Chemically tagging the Hyades stream: does it partly originate from the Hyades cluster?

The Hyades stream has long been thought to be a dispersed vestige of the Hyades cluster. However, recent analyses of the parallax distribution, of the mass function, and of the action-space distribution of stream stars have shown it to be rather composed of orbits trapped at a resonance of a density disturbance. This resonant scenario should leave a clearly different signature in the element abundances of stream stars than the dispersed cluster scenario, since the Hyades cluster is chemically homogeneous. Here, we study the metallicity as well as the element abundances of Li, Na, Mg, Fe, Zr, Ba, La, Ce, Nd and Eu for a random sample of stars belonging to the Hyades stream, and compare them with those of stars from the Hyades cluster. From this analysis: (i) we independently confirm that the Hyades stream cannot be solely composed of stars originating in the Hyades cluster; (ii) we show thatsomestars (namely 2/21) from the Hyades stream nevertheless have abundances compatible with an origin in the cluster; (iii) we emphasize that the use of Li as a chemical tag of the cluster origin of main-sequence stars is very efficient in the range 5500K ≤Teff≤ 6200K, since the Li sequence in the Hyades cluster is very tight, while at the same time spanning a large abundance range; (iv) we show that, while this evaporated population has a metallicity excess of ~0.2 dex with respect to the local thin-disc population, identical to that of the Hyades cluster, the remainder of the Hyades stream population has still a metallicity excess of ~0.06-0.15 dex, consistent with an origin in the inner Galaxy and (v) we show that the Hyades stream can be interpreted as an inner 4:1 resonance of the spiral pattern: this then also reproduces an orbital family compatible with the Sirius stream, and places the origin of the Hyades stream up to 1kpc inwards from the solar radius, which might explain the observed metallicity excess of the stream population. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Tambalacoque. For a formal account of the gist of a scholarly argument

Argumentation as reflected in a short communication from the published literature of botany and zoology is discussed. Trying to capture the logic structure of the argument, however imperfectly, is relevant to information science and depends on a particular goal: namely, to potentially benefit the task of sketching the relationship between bibliographic entries in a better manner than is possible with present-day bibliometric or scientometric practice. This imposes tight limits on the depth of analysis of the text.

Nanoscopic modelling of the adhesion, indentation and fracture characteristics of metallic systems via molecular dynamics simulations

Large-scale molecular dynamics simulations have been performed on canonical ensembles to model the adhesion and indentation characteristics of 3-D metallic nano-scale junctions in tip-substrate geometries, and the crack propagation in 2-D metallic lattices. It is shown that irreversible flows in nano-volumes of materials control the behaviour of the 3-D nano-contacts, and that local diffusional flow constitutes the atomistic mechanism underlying these plastic flows. These simulations show that the force of adhesion in metallic nano-contacts is reduced when adsorbate monolayers are present at the metal—metal junctions. Our results are in agreement with the conclusions of very accurate point-contact experiments carried out in this field. Our fracture simulations reveal that at low temperatures cleavage fractures can occur in both an elemental metal and an alloy. At elevated temperatures, the nucleation of dislocations is shown to cause a brittle-to-ductile transition. Limiting crack propagation velocities are computed for different strain rates and a dynamic instability is shown to control the crack movement beyond this limiting velocity, in line with the recent experimental results.

Scheduling for parallel dedicated machines with a single server

This paper examines scheduling problems in which the setup phase of each operation needs to be attended by a single server, common for all jobs and different from the processing machines. The objective in each situation is to minimize the makespan. For the processing system consisting of two parallel dedicated machines we prove that the problem of finding an optimal schedule is NP-hard in the strong sense even if all setup times are equal or if all processing times are equal. For the case of m parallel dedicated machines, a simple greedy algorithm is shown to create a schedule with the makespan that is at most twice the optimum value. For the two machine case, an improved heuristic guarantees a tight worst-case ratio of 3/2. We also describe several polynomially solvable cases of the later problem. The two-machine flow shop and the open shop problems with a single server are also shown to be NP-hard in the strong sense. However, we reduce the two-machine flow shop no-wait problem with a single server to the Gilmore-Gomory traveling salesman problem and solve it in polynomial time. (c) 2000 John Wiley & Sons, Inc.

