bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous scaling exponents and coherent structures in high Re fluid turbulence
Authors: Camussi R. , Verzicco R.
Published: July 2002

The scaling exponents of the velocity structure functions are predicted by a simple model based on the probability density function (PDF) of the local turbulent kinetic energy fluctuations with no hypotheses on the shape of the most intermittent coherent structures. The energy fluctuations are presumed to be induced by statistically independent coherent structures and, therefore, are characterized by exponential-like PDFs. Accounting also for the scaling of the energy with the scale, a recursive formula is obtained which permits the calculation of the scaling exponents of the velocity structure functions. The predicted exponents are checked to be in good agreement with previous theoretical and experimental results. The main hypotheses behind the present approach are also validated by analyzing experimental velocity time series acquired in a jet flow at moderately high Reλ. It is also shown that present approach allows the calculation of the scaling exponents also in cases of nonhomogeneous turbulence.
Direct numerical simulations of the elliptic instability of a vortex pair
Authors: Laporte F. , Corjon A.
Published: July 2002

The objective of this study is to perform direct numerical simulations (DNS) of the three-dimensional short-wavelength elliptic instability developing in a counter-rotating vortex pair, and to reproduce numerically a water-tank experiment. The main features of the elliptic instability are recovered by the simulations. In particular, the spatial structure and the temporal evolution of the most amplified perturbation mode during the linear regime correspond to both experimental measurements and theoretical predictions. The long-term evolution is also simulated, and the stages leading to transition to turbulence are described. Some elements resulting from simulations related to the interaction between the short-wavelength elliptic instability and the long-wavelength Crow instability are provided.
Three-dimensional propagation and absorption of high frequency Gaussian beams in magnetoactive plasmas
Authors: Nowak S. , Orefice A.
Published: July 2002

In today’s high frequency systems employed for plasma diagnostics, power heating, and current drive the behavior of the wave beams is appreciably affected by the self-diffraction phenomena due to their narrow collimation. In the present article the three-dimensional propagation of Gaussian beams in inhomogeneous and anisotropic media is analyzed, starting from a properly formulated dispersion relation. Particular attention is paid, in the case of electromagnetic electron cyclotron (EC) waves, to the toroidal geometry characterizing tokamak plasmas, to the power density evolution on the advancing wave fronts, and to the absorption features occurring when a beam crosses an EC resonant layer.
Toroidal plasma beta-finite Larmor radius limit in a toroidally linked mirror system
Authors: Wong H. Vernon , Berk H. L. , Ilgisonis V. I. , Pastukhov V. P.
Published: July 2002

The ballooning stability limit in one toroidal section of the recently proposed toroidally linked neutron source is investigated within the framework of the Wentzel–Kramers–Brillouin (WKB) approximation. Rotational effects induced by radial electric fields present in the equilibrium are neglected. The equilibrium pressure and density profiles are taken to be linear in the flux variable. For a reasonable set of design parameters, ideal ballooning instability limits the toroidal plasma beta to less than 1%. However, the inclusion of stabilizing kinetic effects due to finite ion Larmor radius approximately doubles the predicted critical beta limit, and makes possible a choice of design parameters compatible with ballooning stability.
Control of the floating potential fluctuations via limiter biasing in the Saskatchewan Torus-Modified (STOR-M) tokamak
Authors: Zhang W. , Xiao C. , Zhang L. , Hirose A.
Published: July 2002

Limiter biasing experiments have been performed in the STOR-M tokamak (Saskatchewan Torus-Modified) [Phys. Fluids B 4, 3277 (1992)]. It is found that the floating potential fluctuation amplitudes in the scrape-off layer (SOL) depend mainly on the limiter potential and this potential determines the current flowing toward the limiter. The dependence of the fluctuation amplitude on the potential gradient in the SOL is rather weak. For positive limiter bias, a strong suppression of the floating potential fluctuation is observed, while for negative limiter biasing the floating potential fluctuations are significantly enhanced. The observed phenomena are consistent with recent theoretical studies [Phys. Fluids B 5, 3191 (1993)].
A self-adjoint form of linearized Coulomb collision operator for energetic ions
Authors: Jhang Hogun , Chang C. S.
Published: July 2002

A self-adjoint form of linearized Coulomb collision operator for energetic ions is obtained. Background electron and ion species are assumed to have Maxwellian distributions with different temperatures. The result can be used in the kinetic investigations of collisional effects on the energetic ion behavior, including variational studies of the energetic ion Fokker–Planck equation.
Excitation mechanism of standing waves produced by electron beam plasma instability
Authors: Hayashi N. , Tanaka M. , Shinohara S. , Kawai Y.
Published: July 2002

The excitation mechanism of standing waves produced by the electron beam plasma instability is experimentally studied using a Double Plasma device. When an electron beam is injected into the target plasma, standing waves around the electron plasma frequency are excited. A test wave is propagated in an electron beam plasma system and is identified as the beam mode from the dispersion relation. The propagation direction of the beam mode is determined from the wave pattern utilizing a phase shifter. It is found that a reflected beam mode exists as well as a forward beam mode, and is generated by the reflection of the forward beam mode from a potential well produced by the injection of the electron beam. The observed standing waves are formed by superposing the beam modes propagating in opposite directions from each other.
Dynamic and Debye shielding and anti-shielding
Authors: Hansen C. , Reimann A. B. , Fajans J.
Published: July 2002

