bluuebunny/crossref_metadata_2025 huggingface dataset:
Ejector Irreversibility Characteristics
Authors: Arbel A. , Shklyar A. , Hershgal D. , Barak M. , Sokolov M.
Published: January 2003

The present study analyzes and characterizes the irreversibility of the ejector’s internal processes in an effort to improve the understanding of the making of its overall performance. The analysis presented is based on entropy production methodology. Since entropy production is equivalent to performance losses, minimizing entropy production could serve as a tool for performance optimization. The three main internal processes forming sources of ejector irreversibility are mixing, kinetic energy losses, and normal shock wave. Comparison of these with those of an ideal mixing process, an ideal turbine-compressor system and stagnation conditions (of the flow after mixing) provides the benchmarks against which the actual overall performance is measured. By identifying the sources of irreversibility, the analysis provides a diagnostic tool for performance improvements. While irreversibility due to mixing can be eliminated by appropriate choice of gas and/or inlet conditions and an appropriate adjustable throat can eliminate losses associated with normal shock wave–kinetic energy losses can only be reduced but not totally eliminated.
Parallel Particle Simulation of the Near-Continuum Hypersonic Flows Over Compression Ramps
Authors: Wu J.-S. , Tseng K.-C.
Published: January 2003

This paper describes the analysis of the near-continuum hypersonic flow over a compression ramp using the two-dimensional parallel direct simulation Monte Carlo (DSMC) method. Unstructured and triangular solution-based adaptive mesh depending on the local mean free path is used to improve the resolution of solution for the flow field with highly varying properties. In addition, a freestream parameter is defined to help reduced the cell numbers in the freestream area, resulting in appreciable decrease of the computational time (20–30%) without sacrificing the accuracy of the solution. The two-step multilevel graph partition technique is used for physical domain decomposition, employing estimated particle number distribution in each cell as the graph vertex weight. 32 IBM-SP2 processors are used throughout the study unless otherwise specified. The Effect of the outflow vacuum boundary condition, compression ramp angle, freestream condition, and length of the ramp to the flow field are investigated. Computational results are compared with previous numerical results whenever available.
Wake Dynamics of a Yawed Cylinder
Authors: Marshall J. S.
Published: January 2003

A theoretical and computational study is reported of the effect of cylinder yaw angle on the vorticity and velocity field in the cylinder wake. Previous experimental studies for yawed cylinder flows conclude that, sufficiently far away from the cylinder ends and for small and moderate values of the yaw angle, the near-wake region is dominated by vortex structures aligned parallel to the cylinder. Associated with this observation, experimentalists have proposed the so-called Independence Principle, which asserts that the forces and vortex shedding frequency of a yawed cylinder are the same as for a cylinder with no yaw using only the component of the freestream flow oriented normal to the cylinder axis. The current paper examines the structure, consequences and validity for yawed cylinder flows of a quasi-two-dimensional approximation in which the velocity and vorticity have three nonzero components, but have vanishing gradient in the direction of the cylinder axis. In this approximation, the cross-stream velocity field is independent of the axial velocity component, thus reproducing the Independence Principle. Both the axial vorticity and axial velocity components are governed by an advection-diffusion equation. The governing equations for vorticity and velocity in the quasi-two-dimensional theory can be nondimensionalized to eliminate dependence on yaw angle, such that the cross-stream Reynolds number is the only dimensionless parameter. A perturbation argument is used to justify the quasi-two-dimensional approximation and to develop approximate conditions for validity of the quasi-two-dimensional approximation for finite-length cylinder flows. Computations using the quasi-two-dimensional theory are performed to examine the evolution of the cross-stream vorticity and associated axial velocity field. The cross-stream vorticity is observed to shed from the cylinder as thin sheets and to wrap around the Ka´rman vortex structures, which in turn induces an axial velocity deficit within the wake vortex cores. The computational results indicate two physical mechanisms, associated with instability of the quasi-two-dimensional flow, that might explain the experimentally observed breakdown of the Independence Principle for large yaw angles.
Effect of Pressure With Wall Heating in Annular Two-Phase Flow
Authors: Kumar Ranganathan , Trabold Thomas A.
Published: January 2003

The local distributions of void fraction, interfacial frequency, and velocity have been measured in annular flow of R-134a through a wall-heated, high aspect ratio duct. High aspect ratio ducts provide superior optical access to tubes or irregular geometries. This work expands upon earlier experiments conducted with adiabatic flows in the same test section. Use of thin, transparent heater films on quartz windows provided sufficient electrical power capacity to produce the full range of two-phase conditions of interest. With wall vapor generation, the system pressure was varied from 0.9 to 2.4 MPa, thus allowing the investigation of flows with liquid-to-vapor density ratios covering the range of about 7 to 27, far less than studied in air-water and similar systems. There is evidence that for a given cross-sectional average void fraction, the local phase distributions can be different depending on whether the vapor phase is generated at the wall, or upstream of the test section inlet. In wall-heated flows, local void fraction profiles measured across both the wide and narrow test section dimensions illustrate the profound effect that pressure has on the local flow structure; notably, increasing pressure appears to thin the wall-bounded liquid films and redistribute liquid toward the edges of the test section. This general trend is also manifested in the distributions of mean droplet diameter and interfacial area density, which are inferred from local measurements of void fraction, droplet frequency and velocity. At high pressure, the interfacial area density is increased due to the significant enhancement in droplet concentration.
Evaluation of the Turbulence Model Influence on the Numerical Simulations of Unsteady Cavitation
Authors: Coutier-Delgosha O. , Fortes-Patella R. , Reboud J. L.
Published: January 2003

