bluuebunny/crossref_metadata_2025 huggingface dataset:
A calendar conversion method for monthly mean paleoclimate model output with orbital forcing
Authors: Pollard David , Reusch David B.
Published: December 2002

A computationally cheap method is described for estimating monthly means of climatological variables on alternate calendars, given their monthly means on an original calendar. This can be used to convert archived paleoclimatic GCM monthly mean results originally saved on the modern calendar to a more appropriate equi‐angular calendar, thus avoiding spurious orbital signals when comparing monthly means for modern and past simulations. The method is tested using GCM simulations for the present and 126 ka BP. The method works well for temperature, which has relatively smooth seasonal cycles, and satisfactorily for other climatological variables in most regions except mid to high southern latitudes. It is also satisfactory for precipitation in most regions, but in the tropical ITCZ, it fails to significantly reduce the spurious calendar errors. However, this is largely due to high‐frequency natural interannual variability in the 10‐year simulations, and the errors are of the same order as the uncertainty in monthly means on a single calendar.
POAM III retrieval algorithm and error analysis
Authors: Lumpe J. D. , Bevilacqua R. M. , Hoppel K. W. , Randall C. E.
Published: December 2002

This paper describes the operational version 3 algorithms used to analyze data from the Polar Ozone and Aerosol Measurement (POAM) III instrument. We include a thorough discussion of both the forward model and retrieval algorithms, including the algorithms used to derive altitude information and normalize the measured radiances to produce atmospheric transmission profiles. The operational POAM III algorithms retrieve O3, NO2, H2O, and O2 (or total) density, as well as aerosol extinction between 353 and 1018 nm. All atmospheric species are retrieved simultaneously using the technique of optimal estimation. The conversion of transmission data to geophysical profiles is achieved via a two‐step process, beginning with a spectral inversion to partition the various gas and aerosol components of the measured slant optical depth, followed by a spatial inversion to produce altitude profiles of gas density and aerosol extinction from the path‐integrated quantities. A formal error analysis is also presented, yielding estimates of the total random error budget for the retrieved profiles. In addition to the theoretical error analysis, we present results from empirical analyses that quantify error components due to aerosol feedback in the gas retrievals, as well as sunspot artifacts that are sometimes present in the data. Finally, we present a quantitative retrieval characterization based on analysis of the full retrieval averaging kernel matrix. This matrix is used to calculate vertical resolution profiles for all retrieved species, as well as to quantify the information content of the retrievals, including the a priori weighting in the retrievals, the coupling between the various retrieval species, and the spectral resolution of the aerosol retrievals.
A hypothesis for growth of fresh atmospheric nuclei
Authors: Zhang K. Max , Wexler Anthony S.
Published: December 2002

The formation of new atmospheric particles, roughly 1–2 nm in diameter, has drawn a lot of attention recently because of (1) their possibly negative effects on human health and (2) their potential to grow into cloud condensation nuclei, thus affecting cloud formation as well as the global radiation budget. At these small sizes, the Kelvin effect prevents condensation of any compound in sufficient abundance for producing substantial growth. But heterogeneous reactions may play a critical role in helping these nm‐sized nuclei cross the huge Kelvin‐effect barrier and facilitating further condensation of organic vapors. Its implications in the marine boundary layer and engine exhausts are discussed.
Aerosol optical properties from columnar data during the second Aerosol Characterization Experiment on the south coast of Portugal
Authors: Silva Ana Maria , Bugalho Maria Lourdes , Costa Maria Joao , von Hoyningen‐Huene Wolfgang , Schmidt Torsten , Heintzenberg Jost , Henning Sylvia
Published: December 2002

Measurements of aerosol optical properties over the atmospheric column (aerosol optical thickness, spectral angular sky radiance (sky brightness), and downwelling hemispheric flux) have been used to derive climate‐relevant aerosol parameters such as the phase function, the broadband single‐scattering albedo, and the refractive index. These parameters are needed to estimate the direct short‐wave radiative forcing by aerosols and to validate aerosol models in the satellite retrieval algorithms. Values of the broadband single‐scattering albedo obtained in this study range between ω0 = 0.98 (marine aerosols) and 0.90 (continental pollution aerosols). The columnar ambient broadband refractive index is found to be m = 1.39 ± 0.044 − i (<0.003) for marine conditions and m = 1.48 ± 0.058 − i (0.01 ± 0.003) for polluted continental aerosols. Nonsphericity is shown to be important in the case of marine aerosols. Moreover, aerosol nonsphericity gives an additional contribution to the negative short‐wave radiative forcing of marine aerosols under clear‐sky conditions, which can be estimated as being 30 up to 50% of the radiative forcing estimated for spherical marine aerosols. In the case of continental polluted aerosols the optical properties can be represented by spherical particles, and no additional shape effect has to be considered. However, the aerosol absorption leads to an increase of about 40% of the radiative forcing estimated for nonabsorbing aerosol of the same size distribution.
FORTE observations of optical emissions from lightning: Optical properties and discrimination capability
Authors: Davis S. M. , Suszcynsky D. M. , Light T. E. L.
Published: December 2002