While shielding in collisional plasmas obeys the standard Debye result, shielding in collisionless plasmas is far more complex than commonly believed. For example, a one-dimensional (highly magnetized), immobile-ion plasma can, in some circumstances, anti-shield a positive test charge; i.e. the plasma becomes more positive in the vicinity of the test charge. When shielding does occur, it results from electrons dynamically trapped in the neighborhood of the test charge. A new theory of collisionless (Dynamic) shielding in one, two and three dimensions is presented here, and is in excellent agreement with experiments in pure electron plasmas. Because the distribution functions found in Dynamic shielding are highly non-Maxwellian in the non-linear regime, collisionless Dynamic shielding can be substantially less efficacious than collisional Debye shielding.
Alfvén waves and rotation of collisional plasmas in tokamaks
Authors: Tsypin V. S. , Elfimov A. G. , de Azevedo C. A. , de Assis A. S.
Published: July 2002

The effect of radio frequency fields on a plasma rotation in the edge (collisional) region of slightly rippled tokamaks is considered. The expressions for poloidal and toroidal velocities and for quasistationary radial electric fields are obtained as a function of absorbed rf power. The estimations of these quantities for the Phaedrus-T tokamak [N. Hershkovitz et al., 15th International Atomic Energy Agency Conference on Plasma Physics and Controlled Fusion, Seville, 1994 (International Atomic Energy Agency, Vienna, in press)] are also presented. It is shown that Alfvén waves can strongly modify the rotation velocities and radial electric fields in collisional regions of tokamak plasmas.
Comparison of Zakharov simulation and open boundary Vlasov simulation of strong Langmuir turbulence
Authors: Wang J. G. , Payne G. L. , DuBois D. F. , Rose H. A.
Published: July 2002

Both Zakharov equations and Vlasov equations are solved numerically to study the strong Langmuir turbulence developed in a plasma driven by an external pump field oscillating at the plasma frequency. A steady state turbulence in Vlasov simulations is reached by using open boundary conditions under which hot particles generated by strong caviton fields are replaced by initial cold Maxwellian particles when they cross the boundaries of simulation domain. A similar steady turbulent state in Zakharov simulations is easily achieved by implementing a phenomenological damping model and using periodic boundary conditions. Simulation results of these two different models are compared and investigated.
Kinetic analysis of the ion temperature gradient modes in toroidally rotating plasmas
Authors: Zheng L.-J. , Tessarotto M.
Published: July 2002

With the two time scale feature revealed, an analytical method is developed to solve the combined eigenvalue and initial value problem describing the ion temperature gradient (ITG) modes in the toroidally rotating plasmas. With full gyrokinetics and toroidal geometry effects being taken into account in an ordering consistent manner, dispersion relations are obtained for ITG modes both of toroidal and slab-like branches. The results show that the sonic rotation can be harmful for the stability, while subsonic rotation with flow shear can be expected to be stabilizing. The existence of the flow shear leads the time evolution of the fluctuation signals to display two different time scales—a fast oscillating (either fast or slow growing) signal with its amplitude modulated by a slowly varying envelope, resembling fishbone-like fluctuations.
Fast surface waves in an ideal Hall-magnetohydrodynamic plasma slab
Authors: Zhelyazkov Ivan , Debosscher Arnold , Goossens Marcel
Published: July 2002

The propagation of fast sausage and kink magnetohydrodynamic (MHD) surface waves in an ideal magnetized plasma slab is studied taking into account the Hall term in the generalized Ohm’s law. It is found that the Hall effect modifies the dispersion characteristics of MHD surface modes when the Hall term scaling length is not negligible (less than, but comparable to the slab thickness). The dispersion relations for both modes have been derived for parallel propagation (along the ambient equilibrium magnetic field lines).The Hall term imposes some limits on the possible wave number range. It turns out that the space distribution of almost all perturbed quantities in sausage and kink surface waves with Hall effect is rather complicated as compared to that of usual fast MHD surface waves. The applicability to solar wind aspects of the results obtained, is briefly discussed.
Electron transport processes close to magnetic axis in tokamaks
Authors: Shaing K. C. , Hazeltine R. D. , Zarnstorff M. C.
Published: July 2002

Electron transport fluxes valid in the region close to magnetic axis in tokamaks are derived from the moment equation approach. It is found that bootstrap current does not vanish on the axis, electrical conductivity is reduced from its classical value, and particle and heat fluxes are enhanced over those in the conventional neoclassical theory. The reason for the deviation from the conventional theory is because the fraction of the trapped particles is finite in the region close to the magnetic axis. The existence of the bootstrap current on the magnetic axis may reduce or eliminate the need of the seed current.
Density profile consistency, particle pinch, and cold pulse propagation in DIII-D
Authors: Baker D. R.
Published: July 2002

