Stable isotopes applied to the study of the concrete/bentonite interaction in the FEBEX in situ test

Stable isotope analysis was carried out on a set of samples from the concrete-bentonite interface from the FEBEX real-scale in-situ experiment. The concrete and bentonite that simulated the engineering barriers system of a deep geological repository have interacted for 13 years in saturated conditions up to dismantling. The monitoring of the experiment during the years of operation has made possible to know not only the baseline status but also the evolution of the system and the mass transfer processes. Thus, the FEBEX experiment has been a unique opportunity to study concrete degradation within a broader multi-proxy approach under real-scale repository conditions. Analysis of carbon and oxygen isotopes of carbonates in groundwater, concrete and clay have provided evidence of how dissolution and mass transfer processes occur in the Engineered Barrier System (EBS). Spatial distribution of δ13C values points to the existence of a dominant process of diffusion of carbon species from bentonite towards the concrete/bentonite interface. Variations in δ18O values suggest a non-homogeneous geochemical and hydraulic behavior of the EBS in the vicinity of both, the granite-concrete interface and the concrete-bentonite interface. These differences might be related to different degrees of exposure of each sample to bentonite porewater, groundwater and concrete/bentonite leachates. This seem to be in agreement with the existence of different chemical environments depending on the location of the samples in the experiment.The work was financially supported by the European Union's Horizon 2020 grant agreement n° 662147 (www.cebama.eu) and the Annex XLII of the ENRESA-CIEMAT framework agreement. The FEBEX project was financed by ENRESA and the EC Contracts FI4W-CT95-006 and FIKWCT-2000-00016. The FEBEX-DP Consortium (NAGRA, SKB, POSIVA, CIEMAT, KAERI) financed the dismantling operation and onsite determinations in 2015

Retention of Ascorbic Acid and Solid Concentration via Centrifugal Freeze Concentration of Orange Juice

Freeze concentration of liquid foods produces high-quality concentrates while retaining the heat-labile compounds found in fresh samples. Centrifugal freeze concentration is a cryoconcentration method assisted by an external force, centrifugation, to enhance the separation of concentrate from the ice. When applying centrifugal freeze concentration to orange juice, after the third cryoconcentration cycle, the ascorbic acid content in the concentrate showed retention close to 70% of the initial value. After the third cycle, the solutes in the concentrate increased 4 times the initial value of the fresh sample with 70% efficiency. The color evaluation showed that the final concentrated fraction was darker than the fresh juice. The centrifugal freeze concentration in orange juice was effective for obtaining a high-quality concentrate with a higher concentration of solids and ascorbic acid retention

Geochemical interactions at the steel-bentonite interface caused by a hydrothermal gradient

Bentonites are used in deep geological disposal facilities as an engineered barrier to isolate high level radioactive waste, contained in metallic canisters. The present study, performed at laboratory scale, evaluated the behaviour of MX-80 (Na-bentonite) and FEBEX (Ca-Mg-Na-bentonite) in contact with carbon steel, subjected to a hydrothermal gradient. A dominant Na-Cl-SO4 saline solution was injected towards the compacted bentonite from the top, while a heater, located at the bottom in contact with the steel disc, maintained a constant temperature of 100 °C. The cells were studied after one and six months of interaction. Changes in the physical (water content and specific surface area) and chemical (cation exchange capacity and element distribution) properties of the bentonite were observed, as well as the formation of a corrosion layer on the steel, at the interface with bentonite, mainly composed of magnetite, maghemite and hematite. The bentonites were mainly altered at the mm scale, being enriched in iron content, and changing their ion distribution to Ca-dominant smectite (in MX-80 bentonite)This project has received funding from the European Union’s Horizon 2020 research and innovation programme 2014-2018 under grant agreement N◦84759

Challenges and New Approaches to Proving the Existence of Muscle Synergies of Neural Origin

Muscle coordination studies repeatedly show low-dimensionality of muscle activations for a wide variety of motor tasks. The basis vectors of this low-dimensional subspace, termed muscle synergies, are hypothesized to reflect neurally-established functional muscle groupings that simplify body control. However, the muscle synergy hypothesis has been notoriously difficult to prove or falsify. We use cadaveric experiments and computational models to perform a crucial thought experiment and develop an alternative explanation of how muscle synergies could be observed without the nervous system having controlled muscles in groups. We first show that the biomechanics of the limb constrains musculotendon length changes to a low-dimensional subspace across all possible movement directions. We then show that a modest assumption—that each muscle is independently instructed to resist length change—leads to the result that electromyographic (EMG) synergies will arise without the need to conclude that they are a product of neural coupling among muscles. Finally, we show that there are dimensionality-reducing constraints in the isometric production of force in a variety of directions, but that these constraints are more easily controlled for, suggesting new experimental directions. These counter-examples to current thinking clearly show how experimenters could adequately control for the constraints described here when designing experiments to test for muscle synergies—but, to the best of our knowledge, this has not yet been done

