773 research outputs found
Sequential point estimation of parameters in a threshold AR(1) model
AbstractWe show that if an appropriate stopping rule is used to determine the sample size when estimating the parameters in a stationary and ergodic threshold AR(1) model, then the sequential least-squares estimator is asymptotically risk efficient. The stopping rule is also shown to be asymptotically efficient. Furthermore, non-linear renewal theory is used to obtain the limit distribution of appropriately normalized stopping rule and a second-order expansion for the expected sample size. A central result here is the rate of decay of lower-tail probability of average of stationary, geometrically β-mixing sequences
Ribbons Around Mexican Hats
We analyze quasi-topological solitons winding around a mexican-hat potential
in two space-time dimensions.
They are prototypes for a large number of physical excitations, including
Skyrmions of the Higgs sector of the standard electroweak model, magnetic
bubbles in thin ferromagnetic films, and strings in certain non-trivial
backgrounds.
We present explicit solutions, derive the conditions for classical stability,
and show that contrary to the naive expectation these can be satisfied in the
weak-coupling limit. In this limit we can calculate the soliton properties
reliably, and estimate their lifetime semiclassically. We explain why gauge
interactions destabilize these solitons, unless the scalar sector is extended.Comment: 12p. Latex , Ecole Polytechnique preprint A295.02.94 and Crete
preprint 94-1
Injectable dual-gelling cell-laden composite hydrogels for bone tissue engineering
The present work investigated the osteogenic potential of injectable, dual thermally and chemically gelable composite hydrogels for mesenchymal stem cell (MSC) delivery in vitro and in vivo. Composite hydrogels comprising copolymer macromers of N-isopropylacrylamide were fabricated through the incorporation of gelatin microparticles (GMPs) as enzymatically digestible porogens and sites for cellular attachment. High and low polymer content hydrogels with and without GMP loading were shown to successfully encapsulate viable MSCs and maintain their survival over 28 days in vitro. GMP incorporation was also shown to modulate alkaline phosphatase production, but enhanced hydrogel mineralization along with higher polymer content even in the absence of cells. Moreover, the regenerative capacity of 2 mm thick hydrogels with GMPs only, MSCs only, or GMPs and MSCs was evaluated in vivo in an 8 mm rat critical size cranial defect for 4 and 12 weeks. GMP incorporation led to enhanced bony bridging and mineralization within the defect at each timepoint, and direct bone-implant contact as determined by microcomputed tomography and histological scoring, respectively. Encapsulation of both GMPs and MSCs enabled hydrogel degradation leading to significant tissue infiltration and osteoid formation. The results suggest that these injectable, dual-gelling cell-laden composite hydrogels can facilitate bone ingrowth and integration, warranting further investigation for bone tissue engineering
B => \pi \pi \ell \nu decays in a QCD relativistic potential model
In the framework of a QCD relativistic potential model we evaluate the form
factors describing the exclusive decay B => \pi\pi \ell \nu. The calculation is
performed in a phase space region far away from the resonances and therefore is
complementary to other decay mechanisms where the pions are produced by
intermediate particles, e.g. in the chiral approach. We give an estimate of the
contribution of the non resonant channel of the order of BR(B- => \pi+ \pi-
\ell \nu) \approx 2.2 x 10^(-4).Comment: 14 pages LaTeX2e + 3 figures, Napoli Preprint DSF 99/3
B -> K1 gamma and tests of factorization for two-body non leptonic Bdecays with axial-vector mesons
The large branching ratio for B-> K1 gamma recently measured at Belle implies
a large B -> K1 transition form factor and large branching ratios for non
leptonic B decays involving an axial-vector meson. In this paper we present an
analysis of two-body B decays with an axial-vector meson in the final state
using naive factorization and the B -> K1 form factors obtained from the
measured radiative decays. We find that the predicted B -> J/psi K1 branching
ratio is in agreement with experiment. We also suggest that the decay rates of
B -> K1 pi, B -> a1 K and B -> b1 K could be used to test the factorization
ansatz.Comment: 8 pages; 7 new references included and a comment on K2(1430) in the
final state adde
WRIDY: MULTISENSORY WRITING APPROACH IN MOBILE APPLICATION FOR KIDS WITH LEARNING DISABILITIES INCLUDING DYSLEXIA
Handwriting development begins as early as infancy when children are first able to grasp a writing object
