bluuebunny/crossref_metadata_2025 huggingface dataset:
Molekulare Targets beim Kolonkarzinom
Authors: Borner
Published: March 2006

Das Kolonkarzinom ist die zweithäufigste Tumortodesursache in den Industrieländern. In der Schweiz sterben jährlich etwa 1900 Patienten an dieser Krankheit. Der therapeutische Nihilismus, der jahrzehntelang aufgrund der fehlenden Therapieoptionen berechtigt war, hat nun einem großen Enthusiasmus Platz gemacht. Der Grund für diese Veränderung sind die neuen Medikamente, welche die Standardtherapie des Kolonkarzinoms in den letzten zehn Jahren revolutioniert haben. Neue potente Chemotherapeutika wie Irinotecan und Oxaliplatin haben die Lebensdauer der Patienten mit metastasierendem Kolonkarzinom etwa verdreifacht. Zukunftsweisend ist jedoch die Tatsache, dass zunehmend sogenannte molekulare Targets, biologische Unterschiede zwischen Tumor- und Normalgewebe, therapeutisch ausgenützt werden können. Die zur Zeit erfolgreichsten molekularen Targets sind der Epidermal Growth Factor Receptor (EGFR) und der Vascular Endothelial Growth Factor (VEGF). Sie stehen jedoch wahrscheinlich nur für den Anfang einer rasanten Entwicklung.
Tyrosinkinase-Inhibitoren in der Behandlung der chronisch myeloischen Leukämie
Authors: Heim
Published: March 2006

Die chronisch myeloische Leukämie (CML) ist durch das Philadelphia-Chromosom charakterisiert, ein verkürztes Chromosom 22, welches durch die reziproke Translokation t(9;22) entsteht. Auf molekularer Ebene kommt es zu einer Fusion zwischen dem auf 22q11 lokalisierten BCR-Gen und dem auf 9q34 lokalisierten und translozierten ABL-Gen. Das Produkt dieses Fusionsgens ist das p210 BCR-ABL Onkoprotein. Die deregulierte Tyrosinkinase-Aktivität von BCR-ABL ist für die Entstehung eines CML-Phänotyps notwendig und genügend. In Kenntnis dieser molekularen Mechanismen wurde der Tyrosinkinase Inhibitor Imatinib mesylate (Glivec) entwickelt. Imatinib ist ein kleines Molekül das die ATP-Bindungsstelle der ABL-Tyrosinkinase besetzt und dadurch die transformierende Wirkung des BCR-ABL Oncoproteins aufhebt. Klinische Studien haben die Wirksamkeit von Imatinib bei Patienten mit CML in allen Stadien der Krankheit erwiesen. Bei einem deutlich günstigeren Nebenwirkungsprofil ist Imatinib bei Patienten mit CML in chronischer Phase der früheren Standardtherapie mit Interferon-alpha in Bezug auf progressionsfreies Überleben und auf das Erreichen einer hämatologischen oder einer zytogenetischen Remission überlegen. Bei Patienten mit einer CML in akzelerierter Phase oder in Blastenkrise ist die Ansprechrate auf die Imatinibtherapie geringer und die Dauer erreichter Remissionen kürzer. Das schlechtere Ansprechen von Patienten mit einer fortgeschrittenen CML ist häufig auf zusätzliche, erworbene, BCR-ABL unabhängige zytogenetische Anomalien zurückzuführen. Schon früh in der klinischen Erprobung von Imatinib hat sich aber auch gezeigt, dass Mutationen in der BCR-ABL Kinasedomäne zu einer Imatinib-Resistenz führen können. Bereits ist eine zweite Generation von ABL Tyrosinkinase-Inhibitoren in klinischer Erprobung.
Mammakarzinom – therapeutische Fortschritte
Authors: Pestalozzi
Published: March 2006

Die Behandlung des Mammakarzinoms hat in den letzten zehn Jahren wichtige Fortschritte erzielt. Bei der Primäroperation und klinisch negativer Axilla wird heute die Sentinel-Lymphknoten-Biopsie durchgeführt. Bei der Hormontherapie der postmenopausalen Patientin haben sich die selektiven Aromatasehemmer in der metastasierten und in der adjuvanten Situation etabliert. Trastuzumab (Herceptin®) spielt bei der Behandlung des metastasierten und neuerdings auch des kurativ operierten, HER2-positiven Karzinoms eine bedeutende Rolle. Bei der Chemotherapie des metastasierten Leidens zeigen Zytostatika-Kombinationen kaum Vorteile gegenüber der sequentiellen Therapie. Dagegen sind Kombinationen der Standard in der adjuvanten Chemotherapie. Neue Methoden der Gewebsanalyse (Expressionsmuster von mRNA und Proteinen) versprechen weitere diagnostische und therapeutische Fortschritte.
Gewebebanken als Voraussetzung für die Molekulare Diagnostik
Authors: Schraml
Published: March 2006

