1,110 research outputs found
On the Validity of the Imbert-Fick Law: Mathematical Modelling of Eye Pressure Measurement
YesOphthalmologists rely on a device known as the Goldmann applanation tonometer to make intraocular
pressure (IOP) measurements. It measures the force required to press a flat disc against
the cornea to produce a flattened circular region of known area. The IOP is deduced from this
force using the Imbert-Fick principle. However, there is scant analytical justification for this
analysis. We present a mathematical model of tonometry to investigate the relationship between
the pressure derived by tonometry and the IOP. An elementary equilibrium analysis suggests that
there is no physical basis for traditional tonometric analysis. Tonometry is modelled using a hollow
spherical shell of solid material enclosing an elastic liquid core, with the shell in tension and
the core under pressure. The shell is pressed against a rigid flat plane. The solution is found using
finite element analysis. The shell material is anisotropic. Values for its elastic constants are obtained
from literature except where data are unavailable, when reasonable limits are explored.
The results show that the force measured by the Goldmann tonometer depends on the elastic constant
values. The relationship between the IOP and the tonometer readings is complex, showing
potentially high levels of inaccuracy that depend on IOP
On fast CP violating interactions in leptogenesis
We show that when the relevant CP violating interactions in leptogenesis are
fast, the different matter density asymmetries are determined at each instant
by a balance condition between the amount of asymmetry being created and
destroyed. This fact allows to understand in a simple way many features of
leptogenesis in the strong washout regime. In particular, we find some
non-trivial effects of flavour changing interactions that conserve lepton
number, which are specially relevant in models for leptogenesis that rely
heavily on flavour effects.Comment: V2: To match published version in JCAP. Minor changes, including one
figure, with respect to V1. 17 pages, 4 figure
Atmospheric lepton fluxes at ultrahigh energies
In order to estimate the possibility to observe exotic physics in a neutrino
telescope, it is essential to first understand the flux of atmospheric
neutrinos, muons and dimuons. We study the production of these leptons by
high-energy cosmic rays. We identify three main sources of muons of energy E >
10^6 GeV: the weak decay of charm and bottom mesons and the electromagnetic
decay of unflavored mesons. Contrary to the standard assumption, we find that
eta mesons, not the prompt decay of charm hadrons, are the dominant source of
atmospheric muons at these energies. We show that, as a consequence, the ratio
between the neutrino and muon fluxes is significantly reduced. For dimuons,
which may be a background for long-lived staus produced near a neutrino
telescope, we find that pairs of E ~ 10^7 GeV forming an angle above 10^-6 rad
are produced through D (80%) or B (10%) meson decay and through Drell-Yan
proceses (10%). The frequency of all these processes has been evaluated using
the jet code PYTHIA.Comment: 10 pages, 4 figures; published versio
Benchmarking of Academic Departments using Data Envelopment Analysis (DEA)
Keywords: Data Envelopment Analysis; Relative Efficiency; Benchmarking; Resource Allocation; Investment Model; Decision-Support SystemPurpose – The main objective of the paper is to develop an Investment Model using Data Envelopment Analysis (DEA) that provides a decision-making framework to allocate resources efficiently, such that the relative efficiency is improved within an available investment budget.
Design/methodology/approach – DEA models are used to evaluate the efficiency of the departments relative to their peers and providing benchmarks for the less efficient departments. Secondly, the inefficiencies in departments are identified. Finally, for the less efficient departments, a decision-support system is introduced for optimizing resource allocation to improve efficiency.
Findings – Five of the eighteen academic departments were determined to be inefficient, and benchmark departments were found for those departments. The most prevalent causes for inefficiency were the number of Undergraduate Students per Faculty and the Number of Graduate Students. Results from the Investment Model for Department 12 suggest increasing the Number of Faculty by 2 units and H-Index by 0.5 units, thereby, improving the relative efficiency of the department by 6.8% (88% to 94%), using 500,000 investment budget provided.
Originality – When an investment budget is available, no study has used DEA to develop a decision-support framework for resource allocation in academic departments to maximize relative efficiency.Ye
TeV scale resonant leptogenesis from supersymmetry breaking
We propose a model of TeV-scale resonant leptogenesis based upon recent
models of the generation of light neutrino masses from supersymmetry-breaking
effects with TeV-scale right-handed (rhd) neutrinos, . The model leads to
naturally large cosmological lepton asymmetries via the resonant behaviour of
the one-loop self-energy contribution to decay. Our model addresses the
primary problems of previous phenomenological studies of low-energy
leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa
couplings so that the out-of equilibrium condition for decay is
satisfied; the origin of the tiny, but non-zero mass splitting required between
at least two masses; and the necessary non-trivial breaking of flavour
symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos
and their superpartners, and the TeV-scale -terms automatically contained
within the model offer opportunities for partial direct experimental tests of
this leptogenesis mechanism at future colliders.Comment: 10 Pages latex, version for JHE
Soft leptogenesis in the inverse seesaw model
We consider leptogenesis induced by soft supersymmetry breaking terms ("soft
leptogenesis"), in the context of the inverse seesaw mechanism. In this model
there are lepton number (L) conserving and L-violating soft
supersymmetry-breaking B-terms involving the singlet sneutrinos which, together
with the -- generically small-- L-violating parameter responsible of the
neutrino mass, give a small mass splitting between the four singlet sneutrino
states of a single generation. In combination with the trilinear soft
supersymmetry breaking terms they also provide new CP violating phases needed
to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that
in this scenario the lepton asymmetry is proportional to the L-conserving soft
supersymmetry-breaking B-term, and it is not suppressed by the L-violating
parameters. Consequently we find that, as in the standard see-saw case, this
mechanism can lead to sucessful leptogenesis only for relatively small value of
the relevant soft bilinear coupling. The right-handed neutrino masses can be
sufficiently low to elude the gravitino problem. Also the corresponding Yukawa
couplings involving the lightest of the right-handed neutrinos are constrained
to be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that the
neutrino mass spectrum has to be strongly hierarchical.Comment: 28 pages, 1 figure; some references added; final version to appear in
JHE
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