474 research outputs found
Внешнеэкономическая деятельность в системе оценки инвестиционного рейтинга отраслевых предприятий Украины
In this paper we describe a variation of monotone frameworks that enables us to perform approximate typing of Python, in particular for dealing with some of its more dynamic features such as first-class functions and Python’s dynamic class system. We additionally introduce a substantial number of variants of the basic analysis in order to experimentally discover which configurations attain the best balance of cost and precision. For example, the analysis allows us to be selectively flow-insensitive for certain classes of identifiers, and the amount of call-site context is configurable. Results of our evaluation include that adding call-site sensitivity and parameterized types has little effect on precision; in terms of speed call-site sensitivity is very costly. On the other hand, flow-insensitive treatment of module scope identifiers has a strongly positive effect, often both in terms of precision and speed
PaMILO: A Solver for Multi-Objective Mixed Integer Linear Optimization and Beyond
In multi-objective optimization, several potentially conflicting objective
functions need to be optimized. Instead of one optimal solution, we look for
the set of so called non-dominated solutions. An important subset is the set of
non-dominated extreme points. Finding it is a computationally hard problem in
general. While solvers for similar problems exist, there are none known for
multi-objective mixed integer linear programs (MOMILPs) or multi-objective
mixed integer quadratically constrained quadratic programs (MOMIQCQPs). We
present PaMILO, the first solver for finding non-dominated extreme points of
MOMILPs and MOMIQCQPs. PaMILO provides an easy to use interface and is
implemented in C++17. It solves occurring subproblems employing either CPLEX or
Gurobi. PaMILO adapts the dual-benson algorithm for multi-objective linear
programming (MOLP). As it was previously only defined for MOLPs, we describe
how it can be adapted for MOMILPs, MOMIQCQPs and even more problem classes in
the future
Simulations of the Origin and Fate of the Galactic Center Cloud G2
We investigate the origin and fate of the recently discovered gas cloud G2
close to the Galactic Center. Our hydrodynamical simulations focussing on the
dynamical evolution of the cloud in combination with currently available
observations favor two scenarios: a Compact Cloud which started around the year
1995 and a Spherical Shell of gas, with an apocenter distance within the
disk(s) of young stars and a radius of a few times the size of the Compact
Cloud. The former is able to explain the detected signal of G2 in the
position-velocity diagram of the Br gamma emission of the year 2008.5 and
2011.5 data. The latter can account for both, G2's signal as well as the
fainter extended tail-like structure G2t seen at larger distances from the
black hole and smaller velocities. In contrast, gas stripped from a compact
cloud by hydrodynamical interactions is not able to explain the location of the
detected G2t emission in the observed position-velocity diagrams. This favors
the Spherical Shell Scenario and might be a severe problem for the Compact
Cloud as well as the so-called Compact Source Scenario. From these first
idealized simulations we expect a roughly constant feeding of the supermassive
black hole through a nozzle-like structure over a long period, starting shortly
after the closest approach in 2013.51 for the Compact Cloud. If the matter
accretes in the hot accretion mode, we do not expect a significant boost of the
current activity of Sgr A* for the Compact Cloud model, but a boost of the
average infrared and X-ray luminosity by roughly a factor of 80 for the
Spherical Shell scenario with order of magnitude variations on a timescale of a
few months. The near-future evolution of the cloud will be a sensitive probe of
the conditions of the gas distribution in the milli-parsec environment of the
massive black hole in the Galactic Center.Comment: 16 pages, 16 figures, accepted by Ap
An Image Registration-Based Method for EPI Distortion Correction Based on Opposite Phase Encoding (COPE)
Evidence for Warped Disks of Young Stars in the Galactic Center
The central parsec around the super-massive black hole in the Galactic Center
hosts more than 100 young and massive stars. Outside the central cusp (R~1")
the majority of these O and Wolf-Rayet (WR) stars reside in a main clockwise
system, plus a second, less prominent disk or streamer system at large angles
with respect to the main system. Here we present the results from new
observations of the Galactic Center with the AO-assisted near-infrared imager
NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include
the detection of 27 new reliably measured WR/O stars in the central 12" and
improved measurements of 63 previously detected stars, with proper motion
uncertainties reduced by a factor of four compared to our earlier work. We
develop a detailed statistical analysis of their orbital properties and
orientations. Half of the WR/O stars are compatible with being members of a
clockwise rotating system. The rotation axis of this system shows a strong
transition as a function of the projected distance from SgrA*. The main
clockwise system either is either a strongly warped single disk with a
thickness of about 10 degrees, or consists of a series of streamers with
significant radial variation in their orbital planes. 11 out of 61 clockwise
moving stars have an angular separation of more than 30 degrees from the
clockwise system. The mean eccentricity of the clockwise system is 0.36+/-0.06.
