bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameterresonanz in fastkanonischen Systemen
Authors: Starshinski W. M. , Beyreuther J.
Published: May 2007

Nach einer Methode von Jakubowitsch findet man Ungleichungen zur Bestimmung von Bereichen kinetischer Instabilität für ein lineares Differentialgleichungssystem mit (komplexen) periodischen Koeffizienten, die analytisch von einem kleinen Parameter ε abhängen. Für ε = 0 soll das Ausgangssystem in ein kanonisches System mit konstanten Koeffizienten übergehen. Als Anwendungsbeispiel werden Biegeschwingungen zweier koaxialer Wellen mit Schwungscheiben am Ende bei konstanten Drehzahlen untersucht.
Symmetrische Koppelkurven mit zwei Flachpunkten
Authors: Tesar D. , Wunderlich W.
Published: May 2007

Die Konstruktion von Gelenkvierecken, welche symmetrische Koppelkurven, mit zwei Flachpunkten erzeugen, wird auf ein kubisches Problem zurückgeführt und sowohl graphisch als auch rechnerisch gelöst. Gewisse Sonderfälle gestatten eine vereinfachte Behandlung.
Das d'Alembertsche Anfangswertproblem für Zylinderwellen
Authors: Heynatz J. T.
Published: May 2007

Für Zylinderwellen kleiner Amplitude wird eine Darstellung des d' Alembertschen Anfangswertproblems gegeben. Auf dem Wege über die Lösung zweier Abelscher Integralgleichungen und anschließender Integralvertauschungen gelangt man durch die Rückführung der auftretenden elliptischen Integrale auf vollständige Legendresche Normalformen zu einer dem ebenen und dem kugelsymmetrischen Fall entsprechenden Darstellung der linearisierten Potentialgleichung. Während man sich sonst häufig mit der Ausbreitung von Zylinderwellen beschäftigt, die durch eine auf der Zylinderachse als Funktion der Zeit gegebene Quelltätigkeit verursacht werden, handelt es sich hier um die Bestimmung von Strömungsfeldern aus Anfangswerten, die zu einer festen Zeit als Funktionen des Zylinderradius gegeben sind. Die Resultate dienen zur Berechnung der durch einen Drucksprung verursachten Strömung. Der Geschwindigkeitsverlauf und die Druckverteilung entsprechen qualitativ dem kugelsymmetrischen Fall. Es handelt sich um einfache Funktionen von elliptischen Normalintegralen erster, zweiter und dritter Gattung. Für die Abgeschlossenheit von Zylinderwellen unter verschiedenen Voraussetzungen werden Bedingungen aufgestellt.
Ein Verfahren der stochastischen Approximation
Authors: Bunke H.
Published: May 2007

Es wird ein Approximationsverfahren angegeben, mit dessen Hilfe eine gesuchte reelle Zahl auf Grund von Realisierungen gewisser zufälliger Variablen mit vorgegebener Genauigkeit angenähert werden kann.
Linearisierung des schwerebehafteten Gleitproblems
Authors: Stumpf H.
Published: May 2007

Es werden die Zusammenhänge zwischen Bodenform, Druckverteilung und Widerstand einer stationär über die ungestörte Wasseroberfläche bewegten Gleitfläche untersucht, wobei eine Trennung des Geschwindigkeitspotentials in einen von der Erdschwere unabhängigen sowie in einen von der Erdschwere abhängigen Anteil durchgeführt wird. Das schwerefreie Geschwindigkeitspotential, das den Gleitvorgang für unendlich große Froudesche Zahl beschreibt und das alle wesentlichen Irregularitäten des Gleitproblems beinhaltet, liefert die schwerefreie Form der Gleitfläche sowie Spritz‐ und induzierten Widerstand. Der den Schwereeinfluß darstellende Potentialanteil gestattet eine Berechnung der Änderung. die die Form der Druckfläche infolge Wirkung der Erdschwere erfährt und die für breite Gleitflächen und große Froudesche Zahl linearisiert werden kann. Hiermit ergibt sich für das schwerebehaftete Gleiten eine einfache Beziehung zwischen Druckverteilung und Bodenform, wobei man als dritte Widerstandskomponente einen der Erdschwere proportionalen Widerstand erhält.
Abwindkorrekturen für kreisrunde Windkanäle mit Bodenplatte
Authors: Pfeiffer F.
Published: May 2007

Für offene und geschlossene Windkanäle mit Bodenplatte wird ein Verfahren entwickelt, das den Einfluß der endlichen Strahlabmessungen auf die gemessenen aerodynamischen Beiwerte eines Tragflügels mit beliebiger Pfeilung, Streckung und Zuspitzung sowie beliebigem Bodenabstand zu berechnen gestattet.
Endliche elastische Verformungen
Authors: Vocke W.
Published: May 2007

Zur Beschreibung von elastischen Verformungen bis zu Werten von etwa 15% bringt die Berücksichtigung der quadratischen Glieder eine sehr gute Näherung. Es wird dabei das in diesem Bereich für viele Stoffe gültige lineare Realspannungs‐Dehnungs‐Gesetz verwendet.
Asymptotisches Verhalten der Lösungen der modizifierten van der Polschen Differentialgleichung
Authors: Maess G.
Published: May 2007

Die modifizierte van der Polsche Differentialgleichung (1) läßt sich durch die Transformation x2 sgn x = v in eine stückweise lineare Differentialgleichung überführen. Für deren allgemeine Lösung (6) wird die asymptotische Darstellung (μ → ∞) berechnet und daraus die asymptotische Entwicklung der Amplitude a der periodischen Lösung von (1) bestimmt.
Significance of CD44 Expression in Gastrointestinal Stromal Tumors in Relation to Disease Progression and Survival
Authors: Hsu Kai‐Hsi , Tsai Hung‐Wen , Shan Yan‐Shen , Lin Pin‐Wen
Published: May 2007

Background

CD44 is a transmembrane glycoprotein belonging to the cell‐adhesion molecule family. It has been identified as being involved in tumor progression and metastasis, and its expression has been found to be of prognostic significance in several human malignancies. The aim of this study was to assess CD44 expression in gastrointestinal stromal tumors (GISTs), the most common mesenchymal tumor of the gastrointestinal tract.

