2,646 research outputs found
Band gap renormalization in photoexcited semiconductor quantum wire structures in the GW approximation
We investigate the dynamical self-energy corrections of the electron-hole
plasma due to electron-electron and electron-phonon interactions at the band
edges of a quasi-one dimensional (1D) photoexcited electron-hole plasma. The
leading-order dynamical screening approximation is used in the calculation
by treating electron-electron Coulomb interaction and electron-optical phonon
Fr\"{o}hlich interaction on an equal footing. We calculate the
exchange-correlation induced band gap renormalization (BGR) as a function of
the electron-hole plasma density and the quantum wire width. The calculated BGR
shows good agreement with existing experimental results, and the BGR normalized
by the effective quasi-1D excitonic Rydberg exhibits an approximate
one-parameter universality.Comment: 11 pages, 3 figure
Multiple solutions to a magnetic nonlinear Choquard equation
We consider the stationary nonlinear magnetic Choquard equation
[(-\mathrm{i}\nabla+A(x))^{2}u+V(x)u=(\frac{1}{|x|^{\alpha}}\ast |u|^{p})
|u|^{p-2}u,\quad x\in\mathbb{R}^{N}%] where is a real valued vector
potential, is a real valued scalar potential ,
and . \ We assume that both and are
compatible with the action of some group of linear isometries of
. We establish the existence of multiple complex valued
solutions to this equation which satisfy the symmetry condition where
is a given group homomorphism into the unit
complex numbers.Comment: To appear on ZAM
Confined optical phonon modes in polar tetrapod nanocrystals detected by resonant inelastic light scattering
We investigated CdTe nanocrystal tetrapods of different sizes by resonant
inelastic light scattering at room temperature and under cryogenic conditions.
We observe a strongly resonant behavior of the phonon scattering with the
excitonic structure of the tetrapods. Under resonant conditions we detect a set
of phonon modes that can be understood as confined longitudinal-optical
phonons, surface-optical phonons, and transverse-optical phonons in a nanowire
picture.Comment: 12 pages, 4 figure
Age estimation in children by measurement of open apices in teeth
This paper concerns a method for estimating the
age of children based on their teeth. The sample consisted
of 455 Italian white children (213 boys, 242 girls) aged
between 5 and 15 years. The purpose of the present investigation
was to present a method for assessing chronological
age based on the relationship between age and
measurement of the open apices in teeth. Pearson\u2019s correlation
coefficients between age and these variables
showed that the correlations between age and the open
apices in teeth were significant and negative. Furthermore,
gender and the number of teeth with the apical end of the
root canals completely closed (N0) showed a significant
correlation with chronological age. With the aid of a
stepwise multiple regression model, a linear relationship
between open apices, N0, and age was shown. Statistical
analysis indicated that these morphological variables
explain 83.6% of the variations in estimated chronological
age. The median of residual errors between the actual
and estimated ages was 120.035 years [interquartile range
(IQR)=1.18 years]
Variations in pulp/tooth area ratio as an indicator of age: a preliminary study
This paper details for age determination of adult from single rooted theeth. The sample consisted of 100 Italians white Caucasioan patients (46 men, 54 womwn) aged between 18 and 72 years. The single rooted maxillary right canine was utilized in this preliminary study. Pulp/root ration, tooth length ratio, pulp/root area and pulp/root width ratios at three different levels were computed. Pearson's correlation coefficients between age and these variables showed that the ratio between pulp and tooth area correlated best with age (r2 = 0,85). Stepwise multiple regression models yielded a linear relationship between pulp/root width at mid-root level and chronological age and a linear relationship when pulp/tooth area was compared to age. Statistical analysis indicated that these two variables explain 84,9% of variations in estimated chronological age. The median of the absolute value of residual errors between actual and estimated ages was less than four years
Exploring the atomic structure and conformational flexibility of a 320 Å long engineered viral fiber using X-ray crystallography.
