bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermochemical Modelling and Analysis of a Compact Reforming System for PEM FC Application
Authors: Minutillo Mariagiovanna , Jannelli Elio
Published: October 2008

The main objective of this study is to foresee the performance of a PEM fuel cell generator operating as an emergency backup power system. The fuel cell generator is fuelled by hydrogen supplied by a compact reforming system. The reforming system must be able to use a carbon-based fuel, such as natural gas, standard gasoline or diesel to generate hydrogen for clean, on-site electrical power production. Hydrogen generation is provided by a non-catalytic reformer using high-voltage discharges to assist the exothermic partial oxidation process. Thermo-chemical modelling has been implemented considering both reforming system and hydrogen purification unit. The purification and separation unit must be able to produce high purity hydrogen because concentration of CO has to be strongly reduced before entering the fuel cell stack. A comparative performance analysis of different fuels for hydrogen generation has been provided. Thermochemical modelling has been conducted by means of Aspen Plus code.
A Thermodynamic Analysis of Electricity and Hydrogen Co-Production Using a Solid Oxide Fuel Cell
Authors: Leal Elisaˆngela Martins , Brouwer Jacob
Published: October 2008

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41% to 44%, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45% to 80%. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80% and 45% respectively), but lower second law efficiency (61%), indicating potential for cycle improvements.
Production of Hydrogen With Low Carbon Monoxide Formation Via Catalytic Steam Reforming of Methanol
Authors: Patel Sanjay , Pant K. K.
Published: October 2008

The production of hydrogen was investigated in a fixed bed tubular reactor via steam reforming of methanol using CuO/ZnO/Al2O3 catalysts prepared by wet impregnation method and characterized by measuring surface area, pore volume, X-ray diffraction pattern and scanning electron microscopy photographs. The SRM was carried out at atmospheric pressure, temperature 493–573 K, steam to methanol molar ratio 1–1.8 and W/F 3 to 15. Effects of reaction temperature, contact-time, steam to methanol molar ratio and zinc content of catalyst on methanol conversion, selectivity and product yields were evaluated. The addition of zinc enhances the methanol conversion and hydrogen production. The excess steam promotes the methanol conversion and suppresses the carbon monoxide formation. Different strategies have been mentioned to minimize the carbon monoxide formation for the steam reforming of methanol to produce fuel cell grade hydrogen. Optimum operating conditions with appropriate composition of catalyst has been found to produce more selective hydrogen with minimum carbon monoxide. The reaction mechanism has been proposed based on the product distribution. The kinetic model available in literature fitted well with the experimental results.
Modeling of a Direct Carbon Fuel Cell System
Authors: Hemmes K. , Houwing M. , Woudstra N.
Published: October 2008

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO2 produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study the performance of a CO2-producing DCFC system model. The theoretically predicted advantages that are confirmed on a bench scale are also confirmed on a system level, except for the production of pure CO2. Net system efficiencies of around 78 % were found for the developed system. An exergy analysis of the system shows where the losses in the system occur. If the cathode of the DCFC must be operated as a standard MCFC cathode the required CO2 at the cathode is the reason why a large part of the pure CO2 from the anode is recycled and mixed with the incoming air and cannot be used directly for sequestration. Bench scale studies should be performed to test the minimum amount of CO2 needed at the cathode. This might be lower than in standard MCFC operation due to the pure CO2 at the anode side that enhances diffusion towards the cathode.
Numerical Study on Transient Characteristics of a Tubular SOFC Cell
Authors: Shiomi Daisuke , Iwai Hiroshi , Suzuki Kenjiro , Yoshida Hideo
Published: October 2008

Fundamental performance and the transient characteristics of a small tubular SOFC were numerically investigated. The model simultaneously treats momentum, heat and mass transfer, electrochemical phenomena and an electric circuit. Transient characteristics of a cell upon a sudden change of the cell terminal voltage or the air flow rate were examined. During its process, a steady simulation was first conducted and its result was used as the initial condition for the transient calculation. The transient calculation continued until a steady state under the new boundary condition was obtained. Discussions on the time response of the cell performance and thermal field were made in order to find the key factors mainly affecting the transient characteristics. To confirm what factors affect on the transient behavior, calculations were conducted for two different cell geometries, which have different cell diameters, but have same ratios of cell heat capacity to the heat generating area. As a result, it was found that the transient characteristics of a cell are primarily governed by the balance between the heat capacity of a cell and the heat generation by electrochemical reactions. The large heat capacity of the cell is one of the key problems affecting the transient behavior, limiting its quick response. A numerical demonstration is shown in which a rapid cell status change was achieved by controlling its operation conditions.
Fuel Cell Research and Development in Taiwan
Authors: Chan S. H. , Jung G. B. , Weng F. B. , Su A.
Published: October 2008

