bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Electrochemical Impedance Spectroscopy for Fuel Cell Characterization: PEFC and Oxygen Reduction Reaction in Alkaline Solution
Authors: Wagner N. , Friedrich K. A. 
Published: December 2008

AbstractThe most common method used to characterise the electrochemical performance of fuel cells is the recording of current/voltage U(i) curves. Separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques like electrochemical impedance spectroscopy (EIS). The application of EIS is an approach to determine parameters which have proved to be indispensable for the characterisation and development of all types of fuel cell electrodes and electrolyte electrode assemblies [1]. In addition to EIS semi‐empirical approaches based on simplified mathematical models can be used to fit experimental U(i) curves [2].By varying the operating conditions of the fuel cell and by the simulation of the measured EIS with an appropriate equivalent circuit, it is possible to split the cell impedance into electrode impedances and electrolyte resistance. Integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell (PEFC) and the assignment of voltage loss to the different processes. In case of using a three electrode cell configuration with a reference electrode, one can directly determine the corresponding overvoltage. For the evaluation of the measured impedance spectra the porous electrode model of Göhr [3] was used. This porous electrode model includes different impedance contributions like impedance of the interface porous layer/pore, interface porous layer/electrolyte, interface porous layer/bulk, impedance of the porous layer and impedance of the pores filled by electrolyte.
Tunnelkette Perschling – Reiserbergtunnel and Stierschweiffeldtunnel: TBM Success under Difficult Ground Conditions
Authors: Bach Dietmar , Fuchs Werner , Lehner Wolfgang , Obermeier Oskar 
Published: December 2008

AbstractDue to the very difficult geological conditions and the partly low overburden the TBM drives of the “Tunnelkette Perschling” have been a challenge for the persons involved in the project. This paper is a report on the experiences and conclusions gained from two of the three driven tunnels. It deals with the unexpected major occurrences and the related solutions as well as with the adjustment of the concept for backfilling the annular gap in order to achieve sufficient stabilization of the segmental tunnel lining under all conditions encountered.
Extension Hieflau HEP – Economical Solutions for the Headrace Tunnel
Authors: Walter Andreas , Weber Wolfgang , Gappmaier Franz 
Published: December 2008

AbstractThe expansion project for the Hieflau hydropower plant involves the construction of a second headrace tunnel to enhance the capacity from 60 up to 90 m3/s. The second tunnel, located between the weir system Gstatterboden and storage reservoir Wag, is seen as the highlight of the enhancement scheme. The breakthrough of the 4,9 km long TBM‐drive is expected by end of this year.
Technical Challenges During Construction of Alborz Service Tunnel, Iran
Authors: Wenner Dieter , Wannenmacher Helmut 
Published: December 2008

AbstractThe Tehran Shomal Motorway project is one the major infrastructure projects currently ongoing in Iran. The line will connect the capital of Iran, Tehran with the Caspian Sea. The traffic volume is very high and the conditions of the actual roads, especially in the winter and holiday times are dangerous. The Alborz tunnel system, with the actual ongoing excavation of its service tunnel, is the outstanding lot of the Tehran Shomal Motorway project. The project is facing severe and adverse geological conditions like various dangerous gases, water and material inrush and blocked TBM. Depending on the conditions at the remaining length the breakthrough is anticipated by early 2009.
Heading‐vector navigation based on head‐direction cells and path integration
Authors: Kubie John L. , Fenton André A. 
Published: December 2008

