bluuebunny/crossref_metadata_2025 huggingface dataset:
On the computation of the infimum in H∞‐optimization
Authors: Chu Delin
Published: April 2004

In this paper, a new method for the computation of the infimum for a large class of continuous‐time H∞ optimal control problem by state feedback is presented. The main ingredients of the new method include three generalized eigenvalue problems whose coefficient matrices are from a condensed form of the given system. This condensed form is computed using only orthogonal transformations which can be implemented via a numerically stable way. The superiority of the new method over the existing one given in Chen (H∞ Control and its Applications, Chapter 5. Springer: Berlin, 1997) is verified by some numerical examples. Copyright © 2004 John Wiley & Sons, Ltd.
Improved outer inverses for the numerical solution of Euler–Lagrange equations
Authors: Coroian Dan I.
Published: April 2004

In this paper, improved outer inverses are used for solving the overdetermined differential‐algebraic equations that arise in the simulation of mechanical systems. The method is based on Newton‐type iterations using outer inverses. Copyright © 2004 John Wiley & Sons, Ltd.
Evaluations of sex assessment using weighted traits on incomplete skeletal remains
Authors: Kjellström A.
Published: April 2004

Several studies have presented a variety of sexually dimorphic traits on the skeleton offering possibilities to score these traits for sex determination. However, few have discussed how fragmentation of skeletons affects the reliability of the results, and how to assess sex attribution based on a variety of methods. In the present study sex was determined for 354 skeletons from the medieval Swedish town Sigtuna, using well‐recognized sexing techniques on the pelvis, skull and femur. The preservation of the skeletons varied markedly, thus affecting possibilities for sex assessments. An attempt was made to evaluate the result of the sex assessment when weighting of different traits with different scales was used. The resulting estimation for each individual was called total mean value A. In addition, a total mean value B that considers unobservable missing traits was estimated. It can be concluded that both weighting and fragmentation affect sex assessments of incomplete skeletons. Copyright © 2004 John Wiley & Sons, Ltd.
Two neolithic cases of Hyperostosis frontalis interna
Authors: Devriendt W. , Piercecchi‐Marti M.D. , Ardagna Y. , Mahieu E. , Hershkovitz I. , Signoli M. , Dutour O.
Published: April 2004

Bone nodules resulting from Hyperostosis frontalis interna (HFI) were observed on the endocranial surface of the frontal bone of two elderly females in excess of 50 years of age coming from the excavation of the Neolithic hypogeum of Boileau (Vaucluse, France). These observations constituted the first evidence for HFI in the Neolithic periods in Europe. Copyright © 2004 John Wiley & Sons, Ltd.
Aggregation and protein binding of sodium maleate copolymers with varying hydrophobicities
Authors: Hirvonen Sami‐Pekka , Aseyev Vladimir , Chitanu Gabrielle C. , Tenhu Heikki
Published: April 2004

Copolymers of sodium maleate with methyl methacrylate, styrene, or vinyl acetate have been synthesized and studied in aqueous NaCl solutions of various ionic strengths. The polymers are polyelectrolytes with varying hydrophobicities, and their solution properties have been studied using static and dynamic light scattering. Copolymers containing methyl methacrylate or styrene were shown to aggregate in water upon increasing salt concentration. Copolymers of sodium maleate and vinyl acetate do not associate with increasing ionic strength. The binding of bovine serum albumin and cytochrome C to the sodium maleate copolymers was also investigated by light scattering. It was observed that cytochrome C forms complexes with the copolymers containing methyl methacrylate or vinyl acetate whereas albumin does not bind to any of the copolymers studied. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and characterization of SPE membrane based on sulfonated FEP‐g‐acrylic acid by radiation induced graft copolymerization for PEM fuel cell
Authors: Patri M. , Hande Varsha R. , Phadnis Swati , Somaiah B. , Roychoudhury Suhasini , Deb P. C.
Published: April 2004

A Novel solid polymer electrolyte (SPE) membrane containing both COOH and SO3H group has been prepared by simultaneous method of radiation grafting of acrylic acid onto FEP followed by sulfonation. The presence of weakly acidic acrylic acid controls the swelling in water while SO3H group provides conductivity due to its strongly ionic characteristic. FEP‐g‐acrylic acid and its sulfonated derivatives were characterized by their properties. While the mechanical properties decreased, other properties such as ion exchange capacity (IEC), water uptake and ionic conductivity increased with increase in graft content. These properties further changed on sulfonation. Acrylic acid being weakly acidic in nature, conductivity values of the grafted membrane were quite low. However, introduction of strong SO3H group resulted in conductivity closer to Nafion 117. Few sulfonated membranes have been tested with respect to H2/O2 fuel cell performance. Short‐term fuel cell test for 100 hr gave a stable performance. These membranes are less expensive compared to Nafion. Copyright © 2004 John Wiley & Sons, Ltd.
Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates, central Sacramento River, California, USA
Authors: Micheli E. R. , Kirchner J. W. , Larsen E. W.
Published: April 2004

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back‐calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near‐bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios. Copyright © 2004 John Wiley & Sons, Ltd.
Changes in riparian vegetation communities below a large dam in a monsoonal region: Futase Dam, Japan
Authors: Azami Kazuhiro , Suzuki Hitomi , Toki Seiko
Published: April 2004

