76 research outputs found
Residual Stress Measurement by Electronic Speckle Pattern Interferometry
The existence of residual stresses affects both safety and lifetime. Thus the determination of these stresses is very important. The ESPI (Electronic Speckle Pattern Interferometry) and Hole- Drilling combined method seems to be an appropriate technique for their measurement. The theoretical considerations about the applicability of this method based on computations and preliminary experiments are presented. The experiments on specimens simulating known residual stress distributions were carried out on a professional apparatus. These results were compared and are in good accordance with other conventional methods. The proposed technique can be used for residual stress measurements
The speciation and genotyping of Cronobacter isolates from hospitalised patients
The World Health Organization (WHO) has recognised all Cronobacter species as human pathogens. Among premature neonates and immunocompromised infants, these infections can be life-threatening, with clinical presentations of septicaemia, meningitis and necrotising enterocolitis. The neurological sequelae can be permanent and the mortality rate as high as 40 â 80 %. Despite the highlighted issues of neonatal infections, the majority of Cronobacter infections are in the elderly population suffering from serious underlying disease or malignancy and include wound and urinary tract infections, osteomyelitis, bacteraemia and septicaemia. However, no age profiling studies have speciated or genotyped the Cronobacter isolates. A clinical collection of 51 Cronobacter strains from two hospitals were speciated and genotyped using 7-loci multilocus sequence typing (MLST), rpoB gene sequence analysis, O-antigen typing and pulsed- field gel electrophoresis (PFGE). The isolates were predominated by C. sakazakii sequence type 4 (63 %, 32/51) and C. malonaticus sequence type 7 (33 %, 17/51). These had been isolated from throat and sputum samples of all age groups, as well as recal and faecal swabs. There was no apparent relatedness between the age of the patient and the Cronobacter species isolated. Despite the high clonality of Cronobacter , PFGE profiles differentiated strains across the sequence types into 15 pulsotypes. There was almost complete agreement between O-antigen typing and rpoB gene sequence analysis and MLST profiling. This study shows the value of applying MLST to bacterial population studies with strains from two patient cohorts, combined with PFGE for further discrimination of strains
Nonlinear evolution of surface morphology in InAs/AlAs superlattices via surface diffusion
Continuum simulations of self-organized lateral compositional modulation
growth in InAs/AlAs short-period superlattices on InP substrate are presented.
Results of the simulations correspond quantitatively to the results of
synchrotron x-ray diffraction experiments. The time evolution of the
compositional modulation during epitaxial growth can be explained only
including a nonlinear dependence of the elastic energy of the growing epitaxial
layer on its thickness. From the fit of the experimental data to the growth
simulations we have determined the parameters of this nonlinear dependence. It
was found that the modulation amplitude don't depend on the values of the
surface diffusion constants of particular elements.Comment: 4 pages, 3 figures, published in Phys. Rev. Lett.
http://link.aps.org/abstract/PRL/v96/e13610
Surface morphology and magnetic anisotropy in (Ga,Mn)As
Atomic Force Microscopy and Grazing incidence X-ray diffraction measurements
have revealed the presence of ripples aligned along the direction
on the surface of (Ga,Mn)As layers grown on GaAs(001) substrates and buffer
layers, with periodicity of about 50 nm in all samples that have been studied.
