1,115,295 research outputs found
A search for solar-like oscillations in the Am star HD 209625
The goal is to test the structure of hot metallic stars, and in particular
the structure of a near-surface convection zone using asteroseismic
measurements. Indeed, stellar models including a detailed treatement of the
radiative diffusion predict the existence of a near-surface convection zone in
order to correctly reproduce the anomalies in surface abundances that are
observed in Am stars. The Am star HD 209625 was observed with the Harps
spectrograph mounted on the 3.6-m telescope at the ESO La Silla Observatory
(Chile) during 9 nights in August 2005. This observing run allowed us to
collect 1243 radial velocity (RV) measurements, with a standard deviation of
1.35 m/s. The power spectrum associated with these RV measurements does not
present any excess. Therefore, either the structure of the external layers of
this star does not allow excitation of solar-like oscillations, or the
amplitudes of the oscillations remain below 20-30 cm/s (depending on their
frequency range).Comment: 5 pages, 4 figures, A&A accepte
Graphene for Antenna Applications: Opportunities and Challenges from Microwaves to THz
The use of graphene for antennas and other electromagnetic passives could
bring significant benefit such as extreme miniaturization, monolithic
integration with graphene RF nanoelectronics, efficient dynamic tuning, and
even transparency and mechanical flexibility. Though recently different related
theoretical works have been presented, relatively few applications have been
proposed and realistically assessed. In this invited talk we will briefly
review the main properties of graphene and the state of the art in its
theoretical and experimental characterization. Then, we will discuss a number
of potential antenna applications from microwave to THz, providing in each case
a critical assessment of the benefits, limitations, and remaining issues
towards actual real-life implementations. Here we provide a brief overview of
different devices and associated developments in our group discussed in the
talk, including graphene antennas and reflectarrays at microwave and THz,
plasmonic switches, isotropic and anisotropic meta-surfaces, or graphene
RF-NEMS
Review of: Amer EI-Ahraf et al., The Impact of Public Policy on Environmental Quality and Health: The Case of Land Use Management and Planning
Review of the book The Impact of Public Policy on Environmental Quality and Health: The Case of Land Use Management and Planning by Amer El-Ahraf et al., (Quorum Books 1999). Acknowledgments, introduction, appendixes, selected bibliography, index. ISBN 1-56720-065-6 [181 pp. $59.95. Hardbound, 88 Post Road West, Westport, CT 06881]
Asteroseismology of the visual binary 70 Ophiuchi
Convection in stars excites resonant acoustic waves. The frequencies of these
oscillations depend on the sound speed inside the star, which in turn depends
on density, temperature, gas motion, and other properties of the stellar
interior. Therefore, analysis of the oscillations provides an unrivaled method
to probe the internal structure of a star. Solar-like oscillations in the
primary of the visual binary 70 Ophiuchi are investigated. 70 Ophiuchi A was
observed with the Harps spectrograph mounted on the 3.6-m telescope at the ESO
La Silla Observatory (Chile) during 6 nights in July 2004 allowing us to
collect 1758 radial velocity measurements with a standard deviation of about
1.39 m s-1. The power spectrum of the high precision velocity time series
clearly presents several identifiable peaks between 3 and 6 mHz showing
regularity with a large spacing of Delta_nu = 161.7 +- 0.3 uHz. Fourteen
individual modes were identified with amplitudes in the range 11 to 14 cm s-1.Comment: 5 pages, A&A in pres
Americans' Access to Prescription Drugs Stabilizes, 2007-2010
Examines trends in the percentage of Americans reporting difficulty affording prescription drugs by insurance status, age group, income, and health status. Considers contributing factors such as changes in the uninsured population and fewer doctor visits
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Review of standards for biodegradable plastic bags.
The Single Use Carrier Bags Charges (England) Order 2015 requires retailers to charge at least 5p for each single use carrier bag, except where exempted.
Under section 18 of that order, the Secretary of State must—
(a) complete a review of industry standards for the biodegradability of lightweight plastic material; and
(b) lay a copy of a report before Parliament setting out the conclusions of the review, in particular—
(i) whether it appears to the Secretary of State that there exists an industry standard appropriate for the purposes of an exclusion from the obligations specified in Part 2 on grounds of biodegradability; and
(ii) if so, how that exclusion would be implemented.
That review has now been completed. It found that there are a number of standards for plastic bag biodegradability. We will need to conduct further work before any of these could be used to exempt certain types of carrier bags on grounds of biodegradability.
By the end of May 2016 retailers are required to report the number of bags that have been supplied, and the uses to which the proceeds of the charge have been put, after reasonable costs are deducted. The Government will use that opportunity to consider the early impacts of the charge. The Government will continue to consider the technical specification for a genuinely biodegradable bag, and will at that point further report on how an exemption for such a biodegradable bag can be implemented
MEMS-reconfigurable metamaterials and antenna applications
This paper reviews some of our contributions to reconfigurable metamaterials,
where dynamic control is enabled by micro-electro-mechanical systems (MEMS)
technology. First, we show reconfigurable composite right/left handed
transmission lines (CRLH-TLs) having state of the art phase velocity variation
and loss, thereby enabling efficient reconfigurable phase shifters and
leaky-wave antennas (LWA). Second, we present very low loss metasurface designs
with reconfigurable reflection properties, applicable in reflectarrays and
partially reflective surface (PRS) antennas. All the presented devices have
been fabricated and experimentally validated. They operate in X- and Ku-bands.Comment: 8 pages; 8 figures; International Journal of Antennas and Propagatio
Dominant role of many-body effects on the carrier distribution function of quantum dot lasers
The effects of free-carrier-induced shift and broadening on the carrier distribution function are studied considering different extreme cases for carrier statistics (Fermi–Dirac and random carrier distributions) as well as quantum dot (QD) ensemble inhomogeneity and state separation using a Monte Carlo model. Using this model, we show that the dominant factor determining the carrier distribution function is the free carrier effects and not the choice of carrier statistics. By using empirical values of the free-carrier-induced shift and broadening, good agreement is obtained with experimental data of QD materials obtained under electrical injection for both extreme cases of carrier statistics
Impact of doping on the carrier dynamics in graphene
We present a microscopic study on the impact of doping on the carrier
dynamics in graphene, in particular focusing on its influence on the
technologically relevant carrier multiplication in realistic, doped graphene
samples. Treating the time- and momentum-resolved carrier-light,
carrier-carrier, and carrier-phonon interactions on the same microscopic
footing, the appearance of Auger-induced carrier multiplication up to a Fermi
level of 300 meV is revealed. Furthermore, we show that doping favors the
so-called hot carrier multiplication occurring within one band. Our results are
directly compared to recent time-resolved ARPES measurements and exhibit an
excellent agreement on the temporal evolution of the hot carrier multiplication
for n- and p-doped graphene. The gained insights shed light on the ultrafast
carrier dynamics in realistic, doped graphene sample
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