This paper examines the effects of a dam reservoir flood control on riparian plant communities in an Asian monsoon area subjected to large summer floods under natural conditions. We compared riparian plant communities downstream of the Futase Dam located on the Arakawa River, with communities on the Nakatsu River, a tributary of the Arakawa River with no dam. Historical changes in spatial distribution of riparian vegetation communities were analysed using aerial photographs. Stand ages and flood history were also examined to analyse the likelihood of tree erosion in scenarios with and without flood control. Comparison of the two reaches shows that the reduced flood peaks below the Futase Dam led to the expansion of riparian forest area and an increase in species diversity. Reduction in the flood peaks below the dam means that the toppling moment of the trees is no longer exceeded. The result is that the riparian forest below the dam is able to develop into later successional stages. Copyright © 2004 John Wiley & Sons, Ltd.
Does grand multiparity affect fetal outcome?
Authors: Seidman D.S. , Gale R. , Slater P.E. , Ever‐Hadani P. , Harlap S.
Published: April 2004

Low birthweight and stillbirth rates of 16,647 Jerusalem deliveries were examined by birth‐order comparing longitudinal to cross‐sectional data. Six hundred fifty‐seven complete sibships of 7 or more were assessed, including 95 sibships from the socio‐economically homogeneous ultraorthodox Jewish community of Mea Shearim. In both cross‐sectional and longitudinal studies grandmultiparas were not at increased risk for low birthweight, but did have a higher frequency of stillbirths.
A simple painless, dangerless and easily repeatable procedure for endometrium biopsy
Authors: van Bogaert L.‐J.
Published: April 2004

Endometrium biopsies are currently carried out with the Novak curette. The drawbacks of this procedure are well known. The use of a female, disposable, sterile, plastic urinary catheter is a useful, easy, painless, dangerless and repeatable alternative to obtain suitable endometrium samples for histopathologic diagnosis. Since a small endometrial cancer can be overlooked, selection of patients is obligate, but this holds also insofar as all methods of endometrium biopsy are concerned. Accordingly, the procedure is primarily suitable in cases of “dysfunctional” bleeding.
Recurrent endometriosis following hysterectomy and oophorectomy: the role of residual ovarian fragments
Authors: Dmowski W.P. , Radwanska E. , Rana N.
Published: April 2004

Seven women with recurrent endometriosis after definitive surgery were evaluated. Plasma estradiol, FSH and LH indicated that recurrence was stimulated by residual ovarian fragments in six and pseudopregnancy regimen in one. Surgical treatment in two women was followed in one by hypertrophy of another ovarian fragment and reactivation of endometriosis as demonstrated by serial endocrine and ultrasonographic studies. Three patients responded well to hormonal treatment; one required pelvic irradiation. We conclude that: (1) small ovarian fragments may hypertrophy under increased gonadrotropin stimulation, become functional and stimulate recurrence of endometriosis; (2) resection of one such fragment may be followed by reactivation of another.
Endometrial carcinoma and its precursors: Early detection and treatment
Authors: Mencaglia L. , Valle R.F. , Perino A. , Gilardi G.
Published: April 2004

Endometrial carcinoma is the most frequent genital neoplasia in women. Precursors of this condition include endometrial hyperplasia, particularly when cytologic atypia occurs. Among the frequent early clinical manifestations of endometrial carcinoma is abnormal uterine bleeding that must be differentiated from bleeding associated with benign conditions. Early detection of endometrial carcinoma and its precursors in women at risk is the best prophylactic measure in the final therapeutic outcome. In this review, the accuracy of methods of early diagnosis of endometrial carcinoma and its precursors is assessed, in order to provide early therapy and optimum prognosis. The epidemiology of endometrial carcinoma, as well as the risk factors for the development of this neoplasia, are also reviewed. A histologic classification of endometrial hyperplasia and carcinoma of the endometrium, based on current theories of histopathogenesis, is included.
Occurrence of human papillomavirus DNA types 16 and 18 (HPV‐16/18) in cervical smears as compared to cytological findings
Authors: Köchel H.G. , Teichmann A. , Eckardt N. , Arendt P. , Kuhn W. , Thomssen R.
Published: April 2004

Cervical smears from 2336 women were examined for the presence of HPV‐16/18 by dot‐blot hybridization using 32P‐labeled HPV‐16/18 DNA under high stringency conditions. The hybridization data were compared with cytological findings classified according to Papanicolaou. The ages of the patients ranged from under 20 to over 70 years. Ninety‐eight (4.4%) of the 2237 cytologically normal cervical samples (Pap I and II) were HPV‐16/18 positive. Thirteen out of 32 (40.6%) samples showing signs of mild and moderate dysplasia (Pap IIID) were found to be HPV‐16/18 positive. In 5 out of 7 (71.4%) samples from women with severe dysplasia or carcinoma in situ (Pap IV) and in 9 out of 25 (32.1%) samples from patients with invasive cervical carcinoma (Pap V) HPV‐16/18 DNA was detected. Thirty‐two smears were from women with severe unspecific cervical inflammation (Pap III). Two (6.2%) out of them were HPV‐16/18 positive. Normal smears showed an apparent age‐dependent pattern of HPV‐16/18 positivity with a peak prevalence of 10.6% among women younger than 20 years old. The majority of premalignant lesions was detected among women younger than 40 years old; whereas all invasive lesions were from women older than 39 years. Compared to the HPV‐16/18 prevalence rate in normal smears, abnormal smears harbored HPV‐16/18 DNA approximately 9 times more frequently. This finding supports the hypothesis that HPV‐16/18 may be involved in the development of cervical cancer.
Illness appraisals in paediatric patients and their parents: A short scale
Authors: Vollrath Margarete , Landolt Markus A. , Ribi Karin
Published: April 2004

