bluuebunny/crossref_metadata_2025 huggingface dataset:
Methane enrichment in low‐temperature hydrothermal fluids from the Suiyo Seamount in the Izu‐Bonin Arc of the western Pacific Ocean
Authors: Toki Tomohiro , Tsunogai Urumu , Ishibashi Jun‐ichiro , Utsumi Motoo , Gamo Toshitaka
Published: August 2008

The gas geochemistries of high‐temperature and low‐temperature hydrothermal fluids (HTHFs and LTHFs, respectively) were studied for the Suiyo Seamount hydrothermal system (140°39′E, 28°33′N) in the southern Izu‐Bonin (Ogasawara) Arc of the western Pacific Ocean. HTHFs (290 ± 20°C) were collected from four active vents using a gas‐tight fluid sampler, which prevented the loss of volatile components through degassing during sample processing. The end‐member CH4 concentrations were homogeneous across the vent fields. LTHFs were collected from four diffuse flow zones using a funnel, which was deployed on the seafloor with replacement of the seawater inside the funnel by the LTHF. Strong linear relationships were found among the concentrations of CH4, ΣCO2, and Si of the obtained samples, which ensured that the end‐member chemical composition of the LTHFs could be accurately estimated. While the ΣCO2 concentrations of the HTHFs and LTHFs were similar, all four LTHFs showed enrichment of CH4 as compared to the HTHFs. The carbon isotopic composition of CH4 also revealed a significant difference: the LTHFs (δ13C(CH4) = −4.8 ± 0.3‰PDB) showed 13C enrichment, as compared to the HTHFs (δ13C(CH4) = −5.8 ± 0.4‰PDB). The 13C enrichment can be explained by a combination of microbial CH4 production and oxidation after formation of the LTHFs. On the basis of the observed differences in CH4 concentrations and carbon isotopic compositions of the HTHFs and LTHFs, microbial methane oxidation and production are estimated to have comparable impacts. These results support the notion of a subseafloor microbial consortium of methanogens and methanotrophs.
Effects of atmospheric particles from Southern California on the optical properties of seawater
Authors: Stramska Malgorzata , Stramski Dariusz , Cichocka Marta , Cieplak Agnieszka , Woźniak Sławomir B.
Published: August 2008

The role of particles deposited from the atmosphere to the ocean is poorly understood in ocean optics. We examined the light absorption and scattering properties of atmospheric particulate matter, which was collected by dry deposition near the Pacific coastline in La Jolla, Southern California, and then suspended in particle‐free seawater for subsequent laboratory measurements. Within these suspensions, we measured the spectral absorption and beam attenuation coefficients, particle size distribution, and particle mass concentration of atmospheric particles. We also determined the 4‐week average aerosol deposition rates at the experimental site over a period of 9 months. The mass‐specific particle absorption ap*(λ) and scattering bp*(λ) coefficients showed considerable variability among the samples because of the variations in particle size distribution and composition. For example, ap*(440) was on average 0.042 m2 g−1 but exhibited over fivefold range among the samples. At near‐infrared wavelengths (750–800 nm), the magnitude of ap* was significant (>0.02 m2 g−1 for a number of samples) and is likely attributable to the presence of black carbon. The bp*(λ) values were virtually wavelength‐independent because of the significant presence of relatively large particles (>10 μm) in our samples. The magnitude of bp*(λ) varied within a 3.5‐fold range, with an average value of ∼0.27 m2 g−1. Our determinations of absorption and scattering by atmospheric particles coupled with radiative transfer simulations suggest that aerosol deposition may have sizable effect on ocean optical properties, including remote sensing reflectance under certain scenarios of deposition events, residence time of deposited particles within the water column, and particle properties.
Size‐resolved chemical composition of aerosol particles during a monsoonal transition period over the Indian Ocean
Authors: Spencer M. T. , Holecek J. C. , Corrigan C. E. , Ramanathan V. , Prather K. A.
Published: August 2008

An aerosol time‐of‐flight mass spectrometer (ATOFMS) was used to measure the size‐resolved mixing state of particles over the northern Indian Ocean in October and November 2004. This period was chosen to observe the impact of the monsoonal transition on the size, chemistry, sources, and radiative properties of atmospheric aerosols in the region. Overall, elemental carbon with sulfate (EC‐sulfate), biomass/biofuel burning, fresh sea salt (SS), aged sea salt, fly ash, and EC mixed with sea salt were the dominant supermicron particle types, whereas EC‐sulfate, biomass/biofuel burning, and fly ash were the dominant submicron particle types. Interestingly, particles composed mostly of aged organic carbon and nitrate were virtually absent during the campaign. This is possibly from low ozone formation in the region or selective scavenging during transport. Notably, during long‐range transport periods when an aethalometer measured the highest black carbon concentrations, 77% of submicron particles between 0.5 and 2.5 μm and 71% of EC/soot particles contained an intense 39K+ ion (a known tracer for biomass/biofuel combustion). These observations suggest when the air mass originated from India, biofuel combustion represented a significant source of the regional atmospheric brown cloud. The majority (∼80%) of EC and biomass/biofuel burning particles were mixed with significant amounts of sulfate due to extensive secondary processing of these particles during transport. EC mixed with sea salt was also observed suggesting the particles had undergone cloud processing and become internally mixed during transport. These measurements support the use of an internal mixture of sulfate with EC/soot and biomass/biofuel burning in models to accurately calculate radiative forcing by aerosols in this region.
Improved algorithm for MODIS satellite retrievals of aerosol optical depths over western North America
Authors: Drury Easan , Jacob Daniel J. , Wang Jun , Spurr Robert J. D. , Chance Kelly
Published: August 2008

