4,871 research outputs found
On the spectrum of atmospheric velocity fluctuations seen by MST/ST radar and their interpretation
The observations of the spectrum of atmospheric motions over the range of periods from a few minutes to many hours are considered that have been made with stratosphere-troposphere/mesosphere-stratosphere (ST/MST) radars in the past five years. This range of periods includes the periods associated with buoyancy waves and the scale of atmospheric motions often referred to by meteorologists as the mesoscale. The spectra of horizontal and vertical velocities are considered. Their interpretation is examined in terms of buoyancy wave theory and turbulence theory. To help in interpreting these spectra some recently determined aircraft wave number spectra are presented
The Proficiency Illusion
Examines the tests states use to measure academic progress under the No Child Left Behind Act. Explores whether expectations for proficiency in reading and mathematics are consistent between states
The proposed flatland radar
A flexible very high frequency (VHF) stratosphere-troposphere (ST) radar configured for meteorological research is to be constructed near Urbana, Illinois. Measurement of small vertical velocities associated with synoptic-scale meteorology can be performed. A large Doppler microwave radar (CHILL) is located a few km from the site of the proposed ST radar. Since the microwave radar can measure the location and velocity of hydrometeors and the VHF ST radar can measure clear (or cloudy) air velocities, simultaneous observations by these two radars of stratiform or convective weather systems would provide valuable meteorological information
Homomorphisms of quantum hypergraphs
We introduce quantum homomorphisms between quantum hypergraphs through the
existence of perfect strategies for quantum non-local games, canonically
associated with the quantum hypergraphs. We show that the relation of
homomorphism of a given type satisfies natural analogues of the properties of a
pre-order. We show that quantum hypergraph homomorphisms of local type are
closely related, and in some cases identical, to the TRO equivalence of finite
dimensionally acting operator spaces, canonically associated with the
hypergraphs
Quantum hypergraph homomorphisms and non-local games
Using the simulation paradigm in information theory, we define notions of
quantum hypergraph homomorphisms and quantum hypergraph isomorphisms, and show
that they constitute partial orders and equivalence relations, respectively.
Specialising to the case where the underlying hypergraphs arise from non-local
games, we define notions of quantum non-local game homomorphisms and quantum
non-local game isomorphisms, and show that games, isomorphic with respect to a
given correlation type, have equal values and asymptotic values relative to
this type. We examine a new class of no-signalling correlations, which witness
the existence of non-local game homomorphisms, and characterise them in terms
of states on tensor products of canonical operator systems. We define jointly
synchronous correlations and show that they correspond to traces on the tensor
product of the canonical C*-algebras associated with the game parties
Cryptic choice of conspecific sperm controlled by the impact of ovarian fluid on sperm swimming behavior
Despite evidence that variation in male–female reproductive compatibility exists in many fertilization systems, identifying mechanisms of cryptic female choice at the gamete level has been a challenge. Here, under risks of genetic incompatibility through hybridization, we show how salmon and trout eggs promote fertilization by conspecific sperm. Using in vitro fertilization experiments that replicate the gametic microenvironment, we find complete interfertility between both species. However, if either species’ ova were presented with equivalent numbers of both sperm types, conspecific sperm gained fertilization precedence. Surprisingly, the species’ identity of the eggs did not explain this cryptic female choice, which instead was primarily controlled by conspecific ovarian fluid, a semiviscous, protein-rich solution that bathes the eggs and is released at spawning. Video analyses revealed that ovarian fluid doubled sperm motile life span and straightened swimming trajectory, behaviors allowing chemoattraction up a concentration gradient. To confirm chemoattraction, cell migration tests through membranes containing pores that approximated to the egg micropyle showed that conspecific ovarian fluid attracted many more spermatozoa through the membrane, compared with heterospecific fluid or water. These combined findings together identify how cryptic female choice can evolve at the gamete level and promote reproductive isolation, mediated by a specific chemoattractive influence of ovarian fluid on sperm swimming behavior
Criticality for the Gehring link problem
In 1974, Gehring posed the problem of minimizing the length of two linked
curves separated by unit distance. This constraint can be viewed as a measure
of thickness for links, and the ratio of length over thickness as the
ropelength. In this paper we refine Gehring's problem to deal with links in a
fixed link-homotopy class: we prove ropelength minimizers exist and introduce a
theory of ropelength criticality.
Our balance criterion is a set of necessary and sufficient conditions for
criticality, based on a strengthened, infinite-dimensional version of the
Kuhn--Tucker theorem. We use this to prove that every critical link is C^1 with
finite total curvature. The balance criterion also allows us to explicitly
describe critical configurations (and presumed minimizers) for many links
including the Borromean rings. We also exhibit a surprising critical
configuration for two clasped ropes: near their tips the curvature is unbounded
and a small gap appears between the two components. These examples reveal the
depth and richness hidden in Gehring's problem and our natural extension.Comment: This is the version published by Geometry & Topology on 14 November
200
Post-copulatory opportunities for sperm competition and cryptic female choice provide no offspring fitness benefits in externally fertilizing salmon
There is increasing evidence that females can somehow improve their offspring fitness by mating with multiple males, but we understand little about the exact stage(s) at which such benefits are gained. Here, we measure whether offspring fitness is influenced by mechanisms operating solely between sperm and egg. Using externally-fertilising and polyandrous Atlantic salmon (Salmo salar), we employed split-clutch and split-ejaculate in vitro fertilisation experiments to generate offspring using designs that either denied or applied opportunities for sperm competition and cryptic female choice. Following fertilisations, we measured 140 days of offspring fitness after hatch, through growth and survival in hatchery and near-natural conditions. Despite an average composite mortality of 61%, offspring fitness at every life stage was near-identical between groups fertilised under the absence versus presence of opportunities for sperm competition and cryptic female choice. Of the 21,551 and 21,771 eggs from 24 females fertilised under monandrous versus polyandrous conditions, 68% versus 67.8% survived to the 100-day juvenile stage; sub-samples showed similar hatching success (73.1% versus 74.3%), had similar survival over 40 days in near-natural streams (57.3% versus 56.2%), and grew at similar rates throughout. We therefore found no evidence that gamete-specific interactions allow offspring fitness benefits when polyandrous fertilisation conditions provide opportunities for sperm competition and cryptic female choice
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