These samples show the strong symmetry breaking uniaxial magnetic anisotropy
normally observed in such materials. We observe a clear correlation between the
amplitude of the surface ripples and the strength of the uniaxial magnetic
anisotropy component suggesting that these ripples might be the source of such
anisotropy.Comment: 3 pages, 4 figures, 1 table. Replaced with published versio
Mn incorporation in as-grown and annealed (Ga,Mn)As layers studied by x-ray diffraction and standing-wave uorescence
A combination of high-resolution x-ray diffraction and a new technique of
x-ray standing wave uorescence at grazing incidence is employed to study the
structure of (Ga,Mn)As diluted magnetic semiconductor and its changes during
post-growth annealing steps. We find that the film is formed by a uniform,
single crystallographic phase epilayer covered by a thin surface layer with
enhanced Mn concentration due to Mn atoms at random non-crystallographic
positions. In the epilayer, Mn incorporated at interstitial position has a
dominant effect on lattice expansion as compared to substitutional Mn. The
expansion coeffcient of interstitial Mn estimated from our data is consistent
with theory predictions. The concentration of interstitial Mn and the
corresponding lattice expansion of the epilayer are reduced by annealing,
accompanied by an increase of the density of randomly distributed Mn atoms in
the disordered surface layer. Substitutional Mn atoms remain stable during the
low-temperature annealing.Comment: 9 pages, 9 figure
Interband absorption edge in the topological insulators Bi-2(Te1-xSex)(3)
We have investigated the optical properties of thin films of topological insulators Bi2Te3, Bi2Se3, and their alloys Bi-2(Te1-x Se-x)(3) on BaF2 substrates by a combination of infrared ellipsometry and reflectivity in the energy range from 0.06 to 6.5 eV. For the onset of interband absorption in Bi2Se3, after the correction for the Burstein-Moss effect, we find the value of the direct band gap of 215 +/- 10 meV at 10 K. Our data support the picture that Bi2Se3 has a direct band gap located at the Gamma point in the Brillouin zone and that the valence band reaches up to the Dirac point and has the shape of a downward-oriented paraboloid, i.e., without a camel-back structure. In Bi2Te3, the onset of strong direct interband absorption at 10 K is at a similar energy of about 200 meV, with a weaker additional feature at about 170 meV. Our data support the recent GW band-structure calculations suggesting that the direct interband transition does not occur at the Gamma point but near the Z-F line of the Brillouin zone. In the Bi-2(Te1-x Se-x)(3) alloy, the energy of the onset of direct interband transitions exhibits a maximum near x = 0.3 (i.e., the composition of Bi2Te2Se), suggesting that the crossover of the direct interband transitions between the two points in the Brillouin zone occurs close to this composition
Effect of strain on surface diffusion in semiconductor heteroepitaxy
We present a first-principles analysis of the strain renormalization of the
cation diffusivity on the GaAs(001) surface. For the example of
In/GaAs(001)-c(4x4) it is shown that the binding of In is increased when the
substrate lattice is expanded. The diffusion barrier \Delta E(e) has a
non-monotonic strain dependence with a maximum at compressive strain values (e
0) studied.
We discuss the consequences of spatial variations of both the binding energy
and the diffusion barrier of an adatom caused by the strain field around a
heteroepitaxial island. For a simplified geometry, we evaluate the speed of
growth of two coherently strained islands on the GaAs(001) surface and identify
a growth regime where island sizes tend to equalize during growth due to the
strain dependence of surface diffusion.Comment: 10 pages, 8 figures, LaTeX2e, to appear in Phys. Rev. B (2001). Other
related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
Diplolepis rosae (l.) (hymenoptera: Cynipidae): Development, ecology and galls in the brno region
The paper results from two years of studying development and formation of the galls of Diplolepis rosae (L.) on Rosa canina (L.) in the Brno region (Czech Republic). Following the extremely warm and dry growing season of 2015, 70 % of prepupae and 30 % of grown-up 2nd instar larvae hibernated. After the climatically milder growing period of 2016, only 47 % of prepupae and 53 % of grown-up larvae hibernated. Pupae were recorded from mid-March to mid-July and imagoes occurred from April to July. The average percentage of males in the populations was 4.5 %. Eggs were found in the galls from May to July. Larvae of the 1st and 2nd instars were found in the galls from June to August and from July to October (or to next March), respectively. Average cranium width in the 1st instar larvae increased during the growth of larvae from 0.25 to 0.35 mm, i.e. by 38 %. Average cranium width in the 2nd instar larvae was 0.55 mm and practically did not change during the growth of the larvae. 85.1 % of galls were formed on budding leaves, 14.9 % on flowers and fruits. The galls were growing most rapidly in June and July, and their growth ended in October when they reached average height and width of 40 mm and 47 mm, respectively. They consisted of 1 to 20 (on average 7) +- intergrown parts with 1 to 225 (on average 54) cells. 63.5 % of them were localized along the sides of shoots and 36.5 % were found on the shoot tips. The largest cells (3.9 x 3.1 mm) were those with the completed development of gall wasp larvae. Cells inhabited by parasitoids were by 15.0 % smaller and by 24.5 % smaller were cells with dead gallwasp larvae due to natural reasons. As compared with the cells with the completed development of gall wasp, cells with the larvae of inquiline Periclistus brandtii (Ratz.) were by 43.6 % shorter and by 50.6 % narrower. The inquiline was found in 10 % of galls and in 3.6 % of cells. In 2015, parasitoids inhabited on average 15.0 % (in 2016 22.1 %) of cells. Approximately 50 % of the population of D. rosae died in the galls during the preimaginal development.O
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