bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond dissociation dynamics of methyl iodide clusters
Authors: Poth L. , Zhong Q. , Ford J. V. , Castleman A. W.
Published: July 2002

The photodissociation dynamics of methyl iodide clusters using λ=270 nm as pump and λ=405 nm as probe are studied using a femtosecond two color pump–probe laser arrangement combined with a reflectron time-of-flight (RTOF) mass spectrometer. This enables the Ã state and 10s Rydberg state of methyl iodide to be accessed with the pump beam. Of particular interest is a comparison of the femtosecond dynamics of the methyl iodide monomer with the clustered species. Clocking of the monomer dissociation shows a transient which is indicative of a fast C–I bond breakage as is to be expected upon excitation of methyl iodide into the fast dissociating Ã state, or into the predissociative 10s Rydberg state. Clusters, however, show a very different pump–probe transient composed of a fast decay and a subsequent dip in ion signal followed by a rise for pump–probe delay times greater than 2 ps. The cluster ion signal shows an enhancement for pump probe delay times up to 70 ps. The results are interpreted in terms of the electronic state diagram of the methyl iodide monomer and effects resulting from clustering of these species, shifts of electronic energy levels and caging of excited species in the cluster.
Adsorption and abstraction of H(D) on clean and modified Al(111) and Ni(111) surfaces
Authors: Pölzl H. , Strohmeier G. , Winkler A.
Published: July 2002

The kinetics of adsorption and abstraction for the system H(D) on Al(111) and Ni(111) has been investigated using an efficient atomic beam source, thermal desorption spectroscopy, and multiplexed mass spectrometry. The initial sticking coefficient of atomic hydrogen on Ni(111) is 1.0 and independent of the angle of incidence. For H on Al(111) the initial sticking coefficient is 0.6 and increases with increasing angle of incidence (S(φ)∼cos−0.4 φ). On Al(111) preadsorbed oxygen leads to a decrease of the initial sticking coefficient for H down to 0.1; potassium on the other hand has no significant influence on the initial sticking probability. On both surfaces, Ni(111) and Al(111), abstraction of deuterium proceeds at a surface temperature of 150 K due to impinging H atoms (H+D→HD), with an initial abstraction coefficient of 0.20 on Al(111) and 0.12 on Ni(111). In the case of Al(111) this coefficient is nearly independent of the initial D coverage and therefore the abstraction reaction cannot be described by a simple Eley–Rideal process, but rather by a hot-precursor mechanism. In addition to abstraction there is also a small probability for the removal of an adsorbed species by a collision induced desorption process. Abstraction of deuterium by impinging H-atoms is strongly affected by modification of the Al(111) surface, either by oxygen or by potassium. Oxygen decreases the HD abstraction coefficient, probably by inhibiting the hot-precursor state of H on the surface. Potassium increases the HD abstraction rate, most likely by increasing the lifetime of atomic hydrogen in the precursor state.
Molecular dynamics study of the solution of semiflexible telechelic polymer chains with strongly associating end-groups
Authors: Khalatur Pavel G. , Khokhlov Alexei R. , Kovalenko Julia N. , Mologin Dmitrii A.
Published: July 2002

We present the results of molecular dynamics simulations of micelle organization as well as the formation of micellar aggregates in the solutions of semiflexible telechelic chains with strongly attracting end-groups (“sticker sites”). Using the cluster size distribution function, we study associative equilibrium in the system of flexible and semiflexible chains. It is found that this process corresponds to the so-called “open association” model for micelle formation. The critical temperature of micelle formation Tc is calculated as a function of chain rigidity and system density ρ. We find that the value of Tc increases monotonically with the increase of Kuhn segment length A. Such a behavior takes place in wide range of densities, but only if the value of ρ is somewhat smaller than some threshold value. At high density, we observe the opposite tendency; the temperature Tc decreases monotonically as the value of A is increased. The type of equilibrium microstructures, emerging as a result of micellization in the strong segregation regime, depends essentially on the chain rigidity. In the case of flexible telechelic chains, relatively small flowerlike micellar aggregates are observed. For the system of semiflexible chains, we find rather distinctly appearance of microbundles with pronounced liquid-crystalline-like order. In this case, the spatial organization of the system is characterized by a cellular architecture which looks like “ceramics.” Thus, significant morphological changes can be induced by varying of chain rigidity. At fixed system density and T<Tc, the characteristic period rm of locally ordered micellar arrays scales as rm∝Ã1/3, where Ã is the reduced statistical segment length. Also, it is shown that the average aggregation number increases as the chain rigidity is increased. In other words, the gradual stretching out of the chains shifts the association equilibrium to formation of larger clusters. We have performed a comparative analysis of our computer simulation data with theoretical predictions. It is shown that the simple theoretical model is successful enough to explain some basic features observed in simulations.
Numerically exact diffusion coefficients for lattice systems with periodic boundary conditions. I. Theory
Authors: Mercier Jean-François , Slater Gary W. , Guo Hong L.
Published: July 2002

