Testing General Relativity with Atomic Clocks

We discuss perspectives for new tests of general relativity which are based on recent technological developments as well as new ideas. We focus our attention on tests performed with atomic clocks and do not repeat arguments present in the other contributions to the present volume. In particular, we present the scientific motivations of the space projects ACES and SAGAS.Comment: Contribution for "The Nature of Gravity" (eds. F. Everitt et al

Mechanosensing in actin stress fibers revealed by a close correlation between force

The mechanics of the actin cytoskeleton have a central role in the regulation of cells and tissues, but the details of how molecular sensors recognize deformations and forces are elusive. By performing cytoskeleton laser nanosurgery in cultured epithelial cells and fibroblasts, we show that the retraction of stress fibers (SFs) is restricted to the proximity of the cut and that new adhesions form at the retracting end. This suggests that SFs are attached to the substrate. A new computational model for SFs confirms this hypothesis and predicts the distribution and propagation of contractile forces along the SF. We then analyzed the dynamics of zyxin, a focal adhesion protein present in SFs. Fluorescent redistribution after laser nanosurgery and drug treatment shows a high correlation between the experimentally measured localization of zyxin and the computed localization of forces along SFs. Correlative electron microscopy reveals that zyxin is recruited very fast to intermediate substrate anchor points that are highly tensed upon SF release. A similar acute localization response is found if SFs are mechanically perturbed with the cantilever of an atomic force microscope. If actin bundles are cut by nanosurgery in living Drosophila egg chambers, we also find that zyxin redistribution dynamics correlate to force propagation and that zyxin relocates at tensed SF anchor points, demonstrating that these processes also occur in living organisms. In summary, our quantitative analysis shows that force and protein localization are closely correlated in stress fibers, suggesting a very direct force-sensing mechanism along actin bundles

A similar 24-h blood pressure control is obtained by zofenopril and candesartan in primary hypertensive patients

Objective. To compare the antihypertensive effect of treatment with zofenopril vs candesartan by office and ambulatory blood pressure (BP). Design and methods. Following a 2-week wash-out from previous treatment, 236 grade I-II primary hypertensive patients were randomized double-blind to 12 weeks treatment with zofenopril 30 mg or candesartan 8 mg od. After 4 weeks, treatment was doubled in responder non-normalized (office systolic BP≥140 mmHg and office diastolic BP reduction ≥10 mmHg) or non-responder patients (office systolic BP≥140 mmHg and office diastolic BP reduction <10 mmHg). Following a further 4 weeks, non-responder non-normalized patients were withdrawn. Results. In the intention-to-treat population, office systolic BP and diastolic BP reductions after 12 weeks of treatment were similar between the two groups (zofenopril: 21±11/15±8 mmHg, n=114 vs C: 20±11/15±7 mmHg (candesartan; p=NS). Also 24-h ambulatory BPs were equally reduced by zofenopril and candesartan (7±13/ 5±8 mmHg vs 7±12/5±8 mmHg; p=NS). The trough-to-peak ratio and smoothness index were not sigficantly different between zofenopril and candesartan. Tolerability of both drugs was good. Conclusions. Monotherapy with zofenopril and candesartan similary reduced office and 24-h BPs. Since almost 90% of patiens were normalized by either zofenopril or candesartan, this result suppots the importance of considering low- or high-dose monotherapies as initial for most hypertensive patients of mild degree