AbstractInsect navigation is guided by heading vectors that are computed by path integration. Mammalian navigation models, on the other hand, are typically based on map‐like place representations provided by hippocampal place cells. Such models compute optimal routes as a continuous series of locations that connect the current location to a goal. We propose a “heading‐vector” model in which head‐direction cells or their derivatives serve both as key elements in constructing the optimal route and as the straight‐line guidance during route execution. The model is based on a memory structure termed the “shortcut matrix,” which is constructed during the initial exploration of an environment when a set of shortcut vectors between sequential pairs of visited waypoint locations is stored. A mechanism is proposed for calculating and storing these vectors that relies on a hypothesized cell type termed an “accumulating head‐direction cell.” Following exploration, shortcut vectors connecting all pairs of waypoint locations are computed by vector arithmetic and stored in the shortcut matrix. On re‐entry, when local view or place representations query the shortcut matrix with a current waypoint and goal, a shortcut trajectory is retrieved. Since the trajectory direction is in head‐direction compass coordinates, navigation is accomplished by tracking the firing of head‐direction cells that are tuned to the heading angle. Section 1 of the manuscript describes the properties of accumulating head‐direction cells. It then shows how accumulating head‐direction cells can store local vectors and perform vector arithmetic to perform path‐integration‐based homing. Section 2 describes the construction and use of the shortcut matrix for computing direct paths between any pair of locations that have been registered in the shortcut matrix. In the discussion, we analyze the advantages of heading‐based navigation over map‐based navigation. Finally, we survey behavioral evidence that nonhippocampal, heading‐based navigation is used in small mammals and humans. © 2008 Wiley‐Liss, Inc.
Long‐term deficits on a foraging task after bilateral vestibular deafferentation in rats
Authors: Zheng Yiwen , Goddard Matthew , Darlington Cynthia L. , Smith Paul F. 
Published: December 2008

AbstractAnimal studies have shown that bilateral vestibular deafferentation (BVD) causes deficits in spatial memory that may be related to electrophysiological and neurochemical changes in the hippocampus. Recently, human studies have also indicated that human patients can exhibit spatial memory impairment and hippocampal atrophy even 8–10 yr following BVD. Our previous studies have shown that rats with unilateral vestibular deafferentation (UVD) showed an impairment at 3 months after the surgery on a food foraging task that relies on hippocampal integration of egocentric cues, such as vestibular information; however, by 6 months postop, they showed a recovery of function. By contrast, the long‐term effects of BVD on spatial navigation have never been well studied. In this study, we tested BVD or sham rats on a food foraging task at 5 months postop. Under light conditions, BVD rats were able to use visual cues to guide themselves home, but did so with a significantly longer homing time. However, in darkness, BVD rats were severely impaired in the foraging task, as indicated by a significantly longer homing distance and homing time, with more errors and larger heading angles when compared with sham rats. These results suggest that, unlike UVD, BVD causes long‐term deficits in spatial navigation that are unlikely to recover, even with repeated T‐maze training. © 2008 Wiley‐Liss, Inc.
Efficient table lookup without inverse square roots for calculation of pair wise atomic interactions in classical simulations
Authors: Nilsson Lennart 
Published: December 2008

AbstractA major bottleneck in classical atomistic simulations of biomolecular systems is the calculation of the pair wise nonbonded (Coulomb, van der Waals) interactions. This remains an issue even when methods are used (e.g., lattice summation or spherical cutoffs) in which the number of interactions is reduced from O(N2) to O(NlogN) or O(N). The interaction forces and energies can either be calculated directly each time they are needed or retrieved using precomputed values in a lookup table; the choice between direct calculation and table lookup methods depends on the characteristics of the system studied (total number of particles and the number of particle kinds) as well as the hardware used (CPU speed, size and speed of cache, and main memory). A recently developed lookup table code, implemented in portable and easily maintained FORTRAN 95 in the CHARMM program (www.charmm.org), achieves a 1.5‐ to 2‐fold speedup compared with standard calculations using highly optimized FORTRAN code in real molecular dynamics simulations for a wide range of molecular system sizes. No approximations other than the finite resolution of the tables are introduced, and linear interpolation in a table with the relatively modest density of 100 points/Å2 yields the same accuracy as the standard double precision calculations. For proteins in explicit water a less dense table (10 points/Å2) is 10–20% faster than using the larger table, and only slightly less accurate. The lookup table is even faster than hand coded assembler routines in most cases, mainly due to a significantly smaller operation count inside the inner loop. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009
Trends in heavy precipitation in the Czech Republic over 1961–2005
Authors: Kyselý Jan 
Published: December 2008