Fuel cells provide a clean and efficient alternative fuel technology for transportation, residential and portable power applications. From political, social, economic, energy, environmental and technological considerations, the emerging fuel cell technology is undoubtedly well worthy of long-term investment in Taiwan. In view of the success and manufacture capability of electronics and IT industries, Taiwan may play an active role in fuel cell manufacturing and is thus conducive for international strategic alliance, both in R&D and manufacturing activities. This article provides an overview of Taiwan’s technological activities and accomplishments in fuel cells, and makes recommendations for the country’s future development and commercialization of fuel cell applications.
A cascade autocorrelation model of pitch perception
Authors: Balaguer-Ballester Emili , Denham Susan L. , Meddis Ray
Published: October 2008

Autocorrelation algorithms, in combination with computational models of the auditory periphery, have been successfully used to predict the pitch of a wide range of complex stimuli. However, new stimuli are frequently offered as counterexamples to the viability of this approach. This study addresses the issue of whether in the light of these challenges the predictive power of autocorrelation can be preserved by changes to the peripheral model and the computational algorithm. An existing model is extended by the addition of a low-pass filter of the summary integration of the individual within-channel autocorrelations. Other recent developments are also incorporated, including nonlinear processing on the basilar membrane and the use of integration time constants that are proportional to the autocorrelation lags. The modified and extended model predicts with reasonable success the pitches of a range of stimuli that have proved problematic for earlier implementations of the autocorrelation principle. The evaluation stimuli include short tone sequences, click trains consisting of alternating interclick intervals, click trains consisting of mixtures of regular and irregular intervals, shuffled click trains, and transposed tones.
Acoustic analysis of musical intervals in modern Byzantine Chant scales
Authors: Delviniotis Dimitrios , Kouroupetroglou Georgios , Theodoridis Sergios
Published: October 2008

The goal of this work is to investigate experimentally the music intervals in modern Byzantine Chant performance and to compare the obtained results with the equal temperament scales introduced by the Patriarchal Music Committee (PMC). Current measurements resulted from pressure and electroglottographic recordings of 13 famous chanters singing scales of all the music genera. The scales’ microintervals were derived after pitch detection based on autocorrelation, cepstrum, and harmonic product spectrum analysis. The microintervallic differences between the experimental values and the PMC’s ones were statistically analyzed indicating large deviation of the mean values and the standard deviations. Significant interaction effects were identified among some genera and between ascending and descending scale directions.
On the dynamic viscous permeability tensor symmetry
Authors: Perrot Camille , Chevillotte Fabien , Panneton Raymond , Allard Jean-François , Lafarge Denis
Published: October 2008

Based on a direct generalization of a proof given by Torquato for symmetry property in static regime, this express letter clarifies the reasons why the dynamic permeability tensor is symmetric for spatially periodic structures having symmetrical axes which do not coincide with orthogonal pairs being perpendicular to the axis of three-, four-, and sixfold symmetry. This somewhat nonintuitive property is illustrated by providing detailed numerical examples for a hexagonal lattice of solid cylinders in the asymptotic and frequency dependent regimes. It may be practically useful for numerical implementation validation and∕or convergence assessment.
A mode-based technique for estimating uncertainty in range-averaged transmission loss results from underwater acoustic calculations
Authors: Zingarelli R. A.
Published: October 2008

The equivalence of range and frequency averaging of acoustic propagation model results, based on the similarity of their analytic forms in mode calculations, was shown by Harrison [J. Acoust. Soc. Am. 97, 1314–1317 (1995)]. Here it is shown how oceanographic measurement errors and receiver bandwidth can be mapped into uncertainty in the number of modes being propagated. This can be mapped into range boundaries for averaging calculations, thereby giving upper and lower confidence boundaries for frequency-averaged transmission loss calculations. Examples of the application of this technique to synthetic data, where the measurement uncertainties are known and deliberately included, are shown.
Methods for determining infrasound phase velocity direction with an array of line sensors
Authors: Walker Kristoffer T. , Zumberge Mark A. , Hedlin Michael A. H. , Shearer Peter M.
Published: October 2008

Infrasound arrays typically consist of several microbarometers separated by distances that provide predictable signal time separations, forming the basis for processing techniques that estimate the phase velocity direction. The directional resolution depends on the noise level and is proportional to the number of these point sensors; additional sensors help attenuate noise and improve direction resolution. An alternative approach is to form an array of directional line sensors, each of which emulates a line of many microphones that instantaneously integrate pressure change. The instrument response is a function of the orientation of the line with respect to the signal wavefront. Real data recorded at the Piñon Flat Observatory in southern California and synthetic data show that this spectral property can be exploited with multiple line sensors to determine the phase velocity direction with a precision comparable to a larger aperture array of microbarometers. Three types of instrument-response-dependent beamforming and an array deconvolution technique are evaluated. The results imply that an array of five radial line sensors, with equal azimuthal separation and an aperture that depends on the frequency band of interest, provides directional resolution while requiring less space compared to an equally effective array of five microbarometers with rosette wind filters.
Torsional waves propagation along a waveguide of arbitrary cross section immersed in a perfect fluid
Authors: Fan Z. , Lowe M. J. S. , Castaings M. , Bacon C.
Published: October 2008

