bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Approach to the Optimization of Reaction Rate Parameters for Methane Combustion Using Multi-Objective Genetic Algorithms
Authors: Elliott L. , Ingham D. B. , Kyne A. G. , Mera N. S. , Pourkashanian M. , Wilson C. W.
Published: August 2004

This study uses a multi-objective genetic algorithm to determine new reaction rate parameters (A’s, β’s and Ea’s in the non-Arrhenius expressions) for the combustion of a methane/air mixture. The multi-objective structure of the genetic algorithm employed allows for the incorporation of both perfectly stirred reactor and laminar premixed flame data in the inversion process, thus enabling a greater confidence in the predictive capabilities of the reaction mechanisms obtained. Various inversion procedures based on reduced sets of data are investigated and tested on methane/air combustion in order to generate efficient inversion schemes for future investigations concerning complex hydrocarbon fuels. The inversion algorithms developed are first tested on numerically simulated data. In addition, the increased flexibility offered by this novel multi-objective GA has now, for the first time, allowed experimental data to be incorporated into our reaction mechanism development. A GA optimized methane-air reaction mechanism is presented which offers a remarkable improvement over a previously validated starting mechanism in modeling the flame structure in a stoichiometric methane-air premixed flame (http://www.personal.leeds.ac.uk/∼fuensm/project/mech.html). In addition, the mechanism outperforms the predictions of more detailed schemes and is still capable of modeling combustion phenomena that were not part of the optimization process. Therefore, the results of this study demonstrate that the genetic algorithm inversion process promises the ability to assess combustion behavior for fuels where the reaction rate coefficients are not known with any confidence and, subsequently, accurately predict emission characteristics, stable species concentrations and flame characterization. Such predictive capabilities will be of paramount importance within the gas turbine industry.
Interval Approach for the Modeling of Tolerances and Clearances in Mechanism Analysis
Authors: Wu Weidong , Rao S. S.
Published: August 2004

It is important to conduct error analysis of assemblies in order to ensure that the manufactured parts satisfy the design specifications. Traditionally, mechanical tolerances and clearances are modeled as random variables and the analysis is conducted using probabilistic methods. In this work, a new approach, based on interval analysis, is presented for the modeling and analysis of tolerances and clearances. The basic procedure of interval analysis involving solution of simultaneous nonlinear equations is described. The application of the approach in the fuzzy error analysis of planar and spatial mechanisms is also outlined. The treatment of the tolerances and clearances of the mechanism as interval numbers leads to a better and a more realistic estimation of the analysis results. Numerical examples are presented to illustrate the computational procedures. The results of the interval analysis, although philosophically different, are compared with those given by the probabilistic method for comparable input data; the differences found in the two sets of results are explained in terms of the basic characteristics of the two methods. This work denotes the first application of interval methods for the modeling of tolerances and clearances and the fuzzy error analysis of mechanisms.
Bistable Configurations of Compliant Mechanisms Modeled Using Four Links and Translational Joints
Authors: Jensen Brian D. , Howell Larry L.
Published: August 2004

Bistable mechanical devices remain stable in two distinct positions without power input. They find application in valves, switches, closures, and clasps. Mechanically bistable behavior results from the storage and release of energy, typically in springs, with stable positions occurring at local minima of stored energy. Compliant mechanisms offer an elegant way to achieve this behavior by incorporating both motion and energy storage into the same flexible element. Interest in compliant bistable mechanisms has also recently increased because of the advantages of bistable behavior in many micro-electro-mechanical systems (MEMS). Design of compliant or rigid-body bistable mechanisms typically requires simultaneous consideration of both energy storage and motion requirements. This paper simplifies this process by developing theory that provides prior knowledge of mechanism configurations that guarantee bistable behavior. Configurations which include one or more translational, or slider, joints are studied in this work. Several different mechanism types are analyzed to determine compliant segment placement that will ensure bistable mechanism operation. Examples demonstrate the power of the theory in design.
New Analytical Model of Bolted Joints
Authors: Zhang Ouqi , Poirier Jason A.
Published: August 2004

The conventional theory of bolted joints adopts equivalent cylinders, cones or spheres for compression members. In this model, the member deformation is determined by the member stiffness that remains unchanged whether the external load is present. In fact, the external load causes an additional member deformation that is not determined by the member stiffness measured at pre-load. The external load also causes a member rotation, which not only reduces the member stiffness, but also delays the separation of the joint. Based on these observations, a new model of bolted joints is developed. Finite element analyses is performed to verify the proposed model.
Rotor Balancing Without Trial Weights
Authors: El-Shafei A. , El-Kabbany A. S. , Younan A. A.
Published: August 2004

The traditional balancing methods using trial or calibration weights are quite effective, yet too many trials may result in a lengthy balancing process. It had been suggested in the literature that it is possible to balance flexible rotors without the use of trial weights, if a rotor model is available. A procedure is developed in this paper to balance flexible rotors using complex modes and complex vibration measurements. It is shown that a complex rotor model is essential for the success of the technique. Moreover, careful calibration of the rotor model is the major cornerstone of the procedure. Experimental results illustrate the success of the procedure.
Technical and Tariff Scenarios Effect on Microturbine Trigenerative Applications
Authors: Campanari Stefano , Macchi Ennio
Published: August 2004

