bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection Criteria for Hepatectomy in Patients with Hepatocellular Carcinoma Classified as Child‐Pugh Class B
Authors: Kuroda Shintaro , Tashiro Hirotaka , Kobayashi Tsuyoshi , Oshita Akihiko , Amano Hironobu , Ohdan Hideki
Published: December 2010

Background

The appropriate surgical approach for hepatocellular carcinoma (HCC) patients of Child‐Pugh class B is unclear. The aim of this study was to clarify the prognostic factors after hepatectomy in Child‐Pugh class B patients and to delineate the selection criteria for hepatectomy.

Methods

One hundred fifty patients of Child‐Pugh class B who underwent hepatectomy were enrolled in this retrospective study (Hx group). Univariate and multivariate analyses were performed to identify prognostic factors. The prognosis was compared with that of 23 patients of Child‐Pugh class B who underwent liver transplantation (LT group).

Results

The overall survival rate of the Hx group was significantly worse than that of the LT group (5‐year survival: 36.0 vs. 78.3%, p = 0.001). In multivariate analyses, diabetes mellitus (p = 0.011), preoperative total bilirubin level ≥1.5 mg/dl (p = 0.038), and Child‐Pugh score of 8 or 9 (p = 0.038) were independent prognostic factors. Although the overall 5‐year survival rate of patients with none of the three adverse prognostic factors was only 50.3%, that of patients with one or more adverse prognostic factors was only 27.2% (p = 0.001).

Conclusions

Hepatectomy may be the optimal initial treatment for HCC patients classified as Child‐Pugh class B and without any adverse prognostic factors.
Do Soft Skills Predict Surgical Performance?
Authors: Maschuw K. , Schlosser K. , Kupietz E. , Slater E. P. , Weyers P. , Hassan I.
Published: December 2010

Background

Virtual reality (VR) training in minimal invasive surgery (MIS) is feasible in surgical residency and beneficial for the performance of MIS by surgical trainees. Research on stress‐coping of surgical trainees indicates the additional impact of soft skills on VR performance in the surgical curriculum. The aim of this study was to evaluate the impact of structured VR training and soft skills on VR performance of trainees.

Method

The study was designed as a single‐center randomized controlled trial. Fifty first‐year surgical residents with limited experience in MIS (“camera navigation” in laparoscopic cholecystectomy only) were randomized for either 3 months of VR training or no training. Basic VR performance and defined soft skills (self‐efficacy, stress‐coping, and motivation) were assessed prior to randomization using basic modules of the VR simulator LapSim® and standardized psychological questionnaires. Three months after randomization VR performance was reassessed. Outcome measurement was based on the results derived from the most complex of the basic VR modules (“diathermy cutting”) as the primary end point. A correlation analysis of the VR end‐point performance and the psychological scores was done in both groups.

Results

Structured VR training enhanced VR performance of surgical trainees. An additional correlation to high motivational states (P < 0.05) was found. Low levels of self‐efficacy and negative stress‐coping were related to poor VR performance in the untrained control group (P < 0.05). This correlation was absent in the trained intervention group (P > 0.05).

Conclusion

Low self‐efficacy and negative stress‐coping strategies seem to predict poor VR performance. However, structured training along with high motivational states is likely to balance out this impairment.
Robot‐assisted versus Laparoscopic Roux‐en‐Y Gastric Bypass: Is There a Difference in Outcomes?
Authors: Ayloo Subhashini M. , Addeo Pietro , Buchs Nicolas Christian , Shah Galaxy , Giulianotti Pier Cristoforo
Published: December 2010

Background

Application of the robot for Roux‐en‐Y gastric bypass has been slow to evolve, despite its rapid acceptance in other fields. This is largely due to associated costs of technology, reports of increased operative time, and inadequate data available to correlate the benefits of robotics to a clinical outcome. The authors present a comparative study between laparoscopic and robot‐assisted Roux‐en‐Y gastric bypass performed at a specialized institution for robotic surgery.

Materials and method

A total of 135 consecutive Roux‐en‐Y gastric bypass procedures were performed from January 2006 to December 2009 by a single surgeon. The first 45 were performed laparoscopically and the remaining 90 were robot‐assisted. Patient demographics, operative time, complication rate, length of stay, long‐term weight loss, and follow‐up for the two groups were gathered from a prospectively maintained database and statistically analyzed.

Results

The overall operative time was significantly shorter for the robot‐assisted procedures than for the laparoscopic procedures (207 ± 31 vs. 227 ± 31 min) (P = 0.0006). The robotic set‐up time remained constant at 13 ± 4 min. 30 robotic cases were necessary in order to perform the procedure in less time than with the laparoscopic approach (P = 0.047). Mortality was 0% in both groups, with no conversions to open surgery and no transfusions. Early morbidities and percentage of excess weight loss at 1 year were comparable for the two groups.

