bluuebunny/crossref_metadata_2025 huggingface dataset:
Bone changes after maxillary sinus surgery: an experimental scanning electron microscopy study
Authors: Moreno P M , Meseguer D H
Published: July 2007

Aims:

The purpose of this study was to explore the pathogenic role of bone in sinus surgery, and to determine whether mucosal disease after sinus surgery may be induced by underlying disease within the bone.

Material and methods:

Twenty-five rabbits were divided into five groups. In group one, wide surgical removal of the maxillary sinus mucosa and creation of a nasoantral window were undertaken. In group two, only nasoantral window creation was undertaken. In group three, the mucosa of the anterior maxillary sinus was removed. In group four, a strip of mucosa around the ostium was removed. Group five was used as a control.

Results:

After three months, in the groups which had undergone wide surgical removal, the medial sinus walls were observed to be retracted and the inner curtain of the bone disturbed, with alteration of the haversian canal system and osteoclastic bone resorption.

Conclusions:

After radical sinus surgery, electron microscopic changes were observed in the bony walls, similar to those changes seen in osteomyelitis.
Limiting profiles for periodic solutions of scalar delay differential equations
Authors: Chen Y.
Published: July 2007

Let f(·, λ) : R→R be given so that f(0, λ) = 0 and f(x, λ) = (1 + λ)x + ax2 + bx3 + o(x3) as x → 0. We characterize those small values of ε > 0 and λ ∈ R for which there are periodic solutions of periods approximately 1/k with k ∈ N of the delay equations

When a = 0, these periodic solutions approach square waves if b < 0 or pulses if b > 0 as ε → 0. These results are similar to those obtained by Chow et al. and Hale and Huang, where the case of f(x, λ) = −(1 + λ)x + ax2 + bx3 + o(x3) as x → 0 is considered. However, when a ≠ 0, all these periodic solutions approach pulses as ε → 0; an interesting phenomenon that cannot happen in the case considered by Chow et al. and Hale and Huang.
A compactness result in the gradient theory of phase transitions
Authors: DeSimone Antonio , Müller Stefan , Kohn Robert V. , Otto Felix
Published: July 2007

We examine the singularly perturbed variational problem

in the plane. As ε → 0, this functional favours |∇ψ| = 1 and penalizes singularities where |∇∇ψ| concentrates. Our main result is a compactness theorem: if {Eε(ψε)}ε↓0 is uniformly bounded, then {∇ψε}ε↓0 is compact in L2. Thus, in the limit ε → 0, ψ solves the eikonal equation |∇ψ| = 1 almost everywhere. Our analysis uses ‘entropy relations’ and the ‘div-curl lemma,’ adopting Tartar's approach to the interaction of linear differential equations and nonlinear algebraic relations.
On the spreading of characteristics for non-convex conservation laws
Authors: Jenssen Helge Kristian , Sinestrari Carlo
Published: July 2007

We study the spreading of characteristics for a class of one-dimensional scalar conservation laws for which the flux function has one point of inflection. It is well known that in the convex case the characteristic speed satisfies a one-sided Lipschitz estimate. Using Dafermos' theory of generalized characteristics, we show that the characteristic speed in the non-convex case satisfies an Hölder estimate. In addition, we give a one-sided Lipschitz estimate with an error term given by the decrease of the total variation of the solution.
On a class of elliptic problems in R2: symmetry and uniqueness results
Authors: Prajapat J. , Tarantello G.
Published: July 2007

In the plane R2, we classify all solutions for an elliptic problem of Liouville type involving a (radial) weight function. As a consequence, we clarify the origin of the non-radially symmetric solutions for the given problem, as established by Chanillo and Kiessling.

For a more general class of Liouville-type problems, we show that, rather than radial symmetry, the solutions always inherit the invariance of the problem under inversion with respect to suitable circles. This symmetry result is derived with the help of a 'shrinking-sphere' method.
Symmetric solutions for a Neumann problem involving critical exponent
Authors: Cao Daomin , Noussair E. S. , Yan Shusen
Published: July 2007

In this paper, we construct three types of symmetric peaked solutions for a Neumann problem involving critical Sobolev exponent: the interior peaked solution, the boundary peaked solution and the interior-boundary peaked solution.
Comparison theorems and variable speed waves for a scalar reaction–diffusion equation
Authors: Kay Alison L. , Sherratt Jonathan A. , McLeod J. B.
Published: July 2007

This paper concerns the reaction-diffusion equation ut = uxx + u2(1 − u). Previous numerical solutions of this equation have demonstrated various different types of wave front solutions, generated by different initial conditions. In this paper, the authors use a phase-plane form of comparison theorems for partial differential equations (PDEs) to confirm analytically these numerical results. In particular, they show that initial conditions with an exponentially decaying tail evolve to the unique exponentially decaying travelling wave, while initial conditions with algebraically decaying tails evolve either to an algebraically decaying travelling wave, or to the exponentially decaying wave, or to a perpetually accelerating wave, dependent upon the exact form of the decay of the initial conditions. We then focus on the case of accelerating waves and investigate their form in more detail, by approximating the full equation in this case with a hyperbolic PDE, which we solve using the method of characteristics. We use this approximate solution to derive a leading-order approximation to the wave speed.
Analysis of the PML equations in general convex geometry
Authors: Lassas Matti , Somersalo Erkki
Published: July 2007