Guided torsional waves in a bar with a noncircular cross section have been exploited by previous researchers to measure the density of fluids. However, due to the complexity of the wave behavior in the noncircular cross-sectional shape, the previous theory can only provide an approximate prediction; thus the accuracy of the measurement has been compromised. In this paper, a semianalytical finite element method is developed to model accurately the propagation velocity and leakage of guided waves along an immersed waveguide with arbitrary noncircular cross section. An accurate inverse model is then provided to measure the density of the fluid by measuring the change of the torsional wave speed. Experimental results obtained with a rectangular bar in a range of fluids show very good agreement with the theoretical predictions. Finally, the potentials to use the model for sensor optimization are discussed.
Factors contributing to comodulation masking release with dichotic maskers
Authors: Buss Emily , Hall Joseph W.
Published: October 2008

Detection threshold for a pure tone signal centered in a narrow band of noise may be reduced by inclusion of additional flanking masker bands, provided that they share coherent amplitude modulation (AM) across frequency. This comodulation masking release (CMR) associated with coherent AM across frequency is often much smaller if the signal and on-signal masker are presented to one ear and the flanking masker band(s) are presented contralaterally. An experiment was carried out to explore the role of peripheral effects (e.g., suppression) and central effects (e.g., grouping) in this finding. As frequently reported, CMR was smaller when two or more flanking maskers were presented contralaterally to the signal than when presented ipsilaterally. An intermediate condition, where a subset of flanking maskers was presented to each ear, provided comparable benefit to presenting all flankers ipsilateral to the signal. This result suggests that central effects may play a significant role in the reduced dichotic CMR under some conditions.
Radiation force calculations for ultrasonic fields from rectangular weakly focusing transducers
Authors: Beissner K.
Published: October 2008

Knowledge of the theoretical relation between acoustic radiation force and ultrasonic power is important for measuring the emitted power, particularly from medical ultrasonic equipment, using a radiation force balance. A far-field method is applied to calculate the radiation force exerted by rectangular field types on a large absorbing target in a nonabsorbing fluid. This is an extension of previous work on fields with circular symmetry. Pistonlike, apodized, and weakly focusing transducer behavior including diffraction effects is dealt with. If diffraction is neglected, i.e., in the geometric or high-frequency limit, the result can be given as a closed-form expression.
Cochlear nonlinearity in normal-hearing subjects as inferred psychophysically and from distortion-product otoacoustic emissions
Authors: Johannesen Peter T. , Lopez-Poveda Enrique A.
Published: October 2008

The aim was to investigate the correlation between compression exponent, compression threshold, and cochlear gain for normal-hearing subjects as inferred from temporal masking curves (TMCs) and distortion-product otoacoustic emission (DPOAEs) input–output (I/O) curves. Care was given to reduce the influence of DPOAE fine structure on the DPOAE I/O curves. A high correlation between compression exponent estimates obtained with the two methods was found at 4kHz but not at 0.5 and 1kHz. One reason is that the DPOAE I/O curves show plateaus or notches that result in unexpectedly high compression estimates. Moderately high correlation was found between compression threshold estimates obtained with the two methods, although DPOAE-based values were around 7dB lower than those based on TMCs. Both methods show that compression exponent and threshold are approximately constant across the frequency range from 0.5to4kHz. Cochlear gain as estimated from TMCs was found to be ∼16dB greater at 4 than at 0.5kHz. In conclusion, DPOAEs and TMCs may be used interchangeably to infer precise individual nonlinear cochlear characteristics at 4kHz, but it remains unclear that the same applies to lower frequencies.
Simulated head related transfer function of the phyllostomid bat Phyllostomus discolor
Authors: De Mey F. , Reijniers J. , Peremans H. , Otani M. , Firzlaff U.
Published: October 2008

This paper presents a calculation of the head related transfer function (HRTF) for the frontal hemisphere of the phyllostomid bat Phyllostomus discolor using an acoustic field simulation tool based on the boundary element method. From the calculated HRTF results, binaural interaural intensity differences (IIDs) are derived. The results: Region of highest sensitivity, HRTF patterns, and IID patterns are shown to be in good agreement with earlier experimental measurements on other specimens of the same bat species, i.e., the differences are within the interspecies variability range. Next, it is argued that the proposed simulation method offers distinct advantages over acoustic measurements on real bat specimens. To illustrate this, it is shown how computer manipulation of the virtual morphology model allows a more detailed comprehension of bat spatial hearing by investigating the effects of different head parts on the HRTF. From this analysis it is concluded that for this species the pinna has a significantly larger effect on the HRTF and IID patterns than the head itself. This conclusion argues in favor of a series of recent simulation studies based on pinna morphology only [R. Müller, J. Acoust. Soc. Am. 116, 3701–3712 (2004); Müller et al., ibid 119, 4083–4092 (2006)].
Critical ratios of beluga whales (Delphinapterus leucas) and masked signal duration
Authors: Erbe Christine
Published: October 2008

