bluuebunny/crossref_metadata_2025 huggingface dataset:
An examination of Köhler theory resulting in an accurate expression for the equilibrium radius ratio of a hygroscopic aerosol particle valid up to and including relative humidity 100%
Authors: Lewis Ernie R.
Published: February 2008

The equilibrium hygroscopic behavior of an aqueous solution drop is investigated using the Köhler model to relate the radius ratio ξ ≡ r/rdry, where rdry is the volume‐equivalent dry radius, and the fractional relative humidity h. The Köhler equation is derived and results obtained from it are presented for three situations: when the effect of surface tension can be neglected, for h = 1, and for cloud‐drop activation. The exact solution to this equation is presented, as is an accurate approximate solution for h < 1 that yields insight into the dependences of the equilibrium radius on relative humidity, surface tension, and dry radius. The approximations made in the derivation of the Köhler equation are examined, errors in quantities obtained from this equation are quantified, and the so‐called Debye approximation is introduced which allows accurate parameterization of these errors as a function of rdry. Errors in the radius ratio at activation obtained from the Köhler equation are up to 20% for ammonium sulfate solution drops of the size that typically form cloud drops. Attempts to extend the Köhler model to higher concentrations are examined, and it is seen that the primary cause of inaccuracy in the model is the assumption that the practical osmotic coefficient is unity. On the basis of this analysis, a simple two‐parameter expression is presented for the equilibrium radius ratio as a function of h and rdry that is accurate over a wide range of rdry and for h up to and including unity.
Dynamics of groundwater recharge and seepage over the Canadian landscape during the Wisconsinian glaciation
Authors: Lemieux J.‐M. , Sudicky E. A. , Peltier W. R. , Tarasov L.
Published: February 2008

Pleistocene glaciations and their associated dramatic climatic conditions are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow‐related processes involved during a glaciation period, numerical models have become powerful tools for examining groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modeling, such as density‐dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (∼−120 ka to present). The primary objective is to demonstrate the immense impact of glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface‐subsurface water exchanges (i.e., recharge and discharge fluxes) in both the subglacial and the periglacial environments. It is shown that much of the infiltration of subglacial meltwater occurs during ice sheet progression and that during ice sheet regression, groundwater mainly exfiltrates on the surface, in both the subglacial and periglacial environments. The average infiltration/exfiltration fluxes range between 0 and 12 mm/a. Using mixed, ice sheet thickness–dependent boundary conditions for the subglacial environment, it was estimated that 15–70% of the meltwater infiltrated into the subsurface as recharge, with an average of 43%. Considering the volume of meltwater that was generated subsequent to the last glacial maximum, these recharge rates, which are related to the bedrock type and elastic properties, are historically significant and therefore played an immense role in the evolution of groundwater flow system evolution over the Canadian landmass over the last 120 ka. Finally, it is shown that the permafrost extent plays a key role in the distribution of surface‐subsurface interaction because the presence of permafrost acts as a barrier for groundwater flow.
New Episodes of Volcanism at Kilauea Volcano, Hawaii
Authors: Poland Michael , Miklius Asta , Orr Tim , Sutton Jeff , Thornber Carl , Wilson David
Published: February 2008

Mid‐2007 was a time of intense activity at Kilauea Volcano, Hawaii (see Figure 1). In June, the long‐lived Pu'u 'Ō'ō—Kupaianaha eruption, a dual‐vent system along the east rift zone (ERZ) that has been erupting since 1983 [Heliker et al., 2003], paused due to the outbreak of a new vent farther up the rift (see Figure 2). The Pu'u 'Ō'ō vent collapsed following that activity, and the resulting reorganization of the magma plumbing system led to the formation of a second new eruptive vent 2 kilometers downrift of Pu'u 'Ō'ō.

These events were well documented by geological, geophysical, and geochemical monitoring. This article summarizes results from these monitoring efforts and interprets the changes that have occurred at Kilauea since June 2007.
Converting Raw Data Into Ecologically Meaningful Products: Data‐Model Assimilation in Ecology: Techniques and Applications; Norman, Oklahoma, 22–24 October 2007
Authors: Hui Dafeng , Luo Yiqi , Schimel David , Clark James S. , Hastings Alan , Ogle Kiona , Williams Mathew
Published: February 2008

A U.S. National Science Foundation workshop brought together more than 40 researchers from different disciplines to discuss applications of data assimilation techniques in ecology, define major scientific questions to be addressed, and identify future research challenges.

