2,073 research outputs found
Corporate governance of a multinational enterprise: Firm, industry and institutional perspectives
Implications of Variability Patterns observed in TeV Blazars on the Structure of the Inner Jet
The recent long look X-ray observations of TeV blazars have revealed many
important new features concerning their time variability. In this paper, we
suggest a physical interpretation for those features based on the framework of
the internal and external shock scenarios. We present a simplified model
applicable to TeV blazars, and investigate through simulations how each of the
model parameters would affect to the observed light curve or spectrum. In
particular, we show that the internal shock scenario naturally leads to all the
observed variability properties including the structure function, but for it to
be applicable, the fractional fluctuation of the initial bulk Lorentz factors
must be small, with sigma_gamma / gamma_average < 0.01. This implies very low
dynamical efficiency of the internal shock scenario. We also suggest that
several observational quantities -- such as the characteristic time scale, the
relative amplitude of flares as compared to the steady (``offset'') component,
and the slope of the structure function -- can be used to probe the inner jet.
The results are applied to the TeV blazar Mrk421, and this, within the context
of the model, leads to the determination of several physical parameters: the
ejection of a shell with average thickness of ~1E13 cm occurs on average every
10 minutes, and the shells collide ~1E17 cm away from the central source.Comment: 12 pages, 13 figures, to appear in Ap
Ex-vivo HRMAS of adult brain tumours: metabolite quantification and assignment of tumour biomarkers
Background: High-resolution magic angle spinning (HRMAS) NMR spectroscopy allows detailed metabolic analysis
of whole biopsy samples for investigating tumour biology and tumour classification. Accurate biochemical
assignment of small molecule metabolites that are “NMR visible” will improve our interpretation of HRMAS data
and the translation of NMR tumour biomarkers to in-vivo studies.
Results: 1D and 2D 1H HRMAS NMR was used to determine that 29 small molecule metabolites, along with 8 macromolecule signals, account for the majority of the HRMAS spectrum of the main types of brain tumour(astrocytoma grade II, grade III gliomas, glioblastomas, metastases, meningiomas and also lymphomas). Differences in concentration of 20 of these metabolites were statistically significant between these brain tumour types. During the course of an extended 2D data acquisition the HRMAS technique itself affects sample analysis: glycine, glutathione and glycerophosphocholine all showed small concentration changes; analysis of the sample after HRMAS indicated structural damage that may affect subsequent histopathological analysis.
Conclusions: A number of small molecule metabolites have been identified as potential biomarkers of tumour
type that may enable development of more selective in-vivo 1H NMR acquisition methods for diagnosis and prognosis of brain tumours
Radial Velocity Studies of Close Binary Stars. IX
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the eighth set of ten close binary systems: AB
And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP
Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori,
V335 Peg) were discovered photometrically by the Hipparcos mission and all
systems are double-lined (SB2) contact binaries. The broadening function method
permitted improvement of the orbital elements for AB And and V502 Oph. The
other systems have been observed for radial velocity variations for the first
time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918
Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates
for combined light and radial-velocity synthesis solutions.Comment: 17+ pages, 2 tables, 4 figure
A Planet at 5 AU Around 55 Cancri
We report precise Doppler shift measurements of 55 Cancri (G8V) obtained from
1989 to 2002 at Lick Observatory. The velocities reveal evidence for an outer
planetary companion to 55 Cancri orbiting at 5.5 AU. The velocities also
confirm a second, inner planet at 0.11 AU. The outer planet is the first
extrasolar planet found that orbits near or beyond the orbit of Jupiter. It was
drawn from a sample of ~50 stars observed with sufficient duration and quality
to detect a giant planet at 5 AU, implying that such planets are not rare. The
properties of this jupiter analog may be compared directly to those of the
Jovian planets in our Solar System. Its eccentricity is modest, e=0.16,
compared with e=0.05 for both Jupiter and Saturn. Its mass is at least 4.0
jupiter masses (M sin i). The two planets do not perturb each other
significantly. Moreover, a third planet of sub-Jupiter mass could easily
survive in between these two known planets. Indeed a third periodicity remains
in the velocity measurements with P = 44.3 d and a semi-amplitude of 13 m/s.