This article examines the masking of a complex beluga vocalization by natural and anthropogenic noise. The call consisted of six 150ms pulses exhibiting spectral peaks between 800Hz and 8kHz. Comparing the spectra and spectrograms of the call and noises at detection threshold showed that the animal did not hear the entire call at threshold. It only heard parts of the call in frequency and time. From the masked hearing thresholds in broadband continuous noises, critical ratios were computed. Fletcher critical bands were narrower than either 15 or 111 of an octave at the low frequencies of the call (<2kHz), depending on which frequency the animal cued on. From the masked hearing thresholds in intermittent noises, the audible signal duration at detection threshold was computed. The intermittent noises differed in gap length, gap number, and masking, but the total audible signal duration at threshold was the same: 660ms. This observation supports a multiple-looks model. The two amplitude modulated noises exhibited weaker masking than the unmodulated noises hinting at a comodulation masking release.
On the ability to discriminate Gaussian-noise tokens or random tone-burst complexes
Authors: Goossens Tom , van de Par Steven , Kohlrausch Armin
Published: October 2008

This study investigated factors that influence a listeners’ ability to discriminate Gaussian-noise stimuli in a same-different discrimination paradigm. The first experiment showed that discrimination ability increased with bandwidth for noise durations up to 100ms. Duration had a nonmonotonic influence on performance, with a decrease in discriminability for stimuli longer than 40ms. Further experiments investigated the cause for this performance decrease. They showed that discriminability could be improved when using frozen-noise tokens and by instructing listeners to focus on the stimulus endings. A final experiment, using a stimulus consisting of 5ms Hanning-windowed tone-bursts randomly distributed over time, investigated whether stimulus duration and amount of information differently affect the processing capacity of the auditory system. Results showed that the number of degrees of freedom in the stimulus, not its duration, predominantly influenced the ability to discriminate. Overall, the results suggest that the discrimination performance for acoustic stimuli depends strongly on the amount of information per critical band and the capacity to process this information. This capacity seems to be limited in the temporal dimension, while extending the signal over more auditory filters does have a positive effect on performance.
Modeling the impact of soft tissue on axial transmission measurements of ultrasonic guided waves in human radius
Authors: Moilanen Petro , Talmant Maryline , Kilappa Vantte , Nicholson Patrick , Cheng Sulin , Timonen Jussi , Laugier Pascal
Published: October 2008

Recent in vitro and simulation studies have shown that guided waves measured at low ultrasound frequencies (f=200 kHz) can characterize both material properties and geometry of the cortical bone wall. In particular, a method for an accurate cortical thickness estimation from ultrasound velocity data has been presented. The clinical application remains, however, a challenge as the impact of a layer of soft tissue on top of the bone is not yet well established, and this layer is expected to affect the dispersion and relative intensities of guided modes. The present study is focused on the theoretical modeling of the impact of an overlying soft tissue. A semianalytical method and finite-difference time domain simulations were used. The models developed were shown to predict consistently real in vivo data on human radii. As a conclusion, clinical guided wave data are not consistent with in vitro data or related in vitro models, but use of an adequate in vivo model, such as the one introduced here, is necessary. A theoretical model that accounts for the impact of an overlying soft tissue could thus be used in clinical applications.
Impacts of environmental change and direct and indirect harvesting effects on the dynamics of a marine fish community
Authors: Benoît Hugues P. , Swain Douglas P.
Published: October 2008

We describe dramatic shifts in the species composition of the marine fish community of the southern Gulf of St. Lawrence using a 35-year time series of catch rates in an annual bottom-trawl survey. We attempt to understand the causes of these changes using a traits-based approach that relates the similarity among species in their abundance trends to similarities in their ecological traits. We selected traits based on a priori beliefs of how each should reflect susceptibility to changes in a different external factor potentially affecting the community. We found evidence for an effect of ocean climate and top-down effects of fishing and seal predation, but not for bottom-up effects of prey availability on adult fishes. Mean body length in the community decreased dramatically in the 1990s. This reflected the removal of large-bodied fishes by fishing and sharp increases in the abundance of small fishes. The biomass of small fish was inversely correlated with an index of predation on those fish by larger fish, suggesting strong predator control of the abundance of small-bodied fishes. Our results suggest that changes in ocean climate combined with direct and indirect effects of harvesting can dramatically and rapidly alter the composition of marine fish communities.
Effect of changing land use patterns on the distribution of coho salmon (Oncorhynchus kisutch) in the Puget Sound region
Authors: Bilby Robert E. , Mollot Lauren A.
Published: October 2008