The paper considers the use of gas fired micro turbine generators (MTG) for trigeneration (combined production of electricity, heating, and cooling) applications in tertiary buildings. The importance of the adopted MTG technology is investigated, showing that the high electrical efficiency levels achievable by future advanced ceramic MTGs would improve dramatically the economic competitiveness of the application, as well as the primary energy savings and environmental benefits. Calculations are performed by the simulation code TRIGEN, capable of optimizing the plant operating mode in each time step and integrating the results over the entire year. The requirement of a “target” energy saving index on the optimization procedure is also addressed.
Computational Modeling of Natural Gas Injection in a Large Bore Engine
Authors: Kim Gi-Heon , Kirkpatrick Allan , Mitchell Charles
Published: August 2004

The topic of this paper is the computational modeling of gas injection through various poppet valve geometries in a large bore engine. The objective of the paper is to contribute to a better understanding of the significance of the poppet valve and the piston top in controlling the mixing of the injected fuel with the air in the cylinder. In this paper, the flow past the poppet valve into the engine cylinder is computed for both a low (4 bar) and a high pressure (35 bar) injection process using unshrouded and shrouded valves. Experiments using PLIF (planar laser induced fluorescence) are used to visualize the actual fluid flow for the valve geometries considered. The results indicate that for low injection pressures the gas flow around a typical poppet valve collapses to the axis of symmetry of the valve downstream of the poppet. At high pressure, the gas flow from this simple poppet valve does not collapse, but rather expands outward and flows along the cylinder wall. At high pressures, addition of a shroud around the poppet valve was effective in directing the supersonic flow toward the center of the cylinder. Additional computations with a moving piston show that at top dead center, the flammable volume fraction and turbulence intensity with high pressure shrouded injection are larger than for low pressure injection.
Emissions Performance of the Parker Macrolaminate Premixer Tested Under Simulated Engine Conditions
Authors: Mansour Adel , Benjamin Michael A.
Published: August 2004

Single-injector high-pressure rig evaluation of the prototype Parker macrolaminate dual fuel premixer (previously tested at NETL, Mansour et al., 2001) with pressure swirl macrolaminate atomizers was conducted under simulated engine operating conditions running on No. 2 diesel fuel (DF2). Emissions, oscillations and lean blowout (LBO) performance on liquid fuel at high, part and no load operating points (pressures of 160, 100, 120 psig, and inlet temperatures of 690, 570, 590°F, respectively) and various pressure drops (ΔP/P) and air fuel ratio conditions were investigated. The results indicate that the Parker premixer design has the potential to reduce the DF2 NOX emission to below 15 ppmv, 15% O2. At simulated high load conditions with a nominal flame temperature TPZ of 2700°F, the NOX and CO emissions are approximately 10 and 2.5 ppmv at 15% O2, respectively. These NOX results have not been corrected for fuel bound nitrogen (FBN). From the studies of Lee (2000), small amounts of FBN in the liquid fuel generally are completely converted over to fuel NOX under lean premixed conditions. The fuel tested has a nominal 60 ppmw of FBN which converts to an estimated fuel NOX of 4 ppmv at 15% O2. These results compare extremely favorable to existing commercially available premixer technologies tested under similar rig operating conditions. More importantly, the NOX yield for the Parker Macrolaminate premixer appears to be independent of operating conditions (from high to no load and various pressure drop conditions). Variations in combustor pressure, inlet temperature T2 and residence time (τ) or pressure drop (ΔP/P) does not seem to have an effect on the formation of NOX. According to Leonard and Stegmaier (1993), insensitivity of NOX formation to operating conditions is a good indication of high degree of premixing. Additionally, the premixer NOX data is only 1 to 2 ppmv higher than the jet stirred reactor (JSR) results (ran at T2=661°F,PCD=1 atm and TPZ=2762°F with similar DF2) of Lee et al. (2001) further confirming the quality of premixing achieved. Combustion driven oscillations was not investigated by tuning the rig so that oscillations would not be a factor.
Aspects of Cooled Gas Turbine Modeling for the Semi-Closed O2/CO2 Cycle With CO2 Capture
Authors: Jordal Kristin , Bollard Olav , Klang Ake
Published: August 2004

In order to capture the behavior of the oxyfuel cycle operating with high combustor-outlet temperature, the impact of blade and vane cooling on cycle performance must be included in the thermodynamic model. As a basis for a future transient model, three thermodynamic models for the cooled gas turbine are described and compared. The first model, known previously from the literature, models expansion as a continuous process with simultaneous heat and work extraction. The second model is a simple stage-by-stage model and the third is a more detailed stage-by-stage model that includes velocity triangles and enables the use of advanced loss correlations. An airbreathing aeroderivative gas turbine is modeled, and the same gas turbine operating in an oxyfuel cycle is studied. The two simple models show very similar performance trends in terms of variation of pressure ratio and turbine inlet temperature in both cases. With the more detailed model, it was found that, without any change of geometry, the turbine rotational speed increases significantly and performance drops for the maintained geometry and pressure ratio. A tentative increase of blade angles or compressor pressure ratio is found to increase turbine performance and decrease rotational speed. This indicates that a turbine will require redesign for operation in the oxyfuel cycle.
Bacterial Persistence as a Phenotypic Switch
Authors: Balaban Nathalie Q. , Merrin Jack , Chait Remy , Kowalik Lukasz , Leibler Stanislas
Published: August 2004