Unsteady cavitation in a Venturi-type section was simulated by two-dimensional computations of viscous, compressible, and turbulent cavitating flows. The numerical model used an implicit finite volume scheme (based on the SIMPLE algorithm) to solve Reynolds-averaged Navier-Stokes equations, associated with a barotropic vapor/liquid state law that strongly links the density variations to the pressure evolution. To simulate turbulence effects on cavitating flows, four different models were implemented (standard k-ε RNG; modified k-ε RNG; k-ω with and without compressibility effects), and numerical results obtained were compared to experimental ones. The standard models k-ε RNG and k-ω without compressibility effects lead to a poor description of the self-oscillation behavior of the cavitating flow. To improve numerical simulations by taking into account the influence of the compressibility of the two-phase medium on turbulence, two other models were implemented in the numerical code: a modified k-ε model and the k-ω model including compressibility effects. Results obtained concerning void ratio, velocity fields, and cavitation unsteady behavior were found in good agreement with experimental ones. The role of the compressibility effects on turbulent two-phase flow modeling was analyzed, and it seemed to be of primary importance in numerical simulations.
Flow in a Centrifugal Pump Impeller at Design and Off-Design Conditions—Part I: Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) Measurements
Authors: Pedersen Nicholas , Larsen Poul S. , Jacobsen Christian B.
Published: January 2003

Detailed optical measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller of industrial design have been performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). Results include instantaneous and ensemble averaged PIV velocity vector maps as well as bin-resolved LDV data acquired in the midplane between hub and shroud of the impeller. The flow is surveyed at both design load and at severe off-design conditions. At design load, Q=Qd, the mean field of relative velocity is predominantly vane congruent, showing well-behaved flow with no separation. At quarter-load, Q=0.25Qd, a previously unreported “two-channel” phenomenon consisting of alternate stalled and unstalled passages was observed, with distinct flow congruence between every second of the six passages. A large recirculation cell blocked the inlet to the stalled passage while a strong relative eddy dominated the remaining parts of the passage. The stall phenomenon was steady, nonrotating and not initiated via the interaction with stationary components. The study demonstrates that the PIV technique is efficient in providing reliable and detailed velocity data over a full impeller passage, also in the close vicinity of walls due to the use of fluorescent seeding. A quantitative comparison of blade-to-blade distributions of mean fields obtained by PIV and LDV showed a satisfactory agreement.
Flow in a Centrifugal Pump Impeller at Design and Off-Design Conditions—Part II: Large Eddy Simulations
Authors: Byskov Rikke K. , Jacobsen Christian B. , Pedersen Nicholas
Published: January 2003

The flow field in a shrouded six-bladed centrifugal pump impeller has been investigated using large eddy simulation (LES). The effect of the subgrid scales has been modeled through a localized dynamic Smagorinsky model implemented in the commercial CFD code FINE/Turbo. A detailed analysis of the results of LES at design load, Q=Qd, and severe off-design conditions, at quarter-load Q=0.25Qd, is presented. At design load LES reveals a well-behaved flow field with no significant separation. At quarter-load significant differences between adjacent impeller passages are revealed. A steady nonrotating stall phenomenon is observed in the entrance of one passage and a relative eddy develops in the remaining part of the passage. The stall unblocks the adjacent passage which exhibits a flow dominated by rotational effects. Velocities predicted by LES and steady-state Reynolds averaged Navier-Stokes (RANS) simulations based on the Baldwin-Lomax and Chien k-ε turbulence models are compared with experimental data obtained from particle image velocimetry (PIV). The complex two-channel phenomena observed by LES is with satisfactory agreement confirmed by PIV. However, it is found that the two RANS models do not reproduce the stall phenomenon observed at quarterload and are incapable of detecting the differences between the two passages.
Prediction of Turbulent Flow Over Rough Surfaces Using a Force Field in Large Eddy Simulation
Authors: Cui Jie , Patel Virendra C. , Lin Ching-Long
Published: January 2003

