Influence of nonuniform critical current density profile on magnetic field behavior of AC susceptibility in 2D Josephson Junction Arrays

Employing mutual-inductance measurements we study the magnetic field dependence of complex AC susceptibility of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays of unshunted Nb-AlO_x-Nb junctions. The observed behavior can be explained assuming single-plaquette approximation of the overdamped model with an inhomogeneous critical current distribution within a single junction.Comment: 4 pages (REVTEX), 6 figure

Study of magnetic and specific heat measurements at low temperatures in Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3

The magnetization at low temperatures for Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3 samples showed a rapid increase with decreasing temperatures, contrary to a La0.5Ca0.5MnO3 sample. Specific heat measurement at low temperatures showed a Schottky-like anomaly for the first two samples. However, there is not a straight forward correlation between the intrinsic magnetic moment of the Nd3+ ions and the Schottky-like anomaly.Comment: To be presented in the 1 Joint European Magnetic Symposia, Grenoble,France (2001). Also submitted to Journal of Magnetism and Magnetic Material

Exponential Critical State Model Applied To Ac Susceptibility Data For The Superconductor Yba2cu3o7-δ

We derive new expressions for the average magnetization loops, M(H), based on the exponential critical state model. The components χ′ and χ″ of the complex susceptibility are calculated and an algorithm to fit ac susceptibility data is discussed. This algorithm is employed to study the intergranular response χ′(Hm) and χ″(Hm) measured for two samples of YBa2Cu3O7-δ as a function of the ac field amplitude Hm. One sample is a porous sintered cylinder and the other is a very dense melt-textured bar. In both cases good fits of the calculated components χ′ and χ″ are obtained using an algorithm that involves two free parameters, the full penetration field. Hp, and the sample quality factor, p. An interesting result for the melt-textured sample is the observation of a step in χ′(Hm) curves at very low Hm. possibly associated with grain clustering. © 1996 American Institute of Physics.80633903395Goldfarb, R.B., Lelenthal, M., Thomson, C.A., (1991) Susceptibility of Superconductors and Others Spin Systems, p. 204. , edited by R. A. Hein, T. L. Francavilla, and D. H. Lieberger Plenum Press, New YorkCouach, M., Khoder, A.F., Monnier, F., (1989) Cryogenics, 25, p. 695Goldfarb, R.B., Clark, A.F., (1988) Cryogenics, 27, p. 475Chen, D.X., Goldfarb, R.B., (1988) J. Appl. Phys., 63, p. 980Larbalestier, D.C., Babcock, S.E., Cai, X., Daeumling, M., Hampshire, D.P., Kelly, T.F., Lavanier, L.A., Seuntjens, J., (1988) Physica C, 153-155, p. 1580Worthington, T.K., Gallagher, W.J., Dingerm, T.R., (1987) Phys. Rev. Lett., 59, p. 1160Tanaka, S., Itozaki, H., (1988) J. Appl. Phys., 27, pp. L622Dersch, H., Blatter, G., (1988) Phys. Rev. B, 38, p. 11391Moreira, F.M.A., Ortiz, W.A., De Lima, O.F., (1994) Physica C, 245, p. 3205Bean, C.P., (1962) Phys. Rev. Lett., 8, p. 250Bean, C.P., (1964) Rev. Mod. Phys., 36, p. 31London, H., (1963) Phys. Lett., 6, p. 162Kim, Y.B., Hempstead, C.F., Strnad, A.R., (1963) Phys. Rev., 129, p. 528Fietz, W.A., Beasley, M.R., Silcox, J., Webb, W.W., (1964) Phys. Rev., 136, pp. A335Xu, M., Shi, D., Fox, R.F., (1990) Phys. Rev. B, 42, p. 10773Chen, D.X., Goldfarb, R.B., (1989) J. Appl. Phys., 66, p. 2489Chen, D.X., Sanchez, A., Muñoz, J.S., (1990) J. Appl. Phy., 67, p. 3430Chen, J.L., Yang, T.J., (1994) Physica C, 224, p. 345Chen, D.X., Sanchez, A., (1991) J. Appl. Phys., 70, p. 5463Ishida, T., Goldfarb, R.B., (1990) Phys. Rev. B, 41, p. 8937Sanchez, A., (1994) Physica C, 225, p. 136Shi, D., Chen, J.G., Salem-Sugui Jr., S., Goretta, K.C., (1991) Physica C, 185-189, p. 2329Sanchez, A., Chen, D.X., (1991) Susceptibility of Superconductors and Others Spin Systems, p. 251. , edited by R. A. Hein, T. L. Francavilla, and D. H. Lieberger Plenum, New YorkGelfuso, V.C., Ortiz, W.A., unpublishe

Magnetic relaxation and magnetization field dependence measurements in La0.5Ca0.5MnO3