Quantitative evaluation of chemical transport models (CTMs) with aerosol optical depth (AOD) products retrieved from satellite backscattered reflectances can be compromised by inconsistent assumptions of aerosol optical properties and errors in surface reflectance estimates. We present an improved AOD retrieval algorithm for the MODIS satellite instrument using locally derived surface reflectances and CTM aerosol optical properties for the 0.47, 0.65, and 2.13 μm MODIS channels. Assuming negligible atmospheric reflectance at 2.13 μm in cloud‐free conditions, we derive 0.65/2.13 surface reflectance ratios at 1° × 1.25° horizontal resolution for the continental United States in summer 2004 from the subset of top‐of‐atmosphere (TOA) reflectance data with minimal aerosol reflectance. We obtain a mean ratio of 0.57 ± 0.10 for the continental United States, with high values over arid regions and low values over the Midwest prairies. The higher surface reflectance ratios explain the high AOD bias over arid regions found in previous MODIS retrievals. We calculate TOA reflectances for each MODIS scene using local aerosol optical properties from the GEOS‐Chem CTM, and fit these reflectances to the observed MODIS TOA reflectances for a best estimate of AODs for that scene. Comparison with coincident ground‐based (AERONET) AOD observations at 16 sites in the western and central United States in summer 2004 shows poor correlation in the daily data but the correlation improves as averaging time increases. Averaging over the available coincident observations (n = 11–44 days) results in strong correlations (R0.47μm = 0.90, R0.65μm = 0.67) and a 19% low bias, representing considerable improvement over the operational MODIS AOD products in this region.
AGCM experiment of the effect of cumulus suppression on convection center formation over the Bay of Bengal
Authors: Suzuki Tsuneaki , Ninomiya Kozo , Takayabu Yukari N. , Emori Seita
Published: August 2008

We examined the effect of cumulus triggering on the distribution of precipitation during the Indian summer monsoon using the CCSR/NIES/FRCGC atmospheric general circulation model (AGCM) with different cumulus parameterizations. To investigate the effect, we carried out two kinds of simulation. The no‐cumulus‐suppression (NOCS) run used the original AGCM in which we implemented the prognostic Arakawa‐Schubert (AS) scheme. In the other run, we introduced cumulus suppression (CS) as an additional condition of the AS scheme; the CS permitted cumulus convection only when the environmental relative humidity averaged in the modeled cumulus cloud region of the AS scheme exceeded 80%. Special attention was given to the formation of the convection center over the Bay of Bengal (CCBB). The NOCS run could not reproduce the CCBB because the original AS scheme was controlled solely by the convective available potential energy (CAPE). In the CS run, the CS suppressed the unrealistic precipitation simulated in the NOCS run east of the Indian subcontinent (around Sri Lanka) through large‐scale topographical effects and well reproduced the westward propagating disturbances coming from the South China Sea and Indochina Peninsula. The westward propagating disturbances created heavy rain in the Bay of Bengal. As a result, the CS run reproduced the realistic distribution of precipitation during the Indian summer monsoon. The AGCM experiment showed that the triggering of cumulus convection played a key role in the distribution of precipitation in the Indian summer monsoon. For instance, the CS suppressed the unrealistic precipitation east of the Indian subcontinent. In addition, in the CS run, ascending motion orographically produced by the large‐scale horizontal flow triggered cumulus convection around the northeast coast of the Bay of Bengal, and the propagating disturbances brought heavy rainfall to the Bay of Bengal.
The drying of Titan's dunes: Titan's methane hydrology and its impact on atmospheric circulation
Authors: Mitchell Jonathan L.
Published: August 2008

We explore the effect of a finite reservoir of methane on Titan's atmospheric circulation, precipitation patterns, and surface methane content. We develop a soil model that accounts for the methane cycle in the surface‐atmosphere system, and we implement this surface model in a two‐dimensional model of the Titan's atmosphere. Seasonal oscillations in latitude of the large‐scale circulation accomplish net drying of the low‐latitude surface by diverging methane vapor from low latitudes to higher latitudes. Simulations with an initially deep methane reservoir indicate this mechanism is able to dry ∼1.75 meters of liquid methane per Titan year from the low‐latitude surface. The existence of low‐latitude desert morphologies suggests that the system has had sufficient time to completely remove the surface methane by this mechanism. We then varied the reservoir size, focusing on initial depths of 30 meters of liquid methane or less and compared the results to available observations. The climate system has an abrupt transition to a warmer state with less precipitation and nearly global surface drying near the level at which the atmosphere can store the majority of the methane reservoir as vapor or around 6.5 meters of equivalent liquid methane for our particular choice of parameters. A comparison of our model results with Huygens' observations suggests Titan's climate mimics a state in which most of the methane inventory with direct access to the atmosphere (i.e., excluding underground sources) is stored in the atmosphere.
Distribution of the ices exposed near the south pole of Mars using Thermal Emission Imaging System (THEMIS) temperature measurements
Authors: Piqueux Sylvain , Edwards Christopher S. , Christensen Philip R.
Published: August 2008

