bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat kernel coefficients of the Laplace operator on the D-dimensional ball
Authors: Bordag M. , Elizalde E. , Kirsten K.
Published: July 2002

We present a very quick and powerful method for the calculation of heat kernel coefficients. It makes use of rather common ideas, as integral representations of the spectral sum, Mellin transforms, non-trivial commutation of series and integrals and skillful analytic continuation of zeta functions on the complex plane. We apply our method to the case of the heat kernel expansion of the Laplace operator on a D-dimensional ball with either Dirichlet, Neumann or, in general, Robin boundary conditions. The final formulas are quite simple. Using this case as an example, we illustrate in detail our scheme —which serves for the calculation of an (in principle) arbitrary number of heat kernel coefficients in any situation when the basis functions are known. We provide a complete list of new results for the coefficients B3,..., B10, corresponding to the D-dimensional ball with all the mentioned boundary conditions and D=3,4,5.
Friedrichs model with virtual transitions. Exact solution and indirect spectroscopy
Authors: Karpov E. , Prigogine I. , Petrosky T. , Pronko G.
Published: July 2002

The Friedrichs-type model of interaction between matter (multilevel system) and radiation including virtual transitions is considered. The canonical Bogolubov transformation diagonalizing the total Hamiltonian is constructed. It is pointed out that the transformation is improper when the discrete part of the spectrum of system is “dissolved” in the continuous one. The new vacuum state for the total Hamiltonian is obtained. The time evolution of the bare vacuum and the bare operators is calculated. Using the exact solution, the result of Passante, Petrosky, and Prigogine [Physica A 218, 437 (1995)] that the transition from the bare vacuum state to the true vacuum leads to the emission of real photons is confirmed. The dressing of the bare vacuum at the presence of resonances is an irreversible process. The relation of the result with the idea of “indirect spectroscopy” is discussed.
Classical four-vector fields in the relativistic longitudinal gauge
Authors: Woodside Dale A.
Published: July 2002

Minkowski four-space uniqueness theorems are used to develop further the author’s “relativistic longitudinal gauge” [J. Math. Phys. 40, 4911 (1999)] for four-irrotational classical four-vector fields. A theorem is developed which distinguishes between two and only two “physical” classes of classical four-vector fields. One must satisfy the “relativistic transverse gauge,” i.e., the Lorentz condition, while the other must satisfy this new relativistic longitudinal gauge where its four-curl, the Maxwell field tensor itself, is set to zero. The Lagrangian density of the new four-irrotational four-vector field is distinguished from the usual Lorentz constrained Lagrangian density by the incorporation of an additional overall minus sign. Application of the relativistic longitudinal gauge, in the four-irrotational four-vector field case, eliminates the badly behaved terms associated with the spatial degrees of freedom from a most general, fully quadratic, Lagrangian density. The resulting constrained Lagrangian density is bounded from below and therefore a relativistic longitudinal classical four-vector field has the possibility of a physical interpretation.
Separated flow in a driven trapezoidal cavity
Authors: Darr Joseph H. , Vanka S. P.
Published: July 2002

Numerical solutions of the Navier–Stokes equations governing shear flow in a trapezoidal enclosure have been obtained at fine grid resolutions using an efficient multigrid calculation procedure. The effects of flow Reynolds number and wall boundary conditions are studied in detail. Interesting flow patterns are observed to develop, especially at high Reynolds numbers. To the author’s knowledge, such a flow development has not been reported previously.
Laminar flow control of subsonic boundary layers by suction and heat-transfer strips
Authors: Masad J. A. , Nayfeh A. H.
Published: July 2002

The effects of suction and heat-transfer strips on the stability of subsonic boundary layers over flat plates are investigated. The mean flows are calculated by using interacting boundary layers. Then the linear two-dimensional quasiparallel spatial stability theory of compressible flows is used to calculate the growth rates and hence the amplification factors. Using the eN criterion, the optimal location of a suction strip for delaying transition is investigated. Moreover, using the fact that the incremental growth rates due to suction in subsonic flows vary linearly with suction velocity, influence coefficients are calculated that can be used to design ‘‘smart’’ suction configurations. A major finding of the present investigation is the reversal of the effect of heating by strips compared with uniform heating. The present results show that a heating strip located near branch I of the neutral stability curve very much stabilizes the flow, in contrast with uniform heating, which destabilizes the flow. On the other hand, a cooling strip located near branch I of the neutral stability curve destabilizes the flow, in contrast with uniform cooling, which stabilizes the flow. It is also found that a properly placed cooling strip can delay transition in subsonic boundary layers. The optimal locations of heating and cooling strips are determined. The present findings may have important implications for the design of laminar flow control surfaces.
The effect of an electrostatic field on film flow down an inclined plane
Authors: Kim Hyo , Bankoff S. G. , Miksis Michael J.
Published: July 2002

A study of the interaction of an electrostatic field with a thin liquid film flowing under gravity down an inclined plane is presented. First, the effect of the electric field on the stability of the film flow is examined. Next, several limits of the equations of motion are investigated analytically, and then compared with an explicit numerical calculation of the equations of motion. Also, applications of these calculations to a proposed electrostatic liquid film space radiator are discussed.
Kinetic effects in Alfvén wave heating. Part II: Propagation and absorption with a single minority species
Authors: Li Wann-Quan , Ross David W. , Mahajan Swadesh M.
Published: July 2002

