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Owing to the limited supply and pressure margin in the air system, a cooling technique providing efficient heat transfer with lower flow loss is highly desirable for gas turbine blades. Microscale ribs have promised to be a potential cooling candidate. In this work, large eddy simulations are implemented to reveal the scale effect of micro ribs on the near-wall turbulent transport in a cooling channel. Considering a mechanistic study and practical applications, both single-rib and rib-array arrangements are studied with a wide range of dimensionless viscous-scaled rib heights involving the entire boundary layer. The results indicate that the rib-induced destruction and regeneration of coherent structures are, respectively, responsible for the weakened momentum transport and enhanced heat transport in the near-wall region. Using tiny ribs, regenerated quasi-streamwise vortices are mainly located in the buffer layer. The resulting turbulence burst greatly enhances wall heat transfer while keeping a lower flow loss due to the weak form drag. Regenerated hairpin vortices using tall ribs are activated in the log-law layer and intensively interact with mainstream. Along with improved wall heat transfer, the significant form drag results in a remarkably high flow loss. Accordingly, heat transfer and flow loss show different dependencies on the rib height, which contributes to an optimum height interval of ribs (e+ = 20–40) located in the high buffer and low log-law layer for maximizing the overall performance. Furthermore, for the rib-array scheme, adequate inter-rib spacing is essential to achieve turbulence regeneration for enhancing near-wall heat transport. [ABSTRACT FROM AUTHOR]

Chemical dynamics simulations were performed to study the unimolecular dissociation of randomly excited Na+(Bz) and Na+(Bz)2 clusters; Bz = benzene. The simulations were performed at constant energy, and temperatures in the range of 1200-2200 K relevant to combustion, using an analytic potential energy surface (PES) derived in part from MP2/6-311+G* calculations. The clusters decompose with exponential probabilities, consistent with RRKM unimolecular rate theory. Analyses show that intramolecular vibrational energy redistribution is sufficiently rapid within the clusters that their unimolecular dynamics is intrinsically RRKM. Arrhenius parameters, determined from the simulations of the clusters, are unusual in that Ea is ~10 kcal/mol lower the Na+ + (Bz) → Na+ + Bz dissociation energy and the A-factor is approximately two orders-of-magnitude too small. Analyses indicate that temperature dependent anharmonicity is important for the Na+(Bz) cluster's unimolecular rate constants k(T). This is consistent with the temperature dependent anharmonicity found for the Na+(Bz) cluster from a Monte Carlo calculation based on the analytic PES used for the simulations. Apparently temperature dependent anharmonicity is quite important for unimolecular dissociation of the Na+(Bz)1,2 clusters. [ABSTRACT FROM AUTHOR]

1:2 B-site cation ordered Ba(Mg1/3Nb2/3)O3 ceramic was synthesized using conventional solid-state reaction at 1600 °C for 12 h. The structure parameters were obtained through Rietveld refinement of X-ray diffraction data. The Raman peak frequencies were obtained by Lorenz fitting on Raman spectrum. Four-parameter semiquantum model was used to fit the infrared (IR) reflectivity spectrum, and the fitted parameters were used to calculate the dielectric permittivity e and dielectric loss tand. A total of 9 active Raman and 16 active IR modes were obtained using first-principle calculations based on density functional theory with local density approximation. All of the vibrational modes were assigned and represented by linear combinations of the symmetry coordinates deduced using group theory analysis. The Raman mode with the highest frequency A1g (4) (789 cm-1) can be described as the breathing vibration of NbO6. The IR modes Eu (1) (149 cm-1) and A2u (2) (212 cm-1), which can be described as the twisting vibrations of Ba-MgO6/Ba-NbO6 on the a-b plane and the stretching vibrations of Ba-MgO6/Ba-NbO6 along the c direction, respectively, are the dominant contributing modes to e and tand. The dielectric property parameters obtained using IR spectrum fittings, first-principal calculations, and microwave measurements were compared. [ABSTRACT FROM AUTHOR]

Vertically oriented single-crystalline TiO2 nanowires array was grown on transparent conductive oxide glass substrate, and then CdS and CdSe quantum dots (QDs) were deposited on nanowires to form a TiO2/CdS/CdSe core-shell structure films. The optical properties of films with different layers of QDs were compared. The QD sensitized solar cells (QD-SSCs) were assembled and the effect of coating cycles of QDs on the photovoltaic performance was investigated. Under optimum parameters, QD-SSCs assembled with 5 μm thick TiO2 nanowires film exhibited a short-circuit current density of 7.92 mA cm-2, an open-circuit voltage of 0.40 V, and a power conversion efficiency of 1.14%. [ABSTRACT FROM AUTHOR]