Seven illness appraisals (situation and resource appraisals) were examined in paediatric patients with cancer, diabetes, or accidental injuries and their parents. It was hypothesized that situation appraisals but not resource appraisals would co-vary with the diagnosis and other medical variables. It was also expected that corresponding appraisals in children and their parents would be associated. 244 newly hospitalised paediatric patients (aged 6-16 years) with cancer, diabetes or an accidental injury were interviewed regarding illness appraisals. Corresponding parent illness appraisals were assessed by means of a questionnaire. Situation appraisals co-varied with medical diagnosis and other medical variables in both patients and their parents. There were also associations between corresponding parents’ appraisals and paediatric patients’ appraisals. Findings encourage measurement of distinct categories of illness appraisals.
Die Anfänge der Diagnostica
Authors: Brickenkamp Rolf
Published: April 2004

Zusammenfassung. Die Ursprünge und ersten Jahre der Diagnostica werden aus der Perspektive des damaligen Redaktionsassistenten und späteren Mitherausgebers reflektiert. Insbesondere werden die Ziele, die der Gründer dieser Zeitschrift, Kurt Wilde, mit dem Aufbau der Diagnostica verfolgte, beschrieben. Aus dem Vergleich der früheren diagnostica mit der heutigen Diagnostica werden Desiderate für ihre weitere Entwicklung abgeleitet. Dies betrifft insbesondere die Rolle der Diagnostica als Informationsorgan über psychologische Tests und Untersuchungsmethoden.
Photochemical production of odd nitrogen directly from O2, N2 principals: Atmospheric implications and related open issues
Authors: Prasad Sheo S. , Zipf Edward C.
Published: April 2004

The present study examines the effects of atmospheric production of NOX directly from the O2 and N2 principals via the reaction of O2(B3Σ) with N2 and a second process provisionally theorized as absorption of a photon with 190 ≤ λ ≤ 204 nm by O2•N2 collision complex. The NOX production from O2(B3Σ) is ∼12% of the production from the “classical” O(1D) + N2O reaction in the region of their maxima in altitude. The diurnally averaged vmr (volume mixing ratios) of both NOX and NOY are enhanced similarly by 10 to 15% at the most. The NOX/NOY ratio is therefore unaffected. The production of NOX from O2(B 3Σ) compensates for the decrease in the classical production due to the recently discovered faster quenching of O(1D) by N2. In the O2‐poor ancient atmosphere, when the solar UV in the Schumann‐Runge bands penetrated much deeper into the denser lower atmosphere, the contribution of the NOX production from O2(B3Σ) may have been more pronounced than in the O2‐rich present atmosphere. Below 22 km, NOX production from the second process far exceeds the classical production. Such a production would almost certainly lead to NOX and NOY vmr exceeding their observed values and would call for an extensive rethinking of the atmospheric NOX budget. Because these implications of the two new NOX sources are quite serious, attention has been drawn to many, equally serious, open issues at the levels of both laboratory experiments and basic quantal processes that require further studies.
Ionospheric effects upon a satellite navigation system at Mars
Authors: Mendillo Michael , Pi Xiaoqing , Smith Steven , Martinis Carlos , Wilson Jody , Hinson David
Published: April 2004

Trans‐ionospheric radio propagation effects resulting in ranging errors are examined for a potential orbital network of communications and navigational satellites at Mars. Using recent results from the radio science experiment on board the Mars Global Surveyor (MGS) spacecraft and a photochemical model of Mars' ionosphere, we study the total electron content (TEC) at Mars to investigate how its latitude, local time, and solar cycle patterns would contribute to errors in positioning on the planet. In addition, we examine the relationship between TEC and peak density (Nmax) and find that their ratio, called the equivalent slab thickness, shows that integral preserving distortions of the Ne(h) profile can be rather substantial, implying that neutral atmosphere dynamics can have strong effects upon Mars' photochemical ionosphere. We use MGS observations to validate modeling results and determine the extreme cases for TEC at Mars (i.e., when the planet is at perihelion during solar maximum years and at aphelion during solar minimum years). If a proposed Mars Communication and Navigation (MC&N) System used UHF/L‐band (1–2 GHz) transmission frequencies similar to those used for the terrestrial Global Positioning System (GPS) satellites, upper limits to the magnitude and variability of the martian ionosphere (TEC < ∼few × 1016 el m−2, with σ ∼ 10%) would not be of concern unless extremely precise positional information were required (<1 m). The impact of the ionosphere would be greater along slanted ray paths, and especially if lower frequency UHF beacon frequencies (e.g., 400 MHz) were selected for use. Indeed, such effects could be used as a diagnostic for the global structure of Mars' ionosphere, much in the same way as GPS measurements are used in terrestrial ionospheric physics.
PLEIADES: A picosecond Compton scattering x-ray source for advanced backlighting and time-resolved material studies
Authors: Gibson David J. , Anderson Scott G. , Barty Christopher P. J. , Betts Shawn M. , Booth Rex , Brown Winthrop J. , Crane John K. , Cross Robert R. , Fittinghoff David N. , Hartemann Fred V. , Kuba Jaroslav , Le Sage Gregory P. , Slaughter Dennis R. , Tremaine Aaron M. , Wootton Alan J. , Hartouni Edward P. , Springer Paul T. , Rosenzweig James B.
Published: April 2004

