Magnetotransport in quantum cascade detectors: analyzing the current under illumination

Photocurrent measurements have been performed on a quantum cascade detector structure under strong magnetic field applied parallel to the growth axis. The photocurrent shows oscillations as a function of B. In order to describe that behavior, we have developed a rate equation model. The interpretation of the experimental data supports the idea that an elastic scattering contribution plays a central role in the behavior of those structures. We present a calculation of electron lifetime versus magnetic field which suggests that impurities scattering in the active region is the limiting factor. These experiments lead to a better understanding of these complex structures and give key parameters to optimize them further.     

Nanoscale coordination polymers exhibiting luminescence properties and NMR relaxivity

This article presents the first example of ultra-small (3-4 nm) magneto-luminescent cyano-bridged coordination polymer nanoparticles Ln0.33(3+)Gdx3+/[Mo(CN)8]3- (Ln=Eu (x=0.34), Tb (x=0.35)) enwrapped by a natural biocompatible polymer chitosan. The aqueous colloidal solutions of these nanoparticles present a luminescence characteristic of the corresponding lanthanides (5D0→7F0-4 (Eu3+) or the 5D4→7F6-2 (Tb3+)) under UV excitation and a green luminescence of the chitosan shell under excitation in the visible region. Magnetic Resonance Imaging (MRI) efficiency, i.e. the nuclear relaxivity, measurements performed for Ln0.33(3+)Gdx3+/[Mo(CN)8]3- nanoparticles show r1p and r2p relaxivities slightly higher than or comparable to the ones of the commercial paramagnetic compounds Gd-DTPA? or Omniscan? indicating that our samples may potentially be considered as a positive contrast agent for MRI. The in vitro studies performed on these nanoparticles show that they maybe internalized into human cancer and normal cells and well detected by fluorescence at the single cell level. They present high stability even at low pH and lack of cytotoxicity both in human cancer and normal cells.     

Using phase diagrams to deal with moisture expansion

Consensus has it that the post-fabrication moisture expansion of fired clay-based materials is governed by the presence of amorphous and/or vitreous phases. In this work, very simple calculations using the lever rule and the phase diagram of the Al₂O₃–SiO₂–K₂O (A–S–K) system, were used to show that the experimentally observed dependencies between moisture expansion and the A/S and K/A weight ratios in clay-based compositions can be correlated with the amount of liquid phase formed during the initial melting of the composition, which remains in the fired body as a vitreous phase. This correlation might, if judiciously used, help ceramists in the choice of additives and/or processing conditions, while avoiding changes in the firing temperatures. Also, the results obtained throw a sharper light in the dual and, in this respect, antagonistic role played by the liquid phase during firing.     

Electrospun polymeric membranes: Potential removal of endocrine disrupting compounds using solid membrane extraction and filtration processes

The present study aims to prepare polymeric membranes by electrospinning to apply in the removal of estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in aqueous samples. Polymeric membranes of polyamide-6 (PA6), polycaprolactone (PCL), polylactic acid (PLA), and poly (butylene adipate-co-terephthalate) (PBAT) were obtained, characterized, and tested as sorbent material in processes of solid membrane extraction (SME) and membrane filtration. The efficiencies of the membranes after washing and/or conditioning processes were compared. The characterizations showed membranes with nanometer-diameter threads (between 250 and 1200 nm, on average). The four membranes' morphology, chemical composition, and thermal stability were like previous works. PBAT membranes were considered the most effective SME technique as a differential, with 44%–71% removal. For the membrane filtration process, the highest removal values were obtained for the PBAT membrane (82%–91%), which was also efficient in filtering a surface water sample from River Guaíba. PBAT polymeric membrane effectively removes and recovers the studied hormones, lowering production costs and allowing internal and external modifications. These aspects demonstrate that the obtained membranes offer an efficient material in extracting E1, E2, and EE2, of high simplicity, low cost, and green chemistry.     

A sex attractant for the scarab beetle Anomala solida Er

(R,Z)-5-(-)-(Oct-1-enyl)oxacyclopentan-2-one (R-buibuilactone) attracted male Anomala solida Er. (Coleoptera: Scarabaeidae, Rutelinae), a vineyard and orchard pest in Southeastern Europe. The presence of the corresponding (S) enantiomer or of 2-(E)-nonen-1-ol (a frequently found pheromone component in other Anomala spp.) in the bait did not influence catches. Traps baited with (R,Z)-5-(-)-(oct-1-enyl)oxacyclopentan-2-one were successfully used for monitoring the flight of A. solida, and may have practical applications for detection, monitoring, and mass trapping of the pest.     

A theoretical and experimental study of the crossflow microfiltration process of silica particles in an aqueous suspension

This work presents a theoretical and experimental analysis of a crossflow microfiltration process of silica particles in suspension. The silica suspensions were 0.001 M of NaCl with a pH of 6 (to maintain a constant ionic force within the medium to produce a stable silica particle suspension) for three different concentrations of silica particles: 100, 300, and 500 mg L⁻¹. The membrane used in the crossflow microfiltration experiments was a commercial polymeric membrane, microporous, asymmetric with a nominal pore diameter of 0.2 µm, manufactured by OSMONICS (Minnetonka, MN). The experiments were performed in a bench scale crossflow microfiltration system with a flat rectangular membrane cell. The permeate flux was obtained as a function of the transmembrane pressure, the crossflow velocities, and the silica particles concentration. The mathematical model describing the process takes into account the variation of the physical properties of the suspension (dynamic viscosity and mass diffusivity) with the silica concentration. The experimental data are used to predict the maximum silica concentration at the membrane surface as a function of the operating conditions.     