Pyrrole adsorption on Si(111)-(7×7) has been investigated using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy, scanning tunneling microscopy (STM), and theoretical calculations. Compared to physisorbed pyrrole, chemisorption leads to the appearance of N–Si and Si–H vibrational features, together with the absence of N–H stretching mode. This clearly demonstrates the dissociative nature of pyrrole chemically binding on Si(111)-(7×7) through the breakage of N–H bond. Based on STM results, the resulting fragments of pyrrolyl and H atom are proposed to bind with an adatom and an adjacent rest atom, respectively. The STM images further reveal that the adsorption is site selective. The faulted center adatoms are most favored, followed by unfaulted center adatoms, faulted corner adatoms, and unfaulted corner adatoms. In addition, the chainlike pattern of reacted adatoms was observed, implying the possible existence of attractive interaction between adsorbed pyrrolyl and the precursor state. Theoretical calculation confirms that the dissociative adsorption with pyrrolyl bonded to an adatom and H atom to an adjacent rest atom is energetically favored compared to the associative cycloaddition involving the two α-carbon atoms of pyrrole and an adatom–rest atom pair. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Integrated NbN direct current superconducting quantum interference device (DC-SQUID) magnetometers were developed based on high-quality epitaxial NbN/AlN/NbN Josephson junctions for SQUID applications operating at high temperatures. We report the current–voltage and voltage–flux characteristics and the noise performance of the NbN DC-SQUIDs for temperatures ranging from 4.2 to 9K. The critical current and voltage swing of the DC-SQUIDs decreased by 15% and 25%, respectively, as the temperature was increased from 4.2 to 9K. The white flux noise of the DC-SQUID magnetometer at 1 kHz increased from 3.9 μφ0/Hz1/2 at 4.2K to 4.8μφ0/Hz1/2 at 9K with 23% increase, corresponding to the magnetic field noise of 6.6 and 8.1 fT/Hz1/2, respectively. The results show that NbN DC-SQUIDs improve the tolerance of the operating temperatures and temperature fluctuations in SQUID applications. [ABSTRACT FROM AUTHOR]

By the multiple reflections and transmissions in a dielectric on a ferromagnetic metal, color and Kerr rotation correlate with each other. It is revealed that the real refractive index of dielectric plays a major role on the variations of color and Kerr signal, while the absorbing term adjusts the intensive color exhibition and Kerr enhancement at much thinner dielectric thickness. The intensive Kerr signal variation is always accompanied by the color transition with the dielectric thickness changing. Experimental results observed in silicon(or silica)/iron samples are well consistent with calculations. Nanometer dielectric optical coating can not only enhance Kerr effect but also endow magnetic surface with chromatics, which has promising potential applications in anti-fake brands, colorful decorations, camouflages, and even bionics. [ABSTRACT FROM AUTHOR]

In a reversed field pinch device, the conductive shell is placed as close as possible to the plasma so as to balance the plasma during discharge. Plasma instabilities such as the resistive wall mode and certain tearing modes, which restrain the plasma high parameter operation, respond closely with conditions in the wall, in essence the eddy current present. Also, the effect of eddy currents induced by the external coils cannot be ignored when active control is applied to control instabilities. One diagnostic tool, an eddy current probe array, detects the eddy current in the composite shell. Magnetic probes measuring differences between the inner and outer magnetic fields enable estimates of the amplitude and angle of these eddy currents. Along with measurements of currents through the copper bolts connecting the poloidal shield copper shells, we can obtain the eddy currents over the entire shell. Magnetic field and eddy current resolutions approach 2 G and 6 A, respectively. Additionally, the vortex electric field can be obtained by eddy current probes. As the conductivity of the composite shell is high, the eddy current probe array is very sensitive to the electric field and has a resolution of 0.2 mV/cm. In a bench test experiment using a 1/4 vacuum vessel, measurements of the induced eddy currents are compared with simulation results based on a 3D electromagnetic model. The preliminary data of the eddy currents have been detected during discharges in a Keda Torus eXperiment device. The typical value of toroidal and poloidal eddy currents across the magnetic probe coverage rectangular area could reach 3.0 kA and 1.3 kA, respectively. [ABSTRACT FROM AUTHOR]

The unsubstituted copper phthalocyanine (CuPc) single crystal nano columns were fabricated for the first time as chlorine (Cl2) gas sensors in this paper. The nano columns of CuPc have been prepared on different substrates via template-free physical vapor deposition (PVD) approach. The growth mechanism of CuPc nano column on quartz was explored and the same condition used on other substrates including glass, sapphire (C-plane<0001>, M-plane<1010>, R-plane<1102>), Si and SiO2/Si came to a same conclusion, which confirmed that the aligned growth of CuPc nano column is not substrate-dependent. And then the CuPc nano column with special morphology was integrated as in-situ sensor device which exhibits high sensitivity and selectivity towards Cl2 at room temperature with a minimum detection limit as low as 0.08 ppm. The response of sensor was found to increase linearly (26~659%) with the increase for Cl2 within concentration range (0.08~4.0ppm). These results clearly demonstrate the great potential of the nano column growth and device integration approach for sensor device. [ABSTRACT FROM AUTHOR]

