bluuebunny/crossref_metadata_2025 huggingface dataset:
Loss of MicroRNA Targets in the 3′ Untranslated Region as a Mechanism of Retroviral Insertional Activation of Growth Factor Independence 1
Authors: Dabrowska Magdalena Julia , Dybkaer Karen , Johnsen Hans Erik , Wang Bruce , Wabl Matthias , Pedersen Finn Skou
Published: May 2009

The non-oncogene-bearing retrovirus SL3-3 murine leukemia virus induces strictly T-cell lymphomas with a mean latency of 2 to 4 months in mice of the NMRI-inbred (NMRI-i) strain. By high-throughput sequencing of retroviral tags, we have identified the genomic region carrying the transcriptional repressor and oncogene growth factor independence 1 (
Gfi1
) as a frequent target for SL3-3 in the NMRI-i mouse genome. Twenty-four SL3-3 insertions were identified within a 1-kb window of the 3′ untranslated region (3′UTR) of the
Gfi1
gene, a clustering pattern unique for this lymphoma model. Expression analysis determined that the
Gfi1
gene was transcriptionally activated by SL3-3 insertions, and an upregulation of Gfi1 protein expression was detected for tumors harboring insertions in the
Gfi1
3′UTR. Here we provide data in support of a mechanism by which retroviral insertions in the
Gfi1
3′UTR decouple microRNA-mediated posttranscriptional regulation.
Complete Virion Assembly with Scaffolding Proteins Altered in the Ability To Perform a Critical Conformational Switch
Authors: Cherwa James E. , Fane Bentley A.
Published: May 2009

In the φX174 procapsid, 240 external scaffolding proteins form a nonquasiequivalent lattice. To achieve this arrangement, the four structurally unique subunits must undergo position-dependent conformational switches. One switch is mediated by glycine residue 61, which allows a 30° kink to form in α-helix 3 in two subunits, whereas the helix is straight in the other two subunits. No other amino acid should be able to produce a bend of this magnitude. Accordingly, all substitutions for G61 are nonviable but mutant proteins differ vis-à-vis recessive and dominant phenotypes. As previously reported, amino acid substitutions with side chains larger than valine confer dominant lethal phenotypes. Alone, these mutant proteins appear to have little or no biological activity but rather require the wild-type protein to interact with other structural proteins. Proteins with conservative substitutions for G61, serine and alanine, have now been characterized. Unlike the dominant lethal proteins, these proteins do not require wild-type subunits to interact with other viral proteins and cause assembly defects reminiscent of those conferred by the lethal dominant proteins in concert with wild-type subunits. Although atomic structures suggest that only a glycine residue can provide the proper torsion angle for assembly, mutants that can productively utilize the altered external scaffolding proteins were isolated, and the mutations were mapped to the coat and internal scaffolding proteins. Thus, the ability to isolate strains that could utilize the single mutant D protein species would not have been predicted from past structural analyses.
Human Bocavirus Can Be Cultured in Differentiated Human Airway Epithelial Cells
Authors: Dijkman Ronald , Koekkoek Sylvie M. , Molenkamp Richard , Schildgen Oliver , van der Hoek Lia
Published: May 2009

In 2005, a human bocavirus was discovered in children with respiratory tract illnesses. Attempts to culture this virus on conventional cell lines has failed thus far. We investigated whether the virus can replicate on pseudostratified human airway epithelium. This cell culture system mimics the human airway environment and facilitates culturing of various respiratory agents. The cells were inoculated with human bocavirus-positive nasopharyngeal washes from children, and virus replication was monitored by measuring apical release of the virus via real-time PCR. Furthermore, we identified different viral mRNAs in the infected cells. All mRNAs were transcribed from a single promoter but varied due to alternative splicing and alternative polyadenylation, similar to what has been described for bovine parvovirus and minute virus of canines, the other two members of the
Bocavirus
genus. Thus, transcription of human bocavirus displays strong homology to the transcription of the other bocaviruses. In conclusion, we report here for the first time that human bocavirus can be propagated in an in vitro culture system and present a detailed map of the set of mRNAs that are produced by the virus.
The Lipidomes of Vesicular Stomatitis Virus, Semliki Forest Virus, and the Host Plasma Membrane Analyzed by Quantitative Shotgun Mass Spectrometry
Authors: Kalvodova Lucie , Sampaio Julio L. , Cordo Sandra , Ejsing Christer S. , Shevchenko Andrej , Simons Kai
Published: May 2009

Although enveloped virus assembly in the host cell is a crucial step in the virus life cycle, it remains poorly understood. One issue is how viruses include lipids in their membranes during budding from infected host cells. To analyze this issue, we took advantage of the fact that baby hamster kidney cells can be infected by two different viruses, namely, vesicular stomatitis virus and Semliki Forest virus, from the
Rhabdoviridae
and
Togaviridae
families, respectively. We purified the host plasma membrane and the two different viruses after exit from the host cells and analyzed the lipid compositions of the membranes by quantitative shotgun mass spectrometry. We observed that the lipid compositions of these otherwise structurally different viruses are virtually indistinguishable, and only slight differences were detected between the viral lipid composition and that of the plasma membrane. Taken together, the facts that the lipid compositions of the two viruses are so similar and that they strongly resemble the composition of the plasma membrane suggest that these viruses exert little selection in including lipids in their envelopes.
John N. Brady (1952-2009): a Generous Spirit
Authors: Enquist Lynn W.
Published: May 2009