Understanding the present and past water cycle on Mars requires an accurate knowledge of the distribution and amount of H2O available near the surface. In this article, we present a map of the distribution of the surface material exposed between 87°S and 70°S in the summer (e.g., CO2 and H2O ices, dust) based on temperature measurements made by Thermal Emission Imaging System (THEMIS). Our compositional map (100 m per pixel) is in good agreement with spectral mapping returned by Observatoire pour la minéralogie, l'Eau, la Glace et l'activité (OMEGA) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Exposed water ice covers a total surface area of approximately 40,000 km2. A large fraction of the water ice is exposed at the periphery of the CO2 cap. An approximately 25,000‐km2 large patch centered at 83.5°S and 345°E is discovered and represents the largest exposure of water ice in the southern hemisphere. It is not located on the south polar layered deposits but on the surrounding mantled terrains. THEMIS VIS, MOC and HiRISE images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust. Polygonal patterns are observed on the water ice but not exclusively. There is a strong correlation between the surface albedo, the composition of the exposed material, and the timing of the initial seasonal CO2 frost deposition and final removal. These exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere. The spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal CO2 frost, indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere. As water ice is not stable, it may indicate the past location of part of the CO2 perennial cap that has been eroded.
Lagrangian Analysis and Prediction of Coastal Ocean Dynamics
Authors: Malek‐Madani Reza
Published: August 2008

The basic governing equations of geophysical fluid dynamics have been known for many years, but how meaningful these equations are to our understanding of coastal and open oceans depends crucially on the accuracy of constitutive equations that relate the internal and external forces acting on these bodies of water. Field measurements, whether Eulerian or Lagrangian, have played and continue to play a central role in two important aspects of geophysical fluid dynamics. First, the data collected often point to the presence of various stable and coherent structures, eddies, or streams, whose study naturally becomes the focus of analytical and computational efforts. Second, the availability of good data serves to calibrate how the response of bodies of water to forces should be modeled. This book provides a substantial collection of well‐ written articles on how Lagrangian data are collected, analyzed, and eventually assimilated into models.
Hysteresis of the self‐potential response associated with harmonic pumping tests
Authors: Revil A. , Gevaudan C. , Lu N. , Maineult A.
Published: August 2008

Harmonic pumping tests performed in an unconfined aquifer are responsible for a non‐linear and phase shifted behavior of the self‐potential response recorded at the ground surface with respect to the change in the pressure heads of the aquifer. The observed non‐linearity of the transfer function can be reproduced with a petrophysical model in which the permeability, the capillary pressure curve, and the streaming potential coupling coefficient are modelled inside a unified framework approach based on the van Genuchten parametrization including a hysteretic behaviour with the water saturation. The field equations for the hydraulic heads and the self‐potential signals are solved with a finite‐element code, which is used to compute the time variation of the self‐potential variations over time for two numerical experiments accounting or not for hysteresis. Only the model with hysteresis can reproduce the field observations.
Observations of aurorae by SPICAM ultraviolet spectrograph on board Mars Express: Simultaneous ASPERA‐3 and MARSIS measurements
Authors: Leblanc F. , Witasse O. , Lilensten J. , Frahm R. A. , Safaenili Ali , Brain D. A. , Mouginot J. , Nilsson H. , Futaana Y. , Halekas J. , Holmström M. , Bertaux J. L. , Winningham J. D. , Kofman W. , Lundin R.
Published: August 2008

We present a new set of observations of Martian aurorae obtained by Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) on board Mars Express (MEX). Using nadir viewing, several auroral events have been identified on the Martian nightside, all near regions of crustal magnetic fields. For most of these events, two to three consecutive events with variable intensities and separated by a few seconds to several tens of seconds have been observed, whereas simultaneous observations with Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and Analyzer of Space Plasma and Energetic Atoms (ASPERA‐3) have been possible. In this paper, we present the data set for these events and discuss the possible correlation between the measured UV emission by SPICAM, the measured downward and/or upward flux of electrons by ASPERA‐3 and the total electron content recorded by MARSIS. Despite the limited coverage of SPICAM ultraviolet spectrograph (UVS) on the Martian nightside (essentially in regions of high crustal magnetic fields), there is however a very good correlation between the regions with the locally smallest probability to be on closed crustal magnetic field lines, as derived from Mars Global Surveyor/Electron Reflectometer (MGS/MAG‐ER), and the position of an aurora event. This suggests that the crustal magnetic fields, when organized into cusp‐like structure, can trigger the few aurorae identified by SPICAM UVS. It confirms also the good probability, in the cases where SPICAM UVS measured UV emissions, that the increase in the measured total electron content by MARSIS and the simultaneous measured precipitating electron flux by the ASPERA‐3/Electron Spectrometer may be related to each other.
On the Earth's magnetospheric dynamics: Nonequilibrium evolution and the fluctuation theorem
Authors: Consolini Giuseppe , De Michelis Paola , Tozzi Roberta
Published: August 2008