In this work, we study a mesh termination scheme in acoustic scattering, known as the perfectly matched layer (PML) method. The main result of the paper is the following. Assume that the scatterer is contained in a bounded and strictly convex artificial domain. We surround this domain by a PML of constant thickness. On the peripheral boundary of this layer, a homogenous Dirichlet condition is imposed. We show in this paper that the resulting boundary-value problem for the scattered field is uniquely solvable for all wavenumbers and the solution within the artificial domain converges exponentially fast toward the full-space scattering solution when the layer thickness is increased. The proof is based on the idea of interpreting the PML medium as a complex stretching of the coordinates in Rn and on the use of complexified layer potential techniques.
Blow-up for a parabolic system coupled in an equation and a boundary condition
Authors: Deng Keng , Zhao Cheng-Lin
Published: July 2007

In this paper, we consider non-negative solutions of
,
We prove that if pq ≤ 1, every solution is global while if pq > 1, all solutions blow up in finite time. We also show that if p, q ≥ 1, then blow-up can occur only on the boundary.
Maximal extension for linear spaces of real matrices with large rank
Authors: Zhang Kewei
Published: July 2007

For every 0 < k < min{m,n} and any linear subspace E of real m × n matrices whose non-zero elements have rank greater than k, we show that there is a maximal extension Emax satisfying the same rank condition, and that the dimension of Emax is not less than (m – k)(n – k). We apply this result to the study of quasiconvex functions defined on the complement E⊥ of E in the form F(X) = f(PE⊥(X)), where PE⊥ is the orthgonal projection to E⊥.
Travelling fronts in a food-limited population model with time delay
Authors: Gourley S. A. , Chaplain M. A. J.
Published: July 2007

In this paper we study travelling front solutions of a certain food-limited population model incorporating time-delays and diffusion. Special attention is paid to the modelling of the time delays to incorporate associated non-local spatial terms which account for the drift of individuals to their present position from their possible positions at previous times. For a particular class of delay kernels, existence of travelling front solutions connecting the two spatially uniform steady states is established for sufficiently small delays. The approach is to reformulate the problem as an existence question for a heteroclinic connection in R4. The problem is then tackled using dynamical systems techniques, in particular, Fenichel's invariant manifold theory. For larger delays, numerical simulations reveal changes in the front's profile which develops a prominent hump.
Γ-limit for the extended Fisher–Kolmogorov equation
Authors: Hilhorst D. , Peletier L. A. , Schätzle R.
Published: July 2007

We consider the Lyapunov functional,

of the rescaled Extended Fisher-Kolmogorov equation

This is a fourth order generalization of the Fisher–Kolmogorov or Allen–Cahn equation. We prove that if ε → 0, then tends to the area functional in the sense of Γ-limits, where the transition energy is given by the one-dimensional kink of the Extended Fisher–Kolmogorov equation.
A derivation theory for generalized Besicovitch spaces and its application for partial differential equations
Authors: Casado-Díaz Juan , Gayte Inmaculada
Published: July 2007

We present an extension of Besicovitch spaces, which has its origin in the works of Zhikov et al. and Kozlov and Oleinik. We show that these spaces have a similar behaviour to the Lp spaces, and we give a notion of derivative that allows us to treat partial differential problems in this frame. To the best of our knowledge, this is new, even for the usual Besicovitch spaces.
Asymptotic behaviour of solutions of the hydrodynamic model of semiconductors
Authors: Li Hailiang , Markowich Peter , Mei Ming
Published: July 2007

Degond and Markowich discussed the existence and uniqueness of a steady-state solution in the subsonic case for the one-dimensional hydrodynamic model of semiconductors. In the present paper, we reconsider the existence and uniqueness of a globally smooth subsonic steady-state solution, and prove its stability for small perturbation. The proof method we adopt in this paper is based on elementary energy estimates.
On the second-order asymptotic equation of a variational wave equation
Authors: Zhang Ping , Zheng Yuxi
Published: July 2007

We have been interested in studying a nonlinear variational wave equation whose wave speed is a sinusoidal function of the wave amplitude, arising naturally from liquid crystals. High-frequency waves of small amplitudes, the so-called weakly nonlinear waves, near a constant state a are governed by two asymptotic equations: the first-order asymptotic equation if a is not a critical point of the sinusoidal function, or the second-order asymptotic equation if a is either a maximal or a minimal point of the sinusoidal function. Our earlier work on the first-order asymptotic equation has greatly helped the study of the nonlinear variational wave equation with monotone wave speed functions. It is apparent in our research that investigation of the second-order asymptotic equation is both crucial and equally illuminating for the study of the nonlinear variational wave equation with sinusoidal wave speed functions. We succeed in this paper in handling what may be appropriately called the ‘concentration-annihilation’ phenomena in the historical spirit of compensated-compactness (Tartar et al.), concentration-compactness (Lions), and concentration-cancellation or concentration-evanesces (DiPerna and Majda). More precisely, the second-order asymptotic equation has a product term uv2 for which v2 may have concentration on a set where u vanishes in a sequence of approximate solutions, while the product retains no concentration. Although absent in the first-order asymptotic equation, this concentration-annihilation phenomenon has been demonstrated through an explicit example for the nonlinear variational wave equation with sinusoidal wave speed functions in an earlier work. We use this concentration-annihilation to establish the global existence of weak solutions to the second-order asymptotic equation with initial data of bounded total variations.
Positive solutions for the p-Laplacian in annuli
Authors: Ercole Grey , Zumpano Antônio
Published: July 2007

