1,061 research outputs found
Resonance in PSR B1257+12 Planetary System
In this paper we present a new method that can be used for analysis of time
of arrival of a pulsar pulses (TOAs). It is designated especially to detect
quasi-periodic variations of TOAs. We apply our method to timing observations
of PSR B1257+12 and demonstrate that using it it is possible to detect not only
first harmonics of a periodic variations, but also the presence of a resonance
effect. The resonance effect detected, independently of its physical origin,
can appear only when there is a non-linear interaction between two periodic
modes. The explanation of TOAs variations as an effect of the existence of
planets is, till now, the only known and well justified. In this context, the
existence of the resonance frequency in TOAs is the most significant signature
of the gravitational interaction of planets.Comment: AASLaTeX + 5 figures (eps files), 15 pages; submitted to Ap
Influenceof measuring conditions on the quantification of spectroscopic signals inTA-FTIR-MS systems
Simultaneous thermal analysis (TA) and evolved gas analysis by mass spectrometry (MS) and/or Fourier transform infrared spectroscopy (FTIR) is a powerful hyphenated technique combining direct measurement of mass loss and sensitive spectroscopic analysis. In the present study the influence of several experimental parameters which may affect the quantification of FTIR signals have been studied using a combined TA-FTIR-MS system. Parameters studied include: sample mass (1-400 mg), carrier gas flow rate (25-200 mL min-1), resolution of the FTIR spectrometer (1-32 cm-1), and location of injection of the calibrating gas. MS analysis, which was not significantly affected by the experimental conditions, was used as a reference for assessing the accuracy of quantification by FTIR. The quantification of the spectroscopic signals was verified by the decomposition (NaHCO3) or dehydration (CuSO4·5H2O) of compounds with well-known stoichiometry. The systematic study of the parametric sensitivity revealed that spectral resolution and carrier gas flow rate, which affect the acquisition time in the IR-cell, are key parameters that must be adjusted carefully for reliable quantification. The dependence of the reliability of quantification on these parameters is illustrated and conditions leading to proper quantification are discussed. As an example, for a standard spectral resolution of 4 cm-1 and a FTIR gas cell volume of 8.7 mL, the carrier gas flow must be lower than 100 mL min-1 for warranting accurate results (relative deviation <2%). The concentration range of analyzed species is limited but can be extended by proper selection of the wavenumber regions for molecules giving strong IR signal
Supernova Remnant in a Stratified Medium: Explicit, Analytical Approximations for Adiabatic Expansion and Radiative Cooling
We propose simple, explicit, analytical approximations for the kinematics of
an adiabatic blast wave propagating in an exponentially stratified ambient
medium, and for the onset of radiative cooling, which ends the adiabatic era.
Our method, based on the Kompaneets implicit solution and the Kahn
approximation for the radiative cooling coefficient, gives straightforward
estimates for the size, expansion velocity, and progression of cooling times
over the surface, when applied to supernova remnants (SNRs). The remnant shape
is remarkably close to spherical for moderate density gradients, but even a
small gradient in ambient density causes the cooling time to vary substantially
over the remnant's surface, so that for a considerable period there will be a
cold dense expanding shell covering only a part of the remnant. Our
approximation provides an effective tool for identifying the approximate
parameters when planning 2-dimensional numerical models of SNRs, the example of
W44 being given in a subsequent paper.Comment: ApJ accepted, 11 pages, 2 figures embedded, aas style with
ecmatex.sty and lscape.sty package
Application of random coherence order selection in gradient-enhanced multidimensional NMR
Development of multidimensional NMR is essential to many applications, for example in high resolution structural studies of biomolecules. Multidimensional techniques enable separation of NMR signals over several dimensions, improving signal resolution, whilst also allowing identification of new connectivities. However, these advantages come at a significant cost. The Fourier transform theorem requires acquisition of a grid of regularly spaced points to satisfy the Nyquist criterion, while frequency discrimination and acquisition of a pure phase spectrum require acquisition of both quadrature components for each time point in every indirect (non-acquisition) dimension, adding a factor of 2 to the number of free-induction decays which must be acquired, where is the number of dimensions. Compressed sensing (CS) ℓ-norm minimisation in combination with non-uniform sampling (NUS) has been shown to be extremely successful in overcoming the Nyquist criterion. Previously, maximum entropy reconstruction has also been used to overcome the limitation of frequency discrimination, processing data acquired with only one quadrature component at a given time interval, known as random phase detection (RPD), allowing a factor of two reduction in the number of points for each indirect dimension (Maciejewski et al. 2011 108 16640). However, whilst this approach can be easily applied in situations where the quadrature components are acquired as amplitude modulated data, the same principle is not easily extended to phase modulated (P-/N-type) experiments where data is acquired in the form exp () or exp (−), and which make up many of the multidimensional experiments used in modern NMR. Here we demonstrate a modification of the CS ℓ-norm approach to allow random coherence order selection (RCS) for phase modulated experiments; we generalise the nomenclature for RCS and RPD as random quadrature detection (RQD). With this method, the power of RQD can be extended to the full suite of experiments available to modern NMR spectroscopy, allowing resolution enhancements for all indirect dimensions; alone or in combination with NUS, RQD can be used to improve experimental resolution, or shorten experiment times, of considerable benefit to the challenging applications undertaken by modern NMR.This is the final version of the article. It first appeared from IOP Publishing via http://dx.doi.org/10.1088/1742-6596/699/1/01200
[The Impact of Nuclear Star Formation on Gas Inflow to AGN
Our adaptive optics observations of nearby AGN at spatial resolutions as
small as 0.085arcsec show strong evidence for recent, but no longer active,
nuclear star formation. We begin by describing observations that highlight two
contrasting methods by which gas can flow into the central tens of parsecs. Gas
accumulation in this region will inevitably lead to a starburst, and we discuss
the evidence for such events. We then turn to the impact of stellar evolution
on the further inflow of gas by combining a phenomenological approach with
analytical modelling and hydrodynamic simulations. These complementary
perspectives paint a picture in which all the processes are ultimately
regulated by the mass accretion rate into the central hundred parsecs, and the
ensuing starburst that occurs there. The resulting supernovae delay accretion
by generating a starburst wind, which leaves behind a clumpy interstellar
medium. This provides an ideal environment for slower stellar outflows to
accrete inwards and form a dense turbulent disk on scales of a few parsecs.
