bluuebunny/crossref_metadata_2025 huggingface dataset:
Predation on European wild forest reindeer (Rangifer tarandus) by wolves (Canis lupus) in Finland
Authors: Kojola Ilpo , Huitu Otso , Toppinen Katri , Heikura Kalevi , Heikkinen Samuli , Ronkainen Seppo
Published: June 2004

It is generally accepted that predation by wolves Canis lupus is one of the major factors limiting densities of woodland caribou Rangifer tarandus caribou in North America. Conversely, little is known about the role of European wild forest reindeer R. t. fennicus as wolf prey, or about the influence of wolf predation on populations of this rare subspecies. This relationship was examined in east‐central Finland, where wild forest reindeer coexist with moose Alces alces at a numerical ratio of c. 1 reindeer to 1.5 moose. During the study, moose were clearly the primary prey of wolves. Reindeer were, however, an important part of wolf diet in summer, autumn and early winter, when their remains comprised roughly 20–50% of all food items identified in wolf scats. Wolves exhibited a slight preference for reindeer over moose as prey during early winter (November–December) when the reindeer were moving towards their wintering ranges. Virtually no reindeer were killed by wolves during midwinter (January–March). This held also for a pack whose territory was located in the middle of the wintering range of reindeer, where reindeer outnumbered moose during the winter months. After the approximate ratio of wolves to reindeer increased from 0.004 (1998) to 0.02 (2000), wolf predation became the most common source of mortality (50%) for reindeer. The annual net increase in the reindeer population decreased from 13% to 7% because of increased wolf predation. The results indicate that wolf predation was an important factor limiting reindeer population growth. Wolves were, however, unable to prevent entirely the number of reindeer from increasing, partly owing to behavioural traits used by reindeer during winter and calving times.
The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters
Authors: Evans Karen , Hindell Mark A.
Published: June 2004

The age of 86 individuals derived from groups of female sperm whale Physeter macrocephalus involved in three mass strandings on the north and west coasts of Tasmania in 1998 was determined from the number of dentinal growth layer groups in the teeth of individuals. Dorsal total lengths were also measured. Ages of females ranged from 0.75 to 64 years, with the majority (77%) aged between 20 and 45 years. Total lengths of female sperm whales ranged from 417–1200 cm, with 68% of females 1050–1200 cm long. Constraints associated with the age structure observed in this study and the representativeness of the age structure to that of the greater population are discussed. In an effort to assess the effects of underestimation of age estimates on age‐specific demographic parameters, a model simulating changes in age structure as a result of tooth wear was developed and the resulting survival rates compared to those derived from the original age structures of the samples. Survival did not change significantly between the modelled and original age structures. Also, the survival rate calculated from Australian mature female sperm whales was compared to that calculated from sperm whales caught in whaling operations from Japanese waters. Australian mature female sperm whales demonstrated significantly higher survival rates (mean=0.905±0.046 sd range: 0.856–0.986) than mature females from Japanese waters (mean=0.885±0.034 sd; range=0.859–0.970), possibly the reflection of higher fishing mortality on the Japanese whales. Growth equations using Gompertz and von Bertalanffy models were calculated for female Australian sperm whales and compared. Both models described growth in female sperm whales similarly. Changes in the demographic parameters of sperm whales with the cessation of whaling may be reflected in the growth rates of individuals and as such, these equations may provide a useful tool for monitoring continuing changes in the demographic parameters of this species. Without long‐term mark–recapture studies on sperm whales in this region, the frequent stranding of sperm whales in south‐eastern Australia provides an important opportunity to collect data on the life history and demography of this species.
Winter dispersal of leopard seals (Hydrurga leptonyx): environmental factors influencing demographics and seasonal abundance
Authors: Jessopp M. J. , Forcada J. , Reid K. , Trathan P. N. , Murphy E. J.
Published: June 2004

The dynamics of leopard seal Hydrurga leptonyx abundance and residency were investigated both within and between years at Bird Island, South Georgia, using observations of tagged and untagged individuals. Seals belonged to an open population, and were sampled outside the breeding season and during their northward winter dispersal (April–October). Seals at Bird Island were highly transient (41–63%) with only a limited number of individuals making repeat visits across years. A minimum yearly survival for resident seals was estimated to be between 0.61 and 0.85. The physical environment played an important role in leopard seal abundance, with observations following an apparent 4‐year periodicity consistent with the frequency and timing of the Antarctic Circumpolar Wave. Years of low sea‐surface temperature (SST) and extensive pack‐ice corresponded to a higher number of seals present, earlier arrivals, and longer periods of residency. Peak leopard seal arrivals at Bird Island corresponded to periods of low SST, which was consistent with the pagophilic nature of this species.
Feeding resource partitioning among four sympatric carnivores in the Peneda‐Gerês National Park (Portugal)
Authors: Carvalho J. C. , Gomes P.
Published: June 2004

