16,259 research outputs found
Symmetry Constraints and the Electronic Structures of a Quantum Dot with Thirteen Electrons
The symmetry constraints imposing on the quantum states of a dot with 13
electrons has been investigated. Based on this study, the favorable structures
(FSs) of each state has been identified. Numerical calculations have been
performed to inspect the role played by the FSs. It was found that, if a
first-state has a remarkably competitive FS, this FS would be pursued and the
state would be crystal-like and have a specific core-ring structure associated
with the FS. The magic numbers are found to be closely related to the FSs.Comment: 13 pages, 5 figure
Improved Simulation of the Mass Charging for ASTROD I
The electrostatic charging of the test mass in ASTROD I (Astrodynamical Space
Test of Relativity using Optical Devices I) mission can affect the quality of
the science data as a result of spurious Coulomb and Lorentz forces. To
estimate the size of the resultant disturbances, credible predictions of
charging rates and the charging noise are required. Using the GEANT4 software
toolkit, we present a detailed Monte Carlo simulation of the ASTROD I test mass
charging due to exposure of the spacecraft to galactic cosmic-ray (GCR) protons
and alpha particles (3He, 4He) in the space environment. A positive charging
rate of 33.3 e+/s at solar minimum is obtained. This figure reduces by 50% at
solar maximum. Based on this charging rate and factoring in the contribution of
minor cosmic-ray components, we calculate the acceleration noise and stiffness
associated with charging. We conclude that the acceleration noise arising from
Coulomb and Lorentz effects are well below the ASTROD I acceleration noise
limit at 0.1 mHz both at solar minimum and maximum. The coherent Fourier
components due to charging are investigated, it needs to be studied carefully
in order to ensure that these do not compromise the quality of science data in
the ASTROD I mission.Comment: 20 pages, 14 figures, submitted to International Journal of Modern
Physics
Direct neutron capture cross sections of 62Ni in the s-process energy range
Direct neutron capture on 62Ni is calculated in the DWBA and the cross
sections in the energy range relevant for s-process nucleosynthesis are given.
It is confirmed that the thermal value of the capture cross section contains a
subthreshold resonance contribution. Contrary to previous investigations it is
found that the capture at higher energies is dominated by p-waves, thus leading
to a considerably increased cross section at s-process energies and a modified
energy dependence.Comment: 10 pages, 1 figure, corrected typos in Eq. 6 and subsequent paragrap
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Mechanistic Study Of Plasma Damage Of Low k Dielectric Surfaces
Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O-2, N-2/H-2, N-2 and H-2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.Microelectronics Research Cente
Breathing oscillations of a trapped impurity in a Bose gas
Motivated by a recent experiment [J. Catani et al., arXiv:1106.0828v1
preprint, 2011], we study breathing oscillations in the width of a harmonically
trapped impurity interacting with a separately trapped Bose gas. We provide an
intuitive physical picture of such dynamics at zero temperature, using a
time-dependent variational approach. In the Gross-Pitaevskii regime we obtain
breathing oscillations whose amplitudes are suppressed by self trapping, due to
interactions with the Bose gas. Introducing phonons in the Bose gas leads to
the damping of breathing oscillations and non-Markovian dynamics of the width
of the impurity, the degree of which can be engineered through controllable
parameters. Our results reproduce the main features of the impurity dynamics
observed by Catani et al. despite experimental thermal effects, and are
supported by simulations of the system in the Gross-Pitaevskii regime.
Moreover, we predict novel effects at lower temperatures due to self-trapping
and the inhomogeneity of the trapped Bose gas.Comment: 7 pages, 3 figure
Magnetic structure of antiferromagnetic NdRhIn5
The magnetic structure of antiferromagnetic NdRhIn5 has been determined using
neutron diffraction. It has a commensurate antiferromagnetic structure with a
magnetic wave vector (1/2,0,1/2) below T_N = 11K. The staggered Nd moment at
1.6K is 2.6mu_B aligned along the c-axis. We find the magnetic structure to be
closely related to that of its cubic parent compound NdIn3 below 4.6K. The
enhanced T_N and the absence of additional transitions below T_N for NdRhIn5
are interpreted in terms of an improved matching of the
crystalline-electric-field (CEF), magnetocrystalline, and exchange interaction
anisotropies. In comparison, the role of these competing anisotropies on the
magnetic properties of the structurally related compound CeRhIn5 is discussed.Comment: 4 pages, 4 figure
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