The field of ecology has become a data‐rich enterprise, due largely to rapid development of measurement sensors and long‐term accumulation of data from research networks. With the implementation of the National Ecological Observatory Network (NEON), a network with different kinds of sensors at many locations over the nation, large volumes of ecological data will be generated every day. There will be an unprecedented demand to convert the massive raw data into ecologically meaningful products using data assimilation techniques.
European Magellan Workshop Series on Marine Research Drilling
Authors: Spezzaferri Silvia
Published: February 2008

A fundamental and unanswered question facing Earth and life scientists today is: What are the important relationships among the hydrosphere, the geosphere, and the biosphere? The geological setting of mound systems and mud volcanoes furnishes a unique natural laboratory for studying and understanding the dynamic interplay among carbonates, geofluids, and biodiversity, while also providing a window into the deep biosphere where elemental cycles and diagenetic processes can be evaluated. In addition to biogeochemical processes, the genetic or causal link between these two structural types can be explored in order to determine if these modern systems are appropriate analogues for ancient mounds found in the sedimentary record.
McNutt Receives 2007 Maurice Ewing Medal
Authors: Watts Anthony B. , McNutt Marcia K.
Published: February 2008

It is a great honor for me to have the opportunity to deliver this citation for Marcia K. McNutt, the 2007 recipient of AGU's Maurice Ewing Medal. Marcia has made a significant contribution to our understanding of the structure of oceanic lithosphere, served in leadership roles in the marine scientific community, and instigated new directions and technologies for ocean exploration.

Marcia received her undergraduate degree in physics and studied for the Ph.D. with Bob Parker and the late Bill Menard at the Scripps Institution of Oceanography. Her thesis led to two seminal papers on oceanic and continental isostasy. The first showed that flexure due to a young volcanic load could influence the subsidence and uplift history of nearby, preexisting volcanoes. This hypothesis, which explains why some seamounts and oceanic islands show uplift rather than subsidence, has had wide implications for basin development and sea level change. The second used 3‐D spectral methods of analyzing topography and gravity data to argue that the Australian lithosphere responds to loads as a relatively strong structure at short time scales and a weak one at long geological times. This method is now widely used and is at the center of current debates concerning the rheology and strength of continental lithosphere.
AGU Revises Position Statement on Climate Change
Authors: Von Holle Kate
Published: February 2008

Earlier this month, Eos published three of the four position statements that were adopted by the AGU Council at its 14 December 2007 meeting. Last week, AGU released the fourth statement, “Human Impacts on Climate.” AGU formulates and maintains a number of position statements that reflect the concerns of the Union, none of which extends beyond the range of available geophysical data or the norms of legitimate scientific debate.

The climate statement has been extensively revised from its original 2003 version, largely because of the significant amount of scientific data that have become available in the past 4 years. The statement also has been substantiated by the release last year of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report.
Human Impacts on Climate
Authors: Anonymous
Published: February 2008

The Earth's climate is now clearly out of balance and is warming. Many components of the climate system—including the temperatures of the atmosphere, land, and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons—are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century. Global average surface temperatures increased on average by about 0.6°C over the period 1956–2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century. Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained research effort, involving many AGU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate.
Science News for the U.S. Hispanic Audience
Authors: Showstack Randy
Published: February 2008

A science and health news service targeted toward the U.S. Hispanic community was launched on 23 January. ConCiencia, billed as the first Spanish‐language science newswire service in the United States, provides free weekly news feeds to media targeting the U.S. Hispanic population. The news feeds, available to Spanish‐language newspapers and radio stations, include newspaper features, radio segments, and online news content.

ConCiencia science advisor Bob Russell said it is critical to provide Hispanic media with an ongoing source of high‐quality science news that meets the needs and interests of Hispanics. He noted that “Latinos currently achieve lower‐than‐average math and science scores in public schools and are significantly underrepresented in science and engineering professions.”
Applying Rock Physics to Natural Hazards: Euro‐Conference of Rock Physics and Geomechanics on Natural Hazards: Thermo‐Hydro‐Mechanical Processes in Rocks; Erice, Italy, 25–30 September 2007
Authors: Vinciguerra Sergio , Bernabe Yves
Published: February 2008

Natural hazards events such as earthquakes or volcanic eruptions involve activation of coupled thermo‐hydro‐chemo‐mechanical processes in rocks. A conference sponsored by the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV), the French Centre National de la Recherche Scientifique (CNRS), and Exxon Mobil was held in Erice, Italy, to explore how rock physics experiments and models can help scientists understand natural hazards mechanisms, and to foster cross‐ disciplinary collaborations.

The largest part of the conference was devoted to questions related to rock failure and earthquake source mechanisms. Several presentations showed that despite the huge reduction in scale, laboratory experiments sometimes display phenomena strikingly similar to field observations. For example, new very high slip‐rate friction experiments show significantly higher fault weakening than previously observed at the laboratory scale. These exploratory experiments may provide new insights into the mutual interactions of frictional shear failure, heat production, and fluid or melt lubrication. Another study revealed that tremor‐like events are generated in laboratory samples during melt propagation in cracks or dehydration of hydrated minerals, providing physical constraints to the open debate on the origin of volcanic and non‐volcanic deep tremors.
Summer School Seeks to Better Link Atmosphere and Ocean Convection Studies: Fundamental Issues in Geophysical and Environmental Fluid Mechanics: Atmosphere‐Ocean Convection in Climate Dynamics; Valsavaranche, Italy, 18–27 June 2007
Authors: Yano Jun‐Ichi , Griffiths Ross , Bouruet‐Aubertot Pascale
Published: February 2008

To provide Ph.D. students with a coherent overview of the current understanding of atmosphere and ocean convection in the context of global climate modeling, an Alpine summer school was organized in Valsavaranche, Italy, during June 2007. About 50 students from five continents and three islands participated in this unique event. Lectures and class discussions covered topics including asymptotic analyses, computational modeling, field campaigns, and laboratory analogs.