The Iberian Peninsula comprises two distinct biogeographic areas: a temperate Atlantic Eurosiberian (north) and a Mediterranean (centre and south), and they provide very different biotopes, landscapes and prey for carnivores. One example is an abundance of the wild rabbit Orytolagus cuniculus in the Mediterranean zone, which contrasts with the Eurosiberian zone, where the rabbit is scarce. The feeding resource partitioning among four sympatric predators (red fox Vulpes vulpes, wild cat Felis silvestris, genet Genetta genetta and stone marten Martes foina) was analysed in the Peneda‐Gerês National Park (north‐west Portugal), located in the Eurosiberian region. Data on the spatial distribution of three important prey species (Apodemus sylvaticus, Microtus lusitanicus and Talpa occidentalis) were also collected to investigate their possible relationships with the feeding habits of each predator. Rodents are the staple prey for this guild of carnivores. Predators are able to supplement their diets with one or two secondary prey types: rabbits and arthropods by the largest carnivores (the red fox and the wild cat); insectivores by the small predators (the genet and the stone marten). These results contrast with the characteristic Mediterranean predator–prey features, where rabbits are the main support of carnivore communities. The feeding resource partitioning revealed a complex structure characterized by a dynamic niche differentiation and overlap, according to a seasonal pattern. To explain this pattern of resource exploitation two hypotheses are discussed in the light of the body size of predators and their use of space.
River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment
Authors: Martin A. R. , da Silva V. M. F.
Published: June 2004

Habitat use by the boto, or Amazon river dolphin Inia geoffrensis, was investigated in and around the Mamirauá Reserve, Brazil. Largely forested with numerous channels and lakes, Mamirauá comprises a variety of seasonal floodplain habitats known collectively as várzea. The annual cycle of flooding in this region (amplitude 11–15 m) dominates all life. Profound seasonal differences in dolphin density between habitats were consistent with known fish movements, in turn dictated by changes in water level and dissolved oxygen. An exodus of botos from floodplain to river at low water prevents dolphins being trapped in areas that become entirely dry. Densities of botos in floodplain channels were seasonally higher (up to 18 km−2) than reported for any cetacean worldwide. Adults were largely segregated by sex except at low water. Females and calves dominated in chavascal habitat–the areas most remote from rivers, which were preferred by males. Probable causes of this segregation are the energetic requirements of calves and the safety of females and/or calves from male harassment. Some 80% of botos occurring on rivers were within 150 m of the margins. The reliance of adult females and calves on várzea in a region with exceptional dolphin densities demonstrates the importance of floodplain habitats for the boto, and may be the key determinant of this species' distribution.
A comparative test of the correlated evolution of flightlessness and relative brain size in birds
Authors: Iwaniuk Andrew N. , Nelson John E. , James Helen F. , Olson Storrs L.
Published: June 2004

Secondary flightlessness has evolved independently many times in birds. Morphological changes in the pectoral girdle and flight feathers and changes in body size have been associated with the evolution of flightlessness, and it has also been suggested that flightless birds have relatively small brains. We therefore tested whether flightlessness is related to changes in relative brain size. Relative brain size was compared between volant and flightless species using both conventional statistics and modern comparative methods within nine taxonomic groups. No significant difference was found between flightless and volant species in six of these groups, regardless of whether body mass or tibiotarsal measurements were used as estimates of body size. Species with relatively smaller brains compared with their volant relatives were the great auk Pinguinus impennis, the kakapo Strigops habroptilus and some species of penguin. Thus, we found no evidence of a general correlation between the evolution of secondary flightlessness and the evolution of relatively small brains in birds. This suggests that neural requirements are not significantly different between flightless and volant species, although our methods may have overlooked subtle neurological changes that do not result in markedly different endocranial volumes.
Ultrastructure of echimyid and murid rodent spines
Authors: Hoey Kelley A. , Wise Robert R. , Adler Gregory H.
Published: June 2004

Aristiform spines of the rodents Niviventer fulvescens, Maxomys surifer, Hoplomys gymnurus and 17 species of Proechimys (representing both recognized subgenera and all nine species groups) were studied qualitatively using scanning electron microscopy (SEM) and quantitatively by measuring seven linear dimensions. SEM was used to examine spine tips, bases, longitudinal furrows and cross sections. Spines of the murid rodents N. fulvescens and M. surifer differed from those of the echimyid rodents H. gymnurus and Proechimys spp. in possessing a smaller base with a longer, narrower neck, scaled rather than ridged longitudinal furrows, and a solid internal core and large lacunae at the spine margins. Spines of H. gymnurus differed from those of Proechimys spp. in being considerably more robust with a stout neck at the base, an abruptly‐tapering tip and a dense inner layer with a series of smaller lacunae at the spine margins. A factor analysis of spine measurements revealed major differences among N. fulvescens, M. surifer, H. gymnurus, the Proechimys subgenus Trinomys and the nine Proechimys species groups within the subgenus Proechimys. However, all Proechimys species groups clustered closely together. A discriminant function analysis of the nine Proechimys species groups provided generally limited discriminatory power. Although spines are distinct at the generic and subgeneric levels, spines may possess limited diagnostic structure at the level of species within the subgenus Proechimys.
Tob38, a novel essential component in the biogenesis of β‐barrel proteins of mitochondria
Authors: Waizenegger Thomas , Habib Shukry J , Lech Maciej , Mokranjac Dejana , Paschen Stefan A , Hell Kai , Neupert Walter , Rapaport Doron
Published: June 2004