A force field model to simulate turbulent flow over a surface with arbitrary roughness is described. A given roughness is decomposed into resolved and subgrid-scale roughness, conceptually similar to the flow decomposition in large eddy simulation (LES). For a given flow and Reynolds number, a Cartesian grid is selected to satisfy LES requirements. This grid determines the geometric features of the roughness that are formally resolved. The force field used to represent this resolved roughness is determined during the LES solution process, without any empirical input. The subgrid roughness that is not resolved is modeled by a random force distribution in which a drag coefficient is specified. Use of this approach to model surface roughness is demonstrated by calculations of the flow in a duct with a wavy wall with superimposed fine-grain roughness.
Measurements of Heat Transfer to a Massive Cylindrical Calorimeter Engulfed in a Circular Pool Fire
Authors: Kramer M. Alex , Greiner Miles , Koski J. A. , Lopez Carlos , Suo-Anttila Ahti
Published: January 2003

A large-scale experiment was performed to measure heat transfer to a massive cylindrical calorimeter engulfed in a 30 minute circular-pool fire. This test simulated the conditions of a truck-sized nuclear waste transport package in a severe fire. The calorimeter inner surface temperature and the flame environment emissive power were measured at several locations as functions of time. An inverse heat conduction technique was used to estimate the net heat flux to the calorimeter. Tall porous fences surrounded the test facility to reduce the effect of wind on the fire. Outside the fences, 2.9 m/s winds blew across the calorimeter axis at the beginning of the test but decreased with time. The wind tilted and moved the fire so that the initial flame environment emissive power was substantially less on the windward side than the leeward side. The calorimeter became more uniformly engulfed as the winds decreased. The maximum heat flux to the calorimeter was 150 MW/m2 on the leeward side at the beginning of the fire, and generally decreased with time. The local variations of calorimeter temperature and heat flux were closely related to the local flame environment emissive power.
A New 75 kW High-Flux Solar Simulator for High-Temperature Thermal and Thermochemical Research
Authors: Hirsch, D. , Zedtwitz, and P. v. , Osinga T. , Kinamore J. , Steinfeld A.
Published: January 2003

A new high-flux solar simulator, capable of delivering up to 75 kW of continuous radiative power at peak fluxes exceeding 4250 kW/m2, is operational at the ETH-Zurich. Its optical design and performance are described. This unique facility serves principally as an experimental platform for investigating thermal and thermochemical processes at temperatures up to 3000°K.
Solar Chimney Turbine Performance
Authors: Gannon Anthony J. , von Backstro¨m Theodor W.
Published: January 2003

An experimental investigation of the performance of a solar chimney turbine is presented. The design features a single rotor and uses the chimney supports as inlet guide vanes (IGVs) to introduce pre-whirl. This reduces the turbine exit kinetic energy at the diffuser inlet and assists the flow turning in the IGV-to-rotor duct. The rotor configuration allows the supports to be placed directly under the chimney walls. Measurements from a scale model turbine are used to calculate the turbine performance and efficiency. Efficiencies over a wide operating range and detailed performance measurements at two operating points are presented. Total-to-total efficiencies of 85–90% and total-to-static of 77–80% over the design range are measured. The detailed measurements give insight into the turbine performance and possible design improvements. These results allow more accurate simulation of solar chimney power plants.
Aqueous Lithium Bromide TES and R-123 Chiller in Series
Authors: Rizza J. J.
Published: January 2003

This paper presents an analysis of a cold thermal energy storage (TES) system operating in series with an R-123 chiller. A lithium bromide/water LiBr/H2O solution is used both as a refrigerant and as a cold thermal storage material. The refrigerant, liquid water, is extracted from the LiBr/H2O strong solution during the off-peak period. The liquid water and LiBr/H2O weak solution, a byproduct of the refrigerant recovery process, are used during the on-peak period to cool the building. Building waste heat is pumped by the R-123 compressor to a higher temperature during the off-peak period and is used in the generator to recover the thermal storage by reprocessing the stored solution to a higher lithium bromide concentration. The storage volumetric efficiency and system COP are determined and compared to storage systems based on water/ice and liquid water. The storage volumetric efficiency is greater than a water/ice system and far exceeds the value for a liquid water system. The proposed system, which uses an external heat pump as a source of generator heat, is also compared to another LiBr/H2O system that uses a self-contained internal heat pump (the compressor operates independently from the chiller and uses the liberated water refrigerant as its working fluid). The system presented here outperforms both the water/ice system and the internal heat pump LiBr/H2O system but is unable to match the liquid water system COP. However, it has other well-defined advantages over the liquid water system and appears to be a competitive alternative to conventional TES systems.
Natural Convection from a Horizontal Tube Heat Exchanger Immersed in a Tilted Enclosure
Authors: Liu Wei , Davidson Jane H. , Kulacki F. A. , Mantell Susan C.
Published: January 2003

Heat transfer rates of a single horizontal tube immersed in a water-filled enclosure tilted at 30 deg are measured. The results serve as a baseline case for a solar water heating system with a heat exchanger immersed in an integral collector storage. Experiments are conducted for isothermal and stratified enclosures with both adiabatic and uniform heat flux boundary conditions. Natural convection flow in the enclosure is interpreted from measured water temperature distributions. Formation of an appropriate temperature difference that drives natural convection is determined. Correlations for the overall heat transfer coefficient in terms of the Nusselt and Rayleigh numbers are reduced to the form NuD=0.675RaD0.25 for 9×105⩽RaD⩽4×107.
Remote Solar, Wind, and Hybrid Solar/Wind Energy Systems for Purifying Water
Authors: Vick Brian D. , Clark R. Nolan , Ling Junyi , Ling Shitao
Published: January 2003