An open shop scheduling problem with a non-bottleneck machine

This paper considers the problem of processing n jobs in a two-machine non-preemptive open shop to minimize the makespan, i.e., the maximum completion time. One of the machines is assumed to be non-bottleneck. It is shown that, unlike its flow shop counterpart, the problem is NP-hard in the ordinary sense. On the other hand, the problem is shown to be solvable by a dynamic programming algorithm that requires pseudopolynomial time. The latter algorithm can be converted into a fully polynomial approximation scheme that runs in time. An O(n log n) approximation algorithm is also designed whi finds a schedule with makespan at most 5/4 times the optimal value, and this bound is tight.

North Sea Ecosystem: Status Report

The North Sea is a dynamic large marine ecosystem which is bordered by a dense coastal population, contains a productive oil and gas province, has a dense shipping network and has one of the most productive fisheries in the world. An assessment of the state of health of the North Sea was initiated in 1987 as part of a developing series of international initiatives at Ministerial level to address concerns over the impact of these activities on the marine ecosystem. Four North Sea Ministerial Conferences (1984, 1987, 1990, 1995) and an Intermediate Ministerial Meeting (1993) have been held to date to develop a harmonized approach to the sustainable management of the North Sea. In 1988 at the request of Ministers a North Sea Task Force was established to co-ordinate work leading to the production of a Quality Status Report (QSR) on the North Sea in December 1993. In recognition of the large geographical and ecological diversity exhibited, a sub-regional approach was adopted and a total of 13 sub-regional assessment reports were produced to a common protocol. The Task Force established a five-year plan to co-ordinate research, monitoring and modelling and other special topics in the preparations for the QSR. As part of this exercise a ‘Monitoring Master Plan’ was drawn up to provide for the first time reliable spatial information on the distribution of chemical contaminants and biological effects throughout the North Sea. The Task Force was a unique structure in international collaboration with a fixed remit that ended in December 1993. It was successful in bringing together many diverse organisations with interests in the North Sea and co-ordinated to a tight timetable the production of the QSR. The experiences gained are now being applied to the whole north east Atlantic under a new OSPAR Convention and have wide application to other Large Marine Ecosystems.

Physiology, ecological niches and species distribution

Although many studies have debated the theoretical links between physiology, ecological niches and species distribution, few studies have provided evidence for a tight empirical coupling between these concepts at a macroecological scale. We used an ecophysiological model to assess the fundamental niche of a key-structural marine species. We found a close relationship between its fundamental and realized niche. The relationship remains constant at both biogeographical and decadal scales, showing that changes in environmental forcing propagate from the physiological to the macroecological level. A substantial shift in the spatial distribution is detected in the North Atlantic and projections of range shift using IPCC scenarios suggest a poleward movement of the species of one degree of latitude per decade for the 21st century. The shift in the spatial distribution of this species reveals a pronounced alteration of polar pelagic ecosystems with likely implications for lower and upper trophic levels and some biogeochemical cycles.

