404 research outputs found
Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization
Context. The knowledge of abundance distributions is central to understanding
the formation and evolution of galaxies. Most of the relations employed for the
derivation of gas abundances have so far been derived from observations of
outer disk HII regions, despite the known differences between inner and outer
regions. Aims. Using integral field spectroscopy (IFS) observations we aim to
perform a systematic study and comparison of two inner and outer HII regions
samples. The spatial resolution of the IFS, the number of objects and the
homogeneity and coherence of the observations allow a complete characterization
of the main observational properties and differences of the regions. Methods.
We analyzed a sample of 725 inner HII regions and a sample of 671 outer HII
regions, all of them detected and extracted from the observations of a sample
of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey.
Results. We find that inner HII regions show smaller equivalent widths, greater
extinction and luminosities, along with greater values of
[NII]{\lambda}6583/H{\alpha} and [OII]{\lambda}3727/[OIII]{\lambda}5007
emission-line ratios, indicating higher metallicites and lower ionization
parameters. Inner regions have also redder colors and higher photometric and
ionizing masses, although Mion/Mphot is slighty higher for the outer regions.
Conclusions. This work shows important observational differences between inner
and outer HII regions in star forming galaxies not previously studied in
detail. These differences indicate that inner regions have more evolved stellar
populations and are in a later evolution state with respect to outer regions,
which goes in line with the inside-out galaxy formation paradigm.Comment: 16 page
Anomalous Flow Profile due to the Curvature Effect on Slip Length
Einzel, Panzer, and Liu [Phys. Rev. Lett. 64, 2269 (1990)] suggest that the slip boundary condition for a fluid moving near a wall is modified by the radius of curvature of the surface. Using particle simulations of a microscopic flow between concentric cylinders we qualitatively confirm their prediction and point out that the effect is seen in a limiting case derived by Maxwell [Nature (London) 16, 244 (1877)].SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Reply to "Comment on `Validity of path thermodynamic description of reactive systems: Microscopic simulations'
The Comment's author argues that a correct description of reactive systems
should incorporate the explicit interaction with reservoirs, leading to a
unified system-reservoirs entity. However, this proposition has two major
flaws. Firstly, as we will emphasize, this entity inherently follows a
thermodynamic equilibrium distribution. In the Comment, no indication is
provided on how to maintain such a system-reservoirs entity in a
non-equilibrium state. Secondly, contrary to the author's claim, the inclusion
of system-reservoir interaction in traditional stochastic modeling of reactive
systems does not automatically alter the limited applicability of path
thermodynamics to problematic reactive systems. We will provide a simple
demonstration to illustrate that certain elementary reactions may not involve
any changes in reservoir components, which seems to have been overlooked by the
author.Comment: To appear in Physical Review
Inner and outer star forming regions over the disks of spiral galaxies. II. A comparative of physical properties and evolutionary stages
The HII regions are all studied employing the same general prescriptions,
despite the possible influence of their environment in their star formation
processes. Through the analysis of two samples of 725 inner and 671 outer disk
HII region observed spectra, we explore possible systematic differences between
their ionising clusters physical properties (metallicity, mass, and age),
comparing observations and predictions by photoionisation models. Higher
metallicities are confirmed for inner regions, although there are important
discrepancies between the diagnostic diagrams. Calibrations based on the N2
index may underestimate inner regions O/H due to the [NII] saturation at solar
metallicities. The degeneracy between the age and ionisation parameter affects
O/H calibrations based on the O3N2 index. Innermost regions have enhanced N/O
ratios, indicating an increase in the slope of the relation between N/O and
O/H. Ionisation parameter calibrations based on the [SII]/H{\alpha} ratio are
not valid for inner regions due to the bivalued behaviour of this ratio with
O/H. Innermost regions have lower [OII]/[OIII] ratios than expected, indicating
a possible non-linear relation between u and Z. Ionising and non-ionising
populations are present in both inner and outer regions. Inner regions show
larger ionising cluster masses that possibly compose star-forming complexes.