The effects of a heavy minority on Alfvén wave heating are examined in a linearized circular cylindrical tokamak model. It is shown that a suitable minority concentration and radially varying charge profile produces a two-ion hybrid resonance in the plasma interior and an Alfvén wave resonance near the edge. The latter situation, which gives rise to cold plasma surface Alfvén eigenmodes (SAE’s), was described in Part I [Phys. Fluids B 1, 2353 (1989)] for a pure plasma. Here, numerical results, exhibiting substantial absorption in the hybrid layer as a result of the dissipation of these modes, are presented. It is shown that the poloidal mode number strongly affects the amount of the energy absorbed in the hybrid layer. Generally, electron heating due to electron Landau and collisional damping of SAE’s and two-ion hybrid fields [ω>(ωc2)max, with ωc2 being the fundamental minority gyrofrequency] dominates minority heating excepting for cases when k∥, the parallel wavenumber, is large enough that no SAE occurs near the plasma edge. For the larger k∥ system, there occurs a stronger coupling between the two-ion hybrid and fundamental minority gyroresonance layers, resulting in comparable electron and minority heating. The majority heating is zero everywhere because ω<(ωc1)min, where ωc1 is the fundamental majority gyrofrequency.
Self-induced distributed feedback in plasma-filled Čerenkov free electron masers
Authors: Botton M. , Ron Amiram
Published: July 2002

Two strong counterpropagating waves in the cavity of a plasma-filled Čerenkov free electron maser modulate the density of the plasma electrons and ions. These density modulations induce periodic perturbations in the effective high-frequency dielectric constant of the plasma. When the intensity of the waves is high, and the ions can move to reduce the charge separation, the modulations are saturated. The two waves are then coupled by a self-induced distributed feedback. The distributed feedback is shown to resonantly enhance the gain of the Čerenkov amplifier. In the oscillator, the threshold gain is significantly reduced. Estimates of the oscillator efficiency show that the distributed feedback may enhance this efficiency to about eight times more than in a comparable vacuum Čerenkov oscillator.
The mechanism of mixing enhancement and suppression in a circular jet under excitation conditions
Authors: Mankbadi R. R.
Published: July 2002

The present work is a numerical study of the shear layer’s growth in a turbulent round jet under forced axisymmetric periodic disturbances. The forced oscillation is found to either enhance or reduce the momentum thickness along the jet depending on the forcing Strouhal number St, where St is defined as fd/Ue. Here, f is the frequency in Hertz, d is the nozzle exit diameter, and Ue is the jet exit velocity. At low Strouhal numbers (St<0.5), no subharmonic of the forced fundamental is amplified. The momentum thickness is found to increase monotonically with the forcing level, and the effect is pronounced for forcing levels higher than 0.5% of the jet exit velocity. At forcing Strouhal numbers in the range of 0.6–1.0, the first subharmonic of the fundamental is amplified. The increase in the momentum thickness caused by forcing at this Strouhal number range is proportional to the forcing level and is pronounced at low forcing levels in the range of 0.01%–1% of the jet exit velocity. If the forcing Strouhal number is close to the ‘‘shear layer instability mode,’’ Stθ≊0.015, several subharmonics are generated and the forcing is found to result in a reduction in the momentum thickness along the jet.
Reduction of radial losses in a pure electron plasma
Authors: Driscoll C. F. , Fine K. S. , Malmberg J. H.
Published: July 2002

A new pure electron-plasma containment apparatus exhibits radial losses approximately 20 times smaller than the prior apparatus. However, the new containment times show the same (L/B)−2 scaling with plasma column length and magnetic field as obtained previously. The radial transport is apparently induced by small irregularities that break the cylindrical symmetry of the magnetic and electric containment fields. The fact that the two devices show the same (L/B)−2 scaling suggests the dominance of a single generic process, although this process has not yet been identified.
Kinetic theory of binary gas mixtures with large mass disparity
Authors: Fernández de la Mora J. , Fernández-Feria R.
Published: July 2002

The Boltzmann equations for a binary mixture of gases are considered in the asymptotic limit when their molecular weight ratio and the light gas Knudsen number are small quantities. A first mass-ratio expansion reduces the cross-collision operator of the light gas Boltzmann equation to a Lorentz form, uncoupling its kinetic behavior from that of the heavy gas. The light gas distribution function is then determined to first order in the Knudsen number, independently of the degree of nonequilibrium characterizing the heavy gas, whose influence is felt only through its hydrodynamic quantities. All transport coefficients arising are determined variationally for arbitrary interaction potentials using Sonine polynomial expansions as trial functions. A remarkable feature of this analysis is that it yields binary transport information (i.e., diffusion and thermal diffusion coefficients) from considering only the Boltzmann equation for the light gas. A second mass expansion reduces the cross-collision operator of the heavy gas equation to a Fokker–Planck form. The corresponding coefficients involve integrals over the light gas distribution function determined previously and are evaluated explicitly in terms of the hydrodynamic quantities and transport coefficients of the light gas. The heavy gas distribution function can be determined by solving a Fokker–Planck equation at dilutions large enough to make heavy–heavy collisions negligible, or by a new Knudsen number expansion when the molar fraction of the heavy gas is of order 1. In this latter case, the heavy gas kinetic behavior is independent of the light gas, being characterized by the same transport coefficients of the pure heavy gas. The problem is then reduced to a set of two-fluid hydrodynamic equations.
On the solution of Stokes’ equations between confocal ellipses
Authors: Saatdjian Estéban , Midoux Noël , André Jean Claude
Published: July 2002

