bluuebunny/crossref_metadata_2025 huggingface dataset:
The Origin of the Architecture of the Solar System
Authors: Perryman Michael
Published: March 2012

This article relates two topics of central importance in modern astronomy – the discovery some 15 years ago of the first planets around other stars (referred to as exoplanets), and the centuries-old problem of understanding the origin of our own solar system, with its planets, planetary satellites, asteroids, and comets. The surprising diversity of exoplanets, of which more than 500 have already been discovered, has required new models to explain their formation and evolution. In turn, these models explain, rather naturally, a number of important features of our own solar system, amongst them the masses and orbits of the ‘terrestrial’ and ‘gas giant’ planets, the presence and distribution of asteroids and comets, the origin and impact cratering of the Moon, and the existence of water on Earth.
The salience of existential concerns across the cancer control continuum
Authors: Lee Virginia , Loiselle Carmen G.
Published: March 2012

Despite significant improvement in cancer survival, the fear of death still remains rooted in individuals' beliefs about cancer. Existential fears pertaining to cancer cut across the cancer control continuum and taint decisions related to prevention, screening, surveillance, and follow-up recommendations, as well as the overall management of cancer-related issues. However, individuals are innately predisposed to cope with their cancer-related fears through mechanisms such as reliance on the process of meaning making. To better appreciate the potential impact of existential concerns across the cancer control continuum, the Temporal Existential Awareness and Meaning Making (TEAMM) model is proposed. This tripartite model depicts three types of perceived threats to life related to cancer including a “social awareness” (i.e., cancer signals death), “personalized awareness” (i.e., I could die from cancer), and the “lived experience” (i.e., It feels like I am dying from cancer). This construal aims to enhance our understanding of the personal and contextual resources that can be mobilized to manage existential concerns and optimize cancer control efforts. As such, existential discussions should be considered in any cancer-related supportive approach whether preventive, curative, or palliative, and not be deferred only until the advanced stages of cancer or at end of life. Further delineation and validation of the model is needed to explicitly recognize and depict how different levels of existential awareness might unfold as individuals grapple with a potential, actual, or recurrent cancer.
Accounting for unobserved time‐varying quality in recreation demand: An application to a Sonoran Desert wilderness
Authors: Weber Matthew A. , Mozumder Pallab , Berrens Robert P.
Published: March 2012

Environmental variables can be important factors in recreation demand. Analysts wishing to quantify environmental quality impacts face the difficult issue of isolating them from unobserved variables. Quality changes may occur in space, varying between sites, or in time, varying between occasions. In this zonal travel cost analysis, fixed effects are used to control for time‐varying factors at a single site, adapting a technique previously applied to control for unobserved factors across sites. Graphical analysis and a second stage regression on time‐specific constants are used as diagnostic tools to guide a demand specification directly including both environmental and access predictors. The approach is developed and applied using a multiyear panel data set for a wilderness destination in the Sonoran Desert featuring a perennial stream. Empirical estimates are also provided for the recreational value of a trip day to a Sonoran Desert site with instream flows.
Saline pulse test monitoring with the self‐potential method to nonintrusively determine the velocity of the pore water in leaking areas of earth dams and embankments
Authors: Ikard S. J. , Revil A. , Jardani A. , Woodruff W. F. , Parekh M. , Mooney M.
Published: March 2012

A method is proposed to localize preferential fluid flow pathways in porous media on the basis of time‐lapse self‐potential measurements associated with salt tracer injection upstream. This method is first tested using laboratory data. A network of nonpolarizing electrodes located is connected to a highly sensitive voltmeter used to record the resulting electrical field fluctuations occurring over time at the surface of the tank. The transport of the conductive salt plume through the permeable porous materials changes the localized streaming potential coupling coefficient associated with the advective drag of the excess charge of the pore water and is also responsible for a diffusion current associated with the salinity gradient. Monitoring of the electrical potential distribution at the ground surface can be used to localize the pulse of saline water over time and to determine its velocity. This method applies in real time and can be used to track highly localized flow pathways characterized by high permeability. Our sandbox experiment demonstrates the applicability of this new method under well‐controlled conditions with a coarse‐sand channel embedded between fine‐sand banks. A finite element model allows us to reproduce the time‐lapse electrical potential distribution over the channel, but some discrepancies were observed on the banks. Finally, we performed a numerical simulation for a synthetic case study inspired by a recently published field case study. A Markov chain Monte Carlo sampler is used to determine the permeability and the porosity of the preferential fluid flow pathway of this synthetic case study.
Constraining the Jurassic extent of Greater India: Tectonic evolution of the West Australian margin
Authors: Gibbons Ana D. , Barckhausen Udo , van den Bogaard Paul , Hoernle Kaj , Werner Reinhard , Whittaker Joanne M. , Müller R. Dietmar
Published: March 2012

