30 research outputs found
Critical conductance of the chiral 2d random flux model
The two-terminal conductance of a random flux model defined on a square
lattice is investigated numerically at the band center using a transfer matrix
method. Due to the chiral symmetry, there exists a critical point where the
ensemble averaged mean conductance is scale independent. We also study the
conductance distribution function which depends on the boundary conditions and
on the number of lattice sites being even or odd. We derive a critical exponent
for square samples of even width using one-parameter scaling
of the conductance. This result could not be obtained previously from the
divergence of the localization length in quasi-one-dimensional systems due to
pronounced finite-size effects.Comment: EP2DS-17, Genua 2007, accepted for publication in Physica
Using random testing to manage a safe exit from the COVID-19 lockdown
We argue that frequent sampling of the fraction of infected people (either by
random testing or by analysis of sewage water), is central to managing the
COVID-19 pandemic because it both measures in real time the key variable
controlled by restrictive measures, and anticipates the load on the healthcare
system due to progression of the disease. Knowledge of random testing outcomes
will (i) significantly improve the predictability of the pandemic, (ii) allow
informed and optimized decisions on how to modify restrictive measures, with
much shorter delay times than the present ones, and (iii) enable the real-time
assessment of the efficiency of new means to reduce transmission rates.
Here we suggest, irrespective of the size of a suitably homogeneous
population, a conservative estimate of 15000 for the number of randomly tested
people per day which will suffice to obtain reliable data about the current
fraction of infections and its evolution in time, thus enabling close to
real-time assessment of the quantitative effect of restrictive measures. Still
higher testing capacity permits detection of geographical differences in
spreading rates. Furthermore and most importantly, with daily sampling in
place, a reboot could be attempted while the fraction of infected people is
still an order of magnitude higher than the level required for a relaxation of
restrictions with testing focused on symptomatic individuals. This is
demonstrated by considering a feedback and control model of mitigation where
the feed-back is derived from noisy sampling data.Comment: 18 pages, 6 figures, 2 appendices. Phys. Biol. (2020
Counting Majorana zero modes in superconductors
A counting formula for computing the number of (Majorana) zero modes bound to
topological point defects is evaluated in a gradient expansion for systems with
charge-conjugation symmetry. This semi-classical counting of zero modes is
applied to some examples that include graphene and a chiral p-wave
superconductor in two-dimensional space. In all cases, we explicitly relate the
counting of zero modes to Chern numbers.Comment: 21 pages, 3 figure
Case report: rapid and durable response to PDGFR targeted therapy in a child with refractory multiple infantile myofibromatosis and a heterozygous germline mutation of the PDGFRB gene
Timeline. This file shows timeline of both described cases. (PDF 466Ă‚Â kb
Magnetic nano-fluctuations in a frustrated magnet
Frustrated systems exhibit remarkable properties due to the high degeneracy
of their ground states. Stabilised by competing interactions, a rich diversity
of typically nanometre-sized phase structures appear in polymer and colloidal
systems, while the surface of ice pre-melts due to geometrically frustrated
interactions. Atomic spin systems where magnetic interactions are frustrated by
lattice geometry provide a fruitful source of emergent phenomena, such as
fractionalised excitations analogous to magnetic monopoles. The degeneracy
inherent in frustrated systems may prevail all the way down to absolute zero
temperature, or it may be lifted by small perturbations or entropic effects. In
the geometrically frustrated Ising--like magnet Ca3Co2O6, we follow the
temporal and spatial evolution of nanoscale magnetic fluctuations firmly
embedded inside the spin--density--wave magnetic structure. These fluctuations
are a signature of a competing ferrimagnetic phase with an incommensurability
that is different from, but determined by the host. As the temperature is
lowered, the fluctuations slow down into a super-paramagnetic regime of stable
spatiotemporal nano-structures
Effects of Sunitinib and Other Kinase Inhibitors on Cells Harboring a PDGFRB Mutation Associated with Infantile Myofibromatosis
Infantile myofibromatosis represents one of the most common proliferative fibrous tumors of infancy and childhood. More effective treatment is needed for drug-resistant patients, and targeted therapy using specific protein kinase inhibitors could be a promising strategy. To date, several studies have confirmed a connection between the p.R561C mutation in gene encoding platelet-derived growth factor receptor beta (PDGFR-beta) and the development of infantile myofibromatosis. This study aimed to analyze the phosphorylation of important kinases in the NSTS-47 cell line derived from a tumor of a boy with infantile myofibromatosis who harbored the p.R561C mutation in PDGFR-beta. The second aim of this study was to investigate the effects of selected protein kinase inhibitors on cell signaling and the proliferative activity of NSTS-47 cells. We confirmed that this tumor cell line showed very high phosphorylation levels of PDGFR-beta, extracellular signal-regulated kinases (ERK) 1/2 and several other protein kinases. We also observed that PDGFR-beta phosphorylation in tumor cells is reduced by the receptor tyrosine kinase inhibitor sunitinib. In contrast, MAPK/ERK kinases (MEK) 1/2 and ERK1/2 kinases remained constitutively phosphorylated after treatment with sunitinib and other relevant protein kinase inhibitors. Our study showed that sunitinib is a very promising agent that affects the proliferation of tumor cells with a p.R561C mutation in PDGFR-beta
Risk factors for tumors or leukemia development in the first two years of life
Objectives. The objective of this study was to determine the incidence of neoplastic diseases and associated risk factors in the early stages of life. Methods. Data were retrospectively assessed in 730,000 live births between 2000 and 2019. The occurrence of tumors was monitored in the neonatal, infant (1-12 months), and toddler (13-24 months) periods. Risk factors were divided into demographic, internal, and environmental factors. The control group consisted of subjects in the same age category without oncological diseases. Results. A total of 452 neoplastic diseases were diagnosed in the study sample. In total, 24% (110/452) manifested during the neonatal period, 45% (203/452) in infants, and 31% (139/452) at the age of 13-24 months. Any genetic disease (OR 26.68; 95% CI 7.64-93.12) and medications used by the mother (OR 3.07; 95% CI 1.32-7.15) were identified as risk factors. Without adjustment for all factors, asphyxia in the first minute, a younger age of the mother, lower pregnancy, and the presence of a congenital defect manifested themselves as risk factors. Conclusions. The highest risk factors for the development of early childhood tumors were identified as with medications used by the mother before or during pregnancy and genetic diseases