Solar energy, wind energy, and a combination of wind and solar energy have been used successfully to power an UV (ultraviolet) water purification system. Five different solar and wind energy systems have been tested and although these renewable energy systems have been used for water purification, graphs contained in the paper can be used to determine the feasibility of powering other electrical loads. Combining a 100-W solar-PV system with a 500-W wind turbine resulted in pumping and purifying enough water to satisfy the potable water requirements of 4000 people (16000 liters/day) at an estimated equipment cost of $4630.
Measured Versus Predicted Performance of Building Integrated Photovoltaics
Authors: Davis Mark W. , Fanney A. Hunter , Dougherty Brian P.
Published: January 2003

The lack of predictive performance tools creates a barrier to the widespread use of building integrated photovoltaic panels. The National Institute of Standards and Technology (NIST) has created a building integrated photovoltaic (BIPV) test bed to capture experimental data that can be used to improve and validate previously developed computer simulation tools. Twelve months of performance data have been collected for building integrated photovoltaic panels using four different cell technologies—crystalline, polycrystalline, silicon film, and triple-junction amorphous. Two panels using each cell technology were present, one without any insulation attached to its rear surface and one with insulation having a nominal thermal resistance value of 3.5m2s˙K/W attached to its rear surface. The performance data associated with these eight panels, along with meteorological data, were compared to the predictions of a photovoltaic model developed jointly by Maui Solar Software and Sandia National Laboratories (SNL), which is implemented in their IV Curve Tracer software [1]. The evaluation of the predictive performance tools was done in the interest of refining the tools to provide BIPV system designers with a reliable source for economic evaluation and system sizing.
Adaptation in a revised inner-hair cell model
Authors: Sumner Christian J. , Lopez-Poveda Enrique A. , O’Mard Lowel P. , Meddis Ray
Published: January 2003

A revised computational model of the inner-hair cell (IHC) and auditory-nerve (AN) complex was recently presented [Sumner et al., J. Acoust. Soc. Am. 111, 2178–2188 (2002)]. One key improvement is that the model reproduces the rate-intensity functions of low- (LSR), medium- (MSR), and high-spontaneous rate (HSR) fibers in the guinea-pig. Here we describe the adaptation characteristics of the model, and how they vary with model fiber type. Adaptation of the revised model for a HSR fiber is in line with an earlier version of the model [Meddis and Hewitt, J. Acoust. Soc. Am. 90, 904–917 (1991)]. In guinea-pig, poststimulus time histograms (PSTH) have been found to show less adaptation in LSR fibers. Evidence from chinchilla suggests that this is due to chronic adaptation resulting from short interstimulus intervals, and that fully recovered LSR fibers actually show more adaptation. However, the model is able to account for both variations of PSTH shape when fully recovered from adaptation. Interstimulus interval can also affect recovery in the model. The model is further tested against data previously used to evaluate models of AN adaptation. The tests are (i) recovery from adaptation of spontaneous rate and (ii) the recovery of response to acoustic stimuli (“forward masking”), (iii) the response to stimulus increments and (iv) decrements, and (v) the conservation of transient components. A HSR model fiber performs similarly to the earlier version of the model. However, there is considerable variation in response to increments and decrements between different model fibers.
Cochlear nonlinearity between 500 and 8000 Hz in listeners with normal hearing
Authors: Lopez-Poveda Enrique A. , Plack Christopher J. , Meddis Ray
Published: January 2003

Cochlear nonlinearity was estimated over a wide range of center frequencies and levels in listeners with normal hearing, using a forward-masking method. For a fixed low-level probe, the masker level required to mask the probe was measured as a function of the masker-probe interval, to produce a temporal masking curve (TMC). TMCs were measured for probe frequencies of 500, 1000, 2000, 4000, and 8000 Hz, and for masker frequencies 0.5, 0.7, 0.9, 1.0 (on frequency), 1.1, and 1.6 times the probe frequency. Across the range of probe frequencies, the TMCs for on-frequency maskers showed two or three segments with clearly distinct slopes. If it is assumed that the rate of decay of the internal effect of the masker is constant across level and frequency, the variations in the slopes of the TMCs can be attributed to variations in cochlear compression. Compression-ratio estimates for on-frequency maskers were between 3:1 and 5:1 across the range of probe frequencies. Compression did not decrease at low frequencies. The slopes of the TMCs for the lowest frequency probe (500 Hz) did not change with masker frequency. This suggests that compression extends over a wide range of stimulus frequencies relative to characteristic frequency in the apical region of the cochlea.
Differential responses to acoustic damage and furosemide in auditory brainstem and otoacoustic emission measures
Authors: Mills David M.
Published: January 2003