Lightning type identification of temporally coincident optical‐VHF time series event pairs collected by the Fast On‐orbit Recording of Transient Events (FORTE) satellite's photodiode detector (PDD) and VHF instrument allows for the investigation of optical properties as a function of lightning type. General trends in the peak optical irradiance and characteristic pulse widths of PDD‐VHF coincident events are studied as a function of lightning type, using previously established techniques to identify lightning type based on VHF spectogram‐power time series. While lightning type cannot be identified from optical data alone, there are several notable features in the optical record. The distribution of observed characteristic widths of PDD events has a cutoff near 200 μs, which represents a lower limit on the combination of intrinsic optical emission time and pulse broadening due to photon scattering in the intervening clouds. Events with the highest peak optical irradiances observed at FORTE are typically positive initial return strokes. Also, the median value of peak optical irradiance for cloud‐to‐ground lightning events is more than double that for in‐cloud lightning.
Stratigraphic sequence and ages of volcanic units in the Gruithuisen region of the Moon
Authors: Wagner R. , Head J. W. , Wolf U. , Neukum G.
Published: December 2002

Several domes indicative of non‐mare volcanism, morphologically as well as spectrally distinct from surrounding mare and highland units, are located in the Gruithuisen region in northern Oceanus Procellarum. The determination of the nature and age of non‐mare volcanism helps to put constraints on lunar crustal evolution. The ages of the domes were previously thought to be mid‐Imbrian or possibly even Eratosthenian. In order to assess more closely the stratigraphic relationships in this region, we carried out geologic mapping and crater size‐frequency measurements (1) on the Gruithuisen volcanic domes, (2) on the adjacent mare units, and (3) in the highland areas. (4) The nearby Iridum impact event was also dated by means of crater counts. A recently updated and improved version of the lunar production function polynomial was used to fit measured crater size‐frequency distributions of geologic units, and a cratering chronology model was applied in order to assign these units to the periods and epochs of the lunar chronology system. Oceanus Procellarum mare materials in the study area were found to range in age from Late Imbrian to Eratosthenian and show peak cratering model ages at 3.55 Gyr (1 Gyr = 1 billion years), 3.2–3.3 Gyr, and about 2.4 Gyr. Some mare units show evidence for at least two events in their crater size‐frequency distributions; these are most likely due to the superposition of later thin lava flows. Mare volcanism, hence, has lasted over a period of several hundred million years in the Gruithuisen region. The Gruithuisen domes show a much more restricted age range; they were found to range in age from 3.85 to 3.72 Gyr and thus were formed in the early part of the Late Imbrian, an older age than previously thought. Iridum crater, stratigraphically older than the Gruithuisen domes, was formed about 3.7–3.8 Gyr ago. The Iridum impact event and the formation of the two Gruithuisen domes cannot be well separated by means of crater counts. A few stratigraphically older highland units and some mare areas show ages of less than 2.0 Gyr, but these are less reliable due to (1) the crater distributions being close to saturation, (2) less effective crater retention on slopes, and (3) erosional removal of craters.
Saturn's inner satellites: Ice chemistry and magnetosphere effects
Authors: Delitsky Mona L. , Lane Arthur L.
Published: December 2002

The magnetosphere of Saturn contains plasma ions that corotate with the magnetic field of the planet and impact the satellites, changing the chemical nature of their surfaces. The Voyager spacecraft observed ionic species such as O+, H2O+, N+, N2+, H+, and others, as well as electrons. If N+ and N2+ ions from Titan reach the inner satellites Rhea, Dione, Tethys, Enceladus, and Mimas, implanting of these ions into their water‐ice surfaces should induce a complex nitrogen oxides chemistry. Species observed in laboratory experiments of N+ impact into water ice include NO, N2O, NO2, NO3, HNO2, HNO3, NH2OH, HNO, NH, and NH2. Impact of N2+ may yield N2O, HNNO, and N2. If the surfaces also contain CO2, then other species produced as a result of N+ impact into H2O/CO2 ice may be HNCO, NCO, and R‐OCN. Once HNCO (with its C—N bond) is formed, then production of amino acids may occur. Chemical schemes show that successive reaction of HNCO with H and CO could lead to the smallest amino acid, glycine, in only five steps. Energy fluxes for ions, electrons, and photons are summed for each satellite. Column densities of the nitrogen‐containing species are calculated. The simplest molecule, NO, should have an appreciable vapor pressure at Saturnian satellite temperatures. At 90 K, the vapor pressure of NO is ∼4 mbar. At 105 K, its vapor pressure is 98 mbar. These gases may form transient atmospheres on the satellites. This should be observable with high‐resolution instruments.
Stratigraphic profiling with ground‐penetrating radar in permafrost: A review of possible analogs for Mars
Authors: Arcone Steven A. , Prentice Michael L. , Delaney Allan J.
Published: December 2002

