Reactions of N-substituted allylacetic acid amides with selenium and tellurium tetrahalides

The addition of selenium tetrabromide to the olefinic bond of N-substituted allylacetic acid amides (reagent molar ratio 21) proceeds counter to Markownikoff's rule with the formation of tetrahydrofuran derivatives. The addition of tellurium tetrahalides under the same conditions (reagent molar ratio 11) proceeds in accordance with Markownikoff's rule with the formation of tetrahydropyran derivatives.Communication 10 in the series Electrophilic reactions of halides of elements of the sixth group; see [1] for Communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 743–745, June, 1989.     

Note on flow instability in heated ducts

Zusammenfassung Das Problem der Stabilität der Strömung durch beheizte horizontale Kanäle gegen zweidimensionale Störungen wird in linearisierter Form als Variationsaufgabe behandelt. Die Abhängigkeit der Stabilitätsparameter von der Gestalt des Kanals wird untersucht und verglichen mit dem Fall der Stabilität der von unten beheizten Flüssigkeitsschicht.     

Experimental investigation of the 2.1-μm single-mode Tm-Ho:KYF laser

We report on the development and comprehensive characterization of a room-temperature single-mode 2-m Tm-Ho:KYF laser. A maximum CW output power of 70 mW at the central wavelength of 2.078 m has been obtained. Using a 5-mm long intracavity birefringent filter the single-mode emission wavelength can be tuned over a range of 40 nm. Both frequency and relative intensity noise have been investigated showing a 1-ms emission linewidth of 600 kHz and an intensity noise spectrum that is quantum-noise limited for Fourier frequencies higher than 1 MHz. PACS 42.55Xi; 42.55Rz; 42.60Pk; 42.70Hj; 42.60Lh     

Widely tunable continuous-wave diode-pumped 2-microm Tm-Ho:KYF4 laser

Continuous-wave laser action at approximately 2 microm is demonstrated in a Tm-Ho:KYF4 single crystal at room temperature. Crystal growth, spectroscopic measurements, and laser results are presented. An output power in excess of 250 mW is obtained with a tuning range of 99 nm, the largest ever published, to our knowledge, for Tm-Ho in any crystalline host.     

Sub-100-ps amplitude-modulation mode-locked Tm-Ho:BaY2F8 laser at 2.06 microm

We report the generation of sub-100-ps pulse trains near the 2.06-microm wavelength in an actively mode-locked diode-pumped Tm-Ho:BaYF laser operating at room temperature. Transform-limited, 97-ps Gaussian pulses at a 100-MHz repetition rate with an average power in excess of 20 mW and with a carrier wavelength tunable by approximately 50 nm near 2.066 microm are demonstrated.     

Phase evolution and magnetic properties of Co/α-Fe2O3 powder mixtures with different molar ratios treated by mechanical alloying

In this work, we report the phase formation and magnetic properties of Co–hematite powder mixtures with two different molar ratios: Co/α-Fe₂O₃: 1/0.7 and 1/1.3 subjected to high-energy mechanical milling using metallic cobalt and hematite powder as the initial raw material in ambient air atmosphere. The samples were activated with a ball to powder weight ratio (BPR) of 10 and the milled powders were collected after 0, 1, 5, 15, 25 and 30 h. Various characterization techniques such as XRD, HRTEM, VSM and Mössbauer spectroscopy were utilized to study the prepared samples. For the samples with Co/α-Fe₂O₃: 1/0.7 milled for 1 and 5 h the formation of cobalt ferrite was confirmed. However, this was not the case for the samples milled above 5 h for whose both Mössbauer and XRD results confirmed the phase decomposition taken place for the previously formed cobalt ferrite phase. Further, the formation of superparamagnetic nanoclusters of iron oxide, a wustite-like Fe_1?XCo_XO phase and the existence of small amounts of metallic Fe/Fe_1?XCo_X phase/s were also detected for these samples. The presence of the latter phase is not believed to be solely related to contamination from the steel vial/balls used. A mechanochemical-reduction process is assumed to be also possibly responsible for the formation of the observed reduced phases. For the powder mixture with Co/α-Fe₂O₃: 1/1.3, however, increased formation of cobalt ferrite phase was observed by increasing the milling time. The highest maximum magnetization (53 e.m.u/g) and coercive field (500 Oe) was obtained for the sample milled for 25 h among various samples of this series of powder mixture. The lower magnetization obtained for this sample compared to that of the bulk is attributed to the size effect. Furthermore, the structural–magnetic properties relationship of the various powders prepared is discussed in detail.     

