8,906 research outputs found
Density dependence of spin relaxation in GaAs quantum well at room temperature
Carrier density dependence of electron spin relaxation in an intrinsic GaAs
quantum well is investigated at room temperature using time-resolved circularly
polarized pump-probe spectroscopy. It is revealed that the spin relaxation time
first increases with density in the relatively low density regime where the
linear D'yakonov-Perel' spin-orbit coupling terms are dominant, and then tends
to decrease when the density is large and the cubic D'yakonov-Perel' spin-orbit
coupling terms become important. These features are in good agreement with
theoritical predictions by L\"u {\em et al.} [Phys. Rev. B {\bf 73}, 125314
(2006)]. A fully microscopic calculation based on numerically solving the
kinetic spin Bloch equations with both the D'yakonov-Perel' and the
Bir-Aronov-Pikus mechanisms included, reproduces the density dependence of spin
relaxation very well.Comment: 4 pages, 2 figures, Europhys. Lett., in pres
Spin relaxation due to random Rashba spin-orbit coupling in GaAs (110) quantum wells
We investigate the spin relaxation due to the random Rashba spin-orbit
coupling in symmetric GaAs (110) quantum wells from the fully microscopic
kinetic spin Bloch equation approach. All relevant scatterings, such as the
electron-impurity, electron--longitudinal-optical-phonon,
electron--acoustic-phonon, as well as electron-electron Coulomb scatterings are
explicitly included. It is shown that our calculation reproduces the
experimental data by M\"uller {\em et al.} [Phys. Rev. Lett. {\bf 101}, 206601
(2008)] for a reasonable choice of parameter values. We also predict that the
temperature dependence of spin relaxation time presents a peak in the case with
low impurity density, which originates from the electron-electron Coulomb
scattering.Comment: 5 pages, 2 figures, EPL in pres
An Exploratory Study of Lecturers' Views of Out-of-class Academic Collaboration Among Students
This article reports an exploratory study of lecturers' perceptions of out-of-class academic collaboration (OCAC) among students at a large Singapore university. Two types of OCAC were investigated: collaboration initiated by students, e.g., groups decide on their own to meet to prepare for exams, and collaboration required by teachers, e.g., teachers assign students to do projects in groups. Data were collected via one-on-one interviews with 18 faculty members from four faculties at the university. Findings suggest that OCAC, especially of a teacher-required kind, is fairly common at the university. Faculty members' views on factors affecting the success of OCAC are discussed for the light they might shed on practices to enhance the effectiveness of OCAC
Search for Intrinsic Excitations in 152Sm
The 685 keV excitation energy of the first excited 0+ state in 152Sm makes it
an attractive candidate to explore expected two-phonon excitations at low
energy. Multiple-step Coulomb excitation and inelastic neutron scattering
studies of 152Sm are used to probe the E2 collectivity of excited 0+ states in
this "soft" nucleus and the results are compared with model predictions. No
candidates for two-phonon K=0+ quadrupole vibrational states are found. A 2+,
K=2 state with strong E2 decay to the first excited K=0+ band and a probable 3+
band member are established.Comment: 4 pages, 6 figures, accepted for publication as a Rapid Communication
in Physical Review
Synthesis and characterization of core-shell structure silica-coated Fe29.5Ni70.5 nanoparticles
In view of potential applications of magnetic particles in biomedicine and
electromagnetic devices, we made use of the classical Stober method
base-catalysed hydrolysis and condensation of tetraethoxysilane (TEOS) to
encapsulate FeNi nanoparticles within a silica shell. An original stirring
system under high power ultrasounds made possible to disperse the otherwise
agglomerated particles. Sonication guaranteed particles to remain dispersed
during the Stober synthesis and also improved the efficiency of the method. The
coated particles are characterized by electron microscopy (TEM) and
spectroscopy (EDX) showing a core-shell structure with a uniform layer of
silica. Silica-coating does not affect the core magnetic properties. Indeed,
all samples are ferromagnetic at 77 K and room temperature and the Curie point
remains unchanged. Only the coercive force shows an unexpected non-monotonous
dependence on silica layer thickness.Comment: Regular paper submited to international peer-reveiwed journa
Search for flavor-changing neutral currents and lepton-family-number violation in two-body D0 decays
Results of a search for the three neutral charm decays, D0 -> mu e, D0 -> mu
mu, and D0 -> e e, are presented. This study was based on data collected in
Experiment 789 at the Fermi National Accelerator Laboratory using 800 GeV/c
proton-Au and proton-Be interactions. No evidence is found for any of the
decays. Upper limits on the branching ratios, at the 90% confidence level, are
obtained.Comment: 28 pages, 18 figures. Submitted to Physical Review
Quark Delocalization, Color Screening, and Nuclear Intermediate Range Attraction
We consider the effect of including quark delocalization and color screening,
in the nonrelativistic quark cluster model, on baryon-baryon potentials and
phase shifts. We find that the inclusion of these additional effects allows a
good qualitative description of both.Comment: 10 pages, LaTeX, 4 figures in PostScript after text, LA-UR-91-215
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