The analytical solution of Stokes’ equations between two concentric, confocal ellipses is derived here. This bounded flow, similar in certain respects to the journal bearing flow, was imagined in order to investigate two-dimensional mixing and Lagrangian chaos in a bounded flow with two symmetry axis. The derived streamfunction is in the form of a Fourier cosine series and, when the eccentricity ratio of the inner ellipse is not very low, the solution converges very rapidly. When the ellipses turn in opposite directions, there are cases where two saddle points are connected by two different streamlines, a necessary and sufficient condition for structural instability according to Peixoto’s theorem. This flow geometry could be particularly effective for mixing of viscous fluids since the number of low period hyperbolic and elliptical points during time periodic boundary motion is greater than for the eccentric rotating cylinder system. The Poincaré sections obtained with a discontinuous velocity protocol suggest that the size of regions of poor mixing can be reduced by increasing the inner ellipse motion per period. For this geometry, the Poincaré sections indicate that counter-rotation yields a more chaotic long term behavior than co-rotation.
Large eddy simulation of longitudinal stationary vortices
Authors: Sreedhar Madhu , Ragab Saad
Published: July 2002

The response of longitudinal stationary vortices when subjected to random perturbations is investigated using temporal large-eddy simulation. Simulations are obtained for high Reynolds numbers and at a low subsonic Mach number. The subgrid-scale stress tensor is modeled using the dynamic eddy-viscosity model. The generation of large-scale structures due to centrifugal instability and their subsequent breakdown to turbulence is studied. The following events are observed. Initially, ring-shaped structures appear around the vortex core. These structures are counter-rotating vortices similar to the donut-shaped structures observed in a Taylor–Couette flow between rotating cylinders. These structures subsequently interact with the vortex core resulting in a rapid decay of the vortex. The turbulent kinetic energy increases rapidly until saturation, and then a period of slow decay prevails. During the period of maximum turbulent kinetic energy, the normalized mean circulation profile exhibits a logarithmic region, in agreement with the universal inner profile of Hoffman and Joubert [J. Fluid Mech. 16, 395 (1963)].
Caustics of weak shock waves
Authors: Rosales Rodolfo R. , Tabak Esteban G.
Published: July 2002

The caustics of weak shock waves are studied through matched asymptotic expansions. It is shown that these caustics are thinner and more intense than those of smooth waves with a comparable amplitude. This difference in scalings solves a paradox that would have the caustics of weak shock waves behave linearly, even though linear theory for discontinuous fronts predicts infinite amplitudes near the caustic and in the reflected wave. With the new scalings, the behavior of shocks both near the caustic and in the far field is described by nonlinear equations. The new scales are robust, in the sense that they survive the addition of a small amount of viscosity to the equations. As a viscous shock approaches the caustic, its intensity amplifies and its width decreases in such a way that the new scalings are actually reinforced. A new paradox arises, however: The nonlinear Tricomi equation which describes the behavior of the fronts near caustics does not appear to admit the triple shock intersections which have been observed experimentally. This new open problem is closely related to the von Neumann paradox of oblique shock reflection.
Experimental investigation of interaction processes between droplets and hot walls
Authors: Karl A. , Frohn A.
Published: July 2002

A detailed experimental investigation of interaction processes of small liquid droplets with hot walls well above the Leidenfrost temperature has been carried out. The experimental method which uses monodisperse droplet streams in combination with a standard video camera allows very detailed observations and measurements with very high time resolution. The main intent of this paper is to study the mechanical behavior of liquid droplets impacting on hot walls well above the Leidenfrost temperature. A better understanding of this process may lead to a better modeling of two-phase flows, especially for applications in fuel preparation processes, combustion processes, and spray cooling. The loss of momentum of the droplets, the droplet deformation, and the onset of droplet disintegration have been investigated. For all experimental results correlations have been developed, which can be used to improve the numerical modeling of two-phase flows. Using the correlation for the loss of momentum a theoretical approximation for the maximum droplet deformation has been deduced, which yields a very good agreement with our own measurements as well as with results reported in the literature. A minimum impinging angle for droplet disintegration has been discovered for small impinging angles. Below this impinging angle no droplet disintegration is observed. This phenomenon is directly related to the energy dissipation at the wall during the interaction process. With the presented work the understanding of basic interaction processes between droplets and hot walls may be improved.
Laser-driven plasma-based accelerators: Wakefield excitation, channel guiding, and laser triggered particle injection
Authors: Leemans W. P. , Volfbeyn P. , Guo K. Z. , Chattopadhyay S. , Schroeder C. B. , Shadwick B. A. , Lee P. B. , Wurtele J. S. , Esarey E.
Published: July 2002

Plasma-based accelerators are discussed in which high-power short pulse lasers are the power source, suitably tailored plasma structures provide guiding of the laser beam and support large accelerating gradients, and an optical scheme is used to produce time-synchronized ultrashort electron bunches. From scaling laws laser requirements are obtained for development of compact high-energy accelerators. Simulation results of laser guiding and wakefield excitation in plasma channels, as well as laser-based injection of particles into a plasma wake, are presented. Details of the experimental program at Lawrence Berkeley National Laboratory on laser guiding, laser wakefield-based accelerators, and laser triggered injection are given.
Mechanism for dislocation density reduction in GaAs crystals by indium addition
Authors: Ehrenreich H. , Hirth J. P.
Published: July 2002