Characteristics of distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs) were measured in Mongolian gerbil before and after the introduction of two different auditory dysfunctions: (1) acoustic damage with a high-intensity tone, or (2) furosemide intoxication. The goal was to find emission parameters and measures that best differentiated between the two dysfunctions, e.g., at a given ABR threshold elevation. Emission input–output or “growth” functions were used (frequencies f1 and f2, f2/f1=1.21) with equal levels, L1=L2, and unequal levels, with L1=L2+20 dB. The best parametric choice was found to be unequal stimulus levels, and the best measure was found to be the change in the emission threshold level, Δx. The emission threshold was defined as the stimulus level required to reach a criterion emission amplitude, in this case −10 dB SPL. (The next best measure was the change in emission amplitude at high stimulus levels, specifically that measured at L1×L2=90×70 dB SPL.) For an ABR threshold shift of 20 dB or more, there was essentially no overlap in the emission threshold measures for the two conditions, sound damage or furosemide. The dividing line between the two distributions increased slowly with the change in ABR threshold, ΔABR, and was given by Δxt=0.6 ΔABR+8 dB. For a given ΔABR, if the shift in emission threshold was more than the calculated dividing line value, Δxt, the auditory dysfunction was due to acoustic damage, if less, it was due to furosemide.
Disruption of Transforming Growth Factor-β Signaling in ELF β-Spectrin-Deficient Mice
Authors: Tang Yi , Katuri Varalakshmi , Dillner Allan , Mishra Bibhuti , Deng Chu-Xia , Mishra Lopa
Published: January 2003

Disruption of the adaptor protein ELF, a β-spectrin, leads to disruption of transforming growth factor–β (TGF-β) signaling by Smad proteins in mice.
Elf
−/−
mice exhibit a phenotype similar to
smad2
+/−
/
smad3
+/−
mutant mice of midgestational death due to gastrointestinal, liver, neural, and heart defects. We show that TGF-β triggers phosphorylation and association of ELF with Smad3 and Smad4, followed by nuclear translocation. ELF deficiency results in mislocalization of Smad3 and Smad4 and loss of the TGF-β–dependent transcriptional response, which could be rescued by overexpression of the COOH-terminal region of ELF. This study reveals an unexpected molecular link between a major dynamic scaffolding protein and a key signaling pathway.
Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs
Authors: Zeineh Michael M. , Engel Stephen A. , Thompson Paul M. , Bookheimer Susan Y.
Published: January 2003

The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields 2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new memory formation.
The Cellular and Molecular Origins of Beak Morphology
Authors: Schneider R. A. , Helms J. A.
Published: January 2003

Cellular and molecular mechanisms underlying differences in beak morphology likely involve interactions among multiple embryonic populations. We exchanged neural crest cells destined to participate in beak morphogenesis between two anatomically distinct species. Quail neural crest cells produced quail beaks in duck hosts and duck neural crest produced duck bills in quail hosts. These transformations involved morphological changes to non–neural crest host beak tissues. To achieve these changes, donor neural crest cells executed autonomous molecular programs and regulated gene expression in adjacent host tissues. Thus, neural crest cells are a source of molecular information that generates interspecific variation in beak morphology.
Tracheal Respiration in Insects Visualized with Synchrotron X-ray Imaging
Authors: Westneat Mark W. , Betz Oliver , Blob Richard W. , Fezzaa Kamel , Cooper W. James , Lee Wah-Keat
Published: January 2003

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.
Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search
Authors: Beghein Caroline , Trampert Jeannot
Published: January 2003

A technique for searching full model space that was applied to measurements of anomalously split normal modes showed a robust pattern of
P
-wave and
S
-wave anisotropy in the inner core. The parameter describing
P
-wave anisotropy changes sign around a radius of 400 kilometers, whereas
S
-wave anisotropy is small in the upper two-thirds of the inner core and becomes negative at greater depths. Our results agree with observed travel-time anomalies of rays traveling at epicentral distances varying from 150° to 180°. The models may be explained by progressively tilted hexagonal close-packed iron in the upper half of the inner core and could suggest a different iron phase in the center.
Extended Longevity in Mice Lacking the Insulin Receptor in Adipose Tissue
Authors: Blüher Matthias , Kahn Barbara B. , Kahn C. Ronald
Published: January 2003

Caloric restriction has been shown to increase longevity in organisms ranging from yeast to mammals. In some organisms, this has been associated with a decreased fat mass and alterations in insulin/insulin-like growth factor 1 (IGF-1) pathways. To further explore these associations with enhanced longevity, we studied mice with a fat-specific insulin receptor knockout (FIRKO). These animals have reduced fat mass and are protected against age-related obesity and its subsequent metabolic abnormalities, although their food intake is normal. Both male and female FIRKO mice were found to have an increase in mean life-span of ∼134 days (18%), with parallel increases in median and maximum life-spans. Thus, a reduction of fat mass without caloric restriction can be associated with increased longevity in mice, possibly through effects on insulin signaling.
An Evolutionary Advantage of Haploidy in Large Yeast Populations
Authors: Zeyl Clifford , Vanderford Thomas , Carter Michele
Published: January 2003