The Earth's magnetosphere evolves as an out‐of‐equilibrium system due to the continuous coupling with the solar wind and the Earth's ionosphere. We test the validity of the symmetries implied in the Fluctuation Theorem for the magnetospheric dynamics by investigating the long‐term evolution of the Earth's magnetospheric ring current, as monitored by the geomagnetic Dst index. We find that the symmetries implied by the Fluctuation Theorem are all verified, thus providing a proof of the existence of a steady state far from equilibrium for the Earth's magnetosphere. A possible link between the Dst index and the entropy production rate is also proposed and discussed.
Medium‐ to large‐scale density variability as observed by CHAMP
Authors: Bruinsma Sean L. , Forbes Jeffrey M.
Published: August 2008

Atmospheric density accounts for the largest source of error for predicting low‐Earth orbiting satellite positions. Relevant applications include catalog maintenance, collision avoidance, and mission design. In this paper we quantify density model errors due to density variability at submodel grid spatial scales. Densities in the 370–450 km height region inferred from accelerometer measurements on CHAMP between 2001 and 2006 are utilized. Results are presented in terms of root‐mean‐square (RMS) amplitudes of the high‐pass‐filtered density residuals with respect to the trend. RMS one‐sigma amplitudes are found to be on the order of 9% (13%) for low (high) geomagnetic activity and to possess distinct seasonal‐latitudinal and local time patterns. The RMS density amplitude patterns suggest a high‐latitude (i.e., auroral) wave source for many of the density perturbations, dissipation for most waves poleward of 40° latitude, and a preference for penetration to lower latitudes during nighttime and during higher levels of geomagnetic activity and lower levels of solar activity. An unknown fraction of the density variability may also originate from gravity wave sources in the lower atmosphere. The RMS amplitude distributions provide statistical constraints on gravity wave contributions from all sources and in a modeling or theoretical context also help to constrain mean heating and acceleration rates due to wave dissipation. In the context of density model errors, our results can be used to calculate an orbit prediction and attitude dynamics error budget. Other engineering applications such as thruster throttling requirements for a drag‐compensated satellite system are also discussed.
The Incidence Rate of Seizures in Relation to BMI in UK Adults
Authors: Gao Shujun , Juhaeri Juhaeri , Dai Wanju S.
Published: August 2008

A retrospective cohort study using the data from The Health Improvement Network (THIN) database in the United Kingdom was conducted to examine the incidence rates of seizures across different BMI levels in the adult population aged ≥18 years. Poisson regression was used to examine the relationship between BMI and seizures. The overall incidence rate of seizures was found to be 31.2 cases per 100,000 person‐years. The incidence rate of seizures (cases per 100,000 person‐years) in obese patients (BMI ≥ 30 kg/m2) was 34.8 (95% confidence interval (CI), 23.1, 46.4), comparable to that in patients with normal weight (BMI between 18.5 and 24.9 kg/m2) (35.8, 95%CI (26.6, 44.9)). In contrast, underweight patients (<18.5 kg/m2) or extremely obese (≥40 kg/m2) patients tended to have higher incidence rates than those with normal weight. After adjustment for age, gender, and smoking status, compared to patients with normal weight, those who were underweight or extremely obese had a rate ratio (RR) for seizures of 1.6 (95%CI (0.7, 3.8)) and 1.7 (95%CI (0.7, 3.9)), respectively. To date, we have not found any study that examines the associations between BMI or obesity and seizures. In this study, the incidence rates of seizures in the extremely obese and underweight patients tended to be higher than that in the normal‐weight patients.
The Effect of Obesity and Cardiometabolic Risk Factors on Expenditures and Productivity in the United States
Authors: Sullivan Patrick W. , Ghushchyan Vahram , Ben‐Joseph Rami H.
Published: August 2008

Objective: To examine the effect of obesity and cardiometabolic risk factors on medical expenditures and missed work days.

Methods and Procedures: The 2000 and 2002 Medical Expenditure Panel Survey (MEPS), a nationally representative survey of the US population, was used to estimate the marginal effect of obesity (BMI ≥ 30) on annual per‐person medical expenditures and missed work days for patients with diabetes, dyslipidemia, or hypertension using multivariate regression methods controlling for age, sex, race, ethnicity, education, income, insurance, and smoking status. Maximum Likelihood Heckman Selection with Smearing retransformation was used to assess medical expenditures, and Negative Binomial regression was used for missed work days.