The emphasis of the school was on deep convection, the form of convection of greatest importance to global circulation and climate. However, a series of lecturers revealed that atmospheric and oceanographic convection each pose quite different complexities. The presence of water vapor as a minor constituent of the atmosphere substantially alters the thermodynamics, and lecturers discussed how it is necessary to model a water cycle complicated by cloud formation, a variety of ice crystals, precipitation, and reevaporation. Oceanographic convection, on the other hand, is complicated through strong coupling with wind stress forcing, bottom topography, and baroclinic eddies. It still remains a major challenge to identify the various processes governing deep convection in high‐latitude oceans and the tropical atmosphere, and the coupling of this convection with larger‐scale circulation. Parameterization of convection, though clearly essential in climate modeling, is simply too extensively relied upon in both atmosphere and ocean models.
Luhmann Receives 2007 John Adam Fleming Medal
Authors: Russell Christopher T. , Luhmann Janet G.
Published: February 2008

This year's John Adam Fleming medalist quickly established a reputation as an innovative and productive scientist with a broad range of interests. She made early and seminal contributions to aeronomy, cosmic rays, and magnetospheric and planetary physics. She contributed importantly to the understanding of the interaction of the solar wind with the atmosphere and magnetic fields of Mercury, Venus, Earth, and Mars. She has examined the behavior of planetary rings, the interaction of interstellar neutrals with heliospheric plasmas, as well as the interaction of planetary neutrals with the heliosphere. She has led in the study of the interaction of the moon Titan with the Saturn magnetosphere, and most recently she developed a vigorous solar physics effort, leading the implementation of the IMPACT particle and field package on the twin STEREO mission, now entering its second year of successful operation.
Fiscal Year 2009 U.S. Budget Request Unveiled
Authors: Kumar Mohi , Von Holle Kate
Published: February 2008

The Bush administration's proposed budget for fiscal year (FY) 2009, released on 4 February, requested roughly US$40 billion for projects that support research in Earth, environmental, space, and energy‐related sciences through the Department of Energy (DOE) Office of Science, NASA, the U.S. National Oceanic and Atmospheric Administration (NOAA), the U.S. National Science Foundation (NSF), the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (EPA). This request is about 4% more than the amount authorized by Congress to support such research in FY 2008.

A significant portion of this budget increase is for programs that will address global climate change through advancing energy security and monitoring the Earth's dynamic system as global temperatures rise.
U.S. Geological Survey Budget Cuts Funds for Minerals, Hazards, and Water Programs
Authors: Showstack Randy
Published: February 2008

The Bush administration's proposed US$968.5 million budget for the U.S. Geological Survey (USGS) for fiscal year (FY) 2009 is a $38 million decrease from the FY 2008 enacted level.

The proposed budget also includes some increases for high‐priority programs. Funding includes an $8.2 million net increase for a water census that would be the first U.S.‐wide assessment of water availability and human and environmental water use and an increase of $7 million to support the U.S. Department of Interior's Ocean and Coastal Frontiers Initiative, which will acquire key ocean health data while also providing objective scientific data to evaluate U.N. Law of the Sea claims made by other nations.
U.S. Passive Margins: Are We Missing an Important Opportunity?
Authors: Stern Robert J. , Klemperer Simon
Published: February 2008

Understanding passive margins—thick accumulations of sediments built above the juncture between continental and oceanic crusts—has far‐reaching economic and societal implications. Passive margins underlie the coastal regions of most of the conterminous United States, extending continuously from Texas eastward to Florida and northward to Maine. They hide most of the undiscovered hydrocarbon reserves of the United States, and they are excellent sites for sequestering carbon dioxide. Natural hazards of hurricanes, tsunamis, sea level rise, and rapid subsidence, and concerns related to the United Nations Law of the Sea, also make it imperative to better understand passive margins, and how they form and evolve.
Radiation in the Atmosphere: A Course in Theoretical Meteorology
Authors: Hasekamp Otto
Published: February 2008

Radiation transfer theory plays an important role in atmospheric science. Important areas of the application of atmospheric radiative transfer are climate modeling, weather prediction, and atmospheric remote sensing. For these application areas, the radiation transfer equation needs to be solved for a broad spectral range—from the ultraviolet to the infrared part of the electromagnetic spectrum—involving multiple scattering by molecules and cloud/aerosol particles, absorption by atmospheric gases, surface reflection, and emission of radiation by the Earth surface and the atmosphere.
Nitrogen fixation by phyllosphere bacteria associated with higher plants and their colonizing epiphytes of a tropical lowland rainforest of Costa Rica
Authors: Fürnkranz Michael , Wanek Wolfgang , Richter Andreas , Abell Guy , Rasche Frank , Sessitsch Angela
Published: February 2008

