Trypanocidal terpenoids from Laurus nobilis L

Trypanocidal constituents of dried leaves of Laurus nobilis L. (Lauraceae) were examined. Activity-guided fractionation of the methanol extract resulted in the isolation of two guaianolides, dehydrocostus lactone (1) and zaluzanin D (2), and a new p-menthane hydroperoxide, (1R,4S)-1-hydroperoxy-p-menth-2-en-8-ol acetate (3). The minimum lethal concentrations of these compounds against epimastigotes of Trypanosoma cruzi were 6.3, 2.5, and 1.4 microM, respectively.     

New and efficient synthesis of azabicyclo[4.4.0]alkane amino acids by Rh-catalyzed cyclohydrocarbonylation

[reaction: see text] Highly efficient syntheses of azabicyclo[4.4.0]alkane amino acids were achieved by Rh-catalyzed cyclohydrocarbonylation of dipeptides bearing a terminal olefin moiety and a heteroatom nucleophile.     

Extremely low vertical-emittance beam in the accelerator test facility at KEK

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8 x 10(-8) rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.     

Evolution of magnetism in U(Ni 1- xPd x) Si single crystals

Single crystals of U(Ni_1-xPd_x)₂Si₂ with x = 0.05, 0.09 and 0.135 have been grown. Magnetization and electrical resistivity measurements were performed in a wide range of temperatures and magnetic fields in order to study stability of magnetic phases in the solid solutions between UNi₂Si₂ and UPd₂Si₂ with a special emphasis on the type of ground state. In UPd₂Si₂ the simple AFI-type antiferromagnetic structure of U moments is observed at low temperatures. UNi₂Si₂ adopts the uncompensated AF structure (UAF) with the + + - stacking of U moments along the c-axis and consequently this compound exhibits a spontaneous magnetization corresponding to 1/3 of the U moment. The substitution of Pd for Ni leads to a rapid decay of the spontaneous magnetization. The evolution of magnetization and electrical resistivity behavior with Pd doping is tentatively attributed to the coexistence of the AF-I and UAF phases in the ground state of U(Ni_0.91Pd_0.09)₂Si₂ and U(Ni_0.865Pd_0.135)₂Si₂. In this scenario, the volume fraction of the AF-I phase rapidly grows with Pd doping on account of the UAF. At lowest temperatures an irreversible transition to the UAF phase is observed when a sufficiently high magnetic field is applied along the c-axis. Received 28 March 2002 / Received in final form 8 August 2002 Published online 19 December 2002 RID="a" ID="a"e-mail: sech@mag.mff.cuni.cz     

On the chemical states of nitrogen on iron surfaces reacted with ammonia and sodium cyanide,studied by X-ray photoelectron spectroscopy

The reaction products of iron reacted with ammonia gas and molten sodium cyanide are studied using X-ray photoelectron spectroscopy. Ammonia gas dissociates on iron surfaces to form a nitride and a loosely bound NH₃-like species with N 1sB.E.'s at 397.2 and 399.8 eV, respectively. On iron specimens dipped into molten NaCN three species are found at 398.6, 397.8 and 397.2 eV. The 398.6-eV peak is ascribed to adsorbed ?CN, and the 397.8-eV peak to carbonitride formed by the reaction of the cyanide with iron. Decreasing binding energies are found for adsorbed ?CN ligand, carbonitride compound and nitride, which seem to correspond to an apparent order of stronger interaction of nitrogen with iron. An iron sample was scratched with a file and the surface species of nitrogen were observed below 400°C. The nitrogen atoms in the sample diffuse and concentrate on the surface, depending on the nitrogen content in the bulk. Desorption patterns of nitrogen from a heated iron surface are examined with a view to the determination of gaseous constituents in metal samples.     

Thermodynamic properties in the approach to the quantum critical point of the spin-ladder material Na2Co2(C2O4)3(H2O)2

Magnetic susceptibility and heat capacity measurements as a function of temperature on a single-crystal sample of a spin-ladder material, Na2Co2(C2O4)3(H2O)2, are reported. Principal susceptibilities, parallel and perpendicular to the ladder direction, respectively, show broad maxima around 22 and 17 K. Both susceptibilities decay exponentially down to about 5 K and thereafter they are essentially independent of temperature. These findings amount to a signature of a quantum phase transition from a spin-liquid to Néel ordered state previously predicted theoretically. No anomaly is found in the heat capacity around the transition temperature.     

Improving the spectral resolution of wedged etalons and linear variable filters with incidence angle

Compact spectrometers fabricated by placing a wedged etalon or a linear variable filter in front of a linear photodiode array typically do not exhibit the spectral resolution of a parallel filter of the same finesse. A theoretical analysis of the beam emerging from a wedged etalon is shown to predict a comalike aberration, explaining the loss in resolution. This analysis also predicts a focused beam waist whose axial position depends on the incidence angle, indicating that resolution can be improved by placing this waist on the detector. These results are experimentally confirmed in a multicavity linear variable filter to achieve 0.09 nm spectral resolution at 1550 nm.     

Photoassociation spectroscopy of laser-cooled ytterbium atoms

We report the photoassociation spectroscopy of laser-cooled ytterbium atoms in an optical trap. We observed more than 90 photoassociation resonances of vibrational levels in the (1)Sigma(+)(u) state, including 80 consecutive series, up to 490 GHz detuning with respect to the atomic resonance. From the resonance frequencies we derived the atomic radiative lifetime of the (6s6p) 1P1 state to be 5.464+/-0.005 ns, which is about 2 orders of magnitude improvement over previous results. We also observed line broadening of resonances, which is ascribed to the predissociation to the triplet states, and estimated the transition probability to be 0.2. Furthermore, we observed the decrease of the photoassociation signal intensity, from which the scattering length is estimated to be equal to or less than 3 nm.     

Beam-size measurement with optical diffraction radiation at KEK accelerator test facility

An experiment on the investigation of optical diffraction radiation (ODR) from a slit target as a possible tool for noninvasive electron beam-size diagnostics has been performed at the KEK accelerator test facility. The experimental setup has been installed at the diagnostics section of the extraction line. We have performed the first incoherent ODR observation from a slit target. The measured angular distributions are in reasonable agreement with the theoretical expectation. The beam-size effect onto the ODR angular pattern has been observed. Moreover, the sensitivity to the beam size as small as 14 microm has been achieved.