Results: Normal weight individuals with diabetes, dyslipidemia, or hypertension had significantly greater medical expenditures than those without the respective condition ($6,006 (5,124–6,887), $4,760 (4,102–5,417), $3,911 (3,345–4,476)) and obesity significantly exacerbated this effect ($7,986 (7,397–8,574), $7,636 (7,072–8,200), $6,197 (5,745–6,649); $2007; all P < 0.05). In addition, diabetes, dyslipidemia, and hypertension resulted in greater missed work days (3.1 (0.94–6.21), 3.2 (0.42–7.91), 1.4 (0.0–3.52)) (all P < 0.05 except hypertension), which resulted in greater lost productivity ($433, $451, $199) and obesity significantly exacerbated the deleterious effect on work days (8.7 (4.44–15.2), 5.5 (2.18–10.5), 4.5 (2.92–6.34)) and lost productivity ($1,217, $763, $622) (all P < 0.05). In addition, medical expenditures increased for increasing weight category and increasing number of risk factors.

Discussion: Obesity significantly exacerbates the deleterious effect of diabetes, dyslipidemia, and hypertension on medical expenditures and productivity loss in the United States. Obesity is preventable and public health efforts need to be undertaken to prevent its alarming increase in order to reduce the incidence and effect of cardiometabolic risk factors.
Adiposity Measures and Oxidative Stress Among Police Officers
Authors: Charles Luenda E. , Burchfiel Cecil M. , Violanti John M. , Fekedulegn Desta , Slaven James E. , Browne Richard W. , Hartley Tara A. , Andrew Michael E.
Published: August 2008

Our objective was to investigate associations between adiposity measures (BMI, waist circumference, waist‐to‐hip ratio, waist‐to‐height ratio, and abdominal height) and biomarkers of oxidative stress (glutathione (GSH), GSH peroxidase (GSH‐Px), vitamin C, thiobarbituric acid reactive substances (TBARS), and trolox equivalent antioxidant capacity (TEAC)) among police officers. This cross‐sectional study included randomly selected police officers (43 policewomen; 67 policemen) from Buffalo, New York. Adiposity measures were performed using standardized methods. Biomarkers were measured on fasting blood specimens. An oxidative stress score (OSS) was created as a composite of the biomarkers. ANOVAs were used to compare mean levels of biomarkers across tertiles of the adiposity measures. Officers were 26‐ to 61‐years old. GSH was inversely associated with waist circumference (trend P = 0.030) and waist‐to‐hip ratio (trend P = 0.026). GSH‐Px was inversely associated with BMI (trend P = 0.004) and with waist‐to‐height ratio (trend P = 0.017). No associations were observed for TEAC, TBARS, or OSS with any adiposity measure. Significant interactions were observed by physical activity status for GSH with waist circumference and waist‐to‐hip ratio and for vitamin C with waist circumference, waist‐to‐hip and waist‐to‐height ratios. The above associations were inversely related only among officers who reported engaging in physical activity. Inverse associations were observed for BMI and waist circumference with GSH, but only among women; the interaction with gender was significant. Larger indices of adiposity were associated with increased levels of oxidative stress and decreased levels of antioxidant defense.
Multistate vibronic interactions in difluorobenzene radical cations. II. Quantum dynamical simulations
Authors: Faraji Shirin , Meyer H.-D. , Köppel Horst
Published: August 2008

The multistate vibronic dynamics in the X̃-D̃ electronic states of all three difluorobenzene radical cations are investigated theoretically by an ab initio quantum dynamical approach. The vibronic coupling scheme and the ab initio values of the system parameters are adopted from Paper I [S. Faraji and H. Köppel, J. Chem. Phys. 129, 074310 (2008)]. Extensive calculations by wave-packet propagation have been performed with the aid of the multiconfiguration time-dependent Hartree method. Five coupled electronic potential energy surfaces and 10 (11 in the case of the orthoisomer) vibrational degrees of freedom have been included in these calculations. The nonadiabatic interactions lead to the restructuring of the photoelectron spectral envelopes. Ultrafast internal conversion processes within the electronic manifolds in question demonstrate the strength of the nonadiabatic coupling effects and complement the analogous findings for the electronic spectra. The internal conversion dynamics is characterized by a stepwise transfer of the electronic population to the lowest electronic state on a time scale of femtoseconds to picoseconds. A difference between the three isomers is found to be related to the weaker interaction between the sets of X̃-Ã and B̃-C̃-D̃ states (with high-energy conical intersections) in the meta isomer, as compared to the other isomers. The implications of these findings for the qualitative understanding of the fluorescence dynamics of fluorinated benzene radical cations are discussed.
Broadband electrically detected magnetic resonance of phosphorus donors in a silicon field-effect transistor
Authors: Willems van Beveren L. H. , Huebl H. , McCamey D. R. , Duty T. , Ferguson A. J. , Clark R. G. , Brandt M. S.
Published: August 2008

We report electrically detected magnetic resonance of phosphorus donors in a silicon field-effect transistor. An on-chip transmission line is used to generate the oscillating magnetic field allowing broadband operation. At millikelvin temperatures, continuous wave spectra were obtained up to 40GHz, using both magnetic field and microwave frequency modulation. The spectra reveal the hyperfine-split electron spin resonances characteristic for Si:P and a central feature which displays the fingerprint of spin-spin scattering in the two-dimensional electron gas.
Evolutions in time and space of laser ablated species by dual-laser photoabsorption spectroscopy
Authors: Ribière M. , Méès L. , Allano D. , Chéron B. G.
Published: August 2008

