819 research outputs found
Oblique frozen modes in periodic layered media
We study the classical scattering problem of a plane electromagnetic wave
incident on the surface of semi-infinite periodic stratified media
incorporating anisotropic dielectric layers with special oblique orientation of
the anisotropy axes. We demonstrate that an obliquely incident light, upon
entering the periodic slab, gets converted into an abnormal grazing mode with
huge amplitude and zero normal component of the group velocity. This mode
cannot be represented as a superposition of extended and evanescent
contributions. Instead, it is related to a general (non-Bloch) Floquet
eigenmode with the amplitude diverging linearly with the distance from the slab
boundary. Remarkably, the slab reflectivity in such a situation can be very
low, which means an almost 100% conversion of the incident light into the
axially frozen mode with the electromagnetic energy density exceeding that of
the incident wave by several orders of magnitude. The effect can be realized at
any desirable frequency, including optical and UV frequency range. The only
essential physical requirement is the presence of dielectric layers with proper
oblique orientation of the anisotropy axes. Some practical aspects of this
phenomenon are considered.Comment: text and 9 figure
Constraints on a second planet in the WASP-3 system
There have been previous hints that the transiting planet WASP-3 b is
accompanied by a second planet in a nearby orbit, based on small deviations
from strict periodicity of the observed transits. Here we present 17 precise
radial velocity measurements and 32 transit light curves that were acquired
between 2009 and 2011. These data were used to refine the parameters of the
host star and transiting planet. This has resulted in reduced uncertainties for
the radii and masses of the star and planet. The radial-velocity data and the
transit times show no evidence for an additional planet in the system.
Therefore, we have determined the upper limit on the mass of any hypothetical
second planet, as a function of its orbital period.Comment: Accepted for publication in The Astronomical Journa
Transit Variability in Bow Shock-Hosting Planets
We investigate the formation of bow shocks around exoplanets as a result of
the interaction of the planet with the coronal material of the host star,
focusing on physical causes that can lead to temporal variations in the shock
characteristics. We recently suggested that WASP-12b may host a bow shock
around its magnetosphere, similarly to the one observed around the Earth. For
WASP12b, the shock is detected in the near-UV transit light curve.
Observational follow-up suggests that the near-UV light curve presents temporal
variations, which may indicate that the stand-off distance between the shock
and the planet is varying. This implies that the size of the planet's
magnetosphere is adjusting itself in response to variations in the surrounding
ambient medium. We investigate possible causes of shock variations for the
known eccentric (e>0.3) transiting planets. We show that, because the distance
from the star changes along the orbit of an eccentric planet, the shock
characteristics are modulated by orbital phase. We predict time offsets between
the beginnings of the near-UV and optical light curves that are, in general,
less than the transit duration. Variations in shock characteristics caused in
eccentric systems can only be probed if the shock is observed at different
orbital phases, which is, in general, not the case for transit observations.
However, non-thermal radio emission produced by the interaction of the star and
planet should be modulated by orbital phase. We also quantify the response of
the shock to variations in the coronal material itself due to, e.g., a
non-axisymmetric stellar corona, planetary obliquity, intrinsic variations of
the stellar magnetic field. Such variations do not depend on the system
eccentricity. We conclude that, for systems where a shock is detectable through
transit light curve observations, shock variations should be a common
occurrence. (Abridged)Comment: 10 pages, 11 figures, 1 table. MNRAS accepte
Calculation of atomic spontaneous emission rate in 1D finite photonic crystal with defects
We derive the expression for spontaneous emission rate in finite
one-dimensional photonic crystal with arbitrary defects using the effective
resonator model to describe electromagnetic field distributions in the
structure. We obtain explicit formulas for contributions of different types of
modes, i.e. radiation, substrate and guided modes. Formal calculations are
illustrated with a few numerical examples, which demonstrate that the
application of effective resonator model simplifies interpretation of results.Comment: Cent. Eur. J. Phys, in pres
Improved precision on the radius of the nearby super-Earth 55 Cnc e
We report on new transit photometry for the super-Earth 55 Cnc e obtained
with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data
leads to a planet radius of 2.21-0.16+0.15 Rearth, in good agreement with the
values previously derived from the MOST and Spitzer transit discovery data. A
global analysis of both Spitzer transit time-series improves the precision on
the radius of the planet at 4.5 microns to 2.20+-0.12 Rearth. We also performed
an independent analysis of the MOST data, paying particular attention to the
influence of the systematic effects of instrumental origin on the derived
parameters and errors by including them in a global model instead of performing
a preliminary detrending-filtering processing. We deduce an optical planet
radius of 2.04+0.15 Rearth from this reanalysis of MOST data, which is
consistent with the previous MOST result and with our Spitzer infrared radius.
