467 research outputs found
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Zero-Mode Dynamics of String Webs
At sufficiently low energy the dynamics of a string web is dominated by zero
modes involving rigid motion of the internal strings. The dimension of the
associated moduli space equals the maximal number of internal faces in the web.
The generic web moduli space has boundaries and multiple branches, and for webs
with three or more faces the geometry is curved. Webs can also be studied in a
lift to M-theory, where a string web is replaced by a membrane wrapped on a
holomorphic curve in spacetime. In this case the moduli space is complexified
and admits a Kaehler metric.Comment: LaTeX, 17 pages, 5 eps figures; v2: references adde
On spin-1 massive particles coupled to a Chern-Simons field
We study spin one particles interacting through a Chern-Simons field. In the
Born approximation, we calculate the two body scattering amplitude considering
three possible ways to introduce the interaction: (a) a Proca like model
minimally coupled to a Chern-Simons field, (b) the model obtained from (a) by
replacing the Proca's mass by a Chern-Simons term and (c) a complex
Maxwell-Chern-Simons model minimally coupled to a Chern-Simons field. In the
low energy regime the results show similarities with the Aharonov-Bohm
scattering for spin 1/2 particles. We discuss the one loop renormalization
program for the Proca's model. In spite of the bad ultraviolet behavior of the
matter field propagator, we show that, up to one loop the model is power
counting renormalizable thanks to the Ward identities satisfied by the
interaction vertices.Comment: 14 pages, 5 figures, revte
Quivers from Matrix Factorizations
We discuss how matrix factorizations offer a practical method of computing
the quiver and associated superpotential for a hypersurface singularity. This
method also yields explicit geometrical interpretations of D-branes (i.e.,
quiver representations) on a resolution given in terms of Grassmannians. As an
example we analyze some non-toric singularities which are resolved by a single
CP1 but have "length" greater than one. These examples have a much richer
structure than conifolds. A picture is proposed that relates matrix
factorizations in Landau-Ginzburg theories to the way that matrix
factorizations are used in this paper to perform noncommutative resolutions.Comment: 33 pages, (minor changes
Ferromagnetic behavior of ultrathin manganese nanosheets
Ferromagnetic behaviour has been observed experimentally for the first time
in nanostructured Manganese. Ultrathin ( 0.6 nm) Manganese nanosheets
have been synthesized inside the two dimensional channels of sol-gel derived
Na-4 mica. The magnetic properties of the confined system are measured within
2K-300K temperature range. The confined structure is found to show a
ferromagnetic behaviour with a nonzero coercivity value. The coercivity value
remains positive throughout the entire temperature range of measurement. The
experimental variation of susceptibility as a function of temperature has been
satisfactorily explained on the basis of a two dimensional system with a
Heisenberg Hamiltonian involving direct exchange interaction.Comment: 13 pages, 9 figure
Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion
Performing molecular dynamics simulations for all-atom models, we
characterize the conformational and structural relaxations of poly(ethylene
oxide) and poly(propylene oxide) melts. The temperature dependence of these
relaxation processes deviates from an Arrhenius law for both polymers. We
demonstrate that mode-coupling theory captures some aspects of the glassy
slowdown, but it does not enable a complete explanation of the dynamical
behavior. When the temperature is decreased, spatially heterogeneous and
cooperative translational dynamics are found to become more important for the
structural relaxation. Moreover, the transitions between the conformational
states cease to obey Poisson statistics. In particular, we show that, at
sufficiently low temperatures, correlated forward-backward motion is an
important aspect of the conformational relaxation, leading to strongly
nonexponential distributions for the waiting times of the dihedrals in the
various conformational statesComment: 13 pages, 13 figure
Transcriptional Profiling of Bacillus anthracis Sterne (34F2) during Iron Starvation
Lack of available iron is one of many environmental challenges that a bacterium encounters during infection and adaptation to iron starvation is important for the pathogen to efficiently replicate within the host. Here we define the transcriptional response of B. anthracis Sterne (34F2) to iron depleted conditions. Genome-wide transcript analysis showed that B. anthracis undergoes considerable changes in gene expression during growth in iron-depleted media, including the regulation of known and candidate virulence factors. Two genes encoding putative internalin proteins were chosen for further study. Deletion of either gene (GBAA0552 or GBAA1340) resulted in attenuation in a murine model of infection. This attenuation was amplified in a double mutant strain. These data define the transcriptional changes induced during growth in low iron conditions and illustrate the potential of this dataset in the identification of putative virulence determinants for future study
Investor Protection and Share Prices: Evidence from Statutory Rules Governing Variations of Shareholders' Class Rights in Russia
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