MILD: a laser altimeter transmitter for a Mercury planetary orbiter

We report on the design and preliminary development of a micro laser (MILD) breadboard (BB). The laser source is designed to be used as the transmitter unit of a laser altimeter for planetary investigations. The reference scenario is the ESA BepiColombo mission to Mercury (presently scheduled to be launched in 2012) but possible applications to minor solar system bodies may be included. In order to fulfil the laser source requirements for this kind of application we adopted a master-oscillator-power-amplifier (MOPA) scheme. Analysis of the MO efficiency, pulse duration and beam characterisation in different resonator configurations is described together with the preliminary PA performance on a ± 10 °C temperature range. PACS  42.55.Xi; 42.60.By; 42.60.Da     

Asymptotic Information-Theoretic Detection of Dynamical Organization in Complex Systems

The identification of emergent structures in complex dynamical systems is a formidable challenge. We propose a computationally efficient methodology to address such a challenge, based on modeling the state of the system as a set of random variables. Specifically, we present a sieving algorithm to navigate the huge space of all subsets of variables and compare them in terms of a simple index that can be computed without resorting to simulations. We obtain such a simple index by studying the asymptotic distribution of an information-theoretic measure of coordination among variables, when there is no coordination at all, which allows us to fairly compare subsets of variables having different cardinalities. We show that increasing the number of observations allows the identification of larger and larger subsets. As an example of relevant application, we make use of a paradigmatic case regarding the identification of groups in autocatalytic sets of reactions, a chemical situation related to the origin of life problem.     

Synthesis of dialkyl 5-(aryl)-1-phenyl-1H-prazole-3,4-dicarboxylates via a one-pot and four-component reaction

A number of new dialkyl 5-(aryl)-1-phenyl-1H-prazole-3,4-dicarboxylate derivatives have been prepared regiospecifically in moderate to good yield from the cyclocondensation reaction of dialkyl (E)-2-(dialkoxyphosphoryl)-3-(aroyl)-2-butenedioate, derived from the reaction between trimethyl phosphite, an acetylenic ester, and an aroyl chloride, with phenylhydrazine. The reaction is four-component and is carried out under reflux conditions in dry toluene.     

Separation/preconcentration and determination of vanadium with dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) and electrothermal atomic absorption spectrometry

A novel dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) for separation/preconcentration of ultra trace amount of vanadium and its determination with the electrothermal atomic absorption spectrometry (ETAAS) was developed. The DLLME-SFO behavior of vanadium (V) using N-benzoyl-N-phenylhydroxylamine (BPHA) as complexing agent was systematically investigated. The factors influencing the complex formation and extraction by DLLME-SFO method were optimized. Under the optimized conditions: 100 μL, 200 μL and 25 mL of extraction solvent (1-undecanol), disperser solvent (acetone) and sample volume, respectively, an enrichment factor of 184, a detection limit (based on 3S_b/m) of 7 ng L⁻¹ and a relative standard deviation of 4.6% (at 500 ng L⁻¹) were obtained. The calibration graph using the preconcentration system for vanadium was linear from 20 to 1000 ng L⁻¹ with a correlation coefficient of 0.9996. The method was successfully applied for the determination of vanadium in water and parsley.