It has been recently proposed that, for highly turbulent discharges, there exists a consistent density profile for the trapped electrons in a high aspect ratio circular cross-section tokamak, which has a radial variation proportional to 1/q(r), where q is the usual safety factor. It is shown here that this result can be extended to include passing electrons and noncircular cross-section moderate aspect ratio tokamaks. This new prediction for the density profile is compared to the time evolution of the measured electron density profile in low confinement mode (L-mode) shots in the tokamak known as DIII-D [L. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I. p. 159], where the q profile is changed in time during the discharge. Once an expression for the consistent density profile is known, it is trivial to obtain an expression for Vp/D, where Vp is the particle pinch velocity and D is the particle diffusion coefficient. This expression is compared with the value of Vp/D, which is obtained from an analysis, utilizing the ONETWO transport code [R. Dominguez and R. Waltz, Nucl. Fusion 27, 65 (1987)], of certain high confinement mode (H-mode) DIII-D discharges, which are free from edge localized modes. The dependence of density on q can be extended to a dependence of temperature on q through the adiabatic relation. The dependence of temperature on q can then predict one type of cold pulse propagation phenomena. By way of introduction, a simple analogy with a dynamic incompressible fluid system is made.
Exact order reduction method in mode conversion problems
Authors: Swanson D. G. , Kwon T. H.
Published: July 2002

The exact order reduction method solves the fourth-order system of equations from the Vlasov equations that describe mode conversion by breaking the solution into two steps. The first step is to find the numerical solutions of a pair of second-order equations for the fast waves and slow waves, respectively, which are easily obtained. The second step uses an associated integral equation to obtain the coupling between the fast and slow waves. Potential difficulties due to singularities in the kernel of the integral equations near the axis are resolved by altering the integration path. This allows accurate estimates for mode conversion efficiencies in realistic geometries as the integral equation is solved only in a narrow region near resonance, while the global fast wave solution of the reduced second-order equation covers the entire cross section. The method makes virtually no approximations except that it keeps only the lowest nontrivial order terms in the Larmor radius expansion.
The bootstrap current in a tokamak with electron cyclotron heating
Authors: Helander P. , Hastie R. J. , Connor J. W.
Published: July 2002

The bootstrap current in a non-Maxwellian tokamak plasma with electron cyclotron heating is calculated. The calculation is exact in the limit of highly charged ions, where pitch-angle scattering dominates over quasilinear diffusion, and shows that the current is entirely determined by the pressure of the trapped electrons. If the ion charge is finite, the current is shown to consist of two terms: one driven by collisions, and one driven by the heating and losses. The former is calculated approximately by using a model collision operator, and is found to be determined by the distribution of trapped electrons alone; the latter is discussed qualitatively.
Gyrokinetic theory for arbitrary wavelength electromagnetic modes in tokamaks
Authors: Qin H. , Tang W. M. , Rewoldt G.
Published: July 2002

A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfvén eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables one to look at many familiar modes simultaneously, and thus to study the modifications of and the interactions between them in a systematic way. Especially, it is possible to investigate self-consistently the kinetic magnetohydrodynamics (MHD) phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a two-dimensional finite element code has been developed and tested. In this paper, the basic theoretical formalism and some of the preliminary results are presented.
The trap of particles in plasma sheath
Authors: Liu Jinyuan , Wang Dezhen , Ma T. C. , Gong Y. , Sun Qiupu , Ma J. X. , Yu C. X.
Published: July 2002

The traps of isolated dust particles under the action of electrostatic, gravitational, ion-drag, and neutral collision forces are investigated near the boundary of a dusty plasma. It is shown that in the lower sheath (above the lower electrode) the particle traps can exist only for the negatively charged particles. The positions of trapped particle are determined by grain size and forces on it and there are upper and lower critical values for the trapped particle. In the upper sheath (under the upper electrode) there is balance force for the positively charged particles but it is not a stable balance. Still negatively charged particles can be trapped in the upper sheath. In addition, it was shown that two sized grains are trapped in the same position.
Infrared absorption study on carbon and oxygen behavior in Czochralski silicon crystals
Authors: Shimura F. , Baiardo J. P. , Fraundorf P.
Published: July 2002

The behavior of carbon atoms in relation to oxygen precipitation in Czochralski silicon crystals subjected to various heat treatments is investigated by means of infrared (IR) spectroscopy. It is shown that carbon atoms enhance and modify oxygen precipitation both at 750 and at 1000 °C. Perturbed [Oi−Ci] C(3) centers, which are unstable at a high temperature (1250 °C), have been observed in the specimen subjected to 750 °C heat treatment by IR spectroscopy. The enhancement effect of carbon atoms is explained in two ways: (i) C(3) centers act as effective heterogeneous seeding sites for oxygen precipitation, and (ii) carbon atoms play a catalytic role by modifying interfacial energies or the point defect ambient at the oxygen precipitate surface.
Metals on cadmium telluride: Schottky barriers and interface reactions
Authors: Dharmadasa I. M. , Herrenden-Harker W. G. , Williams R. H.
Published: July 2002

