bluuebunny/crossref_metadata_2025 huggingface dataset:
Les stades de la philosophie naturelle d'averroés
Authors: Montada Josep Puig
Published: October 2008

The stages in the development of Averroes' philosophy can be better defined by the revisions Averroes himself made of his works than by the traditional order of his commentaries (short, middle, long); such revisions often take the form of glosses. In his initial stages Averroes' opinions are influenced by the interpretations of Alexander of Aphrodisias and Themistius as well as Avempace. In his final stages, he departs from them and moves closer to Aristotle's original thought. Averroes' reading of the beginning of Physics, Book VIII is an exception: there he agrees with Aristotle in the first stage and moves away from him in the final stage, because he came to believe that Aristotle's purpose in this part of the book was to prove the eternity of heavenly movement. The explanation for the different reading of the introduction to the short commentary can be found in the persecution Averroes and other philosophers suffered in 1197, after which Averroes no longer declared philosophy to be the way to attain human perfection, and he only wanted to illuminate Aristotle's philosophy.
Al-khayyām's Conception of Ratio and Proportionality
Authors: Vahabzadeh Bijan
Published: October 2008

We have attempted in this article to describe the content of al-Khayyām's 11th century Arabic commentary on Book V of Euclid's Elements, and have translated into English what we thought were its most important passages. We have also tried to explain why some Arab mathematicians were opposed to the famous definition of proportional magnitudes found at the beginning of Book V of the Elements.
Ptolemy, Alhazen, and Kepler and the Problem of Optical Images
Authors: Smith A. Mark
Published: October 2008

“Although up to now the [visual] image has been [understood as] a construct of reason,” Kepler observes in the fifth chapter of hisAd Vitellionem Paralipomena(1604), “henceforth the [visible] representations of objects should be considered as paintings [picturae] that are actual[ly projected] on paper or some other screen.” While not intended as a historical generalization (“up to now” having surely been meant within the narrow context of the treatise itself), this claim nonetheless reflects historical reality. Virtually all visual theorists before Kepler did, in fact, conceive of optical images as subjective, not objective constructs – or, to put it in modern terms, as virtual rather than real entities. By current lights, of course, the distinction between virtual and real images is both obvious and common-place: whereas the latter can be physically projected upon a screen, the former cannot.
Métaphysique et science politique les intelligibles volotaires dans leTaḥṣīl al-sa'ādad'al-Fārābī
Authors: Zghal Hatem
Published: October 2008

This study, limited toKitāb Taḥṣīl al-sa'āda, examines two points: the first point concerns the place of political science in the hierarchy of the sciences and its dependence on Metaphysics. This dependence gives it a theoretical status and a proper subject, namely voluntary intelligibles which appear as objective entities and stable essences. The second point to be examined concerns these intelligibles, considered in their relationship to deliberation. From this viewpoint, they appear as formal invariants open to different formulations which correspond to different modes of existence. These formulations are also formal rules to the realisation of intelligibles, and though they are more or less general, they are not universal. They are objects for deliberative discovery and the model of deliberative operations seems similar to the model of ingeniosity present in Algebra and the arts of ingenious devices.
From Sense Perception to the Vision of God: a Path towards Knowledge according to the Ihwān al-Safā'
Authors: Baffioni Carmela
Published: October 2008

The aim of this paper is to identify the position theru'yat Allāhholds within the curriculum of sciences described by the Iḫwān al-Ṣafa'. Their concept of knowledge is first clarified. The Ihwan use the terminology of rational knowledge to describe items of faith too. But faith is only an introduction to a greater knowledge. Now: is the supreme knowledge to be considered as speculative and theoretical, or are theḫawciṣṣ, the only ones entitled to the vision of God, eventually obliged to rely on a kind of divine “revelation” or “inspiration”? If the “vision of God” appears beyond any possible connotation of knowledge in “rational” terms, it is unclear, however, whether the Ihwan use the concepts of “revelation” and “inspiration” as a way of explaining in a theological terminology the utmost degree of human knowledge (perhaps according to the same analogical functionwaḥyandilhāmappear to have in Ibn Sīnā). Moreover, the qualities and moral dispositions attributed to the “Friends of God” remind us of Sufi doctrines. Consequently, the question of the relation between Sufism and imāmite theories could be re-opened: the Iḫwānian definition of the “science of the transcendent” shows that the gnoseological itinerary is not concluded even with the “vision of God.”
Place and Space in Albert of Saxony's Commentaries on the Physics
Authors: Sarnowsky Jürgen
Published: October 2008

Albert of Saxony, master of Arts at Paris from 1351 until 1361/62, has left two commentaries on the Physics of Aristotle. Since he was well aware of the tradition, his writings may serve for an analysis of the transmision of ideas from the ancient and Arabic philosophers into the fourteenth century. In this paper, this is exemplified by the problems of place and space, especially by those of the definition of place and of the immobility of place, of natural place and of the location of the last and outermost sphere. As a result, four modes emerge how an author of the fourteenth century may have been influenced by tradition. Ancient Greek or Pre-Socratic philosophers were mainly known through Aristotle, and thus their opinions were mostly refuted; the same holds true for later ancient or Arabic authors known through the commentaries of Averroes; the influence of the authors of the thirteenth century was present though their texts may not have been directly consulted; and, finally, the contemporary authors were known, but nearly never quoted. Thus, though there was a line of tradition from Aristotle into the fourteenth century, there was also room for proper “medieval” solutions.
fMRI activation during a language task in adolescents with ASD
Authors: KNAUS TRACEY A. , SILVER ANDREW M. , LINDGREN KRISTEN A. , HADJIKHANI NOUCHINE , TAGER-FLUSBERG HELEN
Published: October 2008

