2,111 research outputs found
Controlling surface plasmon polaritons in transformed coordinates
Transformational optics allow for a markedly enhanced control of the
electromagnetic wave trajectories within metamaterials with interesting
applications ranging from perfect lenses to invisibility cloaks, carpets,
concentrators and rotators. Here, we present a review of curved anisotropic
heterogeneous meta-surfaces designed using the tool of transformational
plasmonics, in order to achieve a similar control for surface plasmon
polaritons in cylindrical and conical carpets, as well as cylindrical cloaks,
concentrators and rotators of a non-convex cross-section. Finally, we provide
an asymptotic form of the geometric potential for surface plasmon polaritons on
such surfaces in the limit of small curvature.Comment: 14 pages, 9 figure
On the use of surfaces of section in the Nâbody ring problem
In the Nâbody ring problem, we investigate the motion of a massless body interacting with N bodies of equal masses at the vertices of a regular polygon that rotates around a central mass. In this paper, we analyze the use of different surfaces of section in the numerical exploration of the escape in the Nâbody ring problem in order to get some conclusions about the geometry of the basins of escape in the corresponding configuration spaces
Pengembangan Lembar Kegiatan Siswa (Lks) Kimia Sma/ma Berbasis Learning Cycle 5e Pada Materi Laju Reaksi
Penelitian ini bertujuan untuk: (1) mengembangkan Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E, (2) mengetahui kualitas Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E, (3) mengetahui efektivitas Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E untuk meningkatkan prestasi belajar siswa. Penelitian dan pengembangan Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E menggunakan prosedur penelitian dan pengembangan dari Borg and Gall yang disederhanakan menjadi 9 tahapan yaitu: (1) penelitian pendahuluan dan pengumpulan data, (2) perencanaan, (3) pengembangan produk, (4) uji coba lapangan awal, (5) revisi produk awal, (6) uji coba pelaksanaan lapangan, (7) penyempurnaan produk hasil uji coba lapangan, (8) uji coba pelaksanaan lapangan, (9) penyempurnaan produk akhir. Analisis Data yang digunakan adalah analisis deskriptif kualitatif. Hasil Penelitian menunjukkan: (1) telah berhasil dikembangkan Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E pada materi Laju Reaksi yang dilakukan berdasarkan tahapan penelitian dan pengembangan R&D yang terdiri dari 9 tahapan, (2) kualitas Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E pada materi Laju Reaksi memiliki kualitas sangat baik pada aspek komponen kelayakan isi, bahasa, penyajian dan kegrafisan dengan persentase sebesar 84,06% berdasarkan penilaian siswa dan 90,88% berdasarkan penilaian guru, (hasil uji efektivitas pada aspek pengetahuan terdapat perbedaan antara kelas eksperimen (pembelajaran dengan menggunakan model Learning Cycle 5E disertai Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E ) dan kelas baseline (pembelajaran dengan menggunakan model pembelajaran Learning Cycle 5E tanpa disertai Lembar Kegiatan Siswa (LKS) berbasis Learning Cycle 5E ),, sedangkan pada aspek sikap dan keterampilan tidak terdapat perbedaan
Topological modes bound to dislocations in mechanical metamaterials
Mechanical metamaterials are artificial structures with unusual properties,
such as negative Poisson ratio, bistability or tunable vibrational properties,
that originate in the geometry of their unit cell. At the heart of such unusual
behaviour is often a soft mode: a motion that does not significantly stretch or
compress the links between constituent elements. When activated by motors or
external fields, soft modes become the building blocks of robots and smart
materials. Here, we demonstrate the existence of topological soft modes that
can be positioned at desired locations in a metamaterial while being robust
against a wide range of structural deformations or changes in material
parameters. These protected modes, localized at dislocations, are the
mechanical analogue of topological states bound to defects in electronic
systems. We create physical realizations of the topological modes in prototypes
of kagome lattices built out of rigid triangular plates. We show mathematically
that they originate from the interplay between two Berry phases: the Burgers
vector of the dislocation and the topological polarization of the lattice. Our
work paves the way towards engineering topologically protected nano-mechanical
structures for molecular robotics or information storage and read-out.Comment: 13 pages, 6 figures; changes to text and figures and added analysis
on mode localization; see
http://www.lorentz.leidenuniv.nl/~paulose/dislocation-modes/ for accompanying
video
The Hypothesis of Locality and its Limitations
The hypothesis of locality, its origin and consequences are discussed. This
supposition is necessary for establishing the local spacetime frame of
accelerated observers; in this connection, the measurement of length in a
