Thermal management using the bi-disperse porous medium approach

Thermal management of distributed electronics similar to data centers is studied using a bi-disperse porous medium (BDPM) approach. The BDPM channel comprises heat generating micro-porous square blocks, separated by macro-pores. Laminar forced convection cooling fluid of Pr = 0.7 saturates both the micro- and macro-pores. Bi-dispersion effect is induced by varying the macro-pore volume fraction phi(E), and by changing the number of porous blocks N-2, both representing re-distribution of the electronics. When 0.2 <= phi(E) <= 0.86, the heat transfer No is enhanced twice (from similar to 550 to similar to 1100) while the pressure drop Delta p* reduces almost eightfold. For phi(E) < 0.5, No reduces quickly to reach a minimum at the mono -disperse porous medium (MDPM) limit (phi(E) -> 0). Compared to N-2 = 1 case, No for BDPM configuration is high when N-2 >> 1, i.e., the micro-porous blocks are many and well distributed. The Nu increase with Re changes from non-linear to linear as N-2 increases from 1 to 81, with corresponding insignificant pumping power increase. (C) 2011 Elsevier Ltd. All rights reserved.

Inter-domain interactions influence the stability and catalytic activity of the bi-domain protein tyrosine phosphatase PTP99A

The two protein tyrosine phosphatase (PTP) domains in bi-domain PTPs share high sequence and structural similarity. However, only one of the two PIP domains is catalytically active. Here we describe biochemical studies on the two tandem PTP domains of the bi-domain PTP, PTP99A. Phosphatase activity, monitored using small molecule as well as peptide substrates, revealed that the inactive (D2) domain activates the catalytic (D1) domain. Thermodynamic measurements suggest that the inactive D2 domain stabilizes the bi-domain (D1-D2) protein. The mechanism by which the D2 domain activates and stabilizes the bi-domain protein is governed by few interactions at the inter-domain interface. In particular, mutating Lys990 at the interface attenuates inter-domain communication. This residue is located at a structurally equivalent location to the so-called allosteric site of the canonical single domain PIP, PTP1B. These observations suggest functional optimization in bi-domain PTPs whereby the inactive PTP domain modulates the catalytic activity of the bi-domain enzyme. (C) 2012 Elsevier B.V. All rights reserved.

Effect of Thickness on The Optical Properties Change in Bi/As2S3 Bilayer Thin Films

Bilayer thin films of Bi/As2S3 were prepared from Bi and As2S3 by thermal evaporation technique under high vacuum. We have prepared three bilayer films of 905nm, 910nm and 915nm thickness with with As2S3 as bottom layer (900nm) and Bi as top layer (5,10,15 nm). We have compared the optical changes due to the thickness variation of Bi layer on As2S3 film. The changes were characterized by FTIR and XPS techniques.

Raman & Infrared Study of Bi Filled Co4Sb12

CoSb3 skutterudites are established thermoelectric materials in the 500-800K temperature range. Undoped and Bi filled CoSb3 samples were synthesized by induction melting-annealing process and phase confirmation done by X-Ray diffraction. The role of bismuth as a filler in CoSb3 was investigated by Raman and far infrared reflectance study. It was found that bismuth strengthens Sb vibrations, and can potentially scatter Sb related acoustic phonons effectively. As a result substantial reduction in thermal conductivity may be possible with proper control of Bi filling.

A 12 V Substrate-Integrated PbO2-Activated Carbon Asymmetric Hybrid Ultracapacitor with Silica-Gel-Based Inorganic-Polymer Electrolyte

A 12 V Substrate-Integrated PbO2-Activated Carbon hybrid ultracapacitor (SI-PbO2-AC HUCs) with silica-gel sulfuric acid electrolyte is developed and performance tested. The performance of the silica-gel based hybrid ultracapacitor is compared with flooded and AGM-based HUCs. These HUCs comprise substrate-integrated PbO2 (SI-PbO2) as positive electrodes and high surface-area activated carbon with dense graphite-sheet substrate as negative electrodes. 12 V SI-PbO2-AC HUCs with flooded, AGM and gel electrolytes are found to have capacitance values of 308 F, 184 F, and 269 F at C-rate and can be pulse charged and discharged for 100,000 cycles with only a nominal decrease in their capacitance values. The best performance is exhibited by gel-electrolyte HUCs.

Optical properties change with the addition and diffusion of Bi to As2S3 in the Bi/As2S3 bilayer thin film

The role of Bi layer (thickness similar to 7 nm) on As2S3 film was extensively studied for different optical applications in which Bi (top layer) as active and diffusing layer and As2S3 as barrier (matrix) layer. Bilayer thin films of Bi/As2S3 were prepared from Bi and As2S3 by thermal evaporation technique under high vacuum. The decrease of optical band gap with the addition of Bi to As2S3 has been explained on the basis of density of states and the increase in disorder in the system. It was found that the efficient changes of optical parameters (transmission, optical band gap, refraction) could be realized due to the photo induced diffusion activated by the focused 532 nm laser irradiation and formation of different bonds. The diffusion of Bi into As2S3 matrix increases the optical band gap producing photo bleaching effect. The changes were characterised by different experimental techniques. (C) 2012 Elsevier B.V. All rights reserved.