John N. Brady, Chief of the Virus Tumor Biology Section of the Laboratory of Cellular Oncology, National Institutes of Health, died of cancer on 27 April 2009. John was a stellar member of the virology community. He was a longtime
Journal of Virology
reviewer and a member of the editorial board. He will be missed. Fatah Kashanchi of the George Washington University Medical Center has written John's memorial. Fatah worked with John at the NIH and published more than 30 papers with him. Fatah thanks all the people who contributed to John's obituary, including Kuan-Teh Jeang, Lou Laimins, Mary Loeken, Renaud Mehieux, Paul Lambert, Graziella Piras, Scott Gitlin, Paul Lindholm, Nadia Rosenthal, Sergi Nekhai, Brian Wigdahl, David Price, Susan J. Marriott, Cynthia Masison, Jurgen Dittmer, Eric Verdin, Bassel E. Sawaya, and John's longtime assistants Janet Duvall Grimm and Michael Radonovich, who gave immense support to all the individuals who went through John's lab.
Changes in recruitment of transversus abdominis correlate with disability in people with chronic low back pain
Authors: Ferreira P H , Ferreira M L , Maher C G , Refshauge K , Herbert R D , Hodges P W
Published: May 2009

Objectives

Although motor control exercises have been shown to be effective in the management of low back pain (LBP) the mechanism of action is unclear. The current study investigated the relationship between the ability to recruit transversus abdominis and clinical outcomes of participants in a clinical trial.

Methods

Ultrasonography was used to assess the ability to recruit transversus abdominis in a nested design: a sample of 34 participants with chronic LBP was recruited from participants in a randomised controlled trial comparing the efficacy of motor control exercise, general exercise and spinal manipulative therapy. Perceived recovery, function, disability and pain were also assessed.

Results

Participants with chronic LBP receiving motor control exercise had a greater improvement in recruitment of transversus abdominis (7.8%) than participants receiving general exercise (4.9% reduction) or spinal manipulative therapy (3.7% reduction). The effect of motor control exercise on pain reduction was greater in participants who had a poor ability to recruit transversus abdominis at baseline. There was a significant, moderate correlation between improved recruitment of transversus abdominis and a reduction in disability (r = −0.35; 95% CI 0.02 to 0.62).

Conclusion

These data provide some support for the hypothesised mechanism of action of motor control exercise and suggest that the treatment may be more effective in those with a poor ability to recruit transversus abdominis.
A Deep Excavation and a Raft Foundation in Soft Clay
Authors: Insley A.
Published: May 2009

This is a case history describing a deep braced excavation in which a fully compensated raft foundation was constructed. The foundation soil is the Victoria marine clay, which is a soft normally consolidated deposit 70–100 ft (21–30 m) thick at this site. Observations were made on the deflections of the bracing and the heave of the excavation and were considered a necessary part of the design. Observations have also been kept on the settlement of the building foundation for over [Formula: see text] years. The calculated safety factors used in bracing design and foundation design are compared against the actual performance.
Instrumented Foundations for two 43-storey Buildings on Till, Metropolitan Toronto
Authors: Trow W. , Bradstock J.
Published: May 2009

Settlement records have been obtained for a two-year period during and following construction of two 43-storey buildings in mid-town Metro Toronto, Ontario. One structure is supported on caissons varying in length from 45 to 70 ft (13.7 to 21.3 m) long, belled to a maximum of 12 ft (3.7 m) diameter and supported on dense silt till. The other is supported upon a raft foundation above the till. Protected rods have been inserted in four heavily loaded caissons to determine total settlement as well as differential settlement along the concrete shaft. Settlement devices have been installed at two levels in the till below the raft foundation and a pattern of differential settlement under the building has been established. It appears that all load has reached the base of the caissons and therefore that no load of consequence is being taken by the massive caisson caps or by the shafts. The settlement under the raft follows the flexible foundation pattern only approximately. In both buildings there appears to be load redistribution due to rigidity.
The stability of slopes in soils with nonlinear failure envelopes
Authors: Charles J. A. , Soares M. M.
Published: May 2009

The failure envelopes of many soils are significantly nonlinear and the effect of this curvature on slope stability is examined. Charts, based on circular arc stability analyses, have been prepared and make possible the rapid assessment of the stability of slopes of simple geometry in uniform soils with curved failure envelopes. The effect on the factor of safety against stability failure of (i) the degree of curvature of the failure envelope of the soil, (ii) the magnitude of the pore pressure ratio within the slope, and (iii) the depth to a hard stratum has been investigated. Key words: depth factor, pore pressure, safety factor, shear strength, slope, stability.
The undrained equilibrium behaviour of gassy sediments
Authors: Sobkowicz J. C. , Morgenstern N. R.
Published: May 2009