The strengthening of GaAs single crystals by the substitution of a few percent In on Ga sites is analyzed on the basis of a solid solution hardening model. The hardening entity is an In atom and its four nearest As neighbors. The predicted hardening is substantial and may account for the reduction in dislocation density in as-grown GaAs crystals containing In.
Optical detection of ultrasound at a distance using a confocal Fabry–Perot interferometer
Authors: Monchalin Jean-Pierre
Published: July 2002

A novel scheme to detect ultrasonic motion at the surface of a solid sample is presented. The surface of the sample is illuminated by a laser and the light scattered by the surface is received by a confocal Fabry–Perot interferometer which demodulates the Doppler shift produced by ultrasound. Experimental results, obtained at a distance of 1.5 m from a machined but not polished steel plate, and excited by ultrasound produced by a laser pulse, are presented.
Studies of excimer laser ablation of solids using a Michelson interferometer
Authors: Walkup R. E. , Jasinski J. M. , Dreyfus R. W.
Published: July 2002

A Michelson interferometer has been used as a direct quantitative probe for gas phase plasma formation in the UV excimer laser ablation of solids. Excimer laser fluence thresholds for plasma formation are determined and correlated with optical emission from electronically excited ablation fragments.
Generation and detection of picosecond acoustic pulses in thin metal films
Authors: Eesley Gary L. , Clemens Bruce M. , Paddock Carolyn A.
Published: July 2002

We report on the use of picosecond duration laser pulses to generate picosecond acoustic pulses in metal films on the order of 200 nm thick. The acoustic pulses are detected by means of transient piezoreflectance measurements. We demonstrate the use of a thin metal overlayer to enhance the piezoreflectance signal.
Interfacially initiated crystallization in amorphous germanium films
Authors: Homma Hitoshi , Schuller Ivan K. , Sevenhans Walter , Bruynseraede Yvan
Published: July 2002

The amorphous to microcrystalline phase transition of Ge in Pb/Ge multilayers has been extensively studied. During crystallization, the x-ray diffraction peaks of the modulated structure disappear and the Pb texture improves. It is shown that the crystallization temperature decreases with decreasing amorphous Ge thickness and is strongly affected by the texture of the metallic component. These results imply that the crystallization is interfacially initiated.
Active pulse compression using an integrated electro-optic phase modulator
Authors: Kolner Brian H.
Published: July 2002

We describe a pulse compression technique that uses integrated electro-optic phase modulators to linearly chirp optical pulses for compression by a dispersive delay line. In contrast to passive chirp techniques such as self-phase modulation, this approach of active pulse compression does not depend on the optical power and thus shows promise for application to low-power solid-state lasers as an alternative to mode locking for realizing compact picosecond sources. We have demonstrated this technique by compressing the pulses from a mode-locked neodymium:yttrium aluminum garnet laser from 100 to 45 ps.
A conditional probability analysis of cystic fibrosis transmembrane conductance regulator gating indicates that ATP has multiple effects during the gating cycle
Authors: Hennager Daniel J. , Ikuma Mutsuhiro , Hoshi Toshinori , Welsh Michael J.
Published: July 2002

ATP-binding cassette (ABC) transporters bind and hydrolyze ATP. In
the cystic fibrosis transmembrane conductance regulator
Cl
−
channel, this interaction with ATP generates a gating
cycle between a closed (C) and two open (O1 and O2) conformations. To
understand better how ATP controls channel activity, we examined gating
transitions from the C to the O1 and O2 states and from these open
states to the C conformation. We made three main observations. First,
we found that the channel can open into either the O1 or O2 state, that
the frequency of transitions to both states was increased by ATP
concentration, and that ATP increased the relative proportion of
openings into O1 vs. O2. These results indicate that ATP can interact
with the closed state to open the channel in at least two ways, which
may involve binding to nucleotide-binding domains (NBDs) NBD1 and NBD2.
Second, ATP prolonged the burst duration and altered the way in which
the channel closed. These data suggest that ATP also interacts with the
open channel. Third, the channel showed runs of specific types of
open–closed transitions. This finding suggests a mechanism with more
than one cycle of gating transitions. These data suggest models to
explain how ATP influences conformational transitions in cystic
fibrosis transmembrane conductance regulator and perhaps other ABC
transporters.
Genetic mapping of a naturally occurring hereditary renal cancer syndrome in dogs
Authors: Jónasdóttir Thora J. , Mellersh Cathryn S. , Moe Lars , Heggebø Ragna , Gamlem Hans , Ostrander Elaine A. , Lingaas Frode
Published: July 2002