The Schottky barriers formed for a wide range of metals on (110) n-CdTe surfaces have been studied using current-voltage and capacitance-voltage techniques. The surfaces were prepared by cleaving in ultrahigh vacuum, cleaving in air, and chemical etching. The electrical barriers are drastically influenced by oxide layers on the surface. Most metals on the chemically etched surfaces yield barriers having values around 0.7 eV but Mn, Cr, and V are notable exceptions, yielding ohmic or low barrier contacts. Microscopic interactions of these interfaces have also been studied by soft x-ray photoemission using synchrotron radiation. Detailed comparisons of the microscopic interaction of Ag and Mn with the clean and oxidized surfaces, using photoemission, are presented. In contrast to the behavior of Ag, the Mn overlayer completely reduces the CdTe native oxide layer, resulting in lower barrier contacts.
Characterization of individual electron traps in amorphous Si by telegraph noise spectroscopy
Authors: Rogers C. T. , Buhrman R. A. , Kroger H. , Smith L. N.
Published: July 2002

We have used telegraph noise spectroscopy to study the properties of individual localized electron traps of a particular type in thin layers (t<∼6 nm) of rf sputtered amorphous Si and amorphous Si:H. The results indicate that these traps have bistable ionic configurations: The trapping kinetics are dominated by transitions between two different ionic configurations with an associated change in trapped charge. Above ∼20 K, configurational transitions are by thermally activated hopping; below 20 K, transitions appear to be induced by zero-point oscillations.
Hologram fixing process at room temperature in photorefractive Bi12SiO20 crystals
Authors: Herriau J. P. , Huignard J. P.
Published: July 2002

We present the first demonstration of a room-temperature grating fixing process in a photorefractive Bi12SiO20 crystal. This arises from a space-charge compensation due to a hole conduction when the crystal is placed in the dark for 1–3 min. The grating is optically revealed by redistribution of photoelectrons through the uniform illumination of the crystal. After compensation and optical revelation, the readout time constant of the grating is increased by a factor of 40×. Electrical revelation of fixed gratings and holographic images is also demonstrated.
Compact room-temperature metal vapor laser
Authors: Anders A. K. , Harvey E. C. , Tobin R. C.
Published: July 2002

Laser emission is obtained at room temperature on the copper I (510.6 and 578.2 nm) and gold I (627.8 nm) transitions from a compact device in which the metal vapor is produced by sputtering in the presence of a rapid flow of noble gas. Peak powers of 1 kW and 250 W are obtained for copper I and gold I, respectively.
Novel superconducting thermometer for bolometric applications
Authors: McDonald D. G.
Published: July 2002

The temperature dependence of the magnetic penetration depth in a superconductor, in the kinetic inductance limit, is proposed as a basis for a sensitive thermometer. Considered as a bolometer, the noise equivalent power from the sum of the Johnson noise and the preamplifier noise can be reduced to about 7×10−20 W/(Hz)1/2, which is approximately four orders of magnitude below currently realized values.
Exciton binding energies in GaInAs/InP quantum wells determined by thermally modulated photoluminescence
Authors: Lin Z. H. , Wang T. Y. , Stringfellow G. B. , Taylor P. C.
Published: July 2002

Atmospheric pressure organometallic vapor phase epitaxy has been used for the growth of single InP/GaInAs/InP quantum wells with atomically abrupt interfaces. This has allowed wells as thin as 10 Å to be grown which give sharp photoluminescence (PL) spectra at 10 K. PL and thermally modulated PL have been used to distinguish band-to-band and exciton luminescence transitions allowing an estimation of the exciton binding energy. For the first time, the qualitative trend of an increase in exciton binding energy with decreasing well width for thick wells followed by a distinct maximum and a sharp decrease in binding energy with decreasing well width for very thin wells has been observed. The maximum binding energy of approximately 17 meV is found to occur for a nominal well width of approximately 13 Å.
Time-resolved plasma parameter measurements in a low-frequency rf glow discharge
Authors: Anderson Colin A. , Graham William G. , Hopkins Michael B.
Published: July 2002

A new approach to the use of Langmuir probes in a rf driven plasma is presented. The periodic nature of the rf is utilized to overcome the distortion of the probe characteristics caused by averaging over many rf cycles. Time-resolved measurements of the electron density, electron temperature, plasma potential, and floating potential in the negative portion of the rf cycle are obtained. The technique is used to characterize a low-pressure 100-kHz capacitively coupled rf argon discharge. The measured electron temperature is found to be approximately 0.5 eV.
Multiphoton ionization of aluminum and copper planar target
Authors: Park C. O. , Lee H. W. , Lee T. D. , Kim J. K.
Published: July 2002

The total charge of the emitted ions from the planar metal targets irradiated by the mode-locked ruby laser was measured. The dependence of the total emitted ions on the laser fluence is consistent with the theory of the multiphoton ionization in the low fluence region. However, it shows saturation phenomena at the higher fluence regions. These saturations could be explained by the depletion of the neutral atoms and the level shifting of the intermediate state due to the strong Stark effect.
Searching sequence space for protein catalysts
Authors: Taylor Sean V. , Walter Kai U. , Kast Peter , Hilvert Donald
Published: July 2002