Gassy soils are defined as those soils which contain a relatively large amount of gas dissolved in the pore fluid. Examples include the Alberta Oil Sands, marine sediments from deep ocean locations, geopressure reservoirs along the Gulf Coast, and other naturally occurring, gas-charged reservoirs.The equilibrium behaviour during unloading with undrained boundary conditions is examined. Contrary to conventional experience with soils containing only a small amount of gas, gassy soils exhibit an equilibrium pore pressure response close to zero. Effective stress, and hence strength, decrease commensurately with total stress at the soil boundary.Laboratory observations of gassy soil behaviour are presented, which confirm the predictive accuracy of the theoretical model. Parameters important to the determination of gassy soil behaviour include the in situ state of stress (σ0 and u0), the liquid/gas saturation pressure (ul/g), the gas solubility (H), saturation (S), and the soil and liquid compressibilities (βT and βL). Key words: undrained, pore pressure, compressibility, gas, shear strength, unloading, laboratory, ex-solution.
Repetitive load testing: reversal or rotation
Authors: McDonald L. M. , Raymond G. P.
Published: May 2009

Permanent way support systems (roads, airfields, railways) subject to moving load, soil deposits subject to earthquakes, and soil beneath offshore structures subject to wave loading are classical examples of field situations where the soils will experience varying degrees of principal stress rotation. To assess the effects of this principal stress rotation, comparisons were made between the responses of a dry sand when subjected to stress-controlled repetitive triaxial and repetitive simple shear testing. Based on findings from this test program, an attempt was made to analyse the deformation response of a model footing simulating the railway field situation.Principal stress rotation was shown to be a major factor influencing the behaviour of dry granular material when subjected to repetitive load, the effect of which was to induce permanent deformation while the elastic response remained unchanged. The applicability of repetitive triaxial and repetitive simple shear testing in these circumstances is shown to be complex, and rational design methods for field situations involving repetitive loads have been reevaluated. Key words: principal stress rotation, repetitive load, repeated load, cyclic load, granular, triaxial test, simple shear test.
Geochemical reactions associated with low-temperature thermal energy storage in aquifers
Authors: Palmer Carl D. , Cherry John A.
Published: May 2009

The geochemical mass transfer model WATEGM-SE is used to illustrate by example potential chemical reactions that can occur at a hypothetical low-temperature thermal energy aquifer storage facility. Important processes that control the chemistry include heating and cooling of the water, equilibration of the pumped water with the atmospheric partial pressure of CO2 and O2, and the mixing of the injection water with the native groundwater during the injection, storage, and recovery cycles. For the given example, 0.3 mmol/L of calcite would be precipitated under closed system pumping and heating from 10 to 50 °C while a total of 1.9 mmol/L would be precipitated under the open condition. If this calcite were to form scale within the facility's piping then considerable lengths can be affected depending on the pumping rate. Alternatively, if the precipitate is kept in suspension it will be transported to the injection well and will be filtered out by the aquifer itself. This filtration can result in significant decreases in porosity and hence permeability in the immediate vicinity of the injection well. Mixing of the injection water with the native groundwater changes the water chemistry and can result in mineral supersaturation or undersaturation depending on the composition of these waters and the proportions in which they are mixed. The effect of mixing on the given example is undersaturation with respect to calcite and supersaturation with respect to amorphous Fe(OH)3. The pe values in the simulations of mixtures of an oxidizing injection water and a reducing native groundwater yielded some results with significantly higher pe values than the oxidizing injection water. The use of equilibrium geochemical mass transfer models tempered by an understanding of their limitations may prove to be an effective tool for evaluation of potential chemical reactions associated with low-temperature aquifer thermal energy storage facilities. Key words: thermal energy storage, geochemical equilibria, groundwater, simulation, scale formation, mixing.
On stability of slopes in clays with linearly increasing strength
Authors: Koppula Sivajogi D.
Published: May 2009

The study deals with the analysis, using the circular arc failure mechanism, of the stability of slopes in normally consolidated clays whose strengths are finite at the top and vary linearly with depth. The results are presented in terms of a dimensionless stability number that is dependent on the slope inclination and cohesion ratio. Stability charts are presented for several values of cohesion ratio and slope inclination and will provide the first-order design solution(s) in preparation for more complex numerical analyses. The reappraisal of a case history based on the study results yields reasonable agreement with a previous study. An illustrative procedure for the design of cuttings in normally consolidated clays is provided. Key words: circular failure surface, design example, normally consolidated clays, slope stability.
Unconventional concepts for dykes and dams on soft clay foundation
Authors: Eide O. , Lacasse S. , Kjærnsli B. , Hafskjold P. S.
Published: May 2009

As an alternative to a stage-construction embankment dyke equipped with vertical drains, two buttress-type concrete dams are proposed for deep, soft clay deposits where the building of embankment dykes would involve serious difficulties and sizable expenditures. These concepts avoid the loading of the soft clay deposit with high embankments and thus reduce problems of stability and settlement. High embankment dykes may not be feasible in the case of sloping ground, even gently so, because of the lack of stability in a flake-type sliding. The advantages of the proposed concept include the absence of soil improvement measures, shorter construction time, and reduced settlements. Specific drawbacks relate to the lack of experience with buttress-type dams on soft clay foundations. Key words: dam, clay, concrete, earth pressure, embankment, pile.
The Canadian program for sealing underground nuclear fuel waste vaults
Authors: Lopez R. S. , Cheung S. C. H. , Dixon D. A.
Published: May 2009

