Dynamics in shear flow studied by X-ray Photon Correlation Spectroscopy.

X-ray Photon Correlation Spectroscopy was used to measure the diffusive dynamics of colloidal particles in a shear flow. The results presented here show how the intensity autocorrelation functions measure both the diffusive dynamics of the particles and their flow-induced, convective motion. However, in the limit of low flow/shear rates, it is possible to obtain the diffusive component of the dynamics, which makes the method suitable for the study of the dynamical properties of a large class of complex soft-matter and biological fluids. An important benefit of this experimental strategy over more traditional X-ray methods is the minimization of X-ray-induced beam damage. While the method can be applied also for photon correlation spectroscopy in the visible domain, our analysis shows that the experimental conditions under which it is possible to measure the diffusive dynamics are easier to achieve at higher q values (with X-rays).

SrTiO3 displacive transition revisited via coherent X-ray diffraction.

We present a coherent x-ray diffraction study of the antiferrodistortive displacive transition of SrTiO3, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100-microm-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a approximately 10 mn time scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known central peak seen in inelastic neutron scattering.

Microrheology of polymeric solutions using x-ray photon correlation spectroscopy.

We demonstrate the technique of XPCS microrheology on opaque polymeric solutions (1-20% w/w) using colloidal silica probes. The short time decay of the intensity correlation function provides the mean square displacement (MSD) of the colloidal probes. The MSDs of the probes are subsequently transformed using the generalized Stokes-Einstein equation, allowing the linear viscoelastic spectra of a biopolymer (gellan) and a synthetic polyelectrolyte (polystyrene sulfonate, PSS) to be calculated over two decades of frequency. MSDs can be measured that are two orders of magnitude smaller than those possible with video particle tracking microrheology, with a sensitivity of ∼10 nm s(-1) for displacements of ∼nms. The XPCS data for water, glycerol and PSS combs are in agreement with video particle tracking microrheology experiments performed at lower polymer concentrations.

Accelerated streptokinase--a new thrombolytic regimen in acute myocardial infarction.

Efficiency and safety of an accelerated regimen of streptokinase (1.5 M.U. over 20 min., 109 patients) has been compared with the standard regimen (1.5 M.U. over 60 min, 119 patients) in 218 patients admitted within the first 6 hours after the onset of the symptoms of acute myocardial infarction. Using the noninvasive criteria we found a coronary reperfusion rate of 77.04% in patients belonging to the accelerated regimen group and this value was significantly higher than the one of 57.14% registered in the standard group. No major hemorrhagic events were registered in both groups. Although the hypotension appeared to be more frequent in patients in whom the accelerated regimen was used, however this side effect proved to be transient and well controlled using the rapid infusion of natrium chloride solution. In conclusion, the accelerated regimen of streptokinase is safe and followed by a higher rate of coronary reperfusion as compared to the standard one.

Rapid infusion of streptokinase standard dose in acute myocardial infarction is followed by a higher rate of coronary reperfusion than standard protocol.

There are several opinions asserting that the accelerated t-PA is more efficient than the standard protocol of streptokinase (SK) administration in acute myocardial infarction (AMI). One hundred patients admitted within the first 6 hrs after the onset of the symptoms revealing AMI were divided in two subgroups, as follows: subgroup A (50 patients) in whom a dose of 1.5 M.U. SK was infused in 20 min (accelerated protocol) and subgroup B (50 patients) in whom the same dose was infused in 60 min (standard protocol). In order to assess the efficiency of thrombolytic therapy (TT), we used three noninvasive criteria: the rapid resolution of the chest pain, the rapid decreasing of the ST segment elevation by more than 50% from the initial value, and the rapid increasing of enzymes revealing necrosis. Using the above-mentioned criteria, we considered that coronary reperfusion appeared in 40 patients from subgroup A (80%) and in 29 patients from subgroup B (58%). The speed of coronary reperfusion was 40 +/- 26 min in patients with accelerated SK and this time was significantly shorter than the time of 60 +/- 24 min registered in the control group. No major hemorrhagic events appeared in both subgroups. Although hypotension appeared more frequently in subgroup A, this minor complication was well supported by our patients. The rapid infusion of the standard dose of SK was followed by a higher rate and speed of coronary reperfusion as compared to the standard protocol.