The PLEIADES (Picosecond Laser-Electron Inter-Action for the Dynamical Evaluation of Structures) facility has produced first light at 70 keV. This milestone offers a new opportunity to develop laser-driven, compact, tunable x-ray sources for critical applications such as diagnostics for the National Ignition Facility and time-resolved material studies. The electron beam was focused to 50 μm rms, at 57 MeV, with 260 pC of charge, a relative energy spread of 0.2%, and a normalized emittance of 5 mm mrad horizontally and 13 mm mrad vertically. The scattered 820 nm laser pulse had an energy of 180 mJ and a duration of 54 fs. Initial x rays were captured with a cooled charge-coupled device using a cesium iodide scintillator; the peak photon energy was approximately 78 keV, with a total x-ray flux of 1.3×106 photons/shot, and the observed angular distribution found to agree very well with three-dimensional codes. Simple K-edge radiography of a tantalum foil showed good agreement with the theoretical divergence-angle dependence of the x-ray energy. Optimization of the x-ray dose is currently under way, with the goal of reaching 108 photons/shot and a peak brightness approaching 1020 photons/mm2/mrad2/s/0.1% bandwidth.
Extended x-ray absorption fine structure measurements of laser shocks in Ti and V and phase transformation in Ti
Authors: Yaakobi B. , Meyerhofer D. D. , Boehly T. R. , Rehr J. J. , Remington B. A. , Allen P. G. , Pollaine S. M. , Albers R. C.
Published: April 2004

A laser-source-based extended x-ray absorption fine structure (EXAFS) measurement has been used to study the properties of laser-shocked metals on a nanosecond time scale. The ability of measuring shock-induced temperatures of the order of 0.1 eV is essentially unique to EXAFS. EXAFS measurement of vanadium shocked to ∼0.5 Mbar with a 3 ns laser pulse yields a compression and temperature in good agreement with hydrodynamic simulations and with shock-speed measurements. In laser-shocked titanium at the same pressure, the EXAFS modulation damping is much higher than warranted by the increase in temperature. This is explained by the α-Ti to ω-Ti phase transformation known to occur around ∼0.1 Mbar in the longer (μs) shocks obtained in gas-gun experiments. In the ω-Ti phase, the disparate neighbor distances cause a beating of the modulation frequencies and thus an increased damping. These results demonstrate that EXAFS measurements can be used for the study of nanosecond-scale shocks and phase transformation in metals.
Fast ion absorption of the high harmonic fast wave in the National Spherical Torus Experiment
Authors: Rosenberg A. L. , Menard J. E. , Wilson J. R. , Medley S. S. , Andre R. , Phillips C. K. , Darrow D. S. , LeBlanc B. P. , Redi M. H. , Fisch N. J. , Team NSTX , Harvey R. W. , Mau T. K. , Jaeger E. F. , Ryan P. M. , Swain D. W. , Sabbagh S. A. , Egedal J.
Published: April 2004

Ion absorption of the high harmonic fast wave in a spherical torus [Y.-K. M. Peng et al., Nucl. Fusion 26, 769 (1986)] is of critical importance to assessing the viability of the wave as a means of heating and driving current. Analysis of recent National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] shots has revealed that under some conditions when neutral beam and rf power are injected into the plasma simultaneously, a fast ion population with energy above the beam injection energy is sustained by the wave. In agreement with modeling, these experiments find the rf-induced fast ion tail strength and neutron rate at lower B-fields to be less enhanced, likely due to a larger β profile, which promotes greater off-axis absorption where the fast ion population is small. Ion loss codes find the increased loss fraction with decreased B insufficient to account for the changes in tail strength, providing further evidence that this is a rf interaction effect. Though greater ion absorption is predicted with lower k∥, surprisingly little variation in the tail was observed, along with a neutron rate enhancement with higher k∥. Data from the neutral particle analyzer, neutron detectors, x-ray crystal spectrometer, and Thomson scattering are presented, along with results from the TRANSP [R. J. Hawryluk, Physics of Plasmas Close to Thermonuclear Conditions 1, 19 (1981); J. P. H. E. Ongena et al., Fusion Technol. 33, 181 (1998)] transport analysis code, ray-tracing codes HPRT [J. Menard et al., Phys. Plasmas 6, 2002 (1999)], and CURRAY [T. K. Mau et al., RF Power in Plasmas: 13th Topical Conference (1999), p. 148], full-wave code AORSA [E. F. Jaeger et al., RF Power in Plasmas: 14th Topical Conference, 2001, p. 369], quasilinear code CQL3D [R. W. Harvey et al., in Proceedings of the IAEA TCM on Advances in Simulation and Modeling of Thermonuclear Plasmas, 1992], and ion loss codes EIGOL [D. S. Darrow et al., in Proceedings of the 6th IAEA TCM on Energetic Particles in Magnetic Confinement Systems, 2000, p. 109] and CONBEAM [J. Egedal et al., Phys. Plasmas 10, 2372 (2003)].
Investigation of ion cyclotron range of frequencies mode conversion at the ion–ion hybrid layer in Alcator C-Mod
Authors: Lin Y. , Wukitch S. , Bonoli P. , Nelson-Melby E. , Porkolab M. , Wright J. C. , Basse N. , Hubbard A. E. , Irby J. , Lin L. , Marmar E. S. , Mazurenko A. , Mossessian D. , Parisot A. , Rice J. , Wolfe S. , Phillips C. K. , Schilling G. , Wilson J. R. , Phillips P. , Lynn A.
Published: April 2004

