1,786 research outputs found
Twisted split-ring-resonator photonic metamaterial with huge optical activity
Coupled split-ring-resonator metamaterials have previously been shown to
exhibit large coupling effects, which are a prerequisite for obtaining large
effective optical activity. By a suitable lateral arrangement of these building
blocks, we completely eliminate linear birefringence and obtain pure optical
activity and connected circular optical dichroism. Experiments at around
100-THz frequency and corresponding modeling are in good agreement. Rotation
angles of about 30 degrees for 205nm sample thickness are derived.Comment: 6 pages, 4 figure
Metamaterials proposed as perfect magnetoelectrics
Magnetoelectric susceptibility of a metamaterial built from split ring
resonators have been investigated both experimentally and within an equivalent
circuit model. The absolute values have been shown to exceed by two orders of
magnitude that of classical magnetoelectric materials. The metamaterial
investigated reaches the theoretically predicted value of the magnetoelectric
susceptibility which is equal to the geometric average of the electric and
magnetic susceptibilities.Comment: 5 pages, 3 figure
Nonlinear Elasticity of Single Collapsed Polyelectrolytes
Nonlinear elastic responses of short and stiff polyelectrolytes are
investigated by dynamic simulations on a single molecule level. When a
polyelectrolyte condensate undergoes a mechanical unfolding, two types of
force-extension curves, i.e., a force plateau and a stick-release pattern, are
observed depending on the strength of the electrostatic interaction. We provide
a physical interpretation of such force-extension behavior in terms of
intramolecular structures of the condensates. We also describe a charge
distribution of condensed counterions onto a highly stretched polyelectrolyte,
which clarifies a formation of one-dimensional strongly correlated liquid at
large Coulomb coupling regime where a stick-release pattern is observed. These
findings may provide significant insights into the relationship between a
molecular elasticity and a molecular mechanism of like-charge attractions
observed in a wide range of charged biopolymer systems.Comment: 5pages, 5figure
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Stripper-foil scan studies of the first-turn beam loss mechanism in the LAMPF proton storage ring (PSR)
First-turn beam losses in the LAMPF Proton Storage Ring were measured as a function of the left-right position of the carbon foil used to strip neutral hydrogen atoms to H[sup +] for proton injection into the PSR. Two foil thicknesses, 200 and 300 [mu]g/cm[sup 2], were tested. Results indicated that first-turn loss is caused predominately by magnetic field stripping of a small fraction of the H[sub 0] atoms that pass through the stripper foil without being stripped to protons, and the results were not consistent with a mechanism involving protons originating from atoms in the halo of the neutral beam incident on the stripper foil
Availability of diagnostic services and essential medicines for non-communicable respiratory diseases in African countries
BACKGROUND: The global burden of disease due to asthma and chronic obstructive pulmonary disease (COPD) is substantial and particularly great in lowâ and middleâincome countries, including many African countries. Management is affected by availability of diagnostic tests and essential medicines. The study aimed to explore the availability of spirometry services and essential medicines for asthma and COPD in African countries.
METHOD: Questionnaires were delivered to healthcare workers at the annual meeting of the Pan African Thoracic Society Methods in Epidemiology and Clinical Research (PATS MECOR) and International Multidisciplinary Programme to Address Lung Health and TB in Africa (IMPALA). Data were analysed using simple descriptive statistics.
RESULTS: A total of 37 questionnaires representing 13 African countries were returned. Spirometry availability was 73.0%. The most common reasons for nonâavailability were lack of knowledge of the utility of the test. Within the study sample, 33.3% faced sporadic availability due to maintenance issues. Essential medicines availability ranged from 37.8% for inhaled corticosteroidâlongâacting betaâagonist inhalers to 100% for prednisolone 5 mg tablets, mainly due to supply chain problems.
CONCLUSION: There is varied availability of spirometry and WHO essential medicines for COPD and asthma in African countries. Strategies are needed to improve access to basic effective care for people with nonâcommunicable lung disease in Africa
Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials
We review the basic physics behind light interaction with plasmonic
nanoparticles. The theoretical foundations of light scattering on one metallic
particle (a plasmonic monomer) and two interacting particles (a plasmonic
dimer) are systematically investigated. Expressions for effective particle
susceptibility (polarizability) are derived, and applications of these results
to plasmonic nanoantennas are outlined. In the long-wavelength limit, the
effective macroscopic parameters of an array of plasmonic dimers are
calculated. These parameters are attributable to an effective medium
corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial
where plasmonic monomers or dimers have the function of "meta-atoms". It is
shown that planar dimers consisting of rod-like particles generally possess
elliptical dichroism and function as atoms for planar chiral metamaterials. The
fabricational simplicity of the proposed rod-dimer geometry can be used in the
design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.
Past Achievements and Future Challenges in 3D Photonic Metamaterials
Photonic metamaterials are man-made structures composed of tailored micro- or
nanostructured metallo-dielectric sub-wavelength building blocks that are
densely packed into an effective material. This deceptively simple, yet
powerful, truly revolutionary concept allows for achieving novel, unusual, and
sometimes even unheard-of optical properties, such as magnetism at optical
frequencies, negative refractive indices, large positive refractive indices,
zero reflection via impedance matching, perfect absorption, giant circular
dichroism, or enhanced nonlinear optical properties. Possible applications of
metamaterials comprise ultrahigh-resolution imaging systems, compact
polarization optics, and cloaking devices. This review describes the
experimental progress recently made fabricating three-dimensional metamaterial
structures and discusses some remaining future challenges
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Noninterceptive beam energy measurements in line D of the Los Alamos Meson Physics Facility
Several members of the Accelerator and Operations Technology (AOT) division beam-diagnostics team performed time-of-flight (TOF) beam-energy measurements in line D of the Los Alamos Meson Physics Facility (LAMPF) using developmental beam time. These measurements provided information for a final design of an on-line beam energy measurement. The following paper discusses these measurements and how they apply to the final beam energy measurement design
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