We consider the Dirichlet problem for the equation -Δpu = q(|x|)f(u) in an annulus Ω ⊂ Rn, n ≥ 1, where Δpu = div(|∇u|p−2∇u) is the p-Laplacian operator, p > 1. With no assumption on the behaviour of the nonlinearity f either at zero or at infinity, we prove existence and localization of positive radial solutions for this problem by applying Schauder's fixed-point theorem. Precisely, we show the existence of at least one such solution each time the graph of f passes through an appropriate tunnel. So, it is easy to exhibit multiple, or even infinitely many, positive solutions. Moreover, upper and lower bounds for the maximum value of the solution are obtained. Our results are easily extended to the exterior of a ball, when n > p.
On the spectral theory of a tapered rod
Authors: Stuart C. A.
Published: July 2007

This paper establishes the main features of the spectral theory for the singular two-point boundary-value problem

and

which models the buckling of a rod whose cross-sectional area decays to zero at one end. The degree of tapering is related to the rate at which the coefficient A tends to zero as s approaches 0. We say that there is tapering of order p ≥ 0 when A ∈ C([0, 1]) with A(s) > 0 for s ∈ (0, 1] and there is a constant L ∈ (0, ∞) such that lims→0A(s)/sp = L. A rigorous spectral theory involves relating (1)−(3) to the spectrum of a linear operator in a function space and then investigating the spectrum of that operator. We do this in two different (but, as we show, equivalent) settings, each of which is natural from a certain point of view. The main conclusion is that the spectral properties of the problem for tapering of order p = 2 are very different from what occurs for p < 2. For p = 2, there is a non-trivial essential spectrum and possibly no eigenvalues, whereas for p < 2, the whole spectrum consists of a sequence of simple eigenvalues. Establishing the details of this spectral theory is an important step in the study of the corresponding nonlinear model. The first function space that we choose is the one best suited to the mechanical interpretation of the problem and the one that is used for treating the nonlinear problem. However, we relate this formulation in a precise way to the usual L2 setting that is most common when dealing with boundary-value problems.
On a nonlinear eigenvalue problem in OrliczSobolev spaces
Authors: Gossez J.-P. , Mansevich R.
Published: July 2007

We consider the eigenvalue problem

in an arbitrary OrliczSobolev space. We show that the existence of an eigenvalue can be derived from a generalized version of Lagrange multiplier rule. Our approach also applies to more general problems. We emphasize that no 2 condition is imposed.
Phase field model with a variable chemical potential
Authors: Tonegawa Yoshihiro
Published: July 2007

We study some asymptotic behaviour of phase interfaces with variable chemical potential under the uniform energy bound. The problem is motivated by the Cahn-Hilliard equation, where one has a control of the total energy and chemical potential. We show that the limit interface is an integral varifold with generalized Lp mean curvature. The convergence of interfaces as 0 is in the Hausdorff distance sense.
Submanifolds with constant scalar curvature
Authors: Cheng Qing-Ming
Published: July 2007

In this paper, we study n-dimensional complete submanifolds with constant scalar curvature in the Euclidean space En+p and n-dimensional compact submanifolds with constant scalar curvature in the unit sphere Sn+p(1). We prove that the totally umbilical sphere Sn(r), totally geodesic Euclidean space En and generalized cylinder Sn−1(c) × E1 are the only n-dimensional (n > 2) complete submanifolds Mn with constant scalar curvature n(n − 1)r in the Euclidean space En+p, which satisfy the following condition:

where S denotes the squared norm of the second fundamental form of Mn. For compact submanifolds with constant scalar curvature in the unit sphere Sn+p(1), we also obtain a corresponding result (see theorem 1.3).
Best constants in the L2-Nash inequality
Authors: Humbert Emmanuel
Published: July 2007

We prove that, contrary to the L1-Nash inequality, there exists a second best constant for the L2-Nash inequality on any smooth compact Riemannian manif
Three-space problems in discrete spectra of C*-algebras and dual C*-algebras
Authors: Kusuda Masaharu
Published: July 2007

We discuss the three-space problem on discreteness for the Jacobson topology on the spectrum of a C*-algebra in detail. As an application, it is shown that a C*-algebra A is a dual C*-algebra if and only if a closed ideal I of A and the quotient A/I are dual C*-algebras and the open central projection, in the second dual of A, corresponding to I is a multiplier for A.
𝔻n-forced symmetry breaking of 𝕆(2)-equivariant problems
Authors: Furter Jacques-Elie , Sitta Angela Maria
Published: July 2007

