821 research outputs found
Anomaly Cancellation in Supergravity with Fayet-Iliopoulos Couplings
We review and clarify the cancellation conditions for gauge anomalies which
occur when N=1, D=4 supergravity is coupled to a Kahler non-linear sigma-model
with gauged isometries and Fayet-Iliopoulos couplings. For a flat sigma-model
target space and vanishing Fayet-Iliopoulos couplings, consistency requires
just the conventional anomaly cancellation conditions. A consistent model with
non-vanishing Fayet-Iliopoulos couplings is unlikely unless the Green-Schwarz
mechanism is used. In this case the U(1) gauge boson becomes massive and the
D-term potential receives corrections. A Green-Schwarz mechanism can remove
both the abelian and certain non-abelian anomalies in models with a gauge
non-invariant Kahler potential.Comment: 27 page
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Time-transgressive North Atlantic productivity changes upon Northern Hemisphere glaciation
Marine biological export productivity declined in high-latitude regions in the North Pacific and Southern Ocean 2.7 million years ago, in parallel with the intensification of Northern Hemisphere glaciation. Here we present data from the North Atlantic, which show a similar but time-transgressive pattern of high-latitude productivity decline from 3.3 to 2.5âMa, with productivity decreasing first at 69°N, hundreds of thousands of years before it declined at 58°N. We propose that the cumulative data are best explained by an equatorward migration of the westerly winds, which caused a southward shift in the zone of Ekman divergence and upwelling-associated major nutrient supply over this time interval. We suggest that a similar equatorward migration of the westerly winds may also help explain the productivity changes observed in other high-latitude regions, particularly the Southern Ocean. At 2.7âMa, equatorial and temperate Atlantic sites began to show orbitally paced productivity pulses, consistent with a shoaling and meridional contraction of the nutrient-poor "warm sphere" that characterizes the low latitude upper ocean. This timing coincides with observed productivity changes in Southern Ocean, consistent with previous findings that the Southern Ocean exerts a strong influence on the fertility of the low-latitude Atlantic. Finally, we propose that the unique basin geometry of the North Atlantic caused deep water formation in this region to remain relatively stable despite equatorward migration of winds and ocean fronts
The transfer of fibres in the carding machine
The problem of understanding the transfer of fibres between carding-machine surfaces is addressed by considering the movement of a single fibre in an airflow. The structure of the aerodynamic flow field predicts how and when fibres migrate between the different process surfaces. In the case of a revolving-flats carding machine the theory predicts a âstrongâ aerodynamic mechanism between taker-in and cylinder and a âweakâ mechanism between cylinder and removal cylinder resulting in effective transfer in the first case and a more limited transfer in the second
Continuum theory of vacancy-mediated diffusion
We present and solve a continuum theory of vacancy-mediated diffusion (as
evidenced, for example, in the vacancy driven motion of tracers in crystals).
Results are obtained for all spatial dimensions, and reveal the strongly
non-gaussian nature of the tracer fluctuations. In integer dimensions, our
results are in complete agreement with those from previous exact lattice
calculations. We also extend our model to describe the vacancy-driven
fluctuations of a slaved flux line.Comment: 25 Latex pages, subm. to Physical Review
From Majorana theory of atomic autoionization to Feshbach resonances in high temperature superconductors
The Ettore Majorana paper - Theory of incomplete P triplets- published in
1931, focuses on the role of selection rules for the non-radiative decay of two
electron excitations in atomic spectra, involving the configuration interaction
between discrete and continuum channels. This work is a key step for
understanding the 1935 work of Ugo Fano on the asymmetric lineshape of two
electron excitations and the 1958 Herman Feshbach paper on the shape resonances
in nuclear scattering arising from configuration interaction between many
different scattering channels. The Feshbach resonances are today of high
scientific interest in many different fields and in particular for ultracold
gases and high Tc superconductivity.Comment: 13 pages, 7 figures. Journal of Superconductivity and Novel Magnetism
to be publishe
Poverty and the multiple stakeholder challenge for global leaders
The article presents a case study in which business leaders deal with challenging problems related to poverty, involving multiple stakeholders. This emphasizes the importance of training prospective global leaders to manage stakeholder relationships and engage in stakeholder dialogue. The authors highlight the stakeholder role played by nongovernmental organizations and include a simulation that develops stakeholder dialogue skills. They identify practical lessons and assumptions underlying business education that are not shared by all stakeholders in the context of poverty
PRIMA1 mutation: A new cause of nocturnal frontal lobe epilepsy
Objective
Nocturnal frontal lobe epilepsy (NFLE) can be sporadic or autosomal dominant; some families have nicotinic acetylcholine receptor subunit mutations. We report a novel autosomal recessive phenotype in a single family and identify the causative gene.
Methods
Whole exome sequencing data was used to map the family, thereby narrowing exome search space, and then to identify the mutation.
Results
Linkage analysis using exome sequence data from two affected and two unaffected subjects showed homozygous linkage peaks on chromosomes 7, 8, 13, and 14 with maximum LOD scores between 1.5 and 1.93. Exome variant filtering under these peaks revealed that the affected siblings were homozygous for a novel splice site mutation (c.93+2T>C) in the PRIMA1 gene on chromosome 14. No additional PRIMA1 mutations were found in 300 other NFLE cases. The c.93+2T>C mutation was shown to lead to skipping of the first coding exon of the PRIMA1 mRNA using a minigene system.
Interpretation
PRIMA1 is a transmembrane protein that anchors acetylcholinesterase (AChE), an enzyme hydrolyzing acetycholine, to membrane rafts of neurons. PRiMA knockout mice have reduction of AChE and accumulation of acetylcholine at the synapse; our minigene analysis suggests that the c.93+2T>C mutation leads to knockout of PRIMA1. Mutations with gain of function effects in acetylcholine receptor subunits cause autosomal dominant NFLE. Thus, enhanced cholinergic responses are the likely cause of the severe NFLE and intellectual disability segregating in this family, representing the first recessive case to be reported and the first PRIMA1 mutation implicated in disease
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
A Bayesian analysis of pentaquark signals from CLAS data
We examine the results of two measurements by the CLAS collaboration, one of
which claimed evidence for a pentaquark, whilst the other found no
such evidence. The unique feature of these two experiments was that they were
performed with the same experimental setup. Using a Bayesian analysis we find
that the results of the two experiments are in fact compatible with each other,
but that the first measurement did not contain sufficient information to
determine unambiguously the existence of a . Further, we suggest a
means by which the existence of a new candidate particle can be tested in a
rigorous manner.Comment: 5 pages, 3 figure
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