Tailored Height Gradients in Vertical Nanowire Arrays via Mechanical and Electronic Modulation of Metal‐Assisted Chemical Etching

In current top‐down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask‐dependent material deposition or etching techniques, is usually uniform, and on‐chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect‐ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal‐assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20‐fold on‐chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano‐assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics.     

Evaluation of the functional potential of Weissella and Lactobacillus isolates obtained from Nigerian traditional fermented foods and cow's intestine

The characterisation of 24 lactic acid bacteria (LAB) isolates from Nigerian traditional fermented dairy foods, including some cow's intestine isolates, was conducted in order to select isolates for potential use as probiotics. LAB isolates were identified by partial sequencing the 16S rRNA gene as belonging to the species Lactobacillus paracasei, Lactobacillus brevis and mainly Weissella confusa. At the end of a characterisation process, 2 L. paracasei and 2 W. confusa isolates were selected, and their resistance to a simulated gastrointestinal digestion and their ability to adhere to eukaryotic cell lines were assessed. The survival to the simulated gastrointestinal passage was higher when bacterial suspensions were made in skimmed milk (2.0 ± 0.8 log units reduction) or at the simulated gastric juice pH 3 (2.7 ± 0.9 log units reduction) than at pH 2.0 (5.5 ± 0.7 log units reduction). Adhesion of LAB to both intestinal and vaginal epithelial models was comparable or higher than that of the reference Lactobacillus rhamnosus GG. However, some of the isolates increased the adhesion of the pathogen Escherichia coli LMG2092 to HT-29 and HeLa monolayers. Overall, isolates L. paracasei UI14 and W. confusa UI7 are good candidates for further studying potential benefits that support their use as probiotics. This is one of the few articles reporting the characterisation and the probiotic potential of Weissella, although more studies are needed in order to establish their safety for potential probiotic applications.     

Using hydropower to complement wind energy: a hybrid system to provide firm power

This paper presents a theoretical study of how wind power can be complemented by hydropower. A conceptual framework is provided for a hybrid power station that produces constant power output without the intermittent fluctuations inherent when using wind power. Two hypothetical facilities are considered as case studies. One of them is a hydropower plant located on the “Presidente Benito Juarez” dam in Jalapa del Marques, Oaxaca, Mexico. The other hypothetical facility is a wind farm located near “La Venta”, an area in Juchitan, Oaxaca, Mexico. The wind–hydro-power system is a combined wind and hydro power plant in a region that is rich in both resources. The model shows that the hybrid plant could provide close to 20 MW of firm power to the electrical distribution system. On a techno-economic basis, we obtain the levelized production cost of the hybrid system. Taking into account two different discount rates of 7% and 10%, figures for levelized production cost are developed.     

Evaluation of the water quality in the Guadarrama river at the section of Las Rozas‐Madrid,Spain

The variation of the water quality of the Guadarrama river and its tributaries in a section of Las Rozas‐Madrid, Spain, was studied during the time period between January 2003 and January 2008. The parameter water quality index (WQI) was used to determine the water quality based on the conventional parameters of pollution. It was found that the WQI was slightly affected in the section evaluated. The value of the WQI was in the range of 56–64, which corresponded to the classification of ‘good quality’. It was determined that 64.3% of the organic matter present in the river was removed in the section of Las Rozas‐Madrid. The river acted as a plug flow reactor and a first‐order kinetics governed the ultimate biological oxygen demand (BOD₅) (BOD_U) decay. The value of the first‐order constant demonstrated the river's high self‐purification capacity. In addition, a high linear relationship was found between the WQI and the dissolved oxygen deficit (D). Therefore, a quick determination of WQI may be carried out if the values of D are known. These are easily obtainable by field measurements.     

