bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface and crater‐exposed lithologic units of the Isidis Basin as mapped by coanalysis of THEMIS and TES derived data products
Authors: Tornabene Livio L. , Moersch Jeffrey E. , McSween Harry Y. , Hamilton Victoria E. , Piatek Jennifer L. , Christensen Phillip R.
Published: October 2008

The stratigraphy and mineral heterogeneity of surface and crater‐exposed deposits in the southwestern portion of the Isidis Basin were investigated using spatial, spectral, visible, and thermophysical data sets from both the Mars Global Surveyor and Odyssey missions. Four THEMIS spectral surface units were identified progressing from the Libya Montes highlands to the inner lowland plains of Isidis Planitia. Lithologic determinations of these spectral units were made by linear deconvolution analysis of TES data. Olivine‐rich surface materials correlate with a well‐documented high‐thermal inertia unit. Based on spatial and stratigraphic relationships interpreted from both crater‐exposed and surface exposures, the olivine‐rich unit was determined to have formed subsequent to the Isidis Basin forming event. Morphology, occurrence, and linear deconvolution of this unit suggests that it may represent Noachian age to Hesperian age picritic lavas that erupted as early‐stage lavas originating from sources such as Syrtis Major, beneath Isidis, and as far as Tyrrhena Patera. These lavas are suggested to have partially filled the basin, based on crater‐exposed occurrences, and were subsequently buried by further evolved olivine‐poor lavas. Later, these lavas were exposed by erosion and subsequent impacts into the basin. Crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d/D ratios and the well‐developed positive mass anomaly associated with the basin. This study also demonstrates that the remote sensing of impact craters, in conjunction with surface mapping, is a potent mapping tool for understanding stratigraphy and the petrogenesis of the Martian crust.
Sensitivity of residential water consumption to variations in climate: An intraurban analysis of Phoenix, Arizona
Authors: Balling R. C. , Gober P. , Jones N.
Published: October 2008

Water remains an essential ingredient for the rapid population growth taking place in metropolitan Phoenix, Arizona. Depending upon the municipality, between 60 and 75% of residential water is used outdoors to maintain nonnative, water‐intensive landscapes and swimming pools. Residential water use in Phoenix should be especially sensitive to meteorological and climatic variations because of the strong emphasis on outdoor water use. This study explores the intraurban spatial variations in the sensitivity of residential water consumption to atmospheric conditions. For 230 census tracts in the city, we developed times series of monthly water use anomalies and compared them with monthly anomalies of temperature, precipitation, and the Palmer Drought Hydrological Index. We found that one third of census tracts have little to no sensitivity to climate, while one tract had over 70% of its monthly variance in water use explained by atmospheric conditions. Greater sensitivity to atmospheric conditions occurred in census tracts with large lots, many pools, a high proportion of irrigated mesic landscaping, and a high proportion of high‐income residents. Low climatic sensitivity occurred in neighborhoods with large families and many Hispanics. Results suggest that more affluent, non‐Hispanic neighborhoods will be disproportionately affected by increasing temperatures due to urban heat island effects and the buildup of greenhouse gases.
Montgomery chosen as MacArthur Fellow
Authors: Showstack Randy
Published: October 2008

David Montgomery, a professor in the Department of Earth and Space Sciences at the University of Washington, Seattle, was selected as a MacArthur Fellow, the John D. and Catherine T. MacArthur Foundation announced on 23 September. A geomorphologist, Montgomery was cited for “making fundamental contributions to our understanding of the geophysical forces that determine landscape evolution and of how our use of soils and rivers has shaped civilizations past and present.”
Marine debris plan
Authors: Showstack Randy
Published: October 2008

A new U.S. federal interagency report on preventing and reducing marine debris focuses on responses to debris already in the environment, prevention of debris, research and development, and coordination among agencies. The report, released on 22 September, was prepared by 11 federal agencies and is intended to guide the strategies of federal agencies and the Interagency Marine Debris Coordinating Committee.
Karen L. Von Damm (1955–2008)
Authors: Haymon Rachel , Lilley Marv , Fornari Dan , Bryce Julie , Varner Ruth
Published: October 2008

Karen L. Von Damm, a professor and world‐renowned researcher in marine geochemistry at the University of New Hampshire, passed away at her home in Durham on 15 August 2008, after having been diagnosed with liver cancer in April 2008. She was 53 years old.
Comment on “Unraveling the Causes of Radiation Belt Enhancements”
Authors: Campbell Wallace H.
Published: October 2008

The excellent article by M. W. Liemohn and A. A. Chan on the radiation belts (see Eos, 88(42), 16 October 2007) is misleading in its implication that the disturbance storm‐time (Dst) index is an indicator of a magnetospheric ring current. That index is formed from an average of magnetic data from three or four low‐latitude stations that have been fallaciously “adjusted” to a magnetic equatorial location under the 1960's assumption [Sugiura, 1964] that the fields arrive from the growth and decay of a giant ring of current in the magnetosphere. In truth, the index has a negative lognormal form [Campbell, 1996; Yago and Kamide, 2003] as a result of its composition from numerous negative ionospheric and magnetospheric disturbance field sources, each having normal field amplitude distributions [Campbell, 2004]. Some partial ring currents [Lui et al., 1987] and their associated field‐aligned currents, as well as major ionospheric currents flowing from the auroral zone to equatorial latitudes, are the main contributors to the Dst index.
Reply to Comment on “Unraveling the Causes of Radiation Belt Enhancements”
Authors: Liemohn Michael W. , Chan Anthony A.
Published: October 2008