We review our past and ongoing use of ground‐penetrating radar to investigate permafrost in Alaska and in the Dry Valleys of Antarctica. The results may be relevant to radar efforts on Mars because of arid conditions and the presence of ice. The pulses were centered at 50, 100, and 400 MHz. We interpret profiles from two sites in the eastern Taylor Valley to show glaciolacustrine and glaciofluvial stratigraphy. The maximum depth of stratigraphy profiled there was about 33 m. Near Fairbanks, Alaska, the depth of penetration at 50 MHz was near 80 m in marginally frozen and stratified alluvial sands. At the Fairbanks sites, supplementary drilling was required to differentiate between reflections from conductive bedrock, a graphitic schist, and those from the water table at depths of 20–25 m. At a site on the North Slope of Alaska, we profiled present and remnant freezing fronts in an alluvial floodplain. The relative permittivity at most sites ranged between about 4 and 5.5, which is consistent with dry conditions, the mineralogy, and low ice content. Weak interface reflectivity or the lack of further interfaces may have limited the interpretation of maximum penetration where no water table was present because signal absorption should have been low and scarce diffractions imply that scattering was weak. The interface reflectivities beneath Taylor Valley may be a function of only density contrasts, since free water, and possibly ice, is absent.
An ionospheric obliquity process responsive to line‐of‐sight azimuth and elevation
Authors: Conker Robert S. , El‐Arini M. Bakry
Published: December 2002

This paper describes a one‐directional iterative technique which converts from slant Total Electron Content (TEC) to vertical TEC using information describing the current state of the ionosphere. The method combines the well‐known Chapman function of electron density with a spherical harmonics representation of the peak density over a spherical surface. Several parameters either have restricted movement or are kept constant in order for the problem to remain manageable. This technique is compared to the standard thin shell model obliquity factor in order to assess the degree of improvement in accuracy and the conditions under which this occurs. The Parameterized Ionospheric Model (PIM) is used as a truth model.
Data set generation and inversion simulation of radio waves propagating through a two‐dimensional comet nucleus (CONSERT experiment)
Authors: Benna M. , Piot A. , Barriot J.‐P. , Kofman W.
Published: December 2002

To prepare the Comet Nucleus Sounding Experiment using Radio wave Transmission during the Rosetta mission, we study the electromagnetic wave propagation through a comet nucleus model and tomographic inversion in a two‐dimensional setting. For the propagation, the Ray Tracing Method (RTM) is validated with respect to the Pseudo‐Spectral Time Domain (PSTD) method. For the inverse problem, a Tikhonov‐like inverse RTM method based on weak permittivity assumptions is used, with synthetic data derived from the PSTD algorithm. Reconstruction results show that the Consert data will permit a reliable tomography of the comet nucleus. Surface data will enhance the quality of the imaging.
Improvement of rat liver graft function after storage in University of Wisconsin solution containing testicular hyaluronidase
Authors: Papanikolaou Vassilios , Vrochides Dionisios , Gakis Dimitrios , Patsiaoura Kalliopi , Margari Paraskevi , Dogramatzi Fani , Antoniades Antonios , Heldin Paraskevi
Published: December 2002

Hyaluronan accumulates at sites of inflammation, which affects the organization of matrix and thereby the proliferation, migration, and adherence of cells. In this study we investigated possible beneficial effects of the hyaluronan-degrading enzyme hyaluronidase on rat liver graft viability. Orthotopic rat liver transplantation was performed using a cuff technique in Wistar AL Bacharach Glaxo (WAG) rats grafted with WAG livers, which had been stored in the University of Wisconsin (UW) solution or in UW solution enriched with testicular hyaluronidase. Liver tissue architecture, as well as tissue and serum hyaluronan levels, were determined using immunohistochemistry and biochemical assays. Addition of testicular hyaluronidase (0.4 mg/mL) to livers preserved for 24 hours in cold UW solution followed by brief exposure to Ringer’s lactate both prolonged the function of the grafted livers and improved their viability (4 of 10 grafts survived, compared with 0 of 10 in the control group). Hyaluronidase treatment did not damage the liver tissue architecture, and a reduced edema was observed in the survivors. Furthermore, 10 minutes after restoration of circulation, higher serum hyaluronan levels were observed in nonsuccessful compared with successful transplantations, whereas no differences in the levels of other serum viability markers were detected. We conclude that addition of testicular hyaluronidase to storage UW solution limits liver cell damage and considerably improves graft function. Furthermore, our data suggest that serum hyaluronan level is a better marker than other serum markers for early evaluation of postoperative graft function.
Detection of hepatitis C virus sequences in brain tissue obtained in recurrent hepatitis C after liver transplantation
Authors: Vargas Hugo E. , Laskus Tomasz , Radkowski Marek , Wilkinson Jeff , Balan Vijay , Douglas David D. , Harrison Edwyn M. , Mulligan David C. , Olden Kevin , Adair Debra , Rakela Jorge
Published: December 2002

Patients with chronic hepatitis C frequently report tiredness, easy fatigability, and depression. The aim of this study is to determine whether hepatitis C virus (HCV) replication could be found in brain tissue in patients with hepatitis C and depression. We report two patients with recurrent hepatitis C after liver transplantation who also developed severe depression. One patient died of multiorgan failure and the other, septicemia caused by Staphylococcus aureussis. Both patients had evidence of severe hepatitis C recurrence with features of cholestatic fibrosing hepatitis. We were able to study samples of their central nervous system obtained at autopsy for evidence of HCV replication. The presence of HCV RNA-negative strand, which is the viral replicative form, was determined by strand-specific Tth-based reverse-transcriptase polymerase chain reaction. Viral sequences were compared by means of single-strand conformation polymorphism and direct sequencing. HCV RNA-negative strands were found in subcortical white matter from one patient and cerebral cortex from the other patient. HCV RNA-negative strands amplified from brain tissue differed by several nucleotide substitutions from serum consensus sequences in the 5′ untranslated region. These findings support the concept of HCV neuroinvasion, and we speculate that it may provide a biological substrate to neuropsychiatric disorders observed in patients with chronic hepatitis C. The exact lineage of cells permissive for HCV replication and the possible interaction between viral replication and cerebral function that may lead to depression remain to be elucidated.
Critical points and transitions in an electric power transmission model for cascading failure blackouts
Authors: Carreras B. A. , Lynch V. E. , Dobson I. , Newman D. E.
Published: December 2002

