1,045 research outputs found
Sonic hedgehog functions upstream of disrupted-in-schizophrenia 1 (disc1): implications for mental illness
DISRUPTED-IN-SCHIZOPHRENIA (DISC1) has been one of the most intensively studied genetic risk factors for mental illness since it was discovered through positional mapping of a translocation breakpoint in a large Scottish family where a balanced chromosomal translocation was found to segregate with schizophrenia and affective disorders. While the evidence for it being central to disease pathogenesis in the original Scottish family is compelling, recent genome-wide association studies have not found evidence for common variants at the DISC1 locus being associated with schizophrenia in the wider population. It may therefore be the case that DISC1 provides an indication of biological pathways that are central to mental health issues and functional studies have shown that it functions in multiple signalling pathways. However, there is little information regarding factors that function upstream of DISC1 to regulate its expression and function. We herein demonstrate that Sonic hedgehog (Shh) signalling promotes expression of disc1 in the zebrafish brain. Expression of disc1 is lost in smoothened mutants that have a complete loss of Shh signal transduction, and elevated in patched mutants which have constitutive activation of Shh signalling. We previously demonstrated that disc1 knockdown has a dramatic effect on the specification of oligodendrocyte precursor cells (OPC) in the hindbrain and Shh signalling is known to be essential for the specification of these cells. We show that disc1 is prominently expressed in olig2-positive midline progenitor cells that are absent in smo mutants, while cyclopamine treatment blocks disc1 expression in these cells and mimics the effect of disc1 knock down on OPC specification. Various features of a number of psychiatric conditions could potentially arise through aberrant Hedgehog signalling. We therefore suggest that altered Shh signalling may be an important neurodevelopmental factor in the pathobiology of mental illness
Semileptonic B and Lambda_b Decays and Local Duality in QCD
The inclusive and exclusive semileptonic decay distributions for b -> c decay
are computed in the Shifman-Voloshin limit. The inclusive decay distributions
(computed using an operator product expansion) depend on quark masses, and the
exclusive decay distributions depend on hadron masses. Nevertheless, we show
explicitly how the first two terms in the 1/m expansion match between the
inclusive and exclusive decays. Agreement between the inclusive and exclusive
decay rates requires a minimum smearing region of size Lambda_QCD before local
duality holds in QCD. The alpha_s corrections to the inclusive and exclusive
decay rates are also shown to agree to order (log m)/m^2. The alpha_s/m^2
corrections are used to obtain the alpha_s correction to Bjorken's inequality
on the slope of the Isgur-Wise function.Comment: 22 pages, 3 eps figures, uses revtex (Revision: a discussion of
radiative corrections to the bound K>0 of Section 7.B has been added; some
typos, including labels in fig 2
A Simple Colorimetric Method for the Estimation of Relative Numbers of Lactobacilli in the Saliva
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67295/2/10.1177_00220345400190040101.pd
Photon-photon correlations and entanglement in doped photonic crystals
We consider a photonic crystal (PC) doped with four-level atoms whose
intermediate transition is coupled near-resonantly with a photonic band-gap
edge. We show that two photons, each coupled to a different atomic transition
in such atoms, can manifest strong phase or amplitude correlations: One photon
can induce a large phase shift on the other photon or trigger its absorption
and thus operate as an ultrasensitive nonlinear photon-switch. These features
allow the creation of entangled two-photon states and have unique advantages
over previously considered media: (i) no control lasers are needed; (ii) the
system parameters can be chosen to cause full two-photon entanglement via
absorption; (iii) a number of PCs can be combined in a network.Comment: Modified, expanded text; added reference
MaxEnt power spectrum estimation using the Fourier transform for irregularly sampled data applied to a record of stellar luminosity
The principle of maximum entropy is applied to the spectral analysis of a
data signal with general variance matrix and containing gaps in the record. The
role of the entropic regularizer is to prevent one from overestimating
structure in the spectrum when faced with imperfect data. Several arguments are
presented suggesting that the arbitrary prefactor should not be introduced to
the entropy term. The introduction of that factor is not required when a
continuous Poisson distribution is used for the amplitude coefficients. We
compare the formalism for when the variance of the data is known explicitly to
that for when the variance is known only to lie in some finite range. The
result of including the entropic measure factor is to suggest a spectrum
consistent with the variance of the data which has less structure than that
given by the forward transform. An application of the methodology to example
data is demonstrated.Comment: 15 pages, 13 figures, 1 table, major revision, final version,
Accepted for publication in Astrophysics & Space Scienc
Mid-infrared entangled photon generation in optimised asymmetric semiconductor quantum wells
The optimal design of asymmetric quantum well structures for generation of entangled photons in the mid-infrared range by spontaneous parametric down- conversion is considered, and the efficiency of this process is estimated. Calcu- lations show that a reasonably good degree of entanglement can be obtained, and that the optical interaction length required for optimal conversion is very short, in the few μm range
Glueballs, gluon condensate, and pure glue QCD below T_c
A quasiparticle description of pure glue QCD thermodynamics at T<T_c is
proposed and compared to recent lattice data. Given that a gas of glueballs
with constant mass cannot quantitatively reproduce the early stages of the
deconfinement phase transition, the problem is to identify a relevant mechanism
leading to the observed sudden increase of the pressure, trace anomaly, etc. It
is shown that the strong decrease of the gluon condensate near T_c combined
with the increasing thermal width of the lightest glueballs might be the
trigger of the phase transition.Comment: 5 pages, 5 figures; analysis refined in v2, explanations added; v3 to
appear in EPJ
Solid-state laser system for laser cooling of Sodium
We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with
up to 800 mW output power. The laser relies on sum-frequency generation from
two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a
doubly-resonant cavity. We obtain conversion efficiency as high as 2 W/W^2
after optimization of the cavity parameters. The output wavelength is tunable
over 60 GHz, which is sufficient to lock on the Sodium D2 line. The robustness,
beam quality, spectral narrowness and tunability of our source make it an
alternative to dye lasers for atomic physics experiments with Sodium atoms
Unitarity Constraints on the B and B^* Form Factors from QCD Analyticity and Heavy Meson Spin Symmetry
A method of deriving bounds on the weak meson form factors, based on
perturbative QCD, analyticity and unitarity, is generalized in order to fully
exploit heavy quark spin symmetry in the ground state doublet of
pseudoscalar and vector mesons. All the relevant form factors of
these mesons are taken into account in the unitarity sum. They are treated as
independent functions along the timelike axis, being related by spin symmetry
only near the zero recoil point. Heavy quark vacuum polarisation up to three
loops in perturbative QCD and the experimental cross sections are used as input. We obtain bounds on the charge radius
of the elastic form factor of the meson, which considerably improve
previous results derived in the same framework.Comment: 13 pages LaTex, 1 figure as a separate ps fil
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