Numerous current systems contribute to the magnetic perturbations used to calculate the Dst index. Ionospheric and field‐aligned current effects are minimized, although not always well [e.g., Friedrich et al., 1999], by averaging measurements from a worldwide chain of low‐latitude stations. The index is imperfect, but it has been shown that Biot‐Savart magnetic perturbations from magnetospheric currents derived from in situ particle observations can account for most of the Dst variation [Greenspan and Hamilton, 2000; Turner et al., 2001; Jorgenson et al., 2004].
First Coastal Altimetry Workshop: Cooperative Institute for Oceanographic Satellite Studies/National Oceanic and Atmospheric Administration Coastal Altimeter Workshop; 5–7 February 2008, Silver Spring, Maryland
Authors: Smith Walter H. F. , Strub Ted , Miller Laury
Published: October 2008

Satellite radar altimeter measurements of sea surface height (SSH), significant wave height, and wind speed have many potential applications in coastal zones, despite the common perception that altimetry does not “work” near the coast. The altimeter's primary measurement, the radar travel time from the spacecraft to the sea surface, is reliable seaward of 10 kilometers from the coast, and sometimes closer. The Ocean Surface Topography Mission altimeter on Jason 2, launched on 20 June 2008, has a new tracking mode that may recover more data in the coastal zone, and the launch of CryoSat 2 next year will demonstrate the coastal capabilities of a delay‐Doppler altimeter. Turning radar travel time into accurate SSH requires ancillary water vapor radiometer measurements that may become unreliable within 50 kilometers of the coast. Interpretation of SSH data in the coastal zone is complicated where tides and other SSH corrections may change abruptly over shallow coastal shelves or near land.
Cultural Uses and Impacts of Fire: Past, Present, and Future: Analysis, Integration and Modeling of the Earth System (AIMES), Fourth Young Scholar's Network (YSN) Workshop; Boulder, Colorado, 14–18 July 2008
Authors: Magi Brian , Coughlan Michael , Edwards Andrew , Hurteau Matthew , Petty Aaron , Seijo Francisco , Wiedimyer Christine
Published: October 2008

Fire is a global phenomenon transcending social, economic, and political boundaries. Effective decision making regarding fire policies requires integrating knowledge of human, ecological, and climatic components of fire research over a range of spatial and temporal scales.

The Analysis, Integration and Modeling of the Earth System (AIMES) fourth Young Scholar's Network workshop brought together early‐career researchers representing anthropology, archaeology, atmospheric science, climate modeling, ecology, fire management, geography, paleoclimate, political science, and remote sensing. Goals of the workshop were to explore the drivers, impacts, and feedbacks of human use of fires and to contextualize the management of fires.
Science for Agriculture and Rural Development in Low‐Income Countries
Authors: Barros Vicente
Published: October 2008

During recent months, another sign of the global fragility to sustain the increasing human demand for resources has appeared with merciless cruelty. Increasing food prices, paradoxically driven to a large extent by the rapid economic growth of vast regions of the emerging world, are affecting hundreds of millions of the poorest people in Africa, Asia, and Latin America. As described in Science for Agriculture and Rural Development in Low‐Income Countries, most of the poorest people in these low‐income countries live in rural areas and are engaged in agriculture or related activities. Because many people in these areas are engaged in subsistence agriculture, they do not share in the added income derived from higher market prices for food.
Global lightning activity from the ENSO perspective
Authors: Chronis T. G. , Goodman S. J. , Cecil D. , Buechler D. , Robertson F. J. , Pittman J. , Blakeslee R. J.
Published: October 2008

The recently reprocessed (1998–2006) OTD/LIS space‐based lightning database is used to investigate the global lightning climatology in response to the ENSO cycle. Temporal correlation maps depicting lightning anomalies‐NINO3.4 identify areas that generally follow patterns similar to the widely documented ENSO‐related precipitation anomalies. However, areas having statistically significant lightning anomaly‐NINO3.4 correlations accompanied by non‐significant precipitation anomaly‐NINO3.4 correlations are found over the mid‐latitudes in both hemispheres. Analysis shows that these areas are related to upper level circulation anomalies (enhanced wind shear) induced by the corresponding ENSO phase. A special case is observed over the western Maritime continent where typical drought conditions during the warm ENSO phase are related to enhanced lightning activity. Further attention is given toward identifying areas over which consistent thunderstorm activity is observed during the two major warm and cold ENSO phases of the past decade. Their spatial distribution shows strong regional preference and in general agrees with the already established ENSO‐related precipitation regimes.
Recent trends in the seasonal and temporal behaviour of the El Niño–Southern Oscillation
Authors: Nicholls Neville
Published: October 2008

Trends in the seasonal and temporal behaviour of the El Niño–Southern Oscillation over the period 1958–2007 have been assessed using two indices of the phenomenon, NINO3.4 and a non‐standardised Southern Oscillation Index (SOI). There is no evidence of trends in the variability or the persistence of the indices, nor in their seasonal patterns. There is a trend towards what might be considered more “El Niño‐like” behaviour in the SOI (and more weakly in NINO3.4), but only through the period March–September and not in November–February, the season when El Niño and La Niña events typically peak. The trend in the SOI reflects only a trend in Darwin pressures, with no trend in Tahiti pressures. Apart from this trend, the temporal/seasonal nature of the El Niño–Southern Oscillation has been remarkably consistent through a period of strong global warming.
First measurements of lower mesospheric wind by airborne microwave radiometry
Authors: Flury T. , Hocke K. , Müller S. C. , Kämpfer N.
Published: October 2008

