4,368 research outputs found
Multicomponent fluids of hard hyperspheres in odd dimensions
Mixtures of hard hyperspheres in odd space dimensionalities are studied with
an analytical approximation method. This technique is based on the so-called
Rational Function Approximation and provides a procedure for evaluating
equations of state, structure factors, radial distribution functions, and
direct correlations functions of additive mixtures of hard hyperspheres with
any number of components and in arbitrary odd-dimension space. The method gives
the exact solution of the Ornstein--Zernike equation coupled with the
Percus--Yevick closure, thus extending to arbitrary odd dimension the solution
for hard-sphere mixtures [J. L. Lebowitz, Phys.\ Rev.\ \textbf{133}, 895
(1964)]. Explicit evaluations for binary mixtures in five dimensions are
performed. The results are compared with computer simulations and a good
agreement is found.Comment: 16 pages, 8 figures; v2: slight change of notatio
Solvable Lie algebras are not that hypo
We study a type of left-invariant structure on Lie groups, or equivalently on
Lie algebras. We introduce obstructions to the existence of a hypo structure,
namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy
SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain
associated cohomology groups, determine a first obstruction. We also construct
necessary conditions for the existence of a hypo structure with a fixed
almost-contact form. For non-unimodular Lie algebras, we derive an obstruction
to the existence of a hypo structure, with no choice involved. We apply these
methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational
conflicts eliminated. To appear in Transformation Group
The elliptic genus from split flows and Donaldson-Thomas invariants
We analyze a mixed ensemble of low charge D4-D2-D0 brane states on the
quintic and show that these can be successfully enumerated using attractor flow
tree techniques and Donaldson-Thomas invariants. In this low charge regime one
needs to take into account worldsheet instanton corrections to the central
charges, which is accomplished by making use of mirror symmetry. All the
charges considered can be realized as fluxed D6-D2-D0 and anti-D6-D2-D0 pairs
which we enumerate using DT invariants. Our procedure uses the low charge
counterpart of the picture developed Denef and Moore. By establishing the
existence of flow trees numerically and refining the index factorization
scheme, we reproduce and improve some results obtained by Gaiotto, Strominger
and Yin. Our results provide appealing evidence that the strong split flow tree
conjecture holds and allows to compute exact results for an important sector of
the theory. Our refined scheme for computing indices might shed some light on
how to improve index computations for systems with larger charges.Comment: 37 pages, 12 figure
A MegaCam Survey of Outer Halo Satellites. VI: The Spatially Resolved Star Formation History of the Carina Dwarf Spheroidal Galaxy
We present the spatially resolved star formation history (SFH) of the Carina
dwarf spheroidal galaxy, obtained from deep, wide-field g,r imaging and a
metallicity distribution from the literature. Our photometry covers
deg, reaching up to times the half-light radius of Carina with a
completeness higher than at , more than one magnitude fainter
than the oldest turnoff. This is the first time a combination of depth and
coverage of this quality has been used to derive the SFH of Carina, enabling us
to trace its different populations with unprecedented accuracy. We find that
Carina's SFH consists of two episodes well separated by a star formation
temporal gap. These episodes occurred at old ( Gyr) and intermediate
(- Gyr) ages. Our measurements show that the old episode comprises the
majority of the population, accounting for of the stellar mass
within times the King tidal radius, while the total stellar mass derived
for Carina is , and the stellar
mass-to-light ratio . The SFH derived is consistent with no recent
star formation which hints that the observed blue plume is due to blue
stragglers. We conclude that the SFH of Carina evolved independently of the
tidal field of the Milky Way, since the frequency and duration of its star
formation events do not correlate with its orbital parameters. This result is
supported by the age/metallicity relation observed in Carina, and the gradients
calculated indicating that outer regions are older and more metal poor.Comment: Accepted in ApJ (22 pages, 13 figures
A branch-point approximant for the equation of state of hard spheres
Using the first seven known virial coefficients and forcing it to possess two
branch-point singularities, a new equation of state for the hard-sphere fluid
is proposed. This equation of state predicts accurate values of the higher
virial coefficients, a radius of convergence smaller than the close-packing
value, and it is as accurate as the rescaled virial expansion and better than
the Pad\'e [3/3] equations of state. Consequences regarding the convergence
properties of the virial series and the use of similar equations of state for
hard-core fluids in dimensions are also pointed out.Comment: 6 pages, 4 tables, 3 figures; v2: enlarged version, extension to
