25,180 research outputs found
Multiquark Hadrons
A number of candidate multiquark hadrons, i.e., particle resonances with
substructures that are more complex than the quark-antiquark mesons and
three-quark baryons that are prescribed in the textbooks, have recently been
observed. In this talk I present: some recent preliminary BESIII results on the
near-threshold behavior of sigma(e+e- --> Lambda Lambda-bar) that may or may
not be related to multiquark mesons in the light- and strange-quark sectors;
results from Belle and LHCb on the electrically charged, charmoniumlike
Z(4430)^+ --> pi^+ psi ' resonance that necessarily has a four-quark
substructure; and the recent LHCb discovery of the P_c(4380) and P_c(4450)
hidden-charm resonances seen as a complex structure in the J/psi p invariant
mass distribution for Lambda_b --> K^-J/psi p decays and necessarily have a
five-quark substructure and are, therefore, prominent candidates for pentaquark
baryons.Comment: 12 pages, 9 figures, summary of a talk presented at the 12th
Conference on Hypernuclear and Strange Particle Physics (HYP2015), September
7-12, 2015 Sendai, JAPAN. To appear in the JPS Conference proceeding
A bimodal search strategy for SETI
The search strategy and resultant observational plan which was developed to carry out a comprehensive Search for Extraterrestrial Intelligence (SETI) over that portion of the electromagnetic spectrum known as the terrestrial microwave window is described. The limiting sensitivity achieved was parameterized and calculated for Deep Space Network antennas as well as several radio astronomy observatories. A brief description of the instrumentation to be employed in the search and the classes of signals to be looked for is given. One observational goal is to survey the entire sky over a wide range of frequency to a relatively constant flux level. This survey ensures that all potential life sites are observed to some limiting equivalent isotropic radiated power depending upon their distance. A second goal is to survey a set of potential transmission sites selected a priori to be especially promising, achieving very high sensitivity over a smaller range of frequency
Mesoscopic dynamical differences from quantum state preparation in a Bose-Hubbard trimer
Conventional wisdom is that quantum effects will tend to disappear as the
number of quanta in a system increases, and the evolution of a system will
become closer to that described by mean field classical equations. In this
letter we combine newly developed experimental techniques to propose and
analyse an experiment using a Bose-Hubbard trimer where the opposite is the
case. We find that differences in the preparation of a centrally evacuated
trimer can lead to readily observable differences in the subsequent dynamics
which increase with system size. Importantly, these differences can be detected
by the simple measurements of atomic number.Comment: 5 pages, 4 figures, theor
Cross-Dimensional relaxation in Bose-Fermi mixtures
We consider the equilibration rate for fermions in Bose-Fermi mixtures
undergoing cross-dimensional rethermalization. Classical Monte Carlo
simulations of the relaxation process are performed over a wide range of
parameters, focusing on the effects of the mass difference between species and
the degree of initial departure from equilibrium. A simple analysis based on
Enskog's equation is developed and shown to be accurate over a variety of
different parameter regimes. This allows predictions for mixtures of commonly
used alkali atoms.Comment: 7 pages, 4 figures, uses Revtex 4. This is a companion paper to [PRA
70, 021601(R) (2004)] (cond-mat/0405419
Radio frequency interference survey over the 1.0-10.4 GHz frequency range at the Goldstone-Venus Development Station
The results of a low sensitivity Radio Frequency Interference (RFI) survey carried out at the Venus Station of the Goldstone Communications Complex are reported. The data cover the spectral range from 1 GHz to 10.4 GHz with a 10-kHz instantaneous bandwidth. Frequency and power levels were observed using a sweep-frequency spectrum analyzer connected to a 1-m diameter antenna pointed at zenith. The survey was conducted from February 16, 1987 through February 24, 1987
The NASA SETI sky survey: Recent developments