Genetic selection was used to explore the probability of finding enzymes in protein sequence space. Large degenerate libraries were prepared by replacing all secondary structure units in a dimeric, helical bundle chorismate mutase with simple binary-patterned modules based on a limited set of four polar and four nonpolar residues. Two-stage
in vivo
selection yielded catalytically active variants possessing biophysical and kinetic properties typical of the natural enzyme even though ≈80% of the protein originates from the simplified modules and >90% of the protein consists of only eight different amino acids. This study provides a quantitative assessment of the number of sequences compatible with a given fold and implicates previously unidentified residues needed to form a functional active site. Given the extremely low incidence of enzymes in completely unbiased libraries, strategies that combine chemical information with genetic selection, like the one used here, may be generally useful in designing novel protein scaffolds with tailored activities.
Corticofugal modulation of duration-tuned neurons in the midbrain auditory nucleus in bats
Authors: Ma Xiaofeng , Suga Nobuo
Published: July 2002

Animal sounds, as well as human speech sounds, are characterized by multiple parameters such as frequency, intensity, duration, etc. The central auditory system produces neurons tuned to particular durations and frequencies of sounds emitted by a species. In bats, “duration-tuned” neurons are mostly sensitive to short durations and high frequencies of sounds used for echolocation. They are scattered in the frequency maps of the inferior colliculus and auditory cortex. We found that electric stimulation of cortical duration-tuned neurons modulates collicular duration-tuned neurons in both duration and frequency tuning only when collicular and cortical neurons paired for studies are within ±4 ms in best duration and within ±6 kHz in best frequency. There are four types of modulations: sharpening or broadening of duration tuning, and lengthening or shortening of best duration. Sharpening is observed in “matched” collicular neurons whose best durations are the same as those of stimulated cortical neurons, and it is accompanied by augmentation of the auditory responses at their best durations. The other three types of modulations are observed in “unmatched” collicular neurons whose best durations are different from those of stimulated cortical neurons. Lengthening or shortening of best duration is linearly related to the amount of the difference in best duration between collicular and cortical neurons. Corticofugal modulation is specific and systematic according to relationships in both duration and frequency between stimulated cortical and recorded collicular neurons.
An endogenous rate of time preference, the Penrose effect, and dynamic optimality of environmental quality.
Authors: Uzawa H
Published: July 2002

In the present paper, the endogenous theory of time preference is extended to analyze those processes of capital accumulation and changes in environmental quality that are dynamically optimum with respect to the intertemporal preference ordering of the representative individual of the society in question. The analysis is carried out within the conceptual framework of the dynamic analysis of environmental quality, as has been developed by a number of economists for specific cases of the fisheries and forestry commons. The duality principles on intertemporal preference ordering and capital accumulation are extended to the situation where processes of capital accumulation are subject to the Penrose effect, which exhibit the marginal decrease in the effect of investment in private and social overhead capital upon the rate at which capital is accumulated. The dynamically optimum time-path of economic activities is characterized by the proportionality of two systems of imputed, or efficient, prices, one associated with the given intertemporal ordering and another associated with processes of accumulation of private and social overhead capital. It is particularly shown that the dynamically optimality of the processes of capital accumulation involving both private and social overhead capital is characterized by the conditions that are identical with those involving private capital, with the role of social overhead capital only indirectly exhibited.
Virus-specific CD8+T cell numbers are maintained during γ-herpesvirus reactivation in CD4-deficient mice
Authors: Stevenson Philip G. , Belz Gabrielle T. , Altman John D. , Doherty Peter C.
Published: July 2002

The murine γ-herpesvirus 68 replicates in epithelial sites after intranasal challenge, then persists in various cell types, including B lymphocytes. Mice that lack CD4+T cells (I-Ab−/−) control the acute infection, but suffer an ultimately lethal recrudescence of lytic viral replication in the respiratory tract. The consequences of CD4+T cell deficiency for the generation and maintenance of murine γ-herpesvirus 68-specific CD8+set now have been analyzed by direct staining with viral peptides bound to major histocompatibility complex class I tetramers and by a spectrum of functional assays. Both acutely and during viral reactivation, the CD8+T cell responses in the I-Ab−/−group were no less substantial than in the I-Ab+/+controls. Indeed, virus-specific CD8+T cell numbers were increased in the lymphoid tissue of clinically compromised I-Ab−/−mice, although relatively few of the potential cytotoxic T lymphocyte effectors were recruited back to the site of pathology in the lung. Thus the viral reactivation that occurs in the absence of CD4+T cells was not associated with any exhaustion of the virus-specific cytotoxic T lymphocyte response. It seems that CD8+T cells alone are insufficient to maintain long-term control of this persistent γ-herpesvirus.
A phytochrome from the fern
Adiantum
with features of the putative photoreceptor NPH1
Authors: Nozue Kazunari , Kanegae Takeshi , Imaizumi Takato , Fukuda Shunsuke , Okamoto Haruko , Yeh Kuo-Chen , Lagarias J. Clark , Wada Masamitsu
Published: July 2002