Assuming the achromaticity of the transit depth, we performed a global analysis
combining Spitzer and MOST data that results in a planet radius of 2.17+-0.10
Rearth (13,820+-620 km). These results point to 55 Cnc e having a gaseous
envelope overlying a rocky nucleus, in agreement with previous works. A
plausible composition for the envelope is water which would be in
super-critical form given the equilibrium temperature of the planet.Comment: 7 pages, 7 figures. Submitted to A&A on 21/10/2011. Accepted for
publication in A&A on . 28/12/2011. Accepted version uploade
SPECULOOS exoplanet search and its prototype on TRAPPIST
One of the most significant goals of modern science is establishing whether
life exists around other suns. The most direct path towards its achievement is
the detection and atmospheric characterization of terrestrial exoplanets with
potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs),
i.e. very-low-mass stars and brown dwarfs with effective temperatures lower
than 2700 K, represent a unique opportunity to reach this goal within the next
decade. The potential of the transit method for detecting potentially habitable
Earth-sized planets around these objects is drastically increased compared to
Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby
UCD would be amenable for a thorough atmospheric characterization, including
the search for possible biosignatures, with near-future facilities such as the
James Webb Space Telescope. In this chapter, we first describe the physical
properties of UCDs as well as the unique potential they offer for the detection
of potentially habitable Earth-sized planets suitable for atmospheric
characterization. Then, we present the SPECULOOS ground-based transit survey,
that will search for Earth-sized planets transiting the nearest UCDs, as well
as its prototype survey on the TRAPPIST telescopes. We conclude by discussing
the prospects offered by the recent detection by this prototype survey of a
system of seven temperate Earth-sized planets transiting a nearby UCD,
TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H.
Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure
The efficiency and effectiveness of utilizing diagrams in interviews: an assessment of participatory diagramming and graphic elicitation
Abstract
Background
This paper focuses on measuring the efficiency and effectiveness of two diagramming methods employed in key informant interviews with clinicians and health care administrators. The two methods are 'participatory diagramming', where the respondent creates a diagram that assists in their communication of answers, and 'graphic elicitation', where a researcher-prepared diagram is used to stimulate data collection.
Methods
These two diagramming methods were applied in key informant interviews and their value in efficiently and effectively gathering data was assessed based on quantitative measures and qualitative observations.
Results
Assessment of the two diagramming methods suggests that participatory diagramming is an efficient method for collecting data in graphic form, but may not generate the depth of verbal response that many qualitative researchers seek. In contrast, graphic elicitation was more intuitive, better understood and preferred by most respondents, and often provided more contemplative verbal responses, however this was achieved at the expense of more interview time.
Conclusion
Diagramming methods are important for eliciting interview data that are often difficult to obtain through traditional verbal exchanges. Subject to the methodological limitations of the study, our findings suggest that while participatory diagramming and graphic elicitation have specific strengths and weaknesses, their combined use can provide complementary information that would not likely occur with the application of only one diagramming method. The methodological insights gained by examining the efficiency and effectiveness of these diagramming methods in our study should be helpful to other researchers considering their incorporation into qualitative research designs
Polymorphic residues in rice NLRs expand binding and response to effectors of the blast pathogen
Accelerated adaptive evolution is a hallmark of plant-pathogen interactions. Plant intracellular immune receptors (NLRs) often occur as allelic series with differential pathogen specificities. The determinants of this specificity remain largely unknown. Here, we unravelled the biophysical and structural basis of expanded specificity in the allelic rice NLR Pik, which responds to the effector AVR-Pik from the rice blast pathogen Magnaporthe oryzae. Rice plants expressing the Pikm allele resist infection by blast strains expressing any of three AVR-Pik effector variants, whereas those expressing Pikp only respond to one. Unlike Pikp, the integrated heavy metal-associated (HMA) domain of Pikm binds with high affinity to each of the three recognized effector variants, and variation at binding interfaces between effectors and Pikp-HMA or Pikm-HMA domains encodes specificity. By understanding how co-evolution has shaped the response profile of an allelic NLR, we highlight how natural selection drove the emergence of new receptor specificities. This work has implications for the engineering of NLRs with improved utility in agriculture
Search for a Technicolor omega_T Particle in Events with a Photon and a b-quark Jet at CDF
If the Technicolor omega_T particle exists, a likely decay mode is omega_T ->
gamma pi_T, followed by pi_T -> bb-bar, yielding the signature gamma bb-bar. We
have searched 85 pb^-1 of data collected by the CDF experiment at the Fermilab
Tevatron for events with a photon and two jets, where one of the jets must
contain a secondary vertex implying the presence of a b quark. We find no
excess of events above standard model expectations. We express the result of an
exclusion region in the M_omega_T - M_pi_T mass plane.Comment: 14 pages, 2 figures. Available from the CDF server (PS with figs):
http://www-cdf.fnal.gov/physics/pub98/cdf4674_omega_t_prl_4.ps
FERMILAB-PUB-98/321-
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
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