The Institute of Applied Physics operates an airborne microwave radiometer that measures the rotational transition line of water vapor at 183.3 GHz. A narrowband digital FFT spectrometer is used for the detection of the atmospheric signal with a channel resolution of 12 kHz. For the first time we measure lower mesospheric wind using the wind induced Doppler shift of the spectral line at its center. The Doppler frequency shift is calculated by the center of mass method allowing to retrieve the wind speed in the layer 55–70 km with a precision of 14 m/s. A good agreement with ECMWF operational reanalysis is found. We show that microwave remote sensing is an appropriate technique to fill the current experimental data gap in lower mesospheric winds. Precise wind measurements are of need to improve atmosphere circulation models and medium range weather forecasts.
Effects of wind‐powered hydrogen fuel cell vehicles on stratospheric ozone and global climate
Authors: Jacobson Mark Z.
Published: October 2008

Converting the world's fossil‐fuel onroad vehicles (FFOV) to hydrogen fuel cell vehicles (HFCV), where the H2 is produced by wind‐powered electrolysis, is estimated to reduce global fossil, biofuel, and biomass‐burning emissions of CO2 by ∼13.4%, NOx ∼23.0%, nonmethane organic gases ∼18.9%, black carbon ∼8% H2 ∼3.2% (at 3% leakage), and H2O ∼0.2%. Over 10 years, such reductions were calculated to reduce tropospheric CO ∼5%, NOx ∼5–13%, most organic gases ∼3–15%, OH ∼4%, ozone ∼6%, and PAN ∼13%, but to increase tropospheric CH4 ∼0.25% due to the lower OH. Lower OH also increased upper tropospheric/lower stratospheric ozone, increasing its global column by ∼0.41%. WHFCV cooled the troposphere and warmed the stratosphere, reduced aerosol and cloud surface areas, and increased precipitation. Other renewable‐powered HFCV or battery electric vehicles should have similar impacts.
Seismic and acoustic recordings of an unusually large rockfall at Mount St. Helens, Washington
Authors: Moran S. C. , Matoza R. S. , Garcés M. A. , Hedlin M. A. H. , Bowers D. , Scott W. E. , Sherrod D. R. , Vallance J. W.
Published: October 2008

On 29 May 2006 a large rockfall off the Mount St. Helens lava dome produced an atmospheric plume that was reported by airplane pilots to have risen to 6,000 m above sea level and interpreted to be a result of an explosive event. However, subsequent field reconnaissance found no evidence of a ballistic field, indicating that there was no explosive component. The rockfall produced complex seismic and infrasonic signals, with the latter recorded at sites 0.6 and 13.4 km from the source. An unusual, very long‐period (50 s) infrasonic signal was recorded, a signal we model as the result of air displacement. Two high‐frequency infrasonic signals are inferred to result from the initial contact of a rock slab with the ground and from interaction of displaced air with a depression at the base of the active lava dome.
Correlations between SO2 flux, seismicity, and outgassing activity at the open vent of Villarrica volcano, Chile
Authors: Palma José Luis , Calder Eliza S. , Basualto Daniel , Blake Stephen , Rothery David A.
Published: October 2008

The characteristics of the open vent activity of Villarrica volcano, Chile, were studied in detail by integrating visual observations of the lava lake, analysis of the seismic tremor, and measurements of SO2 flux. The outgassing activity comprises a persistent gas plume emission from the bottom of the crater as well as frequent explosive events. Three main styles of bubble bursting were identified at the surface of the active lava lake: seething magma, small short‐lived lava fountains, and Strombolian explosions. Seething magma consists of continual burst of relatively small bubbles (a few meters in diameter) with varying strength over the entire surface of the lava lake. Small lava fountains, seen as a vigorous extension of seething magma, commonly have durations of 20–120 s and reach 10–40 m high above the lava lake. Correlations between seismicity and visual observations indicate that the seismic tremor is mostly caused by the explosive outgassing activity. Furthermore, for different periods between 2000 and 2006, during which the activity remained comparable, the real‐time seismic amplitude measurement system (RSAM) and SO2 emission rates show a very good correlation. Higher SO2 emissions appeared to be related to higher levels of the lava lake, stronger bubble bursting activity, and changes in the morphology and texture of the crater floor. Background (low) levels of activity correspond to a lava lake located >80 m below the crater rim, small and/or blocky morphology of the roof, seismic amplitude (RSAM) lower than 25 units, few volcano‐tectonic earthquakes, and daily averages of SO2 emissions lower than 600 Mg/d.
Induction of the Wnt Antagonist, Dickkopf-1, Contributes to the Development of Neuronal Death in Models of Brain Focal Ischemia
Authors: Mastroiacovo Federica , Busceti Carla L , Biagioni Francesca , Moyanova Slavianka G , Meisler Miriam H , Battaglia Giuseppe , Caricasole Andrea , Bruno Valeria , Nicoletti Ferdinando
Published: October 2008