The general objective of the Canadian Nuclear Fuel Waste Management Program is the safety assessment of the disposal of nuclear reactor wastes in underground vaults mined in plutonic rock formations of the Canadian Shield. The isolation of waste forms from the surface environment is effected by a system of multiple additive barriers, each one engineered to a high degree of excellence. In successive order, these barriers are the container, the buffer, the backfill of vault openings, shaft and drift seals, and plugs in boreholes.The buffer is primarily a chemical barrier designed to retard the migration of chemical species that may corrode the containers, and also the outward migration of radionuclides in case of container failure. The buffer is an engineered mixture of high-purity expandable clays and sand or crushed rock. The backfill material in drifts and shafts is primarily a physical barrier, designed to stabilize the rock excavations and to retard the movement of radionuclides by advection.Specially designed drift and shaft seals are being considered, to enhance the function of the backfill. The seals are engineered barriers that may include reinforced concrete bulkheads, compacted clay and sand plugs, and grouting of the surrounding rock. Key words: nuclear fuel waste, underground disposal, engineered barriers, swelling clay, buffer, backfill, shaft seals.
IMPACT OF PROCESSING AND POLARIZATION ON DIELECTRIC BEHAVIOR OFNixMn0.4-xZn0.6Fe2O4SPINEL FERRITES
Authors: MATHUR P. , THAKUR A. , SINGH M.
Published: May 2009

In this paper, dielectric properties of NixMn0.4-xZn0.6Fe2O4ferrites with x varying from 0.05 to 0.35 prepared by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. A decrease in the dielectric constant is observed with the increase in Ni concentration except for x = 0.3. This decrease in dielectric constant with the increase in Ni concentration is justified by inverse proportionality between resistivity and dielectric constant. Dispersion in the dielectric constant with frequency in the range of 75 Hz to 30 MHz is observed. Resonance peaks were observed in tan δεversus frequency curve for all the samples. A shift in the resonance frequency toward higher frequency is observed with the increase in temperature. The peak height also increases with an increase in temperature. Phase change is confirmed by differential scanning calorimetry. Structural studies have been done by X-ray diffraction technique and scanning electron microscopy. Possible theories, models, and mechanisms contributing to these processes have been discussed.
POSSIBLE POSITRONIUM FORMATION IN THE COLLISIONS OF POSITRONS WITH CALCIUM AND STRONTIUM POSITIVE IONS
Authors: EL-BAKRY SALAH YASEEN
Published: May 2009

The inelastic collisions of positrons with calcium and strontium positive ions are treated for the first time as a three-channel problem within the framework of the improved coupled-static and frozen-core approximations with the assumption that the elastic, ground positronium and excited-positronium formation channels are open. The calculations of the partial and total cross sections are carried out for eight values of the total angular momentum ℓ (0 ≤ ℓ ≤7), at 20 values of the incident energy lying above the excited positronium formation threshold and extending to a wide region above the ionization threshold of the target ion. The total collisional positronium formation cross sections of e+– Sr+scattering show a peak around the ionization threshold of Sr+but display a peak at 30 eV for e+– Ca+scattering. In both scattering problems the total excited Ps formation cross sections have considerable values in the energy range [Formula: see text].
INFLUENCE OF EXTINCTION RATIO ON THE PERFORMANCE OF RZ-ODPASK MODULATION FORMAT
Authors: LI XIAOJUN , WEN AIJUN , LIU ZENGJI , SHANG TAO
Published: May 2009

The influence of extinction ratio (ER) on the performance of 120 Gbps return-to-zero octal differential phase-amplitude-shift keying (RZ-ODPASK) modulation format in single-channel transmission is investigated. Based on the modulation and demodulation schemes, the structures of RZ-ODPASK transmitter and receiver are presented; and expressions for the output optical fields and electrical currents of amplitude and phase tributaries are analytically acquired. As ER is a tradeoff for good performance of the two tributaries, the optimal ER for back-to-back configuration is theoretically derived as 2.32 dB for the first time, which is verified by simulation. Then the tolerances to residual chromatic dispersion (CD) and fiber nonlinearity of RZ-ODPASK transmission are numerically studied, respectively. The results indicate that phase tributary is more robust against both dispersion and nonlinearity impairment than the amplitude tributary. To balance the performance of the two tributaries, curves of the optimal ER values with the change of residual CD and fiber nonlinearity are also obtained, respectively. The results can be useful for the design of RZ-ODPASK systems; in the meantime, the analytical methodology described in this paper is applicable to other multilevel RZ-DPASK modulation formats.
HE'S ITERATION PERTURBATION METHOD TO NONLINEAR OSCILLATIONS OF MECHANICAL SYSTEMS WITH SINGLE-DEGREE-OF FREEDOM
Authors: GANJI D. D. , KARIMPOUR S. , GANJI S. S.
Published: May 2009