Leaf surfaces (phyllospheres) have been shown to provide appropriate conditions for colonization by microorganisms including diazotrophic bacteria that are able to fix atmospheric nitrogen (N2). In this study, we determined leaf-associated N2 fixation of a range of rainforest plants in Costa Rica, under different environmental conditions, by tracing biomass N incorporation from 15N2. N2-fixing bacterial communities of the plant species Carludovica drudei, Grias cauliflora and Costus laevis were investigated in more detail by analysis of the nifH gene and leaf-associated bacteria were identified by 16S rRNA gene analysis. N2 fixation rates varied among plant species, their growth sites (different microclimatic conditions) and light exposure. Leaf-associated diazotrophic bacterial communities detected on C. drudei and C. laevis were mainly composed of cyanobacteria (Nostoc spp.), whereas on the leaves of G. cauliflora γ-proteobacteria were dominant in addition to cyanobacteria. The complexity of diazotrophic communities on leaves was not correlated with N2 fixation activity. 16S rRNA gene sequence analysis suggested the presence of complex microbial communities in association with leaves, however, cyanobacteria showed only low abundance. Our findings suggest that cyanobacteria as well as γ-proteobacteria associated with leaf-colonizing epiphytes may provide significant nitrogen input into this rainforest ecosystem.
Influence of industrial contamination on mobile genetic elements: class 1 integron abundance and gene cassette structure in aquatic bacterial communities
Authors: Wright Meredith S , Baker-Austin Craig , Lindell Angela H , Stepanauskas Ramunas , Stokes Hatch W , McArthur J Vaun
Published: February 2008

The acquisition of new genetic material via horizontal gene transfer allows bacteria to rapidly evolve. One key to estimating the contribution of horizontal gene transfer to bacterial evolution is to quantify the abundance of mobile genetic elements (MGEs) in bacterial communities under varying degrees of selective pressure. We quantified class 1 integrase (intI1) gene abundance in total community DNA extracted from contaminated and reference riverine and estuarine microhabitats, and in metal- or antibiotic-amended freshwater microcosms. The intI1 gene was more abundant in all contaminant-exposed communities indicating that relative gene transfer potential is higher in these communities. A second key to assessing the contributions of MGEs to bacterial evolution is to examine the structure and function of the MGE-associated gene pool. We determined that the gene cassette pool is a novel and diverse resource available for bacterial acquisition, but that contamination has no discernible effect on cassette richness. Gene cassette profiles were more similar within sites than among sites, yet bacterial community profiles were not, suggesting that selective pressures can shape the structure of the gene cassette pool. Of the 46 sequenced gene cassette products, 37 were novel sequences, while the 9 gene cassettes with similarity to database sequences were primarily to hypothetical proteins. That class 1 integrons are ubiquitous and abundant in environmental bacterial communities indicates that this group of MGEs can play a substantial role in the acquisition of a diverse array of gene cassettes beyond their demonstrated impact in mediating multidrug resistance in clinical bacteria.
On ARS-interacting multifunctional protein p18
Authors: Deineko Viktor
Published: February 2008

Nine aminoacyl-tRNA synthetases with three auxiliary components are forming a multisynthetase complex which is essential component of protein biosynthesis machinery. The smallest auxiliary component p18 takes part in biosynthesis channeling. It is also a regulator of p53 and has tumor suppressing function. Particular structure of this protein is still unknown. Here methods of structural bioinformatics were applied to generate a model of p18 spatial structure suitable for further research. The structure was created using homology modeling. DNA-binding residues of p18 were also derived both from raw sequence and from three-dimensional structure model.
Perceiving Patterns in Parallel Coordinates: Determining Thresholds for Identification of Relationships
Authors: Johansson Jimmy , Forsell Camilla , Lind Mats , Cooper Matthew
Published: February 2008

This article presents a study that investigates the ability of humans to perceive relationships (patterns) in parallel coordinates, an ability that is crucial to the use of this popular visualization technique. It introduces a visual quality metric, acceptable distortions of patterns, which establishes the level of noise that may be present in data while allowing accurate identification of patterns. This metric was used to assess perceptual performance of standard 2D parallel coordinates and multi-relational 3D parallel coordinates in two experiments. In multirelational 3D parallel coordinates the axes are placed on a circle with a focus axis in the centre, allowing a simultaneous analysis between the focus variable and all other variables. The experiments aimed to determine the maximum number of variables that can be, from a user's point of view, efficiently used in a multi-relational 3D parallel coordinates display and to present a first attempt to study users' ability to analyse noisy data in parallel coordinates. The results show that, in terms of the acceptable level of noise in data, a multi-relational 3D parallel coordinates visualization having 11 axes (variables) is as efficient as standard 2D parallel coordinates. Visualizing a larger number of variables would possibly require a greater amount of manipulation of the visualization and thus be less efficient.
Investigation of the dominant hydration structures among the ionic species in aqueous solution: Novel quantum mechanics/molecular mechanics simulations combined with the theory of energy representation
Authors: Takahashi Hideaki , Ohno Hajime , Yamauchi Toshihiko , Kishi Ryohei , Furukawa Shin-ichi , Nakano Masayoshi , Matubayasi Nobuyuki
Published: February 2008

