924 research outputs found
Embedded with the Scientists: The UCLA Experience
In this video article, Lisa Federer, Research Informationist at the UCLA Louise M. Darling Biomedical Library, describes her experience as a research informationist for a National Institutes of Health-funded research team at the University of California, Los Angeles
Modeling physical and chemical climate of the northeastern United States for a geographic information system
A model of physical and chemical climate was developed for New York and New England that can be used in a GIs for integration with ecosystem models. The variables included are monthly average maximum and minimum daily temperatures, precipitation, humidity, and solar radiation, as well as annual atmospheric deposition of sulfur and nitrogen. Equations generated from regional data bases were combined with a digital elevation model of the region to generate digital coverages of each variable
The Arabidopsis mutant feronia disrupts the female gametophytic control of pollen tube reception
Reproduction in angiosperms depends on communication processes of the male gametophyte (pollen) with the female floral organs (pistil, transmitting tissue) and the female gametophyte (embryo sac). Pollen-pistil interactions control pollen hydration, germination and growth through the stylar tissue. The female gametophyte is involved in guiding the growing pollen tube towards the micropyle and embryo sac. One of the two synergids flanking the egg cell starts to degenerate and becomes receptive for pollen tube entry. Pollen tube growth arrests and the tip of the pollen tube ruptures to release the sperm cells. Failures in the mutual interaction between the synergid and the pollen tube necessarily impair fertility. But the control of pollen tube reception is not understood. We isolated a semisterile, female gametophytic mutant from Arabidopsis thaliana, named feronia after the Etruscan goddess of fertility, which impairs this process. In the feronia mutant, embryo sac development and pollen tube guidance were unaffected in all ovules, although one half of the ovules bore mutant female gametophytes. However, when the pollen tube entered the receptive synergid of a feronia mutant female gametophyte, it continued to grow, failed to rupture and release the sperm cells, and invaded the embryo sac. Thus, the feronia mutation disrupts the interaction between the male and female gametophyte required to elicit these processes. Frequently, mutant embryo sacs received supernumerary pollen tubes. We analysed feronia with synergid-specific GUS marker lines, which demonstrated that the specification and differentiation of the synergids was normal. However, GUS expression in mutant gametophytes persisted after pollen tube entry, in contrast to wild-type embryo sacs where it rapidly decreased. Apparently, the failure in pollen tube reception results in the continued expression of synergid-specific genes, probably leading to an extended expression of a potential pollen tube attractant
A Mathematical Theory of Stochastic Microlensing II. Random Images, Shear, and the Kac-Rice Formula
Continuing our development of a mathematical theory of stochastic
microlensing, we study the random shear and expected number of random lensed
images of different types. In particular, we characterize the first three
leading terms in the asymptotic expression of the joint probability density
function (p.d.f.) of the random shear tensor at a general point in the lens
plane due to point masses in the limit of an infinite number of stars. Up to
this order, the p.d.f. depends on the magnitude of the shear tensor, the
optical depth, and the mean number of stars through a combination of radial
position and the stars' masses. As a consequence, the p.d.f.s of the shear
components are seen to converge, in the limit of an infinite number of stars,
to shifted Cauchy distributions, which shows that the shear components have
heavy tails in that limit. The asymptotic p.d.f. of the shear magnitude in the
limit of an infinite number of stars is also presented. Extending to general
random distributions of the lenses, we employ the Kac-Rice formula and Morse
theory to deduce general formulas for the expected total number of images and
the expected number of saddle images. We further generalize these results by
considering random sources defined on a countable compact covering of the light
source plane. This is done to introduce the notion of {\it global} expected
number of positive parity images due to a general lensing map. Applying the
result to microlensing, we calculate the asymptotic global expected number of
minimum images in the limit of an infinite number of stars, where the stars are
uniformly distributed. This global expectation is bounded, while the global
expected number of images and the global expected number of saddle images
diverge as the order of the number of stars.Comment: To appear in JM
Fractal dimension crossovers in turbulent passive scalar signals
The fractal dimension of turbulent passive scalar signals is
calculated from the fluid dynamical equation. depends on the
scale. For small Prandtl (or Schmidt) number one gets two ranges,
for small scale r and =5/3 for large r, both
as expected. But for large one gets a third, intermediate range in
which the signal is extremely wrinkled and has . In that
range the passive scalar structure function has a plateau. We
calculate the -dependence of the crossovers. Comparison with a numerical
