1,269 research outputs found
Advancing the Discipline: Guidelines from the Experience of Colleagues
Introduces articles from the issue about the disciplinary advancement of the communication departments of various colleges and universities
Physics-Based Modeling for Determining Transient Current Flow in Multi-Layer Pcb Pi Designs
A physics-based modeling methodology for determining the transient current flow path in multi-layer PI designs is given in this paper using a commercial board with a complicated structure as an example. Board structure analysis is done first to provide a physical basis of post-layout analytical and equivalent circuit modeling. A match of the PDN impedance between commercial tool simulation, post-layout analytical calculation, and the physics-based equivalent circuit modeling was achieved to support the model for the transient simulation. By analyzing the current response in all the vias, a clear representation of transient current flow across all via segments can be given layer-by-layer. The maximum current density in vertical vias can also be extracted in this process, providing a reference for preventing transient overcurrent design
Making Good Tenure Decisions
This article provides information on decision making on the granting or denial of tenure to a faculty member. It not only has an effect on the professional life of a colleague, it has a major influence on the direction and long-term quality of the department. The tenure decision in made in the sixth year of a tenure-track faculty appointment. If a faculty member has been on the tenure track at two institutions, the years of service at the first institution usually count toward those six years, unless the faculty member and his of her current institution agree in writing at the time of appointment that they will not or that only a certain number of them will. The sooner the person is terminated or helped to find another position, the better for him or her and for the department
Level densities and -ray strength functions in Yb
Level densities and radiative strength functions in Yb and Yb
nuclei have been measured using the
Yb(He,He)Yb and
Yb(He,)Yb reactions. New data on Yb
are compared to a previous measurement for Yb from the
Yb(He,)Yb reaction. Systematics of level
densities and radiative strength functions in Yb are
established. The entropy excess in Yb relative to the even-even nuclei
Yb due to the unpaired neutron quasiparticle is found to be
approximately 2. Results for the radiative strength function from the two
reactions lead to consistent parameters characterizing the ``pygmy''
resonances. Pygmy resonances in the Yb populated by the
(He,) reaction appear to be split into two components for both of
which a complete set of resonance parameters are obtained.Comment: 8 pages, 7 figure
The anomaly line bundle of the self-dual field theory
In this work, we determine explicitly the anomaly line bundle of the abelian
self-dual field theory over the space of metrics modulo diffeomorphisms,
including its torsion part. Inspired by the work of Belov and Moore, we propose
a non-covariant action principle for a pair of Euclidean self-dual fields on a
generic oriented Riemannian manifold. The corresponding path integral allows to
study the global properties of the partition function over the space of metrics
modulo diffeomorphisms. We show that the anomaly bundle for a pair of self-dual
fields differs from the determinant bundle of the Dirac operator coupled to
chiral spinors by a flat bundle that is not trivial if the underlying manifold
has middle-degree cohomology, and whose holonomies are determined explicitly.
We briefly sketch the relevance of this result for the computation of the
global gravitational anomaly of the self-dual field theory, that will appear in
another paper.Comment: 41 pages. v2: A few typos corrected. Version accepted for publication
in CM
Infinite factorization of multiple non-parametric views
Combined analysis of multiple data sources has increasing application interest, in particular for distinguishing shared and source-specific aspects. We extend this rationale of classical canonical correlation analysis into a flexible, generative and non-parametric clustering
setting, by introducing a novel non-parametric hierarchical
mixture model. The lower level of the model describes each source with a flexible non-parametric mixture, and the top level combines these to describe commonalities of the sources. The lower-level clusters arise from hierarchical Dirichlet Processes, inducing an infinite-dimensional contingency table between the views. The commonalities between the sources are modeled by an infinite block
model of the contingency table, interpretable as non-negative factorization of infinite matrices, or as a prior for infinite contingency tables. With Gaussian mixture components plugged in for continuous measurements, the model is applied to two views of genes, mRNA expression and abundance of the produced proteins, to expose groups of genes that are co-regulated in either or both of the views.
