435 research outputs found
A multiobjective continuation method to compute the regularization path of deep neural networks
Sparsity is a highly desired feature in deep neural networks (DNNs) since it
ensures numerical efficiency, improves the interpretability of models (due to
the smaller number of relevant features), and robustness. In machine learning
approaches based on linear models, it is well known that there exists a
connecting path between the sparsest solution in terms of the norm
(i.e., zero weights) and the non-regularized solution, which is called the
regularization path. Very recently, there was a first attempt to extend the
concept of regularization paths to DNNs by means of treating the empirical loss
and sparsity ( norm) as two conflicting criteria and solving the
resulting multiobjective optimization problem. However, due to the
non-smoothness of the norm and the high number of parameters, this
approach is not very efficient from a computational perspective. To overcome
this limitation, we present an algorithm that allows for the approximation of
the entire Pareto front for the above-mentioned objectives in a very efficient
manner. We present numerical examples using both deterministic and stochastic
gradients. We furthermore demonstrate that knowledge of the regularization path
allows for a well-generalizing network parametrization.Comment: 7 pages, 6 figure
A Note on the Slim Accretion Disk Model
We show that when the gravitational force is correctly calculated in dealing
with the vertical hydrostatic equilibrium of black hole accretion disks, the
relationship that is valid for geometrically thin disks, i.e., constant, where is the sound speed, is the Keplerian
angular velocity, and is the half-thickness of the disk, does not hold for
slim disks. More importantly, by adopting the correct vertical gravitational
force in studies of thermal equilibrium solutions, we find that there exists a
maximally possible accretion rate for each radius in the outer region of
optically thick accretion flows, so that only the inner region of these flows
can possibly take the form of slim disks, and strong outflows from the outer
region are required to reduce the accretion rate in order for slim disks to be
realized.Comment: 14 pages, 5 figures, accepted by Ap
Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure
The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. These lines serve as powerful probes for examining
the structure of inner regions of accretion disks. Previous studies of line
emission have considered geometrically thin disks only, where the gas moves
along geodesics in the equatorial plane of a black hole. Here we extend this
work to consider effects on line profiles from finite disk thickness, radial
accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution,
and find that within this framework, turbulent broadening is the dominant new
effect. The most prominent change in the skewed, double-horned line profiles is
a substantial reduction in the maximum flux at both red and blue peaks. The
effect is most pronounced when the inclination angle is large, and when the
accretion rate is high. Thus, the effects discussed here may be important for
future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ;
short results of this paper appeared before as a conference proceedings
(astro-ph/9711214
Estudo preliminar antimicrobiano e fitoquĂmico do Ăłleo essencial foliar da Nectandra grandiflora Ness (canela-amarela).
SBQ SUL
Infrastructure Upgrades and Foreclosure with Coexistence of Service-Based and Facility-Based Firms
Boson Stars as Gravitational Lenses
We discuss boson stars as possible gravitational lenses and study the lensing
effect by these objects made of scalar particles. The mass and the size of a
boson star may vary from an individual Newtonian object similar to the Sun to
the general relativistic size and mass of a galaxy close to its Schwarzschild
radius. We assume boson stars to be transparent which allows the light to pass
through them though the light is gravitationally deflected. We assume boson
stars of the mass to be on non-cosmological distance from
the observer. We discuss the lens equation for these stars as well as the
details of magnification. We find that there are typically three images of a
star but the deflection angles may vary from arcseconds to even degrees. There
is one tangential critical curve (Einstein ring) and one radial critical curve
for tangential and radial magnification, respectively. Moreover, the deflection
angles for the light passing in the gravitational field of boson stars can be
very large (even of the order of degrees) which reflects the fact they are very
strong relativistic objects. We also propose a suitable formula for the lens
equation for such large deflection angles, and with the reservation that large
deflection angle images are highly demagnified but in the area of the
tangential critical curve, their existence may help in observational detection
of suitable lenses possessing characteristic features of boson stars which
could also serve as a direct evidence for scalar fields in the universe.Comment: accepted by Astrophys. J., 31 pages, AASTeX, 6 figure
Bringing to light the physiological and pathological firing patterns of human induced pluripotent stem cell-derived neurons using optical recordings
Human induced pluripotent stem cells (hiPSCs) are a promising approach to study neurological and neuropsychiatric diseases. Most methods to record the activity of these cells have major drawbacks as they are invasive or they do not allow single cell resolution. Genetically encoded voltage indicators (GEVIs) open the path to high throughput visualization of undisturbed neuronal activity. However, conventional GEVIs perturb membrane integrity through inserting multiple copies of transmembrane domains into the plasma membrane. To circumvent large add-ons to the plasma membrane, we used a minimally invasive novel hybrid dark quencher GEVI to record the physiological and pathological firing patterns of hiPSCs-derived sensory neurons from patients with inherited erythromelalgia, a chronic pain condition associated with recurrent attacks of redness and swelling in the distal extremities. We observed considerable differences in action potential firing patterns between patient and control neurons that were previously overlooked with other recording methods. Our system also performed well in hiPSC-derived forebrain neurons where it detected spontaneous synchronous bursting behavior, thus opening the path to future applications in other cell types and disease models including Parkinsonâs disease, Alzheimerâs disease, epilepsy, and schizophrenia, conditions associated with disturbances of neuronal activity and synchrony
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