482 research outputs found
Harnessing poly(ionic liquid)s for sensing applications
The interest in poly(ionic liquid)s for sensing applications is derived from their strong interactions to a variety of analytes. By combining the desirable mechanical properties of polymers with the physical and chemical properties of ILs, new materials can be created. The tunable nature of both ionic liquids and polymers allows for incredible diversity, which is exemplified in their broad applicability. In this article we examine the new field of poly(ionic liquid) sensors by providing a detailed look at the current state-of-the-art sensing devices for solvents, gases, biomolecules, pH, and anions
Tropical polyhedra are equivalent to mean payoff games
We show that several decision problems originating from max-plus or tropical
convexity are equivalent to zero-sum two player game problems. In particular,
we set up an equivalence between the external representation of tropical convex
sets and zero-sum stochastic games, in which tropical polyhedra correspond to
deterministic games with finite action spaces. Then, we show that the winning
initial positions can be determined from the associated tropical polyhedron. We
obtain as a corollary a game theoretical proof of the fact that the tropical
rank of a matrix, defined as the maximal size of a submatrix for which the
optimal assignment problem has a unique solution, coincides with the maximal
number of rows (or columns) of the matrix which are linearly independent in the
tropical sense. Our proofs rely on techniques from non-linear Perron-Frobenius
theory.Comment: 28 pages, 5 figures; v2: updated references, added background
materials and illustrations; v3: minor improvements, references update
An Investigation into the Radial Velocity Variations of CoRoT-7
CoRoT-7b, the first transiting ``superearth'' exoplanet, has a radius of 1.7
R_Earth and a mass of 4.8 M_Earth. Ground-based radial velocity measurements
also detected an additional companion with a period of 3.7 days (CoRoT-7c) and
a mass of 8.4 M_Earth. The mass of CoRoT-7b is a crucial parameter for planet
structure models, but is difficult to determine because CoRoT-7 is a modestly
active star and there is at least one additional companion. A Fourier analysis
was performed on spectral data for CoRoT-7 taken with the HARPS spectrograph.
These data include RV measurements, spectral line bisectors, the full width at
half maximum of the cross-correlation function, and Ca II emission. The latter
3 quantities vary due to stellar activity and were used to assess the nature of
the observed RV variations. An analysis of a sub-set of the RV measurements
where multiple observations were made per night was also used to estimate the
RV amplitude from CoRoT-7b that was less sensitive to activity variations. Our
analysis indicates that the 0.85-d and 3.7-d RV signals of CoRoT-7b and
CoRoT-7c are present in the spectral data with a high degree of statistical
significance. We also find evidence for another significant RV signal at 9
days. An analysis of the activity indicator data reveals that this 9-d signal
most likely does not arise from activity, but possibly from an additional
companion. If due to a planetary companion the mass is m = 19.5 M_Earth,
assuming co-planarity with CoRoT-7b. A dynamical study of the three planet
system shows that it is stable over several hundred millions of years. Our
analysis yields a RV amplitude of 5.04 +/- 1.09 m/s for CoRoT-7b which
corresponds to a planet mass of m = 6.9 +/- 1.4 M_Earth. This increased mass
would make the planet CoRoT-7b more Earth-like in its internal structure.Comment: 20 pages, 20 figure
A phosphorus-rich polymer as a homogeneous catalyst scavenger
© The Royal Society of Chemistry 2017. A soft polymer network prepared through a phosphane-ene reaction successfully sequestered Rh and Ru from hydrogenation and ring closing metathesis reactions, respectively. Scavenging effectively quenches catalytic activity and ultimately removes \u3e98% of the metal
Modulation of DNA damage tolerance in Escherichia coli recG and ruv strains by mutations affecting PriB, the ribosome and RNA polymerase
RecG is a DNA translocase that helps to maintain genomic integrity. Initial studies suggested a role in promoting recombination, a possibility consistent with synergism between recG and ruv null alleles and reinforced when the protein was shown to unwind Holliday junctions. In this article we describe novel suppressors of recG and show that the pathology seen without RecG is suppressed on reducing or eliminating PriB, a component of the PriA system for replisome assembly and replication restart. Suppression is conditional, depending on additional mutations that modify ribosomal subunit S6 or one of three subunits of RNA polymerase. The latter suppress phenotypes associated with deletion of priB, enabling the deletion to suppress recG. They include alleles likely to disrupt interactions with transcription anti-terminator, NusA. Deleting priB has a different effect in ruv strains. It provokes abortive recombination and compromises DNA repair in a manner consistent with PriB being required to limit exposure of recombinogenic ssDNA. This synergism is reduced by the RNA polymerase mutations identified. Taken together, the results reveal that RecG curbs a potentially negative effect of proteins that direct replication fork assembly at sites removed from the normal origin, a facility needed to resolve conflicts between replication and transcription
Removing systematics from the CoRoT light curves: I. Magnitude-Dependent Zero Point
This paper presents an analysis that searched for systematic effects within
the CoRoT exoplanet field light curves. The analysis identified a systematic
effect that modified the zero point of most CoRoT exposures as a function of
stellar magnitude. We could find this effect only after preparing a set of
learning light curves that were relatively free of stellar and instrumental
noise. Correcting for this effect, rejecting outliers that appear in almost
every exposure, and applying SysRem, reduced the stellar RMS by about 20 %,
without attenuating transit signals.Comment: Accepted for publication in Astronomy and Astrophysic
Noise properties of the CoRoT data: a planet-finding perspective
In this short paper, we study the photometric precision of stellar light
curves obtained by the CoRoT satellite in its planet finding channel, with a
particular emphasis on the timescales characteristic of planetary transits.
Together with other articles in the same issue of this journal, it forms an
attempt to provide the building blocks for a statistical interpretation of the
CoRoT planet and eclipsing binary catch to date.
After pre-processing the light curves so as to minimise long-term variations
and outliers, we measure the scatter of the light curves in the first three
CoRoT runs lasting more than 1 month, using an iterative non-linear filter to
isolate signal on the timescales of interest. The bevhaiour of the noise on 2h
timescales is well-described a power-law with index 0.25 in R-magnitude,
ranging from 0.1mmag at R=11.5 to 1mmag at R=16, which is close to the
pre-launch specification, though still a factor 2-3 above the photon noise due
to residual jitter noise and hot pixel events. There is evidence for a slight
degradation of the performance over time. We find clear evidence for enhanced
variability on hours timescales (at the level of 0.5 mmag) in stars identified
as likely giants from their R-magnitude and B-V colour, which represent
approximately 60 and 20% of the observed population in the direction of Aquila
and Monoceros respectively. On the other hand, median correlated noise levels
over 2h for dwarf stars are extremely low, reaching 0.05mmag at the bright end.Comment: 5 pages, 4 figures, accepted for publication in A&
A First-Year Research Experience: The Freshman Project in Physics at Loyola University Chicago
Undergraduate research has become an essential mode of engaging and retaining students in physics. At Loyola University Chicago, first-year physics students have been participating in the Freshman Projects program for over twenty years, which has coincided with a period of significant growth for our department. In this paper, we describe how the Freshman Projects program has played an important role in advancing undergraduate research at Loyola and the profound impact it has made on our program. We conclude with suggestions for adoption of similar programs at other institutions
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