Inhibition of the canonical Wnt pathway has been implicated in the pathophysiology of neuronal death. Here, we report that the secreted Wnt antagonist, Dickkopf-1 (Dkk-1) is rapidly induced in neurons after induction of focal brain ischemia. In rats undergoing transient focal ischemia in response to brain infusion of endothelin-1, Dkk-1 was induced in neurons of the ischemic core and the penumbra region. Induction of Dkk-1 was associated with a reduced expression of β-catenin (a downstream signaling molecule of the canonical Wnt pathway), and was not observed in neurons expressing the protective protein, heat shock protein-70. Treatment with lithium ions, which, inter alia, rescue the canonical Wnt pathway, was highly protective against ischemic damage. Dkk-1 was also induced in cortical neurons of mice undergoing permanent middle cerebral artery (MCA) occlusion. This model allowed us to compare wild-type mice with doubleridge mice, which are characterized by a reduced expression of Dkk-1. Doubleridge mice showed an attenuated reduction of β-catenin and a reduced infarct volume in response to MCA occlusion, providing a direct demonstration that Dkk-1 contributes to the pathophysiology of ischemic neuronal damage. These data rise the interesting possibility that Dkk-1 antagonists or drugs that rescue the Wnt pathway might be neuroprotective in stroke.
Magnetic Resonance Imaging Assessment of Regional Cerebral Blood Flow after Asphyxial Cardiac Arrest in Immature Rats
Authors: Manole Mioara D , Foley Lesley M , Hitchens T Kevin , Kochanek Patrick M , Hickey Robert W , Bayir Hülya , Alexander Henry , Ho Chien , Clark Robert SB
Published: October 2008

Cerebral blood flow (CBF) alterations after asphyxial cardiac arrest (CA) are not defined in developmental animal models or humans. We characterized regional and temporal changes in CBF from 5 to 150 mins after asphyxial CA of increasing duration (8.5, 9, 12 min) in postnatal day (PND) 17 rats using the noninvasive method of arterial spin-labeled magnetic resonance imaging (ASL-MRI). We also assessed blood-brain barrier (BBB) permeability, and evaluated the relationship between CBF and mean arterial pressure after resuscitation. After all durations of asphyxia CBF alterations were region dependent. After 8.5- and 9-min asphyxia, intense subcortical hyperemia at 5 min was followed by return of CBF to baseline values by 10 mins. After 12-min asphyxia, hyperemia was absent and hypoperfusion reached a nadir of 38% to 65% of baselines with the lowest values in the cortex. BBB was impermeable to gadoteridol 150 mins after CA. CBF in the 12-min CA group was blood pressure passive at 60 min assessed via infusion of epinephrine. ASL-MRI assessment of CBF after asphyxial Ca in PND 17 rats reveals marked duration and region-specific reperfusion patterns and identifies possible new therapeutic targets.
Quantitative Assessment of Water Pools by T1p and T2p MRI in Acute Cerebral Ischemia of the Rat
Authors: Jokivarsi Kimmo T , Niskanen Juha-Pekka , Michaeli Shalom , Gröhn Heidi I , Garwood Michael , Kauppinen Risto A , Gröhn Olli H
Published: October 2008

The rotating frame longitudinal relaxation magnetic resonance imaging (MRI) contrast, T1ρ, obtained with on-resonance continuous wave (CW) spin-lock field is a sensitive indicator of tissue changes associated with hyperacute stroke. Here, the rotating frame relaxation concept was extended by acquiring both T1ρ and transverse rotating frame ( T2ρ) MRI data using both CW and adiabatic hyperbolic secant (HSn; n = 1, 4, or 8) pulses in a rat stroke model of middle cerebral artery occlusion. The results show differences in the sensitivity of spinlock T1ρ and T2ρ MRI to detect hyperacute ischemia. The most sensitive techniques were CW- T1ρ and T1ρ using HS4 or HS8 pulses. Fitting a two-pool exchange model to the T1ρ and T2ρ MRI data acquired from the infarcting brain indicated time-dependent increase in free water fraction, decrease in the correlation time of water fraction associated with macromolecules, and increase in the exchange correlation time. These findings are consistent with known pathology in acute stroke, including vasogenic edema, destructive processes, and tissue acidification. Our results show that the sensitivity of the spinlock MRI contrast in vivo can be modified using different spinlock preparation blocks, and that physicochemical models of the rotating frame relaxation may provide insight into progression of ischemia in vivo.
Intracerebral Hemorrhage Leads to Infiltration of Several Leukocyte Populations with Concomitant Pathophysiological Changes
Authors: Loftspring Matthew C , McDole Jeremiah , Lu Aigang , Clark Joseph F , Johnson Aaron J
Published: October 2008

Intracerebral hemorrhage (ICH) is a stroke subtype with high rates of mortality and morbidity. The immune system, particularly complement and cytokine signaling, has been implicated in brain injury after ICH. However, the cellular immunology associated with ICH has been understudied. In this report, we use flow cytometry to quantitatively profile immune cell populations that infiltrate the brain 1 and 4 days post-ICH. At 1 day CD45hi GR-1+ cells were increased 2.0-fold compared with saline controls ( P ≤ 0.05); however, we did not observe changes in any other cell populations analyzed. At 4 days ICH mice presented with a 2.4-fold increase in CD45hi cells, a 1.9-fold increase in CD45hi GR-1 cells, a 3.4-fold increase in CD45hi GR-1+ cells, and most notably, a 1.7-fold increase in CD4+ cells ( P ≤ 0.05 for all groups), compared with control mice. We did not observe changes in the numbers of CD8+ cells or CD45lo cells ( P = 0.43 and 0.49, respectively). Thus, we have shown the first use of flow cytometry to analyze leukocyte infiltration in response to ICH. Our finding of a CD4 T-cell infiltrate is novel and suggests a role for the adaptive immune system in the response to ICH.
Chaotic model and memory in single calcium-activated potassium channel kinetics
Authors: Bandeira Heliovânio T. , Barbosa Catão T. F. , Campos De Oliveira Regina A. , Aguiar José F. , Nogueira Romildo A.
Published: October 2008