Conclusions

The use of the robot for performing the gastrojejunostomy during laparoscopic Roux‐en‐Y gastric bypass does not increase the operative time or the rate of specific complications. The short‐term outcomes of the robot‐assisted procedure are comparable to those found with the conventional laparoscopic method.
Fungal endophyte communities in four Rhizophoraceae mangrove species on the south coast of China
Authors: Xing Xiaoke , Guo Shunxing
Published: December 2010

This study investigated the taxonomic identities and diversity of fungal endophytes isolated from four Rhizophoraceae mangrove plant species, Ceriops tagal, Rhizophoraapiculata, R. stylosa and Bruguiera sexangula var. rhynchopetala, using a combination of morphological and molecular approaches. Two hundred ninety‐five isolates were classified into 38 taxa by morphological characteristics. The representative 38 isolates from each taxa were selected for further molecular identification using nuclear ribosomal DNA sequences, including both the internal transcribed spacers (ITS1 and ITS2) and the 5.8S gene region. The 38 representative endophytes were identified to various taxonomic levels. These results suggest that Pestalotiopsis and Phomopsis were the most frequent endophytes in the four host species. Some of the endophytes exhibit host and tissue specificity. The colonization frequencies of endophytic fungi in the stems of the four host plants are evidently higher than in the roots. The four Rhizophoraceae mangrove species have low similarities of endophyte communities.
Epigenetic mechanisms and genome stability
Authors: Putiri Emily L. , Robertson Keith D.
Published: December 2010

Epigenetic marks are well recognized as heritable chemical modifications of DNA and chromatin that induce chromatin structural changes thereby affecting gene activity. A lesser-known phenomenon is the pervasive effects these marks have on genomic integrity. Remarkably, epigenetic marks and the enzymes that establish them are involved in multiple aspects of maintaining genetic content. These aspects include preserving nucleotide sequences such as repetitive elements, preventing DNA damage, functioning in DNA repair mechanisms and chromatin restoration, and defining chromosomal organization through effects on structural elements such as the centromere. This review discusses these functional aspects of epigenetic marks and their effects on human health and disease.
Working Together to Build a Respectful Workplace: Transforming OR Culture
Authors: Costello Judy , Clarke Cathy , Gravely Gillian , D'Agostino‐Rose Dina , Puopolo Rose
Published: December 2010

Respect is important in the creation of a positive perioperative work environment and effective OR teams. Low scores for respect in the OR on an employee opinion survey and responses on a more customized survey that examined issues associated with respect prompted leaders at the University Health Network to undertake a multiyear organizational strategy to address respect and quality of worklife initiatives. An interprofessional quality of worklife task force convened to create an action plan to address the outcomes of the surveys. The work of the task force included developing and implementing a code of conduct team charter for the OR, empowering leaders to better manage conflict through education and coaching, creating a collaborative, consistent approach to conflict resolution, and designing an education strategy for staff members to enhance communication and conflict resolution. Results of recent employee opinion surveys have reflected positive outcomes. Efforts to sustain the effects of the project include quarterly recognition awards and ongoing education focused on wellness and communication skills.
Perioperative Pharmacology: A Framework for Perioperative Medication Safety
Authors: Hicks Rodney W. , Wanzer Linda , Goeckner BradLee
Published: December 2010

Learning pharmacology is a critical element of any health care practitioner's education to ensure quality and safety in perioperative care. The medication‐use process and safe medication use are two important principles that contribute to the safe use of pharmacological agents in perioperative clinical practice. The medication‐use process consists of procuring, prescribing, transcribing, dispensing, administering, and monitoring; however, variations in the medication‐use process result from demands unique to the perioperative environment, and these variations can sometimes bypass the safety nets within the system. Understanding these variances will help perioperative practitioners recognize threats to patient safety and help ensure the patient's well‐being. Responsibilities of a safe medication‐use system include assuring the public that practitioners use medications efficiently, safely, and effectively, and fully document all medications administered.
Paleoseismological evidence of surface faulting along the northeastern Himalayan front, India: Timing, size, and spatial extent of great earthquakes
Authors: Kumar Senthil , Wesnousky Steven G. , Jayangondaperumal R. , Nakata T. , Kumahara Y. , Singh Vimal
Published: December 2010

