8,893 research outputs found
Optically probing the fine structure of a single Mn atom in an InAs quantum dot
We report on the optical spectroscopy of a single InAs/GaAs quantum dot (QD)
doped with a single Mn atom in a longitudinal magnetic field of a few Tesla.
Our findings show that the Mn impurity is a neutral acceptor state A^0 whose
effective spin J=1 is significantly perturbed by the QD potential and its
associated strain field. The spin interaction with photo-carriers injected in
the quantum dot is shown to be ferromagnetic for holes, with an effective
coupling constant of a few hundreds of micro-eV, but vanishingly small for
electrons.Comment: 5 pages, 3 figure
No Complaining...
It is said that hunger is a great motivator. If only the hunger for knowledge were as great as the hunger for physical sustenance. This statement could be lodged as a complaint, but that would defeat the purpose of this essay. How is it possible to turn the toil of our learning into the enlightenment for self-improvement
Evolution of Thermotolerance and Variation in the Heat Shock Protein, Hsp70
Low to moderate levels of stress induce a class of molecular chaperones called heat shock proteins (Hsps), which protect cells, tissues and whole organisms from more severe stress. In higher Eukaryotes, Hsp70 is one of the principle heat-induced chaperones. This response is general, and how much Hsp70 an animal produces correlates with the level of stress to which it is exposed. Nonetheless, definitively linking high Hsp70 expression as an adaptation to stress tolerance is problematic, because organisms and cells respond to stress in many ways. By molecular manipulation of Hsp70 in one animal group, Drosophila, differences in hsp70 copy number are shown to directly influence heat-induced expression of Hsp70 and tolerance of heat. However, too high an expression level of Hsp70 can harm individuals during periods of rapid growth. This strong physiological relationship between Hsp70 concentration and thermotolerance, along with Hsp70\u27s remarkable degree of interspecific coding sequence conservation, suggest that hsp70 regulatory elements may evolve as an adaptation in diverse species to their thermal environments. To examine this possibility, correlative studies within species and research on phylogenetic covariation between these traits is reviewed with a focus on Drosophila species. However, the techniques and results discussed should broadly apply to other animal groups where evolutionary approaches can be used to test whether genetic variation in both thermotolerance and Hsp expression within and among species select locally on either hsp70 sequence and/or expression
Concentration for One and Two Species One-Dimensional Reaction-Diffusion Systems
We look for similarity transformations which yield mappings between different
one-dimensional reaction-diffusion processes. In this way results obtained for
special systems can be generalized to equivalent reaction-diffusion models. The
coagulation (A + A -> A) or the annihilation (A + A -> 0) models can be mapped
onto systems in which both processes are allowed. With the help of the
coagulation-decoagulation model results for some death-decoagulation and
annihilation-creation systems are given. We also find a reaction-diffusion
system which is equivalent to the two species annihilation model (A + B ->0).
Besides we present numerical results of Monte Carlo simulations. An accurate
description of the effects of the reaction rates on the concentration in
one-species diffusion-annihilation model is made. The asymptotic behavior of
the concentration in the two species annihilation system (A + B -> 0) with
symmetric initial conditions is studied.Comment: 20 pages latex, uuencoded figures at the en
Organizational Chart Inference
Nowadays, to facilitate the communication and cooperation among employees, a
new family of online social networks has been adopted in many companies, which
are called the "enterprise social networks" (ESNs). ESNs can provide employees
with various professional services to help them deal with daily work issues.
Meanwhile, employees in companies are usually organized into different
hierarchies according to the relative ranks of their positions. The company
internal management structure can be outlined with the organizational chart
visually, which is normally confidential to the public out of the privacy and
security concerns. In this paper, we want to study the IOC (Inference of
Organizational Chart) problem to identify company internal organizational chart
based on the heterogeneous online ESN launched in it. IOC is very challenging
to address as, to guarantee smooth operations, the internal organizational
charts of companies need to meet certain structural requirements (about its
depth and width). To solve the IOC problem, a novel unsupervised method Create
(ChArT REcovEr) is proposed in this paper, which consists of 3 steps: (1)
social stratification of ESN users into different social classes, (2)
supervision link inference from managers to subordinates, and (3) consecutive
social classes matching to prune the redundant supervision links. Extensive
experiments conducted on real-world online ESN dataset demonstrate that Create
can perform very well in addressing the IOC problem.Comment: 10 pages, 9 figures, 1 table. The paper is accepted by KDD 201
Magnetic Properties of Epitaxial and Polycrystalline Fe/Si Multilayers
Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown
via ion-beam sputtering on both glass and single-crystal substrates. High-angle
x-ray diffraction measurements show that both sets of films have narrow Fe
peaks, implying a large crystallite size and crystalline iron silicide spacer
layers. Low-angle x-ray diffraction measurements show that films grown on glass
have rougher interfaces than those grown on single-crystal substrates. The
multilayers grown on glass have a larger remanent magnetization than the
multilayers grown on single-crystal substrates. The observation of
magnetocrystalline anisotropy in hysteresis loops and peaks in x-ray
diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The
smaller remanent magnetization in Fe/Si multilayers with better layering
suggests that the remanence is not an intrinsic property.Comment: 9 pages, RevTex, 4 figures available by fax. Send email to
[email protected] for more info. Submitted to '95 MMM proceeding
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Quarterly report, 1 Dec. 1967 - 29 Feb. 1968
Stress corrosion of aluminum alloys and techniques for its detectio
Study of the general mechanism of stress corrosion of aluminum alloys and development of techniques for its detection Annual summary report, 2 Jun. 1967 - 1 Jun. 1968
Stress corrosion cracking of high strength aluminum alloys investigated by electrochemical, mechanical, and electron microscopic technique
Separating Developmental and Environmental Effects on Fluctuating Asymmetry in Lythrum salicaria and Penthorum sedoides
Environmental stress can disrupt developmental processes on biological, physiological, and chemical levels and thereby affect the symmetry of a trait. For this reason, fluctuating asymmetry is often proposed as a measure of stress encountered by an individual. One problem is that asymmetry may have multiple causes, including developmental noise and genetic background, and genetic differences may interact with any physiological stress imposed by the environment. The main objective of this research was to determine whether developmental noise and genetic stress can be separated from environmental effects on leaf asymmetry. The experiments were conducted on two wetland plants, Lythrum salicaria (purple loosestrife) and Penthorum sedoides (ditch stonecrop). Replicates of different genotypes were measured when young and after they matured, with the latter group grown under two nutrient treatments. The largest and healthiest leaf of each plant was measured for length, width, and differences in width between the left and right sides (measuring from the central vein at the widest point). Nutrient enrichment increased leaf asymmetry, while age reduced asymmetry in L. salicaria. However, leaf asymmetry changed only as a consequence of development in P. sedoides and decreased. Genotype did not affect asymmetry in either species
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