Cascading failures in large-scale electric power transmission systems are an important cause of blackouts. Analysis of North American blackout data has revealed power law (algebraic) tails in the blackout size probability distribution which suggests a dynamical origin. With this observation as motivation, we examine cascading failure in a simplified transmission system model as load power demand is increased. The model represents generators, loads, the transmission line network, and the operating limits on these components. Two types of critical points are identified and are characterized by transmission line flow limits and generator capability limits, respectively. Results are obtained for tree networks of a regular form and a more realistic 118-node network. It is found that operation near critical points can produce power law tails in the blackout size probability distribution similar to those observed. The complex nature of the solution space due to the interaction of the two critical points is examined.
Generation of undular bores in the shelves of slowly-varying solitary waves
Authors: El G. A. , Grimshaw R. H. J.
Published: December 2002

We study the long-time evolution of the trailing shelves that form behind solitary waves moving through an inhomogeneous medium, within the framework of the variable-coefficient Korteweg–de Vries equation. We show that the nonlinear evolution of the shelf leads typically to the generation of an undular bore and an expansion fan, which form apart but start to overlap and nonlinearly interact after a certain time interval. The interaction zone expands with time and asymptotically as time goes to infinity occupies the whole perturbed region. Its oscillatory structure strongly depends on the sign of the inhomogeneity gradient of the variable background medium. We describe the nonlinear evolution of the shelves in terms of exact solutions to the KdV–Whitham equations with natural boundary conditions for the Riemann invariants. These analytic solutions, in particular, describe the generation of small “secondary” solitary waves in the trailing shelves, a process observed earlier in various numerical simulations.
The eight fine gradings of sl(4, C) and o(6, C)
Authors: Patera Jiřı́ , Pelantová Edita , Svobodová Milena
Published: December 2002

A grading of a Lie algebra is called fine if it cannot be further refined. Fine gradings provide basic information about the structure of the algebra. There are eight fine gradings of the simple Lie algebra of type A3 over the complex number field. One of them (root decomposition) is the main tool of the theory and applications in working with A3 and with its representations; one other has also been used in the literature, and the rest have apparently not been recognized so far. An explicit description of all the fine gradings of A3 is given in terms of the four-dimensional [sl(4, ℂ)] and six-dimensional orthogonal [o(6, ℂ)] representations of the algebra. These results should be useful generally for choosing bases which reflect structural properties of the Lie algebra, for defining various sets of additive quantum numbers for systems with such symmetries, and for systematic study of grading preserving contractions of this Lie algebra.
An extension to chaos control via Lie derivatives: Fully linearizable systems
Authors: Femat Ricardo
Published: December 2002

The technique of using Lie derivatives to control chaos introduced by Kocarev et al. [Chaos, Solitons Fractals 9, 1359–1366 (1998)] is extended in this contribution. Here, by using Lie derivatives in an extended space state, it is proved that chaos can be practically suppressed via feedback in spite of the Lie derivative being ill-posed at the reference. The main idea is to construct a dynamically equivalent system. In this way, the chaotic system can be practically stabilized around any point of singularity x0. The Lorenz equation is used as an illustrative example to show the application in the chaos control context.
Uniqueness in MHD in divergence form: Right nullvectors and well-posedness
Authors: van Putten Maurice H. P. M.
Published: December 2002

Magnetohydrodynamics in divergence form describes a hyperbolic system of covariant and constraint-free equations. It comprises a linear combination of an algebraic constraint and Faraday’s equations. Here, we study the problem of well-posedness, and identify a preferred linear combination in this divergence formulation. The limit of weak magnetic fields shows the slow magnetosonic and Alfvén waves to bifurcate from the contact discontinuity (entropy waves), while the fast magnetosonic wave is a regular perturbation of the hydrodynamical sound speed. These results are further reported as a starting point for characteristic based shock capturing schemes for simulations with ultra-relativistic shocks in magnetized relativistic fluids.
Magnetic translation groups in an n-dimensional torus and their representations
Authors: Tanimura Shogo
Published: December 2002

A charged particle in a uniform magnetic field in a two-dimensional torus has a discrete noncommutative translation symmetry instead of a continuous commutative translation symmetry. We study topology and symmetry of a particle in a magnetic field in a torus of arbitrary dimensions. The magnetic translation group (MTG) is defined as a group of translations that leave the gauge field invariant. We show that the MTG in an n-dimensional torus is isomorphic to a central extension of a cyclic group Zν1×⋯×Zν2l×Tm by U(1) with 2l+m=n. We construct and classify irreducible unitary representations of the MTG in a three-torus and apply the representation theory to three examples. We briefly describe a representation theory for a general n-torus. The MTG in an n-torus can be regarded as a generalization of the so-called noncommutative torus.
Results on the Wess–Zumino consistency condition for arbitrary Lie algebras
Authors: Barkallil A. , Barnich G. , Schomblond C.
Published: December 2002

