19,887 research outputs found
HI properties and star formation history of a fly-by pair of blue compact dwarf galaxies
A fly-by interaction has been suggested to be one of the major explanations
for enhanced star formation in blue compact dwarf (BCD) galaxies, yet no direct
evidence for this scenario has been found to date. In the HI Parkes all-sky
survey (HIPASS), ESO 435-IG 020 and ESO 435- G 016, a BCD pair were found in a
common, extended gas envelope of atomic hydrogen, providing an ideal case to
test the hypothesis that the starburst in BCDs can be indeed triggered by a
fly-by interaction. Using high-resolution data from the Australia Telescope
Compact Array (ATCA), we investigated HI properties and the spectral energy
distribution (SED) of the BCD pair to study their interaction and star
formation histories. The high-resolution HI data of both BCDs reveal a number
of peculiarities, which are suggestive of tidal perturbation. Meanwhile, 40% of
the HIPASS flux is not accounted for in the ATCA observations with no HI gas
bridge found between the two BCDs. Intriguingly, in the residual of the HIPASS
and the ATCA data, 10% of the missing flux appears to be located between the
two BCDs. While the SED-based age of the most dominant young stellar population
is old enough to have originated from the interaction with any neighbors
(including the other of the two BCDs), the most recent star formation activity
traced by strong H emission in ESO 435-IG 020 and the shear motion of
gas in ESO 435- G 016, suggest a more recent or current tidal interaction.
Based on these and the residual emission between the HIPASS and the ATCA data,
we propose an interaction between the two BCDs as the origin of their recently
enhanced star formation activity. The shear motion on the gas disk, potentially
with re-accretion of the stripped gas, could be responsible for the active star
formation in this BCD pair.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in A&
Probing AdS4/CFT3 proposals beyond chiral rings
We calculate the superconformal Witten index for the Chern-Simons-matter
theory which was proposed to describe multiple M2-branes on . We
consider a variant of this model, which exhibits explicit N=3 supersymmetry and
has the advantage of not having an exotic branch of the moduli space. At ,
we compare the index with that from the proposed gravity dual and find a
disagreement.Comment: references added; introduction modifie
Air-stable n-type operation of Gd-contacted carbon nanotube field effect transistors
We report air-stable n -type operations of the single-walled carbon nanotube field effect transistors (SWNT-FETs) fabricated with Gd electrodes. Unlike previously reported n -type SWNT-FETs, our devices maintained their n -type operation characteristics in ambient atmosphere for more than two months. The shallow Gd films with a thickness below 20 nm are corroded by environmental oxygen, whereas the well-contacted Gd-SWNT interfaces underneath the thick Gd layers are protected from contaminations by air molecules. Theoretical studies based on the first-principles electronic structure calculations confirm that Gd layers have an excellent binding affinity to the SWNTs.open8
Note on Generalized Janus Configurations
We study several aspects of generalized Janus configuration, which includes a
theta term. We investigate the vacuum structure of the theory and find that
unlike the Janus configuration without theta term there is no nontrivial
vacuum. We also discuss BPS soliton configuration both by supersymmetry
analysis and from energy functional. The half BPS configurations could be
realized by introducing transverse (p,q)-strings in original brane
configuration corresponding to generalized Janus configuration. It turns out
the BPS soliton could be taken as modified dyon. We discuss the solution of
half BPS equations for the sharp interface case. Moreover we construct less
supersymmetric Janus configuration with theta term.Comment: 27 pages; References adde
Properties of Central Caustics in Planetary Microlensing
To maximize the number of planet detections, current microlensing follow-up
observations are focusing on high-magnification events which have a higher
chance of being perturbed by central caustics. In this paper, we investigate
the properties of central caustics and the perturbations induced by them. We
derive analytic expressions of the location, size, and shape of the central
caustic as a function of the star-planet separation, , and the planet/star
mass ratio, , under the planetary perturbative approximation and compare the
results with those based on numerical computations. While it has been known
that the size of the planetary caustic is \propto \sqrt{q}, we find from this
work that the dependence of the size of the central caustic on is linear,
i.e., \propto q, implying that the central caustic shrinks much more rapidly
with the decrease of compared to the planetary caustic. The central-caustic
