Simple multiwavelength time-division multiplexed light source for sensing applications

We present a novel multiwavelength, time-division multiplexed laser design that continuously cycles through N spectrally narrow wavelengths, spending a specified, fixed time on each one. The design is based on a matched compressor/stretcher and a custom waveform generator applying modulation preferably to the gain medium. The realization discussed here utilizes a pulsed semiconductor optical amplifier in an all-fiber cavity containing fiber Bragg gratings. The laser cycles through 19 wavelengths in a 44 nm wide spectral band (1333-1377 nm) every 15 micros. The source contains no moving parts, offers high repetition rates, narrow spectral linewidths, and custom spectral profiling of the output.     

Optimal greedy policies for stochastic control models

We introduce the notion of a greedy policy for general stochastic control models. Sufficient conditions for the optimality of the greedy policy for finite and infinite horizon are given. Moreover, we derive error bounds if the greedy policy is not optimal. The main results are illustrated by Bayesian information models, discounted Bayesian search problems, stochastic scheduling problems, single-server queueing networks and deterministic dynamic programs.     

Time-of-flight mass spectrometric analysis of ion formation in hypervelocity impact of organic polymer microspheres: comparison with secondary ion mass spectrometry, (252)Cf mass spectrometry and laser mass spectrometry

Unisized 1.6-microm polystyrene microspheres coated with PEDOT (polyethylene-dioxythiophene) were accelerated to speeds of 6-16 km/s and shot onto a silver target. Either positive or negative ions, both instantaneously formed by the impact process, have been analyzed by time-of-flight mass spectrometry (TOF). Apparently, the processes that control the formation of ions of either polarity depend on the impact velocity. Comparing the results with those of secondary ion mass spectrometry with primary ion energy in both the elastic and the inelastic ((252)Cf-MS) energy loss regimes, some reaction mechanisms of the polymer ions for different energy densities could be elucidated. Some aspects of ion formation are also related to those found in pulsed laser ion generation from these microspheres. This investigation was performed in order to further improve the method of analyzing the organic fraction of interstellar, interplanetary, and cometary dust particles impinging on the targets of the "CIDA" time-of-flight (TOF) mass spectrometers on-board the NASA comet missions "STARDUST" and "CONTOUR".     

Das erste „Lithovanadat”︁: K2{LiVO4}.

The First ?Lithovanadate”?: K₂{LiVO₄} By heating of well ground mixtures of the binary oxides [K₂O, Li₂O, V₂O₅, K:Li: V = 2.2:1.1:1.0; Ni-tube, 900°C, 46 d] colourless monoclinic single crystals of K₂[LiVO₄] have been prepared for the first time: space group C2/m; a = 835.7(1) pm, b = 774.5(1) pm, c = 753,3(1) pm, β = 90.23(1)°. The structure was determined by four-circle diffractometer data [MoKα, 1018 form 1262 I₀ (hkl), R = 8.65%, R_w = 5.67%], parameters see text. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, have been calculated.     

[VCl3(NPPh3)(OPPh3)], ein Phosphaniminato-Komplex von Vanadium(IV)

[VCl₃(NPPh₃)(OPPh₃)], a Phosphorane Iminato Complex of Vanadium(IV) The title compound has been prepared from vanadium tetrachloride and Me₃SiNPPh₃ in the presence of OPPh₃ in CCl₄ solution, forming orange-red, moisture sensitive crystals, which were characterized by an X-ray structure determination. Space group Cc, Z = 4, 2 560 observed unique reflections, R = 0.049. Lattice dimensions at 0°C: a = 1 018(1), b = 1 826(2), c = 1 859(2) pm, β = 93.65(9)° [VCl₃(NPPh₃)(OPPh₃)] forms monomeric molecules, in which the vanadium atom is coordinated in a distorted square pyramidal fashion with the (NPPh₃)^? ligand in apical position. The three chlorine atoms and the oxygen atom of the OPPh₃ molecule occupy the basal positions. The phosphorane iminato group V?N?PPh₃ is nearly linear (bond angle VNP 161.4°), the bond lengths VN (169 pm) and PN (162 pm) correspond with double bonds.     

Assignment of quinone derivatives as the main compound class composing 'interstellar' grains based on both polarity ions detected by the 'Cometary and Interstellar Dust Analyser' (CIDA) onboard the spacecraft STARDUST

The 'Cometary and Interstellar Dust Analyser' (CIDA) is a particle impact time-of-flight mass spectrometer onboard the NASA spacecraft STARDUST. A series of positive and negative ion mass spectra from the impact of (apparently) interstellar dust particles has been collected since 1999. In the meantime laboratory work has been performed to better understand the ion formation processes of organic grains impacting at those speeds (>15 km/s) and to relate them to some other ion formation methods. The key ion types were the negative ions, with some additional information from the positive ions. Here, first the principal ion formation rules are briefly reviewed. Secondly, the common substance class is inferred mainly by the application of exclusion principles, and appears to be partly condensed aromatic and quinonoid compounds with high oxygen and low nitrogen content. Oxygen appears to be present in quinone-type structures with condensed aromatic rings, possibly with furan substructures and some hydroxyl moieties. Some nitrogen may be present in pyrrole- or quinoline-type structures. Considerations of thermodynamics and radiation physics of these dust particles within the solar system are consistent with this interpretation. Quinoenzyme cofactors such as the known compound pyrroloquinoline-quinone (PQQ) and its subconstituents would be expected to yield similar mass spectra.     

Über Vorgänge bei der Bildung des Arsen(V)-sulfids beim Ansäuern von Tetrathioarsenatlösungen

On acidifying of Na₃AsS₄ solution reactive ?AsSH groups are formed which condense under intermolecular elimination of H₂S to form very instable (AsS₃) ions. These intermediary, yellow species give rise to the formation of polymeric As^V sulphide on further acidification.