Mode conversion (MC) of long wavelength fast electromagnetic magnetosonic waves (fast wave, or FW) into shorter wavelength electrostatic (ion-Bernstein, or IBW) or slow electromagnetic (ion cyclotron, or ICW) waves is of great interest in laboratory, magnetic fusion and space physics experiments. Such processes are particularly important in multi-ion species plasmas. In this paper we report recent results from high power ion cyclotron range of frequencies (ICRF) heating experiments in the Alcator C-Mod tokamak. Mode converted waves near the He–H3 hybrid layer have been detected by means of phase contrast imaging in H(3He,D) plasmas [E. Nelson-Melby et al., Phys. Rev. Lett. 90, 155004 (2003)]. The measured wave k spectrum and spatial location are in agreement with theoretical predictions [F. W. Perkins, Nucl. Fusion 17, 1197 (1977)], which showed that in a sheared magnetic field, mode-conversion of FW into ICW may dominate over IBW for appropriate ion species (i.e., D–T, or equivalently, H–3He). Recent modeling with full wave codes, as well as solving the hot plasma dispersion equation in the presence of sheared magnetic fields, verifies the interpretation of such a mode conversion process. Thus, the geometry of the magnetic field, as well as the particular ion species mix, influences the physics of ICRF mode conversion. In this paper, we also report recent results on the study of mode conversion electron heating (MCEH) in D(H) plasmas [Y. Lin et al., Plasmas Phys. Controlled Fusion 45, 1013 (2003)]. By comparing the experimentally measured MCEH profile with modeling, the study shows that the MC ICW may make a significant contribution to the direct electron heating when the D–H hybrid layer is off axis on the high field side. Preliminary results of mode conversion poloidal plasma flow drive experiments in D(3He) are also reported.
Results on intense beam focusing and neutralization from the neutralized beam experiment
Authors: Roy P. K. , Yu S. S. , Eylon S. , Henestroza E. , Anders A. , Bieniosek F. M. , Greenway W. G. , Logan B. G. , Waldron W. L. , Vanecek D. L. , Welch D. R. , Rose D. V. , Davidson R. C. , Efthimion P. C. , Gilson E. P. , Sefkow A. B. , Sharp W. M.
Published: April 2004

Experimental techniques to provide active neutralization for space-charge-dominated beams as well as to prevent uncontrolled ion beam neutralization by stray electrons have been demonstrated. Neutralization is provided by a localized plasma injected from a cathode arc source. Unwanted secondary electrons produced at the wall by halo particle impact are suppressed using a radial mesh liner that is positively biased inside a beam drift tube. Measurements of current transmission, beam spot size as a function of axial position, beam energy, and plasma source conditions are presented along with detailed comparisons with theory.
X-ray diffraction study and Monte Carlo simulation of the relaxation behavior of epitaxially grown wire structures
Authors: Schumacher C. , Bader A. S. , Schallenberg T. , Schwarz N. , Faschinger W. , Molenkamp L. W. , Neder R. B.
Published: April 2004

In this contribution a model for the elastic relaxation of Al0.5Ga0.5As and ZnSe wire structures, respectively, is presented. The wire structures extend along [11̄0] and were characterized by high resolution x-ray diffraction experiments. Based on Monte Carlo simulations, the wire structures, which have been simulated at atomic resolution, were relaxed to reduce the strain caused by the lattice misfit. The x-ray diffraction patterns calculated for the final structures reproduce the observed data. The structures display a two dimensional strain gradient and curved lattice planes. Hence the introduced modeling is a powerful method in particular to resolve the atomic structure of a wet chemically etched or molecular beam epitaxial grown wire by giving a microscopic picture on an atomic scale.
Kinetic effects on the stability properties of field-reversed configurations. II. Nonlinear evolution
Authors: Belova Elena V. , Davidson Ronald C. , Ji Hantao , Yamada Masaaki
Published: April 2004

Results of three-dimensional hybrid simulations of the field-reversed configuration (FRC) are presented. Emphasis of this work is on the nonlinear evolution of magnetohydrodynamic (MHD) instabilities in kinetic FRCs. A wide range of s̄ values is considered, where the s̄ is the FRC kinetic parameter, which measures the number of ion gyroradii in the configuration. The linear and nonlinear stability of MHD modes with toroidal mode numbers n⩾1 is investigated, including the effects of ion rotation, finite electron pressure, and weak toroidal field. Low-s̄ simulations show nonlinear saturation of the n=1 tilt mode. The n⩾2 rotational modes are observed to grow during the nonlinear phase of the tilt instability due to ion spin-up in the toroidal direction. Large-s̄ simulations show no saturation of the tilt mode, and there is a slow nonlinear evolution of the instability after the initial fast linear growth. Overall, the hybrid simulations demonstrate the importance of nonlinear effects, which are responsible for the saturation of instabilities in low-s̄ configurations, and also for the increase in FRC lifetime compared to MHD models in high-s̄ configurations.
Effect of secondary electron emission on the propagation of dust acoustic waves in a dusty plasma
Authors: Gupta M. R. , Sarkar Susmita , Roy Banamali , Karmakar Anupam , Khan Manoranjan
Published: April 2004