We reported a systematic change in the average magnetic relaxation rate, after the application and removal of a 5 T magnetic field, in a polycrystalline sample of La0.5Ca0.5MnO3. Magnetic relaxation measurements and magnetization versus field curves were taken from 10 K to 160 K. The long time behavior of the relaxation curves was approximately logarithmic in all cases. Keywords: Charge Ordering, Relaxation, Magnetic measurementsComment: 2 figures, accepted to be presented in the International Conference on Magnetism 2000 in Recife, also submitted to Journal of Magnetism and Magnetic Material

Probing pairing symmetry of Sm_{1.85}Ce_{0.15}CuO_4 via highly-sensitive voltage measurements: Evidence for strong impurity scattering

Using a highly-sensitive home-made mutual-inductance technique, temperature profiles of the magnetic penetration depth $\lambda (T)$ in the optimally-doped $Sm_{1.85}Ce_{0.15}CuO_4$ thin films have been extracted. The low-temperature behavior of $\lambda (T)$ is found to be best-fitted by linear $\Delta \lambda (T)/\lambda (0)= \ln(2)k_BT/\Delta_0$ and quadratic $\Delta \lambda (T)/\lambda (0)=\Gamma ^{-1/2}\Delta_0^{-3/2}T^2$ laws above and below $T=0.22T_C$, respectively, which clearly indicates the presence of d-wave pairing mechanism dominated by strong paramagnetic scattering at the lowest temperatures. The best fits produce $\Delta_0/k_BT_C=2.07$ and $\Gamma /T_C=0.25(T_C/\Delta_0)^3$ for the estimates of the nodal gap parameter and impurity scattering rate

Manifestation of vortex depinning transition in nonlinear current-voltage characteristics of polycrystalline superconductor Y_{1-x}Pr_{x}Ba_2Cu_3O_7

We present our recent results on the temperature dependence of current-voltage characteristics for polycrystalline Y_{1-x}Pr_{x}Ba_2Cu_3O_7 superconductors with x = 0.0, 0.1 and 0.3. The experimental results are found to be reasonably well fitted for all samples by a power like law. According to the theoretical interpretation of the obtained results, nonlinear deviation of our current-voltage characteristics curves from Ohmic behavior below Tc is attributed to the manifestation of dissipation processes related to the current induced depinning of Abrikosov vortices.Comment: Accepted for publication in PL

An Evolutionary Mono-Objective Approach for Solving the Menu Planning Problem

This work proposes an evolutionary approach to solve the Menu Planning Problem. Our work uses the Brazilian school context and our principal goal is to create menus that minimize the total cost of these menus. However, those menus must also satisfy requirements of the Brazilian government, such as: (i) student age group, (ii) school category, (iii) school duration time, (iv) school location, (v) variety of preparations, (vi) harmony of preparations, (vii) maximum amount to be paid for each meal and, (viii) lower and upper limits of macronutrients. The results demonstrate that the evolutionary approach is not only able to generate a set of inexpensive and healthy menus but also respect the required set of constraints. A constrained deterministic approach is performed to generate 5-day menu through a greedy-based function taking into account the normalized sum of all macronutrients and the monetary cost of the menu. A comparison between the 5-day menu obtained by the proposed approach and the constrained greedy-based approach menu is carried out. Despite the fact the obtained menu outperforms the greed-based menu taking into account the total cost, this difference is not so expressive. However, all macronutrients were outside the pre-defined range at least in one day of the week. The 5-day menu obtained by the proposed approach is evaluated by a nutritionist. The overall quality of the menu is outstanding and the time spent to generate it is 60 seconds

CardNutri:A Software of Weekly Menus Nutritional Elaboration for Scholar Feeding Applying Evolutionary Computation

This paper aims to present and evaluate a software that uses an evolutionary strategy to design weekly nutritional menus for School Feeding. The software ensures the nutritional needs of students and also minimizes the total cost of the menu. We based our nutritional needs on the Brazilian National School Feeding Programme (PNAE). This program takes into account: (i) the age of the student; (ii) some preparations issues as color, consistency and, variety; and also (iii) the maximum amount to be paid per meal. Our software generates, in less than five minutes, a set of menus, and the nutritionist can choose the menu that suits his/her best. We evaluate our algorithm using the Weighted-Sum approach, and our results show that the obtained 5-days menus using the proposed methodology not only comply with the restrictions imposed by the authorities but also produce inexpensive and healthy menus. We also appraise the software itself using an opinion pool among nine nutritionists. The professionals considered our software above expectations

TRIZ: creativity as exact science?