The standard method to study the diffusion of a particle in a system with immobile obstacles is to use Monte Carlo simulations on finite-size lattices with periodic boundary conditions. For example, the diffusion of proteins on the surface of biomembranes in the presence of fractal and random aggregates of obstacles has been studied extensively by M. J. Saxton. In this article, we derive two algebraically exact methods to calculate the diffusion coefficient D for such systems. The first method reduces the problem to that of a first passage problem. The second one uses the Nernst–Einstein relation to transform the problem into a field-driven drift problem where D is related to the zero-field mobility. Systems with closed volumes and multiple independent pathways are discussed. In the second part [Mercier and Slater, J. Chem. Phys. 110, 6057 (1999), following paper], a numerical implementation will be described and tested, and several examples of applications will be given.
Collision induced migration of adsorbates on surfaces
Authors: Romm L. , Asscher M. , Zeiri Y.
Published: July 2002

Collision induced migration (CIM) has been identified as a new surface phenomenon and has been studied for the first time using molecular dynamics simulations. The CIM process was represented by an energetic gas phase argon atom, striking an adsorbed nitrogen molecule on Ru(001). The efficiency of CIM was investigated as a function of the collider initial kinetic energy and angle of incidence. It was found that at low coverages an adsorbed molecule can migrate more than 150 Å following collisions at high energies and grazing angles of incidence. As coverage increases, inter-adsorbate collisions result in significant reduction of migration distances. At high energies, the competing process of collision induced desorption becomes dominant, leaving behind molecules which migrate shorter distances. These competing channels lead to a collision energy for which CIM is maximized. For the N2/Ru system, the CIM process is most effective near collider energy of 2.0 eV. This new surface phenomenon of CIM has to be considered for better understanding the full range of surface processes which govern industrial high pressure catalysis. At the tail of the thermal kinetic energy distribution, energetic colliders from the gas phase lead to CIM and generate high energy inter-adsorbate collisions, sometimes discussed in terms of “hot-particle” chemistry.
Resonant two-photon ionization spectroscopy of jet-cooled PdC
Authors: Langenberg Jon D. , Shao Lian , Morse Michael D.
Published: July 2002

The first optical investigation of the spectra of diatomic PdC has revealed that the ground state has Ω=0+, with a bond length of r0=1.712 Å. The Hund’s case (a) nature of this state could not be unambiguously determined from the experimental data, but dispersed fluorescence studies to be reported in a separate publication, in combination with a comparison to theoretical calculations, demonstrate that it is the 2δ4 12σ2, 1Σ0++ state, which undergoes spin–orbit mixing with a low-lying 2δ4 12σ1 6π1, 3Π0+ state. An excited 3Σ+ state with re=1.754±0.003 Å (r0=1.758±0.002 Å) and ΔG1/2=794 cm−1 is found at T0=17 867 cm−1. Although only the Ω=1 component of this state is directly observed, the large hyperfine splitting of this state for the 105Pd 12C isotopomer implies that an unpaired electron occupies an orbital that is primarily of 5s character on Pd. Comparison to ab initio calculations identifies this state as 2δ4 12σ1 13σ1, 3Σ1+. To higher wavenumbers a number of transitions to states with Ω=0+ have been observed and rotationally analyzed. Two groups of these have been organized into band systems, despite the clear presence of homogeneous perturbations between states with Ω=0+ in the region between 22 000 and 26 000 cm−1.
Rotationally resolved A 2Π←X 2Π electronic spectra of cyanodiacetylene and dicyanoacetylene cations
Authors: Sinclair Wayne E. , Pfluger David , Maier John P.
Published: July 2002

The 000 bands of the A 2Π←X 2Π and A 2Πg←X 2Πu transitions of cyanodiacetylene and dicyanoacetylene cations have been rotationally analyzed at Doppler-limited resolution using frequency modulation absorption spectroscopy. The ions were generated in a liquid-nitrogen cooled hollow cathode modulated discharge incorporated in a White cell. Analysis of the rotational structure yields molecular parameters of the cations in the two electronic states, confirming linear geometries. The inferred spin–orbit and rotational constants are discussed in terms of the electronic structure of the isoelectronic cations. The spectrum of dicyanoacetylene cation reveals Λ-type doubling consistent with the presence of a nearby Σg+2 state. The second order spin-orbit splitting of the A 2Πg state is analyzed to predict the existence of the Σg+2 state below the A 2Πg state.
Dynamics of dissociative methane adsorption on metals: CH4 on Pt{110}(1×2)
Authors: Walker A. V. , King D. A.
Published: July 2002

Supersonic molecular beams have been used to study methane dissociative adsorption on Pt{110}(1×2) at incident translational energies of 20 to 700 meV, incident vibrational temperatures of 300 to 800 K and surface temperatures from 400 to 1000 K. At Et⩽100 meV, the initial dissociative sticking probability, s0, rises sharply. The process is facilitated by vibrational excitation of the deformation modes and surface temperature. At Et>100 meV, an activated adsorption process becomes dominant, with an activation barrier of ∼146 meV. At Et⩾230 meV, s0 attains a limiting value which is strongly enhanced by excitation of the C–H stretch modes in the incident molecule. An increase in the surface temperature also enhances s0, at all incident translational energies. The mechanistic implications are discussed and it is concluded that the low translational energy process is a distinctive steering-assisted direct adsorption pathway.
Poisson maps and canonoid transformations for time-dependent Hamiltonian systems
Authors: Cariñena José F. , Rañada Manuel F.
Published: July 2002

After a new presentation of the geometric theory of time-dependent systems in the Hamiltonian formulation, using Poisson structures, a characterization of canonoid transformations with respect to a dynamical vector field is given. The associated constants of motion and the generating functions of canonoid transformations are also studied. The theory is illustrated with several examples.
The generalized Koszul differential in the BRST quantization
Authors: Constantinescu Radu
Published: July 2002