Population increase in the Pacific Northwest of North America over the last century has led to the removal of forests for various purposes. Evidence of salmon response to these alterations in land use is rare owing to a scarcity of fish population data and a high degree of interannual variation in abundance. We examined the relationship between the spatial distribution of spawning coho salmon ( Oncorhynchus kisutch ) and changes in land use from 1984 through 2001 at 84 sites in four rivers draining into northern Puget Sound. Changes in land use over this period were determined from LandSat imagery, county zoning designations, and aerial photographs. Substantial reduction in forest cover occurred in many of the index watersheds during this time. The proportion of salmon using sites subjected to increased urban land use over the study period declined about 75%. Increases were observed at forested sites and those with increased rural residential use. Maintaining salmon populations in rapidly developing areas may require the identification and protection of sites that support large salmon populations and steering development to areas supporting few fish.
Maternal transfer of carbon and nitrogen to progeny of sea-run and resident brook trout (Salvelinus fontinalis)
Authors: Jardine Timothy D. , Chernoff Eric , Curry R. Allen
Published: October 2008

Early-life history characteristics of sea-run and resident salmonid fishes that co-exist in sympatry are poorly understood. To assess differences in characteristics of offspring of these two strategies following their emergence to the stream, stable isotope ratios (δ13C and δ15N) were used to identify the progeny of resident and sea-run female brook trout ( Salvelinus fontinalis ) in a tributary of the Miramichi River, New Brunswick, Canada. Upon emergence, sea-run progeny captured in emergence traps were longer, heavier, and had higher carbon to nitrogen ratios (C/N, an indicator of lipid content) than resident progeny, but did not have a higher body condition. After some feeding and growth in the stream, sea-run progeny (still identifiable by their δ13C and δ15N) captured in dip-nets became longer, heavier, had higher C/N, and had higher condition than resident progeny. The proportion of fish caught in dip nets at sites where the two forms co-existed was dominated by offspring of sea-run females (sea-run = 56%, resident = 19%, unknown = 25%). These analyses suggest that offspring of sea-run, female trout benefit from maternally derived energy reserves gained at sea and thus have potential adaptive advantages over offspring of residents.
Evaluation of safety and operational impacts of bicycle bypass lanes at modern roundabouts
Authors: Dabbour Essam , Easa Said M.
Published: October 2008

Modern roundabouts have been found to improve safety and reduce overall delay, but they may have negative impacts on the safety of cyclists as other vehicles may cut-off cyclist paths while entering or exiting the roundabout. Several before–after studies have found an increase in traffic collisions involving cyclists at roundabouts after being converted from conventional signalized intersections. Another concern associated with roundabouts is the safety of pedestrians, especially pedestrians with severe vision impairment who may find difficulty in negotiating roundabouts. This paper evaluates safety and operational impacts of using bicycle bypass lanes at roundabouts as a means of increasing the safety of cyclists. The paper also recommends the full utilization of pedestrian traffic signals, proposed by other studies, by incorporating them with the proposed bicycle bypass lanes. An evaluation scheme involving the safety benefits and the costs of the proposed bypass lanes is provided to help practitioners decide when they are warranted. The evaluation scheme is illustrated using an application example.
THE INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS
Authors: HUSSAIN FAHEEM
Published: October 2008

This talk traces in brief the genesis of the Abdus Salam International Centre for Theoretical Physics, Trieste, as one of Prof. Abdus Salam's major achievements. It outlines why Salam felt the necessity for establishing such a centre to help physicists in the developing world. It situates the founding of the Centre within Salam's broader vision of the causes of underdevelopment and of science as an engine for scientific, technological, economic and social development. The talk reviews the successes and failures of the ICTP and gives a brief overall view of the current status of the Centre.
PARALLEL SOLID MODELING USING BSP DATAFLOW
Authors: SCORZELLI GIORGIO , PAOLUZZI ALBERTO , PASCUCCI VALERIO
Published: October 2008

