11,851 research outputs found
A Simple Nested Simulation for SED-ML
This document describes a simple nested Simulation Experiment for SED-ML [1] that is easy to implement and will help to broaden what SED-ML is able to encode
Longitudinal Atomic Beam Spin Echo Experiments: A possible way to study Parity Violation in Hydrogen
We discuss the propagation of hydrogen atoms in static electric and magnetic
fields in a longitudinal atomic beam spin echo (lABSE) apparatus. Depending on
the choice of the external fields the atoms may acquire both dynamical and
geometrical quantum mechanical phases. As an example of the former, we show
first in-beam spin rotation measurements on atomic hydrogen, which are in
excellent agreement with theory. Additional calculations of the behaviour of
the metastable 2S states of hydrogen reveal that the geometrical phases may
exhibit the signature of parity-(P-)violation. This invites for possible future
lABSE experiments, focusing on P-violating geometrical phases in the lightest
of all atoms.Comment: 6 pages, 4 figure
TinkerCell: Modular CAD Tool for Synthetic Biology
Synthetic biology brings together concepts and techniques from engineering
and biology. In this field, computer-aided design (CAD) is necessary in order
to bridge the gap between computational modeling and biological data. An
application named TinkerCell has been created in order to serve as a CAD tool
for synthetic biology. TinkerCell is a visual modeling tool that supports a
hierarchy of biological parts. Each part in this hierarchy consists of a set of
attributes that define the part, such as sequence or rate constants. Models
that are constructed using these parts can be analyzed using various C and
Python programs that are hosted by TinkerCell via an extensive C and Python
API. TinkerCell supports the notion of a module, which are networks with
interfaces. Such modules can be connected to each other, forming larger modular
networks. Because TinkerCell associates parameters and equations in a model
with their respective part, parts can be loaded from databases along with their
parameters and rate equations. The modular network design can be used to
exchange modules as well as test the concept of modularity in biological
systems. The flexible modeling framework along with the C and Python API allows
TinkerCell to serve as a host to numerous third-party algorithms. TinkerCell is
a free and open-source project under the Berkeley Software Distribution
license. Downloads, documentation, and tutorials are available at
www.tinkercell.com.Comment: 23 pages, 20 figure
Metastable states, the adiabatic theorem and parity violating geometric phases II
We discuss and calculate parity conserving (PC) and parity violating (PV)
geometric phases for the metastable 2S states of hydrogen and deuterium. The
atoms are supposed to be subjected to slowly varying electric and magnetic
fields which act as external parameters for the atoms. Geometric flux density
fields are introduced which allow for an easy overview how to choose the paths
in parameter space in order to obtain only PC or only PV geometric phases. The
PV phases are calculated in the Standard Model of particle physics. Even if
numerically they come out small they have interest of principle as a new
manifestation of parity violation in atomic physics.Comment: 63 pages, 8 figures, 10 table
Photoionization Suppression by Continuum Coherence: Experiment and Theory
We present experimental and theoretical results of a detailed study of
laser-induced continuum structures (LICS) in the photoionization continuum of
helium out of the metastable state 2s . The continuum dressing with a
1064 nm laser, couples the same region of the continuum to the {4s }
state. The experimental data, presented for a range of intensities, show
pronounced ionization suppression (by as much as 70% with respect to the
far-from-resonance value) as well as enhancement, in a Beutler-Fano resonance
profile. This ionization suppression is a clear indication of population
trapping mediated by coupling to a contiuum. We present experimental results
demonstrating the effect of pulse delay upon the LICS, and for the behavior of
LICS for both weak and strong probe pulses. Simulations based upon numerical
solution of the Schr\"{o}dinger equation model the experimental results. The
atomic parameters (Rabi frequencies and Stark shifts) are calculated using a
simple model-potential method for the computation of the needed wavefunctions.
The simulations of the LICS profiles are in excellent agreement with
experiment. We also present an analytic formulation of pulsed LICS. We show
that in the case of a probe pulse shorter than the dressing one the LICS
profile is the convolution of the power spectra of the probe pulse with the
usual Fano profile of stationary LICS. We discuss some consequences of
deviation from steady-state theory.Comment: 29 pages, 17 figures, accepted to PR
Extended Gas in Seyfert Galaxies: Near Infrared Observations of NGC 2110 and Circinus
We present results of near--IR long-slit spectroscopy in the J and K bands of
the Seyfert 2 galaxies NGC 2110 and Circinus, investigating the gaseous
distribution, excitation, reddening and kinematics. In NGC 2110, the emission
line ratio [FeII]/Pa beta increases towards the nucleus (to ~ 7). The nuclear
[Fe II]1.257 (microns) and Pa beta lines are broader (FWHM ~ 500 km/s) than the
H2 (2.121) line (FWHM ~ 300 km/s). Both these results suggest that shocks,
driven by the radio jet, are an important source of excitation of [Fe II]. The
H2 excitation appears to be dominated by X-rays from the nucleus. In Circinus,
both [FeII]/Pa beta and H2/Br gamma decrease from ~ 2 at 4 arcsec from the
nucleus to nuclear values of ~ 0.6 and ~ 1, respectively, suggesting that the
starburst dominates the nuclear excitation, while the AGN dominates the
excitation further out (r > 2 arcsec). For both galaxies, the gaseous
kinematics are consistent with circular rotation in the plane of the disk. Our
rotation curves suggest that the nucleus (identified with the peak of the IR
continuum) is displaced from the kinematic centre of the galaxies. This effect
has been observed previously in NGC 2110 based on the kinematics of optical
emission lines, but the displacement is smaller in the infrared, suggesting the
effect is related to obscuration. The continuum J-K colours of the nuclear
region indicate a red stellar population in NGC 2110 and a reddened young
stellar population in Circinus. Right at the nucleus of both galaxies, the
colours are redder, apparently a result of hot dust emission from the inner
edge of a circumnuclear torus.Comment: 11 pages, 14 figures, accepted for publication in MNRA
The Spectral Energy Distribution of Normal, Starburst and Active Galaxies
We present the results of an extensive literature search of multiwavelength
data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's,
5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include
soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared
photometry and radio measurements, selected to match as closely as possible the
IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar
characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts
of Low and High reddening, for which we create average spectral energy
distributions (SED). The individual groups SED's are normalized to the
7000\AA flux and compared, looking for similarities and differences
among them.The bolometric fluxes of different types of galaxies were calculated
integrating their SED's. These values are compared with individual waveband
flux densities, in order to determine the wavebands which contribute most to
the bolometric flux. Linear regressions were performed between the bolometric
and individual band fluxes for each kind of galaxy. These fits can be used in
the calculation of the bolometric flux for other objects of similar activity
type, but with reduced waveband information. We have also collected
multiwavelength data for 4 HII regions, a thermal supernova remnant, and a
non-thermal supernova remnant (SNR), which are compared with the Starburst
SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The
Astronomical Journa
Long-Term Profile Variability of Double-Peaked Emmission Lines in AGNs
An increasing number of AGNs exhibit broad, double-peaked Balmer emission
lines, which arise from the outer regions of the accretion disk which fuels the
AGN. The line profiles vary on timescales of 5--10 years. Our group has
monitored a set of 20 double-peaked emitters for the past 8 years (longer for
some objects). Here we describe a project to characterize the variability
patterns of the double-peaked H alpha line profiles and compare with those of
two simple models: a circular disk with a spiral arm and an elliptical disk.Comment: 2 pages, 1 figure, to appear in the proceedings of "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. T.
Storchi Bergmann, L.C. Ho, and H.R. Schmit
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