The ∼2500 km long Himalayan arc has experienced three large to great earthquakes of Mw 7.8 to 8.4 during the past century, but none produced surface rupture. Paleoseismic studies have been conducted during the last decade to begin understanding the timing, size, rupture extent, return period, and mechanics of the faulting associated with the occurrence of large surface rupturing earthquakes along the ∼2500 km long Himalayan Frontal Thrust (HFT) system of India and Nepal. The previous studies have been limited to about nine sites along the western two‐thirds of the HFT extending through northwest India and along the southern border of Nepal. We present here the results of paleoseismic investigations at three additional sites further to the northeast along the HFT within the Indian states of West Bengal and Assam. The three sites reside between the meizoseismal areas of the 1934 Bihar‐Nepal and 1950 Assam earthquakes. The two westernmost of the sites, near the village of Chalsa and near the Nameri Tiger Preserve, show that offsets during the last surface rupture event were at minimum of about 14 m and 12 m, respectively. Limits on the ages of surface rupture at Chalsa (site A) and Nameri (site B), though broad, allow the possibility that the two sites record the same great historical rupture reported in Nepal around A.D. 1100. The correlation between the two sites is supported by the observation that the large displacements as recorded at Chalsa and Nameri would most likely be associated with rupture lengths of hundreds of kilometers or more and are on the same order as reported for a surface rupture earthquake reported in Nepal around A.D. 1100. Assuming the offsets observed at Chalsa and Nameri occurred synchronously with reported offsets in Nepal, the rupture length of the event would approach 700 to 800 km. The easternmost site is located within Harmutty Tea Estate (site C) at the edges of the 1950 Assam earthquake meizoseismal area. Here the most recent event offset is relatively much smaller (<2.5 m), and radiocarbon dating shows it to have occurred after A.D. 1100 (after about A.D. 1270). The location of the site near the edge of the meizoseismal region of the 1950 Assam earthquake and the relatively lesser offset allows speculation that the displacement records the 1950 Mw 8.4 Assam earthquake. Scatter in radiocarbon ages on detrital charcoal has not resulted in a firm bracket on the timing of events observed in the trenches. Nonetheless, the observations collected here, when taken together, suggest that the largest of thrust earthquakes along the Himalayan arc have rupture lengths and displacements of similar scale to the largest that have occurred historically along the world's subduction zones.
Control of the 2009 L'Aquila earthquake, central Italy, by a high‐velocity structure: A receiver function study
Authors: Bianchi I. , Chiarabba C. , Piana Agostinetti N.
Published: December 2010

Receiver functions (RFs) analyzed at two permanent broadband seismic stations operating in the epicentral area of the Mw 6.3, 2009 L'Aquila earthquake (central Italy) yield insight on crustal structure along the fault rupture. The harmonic decomposition of RFs highlights a subsurface structure in which both isotropic and anisotropic features are present. We model the waveforms using recently developed Monte Carlo methods. The retrieved models display a common depth structure, between 10 and 40 km depth, consistent with the under‐thrusting of the Adria lithosphere underneath the Apennines belt. Along the fault, in the uppermost crust, the S wave velocity structure is laterally heterogeneous. Right above the hypocenter, we find a 4–6 km thick, very high S wave velocity body (Vs as high as 4.2 km/s) that is absent in the SE portion of the fault, where the earthquake propagated. The high‐Vs body is coincident with the area of fewer aftershocks and is anticorrelated with the maximum slip patches of the earthquake, as modeled by differential interferometric synthetic aperture radar (DInSAR) and strong motion data. We interpret this high‐Vs body as a high‐strength barrier responsible for the high peak ground motion in the near field, observed in the L'Aquila city and surroundings, and for the complexity in the rupture evolution. The retrieved seismic S wave velocity of this body far exceeds common Vs values in the upper crust and it is more compatible with values observed in mafic basement rocks.
Frontal dynamics in a California Current System shallow front: 1. Frontal processes and tracer structure
Authors: Pallàs‐Sanz E. , Johnston T. M. S. , Rudnick D. L.
Published: December 2010

The three‐dimensional dynamics in a shallow front are examined using density and current data from two surveys 100 km offshore of Monterey Bay, California. Survey 1 is forced by down‐front winds, and both surveys have considerable cross‐front density gradients and flow curvature. The maximum Rossby numbers on the dense side reached maxima of +0.60 in survey 1 and +0.45 in survey 2. Downwelling occurs in regions of confluence (frontogenesis) associated with potential vorticity (PV) change and thermal wind imbalance. Streamers of particulate matter and PV are advected southeastward by the frontal jet and downward. Nonlinear Ekman currents advect dense water over light water in the presence of down‐front winds, which leads to upwelling along the front and downwelling on the light side of the front. At sites of active ageostrophic secondary circulation (ASC), induced by frontogenesis or Ekman effects, the observed cross‐front ageostrophic velocity is consistent with the diagnosed vertical velocity. Furthermore, in survey 2, ageostrophic divergence may play an important role at the curved front, presumably counteracting quasi‐geostrophic frontogenesis due to isopycnal confluence. Downward frictional vertical PV flux below the surface extracts PV from the pycnocline and reinforces the frontogenetic vertical PV flux. PV destruction at the surface is inferred from a low PV anomaly below the mixed layer in survey 2. Since the magnitude of the frontogenetic ASC is only twice the magnitude of Ekman suction, external forcing may have a considerable impact on the vertical heat and PV fluxes.
Effect of measured surface albedo on modeled Saharan dust solar radiative forcing
Authors: Tegen Ina , Bierwirth Eike , Heinold Bernd , Helmert Jürgen , Wendisch Manfred
Published: December 2010