An atmospheric aluminum laser induced plasma is investigated by means of absorption and emission spectroscopies in the near ultraviolet range. The absorbed radiation is produced by a second aluminum laser induced plasma, which is generated at adjustable time delay. The measurements of both ground and resonant state number densities are derived from the fitting of the experimental 308.21 nm (P21/20−D23/2) and 396.15 nm (P23/20−S21/2) line absorption profiles on the numerical solution of the radiative transfer equation. Owing to the dominant role played by the Stark effect in the line broadening and shifting, the calculation also provides the evolution in time and in space of the free electron density along the line of sight. More classically, the same method is applied to the emission profiles which exhibit strong self-absorbed shapes. The reliability of the results derived from both absorption and emission experiments is analyzed and the origin of the asymmetric shape of the absorption lines is discussed.
Local thermomechanical characterization of phase transitions using band excitation atomic force acoustic microscopy with heated probe
Authors: Jesse S. , Nikiforov M. P. , Germinario L. T. , Kalinin S. V.
Published: August 2008

An approach for thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. We demonstrate a heating protocol which keeps the contact area and contact force constant, thus allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.
Spatial retarding field energy analyzer measurements downstream of a helicon double layer plasma
Authors: Cox W. , Charles C. , Boswell R. W. , Hawkins R.
Published: August 2008

Spatial ion energy measurements using a retarding field energy analyzer are performed in the exhaust of a 0.30mTorr, 250W helicon double layer plasma to investigate the divergence of the argon ion beam formed by acceleration in the double layer. Various divergence angles are computed by considering the radial distribution of beam density; the average beam ion diverging by 9°. The efficiency at which momentum is imparted parallel to the longitudinal axis of the thruster is calculated to be 98%. The results show that a few centimeters downstream of the source, the beam ions do not follow the magnetic field lines.
Type-II behavior in wurtzite InP/InAs/InP core-multishell nanowires
Authors: Pal B. , Goto K. , Ikezawa M. , Masumoto Y. , Mohan P. , Motohisa J. , Fukui T.
Published: August 2008

We study optical transitions from a periodic array of InP/InAs/InP core-multishell nanowires (CMNs) having a wurtzite crystal structure by using photoluminescence (PL) and PL excitation (PLE) spectroscopy. Observing a large Stokes shift between PL and PLE spectra, a blueshift of the PL peak with a cube-root dependence on the excitation power and a slow and nonexponential decay of PL with an effective decay time of 16 ns suggest a type-II band alignment. Band-offset calculation based on the “model-solid theory” of Van de Walle [Phys. Rev. B 39, 1871 (1989)] supports type-II band lineup if the InAs layer in the wurtzite CMNs is assumed to sustain compressive strain in all directions.
Probing OH stretching overtones of CH3OOH through action spectroscopy: Influence of dipole moment dependence on HOOC torsion
Authors: Matthews Jamie , Martínez-Avilés Mónica , Francisco Joseph S. , Sinha Amitabha
Published: August 2008

The OH stretching overtones and OH stretch–HOOC torsion combination bands of methyl hydroperoxide are investigated using action spectroscopy initiated through vibrational state selected photodissociation. Our results for the room temperature spectra covering the 2νOH–5νOH regions suggest that the coarse vibrational structures appearing in the spectra can be understood using a simple two-dimensional vibration-torsion model involving the OH stretch and COOH torsion consistent with what has been previously reported. However, investigation of the jet-cooled spectrum for the 2νOH band along with the results of ab initio calculations using coupled cluster methods reveals that the dependence of the transition dipole moment on the HOOC torsion angle cannot be neglected when simulating intensities of OH stretching overtone bands, as has been suggested by earlier room temperature studies. The present results demonstrate that transitions between torsional levels of different symmetries, which arise from the dependence of the dipole moment μ(r,τ) on the torsional angle, contribute significantly to the intensities of the vibrational overtone bands and are important in interpreting the temperature dependence of the spectral band profiles. Contributions from these transitions are largest for the 2νOH and 3νOH levels and fall off gradually for the higher overtones. In addition, results are presented investigating the orbital interactions in CH3OOH that influence changes in the HOOC adiabatic torsion potential with increased OH stretching excitation.
Methyl group dynamics in glassy, polycrystalline, and liquid coenzyme Q10 studied by quasielastic neutron scattering
Authors: Smuda Christoph , Busch Sebastian , Wagner Bernd , Unruh Tobias
Published: August 2008