We introduce a parallel approach to geometric modeling of complex objects and scenes, combining a dataflow streaming of BSP trees with a partition of the object space into independent portions, to be evaluated in parallel with minimal interprocess communication. Binary Space Partition (BSP) is a space index used in graphics for hidden-surface removal and animation. We use BSP trees with fuzzy leaves as a progressive representation of solid meshes. Our approach is implemented as a dataflow with processes that progress concurrently, where each refinement of the input to a process is mapped instantly to a refinement of the output, so that the result is also a stream of progressive refinements. This framework allows for progressive generation of complex geometric parts and large-scale assemblies. We have adapted several graphics techniques, including BSP, boundary polygons, CSG, splines and subdivision methods, to fit into our dataflow graph, where four types of processes produce, transform, combineor consume mesh cells. This approach is scalable over different kinds of HPC hardware and different number of computing nodes, by way of the decomposition of the object space and of the distribution of computational processes. Compiling a generative geometric expression into a dataflow graph is well suited to SMP machines, whereas a space decomposition into independent portions fits well with computing clusters and grids.
SYNTHESIS AND CHARACTERIZATION OF THIOPHENE-CONTAINING CHROMOPHORES FOR NONLINEAR OPTICAL (NLO) MATERIALS
Authors: SHI ZUOSEN , ZHANG XIAOLONG , CUI ZHANCHEN
Published: October 2008

A series of chromophores based on benzene and thiophene moieties as π-conjugating spacers were designed and synthesized by Horner-Emmons-Wadsworth reaction and Vilsmeier-Haack reaction, followed by Knoevenagel reaction with different electron acceptors. Their structures were confirmed by 1HNMR, FT-IR, HPLC-Ms, UV-visible spectra, and the thermal properties were characterized by differential scanning calorimetry (DSC). Solvatochromic method was used to measure their nonlinear optical properties. The variation of chromophoric structures on NLO properties was investigated, indicating that the cyano substitution on the vinylene bridge of the chromophore produces a considerable red-shift of the absorption maximum, and would greatly enhance the molecular quadratic hyperpolarizability (βμ).
LEARNING FROM GYMNOTIFORM SWIMMERS — DESIGN AND IMPLEMENTATION OF ROBOTIC KNIFEFISH NKF-II
Authors: LOW K. H. , ZHOU CHUNLIN , SEET GERALD G. L. , YU JUNZHI
Published: October 2008

Gymnotiform swimmer uses single undulating anal fin below the rigid body as the propulsor. This special morphological structure is generally thought to have advantages in reducing the friction drag in undulatory movements. The finned body form and the undulatory swimming gait give the inspiration to the design of underwater robot. We have developed a robotic fish (Nanyang KnifeFish, NKF-I), which learns from a Gymnotiform swimmer: Black Ghost Knifefish. A new version of biomimetic robotic fish (NKF-II) is presented in this paper. To mimic the actual flexible fin of real fish, an optimized fin-like propulsion mechanism is modelled with a series of connecting linkages for enhancing its propulsive performance. Workspace of the proposed mechanism is studied and optimized. Swimming motion function is also established for the planning of the undulatory gait movement. The manoeuvrability and buoyancy control has also been achieved by the integration of mechatronics design of a buoyancy module with the undulating fin. The design philosophy of modularity has also been incorporated into the design of the fish. Hence, the modularity of the prototypes not only provides versatility for the robot system and also facilitates in the maintenance and future development of fish with undulating fins/body, as new modules can be added to replace the existing modules easily. By reconfiguring the components of NKF-II, other version of robotic fish with undulating fins/body is derived. This evolution of the undulating fins is also discussed.
Early Milestones in the Evolution of Accelerators
Authors: Courant E. D.
Published: October 2008

About 80 years ago Rutherford [1] expressed the hope that particles could be accelerated to energies exceeding those occurring in radioactivity, enabling the study of nuclei and their constituents. Physicists and engineers have more than met this challenge, and today the LHC (Large Hadron Collider) at CERN, Geneva is about to accelerate protons to 7 trillion (7 × 1012) eV. Here we describe some of the crucial steps that have gotten us there.
Cooling Methods for Charged Particle Beams
Authors: Parkhomchuk V. V. , Skrinsky A. N.
Published: October 2008

We review the basic methods for cooling charged particle beams in storage rings and accelerators. Applications of cooled beams are discussed.
Epigenetics, DNA Methylation, and Chromatin Modifying Drugs
Authors: Szyf Moshe
Published: October 2008

Evidence is emerging that several diseases and behavioral pathologies result from defects in gene function. The best-studied example is cancer, but other diseases such as autoimmune disease, asthma, type 2 diabetes, metabolic disorders, and autism display aberrant gene expression. Gene function may be altered by either a change in the sequence of the DNA or a change in epigenetic programming of a gene in the absence of a sequence change. With epigenetic drugs, it is possible to reverse aberrant gene expression profiles associated with different disease states. Several epigenetic drugs targeting DNA methylation and histone deacetylation enzymes have been tested in clinical trials. Understanding the epigenetic machinery and the differential roles of its components in specific disease states is essential for developing targeted epigenetic therapy.
Immunodrugs: Therapeutic VLP-Based Vaccines for Chronic Diseases
Authors: Jennings Gary T. , Bachmann Martin F.
Published: October 2008