Die Anwendung moderner Technologien in der Genom- und Proteomforschung erlaubt, viele für Krankheiten verantwortliche molekulare Mechanismen zu identifizieren. Um die meist durch Experimente mit Zelllinien oder Tiermodellen gewonnenen Erkenntnisse für neue Diagnose- und Therapiemethoden zu validieren, sind Untersuchungen von zahlreichen menschlichen Geweben notwendig. Solche gut dokumentierte Gewebesammlungen sind vor allem in universitären Pathologie-Instituten anzutreffen. Dabei handelt es sich um fixierte, in Paraffinblöcken eingebettete, aber auch zum Teil unfixierte, tiefgekühlte Gewebeproben, welche für zukünftige diagnostische Zwecke gelagert werden. Die Untersuchung dieser Gewebe mittels der Gewebechip-Technologie und die Verknüpfung mit entsprechenden pathologischen und klinischen Daten ermöglicht es, relativ schnell, neue potentielle Biomarker für Krankheiten zu selektionieren. Mit dem kontinuierlichen Ausbau und der Qualitätssicherung von Gewebebanken wird in Zukunft ein riesiges Potential für die molekulare Diagnostik zur Verfügung gestellt. Dies wird entscheidend dazu beitragen, neue Therapiemöglichkeiten zu etablieren.
Die diagnostische und prädiktive Bedeutung von Kit (CD117)
Authors: Dirnhofer  , Zimpfer  , Went
Published: March 2006

CD117 (Kit) ist eine transmembrane Tyrosinkinase. Es ist ein klassischer Wachstumsfaktorrezeptor und bindet spezifisch den sogenannten Stammzellfaktor (auch Kit-Ligand oder Mastzellwachstumsfaktor genannt). Kit wird physiologischerweise in hämatopoetischen Stammzellen, Keimzellen der Gonaden, den interstitiellen Zellen von Cajal (intestinale Schrittmacherzellen) und Mastzellen sowie Melanozyten exprimiert. Die Kit-mediierte Signaltransduktion reguliert Proliferation, Differenzierung und Apoptose und spielt eine Rolle bei der Gametogenese, Hämatopoiese, Mastzellentwicklung, Melanogenese und Entwicklung der Cajalzellen. Von herausragender diagnostischer Bedeutung ist der Nachweis einer CD117-Expression bei den gastrointestinalen Stromatumoren (GIST). Ungefähr 95% aller GIST sind immunhistochemisch CD117-positiv. Die überwiegende Mehrzahl aller anderen Sarkome sowie Karzinome und auch Lymphome sind CD117-negativ, sodass dieser Marker eine sehr gute Sensitivität und Spezifität für die Diagnose eines GIST aufweist. Darüber hinaus sind aktivierende Mutationen im Kit-Onkogen von entscheidender pathogenetischer Bedeutung der GIST. 80–85% aller GIST weisen derartige Mutationen auf. Da mit dem Medikament Imatinib (Glivec®) ein spezifischer Tyrosinkinase-Hemmer zur Verfügung steht, ist der Nachweis beziehungsweise die Lokalisation einer spezifischen Mutation auch der wichtigste prädiktive Faktor. Neben GIST sind systemische Mastozytosen sowie Seminome am häufigsten CD117-positiv. Diese Neoplasien weisen allerdings Mutationen in anderen Exons des Kit-Gens als GIST auf und sind nur teilweise Imatinib-sensitiv. Die CD117-Expression ist aber nicht spezifisch für diese Entitäten. Andere maligne Tumore, vor allem adenoid-zystische Karzinome, Tymuskarzinome und Melanome können das Protein ebenfalls exprimieren. Ganz selten gilt dies auch noch für andere Entitäten. Bei der überwiegenden Mehrzahl der Fälle liegt aber eine Wild-Typ Kit-Gen-Konfiguration vor und damit fehlt die molekulare Basis für eine erfolgreiche Imatinib-Therapie. Der reine immunhistochemische Nachweis einer CD117-Expression stellt also – mit Ausnahme des GIST – keine verlässliche therapeutische Grundlage dar. Der molekular-pathologische Nachweis der CD117-Expression und des Mutationsstatus bei GIST (und anderen Tumoren) bringt geradezu paradigmatisch die Bedeutung moderner molekularer Diagnostik im Zeitalter der zielgerichteten, individualisierten Therapie zum Ausdruck.
A numerical study on localized volume reduction in elastic media: Some insights on the mechanics of anticracks
Authors: Katsman R. , Aharonov E. , Scher H.
Published: March 2006

Porous rocks, subjected to compressive stress, often undergo mechanical compaction via grain crushing and grain rearrangement, and chemical compaction by pressure solution. Such volume reduction processes are known to spontaneously localize under certain conditions, creating compaction and compacting shear bands, solution seams, and stylolites. However, the localization process is poorly understood. The formation and propagation of compaction bands have recently been studied using an elastoplastic spring network model (Katsman et al., 2005). In this paper, the same technique was employed to systematically analyze localized volume reduction (LVR) defects and their interactions with the surrounding elastic media, i.e., the stress distribution around an LVR region. Simulation results show that LVR regions experience stress concentrations at their tips, reminiscent of mode I cracks. However, aside from this similarity point, comparison of stress around LVR regions to stress around cracks reveals that the stress/strain distribution in such LVR defects is quite different than that surrounding mode I cracks. Implications for stylolites and compaction band are thoroughly discussed.
Sub‐Milankovitch cycles in periplatform carbonates from the early Pliocene Great Bahama Bank
Authors: Reuning Lars , Reijmer John J. G. , Betzler Christian , Timmermann Axel , Steph Silke
Published: March 2006

High‐resolution bulk sediment (magnetic susceptibility and aragonite content) and δ18O records from two different planktonic foraminifera species were analyzed in an early Pliocene core interval from the Straits of Florida (Ocean Drilling Program site 1006). The δ18O record of the shallow‐dwelling foraminifera G. sacculifer and the aragonite content are dominated by sub‐Milankovitch variability. In contrast, magnetic susceptibility and the δ18O record of the deeper‐dwelling foraminifera G. menardii show precession cycles. The relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent Great Bahama Bank was triggered directly by atmospheric processes rather than by sea level change. We propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial Pacific sea surface temperatures under present‐day conditions.
Tectonics and seismicity of the Tindari Fault System, southern Italy: Crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab
Authors: Billi Andrea , Barberi Graziella , Faccenna Claudio , Neri Giancarlo , Pepe Fabrizio , Sulli Attilio
Published: March 2006

