4,882 research outputs found
Comparisons of halogenated ß-nitrostyrenes as antimicrobial agents
The influence of three types of halogen-substituted E-ß-methyl-ß-nitrostyrenes (such as Compounds B, D, H) to overcome bacterial activity that is currently a significant health threat was studied. The evaluations of their bio-potency was measured and related to their structure and activity relationships for the purposes of serving to inhibit and overcoming resistant microorganisms. In particular, fluorine-containing ß-nitrostyrenes were found to be highly active antimicrobial agents. The addition of the ß-bromo group enhanced the antibacterial activity significantly. Our work has illustrated that halogen substituents at both the 4-position in the aromatic ring and also at the ß-position on the alkene side chain of nitropropenyl arenes enhanced the antimicrobial activity of these compounds
Exciton Spin Relaxation Time in Quantum Dots Measured by Continuous-Wave Photoluminescence Spectroscopy
We demonstrate a new method of measuring the exciton spin relaxation time in
semiconductor nanostructures by continuous-wave photoluminescence. We find that
for self-assembled CdTe quantum dots the degree of circular polarization of
emission is larger when exciting polarized excitons into the lower energy spin
state than in the case when the excitons are excited into the higher energy
spin state. A simple rate equation model gives the exciton spin relaxation time
in CdTe quantum dots equal to 4.8+/-0.3 ns, significantly longer than the
quantum dot exciton recombination time 300 ps.Comment: 11 pages, 3 figure
Enhancing students' digital skills through promotion relationship between business and university to digital era integration
The rapid changes in the technology and labour market requires actions in education throughout the world. Currently, the Ministry of Education and Training in Vietnam provides guidelines and encourages universities and colleges to have direct interaction with industry partners to close skill gaps, especially in the digital era when universities lack updated resources for training. To prepare well essential skills for students at 8 higher education institutions in Vietnam, collaboration between industry partners and university is a must. This paper will explore how to develop a sustainable university-industry linkage at Phu Xuan University to enhance the digital capacity of students in the digital era. Reviewing existing university-industry linkages and proposing new activities and solutions for sustainable collaboration based on current practices will be presented in this paper
Optically Induced Magnetization of CdMnTe Self-Assembled Quantum Dots
We demonstrate that resonant excitation of CdMnTe self-assembled quantum dots
creates an ensemble of spin-polarized magnetic polarons at B=0 T. The strong
spatial confinement characteristic of quantum dots significantly increases the
stability of magnetic polarons so that the optically induced spin alignment is
observed for temperatures > 120 K.Comment: accepted for publication in Applied Physics Letter
Resonant Spectroscopy of II-VI Self-Assembled Quantum Dots: Excited States and Exciton-LO Phonon Coupling
Using resonantly excited photoluminescence along with photoluminescence
excitation spectroscopies, we study the carrier excitation processes in
CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots. Photoluminescence
excitation spectra of single CdTe quantum dots reflect two major mechanisms for
carrier excitation: The first, associated with the presence of sharp and
intense lines in the spectrum, is a direct excited state ? ground state
transition. The second, associated with the appearance of up to four much
broader excitation lines, is a LO phonon-assisted absorption directly into the
quantum dot ground states. LO phonons with energies of both quantum dots and
ZnTe barrier material are identified in the photoluminescence excitation
spectra. Resonantly excited PL measurements for the dot ensemble as a function
of excitation energy makes it possible to separate the contributions of these
two mechanisms. We find that for CdTe quantum dots the distribution of excited
states coupled to the ground states reflects the energy distribution of the
quantum dot emission, but shifted up in energy by 100 meV. This large splitting
between excited and ground states in CdTe quantum dots suggests strong spatial
confinement. In contrast, the LO phonon-assisted absorption shows significant
size selectivity. In the case of CdTe dots the exciton-LO phonon coupling is
strongly enhanced for smaller-sized dots which have higher emission energies.
In contrast, for CdSe quantum dots the exciton-LO phonon coupling is uniform
over the ensemble ? that is, the energy distribution determines the intensities
of LO phonon replicas. We show that for CdTe quantum dots after annealing, that
is after an increase in the average dot size, the exciton-LO phonon interaction
reflects the dot energy distribution, as observed for CdSe quantum dots.Comment: 28 pages, 5 figure
Pattern formation in directional solidification under shear flow. I: Linear stability analysis and basic patterns
An asymptotic interface equation for directional solidification near the
absolute stabiliy limit is extended by a nonlocal term describing a shear flow
parallel to the interface. In the long-wave limit considered, the flow acts
destabilizing on a planar interface. Moreover, linear stability analysis
suggests that the morphology diagram is modified by the flow near the onset of
the Mullins-Sekerka instability. Via numerical analysis, the bifurcation
structure of the system is shown to change. Besides the known hexagonal cells,
structures consisting of stripes arise. Due to its symmetry-breaking
properties, the flow term induces a lateral drift of the whole pattern, once
the instability has become active. The drift velocity is measured numerically
and described analytically in the framework of a linear analysis. At large flow
strength, the linear description breaks down, which is accompanied by a
transition to flow-dominated morphologies, described in a companion paper.
Small and intermediate flows lead to increased order in the lattice structure
of the pattern, facilitating the elimination of defects. Locally oscillating
structures appear closer to the instability threshold with flow than without.Comment: 20 pages, Latex, accepted for Physical Review
Nonlinear response of a driven vibrating nanobeam in the quantum regime
We analytically investigate the nonlinear response of a damped doubly clamped
nanomechanical beam under static longitudinal compression which is excited to
transverse vibrations. Starting from a continuous elasticity model for the
beam, we consider the dynamics of the beam close to the Euler buckling
instability. There, the fundamental transverse mode dominates and a quantum
mechanical time-dependent effective single particle Hamiltonian for its
amplitude can be derived. In addition, we include the influence of a
dissipative Ohmic or super-Ohmic environment. In the rotating frame, a
Markovian master equation is derived which includes also the effect of the
time-dependent driving in a non-trivial way. The quasienergies of the pure
system show multiple avoided level crossings corresponding to multiphonon
transitions in the resonator. Around the resonances, the master equation is
solved analytically using Van Vleck perturbation theory. Their lineshapes are
calculated resulting in simple expressions. We find the general solution for
the multiple multiphonon resonances and, most interestingly, a bath-induced
transition from a resonant to an antiresonant behavior of the nonlinear
response.Comment: 25 pages, 5 figures, submitted to NJ
- …