TRIZ is the acronym for the Russian phrase Theory of Inventive Problem Solving. Over two million patents have been examined, classified by level of inventiveness, and analyzed to look for principles of innovation. If these principles could be identified and codified, they could be taught to people to make the process of invention more predictable. In this paper we discuss some ideas to use this method in the preparation of Physics students.TRIZ é a sigla para as palavras russas que, em português, significam Teoria para a Resolução de Problemas Criativos. O estudo de mais de dois milhões de patentes no mundo tem permitido identificar princípios universais de invenção. Ensinando estes princípios e com a ajuda de técnicas psicológicas de geração de idéias, a metodologia TRIZ pretende aprofundar e dinamizar o processo criativo. Neste artigo apresentamos algumas sugestões de como utilizar o método TRIZ na formação de estudantes de Física.205209Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Magnetic And Superconducting Properties Of Ru Sr2 Gd1.5 Ce0.5 Cu2 O10-δ Samples: Dependence On The Oxygen Content And Aging Effects

The magnetic and superconducting properties of Ru Sr2 Gd1.5 Ce0.5 Cu2 O10-δ polycrystalline samples with different oxygen-doping levels are presented. A strong suppression of the superconducting temperature (Tc), as well as a reduction in the superconducting fraction, occurs as the oxygen content is reduced by annealing the samples in oxygen-deprived atmospheres. Drastic changes in the electrical resistivity are observed above Tc, possibly associated with oxygen removal, mainly from grain boundaries. However, the magnetic ordering is relatively less affected by the changes in oxygen content of the samples. The spin-glass transition is enhanced and shifted to higher temperatures with the reduction in oxygen content. This could be correlated with an increase in the spin disorder and frustration for the oxygen-depleted samples. Also, the same oxygen-vacancy-induced disorder could explain the reduction in the fraction of the sample showing antiferromagnetic order. We also report significant changes in the measured properties of the samples as a function of time. © 2005 The American Physical Society.7113Felner, I., Asaf, U., Levi, Y., Millo, O., (1997) Phys. Rev. B, 55, p. 3374. , PRBMDO 0163-1829 10.1103/PhysRevB.55.R3374Bernhard, C., Tallon, J.L., Niedermayer, Ch., Blasius, Th., Golnik, A., Brücher, E., Kremer, R.K., Ansaldo, E.J., (1999) Phys. Rev. B, 59, p. 14099. , PRBMDO. 0163-1829. 10.1103/PhysRevB.59.14099Awana, V.P.S., Karppinen, M., Yamauchi, H., (2003) Studies of High Tc Superconductors, 46, p. 77. , edited by A. V. Narlikar (Nova Science Publishers, New YorkMatvejeff, M., Awana, V.P.S., Jang, L.-Y., Liu, R.S., Yamauchi, H., Karppinen, M., (2003) Physica C, 392-396, p. 87. , PHYCE6 0921-4534Cardoso, C.A., Araujo-Moreira, F.M., Awana, V.P.S., Kishan, H., Takayama-Muromachi, E., De Lima, O.F., (2004) Physica C, 405, p. 212. , PHYCE6 0921-4534Cardoso, C.A., Araujo-Moreira, F.M., Awana, V.P.S., Takayama-Muromachi, E., De Lima, O.F., Yamauchi, H., Karppinen, M., (2003) Phys. Rev. B, 67, p. 020407. , PRBMDO 0163-1829 10.1103/PhysRevB.67.020407Shi, L., Li, G., Fan, X.J., Feng, S.J., Li, X.-G., (2003) Physica C, 399, p. 69. , PHYCE6 0921-4534Felner, I., Asaf, U., Ritter, F., Klamut, P.W., Dabrowski, B., (2001) Physica C, 364-365, p. 368. , PHYCE6 0921-4534Felner, I., Asaf, U., Galstyan, E., (2002) Phys. Rev. B, 66, p. 024503. , PRBMDO 0163-1829 10.1103/PhysRevB.66.024503Felner, I., Asaf, U., Levi, Y., Millo, O., (2000) Physica C, 334, p. 141. , PHYCE6 0921-4534 10.1016/S0921-4534(00)00250-1Awana, V.P.S., Ansari, M.A., Gupta, A., Saxena, R.B., Kishan, H., Buddhikot, D., Malik, S.K., (2004) Phys. Rev. B, 70, p. 104520. , PRBMDO 0163-1829 10.1103/PhysRevB.70.104520Yoshizawa, H., Mitsuda, S., Aruga, H., Ito, A., (1987) Phys. Rev. Lett., 59, p. 2364. , PRLTAO 0031-9007 10.1103/PhysRevLett.59.2364Binder, K., Young, A.P., (1986) Rev. Mod. Phys., 58, p. 801. , RMPHAT 0034-6861 10.1103/RevModPhys.58.801Mydosh, J.A., (1993) Spin Glasses An Experimental Introduction, , Taylor & Francis, LondonFelner, I., Galstyan, E., Herber, R.H., Nowik, I., (2004) Phys. Rev. B, 70, p. 094504. , PRBMDO 0163-1829 10.1103/PhysRevB.70.094504Shengelaya, A., Khasanov, R., Eschenko, D.G., Felner, I., Asaf, U., Savić, I.M., Keller, H., Müller, K.A., (2004) Phys. Rev. B, 69, p. 024517. , PRBMDO. 0163-1829. 10.1103/PhysRevB.69.024517Xue, Y.Y., Cao, D.H., Lorenz, B., Chu, C.W., (2002) Phys. Rev. B, 65, p. 020511. , PRBMDO 0163-1829 10.1103/PhysRevB.65.02051