Isotropic Loop Quantum Cosmology with Matter

A free massless scalar field is coupled to homogeneous and isotropic loop quantum cosmology. The coupled model is investigated in the vicinity of the classical singularity, where discreteness is essential and where the quantum model is non-singular, as well as in the regime of large volumes, where it displays the expected semiclassical features. The particular matter content (massless, free scalar) is chosen to illustrate how the discrete structure regulates pathological behavior caused by kinetic terms of matter Hamiltonians (which in standard quantum cosmology lead to wave functions with an infinite number of oscillations near the classical singularity). Due to this modification of the small volume behavior the dynamical initial conditions of loop quantum cosmology are seen to provide a meaningful generalization of DeWitt's initial condition.Comment: 18 pages, 4 figure

On the Dynamics of Bianchi IX cosmological models

A cosmological description of the universe is proposed in the context of Hamiltonian formulation of a Bianchi IX cosmology minimally coupled to a massless scalar field. The classical and quantum results are studied with special attention to the case of closed Friedmann-Robertson-Walker model.Comment: 11 pages, 1 figur

Vortex Dynamics Differences Due To Twin-boundary Pinning Anisotropy In Yba 2cu 3o X At Low Temperatures For H∥ab Planes

We measured the magnetization M of a twin-aligned single crystal of YBa 2Cu 3O x (YBaCuO), with T c =91 K, as a function of temperature T and magnetic field H, with H applied along the ab planes. Isothermal M-vs-H and M-vs-time curves were obtained with H applied parallel (∥) and perpendicular (⊥) to the twin boundary (TB) direction. M-vs-H curves exhibited two minima below 38 K, which resembled similar curves that have been obtained in YBaCuO for H∥c axis. Above 12 K, the field positions of the minima for H∥TB and H⊥TB were quite similar. Below 12 K, the position of the second minimum H min occurred at a higher field value with H∥TB. Below 6 K, only one minimum appeared for both field directions. At low temperatures, these minima in the M-vs-H curves produced maxima in the critical current. It was determined that vortex lines were expelled more easily for H∥TB than for H⊥TB and, therefore, below a certain field value, that J c(H⊥TB) was larger than J c(H∥TB). At T<12 K with H∥TB, the relaxation rate for flux lines leaving the crystal was found to be different from that for flux entering the crystal. We also observed flux jumps at low temperatures, with their sizes depending on the orientation of magnetic field with respect to the TB's. © 2005 The American Physical Society.712Sarikaya, M., Stern, E.A., (1988) Phys. Rev. B, 37, p. 9373Van Bakel, G.P.E.M., Hof, P.A., Van Engelen, J.P.M., Bronsveld, P.M., De Hosson, J.Th.M., (1990) Phys. Rev. B, 41, p. 9502Liu, J.Z., Jia, Y.X., Shelton, R.N., Fluss, M.J., (1991) Phys. Rev. Lett., 66, p. 1354Swartzendruber, L.J., Roitburd, A., Kaiser, D.L., Gayle, F.W., Bennett, L.H., (1990) Phys. Rev. Lett., 64, p. 483Kwok, W.K., Welp, U., Crabtree, G.W., Vandervoort, K.G., Hulscher, R., Liu, J.Z., (1990) Phys. Rev. Lett., 64, p. 966Duran, C.A., Gammel, P.L., Wolfe, R., Fratello, V.J., Bishop, D.J., Rice, J.P., Ginsberg, D.M., (1992) Nature (London), 357, p. 474Gyorgy, E.M., Van Dover, R.B., Schneemeyer, L.F., White, A.E., O'Bryan, H.M., Felder, R.J., Waszczak, J.V., Rhodes, W.W., (1990) Appl. Phys. Lett., 56, p. 2465Oussena, M., De Groot, P.A.J., Porter, S.J., Gagnon, R., Taillefer, L., (1995) Phys. Rev. B, 51, p. 1389Oussena, M., De Groot, P.A.J., Deligiannis, K., Volkozub, A.V., Gagnon, R., Taillefer, L., (1996) Phys. Rev. Lett., 76, p. 2559Vlasko-Vlasov, V.K., Dorosinskii, L.A., Polyanskii, A.A., Nikitenko, V.I., Welp, U., Veal, B.W., Crabtree, G.W., (1994) Phys. Rev. Lett., 72, p. 3246Wijngaarden, R.J., Griessen, R., Fendrich, J., Kwok, W.K., (1997) Phys. Rev. B, 55, p. 3268Duran, C.A., Gammel, P.L., Bishop, D.J., Rice, J.P., Ginsberg, D.M., (1995) Phys. Rev. Lett., 74, p. 3712Pastoriza, H., Candia, S., Nieva, G., (1999) Phys. Rev. Lett., 83, p. 1026Herbsommer, J.A., Nieva, G., Luzuriaga, J., (2000) Phys. Rev. B, 62, p. 3534Jorge, G.A., Rodriguez, E., (2000) Phys. Rev. B, 61, p. 103Bondareko, A.V., (2001) Low Temp. Phys., 27, p. 339(2001) Phys. Rev. B, 27, p. 201Esquinazi, P., Setzer, A., Fuchs, D., Kopelevich, Y., Zeldov, E., Assmann, C., (1999) Phys. Rev. B, 60, p. 12454Mints, R.G., Brandt, E.H., (1996) Phys. Rev. B, 54, p. 12421Muller, K.-H., Andrikidis, C., (1994) Phys. Rev. B, 49, p. 1294Guillot, M., Potel, M., Gougeon, P., Noel, H., Levet, J.C., Chouteau, G., Tholence, J.L., (1988) Phys. Lett. A, 127, p. 363Salem-Sugui Jr., S., Alvarenga, A.D., Friesen, M., Veal, B., Paulikas, P., (2001) Phys. Rev. B, 63, p. 216502Bean, C.P., (1962) Phys. Rev. Lett., 8, p. 250Tinkham, M., (1996) Introduction to Superconductivity, 2nd Ed., , McGraw-Hill, New YorkDe Andrade, M.C., Dilley, N.R., Ruess, F., Maple, M.B., (1998) Phys. Rev. B, 57, pp. R708Abulafia, Y., Shaulov, A., Wolfus, Y., Prozorov, R., Burlachkov, L., Yeshurun, Y., Majer, D., Vinokur, V.M., (1995) Phys. Rev. Lett., 75, p. 2404Maley, M.P., Willis, J.O., Lessure, H., McHenry, M.E., (1990) Phys. Rev. B, 42, p. 2639Shi, D., Salem-Sugui Jr., S., (1991) Phys. Rev. B, 44, p. 7647Beasley, M.R., Labash, R., Weeb, W.W., (1969) Phys. Rev., 181, p. 682Burlachkov, L., (1993) Phys. Rev. B, 47, p. 8056Alvarenga, A.D., Salem-Sugui Jr., S., (1994) Physica C, 235, p. 2811Junod, A., (1989) Physica C, 162-164, p. 482Triscone, G., (1990) Physica C, 168, p. 40Genoud, J.Y., (1991) Physica C, 177, p. 31