and leave a mark on the paper. Handwriting is linked with brain functioning; experts suggest that
handwriting skill lightens a student’s cognitive load. With consistent handwriting practice, it becomes
less demanding and more automatic, enabling students critical thinking and thought organization. The
lack of writing skill decreases kids’ capacity to carry out higher-order skills. Most of the writing
intervention approaches are not multisensory and some are using substances that may be dangerous
for kids such as sand or shaving cream or pipe cleaners or play-doh etc. These issues become more
challenging for kids with a learning disability such as dyslexia. This empirical gap in the multisensory
writing system is the target of this research. A multisensory mobile application (Wridy) is designed and
developed to support kids with learning disabilities. Wridy is an early-stage multisensory writing
intervention tool. It uses a dyslexia-friendly user interface, fonts and colour. Wridy is demonstrated to
the teachers of the Dyslexia Association Kuching, Malaysia. The results of the survey show that Wridy
is helpful and useful in learning writing alphabets especially for kids with learning disabilities such as
dyslexia
On the statistical significance of the conductance quantization
Recent experiments on atomic-scale metallic contacts have shown that the
quantization of the conductance appears clearly only after the average of the
experimental results. Motivated by these results we have analyzed a simplified
model system in which a narrow neck is randomly coupled to wide ideal leads,
both in absence and presence of time reversal invariance. Based on Random
Matrix Theory we study analytically the probability distribution for the
conductance of such system. As the width of the leads increases the
distribution for the conductance becomes sharply peaked close to an integer
multiple of the quantum of conductance. Our results suggest a possible
statistical origin of conductance quantization in atomic-scale metallic
contacts.Comment: 4 pages, Tex and 3 figures. To be published in PR
Resistivity of a Metal between the Boltzmann Transport Regime and the Anderson Transition
We study the transport properties of a finite three dimensional disordered
conductor, for both weak and strong scattering on impurities, employing the
real-space Green function technique and related Landauer-type formula. The
dirty metal is described by a nearest neighbor tight-binding Hamiltonian with a
single s-orbital per site and random on-site potential (Anderson model). We
compute exactly the zero-temperature conductance of a finite size sample placed
between two semi-infinite disorder-free leads. The resistivity is found from
the coefficient of linear scaling of the disorder averaged resistance with
sample length. This ``quantum'' resistivity is compared to the semiclassical
Boltzmann expression computed in both Born approximation and multiple
scattering approximation.Comment: 5 pages, 3 embedded EPS figure
Accumulation and persistence of ivacaftor in airway epithelia with prolonged treatment
Background: Current dosing strategies of CFTR modulators are based on serum pharmacokinetics, but drug concentrations in target tissues such as airway epithelia are not known. Previous data suggest that CFTR modulators may accumulate in airway epithelia, and serum pharmacokinetics may not accurately predict effects of chronic treatment. Methods: CF (F508del homozygous) primary human bronchial epithelial (HBE) cells grown at air-liquid interface were treated for 14 days with ivacaftor plus lumacaftor or ivacaftor plus tezacaftor, followed by a 14-day washout period. At various intervals during treatment and washout phases, drug concentrations were measured via mass spectrometry, electrophysiological function was assessed in Ussing chambers, and mature CFTR protein was quantified by Western blotting. Results: During treatment, ivacaftor accumulated in CF-HBEs to a much greater extent than either lumacaftor or tezacaftor and remained persistently elevated even after 14 days of washout. CFTR activity peaked at 7 days of treatment but diminished with further ivacaftor accumulation, though remained above baseline even after washout. Conclusions: Intracellular accrual and persistence of CFTR modulators during and after chronic treatment suggest complex pharmacokinetic and pharmacodynamic properties within airway epithelia that are not predicted by serum pharmacokinetics. Direct measurement of drugs in target tissues may be needed to optimize dosing strategies, and the persistence of CFTR modulators after treatment cessation has implications for personalized medicine approaches
- …