A fraction of a genetically homogeneous microbial population may survive exposure to stress such as antibiotic treatment. Unlike resistant mutants, cells regrown from such persistent bacteria remain sensitive to the antibiotic. We investigated the persistence of single cells of
Escherichia coli
with the use of microfluidic devices. Persistence was linked to preexisting heterogeneity in bacterial populations because phenotypic switching occurred between normally growing cells and persister cells having reduced growth rates. Quantitative measurements led to a simple mathematical description of the persistence switch. Inherent heterogeneity of bacterial populations may be important in adaptation to fluctuating environments and in the persistence of bacterial infections.
The
eutT
Gene of
Salmonella enterica
Encodes an Oxygen-Labile, Metal-Containing ATP:Corrinoid Adenosyltransferase Enzyme
Authors: Buan Nicole R. , Suh Sang-Jin , Escalante-Semerena Jorge C.
Published: August 2004

The
eutT
gene of
Salmonella enterica
was cloned and overexpressed, and the function of its product was established in vivo and in vitro. The EutT protein has an oxygen-labile, metal-containing ATP:co(I)rrinoid adenosyltransferase activity associated with it. Functional redundancy between EutT and the housekeeping ATP:co(I)rrinoid adenosyltransferase CobA enzyme was demonstrated through phenotypic analyses of mutant strains. Lack of CobA and EutT blocked ethanolamine utilization. EutT was necessary and sufficient for growth of an
S. enterica cobA eutT
strain on ethanolamine as a carbon and energy or nitrogen source. A

eutT
+

gene provided in
trans
corrected the adenosylcobalamin-dependent transcription of a
eut
-
lacZ
operon fusion in a
cobA
strain. Cell extracts enriched for EutT protein contained strong, readily detectable ATP:co(I)rrinoid adenosyltransferase activity. The activity was only detected in extracts maintained under anoxic conditions, with complete loss of activity upon exposure to air or treatment with the Fe
2+
ion chelator bathophenanthroline. While the involvement of another metal ion cannot be ruled out, the observed sensitivity to air and bathophenanthroline suggests involvement of Fe
2+
. We propose that the EutT protein is a unique metal-containing ATP:co(I)rrinoid adenosyltransferase. It is unclear whether the metal ion plays a structural or catalytic role.
Sequence Diversity and Molecular Evolution of the Heat-Modifiable Outer Membrane Protein Gene (
ompA
) of
Mannheimia
(
Pasteurella
)
haemolytica
,
Mannheimia glucosida
, and
Pasteurella trehalosi
Authors: Davies Robert L. , Lee Inkyoung
Published: August 2004

The OmpA (or heat-modifiable) protein is a major structural component of the outer membranes of gram-negative bacteria. The protein contains eight membrane-traversing β-strands and four surface-exposed loops. The genetic diversity and molecular evolution of OmpA were investigated in 31
Mannheimia
(
Pasteurella
)
haemolytica
, 6
Mannheimia glucosida
, and 4
Pasteurella trehalosi
strains by comparative nucleotide sequence analysis. The OmpA proteins of
M. haemolytica
and
M. glucosida
contain four hypervariable domains located at the distal ends of the surface-exposed loops. The hypervariable domains of OmpA proteins from bovine and ovine
M. haemolytica
isolates are very different but are highly conserved among strains from each of these two host species. Fourteen different alleles representing four distinct phylogenetic classes, classes I to IV, were identified in
M. haemolytica
and
M. glucosida
. Class I, II, and IV alleles were associated with bovine
M. haemolytica
, ovine
M. haemolytica
, and
M. glucosida
strains, respectively, whereas class III alleles were present in certain
M. haemolytica
and
M. glucosida
isolates. Class I and II alleles were associated with divergent lineages of bovine and ovine
M. haemolytica
strains, respectively, indicating a history of horizontal DNA transfer and assortative (entire gene) recombination. Class III alleles have mosaic structures and were derived by horizontal DNA transfer and intragenic recombination. Our findings suggest that OmpA is under strong selective pressure from the host species and that it plays an important role in host adaptation. It is proposed that the OmpA protein of
M. haemolytica
acts as a ligand and is involved in binding to specific host cell receptor molecules in cattle and sheep.
P. trehalosi
expresses two OmpA homologs that are encoded by different tandemly arranged
ompA
genes. The
P. trehalosi ompA
genes are highly diverged from those of
M. haemolytica
and
M. glucosida
, and evidence is presented to suggest that at least one of these genes was acquired by horizontal DNA transfer.
DETECTING MULTIFRACTAL PROPERTIES IN ASSET RETURNS: THE FAILURE OF THE "SCALING ESTIMATOR"
Authors: LUX THOMAS
Published: August 2004

It has become popular recently to apply the multifractal formalism of statistical physics (scaling analysis of structure functions and f(α) singularity spectrum analysis) to financial data. The outcome of such studies is a nonlinear shape of the structure function and a nontrivial behavior of the spectrum. Eventually, this literature has moved from basic data analysis to estimation of particular variants of multifractal models for asset returns via fitting of the empirical τ(q) and f(α) functions. Here, we reinvestigate earlier claims of multifractality using four long time series of important financial markets. Taking the recently proposed multifractal models of asset returns as our starting point, we show that the typical "scaling estimators" used in the physics literature are unable to distinguish between spurious and "true" multiscaling of financial data. Designing explicit tests for multiscaling, we can in no case reject the null hypothesis that the apparent curvature of both the scaling function and the Hölder spectrum are spuriously generated by the particular fat-tailed distribution of financial data. Given the well-known overwhelming evidence in favor of different degrees of long-term dependence in the powers of returns, we interpret this inability to reject the null hypothesis of multiscaling as a lack of discriminatory power of the standard approach rather than as a true rejection of multiscaling. However, the complete "failure" of the multifractal apparatus in this setting also raises the question whether results in other areas (like geophysics) suffer from similar shortcomings of the traditional methodology.
HIGH-ORDER HARMONIC GENERATION OF HYDROGEN IN INTENSE LASER FIELD AND STRONG MAGNETIC FIELD
Authors: QIAO H. X. , ZOU Y. C. , ZHANG Z. J.
Published: August 2004

