166 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
Comparing the performance of 850 GHz integrated bias-tee superconductor-insulator-superconductor (SIS) mixers with single- and parallel-junction tuner
We present and compare the design and performance of two 850 GHz radial probe fed superconductor-insulator-superconductor mixers, where the antenna is aligned perpendicular to the E-Plane of the input full-height rectangular waveguide connected to a multiple flare-angles smooth-walled horn. Both designs are comprised of 0.5 µm2 hybrid niobium/aluminium-nitride/niobium-nitride tunnel junction, fabricated on top of a niobium titanium nitride ground plane with an Al wiring layer. The entire superconducting circuit is supported with a 40 µm thick quartz substrate. The major difference between the two designs is the method used to cancel out the parasitic junction capacitance for broadband performance. The first design utilises two identical junctions connected in parallel with a short transmission line to convert the capacitance of one junction into the equivalent inductance of the other junction, commonly known as the twin-junction tuning scheme; whilst the second design employs an end-loaded scheme with only one tunnel junction. We found that both methods offer similar radio frequency performances, with close to 2× the double sideband quantum noise temperature, but the twin-junction design is more resilient to fabrication tolerances. However, the end-loaded design offers a much better intermediate frequency (IF) bandwidth performance, made possible by the sub-micron and high current density tunnel junction technology. The improved IF performance is important for many millimetre (mm) and sub-mm observatories, such as future upgrades of Atacama Large Millimetre/sub-mm Array receivers, as well as forthcoming space-borne far-infrared missions. Therefore, we conclude that the single-junction mixer design is the preferred option for THz applications, as long as the fabrication error can be minimised within a certain limit
Computational structural and functional proteomics 235 IDENTIFICATION AND STRUCTURE-FUNCTIONAL ANALYSIS OF THE SPECIFICITY DETERMINING RESIDUES OF THE ALPHA SUBUNITS OF THE PROTEOSOMAL COMPLEX
SUMMARY Motivation: Proteosomes are polyenzymatic proteolytic structures that provide the degradation of the bulk of cytoplasmic proteins to oligopeptides. The proteosomal genes in the eukaryotes all arose by duplication of a single ancestral gene encoding the proteosomal subunits in the bacteria. The analysis of evolutionary events after duplication may be useful for discovering new information about proteosomal structural and functional properties. Results: We confine our study here to the detection of the positions of the α-subunits whose amino acid substitutions are specific to particular subunits of the proteosomal alpha-rings. We detected a set of the α-subunit positions whose substitutions are specific to the genes that encode the various proteosomal subunits. It was demonstrated that these specific amino acid substitutions are the features of residues that form the subunit contacts in the α-ring of the proteosomes. Availability: The proteosomal sequences, multiple sequence alignments and phylogenetic tree used in analysis are available upon request
Characterization of superconducting NbTiN films using a dispersive Fourier transform spectrometer
We have built a Terahertz Dispersive Fourier Transform Spectrometer
\cite{Birch1987} to study frequency properties of superconducting films used
for fabrication of THz detectors. The signal reflected from the tested film is
measured in time domain, which allows to separate it from the other
reflections. The complex conductivity of the film depends on frequency and
determines the reflection coefficient. By comparing the film reflection in the
superconducting state (temperature is below ) with the reflection of the
normal state, we characterise the film quality at terahertz frequencies. The
method was applied to 70 and 200nm thick Nb films on a silicon wafer and to
360nm thick NbTiN films on silicon and quartz wafers. The strong-coupling
coefficient, , was found to be 3.52 for Nb, and 3.71-4.02 for the NbTiN
films. The experimental results were fitted using extended Mattis-Bardeen
theory \cite{Noguchi2012} and show a good agreement.Comment: The following article has been accepted by Applied Physics Letters.
After it is published, it will be found at
https://aip.scitation.org/journal/ap
Exact isotropic cosmologies with local fractal number counts
We construct an exact relativistic cosmology in which an inhomogeneous but
isotropic local region has fractal number counts and matches to a homogeneous
background at a scale of the order of Mpc. We show that Einstein's
equations and the matching conditions imply either a nonlinear Hubble law or a
very low large-scale density.Comment: revised version, to appear Class. Q. Grav.; minor corrections
following eqn 16, additional comments on relation to other work, some new
reference
The Influence of Melt State on Atomization Process and Quality of Powders on Iron and Nickel Base
The analysis of the results of physical and chemical properties and structure investigation in liquid multicomponent steels and alloys indicates that after melting their state is generally not in equilibrium. Heating to the critical temperatures helps the system to transform into the equilibrium state or the state close to it. Melt preparing before atomization affects the process of liquid metal dispersion and helps to improve the structure and properties of the powder. The optimum melt preparing technology before atomization leads to formation the dispersion dendritic structure, optimum morphology, quantity and size of primary and eutectic phases in the powders particles and increase in properties. © 2008 IOP Publishing Ltd
NIKA: A millimeter-wave kinetic inductance camera
Current generation millimeter wavelength detectors suffer from scaling limits
imposed by complex cryogenic readout electronics. To circumvent this it is
imperative to investigate technologies that intrinsically incorporate strong
multiplexing. One possible solution is the kinetic inductance detector (KID).
In order to assess the potential of this nascent technology, a prototype
instrument optimized for the 2 mm atmospheric window was constructed. Known as
the N\'eel IRAM KIDs Array (NIKA), it was recently tested at the Institute for
Millimetric Radio Astronomy (IRAM) 30-meter telescope at Pico Veleta, Spain.
The measurement resulted in the imaging of a number of sources, including
planets, quasars, and galaxies. The images for Mars, radio star MWC349, quasar
3C345, and galaxy M87 are presented. From these results, the optical NEP was
calculated to be around WHz. A factor of 10
improvement is expected to be readily feasible by improvements in the detector
materials and reduction of performance-degrading spurious radiation.Comment: Accepted for publication in Astronomy & Astrophysic
Optical Tamm states in one-dimensional magnetophotonic structures
We demonstrate the existence of a spectrally narrow localized surface state,
the so-called optical Tamm state, at the interface between a 1D magnetophotonic
and non-magnetic photonic crystals. The state is spectrally located inside the
photonic band gaps of each of the photonic crystals comprising this
magnetophotonic structure. This state is associated with a sharp transmission
peak through the sample and is responsible for the substantial enhancement of
the Faraday rotation for the corresponding wavelength. The experimental results
are in excellent agreement with the theoretical predictions
Symmetry properties of the metric energy-momentum tensor in classical field theories and gravity
We derive a generic identity which holds for the metric (i.e. variational)
energy-momentum tensor under any field transformation in any generally
covariant classical Lagrangian field theory. The identity determines the
conditions under which a symmetry of the Lagrangian is also a symmetry of the
energy-momentum tensor. It turns out that the stress tensor acquires the
symmetry if the Lagrangian has the symmetry in a generic curved spacetime. In
this sense a field theory in flat spacetime is not self-contained. When the
identity is applied to the gauge invariant spin-two field in Minkowski space,
we obtain an alternative and direct derivation of a known no-go theorem: a
linear gauge invariant spin-2 field, which is dynamically equivalent to
linearized General Relativity, cannot have a gauge invariant metric
energy-momentum tensor. This implies that attempts to define the notion of
gravitational energy density in terms of the metric energy--momentum tensor in
a field-theoretical formulation of gravity must fail.Comment: Revised version to match the published version in Class. Quantum Gra
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