Measurement of the helicity of W bosons in top quark decays

We use the transverse momentum spectrum of leptons in the decay chain t-->bW with W-->lnu to measure the helicity of the W bosons in the top quark rest frame. Our measurement uses a t&tmacr; sample isolated in 106+/-4 pb(-1) of data collected in p&pmacr; collisions at sqrt[s] = 1.8 TeV with the CDF detector at the Fermilab Tevatron. Assuming a standard V-A weak decay, we find that the fraction of W's with zero helicity in the top rest frame is F0 = 0.91+/-0. 37(stat)+/-0.13(syst), consistent with the standard model prediction of F0 = 0.70 for a top mass of 175 GeV/c(2).     

Search for scalar top quark production in p&pmacr; collisions at sqrt

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb(-1) of p&pmacr; collisions at sqrt[s] = 1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c(2) and scalar neutrino masses of at least 40 GeV/c(2), we find no evidence for scalar top production and present upper limits on the production cross section in both decay scenarios.     

Lipolysis by phospholipase A2 of monomolecular mixed films of natural lipids

A study is made of the enzymatic lipolysis by pancreatic phospholipase A₂ and by phospholipase A₂ of Vipera berus on monomolecular films of mixture of natural lipids: cholesterol-egg lecithin and triolein-egg lecithin, by adding serumalbumin to the aqueous subphase in order to imitate the physiological conditions. The influence of the composition of the mixed film and the quantity of the added serumalbumin exerts on the velocity of lipolysis is studied, as well as the surface pressure of the film and the type and the quantity of the injected enzyme. The results obtained are discussed.     

Robustness for Stable Impulsive Equations via Quadratic Lyapunov Functions

For a linear impulsive differential equation, we give a complete characterization of the existence of a nonuniform exponential contraction in terms of quadratic Lyapunov functions and of the operators defining them. This corresponds to consider a nonuniform exponential stability of the dynamics, which is typical for example in the context of ergodic theory. As an application, we use this characterization to establish in a very simple manner the robustness property of a nonuniform exponential contraction under sufficiently small linear perturbations. In addition, we obtain versions of the robustness property for perturbations of the jumping times and of a strong nonuniform exponential contraction. The latter corresponds to consider not only an upper bound for the dynamics but also a lower bound.     

Synthèse de derivès du nitro-5 imidazole potentiellement actifs en chimiothèrapie

The synthesis of six derivatives of 2-methyl-5-nitroimidazole 1-substituted by a CH₂CH₂Het group (Het being a pyridinium or a 1-substituted imidazolium) has been carried out. A careful ¹H and ¹³C nmr study of these compounds and other nitroimidazoles has been made. None of the synthesized compounds show any significant cytostatic kactivity.     

Characterization of cationic surfactant markers and their abiotic degradation products by CGC-EI/PICI MS

Summary The electronic impact (EI) and positive ion chemical ionization (PICI) mechanisms of a variety of environmental relevant secondary and tertiary trialkylamines (TAMs) (NR₁R₂R₃, where R_n=H, CH₃, C₁₄H₂₉, C₁₆H₃₃ or C₁₈H₃₇) have been determined. The base peak of EI mass spectra corresponds to the carbon-carbon bond -cleavage with respect to nitrogen, contrasting with a low abundant molecular ion [M]⁺. On the other hand, the [M-1]⁺ was the base peak of the PICI. In addition, the photoproduct composition of irradiated (>290 nm) TAMs ((CH₃)₂NR, R=C₁₆H₃₃ and C₁₈H₃₇) aqueous solutions in the presence of hydrogen peroxide has been characterized by CGC-MS. In this regard, oxidation products in the vicinal carbons with respect to nitrogen and a variety of photolysis products including fatty acids, aldehydes, alkenes, alkanes and 2-methylketones were identified as major components.     

Analysis of high molecular weight esters and ketones in thymus

A crystalline mixture of esters from Thymus chamaedris is analyzed by mass spectrometry, and after hydrolysis, by gas chromatography. Two series of straight chain even aliphatic acids from C₁₆ to C₂₆, and from C₄₀ to C₄₈, and a series of straight chain even saturated primary alcohols, from C₈ to C₃₀, are its main constituents. Another crystalline mixture, isolated from Thymus caespititius, is shown by mass spectrometry and gas chromatography to be composed of a straight chain series of aliphatic ketones, from C₂₅ to C₃₇.     

Syntheses of both the putative and revised structures of aeruginosin EI461 bearing a new bicyclic alpha-amino acid

[structure: see text] The putative structure of the naturally occurring aquatic peptide aeruginosin EI461 has been prepared from d-tyrosine. A corrected structure for aeruginosin EI461 is proposed, and the structure is proven by synthesis, which was accomplished using the new alpha-amino acid (2S,3aR,6R,7aR)-6-hydroxy-2-carboxyoctahydroindole, prepared from l-tyrosine. Succesive couplings of the dipeptide d-Leu-3a,7a-diepi-l-Choi with l-Hpla and NH(4)OH and a deprotection step gave aeruginosin EI461.