The Determination of Oxidation-Reduction Potentials from Equilibrium Data

The determination of the oxidation-reduction potentials is more reliable from equilibrium data than from electromotive force data. The potential of the ferric-ferrous electrode was calculated from the experimentally determined equilibrium constant of the reaction: 2Fe (ClO4)3 +2Hg⇔ 2Fe (ClO4)2+Hg2 (ClO4)2 The perchlorates, mercury, and perchloric acid are better suited for the determination of the equilibrium constant than the nitrates, silver and nitric acid employed by A. A. Noyes and Braun (J. Arn. Chem. Soc. 34, 1016, 1912). The true equilibrium constant of the reaction was determined by suitable experimental procedure and subsequent mathematical and graphical analysis

The Schr\"odinger operator on an infinite wedge with a tangent magnetic field

We study a model Schr\"odinger operator with constant magnetic field on an infinite wedge with Neumann boundary condition. The magnetic field is assumed to be tangent to a face. We compare the bottom of the spectrum to the model spectral quantities coming from the regular case. We are particularly motivated by the influence of the magnetic field and the opening angle of the wedge on the spectrum of the model operator and we exhibit cases where the bottom of the spectrum is smaller than in the regular case. Numerical computations enlighten the theoretical approach

Finite size effects, super-and sub-poissonian noise in a nanotube connected to leads

The injection of electrons in the bulk of carbon nanotube which is connected to ideal Fermi liquid leads is considered. While the presence of the leads gives a cancellation of the noise cross-correlations, the auto-correlation noise has a Fano factor which deviates strongly from the Schottky behavior at voltages where finite size effects are expected. Indeed, as the voltage is increased from zero, the noise is first super-poissonian, then sub-poissonian, and eventually it reaches the Schottky limit. These finite size effects are also tested using a diagnosis of photo-assisted transport, where a small AC modulation is superposed to the DC bias voltage between the injection tip and the nanotube. When finite size effects are at play, we obtain a stepwise behavior for the noise derivative, as expected for normal metal systems, whereas in the absence of finite size effects, due to the presence of Coulomb interactions, a smoothed staircase is observed. The present work shows that it is possible to explore finite size effects in nanotube transport via a zero frequency noise measurement

Controlling Light Through Optical Disordered Media : Transmission Matrix Approach

We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and we study the effect of noise on the reconstruction method. We also extracted from the TM informations about the statistical properties of the medium and the light transport whitin it. In particular, we are able to isolate the contributions of the Memory Effect (ME) and measure its attenuation length

Minimally invasive mitral valve surgery: State-of-the-art and our experience

The minimally invasive approach is becoming the standard-of-care for surgery of the mitral valve. As any less invasive strategy, it entails an increased surgical complexity. Standard-of-care mitral repair using the totally videoscopic approach is indeed reproducible; however, few specific data on patients with complex mitral valve disease are available in the published literature. The purpose of the present paper is to provide an overview of the current state-of-the-art in minimally invasive cardiac surgery, and a summary of recent evidence on the topic, with particular regard to the surgical techniques and comparisons with conventional surgery. The experience of the GVM Care and Research network in the field is also briefly reported

Human Ape2 protein has a 3′–5′ exonuclease activity that acts preferentially on mismatched base pairs

DNA damage, such as abasic sites and DNA strand breaks with 3′-phosphate and 3′-phosphoglycolate termini present cytotoxic and mutagenic threats to the cell. Class II AP endonucleases play a major role in the repair of abasic sites as well as of 3′-modified termini. Human cells contain two class II AP endonucleases, the Ape1 and Ape2 proteins. Ape1 possesses a strong AP-endonuclease activity and weak 3′-phosphodiesterase and 3′–5′ exonuclease activities, and it is considered to be the major AP endonuclease in human cells. Much less is known about Ape2, but its importance is emphasized by the growth retardation and dyshematopoiesis accompanied by G2/M arrest phenotype of the APE2-null mice. Here, we describe the biochemical characteristics of human Ape2. We find that Ape2 exhibits strong 3′–5′ exonuclease and 3′-phosphodiesterase activities and has only a very weak AP-endonuclease activity. Mutation of the active-site residue Asp 277 to Ala in Ape2 inactivates all these activities. We also demonstrate that Ape2 preferentially acts at mismatched deoxyribonucleotides at the recessed 3′-termini of a partial DNA duplex. Based on these results we suggest a novel role for human Ape2 as a 3′–5′ exonuclease

