bluuebunny/crossref_metadata_2025 huggingface dataset:
Unusual Grüneisen and Bridgman parameters of low-density amorphous ice and their implications on pressure induced amorphization
Authors: Andersson Ove , Inaba Akira
Published: March 2005

The low-temperature limiting value of the Grüneisen parameter for low-frequency phonons and the density dependence of the thermal conductivity (Bridgman parameter) of low-density amorphous (LDA) ice, high-density amorphous (HDA) ice, hexagonal ice Ih, and cubic ice Ic were calculated from high-pressure sound velocity and thermal conductivity measurements, yielding negative values for all states except HDA ice. LDA ice is the first amorphous state to exhibit a negative Bridgman parameter, and negative Grüneisen parameters are relatively unusual. Since Ih, Ic, and LDA ice all transform to HDA upon pressurization at low temperatures and share the unusual feature of negative Grüneisen parameters, this seems to be a prerequisite for pressure induced amorphization. We estimate that the Grüneisen parameter increases at the ice Ih to XI transition, and may become positive in ice XI, which indicates that proton-ordered ice XI does not amorphize like ice Ih on pressurization.
Quantum dynamics in the highly discrete, commensurate Frenkel Kontorova model: A path-integral molecular dynamics study
Authors: Krajewski Florian R. , Müser Martin H.
Published: March 2005

The commensurate Frenkel Kontorova (FK) model is studied using path-integral molecular dynamics (PIMD). We focus on the highly discrete case, in which the embedding potential has a much greater maximum curvature than the harmonic potential connecting two particles in the FK chain. When efficient sampling methods are used, the dynamical interpretation of adiabatic PIMD appears to represent quite accurately the true time correlation functions of this highly correlated many-body system. We have found that the discrete, quantum FK model shows different behavior than its continuum version. The spectral density does not show the characteristic ω−2Θ(ω−ωc) cusp of the continuum solution in the pinned phase (m>mc). We also identify a dynamical quantum hysteresis in addition to the regular classical hysteresis when an external force is applied to the FK chain. In the unpinned phase (m⩽mc), we find a linear response damping coefficient which is finite and only weakly dependent on temperature T at small values of T.
A coarse-grained model for double-helix molecules in solution: Spontaneous helix formation and equilibrium properties
Authors: Tepper Harald L. , Voth Gregory A.
Published: March 2005

A new reductionist coarse-grained model is presented for double-helix molecules in solution. As with such models for lipid bilayers and micelles, the level of description is both particulate and mesoscopic. The particulate (bead-and-spring) nature of the model makes for a simple implementation in standard molecular dynamics simulation codes and allows for investigation of thermomechanic properties without preimposing any (form of) response function. The mesoscopic level of description—where groups of atoms are condensed into coarse-grained beads—causes long-range interactions to be effectively screened, which greatly enhances the efficiency and scalability of simulations. Without imposing local or global order parameters, a linear initial configuration of the model molecule spontaneously assembles into a double helix due to the interplay between three contributions: hydrophobic/hydrophilic interactions between base pairs, backbone, and solvent; phosphate-phosphate repulsion along the backbone; and favorable base-pair stacking energy. We present results for the process of helix formation as well as for the equilibrium properties of the final state, and investigate how both depend on the input parameters. The current model holds promise for two routes of investigation: First, within a limited set of generic parameters, the effect of local (atomic-scale) perturbations on overall helical properties can be systematically studied. Second, since the efficiency allows for a direct simulation of both small and large (>100 base pairs) systems, the model presents a testground for systematic coarse-graining methods.
A comparative ab initio study of intramolecular proton transfer in model α-hydroxyalkoxides
Authors: Parra Rubén D. , Dukarevich Igor
Published: March 2005

A comparative ab initio study was performed on the intramolecular proton-transfer reaction that occurs in α-hydroxyethanoxy, α-hydroxyphenoxide, and α-hydroxyethenoxy anions. The intramolecular proton transfer occurs in a five-member atom arrangement, between two oxygen atoms separated by a carbon–carbon bond. The chosen systems serve as models for α-hydroxyalkoxide molecules where the carbon–carbon bond varies from a single bond (the glycolate anion or α-hydroxyethanoxide anion) to a part of an aromatic ring (the α-hydroxyphenoxide anion), and finally to a double bond (the α-hydroxyethenoxide anion). Particular attention was given to the evolution along the intrinsic reaction coordinate of such properties as energies, relevant structural parameters, Mulliken charges, dipole moments, and H1-NMR chemical shifts to reveal the similarities and differences for the proton transfer in the model systems.
The quadrupole moment of the 3∕2+ nuclear ground state of Au197 from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state
Authors: Schwerdtfeger Peter , Bast Radovan , Gerry Michael C. L. , Jacob Christoph R. , Jansen Martin , Kellö Vladimir , Mudring Anja V. , Sadlej Andrzej J. , Saue Trond , Söhnel Tilo , Wagner Friedrich E.
Published: March 2005

An attempt is made to improve the currently accepted muonic value for the Au197 nuclear quadrupole moment [+0.547(16)×10−28m2] for the 3∕2+ nuclear ground state obtained by Powers et al. [Nucl. Phys. A230, 413 (1974)]. From both measured Mössbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60×10−28m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the Au197 isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the Au197 nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples [CCSD(T) level of theory] for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD(T) procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers [Inorg. Chem. 40, 6123 (2001)] a significantly enhanced Au197 nuclear quadrupole coupling constant in (CO)AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD(T) calculations finally give a nuclear quadrupole moment of +0.64×10−28m2 for Au197. It is argued that it is currently very difficult to improve on the already published muonic value for the Au197 nuclear quadrupole moment.
Laser spectroscopy of Si3C
Authors: Stanton John F. , Dudek John , Theulé Patrice , Gupta Harshal , McCarthy M. C. , Thaddeus P.
Published: March 2005