Insertion of β‐barrel proteins into the outer membrane of mitochondria is mediated by the TOB complex. Known constituents of this complex are Tob55 and Mas37. We identified a novel component, Tob38. It is essential for viability of yeast and the function of the TOB complex. Tob38 is exposed on the surface of the mitochondrial outer membrane. It interacts with Mas37 and Tob55 and is associated with Tob55 even in the absence of Mas37. The Tob38–Tob55 core complex binds precursors of β‐barrel proteins and facilitates their insertion into the outer membrane. Depletion of Tob38 results in strongly reduced levels of Tob55 and Mas37 and the residual proteins no longer form a complex. Tob38‐depleted mitochondria are deficient in the import of β‐barrel precursor proteins, but not of other outer membrane proteins or proteins of other mitochondrial subcompartments. We conclude that Tob38 has a crucial function in the biogenesis of β‐barrel proteins of mitochondria.
Membrane protein turnover by the m‐AAA protease in mitochondria depends on the transmembrane domains of its subunits
Authors: Korbel Daniel , Wurth Stephanie , Käser Michael , Langer Thomas
Published: June 2004

AAA proteases are membrane‐bound ATP‐dependent proteases that are present in eubacteria, mitochondria and chloroplasts and that can degrade membrane proteins. Recent evidence suggests dislocation of membrane‐embedded substrates for proteolysis to occur in a hydrophilic environment; however, next to nothing is known about the mechanism of this process. Here, we have analysed the role of the membrane‐spanning domains of Yta10 and Yta12, which are conserved subunits of the hetero‐oligomeric m‐AAA protease in the mitochondria of Saccharomyces cerevisiae. We demonstrate that the m‐AAA protease retains proteolytic activity after deletion of the transmembrane segments of either Yta10 or Yta12. Although the mutant m‐AAA protease is still capable of processing cytochrome c peroxidase and degrading a peripheral membrane protein, proteolysis of integral membrane proteins is impaired. We therefore propose that transmembrane segments of m‐AAA protease subunits have a direct role in the dislocation of membrane‐embedded substrates.
Effect of electron inertia on the speed and shape of ion-acoustic solitary waves in plasma
Authors: Chatterjee Prasanta , Das Brindaban
Published: June 2004

Conditions for the existence of ion-acoustic solitary waves are investigated in a cold collisionless plasma taking into account the electron inertia. The Sagdeev’s pseudopotential is derived in terms of u, the ion velocity. It is found that there exists a critical value of u0(≠0), the value of u at which (u′)2=0, beyond which the soliton solution ceases to exist and the electron inertia plays a non-insignificant role in determining this critical value. This result reproduces the result of Johnston and Epstein [Phys. Plasmas. 7, 906 (2000)] when the effect of electron inertia is neglected.
Electrical study of Ge-nanocrystal-based metal-oxide-semiconductor structures for p-type nonvolatile memory applications
Authors: Kanoun M. , Souifi A. , Baron T. , Mazen F.
Published: June 2004

Nonvolatile memory structures using Ge nanocrystals embedded in SiO2 have been characterized by room and low temperature current–voltage and capacitance–voltage measurements. The Ge nanocrystals have been fabricated by low pressure chemical vapor deposition process which is shown to be well suited for a real control of the tunnel oxide thickness. The deposition conditions allow a separate control of nc-Ge density and size. Using capacitance–voltage characterizations on nonvolatile memory structures, we have measured the charging and discharging kinetics of holes for tunnel oxides in the range 1.2–2.5 nm. Using current–voltage measurements and simulations, we have also shown that nc-Ge are at the origin of a tunnel-assisted current. Simulations have demonstrated that the hole’s charging effects strongly reduce the current density across the nonvolatile memory structure. Combined with a good control of nc-Ge properties, the use of Ge dots with large diameters (>10 nm) seems to be a promising way for p-type memory applications.
Numerical simulation of supernova-relevant laser-driven hydro experiments on OMEGA
Authors: Miles A. R. , Braun D. G. , Edwards M. J. , Robey H. F. , Drake R. P. , Leibrandt D. R.
Published: June 2004

In ongoing experiments performed on the OMEGA laser [J. M. Soures et al., Phys. Plasmas 5, 2108 (1996)] at the University of Rochester Laboratory for Laser Energetics, nanosecond laser pulses are used to drive strong blast waves into two-layer targets. Perturbations on the interface between the two materials are unstable to the Richtmyer–Meshkov instability as a result of shock transit and the Rayleigh–Taylor instability during the deceleration-phase behind the shock front. These experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen–helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. The authors are, at present, particularly interested in the development of the Rayleigh–Taylor instability through the late nonlinear stage, the transition to turbulence, and the subsequent transport of material within the turbulent region. In this paper, the results of numerical simulations of two-dimensional (2D) single and multimode experiments are presented. These simulations are run using the 2D Arbitrary Lagrangian Eulerian radiation hydrodynamics code CALE [R. T. Barton, Numerical Astrophysics (Jones and Bartlett, Boston, 1985)]. The simulation results are shown to compare well with experimental radiography. A buoyancy-drag model captures the behavior of the single-mode interface, but gives only partial agreement in the multimode cases. The Richtmyer–Meshkov and target decompression contributions to the perturbation growth are both estimated and shown to be significant. Significant dependence of the simulation results on the material equation of state is demonstrated, and the prospect of continuing the experiments to conclusively demonstrate the transition to turbulence is discussed.
Comparison between experiment and two simulation strategies for the extraction of focused ion beams
Authors: Sutherland Orson , Keller John , Irzyk Michael , Boswell Rod
Published: June 2004