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by language and communication impairments, social impairments, and repetitive behaviors or restricted interests. Previous studies of semantic functions have found differences in semantic processing and differences in the activation of the language network in adults with ASD compared to controls. The goal of this study is to examine semantic functions in adolescents with ASD compared to typically developing adolescents. We utilized fMRI with a reading version of a response-naming task to investigate activation in 12 right-handed adolescent boys with ASD and 12 typically developing boys. Both groups performed the task at ceiling levels. Boys with ASD had significantly stronger activation than controls in Broca's area, which was less left lateralized in ASD individuals. Controls had a significant correlation between frontal and temporal language area activation in the left hemisphere, whereas ASD adolescents did not. Direct group comparisons revealed additional regions activated in the ASD group relative to the control group. These results suggest differences in semantic organization, approaches to the semantic task, or efficiency in semantic processing in ASD adolescents relative to typically developing adolescents. (JINS, 2008,14, 967–979.)
Subjective memory complaints and concurrent memory performance in older patients of primary care providers
Authors: SNITZ BETH E. , MORROW LISA A. , RODRIGUEZ ERIC G. , HUBER KIMBERLY A. , SAXTON JUDITH A.
Published: October 2008

Subjective memory complaints (SMCs) are known to be inconsistently related to current memory impairment in older adults but this association has not been well investigated in primary care provider (PCP) settings. To characterize the complexity of the relationship between SMCs and objective memory in older outpatients of PCPs, we collected neuropsychological, subjective memory, depression and medical chart data from outpatients aged 65 and older, without documented dementia diagnoses, in eleven PCP offices in and around the Pittsburgh metropolitan area. Results indicated that self-estimates of current memory ability were most strongly associated with objective memory performance; in contrast, perception of worsening memory over the past year showed no association; and specific memory-related activities were only weakly associated. Women were more likely than men to show inconsistency between SMCs and objective memory performance. Only two of the 11 most significantly memory-impaired participants endorsed SMCs and only four had PCP chart documentation of memory problems. Eliciting SMCs in non-demented older adults can be of clinical value in a PCP setting, but significant limitations of patient self-report in more memory-impaired patients underscore the need to develop brief, objective indicators of memory impairment for PCP office use when there is suspicion of decline. (JINS, 2008,14, 1004–1013.)
Neurocognitive predictors of social and communicative developmental trajectories in preschoolers with autism spectrum disorders
Authors: MUNSON JEFFREY , FAJA SUSAN , MELTZOFF ANDREW , ABBOTT ROBERT , DAWSON GERALDINE
Published: October 2008

Currently, the heterogeneity in the developmental trajectories of autism spectrum disorders (ASD) is poorly understood. Preschool children with ASD participating in a longitudinal study received a battery of neurocognitive tasks that measured the learning of reward associations (Lrn-Rew), spatial working memory (SpatWM), and imitation from memory and novelty preference (Mem/Nov), as well as a measure of nonverbal problem-solving ability (NVDQ). Growth curve analyses via HLM were used to predict the variability in growth rates between age 4 to age 6.5 in Vineland Socialization and Communication scores. Individual differences in both Lrn-Rew and Mem/Nov were significantly related to Socialization and Communication growth rates above and beyond NVDQ, whereas SpatWM was not. Thus, specific aspects of neurocognitive functioning appear to be important predictors of developmental variability during the preschool years in children with ASD. We speculate that these findings support the combined role of ventromedial prefrontal and medial temporal lobe systems in the early pathogenesis of ASD and may be useful in predicting developmental trajectory. The benefits and challenges of assessing specific neurocognitive functions in children with autism is discussed with regard to general cognitive/developmental ability and the behavioral requirements of most assessment settings. (JINS, 2008, 14, 956–966.)
A model of earthquake triggering probabilities and application to dynamic deformations constrained by ground motion observations
Authors: Gomberg Joan , Felzer Karen
Published: October 2008

We have used observations from Felzer and Brodsky (2006) of the variation of linear aftershock densities (i.e., aftershocks per unit length) with the magnitude of and distance from the main shock fault to derive constraints on how the probability of a main shock triggering a single aftershock at a point,P(r,D), varies as a function of distance,r, and main shock rupture dimension,D. We find thatP(r,D) becomes independent ofDas the triggering fault is approached. Whenr≫D P(r,D) scales asDmwherem∼2 and decays with distance approximately asr−nwithn= 2, with a possible change tor−(n−1)atr>h, wherehis the closest distance between the fault and the boundaries of the seismogenic zone. These constraints may be used to test hypotheses about the types of deformations and mechanisms that trigger aftershocks. We illustrate this using dynamic deformations (i.e., radiated seismic waves) and a posited proportionality withP(r,D). Deformation characteristics examined include peak displacements, peak accelerations and velocities (proportional to strain rates and strains, respectively), and two measures that account for cumulative deformations. Our model indicates that either peak strains alone or strain rates averaged over the duration of rupture may be responsible for aftershock triggering.
Structural features of the subducting slab beneath the Kii Peninsula, central Japan: Seismic evidence of slab segmentation, dehydration, and anisotropy
Authors: Shiomi Katsuhiko , Park Jeffrey
Published: October 2008

