Filament temperature stabilizer for a thermal ionization mass spectrometer

A major enhancement in temperature stabilization of a filament has recently been achieved by means of the Halas–Kami ski bridge, in which the reference resistance of one leg is directly proportional to the filament temperature. In this article we describe a novel version of this type of electronic circuit which feeds dc power voltage to the filament via a switching transistor. The switching frequency is regulated by means of a triangular waveform generator incorporated into the system. The duration of the heating peak (square wave) is automatically adjusted properly once at each break between two subsequently appearing heating peaks, which is the interval when the bridge imbalance signal is measured. At the end of each break the bridge imbalance signal is kept on the output of the sample-and-hold amplifier. This signal compared with the generator output voltage provides the square wave for the switching transistor. The application of this circuit for a thermal ionization mass spectrometry is simple and straightforward. The filament temperature is set by two decade low-ohm resistors. Long-term variance of the ion current is approximately 5 times lower than that obtained by use of a commercial voltage stabilizer for the filament supply. It is shown theoretically that stabilization of the filament resistance results in the lowest possible variance of temperature.     

Boundary Hemivariational Inequalities of Hyperbolic Type and Applications

In this paper we examine two classes of nonlinear hyperbolic initial boundary value problems with nonmonotone multivalued boundary conditions characterized by the Clarke subdifferential. We prove two existence results for multidimensional hemivariational inequalities: one for the inequalities with relation between reaction and velocity and the other for the expressions containing the reaction–displacement law. The existence of weak solutions is established by using a surjectivity result for pseudomonotone operators and a priori estimates. We present also an example of dynamic viscoelastic contact problem in mechanics which illustrate the applicability of our results.Mathematics Subject Classifications (2000). 34G20, 35A15, 35L85, 35L70, 74H20     

On approximation methods of Leonardo Fibonacci

As is well known, Leonardo da Pisa gave a very precise approximation for the only irrational root of the equation x³ + 2x² + 10x = 20. Two hypotheses concerning his method were put forward in the XIX century. With good reason they were criticized by M. Cantor in his Vorlesungen. In the present paper it is argued that Leonardo calculated his approximate value using step-by-step the rule of two false positions. Our argument is based on an analysis of all approximation methods used by him.     

Twisted homology of symmetric groups

We study the homology of symmetric groups with coefficients coming from the functor . We are primarily interested in the limit where . Our main goal is to compare the described above situation with the case of general linear groups.

     

Nucleic acid related compounds. 114. Synthesis of 2,6‐(disubstituted)purine 2′,3′‐dideoxynucleosides and selected cytotoxic,anti‐hepatitis b,and adenosine deaminase substrate activities

Selected 2,6‐(disubstituted)purine 2′,3′‐didehydro‐2′,3′‐dideoxynucleosides and 2′,3′‐dideoxynucleosides were prepared and evaluated. Treatment of 5′‐protected ribonucleosides with phenoxythiocarbonyl chloride and 4‐(dimethylamino)pyridine, or under Schotten‐Baumann conditions, gave high yields of 2′,3′‐O‐thiono‐carbonates that underwent Corey‐Winter elimination. Treatment of unprotected ribonucleosides with α‐ace‐toxyisobutyryl bromide in “moist” acetonitrile gave trans 2′,3′‐bromohydrin acetate mixtures that underwent reductive elimination with zinc‐copper couple or zinc/acetic acid. Catalytic hydrogenation of the resulting 2′,3′‐enes gave 2′,3′‐dideoxynucleosides. Treatment of the 2‐amino‐6‐chloropurine and 6‐amino‐2‐fluoro‐purine derivatives with nucleophiles gave 2,6‐(disubstituted)purine 2′,3′‐dideoxynucleosides. 2′,3′‐Dideoxyguanosine and the 2‐amino‐6‐[amino ( 16d ), methoxy ( 16b ), ethoxy ( 16c ), and methylamino ( 16j )]purine 2′,3′‐dideoxynucleosides showed good anti‐hepatitis B activity with infected primary duck hepatocytes. Cytotoxic effects with selected analogues were evaluated in human T‐lymphoblastic and promyelocytic leukemia cell lines. The 2‐amino‐6‐fluoro derivative 16m was the most cytotoxic of the 2‐amino‐6‐(substituted)purine 2′,3′‐dideoxynucleosides, and 2‐fluoro‐2′,3′‐dideoxyadenosine ( 21a ) was the most cytotoxic compound. The order of efficiency of hydrolysis of the 6‐substituent from 2‐amino‐6‐(sub‐stituted)purine 2′,3′‐dideoxynucleosides (V_max/K_m) with adenosine deaminase from calf intestine was: 2‐amino‐6‐[amino ( 16d ) > methoxy ( 16b ) > ethoxy ( 16c )], all of which were ≤3% of the efficiency with adenosine. The 6‐methylamino derivative 16j , as well as 16b , 16c , and 16d were readily converted into 2′,3′‐dideoxyguanosine by duck cell supernatants.     

Biodegradable Polyesters for Tissue Engineering

Summary: Paper describes basic characteristics of synthesis and properties of aliphatic polyesters used for tissue engineering. Described is also synthesis of polyester containing block copolymers suitable for surface modification. Described are methods used for scaffold fabrication with required porosity. In particular, presented are methods according to which scaffolds are made from prefabricated polyester micro- and nanoparticles.     

Polycondensation of diglycerol with H3PO4. Reversibly degradable gels giving multireactive,highly branched macromolecules

Polycondensation of H₃PO₄ with diglycerol (DGL) involves biobased, commercial products and leads, via hydrolyzable gels, to highly branched reactive macromolecules. These reactive macromolecules have been applied as multiacidic catalysts with hydroxyl groups in polymerization of l ‐lactide, consuming entirely the starting highly branched macromolecules. Polycondensation was performed in bulk, at 110–120 °C with efficient elimination of water under vacuum. The process with DGL differs substantially from the previously studied polycondensation with ethylene glycol and glycerol. Formation of pyrophosphoric acid (PY) constitutes the rate determining step: the rate of PY formation is the same in the absence and presence of DGL. Kinetic studies explained why the rate of monoesters (M) accumulation may be the same as the rate of accumulation of di‐ (D), and triesters (T). This is because the rate of M formation is relatively low when compared with rates of further reactions of M, leading to D and T. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3303–3317     

Criterion on stability for Markov processes applied to a model with jumps

We formulate and prove a new criterion for stability of e-processes. In particular we show that any e-process which is averagely bounded and concentrating is asymptotically stable. This general result is applied to a stochastic process with jumps that is a continuous counterpart of the chain considered in Szarek (Ann. Probab. 34:1849–1863, 2006).