3,327 research outputs found
Giving and Receiving Peer Advice in an Online Breast Cancer Support Group
People have access to experiential information and advice about health online. The types of advice exchanged affect the nature of online communities and potentially patient decision making. The aim of this study was to examine the ways in which peers exchange advice within an online health forum in order to better understand online groups as a resource for decision making. Messages collected over a one-month period from an online breast cancer support forum were analyzed for examples of advice exchange. The majority of the messages solicited advice through problem disclosure or requests for information and opinion. A novel form of advice solicitationââanyone in the same boat as meââwas noted as was the use of personal experience as a form of advice giving. Women construct their advice requests to target like-minded people. The implications in terms of decision making and support are discussed
Holomorphic Anomaly in Gauge Theories and Matrix Models
We use the holomorphic anomaly equation to solve the gravitational
corrections to Seiberg-Witten theory and a two-cut matrix model, which is
related by the Dijkgraaf-Vafa conjecture to the topological B-model on a local
Calabi-Yau manifold. In both cases we construct propagators that give a
recursive solution in the genus modulo a holomorphic ambiguity. In the case of
Seiberg-Witten theory the gravitational corrections can be expressed in closed
form as quasimodular functions of Gamma(2). In the matrix model we fix the
holomorphic ambiguity up to genus two. The latter result establishes the
Dijkgraaf-Vafa conjecture at that genus and yields a new method for solving the
matrix model at fixed genus in closed form in terms of generalized
hypergeometric functions.Comment: 34 pages, 2 eps figures, expansion at the monopole point corrected
and interpreted, and references adde
Scaling in the structure of directory trees in a computer cluster
We describe the topological structure and the underlying organization
principles of the directories created by users of a computer cluster when
storing his/her own files. We analyze degree distributions, average distance
between files, distribution of communities and allometric scaling exponents of
the directory trees. We find that users create trees with a broad, scale-free
degree distribution. The structure of the directories is well captured by a
growth model with a single parameter. The degree distribution of the different
trees has a non-universal exponent associated with different values of the
parameter of the model. However, the distribution of community sizes has a
universal exponent analytically obtained from our model.Comment: refined data analysis and modeling, completely reorganized version, 4
pages, 2 figure
MQCD, ('Barely') G_2 Manifolds and (Orientifold of) a Compact Calabi-Yau
We begin with a discussion on two apparently disconnected topics - one
related to nonperturbative superpotential generated from wrapping an M2-brane
around a supersymmetric three cycle embedded in a G_2-manifold evaluated by the
path-integral inside a path-integral approach of [1], and the other centered
around the compact Calabi-Yau CY_3(3,243) expressed as a blow-up of a degree-24
Fermat hypersurface in WCP^4[1,1,2,8,12]. For the former, we compare the
results with the ones of Witten on heterotic world-sheet instantons [2]. The
subtopics covered in the latter include an N=1 triality between Heterotic, M-
and F-theories, evaluation of RP^2-instanton superpotential, Picard-Fuchs
equation for the mirror Landau-Ginsburg model corresponding to CY_3(3,243),
D=11 supergravity corresponding to M-theory compactified on a `barely' G_2
manifold involving CY_3(3,243) and a conjecture related to the action of
antiholomorphic involution on period integrals. We then show an indirect
connection between the two topics by showing a connection between each one of
the two and Witten's MQCD [3]. As an aside, we show that in the limit of
vanishing "\zeta", a complex constant that appears in the Riemann surfaces
relevant to definining the boundary conditions for the domain wall in MQCD, the
infinite series of [4] used to represent a suitable embedding of a
