Search Results
Rejuvenation through plastic deformation of a La-based metallic glass measured by fast-scanning calorimetry
We explore the glassy states achievable after a metallic glass is formed on liquid quenching. Samples of La55Al25Ni20 (at.%) metallic glass (rod and ribbon) are studied. The extent of structural relaxation at room temperature is characterized for this low-glass-transition temperature glass. Plastic deformation (uniaxial compression) rejuvenates the glass to states of higher enthalpy characteristic of glass formation at high cooling rate. Deformation increases the heterogeneity of the glass, widening the spectrum of relaxation times. The extent of rejuvenation in samples of low aspect ratio is compared with that under conditions of high constraint in notched samples. The deformation-induced rejuvenation is particularly susceptible to reduction on subsequent ageing. Fast-scanning calorimetry is useful in characterizing the dynamics of structural relaxation. The shadow glass transition is more evident on fast heating, and is observed in this glass for the first time. A new excess exothermic effect is observed before the glass transition.
β-adrenoceptor-mediated relaxation of urinary bladder muscle in β2-adrenoceptor knockout mice
Background and Objective: In order to characterize the β-adrenoceptor (AR) subtypes involved in agonist-stimulated relaxation of murine urinary bladder we studied the effects of (-)-isoprenaline and CL 316,243 on tonic contraction and spontaneous contractions in detrusor strips of wild-type (WT) and β2-AR knockout (β2-AR KO) mice. Materials and Methods: Urinary bladders were isolated from male WT and β2-AR KO mice. β-AR subtype expression was determined with quantitative real-time PCR. Intact muscle strips pre-contracted with KCl (40 mM) were exposed to cumulatively increasing concentrations of (-)-isoprenaline or β3-AR agonist CL 316,243 in the presence and absence of the subtype-selective β-AR blockers CGP 20712A (β1-ARs), ICI 118,551 (β2-ARs), and L748,337 (β3-ARs). Results: Quantitative real-time PCR confirmed lack of β2-AR expression in bladder tissue from β2-AR KO mice. In isolated detrusor strips, pre-contraction with KCl increased basal tone and enhanced spontaneous activity significantly more in β2-AR KO than in WT. (-)-Isoprenaline relaxed tonic tension and attenuated spontaneous activity with similar potency, but the concentrations required were two orders of magnitude higher in β2-AR KO than WT. The concentration-response curves (CRCs) for relaxation were not affected by CGP 20712A (300 nM), but were shifted to the right by ICI 118,551 (50 nM) and L748,337 (10 μM). The -logEC50 values for (-)-isoprenaline in WT and β2-AR KO tissue were 7.98 and 6.00, respectively, suggesting a large receptor reserve of β2-AR. (-)-CL 316,243 relaxed detrusor and attenuated spontaneous contractions from WT and β2-AR KO mice with a potency corresponding to the drug’s affinity for β3-AR. L743,337 shifted the CRCs to the right. Conclusion: Our findings in β2-AR KO mice suggest that there is a large receptor reserve for β2-AR in WT mice so that this β-AR subtype will mediate relaxation of tone and attenuation of spontaneous activity under physiological conditions. Nevertheless, upon removal of this reserve, β3-AR can also mediate murine detrusor relaxation.
A function space framework for structural total variation regularization with applications in inverse problems
In this work, we introduce a function space setting for a wide class of structural/weighted total variation (TV) regularization methods motivated by their applications in inverse problems. In particular, we consider a regularizer that is the appropriate lower semi-continuous envelope (relaxation) of a suitable total variation type functional initially defined for sufficiently smooth functions. We study examples where this relaxation can be expressed explicitly, and we also provide refinements for weighted total variation for a wide range of weights. Since an integral characterization of the relaxation in function space is, in general, not always available, we show that, for a rather general linear inverse problems setting, instead of the classical Tikhonov regularization problem, one can equivalently solve a saddle-point problem where no a priori knowledge of an explicit formulation of the structural TV functional is needed. In particular, motivated by concrete applications, we deduce corresponding results for linear inverse problems with norm and Poisson log-likelihood data discrepancy terms. Finally, we provide proof-of-concept numerical examples where we solve the saddle-point problem for weighted TV denoising as well as for MR guided PET image reconstruction.