Outer regions might be affected by stochastic effects. Equivalent widths
indicate younger ages for outer regions, but degeneracy between evolution and
underlying population effects prevent a quantitative determination. Inner
regions have larger angular sizes, lower filling factors, and larger ionised
hydrogen masses. The confirmed systematic differences between ionising clusters
of inner and outer HII regions condition the validity and range of reliability
of O/H and u calibrations commonly applied to the study of HII regions.Comment: Accepted for publication in A&A. 14 pages, 12 figure
On the True Cramer-Rao Lower Bound for the DA Joint Estimation of Carrier Phase and Timing Offsets
The Cramer-Rao lower bound (CRLB) plays a pivotal role in parameter estimation theory, such as timing, frequency and phase synchronization. Therefore, it receives considerable attention in the literature. This paper concerns the CRLB for data-aided (DA) timing and/or phase recovery, i.e. the parameter synchronization is aided by a training sequence known to the receiver. For DA parameter synchronization, the CRLB typically varies with the training sequence. This indicates that different training sequences offer fundamental different performance. Therefore, it is very important to be able to compute the CRLB for any particular training sequence to understand the fundamental limit that a particular training sequence has. However, in the literature, the closed-form CRLB for an arbitrary training sequence is not available. In principle, it is possible to use brute-force numerical approach to compute CRLB for any given training sequence. Such brute-force computation involves evaluation of derivatives numerically and matrix inversion. Besides the computational complexity, brute-force approach does not provide any insight on the interaction between training sequence and the resultant CRLB. In the literature, the widely cited close-form data-aided CRLB for timing and phase recovering was derived under the assumption that the training sequence is independently identical distributed (i.i.d.) and the length of the training sequence is sufficiently long. We found that the CRLB for a particular training sequence can be significantly lower than that with the long i.i.d. assumption. Therefore, the widely cited data-aided CRLB actually does not give the fundamental limit for a particular training sequence. In this manuscript, we derive a closed-form formula for data-aided CRLB for timing and phase synchronization with respect to arbitrary training sequence. The bound illustrates the close relation between the training sequence and the fundamental limit on timing and phase synchronization. This bound provides additional insights on the sequence design. 2000 IEEE International Conference on Communication
Oscillatory behaviour in a lattice prey-predator system
Using Monte Carlo simulations we study a lattice model of a prey-predator
system. We show that in the three-dimensional model populations of preys and
predators exhibit coherent periodic oscillations but such a behaviour is absent
in lower-dimensional models. Finite-size analysis indicate that amplitude of
these oscillations is finite even in the thermodynamic limit. In our opinion,
this is the first example of a microscopic model with stochastic dynamics which
exhibits oscillatory behaviour without any external driving force. We suggest
that oscillations in our model are induced by some kind of stochastic
resonance.Comment: 7 pages, 10 figures, Phys.Rev.E (Nov. 1999
Spurious diffusion in particle simulations of the Kolmogorov flow
Particle simulations of the Kolmogorov flow are analyzed by the
Landau-Lifshitz fluctuating hydrodynamics. It is shown that a spurious
diffusion of the center of mass corrupts the statistical properties of the
flow. The analytical expression for the corresponding diffusion coefficient is
derived.Comment: 10 pages, no figure
Behaviour and passage of European silver eels (Anguilla anguilla) at a small hydropower plant during their downstream migration
Between 2004 and 2007, 116 downstream migrant silver eels (Anguilla anguilla) were monitored at a hydropower plant on the Gave de Pau river in South-West France using radio and PIT telemetry. The objectives of the study were: (i) to determine the environmental conditions when eels arrived and passed the facility; (ii) to determine the rate of eel escapement (passage other than via the turbines); (iii) to describe the behaviour of eels faced with the intake structure and the permeability of the intake trashracks for the different sizes of eel; and (iv) to determine whether surface bypasses originally designed for salmon could be effective for eels. Five types of behaviour of silver eels in the forebay and at the plant intakes were identified. The study showed the key factor influencing both eel behaviour and the route taken through the plant was variation in river discharge. Escapement rate was related to eel length and the spill flow to river flow ratio, which could be described by a logistic regression model. The surface bypasses originally designed for salmon were found to aid downstream eel migration significantly. At velocities < 0.40 m·s−1, no eels, even the largest, for which the racks are a physical barrier, were found impinged
on the trashracks
Potentiation of the anticancer effect of valproic acid, an antiepileptic agent with histone deacetylase inhibitory activity, by the kinase inhibitor Staurosporine or its clinically relevant analogue UCN-01
Histone deacetylase inhibitors (HDACIs) are novel anticancer agents with potent cytotoxicity against a wide range of malignancies. We have previously demonstrated that either Calphostin C (CC) (a protein kinase C (PKC) inhibitor) or Parthenolide (an NF-κB inhibitor) abrogates HDACI-induced transcriptional activation of NF-κB and p21, which is associated with profound potentiation of HDACI-mediated induction of apoptosis. Valproic acid (VA), a commonly used antiepileptic agent, has recently been shown to be an HDACI. This study was aimed to evaluate the anticancer property of VA in thoracic cancer cells and the development of clinically relevant strategies to enhance VA-mediated induction of apoptosis using kinase inhibitors Staurosporine (STP) or its analogue UCN-01. Treating cultured thoracic cancer cells with VA (0.62–10.0 mM) resulted in significant cell line- and dose-dependent growth inhibition (IC50 values: 4.1–6.0 mM) and cell cycle arrest at G1/S checkpoint with profound accumulation of cells at G0/G1 phase but little induction of apoptosis. Valproic acid, being an HDACI, caused significant dose-dependent accumulation of hyperacetylated histones, following 24 h of treatment. Valproic acid-mediated 5–20-fold upregulation of transcriptional activity of NF-κB was substantially (50–90%) suppressed by cotreatment with CC, STP or UCN-01. Whereas minimal death (<20%) was observed in cells treated with either VA (1.0 or 5.0 mM) alone or kinase inhibitors alone, 60–90% of cells underwent apoptosis following exposure to combinations of VA+kinase inhibitors. Kinase inhibitor-mediated suppression of NF-κB transcriptional activity played an important role in sensitising cancer cells to VA as direct inhibition of NF-κB by Parthenolide drastically synergised with VA to induce apoptosis (VA+Parthenolide: 60–90% compared to <20% following single-drug treatments). In conclusion, VA, a well-known antiepileptic drug, has mild growth-inhibitory activity on cultured cancer cells. The weak VA-mediated induction of apoptosis of thoracic cancer cells can be profoundly enhanced either by Parthenolide, a pharmacologic inhibitor of NF-κB, or by UCN-01 a kinase inhibitor that has already undergone phase I clinical development. Combinations of VA with either a PKC inhibitor or an NF-κB inhibitor are promising novel molecularly targeted therapeutics for thoracic cancers
- …