Alternative reconstructions of the Jurassic northern extent of Greater India differ by up to several thousand kilometers. We present a new model that is constrained by revised seafloor spreading anomalies, fracture zones and crustal ages based on drillsites/dredges from all the abyssal plains along the West Australian margin and the Wharton Basin, where an unexpected sliver of Jurassic seafloor (153 Ma) has been found embedded in Cretaceous (95 My old) seafloor. Based on fracture zone trajectories, this NeoTethyan sliver must have originally formed along a western extension of the spreading center that formed the Argo Abyssal Plain, separating a western extension of West Argoland/West Burma from Greater India as a ribbon terrane. The NeoTethyan sliver, Zenith and Wallaby plateaus moved as part of Greater India until westward ridge jumps isolated them. Following another spreading reorganization, the Jurassic crust resumed migrating with Greater India until it was re‐attached to the Australian plate ∼95 Ma. The new Wharton Basin data and kinematic model place strong constraints on the disputed northern Jurassic extent of Greater India. Late Jurassic seafloor spreading must have reached south to the Cuvier Abyssal Plain on the West Australian margin, connected to a spreading ridge wrapping around northern Greater India, but this Jurassic crust is no longer preserved there, having been entirely transferred to the conjugate plate by ridge propagations. This discovery constrains the major portion of Greater India to have been located south of the large‐offset Wallaby‐Zenith Fracture Zone, excluding much larger previously proposed shapes of Greater India.
Topographic/isostatic evaluation of new‐generation GOCE gravity field models
Authors: Hirt C. , Kuhn M. , Featherstone W. E. , Göttl F.
Published: March 2012

We use gravity implied by the Earth's rock‐equivalent topography (RET) and modeled isostatic compensation masses to evaluate the new global gravity field models (GGMs) from European Space Agency (ESA)'s Gravity Field and Steady‐State Ocean Circulation Explorer (GOCE) satellite gravimetry mission. The topography is now reasonably well‐known over most of the Earth's landmasses, and also where conventional GGM evaluation is prohibitive due to the lack (or unavailability) of ground‐truth gravity data. We construct a spherical harmonic representation of Earth's RET to derive band‐limited topography‐implied gravity, and test the somewhat simplistic Airy/Heiskanen and Pratt/Hayford hypotheses of isostatic compensation, but which did not improve the agreement between gravity from the uncompensated RET and GOCE. The third‐generation GOCE GGMs (based on 12 months of space gravimetry) resolve the Earth's gravity field effectively up to spherical harmonic degree ∼200–220 (∼90–100 km resolution). Such scales could not be resolved from satellites before GOCE. From the three different GOCE processing philosophies currently in use by ESA, the time‐wise and direct approaches exhibit the highest sensitivity to short‐scale gravity recovery, being better than the space‐wise approach. Our topography‐implied gravity comparisons bring evidence of improvements from GOCE to gravity field knowledge over the Himalayas, Africa, the Andes, Papua New Guinea and Antarctic regions. In attenuated form, GOCE captures topography‐implied gravity signals up to degree ∼250 (∼80 km resolution), suggesting that other signals (originating, e.g., from the crust‐mantle boundary and buried loads) are captured as well, which might now improve our knowledge on the Earth's lithosphere structure at previously unresolved spatial scales.
QBO modulation of traveling planetary waves during northern winter
Authors: Lu Hua , Pancheva Dora , Mukhtarov Plamen , Cnossen Ingrid
Published: March 2012

This study analyzes geopotential height data from the ERA‐40 and ERA‐Interim reanalyses for the period of 1958–2009 to provide some new insights on the stratospheric Quasi‐Biennial Oscillation (QBO) modulation of traveling planetary waves during Northern Hemisphere (NH) winter. In the stratosphere, the zonal wave number 1–3 waves with periods of 22.5–30 days and 45–60 days are found to be significantly stronger at midlatitudes when the QBO at 50 hPa is in its westerly phase than when it is in its easterly phase. The modulation is stronger for eastward propagating and standing waves and weaker for westward propagating waves. A QBO modulation of 11–13 day planetary waves is also found but the effect is dominated by post‐satellite data. In the troposphere, significant QBO modulation is only detected in westward propagating waves at zonal wave number 2 with periods of 22.5–30 days in early winter (Oct‐Dec). Consistent results in the stratosphere are obtained using the temperature data from SABER/TIMED. The SABER data also show that the QBO effect on the eastward propagating 23‐day waves extends into the mesosphere (∼70 km) for wave number 1 and only up to the stratopause (∼45 km) for wave numbers 2 and 3. We suggest that the 22.5–30 day planetary waves are secondary waves generated by a nonlinear coupling between zonal‐mean intraseasonal oscillations (ISO) and the well‐known 16‐day planetary waves. The QBO modulation of those planetary waves is due to a QBO‐ISO interaction. Further studies are needed to prove this hypothesis.
Analytic solution for the morphology of a soil‐mantled valley undergoing steady headward growth: Validation using case studies in southeastern Arizona
Authors: Pelletier Jon D. , Perron J. Taylor
Published: March 2012