TiN coatings were deposited with various Ar/N2 gas flow ratios by arc ion plating. Coating microstructure and mechanical properties were investigated through grazing incidence x-ray diffraction (GIXRD), scanning electron microscopy, digital microscopy, nanoindentation, and nanoscratch test. GIXRD indicated that TiN coatings initially grew along the (111) and (200) planes, and then the intensity of the peaks decreased as the Ar/N2 gas flow ratio was reduced. TiN coatings exhibited a high hardness value (22.3-26.3GPa). Coatings with a high hardness-to-modulus ratio (H/Er) were found to crack dramatically under low critical load. The depth of the nanoscratches decreased as the H/Er ratio was reduced, indicating that the wear resistance of the coatings increased as the Ar/N2 gas flow ratio was augmented. TiN coatings with high Ar/N2 gas flow ratio achieved high hardness value, excellent elastic recovery under low loads, high adhesive strength, and strong wear resistance. [ABSTRACT FROM AUTHOR]

The flux modulation scheme (FMS) is the standard readout technique of dc SQUIDs, where a step-up transformer links the SQUID to the preamplifier. The transformer's primary winding shunts the SQUID via a large capacitor while the secondary winding connects it to the preamplifier. A modulation flux having a frequency of typically 100 kHz generates an ac voltage across the SQUID, stepped up by the transformer. The SQUID with FMS is customarily operated in the current bias mode, because a constant dc bias current flows only through the SQUID due to the capacitor isolation. With FMS, however, the transformer ac shunts the SQUID so that in reality the operating mode is neither purely current-biased nor voltage-biased but rather nominal currentbiased or "mixed biased." Our objective is to experimentally investigate the consequences of ac shunting of the dc SQUID in FMS and the transformer's transfer characteristics. For different shunt values we measure the change in the SQUID bias current due to the ac shunt using another SQUID in the two-stage readout scheme, and simultaneously monitor the SQUID output voltage signal. We then explain our measurements by a simplified graphic analysis of SQUID intrinsic current-voltage (I-V) characteristics. Since the total current flowing through the SQUID is not constant due to the shunting effect of the transformer, the amplitude of SQUID flux-to-voltage characteristics V(U) is less as compared to the direct readout scheme (DRS). Furthermore, we analyze and compare V(U) obtained by DRS and FMS. We show that in FMS, the transfer characteristics of the SQUID circuit also depend on the isolation capacitance and the dynamic resistance of the SQUID. [ABSTRACT FROM AUTHOR]

The authors describe an electroless deposition method for thin films, based on the irradiation by an x-ray beam emitted by a synchrotron source. Specifically, Ni–P films were deposited at room temperature. This synthesis is a unique combination of photochemical and electrochemical processes. The influence of the pH value on the formation and structural properties of the films was examined by various characterization tools including scanning electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Real time monitoring of the deposition process by coherent x-ray microscopy reveals that the formation of hydrogen bubbles leads to a self-catalysis effect without a preexisting catalyst. The mechanisms underlying the deposition process are discussed in details. [ABSTRACT FROM AUTHOR]

An increased absorption of regioregular poly(3-hexylthiophene) due to surface plasmons (SPs) has been studied by steady state fluorescence spectra measurements and femtosecond transient absorption (TA) technique. The SPs were excited by periodic Ag grating structures transferred from the photoresist gratings which were fabricated by two-beam laser interference. The steady state fluorescence measurements show a maximum enhanced fluorecence of about 16 times larger arising from the absorption enhancement. Further investigation by TA technique reveals that the yield of the polaron pairs on Ag gratings significantly increase, much bigger than that of the pure sample, which also confirms the enhanced absorption efficiency as resulting from the excited SPs. [ABSTRACT FROM AUTHOR]

A 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine thin film doped with Fe3O4 has been demonstrated an efficient p-type hole-injection layer (HIL) in organic light-emitting devices (OLEDs). The tris-(8-hydroxyquinoline) aluminum-based OLEDs with the p-type HIL exhibit a very low turn-on voltage of 2.4 V and a high luminance of 29 360 cd/m2 at 8 V, while it is 3 V and 6005 cd/m2, respectively, for the nondoped devices. The improvement in the device performance is clarified as arising from the improved hole injection and transport by the results of ultraviolet/visible/near-infrared absorption, x-ray photoelectron spectra and current density-voltage characteristics of hole-only devices. [ABSTRACT FROM AUTHOR]

Here we report a frontside illuminated TiO2 nanotube based dye-sensitized solar cell (DSSC). The photoanode with inclined microchannels (IMCs) formed by laser drilling acted as a multifunctional role for enhancing the cell’s efficiency; light trapping, pathway for transporting electrolyte, and extra surface area for dye loading. The amount of N719 dye absorbed on IMCs photoanode was measured to be 3.83×10-7 mol/cm2, which was almost 1.82 times as high as that of the flat photoanode. The frontside illuminated DSSC showed an energy conversion efficiency of 4.1% under AM1.5 condition, which was much higher compared to that (3.1%) of the backside illuminated DSSC. [ABSTRACT FROM AUTHOR]

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell’s characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode. [ABSTRACT FROM AUTHOR]