Characterisation of a Bifidobacterium strain with acquired resistance to cholate--a preliminary study

The susceptibility levels against bile salts (ox gall) and sodium cholate of 19 Bifidobacterium strains from different origins ranged between 0.125% and 2.0% and 0.05% and 0.4%, respectively. Seven of these strains were subsequently selected for the isolation of sodium cholate resistant derivatives by exposure to gradually increasing concentrations of this compound. Derivatives resistant to at least 1.2% of cholate were obtained from Bifidobacterium bifidum CECT 4549 and B. bifidum M6. Further analysis of the CECT 4549 derivative indicated that the phenotype induced was stable; the enzymatic activities analysed remained unchanged and no major rearrangements of chromosomal DNA were produced. However, the cells of the resistant derivative were smaller and more regular in average size than those of the original strain. In addition, the derivative had lost the ability to use lactose, fructose and galactose, and showed reduced expression levels of two membrane proteins of 78 and 114 kDa. Finally, the resistant strain displayed higher survival and lower growth inhibition in the presence of cholate than the original strain.     

Dynamic Accessibility using Big Data: The Role of the Changing Conditions of Network Congestion and Destination Attractiveness

Accessibility is essentially a dynamic concept. However, most studies on urban accessibility take a static approach, overlooking the fact that accessibility conditions change dramatically throughout the day. Due to their high spatial and temporal resolution, the new data sources (Big Data) offer new possibilities for the study of accessibility. The aim of this paper is to analyse urban accessibility considering its two components –the performance of the transport network and the attractiveness of the destinations– using a dynamic approach using data from TomTom and Twitter respectively. This allows us to obtain profiles that highlight the daily variations in accessibility in the city of Madrid, and identify the influence of congestion and the changes in location of the population. These profiles reveal significant variations according to transport zones. Each transport zone has its own accessibility profile, and thus its own specific problems, which require solutions that are also specific.     

Variants of the 3' region of the cagA gene in Helicobacter pylori isolates from patients with different H. pylori-associated diseases

The CagA protein of Helicobacter pylori is an immunogenic antigen of variable size and unknown function that has been associated with increased virulence as well as two mutually exclusive diseases, duodenal ulcer and gastric carcinoma. The 3' region of the cagA gene contains repeated sequences. To determine whether there are structural changes in the 3' region of cagA that predict outcome of H. pylori infection, we examined 155 cagA gene-positive H. pylori isolates from Japanese patients including 50 patients with simple gastritis, 40 with gastric ulcer, 35 with duodenal ulcer, and 30 with gastric cancer. The 3' region of the cagA gene was amplified by PCR followed by sequencing. CagA proteins were detected by immunoblotting using a polyclonal antibody against recombinant CagA. One hundred forty-five strains yielded PCR products of 642 to 651 bp; 10 strains had products of 756 to 813 bp. The sequence of the 3' region of the cagA gene in Japan differs markedly from the primary sequence of cagA genes from Western isolates. Sequence analysis of the PCR products showed four types of primary gene structure (designated types A, B, C, and D) depending on the type and number of repeats. Six of the seven type C strains were found in patients with gastric cancer (P < 0.01 in comparison to noncancer patients). Comparison of type A and type C strains from patients with gastric cancer showed that type C was associated with higher levels of CagA antibody and more severe degrees of atrophy. Differences in cagA genotype may be useful for molecular epidemiology and may provide a marker for differences in virulence among cagA-positive H. pylori strains.     

Zeolite sensitized photoelectron transfer: Modulation of reduction potentials

The remarkable efficiency of conversion of light to chemical energy observed in green plant photosynthesis arises due to the spatial positioning of the sensitizers and the molecules involved in the electron relay. The architecture of zeolite cages also allows for positioning of molecules spatially, and in a primitive sense mimics photosynthesis. Using entrapped RU(bpy)₃²⁺ as sensitizer, directional electron transfer to propylviologen sulfonate (PVS) in solution is possible if the mediating viologen in the zeolite has the appropriate reduction potential e.g. N,N'-tetramethylene-2,2' bipyridinium (DQ²⁺). The reduction potentials of viologens is controlled by introducing steric effects in the molecule such that planarity of the two bipyridyl rings upon one-electron reduction is difficult to achieve. We show that by using viologen molecules that span several supercages of a zeolite e.g. benzylviologen (BV²⁺), we can also alter the reduction potential, but because of the steric constraints imposed by the zeolite framework. Thus, in this example, not only does the zeolite provide spatial orientation, but also modulates the reduction potential of the encapsulated viologen.