Phonon dominated heat conduction normal to Mo/Si multilayers with period below 10 nm

Thermal conduction in periodic multilayer composites can be strongly influenced by nonequilibrium electron-phonon scattering for periods shorter than the relevant free paths. Here we argue that two additional mechanisms-quasiballistic phonon transport normal to the metal film and inelastic electron-interface scattering-can also impact conduction in metal/dielectric multilayers with a period below 10 nm. Measurements use the 3ω method with six different bridge widths down to 50 nm to extract the in- and cross-plane effective conductivities of Mo/Si (2.8 nm/4.1 nm) multilayers, yielding 15.4 and 1.2 W/mK, respectively. The cross-plane thermal resistance is lower than can be predicted considering volume and interface scattering but is consistent with a new model built around a film-normal length scale for phonon-electron energy conversion in the metal. We introduce a criterion for the transition from electron to phonon dominated heat conduction in metal films bounded by dielectrics.     

Detection of nano-oxidation sites on the surface of hemoglobin crystals using tip-enhanced Raman scattering

Hemoglobin nanocrystals were analyzed with tip-enhanced Raman scattering (TERS), surface-enhanced resonance Raman scattering (SERRS) and conventional resonance Raman scattering (RRS) using 532 nm excitation. The extremely high spatial resolution of TERS enables selective enhancement of heme, protein, and amino acid bands from the crystal surface not observed in the SERRS or RRS spectra. Two bands appearing at 1378 and 1355 cm(-1) assigned to the ferric and ferrous oxidation state marker bands, respectively, were observed in both TERS and SERRS spectra but not in the RRS spectrum of the bulk sample. The results indicate that nanoscale oxidation changes are occurring at the hemoglobin crystal surface. These changes could be explained by oxygen exchange at the crystal surface and demonstrate the potential of the TERS technique to obtain structural information not possible with conventional Raman microscopy.     

Experimental identification of the phenomenon triggering the net vapor generation in upward subcooled flow boiling of water at low pressure

Observation of the bubble behavior was made using a high-speed camera to investigate the mechanisms to cause the net vapor generation in subcooled flow boiling. In the experiments, water was used as the test fluid, the flow direction was vertical upward, and the pressure was kept close to the atmospheric pressure. At high liquid subcooling close to the condition of the onset of nucleate boiling, all the bubbles were lifted off the heated surface immediately after the nucleation to disappear quickly in the subcooled bulk liquid due to condensation. It was found that the void fraction did not increase significantly unless the liquid subcooling became low enough for some bubbles to be reattached to the heated surface after the lift-off. When the reattachment took place, the bubble lifetime was substantially elongated since the bubbles slid up the vertical heated surface for a long distance after the reattachment. The reattachment therefore contributed to an increase in the void fraction. It was concluded that in the experimental conditions tested in this work, the bubble reattachment to the heated surface was a key phenomenon to cause the sharp increase of the void fraction at the point of net vapor generation.     

The effects of TiO2 pigmented coatings characteristics on temperature and brightness of a coated black substrate

The high visible reflectivity of the cool coatings made by typical white pigment particles produces high glare, which is unpleasant to the human eye and possibly distorts the view of coated objects. A new approach to optimizing pigmented coatings considering both thermal and esthetic effects was proposed in previous works. For an accurate thermal analysis, a full spectral evaluation of radiative properties of pigmented coatings from UV to far IR wavelengths is required. We made a full spectral analysis of TiO₂ pigment particles in polyethylene resin as the host medium in the wavelength range of 0.3–36 μm. To find the spectral transmittance and reflectance of the pigmented layer, we conducted a radiation analysis using the radiation element method by ray emission model (REM²). The effects of characteristics of the coating layer, including size and volume concentration of pigment particles and coating thickness on esthetic and thermal behaviors were studied. The results show that by using the proposed optimum particle size, i.e., 0.8 μm, it is possible to design a coating with reasonable temperature and moderate brightness.     

