445 research outputs found
Decisions, Decisions: Noise and its Effects on Integral Monte Carlo Algorithms
In the present paper we examine the effects of noise on Monte Carlo
algorithms, a problem raised previously by Kennedy and Kuti (Phys. Rev. Lett.
{\bf 54}, 2473 (1985)). We show that the effects of introducing unbiased noise
into the acceptance/rejection phase of the conventional Metropolis approach are
surprisingly modest, and, to a significant degree, largely controllable. We
present model condensed phase numerical applications to support these
conclusions.Comment: Chemical Physics Letters, 12 pages text, 5 figure
In vivo imaging of cellular proliferation in colorectal cancer using positron emission tomography
Background and aims: Positron emission tomography (PET) using 18F labelled 2-fluoro-2-deoxy-D-glucose (18FDG) is an established imaging tool, although the recent development of a biologically stable thymidine analogue [18F] 3'-deoxy-3-fluorothymidine (18FLT) has allowed PET to image cellular proliferation by utilising the salvage pathway of DNA synthesis. In this study, we have compared uptake of 18FLT and 18FDG with MIB-1 immunohistochemistry to evaluate the role of PET in quantifying in vivo cellular proliferation in colorectal cancer (CRC).
Patients and methods: Patients with resectable, primary, or recurrent CRC were prospectively studied. Thirteen lesions from 10 patients (five males, five females), median age 68 years (range 54â87), were evaluated. Patients underwent 18FDG and 18FLT PET scanning. Tracer uptake within lesions was quantified using standardised uptake values (SUVs). Histopathological examination and MIB-1 immunohistochemistry were performed on all lesions, and proliferation quantified by calculating a labelling index (% of MIB-1 positively stained nuclei within 1500 tumour cells).
Results: Histology confirmed adenocarcinoma in 12 of 13 lesions; the remaining lesion was reactive. All eight extrahepatic lesions were visualised using both 18FLT and 18FDG. Three of the five resected liver metastases were also avid for 18FLT and showed high proliferation, while the remaining two lesions which demonstrated no uptake of 18FLT had correspondingly very low proliferation. There was a statistically significant positive correlation (r =0.8, p<0.01) between SUVs of the tumours visualised with 18FLT and the corresponding MIB-1 labelling indices. No such correlation was demonstrated with 18FDG avid lesions (r =0.4).
Conclusions: 18FLT PET correlates with cellular proliferation markers in both primary and metastatic CRC. This technique could provide a mechanism for in vivo grading of malignancy and early prediction of response to adjuvant chemotherapy
The Construction of Double-Ended Classical Trajectories
In the present paper we describe relaxation methods for constructing
double-ended classical trajectories. We illustrate our approach with an
application to a model anharmonic system, the Henon-Heiles problem.
Trajectories for this model exhibit a number of interesting energy-time
relationships that appear to be of general use in characterizing the dynamics.Comment: (12 pages, submitted to Chemical Physics Letters. Figures are too
large for convenient e-mail access. they are available via anonymous ftp on
willie.chem.brown.edu and reside in the directory pub/chem-ph/9407 as the
compressed tar file 9407001.tar.Z. If you have difficulty retrieving the
figures, please contact J. Doll ([email protected]) for assistance
The Approach to Ergodicity in Monte Carlo Simulations
The approach to the ergodic limit in Monte Carlo simulations is studied using
both analytic and numerical methods. With the help of a stochastic model, a
metric is defined that enables the examination of a simulation in both the
ergodic and non-ergodic regimes. In the non-ergodic regime, the model implies
how the simulation is expected to approach ergodic behavior analytically, and
the analytically inferred decay law of the metric allows the monitoring of the
onset of ergodic behavior. The metric is related to previously defined measures
developed for molecular dynamics simulations, and the metric enables the
comparison of the relative efficiencies of different Monte Carlo schemes.
Applications to Lennard-Jones 13-particle clusters are shown to match the model
for Metropolis, J-walking and parallel tempering based approaches. The relative
efficiencies of these three Monte Carlo approaches are compared, and the decay
law is shown to be useful in determining needed high temperature parameters in
parallel tempering and J-walking studies of atomic clusters.Comment: 17 Pages, 7 Figure
Responsible agriculture must adapt to the wetland character of midâlatitude peatlands
Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yrâ1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Reducing drainage depths is, therefore, essential for responsible peatland management. Peatland restoration can substantially reduce emissions. However, this may conflict with societal needs to maintain productive use, to protect food security and livelihoods. Wetland agriculture strategies will, therefore, be required to adapt agriculture to the wetland character of peatlands, and balance GHG mitigation against productivity, where halting emissions is not immediately possible. Paludiculture may substantially reduce GHG emissions but will not always be viable in the current economic landscape. Reduced drainage intensity systems may deliver partial reductions in the rate of emissions, with smaller modifications to existing systems. These compromise systems may face fewer hurdles to adoption and minimize environmental harm until societal conditions favour strategies that can halt emissions. Wetland agriculture will face agronomic, socio-economic and water management challenges, and careful implementation will be required. Diversity of values and priorities among stakeholders creates the potential for conflict. Successful implementation will require participatory research approaches and co-creation of workable solutions. Policymakers, private sector funders and researchers have key roles to play but adoption risks would fall predominantly on land managers. Development of a robust wetland agriculture paradigm is essential to deliver resilient production systems and wider environmental benefits. The challenge of responsible use presents an opportunity to rethink peatland management and create thriving, innovative and green wetland landscapes for everyone's future benefit, while making a vital contribution to global climate change mitigation
Thermodynamic properties of thin films of superfluid 3He-A
The pairing correlations in superfluid He-3 are strongly modified by
quasiparticle scattering off a surface or an interface. We present theoretical
results and predictions for the order parameter, the quasiparticle excitation
spectrum and the free energy for thin films of superfluid He-3. Both specular
and diffuse scattering by a substrate are considered, while the free surface is
assumed to be a perfectly reflecting specular boundary. The results are based
on self-consistent calculations of the order parameter and quasiparticle
excitation spectrum at zero pressure. We obtain new results for the phase
diagram, free energy, entropy and specific heat of thin films of superfluid
He-3.Comment: Replaced with an updated versio
Modified gravity without dark matter
On an empirical level, the most successful alternative to dark matter in
bound gravitational systems is the modified Newtonian dynamics, or MOND,
proposed by Milgrom. Here I discuss the attempts to formulate MOND as a
modification of General Relativity. I begin with a summary of the
phenomenological successes of MOND and then discuss the various covariant
theories that have been proposed as a basis for the idea. I show why these
proposals have led inevitably to a multi-field theory. I describe in some
detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and
discuss its successes and shortcomings. This lecture is primarily pedagogical
and directed to those with some, but not a deep, background in General
RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School,
The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected,
references update
Microfluidic and Nanofluidic Cavities for Quantum Fluids Experiments
The union of quantum fluids research with nanoscience is rich with
opportunities for new physics. The relevant length scales in quantum fluids,
3He in particular, are comparable to those possible using microfluidic and
nanofluidic devices. In this article, we will briefly review how the physics of
quantum fluids depends strongly on confinement on the microscale and nanoscale.
Then we present devices fabricated specifically for quantum fluids research,
with cavity sizes ranging from 30 nm to 11 microns deep, and the
characterization of these devices for low temperature quantum fluids
experiments.Comment: 12 pages, 3 figures, Accepted to Journal of Low Temperature Physic
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