570 research outputs found
Conceptual Problems of Fractal Cosmology
This report continues recent Peebles-Turner debate "Is cosmology solved?" and
considers the first results for Sandage's program for "Practical cosmology". A
review of conceptual problems of modern cosmological models is given, among
them: the nature of the space expansion; recession velocities of distant
galaxies more than velocity of light; cosmological Friedmann force; continuous
creation of gravitating mass in Friedmann's equation; cosmological pressure is
not able to produce a work; cosmological gravitational frequency shift;
Friedmann-Holtsmark paradox; the problem of the cosmological constant;
Einstein's and Mandelbrot's Cosmological Principles; fractality of observed
galaxy distribution; Sandage's 21st problem: Hubble - de Vaucouleurs paradox;
quantum nature of gravity force.Comment: 17 pages, no Figures, report presented at Gamow Memorial Conference,
August 1999, St.-Petersburg, Russi
Performance of Hybrid NbTiN-Al Microwave Kinetic Inductance Detectors as Direct Detectors for Sub-millimeter Astronomy
In the next decades millimeter and sub-mm astronomy requires large format
imaging arrays and broad-band spectrometers to complement the high spatial and
spectral resolution of the Atacama Large Millimeter/sub-millimeter Array. The
desired sensors for these instruments should have a background limited
sensitivity and a high optical efficiency and enable arrays thousands of pixels
in size. Hybrid microwave kinetic inductance detectors consisting of NbTiN and
Al have shown to satisfy these requirements. We present the second generation
hybrid NbTiN-Al MKIDs, which are photon noise limited in both phase and
amplitude readout for loading levels fW. Thanks to the
increased responsivity, the photon noise level achieved in phase allows us to
simultaneously read out approximately 8000 pixels using state-of-the-art
electronics. In addition, the choice of superconducting materials and the use
of a Si lens in combination with a planar antenna gives these resonators the
flexibility to operate within the frequency range THz. Given
these specifications, hybrid NbTiN-Al MKIDs will enable astronomically usable
kilopixel arrays for sub-mm imaging and moderate resolution spectroscopy.Comment: 7 pages, 3 figures. Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VI
Photon noise limited radiation detection with lens-antenna coupled Microwave Kinetic Inductance Detectors
Microwave Kinetic Inductance Detectors (MKIDs) have shown great potential for
sub-mm instrumentation because of the high scalability of the technology. Here
we demonstrate for the first time in the sub-mm band (0.1...2 mm) a photon
noise limited performance of a small antenna coupled MKID detector array and we
describe the relation between photon noise and MKID intrinsic
generation-recombination noise. Additionally we use the observed photon noise
to measure the optical efficiency of detectors to be 0.8+-0.2.Comment: The following article has been submitted to AP
Classical Cosmological Tests for Galaxies of the Hubble Ultra Deep Field
Images of the Hubble Ultra Deep Field are analyzed to obtain a catalog of
galaxies for which the angular sizes, surface brightness, photometric
redshifts, and absolute magnitudes are found. The catalog contains a total of
about 4000 galaxies identified at a high signal-to-noise ratio, which allows
the cosmological relations angular size{redshift and surface
brightness-redshift to be analyzed. The parameters of the evolution of linear
sizes and surface brightness of distant galaxies in the redshift interval
0.5-6.5 are estimated in terms of a grid of cosmological models with different
density parameters. The distribution of photometric redshifts of galaxies is
analyzed and possible superlarge inhomogeneities in the radial distribution of
galaxies are found with scale lengths as large as 2000 Mpc.Comment: 23 pages, 9 figures, 1 tabl
An SIS-based sideband-separating heterodyne mixer optimized for the 600 to 720 GHz band
The Atacama Large Millimeter Array (ALMA) is the largest radio astronomical enterprise ever proposed. When completed, each of its 64 constituting radio-telescopes will be able to hold 10 heterodyne receivers covering the spectroscopic windows allowed by the atmospheric transmission at the construction site, the altiplanos of the northern Chilean Andes. In contrast to the sideband-separating (2SB) receivers being developed at low frequencies, double-side-band (DSB) receivers are being developed for the highest two spectroscopic windows (bands 9 and 10). Despite of the well known advantages of 2SB mixers over their DSB counterparts, they have not been implemented at the highest-frequency bands as the involved dimensions for some of the radio frequency components are prohibitory small. However, the current state-of-the-art micromachining technology has proved that the structures necessary for this development are attainable. Here we report the design, modeling, realization, and characterization of a 2SB mixer for band 9 of ALMA (600 to 720 GHz). At the heart of the mixer, two superconductor-insulator-superconductor (SIS) junctions are used as mixing elements. The constructed instrument presents an excellent performance as shown by two important figures of merit: noise temperature of the system and side band ratio, both of them within ALMA specifications
Properties of Quasar-Galaxy Associations and Gravitational Mesolensing by Halo Objects
A new catalog of 8382 close quasar-galaxy pairs is presented. The catalog was
composed using published catalogs of quasars and active galactic nuclei
containing 11358 objects, as well as the LEDA catalog of galaxies, which
contains on the order of 100 thousand objects. The search for pairs was carried
out in such a way that the linear distance between the galaxy and projected
quasar does not exceed 150kpc. Based on these new data, the dependence of the
number of pairs on a=z_G/z_Q is analysed, where z_G and z_Q are the redshifts
of the galaxy and quasar, respectively, revealing an excess of pairs with a<0.1
and a>0.9. This means that the galaxies in pairs are preferably located close
to either the observer or the quasar and avoid intermediate distances along the
line of sight to the quasar. Computer simulations demonstrate that it is not
possible to explain this number of pairs with the observed distribution in a as
the result of chance positional coincidences with a uniform spatial
distribution of galaxies. Data on globular clusters show that the excess of
pairs with a0.9 is consistent with the hypothesis that we are
observing distant compact objects that are strongly gravitationally lensed by
transparent lenses with a King mass distribution located in the halos of nearby
galaxies. The Hubble diagram for galaxies and quasars is presented.
Observational tests of the mesolensing hypothesis are formulated.Comment: 11 pages, 7 figure
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