In the present work, we have performed quantum chemical calculations to determine preferable species among the ionic complexes that are present in ambient water due to the autodissociation of water molecule. First, we have formulated the relative population of the hydrated complexes with respect to the bare ion (H3O+ or OH−) in terms of the solvation free energies of the relevant molecules. The solvation free energies for various ionic species (H3O+, H5O2+, H7O3+, H9O4+ or OH−, H3O2−, H5O3−, H7O4−, H9O5−), categorized as proton or hydroxide ion in solution, have been computed by employing the QM/MM-ER method recently developed by combining the quantum mechanical/molecular mechanical (QM/MM) approach with the theory of energy representation (ER). Then, the computed solvation free energies have been used to evaluate the ratio of the populations of the ionic complexes to that of the bare ion (H3O+ or OH−). Our results suggest that the Zundel form, i.e., H5O2+, is the most preferable in the solution among the cationic species listed above though the Eigen form (H9O4+) is very close to the Zundel complex in the free energy, while the anionic fragment from water molecules mostly takes the form of OH−. It has also been found that the loss of the translational entropy of water molecules associated with the formation of the complex plays a role in determining the preferable size of the cluster.
Comparative study of two- and three-dimensional modeling on arc discharge phenomena inside a thermal plasma torch with hollow electrodes
Authors: Kim Keun Su , Park Jin Myung , Choi Sooseok , Kim Jongin , Hong Sang Hee
Published: February 2008

A comparative study between two- and three-dimensional (2D and 3D) modeling is carried out on arc discharge phenomena inside a thermal plasma torch with hollow electrodes, in order to evaluate the effects of arc root configuration characterized by either 2D annular or 3D highly localized attachment on the electrode surface. For this purpose, a more precise 3D transient model has been developed by taking account of 3D arc current distribution and arc root rotation. The 3D simulation results apparently reveal that the 3D arc root attachment brings about the inherent 3D and turbulence nature of plasma fields inside the torch. It is also found that the constricted arc column near the vortex chamber plays an important role in heating and acceleration of injected arc gases by concentrating arc currents on the axis of the hollow electrodes. The inherent 3D nature of arc discharge is well preserved inside the cathode region, while these 3D features slowly diminish behind the vortex chamber where the turbulent flow begins to be developed in the anode region. Based on the present simulation results, it is noted that the mixing effects of the strong turbulent flow on the heat and mass transfer are mainly responsible for the gradual relaxation of the 3D structures of plasma fields into the 2D axisymmetric ones that eventually appear in the anode region near the torch exit. From a detailed comparison of the 3D results with the 2D ones, the arc root configuration seems to have a significant effect on the heat transfer to the electrode surfaces interacting with the turbulent plasma flow. That is, in the 2D simulation based on an axisymmetric stationary model, the turbulence phenomena are fairly underestimated and the amount of heat transferred to the cold anode wall is calculated to be smaller than that obtained in the 3D simulation. For the validation of the numerical simulations, calculated plasma temperatures and axial velocities are compared with experimentally measured ones, and the 3D simulation turns out to be more accurate than the 2D simulation as a result of a relatively precise description of the turbulent phenomena inside the torch using a more realistic model of arc root attachment. Finally, it is suggested that the 3D transient formulation is indeed required for describing the real arc discharge phenomena inside the torch, while the 2D stationary approach is sometimes useful for getting practical information about the time-averaged plasma characteristics outside the torch because of its simplicity and rapidness in computation.
Atomic partition of the optical rotatory power of methylhydroperoxide
Authors: Sánchez Marina , Ferraro Marta B. , Alkorta Ibon , Elguero José , Sauer Stephan P. A.
Published: February 2008

We applied a methodology capable of resolving the optical rotatory power into atomic contributions. The individual atomic contributions to the optical rotatory power and molecular chirality of the methylhydroperoxide are obtained via a canonical transformation of the Hamiltonian by which the electric dipolar moment operator is transformed to the acceleration gauge formalism and the magnetic dipolar moment operator to the torque formalism. The gross atomic isotropic contributions have been evaluated for the carbon, the nonequivalent oxygen, and the nonequivalent hydrogen atoms of methylhydroperoxide, employing a very large Gaussian basis set which is close to the Hartree-Fock limit.
Structure prediction of an S-layer protein by the mean force method
Authors: Horejs C. , Pum D. , Sleytr U. B. , Tscheliessnig R.
Published: February 2008