Protein fibers are widespread in nature, but only a limited number of high-resolution structures have been determined experimentally. Unlike globular proteins, fibers are usually recalcitrant to form three-dimensional crystals, preventing single-crystal X-ray diffraction analysis. In the absence of three-dimensional crystals, X-ray fiber diffraction is a powerful tool to determine the internal symmetry of a fiber, but it rarely yields atomic resolution structural information on complex protein fibers. An 85-residue-long minimal coiled-coil repeat unit (MiCRU) was previously identified in the trimeric helical core of tail needle gp26, a fibrous protein emanating from the tail apparatus of the bacteriophage P22 virion. Here, evidence is provided that an MiCRU can be inserted in frame inside the gp26 helical core to generate a rationally extended fiber (gp26-2M) which, like gp26, retains a trimeric quaternary structure in solution. The 2.7 Å resolution crystal structure of this engineered fiber, which measures ∼320 Å in length and is only 20-35 Å wide, was determined. This structure, the longest for a trimeric protein fiber to be determined to such a high resolution, reveals the architecture of 22 consecutive trimerization heptads and provides a framework to decipher the structural determinants for protein fiber assembly, stability and flexibility
Role of anisotropy in the F\"orster energy transfer from a semiconductor quantum well to an organic crystalline overlayer
We consider the non-radiative resonant energy transfer from a two-dimensional
Wannier exciton (donor) to a Frenkel exciton of a molecular crystal overlayer
(acceptor). We characterize the effect of the optical anisotropy of the organic
subsystem on this process. Using realistic values of material parameters, we
show that it is possible to change the transfer rate within typically a factor
of two depending on the orientation of the crystalline overlayer. The resonant
matching of donor and acceptor energies is also partly tunable via the organic
crystal orientation.Comment: 6 pages, 8 figure
Valence band spectroscopy in V-grooved quantum wires
We present a combined theoretical and experimental study of the anisotropy in
the optical absorption of V-shaped quantum wires. By means of realistic band
structure calculations for these structures, we show that detailed information
on the heavy- and light-hole states can be singled out from the anisotropy
spectra {\em independently of the electron confinement}, thus allowing accurate
valence band spectroscopy.Comment: To be published in Appl. Phys. Lett. (8 pages in REVTeX, two
postscipt figures
Carpals and epiphysis of radius and ulna as age indicators
Estimation of skeletal age using radiographic
images is widely used for assessing biological growth in
clinical and auxological studies. The most frequent areas
used for age estimation in children and adolescents are
tooth and wrist/hand, both giving good results with only a
low level of radiation. In particular, ossification of the
carpals shows good agreement with chronological age. This
study of a sample of 150 Italian children and adolescents
aged between 5 and 17 years focused on analyzing the
possible applications of the proportion of carpal area (Ca)
mineralization as a criterion of age estimation. The ratio
between the total area of carpal bones and epiphyses of the
ulna and radius (Bo) andCa was calculated. This ratio (Bo/Ca)
was used for linear regression analysis. The regression model,
describing age as a linear function of the ratio Bo/Ca, yielded
the following equation: Age= 123.253+0.719g+20.610 Bo/Ca,
and explained 83% of the total variance (R2=0.83). The
median of the absolute values of residuals (observed age
minus predicted age) was 0.08 years, with a quartile deviation
of 1.59 years, and a standard error of estimate of 1.19 years
Detection and quantitation analysis of cocaine and metabolites in fixed liver tissue and formalin solutions.
This study reports the results of the detection and quantitation of
cocaine and its metabolites in liver tissues fixed in formalin and in
the formalin solutions in which the same tissues were fixed.
Toxicological analyses were performed on formalin-fixed liver
samples from four cases of death of cocaine abusers and on
formalin solutions (10% buffered, pH 7) in which the samples were
preserved. Analyses carried out at the time of autopsy on body
fluids and tissues allowed identification of cocaine and the
metabolite benzoylecgonine. Liver tissue samples were preserved in formalin solutions for four weeks before analysis. Results only
showed the presence of benzoylecgonine in the studied materials.
The mean levels of recovery of benzoylecgonine in fixed tissues
were 12.31% in liver and 84.47% in formalin from liver. Results
indicated that benzoylecgonine has good stability, even in
biological specimens subjected to chemical fixation
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