A new geometrical structure is proposed for a differential complex of the Koszul type. The generators of the complex are structured on more levels and new graduations are used. A generalized differential that can be split in many pieces acts on the generators. The first two items are identified with the Koszul operators from the sp(2) BRST quantization. This result suggests the possibility of the implementation of a symmetry bigger than sp(2). The third order Koszul differential is effectively constructed. As an application of this construction, the BRST charges and the extended Hamiltonian suitable for the sp(3) BRST quantization of a first rank gauge theory are presented.
Homogeneous scalar field cosmologies with an exponential potential
Authors: Coley A. A. , Ibáñez J. , van den Hoogen R. J.
Published: July 2002

We shall study spatially homogeneous cosmological models containing a self-interacting scalar field with an exponential potential of the form V(φ)=Λekφ. The asymptotic properties of these models are discussed. In particular, their possible isotropization and inflation are investigated for all values of the parameter k. A particular class of models is analyzed qualitatively using the theory of dynamical systems, illustrating the general asymptotic behavior.
Onset of superconductivity in decreasing fields for general domains
Authors: Bernoff Andrew , Sternberg Peter
Published: July 2002

Ginzburg–Landau theory has provided an effective method for understanding the onset of superconductivity in the presence of an external magnetic field. In this paper we examine the instability of the normal state to superconductivity with decreasing magnetic field for a closed smooth cylindrical region of arbitrary cross-section subject to a vertical magnetic field. We examine the problem asymptotically in the boundary layer limit (i.e., when the Ginzburg–Landau parameter, k, is large). We demonstrate that instability first occurs in a region exponentially localized near the point of maximum curvature on the boundary. The transition occurs at a value of the magnetic field associated with the half-plane at leading order, with a small positive correction due to the curvature (which agrees with the transition problem for the disc), and a smaller correction due to the second derivative of the curvature at the maximum.
Bose–Einstein condensation in an external potential at zero temperature: Solitary-wave theory
Authors: Margetis Dionisios
Published: July 2002

For a trapped, dilute atomic gas of short-range, repulsive interactions at extremely low temperatures, when Bose–Einstein condensation is nearly complete, some special forms of the time-dependent condensate wave function and the pair-excitation function, the latter being responsible for phonon creation, are investigated. Specifically, (i) a class of external potentials Ve(r,t) that allow for localized, shape-preserving solutions to the nonlinear Schrödinger equation for the condensate wave function, each recognized as a solitary wave moving along an arbitrary trajectory, is derived and analyzed in any number of space dimensions; and (ii) for any such external potential and condensate wave function, the nonlinear integro-differential equation for the pair-excitation function is shown to admit solutions of the same nature. Approximate analytical results are presented for a sufficiently slowly varying trapping potential. Numerical results are obtained for the condensate wave function when Ve is a time-independent, spherically symmetric harmonic potential.
Maximum stable length of nonisothermal liquid bridges
Authors: Chen J. C. , Sheu J. C. , Lee Y. T.
Published: July 2002

The maximum stable length of nonisothermal liquid bridges is predicted through a series of numerical computations. The results show that the maximum length of the bridges is less than the Rayleigh limit determined by the isothermal capillary stability analysis. It is enhanced by increasing the strength of the thermocapillary convection, while it is reduced for higher percentage change of surface-tension force or stronger buoyancy-driven convection. For the cases of small parameters, the predictions are in qualitative and quantitative agreement with the previous asymptotic results.
Combined effects of riblets and polymers on drag reduction in pipes
Authors: Christodoulou C. , Liu K. N. , Joseph D. D.
Published: July 2002

In the present Brief Communication, experiments are reported establishing a superposition of drag reduction due to riblets on drag reduction due to polymers, in fully developed turbulent flow of dilute aqueous solutions of polymers (2–50 ppm) through 25.4 mm (1 in.) diameter pipes, lined with a film of grooved isosceles triangles of equal height and base (S=0.11 mm). The range of S+ (which is the base and height of the riblets expressed in wall units), where drag reduction is superimposed, changes with polymer concentration. The higher the concentration, the narrower the range of S+. Also, the amount of superimposed drag reduction changes with the type of polymer used.
Statistical inelastic cross-section model for the Monte Carlo simulation of molecules with discrete internal energy
Authors: Koura Katsuhisa
Published: July 2002

The statistical inelastic cross-section (SICS) model based on the statistical uncorrelation assumption is derived using the microscopic reversibility relation for the Monte Carlo simulation of molecules with discrete internal energy. The SICS model is specified for rotationally inelastic collisions by employing Parker’s rotational energy gain function and applied to the calculation of the rotational distribution through a nitrogen shock wave with the null-collision direct-simulation Monte Carlo method. It is shown that the SICS model produces the Boltzmann and bimodal rotational distributions in low and high Mach number shock waves, respectively, consistent with the experimental results of Robben and Talbot [Phys. Fluids 9, 653 (1966)]. Quantitative agreement between the Monte Carlo and experimental results of the rotational distribution as well as the density and rotational temperature profiles is reasonable for available values of the SICS parameters.
Chaotic dynamics of particle dispersion in fluids
Authors: Wang L. P. , Maxey M. R. , Burton T. D. , Stock D. E.
Published: July 2002