Thermoelectric properties of Bi-added Co4Sb12 skutterudites

Void filling in (I) Bi-x-added Co4Sb12 or (II) Sb/Bi substitution of Co4Sb12-xBix has been investigated for structural and thermoelectric properties evaluation. X-ray powder data Rietveld refinements combined with electron probe microanalyses showed a polycrystalline and practically Bi-free CoSb3 skutterudite phase as the major constituent as well as a secondary Bi phase in the grain boundaries. For series I alloys, the electrical conductivity, Seebeck coefficient and thermal conductivity were measured as a function of temperature in the range from 450 to 750 K. The electrical conductivity of all the samples increased with increasing temperature, showing a semiconducting nature with smaller values of the Seebeck coefficient for higher Bi fractions. Conduction over the entire temperature range was found to arise from a single p-type carrier. Thermal conductivity showed a reduction with Bi added in all the samples, except for Bi0.75Co4Sb12, and the lowest lattice thermal conductivity was found for a Bi-added fraction of 0.5. The maximum zT value of 0.53 at 632 K is higher than that of Co4Sb12.

Comparison of one cycle control of charge and current for bi-directional boost rectifiers

Classical control and one cycle control of current are popular methods used to modulate pulses in active rectifiers for ac-dc power conversion. One cycle control has lower control complexity and can be implemented using linear analog circuits when compared with the classical approach. However, it also suffers from problems such as instability and offsets in current that is severe at light load conditions. A control strategy for bidirectional boost rectifiers based on one cycle control of charge is proposed for that overcomes these limitations. The integral of sensed current, which represents charge, is compared with a non-linear carrier, which is modified for ac-dc power conversion. This generates the gating signals for the switching devices. The modifications required for the control law governing one cycle control of charge is derived in the paper. Detailed simulation studies are carried out to compare one cycle control of current with the proposed method for ac-dc power conversion, which are validated on a laboratory hardware prototype.

Thermoelectric properties of PbTe with encapsulated bismuth secondary phase

Lead Telluride (PbTe) with bismuth secondary phase embedded in the bulk has been prepared by matrix encapsulation technique. X-Ray Diffraction results indicated crystalline PbTe, while Rietveld analysis showed that Bi did not substitute at either Pb or Te site, which was further confirmed by Raman and X-Ray Photoelectron Spectroscopy. Scanning Electron Microscopy showed the expected presence of a secondary phase, while Energy Dispersive Spectroscopy results showed a slight deficiency of tellurium in the PbTe matrix, which might have occurred during synthesis due to higher vapor pressure of Te. Transmission Electron Microscopy results did not show any nanometer sized Bi phase. Seebeck coefficient (S) and electrical conductivity (sigma) were measured from room temperature to 725 K. A decrease in S and sigma with increasing Bi content showed an increased scattering of electrons from PbTe-Bi interfaces, along with a possible electron acceptor role of Bi secondary phase. An overall decrease in the power factor was thus observed. Thermal conductivity, measured from 400K to 725K, was smaller at starting temperature with increasing Bi concentration, and almost comparable to that of PbTe at higher temperatures, indicating a more important role of electrons as compared to phonons at PbTe-Bi interfaces. Still, a reasonable zT of 0.8 at 725K was achieved for undoped PbTe, but no improvement was found for bismuth added samples with micrometer inclusions. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4796148]

Bismuth carboxylates with Brucite- and Fluorite-related structures: synthesis structure and properties

Three new compounds of bismuth, C4N2H10]center dotBi(C7H4NO4)(C7H3NO4)]center dot H2O, I, Bi(C5H3N2O4) (C5H2N2O4)], II, and Bi(mu(2)-OH)(C7H3NO4)], III, have been prepared by the reaction between bismuth nitrate and heterocyclic aromatic dicarboxylic acids, 2,6-pyridinedicarboxylic acid, 4,5-imidazoledicarboxylic acid, and 3,4-pyridinedicarboxylic acid, respectively, under hydrothermal conditions. The structures of all the compounds have linkages between Bi2O2 and the corresponding dicarboxylate forming a simple molecular unit in I, a bilayer arrangement in II, and a three-dimensional extended structure in III. The topological arrangement of the nodal building units in the structures indicates that a brucite-related layer (II) and fluorite-related arrangement (III) can be realized in these structures. By utilizing the secondary interactions, one can correlate the structure of III to a Kagome-related one. The observation of such classical inorganic related structures in the bismuth carboxylates is noteworthy. Lewis acid catalytic studies on the formation of ketal suggest the possible participatory role of the lone pair of electrons. All the compounds are characterized employing elemental analysis, IR, UV-vis, and thermal studies.

