922,313 research outputs found
The evolution and comparative neurobiology of endocannabinoid signalling
CB(1)- and CB(2)-type cannabinoid receptors mediate effects of the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide in mammals. In canonical endocannabinoid-mediated synaptic plasticity, 2-AG is generated postsynaptically by diacylglycerol lipase alpha and acts via presynaptic CB(1)-type cannabinoid receptors to inhibit neurotransmitter release. Electrophysiological studies on lampreys indicate that this retrograde signalling mechanism occurs throughout the vertebrates, whereas system-level studies point to conserved roles for endocannabinoid signalling in neural mechanisms of learning and control of locomotor activity and feeding. CB(1)/CB(2)-type receptors originated in a common ancestor of extant chordates, and in the sea squirt Ciona intestinalis a CB(1)/CB(2)-type receptor is targeted to axons, indicative of an ancient role for cannabinoid receptors as axonal regulators of neuronal signalling. Although CB(1)/CB(2)-type receptors are unique to chordates, enzymes involved in biosynthesis/inactivation of endocannabinoids occur throughout the animal kingdom. Accordingly, non-CB(1)/CB(2)-mediated mechanisms of endocannabinoid signalling have been postulated. For example, there is evidence that 2-AG mediates retrograde signalling at synapses in the nervous system of the leech Hirudo medicinalis by activating presynaptic transient receptor potential vanilloid-type ion channels. Thus, postsynaptic synthesis of 2-AG or anandamide may be a phylogenetically widespread phenomenon, and a variety of proteins may have evolved as presynaptic (or postsynaptic) receptors for endocannabinoids
Arithmetic and Geometric Progressions in Productsets over Finite Fields
Given two sets \cA, \cB \subseteq \F_q of elements of the finite field
\F_q of elements, we show that the productset \cA\cB = \{ab | a \in
\cA, b \in\cB\} contains an arithmetic progression of length
provided that , where is the characteristic of \F_q, and # \cA #
\cB \ge 3q^{2d-2/k}. We also consider geometric progressions in a shifted
productset \cA\cB +h, for f \in \F_q, and obtain a similar result
Human umbilical cord blood-borne fibroblasts contain marrow niche precursors that form a bone/marrow organoid in vivo
Human umbilical cord blood (CB) has attracted much attention as a reservoir for functional hematopoietic stem and progenitor cells, and, recently, as a source of blood-borne fibroblasts (CB-BFs). Previously, we demonstrated that bone marrow stromal cell (BMSC) and CB-BF pellet cultures make cartilage in vitro. Furthermore, upon in vivo transplantation, BMSC pellets remodelled into miniature bone/marrow organoids. Using this in vivo model, we asked whether CB-BF populations that express characteristics of the hematopoietic stem cell (HSC) niche contain precursors that reform the niche. CB ossicles were regularly observed upon transplantation. Compared with BM ossicles, CB ossicles showed a predominance of red marrow over yellow marrow, as demonstrated by histomorphological analyses and the number of hematopoietic cells isolated within ossicles. Marrow cavities from CB and BM ossicles included donor-derived CD146-expressing osteoprogenitors and host-derived mature hematopoietic cells, clonogenic lineage-committed progenitors and HSCs. Furthermore, human CD34+ cells transplanted into ossicle-bearing mice engrafted and maintained human HSCs in the niche. Our data indicate that CB- BFs are able to recapitulate the conditions by which the bone marrow microenvironment is formed and establish complete HSC niches, which are functionally supportive of hematopoietic tissue
Separability and entanglement in 2x3xN composite quantum systems
The separability and entanglement of quantum mixed states in \Cb^2 \otimes
\Cb^3 \otimes \Cb^N composite quantum systems are investigated. It is shown
that all quantum states with positive partial transposes and rank
are separable.Comment: Latex, 15 page
Identifying Transiting Circumbinary Planets
Transiting planets manifest themselves by a periodic dimming of their host
star by a fixed amount. On the other hand, light curves of transiting
circumbinary (CB) planets are expected to be neither periodic nor to have a
single depth while in transit, making BLS [Kovacs et al. 2002] almost
ineffective. Therefore, a modified version for the identification of CB planets
was developed - CB-BLS. We show that using CB-BLS it is possible to find CB
planets in the residuals of light curves of eclipsing binaries (EBs) that have
noise levels of 1% or more. Using CB-BLS will allow to easily harness the
massive ground- and space- based photometric surveys to look for these objects.
Detecting transiting CB planets is expected to have a wide range of
implications, for e.g.: The frequency of CB planets depend on the planetary
formation mechanism - and planets in close pairs of stars provides a most
restrictive constraint on planet formation models. Furthermore, understanding
very high precision light curves is limited by stellar parameters - and since
for EBs the stellar parameters are much better determined, the resultant
planetary structure models will have significantly smaller error bars, maybe
even small enough to challenge theory.Comment: To appear on the IAU Symposium 253 proceedings. 4 pages, 4 figure
A 1993 Look at the Lower Bound on the Top Quark Mass from CP Violation
We point out that the lower bound on from the CP violation parameter
has increased considerably. Using Wolfenstein parametrization of
the CKM matrix we derive an analytic expression for this bound as a function of
and the non-perturbative parameter
. For and we find . However, for and the
bound is raised to . The lower bound on from mixing is also reconsidered.Comment: latex, 8p, 3 figs not included, MPI-Ph/93-52 and TUM-T31-45/9
A More Precise Extraction of |V_{cb}| in HQEFT of QCD
The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure
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