An effective one-dimensional model approach combining time-dependent pseudospectral method and Taylor expansion [Haoxue Qiao et al., Phys. Rev. A65, 063403 (2002)] is generalized to study a real hydrogen atom in an intense laser field. High-order harmonic generations are calculated in several cases of different laser field parameters. The ionization probability is also calculated. The influence of the strong magnetic field on harmonic generations is investigated. It is found that the plateau of high harmonics can be extended by the magnetic field and the cutoff order increases with the increase of the field intensity.
DYNAMICAL SIMULATIONS OF CARBON NANOTUBE BENDING
Authors: HUHTALA MARIA , KURONEN ANTTI , KASKI KIMMO
Published: August 2004

In this paper we present the results of a dynamical nanotube bending study. Carbon nanotube structures under constant rate bending have been studied using classical molecular dynamics simulations method, with the inter-atomic forces described by Brenner's empirical model potential. We show that the tube diameter and the prevalent temperature play an important role in the outcome. Some of the results have been assessed by letting the most deformed part of the nanotube further relax by using a dynamical tight binding method. Significant difference was found between the empirical and the tight binding models in predicting the structure.
EULER–LAGRANGE CORRESPONDENCE OF GENERALIZED BURGERS CELLULAR AUTOMATON
Authors: MATSUKIDAIRA JUNTA , NISHINARI KATSUHIRO
Published: August 2004

Recently, we have proposed a Euler–Lagrange transformation for cellular automata (CA) by developing new transformation formulas. Applying this method to the Burgers CA (BCA), we have succeeded in obtaining the Lagrange representation of the BCA. In this paper, we apply this method to multi-value generalized Burgers CA (GBCA) which include the Fukui–Ishibashi model and the quick-start model associated with traffic flow. As a result, we have succeeded in clarifying the Euler–Lagrange correspondence of these models. It turns out moreover that the GBCA can naturally be considered as a simple model of a multi-lane traffic flow.
SYMBOLIC COMPUTATION AND POSSIBLY OBSERVABLE EFFECTS FOR THE SOLITON-LIKE LIQUID WAVE PROPAGATION IN THE PRESENCE OF SURFACE TENSION
Authors: TIAN BO , GAO YI-TIAN
Published: August 2004

Phenomena on the liquid surfaces are of current importance, such as those for rivers, oceans, liquid propellant for rockets and aviation kerosene. Wave propagation on a liquid surface in the presence of surface tension is hereby investigated. Computerized symbolic computation, generalized hyperbolic-function method and Wu method are combined. Some soliton-like, exact analytic solutions are obtained for a recently-proposed (2+1)-dimensional 6th-order model. Possibly observable effects are also proposed, which certain future experiments may hopefully discover.
TWO-LANE TRAFFIC WITH PLACES OF OBSTRUCTION TO TRAFFIC
Authors: EBERSBACH ANJA , SCHNEIDER JOHANNES J.
Published: August 2004

As the Nagel–Schreckenberg model (NaSch model) became known as a realistic approach to describe traffic flow on single-lane streets, this model was extended to two-lane traffic by several groups. On the base of our two-lane model, we will now investigate the impact of a place of obstruction, e.g., because of road works, on partial fractions, densities and mean velocities.
CONTROLLING THE STATES OF TRAFFIC FLOW AT THE INTERSECTIONS
Authors: LI KEPING , GAO ZIYOU
Published: August 2004

In city network, the state of the traffic flow which is in front of each intersection is random and disorder. It usually leads to some traffic problems. In this paper, we propose a new technique to control such dynamical state of the traffic flow on a main road. A type of the control signal has been designated at a given site (signal point) in front of each intersection. Under the effect of the control signal, the velocities of the vehicles which pass the signal point will be changed. Our method is tested for the "unified" CA traffic model which is the marriage of the NaSch model and the BML model. The simulation results demonstrate that using this control strategy, when the traffic light is green, the disorder state of the traffic flow which is in front of each intersection can be suppressed, and the periodic state of the traffic flow will occur.
PATTERN RECOGNITION OF ONE-DIMENSIONAL CELLULAR AUTOMATA USING MARKOV CHAINS
Authors: SANCHEZ JUAN R.
Published: August 2004

A technique is presented for the identification of rule that generates a given complex pattern of linear one-dimensional cellular automata (LCA). The technique is based on the construction of a Markov transition matrix for the Markov chains that correspond to the evolution of the automaton. Such chain is generated by the evolution of a sequence of symbols representing the value of a string composed by small portion of the sites of the automaton. Excellent results are obtained for the identification of the rules that generate different complex patterns.
ADVERTISING, CONSENSUS, AND AGING IN MULTILAYER SZNAJD MODEL
Authors: SCHULZE CHRISTIAN
Published: August 2004

In the Sznajd consensus model on the square lattice, two people who agree in their opinions convince their neighbors of this opinion. We generalize it to many layers representing many age levels, and check if a consensus among all layers is possible. Advertising sometimes, but not always, produces a consensus on the advertised opinion.
CONTINUUM SPACE MODEL FOR FOLDING OF THE PROTEIN CRAMBIN
Authors: TANERI SENCER
Published: August 2004