The Tindari Fault System (southern Tyrrhenian Sea, Italy) is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab. Onshore structural data, an offshore seismic reflection profile, and earthquake data are analyzed to constrain the present geometry of the Tindari Fault System and its tectonic evolution since Neogene, including the present seismicity. Results show that this zone of deformation consists of a broad NNW trending system of faults including sets of right‐lateral, left‐lateral, and extensional faults as well as early strike‐slip faults reworked under late extension. Earthquakes and other neotectonic data provide evidence that the Tindari Fault System is still active in the central and northern sectors and mostly accommodates extensional or right‐lateral transtensional displacements on a diffuse array of faults. From these data, a multiphase tectonic history is inferred, including an early phase as a right‐lateral strike‐slip fault and a late extensional reworking under the influence of the subduction‐related processes, which have led to the formation of the Tyrrhenian back‐arc basin. Within the present, regional, geodynamic context, the Tindari Fault System is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments, these tectonic compartments relating to the complex processes of plate convergence occurring in the region. The Tindari Fault System might also be included in an incipient, oblique‐extensional, transfer zone linking the ongoing contractional belts in the Calabrian‐Ionian and southern Tyrrhenian compartments.
Toward resolving an earthquake ground motion mystery in west Seattle, Washington State: Shallow seismic focusing may cause anomalous chimney damage
Authors: Stephenson William J. , Frankel Arthur D. , Odum Jack K. , Williams Robert A. , Pratt Thomas L.
Published: March 2006

A shallow bedrock fold imaged by a 1.3‐km long high‐resolution shear‐wave seismic reflection profile in west Seattle focuses seismic waves arriving from the south. This focusing may cause a pocket of amplified ground shaking and the anomalous chimney damage observed in earthquakes of 1949, 1965 and 2001. The 200‐m bedrock fold at ∼300‐m depth is caused by deformation across an inferred fault within the Seattle fault zone. Ground motion simulations, using the imaged geologic structure and northward‐propagating north‐dipping plane wave sources, predict a peak horizontal acceleration pattern that matches that observed in strong motion records of the 2001 Nisqually event. Additionally, a pocket of chimney damage reported for both the 1965 and the 2001 earthquakes generally coincides with a zone of simulated amplification caused by focusing. This study further demonstrates the significant impact shallow (<1km) crustal structures can have on earthquake ground‐motion variability.
Global climate signals and equatorial SST variability in the Indian, Pacific and Atlantic oceans during the 20th century
Authors: Tourre Yves M. , White Warren B.
Published: March 2006

Oceanic global and individual basin (i.e., Indian, Pacific and Atlantic oceans) sea surface temperature (SST) and sea level pressure (SLP) are analyzed jointly, using MTM/SVD technique. Besides global and individual secular variability, differences in low‐frequency climate signals are evidenced: that is, an inter‐decadal signal dominates in the Indian and Pacific oceans, while a quasi‐decadal signal dominates in the Pacific and Atlantic oceans. Two inter‐annual global and individual climate signals dominate: i.e., ENSO and quasi‐biennial (QB). Moreover, significant correlations are found between three known equatorial SST indices (i.e., IO1 in Indian Ocean, NINO3 in Pacific Ocean, and ATL2 in Atlantic Ocean), and SST time‐series obtained by summing‐up only global lead‐frequency signals identified here: i.e., 0.74, 0.82, and 0.56 respectively. These results should help improving long‐term climate numerical forecasts and mitigating societal impacts by using observed specific equatorial SSTs time‐series, in a climate change context.
Low‐energy (order 10 eV) ion flow in the magnetotail lobes inferred from spacecraft wake observations
Authors: Engwall E. , Eriksson A. I. , André M. , Dandouras I. , Paschmann G. , Quinn J. , Torkar K.
Published: March 2006

Cold ionospheric ions with eV energies are common in the magnetosphere and can travel far out in the magnetotail. However, they are difficult to measure with conventional ion spectrometers mounted on spacecraft, since the potential of a sunlit spacecraft often reaches several tens of volts. In this paper we present two alternative methods of measuring the cold‐ion flow with the Cluster spacecraft and apply them on one case in the magnetotail at 18 RE: 1. Ion spectrometer in combination with artificial spacecraft potential control; 2. Deriving ion flow velocity (both perpendicular and parallel) from electric field instruments. The second method takes advantage of the effect on the double‐probe instrument of the wake formed behind a spacecraft in a plasma flow. The results from the two methods show good agreement and are also consistent with polar wind models and previous measurements at lower altitudes, confirming the continuation of low‐energy ion outflows.
Reconciling a geophysical model to data using a Markov chain Monte Carlo algorithm: An application to the Yellow Sea–Korean Peninsula region
Authors: Pasyanos Michael E. , Franz Gregory A. , Ramirez Abelardo L.
Published: March 2006