Seismic evidence of lithospheric slab segmentation, dehydration, and anisotropic rocks beneath the Kii Peninsula, central Japan, is detected with receiver function (RF) analyses. By stacking radial and transverse RFs with moveout perturbations, we estimate the downdip azimuth, dip angle, and depth of the slab Moho beneath each seismic station. Comparing the downdip azimuth to the slab convergence azimuth, we can classify the slab into three segments. The segments correspond to both the fault zones of past megathrust earthquakes and to the spatial distribution of intraslab seismicity. The slab Moho lies just above the intraslab seismicity in the southwestern Kii Peninsula. Slab Moho lies deeper at the eastern part of the peninsula, at the bottom of seismicity. This suggests that earthquakes occur only within the slab mantle under the southern Kii Peninsula. The dip angle of slab Moho becomes steeper at 40‐ to 50‐km depth, perhaps caused by dehydration transformation of basalt to eclogite. At some stations located in the western part of the Kii Peninsula, RF‐estimated dip angle of the interface is much steeper than that estimated by spatial trends in seismicity. Since the local seismicity distribution reflects well the larger‐scale geometry of the slab, the RF‐estimated dip angle may imply anisotropic wave speeds within strongly sheared and/or hydrated media around the slab Moho. These detailed features of the slab may be one key in distinguishing the source regions of megathrust earthquakes in the Nankai region.
A benchmark study on mantle convection in a 3‐D spherical shell using CitcomS
Authors: Zhong Shijie , McNamara Allen , Tan Eh , Moresi Louis , Gurnis Michael
Published: October 2008

As high‐performance computing facilities and sophisticated modeling software become available, modeling mantle convection in a three‐dimensional (3‐D) spherical shell geometry with realistic physical parameters and processes becomes increasingly feasible. However, there is still a lack of comprehensive benchmark studies for 3‐D spherical mantle convection. Here we present benchmark and test calculations using a finite element code CitcomS for 3‐D spherical convection. Two classes of model calculations are presented: the Stokes' flow and thermal and thermochemical convection. For Stokes' flow, response functions of characteristic flow velocity, topography, and geoid at the surface and core‐mantle boundary (CMB) at different spherical harmonic degrees are computed using CitcomS and are compared with those from analytic solutions using a propagator matrix method. For thermal and thermochemical convection, 24 cases are computed with different model parameters including Rayleigh number (7 × 103 or 105) and viscosity contrast due to temperature dependence (1 to 107). For each case, time‐averaged quantities at the steady state are computed, including surface and CMB Nussult numbers, RMS velocity, averaged temperature, and maximum and minimum flow velocity, and temperature at the midmantle depth and their standard deviations. For thermochemical convection cases, in addition to outputs for thermal convection, we also quantified entrainment of an initially dense component of the convection and the relative errors in conserving its volume. For nine thermal convection cases that have small viscosity variations and where previously published results were available, we find that the CitcomS results are mostly consistent with these previously published with less than 1% relative differences in globally averaged quantities including Nussult numbers and RMS velocities. For other 15 cases with either strongly temperature‐dependent viscosity or thermochemical convection, no previous calculations are available for comparison, but these 15 test calculations from CitcomS are useful for future code developments and comparisons. We also presented results for parallel efficiency for CitcomS, showing that the code achieves 57% efficiency with 3072 cores on Texas Advanced Computing Center's parallel supercomputer Ranger.
A study of the alkenone, TEX86, and planktonic foraminifera in the Benguela Upwelling System: Implications for past sea surface temperature estimates
Authors: Lee Kyung Eun , Kim Jung‐Hyun , Wilke Iris , Helmke Peer , Schouten Stefan
Published: October 2008

Suspended particulate matter from seawater and core top sediments were collected during 2003 Meteor cruise M57/1 in January–February from the continental margin off western South Africa for analysis of alkenones, glycerol dibiphytanyl glycerol tetraether (GDGT) lipids, and planktonic foraminifera. Alkenone analysis of suspended particulates in seawater and core top sediments indicates that U37K′ temperatures were representative of annual mean sea surface temperature. In contrast, GDGT analysis suggests that TEX86 temperatures are cold‐biased due to upward transports of GDGTs produced below the mixed layer. The analysis of plankton tow samples revealed that the δ18O of Globorotalia inflata in core top sediments could be biased toward lower temperatures due to subsurface calcification. Accordingly, our study shows that each paleotemperature proxy may record different temperature signals in the Benguela upwelling system emphasizing the general need to constrain potential biases in each proxy for better interpreting paleoclimate records.
Nitrogen trifluoride in the global atmosphere
Authors: Weiss Ray F. , Mühle Jens , Salameh Peter K. , Harth Christina M.
Published: October 2008

