1,801 research outputs found
Complex Line Bundles over Simplicial Complexes and their Applications
Discrete vector bundles are important in Physics and recently found
remarkable applications in Computer Graphics. This article approaches discrete
bundles from the viewpoint of Discrete Differential Geometry, including a
complete classification of discrete vector bundles over finite simplicial
complexes. In particular, we obtain a discrete analogue of a theorem of Andr\'e
Weil on the classification of hermitian line bundles. Moreover, we associate to
each discrete hermitian line bundle with curvature a unique piecewise-smooth
hermitian line bundle of piecewise constant curvature. This is then used to
define a discrete Dirichlet energy which generalizes the well-known cotangent
Laplace operator to discrete hermitian line bundles over Euclidean simplicial
manifolds of arbitrary dimension
A Note on the Equality of Algebraic and Geometric D-Brane Charges in WZW Models
The algebraic definition of charges for symmetry-preserving D-branes in
Wess-Zumino-Witten models is shown to coincide with the geometric definition,
for all simple Lie groups. The charge group for such branes is computed from
the ambiguities inherent in the geometric definition.Comment: 12 pages, fixed typos, added references and a couple of remark
Romantic Partnerships and the Dispersion of Social Ties: A Network Analysis of Relationship Status on Facebook
A crucial task in the analysis of on-line social-networking systems is to
identify important people --- those linked by strong social ties --- within an
individual's network neighborhood. Here we investigate this question for a
particular category of strong ties, those involving spouses or romantic
partners. We organize our analysis around a basic question: given all the
connections among a person's friends, can you recognize his or her romantic
partner from the network structure alone? Using data from a large sample of
Facebook users, we find that this task can be accomplished with high accuracy,
but doing so requires the development of a new measure of tie strength that we
term `dispersion' --- the extent to which two people's mutual friends are not
themselves well-connected. The results offer methods for identifying types of
structurally significant people in on-line applications, and suggest a
potential expansion of existing theories of tie strength.Comment: Proc. 17th ACM Conference on Computer Supported Cooperative Work and
Social Computing (CSCW), 201
Physical States at the Tachyonic Vacuum of Open String Field Theory
We illustrate a method for computing the number of physical states of open
string theory at the stable tachyonic vacuum in level truncation approximation.
The method is based on the analysis of the gauge-fixed open string field theory
quadratic action that includes Fadeev-Popov ghost string fields. Computations
up to level 9 in the scalar sector are consistent with Sen's conjecture about
the absence of physical open string states at the tachyonic vacuum. We also
derive a long exact cohomology sequence that relates relative and absolute
cohomologies of the BRS operator at the non-perturbative vacuum. We use this
exact result in conjunction with our numerical findings to conclude that the
higher ghost number non-perturbative BRS cohomologies are non-empty.Comment: 43 pages, 16 eps figures, LaTe
RationalMaps, a package for Macaulay2
This paper describes the RationalMaps package for Macaulay2. This package
provides functionality for computing several aspects of rational maps such as
whether a map is birational, or a closed embedding.Comment: 8 pages. The current version of the package (and other necessary
files) can be accessed at
https://github.com/Macaulay2/Workshop-2016-Utah/tree/master/RationalMap
Chern-Simons Theory on S^1-Bundles: Abelianisation and q-deformed Yang-Mills Theory
We study Chern-Simons theory on 3-manifolds that are circle-bundles over
2-dimensional surfaces and show that the method of Abelianisation,
previously employed for trivial bundles , can be adapted to
this case. This reduces the non-Abelian theory on to a 2-dimensional
Abelian theory on which we identify with q-deformed Yang-Mills theory,
as anticipated by Vafa et al. We compare and contrast our results with those
obtained by Beasley and Witten using the method of non-Abelian localisation,
and determine the surgery and framing presecription implicit in this path
integral evaluation. We also comment on the extension of these methods to BF
theory and other generalisations.Comment: 37 pages; v2: references adde
Formation of Episodic Magnetically Driven Radiatively Cooled Plasma Jets in the Laboratory
We report on experiments in which magnetically driven radiatively cooled
plasma jets were produced by a 1 MA, 250 ns current pulse on the MAGPIE pulsed
power facility. The jets were driven by the pressure of a toroidal magnetic
field in a ''magnetic tower'' jet configuration. This scenario is characterized