The clear‐sky solar radiative forcing of Saharan dust is computed for a case study during the SAharan Mineral dUst experiMent (SAMUM) in May 2006. Size‐resolved dust concentrations simulated with a regional model and spectrally resolved surface albedo measurements were used as input for a 1‐D radiative transfer model to study the dependence of the dust radiative forcing at solar wavelengths on surface albedo and particle optical properties. Within the considered parameter range, the surface albedo can have a larger impact on the solar radiative forcing of dust at the top of atmosphere (TOA) than the variations of optical properties. At the location of Ouarzazate in Morocco, different measured surface albedo values lead to differences in instantaneous solar TOA solar forcing of up to 15 W m−2 for identical dust properties. This highlights the importance of using an accurate characterization of surface albedo values for estimating solar dust forcing over land. In the regional average over the Sahara using either the standard model values or satellite‐based surface albedos leads to differences in the order of 9 W m−2 in the instantaneous solar forcing at TOA, and 5 W m−2 for the diurnal mean TOA forcing.
R/V Marcus G. Langseth seismic source: Modeling and calibration
Authors: Diebold John B. , Tolstoy Maya , Doermann Lindsey , Nooner Scott L. , Webb Spahr C. , Crone Timothy J.
Published: December 2010

This paper presents analyses of calibration data of the R/V Marcus G. Langseth seismic sources that were collected in 2007–2008. The analysis includes measurements of the levels and azimuthal directivity of the Langseth two‐string source, which is used for 3‐D seismic surveys and compares these data with multichannel seismic hydrophone array data in shallow water. The analysis also shows the important contribution of seafloor and subseafloor reflected and refracted arrivals and the associated effects of water depth and seafloor slope. As expected and predicted by modeling, azimuthal directivity depends greatly on the “footprint” dimensions of the seismic array. In shallow water, where the acoustic field is dominated by near‐vertically traveling reflected and refracted waves, data recorded using a towed MCS array are a useful proxy for single hydrophone calibration data. In deeper water, the easily modeled direct arrivals are exceeded in amplitude by seafloor reflected and subseafloor refracted energy at offsets which depend upon the water depth, limiting the applicability of a priori modeling that does not include these interactions. In addition, in a seafloor sloping environment, amplitudes depend greatly on whether the receivers are upslope or downslope from the source.
Determination of Mg isotopes in chlorophyll a for marine bulk phytoplankton from the northwestern Pacific Ocean
Authors: Ra Kongtae
Published: December 2010

We present Mg isotope data of chlorophyll a extracted from marine phytoplankton samples. Thirty‐eight samples of phytoplankton were collected at three different regions (inner bay and the Kuroshio and Oyashio regions) from the northwestern Pacific Ocean. Even though the dominant class of phytoplankton samples is mainly diatom, large variation (2.37‰) of δ26Mg values was observed. Variation of δ26Mg values in marine phytoplankton collected in the Oyashio region during a spring bloom was smaller than in the Kuroshio region (2.37‰) and within a bay (2.03‰). There is no clear relationship between δ26Mg values and other oceanographic parameters such as temperature, salinity, chlorophyll a concentration, and nutrients. We conclude that interspecies variability of diatoms is the most likely cause of variability in δ26Mg values. Further experiments can allow us to explore which oceanographic parameters control Mg isotopic composition of chlorophyll a. More Mg isotope data are necessary to assess the usage of Mg isotopes of chlorophyll as a potential oceanographic indicator preserved not only in marine phytoplankton but also in other photosynthetic organisms.
High‐velocity frictional properties of clay‐rich fault gouge in a megasplay fault zone, Nankai subduction zone
Authors: Ujiie Kohtaro , Tsutsumi Akito
Published: December 2010

We conducted high‐velocity friction experiments on clay‐rich fault gouge taken from the megasplay fault zone in the Nankai subduction zone under dry and wet conditions. In the dry tests, dehydration of clay minerals occurred by frictional heating, and slip weakening is related to thermal pressurization associated with water vaporization, resulting in a random distribution of clay‐clast aggregates in the gouge matrix. In the wet tests, slip weakening is caused by pore‐fluid pressurization via shear‐enhanced compaction and frictional heating, and there is a very weak dependence of the steady‐state shear stress on the normal stress. The resulting microstructure reflects the grain size segregation in a granular‐fluid shear flow at high shear rates. These results suggest that earthquake rupture propagates easily through clay‐rich fault gouge by high‐velocity weakening, potentially leaving the microstructures resulting from the frictional heating or the flow sorting at high slip rates.
Formation of fingerlike structures in fragmentation of small‐scale patchy aurora
Authors: Hiraki Yasutaka , Sakaguchi Kaori
Published: December 2010