The geomorphic literature contains many analytic solutions for the topographic evolution of gently sloping soil‐mantled hillslopes responding to base level changes. Most of these solutions are limited to vertical base level changes and/or to simplified geometries, however. In this paper we present an analytic solution for the morphology of a valley and its adjacent hillslopes undergoing steady headward growth. The mathematics of this problem were first solved by Ivantsov (1947) in the context of heat flow near a parabolic solidification boundary. Here we test whether the Ivantsov solution provides an accurate first‐order prediction of the morphology of valley heads and their adjacent hillslopes by comparing the model predictions to survey data from two study sites in southeastern Arizona. The model predicts that elevation contours of valley heads are parabolas and that topographic transects normal to contour lines are error functions. High‐resolution Digital Elevation Models (DEMs) were constructed for the two study sites using Real‐Time Kinematic Global Positioning System (RTK‐GPS) measurements and a Terrestrial Laser Scanner (TLS). Our analyses show that the model reproduces the first‐order morphology of headward‐growing valleys and their adjacent hillslopes. We also show that by analyzing hillslope profiles at different distances from the valley head, the model framework can be used to infer likely changes in the valley head migration rate through time.
A review of global terrestrial evapotranspiration: Observation, modeling, climatology, and climatic variability
Authors: Wang Kaicun , Dickinson Robert E.
Published: March 2012

This review surveys the basic theories, observational methods, satellite algorithms, and land surface models for terrestrial evapotranspiration, E (or λE, i.e., latent heat flux), including a long‐term variability and trends perspective. The basic theories used to estimate E are the Monin‐Obukhov similarity theory (MOST), the Bowen ratio method, and the Penman‐Monteith equation. The latter two theoretical expressions combine MOST with surface energy balance. Estimates of E can differ substantially between these three approaches because of their use of different input data. Surface and satellite‐based measurement systems can provide accurate estimates of diurnal, daily, and annual variability of E. But their estimation of longer time variability is largely not established. A reasonable estimate of E as a global mean can be obtained from a surface water budget method, but its regional distribution is still rather uncertain. Current land surface models provide widely different ratios of the transpiration by vegetation to total E. This source of uncertainty therefore limits the capability of models to provide the sensitivities of E to precipitation deficits and land cover change.
HF propagation modeling within the polar ionosphere
Authors: Warrington E. M. , Zaalov N. Y. , Naylor J. S. , Stocker A. J.
Published: March 2012

This paper illustrates the importance of understanding and taking into account the presence of various structural features in the polar ionosphere (in particular, patches and arcs of enhanced electron density) when planning and operating HF radio links. These features result in radio waves propagating over paths well displaced from the great circle direction and impact on almost any HF communications system where the signal reflects from the ionosphere within the region poleward of the subauroral trough. The off–great circle mechanisms give rise to propagation at times that are not predicted by current prediction codes and may also suppress propagation at times that are expected. Techniques to account for this type of propagation are therefore required. A ray‐tracing model that accurately reproduces many of the direction of arrival features observed in experimental measurements has been developed. Particular attention will be given in this paper to area coverage estimations undertaken by means of the ray‐tracing model.
Interpreting seasonal convective mixing in Devils Hole, Death Valley National Park, from temperature profiles observed by fiber‐optic distributed temperature sensing
Authors: Hausner Mark B. , Wilson Kevin P. , Gaines D. Bailey , Tyler Scott W.
Published: March 2012

Devils Hole, a groundwater‐filled fracture in the carbonate aquifer of the southern Nevada Mojave Desert, represents a unique ecohydrological setting, as home to the only extant population of Cyprinodon diabolis, the endangered Devils Hole pupfish. Using water column temperatures collected with a fiber‐optic distributed temperature sensor (DTS) during four field campaigns in 2009, evidence of deep circulation and nutrient export are, for the first time, documented. The DTS was deployed to measure vertical temperature profiles in the system, and the raw data returned were postprocessed to refine the calibration beyond the precision of the instrument's native calibration routines. Calibrated temperature data serve as a tracer for water movement and reveal a seasonal pattern of convective mixing that is supported by numerical simulations of the system. The periodic presence of divers in the water is considered, and their impacts on the temperature profiles are examined and found to be minimal. The seasonal mixing cycle may deplete the pupfish's food supplies when nutrients are at their scarcest. The spatial and temporal scales of the DTS observations make it possible to observe temperature gradients on the order of 0.001°C m−1, revealing phenomena that would have been lost in instrument noise and uncertainty.
A log‐sinh transformation for data normalization and variance stabilization
Authors: Wang Q. J. , Shrestha D. L. , Robertson D. E. , Pokhrel P.
Published: March 2012

When quantifying model prediction uncertainty, it is statistically convenient to represent model errors that are normally distributed with a constant variance. The Box‐Cox transformation is the most widely used technique to normalize data and stabilize variance, but it is not without limitations. In this paper, a log‐sinh transformation is derived based on a pattern of errors commonly seen in hydrological model predictions. It is suited to applications where prediction variables are positively skewed and the spread of errors is seen to first increase rapidly, then slowly, and eventually approach a constant as the prediction variable becomes greater. The log‐sinh transformation is applied in two case studies, and the results are compared with one‐ and two‐parameter Box‐Cox transformations.
Near Infrared Reflectance Spectroscopy (NIRS) Determination of Isoflavone Contents for Selected Soybean Accessions
Authors: Baianu I. , Guo Jun , You Tiefeng , Nelson Randall
Published: March 2012