Canine hereditary multifocal renal cystadenocarcinoma and nodular dermatofibrosis (RCND) is a rare, naturally occurring inherited cancer syndrome observed in dogs. Genetic linkage analysis of an RCND-informative pedigree has identified a linkage group flankingRCND(CHP14-C05.377-C05.414-FH2383-C05.771-[RCND-CPH18]-C02608-GLUT4-TP53-ZuBeCa6-AHT141-FH2140-FH2594) thus localizing the disease to a small region of canine chromosome 5. The closest marker, C02608, is linked toRCNDwith a recombination fraction (θ) of 0.016, supported by a logarithm of odds score of 16.7. C02608 and the adjacent linked markers map to a region of the canine genome corresponding to portions of human chromosomes 1p and 17p. A combination of linkage analysis and direct sequencing eliminate several likely candidate genes, including tuberous sclerosis 1 and 2 genes (TSC1andTSC2) and the tumor suppressor geneTP53.These data suggest that RCND may be caused by a previously unidentified tumor suppressor gene and highlight the potential for canine genetics in the study of human disease predisposition.
Cytoskeletal microdifferentiation: A mechanism for organizing morphological plasticity in dendrites
Authors: Kaech Stefanie , Parmar Hema , Roelandse Martijn , Bornmann Caroline , Matus Andrew
Published: July 2002

Experimental evidence suggests that microfilaments and microtubules play contrasting roles in regulating the balance between motility and stability in neuronal structures. Actin-containing microfilaments are associated with structural plasticity, both during development when their dynamic activity drives the exploratory activity of growth cones and after circuit formation when the actin-rich dendritic spines of excitatory synapses retain a capacity for rapid changes in morphology. By contrast, microtubules predominate in axonal and dendritic processes, which appear to be morphologically relatively more stable. To compare the cytoplasmic distributions and dynamics of microfilaments and microtubules we made time-lapse recordings of actin or the microtubule-associated protein 2 tagged with green fluorescent protein in neurons growing in dispersed culture or in tissue slices from transgenic mice. The results complement existing evidence indicating that the high concentrations of actin present in dendritic spines is a specialization for morphological plasticity. By contrast, microtubule-associated protein 2 is limited to the shafts of dendrites where time-lapse recordings show little evidence for dynamic activity. A parallel exists between the partitioning of microfilaments and microtubules in motile and stable domains of growing processes during development and between dendrite shafts and spines at excitatory synapses in established neuronal circuits. These data thus suggest a mechanism, conserved through development and adulthood, in which the differential dynamics of actin and microtubules determine the plasticity of neuronal structures.
A role for Src kinase in spontaneous epileptiform activity in the CA3 region of the hippocampus
Authors: Sanna Pietro Paolo , Berton Fulvia , Cammalleri Maurizio , Tallent Melanie K. , Siggins George R. , Bloom Floyd E. , Francesconi Walter
Published: July 2002

Members of the Src family of nonreceptor protein tyrosine kinases (PTKs) have been implicated in the regulation of cellular excitability and synaptic plasticity. We have investigated the role of these PTKs in
in vitro
models of epileptiform activity. Spontaneous epileptiform discharges were induced
in vitro
in the CA3 region of rat hippocampal slices by superfusion with the potassium channel blocker 4-aminopyridine in Mg
2+
-free medium. In hippocampal slices treated in this fashion, Src kinase activity was increased and the frequency of epileptiform discharges could be greatly reduced by inhibitor of the Src family of PTKs, 4-amino-5-(4-chlorophenyl)-7-(
t
-butyl)pyrazolo[3,4-d]pyrimidine (PP2), but not by the inactive structural analog 4-amino-7-phenylpyrazol[3,4-d]pyrimidine (PP3). 4-Amino-5-(4-chlorophenyl)-7-(
t
-butyl)pyrazolo[3,4-d]pyrimidine also reduced epileptiform activity induced by either 4-aminopyridine or Mg
2+
-free medium alone. These observations demonstrate a role for Src family PTKs in the pathophysiology of epilepsy and suggest potential therapeutic targets for antiepileptic therapy.
Two
Plasmodium falciparum
genes express merozoite proteins that are related to
Plasmodium vivax
and
Plasmodium yoelii
adhesive proteins involved in host cell selection and invasion
Authors: Rayner Julian C. , Galinski Mary R. , Ingravallo Paul , Barnwell John W.
Published: July 2002

Two related
Plasmodium falciparum
genes and their encoded proteins have been identified by comparative analyses with
Plasmodium vivax
reticulocyte binding protein 2 (PvRBP-2). The
P. falciparum
genes have a structure which suggests that they may be the result of an evolutionary duplication event, as they share more than 8 kb of closely related nucleotide sequence but then have quite divergent unique 3′ ends. Between these shared and unique regions is a complex set of repeats, the nature and number of which differs between the two genes, as well as between different
P. falciparum
strains. Both genes encode large hydrophilic proteins, which are concentrated at the invasive apical end of the merozoite and are predicted to be more than 350 kDa, with an N-terminal signal sequence and a single transmembrane domain near their C termini. Importantly, they also share gene structure and amino acid homology with the
Plasmodium yoelii
235-kDa rhoptry protein family, which is also related to PvRBP-2. Together these
Plasmodium
proteins define an extended family of proteins that appear to function in erythrocyte selection and invasion. As such, they may prove to be essential components of malaria vaccine preparations.
Disruption of
Sur2
-containing K
ATP
channels enhances insulin-stimulated glucose uptake in skeletal muscle
Authors: Chutkow William A. , Samuel Varman , Hansen Polly A. , Pu Jielin , Valdivia Carmen R. , Makielski Jonathan C. , Burant Charles F.
Published: July 2002