NASA's Search for Extraterrestrial Intelligence (SETI) project utilizes two complementary search strategies: a sky survey and a targeted search. The SETI team at the Jet Propulsion Laboratory (JPL) in Pasadena, California, has primary responsibility to develop and carry out the sky survey part. Described here is progress that has been made developing the major elements of the survey including a 2-million channel wideband spectrum analyzer system that is being designed and constructed by JPL for the Deep Space Network (DSN). The system will be a multiuser instrument; it will serve as a prototype for the SETI sky survey processor. This prototype system will be used to test the signal detection and observational strategies on DSN antennas in the near future
Saturn's microwave spectrum: Implications for the atmosphere and the rings
Measurements of Saturn's disk temperature are compiled to determine the planet's microwave spectrum from 1 mm to 100 cm wavelength. The data were adjusted to conform with a common flux density scale. A model of Saturn's rings is used to remove the effects of the rings from the atmospheric component at centimeter and decimeter wavelengths. Theoretical spectra for a number of convective atmospheric models were computed and compared with the observed spectrum. Radiative-convective models with approximately solar composition and with an effective temperature of approximately 89 K are in good agreement with the observations. The agreement between the observed and theoretical spectra is a strong indication that gaseous ammonia is present in Saturn's atmosphere. A good fit to the data is obtained with an ammonia mixing ratio of approximately 5 x 10,0001. A comparison of the millimeter wavelength data with the best-fitting atmospheric spectrum indicates that the thermal component of the ring brightness temperature near 1 mm wavelength is approximately 25 k
SIGAME simulations of the [CII], [OI] and [OIII] line emission from star forming galaxies at z ~ 6
Of the almost 40 star forming galaxies at z>~5 (not counting QSOs) observed
in [CII] to date, nearly half are either very faint in [CII], or not detected
at all, and fall well below expectations based on locally derived relations
between star formation rate (SFR) and [CII] luminosity. Combining cosmological
zoom simulations of galaxies with SIGAME (SImulator of GAlaxy
Millimeter/submillimeter Emission) we have modeled the multi-phased
interstellar medium (ISM) and its emission in [CII], [OI] and [OIII], from 30
main sequence galaxies at z~6 with star formation rates ~3-23Msun/yr, stellar
masses ~(0.7-8)x10^9Msun, and metallicities ~(0.1-0.4)xZsun. The simulations
are able to reproduce the aforementioned [CII]-faintness at z>5, match two of
the three existing z>~5 detections of [OIII], and are furthermore roughly
consistent with the [OI] and [OIII] luminosity relations with SFR observed for
local starburst galaxies. We find that the [CII] emission is dominated by the
diffuse ionized gas phase and molecular clouds, which on average contribute
~66% and ~27%, respectively. The molecular gas, which constitutes only ~10% of
the total gas mass is thus a more efficient emitter of [CII] than the ionized
gas making up ~85% of the total gas mass. A principal component analysis shows
that the [CII] luminosity correlates with the star formation activity as well
as average metallicity. The low metallicities of our simulations together with
their low molecular gas mass fractions can account for their [CII]-faintness,
and we suggest these factors may also be responsible for the [CII]-faint normal
galaxies observed at these early epochs.Comment: 24 pages, 14 figures. Accepted for publication in the Astrophysical
Journa
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
Frequency Dependent Specific Heat from Thermal Effusion in Spherical Geometry
We present a novel method of measuring the frequency dependent specific heat
at the glass transition applied to 5-polyphenyl-4-ether. The method employs
thermal waves effusing radially out from the surface of a spherical thermistor
that acts as both a heat generator and thermometer. It is a merit of the method
compared to planar effusion methods that the influence of the mechanical
boundary conditions are analytically known. This implies that it is the
longitudinal rather than the isobaric specific heat that is measured. As
another merit the thermal conductivity and specific heat can be found
independently. The method has highest sensitivity at a frequency where the
thermal diffusion length is comparable to the radius of the heat generator.
This limits in practise the frequency range to 2-3 decades. An account of the
3omega-technique used including higher order terms in the temperature
dependency of the thermistor and in the power generated is furthermore given.Comment: 17 pages, 15 figures, Substantially revised versio
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