Soybean isoflavones are of considerable interest in relation to their possible health effects in human diets. The rapid and economical determination of soybean isoflavone concentrations is essential for the investigation and development of soybean health foods as well as the selection of soybean seeds with optimal isoflavone levels for such foods. Fourier transforms near infrared reflectance spectroscopy (FT-NIRS) calibrations were developed for the rapid and cost-effective analysis of isoflavones in soybean seeds. FT-NIRS measurements were carried out in quadruplicate for 50 soybean lines selected from the USDA Soybean Germplasm Collection. The selected soybean seeds provided a wide range of isoflavone concentrations (from 0.3 to 6.0 mg/g) that is necessary for development of high-quality calibrations. Laboratory reference values of isoflavone composition were obtained by HPLC analysis of extracted soybean powders. Single soybean seeds were selected for each standard sample and were cut in half in order to avoid screening of the isoflavones NIR absorption bands by the seed coat. For comparison purposes, measurements were also made on soybean powders of the same samples. FT -NIR spectra were collected with a spectral range from 4000 to 12000 cm-1 at a resolution of 8 cm-1 on a Perkin-Elmer Spectrum one NTS spectrometer model. This spectrometer is optimized for high sensitivity analysis of single seed composition, being equipped with an NIRA, integrating sphere accessory and an extended range InGaAs detector.
Nucleon–nucleon correlations in p–He4?
Authors: Lubkin Gloria B.
Published: March 2012

A recent experiment at Saclay suggests that to explain the behavior of 1-GeV protons elastically scattering off He4 it is necessary to include the effect of correlations between the nucleons. When we recently visited Jacques Thirion at Saclay he told us of the results, which have just been reported in the 15 April issue of Phys. Rev. Letters. Herman Feshbach (MIT) has found that the explanation of the Saclay results would require the inclusion of nucleon–nucleon correlations in the nuclear wave function.
Is there a pecking order in physics journals?
Authors: Inhaber Herbert
Published: March 2012

When physicists wish to communicate their work by means of publication, several considerations are weighed before choosing the appropriate journal. There is the matter of audience; of the probable delay between acceptance and publication; of article format (letter, review, standard research report). If the article is potentially controversial, the author may estimate its chances of being accepted by different journals. Considerations of national pride may sway the choice: An author may submit a work to a journal in his own country rather than to one that has a greater circulation and impact but is published in a foreign country.
Rotation induced nonlinear dispersive dust drift waves can be the progenitors of spokes
Authors: Masood W. , Rizvi H. , Hasnain H. , Haque Q.
Published: March 2012

Rotation induced dispersive dust drift waves are suggested as the possible cause of the formation of spokes in the Saturn’s B ring. Using the plasma parameters found in the Saturn’s B ring, it has been shown that the theoretically predicted spatio-temporal scalelengths agree well with the satellites and Hubble Space telescope observations of the spokes.
Measurement of plasma current dependent changes in impurity transport and comparison with nonlinear gyrokinetic simulation
Authors: Howard N. T. , Greenwald M. , Mikkelsen D. R. , White A. E. , Reinke M. L. , Ernst D. , Podpaly Y. , Candy J.
Published: March 2012

Measured impurity transport coefficients are found to demonstrate a strong dependence on plasma current in the core of Alcator C-Mod. These measurements are compared directly with linear and nonlinear gyrokinetic simulation in an attempt to both qualitatively and quantitatively reproduce the measured impurity transport. Discharges constituting a scan of plasma current from 0.6 to 1.2 MA were performed during the 2010 run campaign. The impurity transport from these discharges was determined using a novel set of spectroscopic diagnostics available on Alcator C-Mod. This diagnostic suite allowed for the effective constraint of impurity transport coefficient profiles inside of r/a = 0.6. A decrease in the measured impurity diffusivity and inward convection is found with increased plasma current. Global, nonlinear gyrokinetic simulations were performed using the GYRO code [J. Candy and R. E. Waltz, J Comput. Phys. 186, 545 (2003)] for all discharges in the experimental scan and are found to reproduce the experimental trends, while demonstrating good quantitative agreement with measurement. A more comprehensive quantitative comparison was performed on the 0.8 MA discharge of the current scan which demonstrates that simultaneous agreement between experiment and simulation in both the impurity particle transport and ion heat transport channels is attainable within experimental uncertainties.
Effects of beam temperature and density variation on the growth rate of a two-stream free electron laser
Authors: Aghamir F. M. , Mahdizadeh N.
Published: March 2012

The effect of beam temperature and density variation on the growth rate of a two-stream free electron laser (TSFEL) with planer wiggler pump has been verified. With the aid of momentum transfer, Poisson, continuity, and Maxwell’s equations, the dispersion relation was derived. The eighth order dispersion equation has been solved numerically. The two FEL along with the TS instabilities occur simultaneously. The analysis shows that when the effect of the temperature is taken into account, both instable bands of wave-number and peak growth rate in TS instability increase, but peak growth of FEL instabilities decreases. The growth rate increases with an increase in the strength of the wiggler field. In addition, the growth sensitivity to density variation has been noticed.
Atomistic elucidation of the effect of surface roughness on curvature-dependent surface energy, surface stress, and elasticity
Authors: Mohammadi P. , Sharma P.
Published: March 2012