Dimensionless cosmology

Although it is well known that any consideration of the variations of fundamental constants should be restricted to their dimensionless combinations, the literature on variations of the gravitational constant $G$ is entirely dimensionful. To illustrate applications of this to cosmology, we explicitly give a dimensionless version of the parameters of the standard cosmological model, and describe the physics of Big Bang Neucleosynthesis and recombination in a dimensionless manner. The issue that appears to have been missed in many studies is that in cosmology the strength of gravity is bound up in the cosmological equations, and the epoch at which we live is a crucial part of the model. We argue that it is useful to consider the hypothetical situation of communicating with another civilization (with entirely different units), comparing only dimensionless constants, in order to decide if we live in a Universe governed by precisely the same physical laws. In this thought experiment, we would also have to compare epochs, which can be defined by giving the value of any {\it one} of the evolving cosmological parameters. By setting things up carefully in this way one can avoid inconsistent results when considering variable constants, caused by effectively fixing more than one parameter today. We show examples of this effect by considering microwave background anisotropies, being careful to maintain dimensionlessness throughout. We present Fisher matrix calculations to estimate how well the fine structure constants for electromagnetism and gravity can be determined with future microwave background experiments. We highlight how one can be misled by simply adding $G$ to the usual cosmological parameter set

Dynamics Of An Articulated Towboat

It is considerable the number of research around the subject of motorization of conventional manual wheechairs, however the found models don't take care of the real necessities of the wheelchair users. In the manufacture the necessity of an independent vehicle for the load transport exists. With the increasing necessity in Brazil to develop the knowledge in the area of independent vehicles and not being still available a towboat of tests adjusted to approach such problems. The articulated towboat is an intelligent independent vehicle to tow loads. The users of conventional manual wheelchairs will go to use this vehicle when to need motorization, that is in ascent cases, descending of ramps, or long distances. This vehicle possesss practical applications that they can assist systems of support to the rehabilitation of physical and motor deficiencies and also systems automatized of manufacture. The purpose of this paper is to develop some important contribution in the area of independent vehicles in the aid for the people with special needs. Copyright © 2004 Society of Automotive Engineers, Inc.Alvarenga, F.B., Dedini, F.G., Analysis of the possibilities of the Conventional Wheelchairs Motorization (2001) Proceedings of COBEM 2001- XVI Brazilian Congress on Mechanical Engineering, , Uberlândia -MG, Brasil, Nov. 26-30Alvarenga, F.B., (2002) Desenvolvimento de Sistemas de Motorização Alternativa Para Cadeiras de Rodas Convencionais, p. 192. , Máster Thesis Faculty of Mechanical Engineering, Unicamp, Campinas,SP, BrazilHaubenwallner, G., (1988) Drive Motor, Which is Supplied by an Energy Source, for Disk-Shaped or Wheel-Shaped Members with a Control Mechanism, , US 4,773,495, September 27Dudley, F.E.A., (1975) Motorized Wheel, , US 3,908,776, September 30Brudermann, (1984) Chassis for Invalid Wheelchairs, , US 4,436,320, March 13Jones, G.C., (1990) Kit for Converting a Hand-Powered Wheelchair to an Electric Motor-Power Wheelchair, , US 4,961,473, October 9Iii, G., (1992) Wheelchair Drive Assembly, , US 5,161,630, November 10Alvarenga, F.B., Dedini, F.G., Development of systems of alternative motorization for conventional wheelchairs SAE Technical Paper Series, 2003-01-3563-E, pp. 1-10. , Danvers, MA(1985) Associação Brasileira de Normas Técnicas, NBR 9050, , Adequação das edificações e do mobiliário urbano à pessoa deficiente. Rio de JaneiroJarosz, E., Determination of the workspace of wheelchair users (1996) International Journal of Industrial Ergonomics, 17 (2), pp. 123-133. , DOI 10.1016/0169-8141(95)00044-5Fisette, P., Ferriere, L., Raucent, B., Vaneghem, B., Multibody approach for modelling universal wheels of mobile robots (2000) Mechanism and Machine Theory, 35 (3), pp. 329-351. , DOI 10.1016/S0094-114X(99)00017-8Campion, G., Bastin, G., D'Andrea-Novel, B., Structural properties and classification of kinematic and dynamic models of wheeled mobile robots (1996) IEEE Transactions on Robotics and Automation, 12 (1), pp. 47-62. , PII S1042296X96004976Sasi, S., High mobility platform (2002) Technical Report of Department of Mechanical Engineering, , Adoo

