237 research outputs found
Mode-selective quantization and multimodal effective models for spherically layered systems
We propose a geometry-specific, mode-selective quantization scheme in coupled
field-emitter systems which makes it easy to include material and geometrical
properties, intrinsic losses as well as the positions of an arbitrary number of
quantum emitters. The method is presented through the example of a spherically
symmetric, non-magnetic, arbitrarily layered system. We follow it up by a
framework to project the system on simpler, effective cavity QED models.
Maintaining a well-defined connection to the original quantization, we derive
the emerging effective quantities from the full, mode-selective model in a
mathematically consistent way. We discuss the uses and limitations of these
effective models
The Calar Alto lunar occultation program: update and new results
We present an update of the lunar occultation program which is routinely
carried out in the near-IR at the Calar Alto Observatory. A total of 350 events
were recorded since our last report (Fors et al. 2004). In the course of eight
runs we have observed, among others, late-type giants, T-Tauri stars, and
infrared sources. Noteworthy was a passage of the Moon close to the galactic
center, which produced a large number of events during just a few hours in July
2004. Results include the determinations of the angular diameter of RZ Ari, and
the projected separations and brightness ratios for one triple and 13 binary
stars, almost all of which representing first time detections. Projected
separations range from 0.09arcsec to 0.007arcsec. We provide a quantitative
analysis of the performance achieved in our observations in terms of angular
resolution and sensitivity, which reach about 0.003arcsec and K~8.5mag,
respectively. We also present a statistical discussion of our sample, and in
particular of the frequency of detection of binaries among field stars.Comment: 8 pages, 2 figures. Accepted for publication in A&
Stimulated emission from ZnO thin films with high optical gain and low loss
Stimulated surface- and edge-emission were investigated for ZnO thin films
grown epitaxially by pulsed laser deposition. The lasing threshold was 0.32
MW/cm2 for surface pumping and 0.5 MW/cm2 for edge pumping, which is
significantly lower than thresholds observed previously. A modified variable
stripe length method was used to measure the gain, which was 1369 cm-1 for
N-band emission. Losses were measured using the shifting excitation spot method
and values of 6.2 cm-1 and 6.3 cm-1 were found for the N-band and P-band,
respectively. The measured gain and loss were the highest and lowest
(respectively) ever reported for ZnO films
On the Dynamical Ferromagnetic, Quantum Hall, and Relativistic Effects on the Carbon Nanotubes Nucleation and Growth Mechanism
The mechanism of carbon nanotube (CNT) nucleation and growth has been a
mystery for over 15 years. Prior models have attempted the extension of older
classical transport mechanisms. In July 2000, a more detailed and accurate
nonclassical, relativistic mechanism was formulated considering the detailed
dynamics of the electronics of spin and orbital rehybridization between the
carbon and catalyst via novel mesoscopic phenomena and quantum dynamics.
Ferromagnetic carbon was demonstrated. Here, quantum (Hall) effects and
relativistic effects of intense many body spin-orbital interactions for novel
orbital rehybridization dynamics (Little Effect) are proposed in this new
dynamical magnetic mechanism. This dynamic ferromagnetic mechanism is proven by
imposing dynamic and static magnetic fields during CNT syntheses and observing
the different influence of these external magnetic environments on the
catalyzing spin currents and spin waves and the resulting CNT formation
Visual Binaries in the Orion Nebula Cluster
We have carried out a major survey for visual binaries towards the Orion
Nebula Cluster using HST images obtained with an H-alpha filter. Among 781
likely ONC members more than 60" from theta-1 Ori C, we find 78 multiple
systems (75 binaries and 3 triples), of which 55 are new discoveries, in the
range from 0.1" to 1.5". About 9 binaries are likely line-of-sight
associations. We find a binary fraction of 8.8%+-1.1% within the limited
separation range from 67.5 to 675 AU. The field binary fraction in the same
range is a factor 1.5 higher. Within the range 150 AU to 675 AU we find that T
Tauri associations have a factor 2.2 more binaries than the ONC. The binary
separation distribution function of the ONC shows unusual structure, with a
sudden steep decrease in the number of binaries as the separation increases
beyond 0.5", corresponding to 225 AU. We have measured the ratio of binaries
wider than 0.5" to binaries closer than 0.5" as a function of distance from the
Trapezium, and find that this ratio is significantly depressed in the inner
region of the ONC. The deficit of wide binaries in the central part of the
cluster is likely due to dissolution or orbital change during their passage
through the potential well of the inner cluster region. Many of the companions
are likely to be brown dwarfs.Comment: 27 pages, 10 figures, 2 tables, accepted by the Astronomical Journa
PHASES High Precision Differential Astrometry of delta Equulei
delta Equulei is among the most well-studied nearby binary star systems.
