3,201 research outputs found
Hadron Mass Spectrum from Lattice QCD
Finite temperature lattice simulations of quantum chromodynamics (QCD) are
sensitive to the hadronic mass spectrum for temperatures below the "critical"
temperature T_c ~ 160 MeV. We show that a recent precision determination of the
QCD trace anomaly shows evidence for the existence of a large number of hadron
states beyond those known from experiment. The lattice results are well
represented by an exponentially growing hadron mass spectrum up to a
temperature T = 155 MeV. Using simple parametrizations we show how one may
estimate the total spectral weight in these yet undermined states
Ultraviolet light emission from Si in a scanning tunneling microscope
Ultraviolet and visible radiation is observed from the contacts of a scanning
tunneling microscope with Si(100) and (111) wafers. This luminescence relies on
the presence of hot electrons in silicon, which are supplied, at positive bias
on n- and p-type samples, through the injection from the tip, or, at negative
bias on p-samples, by Zener tunneling. Measured spectra reveal a contribution
of direct optical transitions in Si bulk. The necessary holes well below the
valence band edge are injected from the tip or generated by Auger processes
Controlling the Kondo Effect in CoCu_n Clusters Atom by Atom
Clusters containing a single magnetic impurity were investigated by scanning
tunneling microscopy, spectroscopy, and ab initio electronic structure
calculations. The Kondo temperature of a Co atom embedded in Cu clusters on
Cu(111) exhibits a non-monotonic variation with the cluster size. Calculations
model the experimental observations and demonstrate the importance of the local
and anisotropic electronic structure for correlation effects in small clusters.Comment: 4 pages, 4 figure
Nilpotent Classical Mechanics
The formalism of nilpotent mechanics is introduced in the Lagrangian and
Hamiltonian form. Systems are described using nilpotent, commuting coordinates
. Necessary geometrical notions and elements of generalized differential
-calculus are introduced. The so called geometry, in a special case
when it is orthogonally related to a traceless symmetric form, shows some
resemblances to the symplectic geometry. As an example of an -system the
nilpotent oscillator is introduced and its supersymmetrization considered. It
is shown that the -symmetry known for the Graded Superfield Oscillator (GSO)
is present also here for the supersymmetric -system. The generalized
Poisson bracket for -variables satisfies modified Leibniz rule and
has nontrivial Jacobiator.Comment: 23 pages, no figures. Corrected version. 2 references adde
Vacuum Polarization and the Electric Charge of the Positron
We show that higher-order vacuum polarization would contribute a measureable
net charge to atoms, if the charges of electrons and positrons do not balance
precisely. We obtain the limit for the sum of
the charges of electron and positron. This also constitutes a new bound on
certain violations of PCT invariance.Comment: 9 pages, 1 figure attached as PostScript file, DUKE-TH-92-38. Revised
versio
Cattle Grubs and Their Control in South Dakota
The purposes of the research work carried on from 1947 to 1953 by the South Dakota Agricultural Experiment Station were: to study the distribution and seasonal abundance of cattle grubs in South Dakota; to measure effects of grub infestations and methods of control on rates of gain of feed lot cattle; to evaluate and improve methods of control; and to investigate the practicability of cattle grub control on an area or community-wide basis
Two-Site Kondo Effect in Atomic Chains
Linear CoCu_nCo clusters on Cu(111) are fabricated by means of atomic
manipulation. They represent a two-site Kondo system with tunable interaction.
Scanning tunneling spectroscopy reveals oscillations of the Kondo temperature
T_K with the number n of Cu atoms for n>=3. Density functional calculations
show that the Ruderman-Kittel-Kasuya-Yosida interaction mediated by the Cu
chains causes the oscillations. Calculations find ferromagnetic and
antiferromagnetic interaction for n=1 and 2, respectively. Both interactions
lead to a decrease of T_K as experimentally observed.Comment: 5 pages, 3 figure
Technical Change, Investment and Energy Intensity
Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).This paper analyzes the role of different components of technical change on energy intensity by applying a Translog variable cost function setting to the new EU KLEMS dataset for 3 selected EU countries (Italy, Finland and Spain). The framework applied represents an accounting of technical change components, comprising autonomous as well as embodied and induced technical change. The inducement of embodied technical change is introduced by an equation for the physical capital stock that is a fixed factor in the short-run. The dataset on capital services and user costs of capital in EUKLEMS enables explaining capital accumulation depending on factor prices. The model can be used for explaining and tracing back the long-run impact of prices and technical change on energy intensity.This paper is based on the EU KLEMS database, which has been funded by the European Commission, Research Directorate General as part of the 6th Framework Programme, Priority 8, âPolicy Support and Anticipating Scientific and Technological Needsâ (project 502049)
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