Cluster analysis of co-expression is a standard simple way of screening for co-regulation, and the two-view analysis extends the approach to distinguishing between pre- and post-translational regulation
Noncyclic geometric phase for neutrino oscillation
We provide explicit formulae for the noncyclic geometric phases or
Pancharatnam phases of neutrino oscillations. Since Pancharatnam phase is a
generalization of the Berry phase, our results generalize the previous findings
for Berry phase in a recent paper [Phys. Lett. B, 466 (1999) 262]. Unlike the
Berry phase, the noncyclic geometric phase offers distinctive advantage in
terms of measurement and prediction. In particular, for three-flavor mixing,
our explicit formula offers an alternative means of determining the
CP-violating phase. Our results can also be extended easily to explore
geometric phase associated with neutron-antineutron oscillations
Dominance of photo over chromatic acclimation strategies by habitat-forming mesophotic red algae
Funding was provided by a Leverhulme Trust Research Project grant no. (RPG-2018-113) to H.L.B., G.A.T. and I.D.W.S., an Engineering and Physical Sciences Research Council grant (EP/L017008/1) to G.A.T. and I.D.W.S., and a São Paulo Research Foundation (FAPESP) individual grant (#2016/14017-0) to G.H.P.-F.Red coralline algae are the deepest living macroalgae, capable of creating spatially complex reefs from the intertidal to 100+ m depth with global ecological and biogeochemical significance. How these algae maintain photosynthetic function under increasingly limiting light intensity and spectral availability is key to explaining their large depth distribution. Here, we investigated the photo- and chromatic acclimation and morphological change of free-living red coralline algae towards mesophotic depths in the Fernando do Noronha archipelago, Brazil. From 13 to 86 m depth, thalli tended to become smaller and less complex. We observed a dominance of the photo-acclimatory response, characterized by an increase in photosynthetic efficiency and a decrease in maximum electron transport rate. Chromatic acclimation was generally stable across the euphotic-mesophotic transition with no clear depth trend. Taxonomic comparisons suggest these photosynthetic strategies are conserved to at least the Order level. Light saturation necessitated the use of photoprotection to 65 m depth, while optimal light levels were met at 86 m. Changes to the light environment (e.g. reduced water clarity) due to human activities therefore places these mesophotic algae at risk of light limitation, necessitating the importance of maintaining good water quality for the conservation and protection of mesophotic habitats.Publisher PDFPeer reviewe
Ecosystem engineer morphological traits and taxon identity shape biodiversity across the euphotic-mesophotic transition
Funding was provided by a Leverhulme Trust Research Project grant (no. RPG-2018-113) to H.L.B., G.A.T. and I.D.W.S., an Engineering and Physical Sciences Research Council grant (no. EP/L017008/1) to G.A.T. and I.D.W.S., and a São Paulo Research Foundation (FAPESP) individual grant (no. 2016/14017-0) to G.H.P.F.The euphotic-mesophotic transition is characterized by dramatic changes in environmental conditions, which can significantly alter the functioning of ecosystem engineers and the structure of their associated communities. However, the drivers of biodiversity change across the euphotic-mesophotic transition remain unclear. Here, we investigated the mechanisms affecting the biodiversity-supporting potential of free-living red coralline algae-globally important habitat creators-towards mesophotic depths. Across a 73 m depth gradient, we observed a general decline in macrofaunal biodiversity (fauna abundance, taxon richness and alpha diversity), but an increase in beta-diversity (i.e. variation between assemblages) at the deepest site (86 m depth, where light levels were less than 1% surface irradiance). We identified a gradient in abundance decline rather than distinct ecological shifts, driven by a complex interaction between declining light availability, declining size of the coralline algal host individuals and a changing host taxonomy. However, despite abundance declines, high between-assemblage variability at deeper depths allowed biodiversity-supporting potential to be maintained, highlighting their importance as coastal refugia.PostprintPeer reviewe
Bright triplet excitons in lead halide perovskites
Nanostructured semiconductors emit light from electronic states known as
excitons[1]. According to Hund's rules[2], the lowest energy exciton in organic
materials should be a poorly emitting triplet state. Analogously, the lowest
exciton level in all known inorganic semiconductors is believed to be optically
inactive. These 'dark' excitons (into which the system can relax) hinder
light-emitting devices based on semiconductor nanostructures. While strategies
to diminish their influence have been developed[3-5], no materials have been
identified in which the lowest exciton is bright. Here we show that the lowest
exciton in quasi-cubic lead halide perovskites is optically active. We first
use the effective-mass model and group theory to explore this possibility,
which can occur when the strong spin-orbit coupling in the perovskite
conduction band is combined with the Rashba effect [6-10]. We then apply our
model to CsPbX3 (X=Cl,Br,I) nanocrystals[11], for which we measure size- and
composition-dependent fluorescence at the single-nanocrystal level. The bright
character of the lowest exciton immediately explains the anomalous
photon-emission rates of these materials, which emit 20 and 1,000 times
faster[12] than any other semiconductor nanocrystal at room[13-16] and
cryogenic[17] temperatures, respectively. The bright exciton is further
confirmed by detailed analysis of the fine structure in low-temperature
fluorescence spectra. For semiconductor nanocrystals[18], which are already
used in lighting[19,20], lasers[21,22], and displays[23], these optically
active excitons can lead to materials with brighter emission and enhanced
absorption. More generally, our results provide criteria for identifying other
semiconductors exhibiting bright excitons with potentially broad implications
for optoelectronic devices.Comment: 14 pages and 3 figures in the main text, Methods and extended data 16
pages which include 11 figures, and supporting information 28 page
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