The so-called covariant Poincaré lemma on the induced cohomology of the space–time exterior derivative in the cohomology of the gauge part of the BRST differential is extended to cover the case of arbitrary, nonreductive Lie algebras. As a consequence, the general solution of the Wess–Zumino consistency condition with a nontrivial descent can, for arbitrary (super) Lie algebras, be computed in the small algebra of the one-form potentials, the ghosts and their exterior derivatives. For particular Lie algebras that are the semidirect sum of a semisimple Lie subalgebra with an ideal, a theorem by Hochschild and Serre is used to characterize more precisely the cohomology of the gauge part of the BRST differential in the small algebra. In the case of an Abelian ideal, this leads to a complete solution of the Wess–Zumino consistency condition in this space. As an application, the consistent deformations of 2+1 dimensional Chern–Simons theory based on iso(2,1) are rediscussed.
Black-brane solution for C2 algebra
Authors: Grebeniuk M. A. , Ivashchuk V. D. , Kim S.-W.
Published: December 2002

Black p-brane solutions for a wide class of intersection rules and Ricci-flat “internal” spaces are considered. They are defined up to moduli functions Hs obeying nonlinear differential equations with certain boundary conditions imposed. A new solution with intersections corresponding to the Lie algebra C2 is obtained. The functions H1 and H2 for this solution are polynomials of degree 3 and 4.
Central limit theorem for fluctuations in the high temperature region of the Sherrington–Kirkpatrick spin glass model
Authors: Guerra Francesco , Lucio Toninelli Fabio
Published: December 2002

In a region above the Almeida–Thouless line, where we are able to control the thermodynamic limit of the Sherrington–Kirkpatrick model and to prove replica symmetry, we show that the fluctuations of the overlaps and of the free energy are Gaussian, on the scale 1/N, for large N. The method we employ is based on the idea we recently developed of introducing quadratic coupling between two replicas. The proof makes use of the cavity equations and of concentration of measure inequalities for the free energy.
P-type macroporous silicon for two-dimensional photonic crystals
Authors: Bettotti P. , Dal Negro L. , Gaburro Z. , Pavesi L. , Lui A. , Galli M. , Patrini M. , Marabelli F.
Published: December 2002

Macroporous silicon with two-dimensional periodicity has been produced by electrochemical etching, using a p-type doped silicon substrate. The structure shows photonic energy gaps in the infrared region, as demonstrated by variable angle reflectance measurements. The agreement between measurement and band calculations confirms the high quality of the samples. The use of an optimized electrolyte allows the fabrication of very high quality samples, with high aspect ratio and low roughness both at the surface and on the pore walls. The best results are obtained with aprotic and protophilic solvents.
Extension of Bethe ansatz to multiple occupancies for one-dimensional SU(4) fermions with δ-function interaction
Authors: Ying Zu-Jian , Li You-Quan , Gu Shi-Jian , Chen Bin
Published: December 2002

We consider the problem of consistence between the Bethe ansatz (BA) wave function and the multiparticle (more than two) scattering in one-dimensional δ-function interacting SU(4) fermions, which the approach of BA does not explicitly take into account. We find the scattering conditions of three and four particles located at the same position and show that the conditions can be fulfilled by the two-particle connection conditions of the BA wave function. So the definition of the BA wave function can be exactly extended to those cases with multiple occupancies. The inconsistence between the BA and multiparticle interacting on a same site in the degenerate Hubbard model, which makes the BA fail for the model, is shown to vanish in the limit of small site spacing. A correspondence relation of the BA equation and SU(4) symmetry of the system is also indicated for the fermions. The degeneracy of state with BA eigenenergy is given. Singlet lies in the case when there are equal numbers of particles in each inner component.
Convexity and potential sums for Salpeter-type Hamiltonians
Authors: Hall Richard L. , Lucha Wolfgang , Schöberl Franz F.
Published: December 2002

The semirelativistic Hamiltonian H=βm2+p2+V(r), where V(r) is a central potential in R3, is concave in p2 and convex in p≡p2. This fact enables us to obtain complementary energy bounds for the discrete spectrum of H. By extending the notion of “kinetic potential” we are able to find general energy bounds on the ground-state energy E corresponding to potentials with the form V=∑iaif(i)(r). In the case of sums of powers and the log potential, where V(r)=∑q≠0a(q)sgn(q)r q+a(0)ln(r), the bounds can all be expressed in the semiclassical form E≈minr{βm2+(1/r2)+∑q≠0a(q)sgn(q)(rP(q))q+a(0)ln(rP(0))}. “Upper” and “lower” P numbers are provided for q=−1,1,2, and for the log potential q=0. Some specific examples are discussed, to show the quality of the bounds.
Submicrometer-resolution three-dimensional imaging with hard x-ray imaging microtomography
Authors: Takeuchi Akihisa , Uesugi Kentaro , Takano Hidekazu , Suzuki Yoshio
Published: December 2002