S-layer proteins have a wide range of application potential due to their characteristic features concerning self-assembling, assembling on various surfaces, and forming of isoporous structures with functional groups located on the surface in an identical position and orientation. Although considerable knowledge has been experimentally accumulated on the structure, biochemistry, assemble characteristics, and genetics of S-layer proteins, no structural model at atomic resolution has been available so far. Therefore, neither the overall folding of the S-layer proteins—their tertiary structure—nor the exact amino acid or domain allocations in the lattices are known. In this paper, we describe the tertiary structure prediction for the S-layer protein SbsB from Geobacillus stearothermophilus PV72/p2. This calculation was based on its amino acid sequence using the mean force method (MF method) achieved by performing molecular dynamic simulations. This method includes mainly the thermodynamic aspects of protein folding as well as steric constraints of the amino acids and is therefore independent of experimental structure analysis problems resulting from biochemical properties of the S-layer proteins. Molecular dynamic simulations were performed in vacuum using the simulation software NAMD. The obtained tertiary structure of SbsB was systematically analyzed by using the mean force method, whereas the verification of the structure is based on calculating the global free energy minimum of the whole system. This corresponds to the potential of mean force, which is the thermodynamically most favorable conformation of the protein. Finally, an S-layer lattice was modeled graphically using CINEMA4D and compared with scanning force microscopy data down to a resolution of 1nm. The results show that this approach leads to a thermodynamically favorable atomic model of the tertiary structure of the protein, which could be verified by both the MF Method and the lattice model.
Pressure and size effects in endohedrally confined hydrogen clusters
Authors: Soullard Jacques , Santamaria Ruben , Jellinek Julius
Published: February 2008

Density functional theory is used to carry out a systematic study of zero-temperature structural and energy properties of endohedrally confined hydrogen clusters as a function of pressure and the cluster size. At low pressures, the most stable structural forms of (H2)n possess rotational symmetry that changes from C4 through C5 to C6 as the cluster grows in size from n=8 through n=12 to n=15. The equilibrium configurational energy of the clusters increases with an increase of the pressure. The rate of this increase, however, as gauged on the per atom basis is different for different clusters sizes. As a consequence, the size dependencies of the configurational energies per atom at different fixed values of pressure are nonmonotonic functions. At high pressures, the molecular (H2)n clusters gradually become atomic or dominantly atomic. The pressure-induced changes in the HOMO-LUMO gap of the clusters indicate a finite-size analog of the pressure-driven metallization of the bulk hydrogen. The ionization potentials of the clusters decrease with the increase of pressure on them.
A theoretical study of the TiC5 cluster
Authors: Yuan Yongbo , Deng Kaiming , Liu Yuzhen , Tang Chunmei , Tan Weishi , Huang Decai , Yang Jinlong , Wang Xin
Published: February 2008

The geometric and electronic properties of the titanium carbide TiC5 cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or “butterflylike” structures are found to be the equilibrium geometric structures of TiC5 and TiC5−. Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data.
Thermal conductance of bimaterial microcantilevers
Authors: Shen Sheng , Narayanaswamy Arvind , Goh Shireen , Chen Gang
Published: February 2008

In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we demonstrate that the effective thermal conductance of the cantilever and the temperature at the tip of the cantilever can be determined by measuring the bending of the cantilever in response to two different thermal inputs: power absorbed at the tip and ambient temperature.
Interactions between anionic and neutral bromine and rare gas atoms
Authors: Buchachenko Alexei A. , Grinev Timur A. , Wright Timothy G. , Viehland Larry A.
Published: February 2008

High-quality, ab initio potential energy functions are obtained for the interaction of bromine atoms and anions with atoms of the six rare gases (Rg) from He to Rn. The potentials of the nonrelativistic Σ+2 and Π2 electronic states arising from the ground-state Br(P2)–Rg interactions are computed over a wide range of internuclear separations using a spin-restricted version of the coupled cluster method with single and double excitations and noniterative correction to triple excitations [RCCSD(T)] with an extrapolation to the complete basis set limit, from basis sets of d-aug-cc-pVQZ and d-aug-cc-pV5Z quality. These are compared with potentials derived previously from experimental measurements and ab initio calculations. The same approach is used also to refine the potentials of the Br−–Rg anions obtained previously [Buchachenko et al., J. Chem. Phys. 125, 064305 (2006)]. Spin-orbit coupling in the neutral species is included both ab initio and via an atomic approximation; deviations between two approaches that are large enough to affect the results significantly are observed only in the Br–Xe and Br–Rn systems. The resulting relativistic potentials are used to compute anion zero electron kinetic energy photoelectron spectra, differential scattering cross sections, and the transport coefficients of trace amounts of both anionic and neutral bromine in the rare gases. Comparison with available experimental data for all systems considered proves a very high precision of the present potentials.
Thermal expansion of Fe-TM-B (TM=transition metal) bulk amorphous forming alloys
Authors: Hatate M. , Garitaonandia J. S. , Suzuki K.
Published: February 2008

In order to clarify the potential of bulk amorphous alloys as a new class of structural materials with high dimensional stability, the thermal expansion and magnetic properties of amorphous Fe56Co7Ni7Zr10B20 doped with Cr have been investigated. Both the magnetic moment and the Curie point of amorphous Fe56Co7Ni7Zr10B20 were suppressed by Cr addition. The effect of Cr on the magnetic moment was well described by assuming a reduction of 4μB∕Cr atom. It was found that the Curie temperature can be controlled by Cr content over a wide range of 200K in the vicinity of room temperature. Although Invar characteristics were absent from the thermal expansion curves, amorphous Fe56Co7Ni7Zr10B20 doped with 1at.% Cr was found to exhibit a small coefficient of thermal expansion comparable to Kovar alloys, indicating that bulk amorphous alloys may have a potential for commercial low expansion materials.
Magnetic property and magnetocaloric effect of Gd(In) solid solutions
Authors: Ren W. J. , Li D. , Liu W. , Li J. , Zhang Z. D.
Published: February 2008