We use singularity theory to classify forced symmetry-breaking bifurcation problems

where f1 is 𝕆(2)-equivariant and f2 is 𝔻n-equivariant with the orthogonal group actions on z ∈ ℝ2. Forced symmetry breaking occurs when the symmetry of the equation changes when parameters are varied. We explicitly apply our results to the branching of subharmonic solutions in a model periodic perturbation of an autonomous equation and sketch further applications.
Special issue on English dialect syntax
Authors: TROUSDALE GRAEME , ADGER DAVID
Published: July 2007

This special volume is concerned with the syntax of nonstandard varieties of (mainly British) English, and how such syntactic variation is accounted for within a range of theoretical models. There has been a growing interest in the modelling of dialect syntax (a) in a number of languages and (b) in a number of syntactic theories (see, for instance, the research on syntactic microvariation in some Germanic languages in Barbiers, Cornips & van der Kelij, 2002, or the construction-based approach to variation in Leino & Östman, 2005). We have brought together five articles written in different theoretical frameworks (Principles and Parameters, Stochastic Optimality Theory, Head-driven Phrase Structure Grammar, Word Grammar, and Construction Grammar), together with an introduction written by the editors, who themselves adopt very different theoretical frameworks.
A new approach to transitive expletives: evidence from Belfast English
Authors: HENRY ALISON , COTTELL SIOBHAN
Published: July 2007

This article discusses the existence of transitive expletives in a variety of English. Belfast English has none of the features previously proposed as licensing transitive expletives, but nevertheless allows these, calling into question previous analyses of the licensing of this structure. This article considers the properties of transitive expletives in this variety, showing that they are restricted to sentences where the associate is quantified, and that the associate can appear in a range of positions, similar but not identical to those available to ‘floated’ quantifiers. It is argued that Belfast English has a higher merge position for the expletive than does Standard English, and that the general availability in English of quantifier positions between T and vP – perhaps because auxiliaries in English head phases, and phases can be closed by a quantification – means that, even though Belfast English is not a Verb Second language, a position is available for both the expletive and the associate.
English dialect syntax in Word Grammar
Authors: HUDSON RICHARD A.
Published: July 2007

The article focuses on inherent variability in syntax and the challenge that it presents for theories of language structure, using illustrative data from the Scottish town of Buckie (Smith, 2000). Inherent variability challenges a linguistic theory at three levels of theoretical adequacy: structural (Does the theory distinguish the relevant structures?), contextual (Does it allow structures to be related directly to their social context?), and behavioural (Does it allow an explanation for the observed frequencies?). The article summarizes the relevant claims of Word Grammar and shows (1) that it has at least as much structural adequacy as any other theory, (2) that it has more contextual adequacy than other theories because it formalizes the theory of Acts of Identity, and (3) that it at least provides a theoretical foundation for future advances towards behavioural adequacy. The article also argues against the minimalist analysis of the was/were alternation in Buckie (Adger, 2006).
Overview of Multiple–Aperture Interferometry Binary Star Results from the Northern Hemisphere
Authors: McAlister Harold A.
Published: July 2007

Long-baseline optical interferometry (LBI) can nearly close the gap in selection space between astrometric and spectroscopic detection of binary star systems, bringing the complementary powers of astrometry and spectroscopy to bear on a complete dynamical understanding of such systems, particularly including the determination of the masses of the individual stellar components. In the case of double-lined spectroscopic systems, their resolution by long-baseline interferometry also yields the orbital parallax and hence the luminosities of the individual stars. In some of these cases, the angular diameters of one or more components are accessible, and so a complete specification of a star in terms of its mass, radius and luminosity is made.

The northern hemisphere is now equipped with several interferometers of unprecedented capability in terms of their baseline sizes, numbers of telescopes and telescope apertures. These instruments, most notably the Palomar Testbed Interferometer at Mt. Palomar Observatory, have produced very significant results of a number of interesting systems fulfilling interferometry's promise to produce fundamental astrophysical data at levels of accuracy that challenge or confirm astrophysical theory.

This paper presents basic principles of long-baseline interferometric study of binary stars and summarizes results from northern interferometers with specific examples of their broad impact on binary star astronomy.
Doppler Tomography of Accretion Disks and Streams in Close Binaries
Authors: Richards Mercedes T.
Published: July 2007

The application of tomography to the study of gas flows in interacting binaries has led to fascinating images of the Cataclysmic Variables and Algol-type binaries. Such detailed images are currently unachievable using direct-imaging techniques. Numerous images of accretion flows have now been derived from optical and ultraviolet spectra and they have been used to identify multiple emission sources including the gas stream, accretion disk, accretion annulus, shock regions, and the chromosphere of the mass loser. It was difficult to distinguish between the separate sources of emission since these sources have overlapping velocities in the Doppler tomogram. However, with the aid of a new spectral synthesis code, we can now systematically extract the individual emission sources to sequentially isolate the images of the disk and gas stream. With these new tools, we have begun to extract the critical properties of the disk and gas stream more accurately than previously possible.
Reducing Binary Star Data from Long-Baseline Interferometers
Authors: ten Brummelaar Theo A.
Published: July 2007

