7,000 research outputs found
Grain refinement of DC cast magnesium alloys with intensive melt shearing
A new direct chill (DC) casting process, melt conditioned DC (MC-DC) process, has been developed for the production of high quality billets/slabs of light alloys by application of intensive melt shearing through a rotor-stator high shear device during the DC casting process. The rotor-stator high shear device provides intensive melt shearing to disperse the naturally occurring oxide films, and other inclusions, while creating a microscopic flow pattern to homogenize the temperature and composition fields in the sump. In this paper, we report the grain refining effect of intensive melt shearing in the MC-DC casting processing. Experimental results on DC casting of Mg-alloys with and without intensive melt shearing have demonstrated that the MC-DC casting process can produce magnesium alloy billets with significantly refined microstructure. Such grain refinement in the MC-DC casting process can be attributed to enhanced heterogeneous nucleation by dispersed naturally occurring oxide particles, increased nuclei survival rate in uniform temperature and compositional fields in the sump, and potential contribution from dendrite arm fragmentation
Refining grain structure and porosity of an aluminium alloy with intensive melt shearing
The official published version of the article can be obtained at the link below.Intensive melt shearing was achieved using a twin-screw machine to condition an aluminium alloy prior to solidification. The results show that intensive melt shearing has a significant grain-refining effect. In addition, the intensive melt shearing reduces both the volume fraction and the size of porosity. It can reduce the density index from 10.50% to 2.87% and the average size of porosity in the samples solidified under partial vacuum from around 1 mm to 100 ÎŒm.Financial support was obtained from the EPSRC and the Technology Strategy Board
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Advances and challenges in commercializing radiative cooling
Radiative cooling (RC) dissipates terrestrial heat to outer space through the atmospheric window, without external energy input and production of environmental pollutants. More and more efforts have been devoted to this clean promising cooling technology; thus diverse radiative coolers have emerged. However, the performance, cost, and effectiveness of various radiative coolers are not exactly the same. In addition, the large-scale application of RC technology is impeded by the low energy density, uncontrollable cooling power, and limited sky-facing area. Here, we critically review the recent progress of RC technology, evaluate the cooling performance of various radiative coolers, and discuss the challenges and feasible solutions to commercialize RC technology. Furthermore, valuable insights are provided to make new breakthroughs in this field
Induced Growth of Asymmetric Nanocantilever Arrays on Polar Surfaces
©2003 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevLett.91.185502DOI: 10.1103/PhysRevLett.91.185502We report that the Zn-terminated ZnO (0001) polar surface is chemically active and the oxygenterminated (0001) polar surface is inert in the growth of nanocantilever arrays. Longer and wider "comblike" nanocantilever arrays are grown from the (0001)-Zn surface, which is suggested to be a self-catalyzed process due to the enrichment of Zn at the growth front. The chemically inactive
(0001)-O surface typically does not initiate any growth, but controlling experimental conditions could lead to the growth of shorter and narrower nanocantilevers from the intersections between (0001)-O with (0110) surfaces
Nuclear Three-body Force Effect on a Kaon Condensate in Neutron Star Matter
We explore the effects of a microscopic nuclear three-body force on the
threshold baryon density for kaon condensation in chemical equilibrium neutron
star matter and on the composition of the kaon condensed phase in the framework
of the Brueckner-Hartree-Fock approach. Our results show that the nuclear
three-body force affects strongly the high-density behavior of nuclear symmetry
energy and consequently reduces considerably the critical density for kaon
condensation provided that the proton strangeness content is not very large.
