Ultrasonography-guided identification of the lumbar epidural space

The study was designed to assess the reliability of sonographic evaluation in the prediction of the depth of the lumbar epidural space. Forty males, scheduled for epidural anesthesia for surgical repair of inguinal hernia, were prospectively studied. Patients were placed in a sitting position and sagittal scanning of the lumbar spine was performed with a 5-MHz transducer over the fourth or fifth interspace in order to identify the deeper hyperechogen interface, which represents the landmark between the ligamentum flavum and the epidural space. Ultrasound depth was measured and transducer removed. A Tuohy needle 18 G was then introduced percutaneously according to the standard technique and a rubber slide placed over it, so that it depth of insertion could be accurately measured. The potential for using ultrasounds for prediction of the distance from skin to epidural space was analyzed using a simple linear regression analysis; p values < 0.05 were considered significant. Mean values of ultrasound depth and needle depth were respectively 51 mm (SD 6.3) and 50.9 mm (SD 6.2); the correlation coefficient was 0.99. Ultrasound scanning of the lumbar spine provides an accurate measurement of the depth of the epidural space, which can facilitate the performance of the epidural anaesthesia and may decrease the complication rate, particularly in those patients in which anatomic landmarks are obscured.     

A finger-tapping task and a reaction time task as behavioral measures of the transition from wakefulness to sleep: which task interferes less with the sleep onset process

The aim of this study was to assess whether a finger-tapping task (FTT), in which normal subjects repeatedly tap on a button while falling asleep, could be less disturbing and provide comparable information on the sleep onset period (SOP) with respect to a reaction-time task (RTT) to acoustic stimuli, in which the onset of sleep can be delayed by the arousing effect of the acoustic stimuli. Twelve subjects slept at their homes and six slept in a sleep laboratory for four consecutive nights. After one adaptation night and one baseline night, subjects were required to fall asleep in the third and fourth nights, bimanually performing either a RTT or a FTT. The results indicate that the FTT interfaces less with the SOP compared to the RTT and suggest that the FTT provides further advantages as a behavioral measure of the transition from wakefulness to sleep. In fact, the tapping task is associated with significantly shorter behavioral and polysomnographic sleep onset latencies and with a greater proportion of slow-wave sleep (SWS) during the transition from wakefulness to sleep compared with the RTT. Furthermore, correlations among subjective, behavioral, and electroencephalograph (EEG) latencies confirm the validity of the finger-tapping task as a behavioral measure of sleep onset.     

An ASM-based characterisation of starvation-free systems

Abstract State Machines (ASMs) have been successfully applied for modeling critical and complex systems in a wide range of application domains. However, unlike other well-known formalisms, e.g. Petri nets, ASMs lack inherent, domain-independent characterisations of computationally important properties. Here, we provide an ASM-based characterisation of the starvation-free property. The classic, informal notion of starvation, usually provided in literature, is analysed and expressed as a necessary condition in terms of ASMs. Thus, we enrich the ASM framework with the notion of vulnerable rule as a practical tool for analysing starvation issues in an operational fashion.     

Surface Instability and Chemical Reactivity of ZrSiS and ZrSiSe Nodal‐Line Semimetals

Materials exhibiting nodal‐line fermions promise superb impact on technology for the prospect of dissipationless spintronic devices. Among nodal‐line semimetals, the ZrSiX (X = S, Se, Te) class is the most suitable candidate for such applications. However, the surface chemical reactivity of ZrSiS and ZrSiSe has not been explored yet. Here, by combining different surface‐science tools and density functional theory, it is demonstrated that the formation of ZrSiS and ZrSiSe surfaces by cleavage is accompanied by the washing up of the exotic topological bands, giving rise to the nodal line. Moreover, while the ZrSiS has a termination layer with both Zr and S atoms, in the ZrSiSe surface, reconstruction occurs with the appearance of Si surface atoms, which is particularly prone to oxidation. It is demonstrated that the chemical activity of ZrSiX compounds is mostly determined by the interaction of the Si layer with the ZrX sublayer. A suitable encapsulation for ZrSiX should not only preserve their surfaces from interaction with oxidative species, but also provide a saturation of dangling bonds with minimal distortion of the surface.     