The effect of secondary electron emission on dust acoustic wave (DA) propagation has been investigated based on orbit motion limited theory of dust grain charging. The emitted secondaries are assumed to have the same temperature as that of the ambient plasma electrons so that the plasma effectively consists of three components: the ions, electrons, and the variable charge dusts. Together with the effect of secondary emission, the effect of ion and electron capture and ionization of neutral atoms and recombination have been included in the ion and electron fluid equations. Small amplitude perturbation is considered about a charge neutral steady state. It is seen that if the dust charge is positive there may occur under certain conditions zero frequency exponentially growing perturbation about the equilibrium. The possibility of the occurrence of such purely growing mode in a dusty plasma was not noted earlier. The frequency and damping decrement of DA waves in dusty plasmas with negatively charged dust and also of DA waves with positively charged dust, when they exist, are determined. Comparisons with corresponding results of DA waves in the absence of secondary emission are exhibited graphically.
Simple analysis of the nonlinear saturation of the tearing mode
Authors: Militello F. , Porcelli F.
Published: April 2004

A simple nonlinear treatment of the reduced magnetohydrodynamics equations, that describes the saturation of small width magnetic island, is presented. This procedure is an extension of Rutherford’s theory. It is found that the tearing mode saturates at a finite amplitude, ws, which is proportional to the linear stability parameter, Δ′. The correct value of the proportionality coefficient between ws and Δ′ is obtained in this paper, in agreement with numerical simulations.
Prospects for high-gain, high yield National Ignition Facility targets driven by 2ω (green) light
Authors: Suter L. J. , Glenzer S. , Haan S. , Hammel B. , Manes K. , Meezan N. , Moody J. , Spaeth M. , Divol L. , Oades K. , Stevenson M.
Published: April 2004

The National Ignition Facility (NIF) [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, 755 (1994)], operating at green (2ω) light, has the potential to drive ignition targets with significantly more energy than the 1.8 MJ it will produce with its baseline, blue (3ω) operations. This results in a greatly increased “target design space,” providing a number of exciting opportunities for fusion research. These include the prospect of ignition experiments with capsules absorbing energies in the vicinity of 1 MJ. This significant increase in capsule absorbed energy over the original designs at ∼150 kJ could allow high-gain, high yield experiments on NIF. This paper reports the progress made exploring 2ω for NIF ignition, including potential 2ω laser performance, 2ω ignition target designs, and 2ω laser plasma interaction studies.
Compressive and rarefactive ion-acoustic solitons in bi-ion plasmas
Authors: McKenzie J. F. , Verheest F. , Doyle T. B. , Hellberg M. A.
Published: April 2004

Nonlinear propagation of ion-acoustic solitary structures in plasmas with an admixture of heavy ions is studied in the wave frame, where they are stationary, using a recently developed gas-dynamic approach, as an alternative to the conventional Sagdeev pseudopotential method. This viewpoint brings out the gas-dynamic aspects, which then allow a characterization of the solitary wave structures in terms of the species’ sonic points, the global charge neutral points, and critical collective Mach numbers. It is shown that the concepts of a critical density in the Korteweg–de Vries (KdV) treatment, and of a changeover from compressive to rarefactive soliton character, correspond to the formation of a second charge neutral point (outside equilibrium) in the rarefactive regime, at which the electric stresses maximize. It is possible therefore that in certain regions of parameter space compressive and rarefactive solitons can co-exist. The compressive solitons are not predicted by a weakly nonlinear KdV treatment, except very close to the changeover region at sufficiently small enough amplitudes, as typified by the “modified” KdV (mKdV) equation. Their prediction requires a fully nonlinear treatment. Existence criteria are deduced and evaluated numerically in the parameter space of soliton Mach number and normalized density of the heavy species for compressive and rarefactive ion-acoustic solitons in a plasma with negative ion admixture.
Characteristics of transport in electron internal transport barriers and in the vicinity of rational surfaces in the Large Helical Device
Authors: Ida K. , Inagaki S. , Shimozuma T. , Tamura N. , Funaba H. , Narihara K. , Kubo S. , Murakami S. , Wakasa A. , Yokoyama M. , Takeiri Y. , Watanabe K. Y. , Tanaka K. , Yoshinuma M. , Liang Y. , Ohyabu N. , Akiyama T. , Ashikawa N. , Emoto M. , Fujita T. , Fukuda T. , Goncharov P. , Goto M. , Idei H. , Ikeda K. , Isayama A. , Isobe M. , Kaneko O. , Kawahata K. , Kawazome H. , Kobuchi T. , Komori A. , Kumazawa R. , Masuzaki S. , Minami T. , Miyazawa J. , Morisaki T. , Morita S. , Muto S. , Mutoh T. , Nagayama Y. , Nakamura Y. , Nakanishi H. , Narushima Y. , Nishimura K. , Noda N. , Notake T. , Nozato H. , Ohdachi S. , Oka Y. , Okajima S. , Osakabe M. , Ozaki T. , Peterson B. J. , Sagara A. , Saida T. , Saito K. , Sakakibara S. , Sakamoto R. , Sakamoto Y. , Sasao M. , Sato K. , Sato M. , Seki T. , Shoji M. , Suzuki H. , Takeuchi N. , Toi K. , Tokuzawa T. , Torii Y. , Tsumori K. , Watari T. , Yamada H. , Yamada I. , Yamamoto S. , Yamamoto T. , Yoshimura Y. , Itoh K. , Matsuoka K. , Ohkubo K. , Sudo S. , Uda T. , Yamazaki K. , Motojima O.
Published: April 2004

