By using a fixed point theorem of strict-set-contraction, some sufficient conditions are obtained for the existence of positive periodic solutions for a periodic neutral Lotka-Volterra competition system on time scales of the form x ∆ i (t) = x i (t) r i (t) − n j=1 a ij (t)x j (t) − n j=1 b ij (t)x j (t − τ ij (t, x 1 (t),. .. , x n (t))) − n j=1 c ij (t)x

We give a complete characterization of the closed subsets of the complex plane that can serve as spectra of completely nonunitary contractions of class Cu. Let Jfbe a complex Hilbert space, and denote by £^(Jff) the algebra of all (continuous, linear) operators acting onJf. An operator T g Sí'(Jíf) is a contraction if \\T\\ < 1. A contraction T g J¡f( Jf ) is said to be a C,,-contraction if lim...

Naive Ag-specific CD8(+) T cells expand, contract, and become memory cells after infection and/or vaccination. Memory CD8(+) T cells provide faster, more effective secondary responses against repeated exposure to the same pathogen. Using an adoptive transfer system with low numbers of trackable nontransgenic memory CD8(+) T cells, we showed that secondary responses can be comprised of both prim...

The mechanical response of PC12 neurites under tension is investigated using a microneedle technique. Elastic response, viscoelastic relaxation, and active contraction are observed. The mechanical model proposed by Dennerll et al. [J. Cell Biol. 109, 3073 (1989).10.1083/jcb.109.6.3073], which involves three mechanical devices--a stiff spring kappa coupled with a Voigt element that includes a le...

In the present study, cardiac contraction was regionally impaired to investigate the relationship between contractility [maximum first time derivative of left ventricular pressure (dPLV/d t max)] and PLV on epicardial lymph pressure (Plymph) generation. Measurements were performed in open-chest anesthetized dogs under control conditions and while local contraction was abolished by intracoronary...

OBJECTIVE Exercise is an important strategy for the treatment of type 2 diabetes. This is due in part to an increase in glucose transport that occurs in the working skeletal muscles. Glucose transport is regulated by GLUT4 translocation in muscle, but the molecular machinery mediating this process is poorly understood. The purpose of this study was to 1) use a novel imaging system to elucidate ...

In contrast to many developing muscles which contain a spectrum of cells at different stages of differentiation, cell development in the locust abdominal intersegmental muscle tends to be synchronous, so that at any stage of development the cells are at the same stage of differentiation. This makes it feasible to relate the properties of the developing tissue as a whole to changes occurring wit...

The membrane potential of isolated muscle fibers was controlled with a two-electrode voltage clamp, and the radial extent of contraction elicited by depolarizing pulses of increasing magnitude was observed microscopically. Depolarizations of the fiber surface only 1-2 mv greater than the contraction threshold produced shortening throughout the entire cross-section of the muscle fiber. The radia...

BACKGROUND The mechanisms by which ventricular function is altered during cardiac transplant rejection are not well understood. Therefore, an in vitro model system has been developed to facilitate investigation of lymphocyte-mediated myocyte injury. METHODS AND RESULTS Splenic lymphoid cells were obtained from mice 8-10 days after placement of a vascularized abdominal cardiac allograft and we...

Mechanisms linked to actin filaments have long been thought to cooperate in smooth muscle contraction, although key molecules were unclear. We show evidence that cardiac troponin T (cTnT) substantially contributes to Ca(2+)-mediated contraction in a physiological range of cytosolic Ca(2+) concentration ([Ca(2+)](i)). cTnT was detected in various smooth muscles of the aorta, trachea, gut and uri...