5,504 research outputs found
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
Ideal Bose gas in fractal dimensions and superfluid He 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
Gunnera herteri - developmental morphology of a dwarf from Uruguay and S Brazil (Gunneraceae)
Abstract.: New morphological and developmental observations are presented of Gunnera herteri (subgenus Ostenigunnera) which is, according to molecular studies, sister to the other species of Gunnera. It is an annual dwarf (up to 4 cm long) whereas the other Gunnera spp. are perennial and slightly to extremely larger. External stem glands are combined with channels into the stem cortex serving as entrance path for symbiotic Nostoc cells. Young stem zones show globular regions of cytoplasm-rich cortex cells, prepared for invasion by Nostoc. The leaf axils contain 2-5 inconspicuous colleters (glandular scales) which can be taken as homologous to the more prominent scales of G. manicata (subg. Panke) and G. macrophylla (subg. Pseudogunnera). Foliage leaves of G. herteri have tooth-like sheath lobes which may be homologous to stipules. Adult plants have extra-axillary inflorescences arising from leaf nodes. The main stem is interpreted as a chain of sympodial units, each one consisting of a leaf and an extra-axillary inflorescence. This "sympodium hypothesis” may be also valid for other species of Gunnera. Each globular inflorescence of G. herteri contains several female flowers and 2-7 stamens at the top, perhaps equalling a single male flower. There are neither bracts nor bracteoles. The ovary is inferior, bicarpellary and unilocular. Its single hanging ovule develops into a dry and endosperm-rich see
Boundary quantum critical phenomena with entanglement renormalization
We extend the formalism of entanglement renormalization to the study of
boundary critical phenomena. The multi-scale entanglement renormalization
ansatz (MERA), in its scale invariant version, offers a very compact
approximation to quantum critical ground states. Here we show that, by adding a
boundary to the scale invariant MERA, an accurate approximation to the critical
ground state of an infinite chain with a boundary is obtained, from which one
can extract boundary scaling operators and their scaling dimensions. Our
construction, valid for arbitrary critical systems, produces an effective chain
with explicit separation of energy scales that relates to Wilson's RG
formulation of the Kondo problem. We test the approach by studying the quantum
critical Ising model with free and fixed boundary conditions.Comment: 8 pages, 12 figures, for a related work see arXiv:0912.289
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