bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal effects during magma ascent in conduits
Authors: Costa A. , Melnik O. , Vedeneeva E.
Published: December 2007

Because of strong coupling between viscosity and temperature, the dynamics of magma flows in conduits are drastically controlled by thermal effects due to heat generation by viscous dissipation and loss to the walls by conduction. Here we present analytical solutions and a practical procedure based on an order of magnitude analysis that permits the characterization of the regime and estimation of the main features of the flow. The ranges of validity of analytical and asymptotic solutions were bounded by using results from fully two‐dimensional (2‐D) numerical solutions of mass, momentum, and energy equations for magma flow inside a cylindrical conduit and the heat conduction in the surrounding host rocks. The results permitted the identification of three regimes: a conductive‐heat‐loss‐dominated regime, an intermediate regime, and a viscous‐heating‐dominated regime. Some useful analytical parameterizations are proposed for estimating friction in simplified 1‐D models. Temperature layering due to heat loss by conduction can lead to local crystal growth and magma solidification whereas heat generated by viscous dissipation can be responsible for crystal resorption and remelting of wall rocks.
Role of aquifer heterogeneity in fresh groundwater discharge and seawater recycling: An example from the Carmel coast, Israel
Authors: Weinstein Y. , Burnett W. C. , Swarzenski P. W. , Shalem Y. , Yechieli Y. , Herut B.
Published: December 2007

A case study is shown in which the pattern of submarine groundwater discharge and of seawater recycling is controlled by local hydrogeological variability. The coastal aquifer in Dor Bay is composed of two units: a partly confined calcaranitic sandstone (Kurkar) and an overlying loose sand. Groundwater in the Kurkar has elevated activities of 222Rn (∼390 dpm/L) and relatively low 224Ra/223Ra activity ratios (3–4), while the sand groundwater is significantly less radiogenic (6–90 dpm/L) and shows higher 224Ra/223Ra ratios. Groundwater discharging from sand‐covered areas of the bay has salinities of 16–31 and an average 222Rn activity of 168 dpm/L, which lies on a mixing line between Rn‐rich Kurkar fresh water and Rn‐poor seawater. Another key observation is that seawater infiltrates to some extent into onshore sand groundwater, while the fresh water within the submarine Kurkar can be traced up to 40 m offshore. This implies that while fresh water mainly discharges from the Kurkar unit, seawater recycling is limited to the loose sand, and that the discharge from sand‐covered areas is a mixture of Kurkar water with recycled seawater. Advection rates from the bay floor were calculated from Rn time series and found to vary between 0 and 36 cm/d, correlating negatively with bay water depth. The average flux was 8.1 cm/d, and it did not seem to change much during March, May, and July 2006. The average amount of fresh water discharging to the bay was 5.0 m3/d per meter of shoreline. Radon activity in the sand groundwater also fluctuates due to influx of Kurkar‐type groundwater.
Light absorption by soluble chemical species in Arctic and Antarctic snow
Authors: Anastasio Cort , Robles Tony
Published: December 2007

Using a liquid core waveguide spectrophotometer we have quantified the very low light absorption of dissolved chromophores (light absorbing trace species) in filtered samples of melted polar snows. Light absorption coefficients at 280 nm span the ranges of 0.005–0.029 m−1 and 0.002–0.027 m−1 for samples from Summit, Greenland, and Dome C, Antarctica, respectively. Absorption coefficients decrease with increasing wavelength and also decrease with depth in the snowpack. At both sites, NO3− and H2O2 together account for approximately half of the summed light absorption coefficients for wavelengths of 280 nm and above; the remaining ∼50% of light absorption is due to unknown, probably organic, chromophores. Rates of sunlight absorption by soluble chromophores in surface snows are approximately (1–4) × 1011 and (0.5–9) × 1011 photons cm−3 s−1 during summer at Summit and Dome C, respectively. Approximately 50–90% of this sunlight absorption is due to unknown chromophores, while the remainder is due to hydrogen peroxide and nitrate. Although we do not know quantum yields for the photochemical reactions of the unknown chromophores, their large contribution to the rate of sunlight absorption suggests that they play an important role in the photochemistry of polar snowpacks. In addition, at Summit it appears that up to 60% of the unknown chromophores are emitted from the snow into the boundary layer during the day and redeposited at night. This flux might affect the composition and chemistry of both the snowpack and boundary layer.
Regional probabilistic climate forecasts from a multithousand, multimodel ensemble of simulations
Authors: Piani C. , Sanderson B. , Giorgi F. , Frame D. J. , Christensen C. , Allen M. R.
Published: December 2007

A methodology for constraining climate forecasts, developed for application to the multithousand member perturbed physics ensemble of simulations completed by the distributed computing project ClimatePrediction.net, is here presented in detail. The methodology is extended to produce constrained forecasts of mean surface temperature and precipitation within 21 land‐based regions and is validated with climate simulations from other models available from the IPCC (AR4) data set. The mean forecasted values of temperature and precipitation largely confirm prior results for the same regions. In particular, precipitation in the Mediterranean basin is shown to decrease and temperature over northern Europe is shown to increase with comparatively little uncertainty in the forecast (i.e., with tight constraints). However, in some cases the forecasts show large uncertainty, and there are a few cases where the forecasts cannot be constrained at all. These results illustrate the effectiveness of the methodology and its applicability to regional climate variables.
Influence of disturbance on carbon exchange in a permafrost collapse and adjacent burned forest
Authors: Myers‐Smith Isla H. , McGuire A. David , Harden Jennifer W. , Chapin F. Stuart
Published: December 2007