Computer simulation codes for the extraction of ion beams have been used for over three decades. Here we describe medium current extraction (∼1 mA) from a high density plasma source (>1012 cm−3) with a three electrode extraction system and compare the extracted current and the angular divergence with the results of two computer simulation programs. The first is called PBgun and is a commercially available ray tracing code; the second, called simulation d’extraction de faisceaux d’ions (SEFI) uses a particle-in-cell code to simulate the plasma and ion beam. It is the purpose of this article to ascertain whether these codes can adequately model the plasma/beam interface and hence successfully predict the extracted current and beam form across a broad range of extraction parameters. We found that SEFI could accurately predict the function of extracted current versus extraction voltage and that PBgun gave accurate simulations when the current or current density could be specified near the meniscus. Also for a thin plasma aperture and a fixed current at the meniscus, PBgun gave roughly 60% of the functional dependence of the extracted current on the extraction voltage and the other 40% on variations in the plasma pre-sheath. Both codes had some error from beam crossing near the axis which changed the amount of meniscus curvature predicted.
High efficiency apparatus for spin polarized inverse photoemission
Authors: Cantoni M. , Bertacco R.
Published: June 2004

Spin polarized inverse photoemission is a powerful but demanding technique for investigating the interplay between surface magnetism and the spin polarized electronic structure of unoccupied states. We have developed a compact apparatus five times more efficient than similar existing systems, with a sizable reduction of the acquisition time. It consists of an electron source based on a negative electron affinity GaAs photocathode coupled to an appropriate transport electron optics and a bandpass photon detector at fixed energy (9.3 eV) employing a KBr photocathode and a SrF2 window. The detector is placed all around the electron gun, thus providing a sizable increase of the solid collection angle for photons. For calibration and as examples of application, spin integrated/resolved spectra from Ag(001)/Fe(001)-p(1×1)O surfaces are reported.
Equilibrium shape of SiGe Stranski–Krastanow islands on silicon grown by liquid phase epitaxy
Authors: Hanke M. , Schmidbauer M. , Köhler R. , Syrowatka F. , Gerlitzke A.-K. , Boeck T.
Published: June 2004

SiGe Stranski–Krastanow islands coherently grown on Si(001) substrates by liquid phase epitaxy are typically made of truncated pyramids with {111} side facets, whereas the persistent presence of an (001) top facet indicates an energetical disadvantage of complete pyramids compared to truncated ones. We attribute this to a surface minimization process during the island evolution under the assumption of isotropically distributed surface energies and stable island facets. For the presence of {111} side facets we have theoretically derived a final geometrical aspect ratio of island base versus island height of 1.96, which is in excellent agreement with the experimentally derived averaged value of 2.08±0.10 within a concentration window between 9% and 30% germanium.
Comment on “Statistical analysis of turbulent flux and intermittency in the nonfusion magnetoplasma Blaamann” [Phys. Plasmas 10, 4335 (2003)]
Authors: Rypdal K. , Ratynskaia S.
Published: June 2004

In a recent paper Fredriksen et al. claim the nonexistence of long-range dependence in a particular state in the plasma torus “Blaamann” based on estimates in the mesoscale regime of the Hurst exponent from data sampled from different positions within the plasma column. The data analyzed were records of 104 sample points of local quantities like electron density, electric field, and particle flux. In this Comment the physical interpretation of these estimates is discussed, and it is pointed out that a work cited in that paper, based on data records of 106 sample points from the same state, has demonstrated the existence of strong long-range dependence (H=0.75) in plasma potential due to global fluctuations, and only weak dependence in local quantities. This Comment also demonstrates that the length of the data records, as well as the method employed by Fredriksen et al. to obtain the Hurst exponent, are inadequate to eliminate the influence of the strong cyclic components in the signal. The methods employed are also inadequate in the sense that they cannot distinguish between Lévy statistics and long-range dependence as a cause of elevated Hurst exponent.
Gyroscopic effect in compact toroidal plasmas
Authors: Geren Preston , Steinhauer Loren
Published: June 2004

The gyroscopic effect in compact toroidal plasmas is investigated using a minimum energy principle in which the angular momentum is added as a constraint. If attention is limited to incompressible plasmas, the flow and field vectors can be expanded in eigenfunctions of the curl (Beltrami functions). Then the flow and field appear, in general, as a spectrum of Beltrami vectors. Adding the angular momentum as a constraint has a strong effect on the energy ordering of the system. Without this constraint, the state with lowest “ordered” energy has a fine structure element that would, in practice, decay, leading to a force-free state. However, if a nonzero angular momentum is specified, then the lowest-energy state has finite pressure and significant flow. For angular momentum of sufficient magnitude, this is a “smooth” state that should have good magnetic confinement. These effects may be an indicator that the gyroscopic effect improves the stability. However, this is by no means certain since a rigorous link between minimum energy and stability in a flowing plasma has not yet been established.
Linear and nonlinear dispersive dust Alfvén waves in plasmas with opposite polarity dust grains
Authors: Shukla P. K.
Published: June 2004

