793 research outputs found
Establishing Telepathology in Africa: Lessons From Botswana
Few reports of telepathology in Africa exist in the medical literature. With the strong need for improvement in health care infrastructure and personnel training in many African nations, telepathology provides a rapid and versatile tool to improve clinical care and foster educational and research opportunities. We describe the challenges faced in establishing robotic telepathology (RT) services at a government referral center in Botswana and reflect on conditions under which such initiatives may be most likely to succeed in sub-Saharan Africa and other parts of the developing world
Mean field theory of hard sphere glasses and jamming
Hard spheres are ubiquitous in condensed matter: they have been used as
models for liquids, crystals, colloidal systems, granular systems, and powders.
Packings of hard spheres are of even wider interest, as they are related to
important problems in information theory, such as digitalization of signals,
error correcting codes, and optimization problems. In three dimensions the
densest packing of identical hard spheres has been proven to be the FCC
lattice, and it is conjectured that the closest packing is ordered (a regular
lattice, e.g, a crystal) in low enough dimension. Still, amorphous packings
have attracted a lot of interest, because for polydisperse colloids and
granular materials the crystalline state is not obtained in experiments for
kinetic reasons. We review here a theory of amorphous packings, and more
generally glassy states, of hard spheres that is based on the replica method:
this theory gives predictions on the structure and thermodynamics of these
states. In dimensions between two and six these predictions can be successfully
compared with numerical simulations. We will also discuss the limit of large
dimension where an exact solution is possible. Some of the results we present
here have been already published, but others are original: in particular we
improved the discussion of the large dimension limit and we obtained new
results on the correlation function and the contact force distribution in three
dimensions. We also try here to clarify the main assumptions that are beyond
our theory and in particular the relation between our static computation and
the dynamical procedures used to construct amorphous packings.Comment: 59 pages, 25 figures. Final version published on Rev.Mod.Phy
Orthorhombic Phase of Crystalline Polyethylene: A Constant Pressure Path Integral Monte Carlo Study
In this paper we present a Path Integral Monte Carlo (PIMC) simulation of the
orthorhombic phase of crystalline polyethylene, using an explicit atom force
field with unconstrained bond lengths and angles. This work represents a
quantum extension of our recent classical simulation (J. Chem. Phys. 106, 8918
(1997)). It is aimed both at exploring the applicability of the PIMC method on
such polymer crystal systems, as well as on a detailed assessment of the
importance of quantum effects on different quantities. We used the
ensemble and simulated the system at zero pressure in the temperature range 25
- 300 K, using Trotter numbers between 12 and 144. In order to investigate
finite-size effects, we used chains of two different lengths, C_12 and C_24,
corresponding to the total number of atoms in the super-cell being 432 and 864,
respectively. We show here the results for structural parameters, like the
orthorhombic lattice constants a,b,c, and also fluctuations of internal
parameters of the chains, such as bond lengths and bond and torsional angles.
We have also determined the internal energy and diagonal elastic constants
c_11, c_22 and c_33. We discuss the temperature dependence of the measured
quantities and compare to that obtained from the classical simulation. For some
quantities, we discuss the way they are related to the torsional angle
fluctuation. In case of the lattice parameters we compare our results to those
obtained from other theoretical approaches as well as to some available
experimental data. In order to study isotope effects, we simulated also a
deuterated polyethylene crystal at a low temperature. We also suggest possible
ways of extending this study and present some general considerations concerning
modeling of polymer crystals.Comment: 18 pages, RevTex, 18 figures, 3 tables, submitted to Phys. Rev.
