Near-field optical patterning and structuring based on local-field enhancement at the extremity of a metal tip

We present a particular approach and the associated results allowing the nanostructuration of a thin photosensitive polymer film. This approach based on a scanning near-field optical microscopy configuration uses the field-enhancement (FE) effect, a so-called lightning-rod effect appearing at the extremity of a metallic tip when illuminated with an incident light polarized along the tip axis. The local enhancement of the electromagnetic field straight below the tip's apex is observed directly through a photoisomerization reaction, inducing the growth of a topographical nanodot characterized in situ by atomic-force microscopy using the same probe. From a survey of the literature, we first review the different experimental approaches offered to nanostructure materials by near-field optical techniques. We describe more particularly the FE effect approach. An overview of the theoretical approach of this effect is then given before presenting some experimental results so as theoretical results using the finite-element method. These results show the influence on the nanostructuration of the polymer of a few experimental parameters such as the polarization state, the illumination mode and the tip's geometry. Finally, the potentiality of this technique for some applications in the field of lithography and high-density data storage is shown via the fabrication of nano-patterns.     

Polarized second harmonic response of square, hexagonal and random arrays of gold metallic nanocylinders

The vertically and horizontally polarized second harmonic responses from arrays of gold metallic nanocylinders with different two-dimensional spatial organization, namely square, hexagonal and random arrangements, have been determined in transmission as a function of the input fundamental polarization angle. The results demonstrate that the second harmonic response is incoherent, resulting from the breaking of the centrosymmetry of the shape of the nanocylinders by surface defects. As a result, no effect from the geometrical arrangement of the nanocylinders on the substrate is observed.     

Theoretical and experimental investigations of lateral modes in 1-3piezocomposites

Materials with a periodic microstructure show resonances caused by the elastic wave Bragg diffraction. This paper presents a simple approach to describe these resonances (called lateral resonances) in 1-3 piezoelectric composite materials which have a 2-D periodicity. Our model is based on the analysis of the propagation of transverse waves in a 2-D periodic medium of infinite thickness and takes into account the periodic and interfacial boundary conditions. This model predicts the displacement field vectors and frequencies of lateral resonances from which the phase velocity of lateral waves is determined. The theoretical and experimental variations of this velocity versus the ceramic rod width to pitch ratio are compared. It is shown that the first lateral mode frequency is maximum when the ceramic volume fraction is around 0.65. Theoretical predictions of the mechanical displacement at the composite surface are compared with measurements obtained by an interferometric laser technique. A good agreement is observed, showing that lateral waves are mainly vertically polarized     

A liquid level sensor using the absorption of guided acoustic waves

This liquid level sensor consists of a vertically movable 10-cm-long hollow cylinder with an impedance matching conic section suspended at one end of a few-meters-long magnetorestrictive wire. The wire is automatically wound up or unwound such that the cylindrical sensor element at the bottom of the wire is immersed by just a small and measurable distance into the liquid whose level is sought. Acoustic waves are launched in the wire by a pulse of current in a coil and are transmitted to the hollow cylinder through the cylindrical horn. The carrier frequency of the wave trains and the thickness of the tube are chosen so that the elastic waves strongly leak into the liquid when the hollow cylinder is immersed. The level is then determined by measuring the time-of-flight of the echo reflected at the junction between the wire and the horn, followed by taking into account a small correction term computed from the attenuation of the end echo.     

Probing the contribution of internal cavities to the volume change of protein unfolding under pressure

BACKGROUND: Testicular dysfunction with elevated follicle-stimulating hormone (FSH) levels (indicating oligospermia and/or azoospermia) is a major late sequelae after treatment for Hodgkin's disease (HD) with high cumulative doses of procarbazine, cyclophosphamide, or chlorambucil. Etoposide is a newer antineoplastic agent that is effective in the treatment of HD. However, little is known regarding its testicular toxicity, especially in the pediatric age group. METHODS: The authors evaluated testicular function in 46 young adults in first continuous complete remission after stage-dependent treatment for HD with the vincristine, etoposide, prednisone, and doxorubicin (OEPA) or OEPA/cyclophosphamide, vincristine, procarbazine, and prednisone [COPP] chemotherapy regimens and involved field irradiation, excluding patients with ilioinguinal radiotherapy. Pubertal development was documented and a standardized intravenous gonadotropin-releasing hormone test was performed measuring testosterone and basal and stimulated levels of FSH and luteinizing hormone (LH). RESULTS: Testicular volumes, Tanner stages of pubic hair, and genital development were found to be appropriate or slightly delayed for the patients' chronologic age. All 27 patients had normal basal levels of FSH and LH after treatment of Ann Arbor Stage I-IIA HD with 2 courses of OEPA. Stimulated FSH and LH levels were found to be elevated only in rare patients, thus indicating normal endocrine function and spermatogenesis. However, basal and stimulated FSH levels were outside the +2 standard deviation range in 37.5% and 83.3% of patients receiving 2 cycles of OEPA and 2 cycles of COPP chemotherapy, and in 36.4% and 66.7% of patients receiving 2 cycles of OEPA and 4 cycles of COPP chemotherapy, demonstrating a high risk of oligospermia or azoospermia with these regimens. Basal LH levels essentially were normal, whereas stimulated LH levels frequently were elevated. CONCLUSIONS: Testicular function was found to be normal in patients with Stage I-IIA HD when etoposide was used in combination with vincristine, prednisone, and doxorubicin (2 cycles of OEPA). Additional chemotherapy with cyclophosphamide and procarbazine (2 cycles of OEPA and 2 or 4 cycles of COPP) negatively affected spermatogenesis and possibly Leydig cell function in a considerable number of patients. This major gonadotoxic effect most likely is due to procarbazine, although an additional effect of etoposide and cyclophosphamide cannot be excluded.     

Stimulus variables in the block design task: A commentary on Schorr, Bower, and Kiernan.

Contends that the block design task by D. Schorr et al (see record 1982-27118-001) replicates the earlier findings of the author and his colleague K. Weitzel (see PA, Vols 58:2589; 61:10327; and 61:12312). In addition, Schorr et al introduce a new paradigm to continue isolating information-processing components of the task. The present author takes issue with their finding regarding synthetic and analytic strategies because these terms are too global to advance knowledge of cognitive processes. (6 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lamb wave graphic tablet

A graphic sensor based on the measurement of the propagation time of an acoustic wave train is described. Lamb waves are launched in a plate of ordinary glass by piezoelectric bars bonded to the edges of the plate. They are detected at their arrival under the tip of the drawing pencil by a small piezoelectric disc placed in the pencil body. The useful area of the tablet is 19×27 cm2; the resolution is about 0.2 mm.