epi-Aszonalenins A, B, and C from Aspergillus novofumigatus

Three new benzodiazepines have been isolated from an unusual chemotype of Aspergillus novofumigatus: epi-aszonalenins A, B, and C. The structures were elucidated by use of one- and two-dimensional NMR spectroscopic techniques and HR ESI MS. The relative configuration was established on the basis of a single crystal X-ray diffraction study of epi-aszonalenin A and the absolute configuration was determined by optical rotation comparison with the literature data. The absolute configurations of epi-aszonalenins B and C were determined by circular dichroism comparison to epi-aszonalenin A.     

Absorption kinetics of uranium tri-n-butyl phosphate in the rat: Implications for occupational exposure

The absorption kinetics for uranium into blood after deposition as tri-n-butylphosphate (UTBP) in the rat lung were combined with human data on particle deposition and clearance from the ICRP Publication 66 respiratory tract model and information from the most recent ICRP biokinetic model for uranium to predict the consequences for exposure of workers. These predictions suggest that, (1) the biokinetics of UTBP are similar to those for a Type F compound as defined by ICRP, (2) the dose coefficient is essentially independent of the aerosol size and isotopic composition, (3) the mass of uranium equivalent to the ALI can vary by 13 fold depending upon the isotopic composition, (4) intakes of uranium as UTBP other than chronic intakes as highly enriched forms should be restricted on the basis of the chemical toxicity of uranium, (5) the assessment of intake by urine bioassay measurements should be interpreted with caution unless the exposure conditions are well defined and (6) severe kidney damage is unlikely at intakes corresponding to the ALI or daily limit.     

Cytosporones O, P and Q from an endophytic Cytospora sp.

Cytosporones O, P and Q, together with the known compounds cytosporones B, C, D, E and dothiorelones A, B, C, and H were isolated from the ascomycete fungus Cytospora sp. during a chemotaxonomic study of fungal endophytes belonging to the related genera Cytospora and Phomopsis from Brazil. The structures were determined by NMR spectroscopy and mass spectrometry. With exception of cytosporones D, E, Q, and dothiorelone B, all compounds were consistently detected in the metabolite profiles of eight Cytospora isolates investigated; and were also produced by a distinct chemotype of Phomopsis.     

FTIR Emission Spectra, Molecular Constants, and Potential Curve of Ground State GeO

Extensive new high-temperature, high-resolution FTIR emission spectroscopy measurements for the five common isotopomers of GeO are combined with previous diode laser and microwave measurements in combined isotopomer analyses. New Dunham expansion parameters and an accurate analytical potential energy function are determined for the ground X1Sigma+ state. Copyright 1999 Academic Press.     

Electrostatically-directed Pd-catalysis in combination with C–H activation: site-selective coupling of remote chlorides with fluoroarenes and fluoroheteroarenes

Systems incorporating catalyst–substrate non-covalent interactions are emerging as a versatile approach to address site-selectivity challenges in remote functionalization reactions. Given the achievements that have been made in this regard using metals such as iridium, manganese and rhodium, it is surprising that non-covalent catalyst direction has not been utilized in reactions incorporating palladium-catalyzed C–H activation steps, despite palladium being arguably the most versatile metal for C–H activation. Herein, we demonstrate that electrostatically directed, site-selective C–Cl oxidative addition is compatible with a subsequent C–H activation step, proceeding via a concerted metalation deprotonation-type mechanism. This results in site-selective cross-coupling of dichloroarenes with fluoroarenes and fluoroheteroarenes, with selectivity controlled by catalyst structure. This study demonstrates that Pd-catalyzed C–H activation can be used productively in combination with a non-covalently-directed mode of catalysis, with important implications in both fields.

Electrostatically-directed oxidative addition is compatible with a subsequent C–H activation step, enabling site-selective coupling of remote chlorides with fluoroarenes and fluoroheteroarenes.     

Micropropulsion using laser ablation

The micro-laser plasma thruster (LPT) is a new micropropulsion device that uses laser ablation to create very small thrusts (0.1–100 N) for pointing and positioning micro- and nano-satellites. In this paper, we discuss the expected performance of the LPT. For a ms-pulse device, target materials are restricted to those of low thermal conductivity, e.g. polymers. Volume ablation theory adequately describes their behavior. In a ns-pulse version, exhaust velocity can be an order of magnitude higher with correspondingly lower thrust-to-power ratio. The theory for surface absorbers describes the observed behavior. PACS 45.55.Px; 42.70.Jk; 52.50.Jm; 42.62.Cf; 42.70.Km; 78.66.Qr     

Laser plasma thruster

The laser plasma thruster (LPT) is a new microthruster for small satellites. We report on development and testing of a prototype LPT. Some advantages of the LPT are: thruster voltage 4 V, mass less than 1 kg, power-to-thrust ratio 10 kW/N, and I_sp up to 1000 s. Typical thrust level is 250 μN with PVC fuel. Thrust of 1 mN is expected with energetic fuel. The pre-prototype continuous-thrust experiment includes the laser mount and heat sink, lens mounts, and focusing mechanism, which are coupled to the target-material transport mechanism. The target material is applied to a transparent plastic tape, and the laser is focused on a series of tracks on the tape. The tape-drive hardware and laser-drive electronics are described. Design, construction, and calibration of the thrust stand are described. During continuous operation, the exhaust plume is deflected in the direction of the moving tape. When the laser is operated in pulsed mode, the exhaust plume is perpendicular to the tape (parallel to the optical axis). This provides some thrust-vector control. Measured thrust is 70 μN with PVC fuel, and 550 μN with energetic fuel, with a specific impulse of 350 s. Received: 7 October 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-505-272-7203, E-mail: luke@iera.nmt.edu     

Do metric standards contract?

We address the question: By what class of force-application programs must a meter stick initially at rest in an inertial frame be moved in order to transfer it to a relatively moving inertial frame without altering the internal energy state of the structure in the process? Such stress-free transfer of a metric standard is essential for moving-axis calibration (a neglected art in established relativity theory). In order to deduce the answer by reasonings appropriate to kinematics, it proves necessary to make an extension of the relativity principle to rectilinear (irrotational) accelerated motions, and to enhance the kinematic motion group accordingly. Since the physical motion groups differ, the answers we obtain to this and to the title question differ from those of special relativity. Our alternative kinematics thus leads to discrepancies that should be measurable atO(v ²/c ²).