948 research outputs found
Constraining the False Positive Rate for Kepler Planet Candidates with Multi-Color Photometry from the GTC
Using the OSIRIS instrument installed on the 10.4-m Gran Telescopio Canarias
(GTC) we acquired multi-color transit photometry of four small (Rp < 5 R_Earth)
short-period (P < 6 days) planet candidates recently identified by the Kepler
space mission. These observations are part of a program to constrain the false
positive rate for small, short-period Kepler planet candidates. Since planetary
transits should be largely achromatic when observed at different wavelengths
(excluding the small color changes due to stellar limb darkening), we use the
observed transit color to identify candidates as either false positives (e.g.,
a blend with a stellar eclipsing binary either in the background/foreground or
bound to the target star) or validated planets. Our results include the
identification of KOI 225.01 and KOI 1187.01 as false positives and the
tentative validation of KOI 420.01 and KOI 526.01 as planets. The probability
of identifying two false positives out of a sample of four targets is less than
1%, assuming an overall false positive rate for Kepler planet candidates of 10%
(as estimated by Morton & Johnson 2011). Therefore, these results suggest a
higher false positive rate for the small, short-period Kepler planet candidates
than has been theoretically predicted by other studies which consider the
Kepler planet candidate sample as a whole. Furthermore, our results are
consistent with a recent Doppler study of short-period giant Kepler planet
candidates (Santerne et al. 2012). We also investigate how the false positive
rate for our sample varies with different planetary and stellar properties. Our
results suggest that the false positive rate varies significantly with orbital
period and is largest at the shortest orbital periods (P < 3 days), where there
is a corresponding rise in the number of detached eclipsing binary stars...
(truncated)Comment: 13 pages, 12 figures, 3 tables; revised for MNRA
Synthesis and Characterization of LnAg(WO4)(MoO4)
Polycrystalline LnAg(WO4)(MoO4) powders, with Ln = La to Lu and Y, have been obtained by ceramic method. Rietveld refinement for all compounds reveals that they present tetragonal symmetry, space group I41/a (No. 88), where the Ln3+/Ag+ ions are located in the 4a atomic positions, since the W/Mo are randomly distributed into 4b crystal sites.
In these compounds, a and b lattice parameters take values between those corresponding to tungstate and molybdate compounds. A progressive decrease in the lattice parameters is observed in going from La to Lu derivatives as a consequence of the well-known lanthanide contraction
A priori mixing of mesons and the |Delta I|=1/2 rule in K\to\pi\pi
We consider the hypothesis of a priori mixings in the mass eigenstates of
mesons to obtain the |Delta I|=1/2 rule in K\to\pi\pi. The Hamiltonian
responsible for the transition is the strong interacting one. The experimental
data are described using the isospin symmetry relations between the strong
coupling constants
Constitutionalising the Senate: A Modest Democratic Proposal
The Senate Reference did not provide an ideal situation for clarifying the nature and limits of the power of constitutional reform in Canada. The facts gave the Court no choice but to recognize the fundamental role that the Senate plays in the Canadian constitutional order, and therefore to place some of its main features outside the scope of section 44 of the Constitution Act, 1982, even if they ran contrary to basic democratic values. For example, in order to explain that the implementation of consultative elections would alter the constitution’s basic structure, the Court was forced to construe in a negative light the prospect of a democratically legitimate Senate. In this paper, rather than attack or defend bicameralism, we will argue in favour of attributing a democratically reconstituted Senate with the primary responsibility of reviewing the constitutionality of legislation (as opposed to acting as a chamber of “sober second thought” with respect to the policy decisions of the House of Commons). Such an approach, we suggest, would augment the overall democratic legitimacy of the constitutional order
Constitutionalising the Senate: A Modest Democratic Proposal
The Senate Reference did not provide an ideal situation for clarifying the nature and limits of the power of constitutional reform in Canada. The facts gave the Court no choice but to recognize the fundamental role that the Senate plays in the Canadian constitutional order, and therefore to place some of its main features outside the scope of section 44 of the Constitution Act, 1982, even if they ran contrary to basic democratic values. For example, in order to explain that the implementation of consultative elections would alter the constitution’s basic structure, the Court was forced to construe in a negative light the prospect of a democratically legitimate Senate. In this paper, rather than attack or defend bicameralism, we will argue in favour of attributing a democratically reconstituted Senate with the primary responsibility of reviewing the constitutionality of legislation (as opposed to acting as a chamber of “sober second thought” with respect to the policy decisions of the House of Commons). Such an approach, we suggest, would augment the overall democratic legitimacy of the constitutional order
Stochastic Invariants for Probabilistic Termination
Termination is one of the basic liveness properties, and we study the
termination problem for probabilistic programs with real-valued variables.
Previous works focused on the qualitative problem that asks whether an input
program terminates with probability~1 (almost-sure termination). A powerful
approach for this qualitative problem is the notion of ranking supermartingales
with respect to a given set of invariants. The quantitative problem
(probabilistic termination) asks for bounds on the termination probability. A
fundamental and conceptual drawback of the existing approaches to address
probabilistic termination is that even though the supermartingales consider the
probabilistic behavior of the programs, the invariants are obtained completely
ignoring the probabilistic aspect.
In this work we address the probabilistic termination problem for
linear-arithmetic probabilistic programs with nondeterminism. We define the
notion of {\em stochastic invariants}, which are constraints along with a
probability bound that the constraints hold. We introduce a concept of {\em
repulsing supermartingales}. First, we show that repulsing supermartingales can
be used to obtain bounds on the probability of the stochastic invariants.
Second, we show the effectiveness of repulsing supermartingales in the
following three ways: (1)~With a combination of ranking and repulsing
supermartingales we can compute lower bounds on the probability of termination;
(2)~repulsing supermartingales provide witnesses for refutation of almost-sure
termination; and (3)~with a combination of ranking and repulsing
supermartingales we can establish persistence properties of probabilistic
programs.
We also present results on related computational problems and an experimental
evaluation of our approach on academic examples.Comment: Full version of a paper published at POPL 2017. 20 page
Spectroscopic Characteristics of Carbon Dots (C-Dots) Derived from Carbon Fibers and Conversion to Sulfur-Bridged C-Dots Nanosheets
We synthesized sub‐10 nm carbon nanoparticles (CNPs) consistent with photoluminescent carbon dots (C-dots) from carbon fiber starting material. The production of different C-dots fractions was monitored over seven days. During the course of the reaction, one fraction of C-dots species with relatively high photoluminescence was short-lived, emerging during the first hour of reaction but disappearing after one day of reaction. Isolation of this species during the first hour of the reaction was crucial to obtaining higher-luminescent C-dots species. When the reaction proceeded for one week, the appearance of larger nanostructures was observed over time, with lateral dimensions approaching 200 nm. The experimental evidence suggests that these larger species are formed from small C-dot nanoparticles bridged together by sulfur-based moieties between the C-dot edge groups, as if the C-dots polymerized by cross-linking the edge groups through sulfur bridges. Their size can be tailored by controlling the reaction time. Our results highlight the variety of CNP products, from sub‐10 nm C-dots to ~200 nm sulfur-containing carbon nanostructures, that can be produced over time during the oxidation reaction of the graphenic starting material. Our work provides a clear understanding of when to stop the oxidation reaction during the top-down production of C-dots to obtain highly photoluminescent species or a target average particle size
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