27,184 research outputs found
Graphs Identified by Logics with Counting
We classify graphs and, more generally, finite relational structures that are
identified by C2, that is, two-variable first-order logic with counting. Using
this classification, we show that it can be decided in almost linear time
whether a structure is identified by C2. Our classification implies that for
every graph identified by this logic, all vertex-colored versions of it are
also identified. A similar statement is true for finite relational structures.
We provide constructions that solve the inversion problem for finite
structures in linear time. This problem has previously been shown to be
polynomial time solvable by Martin Otto. For graphs, we conclude that every
C2-equivalence class contains a graph whose orbits are exactly the classes of
the C2-partition of its vertex set and which has a single automorphism
witnessing this fact.
For general k, we show that such statements are not true by providing
examples of graphs of size linear in k which are identified by C3 but for which
the orbit partition is strictly finer than the Ck-partition. We also provide
identified graphs which have vertex-colored versions that are not identified by
Ck.Comment: 33 pages, 8 Figure
Dense Packings of Congruent Circles in Rectangles with a Variable Aspect Ratio
We use computational experiments to find the rectangles of minimum area into
which a given number n of non-overlapping congruent circles can be packed. No
assumption is made on the shape of the rectangles. Most of the packings found
have the usual regular square or hexagonal pattern. However, for 1495 values of
n in the tested range n =< 5000, specifically, for n = 49, 61, 79, 97, 107,...
4999, we prove that the optimum cannot possibly be achieved by such regular
arrangements. The evidence suggests that the limiting height-to-width ratio of
rectangles containing an optimal hexagonal packing of circles tends to
2-sqrt(3) as n tends to infinity, if the limit exists.Comment: 21 pages, 13 figure
The application of self-limiting transgenic insects in managing resistance in experimental metapopulations
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.Data sharing: raw data for this study are available as supplementary data files.1. The mass release of transgenic insects carrying female lethal self-limiting genes can
reduce pest insect populations. Theoretically, substantial releases can be a novel
resistance management tool, since wild type alleles conferring susceptibility to
pesticides can dilute resistance alleles in target populations. A potential barrier to the
deployment of this technology is the need for large-scale area wide releases. Here we
address whether localized releases of transgenic insects could provide an alternative,
means of population suppression and resistance management, without serious loss of
efficacy.
2. We used experimental mesocosms constituting insect metapopulations to explore the
evolution of resistance to the Bacillus thuringiensis toxin Cry1Ac in a high-dose/refugia
landscape in the insect Plutella xylostella. We ran two selection experiments, the first
compared the efficacy of ‘everywhere’ releases and negative controls to a spatially
density-dependent or ‘whack-a-mole’ strategy that concentrated release of transgenic
insects in sub-populations with high levels of resistance. The second experiment tested
the relative efficacy of whack-a-mole and everywhere releases under spatially
homogenous and heterogeneous selection pressure.
3. The whack-a-mole releases were less effective than everywhere releases in terms of
slowing the evolution of resistance, which in the first experiment, largely prevented the
evolution of resistance. In contrast to predictions, heterogeneous whack-a-mole releases
were not more effective under heterogeneous selection pressure. Heterogeneous
selection pressure did, however, reduce total insect population sizes
4. Whack-a-mole releases provided early population suppression that was
indistinguishable from homogeneous everywhere releases. However, insect population
densities tracked the evolution of resistance in this system, as phenotypic resistance
provides access to the 90% of experimental diet containing the toxin Cry1Ac. Thus, as
resistance levels diverged between treatments, carrying capacities diverged and
population sizes increased under the whack- a-mole approach.