Characteristics of transport in electron internal transport barriers (ITB) and in the vicinity of a rational surface with a magnetic island are studied with transient transport analysis as well as with steady state transport analysis. Associated with the transition of the radial electric field from a small negative value (ion-root) to a large positive value (electron-root), an electron ITB appears in the Large Helical Device [M. Fujiwara et al., Nucl. Fusion 41, 1355 (2001)], when the heating power of the electron cyclotron heating exceeds a power threshold. Transport analysis shows that both the standard electron thermal diffusivity, χe, and the incremental electron thermal diffusivity, χeinc (the derivative of normalized heat flux to temperature gradient, equivalent to heat pulse χe), are reduced significantly (a factor 5–10) in the ITB. The χeinc is much lower than the χe by a factor of 3 just after the transition, while χeinc is comparable to or even higher than χe before the transition, which results in the improvement of electron transport with increasing power in the ITB, in contrast to its degradation outside the ITB. In other experiments without an ITB, a significant reduction (by one order of magnitude) of χeinc is observed at the O-point of the magnetic island produced near the plasma edge using error field coils. This observation gives significant insight into the mechanism of transport improvement near the rational surface and implies that the magnetic island serves as a poloidally asymmetric transport barrier. Therefore the radial heat flux near the rational surface is focused at the X-point region, and that may be the mechanism to induce an ITB near a rational surface.
Evolution of nonlocal ideal helical perturbations in cylindrical plasma
Authors: Zhang Wenlu , Li Ding
Published: April 2004

The evolution and the stability property of a helical perturbation for arbitrary magnetic shear configurations are investigated. An analytic stability criterion has been obtained and predicts that nonlocal perturbations exhibit stronger instabilities than local perturbations. A weak positive magnetic shear is favorable to the stability, while a strong negative magnetic shear contributes little to the instability for reversed magnetic shear configurations, which do not show better stabilities than positive shear configurations. Instability is stronger in the decreasing region of the r-direction perturbation amplitude than in the increasing region and perturbations with a steep negative slope produces strong localized instabilities. A larger poloidal or toroidal mode number of the perturbations relates to a stronger instability. Instability is weaker in the core than in other regions.
Nonlinear model for magnetosonic shocklets in plasmas
Authors: Shukla P. K. , Eliasson B. , Marklund M. , Bingham R.
Published: April 2004

Exact nonlinear equations for magnetosonic shocklets in a uniform hot magnetoplasma are derived by using the nonlinear magnetohydrodynamic equations. Analytic, as well as numerical, solutions of the nonlinear equations are presented. Shocklike structures of the ion fluid velocity and magnetic field (or the plasma density) perturbations are obtained. The results may have relevance to the understanding of fast magnetosonic shocklets that have been recently observed by onboard instruments of the Cluster spacecraft at the Earth’s bow shock.
Local shear damping of ion and electron temperature gradient modes
Authors: Kendl Alexander
Published: April 2004

The influence of local magnetic field line shear on linear toroidal ion and electron temperature gradient drift modes is studied within a local gyrokinetic model. Elementary representations of local shear functions are constructed to resemble generic geometric aspects of low-shear stellarators and divertor tokamaks. Modes are damped for all these local shear structures although the amount of reduction of growth rates depends strongly on the form and magnitude of the structure.
An investigation into the cap deformation of carbon nanotube tips using tight-binding molecular dynamics simulation
Authors: Ju Shin-Pon , Weng Cheng-I , Lin Chia-Hua
Published: April 2004

This article employs a tight-binding molecular dynamics simulation approach to investigate the cap deformation of a carbon nanotube tip when used as a probe in a tapping mode measurement process. The simulation results indicate that the deformation behavior of the cap during its interaction with a rigid graphite surface obeys Hooke’s law until a critical repulsive force is attained. At this point, a radial deformation of the cap occurs as the bond orientations and lengths change. This deformation causes a reduction in the magnitude of the repulsive force, and is accompanied by an increase in the axial compression. Consequently, the cap deformation no longer conforms to Hooke’s law. It is observed that when the capped carbon nanotube is withdrawn from the graphite surface, the cap recovers its original shape. By considering the deformation within the Hookean region, this study derives the spring constants of caps of different radii. It is shown that the spring constant decreases as the radius of the carbon nanotube increases toward that of an (8,8) carbon nanotube. Thereafter, there is no significant change in the spring constant as the radius of the nanotube continues to increase. Specifically, the results indicate that the spring constant of a (4,4) armchair carbon nanotube is approximately 1.4 nN/Å, and that this value reduces to 0.4 nN/Å for carbon nanotubes of radii greater than that of an (8,8) carbon nanotube.
Dielectric property-microstructure relationship for nanoporous silica based thin films
Authors: Fisher I. , Kaplan W. D. , Eizenberg M.
Published: April 2004

