82 research outputs found
SMA observations of the proto brown dwarf candidate SSTB213 J041757
Context. The previously identified source SSTB213 J041757 is a proto brown
dwarf candidate in Taurus, which has two possible components A and B. It was
found that component B is probably a class 0/I proto brown dwarf associated
with an extended envelope.
Aims. Studying molecular outflows from young brown dwarfs provides important
insight into brown dwarf formation mechanisms, particularly brown dwarfs at the
earliest stages such as class 0, I. We therefore conducted a search for
molecular outflows from SSTB213 J041757.
Methods. We observed SSTB213 J041757 with the Submillimeter Array to search
for CO molecular outflow emission from the source.
Results. Our CO maps do not show any outflow emission from the proto brown
dwarf candidate.
Conclusions. The non-detection implies that the molecular outflows from the
source are weak; deeper observations are therefore needed to probe the outflows
from the source.Comment: 7 pages, 4 figures, accepted for publication in A&
Rectification and Flux Reversals for Vortices Interacting with Triangular Traps
We simulate vortices in superconductors interacting with two-dimensional
arrays of triangular traps. We find that, upon application of an ac drive, a
net dc flow can occur which shows current reversals with increasing ac drive
amplitude for certain vortex densities, in agreement with recent experiments
and theoretical predictions. We identify the vortex dynamics responsible for
the different rectification regimes. We also predict the occurrence of a novel
transverse rectification effect in which a dc flow appears that is transverse
to the direction of the applied ac drive.Comment: 4 pages, 4 postscript figure
Fano-type interpretation of red shifts and red tails in hole array transmission spectra
We present a unifying point of view which allows to understand spectral
features reported in recent experiments with two-dimensional arrays of
subwavelength holes in metal films. We develop a Fano analysis of the related
scattering problem by distinguishing two interfering contributions to the
transmission process, namely a non-resonant contribution (direct scattering)
and a resonant contribution (surface plasmon excitation). The introduction of a
coupling strength between these two contributions naturally induces resonance
shifts and asymmetry of profiles which satisfy simple scaling relations. We
also report an experiment to confirm this analysis.Comment: 5 page
BRST invariant formulation of spontaneously broken gauge theory in generalized differential geometry
Noncommutative geometry(NCG) on the discrete space successfully reproduces
the Higgs mechanism of the spontaneously broken gauge theory, in which the
Higgs boson field is regarded as a kind of gauge field on the discrete space.
We could construct the generalized differential geometry(GDG) on the discrete
space which is very close to NCG in case of .
GDG is a direct generalization of the differential geometry on the ordinary
manifold into the discrete one. In this paper, we attempt to construct the BRST
invariant formulation of spontaneously broken gauge theory based on GDG and
obtain the BRST invariant Lagrangian with the t'Hooft-Feynman gauge fixing
term.Comment: 15 page
Logistic regression for simulating damage occurrence on a fruit grading line
Many factors influence the incidence of mechanical damage in fruit handled on a grading line. This makes it difficult to address damage estimation from an analytical point of view. During fruit transfer from one element of a grading line to another, damage occurs as a combined effect of machinery roughness and the intrinsic susceptibility of fruit. This paper describes a method to estimate bruise probability by means of logistic regression, using data yielded by specific laboratory tests. Model accuracy was measured via the statistical significance of its parameters and its classification ability. The prediction model was then linked to a simulation model through which impacts and load levels, similar to those of real grading lines, could be generated. The simulation output sample size was determined to yield reliable estimations. The process makes it possible to derive a suitable line design and the type of fruit that should be handled to maintain bruise levels within European Union (EU) Standards. A real example with peaches was carried out with the aid of the software implementation SIMLIN®, developed by the authors and registered by Madrid Technical University. This kind of tool has been demanded by inter-professional associations and grading lines designers in recent year
Conductance properties of nanotubes coupled to superconducting leads: signatures of Andreev states dynamics
We present a combined experimental and theoretical analysis of the low bias
conductance properties of carbon nanotubes coupled to superconducting leads. In
the Kondo regime the conductance exhibits a zero bias peak which can be several
times larger than the unitary limit in the normal case. This zero bias peak can
be understood by analyzing the dynamics of the subgap Andreev states under an
applied bias voltage. It is shown that the existence of a linear regime is
linked to the presence of a finite relaxation rate within the system. The
theory provides a good fitting of the experimental results.Comment: 6 revtex4 pages, 6 figures, to appear in SS
A Generalization of Chetaev's Principle for a Class of Higher Order Non-holonomic Constraints
The constraint distribution in non-holonomic mechanics has a double role. On
one hand, it is a kinematic constraint, that is, it is a restriction on the
motion itself. On the other hand, it is also a restriction on the allowed
variations when using D'Alembert's Principle to derive the equations of motion.
