Granular discharge rate for submerged hoppers

The discharge of spherical grains from a hole in the bottom of a right circular cylinder is measured with the entire system underwater. We find that the discharge rate depends on filling height, in contrast to the well-known case of dry non-cohesive grains. It is further surprising that the rate increases up to about twenty five percent, as the hopper empties and the granular pressure head decreases. For deep filling, where the discharge rate is constant, we measure the behavior as a function of both grain and hole diameters. The discharge rate scale is set by the product of hole area and the terminal falling speed of isolated grains. But there is a small-hole cutoff of about two and half grain diameters, which is larger than the analogous cutoff in the Beverloo equation for dry grains

Representational Account of Memory: Insights from Aging and Synesthesia

The representational account of memory envisages perception and memory to be on a continuum rather than in discretely divided brain systems [Bussey, T. J., & Saksida, L. M. Memory, perception, and the ventral visual-perirhinal-hippocampal stream: Thinking outside of the boxes. Hippocampus, 17, 898–908, 2007]. We tested this account using a novel between-group design with young grapheme-color synesthetes, older adults, and young controls. We investigated how the disparate sensory-perceptual abilities between these groups translated into associative memory performance for visual stimuli that do not induce synesthesia. ROI analyses of the entire ventral visual stream showed that associative retrieval (a pair-associate retrieved in the absence of a visual stimulus) yielded enhanced activity in young and older adults' visual regions relative to synesthetes, whereas associative recognition (deciding whether a visual stimulus was the correct pair-associate) was characterized by enhanced activity in synesthetes' visual regions relative to older adults. Whole-brain analyses at associative retrieval revealed an effect of age in early visual cortex, with older adults showing enhanced activity relative to synesthetes and young adults. At associative recognition, the group effect was reversed: Synesthetes showed significantly enhanced activity relative to young and older adults in early visual regions. The inverted group effects observed between retrieval and recognition indicate that reduced sensitivity in visual cortex (as in aging) comes with increased activity during top–down retrieval and decreased activity during bottom–up recognition, whereas enhanced sensitivity (as in synesthesia) shows the opposite pattern. Our results provide novel evidence for the direct contribution of perceptual mechanisms to visual associative memory based on the examples of synesthesia and aging

Ideal Bose gas in fractal dimensions and superfluid 4^4He in porous media

Physical properties of ideal Bose gas with the fractal dimensionality between D=2 and D=3 are theoretically investigated. Calculation shows that the characteristic features of the specific heat and the superfluid density of ideal Bose gas in fractal dimensions are strikingly similar to those of superfluid Helium-4 in porous media. This result indicates that the geometrical factor is dominant over mutual interactions in determining physical properties of Helium-4 in porous media.Comment: 13 pages, 6 figure

Multi MeV protons, deuterons and carbon ions produced by the PALS laser system

Multi MeV ions and fusion neutrons were generated by focused radiation of the 3 TW Prague Asterix Laser System (PALS). The use of 8 μm Al foil as XUV filter positioned in front of an ion collector allowed measuring currents of 4-MeV protons emitted behind a thin target in the forward direction. The proton energy of 4 MeV generated by a PALS laser irradiance Iλ2~5×1016 W cm-2 μm2 on target is nominally reachable for picosecond lasers when they deliver the intensity Iλ2~3×1018 W cm-2 μm2. The enhanced maximum proton energy is favoured by a non-linear interaction of the laser beam with the pre-generated plasma. Nonlinear processes also cause enhancement in the yield of fusion neutrons per focused laser energy from the CD2 plasma. The obtained results show that an equivalent neutron yield was reached by ps- and sub-ps laser beams for Iλ2~1019 W cm-2 μm2. The hampering influence of the electromagnetic pulse generated within the interaction chamber on diagnostics signals was eliminated

Numerical study of multilayer adsorption on fractal surfaces

We report a numerical study of van der Waals adsoprtion and capillary condensation effects on self-similar fractal surfaces. An assembly of uncoupled spherical pores with a power-law distributin of radii is used to model fractal surfaces with adjustable dimensions. We find that the commonly used fractal Frankel-Halsey-Hill equation systematically fails to give the correct dimension due to crossover effects, consistent with the findings of recent experiments. The effects of pore coupling and curvature dependent surface tension were also studied.Comment: 11 pages, 3 figure