In this study, an accurate analytical solution for the nonlinear free vibration of a conservative oscillator with inertia and static type cubic nonlinearities is derived. This solution has been obtained using Iteration Perturbation method (IPM). This study shows that IPM leads to an accurate analytical solution, which is valid for a wide range of considered system parameters. The excellent accuracy of current results is demonstrated by comparing with available analytical and numerical results.
JOINT ENTROPY OF THE HARMONIC OSCILLATOR WITH TIME-DEPENDENT MASS AND/OR FREQUENCY
Authors: AKTÜRK ETHEM , ÖZCAN ÖZGÜR , SEVER RAMAZAN
Published: May 2009

Time-dependent joint entropy is obtained for harmonic oscillator with the time-dependent mass and frequency case. It is calculated by using time-dependent wave function obtained via Feynman path integral method. Variation of time dependence is investigated for various cases.
NONLOCAL ELECTRONIC SPIN DETECTION, SPIN ACCUMULATION AND THE SPIN HALL EFFECT
Authors: VALENZUELA SERGIO O.
Published: May 2009

In recent years, electrical spin injection and detection has grown into a lively area of research in the field of spintronics. Spin injection into a paramagnetic material is usually achieved by means of a ferromagnetic source, whereas the induced spin accumulation or associated spin currents are detected by means of a second ferromagnet or the reciprocal spin Hall effect, respectively. This article reviews the current status of this subject, describing both recent progress and well-established results. The emphasis is on experimental techniques and accomplishments that brought about important advances in spin phenomena and possible technological applications. These advances include, amongst others, the characterization of spin diffusion and precession in a variety of materials, such as metals, semiconductors and graphene, the determination of the spin polarization of tunneling electrons as a function of the bias voltage, and the implementation of magnetization reversal in nanoscale ferromagnetic particles with pure spin currents.
PULSATING INSTABILITIES OF COMBUSTION WAVES IN A CHAIN-BRANCHING REACTION MODEL
Authors: GUBERNOV V. V. , KOLOBOV A. V. , POLEZHAEV A. A. , SIDHU H. S. , MERCER G. N.
Published: May 2009

In this paper we investigate the properties and linear stability of traveling premixed combustion waves and the formation of pulsating combustion waves in a model with two-step chain-branching reaction mechanism. These calculations are undertaken in the adiabatic limit, in one spatial dimension and for the case of arbitrary Lewis numbers for fuel and radicals. It is shown that the Lewis number for fuel has a significant effect on the properties and stability of premixed flames, whereas varying the Lewis number for the radicals has only qualitative (but not qualitative) effect on the combustion waves. We demonstrate that when the Lewis number for fuel is less than unity, the flame speed is unique and is a monotonically decreasing function of the dimensionless activation energy. Moreover, in this case, the combustion wave is stable and exhibits extinction for finite values of activation energy as the flame speed decreases to zero. However, for the fuel Lewis number greater than unity, the flame speed is a C-shaped and double valued function. The linear stability of the traveling wave solution was determined using the Evans function method. The slow solution branch is shown to be unstable whereas the fast solution branch is stable or exhibits the onset of pulsating instabilities via a Hopf bifurcation. The critical parameter values for the Hopf bifurcation and extinction are found and the detailed map for the onset of pulsating instabilities is determined. We show that a Bogdanov—Takens bifurcation is responsible for both the change in the behavior of the traveling wave solution near the point of extinction from unique to double valued type as well as for the onset of pulsating instabilities. We investigate the properties of the Hopf bifurcation and the emerging pulsating combustion wave solutions. It is demonstrated that the Hopf bifurcation observed in our present study is of supercritical type. We show that the pulsating combustion wave propagates with the average speed smaller than the speed of the traveling combustion wave and at certain parameter values the pulsating wave exhibits a period doubling bifurcation.
THE DISCRETE HYPERCHAOTIC DOUBLE SCROLL
Authors: ELHADJ ZERAOULIA , SPROTT J. C.
Published: May 2009

In this paper we present and analyze a new piecewise linear map of the plane capable of generating chaotic attractors with one and two scrolls. Due to the shape of the attractor and its hyperchaoticity, we call it "the discrete hyperchaotic double scroll." It has the same nonlinearity as used in the well-known Chua circuit. A rigorous proof of the hyperchaoticity of this attractor is given and numerically justified.
BOUNDING A DOMAIN THAT CONTAINS ALL COMPACT INVARIANT SETS OF THE BLOCH SYSTEM
Authors: STARKOV KONSTANTIN E.
Published: May 2009

In this paper we consider the localization problem of compact invariant sets of the Bloch system describing dynamics of an ensemble of spins in an external magnetic field. Our main results are related to finding a domain containing all compact invariant sets of the Bloch system. This domain is described as an intersection of one-parameter set of balls with two half spaces. Further, we describe the location of periodic orbits respecting two circular paraboloids and one semipermeable plane. In addition, we find conditions under which the origin is the unique compact invariant set. Finally, taking the Bloch system in cylindrical coordinates we construct one first integral for some specific restriction imposed on its parameters and, we also establish conditions under which this system has no compact invariant sets.
A MULTI-VARIABLE POLYNOMIAL INVARIANT FOR UNORIENTED VIRTUAL KNOTS AND LINKS
Authors: MIYAZAWA YASUYUKI
Published: May 2009

