4,825 research outputs found
On Schwarzschild's Topology in Brane-Worlds
The topological structure of Schwarzschild's space-time and its maximal
analytic extension are investigated in context of brane-worlds. Using the
embedding coordinates, these geometries are seen as different states of the
evolution of a single brane-world. Comparing the topologies and the embeddings
it is shown that this evolution must be followed by a signature change in the
bulk.Comment: 6 page
Mass distribution and structural parameters of Small Magellanic Cloud star clusters
In this work we estimate, for the first time, the total masses and mass
function slopes of a sample of 29 young and intermediate-age SMC clusters from
CCD Washington photometry. We also derive age, interstellar reddening and
structural parameters for most of the studied clusters by employing a
statistical method to remove the unavoidable field star contamination. Only
these 29 clusters out of 68 originally analysed cluster candidates present
stellar overdensities and coherent distribution in their colour-magnitude
diagrams compatible with the existence of a genuine star cluster. We employed
simple stellar population models to derive general equations for estimating the
cluster mass based only on its age and integrated light in the B, V, I, C and
T1 filter. These equations were tested against mass values computed from
luminosity functions, showing an excellent agreement. The sample contains
clusters with ages between 60 Myr and 3 Gyr and masses between 300 and 3000 Mo
distributed between ~0.5 deg. and ~2 deg. from the SMC optical centre. We
determined mass function slopes for 24 clusters, of which 19 have slopes
compatible with that of Kroupa IMF (2.3 +/- 0.7), considering the
uncertainties. The remaining clusters - H86-188, H86-190, K47, K63 and NGC242 -
showed flatter MFs. Additionally, only clusters with masses lower than ~1000 Mo
and flatter MF were found within ~0.6 deg. from the SMC rotational centre.Comment: 12 pages, 19 figures. Includes another 29 full-page figures of
supplementary material. Accepted for publication in the MNRA
Incomplete Transition Complexity of Basic Operations on Finite Languages
The state complexity of basic operations on finite languages (considering
complete DFAs) has been in studied the literature. In this paper we study the
incomplete (deterministic) state and transition complexity on finite languages
of boolean operations, concatenation, star, and reversal. For all operations we
give tight upper bounds for both description measures. We correct the published
state complexity of concatenation for complete DFAs and provide a tight upper
bound for the case when the right automaton is larger than the left one. For
all binary operations the tightness is proved using family languages with a
variable alphabet size. In general the operational complexities depend not only
on the complexities of the operands but also on other refined measures.Comment: 13 page
Thermal Casimir Effect in the Plane-Sphere Geometry
The thermal Casimir force between two metallic plates is known to depend on
the description of material properties. For large separations the dissipative
Drude model leads to a force a factor of 2 smaller than the lossless plasma
model. Here we show that the plane-sphere geometry, in which current experiment
are performed, decreases this ratio to a factor of 3/2, as revealed by exact
numerical and large distance analytical calculations. For perfect reflectors,
we find a repulsive contribution of thermal photons to the force and negative
entropy values at intermediate distances.Comment: 4 pages, 3 figure
GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle
Physical properties were derived for the candidate open cluster La Serena 94,
recently unveiled by the VVV collaboration. Thanks to the exquisite angular
resolution provided by GeMS/GSAOI, we could characterize this system in detail,
for the first time, with deep photometry in JHK - bands. Decontaminated
JHK diagrams reach about 5 mag below the cluster turnoff in H. The locus
of red clump giants in the colour - colour diagram, together with an extinction
law, was used to obtain an average extinction of . The
same stars were considered as standard - candles to derive the cluster
distance, kpc. Isochrones were matched to the cluster colour -
magnitude diagrams to determine its age, , and
metallicity, . A core radius of pc was
found by fitting King models to the radial density profile. By adding up the
visible stellar mass to an extrapolated mass function, the cluster mass was
estimated as M, consistent with an
integrated magnitude of and a tidal radius of
pc. The overall characteristics of La Serena 94 confirm that
it is an old open cluster located in the Crux spiral arm towards the fourth
Galactic quadrant and distant kpc from the Galactic centre. The
cluster distorted structure, mass segregation and age indicate that it is a
dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo
Evaluating evolutionary multiobjective algorithms for the in silico optimization of mutant strains
In Metabolic Engineering, the identification of genetic manipulations that lead to mutant strains able to produce a given compound of interest is a promising, while still complex process. Evolutionary Algorithms (EAs) have been a successful approach for tackling the underlying in silico optimization problems. The most common task is to solve a bi-level optimization problem, where the strain that maximizes the production of some compound is sought, while trying to keep the organism viable (maximizing biomass). In this work, this task is viewed as a multiobjective optimization problem and an approach based on multiobjective EAs is proposed. The algorithms are validated with a real world case study that uses E. coli to produce succinic acid. The results obtained are quite promising when compared to the available single objective algorithms.This work was supported by the Portuguese FCT project POSC/EIA/59899/200
Open Cluster Characterization via Cross-Correlation with Spectral Library
We present a characterization method based on spectral cross-correlation to
obtain the physical parameters of the controversial stellar aggregate
ESO442-SC04. The data used was obtained with GMOS at Gemini-South telescope
including 17 stars in the central region of the ob ject and 6 standard-stars.
FXCOR was used in an iterative process to obtain self-consistent radial
velocities for the standard-stars and averaged radial velocities for the
science spectra. Spectral types, effective temperature, suface gravity and
metallicities parameters were determined using FXCOR to correlate cluster
spectra with ELODIE spectral library and selecting the best correlation matches
using the Tonry and Davis Ratio (TDR). Analysis of the results suggests that
the stars in ESO442-SC04 are not bound and therefore they do not constitute a
physical system.Comment: 4-page paper from IAU symposium 266. Contains 3 eps figures and IAU
document class file 'iau.cls
Multi-criterion approaches for the in silico optimization of mutant microorganisms
create mutants for the production of valuable compounds is, in Metabolic Engineering,
a promising, while complex task. Approaches to tackle this problem have been
proposed and included MILP-based techniques (OptKnock [1]), that lacked the
possibility of including non-linear objective functions. More recently, meta-heuristic
approaches like Evolutionary Algorithms (EAs) (OptGene [2]) have been put forward.
Although these are more flexible and have provided good results in some cases, they
relied on objective functions that aggregate several potentially conflicting optimization
goals.
In this work, the problem is interpreted as a Multi-Objective task and an approach based
on Multi-Objective EAs (MOEAs) is proposed. The Strength Pareto Evolutionary
Algorithm 2 (SPEA2) and the Non-dominated Sorting Genetic Algorithm II (NSGA-II),
two state-of-the-art MOEAs were adapted to conduct this task. The optimization goals
are to simultaneously maximize the biomass and also the concentration of a desired
compound (bi-objective optimization problems). Next, we took the problem further and
added two new objectives: minimizing either the number of knockouts in the solution or
the sum of all the fluxes present in the model (tri-objective optimization problems).
These algorithms are validated using three real world case studies. The selected
organisms are S.cerevisiae for the production of succinate and E.coli for the production
of both succinate and lactate. The results are quite promising when compared with the
available single-objective approaches
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