A simple and effective method for the analytic description of important optical beams, when truncated by finite apertures

In this paper we present a simple and effective method, based on appropriate superpositions of Bessel-Gauss beams, which in the Fresnel regime is able to describe in analytic form the 3D evolution of important waves as Bessel beams, plane waves, gaussian beams, Bessel-Gauss beams, when truncated by finite apertures. One of the byproducts of our mathematical method is that one can get in few seconds, or minutes, high-precision results which normally require quite long times of numerical simulation. The method works in Electromagnetism (Optics, Microwaves,...), as well as in Acoustics. OCIS codes: (999.9999) Non-diffracting waves; (260.1960) Diffraction theory; (070.7545) Wave propagation; (070.0070) Fourier optics and signal processing; (200.0200) Optics in computing; (050.1120) Apertures; (070.1060) Acousto-optical signal processing; (280.0280) Remote sensing and sensors; (050.1755) Computational electromagnetic methods.Comment: Paper of 21 pages with 13 Figures. Source file in LaTe

Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at T=0KT=0 K

In this paper we analyze different contributions to the magnetoresistance of magnetic tunneling junctions at low voltages. A substantial fraction of the resistance drop with voltage can be ascribed to variations of the density of states and the barrier transmission with the bias. However, we found that the anomaly observed at zero bias and the magnetoresistance behavior at very small voltages, point to the contribution of inelastic magnon-assisted tunneling. The latter is described by a transfer parameter $T^{J}$, which is one or two orders of magnitude smaller than $T^{d}$, the direct transmission for elastic currents. Our theory is in excellent agreement with experimental data, yielding estimated values of $T^{J}$ which are of the order of $T^{d}$ / $T^{J}$ ~ 40.Comment: 13 pages, 4 figures (in postscript format). PACS numbers: 72.25.-b, 73.23.-b, 72.10.D

Is the SARS-COV2 mortality rate coefficient decreasing over time?

The outbreak of novel SARS-COV2, which started in China late 2019, rapidly gained the pandemic status. Mathematical models are required to have good accuracy in predicting the outbreak evolution, to allow governments and local authorities to take actions aiming at minimizing the damage for the public health. In the current context, there are many uncertainties concerning the parameters entering the SIR model. Here we analyze the evolution of the death rate coefficient in Italy, USA, and Brazil. Experimental data support the conclusion that it is decreasing over time

Magnetization, Spin Current, And Spin-transfer Torque From Su (2) Local Gauge Invariance Of The Nonrelativistic Pauli-schrödinger Theory

