1,995 research outputs found
Nonsupersymmetric Brane/Antibrane Configurations in Type IIA and M Theory
We study metastable nonsupersymmetric configurations in type IIA string
theory, obtained by suspending D4-branes and anti-D4-branes between
holomorphically curved NS5's, which are related to those of hep-th/0610249 by
T-duality. When the numbers of branes and antibranes are the same, we are able
to obtain an exact M theory lift which can be used to reliably describe the
vacuum configuration as a curved NS5 with dissolved RR flux for g_s<<1 and as a
curved M5 for g_s>>1. When our weakly coupled description is reliable, it is
related by T-duality to the deformed IIB geometry with flux of hep-th/0610249
with moduli exactly minimizing the potential derived therein using special
geometry. Moreover, we can use a direct analysis of the action to argue that
this agreement must also hold for the more general brane/antibrane
configurations of hep-th/0610249. On the other hand, when our strongly coupled
description is reliable, the M5 wraps a nonholomorphic minimal area curve that
can exhibit quite different properties, suggesting that the residual structure
remaining after spontaneous breaking of supersymmetry at tree level can be
further broken by the effects of string interactions. Finally, we discuss the
boundary condition issues raised in hep-th/0608157 for nonsupersymmetric IIA
configurations, their implications for our setup, and their realization on the
type IIB side.Comment: 84 pages (57 pages + 4 appendices), 18 figure
Engineering simulations for cancer systems biology
Computer simulation can be used to inform in vivo and in vitro experimentation, enabling rapid, low-cost hypothesis generation and directing experimental design in order to test those hypotheses. In this way, in silico models become a scientific instrument for investigation, and so should be developed to high standards, be carefully calibrated and their findings presented in such that they may be reproduced. Here, we outline a framework that supports developing simulations as scientific instruments, and we select cancer systems biology as an exemplar domain, with a particular focus on cellular signalling models. We consider the challenges of lack of data, incomplete knowledge and modelling in the context of a rapidly changing knowledge base. Our framework comprises a process to clearly separate scientific and engineering concerns in model and simulation development, and an argumentation approach to documenting models for rigorous way of recording assumptions and knowledge gaps. We propose interactive, dynamic visualisation tools to enable the biological community to interact with cellular signalling models directly for experimental design. There is a mismatch in scale between these cellular models and tissue structures that are affected by tumours, and bridging this gap requires substantial computational resource. We present concurrent programming as a technology to link scales without losing important details through model simplification. We discuss the value of combining this technology, interactive visualisation, argumentation and model separation to support development of multi-scale models that represent biologically plausible cells arranged in biologically plausible structures that model cell behaviour, interactions and response to therapeutic interventions
Does urinary peptide content differ between COPD patients with and without inherited alpha-1 antitrypsin deficiency?
Differentiating between chronic obstructive pulmonary disease (COPD) patients with normal (PiMM) or deficient (PiZZ) genetic variants of alpha-1 antitrypsin (A1AT) is important not only for understanding the pathobiology of disease progression but also for improving personalized therapies. This pilot study aimed to investigate whether urinary peptides reflect the A1AT-related phenotypes of COPD. Urine samples from 19 clinically stable COPD cases (7 PiMM and 12 PiZZ A1AT) were analyzed by capillary electrophoresis coupled to mass spectrometry. We identified 66 peptides (corresponding to 36 unique proteins) that differed between PiZZ and PiMM COPD. Among these, peptides from the collagen family were the most abundant and divergent. A logistic regression model based on COL1A1 or COL5A3 peptides enabled differentiation between PiMM and PiZZ groups, with a sensitivity of 100% and specificity of 85.71% for COL1A1 and a sensitivity of 91.67% and specificity of 85.71% for COL5A3. Furthermore, patients with PiZZ presented low levels of urinary peptides involved in lipoproteins/lipids and retinoic acid metabolism, such as apolipoprotein A-I and C4, retinol-binding protein 4 and prostaglandin-H2 d-isomerase. However, peptides of MDS1 and EVII complex locus, gelsolin and hemoglobin alpha were found in the urine of COPD cases with PiZZ, but not with PiMM. These capillary electrophoresis coupled to mass spectrometry-based results provide the first evidence that urinary peptide content differs between PiMM and PiZZ patients with COPD
Emergence and Correspondence for String Theory Black Holes
This is one of a pair of papers that give a
historical-\emph{cum}-philosophical analysis of the endeavour to understand
black hole entropy as a statistical mechanical entropy obtained by counting
string-theoretic microstates. Both papers focus on Andrew Strominger and Cumrun
Vafa's ground-breaking 1996 calculation, which analysed the black hole in terms
of D-branes. The first paper gives a conceptual analysis of the Strominger-Vafa
argument, and of several research efforts that it engendered. In this paper, we
assess whether the black hole should be considered as emergent from the D-brane
system, particularly in light of the role that duality plays in the argument.
We further identify uses of the quantum-to-classical correspondence principle
in string theory discussions of black holes, and compare these to the
heuristics of earlier efforts in theory construction, in particular those of
the old quantum theory.Comment: 40 page
Soft matrix models and Chern-Simons partition functions
We study the properties of matrix models with soft confining potentials.
Their precise mathematical characterization is that their weight function is
not determined by its moments. We mainly rely on simple considerations based on
orthogonal polynomials and the moment problem. In addition, some of these
models are equivalent, by a simple mapping, to matrix models that appear in
Chern-Simons theory. The models can be solved with q deformed orthogonal
polynomials (Stieltjes-Wigert polynomials), and the deformation parameter turns
out to be the usual parameter in Chern-Simons theory. In this way, we give
a matrix model computation of the Chern-Simons partition function on
and show that there are infinitely many matrix models with this partition
function.Comment: 13 pages, 3 figure
Conceptual Analysis of Black Hole Entropy in String Theory
The microscopic state counting of the extremal Reissner-Nordstr\"om black
hole performed by Andrew Strominger and Cumrun Vafa in 1996 has proven to be a
central result in string theory. Here, with a philosophical readership in mind,
the argument is presented in its contemporary context and its rather complex
conceptual structure is analysed. In particular, we will identify the various
inter-theoretic relations, such as duality and linkage relations, on which it
depends. We further aim to make clear why the argument was immediately
recognised as a successful accounting for the entropy of this black hole and
how it engendered subsequent work that intended to strengthen the string
theoretic analysis of black holes. Its relation to the formulation of the
AdS/CFT conjecture will be briefly discussed, and the familiar reinterpretation
of the entropy calculation in the context of the AdS/CFT correspondence is
given. Finally, we discuss the heuristic role that Strominger and Vafa's
microscopic account of black hole entropy played for the black hole information
paradox. A companion paper analyses the ontology of the Strominger-Vafa black
hole states, the question of emergence of the black hole from a collection of
D-branes, and the role of the correspondence principle in the context of string
theory black holes.Comment: 70 page
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