Methods

Between January 1995 and March 2006, 92 patients undergoing surgical resection for GIST in National Cheng Kung University Hospital were evaluated. To study the significance of CD44 expression, immunohistochemical staining of CD44 in tumor specimens was performed, and the clinicopathological information of patients was reviewed.

Results

Fifty‐nine of 81 patients (73%) showed positive CD44 expression. Loss of CD44 expression was associated with disease progression (p = 0.019). Kaplan‐Meier analysis revealed better progression‐free survival among patients with strong CD44 expression (++ and +++) (p = 0.034), absence of disease progression (p < 0.001), and lower risk, according to National Institutes of Health (NIH) Consensus Criteria for GIST risk stratification (p = 0.003). Multivariate analysis demonstrated that high‐risk status was the only independent risk factor for disease progression and the only independent predictor for a poor progression‐free survival (p = 0.023 and 0.045, respectively).

Conclusions

It is demonstrated that high‐risk status by NIH criteria is significantly associated with disease progression and poor progression‐free survival in GIST.
Humangenetische Beratung
Authors: Zerres K. , Grimm T. , Rudnik-Schöneborn S.
Published: May 2007

Mit den wachsenden Möglichkeiten der genetischen Diagnostik gewinnt die humangenetische Beratung in der klinischen Medizin an Bedeutung. Sie soll Ratsuchenden helfen, Fragen im Zusammenhang mit einer evtl. erblich bedingten Krankheit oder Entwicklungsstörung zu beantworten und mögliche Probleme zu lösen. Wichtige Anlässe einer solchen Beratung sind u. a. eine Erkrankung oder Entwicklungsstörung eines Kindes, eines Ratsuchenden oder Verwandten, so genannte altersbedingte Risiken, eine Blutsverwandtschaft, habituelle Aborte, Totgeburten, Fertilitätsstörungen sowie die Sorge vor möglichen teratogenen oder mutagenen Risiken. Ergebnisse der pränatalen, der prädiktiven sowie der Heterozygotendiagnostik können eine Tragweite besitzen, die sich von der Diagnostik im Rahmen der Abklärung einer klinischen Symptomatik unterscheidet. Die Entscheidung hierzu sollte nach einer vorangegangen humangenetischen Beratung „informiert“ erfolgen. Der Beitrag informiert über die Ziele, die Durchführung und mögliche Anlässe einer humangenetischen Beratung.
NONHOLONOMIC SIMPLE D-MODULES FROM SIMPLE DERIVATIONS
Authors: COUTINHO S. C.
Published: May 2007

We give new examples of affine sufaces whose rings of coordinates are d-simple and use these examples to construct simple nonholonomic D-modules over these surfaces.
ISOPERIMETRIC FUNCTIONS OF GROUPS ACTING ON Lδ-SPACES
Authors: CORSON JON , RYANG DOHYOUNG
Published: May 2007

A finitely generated group acting properly, cocompactly, and by isometries on an Lδ-metric space is finitely presented and has a sub-cubic isoperimetric function.
BLOCKS WITH A QUATERNION DEFECT GROUP OVER A 2-ADIC RING: THE CASEÃ4
Authors: HOLM THORSTEN , KESSAR RADHA , LINCKELMANN MARKUS
Published: May 2007

Except for blocks with a cyclic or Klein four defect group, it is not known in general whether the Morita equivalence class of a block algebra over a field of prime characteristic determines that of the corresponding block algebra over ap-adic ring. We prove this to be the case when the defect group is quaternion of order 8 and the block algebra over an algebraically closed fieldkof characteristic 2 is Morita equivalent tokÃ4. The main ingredients are Erdmann's classification of tame blocks [6] and work of Cabanes and Picaronny [4, 5] on perfect isometries between tame blocks.
ON BRANNAN'S COEFFICIENT CONJECTURE AND APPLICATIONS
Authors: RUSCHEWEYH STEPHAN , SALINAS LUIS
Published: May 2007

D. Brannan's conjecture says that for 0 <α,β≤1, |x|=1, and n∈N one has |A2n−1(α,β,x)|≤|A2n−1(α,β,1)|, where

We prove this for the case α=β, and also prove a differentiated version of the Brannan conjecture. This has applications to estimates for Gegenbauer polynomials and also to coefficient estimates for univalent functions in the unit disk that are ‘starlike with respect to a boundary point’. The latter application has previously been conjectured by H. Silverman and E. Silvia. The proofs make use of various properties of the Gauss hypergeometric function.
COMMON SOURCE OF NUMEROUS THETA FUNCTION IDENTITIES
Authors: WENCHANG CHU
Published: May 2007