Gd 1 − x In x  (0⩽x⩽0.06) alloys were prepared by arc melting and subsequent quenching. Gd(In) solid solution free of impurity forms for the alloys up to x=0.04. When 0.04⩽x⩽0.06, impurity phases appear. The lattice constants a and c, the unit cell volume V, and the Curie temperature of the Gd1−xInx solid solutions decrease with increasing the In content x as 0⩽x⩽0.04. The magnetization at 5K of the Gd1−xInx solid solutions decreases with increasing x when x⩽0.02. The magnetization of Gd0.96In0.04 solid solution is larger than that of Gd0.99In0.01 and Gd0.98In0.02, which may be attributed to the oscillatory character of the Ruderman–Kittel–Kasuya–Yosida exchange interaction. The magnetic transition in all the Gd(In) solid solutions has the second-order nature. The magnetic entropy change of the Gd1−xInx solid solutions decreases slightly when x⩽0.02, compared with that of pure Gd.
Effect of shape anisotropy on the magnetization reversal process of (Ga,Mn)As ferromagnetic semiconductors
Authors: Yoo Taehee , Shin Dongyun , Kim Jungtaek , Kim Hyungchan , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: February 2008

We have carried out the planar Hall effect measurement on two different sizes of Hall bar devices fabricated from GaMnAs ferromagnetic films. The detailed information on the magnetic anisotropy properties including the shape anisotropy field were obtained from the angular dependence of planar Hall resistance. The shape anisotropy field per magnetization in the device with 10μm channel width was about 39G. Though the value of shape anisotropy is small, it affects the magnetization reversal processes of the 10μm Hall device by showing steplike feature in the angular dependence of switching fields.
Microwave absorption of λ∕4 wave absorbers using high permeability magnetic composites in quasimicrowave frequency band
Authors: Lee Kyung-Sub , Yun Yeo-Chun , Kim Sang-Woo , Kim Sung-Soo
Published: February 2008

For the aim of thin electromagnetic wave absorbers used in quasimicrowave frequency band, this study proposes the high-permeability magnetic composite sheets of quarter wavelength thickness (λ∕4 spacer) coated with resistive film of 377Ω∕sq (impedance transformer). For the λ∕4 spacer, flexible magnetic composite sheets containing Fe85Si9.5Al5.5 flake particles are used. Due to high permeability and high permittivity of the composite sheets, λ∕4 thickness can be reduced as low as 0.5mm in 2GHz. By coating the conductive paste with surface resistance close to 377Ω∕sq on the λ∕4 spacer, the reflection loss can be reduced to as low as −11dB (90% power absorption). This is attributed to the wave impedance matching led by the resistive film of free-space impedance combined with a λ∕4 thickness of high-permeability magnetic spacer.
Band-structure and correlation effects in the Co(111) planes of CoO
Authors: Skomski Ralph , Wei Xiaohui , Sellmyer D. J.
Published: February 2008

The origin of the striking magnetic anisotropy of cobaltous oxide (CoO) is investigated by model calculations. A key feature of the electronic structure of the antiferromagnetic compound is the accommodation of Co 3d electrons in the (111) Co planes, with parallel and antiparallel intra- and interplane spin orientations and reminiscent of Cu 3d electrons in the CuO2 planes in high-temperature superconductors. The strong correlations of the Co 3d electrons lead to a picture intermediate between traditional crystal-field and itinerant-electron descriptions of the magnetic anisotropy. Using a simple configuration-interaction approach, we analyze the effect of 3d8-3d6 bonds and their interplay with 3d7-3d7 configurations.
Mn composition dependence of phase stability of Ga1−xMnxAs alloys from first principles
Authors: Kim Miyoung
Published: February 2008

The Ga1−xMnxAs alloy is one of the most intensively studied spintronics materials, but its best known Curie temperature TC is still low for practical application. The phase instability of the zincblende Ga1−xMnxAs is known to be one of the main issues hindering the increase of the Mn incorporation, which is crucial in realizing the high TC at room temperature level. While the substitutional dilute Mn incorporation in this alloy indicates a zincblende structure (alpha phase), a single phase bulk alpha-MnAs has not yet been grown—instead, the bulk MnAs exists in a NiAs structure (beta phase) in nature. Here, we determine the phase stability of the alpha- and beta-phase Ga1−xMnxAs alloys for various Mn compositions through the fully optimized total energy calculations using the all-electron full-potential linearized augmented plane-wave method. The alpha phase is found to be energetically more stable over the beta phase for the Mn composition of less than 10% in agreement with experiment. We also find that this stability of alpha phase diminishes as Mn composition further increases, and, finally, the beta phase becomes favored over the alpha phase for Mn composition bigger than 50%.
Influence of seed layer on magnetic properties of laminated Co65Fe35 films
Authors: Ladak S. , Fernández-Outón L. E. , O’Grady K.
Published: February 2008

