1,391 research outputs found
A comparative study of online news retrieval and presentation strategies
We introduce a news retrieval system on which we evaluated three alternative presentation strategies for online news retrieval. We used a user-oriented and task-oriented evaluation framework. The interfaces studied were Image, giving a grid of thumbnails for each story together with query-based summaries presented as tooltips, Summary, which displayed the summary information alongside each thumbnail, and Cluster, which grouped similar stories together and used the same display format as Image. The evaluation showed that the Summary Interface was preferred to the Image Interface, and that the Cluster Interface was helpful to users with a set task to complete. The implications of this study are also discussed in this paper
Examination of actin and microtubule dependent APC localisations in living mammalian cells
Abstract (provisional)
Background
The trafficking of the adenomatous polyposis coli (APC) tumour suppressor protein in mammalian cells is a perennially controversial topic. Immunostaining evidence for an actin-associated APC localisation at intercellular junctions has been previously presented, though live imaging of mammalian junctional APC has not been documented.
Results
Using live imaging of transfected COS-7 cells we observed intercellular junction-associated pools of GFP-APC in addition to previously documented microtubule-associated GFP-APC and a variety of minor localisations. Although both microtubule and junction-associated populations could co-exist within individual cells, they differed in their subcellular location, dynamic behaviour and sensitivity to cytoskeletal poisons. GFP-APC deletion mutant analysis indicated that a protein truncated immediately after the APC armadillo repeat domain retained the ability to localise to adhesive membranes in transfected cells. Supporting this, we also observed junctional APC immunostaining in cultures of human colorectal cancer cell line that express truncated forms of APC.
Conclusions
Our data indicate that APC can be found in two spatially separate populations at the cell periphery and these populations can co-exist in the same cell. The first localisation is highly dynamic and associated with microtubules near free edges and in cell vertices, while the second is comparatively static and is closely associated with actin at sites of cell-cell contact. Our imaging confirms that human GFP-APC possesses many of the localisations and behaviours previously seen by live imaging of Xenopus GFP-APC. However, we report the novel finding that GFP-APC puncta can remain associated with the ends of shrinking microtubules. Deletion analysis indicated that the N-terminal region of the APC protein mediated its junctional localisation, consistent with our observation that truncated APC proteins in colon cancer cell lines are still capable of localising to the cell cortex. This may have implications for the development of colorectal cancer
Stable sheaves on elliptic fibrations
We characterize the subscheme of the moduli space of torsion-free sheaves on
an elliptic surface which are stable of relative degree zeero (with respect to
a polarization of type aH+bf, H being the section and f the elliptic fibre)
which is isomorphic, via the relative Fourier-Mukai transform, with the
relative compactified Simpson Jacobian of the family of those curves D in the
surface which are flat over the base of the elliptic fibration. This
generalizes and completes earlier constructions due to Friedman, Morgan and
Witten. We also study the relative moduli scheme of sheaves whose restriction
to each fibre is torsion-free and semistable of rank n and degree zero for
higher dimensional elliptic fibrations. The relative Fourier-Mukai transform
induces an isomorphic between this relative moduli space and the relative n-th
symmetric product of the fibration.Comment: AMS-LaTeX, 18 pages, XY-pic; new title, some modifications; final
version as accepted in J. Geom. Phy
Source Parameters from Identified Hadron Spectra and HBT Radii for Au-Au Collisions at sqrt(s_NN)=200 GeV in PHENIX
The characteristics of the particle emitting source are deduced from low
transverse momentum identified hadron spectra (transverse mass less than 1 GeV)
and HBT radii using a hydrodynamic interpretation. From the most peripheral to
the most central data, the single particle spectra are fit simultaneously for
all pions, kaons, and (anti-)protons using the parameterization in [1] and
assuming a linear transverse flow profile. Within the systematic uncertainties,
the expansion parameters called the freeze-out temperature and flow velocity,
respectively decrease and increase with the number of participants, saturating
for both at mid-centrality. The expansion using analytic calculations of the kT
dependence of HBT radii in [2] is fit to the data but no chi-squared minimum is
found.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Half-BPS quotients in M-theory: ADE with a twist
We classify Freund-Rubin backgrounds of eleven-dimensional supergravity of
the form AdS_4 x X^7 which are at least half BPS; equivalently, smooth
quotients of the round 7-sphere by finite subgroups of SO(8) which admit an
