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An innovative numerical prediction method of flow-induced noise is implemented to overcome the defect that the traditional acoustic analogy method cannot reflect the interaction between turbulence vortex and sound. The classical cylindrical–airfoil interference model is used to perform the simulation and compared with the experimental results. To start with the derivation of Powell's vortex sound equation, an implicit three-dimensional model of the fluid–acoustic coupling field is established to process the unsteady iterative calculation. The large eddy simulation method is adopted to solve the unsteady flow, and the acoustic information is then calculated using the vortex acoustic equation at each iteration step. The vortex structures around the cylinder airfoil are identified and captured by the Q-criterion for further analysis of vortex–noise correlation mechanism. The flow-induced noise prediction results are finally compared with Ffowcs Williams–Hawkings (FW–H) acoustic analogy approach. The results show that the vortex shedding from the cylinder and the interaction between vortex shedding and airfoil have the greatest influence on the acoustic, and the far-field noise of the cylinder airfoil shows a partial "eight" dipole distribution. The calculated results of the vortex sound theory are closer to the experimental ones than the FW–H method. The research helps understand the vortex acoustic coupling mechanism of the cylinder–airfoil model and provides a more accurate numerical prediction of flow-induced noise. [ABSTRACT FROM AUTHOR]

This paper presents an explanation based on torsionally mediated proton-spin-overall-rotation interaction for the observation of doublet hyperfine splittings in some Lamb-dip sub-millimeter-wave transitions between ground-state torsion-rotation states of E symmetry in methanol. These unexpected doublet splittings, some as large as 70 kHz, were observed for rotational quantum numbers in the range of J = 13 to 34, and K = -2 to +3. Because they increase nearly linearly with J for a given branch, we confined our search for an explanation to hyperfine operators containing one nuclear-spin angular momentum factor I and one overall-rotation angular momentum factor J (i.e., to spin-rotation operators) and ignored both spin-spin and spin-torsion operators, since they contain no rotational angular momentum operator. Furthermore, since traditional spin-rotation operators did not seem capable of explaining the observed splittings, we constructed totally symmetric "torsionally mediated spin-rotation operators" by multiplying the E-species spin-rotation operator by an E-species torsional-coordinate factor of the form e±nia. The resulting operator is capable of connecting the two components of a degenerate torsion-rotation E state. This has the effect of turning the hyperfine splitting pattern upside down for some nuclear-spin states, which leads to bottom-to-top and top-to-bottom hyperfine selection rules for some transitions, and thus to an explanation for the unexpectedly large observed hyperfine splittings. The constructed operator cannot contribute to hyperfine splittings in the A-species manifold because its matrix elements within the set of torsion-rotation A1 and A2 states are all zero. The theory developed here fits the observed large doublet splittings to a root-mean-square residual of less than 1 kHz and predicts unresolvable splittings for a number of transitions in which no doublet splitting was detected. [ABSTRACT FROM AUTHOR]

We report the structural and magnetotransport properties of ultrathin superparamagnetic Co/ZnO and Co/ZnAlO films deposited by sequentially sputtering Co layers and semiconductor layers. The films consisting of Co nanodots embedded in an amorphous semiconductor matrix exhibit large room temperature tunneling magnetoresistance with a maximum value of over 7%. The singlelayer- nanodot structures gradually develop in the films with thicknesses below 8 nm, where tunneling processes existing only between nanodots that lie in a plane are realized. The tunneling magnetoresistance ratio at room temperature is as high as 5% although the thickness of the Co/ZnAlO film is as thin as 3.2 nm. These single-layer-nanodot films having high tunneling magnetoresistance ratios and superparamagnetic behavior can be used in transparent nano-granular in gap sensors. [ABSTRACT FROM AUTHOR]

Fe-doped In2O3 thin films are deposited on sapphire substrates using pulsed laser ablation. The effects of Fe concentration and oxygen partial pressure on the structure, magnetism and transport properties of (In1-xFex)2O3 films are studied systematically. A detailed analysis of the structural properties suggests the substitution of Fe dopant ions with mixture valences and rules out the presence of clusters and secondary phases as the source of ferromagnetism. Systematic investigations of transport properties for (In1-xFex)2O3 films with a wide range of carrier densities reveal that they occur in both metallic and insulating regimes. The insulating films exhibit variable range hopping at low temperatures and show temperature dependent ferromagnetism, which can be explained by bound magnetic polarons mechanism. For the metallic films, the carrier densities play a crucial role in their robust ferromagnetism and the resistivity and magnetization are independent of temperature; the carrier-mediated exchange mechanism has been suggested as responsible for magnetic ordering in these metallic films. Optical absorption and magneto-optic studies of (In1-xFex)2O3 films indicate further differences between metallic and semiconducting films and show significant magnetic circular dichroism below the In2O3 bandedge at room temperature, which also implies intrinsic ferromagnetism. [ABSTRACT FROM AUTHOR]

