15,211 research outputs found
Larvae of the three common North American species of Phylocentropus (Trichoptera: Dipseudopsidae)
The caddisfly genus Phylocentropus includes 7 extant species globally, of which 5 occur in eastern North America and 2 in eastern Asia. Larvae of the 3 most common North American species [Phylocentropus carolinus Carpenter, P. lucidus (Hagen), and P. placidus (Banks)] were associated with identifiable adults and diagnostic characters are described. Larvae ofthese 3 species may be distinguished by overall length of mature larvae, head color pattern, and number of spines on the hind tibiae. Larvae of other species of this genus are unknown
Distance and intersection number in the curve graph of a surface
In this work, we study the cellular decomposition of induced by a filling
pair of curves and , , and its connection
to the distance function in the curve graph of a closed orientable
surface of genus . Efficient geodesics were introduced by the first
author in joint work with Margalit and Menasco in 2016, giving an algorithm
that begins with a pair of non-separating filling curves that determine
vertices in the curve graph of a closed orientable surface and
computing from them a finite set of {\it efficient} geodesics. We extend the
tools of efficient geodesics to study the relationship between distance
, intersection number , and . The main result is
the development and analysis of particular configurations of rectangles in
called \textit{spirals}. We are able to show that, in some
special cases, the efficient geodesic algorithm can be used to build an
algorithm that reduces while preserving . At the end of the
paper, we note a connection of our work to the notion of extending geodesics.Comment: 20 pages, 17 figures. Changes: A key lemma (Lemma 5.6) was revised to
be more precise, an irrelevant proposition (Proposition 2.1) and example were
removed, unnecessary background material was taken out, some of the
definitions and cited results were clarified (including added figures,) and
Proposition 5.7 and Theorem 5.8 have been merged into a single theorem,
Theorem 4.
A Hybrid Observer for a Distributed Linear System with a Changing Neighbor Graph
A hybrid observer is described for estimating the state of an channel,
-dimensional, continuous-time, distributed linear system of the form
. The system's state is
simultaneously estimated by agents assuming each agent senses and
receives appropriately defined data from each of its current neighbors.
Neighbor relations are characterized by a time-varying directed graph
whose vertices correspond to agents and whose arcs depict
neighbor relations. Agent updates its estimate of at "event
times" using a local observer and a local parameter
estimator. The local observer is a continuous time linear system whose input is
and whose output is an asymptotically correct estimate of
where a matrix with kernel equaling the unobservable space of .
The local parameter estimator is a recursive algorithm designed to estimate,
prior to each event time , a constant parameter which satisfies the
linear equations , where is a small
positive constant and is the state estimation error of local observer
. Agent accomplishes this by iterating its parameter estimator state
, times within the interval , and by making use of
the state of each of its neighbors' parameter estimators at each iteration. The
updated value of at event time is then . Subject to the assumptions that (i) the neighbor graph
is strongly connected for all time, (ii) the system whose state
is to be estimated is jointly observable, (iii) is sufficiently large, it
is shown that each estimate converges to exponentially fast as
at a rate which can be controlled.Comment: 7 pages, the 56th IEEE Conference on Decision and Contro
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Numerical modelling of microwave sintering of lunar simulants under near lunar atmospheric condition
Ion Trap Mass Spectrometers for Identity, Abundance and Behavior of Volatiles on the Moon
NASA GSFC and The Open University (UK) are collaborating to deploy an Ion Trap Mass Spectrometer on the Moon to investigate the lunar water cycle. The ITMS is flight-proven throughthe Rosetta Philae comet lander mission. It is also being developed under ESA funding to analyse samples drilled from beneath the lunar surface on the Roscosmos Luna-27 lander (2025).Now, GSFC and OU will now develop a compact ITMS instrument to study the near-surface lunar exosphere on board a CLPS Astrobotic lander at Lacus Mortis in 2021
Anomalous fluctuations of active polar filaments
Using a simple model, we study the fluctuating dynamics of inextensible,
semiflexible polar filaments interacting with active and directed force
generating centres such as molecular motors. Taking into account the fact that
the activity occurs on time-scales comparable to the filament relaxation time,
we obtain some unexpected differences between both the steady-state and
dynamical behaviour of active as compared to passive filaments. For the
statics, the filaments have a {novel} length-scale dependent rigidity.
Dynamically, we find strongly enhanced anomalous diffusion.Comment: 5 pages, 3 figure
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
Magnetic Helicity in Sphaleron Debris
We develop an analytical technique to evaluate the magnetic helicity in the
debris from sphaleron decay. We show that baryon number production leads to
left-handed magnetic fields, and that the magnetic helicity is conserved at
late times. Our analysis explicitly demonstrates the connection between
sphaleron-mediated cosmic baryogenesis and cosmic magnetogenesis.Comment: 9 pages, 1 figure. v2: Minor revisions; matches published version in
Physical Review
Renormalization of the one-loop theory of fluctuations in polymer blends and diblock copolymer melts
Attempts to use coarse-grained molecular theories to calculate corrections to
the random-phase approximation (RPA) for correlations in polymer mixtures have
been plagued by an unwanted sensitivity to the value of an arbitrary cutoff
length, {\it i.e.}, by an ultraviolet (UV) divergence. We analyze the UV
divergence of the inverse structure factor predicted by a
`one-loop' approximation similar to that used in several previous studies. We
consider both miscible homopolymer blends and disordered diblock copolymer
melts. We show, in both cases, that all UV divergent contributions can be
absorbed into a renormalization of the values of the phenomenological
parameters of a generalized self-consistent field theory (SCFT). This
observation allows the construction of a UV convergent theory of corrections to
SCFT phenomenology. The UV-divergent one-loop contribution to are
shown to be the sum of: (i) a -independent contribution that arises from a
renormalization of the effective parameter, (ii) a -dependent
contribution that arises from a renormalization of monomer statistical segment
lengths, (iii) a contribution proportional to that arises from a
square-gradient contribution to the one-loop fluctuation free energy, and (iv)
a -dependent contribution that is inversely proportional to the degree of
polymerization, which arises from local perturbations in fluid structure near
chain ends and near junctions between blocks in block copolymers.Comment: 35 pages, 2 figure
Hall of Mirrors Scattering from an Impurity in a Quantum Wire
This paper develops a scattering theory to examine how point impurities
affect transport through quantum wires. While some of our new results apply
specifically to hard-walled wires, others--for example, an effective optical
theorem for two-dimensional waveguides--are more general. We apply the method
of images to the hard-walled guide, explicitly showing how scattering from an
impurity affects the wire's conductance. We express the effective cross section
of a confined scatterer entirely in terms of the empty waveguide's Green's
function, suggesting a way in which to use semiclassical methods to understand
transport properties of smooth wires. In addition to predicting some new
phenomena, our approach provides a simple physical picture for previously
observed effects such as conductance dips and confinement-induced resonances.Comment: 19 pages, 8 figures. Accepted for publication in Physical Review B.
Minor additions to text, added reference
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