AbstractTrends in multiple characteristics of heavy precipitation over the area of the Czech Republic are evaluated using a new dataset from 175 rain‐gauge stations covering the period 1961–2005. The temporal changes are generally more pronounced in the western than eastern part of the country. Spatially coherent increasing trends are identified for all indices of heavy precipitation in winter in the western region, the relative trend magnitudes being mostly between 20 and 30% over the 45 years. Increasing but insignificant and spatially less coherent trends in heavy precipitation prevail also in summer. Opposite trends occur in spring (when they are related to declines in seasonal precipitation totals), and the changes are spatially least coherent and insignificant in autumn (in spite of the increase in mean precipitation). The differences between winter and summer on the one hand and the transition seasons on the other highlight the need for involving spring and autumn into studies of temporal changes of climatic variables, to avoid simplified views. It is also shown that trends in heavy precipitation at Prague‐Klementinum, the most frequently analysed long‐term station in the Czech Republic [and the only one available in continental‐scale analyses within the European Climate Assessment (ECA) project and related activities], are particularly unrepresentative for a wider area. The analysis partly supports an emerging global picture of prevailing positive trends in precipitation extremes over the mid‐latitudinal land areas of the Northern Hemisphere in winter. However, the cut‐off between the western and eastern parts of the Czech Republic in many precipitation characteristics, including the trends in wintertime indices of precipitation extremes, may indicate that the pattern of changes is more complex and less coherent in eastern than in western Europe. Copyright © 2008 Royal Meteorological Society
Annual and seasonal mapping of peak intensity, magnitude and duration of extreme precipitation events across a climatic gradient, northeast Spain
Authors: Beguería Santiago , Vicente‐Serrano Sergio M. , López‐Moreno Juan I. , García‐Ruiz José M. 
Published: December 2008

AbstractAssessing the characteristics of extreme precipitation over large regions has a great interest, mainly due to its applications in hazard analysis. However, most of the analyses are reduced to daily rainfall intensity due to the fact that most long precipitation records were collected on a daily basis. Hazardous situations related to extreme precipitation events, however, can be originated either by very intense rainfall, or by large accumulated precipitation due to the persistence of the rainy conditions over a long period of time. In this paper, we show the use of a methodology based on the extreme‐value theory to obtain continuous maps of quantiles of precipitation event parameters—peak intensity, magnitude and duration—for a large region with contrasted climatic characteristics in the northeastern Iberian Peninsula. Spatial models of the probability distributions parameters were calculated, which allowed constructing the regional probability models. The analysis was based on time series of precipitation events, which were obtained from the original daily series. In addition to the usual annual‐based analysis, seasonal analyses were also performed. This allowed assessing the differences in the spatial distribution of the probability of extreme events at different times of the year. Copyright © 2008 Royal Meteorological Society
Rainfall trends in the KwaZulu‐Natal Drakensberg region of South Africa during the twentieth century
Authors: Nel Werner 
Published: December 2008

AbstractThis study assesses long‐term rainfall records in the KwaZulu‐Natal Drakensberg, South Africa's most valuable source of surface runoff. Records from 11 stations covering the Drakensberg region in South Africa indicate that no statistically significant trend in interannual variability existed during the last half of the twentieth century. Annual rainfall in the Drakensberg is highly seasonal, and analysis of monthly rainfall indicates an increase in the variability of the distribution of monthly rainfall and the strengthening of rainfall seasonality in the Drakensberg through a significant decrease in autumn rainfall. The El Niño/Southern Oscillation (ENSO) influences summer rainfall variability of the KwaZulu‐Natal Drakensberg, and a strong correlation also exists between summer rainfall and the Southern Oscillation Index (SOI) for preceding periods. This correlation between summer rainfall and ENSO events suggests that changes in the frequency and intensity of the ENSO should affect the rainfall in the Drakensberg. The lagged correlation between summer rainfall in the Drakensberg and the SOI could be used as an indicator for seasonal forecasting. Copyright © 2008 Royal Meteorological Society
Summer daily precipitation variability over the East Anglian region of Great Britain
Authors: Neal Robert A. , Phillips Ian D. 
Published: December 2008

