320 research outputs found
Fractional Diffusion and Medium Heterogeneity: The Case of the Continuos Time Random Walk
In this contribution we show that fractional diffusion emerges from a simple Markovian Gaussian random walk when the medium displays a power-law heterogeneity. Within the framework of the continuous time random walk, the heterogeneity of the medium is represented by the selection, at any jump, of a different time-scale for an exponential survival probability. The resulting process is a non-Markovian non-Gaussian random walk. In particular, for a power-law distribution of the time-scales, the resulting random walk corresponds to a time-fractional diffusion process. We relates the power-law of the medium heterogeneity to the fractional order of the diffusion. This relation provides an interpretation and an estimation of the fractional order of derivation in terms of environment heterogeneity. The results are supported by simulations
Langevin equation in complex media and anomalous diffusion
The problem of biological motion is a very intriguing and topical issue.
Many efforts are being focused on the development of novel modelling
approaches for the description of anomalous diffusion in biological systems,
such as the very complex and heterogeneous cell environment. Nevertheless,
many questions are still open, such as the joint manifestation of statistical
features in agreement with different models that can also be somewhat alternative to each other, e.g. continuous time random walk and fractional Brownian
motion. To overcome these limitations, we propose a stochastic diffusion
model with additive noise and linear friction force (linear Langevin equation),
thus involving the explicit modelling of velocity dynamics. The complexity of
the medium is parametrized via a population of intensity parameters (relaxation time and diffusivity of velocity), thus introducing an additional
randomness, in addition to white noise, in the particleâs dynamics. We
prove that, for proper distributions of these parameters, we can get both
Gaussian anomalous diffusion, fractional diffusion and its generalizations.V.S. acknowledges BCAM Internship Program, Bilbao, for the financial support to her internship research period during which she developed her masterâs thesis research
useful for her masterâs degree in Physics at University of Bologna.
S.V. acknowledges the University of Bologna for the financial support
through the âMarco Polo Programmeâ for her PhD research period
abroad spent at BCAM, Bilbao, useful for her PhD degree in Physics
at University of Bologna.
P.P. acknowledges financial support from Bizkaia Talent and European Commission
through COFUND scheme, 2015 Financial Aid Program for Researchers, project number
AYDâ000â252 hosted at BCAM, Bilbao
Microwave-assisted vacuum synthesis of tio2 nanocrystalline powders in one-pot, one-step procedure
A new method for fast and simple synthesis of crystalline TiO2 nanoparticles with photocat-alytic activity was developed by carrying out a classic solâgel reaction directly under vacuum. The use of microwaves for fast heating of the reaction medium further reduces synthesis times. When the solvent is completely removed by vacuum, the product is obtained in the form of a powder that can be easily redispersed in water to yield a stable nanoparticle suspension, exhibiting a comparable photocatalytic activity with respect to a commercial product. The present methodology can, therefore, be considered a process intensification procedure for the production of nanotitania
Centre-of-mass like superposition of Ornstein-Uhlenbeck processes: A pathway to non-autonomous stochastic differential equations and to fractional diffusion
We consider an ensemble of OrnsteinâUhlenbeck processes featuring a population of relaxation times and a population of noise amplitudes that characterize the heterogeneity of the ensemble. We show that the centre-of-mass like variable corresponding to this ensemble is statistically equivalent to a process driven by a non-autonomous stochastic differential equation with time-dependent drift and a white noise. In particular, the time scaling and the density function of such variable are driven by the population of timescales and of noise amplitudes, respectively. Moreover, we show that this variable is equivalent in distribution to a randomly-scaled Gaussian process, i.e., a process built by the product of a Gaussian process times a non-negative independent random variable. This last result establishes a connection with the so-called generalized grey Brownian motion and suggests application to model fractional anomalous diffusion in biological systems.âMarco Polo Programmeâ (University of Bologna
Effect of FCNC mediated Z boson on lepton flavor violating decays
We study the three body lepton flavor violating (LFV) decays , and the semileptonic decay in the flavor changing neutral current (FCNC) mediated boson
model. We also calculate the branching ratios for LFV leptonic B decays,
, , and the
conversion of muon to electron in Ti nucleus. The new physics parameter space
is constrained by using the experimental limits on and
. We find that the branching ratios for and processes could be as large as and . For other LFV B decays the branching ratios are found to be too
small to be observed in the near future.Comment: 15 pages, 8 figures, typos corrected, one more section added, version
to appear in EPJ