Such a scenario may resolve the discrepancy between the larger scale structure
seen with adaptive optics and the small scale structure seen with VLTI.Comment: to appear in: Co-Evolution of Central Black Holes and Galaxies; 7
page
The activity and immunoexpression of cathepsin D in rat male reproductive organs
Cathepsin D is a cysteine endopeptidase that belongs to the lysosomal enzyme
family. The aim of the study was to evaluate the enzyme immunoexpression and
activity in selected male genital organs in mature Wistar rats. The activity of
cathepsin D was measured spectrophotometrically in homogenates of the testis,
epididymis, seminal vesicle and prostate. Immunohistochemical staining was
also performed in the ductus deferens. Enzyme activity was found in the following
sequence: testis>epididymis>dorsal prostatic lobe>seminal
vesicle>lateral prostatic lobe>ventral prostatic lobe. Although there were differences
in enzyme activity between various organs of the male reproductive
system, cathepsin D immunoreactivity was seen exclusively in the Sertoli and
Leydig cells in the testis
Phase-space structures II: Hierarchical Structure Finder
A new multi-dimensional Hierarchical Structure Finder (HSF) to study the
phase-space structure of dark matter in N-body cosmological simulations is
presented. The algorithm depends mainly on two parameters, which control the
level of connectivity of the detected structures and their significance
compared to Poisson noise. By working in 6D phase-space, where contrasts are
much more pronounced than in 3D position space, our HSF algorithm is capable of
detecting subhaloes including their tidal tails, and can recognise other
phase-space structures such as pure streams and candidate caustics. If an
additional unbinding criterion is added, the algorithm can be used as a
self-consistent halo and subhalo finder. As a test, we apply it to a large halo
of the Millennium Simulation, where 19 % of the halo mass are found to belong
to bound substructures, which is more than what is detected with conventional
3D substructure finders, and an additional 23-36 % of the total mass belongs to
unbound HSF structures. The distribution of identified phase-space density
peaks is clearly bimodal: high peaks are dominated by the bound structures and
low peaks belong mostly to tidal streams. In order to better understand what
HSF provides, we examine the time evolution of structures, based on the merger
tree history. Bound structures typically make only up to 6 orbits inside the
main halo. Still, HSF can identify at the present time at least 80 % of the
original content of structures with a redshift of infall as high as z <= 0.3,
which illustrates the significant power of this tool to perform dynamical
analyses in phase-space.Comment: Submitted to MNRAS, 24 pages, 18 figure
Necessary conditions for classical super-integrability of a certain family of potentials in constant curvature spaces
We formulate the necessary conditions for the maximal super-integrability of
a certain family of classical potentials defined in the constant curvature
two-dimensional spaces. We give examples of homogeneous potentials of degree -2
on as well as their equivalents on and for which these
necessary conditions are also sufficient. We show explicit forms of the
additional first integrals which always can be chosen polynomial with respect
to the momenta and which can be of an arbitrary high degree with respect to the
momenta
Straight Line Orbits in Hamiltonian Flows
We investigate periodic straight-line orbits (SLO) in Hamiltonian force
fields using both direct and inverse methods. A general theorem is proven for
natural Hamiltonians quadratic in the momenta in arbitrary dimension and
specialized to two and three dimension. Next we specialize to homogeneous
potentials and their superpositions, including the familiar H\'enon-Heiles
problem. It is shown that SLO's can exist for arbitrary finite superpositions
of -forms. The results are applied to a family of generalized H\'enon-Heiles
potentials having discrete rotational symmetry. SLO's are also found for
superpositions of these potentials.Comment: laTeX with 6 figure
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