7,491 research outputs found
Factors influencing the start of development in Daphnia pulex winter eggs [Translation from: Biological Reviews Vol. 13, 24-26, 1951]
The winter eggs of Daphnia pulex, after passing safely through the winter , develop and hatch in the spring, multiplying by themselves, while some males emerging among them with the changes in environment produce fertile eggs, which are universally known as winter eggs . This study researches the factors governing the development of winter eggs through experiments
On the Chandra X-ray Sources in the Galactic Center
Recent deep Chandra surveys of the Galactic center region have revealed the
existence of a faint, hard X-ray source population. While the nature of this
population is unknown, it is likely that several types of stellar objects
contribute. For sources involving binary systems, accreting white dwarfs and
accreting neutron stars with main sequence companions have been proposed. Among
the accreting neutron star systems, previous studies have focused on stellar
wind-fed sources. In this paper, we point out that binary systems in which mass
transfer occurs via Roche lobe overflow (RLOF) can also contribute to this
X-ray source population.
A binary population synthesis study of the Galactic center region has been
carried out, and it is found that evolutionary channels for neutron star
formation involving the accretion induced collapse of a massive ONeMg white
dwarf, in addition to the core collapse of massive stars, can contribute to
this population. The RLOF systems would appear as transients with quiescent
luminosities, above 2 keV, in the range from 10^31-10^32 ergs/s. The results
reveal that RLOF systems primarily contribute to the faint X-ray source
population in the Muno et al. (2003) survey and wind-fed systems can contribute
to the less sensitive Wang et al. (2002) survey. However, our results suggest
that accreting neutron star systems are not likely to be the major contributor
to the faint X-ray source population in the Galactic center.Comment: 12 pages, 3 figures, 1 table ApJ in press (Dec 2004). Substantial
change
Solution of Orthopositronium lifetime Puzzle
The intrinsic decay rate of orthopositronium formed in powder
is measured using the direct correction method such that the time
dependence of the pick-off annihilation rate is precisely determined. The decay
rate of orthopositronium is found to be , which is consistent with our previous measurements with
about twice the accuracy. Results agree well with the QED
prediction, and also with a result reported very recently using nanoporous
film
Large amplitude oscillation of an erupting filament as seen in EUV, H-alpha and microwave observations
We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which has been reported by Isobe and Tripathi (Astron. Astrophys. 449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation. The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated
Quasi-Superradiant Soliton State of Matter in Quantum Metamaterials
Strong interaction of a system of quantum emitters (e.g., two-level atoms)
with electromagnetic field induces specific correlations in the system
accompanied by a drastic insrease of emitted radiation (superradiation or
superfluorescence). Despite the fact that since its prediction this phenomenon
was subject to a vigorous experimental and theoretical research, there remain
open question, in particular, concerning the possibility of a first order phase
transition to the superradiant state from the vacuum state. In systems of
natural and charge-based artificial atome this transition is prohibited by
"no-go" theorems. Here we demonstrate numerically a similar transition in a
one-dimensional quantum metamaterial - a chain of artificial atoms (qubits)
strongly interacting with classical electromagnetic fields in a transmission
line. The system switches from vacuum state with zero classical electromagnetic
fields and all qubits being in the ground state to the quasi-superradiant (QS)
phase with one or several magnetic solitons and finite average occupation of
qubit excited states along the transmission line. A quantum metamaterial in the
QS phase circumvents the "no-go" restrictions by considerably decreasing its
total energy relative to the vacuum state by exciting nonlinear electromagnetic
solitons with many nonlinearly coupled electromagnetic modes in the presence of
external magnetic field.Comment: 6 pages, 4 figure
A model for the interaction of high-energy particles in straight and bent crystals implemented in Geant4
A model for the simulation of orientational effects in straight and bent
periodic atomic structures is presented. The continuum potential approximation
has been adopted.The model allows the manipulation of particle trajectories by
means of straight and bent crystals and the scaling of the cross sections of
hadronic and electromagnetic processes for channeled particles. Based on such a
model, an extension of the Geant4 toolkit has been developed. The code has been
validated against data from channeling experiments carried out at CERN
Vertex operator approach for form factors of Belavin's -symmetric model
Belavin's -symmetric model is considered on the
basis of bosonization of vertex operators in the model and
vertex-face transformation. Free field representations of nonlocal tail
operators are constructed for off diagonal matrix elements with respect to the
ground state sectors. As a result, integral formulae for form factors of any
local operators in the -symmetric model can be
obtained, in principle.Comment: 24 pages, 4 figures, published in J. Phys. A: Math. Theor. 43 (2010)
085202. For the next thirty days from Feb 5 2010, the full text of the
article will be completely free to access through our 'This Month's Papers'
service (www.iop.org/journals/thismonth), helping you to benefit from maximum
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