We measured CO2 and CH4 exchange from the center of a Sphagnum‐dominated permafrost collapse, through an aquatic moat, and into a recently burned black spruce forest on the Tanana River floodplain in interior Alaska. In the anomalously dry growing season of 2004, both the collapse and the surrounding burned area were net sinks for CO2, with a mean daytime net ecosystem exchange of −1.4 μmol CO2 m−2 s−1, while the moat was a CH4 source with a mean flux of 0.013 μmol CH4 m−2 s−1. Regression analyses identified temperature as the dominant factor affecting intragrowing season variation in CO2 exchange and soil moisture as the primary control influencing CH4 emissions. CH4 emissions during the wettest portion of the growing season were four times higher than during the driest periods. If temperatures continue to warm, peatland vegetation will likely expand with permafrost degradation, resulting in greater carbon accumulation and methane emissions for the landscape as a whole.
Changes in the alpine forest‐tundra ecotone commensurate with recent warming in southcentral Alaska: Evidence from orthophotos and field plots
Authors: Dial Roman J. , Berg Edward E. , Timm Katriina , McMahon Alissa , Geck Jason
Published: December 2007

The complex response of the forest‐tundra ecotone (FT) to climate change may not generalize well geographically. We document FT changes in a nonpermafrost region of southcentral Alaska during a known warming period. Using 1951 and 1996 orthophotos overlain on digital elevation models across 800 km2 of the west Kenai Mountains, we identified cover classes and topography for 978 random points and the highest closed‐canopy conifer patches along 205 random altitudinal gradients. Results show 29% of FT area increased in woodiness, with closed‐canopy forest expanding 14%/decade and shrubs 4%/decade; unvegetated areas decreased 17.4%/decade and tundra 5%/decade. Area of open woodland remained constant but changed location. Timberline, estimated using both the 205 altitudinal gradients and the upper quartile elevations of closed‐canopy forest among the 978 points, rose very little. Tree line, identified using upper quartiles of open woodland, rose ∼50 m on cool, northerly aspects, but not on other aspects. Dendrochronology on high‐elevation seedlings showed a congruence between decadal recruitment and regional changes in climate from 1945 to 2005. Patterns observed in the climatic FT of the Kenai Mountains corroborate other studies that show regional and landscape specificity of the structural response of FT to climate change. FT shifted upwards on cooler, presumably more mesic aspects near seed sources; however, on warm aspects the density of shrubs and trees increased, but FT did not rise. If current conditions continue for the next 50–100 years, the Kenai FT will markedly change to a far woodier landscape with less tundra and more closed‐canopy forest.
Experimental verification of radio frequency interference mitigation with a focal plane array feed
Authors: Nagel James R. , Warnick Karl F. , Jeffs Brian D. , Fisher J. Richard , Bradley Richard
Published: December 2007

We demonstrate the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane array of electrically small elements. The array consists of a seven‐element hexagonal arrangement of thickened dipole antennas with 1600 MHz designed center frequency backed by a circular ground plane at the focal plane of a 3 m parabolic reflector. Rooftop‐mounted signal sources were used to simulate a weak signal of interest at boresight and a strong, broadband interferer in the reflector sidelobes. Using an adaptive beamformer, the amplitude of the interfering signal was reduced sufficiently to recover the signal of interest. For an interference to noise ratio of 15 dB as measured at the center array element, the interferer was suppressed to the level of the fluctuations of the 10‐s integrated noise floor (the minimum detectable signal level was interference‐limited and no longer decreased after 10 s integration). Similar cancellation performance was demonstrated for a nonstationary interferer moving at an angular velocity of 0.1° per second. Pattern rumble due to beamformer adaptation was observed and quantified. For a moving RFI source, the degree of pattern rumble was found to be unacceptably large in terms of its effects on the maximum stable integration time and receiver sensitivity. An array feed with more elements together with specialized signal processing algorithms designed to suppress pattern rumble will likely be required in order to use adaptive spatial filtering for astronomical observations.
A method for detecting ionospheric disturbances and estimating their propagation speed and direction using a large GPS network
Authors: Garrison James L. , Lee See‐Chen G. , Haase Jennifer S. , Calais Eric
Published: December 2007