The dependence of the threshold density on the symmetry energy becomes weaker
as the proton strangeness content increases. The kaon condensed phase of
neutron star matter turns out to be proton-rich instead of neutron-rich. The
three-body force has an important influence on the composition of the kaon
condensed phase. Inclusion of the three-body force contribution in the nuclear
symmetry energy results in a significant reduction of the proton and kaon
fractions in the kaon condensed phase which is more proton-rich in the case of
no three-body force. Our results are compared to other theoretical predictions
by adopting different models for the nuclear symmetry energy. The possible
implications of our results for the neutron star structure are also briefly
discussed.Comment: 15 pages, 5 figure
Guided atom laser : a new tool for guided atom optics
We present a guided atom laser. A Bose-Einstein condensate (BEC) is created
in a crossed hybrid magnetic and an elongated optical trap, which acts as a
matterwave guide. Atoms are extracted from the BEC by radio frequency (rf)
outcoupling and then guided in the horizontal optical matterwave guide. This
method allows to control the acceleration of the beam and to achieve large de
Broglie wavelength. We also measure the longitudinal energy of the guided atom
laser using atom optical elements based on a blue light barrier
Globally Polarized Quark-gluon Plasma in Non-central A+A Collisions
Produced partons have large local relative orbital angular momentum along the
direction opposite to the reaction plane in the early stage of non-central
heavy-ion collisions. Parton scattering is shown to polarize quarks along the
same direction due to spin-orbital coupling. Such global quark polarization
will lead to many observable consequences, such as left-right asymmetry of
hadron spectra, global transverse polarization of thermal photons, dileptons
and hadrons. Hadrons from the decay of polarized resonances will have azimuthal
asymmetry similar to the elliptic flow. Global hyperon polarization is
predicted within different hadronization scenarios and can be easily tested.Comment: 4 pages in RevTex with 2 postscript figures, an erratum is added to
the final published versio
Hot Nuclear Matter Equation of State with a Three-body Force
The finite temperature Brueckner-Hartree-Fock approach is extended by
introducing a microscopic three-body force. In the framework of the extended
model, the equation of state of hot asymmetric nuclear matter and its isospin
dependence have been investigated. The critical temperature of liquid-gas phase
transition for symmetric nuclear matter has been calculated and compared with
other predictions. It turns out that the three-body force gives a repulsive
contribution to the equation of state which is stronger at higher density and
as a consequence reduces the critical temperature of liquid-gas phase
transition. The calculated energy per nucleon of hot asymmetric nuclear matter
is shown to satisfy a simple quadratic dependence on asymmetric parameter
as in the zero-temperature case. The symmetry energy and its density
dependence have been obtained and discussed. Our results show that the
three-body force affects strongly the high-density behavior of the symmetry
energy and makes the symmetry energy more sensitive to the variation of
temperature. The temperature dependence and the isospin dependence of other
physical quantities, such as the proton and neutron single particle potentials
and effective masses are also studied. Due to the additional repulsion produced
by the three-body force contribution, the proton and neutron single particle
potentials are correspondingly enhanced as similar to the zero-temperature
case.Comment: 16 pages, 8 figure
The effects of dog management on Echinococcus spp. prevalence in villages on the eastern Tibetan Plateau, China
Background The pastoral area of the eastern Tibetan plateau is a very important human echinococcosis endemic region. Domestic dogs are the main definitive host for the transmission of Echinococcus granulosus sensu lato (s.1.) and E. multilocularis to humans. To control the infection risks, a national-level canine echinococcosis prevention and control program has been implemented since 2015 in Shiqu County, Sichuan, China, The objective of this investigation was to evaluate its effect on Echinococcus spp. prevalence in dogs. Methods We surveyed 69 households with 84 owned dogs, for dog keeping information in the villages of Rizha and Eduoma. A total of 105 dog fecal samples, consisting of 75 from owned dogs and 30 unknown dog fecal samples were collected between 2015 and 2017 to determine Echinococcus spp. prevalence using copro-PCR. Eight variables based on household surveys were included into a logistic regression model for significantly relevant factors to canine echinococcosis prevalence in dogs. Results The overall Echinococcus spp. copro-DNA prevalence decreased significantly in dogs from 51.2% (2015) to 20.0% (2017) in Rizha, and insignificantly from 11.5% (2016) to 4.3% (2017) in Eduoma. Echinococcus multilocularis was the most prevalent species continually detected during the entire research period, while E. granulosus was rare and not detected in 2017. Echinococcus shiquicus prevalence was as high as E. multilocularis , although only detected in 2015 in Rizha. Unleashed dog feces were mainly collected in Rizha Village in 2015. Although 93.2% of owned dogs were leashed, and the monthly praziquantel dosing rate reached 97%, E. multilocularis infection could still be detected in 11.1% of owned dogs in 2017. Monthly deworming, leashing dogs 24h per day, and the avoidance of dogs feeding on livestock viscera are significant measures to prevent canine echinococcosis infection in owned dogs. Conclusion Carrying out a canine echinococcosis prevention and control program can significantly decrease the Echinococcus prevalence. The potential contact between leashed dogs and wild small mammals is still a risk to re-infect owned dogs. This study shows that the long term application of regular dog dosing in the vast remote echinococcosis endemic areas of west China is still challenging
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