Although seed plants and multicellular animals are predominantly diploid, the prominence of diploidy varies greatly among eukaryote life cycles, and no general evolutionary advantage of diploidy has been demonstrated. By doubling the copy number of each gene, diploidy may increase the rate at which adaptive mutations are produced. However, models suggest that this does not necessarily accelerate adaptation by diploid populations. We tested model predictions regarding rates of adaptation using asexual yeast populations. Adaptive mutations were on average partially recessive. As predicted, diploidy slowed adaptation by large populations but not by small populations.
Deciphering the Reaction Dynamics Underlying Optimal Control Laser Fields
Authors: Daniel Chantal , Full Jürgen , González Leticia , Lupulescu Cosmin , Manz Jörn , Merli Andrea , Vajda Štefan , Wöste Ludger
Published: January 2003

Femtosecond high-resolution pump-probe experiments have been used together with theoretical ab initio quantum calculations and wave packet dynamics simulations to decode an optimal femtosecond pulse that is generated from adaptive learning algorithms. This pulse is designed to maximize the yield of the organometallic ion CpMn(CO)5while hindering the competing fragmentation. The sequential excitation and ionization of the target ion are accomplished by an optimized field consisting of two dominant subpulses with optimal frequencies and time delays.
Long-Range Correlations in the Diffuse Seismic Coda
Authors: Campillo Michel , Paul Anne
Published: January 2003

The late seismic coda may contain coherent information about the elastic response of Earth. We computed the correlations of the seismic codas of 101 distant earthquakes recorded at stations that were tens of kilometers apart. By stacking cross-correlation functions of codas, we found a low-frequency coherent part in the diffuse field. The extracted pulses have the polarization characteristics and group velocities expected for Rayleigh and Love waves. The set of cross-correlations has the symmetries of the surface-wave part of the Green tensor. This seismological example shows that diffuse waves produced by distant sources are sufficient to retrieve direct waves between two perfectly located points of observation. Because it relies on general properties of diffuse waves, this result has potential applications in other fields.
Vibrationally Resolved Fluorescence Excited with Submolecular Precision
Authors: Qiu X. H. , Nazin G. V. , Ho W.
Published: January 2003

Tunneling electrons from a scanning tunneling microscope (STM) were used to excite photon emission from individual porphyrin molecules adsorbed on an ultrathin alumina film grown on a NiAl(110) surface. Vibrational features were observed in the light-emission spectra that depended sensitively on the different molecular conformations and corresponding electronic states obtained by scanning tunneling spectroscopy. The high spatial resolution of the STM enabled the demonstration of variations in light-emission spectra from different parts of the molecule. These experiments realize the feasibility of fluorescence spectroscopy with the STM and enable the integration of optical spectroscopy with a nanoprobe for the investigation of single molecules.
Chromatin Loosening by Poly(ADP)-Ribose Polymerase (PARP) at
Drosophila
Puff Loci
Authors: Tulin Alexei , Spradling Allan
Published: January 2003

Steroid response and stress-activated genes such as
hsp70
undergo puffing in
Drosophila
larval salivary glands, a local loosening of polytene chromatin structure associated with gene induction. We find that puffs acquire elevated levels of adenosine diphosphate (ADP)-ribose modified proteins and that poly(ADP)-ribose polymerase (PARP) is required to produce normal-sized puffs and normal amounts of Hsp70 after heat exposure. We propose that chromosomal PARP molecules become activated by developmental or environmental cues and strip nearby chromatin proteins off DNA to generate a puff. Such local loosening may facilitate transcription and may transiently make protein complexes more accessible to modification, promoting chromatin remodeling during development.
Functional Mapping of the Primate Auditory System
Authors: Poremba Amy , Saunders Richard C. , Crane Alison M. , Cook Michelle , Sokoloff Louis , Mishkin Mortimer
Published: January 2003

Cerebral auditory areas were delineated in the awake, passively listening, rhesus monkey by comparing the rates of glucose utilization in an intact hemisphere and in an acoustically isolated contralateral hemisphere of the same animal. The auditory system defined in this way occupied large portions of cerebral tissue, an extent probably second only to that of the visual system. Cortically, the activated areas included the entire superior temporal gyrus and large portions of the parietal, prefrontal, and limbic lobes. Several auditory areas overlapped with previously identified visual areas, suggesting that the auditory system, like the visual system, contains separate pathways for processing stimulus quality, location, and motion.
Phosphorus Limitation of Coastal Ecosystem Processes
Authors: Sundareshwar P. V. , Morris J. T. , Koepfler E. K. , Fornwalt B.
Published: January 2003

Primary production in coastal wetlands is conventionally thought to be limited by nitrogen. Although the plant community in a pristine salt marsh was found to be limited primarily by nitrogen availability, the bacterial community in the soil was limited by phosphorus. Hence, in coastal wetlands, and possibly in many ecosystems, individual trophic groups may respond differently to nitrogen and phosphorus loading. Phosphorus limitation of the growth of nitrogen-transforming bacteria will affect carbon fixation, storage, and release mediated by plants, a result that has important implications for ecosystem management.
A Different Approach to Modeling
Authors: Stenseth Nils Chr. , Mysterud Atle
Published: January 2003

Adaptive Herbivore Ecology
. From Resources to Populations in Variable Environments. Norman Owen-Smith. Cambridge University Press, Cambridge, 2002. 390 pp. $90, £65. ISBN 0-521-81061-2.