Motivated by the recent work due to Warnaar (2005), two new and elementary proofs are presented for a very useful q-difference equation on eight shifted factorials of infinite order. As the common source of theta function identities, this q-difference equation is systematically explored to review old and establish new identities on Ramanujan's partition functions. Most of the identities obtained can be interpreted in terms of theorems on classical partitions.
LINEAR ASYMPTOTIC BEHAVIOUR OF SECOND ORDER ORDINARY DIFFERENTIAL EQUATIONS
Authors: EHRNSTRÖM MATS
Published: May 2007

We study the semilinear differential equation u″ + F(t,u,u′)=0 on a half-line. Under different growth conditions on the function F, equations with globally defined solutions asymptotic to lines are characterized. Both fixed initial data and fixed asymptote are considered.
URSCM OR BI-URSCM FOR p-ADIC ANALYTIC OR MEROMORPHIC FUNCTIONS INSIDE A DISK
Authors: BOUTABAA ABDELBAKI , ESCASSUT ALAIN
Published: May 2007

Let K be an algebraically closed field of characteristic zero, complete with respect to an ultrametric absolute value. In a previous paper, we had found URSCM of 7 points for the whole set of unbounded analytic functions inside an open disk. Here we show the existence of URSCM of 5 points for the same set of functions. We notice a characterization of BI-URSCM of 4 points (and infinity) for meromorphic functions in K and can find BI-URSCM for unbounded meromorphic functions with 9 points (and infinity). The method is based on the p-Adic Nevanlinna Second Main Theorem on 3 Small Functions applied to unbounded analytic and meromorphic functions inside an open disk and we show a more general result based upon the hypothesis of a finite symmetric difference on sets of zeros, counting multiplicities.
The hydrodynamic structure of unstable cellular detonations
Authors: RADULESCU MATEI I. , SHARPE GARY J. , LAW CHUNG K. , LEE JOHN H. S.
Published: May 2007

The study analyses the cellular reaction zone structure of unstable methane–oxygen detonations, which are characterized by large hydrodynamic fluctuations and unreacted pockets with a fine structure. Complementary series of experiments and numerical simulations are presented, which illustrate the important role of hydrodynamic instabilities and diffusive phenomena in dictating the global reaction rate in detonations. The quantitative comparison between experiment and numerics also permits identification of the current limitations of numerical simulations in capturing these effects. Simulations are also performed for parameters corresponding to weakly unstable cellular detonations, which are used for comparison and validation. The numerical and experimental results are used to guide the formulation of a stochastic steady one-dimensional representation for such detonation waves. The numerically obtained flow fields were Favre-averaged in time and space. The resulting one-dimensional profiles for the mean values and fluctuations reveal the two important length scales, the first being associated with the chemical exothermicity and the second (the ‘hydrodynamic thickness’) with the slower dissipation of the hydrodynamic fluctuations, which govern the location of the average sonic surface. This second length scale is found to be much longer than that predicted by one-dimensional reaction zone calculations.
Theory of vaporization of a rigid spherical droplet in slowly varying rectilinear flow at low Reynolds numbers
Authors: DEL ÁLAMO G. , WILLIAMS F. A.
Published: May 2007

The vaporization of a droplet in rectilinear motion relative to a stagnant gaseous atmosphere is addressed for the limit of low Reynolds numbers and slow variation of the droplet velocity. Approximations are introduced that enable a formal asymptotic analysis to be performed with a minimum of complexity. It is shown that, under the conditions addressed, there is an inner region in the vicinity of the droplet within which the flow is nearly quasi-steady except during short periods of time when the acceleration changes abruptly, and there is a fully time-dependent outer region in which departures of velocities and temperatures from those of the ambient medium are small. Matched asymptotic expansions, followed by a Green's function analysis of the outer region enable expressions to be obtained for the velocity and temperature fields and for the droplet drag and vaporization rate. The results are applied to problems in which the droplet experiences constant acceleration, constant deceleration and oscillatory motion. The results, which identify dependences on the Prandtl number and the transfer number, are intended to be compared with experimental measurements on droplet behaviours in time-varying flows.
Optimal control of mixing in Stokes fluid flows
Authors: MATHEW GEORGE , MEZIĆ IGOR , GRIVOPOULOS SYMEON , VAIDYA UMESH , PETZOLD LINDA
Published: May 2007

Motivated by the problem of microfluidic mixing, optimal control of advective mixing in Stokes fluid flows is considered. The velocity field is assumed to be induced by a finite set of spatially distributed force fields that can be modulated arbitrarily with time, and a passive material is advected by the flow. To quantify the degree of mixedness of a density field, we use a Sobolev space norm of negative index. We frame a finite-time optimal control problem for which we aim to find the modulation that achieves the best mixing for a fixed value of the action (the time integral of the kinetic energy of the fluid body) per unit mass. We derive the first-order necessary conditions for optimality that can be expressed as a two-point boundary value problem (TPBVP) and discuss some elementary properties that the optimal controls must satisfy. A conjugate gradient descent method is used to solve the optimal control problem and we present numerical results for two problems involving arrays of vortices. A comparison of the mixing performance shows that optimal aperiodic inputs give better results than sinusoidal inputs with the same energy.
A wave propagation model of blood flow in large vessels using an approximate velocity profile function
Authors: BESSEMS DAVID , RUTTEN MARCEL , VAN DE VOSSE FRANS
Published: May 2007

Lumped-parameter models (zero-dimensional) and wave-propagation models (one-dimensional) for pressure and flow in large vessels, as well as fully three-dimensional fluid–structure interaction models for pressure and velocity, can contribute valuably to answering physiological and patho-physiological questions that arise in the diagnostics and treatment of cardiovascular diseases. Lumped-parameter models are of importance mainly for the modelling of the complete cardiovascular system but provide little detail on local pressure and flow wave phenomena. Fully three-dimensional fluid–structure interaction models consume a large amount of computer time and must be provided with suitable boundary conditions that are often not known. One-dimensional wave-propagation models in the frequency and time domain are well suited to obtaining clinically relevant information on local pressure and flow waves travelling through the arterial system. They can also be used to provide boundary conditions for fully three-dimensional models, provided that they are defined in, or transferred to, the time domain.

