16,219 research outputs found
Modelling the kinetics of thermal inactivation of apple polyphenoloxidase
The enzymatic browning of fruits and vegetables caused by mechanical injury during postharvest storage or processing is initiated by the catalytic action of polyphenoloxidase (PPO). A bleaching
treatment prior to processing is still considered mostly effective in inhibiting the catalytic activity of PPO,
and thus controlling undesirable enzymatic browning. In this work, different mathematical routines were
assessed in terms of their adequacy to describe the thermal inactivation of PPO from Golden apples over a
range of temperatures from 62.5 to 72.5 ĀŗC. The classical approach to kinetic modelling of the decay activity
of apple PPO, commonly reported to follow a first-order model, employs a two-step procedure, in which the
model parameters are individually obtained, by each temperature studied, using non-linear or linear
regressions. Thereafter, the estimated parameters are further used to calculate their temperature dependence.
Alternatively, a one-step method provides a regression fit to all experimental data sets, with the temperature
dependence equation being directly built in the kinetic model. This fitting technique thus, (a) avoids the
estimation of intermediate parameters and, (b) substantially increases the degrees of freedom and hence the
precision of parametersā estimates. Within this issue was further explored the logarithmic transformation of
the mathematical equations used on the adequacy of the model to describe experimental data. In all cases
non-weighted least-squares regression procedures were used. Both the examination and criticism of the
current modelling strategies were done by assessing statistical data obtained, such as the confidence intervals
of the estimates, correlation coefficients, sum of squares, and residuals normality
Phase transition for the frog model
We study a system of simple random walks on graphs, known as frog model. This
model can be described as follows: There are active and sleeping particles
living on some graph G. Each active particle performs a simple random walk with
discrete time and at each moment it may disappear with probability 1-p. When an
active particle hits a sleeping particle, the latter becomes active. Phase
transition results and asymptotic values for critical parameters are presented
for Z^d and regular trees
Light trapping and guidance in plasmonic nanocrystals
We illustrate the possibility of light trapping and funneling in periodic
arrays of metallic nanoparticles. A controllable minimum in the transmission
spectra of such constructs arises from a collective plasmon resonance
phenomenon, where an incident plane wave sharply localizes in the vertical
direction, remaining delocalized in the direction parallel to the crystal
plane. Using hybrid arrays of different structures or different materials, we
apply the trapping effect to structure the eigen-mode spectrum, introduce
overlapping resonances, and hence direct the light in space in a
wavelength-sensitive fashion
Quantiles for Fractions and Other Mixed Data
This paper studies the estimation of quantile regression for fractional data, focusing on the case where there are mass-points at zero or/and one. More generally, we propose a simple strategy for the estimation of the conditional quantiles of data from mixed distributions, which combines standard results on the estimation of censored and Box-Cox quantile regressions. The implementation of the proposed method is illustrated using a well-known dataset.
Coulomb corrections to inclusive cross sections at the future Electron - Ion Collider
The experimental results of the future electron -- ion () collider are
expected to constrain the dynamics of the strong interactions at small values
of the Bjorken -- variable and large nuclei. Recently it has been suggested
that Coulomb corrections can be important in inclusive and diffractive
interactions. In this paper we present a detailed investigation of the impact
of the Coulomb corrections to some of the observables that will be measured in
the future collider. In particular, we estimate the magnitude of these
corrections for the charm and longitudinal cross sections in inclusive and
diffractive interactions. Our results demonstrate that the Coulomb corrections
for these observables are negligible, which implies that they can be used to
probe the QCD dynamics.Comment: 9 pages, 6 figures. Improved version to be published in Physical
Review
The type N Karlhede bound is sharp
We present a family of four-dimensional Lorentzian manifolds whose invariant
classification requires the seventh covariant derivative of the curvature
tensor. The spacetimes in questions are null radiation, type N solutions on an
anti-de Sitter background. The large order of the bound is due to the fact that
these spacetimes are properly , i.e., curvature homogeneous of order 2
but non-homogeneous. This means that tetrad components of are constant, and that essential coordinates first appear as
components of . Covariant derivatives of orders 4,5,6 yield one
additional invariant each, and is needed for invariant
classification. Thus, our class proves that the bound of 7 on the order of the
covariant derivative, first established by Karlhede, is sharp. Our finding
corrects an outstanding assertion that invariant classification of
four-dimensional Lorentzian manifolds requires at most .Comment: 7 pages, typos corrected, added citation and acknowledgemen
- ā¦