392 research outputs found
Traces for star products on the dual of a Lie algebra
In this paper, we describe all traces for the BCH star-product on the dual of
a Lie algebra. First we show by an elementary argument that the BCH as well as
the Kontsevich star-product are strongly closed if and only if the Lie algebra
is unimodular. In a next step we show that the traces of the BCH star-product
are given by the \ad-invariant functionals. Particular examples are the
integration over coadjoint orbits. We show that for a compact Lie group and a
regular orbit one can even achieve that this integration becomes a positive
trace functional. In this case we explicitly describe the corresponding GNS
representation. Finally we discuss how invariant deformations on a group can be
used to induce deformations of spaces where the group acts on.Comment: 18 pages, LaTeX2e. Updated reference
Infinitesimal deformations of a formal symplectic groupoid
Given a formal symplectic groupoid over a Poisson manifold ,
we define a new object, an infinitesimal deformation of , which can be
thought of as a formal symplectic groupoid over the manifold equipped with
an infinitesimal deformation of the Poisson bivector
field . The source and target mappings of a deformation of are
deformations of the source and target mappings of . To any pair of natural
star products having the same formal symplectic groupoid
we relate an infinitesimal deformation of . We call it the deformation
groupoid of the pair . We give explicit formulas for the
source and target mappings of the deformation groupoid of a pair of star
products with separation of variables on a Kaehler- Poisson manifold. Finally,
we give an algorithm for calculating the principal symbols of the components of
the logarithm of a formal Berezin transform of a star product with separation
of variables. This algorithm is based upon some deformation groupoid.Comment: 22 pages, the paper is reworked, new proofs are adde
The Stability of Bredigite and Other Ca-Mg Silicates
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65844/1/j.1151-2916.1980.tb10213.x.pd
Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers
We study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibility of the method. We present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system
Nanoscale transient magnetization gratings excited and probed by femtosecond extreme ultraviolet pulses
We utilize coherent femtosecond extreme ultraviolet (EUV) pulses derived from
a free electron laser (FEL) to generate transient periodic magnetization
patterns with periods as short as 44 nm. Combining spatially periodic
excitation with resonant probing at the dichroic M-edge of cobalt allows us to
create and probe transient gratings of electronic and magnetic excitations in a
CoGd alloy. In a demagnetized sample, we observe an electronic excitation with
50 fs rise time close to the FEL pulse duration and ~0.5 ps decay time within
the range for the electron-phonon relaxation in metals. When the experiment is
performed on a sample magnetized to saturation in an external field, we observe
a magnetization grating, which appears on a sub-picosecond time scale as the
sample is demagnetized at the maxima of the EUV intensity and then decays on
the time scale of tens of picoseconds via thermal diffusion. The described
approach opens prospects for studying dynamics of ultrafast magnetic phenomena
on nanometer length scales
Global Drivers on Southern Ocean Ecosystems: Changing Physical Environments and Anthropogenic Pressures in an Earth System
Copyright © 2020 Morley, Abele, Barnes, Cárdenas, Cotté, Gutt, Henley, Höfer, Hughes, Martin, Moffat, Raphael, Stammerjohn, Suckling, Tulloch, Waller and Constable. The manuscript assesses the current and expected future global drivers of Southern Ocean (SO) ecosystems. Atmospheric ozone depletion over the Antarctic since the 1970s, has been a key driver, resulting in springtime cooling of the stratosphere and intensification of the polar vortex, increasing the frequency of positive phases of the Southern Annular Mode (SAM). This increases warm air-flow over the East Pacific sector (Western Antarctic Peninsula) and cold air flow over the West Pacific sector. SAM as well as El Niño Southern Oscillation events also affect the Amundsen Sea Low leading to either positive or negative sea ice anomalies in the west and east Pacific sectors, respectively. The strengthening of westerly winds is also linked to shoaling of deep warmer water onto the continental shelves, particularly in the East Pacific and Atlantic sectors. Air and ocean warming has led to changes in the cryosphere, with glacial and ice sheet melting in both sectors, opening up new ice free areas to biological productivity, but increasing seafloor disturbance by icebergs. The increased melting is correlated with a salinity decrease particularly in the surface 100 m. Such processes could increase the availability of iron, which is currently limiting primary production