Background atmospheric abundances and trends of nitrogen trifluoride (NF3), a potent anthropogenic greenhouse gas, have been measured for the first time. The mean global tropospheric concentration of NF3 has risen quasi‐exponentially from about 0.02 ppt (parts‐per‐trillion, dry air mole fraction) at the beginning of our measured record in 1978, to a July 1, 2008 value of 0.454 ppt, with a rate of increase of 0.053 ppt yr−1, or about 11% per year, and an interhemispheric gradient that is consistent with these emissions occurring overwhelmingly in the Northern Hemisphere, as expected. This rise rate corresponds to about 620 metric tons of current NF3 emissions globally per year, or about 16% of the poorly‐constrained global NF3 production estimate of 4,000 metric tons yr−1. This is a significantly higher percentage than has been estimated by industry, and thus strengthens the case for inventorying NF3 production and for regulating its emissions.
Modeling magnetospheric current response to solar wind dynamic pressure enhancements during magnetic storms: 1. Methodology and results of the 25 September 1998 peak main phase case
Authors: Shi Yong , Zesta Eftyhia , Lyons Larry R.
Published: October 2008

We present a methodology for using the modular Tsyganenko storm magnetic field model (TS04) as a tool to investigate the response of magnetospheric currents to solar wind dynamic pressure enhancements during magnetic storms. We demonstrate the technique by examining the contribution of each model current to the observed dawn‐dusk asymmetric ground H perturbation during a peak storm main phase event. We add present pressure terms to the parameterizations of several individual model currents and fit them to the observed low‐latitude and midlatitude H perturbations. We find that the asymmetric H perturbation for this case is primarily due to a net field‐aligned current (FAC) system, with upward FACs peaking in the evening and downward FACs peaking in the morning, and the equatorial portion of the partial ring current (PRC). This net FAC system includes the region 1 and region 2 FACs and the closure FAC of the PRC, with the largest contribution from the PRC closure FACs. The model results show that in this main phase case, the PRC played a more important role in causing the dawn‐dusk asymmetric H perturbation than did the other currents owing to its strength and asymmetry. The model results do not show significant contributions from the symmetric ring current and tail current, but the magnetopause current gives a significant positive perturbation at all MLTs. In the companion paper, our methodology is applied to obtain a more complete picture of the storm time current response to pressure enhancements by examining pressure increases occurring during different storm phases.
Particle acceleration at coronal mass ejection–driven interplanetary shocks and the Earth's bow shock
Authors: Desai M. I. , Burgess D.
Published: October 2008

Particle acceleration in space plasmas, particularly at collisionless shocks, remains a fundamental yet poorly understood problem in space physics. The most important questions that need to be addressed include (1) where are the particles accelerated, (2) what source material is available for acceleration, (3) what mechanisms are responsible for injecting and accelerating the particles, and (4) how are the particle properties modified during their propagation from the acceleration sites to the observation point? Answering these questions will enable further development of the theoretical framework and models that will facilitate quantitative predictions of key properties of the accelerated particles. In this paper, we review recent observations associated with two distinct but widely studied energetic ion populations: (1) solar energetic particles associated with coronal mass ejection–driven interplanetary shocks and (2) energetic ions observed upstream of the Earth's bow shock. We review the common theoretical concepts and physical processes that are believed to be responsible for accelerating particles at these two types of collisionless shocks, emphasizing the commonalities between these distinct structures and their associated particle populations.
Resonant drift echoes in electron phase space density produced by dayside Pc5 waves following a geomagnetic storm
Authors: Degeling A. W. , Rankin R.
Published: October 2008

The interaction between relativistic, equatorially mirroring electrons and Pc5 Ultra Low Frequency (ULF) waves in the magnetosphere is investigated using a numerical MagnetoHydroDynamic (MHD) model for waves and a test‐kinetic model for electron phase space density (PSD). The temporal and spatial characteristics of a ULF wave packet are constrained using ground‐based observations of narrowband ULF activity following a geomagnetic storm on 24 March 1991, which occurred from 1200 to 1340 Universal Time (UT). A salient feature of the ULF waves during this interval was the apparent localization of the ULF wave power to the dayside of the magnetosphere and the antisunward propagation of ULF wave phase in the morning and afternoon sectors. This is interpreted to imply a localized source of ULF wave power close to noon Magnetic Local Time (MLT) at the magnetopause. The expected electron dynamics are investigated using model wavefields to predict the observable characteristics of the interaction in satellite electron flux data. The wave and kinetic models show that the localized radial motion of magnetic field lines associated with MHD fast waves propagating from the ULF source region acts to periodically inject electrons from high L to lower L within the magnetosphere. This action becomes resonant when the drift period of the electrons matches a multiple of the ULF wave period and leads to an enhancement in radial transport.
Global distribution of cirrus clouds from CloudSat/Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements
Authors: Sassen Kenneth , Wang Zhien , Liu Dong
Published: October 2008

