430 research outputs found
Low-Power Testing of Losses in Millimeter-Wave Transmission Lines for High-Power Applications
We report the measurement of small losses in transmission line (TL) components intended for high-power millimeter-wave applications. Measurements were made using two different low-power techniques: a coherent technique using a vector network analyzer (VNA) and an incoherent technique using a radiometer. The measured loss in a 140 GHz 12.7 mm diameter TL system, consisting of 1.7 m of circular corrugated waveguide and three miter bends, is dominated by the miter bend loss. The measured loss was 0.3±0.1 dB per miter bend using a VNA; and 0.22±0.1 dB per miter bend using a radiometer. Good agreement between the two measurement techniques implies that both are useful for measuring small losses. To verify the methodology, the VNA technique was employed to measure the extremely small transmission loss in a 170 GHz ITER prototype TL system consisting of three lengths of 1 m, 63.5 mm diameter, circular corrugated waveguide and two miter bends. The measured loss of 0.05±0.02 dB per miter bend may be compared with the theoretical loss of 0.027 dB per miter bend. These results suggest that low-power testing of TL losses, utilizing a small, simple TL system and a VNA, is a reliable method for evaluating performance of low-loss millimeter-wave TL components intended for use in high-power applications
Coherence as ultrashort pulse train generator
Intense, well-controlled regular light pulse trains start to play a crucial
role in many fields of physics. We theoretically demonstrate a very simple and
robust technique for generating such periodic ultrashort pulses from a
continuous probe wave which propagates in a dispersive thermal gas media
The Future Evolution of White Dwarf Stars Through Baryon Decay and Time Varying Gravitational Constant
Motivated by the possibility that the fundamental ``constants'' of nature
could vary with time, this paper considers the long term evolution of white
dwarf stars under the combined action of proton decay and variations in the
gravitational constant. White dwarfs are thus used as a theoretical laboratory
to study the effects of possible time variations, especially their implications
for the future history of the universe. More specifically, we consider the
gravitational constant to vary according to the parametric relation , where the time scale is the same order as
the proton lifetime. We then study the long term fate and evolution of white
dwarf stars. This treatment begins when proton decay dominates the stellar
luminosity, and ends when the star becomes optically thin to its internal
radiation.Comment: 12 pages, 10 figures, accepted to Astrophysics and Space Scienc
On Properties of Vacuum Axial Symmetric Spacetime of Gravitomagnetic Monopole in Cylindrical Coordinates
We investigate general relativistic effects associated with the
gravitomagnetic monopole moment of gravitational source through the analysis of
the motion of test particles and electromagnetic fields distribution in the
spacetime around nonrotating cylindrical NUT source. We consider the circular
motion of test particles in NUT spacetime, their characteristics and the
dependence of effective potential on the radial coordinate for the different
values of NUT parameter and orbital momentum of test particles. It is shown
that the bounds of stability for circular orbits are displaced toward the event
horizon with the growth of monopole moment of the NUT object. In addition, we
obtain exact analytical solutions of Maxwell equations for magnetized and
charged cylindrical NUT stars.Comment: 16 pages, 3 figures, 1 tabl
Preparation of facilities for fundamental research with ultracold neutrons at PNPI
The WWR-M reactor of PNPI offers a unique opportunity to prepare a source for
ultracold neutrons (UCN) in an environment of high neutron flux (about 3*10^12
n/cm^2/s) at still acceptable radiation heat release (about 4*10^-3 W/g). It
can be realized within the reactor thermal column situated close to the reactor
core. With its large diameter of 1 m, this channel allows to install a 15 cm
thick bismuth shielding, a graphite premoderator (300 dm^3 at 20 K), and a
superfluid helium converter (35 dm^3). At a temperature of 1.2 K it is possible
to remove the heat release power of about 20 W. Using the 4pi flux of cold
neutrons within the reactor column can bring more than a factor 100 of cold
neutron flux incident on the superfluid helium with respect to the present cold
neutron beam conditions at the ILL reactor. The storage lifetime for UCN in
superfluid He at 1.2 K is about 30 s, which is sufficient when feeding
experiments requiring a similar filling time. The calculated density of UCN
with energy between 50 neV and 250 neV in an experimental volume of 40 liters
is about 10^4 n/cm^3. Technical solutions for realization of the project are
discussed.Comment: 10 pages, more detail
Laws of large numbers for eigenvectors and eigenvalues associated to random subspaces in a tensor product
Given two positive integers and and a parameter , we
choose at random a vector subspace of dimension . We show that the
set of -tuples of singular values of all unit vectors in fills
asymptotically (as tends to infinity) a deterministic convex set
that we describe using a new norm in .
Our proof relies on free probability, random matrix theory, complex analysis
and matrix analysis techniques. The main result result comes together with a
law of large numbers for the singular value decomposition of the eigenvectors
corresponding to large eigenvalues of a random truncation of a matrix with high
eigenvalue degeneracy.Comment: v3 changes: minor typographic improvements; accepted versio
Performance Issues in U.S.–China Joint Ventures
Based on an in-depth study of U.S.-China joint ventures, this article offers some insights into the performance of such international business relationships. While the conventional literature treats government as an amorphous aspea of the political-legal environment, in this case government is an active participant and influence in the performance of international joint ventures (UVs). It has both a constraining and enabling effect on LJV structure, strategy, and performance. For example, limits can be placed on ownership shares of joint ventures and on prices of the output. At the same time, government can cooperate with LJVs and foreign parent companies by creating partners for foreign parent companies, acting as major customers, and improving financial performance by lowering taxes
Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73799/1/j.1467-2979.2005.00184.x.pd
Search for Third Generation Vector Leptoquarks in p anti-p Collisions at sqrt(s) = 1.96 TeV
We describe a search for a third generation vector leptoquark (VLQ3) that
decays to a b quark and tau lepton using the CDF II detector and 322 pb^(-1) of
integrated luminosity from the Fermilab Tevatron. Vector leptoquarks have been
proposed in many extensions of the standard model (SM). Observing a number of
events in agreement with SM expectations, assuming Yang-Mills (minimal)
couplings, we obtain the most stringent upper limit on the VLQ3 pair production
cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317
GeV/c^2 (251 GeV/c^2) at 95% C.L.Comment: 7 pages, 2 figures, submitted to PR
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