The methyl group rotation of coenzyme Q10 confined in nanosized droplets was studied using quasielastic neutron scattering (QENS). Q10 as an oligoisoprene derivative with ten isoprene units can easily be supercooled in nanodroplets. Fixed window scans and QENS spectra at several temperatures of glassy Q10 were recorded to study the methyl group rotation which can be described by a logarithmic Gaussian distribution of hopping rates for temperatures below the glass transition temperature (Tg≈200 K). A mean activation energy of 4.8 kJ/mol with a distribution width of 2.1 kJ/mol was obtained from the evaluation of the QENS spectra. A corresponding analysis of a fixed window scan yielded an average activation energy of 5.1 kJ/mol with a distribution width of 1.8 kJ/mol. The results are compared and discussed with those of chain deuterated polyisoprene-d5. For polycrystalline Q10, the QENS spectra could be described by the same model yielding a similar average activation energy as found for glassy Q10. However, no temperature dependence of the distribution width was observed. Based on the performed low-temperature measurements, the correlation times for the methyl group rotation were extrapolated to temperatures of liquid Q10. The complex dynamics of liquid Q10 could be described by a model yielding an apparent diffusion coefficient, the jump rate of the methyl groups, as well as an overall molecular rotational diffusion coefficient. The correlation times of the methyl group rotation in liquid Q10 at a given temperature T0 coincide with values determined in the glassy phase and extrapolated to T0.
ArF laser-based quantum well intermixing in InGaAs/InGaAsP heterostructures
Authors: Genest Jonathan , Béal Romain , Aimez Vincent , Dubowski Jan J.
Published: August 2008

Radiation from a 193 nm ArF laser was investigated to modify surface properties of InGaAs/InGaAsP quantum well (QW) heterostructures and introduce defects required to enhance intermixing during the annealing process. A top 200 nm thick sacrificial layer of InP served as a reservoir for laser generated defects. The irradiation with up to 90 pulses at 65–150 mJ/cm2 allowed to generate an array of 1.2×1 mm2 sites of QW intermixed material, with bandgap energy blueshifted up to 107 nm. We discuss the mechanism and advantages of this approach for postgrowth wafer level fabrication of multibandgap QW material.
Tunable upconversion photon detector
Authors: Thew R. T. , Zbinden H. , Gisin N.
Published: August 2008

We introduce a simple approach for a tunable upconversion detector. This scheme is relevant for both single photon detection or anywhere where low light levels at telecom wavelengths need to be detected with a high degree of temporal resolution or where high count rates are desired. A system combining a periodically poled lithium niobate waveguide for the nonlinear wavelength conversion and a low jitter silicon avalanche photodiode is used in conjunction with a tunable pump source. We report more than a tenfold increase in the detectable bandwidth using this tuning scheme.
A novel pressure-driven piezodispenser for nanoliter volumes
Authors: McGuire Shawn , Fisher Charles , Holl Mark , Meldrum Deirdre
Published: August 2008

A successful dispensing device has been built for use in biotechnology applications requiring nanoliter volume liquid transfer. Air pressure is used as the primary driving force and is controlled via a high speed miniature solenoid valve as opposed to many existing systems that use a valve in line with constantly pressurized fluid to start and stop the dispensing action. This automated pressure-driven system is used to improve a typical piezodriven microdispenser. The resulting system is much less prone to failures resulting from air entrainment and can dispense much higher viscosity fluids than the microdispenser alone.
The dynamics of single enzyme reactions: A reconsideration of Kramers' model for colored noise processes
Authors: Chaudhury Srabanti , Chatterjee Debarati , Cherayil Binny J.
Published: August 2008

The utility of an approximate heuristic version of Kramers’ theory of reaction rates that was earlier used [Chaudhury and Cherayil, J. Chem. Phys. 125, 024904 (2006)] to successfully describe the nonexponential waiting time distributions of the enzyme β-galactosidase is reassessed. The original model, based on the Smoluchowski equation, is reformulated in terms of the phase space variables of the reaction coordinate, without neglecting inertial contributions. A new derivation of the Fokker–Planck equation (FPE) that describes the dynamics of this coordinate is presented. This derivation, based on functional methods, provides a more direct alternative to the existing distribution function approach used by Hanggi and Mojtabai [Phys. Rev. A 26, 1168 (1982)]. The time-dependent coefficients in the FPE, when incorporated into the exact expression for the transmission coefficient obtained from a reactive-flux formalism [Kohen and Tannor, J. Chem. Phys. 103, 6013 (1995)], are found to yield virtually the same results as the earlier heuristic model.
Enhanced flux pinning and critical currents in YBa2Cu3O7−δ films by nanoparticle surface decoration: Extension to coated conductor templates
Authors: Aytug T. , Paranthaman M. , Leonard K. J. , Kim K. , Ijaduola A. O. , Zhang Y. , Tuncer E. , Thompson J. R. , Christen D. K.
Published: August 2008

Interfacial engineering via nanoparticle substrate surface decoration has been extended to coated conductor templates. Preformed BaTiO3 and BaZrO3 nanoparticles were applied to substrate surfaces, prior to YBa2Cu3O7−δ (YBCO) deposition, by using a scalable and inexpensive technique of solution-based suspension. Compared to untreated reference samples, nanodecoration yields improved in-field critical current density (Jc) as well as strong correlated pinning along the c-axis direction of the YBCO film. Accordingly, a much reduced falloff of Jc with magnetic field strength was observed in all of the modified samples. In addition, scaling behavior of the normalized volume pinning force density (Fp) with respect to temperature provided insight as to the differences in flux pinning mechanisms dependent on the decoration technique. Finally, with these results our earlier proof-of-concept demonstrations on nanoparticle modified single crystal substrates were replicated on technological substrates, pointing to the versatility of this simple technique for realization of enhanced high temperature superconductor performance.
Drift kink instability in the current sheet with a kappa-distribution
Authors: Hu Youjun , Yang Weihong , Chen Yinhua , Huang Feng , Zhang Yu
Published: August 2008