The cirrus clouds of the upper troposphere are globally widespread and are important regulators of the radiative balance, and hence climate, of the Earth‐atmosphere system. Despite their wide distribution, however, cirrus are difficult to study from satellite radiance measurements or from scattered ground observing sites because they can occur as part of multilayered cloud systems and are characteristically optically thin. The need to better characterize the global distribution of cirrus clouds was therefore a major justification for the formation flying of the CloudSat and CALIPSO satellites, which support a cloud radar and polarization lidar, respectively. Measurements by these active remote sensors, when analyzed by appropriate algorithms, have the ability to identify and accurately measure the locations and heights of this category of clouds. The combined CloudSat/Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data cirrus cloud algorithm used in this study is aimed at identifying those clouds that would likely be classified as cirrus by a surface weather observer: it is based on previous experience with multiple remote sensor approaches and knowledge gleaned from extensive surface lidar and radar observations of visually identified cirrus clouds with a minimum of a priori assumptions. We report on the global and seasonal frequencies of cirrus clouds, and on their heights and thicknesses obtained over the initial 1 year of data collected. We find a global average frequency of cirrus cloud occurrence of 16.7%. These new results are compared with other cirrus cloud climatologies and are interpreted in terms of local cirrus cloud formation mechanisms and the responsible global weather phenomena.
Estimating fractional sky cover from spectral measurements
Authors: Min Qilong , Wang Tianhe , Long Charles N. , Duan Minzheng
Published: October 2008

A method for estimating fractional sky cover from spectral measurements has been developed. The spectral characteristics of clouds and clear‐sky aerosols are utilized to partition sky fraction. As illustrated in our sensitivity study and demonstrated in real measurements, the transmittance ratio at selected wavelengths is insensitive to solar zenith angle and major atmospheric gaseous absorption. With a localized baseline procedure, retrievals of this ratio method are independent of absolute calibration and weakly sensitive to changes in cloud and aerosol optical properties. Therefore this method substantially reduces the retrieval uncertainty. The uncertainty of this method, estimated through the sensitivity study and intercomparison, is less than 10%. With globally deployed narrowband radiometers, this simple ratio method can substantially enhance the current capability for monitoring fractional sky cover.
Simultaneous remote electric and magnetic field measurements of lightning continuing currents
Authors: Ross Manus , Cummer Steven A. , Nielsen Thomas K. , Zhang Yongming
Published: October 2008

Remote detection and measurement of the slowly varying continuing current that follows some lightning return strokes is difficult. Slow changes in quasi‐static electric fields have been most frequently used to remotely measure continuing current. Because of the rapid attenuation of dipole electric fields with distance, though, the range over which the current will produce a measurable signature in the field is limited. Here we report the analysis of continuing current signatures observed in both the quasi‐static electric and magnetic fields from four lightning strokes that were recorded from a range of 52 to 96 km at a measurement site near Fort Collins, Colorado on 15 July 2005. Electro‐ and magnetostatic analyses show that the distinct magnetic and electric field signatures are produced by the continuing current and the associated net charge transfer, respectively. The measurements confirm that the quasi‐static magnetic fields that follow some return strokes are signatures of continuing current. Using realistic noise estimates based on our measurements, we also show that modest to large continuing currents can be reliably detected and measured from long ranges (more than 1000 km for 1 kA) using quasi‐static magnetic field signatures.
Atmospheric and surface retrievals in the Mars polar regions from the Thermal Emission Spectrometer measurements
Authors: Eluszkiewicz Janusz , Moncet Jean‐Luc , Shephard Mark W. , Cady‐Pereira Karen , Connor Thomas , Uymin Gennady
Published: October 2008

Retrievals of atmospheric temperatures, surface emissivities, and dust opacities in the Mars polar regions from the Thermal Emission Spectrometer (TES) spectra are presented. The retrievals correspond to two types of spectra, characterized by small and large band depths BD25 in the 25‐μm band of solid CO2. These two types of spectra have previously been identified with locations covered by slab ice and fluffy CO2 frost, respectively. Above the first atmospheric scale height, there is a correlation between the degree of saturation in the retrieved atmospheric temperatures and the two types of surface, with the high BD25 spectra (“cold spots”) showing larger supersaturations around 1 mbar. This supports the hypothesis that cold spots correspond to locations with potential or actual atmospheric precipitation. Furthermore, the retrieved temperature profiles exhitbit a warming above 1 mbar (15 km), which appears real even when the limited number of independent pieces of information from the measurement (∼3) and coarse vertical resolution of the TES instrument above 15 km are considered. The spectral shape of the retrieved surface emissivities in the cold spot locations is consistent with modeling results attributing high BD25 to porosity. For the low BD25 spectra, the retrieved emissivities are spectrally flat but significantly less than unity (0.8–0.9). The cause of these spectrally uniform deviations from blackbody behavior (which are not supported by modeling) remains to be investigated, with a noticeable reduction in the deviation from the blackbody behavior achieved through a zero‐radiance‐level correction to the TES spectra available from the Planetary Data System.
Sahel megadroughts triggered by glacial slowdowns of Atlantic meridional overturning
Authors: Mulitza Stefan , Prange Matthias , Stuut Jan‐Berend , Zabel Matthias , von Dobeneck Tilo , Itambi Achakie C. , Nizou Jean , Schulz Michael , Wefer Gerold
Published: October 2008

