539 research outputs found
Discrete skew selfadjoint canonical systems and the isotropic Heisenberg magnet model
A discrete analog of a skew selfadjoint canonical (Zakharov-Shabat or AKNS)
system with a pseudo-exponential potential is introduced. For the corresponding
Weyl function the direct and inverse problem are solved explicitly in terms of
three parameter matrices. As an application explicit solutions are obtained for
the discrete integrable nonlinear equation corresponding to the isotropic
Heisenberg magnet model. State space techniques from mathematical system theory
play an important role in the proofs
A matrix pencil approach to the existence of compactly supported reconstruction functions in average sampling
The aim of this work is to solve a question raised for average sampling in shift-invariant spaces by using the well-known matrix pencil theory. In many common situations in sampling theory, the available data are samples of some convolution operator acting on the function itself: this leads to the problem of average sampling, also known as generalized sampling. In this paper we deal with the existence of a sampling formula involving these samples and having reconstruction functions with compact support. Thus, low computational complexity is involved and truncation errors are avoided. In practice, it is accomplished by means of a FIR filter bank. An answer is given in the light of the generalized sampling theory by using the oversampling technique: more samples than strictly necessary are used. The original problem reduces to finding a polynomial left inverse of a polynomial matrix intimately related to the sampling problem which, for a suitable choice of the sampling period, becomes a matrix pencil. This matrix pencil approach allows us to obtain a practical method for computing the compactly supported reconstruction functions for the important case where the oversampling rate is minimum. Moreover, the optimality of the obtained solution is established
Ionic current changes underlying action potential repolarization responses to physiological pacing and adrenergic stimulation in adult rat ventricular myocytes
This study aimed to simulate ventricular responses to elevations in myocyte pacing and adrenergic stimulation using a novel electrophysiological rat model and investigate ion channel responses underlying action potential (AP) modulations. Peak ion currents and AP repolarization to 50% and 90% of full repolarization (APD50-90) were recorded during simulations at 1–10 Hz pacing under control and adrenergic stimulation conditions. Further simulations were performed with incremental ion current block (L-type calcium current, ICa; transient outward current, Ito; slow delayed rectifier potassium current, IKs; rapid delayed rectifier potassium current, IKr; inward rectifier potassium current, IK1) to identify current influence on AP response to exercise. Simulated APD50-90 closely resembled experimental findings. Rate-dependent increases in IKs (6%–101%), IKr (141%–1339%), and ICa (0%–15%) and reductions in Ito (11%–57%) and IK1 (1%–9%) were observed. Meanwhile, adrenergic stimulation triggered moderate increases in all currents (23%–67%) except IK1. Further analyses suggest AP plateau is most sensitive to modulations in Ito and ICa while late repolarization is most sensitive to IK1, ICa, and IKs, with alterations in IKs predominantly stimulating the greatest magnitude of influence on late repolarization (35%–846% APD90 prolongation). The modified Leeds rat model (mLR) is capable of accurately modeling APs during physiological stress. This study highlights the importance of ICa, Ito, IK1, and IKs in controlling electrophysiological responses to exercise. This work will benefit the study of cardiac dysfunction, arrythmia, and disease, though future physiologically relevant experimental studies and model development are required
On ordinal utility, cardinal utility, and random utility
Though the Random Utility Model (RUM) was conceived
entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties of
cardinal utility. The adoption of cardinal utility as a
working operation of ordinal is perfectly valid, provided
interpretations drawn from that operation remain faithful
to ordinal utility. The paper considers whether the latterrequirement holds true for several measurements commonly
derived from RUM. In particular it is found that
measurements of consumer surplus change may depart from
ordinal utility, and exploit the cardinality inherent in
the practical apparatus.
Recent developments in the characterization of superconducting films by microwaves
We describe and analyze selected surface impedance data recently obtained by
different groups on cuprate, ruthenate and diboride superconducting films on
metallic and dielectric substrates for fundamental studies and microwave
applications. The discussion includes a first review of microwave data on MgB2,
the weak-link behaviour of RABiTS-type YBa2Cu3O7-d tapes, and the observation
of a strong anomalous power-dependence of the microwave losses in MgO at low
temperatures. We demonstrate how microwave measurements can be used to
investigate electronic, magnetic, and dielectric dissipation and relaxation in
the films and substrates. The impact of such studies reaches from the
extraction of microscopic information to the engineering of materials and
further on to applications in power systems and communication technology.Comment: Invited contribution to EUCAS2001, accepted for publication in
Physica C in its present for
Rethinking organoid technology through bioengineering
In recent years considerable progress has been made in the development of faithful procedures for the differentiation of human pluripotent stem cells (hPSCs). An important step in this direction has also been the derivation of organoids. This technology generally relies on traditional three-dimensional culture techniques that exploit cell-autonomous self-organization responses of hPSCs with minimal control over the external inputs supplied to the system. The convergence of stem cell biology and bioengineering offers the possibility to provide these stimuli in a controlled fashion, resulting in the development of naturally inspired approaches to overcome major limitations of this nascent technology. Based on the current developments, we emphasize the achievements and ongoing challenges of bringing together hPSC organoid differentiation, bioengineering and ethics. This Review underlines the need for providing engineering solutions to gain control of self-organization and functionality of hPSC-derived organoids. We expect that this knowledge will guide the community to generate higher-grade hPSC-derived organoids for further applications in developmental biology, drug screening, disease modelling and personalized medicine.This Review provides an overview of bioengineering technologies that can be harnessed to facilitate the culture, self-organization and functionality of human pluripotent stem cell-derived organoids.Stem cells & developmental biolog
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
Observation of Orbitally Excited B_s Mesons
We report the first observation of two narrow resonances consistent with
states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar
collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the
Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed
as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+,
\bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1})
= 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
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