4,161 research outputs found
Singular Vertices and the Triangulation Space of the D-sphere
By a sequence of numerical experiments we demonstrate that generic
triangulations of the sphere for contain one {\it singular}
simplex. The mean number of elementary simplices sharing this
simplex increases with the volume of the triangulation according to a simple
power law. The lower dimension subsimplices associated with this
simplex also show a singular behaviour. Possible consequences for the
DT model of four-dimensional quantum gravity are discussed.Comment: 15 pages, 9 figure
Issues in student training and use of electronic bibliographic databases
In an article in this journal Ottewill and Hudson (1997) raised a number of issues concerning students’ use of electronic bibliographic databases. They emphasized the need for co‐operation between academics and librarians in database training and in coursework where databases would be used. We report a project on students’ use of bibliographic databases. Our findings reveal that access to these databases, whilst solving many of the problems students experience in sourcing reference material for coursework and research, raises new intellectual problems due to the sheer breadth and depth of their coverage of subject matter. Typically database training programmes focus on search skills and the use of different interfaces. However, our findings demonstrate that students should be encouraged to develop a more critical perspective on databases since these can be seductive, time‐consuming and, in certain circumstances, counterproductive resources. Students would benefit from more guidance on the quality cues that academics and librarians employ when evaluating different databases and their contents
N=4 Supersymmetry on a Space-Time Lattice
Maximally supersymmetric Yang--Mills theory in four dimensions can be
formulated on a space-time lattice while exactly preserving a single
supersymmetry. Here we explore in detail this lattice theory, paying particular
attention to its strongly coupled regime. Targeting a theory with gauge group
SU(N), the lattice formulation is naturally described in terms of gauge group
U(N). Although the U(1) degrees of freedom decouple in the continuum limit we
show that these degrees of freedom lead to unwanted lattice artifacts at strong
coupling. We demonstrate that these lattice artifacts can be removed, leaving
behind a lattice formulation based on the SU(N) gauge group with the expected
apparently conformal behavior at both weak and strong coupling
Twisted lattice supersymmetry and applications to AdS/CFT
I review recent approaches to constructing supersymmetric lattice theories
focusing in particular on the concept of topological twisting. The latter
technique is shown to expose a nilpotent, scalar supersymmetry which can be
implemented exactly in the lattice theory. Using these ideas a lattice action
for super Yang-Mills in four dimensions can be written down
which is gauge invariant, free of fermion doublers and respects one out of a
total of 16 continuum supersymmetries. It is shown how these exact symmetries
together with the large point group symmetry of the lattice strongly constrain
the possible counterterms needed to renormalize the theory and hence determine
how much residual fine tuning will be needed to restore all supersymmetries in
the continuum limit. We report on progress to study these renormalization
effects at one loop. We go on to give examples of applications of these
supersymmetric lattice theories to explore the connections between gauge
theories and gravity.Comment: 16 pages. Plenary talk at Lattice 201
Spectrum of orientifold QCD in the strong coupling and hopping expansion approximation
We use the strong coupling and hopping parameter expansions to calculate the
pion and rho meson masses for lattice Yang-Mills gauge theories with fermions
in irreducible two-index representations, namely the adjoint, symmetric and
antisymmetric. The results are found to be consistent with orientifold planar
equivalence, and leading order 1/N corrections are calculated in the lattice
phase. An estimate of the critical bare mass, for which the pion is massless,
is obtained as a function of the bare coupling. A comparison to data from the
two-flavour SU(2) theory with adjoint fermions gives evidence for a bulk phase
transition at beta~2, separating a pure lattice phase from a phase smoothly
connected to the continuum.Comment: 16 page
From Dynamic to Expressionism: An Arts Integration Study
The classroom based study “From Dynamic to Expressionism: An Arts Integration Study” was designed to answer the question; Will implementing an interdisciplinary art and music unit affect the level of student confidence in understanding expressionism in art? The researcher implemented an interdisciplinary art unit in two inner-city second grade classes. Throughout the study a survey was used for students to assess their confidence level and a checklist was used to observe student confidence during class time
Behavioral Comorbidities and Drug Treatments in a Zebrafish scn1lab Model of Dravet Syndrome.
Loss-of-function mutations in SCN1A cause Dravet syndrome (DS), a catastrophic childhood epilepsy in which patients experience comorbid behavioral conditions, including movement disorders, sleep abnormalities, anxiety, and intellectual disability. To study the functional consequences of voltage-gated sodium channel mutations, we use zebrafish with a loss-of-function mutation in scn1lab, a zebrafish homolog of human SCN1A. Homozygous scn1labs552/s552 mutants exhibit early-life seizures, metabolic deficits, and early death. Here, we developed in vivo assays using scn1labs552 mutants between 3 and 6 d postfertilization (dpf). To evaluate sleep disturbances, we monitored larvae for 24 h with locomotion tracking software. Locomotor activity during dark (night phase) was significantly higher in mutants than in controls. Among anticonvulsant drugs, clemizole and diazepam, but not trazodone or valproic acid, decreased distance moved at night for scn1labs552 mutant larvae. To monitor exploratory behavior in an open field, we tracked larvae in a novel arena. Mutant larvae exhibited impaired exploratory behavior, with increased time spent near the edge of the arena and decreased mobility, suggesting greater anxiety. Both clemizole and diazepam, but not trazodone or valproic acid, decreased distance moved and increased time spent in the center of the arena. Counting inhibitory neurons in vivo revealed no differences between scn1labs552 mutants and siblings. Taken together, our results demonstrate conserved features of sleep, anxiety, and movement disorders in scn1lab mutant zebrafish, and provide evidence that a zebrafish model allows effective tests of treatments for behavioral comorbidities associated with DS
Chaperone-mediated native folding of a β-scorpion toxin in the periplasm of E.coli
Background: Animal neurotoxin peptides are valuable probes for investigating ion channel structure/function relationships and represent lead compounds for novel therapeutics and insecticides. However, misfolding and aggregation are common outcomes when toxins containing multiple disulfides are expressed in bacteria.
Methods: The ß-scorpion peptide toxin Bj-xtrIT from Hottentotta judaica and four chaperone enzymes (DsbA, DsbC, SurA and FkpA) were co-secreted into the oxidizing environment of the E.coli periplasm. Expressed Bj-xtrIT was purified and analyzed by HPLC and FPLC chromatography. Its thermostability was assessed using synchrotron radiation circular dichroism spectroscopy and its crystal structure was determined.
Results: Western blot analysis showed that robust expression was only achieved when cells co-expressed the chaperones. The purified samples were homogenous and monodisperse and the protein was thermostable. The crystal structure of the recombinant toxin confirmed that it adopts the native disulfide connectivity and fold.
Conclusions: The chaperones enabled correct folding of the four-disulfide-bridged Bj-xtrIT toxin. There was no apparent sub-population of misfolded Bj-xtrIT, which attests to the effectiveness of this expression method.
General Significance: We report the first example of a disulfide-linked scorpion toxin natively folded during bacterial expression. This method eliminates downstream processing steps such as oxidative refolding or cleavage of a fusion-carrier and therefore enables efficient production of insecticidal Bj-xtrIT. Periplasmic chaperone activity may produce native folding of other extensively disulfide-reticulated proteins including animal neurotoxins. This work is therefore relevant to venomics and studies of a wide range of channels and receptors
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