Impact of the COVID-19 pandemic on ovarian tissue cryopreservation planning in the Bologna clinical center
Introduction: Treatment of patients with COVID-19 has been a priority by competing with the treatment of any other disease due to limited hospital resources. The current pandemic situation has focused the attention of healthcare providers around the world away from all other non-emergency health problems, including oncofertility. The aim of the study was to evaluate the repercussions of the COVID-19 pandemic on the activity levels of ovarian tissue cryopreservation (OTC) in the our center. Methods: The study analyzed the number of patients treated for OTC in our center during three periods: pre-pandemic period: March 2019-February 2020, pandemic period: March 2020-February 2021 and post-pandemic period: March 2021-February 2022. Results: In our center routine hospital operation was completely reorganized, allowing only urgent interventions. Continuing to urgently preserve fertility during the pandemic required rapid changes to our standard practices for the care of these vulnerable patients. Despite the modifications, there was no difference in the number of OTC performed among the periods analyzed. Similarly, the number of patients who did not perform OTC was the same over the three years analyzed. Discussion: Despite the local and national restructuring of care to conserve resources and protect the community, it is significant to continue offering fertility-sparing treatment to cancer patients. This emphasis on the importance of preserving fertility despite the pandemic further highlights the essential and urgent nature of this procedure
Extreme value statistics from the Real Space Renormalization Group: Brownian Motion, Bessel Processes and Continuous Time Random Walks
We use the Real Space Renormalization Group (RSRG) method to study extreme
value statistics for a variety of Brownian motions, free or constrained such as
the Brownian bridge, excursion, meander and reflected bridge, recovering some
standard results, and extending others. We apply the same method to compute the
distribution of extrema of Bessel processes. We briefly show how the continuous
time random walk (CTRW) corresponds to a non standard fixed point of the RSRG
transformation.Comment: 24 pages, 5 figure
The Physics of Heavy Flavours at SuperB
This is a review of the SuperB project, covering the accelerator, detector,
and highlights of the broad physics programme. SuperB is a flavour factory
capable of performing precision measurements and searches for rare and
forbidden decays of , , and
particles. These results can be used to test fundamental symmetries and
expectations of the Standard Model, and to constrain many different
hypothesised types of new physics. In some cases these measurements can be used
to place constraints on the existence of light dark matter and light Higgs
particles with masses below . The potential impact of the
measurements that will be made by SuperB on the field of high energy physics is
also discussed in the context of data taken at both high energy in the region
around the \Upsilon({\mathrm{4S}})$, and near charm threshold.Comment: 49 pages, topical review submitted to J. Phys
Muon Physics: A Pillar of the Standard Model
Since its discovery in the 1930s, the muon has played an important role in
our quest to understand the sub-atomic theory of matter. The muon was the first
second-generation standard-model particle to be discovered, and its decay has
provided information on the (Vector -Axial Vector) structure of the weak
interaction, the strength of the weak interaction, G_F, and the conservation of
lepton number (flavor) in muon decay. The muon's anomalous magnetic moment has
played an important role in restricting theories of physics beyond the standard
standard model, where at present there is a 3.4 standard-deviation difference
between the experiment and standard-model theory. Its capture on the atomic
nucleus has provided valuable information on the modification of the weak
current by the strong interaction which is complementary to that obtained from
nuclear beta decay.Comment: 8 pages, 9 figures. Invited paper for the Journal of Physical Society
in Japan (JPSJ), Special Topics Issue "Frontiers of Elementary Particle
Physics, The Standard Model and beyond
MFV Reductions of MSSM Parameter Space
The 100+ free parameters of the minimal supersymmetric standard model (MSSM)
make it computationally difficult to compare systematically with data,
motivating the study of specific parameter reductions such as the cMSSM and
pMSSM. Here we instead study the reductions of parameter space implied by using
minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with
a view towards systematically building in constraints on flavour-violating
physics. Within this framework the space of parameters is reduced by expanding
soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a
24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42
respectively), depending on the order kept in the expansion. We provide a
Bayesian global fit to data of the MSSM-30 parameter set to show that this is
manageable with current tools. We compare the MFV reductions to the
19-parameter pMSSM choice and show that the pMSSM is not contained as a subset.
The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs
boson and with multi-TeV sparticles.Comment: 2nd version, minor comments and references added, accepted for
publication in JHE
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