11,449 research outputs found
Large-scale anisotropy in stably stratified rotating flows
We present results from direct numerical simulations of the Boussinesq
equations in the presence of rotation and/or stratification, both in the
vertical direction. The runs are forced isotropically and randomly at small
scales and have spatial resolutions of up to grid points and Reynolds
numbers of . We first show that solutions with negative energy
flux and inverse cascades develop in rotating turbulence, whether or not
stratification is present. However, the purely stratified case is characterized
instead by an early-time, highly anisotropic transfer to large scales with
almost zero net isotropic energy flux. This is consistent with previous studies
that observed the development of vertically sheared horizontal winds, although
only at substantially later times. However, and unlike previous works, when
sufficient scale separation is allowed between the forcing scale and the domain
size, the total energy displays a perpendicular (horizontal) spectrum with
power law behavior compatible with , including in the
absence of rotation. In this latter purely stratified case, such a spectrum is
the result of a direct cascade of the energy contained in the large-scale
horizontal wind, as is evidenced by a strong positive flux of energy in the
parallel direction at all scales including the largest resolved scales
Galaxy Evolution in Local Group Analogs. I. A GALEX study of nearby groups
Understanding the astrophysical processes acting within galaxy groups and
their effects on the evolution of the galaxy population is one of the crucial
topic of modern cosmology, as almost 60% of galaxies in the Local Universe are
found in groups. We imaged in the far (FUV 1539 A) and near ultraviolet (NUV
2316 A) with GALEX three nearby groups, namely LGG93, LGG127 and LGG225. We
obtained the UV galaxy surface photometry and, for LGG225, the only group
covered by the SDSS, the photometry in u, g, r, i, z bands. We discuss galaxy
morphologies looking for interaction signatures and we analyze the SED of
galaxies to infer their luminosity-weighted ages. The UV and optical photometry
was also used to perform a kinematical and dynamical analysis of each group and
to evaluate the stellar mass. A few member galaxies in LGG225 show a distorted
UV morphology due to ongoing interactions. (FUV-NUV) colors suggest that
spirals in LGG93 and LGG225 host stellar populations in their outskirts younger
than that of M31 and M33 in the LG or with less extinction. The irregular
interacting galaxy NGC3447A has a significantly younger stellar population (few
Myr old) than the average of the other irregular galaxies in LGG225 suggesting
that the encounter triggered star formation. The early-type members of LGG225,
NGC3457 and NGC3522, have masses of the order of a few 10^9 Mo, comparable to
the Local Group ellipticals. For the most massive spiral in LGG225, we estimate
a stellar mass of ~4x10 Mo, comparable to M33 in the LG. Ages of stellar
populations range from a few to ~7 Gyr for the galaxies in LGG225. The
kinematical and dynamical analysis indicates that LGG127 and LGG225 are in a
pre-virial collapse phase, i.e. still undergoing dynamical relaxation, while
LGG93 is likely virialized. (Abridged)Comment: 20 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Vanishing conductivity of quantum solitons in polyacetylene
Quantum solitons or polarons are supposed to play a crucial role in the
electric conductivity of polyacetylene, in the intermediate doping regime. We
present an exact fully quantized calculation of the quantum soliton
conductivity in polyacetylene and show that it vanishes exactly. This is
obtained by applying a general method of soliton quantization, based on
order-disorder duality, to a Z(2)-symmetric complex extension of the TLM
dimerization effective field theory. We show that, in this theory,
polyacetylene solitons are sine-Gordon solitons in the phase of the complex
field.Comment: To appear in J. Phys. A: Math. Theor., 15 page
Inverter-converter automatic paralleling and protection
Electric control and protection circuits for parallel operation of inverter-converte
Impact of gene polymorphisms of gonadotropins and their receptors on human reproductive success
Gonadotropins and their receptors' genes carry several single-nucleotide polymorphisms resulting in endocrine genotypes modulating reproductive parameters, diseases, and lifespan leading to important implications for reproductive success and potential relevance during human evolution. Here we illustrate common genotypes of the gonadotropins and gonadotropin receptors' genes and their clinical implications in phenotypes relevant for reproduction such as ovarian cycle length, age of menopause, testosterone levels, polycystic ovary syndrome, and cancer. We then discuss their possible role in human reproduction and adaptation to the environment. Gonadotropins and their receptors' variants are differently distributed among human populations. Some hints suggest that they may be the result of natural selection that occurred in ancient times, increasing the individual chance of successful mating, pregnancy, and effective post-natal parental cares. The gender-related differences in the regulation of the reproductive endocrine systems imply that many of these genotypes may lead to sex-dependent effects, increasing the chance of mating and reproductive success in one sex at the expenses of the other sex. Also, we suggest that sexual conflicts within the FSH and LH-choriogonadotropin receptor genes contributed to maintain genotypes linked to subfertility among humans. Because the distribution of polymorphic markers results in a defined geographical pattern due to human migrations rather than natural selection, these polymorphisms may have had only a weak impact on reproductive success. On the contrary, such genotypes could acquire relevant consequences in the modern, developed societies in which parenthood attempts often occur at a later age, during a short, suboptimal reproductive window, making clinical fertility treatments necessary
Quantum global vortex strings in a background field
We consider quantum global vortex string correlation functions, within the
Kalb-Ramond framework, in the presence of a background field-strength tensor
and investigate the conditions under which this yields a nontrivial
contribution to those correlation functions. We show that a background field
must be supplemented to the Kalb-Ramond theory, in order to correctly describe
the quantum properties of the vortex strings. The explicit form of this
background field and the associated quantum vortex string correlation function
are derived. The complete expression for the quantum vortex creation operator
is explicitly obtained. We discuss the potential applicability of our results
in the physics of superfluids and rotating Bose-Einstein condensates.Comment: To appear in Journal of Physics A: Mathematical and Genera
MUSE-inspired view of the quasar Q2059-360, its Lyman alpha blob, and its neighborhood
The radio-quiet quasar Q2059-360 at redshift is known to be close to
a small Lyman blob (LAB) and to be absorbed by a proximate damped
Ly (PDLA) system.