Co/ZnO films were deposited on glass substrates by magnetron sputtering at room temperature. The structure of the as-deposited films is studied by means of x-ray diffraction, x-ray photoelectron spectroscopy, and the zero-field-cooled and field-cooled magnetization curves. It is shown that the as-deposited samples consist of a mixture of regions of metallic Co and semiconducting ZnO. Large negative magnetoresistance of 26% and 11.9% are observed in the as-deposited Co/ZnO film with Co concentration of 50.7 at. % at 10 K and room temperature, respectively. Structural analysis, the temperature dependence of the conductivity and magnetoresistance reveal that the magnetoresistance is induced by spin-dependent tunneling between regions of conducting magnetic Co through the ZnO semiconducting barriers. The enhanced magnetoresistance in the low temperature regime may be related to the existence of higher-order tunneling processes between large Co regions mediated by small Co particles. [ABSTRACT FROM AUTHOR]

We report saturation dip spectroscopy in the C–N stretching band of CH3NH2 with a resolution of 0.4 MHz and an accuracy of 0.1 MHz by use of a CO2-laser/microwave-sideband spectrometer. The wide tunability, Lamb-dip resolution, absolute frequency accuracy, and high sensitivity of our dual-mode instrument were all key features in making precise measurements for a range of lines in the densely crowded spectrum with its complex pattern of splittings arising from the large-amplitude CH3 torsion and NH2 inversion. We focused on achieving resolution and assignment of transitions within the highly blended Q branch of the C–N stretch and on observations of the important K=0 sequences of Aa and Ea torsion-inversion symmetry. Term values of the latter were fitted to J(J+1) power-series expansions to obtain the K=0 C–N stretching effective B values and substate origins, from which calculated ground-state substate energies were subtracted to yield values of 1044.7061 and 1044.8011 cm-1 for the Aa and Ea subband origins, respectively. We thereby estimate a mean value of 1044.75(5) cm-1 for the vibrational band origin and 0.7323(5) cm-1 for the effective upper-state B value for the C–N stretching fundamental of CH3NH2. [ABSTRACT FROM AUTHOR]

Polycoordinate planar B compounds BXn (X=B, Al, C, N and Si; n=3–8) are optimized at B3LYP/6-311++G (3df,p) theoretical level. For X=B, center B atom can coordinate three to eight atoms, while for X=Al, C, Si, and N, it can only coordinate three to five atoms. The natural bond orbital analysis shows that the center B atom does not violate the octet rule, though the numbers of coordinated atom even reach 8. According to molecular orbital analysis and nucleus independent chemical shift value calculation, it seems that these polycoordinate planar B compounds BXn (X=B, Al, C, N, and Si; n=3–8) hold twofold (α and π) aromatic, which play an important role in their stability and keeping all atoms in one plane. [ABSTRACT FROM AUTHOR]

Studies equilibrium structural constants and torsion-rotation interaction parameters for methanol and acetaldehyde. Molecular flexing in the torsional potential barrier; Coefficients of torsion-rotation terns; Agreement between the Gaussian and global fit results for methanol and acetaldehyde.

The Prussian blue/ionic liquid-polyaniline / multiwall carbon nanotubes (PB/IL-PANI/ MWNTs) composite lm was fabricated by using cyclic voltammetry. The ion liquid acting as a lubricating agent, could enhance the electron delocalization degree and reduce the structural defects of the polyaniline. The surface morphology of the composite lm revealed that the PB nanoparticles have smaller size than that in pure PB lm. Due to the introduction of ion liquid, the PB/IL-PANI/MWNTs composite lm showed wonderful synergistic e ect which can remarkably enhance sensitivity, expand linear range and broaden acidic adaptability for hydrogen peroxide detection. The composite lm demonstrated good stability in neutral solution contrast to pure PB lm, with a linear range from 2.5 mol/L to 0.5 mmol/L and a high sensitivity of 736.8 μA∙(mmol/L)-1∙cm-2 for H2O2 detection. Based on the composite lm, an amperometric glucose biosensor was then fabricated by immobilizing glucose oxidase. Under the optimal conditions, the biosensor also exhibits excellent response to glucose with the linear range from 12.5 μmol/L to 1.75 mmol/L and a high sensitivity of 94.79 μA∙(mmol/L)-1∙cm2 for H2O2. The detection limit was estimated 1.1 μmol/L. The resulting biosensor was applied to detect the blood sugar in human serum samples without any pretreatment, and the results were comparatively in agreement with the clinical assay. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) of Fe3O4 nanoparticle was observed from the visible to near-infrared (NIR) range by laser irradiation at 407 nm. PL spectra of ~10 nm diameter Fe3O4 nanoparticles organized in different spatial configuration, showed characteristic emissions with a major peak near 560 nm, and two weak peaks near 690 nm and 840 nm. Different band gap energies were determined for these Fe3O4 nanoparticle samples corresponding to, respectively, the electron band structures of the octahedral site (2.2 eV) and the tetrahedral site (0.9 eV). Photothermal effect of Fe3O4 nanoparticles was found to be associated with the photoluminescence emissions in the NIR range. Also discussed is the mechanism responsible for the photothermal effect of Fe3O4nanoparticles in medical therapy. [ABSTRACT FROM AUTHOR]