Building on his field studies of African herbivores, Owen-Smith develops a new modeling approach for studying the population dynamics of large mammals.
A Nebular Origin for Chondritic Fine-Grained Phyllosilicates
Authors: Ciesla Fred J. , Lauretta Dante S. , Cohen Barbara A. , Hood Lon L.
Published: January 2003

Hydrated minerals occur in accretionary rims around chondrules in CM chondrites. Previous models suggested that these phyllosilicates did not form by gas-solid reactions in the canonical solar nebula. We propose that chondrule-forming shock waves in icy regions of the nebula produced conditions that allowed rapid mineral hydration. The time scales for phyllosilicate formation are similar to the time it takes for a shocked system to cool from the temperature of phyllosilicate stability to that of water ice condensation. This scenario allows for simultaneous formation of chondrules and their fine-grained accretionary rims.
High-Accuracy ab Initio Rotation-Vibration Transitions for Water
Authors: Polyansky Oleg L. , Császár Attila G. , Shirin Sergei V. , Zobov Nikolai F. , Barletta Paolo , Tennyson Jonathan , Schwenke David W. , Knowles Peter J.
Published: January 2003

The spectrum of water vapor is of fundamental importance for a variety of processes, including the absorption and retention of sunlight in Earth's atmosphere. Therefore, there has long been an urgent need for a robust and accurate predictive model for this spectrum. In our work on the high-resolution spectrum of water, we report first-principles calculations that approach experimental accuracy. To achieve this, we performed exceptionally large electronic structure calculations and considered a variety of effects, including quantum electrodynamics, which have routinely been neglected in studies of small many-electron molecules. The high accuracy of the resulting ab initio procedure is demonstrated for the main isotopomers of water.
Spongiform Degeneration in
mahoganoid
Mutant Mice
Authors: He Lin , Lu Xin-Yun , Jolly Aaron F. , Eldridge Adam G. , Watson Stanley J. , Jackson Peter K. , Barsh Gregory S. , Gunn Teresa M.
Published: January 2003

mahoganoid
is a mouse coat-color mutation whose pigmentary phenotype and genetic interactions resemble those of
Attractin
(
Atrn
).
Atrn
mutations also cause spongiform neurodegeneration. Here, we show that a null mutation for
mahoganoid
causes a similar age-dependent neuropathology that includes many features of prion diseases but without accumulation of protease-resistant prion protein. The gene mutated in
mahoganoid
encodes a RING-containing protein with E3 ubiquitin ligase activity in vitro. Similarities in phenotype, expression, and genetic interactions suggest that
mahoganoid
and
Atrn
genes are part of a conserved pathway for regulated protein turnover whose function is essential for neuronal viability.
RacA, a Bacterial Protein That Anchors Chromosomes to the Cell Poles
Authors: Ben-Yehuda Sigal , Rudner David Z. , Losick Richard
Published: January 2003

Eukaryotic chromosomes are anchored to a spindle apparatus during mitosis, but no such structure is known during chromosome segregation in bacteria. When sister chromosomes are segregated during sporulation in
Bacillus subtilis
, the replication origin regions migrate to opposite poles of the cell. If and how origin regions are fastened at the poles has not been determined. Here we describe a developmental protein, RacA, that acts as a bridge between the origin region and the cell poles. We propose that RacA assembles into an adhesive patch at a centromere-like element near the origin, causing chromosomes to stick at the poles.
A Premodern Synthesis
Authors: Laubichler Manfred D.
Published: January 2003

The Romantic Conception of Life
. Science and Philosophy in the Age of Goethe. Robert J. Richards. University of Chicago Press, Chicago, 2002. 607 pp. $35, £24.50. ISBN 0-226-71210-9.

Richards explores the interdependency of the lives and ideas of the German Romantics and the development of their biology. He finds their work to lie at the roots of much of 19th-century biology, including Darwin's conceptions of nature and evolution.
A Glutamate Mutase Is Involved in the Biosynthesis of the Lipopeptide Antibiotic Friulimicin in
Actinoplanes friuliensis
Authors: Heinzelmann E. , Berger S. , Puk O. , Reichenstein B. , Wohlleben W. , Schwartz D.
Published: January 2003