A technique is developed for detecting short period (3–10 min) ionospheric disturbances and estimating their propagation speed and direction using data from a large GPS network (a hundred or more receivers). This method increases the signal‐to‐noise ratio of small signals and could be applied, autonomously, to process a large set of data for the study of the potential signal sources and statistical distributions of these disturbances. The integral electron content (IEC) for every satellite‐station pair in the network is extracted from dual frequency phase data. These IEC time series are then band‐pass‐filtered and cross‐correlated with each other. The resulting correlation power is an indication of the presence of a common disturbance recorded at the two stations, and the delay to the maximum correlation is a measurement of the propagation time between the ionospheric pierce points of the respective stations. A threshold on correlation power is used to select a subset of these delay measurements. The velocity of the detected perturbation is then estimated by fitting a two‐dimensional plane wave model to this subset of measurements. A technique is developed to remove the effects of time‐varying satellite motion and to reconstruct the waveform that would have been observed at a fixed point within the ionosphere. Consistency of the resulting velocity estimates is checked using a stacking‐alignment method and a time‐distance mapping that accounts for the motion of the GPS satellites. The sensitivity of the velocity estimate to both the assumed height of a thin‐layer ionosphere and the detection threshold value is studied. A simulation is used to demonstrate the IEC waveform distortion due to satellite motion, and an example is shown in which this distortion is able to shift the dominant frequencies of an actual disturbance outside of the passband of the filter, thereby preventing detection. Four weeks of data, in different seasons, collected using the Southern California Integrated GPS Network (SCIGN), were processed. Over the total of 28 days, 127 significant disturbances were detected, most with horizontal propagation speeds between 50–1000 m/s and westward directions of propagation. A few cases with exceptionally high speed (>2000 m/s) were observed. It is hypothesized that these are manifestations of disturbances that occur simultaneously throughout the ionosphere, rather than traveling waves. The rate of occurrence of disturbances in the 3–10 min band was found to be larger than expected. Observational biases of this method are discussed.
Inner stationary phase point contribution of physical optic in terms of the modified edge representation line integrals (curved surfaces)
Authors: Rodriguez Luis , Yukimasa Koji , Shijo Tetsu , Ando Makoto
Published: December 2007

The unique concept of the modified edge representation (MER) was proposed for the surface to the line integral reduction of the physical optic (PO). The equivalence between the MER line and the PO surface integration was analytically derived by using the Stokes theorem relations as well as asymptotic treatments, for the smooth scattering surfaces without inner stationary phase points (SPP). Later on, for the planar surface, the MER line integration around the inner SPP was investigated, and it was identified as the scattering geometrical optics (SGO). In this paper, findings related with the MER line integration around the inner SPP are extended to curved surfaces. The accuracy and the applicability of the SGO extraction in terms of the MER line integration are numerically investigated for different radii of curvatures of the scattering surfaces. Authors introduce a geometrical criterion for the applicability of the method. The MER line integration provides an alternative way to the stationary phase method or the classical geometrical optics for calculating SGO. In addition, this numerical result indirectly identifies the entity of the MER line integration along the periphery of the scattering illuminated region, irrespective of the position of observer, as not other than diffraction.
A high‐sensitivity laboratory system for measuring the microwave properties of gases under simulated conditions for planetary atmospheres
Authors: Hanley Thomas R. , Steffes Paul G.
Published: December 2007

A system for measuring the microwave properties of gases under simulated conditions for planetary atmospheres has been under continuous development at Georgia Tech for over 2 decades (see, e.g., DeBoer and Steffes, 1996). The measurements from this system form the basis for accurately modeling the microwave properties of gases under various planetary conditions, which are essential in determining the presence and concentration of such gases through various microwave remote sensing techniques. This system consists of two independent configurations, one capable of measuring gas mixtures up to pressures of 3 bars at frequencies from 22 to 40 GHz, and another capable of pressures up to 12 bars over the frequency range from 1.5 to 24.1 GHz. The former configuration exhibits maximum 2‐σ sensitivities in absorptivity of 0.25 dB/km and in refractivity of 2.0, while the latter configuration exhibits maximum 2‐σ sensitivities in absorptivity ranging from 0.01 dB/km at 1.5 GHz (20 cm) to 1.0 dB/km at 24.1 GHz (1.25 cm) and in refractivity from 0.05 at 1.5 GHz to 3.13 at 24.1 GHz.
A comparison of CADI‐inferred F region plasma convection and DMSP ion drift above Resolute Bay
Authors: Koustov A. V. , MacDougall J. W. , Kadochnikov G. E.
Published: December 2007

CADI ionosonde estimates of the F region plasma convection over Resolute Bay (NWT, Canada, MLAT = 83.5°) are compared with nearly simultaneous ion drift measurements on board DMSP satellites passing in the vicinity of the station. First, CADI vectors are projected onto the cross‐track directions of DMSPs for 141 events and compared with ion drifts measured by DMSPs in these directions. The best linear fit line is found to have a slope of 0.75 and a shift of −13 m/s indicating good correspondence between the instruments with CADI showing minor underestimation. Then, a fully two‐dimensional comparison is performed by considering (1) magnitudes and azimuths and (2) eastward and northward components of the CADI and DMSP vectors. Reasonable agreement is shown as well. For both comparisons, the data spread is small; the correlation coefficients are of the order of 0.7–0.8. The strongest differences between the instruments were found to occur for the periods with spotty enhancement of the plasma flow detected by one or both instruments.
Measurement of interfacial area per volume for drainage and imbibition
Authors: Chen Daiquan , Pyrak‐Nolte Laura J. , Griffin Jessica , Giordano Nicholas J.
Published: December 2007

We investigate experimentally the functional relationship between capillary pressure, Pc, wetting phase saturation, Sw, and interfacial area per volume between the wetting and nonwetting phases, awn, for drainage and imbibition processes in micromodels of two‐dimensional pore structures. Within the experimental and analysis error (around 10–15%), the resulting Pc‐Sw‐awn surfaces were the same. This suggests that data obtained from either the drainage process or the imbibition process are sufficient to generate the complete functional relationship among Pc‐Sw‐awn and that the observed hysteresis in Pc‐Sw‐awn can be modeled by including interfacial area as an additional state variable.
Attenuation of inflammation and cytokine production in rat colitis by a novel selective inhibitor of leukotriene A4 hydrolase
Authors: Whittle B J R , Varga C , Berko A , Horvath K , Posa A , Riley J P , Lundeen K A , Fourie A M , Dunford P J
Published: December 2007