In an effort to build seismic models that are the most consistent with multiple data sets we have applied a new probabilistic inverse technique. This method uses a Markov chain Monte Carlo (MCMC) algorithm to sample models from a prior distribution and test them against multiple data types to generate a posterior distribution. While computationally expensive, this approach has several advantages over deterministic models, notably the seamless reconciliation of different data types that constrain the model, the proper handling of both data and model uncertainties, and the ability to easily incorporate a variety of prior information, all in a straightforward, natural fashion. A real advantage of the technique is that it provides a more complete picture of the solution space. By mapping out the posterior probability density function, we can avoid simplistic assumptions about the model space and allow alternative solutions to be identified, compared, and ranked. Here we use this method to determine the crust and upper mantle structure of the Yellow Sea and Korean Peninsula region. The model is parameterized as a series of seven layers in a regular latitude‐longitude grid, each of which is characterized by thickness and seismic parameters (Vp, Vs, and density). We use surface wave dispersion and body wave traveltime data to drive the model. We find that when properly tuned (i.e., the Markov chains have had adequate time to fully sample the model space and the inversion has converged), the technique behaves as expected. The posterior model reflects the prior information at the edge of the model where there is little or no data to constrain adjustments, but the range of acceptable models is significantly reduced in data‐rich regions, producing values of sediment thickness, crustal thickness, and upper mantle velocities consistent with expectations based on knowledge of the regional tectonic setting.
Modification of surface winds near ocean fronts: Effects of Gulf Stream rings on scatterometer (QuikSCAT, NSCAT) wind observations
Authors: Park Kyung‐Ae , Cornillon Peter , Codiga Daniel L.
Published: March 2006

Modifications to surface winds by currents and sea surface temperature (SST) gradients near frontal boundaries of Gulf Stream rings are analyzed using satellite SST and scatterometer (NASA's Quick Scatterometer (QuikSCAT), NASA scatterometer (NSCAT)) wind observations. A component of scatterometer wind approximately equal and opposite to the surface current vector is observed and attributed to the fact that scatterometers detect relative motion of water and air. Warm‐core ring (WCR) SSTs act to destabilize the marine atmospheric boundary layer (MABL), increasing surface wind magnitude by 10–15% and decreasing veering angle by 5–15° relative to large‐scale mean winds. Cold‐core ring (CCR) SSTs cause impacts of similar magnitude and opposite sense. Magnitudes and directions of modifications are accounted for by MABL dynamics of a nonlinear planetary boundary layer model forced by air‐sea temperature differences. Wind modifications occur within tens of kilometers of SST fronts, implying a wind response timescale of order 1 hour. By contrast, uniformity of modified winds across the larger area within rings suggests the response time for the MABL to return to equilibrium downstream from a front exceeds 10 hours. Over WCRs, strong divergence (convergence) occurs on the upwind (downwind) side; curl is strongly negative (positive) to the right (left) side facing downwind. Opposite patterns are generally seen over CCRs. Divergence (curl) peaks where winds blow perpendicular (parallel) to SST fronts. SST image analysis indicates enhanced cloudiness occurs with downwind convergence over WCRs. Wind stress curl due to ring modifications causes dipolar Ekman pumping sufficient to influence ring translation and decay processes.
Interannual variability of the South China Sea associated with El Niño
Authors: Wang Chunzai , Wang Weiqiang , Wang Dongxiao , Wang Qi
Published: March 2006

Interannual sea surface temperature (SST) anomalies in the South China Sea (SCS) are largely influenced by El Niño through El Niño–driven atmospheric and oceanic changes. This paper discovers a new observed feature of the SCS SST anomalies: a double‐peak evolution following an El Niño event. The first and second peaks occur around February and August, respectively, in the subsequent year of the El Niño year (denoted by February [+1] and August [+1]). During and after the mature phase of El Niño, a change of atmospheric circulation alters the local SCS near‐surface air temperature, humidity, cloudiness, and monsoon wind. These factors influence surface heat fluxes and oceanic flows over the SCS that can either warm or cool the SCS depending upon stages of SST anomaly evolution. The shortwave radiation and latent heat flux anomalies are major contributions to the first peak of the SCS SST anomalies, although the geostrophic heat advections warm the western boundary region of the SCS. After the first peak of February [+1], both the Ekman and geostrophic heat advections, assisted with a reduction of the net heat flux anomalies, cool the SCS SST anomalies. In August [+1], the mean meridional geostrophic heat advection makes the SCS SST anomalies peak again. Then, the latent heat flux anomalies (mainly attributed to anomalous air‐sea difference in specific humidity) and the mean zonal geostrophic heat advection take over for the cooling of the SCS after the second peak.
Determination of multiple aquifer parameters using generated water level disturbances
Authors: Lal A. M. Wasantha
Published: March 2006

A method was developed to determine bulk values of aquifer and sediment resistance parameters in a coupled canal‐aquifer system using generated sinusoidal hydraulic disturbances. The method is based on analytical solutions to the canal‐aquifer interaction problem derived assuming small perturbations, linear analysis, and spectral methods. Results were obtained in terms of dimensionless parameters so that they can be applied to many practical problems. Numerical models were used to verify the solutions in selected test problems. The method was applied to determine physical parameters of the L‐31W canal in Miami‐Dade County, Florida, near the Everglades in both dimensionless and dimensional forms. The field experiment was carried out using operational control features of the south Florida conveyance system. Results of the analysis show that various dimensionless parameter groups determine various dynamic behaviors in both confined and unconfined aquifers. Which flow component dominates in the system depends on the range of a particular dimensionless parameter. The analytical solutions derived during the analysis are useful in calculating parameters in regional systems where the historical data are noisy or questionable. Calculation of parameters is accomplished by designing field experiments in which input and output signals of a particular frequency can be used with analytical equations to obtain parameters.
Toward a unified science of the Earth's surface: Opportunities for synthesis among hydrology, geomorphology, geochemistry, and ecology
Authors: Paola Chris , Foufoula‐Georgiou Efi , Dietrich William E. , Hondzo Miki , Mohrig David , Parker Gary , Power Mary E. , Rodriguez‐Iturbe Ignacio , Voller Vaughan , Wilcock Peter
Published: March 2006