Surface Reconstruction,Oxidation Mechanism,and Stability of Cd3As2

Cadmium arsenide (Cd₃As₂) has recently attracted considerable interest for the presence of 3D massless Dirac fermions with ultrahigh mobility and magnetoresistance. However, its surface properties are currently largely unexplored both theoretically and experimentally, due to the very large unit cell and the challenging growth of single‐crystal samples, respectively. Here, by combining ab initio calculations with surface‐science spectroscopic experiments, the presence of a surface reconstruction is unveiled in centimeter‐scale (112)‐oriented Cd₃As₂ single‐crystal foils produced by the self‐selecting vapor growth. Outermost Cd atoms descend into the As‐sublayer with a subsequent self‐passivation of the dangling bonds with As atoms, forming the triangle lattice previously imaged by scanning tunneling microscopy. Moreover, the oxidation mechanism of this reconstructed surface, dominated by the formation of As? O? Cd bonds, is revealed. Interestingly, it is found that the band structure of the reconstructed surface of Cd₃As₂ is quite robust against surface oxidation. Both computational and experimental findings point to a successful exploitation in technology of Cd₃As₂ single crystals.     

Molecular basis of phospholipase A2 inhibition by petrosaspongiolide M

Petrosaspongiolide M (PM) is an anti-inflammatory marine metabolite that displays a potent inhibitory activity toward group II and III secretory phospholipase A(2) (PLA(2)) enzymes. The details of the mechanism, which leads to a covalent adduct between PLA(2) and gamma-hydroxybutenolide-containing molecules such as PM, are still a matter of debate. In this paper the covalent binding of PM to bee venom PLA(2) has been investigated by mass spectrometry and molecular modeling. The mass increment observed for the PM-PLA(2) adduct is consistent with the formation of a Schiff base by reaction of a PLA(2) amino group with the hemiacetal function (masked aldehyde) at the C-25 atom of the PM gamma-hydroxybutenolide ring. Proteolysis of the modified PLA(2) by the endoprotease LysC followed by HPLC MS analysis allowed us to establish that the PLA(2) alpha-amino terminal group of the Ile-1 residue was the only covalent binding site for PM. The stoichiometry of the reaction between PM and PLA(2) was also monitored and results showed that even with excess inhibitor, the prevalent product is a 1:1 (inhibitor:enzyme) adduct, although a 2:1 adduct is present as a minor component. The 2:1 adduct was also characterized, which showed that the second site of reaction is located at the epsilon -amino group of the Lys-85 residue. Similar results in terms of the reaction profile, mass increments, and location of the PLA(2) binding site were obtained for manoalide, a paradigm for irreversible PLA(2) inhibitors, which suggests that the present results may be considered of more general interest within the field of anti-inflammatory sesterterpenes that contain the gamma-hydroxybutenolide pharmacophore. Finally, a 3D model, constrained by the above experimental results, was obtained by docking the inhibitor molecule into the PLA(2) binding site through AFFINITY calculations. The model provides an interesting insight into the PM-PLA(2) inhibition process and may prove useful in the design of new anti-inflammatory agents that target PLA(2) secretory enzymes.     

