2,816 research outputs found
Diffusion and activation of n-type dopants in germanium
The diffusion and activation of -type impurities (P and As) implanted into
-type Ge(100) substrates were examined under various dose and annealing
conditions. The secondary ion mass spectrometry profiles of chemical
concentrations indicated the existence of a sufficiently high number of
impurities with increasing implanted doses. However, spreading resistance probe
profiles of electrical concentrations showed electrical concentration
saturation in spite of increasing doses and indicated poor activation of As
relative to P in Ge. The relationships between the chemical and electrical
concentrations of P in Ge and Si were calculated, taking into account the
effect of incomplete ionization. The results indicated that the activation of P
was almost the same in Ge and Si. The activation ratios obtained experimentally
were similar to the calculated values, implying insufficient degeneration of
Ge. The profiles of P in Ge substrates with and without damage generated by Ge
ion implantation were compared, and it was clarified that the damage that may
compensate the activated -type dopants has no relationship with the
activation of P in Ge.Comment: 6 pages, 4 figure
Electronic and optical properties of LiBC
LiBC, a semiconducting ternary borocarbide constituted of the lightest
elements only, has been synthesized and characterized by x-ray powder
diffraction, dielectric spectroscopy, and conductivity measurements. Utilizing
an infrared microscope the phonon spectrum has been investigated in single
crystals. The in-plane B-C stretching mode has been detected at 150 meV,
noticeably higher than in AlB2, a non-superconducting isostructural analog of
MgB2. It is this stretching mode, which reveals a strong electron-phonon
coupling in MgB2, driving it into a superconducting state below 40 K, and is
believed to mediate predicted high-temperature superconductivity in hole-doped
LiBC [H. Rosner, A. Kitaigorodsky, and W. E. Pickett, Phys. Rev. Lett. 88,
127001 (2002)].Comment: 4 pages, 4 figure
Tracking System with Re-identification Using a RGB String Kernel
International audiencePeople re-identification consists to identify a person which comes back in a scene where it has been previously detected. This key problem in visual surveillance applications may concern single or multi camera systems. Features encoding each person should be rich enough to provide an efficient re-identification while being sufficiently robust to remain significant through the different phenomena which may alter the appearance of a person in a video. We propose in this paper a method which encodes people's appearance through a string of salient points. The similarity between two such strings is encoded by a kernel. This last kernel is combined with a tracking algorithm in order to associate a set of strings to each person and to measure similarities between persons entering into the scene and persons who left it
Identification of âCandidatus Phytoplasmaâ species in âhuanglongbingâ infected citrus orchards in the Caribbean
âHuanglongbingâ (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from 183 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in three Caribbean countries (Cuba, Jamaica, and Guadeloupe-France), were collected to verify the possible co-infection of âCandidatus Phytoplasmaâ and âCandidatus Liberibacterâ species. The 64% of the samples resulted positive to the âCa. L. asiaticusâ and the 27% to diverse âCa. Phytoplasmaâ-related species, moreover about the 14% of the samples infected with âCa. Liberibacterâ were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Moreover the detection of only phytoplasmas in 11 symptomatic citrus samples collected from Cuba and Guadeloupe without âCa. Liberibacterâ detection, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular detection is necessary to identify single or mixed infections. Diaphorina citri insects collected from Cuba and Guadeloupe resulted infected with âCa. L. asiaticusâ confirming its active role in the dissemination of the pathogen. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Considering that the phytoplasmas belonging to some âCandidatus speciesâ were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attribute to citrus orchards
RVB Contribution to Superconductivity in
We view as electronically equivalent to (non-staggered) graphite
( layer) that has undergone a zero gap semiconductor to a superconductor
phase transition by a large c-axis (chemical) pressure due to layers.