ATP-sensitive potassium channels (K
ATP
) are involved in
a diverse array of physiologic functions including protection of tissue
against ischemic insult, regulation of vascular tone, and modulation of
insulin secretion. To improve our understanding of the role of
K
ATP
in these processes, we used a gene-targeting strategy
to generate mice with a disruption in the muscle-specific
K
ATP
regulatory subunit, SUR2. Insertional mutagenesis of
the
Sur2
locus generated homozygous null
(
Sur2
−/−
) mice and heterozygote
(
Sur2
+/−
) mice that are viable and
phenotypically similar to their wild-type littermates to 6 weeks of age
despite, respectively, half or no SUR2 mRNA expression or channel
activity in skeletal muscle or heart.
Sur2
−/−
animals had lower fasting and fed
serum glucose, exhibited improved glucose tolerance during a glucose
tolerance test, and demonstrated a more rapid and severe hypoglycemia
after administration of insulin. Enhanced glucose use was also observed
during
in vivo
hyperinsulinemic euglycemic clamp studies
during which
Sur2
−/−
mice required a
greater glucose infusion rate to maintain a target blood glucose level.
Enhanced insulin action was intrinsic to the skeletal muscle, as
in vitro
insulin-stimulated glucose transport was
1.5-fold greater in
Sur2
−/−
muscle than in
wild type. Thus, membrane excitability and K
ATP
activity,
to our knowledge, seem to be new components of the insulin-stimulated
glucose uptake mechanism, suggesting possible future therapeutic
approaches for individuals suffering from diabetes mellitus.
Direct atomic force microscope imaging of EcoRI endonuclease site specifically bound to plasmid DNA molecules.
Authors: Allison D P , Kerper P S , Doktycz M J , Spain J A , Modrich P , Larimer F W , Thundat T , Warmack R J
Published: July 2002

Direct imaging with the atomic force microscope has been used to identify specific nucleotide sequences in plasmid DNA molecules. This was accomplished using EcoRI (Gln-111), a mutant of the restriction enzyme that has a 1000-fold greater binding affinity than the wild-type enzyme but with cleavage rate constants reduced by a factor of 10(4). ScaI-linearized plasmids with single (pBS+) and double (pGEM-luc and pSV-beta-galactosidase) EcoRI recognition sites were imaged, and the bound enzyme was localized to a 50- to 100-nt resolution. The high affinity for the EcoRI binding site exhibited by this mutant endonuclease, coupled with an observed low level of nonspecific binding, should prove valuable for physically mapping large DNA clones by direct atomic force microscope imaging.
Gly-63 → Gln substitution adjacent to His-64 in rodent carbonic anhydrase IVs largely explains their reduced activity
Authors: Tamai Shinya , Waheed Abdul , Cody Lee B. , Sly William S.
Published: July 2002

Carbonic anhydrase (CA) IV is a
glycosylphosphatidylinositol-anchored isozyme expressed on
plasma membranes of capillary endothelial cells and certain epithelial
cells of the nephron, the colon, and the genitourinary tract. CA IVs
purified from bovine and rabbit lungs are high-activity enzymes, like
human CA IV, while CA IV from mouse and rat lungs had only 10–20% as
much catalytic activity. To explain the molecular basis for these
differences in activity, we isolated and characterized the full-length
cDNAs for bovine and rabbit CA IVs and compared their sequences to
those we previously reported for human, murine, and rat CA IVs. These
comparisons led us to postulate that a Gly-63 → Gln substitution
adjacent to His-64 in the rodent enzymes accounts for their lower
activity. To test this hypothesis, we made the Gly-63 → Gln mutants
of bovine and rabbit CA IVs and the Gln-63 → Gly mutant of murine CA
IV by site-directed mutagenesis, and compared the activities of mutant
and wild-type CA IVs expressed in COS-7 cells. In addition, we produced
recombinant cDNAs expressing secretory forms of the Gly-63 and Gln-63
forms of each of the three enzymes and compared the activities of the
enzymes purified from transfected COS-7 cell secretions with the
activities of CA IVs purified from lungs. These studies demonstrated
that Gly-63 is important for the high activity of bovine and rabbit CA
IVs, and they showed that the low activity of murine CA IV could be
improved by the Gln-63 → Gly substitution. We suggest that the lower
activity of the rodent CA IVs can be largely explained by the Gln-63
substitution which reduces the efficiency of proton transfer by the
adjacent His-64.
Production of active bovine tracheal antimicrobial peptide in milk of transgenic mice
Authors: Yarus S. , Rosen J. M. , Cole A. M. , Diamond G.
Published: July 2002

Tracheal antimicrobial peptide (TAP) is a member of the
β-defensin family of antibiotic peptides found in the tracheal mucosa
of the cow. TAP gene expression in the bovine airway is inducible by
lipopolysaccharide and inflammatory mediators, suggesting that it
functions to protect the upper airway from infection. Limited
availability of bovine TAP (bTAP) has precluded investigation of its
potential utility in agriculture and medicine. To overcome this
problem, transgenic mice expressing bTAP using an expression vector
driven by control sequences from the murine whey acidic protein (WAP)
gene have been generated. The WAP/bTAP transcript was detected in RNA
isolated from mammary tissue of transgenic females. bTAP was
purified to homogeneity from milk via acid precipitation,
reverse-phase HPLC, and ion-exchange chromatography. This milk-derived
bTAP had antimicrobial activity against
Escherichia
coli
. Amino-terminal peptide sequencing confirmed the identity
of this material as a bTAP isoform. bTAP available from a mammary gland
bioreactor will allow evaluation of bTAP for use as an antibiotic in
agriculture and medicine.
An auxiliary factor containing a 240-kDa protein complex is involved in apolipoprotein B RNA editing.
Authors: Schock D , Kuo S R , Steinburg M F , Bolognino M , Sparks J D , Sparks C E , Smith H C
Published: July 2002

