11,571 research outputs found
Bioremediation of lead using spore surface displayed proteins
Lead is a toxic pollutant very harmful to human health since it accumulates in the body and affects the brain, liver, kidney, and bones. Fetuses can be exposed to lead during pregnancy, which can cause problems with learning later on in the babyâs life. The purpose of this project is to display a lead binding protein on bacterial spore surface for the bioremediation of lead from water. Spores from Bacillus subtilis are very robust and resistant to various harsh environments. Genetically fused to a spore surface protein, the displayed proteins demonstrate enhanced robustness and can be easily produced through sporulation without the need of further purification. PbrR is a regulatory protein that modulates the lead resistance in bacteria. In this project, we fused seven variants of PbrR to the spore surface protein CotC (CotC-PbrRs). The lead binding affinity and specificity of these PbrR variants on the spore surface will be characterized. The robustness of these spores with PbrR will be also evaluated using wastewater samples
Isospin in Reaction Dynamics. The Case of Dissipative Collisions at Fermi Energies
A key question in the physics of unstable nuclei is the knowledge of the
for asymmetric nuclear matter () away from normal conditions. We
recall that the symmetry energy at low densities has important effects on the
neutron skin structure, while the knowledge in high densities region is crucial
for supernovae dynamics and neutron star properties. The way to probe
such region of the isovector in terrestrial laboratories is through very
dissipative collisions of asymmetric (up to exotic) heavy ions from low to
relativistic energies. A general introduction to the topic is firstly
presented. We pass then to a detailed discussion on the
process as the main dissipative mechanism at the Fermi energies and to the
related isospin dynamics. From Stochastic Mean Field simulations the isospin
effects on all the phases of the reaction dynamics are thoroughly analysed,
from the fast nucleon emission to the mid-rapidity fragment formation up to the
dynamical fission of the residues. Simulations have been performed
with an increasing stiffness of the symmetry term of the .
Some differences have been noticed, especially for the fragment charge
asymmetry. New isospin effects have been revealed from the correlation of
fragment asymmetry with dynamical quantities at the freeze-out time. A series
of isospin sensitive observables to be further measured are finally listed.Comment: 16 pages, 6 figures, Contribution to the 5th Italy-Japan Symposium,
Recent Achievements and Perspectives in Nuclear Physics, Naples Nov.3-7 2004,
World Sci. in press. Latex in WorldSci/proc/styl
On the Analytic Wavelet Transform
An exact and general expression for the analytic wavelet transform of a
real-valued signal is constructed, resolving the time-dependent effects of
non-negligible amplitude and frequency modulation. The analytic signal is first
locally represented as a modulated oscillation, demodulated by its own
instantaneous frequency, and then Taylor-expanded at each point in time. The
terms in this expansion, called the instantaneous modulation functions, are
time-varying functions which quantify, at increasingly higher orders, the local
departures of the signal from a uniform sinusoidal oscillation. Closed-form
expressions for these functions are found in terms of Bell polynomials and
derivatives of the signal's instantaneous frequency and bandwidth. The analytic
wavelet transform is shown to depend upon the interaction between the signal's
instantaneous modulation functions and frequency-domain derivatives of the
wavelet, inducing a hierarchy of departures of the transform away from a
perfect representation of the signal. The form of these deviation terms
suggests a set of conditions for matching the wavelet properties to suit the
variability of the signal, in which case our expressions simplify considerably.
One may then quantify the time-varying bias associated with signal estimation
via wavelet ridge analysis, and choose wavelets to minimize this bias
Analysis of Modulated Multivariate Oscillations
The concept of a common modulated oscillation spanning multiple time series
is formalized, a method for the recovery of such a signal from potentially
noisy observations is proposed, and the time-varying bias properties of the
recovery method are derived. The method, an extension of wavelet ridge analysis
to the multivariate case, identifies the common oscillation by seeking, at each
point in time, a frequency for which a bandpassed version of the signal obtains
a local maximum in power. The lowest-order bias is shown to involve a quantity,
termed the instantaneous curvature, which measures the strength of local
quadratic modulation of the signal after demodulation by the common oscillation
frequency. The bias can be made to be small if the analysis filter, or wavelet,
can be chosen such that the signal's instantaneous curvature changes little
over the filter time scale. An application is presented to the detection of
vortex motions in a set of freely-drifting oceanographic instruments tracking
the ocean currents
The meaning of S-D dominance
The dominance of S and D pairs in the description of deformed nuclei is one
of the facts that provided sustain to the Interacting Boson Approximation. In
Ref.(J. Dukelsky and S. Pittel, Phys. Rev. Lett. 86, 4791, 2001.), using an
exactly solvable model with a repulsive pairing interaction between bosons it
has been shown that the ground state is described almost completely in terms of
S and D bosons. In the present paper we study the excited states obtained
within this exactly solvable hamiltonian and show that in order to obtain a
rotational spectra all the other degrees of freedom are needed.Comment: Are S and D pairs enough to describe deformed nuclei
Generalized Morse Wavelets as a Superfamily of Analytic Wavelets
The generalized Morse wavelets are shown to constitute a superfamily that
essentially encompasses all other commonly used analytic wavelets, subsuming
eight apparently distinct types of analysis filters into a single common form.