An analysis of the Lagrangian motion for small particles denser than surrounding fluid in a two-dimensional steady cellular flow is presented. The Stokes drag, fluid acceleration, and added mass effect are included in the particle equation of motion. Although the fluid motion is regular, the particle motion can be either chaotic or regular depending on the Stokes number and density ratio. The implications of chaotic motion to particle mixing and dispersion are discussed. Chaotic orbits lead to the dispersion of particle clouds which has many of the features of turbulent dispersion. The mixing process of particles is greatly enhanced since the chaotic advection has the property of ergodicity. However, a high dispersion rate was found to be correlated with low fractal dimension and low mixing efficiency. A similar correlation between dispersion and mixing was found for particles convected by a plane shear mixing layer.
Role of large-scale structure in a nonreacting turbulent CH4 jet
Authors: Schefer R. W. , Kerstein A. R. , Namazian M. , Kelly J.
Published: July 2002

The existence of organized large-scale structure in jet flows has been studied using planar imaging of the CH4 concentration in a turbulent CH4 jet. The measurements show the development of large-scale vortical structures in the mixing region adjacent to the central jet. These structures result in instantaneous radial profiles that differ considerably from the classical time-averaged Gaussian profiles measured previously using single-point measurements. The profiles typically consist of one or two plateau regions of relatively uniform concentration and are consistent with planar measurements obtained by other investigators in constant density and reacting flows. The results suggest a mixing model in which the dominant mechanism for entrainment is large-scale engulfment of surrounding air by the vortical structures, followed by rapid mixing with jet fluid. Conventional time-averaged statistics (mean, RMS fluctuations, and probability distributions) can be interpreted in terms of this large-scale structure.
Numerical simulations of the translational and shape oscillations of a liquid drop in an acoustic field
Authors: Feng Z. C. , Su Y. H.
Published: July 2002

In this work, the boundary element method combined with the fourth order Runge–Kutta scheme as time integrator is used to simulate the dynamics of an acoustically levitated axisymmetric liquid drop. For a given set of dimensionless parameters—wavenumber, Bond number, and acoustic Bond number—the drop dynamics in an acoustic field is studied in terms of the shape oscillation and the translational motion of the drop. The shape oscillation of the drop is characterized by using the equatorial radius and its rate of change as two phase variables. Fixed points on this phase plane represent the static equilibrium shapes. The translational motion is characterized by using the position and the velocity of the drop centroid as two phase variables. The fixed points on this phase plane represent the equilibrium positions of the drop in the acoustic field. It is found that fixed points corresponding to both translational and shape oscillations undergo saddle-node bifurcations with the acoustic Bond number as a parameter. These saddle-node bifurcations define an upper and a lower limit on the acoustic Bond number that can be used in acoustic levitation. We also investigate the coupling effect between the translational oscillation and the shape oscillation. It is found that owing to the order-of-magnitude difference between the period of translational oscillation and that of shape oscillation the coupling effect is only significant at the boundary of the trapping region.
Electron heat transport with non-Maxwellian distributions
Authors: Liu J. M. , De Groot J. S. , Matte J. P. , Johnston T. W. , Drake R. P.
Published: July 2002

Measurements are presented of electron heat transport with non-Maxwellian (flattopped) distributions due to inverse bremsstrahlung absorption of intense microwaves in the University of California at Davis Aurora II device [Rogers et al., Phys. Fluids B 1, 741 (1989)]. The plasma is created by pulsed discharge in a cylindrical vacuum chamber with surface magnets arranged to create a density gradient. The ionization fraction (∼1%) is high enough that charged particle collisions are strongly dominant in the afterglow plasma. A short microwave pulse (∼2 μs) heats a region of the afterglow plasma (ne/ncr≤0.5) creating a steep axial (LT∼1–10λei) temperature gradient. Langmuir probes are used to measure the relaxation of the heat front after the microwave pulse. Time and space resolved measurements show that the isotropic component of the electron velocity distribution is flat topped (∼exp[−(v/vm)m], m≳2) in agreement with Fokker–Planck calculations using the measured density profile. Classical heat transport theory is not valid both because the isotropic component of the electron velocity distribution is flattopped and the temperature gradients are very steep.
Nonlinear evolution of multimode Rayleigh–Taylor instability in two and three dimensions
Authors: Shvarts D. , Alon U. , Ofer D. , McCrory R. L. , Verdon C. P.
Published: July 2002

The nonlinear evolution of the Rayleigh–Taylor instability from multimode initial perturbations is studied by two complementary approaches. First, a statistical-mechanics bubble-merger model is presented, that enables determination of the late-time scaling properties based on single-mode and two-bubble interaction physics. The results for Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) bubble and spike front penetrations are given, as well as scaling laws for mixing under a time-dependent driving acceleration. The second approach is a modal model, in which nonlinear mode coupling and saturation are included in an equation for effective modes that describe the mixed region. The importance of mode coupling in the generation of large structure that dominates the late stage evolution, and the relative importance of long-wavelength components in the initial perturbation spectra on the late-stage evolution are studied. Finally, multimode RT instability in three dimensions is studied by both full-scale simulations and the modal model. The effect and late-stage memory loss of different aspect ratios in the initial perturbation are demonstrated.
Transient enhanced diffusion of phosphorus in silicon
Authors: Cowern N. E. B. , Godfrey D. J. , Sykes D. E.
Published: July 2002