AbstractDaily precipitation totals for five consecutive summers (1994–1998) were obtained for 136 stations in East Anglia to explore geographic variations in rainfall. S‐mode principal components analysis (PCA) was used to identify the main spatial modes of variability in the region's precipitation field. The components were interpreted physically by examining synoptic charts and the British Isles' circulation variables for the days with high PC scores. Whilst seven principal components have eigenvalues greater than 1, and collectively explain 86.3% of the variance, only the first 5 PCs have well defined rainfall patterns that can be attributed to specific circulation patterns. The most dominant pattern (PC 1) shows a gradient between wetter conditions in NE Norfolk and drier conditions in Cambridgeshire and Essex, which is favoured by a cyclonic northerly airflow. PC 2 is almost as dominant, and shows a west to east decay in rainfall totals that is typically associated with active zonal W–SW flows. PC 3 sees the highest totals occurring in Essex. Wetter conditions in the south of East Anglia tend to occur when areas of low pressure follow a southerly track along the English Channel and southern North Sea. PC 4 shows a maximum in convective activity that occurs furthest inland in SE Cambridgeshire and west Suffolk, with the convection being triggered or accentuated by the East Anglian Heights (the highest land in East Anglia). PC 5 shows the rainfall distribution under a cyclonic N–NW, whereby showers generated over The Wash penetrate inland and produce the most rainfall in west Norfolk. Finally, a summer precipitation regionalization was derived by applying agglomerative hierarchical cluster analysis to the loadings of PCs 1–7. It is concluded that a location's precipitation climatology is more strongly determined by the orientation of the nearest coastline rather than simply the site's distance from the North Sea. Copyright © 2008 Royal Meteorological Society
The role of surgical margin status in retroperitoneal sarcoma
Authors: Anaya Daniel A. , Lev Dina C. , Pollock Raphael E. 
Published: December 2008

AbstractRetroperitoneal sarcomas (RPS) represent approximately 15% of all soft tissue sarcomas (STS). Clinical and prognostic features as well as oncologic outcomes are well known in this group of patients. Post‐operative margin status specifically, is a major predictor of local and distant recurrence and survival. The purpose of this review is to define complete resection as it applies to RPS and evaluate its effect on future outcomes in these patients. J. Surg. Oncol. 2008;98:607–610. © 2008 Wiley‐Liss, Inc.
Multimodality management of desmoid tumors: How important is a negative surgical margin?
Authors: Melis Marcovalerio , Zager Jonathan S. , Sondak Vernon K. 
Published: December 2008

AbstractDesmoid tumors are rare, locally invasive mesenchymal tumors without metastatic potential. Their clinical behavior is heterogeneous and characteristically unpredictable; outcomes are influenced by anatomic location, proximity to vital organs, association with familial adenomatous polyposis. Surgery is the main treatment modality, but the significance of positive resection margins remains controversial since they may not increase the risk of recurrence: in this setting re‐resection, adjuvant radiation or close clinical follow‐up could all be appropriate options. We reviewed the current evidence for multimodality therapy of desmoids, with a focus on the importance of resection margins, and present our own algorithm for treatment. J. Surg. Oncol. 2008;98:594–602. © 2008 Wiley‐Liss, Inc.
Margin status after breast‐conserving treatment of breast cancer: How much free margin is enough?
Authors: von Smitten Karl 
Published: December 2008

AbstractIn breast conserving surgery the margins of the specimen have to be tumor free. There is no universal agreement on the width of the tumor free margin. The width has some impact on recurrence rate, and at least 5 mm seems to be preferred and this is especially important in extensive intraductal component. In ductal cancer in situ the free margin should be at least 5 mm, preferably 10 mm. Oncoplastic surgery is beneficial for reaching adequate margins. J. Surg. Oncol. 2008;98:585–587. © 2008 Wiley‐Liss, Inc.
Ultrafast exciton relaxation dynamics in silicon quantum dots
Authors: Cimpean C. , Groenewegen V. , Kuntermann V. , Sommer A. , Kryschi C. 
Published: December 2008