Development Of Systems Of Alternative Motorization For Conventional Wheelchairs

In this work the main objective is the development of systems for motorization of conventional wheelchairs, and the great mass of wheelchairs now available in Brazil of the simplest type than they don't allow the pure and simple conversion for motorization. In this aspect the problem comes as a challenge because the great variety of models and types of wheelchairs and the lack of a rigorous normalization impose the use of technologies of search of solutions and the application of methodology knowledge and systematic of project. In this way, firstly a study will be accomplished on the object wheelchair, containing: historical, origin, types and characteristics. The following step will be the search of the possibilities of motorizing conventional wheelchairs, limitations and applications. Eventually, after the definition of a basic type to serve as model, the systematic of project will be applied for development of a product and the execution of a prototype in scale or functional for evaluation of possibilities. In the development of the product a methodology will be used and systematic of project. The objective of this work is study the possibilities to motorize a conventional wheelchair. This article analyses the possibilities of motorization. Copyright © 2003 Society of Automotive Engineers, Inc.Cooper, R.A., Wheelchairs and related technology for the millennium (2000) Journal of Rehabilitation Research and Development, 37 (3)Weelman, P., Design of a wheelchair with legs for people with motor disabilities (1995) IEEE Trans. Rehabilitation Engineering, 3 (4)Becker, M., (2000) Suspension System for An All-terrain Wheelchair, pp. 462-464. , ResnaBecker, M., (2000), p. 136. , Aplicação de Tecnologias Assistivas e Técnicas de Controle em Cadeiras de Rodas Inteligentes". Campinas: Faculdade de Engenharia Mecânica, Universidade Estadual de Campinas, Tese (Doutorado)Abledata Fact Sheet (1994) Manual Wheelchair, (23). , www.abledata.com/text2/manwhch.htm, July, ""Alvarenga, F.B., Dedini, F.G., Analysis of the possibilities of the Conventional Wheelchairs Motorization (2001) Proceedings of COBEM 2001- XVI Brazilian Congress on Mechanical Engineering, , Uberlândia-MG, Brasil, Nov. 26-30Abledata Fact Sheet (1994) Powerd Wheelchair, (24). , www.abledata.com/text2/powwch.htm, July, ""Alvarenga, F.B., (2002), p. 192. , Desenvolvimento de Sistemas de Motorização Alternativa para Cadeiras de Rodas Convencionais", Dissertação de Mestrado, Unicamp, BrazilKirby, R.L., Wheelchair stability: Important, measurable and modifiable (1996) Technology and Disability, 5 (1), pp. 75-80Zwicky, F., Creative Morphology, , ourworld.compuserve.com/homepages/canmor/"Akao, Y., (1996) Qualitv Function Deployment: Integrating, Customer's Requirements into Product Design, , Cambridge: Massachusetts, Productivity PressCheng, L.C., (1995), QFD: planejamento da qualidade. Belo Horizonte: Fundação Christiano OttoniOhfuji, T., Ono, M., Akao, Y., (1997), Métodos de desdobramento da qualidade. Belo Horizonte: Fundação Christiano OttoniMiguel, P.C., Cheng, L.C., QFD in Brazil: Present status and future perspectives (2001) 7th International Symposium on Quality Function Deployment, pp. 147-152. , TóquioDedini, F.G., (2000), p. 128. , Metodologia e sistemática de projeto.Campinas: Universidade Estadual de Campinas, ApostilaCsillag, J.M., (1996), Análise do valor: metodologia do valor. São Paulo: Atla