Superthermal particle distributions well-described by the family of κ-distributions have been observed in various astrophysical plasmas. In this paper, the drift kink instability in the current sheet with a κ-distribution is investigated in the framework of linear kinetic theory. The orbit integrals are treated numerically using the exact unperturbed particle orbits, and the resulting eigenvalue problem of the integro-differential equations is solved using the spectral method. The growth rate, eigenmode structure, and parametric dependencies of the kink mode are examined and compared with the case of the standard Harris current sheet. The results show that the drift kink instability in the κ-distribution current sheet resembles its counterpart in the standard Harris sheet, but has a smaller growth rate and real frequency for small value of κ. It is also demonstrated that a background population can enhance the growth rate of the kink mode, making the growth rate significant at the physical value of the ion-electron mass ratio.
Pattern formation in a rotating suspension of non-Brownian buoyant particles
Authors: Kalyankar Makrand G. , Matson W. R. , Tong Penger , Ackerson Bruce J.
Published: August 2008

This study examines the concentration and velocity patterns observed in a horizontal rotating cylinder completely filled with a monodisperse suspension of non-Brownian buoyant particles. The unique patterns or phases are mapped by varying both the rotation rate and the solvent viscosity. Individual phases are identified using both frontal (θ-z plane) and axial (r-θ plane) views. Phase boundaries are compared to those obtained recently for suspensions of nonbuoyant particles. Expressing the boundaries in terms of dimensionless parameters unifies the data for several samples at low rotation rates. When centrifugal force dominates, the behavior becomes quite different from previous studies.
An advanced magnetic reflectometer
Authors: Brück Sebastian , Bauknecht Steffen , Ludescher Bernd , Goering Eberhard , Schütz Gisela
Published: August 2008

A new experimental setup dedicated to the measurement of soft-x-ray magnetic absorption spectroscopy and soft-x-ray resonant magnetic reflectometry (soft-XRMR) is presented. XRMR is the combination of standard x-ray reflectometry with x-ray magnetic circular dichroism which provides chemical and magnetic depth profiles of layered thin-film samples. This new diffractometer is optimized for a broad variety of sample systems. Therefore a balanced design focusing on high magnetic fields, low temperatures, and full freedom of rotation has been realized in UHV. First experimental results obtained on a NiCoO/Co bilayer sample are presented showing the potential of the setup.
Research of areal density diagnostic technique on Shenguang III laser prototype facility
Authors: Kang Xiaotao , Chen Jiabin , Deng Caibo , Liu Zhongjie , Zhan Xiayu , Chen Ming
Published: August 2008

In the test run of Shenguang III laser prototype facility, under the low density condition, the yield ratio method was used to measure the fuel areal density. Considering the uncertainty of the neutron yield, detectors with different efficiencies were used. The clear secondary-neutron signals in inertial confinement fusion experiments were obtained for the first time in China, and the values of the areal density were deduced.
Effects of the Fe–Co interaction on the growth of multiwall carbon nanotubes
Authors: Li Zhongrui , Dervishi Enkeleda , Xu Yang , Ma Xiaodong , Saini Viney , Biris Alexandru S. , Little Reginald , Biris Alexandru R. , Lupu Dan
Published: August 2008

The influences of active species Fe–Co composition on the growth of carbon nanotubes (CNTs) were systemically investigated. CNTs were grown from the pyrolytic decomposition of C2H2 over Fe–Co/CaCO3 catalysts by radio frequency chemical vapor deposition (CVD). The catalyst stoichiometry was found to strongly influence the carbon deposition rate as well as the nanotube crystallinity characteristics. Compared to the CNTs synthesized over the Co/CaCO3 catalyst, those produced by Fe-containing catalysts have less amorphous carbon. The maximum yield of high-quality CNTs was achieved at the Fe/Co atomic ratio of 2:1 due to a suitable concentration of benzene generated from acetylene CVD on such catalytic system. Fe and Co can form alloy and therefore the d-electron interaction between Fe and Co was believed to play an important role in the CNT growth.
Resonance effects in broadband acoustic cloak with multilayered homogeneous isotropic materials
Authors: Cheng Y. , Liu X. J.
Published: August 2008

The frequency response of the multilayered acoustic cloak made of isotropic materials is analyzed by the acoustic scattering theory. When concealing a rigid cylinder, the acoustic total scattering cross section (TSCS) monotonically increases with frequency. If concealing penetrable materials, the cloak-induced reverse-phase monopole and dipole resonances can increase the TSCS around the resonant frequencies, while the in-phase monopole resonance decreases the TSCS. The results are confirmed by numerical simulations of the finite element method.