On Descartes’ rule for polynomials with two variations of signs

Lithuanian Mathematical Journal - For sequences of d + 1 signs + and ? beginning with a + and having exactly two variations of sign, we give some sufficient conditions for the (non)existence...     

Isomeric transitions between shape coexisting states in iodine isotopes withA=115, 119 and 121

Applying delayed- r.f. coincidences and generalized centroid-shift analysis, nanosecond isomers in some odd-A iodine isotopes are studied in-beam. The reactions¹⁰⁶Cd(¹²C,p2n) and^116,118Sn(⁶Li,3n) have been used. The following half-lives were determined:T _1/2(565 keV)=0.50±0.10 ns andT _1/2(837 keV) =0.90±0.20 ns in¹¹⁵I,T _1/2(687 keV)=5.50±0.50 ns andT _1/2(2418 keV)=4.0±0.50 ns in¹¹⁹I as well asT _1/2(812 keV)=0.35±0.20 ns andT _1/2(445 keV)<0.10 ns=">¹²¹I. A systematics of the absolute probabilities for the transitions deexciting theg _9/2 9/2⁺ and _11/2 11/2 ₁ ^– band heads in^115–125I is presented and discussed.Partly supported by the Bulgarian National Research Foundation under contracts PH14, and PH31 and Kernforschungszentrum Karlsruhe, Stabsabteilung Internationale Beziehungen     

Novel fluoroacrylated copolymers: synthesis, characterization and properties

The development of polymer waveguides leads to synthesis of fluorinated amorphous polymers with high transmission capacity, potential to tune their optical properties by tailoring the molecular structure, together with good processability, easy handling, good flexibility and low cost.In this work we have investigated new thermoplastic fluoroacrylated copolymers, synthesized by radical copolymerization of fluoroalkene(s) with five-membered cyclic carbonate and a third monomer or transfer agent, both containing OH group susceptible to be used for grafting of photocrosslinkable groups. The reaction of hydroxy functionalized copolymers with different acrylating agents results in fluoroacrylated resins with molecular weight in the range of 2000-3000 g mol⁻¹, yield >75% and good solubility in reactive diluents. In the presence of photoinitiator(s), they were crosslinked under UV-radiation in order to obtain optical waveguides.The copolymers synthesized were characterized by ¹H, ¹⁹F and ¹³C NMR as well as FT-IR spectroscopies and have good thermal stability (T_d > 200 °C). The refractive indeces of hydroxy functionalized fluorooligomers and acrylated resins were found to range from 1.44 to 1.45 at 23 °C and the T_gs (by DSC) varied from 40 to 110 °C depending on the content of the cyclic monomer. The optical characteristics of these thermoplastic fluoroacrylated copolymers are under progress.     

Acetylene adsorption on a clean iridium surface

The interaction of C₂H₂ with a polycrystalline iridium surface at 140 KT500 K has been studied by AES, XPS and UPS. A model of the bonding between C₂H₂ and Ir by the 1 orbitals of the hydrocarbon is proposed. The more pronounced energy splitting between the orbitals of acetylene during adsorption compared to that in the gas phase is ascribed to deformation of the acetylene molecule.

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C₂H₂ . 140 KT500 K AES, XPS UPS. C₂H₂ Ir 1- . - , , .

     

The half-life of the 1437 keV 11/2− state in97Mo

Using the (,n) reaction, the half-life of the first 11/2^– level in⁹⁷Mo has been determined as T_1/2(1437.0 keV)=2.5±0.3 ns by means of the pulsed beam method. The experimentally obtainedB(M2) value between theh _11/2 andg _7/2 configurations in⁹⁷Mo has been satisfactorily described within the quasiparticle-phonon model usingg _s ^eff =0.6g _s ^free . Similar calculations and comparisons with experminental data have been performed also for^95,99Mo as well as for⁹⁹Ru and¹⁰¹Pd.This work is partly supported by the Bulgarian National Research Foundation     

A functional model for polynomially posinormal operators

In this paper we introduce a class of operators naturally extending the classes of hyponormal and posinormal operators. For this class we construct a generating family of eigendistributions, unitary invariants and a functional model.     

Reversible unfolding of poplar iso-plastocyanins

We attempted to determine the experimental conditions under which poplar plastocyanin iso-forms PCa and PCb undergo reversible thermal unfolding studied by differential scanning calorimetry (DSC). Our results indicate that an exothermic unfolding process exists always in the presence of molecular oxygen. Reversible unfolding and almost perfect two-state transitions were exhibited in the presence of TCEP under anaerobic conditions. This suggests that the second endothermic peak is due to copper-site disulfide dimmers formed during thermal denaturation. The conformational thermal stability of reduced PCb (ΔG (25 °C) = 33.9 kJ mol⁻¹) has proven to be higher than that of reduced PCa (ΔG(25 °C) = 22.9 kJ mol⁻¹).     

Some kinetic aspects regarding the preparation of telomeric ω-hydroperfluoroalkanols

Telomerization of tetrafluoroethylene (TFE) with methanol in the presence of a free-radical initiator such as α, α′-azoisobutyronitrile (AIBN) has been carried out. The product composition was related to kinetic equations involving the chaintransfer coefficients and the concentration of telomeric fluoroalkanols obtained.