A protein complex involved in apolipoprotein B (apoB) RNA editing, referred to as AUX240 (auxiliary factor containing p240), has been identified through the production of monoclonal antibodies against in vitro assembled 27S editosomes. The 240-kDa protein antigen of AUX240 colocalized with editosome complexes on immunoblots of native gels. Immunoadsorbed extracts were impaired in their ability to assemble editosomes beyond early intermediates and in their ability to edit apoB RNA efficiently. Supplementation of adsorbed extract with AUX240 restored both editosome assembly and editing activities. Several proteins, in addition to p240, ranging in molecular mass from 150 to 45 kDa coimmunopurify as AUX240 under stringent wash conditions. The activity of the catalytic subunit of the editosome APOBEC-1 and mooring sequence RNA binding proteins of 66 and 44 kDa could not be demonstrated in AUX240. The data suggest that p240 and associated proteins constitute an auxiliary factor required for efficient apoB RNA editing. We propose that the role of AUX240 may be regulatory and involve mediation or stabilization of interactions between APOBEC-1 subunits and editing site recognition proteins leading the assembly of the rat liver C/U editosome.
Equine rhinovirus 1 is more closely related to foot-and-mouth disease virus than to other picornaviruses.
Authors: Li F , Browning G F , Studdert M J , Crabb B S
Published: July 2002

Equine rhinovirus 1 (ERhV1) is a respiratory pathogen of horses which has an uncertain taxonomic status. We have determined the nucleotide sequence of the ERhV1 genome except for a small region at the 5' end. The predicted polyprotein was encoded by 6741 nucleotides and possessed a typical picornavirus proteolytic cleavage pattern, including a leader polypeptide. The genomic structure and predicted amino acid sequence of ERhV1 were more similar to those of foot-and-mouth disease viruses (FMDVs), the only members of the aphthovirus genus, than to those of other picornaviruses. Features which were most similar to FMDV included a 16-amino acid 2A protein which was 87.5% identical in sequence of FMDV 2A, a leader (L) protein similar in size to FMDV Lab and the possibility of a truncated L protein similar in size to FMDV Lb, and a 3C protease which recognizes different cleavage sites. However, unlike FMDV, ERhV1 had only one copy of the 3B (VPg) polypeptide. The phylogenetic relationships of the ERhV1 sequence and nucleotide sequences of representative species of the five genera of the family Picornaviridae were examined. Nucleotide sequences coding for the complete polyprotein, the RNA polymerase, and VP1 were analyzed separately. The phylogenetic trees confirmed that ERhV1 was more closely related to FMDV than to other picornaviruses and suggested that ERhV1 may be a member, albeit very distant, of the aphthovirus genus.
Expression of the CD36 homolog (FAT) in fibroblast cells: effects on fatty acid transport.
Authors: Ibrahimi A , Sfeir Z , Magharaie H , Amri E Z , Grimaldi P , Abumrad N A
Published: July 2002

An adipocyte membrane glycoprotein, (FAT), homologous to human CD36, has been previously implicated in the binding/transport of long-chain fatty acids. It bound reactive derivatives of long-chain fatty acids and binding was specific and associated with significant inhibition of fatty acid uptake. Tissue distribution of the protein and regulation of its expression were also consistent with its postulated role. In this report, we have examined the effects of FAT expression on rates and properties of fatty acid uptake by Ob17PY fibroblasts lacking the protein. Three clones (P21, P22, and P25) were selected based on FAT mRNA and protein levels. Cell surface labeling could be demonstrated with the anti-CD36 antibody FITC-OKM5. In line with this, the major fraction of immunoreactive FAT was associated with the plasma membrane fraction. Assays of oleate and/or palmitate uptake demonstrated higher rates in the three FAT-expressing clones, compared to cells transfected with the empty vector. Clone P21, which had the highest protein levels on Western blots, exhibited the largest increase in transport rates. Fatty acid uptake in FAT-expressing P21 cells reflected two components, a phloretin-sensitive high-affinity saturable component with a Km of 0.004 microM and a basal phloretin-insensitive component that was a linear function of unbound fatty acid. P21 cells incorporated more exogenous fatty acid into phospholipids, indicating that binding of fatty acids was followed by their transfer into the cell and that both processes were increased by FAT expression. The data support the interpretation that FAT/CD36 functions as a high-affinity membrane receptor/transporter for long-chain fatty acids.
Major histocompatibility complex gene mapping in the amphibianXenopusimplies a primordial organization
Authors: Nonaka Masaru , Namikawa Chisato , Kato Yoichi , Sasaki Makoto , Salter-Cid Luisa , Flajnik Martin F.
Published: July 2002

