373 research outputs found
Super-gauge Field in de Sitter Universe
The Gupta-Bleuler triplet for vector-spinor gauge field is presented in de
Sitter ambient space formalism. The invariant space of field equation solutions
is obtained with respect to an indecomposable representation of the de Sitter
group. By using the general solution of the massless spin- field
equation, the vector-spinor quantum field operator and its corresponding Fock
space is constructed. The quantum field operator can be written in terms of the
vector-spinor polarization states and a quantum conformally coupled massless
scalar field, which is constructed on Bunch-Davies vacuum state. The two-point
function is also presented, which is de Sitter covariant and analytic.Comment: 21 page
Friction-stir welding of ultrafine grained austenitic 304L stainless steel produced by martensitic thermomechanical processing
An ultrafine grained 304L austenitic stainless steel was produced by martensitic thermomechanical processing and joined by applying Friction Stir Welding (FSW). The thermomechanical processing comprised a cold roll procedure up to 80% reduction followed by annealing. After FSW, different grain structures in different regions of the weld nugget were observed due to the asymmetry in the heat generation during the welding process. Grain growth was found to be the most predominant phenomena in the region just ahead of the rotating tool during the thermal cycle of FSW. A banded structure was observed in the advancing side of the weld nugget. TEM observations revealed that nanometric sigma phase precipitates were present both in the grain boundaries and inside the grains of this region. Shear textures were clearly identified in the weld center. The lack of rotated cube texture shows that the discontinuous dynamic recrystallization (DDRX) is not active in the final microstructure. Increasing the welding speed can reduce the final grain size of the weld nugget leading to higher hardness. Hardness is found to increase in the weld and this is not just a grain refinement effect, but also due to the presence of sub-boundaries and a high density of dislocations.postprin
The role of martensitic transformation on bimodal grain structure in ultrafine grained AISI 304L stainless steel
In the present study, metastable AISI 304L austenitic stainless steel samples were subjected to different cold rolling reductions from 70% to 93%, followed by annealing at 700 °C for 300 min to form ultrafine grained (UFG) austenite with different grain structures. Transmission electron microscopy (TEM) and nanoindentation were used to characterize the martensitic transformation, in order to relate it to the bimodal distribution of the austenite grain size after subsequent annealing. The results showed that the martensite morphology changed from lath type in the 60% rolled sample to a mixture of lath and dislocation-cell types in the higher rolling reductions. Calculation of the Gibbs free energy change during the reversion treatment showed that the reversion mechanism is shear controlled at the annealing temperature and so the morphology of the reverted austenite is completely dependent on the morphology of the deformation induced martensite. It was found that the austenite had a bimodal grain size distribution in the 80% rolled and annealed state and this is related to the existence of different types of martensite. Increasing the rolling reduction to 93% followed by annealing caused changing of the grain structure to a monomodal like structure, which was mostly covered with small grains of around 300 nm. The existence of bimodal austenite grain size in the 80% rolled and annealed 304L stainless steel led to the improvement of ductility while maintaining a high tensile strength in comparison with the 93% rolled and annealed sample.postprin
Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2Cu4O8
In the quasi-one-dimensional cuprate PrBaCuO, the Pr cations
order antiferromagnetically at 17 K in zero field. Through a combination of
magnetic susceptibility, torque magnetometry, specific heat and interchain
transport measurements, the anisotropic temperature-magnetic field phase
diagram associated with this ordering has been mapped out. A low-temperature
spin-flop transition in the Pr sub-lattice is found to occur at the same
magnetic field strength and orientation as a dimensional crossover in the
ground state of the metallic CuO chains. This coincidence suggests that the
spin reorientation is driven by a change in the anisotropic
Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding
change in effective dimensionality of the conduction electrons.Comment: 8 pages, 8 figure
Possible co-existence of local itinerancy and global localization in a quasi-one-dimensional conductor
In the chain compound PrBaCuO localization appears simultaneously
with a dimensional crossover in the electronic ground state when the scattering
rate in the chains exceeds the hopping rate between the chains. Here we report
the discovery of a large, transverse magnetoresistance in PrBaCuO
in the localized regime. This result suggests a novel form of localization
whereby electrons retain their metallic (quasi-one-dimensional) character over
a microscopic length scale despite the fact that macroscopically, they exhibit
localized (one-dimensional) behavior.Comment: 4 pages, 4 Figure
Irradiation-induced confinement in a quasi-one-dimensional metal
The anisotropic resistivity of PrBaCuO has been measured as a
function of electron irradiation fluence. Localization effects are observed for
extremely small amounts of disorder corresponding to electron mean-free-paths
of order 100 unit cells. Estimates of the localization corrections suggest that
this anomalous localization threshold heralds a crossover to a ground state
with pronounced one-dimensional character in which conduction electrons become
confined to a small cluster of chains.Comment: 4 pages, 4 figure
Fragile three-dimensionality in the quasi-one-dimensional cuprate PrBa_2Cu_4O_8
In this article we report on the experimental realization of dimensional
crossover phenomena in the chain compound PrBaCuO using
temperature, high magnetic fields and disorder as independent tuning
parameters. In purer crystals of PrBaCuO, a highly anisotropic
three-dimensional Fermi-liquid state develops at low temperatures. This
metallic state is extremely susceptible to disorder however and localization
rapidly sets in. We show, through quantitative comparison of the relevant
energy scales, that this metal/insulator crossover occurs precisely when the
scattering rate within the chain exceeds the interchain hopping rate(s), i.e.
once carriers become confined to a single conducting element.Comment: 12 pages, 5 figures, published at
http://www.iop.org/EJ/article/1367-2630/8/9/172/njp6_9_172.htm
Anxiety as a consequence of modern dietary pattern in adults in Tehran-Iran
Food intake patterns in relation to mental health have already been revealed. To investigate the relationship between processed food consumption behavior and anxiety disorder, a cross sectional study was conducted. Overall, 1782 young adults aged 18-35 years were randomly selected using cluster sampling method from 22 districts of Tehran Iran in 2011. Diet assessment was done using a 24 hour recall questionnaire in two times with a week interval. Anxiety level was determined using the validated Speilburger test (Persian version). A proportional odds regression model was used to assess the effect of processed food consumption on anxiety variables. A significant statistical difference was found between men and women in terms of processed food consumption (p<0.001). Adjusting for age, total calorie intake, gender, body mass index, socioeconomic status, and history of sedative drug consumption as well as mental health disorders, the proportional odds regression model showed a significant relationship between increased consumption of processed foods and anxiety (OR = 4.73, 95 CI: 2.89-12.54 for state and OR = 4.91, 95 CI: 2.88-13.99 for trait). Identification, modification and adjusting incorrect food patterns in the community could be considered as valuable steps to turn down nutritional-based health difficulties. (C) 2012 Elsevier Ltd. All rights reserved
Influence of Ca²⁺ ions on the habit of KDP crystals
A few KDP (KH₂PO₄) and KDP:Ca²⁺ (CaCl₂) single crystals were grown
based on the temperature reduction method. Investigations show that the presence of
bivalent ions like Ca²⁺ could be a cause of retarded growth rate and induced crystalline
lattice defects. Here the pure KDP crystals are compared with KDP:CaCl₂. Crystals of
both types were also studied in aspect of other structural and optical properties
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