1,083,438 research outputs found
Selective Control of the Symmetric Dicke Subspace in Trapped Ions
We propose a method of manipulating selectively the symmetric Dicke subspace
in the internal degrees of freedom of N trapped ions. We show that the direct
access to ionic-motional subspaces, based on a suitable tuning of
motion-dependent AC Stark shifts, induces a two-level dynamics involving
previously selected ionic Dicke states. In this manner, it is possible to
produce, sequentially and unitarily, ionic Dicke states with increasing
excitation number. Moreover, we propose a probabilistic technique to produce
directly any ionic Dicke state assuming suitable initial conditions.Comment: 5 pages and 1 figure. New version with minor changes and added
references. Accepted in Physical Review
Observation of a (2X8) surface reconstruction on Si_(1-x)Ge_x alloys grown on (100) Si by molecular beam epitaxy
We present evidence supporting the formation of a new, (2Ă8) surface reconstruction on Si_(1âx)Ge_x alloys grown on (100) Si substrates by molecularâbeam epitaxy. Surfaces of Si_(1âx)Ge_x alloys were studied using reflection highâenergy electron diffraction (RHEED) and lowâenergy electron diffraction (LEED) techniques. RHEED patterns from samples with Ge concentrations, x, falling within the range 0.10â0.30 and grown at temperatures between 350 and 550â°C, exhibit n/8 fractionalâorder diffraction streaks in addition to the normal (2Ă1) pattern seen on (100) Si. The presence of fractionalâorder diffracted beams is indicative of an eightâfoldâperiodic modulation in electron scattering factor across the alloy surface. LEED patterns from surfaces of samples grown under similar conditions are entirely consistent with these results. In addition, the LEED patterns support the conclusion that the modulation is occurring in the direction of the dimer chains of a (2Ă1) reconstruction. We have examined the thermal stability of the (2Ă8) reconstruction and have found that it reverts to (2Ă1) after annealing to 700â°C and reappears after the sample temperature is allowed to cool below 600â°C. Such behavior suggests that the reconstruction is a stable, ordered phase for which the pairâcorrelation function of surface Ge atoms exhibits an eightfold periodicity in the "1" direction of a Siâlike (2Ă1) reconstruction. We also present a simulation in the kinematic approximation, confirming the validity of our interpretation of these finding
Conditioning of pulses from aerosol-particle detectors
Pulse-conditioner translates pulses generated by aerosol-particle detectors to a form acceptable by commercially available pulse height analyzers designed for nuclear-energy spectroscopy
Epitaxial silicon grown on CeO2/Si(111) structure by molecular beam epitaxy
Using electron beam evaporation, a Si/CeO2/Si(111) structure has been grown in a molecular beam epitaxy machine. In situ low energy electron diffraction, cross sectional transmission electron microscopy, selected area diffraction, and atomic force microscopy have been used to structurally characterize the overlying silicon layer and show it to be single crystalline and epitaxially oriented. Rutherford backscattering and energy dispersive x-ray analysis have been used to confirm the presence of a continuous 23 Ă
CeO2 layer at the interface. Rutherford backscattering and x-ray photoemission spectroscopy show an additional presence of cerium both at the exposed silicon surface and incorporated in low levels (~ 1%) within the silicon film, suggesting a growth mechanism with cerium riding atop the silicon growth front leaving behind small amounts of cerium incorporated in the growing silicon crystal
Quantum fluctuations in the spiral phase of the Hubbard model
We study the magnetic excitations in the spiral phase of the two--dimensional
Hubbard model using a functional integral method. Spin waves are strongly
renormalized and a line of near--zeros is observed in the spectrum around the
spiral pitch . The possibility of disordered spiral states is
examined by studying the one--loop corrections to the spiral order parameter.
We also show that the spiral phase presents an intrinsic instability towards an
inhomogeneous state (phase separation, CDW, ...) at weak doping. Though phase
separation is suppressed by weak long--range Coulomb interactions, the CDW
instability only disappears for sufficiently strong Coulomb interaction.Comment: Figures are NOW appended via uuencoded postscript fil
Dynamics of hadron strong production and decay
We generalize results of lattice QCD to determine the spin-dependent
symmetries and factorization properties of meson production in OZI allowed
processes. This explains some conjectures previously made in the literature
about axial meson decays and gives predictions for exclusive decays of vector
charmonia, including ways of establishing the structure of Y(4260) and Y(4325)
from their S-wave decays. Factorization gives a selection rule which forbids
near threshold with the tensor meson in helicity 2. The
relations among amplitudes for double charmonia production \e^+e^-\to
\psi\chi_{0,1,2} are expected to differ from the analagous relations among
light flavour production such as \e^+e^-\to \omega f_{0,1,2}.Comment: 13 pages; journal versio
Seasonal Flight Patterns of Miridae (Hemiptera) in a Southern Illinois Black Walnut Plantation
The seasonal flight patterns of 92 species of Miridae collected in window traps in a southern Illinois black walnut plantation are compared with similar data from a North Carolina black walnut plantation. Flying height distributions and seasonal flight activities of Amblytylus nasutus, Deraeocoris nebulosus, Leptopterna dolabrata, Lopidea heidemanni, Lygus lineolaris, and Plagiognathus politus are considered in detail. Six species are newly recorded for Illinois
Stability Analysis of a Rigid Body with Attached Geometrically Nonlinear Rod by the Energy-Momentum Method
This paper applies the energy-momentum method to the problem of nonlinear stability of relative equilibria of a rigid body with attached flexible appendage in a uniformly rotating state. The appendage is modeled as a geometrically exact rod which allows for finite bending, shearing and twist in three dimensions. Application of the energy-momentum method to this example depends crucially on a
special choice of variables in terms of which the second variation block diagonalizes into blocks associated with rigid body modes and internal vibration modes respectively. The analysis yields a nonlinear stability result which states that relative equilibria are nonlinearly stable provided that; (i) the angular velocity is bounded above by the square root of the minimum eigenvalue of an associated
linear operator and, (ii) the whole assemblage is rotating about the minimum axis of inertia
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