Recent high‐resolution video imagery reveals a dynamic feature of small‐scale (< 20 km) patchy aurora during a substorm recovery phase, that is, fingerlike structures with a few kilometers' scale are formed through the patch fragmentation. Various kinetic processes such as ion finite Larmor radius effects can be involved because the scale mapped into the plasma sheet is much smaller than the ion inertia length. However, such a scale is likely to be strongly damped in a high‐β plasma regime by the ion gyroviscosity effect. In this study, we make several 2.5‐dimensional simulations at the system of each position s along a field line, perpendicular to the ambient magnetic field, by means of the three‐field reduced magnetohydrodynamic equations. The model includes the effects of ion diamagnetic drift and electron parallel motion. In a low‐β regime of s = 4 RE, we find that an ion diamagnetic drift wave grows isotropically to form a patchy structure with a scale of ≈10 km. As the field‐aligned current increases, these patches are fragmented and fingerlike structures with scales of 2–5 km appear owing to the nonlinear electron inertia effect. The scales of patches and fingers and the east–westward finger development, as well as the time scale, are fairly consistent with those of recent observations. On the other hand, at the plasma sheet (ion beta βi = 1, s = 7.5 RE), fingerlike patterns cannot be formed owing to a predominance of large‐scale vortex patterns.
Low‐temperature magnetism of synthetic Fe‐Ti oxide assemblages
Authors: Engelmann Ralf , Kontny Agnes , Lattard Dominique
Published: December 2010

Low‐T magnetometry (<300 K) is increasingly used to identify magnetic mineral assemblages. The present work aims at establishing a robust data basis for the characterization of polycrystalline synthetic Fe‐Ti oxide assemblages from low‐T magnetic measurements. The two‐phase samples contained ilmenite‐hematite solid solutions (ilmenitess) with compositions near to the ilmenite end‐member (XIlm > 0.69), that coexisted either with titanomagnetites or with pseudobrookitess of intermediate to Ti‐rich compositions (XUsp > 0.6; XFpb > 0.57). Single‐phase samples of ilmenitess and titanomagnetite were also prepared and measured to underpin the results on the two‐phase assemblages. We have concentrated on in‐phase and out‐of‐phase AC susceptibility and saturation remanence and some hysteresis measurements. The temperature‐dependent susceptibility and remanence curves reveal diagnostic, composition dependent signals for both ilmenitess and titanomagnetite. In particular, titanomagnetite is distinguished by frequency‐dependent signals in the in‐phase and out‐of‐phase susceptibility curves. We have focused on critical transition temperatures for ilmenitess such as Curie (TC) and Néel temperatures (TN), the spin glass transition temperature (TG) and the blocking temperature (TB). We observe a continuous decrease of TC with increasing XIlm down to about 0.93 and a slight increase of TN for XIlm between 0.95 and 1.0. TG is constant for XIlm between 0.76 and 0.95 and absent for 0.98 < XIlm < 1.0, where antiferromagnetic behavior occurs. TB is only slightly lower than TC for 0.84 < XIlm < 0.94, indicating a very restricted “superparamagnetic” field that vanishes for higher XIlm values. The new data for ilmenitess allow the construction of a revised, more physically appealing low‐temperature phase diagram for this system. We observe two very good linear correlations between the peak temperature in the χ′‐T curves and XIlm, one for the range 0.69–0.92 and one for 0.95–1.00, which can be useful for simple estimates of ilmenitess compositions.
Observations of mesoscale eddies in the South Atlantic Cape Basin: Baroclinic and deep barotropic eddy variability
Authors: Baker‐Yeboah S. , Byrne D. A. , Watts D. R.
Published: December 2010

Anticyclones and cyclones in the eastern South Atlantic are characterized based on data collected during January 2003 to March 2005, along a Jason 1 satellite altimeter ground track, as part of the Agulhas South Atlantic Thermohaline Transport Experiment. Large and small cyclones and anticyclones were ubiquitous in the deep ocean of the eastern South Atlantic, as well as in the upper ocean. Eddy structures jointly corotating in the upper and deep water column were common; most of the time (94%) these were not axially aligned as they copropagated. The Agulhas rings and cyclones that populate the region generally carry both a steric component (baroclinic) and a mass loading component (deep barotropic structure). Average translation speeds were 7.5 cm s−1 for baroclinic eddies and twice as fast for barotropic eddies, irrespective of polarity. Translation speeds were higher than advection by the mean background flow field. In addition, large mixed baroclinic‐barotropic rings crashed into the Agulhas Ridge and nearby seamounts and split into two or more parts. Some ring parts were also observed to fuse together. Deep cyclones, as well as interactions with topography, were observed to play a role in the fission process of Agulhas rings. These processes can increase the population of Agulhas rings and their remnant eddies, which took three pathways from the Agulhas and into the Cape Basin: (1) a deep pathway between the continental slope and Erica Seamount, (2) a shallower pathway over or near the Agulhas Ridge and Schmitt‐Otto Seamount, and (3) a deep seaward pathway around the Agulhas Ridge.
Development of a curved ray tracing method for modeling of phase paths from GPS radio occultation: A two‐dimensional study
Authors: Wee Tae‐Kwon , Kuo Ying‐Hwa , Lee Dong‐Kyou
Published: December 2010

