27,248 research outputs found
Requirement for Slit-1 and Robo-2 in zonal segregation of olfactory sensory neuron axons in the main olfactory bulb
The formation of precise stereotypic connections in sensory systems is critical for the ability to detect and process signals from the environment. In the olfactory system, olfactory sensory neurons (OSNs) project axons to spatially defined glomeruli within the olfactory bulb (OB). A spatial relationship exists between the location of OSNs within the olfactory epithelium (OE) and their glomerular targets
along the dorsoventral axis in the OB. The molecular mechanisms underlying the zonal segregation of OSN axons along the dorsoventral axis of the OB are poorly understood. Using robo-2/ (roundabout) and slit-1/ mice, we examined the role of the Slit family of axon
guidance cues in the targeting of OSN axons during development. We show that a subset of OSN axons that normally project to the dorsal region of the OB mistarget and form glomeruli in the ventral region in robo-2/ and slit-1/ mice. In addition, we show that the Slit
receptor, Robo-2, is expressed in OSNs in a high dorsomedial to low ventrolateral gradient across the OE and that Slit-1 and Slit-3 are expressed in the ventral region of the OB. These results indicate that the dorsal-to-ventral segregation of OSN axons are not solely defined
by the location of OSNs within the OE but also relies on axon guidance cues
On the distribution of the nodal sets of random spherical harmonics
We study the length of the nodal set of eigenfunctions of the Laplacian on
the \spheredim-dimensional sphere. It is well known that the eigenspaces
corresponding to \eigval=n(n+\spheredim-1) are the spaces \eigspc of
spherical harmonics of degree , of dimension \eigspcdim. We use the
multiplicity of the eigenvalues to endow \eigspc with the Gaussian
probability measure and study the distribution of the \spheredim-dimensional
volume of the nodal sets of a randomly chosen function. The expected volume is
proportional to \sqrt{\eigval}. One of our main results is bounding the
variance of the volume to be O(\frac{\eigval}{\sqrt{\eigspcdim}}).
In addition to the volume of the nodal set, we study its Leray measure. For
every , the expected value of the Leray measure is .
We are able to determine that the asymptotic form of the variance is
\frac{const}{\eigspcdim}.Comment: 47 pages, accepted for publication in the Journal of Mathematical
Physics. Lemmas 2.5, 2.11 were proved for any dimension, some other,
suggested by the referee, modifications and corrections, were mad
A Paraconsistent Higher Order Logic
Classical logic predicts that everything (thus nothing useful at all) follows
from inconsistency. A paraconsistent logic is a logic where an inconsistency
does not lead to such an explosion, and since in practice consistency is
difficult to achieve there are many potential applications of paraconsistent
logics in knowledge-based systems, logical semantics of natural language, etc.
Higher order logics have the advantages of being expressive and with several
automated theorem provers available. Also the type system can be helpful. We
present a concise description of a paraconsistent higher order logic with
countable infinite indeterminacy, where each basic formula can get its own
indeterminate truth value (or as we prefer: truth code). The meaning of the
logical operators is new and rather different from traditional many-valued
logics as well as from logics based on bilattices. The adequacy of the logic is
examined by a case study in the domain of medicine. Thus we try to build a
bridge between the HOL and MVL communities. A sequent calculus is proposed
based on recent work by Muskens.Comment: Originally in the proceedings of PCL 2002, editors Hendrik Decker,
Joergen Villadsen, Toshiharu Waragai (http://floc02.diku.dk/PCL/). Correcte
The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter Photometry
The nature of far-infrared dust emission toward main sequence stars, whether
interstellar or circumstellar, can be deduced from submillimeter photometry. We
present JCMT/SCUBA flux measurements at 850 microns toward 8 stars with large
photospheric excesses at 60-100 microns. 5 sources were detected at 3-sigma or
greater significance and one was marginally detected at 2.5-sigma. The inferred
dust masses and temperatures range from 0.033 to 0.24 Earth masses and 43-65 K
respectively. The frequency behavior of the opacity, tau_nu ~ nu^beta, is
relatively shallow, beta < 1. These dust properties are characteristic of
circumstellar material, most likely the debris from planetesimal collisions.