Ion channels are pores formed by proteins and responsible for carrying ion fluxes through cellular membranes. The ion channels can assume conformational states thereby controlling ion flow. Physically, the conformational transitions from one state to another are associated with energy barriers between them and are dependent on stimulus, such as, electrical field, ligands, second messengers, etc. Several models have been proposed to describe the kinetics of ion channels. The classical Markovian model assumes that a future transition is independent of the time that the ion channel stayed in a previous state. Others models as the fractal and the chaotic assume that the rate of transitions between the states depend on the time that the ionic channel stayed in a previous state. For the calcium activated potassium channels of Leydig cells the R/S Hurst analysis has indicated that the channels are long-term correlated with a Hurst coefficient H around 0.7, showing a persistent memory in this kinetic. Here, we applied the R∕S analysis to the opening and closing dwell time series obtained from simulated data from a chaotic model proposed by L. Liebovitch and T. Tóth [J. Theor. Biol. 148, 243 (1991)] and we show that this chaotic model or any model that treats the set of channel openings and closings as independent events is inadequate to describe the long-term correlation (memory) already described for the experimental data.
Translocation of a knotted polypeptide through a pore
Authors: Huang Lei , Makarov Dmitrii E.
Published: October 2008

We use Langevin dynamics simulations to study how the presence of a deep knot affects the time it takes to thread a polypeptide chain through a narrow pore by pulling mechanically at its end. The polypeptide was designed to contain a knotted unstructured segment inserted between two β-hairpins, which prevented the knot from slipping off the chain ends. In the range of forces studied (40–200pN), the mean translocation time increased with the knot complexity. The type 52 knot, which was recently discovered in the structure of human ubiquitin hydrolase and is the most complex knot found in the protein databank, slows down translocation by about two orders of magnitude, as compared to the unknotted chain. In contrast to the unknotted chain case, the translocation mechanism of knotted chains involves multiple slippage events suggesting that the corresponding free energy landscape is rugged and involves multiple metastable minima.
Single-chip detector for electron spin resonance spectroscopy
Authors: Yalcin T. , Boero G.
Published: October 2008

We have realized an innovative integrated detector for electron spin resonance spectroscopy. The microsystem, consisting of an LC oscillator, a mixer, and a frequency division module, is integrated onto a single silicon chip using a conventional complementary metal-oxide-semiconductor technology. The implemented detection method is based on the measurement of the variation of the frequency of the integrated LC oscillator as a function of the applied static magnetic field, caused by the presence of a resonating sample placed over the inductor of the LC-tank circuit. The achieved room temperature spin sensitivity is about 1010spins∕GHz1∕2 with a sensitive volume of about (100μm)3.
The Prigogine–Defay ratio and the microscopic theory of supercooled liquids
Authors: Pick R. M.
Published: October 2008

Prigogine–Defay ratios and, more recently, their frequency extension have been proposed to be a measure of the number of nonmacroscopic processes involved in the relaxation dynamics of supercooled liquids. We show that the microscopic theory of the Navier–Stokes equations of those liquids provides a consistent thermodynamic framework in which all possible dynamical Prigogine–Defay ratios can be expressed in terms of the same relaxation functions and that these ratios provide less information than the microscopic theory itself. The latter shows that more than one relaxation process is certainly always involved in this relaxation dynamics, whatever is the molecular dynamics, or experimental, technique used to determine the latter.
Partial multicanonical algorithm for molecular dynamics and Monte Carlo simulations
Authors: Okumura Hisashi
Published: October 2008

Partial multicanonical algorithm is proposed for molecular dynamics and Monte Carlo simulations. The partial multicanonical simulation samples a wide range of a part of the potential-energy terms, which is necessary to sample the conformational space widely, whereas a wide range of total potential energy is sampled in the multicanonical algorithm. Thus, one can concentrate the effort to determine the weight factor only on the important energy terms in the partial multicanonical simulation. The partial multicanonical, multicanonical, and canonical molecular dynamics algorithms were applied to an alanine dipeptide in explicit water solvent. The canonical simulation sampled the states of PII, C5, αR, and αP. The multicanonical simulation covered the αL state as well as these states. The partial multicanonical simulation also sampled the C7ax state in addition to the states that were sampled by the multicanonical simulation. In the partial multicanonical simulation, furthermore, backbone dihedral angles ϕ and ψ rotated more frequently than those in the multicanonical and canonical simulations. These results mean that the partial multicanonical algorithm has a higher sampling efficiency than the multicanonical and canonical algorithms.
Quantum streamlines within the complex quantum Hamilton–Jacobi formalism
Authors: Chou Chia-Chun , Wyatt Robert E.
Published: October 2008