We construct a multi-variable polynomial invariant Y for unoriented virtual links as a certain weighted sum of polynomials, which are derived from virtual magnetic graphs with oriented vertices, on oriented virtual links associated with a given virtual link. We show some features of the Y-polynomial including an evaluation of the virtual crossing number of a virtual link.
A VIRTUAL LINK POLYNOMIAL AND THE VIRTUAL CROSSING NUMBER
Authors: MIYAZAWA YASUYUKI
Published: May 2009

We construct a multi-variable polynomial invariant for virtual knots and links by using the concepts of a decorated virtual magnetic graph diagram and a weight map. We show that the invariant is a variety of virtual link polynomial with multiple variables introduced in [16] by the author and it gives a sharpened evaluation of the virtual crossing number of a virtual knot or link.
THE QUANTUM TEICHMÜLLER SPACE AS A NONCOMMUTATIVE ALGEBRAIC OBJECT
Authors: LIU XIAOBO
Published: May 2009

We consider the quantum Teichmüller space of the punctured surface introduced by Chekhov–Fock–Kashaev, and formalize it as a noncommutative deformation of the space of algebraic functions on the Teichmüller space of the surface. In order to apply it in 3-dimensional topology, we put more attention to the details involving small surfaces.
QUINTOM COSMOLOGY WITH GENERAL POTENTIALS
Authors: SETARE M. R. , SARIDAKIS E. N.
Published: May 2009

We investigate the phase space structure of the quintom paradigm in the framework of a spatially flat, open or closed isotropic and homogeneous universe. We examine the dynamical evolution under the assumption of late time dark energy domination, without specifying the explicit quintom potential form. The obtained cosmological behavior is qualitatively different than that acquired from the single phantom model.
CAN A HYPERBOLIC PHASE OF THE BRANS–DICKE FIELD ACCOUNT FOR DARK MATTER?
Authors: ARIK M. , ÇALIK M. , ÇIFTER F.
Published: May 2009

We show that the introduction of a hyperbolic phase of the Brans–Dicke (BD) field results in a flat vacuum cosmological solution of the Hubble parameter H and a fractional rate of change of the BD scalar field F, which asymptotically approach constant values. At later stages, the hyperbolic phase of the BD field behaves like dark matter.
ON KALUZA–KLEIN SPACE–TIME IN EINSTEIN–GAUSS–BONNET GRAVITY
Authors: MOLINA ALFRED , DADHICH NARESH
Published: May 2009

By considering the product of the usual four-dimensional space–time with two dimensional space of constant curvature, an interesting black hole solution has recently been found for Einstein–Gauss–Bonnet gravity. It turns out that this as well as all others could easily be made to radiate Vaidya null dust. However, there exists no Kerr analog in this setting. To get the physical feel of the four-dimensional black hole space–times, we study asymptotic behavior of stresses at the two ends, r → 0 and r → ∞.
ON THE DYNAMICS OF A QUADRATIC SCALAR FIELD POTENTIAL
Authors: UREÑA-LÓPEZ L. ARTURO , REYES-IBARRA MAYRA J.
Published: May 2009

We review the attractor properties of the simplest chaotic model of inflation, in which a minimally coupled scalar field is endowed with a quadratic scalar potential. The equations of motion in a flat Friedmann–Robertson–Walker universe are written as an autonomous system of equations, and the solutions of physical interest appear as critical points. This new formalism is then applied to the study of inflation dynamics, in which we can go beyond the known slow-roll approximation.
RECORDS THEORY
Authors: ANDERSON EDWARD
Published: May 2009

In quantum gravity, one seeks to combine quantum mechanics and general relativity. In attempting to do so, one comes across the "problem of time" impasse: the notion of time is conceptually different in each of these theories. In this paper, I consider the timeless records approach to resolving this. Records are localized, information-containing subconfigurations of a single instant. Records theory is the study of these and of how science (or history) is to be abstracted from correlations between them. I critically evaluate motivations for this approach that have previously appeared in the literature. I provide a ground-level structure for records theory and discuss what kind of further tools are needed, illustrated with some toy models: ordinary mechanics, relational particle dynamics, detector models and inhomogeneous perturbations about homogeneous cosmology.
GRAVITATION AND THERMODYNAMICS: THE EINSTEIN EQUATION OF STATE REVISITED
Authors: MÄKELÄ JARMO , PELTOLA ARI
Published: May 2009

We perform an analysis where Einstein's field equation is derived by means of very simple thermodynamical arguments. Our derivation is based on a consideration of the properties of a very small, spacelike two-plane in a uniformly accelerating motion.
ENTREPRENEURIAL INCLINATIONS OF VOCATIONAL EDUCATION STUDENTS: A COMPARATIVE STUDY OF MALE AND FEMALE TRAINEES IN IRINGA REGION, TANZANIA
Authors: OLOMI DONATH R. , SINYAMULE ROSE S.
Published: May 2009