over much of the SO. Increasing CO2 is one of the most important SO anthropogenic drivers and is likely to affect marine ecosystems in the coming decades. While levels of many pollutants are lower than elsewhere, persistent organic pollutants (POPs) and plastics have been detected in the SO, with concentrations likely enhanced by migratory species. With increased marine traffic and weakening of ocean barriers the risk of the establishment of non-indigenous species is increased. The continued recovery of the ozone hole creates uncertainty over the reversal in sea ice trends, especially in the light of the abrupt transition from record high to record low Antarctic sea ice extent since spring 2016. The current rate of change in physical and anthropogenic drivers is certain to impact the Marine Ecosystem Assessment of the Southern Ocean (MEASO) region in the near future and will have a wide range of impacts across the marine ecosystem
Haplotype Structure of the ENPP1 Gene and Nominal Association of the K121Q Missense Single Nucleotide Polymorphism With Glycemic Traits in the Framingham Heart Study
OBJECTIVE—A recent meta-analysis demonstrated a nominal association of the ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) K→Q missense single nucleotide polymorphism (SNP) at position 121 with type 2 diabetes. We set out to confirm the association of ENPP1 K121Q with hyperglycemia, expand this association to insulin resistance traits, and determine whether the association stems from K121Q or another variant in linkage disequilibrium with it
Configuration of the Northern Antarctic Peninsula Ice Sheet at LGM based on a new synthesis of seabed imagery
We present a new seafloor map for the northern
Antarctic Peninsula (AP), including swath multibeam data
sets from five national programs. Our map allows for the
examination and interpretation of Last Glacial Maximum
(LGM) paleo-ice-flow paths developed on the seafloor from
the preservation of mega-scale glacial lineations, drumlinized
features, and selective linear erosion. We combine this
with terrestrial observations of flow direction to place constraints
on ice divides and ice domes on the AP continental
shelf during the LGM time interval. The results show a flow
bifurcation as ice exits the Larsen B embayment. Flow emanating
off the Seal Nunataks (including Robertson Island)
is directed toward the southeast, then eastward as the flow
transits toward the Robertson Trough. A second, stronger
“streaming flow” is directed toward the southeast, then southward
as ice overflowed the tip of the Jason Peninsula to reach
the southern perimeter of the embayment. Our reconstruction
also refines the extent of at least five other distinct paleo-icestream
systems that, in turn, serve to delineate seven broad
regions where contemporaneous ice domes must have been
centered on the continental shelf at LGM. Our reconstruction
is more detailed than other recent compilations because we
followed specific ice-flow indicators and have kept tributary
flow paths parallel
Dimensional analysis of MINMOD leads to definition of the disposition index of glucose regulation and improved simulation algorithm
BACKGROUND: Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT) together with its mathematical model, the minimal model (MINMOD), have become important clinical tools to evaluate the metabolic control of glucose in humans. Dimensional analysis of the model is up to now not available. METHODS: A formal dimensional analysis of MINMOD was carried out and the degree of freedom of MINMOD was examined. Through re-expressing all state variable and parameters in terms of their reference scales, MINMOD was transformed into a dimensionless format. Previously defined physiological indices including insulin sensitivity, glucose effectiveness, and first and second phase insulin responses were re-examined in this new formulation. Further, the parameter estimation from FSIVGTT was implemented using both the dimensional and the dimensionless formulations of MINMOD, and the performances were compared utilizing Monte Carlo simulation as well as real human FSIVGTT data. RESULTS: The degree of freedom (DOF) of MINMOD was found to be 7. The model was maximally simplified in the dimensionless formulation that normalizes the variation in glucose and insulin during FSIVGTT. In the new formulation, the disposition index (Dl), a composite parameter known to be important in diabetes pathology, was naturally defined as one of the dimensionless parameters in the system. The numerical simulation using the dimensionless formulation led to a 1.5–5 fold gain in speed, and significantly improved accuracy and robustness in parameter estimation compared to the dimensional implementation. CONCLUSION: Dimensional analysis of MINMOD led to simplification of the model, direct identification of the important composite factors in the dynamics of glucose metabolic control, and better simulations algorithms
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