Alexander Nesterov

Influence of beam polarization on laser cutting efficiency

The three-dimensional (3D) theory of laser cutting is presented. The cutting efficiency determined by its ultimate parameters at different types of polarization is estimated. The physical reasons for limitations of ultimate cutting parameters at a plane P-polarized beam are displayed. In the case of cutting metals with a large ratio of sheet thickness to width of the cut, the laser cutting efficiency for a radially polarized beam is 1.5 - 2 times larger than for plane P-polarized and circularly polarized beams. The possibility of generating the radially polarized beam is discussed.

Generation of high-power radially polarized beam

Radially polarized radiation of 1.8 kW was first obtained in an industrial high-power CO2 laser. Special reflective elements with an axial polarization selectivity of 22% were used as a rear mirror in the laser. The output radiation consisted mainly of an unpolarized mode TEM00 and a radially polarized mode R-TEM01*.

Combinatorial Synthesis of Peptide Arrays onto a Microchip

Arrays promise to advance biology through parallel screening for binding partners. We show the combinatorial in situ synthesis of 40,000 peptide spots per square centimeter on a microchip. Our variant Merrifield synthesis immobilizes activated amino acids as monomers within particles, which are successively attracted by electric fields generated on each pixel electrode of the chip. With all different amino acids addressed, particles are melted at once to initiate coupling. Repetitive coupling cycles should allow for the translation of whole proteomes into arrays of overlapping peptides that could be used for proteome research and antibody profiling.

Combinatorial synthesis of peptide arrays with a laser printer

however, thedecodingofpeptidebindersislaborintensive.Furthermore,problematicpeptides,forexample,hydrophobicpeptidesthatbind nonspecifically to any protein, are also synthesizedduringlibrarypreparationbythesemethods.Arrays do not have these drawbacks. The position of agivenpeptideonanarraycorrespondsdirectlytoitssequence,and problematic peptides can be omitted in subsequentarrays. Peptide arrays were first described by Frank, whosespotsynthesisdominatesthefieldbecauseofitsreliabilityandwideapplicability.

High-density peptide arrays.

Arrays promise to advance biology by allowing parallel screening for many different binding partners. Meanwhile, lithographic methods enable combinatorial synthesis of > 50,000 oligonucleotides per cm(2), an advance that has revolutionized the whole field of genomics. A similar development is expected for the field of proteomics, provided that affordable, very high-density peptide arrays are available. However, peptide arrays lag behind oligonucleotide arrays. This review discusses recent developments in the field with an emphasis on methods that lead to very high-density peptide arrays.

Simulation study of the influence of polymer modified anodes on organic LED performance

Abstract It is well known from the literature that the performance of organic light-emitting diodes (OLEDs) can be improved significantly by introducing a highly (p + ) doped polymer layer between the (ITO) anode and the hole transport layer (HTL). Until now for the origin of such improved performance, only descriptive explanations have been presented. Therefore, in this paper numerical simulations of the diode currents and of the corresponding internal profiles of concentrations and potentials are presented. The main parameters, anode work function determining the hole barrier, doping of the HTL and of the p + -layer, thickness of the layers, mobility, and the valence band edge (or the ionization energy) of the p + -layer have been varied. Already for the mono-HTL device the current characteristics exhibits a large variety of peculiarities which are explained on the basis of the internal potential and concentration profiles. Conditions are formulated under which a p + -layer at the anode does lead to higher currents. If the p + -layer is made from the same material as the HTL, a moderate increase is possible if the barrier between the anode and the HTL is large. In this case, an increase of the mobility due to the doping will lead to an additional (roughly proportional) increase of the current. Introduction of a p + -hetero-layer with a lower ionization energy (the valence band edge higher than in the HTL) reduces the barrier at the anode and at the same time, an additional barrier does occur at the hetero-junction to the HTL. Both influence the current in opposite directions and hence there will exist an optimum for the valence band offset between the p + -layer and the HTL. If one has from the beginning a rather low barrier between the anode and the HTL (or sufficiently large anode work function) one has already an accumulation contact which cannot be significantly improved by higher doping of the HTL near the anode and becomes even worse by using for the p + -layer a material with an ionization energy lower than that one of the HTL.

Particle-Based Synthesis of Peptide Arrays

High‐density peptide arrays with solid amino acid particles: Intermittent “freezing” of activated amino acid derivatives within solid particles allows a laser printer or a chip to spatially address these “postal packages”. Subsequent parallel coupling is started simply by melting a whole layer of 20 different amino acid particles, freeing the hitherto immobilized amino acids and resulting in the coupling of all 20 different amino acids to the support in a single coupling step.

A plane-wave boundary method for analysis of bent optical waveguides

A plane-wave boundary method is proposed for the analysis of bent optical waveguides. The realization of the method is based on the equivalent straight waveguide approach and consists of two steps. At first, the plane-wave boundary condition is introduced at the computational boundary where the outgoing wave is expected. Then, the optimum location of the computational boundary is determined, corresponding to the maximum of radiation power loss. The optimized computational window helps to significantly reduce the influence of the nonphysical reflections of the outgoing wave caused by the particular index profile of bent waveguide structures in the straight waveguide approach. Using this method, the propagation constants and radiation losses are determined for waveguides with different bend radii. In contrast to methods based on the absorption concept, the proposed method does not require the introduction of additional parameters.

Simulation of organic light emitting diodes: influence of charges localized near the electrodes

In spite of experimental evidence for the formation of charged layers near the electrodes of organic light emitting diodes (OLED), the influence of such layers on the OLED performance has not yet been clarified. This article presents a simulation study of this subject, utilizing the drift-diffusion model. In order to understand the principal mechanism of the influence of such layers, only monolayer devices with unintentional low p-doping are considered. In this case, positively charged layers near the anode or the cathode modify the current voltage characteristics for areal charges above some critical value. Effectively, such areal charges create an additional barrier of a magnitude which depends on the applied bias. A fixed positive areal charge near the anode decreases the current. However, due to the additional bias-dependent barrier, with increasing forward bias one has then a rather strong increase of the current resembling trap assisted space charge limited current. A fixed positive areal charge near the cathode leads to an increase of the build-in potential compared to the ideal thin-layer value which is given by the work function difference of the electrodes. The possibility of compensating the effect of the fixed positive charge with the help of a p-doped layer is discussed.

Noncontact charge measurement of moving microparticles contacting dielectric surfaces

In this study examples for a noncontact procedure that allow the description of instant electric charging of moving microparticles that contact dielectric surfaces, for instance, of a flow hose are presented. The described principle is based on the measurement of induced currents in grounded metal wire probes, as moving particles pass close to the probe. The feasibility of the approach was tested with laser printer toner particles of a given size for different basic particle flow and charging conditions. An analytic description for the induced currents was developed and compared to observed effects in order to interpret the results qualitatively. The implementation of the presented procedure can be applied to transparent and nontransparent particle containers and flow lines of complex geometry which can be composed from the presented basic flow stream configurations.