The distribution of the counter-clockwise WR/O star is not isotropic at the 98%
confidence level. It is compatible with a coherent structure such as stellar
filaments, streams, small clusters or possibly a disk in a dissolving state.
The observed disk warp and the steep surface density distribution favor in situ
star formation in gaseous accretion disks as the origin of the young stars.Comment: ApJ in pres
Resonant relaxation and the warp of the stellar disc in the Galactic centre
Observations of the spatial distribution and kinematics of young stars in the
Galactic centre can be interpreted as showing that the stars occupy one, or
possibly two, discs of radii ~0.05-0.5 pc. The most prominent (`clockwise')
disc exhibits a strong warp: the normals to the mean orbital planes in the
inner and outer third of the disc differ by ~60 deg. Using an analytical model
based on Laplace-Lagrange theory, we show that such warps arise naturally and
inevitably through vector resonant relaxation between the disc and the
surrounding old stellar cluster.Comment: 24 pages, 8 figures, accepted by MNRA
An extremely top-heavy initial mass function in the galactic center stellar disks
Composite armors, having two or more different materials, contain a ceramic layer in the front face and a metallic or polymer matrix composite as support on the back side backing. The function of the ceramic layer is to erode and break up the projectile and to increase the contact surface of the metallic plate by forming a hard cone. The role of the metallic backing layer is to absorb the kinetic energy of the projectile and support the fragmented ceramic. The most impportant advantage of these materials over monolithic metallic armors is to reduce the thickness by using the ceramic layer in front of the metallic layer. This provides reducing the weight of armor. In this study, experiments have been conducted to describe ballistic performance of polymer matrix composites having different geometrical shapes. To do these experiments, aramid and polyethilen composite specimens were first fabricated as laminates in different geometrical shapes. Then, these composite plates at charpy harms were investigeted in varios speed bullet to cover the impact damageKompozit zırhlar iki veya daha fazla farklı malzemeden oluşan, yüzeyde seramik katman ile arkada metal veya polimer matrisli kompozit destek içeren malzemelerdir. Seramik katmanın işlevi mermiyi aşındırma ve parçalamanın yanısıra sert koni oluşturarak metal katmanın temas yüzeyini artırmaktır. Metal destek katmanının görevi ise merminin kinetik enerjisini emmek ve darbe sonrası oluşacak seramik parçaları tutmaktır. Bu malzemelerin, tamamen metalik olan zırhlara göre en önemli avantajı, metalik katmandan önce seramik katmanın kullanılması yoluyla zırh kalınlığının, dolayısı ile zırhın ağırlığının azalmasını sağlamaktadır. Bu çalışmada değişik geometriye sahip, polimer matrisli kompozitlerin, balistik performansını ölçmek için deneyler yapılmıştır. Bunun için önce Aramid ve polietilen numuneler düz, iki değişik çapta silindirik ve küre plakalar halinde üretilmiştir. Bu kompozit plakalara atış poligonunda atışlar yapılmış ve oluşan darbe hasarları incelenmiştir
Near-infrared proper motions and spectroscopy of infrared excess sources at the Galactic Center
There are a number of faint compact infrared excess sources in the central
stellar cluster of the Milky Way. Their nature and origin is unclear. In
addition to several isolated objects of this kind we find a small but dense
cluster of co-moving sources (IRS13N) about 3" west of SgrA* just 0.5" north of
the bright IRS13E cluster of WR and O-type stars. Based on their color and
brightness, there are two main possibilities: (1) they may be dust embedded
stars older than few Myr, or (2) extremely young, dusty stars with ages less
than 1Myr. We present fist H- and Ks-band identifications or proper motions of
the IRS13N members, the high velocity dusty S-cluster object (DSO), and other
infrared excess sources in the central field. We also present results of NIR H-
and Ks-band ESO-SINFONI integral field spectroscopy of ISR13N. We show that
within the uncertainties, the proper motions of the IRS13N sources in Ks- and