The hydrodynamic equations for opposite polarity dust grains in a quasineutral magnetoplasma, together with Ampère’s law, are used to derive nonlinear equations for ultralow-frequency (in comparison with the dust gyrofrequency) dispersive dust Alfvén waves (DDAWs). In the linear approximation, the frequency of the DDAWs is obtained. The governing equations for the DDAWs admit a tearing instability as well as a dipolar vortex solution.
Effect of ion cyclotron parametric turbulence on the generation of edge suprathermal ions during ion cyclotron plasma heating
Authors: Mikhailenko V. S. , Scime E. E.
Published: June 2004

The effect of parametric ion cyclotron turbulence on the heating of cold and suprathermal ions in the edge of a tokamak plasma during injection of high radio frequency (rf) power in the ion cyclotron resonance frequency range is studied. The maximum turbulent heating rates for cold edge ions and suprathermal edge ions are calculated analytically for ion cyclotron turbulence driven by rf heating at the plasma edge. It is demonstrated that the maximum turbulent ion-heating rate for suprathermal ions is insufficient to explain the observed heating of edge ions. Therefore, the excitation of ion cyclotron turbulence by rf heating systems in the plasma edge is unlikely to be responsible for the experimentally observed large population of suprathermal ions in the edge of tokamak plasmas.
Phenomenology of compressional Alfvén eigenmodes
Authors: Fredrickson E. D. , Gorelenkov N. N. , Menard J.
Published: June 2004

Coherent oscillations with frequency 0.3⩽ω/ωci⩽1, are seen in the National Spherical Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)]. This paper presents new data and analysis comparing characteristics of the observed modes to the model of compressional Alfvén eigenmodes (CAE). The toroidal mode number has been measured and is typically between 7<n<9. The polarization of the modes, measured using an array of four Mirnov coils, is found to be compressional. The frequency scaling of the modes agrees with the predictions of a numerical two-dimensional code, but the detailed structure of the spectrum is not captured with the simple model. The fast ion distribution function, as calculated with the beam deposition code in TRANSP [R. V. Budny, Nucl. Fusion 34, 1247 (1994)], is shown to be qualitatively consistent with the constraints of the Doppler-shifted cyclotron resonance drive model. This model also predicts the observed scaling of the low frequency limit for CAE.
Low threshold room-temperature continuous-wave operation of 2.24–3.04 μm GaInAsSb/AlGaAsSb quantum-well lasers
Authors: Lin C. , Grau M. , Dier O. , Amann M.-C.
Published: June 2004

3.04 μm emission has been achieved in GaInAsSb/AlGaAsSb double-quantum-well ridge waveguide diode lasers in continuous-wave mode up to 20 °C. A threshold current density of 343 A/cm2 was recorded from a laser with 2 mm cavity length and 30 μm ridge width in pulsed-mode operation. A characteristic temperature of 30 K was measured from a 1.2 mm long device. Threshold current densities and characteristic temperatures of GaInAsSb/AlGaAsSb laser diodes with wavelengths from 2.24 to 3.04 μm are summarized. The threshold current density per quantum well increases strongly with wavelength; at 3.04 μm, it is three times that value of a 2.24 μm device.
Hydrogen incorporation in titanium via laser irradiation
Authors: Schwickert M. , Carpene E. , Lieb K. P. , Uhrmacher M. , Schaaf P.
Published: June 2004

We have applied the technique of direct laser synthesis to the hydrogen–titanium system. Large amounts of hydrogen are incorporated into the sample surface by laser irradiating the samples in a hydrogen atmosphere at elevated gas pressures. The process of “laser hydriding” leads to the formation of TiH2 and the amount of incorporated hydrogen was found to be independent of the hydrogen gas pressure. Similarities to the laser nitriding process are briefly discussed and the results are interpreted with the help of thermodynamic simulations of the laser–material interaction.
Dense and strong plasma initiated by Ca0.7Sr0.3TiO3 ceramic
Authors: Li Ruixing , Tang Qing , Yin Shu , Yamaguchi Yukishige , Sato Tsugio
Published: June 2004

In order to find a kind of material that is able to initiate plasma avalanches, Ca0.7Sr0.3TiO3 ceramic, which possesses high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier to decompose CO2 in order to investigate the efficiency and characteristics of this ceramic. The results were compared with commercial alumina and silica glass, which possess lower permittivities, but however, were widely used in previous studies. The mechanical and dielectric properties of Ca0.7Sr0.3TiO3 were greatly enhanced by adding 0.5 wt. % Li2Si2O5 as a sintering additive. Although Ca0.7Sr0.3TiO3 without an additive was fractured before the arcing plasma, that which was sintered with 0.5 wt. % Li2Si2O5 successfully generated a dielectric barrier discharge (DBD) plasma and the CO2 conversion was much higher than with those using an alumina or silica glass barrier. The plasma behaviors of using different dielectric materials were studied during the processes of the DBD plasma burst. It was found that the density and strength of current pulses increased with increasing permittivity, and as a consequence, very dense and strong current pulses were initiated by this Ca0.7Sr0.3TiO3 with 0.5 wt. % Li2Si2O5 ceramic because of its high permittivity; likewise, they were efficient in reducing CO2. The density and strength of current pulses are also found to be the dominative parameters of the plasma reaction. This Ca0.7Sr0.3TiO3 ceramic was sintered using Li2Si2O5 as a sintering additive and used as a dielectric barrier of DBD for the first time.
Characterization of preplasma produced by an ultrahigh intensity laser system
Authors: Adumi K. , Tanaka K. A. , Matsuoka T. , Kurahashi T. , Yabuuchi T. , Kitagawa Y. , Kodama R. , Sawai K. , Suzuki K. , Okabe K. , Sera T. , Norimatsu T. , Izawa Y.
Published: June 2004

