Screening of the quantum-confined Stark effect in AlN/GaN nanowire superlattices by Germanium doping

We report on electrostatic screening of polarization-induced internal electric fields in AlN/GaN nanowire heterostructures with Germanium-doped GaN nanodiscs embedded between AlN barriers. The incorporation of Germanium at concentrations above $10^{20}\,\text{cm}^{-3}$ shifts the photoluminescence emission energy of GaN nanodiscs to higher energies accompanied by a decrease of the photoluminescence decay time. At the same time, the thickness-dependent shift in emission energy is significantly reduced. In spite of the high donor concentration a degradation of the photoluminescence properties is not observed.Comment: Manuscript including Supplemental material (15 pages, 5 figures

Influence of the Delta Phase in the Microstructure of the Inconel 718 subjected to “Delta-processing” Heat Treatment and Hot Deformed

AbstractInconel 718 (IN718) is a nickel base alloy widely used in the aerospace industry due to its mechanical stability at elevated temperatures. Stable δ phase with acicular morphology weakens the IN718, however, it has been found that a spherical morphology distributed in the grain boundaries acts as an anchor preventing grain growth during hot deformation. The delta processing (DP718) is a saturation of δ phase in the alloy by thermal treatment followed by thermomechanical working to control the grain growth and morphology during deformation. Two specimens (A and B) of IN718 alloy were solubilized for 1h at 1100°C WQ and aging at 900°C for 24hWQ thermal treatment, following bythermomechanical deformation. Sample A was deformed at 0.001 s -1 and sample Bat 0.01 s-1, both deformations were carried out at 960°C and the final microstructures were characterized by optical microscopy and scanning electron microscopy (SEM) in order to evaluate morphology and grainsize distribution

Development of sandwich ELISA and lateral flow immunoassay to detect almond in processed food

Almond (Prunus dulcis) represents a potential allergenic hazard that should be included in Allergen Control Plans. In this study, sandwich ELISA and lateral flow immunoassay (LFIA), using amandin (Pru du 6) as the target protein, were developed to detect almond in processed food and validated according to international guides. ELISA could detect 2 ng/mL and LFIA 30 ng/mL of pure amandin. No cross-reactivity was found on a panel of 50 food commodities with the exception of Pecan nut, Brazil nut and chestnut for which the cross-reactivity was lower than 0.02%. Furthermore, ELISA and LFIA were able to detect 0.12 and 0.70 ppm of almond protein in foods spiked with almond extract whereas 0.20 and 2.0 ppm could be detected in baked cookies incurred with almond, respectively. Both techniques could be applied for food manufacturers and control agencies for monitoring the presence of almond traces in food and working surfaces. © 2021 The Author(s

Long-lived excitons in GaN/AlN nanowire heterostructures

GaN/AlN nanowire heterostructures can display photoluminescence (PL) decay times on the order of microseconds that persist up to room temperature. Doping the GaN nanodisk insertions with Ge can reduce these PL decay times by two orders of magnitude. These phenomena are explained by the three-dimensional electric field distribution within the GaN nanodisks, which has an axial component in the range of a few MV/cm associated to the spontaneous and piezoelectric polarization, and a radial piezoelectric contribution associated to the shear components of the lattice strain. At low dopant concentrations, a large electron-hole separation in both the axial and radial directions is present. The relatively weak radial electric fields, which are about one order of magnitude smaller than the axial fields, are rapidly screened by doping. This bidirectional screening leads to a radial and axial centralization of the hole underneath the electron, and consequently, to large decreases in PL decay times, in addition to luminescence blue shifts

The transcriptional cycle of HIV-1 in real-time and live cells

RNA polymerase II ( RNAPII) is a fundamental enzyme, but few studies have analyzed its activity in living cells. Using human immunodeficiency virus ( HIV) type 1 reporters, we study real- time messenger RNA ( mRNA) biogenesis by photobleaching nascent RNAs and RNAPII at specific transcription sites. Through modeling, the use of mutant polymerases, drugs, and quantitative in situ hybridization, we investigate the kinetics of the HIV- 1 transcription cycle. Initiation appears efficient because most polymerases demonstrate stable gene association. We calculate an elongation rate of approximately 1.9 kb/ min, and, surprisingly, polymerases remain at transcription sites 2.5 min longer than nascent RNAs. With a total polymerase residency time estimated at 333 s, 114 are assigned to elongation, and 63 are assigned to 3'- end processing and/ or transcript release. However, mRNAs were released seconds after polyadenylation onset, and analysis of polymerase density by chromatin immunoprecipitation suggests that they pause or lose processivity after passing the polyA site. The strengths and limitations of this kinetic approach to analyze mRNA biogenesis in living cells are discussed

COMPARING GC×GC-TOFMS-BASED METABOLOMIC PROFILING AND WOOD ANATOMY FOR FORENSIC IDENTIFICATION OF FIVE MELIACEAE (MAHOGANY) SPECIES

