1,596 research outputs found
GaAs(111)A and B in hydrazine sulfide solutions : extreme polarity dependence of surface adsorption processes
Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were
studied by synchrotron photoemission spectroscopy. At the B surface, the top
arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by
sulfur, also bonded to underlying gallium, despite the sulfide molar
concentration being 103 times smaller than that of the hydrazine. This extreme
dependence on surface polarity is explained by competitive adsorption processes
of HS- and OH- anions and of hydrazine molecules, on Ga- adsorption sites,
which have distinct configurations on the A and B surfaces
Absence of an intrinsic value for the surface recombination velocity in doped semiconductors
A self-consistent expression for the surface recombination velocity and
the surface Fermi level unpinning energy as a function of light excitation
power () is presented for n- and p-type semiconductors doped above the
10 cm range. Measurements of on p-type GaAs films using a
novel polarized microluminescence technique are used to illustrate two limiting
cases of the model. For a naturally oxidized surface is described by a
power law in whereas for a passivated surface varies
logarithmically with . Furthermore, the variation in with surface state
density and bulk doping level is found to be the result of Fermi level
unpinning rather than a change in the intrinsic surface recombination velocity.
It is concluded that depends on throughout the experimentally
accessible range of excitation powers and therefore that no instrinsic value
can be determined. Previously reported values of on a range of
semiconducting materials are thus only valid for a specific excitation power.Comment: 10 pages, 7 figure
Assessment of the inclusion of vaccination as an intervention to reduce antimicrobial resistance in AMR national action plans:a global review
BACKGROUND: Vaccination can reduce antibiotic use by decreasing bacterial and viral infections and vaccines are highlighted in the WHO Global Action Plan on Antimicrobial Resistance (AMR) as an infection prevention measure to reduce AMR. Our study aimed to analyze whether WHO Member States have developed AMR national action plans that are aligned with the Global Action Plan regarding objectives on vaccination. METHODS: We reviewed 77 out of 90 AMR national action plans available in the WHO library that were written after publication of the Global Action Plan in 2015. Each plan was analyzed using content analysis, with a focus on vaccination and key components as defined by WHO (I. Strategic plan (e.g. goals and objectives), II. Operational plan, III. Monitoring and Evaluation plan). RESULTS: Vaccination was included in 67 of 77 AMR plans (87%) across all WHO Regions (Africa: n = 13/13, the Eastern Mediterranean: n = 15/16, Europe: n = 10/14, the Americas: n = 8/8, South-East Asia: n = 8/11, and the Western Pacific: n = 13/15). Pneumococcal and influenza vaccination were most frequently highlighted (n = 12 and n = 11). We found indications that vaccination objectives are more often included in AMR plans from higher income countries, while lower income countries more often include specific vaccines. The key WHO components of national action plans were frequently not covered (I. 47% included, II. 57%, III. 40%). In total, 33 countries (43%) included indicators (e.g. strategic objectives) to capture the role of vaccines against AMR. CONCLUSIONS: While vaccination to reduce AMR is seen as an important global public health issue by WHO, there appears to be a gap in its adoption in national AMR plans. Country income levels seem to influence the progress, implementation and focus of national action plans, guided by a lack of funding and prioritization in developing countries. To better align the global response to AMR, our review suggests there is a need to update national action plans to include objectives on vaccination with more focus on specific vaccines that impact antibiotic use
Coulomb "blockade" of Nuclear Spin Relaxation in Quantum Dots
We study the mechanism of nuclear spin relaxation in quantum dots due to the
electron exchange with 2D gas. We show that the nuclear spin relaxation rate is
dramatically affected by the Coulomb blockade and can be controlled by gate
voltage. In the case of strong spin-orbit coupling the relaxation rate is
maximal in the Coulomb blockade valleys whereas for the weak spin-orbit
coupling the maximum of the nuclear spin relaxation rate is near the Coulomb
blockade peaks.Comment: 4 pages, 3 figure
Spin-dependent electron dynamics and recombination in GaAs(1-x)N(x) alloys at room temperature
We report on both experimental and theoretical study of conduction-electron
spin polarization dynamics achieved by pulsed optical pumping at room
temperature in GaAs(1-x)N(x) alloys with a small nitrogen content (x = 2.1,
2.7, 3.4%). It is found that the photoluminescence circular polarization
determined by the mean spin of free electrons reaches 40-45% and this giant
value persists within 2 ns. Simultaneously, the total free-electron spin decays
rapidly with the characteristic time ~150 ps. The results are explained by
spin-dependent capture of free conduction electrons on deep paramagnetic
centers resulting in dynamical polarization of bound electrons. We have
developed a nonlinear theory of spin dynamics in the coupled system of
spin-polarized free and localized carriers which describes the experimental
dependencies, in particular, electron spin quantum beats observed in a
transverse magnetic field.Comment: 5 pages, 4 figures, Submitted to JETP Letter
Niche inheritance: a cooperative pathway to enhance cancer cell fitness though ecosystem engineering
Cancer cells can be described as an invasive species that is able to
establish itself in a new environment. The concept of niche construction can be
utilized to describe the process by which cancer cells terraform their
environment, thereby engineering an ecosystem that promotes the genetic fitness
of the species. Ecological dispersion theory can then be utilized to describe
and model the steps and barriers involved in a successful diaspora as the
cancer cells leave the original host organ and migrate to new host organs to
successfully establish a new metastatic community. These ecological concepts
can be further utilized to define new diagnostic and therapeutic areas for
lethal cancers.Comment: 8 pages, 1 Table, 4 Figure
Creation of Entanglement between Two Electron Spins Induced by Many Spin Ensemble Excitations
We theoretically explore the possibility of creating spin entanglement by
simultaneously coupling two electronic spins to a nuclear ensemble. By
microscopically modeling the spin ensemble with a single mode boson field, we
use the time-dependent Fr\"{o}hlich transformation (TDFT) method developed most
recently [Yong Li, C. Bruder, and C. P. Sun, Phys. Rev. A \textbf{75}, 032302
(2007)] to calculate the effective coupling between the two spins. Our
investigation shows that the total system realizes a solid state based
architecture for cavity QED. Exchanging such kind effective boson in a virtual
process can result in an effective interaction between two spins. It is
discovered that a maximum entangled state can be obtained when the velocity of
the electrons matches the initial distance between them in a suitable way.
Moreover, we also study how the number of collective excitations influences the
entanglement. It is shown that the larger the number of excitation is, the less
the two spins entangle each other.Comment: 8 pages, 4 figure
Fine structure and optical pumping of spins in individual semiconductor quantum dots
We review spin properties of semiconductor quantum dots and their effect on
optical spectra. Photoluminescence and other types of spectroscopy are used to
probe neutral and charged excitons in individual quantum dots with high
spectral and spatial resolution. Spectral fine structure and polarization
reveal how quantum dot spins interact with each other and with their
environment. By taking advantage of the selectivity of optical selection rules
and spin relaxation, optical spin pumping of the ground state electron and
nuclear spins is achieved. Through such mechanisms, light can be used to
process spins for use as a carrier of information
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