Interfacing capillary gel microfluidic chips with infrared laser desorption mass spectrometry

We report on the fabrication and performance of a gel microfluidic chip interfaced to laser desorption/ionization (LDI) mass spectrometry with a time-of-flight mass analyzer. The chip was fabricated from poly(methylmethacrylate) with a poly(dimethyl siloxane) cover. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was performed in the channel of the microfluidic chip. After electrophoresis, the cover was removed and either the PDMS chip or the PMMA cover was mounted in a modified MALDI ion source for analysis. Ions were formed by irradiating the channel with 2.95 microm radiation from a pulsed optical parametric oscillator (OPO), which is coincident with IR absorption by N-H and O-H stretch of the gel components. No matrix was added. The microfluidic chip design allowed a decrease in the volume of material required for analysis over conventional gel slabs, thus enabling improvement in the detection limit to a pmol level, a three orders of magnitude improvement over previous studies in which desorption was achieved from an excised section of a conventional gel.     

Optical characteristics of m-plane InGaN/GaN multiple quantum well grown on LiAlO2 (1 0 0) by MOVPE

We investigate the optical properties of m-plane InGaN/GaN multiple quantum well grown on LiAlO₂ substrate by metal organic vapor phase epitaxy. Polarization-dependent photoluminescence and polarization-dependent photoluminescence excitation measurements have been performed at low temperature to study the optical absorption and emission characteristics. The main emission band possesses large polarization anisotropy which may be attributed to the anisotropic biaxial strain. We found the optical emission is not influenced by the polarization-induced electric field from the excitation-dependent photoluminescence measurements. From our results, we attribute the low-temperature emission band around 3.2 eV to interband transition in the quantum well. Besides, the mechanism of the main emission band is associated with interband transition and subsequent carrier localization. The realization of good-quality non-polar GaN-based devices can then be expected in near future.     

High-lift airfoil trailing edge separation control using a single dielectric barrier discharge plasma actuator

Control of flow separation from the deflected flap of a high-lift airfoil up to Reynolds numbers of 240,000 (15 m/s) is explored using a single dielectric barrier discharge (DBD) plasma actuator near the flap shoulder. Results show that the plasma discharge can increase or reduce the size of the time-averaged separated region over the flap depending on the frequency of actuation. High-frequency actuation, referred to here as quasi-steady forcing, slightly delays separation while lengthening and flattening the separated region without drastically increasing the measured lift. The actuator is found to be most effective for increasing lift when operated in an unsteady fashion at the natural oscillation frequency of the trailing edge flow field. Results indicate that the primary control mechanism in this configuration is an enhancement of the natural vortex shedding that promotes further momentum transfer between the freestream and separated region. Based on these results, different modulation waveforms for creating unsteady DBD plasma-induced flows are investigated in an effort to improve control authority. Subsequent measurements show that modulation using duty cycles of 50–70% generates stronger velocity perturbations than sinusoidal modulation in quiescent conditions at the expense of an increased power requirement. Investigation of these modulation waveforms for trailing edge separation control similarly shows that additional increases in lift can be obtained. The dependence of these results on the actuator carrier and modulation frequencies is discussed in detail.     

Theory of polarization rotation and conversion in verticallycoupled microresonators

Two orthogonally polarized waveguide modes can exchange power through an intermediate level, if the polarization state of that level is tilted with respect to the polarization states of the waveguide. Microrings with modest sidewall angles support such tilted modes. Ultracompact, wavelength selective polarization rotators might be achieved. Simple analytic expressions are derived for polarization rotation by vertically-coupled resonators in terms of geometrical factors     

A microwave-excited strontium-ion (λ430.5 nm) recombination laser

Laser oscillation on the 430.5 nm transition of Sr⁺, which replies on three-body electron-ion recombination for its excitation, has been achieved in a pulsed, selfheated, microwave-pumped discharge.     

A simple multiple beam lo coupler for SIS heterodyne arrays

The construction of SIS heterodyne imaging arrays for submillimetre wave-lengths requires multiple coupling of the local oscillator signal. The quasi-optical analogue of a multiple cross-guide coupler, employing 45° beam-splitters successively stacked along the local oscillator beam, allows for individual adjustment of local oscillator power to each channel. We analyse the coupling as a function of the focal ratio of the incident beams and the number of beam widths off-axis through which the coupler is extended, and describe a simple construction method to realise a compact and effective design.     

No graph has a maximal 3-ring of bonds

It is shown that no graph contains a maximal 3-ring of bonds.     

Matrix-free infrared soft laser desorption/ionization

Infrared soft laser desorption/ionization was performed using a 2.94 µm Er : YAG laser and a commercial reflectron time-of-flight mass spectrometer. The instrument was modified so that a 337 nm nitrogen laser could be used concurrently with the IR laser to interrogate samples. Matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization and desorption/ionization on silicon with UV and IR lasers were compared. Various target materials were tested for IR soft desorption ionization, including stainless steel, aluminum, copper, silicon, porous silicon and polyethylene. Silicon surfaces gave the best performance in terms of signal level and low-mass interference. The internal energy resultant of the desorption/ionization was assessed using the easily fragmented vitamin B₁₂ molecule. IR ionization produced more analyte fragmentation than UV-MALDI analysis. Fragmentation from matrix-free IR desorption from silicon was comparable to that from IR-MALDI. The results are interpreted as soft laser desorption and ionization resulting from the absorption of the IR laser energy by the analyte and associated solvent molecules. Copyright © 2004 John Wiley & Sons, Ltd.     

Characteristics of pulsed discharges in copper bromide and copperHyBrID lasers

Comparative measurements of discharge electrical waveforms have been carried out with a Ne-H₂-CuBr laser, a Ne-CuBr laser, and a Cu HyBrID laser, each of the same size and geometry, and under the same conditions of excitation. From the general similarity of the electrical characteristics of the HyBrID laser and the Ne-H₂-CuBr laser, together with a reappraisal of the role of hydrogen, it is concluded that the main characteristics of these lasers (high efficiency, high average output power, and special features of their excitation pulse waveforms) can all be qualitatively explained if we assume that HBr and not hydrogen (molecular, atomic, or ionic) is the responsible agent which acts via the process of dissociative attachment of electrons to HBr during the interpulse period and during the early stages of the discharge current pulse     

On a Conjecture on Directed Cycles in a Directed Bipartite Graph

Let D = (V ₁, V ₂; A) be a directed bipartite graph with |V ₁| = |V ₂| = n ≥ 2. Suppose that d _D (x) + d _D (y) ≥ 3n for all x ∈ V ₁ and y ∈ V ₂. Then, with one exception, D contains two vertex-disjoint directed cycles of lengths 2n ₁ and 2n ₂, respectively, for any positive integer partition n = n ₁ + n ₂. This proves a conjecture proposed in [9].