The influence of the large‐scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.
Shotgun metaproteomics of the human distal gut microbiota
Authors: Verberkmoes Nathan C , Russell Alison L , Shah Manesh , Godzik Adam , Rosenquist Magnus , Halfvarson Jonas , Lefsrud Mark G , Apajalahti Juha , Tysk Curt , Hettich Robert L , Jansson Janet K
Published: October 2008

The human gut contains a dense, complex and diverse microbial community, comprising the gut microbiome. Metagenomics has recently revealed the composition of genes in the gut microbiome, but provides no direct information about which genes are expressed or functioning. Therefore, our goal was to develop a novel approach to directly identify microbial proteins in fecal samples to gain information about the genes expressed and about key microbial functions in the human gut. We used a non-targeted, shotgun mass spectrometry-based whole community proteomics, or metaproteomics, approach for the first deep proteome measurements of thousands of proteins in human fecal samples, thus demonstrating this approach on the most complex sample type to date. The resulting metaproteomes had a skewed distribution relative to the metagenome, with more proteins for translation, energy production and carbohydrate metabolism when compared to what was earlier predicted from metagenomics. Human proteins, including antimicrobial peptides, were also identified, providing a non-targeted glimpse of the host response to the microbiota. Several unknown proteins represented previously undescribed microbial pathways or host immune responses, revealing a novel complex interplay between the human host and its associated microbes.
Genomic comparison ofBradyrhizobium japonicumstrains with different symbiotic nitrogen-fixing capabilities and other Bradyrhizobiaceae members
Authors: Itakura Manabu , Saeki Kazuhiko , Omori Hirofumi , Yokoyama Tadashi , Kaneko Takakazu , Tabata Satoshi , Ohwada Takuji , Tajima Shigeyuki , Uchiumi Toshiki , Honnma Keina , Fujita Konosuke , Iwata Hiroyoshi , Saeki Yuichi , Hara Yoshino , Ikeda Seishi , Eda Shima , Mitsui Hisayuki , Minamisawa Kiwamu
Published: October 2008

Comparative genomic hybridization (CGH) was performed with nine strains of Bradyrhizobium japonicum (a symbiotic nitrogen-fixing bacterium associated with soybean) and eight other members of the Bradyrhizobiaceae by DNA macroarray of B. japonicum USDA110. CGH clearly discriminated genomic variations in B. japonicum strains, but similar CGH patterns were observed in other members of the Bradyrhizobiaceae. The most variable regions were 14 genomic islands (4–97 kb) and low G+C regions on the USDA110 genome, some of which were missing in several strains of B. japonicum and other members of the Bradyrhizobiaceae. The CGH profiles of B. japonicum were classified into three genome types: 110, 122 and 6. Analysis of DNA sequences around the boundary regions showed that at least seven genomic islands were missing in genome type 122 as compared with type 110. Phylogenetic analysis for internal transcribed sequences revealed that strains belonging to genome types 110 and 122 formed separate clades. Thus genomic islands were horizontally inserted into the ancestor genome of type 110 after divergence of the type 110 and 122 strains. To search for functional relationships of variable genomic islands, we conducted linear models of the correlation between the existence of genomic regions and the parameters associated with symbiotic nitrogen fixation in soybean. Variable genomic regions including genomic islands were associated with the enhancement of symbiotic nitrogen fixation in B. japonicum USDA110.
Energetics, structure, and charge distribution of reduced and oxidized n-pyrrole oligomers: A density functional approach
Authors: Dai Yafei , Blaisten-Barojas Estela
Published: October 2008

Polypyrrole is a conjugated polymer prototype of conducting polymers. The energetically preferred spatial conformation of n-pyrrole oligomers (n=1–24) in both the reduced and oxidized phases is obtained and analyzed in this paper within the hybrid density functional theory. Binding energies, gap energies, radius of gyration, end-to-end distance, and vibrational frequencies are reported as functions of oligomer length. Reduced n-pyrrole are bent chains for all sizes showing a dramatic departure from planarity. Vibrational spectra of n-pyrrole oligomers indicate the presence of two fairly size-insensitive frequency regions, which increase in intensity with increasing oligomer size. Several oxidation levels were analyzed for n-pyrrole through the distribution of the carbon-carbon bond orders and single/double bond lengths. It is shown that the oxidation level is directly related to the way positive charge localizes along the n-pyrrole oligomer chain. If charge/n<1∕3, the oligomers are bent and charge is delocalized; if charge/n⩾1∕3, the oligomers are planar and charge notoriously localizes in n/charge regions along the backbone. Calculations with electronegative dopants show that charge localizes in the neighborhood of the dopant. It is demonstrated that one localized state in the gap between the highest occupied and lowest-unoccupied states appears for every +2e in the oxidation level. The band structure of infinite reduced polypyrrole gives a band gap energy in excellent agreement with experiment. The evolution of the band gap and the charge-localized band as a function of polypyrrole oxidation level is reported.
Observation of fast-ion Doppler-shifted cyclotron resonance with shear Alfvén waves
Authors: Zhang Yang , Heidbrink W. W. , Boehmer H. , McWilliams R. , Vincena S. , Carter T. A. , Gekelman W. , Leneman D. , Pribyl P.
Published: October 2008

