2,670 research outputs found
Cooperative Relaying with CPFSK and Distributed Space-Time Trellis Codes
Cooperative relaying allows single antenna users to achieve diversity and coding gains by utilizing nearby users' transmitting capabilities. We consider a relay system employing constant envelope continuous phase frequency shift keying. Distributed space-time trellis codes are implemented with a novel multiple relay protocol
Developing an ancient epithelial appendage: FGF signalling regulates early tail denticle formation in sharks
Background: Vertebrate epithelial appendages constitute a diverse group of organs that includes integumentary
structures such as reptilian scales, avian feathers and mammalian hair. Recent studies have provided new evidence for
the homology of integumentary organ development throughout amniotes, despite their disparate fnal morphologies.
These structures develop from conserved molecular signalling centres, known as epithelial placodes. It is not yet
certain whether this homology extends beyond the integumentary organs of amniotes, as there is a lack of knowledge
regarding their development in basal vertebrates. As the ancient sister lineage of bony vertebrates, extant chondrichthyans
are well suited to testing the phylogenetic depth of this homology. Elasmobranchs (sharks, skates and
rays) possess hard, mineralised epithelial appendages called odontodes, which include teeth and dermal denticles
(placoid scales). Odontodes constitute some of the oldest known vertebrate integumentary appendages, predating
the origin of gnathostomes. Here, we used an emerging model shark (Scyliorhinus canicula) to test the hypothesis that
denticles are homologous to other placode-derived amniote integumentary organs. To examine the conservation
of putative gene regulatory network (GRN) member function, we undertook small molecule inhibition of fbroblast
growth factor (FGF) signalling during caudal denticle formation.
Results: We show that during early caudal denticle morphogenesis, the shark expresses homologues of conserved
developmental gene families, known to comprise a core GRN for early placode morphogenesis in amniotes. This
includes conserved expression of FGFs, sonic hedgehog (shh) and bone morphogenetic protein 4 (bmp4). Additionally,
we reveal that denticle placodes possess columnar epithelial cells with a reduced rate of proliferation, a conserved
characteristic of amniote skin appendage development. Small molecule inhibition of FGF signalling revealed
placode development is FGF dependent, and inhibiting FGF activity resulted in downregulation of shh and bmp4
expression, consistent with the expectation from comparison to the amniote integumentary appendage GRN.
Conclusion: Overall, these fndings suggest the core GRN for building vertebrate integumentary epithelial appendages
has been highly conserved over 450 million years. This provides evidence for the continuous, historical homology
of epithelial appendage placodes throughout jawed vertebrates, from sharks to mammals. Epithelial placodes
constitute the shared foundation upon which diverse vertebrate integumentary organs have evolved
High power 946nm Nd:YAG laser, longitudinally-pumped by a diode bar
We report efficient quasi-three-level operation of a Nd:YAG laser at 946nm pumped by a 20W diode bar. An output power of ~2.6W has been obtained for 14.4W of incident pump power
A pilot study of MBA programmes in South Africa
In recent years, Master of Business Administration (MBA) programmes and their curricula have been subjected to substantial scrutiny. However, the majority of studies have been confined to business schools in Western countries. By comparison, much less research is available on MBA programmes in developing countries, particularly those in Africa. In an effort to address this gap, this article examines MBA programmes in South Africa by first situating them within the global MBA curriculum debate. It then notes the need to move away from a generalist MBA programme to a specialized MBA in line with emerging global trends. Finally, it suggests a multidisciplinary approach to the redesign of the MBA curriculum
Quantum tunneling of superconducting string currents
We investigate the decay of current on a superconducting cosmic string
through quantum tunneling. We construct the instanton describing tunneling in a
simple bosonic string model, and estimate the decay rate. The tunneling rate
vanishes in the limit of a chiral current. This conclusion, which is supported
by a symmetry argument, is expected to apply in general. It has important
implications for the stability of chiral vortons.Comment: 16 pages, 2 figure
Dependent Types for Pragmatics
This paper proposes the use of dependent types for pragmatic phenomena such
as pronoun binding and presupposition resolution as a type-theoretic
alternative to formalisms such as Discourse Representation Theory and Dynamic
Semantics.Comment: This version updates the paper for publication in LEU
Artenreiches Rauhfutter als Alleinfutter und Fettsäurenmuster der Milch
In two experiments it was investigated which factors to what extent determine the fatty acid composition milk when cows are grazing high alpine pastures. The influences of altitude per se, of alpine forage quality, of concentrate-free diet type and of the overall grazing effect were separated by the experimental design. The most important factor which significantly elevated the concentrations of CLA, α-linolenic acid (ALA) and n-3 PUFA in milk fat was found to be the alpine diet type, i.e. the feeding of roughage-only (as well hay as pasture of as well lowland as alpine origin) with omission of concentrates and maize. Additionally a clear positive effect of the forage quality of alpine pastures on ALA concentration in milk fat was found. The latter effect is assumed to be linked to specific plant ingredients (eg. tannins) and to the low energy density of the alpine flora, which may influence the ruminal biohydrogenation of native ALA. An effect of altitude per se (hypoxia) was not found
Accessing transversity with interference fragmentation functions
We discuss in detail the option to access the transversity distribution
function by utilizing the analyzing power of interference
fragmentation functions in two-pion production inside the same current jet. The
transverse polarization of the fragmenting quark is related to the transverse
component of the relative momentum of the hadron pair via a new azimuthal
angle. As a specific example, we spell out thoroughly the way to extract
from a measured single spin asymmetry in two-pion inclusive
lepton-nucleon scattering. To estimate the sizes of observable effects we
employ a spectator model for the fragmentation functions. The resulting
asymmetry of our example is discussed as arising in different scenarios for the
transversity.Comment: 17 pages, 15 figures in .eps format included, typesetted in RevTeX
and epsfig.sty, submitted to Phys. Rev.
Bacillus subtilis vegetative isolate surviving chlorine dioxide exposure: an elusive mechanism of resistance
Aims
Oxidizing agents such as chlorine dioxide are widely used microbicides, including for disinfection of medical equipment. We isolated a Bacillus subtilis isolate from a washer-disinfector whose vegetative form demonstrated unique resistance to chlorine dioxide (0·03%) and hydrogen peroxide (7·5%). The aim of this study was to understand the mechanisms of resistance expressed by this isolate.
Methods and Results
A range of resistance mechanisms were investigated in the B. subtilis isolate and a reference B. subtilis strain (ATCC 6051) to include bacterial cell aggregation, the presence of profuse exopolysaccharide (EPS), and the expression of detoxification enzymes. The basis of resistance of the isolate to high concentrations of oxidizing agents was not linked to the presence of endospores. Although, the presence of EPS, aggregation and expression of detoxification enzymes may play a role in bacterial survival to low concentrations of chlorine dioxide, it is unlikely that the mechanisms helped tested to survive the bactericidal effect of higher oxidizer concentrations.
Conclusions
Overall, the mechanisms conferring resistance to chlorine dioxide and hydrogen peroxide remains elusive. Based on recent advances in the mode of action of oxidizing agents and notably hydrogen peroxide, we postulate that additional efficient intracellular mechanisms may be involved to explain significant resistance to in-use concentrations of commonly used high-level disinfectants
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