Processing long-baseline interferometry data presents a unique set of complications: How does one derive relative astrometry from interferometric data? How can 1-D interferometric results be used to solve a 2-D orbit? How can baseline-only solutions be combined with historical data and how should interferometric data be published so that they can be combined with archived data? What new techniques for interferometers are coming on line? This paper contains a brief review of interferometric data analysis in the context of binary star astrometry.
Line-Profile Variations on Massive Binary Systems: Determining η Carinae Orbital Parameters
Authors: Falceta-Gonçalves D. , Abraham Z. , Jatenco-Pereira V.
Published: July 2007

When the winds of two massive stars orbiting each other collide, an interaction zone is created consisting of two shock fronts at both sides of a contact surface. During the cooling process, elements may recombine generating spectral lines. These lines may be Doppler shifted, as the gas stream flows over the interaction zone. To calculate the stream velocity projected into the line of sight we use a simplified conical geometry for the shock fronts and, to determine the synthetic line profile, we have to sum the amount of emitting gas elements with the same Doppler shifted velocity. We show that the stellar mass loss rates and wind velocities, and the orbital inclination and eccentricity, are the main parameters on this physical process. By comparing observational data to the synthetic line profiles it is possible to determine these parameters. We tested this process to Brey 22 WR binary system, and applied to the enigmatic object of η Carinae.
Pipeline Reduction of Binary Light Curves from Large–Scale Surveys
Authors: Prša Andrej , Zwitter Tomaž
Published: July 2007

One of the most important changes in observational astronomy of the 21stCentury is a rapid shift from classical object-by-object observations to extensive automatic surveys. As CCD detectors are getting better and their prices are getting lower, more and more small and medium-size observatories are refocusing their attention to detection of stellar variability through systematic sky-scanning missions. This trend is aditionally powered by the success of pioneering surveys such as ASAS, DENIS, OGLE, TASS, their space counterpart Hipparcos and others. Such surveys produce massive amounts of data and it is not at all clear how these data are to be reduced and analysed. This is especially striking in the eclipsing binary (EB) field, where most frequently used tools are optimized for object-by-object analysis. A clear need for thorough, reliable and fully automated approaches to modeling and analysis of EB data is thus obvious. This task is very difficult because of limited data quality, non-uniform phase coverage and solution degeneracy. This paper reviews recent advancements in putting together semi-automatic and fully automatic pipelines for EB data processing. Automatic procedures have already been used to process Hipparcos data, LMC/SMC observations, OGLE and ASAS catalogs etc. We discuss the advantages and shortcomings of these procedures.
The Incidence of Multiplicity Among Bright Stellar Systems
Authors: Eggleton Peter P. , Kisseleva-Eggleton Ludmila , Dearborn Xander
Published: July 2007

We consider the multiplicity of stellar systems with (combined) magnitude brighter than 6.00 in Hipparcos magnitudes. We identify 4555 such bright systems, and the frequencies of multiplicities 1, 2, . . , 7 are found to be 2722, 1412, 299, 86, 22, 12 and 2. We also consider the distributions of periods of orbits and sub-orbits. For the even more restricted set of 474 systems with VH ≤ 4.00 the proportions of higher multiples up to sextuple are progressively larger, suggesting incompleteness in even the relatively well-studied larger sample.

We construct a Monte-Carlo algorithm that will generate systems with roughly the observed multiplicities and orbital parameters, taking account of selection effects.
The Frequency Distribution of Semimajor Axes of Wide Binaries: Cosmogony and Dynamical Evolution
Authors: Poveda Arcadio , Allen Christine , Hernández-Alcántara A.
Published: July 2007

The frequency distribution f(a) of semimajor axes of double and multiple systems, and their eccentricities and mass ratios, contain valuable fossil information about the process of star formation and the dynamical history of the systems. In order to advance in the understanding of these questions, we made an extensive analysis of the frequency distribution f(a) for wide binaries (a > 25 AU) in various published catalogues, as well as in our own (Poveda et al 1994; Allen et al 2000; (Poveda & Hernández–Alcántara 2003). Based upon all these studies we have established that the frequency distribution f(a) is a function of the age of the system and follows Öpik's distribution f(a) ∼ 1/a in the range of 100 AU < a < ac(t), where ac (t) are the critical semimajor axes beyond which binaries have been dissociated by encounters with massive objects. We argue that the physics behind the distribution f(a) ∼ 1/a is a process of energy relaxation, analogous to those present in stellar clusters (secular relaxation) or in the early stages of spherical galaxies (violent relaxation). The existence of runaway stars indicates that both types of relaxation are important in the process of binary and multiple star dynamical evolution.
Long‐term trend analysis of aerosol variables at the high‐alpine site Jungfraujoch
Authors: Collaud Coen M. , Weingartner E. , Nyeki S. , Cozic J. , Henning S. , Verheggen B. , Gehrig R. , Baltensperger U.
Published: July 2007