Background and purpose:

Leukotriene B4 (LTB4), formed by the sequential actions of the 5‐lipoxygenase (5‐LO) and leukotriene A4 hydrolase (LTA4H), is a pro‐inflammatory mediator implicated in the pathogenesis of inflammatory bowel disease. However, inhibitors of 5‐LO have not proved to be consistent in their therapeutic efficacy in colitis. Another approach to inhibiting LTB4 synthesis is through the use of inhibitors of LTA4H, such as the novel, potent and selective compound, JNJ 26993135.

Experimental approach:

The effect of oral administration of JNJ 26993135 has been evaluated in a rat model of colitis provoked by colonic instillation of trinitrobenzenesulphonic acid (TNBS). The extent and severity of the macroscopic inflammatory response, the colonic levels of myeloperoxidase (MPO) and LTB4 and of the pro‐inflammatory cytokines, tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) were measured.

Key results:

Oral administration of JNJ 26993135 (5, 15 and 30 mg kg−1, twice a day) dose‐dependently reduced both the extent and intensity of the colonic inflammatory damage observed 3 days after TNBS challenge. JNJ 26993135 also dose‐dependently reduced the elevated colonic levels of LTB4, as well as the inflammatory biomarkers, MPO, IL‐6 and TNF‐α. This dosing regimen was supported by the pharmacokinetic profile of JNJ 26993135, along with the demonstration of the inhibition of ex vivo production of LTB4 in whole blood following oral administration.

Conclusions and implications:

These results with JNJ 26993135 in the rat TNBS model support the role of LTB4 in colitis and the potential value of targeting LTA4H for the treatment of inflammatory bowel diseases.

British Journal of Pharmacology (2008) 153, 983–991; doi:10.1038/sj.bjp.0707645; published online 24 December 2007
Rimonabant (SR141716) exerts anti‐proliferative and immunomodulatory effects in human peripheral blood mononuclear cells
Authors: Malfitano A M , Laezza C , Pisanti S , Gazzerro P , Bifulco M
Published: December 2007

Background and purpose:

Rimonabant (SR141716) is the first selective cannabinoid receptor CB1antagonist described. Along with its anti‐obesity action, emerging findings show potential anti‐proliferative and anti‐inflammatory action of SR141716 in severalin vitroandin vivomodels. In this study we have investigated the anti‐proliferative and immunomodulatory effects of SR141716 in human peripheral blood mononuclear cells (PBMCs).

Experimental approach:

We have evaluatedin vitrothe effect of SR141716 in human PBMCs stimulated with different mitogens. Cell proliferation was assessed by3H‐thymidine incorporation. Cell cycle, cell death and apoptosis were analysed by flow cytometry. Protein expression was investigated by Western blot.

Key results:

SR141716 significantly inhibited the proliferative response of PBMCs and this effect was accompanied by block of G1/S phase of the cell cycle without induction of apoptosis and cell death. SR141716 used in combination with 2‐methyl‐arachidonyl‐2′‐fluoro‐ethylamide (Met‐F‐AEA), a stable analogue of the endogenous cannabinoid anandamide, showed synergism rather than antagonism of the inhibition of cell proliferation. The immunomodulatory effects of SR141716 were associated with increased expression of IκB, phosphorylated AKT (p‐AKT) and decreased expression of NF‐κB, p‐IκB, p‐ERK, COX‐2 and iNOS.

Conclusions and implications:

Our findings suggest SR141716 is a novel immunomodulatory drug with anti‐inflammatory properties.

British Journal of Pharmacology(2008)153, 1003–1010; doi:10.1038/sj.bjp.0707651; published online 24 December 2007
Tuning LDA+U for electron localization and structure at oxygen vacancies in ceria
Authors: Castleton C. W. M. , Kullgren J. , Hermansson K.
Published: December 2007

We examine the real space structure and the electronic structure (particularly Ce4f electron localization) of oxygen vacancies in CeO2 (ceria) as a function of U in density functional theory studies with the rotationally invariant forms of the LDA+U and GGA+U functionals. The four nearest neighbor Ce ions always relax outwards, with those not carrying localized Ce4f charge moving furthest. Several quantification schemes show that the charge starts to become localized at U≈3eV and that the degree of localization reaches a maximum at ∼6eV for LDA+U or at ∼5.5eV for GGA+U. For higher U it decreases rapidly as charge is transferred onto second neighbor O ions and beyond. The localization is never into atomic corelike states; at maximum localization about 80–90% of the Ce4f charge is located on the two nearest neighboring Ce ions. However, if we look at the total atomic charge we find that the two ions only make a net gain of (0.2–0.4)e each, so localization is actually very incomplete, with localization of Ce4f electrons coming at the expense of moving other electrons off the Ce ions. We have also revisited some properties of defect-free ceria and find that with LDA+U the crystal structure is actually best described with U=3–4eV, while the experimental band structure is obtained with U=7–8eV. (For GGA+U the lattice parameters worsen for U>0eV, but the band structure is similar to LDA+U.) The best overall choice is U≈6eV with LDA+U and ≈5.5eV for GGA+U, since the localization is most important, but a consistent choice for both CeO2 and Ce2O3, with and without vacancies, is hard to find.
Stability of small Pdn (n=1–7) clusters on the basis of structural and electronic properties: A density functional approach
Authors: Kalita Bulumoni , Deka Ramesh C.
Published: December 2007