The C̃B11←X̃A11 band system of the potential interstellar species Si3C has been recorded in a silane/acetylene discharge by resonant two-color two-photon ionization spectroscopy. The origin band is located near 24925cm−1 (3.09eV). Several other features in the spectrum are assigned to progressions in the Si–Si stretching modes as well as to sequence and hot band transitions. The assignment was facilitated by ab initio calculations, which also indicate that this is the strongest electronic transition of Si3C in the visible region of the spectrum. Features in the spectrum are broadened considerably (ca. 10cm−1), and suggest an excited state lifetime of a few picoseconds. Possible reasons for the short-lived nature of the excited state are discussed.
Rydberg electron transfer to C6H5NO2: Lifetimes and characteristics of the product C6H5NO2− ions
Authors: Suess L. , Liu Y. , Parthasarathy R. , Dunning F. B.
Published: March 2005

The nature of electron binding in C6H5NO2− ions produced by Rydberg electron transfer in K(np)∕C6H5NO2 collisions is investigated through measurements of the number and the lifetimes of the product ions and their dependence on Rydberg atom velocity and principal quantum number n in the range 12≲n≲30. The data are interpreted by comparison to results obtained using well-known dipole-bound and valence-bound anions. At high n direct capture into valence-bound states with a lifetime of ∼1.6ms is observed. At low n the data suggest that, while direct capture into valence-bound states is still possible, the majority of the observed C6H5NO2− ions result from the onset of a second reaction channel that involves the formation of a dipole-bound “doorway” state that rapidly evolves into a state with predominantly valence-bound character. These findings are discussed in the light of earlier work on electron binding to C6H5NO2.
Theoretical modeling of vibroelectronic quantum states in complex molecular systems: Solvated carbon monoxide, a test case
Authors: Amadei Andrea , Marinelli Fabrizio , D’Abramo Marco , D’Alessandro Maira , Anselmi Massimiliano , Di Nola Alfredo , Aschi Massimiliano
Published: March 2005

In this paper we extend the perturbed matrix method by explicitly including the nuclear degrees of freedom, in order to treat quantum vibrational states in a perturbed molecule. In a previous paper we showed how to include, in a simple way, nuclear degrees of freedom for the calculation of molecular polarizability. In the present work we extend and generalize this approach to model vibroelectronic transitions, requiring a more sophisticated treatment.
Ground and excited electronic state thermodynamics of aqueous carbon monoxide: A theoretical study
Authors: D’Alessandro Maira , Marinelli Fabrizio , D’Abramo Marco , Aschi Massimiliano , Di Nola Alfredo , Amadei Andrea
Published: March 2005

By using the quasi Gaussian entropy theory in combination with molecular dynamics simulations and the perturbed matrix method, we investigate the ground and excited state thermodynamics of aqueous carbon monoxide. Results show that the model used is rather accurate and provides a great detail in the description of the excitation thermodynamics.
Stochastic fluctuations in gene expression far from equilibrium: Ω expansion and linear noise approximation
Authors: Tao Yi , Jia Yuting , Dewey T. Gregory
Published: March 2005

The Ω expansion of the master equation is used to investigate the intrinsic noise in an autoregulatory gene expression system. This Ω expansion provides a mesoscale description of the system and is used to analyze the effect of feedback regulation on intrinsic noise when the system state is far from equilibrium. Using the linear noise approximation, analytic results are obtained for a single gene system with linear feedback that is far from equilibrium. Additionally, analytic expressions are obtained for nonlinear systems near equilibrium. Simulations of such autoregulatory reaction schemes with nonlinear feedback show that during the approach to equilibrium the noise is not always reduced by the strength of the feedback. This is contrary to results seen in the equilibrium limit which show decreased noise with feedback strength. These results demonstrate that the behavior of linearized systems near equilibrium cannot be readily applied to systems far from equilibrium and highlight the need to explore nonequilibrium domains in mesoscopic systems.
Colloid-induced structure in liquid crystal media
Authors: Sokolovska T. G. , Sokolovskii R. O. , Patey G. N.
Published: March 2005

The structural perturbations induced by colloidal particles immersed in a model nematic subjected to an external field are calculated employing integral equation methods. Maps of the density-orientational distribution about a colloidal particle are obtained, and these provide a microscopic picture of the colloid’s nematic coat. We focus on colloidal particles that favor homeotropic anchoring, but planar anchoring cases are also considered. The range and structure of the nematic coat is shown to be significantly influenced by the nature of the anchoring, the size of the colloidal particle, the range and strength of the colloid-nematogen interaction, and the external field strength. All of these factors are discussed.
Integral encounter theory of strong electron transfer
Authors: Feskov S. V. , Ivanov A. I. , Burshtein A. I.
Published: March 2005

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong.
On toric geometry, Spin(7) manifolds, and type II superstring compactifications
Authors: Belhaj Adil , Rasmussen Jørgen
Published: March 2005

We consider type II superstring compactifications on the singular Spin(7) manifold constructed as a cone on SU(3)∕U(1). Based on a toric realization of the projective space CP2, we discuss how the manifold can be viewed as three intersecting Calabi–Yau conifolds. The geometric transition of the manifold is then addressed in this setting. The construction is readily extended to higher dimensions where we speculate on possible higher-dimensional geometric transitions. Armed with the toric description of the Spin(7) manifold; we discuss a brane∕flux duality in both type II superstring theories compactified on this manifold.
On a classification of irreducible almost commutative geometries, a second helping
Authors: Jureit Jan-Hendrik , Stephan Christoph A.
Published: March 2005