In plant photomorphogenesis, it is well accepted that the perception of red/far-red and blue light is mediated by distinct photoreceptor families, i.e., the phytochromes and blue-light photoreceptors, respectively. Here we describe the discovery of a photoreceptor gene from the fern
Adiantum
that encodes a protein with features of both phytochrome and NPH1, the putative blue-light receptor for second-positive phototropism in seed plants. The fusion of a functional photosensory domain of phytochrome with a nearly full-length NPH1 homolog suggests that this polypeptide could mediate both red/far-red and blue-light responses in
Adiantum
normally ascribed to distinct photoreceptors.
Nas–Walras equilibria of a large economy
Authors: Minelli E. , Polemarchakis H. M.
Published: July 2002

Individuals exchange contracts for the delivery of commodities in competitive markets and, simultaneously, act strategically; actions affect utilities across individuals directly or through the payoffs of contracts. This encompasses economies with asymmetric information. Nash–Walras equilibria exist for large economies, even if utility functions are not quasi-concave and choice sets are not convex, which is the case in standard settings; the separation of the purchase from the sale of contracts and the pooling of the deliveries on contracts guarantee that the markets for commodities clear.
A relation between the principal axes of inertia and ligand binding
Authors: Foote Jefferson , Raman Anandi
Published: July 2002

The principal axes of inertia are eigenvectors that can be calculated for any rigid body. We report studies of the position of the principal axes in crystallographically solved protein molecules. We find with high frequency that at least one principal axis penetrates the surface of the respective protein in a region used for ligand binding. In antibody variable regions, an axis goes through the third hypervariable loop of the heavy chain. In major histocompatibility complex proteins, an axis goes through the peptide-binding groove. In protein–protein heterodimers, a principal axis of one subunit will often penetrate the interface formed with the other subunit. In many of these protein–protein complexes, the axis specifically intersects residues known to be critical for molecular recognition.
On Expressing Lexical Generalizations in HPSG
Authors: Meurers W. Detmar
Published: July 2002

This paper investigates the status of the lexicon and the possibilities for expressing lexical generalizations in the paradigm of Head-Driven Phrase Structure Grammar (HPSG). We illustrate that the architecture readily supports the use of implicational principles to express generalizations over a class of word objects. A second kind of lexical generalizations expressing relations between classes of words is often expressed in terms of lexical rules. We show how lexical rules can be integrated into the formal setup for HPSG developed by King (1989, 1994), investigate a lexical rule specification language allowing the linguist to only specify those properties which are supposed to differ between the related classes, and define how this lexical rule specification language is interpreted. We thereby provide a formalization of lexical rules as used in HPSG.
The Tlg SNARE complex is required for TGN homotypic fusion
Authors: Brickner Jason H. , Blanchette Jennifer M. , Sipos György , Fuller Robert S.
Published: July 2002

Using a new assay for membrane fusion between late Golgi/endosomal compartments, we have reconstituted a rapid, robust homotypic fusion reaction between membranes containing Kex2p and Ste13p, two enzymes resident in the yeast trans-Golgi network (TGN). Fusion was temperature, ATP, and cytosol dependent. It was inhibited by dilution, Ca+2 chelation, N-ethylmaleimide, and detergent. Coimmunoisolation confirmed that the reaction resulted in cointegration of the two enzymes into the same bilayer. Antibody inhibition experiments coupled with antigen competition indicated a requirement for soluble NSF attachment protein receptor (SNARE) proteins Tlg1p, Tlg2p, and Vti1p in this reaction. Membrane fusion also required the rab protein Vps21p. Vps21p was sufficient if present on either the Kex2p or Ste13p membranes alone, indicative of an inherent symmetry in the reaction. These results identify roles for a Tlg SNARE complex composed of Tlg1p, Tlg2p, Vti1p, and the rab Vps21p in this previously uncharacterized homotypic TGN fusion reaction.
The Thrombopoietin Receptor Can Mediate Proliferation without Activation of the Jak-STAT Pathway
Authors: Dorsch Marion , Fan Pang-Dian , Danial Nika N. , Rothman Paul B. , Goff Stephen P.
Published: July 2002

Cytokine receptors of the hematopoietic receptor superfamily lack intrinsic tyrosine kinase domains for the intracellular transmission of their signals. Instead all members of this family associate with Jak family nonreceptor tyrosine kinases. Upon ligand stimulation of the receptors, Jaks are activated to phosphorylate target substrates. These include STAT (signal transducers and activators of transcription) proteins, which after phosphorylation translocate to the nucleus and modulate gene expression. The exact role of the Jak-STAT pathway in conveying growth and differentiation signals remains unclear. Here we describe a deletion mutant of the thrombopoietin receptor (c-mpl) that has completely lost the capacity to activate Jaks and STATs but retains its ability to induce proliferation. This mutant still mediates TPO-induced phosphorylation of Shc, Vav, mitogen-activated protein kinase (MAPK) and Raf-1 as well as induction of c-fos and c-myc, although at somewhat reduced levels. Furthermore, we show that both wild-type and mutant receptors activate phosphatidylinositol (PI) 3-kinase upon thrombopoietin stimulation and that thrombopoietin-induced proliferation is inhibited in the presence of the PI 3-kinase inhibitor wortmannin. These results demonstrate that the Jak-STAT pathway is dispensable for the generation of mitogenic signals by a cytokine receptor.
Indecomposable continua in exponential dynamics
Authors: Devaney Robert , Jarque Xavier
Published: July 2002

