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Gullies on Mars: Origin by snow and ice melting and potential for life based on possible analogs from Devon Island, High Arctic
Gullies on Devon Island, High Arctic, which form by melting of transient surface ice and snow covers and offer morphologic and contextual analogs for gullies reported on Mars are reported to display enhancements in biological activity in contrast to surrounding polar desert terrain
Noncommutative GUT inspired theories and the UV finiteness of the fermionic four point functions
We show at one-loop and first order in the noncommutativity parameters that
in any noncommutative GUT inspired theory the total contribution to the
fermionic four point functions coming only from the interaction between
fermions and gauge bosons, though not UV finite by power counting, is UV finite
at the end of the day. We also show that this is at odds with the general case
for noncommutative gauge theories --chiral or otherwise-- defined by means of
Seiberg-Witten maps that are the same --barring the gauge group
representation-- for left-handed spinors as for right-handed spinors. We
believe that the results presented in this paper tilt the scales to the side of
noncommutative GUTS and noncommutative GUT inspired versions of the Standard
Model.Comment: 11 pages, 3 figures. Version 2: references fixed and completed.
Version 3: Comments adde
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New Program Abstractions for Privacy
Static program analysis, once seen primarily as a tool for optimising programs, is now increasingly important as a means to provide quality guarantees about programs. One measure of quality is the extent to which programs respect the privacy of user data. Differential privacy is a rigorous quantified definition of privacy which guarantees a bound on the loss of privacy due to the release of statistical queries. Among the benefits enjoyed by the definition of differential privacy are compositionality properties that allow differentially private analyses to be built from pieces and combined in various ways. This has led to the development of frameworks for the construction of differentially private program analyses which are private-by-construction. Past frameworks assume that the sensitive data is collected centrally, and processed by a trusted curator. However, the main examples of differential privacy applied in practice - for example in the use of differential privacy in Google Chrome’s collection of browsing statistics, or Apple’s training of predictive messaging in iOS 10 -use a purely local mechanism applied at the data source, thus avoiding the collection of sensitive data altogether. While this is a benefit of the local approach, with systems like Apple’s, users are required to completely trust that the analysis running on their system has the claimed privacy properties.
In this position paper we outline some key challenges in developing static analyses for analysing differential privacy, and propose novel abstractions for describing the behaviour of probabilistic programs not previously used in static analyses
Size-sorting dust grains in the surface layers of protoplanetary disks
Aims: We wish to investigate what the effect of dust sedimentation is on the
observed 10 mum feature of protoplanetary disks and how this may affect the
interpretation of the observations.
Methods: Using a combination of modeling tools, we simulated the
sedimentation of a dust grain size distribution in an axisymmetric 2-D model of
a turbulent protoplanetary disk, and we used a radiative transfer program to
compute the resulting spectra.
Results: We find that the sedimentation can turn a flat feature into a pointy
one, but only to a limited degree and for a very limited set of particle size
distributions. Only if we have a bimodal size distribution, i.e. a very small
grain population and a bigger grain population, do we find that the
transformation from a flat to a pointy feature upon dust sedimentation is
strong. However, our model shows that, if sedimentation is the sole reason for
the variety of silicate feature strengths observed in protoplanetary disks,
then we would expect to find a correlation such that disks with weak mid- to
far-infrared excess have a stronger 10 mum silicate feature than disks with a
strong mid- to far-infrared excess. If this is contrary to what is observed,
then this would indicate that sedimentation cannot be the main reason for the
variety of 10 mum silicate features observed in protoplanetary disks.Comment: Astronomy and Astrophysics, in pres
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