(N>3)-dimensional subspace of Killing spinors. The classification is given in
terms of pairs consisting of an ADE subgroup of SU(2) and an automorphism
defining its embedding in SO(8). In particular we find novel half-BPS quotients
associated with the subgroups of type D_n (for n>5), E_7 and E_8 and their
outer automorphisms.Comment: 16 pages; V2: notational inconsistencies addressed, final version to
be published in JHE
The Iliad’s big swoon: a case of innovation within the epic tradition
In book 5 of the Iliad Sarpedon suffers so greatly from a wound that his ‘‘ψυχή leaves him’. Rather than dying, however, Sarpedon lives to fight another day. This paper investigates the phrase τὸν δὲ λίπε ψυχή in extant archaic Greek poetry to gain a sense of its traditional referentiality and better assess the meaning of Sarpedon’s swoon. Finding that all other instances of the ψυχή leaving the body signify death, it suggests that the Iliad exploits a traditional unit of utterance to flag up the importance of Sarpedon to this version of the Troy story
Quantum Deconstruction of a 5D SYM and its Moduli Space
We deconstruct the fifth dimension of the 5D SYM theory with SU(M) gauge
symmetry and Chern-Simons level k=M and show how the 5D moduli space follows
from the non-perturbative analysis of the 4D quiver theory. The 5D coupling
h=1/(g_5)^2 of the un-broken SU(M) is allowed to take any non-negative values,
but it cannot be continued to h<0 and there are no transitions to other phases
of the theory. The alternative UV completions of the same 5D SYM -- via M
theory on the C^3/Z_2M orbifold or via the dual five-brane web in type IIB
string theory -- have identical moduli spaces: h >= 0 only, and no flop
transitions. We claim these are intrinsic properties of the SU(M) SYM theory
with k=M.Comment: 46 Page
Perturbative Gauge Theory and Closed String Tachyons
We find an interesting connection between perturbative large N gauge theory
and closed superstrings. The gauge theory in question is found on N D3-branes
placed at the tip of the cone R^6/Gamma. In our previous work we showed that,
when the orbifold group Gamma breaks all supersymmetry, then typically the
gauge theory is not conformal because of double-trace couplings whose one-loop
beta functions do not possess real zeros. In this paper we observe a precise
correspondence between the instabilities caused by the flow of these
double-trace couplings and the presence of tachyons in the twisted sectors of
type IIB theory on orbifolds R^{3,1}x R^6/Gamma. For each twisted sectors that
does not contain tachyons, we show that the corresponding double-trace coupling
flows to a fixed point and does not cause an instability. However, whenever a
twisted sector is tachyonic, we find that the corresponding one-loop beta
function does not have a real zero, hence an instability is likely to exist in
the gauge theory. We demonstrate explicitly the one-to-one correspondence
between the regions of stability/instability in the space of charges under
Gamma that arise in the perturbative gauge theory and in the free string
theory. Possible implications of this remarkably simple gauge/string
correspondence are discussed.Comment: 25 pages, Latex; V2: Clarifications and references adde
Penrose Limits of Orbifolds and Orientifolds
We study the Penrose limit of various AdS_p X S^q orbifolds. The limiting
spaces are waves with parallel rays and singular wave fronts. In particular, we
consider the orbifolds AdS_3 X S^3/\Gamma, AdS_5 X S^5/\Gamma and AdS_{4,7} X
S^{7,4}/\Gamma where \Gamma acts on the sphere and/or the AdS factor. In the
pp-wave limit, the wave fronts are the orbifolds C^2/\Gamma, C^4/\Gamma and R
XC^4/\Gamma, respectively. When desingularization is possible, we get
asymptotically locally pp-wave backgrounds (ALpp). The Penrose limit of
orientifolds are also discussed. In the AdS_5 X RP^5 case, the limiting
singularity can be resolved by an Eguchi-Hanson gravitational instanton. The
pp-wave limit of D3-branes near singularities in F-theory is also presented.
Finally, we give the embedding of D-dimensional pp-waves in flat M^{2,D} space.Comment: 20 pages, references adde
Baryon Spectra and AdS/CFT Correspondence
We provide a detailed map between wrapped D3-branes in Anti-de Sitter (AdS)
backgrounds and dibaryon operators in the corresponding conformal field theory
(CFT). The effective five dimensional action governing the dynamics of AdS
space contains a gauge field that mediates interactions between
objects possessing R-charge. We show that the charge of these wrapped
D3-branes as measured by the gauge field matches the R-charge of the dibaryons
expected from field theory considerations. We are able, through a careful probe
brane calculation in an background, to understand the
exact relation between the mass of the wrapped D3-brane and the dimension of
the corresponding dibaryon. We also make some steps toward matching the
counting of dibaryon operators in the CFT with the ground states of a
supersymmetric quantum mechanical system whose target space is the moduli space
of D-branes. Finally, we discuss BPS excitations of the D3-brane and compare
them with higher dimension operators in the CFT.Comment: 24 pages, typos correcte
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