4,564 research outputs found
The elusive old population of the dwarf spheroidal galaxy Leo I
We report the discovery of a significant old population in the dwarf
spheroidal (dSph) galaxy Leo I as a result of a wide-area search with the ESO
New Technology Telescope. Studies of the stellar content of Local Group dwarf
galaxies have shown the presence of an old stellar population in almost all of
the dwarf spheroidals. The only exception was Leo I, which alone appeared to
have delayed its initial star formation episode until just a few Gyr ago. The
color-magnitude diagram of Leo I now reveals an extended horizontal branch,
unambiguously indicating the presence of an old, metal-poor population in the
outer regions of this galaxy. Yet we find little evidence for a stellar
population gradient, at least outside R > 2' (0.16 kpc), since the old
horizontal branch stars of Leo I are radially distributed as their more
numerous intermediate-age helium-burning counterparts. The discovery of a
definitely old population in the predominantly young dwarf spheroidal galaxy
Leo I points to a sharply defined first epoch of star formation common to all
of the Local Group dSph's as well as to the halo of the Milky Way.Comment: 4 pages, 3 postscript figures, uses apjfonts.sty, emulateapj.sty.
Accepted for publication in ApJ Letter
Magellanic Cloud Periphery Carbon Stars IV: The SMC
The kinematics of 150 carbon stars observed at moderate dispersion on the
periphery of the Small Magellanic Cloud are compared with the motions of
neutral hydrogen and early type stars in the Inter-Cloud region. The
distribution of radial velocities implies a configuration of these stars as a
sheet inclined at 73+/-4 degrees to the plane of the sky. The near side, to the
South, is dominated by a stellar component; to the North, the far side contains
fewer carbon stars, and is dominated by the neutral gas. The upper velocity
envelope of the stars is closely the same as that of the gas. This
configuration is shown to be consistent with the known extension of the SMC
along the line of sight, and is attributed to a tidally induced disruption of
the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr
ago. The dearth of gas on the near side of the sheet is attributed to ablation
processes akin to those inferred by Weiner & Williams (1996) to collisional
excitation of the leading edges of Magellanic Stream clouds. Comparison with
pre LMC/SMC encounter kinematic data of Hardy, Suntzeff, & Azzopardi (1989) of
carbon stars, with data of stars formed after the encounter, of Maurice et al.
(1989), and Mathewson et al. (a986, 1988) leaves little doubt that forces other
than gravity play a role in the dynamics of the H I.Comment: 30 pages; 7 figures, latex compiled, 1 table; to appear in AJ (June
2000
USE OF INHALANT ANESTHETICS IN THREE SNAKE SPECIES
Different snake species respond differently to various anesthetic agents. Hence, an anesthetic procedure developed for one species cannot necessarily be safely transferred to another species. The goal of this paper is to summarize our experience using inhalant anesthetics on three snake species, including both procedures that were successful and those we found to be less satisfactory. We found isoflurane delivered with a precision vaporizer to be the best agent to anesthetize black rat snakes (Elaphe o. obsoleta). Sex and mass did not seem to affect induction times in black rat snakes, but larger female rat snakes recovered faster from anesthesia than smaller females. Halothane delivered in the open method provided consistent anesthesia in northern water snakes (Nerodia s. sipedon), although it caused some mortality and should not be used on debilitated patients. Halothane delivered with a precision vaporizer may be used to anesthetize eastern massasauga rattlesnakes (Sistrurus c. catenatus). However, care must be taken to prevent mortality resulting from anesthetic overdose. Sex and mass had no effect on induction and recovery times in the rattlesnakes, but stressed animals require longer induction and recovery times
Peeping at chaos: Nondestructive monitoring of chaotic systems by measuring long-time escape rates
One or more small holes provide non-destructive windows to observe
corresponding closed systems, for example by measuring long time escape rates
of particles as a function of hole sizes and positions. To leading order the
escape rate of chaotic systems is proportional to the hole size and independent
of position. Here we give exact formulas for the subsequent terms, as sums of
correlation functions; these depend on hole size and position, hence yield
information on the closed system dynamics. Conversely, the theory can be
readily applied to experimental design, for example to control escape rates.Comment: Originally 4 pages and 2 eps figures incorporated into the text; v2
has more numerical results and discussion: now 6 pages, 4 figure
Strengthening of the net section of steel elements under tensile loads with bonded CFRP strips
Abstract : The use of CFRP is increasingly common as a solution for the strengthening of structures, but the majority of research and applications have focused on the retrofit of concrete structures. The application of CFRP adhesively bonded to enhance the load carrying capacity of metallic elements has been widely studied in the aeronautical industry but is also a promising technique for the civil engineering area. This paper presents an experimental study to verify the effectiveness of the use of CFRP for the strengthening of the net section of steel elements under tensile loading. A series of tensile tests were conducted with different bond lengths, different number of layers and different surface preparation of steel elements in double lap joints and steel plates. The ultimate load, the failure mode and the effective bond length for CFRP strengthened specimens were determined. The results showed that using CFRP sheets for the strengthening against net area failure provides no gain on the ultimate state, provides a small gain at the elastic limit, and provides a larger gain if the designer accepts to increase the capacity from the elastic limit to the debondig limit
Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by Dip Pen Nanolithography
We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel
Au-Ag micro patterned template stripped surface. DNA arrays have been
investigated by atomic force microscopy (AFM) and scanning tunnelling
microscopy (STM) showing that the patterned template stripped substrate enables
easy retrieval of the DPN-functionalized zone with a standard optical
microscope permitting a multi-instrument and multi-technique local detection
and analysis. Moreover the smooth surface of the Au squares (abput 5-10
angstrom roughness) allows to be sensitive to the hybridization of the
oligonucleotide array with label-free target DNA. Our Au-Ag substrates,
combining the retrieving capabilities of the patterned surface with the
smoothness of the template stripped technique, are candidates for the
investigation of DPN nanostructures and for the development of label free
detection methods for DNA nanoarrays based on the use of scanning probes.Comment: Langmuir (accepted
On the resonance eigenstates of an open quantum baker map
We study the resonance eigenstates of a particular quantization of the open
baker map. For any admissible value of Planck's constant, the corresponding
quantum map is a subunitary matrix, and the nonzero component of its spectrum
is contained inside an annulus in the complex plane, . We consider semiclassical sequences of eigenstates, such that the
moduli of their eigenvalues converge to a fixed radius . We prove that, if
the moduli converge to , then the sequence of eigenstates
converges to a fixed phase space measure . The same holds for
sequences with eigenvalue moduli converging to , with a different
limit measure . Both these limiting measures are supported on
fractal sets, which are trapped sets of the classical dynamics. For a general
radius , we identify families of eigenstates with
precise self-similar properties.Comment: 32 pages, 2 figure
Escape Rates and Physically Relevant Measures for Billiards with Small Holes
We study the billiard map corresponding to a periodic Lorentz gas in
2-dimensions in the presence of small holes in the table. We allow holes in the
form of open sets away from the scatterers as well as segments on the
boundaries of the scatterers. For a large class of smooth initial
distributions, we establish the existence of a common escape rate and
normalized limiting distribution. This limiting distribution is conditionally
invariant and is the natural analogue of the SRB measure of a closed system.
Finally, we prove that as the size of the hole tends to zero, the limiting
distribution converges to the smooth invariant measure of the billiard map.Comment: 39 pages, 4 figure
Translation and Community in the work of Elizabeth Cary
Explores the role of female community within Elizabeth Cary\u27s translations and her play, The Tragedy of Mariam
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