Density functional calculations within the generalized gradient approximation have been used to investigate the lowest energy electronic and geometric structures of neutral, cationic, and anionic Pdn (n=1–7) clusters in the gas phase. In this study, we have examined three different spin multiplicities (M=1, 3, and 5) for different possible structural isomers of each neutral cluster. The calculated lowest energy structures of the neutral clusters are found to have multiplicities, M=1 for Pd1, Pd3, Pd5, Pd6, and Pd7, while M=3 for Pd2 and Pd4. We have also determined the lowest energy states of cationic and anionic Pdn (n=1–7) clusters, formed from the most stable neutral clusters, in three spin multiplicities (M=2, 4, and 6). Bond length, coordination number, binding energy, fragmentation energy, bond dissociation energy, ionization potential, electron affinity, chemical hardness, and electric dipole moment of the optimized clusters are compared with experimental and other theoretical results available in the literature. Based on these criteria, we predict the four-atom palladium cluster to be a magic-number cluster.
Helix formation inside a nanotube: Possible influence of backbone-water hydrogen bonding by the confining surface through modulation of water activity
Authors: Zhou Huan-Xiang
Published: December 2007

Recent molecular dynamics simulations of Sorin and Pande [J. Am. Chem. Soc. 128, 6316 (2006)] in explicit solvent found that helix formation of an alanine peptide is disfavored inside a nanotube relative to that in bulk solution. Here, we present a theory to quantitatively rationalize their simulation results. The basic idea is that the nonpolar inner surface of the nanotube creates a depletion layer and raises the activity of the confined water. The raised water activity, in turn, stabilizes the coil state through hydrogen bonding with the backbone amides and carbonyls. We account for the influence of water activity on helix formation within the Lifson-Roig theory. With physically reasonable parameters, the dependence of the helical content on the diameter of the nanotube obtained in the simulations is well reproduced.
Supersonic molecular beam studies of dissociative adsorption of H2 on Ru(0001)
Authors: Groot I. M. N. , Ueta H. , van der Niet M. J. T. C. , Kleyn A. W. , Juurlink L. B. F.
Published: December 2007

We examined reactivity of H2 on Ru(0001) using molecular beam techniques and we compared our results to experimental results for similar systems. The dissociative adsorption of H2 on Ru(0001) is similar to that on Pt(111) and Ni(111), although on ruthenium nonactivated adsorption is strongly suggested. However, we find no clear signature of a steering- or precursor-based mechanism that favors nonactivated reaction paths at low kinetic energy. In comparison to Pd(111) and Rh(111) our results indicate that a universal mechanism enhancing reactivity at low energy does not have a mass dependence. In addition, we have compared our results to predictions of reactivity for H2 on Ru(0001) from six-dimensional dynamical calculations using two different generalized gradient approximation functionals. It leads us to conclude that the PW91 functional yields a more accurate value for the minimum energy path but does not impose enough corrugation in the potential. The revised-Perdew-Burke-Ernzerhof (RPBE) functional appears to behave slightly better at higher energies, but we find significant quantitative disagreement. We show that the difference is not due to different energy resolutions between experiment and theory. However, it may be due to a dependence of the reactivity on rotational state or on omission of relevant dimensions in the theoretical description.
Growth-related properties and postgrowth phenomena in organic molecular thin films
Authors: Campione M. , Borghesi A. , Laicini M. , Sassella A. , Goletti C. , Bussetti G. , Chiaradia P.
Published: December 2007

The problem of monitoring the structural and morphological evolutions of thin films of organic molecular materials during their growth by organic molecular beam epitaxy and in the postgrowth stage is addressed here by a combination of in situ optical reflectance anisotropy measurements, ex situ optical and morphological investigations, and theoretical simulation of the material optical response. For α-quaterthiophene, a representative material in the class of organic molecular semiconductors, the results show that molecules crystallize in the first stage of growth in metastable structures, even when deposition is carried out at room temperature. In the postdeposition stage, the film structure evolves within a few days to the known equilibrium structure of the low temperature polymorph. When deposition is carried out at low substrate temperatures, an evolution of the film morphology is also demonstrated.
Efficient GeV ion generation by ultraintense circularly polarized laser pulse
Authors: Zhang Xiaomei , Shen Baifei , Li Xuemei , Jin Zhangying , Wang Fengchao , Wen Meng
Published: December 2007

The interaction of an ultraintense circularly polarized laser pulse and a solid target is studied by one-dimensional particle-in-cell simulations. Ions at the front of the target are reflected by a moving quasisteady electrostatic field and obtain a relativistic velocity. At a laser intensity of 1022W∕cm2, almost half of the laser energy is transferred to ions and GeV ions are obtained. Effects of laser polarization state and target thickness on the laser energy conversion are investigated. It is found that a circularly polarized laser pulse can accelerate ions more efficiently than a linearly polarized laser pulse at the same laser and target parameters. A monoenergetic ion bunch is obtained for the ultrathin target, which is accelerated as a single entity.
Raman and electron microscopic studies of Si1−xGex alloy nanowires grown by chemical vapor deposition
Authors: Kawashima Takahiro , Imamura Goh , Fujii Minoru , Hayashi Shinji , Saitoh Tohru , Komori Kazunori
Published: December 2007