Here, we present the Multi Unit Spectroscopic Explorer (MUSE) integral field
spectroscopy follow-up of this quasi-stellar object (QSO). Our primary goal is
to characterize this LAB in detail by mapping it both spatially and spectrally
using the Ly line, and by looking for high-ionization lines to
constrain the emission mechanism.
Combining the high sensitivity of the MUSE integral field spectrograph
mounted on the Yepun telescope at ESO-VLT with the natural coronagraph provided
by the PDLA, we map the LAB down to the QSO position, after robust subtraction
of QSO light in the spectral domain.
In addition to confirming earlier results for the small bright component of
the LAB, we unveil a faint filamentary emission protruding to the south over
about 80 pkpc (physical kpc); this results in a total size of about 120 pkpc.
We derive the velocity field of the LAB (assuming no transfer effects) and map
the Ly line width. Upper limits are set to the flux of the N V , C IV , He II , and C III] lines. We have discovered two probable Ly emitters at the
same redshift as the LAB and at projected distances of 265 kpc and 207 kpc from
the QSO; their Ly luminosities might well be enhanced by the QSO
radiation. We also find an emission line galaxy at near the line of
sight to the QSO.
This LAB shares the same general characteristics as the 17 others surrounding
radio-quiet QSOs presented previously. However, there are indications that it
may be centered on the PDLA galaxy rather than on the QSO.Comment: Accepted for publication in Astronomy & Astrophysics; 16 pages, 19
figure
Reverse engineering the euglenoid movement
Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large-amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these deformations. Unlike ciliary or flagellar motility, the biophysics of this mode is not well understood, including its efficiency and molecular machinery. We quantitatively examine video recordings of four euglenids executing such motions with statistical learning methods. This analysis reveals strokes of high uniformity in shape and pace. We then interpret the observations in the light of a theory for the pellicle kinematics, providing a precise understanding of the link between local actuation by pellicle shear and shape control. We systematically understand common observations, such as the helical conformations of the pellicle, and identify previously unnoticed features of metaboly. While two of our euglenids execute their stroke at constant body volume, the other two exhibit deviations of about 20% from their average volume, challenging current models of low Reynolds number locomotion. We find that the active pellicle shear deformations causing shape changes can reach 340%, and estimate the velocity of the molecular motors. Moreover, we find that metaboly accomplishes locomotion at hydrodynamic efficiencies comparable to those of ciliates and flagellates. Our results suggest new quantitative experiments, provide insight into the evolutionary history of euglenids, and suggest that the pellicle may serve as a model for engineered active surfaces with applications in microfluidics
A Hybrid-Electric Passenger Vessel for Inland Waterway
The problem of air pollution is one of the biggest issues discussed worldwide: due to this reason, various measures to reduce global pollution, especially CO2 emissions, are being taken by Governments. One of the main causes of pollution is represented by the transport sector, which includes also maritime transport. Therefore, it is necessary to study and find new types of propulsion that ensure a reduction of pollutant emissions. A way to achieve this aim is represented by hybrid-electric propulsion systems, capable of ensuring a good range in ZEM - Zero Emission Mode - navigation. In this paper, the application of hybrid-electric propulsion on a small boat for passenger transport in inland waters has been analysed. Based on the results of preliminary studies, a prototype of the vessel was built; the boat has been a useful and remarkable test bench to validate such a technology, in terms of eco-friendliness, energy efficiency, and reliability. Here, the theoretical estimates carried out in the early stage of design have been compared with the experimental data obtained on the prototype during a sea trials campaign carried out in a real operative environment
Galaxy evolution in nearby groups. II. Galaxy evolution in nearby loose groups. II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud
We present the photometric and kinematic characterization of two groups, USGC
U268 and USGC U376 located in different regions of the Leo cloud. U268,
composed of 10 catalogued members and 11 new added members, has a small
fraction (~24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added
members, with ~38% of ETGs. We find the presence of significant substructures
in both groups suggesting that they are likely accreting galaxies. U268 is
located in a more loose environment than U376. For each member galaxy, broad
band integrated and surface photometry have been obtained in far-UV and near-UV
with GALEX, and in u,g, r, i, z (SDSS) bands. H_alpha imaging and 2D high
resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot
interferometer at the 2.12 m telescope in San Pedro M\'artir, (Baja California,
M\'exico). We improved the galaxy classification and we detected morphological
and kinematical distortions that may be connected to either on-going and/or
past interaction/accretion events or environmental induced secular evolution.
U268 appears more active than U376, with a large fraction of galaxies showing
interaction signatures (60% vs. 13%). The presence of bars among late-type
galaxies is ~10% in U268 and ~$29% in U376. The cumulative distribution of (FUV
- NUV) colours of galaxies in U268 is significantly different than that in U376
with galaxies in U268 bluer than those in U376. In the (FUV-r vs. M_r) and
(NUV-r vs. M_r) planes no members of U268 are found in the `red sequence', even
early-type galaxies lie in the `blue sequence' or in the `green valley'. Most
(80%) of the early-type members in U376 inhabits the `red sequence, a large
fraction of galaxies, of different morphological types, are located in the
`green valley', while the `blue sequence' is under-populated with respect to
U268.Comment: 27 pages, 11 figures, 8 tables, accepted for publication in MNRAS
(abridged abstract
- …