Ultra intense laser interaction with solids is crucially modified by the presence of the plasma layer created by the prepulse associated with the peak intensity pulse. Here interferometric measurements of the preplasma created by a 40 TW, 600 fs Nd-glass laser are reported. Density profile and its target dependence are measured and the predicted scale length dependence on target atomic number is confirmed.
Experimental investigations of void dynamics in a dusty discharge
Authors: Mikikian Maxime , Boufendi Laïfa
Published: June 2004

The first electrical and spectroscopic characterizations of an instability, usually called the “heartbeat” instability, occurring in a laboratory dusty plasma are reported. The heartbeat instability consists of successive contractions and expansions of the central dust free region observed in a dense cloud of dust particles. This cloud is formed in a radio-frequency plasma by sputtering polymer material deposited on the electrodes. The evolution of the discharge current reveals the relatively complex shape of the instability and allows one to measure its evolution as a function of gas pressure and radio-frequency power.
Resistive magnetohydrodynamic equilibrium and stability of a rotating plasma with particle sources
Authors: Huang Yi-Min , Hassam A. B.
Published: June 2004

Particle sources and resulting density profiles are shown to play an important role in the magnetohydrodynamic (MHD) stability of azimuthally rotating axially magnetized plasmas. In the absence of particle sources, density profiles relax under resistive diffusion to pile up to the outside of the system consistent with the outward centrifugal forces. In particular, particle sources would have to be placed appropriately to maintain desired density profiles for fusion applications of centrifugally confined systems. Tailoring of the density profiles could, however, be used to achieve control over MHD stability. Long wavelength Kelvin–Helmholtz modes as well as short wavelength interchange modes are studied in relation to profile tailoring and efficacy of velocity shear. It is concluded that judiciously placed particle sources could be used to enhance stability.
Assessment of room-temperature phonon-limited mobility in gated silicon nanowires
Authors: Kotlyar R. , Obradovic B. , Matagne P. , Stettler M. , Giles M. D.
Published: June 2004

The technologically important question of whether the reduced density of electron states (DOS) for scattering in one-dimensional (1D) wire transport devices gives an advantage over the planar metal–oxide–semiconductor field-effect-transistor (MOSFET) for electron mobility is assessed by simulations. We self-consistently solve the Schrödinger–Poisson equations to calculate phonon-limited electron mobility in a multisubband cylindrical Si gated wire. We find that the benefit of reduced 1D DOS is offset by an increased phonon scattering rate due to increased electron–phonon wave function overlap and results in a degraded mobility in narrow wires. The applied gate bias voltage and the wire size control the transition from wire geometry to surface field-dominated confinement. The size scale for this 1D to two-dimensional (2D) transition is also found to be surprisingly small: A wire with a 75 A radius has an essentially 2D DOS and has a 2D mobility that is degraded from the planar (100) MOSFET due to the anisotropy of the inversion mobility in different Si crystallographic planes.
Force-gradient detected nuclear magnetic resonance
Authors: Garner Sean R. , Kuehn Seppe , Dawlaty Jahan M. , Jenkins Neil E. , Marohn John A.
Published: June 2004

We have detected nuclear magnetic resonance in GaAs by selectively inverting Ga71 spins to create a local force gradient which shifts the mechanical resonance frequency of a nearby magnet tipped microcantilever. Employing a low spring constant cantilever (60 μN/m) at 4.4 K and 7 T, we demonstrate a magnetic moment sensitivity of 7.5×10−21 J/T, equal to the Curie Law magnetization from 7.1×108 Ga71 spins. The method obviates the need to spin-lock sample magnetization during detection, allowing the signal to be collected for a time approaching the full spin-lattice relaxation time.
Ferroelectric properties of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method below the Curie temperature
Authors: Morita Takeshi , Wagatsuma Yasuo , Cho Yasuo , Morioka Hitoshi , Funakubo Hiroshi , Setter Nava
Published: June 2004

Deposition of a hydrothermal method has a number of advantages; low deposition temperature, high-purity, deposition on a three-dimensional structure, and a large thickness. The present paper investigates the improvement of an epitaxial lead zirconate titanate (PZT) thin film deposited via hydrothermal synthesis. The critical parameter contributing to the film morphology was revealed to be the holding position of the reaction solution during deposition. In addition to this improvement, the SrRuO3 bottom electrode was confirmed to be able to withstand high alkali concentrations during the hydrothermal reaction. A hydrothermal synthesis time of 24 h yielded a PZT film with a thickness of 500 nm on SrRuO3/SrTiO3 (100) at 150 °C. The remanent polarization 2Pr and coercive electric field were 38.4 μC/cm2 and 21.8 kV/cm, respectively.
Enhancement in screening throughput and density of combinatorial libraries using wavelet analysis
Authors: Potyrailo Radislav A.
Published: June 2004