Low dielectric constant silica based films which incorporate a large amount of nanometer sized pores are attractive candidates as interlayer dielectrics in future gigascale integrated circuits chip technology. Nanoporous silica based films were deposited by surfactant templated self-assembly spin-on deposition (SOD). Other low-k materials with relatively low density silica based films were deposited by plasma enhanced chemical vapor deposition (PECVD), and some silica films were deposited by a CVD process. The SOD films have a higher porosity, compared to the PECVD/CVD films, as measured by x-ray reflectivity, Rutherford back scattering, and ellipsometry measurements. The SOD films have lower dielectric constants compared to the PECVD/CVD films, as derived from electrical (1 MHz) and optical (5×1014 Hz) measurements. The correlation between the dielectric constant and the porosity for the SOD films fits well to the lower prediction of the Lorentz–Lorenz model, and the PECVD/CVD films agree with the higher prediction of the Rayleigh model. These results suggest that the dielectric constant of the inhomogeneous two phase nanoporous silica based films deposited by SOD is significantly lowered by forming air voids, whereas the PECVD/CVD films consist of a homogeneous low density loose microstructure originating from the bonding nature alone, and therefore their dielectric constant is lowered to a smaller extent.
Luminescence of ZnSe nanowires grown by metalorganic vapor phase deposition under different pressures
Authors: Zhang X. T. , Liu Z. , Ip K. M. , Leung Y. P. , Li Quan , Hark S. K.
Published: April 2004

Quasi-one-dimensional ZnSe nanowires have been synthesized by metalorganic chemical vapor deposition on Si (001) substrates, sputter coated with gold catalyst, at various pressures using diethylzinc and diisopropylselendie. The nanowires appear to be randomly oriented on the substrate and some are slightly bent along their length. X-ray diffraction and scanning electron microscopy studies show that the nanowires are zincblende in structure and have a uniform cross section along its length, and an average diameter about 30 nm, regardless of growth pressure. Individual strands of the nanowires were examined by high-resolution transmission electron microscopy and were found to be single crystals elongated along the 〈112〉 crystallographic direction. Gold particles at the tips of the nanowires identified by transmission electron microscopy and atomic force microscopy indicate that the nanowires grow via the vapor–liquid–solid process. Room-temperature photoluminescence spectra of the ZnSe nanowires grown under different pressures show variations in their optical properties, despite their similarity in morphology and crystalline structure. At the optimal pressure of growth, strong near band-edge emission and very weak deep-level emissions are observed, indicating the low level of nonstoichiometric defects in the resulting ZnSe nanowires.
Coupled magnetodielectric properties of laminated PbZr0.53Ti0.47O3/NiFe2O4 ceramics
Authors: Zhai Junyi , Cai Ning , Shi Zhan , Lin Yuanhua , Nan Ce-Wen
Published: April 2004

Simple multiferroic laminated ceramics of lead–zirconate–titanate PbZr0.53Ti0.47O3(PZT)/NiFe2O4 were prepared by a conventional ceramic processing. The measured magnetodielectric properties demonstrated strong dependence on the relative thickness of the PZT layers, magnetic bias, and angle between the bias and polarization in the laminated ceramics. Recent theoretical approaches were employed to explain these observed behaviors. The maximum magnetoelectric sensitivity (αE31) of the ceramics samples could reach up to as high as 0.21 V/A at 11.9 kA/m. In particular, at low magnetic bias, the laminated ceramics were found to have a very large magnetoelectric sensitivity linearly varying with the bias.
Investigation of polarization switching in (001)c, (110)c, and (111)c oriented Pb(Zn1/3Nb2/3)O3–4.5%PbTiO3 crystals
Authors: Jullian Christelle , Li J. F. , Viehland D.
Published: April 2004

The dynamics of polarization switching have been investigated over extremely broad time (10−8<t<102 s) and field ranges for (001)c, (110)c, and (111)c-oriented Pb(Zn1/3Nb2/3)O3–4.5%PbTiO3 crystals. The results demonstrate the presence of broad relaxation time distributions that can extend over a decade(s) in orders of magnitude in time, and which sharpen significantly with increasing field. The polarization transients have been fit to stretched exponential functions, which are typical of disordered systems.
In situ micro Raman investigation of the laser crystallization in Si thin films plasma enhanced chemical vapor deposition-grown from He-diluted SiH4
Authors: Santato Clara , Mattei Giorgio , Ruihua Wu , Mecarini Federico
Published: April 2004

A cw Ar+ laser crystallization has been performed locally (on a 2 μm sized spot), using a Raman microscope, on plasma enhanced chemical vapor deposition-grown Si films. The deposition has been carried out from differently He-diluted SiH4 so that no high temperature dehydrogenation has been required before the laser treatment. X-ray diffraction patterns and Raman spectra of the deposited films reveal their amorphous nature whereas infrared spectra would indicate a larger degree of local order in the high dilution (HD) material (SiH4/He=0.02) if compared to the low dilution (LD) one (SiH4/He≈3). Atomic force microscopy and scanning electron microscopy images show large, well defined outgrowths, few hundreds of nanometers-sized, on the surface of the HD film whereas these are few tens of nanometers-sized in the case of the LD film. The threshold laser power densities (LPDs) required to attain the crystallization of the HD and the LD materials (in the range of times of irradiation investigated) are 1.2×105 and 2.0×105 W cm−2, respectively. The relative ease to crystallize the HD material possibly originates from the fact that the heavy dilution of the reacting gas implies a lower rate of growth and so a larger degree of order. Large crystalline fractions (∼0.8) have been observed for the laser-treated HD material. Using a phenomenological model, the diameters of the nanocrystallites from the Raman shift of the crystalline peaks have been estimated. The size of the small crystals increases with the time of irradiation (up to a certain time). The smallest nanocrystals would have been fabricated irradiating the LD material at the threshold LPD for the shortest time of irradiation considered in this work. This low temperature process is of great technological interest (e.g., optoelectronics, microelectronics) because it allows the patterning down to a micrometric scale of (amorphous) a-Si:H films deposited onto glass and/or plastic substrates.