Most of the one-dimensional wave propagation models in the time domain described in the literature assume velocity profiles and therefore frictional forces to be in phase with the flow, whereas from exact solutions in the frequency domain a phase difference between the flow and the wall shear stress is known to exist. In this study an approximate velocity profile function more suitable for one-dimensional wave propagation is introduced and evaluated. It will be shown that this profile function provides first-order approximations for the wall shear stress and the nonlinear term in the momentum equation, as a function of local flow and pressure gradient in the time domain. The convective term as well as the approximate friction term are compared to their counterparts obtained from Womersley profiles and show good agreement in the complete range of the Womersley parameter α. In the limiting cases, for Womersley parameters α → 0 and α → ∞, they completely coincide. It is shown that in one-dimensional wave propagation, the friction term based on the newly introduced approximate profile function is important when considering pressure and flow wave propagation in intermediate-sized vessels.
Falling clouds of particles in viscous fluids
Authors: METZGER BLOEN , NICOLAS MAXIME , GUAZZELLI ÉLISABETH
Published: May 2007

We have investigated both experimentally and numerically the time evolution of clouds of particles settling under the action of gravity in an otherwise pure liquid at low Reynolds numbers. We have found that an initially spherical cloud containing enough particles is unstable. It slowly evolves into a torus which breaks up into secondary droplets which deform into tori themselves in a repeating cascade. Owing to the fluctuations in velocity of the interacting particles, some particles escape from the cloud toroidal circulation and form a vertical tail. This creates a particle deficit near the vertical axis of the cloud and helps in producing the torus which eventually expands. The rate at which particles leak from the cloud is influenced by this change of shape. The evolution toward the torus shape and the subsequent evolution is a robust feature. The nature of the breakup of the torus is found to be intrinsic to the flow created by the particles when the torus aspect ratio reaches a critical value. Movies are available with the online version of the paper.
Buoyancy-driven crack propagation: the limit of large fracture toughness
Authors: ROPER S. M. , LISTER J. R.
Published: May 2007

We study steady vertical propagation of a crack filled with buoyant viscous fluid through an elastic solid with large effective fracture toughness. For a crack fed by a constant flux Q, a non-dimensional fracture toughness K=Kc/(3μQm3/2)1/4 describes the relative magnitudes of resistance to fracture and resistance to viscous flow, where Kc is the dimensional fracture toughness, μ the fluid viscosity and m the elastic modulus. Even in the limit K ≫ 1, the rate of propagation is determined by viscous effects. In this limit the large fracture toughness requires the fluid behind the crack tip to form a large teardrop-shaped head of length O(K2/3) and width O(K4/3), which is fed by a much narrower tail. In the head, buoyancy is balanced by a hydrostatic pressure gradient with the viscous pressure gradient negligible except at the tip; in the tail, buoyancy is balanced by viscosity with elasticity also playing a role in a region within O(K2/3) of the head. A narrow matching region of length O(K−2/5) and width O(K−4/15), termed the neck, connects the head and the tail. Scalings and asymptotic solutions for the three regions are derived and compared with full numerical solutions for K ≤ 3600 by analysing the integro-differential equation that couples lubrication flow in the crack to the elastic pressure gradient. Time-dependent numerical solutions for buoyancy-driven propagation of a constant-volume crack show a quasi-steady head and neck structure with a propagation rate that decreases like t−2/3 due to the dynamics of viscous flow in the draining tail.
The rough-wall turbulent boundary layer from the hydraulically smooth to the fully rough regime
Authors: SCHULTZ M. P. , FLACK K. A.
Published: May 2007

Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a three-dimensional rough surface geometrically similar to the honed pipe roughness used by Shockling, Allen & Smits (J. Fluid Mech. vol. 564, 2006, p. 267). The present work covers a wide Reynolds-number range (Reθ = 2180–27 100), spanning the hydraulically smooth to the fully rough flow regimes for a single surface, while maintaining a roughness height that is a small fraction of the boundary-layer thickness. In this investigation, the root-mean-square roughness height was at least three orders of magnitude smaller than the boundary-layer thickness, and the Kármán number (δ+), typifying the ratio of the largest to the smallest turbulent scales in the flow, was as high as 10100. The mean velocity profiles for the rough and smooth walls show remarkable similarity in the outer layer using velocity-defect scaling. The Reynolds stresses and higher-order turbulence statistics also show excellent agreement in the outer layer. The results lend strong support to the concept of outer layer similarity for rough walls in which there is a large separation between the roughness length scale and the largest turbulence scales in the flow.
The structure of shock waves as a test of Brenner's modifications to the Navier–Stokes equations
Authors: GREENSHIELDS CHRISTOPHER J. , REESE JASON M.
Published: May 2007