In this paper we prove the existence of uncountably many indecomposable continua in the dynamics of complex exponentials of the form

E
λ

(
z
)
=
λ

e
z

E_\lambda (z) = \lambda e^z

with

λ
>
1

/

e

\lambda > 1/e

. These continua contain points that share the same itinerary under iteration of

E
λ

E_\lambda

. These itineraries are bounded but consist of blocks of

0
0

’s whose lengths increase, and hence these continua are never periodic.
Firm Size, Earnings, and Displacement Risk
Authors: Winter‐Ebmer Rudolf
Published: July 2002

Analogous to the well‐documented firm size‐wage differential, there also exists a differential in layoff risk according to firm size. Using Austrian data I discuss several reasons for this puzzle, including on‐the‐job training and workers' heterogeneity. If less stable (and also less able) workers select themselves into small, unstable, and low‐paying firms, predicted layoff risk of workers can be used as a proxy for heterogeneity of workers and therefore be included in wage regressions. Doing this, one half of the size earnings premium can be explained.
The susceptibility of Streptococcus pneumoniae to levofloxacin and other antibiotics
Authors: Keller N. , Smollen G. , Davidson Y. , Barzilai A. , Keren G. , Rubinstein E.
Published: July 2002

The aim of this study was to determine the in-vitro susceptibility of Streptococcus pneumoniae to levofloxacin, ciprofloxacin, sparfloxacin, ofloxacin, amoxycillin, cefepime and cefuroxime. In total, 105 isolates (clinical blood and sputum isolates from 1995–96) were selected from the collection of the Department of Clinical Microbiology of the Chaim Sheba Medical Centre. MICs were determined with an agar dilution method according to NCCLS guidelines. The MIC ranges with the test antibiotics against the pneumococcal isolates were: 0.5 mg/L, levofloxacin; 0.12–0.5 mg/L, sparfloxacin; 0.5–2 mg/L, ciprofloxacin; 0.5–1 mg/L, ofloxacin; <0.03–2 mg/L, amoxycillin; <0.03–2 mg/L, cefepime; <0.03–2 mg/L, cefuroxime. The results indicated that although all isolates were susceptible to all the fluoroquinolone agents except ciprofloxacin, some isolates had reduced susceptibility to amoxycillin, cefepime and cefuroxime. We conclude that all S. pneumoniae isolates tested were susceptible to levofloxacin, ofloxacin and sparfloxacin. However, about 85% were susceptible to amoxycillin and the other β -lactam antibiotics tested.
Patterns of pair formation and mating in an ectoparasitic caligid copepod Lepeophtheirus salmonis (Krøyer 1837): implications for its sensory and mating biology
Authors: Hull M. Q. , Pike A. W. , Mordue A. J. , Rae G. H.
Published: July 2002

Non–invasive observations of single cohort and manipulated populations of the sealouse on laboratory–maintained salmon established the sequence of reproductive events and mating. Protandry occurs with adult male emergence synchronized with pre–adult II female emergence, the stage at which most pair formation and pre–copular guarding takes place. Male competence for pair formation and mating was achieved within 24 h of the final moult and pairing occurred according to the preference hierarchy, virgin adult females greater than pre–adult II females much greater than pre–adult I females. This hierarchy broke down when the adult male to unmated female ratio increased rapidly. Males mated successfully not only with newly moulted adult females, but also with older virgin females in which enlargement of the genital complex and premature extrusion of egg strings had occurred. Multiple mating by adult males was demonstrated and may be widespread. Significant inter–host transfer was also demonstrated. Adult males were more mobile than adult females and showed significantly more inter–host transfer. Ablation of the distal tip of the antennules significantly reduced the success of host–finding, pair formation and males' mating.
Vision in hydrothermal vent shrimp
Authors: Chamberlain Steven C.
Published: July 2002

Bresiliid shrimp from hydrothermal vents on the Mid–Atlantic Ridge have non–imaging eyes adapted for photodetection in light environments of very low intensity. Comparison of retinal structures between both vent shrimp and surface–dwelling shrimp with imaging eyes, and between juvenile and adult vent shrimp, suggests that vent shrimp have evolved from ancestors that lived in a light environment with bright cyclic lighting. Whether the vent shrimp live in swarms and have large dorsal eyes or live in sparse groupings and have large anterior eyes, the basic retinal adaptations are the same across species. Retinal adaptations in adult vent shrimp include the loss of dioptrics, enlargement of both the rhabdomeral segment of the photoreceptors and the light–sensitive rhabdomere therein, attenuation of the arhabdomeral segment of the photoreceptors, reduction of black screening pigment, development of a white diffusing layer behind the photoreceptors, and the loss of rhabdom turnover.
A three‐dimensional algorithm for optimizing beam weights and wedge filters
Authors: Xing Lei , Hamilton R. J. , Pelizzari C. , Chen G. T. Y.
Published: July 2002