This superfamily of analytic wavelets provides a framework for systematically
investigating wavelet suitability for various applications. In addition to a
parameter controlling the time-domain duration or Fourier-domain bandwidth, the
wavelet {\em shape} with fixed bandwidth may be modified by varying a second
parameter, called . For integer values of , the most symmetric,
most nearly Gaussian, and generally most time-frequency concentrated member of
the superfamily is found to occur for . These wavelets, known as
"Airy wavelets," capture the essential idea of popular Morlet wavelet, while
avoiding its deficiencies. They may be recommended as an ideal starting point
for general purpose use
Variation of the Diameter of the Sun as Measured by the Solar Disk Sextant (SDS)
The balloon-borne Solar Disk Sextant (SDS) experiment has measured the
angular size of the Sun on seven occasions spanning the years 1992 to 2011. The
solar half-diameter -- observed in a 100-nm wide passband centred at 615 nm --
is found to vary over that period by up to 200 mas, while the typical estimated
uncertainty of each measure is 20 mas. The diameter variation is not in phase
with the solar activity cycle; thus, the measured diameter variation cannot be
explained as an observational artefact of surface activity. Other possible
instrument-related explanations for the observed variation are considered but
found unlikely, leading us to conclude that the variation is real. The SDS is
described here in detail, as is the complete analysis procedure necessary to
calibrate the instrument and allow comparison of diameter measures across
decades.Comment: 41 pages; appendix and 2 figures added plus some changes in text
based on referee's comments; to appear in MNRA
Solar radius and luminosity variations induced by the internal dynamo magnetic fields
Although the occurrence of solar irradiance variations induced by magnetic
surface features (e.g., sunspots, faculae, magnetic network) is generally
accepted, the existence of intrinsic luminosity changes due to the internal
magnetic fields is still controversial. This additional contribution is
expected to be accompanied by radius variations, and to be potentially
significant for the climate of the Earth. We aim to constrain theoretically the
radius and luminosity variations of the Sun that are due to the effect of the
variable magnetic fields in its interior associated with the dynamo cycle. We
have extended a one-dimensional stellar evolution code to include several
effects of the magnetic fields on the interior structure. We investigate
different magnetic configurations, based on both observational constraints and
on the output of state-of-the-art mean field dynamo models. We explore both
step-like and simply periodic time dependences of the magnetic field peak
strength. We find that the luminosity and radius variations are in anti-phase
and in phase, respectively, with the magnetic field strength. For peak magnetic
field strengths of the order of tens of kilogauss, luminosity variations
ranging between 10^{-6} and 10^{-3} (in modulus) and radius variations between
10^{-6} and 10^{-5} are obtained. Modest but significant radius variations (up
to 10^{-5} in relative terms) are obtained for magnetic fields of realistic
strength and geometry, providing a potentially observable signature of the
intrinsic variations. Establishing their existence in addition to the accepted
surface effects would have very important implications for the understanding of
solar-induced long-term trends on climate.Comment: 18 pages, 7 figures; accepted for publication in Astronomische
Nachrichte
Optimal control of a dengue epidemic model with vaccination
We present a SIR+ASI epidemic model to describe the interaction between human
and dengue fever mosquito populations. A control strategy in the form of
vaccination, to decrease the number of infected individuals, is used. An
optimal control approach is applied in order to find the best way to fight the
disease.Comment: This is a preprint of a paper accepted for presentation at ICNAAM
2011, Halkidiki, Greece, 19-25 September 2011, and to appear in AIP
Conference Proceedings, volume 138
Modeling and Optimal Control Applied to a Vector Borne Disease
A model with six mutually-exclusive compartments related to Dengue disease is
presented. In this model there are three vector control tools: insecticides
(larvicide and adulticide) and mechanical control. The problem is studied using
an Optimal Control (OC) approach. The human data for the model is based on the
Cape Verde Dengue outbreak. Some control measures are simulated and their
consequences analyzed
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