other dimensionalities; v3: typos in references correcte
Evaluation of the influence of toll systems on energy consumption and CO2 emissions: A case study of a Spanish highway
This paper studies the energy consumption and subsequent CO2 emissions of road highway transportation under three toll systems in Spain for four categories of vehicles: cars, vans, buses and articulated trucks. The influence of toll systems is tested for a section of AP-41 highway between Toledo and Madrid. One system is free flow, other is traditional stop and go and the last toll system operates with an electronic toll collection (ETC) technology. Energy consumption and CO2 emissions were found to be closely related to vehicle mass, wind exposure, engine efficiency and acceleration rate. These parameters affect, directly or indirectly, the external forces which determine the energy consumption. Reducing the magnitude of these forces through an appropriate toll management is an important way of improving the energy performance of vehicles. The type of toll system used can have a major influence on the energy efficiency of highway transportation and therefore it is necessary to consider free flow
Towards a fundamental astrometric reference system behind the Malleganic clouds : spectroscopic confirmation of new quasar candidates selected in the near-infrared
Quasi-stellar objects (quasars) located behind nearby galaxies provide an excellent absolute reference system for astrometric studies, but they are difficult to identify because of fore- and background contamination. We have embarked on a programme to expand the quasar reference system behind the Large and Small Magellanic Clouds, the Magellanic Bridge and Magellanic Stream. Hundreds of quasar candidates were selected, based on their near-infrared colours and variability properties from the ESO VISTA Magellanic Clouds (VMC) Public Survey. A subset of 49 objects was followed up with optical spectroscopy with FORS2. We confirmed the quasar nature of 37 objects (34 new identifications) that span a redshift range from z ~ 0.5 to 4.1
In vivo inhibition of c-MYC in myeloid cells impairs tumor-associated macrophage maturation and pro-tumoral activities
Although tumor-associated macrophages (TAMs) are involved in tumor growth and metastasis, the mechanisms controlling their pro-tumoral activities remain largely unknown. The transcription factor c-MYC has been recently shown to regulate in vitro human macrophage polarization and be expressed in macrophages infiltrating human tumors. In this study, we exploited the predominant expression of LysM in myeloid cells to generate c-Myc(fl/fl) LysM(cre/+) mice, which lack c-Myc in macrophages, to investigate the role of macrophage c-MYC expression in cancer. Under steady-state conditions, immune system parameters in c-Myc(fl/fl) LysM(cre/+) mice appeared normal, including the abundance of different subsets of bone marrow hematopoietic stem cells, precursors and circulating cells, macrophage density, and immune organ structure. In a model of melanoma, however, TAMs lacking c-Myc displayed a delay in maturation and showed an attenuation of pro-tumoral functions (e.g., reduced expression of VEGF, MMP9, and HIF1α) that was associated with impaired tissue remodeling and angiogenesis and limited tumor growth in c-Myc(fl/fl) LysM(cre/+) mice. Macrophage c-Myc deletion also diminished fibrosarcoma growth. These data identify c-Myc as a positive regulator of the pro-tumoral program of TAMs and suggest c-Myc inactivation as an attractive target for anti-cancer therapy
Developmental axon degeneration requires trpv1-dependent Ca 2+ influx
Development of the nervous system relies on a balance between axon and dendrite growth and subsequent pruning and degeneration. The developmental degeneration of dorsal root ganglion (DRG) sensory axons has been well studied in part because it can be readily modeled by removing the trophic support by nerve growth factor (NGF) in vitro. We have recently reported that axonal fragmentation induced by NGF withdrawal is dependent on Ca2+, and here, we address the mechanism of Ca2+ entry required for developmental axon degeneration of mouse embryonic DRG neurons. Our results show that the transient receptor potential vanilloid family member 1 (TRPV1) cation channel plays a critical role mediating Ca2+ influx in DRG axons withdrawn from NGF. We further demonstrate that TRPV1 activation is dependent on reactive oxygen species (ROS) generation that is driven through protein kinase C (PKC) and NADPH oxidase (NOX)-dependent pathways that become active upon NGF withdrawal. These findings demonstrate novel mechanistic links between NGF deprivation, PKC activation, ROS generation, and TRPV1-dependent Ca2+ influx in sensory axon degeneration.Fil: Johnstone, Aaron D.. University of British Columbia; Canadá. McGill University; CanadáFil: de Léon, Andrés. University of British Columbia; Canadá. McGill University; CanadáFil: Unsain, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Gibon, Julien. University of British Columbia; CanadáFil: Barker, Philip A.. University of British Columbia; Canad
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