Results of its observation have been applied to a wide range of fundamental
studies of binary systems and stellar astrophysics. It is widely used to
calibrate and constrain theoretical models of the physics of stars. We report
27 high precision differential astrometry measurements of delta Equulei from
the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES).
The median size of the minor axes of the uncertainty ellipses for these
measurements is 26 micro-arcseconds. These data are combined with previously
published radial velocity data and other previously published differential
astrometry measurements using other techniques to produce a combined model for
the system orbit. The distance to the system is determined to within a
twentieth of a parsec and the component masses are determined at the level of a
percent. The constraints on masses and distance are limited by the precisions
of the radial velocity data; we outline plans improve this deficiency and
discuss the outlook for further study of this binary.Comment: Accepted by AJ. Complete versions of tables 2-7 now available at
http://stuff.mit.edu/~matthew1/deltaEquTables/ (removed from astroph server
Using Nonlinear Response to Estimate the Strength of an Elastic Network
Disordered networks of fragile elastic elements have been proposed as a model
of inner porous regions of large bones [Gunaratne et.al., cond-mat/0009221,
http://xyz.lanl.gov]. It is shown that the ratio of responses of such
a network to static and periodic strain can be used to estimate its ultimate
(or breaking) stress. Since bone fracture in older adults results from the
weakening of porous bone, we discuss the possibility of using as a
non-invasive diagnostic of osteoporotic bone.Comment: 4 pages, 4 figure
Candidate Disk Wide Binaries in the Sloan Digital Sky Survey
Using SDSS Data Release 6, we construct two independent samples of candidate
stellar wide binaries selected as i) pairs of unresolved sources with angular
separation in the range 3'' - 16'', ii) common proper motion pairs with 5'' -
30'' angular separation, and make them publicly available. These samples are
dominated by disk stars, and we use them to constrain the shape of the
main-sequence photometric parallax relation M_r(r-i) and to study the
properties of wide binary systems. We estimate M_r(r-i) by searching for a
relation that minimizes the difference between distance moduli of primary and
secondary components of wide binary candidates. We model M_r(r-i) by a fourth
degree polynomial and determine the coefficients using Markov Chain Monte Carlo
fitting, independently for each sample. Aided by the derived photometric
parallax relation, we construct a series of high-quality catalogs of candidate
main-sequence binary stars. Using these catalogs, we study the distribution of
semi-major axes of wide binaries, a, in the 2,000 < a < 47,000 AU range. We
find the observations to be well described by the Opik distribution, f(a)~1/a,
for a<a_{break}, where a_{break} increases roughly linearly with the height Z
above the Galactic plane (a_{break}~12,300 Z[kpc]^0.7 AU). The number of wide
binary systems with 100 AU < a < a_{break}, as a fraction of the total number
of stars, decreases from 0.9% at Z=0.5 kpc to 0.5% at Z=3 kpc. The probability
for a star to be in a wide binary system is independent of its color. Given
this color, the companions of red components seem to be drawn randomly from the
stellar luminosity function, while blue components have a larger blue-to-red
companion ratio than expected from luminosity function.Comment: emulateApJ, 47 pages, 28 figures, accepted to Ap
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