Operative and middle-term results of cardiac surgery in nonagenarians: A bridge toward routine practice

Background: Age >90 years represents in many centers an absolute contraindication to cardiac surgery. Nonagenarians are a rapidly growing subset of the population posing an expanding clinical problem. To provide helpful information in regard to this complex decision, we analyzed the operative and 5-year results of coronary and valvular surgical procedures in these patients. Methods and Results: We retrospectively reviewed 127 patients aged ≥90 years who underwent cardiac surgery within our hospital group in the period 1998 to 2008. Kaplan-Meier and multiple logistic regression analyses were performed. A longer follow-up than most published studies and the largest series published thus far are presented. Mean age was 92 years (range, 90 to 103 years). Mean logistic EuroSCORE was 21.3±6.1. Sixty patients had valvular surgery (including 11 valve repairs), 49 patients had coronary artery bypass grafting, and 18 had valvular plus coronary artery bypass grafting surgery (55 left mammary artery grafts implanted). Forty-five patients (35.4%) were operated on nonelectively. Operative mortality was 13.4% (17 cases). Fifty-four patients (42.5%) had a complicated postoperative course. There were no statistically significant differences in the rate and type of complications between patient strata on the basis of type of surgery performed. Nonelective priority predicted a complicated postoperative course. Predictors of operative mortality were nonelective priority and previous myocardial infarction. Kaplan-Meier survival estimates at 5 years were comparable between patient groups on the basis of procedure performed. Conclusions: Although the rate of postoperative complications remains high, cardiac surgery in nonagenarians can achieve functional improvement at the price of considerable operative and follow-up mortality rates. Cardiac operations in these very elderly subjects are supported if appropriate selection is made and if the operation is performed earlier and electively. Our results should contribute to the development of guidelines for cardiac operations in nonagenarians. © 2010 American Heart Association. All rights reserved

Structural insights into Clostridium perfringens delta toxin pore formation

Clostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins

Susceptibility of hamsters to clostridium difficile isolates of differing toxinotype

Clostridium difficile is the most commonly associated cause of antibiotic associated disease (AAD), which caused ~21,000 cases of AAD in 2011 in the U.K. alone. The golden Syrian hamster model of CDI is an acute model displaying many of the clinical features of C. difficile disease. Using this model we characterised three clinical strains of C. difficile, all differing in toxinotype; CD1342 (PaLoc negative), M68 (toxinotype VIII) and BI-7 (toxinotype III). The naturally occurring non-toxic strain colonised all hamsters within 1-day post challenge (d.p.c.) with high-levels of spores being shed in the faeces of animals that appeared well throughout the entire experiment. However, some changes including increased neutrophil influx and unclotted red blood cells were observed at early time points despite the fact that the known C. difficile toxins (TcdA, TcdB and CDT) are absent from the genome. In contrast, hamsters challenged with strain M68 resulted in a 45% mortality rate, with those that survived challenge remaining highly colonised. It is currently unclear why some hamsters survive infection, as bacterial and toxin levels and histology scores were similar to those culled at a similar time-point. Hamsters challenged with strain BI-7 resulted in a rapid fatal infection in 100% of the hamsters approximately 26 hr post challenge. Severe caecal pathology, including transmural neutrophil infiltrates and extensive submucosal damage correlated with high levels of toxin measured in gut filtrates ex vivo. These data describes the infection kinetics and disease outcomes of 3 clinical C. difficile isolates differing in toxin carriage and provides additional insights to the role of each toxin in disease progression