5,833 research outputs found
Euclidean Dynamical Symmetry in Nuclear Shape Phase Transitions
The Euclidean dynamical symmetry hidden in the critical region of nuclear
shape phase transitions is revealed by a novel algebraic F(5) description. With
a nonlinear projection, it is shown that the dynamics in the critical region of
the spherical--axial deformed and the spherical-- soft shape phase
transitions can indeed be manifested by this description, which thus provides a
unified symmetry--based interpretation of the critical phenomena in the region.Comment: 5 pages, 2 figures, 2 table
Mitochondrial metagenomics: letting the genes out of the bottle
‘Mitochondrial metagenomics’ (MMG) is a methodology for shotgun sequencing of total DNA from specimen mixtures and subsequent bioinformatic extraction of mitochondrial sequences. The approach can be applied to phylogenetic analysis of taxonomically selected taxa, as an economical alternative to mitogenome sequencing from individual species, or to environmental samples of mixed specimens, such as from mass trapping of invertebrates. The routine generation of mitochondrial genome sequences has great potential both for systematics and community phylogenetics. Mapping of reads from low-coverage shotgun sequencing of environmental samples also makes it possible to obtain data on spatial and temporal turnover in whole-community phylogenetic and species composition, even in complex ecosystems where species-level taxonomy and biodiversity patterns are poorly known. In addition, read mapping can produce information on species biomass, and potentially allows quantification of within-species genetic variation. The success of MMG relies on the formation of numerous mitochondrial genome contigs, achievable with standard genome assemblers, but various challenges for the efficiency of assembly remain, particularly in the face of variable relative species abundance and intra-specific genetic variation. Nevertheless, several studies have demonstrated the power of mitogenomes from MMG for accurate phylogenetic placement, evolutionary analysis of species traits, biodiversity discovery and the establishment of species distribution patterns; it offers a promising avenue for unifying the ecological and evolutionary understanding of species diversity
The entropy puzzle and the quark combination model
We use two available methods, the Duhem-Gibbs relation and the entropy
formula in terms of particle phase space distributions, to calculate the
entropy in a quark combination model. The entropy of the system extracted from
the Duhem-Gibbs relation is found to increase in hadronization if the average
temperature of the hadronic phase is lower than that of the quark phase. The
increase of the entropy can also be confirmed from the entropy formula if the
volume of the hadronic phase is larger than 2.5-3.0 times that of the quark
phase. So whether the entropy increases or decreases during combination depends
on the temperature before and after combination and on how much expansion the
system undergoes during combination. The current study provides an example to
shed light on the entropy issue in the quark combination model.Comment: RevTex 4, 4 pages, 2 tables, 4 figures, discussions and references
added, to appear in PR
Critical point symmetries in deformed odd-A nuclei
A scheme that elucidates the nature of critical point symmetries in deformed odd-A nuclei by linking them to critical point symmetries of neighboring even-even nuclei is introduced. Specifically, a new symmetry, called SX(3), is advanced that shows primary characteristics of an assumed strong-coupling limit for odd-A systems. It is found that the SX(3) symmetry can be used to identify the soft collective structures in odd-A system. A preliminary application of the new scheme to describe the lowest positive parity bands of 193Ir is also shown. © 2011 American Physical Society
A Peculiar Flaring Episode of Cygnus X-1
Recent monitoring of Cyg X-1 with {\em RXTE} revealed a period of intense
flaring, which started in October of 2000 and lasted until March of 2001. The
source exhibited some quite unusual behaviors during this period. The soft
X-ray flux of the source went up and down three times on a timescale of about
one month, as discovered by the ASM aboard RXTE, before finally returning to
the normal level (of the hard state). The observed spectral and temporal X-ray
properties of Cyg X-1 are mostly intermediate between the canonical hard and
soft states. This is known previously for strong X-ray flares, however, we show
that the source did enter a period that resembles, in many ways, a sustained
soft state during the last of the three flares. We make detailed comparisons
between this flare and the 1996 state transition, in terms of the observed
X-ray properties, such as flux--hardness correlation, X-ray spectrum, and power
density spectrum. We point out the similarities and differences, and discuss
possible implications of the results on our understanding of the phenomena of
flares and state transitions associated with Cyg X-1.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Theoretical Study on Rotational Bands and Shape Coexistence of {Tl} in the Particle Triaxial-Rotor Model
By taking the particle triaxial-rotor model with variable moment of inertia,
we investigate the energy spectra, the deformations and the single particle
configurations of the nuclei Tl systemically. The calculated
energy spectra agree with experimental data quite well. The obtained results
indicate that the aligned bands observed in Tl originate from
the , , proton
configuration coupled to a prolate deformed core, respectively. Whereas, the
negative parity bands built upon the isomeric states in
Tl are formed by a proton with the
configuration coupled to a core with triaxial oblate deformation, and the
positive parity band on the isomeric state in Tl is
generated by a proton with configuration coupled to a
triaxial oblate core.Comment: 16 pages, 5 figures. To appear in Physical Review
A new parametric equation of state and quark stars
It is still a matter of debate to understand the equation of state of cold
supra-nuclear matter in compact stars because of unknown on-perturbative strong
interaction between quarks. Nevertheless, it is speculated from an
astrophysical view point that quark clusters could form in cold quark matter
due to strong coupling at realistic baryon densities. Although it is hard to
calculate this conjectured matter from first principles, one can expect the
inter-cluster interaction to share some general features to nucleon-nucleon
interaction. We adopt a two-Gaussian component soft-core potential with these
general features and show that quark clusters can form stable simple cubic
crystal structure if we assume Gaussian form wave function. With this
parameterizing, Tolman-Oppenheimer-Volkoff equation is solved with reasonable
constrained parameter space to give mass-radius relation of crystalline solid
quark star. With baryon densities truncated at 2 times nuclear density at
surface and range of interaction fixed at 2fm we can reproduce similar
mass-radius relation to that obtained with bag model equations of state. The
maximum mass ranges from about 0.5 to 3 solar mass. Observed maximum pulsar
mass (about 2 solar mass) is then used to constrain parameters of this simple
interaction potential.Comment: 5 pages, 2 figure
γ -rigid solution of the Bohr Hamiltonian for the critical point description of the spherical to γ -rigidly deformed shape phase transition
The γ-rigid solution of the Bohr Hamiltonian with the β-soft potential and 0 ≤γ≤30 is worked out. The resulting model, called T(4), provides a natural dynamical connection between the X(4) and the Z(4) critical-point symmetries, which thus serves as the critical-point symmetry of the spherical to γ-rigidly deformed shape phase transition. This point is further justified through comparing the model dynamics with those of the interacting boson model. As a preliminary test, the low-lying structures of Er158 are taken to compare the theoretical calculations, and the results indicate that this nucleus could be considered as the candidate of the T(4) model with an intermediate γ deformation
- …