Illegal logging and associated trade have increased worldwide. Such environmental crimes represent a major threat to forest ecosystems and society, causing distortions in market prices, economic instability, ecological deterioration, and poverty. To prevent illegal imports of forest products, there is a need to develop wood identification methods for identifying tree species regulated by the Convention on International Trade in Species of Wild Fauna andFlora in Trade (CITES) and other look-alike species. In this exploratory study, we applied metabolomic profiling of five species (Swietenia mahagoni, Swietenia macrophylla, Cedrela odorata, Khaya ivorensis, and Toona ciliata) using two-dimensional gas chromatog- raphy combined with time-of-flight mass spectrometry (GC3GC-TOFMS). We also performed qualitative, quantitative (based on the measurement of vessel area, tangential vessel lumina diameter,vessel element length, ray height, and ray width), and machine-vision aided (XyloTron) wood anatomy on a subsample of wood specimens to explore thepotential and limits of each approach. Fifty dried xylaria wood specimens were ground, extracted with methanol, and subsequently analyzed by GC3GC-TOFMS. In this study, the four genera could easily be identified using qualitative wood anatomy and chemical profiling. At the spe- cies level, Swietenia macrophylla and Swietenia mahagoni specimens were found to share many major metabolites and could only be differentiated after feature selection guided by cluster resolution (FS-CR) and visualization using Principal Component Analysis (PCA). Expectedly, specimens from the two Swiete- nia spp. could not be distinguished based on qualitative wood anatomy. However, significant differences in quantitative anatomical features were obtained for these two species. Excluding T. ciliata that was not included in the reference database of end grain images at the time of testing (2021), the XyloTron could successfully identify the majority of the specimens to the right genus and 50% of the specimens to the right species. The machine-vision tool was particularly successful at identifying Cedrela odorata samples, where all samples were correctly identified. Despite the limited number of specimens available for thisstudy, our preliminary results indicate that GC3GC-TOFMS-based metabolomic profiles could be used as comple- mentary method to differentiate CITES-regulated wood specimens at the genus and species levels.

Evaluación del nivel de estrés en leoncillos (Cebuella pygmaea) mediante la medición de cortisol en heces

The pygmy marmoset (Cebuella pygmaea) is the smallest platyrrhine primate. It lives in gallery forests in the Upper Amazon basin of Colombia, Ecuador, Peru, Bolivia and Brazil. Although all the Ecuadorian primate species are threatened by human activities, the pygmy marmoset is one of the most vulnerable due to its high specialization in diet and habitat. It is included in the list of vulnerable species in Ecuador. Anthropogenic alteration of the habitats is a stress factor for pygmy marmosets. In this context this study aimed to establish a protocol to measure cortisol concentration in feces (ng/g), as an indicator of the stress level of the individuals, and to make a preliminary comparison of the levels of cortisol and stress of three populations of pygmy marmosets in Amazonian Ecuador. Fifty two fecal samples from the wild populations of Tiputini and San Pablo, and one captive population from Puyo were analyzed. The samples analyzed had a dry weight between 0.05 and 0.07 g. The biological validation made with the fecal samples of an individual quarantined, showed that cortisol levels were higher in times closer to its death. The preliminary results suggest that the captive population from Puyo has higher levels of stress than the wild populations. These results have to be confirmed by analyzing a larger number of samples with information about the time of fecal deposition, the sex, age and previous activities of the individuals.El leoncillo (Cebuella pygmaea), es la especie más pequeña de primate platirrino. Habita en bosques de la Amazonía alta en Colombia, Ecuador, Perú, Bolivia y Brasil. Aunque todas las especies de primates en el Ecuador están amenazadas por las actividades humanas, ésta es una de las más vulnerables, debido a la especificidad de su alimentación y hábitat. C. pygmaea actualmente ha sido incluida en la lista de especies vulnerables en el Ecuador. La alteración antropogénica de los hábitats es un factor de estrés para los leoncillos. En este contexto, los objetivos de esta investigación fueron establecer un protocolo para medir el cortisol en heces, como un indicador del nivel de estrés de los individuos, y realizar una comparación preliminar de los niveles de cortisol y estrés de tres poblaciones de leoncillos en la Amazonía ecuatoriana. Se analizaron 52 muestras provenientes de las poblaciones silvestres de Tiputini y San Pablo y de una población en cautiverio en Puyo. Las muestras analizadas tuvieron pesos secos entre 0.05 y 0.07 g. La validación biológica realizada con muestras de heces de un individuo en cuarentena, evidenció que los niveles de cortisol fueron más elevados en los días más próximos a su muerte. Los resultados preliminares sugieren que la población en cautiverio de Puyo tiene niveles de estrés significativamente más altos que los de las poblaciones silvestres. Estos resultados deben ser confirmados analizando un mayor número de muestras de las que se tenga información completa sobre la hora de deposición y sobre los individuos de los que se tomaron las muestras

X-ray determination of compressive residual Stresses in spring steel generated by high-speed water Quenching

Automotive components manufacturers use the 5160 steel in leaf and coil springs. The industrial heat treatment process consists in austenitizing followed by the oil quenching and tempering process. Typically, compressive residual stresses are induced by shot peening on the surface of automotive springs to bestow compressive residual stresses that improve the fatigue resistance and increase the service life of the parts after heat treatment. In this work, a high-speed quenching was used to achieve compressive residual stresses on the surface of AISI/SAE 5160 steel samples by producing high thermal gradients and interrupting the cooling in order to generate a case-core microstructure. A special laboratory equipment was designed and built, which uses water as the quenching media in a high-speed water chamber. The severity of the cooling was characterized with embedded thermocouples to obtain the cooling curves at different depths from the surface. Samples were cooled for various times to produce different hardened case depths. The microstructure of specimens was observed with a scanning electron microscope (SEM). X-ray diffraction (XRD) was used to estimate the magnitude of residual stresses on the surface of the specimens. Compressive residual stresses at the surface and sub-surface of about -700 MPa were obtained.Peer ReviewedPostprint (published version