An essential step towards optimizing and automating radiation therapy treatment planning is to develop an effective algorithm to find the optimal beam weights and wedge filters for a given set of beam directions and modalities. This problem is solved by introducing a variable transformation based on the universal and omni wedge principles. Instead of directly optimizing an objective function with respect to wedge angles and orientations, each field is first decomposed into a superposition of an open field and two orthogonal wedged fields. This transforms the problem of finding J beam weights, wedge angles, and orientations to that of optimizing a system with beam weights (J open beams and nominal wedged beams), where J is the total number of incident beam directions. An iterative algorithm based on a method originally developed for image reconstruction is used to find the beam weights. The technique is applied to a few clinical cases. Treatment plans are improved compared to those obtained through the conventional manual trial and error planning process. In addition, planning time and effort are greatly reduced.
Neutron dosimetry, moderated energy spectrum, and neutron capture therapy for medical sources
Authors: Rivard Mark J.
Published: July 2002

dosimetry was examined by calculative and experimental means. The Monte Carlo N‐Particle (MCNP) transport code was used in a distributed computing environment (PVM) to determine neutron dose and neutron energy spectrum from in a variety of clinically relevant materials. A Maxwellian spectrum was used to model neutron emissions in these materials. Mixed‐field dosimetry of applicator tube (AT) sources was measured using tissue‐equivalent ion chambers and a miniature GM counter to formulate a dosimetry protocol. Neutron dose was determined using the AAPM TG‐43 dosimetry protocol. Results demonstrate the overwhelming dependence of dosimetry on the source geometry and no significant neutron attenuation by the source or encapsulation. Gold foils and TLDs were used to measure thermal neutron flux near AT sources and compared with MCNP results. The fast neutron energy spectrum did not change markedly at greater distances from the AT source. Calculations of moderated neutron energy spectrum with various loadings of and were performed, in addition to analysis of neutron capture therapy dosimetry. Radiological concerns such as personnel exposure and shielding of emissions were examined. Feasibility of a high specific‐activity HDR source was investigated through radiochemical and metallurgical studies using stand‐ins such as Tb, Gd, and Issues such as capsule burst strength due to helium production for a variety of proposed HDR sources were addressed. At least 1 mg of was necessary for a HDR source.
Analysis of the acoustic scattering at variable incidences from an extra thin cylindrical shell bounded by hemispherical endcaps
Authors: Touraine N. , Haumesser L. , Décultot D. , Maze G. , Klauson A. , Metsaveer J.
Published: July 2002

Through an experimental approach, in this paper we investigate the acoustic wave scattering processes involved in the acoustic backscattering at variable incidences from an air-filled submerged cylindrical shell with hemispherical endcaps. Given the 1% shell thickness and the explored low frequency domain, the wave types studied are the circumferential or helical S0 wave and the helical T0 wave only. Between the axial (in the direction of the main axis of the object) and the normal incidences (normal to the main axis), two distinct angular zones can be observed depending on hemispherical or cylindrical excitation. In these zones, after a pressure wave excitation, different series of echoes on the echo wave forms are identified by their arrival times and related wave types. From results in the time domain and those obtained in the frequency domain, each acoustic response from the target corresponding to the two zones of excitation is compared with the acoustic response of canonical objects (spherical shell for axial excitation and tube for normal excitation). This analysis of the acoustic response from the target at various incidences, highlights the influence of both the endcaps and the finite length for a cylindrical shell on scattering. The study is intended to make a contribution to the knowledge of the identification of such geometrically complex objects.
Effects of ipsilateral and contralateral precursors on overshoot
Authors: Bacon Sid P. , Liu Li
Published: July 2002

Overshoot is defined as the decrease in threshold as a brief signal is moved from the beginning to near the temporal center of a longer duration, broadband noise masker. Overshoot can be reduced when another noise (a precursor) is presented just prior to the masker. The purpose of the present investigation was to follow up on a recent psychophysical study which showed that overshoot could be reduced by a precursor presented to the ear contralateral to that receiving the masker and signal. The signal was a 20-ms, 4000-Hz tone that was presented at the beginning or in the temporal center of a 400-ms broadband noise masker. In the first experiment, a 200-ms broadband precursor was presented either to the ipsilateral or to the contralateral ear. The ipsilateral precursor reduced overshoot for all ten subjects, but the contralateral precursor reduced overshoot for only four of the ten subjects. In a supplementary experiment, the contralateral precursor failed to reduce overshoot in a new group of five subjects, both when tested with supra-aural headphones and with insert earphones. In the second experiment, the four subjects who showed an effect of the contralateral precursor in experiment 1 were tested under conditions where the bandwidth of the precursor was manipulated, resulting in either a narrow-band precursor centered at 4000 Hz, a low-band precursor with energy primarily below 4000 Hz, or a high-band precursor with energy primarily above 4000 Hz. There was a tendency for the effectiveness of the ipsilateral and contralateral precursors to be affected similarly (though to different degrees) by changes in the spectral content of the precursor. These results suggest that the effect of the contralateral precursor is not due to a timing cue, and that the processing underlying the effectiveness of ipsilateral and contralateral precursors may be largely the same.