The diffusion of phosphorus implanted at low dose into crystalline silicon has been investigated as a function of dose and furnace anneal time. A major feature is an initial transient diffusion enhancement, comparable with the well-known transient in boron diffusion. The transient is larger than expected from published studies using rapid thermal annealing.
Vibrational characteristics of acceptor-hydrogen complexes in silicon
Authors: Stavola Michael , Pearton S. J. , Lopata J. , Dautremont-Smith W. C.
Published: July 2002

Acceptor-hydrogen complexes for the group III acceptors, B, Al, and Ga, in Si have been studied with low-temperature infrared spectroscopy. The Si-H stretching band narrows dramatically upon cooling to low temperature thereby aiding the detection of the vibrations of the Al and Ga acceptor-H complexes. The frequency 2201 cm−1 we have measured for the Al-H complex is in reasonable agreement with the prediction made by G. G. DeLeo and W. B. Fowler [Phys. Rev. B 31, 6861 (1985)] (2220 cm−1 for a 〈111〉 interstitial configuration for the H). Assignment of the new vibrational bands is confirmed by isotopic substitution. The strength of the absorption provides evidence that the passivation is not the result of compensation alone and that a major fraction of the passivated acceptors result in acceptor-H complexes. A new, low-energy excitation of the acceptor-hydrogen complexes gives rise to a sideband to the main stretching vibration and explains the pronounced energy shift and narrowing of the spectra upon cooling to He temperature.
High-power conversion efficiency quantum well diode lasers
Authors: Waters R. G. , Wagner D. K. , Hill D. S. , Tihanyi P. L. , Vollmer B. J.
Published: July 2002

cw power conversion efficiencies of 57% have been obtained on uncoated diode lasers emitting nearly 300 mW per facet. This performance is achieved by using a low-resistance graded index separate confinement single quantum well AlGaAs/GaAs structure with high (84%) differential quantum efficiency and low threshold current.
Brittle-to-ductile transition in laser-induced spall at ultrahigh strain rate in 6061-T6 aluminum alloy
Authors: Gilath I. , Eliezer S. , Dariel M. P. , Kornblit L.
Published: July 2002

Experimental confirmation is provided for a brittle-to-ductile transition of the spall failure mode in a 6061-T6 aluminum alloy, at a strain rate of 107 s−1 , caused by laser-induced shock waves. This result is consistent with the prediction of a theory that has been put forward recently by Grady. The experimental approach that was used allowed determination of the maximum elongation associated with the spall failure in the alloy and pure aluminum.
Photochemical hole burning of tetraphenylporphine derivatives
Authors: Kishii N. , Asai N. , Kawasumi K. , Tamura S. , Seto J.
Published: July 2002

The substituent effect on photochemical hole burning (PHB) for tetraphenylporphine was studied and the PHB efficiency was related to the electron donating and/or withdrawing properties of the substituents of the phenyl ring. The Hammett-sigma constants of the substituents were related to the efficiency of the photochemical hole burning reaction. Compounds with a low Hammett-sigma constant such as tetra-(4-methoxyphenyl)porphine had a higher PHB reaction efficiency than derivatives with a higher value such as tetraphenylporphine. We have also demonstrated multiple photochemical hole burning using this high efficiency compound tetra-(4-methoxyphenyl)porphine as a guest material.
The expression of the γ subunit of Na-K-ATPase is regulated by osmolality via C-terminal Jun kinase and phosphatidylinositol 3-kinase-dependent mechanisms
Authors: Capasso J. M. , Rivard C. , Berl T.
Published: July 2002

The α and β subunits of Na-K-ATPase are up-regulated by hypertonicity in inner-medullary collecting duct cells adapted to survive in hypertonic conditions. We examined the regulation of the γ subunit by hypertonicity. Although cultured inner-medullary collecting duct cells lacked the γ subunits, both variants γ
a
and γ
b
were expressed in cells adapted to 600 and 900 mosmol/KgH
2
O. This expression was reversible with a half-time of 17.2 ± 0.5 h. The message of the γ subunit was absent in isotonic conditions and increased with higher tonicity in adapted cells. In acute experiments the appearance of the γ subunit was found to be both time-dependent (≥24 h) and osmolality-dependent (≥500 mosmol/KgH
2
O). No induction was noted with urea and only minimal induction with mannitol. Increasing concentrations of the phosphatidylinositol 3-kinase inhibitor LY294002 resulted in a dose-dependent decrement in the expression of the γ subunit with total abolition at 10 μM. This was associated with a decrease in cell viability as <20% survived the treatment with 10 μM of LY294002. Neither inhibition of extracellular response kinase nor p38 mitogen-activated protein kinase inhibited osmotic induction of the γ subunit. In contrast, cells transfected with a dominant negative c-Jun N-terminal kinase 2-APF construct displayed complete inhibition of the γ subunit. Such cells have accelerated loss of viability in hypertonic conditions. This study describes the regulation of the γ subunit of Na-K-ATPase by hypertonicity. This regulation is transcriptionally regulated and involves signaling mediated by phosphatidylinositol 3-kinase and c-Jun N-terminal kinase 2 pathways.
A genetic screen identifies a cellular regulator of adeno-associated virus
Authors: Cathomen Toni , Stracker Travis H. , Gilbert Luz Beatriz , Weitzman Matthew D.
Published: July 2002