Brenner (Physica A, vol. 349, 2005a, b, pp. 11, 60) has recently proposed modifications to the Navier–Stokes equations that are based on theoretical arguments but supported only by experiments having a fairly limited range. These modifications relate to a diffusion of fluid volume that would be significant for flows with high density gradients. So the viscous structure of shock waves in gases should provide an excellent test case for this new model. In this paper we detail the shock structure problem and propose exponents for the gas viscosity–temperature relation based on empirical viscosity data that is independent of shock experiments. We then simulate monatomic gas shocks in the range Mach 1.0–12.0 using the Navier–Stokes equations, both with and without Brenner's modifications. Initial simulations showed that Brenner's modifications display unphysical behaviour when the coefficient of volume diffusion exceeds the kinematic viscosity. Our subsequent analyses attribute this behaviour to both an instability to temporal disturbances and a spurious phase velocity–frequency relationship. On equating the volume diffusivity to the kinematic viscosity, however, we find the results with Brenner's modifications are significantly better than those of the standard Navier–Stokes equations, and broadly similar to those from the family of extended hydrodynamic models that includes the Burnett equations. Brenner's modifications add only two terms to the Navier–Stokes equations, and the numerical implementation is much simpler than conventional extended hydrodynamic models, particularly in respect of boundary conditions. We recommend further investigation and testing on a number of different benchmark non-equilibrium flow cases.
Flow features resulting from shock wave impact on a cylindrical cavity
Authors: SKEWS BERIC W. , KLEINE HARALD
Published: May 2007

The complex flow features that arise from the impact of a shock wave on a concave cavity are determined by means of high-speed video photography. Besides additional information on features that have previously been encountered in specific studies, such as those relating to shock wave reflection from a cylindrical wall and those associated with shock wave focusing, a number of new features become apparent when the interaction is studied over longer times using time-resolved imaging. The most notable of these new features occurs when two strong shear layers meet that have been generated earlier in the motion. Two jets can be formed, one facing forward and the other backward, with the first one folding back on itself. The shear layers themselves develop a Kelvin–Helmholtz instability which can be triggered by interaction with weak shear layers developed earlier in the motion. Movies are available with the online version of the paper.
Mycocalicium llimonae, a new species from the Iberian Peninsula
Authors: MUÑIZ Diana , HLADUN Néstor L.
Published: May 2007

The new species, Mycocalicium llimonae, is described based on specimens collected from cones of Pinus halepensis in the west of the Iberian Peninsula. The new taxon is compared with the other species of the genus Mycocalicium in the Iberian Peninsula, particularly Mycocalicium subtile, and also with other genera in the Mycocaliciaceae.
Corticifraga santessonii and C. chugachiana (Lecanoromycetes, Ascomycota), new species of lichenicolous fungi from the Holarctic
Authors: ZHURBENKO Mikhail
Published: May 2007

Two new lichenicolous ascomycetes, Corticifraga santessonii and C. chugachiana, are described from Lobaria and Nephroma species. The new species are readily distinguished by narrow ascospores and are known from the USA, Canada and Russia. A Table with the distinguishing characteristics of all known Corticifraga species is presented.
A new species of Graphis (Graphidaceae) from India
Authors: JAGADEESH RAM T. A. M. , SINHA G. P. , SINGH K. P.
Published: May 2007

A new species of lichen, Graphis sundarbanensis, is described from India. It is characterized by ascomata with a pruinose wide-open disc, a laterally carbonized apically convergent exciple and 6–8 locular halonate ascospores.
New or interesting saxicolous Pertusaria species (Pertusariales: Pertusariaceae) from Zimbabwe
Authors: MESSUTI María Inés , BECKER Uwe , ARCHER Alan W.
Published: May 2007

%The new saxicolous species P. clercii Messuti & A. W. Archer is described. The following two taxa are reported for the first time from Africa: P. petrophyes C. Knight and P. subventosa var. deficiens A. W. Archer & Elix. A brief description of each species is given together with notes on their chemistry, distribution, ecology and taxonomy.
Predicting the potential spatial distributions of epiphytic lichen species at the landscape scale
Authors: BOLLIGER Janine , BERGAMINI Ariel , STOFER Silvia , KIENAST Felix , SCHEIDEGGER Christoph
Published: May 2007

The potential spatial distributions of six epiphytic lichen species were assessed in Switzerland (41 000 km2) as a function of various key climatic drivers and forest types using logistic regression models. Cetrelia cetrarioides is ‘near threatened’, Lobaria pulmonaria is ‘vulnerable’, and Graphis scripta, Hypogymnia physodes, Lecanora cadubriae, Letharia vulpina are not endangered according to the Red List assessment based on IUCN criteria. Lichen presence and absence were derived from the SwissLichens database that contains spatially explicit information on both species presence and absence.

The spatial lichen niches are predicted with R2 values between 0·5 and 0·75 and AUC values between 0·63 and 0·94. Model evaluation shows that the models perform well.