The Doppler-shifted cyclotron resonance (ω−kzvz=Ωf) between fast ions and shear Alfvén waves is experimentally investigated (ω, wave frequency; kz, axial wavenumber; vz, fast-ion axial speed; Ωf, fast-ion cyclotron frequency). A test particle beam of fast ions is launched by a Li+ source in the helium plasma of the LArge Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)], with shear Alfvén waves (SAW) (amplitude δ B/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the nonclassical spreading of the beam, which is proportional to the resonance with the wave. A resonance spectrum is observed by launching SAWs at 0.3–0.8ωci. Both the magnitude and frequency dependence of the beam-spreading are in agreement with the theoretical prediction using a Monte Carlo Lorentz code that launches fast ions with an initial spread in real/velocity space and random phases relative to the wave. Measured wave magnetic field data are used in the simulation.
A measurable Lawson criterion and hydro-equivalent curves for inertial confinement fusion
Authors: Zhou C. D. , Betti R.
Published: October 2008

It is shown that the ignition condition (Lawson criterion) for inertial confinement fusion (ICF) can be cast in a form dependent on the only two parameters of the compressed fuel assembly that can be measured with existing techniques: the hot spot ion temperature (Tih) and the total areal density (ρRtot), which includes the cold shell contribution. A marginal ignition curve is derived in the ρRtot, Tih plane and current implosion experiments are compared with the ignition curve. On this plane, hydrodynamic equivalent curves show how a given implosion would perform with respect to the ignition condition when scaled up in the laser-driver energy. For 3<⟨Tih⟩n<6keV, an approximate form of the ignition condition (typical of laser-driven ICF) is ⟨Tih⟩n2.6⋅⟨ρRtot⟩n>50keV2.6⋅g∕cm2, where ⟨ρRtot⟩n and ⟨Tih⟩n are the burn-averaged total areal density and hot spot ion temperature, respectively. Both quantities are calculated without accounting for the alpha-particle energy deposition. Such a criterion can be used to determine how surrogate D2 and subignited DT target implosions perform with respect to the one-dimensional ignition threshold.
The simulator for icy world interiors: A 700 MPa pressure system for impulsive stimulated scattering and other optical measurements, with thermal control from −20 to 100 °C
Authors: Vance Steve , Brown J. Michael
Published: October 2008

The simulator for icy world interiors (SIWI) was developed for sound velocity measurements in simulated extraterrestrial ocean materials by the method of impulsive stimulated scattering (ISS). The design and operation of SIWI are described. Optical measurements at low temperature in corrosive solution were enabled by enclosing sample fluid in a stoppered spectrophotometric cuvette. To maintain minimum optical density it was necessary to limit contact of the dioctyl sebacate hydraulic fluid with nitrile o-rings, which caused discoloring enhanced absorption of the 532 nm ISS probe pulses. Dilution of hydraulic fluid with kerosene in the amount of 5% by volume prevented clouding at high pressures and at low temperatures. Pure kerosene was found to attenuate the ISS signal, and so was deemed unsatisfactory at low temperatures where the lower thermal expansion of water leads to weaker density contrasts between heated and unheated regions in the sample fluid. When 50 cS silicone oil was used as a hydraulic medium, clouding was observed at pressures above 400 MPa when temperatures were raised above ∼50 °C and lowered to less than ∼10 °C. To our knowledge, such clouding has not been reported previously for dioctyl sebacate, nor for silicone at such low pressures.
Stability of electrical switching properties in vanadium dioxide thin films under multiple thermal cycles across the phase transition boundary
Authors: Ko Changhyun , Ramanathan Shriram
Published: October 2008

The influence of successive thermally induced metal-insulator transition (MIT) on electrical transition characteristics in high quality vanadium dioxide (VO2) thin films synthesized by reactive sputtering was investigated in conjunction with structural studies. We show that the transition quality of VO2 thin films was largely unaffected up to ∼100 heating-cooling cycles with respect to hysteresis width, resistivity ratio, and MIT onset temperature. The hysteresis width decreased by ∼3% along with an enhancement in film texture, while no reduction in resistivity ratio or MIT temperature was observed, implying that the stoichiometry of overall VO2 thin film did not degrade under multiple thermally induced transitions. The results are of potential relevance to solid state sensing elements utilizing vanadium oxide.
Controlled manipulation of individual vortices in a superconductor
Authors: Straver E. W. J. , Hoffman J. E. , Auslaender O. M. , Rugar D. , Moler Kathryn A.
Published: October 2008

We report controlled local manipulation of single vortices by low temperature magnetic force microscopy in a thin film of superconducting Nb. We are able to position the vortices in arbitrary configurations and to measure the distribution of local depinning forces. This technique opens up possibilities for the characterization and use of vortices in superconductors.
Simulation of Joint European Torus beta scan experiments using theory-based models
Authors: Laborde L. , McDonald D. C. , Voitsekhovitch I. ,   JET EFDA Contributors
Published: October 2008