In this Brief Report, we consider local gauge symmetries of the nonrelativistic Pauli-Schrödinger theory. From the simplest free Lagrangian density for Pauli two-component spinors, we obtain the spin interaction with a magnetic field and define the spin-current vector without invoking relativistic theory. Applying U (1) ×SU (2) local gauge symmetry, and proceeding via the Noether's theorem, we are able to construct a covariant conserved spin-current density in a natural way. Our approach allow us to understand the main features of spin transport properties and suggests that SU (2) is a fundamental symmetry of nonrelativistic quantum mechanics. © 2008 The American Physical Society.781Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., Von Molnar, S., Roukes, M.L., Chtchelkanova, A.Y., Treger, D.M., (2001) Science, 294, p. 1488. , SCIEAS 0036-8075 10.1126/science.1065389Zutic, I., Fabian, J., Das Sarma, S., (2004) Rev. Mod. Phys., 76, p. 323. , RMPHAT 0034-6861 10.1103/RevModPhys.76.323Zhang, S., Levy, P.M., Marley, A.C., Parkin, S.S.P., (1997) Phys. Rev. Lett., 79, p. 3744. , See, for instance, PRLTAO 0031-9007 10.1103/PhysRevLett.79.3744Dartora, C.A., Cabrera, G.G., (2004) J. Appl. Phys., 95, p. 6058. , JAPIAU 0021-8979 10.1063/1.1703825Dartora, C.A., Cabrera, G.G., (2005) Phys. Rev. B, 72, p. 064456. , PRBMDO 0163-1829 10.1103/PhysRevB.72.064456Petit, S., Baraduc, C., Thirion, C., Ebels, U., Liu, Y., Li, M., Wang, P., Dieny, B., (2007) Phys. Rev. Lett., 98, p. 077203. , PRLTAO 0031-9007 10.1103/PhysRevLett.98.077203Berger, L., (1996) Phys. Rev. B, 54, p. 9353. , PRBMDO 0163-1829 10.1103/PhysRevB.54.9353Slonczewski, J., (1996) J. Magn. Magn. Mater., 159, p. 1. , JMMMDC 0304-8853 10.1016/0304-8853(96)00062-5Murakami, S., Nagaosa, N., Zhang, S.-C., (2003) Science, 301, p. 1348. , SCIEAS 0036-8075 10.1126/science.1087128Murakami, S., Nagaosa, N., Zhang, S.-C., (2004) Phys. Rev. B, 69, p. 235206. , PRBMDO 0163-1829 10.1103/PhysRevB.69.235206Jiang, Z.F., Li, R.D., Zhang, S.-C., Liu, W.M., (2005) Phys. Rev. B, 72, p. 045201. , PRBMDO 0163-1829 10.1103/PhysRevB.72.045201Sinova, J., Culcer, D., Niu, Q., Sinitsyn, N.A., Jungwirth, T., MacDonald, A.H., (2004) Phys. Rev. Lett., 92, p. 126603. , PRLTAO 0031-9007 10.1103/PhysRevLett.92.126603Shen, S.Q., Ma, M., Xie, X.C., Zhang, F.C., (2004) Phys. Rev. Lett., 92, p. 256603. , PRLTAO 0031-9007 10.1103/PhysRevLett.92.256603Barnes, S.E., Maekawa, S., (2007) Phys. Rev. Lett., 98, p. 246601. , PRLTAO 0031-9007 10.1103/PhysRevLett.98.246601Hirsch, J.E., (1990) Phys. Rev. B, 42, p. 4774. , PRBMDO 0163-1829 10.1103/PhysRevB.42.4774Meier, F., Loss, D., (2003) Phys. Rev. Lett., 90, p. 167204. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.167204Schutz, F., Kollar, M., Kopietz, P., (2003) Phys. Rev. Lett., 91, p. 017205. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.017205Sun, Q.-F., Guo, H., Wang, J., (2004) Phys. Rev. B, 69, p. 054409. , PRBMDO 0163-1829 10.1103/PhysRevB.69.054409Vernes, A., Gyorffy, B.L., Weinberger, P., (2007) Phys. Rev. B, 76, p. 012408. , PRBMDO 0163-1829 10.1103/PhysRevB.76.012408Sakurai, J.J., (1994) Advanced Quantum Mechanics, , Revised ed. (Addison-Wesley, Reading, MABjorken, J.D., Drell, S.D., (1964) Relativistic Quantum Mechanics, , McGraw-Hill, New YorkGreiner, W., Reinhardt, J., (2002) Quantum Electrodynamics, , 3rd ed. (Springer-Verlag, BerlinWang, Y., Xia, K., Su, Z.B., Ma, Z., (2006) Phys. Rev. Lett., 96, p. 066601. , PRLTAO 0031-9007 10.1103/PhysRevLett.96.066601Sun, Q.F., Xie, X.C., (2005) Phys. Rev. B, 72, p. 245305. , PRBMDO 0163-1829 10.1103/PhysRevB.72.245305Fröhlich, J., Studer, U.M., (1992) Commun. Math. Phys., 148, p. 553. , CMPHAY 0010-3616 10.1007/BF02096549Fröhlich, J., Studer, U.M., (1992) Int. J. Mod. Phys. B, 6, p. 2201. , IJPBEV 0217-9792 10.1142/S0217979292001092Fröhlich, J., Studer, U.M., (1993) Rev. Mod. Phys., 65, p. 733. , RMPHAT 0034-6861 10.1103/RevModPhys.65.733Yang, C.N., Mills, R.L., (1954) Phys. Rev., 96, p. 191. , PHRVAO 0031-899X 10.1103/PhysRev.96.191Weinberg, S., (1996) The Quantum Teory of Fields, 1-2. , Cambridge University Press, CambridgeRyder, L.H., (1996) Quantum Field Theory, , 2nd ed. (Cambridge University Press, CambridgeLove, P.J., Boghosian, B.M., (2004) Physica a, 332, p. 47. , PHYADX 0378-4371 10.1016/j.physa.2003.09.055Wiese, U.-J., (2005) Nucl. Phys. B, Proc. Suppl., 141, p. 143. , 0920-5632Watts, S.M., Grollier, J., Van Der Wal, C.H., Van Wees, B.J., (2006) Phys. Rev. Lett., 96, p. 077201. , PRLTAO 0031-9007 10.1103/PhysRevLett.96.07720

Caracterização da disseminação da epidemia de COVID-19 e previsões para Curitiba-BR utilizando modelo SIR modificado

The epidemic outbreak of the new coronavirus has fastly reached a pandemic status. That has awaken interest from the academy on mathematical models that alow for contagion curves previsions. A SIR model with modied solutions has been presented and numerical solutions of R0 and τ for data corrected including probable non-notied cases has been reached. Previsions have been made to support government decision-makers on strategies to ght the pandemic. Main topics discussed were state-wide inward dissemination and probable second waves of dissemination in large urban areas taking Curitiba-PR, Manaus-Am and the state of Parana as study cases. Also, a correlation between susceptibles urban density and dissemination parameters R0 and τ are shown to be precise do a 10% error margin. That was quite instrumental on previewing second wave parameters. Were considered data available up to may, 8, 2020.O surto epidêmico do novo coronavírus, que rapidamente alcançou o status de pandemia, despertou o interesse por modelos matemáticos que permitam realizar previsões de desenvolvimento das curvas de contágio. Um modelo SIR com soluções modificadas foi apresentado e soluções numéricas dos parâmetros de disseminação R0 e tempo de recuperação baseadas em dados corrigidos com prováveis não-notificados foram alcançadas. Previsões foram feitas para amparar as autoridades públicas na adoção de estratégias para o combate a pandemia quanto a interiorização da disseminação e análise de prováveis segundas ondas em centro urbanos tomando Curitiba-PR, Manaus-Am e o estado do Paraná como casos de estudo. Uma correlação entre densidade urbana de susceptíveis e os parâmetros de disseminação R0 e tempo de recuperação foram levantadas com margem de erro de 10% o que permitiu ótima previsão dos parâmetros de segundas ondas. Foram considerandos os dados disponíveis para o Brasil até 08 de maio de 2020

Wess–Zumino supersymmetric phase and superconductivity in graphene

AbstractSupersymmetry is expected to exist in nature at high energies, but must be spontaneously broken at ordinary energy scales. The required energy scale in elementary particle physics is currently inaccessible, but condensed matter could furnish low energy realizations of supersymmetry. In graphene, electrons behave as ‘relativistic’ massless fermions in 1+2 dimensions. Here we propose phenomenologically, assuming that some microscopic parameters can be fine-tuned in graphene, the existence of a supersymmetric Wess–Zumino phase. The supersymmetry breaking leads to a superconductor phase, described by a relativistic Ginzburg–Landau phenomenology