8,248 research outputs found
A Time-Periodic Lyapunov Approach for Motion Planning of Controllable Driftless Systems on SU(n)
For a right-invariant and controllable driftless system on SU(n), we consider
a time-periodic reference trajectory along which the linearized control system
generates su(n): such trajectories always exist and constitute the basic
ingredient of Coron's Return Method. The open-loop controls that we propose,
which rely on a left-invariant tracking error dynamics and on a fidelity-like
Lyapunov function, are determined from a finite number of left-translations of
the tracking error and they assure global asymptotic convergence towards the
periodic reference trajectory. The role of these translations is to avoid being
trapped in the critical region of this Lyapunov-like function. The convergence
proof relies on a periodic version of LaSalle's invariance principle and the
control values are determined by numerical integration of the dynamics of the
system. Simulations illustrate the obtained controls for and the
generation of the C--NOT quantum gate.Comment: Submitte
Thermal treatment of superconductor thin film of the BSCCO system using domestic microwave oven
In this work, we report the preparation of a superconductor thin film of the
BSCCO system using a good quality powder with nominal composition
Bi_{1.8}Pb_{0.4}Sr_2CaCu_2O_x which was thermally treated using a domestic
microwave oven (2.45 GHz, 800 W). This film was grew on a single crystal of
LaAlO_3(100) substrate and exhibited a crystalline structure with the c-axis
perpendicular to the plane of the substrate. An onset superconducting
transition temperature was measured at 80 K.Comment: 4 pages, 5 figure
Concepções de professores paranaenses sobre a natureza do conhecimento científico: permanências e rupturas
Apresenta resultados de pesquisa com professores de química da rede pública de ensino do Estado do Paraná no Brasil. Estudamos as concepções desses docentes sobre a natureza do conhecimento científico e identificamos rupturas e permanências da visão geral que docentes têm sobre ciência. Aplicamos questionário a 62 professores com questões sobre a ciência e sua natureza. A maioria dos professores revela visões de ciência empírico-indutivista. Indicam a melhoria das atividades didáticas exclusivamente pela inserção de experimentos guiados pelo método científico. Este trabalho aponta para a necessidade de inserirmos na formação de professores a história e filosofia da ciência no intuito de melhorar a concepção docente sobre a ciência
Mg/Ti multilayers: structural, optical and hydrogen absorption properties
Mg-Ti alloys have uncommon optical and hydrogen absorbing properties,
originating from a "spinodal-like" microstructure with a small degree of
chemical short-range order in the atoms distribution. In the present study we
artificially engineer short-range order by depositing Pd-capped Mg/Ti
multilayers with different periodicities and characterize them both
structurally and optically. Notwithstanding the large lattice parameter
mismatch between Mg and Ti, the as-deposited metallic multilayers show good
structural coherence. Upon exposure to H2 gas a two-step hydrogenation process
occurs, with the Ti layers forming the hydride before Mg. From in-situ
measurements of the bilayer thickness L at different hydrogen pressures, we
observe large out-of-plane expansions of the Mg and Ti layers upon
hydrogenation, indicating strong plastic deformations in the films and a
consequent shortening of the coherence length. Upon unloading at room
temperature in air, hydrogen atoms remain trapped in the Ti layers due to
kinetic constraints. Such loading/unloading sequence can be explained in terms
of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by
diffusion calculations on a model multilayered systems. Absorption isotherms
measured by hydrogenography can be interpreted as a result of the elastic
clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces
Effect of antibodies on the expression of Plasmodium falciparum circumsporozoite protein gene
Antibodies are known to play an important role in the control of malaria infection. However, they can modulate parasite development enhancing infection. The effect of anti-Plasmodium antibodies on the expression of circumsporozoite protein gene (csp) was investigated. Plasmodium falciparum 3D7 in vitro cultures were submitted to: i) anti- circumsporozoite protein monoclonal antibody (anti-CSP-mAb) [1μg/ml, 0.1μg/ml, 0.01μg/ml and 0.001μg/ml] and ii) purified IgG Fab fragment from a pool of malaria patients [1mg/ml and 1μg/ml]; and compared to control cultures. After 24h the number of ring infected erythrocytes was determined in order to calculate invasion efficacy. At 48h culture supernatant was collected, and the amount of circumsporozoite protein determined by ELISA, parasitaemia was calculated and cells were processed for RNA preparation. Expression of csp gene was quantified using Real time RT-PCR. There was an increase in parasite growth when treated with lower anti-CSP-mAb concentration, which was associated with lower csp expression, while 1μg/ml anti-CSP-mAb treatment presented a growth inhibitory effect accompanied by high csp expression
Dynamics of Counterion Condensation
Using a generalization of the Poisson-Boltzmann equation, dynamics of
counterion condensation is studied. For a single charged plate in the presence
of counterions, it is shown that the approach to equilibrium is diffusive. In
the far from equilibrium case of a moving charged plate, a dynamical counterion
condensation transition occurs at a critical velocity. The complex dynamic
behavior of the counterion cloud is shown to lead to a novel nonlinear
force-velocity relation for the moving plate.Comment: 5 pages, 1 ps figure included using eps
Anisotropic elastic theory of preloaded granular media
A macroscopic elastic description of stresses in static, preloaded granular
media is derived systematically from the microscopic elasticity of individual
inter-grain contacts. The assumed preloaded state and friction at contacts
ensure that the network of inter-grain contacts is not altered by small
perturbations. The texture of this network, set by the preparation of the
system, is encoded in second and fourth order fabric tensors. A small
perturbation generates both normal and tangential inter-grain forces, the
latter causing grains to reorient. This reorientation response and the
incremental stress are expressed in terms of the macroscopic strain.Comment: 7 pages, 2 figures. Accepted version. [email protected]
[email protected]
- …