Lichenologists reviewed the spatial predictions of lichen species on the basis of their expert knowledge and concluded that parsimonious regression models may suffice for successful prediction of the potential spatial niche distributions of epiphytic lichen species.
The putative role of fumarprotocetraric acid in the manganese tolerance of the lichen Lecanora conizaeoides
Authors: Hauck Markus , Huneck Siegfried
Published: May 2007

Hauck & Huneck (2007) and Hauck et al. (2007) established that lichen secondary chemistry is related to metal absorption in the apoplast of lichens. Depsidones occurring in the medulla of the Mn2+ and Cu2+-sensitive epiphytic lichen Hypogymnia physodes were found to reduce the absorption of Mn2+ and Cu2+ at cation exchange sites (Hauck & Huneck 2007). Several lichen substances, belonging to the depsidones, depsides, anthraquinones, or pulvinic acid derivatives, are known to absorb Fe3+ (Engstrom et al. 1980; Hauck et al. 2007). Occurrence of such lichen substances in lichens of Fe-poor sites, but rarity in lichens from Fe-rich sites suggests that they promote the intracellular uptake of Fe3+ (Hauck et al. 2007). In Acarosporion sinopicae lichens specialized on Fe-rich rock and slag, only two efficient Fe3+ absorbers are known, viz. the depsidone norstictic acid and the pulvinic acid derivative rhizocarpic acid. Their occurrence in Acarosporion sinopicae lichens is attributed to the fact that they reduce the absorption of Fe2+ at cation exchange sites despite their high affinity to Fe3+ (Hauck et al. 2007). The observations by Engstrom et al. (1980), Hauck & Huneck (2007) and Hauck et al. (2007), which were made in experiments with isolated lichen substances, suggest that these secondary metabolites control metal homeostasis in lichens by reducing the absorption of selected metal ions in the apoplast and by promoting the uptake of Fe3+.
Lecidea grisella sympatric with Lecidea fuscoatra, differing in its rimose instead of areolate thallus
Authors: Aptroot André , van Herk C. M. (Kok)
Published: May 2007

Lecidea fuscoatra (L.) Ach. is one of the earliest lichen species described, and is very common and widespread in Europe. Lecidea grisella Flörke, described from Germany, was kept separate at species level in many floras until the 1950s. In recent lichen floras, however, and in the most recent key to the genus (Hertel 1995), L. grisella is no longer accepted at species level, although it is keyed out and recognized by Hertel as L. fuscoatra var. grisella (Floerke) Nyl. The main difference is usually reported to be the thallus colour; brown and shiny in L. fuscoatra, grey and opaque in L. grisella. Some authors, for example Hertel (1995) and Wirth (1995), report that the two taxa have different habitat preferences: L. fuscoatra occurring mainly on acid substrata, while L. grisella is reported to prefer more neutral, often dust-impregnated rock and to be common on roof tiles.
Content of secondary compounds depends on thallus size in the foliose lichen Lobaria pulmonaria
Authors: ASPLUND Johan , GAUSLAA Yngvar
Published: May 2007

Thalli of Lobaria pulmonaria of different sizes were collected from the trunks of two specimens of Populus tremula. The secondary lichen compounds, stictic, constictic, norstictic, peristictic, cryptostictic and methyl stictic acid were quantified by HPLC and ranked in order of decreasing concentration. There was a highly significant positive correlation between thallus size and the total concentration of secondary compounds, as well as the total content per unit area for specimens from the two sampled trees. According to hypotheses inferring a herbivore deterrent role of secondary lichen compounds, small, juvenile thalli should be more susceptible to herbivores than larger thalli. Thus herbivory might limit survival of young specimens in habitats rich in lichen-feeding molluscs and thereby reduce reproductive success.
Bacidia coprodes—resurrecting a misinterpreted species
Authors: LLOP Esteve , EKMAN Stefan
Published: May 2007

Bacidia coprodes (Körb.) Lettau, until now treated as a synonym of Bacidia trachona (Ach.) Lettau, is resurrected. Morphological, chemical and ecological characteristics place this species close to Toninia in the Ramalinaceae, but we retain it in Bacidia because of uncertainties in the generic taxonomy of this family. Bacidia coprodes is fairly widespread on calcareous and enriched siliceous rock in Europe and eastern North America. In North America the species has also been known under the synonyms Bacidia granosa (Tuck.) Zahlbr. (basionym: Lecidea granosa Tuck.) and Bacidia pammellii (Fink) Zahlbr. (basionym: Bilimbia pammellii Fink). Morphological and chemical features, together with molecular data, suggest that B. trachona does not belong to Bacidia, but rather in the Pilocarpaceae.
New evidence corroborates population differentiation in Xanthoria parietina
Authors: LINDBLOM Louise , EKMAN Stefan
Published: May 2007

In order to examine genetic variation and population structure of the widespread lichen-forming ascomycete Xanthoria parietina from similar habitats, but different sites in Scandinavia, we investigated seven populations in Scania, southernmost Sweden, and compared the results with a corresponding study on Storfosna, central Norway. Sequence variations of the nuclear ribosomal DNA were used as molecular markers, for both a part of the IGS region and the complete ITS1-5.8S-ITS2 region. The amount of genetic variability observed was comparable in the two investigations. Divergence between populations in different habitats found in the previous study was also present in this study. Xanthoria parietina is genetically differentiated between habitats with no evidence of restricted gene flow between populations in the same habitat at the present spatial scale, at least at sites along the coast of Scandinavia. Differentiation between habitats is considerable at both study sites, which we attribute to restricted gene flow between habitats, i.e. habitat isolation.
The Genesis of the Civilian
Authors: ALEXANDER AMANDA
Published: May 2007