Adeno-associated virus type 2 (AAV2) is a human parvovirus
that has attracted attention as a vector for gene transfer. Replication
and site-specific integration of the wild-type virus requires
binding of the AAV2 Rep proteins to a cis-regulatory element named
the Rep recognition sequence (RRS). RRS motifs are found within the
cellular
AAVS1
integration locus, the viral p5 promoter,
and the inverted terminal repeats (ITRs). Here we report the
design of a genetic screen based on the yeast one-hybrid assay to
identify cellular RRS-binding proteins. We show that the human zinc
finger 5 protein (ZF5) binds specifically to RRS motifs
in
vitro
and
in vivo
. ZF5 is a highly conserved and
ubiquitously expressed transcription factor that contains five
C-terminal zinc fingers and an N-terminal POZ domain. Ectopic
expression of ZF5 leads to an ITR-dependent repression of the
autologous p5 promoter and reduces both AAV2 replication and the
production of recombinant AAV2. By using deletion and substitution
mutants we show that two different domains of ZF5 contribute to AAV2
repression. Negative regulation of the p5 promoter requires the POZ
domain, whereas viral replication is inhibited by the zinc finger
domain, likely by competing with Rep for binding to the ITR.
Identification and characterization of proteins that bind the ITR, the
only viral genetic element retained in AAV2 vectors, will lead to new
insights into the unique life cycle of AAV2 and will suggest
improvements important for its application as a gene therapy vector.
Reciprocal regulation of G
sα
by palmitate and the βγ subunit
Authors: Iiri Taroh , Backlund Peter S. , Jones Teresa L. Z. , Wedegaertner Philip B. , Bourne Henry R.
Published: July 2002

Hormonal activation of G
s
, the stimulatory regulator of
adenylyl cyclase, promotes dissociation of α
s
from
Gβγ, accelerates removal of covalently attached palmitate from the
Gα subunit, and triggers release of a fraction of α
s
from the plasma membrane into the cytosol. To elucidate relations among
these three events, we assessed biochemical effects
in
vitro
of attached palmitate on recombinant α
s
prepared from Sf9 cells. In comparison to the unpalmitoylated protein
(obtained from cytosol of Sf9 cells, treated with a palmitoyl esterase,
or expressed as a mutant protein lacking the site for palmitoylation),
palmitoylated α
s
(from Sf9 membranes, 50% palmitoylated)
was more hydrophobic, as indicated by partitioning into TX-114, and
bound βγ with 5-fold higher affinity. βγ protected GDP-bound
α
s
, but not α
s
· GTP[γS], from
depalmitoylation by a recombinant esterase. We conclude that βγ
binding and palmitoylation reciprocally potentiate each other in
promoting membrane attachment of α
s
and that dissociation
of α
s
·GTP from βγ is likely to mediate
receptor-induced α
s
depalmitoylation and translocation of
the protein to cytosol in intact cells.
Gene targeting by linear duplex DNA frequently occurs by assimilation of a single strand that is subject to preferential mismatch correction
Authors: Leung W.-Y. , Malkova A. , Haber J. E.
Published: July 2002

To study targeted recombination, a single linear 2-kb fragment of
LEU2
DNA was liberated from a chromosomal site within the nucleus of
Saccharomyces cerevisiae
, by expression of the site-specific HO endonuclease. Gene targeting was scored by gene conversion of a chromosomal
leu2
mutant allele by the liberated
LEU2
fragment. This occurred at a frequency of only 2 × 10
−4
, despite the fact that nearly all cells successfully repaired, by single-strand annealing, the chromosome break created by liberating the fragment. The frequency of Leu
+
recombinants was 6- to 25-fold higher in
pms1
strains lacking mismatch repair. In 70% of these cases, the colony was sectored for Leu
+
/Leu
−
. Similar results were obtained when a 4.1-kb fragment containing adjacent
LEU2
and
ADE1
genes was liberated, to convert adjacent
leu2
and
ade1
mutations on the chromosome. These results suggest that a linear fragment is not assimilated into the recipient chromosome by two crossovers each close to the end of the fragment; rather, heteroduplex DNA between the fragment and the chromosome is apparently formed over the entire region, by the assimilation of one of the two strands of the linear duplex DNA. Moreover, the recovery of Leu
+
transformants is frequently defeated by the cell’s mismatch repair machinery; more than 85% of mismatches in heteroduplex DNA are corrected in favor of the resident, unbroken (mutant) strand.
Targeted inactivation of αi2or αi3disrupts activation of the cardiac muscarinic K+channel, IK+Ach, in intact cells
Authors: Sowell Margaret O. , Ye Chianping , Ricupero Dennis A. , Hansen Sherry , Quinn Stephen J. , Vassilev Peter M. , Mortensen Richard M.
Published: July 2002