An interlaboratory comparison for the quantification of aqueous dimethylsulfide

An interlaboratory comparison (ILC) was conducted to evaluate the proficiency of multiple laboratories to quantify dimethylsulfide (DMS) in aqueous solution. Ten participating laboratories were each supplied with blind duplicate test solutions containing dimethylsulfoniopropionate hydrochloride (DMSP HCl) dissolved in acidified artificial seawater. The test solutions were prepared by the coordinating laboratory from a DMSP HCl reference material that was synthesized and purity certified for this purpose. A concentration range was specified for the test solutions and the participating laboratories were requested to dilute them as required for their analytical procedure, together with the addition of excess alkali under gas-tight conditions to convert the DMSP to DMS. Twenty-two DMS concentrations and their estimated expanded measurement uncertainties (95% confidence level) were received from the laboratories. With two exceptions, the within-laboratory variability was 5% or less and the between-laboratory variability was ~ 25%. The magnitude of expanded measurement uncertainties reported from all participants ranged from 1% to 33% relative to the result. The information gained from this pilot ILC indicated the need for further test sample distribution studies of this type so that participating laboratories can identify systematic errors in their analysis procedures and realistically evaluate their measurement uncertainty. The outcome of ILC studies provides insights into the comparability of data in the global surface seawater DMS database.

THE ROLE OF LIPOPROTEIN(a)/APOLIPOPROTEIN(a) IN ENDOTHELIAL DYSFUNCTION: MECHANISTIC STUDIES IN VASCULAR ENDOTHELIUM

Multiple lines of evidence suggest that elevated plasma lipoprotein(a) (Lp(a)) concentrations are a significant risk factor for the development of a number of vascular diseases including coronary heart disease and stroke. Lp(a) consists of a low-density lipoprotein (LDL)-like moiety and an unique glycoprotein, apolipoprotein(a) (apo(a)), that is covalently attached to the apolipoproteinB-100 (apoB-100) component of LDL by a single disulfide bond. Many studies have suggested a role for Lp(a) in the process of endothelial dysfunction. Indeed, Lp(a) has been shown to increase both the expression of adhesion molecules on endothelial cells (EC), as well as monocyte and leukocyte chemotactic activity in these cells. We have previously demonstrated that Lp(a), through its apo(a) moiety, increases actomyosin-driven EC contraction which, as a consequence, increases EC permeability. In this thesis, we have demonstrated a role for the strong lysine-binding site in the kringle IV type 10 domain of apo(a) in increasing EC permeability, which occurs through a Rho/Rho kinase-dependent pathway. We have further validated these findings using mouse mesenteric arteries in a pressure myograph system. We also have dissected another major signaling pathway initiated by apo(a) that involves in a disruption of adherens junctions in EC. In this pathway, apo(a)/Lp(a) activates the PI3K/Akt/GSK3β-dependent pathway to facilitate nuclear translocation of beta-catenin. In the nucleus beta-catenin induced the expression of cyclooxygenase-2 (COX-2) and the secretion of prostaglandin E2 (PGE2) from the EC. Finally, we have presented data to suggest a novel inflammatory role for apo(a) in which it induces the activation of nuclear factor-kappaB through promotion of the dissociation of IkappaB from the inactive cytoplasmic complex; this allows the nuclear translocation of NFkappaB with attendant effects on the transcription of pro-inflammatory genes. Taken together, our findings may facilitate the development of new drug targets for mitigating the harmful effects of Lp(a) on vascular EC which corresponds to an early step in the process of atherogenesis.

Endostatin modulates VEGF-mediated barrier dysfunction in the retinal microvascular endothelium

Recent evidence indicates that the anti-angiogenic peptide endostatin may modulate some of the vasomodulatory effects of vascular endothelial growth factor (VEGF) in the retina, including reduction of blood retinal barrier function although it remains uncertain how endostatin promotes endothelial barrier properties. The current study has sought to examine how physiological levels of endostatin alters VEGF-induced inner BRB function using an in vitro model system and evaluation of occludin and ZO-1 regulatory responses. In addition, the ability of exogenous endostatin to regulate VEGF-mediated retinal vascular permeability in vivo was investigated.

Retinal microvascular endothelial cells (RMEC's) were exposed to various concentrations of endostatin. In parallel studies, RMEC monolayers were treated with vascular endothelial growth factor (VEGF165). Vasopermeability of RMEC monolayers and occludin expression were determined.

Blood retinal barrier integrity was quantified in mouse retina using Evans Blue assay following intravitreal delivery of VEGF165, endostatin or a VEGF/endostatin combination.

