351 research outputs found
Dehydration-induced tps gene transcripts from an anhydrobiotic nematode contain novel spliced leaders and encode atypical GT-20 family proteins
Accumulation of the non-reducing disaccharide trehalose is associated with desiccation tolerance during anhydrobiosis in a number of invertebrates, but there is little information on trehalose biosynthetic genes in these organisms.We have identified two trehalose-6-phosphate
synthase (tps) genes in the anhydrobiotic nematode Aphelenchus avenae and determined full length cDNA sequences for both; for comparison, full length tps cDNAs from the model nematode, Caenorhabditis elegans, have also been obtained. The A. avenae genes encode very
similar proteins containing the catalytic domain characteristic of the GT-20 family of glycosyltransferases and are most similar to tps-2 of C. elegans; no evidence was found for a gene in A. avenae corresponding to Ce-tps-1. Analysis of A. avenae tps cDNAs revealed several
features of interest, including alternative trans-splicing of spliced leader sequences in Aav-tps-1, and four different, novel SL1-related transspliced leaders, which were different to the canonical SL1 sequence found in all other nematodes studied. The latter observation suggests that A. avenae does not comply with the strict evolutionary conservation of SL1 sequences observed in other species. Unusual features were also noted in predicted nematode TPS proteins, which distinguish them from homologues in other higher eukaryotes (plants and insects) and in
micro-organisms. Phylogenetic analysis confirmed their membership of the GT-20 glycosyltransferase family, but indicated an accelerated rate of molecular evolution. Furthermore, nematode TPS proteins possess N- and C-terminal domains, which are unrelated to those of other
eukaryotes: nematode C-terminal domains, for example, do not contain trehalose-6-phosphate phosphatase-like sequences, as seen in plant and insect homologues. During onset of anhydrobiosis, both tps genes in A. avenae are upregulated, but exposure to cold or increased osmolarity
also results in gene induction, although to a lesser extent. Trehalose seems likely therefore to play a role in a number of stress responses in nematodes
Nonperturbative ghost dynamics in the maximal Abelian gauge
We construct the effective potential for the ghost condensate
in the maximal Abelian gauge. This condensate is an
order parameter for a global continuous symmetry, which is spontaneously broken
since a nonvanishing value of lowers the vacuum energy.
The associated Goldstone mode turns out to be unphysical.Comment: 16 pages. v2: version accepted for publication in JHE
The validity and reliability of the exposure index as a metric for estimating the radiation dose to the patient
Introduction
With the introduction of digital radiography, the feedback between image quality and over-exposure has been partly lost which in some cases has led to a steady increase in dose. Over the years the introduction of exposure index (EI) has been used to resolve this phenomenon referred to as âdose creepâ. Even though EI is often vendor specific it is always a related of the radiation exposure to the detector. Due to the nature of this relationship EI can also be used as a patient dose indicator, however this is not widely investigated in literature.
Methods
A total of 420 dose-area-product (DAP) and EI measurements were taken whilst varying kVp, mAs and body habitus on two different anthropomorphic phantoms (pelvis and chest). Using linear regression, the correlation between EI and DAP were examined. Additionally, two separate region of interest (ROI) placements/per phantom where examined in order to research any effect on EI.
Results
When dividing the data into subsets, a strong correlation between EI and DAP was shown with all R-squared values > 0.987. Comparison between the ROI placements showed a significant difference between EIs for both placements.
Conclusion
This research shows a clear relationship between EI and radiation dose which is dependent on a wide variety of factors such as ROI placement, body habitus. In addition, pathology and manufacturer specific EIâs are likely to be of influence as well.
Implications for practice
The combination of DAP and EI might be used as a patient dose indicator. However, the influencing factors as mentioned in the conclusion should be considered and examined before implementation
One loop renormalization of the non-local gauge invariant operator min_U (A^U_mu)^2 in QCD
We compute the one loop anomalous dimension of the gauge invariant dimension
two operator min_U (A^U_mu)^2, where U is an element of the gauge group, by
exploiting Zwanziger's expansion of the operator in terms of gauge invariant
non-local n leg operators. The computation is performed in an arbitrary linear
covariant gauge and the cancellation of the gauge parameter in the final
anomalous dimension is demonstrated explicitly. The result is equivalent to the
one loop anomalous dimension of the local dimension two operator (A^a_mu)^2 in
the Landau gauge.Comment: 8 latex page
Renormalizability of the local composite operator A^2 in linear covariant gauges
The local composite operator is analysed within the algebraic
renormalization in Yang-Mills theories in linear covariant gauges. We establish
that it is multiplicatively renormalizable to all orders of perturbation
theory. Its anomalous dimension is computed to two-loops in the MSbar scheme.Comment: 10 pages, LaTeX, final version to appear in Phys. Lett.