We will show that many systems of physical interest where D'Alembert's
Principle does not apply can be conveniently modeled within the general idea of
the Principle of Virtual Work by the introduction of both kinematic constraints
and variational constraints as being independent entities. This includes, for
example, elastic rolling bodies and pneumatic tires. Also, D'Alembert's
Principle and Chetaev's Principle fall into this scheme. We emphasize the
geometric point of view, avoiding the use of local coordinates, which is the
appropriate setting for dealing with questions of global nature, like
reduction.Comment: 27 pages. Journal of Mathematical Physics (to zappear
Small vertebrate taphonomy of La Cueva del Llano, a volcanic cave on Fuerteventura (Canary Islands, Spain). Palaeoecological implications
Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island. A strand of it (Ramal Nuevo) contains a complex sedimentary infill which has been divided into three sedimentary units and contains at least eight fossiliferous levels of Holocene age. The taphonomic analysis of small vertebrates found in the sediments revealed a scatological origin for the vertebrate assemblage, and that the barn owl (Tyto alba) is the main agent responsible for this concentration of bone remains. Furthermore, the taphonomic analysis allows to reconstruct the changes in the palaeodiet of barn owls during the Holocene of Fuerteventura (Canary Islands) and infer the alterations produced in the vertebrate comunity during that time. In the upper units of the sedimentary infill, the appearance of the house mouse (Mus musculus) is observed. This immigration is correlated that is associated to a decrease of the lava mouse (Malpaisomys insularis) proportions in the fossil assemblage. Also, the study of small vertebrate accumulation in Ramal Nuevo shows that volcanic tubes can be referred to as very useful concentration trap for taphonomic studies
Residence and redistribution of REE, Y, Zr, Th and U during granulite-facies metamorphism: behaviour of accessory and major phases in peraluminous granulites of central Spain
Accessory minerals are thought to play a key role in controlling the behaviour of certain trace elements such as REE, Y, Zr,
Th and U during crustal melting processes under high-grade metamorphic conditions. Although this is probably the case at
middle crustal levels, when a comparison is made with granulite-facies lower crustal levels, differences are seen in trace element
behaviour between accessory minerals and some major phases. Such a comparison can be made in Central Spain where two
granulite-facies terranes have equilibrated under slightly different metamorphic conditions and where lower crustal xenoliths are
also found. Differences in texture and chemical composition between accessory phases found in leucosomes and leucogranites
and those of melanosomes and protholiths indicate that most of the accessory minerals in melt-rich migmatites are newly
crystallized. This implies that an important redistribution of trace elements occurs during the early stages of granulite-facies
metamorphism. In addition, the textural position of the accessory minerals with respect to the major phases is crucial in the
redistribution of trace elements when melting proceeds via biotite dehydration melting reactions. In granulitic xenoliths from
lower crustal levels, the situation seems to be different, as major minerals show high concentration of certain trace elements, the
distribution of which is thus controlled by reactions involving final consumption of Al-Ti-phlogopite. A marked redistribution
of HREE–Y–Zr between garnet and xenotime (where present) and zircon, but also of LREE between feldspars (K-feldspar and
plagioclase) and monazite, is suggested
- …