Further, like the \ppi bonded planar organic molecules, graphite is an old
resonating valence bond (RVB) system. The RVB's are the `preexisting cooper
pairs' in the `parental' zero gap semiconducting (graphite) sheets that
manifests themselves as a superconducting ground state of the transformed
metal. Some consequences are pointed out.Comment: 4 pages, 2 figure, RevTex. Based on a talk given at the Institute
Seminar Week, IMSc, Madras (12-16, Feb. 2001
Soft x-ray spectroscopy experiments on the near K-edge of B in MB2 (M=Mg, Al, Ta, and Nb)
Soft X-ray absorption and emission measurements are performed for the K- edge
of B in MB (M=Mg, Al, Ta and Nb). Unique feature of MgB with a high
density of B 2-state below and above the Fermi edge, which
extends to 1 eV above the edge, is confirmed. In contrast, the B 2 density
of states in AlB and TaB, both of occupied and unoccupied states,
decreased linearly towards the Fermi energy and showed a dip at the Fermi
energy. Furthermore, there is a broadening of the peaks with
-character in XES and XAS of AlB, which is due to the increase of
three dimensionality in the -band in AlB. The DOS of NbB has a
dip just below the Fermi energy. The present results indicate that the large
DOS of B-2 states near the Fermi energy are crucial for the
superconductivity of MgB.Comment: 3 pages text and 4 pages figures. accepted for publication to Phys.
Rev.
The Role of Nrf2 in Cardiovascular Function and Disease
Free radicals, reactive oxygen/nitrogen species (ROS/RNS), hydrogen sulphide and hydrogen peroxide play an important role in both intracellular and intercellular signalling, however their production and quenching needs to be closely regulated to prevent cellular damage. An imbalance, due to exogenous sources of free radicals and chronic upregulation of endogenous production, contributes to many pathological conditions including cardiovascular disease and also the more general processes involved in aging. Nuclear factor erythroid 2 -like 2 (NFE2L2; commonly known as Nrf2) is a transcription factor that plays a major role in the dynamic regulation of a network of anti-oxidant and cytoprotective genes, through binding to, and activating expression of promoters containing the antioxidant response element (ARE). Nrf2 activity is regulated by many mechanisms, suggesting that tight control is necessary for normal cell function and both hypo- and hyperactivation of Nrf2 are indicated in playing a role in different aspects of cardiovascular disease. Targeted activation of Nrf2, or downstream genes may prove to be a useful avenue in developing therapeutics to reduce the impact of cardiovascular disease. We will review the current status of Nrf2 and related signalling in cardiovascular disease and its relevance to current and potential treatment strategies
Small Fermi energy and phonon anharmonicity in MgB_2 and related compounds
The remarkable anharmonicity of the E_{2g} phonon in MgB_2 has been suggested
in literature to play a primary role in its superconducting pairing. We
investigate, by means of LDA calculations, the microscopic origin of such an
anharmonicity in MgB_2, AlB_2, and in hole-doped graphite. We find that the
anharmonic character of the E_{2g} phonon is essentially driven by the small
Fermi energy of the sigma holes. We present a simple analytic model which
allows us to understand in microscopic terms the role of the small Fermi energy
and of the electronic structure. The relation between anharmonicity and
nonadiabaticity is pointed out and discussed in relation to various materials.Comment: 5 pages, 2 figures replaced with final version, accepted on Physical
Review
Structural and Superconducting Transitions in Mg_{1-x}Al_{x}B_2
From systematic ab initio calculations of the alloy system Mg_{1-x}Al_{x}B_2,
we find a strong tendency for the formation of a superstructure characterized
by Al-rich layers. We also present a simple model, based on calculated energies
and an estimate of the configurational entropy, which suggests that the alloy
has two separate concentration regimes of phase separation, with critical
points near x = 0.25 and x = 0.75. These results, together with calculations of
electronic densities of states in several ionic arrangements, give a
qualitative explanation for the observed structural instabilities, as well as
the x-dependence of the superconducting T_c for x<0.6.Comment: 4 pp./4 figs.; revisions in responce to Referee comment
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