It is well known that surface energy and the associated properties such as surface stress and surface elasticity have a significant effect on the physical behavior of nanostructures. In this letter, using a combination of atomistic simulations and a simple continuum model, we elucidate the role of surface roughness on the renormalization of surface stress, surface elastic constants, as well as the (generally ignored) term that represents the curvature dependence of surface energy (crystalline Tolman’s length). We find, consistent with a recent theoretical prediction and in sharp contrast to few others, that the surface stress is negligibly impacted by roughness. However, even moderate roughness is seen to dramatically alter the surface elasticity modulus as well as the crystalline Tolman’s length. We illustrate a simple application on the impact of roughness on nanosensors.
Comparison of anomalous Doppler resonance effects with molybdenum and graphite limiters on HT-7
Authors: Wang Y. M. , Gao X. , Ling B. L. , Liu Y. , Zhang S. B. , Han X. , Ti A. , Li E. Z. ,   HT-7 Team
Published: March 2012

The material of limiter in HT-7 tokamak was changed from graphite to molybdenum in the last experimental campaign. The pitch angle scattering of runaway electrons due to anomalous Doppler resonance effects was observed. The experimental results agree very well with the stable boundary condition expected from the linear resistive theory but only agree with that from the nonlinear evolutionary of runaway-electron distribution theory in low electric field region. The current carried by runaway electrons is the same under different limiter conditions.
Thermal plasma and fast ion transport in electrostatic turbulence in the large plasma device
Authors: Zhou Shu , Heidbrink W. W. , Boehmer H. , McWilliams R. , Carter T. A. , Vincena S. , Tripathi S. K. P. , Van Compernolle B.
Published: March 2012

The transport of thermal plasma and fast ions in electrostatic microturbulence is studied. Strong density and potential fluctuations (δn/n∼δφ/kTe ∼ 0.5, f ∼ 5–50 kHz) are observed in the large plasma device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] in density gradient regions produced by obstacles with slab or cylindrical geometry. Wave characteristics and the associated plasma transport are modified by driving sheared E × B drift through biasing the obstacle and by modification of the axial magnetic fields (Bz) and the plasma species. Cross-field plasma transport is suppressed with small bias and large Bz and is enhanced with large bias and small Bz. The transition in thermal plasma confinement is well explained by the cross-phase between density and potential fluctuations. Large gyroradius lithium fast ion beam (ρfast/ρs ∼ 10) orbits through the turbulent region. Scans with a collimated analyzer give detailed profiles of the fast ion spatial-temporal distribution. Fast-ion transport decreases rapidly with increasing fast-ion energy and gyroradius. Background waves with different scale lengths also alter the fast ion transport. Experimental results agree well with gyro-averaging theory. When the fast ion interacts with the wave for most of a wave period, a transition from super-diffusive to sub-diffusive transport is observed, as predicted by diffusion theory. Besides turbulent-wave-induced fast-ion transport, the static radial electric field (Er) from biasing the obstacle leads to drift of the fast-ion beam centroid. The drift and broadening of the beam due to static Er are evaluated both analytically and numerically. Simulation results indicate that the Er induced transport is predominately convective.
In-situ and ex-situ characterization of TiO2 and Au nanoparticle incorporated TiO2 thin films for optical gas sensing at extreme temperatures
Authors: Ohodnicki Paul R. , Wang Congjun , Natesakhawat Sittichai , Baltrus John P. , Brown Thomas D.
Published: March 2012

Sensor technologies that can operate under extreme conditions including high temperatures, high pressures, highly reducing and oxidizing environments, and corrosive gases are needed for process monitoring and control in advanced fossil energy applications. Sensor technologies based on optical waveguide-based techniques are highly attractive for passive, embedded, and remote sensing. A critical enabling technology for optical waveguide sensors is the development of advanced optical thin film coatings which have a desired set of optical properties that change in a rapid, selective, and sensitive manner to a particular quantity of interest. TiO2 and Au nanoparticle incorporated TiO2 nanocomposite thin films were prepared through sol-gel deposition techniques and their respective optical responses to a 4% H2/N2 mixture were investigated in the visible / near-IR range of 400–1000 nm. A tendency for Au nanoparticles to occupy special sites on the TiO2 microstructure, such as grain boundaries, twin boundaries, and triple points is rationalized in terms of basic surface energy arguments. The Au / TiO2 nanocomposite films showed a useful optical response due to a reversible, rapid, and repeatable shift in the localized surface plasma resonance peak of Au nanoparticles at a temperature of 650 °C and 850 °C. In contrast, high temperature exposure of TiO2 films to reducing gases at 850 °C resulted in the growth of abnormally large grains or “hillocks” that protruded from the sample surface and resulted in light scattering and an irreversible decrease in transmission at short wavelengths. The origin of the observed optical response of Au / TiO2 nanocomposite films is discussed in the context of work by prior investigators in the Au / yttria-stabilized Zirconia (YSZ) system and needs for future research in this area is highlighted.
On the role of grain boundaries in nanocrystalline γ-Fe2O3 under high pressure
Authors: Zhang Dongmei , Zhang Yongsheng , Gao Yang , Han Yonghao , Gao Chunxiao , Ma Yanzhang , Cheng Chunxiao , Yu Ke
Published: March 2012