Common Origin for Surface Reconstruction and the Formation of Chains of Metal Atoms

During the fracture of nanocontacts gold spontaneously forms freely suspended chains of atoms, which is not observed for the iso-electronic noble metals Ag and Cu. Au also differs from Ag and Cu in forming reconstructions at its low-index surfaces. Using mechanically controllable break junctions we show that all the 5d metals that show similar reconstructions (Ir, Pt and Au) also form chains of atoms, while both properties are absent in the 4d neighbor elements (Rh, Pd, Ag), indicating a common origin for these two phenomena. A competition between s and d bonding is proposed as an explanation

Observation of Supershell Structure in Alkali Metal Nanowires

Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross-section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles, such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure.Comment: Phys. Rev. Lett., in prin

Transition from tunneling to direct contact in tungsten nanojunctions

We apply the mechanically controllable break junctions technique to investigate the transition from tunneling to direct contact in tungsten. This transition is quite different from that of other metals and is determined by the local electronic properties of the tungsten surface and the relief of the electrodes at the point of their closest proximity. The conductance traces show a rich variety of patterns from the avalanche-like jump to a mesoscopic contact to the completely smooth transition between direct contact and tunneling. Due to the occasional absence of an adhesive jump the conductance of the contact can be continuously monitored at ultra-small electrode separations. The conductance histograms of tungsten are either featureless or show two distinct peaks related to the sequential opening of spatially separated groups of conductance channels. The role of surface states of tungsten and their contribution to the junction conductance at sub-Angstrom electrode separations are discussed.Comment: 6 pages, 6 figure

Assessment of oxidative damage to proteins and DNA in urine of newborn infants by a validated UPLC-MS/MS approach

The assessment of oxidative stress is highly relevant in clinical Perinatology as it is associated to adverse outcomes in newborn infants. This study summarizes results from the validation of an Ultra Performance Liquid Chromatography-tandem Mass Spectrometry (UPLC-MS/MS) method for the simultaneous quantification of the urinary concentrations of a set of endogenous biomarkers, capable to provide a valid snapshot of the oxidative stress status applicable in human clinical trials, especially in the field of Perinatology. The set of analytes included are phenylalanine (Phe), para-tyrosine (p-Tyr), ortho-tyrosine (o-Tyr), meta-tyrosine (m-Tyr), 3-NO2-tyrosine (3NO 2-Tyr), 3-Cl-tyrosine (3Cl-Tyr), 2′-deoxyguanosine (2dG) and 8-hydroxy-2′-deoxyguanosine (8OHdG). Following the FDA-based guidelines, appropriate levels of accuracy and precision, as well as adequate levels of sensitivity with limits of detection (LODs) in the low nanomolar (nmol/L) range were confirmed after method validation. The validity of the proposed UPLC-MS/MS method was assessed by analysing urine samples from a clinical trial in extremely low birth weight (ELBW) infants randomized to be resuscitated with two different initial inspiratory fractions of oxygen

Quantum Conductance in Semimetallic Bismuth Nanocontacts

Electronic transport properties of bismuth nanocontacts are analyzed by means of a low temperature scanning tunneling microscope. The subquantum steps observed in the conductance versus elongation curves give evidence of atomic rearrangements in the contact. The underlying quantum nature of the conductance reveals itself through peaks in the conductance histograms. The shape of the conductance curves at 77 K is well described by a simple gliding mechanism for the contact evolution during elongation. The strikingly different behaviour at 4 K suggests a charge carrier transition from light to heavy ones as the contact cross section becomes sufficiently small.Comment: 5 pages including 4 figures. Accepted for publication in Phys. Rev. Let

Urethro-cutaneous fistula: a rare complication in anti-incontinence surgery with trans-obturator tapes sling

This case report presents a rare complication of tension-free mid-urethral tape surgery by the obturator approach (TOT) in the form of a urethro-cutaneous fistula. The patient underwent successful surgical repair, highlighting the importance of intraoperative cystoscopy to minimize surgical risks and complications. Tension-free mid-urethral tape surgery is a commonly performed procedure for the treatment of stress urinary incontinence (SUI). However, complications can occur, albeit rarely. In this case, a 52-year-old female patient developed a urethro-cutaneous fistula following TOT surgery. The fistula was identified by the presence of urine leakage at the right inguinal level, leading to significant distress and discomfort for the patient. Prompt diagnosis and appropriate management are crucial in such cases. The patient underwent surgical repair, which involved excision of the fistulous tract. The procedure was successful, resulting in complete resolution of the fistula and restoration of normal urinary function. In conclusion, this case report highlights the occurrence of a rare complication, namely a urethro-cutaneous fistula, following TOT surgery. The successful surgical repair emphasizes the importance of prompt diagnosis and appropriate management. Furthermore, the authors propose that an intraoperative cystoscopic evaluation be considered, even after a TOT procedure. Especially in cases that present risk factors or in hospital-school institutions. By implementing this practice, surgeons can enhance patient safety and improve surgical outcomes in anti-incontinence procedures