3,563 research outputs found
Numerical study on diverging probability density function of flat-top solitons in an extended Korteweg-de Vries equation
We consider an extended Korteweg-de Vries (eKdV) equation, the usual
Korteweg-de Vries equation with inclusion of an additional cubic nonlinearity.
We investigate the statistical behaviour of flat-top solitary waves described
by an eKdV equation in the presence of weak dissipative disorder in the linear
growth/damping term. With the weak disorder in the system, the amplitude of
solitary wave randomly fluctuates during evolution. We demonstrate numerically
that the probability density function of a solitary wave parameter
which characterizes the soliton amplitude exhibits loglognormal divergence near
the maximum possible value.Comment: 8 pages, 4 figure
The Origin of X-shaped Radio Galaxies: Clues from the Z-symmetric Secondary Lobes
Existing radio images of a few X-shaped radio galaxies reveal Z-symmetric
morphologies in their weaker secondary lobes which cannot be naturally
explained by either the galactic merger or radio-lobe backflow scenarios, the
two dominant models for these X-shaped radio sources. We show that the merger
picture can explain these morphologies provided one takes into account that,
prior to the coalescence of their supermassive black holes, the smaller galaxy
releases significant amounts of gas into the ISM of the dominant active galaxy.
This rotating gas, whose angular momentum axis will typically not be aligned
with the original jets, is likely to provide sufficient ram pressure at a
distance ~10 kpc from the nucleus to bend the extant jets emerging from the
central engine, thus producing a Z-symmetry in the pair of radio lobes. Once
the two black holes have coalesced some 10^7 yr later, a rapid reorientation of
the jets along a direction close to that of the orbital angular momentum of the
swallowed galaxy relative to the primary galaxy would create the younger
primary lobes of the X-shaped radio galaxy. This picture naturally explains why
such sources typically have powers close to the FR I/II break. We suggest that
purely Z-symmetric radio sources are often en route to coalescence and the
concomitant emission of substantial gravitational radiation, while X-shaped
ones have already merged and radiated.Comment: 12 pages, 1 compressed figure; accepted for publication in ApJ
Letter
Diffusive counter dispersion of mass in bubbly media
We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles
are immovably trapped in a porous matrix by surface-tension forces, the
dominant mechanism of transfer of gas mass becomes the diffusion of gas
molecules through the liquid. Essentially, the gas solution is in local
thermodynamic equilibrium with vapor phase all over the system, i.e., the
solute concentration equals the solubility. When temperature and/or pressure
gradients are applied, diffusion fluxes appear and these fluxes are faithfully
determined by the temperature and pressure fields, not by the local solute
concentration, which is enslaved by the former. We derive the equations
governing such systems, accounting for thermodiffusion and gravitational
segregation effects which are shown not to be neglected for geological
systems---marine sediments, terrestrial aquifers, etc. The results are applied
for the treatment of non-high-pressure systems and real geological systems
bearing methane or carbon dioxide, where we find a potential possibility of the
formation of gaseous horizons deep below a porous medium surface. The reported
effects are of particular importance for natural methane hydrate deposits and
the problem of burial of industrial production of carbon dioxide in deep
aquifers.Comment: 10 pages, 5 figures, 1 table, Physical Review
Earth Radiation Budget Experiment (ERBE) scanner instrument anomaly investigation
The results of an ad-hoc committee investigation of in-Earth orbit operational anomalies noted on two identical Earth Radiation Budget Experiment (ERBE) Scanner instruments on two different spacecraft busses is presented. The anomalies are attributed to the bearings and the lubrication scheme for the bearings. A detailed discussion of the pertinent instrument operations, the approach of the investigation team and the current status of the instruments now in Earth orbit is included. The team considered operational changes for these instruments, rework possibilities for the one instrument which is waiting to be launched, and preferable lubrication considerations for specific space operational requirements similar to those for the ERBE scanner bearings
On the connection between gamma and radio radiation spectra in pulsars
The model of pulsar radio emission is discussed in which a coherent radio
emis-sion is excited in a vacuum gap above polar cap of neutron star. Pulsar X
and gamma radiation are considered as the result of low-frequency radio
emission inverse Comp-ton scattering on ultra relativistic electrons
accelerated in the gap. The influence of the pulsar magnetic field on Compton
scattering is taken into account. The relation of radio and gamma radiation
spectra has been found in the framework of the model.Comment: 15 pages, 3 figures, Russian version accepted to JETP, partly
published in JETP Letters, Vol. 85, #6 (2007
Bright X-ray radiation from plasma bubbles in an evolving laser wakefield accelerator
We show that the properties of the electron beam and bright x-rays produced