This paper argues that the concept of the civilian is a specific way of viewing non-combatants that can be traced to the First World War. Before the war, non-combatants were seen by the law and the prevailing culture as citizens. The citizen was potentially and probably aggressive, bound to the fate of his or her state and, therefore, granted only minimal protection by law. The war, however, brought technological changes and a propaganda effort that transformed these citizens into a civilian population. Civilians were essential to the war effort, which meant that they were a target. Yet, at the same time, they were feminized, described as vulnerable and deserving of protection. This cultural shift influenced the way in which the laws of war were understood, leading to the replacement of the traditional categories of law with a military/civilian distinction in the 1923 Hague Draft Rules of Aerial Warfare. In this way the concept of the civilian entered international law.
The Ambivalences of Power: Launching the American Journal of International Law in an Era of Empire and Globalization
Authors: LANDAUER CARL
Published: May 2007

This article uses the first issue of the American Journal of International Law, one hundred years after its creation in 1907, to analyse the state of American international legal thought following the acquisition of Pacific and Caribbean island territories in the Spanish–American War and the creation of a new international identity. Traditionally, the American Society of International Law (of which the journal was the organ) has been placed in the context of the US peace movement. However, both the society and the journal were led by individuals occupying major positions in the administration of Theodore Roosevelt and earlier administrations, including the sitting and a former secretary of war. The society and its journal were vehicles of the US foreign policy establishment. Despite a mixture of imperialists and anti-imperialists, a cultural coherence is discernable in the journal's pages. In essence, the journal can be placed within what the article calls the genteel tradition of US international law, involving an effort at educating the public away from over-excitement, adopting science in the newly professionalized administrative state, and advocating an arbitrational model of legal ordering to promote international peace.
Non-proliferation Law and the United Nations System: Resolution 1540 and the Limits of the Power of the Security Council
Authors: JOYNER DANIEL H.
Published: May 2007

This article argues that in passing Resolution 1540, the UN Security Council has confused the proper scope of its enforcement powers under Chapter VII with the proper scope of its long unused, limited, lawmaking powers under Article 26. It has thereby taken to itself by unilateral exercise of its Chapter VII powers a role which, under the Charter system, it is to share with both the General Assembly, in the exercise of its Article 11(1) powers, and the general membership of the United Nations, to whom it is directed under Article 26 to submit proposals for the creation of new international laws in the area of weapons proliferation.
Theoretical modeling of convection II. Reynolds Stress Model
Authors: Canuto V. M.
Published: May 2007

The Reynolds Stress Model (RSM) yields the dynamic equations for the second-order moments (e.g., heat fluxes) needed in the equations for the mean variables (e.g., mean temperature). The RSM equations are in general time dependent and non-local. We first discuss the “buoyancy only” case and the tests of the non-local model against a variety of data. We also “plumenize” the model in order to exhibit the up-down flows that characterize convection so as to show that a non-local RSM is fully equipped to account for the “plume aspect” of buoyant flows. Next, we extend the RSM to account for stable and/or unstable stratification and shear, a formalism that is needed to describe the overshooting region contributed by differentail rotation. We conclude by discussing the equation for the dissipation of turbulent kinetic energy which plays a key role in any RSM.
Challenges to the theory of solar convection
Authors: Cattaneo F.
Published: May 2007

Turbulent convection carries most of the solar luminosity from the stable radiative interior to the visible surface over a substantial fraction of the solar radius. The turbulent motions are highly nonlinear displaying activity on several spatial and temporal scales. The effects of these motions are to redistribute angular momentum, mix light elements, excite gravity waves and power magnetic activity. In this talk, I shall review some of the recent efforts, mostly based on numerical simulations, to model turbulent convection spanning multiple scale heights. I will discuss what we have learnt about the nature of convective transport, and what the relevant timescales are on which convection operates.
Radiative hydrodynamics models of stellar convection
Authors: Steffen Matthias
Published: May 2007

In the quest for a better theoretical understanding of the dynamical processes operating in stellar envelopes, increasingly more realistic hydrodynamical models of stellar convection have been developed over the last 25 years. Based on 3D state-of-the-art simulations performed recently with the radiation hydrodynamics code CO5BOLD, we review the present status of hydrodynamical modeling of stellar surface convection and demonstrate the basic differences between 3D hydrodynamical models and 1D ‘classical’ hydrostatic atmospheres where convection is treated by the mixing-length theory. We briefly discuss some of the many possible applications across the Hertzsprung-Russell diagram, including spectroscopic abundance determinations using 3D stellar atmospheres, particularly with regard to the much debated question of the solar oxygen abundance.
Dynamic models of the sun from the convection zone to the chromosphere
Authors: Wedemeyer-Böhm Sven
Published: May 2007

The chromosphere in internetwork regions of the quiet Sun was regarded as a static and homogeneous layer for a long time. Thanks to advances in observations and numerical modelling, the wave nature of these atmospheric regions received increasing attention during the last decade. Recent three-dimensional radiation magnetohydrodynamic simulations with CO5BOLD feature the chromosphere of internetwork regions as a dynamic and intermittent phenomenon. It is a direct product of interacting waves that form a mesh-like pattern of hot shock fronts and cool post-shock regions. The waves are excited self-consistently at the top of the convection zone. In the middle chromosphere above an average height of 1000 km, plasma beta gets larger than one and magnetic fields become more important. The model chromosphere exhibits a magnetic field that is much more homogeneous than in the layers below and evolves much faster. That includes fast propagating (MHD) waves. Further improvements of the simulations like time-dependent hydrogen ionisation are currently in progress. This class of models is capable of explaining apparently contradicting diagnostics such as carbon monoxide and UV emission at the same time.
3-D hydrodynamic simulations of convection in A stars
Authors: Kochukhov O. , Freytag B. , Piskunov N. , Steffen M.
Published: May 2007