The Earth's surface is shaped by the interaction of tectonics, water, sediment, solutes, and biota over a wide range of spatial and temporal scales and across diverse environments. Development of a predictive science of Earth surface dynamics integrates many disciplines and approaches, including hydrology, geomorphology, ocean and atmospheric science, sedimentary and structural geology, geochemistry, and ecology. This paper discusses challenges, opportunities, and a few example problems that can serve as pathways toward this integration.
Relationship between river size and nutrient removal
Authors: Wollheim W. M. , Vörösmarty C. J. , Peterson B. J. , Seitzinger S. P. , Hopkinson C. S.
Published: March 2006

We present a conceptual approach for evaluating the biological and hydrological controls of nutrient removal in different sized rivers within an entire river network. We emphasize a per unit area biological parameter, the nutrient uptake velocity (νf), which is mathematically independent of river size in benthic dominated systems. Standardization of biological parameters from previous river network models to νf reveals the nature of river size dependant biological activity in these models. We explore how geomorphic, hydraulic, and biological factors control the distribution of nutrient removal in an idealized river network, finding that larger rivers within a basin potentially exert considerable influence over nutrient exports.
Protective Effect of the 20-HETE Inhibitor HET0016 on Brain Damage after Temporary Focal Ischemia
Authors: Poloyac Samuel M , Zhang Yuqing , Bies Robert R , Kochanek Patrick M , Graham Steven H
Published: March 2006

Cytochrome P450 metabolism of arachidonic acid produces the potent vasoconstrictive metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE). Recent studies have implicated 20-HETE as a vasoconstrictive mediator in hemorrhagic stroke. The purpose of this study was to determine the effect of the 20-HETE inhibitor, HET0016, on lesion volume and cerebral blood flow (CBF) after temporary middle cerebral artery occlusion (MCAO) in rats. Plasma pharmacokinetics and tissue concentrations of HET0016 were determined after a 10 mg/kg intraperitoneal dose. Separate rats were treated with HET0016 or vehicle before 90mins of MCAO. Lesion volume was assessed by 2,3,5-triphenyl-tetrazolium-chloride and cerebral flow was determined using laser Doppler flow. The effect of MCAO on in vitro microsomal formation of mono-oxygenated arachidonic acid metabolites was also determined. Results show that HET0016 has a short biologic half-life, distributes into the brain, and is associated with a 79.6% reduction in 20-HETE concentration in the cortex. Lesion volume was greatly reduced in HET0016-treated (9.1%±4.9%) versus vehicle-treated (57.4%±9.8%; n = 6; P < 0.001) rats. An attenuation of the observed decrease in CBF was observed in HET0016-treated (180 mins 89.2%±6.2%; 240 mins 88.1%±5.7% of baseline flow) versus vehicle control (180 mins 57.6%±19.0%; 240 mins 53.8%±20.0% of baseline flow; n=6; P < 0.05). Brain cortical microsomal formation rate of 20-HETE was also reduced at 24 h in the ipsilateral hemisphere after MCAO. These data support a significant role for 20-HETE in the pathogenesis of ischemic stroke.
Strain relief by periodic misfit arrays for low defect density GaSb on GaAs
Authors: Huang S. H. , Balakrishnan G. , Khoshakhlagh A. , Jallipalli A. , Dawson L. R. , Huffaker D. L.
Published: March 2006

We demonstrate the growth of a low dislocation density, relaxed GaSb bulk layer on a (001) GaAs substrate. The strain energy generated by the 7.78% lattice mismatch is relieved by a periodic array of 90° misfit dislocations. The misfit array is localized at the GaSb∕GaAs interface and has a period of 5.6nm which is determined by transmission electron microscope images. No threading dislocations are visible. The misfits are identified as 90°, rather than 60°, using Burger’s circuit analysis, and are therefore not associated with generation of threading dislocations. A low dislocation density and planar growth mode is established after only 3 monolayers of GaSb deposition as revealed by reflection high-energy electron diffraction patterns. Calculations corroborate the materials characterization and indicate the strain energy generated by the 7.78% lattice mismatch is almost fully dissipated by the misfit array. The low dislocation density bulk GaSb material on GaAs enabled by this growth mode will lead to new devices, especially in the infrared regime, along with novel integration schemes.
Electron attachment to POCl3: Measurement and theoretical analysis of rate constants and branching ratios as a function of gas pressure and temperature, electron temperature, and electron energy
Authors: Van Doren Jane M. , Friedman Jeffery F. , Miller Thomas M. , Viggiano A. A. , Denifl S. , Scheier P. , Märk T. D. , Troe J.
Published: March 2006