In situ impedance spectroscopy of nanophase and bulk γ-Fe2O3 were performed using a fabricated microcircuit on a diamond anvil cell. The results provide evidence for the existence of grain and grain boundary effects that are separated in the frequency region. The analysis establishes that the grain boundary conductance of nanocrystalline γ-Fe2O3 is higher than that of the bulk material. Both the grain and grain boundary resistances of γ-Fe2O3 smoothly decrease with pressure. A remarkable phenomenon of discontinuity appears at 7.4 GPa for the nanocrystals. This critical value is interpreted by the space charge model and changes in charge densities between the grain boundaries. The impedance analysis further reveals that the relaxation frequency gradually increased with the effect of pressure and the γ-Fe2O3 samples’ impedance imaginary part exhibits a typical capacitive characteristic. Within the given pressure range, the relaxation frequency of γ-Fe2O3 follows the Arrhenius behavior. This result was attributed to a dominant interfacial effect.
Fe3O4-citrate-curcumin: Promising conjugates for superoxide scavenging, tumor suppression and cancer hyperthermia
Authors: Kitture Rohini , Ghosh Sougata , Kulkarni Parag , Liu X. L. , Maity Dipak , Patil S. I. , Jun Ding , Dushing Yogesh , Laware S. L. , Chopade B. A. , Kale S. N.
Published: March 2012

Fe3O4 nanoparticles have been conjugated to curcumin (CU) molecules via a citrate (CA) linker (Fe-CA-CU) and have been explored for superoxide scavenging, tumor suppression, and cancer hyperthermia. The conjugation chemistry reveals that Fe3+ ions on the nanoparticle surface readily conjugates to the available carboxyl sites on the CA molecule, which further conjugates to CU at its central enol -OH group. As seen from the UV-vis spectroscopy, the therapeutically active chromophore group of CU, which is seen at 423 nm, was intact, ensuring the activity the molecule. Magnetization measurements showed good hysteresis curves of Fe3O4 and Fe-CA-CU, indicating the presence of magnetism after conjugation. The loading percentage of citrate-curcumin was seen to be ∼10% from the thermo-gravimetric analysis. The systems when subjected to radio-frequency fields of 240 KHz, were seen to get heated up. The Fe3O4 heating exhibited better slope (1 °C/s) as compared to the Fe-CA-CU system (∼0.7 °C/s) for a sample of concentration 10 mg/ml in average time of ∼20 s to reach the required hyperthermia threshold temperature of ∼45 °C. Tumor suppression studies were done using potato assay, which showed that while only CU showed 100% suppression in 7 days, it was about 89% by the Fe-CA-CU. Upon subjecting these systems to the superoxide anion scavenging assay and superoxide radical scavenging assay (riboflavin), it was observed that the activity was enhanced in the Fe-CA-CU to 40% (from 38% in only CU) and 100% (from 5.75% in only CU). These studies promise Fe-CA-CU as a good cancer hyperthermia-cum-tumor suppressant and antioxidant agent.
Studies of structural, dynamical, and interfacial properties of 1-alkyl-3-methylimidazolium iodide ionic liquids by molecular dynamics simulation
Authors: Ghatee Mohammad Hadi , Zolghadr Amin Reza , Moosavi Fatemeh , Ansari Younes
Published: March 2012

Bulk and surface properties of the ionic liquids 1-alkyl-3-methyl-imidazolium iodides ([Cnmim]I) were simulated by classical molecular dynamics using all atom non-polarizable force field (n = 4, butyl; 6, hexyl; 8, octyl). The structure of ionic liquids were initially optimized by density functional theory and atomic charges obtained by CHELPG method. Reduction of partial atomic charges (by 20% for simulation of density and surface tension, and by 10% for viscosity) found to improve the accuracy, while a non-polarizable force field was applied. Additionally, the simulation ensembles approach the equilibrium faster when the charge reduction is applied. By these refined force field parameters, simulated surface tensions in the range of 323–393 k are quite in agreement with the experiments. Simulation of temperature dependent surface tension of [C4mim]I well beyond room temperature (up to 700 K) permits prediction of the critical temperature in agreement with that predicted from experimental surface tension data. Simulated densities in the range of 298–450 K for the three ionic liquids are within 0.8% of the experimental data. Structural properties for [C4mim]I were found to be in agreement with the results of Car-Parrinello molecular dynamics simulation we performed, which indicates a rather well-structured cation-anion interaction and occurs essentially through the imidazolium ring cation. Diffusion coefficient changes with alkyl chain length in the order of [C8mim]I > [C6mim]I > [C4mim]I for the cation and the anion. Formation of a dense domain in subsurface region is quite evident, and progressively becomes denser as the alkyl chain length increases. Bivariate orientational analysis was used to determine the average orientation of molecule in ionic liquids surface, subsurface, and bulk regions. Dynamic bisector-wise and side-wise movement of the imodazolium ring cation in the surface region can be deduced from the bivariate maps. Atom-atom density profile and bivariate analysis indicate that the imidazolium cation takes a spoon like configuration in the surface region and the tilt of alkyl group is a function length of alkyl chain exposing as linear as possible to the vapor phase.
M + Ng potential energy curves including spin-orbit coupling for M = K, Rb, Cs and Ng = He, Ne, Ar
Authors: Blank L , Weeks David E. , Kedziora Gary S.
Published: March 2012

