A Comment on "The Far Future of Exoplanet Direct Characterization" - the Case for Interstellar Space Probes

Following on from ideas presented in a recent paper by Schneider et al. (2010) on "The Far Future of Exoplanet Direct Characterization", I argue that they have exaggerated the technical obstacles to performing such 'direct characterization' by means of fast (order 0.1c) interstellar space probes. A brief summary of rapid interstellar spaceflight concepts that may be found in the literature is presented. I argue that the presence of interstellar dust grains, while certainly something which will need to be allowed for in interstellar vehicle design, is unlikely to be the kind of 'show stopper' suggested by Schneider et al. Astrobiology as a discipline would be a major beneficiary of developing an interstellar spaceflight capability, albeit in the longer term, and I argue that astrobiologists should keep an open mind to the possibilities.Comment: Accepted for publication in Astrobiolog

The local structure of SO2 and SO3 on Ni(1 1 1): a scanned-energy mode photoelectron diffraction study

O 1s and S 2p scanned-energy mode photoelectron diffraction (PhD) data, combined with multiple-scattering simulations, have been used to determine the local adsorption geometry of the SO2 and SO3 species on a Ni(1 1 1) surface. For SO2, the application of reasonable constraints on the molecular conformation used in the simulations leads to the conclusion that the molecule is centred over hollow sites on the surface, with the molecular plane essentially parallel to the surface, and with both S and O atoms offset from atop sites by almost the same distance of 0.65 Å. For SO3, the results are consistent with earlier work which concluded that surface bonding is through the O atoms, with the S atom higher above the surface and the molecular symmetry axis almost perpendicular to the surface. Based on the O 1s PhD data alone, three local adsorption geometries are comparably acceptable, but only one of these is consistent with the results of an earlier normal-incidence X-ray standing wave (NIXSW) study. This optimised structural model differs somewhat from that originally proposed in the NIXSW investigation

Two Unrelated 8-Vinyl Reductases Ensure Production of Mature Chlorophylls in Acaryochloris marina

The major photopigment of the cyanobacterium Acaryochloris marina is chlorophyll d , while its direct biosynthetic precursor, chlorophyll a , is also present in the cell. These pigments, along with the majority of chlorophylls utilized by oxygenic pho- totrophs, carry an ethyl group at the C-8 position of the molecule, having undergone reduction of a vinyl group during biosyn- thesis. Two unrelated classes of 8-vinyl reductase involved in the biosynthesis of chlorophylls are known to exist, BciA and BciB. The genome of Acaryochloris marina contains open reading frames (ORFs) encoding proteins displaying high sequence similarity to BciA or BciB, although they are annotated as genes involved in transcriptional control ( nmrA ) and methanogenesis ( frhB ), respectively. These genes were introduced into an 8-vinyl chlorophyll a -producing delta bciB strain of Synechocystis sp. strain PCC 6803, and both were shown to restore synthesis of the pigment with an ethyl group at C-8, demonstrating their activities as 8-vinyl reductases. We propose that nmrA and frhB be reassigned as bciA and bciB , respectively; transcript and proteomic analysis of Acaryochloris marina reveal that both bciA and bciB are expressed and their encoded proteins are present in the cell, possibly in order to ensure that all synthesized chlorophyll pigment carries an ethyl group at C-8. Potential reasons for the presence of two 8-vinyl reductases in this strain, which is unique for cyanobacteria, are discussed

Aircraft System and Product Development: Teaching the Conceptual Phase

This paper reports the first offering of a graduate level subject covering the conceptual phase of aircraft product development. The output of the conceptual phase is a system level specification that usually serves as the input for a traditional undergraduate capstone subject on aircraft design. Of critical importance in the conceptual phase is addressing the business case for the candidate product. The conceptual phase spans a much wider range of topics than the technical issues which dominate preliminary design. These include user needs, investment and business requirements, market analysis, operational issues, exogenous constraints (certification, regulation, political, etc.), as well as engineering and manufacturing requirements. Students in the subject were required to Prepare for the Board of Directors of a large aerospace company a compelling business case and specification for a large jet transport product. Three student teams produced original responses to the challenge and have reported their findings in a companion AIAA paper. This paper addresses the pedagogical approaches and outcomes. These encompass the use of distance learning technology and techniques for several off-campus practicing engineering students. Overall, the outcome was very gratifying. The class will be offered in the spring of 2001, focusing on a supersonic business jet

Effect of Potassium Salts on Extractable Soil Manganese

Incubation experiments with an acid, poorly drained soil (Typic Albaqualf) showed that the level of extractable Mn was increased by salt treatments. The relative order of the salt effect was KBr > KCl > KNO? > K?SO?. Soil pH changes accounted for the majority of the KNO? and K?SO? treatment effects, but the KCl and KBr effects could not be explained on this basis. In addition, ionic strength considerations and differential biological activities were not found to be factors influencing the K salt effects in the soil system. A hypothesis is presented to explain the KCl or KBr effect, in which the anion would function in an oxidation-reduction reaction. This hypothesis is supported by the fact that the soil treated with KBr contained more extractable Mn than that treated with KCl, in accordance with theory. Theoretical calculations also suggested the possibility that both Cl- and Br- could reduce the lower valency Mn oxides under the experimental soil conditions