Quantum streamlines are investigated in the framework of the quantum Hamilton–Jacobi formalism. The local structures of the quantum momentum function (QMF) and the Pólya vector field near a stagnation point or a pole are analyzed. Streamlines near a stagnation point of the QMF may spiral into or away from it, or they may become circles centered on this point or straight lines. Additionally, streamlines near a pole display east-west and north-south opening hyperbolic structure. On the other hand, streamlines near a stagnation point of the Pólya vector field for the QMF display general hyperbolic structure, and streamlines near a pole become circles enclosing the pole. Furthermore, the local structures of the QMF and the Pólya vector field around a stagnation point are related to the first derivative of the QMF; however, the magnitude of the asymptotic structures for these two fields near a pole depends only on the order of the node in the wave function. Two nonstationary states constructed from the eigenstates of the harmonic oscillator are used to illustrate the local structures of these two fields and the dynamics of the streamlines near a stagnation point or a pole. This study presents the abundant dynamics of the streamlines in the complex space for one-dimensional time-dependent problems.
A simple classical model for predicting onset crystallization temperatures on curved substrates and its implications for phase transitions in confined volumes
Authors: Cooper Sharon J. , Nicholson Catherine E. , Liu Jian
Published: October 2008

For small confinement volumes, phase transition temperatures are determined by the scarcity of the crystallizing material, rather than the magnitude of the energy barrier, as the supply of molecules undergoing the phase transition can be depleted before a stable nucleus is attained. We show this for the case of crystallization from the melt and from the solution by using a simple model based on an extended classical nucleation theory. This has important implications because it enables a simple and direct measurement of the critical nucleus size in crystallization. It also highlights that predicting the observable melting points of nanoparticles by using the Gibbs–Thomson equation can lead to substantial errors.
Critical adsorption and critical Casimir forces for geometrically structured confinements
Authors: Tröndle M. , Harnau L. , Dietrich S.
Published: October 2008

We study the behavior of fluids, confined by geometrically structured substrates, upon approaching a critical point at T=Tc in their bulk phase diagram. As generic substrate structures periodic arrays of wedges and ridges are considered. Based on general renormalization group arguments we calculate, within mean field approximation, the universal scaling functions for order parameter profiles of a fluid close to a single structured substrate and discuss the decay of its spatial variation into the bulk. We compare the excess adsorption at corrugated substrates to the one at planar walls. The confinement of a critical fluid by two walls generates effective critical Casimir forces between them. We calculate corresponding universal scaling functions for the normal critical Casimir force between a flat and a geometrically structured substrate as well as the lateral critical Casimir force between two identically patterned substrates.
Evolution of neutral and charged droplets in an electric field
Authors: Fontelos M. A. , Kindelán U. , Vantzos O.
Published: October 2008

We study the evolution of drops of a very viscous and conducting fluid under the influence of an external electric field. The drops may be neutral or may be charged with some amount of electric charge. If both the external electric field and total drop charge are sufficiently small, then prolate spherical shapes develop according to Taylor’s observations. For sufficiently large charge and/or external field a self-similar conelike singularity develops in a mechanism different from Taylor’s prediction. The opening semiangle of the cones both for uncharged and charged drops in a constant electric field is typically around 30° with a very slight dependence on the viscosity ratio and independence from both total charge and external field. We also discuss the structure of electric and velocity fields near the tip.
Pseudo-Jahn-Teller origin of the low barrier hydrogen bond in N2H7+
Authors: García-Fernández P. , García-Canales L. , García-Lastra J. M. , Junquera J. , Moreno M. , Aramburu J. A.
Published: October 2008

The microscopic origin and quantum effects of the low barrier hydrogen bond (LBHB) in the proton-bound ammonia dimer cation N2H7+ were studied by means of ab initio and density-functional theory (DFT) methods. These results were analyzed in the framework of vibronic theory and compared to those obtained for the Zundel cation H5O2+. All geometry optimizations carried out using wavefunction-based methods [Hartree–Fock, second and fourth order Möller–Plesset theory (MP2 and MP4), and quadratic configuration interaction with singles and doubles excitations (QCISD)] lead to an asymmetrical H3N–H+⋯NH3 conformation (C3v symmetry) with a small energy barrier (1.26kcal∕mol in MP4 and QCISD calculations) between both equivalent minima. The value of this barrier is underestimated in DFT calculations particularly at the local density approximation level where geometry optimization leads to a symmetric H3N⋯H+⋯NH3 structure (D3d point group). The instability of the symmetric D3d structure is shown to originate from the pseudo-Jahn–Teller mixing of the electronic A1g1 ground state with five low lying excited states of A2u symmetry through the asymmetric α2u vibrational mode. A molecular orbital study of the pseudo-Jahn–Teller coupling has allowed us to discuss the origin of the proton displacement and the LBHB formation in terms of the polarization of the NH3 molecules and the transfer of electronic charge between the proton and the NH3 units (rebonding). The parallel study of the H5O2+ cation, which presents a symmetric single-well structure, allows us to analyze why these similar molecules behave differently with respect to proton transfer. From the vibronic analysis, a unified view of the Rudle–Pimentel three-center four-electron and charge transfer models of LBHBs is given. Finally, the large difference in the N–N distance in the D3d and C3v configurations of N2H7+ indicates a large anharmonic coupling between α2u-α1g modes along the proton-transfer dynamics. This issue was explored by solving numerically the vibrational Schrödinger equation corresponding to the bidimensional E[Q(α2u),Q(α1g)] energy surface calculated at the MP4∕6-311++G** level of theory.
The Rossby-inertia-buoyancy instability in baroclinic vortices
Authors: Hodyss Daniel , Nolan David S.
Published: October 2008

