7,362 research outputs found
Subalgebra depths within the path algebra of an acyclic quiver
Constraints are given on the depth of diagonal subalgebras in generalized
triangular matrix algebras. The depth of the top subalgebra B = A /rad A in a
finite, connected, acyclic quiver algebra A over an algebraically closed field
K is then computed. Also the depth of the primary arrow subalgebra 1K + rad A =
B in A is obtained. The two types of subalgebras have depths 3 and 4
respectively, independent of the number of vertices. An upper bound on depth is
obtained for the quotient of a subalgebra pair.Comment: 14 pp. to appear in Proceedings A.G.M.P. Conf. Mulhouse, 2011,
Springe
Waveform complexity in teleseismic broadband SH displacements: Slab diffractions or deep mantle reflections?
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95458/1/grl4356.pd
Increasing Light Absorption and Collection Using Engineered Structures
In recent years we have witnessed an explosion of interest in two dimensional (2D) materials, due to their unique physical properties. Excitement surrounds the promise of replacing conventional bulk photodetectors with devices based on 2D materials, allowing better integration, flexibility and potentially improving performance. However, the low inherent light absorption of 2D materials is an outstanding issue to be solved. In this chapter we review two independent approaches to tackling this problem, which have the potential to be combined to find a robust solution. The first approach involves patterning the substrate with a rod-type photonic crystal (PhC) cavity structure, which is shown to increase the light absorption into a 2D material flake coupled spatially to the cavity mode. Secondly, we review 2Dâcompatible solid immersion lenses (SILs) and their ability to increase both the optical magnification of the structures they encapsulate, and the longevity of the material. SILs have been shown to reduce the requirements for complex optics in the implementation of 2D materials in optoelectronic devices, and also in preserving the photodetectorâs optical performance over long periods of time. Finally, we show how by combining rod-type PhC cavities with SILs, we can improve the performance of 2D material-based photodetectors
Mean shear flows generated by nonlinear resonant Alfven waves
In the context of resonant absorption, nonlinearity has two different
manifestations. The first is the reduction in amplitude of perturbations around
the resonant point (wave energy absorption). The second is the generation of
mean shear flows outside the dissipative layer surrounding the resonant point.
Ruderman et al. [Phys. Plasmas 4, 75 (1997)] studied both these effects at the
slow resonance in isotropic plasmas. Clack et al. [Astron. Astrophys. 494}, 317
(2009)] investigated nonlinearity at the Alfven resonance, however, they did
not include the generation of mean shear flow. In this present paper, we
investigate the mean shear flow, analytically, and study its properties. We
find that the flow generated is parallel to the magnetic surfaces and has a
characteristic velocity proportional to , where is
the dimensionless amplitude of perturbations far away from the resonance. This
is, qualitatively, similar to the flow generated at the slow resonance. The
jumps in the derivatives of the parallel and perpendicular components of mean
shear flow across the dissipative layer are derived. We estimate the generated
mean shear flow to be of the order of in both the solar
upper chromosphere and solar corona, however, this value strongly depends on
the choice of boundary conditions. It is proposed that the generated mean shear
flow can produce a Kelvin--Helmholtz instability at the dissipative layer which
can create turbulent motions. This instability would be an additional effect,
as a Kelvin--Helmholtz instability may already exist due to the velocity field
of the resonant Alfven waves. This flow can also be superimposed onto existing
large scale motions in the solar upper atmosphere.Comment: 11 page
Is Agricultural Policy Decoupling against Human Nature? Experimental Evidence of Fairness Expectationsâ Contributions to Payment Incidence
The objective of this research is to measure individualsâ fairness expectations and relate them to their market behavior in a private-negotiation institution. By doing this, we may inform model parameterization of field data and increase understanding of payment incidence causation. We hypothesize agents will change both their market and UG behavior when the tenant/proposer receives a subsidy following a successful negotiation. We also hypothesize that agentsâ market behavior does relate to their fairness expectations in the UG. Two economic experiments were developed to test our hypotheses, a market and an ultimatum bargaining game experiment. We recruited 106 undergraduate students and conducted the experiments in an experimental laboratory using a computer based market mechanism. Our findings suggest fairness expectations need to be considered as a possible constraint on agentsâ profit maximization behavior in land markets. The experimental evidence indicates market sellers or landlords demand higher land rental prices when tenants receive per-unit subsidies. Their ability to obtain a higher price appears to be more formidable in markets with limited matching opportunities. We conclude fairness expectations may constrain individualsâ profit-maximization behavior in the land market and, in turn, affect payment incidence in this market.Agricultural and Food Policy,
The Environments around Long-Duration Gamma-Ray Burst Progenitors
Gamma-ray burst (GRB) afterglow observations have allowed us to significantly
constrain the engines producing these energetic explosions. Te redshift and
position information provided by these afterglows have already allowed us to
limit the progenitors of GRBs to only a few models. The afterglows may also
provide another observation that can place further constraints on the GRB
progenitor: measurements telling us about the environments surrounding GRBs.
Current analyses of GRB afterglows suggest that roughly half of long-duration
gamma-ray bursts occur in surroundings with density profiles that are uniform.
We study the constraints placed by this observation on both the classic
``collapsar'' massive star progenitor and its relative, the ``helium-merger''
progenitor. We study several aspects of wind mass-loss and find that our
modifications to the standard Wolf-Rayet mass-loss paradigm are not sufficient
to produce constant density profiles. Although this does not rule out the
standard ``collapsar'' progenitor, it does suggest a deficiency with this
model. We then focus on the He-merger models and find that such progenitors can
fit this particular constraint well. We show how detailed observations can not
only determine the correct progenitor for GRBs, but also allow us to study
binary evolution physics.Comment: 44 pages including 11 figure
Recommended from our members
Extreme morning chronotypes are often familial and not exceedingly rare: the estimated prevalence of advanced sleep phase, familial advanced sleep phase, and advanced sleep-wake phase disorder in a sleep clinic population.
Study objectivesReport the first prevalence estimates of advanced sleep phase (ASP), familial advanced sleep phase (FASP), and advanced sleep-wake phase disorder (ASWPD). This can guide clinicians on the utility of screening for extreme chronotypes both for clinical decision-making and to flag prospective participants in the study of the genetics and biology of FASP.MethodsData on morning or evening sleep schedule preference (chronotype) were collected from 2422 new patients presenting to a North American sleep center over 9.8 years. FASP was determined using a severity criterion that has previously identified dominant circadian mutations in humans. All patients were personally seen and evaluated by one of the authors (C.R.J.).ResultsOur results demonstrate an ASP prevalence of 0.33%, an FASP prevalence of 0.21%, and an ASWPD prevalence of at least 0.04%. Most cases of young-onset ASP were familial.ConclusionsAmong patients presenting to a sleep clinic, conservatively 1 out of every 300 patients will have ASP, 1 out of every 475 will have FASP, and 1 out of every 2500 will have ASWPD. This supports obtaining a routine circadian history and, for those with extreme chronotypes, obtaining a family history of circadian preference. This can optimize treatment for evening sleepiness and early morning awakening and lead to additional circadian gene discovery. We hope these findings will lead to improved treatment options for a wide range of sleep and medical disorders in the future
- âŠ