Transport modeling of beta (β) scaling experiments performed in the Joint European Torus (JET) [P. H. Rebut et al., Nucl. Fusion 25 1011 (1985)] is presented. Two theory-based models are used: the Weiland model [F. D. Halpern et al., Phys. Plasmas 15, 012304 (2008)] and the gyro-Landau-fluid model GLF23 [J. E. Kinsey et al., Phys. Plasmas 12, 062302 (2005)]. First, the β dependence of energy transport in each model is illustrated by running them stand-alone with imposed plasma profiles obtained in JET β scaling experiments. Both models show a stabilization of ion temperature gradient modes with increasing β up to a critical β value for which ballooning modes become unstable, leading to a strong degradation of the core confinement. Second, the models are used in predictive simulations of heat transport in order to test the capability of the models to reproduce experimental results. A good agreement between the Weiland model and experimental results is found, but the model sensitivity to dimensionless parameters mismatches throughout the experimental scan strongly affects the apparent scaling. This is tested by running predictive simulations using modified input parameters in order to correct the mismatch. In order to identify which dimensionless parameter mismatches are responsible for the apparent scaling, a sensitivity analysis of the Weiland model is performed. A comparison with modeling of previous experimental results is also presented.
Molecular beam epitaxy and structural anisotropy of m-plane InN grown on free-standing GaN
Authors: Koblmüller G. , Hirai A. , Wu F. , Gallinat C. S. , Metcalfe G. D. , Shen H. , Wraback M. , Speck J. S.
Published: October 2008

This study reports on the growth of high-quality nonpolar m-plane [11¯00] InN films on free-standing m-plane GaN substrates by plasma-assisted molecular beam epitaxy. Optimized growth conditions (In/N ratio ∼1 and T=390–430 °C) yielded very smooth InN films with undulated features elongated along the [112¯0] orientation. This directionality is associated with the underlying defect structure shown by the anisotropy of x-ray rocking curve widths parallel to the [112¯0] (i.e., 0.24°–0.34°) and [0001] (i.e., 1.2°–2.7°) orientations. Williamson–Hall analysis and transmission electron microscopy identified the mosaic tilt and lateral coherence length and their associations with different densities of dislocations and basal-plane stacking faults. Ultimately, very low band gap energies of ∼0.67 eV were measured by optical absorption similar to the best c-plane InN.
Study of the influence of ester orientation on the thermal stability of the smectic C phase: Simulation investigation
Authors: Vadnais Richard , Beaudoin Marc-André , Soldera Armand
Published: October 2008

Two series of mesogenic molecules have been simulated using molecular dynamics with a full atomistic representation. The two series differ from each other only with the orientation of an ester linker inside the rigid core. Experimentally, this small difference leads to drastically different polymorphisms: one displays the smectic A phase while the other exhibits the smectic C and the smectic A phase. From molecular dynamics trajectories, intermolecular potentials are extracted and analyzed. It is then found that the minor difference inside the rigid core can be related to these various interactions. Finally, experimental and simulation results are integrated in a coherent analysis. The correlation between both types of data offers interesting insights in the role of the Coulomb and van der Waals interactions in the molecular origin of the smectic C phase.
Dependence of the mobility on charge carrier density and electric field in poly(3-hexylthiophene) based thin film transistors: Effect of the molecular weight
Authors: Fumagalli L. , Binda M. , Natali D. , Sampietro M. , Salmoiraghi E. , Di Gianvincenzo P.
Published: October 2008

We present a study performed on organic thin film transistors based on poly(3-hexylthiophene) with molecular weights ranging from 20 to 80 kDa as active material. Besides having a strong influence on the absolute value of the mobility, we show that the molecular weight also drastically affects the mobility functional dependence on the gate voltage and on the longitudinal electric field. While the medium range of molecular weight (37–53 kDa) yields a high (about 10−2 cm2/V s) and practically constant mobility, the low and high ranges yield a lower mobility, which in addition shows a strong dependence on both the charge density and the electric field. By means of a detailed analysis of experimental transfer characteristics of transistors, this behavior is traced back to the broadness of the density of states, which turns out to be higher for low mobility polymers. Finally, consequences on transistor modeling due to the simultaneous dependence of the mobility on charge density and electric field are discussed.
An equivalent-circuit model for shunt-connected coplanar microelectromechanical system switches for high frequency applications
Authors: Bartolucci Giancarlo , Marcelli Romolo , Catoni Simone , Margesin Benno , Giacomozzi Flavio , Mulloni Viviana , Farinelli Paola
Published: October 2008

In this paper, a circuit model to predict the microwave response of a shunt-connected capacitive microelectromechanical coplanar switch is proposed. The numerical values of the lumped elements composing the equivalent circuit are computed by means of a fully analytic approach. In particular, the contribution of resistive and inductive parasitic elements has been evaluated by using closed-form expressions. Configurations characterized by different technological solutions have been obtained and modeled. Simulations performed with the proposed approach correlate very well with actual measurements.