Si 1 − x Ge x alloy nanowires (SiGeNWs) were grown by Au-catalyzed chemical vapor deposition and studied by Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS) in TEM (TEM-EDS). The relationship between the growth parameters and the structure of the SiGeNWs was clarified by systematically changing the growth conditions over a wide range. Raman and TEM-EDS results demonstrated that the SiGeNWs consist of a lower Ge composition core and a higher Ge composition shell epitaxially grown on the surface of the core. The effects of oxidation on the structure of the SiGeNWs were studied. It was found that oxidation leads to segregation of the Ge atoms at the interface between the SiGeNWs and SiO2, which in turn results in a large inhomogeneity in Ge composition. Oxidation at a very low rate in a diluted oxygen gas atmosphere is required to avoid the formation of Ge particles and minimize the inhomogeneity.
The ion-optical prototype of the low energy neutral atom sensor of the Interstellar Boundary Explorer Mission (IBEX)
Authors: Wieser M. , Wurz P. , Moebius E. , Fuselier S. A. , Hertzberg E. , McComas D. J.
Published: December 2007

The direct measurement of the energetic neutral atoms originating from the heliospheric termination shock and beyond as well as neutral interstellar gas penetrating into the heliosphere requires a very sensitive neutral particle imaging instrument in the energy range of 10–1000eV. We present the development of the prototype of the low energy sensor for the Interstellar Boundary Explorer (IBEX) mission: IBEX-Lo is a neutral particle mass spectrometer dedicated to the measurement of energetic neutral atoms in this energy range. The response of the sensor to incident neutral hydrogen, helium, and oxygen atoms is discussed as well as the properties of the sensor’s ion optics, the neutral-to-negative conversion surfaces, and other instrumental parameters.
Linear analysis of generalized turbulent hyperbolic flow in a rotating frame
Authors: Langer C. A. , Akylas E. , Kassinos S. C.
Published: December 2007

We apply inviscid rapid distortion theory to the generalized case of turbulent hyperbolic flow in a rotating frame and investigate the dependence of the evolution of the turbulent kinetic energy on the frame rotation rate. We derive an analytical two-dimensional solution which allows for an accurate approximation of the three-dimensional initially isotropic problem. From the analytical solutions we determine a new generalized stability criterion for the evolution of the turbulent kinetic energy in this class of flows.
A differential effective medium model for piezoelectret foams
Authors: Haberman Michael R. , Berthelot Yves H.
Published: December 2007

Polymer foams with piezoelectric properties, called piezoelectrets, have recently gained interest in the acoustics and scientific community. These foams are heterogeneous materials consisting of a continuous polymer containing electrically polarized elliptical voids. The macroscopically observable piezoelectric behavior results from the unique combination of the high void-polymer elastic contrast and the void polarization. Existing modeling methods to approximate the macroscopic piezoelectric properties of these foams are elementary one-dimensional noncoupled electrostatic models. In this study, a coupled mean field microelectromechanical model has been developed as a predictive tool of the macroscopically observed piezoelectric material behavior. This technique employs Green’s function solutions of the three-dimensional (3D) stress equilibrium equations and Gauss’ Law. The result is a multiscale differential effective medium model approximating the 3D effective stiffness, dielectric permittivity, and piezoelectric coupling coefficients as a function of the constituent material properties, void shape and orientation, and deposited charge density. The model is employed to study the sensitivity of macroscopic foam behavior to various constituent material and void variables. This approach improves the approximation of the true piezoelectret behavior by capturing the influence of microscopic material structure and properties on macroscopic piezoelectric performance.
Phase-referenced probe interferometer for biological surface profiling and displacement measurements
Authors: Fang-Yen Christopher , Chu Mark C. , Seung H. Sebastian , Dasari Ramachandra R. , Feld Michael S.
Published: December 2007

We present a probe-based, phase-referenced low coherence interferometer in which the reference field is provided by a fiber end reflection. A gradient-index microlens focuses light onto a sample and collects reflected light. We use the probe interferometer to measure surface profiles of the compound eye of a housefly (Musca domestica) and measure nanometer-scale vibrations in a test sample.
A new approach to the preionization of flash lamps in power lasers
Authors: Samek Stefan , Le Galloudec Bruno , McDaniel William
Published: December 2007

As long as neodymium amplifiers will be used in high-energy lasers, preionization problems will be present in firing the flash lamps. It is difficult to find papers describing technical solutions using preionization concept; only a few internal reports and proceedings from Pulsed Power conferences describe the usage of such circuits in power laser facilities. In all of them, a special negative high voltage power supply is used. A new simple solution, without any additional power supply, using only a small part of the energy gathered in the main capacitor bank for generating a preionization pulse is used. The firing order is split into two signals; the first one is triggering preionization circuit and the second one, after delaying, is triggering the main discharging circuit.
Front propagation and critical gradient transport models
Authors: Garbet X. , Sarazin Y. , Imbeaux F. , Ghendrih P. , Bourdelle C. , Gürcan Ö. D. , Diamond P. H.
Published: December 2007