Actinoplanes friuliensis
produces the lipopeptide antibiotic friulimicin. This antibiotic is active against gram-positive bacteria such as multiresistant
Enterococcus
and
Staphylococcus
strains. It consists of 10 amino acids that form a ring structure and 1 exocyclic amino acid to which an acyl residue is attached. By a reverse genetic approach, biosynthetic genes were identified that are required for the nonribosomal synthesis of the antibiotic. In close proximity two genes (
glmA
and
glmB
) were found which are involved in the production of methylaspartate, one of the amino acids of the peptide core. Methylaspartate is synthesized by a glutamate mutase mechanism, which was up to now only described for glutamate fermentation in
Clostridium
sp. or members of the family
Enterobacteriaceae
. The active enzyme consists of two subunits, and the corresponding genes overlap each other. To demonstrate enzyme activity in a heterologous host, it was necessary to genetically fuse
glmA
and
glmB
. The resulting gene was overexpressed in
Streptomyces lividans
, and the fusion protein was purified in an active form. For gene disruption mutagenesis, a host-vector system was established which enables genetic manipulation of
Actinoplanes
spp. for the first time. Thus, targeted inactivation of biosynthetic genes was possible, and their involvement in friulimicin biosynthesis was demonstrated.
Biological Properties of Novel Antistaphylococcal Quinoline-Indole Agents
Authors: Oliva Brunello , Miller Keith , Caggiano Nico , O'Neill Alexander J. , Cuny Gregory D. , Hoemann Michael Z. , Hauske James R. , Chopra Ian
Published: January 2003

The antibacterial properties of novel quinoline-indole (QI) agents were examined. QI agents demonstrated potent bactericidal activities against
Staphylococcus aureus
, killing by lytic and nonlytic mechanisms.
S. aureus
mutants resistant to a lytic QI agent (SEP 155342) and a nonlytic QI agent (SEP 118843) arose at frequencies of 1.4 × 10
−9
and 1.2 × 10
−8
, respectively, by selection at four times the MICs. Mutants resistant to QI agent SEP 155342 were unstable, but mutants resistant to QI agent SEP 118843 displayed stable resistance. Mutants resistant to QI agent SEP 118843 were not cross resistant to other inhibitors, including QI agent SEP 155342. Addition of QI agents SEP 118843 and SEP 155342 at four times the MIC caused nonspecific inhibition of several macromolecular biosynthetic pathways in
S. aureus
. Within 10 min, QI agents SEP 118843 and SEP 155342 both interfered with bacterial membrane integrity, as measured by uptake of propidium iodide. Agents from the two classes of the QI agents probably kill staphylococci by separate mechanisms which, nevertheless, both involve interference with cytoplasmic membrane function. Precise structure-activity relationships for the division of QI agents into two classes could not be determined. However, lytic activity was often associated with substitution of a basic amine at position 4 of the quinoline nucleus, whereas compounds with nonlytic activity usually contained an aromatic ring with or without a methoxy substituent at position 4. Nonlytic QI agents such as SEP 118843 may possess selective activity against the prokaryotic membrane since this compound failed to lyse mouse erythrocytes when it was added at a concentration equivalent to four times the MIC for
S. aureus.
In Vitro Parasiticidal Effect of Nitazoxanide against
Echinococcus multilocularis
Metacestodes
Authors: Stettler Marianne , Fink Renate , Walker Mirjam , Gottstein Bruno , Geary Timothy G. , Rossignol Jean François , Hemphill Andrew
Published: January 2003

When humans serve as inadvertent intermediate hosts for
Echinococcus multilocularis
, disease (alveolar echinococcosis [AE]) may result from the expanding parasite metacestode in visceral organs, mostly in the liver. Benzimidazole carbamate derivatives such as mebendazole and albendazole are used for chemotherapeutic treatment of AE. However, these treatments are, in most cases, parasitistatic rather than parasiticidal. As treatment is discontinued, a recurrence of parasite growth has been observed in many AE patients with nonradical resections. The only curative treatment for AE is radical surgical resection of the parasite tissue and support by chemotherapy. As there is a need for new treatment options for AE, the in vitro efficacy of nitazoxanide (NTZ), a broad-spectrum drug used against intestinal parasites and bacteria, was investigated. We showed that in vitro treatment of
E. multilocularis
metacestodes with NTZ induced high levels of alkaline phosphatase activity in the medium. Concurrently, distinct morphological and ultrastructural alterations were detected. Most significantly, two distinct types of alterations were observed as soon as after 3 h of NTZ treatment. At first, the drug induced a peripheral output of membranous vesicles from the tegumental membrane into the laminated layer. Simultaneously, germinal layer-associated undifferentiated cells produced large vacuoles filled with lipid-like and often electron-dense membranous segments. Other alterations were observed at later time points, including vacuolization of the germinal layer, accumulation of lipid droplets, and lastly, loss of microtriches and separation of the laminated and germinal layers. The pattern of damage induced by NTZ was different from the alterations earlier observed in albendazole sulfoxide-treated vesicles. The nonviability of NTZ-treated metacestodes was confirmed through bioassay, i.e., inoculation of treated and untreated parasites into mice. These experiments demonstrate the in vitro parasiticidal effect of NTZ on
E. multilocularis
metacestodes.