625 research outputs found
Shot noise in diffusive ferromagnetic metals
We show that shot noise in a diffusive ferromagnetic wire connected by tunnel
contacts to two ferromagnetic electrodes can probe the intrinsic density of
states and the extrinsic impurity scattering spin-polarization contributions in
the polarization of the wire conductivity. The effect is more pronounced when
the electrodes are perfectly polarized in opposite directions. While in this
case the shot noise has a weak dependence on the impurity scattering
polarization, it is strongly affected by the polarization of the density of
states. For a finite spin-flip scattering rate the shot noise increases well
above the normal state value and can reach the full Poissonian value when the
density of states tends to be perfectly polarized. For the parallel
configuration we find that the shot noise depends on the relative sign of the
intrinsic and the extrinsic polarizations.Comment: 4 pages, 3 figure
Taguchi parametric study on the radial and tangential cutting forces in Dry High Speed Machining (DHSM)
In this paper, L8 Taguchi array is applied to find the most important parameters effects on the radial and tangential cutting forces of a Ti–6Al-4V ELI titanium alloy in dry high speed machining (DHSM). The experiments are performed in four cutting speeds of 150, 200, 250, and 300 m/min and two feed rates of 0.03 and 0.06 mm/rev. Also, two cutting tools in types of XOMX090308TR-ME06 of uncoated (H25) and TiAlN+TiN coated (F40M) are used. Results confirm that to minimize the resultant cutting force and radial cutting force, utilizing the lower feed rate and higher cutting speeds were considered as the best levels of factors to reach to its goal
The study of nano technology utilization in upgrading the quality of construction industry with fire-engineering approach
Today, the first requirement for increasing quality and strength in construction industry is utilization of appropriate and high quality materials so that usage of these materials, in addition to reducing maintenance costs and also upgrading the structure's longevity, in engineering respect through change on weight reduction and increasing strength in used materials, can cause general strength of the structure against earthquakes and probable runs due to natural disasters. This requirement is very significant in passive defense scope and this task will be considered in used material in main structure of a building and also in used materials in its frontage and in terminology elaborate work. Given that one of the effects of fire on the building part and parcel of passive defense, so, this look from the perspective of fire engineering is also of particular significance. Wide studies have been performed in this ground and various factories are trying to increase their produced materials quality in today competitive world with utilization of various technologies. One of technologies considered today is Nano technology which in fact by changing the molecular structure of a material causes creating special properties in it and utilization of these properties can answer needs of producers and users for increasing quality, longevity, strength and weight reduction. In this study, it is tried to introduce materials produced by Nano technology which have special properties like resistance against fire, settlement and weight reduction and increasing resistance in tolerance of strike and injected loads to the structure in defensive point of view in civil engineering scope. Keywords: Nano technology; passive defense; building material
Biosuper as a phosphate fertilizer in a calcareous soil with low available phosphorus
Laboratory assays were conducted to produce phosphorus (P) biofertilizers from rock phosphate (RP), applying sulphur at different rates of 10, 15 and 20% and inoculated with Thiobacillus. A greenhouse experiment was carried out to evaluate the effect of the biofertilizers in a calcareous soil with low available P from the Qazvin plain of “Qazvin State”, grown with corn (Zea mays L.). The treatments were: rock phosphate (RP), biofertilizers produced in laboratory with sulphur and Thiobacillus (Biof1, Biof2 and Biof3), rock phosphate with sulphur (10, 15 and 20%) without Thiobacillus (Nbiof1, Nbiof2 and Nbiof3), Triple Super Phosphate (TSP) and a control without phosphorus. In this experiment, shoot dry matter, total P, Fe and Zn in shoots, and also soil available P, Fe and Zn were determined. Higher rates of measured parameters were obtained from biofertilizers with sulphur and Thiobacillus (Biof) and in Triple Super Phosphate (TSP). Biofertilizers with sulphur and Thiobacillus (Biof) and TSP increased plant parameters significantly compared with control or rock phosphate
Counting flags in triangle-free digraphs
Motivated by the Caccetta-Haggkvist Conjecture, we prove that every digraph
on n vertices with minimum outdegree 0.3465n contains an oriented triangle.
This improves the bound of 0.3532n of Hamburger, Haxell and Kostochka. The main
new tool we use in our proof is the theory of flag algebras developed recently
by Razborov.Comment: 19 pages, 7 figures; this is the final version to appear in
Combinatoric
Integrality gaps of semidefinite programs for Vertex Cover and relations to ell embeddability of negative type metrics
We study various SDP formulations for Vertex Cover by adding different constraints to the standard formulation. We rule out approximations better than
even when we add the so-called pentagonal inequality constraints to the standard SDP formulation, and thus almost meet the
best upper bound known due to Karakostas, of
. We further show the surprising fact that by strengthening the SDP with the (intractable) requirement that the metric interpretation
of the solution embeds into ℓ1 with no distortion, we get an exact relaxation (integrality gap is 1), and on the other hand if the solution is arbitrarily
close to being ℓ1 embeddable, the integrality gap is 2 − o(1). Finally, inspired by the above findings, we use ideas from the integrality gap construction of Charikar to provide a
family of simple examples for negative type metrics that cannot be embedded into ℓ1 with distortion better than 8/7 − ε. To this end we prove a new isoperimetric inequality for the hypercube.
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Conductance of bilayer graphene in the presence of a magnetic field: Effects of disorder
We investigate the electronic transport properties of unbiased and biased
bilayer graphene nanoribbon in n-p and n-n junctions subject to a perpendicular
magnetic field. Using the non-equilibrium Green's function method and the
Landauer-B\"{u}ttiker formalism, the conductance is studied for the cases of
clean, on-site, and edge disordered bilayer graphene. We show that the lowest
Hall plateau remains unchanged in the presence of disorder, whereas asymmetry
destroys both the plateaus and conductance quantization. In addition, we show
that disorder induces an enhancement of the conductance in the n-p region in
the presence of magnetic fields. Finally, we show that the equilibration of
quantum Hall edge states between distinctively doped regions causes Hall
plateaus to appear in the regime of complete mode mixing.Comment: 8 pages, 7 figures. Accepted to Phys. Rev.
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