An x-ray microtomography method combined with hard x-ray imaging microscopy was developed that has a potential spatial resolution of the order of 10–100 nm. The system consists of a high-brilliance undulator source of SPring-8, a beam diffuser plate to reduce the coherence of the illumination, a high-precision rotating sample stage, a Fresnel zone plate objective, and a high-resolution x-ray imaging detector. The three-dimensional images of several samples were observed and successfully reconstructed with a pitch pattern of 0.6 μm.
Mechanical characteristics of ionic polymer-metal composite in the process of self-bending
Authors: Tamagawa Hirohisa , Yagasaki Kazuyuki , Nogata Fumio
Published: December 2002

An ionic polymer-metal composite (IPMC) consisting of a thin Nafion sheet sandwiched between two thin metallic plates like platinum, silver, and copper ones exhibits a large self-bending motion in its transversal direction upon such a small voltage as 1 V. Estimating Young’s moduli and generated force, which are time dependent and difficult to measure by standard methods, is fundamental for understanding their mechanical properties. We propose a simple method to estimate the time-dependent nominal Young’s moduli and generated force in experiments. We use cantilever beams of IPMCs and obtain their Young’s moduli and generated force (bending moments) from their shapes and vertical force at the tips by neglecting their inertia and viscosity property. The validity of the method is demonstrated by numerical simulation results. For an IPMC consisting of a Nafion sheet and two thin silver plates we give experimental results, which are considerably consistent with ones previously reported. Moreover, we see that its Young’s modulus and generated force have large variations in the process of its self-bending.
Classicality criteria
Authors: Dias Nuno Costa
Published: December 2002

We present two possible criteria quantifying the degree of classicality of an arbitrary (finite dimensional) dynamical system. The inputs for these criteria are the classical dynamical structure of the system together with the quantum and the classical data providing the two alternative descriptions of its initial time configuration. It is proved that a general quantum system satisfying the criteria up to some extend displays a time evolution consistent with the classical predictions up to some degree and thus it is argued that the criteria provide a suitable measure of classicality. The features of the formalism are illustrated through two simple examples.
Magnon scattering and tunneling through localized states in magnetic tunnel junctions
Authors: Wingbermühle J. , Stein S. , Kohlstedt H.
Published: December 2002

Spin-dependent tunnel junctions with Co75Fe25 electrodes and a Fe50Mn50 pinning layer were fabricated with tunneling magnetoresistance of about 20% at room temperature. The Al2O3 barriers were formed by ultra-violet light assisted oxidation. The resistance × area (R×A) product was about 375 kΩ μm2 in the parallel alignment of the magnetizations. The effect of barrier impurities has been investigated via tunneling conductance as a function of temperature and bias voltage for as-deposited and annealed samples. The spin wave parameter α was determined to be 3.06×10−5 and 2.03×10−5 K−3/2 before and after annealing, respectively. The improved barrier properties after annealing are explained by inelastic hopping via several localized states and reduced magnon scattering. We propose a qualitative model of the barrier homogenization during annealing which supports former Rutherford backscattering and x-ray photoelectron spectroscopy studies.
Nonscanning Brillouin spectroscopy applied to solid materials
Authors: Ko Jae-Hyeon , Kojima Seiji
Published: December 2002

We report the first observation of Brillouin spectra of solid samples by using a nonscanning one-pass Fabry-Perot interferometer with a high finesse of 80. Obtained acoustic parameters of a quartz glass are in good agreement with those measured by a conventional scanning multipass Fabry-Perot interferometer. The acquisition time of the present nonscanning interferometer for measuring one meaningful Brillouin spectrum is remarkably reduced in comparison with the scanning one. It has been demonstrated that the present spectrometer is a very powerful tool in the real-time monitoring of transient acoustic properties of condensed matters, like changes in the sound velocity and the damping factor during liquid-glass transitions.
Operation of a single mode external-cavity laser diode array near 780 nm
Authors: Bayram S. B. , Chupp T. E.
Published: December 2002

We have narrowed the spectral bandwidth of a commercial 2 W laser diode array to be less than 120 MHz near 780 nm. The external-cavity laser diode array system is a standard double-pass Littman–Metcalf configuration operating on a dominant single longitudinal mode.
A combined confocal and magnetic resonance microscope for biological studies
Authors: Majors Paul D. , Minard Kevin R. , Ackerman Eric J. , Holtom Gary R. , Hopkins Derek F. , Parkinson Christopher I. , Weber Thomas J. , Wind Robert A.
Published: December 2002

Complementary data acquired with different microscopy techniques provide a basis for establishing a more comprehensive understanding of cell function in health and disease, particularly when results acquired with different methodologies can be correlated in time and space. In this article, a novel microscope is described for studying live cells simultaneously with both confocal scanning laser fluorescence optical microscopy and magnetic resonance microscopy. The various design considerations necessary for integrating these two complementary techniques are discussed, the layout and specifications of the instrument are given, and examples of confocal and magnetic resonance images of large frog cells and model tumor spheroids obtained with the compound microscope are presented.
High-resolution scattering apparatus for surface studies
Authors: Pedemonte L. , Gussoni A. , Tatarek R. , Bracco G.
Published: December 2002