size depends also on the star-planet separation. If the size of the caustic is
defined as the separation between the two cusps on the star-planet axis
(horizontal width), we find that the dependence of the central-caustic size on
the separation is \propto (s+1/s). While the size of the central caustic
depends both on and q, its shape defined as the vertical/horizontal width
ratio, R_c, is solely dependent on the planetary separation and we derive an
analytic relation between R_c and s. Due to the smaller size of the central
caustic combined with much more rapid decrease of its size with the decrease of
q, the effect of finite source size on the perturbation induced by the central
caustic is much more severe than the effect on the perturbation induced by the
planetary caustic. Abridged.Comment: 5 pages, 4 figures, ApJ accepte
Carbon nanotube diode fabricated by contact engineering with self-assembled molecules
The authors report the construction of carbon nanotube Schottky diodes by covering a selectively exposed area of the electrode with self-assembling molecules. Two self-assembling molecules with different polarities, 2-aminoethanethiol and 3-mercaptopropionic acid, were used to modify the Fermi level lineup at the selected contact. The devices showed p -type behavior with symmetric I-V showing clear rectifying behavior after treatment of one contact with 2-aminoethanethiol. Their experiment, in conjunction with the results of ab initio electronic structure calculations, suggests that the diode action stems from the asymmetric Fermi level lineup between the bare and engineered contacts.open131
Process Development for the Formation of Post-Bonding Biorecognition Layers in Microfluidic Biosensors
Formation of the biorecognition layers within microfluidic sensor channels must be done after the completion of the channel structure since these layers cannot withstand the wafer bonding temperature. We propose a new post-bonding immobilization process to prepare the enzyme layers within microfluidic channels of electrochemical biosensors. An array of Pt vertical electrodes is electroplated using a SU-8 mold. The cured SU-8 is then removed by plasma etching to expose the Pt electrode and to define the fluidic channel cavity simultaneously. An array of enzyme posts is formed on the Pt surface by either electropolymerizing or photopolymerizing enzyme precursor solutions injected into the channel. Very little report is available about the reactive ion etching (RIE) of SU-8 that is the most critical step in this process. A systematic investigation on the RIE of SU-8 is conducted to obtain the maximum etch rate (1.2 ¿m/min.) based on different combinations of parameters of CF4 and O2 gas flow, RF power and time
One-loop Effective Actions in Shape-invariant Scalar Backgrounds
The field-theoretic one-loop effective action in a static scalar background
depending nontrivially on a single spatial coordinate is related, in the
proper-time formalism, to the trace of the evolution kernel (or heat kernel)
for an appropriate, one dimensional, quantum-mechanical Hamiltonian. We
describe a recursive procedure applicable to these traces for shape-invariant
Hamiltonians, resolving subtleties from the continuum mode contributions by
utilizing the expression for the regularized Witten index. For some cases which
include those of domain-wall-type scalar backgrounds, our recursive procedure
yields the full expression for the scalar or fermion one-loop effective action
in both (1+1) and (3+1)-dimensions.Comment: 11 pages, LaTeX2
The Globular Cluster System of M60 (NGC 4649). I. CFHT MOS Spectroscopy and Database
We present the measurement of radial velocities for globular clusters in M60,
giant elliptical galaxy in the Virgo cluster. Target globular cluster
candidates were selected using the Washington photometry based on the deep
16\arcmin \times 16\arcmin images taken at the KPNO 4m and using the
photometry derived from the HST/WFPC2 archive images. The spectra of the target
objects were obtained using the Multi-Object Spectrograph (MOS) at the
Canada-France-Hawaii Telescope (CFHT). We have measured the radial velocity for
111 objects in the field of M60: 93 globular clusters (72 blue globular
clusters with and 21 red globular clusters with
), 11 foreground stars, 6 small galaxies, and the nucleus of
M60. The measured velocities of the 93 globular clusters range from
km s to km s, with a mean value of
km s, which is in good agreement with the velocity of the nucleus of M60
( km s). Combining our results with data in the
literature, we present a master catalog of radial velocities for 121 globular
clusters in M60. The velocity dispersion of the globular clusters in the master
catalog is found to be km s for the entire sample,
km s for 83 blue globular clusters, and
km s for 38 red globular clusters.Comment: 29 pages, 8 figures. To appear in Ap
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