1,402 research outputs found
A baseline evaluation of oceanographic and sea ice conditions in the Hudson Bay Complex during 2016-2018
In this paper, we examine sea surface temperatures (SSTs) and sea ice conditions in the Hudson Bay Complex as a baseline evaluation for the BaySys 2016–2018 field program time frame. Investigated in particular are spatiotemporal patterns in SST and sea ice state and dynamics, with rankings of the latter to highlight extreme conditions relative to the examined 1981–2010 climatology. Results from this study show that SSTs in northwestern Hudson Bay from May to July, 2016–2018, are high relative to the climatology for SST (1982–2010). SSTs are also warmer in 2016 and 2017 than in 2018 relative to their climatology. Similarly, unusually low sea ice cover existed from August to December of 2016 and July to September of 2017, while unusually high sea ice cover existed in January, February, and October of 2018. The ice-free season was approximately 20 days longer in 2016 than in 2018. Unusually high ice-drift speeds occurred in April of 2016 and 2017 and in May of 2018, coinciding with strong winds in 2016 and 2018 and following strong winds in March 2017. Strong meridional circulation was observed in spring of 2016 and winter of 2017, while weak meridional circulation existed in 2018. In a case study of an extreme event, a blizzard from 7 to 9 March 2017, evaluated using Lagrangian dispersion statistics, is shown to have suppressed sea ice deformation off the coast of Churchill. These results are relevant to describing and planning for possible future pathways and scenarios under continued climate change and river regulation
Quasinormal modes of massive charged flavor branes
We present an analysis and classification of vector and scalar fluctuations
in a D3/D7 brane setup at finite termperature and baryon density. The system is
dual to an N=2 supersymmetric Yang-Mills theory with SU(N_c) gauge group and
N_f hypermultiplets in the fundamental representation in the quenched
approximation. We improve significantly over previous results on the
quasinormal mode spectrum of D7 branes and stress their novel physical
interpretation. Amongst our findings is a new purely imaginary scalar mode that
becomes tachyonic at sufficiently low temperature and baryon density. We
establish the existence of a critical density above which the scalar mode stays
in the stable regime for all temperatures. In the vector sector we study the
crossover from the hydrodynamic to the quasiparticle regime and find that it
moves to shorter wavelengths for lower temperatures. At zero baryon density the
quasinormal modes move toward distinct discrete attractor frequencies that
depend on the momentum as we increase the temperature. At finite baryon
density, however, the trajectories show a turning behavior such that for low
temperature the quasinormal mode spectrum approaches the spectrum of the
supersymmetric zero temperature normal modes. We interpret this as resolution
of the singular quasinormal mode spectrum that appears at the limiting D7 brane
embedding at vanishing baryon density.Comment: 56 pages, 40 figure
Efficient Bayesian-based Multi-View Deconvolution
Light sheet fluorescence microscopy is able to image large specimen with high
resolution by imaging the sam- ples from multiple angles. Multi-view
deconvolution can significantly improve the resolution and contrast of the
images, but its application has been limited due to the large size of the
datasets. Here we present a Bayesian- based derivation of multi-view
deconvolution that drastically improves the convergence time and provide a fast
implementation utilizing graphics hardware.Comment: 48 pages, 20 figures, 1 table, under review at Nature Method
A baseline evaluation of atmospheric and river discharge conditions in the Hudson Bay Complex during 2016-2018
In this article, we examine atmospheric and river discharge conditions within the Hudson Bay Complex for the BaySys 2016–2018 field program time frame. Investigated in particular is a subset of European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis - Interim (ERA-Interim) atmospheric forcing variables, namely 2-m surface temperature, 10-m surface winds, precipitation, and sea-level pressure, in addition to river discharge. Results from this assessment show that 2016 was characterized by unusually warm conditions (terrestrial and marine) throughout the annual cycle; 2017 by strong cyclone activity in March and high precipitation in January, October, and November; and 2018 by cold and windy conditions throughout the annual cycle. Evaluation of terrestrial conditions showed higher than normal land surface temperatures (the Hudson Bay physical watershed) for all of the 2016–2018 period (excluding a colder than normal spell August–November 2018), particularly in January (2016 and 2017), higher than normal precipitation in October (2016 and 2017), and higher than normal terrestrial discharge to the Hudson Bay Complex in March (2016 and 2017), with drier than average June through October (2016–2018)
Simulated impacts of relative climate change and river discharge regulation on sea ice and oceanographic conditions in the Hudson Bay Complex