by a laser wakefield accelerator can be predicted if the distance over which
the laser self-focuses and compresses prior to self-injection is taken into
account. A model based on oscillations of the beam inside a plasma bubble shows
that performance is optimised when the plasma length is matched to the laser
depletion length. With a 200~TW laser pulse this results in an x-ray beam with
median photon energy of \unit[20]{keV}, photons above
\unit[1]{keV} per shot and a peak brightness of \unit[3 \times
10^{22}]{photons~s^{-1}mrad^{-2}mm^{-2} (0.1\% BW)^{-1}}.Comment: 5 pages, 4 figure
Contextual factors among indiscriminate or larger attacks on food or water supplies, 1946-2015
This research updates previous inventories of malicious attacks on food and water to include data from 1946 through mid-2015. A systematic search of news reports, databases and previous inventories of poisoning events was undertaken. Incidents that threatened or were intended to achieve direct harm to humans, and that were either relatively large (number of victims > 4 or indiscriminate in intent or realisation were included. Agents could be chemical, biological or radio-nuclear. Reports of candidate incidents were subjected to systematic inclusion and exclusion criteria as well as validity analysis (not always clearly undertaken in previous inventories of such attacks). We summarise contextual aspects of the attacks that may be important for scenario prioritisation, modelling and defensive preparedness. Opportunity is key to most realised attacks, particularly access to dangerous agents. The most common motives and relative success rate in causing harm were very different between food and water attacks. The likelihood that people were made ill or died also varied by food/water mode, and according to motive and opportunity for delivery of the hazardous agent. Deaths and illness associated with attacks during food manufacture and prior to sale have been fewer than those in some other contexts. Valuable opportunities for food defence improvements are identified in other contexts, especially food prepared in private or community settings
Si3AlP: A new promising material for solar cell absorber
First-principles calculations are performed to study the structural and
optoelectronic properties of the newly synthesized nonisovalent and
lattice-matched (Si2)0.6(AlP)0.4 alloy [T. Watkins et al., J. Am. Chem. Soc.
2011, 133, 16212.] We find that the ordered CC-Si3AlP with a basic unit of one
P atom surrounded by three Si atoms and one Al atom is the most stable one
within the experimentally observed unit cell.1 Si3AlP has a larger fundamental
band gap and a smaller direct band gap than Si, thus it has much higher
absorption in the visible light region. The calculated properties of Si3AlP
suggest that it is a promising candidate for improving the performance of the
existing Si-based solar cells. The understanding on the stability and band
structure engineering obtained in this study is general and can be applied for
future study of other nonisovalent and lattice-matched semiconductor alloys
The origin of the Narrow Line Region of Mrk 3: an overpressured jet cocoon
We have obtained HST FOC long-slit optical spectroscopy of the Narrow Line
Region of the Seyfert 2 galaxy Mrk 3. In the region cospatial with the
radio-jet the velocity field is highly perturbed and shows two velocity systems
separated by as much as 1700 km/s. We interpret this to be the consequence of
the rapid expansion of a cocoon of hot gas, shocked and heated by the
radio-emitting outflow, which compresses and accelerates the ambient gas. The
NLR itself is essentially a cylindrical shell expanding supersonically. From
the size and velocity of the expanding region, we derive an upper limit to the
radio-source age, ~ 2
E42 erg/s required to inflate the cocoon and estimate that the jet minimum
advance speed is 3 E-3 pc per year. The total kinetic energy of the high
velocity NLR gas can be estimated as ~6 E54 erg, comparable to the total energy
carried by the jet over its lifetime and this quantitatively supports the idea
that the NLR gas is accelerated by the jet. If the advance speed of Mrk 3 is
representative of the Seyfert population then these sources must also be short
lived and probably recurrent. The jet kinetic luminosity of Mrk 3 is between 2
and 3 orders of magnitude smaller than that derived for radio-loud AGNs with
similar emission-line luminosity. On the other hand, the fraction of jet power
dissipated in radio-emission is similar. We speculate that the main distinction
between radio-quiet and radio-loud AGN is ascribed to a difference in jet power
rather than to a different efficiency in synchrotron emission production.Comment: 13 pages, 8 figures, Astrophysical Journal in pres
Magnetoplasmonic design rules for active magneto-optics
Light polarization rotators and non-reciprocal optical isolators are
essential building blocks in photonics technology. These macroscopic passive
devices are commonly based on magneto-optical Faraday and Kerr polarization
rotation. Magnetoplasmonics - the combination of magnetism and plasmonics - is
a promising route to bring these devices to the nanoscale. We introduce design
rules for highly tunable active magnetoplasmonic elements in which we can
tailor the amplitude and sign of the Kerr response over a broad spectral range
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