We complete the classification of almost commutative geometries from a particle physics point of view given by Iochum, Schücker, and Stephan, J. Math. Phys. (to be published). Four missing Krajewski diagrams will be presented after a short introduction into irreducible, nondegenerate spectral triples.
Improvement of uncertainty relations for mixed states
Authors: Park Yong Moon
Published: March 2005

We study a possible improvement of uncertainty relations. The Heisenberg uncertainty relation employs commutator of a pair of conjugate observables to set the limit of quantum measurement of the observables. The Schrödinger uncertainty relation improves the Heisenberg uncertainty relation by adding the correlation in terms of anti-commutator. However both relations are insensitive whether the state used is pure or mixed. We improve the uncertainty relations by introducing additional terms which measure the mixtureness of the state. For the momentum and position operators as conjugate observables and for the thermal state of quantum harmonic oscillator, it turns out that the equalities in the improved uncertainty relations hold.
Subpicosecond optical switching in polystyrene opal
Authors: Liu Yuanhao , Hu Xiaoyong , Zhang Dongxiang , Cheng Bingying , Zhang Daozhong , Meng Qingbo
Published: April 2005

An ultrafast all-optical switching is demonstrated in an organic three-dimensional nonlinear photonic crystal with a response time as short as 120 fs. The operating wavelength of the optical switching is in the visible spectrum. The switching function is realized by a shift of the photonic band gap under optical pumping. It is found that the photonic band gap shifts about 10 nm with the excitation of 27.5GW∕cm2 pump laser.
Effect of hydrogen passivation on charge storage in silicon quantum dots embedded in silicon nitride film
Authors: Cho Chang-Hee , Kim Baek-Hyun , Kim Tae-Wook , Park Seong-Ju , Park Nae-Man , Sung Gun-Yong
Published: March 2005

The effect of hydrogen passivation on the charge storage characteristics of two types of silicon nitride films containing silicon quantum dots (Si QDs) grown by SiH4+N2 and SiH4+NH3 plasma was investigated. The transmission electron microscope analysis and the capacitance-voltage measurement showed that the silicon nitride film grown by SiH4+NH3 plasma has a lower interface trap density and a higher density of Si QDs compared to that grown by SiH4+N2 plasma. It was also found that the charge retention characteristics in the Si QDs were greatly enhanced in the samples grown by means of SiH4+NH3 plasma, due to the hydrogen passivation of the defects in the silicon nitride films by NH3 during the growth of the Si QDs.
Controlled orientation of liquid-crystalline polythiophene semiconductors for high-performance organic thin-film transistors
Authors: Wu Yiliang , Liu Ping , Ong Beng S. , Srikumar Tharan , Zhao Ni , Botton Gianluigi , Zhu Shiping
Published: March 2005

The silane self-assembled monolayer (SAM) modification of a SiO2 gate dielectric surface improved the molecular ordering of organic channel semiconductor in organic thin-film transistors (OTFTs), leading to a significant improvement in transistor performance. Mobility of up to 0.18cm2∕Vs (current on∕off ratio of 107) was obtained for OTFTs with a liquid-crystalline polythiophene semiconductor built on an octyltrichlorosilane-modified SiO2 gate dielectric layer, a 450 times improvement over those built on a nonmodified dielectric layer. The mobility enhancement was attributed to the edge-on orientation of the polythiophene molecules induced by the silane SAM layer as deduced from the crystal domain structures in the atomic force microscopic images.
Tuning of spontaneous emission of two-dimensional photonic crystal microcavities by accurate control of slab thickness
Authors: Alija A. R. , Martínez L. J. , García-Martín A. , Dotor M. L. , Golmayo D. , Postigo P. A
Published: March 2005

We have found a blueshift in the cavity modes confined in two-dimensional photonic crystal microcavities when the thickness of the slab was varied uniformly by accurate dry etching. The shifts in the wavelength of the cavity modes were around 2nm towards shorter wavelengths per nanometer reduced in the thickness of the slab. Three-dimensional plane wave expansion calculations showed that the observed shifts are inside the calculated photonic band gap of the structures. The variation in the energy position of the peaks with the thickness has been analyzed by three-dimensional finite difference time domain calculations for a one missing hole microcavity. This tuning of the emission wavelength with the change in the thickness slab shows the important effect of the third dimension in photonic crystals made out of semiconductor slabs and it can be of interest for its application in the final processed photonic devices like photonic crystal lasers.
Giant magnetoresistance in an epitaxial NiMnSb∕Cu∕CoFe multilayer
Authors: Girgis E. , Bach P. , Rüster C. , Gould C. , Schmidt G. , Molenkamp L. W.
Published: March 2005

We have fabricated current-in-plane giant magnetoresistive (GMR) devices based on multilayers of epitaxial NiMnSb and sputtered Cu and CoFe. The devices show a magnetoresistance of up to 3.5% at room temperature. The amplitude of the current-in-plane GMR signal and the nature of the coupling between the two magnetic layers depend on the thickness of the Cu layer. For a 1.5nm thick Cu layer, the device exhibits antiferromagnetic coupling, whereas a parallel alignment is observed for 2.2 or 3nm thick Cu layers at low field.
Domain decoration in dipolar coupled ferromagnetic stacks with perpendicular anisotropy
Authors: Wiebel S. , Jamet J.-P. , Vernier N. , Mougin A. , Ferré J. , Baltz V. , Rodmacq B. , Dieny B.
Published: March 2005

The dipolar stray field effects between two nonuniformly magnetized ferromagnetic Co∕Pt stacks with perpendicular anisotropy are investigated by polar magneto-optical Kerr effect microscopy. Decoration of a reversed domain in the hard stack by a domain ring in the soft stack is evidenced and interpreted by magnetostatic calculations. Mirrored 360° domain walls are strongly stabilized by these interactions.
Selective etching of InGaAs∕GaAs(100) multilayers of quantum-dot chains
Authors: Wang Zh. M. , Zhang L. , Holmes K. , Salamo G. J.
Published: March 2005