Cardiac muscarinic receptors activate an inwardly rectifying K+channel, IK+Ach, via pertussis toxin (PT)-sensitive heterotrimeric G proteins (in heart Gi2, Gi3, or Go). We have used embryonic stem cell (ES cell)-derived cardiocytes with targeted inactivations of specific PT-sensitive α subunits to determine which G proteins are required for receptor-mediated regulation of IK+Achin intact cells. The muscarinic agonist carbachol increased IK+Achactivity in ES cell-derived cardiocytes from wild-type cells, in cells lacking αo, and in cells lacking the PT-insensitive G protein αq. In cells with targeted inactivation of αi2or αi3, channel activation by both carbachol and adenosine was blocked. Carbachol-induced channel activation was restored in the αi2- and αi3-null cells by reexpressing the previously targeted gene and guanosine 5′-[γ-thio] triphosphate was able to fully activate IK+Achin excised membranes patches from these mutants. In contrast, negative chronotropic responses to both carbachol and adenosine were preserved in cells lacking αi2or αi3. Our results show that expression of two specific PT-sensitive α subunits (αi2and αi3but not αo) is required for normal agonist-dependent activation of IK+Achand suggest that both αi2- and αi3-containing heterotrimeric G proteins may be involved in the signaling process. Also the generation of negative chronotropic responses to muscarinic or adenosine receptor agonists do not require activation of IK+Achor the expression of αi2or αi3.
Solid and liquid phase59Co NMR studies of cobalamins and their derivatives
Authors: Medek Ales , Frydman Veronica , Frydman Lucio
Published: July 2002

We describe the application of59Co NMR to the study of naturally occurring cobalamins. Targets of these investigations included vitamin B12, the B12coenzyme, methylcobalamin, and dicyanocobyrinic acid heptamethylester. These measurements were carried out on solutions and powders of different origins, and repeated at a variety of magnetic field strengths. Particularly informative were the solid-state central transition NMR spectra, which when combined with numerical line shape analyses provided a clear description of the cobalt coupling parameters. These parameters showed a high sensitivity to the type of ligands attached to the metal and to the crystallization history of the sample.59Co NMR determinations also were carried out on synthetic cobaloximes possessing alkyl, cyanide, aquo, and nitrogenated axial groups, substituents that paralleled the coordination of the natural compounds. These analogs displayed coupling anisotropies comparable to those of the cobalamins, as well as systematic up-field shifts that can be rationalized in terms of their stronger binding affinity to the cobalt atom. Cobaloximes also displayed a higher regularity in the relative orientations of their quadrupole and shielding coupling tensors, reflecting a higher symmetry in their in-plane coordination. For the cobalamines, poor correlations were observed between the values measured for the quadrupole couplings in the solid and the line widths observed in the corresponding solution59Co NMR resonances.
Impairment of antigen-specific antibody production in transgenic mice expressing a dominant-negative form of gp130
Authors: Kumanogoh Atsushi , Marukawa Satoko , Kumanogoh Takayuki , Hirota Hisao , Yoshida Kenji , Lee Ihn-Sook , Yasui Teruhito , Yoshida Kanji , Taga Tetsuya , Kishimoto Tadamitsu
Published: July 2002

gp130 is a common signal-transducing receptor component for the interleukin 6 family of cytokines functioning in, for example, immune, hematopoietic, and nervous systems. In this study, to investigate the physiological functions of gp130 and to determine the pathological consequences of impaired gp130 signals, we have generated transgenic mice expressing a cytoplasmically truncated form of mouse gp130. Expression of this form of gp130 in lymphocytes significantly suppressed interleukin 6-induced tyrosine phosphorylation of endogenous gp130 and a downstream signaling molecule, signal transducer and activator of transcription 3, indicating that this form has a dominant negative function. In spite of the impaired gp130 signals, the development of lymphocytes in the transgenic mice appeared normal in terms of surface marker phenotypes. These mice, however, exhibited severe defects in antigen-specific antibody production of most immunoglobulin isotypes other than IgM after immunization with 2,4-dinitrophenol-conjugated ovalbumin. These results demonstratein vivothat gp130 is essential for antigen-specific antibody production.
Orientation in operator algebras
Authors: Alfsen Erik M. , Shultz Frederic W.
Published: July 2002

A concept of orientation is relevant for the passage from Jordan structure to associative structure in operator algebras. The research reported in this paper bridges the approach of Connes for von Neumann algebras and ourselves for C*-algebras in a general theory of orientation that is of geometric nature and is related to dynamics.
Padlock oligonucleotides for duplex DNA based on sequence-specific triple helix formation
Authors: Escudé Christophe , Garestier Thérèse , Hélène Claude
Published: July 2002

An oligonucleotide was circularized around double-stranded DNA thanks to triple helix formation. Short oligonucleotides are known to be able to form DNA triple helices by binding into the DNA major groove at an oligopurine⋅oligopyrimidine sequence. After sequence-specific recognition of a double-stranded DNA target through triple helix formation, the ends of the triplex-forming oligonucleotide were joined through the action of T4 DNA ligase, thus creating a circular DNA molecule catenated to the plasmid containing the target sequence. The labeling of the double-stranded DNA sequence has been carried out without any chemical or enzymatic modification of this sequence. These “padlock” oligonucleotides provide a tool to attach a noncovalent tag in an irreversible way to supercoiled plasmid or other double-stranded DNAs. Such a complex may find applications in the development of new techniques for duplex DNA detection or plasmid delivery methods for gene therapy.
Interaction of calicheamicin γ
1
I
and its related carbohydrates with DNA–protein complexes
Authors: Sissi Claudia , Aiyar Jayshree , Boyer Serge , Depew Kris , Danishefsky Samuel , Crothers Donald M.
Published: July 2002