CoFe alloys have important applications in recording heads since they have a high MS which enables writing to high coercivity media. They also can have a high coercivity which can hinder applications. Previous studies have attempted to reduce the coercivity by the use of seed layers, process conditions, or lamination. We have used a high target utilization sputtering system that allows control of grain size to study laminated Co35Fe65 films with 15Å Al2O3 spacer layers. Samples were fabricated with Ru, Ni81Fe19, and Ta seed layers, as a single layer, a bilayer, or a trilayer. For samples with Ru and Ni81Fe19 seed layers, the grain size was reduced with increasing lamination resulting in a significantly reduced coercivity. Samples with a Ta seed layer showed the opposite trend and an increase of coercivity was found as the number of laminations increased.
Modification of critical spin torque current induced by rf excitation
Authors: Florez S. H. , Katine J. A. , Carey M. , Folks L. , Terris B. D.
Published: February 2008

We characterize the spin transfer torque induced reversal for current-perpendicular-to-plane spin valves with in-plane magnetic anisotropy at low temperature when driven by both direct and rf currents. We find that for rf currents with frequencies in the range of the dc driven resonances, the rf current strongly influences the preswitching precessional modes leading to a clear dependence of the critical dc switching current on the external rf frequency excitation.
Evaluation of the magnetic coupling degree and performance of an axial-axial flux compound-structure permanent-magnet synchronous machine used for hybrid electric vehicles
Authors: Zheng Ping , Zhao Jing , Wu Qian , Fan Weiguang , Shen Lin , Li Lina , Liu Ranran
Published: February 2008

A novel axial-axial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), which is a hybrid electric vehicle (HEV) power train concept, is integrated by two axial flux disk machines. As the two machines share a common rotor [a magnet rotor with permanent magnets (PMs) on both sides], there may be magnetic coupling between them. Three-dimensional (3D) finite-element method (FEM) calculation shows that the two machines have little magnetic coupling if they have the same pole number and consistent magnetization direction of the two layers of PMs on the common rotor. The performance of the CS-PMSM is evaluated on criteria such as power, power per unit volume and mass, torque, and torque ripple. The power and torque equations of this type of machine are deduced and verified with 3D FEM. After the optimization of diameter ratio and pole number, the power and power per unit active volume and mass are high. The torque ripple is much reduced due to the optimization of the pole arc embrace and magnet skewing angle.
Effect of annealing and barrier thickness on MgO-based magnetic tunnel junctions with perpendicular anisotropy
Authors: Ye Lin-Xiu , Lee Ching-Ming , Chang Yao-Jen , Wu Te-ho
Published: February 2008

The effect of annealing conditions on the magnetic characteristics of multilayered perpendicular magnetic tunnel junctions (pMTJs) of the structures SiNx∕Pt∕TbFeCo∕MgO∕(Co∕Pt)5 and SiNx∕Pt∕TbFeCo∕Mg∕MgO∕(Co∕Pt)5 with various MgO barrier thicknesses are explored. We found that both the hard and free layers have coercivity reduction with increasing annealing temperature. However, annealing at median temperature could improve the squareness of the hysteresis loop of the hard layer (TbFeCo). More interestingly, the annealing temperature at which the free layer (Co∕Pt) lost the perpendicular magnetic anisotropy (PMA) depends on the thickness of the MgO layer. Insertion of a thin Mg layer of thickness 0.4nm between the barrier and the hard layer can assist the junction in keeping the PMA at higher annealing temperature. The experimental results suggest that 150°C could be the suitable annealing temperature for these pMTJs.
Structural, optical, and magnetic characterization of monodisperse Fe-doped ZnO nanocrystals
Authors: Parra-Palomino A. , Perales–Perez O. , Singhal R. , Tomar M. , Hwang Jinwoo , Voyles P. M.
Published: February 2008

The results on the synthesis and characterization of highly monodisperse Fe-doped ZnO nanocrystals are presented. Stable suspensions of these materials were produced in an ethanol solution at room temperature. To promote crystal growth, the suspensions of nanocrystals were aged in contact with their mother liquors. X-ray diffraction characterization of doped systems at various Fe-atomic fractions x confirmed the exclusive formation of the host ZnO with the wurtzite structure. High resolution transmission electron microscopy analyses of the suspensions revealed the high monodispersity and crystallinity of the 6–8nm nanocrystals. Ultraviolet-visible measurements confirmed not only the nanocrystalline nature of the samples but also evidenced the continuous growth of the crystals when aged in their mother liquors. Room-temperature magnetic measurements indicated that the ferromagnetic behavior of doped ZnO was dependent on composition and crystal size of produced nanocrystals. Room-temperature ferromagnetism was established in the nanocrystals synthesized at x=0.05 and 0.08 aged for 24 and 360h, respectively. The corresponding room-temperature coercivity values were 45 and 78Oe.