We report selective chemical etching as a promising procedure to study the buried quantum dots in multiple InGaAs∕GaAs layers. The dot layer-by-dot layer etching is demonstrated using a mixed solution of NH4OH:H2O2:H2O. Regular plan-view atomic force microscopy reveals that all of the exposed InGaAs layers have a chain-like lateral ordering despite the potential of significant In–Ga intermixing during capping. The vertical self-correlation of quantum dots in the chains is observed.
Microdischarges of xenon sustained by microwaves: Determination of scaling laws
Authors: Lacoste A. , Maulat O. , Latrasse L. , Arnal Y. , Pelletier J.
Published: March 2005

The threshold conditions to maintain millimeter and submillimeter-size discharges of xenon with microwaves are experimentally determined. The threshold electric field required to sustain the plasma is reported as a function of gas pressure. The influence of the size of the dielectric cell in which the discharge is produced is also shown. The scaling laws are deduced from the threshold electric field measurements, assuming a few additional simplifying assumptions. The results are compared with data obtained with argon discharges sustained by surface waves in capillary tubes and the hypotheses assumed for the calculations are discussed.
Strong photoluminescence of nanostructured crystalline tungsten oxide thin films
Authors: Feng M. , Pan A. L. , Zhang H. R. , Li Z. A. , Liu F. , Liu H. W. , Shi D. X. , Zou B. S. , Gao H. J.
Published: March 2005

Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.
Femtosecond spectroscopy of unipolar nanometer-scale high-field transport of holes in Al0.08Ga0.92As
Authors: Trumm S. , Betz M. , Sotier F. , Leitenstorfer A. , Schwanhäußer A. , Eckardt M. , Malzer S. , Hanson M. , Driscoll D. , Gossard A. C. , Döhler G. H.
Published: March 2005

High-field transport in GaAs is investigated tracing ultrafast modifications of the Franz–Keldysh absorption spectrum of a AlxGa1−xAs heterostructure diode. A sophisticated sample design allows us to isolate the unipolar tranport properties of holes in combination with a nanometer scale definition of layers for both photoexcitation and detection of the propagating carrier distribution. Transient velocities and spatial broadening of the hole ensemble are directly measured for electric fields between 15 and 200 kV∕cm comparing room temperature operation to results for TL=4K. Even at low temperatures, the transient hole velocities are found not to exceed a value of 1.2×107cm∕s which is a result of ultrafast optical phonon emission with a scattering time below 25 fs.
Intrinsic effective piezoelectric coefficient e31,f for ferroelectric thin films
Authors: Ouyang Jun , Ramesh R. , Roytburd A. L.
Published: April 2005

As a function of film orientation, the intrinsic effective piezoelectric coefficient e31,f is generally formulated for a substrate-constrained ferroelectric film. Numerical results are obtained for Pb(ZrxTi1−x)O3 (PZT) thin films with tetragonal and rhombohedral compositions. It is illustrated that the optimal orientation for e31,f are close to [001] orientation in both tetragonal and rhombohedral PZT films and the maximum calculated e31,f is about −30C∕m2 on the rhombohedral side of the morphotropic phase boundary.
Control of the vortex movement and arrangement by out-of-plane magnetic structures in twinned YBa2Cu3O7−x∕La0.67Sr0.33MnO3 bilayer
Authors: Laviano F. , Gozzelino L. , Mezzetti E. , Przyslupski P. , Tsarev A. , Wisniewski A.
Published: April 2005

In this article, we consider the magnetic interaction exerted on vortices in a thin YBa2Cu3O7−x film by a La0.67Sr0.33MnO3 layer. The magnetic coupling of the bilayer system was studied and locally imaged by means of magneto-optics. Twin boundaries in the LaAlO3 substrate cause a clear splitting of the manganite magnetic domains with well-defined in-plane magnetization separated by pinned out-of-plane magnetic structures. The vortices nucleated by the external magnetic field interact with the out-of-plane magnetic moments depending on their local structure and magnetic polarization. Different blocking mechanisms (sink or reservoir) are found for the vortex motion perpendicular to twin boundaries, whereas for vortices moving parallel to the out-of-plane magnetic structures either blocking or channelling effect is observed.
β1 integrin and IL-3R coordinately regulate STAT5 activation and anchorage-dependent proliferation
Authors: Defilippi Paola , Rosso Arturo , Dentelli Patrizia , Calvi Cristina , Garbarino Giovanni , Tarone Guido , Pegoraro Luigi , Brizzi Maria Felice
Published: March 2005

We previously demonstrated that integrin-dependent adhesion activates STAT5A, a well known target of IL-3–mediated signaling. Here, we show that in endothelial cells the active β1 integrin constitutively associates with the unphosphorylated IL-3 receptor (IL-3R) β common subunit. This association is not sufficient for activating downstream signals. Indeed, only upon fibronectin adhesion is Janus Kinase 2 (JAK2) recruited to the β1 integrin–IL-3R complex and triggers IL-3R β common phosphorylation, leading to the formation of docking sites for activated STAT5A. These events are IL-3 independent but require the integrity of the IL-3R β common. IL-3 treatment increases JAK2 activation and STAT5A and STAT5B tyrosine and serine phosphorylation and leads to cell cycle progression in adherent cells. Expression of an inactive STAT5A inhibits cell cycle progression upon IL-3 treatment, identifying integrin-dependent STAT5A activation as a priming event for IL-3–mediated S phase entry. Consistently, overexpression of a constitutive active STAT5A leads to anchorage-independent cell cycle progression. Therefore, these data provide strong evidence that integrin-dependent STAT5A activation controls IL-3–mediated proliferation.
A systems analysis of importin-α–β mediated nuclear protein import
Authors: Riddick Gregory , Macara Ian G.
Published: March 2005