The \documentclass[12pt]{minimal}\begin{document}$X^2\Sigma _{1/2}^+$\end{document}X2Σ1/2+, A2Π1/2, A2Π3/2, and \documentclass[12pt]{minimal}\begin{document}$B^2\Sigma _{1/2}^+$\end{document}B2Σ1/2+ potential energy curves and associated dipole matrix elements are computed for M + Ng at the spin-orbit multi-reference configuration interaction level, where M = K, Rb, Cs and Ng = He, Ne, Ar. Dissociation energies and equilibrium positions for all minima are identified and corresponding vibrational energy levels are computed. Difference potentials are used together with the quasistatic approximation to estimate the position of satellite peaks of collisionally broadened D2 lines. The comparison of potential energy curves for different alkali atom and noble gas atom combinations is facilitated by using the same level of theory for all nine M + Ng pairs.
Hundreds MeV monoenergetic proton bunch from interaction of 1020–21 W/cm2 circularly polarized laser pulse with tailored complex target
Authors: Zhang Z. M. , He X. T. , Sheng Z. M. , Yu M. Y.
Published: March 2012

A complex target (CT) configuration tailored for generating high quality proton bunch by circularly polarized laser pulses at intensities of 1020-21 W/cm2 is proposed. Two-dimensional particle-in-cell simulations show that both the collimation and mono-energetic qualities of the accelerated proton bunch obtained using a front-shaped thin foil can be greatly enhanced by the backside inhomogeneous plasma layer. The main mechanisms for improving the accelerated protons are identified and discussed. These include stabilization of the photon cavity, providing hole-boring supplementary acceleration and suppressing the thermal-electron effects. A theory for tailoring the CT parameters is also presented.
Photoinduced modification of surface states in nanoporous InP
Authors: Lloyd-Hughes J. , Müller S. , Scalari G. , Bishop H. , Crossley A. , Enachi M. , Sirbu L. , Tiginyanu I. M.
Published: March 2012

Porous honeycombs of n-type InP were investigated by terahertz time-domain and x-ray photoemission spectroscopies. After photoexcitation the dark conductivity was found to increase quasi-irreversibly, recovering only after several hours in air. The calculated electron density for different surface pinning energies suggests that photoexcitation may reduce the density of surface states.
Generalized Flory-Huggins theory-based equation of state for ring and chain fluids
Authors: Jiang Jian , Cao Dapeng
Published: March 2012

By modeling the ring-like molecule as a pearl necklace of freely jointed hard sphere, we develop a new equation of state (EOS) for the ring-like fluids on the basis of generalized Flory-Huggins (GFH) theory. Before proposing the new EOS of the ring-like fluids, we first modify the generalized Flory-Huggins theory for the chain fluids by incorporating a function related to the packing fraction into the insertion probability. The results indicate that the modified GFH EOS can predict the compressibility factors more accurately than the GFH EOS, especially for the intermediate and high packing fractions (η ⩾ 0.157). Subsequently, the modified GFH theory-based EOS for the ring-like fluids is proposed. Compared to the Monte Carlo data of 3-mer, 4-mer, 5-mer, 6-mer, 16-mer, and 32-mer ring-like fluids, our EOS exhibits the best prediction among four EOSs for the compressibility factors at intermediate and high packing fractions (η ⩾ 0.157), although our EOS also shows a slight underestimation for the compressibility factors at low packing fractions. In summary, this is the first report on the generalized Flory-Huggins theory-based EOS for the ring-like fluids. It is expected that the same strategy can be applied to these fluids with more complex architectures.
An isotopic-independent highly accurate potential energy surface for CO2 isotopologues and an initial 12C16O2 infrared line list
Authors: Huang Xinchuan , Schwenke David W. , Tashkun Sergey A. , Lee Timothy J.
Published: March 2012