This periodicity is caused either by a third planet at a=0.24 AU or by
inhomogeneities on the stellar surface that rotates with period 42 d. The
planet interpretation is more likely, as the stellar surface is quiet,
exhibiting log(R'_{HK}) = -5.0 and brightness variations less than 1 millimag,
and any hypothetical surface inhomogeneity would have to persist in longitude
for 14 yr. Even with all three planets, an additional planet of
terrestrial--mass could orbit stably at ~1 AU. The star 55 Cancri is apparently
a normal, middle-aged main sequence star with a mass of 0.95 solar masses, rich
in heavy elements ([Fe/H] = +0.27). This high metallicity raises the issue of
the relationship between its age, rotation, and chromosphere.Comment: 47 pages, 4 tables, 12 figures, uses AASTE
A vortex description of the first-order phase transition in type-I superconductors
Using both analytical arguments and detailed numerical evidence we show that
the first order transition in the type-I 2D Abelian Higgs model can be
understood in terms of the statistical mechanics of vortices, which behave in
this regime as an ensemble of attractive particles. The well-known
instabilities of such ensembles are shown to be connected to the process of
phase nucleation. By characterizing the equation of state for the vortex
ensemble we show that the temperature for the onset of a clustering instability
is in qualitative agreement with the critical temperature. Below this point the
vortex ensemble collapses to a single cluster, which is a non-extensive phase,
and disappears in the absence of net topological charge. The vortex description
provides a detailed mechanism for the first order transition, which applies at
arbitrarily weak type-I and is gauge invariant unlike the usual field-theoretic
considerations, which rely on asymptotically large gauge coupling.Comment: 4 pages, 6 figures, uses RevTex. Additional references added, some
small corrections to the tex
“Top-Down-Bottom-Up” Methodology as a Common Approach to Defining Bespoke Sets of Sustainability Assessment Criteria for the Built Environment
YesThe top-down-bottom-up (TDBU) methodology for defining bespoke sets of sustainability criteria for specific civil engineering project types is introduced and discussed. The need to define sustainability criteria for specific civil engineering project types occurs mainly in one or both of the following cases: (1) when a more comprehensive and indicative assessment of the sustainability of the project type in question is required; and/or (2) there is no readily available bespoke sustainability assessment tool, or set of criteria, for assessing the sustainability of the project type. The construction of roads, buildings, airports, tunnels, dams, flood banks, bridges, water supply, and sewage systems and their supporting systems are considered to be unique civil engineering/infrastructure project types. The normative definition of sustainable civil engineering/infrastructure projects and the framework for assessing its sustainability is defined and provided by the authors. An example of the TDBU methodology being applied to define sustainability criteria for transport noise reducing devices is presented and discussed. The end result of applying the methodology is a systematically researched and industry validated set of criteria that denotes assessing the sustainability of the civil engineering/infrastructure project type. The paper concludes that the top-down-bottom-up will support stakeholders and managers involved in assessing sustainability to consider all major research methods to define general and unique sustainability criteria to assess and so maximize sustainability
Eight common genetic variants associated with serum dheas levels suggest a key role in ageing mechanisms
Dehydroepiandrosterone sulphate (DHEAS) is the most abundant circulating steroid secreted by adrenal glands-yet its function is unknown. Its serum concentration declines significantly with increasing age, which has led to speculation that a relative DHEAS deficiency may contribute to the development of common age-related diseases or diminished longevity. We conducted a meta-analysis of genome-wide association data with 14,846 individuals and identified eight independent common SNPs associated with serum DHEAS concentrations. Genes at or near the identified loci include ZKSCAN5 (rs11761528; p = 3.15×10-36), SULT2A1 (rs2637125; p = 2.61×10-19), ARPC1A (rs740160; p = 1.56×10-16), TRIM4 (rs17277546; p = 4.50×10-11), BMF (rs7181230; p = 5.44×10-11), HHEX (rs2497306; p = 4.64×10-9), BCL2L11 (rs6738028; p = 1.72×10-8), and CYP2C9 (rs2185570; p = 2.29×10-8). These genes are associated with type 2 diabetes, lymphoma, actin filament assembly, drug and xenobiotic metabolism, and zinc finger proteins. Several SNPs were associated with changes in gene expression levels, and the related genes are connected to biological pathways linking DHEAS with ageing. This study provides much needed insight into the function of DHEAS
Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter (β) for Stellar Halos
The velocity anisotropy parameter, β, is a measure of the kinematic state of orbits in the stellar halo, which holds promise for constraining the merger history of the Milky Way (MW). We determine global trends for β as a function of radius from three suites of simulations, including accretion-only and cosmological hydrodynamic simulations. We find that the two types of simulations are consistent and predict strong radial anisotropy () for Galactocentric radii greater than 10 kpc. Previous observations of β for the MW's stellar halo claim a detection of an isotropic or tangential "dip" at r ~ 20 kpc. Using the N-body+SPH simulations, we investigate the temporal persistence, population origin, and severity of "dips" in β. We find that dips in the in situ stellar halo are long-lived, while dips in the accreted stellar halo are short-lived and tied to the recent accretion of satellite material. We also find that a major merger as early as z ~ 1 can result in a present-day low (isotropic to tangential) value of β over a broad range of radii and angles. While all of these mechanisms are plausible drivers for the β dip observed in the MW, each mechanism in the simulations has a unique metallicity signature associated with it, implying that future spectroscopic surveys could distinguish between them. Since an accurate knowledge of β(r) is required for measuring the mass of the MW halo, we note that significant transient dips in β could cause an overestimate of the halo's mass when using spherical Jeans equation modeling
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