Transient behaviour of perovskite-based monolithic reactors in the catalytic combustion of methane

The transient behaviour of perovskite-based catalysts prepared via active phase dispersion on La/γ-Al₂O₃ washcoated cordierite monoliths has been investigated in the autothermal combustion of lean methane mixtures. During start-up and shut-down operations, the reaction front moves from the outlet towards the inlet (ignition) or vice versa (extinction), with a time scale significantly higher than space time. The CH₄/O₂/N₂ feed mixture is completely converted to CO₂ and H₂O provided its inlet temperature is about 500°C, a value not affected by catalyst length and gas flow rate, the phenomenon being kinetically controlled. Gas flow rate significantly affects solid steady-state temperature, as at higher flow rates the thermal power produced by combustion is higher in comparison with heat losses by radiation and conduction and temperature rise is closer to the adiabatic value. The fresh catalysts weakly deactivate during the first 60 h of operation under reaction conditions, but after 120 h the activity is still very high and not significantly affected by further ageing. The transient behaviour of the system has been simulated by a mathematical model, characterised by an increased solid thermal conductivity to take into account the relevant contribution of internal radiation between channel surfaces.     

Bulk functionalization of ethylene–propylene copolymers. II. Influence of the initiator concentration and of the copolymer composition and chain microstructure on the reaction kinetics

The effect of the dicumylperoxide (DCPO) concentration on the kinetics of the bulk functionalization of an ethylene-propylene copolymer (EPR) has been studied. It has been found that, enhancing the DCPO initial concentration in the reaction mixture, results in both increased initial reaction rate and grafting process efficiency. DCPO content also affects degradation, which always accompanies the grafting reaction. At high DCPO content, products with a high degree of grafting and intrinsic viscosity close to that of the parent copolymer can be obtained. Furthermore, the influence of the EPR composition and chain microstructure on the functionalization as well as on the degradation processes has been investigated. By increasing the C₂ content in EPRs prepared by using vanadium-based conventional catalysts, obtains faster functionalization kinetics and a less pronounced degradation of the products. At fixed experimental conditions, the highest grafting degrees have been obtained by using EPRs prepared by high-yield titanium catalysts and characterized as a block-like microstructure. The experimental results have been interpreted on the basis of a proposed reaction mechanism.     

AMnO3 (A=La, Nd, Sm) and Sm1−xSrxMnO3 perovskites as combustion catalysts: structural, redox and catalytic properties

Catalytic combustion of methane has been investigated over AMnO₃ (A = La, Nd, Sm) and Sm_1−xSr_xMnO₃ (x = 0.1, 0.3, 0.5) perovskites prepared by citrate method. The catalysts were characterized by chemical analysis, XRD and TPR techniques. Catalytic activity measurements were carried out with a fixed bed reactor at T = 623–1023 K, space velocity = 40 000 N cm³ g⁻¹ h⁻¹, CH₄ concentration = 0.4% v/v, O₂ concentration = 10% v/v.

Specific surface areas of perovskites were in the range 13–20 m² g⁻¹. XRD analysis showed that LaMnO₃, NdMnO₃, SmMnO₃ and Sm_1−xSr_xMnO₃ (x = 0.1) are single phase perovskite type oxides. Traces of Sm₂O₃ besides the perovskite phase were detected in the Sm_1−xSr_xMnO₃ catalysts for x = 0.3, 0.5. Chemical analysis gave evidence of the presence of a significant fraction of Mn(IV) in AMnO₃. The fraction of Mn(IV) in the Sm_1−xSr_xMnO₃ samples increased with x. TPR measurements on AMnO₃ showed that the perovskites were reduced in two steps at low and high temperature, related to Mn(IV) → Mn(III) and Mn(III) → Mn(II) reductions, respectively. The onset temperatures were in the order LaMnO₃ > NdMnO₃ > SmMnO₃. In Sm_1−xSr_xMnO₃ the Sr substitution for Sm caused the formation of Mn(IV) easily reducible to Mn(II) even at low temperature. Catalytic activity tests showed that all samples gave methane complete conversion with 100% selectivity to CO₂ below 1023 K. The activation energies of the AMnO₃ perovskites varied in the same order as the onset temperatures in TPR experiments suggesting that the catalytic activity is affected by the reducibility of manganese. Sr substitution for Sm in SmMnO₃ perovskites resulted in a reduction of activity with respect to the unsubstituted perovskite. This behaviour was related to the reduction of Mn(IV) to Mn(II), occurring under reaction conditions, hindering the redox mechanism.