The rheological behavior and especially the rheopexy phenomena of dilute self-assembled solutions in the presence of a counterion are examined in stationary and transient shear flows. In the first part, a continuous and gradually increasing strain is applied on the same sample. We study the effect of the initial shear rate, the temporal variation of the viscosity, and the hysterisis between charge and discharge curves. The results show that the properties of shear thickening are independent of the initial shear rate. In the second part, fresh samples are successively subjected to increasing shear strains; this method allows us to follow the evolution of the rheological characteristics during long measuring durations and gives us a distinct picture of the behavior per shear rate. In both cases, we confirm that the chain length has a strong influence on the emergence and amplitude of the shear thickening. It was also found by studying the start-up flow behavior that the structure at equilibrium is composed of bigger structures for longer chain lengths. The maximum of the viscosity in the shear thickening transition occurs in a range of lower shear rates when enough time is given to the system to undertake the formation of the shear induced structure. Considering this result, we introduce the concept of “temporal shear thickening transition.” [ABSTRACT FROM AUTHOR]

This work reports dual-mode operation of a broadly tunable CO[sub 2]-laser/microwave-sideband spectrometer employing a Cheo waveguide modulator and a CO[sub 2] laser that can operate on hot and sequence band lines as well as low- and high-J regular band lines. The spectrometer has a broadband scanning mode at Doppler-limited resolution for spectral searching and assignment, and a narrow-band sub-Doppler mode for precision measurements. In broadband mode, a 6.7–18.5 GHz (∼0.4 cm[sup -1]) window can be covered for each sideband in a single microwave sweep with a tracking Fabry–Perot etalon filter under computer control. In sub-Doppler mode, saturation-dip spectra are obtained at sub-MHz resolution with absolute frequency measurement accuracy of the order of ±200 kHz. The instrumental performance is demonstrated via spectra of the C–O stretching fundamental vibrational band of methanol. Doppler-limited broadband scans have been recorded with good signal-to-noise ratio in both the low- and high-J regions of the 9.6-μm-CO[sub 2] laser band, while narrow-band sub-Doppler scans have permitted clean separation of very close-lying lines in the CH[sub 3]OH spectrum. The measurement precision is confirmed for several CH[sub 3]OH transition systems through closure of combination loops. Our results illustrate the wide coverage and excellent resolution obtainable with CO[sub 2]-sideband infrared laser radiation in a broadly tunable and convenient infrared source with high potential for spectroscopic applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) in a two-dimensional periodically poled congruent LiTaO3 crystal was investigated experimentally. Multiple conical and dotted SHG have been observed, which features phase-tuned Cherenkov radiation, elastic scattering quasi-phase matching process, and random phase matching process. These results are closely connecting with the domain structure and can be utilized as characterization methods for practical purposes. [ABSTRACT FROM AUTHOR]

Mn and Cr-doped In2O3 films with Sn codoping were deposited on sapphire substrate by pulsed laser deposition. The ferromagnetism of Mn-doped In2O3 films shows reversible behavior, which can be switched between “on” and “off” states by controlling the carrier density via varying Sn concentration. The enhanced ferromagnetism in Cr-doped In2O3 films is observed due to the significant increase in the carrier density with Sn doping, and the saturation magnetization can reach 2.10 μB/Cr. Most importantly, both of the experiment results reveal that the carrier density and the net spin are two crucial factors for producing and tuning ferromagnetism. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin films deposited on c-cut sapphire substrates by pulsed laser deposition. Structure, magnetism, composition, and transport studies indicated that Fe occupied the In sites of the In2O3 lattice rather than formed any metallic Fe or other magnetic impurity phases. Magnetic moments of films were proved to be intrinsic and showed to have a strong dependence on the carrier densities, which depended on the Fe concentration and its valence state as well as oxygen pressure. [ABSTRACT FROM AUTHOR]

The torsional dependence of the CH[sub 3] stretching and bending modes of methanol has been explored in terms of a local mode internal coordinate picture [X. Wang and D. S. Perry, J. Chem. Phys. 109, 10795 (1998)]. First, the torsional variations of the small-amplitude vibrational frequencies along the mass weighted intrinsic reaction coordinate from the top to the bottom of the torsional potential barrier were calculated by means of ab initio frequency projection utilizing GAUSSIAN 98. The resulting curves for the three C-H stretch ab initio frequencies as functions of the torsional angle cannot be reproduced by the original 3x3 local mode model incorporating stretch-torsion and stretch-stretch couplings at lowest-order only, but are well-fitted if the model is extended to include higher-order coupling terms. For the CH-bending modes, with internal coordinates chosen to give a high degree of localization, bend-torsion and bend-bend coupling parameters were determined from the ab initio projected frequencies, and were then used to predict torsional tunneling splittings. Just as observed for the C-H stretch modes, the two higher-frequency asymmetric CH-bend modes are predicted to have inverted tunneling splittings with reduced amplitudes, while the splitting pattern for the lower frequency symmetric-bend mode is predicted to be normal. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]