2,650 research outputs found
The W_N minimal model classification
We first rigourously establish, for any N, that the toroidal modular
invariant partition functions for the (not necessarily unitary) W_N(p,q)
minimal models biject onto a well-defined subset of those of the SU(N)xSU(N)
Wess-Zumino-Witten theories at level (p-N,q-N). This permits considerable
simplifications to the proof of the Cappelli-Itzykson-Zuber classification of
Virasoro minimal models. More important, we obtain from this the complete
classification of all modular invariants for the W_3(p,q) minimal models. All
should be realised by rational conformal field theories. Previously, only those
for the unitary models, i.e. W_3(p,p+1), were classified. For all N our
correspondence yields for free an extensive list of W_N(p,q) modular
invariants. The W_3 modular invariants, like the Virasoro minimal models, all
factorise into SU(3) modular invariants, but this fails in general for larger
N. We also classify the SU(3)xSU(3) modular invariants, and find there a new
infinite series of exceptionals.Comment: 25 page
Spectral emissivity of metals after damage by particle impact
The reflectance, R, solar absorption, alpha, thermal emittance epsilon, and the alpha/epsilon ratio were determined for several metals before and after bombardment by high velocity microprojectiles. Observed decreases of 1 to 26 percent in the reflectance of various metals were apparently dependent on the amount of surface area damaged as well as on the velocity of the impinging projectiles. The thermal emittance was observed to increase more than the solar absorptance, which resulted in a net decrease in the alpha/epsilon ratio in all metals investigated except stainless steel 304. In the case of stainless steel 304, alpha and epsilon were observed to increase equally, resulting in an alpha/epsilon ratio apparently insensitive to microprojectile bombardment. Recommendations for the continuation of these investigations are outlined
Political risk in light rail transit PPP projects
Since 2003 public-private partnerships (PPPs) have
represented between 10 and 13.5% of the total investment
in public services in the UK. The macro-economic and
political benefits of PPPs were among the key drivers for
central government's decision to promote this form of
procurement to improve UK public services. Political
support for a PPP project is critical and is frequently cited as the most important critical success factor. This paper investigates the significance of political support and reviews the treatment of political risk in a business case by the public sector project sponsor for major UK-based light rail transit PPP projects during their development stage. The investigation demonstrates that in the early project stages it is not traditional quantitative Monte Carlo risk analysis that is important; rather it is the identification and representation of political support within a business case together with an understanding of how this information is then used to inform critical project decisions
Charges of Exceptionally Twisted Branes
The charges of the exceptionally twisted (D4 with triality and E6 with charge
conjugation) D-branes of WZW models are determined from the microscopic/CFT
point of view. The branes are labeled by twisted representations of the affine
algebra, and their charge is determined to be the ground state multiplicity of
the twisted representation. It is explicitly shown using Lie theory that the
charge groups of these twisted branes are the same as those of the untwisted
ones, confirming the macroscopic K-theoretic calculation. A key ingredient in
our proof is that, surprisingly, the G2 and F4 Weyl dimensions see the simple
currents of A2 and D4, respectively.Comment: 19 pages, 2 figures, LaTex2e, complete proofs of all statements,
updated bibliograph
FEDERAL TORT CLAIMS ACT—SEEKING REDRESS AGAINST THE SOVEREIGN; BALANCING THE RIGHTS OF PLAINTIFFS AND THE GOVERNMENT WHEN APPLYING FEDERAL RULE OF CIVIL PROCEDURE 15(c) TO FTCA CLAIMS
Mdm2-p53 Signaling in Tissue Homeostasis and the DNA Damage Response: A Dissertation
The p53 transcription factor responds to various cellular stressors by regulating the expression of numerous target genes involved in cellular processes such as cell cycle arrest, apoptosis, and senescence. As these downstream pathways are harmful to the growth and development of normal cells when prolonged or deregulated, p53 activity needs to be under tight regulatory control. The Mdm2 oncoprotein is the chief negative regulator of p53, and many mouse models have demonstrated that absence of Mdm2 expression leads to constitutive p53 activation in a variety of cell types. While unregulated p53 can be deleterious to cells, functional p53 is essential for tumor suppression, as many human cancers harbor p53 mutations and p53 knockout mice rapidly develop spontaneous tumors. Therefore, the mechanisms that control p53 regulation by Mdm2 are critical to ensure p53 activity in the appropriate cellular context.
Many genetically engineered mouse models have been created to analyze p53 and Mdm2 functions and these studies have yielded valuable insights into their physiological roles. This dissertation will describe the generation and characterization of novel mutant Mdm2 mouse models and their use to interrogate the roles of p53-Mdm2 signaling in tissue homeostasis and cell stress responses. Deletion of Mdm2 in epidermal progenitor cells of the skin and hair follicles resulted in progressive hair loss and decreased skin integrity, phenotypes that are characteristic of premature aging. Furthermore, p53 protein levels, p53 target gene expression, and cellular senescence were all upregulated in the skins of these mice, and epidermal stem cell numbers and function were diminished. These results indicate that Mdm2 is necessary to limit p53 activity in adult tissues to ensure normal stem cell function.
Additional mouse models used to determine the role of Mdm2 phosphorylation will also be presented. DNA damage triggers an extensive cellular response, including activation of the ATM kinase. ATM activity is necessary for p53 protein stabilization and, therefore, p53 activation, but in vivo evidence suggests that phosphorylation of p53 itself had little effect on p53 stability. ATM was previously shown to phosphorylate MDM2 at serine residue 395 (394 in mice), and we generated knock-in mutant mouse models to study the role of this posttranslational modification in vivo. Absence of this phosphorylation site led to greatly diminished p53 stability and function in response to γ-irradiation and increased spontaneous tumorigenesis in mice. Conversely, a phosphomimic model demonstrated prolonged p53 activation in cells treated with γ-irradiation, which revealed that phosphorylation of this Mdm2 residue controls the duration of the DNA damage response. Therefore, these mouse models have uncovered new roles for the p53-Mdm2 regulatory axis in vivo and will be useful reagents in future studies of posttranslational modifications in oncogene and DNA damage-induced tumorigenesis
Can a Lattice String Have a Vanishing Cosmological Constant?
We prove that a class of one-loop partition functions found by Dienes, giving
rise to a vanishing cosmological constant to one-loop, cannot be realized by a
consistent lattice string. The construction of non-supersymmetric string with a
vanishing cosmological constant therefore remains as elusive as ever. We also
discuss a new test that any one-loop partition function for a lattice string
must satisfy.Comment: 14 page
Nucleation Induced Undulative Instability in Thin Films of nCB Liquid Crystals
A surface instability is reported in thin nematic films of 5CB and 8CB,
occurring near the nematic--isotropic phase transition.
Although this instability leads to patterns reminiscent of spinodal
dewetting, we show that it is actually based on a nucleation mechanism. Its
characteristic wavelength does not depend markedly on film thickness, but
strongly on the heating rate.Comment: 4 pages, 5 figure
Symmetries of the Kac-Peterson Modular Matrices of Affine Algebras
The characters of nontwisted affine algebras at fixed level define
in a natural way a representation of the modular group . The
matrices in the image are called the Kac-Peterson modular
matrices, and describe the modular behaviour of the characters. In this paper
we consider all levels of , and for
each of these find all permutations of the highest weights which commute with
the corresponding Kac-Peterson matrices. This problem is equivalent to the
classification of automorphism invariants of conformal field theories, and its
solution, especially considering its simplicity, is a major step toward the
classification of all Wess-Zumino-Witten conformal field theories.Comment: 16 pp, plain te
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