20,335 research outputs found
Photoemission Spectra in t-J Ladders with Two Legs
Photoemission spectra for the isotropic two-leg t-J ladder are calculated at
various hole-doping levels using exact diagonalization techniques. Low-energy
sharp features caused by short-range antiferromagnetic correlations are
observed at finite doping levels close to half-filling, above the naive Fermi
momentum. These features should be observable in angle-resolved photoemission
experiments. In addition, the formation of a d-wave pairing condensate as the
ratio J/t is increased leads to dynamically generated spectral weight for
momenta close to where the -order parameter is large.Comment: 9 pages, RevTex, to be published in Phys. Rev. B (RC
On the linearization of the generalized Ermakov systems
A linearization procedure is proposed for Ermakov systems with frequency
depending on dynamic variables. The procedure applies to a wide class of
generalized Ermakov systems which are linearizable in a manner similar to that
applicable to usual Ermakov systems. The Kepler--Ermakov systems belong into
this category but others, more generic, systems are also included
Electron heating mechanisms in dual frequency capacitive discharges
We discuss electron heating mechanisms in the sheath regions of dual-frequency capacitive discharges, with the twin aims of identifying the dominant mechanisms and supplying closed-form expressions from which the heating power can be estimated. We show that the heating effect produced by either Ohmic or collisionless heating is much larger when the discharge is excited by a superposition of currents at two frequencies than if either current had acted alone. This coupling effect occurs because the lower frequency current, while not directly heating the electrons to any great extent, strongly affects the spatial structure of the discharge in the sheath regions
Small coherence peak near in unconventional superconductors
It is usually believed that a coherence peak just below T in the
nuclear spin lattice relaxation rate T in superconducting materials
is a signature of conventional s-wave pairing. In this paper we demonstrate
that any unconventional superconductor obeying BCS pure-case weak-coupling
theory should show a small T coherence peak near T, generally
with a height between 3 and 15 percent greater than the normal state
T at T. It is largely due to impurity effects that this peak
has not commonly been observed.Comment: 4 pages, 5 figure
Monitoring the Vernal Advancement and Retrogradation (Green Wave Effect) of Natural Vegetation
The author has identified the following significant results. The Great Plains Corridor rangeland project successfully utilized natural vegetation systems as phenological indicators of seasonal development and climatic effects upon regional growth conditions. An effective method was developed for quantitative measurement of vegetation conditions, including green biomass estimates, recorded in bands 5 and 6, corrected for sun angle, were used to compute a ratio parameter (TV16) which is shown to be highly correlated with green biomass and vegatation moisture content. Analyses results of ERTS-1 digital data and correlated ground data are summarized. Attention was given to analyzing weather influences and test site variables on vegetation condition measurements with ERTS-1 data
Nuclear alpha-clustering, superdeformation, and molecular resonances
Nuclear alpha-clustering has been the subject of intense study since the
advent of heavy-ion accelerators. Looking back for more than 40 years we are
able today to see the connection between quasimolecular resonances in heavy-ion
collisions and extremely deformed states in light nuclei. For example
superdeformed bands have been recently discovered in light N=Z nuclei such as
Ar, Ca, Cr, and Ni by -ray spectroscopy.
The search for strongly deformed shapes in N=Z nuclei is also the domain of
charged-particle spectroscopy, and our experimental group at IReS Strasbourg
has studied a number of these nuclei with the charged particle multidetector
array {\sc Icare} at the {\sc Vivitron} Tandem facility in a systematical
manner. Recently the search for -decays in Mg has been
undertaken in a range of excitation energies where previously nuclear molecular
resonances were found in C+C collisions. The breakup reaction
MgC has been investigated at E(Mg) = 130 MeV, an
energy which corresponds to the appropriate excitation energy in Mg for
which the C+C resonance could be related to the breakup
resonance. Very exclusive data were collected with the Binary Reaction
Spectrometer in coincidence with {\sc Euroball IV} installed at the {\sc
Vivitron}.Comment: 10 pages, 4 eps figures included. Invited Talk 10th Nuclear Physics
Workshop Marie and Pierre Curie, Kazimierz Dolny Poland, Sep. 24-28, 2003; To
be published in International Journal of Modern Physics
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