AbstractThe photoluminescence properties of silicon quantum dots may be tailored by surface states via efficient coupling to resonant bulk states. Therefore various wet‐chemistry procedures were developed to fabricate silicon quantum dots with adjustable sizes and surface properties. While the energy gap of the Si core is tuned by the size, resonant electronic surface states may be attained by varying the structure and chemical composition of the grafting. The strength of electronic couplings between surface and bulk states determines the timescale of both photo‐induced electron transfer from excited surface states to conduction band states and capture of conduction band electrons by surface states. Whereas the origin of photoluminescence and therewith the quantum dot size distribution may be elucidated by stationary luminescence spectroscopy, ultrafast optical spectroscopy techniques, for instance the femtosecond transient absorption spectroscopy, allow to monitor photo‐induced electron transfer between surface and bulk states and carrier trapping on the subpicosecond timescale.
Femtosecond laser near field ablation
Authors: Plech A. , Leiderer P. , Boneberg J. 
Published: December 2008

AbstractThe high field strength of femtosecond laser pulses leads to nonlinear effects during the interaction with condensed matter. One such effect is the ablation process, which can be initiated below the threshold of common thermal ablation if the excitation pulses are sufficiently short. This effect leads to structure formation, which is anisotropic because of the polarization properties of the near field and can result in pattern sizes below the resolution limit of light. These effects are explored by temporally resolved scattering methods and by post‐mortem analysis to show the non‐thermal and anisotropic nature of this process. The near‐field distribution of plasmon modes can be tailored to a large extent in order to obtain control of the pattern formation.
Ultrafast laser written active devices
Authors: Ams M. , Marshall G.D. , Dekker P. , Piper J.A. , Withford M.J. 
Published: December 2008

AbstractDirect‐write optical waveguide device fabrication is probably the most widely studied application of femtosecond laser micromachining in transparent dielectrics at the present time. Devices such as buried waveguides, power splitters, couplers, gratings, optical amplifiers and laser oscillators have all been demonstrated. This paper reviews the application of the femtosecond laser direct‐write technique to the fabrication of active waveguide devices in bulk glass materials.
Structural Analysis of Proteinaceous Components in Byssal Threads of the Mussel Mytilus galloprovincialis
Authors: Hagenau Anja , Scheidt Holger A. , Serpell Louise , Huster Daniel , Scheibel Thomas 
Published: December 2008

AbstractThe mussel byssus is a unique holdfast structure employed by marine mussels to colonize diverse substrates. The byssus consists of extracellular threads with mainly proteinaceous components. Individual threads reveal high tensile strength at their distal end and high elasticity in their proximal portion. Our studies show that proteins of the distal part are oriented along the thread axis and are well‐ordered with a high β‐structural content. In contrast, proteins of the proximal part are less ordered and are not as well‐oriented with primarily α‐helical structure. The detected differences in the structural features of the proteins along a byssus thread are likely an important basis for its gradual mechanical properties.magnified image
Gas Diffusion in Anisotropic Nonhomogeneous Polymers
Authors: Grisafi Steven 
Published: December 2008

AbstractIn an effort to address the situation of gas diffusion in polymers that undergo swelling during the absorption process, two mass flux constitutive relations, independent of Fick's law, are evaluated. Both mass flux relations utilize the mass diffusivity as a tensor quantity. The diffusivity tensor considered can be a function of both time and spatial coordinates. For the case of one‐dimensional diffusion, approximations are found relating the diffusivity, when it is considered to be time varying and a function of position in the polymer, to the constant diffusivity assumed by Fick's law and its predicted concentration profile. Analyzing a case of oxygen absorption by glassy poly(ethylene terephthalate) shows a time‐dependent diffusivity with negligible spatial variation.magnified image