We report an approach to increase the measurement rate in the real-time monitoring of parallel combinatorial reactions with a single scanning device. The wavelet transform is applied to collected data to reduce the integration time needed to achieve a predetermined signal-to-noise. As an example, we analyzed Raman spectra of diphenyl carbonate, one of the starting components in a melt-polymerization reaction of polycarbonate performed on combinatorial (150 μL volume) scale. The time reduction after the wavelet analysis of each measured spectrum permitted sampling of full spectra from each combinatorial reaction with an up-sampling factor N=20–90. Such up-sampling capability is critical for increasing the density of combinatorial libraries during their dynamic analysis where each library element is measured multiple times during combinatorial reactions.
Two-color heterodyne optical zooming method for nanometer measurement
Authors: Wu Guanhao , Zeng Lijiang
Published: June 2004

A two-color heterodyne optical zooming method is proposed to improve the signal-to-noise ratio in nanometer interferometry. By phase-compensation technique, a small displacement in the sensing arm results in an enlarged displacement in the reference arm. The latter displacement can be measured easily and accurately. The zoom factor K, which is determined by the two wavelengths that produce the synthetic wavelength, can be easily changed. Using the heterodyne technique, phase changes caused by the displacement can be measured with high accuracy. A linearity of 0.9997 and a standard deviation of 1.8 nm were experimentally obtained in a measurement range of 0.17 μm.
Method for acquiring extended real-time kinetic signals in nanosecond laser flash photolysis experiments
Authors: Banderini Andrea , Sottini Silvia , Viappiani Cristiano
Published: June 2004

We report a data acquisition method for detecting transient absorbance signals extended in time which require nanosecond resolution and need to span several decades in time up to the hundreds of milliseconds. A microprocessor is used to generate a sequence of up to 100, 2.120 μs wide radio frequency signals at 500 MHz which are used to trigger the analog-to-digital conversion on a digital oscilloscope, operating in the external clock mode. During these radio frequency bursts the data are sampled at a sampling rate of 500 Ms/s. The delay of each sampling burst can be set at arbitrary values with respect to the first signal, with a minimum delay of 0.96 μs for the second pulse, and 1.2 μs for all other pulses. The microprocessor provides accessory synchronization outputs for laser triggering and for shutter opening and closing. This data acquisition system allows measuring the complete time course of extended kinetics after each laser shot, thus reducing acquisition times and data size. We prove the complete equivalence of the proposed acquisition method with standard methods, where several time bases are acquired to cover the complete kinetic trace for the ligand rebinding to myoglobin after photolysis of a gel embedded myoglobin-CO complex.
Spherical sapphire single-crystal synthesis by aerodynamic levitation with high growth rate
Authors: Arai Yasutomo , Aoyama Tomotsugu , Yoda Shinichi
Published: June 2004

This article describes a technique for forming spherical Al2O3 single crystals by an aerodynamic levitator by applying the unidirectional solidification method. A levitation method intrinsically produces a spherical material. In addition, both the focused laser beam heating and the gas flows to the sample trapped in the levitator generate a steep temperature gradient in the molten sample, enabling the sample to grow with high growth rate. Spherical sapphire single-crystal production consists of two processes. First step is to solidify the molten sample unidirectionally from polycrystalline parts at the bottom of the sample. This sample was almost a single crystal with polycrystalline parts remaining just around the bottom. The crystal is then revolved before the second step. In the second step the revolved crystal was remelted from the polycrystalline part and solidified from the seed, resulting in complete single-crystal production. The x-ray Laue and crossed nicol experiment results for the Al2O3 spherical crystal with 2 mm diameter demonstrated that twin-free bulk single crystal had been produced. There were no macroscopic voids or cracks in the crystal at 60 mm/h growth rates in both steps. In addition, a hexagonal shape of the crystal seems to be the habit-plane of a natural corundum. This indicates the growth direction was along the c-axis of a sapphire.
Measurement of the group-delay dispersion of femtosecond optics using white-light interferometry
Authors: Imran Tayyab , Hong Kyung-Han , Yu Tae Jun , Nam Chang Hee
Published: June 2004

A compact and practical white-light cross-correlator suitable for fast evaluation of femtosecond optics, in terms of group-delay dispersion, was developed. A 40-W tungsten-halogen lamp was used as a white-light source and the detector selection was made so as to have adequate spectral sensitivity from 600 to 1050 nm, peaked at 800 nm. Group-delay dispersion was obtained, with femtosecond time resolution, from the Fourier transform of the cross-correlation interferogram. The dispersion characteristics of a borosilicate glass plate, broadband femtosecond mirrors, broadband chirped mirrors, and output couplers of different reflectivity have been determined in the wavelength range of 650 to 1050 nm.
Parallel-plate ion trap useful for optical studies of microparticles
Authors: Tona Masahide , Kimura Masahiro
Published: June 2004