Importin-β (Impβ) is a major transport receptor for Ran-dependent import of nuclear cargo. Impβ can bind cargo directly or through an adaptor such as Importin-α (Impα). Factors involved in nuclear transport have been well studied, but systems analysis can offer further insight into regulatory mechanisms. We used computer simulation and real-time assays in intact cells to examine Impα–β-mediated import. The model reflects experimentally determined rates for cargo import and correctly predicts that import is limited principally by Impα and Ran, but is also sensitive to NTF2. The model predicts that CAS is not limiting for the initial rate of cargo import and, surprisingly, that increased concentrations of Impβ and the exchange factor, RCC1, actually inhibit rather than stimulate import. These unexpected predictions were all validated experimentally. The model revealed that inhibition by RCC1 is caused by sequestration of nuclear Ran. Inhibition by Impβ results from depletion nuclear RanGTP, and, in support of this mechanism, expression of mRFP-Ran reversed the inhibition.
Three-dimensional EM structure of the ectodomain of integrin αVβ3 in a complex with fibronectin
Authors: Adair Brian D. , Xiong Jian-Ping , Maddock Catherine , Goodman Simon L. , Arnaout M. Amin , Yeager Mark
Published: March 2005

Integrins are αβ heterodimeric cell surface receptors that mediate transmembrane signaling by binding extracellular and cytoplasmic ligands. The ectodomain of integrin αVβ3 crystallizes in a bent, genuflexed conformation considered to be inactive (unable to bind physiological ligands in solution) unless it is fully extended by activating stimuli. We generated a stable, soluble complex of the Mn2+-bound αVβ3 ectodomain with a fragment of fibronectin (FN) containing type III domains 7 to 10 and the EDB domain (FN7-EDB-10). Transmission electron microscopy and single particle image analysis were used to determine the three-dimensional structure of this complex. Most αVβ3 particles, whether unliganded or FN-bound, displayed compact, triangular shapes. A difference map comparing ligand-free and FN-bound αVβ3 revealed density that could accommodate the RGD-containing FN10 in proximity to the ligand-binding site of β3, with FN9 just adjacent to the synergy site binding region of αV. We conclude that the ectodomain of αVβ3 manifests a bent conformation that is capable of stably binding a physiological ligand in solution.
ArfGAP1 dynamics and its role in COPI coat assembly on Golgi membranes of living cells
Authors: Liu Wei , Duden Rainer , Phair Robert D. , Lippincott-Schwartz Jennifer
Published: March 2005

Secretory protein trafficking relies on the COPI coat, which by assembling into a lattice on Golgi membranes concentrates cargo at specific sites and deforms the membranes at these sites into coated buds and carriers. The GTPase-activating protein (GAP) responsible for catalyzing Arf1 GTP hydrolysis is an important part of this system, but the mechanism whereby ArfGAP is recruited to the coat, its stability within the coat, and its role in maintenance of the coat are unclear. Here, we use FRAP to monitor the membrane turnover of GFP-tagged versions of ArfGAP1, Arf1, and coatomer in living cells. ArfGAP1 underwent fast cytosol/Golgi exchange with ∼40% of the exchange dependent on engagement of ArfGAP1 with coatomer and Arf1, and affected by secretory cargo load. Permanent activation of Arf1 resulted in ArfGAP1 being trapped on the Golgi in a coatomer-dependent manner. These data suggest that ArfGAP1, coatomer and Arf1 play interdependent roles in the assembly–disassembly cycle of the COPI coat in vivo.
The yeast S phase checkpoint enables replicating chromosomes to bi-orient and restrain spindle extension during S phase distress
Authors: Bachant Jeff , Jessen Shannon R. , Kavanaugh Sarah E. , Fielding Candida S.
Published: March 2005

The budding yeast S phase checkpoint responds to hydroxyurea-induced nucleotide depletion by preventing replication fork collapse and the segregation of unreplicated chromosomes. Although the block to chromosome segregation has been thought to occur by inhibiting anaphase, we show checkpoint-defective rad53 mutants undergo cycles of spindle extension and collapse after hydroxyurea treatment that are distinct from anaphase cells. Furthermore, chromatid cohesion, whose dissolution triggers anaphase, is dispensable for S phase checkpoint arrest. Kinetochore–spindle attachments are required to prevent spindle extension during replication blocks, and chromosomes with two centromeres or an origin of replication juxtaposed to a centromere rescue the rad53 checkpoint defect. These observations suggest that checkpoint signaling is required to generate an inward force involved in maintaining preanaphase spindle integrity during DNA replication distress. We propose that by promoting replication fork integrity under these conditions Rad53 ensures centromere duplication. Replicating chromosomes can then bi-orient in a cohesin-independent manner to restrain untimely spindle extension.
The extracellular domains of FasL and Fas are sufficient for the formation of supramolecular FasL-Fas clusters of high stability
Authors: Henkler Frank , Behrle Eva , Dennehy Kevin M. , Wicovsky Andreas , Peters Nathalie , Warnke Clemens , Pfizenmaier Klaus , Wajant Harald
Published: March 2005