A two‐dimensional curved ray tracer (CRT) is developed to study the propagation path of radio signals across a heterogeneous planetary atmosphere. The method, designed to achieve improvements in both computational efficiency and accuracy over conventional straight‐line methods, takes rays' first‐order bending into account to better describe curved raypaths in the stratified atmosphere. CRT is then used to simulate the phase path from GPS radio occultation (RO). The merit of the ray tracing approach in GPS RO is explicit consideration of horizontal variation in the atmosphere, which may lead to a sizable error but is disregarded in traditional retrieval schemes. In addition, direct modeling of the phase path takes advantage of simple error characteristics in the measurement. With provision of ionospheric and neutral atmospheric refractive indices, in this effort, rays are traced along the full range of GPS‐low Earth orbiting (LEO) radio links just as the measurements are made in real life. Here, ray shooting is employed to realize the observed radio links with controlled accuracy. CRT largely reproduces the very measured characteristics of GPS signals. When compared, the measured and simulated phases show remarkable agreement. The cross validation between CRT and GPS RO has confirmed not only the strength of CRT but also the high accuracy of GPS RO measurements. The primary motivation for this study is enabling effective quality control for GPS RO data, overcoming a complicated error structure in the high‐level data. CRT has also shown a great deal of potential for improved utilization of GPS RO data for geophysical research.
Spatial and temporal melt variability at Helheim Glacier, East Greenland, and its effect on ice dynamics
Authors: Andersen M. L. , Larsen T. B. , Nettles M. , Elosegui P. , van As D. , Hamilton G. S. , Stearns L. A. , Davis J. L. , Ahlstrøm A. P. , de Juan J. , Ekström G. , Stenseng L. , Khan S. A. , Forsberg R. , Dahl‐Jensen D.
Published: December 2010

Understanding the behavior of large outlet glaciers draining the Greenland Ice Sheet is critical for assessing the impact of climate change on sea level rise. The flow of marine‐terminating outlet glaciers is partly governed by calving‐related processes taking place at the terminus but is also influenced by the drainage of surface runoff to the bed through moulins, cracks, and other pathways. To investigate the extent of the latter effect, we develop a distributed surface‐energy‐balance model for Helheim Glacier, East Greenland, to calculate surface melt and thereby estimate runoff. The model is driven by data from an automatic weather station operated on the glacier during the summers of 2007 and 2008, and calibrated with independent measurements of ablation. Modeled melt varies over the deployment period by as much as 68% relative to the mean, with melt rates approximately 77% higher on the lower reaches of the glacier trunk than on the upper glacier. We compare melt variations during the summer season to estimates of surface velocity derived from global positioning system surveys. Near the front of the glacier, there is a significant correlation (on >95% levels) between variations in runoff (estimated from surface melt) and variations in velocity, with a 1 day delay in velocity relative to melt. Although the velocity changes are small compared to accelerations previously observed following some calving events, our findings suggest that the flow speed of Helheim Glacier is sensitive to changes in runoff. The response is most significant in the heavily crevassed, fast‐moving region near the calving front. The delay in the peak of the cross‐correlation function implies a transit time of 12–36 h for surface runoff to reach the bed.
Two-parameter asymptotics in magnetic Weyl calculus
Authors: Lein Max
Published: December 2010

This paper is concerned with small parameter asymptotics of magnetic quantum systems. In addition to a semiclassical parameter ε, the case of small coupling λ to the magnetic vector potential naturally occurs in this context. Magnetic Weyl calculus is adapted to incorporate both parameters, at least one of which needs to be small. Of particular interest is the expansion of the Weyl product which can be used to expand the product of operators in a small parameter, a technique which is prominent to obtain perturbation expansions. Three asymptotic expansions for the magnetic Weyl product of two Hörmander class symbols are proven as (i) ε ≪ 1 and λ ≪ 1, (ii) ε ≪ 1 and λ = 1, as well as (iii) ε = 1 and λ ≪ 1. Expansions (i) and (iii) are impossible to obtain with ordinary Weyl calculus. Furthermore, I relate the results derived by ordinary Weyl calculus with those obtained with magnetic Weyl calculus by one- and two-parameter expansions. To show the power and versatility of magnetic Weyl calculus, I derive the semirelativistic Pauli equation as a scaling limit from the Dirac equation up to errors of fourth order in 1/c.
Local CC2 response method for triplet states based on Laplace transform: Excitation energies and first-order properties
Authors: Freundorfer Katrin , Kats Daniel , Korona Tatiana , Schütz Martin
Published: December 2010