Temporal Aggregation of Lognormal AR processes

We consider temporal aggregation of lognormal autoregressive (AR) processes. More specifically, we develop a novel moment‐matching approximation for temporally aggregated lognormal AR processes. In addition, we show that our approximation provides the closest lognormal AR process in terms of Kullback–Leibler divergence. Moreover, we perform a simulation study to compare our proposed approximation with two competing approximations. This study shows that in terms of L¹‐ and L²‐norm distances our approximation provides superior results. Our results have an important practical application and one main practical implication. In terms of practical application, our approximation can provide possible candidate solutions for simulation‐based algorithms such as the Metropolis–Hastings algorithm. The practical implication gives support to common practice: when the original fine‐level process follows a lognormal AR process but only aggregated data are available, then instead of assuming a Gaussian process it is better to assume a lognormal AR process at the aggregated level. Finally, we illustrate the utility of our results with two applications. The first example considers a simulated dataset whereas the second example examines the number of yearly sunspots in the period 1700–1984.     

Theoretical analysis of the hydration of C60 in normal and supercritical conditions

Thermodynamics of hydration of the C₆₀ fullerene in normal and supercritical conditions is studied through the use of molecular dynamics simulations. The hydration free energy is calculated using the thermodynamic integration technique. It is observed that the hydrophobicity of the C₆₀ in normal water is entropy-driven and characterized by a free energy of about 58 kJ mol⁻¹. Our thermodynamic results indicate that this hydrophobic character is sensitively reduced in a supercritical state near of the critical point and that the solubility of the C₆₀ can be found in the supercritical region by varying pressure and temperature. The simulations reveal that for pressures above 570 bar (at 673 K) and temperatures above 770 K (at pressures of 250 and 350 bar) the solubilization process becomes favorable. Structural and dynamical aspects of supercritical solutions were also analyzed.     

Progress in the understanding of surface structure and surfactant influence on the electrocatalytic activity of gold nanoparticles

The preparation of gold nanoparticles (Au-NPs) displaying specific shape, size and surface crystallographic domains has been investigated aiming to clarify the effect of the surface crystallographic orientation, of the synthesised nanoparticles, and surfactant influence on the electrochemical response of the ITO/Au-NPs modified electrodes. Polymorphic and nanorod-shaped Au-NPs have been obtained using distinct synthetic procedures in the presence of cetyltrimethylammonium bromide (CTAB), through seed-mediated growth methods, displaying distinct surface crystallographic domains confirmed by transmission electron microscopy, X-ray diffraction analysis and under potential deposition (UPD) of lead.The nanoparticles have been physically immobilised by casting on indium tin oxide (ITO) surfaces and the electrocatalytic activity of the Au-NPs evaluated using the ascorbic acid (AA) oxidation reaction, by cyclic voltammetry. The polymorphic and distinct surface crystallographic orientations of the Au-NPs were reflected in an irreproducible electrochemical response. Using gold nanorods comprising (1 1 1) and (1 1 0) facets and gold nanocubes consisting of faces displaying (1 0 0) surface domains, by contrasting the behaviour of CTAB-stabilised and clean particles, it has been possible to verify that the distinct voltammetric results are due to the exposure of specific crystallographic orientations owing to dissimilar interaction strength of CTAB with those facets.     

Aerobic Exercise Improves Reverse Cholesterol Transport in Cholesteryl Ester Transfer Protein Transgenic Mice

We analyzed the effect of a 6-week aerobic exercise training program on the in vivo macrophage reverse cholesterol transport (RCT) in human cholesteryl ester transfer protein (CETP) transgenic (CETP-tg) mice. Male CETP-tg mice were randomly assigned to a sedentary group or a carefully supervised exercise training group (treadmill 15 m/min, 30 min sessions, five sessions per week). The levels of plasma lipids were determined by enzymatic methods, and the lipoprotein profile was determined by fast protein liquid chromatography (FPLC). CETP activity was determined by measuring the transfer rate of ¹⁴C-cholesterol from HDL to apo-B containing lipoproteins, using plasma from CETP-tg mice as a source of CETP. The reverse cholesterol transport was determined in vivo by measuring the [³H]-cholesterol recovery in plasma and feces (24 and 48 h) and in the liver (48 h) following a peritoneal injection of [³H]-cholesterol labeled J774-macrophages into both sedentary and exercise trained mice. The protein levels of liver receptors were determined by immunoblot, and the mRNA levels for liver enzymes were measured using RT-PCR. Exercise training did not significantly affect the levels of plasma lipids or CETP activity. The HDL fraction assessed by FPLC was higher in exercise-trained compared to sedentary mice. In comparison to the sedentary group, a greater recovery of [³H]-cholesterol from the injected macrophages was found in the plasma, liver and feces of exercise-trained animals. The latter occurred even with a reduction in the liver CYP7A1 mRNA level in exercised trained animals. Exercise training increased the liver LDL receptor and ABCA-1 protein levels, although the SR-BI protein content was unchanged. The RCT benefit in CETP-tg mice elicited by exercise training helps to elucidate the role of exercise in the prevention of atherosclerosis in humans.