L'-band are identical. This indicates that the bright L'-band IRS13N sources
are indeed dust enshrouded stars rather than core-less dust clouds. The proper
motions show that the IRS13N sources are not strongly gravitationally bound to
each other implying that they have been formed recently. We also present a
first H- and Ks-band identification as well as proper motions and HKsL'-colors
of a fast moving DSO which was recently found in the cluster of high speed
S-stars that surround the super-massive black hole Sagittarius A* (SgrA*). Most
of the compact L'-band excess emission sources have a compact H- or Ks-band
counterpart and therefore are likely stars with dust shells or disks. Our new
results and orbital analysis from our previous work favor the hypothesis that
the infrared excess IRS13N members and other dusty sources close to SgrA* are
very young dusty stars and that star formation at the GC is a continuously
ongoing process.Comment: 20 pages, 18 figures, 4 tables plus appendix with 16 figures and 3
tables accepted by A&
Fine spatial pattern of an epiphytic lichen species is affected by habitat conditions in two forest types in the Iberian Mediterranean region
Persistence and abundance of species is determined by habitat availability and the ability to disperse and colonize habitats at contrasting spatial scales. Favourable habitat fragments are also heterogeneous in quality, providing differing opportunities for establishment
and affecting the population dynamics of a species. Based on these principles, we suggest that the presence and abundance of epiphytes may reflect their dispersal ability,
which is primarily determined by the spatial structure of host trees, but also by host quality.
To our knowledge there has been no explicit test of the importance of host tree spatial pattern for epiphytes in Mediterranean forests. We hypothesized that performance and
host occupancy in a favourable habitat depend on the spatial pattern of host trees, because this pattern affects the dispersal ability of each epiphyte and it also determines the availability of suitable sites for establishment. We tested this hypothesis using new point pattern analysis tools and generalized linear mixed models to investigate the spatial distribution and performance of the epiphytic lichen Lobaria pulmonaria, which inhabits
two types of host trees (beeches and Iberian oaks). We tested the effects on L. pulmonaria distribution of tree size, spatial configuration, and host tree identity. We built a model including tree size, stand structure, and several neighbourhood predictors to understand the effect of host tree on L. pulmonaria. We also investigated the relative importance of spatial patterning on the presence and abundance of the species, independently of the host
tree configuration. L. pulmonaria distribution was highly dependent on habitat quality for successful establishment, i.e., tree species identity, tree diameter, and several forest stand structure surrogates. For beech trees, tree diameter was the main factor influencing presence and cover of the lichen, although larger lichen-colonized trees were located close to focal trees, i.e., young trees. However, oak diameter was not an important factor, suggesting
that bark roughness at all diameters favoured lichen establishment. Our results indicate that L. pulmonaria dispersal is not spatially restricted, but it is dependent on habitat quality. Furthermore, new spatial analysis tools suggested that L. pulmonaria cover exhibits a distinct pattern, although the spatial pattern of tree position and size was random
Laplace Operators on Fractals and Related Functional Equations
We give an overview over the application of functional equations, namely the
classical Poincar\'e and renewal equations, to the study of the spectrum of
Laplace operators on self-similar fractals. We compare the techniques used to
those used in the euclidean situation. Furthermore, we use the obtained
information on the spectral zeta function to define the Casimir energy of
fractals. We give numerical values for this energy for the Sierpi\'nski gasket
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