This study reports the first long‐term trend analysis of aerosol optical measurements at the high‐alpine site Jungfraujoch, which started 10.5 years ago. Since the aerosol variables are approximately lognormally distributed, the seasonal Kendall test and Sen's slope estimator were applied as nonparametric methods to detect the long‐term trends for each month. The yearly trend was estimated by a least‐mean‐square fit, and the number of years necessary to detect this trend was calculated. The most significant trend is the increase (4–7% yr−1) in light‐scattering coefficients during the September to December period. The light absorption and backscattering coefficients and the aerosol number concentration also show a positive trend during this time of the year. The hemispheric backscattering fraction and the scattering exponent calculated with the smaller wavelengths (450 and 550 nm), which relate to the small aerosol size fraction, decrease except during the summer, whereas the scattering exponent calculated with the larger wavelengths (550 and 700 nm) remains constant. Generally, the summer months at the Jungfraujoch, which are strongly influenced by planetary boundary layer air masses, do not show any long‐term trend. The trends determined by least‐mean‐square fits of the scattering and backscattering coefficients, the hemispheric backscattering fractions, and the scattering exponent are significant, and the number of years necessary to detect them is shorter than 10 years. For these variables, the trends and the slopes estimated by the seasonal Kendall test are therefore confirmed by the least‐mean‐square fit results.
Correcting first‐order errors in snow water equivalent estimates using a multifrequency, multiscale radiometric data assimilation scheme
Authors: Durand Michael , Margulis Steven A.
Published: July 2007

A season‐long, multiscale, multifrequency radiometric data assimilation experiment is performed to test the feasibility of snow water equivalent (SWE) estimation. Synthetic passive microwave (PM) observations at Advanced Microwave Scanning Radiometer‐Earth Observing System frequencies and 25 km resolution and synthetic near infrared (NIR) narrowband albedo observations corresponding to Moderate Resolution Imaging Spectroradiometer band 5 (1230–1250 μm) and 1 km resolution are assimilated into a land surface model snow scheme using the ensemble Kalman filter. First‐order sources of model uncertainty, including error in precipitation quantity, grain size evolution, precipitation spatial distribution, and vegetation leaf area index are modeled. SWE remote sensing retrieval schemes would be of limited value for these scenarios where snow depth ranged between 1.0 and 2.0 m, grain size varied in space, significant vegetation was present, and the snowpack sometimes contained liquid water. Nevertheless, the true basinwide SWE is recovered, in general, within a root‐mean‐square error (RMSE) of approximately 2 cm. Synergy is observed between the PM and NIR measurements because of the complementary nature of the multiscale, multifrequency measurements. Results from the assimilation are compared to those from a pure modeling approach and from a remote sensing retrieval approach. The effects of model uncertainty, measurement error, and ensemble size are investigated.
On the origin of gypsum in the Mars north polar region
Authors: Fishbaugh Kathryn E. , Poulet François , Chevrier Vincent , Langevin Yves , Bibring Jean‐Pierre
Published: July 2007

We describe the distribution and concentration of the largest Martian gypsum deposit discovered to date by the Mars Express OMEGA (Observatoire pour le Mineralogie, l'Eau, les Glaces et l'Activité) imaging spectrometer, its relationship to the late Amazonian‐aged north polar dunes in which it is found, and its likely origin. Gypsum has not been discovered anywhere within the north polar region outside of the Olympia Undae dune sea. In the areas of highest gypsum a concentration, 35% pure gypsum grains of a few tens of micrometers in size, mixed with 65% millimeter‐sized gypsum grains containing, dark, spectrally featureless inclusions best fit the OMEGA observations. The gypsum‐rich dunes contain no significant average albedo, temperature, or morphological anomalies. We propose that water emanating from nearby channels, carved during melting of the polar layered deposits, infiltrated the eastern end of the polar dune sea, percolating through the dunes. Deposits of gypsum resulted from a combination of direct, in situ alteration of sulfide‐ and high‐calcium‐pyroxene‐bearing dunes and from formation of evaporitic gypsum crystals in the pore spaces of these dunes. This gypsum deposit formed in a unique local environment and is disconnected from sulfate‐forming events elsewhere on Mars which are thought to have occurred much earlier, during the late Noachian and Hesperian, by various means. Sulfates have not been discovered in any other collection of dunes on Mars.
Effect of missing data on performance of learning algorithms for hydrologic predictions: Implications to an imputation technique
Authors: Gill M. Kashif , Asefa Tirusew , Kaheil Yasir , McKee Mac
Published: July 2007

A common practice in preprocessing of data for use in hydrological modeling is to ignore observations with any missing variable values at any given time step, even if it is only one of the independent variables that is missing. In most cases, these rows of data are labeled incomplete and would not be used in either model building or subsequent model testing and verification. We argue that this is not necessarily an optimal approach for dealing with missing data because significant information could be lost when incomplete rows of data are discarded. Learning algorithms are affected by such problems more than physically based models because they rely heavily on data to learn the underlying input/output relationships of the systems being modeled. In this study, the extent of damage to the performance of learning algorithms due to missing data is explored in a field‐scale application. To do so, we employed two well‐known learning algorithms, namely artificial neural networks (ANNs) and support vector machines (SVMs) for short‐term prediction of groundwater levels at a well field. Performance comparison is made by subjecting these algorithms to various levels of missing data. In addition to understanding the relative strengths of these algorithms in dealing with missing data, an approach for filling the data gaps in the form of an imputation methodology is proposed and tested against observed data. The utility of the current approach is further demonstrated by analyzing model runs obtained with and without imputed data. It is shown that as the percentage of missing data increases, the forecasting accuracy of ANNs is compromised more than that of SVMs. However, ANNs also derive the greater benefit from the use of imputed data.
A method to estimate groundwater depletion from confining layers
Authors: Konikow L. F. , Neuzil C. E.
Published: July 2007

