Nonparaxial shape-preserving Airy beams with Bessel signature

Spatially accelerating beams that are solutions to the Maxwell equations may propagate along incomplete circular trajectories, after which diffraction broadening takes over and the beams spread out. Taking these truncated Bessel wave fields to the paraxial limit, some authors sustained that it is recovered the known Airy beams (AiBs). Based on the angular spectrum representation of optical fields, we demonstrated that the paraxial approximation rigorously leads to off-axis focused beams instead of finite-energy AiBs. The latter will arise under the umbrella of a nonparaxial approach following elliptical trajectories in place of parabolas. Deviations from full-wave simulations appear more severely in beam positioning rather than its local profile

Light capsules shaped by curvilinear meta-surfaces

We propose a simple yet efficient method for generating in-plane hollow beams with a nearly-full circular light shell without the contribution of backward propagating waves. The method relies on modulating the phase in the near field of a centro-symmetric optical wavefront, such as that from a high-numericalaperture focused wave field. We illustrate how beam acceleration may be carried out by using an ultranarrow non-flat meta-surface formed by engineered plasmonic nanoslits. A mirrorsymmetric, with respect to the optical axis, circular caustic surface is numerically demonstrated that can be used as an optical bottle

La eficacia de las estrategias de andamiaje y la orientación de tareas sobre el conocimiento receptivo y productivo de las colocaciones léxicas

The present study aimed at investigating the effects of scaffolding strategies using input and output-oriented tasks on Iranian EFL learners' receptive and productive knowledge of lexical collocations. For this purpose, 540 adult intermediate-level EFL learners- both male and female- were selected and divided into six experimental groups; three input-oriented and three output-oriented tasks. Each experimental group received treatment under one of the three scaffolding strategies of direct corrective feedback, cooperative group technique, and visual cues. After the treatment period, a 40-item multiple-choice test and a 40-item fill-in-the-blanks test were administered to assess the participants' receptive and productive collocations knowledge. To analyze the data, two separate two-way ANOVA procedures were used. The results indicated that visual cues were the most effective scaffolding strategy in teaching lexical collocations. Moreover, the cooperative group technique had a significant positive impact on learning collocations compared to direct corrective feedback. The results also showed that the participants in the output-oriented tasks group significantly outperformed those in the input-oriented tasks group. These findings can have practical implications for language learners, teachers, and materials developers, and theoretical implications for researchers.El presente estudio tuvo como objetivo investigar los efectos de las estrategias de andamiaje que utilizan tareas orientadas a insumos y resultados en el conocimiento receptivo y productivo de las colocaciones léxicas de los estudiantes iraníes de inglés como lengua extranjera. Para este propósito, 540 aprendices adultos en nivel intermedio, tanto hombres como mujeres fueron seleccionados y divididos en seis grupos experimentales; tres en la categoría de insumos y tres en la categoría de resultados. Cada grupo experimental recibió un tratamiento bajo una de tres estrategias de andamiaje, tales como:  retroalimentación directa correctiva, técnica grupal cooperativa y señales visuales. Después del periodo de tratamiento, se administró una prueba de 40 preguntas de múltiple respuesta y una prueba de 40 preguntas de llenar espacios para evaluar el conocimiento de las colocaciones receptivas y productivas de los participantes. Para analizar los datos, se utilizaron dos procedimientos ANOVA bidireccionales separados. Los resultados indicaron que las señales visuales fueron la estrategia más efectiva en la enseñanza de colocaciones léxicas. Además, la técnica de cooperación grupal tuvo un impacto significativo en el aprendizaje de colocaciones comparado con la retroalimentación directa correctiva. Los resultados también mostraron que los participantes en el grupo de tareas orientadas a resultados superaron significativamente a los del grupo de tareas orientadas a insumos. Estos hallazgos pueden tener implicaciones prácticas para los aprendices de lengua, docentes, desarrolladores de materiales e implicaciones teoréticas para los investigadores

Prevalence of Clarithromycin-Resistant Helicobacter pylori in Patients With Chronic Tonsillitis by Allele-Specific Scorpion Real-Time Polymerase Chain Reaction Assay

Objectives/Hypothesis: To investigate the allelic prevalence of resistance to clarithromycin in the DNA of clinical isolates of Helicobacter pylori obtained from biopsy specimens of patients with chronic tonsillitis by Scorpion real-time polymerase chain reaction (PCR). Study Design: Pathologic specimens of patients with chronic tonsillitis were used for rapid urease test, and blocks of paraffin-embedded tonsillar tissue were used for McMullen staining, rapid urease test, and Scorpion real-time PCR test. Methods: A total of 103 biopsy samples were obtained from patients with chronic tonsillitis and examined for the presence of clarithromycin resistant H. pylori. Modified McMullen staining and rapid urease test were done on the all the samples. The DNA of specimens was extracted from the pathology blocks, and Scorpion real-time PCR was performed on a final volume of 25 lL. Results: Of 103 biopsy specimens, 22 samples were identified as infected by H. pylori, of which none were sensitive to clarithromycin. One had the A2143G genotype, and four had the A2142G genotype. Two had a mixed sensitive and the A2143G genotype, and five had a mixed sensitive and A2142G genotype. One strain had a mixed genotype of sensitive, A2143G, and A2142G. Conclusions: The reported rate of resistance to clarithromycin is of great variation among H. pylori strains isolated from specimens in different countries. Our study showed that the most prevalent genotypes in our H. pylori-positive specimens was A2142G followed by A2143G, which is different from reported results of allele-specific genotyping of H. pylori strains isolated from gastric biopsy and may be a result of cross-resistance to erythromycin and other macrolides. Key Words: Scorpion real-time polymerase chain reaction, chronic tonsillitis, clarithromycin