by the formation of a magnetically collimated plasma jet on the axis of a
magnetic ''bubble'', confined by the ambient medium. The use of a radial
metallic foil instead of the radial wire arrays employed in our previous work
allows for the generation of episodic magnetic tower outflows which emerge
periodically on timescales of ~30 ns. The subsequent magnetic bubbles propagate
with velocities reaching ~300 km/s and interact with previous eruptions leading
to the formation of shocks.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics & Space
Scienc
Constraints on Low-Dimensional String Compactifications
We study the restrictions imposed by cancellation of the tadpoles for two,
three, and four-form gauge fields in string theory, M-theory and F-theory
compactified to two, three and four dimensions, respectively. For a large class
of supersymmetric vacua, turning on a sufficient number of strings, membranes
and three-branes, respectively, can cancel the tadpoles, and preserve
supersymmetry. However, there are cases where the tadpole cannot be removed in
this way, either because the tadpole is fractional, or because of its sign. For
M-theory and F-theory compactifications, we also explore the relation of the
membranes and three-branes to the nonperturbative space-time superpotential.Comment: 16 pages, harvma
Vascular Endothelial Growth Factor and Kinase Domain Region Receptor Are Involved in Both Seminiferous Cord Formation and Vascular Development During Testis Morphogenesis in the Rat
Morphological male sex determination is dependent on migration of endothelial and preperitubular cells from the adjacent mesonephros into the developing testis. Our hypothesis is that VEGFA and its receptor KDR are necessary for both testicular cord formation and neovascularization. The Vegfa gene has 8 exons with many splice variants. Vegfa120, Vegfa164, and Vegfa188 mRNA isoforms were detected on Embryonic Day (E) 13.5 (plug date = E0) in the rat. Vegfa120, Vegfa144, Vegfa164, Vegfa188, and Vegfa205 mRNA were detected at E18 and Postnatal Day 3 (P3). Kdr mRNA was present on E13.5, whereas Fms-like tyrosine kinase 1 receptor (Flt1) mRNA was not detected until E18. VEGFA protein was localized to Sertoli cells at cord formation and KDR to germ and interstitial cells. The VEGFA signaling inhibitors SU1498 (40 μM) and VEGFR-TKI (8 μM) inhibited cord formation in E13 testis cultures with 90% reduced vascular density (P \u3c 0.01) in VEGFR-TKI-treated organs. Furthermore, Je-11 (10 μM), an antagonist to VEGFA, also perturbed cord formation and inhibited vascular density by more than 50% (P \u3c 0.01). To determine signal transduction pathways involved in VEGFA’s regulation of testis morphogenesis, E13 testis were treated with LY 294002 (15 μM), a phosphoinositide 3-kinase (PI3K) pathway inhibitor, resulting in inhibition of both vascular density (46%) and cord formation. Thus, we support our hypothesis and conclude that VEGFA, secreted by the Sertoli cell, is involved in both neovascularization and cord formation and potentially acts through the PI3K pathway during testis morphogenesis to elicit its effects
Vascular Endothelial Growth Factor and Kinase Domain Region Receptor Are Involved in Both Seminiferous Cord Formation and Vascular Development During Testis Morphogenesis in the Rat
Morphological male sex determination is dependent on migration of endothelial and preperitubular cells from the adjacent mesonephros into the developing testis. Our hypothesis is that VEGFA and its receptor KDR are necessary for both testicular cord formation and neovascularization. The Vegfa gene has 8 exons with many splice variants. Vegfa120, Vegfa164, and Vegfa188 mRNA isoforms were detected on Embryonic Day (E) 13.5 (plug date = E0) in the rat. Vegfa120, Vegfa144, Vegfa164, Vegfa188, and Vegfa205 mRNA were detected at E18 and Postnatal Day 3 (P3). Kdr mRNA was present on E13.5, whereas Fms-like tyrosine kinase 1 receptor (Flt1) mRNA was not detected until E18. VEGFA protein was localized to Sertoli cells at cord formation and KDR to germ and interstitial cells. The VEGFA signaling inhibitors SU1498 (40 μM) and VEGFR-TKI (8 μM) inhibited cord formation in E13 testis cultures with 90% reduced vascular density (P \u3c 0.01) in VEGFR-TKI-treated organs. Furthermore, Je-11 (10 μM), an antagonist to VEGFA, also perturbed cord formation and inhibited vascular density by more than 50% (P \u3c 0.01). To determine signal transduction pathways involved in VEGFA’s regulation of testis morphogenesis, E13 testis were treated with LY 294002 (15 μM), a phosphoinositide 3-kinase (PI3K) pathway inhibitor, resulting in inhibition of both vascular density (46%) and cord formation. Thus, we support our hypothesis and conclude that VEGFA, secreted by the Sertoli cell, is involved in both neovascularization and cord formation and potentially acts through the PI3K pathway during testis morphogenesis to elicit its effects
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