1,206 research outputs found
Infinite non-causality in active cancellation of random noise
Active cancellation of broadband random noise requires the detection of the
incoming noise with some time advance. In an duct for example this advance must
be larger than the delays in the secondary path from the control source to the
error sensor. In this paper it is shown that, in some cases, the advance
required for perfect noise cancellation is theoretically infinite because the
inverse of the secondary path, which is required for control, can include an
infinite non-causal response. This is shown to be the result of two mechanisms:
in the single-channel case (one control source and one error sensor), this can
arise because of strong echoes in the control path. In the multi-channel case
this can arise even in free field simply because of an unfortunate placing of
sensors and actuators. In the present paper optimal feedforward control is
derived through analytical and numerical computations, in the time and
frequency domains. It is shown that, in practice, the advance required for
significant noise attenuation can be much larger than the secondary path
delays. Practical rules are also suggested in order to prevent infinite
non-causality from appearing
Mathematical modeling and numerical simulation of a bioreactor landfill using Feel++
In this paper, we propose a mathematical model to describe the functioning of
a bioreactor landfill, that is a waste management facility in which
biodegradable waste is used to generate methane. The simulation of a bioreactor
landfill is a very complex multiphysics problem in which bacteria catalyze a
chemical reaction that starting from organic carbon leads to the production of
methane, carbon dioxide and water. The resulting model features a heat equation
coupled with a non-linear reaction equation describing the chemical phenomena
under analysis and several advection and advection-diffusion equations modeling
multiphase flows inside a porous environment representing the biodegradable
waste. A framework for the approximation of the model is implemented using
Feel++, a C++ open-source library to solve Partial Differential Equations. Some
heuristic considerations on the quantitative values of the parameters in the
model are discussed and preliminary numerical simulations are presented
Left ventricular systolic function in sickle cell anaemia: an echocardiographic evaluation in adult Nigerian patients.
Background: Reliable diagnostic measures for the evaluation of left
ventricular systolic performance in the setting of altered myocardial
loading characteristics in sickle cell anaemia remains unresolved.
Objective: The study was designed to assess left ventricular systolic
function in adult sickle cell patients using non-invasive endsystolic
stress \u2013 end-systolic volume index ratio. Methods: A descriptive
cross sectional comparative study was done using 52 patients recruited
at the adult sickle cell anaemia clinic of the University of Nigeria
Teaching Hospital Enugu. An equal number of age and sex-matched healthy
volunteers served as controls. All the participants had haematocrit
estimation, haemoglobin electrophoresis, as well as echocardiographic
evaluation. Result: The mean age of the patients and controls were
23.93 \ub1 5.28 (range 18-42) and 24.17 \ub1 4.39 (range 19 -42)
years respectively, (t = 0.262; p= .794). No significant difference was
seen in estimate of fractional shortening, and ejection fraction. The
cardiac out-put, cardiac index and velocity of circumferential
shortening were all significantly increased in the cases compared with
the controls. The end systolic stress \u2013 end systolic volume index
ratio (ESS/ESVI) was significantly lower in cases than controls. There
were strong positive correlation between the ejection phase indices
(ejection fraction and fractional shortening) and end systolic stress
and ESS/ESVI. Conclusion: The study findings suggest the presence of
left ventricular systolic dysfunction in adult sickle cell anaemia.
This is best detected using the loading-pressures independent
force-length relationship expressed in ESS/ESVI ratio
A Guild of 45 CRISPR-Associated (Cas) Protein Families and Multiple CRISPR/Cas Subtypes Exist in Prokaryotic Genomes
Clustered regularly interspaced short palindromic repeats (CRISPRs) are a family of DNA direct repeats found in many prokaryotic genomes. Repeats of 21–37 bp typically show weak dyad symmetry and are separated by regularly sized, nonrepetitive spacer sequences. Four CRISPR-associated (Cas) protein families, designated Cas1 to Cas4, are strictly associated with CRISPR elements and always occur near a repeat cluster. Some spacers originate from mobile genetic elements and are thought to confer “immunity” against the elements that harbor these sequences. In the present study, we have systematically investigated uncharacterized proteins encoded in the vicinity of these CRISPRs and found many additional protein families that are strictly associated with CRISPR loci across multiple prokaryotic species. Multiple sequence alignments and hidden Markov models have been built for 45 Cas protein families. These models identify family members with high sensitivity and selectivity and classify key regulators of development, DevR and DevS, in Myxococcus xanthus as Cas proteins. These identifications show that CRISPR/cas gene regions can be quite large, with up to 20 different, tandem-arranged cas genes next to a repeat cluster or filling the region between two repeat clusters. Distinctive subsets of the collection of Cas proteins recur in phylogenetically distant species and correlate with characteristic repeat periodicity. The analyses presented here support initial proposals of mobility of these units, along with the likelihood that loci of different subtypes interact with one another as well as with host cell defensive, replicative, and regulatory systems. It is evident from this analysis that CRISPR/cas loci are larger, more complex, and more heterogeneous than previously appreciated
Geometrical CP violation from non-renormalisable scalar potentials
We consider in detail the non-renormalisable scalar potential of three Higgs
doublets transforming as an irreducible triplet of Delta(27) or Delta(54). We
start from a renormalisable potential that spontaneously leads to a vacuum with
CP-violating phases independent of arbitrary parameters - geometrical CP
violation. Then we analyse to arbitrarily high order non-renormalisable terms
that are consistent with the symmetry and we demonstrate that inclusion of
non-renormalisable terms in the potential can preserve the geometrical
CP-violating vacuum.Comment: 5 pages, 2 figures. v2: references added, accepted by PL
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