We report studies of the contribution of DNA structure, holding the sequence constant, to the affinity of calicheamicin γ
1
I
and its aryltetrasaccharide moiety for DNA. We used polynucleotide chains as models of known protein-binding sequences [the catabolite activator protein (CAP) consensus sequence, AP-1 and cAMP response element (CRE) sites] in their free and protein-bound forms. The proteins were selected to provide examples in which the minor-groove binding site for the carbohydrate is (CAP) or is not (GCN4) covered by the protein. Additionally, peptides related to the GCN4 and CREB families, which have different bending effects on their DNA-binding sites, were used. We observe that proteins of the CREB class, which induce a tendency to bend toward the minor groove at the center of the site, inhibit drug-cleavage sites located at the center of the free AP-1 or CRE DNA sites. In the case of GCN4, which does not induce DNA bending, there is no effect on calicheamicin cleavage of the CRE site, but we observe a GCN4-induced rearrangement of the cutting pattern in the AP-1 site. This effect may arise from either a subtle local conformational rearrangement not accompanied by bending or a localized reduction in DNA flexibility. Whereas GCN4 binding is not inhibited by the calicheamicin aryltetrasaccharide, binding of CAP to its DNA target is significantly inhibited, and calicheamicin cutting of DNA at the center of the CAP–DNA complex site is strongly reduced by protein binding. This result probably reflects steric inhibition of drug binding by the protein.
Expression of guanylin in “pars tuberalis-specific cells” and gonadotrophs of rat adenohypophysis
Authors: D'Este Loredana , Kulaksiz Hasan , Rausch Ulrich , Vaccaro Rosa , Wenger Tibor , Tokunaga Yoshimitsu , Renda Tindaro G. , Cetin Yalcin
Published: July 2002

The intestinal peptide guanylin regulates the electrolyte/water transport in the gastrointestinal epithelium by paracrine/luminocrine mechanisms. Because guanylin also circulates in the blood, we investigated the rat hypothalamo-pituitary region for expression and cellular localization of this peptide. Reverse transcriptase–PCR analyses with guanylin-specific primers revealed expression of the peptide in the pars tuberalis and pars distalis of the pituitary. Western blotting analyses in hypophyseal tissue extracts identified the expected 12.5-kDa immunoreactive peptide by using two different region-specific guanylin antisera. Light and electron microscopic immunocytochemistry with the same antisera localized guanylin in “pars tuberalis-specific cells” in the juxtaneural pars tuberalis adjacent to nerve endings and blood vessels of the hypothalamo-pituitary portal system and in gonadotrophic cells within the distal pars tuberalis and ventrolateral part of the pars distalis. The presence and cell-specific localization of guanylin within the hypothalamo-hypophyseal system indicate that this peptide may be specifically involved in paracrine and endocrine regulatory mechanisms.
Liver cirrhosis mortality trends in Eastern Europe, 1970–1989. Analyses of age, period and cohort effects and of latency with alcohol consumption
Authors: Corrao Giovanni
Published: July 2002

There is evidence that in some Eastern European countries alcohol‐related deaths have an important impact on mortality. In the whole European population increasing trends in mortality were observed until the second half of the 1970s, followed by a decline in the following decades. By contrast, in Eastern Europe continuously rising trends have been observed. The aim of the present study is to describe cirrhosis mortality trends in Eastern European countries between 1970 and 1989. This is a descriptive study in seven European countries, compared with Europe as a whole. A Poisson's log‐linear age‐period‐cohort model is used to ascertain whether the recent trend in mortality represents a short‐term fluctuation or an emerging long‐term trend. In addition, changes in cirrhosis death rates were regressed onto changes in per capita alcohol consumption (1961–89) in order to evaluate the latency period between trends. The birth‐cohort effects suggested that in Eastern Europe as a whole, and in particular in Hungary, Bulgaria and Romania, the mortality will probably increase in the next decade. Eastern European countries showed a latency period between trends in alcohol consumption and in mortality rates of many years, whereas in Europe as a whole the cirrhosis mortality rates were explained by their relationship with per capita alcohol consumption which lagged by only a few years. Further increases in cirrhosis mortality, and probably in other alcohol‐related problems, are expected in several Eastern European countries. Epidemiological studies aimed to estimate the proportion of disease attributable to known risk factors of cirrhosis, and monitoring programmes of viral infections and of alcohol consumption and alcohol‐related problems, should be implemented to address the planning of public health programmes.
Purification and Characterization of an Extracellular Serine Proteinase from Acanthamoeba castellanii
Authors: Cho Jung‐Hwa , Na Byoung‐Kuk , Kim Tong‐Soo , Song Chul‐Yong
Published: July 2002

An extracellular proteinase of Acanthamoeba castellanii was purified and its biochemical and pathological properties were characterized. The molecular mass of the purified enzyme was ˜ 42 kDa as estimated by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Sephacryl S‐200 HR gel‐filtration chromatography. Therefore, its structure seemed to be monomeric with a single polypeptide. Its activity was inhibited by the serine proteinase inhibitors diisopropyl fluorophosphate and phenylmethanesulfonyl fluoride. Its activity was optimum at 30 to 50 °C with a maximum at 50 °C; optimal pH was 8.0. As much as 70% of the enzyme activity was maintained at 50 °C for at least 12 h but was rapidly inactivated thereafter. The purified enzyme degraded collagen and rabbit corneal extract. Furthermore, it exhibited strong cytopathic effects on human corneal epithelial cells and fibroblast cells. These suggest the possible role of this enzyme in the pathogenesis of Acanthamoeba.