11,500 research outputs found
Electromagnetic power absorber
A structure is presented with a surface portion of dielectric material which passes electromagnetic radiation and with a portion below the surface which includes material that absorbs the radiation, the face of the structure being formed with numerous steep ridges. The steepness of the dielectric material results in a high proportion of the electromagnetic energy passing through the surface for absorption by the absorbing material under the surface. A backing of aluminum or other highly heat-conductive and reflective material lies under the face and has very steep protuberances supporting the absorbing and dielectric materials
Chiral Phase Transition in Lattice QCD with Wilson Quarks
The nature of the chiral phase transition in lattice QCD is studied for the
cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice
with the temporal direction extension . We find that the chiral phase
transition is continuous for the case of 2 flavors, while it is of first order
for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure
QCD Phase Transition with Strange Quark in Wilson Formalism for Fermions
The nature of QCD phase transition is studied with massless up and down
quarks and a light strange quark, using the Wilson formalism for quarks on a
lattice with the temporal direction extension . We find that the phase
transition is first order in the cases of both about 150 MeV and 400 MeV for
the strange quark mass. These results together with those for three degenerate
quarks suggest that QCD phase transition in nature is first order.Comment: uuencoded compressed tar file, LaTeX, 13 pages, 9 figures, Minor
errors for quoting references are corrected and a reference is adde
Hadron spectroscopy and static quark potential in full QCD: A comparison of improved actions on the CP-PACS
We present first results from a full QCD calculation on the CP-PACS,
comparing various actions at and --0.9. We use the plaquette and a renormalization group improved action for
the gluons, and the Wilson and the SW-Clover action for quarks. We find that
significant improvements in the hadron spectrum results from improving the
quarks, while the gluon improvement is required for a rotationally invariant
static potential. An ongoing effort towards exploring the chiral limit in full
QCD is described.Comment: 6 pages, based on talks presented by R. Burkhalter and T. Kaneko at
Lattice97, Edinburg
Shuttle orbiter Ku-band radar/communications system design evaluation: High gain antenna/widebeam horn
The physical characteristics of the high gain antenna reflector and feed elements are described. Deficiencies in the sum feed are discussed, and lack of atmospheric venting is posed as a potential problem area. The measured RF performance of the high gain antenna is examined and the high sidelobe levels measured are related to the physical characteristics of the antenna. An examination of the attributes of the feed which might be influenced by temperature extremes shows that the antenna should be insensitive to temperature variations. Because the feed support bipod structure is considered a significant contributor to the high sidelobe levels measured in the azimuth plane, pod relocation, material changes, and shaping are suggested as improvements. Alternate feed designs are presented to further improve system performance. The widebeam horn and potential temperature effects due to the polarizer are discussed as well as in the effects of linear polarization on TDRS acquisition, and the effects of circular polarization on radar sidelobe avoidance. The radar detection probability is analyzed as a function of scan overlap and target range
Phase structure of lattice QCD for general number of flavors
We investigate the phase structure of lattice QCD for the general number of
flavors in the parameter space of gauge coupling constant and quark mass,
employing the one-plaquette gauge action and the standard Wilson quark action.
Performing a series of simulations for the number of flavors --360 with
degenerate-mass quarks, we find that when there is a line of a bulk
first order phase transition between the confined phase and a deconfined phase
at a finite current quark mass in the strong coupling region and the
intermediate coupling region. The massless quark line exists only in the
deconfined phase. Based on these numerical results in the strong coupling limit
and in the intermediate coupling region, we propose the following phase
structure, depending on the number of flavors whose masses are less than
which is the physical scale characterizing the phase transition in
the weak coupling region: When , there is only a trivial IR fixed
point and therefore the theory in the continuum limit is free. On the other
hand, when , there is a non-trivial IR fixed point and
therefore the theory is non-trivial with anomalous dimensions, however, without
quark confinement. Theories which satisfy both quark confinement and
spontaneous chiral symmetry breaking in the continuum limit exist only for .Comment: RevTeX, 20 pages, 43 PS figure
Preliminary Centaur Systems Analysis
The Centaur is stored in the Orbiter payload bay on the Centaur Integrated Support System (CISS). The CISS not only cradles the Centaur prior to deployment but also provides any signal conditioning required to make the Centaur/Orbiter hardwire interfaces compatible. In addition, the CISS provides other Centaur functions such as controlling all the avionics safety features and providing all the helium supplies for tank pressurizations. Problems associated with a Centaur design concept using a transponder and two switchable antennas are defined. Solutions to these problems are presented
A Gaussian Weave for Kinematical Loop Quantum Gravity
Remarkable efforts in the study of the semi-classical regime of kinematical
loop quantum gravity are currently underway. In this note, we construct a
``quasi-coherent'' weave state using Gaussian factors. In a similar fashion to
some other proposals, this state is peaked in both the connection and the spin
network basis. However, the state constructed here has the novel feature that,
in the spin network basis, the main contribution for this state is given by the
fundamental representation, independently of the value of the parameter that
regulates the Gaussian width.Comment: 15 pages, 3 figures, Revtex file. Comments added and references
updated. Final version to appear in IJMP-
Finite Temperature Transitions in Lattice QCD with Wilson Quarks --- Chiral Transitions and the Influence of the Strange Quark ---
The nature of finite temperature transitions in lattice QCD with Wilson
quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of
degenerate quarks (, 3, and 6) and also for the case of massless up and
down quarks and a light strange quark (). Our simulations mainly
performed on lattices with the temporal direction extension indicate
that the finite temperature transition in the chiral limit (chiral transition)
is continuous for , while it is of first order for and 6. We
find that the transition is of first order for the case of massless up and down
quarks and the physical strange quark where we obtain a value of
consistent with the physical value. We also discuss the phase
structure at zero temperature as well as that at finite temperatures.Comment: uuencoded compressed tar file, 70 pages, 32 figure
QCD Thermodynamics with Improved Actions
The thermodynamics of the SU(3) gauge theory has been analyzed with tree
level and tadpole improved Symanzik actions. A comparison with the continuum
extrapolated results for the standard Wilson action shows that improved actions
lead to a drastic reduction of finite cut-off effects already on lattices with
temporal extent . Results for the pressure, the critical temperature,
surface tension and latent heat are presented. First results for the
thermodynamics of four-flavour QCD with an improved staggered action are also
presented. They indicate similarly large improvement factors for bulk
thermodynamics.Comment: Talk presented at LATTICE96(finite temperature) 4 pages, LaTeX2e
file, 6 eps-file
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