Although depletion of storage in low‐permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems, it is all too frequently overlooked or ignored. This makes effective management of groundwater resources difficult by masking how much water has been derived from storage and, in some cases, the total amount of water that has been extracted from an aquifer system. Analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known. In this paper we propose a simplified method for computing estimates of confining layer depletion, as well as procedures for approximating confining layer hydraulic conductivity (K) and specific storage (Ss) using geologic information. The latter makes the technique useful in developing countries and other settings where minimal data are available or when scoping calculations are needed. As such, our approach may be helpful for estimating the global transfer of groundwater to surface water. A test of the method on a synthetic system suggests that the computational errors will generally be small. Larger errors will probably result from inaccuracy in confining layer property estimates, but these may be no greater than errors in more sophisticated analyses. The technique is demonstrated by application to two aquifer systems: the Dakota artesian aquifer system in South Dakota and the coastal plain aquifer system in Virginia. In both cases, depletion from confining layers was substantially larger than depletion from the aquifers.
Error analysis of dynamical seasonal predictions of summer precipitation over the East Asian‐western Pacific region
Authors: Kang Hongwen , Park Chung‐Kyu
Published: July 2007

In the East Asian‐western Pacific (EAWP) region, six climate prediction models which are currently used in APEC Climate Center (APCC) Multi‐Model Ensemble (MME) prediction system show low skill in predicting summer precipitation. In order to diagnose the dominant error in the prediction, an error decomposition method is developed. Using this method, the total error is decomposed into three parts: errors due to conditional bias, unconditional bias and atmospheric internal processes (AIP). The bias‐error can be corrected while the AIP error cannot. It is found that the sum of both bias‐errors is about 3 to 20 times larger than the AIP error over the EAWP region for these models. This suggests that the AIP error is not the main cause for the loss of predictability, therefore there is potential to improve the predictions by correcting the bias‐errors.
A bivariate frequency analysis of extreme rainfall with implications for design
Authors: Kao Shih‐Chieh , Govindaraju Rao S.
Published: July 2007

Analysis of extreme rainfall events has conventionally been performed by prespecifying rainfall duration as a filter to abstract annual maximum rainfall depths as the only variable for analysis. However, this univariate approach does not account for dependence between rainfall properties. To characterize extreme rainfall events, a bivariate analysis is conducted in this study using hourly precipitation data from Indiana, USA. Samples of extreme rainfall events are chosen on the basis of three different criteria: annual maximum volume (AMV), annual maximum peak intensity (AMI), and annual maximum cumulative probability (AMP) based on empirical copulas. Rainfall characteristics, such as total depth, duration, and peak intensity are analyzed using copulas to describe the dependence structures between rainfall variables and to construct their joint distribution for extreme rainfall events. Results from the derived bivariate models are compared to those from conventional univariate analysis by computing the corresponding conditional distributions. Traditional univariate analysis seems to provide reasonable estimates of rainfall depths for durations greater than 10 hours. For shorter durations, a bivariate analysis with extreme events defined on the basis of AMP is recommended. The univariate analysis combined with Huff curves grossly underestimates peak intensities, and again AMP estimates are recommended. Results of this study have implications for current hydrologic design in that they provide better estimates of design rainfall.
Experimental demonstration of chaotic instability in biological nitrification
Authors: Graham David W , Knapp Charles W , Van Vleck Erik S , Bloor Katie , Lane Teresa B , Graham Christopher E
Published: July 2007

Biological nitrification (that is, NH3 → NO2− → NO3−) is a key reaction in the global nitrogen cycle (N-cycle); however, it is also known anecdotally to be unpredictable and sometimes fails inexplicably. Understanding the basis of unpredictability in nitrification is critical because the loss or impairment of this function might influence the balance of nitrogen in the environment and also has biotechnological implications. One explanation for unpredictability is the presence of chaotic behavior; however, proving such behavior from experimental data is not trivial, especially in a complex microbial community. Here, we show that chaotic behavior is central to stability in nitrification because of a fragile mutualistic relationship between ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), the two major guilds in nitrification. Three parallel chemostats containing mixed microbial communities were fed complex media for 207 days, and nitrification performance, and abundances of AOB, NOB, total bacteria and protozoa were quantified over time. Lyapunov exponent calculations, supported by surrogate data and other tests, showed that all guilds were sensitive to initial conditions, suggesting broad chaotic behavior. However, NOB were most unstable among guilds and displayed a different general pattern of instability. Further, NOB variability was maximized when AOB were most unstable, which resulted in erratic nitrification including significant NO2− accumulation. We conclude that nitrification is prone to chaotic behavior because of a fragile AOB–NOB mutualism, which must be considered in all systems that depend on this critical reaction.
Looking at the Beginnings: Enquiries about Emergence of Cognition in Evolution
Authors: Riofrio Walter
Published: July 2007