One of the most provocative recent discoveries in immunology was the description of a genetic linkage in the major histocompatibility complex (MHC) between structurally unrelated genes whose products are involved in processing and presentation of antigens for recognition by T lymphocytes. Genes encoding MHC class I molecules, which bind and present at the cell surface proteolytic fragments of cytosolic proteins, are linked to nonhomologous genes whose products are involved in the production and subsequent transfer of such fragments into the endoplasmic reticulum. In mammals, the class I presentation and processing genes are found in different regions of the MHC. To examine the evolutionary origins of this genetic association, linkage studies were carried out withXenopus, an amphibian last sharing an ancestor with mammals over 350 million years ago. In contrast to mammals, the single copyXenopusclass I gene is located between the class II and III regions, speculated to be in close linkage with the processing and transport genes. In addition to suggesting a primordial organization of genes involved in class I antigen presentation, these linkage studies further provide insight into the origins of the MHC class III region and the phenomenon of class I gene instability in the mammalian MHC.
Equilibration of the terrestrial water, nitrogen, and carbon cycles
Authors: Schimel David S. , Braswell B. H. , Parton W. J.
Published: July 2002

Recent advances in biologically based ecosystem models of the
coupled terrestrial, hydrological, carbon, and nutrient cycles have
provided new perspectives on the terrestrial biosphere’s behavior
globally, over a range of time scales. We used the terrestrial
ecosystem model Century to examine relationships between carbon,
nitrogen, and water dynamics. The model, run to a quasi-steady-state,
shows strong correlations between carbon, water, and nitrogen fluxes
that lead to equilibration of water/energy and nitrogen limitation of
net primary productivity. This occurs because as the water flux
increases, the potentials for carbon uptake (photosynthesis), and
inputs and losses of nitrogen, all increase. As the flux of carbon
increases, the amount of nitrogen that can be captured into organic
matter and then recycled also increases. Because most plant-available
nitrogen is derived from internal recycling, this latter process is
critical to sustaining high productivity in environments where water
and energy are plentiful. At steady-state, water/energy and nitrogen
limitation “equilibrate,” but because the water, carbon, and
nitrogen cycles have different response times, inclusion of nitrogen
cycling into ecosystem models adds behavior at longer time scales than
in purely biophysical models. The tight correlations among nitrogen
fluxes with evapotranspiration implies that either climate change or
changes to nitrogen inputs (from fertilization or air pollution) will
have large and long-lived effects on both productivity and nitrogen
losses through hydrological and trace gas pathways. Comprehensive
analyses of the role of ecosystems in the carbon cycle must consider
mechanisms that arise from the interaction of the hydrological, carbon,
and nutrient cycles in ecosystems.
Characterization of mammalian translocase of inner mitochondrial membrane (Tim44) isolated from diabetic newborn mouse kidney
Authors: Wada Jun , Kanwar Yashpal S.
Published: July 2002

Mammalian translocase of mitochondrial inner membrane (mTim44) was isolated during representational difference analysis of cDNA from diabetic mouse kidney. Streptozotocin-induced diabetic mouse kidney cDNA was prepared and subtracted by normal mouse kidney cDNA. By using one of the isolated cDNA fragments as a screening probe, full-length cDNA of mTim44 was isolated from λZAP kidney cDNA library. At the nucleotide level, mTim44 did not exhibit significant homology with any known genes; however, at the amino acid level, it had 50% similarity and 29% identity with yeast Tim44. C-terminal FLAG epitope-tagged mTim44 fusion protein was transiently expressed in COS7 cells. By using anti-FLAG epitope M2 monoclonal antibody, mTim44 was found to have its subcellular localization associated with mitochondria. By immunoelectron microscopy, mTim44 was seen in the paracrystalline structures within the mitochondria, as well as in their cristae. Mitochondrial import assay of
in vitro
translated mTim44 indicated that its precursor product (≈50 kDa) was imported and proteolytically processed to a mature ≈44-kDa protein, and its translocation was inner membrane potential (ΔΨ)-dependent. Imported mTim44 was protected from protease digestion in which outer membranes were selectively permeabilized with digitonin. The mature form of mTim44 could be recovered in the supernatant of sonicated mitochondrial membrane fraction treated with 0.1 M Na
2
CO
3
, pH 11.5. The data indicate that mTim44 is a mitochondrial inner membrane protein, one of the members of the mammalian TIM complex and up-regulated in hyperglycemic states.
Molecular analysis of CaMnt1p, a mannosyl transferase important for adhesion and virulence of
Candida albicans
Authors: Buurman Ed T. , Westwater Caroline , Hube Bernhard , Brown Alistair J. P. , Odds Frank C. , Gow Neil A. R.
Published: July 2002

There is an immediate need for identification of new antifungal targets in opportunistic pathogenic fungi like
Candida albicans
. In the past, efforts have focused on synthesis of chitin and glucan, which confer mechanical strength and rigidity upon the cell wall. This paper describes the molecular analysis of
CaMNT1
, a gene involved in synthesis of mannoproteins, the third major class of macromolecule found in the cell wall.
CaMNT1
encodes an α-1,2-mannosyl transferase, which adds the second mannose residue in a tri-mannose oligosaccharide structure which represents O-linked mannan in
C. albicans
. The deduced amino acid sequence suggests that CaMnt1p is a type II membrane protein residing in a medial Golgi compartment. The absence of CaMnt1p reduced the ability of
C. albicans
cells to adhere to each other, to human buccal epithelial cells, and to rat vaginal epithelial cells. Both heterozygous and homozygous
Camnt1
null mutants of
C. albicans
showed strong attenuation of virulence in guinea pig and mouse models of systemic candidosis, which, in guinea pigs, could be attributed to a decreased ability to reach and/or adhere internal organs. Therefore, correct CaMnt1p-mediated O-linked mannosylation of proteins is critical for adhesion and virulence of
C. albicans
.