The 2 non-detections have lower temperatures, 35-38 K and steeper opacity
indices, beta > 1.5, that are more typical of interstellar cirrus. The
confirmed disks all have inferred diameters > 2'', most lie near the upper
envelope of the debris disk mass distribution, and 4 are bright enough to be
feasible for high resolution imaging.Comment: accepted by Ap
Properties of Non-Abelian Fractional Quantum Hall States at Filling
We compute the physical properties of non-Abelian Fractional Quantum Hall
(FQH) states described by Jack polynomials at general filling
. For , these states are identical to the
Read-Rezayi parafermions, whereas for they represent new FQH states. The
states, multiplied by a Vandermonde determinant, are a non-Abelian
alternative construction of states at fermionic filling . We
obtain the thermal Hall coefficient, the quantum dimensions, the electron
scaling exponent, and show that the non-Abelian quasihole has a well-defined
propagator falling off with the distance. The clustering properties of the Jack
polynomials, provide a strong indication that the states with can be
obtained as correlators of fields of \emph{non-unitary} conformal field
theories, but the CFT-FQH connection fails when invoked to compute physical
properties such as thermal Hall coefficient or, more importantly, the quasihole
propagator. The quasihole wavefuntion, when written as a coherent state
representation of Jack polynomials, has an identical structure for \emph{all}
non-Abelian states at filling .Comment: 2 figure
Terahertz surface plasmon polariton propagation and focusing on periodically corrugated metal wires
In this letter we show how the dispersion relation of surface plasmon
polaritons (SPPs) propagating along a perfectly conducting wire can be tailored
by corrugating its surface with a periodic array of radial grooves. In this
way, highly localized SPPs can be sustained in the terahertz region of the
electromagnetic spectrum. Importantly, the propagation characteristics of these
spoof SPPs can be controlled by the surface geometry, opening the way to
important applications such as energy concentration on cylindrical wires and
superfocusing using conical structures.Comment: accepted at PRL, submitted 29th May 200
Fermionic characters for graded parafermions
Fermionic-type character formulae are presented for charged
irreduciblemodules of the graded parafermionic conformal field theory
associated to the coset . This is obtained by counting the
weakly ordered `partitions' subject to the graded exclusion principle.
The bosonic form of the characters is also presented.Comment: 24 p. This corrects typos (present even in the published version) in
eqs (4.4), (5.23), (5.24) and (C.4
SM(2,4k) fermionic characters and restricted jagged partitions
A derivation of the basis of states for the superconformal minimal
models is presented. It relies on a general hypothesis concerning the role of
the null field of dimension . The basis is expressed solely in terms of
modes and it takes the form of simple exclusion conditions (being thus a
quasi-particle-type basis). Its elements are in correspondence with
-restricted jagged partitions. The generating functions of the latter
provide novel fermionic forms for the characters of the irreducible
representations in both Ramond and Neveu-Schwarz sectors.Comment: 12 page
An assessment of the effects of neurokinin<sub>1</sub> receptor antagonism against nausea and vomiting: Relative efficacy, sites of action and lessons for future drug development.
A âbroad-spectrumâ anti-vomiting effect of neurokinin1 receptor antagonists (NK1RA), shown in preclinical animal studies, has been supported by a more limited range of clinical studies in different indications. However, this review suggests that compared with vomiting, the self-reported sensation of nausea is less affected or possibly unaffected (depending on the stimulus) by NK1 receptor antagonism, a common finding for âanti-emeticsâ.
The stimulus-independent effects of NK1RAs against vomiting are explicable by actions within the central pattern generator (CPG; ventral brainstem) and the nucleus tractus solitarius (NTS; dorsal brainstem), with additional effects on vagal afferent activity for certain stimuli (e.g., highly emetogenic chemotherapy). The CPG and NTS neurones are multifunctional so the notable lack of obvious effects of NK1RAs on other reflexes mediated by the same neurones suggests that their anti-vomiting action is dependent on the activation state of the pathway leading to vomiting.
Nausea requires activation of cerebral pathways by projection of information from the NTS. Although NK1 receptors are present in cerebral nuclei implicated in nausea, and imaging studies show very high receptor occupancy at clinically used doses, the variable or limited ability of NK1RAs to inhibit nausea emphasises (a) our inadequate understanding of the mechanisms of nausea and (b) that classification of a drug as an âanti-emeticâ may give a false impression of efficacy against nausea versus vomiting.
We discuss the potential mechanisms for the differential efficacy of NK1RA and the implications for future development of drugs which can effectively treat nausea, an area of unmet clinical need
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