470 research outputs found
Effects of Acute and Chronic Cold Stress on Expression of Cyclooxygenase-2 and Prostaglandin E Synthase mRNA in Quail Intestine
The cold temperature, a common environmental stress, reduces the immunity and re-production activities of the poultry. This study aims to investigate the role of acute and chronic cold exposure in the regulation of cyclooxygenase-2 (COX-2) and prostaglandin E synthase (PTGES) expression in the duodenum, jejunum, and ileum of quail. A total of 96 quail with 15 days of age were randomly allocated into 12 groups (8 each group) for exposure to acute (up to 12 h) and chronic (up to 20 days) cold temperature (12±1°C). After that, different segments of the intestine were harvested and subjected to morphology observations under the light and electronic microscopes. qRT-PCR was performed to analyze expression of COX-2 and PTGES, and DNA sequencing was performed to analyze PCR products. The data showed that under acute cold stress, expression of COX-2 and PTGES mRNA was first decreased and then increased in the duodenum, jejunum, and ileum of quail. However, chronic cold stress induced expression of COX-2 and PTGES mRNA in the duodenum, jejunum and ileum of quail, which was then reduced after 20 days of cold exposure. Morphologically, significant changes were also observed in the duodenum, jejunum and ileum after both acute and chronic cold stresses to the animals. The data from the current study indicated that both acute and chronic cold stresses were able to induce inflammation responses in the duodenum, jejunum and ileum, which might be due to the cold-damaged intestinal morphology
Radiographic Image Enhancement by Wiener Decorrelation
The primary focus of the application of image processing to radiography is the problem of segmentation. The general segmentation problem has been attacked on a broad front [1, 2], and thresholding, in particular, is a popular method [1, 3-6]. Unfortunately, geometric unsharpness destroys the crisp edges needed for unambiguous decisions, and this difficulty can be considered a problem in filtering in which the object is to devise a high-pass (sharpening) filter. This approach has been studied for more than 20 years [7-13]
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Finite element analysis and calculation method of residual flexural capacity of post-fire RC beams
Fire tests and subsequent bending tests of fourreinforced concrete (RC) beamswere performed. Based on these tests, the post-fire performance of RCbeams was further studied using finite element simulation through reasonable selection of suitable thermal and thermodynamic parameters of steel and concrete materials. A thermodynamic model of RC beams with three sides under fire was built using finite element analysis(FEA)software ABAQUS. The FEA model was validated with the results of fire tests. Different factors were taken into account for further parametric studies in fire using the proposed FE model.The results show that the main factors affecting the fire resistance of the beamsare the thickness of the concretecover, reinforcement ratio of longitudinal steel,the fire exposure timeandthe fire exposure sides. Based on the strength reduction formula at high temperature of steel and concrete, animproved section method was proposed to develop a calculation formula to calculate the flexural capacity of RC beams after fire. The theoretical calculation method proposed in this paper shows good agreement with FEA results, which can be used to calculate the flexuralcapacity of RC beams after fire
Near-Infrared Super Resolution Imaging with Metallic Nanoshell Particle Chain Array
We propose a near-infrared super resolution imaging system without a lens or
a mirror but with an array of metallic nanoshell particle chain. The imaging
array can plasmonically transfer the near-field components of dipole sources in
the incoherent and coherent manners and the super resolution images can be
reconstructed in the output plane. By tunning the parameters of the metallic
nanoshell particle, the plasmon resonance band of the isolate nanoshell
particle red-shifts to the near-infrared region. The near-infrared super
resolution images are obtained subsequently. We calculate the field intensity
distribution at the different planes of imaging process using the finite
element method and find that the array has super resolution imaging capability
at near-infrared wavelengths. We also show that the image formation highly
depends on the coherence of the dipole sources and the image-array distance.Comment: 15 pages, 6 figure
Microstructure and properties of a deformation-processed Cu-Cr-Ag in situ composite by directional solidification
Cu-7Cr-0.07Ag alloys were prepared by casting and directional solidification, from which deformation-processed in situ composites were prepared by thermo-mechanical processing. The microstructure, mechanical properties, and electrical properties were investigated using optical microscopy, scanning electronic microscopy, tensile testing, and a micro-ohmmeter. The second-phase Cr grains of the directional solidification Cu-7Cr-0.07Ag in situ composite were parallel to the drawing direction and were finer, which led to a higher tensile strength and a better combination of properties
Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica
Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a coreâshell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50â200 nm and the length from tens to hundreds of micrometers. The vaporâsolid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough coreâshell interface
Evolutionary and pulsational properties of white dwarf stars
Abridged. White dwarf stars are the final evolutionary stage of the vast
majority of stars, including our Sun. The study of white dwarfs has potential
applications to different fields of astrophysics. In particular, they can be
used as independent reliable cosmic clocks, and can also provide valuable
information about the fundamental parameters of a wide variety of stellar
populations, like our Galaxy and open and globular clusters. In addition, the
high densities and temperatures characterizing white dwarfs allow to use these
stars as cosmic laboratories for studying physical processes under extreme
conditions that cannot be achieved in terrestrial laboratories. They can be
used to constrain fundamental properties of elementary particles such as axions
and neutrinos, and to study problems related to the variation of fundamental
constants.
In this work, we review the essentials of the physics of white dwarf stars.
Special emphasis is placed on the physical processes that lead to the formation
of white dwarfs as well as on the different energy sources and processes
responsible for chemical abundance changes that occur along their evolution.
Moreover, in the course of their lives, white dwarfs cross different
pulsational instability strips. The existence of these instability strips
provides astronomers with an unique opportunity to peer into their internal
structure that would otherwise remain hidden from observers. We will show that
this allows to measure with unprecedented precision the stellar masses and to
infer their envelope thicknesses, to probe the core chemical stratification,
and to detect rotation rates and magnetic fields. Consequently, in this work,
we also review the pulsational properties of white dwarfs and the most recent
applications of white dwarf asteroseismology.Comment: 85 pages, 28 figures. To be published in The Astronomy and
Astrophysics Revie
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