Anomalous magnetic behavior of La0.6Sr0.4MnO3 nano-tubes constituted with 3-12 nm particles

Uniform La0.6Sr0.4MnO3 (LSMO) nanotubes of an average diameter 180 nm were synthesized by a modified sol-gel method employing nanochannel porous anodic alumina templates. The nanotubes were characterized chemically and structurally by XRD, SEM, EDX, and TEM. Postannealed (700 degrees C for 1 h hour) nanotubes were found to be polycrystalline from XRD and SAED studies. To get further insight into the nanotube structure, HRTEM studies were done, which revealed that obtained LSMO nanotubes were structurally constituted with nanoparticles of 3-12 nm size. These constituent nanoparticles were randomly aligned and self-knitted to build the nanotube wall. Investigation of magnetic properties at this structured nanoscale revealed remarkable irreversibility between the zero field cooling (ZFC) and field cooling (FC) magnetization curves accompanied with a peak in the ZFC curve indicating spin-glass-like behavior. Structural defects and compositional variations at surfaces and grain-boundaries of constituent nanoparticles might be responsible for this anomalous magnetic behavior.

Does aluminium bind to histidine? an NMR investigation of Amyloid beta 12 and Amyloid beta 16 fragments

Aluminium and zinc are known to be the major triggering agents for aggregation of amyloid peptides leading to plaque formation in Alzheimer's disease. While zinc binding to histidine in A (amyloid ) fragments has been implicated as responsible for aggregation, not much information is available on the interaction of aluminium with histidine. In the NMR study of the N-terminal A fragments, DAEFRHDSGYEV (A12) and DAEFRHDSGYEVHHQK (A16) presented here, the interactions of the fragments with aluminium have been investigated. Significant chemical shifts were observed for few residues near the C-terminus when aluminium chloride was titrated with A12 and A16 peptides. Surprisingly, it is nonhistidine residues which seem to be involved in aluminium binding. Based on NMR constrained structure obtained by molecular modelling, aluminium-binding pockets in A12 were around charged residues such as Asp, Glu. The results are discussed in terms of native structure propagation, and the relevance of histidine residues in the sequences for metal-binding interactions. We expect that the study of such short amyloid peptide fragments will not only provide clues for plaque formation in aggregated conditions but also facilitate design of potential drugs for these targets.

Hydrodynamic energy harvesting using an ionic polymer-metal composite stack for underwater applications

Ionic Polymer Metal Composites (IPMCs) are a class of Electro-Active Polymers (EAPs) consisting of a base polymer (usually Nafion), sandwiched between thin films of electrodes and an electrolyte. Apart from fuel cell like proton exchange process in Nafion, these IPMCs can act both as an actuator and a sensor. Typically, IPMCs have been known for their applications in fuel cell technology and in artificial muscles for robots. However, more recently, sensing properties of IPMC have opened up possibilities of mechanical energy harvesting. In this paper, we consider a bi-layer stack of IPMC membranes where fluid flow induced cyclic oscillation allows collection of electronic charge across a pair of functionalized electrode on the surface of IPMC layers/stacks. IPMCs work well in hydrated environment; more specifically, in presence of an electrolyte, and therefore, have great potential in underwater applications like hydrodynamic energy harvesting. Hydrodynamic forces produce bending deformation, which can induce transport of cations via polymer chains of the base polymer of Nafion or PTFE. In our experimental set-up, the deformation is induced into the array of IPMC membranes immersed in electrolyte by water waves caused by a plunger connected to a stepper motor. The frequency and amplitude of the water waves is controlled by the stepper motor through a micro-controller. The generated electric power is measured across a resistive load. Few orders of magnitude increase in the harvested power density is observed. Analytical modeling approach used for power and efficiency calculations are discussed. The observed electro-mechanical performance promises a host of underwater energy harvesting applications.

Wurtzite InN nanodots on Si(100) by molecular beam epitaxy

Studies were carried on the growth behavior of InN nanodots by plasma assisted molecular beam epitaxy on bare Si(100) substrates and their structural, optical, electrical properties. The growth was carried out by two different methods such as, (i) mono-step growth process at a low temperature and a (ii) bi-step growth process with the combination of low and high temperatures for the formation of single crystalline nanodots with well defined crystallographic facets due to cluster migration. Low temperature photoluminescence shows a free excitonic (FE) luminescence at 0.80 eV. The Raman spectroscopy and X-ray diffraction studies reveal that the nanodots as well as the film were of wurtzite structure and strain free.

A nearly constant switching frequency current hysteresis controller with generalized parabolic boundaries using 12-sided polygonal voltage space vectors for IM drives

In this paper, a current hysteresis controller with parabolic boundaries for a 12-sided polygonal voltage space vector inverter fed induction motor (IM) drive is proposed. Parabolic boundaries with generalized vector selection logic, valid for all sectors and rotational direction, is used in the proposed controller. The current error space phasor boundary is obtained by first studying the drive scheme with space vector based PWM (SVPWM) controller. Four parabolas are used to approximate this current error space phasor boundary. The system is then run with space phasor based hysteresis PWM controller by limiting the current error space vector (CESV) within the parabolic boundary. The proposed controller has simple controller implementation, nearly constant switching frequency, extended modulation range and fast dynamic response with smooth transition to the over modulation region.