Imaging in turbid media using quasi-ballistic photons

We study by means of experiments and Monte Carlo simulations, the scattering of light in random media, to determine the distance upto which photons travel along almost undeviated paths within a scattering medium, and are therefore capable of casting a shadow of an opaque inclusion embedded within the medium. Such photons are isolated by polarisation discrimination wherein the plane of linear polarisation of the input light is continuously rotated and the polarisation preserving component of the emerging light is extracted by means of a Fourier transform. This technique is a software implementation of lock-in detection. We find that images may be recovered to a depth far in excess of what is predicted by the diffusion theory of photon propagation. To understand our experimental results, we perform Monte Carlo simulations to model the random walk behaviour of the multiply scattered photons. We present a new definition of a diffusing photon in terms of the memory of its initial direction of propagation, which we then quantify in terms of an angular correlation function. This redefinition yields the penetration depth of the polarisation preserving photons. Based on these results, we have formulated a model to understand shadow formation in a turbid medium, the predictions of which are in good agreement with our experimental results.Comment: LaTex 19 pages, 10 ps figures and 8 eps figures. psfig.sty included. (submitted to Optics Commumications

Deacylated tRNA is released from the E site upon A site occupation but before GTP is hydrolyzed by EF-Tu

The presence or absence of deacylated tRNA at the E site sharply influences the activation energy required for binding of a ternary complex to the ribosomal A site indicating the different conformations that the E-tRNA imparts on the ribosome. Here we address two questions: (i) whether or not peptidyltransferase—the essential catalytic activity of the large ribosomal subunit—also depends on the occupancy state of the E site and (ii) at what stage the E-tRNA is released during an elongation cycle. Kinetics of the puromycin reaction on various functional states of the ribosome indicate that the A-site substrate of the peptidyltransferase center, puromycin, requires the same activation energy for peptide-bond formation under all conditions tested. We further demonstrate that deacylated tRNA is released from the E site by binding a ternary complex aminoacyl-tRNA•EF-Tu•GDPNP to the A site. This observation indicates that the E-tRNA is released after the decoding step but before both GTP hydrolysis by EF-Tu and accommodation of the A-tRNA. Collectively these results reveal that the reciprocal linkage between the E and A sites affects the decoding center on the 30S subunit, but does not influence the rate of peptide-bond formation at the active center of the 50S subunit

Investigating the entire course of telithromycin binding to Escherichia coli ribosomes

Applying kinetics and footprinting analysis, we show that telithromycin, a ketolide antibiotic, binds to Escherichia coli ribosomes in a two-step process. During the first, rapidly equilibrated step, telithromycin binds to a low-affinity site (KT = 500 nM), in which the lactone ring is positioned at the upper portion of the peptide exit tunnel, while the alkyl–aryl side chain of the drug inserts a groove formed by nucleotides A789 and U790 of 23S rRNA. During the second step, telithromycin shifts slowly to a high-affinity site (KT* = 8.33 nM), in which the lactone ring remains essentially at the same position, while the side chain interacts with the base pair U2609:A752 and the extended loop of protein L22. Consistently, mutations perturbing either the base pair U2609:A752 or the L22-loop hinder shifting of telithromycin to the final position, without affecting the initial step of binding. In contrast, mutation Lys63Glu in protein L4 placed on the opposite side of the tunnel, exerts only a minor effect on telithromycin binding. Polyamines disfavor both sequential steps of binding. Our data correlate well with recent crystallographic data and rationalize the changes in the accessibility of ribosomes to telithromycin in response to ribosomal mutations and ionic changes

Revealing the ancient city of Sikyon through the application of integrated geophysical approaches and 3D modelling

The ancient city of Sikyon is located in the northern Peloponnese covering an area of 250 ha on a plateau that rises about 4 km southwest of the Corinthian gulf.  Previous archaeological excavations revealed a limited number of monuments within the surroundings of the ancient agora. Since 2004, a consortium led by the University of Thessaly, the Institute for Mediterranean Studies/FORTH, the University of York and the 37th Ephorate of Prehistoric and Classical Antiquities initiated the Sikyon..

Early mobilization in patients on venoarterial extracorporeal membrane oxygenation: A scoping review

BACKGROUNDExtracorporeal membrane oxygenation (ECMO) is mainly applied to patients with significant cardiorespiratory failure who do not respond to existing conventional treatments. Patients that are supported with veno-arterial ECMO (VA-ECMO) are considered very-high risk patients to participate in any type of physical therapy (PT) or mobilization. However, cumulative evidence suggests that early mobilization of critically ill patients is feasible, safe, and efficient under certain circumstances.AIMTo summarize the existing evidence on the impact of early mobilization and physiotherapy on VA-ECMO patients.METHODSThis is a scoping review that used systematic electronic literature searches (from inception until January 2025) on MEDLINE (PubMed), PEDro, DynaMed, CINAHL, Scopus, Science direct and Hellenic Academic Libraries. Snowball searching method was also applied. Eligible studies included those reporting patients on VA-ECMO who participated in early mobilization or PT, published in English and utilized any primary evidence study design. Studies on children, animals and patients placed on any other ECMO, secondary evidence, and ‘grey’ literature were excluded.RESULTSA total of 316 articles were retrieved and 13 were included in the study. Of those, 1 study was a randomized control trial, 4 retrospective studies, 4 retrospective cohort studies, 1 case series and 3 case reports. The sample size of the included studies ranged from 1 to 104 VA-ECMO patients, who were ambulated or received PT interventions, and mobilization frequency ranged from 2 per day to 4 per week. Mobilization of VA-ECMO patients seems to be safe regardless the cannula’s position. PT and early mobilization were associated with better weaning from mechanical ventilation, gradual reduction of inotropes and functional capacity improvement after ECMO discharge.CONCLUSIONEarly mobilization in VA-ECMO seems to be safe and can potentially help reduce vasoconstrictors and speed up rehabilitation times. High quality research on early mobilization in VA-ECMO patients is warranted