Worldwide, the prevalence of noncommunicable chronic diseases is increasing. The use of vaccines to induce autoantibodies that neutralize disease-related proteins offers a means to effectively and affordably treat such diseases. Twenty vaccines designed to induce therapeutic autoantibodies were clinically tested in the past 12 years. Immunodrugs are therapeutic vaccines comprising virus-like particles (VLPs) covalently conjugated with self-antigens that induce neutralizing autoantibody responses. Four such VLP-based vaccines have been clinically tested and one has achieved proof of principle: a reduction of blood pressure in hypertensive patients. To facilitate preliminary clinical testing, novel nonclinical study programs have been developed. Safety study designs have considered the underlying B and T cell immunology and have examined potential toxicities of vaccine components and primary and secondary pharmacodynamic action of the vaccines.
Dynamics of Liquids, Molecules, and Proteins Measured with Ultrafast 2D IR Vibrational Echo Chemical Exchange Spectroscopy
Authors: Fayer M.D.
Published: October 2008

A wide variety of molecular systems undergo fast structural changes under thermal equilibrium conditions. Such transformations are involved in a vast array of chemical problems. Experimentally measuring equilibrium dynamics is a challenging problem that is at the forefront of chemical research. This review describes ultrafast 2D IR vibrational echo chemical exchange experiments and applies them to several types of molecular systems. The formation and dissociation of organic solute-solvent complexes are directly observed. The dissociation times of 13 complexes, ranging from 4 ps to 140ps, are shown to obey a relationship that depends on the complex's formation enthalpy. The rate of rotational gauche-trans isomerization around a carbon-carbon single bond is determined for a substituted ethane at room temperature in a low viscosity solvent. The results are used to obtain an approximate isomerization rate for ethane. Finally, the time dependence of a well-defined single structural transformation of a protein is measured.
Histones: Annotating Chromatin
Authors: Campos Eric I. , Reinberg Danny
Published: October 2008

Chromatin is a highly regulated nucleoprotein complex through which genetic material is structured and maneuvered to elicit cellular processes, including transcription, cell division, differentiation, and DNA repair. In eukaryotes, the core of this structure is composed of nucleosomes, or repetitive histone octamer units typically enfolded by 147 base pairs of DNA. DNA is arranged and indexed through these nucleosomal structures to adjust local chromatin compaction and accessibility. Histones are subject to multiple covalent posttranslational modifications, some of which alter intrinsic chromatin properties, others of which present or hinder binding modules for non-histone, chromatin-modifying complexes. Although certain histone marks correlate with different biological outputs, we have yet to fully appreciate their effects on transcription and other cellular processes. Tremendous advancements over the past years have uncovered intriguing histone-related matters and raised important related questions. This review revisits past breakthroughs and discusses novel developments that pertain to histone posttranslational modifications and the affects they have on transcription and DNA packaging.
Diatoms—From Cell Wall Biogenesis to Nanotechnology
Authors: Kröger Nils , Poulsen Nicole
Published: October 2008

Diatoms are single-celled algae that produce intricately structured cell walls made of nanopatterned silica (SiO2). The cell wall structure is a species-specific characteristic demonstrating that diatom silica morphogenesis is genetically encoded. Understanding the molecular mechanisms by which a single cell executes the morphogenetic program for the formation of an inorganic material (biomineralization) is not only a fascinating biological problem, but also of great interest for nanomaterials science and technology. Recently, analysis of the organic components associated with diatom silica, the development of techniques for molecular genetic manipulation of diatoms, and two diatom genome sequencing projects are providing insight into the composition and mechanism of the remarkable biosilica-forming machinery.
Genomics and Evolution of Heritable Bacterial Symbionts
Authors: Moran Nancy A. , McCutcheon John P. , Nakabachi Atsushi
Published: October 2008

Insect heritable symbionts have proven to be ubiquitous, based on molecular screening of various insect lineages. Recently, molecular and experimental approaches have yielded an immensely richer understanding of their diverse biological roles, resulting in a burgeoning research literature. Increasingly, commonalities and intermediates are being discovered between categories of symbionts once considered distinct: obligate mutualists that provision nutrients, facultative mutualists that provide protection against enemies or stress, and symbionts such as Wolbachia that manipulate reproductive systems. Among the most far-reaching impacts of widespread heritable symbiosis is that it may promote speciation by increasing reproductive and ecological isolation of host populations, and it effectively provides a means for transfer of genetic information among host lineages. In addition, insect symbionts provide some of the extremes of cellular genomes, including the smallest and the fastest evolving, raising new questions about the limits of evolution of life.
Molecular Determinants of a Symbiotic Chronic Infection
Authors: Gibson Katherine E. , Kobayashi Hajime , Walker Graham C.
Published: October 2008