Synthesis and Applications Spatially density-dependent releases of transgenic insects,
particularly those targeting source populations at landscape level, could suppress pest
populations in the absence of blanket area-wide management. The resistance
management benefits of self-limiting transgenic insects are, however, reduced in
spatially localized releases, suggesting that they are not best suited for spatially
restricted ‘spot’ treatment of problematic resistance. Nevertheless, area-wide and
spatially heterogeneous releases could be used to support other resistance management
interventions.This work was supported by the Biotechnology and Biological Sciences Research Council
[grant numbers BB/L00948X/1 to MBB and NA, and BB/L00819X/1&2 to BR]
Point-Coupling Models from Mesonic Hypermassive Limit and Mean-Field Approaches
In this work we show how nonlinear point-coupling models, described by a
Lagrangian density that presents only terms up to fourth order in the fermion
condensate , are derived from a modified meson-exchange
nonlinear Walecka model. The derivation can be done through two distinct
methods, namely, the hypermassive meson limit within a functional integral
approach, and the mean-field approximation in which equations of state at zero
temperature of the nonlinear point-coupling models are directly obtained.Comment: 18 pages. Accepted for publication in Braz. J. Phy
Kaons production at finite temperature and baryon density in an effective relativistic mean field model
We investigate the kaons production at finite temperature and baryon density
by means of an effective relativistic mean-field model with the inclusion of
the full octet of baryons. Kaons are considered taking into account of an
effective chemical potential depending on the self-consistent interaction
between baryons. The obtained results are compared with a minimal coupling
scheme, calculated for different values of the anti-kaon optical potential.Comment: 3 pages, contribution presented to the International Conference on
Exotic Atoms and Related Topic
Automatic correction of hand pointing in stereoscopic depth
In order to examine whether stereoscopic depth information could drive fast automatic correction of hand pointing, an experiment was designed in a 3D visual environment in which participants were asked to point to a target at different stereoscopic depths as quickly and accurately as possible within a limited time window (≤300 ms). The experiment consisted of two tasks: "depthGO" in which participants were asked to point to the new target position if the target jumped, and "depthSTOP" in which participants were instructed to abort their ongoing movements after the target jumped. The depth jump was designed to occur in 20% of the trials in both tasks. Results showed that fast automatic correction of hand movements could be driven by stereoscopic depth to occur in as early as 190 ms.This work was supported by the Grants from the National Natural Science Foundation of China (60970062 and 61173116) and the Doctoral Fund of Ministry of Education of China (20110072110014)
A "kilonova" associated with short-duration gamma-ray burst 130603B
Short-duration gamma-ray bursts (SGRBs) are intense flashes of cosmic
gamma-rays, lasting less than ~2 s, whose origin is one of the great unsolved
questions of astrophysics today. While the favoured hypothesis for their
production, a relativistic jet created by the merger of two compact stellar
objects (specifically, two neutron stars, NS-NS, or a neutron star and a black
hole, NS-BH), is supported by indirect evidence such as their host galaxy
properties, unambiguous confirmation of the model is still lacking. Mergers of
this kind are also expected to create significant quantities of neutron-rich
radioactive species, whose decay should result in a faint transient in the days
following the burst, a so-called "kilonova". Indeed, it is speculated that this
mechanism may be the predominant source of stable r-process elements in the
Universe. Recent calculations suggest much of the kilonova energy should appear
in the near-infrared (nIR) due to the high optical opacity created by these
heavy r-process elements. Here we report strong evidence for such an event
accompanying SGRB 130603B. If this simplest interpretation of the data is
correct, it provides (i) support for the compact object merger hypothesis of
SGRBs, (ii) confirmation that such mergers are likely sites of significant
r-process production and (iii) quite possibly an alternative, un-beamed
electromagnetic signature of the most promising sources for direct detection of
gravitational waves.Comment: preprint of paper appearing in Nature (3 Aug 2013
Realization of a single Josephson junction for Bose-Einstein condensates
We report on the realization of a double-well potential for Rubidium-87
Bose-Einstein condensates. The experimental setup allows the investigation of
two different dynamical phenomena known for this system - Josephson
oscillations and self-trapping. We give a detailed discussion of the
experimental setup and the methods used for calibrating the relevant
parameters. We compare our experimental findings with the predictions of an
extended two-mode model and find quantitative agreement
Comments on black holes I: The possibility of complementarity
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who
argue against black hole complementarity based on the claim that an infalling
observer 'burns' as he approaches the horizon. We show that in fact
measurements made by an infalling observer outside the horizon are
statistically identical for the cases of vacuum at the horizon and radiation
emerging from a stretched horizon. This forces us to follow the dynamics all
the way to the horizon, where we need to know the details of Planck scale
physics. We note that in string theory the fuzzball structure of microstates
does not give any place to 'continue through' this Planck regime. AMPS argue
that interactions near the horizon preclude traditional complementarity. But
the conjecture of 'fuzzball complementarity' works in the opposite way: the
infalling quantum is absorbed by the fuzzball surface, and it is the resulting
dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde
An early Little Ice Age brackish water invasion along the south coast of the Caspian Sea (sediment of Langarud wetland) and its wider impacts on environment and people
Caspian Sea level has undergone significant changes through time with major impacts not only on the surrounding coasts, but also offshore. This study reports a brackish water invasion on the southern coast of the Caspian Sea constructed from a multi-proxy analysis of sediment retrieved from the Langarud wetland. The ground surface level of wetland is >6 m higher than the current Caspian Sea level (at -27.41 m in 2014) and located >11 km far from the coast. A sequence covering the last millennium was dated by three radiocarbon dates. The results from this new study suggest that Caspian Sea level rose up to at least -21.44 m (i.e. >6 m above the present water level) during the early Little Ice Age. Although previous studies in the southern coast of the Caspian Sea have detected a high-stand during the Little Ice Age period, this study presents the first evidence that this high-stand reached so far inland and at such a high altitude. Moreover, it confirms one of the very few earlier estimates of a high-stand at -21 m for the second half of the 14th century. The effects of this large-scale brackish water invasion on soil properties would have caused severe disruption to regional agriculture, thereby destabilizing local dynasties and facilitating a rapid Turko-Mongol expansion of Tamerlane’s armies from the east.N Ghasemi (INIOAS), V Jahani (Gilan Province Cultural Heritage and Tourism Organisation) and A Naqinezhad (University of Mazandaran), INQUA QuickLakeH project (no. 1227) and to the European project Marie Curie, CLIMSEAS-PIRSES-GA-2009-24751
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