A new multistate local CC2 response method for calculating excitation energies and first-order properties of excited triplet states in extended molecular systems is presented. The Laplace transform technique is employed to partition the left/right local CC2 eigenvalue problems as well as the linear equations determining the Lagrange multipliers needed for the properties. The doubles part in the equations can then be inverted on-the-fly and only effective equations for the singles part must be solved iteratively. The local approximation presented here is adaptive and state-specific. The density-fitting method is utilized to approximate the electron-repulsion integrals. The accuracy of the new method is tested by comparison to canonical reference values for a set of 12 test molecules and 62 excited triplet states. As an illustrative application example, the lowest four triplet states of 3-(5-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophene-2-yl)thiophene-2-yl)-2-cyanoacrylic acid, an organic sensitizer for solar-cell applications, are computed in the present work. No triplet charge-transfer states are detected among these states. This situation contrasts with the singlet states of this molecule, where the lowest singlet state has been recently found to correspond to an excited state with a pronounced charge-transfer character having a large transition strength.
Communication: Decoherence in a nonequilibrium environment: An analytically solvable model
Authors: Martens Craig C.
Published: December 2010

We describe an analytically solvable model of quantum decoherence in a nonequilibrium environment. The model considers the effect of a bath driven from equilibrium by, for example, an ultrafast excitation of a quantum chromophore. The nonequilibrium response of the environment is represented by a nonstationary random function corresponding to the fluctuating transition frequency between two quantum states coupled to the surroundings. The nonstationary random function is characterized by a Fourier series with the phase of each term starting initially with a definite value across the ensemble but undergoing random diffusion with time. The decay of the off-diagonal density matrix element is shown to depend significantly on the particular pattern of initial phases of the terms in the Fourier series, or equivalently, the initial phases of bath modes coupled to the quantum subsystem. This suggests the possibility of control of quantum decoherence by the detailed properties of an environment that is driven from thermal equilibrium.
A smooth, nonsingular, and faithful discretization scheme for polarizable continuum models: The switching/Gaussian approach
Authors: Lange Adrian W. , Herbert John M.
Published: December 2010

Polarizable continuum models (PCMs) are a widely used family of implicit solvent models based on reaction-field theory and boundary-element discretization of the solute/continuum interface. An often overlooked aspect of these theories is that discretization of the interface typically does not afford a continuous potential energy surface for the solute. In addition, we show that discretization can lead to numerical singularities and violations of exact variational conditions. To fix these problems, we introduce the switching/Gaussian (SWIG) method, a discretization scheme that overcomes several longstanding problems with PCMs. Our approach generalizes a procedure introduced by York and Karplus [J. Phys. Chem. A 103, 11060 (1999)], extending it beyond the conductor-like screening model. Comparison to other purportedly smooth PCM implementations reveals certain artifacts in these alternative approaches, which are avoided using the SWIG methodology. The versatility of our approach is demonstrated via geometry optimizations, vibrational frequency calculations, and molecular dynamics simulations, for solutes described using quantum mechanics and molecular mechanics.
Electrical double layers at shock fronts in glow discharges and afterglows
Authors: Siefert Nicholas S.
Published: December 2010

This paper examines the propagation of spark-generated shockwaves (1.0<Mach<2.0) into argon and nitrogen glow discharges and their afterglow. Diagnostic methods were employed and expanded in order to capture the dynamics of the shock front in these weakly-ionized, nonmagnetized, collisional plasmas. We used a microwave hairpin resonator to measure the electron number density, and, for all cases, we measured an increase in the electron number density at the shock front. By comparing the increase in electron number density at the shock front in the active discharge and in the afterglow, we conclude that electrons with a temperature much greater than room temperature can be compressed at the shock front. The ratio of electron number density before and after the shock front can be approximately predicted using the Rankine–Hugoniot relationship. The large gradient in electron density, and hence a large gradient in the flux of charged species, created a region of space-charge separation, i.e., a double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s5 metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine–Hugoniot relationship.
Multidimensional electron beam-plasma instabilities in the relativistic regime
Authors: Bret A. , Gremillet L. , Dieckmann M. E.
Published: December 2010

The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.
An adaptive coupled-cluster theory: @CC approach
Authors: Lyakh Dmitry I. , Bartlett Rodney J.
Published: December 2010

A formulation of an adaptive coupled-cluster theory is presented. The method automatically “adjusts” to any state of an electronic system and converges to the full CI limit, thus being capable of describing both single- and multireference phenomena. Adaptivity is accomplished through a guided selection of a compact set of cluster amplitudes as required for a proper description of the electronic system under consideration. The approach suggested is of “black-box” type. A special importance-selection function (discriminatory function) is explicitly introduced for the guided selection of variables involved in the theoretical model. The method is tested on molecules which exhibit strong multireference character in the region of chemical bond elongation. An unambiguous comparison with formally exact full CI solutions shows that the method is capable of providing mHartee accuracy using a rather compact set of cluster amplitudes.
Density-functional expansion methods: Evaluation of LDA, GGA, and meta-GGA functionals and different integral approximations
Authors: Giese Timothy J. , York Darrin M.
Published: December 2010