We have studied the chain length dependence of folding time for proteins by implementing a novel Monte Carlo (MC) method. The physical parameters in our model are derived from the statistics for bending and torsion angles and distances between the centers of the monomers up to the fourth neighborhood. By assigning potential wells to each of the physical parameters, we are able to use a modified Metropolis algorithm to efficiently trace the later conformations of the proteins as time evolves. Our prescription for microscopic dynamics of the protein "Crambin" results in an increase of folding times with increasing chain length. The folding times are determined via Debye relaxation process.
CONSTRUCTING FAMILIES TRAVELING WAVE SOLUTIONS IN TERMS OF SPECIAL FUNCTION FOR THE ASYMMETRIC NIZHNIK–NOVIKOV–VESSELOV EQUATION
Authors: CHEN YONG , WANG QI
Published: August 2004

By means of a more general ansatz and the computerized symbolic system Maple, a generalized algebraic method to uniformly construct solutions in terms of special function of nonlinear evolution equations (NLEEs) is presented. We not only successfully recover the previously-known traveling wave solutions found by Fan's method, but also obtain some general traveling wave solutions in terms of the special function for the asymmetric Nizhnik–Novikov–Vesselov equation.
THE EQUILIBRIUM THERMODYNAMICS OF VARIOUS PEPTIDE SEQUENCES
Authors: YAŞAR FATİH
Published: August 2004

The equilibrium thermodynamic properties of two peptide sequences of β-casein in the α-helix regions were studied by three-dimensional molecular modeling in vacuum. All the three-dimensional conformations of each peptide sequences were obtained by multicanonical simulations using ECEPP/2 force field and each simulation was started from completely random initial conformation. No a-priori information about ground-state is used in the simulations. In the present study, we calculated the average values of total energy, specific heat, fourth-order cumulant for two peptide sequences of β-casein as a function of temperature. We observed that the specific heat shows two peaks as a function of temperature for both peptides. Because our sequences have highly helical structure and two peaks in the specific heat, we have also studied the helix–coil transitions to determine these peaks. Our data indeed show these peptides have highly helical structure and better agreement with the results of spectroscopic techniques and other prediction methods.
PARTICLE SPECTRUM OF THE SUPERSYMMETRIC STANDARD MODEL FROM THE MASSLESS EXCITATIONS OF A FOUR-DIMENSIONAL SUPERSTRING
Authors: DEO B. B. , MAHARANA L.
Published: August 2004

A superstring action is quantised with Neveu–Schwarz (NS) and Ramond (R) boundary conditions. The zero mass states of the NS sector are classified as the vector gluons, W-mesons, Bμ-mesons and scalars containing Higgs. 15 zero mass fermions are obtained from the Ramond sector. A spacetime supersymmetric Hamiltonian of the Standard Model is presented without any conventional SUSY particles.
A NEW ALTERNATIVE MODEL TO DARK ENERGY
Authors: GONG YUNGUI , CHEN XI-MING , DUAN CHANG-KUI
Published: August 2004

The recent observations of type Ia supernovae strongly support that the universe is accelerating now and decelerated in the recent past. This may be the evidence of the breakdown of the standard Friedmann equation. Instead of a linear function of the matter density, we consider a general function of the matter density to modify the Freidmann equation. We propose a new model which explains the recent acceleration and the past deceleration. Furthermore, the new model also gives a decelerated universe in the future. The new model gives Ω m 0=0.46 and z T =0.44.
SURVEILLANCE ON THE LIGHT-FRONT GAUGE-FIXING LAGRANGIANS
Authors: SUZUKI A. T. , SALES J. H. O.
Published: August 2004

In this work we propose two Lagrange multipliers with distinct coefficients for the light-front gauge that leads to the complete (non-reduced) propagator. This is accomplished via (n·A)2+(∂·A)2 terms in the Lagrangian density. These lead to a well-defined and exact though Lorentz non invariant light-front propagator.
CHIRAL N=1 4D ORIENTIFOLDS WITH D-BRANES AT ANGLES
Authors: HONECKER GABRIELE
Published: August 2004

D6-branes intersecting at angles allow for phenomenologically appealing constructions of four-dimensional string theory vacua. While it is straightforward to obtain non-supersymmetric realizations of the standard model, supersymmetric and stable models with three generations and no exotic chiral matter require more involved orbifold constructions. The T6/(ℤ4×ℤ2×Ωℛ) case is discussed in detail. Other orbifolds including fractional D6-branes are treated briefly.
EVENTS WITH ISOLATED CHARGED LEPTONS AND LARGE MISSING TRANSVERSE MOMENTUM AT HERA
Authors: CARLI TANCREDI , DANNHEIM DOMINIK , BELLAGAMBA LORENZO
Published: August 2004

Striking events with isolated charged leptons, large missing transverse momentum and large transverse momentum of the hadronic final state [Formula: see text] were observed at the electron proton collider HERA in a data sample corresponding to an integrated luminosity of about 130 pb-1. The H1 collaboration observed 11 events with isolated electrons or muons and with [Formula: see text]. Only 3.4±0.6 events were expected from Standard Model (SM) processes. Six of these events have [Formula: see text], while 1.3±0.3 events were expected. The ZEUS collaboration observed good agreement with the SM. However, ZEUS found two events with a similar event topology, but tau leptons instead of electrons or muons in the final state. Only 0.2±0.05 events were expected from SM processes. For various hypotheses, the compatibility of the experimental results was investigated with respect to the SM and with respect to possible explanations beyond the SM. Prospects for the high-luminosity HERA-II data taking period are given.
DIRECT CP VIOLATION AND NEW PHYSICS EFFECTS IN THE DECAY MODE B+→ϕK+
Authors: GIRI ANJAN K. , MOHANTA RUKMANI
Published: August 2004