An isotopic-independent, highly accurate potential energy surface (PES) has been determined for CO2 by refining a purely ab initio PES with selected, purely experimentally determined rovibrational energy levels. The purely ab initio PES is denoted Ames-0, while the refined PES is denoted Ames-1. Detailed tests are performed to demonstrate the spectroscopic accuracy of the Ames-1 PES. It is shown that Ames-1 yields σrms (root-mean-squares error) = 0.0156 cm−1 for 6873 J = 0–117 12C16O2 experimental energy levels, even though less than 500 12C16O2 energy levels were included in the refinement procedure. It is also demonstrated that, without any additional refinement, Ames-1 yields very good agreement for isotopologues. Specifically, for the 12C16O2 and 13C16O2 isotopologues, spectroscopic constants Gv computed from Ames-1 are within ±0.01 and 0.02 cm−1 of reliable experimentally derived values, while for the 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 12C18O2, 17O12C18O, 12C17O2, 13C18O2, 13C17O2, 17O13C18O, and 14C16O2 isotopologues, the differences are between ±0.10 and 0.15 cm−1. To our knowledge, this is the first time a polyatomic PES has been refined using such high J values, and this has led to new challenges in the refinement procedure. An initial high quality, purely ab initio dipole moment surface (DMS) is constructed and used to generate a 296 K line list. For most bands, experimental IR intensities are well reproduced for 12C16O2 using Ames-1 and the DMS. For more than 80% of the bands, the experimental intensities are reproduced with σrms(ΔI) < 20% or σrms(ΔI/δobs) < 5. A few exceptions are analyzed and discussed. Directions for future improvements are discussed, though it is concluded that the current Ames-1 and the DMS should be useful in analyzing and assigning high-resolution laboratory or astronomical spectra.
Development of autonomous gamma dose logger for environmental monitoring
Authors: Jisha N. V. , Krishnakumar D. N. , Surya Prakash G. , Kumari Anju , Baskaran R. , Venkatraman B.
Published: March 2012

Continuous monitoring and archiving of background radiation levels in and around the nuclear installation is essential and the data would be of immense use during analysis of any untoward incidents. A portable Geiger Muller detector based autonomous gamma dose logger (AGDL) for environmental monitoring is indigenously designed and developed. The system operations are controlled by microcontroller (AT89S52) and the main features of the system are software data acquisition, real time LCD display of radiation level, data archiving at removable compact flash card. The complete system operates on 12 V battery backed up by solar panel and hence the system is totally portable and ideal for field use. The system has been calibrated with Co-60 source (8.1 MBq) at various source-detector distances. The system is field tested and performance evaluation is carried out. This paper covers the design considerations of the hardware, software architecture of the system along with details of the front-end operation of the autonomous gamma dose logger and the data file formats. The data gathered during field testing and inter comparison with GammaTRACER are also presented in the paper. AGDL has shown excellent correlation with energy fluence monitor tuned to identify 41Ar, proving its utility for real-time plume tracking and source term estimation.
Multi-chord fiber-coupled interferometer with a long coherence length laser
Authors: Merritt Elizabeth C. , Lynn Alan G. , Gilmore Mark A. , Hsu Scott C.
Published: March 2012

This paper describes a 561 nm laser heterodyne interferometer that provides time-resolved measurements of line-integrated plasma electron density within the range of 1015−1018 cm−2. Such plasmas are produced by railguns on the plasma liner experiment, which aims to produce μs-, cm-, and Mbar-scale plasmas through the merging of 30 plasma jets in a spherically convergent geometry. A long coherence length, 320 mW laser allows for a strong, sub-fringe phase-shift signal without the need for closely matched probe and reference path lengths. Thus, only one reference path is required for all eight probe paths, and an individual probe chord can be altered without altering the reference or other probe path lengths. Fiber-optic decoupling of the probe chord optics on the vacuum chamber from the rest of the system allows the probe paths to be easily altered to focus on different spatial regions of the plasma. We demonstrate that sub-fringe resolution capability allows the interferometer to operate down to line-integrated densities of the order of 5 × 1015 cm−2.
Design and performance of a versatile curved-crystal spectrometer for high-resolution spectroscopy in the tender x-ray range
Authors: Kavčič M. , Budnar M. , Mühleisen A. , Gasser F. , Žitnik M. , Bučar K. , Bohinc R.
Published: March 2012

A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.
Fast scanning mode and its realization in a scanning acoustic microscope
Authors: Ju Bing-Feng , Bai Xiaolong , Chen Jian
Published: March 2012

The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.
The solvation of two electrons in the gaseous clusters of Na−(NH3)n and Li−(NH3)n
Authors: Zhang Han , Liu Zhi-Feng
Published: March 2012

Alkali metal ammonia clusters, in their cationic, neutral, and anionic form, are molecular models for the alkali-ammonia solutions, which have rich variation of phases with the solvated electrons playing an important role. With two s electrons, the Na−(NH3)n and Li−(NH3)n clusters are unique in that they capture the important aspect of the coupling between two solvated electrons. By first principles calculations, we demonstrate that the two electrons are detached from the metal by n = 10, which produces a cluster with a solvated electron pair in the vicinity of a solvated alkali cation. The coupling of the two electrons leads to either the singlet or triplet state, both of which are stable. They are also quite distinct from the hydrated anionic clusters Na−(H2O)n and Li−(H2O)n, in that the solvated electrons are delocalized and widely distributed among the solvent ammonia molecules. The Na−(NH3)n and Li−(NH3)n series, therefore, provide another interesting type of molecular model for the investigation of solvated electron pairs.