In this analysis, we examine relative contributions from climate change and river discharge regulation to changes in marine conditions in the Hudson Bay Complex using a subset of five atmospheric forcing scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5), river discharge data from the Hydrological Predictions for the Environment (HYPE) model, both naturalized (without anthropogenic intervention) and regulated (anthropogenically controlled through diversions, dams, reservoirs), and output from the Nucleus for European Modeling of the Ocean Ice-Ocean model for the 1981–2070 time frame. Investigated in particular are spatiotemporal changes in sea surface temperature, sea ice concentration and thickness, and zonal and meridional sea ice drift in response to (i) climate change through comparison of historical (1981–2010) and future (2021–2050 and 2041–2070) simulations, (ii) regulation through comparison of historical (1981–2010) naturalized and regulated simulations, and (iii) climate change and regulation combined through comparison of future (2021–2050 and 2041–2070) naturalized and regulated simulations. Also investigated is use of the diagnostic known as e-folding time spatial distribution to monitor changes in persistence in these variables in response to changing climate and regulation impacts in the Hudson Bay Complex. Results from this analysis highlight bay-wide and regional reductions in sea ice concentration and thickness in southwest and northeast Hudson Bay in response to a changing climate, and east-west asymmetry in sea ice drift response in support of past studies. Regulation is also shown to amplify or suppress the climate change signal. Specifically, regulation amplifies sea surface temperatures from April to August, suppresses sea ice loss by approximately 30% in March, contributes to enhanced sea ice drift speed by approximately 30%, and reduces meridional circulation by approximately 20% in January due to enhanced zonal drift. Results further suggest that the offshore impacts of regulation are amplified in a changing climate
Flux and Instanton Effects in Local F-theory Models and Hierarchical Fermion Masses
We study the deformation induced by fluxes and instanton effects on Yukawa
couplings involving 7-brane intersections in local F-theory constructions. In
the absence of non-perturbative effects, holomorphic Yukawa couplings do not
depend on open string fluxes. On the other hand instanton effects (or gaugino
condensation on distant 7-branes) do induce corrections to the Yukawas. The
leading order effect may also be captured by the presence of closed string
(1,2) IASD fluxes, which give rise to a non-commutative structure. We check
that even in the presence of these non-perturbative effects the holomorphic
Yukawas remain independent of magnetic fluxes. Although fermion mass
hierarchies may be obtained from these non-perturbative effects, they would
give identical Yukawa couplings for D-quark and Lepton masses in SU(5) F-theory
GUT's, in contradiction with experiment. We point out that this problem may be
solved by appropriately normalizing the wavefunctions. We show in a simple toy
model how the presence of hypercharge flux may then be responsible for the
difference between D-quarks and Lepton masses in local SU(5) GUT's.Comment: 84 pages, 1 figure. v2: minor corrections and references adde
Soft branes in supersymmetry-breaking backgrounds
We revisit the analysis of effective field theories resulting from
non-supersymmetric perturbations to supersymmetric flux compactifications of
the type-IIB superstring with an eye towards those resulting from the
backreaction of a small number of anti-D3-branes. Independently of the
background, we show that the low-energy Lagrangian describing the fluctuations
of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite
perturbations to marginal operators that were not fully considered in some
previous treatments. We take this as an indication that the breaking of
supersymmetry by anti-D3-branes or other sources may be spontaneous rather than
explicit. In support of this, we consider the action of an anti-D3-brane
probing an otherwise supersymmetric configuration and identify a candidate for
the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte
f(R) Gravities, Killing Spinor Equations, "BPS" Domain Walls and Cosmology
We derive the condition on f(R) gravities that admit Killing spinor equations
and construct explicit such examples. The Killing spinor equations can be used
to reduce the fourth-order differential equations of motion to the first order
for both the domain wall and FLRW cosmological solutions. We obtain exact "BPS"
domain walls that describe the smooth Randall-Sundrum II, AdS wormholes and the
RG flow from IR to UV. We also obtain exact smooth cosmological solutions that
describe the evolution from an inflationary starting point with a larger
cosmological constant to an ever-expanding universe with a smaller cosmological
constant. In addition, We find exact smooth solutions of pre-big bang models,
bouncing or crunching universes. An important feature is that the scalar
curvature R of all these metrics is varying rather than a constant. Another
intriguing feature is that there are two different f(R) gravities that give
rise to the same "BPS" solution. We also study linearized f(R) gravities in
(A)dS vacua.Comment: 37 pages, discussion on gravity trapping in RSII modified, typos
corrected, further comments and references added; version to appear in JHE
Med5(Nut1) and Med17(Srb4) Are Direct Targets of Mediator Histone H4 Tail Interactions
The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. In addition to its canonical role in transcriptional activation, recent studies have demonstrated that S. cerevisiae Mediator can interact directly with nucleosomes, and their histone tails. Mutations in Mediator subunits have shown that Mediator and certain chromatin structures mutually impact each other structurally and functionally in vivo. We have taken a UV photo cross-linking approach to further delineate the molecular basis of Mediator chromatin interactions and help determine whether the impact of certain Mediator mutants on chromatin is direct. Specifically, by using histone tail peptides substituted with an amino acid analog that is a UV activatible crosslinker, we have identified specific subunits within Mediator that participate in histone tail interactions. Using Mediator purified from mutant yeast strains we have evaluated the impact of these subunits on histone tail binding. This analysis has identified the Med5 subunit of Mediator as a target for histone tail interactions and suggests that the previously observed effect of med5 mutations on telomeric heterochromatin and silencing is direct
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