Dimension two gluon condensates in a variety of gauges and a gauge invariant Yang-Mills action with a mass
We give a short overview of our work concerning the dimension two operator
A^2 in the Landau gauge and its generalizations to other gauges. We conclude by
discussing recent work that leads to a renormalizable gauge invariant action
containing a mass parameter, based on the operator F 1/D^2 F.Comment: 4 pages. espcrc2.sty is used. Talk given at "13th International
Conference In QCD (QCD 06), 3-7 Jul 2006, Montpellier, France
Functional and molecular analysis of proprioceptive sensory neuron excitability in mice
Neurons located in dorsal root ganglia (DRG) are crucial for transmitting peripheral sensations such as proprioception, touch, temperature, and nociception to the spinal cord before propagating these signals to higher brain structures. To date, difficulty in identifying modality-specific DRG neurons has limited our ability to study specific populations in detail. As the calcium-binding protein parvalbumin (PV) is a neurochemical marker for proprioceptive DRG cells we used a transgenic mouse line expressing green fluorescent protein (GFP) in PV positive DRGs, to study the functional and molecular properties of putative proprioceptive neurons. Immunolabeled DRGs showed a 100% overlap between GFP positive (GFP+) and PV positive cells, confirming the PVeGFP mouse accurately labeled PV neurons. Targeted patch-clamp recording from isolated GFP+ and GFP negative (GFPâ) neurons showed the passive membrane properties of the two groups were similar, however, their active properties differed markedly. All GFP+ neurons fired a single spike in response to sustained current injection and their action potentials (APs) had faster rise times, lower thresholds and shorter half widths. A hyperpolarization-activated current (Ih) was observed in all GFP+ neurons but was infrequently noted in the GFPâ population (100% vs. 11%). For GFP+ neurons, Ih activation rates varied markedly, suggesting differences in the underlying hyperpolarization-activated cyclic nucleotide-gated channel (HCN) subunit expression responsible for the current kinetics. Furthermore, quantitative polymerase chain reaction (qPCR) showed the HCN subunits 2, 1, and 4 mRNA (in that order) was more abundant in GFP+ neurons, while HCN 3 was more highly expressed in GFPâ neurons. Likewise, immunolabeling confirmed HCN 1, 2, and 4 protein expression in GFP+ neurons. In summary, certain functional properties of GFP+ and GFPâ cells differ markedly, providing evidence for modality-specific signaling between the two groups. However, the GFP+ DRG population demonstrates considerable internal heterogeneity when hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel) properties and subunit expression are considered. We propose this heterogeneity reflects the existence of different peripheral receptors such as tendon organs, muscle spindles or mechanoreceptors in the putative proprioceptive neuron population
Renormalization properties of the mass operator A^2 in three dimensional Yang-Mills theories in the Landau gauge
Massive renormalizable Yang-Mills theories in three dimensions are analysed
within the algebraic renormalization in the Landau gauge. In analogy with the
four dimensional case, the renormalization of the mass operator A^2 turns out
to be expressed in terms of the fields and coupling constant renormalization
factors. We verify the relation we obtain for the operator anomalous dimension
by explicit calculations in the large N_f. The generalization to other gauges
such as the nonlinear Curci-Ferrari gauge is briefly outlined.Comment: 15 pages, 3 figure
One loop MSbar gluon pole mass from the LCO formalism
We compute the one loop corrections to the pole mass of the gluon in the
MSbar scheme in the Landau gauge in both the Curci-Ferrari model and the local
composite operator formalism with Nf flavours of massless quarks. For the
latter we determine an estimate for the gluon mass using the effective
potential of a local dimension two composite operator and find, for example,
m_{gluon} = 2.10 Lambda_MSbar in Yang-Mills theory.Comment: 7 latex page
A determination of <A^2> and the non-perturbative vacuum energy of Yang-Mills theory in the Landau gauge
We discuss the 2-point-particle-irreducible (2PPI) expansion, which sums
bubble graphs to all orders, in the context of SU(N) Yang-Mills theory in the
Landau gauge. Using the method we investigate the possible existence of a gluon
condensate of mass dimension two, , and the corresponding non-zero vacuum
energy. This condensate gives rise to a dynamically generated mass for the
gluon.Comment: 12 pages, 3 eps figures; v2 : wrong use of "enhancement" instead of
"suppression" corrected; v3: version accepted for publication in Phys.Lett.
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