Rhizobial bacteria colonize legume roots for the purpose of biological nitrogen fixation. A complex series of events, coordinated by host and bacterial signal molecules, underlie the development of this symbiotic interaction. Rhizobia elicit de novo formation of a novel root organ within which they establish a chronic intracellular infection. Legumes permit rhizobia to invade these root tissues while exerting control over the infection process. Once rhizobia gain intracellular access to their host, legumes also strongly influence the process of bacterial differentiation that is required for nitrogen fixation. Even so, symbiotic rhizobia play an active role in promoting their goal of host invasion and chronic persistence by producing a variety of signal molecules that elicit changes in host gene expression. In particular, rhizobia appear to advocate for their access to the host by producing a variety of signal molecules capable of suppressing a general pathogen defense response.
Genetics of Sleep
Authors: Andretic Rozi , Franken Paul , Tafti Mehdi
Published: October 2008

Molecular and genetic approaches in several species have provided new insights into the mechanisms of rest-activity and sleep-wake regulation. Many of these discoveries are believed to support hypotheses about sleep functions, which nevertheless remain elusive. In this review we discuss the specific contribution of both mammalian and invertebrate models to our understanding of the molecular basis of sleep.
Quantitative Disease, Drug, and Trial Models
Authors: Gobburu Jogarao V.S. , Lesko Lawrence J.
Published: October 2008

Quantitative disease-drug-trial models allow learning from prior experience and summarize the knowledge in a ready to apply format. Employing these models to plan future development is proposed as a powerful solution to improve pharmaceutical R&D productivity. The disease and trial models are, to a large extent, independent of the product, but the drug model is not. The goals are to apply the disease and trial models to future development and regulatory decisions, and publicly share them. We propose working definitions of these models, describe the various subcomponents, provide examples, and discuss the challenges and potential solutions for developing such models. Building useful disease-drug-trial models is a challenging task and cannot be achieved by any single organization. It requires a consorted effort by industry, academic, and regulatory scientists. We also describe the strategic goals of the FDA Pharmacometrics group.
Photofragment Spectroscopy and Predissociation Dynamics of Weakly Bound Molecules
Authors: Reisler Hanna
Published: October 2008

Photofragment spectroscopy is combined with imaging techniques and time-resolved measurements of photoions and photoelectrons to explore the predissociation dynamics of weakly bound molecules. Recent experimental advances include measurements of pair-correlated distributions, in which energy disposal in one cofragment is correlated with a state-selected level of the other fragment, and femtosecond pump-probe experiments, in some cases with coincidence detection. An application in which coincident measurements are carried out in the molecular frame is also described. To illustrate these state-selective and time-resolved techniques, we review two recent applications: (a) the photoinitiated dissociation of the covalently bound NO dimer on the ground and excited electronic states and the role of state couplings and (b) the state-selected vibrational predissociation of hydrogen-bonded acetylene dimers with HCl (acid) and ammonia (base) and the importance of angular momentum constraints. We highlight the crucial role of theoretical models in interpreting results.
Signaling at Purinergic P2X Receptors
Authors: Surprenant Annmarie , North R. Alan
Published: October 2008

P2X receptors are membrane cation channels gated by extracellular ATP. Seven P2X receptor subunits (P2X1-7) are widely distributed in excitable and nonexcitable cells of vertebrates. They play key roles in inter alia afferent signaling (including pain), regulation of renal blood flow, vascular endothelium, and inflammatory responses. We summarize the evidence for these and other roles, emphasizing experimental work with selective receptor antagonists or with knockout mice. The receptors are trimeric membrane proteins: Studies of the biophysical properties of mutated subunits expressed in heterologous cells have indicated parts of the subunits involved in ATP binding, ion permeation (including calcium permeability), and membrane trafficking. We review our current understanding of the molecular properties of P2X receptors, including how this understanding is informed by the identification of distantly related P2X receptors in simple eukaryotes.
Social Withdrawal in Childhood
Authors: Rubin Kenneth H. , Coplan Robert J. , Bowker Julie C.
Published: October 2008

Socially withdrawn children frequently refrain from social activities in the presence of peers. The lack of social interaction in childhood may result from a variety of causes, including social fear and anxiety or a preference for solitude. From early childhood through to adolescence, socially withdrawn children are concurrently and predictively at risk for a wide range of negative adjustment outcomes, including socio-emotional difficulties (e.g., anxiety, low self-esteem, depressive symptoms, and internalizing problems), peer difficulties (e.g., rejection, victimization, poor friendship quality), and school difficulties (e.g., poor-quality teacher-child relationships, academic difficulties, school avoidance). The goals of the current review are to (a) provide some definitional, theoretical, and methodological clarity to the complex array of terms and constructs previously employed in the study of social withdrawal; (b) examine the predictors, correlates, and consequences of child and early-adolescent social withdrawal; and (c) present a developmental framework describing pathways to and from social withdrawal in childhood.