We study the direct CP violation effect in the decay mode B+→ϕK+. This decay mode is dominated by the loop induced [Formula: see text] penguin diagram with a tiny contribution from the annihilation diagram. Therefore, the standard model expectation of direct CP violation is negligibly small. Using QCD factorization approach we find the CP asymmetry in the standard model to be at percent level. We consider then two scenarios beyond the standard model, the model with an extra vector-like down quark (VLDQ) and the R-parity violating supersymmetric model (RPV) and show that the direct CP violating asymmetry in B+→ϕK+ could be as large as ~ 85% (70%) in VLDQ (RPV) model.
A HYDROGENIC MOLECULAR ATMOSPHERE OF A NEUTRON STAR
Authors: TURBINER A. V. , LÓPEZ VIEYRA J. C.
Published: August 2004

A model of a hydrogenic content of atmosphere of the isolated neutron star 1E1207.4-5209 is proposed. It is based on the assumption that the main component in the atmosphere is the exotic molecular ion [Formula: see text] and that there exists a magnetic field in the range of (4±2)×1014 G . Photoionization [Formula: see text] and photodissociation [Formula: see text] correspond to two absorption features at 0.7 keV and 1.4 keV, respectively, discovered by Chandra observatory1 and confirmed by XMM–Newton.11 The model predicts one more absorption feature at 80–150 eV corresponding to photodissociation [Formula: see text].
PCR BY THERMAL CONVECTION
Authors: BRAUN DIETER
Published: August 2004

The Polymerase Chain Reaction (PCR) allows for highly sensitive and specific amplification of DNA. It is the backbone of many genetic experiments and tests. Recently, three labs independently uncovered a novel and simple way to perform a PCR reaction. Instead of repetitive heating and cooling, a temperature gradient across the reaction vessel drives thermal convection. By convection, the reaction liquid circulates between hot and cold regions of the chamber. The convection triggers DNA amplification as the DNA melts into two single strands in the hot region and replicates into twice the amount in the cold region. The amplification progresses exponentially as the convection moves on. We review the characteristics of the different approaches and show the benefits and prospects of the method.
COLLECTIVE DYNAMICS OF LIQUID Al
Authors: TEWARI S. P. , SOOD JYOTI
Published: August 2004

The recently suggested modified microscopic theory of liquids has been used successfully to explain the collective dynamics of liquid Al near its melting point. Considering the frequency-dependent self-diffusion coefficient occurring in the intermediate self-correlation function, which is inextricably linked with the collective dynamics of the system, the observed variation in dynamical structure factor of Al can be quantitatively reproduced for wave vector range 0.42 Å-1 to 1.38 Å-1 taking into account single relaxation time.
WHY DNA ELECTRICAL PROPERTIES CHANGE ON MOLECULAR OXYGEN DOPING: A QUANTUM-CHEMICAL STUDY
Authors: STARIKOV E. B.
Published: August 2004

A detailed semiempirical quantum-chemical study is reported on homogeneous adenosine-thymidine and guanosine-cytidine base pair steps, both pure ones and their complexes with oxygen molecules. The results of this study help gain detailed insight into physico-chemical mechanisms of electrical conduction control in DNA molecules when doping them with molecular oxygen or related molecules.
ANNEALING EFFECTS ON STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF MgB2/Fe WIRES
Authors: BALAMURUGAN S. , NAKAMURA T. , OSAMURA K. , MUTA I. , HOSHINO T.
Published: August 2004

We report the results of annealing effects on structural and superconducting properties (Tc and Jc) of various MgB 2/ Fe wires that are produced by different conditions. Good quality superconducting MgB 2/ Fe wires are fabricated by the powder-in-tube (PIT) technique at ambient pressure. XRD data confirms that they are hexagonal MgB 2 structure. All the annealed samples show higher Tc values in the range of 34.6–38.4 K with Jc higher than the as-rolled wire. The annealed samples show significant change in the Jc values as well as in micro-structural features due to variable sintering temperature. On annealing at 1050°C for 10 min, we obtain the best quality sample with a Jc of 37.2 kA/cm 2 at 33.1 K and self-field with a maximum Tc of 38.4 K. Among the samples annealed at 1050°C for 5–20 min, the 20 min sample shows lower Jc. Longer annealing time (at 1050°C) reduced Jc, indicating a possible interfacial reaction between the Fe sheath and the MgB 2 core.
STRUCTURE AND OPTICAL DAMAGE RESISTANCE IN In:Mn:Fe:LiNbO3 CRYSTALS
Authors: ZHEN XIHE , LI QIANG , XU YUHENG
Published: August 2004

A series of In : Mn : Fe : LiNbO 3 crystals were prepared with fixed concentrations of Fe 2 O 3, MnCO 3 and various concentrations of In 2 O 3. Their ultraviolet-visible (UV-Vis) absorption spectra were measured in order to investigate their defect structure. The optical damage resistance of In : Mn : Fe : LiNbO 3 crystals was characterized by the transmitted beam pattern distortion method. It increases remarkably when the concentration of In 2 O 3 is over its threshold concentration. The optical damage resistance of In (3.0 mol %): Mn : Fe : LiNbO 3 crystal is two orders of magnitude higher that of the Mn : Fe : LiNbO 3 crystal. The dependence of the defects on the optical damage resistance of the In : Mn : Fe : LiNbO 3 crystals was discussed.
IMPORTANCE OF CHARGE TRANSFER EXCITATIONS IN DNA ELECTRON SPECTRUM: A ZINDO SEMIEMPIRICAL QUANTUM-CHEMICAL STUDY
Authors: STARIKOV E. B.
Published: August 2004