Two experimental techniques, electron swarm and electron beam, have been applied to the problem of electron attachment to POCl3, with results indicating that there is a competition between dissociation of the resonant POCl3−* state and collisional stabilization of the parent anion. In the electron beam experiment at zero electron energy, the fragment ion POCl2− is the dominant ion product of attachment (96%), under single-collision conditions. Small amounts (∼2% each) of POCl3− and Cl− were observed. POCl3− and POCl2− ion products were observed only at zero electron energy, but higher-energy resonances were recorded for POCl−, Cl−, and Cl2− ion products. In the electron swarm experiment, which was carried out in 0.4–7Torr of He buffer gas, the parent anion branching ratio increased significantly with pressure and decreased with temperature. The electron attachment rate constant at 297K was measured to be (2.5±0.6)×10−7cm3s−1, with ion products POCl2− (71%) and POCl3− (29%) in 1Torr of He gas. The rate constant decreased as the electron temperature was increased above 1500K. Theory is developed for (a) the unimolecular dissociation of the nascent POCl3−* and (b) a stepladder collisional stabilization mechanism using the average energy transferred per collision as a parameter. These ideas were then used to model the experimental data. The modeling showed that D0o(Cl–POCl2−) and EA(POCl3) must be the same within ±0.03eV.
Self-recognition and aggregation between diblock (charged/neutral) polyelectrolytes by Monte Carlo simulations
Authors: Feng Jie , Ruckenstein Eli
Published: March 2006

The self-recognition between oppositely charged polyelectrolyte-neutral diblock copolymers and aggregate formation is investigated by Monte Carlo simulations. Both matched lengths and charge numbers are critical conditions for self-recognition. The optimum self-recognition occurs between oppositely charged chains with matched charged block lengths and charge numbers. The size of aggregates increases, as the total length and the ratio of charged to neutral beads become larger. Polyelectrolyte networks were observed in some cases containing unmatched chains. The molecular configurations of the entire chains and of the charged and neutral blocks as well as the radial distribution functions of the charged beads are also investigated.
Kinetic theory of binary nucleation based on a first passage time analysis
Authors: Djikaev Yuri , Ruckenstein Eli
Published: March 2006

The binary classical nucleation theory (BCNT) is based on the Gibbsian thermodynamics and applies the macroscopic concept of surface tension to nanosize clusters. This leads to severe inconsistencies and large discrepancies between theoretical predictions and experimental results regarding the nucleation rate. We present an alternative approach to the kinetics of binary nucleation which avoids the use of classical thermodynamics for clusters. The new approach is an extension to binary mixtures of the kinetic theory previously developed by Narsimhan and Ruckenstein and Ruckenstein and Nowakowski [J. Colloid Interface Sci. 128, 549 (1989); 137, 583 (1990)] for unary nucleation which is based on molecular interactions and in which the rate of emission of molecules from a cluster is determined via a mean first passage time analysis. This time is calculated by solving the single-molecule master equation for the probability distribution of a “surface” molecule moving in a potential field created by the cluster. The starting master equation is a Fokker-Planck equation for the probability distribution of a surface molecule with respect to its phase coordinates. Owing to the hierarchy of characteristic time scales in the evolution of the molecule, this equation can be reduced to the Smoluchowski equation for the distribution function involving only the spatial coordinates. The new theory is combined with density functional theory methods to determine the density profiles. This is essential for nucleation in binary systems particularly when one of the components is surface active. Knowing these profiles, one can determine the potential fields created by the cluster, its rate of emission of molecules, and the nucleation rate more accurately than by using the uniform density approximation. The new theory is illustrated by numerical calculations for a model binary mixture of Lennard-Jones monomers and rigidly bonded dimers of Lennard-Jones atoms. The amphiphilic character of the dimer component (i.e., its surface activity) is induced by the asymmetry in the interaction between a monomer and the two different sites of a dimer. The inconsistencies of the BCNT are avoided in the new theory.
Normal transmission of phonons with anomalous dispersion through the interface of two continuous media
Authors: Adamenko I. N. , Nemchenko K. E. , Tanatarov I. V.
Published: March 2006

The problem of normal transmission of quasiparticles through the interface of two continuous media, one of which is a quantum fluid, is solved. The quantum fluid is described as a continuous medium with correlations. Within the framework of this approach the dispersion relation of the quantum fluid Ω(k) can be arbitrary. The integral equation describing it in a half-space is solved by the Wiener–Hopf method, and its general solution is obtained. This approach is applied to the dispersion relation of the Bose–Einstein condensate. It is shown that the solutions of equations of quantum fluid in a half-space are traveling waves deformed near the border by specific surface standing waves. By means of boundary conditions the general solution in the whole space is obtained. Expressions for transmission and reflection factors of waves in both directions are derived, depending on their frequency. The results are important for describing the creation of helium II phonons on the boundary with a solid, and are of interest for classical acoustics.
Magnetic flux creep in YBa2Cu3O7−δ high-Tc superconducting thin films near the critical temperature
Authors: Chernomorets M. P. , Kovalchuk D. G. , Ryabchenko S. M. , Semenov A. V.
Published: March 2006

The temperature dependence of the dynamic relaxation rate Q for epitaxial thin films of YBa2Cu3O7−δ is obtained from measurements of the ac magnetic susceptibility at different frequencies in the temperature range from 77K to the critical temperature Tc. The critical current density is determined from the measurements according to two known methods: using the “loss maximum” and a “high constant amplitude” of the ac exciting field. The results obtained by these two methods are compared to each other and with the theoretical predictions of the critical state model as modified by Clem and Sanchez. It is found that for the temperature and field conditions used in the loss maximum measurements, the deviations from that model are small and independent of temperature right up to Tc. Under these conditions the value of Q is determined correctly and is found to be independent of temperature. The results obtained from the measurements by the method of high constant amplitude of the ac field cannot be interpreted correctly because of practical limitations encountered in the whole range of temperatures studied. With increasing distance from Tc the approximate formulas used in that method diverge rapidly from the exact formulas of the critical state model. On approach to Tc the amplitude of the ac field becomes much greater than the corresponding loss maximum, and it is shown that under those conditions the relations among the parameters obtained diverge from the predictions of the Clem–Sanchez theory. It is concluded that this last circumstance is due to the deviations from the critical state model at such high amplitudes of the ac field. As a result, the use of this theory to obtain data on Q becomes incorrect. At high amplitudes of the ac field there is a region about 1K wide below Tc in which one observes a regime where the real part of the complex magnetic susceptibility falls off practically to zero and only the imaginary part remains. This corresponds to a flux-flow-induced resistive state of the superconductor.
Phase transitions in a ferromagnet with an anisotropic biquadratic exchange interaction
Authors: Fridman Yu. A. , Kosmachev O. A. , Klevets F. N.
Published: March 2006