We report an electrodynamic ion trap composed of four disk electrodes with a hole at the center of each electrode. This ion trap has been developed in order to suspend single micrometer sized droplets. To levitate a droplet, an ac voltage was applied to the two middle electrodes, and the two end electrodes were used to form an additional dc field to balance the gravitational force on the droplet. By further applying compensating dc voltages to the rods which support the disks, the droplet could be maintained at the center of the ion trap with a positional fluctuation of less than 1 μm. It is shown here that this is useful for obtaining both spatial images and emission spectra of dye-doped droplets with higher spatial resolutions than those obtained in systems without such compensation.
Weakly nonlinear vertical dust grain oscillations in dusty plasma crystals in the presence of a magnetic field
Authors: Kourakis I. , Shukla P. K.
Published: June 2004

The weakly nonlinear regime of transverse paramagnetic dust grain oscillations in dusty (complex) plasma crystals is discussed. The nonlinearity, which is related to the sheath electric/magnetic field(s) and to the intergrain (electrostatic/magnetic dipole) interactions, is shown to lead to the generation of phase harmonics and, in the case of propagating transverse dust-lattice modes, to the modulational instability of the carrier wave due to self-interaction. The stability profile depends explicitly on the form of the electric and magnetic fields in the plasma sheath. The long term evolution of the modulated wave packet, which is described by a nonlinear Schrödinger-type equation, may lead to propagating localized envelope structures whose exact forms are presented and discussed. Explicit suggestions for experimental investigations are put forward.
Compression of polyhedral graphite up to 43 GPa and x-ray diffraction study on elasticity and stability of the graphite phase
Authors: Nakayama Atsuko , Iijima Sumio , Koga Yoshinori , Shimizu Katsuya , Hirahara Kaori , Kokai Fumio
Published: June 2004

The crystal structure of polyhedral graphite particles (“G balls”) has been investigated under pressure up to 43 GPa and at room temperature by x-ray powder diffraction measurements. The polyhedra maintain the graphite phase under pressure higher than 40 GPa. A 29% compression in volume at 43 GPa involves an unusual decrease in the interlayer distance of 25%. The polyhedra recover their original crystal structure by releasing the pressure. A closed and solid structure of the polyhedra, suppressing a transition into another phase, causes them to become metallic under pressures higher than 20 GPa.
Effect of In0.2Ga0.8As and In0.2Al0.8As combination layer on band offsets of InAs quantum dots
Authors: He J. , Xu B. , Wang Z. G.
Published: June 2004

We demonstrate the self-organized InAs quantum dots capped with thin and In0.2Al0.8As and In0.2Ga0.8As combination layers with a large ground and first excited energy separation emission at 1.35μm at room temperature. Deep level transient spectroscopy is used to obtain quantitative information on emission activation energies and capture barriers for electrons and holes. For this system, the emission activation energies are larger than those for InAs∕GaAs quantum dots. With the properties of wide energy separation and deep emission activation energies, self-organized InAs quantum dots capped with In0.2Al0.8As and In0.2Ga0.8As combination layers are one of the promising epitaxial structures of 1.3μm quantum dot devices.
Photoluminescence study of Si-doped GaN∕Al0.07Ga0.93N multiple quantum wells with different dopant position
Authors: Haratizadeh H. , Monemar B. , Paskov P. P. , Bergman J. P. , Sernelius B. E. , Holtz P. O. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I.
Published: June 2004

The effects of Si doping on the emission energy and recombination dynamics in a set of GaN∕Al0.07Ga0.93N multiple quantum well (MQW) samples with different position of the dopant layer were studied by means of photoluminescence (PL) and time-resolved PL measurements. When the doping is in the barrier and in both barrier and well, the MQW emission appears above the GaN band gap, while the sample doped in the well shows a redshifted emission. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature a longer PL decay time, 760ps, was measured for the sample doped in the well, a factor of 2 longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures.
Resonant two-photon photoemission in quantum-well infrared photodetectors
Authors: Maier Thomas , Schneider Harald , Walther Martin , Koidl Peter , Liu Hui Chun
Published: June 2004

We report the nonlinear behavior of quantum-well infrared photodetectors with three energetically equidistant energy levels. The giant resonant nonlinearity leads to a quadratic power dependence of the photocurrent down to excitation power densities as low as 0.1W∕cm2. Using these highly sensitive two-photon detectors, second-order autocorrelation measurements of ultrashort midinfrared laser pulses in the pJ regime are demonstrated. The dynamical behavior is studied by a numerical analysis of these measurements. At high bias voltages we observe a dominating linear contribution to the photocurrent arising from tunneling processes.
Scanning photoluminescence spectroscopy in InAs∕InGaAs quantum-dot structures
Authors: Dybiec M. , Ostapenko S. , Torchynska T. V. , Velasquez Losada E.
Published: June 2004

Spatially-resolved photoluminescence (PL) spectroscopy was performed at different temperatures on self-assembled InAs quantum dots embedded into MBE-grown In0.15Ga0.85As∕GaAs multiquantum-well heterostructures. Strong inhomogeneity of the PL intensity is observed by mapping samples with different In∕Ga composition of the InxGa1−xAs capping layers (0.1⩽x⩽0.2). Two different behaviors in the quantum-dot PL maps are observed: (1) a reduction of the PL intensity is accompanied by a gradual “blue” shift of the luminescence maximum at 300K and “red” shift at 80K, and (2) PL intensity variation occurs at a stable peak position of the PL maximum. Two separate mechanisms are suggested to account for the observed intensity variation of the quantum-dot luminescence.