On a Order Reduction Theorem in the Lagrangian Formalism

We provide a new proof of a important theorem in the Lagrangian formalism about necessary and sufficient conditions for a second-order variational system of equations to follow from a first-order Lagrangian.Comment: 9 pages, LATEX, no figures; appear in Il Nuovo Cimento

Nonlinear optical properties of functionalized DNA

Third-order nonlinear optical properties of functionalized deoxyribonucleic acid (DNA) are studied by optical third harmonic generation at 1 0642 nm fundamental wavelength. The studies were performed on thin films of DNA-CTMA and DNA-CTMA doped with a charge transfer molecules DR1 and with a cobalt phthalocyanine. They show that DNA, similarly as synthetic polymers, can be used as matrix for highly active NLO chromophores

Influence of roughness on ZDDP tribofilm formation in boundary lubricated fretting

Influence of initial surface topography on tribofilm formation in ZDDP lubricated contact was analysed. A small displacement fretting tests with sinusoidal motion were carried out in classical sphere/plane configuration. A range of surfaces with different initial roughness were prepared by milling and grinding processes. Tests were carried out using variable displacement method where amplitude of imposed displacement was gradually increased after every 1000 cycles from 2 to 30 µm. The surfaces after tribological tests were measured by interferometric profiler. Main findings confirm that initial roughness has a significant influence on antiwear tribofilm formation in boundary lubricated contact. Tribofilm form faster and require less energy to activate in case of rough surface obtained by milling process than in case of smooth grinded surface. However, in contact lubricated by ZDDP additive a significant transfer of material occurred from plane to sphere specimen

Third-order nonlinear optical response of push-pull azobenzene polymers

The nonlinear optical response of a series of azo-containing side-chain polymers is investigated using Z-scan technique, employing 35 ps and 4 ns laser pulses, at 532 nm. The systems were found to exhibit strong nonlinear optical response, dominated by nonlinear refraction. In all cases, the nonlinear absorption and refraction have been determined and are compared with those of disperse red 1 considered as reference. The corresponding third-order susceptibilities chi((3)) were determined to be as large as 10 (7) and 10 (5) esu under ps and ns laser excitation, respectively. Finally, the results are discussed and compared with other reported data

Effect of poling in Polymers Containing Azobenzene Push–Pull Chromophores on nonlinear optic of second and third order

International audienc

Biopolymer-based material for optical phase conjugation

We present results of optical phase conjugation experiments in modified DNA (deoxyribonucleic acid) - dye system. The system consisted of a biopolymeric matrix made of DNA blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride (CTMA) and doped with a photochromic dye Disperse Red 1. Results were obtained in a typical degenerate four wave mixing experiment. For sample excitation we used linearly polarized light at a wavelength 514.5 nm, delivered by an argon ion (Ar+) laser. The phase conjugated signal which emerged from the sample had rise and fall time constants of a few milliseconds with an excellent reversibility

NLO properties of functionalized DNA thin films

In this paper we investigate the third-order nonlinear optical properties of spin deposited thin films of DNA-based complexes using the optical third harmonic generation (THG) technique at a fundamental wavelength of 1064 nm. We found that the third-order susceptibility, χ(3)(− 3ω;ω,ω,ω), of DNA-based films was about one order of magnitude larger than that of our reference, a pure silica slab. In thin films doped with 5% of the chromophore disperse red 1 (DR1), a two order of magnitude larger value of χ(3)(− 3ω;ω,ω,ω) was observed

Nonlinear Optical Properties of Functionalized DNA-CTMA complexes

International audienc

Gauge Formalism for General Relativity and Fermionic Matter

A new formalism for spinors on curved spaces is developed in the framework of variational calculus on fibre bundles. The theory has the same structure of a gauge theory and describes the interaction between the gravitational field and spinors. An appropriate gauge structure is also given to General Relativity, replacing the metric field with spin frames. Finally, conserved quantities and superpotentials are calculated under a general covariant form.Comment: 18 pages, Plain TEX, revision, explicit expression for superpotential has been adde

Photoinduced Gratings in Functionalized Azo-Carbazole Compounds in Picosecond Regime

We report results of diffraction grating inscription on thin films prepared from epoxy resin doped with azo-carbazole based dyes. Diffraction gratings were recorded at the wavelength 532 nm and monitored through intensity of first order of diffraction (632 nm). Atomic force microscope scans of the gratings show that a surface relief grating also appeared