We extend the Kohn–Sham potential energy expansion (VE) to include variations of the kinetic energy density and use the VE formulation with a 6-31G* basis to perform a “Jacob's ladder” comparison of small molecule properties using density functionals classified as being either LDA, GGA, or meta-GGA. We show that the VE reproduces standard Kohn–Sham DFT results well if all integrals are performed without further approximation, and there is no substantial improvement in using meta-GGA functionals relative to GGA functionals. The advantages of using GGA versus LDA functionals becomes apparent when modeling hydrogen bonds. We furthermore examine the effect of using integral approximations to compute the zeroth-order energy and first-order matrix elements, and the results suggest that the origin of the short-range repulsive potential within self-consistent charge density-functional tight-binding methods mainly arises from the approximations made to the first-order matrix elements.
Electronic and vibrational contributions to first hyperpolarizability of donor–acceptor-substituted azobenzene
Authors: Zaleśny Robert , Bulik Ireneusz W. , Bartkowiak Wojciech , Luis Josep M. , Avramopoulos Aggelos , Papadopoulos Manthos G. , Krawczyk Przemysław
Published: December 2010

In this study we report on the electronic and vibrational (hyper)polarizabilities of donor–acceptor-substituted azobenzene. It is observed that both electronic and vibrational contributions to the electric dipole first hyperpolarizability of investigated photoactive molecule substantially depend on the conformation. The contributions to the nuclear relaxation first hyperpolarizability are found to be quite important in the case of two considered isomers (cis and trans). Although the double-harmonic term is found to be the largest in terms of magnitude, it is shown that the total value of the nuclear relaxation contribution to vibrational first hyperpolarizability is a result of subtle interplay of higher-order contributions. As a part of the study, we also assess the performance of long-range-corrected density functional theory in determining vibrational contributions to electric dipole (hyper)polarizabilities. In most cases, the applied long-range-corrected exchange-correlation potentials amend the drawbacks of their conventional counterparts.
Infrared and Raman line shapes for ice Ih. II. H2O and D2O
Authors: Li F. , Skinner J. L.
Published: December 2010

We present a theoretical study of infrared and Raman line shapes of polycrystalline and single crystal ice Ih, for both water and heavy water, at 1, 125, and 245 K. Our calculations involve a mixed quantum/classical approach, a new water simulation model with explicit three-body interactions, transition frequency and dipole maps, and intramolecular and intermolecular vibrational coupling maps. Our theoretical spectra are in reasonable agreement with experimental spectra (available only near the two higher temperatures). We trace the origins of the different spectral peaks to weak and strong intermolecular couplings. We also discuss the delocalization of the vibrational eigenstates in terms of the competing effects of disorder and coupling.
The efficiency limit of solar cells with molecular absorbers: A master equation approach
Authors: Tayebjee Murad J. Y. , Hirst Louise C. , Ekins-Daukes N. J. , Schmidt Timothy W.
Published: December 2010

A master equation approach to the limiting efficiencies of solar cells with molecular absorbers is presented. A number of model absorbers are analyzed that possess identical absorption spectra, but with differing numbers of electronic excited states. The Shockley–Queisser limit is reproduced for a molecule resembling a semiconductor, with an infinity of electronic levels in the excited state manifold. However, when only a few electronic states contribute to the absorption spectrum, the limiting efficiency is reduced. In the extreme case, where only a single electronic excited state participates in the absorption spectrum, the efficiency limit is 28.9%. At high energy thresholds, built-in thermal up-conversion results in solar cells with efficiencies exceeding the Shockley–Queisser curve. The analysis is applicable to any single threshold photovoltaic device, including those based on semiconductor, polymer, and small molecule absorbers.
Expression of picogram sensitive bending modes in piezoelectric cantilever sensors with nonuniform electric fields generated by asymmetric electrodes
Authors: Johnson Blake N. , Mutharasan Raj
Published: December 2010

Single-layer uniform cross-sectioned piezoelectric macro-cantilevers fabricated with an asymmetric electrode configuration enabled electrical measurement of picogram-sensitive resonant bending modes in liquids. Bending modes were otherwise not electrically measurable without excitation by a nonuniform electric field created by the geometric asymmetry in electrode design used. Electrode modification was confirmed by energy-dispersive X-ray spectroscopy (EDS). Mass-change sensitivity was tested using both bulk density changes and surface chemisorption experiments in a continuous flow apparatus. Significant response to density changes as small as 0.004 g/mL was measured. A sensitivity limit of ∼1 picogram in liquid was determined from 1-dodecanethiol chemisorption experiments. The sensitivity decreased with chemisorbed mass and was log-linear over five orders of magnitude. The observed resonance responses were in agreement with previously reported models of resonating cantilever sensors. This work demonstrates experimentally for the first time that introducing electrode asymmetry enables measurement of bending modes in cantilevers containing only a single piezoelectric layer.