Using fluorescent variants of Fas and FasL, we show that membrane FasL and Fas form supramolecular clusters that are of flexible shape, but nevertheless stable and persistent. Membrane FasL-induced Fas clusters were formed in caspase-8– or FADD-deficient cells or when a cytoplasmic deletion mutant of Fas was used suggesting that cluster formation is independent of the assembly of the cytoplasmic Fas signaling complex and downstream activated signaling pathways. In contrast, cross-linked soluble FasL failed to aggregate the cytoplasmic deletion mutant of Fas, but still induced aggregation of signaling competent full-length Fas. Moreover, membrane FasL-induced Fas cluster formation occurred in the presence of the lipid raft destabilizing component methyl-β-cyclodextrin, whereas Fas aggregation by soluble FasL was blocked. Together, these data suggest that the extracellular domains of Fas and FasL alone are sufficient to drive membrane FasL-induced formation of supramolecular Fas–FasL complexes, whereas soluble FasL-induced Fas aggregation is dependent on lipid rafts and mechanisms associated with the intracellular domain of Fas.
Secondary Structure and Gating Rearrangements of Transmembrane Segments in Rat P2X4 Receptor Channels
Authors: Silberberg Shai D. , Chang Tsg-Hui , Swartz Kenton J.
Published: March 2005

P2X receptors are cation selective channels that are activated by extracellular nucleotides. These channels are likely formed by three identical or related subunits, each having two transmembrane segments (TM1 and TM2). To identify regions that undergo rearrangement during gating and to probe their secondary structure, we performed tryptophan scanning mutagenesis on the two putative TMs of the rat P2X4 receptor channel. Mutant channels were expressed in Xenopus oocytes, concentration–response relationships constructed for ATP, and the EC50 estimated by fitting the Hill equation to the data. Of the 22 mutations in TM1 and 24 in TM2, all but one in TM1 and seven in TM2 result in functional channels. Interestingly, the majority of the functional mutants display an increased sensitivity to ATP, and in general these perturbations are more pronounced for TM2 when compared with TM1. For TM1 and for the outer half of TM2, the perturbations are consistent with these regions adopting α-helical secondary structures. In addition, the greatest perturbations in the gating equilibrium occur for mutations near the outer ends of both TM1 and TM2. Surface biotinylation experiments reveal that all the nonfunctional mutants traffic to the surface membrane at levels comparable to the WT channel, suggesting that these mutations likely disrupt ion conduction or gating. Taken together, these results suggest that the outer parts of TM1 and TM2 are helical and that they move during activation. The observation that the majority of nonconducting mutations are clustered toward the inner end of TM2 suggests a critical functional role for this region.
Type-3 Ryanodine Receptors Mediate Hypoxia-, but Not Neurotransmitter-induced Calcium Release and Contraction in Pulmonary Artery Smooth Muscle Cells
Authors: Zheng Yun-Min , Wang Qing-Song , Rathore Rakesh , Zhang Wan-Hui , Mazurkiewicz Joseph E. , Sorrentino Vincenzo , Singer Harold A. , Kotlikoff Michael I. , Wang Yong-Xiao
Published: March 2005

In this study we examined the expression of RyR subtypes and the role of RyRs in neurotransmitter- and hypoxia-induced Ca2+ release and contraction in pulmonary artery smooth muscle cells (PASMCs). Under perforated patch clamp conditions, maximal activation of RyRs with caffeine or inositol triphosphate receptors (IP3Rs) with noradrenaline induced equivalent increases in [Ca2+]i and Ca2+-activated Cl− currents in freshly isolated rat PASMCs. Following maximal IP3-induced Ca2+ release, neither caffeine nor chloro-m-cresol induced a response, whereas prior application of caffeine or chloro-m-cresol blocked IP3-induced Ca2+ release. In cultured human PASMCs, which lack functional expression of RyRs, caffeine failed to affect ATP-induced increases in [Ca2+]i in the presence and absence of extracellular Ca2+. The RyR antagonists ruthenium red, ryanodine, tetracaine, and dantrolene greatly inhibited submaximal noradrenaline– and hypoxia-induced Ca2+ release and contraction in freshly isolated rat PASMCs, but did not affect ATP-induced Ca2+ release in cultured human PASMCs. Real-time quantitative RT-PCR and immunofluorescence staining indicated similar expression of all three RyR subtypes (RyR1, RyR2, and RyR3) in freshly isolated rat PASMCs. In freshly isolated PASMCs from RyR3 knockout (RyR3−/−) mice, hypoxia-induced, but not submaximal noradrenaline–induced, Ca2+ release and contraction were significantly reduced. Ruthenium red and tetracaine can further inhibit hypoxic increase in [Ca2+]i in RyR3−/− mouse PASMCs. Collectively, our data suggest that (a) RyRs play an important role in submaximal noradrenaline– and hypoxia-induced Ca2+ release and contraction; (b) all three subtype RyRs are expressed; and (c) RyR3 gene knockout significantly inhibits hypoxia-, but not submaximal noradrenaline–induced Ca2+ and contractile responses in PASMCs.
Good measures on Cantor space
Authors: Akin Ethan
Published: March 2005

While there is, up to homeomorphism, only one Cantor space, i.e. one zero-dimensional, perfect, compact, nonempty metric space, there are many measures on Cantor space which are not topologically equivalent. The clopen values set for a full, nonatomic measure

μ
\mu

is the countable dense subset

{
μ
(
U
)
:
U

\{ \mu (U) : U

is clopen

}
\}

of the unit interval. It is a topological invariant for the measure. For the class of good measures it is a complete invariant. A full, nonatomic measure

μ
\mu

is good if whenever

U
,
V

U, V

are clopen sets with

μ
(
U
)
>
μ
(
V
)

\mu (U) > \mu (V)

, there exists

W
W

a clopen subset of

V
V

such that

μ
(
W
)
=
μ
(
U
)

\mu (W) = \mu (U)

. These measures have interesting dynamical properties. They are exactly the measures which arise from uniquely ergodic minimal systems on Cantor space. For some of them there is a unique generic measure-preserving homeomorphism. That is, within the Polish group of such homeomorphisms there is a dense,