The behavior of vortex Rossby (VR) waves undergoing inertia-buoyancy (IB) wave emission on vortices with baroclinic vertical structures is studied. We consider monotonic vortices, where the potential vorticity (PV) decays monotonically with radial distance from the vortex center, and “single-peak” vortices, where the PV reaches a single radial maximum off the vortex center. A linear anelastic model is numerically solved as an eigenvalue problem. The difference between Rossby-inertia-buoyancy (RIB) waves and traditional coupled VR wave barotropic instability is shown to be associated with the region of the vortex where the mode extracts its energy for growth. The dependence of the growth rate of these RIB modes on the radial and vertical PV gradients of the vortex is studied. New interpretations of the damping of RIB modes on baroclinic, monotonic vortices are found to be as follows: (1) RIB mode growth depends on a sensitive arrangement of radial momentum fluxes such that it is disrupted by the vertical tilting of the mode by the vortex vertical shear and (2) RIB modes have a more complicated structure than traditional barotropic instabilities such that eddy viscosity acts more strongly. It is also found that single-peak vortices with annular PV regions that are very thin favor barotropic instabilities with weak IB wave emission, but in contrast, relatively wider annular regions favor barotropic instabilities with strong IB wave emission. The modification of the vortex induced by RIB mode growth is briefly explored in a fully nonlinear model.
Spin-dependent transport and spin polarization in coupled quantum wells
Authors: Liu Genhua , Chen Yonghai , Liu Yu , Jia Caihong , Wang Zhanguo
Published: October 2008

We theoretically investigate the electron transport and spin polarization of two coupled quantum wells with Dresselhaus spin-orbit interaction. In analogy with the optical dual-channel directional coupler, the resonant tunneling effect is treated by the coupled-mode equations. We demonstrate that spin-up and -down electrons can be completely separated from each other for the system with an appropriate system geometry and a controllable barrier. Our result provides a new approach to construct spin-switching devices without containing any magnetic materials or applying a magnetic field.
Digitally synthesized high purity, high-voltage radio frequency drive electronics for mass spectrometry
Authors: Schaefer R. T. , MacAskill J. A. , Mojarradi M. , Chutjian A. , Darrach M. R. , Madzunkov S. M. , Shortt B. J.
Published: October 2008

Reported herein is development of a quadrupole mass spectrometer controller (MSC) with integrated radio frequency (rf) power supply and mass spectrometer drive electronics. Advances have been made in terms of the physical size and power consumption of the MSC, while simultaneously making improvements in frequency stability, total harmonic distortion, and spectral purity. The rf power supply portion of the MSC is based on a series-resonant LC tank, where the capacitive load is the mass spectrometer itself, and the inductor is a solenoid or toroid, with various core materials. The MSC drive electronics is based on a field programmable gate array (FPGA), with serial peripheral interface for analog-to-digital and digital-to-analog converter support, and RS232/RS422 communications interfaces. The MSC offers spectral quality comparable to, or exceeding, that of conventional rf power supplies used in commercially available mass spectrometers; and as well an inherent flexibility, via the FPGA implementation, for a variety of tasks that includes proportional-integral derivative closed-loop feedback and control of rf, rf amplitude, and mass spectrometer sensitivity. Also provided are dc offsets and resonant dipole excitation for mass selective accumulation in applications involving quadrupole ion traps; rf phase locking and phase shifting for external loading of a quadrupole ion trap; and multichannel scaling of acquired mass spectra. The functionality of the MSC is task specific, and is easily modified by simply loading FPGA registers or reprogramming FPGA firmware.
Diffused phase transition and multiferroic properties of 0.57(Bi1−xLax)FeO3−0.43PbTiO3 crystalline solutions
Authors: Chen Jianguo , Qi Yufa , Shi Guiyang , Yan Xiaolong , Yu Shengwen , Cheng Jinrong
Published: October 2008

Crystalline solutions of 0.57(Bi1−xLax)FeO3−0.43PbTiO3 (BLF-PT) for x=0, 0.1, 0.2, and 0.3 have been fabricated by the solid state reaction method. The dielectric constant of BLF-PT was significantly enhanced by using La substitutions, reaching about 1850 for x=0.3. The ferroelectric-paraelectric phase transition of BLF-PT becomes more diffused with a decreased transition temperature for higher La concentration. BLF-PT of x=0.2 exhibits multiferroic characteristics with the simultaneously enhanced remnant magnetization and polarization of 0.119 emu/g and 33.5 μC/cm2, respectively.
Plasma dynamics during relativistic S-band magnetron operation
Authors: Hadas Y. , Sayapin A. , Krasik Ya. E. , Bernshtam V. , Schnitzer I.
Published: October 2008