Separation of polypeptides by isoelectric point focusing in electrospray-friendly solution using a multiple-junction capillary fractionator

We introduce an online multiple-junction capillary isoelectric focusing fractionator (OMJ-CIEF) for separation of biological molecules in solution by pI. In OMJ-CIEF, the separation capillary is divided into seven equal sections joined with each other via tubular Nafion membrane insertions. Each junction is communicated with its own external electrolytic buffer which is used both to supply electrical contact and for solvent exchange. The performance of the fractionator was explored using protein and peptide samples covering broad pI range. Separation was achieved in ionic and ampholytic buffers, including ammonium formate, ammonium hydroxide, histidine, and arginine. By maintaining electric potential across upstream segments of the capillary after the focusing stage, selective release of downstream analyte fractions could be achieved. The selective release mode circumvents the problem of peak broadening during mobilization and enables convenient comprehensive sampling for orthogonal separation methods. Using single-component ampholyte buffers with well-defined pI cutoff values, controlled separation of protein mixture into basic and acidic fractions was demonstrated. The device is cheap and easy to fabricate in-house, simple in operation, and straightforward in interfacing to hyphened analytical platforms. OMJ-CIEF has a potential of becoming a practical add-on unit in a wide range of bioanalytical setups, in particular as a first-dimension separation in mass spectrometry based proteomics or as a preparative tool for analyte purification, fractionation, and preconcentration.     

A Learning Automata Based Area Coverage Algorithm for Wireless Sensor Networks

One way to reduce energy consumption in wireless sensor networks is to reduce the number of active nodes in the network. When sensors are redundantly deployed, a subset of sensors should be selected to actively monitor the field （referred to as a ＂cover＂）, whereas the rest of the sensors should be put to sleep to conserve their batteries. In this paper, a learning automata based algorithm for energy-efficient monitoring in wireless sensor networks （EEMLA） is proposed. Each node in EEMLA algorithm is equipped with a learning automaton which decides for the node to be active or not at any time during the operation of the network. Using feedback received from neighboring nodes, each node gradually learns its proper state during the operation of the network. Experimental results have shown that the proposed monitoring algorithm in comparison to other existing methods such as Tian and LUC can better prolong the network lifetime.     

Prevalence and antimicrobial resistance of Campylobacter isolated from retail raw chicken and beef meat, Tehran, Iran

Campylobacter spp. is a leading cause of human diarrhea. The common source of infection is contaminated food, particularly poultry. The veterinary use of antimicrobial drugs has been suggested to be largely responsible for resistance in human isolates of this zoonotic pathogen. From April to October 2004, 241 samples of chicken and beef meat for sale in retail outlets in Tehran (Iran) were analyzed for the presence of Campylobacter. Totally, 88 (36.5%) Campylobacter strains were isolated. Campylobacter was isolated from a significantly larger number of chicken (63%) than beef (10%) meat (P < 0.0001). Susceptibilities of 72 strains were determined for eight antimicrobial drugs using the disk diffusion assay. Resistance to nalidixic acid was the most common finding (75%), followed by resistance to ciprofloxacin (69.4%), tetracycline (45.8%), amoxicillin (11.1%), streptomycin (4.2%), chloramphenicol (2.8%) and gentamicin (1.4%). None of the isolates was resistant to erythromycin. Multidrug resistance was seen in 75% of the Campylobacter strains.     

Buckling behavior improvement of steel plate shear wall systems

To improve buckling stability and to prevent early elastic buckling of infill plates, vertical and horizontal plate stiffeners are designed for steel plate shear wall (SPSW) systems. Furthermore, effective design of stiffeners for SPSW systems results in improved structural behavior, such as increase of stiffness, capacity and energy absorption. In this paper, the effect of stiffeners is studied on SPSW structural behavior and consequently a rational method is proposed to determine the minimum required moment of inertia for stiffeners resulting in local buckling mode of the infill plate. The proposed requirement is then compared to results obtained from tests previously conducted, as well as those gained from finite element (FE) analyses performed for this study. Copyright © 2007 John Wiley & Sons, Ltd.     

Mechanical properties of NBR/clay nanocomposites by using a novel testing system

NBR/clay nanocomposites are prepared by two different filler types: clay microparticles and clay nanoparticles. The morphology properties of all specimens are explored by XRD and SEM. The mechanical properties are characterized by means of a novel video-controlled method under uniaxial tension. Apart a limited increase in tensile stress at small strains, the ultimate stress at rupture of nanocomposites is much higher than microcomposites. The most dramatic phenomenon is the development of volume strain while the materials are stretched. The nucleation of voids is much more active in composites containing the filler with higher specific surface when the cavitation occurs at the poor interface between the clay platelets and the rubber matrix. In turn, the existence of very diffuse voids hinders the propagation of cracks and retards the rupture process. DMA results reveal that the interfacial action of NBR molecules with layered silicates increases with the degree of intercalation.