Open problems in queueing theory inspired by datacenter computing

Queueing Systems - Datacenter operations today provide a plethora of new queueing and scheduling problems. The notion of a “job” has become more general and multi-dimensional. The ways...     

Crystal and anion structure, TGA, DTA, and infrared and Raman spectra of managanese(II) nitroprusside dihydrate, Mn [Fe(CN)5NO]·2H2O

The single crystal and anion structure of Mn[Fe(CN)₅NO·2H₂O, obtained by slow interdiffusion of reactant solutions through a TMS gel, was solved by X-ray diffraction methods and refined toR1=0.036. Spatial group: orthorhombic,Pnma,a=14.069(2),b=7.538(1),c=10.543(1)Å,Z=4. The Mn(II) ion and the water molecules are sited on mirror planes, which bisect the nitroprusside ions. One of the water molecules is coordinated to Mn(II) and the other, strongly hydrogen (as acceptor) bonded to the first molecule. The IR spectrum confirms the bonding of the water molecules and TGA results are in accordance with the dihydrate character of the substance and its dehydration in two successive steps. DTA results and the Raman spectrum agree with other results and the comparison between IR and RamanvNO wavenumbers confirms the expected strong vibrational interaction between the closely packed antiparallel (eclipsed) NO groups. There is a topotactic relationship between the dihydrate and the trihydrate, which crystallizes in the space subgroupP2 _1/n.     

Operators of Hankel type

Hankel operators and their symbols, as generalized by V. Pták and P. Vrbová, are considered. The present note provides a parametric labeling of all the Hankel symbols of a given Hankel operator X by means of Schur class functions. The result includes uniqueness criteria and a Schur like formula. As a by-product, a new proof of the existence of Hankel symbols is obtained. The proof is established by associating to the data of the problem a suitable isometry V so that there is a bijective correspondence between the symbols of X and the minimal unitary extensions of V.     

A new synthesis and the electrochemical behaviour of nickel(II) dithiophosphate and dithiophosphinate complexes

Summary The [Ni(S₂PR₂)₂] complexes (R=i-PrO, PhO, or Et) can be conveniently prepared by reaction of [Ni{P(OPh)₃}₄] with [R₂P(S)S]₂ (R=i-PrO, PhO, or Et) in refluxing CHCl₃. The electrochemical behaviour of the complexes in CH₂Cl₂ and MeCN has been studied by cyclic voltammetry and coulometry. The oxidation of complexes at a glassy carbon reveals an e.c. mechanism. The [Ni(S₂PR₂)₂] complexes undergo a one-electron irreversible reduction.     

Synthesis and characterization of cyclopentadienyl transition metal halides,part I,vanadium halides

Summary Reactions between -Cp₂V and PX₃ (X=Cl, Br or I) yield the corresponding dihalogenated derivatives -Cp₂VX₂ (X=Cl, Br or I). The oxidative addition of ICl and IBr to -Cp₂V gives mixed halogenated derivatives -Cp₂VIX (X=Cl or Br). All the compounds have been characterized by elemental analyses, magnetic moment measurements and i.r. and e.p.r. spectra.     

An automatic gas-chromatographic analyser for the determination of the radioactivity of argon,krypton and xenon

An instrumental procedure for the determination of the amount and the radio-activity of argon, krypton and xenon has been worked out and an automatic analyser has been designed. A sample was taken from the residual gases remaining after absorption in a solution of potassium hydroxide. Oxygen was catalytically combusted and carbon monoxide converted to methane in a stream of hydrogen. Argon and krypton were separated on a 5.5 m long column packed with Porapak Q, and xenon was analyzed on a 0.4 m long column of Synachrom G-5 at 0°. The radioactivity of the pure components was measured with a flow-type proportional counter. The system proposed and the analyser can be simply adapted to run off determinations of other admixtures in the coolants of nuclear power plants.     

Copper oxide on Cu/Al2O3-TiO2 catalystsTG,FTIR-CO absorption and catalytic activity in the NO reduction by CO

TG, FTIR-(CO absorption), and catalytic activity in the NO reduction by CO were used to characterize Cu/Al₂O₃-TiO₂ catalysts prepared by co-gelling aluminum tri-sec-butoxide and titanium iso-propoxide at pH 9 and at pH 3 gelling conditions. Under nitrogen flow, copper oxide decomposition, oxygen storage capacity (OSC) and sample dehydroxylation (total mass loss) was followed by TG. The CuO decomposition forming Cu⁰, Cu⁺¹ was observed by means of FTIR (CO absorption) spectra. In pH 9 sample the large amount of Cu⁰ was observed. At low total mass loss and high Cu⁰/Cu⁺¹+Cu⁺² ratio (pH 9 sample) a lowest light-off in the NO reduction by CO was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ionic vs pericyclic transition states for the cyclization reactions of C alpha-N anions derived from amides and phosphinamides

[structure: see text] Ab initio and DFT calculations indicate that the anionic cyclization of vinyl- and phenyl-carboxamides and phosphinamides metalated at the C(alpha)-N carbon fits better to a Michael-type ionic addition than to an electrocyclic ring closure. The lithium atom has no influence on the type of reaction mechanism.     

Thermal and spectral behaviour of a light-cured methacrylate-based composite material used in dentistry

The evolution of the polymerization of a light-cured methacrylate-based composite material (Pekalite) used in dentistry was studied. Fourier transform infrared spectroscopy and thermal analysis (TA) showed that with increasing the photo-polymerization time from 5 to 60 s, the degree of conversion increases from 32.5 to 59.6 % and thermal stability of the composite material increases from 144.6 to 270 °C. Growth of photo-polymerization time from 5 to 60 s produces an improvement in the mechanical strength of the composite material from 153 to 248 MPa. Spectral analysis and TA are two complementary and rapid methods for determining the degree of polymerization of composite materials used in dentistry.