G

δ

G_{\delta }

conjugacy class.
Homotopical localizations of module spectra
Authors: Casacuberta Carles , Gutiérrez Javier
Published: March 2005

We prove that stable

f
f

-localizations (where

f
f

is any map of spectra) preserve ring spectrum structures and module spectrum structures, under suitable hypotheses, and we use this fact to describe all possible localizations of the integral Eilenberg–Mac Lane spectrum

H

Z

H{\mathbb {Z}}

. As a consequence of this study, we infer that localizations of stable GEMs are stable GEMs, and it also follows that there is a proper class of nonequivalent stable localizations.
Brauer groups of genus zero extensions of number fields
Authors: Sonn Jack , Swallow John
Published: March 2005

We determine the isomorphism class of the Brauer groups of certain nonrational genus zero extensions of number fields. In particular, for all genus zero extensions

E
E

of the rational numbers

Q

\mathbb {Q}

that are split by

Q

(

2

)

\mathbb {Q}(\sqrt {2})

,

Br
⁡
(
E
)
≅
Br
⁡
(

Q

(
t
)
)

\operatorname {Br}(E)\cong \operatorname {Br}(\mathbb {Q}(t))

.
Finite dimensional representations of invariant differential operators
Authors: Musson Ian , Rueda Sonia
Published: March 2005

Let

k
k

be an algebraically closed field of characteristic

0
0

,

Y
=

k

r

×

(

k

×

)

s

Y=k^{r}\times {(k^{\times })}^{s}

, and let

G
G

be an algebraic torus acting diagonally on the ring of algebraic differential operators

D

(
Y
)

\mathcal {D} (Y)

. We give necessary and sufficient conditions for

D

(
Y

)
G

\mathcal {D}(Y)^G

to have enough simple finite dimensional representations, in the sense that the intersection of the kernels of all the simple finite dimensional representations is zero. As an application we show that if

K
⟶
G
L
(
V
)

K\longrightarrow GL(V)

is a representation of a reductive group

K
K

and if zero is not a weight of a maximal torus of

K
K

on

V
V

, then

D

(
V

)
K

\mathcal {D} (V)^K

has enough finite dimensional representations. We also construct examples of FCR-algebras with any integer GK dimension

≥
3

\geq 3

.
Commutative ideal theory without finiteness conditions: Primal ideals
Authors: Fuchs Laszlo , Heinzer William , Olberding Bruce
Published: March 2005

Our goal is to establish an efficient decomposition of an ideal

A
A

of a commutative ring

R
R

as an intersection of primal ideals. We prove the existence of a canonical primal decomposition:

A
=

⋂

P
∈

X

A

A

(
P
)

A = \bigcap _{P \in \mathcal {X}_A}A_{(P)}

, where the

A

(
P
)

A_{(P)}

are isolated components of

A
A

that are primal ideals having distinct and incomparable adjoint primes

P
P

. For this purpose we define the set

Ass
⁡
(
A
)

\operatorname {Ass}(A)

of associated primes of the ideal

A
A

to be those defined and studied by Krull. We determine conditions for the canonical primal decomposition to be irredundant, or residually maximal, or the unique representation of

A
A

as an irredundant intersection of isolated components of

A
A

. Using our canonical primal decomposition, we obtain an affirmative answer to a question raised by Fuchs, and also prove for

P
∈
Spec
⁡
R

P \in \operatorname {Spec}R

that an ideal

A
⊆
P

A \subseteq P

is an intersection of

P
P

-primal ideals if and only if the elements of

R
∖
P

R \setminus P

are prime to

A
A

. We prove that the following conditions are equivalent: (i) the ring

R
R

is arithmetical, (ii) every primal ideal of

R
R

is irreducible, (iii) each proper ideal of

R
R

is an intersection of its irreducible isolated components. We classify the rings for which the canonical primal decomposition of each proper ideal is an irredundant decomposition of irreducible ideals as precisely the arithmetical rings with Noetherian maximal spectrum. In particular, the integral domains having these equivalent properties are the Prüfer domains possessing a certain property.
Poisson brackets associated to the conformal geometry of curves
Authors: Marí Beffa G.
Published: March 2005

In this paper we present an invariant moving frame, in the group theoretical sense, along curves in the Möbius sphere. This moving frame will describe the relationship between all conformal differential invariants for curves that appear in the literature. Using this frame we first show that the Kac-Moody Poisson bracket on

L
o
(
n
+
1
,
1

)
∗

Lo(n+1,1)^\ast

can be Poisson reduced to the space of conformal differential invariants of curves. The resulting bracket will be the conformal analogue of the Adler–Gel’fand–Dikii bracket. Secondly, a conformally invariant flow of curves induces naturally an evolution on the differential invariants of the flow. We give the conditions on the invariant flow ensuring that the induced evolution is Hamiltonian with respect to the reduced Poisson bracket. Because of a certain parallelism with the Euclidean case we study what we call Frenet and natural cases. We comment on the implications for completely integrable systems, and describe conformal analogues of the Hasimoto transformation.
Weighted estimates in 𝐿² for Laplace’s equation on Lipschitz domains
Authors: Shen Zhongwei
Published: March 2005

Let

Ω
⊂

R

d

\Omega \subset \mathbb {R}^{d}

,

d
≥
3

d\ge 3

, be a bounded Lipschitz domain. For Laplace’s equation

Δ
u
=
0

\Delta u=0

in

Ω
\Omega

, we study the Dirichlet and Neumann problems with boundary data in the weighted space

L

2

(
∂
Ω
,

ω

α

d
σ
)

L^{2}(\partial \Omega ,\omega _{\alpha }d\sigma )