This study examined entrepreneurial inclinations among vocational training centres (VTCs) using a sample of 508 trainees from 12 VTCs in Iringa region, central Tanzania. A majority of VTC trainees have interest in starting own businesses, motivated primarily by the need to have control over their own lives. While gender and having taken entrepreneurship courses have no significant effects on start-up inclinations, perceived chances of getting a job and background of entrepreneurial family are positively associated with interest in entrepreneurial intention. Results suggest a need to re-examine entrepreneurship training in VET and for policy makers to be careful in promoting entrepreneurship as an alternative career for those unable to secure paid jobs.
DOES PERCEPTUAL ACUITY MATTER? — AN INVESTIGATION OF ENTREPRENEURIAL ORIENTATION, PERCEPTUAL ACUITY, AND FIRM PERFORMANCE
Authors: TANG ZHI , ROTHENBERG SANDRA
Published: May 2009

One critical proposition in normative strategic management research is that an accurate perception of the environment by top managers is a prerequisite to attaining better organizational performance. However, recent entrepreneurship studies suggest that entrepreneurs are often leading or even causing environmental changes, and thus they may perceive greater industrial instability than there actually is. In this project, we examine if an over-perception of industrial instability exists among entrepreneurs. If it does, which perceptual mode (accurate perception versus over-perception) will benefit firm performance? We conducted the study in a highly volatile environment — China — and found that entrepreneurial orientation (EO) had an inverse U-shape relationship with perceptual acuity of industrial instability, indicating that a greater level of EO indeed led to an over-perception of industrial instability. However, we found that although perceptual acuity of industrial instability improved firm sales, it was negatively associated with organizational effectiveness evaluated by top managers. Additional analyses were conducted and implications were provided in the end.
THE DEVELOPMENT OF ENTREPRENEURSHIP AND PRIVATE ENTERPRISE IN THE PEOPLE'S REPUBLIC OF CHINA AND ITS RELEVANCE TO TRANSITIONAL ECONOMIES
Authors: HE XIAOHONG
Published: May 2009

This paper aims to study the issues and unique characteristics surrounding the birth and development of the private sector in the People's Republic of China (China); analyze the interaction of entrepreneurial behavior and the country's unique and continuously changing regulatory and institutional environment; examine the actions, outcomes, and composition of this emerging entrepreneurial class; and analyze the implications for entrepreneurship research in transitional economies. The paper offers a model built on a dynamic and transitional cycle. Using this model, the paper examines how uncertainties, ambiguities, and changing regulatory environments may create opportunities, bolstering the entrepreneurial class as well as an impressive private sector in a country where entrepreneurs and private business can be at odds with socialist ideology and culture in addition to many regulatory and institutional obstacles. Rather than relying upon limited survey data targeted at specific locations, industries, or time periods, this study is based on seven large-scale surveys conducted from 1993 to 2006 in both urban and rural areas extending horizontally across different industries in China, with a primary focus on private business. The findings are relevant for future research and government policy in transitional economies.
EVALUATING THE MOTIVES OF INFORMAL ENTREPRENEURS: SOME LESSONS FROM UKRAINE
Authors: WILLIAMS COLIN C. , ROUND JOHN , RODGERS PETER
Published: May 2009

To understand entrepreneurs' motivations, it has become increasingly common to distinguish between those driven by necessity (or pushed) and those driven by opportunity (or pulled) into entrepreneurship. Until now, entrepreneurs operating wholly or partially in the informal economy have been widely assumed to be necessity-driven, pushed into this enterprise as a survival strategy in the absence of alternatives. To evaluate whether this is indeed the case, this paper reports one of the first surveys of informal entrepreneurs' motives. Reporting face-to-face interviews conducted in Ukraine during 2005–06 with 298 informal entrepreneurs, the finding is although most identified themselves as necessity entrepreneurs when initially asked whether they were either pushed or pulled, subsequent questions reveal in the vast majority of cases, there were not only both push and pull factors driving their original decision to start-up informal enterprises, but also a clear shift among these entrepreneurs as their business became established away from necessity-oriented motivations and toward more opportunity-oriented motivations. The outcome is a call for a transcendence of a static either/or approach and the adoption of a dynamic both/and approach that recognizes the coexistence of necessity- and opportunity-drivers as well as the fluidity of entrepreneurs' motivations.
FORCE GENERATION BY MICROTUBULE BUNDLES
Authors: HUSSON JULIEN , LAAN LIEDEWIJ , DOGTEROM MARILEEN
Published: May 2009

Dynamic microtubule bundles are involved in several motility processes in cells, for instance by interacting with mitotic chromosomes. The study of microtubule bundle dynamics and force generation can help understanding the mechanisms underlying these complex processes. Here we discuss experimental results on the force-generating capabilities of bundles of non-crosslinked growing microtubules obtained using an optical tweezers technique in vitro. We discuss the possible effects on force generation by these microtubule bundles of specific (with microtubule-associated proteins) and aspecific (with ions or crowding agents) ways of crosslinking microtubules. We present preliminary results showing that force generation by microtubule bundles is enhanced in the presence of polyethylene glycol used as a crowding agent, and discuss possible explanations for this observation.
MICROTUBULE-KINESIN MECHANICS BY MOLECULAR MODELING
Authors: SONCINI MONICA , VOTTA EMILIANO , APRODU IULIANA , ENEMARK SØREN , REDAELLI ALBERTO , DERIU MARCO A. , MONTEVECCHI FRANCO M.
Published: May 2009

The cellular cytoskeleton contains microtubules which function both as fundamental structural elements as well as motor protein tracks. While the structural property is connected to the properties of the tubulin dimer, its interactions with surrounding dimers and the geometric organization within the microtubule, the transport track properties are related to the interactions between the tubulin dimer and kinesin.