supersymmetric 3-cycle in a G_2-mannifold, can be summed.Comment: 37 pages, LaTex; PARTLY based on talks given at ``Seventh Workshop on
QCD" [session on "Strings, Branes and (De-)Construction"], Jan 6-10, 2003, La
Cittadelle, Villefranche-sur-Mer, France; Fourth Workshop on ``Gauge Fields
and Strings", Feb 25-Mar 1, 2003, Jena, Germany; ``XII Oporto Meeting on
Geometry, Topology and Strings", July 17-20, 2003, Oporto, Portugal; "SQS03"
- International Workshop on "Supersymmetries and Quantum Symmetries', July
24-29, 2003, JINR, Dubna, Russia; poster presented at ``XIV International
Congress on Mathematical Physics", July 28-Aug 2, 2003, Lisbon, Portuga
Possible indicators for low dimensional superconductivity in the quasi-1D carbide Sc3CoC4
The transition metal carbide Sc3CoC4 consists of a quasi-one-dimensional (1D)
structure with [CoC4]_{\inft} polyanionic chains embedded in a scandium
matrix. At ambient temperatures Sc3CoC4 displays metallic behavior. At lower
temperatures, however, charge density wave formation has been observed around
143K which is followed by a structural phase transition at 72K. Below T^onset_c
= 4.5K the polycrystalline sample becomes superconductive. From Hc1(0) and
Hc2(0) values we could estimate the London penetration depth ({\lambda}_L ~=
9750 Angstroem) and the Ginsburg-Landau (GL) coherence length ({\xi}_GL ~= 187
Angstroem). The resulting GL-parameter ({\kappa} ~= 52) classifies Sc3CoC4 as a
type II superconductor. Here we compare the puzzling superconducting features
of Sc3CoC4, such as the unusual temperature dependence i) of the specific heat
anomaly and ii) of the upper critical field H_c2(T) at T_c, and iii) the
magnetic hysteresis curve, with various related low dimensional
superconductors: e.g., the quasi-1D superconductor (SN)_x or the 2D
transition-metal dichalcogenides. Our results identify Sc3CoC4 as a new
candidate for a quasi-1D superconductor.Comment: 4 pages, 5 figure
On Semi-Periods
The periods of the three-form on a Calabi-Yau manifold are found as solutions
of the Picard-Fuchs equations; however, the toric varietal method leads to a
generalized hypergeometric system of equations which has more solutions than
just the periods. This same extended set of equations can be derived from
symmetry considerations. Semi-periods are solutions of this extended system.
They are obtained by integration of the three-form over chains; these chains
can be used to construct cycles which, when integrated over, give periods. In
simple examples we are able to obtain the complete set of solutions for the
extended system. We also conjecture that a certain modification of the method
will generate the full space of solutions in general.Comment: 18 pages, plain TeX. Revised derivation of system of
equations; version to appear in Nuclear Physics
Noether-Lefschetz theory and the Yau-Zaslow conjecture
The Yau-Zaslow conjecture determines the reduced genus 0 Gromov-Witten
invariants of K3 surfaces in terms of the Dedekind eta function. Classical
intersections of curves in the moduli of K3 surfaces with Noether-Lefschetz
divisors are related to 3-fold Gromov-Witten theory via the K3 invariants.
Results by Borcherds and Kudla-Millson determine the classical intersections in
terms of vector-valued modular forms. Proven mirror transformations can often
be used to calculate the 3-fold invariants which arise.
Via a detailed study of the STU model (determining special curves in the
moduli of K3 surfaces), we prove the Yau-Zaslow conjecture for all curve
classes on K3 surfaces. Two modular form identities are required. The first,
the Klemm-Lerche-Mayr identity relating hypergeometric series to modular forms
after mirror transformation, is proven here. The second, the Harvey-Moore
identity, is proven by D. Zagier and presented in the paper.Comment: 40 page
The Vacuum Structure and Spectrum of N=2 Supersymmetric SU(N) Gauge Theory
We present an exact description of the metric on the moduli space of vacua
and the spectrum of massive states for four dimensional N=2 supersymmetric
SU(n) gauge theories. The moduli space of quantum vacua is identified with the
moduli space of a special set of genus n-1 hyperelliptic Riemann surfaces.Comment: 11 pages, Revtex, 2 figures. Reference adde
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