1,858 research outputs found
Orbital Magnetism in Ensembles of Parabolic Potentials
We study the magnetic susceptibility of an ensemble of non-interacting
electrons confined by parabolic potentials and subjected to a perpendicular
magnetic field at finite temperatures. We show that the behavior of the average
susceptibility is qualitatively different from that of billiards. When averaged
over the Fermi energy the susceptibility exhibits a large paramagnetic response
only at certain special field values, corresponding to comensurate classical
frequencies, being negligible elsewhere. We derive approximate analytical
formulae for the susceptibility and compare the results with numerical
calculations.Comment: 4 pages, 4 figures, REVTE
Protecting infrastructure networks from cost-based attacks
It has been known that heterogeneous networks are vulnerable to the
intentional removal of a small fraction of highly connected or loaded nodes,
which implies that, to protect a network effectively, a few important nodes
should be allocated with more defense resources than the others. However, if
too many resources are allocated to the few important nodes, the numerous
less-important nodes will be less protected, which, when attacked all together,
still capable of causing a devastating damage. A natural question therefore is
how to efficiently distribute the limited defense resources among the network
nodes such that the network damage is minimized whatever attack strategy the
attacker may take. In this paper, taking into account the factor of attack
cost, we will revisit the problem of network security and search for efficient
network defense against the cost-based attacks. The study shows that, for a
general complex network, there will exist an optimal distribution of the
defense resources, with which the network is well protected from cost-based
attacks. Furthermore, it is found that the configuration of the optimal defense
is dependent on the network parameters. Specifically, network that has a larger
size, sparser connection and more heterogeneous structure will be more
benefited from the defense optimization.Comment: 5 pages, 4 figure
Transversality of Electromagnetic Waves in the Calculus-Based Introductory Physics Course
Introductory calculus-based physics textbooks state that electromagnetic
waves are transverse and list many of their properties, but most such textbooks
do not bring forth arguments why this is so. Both physical and theoretical
arguments are at a level appropriate for students of courses based on such
books, and could be readily used by instructors of such courses. Here, we
discuss two physical arguments (based on polarization experiments and on lack
of monopole electromagnetic radiation), and the full argument for the
transversality of (plane) electromagnetic waves based on the integral Maxwell
equations. We also show, at a level appropriate for the introductory course,
why the electric and magnetic fields in a wave are in phase and the relation of
their magnitudes.Comment: 10 pages, 6 figure
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Tropical cyclone projections: changing climate threats for Pacific island defense installations
Potential changing climate threats in the tropical and subtropical North Pacific Ocean were assessed, using coupled ocean-atmosphere and atmosphere-only general circulation models, to explore their response to projected increasing greenhouse gas emissions. Tropical cyclone occurrence, described by frequency and intensity, near islands housing major U.S. defense installations was the primary focus. Four island regions-Guam and Kwajalein Atoll in the tropical northwestern Pacific, Okinawa in the subtropical northwestern Pacific, and Oahu in the tropical north-central Pacific-were considered, as they provide unique climate and geographical characteristics that either enhance or reduce the tropical cyclone risk. Guam experiences the most frequent and severe tropical cyclones, which often originate as weak systems close to the equator near Kwajalein and sometimes track far enough north to affect Okinawa, whereas intense storms are the least frequent around Oahu. From assessments of models that simulate well the tropical Pacific climate, it was determined that, with a projected warming climate, the number of tropical cyclones is likely to decrease for Guam and Kwajalein but remain about the same near Okinawa and Oahu; however, the maximum intensity of the strongest storms may increase in most regions. The likelihood of fewer but stronger storms will necessitate new localized assessments of the risk and vulnerabilities to tropical cyclones in the North Pacific
Electrorotation of a pair of spherical particles
We present a theoretical study of electrorotation (ER) of two spherical
particles under the action of a rotating electric field. When the two particles
approach and finally touch, the mutual polarization interaction between the
particles leads to a change in the dipole moment of the individual particle and
hence the ER spectrum, as compared to that of the well-separated particles. The
mutual polarization effects are captured by the method of multiple images. From
the theoretical analysis, we find that the mutual polarization effects can
change the characteristic frequency at which the maximum angular velocity of
electrorotation occurs. The numerical results can be understood in the spectral
representation theory.Comment: Minor revisions; accepted by Phys. Rev.
Reconstructing phylogenetic level-1 networks from nondense binet and trinet sets
Binets and trinets are phylogenetic networks with two and three leaves, respectively. Here we consider the problem of deciding if there exists a binary level-1 phylogenetic network displaying a given set T of binary binets or trinets over a taxon set X, and constructing such a network whenever it exists. We show that this is NP-hard for trinets but polynomial-time solvable for binets. Moreover, we show that the problem is still polynomial-time solvable for inputs consisting of binets and trinets as long as the cycles in the trinets have size three. Finally, we present an O(3^{|X|} poly(|X|)) time algorithm for general sets of binets and trinets. The latter two algorithms generalise to instances containing level-1 networks with arbitrarily many leaves, and thus provide some of the first supernetwork algorithms for computing networks from a set of rooted 1 phylogenetic networks
Second-line agents in myositis: 1-year factorial trial of additional immunosuppression in patients who have partially responded to steroids.
Ciclosporin and MTX are used in idiopathic inflammatory myopathies (DM and PM) when patients incompletely respond to glucocorticoids. Their effectiveness is unproved in randomized controlled trials (RCTs). We evaluated their benefits in a placebo-controlled factorial RCT
The Flint Food Store Survey: combining spatial analysis with a modified Nutrition Environment Measures Survey in Stores (NEMS-S) to measure the community and consumer nutrition environments
Objective The goal of the present study was to use a methodology that accurately and reliably describes the availability, price and quality of healthy foods at both the store and community levels using the Nutrition Environment Measures Survey in Stores (NEMS-S), to propose a spatial methodology for integrating these store and community data into measures for defining objective food access. Setting Two hundred and sixty-five retail food stores in and within 2 miles (3·2 km) of Flint, Michigan, USA, were mapped using ArcGIS mapping software. Design A survey based on the validated NEMS-S was conducted at each retail food store. Scores were assigned to each store based on a modified version of the NEMS-S scoring system and linked to the mapped locations of stores. Neighbourhood characteristics (race and socio-economic distress) were appended to each store. Finally, spatial and kernel density analyses were run on the mapped store scores to obtain healthy food density metrics. Results Regression analyses revealed that neighbourhoods with higher socio-economic distress had significantly lower dairy sub-scores compared with their lower-distress counterparts (β coefficient=−1·3; P=0·04). Additionally, supermarkets were present only in neighbourhoods with \u3c60 % African-American population and low socio-economic distress. Two areas in Flint had an overall NEMS-S score of 0. Conclusions By identifying areas with poor access to healthy foods via a validated metric, this research can be used help local government and organizations target interventions to high-need areas. Furthermore, the methodology used for the survey and the mapping exercise can be replicated in other cities to provide comparable results
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