Endostatin increased the levels of expression of occludin whilst causing no significant change in FITC-dextran flux across the RMEC monolayer. Endostatin reversed the effects of VEGF165-enhanced permeability between microvascular endothelial cells and induced phosphorylation of occludin. Evans Blue leakage from retinas treated with VEGF was 2.0 fold higher than that of contra-lateral untreated eyes (P<0.05) while leakage of eyes from endostatin treated animals was unchanged. When eyes were injected with a combination of VEGF165 and endostatin there was a significant reduction in retinal vasopermeability when compared to VEGF-injected eyes (P<0.05).

We conclude that endostatin can promote integrity of the retinal endothelial barrier, possibly by preventing VEGF-mediated alteration of tight junction integrity. This suggests that endostatin may be of clinical benefit in ocular disorders where significant retinal vasopermeability changes are present.

A stabilization mechanism of zirconia based on oxygen vacancies only

The microscopic mechanism leading to stabilization of cubic and tetragonal forms of zirconia (ZrO2) is analyzed by means of a self-consistent tight-binding model. Using this model, energies and structures of zirconia containing different vacancy concentrations are calculated, equivalent in concentration to the charge compensating vacancies associated with dissolved yttria (Y2O3) in the tetragonal and cubic phase fields (3.2 and 14.4% mol, respectively). The model is shown to predict the large relaxations around an oxygen vacancy, and the clustering of vacancies along the 111 directions, in good agreement with experiments and first principles calculations. The vacancies alone are shown to explain the stabilization of cubic zirconia, and the mechanism is analyzed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Free energy and molecular dynamics calculations for the cubic-tetragonal phase transition in zirconia

The high-temperature cubic-tetragonal phase transition of pure stoichiometric zirconia is studied by molecular dynamics (MD) simulations and within the framework of the Landau theory of phase transformations. The interatomic forces are calculated using an empirical, self-consistent, orthogonal tight-binding model, which includes atomic polarizabilities up to the quadrupolar level. A first set of standard MD calculations shows that, on increasing temperature, one particular vibrational frequency softens. The temperature evolution of the free-energy surfaces around the phase transition is then studied with a second set of calculations. These combine the thermodynamic integration technique with constrained MD simulations. The results seem to support the thesis of a second-order phase transition but with unusual, very anharmonic behavior above the transition temperature.

K alpha yields from Ti foils irradiated with ultrashort laser pulses

We have studied the emission of Kalpha radiation from Ti foils irradiated with ultrashort (45 fs) laser pulses. We utilized the fundamental (800 nm) light from a Ti:sapphire laser on bare foils and foils coated with a thin layer of parylene E (CH). The focusing was varied widely to give a range of intensities from approximately 10(15)-10(19) W cm(-2). Our results show a conversion efficiency of laser to Kalpha energy of similar to 10(-4) at tight focus for both types of targets. In addition, the coated targets exhibited strong secondary peaks of conversion at large defocus, which we believe are due to modification of the extent of preformed plasma due to the dielectric nature of the plastic layer. This in turn affects the level of resonance absorption. A simple model of Kalpha production predicts a much higher conversion than seen experimentally and possible reasons for this are discussed.

Independent particle descriptions of tunneling using the many-body quantum transport approach

Currents across thin insulators are commonly taken as single electrons moving across classically forbidden regions; this independent particle picture is well-known to describe most tunneling phenomena. Examining quantum transport from a different perspective, i.e., by explicit treatment of electron-electron interactions, we evaluate different single particle approximations with specific application to tunneling in metal-molecule-metal junctions. We find maximizing the overlap of a Slater determinant composed of single-particle states to the many-body current-carrying state is more important than energy minimization for defining single-particle approximations in a system with open boundary conditions. Thus the most suitable single particle effective potential is not one commonly in use by electronic structure methods, such as the Hartree-Fock or Kohn-Sham approximations.