A high-resolution apparatus designed to study the structural and dynamical surface properties is described. The apparatus combines the thermal energy He atom- and the low energy ion-scattering techniques both with time-of-flight detection of the scattered fraction. The energy spread of the supersonic He beam is less than 100 μeV at source temperatures below 35 K. The source temperature can be varied between 22 and 300 K to perform elastic, inelastic, and quasielastic scattering studies over a broad range of incident energies. The scattered beam is detected by a homemade quadrupole mass spectrometer designed to have high efficiency for He. The ion source works between 2 and 5 keV and the ion beam is mass selected by a Wien filter which also separates the transmitted ions from fast neutral species. The beam is detected at a scattering angle of 160° and therefore neutral impact collision ion scattering spectroscopy studies can be performed. The base pressure in the target chamber is in the 10−11 mbar range. The capabilities of the apparatus are tested, and the evolution of surface disorder on Ag(110) up to 800 K is characterized.
Free energy disconnectivity graphs: Application to peptide models
Authors: Krivov Sergei V. , Karplus Martin
Published: December 2002

Disconnectivity graphs are widely used for understanding the multidimensional potential energy surfaces (PES) of complex systems. Since entropic contributions to the free energy can be important, particularly for polypeptide chains and other polymers, conclusions concerning the equilibrium properties and kinetics of the system based on potential energy disconnectivity graphs (PE DG) can be misleading. We present an approach for constructing free energy surfaces (FES) and free energy disconnectivity graphs (FE DG) and give examples of their applications to peptides. They show that the FES and FE DG can differ significantly from the PES and PE DG.
Time domain characterization of oscillating sensors: Application of frequency counting to resonance frequency determination
Authors: Zeng Kefeng , Ong Keat G. , Mungle Casey , Grimes Craig A.
Published: December 2002

A frequency counting technique is described for determining the resonance frequency of a transiently excited sensor; the technique is applicable to any sensor platform where the characteristic resonance frequency is the parameter of interest. The sensor is interrogated by a pulse-like excitation signal, and the resonance frequency of the sensor subsequently determined by counting the number of oscillations per time during sensor ring-down. A repetitive time domain interrogation technique is implemented to overcome the effects of sensor damping, such as that associated with mass loading, which reduces the duration of the sensor ring-down and hence the measurement resolution. The microcontroller based, transient frequency counting technique is detailed with application to the monitoring of magnetoelastic sensors [C. A. Grimes, D. Kouzoudis, and C. Mungle, Rev. Sci. Instrum. 71, 3822 (2000)], with a measurement resolution of 0.001% achieved in approximately 40 ms.
Influence of x-ray beam spatial coherence on the diffuse scattering from multilayer mirrors
Authors: Chernov V. A. , Kondratiev V. I. , Kovalenko N. V. , Mytnichenko S. V. , Zolotarev K. V.
Published: December 2002

The improved spatial coherence of a synchrotron radiation beam was shown experimentally to stimulate additional diffuse scattering of x rays diffracted from x-ray multilayer mirrors. Although the large-scale (tens of microns) roughness does not affect Bragg diffraction from multilayers, its presence causes phase shifts at the wave packet front. This leads to partial decay of the coherent wave packet and creates additional diffuse scattering. Additional scattering from this mechanism was observed at angles of incidence corresponding to the Bragg and Kiessig maximum angles. The properties of this scattering caused by large-scale roughness, observed due to improved x-ray beam spatial coherence, were shown experimentally to be different from those of diffuse scattering previously reported when the incoming or outgoing angle is equal to the Bragg angle. Typical breaks in the diffuse scattering intensity due to the standing-wave effect are absent, and there is obvious asymmetry of the diffuse scattering cross section around the incoming and outgoing angles. Due to the small angle of incidence, the coherently irradiated area has very different dimensions parallel and perpendicular to the beam, which leads to the observed scattering being concentrated in the specular diffraction plane defined by the incident and reflected wave vectors.
X-ray photoelectron spectroscopic investigation of surface chemistry of ternary As–S–Se chalcogenide glasses
Authors: Li Wenyan , Seal Sudipta , Lopez Cedric , Richardson Kathleen A.
Published: December 2002

Chalcogenide glasses belong to an important class of materials, due to their good infrared transmission, and low-phonon energy as compared to other oxide glasses. Structural and chemical variations imposed by glass processing conditions, e.g., film deposition, can lead to changes in the linear and nonlinear optical properties. X-ray photoelectron spectroscopy (XPS) has been employed to study As–S–Se glasses of differing chemical compositions, in the film and the bulk form, to understand any variations in chemical bond configuration and their electronic structure. The molecular environments of As and Se for As–S–Se samples with varying S/Se ratio (fixed As content) and As content (fixed S/Se ratio) are studied by monitoring the XPS chemical shifts. The surface chemistry of the bulk and thin-film chalcogenide glasses are also compared to determine the effect of glass processing conditions for better chalcogenides for potential waveguide applications.
Continuous spin representations of the Poincaré and super-Poincaré groups
Authors: Brink Lars , Khan Abu M. , Ramond Pierre , Xiong Xiaozhen
Published: December 2002