, where

ω

α

(
Q
)
=

|

Q
−

Q

0

|

α

\omega _{\alpha }(Q) =|Q-Q_{0}|^{\alpha }

,

Q

0

Q_{0}

is a fixed point on

∂
Ω

\partial \Omega

, and

d
σ

d\sigma

denotes the surface measure on

∂
Ω

\partial \Omega

. We prove that there exists

ε
=
ε
(
Ω
)
∈
(
0
,
2
]

\varepsilon =\varepsilon (\Omega )\in (0,2]

such that the Dirichlet problem is uniquely solvable if

1
−
d
>
α
>
d
−
3
+
ε

1-d>\alpha >d-3+\varepsilon

, and the Neumann problem is uniquely solvable if

3
−
d
−
ε
>
α
>
d
−
1

3-d-\varepsilon >\alpha >d-1

. If

Ω
\Omega

is a

C

1

C^{1}

domain, one may take

ε
=
2

\varepsilon =2

. The regularity for the Dirichlet problem with data in the weighted Sobolev space

L

1

2

(
∂
Ω
,

ω

α

d
σ
)

L^{2}_{1}(\partial \Omega ,\omega _{\alpha }d\sigma )

is also considered. Finally we establish the weighted

L

2

L^{2}

estimates with general

A

p

A_{p}

weights for the Dirichlet and regularity problems.
Saddle surfaces in singular spaces
Authors: Kalikakis Dimitrios
Published: March 2005

The notion of a saddle surface is well known in Euclidean space. In this work we extend the idea of a saddle surface to geodesically connected metric spaces. We prove that any solution of the Dirichlet problem for the Sobolev energy in a nonpositively curved space is a saddle surface. Further, we show that the space of saddle surfaces in a nonpositively curved space is a complete space in the Fréchet distance. We also prove a compactness theorem for saddle surfaces in spaces of curvature bounded from above; in spaces of constant curvature we obtain a stronger result based on an isoperimetric inequality for a saddle surface. These results generalize difficult theorems of S.Z. Shefel′ on compactness of saddle surfaces in a Euclidean space.
Dimension of families of determinantal schemes
Authors: Kleppe Jan , Miró-Roig Rosa
Published: March 2005

A scheme

X
⊂

P

n
+
c

X\subset \mathbb {P}^{n+c}

of codimension

c
c

is called standard determinantal if its homogeneous saturated ideal can be generated by the maximal minors of a homogeneous

t
×
(
t
+
c
−
1
)

t \times (t+c-1)

matrix and

X
X

is said to be good determinantal if it is standard determinantal and a generic complete intersection. Given integers

a
0

,

a
1

,
.
.
.
,

a

t
+
c
−
2

a_0,a_1,...,a_{t+c-2}

and

b
1

,
.
.
.
,

b
t

b_1,...,b_t

we denote by

W
(

b
_

;

a
_

)
⊂

Hilb
p

⁡
(

P

n
+
c

)

W(\underline {b};\underline {a})\subset \operatorname {Hilb} ^p(\mathbb {P}^{n+c})

(resp.

W
s

(

b
_

;

a
_

)

W_s(\underline {b};\underline {a})

) the locus of good (resp. standard) determinantal schemes

X
⊂

P

n
+
c

X\subset \mathbb {P}^{n+c}

of codimension

c
c

defined by the maximal minors of a

t
×
(
t
+
c
−
1
)

t\times (t+c-1)

matrix

(

f

i
j

)

j
=
0
,
.
.
.
,
t
+
c
−
2

i
=
1
,
.
.
.
,
t

(f_{ij})^{i=1,...,t}_{j=0,...,t+c-2}

where

f

i
j

∈
k
[

x
0

,

x
1

,
.
.
.
,

x

n
+
c

]

f_{ij}\in k[x_0,x_1,...,x_{n+c}]

is a homogeneous polynomial of degree

a
j

−

b
i

a_j-b_i

. In this paper we address the following three fundamental problems: To determine (1) the dimension of

W
(

b
_

;

a
_

)

W(\underline {b};\underline {a})

(resp.

W
s

(

b
_

;

a
_

)

W_s(\underline {b};\underline {a})

) in terms of

a
j

a_j

and

b
i

b_i

, (2) whether the closure of

W
(

b
_

;

a
_

)

W(\underline {b};\underline {a})

is an irreducible component of

Hilb
p

⁡
(

P

n
+
c

)

\operatorname {Hilb} ^p(\mathbb {P}^{n+c})

, and (3) when

Hilb
p

⁡
(

P

n
+
c

)

\operatorname {Hilb} ^p(\mathbb {P}^{n+c})

is generically smooth along

W
(

b
_

;

a
_

)

W(\underline {b};\underline {a})

. Concerning question (1) we give an upper bound for the dimension of

W
(

b
_

;

a
_

)

W(\underline {b};\underline {a})

(resp.

W
s

(

b
_

;

a
_

)

W_s(\underline {b};\underline {a})

) which works for all integers

a
0

,

a
1

,
.
.
.
,

a

t
+
c
−
2

a_0,a_1,...,a_{t+c-2}

and

b
1

,
.
.
.
,

b
t

b_1,...,b_t

, and we conjecture that this bound is sharp. The conjecture is proved for

2
≤
c
≤
5

2\le c\le 5

, and for

c
≥
6

c\ge 6

under some restriction on

a
0

,

a
1

,
.
.
.
,

a

t
+
c
−
2

a_0,a_1,...,a_{t+c-2}

and

b
1

,
.
.
.
,

b
t

b_1,...,b_t

. For questions (2) and (3) we have an affirmative answer for

2
≤
c
≤
4

2\le c \le 4

and

n
≥
2

n\ge 2

, and for

c
≥
5

c\ge 5

under certain numerical assumptions.