The phase states of a non-Heisenberg ferromagnet with anisotropy of both the Heisenberg and biquadratic interactions are investigated. Limiting cases of the model are the XY model with a biquadratic interaction and the three-component non-Heisenberg ferromagnet. The phase transitions both in respect to the material constants and in temperature are investigated for the 2D and 3D magnets. The phase diagrams of the system are constructed for various relations of the system parameters. It is shown that in the given model the soft mode is a branch of quasimagnetic and not quasielastic excitations.
Magnetoelastic generation of electromagnetic fields by sound waves in weak ferromagnets
Authors: Kolesnichenko Yu. A. , Stepanenko D. I.
Published: March 2006

A study is made of the generation of electromagnetic oscillations by a sound wave in a weak ferromagnet with a higher-order symmetry axis. The electric fields are calculated for different states with different orientations of the antiferromagnetic vector. It is shown that the magnetoelastic interaction leads to an additional phase difference between the electromagnetic and sound waves.
Magnetic resonance properties of the low-dimensional antiferromagnet Mn[C10H6(OH)(COO−)]2∙2H2O
Authors: Dergachev K. G. , Kobets M. I. , Khats’ko E. N. , Lang M. , Pashchenko V. A.
Published: March 2006

Magnetic resonance studies of the metalorganic antiferromagnet Mn[C10H6(OH)(COO−)]2∙2H2O are carried out over a wide range of frequencies (25–12GHz) and temperatures (1.8–300K). The data on the temperature dependence of the magnetic susceptibility attest to a low-dimensional magnetic structure of this crystal. The results of resonance studies at a temperature of 1.8K are used to construct the frequency–field diagram of the antiferromagnetic resonance spectrum of this compound; it is described by the model of a biaxial rhombic antiferromagnet with the following parameters: ν01=14.1±0.1GHz, ν02=44.2±0.1GHz, Ha1=0.25kOe, Ha2=2.53kOe, Hsf=5.1±0.1kOe, 2He=98±1kOe. Two-magnon and nonresonance three-magnon absorption is observed, and the weakest interchain exchange interaction is estimated as J′=6.2×10−3K.
On magnetic collapse in solid oxygen under high pressure
Authors: Kalita V. M. , Loktev V. M.
Published: March 2006

An attempt is made at a theoretical interpretation of the observed collapse of the magnetic state in solid oxygen under pressure. The basic premise rests on a growing role of the biquadratic intermolecular exchange with increasing pressure, leading to instability of the initial antiferromagnetic state.
A contribution to the theory of magnetoplasma waves in quantum wires
Authors: Ermolaev A. M. , Rashba G. I.
Published: March 2006

The problem of plasma waves in a thick wire in the presence of a magnetic field perpendicular to the wire is considered in the random phase approximation. The standard model of a wire, with a parabolic confinement potential, is used. The polarization operator of a degenerate and a nondegenerate electron gas in the wire is calculated for an arbitrary width of that potential. Formulas are obtained for the spectrum and damping of intrasubband and intersubband magnetoplasmons in wires with a degenerate and nondegenerate electron gas for an arbitrary number of filled confinement subbands. The anisotropy of the magnetoplasmon spectrum in a thick wire and the screening of the Coulomb field of an electric charge in the wire are considered.
Heterogeneous cluster formation in a supersonic argon-krypton jet according to cathodoluminescence data in the vacuum ultraviolet
Authors: Doronin Yu. S. , Samovarov V. N. , Bondarenko E. A.
Published: March 2006

Processes of cluster formation in a supersonic argon-krypton jet at low concentrations of the krypton impurity (down to 1×10−3%) are investigated by a luminescence method. VUV diagnostics of the picture of heterogeneous nucleation, including its earliest stages, is employed for the first time. Attention is focused mainly on the behavior of the emission bands belonging to the neutral excimers Ar2* and Kr2* and the charged homoatomic complexes (Ar4+)* and (Kr4+)* and the heteroatomic exciplexes (Ar∕Kr)*. In the first stage of heterogeneous nucleation the nuclei can be krypton atoms (dimers). Beginning at krypton concentrations in the gas mixture of 0.02% and higher a multiatomic krypton core is formed in the cluster. When such clusters are ionized the ion is located in the krypton core, and its electric field has a substantial influence on the parameters of the emission band of an Ar∕Kr molecule found at the argon/krypton boundary. The results of this study demonstrate the high efficiency of VUV spectroscopy for studying processes of heteroatomic cluster formation in supersonic jets.
Local vibrational modes in crystal lattices with a simply connected region of the quasi-continuous phonon spectrum
Authors: Kotlyar A. V. , Feodosyev S. B.
Published: March 2006