We construct Wigner’s continuous spin representations of the Poincaré algebra for massless particles in higher dimensions. The states are labeled both by the length of a spacelike translation vector and the Dynkin indices of the short little group SO(d−3), where d is the space–time dimension. Continuous spin representations are in one-to-one correspondence with representations of the short little group. We also demonstrate how combinations of the bosonic and fermionic representations form supermultiplets of the super-Poincaré algebra. If the light-cone translations are nilpotent, these representations become finite dimensional, but contain zero or negative norm states, and their supersymmetry algebra contains a central charge in four and ten dimensions.
A time-of-flight resonance ionization mass spectrometer for elemental analysis of precious metals in minerals
Authors: Dimov S. S. , Chryssoulis S. L. , Lipson R. H.
Published: December 2002

An instrument for time-of-flight resonance ionization mass spectrometry (TOF-RIMS) developed at the Advanced Mineral Technology Laboratory (Ontario, Canada) is described which has been applied to the quantitative trace analysis of metals in minerals. The instrument incorporates new pulsed ion optics which provide fast switching of polarity and potentials of acceleration and ion lens optics between the two consecutive laser ablation and laser photoionization steps. Pulsed mode operation allows the time-of-flight mass spectrometer to be operated at higher laser ablation powers with more efficient suppression of the primary ions which are a source of noise that degrades the ultimate sensitivity of detection. The performance of the TOF-RIMS apparatus was assessed by analyzing trace amounts of gold (Au) in sulphide, iron oxide, and silicate mineral samples. Quantification of the TOF-RIMS measurements was established on the basis of calibration curves obtained using reference samples covering three orders of magnitude in concentration. Reproducible minimum detection limits (2σ) of ⩽10 parts per billion with a precision of ∼±15% were obtained.
Tests of potential energy surfaces for H+CH4↔CH3+H2: Deuterium and muonium kinetic isotope effects for the forward and reverse reaction
Authors: Pu Jingzhi , Truhlar Donald G.
Published: December 2002

In previous work, three implicit potential energy surfaces with specific reaction parameters (SRP), namely MPW60, MC-QCISD-SRP, and MCG3-SRP, were developed for the reaction CH4+H→CH3+H2. Forward reaction rate constants obtained by variational transition state theory with multidimensional tunneling (VTST/MT) dynamics calculations on these surfaces give good agreement with recently re-analyzed experimental results. In the present work, again employing VTST/MT, kinetic isotope effects (KIEs) for isotopic variants of the title reaction in both the forward and reverse directions are examined on these SRP surfaces. Various primary and secondary deuterium (D) kinetic isotope reactions are studied; we also calculated the KIE for the reaction between methane and muonium (Mu), which is an ultralight isotope of protium with the Mu/H mass ratio being 0.113. The results are compared with several sets of experimental studies. With the VTST/MT dynamical method and harmonic vibrations, the proposed surfaces predict the KIE quite well, probably within experimental error, for seven different isotopic combinations involving substitution of one to five deuteriums for protium. The calculations also reproduce quite well the high Arrhenius activation energy for Mu+CH4, and the KIE for muonium atom attack is correctly predicted to be inverse, but the predicted values of the Mu KIE over the experimental temperature range are 0.012–0.06 (without scaling force constants) or 0.021–0.09 (when the force constant of the making bond is scaled), whereas the experimental values in the same temperature range are 0.05–0.3. Several possible reasons for this are discussed.
Optical spectroscopic studies of the dispersibility of gold nanoparticle solutions
Authors: Huang Shujuan , Minami Kazuyuki , Sakaue Hiroyuki , Shingubara Shoso , Takahagi Takayuki
Published: December 2002

We present an in situ study on the dispersibility of gold nanoparticles in different solvents by comparing the measured optical absorption spectra to the calculated absorption. Both uncapped and capped particles dispersed in a variety of solvents are investigated. In organic solvents such as chloroform and alcohols, dodecanethiol-capped particles can be dissolved better and with more stability than uncapped nanoparticles. The results of this work demonstrate that surface capping with alkanethiol molecules can dramatically improve the dispersibility of gold nanoparticles in organic solvents. The dissolution nature of the capper and the solvent dominate the dispersibility. We propose a useful method for selecting solvents in order to achieve a high dispersibility of nanoparticle solutions.
Intrinsic anisotropy-defined magnetization reversal in submicron ring magnets
Authors: Li S. P. , Lew W. S. , Bland J. A. C. , Natali M. , Lebib A. , Chen Y.
Published: December 2002

We report a study of the effect of magnetocrystalline anisotropy in the magnetization reversal of submicron Co rings fabricated by nanoimprint lithography. For weak magnetocrystalline anisotropy, the complete reversal takes place via a transition from saturation at large negative fields, into a vortex configuration at small fields, and back to reverse saturation at large positive fields. When the anisotropy strength is increased to a critical value, the intermediate vortex configuration no longer exists in the magnetization reversal along the easy axis; instead, the reversal occurs through a rapid jump. However, when the applied field direction is far from the easy axis, the presence of the magnetocrystalline anisotropy favors local vortex nucleation, and this leads to a similar switching process as found for low anisotropy. Micromagnetic simulations indicate that the magnetization reversal process of the rings, starts from a buckling-like reverse domain nucleation, followed by local vortex formation and an avalanche process of local vortex nucleation.