Thermal multifragmentation in p + Au interactions at 2.16, 3.6 and 8.1 GeV incident energies

Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively. The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The results support a scenario of true thermal multifragmentation of a hot and expanded target spectator. Received: 15 December 1997 / Revised version: 24 April 1998     

Lewis Acid Catalyzed Condensation–Cyclization Cascade: Direct Synthesis of Di/Trifluoromethyl‐1,2,3,4‐tetrahydroquinazolines

Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine‐containing drugs in the market today. Therefore, finding an efficient and cost‐effective method for the direct synthesis of fluorine‐tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one‐pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6‐31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally.     

Bilinear optimality constraints for the cone of positive polynomials

For a proper cone \({{\mathcal K}\subset\mathbb{R}^n}\) and its dual cone \({{\mathcal K}^*}\) the complementary slackness condition \({\langle{\rm {\bf x}},{\rm {\bf s}}\rangle=0}\) defines an n-dimensional manifold \({C({\mathcal K})}\) in the space \({{\mathbb R}^{2n}}\) . When \({{\mathcal K}}\) is a symmetric cone, points in \({C({\mathcal K})}\) must satisfy at least n linearly independent bilinear identities. This fact proves to be useful when optimizing over such cones, therefore it is natural to look for similar bilinear relations for non-symmetric cones. In this paper we define the bilinearity rank of a cone, which is the number of linearly independent bilinear identities valid for points in \({C({\mathcal K})}\) . We examine several well-known cones, in particular the cone of positive polynomials \({{\mathcal P}_{2n+1}}\) and its dual, and show that there are exactly four linearly independent bilinear identities which hold for all \({({\rm {\bf x}},{\rm {\bf s}})\in C({\mathcal P}_{2n+1})}\), regardless of the dimension of the cones. For nonnegative polynomials over an interval or half-line there are only two linearly independent bilinear identities. These results are extended to trigonometric and exponential polynomials. We prove similar results for Müntz polynomials.     

Traditional uses of medicinal plants for respiratory diseases in Transylvania

Inhabitants of some Transylvanian farms in Romania have a valuable archaic knowledge of medicinal plants because of their isolation and the insufficiency of official medical treatment. In this work we present ethnobotanical data about the use of medicinal plant taxa for various respiratory diseases in the villages L?véte and Nagybacon. Altogether 34 plant taxa were documented in L?véte and 26 species in Nagybacon with 15 concordant data of the villages. This information plays an important role in the documentation of the disappearing indigenous medical information of the villages.     

The adsorption of Xe and CO on a Cu (311) single crystal surface

LEED, electron energy loss spectroscopy and surface potential measurements have been used to study the adsorption of Xe and CO on Cu (311). Xe is adsorbed with a heat of 19 ± 2 kJ mol^/t-1. The complete monolayer has a surface potential of 0.58 V and a hexagonal close-packed structure with an interatomic distance of 4.45 ± 0.05 Å. CO gives a positive surface potential increasing with coverage to a maximum of 0.34 V and then falling to 0.22 V at saturation. The heat of adsorption is initially 61 ± 2 kJ mol^?1, falling as the surface potential maximum is approached to about 45 kJ mol^?1. At this coverage streaks appear in the LEED pattern corresponding to an overlayer which is one-dimensionally ordered in the [011̄] direction. Additional CO adsorption causes the heat of adsorption to decrease further and the overlayer structure to be compressed in the [011̄] direction. At saturation the LEED pattern shows extra spots which are tentatively attributed to domains of a new overlayer structure coexisting with the first. Electron energy loss spectra (EELS) of adsorbed CO show two characteristic peaks at 4.5 and 13.5 eV probably arising from transitions between the electronic levels of chemisorbed CO.     

Electron energy loss spectra of the system Cu(311)/CO,Xe

The electron energy loss spectrum of a clean Cu(311) surface has been studied by reflected electrons using primary energies between 30 and 300 eV. The losses obtained are compared with literature values. Loss spectra with adsorbed CO and Xe are also reported. Some assignments of the loss mechanisms have been attempted.     

Quantum mechanical stability approach to the Coulomb quasipotential

The critical coupling constant characterizing the stability behaviour of the Coulomb quasipotential has been evaluated as α ? α_c = 2. The present stability approach is based on the quantum-mechanical controllability requirement of the dispersion shifts due to the interactions. The dispersions characterizing the Coulomb quasipotential have been established suitably within the high-energy euclidian region.     

Observation of heteronuclear Feshbach molecules from a 85Rb-87Rb gas

We report on the observation of ultracold heteronuclear Feshbach molecules. Starting with a 87Rb Bose-Einstein condensate and a cold atomic gas of 85Rb, we utilize previously unobserved interspecies Feshbach resonances to create up to 25,000 molecules. Even though the 85Rb gas is nondegenerate, we observe a large molecular conversion efficiency due to the presence of a quantum degenerate 87Rb gas; this represents a key feature of our system. We compare the molecule creation at two different Feshbach resonances with different magnetic-field widths. The two Feshbach resonances are located at 265.44+/-0.15 G and 372.4+/-1.3 G. We also directly measure the small binding energy of the molecules through resonant magnetic-field association.