3,386 research outputs found
A New Method for the High-Precision Assessment of Tumor Changes in Response to Treatment
Imaging demonstrates that preclinical and human tumors are heterogeneous,
i.e. a single tumor can exhibit multiple regions that behave differently during
both normal development and also in response to treatment. The large variations
observed in control group tumors can obscure detection of significant
therapeutic effects due to the ambiguity in attributing causes of change. This
can hinder development of effective therapies due to limitations in
experimental design, rather than due to therapeutic failure. An improved method
to model biological variation and heterogeneity in imaging signals is
described. Specifically, Linear Poisson modelling (LPM) evaluates changes in
apparent diffusion co-efficient (ADC) before and 72 hours after radiotherapy,
in two xenograft models of colorectal cancer. The statistical significance of
measured changes are compared to those attainable using a conventional t-test
analysis on basic ADC distribution parameters. When LPMs were applied to
treated tumors, the LPMs detected highly significant changes. The analyses were
significant for all tumors, equating to a gain in power of 4 fold (i.e.
equivelent to having a sample size 16 times larger), compared with the
conventional approach. In contrast, highly significant changes are only
detected at a cohort level using t-tests, restricting their potential use
within personalised medicine and increasing the number of animals required
during testing. Furthermore, LPM enabled the relative volumes of responding and
non-responding tissue to be estimated for each xenograft model. Leave-one-out
analysis of the treated xenografts provided quality control and identified
potential outliers, raising confidence in LPM data at clinically relevant
sample sizes
Quasars: What turns them off?
(Abridged) We explore the idea that the anti-hierarchical turn-off observed
in the quasar population arises from self-regulating feedback, via an outflow
mechanism. Using a detailed hydrodynamic simulation we calculate the luminosity
function of quasars down to a redshift of z=1 in a large, cosmologically
representative volume. Outflows are included explicitly by tracking halo
mergers and driving shocks into the surrounding intergalactic medium. Our
results are in excellent agreement with measurements of the spatial
distribution of quasars, and we detect an intriguing excess of galaxy-quasar
pairs at very short separations. We also reproduce the anti-hierarchical
turnoff in the quasar luminosity function, however, the magnitude of the
turn-off falls short of that observed as well as that predicted by analogous
semi-analytic models. The difference can be traced to the treatment of gas
heating within galaxies. The simulated galaxy cluster L_X-T relationship is
close to that observed for z~1 clusters, but the simulated galaxy groups at z=1
are significantly perturbed by quasar outflows, suggesting that measurements of
X-ray emission in high-redshift groups could well be a "smoking gun" for the
AGN heating hypothesis.Comment: 16 pages, 11 figures, submitted to ApJ, comments welcome
Managed moves: schools collaborating for collective gain
Government guidance in the United Kingdom encourages groups of schools to take collective responsibility for supporting and making provision for excluded pupils and those at risk of exclusion. Managed-moves are one way that some schools and authorities are enacting such guidance. This paper presents the results of an evaluation of one such scheme. The scheme, involving seven neighbouring secondary schools, was nearing its first year of completion. The paper draws primarily on interview data with pupils, parents and school staff to describe a number of positive outcomes associated with the scheme and to explore how these were achieved. We found that while some of these could be attributed directly to the managed-move, others arose from the more inclusive ethos and practices of particular schools. The concepts of tailored support, care and commitment emerged as strong themes that underpinned the various practical ways in which some schools in the cluster were able to re-engage 'at-risk' pupils. As managed moves become more widely practiced it will be important to remember that it is how the move proceeds and develops rather than the move itself that will ultimately make the difference for troubled and troublesome pupils
f_B with lattice NRQCD including O(1/m_Q^2) corrections
We calculate the heavy-light meson decay constant using lattice NRQCD action
for the heavy quark and Wilson quark action for the light quark over a wide
range in the heavy quark mass. Simulations are carried out on a 16^3 x 32
lattice with 120 quenched gauge configurations generated with the plaquette
action at beta=5.8. For the heavy quark part of the calculation, two sets of
lattice NRQCD action and current operator are employed. The first set includes
terms up to O(1/m_Q) both in the action and the current operator, and the
second set up to O(1/m_Q^2), where m_Q is the bare mass of the heavy quark.
Tree-level values with tadpole improvement are employed for the coefficients in
the expansion. We compare the results obtained from the two sets in detail and
find that the truncation error of higher order relativistic corrections for the
decay constant are adequately small around the mass of the b quark. We also
calculate the 1S hyperfine splitting of B meson, M_{B_s} - M_B and f_{B_s}/f_B
with both sets and find that the 1/m_Q^2 corrections are negligible. Remaining
systematic errors and the limitation of NRQCD theory are discussed.Comment: 27 pages, 15 figures, RevTex, psfig.sty require
Strings on type IIB pp-wave backgrounds with interacting massive theories on the worldsheet
We consider superstring theories on pp-wave backgrounds which result in an
integrable supersymmetric Landau-Ginzburg theory on the
worldsheet. We obtain exact eigenvalues of the light-cone gauge superstring
hamiltonian in the massive and interacting world-sheet theory with
superpotential . We find the modes of the supergravity part of the
string spectrum, and their space-time interpretation. Because the system is
effectively at strong coupling on the worldsheet, these modes are not in
one-to-one correspondence with the usual type IIB supergravity modes in the
limit. However, the above correspondence holds in the limit.Comment: 20 pages, 1 figure; minor changes, comments adde
Unquenched Charmonium with NRQCD - Lattice 2000
We present results from a series of NRQCD simulations of the charmonium
system, both in the quenched approximation and with n_f = 2 dynamical quarks.
The spectra show evidence for quenching effects of ~10% in the S- and
P-hyperfine splittings. We compare this with other systematic effects.
Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20
MeV, and we estimate radiative corrections may be as large as 40%.Comment: Lattice 2000 (Heavy Quark Physics
Study of Charmonia near the deconfining transition on an anisotropic lattice with O(a) improved quark action
We study hadron properties near the deconfining transition in the quenched
lattice QCD simulation. This paper focuses on the heavy quarkonium states, such
as meson. In order to treat heavy quarks at , we adopt the
improved Wilson action on anisotropic lattice. We discuss bound
state observing the wave function and compare the meson correlators at above
and below . Although we find a large change of correlator near the ,
the strong spatial correlation which is almost the same as confinement phase
survives even .Comment: 19 pages, 10 figure
S and P-wave heavy-light mesons in lattice NRQCD
The mass spectrum of S and P-wave mesons containing a single heavy quark is
computed in the quenched approximation, using NRQCD up to third order in the
inverse heavy quark mass expansion. Previous results found third order
contributions which are as large in magnitude as the total second order
contribution for the charmed S-wave spin splitting. The present work considers
variations such as anisotropic lattices, Landau link tadpole improvement, and a
highly-improved light quark action, and finds that the second order correction
to the charmed S-wave spin splitting is about 20% of the leading order
contribution, while the third order correction is about 20%(10%) for
D^*-D(D_s^*-D_s). Nonleading corrections are very small for the bottom meson
spectrum, and are statistically insignificant for the P-wave charmed masses.
The relative orderings among P-wave charmed and bottom mesons, and the sizes of
the mass splittings, are discussed in light of experimental data and existing
calculations.Comment: 21 pages including 6 figures, changed method of fitting correlators,
this version to be published in Phys Rev
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