Electron spectra of DNA model compounds, adenosine-thymidine and guanosine-cytidine nucleoside base pairs, as well as the relevant homogeneous stacked base pair steps in A-DNA and B-DNA conformations, were investigated using ZINDO semiempirical quantum-chemical method. This work confirms that, in DNA with intact Watson–Crick hydrogen bonding and base stacking, the highest occupied molecular orbitals (HOMO) are residing on purine base residues, whereas the lowest unoccupied molecular orbitals (LUMO) — on pyrimidine base residues. In general, the present results are satisfactorily comparable with the available experimental data. The role of charge transfer excitations in the polymer DNA 260 nm spectral band is discussed.
METHODS OF SHARED KEY AGREEMENT IN COHERENT MULTIPLEXING
Authors: KIM AJUNG
Published: August 2004

A method of shared secret key distribution applicable to optical coherent multiplexing systems is proposed. It provides ways to detect the extent of eavesdropping. Detecting test factors and system design rules are suggested, and performance evaluation is performed in terms of mutual information between legitimate users and an eavesdropper. This scheme devises a new way of attaining secure optical communications without entirely relying on computational complexity.
THE TRANSPORT PROPERTIES OF NANOTUBES AND ITS CURVATURE EFFECTS
Authors: ZHANG SHENGLI , ZHANG ERHU , ZHAO SHUMIN , XIA MINGGANG
Published: August 2004

The transport properties across contacts between quantum tubes and metals are studied. The curvature effects on the transmission are also considered. We find that the transmission probability of an electron transporting from the tube into the metal through the contact can be close to 100%. The curvature has a larger effect on the transmission for smaller radii and the effects decrease as the radii increase.
STRUCTURAL INVESTIGATIONS OF CuO–B2O3–Bi2O3 GLASSES BY MEANS OF EPR AND FT-IR SPECTROSCOPIES
Authors: ARDELEAN I. , CORA SIMONA , CICEO-LUCACEL RALUCA
Published: August 2004

EPR and FT-IR spectroscopy have been used to investigate the B 2 O 3– Bi 2 O 3 glass matrix containing CuO in order to obtain more information about the local structure of these glasses. The EPR absorption spectra revealed the presence in the glass structure of the Cu 2+ ions in axially distorted octahedral environments. No superexchange interaction of Cu 2+ was detected. In the samples with x≥5 mol%, mixed valence states of copper ions were revealed. The FT-IR measurements indicate the presence in the glass structure of the distorted [ BiO 6] polyhedra, tri- and tetra-borate units ( BO 3, BO 4) and its dependence by the copper content.
Detection of intracellular superoxide formation in endothelial cells and intact tissues using dihydroethidium and an HPLC-based assay
Authors: Fink Bruno , Laude Karine , McCann Louise , Doughan Abdul , Harrison David G. , Dikalov Sergey
Published: August 2004

Recently, it was demonstrated that superoxide oxidizes dihydroethidium to a specific fluorescent product (oxyethidium) that differs from ethidium by the presence of an additional oxygen atom in its molecular structure (Zhao H, Kalivendi S, Zhang H, Joseph J, Nithipatikom K, Vásquez-Vivar J, and Kalyanaraman B. Free Radic Biol Med 34: 1359–1368, 2003). We have adapted this new HPLC-based assay to quantify this product as a tool to estimate intracellular superoxide in intact tissues. Ethidium and oxyethidium were separated using a C-18 column and quantified using fluorescence detection. Initial cell-free experiments with potassium superoxide and xanthine oxidase confirmed the formation of oxyethidium from dihydroethidium. The formation of oxyethidium was inhibited by superoxide dismutase but not catalase and did not occur upon the addition of H2O2, peroxynitrite, or hypochlorous acid. In bovine aortic endothelial cells (BAEC) and murine aortas, the redox cycling drug menadione increased the formation of oxyethidium from dihydroethidium ninefold (0.4 nmol/mg in control vs. 3.6 nmol/mg with 20 μM menadione), and polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) significantly inhibited this effect. Treatment of BAEC with angiotensin II caused a twofold increase in oxyethidium formation, and this effect also was reduced by PEG-SOD (0.5 nmol/mg). In addition, in the aortas of mice with angiotensin II-induced hypertension and DOCA-salt hypertension, the formation of oxyethidium was increased in a manner corresponding to superoxide production estimated on the basis of cytochrome c reduction. Detection of oxyethidium using HPLC represents a new, convenient, quantitative method for the detection of superoxide in intact cells and tissues.
Hypothesis: one rate-limiting step controls the magnitude of both phases of glucose-stimulated insulin secretion
Authors: Straub Susanne G. , Sharp Geoffrey W. G.
Published: August 2004