Trying to understand when and how the cognitive phenomena arise in evolution continues being a hard problem of confronting. One important task is to find the ways in which we will be able to arrive at those explanations that will enable us to understand how living beings put together perceived sensory information as well as how they represent it. In this presentation, we address some conceptual questions involved in the relationships between sensorial information perceived by brains and its representational capacities.
Attenuation by Butalbital of Capsaicin‐Induced C‐fos—like Immunoreactivity in Trigeminal Nucleus Caudalis
Authors: Cutrer F. Michael , Mitsikostas Dimos D. , Ayata Gamze , Sanchez del Rio Margarita
Published: July 2007

We examined the effects of butalbital (30, 100, and 1000 μg/kg) on the number of cells expressing c‐fos—like immunoreactivity (c‐fos—LI), a marker of neuronal activation, within lamina I, II0 of the trigeminal nucleus caudalis and the nucleus of the solitary tract 2 hours after the intracisternal injection of capsaicin (0.1 mL; 15.25 mg/mL) or vehicle in urethane‐anesthetized guinea pigs (N=45). Robust c‐fos—LI was observed within nuclei of cells in the trigeminal nucleus caudalis after capsaicin (329 ± 35). Butalbital dose‐dependently reduced the number of labeled cells to a maximum of 66% (1000 μg/kg intraperitoneally [IP], P<.01) in lamina I, II0 but not within area postrema, medial reticular nucleus, or the nucleus of the solitary tract. Pretreatment with bicuculline (30 μg/kg IP) blocked the effect of butalbital, thereby suggesting the importance of the GABAA receptor to activation involved in the transmission of nociceptive information. Our studies suggest the possibility that GABAA, receptors might provide an important therapeutic target in migraine and related headache disorders.
Chronic Daily Bilateral Headache Responsive to Indomethacin
Authors: Solomon Seymour , Newman Lawrence C.
Published: July 2007

Indomethacin is known to be specifically effective for chronic paroxysmal hemicrania, episodic paroxysmal hemicrania, and hemicrania continua. Different forms of idiopathic stabbing headaches have also been responsive to indomethacin, but less consistently than the others.

Two cases of indomethacin‐responsive headache are reported. One patient presented with what appeared to be new‐onset, chronic, daily, bilateral headache aggravated by coughing. Both the chronic daily headache and the exacerbations induced by coughing were suppressed with indomethacin therapy. The second patient experienced hemicrania continua responsive to indomethacin, and the response persisted even when the headache evolved into bilateral continuous pain.

There may be other idiopathic primary headache disorders that are peculiarly responsive to indomethacin. When any primary headache disorder does not respond to standard therapy, a brief therapeutic trial of indomethacin is warranted.
Addition by subtraction in coupled cluster theory. II. Equation-of-motion coupled cluster method for excited, ionized, and electron-attached states based on the nCC ground state wave function
Authors: Musiał Monika , Bartlett Rodney J.
Published: July 2007

New iterative double and triple excitation corrections to the equation-of-motion coupled cluster (EOM-CC) based upon the recently developed nCC methods [Bartlett and Musiał, J. Chem. Phys. 125, 204105–1 (2006)] are applied to excitation energies (EEs), ionization potentials (IPs), and electron affinities (EAs). The methods have been tested by the evaluation of the vertical EEs, IPs, and EAs for Ne, BH, CH2, H2O, N2, C2, CH+, CO, and C2H4 compared to full configuration interaction, EOM-CCSD, EOM-CCSDT, and experimental data.
Transient flow caused by a sudden impulse or twist applied to a sphere immersed in a viscous incompressible fluid
Authors: Felderhof B. U.
Published: July 2007

An analytic solution of the linearized Navier-Stokes equations is presented for the flow of an incompressible viscous fluid about a sphere suddenly set in motion by an impulse or twist. Mixed slip-stick boundary conditions are assumed to hold at the surface of the sphere. The transient flow pattern depends on the mass and moment of inertia of the sphere. The impulsive translational motion of the sphere generates an expanding vortex ring. Conservation of total momentum is discussed and the momentum of the fluid is expressed as a sum of a potential and a viscous contribution. Conservation of total angular momentum is verified in the case of rotational motion.
On the shear flow instability and its applications to multicomponent plasmas
Authors: Saleem H. , Vranjes J. , Poedts S.
Published: July 2007

The classic shear flow instability is discussed and, in particular, the effect of the cancellation of the contribution of the diamagnetic drift in the convective derivative of the polarization drift against the relevant collisionless stress tensor part. This cancellation shows that the shear flow instability in a nonuniform plasma is basically the drift wave instability. If ions are considered to be hot, the shear flow instability criterion is modified even in the homogeneous limit due to the contribution of collisionless ion stress tensor. A comparison of our results with the existing literature on this topic is presented. The shear flow instability criteria are also investigated for electron-positron-ion plasma and for dusty plasma. In a dusty plasma with negatively charged dust grains, the instability appears in the presence of a negative shear flow gradient.