rotating system is considered in detail. Various limitations of the hypothesis
of locality are examined.Comment: LaTeX file, no figures, 14 pages, to appear in: "Relativity in
Rotating Frames", edited by G. Rizzi and M.L. Ruggiero (Kluwer Academic
Publishers, Dordrecht, 2003
On the Maxwell-Stefan approach to multicomponent diffusion
We consider the system of Maxwell-Stefan equations which describe
multicomponent diffusive fluxes in non-dilute solutions or gas mixtures. We
apply the Perron-Frobenius theorem to the irreducible and quasi-positive matrix
which governs the flux-force relations and are able to show normal ellipticity
of the associated multicomponent diffusion operator. This provides
local-in-time wellposedness of the Maxwell-Stefan multicomponent diffusion
system in the isobaric, isothermal case.Comment: Based on a talk given at the Conference on Nonlinear Parabolic
Problems in Bedlewo, Mai 200
Henri Poincaré: The Status of Mechanical Explanations and the Foundations of Statistical Mechanics
The first goal of this paper is to show the evolution of PoincarĂ©âs opinion on the mechanistic reduction of the principles of thermodynamics, placing it in the context of the science of his time. The second is to present some of his work in 1890 on the foundations of statistical mechanics. He became interested first in thermodynamics and its relation with mechanics, drawing on the work of Helm-holtz on monocyclic systems. After a period of skepticism concerning the kinetic theory, he read some of Maxwellâs memories and contributed to the foundations of statistical mechanics. I also show that PoincarĂ©'s contributions to the founda-tions of statistical mechanics are closely linked to his work in celestial mechanics and its interest in probability theory and its role in physics
Mosquito Abundance, Bed net Coverage and Other Factors Associated with Variations in Sporozoite Infectivity Rates in Four Villages of Rural Tanzania.
Entomological surveys are of great importance in decision-making processes regarding malaria control strategies because they help to identify associations between vector abundance both species-specific ecology and disease intervention factors associated with malaria transmission. Sporozoite infectivity rates, mosquito host blood meal source, bed net coverage and mosquito abundance were assessed in this study. A longitudinal survey was conducted in four villages in two regions of Tanzania. Malaria vectors were sampled using the CDC light trap and pyrethrum spray catch methods. In each village, ten paired houses were selected for mosquitoes sampling. Sampling was done in fortnight case and study was undertaken for six months in both Kilimanjaro (Northern Tanzania) and Dodoma (Central Tanzania) regions. A total of 6,883 mosquitoes were collected including: 5,628 (81.8%) Anopheles arabiensis, 1,100 (15.9%) Culex quinquefasciatus, 89 (1.4%) Anopheles funestus, and 66 (0.9%) Anopheles gambiae s.s. Of the total mosquitoes collected 3,861 were captured by CDC light trap and 3,022 by the pyrethrum spray catch method. The overall light trap: spray catch ratio was 1.3:1. Mosquito densities per room were 96.5 and 75.5 for light trap and pyrethrum spray catch respectively. Mosquito infectivity rates between villages that have high proportion of bed net owners and those without bed nets was significant (P < 0.001) and there was a significant difference in sporozoite rates between households with and without bed nets in these four villages (P < 0.001). Malaria remains a major problem in the study areas characterized as low transmission sites. Further studies are required to establish the annual entomological inoculation rates and to observe the annual parasitaemia dynamics in these communities. Outdoor mosquitoes collection should also be considered
Reversible viscosity and Navier--Stokes fluids
Exploring the possibility of describing a fluid flow via a time-reversible
equation and its relevance for the fluctuations statistics in stationary
turbulent (or laminar) incompressible Navier-Stokes flows.Comment: 7 pages 6 figures, v2: replaced Fig.6 and few changes. Last version:
appendix cut shorter, because of a computational erro
Self-Organization and the Physics of Glassy Networks
Network glasses are the physical prototype for many self-organized systems,
ranging from proteins to computer science. Conventional theories of gases,
liquids, and crystals do not account for the strongly material-selective
character of the glass-forming tendency, the phase diagrams of glasses, or
their optimizable properties. A new topological theory, only 25 years old, has
succeeded where conventional theories have failed. It shows that (probably all
slowly quenched) glasses, including network glasses, are the result of the
combined effects of a few simple mechanisms. These glass-forming mechanisms are
topological in nature, and have already been identified for several important
glasses, including chalcogenide alloys, silicates (window glass, computer
chips), and proteins.Comment: One PDF file contains 10 figures and tex
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