14,828 research outputs found
Possible multiple evolution of indirect telencephalo-cerebellar pathways in teleosts: studies in Carassius auratus and Pantodon buchholzi
Among vertebrates, telencephalo-pontine systems exist only in birds and mammals. However, three nuclei in the diencephalon and mesencephalon of teleost fishes have been indicated — analogous to the pons — to represent relay stations between telencephalon and cerebellum. Since two of these nuclei (dorsal preglomerular nucleus, dorsal tegmental nucleus) have only been described in the highly derived, electrosensory mormyrids, we investigated telencephalic connections in two nonelectrosensory teleosts, the goldfish Carassius auratus and the freshwater butterflyfish Pantodon buchholzi, and cerebellar connections only in the latter species, since for C. auratus these connections are already established. Horseradish peroxidase tracing reveals that C. auratus has a dorsal tegmental nucleus and a paracommissural nucleus both of which are telencephalo-recipient and project to the cerebellum, and that P. buchholzi has a dorsal preglomerular nucleus with such connections. These results extend our knowlegde of the distribution and, therefore, the phylogeny of telencephalo-cerebellar systems in teleosts. Similar to tetrapods, teleosts appear to have developed telencephalo-cerebellar systems several times independently
Critical Casimir Forces in Colloidal Suspensions
Some time ago, Fisher and de Gennes pointed out that long-ranged correlations
in a fluid close to its critical point Tc cause distinct forces between
immersed colloidal particles which can even lead to flocculation [C. R. Acad.
Sc. Paris B 287, 207 (1978)]. Here we calculate such forces between pairs of
spherical particles as function of both relevant thermodynamic variables, i.e.,
the reduced temperature t = (T-Tc)/Tc and the field h conjugate to the order
parameter. This provides the basis for specific predictions concerning the
phase behavior of a suspension of colloidal particles in a near-critical
solvent.Comment: 29 pages, 14 figure
Colloidal hard-rod fluids near geometrically structured substrates
Density functional theory is used to study colloidal hard-rod fluids near an
individual right-angled wedge or edge as well as near a hard wall which is
periodically patterned with rectangular barriers. The Zwanzig model, in which
the orientations of the rods are restricted to three orthogonal orientations
but their positions can vary continuously, is analyzed by numerical
minimization of the grand potential. Density and orientational order profiles,
excess adsorptions, as well as surface and line tensions are determined. The
calculations exhibit an enrichment [depletion] of rods lying parallel and close
to the corner of the wedge [edge]. For the fluid near the geometrically
patterned wall, complete wetting of the wall -- isotropic liquid interface by a
nematic film occurs as a two-stage process in which first the nematic phase
fills the space between the barriers until an almost planar isotropic --
nematic liquid interface has formed separating the higher-density nematic fluid
in the space between the barriers from the lower-density isotropic bulk fluid.
In the second stage a nematic film of diverging film thickness develops upon
approaching bulk isotropic -- nematic coexistence.Comment: 9 pages, 9 figure
Light Composite Higgs from Higher Representations versus Electroweak Precision Measurements -- Predictions for LHC
We investigate theories in which the technifermions in higher dimensional
representations of the technicolor gauge group dynamically break the
electroweak symmetry of the standard model. For the two-index symmetric
representation of the gauge group the lowest number of techniflavors needed to
render the underlying gauge theory quasi conformal is two. We confront the
models with the recent electroweak precision measurements and demonstrate that
the two technicolor theory is a valid candidate for a dynamical breaking of the
electroweak symmetry. The electroweak precision measurements provide useful
constraints on the relative mass splitting of the new leptons needed to cure
the Witten anomaly. In the case of a fourth family of leptons with ordinary
lepton hypercharge the new heavy neutrino can be a natural candidate of cold
dark matter. We also propose theories in which the critical number of flavors
needed to enter the conformal window is higher than the one with fermions in
the two-index symmetric representation, but lower than in the walking
technicolor theories with fermions only in the fundamental representation of
the gauge group. Due to the near conformal/chiral phase transition, we show
that the composite Higgs is very light compared to the intrinsic scale of the
technicolor theory. For the two technicolor theory we predict the composite
Higgs mass not to exceed 150 GeV.Comment: RevTex, 53 pages, 7 figures and two table
Effects of Simulated Flight on Fan Noise Suppression
Attenuation properties of three treated fan inlets were evaluated. Tunnel flow simulated the inflow clean-up effect on source noise observed in flight and allowed observation of the blade passage frequency tone cut-off phenomenon. Acoustic data consisted of isolated inlet noise measured in the far field at two fixed positions and with traverses at four frequencies. Attenuation and source noise properties with and without flight simulation are compared and discussed. Averaged attenuation properties showed relative agreement of the inlets with their design intent, however, tunnel flow significantly affected the attenuation spectra
Attractions between charged colloids at water interfaces
The effective potential between charged colloids trapped at water interfaces
is analyzed. It consists of a repulsive electrostatic and an attractive
capillary part which asymptotically both show dipole--like behavior. For
sufficiently large colloid charges, the capillary attraction dominates at large
separations.
The total effective potential exhibits a minimum at intermediate separations
if the Debye screening length of water and the colloid radius are of comparable
size.Comment: 8 pages, 1 figure, revised version (one paragraph added) accepted in
JPC
The valvula cerebelli of the spiny eel, Macrognathus aculeatus, receives primary lateral-line afferents from the rostrum of the upper jaw
In the spiny eel, Macrognathus aculeatus, anterodorsal and (to a lesser degree) anteroventral lateralline nerves project massively to the granular layer of the valvula cerebelli, throughout its rostrocaudal extent. The posterior lateral-line nerve terminates in the corpus cerebelli. Thus, valvula and corpus cerebelli are supplied with mechanosensory input of different peripheral origins. An analysis of the taxonomic distribution of experimentally determined primary lateral-line input to the three parts of the teleostean cerebellum reveals that the eminentia granularis always receives such input, and that the corpus cerebelli is the recipient of primary lateral-line input in many teleosts. The valvula, however, receives primary lateral-line afferents in only two examined species. In M. aculeatus, the massive lateral-line input to the valvula probably originates in mechanoreceptors located in the elongated rostrum of the upper jaw, a characteristic feature of mastacembeloid fishes. This projection to the valvula may therefore represent a unique specialization that arose with the evolution of the peculiar rostrum
Critical Casimir interactions around the consolute point of a binary solvent
Spatial confinement of a near-critical medium changes its fluctuation
spectrum and modifies the corresponding order parameter distribution. These
effects result in effective, so-called critical Casimir forces (CCFs) acting on
the confining surfaces. These forces are attractive for like boundary
conditions of the order parameter at the opposing surfaces of the confinement.
For colloidal particles dissolved in a binary liquid mixture acting as a
solvent close to its critical point of demixing, one thus expects the emergence
of phase segregation into equilibrium colloidal liquid and gas phases. We
analyze how such phenomena occur asymmetrically in the whole thermodynamic
neighborhood of the consolute point of the binary solvent. By applying
field-theoretical methods within mean-field approximation and the
semi-empirical de Gennes-Fisher functional, we study the CCFs acting between
planar parallel walls as well as between two spherical colloids and their
dependence on temperature and on the composition of the near-critical binary
mixture. We find that for compositions slightly poor in the molecules
preferentially adsorbed at the surfaces, the CCFs are significantly stronger
than at the critical composition, thus leading to pronounced colloidal
segregation. The segregation phase diagram of the colloid solution following
from the calculated effective pair potential between the colloids agrees
surprisingly well with experiments and simulations
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