This paper analyzes the properties of a two-field critical gradient model that couples a heat equation to an evolution equation for the turbulence intensity. It is shown that the dynamics of a perturbation is ballistic or diffusive depending on the shape of the pulse and also on the distance of the temperature gradient to the instability threshold. This dual character appears in the linear response of this model for a wave packet. It is recovered when investigating the nonlinear solutions of this system. Both self-similar diffusive fronts and ballistic fronts are shown to exist. When the propagation is ballistic, it is found that the front velocity is the geometric mean between the turbulent diffusion coefficient and a microinstability growth rate.
Low temperature grown carbon nanotube interconnects using inner shells by chemical mechanical polishing
Authors: Yokoyama Daisuke , Iwasaki Takayuki , Yoshida Tsuyoshi , Kawarada Hiroshi , Sato Shintaro , Hyakushima Takashi , Nihei Mizuhisa , Awano Yuji
Published: December 2007

Vertically aligned multiwalled carbon nanotubes (MWCNTs) were synthesized by remote plasma chemical vapor deposition at a low temperature of 390°C, which meets the requirement of the large scale integration (LSI) process. For wiring application, we measured the electrical properties of MWCNT-via structures with and without chemical mechanical polishing (CMP). The via resistances were reduced using inner shells of MWCNTs whose caps were opened due to CMP. The improved resistance after annealing at 400°C was 0.6Ω for 2μm vias. Our process is suitable for LSI because the temperature never exceeds the allowable temperature of 400°C in the Si LSI process.
A large-area bent crystal shield for deflection of high-energy ions
Authors: Breese M. B. H.
Published: December 2007

A large-area bent crystal shield which is capable of deflecting high-energy ions of all atomic numbers is described. Its effect on the transmitted angular distribution of high-energy ions is characterized using Monte Carlo channeling simulations. Ions up to an energy limit set by the bent crystal curvature radius are deflected by the full bend angle. A shield with a surface area of 1×1cm2 which is capable of deflecting ions with energies up to 100GeV/nucleon has been fabricated in which the lattice planes across the entrance surface are uniformly aligned.
Electron mobility in InGaN channel heterostructure field effect transistor structures with different barriers
Authors: Xie J. , Leach J. H. , Ni X. , Wu M. , Shimada R. , Özgür Ü. , Morkoç H.
Published: December 2007

InGaN possesses higher electron mobility and velocity than GaN, and therefore is expected to lead to relatively better performances for heterostructure field effect transistors (HFETs). However, the reported mobilities for AlGaN∕InGaN HFETs are lower than GaN channel HFETs. To address this issue, we studied the effect of different barriers on the Hall mobility for InGaN channel HFETs grown by metal organic chemical vapor deposition. Unlike the conventional AlGaN barrier, the AlInN barrier can be grown at the same temperature as the InGaN channel layer, alleviating some of the technological roadblocks. Specifically, this avoids possible degradation of the thin InGaN channel during AlGaN growth at high temperatures; and paves the way for better interfaces. An undoped In0.18Al0.82N∕AlN∕In0.04Ga0.96N HFET structure exhibited a μH=820cm2∕Vs, with a ns=2.12×1013cm−2 at room temperature. Moreover, with an In-doped AlGaN barrier, namely, Al0.24In0.01Ga0.75N, grown at 900°C, the μH increased to 1230cm2∕Vs with a ns of 1.09×1013cm−2 for a similar InGaN channel. Furthermore, when the barrier was replaced by Al0.25Ga0.75N grown at 1030°C, μH dropped to 870cm2∕Vs with ns of 1.26×1013cm−2 at room temperature. Our results suggest that to fully realize the potential of the InGaN channel HFETs, AlInN or AlInGaN should be used as the barrier instead of the conventional AlGaN barrier.
Interface electronic structure of the organic light-emitting devices: Photoemission and x-ray absorption studies of Al∕KF∕Alq3 interface
Authors: Lee J. , Lim J. S. , Shin H. J. , Park Y.
Published: December 2007

The chemistry of organic light-emitting diode interface composed of KF sandwiched between the Al and Alq3 was investigated using near-edge x-ray absorption fine structure (NEXAFS) as well as x-ray and ultraviolet photoelectron spectroscopy techniques. At the earliest stages of KF deposition on Alq3, changes in F K-edge NEXAFS spectra indicated a strong chemical reaction, which is responsible for the dipole layer formation seen in valence-band spectra. For Al deposition on KF∕Alq3, the reactions inferred from observed spectral changes are not consistent with the commonly believed KF dissociation and AlF3 formation scenarios.
X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier
Authors: Saito Toshiaki , Katayama Toshikazu , Ishikawa Takayuki , Yamamoto Masafumi , Asakura Daisuke , Koide Tsuneharu
Published: December 2007

