751 research outputs found
Magnetic nanowires as permanent magnet materials
We present the fabrication of metallic magnetic nanowires using a low
temperature chemical process. We show that pressed powders and magnetically
oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe
at 300 K). We discuss the magnetic properties of these metamaterials and show
that they have the suitable properties to realize "high temperature magnets"
competitive with AlNiCo or SmCo permanent magnets. They could also be used as
recording media for high density magnetic recording.Comment: 5 pages, 5 figure
Reaching in reality and virtual reality: a comparison of movement kinematics in healthy subjects and in adults with hemiparesis
BACKGROUND: Virtual reality (VR) is an innovative tool for sensorimotor rehabilitation increasingly being employed in clinical and community settings. Despite the growing interest in VR, few studies have determined the validity of movements made in VR environments with respect to real physical environments. The goal of this study was to compare movements done in physical and virtual environments in adults with motor deficits to those in healthy individuals. METHODS: The participants were 8 healthy adults and 7 adults with mild left hemiparesis due to stroke. Kinematics of functional arm movements involving reaching, grasping and releasing made in physical and virtual environments were analyzed in two phases: 1) reaching and grasping the ball and 2) ball transport and release. The virtual environment included interaction with an object on a 2D computer screen and haptic force feedback from a virtual ball. Temporal and spatial parameters of reaching and grasping were determined for each phase. RESULTS: Individuals in both groups were able to reach, grasp, transport, place and release the virtual and real ball using similar movement strategies. In healthy subjects, reaching and grasping movements in both environments were similar but these subjects used less wrist extension and more elbow extension to place the ball on the virtual vertical surface. Participants with hemiparesis made slower movements in both environments compared to healthy subjects and during transport and placing of the ball, trajectories were more curved and interjoint coordination was altered. Despite these differences, patients with hemiparesis also tended to use less wrist extension during the whole movement and more elbow extension at the end of the placing phase. CONCLUSION: Differences in movements made by healthy subjects in the two environments may be explained by the use of a 2D instead of a 3D virtual environment and the absence of haptic feedback from the VR target. Despite these differences, our findings suggest that both healthy subjects and individuals with motor deficits used similar movement strategies when grasping and placing a ball in the two reality conditions. This suggests that training of arm movements in VR environments may be a valid approach to the rehabilitation of patients with motor disorders
An implicit method for radiative transfer with the diffusion approximation in SPH
An implicit method for radiative transfer in SPH is described. The diffusion
approximation is used, and the hydrodynamic calculations are performed by a
fully three--dimensional SPH code. Instead of the energy equation of state for
an ideal gas, various energy states and the dissociation of hydrogen molecules
are considered in the energy calculation for a more realistic temperature and
pressure determination. In order to test the implicit code, we have performed
non--isothermal collapse simulations of a centrally condensed cloud, and have
compared our results with those of finite difference calculations performed by
MB93. The results produced by the two completely different numerical methods
agree well with each other.Comment: 25 pages, 9 figure
Impact behavior of injected PP/nanoclay parts
This work attempts to contribute to bridge the gap between scientific challenges and industrial stakes regarding
PP/nanoclay composites. Pieces of nanocomposites were obtained by direct injection of commercial PP mixed with a
commercial MB of PP with 50% of organoclay, with a double-gated hot runner mould, which produced mouldings with
a weld line. The moulding microstructure was assessed by POM and XRD, while the distribution and exfoliation grade
of clay was evaluated by TEM and XRD. The typical skin-core structure was found, with a skin thickness wider in bulk
than in weld line zones. Regarding clay platelets mostly intercalated structures were seen. The impact properties at
room temperature were assessed by means of tensile and biaxial tests. Properties were monitored at different sites of the
mouldings. At the weld line zone less energy was consumed under tensile conditions and exhibited higher apparent
impact toughness under biaxial conditions than the bulk zone. Visual inspection of biaxially impacted samples showed
that the orientation of polymer molecules and clay platelets induced by melt flow prevailed, and the weld line was not
the determinant of the toughness of the mouldings. An optimum in impact performance was found for moulding with
3% of clay, since at larger clay contents platelets agglomerated and acted as stress raisers
Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings
Polypopylene/nanoclay three-dimensional parts were
produced without intermediate steps by direct injection
molding to explore the influence of flow features and
nanoclay incorporation in their impact performance.
The nanocomposite was obtained by direct compounding
of commercial PP with nanoclay masterbatch. The
as-molded morphology was analyzed by X-ray and
TEM analyses in terms of skin-core structure and
nanoclay particle dispersion. The nanoclay particles
induced the reduction of b-form spherulites, a known
toughener. The impact behavior was assessed in tensile
and biaxial modes. The PP nanocomposite molding
toughness was practically unaffected by the processing
melt temperature and flow rate. Conversely the
nanoclay presence is influent in the impact performance.
Under biaxial stress impact, the regions close to
weld lines are tougher than the bulk and the fracture
develops with main crack paths along the flow direction
and the weld line. Cracking along the weld line
results from less macromolecular interpenetration and
chain entanglement, and unfavorable nanoparticle orientation.
It seems that a failure mechanism which
involves nanoclay delamination and multiple matrix
crazing explains the toughening of PP in the directions
where the nanoparticle orientation with respect to
loading is adequate.Contract grant sponsors: CONICET, ANPCyT from Argentina, MINCyT (Argentina) - FCT (Portugal), Universities Nacional de Mar del Plata and Minho
Characterization of cadmium proteinuria in man and rat.
In workers chronically exposed to cadmium and without signs of renal insufficiency, plasma proteins with molecular weight ranging from 11,800 to 450,000 are excreted in greater amount in urine. Increased urinary excretion of low and high molecular weight proteins can occur independently. Because of its greater stability in urine and provided a sensitive immunological technique is used, the determination of retinol-binding protein is a more practical and reliable test of proximal tubular function than beta 2-microglobulin. The evaluation of renal function of workers removed from cadmium exposure indicates that cadmium-induced renal lesions, albeit of slow progression, are not reversible when exposures ceases. In workers chronically exposed to cadmium or removed from cadmium exposure, metallothionein in urine is directly correlated with cadmium in urine but not with cadmium in blood or years of cadmium exposure. The association between cadmium in urine and metallothionein in urine is independent of the status of renal function and the intensity of current exposure to cadmium. Whereas the repeated IP injection of high doses of cadmium to rat gives rise to a mixed or tubular type proteinuria, the prolonged oral administration of cadmium results mainly in the development of a glomerular type proteinuria. The former is usually reversible after cessation of treatment whereas the latter is not. Circulating antiglomerular basement membrane antibodies have been found in man and in rat chronically exposed to cadmium. The pathogenic significance of this finding deserves further investigation
Medición del índice de refracción del agua usando materiales sencillos
Palabras clave: índice de refracción; ley de Snell; comportamiento de la luz; experiencias físicas sencillas.Measuring the index of refraction of water using simple materialsKeywords: index of refraction; Snell’s law; behaviour of light; simple physical experiences
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