Results of a time- and space-resolved spectroscopic research studies of an S-band relativistic magnetron generating 1.5×108 W microwave power at f=2950 MHz, powered by a linear induction accelerator (450 kV, 4 kA, 150 ns), are presented. The cathode plasma electron density and temperature were obtained by analyzing Hα and Hβ hydrogen Ballmer series and carbon C II and C III ion spectral lines and the results of collision radiative modeling. It was shown that the microwave generation is accompanied by a significant increase in plasma density and ion temperature, up to ∼5×1016 cm−3 and ∼8 eV, respectively. The plasma electron temperature was found to be ∼8 eV. It was shown that the plasma expansion velocity in the axial direction reaches ∼107 cm/s and does not exceed ∼2×105 cm/s in the radial direction. In addition, it was shown that the plasma is not uniform and consists of separate plasma spots whose number increases during the accelerating pulse. Estimates of the plasma transport parameters and its interaction with microwave radiation are also discussed.
A numerical model and scaling relationship for energetic electron beams propagating in air
Authors: Fernsler R. F. , Slinker S. P. , Lambrakos S. G.
Published: October 2008

Scaling relationships for energy loss and scattering are combined with a particle code to construct a purely algebraic expression for the energy deposited by an energetic electron beam injected into field-free homogeneous air. An algebraic formulation is possible because the mean free paths for the major collisional processes depend similarly on density and energy above 1 keV. Accordingly, the spatial behavior of an initially cold pencil beam is approximately self-similar when expressed in terms of the nominal beam range, provided the beam energy at injection exceeds several keV. Since a warm and broad beam can always be decomposed into a series of cold pencil beams, the total energy deposited can be obtained through a simple sum. With such a model, the ionization and excitation generated by a beam can be computed quickly and easily at every point in space. Similar formulations can be developed for other media using particle codes or experimental data. In liquids or solids, the energy deposited is quickly converted to heat and ultimately to melting and/or vaporization of the material.
Mass flux through asymmetric nanopores: Microscopic versus hydrodynamic motion
Authors: Chinappi Mauro , Melchionna Simone , Casiola Carlo Massimo , Succi Sauro
Published: October 2008

The crossover from hydrodynamic to microscopic motion in nanoscopic channels with broken spatial symmetry is investigated by means of many-body molecular dynamics simulations at various pore diameters. It is found that both hydrodynamic and microscopic regimes favor motion along the convergent over the divergent directions, although with a different scaling of the mass flow with the pore diameter. In either cases, departure from linear response and the ensuing detection of spatial asymmetry seems to respond more to the intensity of the external drive than to the granularity of the flowing system. Our simulations suggest that this property lies at the heart of microscopic ratchet motion and its capability of echoing the symmetry-breaking detection realized by macroscopic fluids at nonzero Reynolds numbers.
Superintegrability of the caged anisotropic oscillator
Authors: Evans N. W. , Verrier P. E.
Published: October 2008

We study the caged anisotropic harmonic oscillator, which is a new example of a superintegrable or accidentally degenerate Hamiltonian. The potential is that of the harmonic oscillator with rational frequency ratio (l:m:n) but additionally with barrier terms describing repulsive forces from the principal planes. This confines the classical motion to a sector bounded by the principal planes, or a cage. In three degrees of freedom, there are five isolating integrals of motion, ensuring that all bound trajectories are closed and strictly periodic. Three of the integrals are quadratic in the momenta, the remaining two are polynomials of order 2(l+m−1) and 2(l+n−1). In the quantum problem, the eigenstates are multiply degenerate, exhibiting l2m2n2 copies of the fundamental pattern of the symmetry group SU(3).
The extraordinary wave excitation in microwave gas breakdown in the adiabatic approximation
Authors: Ghorbanalilu M. , Shokri B.
Published: October 2008

Making use of the electron distribution function formed in the interaction of high-frequency microwave (MW) pulsed fields with a rarefied neutral gas [M. Ghorbanalilu, Phys. Plasmas. 13, 102110 (2006)], the dielectric permittivity tensor of the produced plasma is derived under the condition that the ions are cold and nonmagnetized. According to the adiabatic approximation and using the dielectric permittivity tensor elements the dispersion relations for ordinary and extraordinary excited waves are found. The numerical solution of the dispersion relation shows that the extraordinary modes are unstable in such a nonequilibrium system. These modes are generated in a wide range of wavelengths by tuning the MW field amplitude and magnetic field strength.
Light focusing from large refractive indices in ionized air
Authors: Robledo-Martinez A. , Sobral H. , Villagrán-Muniz M. , Bredice F.
Published: October 2008

The sheath that surrounds a laser-induced plasma in air was investigated with a light probe. The sheath is a 3-mm-thick halo of ionized gas created by ultraviolet light emitted from the plasma core. A beam of laser light tracked with a streak camera was employed to probe it. It was found that in the first hundreds of a nanosecond after plasma inception, the beam is deflected towards the plasma center. This result points to a high refractive index inside the sheath. The index values obtained (up to 2.0) are due to an increased susceptibility caused by a bulk electric polarization. Using previous results on the sheath’s electric polarizability values, the refractive index was calculated and was found to agree with the observed indices. The application of the electric polarization model to the guiding of laser beams and to plasma lenses is also discussed.
On the observability of “out-of-plane” quadrupolar magnetic perturbations in two-dimensional force-free reconnection
Authors: Wang Jiaqi , Wang Xiaogang
Published: October 2008

Nonlinear studies for “out-of-plane” magnetic perturbations in two-dimensional force-free magnetic reconnection are carried out to analyze if they are significant enough to be observable in concerned regimes. It is found that though in linear analysis [Bian et al., Phys. Plasmas 14, 120702 (2007)] the “out-of-plane” quadrupolar magnetic perturbation can be generated in the “standard magnetohydrodynamics regime,” it is too weak to be detected in observations.