We element specifically studied the electronic and magnetic states of epitaxially grown full-Heusler alloy Co2MnSi (CMS) 1.1nm (4 ML) thick ultrathin films facing an epitaxial MgO(001) tunnel barrier by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). In situ reflection high-energy electron-diffraction observations indicated that the CMS films grew into the L21 structure. The observed XAS and XMCD spectra revealed that the CMS ultrathin film was not oxidized. The ratio of Mn and Co spin magnetic moments obtained by applying the sum rules was about 2.7, close to a theoretical value of 2.8 for CMS with the L21 structure.
Effects of plasma surface modification on interfacial behaviors and mechanical properties of carbon nanotube-Al2O3 nanocomposites
Authors: Guo Yan , Cho Hoonsung , Shi Donglu , Lian Jie , Song Yi , Abot Jandro , Poudel Bed , Ren Zhifeng , Wang Lumin , Ewing Rodney C.
Published: December 2007

The effects of plasma surface modification on interfacial behaviors in carbon nanotube (CNT) reinforced alumina (Al2O3) nanocomposites were studied. A unique plasma polymerization method was used to modify the surfaces of CNTs and Al2O3 nanoparticles. The CNT-Al2O3 nanocomposites were processed by both ambient pressure and hot-press sintering. The electron microscopy results showed ultrathin polymer coating on the surfaces of CNTs and Al2O3 nanoparticles. A distinctive stress-strain curve difference related to the structural interfaces and plasma coating was observed from the nanocomposites. The mechanical performance and thermal stability of CNT-Al2O3 nanocomposites were found to be significantly enhanced by the plasma-polymerized coating.
Parametric instabilities of parallel propagating incoherent Alfvén waves in a finite ion beta plasma
Authors: Nariyuki Y. , Hada T. , Tsubouchi K.
Published: December 2007

Large amplitude, low-frequency Alfvén waves constitute one of the most essential elements of magnetohydrodynamic (MHD) turbulence in the fast solar wind. Due to small collisionless dissipation rates, the waves can propagate long distances and efficiently convey such macroscopic quantities as momentum, energy, and helicity. Since loading of such quantities is completed when the waves damp away, it is important to examine how the waves can dissipate in the solar wind. Among various possible dissipation processes of the Alfvén waves, parametric instabilities have been believed to be important. In this paper, we numerically discuss the parametric instabilities of coherent/incoherent Alfvén waves in a finite ion beta plasma using a one-dimensional hybrid (superparticle ions plus an electron massless fluid) simulation, in order to explain local production of sunward propagating Alfvén waves, as suggested by Helios/Ulysses observation results. Parameter studies clarify the dependence of parametric instabilities of coherent/incoherent Alfvén waves on the ion and electron beta ratio. Parametric instabilities of coherent Alfvén waves in a finite ion beta plasma are vastly different from those in the cold ions (i.e., MHD and/or Hall-MHD systems), even if the collisionless damping of the Alfvén waves are neglected. Further, “nonlinearly driven” modulational instability is important for the dissipation of incoherent Alfvén waves in a finite ion beta plasma regardless of their polarization, since the ion kinetic effects let both the right-hand and left-hand polarized waves become unstable to the modulational instability. The present results suggest that, although the antisunward propagating dispersive Alfvén waves are efficiently dissipated through the parametric instabilities in a finite ion beta plasma, these instabilities hardly produce the sunward propagating waves.
Exchange bias in self-organized Nd0.5Sr0.5MnO3 bilayer film
Authors: Hyun Y. H. , Park S. Y. , Lee Y. P. , Prokhorov V. G. , Svetchnikov V. L.
Published: December 2007

The self-organized Nd0.5Sr0.5MnO3 bilayer film with a homogeneous chemical composition and different microstructures has been prepared by rf-magnetron sputtering. The top layer of the film has a columnlike nanostructure while the bottom one forms an epitaxial crystal structure. The magnetic properties of the film mimic the behavior of superparamagnetic particles grown onto the ferromagnetic layer. An exchange-bias effect was observed at a temperature below the blocking one, even in the present ferromagnetic hybrid system.
The effect of spanwise wall oscillation on turbulent pipe flow structures resulting in drag reduction
Authors: Duggleby A. , Ball K. S. , Paul M. R.
Published: December 2007

The results of a comparative analysis based upon a Karhunen–Loève expansion of turbulent pipe flow and drag reduced turbulent pipe flow by spanwise wall oscillation are presented. The turbulent flow is generated by a direct numerical simulation at a Reynolds number Reτ=150. The spanwise wall oscillation is imposed as a velocity boundary condition with an amplitude of A+=20 and a period of T+=50. The wall oscillation results in a 27% mean velocity increase when the flow is driven by a constant pressure gradient. The peaks of the Reynolds stress and root-mean-squared velocities shift away from the wall and the Karhunen–Loève dimension of the turbulent attractor is reduced from 2763 to 1080. The coherent vorticity structures are pushed away from the wall into higher speed flow, causing an increase of their advection speed of 34% as determined by a normal speed locus. This increase in advection speed gives the propagating waves less time to interact with the roll modes. This leads to less energy transfer and a shorter lifespan of the propagating structures, and thus less Reynolds stress production which results in drag reduction.
Tailoring the carrier mobility of semiconductor nanowires by remote dielectrics
Authors: Konar Aniruddha , Jena Debdeep
Published: December 2007

The dielectric environment of thin semiconductor nanowires can affect the charge transport properties inside the wire. In this work, it is shown that Coulomb impurity scattering in thin nanowires can be damped strongly by coating the wire with a high-κ dielectric. This leads to an increase in the mobility of free charges inside the wire and can be used as a post-growth technique to improve the conductivity of thin nanowires.