It is shown that the use of the mode classification adopted in the Jacobi matrix method and which is the most natural one for describing localized states leads to extremely rapid convergence of the Green functions for frequencies lying outside the quasi-continuum band of the crystal. This has made it possible to obtain rather general analytical expressions for the conditions of formation and the characteristics of local modes due to the presence of light impurity atoms in crystal lattices having a simply connected region of the quasi-continuous phonon spectrum. The accuracy with which the frequencies and intensities of the local modes are determined using these expressions is illustrated for examples of light substitutional impurities (isotopic and weakly coupled) and close-packed structures (fcc and hcp) and also isolated pairs of isotopic impurities in an fcc crystal lattice. In particular, the results permit simple and extremely accurate evaluation of the parameters of the host lattice and defect from the known values of the local frequencies.
Density dependences of long-range fluctuations and short-range correlation lengths of CHF3 and CH2F2 in supercritical states
Authors: Morita Takeshi , Takahashi Yoshihiro , Tanaka Yoshitada , Arai Asako Ayusawa , Nishikawa Keiko
Published: March 2006

Small-angle x-ray scattering (SAXS) measurements are carried out for supercritical polar fluorocarbons, CHF3 and CH2F2, along the isotherm of 1.04 in reduced temperatures with the density range from 0.3 to 1.5 in reduced units. A novel apparatus for determination of absorption factors of the sample fluids is used in the present measurements. The apparatus enables us to detect simultaneously the accurate factors during the observation of the SAXS signals. Long-range fluctuations such as density fluctuations and correlation lengths are evaluated from the obtained SAXS data. The reduced correlation lengths are obtained by normalization by each molecular size, in order to discuss the fluctuations independent of the difference of the individual molecular size. The density fluctuations and the reduced correlation lengths of CHF3 and CH2F2 are compared with those of CO2 and H2O. The results are as follows: H2O>CH2F2>CHF3∼CO2 in the order of magnitude. The fluctuations of CH2F2 are significantly distinguishable from those of CHF3 and show intermediate aspect between H2O and a group of CO2 and CHF3. In addition, the short-range correlation lengths, i.e., the Ornstein-Zernike direct correlation lengths, are firstly discussed from both viewpoints of density and substance dependences. The reduced short-range correlation lengths normalized by individual molecular size are found to trace a universal curve as a function of the reduced density.
The formation of low-dimensional inorganic nanotube crystallites in carbon nanotubes
Authors: Wilson Mark
Published: March 2006

The filling of carbon nanotubes, which vary in diameter and morphology, is directly observed by molecular dynamics computer simulation with a potential model which thermodynamically favors a four-coordinate bulk crystal structure. Inorganic nanotube (INT) structures form which are based on percolating hexagonal nets. For small carbon nanotube diameters the filling is shown to proceed via an “internal wetting” mechanism, which depends on the internal carbon nanotube area rather than the free volume. Both single- and double-walled INTs are predicted to form. The atomistic formation mechanisms are discussed and an intermediate structure identified. The INT structures, including the observed intermediate, are discussed by reference to a simple energy landscape. The formation energetics are discussed in terms of a simple analytical model which combines the INT strain energy and the tube-tube interactions. An effective phase diagram, which predicts the INT morphologies as a function of carbon nanotube diameter, is derived and discussed with respect to the analytical model.
A comparison of experimental and calculated spectra of HNO3 in the near-infrared using Fourier transform infrared spectroscopy and vibrational perturbation theory
Authors: Feierabend Karl J. , Havey Daniel K. , Varner Mychel E. , Stanton John F. , Vaida Veronica
Published: March 2006

This work combines new laboratory studies of the near-infrared vibrational spectra of HNO3 with theoretical predictions of these spectra as a means to understand the properties of this molecule at energies well above the fundamental region. Trends in overtone and combination band energy levels and intensities are compiled and examined. The theoretical calculations are in excellent agreement with the observed frequencies and intensities of the transitions in this spectral region. The calculations also serve as a valuable aid for assigning many of the transitions. This work validates the ab initio generated potential energy surface for HNO3 by comparing vibrational perturbation theory calculations to experimental spectra focused on combination band and overtone absorptions.
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Racah coefficients: Type I representations
Authors: Krasnov Kirill , Louko Jorma
Published: March 2006

We use AdS/CFT inspired methods to study the Racah coefficients for type I representations of the Lorentz group SO0(1,d+1) with d>1. For such representations (a multiple of) the Racah coefficient can be represented as an integral of a product of six bulk-to-bulk propagators over four copies of the hyperbolic space Hd+1. To compute the integrals we represent the bulk-to-bulk propagators in terms of bulk-to-boundary ones. The bulk integrals can be computed explicitly, and the boundary integrations are carried out by introducing Feynman parameters. The final result is an integral representation of the Racah coefficient given by four Barnes-Mellin type integrals.
Soliton solutions of the Kadomtsev-Petviashvili II equation
Authors: Biondini Gino , Chakravarty S.
Published: March 2006

We study a general class of line-soliton solutions of the Kadomtsev-Petviashvili II (KPII) equation by investigating the Wronskian form of its tau-function. We show that, in addition to the previously known line soliton solutions of KPII, this class also contains a large variety of multisoliton solutions, many of which exhibit nontrivial spatial interaction patterns. We also show that, in general, such solutions consist of unequal numbers of incoming and outgoing line solitons. From the asymptotic analysis of the tau function, we explicitly characterize the incoming and outgoing line solitons of this class of solutions. We illustrate these results by discussing several examples.