Microstructure and Properties of Laser-Selected Melt-Formed AlSi10Mg Alloy

The AlSi10Mg alloy samples were prepared by laser selective melting technology, and the effects of laser power, scanning distance and powder thickness on the microstructure, density and mechanical properties of the formed AlSi10Mg alloy samples were studied. The results showed that the phases of the AlSi10Mg alloy formed by laser melting in the selected area are mainly α-Al matrix and eutectic Si; the forming parallel to the direction of the component forms a typical fish scale structure, which is formed after the laser scanning molten pool solidifies , Its growth direction is parallel to the direction of heat dissipation; as the laser energy density decreases, the height of the fish scale tissue decreases and the width increases; when the laser power is higher, the density of the formed sample is also higher; the laser power is 900W, The sample with a scanning distance of 0.09mm and a spreading thickness of 0.05mm has better performance. The tensile strength and elongation of the sample parallel to the component direction are 288MPa and 2.1%, respectively.

Properties of pattern and component direction-selective cells in area MT of the macaque

Neurons in area MT/V5 of the macaque visual cortex encode visual motion. Some cells are selective for the motion of oriented features (component direction-selective, CDS); others respond to the true direction of complex patterns (pattern-direction selective, PDS). There is a continuum of selectivity in MT, with CDS cells at one extreme and PDS cells at the other; we compute a pattern index that captures this variation. It is unknown how a neuron's pattern index is related to its other tuning characteristics. We therefore analyzed the responses of 792 MT cells recorded in the course of other experiments from opiate-anesthetized macaque monkeys, as a function of the direction, spatial frequency, drift rate, size, and contrast of sinusoidal gratings and of the direction and speed of random-dot textures. We also compared MT responses to those of 718 V1 cells. As expected, MT cells with higher pattern index tended to have stronger direction selectivity and broader direction tuning to gratings, and they responded better to plaids than to gratings. Strongly PDS cells also tended to have smaller receptive fields and stronger surround suppression. Interestingly, they also responded preferentially to higher drift rates and higher speeds of moving dots. The spatial frequency preferences of PDS cells depended strongly on their preferred temporal frequencies, whereas these preferences were independent in component-selective cells. Pattern direction selectivity is statistically associated with many response properties of MT cells but not strongly associated with any particular property. Pattern-selective signals are thus available in association with most other signals exported by MT.

TOPOLOGICAL FIELD THEORY OF VORTICES OVER CLOSED KÄHLER MANIFOLD

We show that the vortex equations of the n-dimensional closed Kähler manifolds can be derived from Einstein-Hermitian equations of the (n+1)-dimensional closed Kähler manifolds by setting invariance under translation in the (n+1)th component direction. We construct the topological theory about the vortex pair model through the dimensional reduction of the topological BRST structure.

Evidence for metamorphic remagnetisation of upper Precambrian tillite in the Dalradian Supergroup of Scotland

ABSTRACTA conglomerate test using 36 clast cores (76 specimens) from the upper Precambrian Port Askaid Tillite of the Dalradian Supergroup in the Garvellach–Islay region of Scotland shows that the tillite was remagnetised during orogenic activity in Lower Ordovician time. After 550°C thermal demagnetisation, the clast remanence directions give a mean of 155°, 14° (α95—12°). This is similar to the mean from four tillite matrix sites of 162°, 4° (α95—9°) and the mean ‘primary component direction’ of 166°, −12° (α95—6°) previously determined from the interbedded siltstones. This indicates that the matrix and siltstones were also remagnetised. These mean directions give virtual geomagnetic poles after tilt correction that fall within the cluster of British Ordovician poles from rocks in the Caledonian orogen, and thereby indicate a prefolding Ordovician age for the remagnetisation. Thermal demagnetisation studies and observations from polished and thin sections of tillite clast and matrix specimens show that secondary hematite derived from partially to completely altered magnetite is the dominant carrier of the metamorphic remagnetisation. These results show that remanence data from the Port Askaid Tillite cannot be used to support the hypothesis that a worldwide glaciation occurred during the Late Precambrian.