Structure determination of PF3 adsorption on Cu(100) using X-ray standing waves

The local structure of the Cu(100)c(4x2)-PF3 adsorption phase has been investigated through the use of normal-incidence X-ray standing waves (NIXSW), monitored by P 1s and F 1s photoemission, together with P K-edge near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows the molecule to be oriented with its C3v symmetry axis essentially perpendicular to the surface, while the P NIXSW data show the molecule to be adsorbed in atop sites 2.37±0.04 Å above the surface, this distance corresponding to the Cu-P nearest-neighbour distance in the absence of any surface relaxation. F NIXSW indicates a surprisingly small height difference of the P and F atoms above the surface 0.44±0.06 Å, compared with the value expected for an undistorted gas-phase geometry of 0.77 Å, implying significant increases in the F-P-F bond angles. In addition, however, the F NIXSW data indicate that the molecules have a well-defined azimuthal orientation with a molecular mirror plane aligned in a substrate mirror plane, and with a small (5-10°) tilt of the molecule in this plane such that the two symmetrically-equivalent F atoms in each molecule are tilted down towards the surface

The local adsorption structure of methylthiolate and butylthiolate on Au(1 1 1): a photoemission core-level shift investigation

Measurements of the core-level shifts in Au 4f photoemission spectra from Au(1 1 1) at different coverages of methylthiolate and butylthiolate are reported. Adsorption leads to two components in addition to that from the bulk, one at lower photoelectron binding energy attributed to surface atoms not bonded to thiolate species, while the second component has a higher binding energy and is attributed to Au atoms bonded to the surface thiolate. The relative intensities of these surface components for the saturation coverage (mainly (√3 × √3)R30°) phases are discussed in terms of different local adsorption sites in a well-ordered surface, and favour adsorption of the thiolate species atop Au adatoms. Alternative interpretations that might be consistent with an Au-adatom-dithiolate model are discussed, particularly in the context of the possible influence of reduced coverage associated with a disordered surface. Marked differences from previously-reported results for longer-chain alkylthiolate layers are highlighted

Parallel flow in Hele-Shaw cells with ferrofluids

Parallel flow in a Hele-Shaw cell occurs when two immiscible liquids flow with relative velocity parallel to the interface between them. The interface is unstable due to a Kelvin-Helmholtz type of instability in which fluid flow couples with inertial effects to cause an initial small perturbation to grow. Large amplitude disturbances form stable solitons. We consider the effects of applied magnetic fields when one of the two fluids is a ferrofluid. The dispersion relation governing mode growth is modified so that the magnetic field can destabilize the interface even in the absence of inertial effects. However, the magnetic field does not affect the speed of wave propagation for a given wavenumber. We note that the magnetic field creates an effective interaction between the solitons.Comment: 12 pages, Revtex, 2 figures, revised version (minor changes

Prevention of restenosis after coronary balloon angioplasty: rationale and design of the Fluvavastatin Angioplasty Restenosis (FLARE) Trial

Prevention of restenosis after successful percutaneous transluminal coronary balloon angioplasty (PTCA) continues to present the greatest therapeutic challenge in interventional cardiology. Experimental and pathological studies describe restenosis as no more than the biologic healing response to arterial injury. Studies of serial quantitative coronary angiography have demonstrated that this biologic process may be measured as the loss in minimal luminal diameter (MLD) from post-PTCA to follow-up angiography and that it is essentially ubiquitous and normally distributed. Thus, quantitative coronary angiography has become the gold standard for evaluation of the angiographic outcome of clinical trials of new agents and devices aimed at prevention of restenosis. The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors inhibit biosynthesis of mevalonate, a precursor of non-sterol compounds involved in cell proliferation, and thus may control the neointimal response, which forms the kernel of restenosis. Experimental evidence suggests that fluvastatin may exert a greater direct inhibitory effect on proliferating vascular myocytes than other HMG-CoA reductase inhibitors, independent of any lipid-lowering action. The Fluvastatin Angioplasty Restenosis (FLARE) Trial was conceived, in collaboration between the Thoraxcenter, Erasmus University, Rotterdam, The Netherlands, and Sandoz Pharma, to evaluate the ability of fluvastatin 40 mg twice daily to reduce restenosis after successful single-lesion PTCA. Treatment of suitable patients begins 2 weeks before PTCA and continues after successful PTCA (residual diameter stenosis < 50%, without major cardiac complications) to follow-up angiography at 26 +/- 2 weeks. Restenosis is measured by quantitative coronary angiography at a core laboratory as the loss in MLD from post-PTCA to follow-up angiography. It is calculated (90% power, alpha = 0.05) that 730 evaluable patients will be needed to tes

Methylthiolate-induced reconstruction of Ag(1 1 1): A medium energy ion scattering study

Medium energy ion scattering (MEIS), using 100 keV H+ incident ions, has been used to investigate the structure of the Ag(1 1 1)(√7 × √7)R19° –CH3S surface phase. The results provide the first direct evidence that this structure does involve substantial reconstruction of the Ag surface layer. The measured absolute scattered ion yields and blocking curves are in generally good agreement with a specific structural model of the surface based on a reconstructed layer containing 3/7 ML Ag atoms, previously suggested on the basis of scanning tunnelling microscopy (STM) and normal incidence X-ray standing wave (NIXSW) studies. However, the MEIS data indicate that any rumpling of the thiolate layer, is small, and probably 0.2 Å. This value is smaller than the amplitude suggested in the STM and NIXSW studies, but could be entirely consistent with the earlier experimental data