Based on the atomistic structures of kinesin and the tubulin dimer, we used molecular modeling to examine the interaction energy and force as function of a spatial distance of separation. From the results, elastic constants describing the system stiffness are obtained. By using the results related to the structure alone, a model of a 1 μm long microtubule is constructed as a network of elastic elements, and its mechanical properties were obtained via finite element method and compared to experimental results.

Concerning microtubule-kinesin complex, the interaction strength during a complete cycle of ATP hydrolysis was investigated. As expected, the affinity between the proteins is modulated by the type of nucleotide occupying the nucleotide binding pocket of the motor protein. The work underscores how molecular modeling can provide fundamental protein information in terms of the relation between mechanical properties and structural changes.
ON THE RELEVANCE OF THE CORE HELIX ALPHA 6 TO KINESIN ACTIVITY GENERATION
Authors: KALCHISHKOVA NIKOLINA , BÖHM KONRAD J.
Published: May 2009

KIF5A and Eg5 are plus-end directed motor proteins with conserved motor domains. The catalytic cores of both motors comprise a central β-sheet consisting of eight β-strands surrounded by six α-helices. Notwithstanding the high level of similarity in their structural organization, Eg5 moves significantly slower than KIF5A. Recently, we reported that neck linker and neck elements of KIF5A and Eg5 contribute to velocity regulation. As the neck linker of both motors is known to be connected to the catalytic core via helix α6, the question arises if also helix α6 and strand β8 as the last core elements might be involved in velocity regulation. To elucidate the role these structures in kinesin activity generation we constructed KIF5A- and Eg5-based chimeras in which the β8 strand, helix α6, the neck linker, and the neck were interchanged. Additionally, we studied the role of α6 and β8 in ATP hydrolysis and microtubule binding by expression of truncated KIF5A and Eg5 constructs lacking both strand β8 and helix α6, or α6 only. The results obtained suggest that strand β8 and helix α6 are not involved in microtubule-binding, but α6 is an obligate and kinesin type-specific structure required to generate ATPase activity.
MOTOR PROTEIN DRIVEN MICROTUBULE TRANSPORT ON GOLD PARTICLE NANOPATTERNS
Authors: BLÜMMEL JACQUES , CAHU JULIE , SANDBLAD LINDA , SCHMITZ CHRISTIAN , SURREY THOMAS , SPATZ JOACHIM P.
Published: May 2009

Novel glass surfaces with quasi-hexagonally arranged gold nanoparticles to control motor protein immobilisation and motor protein dependent microtubule transport were applied. We first show that the kinesin-like motor protein Eg5 adsorbs efficiently and selectively to gold nanodots comprising a molecular motor nanopattern, while the glass surface between nanodots is passivated by a layer of polyethylene glycol in order to reduce non-specific interactions of individual motors with the substrate. We show that the motor nanopattern and density is indeed controlled by the gold nanodot density. We then use these motor protein arrays to investigate the kinetics of microtubule transport and find that the characteristics of the molecular motor nanopattern influence the characteristics of microtubule transport. This finding describes new biomimetic surfaces of molecularly controlled motor protein surface densities.
Importance of melastatin-like transient receptor potential 7 and magnesium in the stimulation of osteoblast proliferation and migration by platelet-derived growth factor
Authors: Abed Elie , Moreau Robert
Published: May 2009

Bone is a dynamic tissue that is continuously being remodeled throughout life. Specialized cells called osteoclasts transiently break down old bone (resorption process) at multiple sites as other cells known as osteoblasts are replacing it with new tissue (bone formation). Usually, both resorption and formation processes are in balance and thereby maintain skeletal strength and integrity. This equilibrium is assured by the coordination of proliferation, migration, differentiation, and secretory functions of the osteoblasts, which are essential for adequate formation and resorption processes. Disturbances of this equilibrium may lead to decreased bone mass (osteoporosis), increased bone fragility, and susceptibility to fractures. Epidemiological studies have linked insufficient dietary magnesium (Mg2+) intake in humans with low bone mass and osteoporosis. Here, we investigated the roles of Mg2+ and melastatin-like transient receptor potential 7 (TRPM7), known as Mg2+ channels, in human osteoblast cell proliferation and migration induced by platelet-derived growth factor (PDGF), which has been involved in the bone remodeling process. PDGF promoted an influx of Mg2+, enhanced cell migration, and stimulated the gene expression of TRPM7 channels in human osteoblast MG-63 cells. The stimulation of osteoblast proliferation and migration by PDGF was significantly reduced under culture conditions of low extracellular Mg2+ concentrations. Silencing TRPM7 expression in osteoblasts by specific small interfering RNA prevented the induction by PDGF of Mg2+ influx, proliferation, and migration. Our results indicate that extracellular Mg2+ and TRPM7 are important for PDGF-induced proliferation and migration of human osteoblasts. Thus Mg2+ deficiency, a common condition among the general population, may be associated with altered osteoblast functions leading to inadequate bone formation and the development of osteoporosis.