Broadening and asymmetry of spectral lines in slowly rotating late A-type stars provide evidence for high-amplitude convective motions. The properties of turbulence observed in the A-star atmospheres are not understood theoretically and contradict results of previous numerical simulations of convection. Here we describe an ongoing effort to understand the puzzling convection signatures of A stars with the help of 3-D hydrodynamic simulations. Our approach combines realistic spectrum synthesis and non-grey hydrodynamic models computed with the CO5BOLD code. We discuss these theoretical predictions and confront them with high-resolution spectra of A stars. Our models have, for the first time, succeeded in reproducing the observed profiles of weak spectral lines without introducing fudge broadening parameters.
Coherent structures in granulation convection and their importance for higher order closure models
Authors: Kupka F. , Robinson F. J.
Published: May 2007

We use numerical simulations of granulation in the Sun and a K dwarf to study the effects of coherent structures on higher order moments. The latter need to be calculated in non-local Reynolds stress models of turbulent convection. Models that explicitly account for the asymmetry between up- and downflows as well as hot and cold drafts provide a substantial improvement over traditional ones, such as the quasi-normal approximation, which is only able to provide order of magnitude estimates for this type of flow.
Reynolds stress models of convection in convective cores
Authors: Roxburgh Ian W , Kupka Friedrich
Published: May 2007

We investigate the properties of non-local Reynolds stress models of turbulent convection in a spherical geometry. Regularity at the centre r=0 places constraints on the behaviour of 3rd order moments. Some of the down-gradient and algebraic closure models have inconsistent behaviour at r=0. A combination of down-gradient and algebraic closures gives a consistent prescription that can be used to model convection in stellar cores.
Probing Reynolds stress models of convection with numerical simulations: I. Overall properties: fluxes, mean profiles
Authors: Kupka F. , Muthsam H. J.
Published: May 2007

We introduce an extended 3D numerical simulation study of Reynolds stress models of stellar convection and probe fluxes as well as mean temperature gradient profiles.
Probing Reynolds stress models of convection with numerical simulations: II. Non-locality and third order moments.
Authors: Kupka F. , Muthsam H. J.
Published: May 2007

We provide results from an extended numerical simulation study of Reynolds stress models of stellar convection and probe the modelling of third order moments and non-locality.
Probing Reynolds stress models of convection with numerical simulations: III. Compressibility modelling and dissipation
Authors: Kupka F. , Muthsam H. J.
Published: May 2007

We provide results from an extended 3D numerical simulation study of Reynolds stress models of stellar convection and probe the modelling of compressibility, pressure fluctuations, and dissipation of turbulent kinetic energy.
Some open questions concerning the modelling of non-locality in Reynolds stress type models of stellar convection.
Authors: Kupka F.
Published: May 2007

We discuss some benefits and pitfalls when combining conceptually different types of closure approximations into complete Reynolds stress models of stellar convection.
The impact of non grey atmospheric treatment and convective modelling on the solar structure
Authors: Penza Valentina , Ventura Paolo
Published: May 2007

The comparison between the observed and theoretical p-mode oscillation frequencies of many orders and degrees allows a detailed determination of the internal solar structure (Christensen-Dalsgaard et al. 1996). The most recent analysis shows that one source of error in the modern description of the Sun is located in the convective layers close to the surface, in the superadiabatic region (Gabriel 1994).
Mixing length model of convection in stellar cores
Authors: Roxburgh Ian W , Kupka Friedrich
Published: May 2007

The standard mixing length model of convection is ill behaved at the centre of a star since the pressure scale height Hp=P/(ρg)→∞ as r→0, and the convective flux remains non zero at r=0. We propose a modifcation of this model of convection that has the correct behaviour in the central regions of a star and smoothly changes to the standard MLT away from the centre.
Convection and the solar abundances: Does the sun have a sub-solar metallicity?
Authors: Asplund Martin
Published: May 2007

In the Sun, the convection zone reaches up to the solar photosphere and can thus directly influence the emergent spectrum. Traditionally, the effects of convection has been modelled with the local mixing length theory in theoretical 1D hydrostatic model atmospheres. In a different approach, we have performed realistic time-dependent, 3D, radiative-hydrodynamical simulations of the outer layers of the solar convection zone, including the photosphere. Both the different mean stratification and the presence of atmospheric inhomogeneities in 3D impact the spectral line formation. In a series of papers, we have applied our 3D solar model atmosphere to the problem of the solar chemical composition. Furthermore, we have adopted the best possible atomic and molecular line data and taken into account departures from LTE in the line formation when necessary. The inferred C, N, O and Ne abundances are all significantly lower than estimated from previous 1D modelling by 0.2-0.3 dex. These results have significant implications for a range of topics in contemporary astrophysics, including causing a severe headache for helioseismology.
What can we learn about convection from asteroseismology?
Authors: Kjeldsen Hans , Bedding Timothy R.
Published: May 2007

Asteroseismology—using stellar oscillations to study the interiors of stars—is a relatively new and growing research field in astrophysics. Oscillations are found in stars of most masses and essentially all stages of evolution. Their frequencies are determined by the internal sound speed and density structure of the star, as well as rotation, convection processes and possibly effects of magnetic fields. Recent developments have led to a breakthrough in our ability to study the details of cores of solar-like stars and it is foreseen that a number of key science questions will be addressed through the analysis of frequencies and other properties of stellar oscillations. In this paper we review some of the latest results from asteroseismology of solar-like stars, with the focus on properties of convection.