Metastable lifetimes in a kinetic Ising model: Dependence on field and system size
The lifetimes of metastable states in kinetic Ising ferromagnets are studied
by droplet theory and Monte Carlo simulation, in order to determine their
dependences on applied field and system size. For a wide range of fields, the
dominant field dependence is universal for local dynamics and has the form of
an exponential in the inverse field, modified by universal and nonuniversal
power-law prefactors. Quantitative droplet-theory predictions are numerically
verified, and small deviations are shown to depend nonuniversally on the
details of the dynamics. We identify four distinct field intervals in which the
field dependence and statistical properties of the lifetimes are different. The
field marking the crossover between the weak-field regime, in which the decay
is dominated by a single droplet, and the intermediate-field regime, in which
it is dominated by a finite droplet density, vanishes logarithmically with
system size. As a consequence the slow decay characteristic of the former
regime may be observable in systems that are macroscopic as far as their
equilibrium properties are concerned.Comment: 18 pages single spaced. RevTex Version 3. FSU-SCRI-94-1
Festschrift Symposium: Honoring Professor Samuel Pillsbury
The Loyola of Los Angeles Law Review is pleased to publish this Festschrift Symposium Honoring Professor Samuel Pillsbury. The following is an edited transcript of the live symposium held at LMU Loyola Law School on Friday, March 25, 2022
Corporate Security Responsibility: Towards a Conceptual Framework for a Comparative Research Agenda
The political debate about the role of business in armed conflicts has increasingly raised expectations as to governance contributions by private corporations in the fields of conflict prevention, peace-keeping and postconflict peace-building. This political agenda seems far ahead of the research agenda, in which the negative image of business in conflicts, seen as fuelling, prolonging and taking commercial advantage of violent conflicts,still prevails. So far the scientific community has been reluctant to extend the scope of research on ‘corporate social responsibility’ to the area of security in general and to intra-state armed conflicts in particular. As a consequence, there is no basis from which systematic knowledge can be generated about the conditions and the extent to which private corporations can fulfil the role expected of them in the political discourse. The research on positive contributions of private corporations to security amounts to unconnected in-depth case studies of specific corporations in specific conflict settings. Given this state of research, we develop a framework for a comparative research agenda to address the question: Under which circumstances and to what extent can private corporations be expected to contribute to public security
Diverse sediment microbiota shape methane emission temperature sensitivity in Arctic lakes
Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH4) from sediments. Ebullitive CH4 flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH4 flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH4 emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH4 emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH4-cycling microorganisms and syntrophs, were predictive of porewater CH4 concentrations. Results suggest that deeper lake regions, which currently emit less CH4 than shallower edges, could add substantially to CH4 emissions in a warmer Arctic and that CH4 emission predictions may be improved by accounting for spatial variations in sediment microbiota
Ninth and Tenth Order Virial Coefficients for Hard Spheres in D Dimensions
We evaluate the virial coefficients B_k for k<=10 for hard spheres in
dimensions D=2,...,8. Virial coefficients with k even are found to be negative
when D>=5. This provides strong evidence that the leading singularity for the
virial series lies away from the positive real axis when D>=5. Further analysis
provides evidence that negative virial coefficients will be seen for some k>10
for D=4, and there is a distinct possibility that negative virial coefficients
will also eventually occur for D=3.Comment: 33 pages, 12 figure
Tunneling of quantum rotobreathers
We analyze the quantum properties of a system consisting of two nonlinearly
coupled pendula. This non-integrable system exhibits two different symmetries:
a permutational symmetry (permutation of the pendula) and another one related
to the reversal of the total momentum of the system. Each of these symmetries
is responsible for the existence of two kinds of quasi-degenerated states. At
sufficiently high energy, pairs of symmetry-related states glue together to
form quadruplets. We show that, starting from the anti-continuous limit,
particular quadruplets allow us to construct quantum states whose properties
are very similar to those of classical rotobreathers. By diagonalizing
numerically the quantum Hamiltonian, we investigate their properties and show
that such states are able to store the main part of the total energy on one of
the pendula. Contrary to the classical situation, the coupling between pendula
necessarily introduces a periodic exchange of energy between them with a
frequency which is proportional to the energy splitting between
quasi-degenerated states related to the permutation symmetry. This splitting
may remain very small as the coupling strength increases and is a decreasing
function of the pair energy. The energy may be therefore stored in one pendulum
during a time period very long as compared to the inverse of the internal
rotobreather frequency.Comment: 20 pages, 11 figures, REVTeX4 styl
Taming trilogues: the EU's law-making process in a comparative perspective.
Trilogues have become the modus operandi of EU decision-making. They are an informal but institutionalised mechanism providing for in camera discussions of legislative texts between the three main EU decision-making institutions, with a view to securing legislative compromises. Trilogues present risks to an organ of parliamentary representation through their potential to depoliticise conflict and by reducing the accountability and transparency of the decision-making process. We examine how the European Parliament (EP) has responded to trilogues and what this response tells us about the development of the EP as an institutionalised organ of representative democracy. We compare these with arrangements for bicameral conflict resolution in the United States, where similar issues are presented by informal mechanisms of decision-making. We assess the institutionalisation of trilogues from a democratic perspective, highlighting achievements and future challenges, and the value of these findings for the ongoing reflection on the EP as a normal parliament and the role of informal institutions in EU law-making
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