reduced wave vector set calculation gives good agreement with our predictions.Comment: 7 pages, Revtex, 3 figures (postscript file on request
The enclosure method for the heat equation
This paper shows how the enclosure method which was originally introduced for
elliptic equations can be applied to inverse initial boundary value problems
for parabolic equations. For the purpose a prototype of inverse initial
boundary value problems whose governing equation is the heat equation is
considered. An explicit method to extract an approximation of the value of the
support function at a given direction of unknown discontinuity embedded in a
heat conductive body from the temperature for a suitable heat flux on the
lateral boundary for a fixed observation time is given.Comment: 12pages. This is the final versio
On a microcanonical relation between continuous and discrete spin models
A relation between a class of stationary points of the energy landscape of
continuous spin models on a lattice and the configurations of a Ising model
defined on the same lattice suggests an approximate expression for the
microcanonical density of states. Based on this approximation we conjecture
that if a O(n) model with ferromagnetic interactions on a lattice has a phase
transition, its critical energy density is equal to that of the n = 1 case,
i.e., a system of Ising spins with the same interactions. The conjecture holds
true in the case of long-range interactions. For nearest-neighbor interactions,
numerical results are consistent with the conjecture for n=2 and n=3 in three
dimensions. For n=2 in two dimensions (XY model) the conjecture yields a
prediction for the critical energy of the Berezinskij-Kosterlitz-Thouless
transition, which would be equal to that of the two-dimensional Ising model. We
discuss available numerical data in this respect.Comment: 5 pages, no figure
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Ghosts and Lovers
Ghosts and Lovers is a collection of short stories told from the points-of-view of four related characters. Travis is a bisexual restaurant owner who fears commitment and longs for the idealistic version of love that he remembers from his past. Ezra, his boyfriend, is an artist struggling to accept the inherent imperfections of life. Travis's ex-girlfriend, Beth, attempts to come to terms with the life that she has chosen for herself. Her husband, Richard, deals with feelings of helplessness as he watches the events of his life unfold before him. By depicting the events of the story from multiple perspectives, the collection attempts to create a more objective view of reality than is ordinarily possible in fiction. An introductory preface examines the role of unreliable narrators and how reality is presented in fiction
Effectiveness of selection based on variability uncomplicated by heterotic effects
Effectiveness of selection based on variability uncomplicated by heterotic effect
Linking Gulf Stream air–sea interactions to the exceptional blocking episode in February 2019: a Lagrangian perspective
The development of atmospheric blocks over the North Atlantic–European region can lead to extreme weather events like heat waves or cold air outbreaks. Despite their potential severe impact on surface weather, the correct prediction of blocking lifecycles remains a key challenge in cur-
rent numerical weather prediction (NWP) models. Increasing evidence suggests that latent heat release in cyclones, the advection of cold air (cold air outbreaks, CAOs) from the Arctic over the North Atlantic, and associated air–sea interactions over the Gulf Stream are key processes contribut-
ing to the onset, maintenance, and persistence of such flow regimes. To better understand the mechanism connecting air-sea interactions over the Gulf Stream with changes in the large-scale flow, we focus on an episode between 20 and 27 February 2019, when a quasi-stationary upper-level ridge was established over western Europe accompanied by an intensified storm track in the northwestern North Atlantic. During that time, a record-breaking winter warm spell occurred over western Europe bringing temperatures above 20C to the United Kingdom, the Netherlands, and northern France. The event was preceded and accompanied by the develop-
ment of several rapidly intensifying cyclones that originated in the Gulf Stream region and traversed the North Atlantic. To explore the mechanistic linkage between the formation of this block and air–sea interactions over the Gulf Stream, we adopt a Lagrangian perspective, using kinematic trajec-
tories. This allows us to study the pathways and transformations of air masses that form the upper-level potential vorticity anomaly and interact with the ocean front. We establish that more than one-fifth of these air masses interact with the Gulf Stream in the lower troposphere, experiencing intense heating and moistening over the region due to the frequent
occurrence of CAOs behind the cold front of the cyclones. Trajectories moistened by the advection of cold air over a warm ocean by one cyclone later ascend into the upper troposphere with the ascending airstream of a subsequent cyclone, fueled by the strong surface fluxes. These findings highlight the importance of CAOs in the Gulf Stream region, indicat-
ing that their intense coupling between the ocean and atmosphere plays a role in block development. Additionally, they provide a mechanistic pathway linking air–sea interactions in the lower troposphere and the upper-level flow
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