2,264 research outputs found
Geometry of Banach spaces and biorthogonal systems
A separable Banach space X contains isomorphically if and only if X
has a bounded wc_0^*-stable biorthogonal system. The dual of a separable Banach
space X fails the Schur property if and only if X has a bounded
wc_0^*-biorthogonal system
Clump stars in the Solar Neighbourhood
Hipparcos data has allowed the identification of a large number of clump
stars in the Solar Neighbourhood. We discuss our present knowledge about their
distributions of masses, ages, colours, magnitudes, and metallicities. We point
out that the age distribution of clump stars is ``biased'' towards
intermediate-ages. Therefore, the metallicity information they contain is
different from that provided by the local G dwarfs. Since accurate abundance
determinations are about to become available, these may provide useful
constraints to chemical evolution models of the local disc.Comment: 6 pages, proc. of the Sept. 20-24, 1999 Vulcano Workshop "The
chemical evolution of the Milky Way: stars vs. clusters", eds. F. Matteucci,
F. Giovanell
Dynamic Transitions in a Two Dimensional Associating Lattice Gas Model
Using Monte Carlo simulations we investigate some new aspects of the phase
diagram and the behavior of the diffusion coefficient in an associating lattice
gas (ALG) model on different regions of the phase diagram. The ALG model
combines a two dimensional lattice gas where particles interact through a soft
core potential and orientational degrees of freedom. The competition between
soft core potential and directional attractive forces results in a high density
liquid phase, a low density liquid phase, and a gas phase. Besides anomalies in
the behavior of the density with the temperature at constant pressure and of
the diffusion coefficient with density at constant temperature are also found.
The two liquid phases are separated by a coexistence line that ends in a
bicritical point. The low density liquid phase is separated from the gas phase
by a coexistence line that ends in tricritical point. The bicritical and
tricritical points are linked by a critical -line. The high density
liquid phase and the fluid phases are separated by a second critical
line. We then investigate how the diffusion coefficient behaves on different
regions of the chemical potential-temperature phase diagram. We find that
diffusivity undergoes two types of dynamic transitions: a fragile-to-strong
trans ition when the critical -line is crossed by decreasing the
temperature at a constant chemical potential; and a strong-to-strong transition
when the -critical line is crossed by decreasing the temperature at a
constant chemical potential.Comment: 22 page
Liquid polymorphism and density anomaly in a three-dimensional associating lattice gas
We investigate the phase diagram of a three-dimensional associating gas
model. This model combines orientational ice-like interactions and
``van der Waals'' that might be repulsive, representing, in this case, a
penalty for distortion of hydrogen bonds. These interactions can be interpreted
as two competing distances making the connection between this model and
continuous isotropic soft-core potentials. We present Monte Carlo studies of
the model showing the presence of two liquid phase, two critical points
and A density anomaly
Evolution of stellar structure in the Small Magellanic Cloud
The projected distribution of stars in the Small Magellanic Cloud (SMC) from
the Magellanic Clouds Photometric Survey is analysed. Stars of different ages
are selected via criteria based on V magnitude and V-I colour, and the degree
of `grouping' as a function of age is studied. We quantify the degree of
structure using the two-point correlation function and a method based on the
Minimum Spanning Tree and find that the overall structure of the SMC is
evolving from a high degree of sub-structure at young ages (~10 Myr) to a
smooth radial density profile. This transition is gradual and at ~75 Myr the
distribution is statistically indistinguishable from the background SMC
distribution. This time-scale corresponds to approximately the dynamical
crossing time of stars in the SMC. The spatial positions of the star clusters
in the SMC show a similar evolution of spatial distribution with age. Our
analysis suggests that stars form with a high degree of (fractal)
sub-structure, probably imprinted by the turbulent nature of the gas from which
they form, which is erased by random motions in the galactic potential on a
time-scale of a galactic crossing time.Comment: Updated to match final journal styl
Lie Superalgebras and the Multiplet Structure of the Genetic Code II: Branching Schemes
Continuing our attempt to explain the degeneracy of the genetic code using
basic classical Lie superalgebras, we present the branching schemes for the
typical codon representations (typical 64-dimensional irreducible
representations) of basic classical Lie superalgebras and find three schemes
that do reproduce the degeneracies of the standard code, based on the
orthosymplectic algebra osp(5|2) and differing only in details of the symmetry
breaking pattern during the last step.Comment: 34 pages, 9 tables, LaTe
The Asymptotic Giant Branch and the Tip of the Red Giant Branch as Probes of Star Formation History: The Nearby Dwarf Irregular Galaxy KKH 98
We investigate the utility of the asymptotic giant branch (AGB) and the red
giant branch (RGB) as probes of the star formation history (SFH) of the nearby
(D=2.5 Mpc) dwarf irregular galaxy, KKH 98. Near-infrared (IR) Keck Laser Guide
Star Adaptive Optics (AO) images resolve 592 IR bright stars reaching over 1
magnitude below the Tip of the Red Giant Branch. Significantly deeper optical
(F475W and F814W) Hubble Space Telescope images of the same field contain over
2500 stars, reaching to the Red Clump and the Main Sequence turn-off for 0.5
Gyr old populations. Compared to the optical color magnitude diagram (CMD), the
near-IR CMD shows significantly tighter AGB sequences, providing a good probe
of the intermediate age (0.5 - 5 Gyr) populations. We match observed CMDs with
stellar evolution models to recover the SFH of KKH 98. On average, the galaxy
has experienced relatively constant low-level star formation (5 x 10^-4 Mo
yr^-1) for much of cosmic time. Except for the youngest main sequence
populations (age < 0.1 Gyr), which are typically fainter than the AO data flux
limit, the SFH estimated from the the 592 IR bright stars is a reasonable match
to that derived from the much larger optical data set. Differences between the
optical and IR derived SFHs for 0.1 - 1 Gyr populations suggest that current
stellar evolution models may be over-producing the AGB by as much as a factor
of three in this galaxy. At the depth of the AO data, the IR luminous stars are
not crowded. Therefore these techniques can potentially be used to determine
the stellar populations of galaxies at significantly further distances.Comment: 15 pages, 14 figs, accepted for publication in Ap
- …