The biphasic secretory response of pancreatic β-cells to abrupt and sustained exposure to glucose is well documented. Some of the ATP-sensitive K+ (KATP) channel-dependent mechanisms underlying the first phase of insulin release are known; the mechanisms underlying the second phase are less well known. The hypothesis we propose is that one rate-limiting step, controlling the conversion of granules in a readily releasable (RR) docked granule pool to an immediately releasable (IR) pool, is responsible for the magnitude of both phases of release. Furthermore, we propose that the KATP channel-independent signaling pathway regulates this rate-limiting step. The size of the IR pool of granules that constitutes the first phase is determined under resting conditions by the forward and reverse rates of conversion of granules in the RR and IR pools. The resulting equilibrium position determines the maximum number of β-cell granules available for release during the first phase upon exposure to glucose. At the nadir between the two phases, the IR pool has been depleted so that the rate of granule release is equal to the low forward rate for the conversion of RR to IR granules. After the nadir, the forward rate is accelerated during the rising portion of the second phase until it reaches a maximum rate at the plateau.
Functional expression of heterologous proteins in yeast: insights into Ca2+ signaling and Ca2+-transporting ATPases
Authors: Ton Van-Khue , Rao Rajini
Published: August 2004

The baker's yeast Saccharomyces cerevisiae is a well-developed, versatile, and widely used model organism. It offers a compact and fully sequenced genome, tractable genetics, simple and inexpensive culturing conditions, and, importantly, a conservation of basic cellular machinery and signal transducing pathways with higher eukaryotes. In this review, we describe recent technical advances in the heterologous expression of proteins in yeast and illustrate their application to the study of the Ca2+ homeostasis machinery, with particular emphasis on Ca2+-transporting ATPases. Putative Ca2+-ATPases in the newly sequenced genomes of organisms such as parasites, plants, and vertebrates have been investigated by functional complementation of an engineered yeast strain lacking endogenous Ca2+ pumps. High-throughput screens of mutant phenotypes to identify side chains critical for ion transport and selectivity have facilitated structure-function analysis, and genomewide approaches may be used to dissect cellular pathways involved in Ca2+ transport and trafficking. The utility of the yeast system is demonstrated by rapid advances in the study of the emerging family of Golgi/secretory pathway Ca2+,Mn2+-ATPases (SPCA). Functional expression of human SPCA1 in yeast has provided insight into the physiology, novel biochemical characteristics, and subcellular localization of this pump. Haploinsufficiency of SPCA1 leads to Hailey-Hailey disease (HDD), a debilitating blistering disorder of the skin. Missense mutations, identified in patients with HHD, may be conveniently assessed in yeast for loss-of-function phenotypes associated with the disease.
Effect of intracellular pH on depolarization-evoked calcium influx in human sperm
Authors: Fraire-Zamora Juan J. , González-Martínez Marco T.
Published: August 2004

Human sperm are endowed with putative voltage-dependent calcium channels (VDCC) that produce measurable increases in intracellular calcium concentration ([Ca2+]i) in response to membrane depolarization with potassium. These channels are blocked by nickel, inactivate in 1–2 min in calcium-deprived medium, and are remarkably stimulated by NH4Cl, suggesting a role for intracellular pH (pHi). In a previous work, we showed that calcium permeability through these channels increases approximately onefold during in vitro “capacitation,” a calcium-dependent process that sperm require to fertilize eggs. In this work, we have determined the pHi dependence of sperm VDCC. Simultaneous depolarization and pHi alkalinization with NH4Cl induced an [Ca2+]i increase that depended on the amount of NH4Cl added. VDCC stimulation as a function of pHi showed a sigmoid curve in the 6.6–7.2 pHi range, with a half-maximum stimulation at pH ∼7.00. At higher pHi (≥7.3), a further stimulation occurred. Calcium release from internal stores did not contribute to the stimulating effect of pHi because the [Ca2+]i increase induced by progesterone, which opens a calcium permeability pathway that does not involve gating of VDCC, was unaffected by ammonium. The ratio of pHi-stimulated-to-nonstimulated calcium influx was nearly constant at different test depolarization values. Likewise, depolarization-induced calcium influx in pHi-stimulated and nonstimulated cells was equally blocked by nickel. In our capacitating conditions pHi increased 0.11 pH units, suggesting that the calcium influx stimulation observed during sperm capacitation might be partially caused by pHi alkalinization. Additionally, a calcium permeability pathway triggered exclusively by pHi alkalinization was detected.
The behavior of peroxisomes in vitro: mammalian peroxisomes are osmotically sensitive particles
Authors: Antonenkov Vasily D. , Sormunen Raija T. , Hiltunen J. Kalervo
Published: August 2004

It has been known for a long time that mammalian peroxisomes are extremely fragile in vitro. Changes in the morphological appearance and leakage of proteins from purified particles demonstrate that peroxisomes are damaged during isolation. However, some properties of purified peroxisomes, e.g., the latency of catalase, imply that their membranes are not disrupted. In the current study, we tried to ascertain the mechanism of this unusual behavior of peroxisomes in vitro. Biochemical and morphological examination of isolated peroxisomes subjected to sonication or to freezing and thawing showed that the membrane of the particles seals after disruption, restoring permeability properties. Transient damage of the membrane leads to the formation of peroxisomal “ghosts” containing nucleoid but nearly devoid of matrix proteins. The rate of leakage of matrix proteins from broken particles depended inversely on their molecular size. The effect of polyethylene glycols on peroxisomal integrity indicated that these particles are osmotically sensitive. Peroxisomes suffered an osmotic lysis during isolation that was resistant to commonly used low-molecular-mass osmoprotectors, e.g., sucrose. Damage to peroxisomes was partially prevented by applying more “bulky” osmoprotectors, e.g., polyethylene glycol 1500. A method was developed for the isolation of highly purified and nearly intact peroxisomes from rat liver by using polyethylene glycol 1500 as an osmoprotector.