Scattering length of the ground state Mg+Mg collision

We have constructed the X 1SIGMAg+ potential for the collision between two ground state Mg atoms and analyzed the effect of uncertainties in the shape of the potential on scattering properties at ultra-cold temperatures. This potential reproduces the experimental term values to 0.2 inverse cm and has a scattering length of +1.4(5) nm where the error is prodominantly due to the uncertainty in the dissociation energy and the C6 dispersion coefficient. A positive sign of the scattering length suggests that a Bose-Einstein condensate of ground state Mg atoms is stable.Comment: 15 pages, 3 figures, Submitted Phys. Rev.

Radiation transport and scaling of optical depth in Nd:YAG laser-produced microdroplet-tin plasma

Experimental scaling relations of the optical depth are presented for the emission spectra of a tin-droplet-based, 1-μm-laser-produced plasma source of extreme-ultraviolet (EUV) light. The observed changes in the complex spectral emission of the plasma over a wide range of droplet diameters (16-65 μm) and laser pulse durations (5-25 ns) are accurately captured in a scaling relation featuring the optical depth of the plasma as a single, pertinent parameter. The scans were performed at a constant laser intensity of 1.4 × 1011 W/cm2, which maximizes the emission in a 2% bandwidth around 13.5 nm relative to the total spectral energy, the bandwidth relevant for industrial EUV lithography. Using a one-dimensional radiation transport model, the relative optical depth of the plasma is found to linearly increase with the droplet size with a slope that increases with the laser pulse duration. For small droplets and short laser pulses, the fraction of light emitted in the 2% bandwidth around 13.5 nm relative to the total spectral energy is shown to reach high values of more than 14%, which may enable conversion efficiencies of Nd:YAG laser light into - industrially - useful EUV radiation rivaling those of current state-of-the-art CO2-laser-driven sources

The Second Cambridge Pulsar Survey at 81.5 MHz

We have searched the northern sky for pulsars at the low radio frequency of 81.5 MHz, using the 3.6-hectare array at Cambridge, England. The survey covered most of the sky north of declination -20 deg and provided sensitivities of order 200 mJy for pulsars not too close to the galactic plane. A total of 20 pulsars were detected, all of them previously known. The effective post-detection sampling rate was 1.3 kHz, and the sensitivity to low-dispersion millisecond pulsars was sufficient to allow the detection of objects similar to PSR J0437-4715 (period 5.7 ms, dispersion measure 2.6 cm^-3 pc, mean flux density 1 Jy). No such pulsars were found.Comment: 19 pages, 5 figure

Cohesive properties of alkali halides

We calculate cohesive properties of LiF, NaF, KF, LiCl, NaCl, and KCl with ab-initio quantum chemical methods. The coupled-cluster approach is used to correct the Hartree-Fock crystal results for correlations and to systematically improve cohesive energies, lattice constants and bulk moduli. After inclusion of correlations, we recover 95-98 % of the total cohesive energies. The lattice constants deviate from experiment by at most 1.1 %, bulk moduli by at most 8 %. We also find good agreement for spectroscopic properties of the corresponding diatomic molecules.Comment: LaTeX, 10 pages, 1 figure, accepted by Phys. Rev.

Setting Financial Accounting Standards for the Twenty-first Century

This paper was prepared for the purpose of facilitating discussion at the Symposium on Financial Reporting and Standard Setting sponsored by the American Institute of Certified Public Accountants. The authors of the paper believe that the changing environment necessitates a thorough reexamination of financial accounting standard-setting processes in the United States. The following observations underlie the propositions offered in the paper: * The increasing demand for and availability of alternative information is decreasing the demand for traditional financial accounting information. * The conventional historical-cost-based accounting model is becoming increasingly inadequate for decision-support purposes

Correlation effects in MgO and CaO: Cohesive energies and lattice constants

A recently proposed computational scheme based on local increments has been applied to the calculation of correlation contributions to the cohesive energy of the CaO crystal. Using ab-initio quantum chemical methods for evaluating individual increments, we obtain 80% of the difference between the experimental and Hartree-Fock cohesive energies. Lattice constants corrected for correlation effects deviate by less than 1% from experimental values, in the case of MgO and CaO.Comment: LaTeX, 4 figure

Biogeochemical signatures in the lichen Hypogymnia physodes in the mid Urals

Abstract Multi-element content and uranium (U) isotopes were investigated in the lichen Hypogymnia physodes (native and transplants) sampled across a 60-km transect, centred on Karabash smelter town, from Turgoyak Lake (SW) to Kyshtym (NE) to investigate the origin of U. Kyshtym was the site of a major nuclear accident in 1957. 234 U/ 238 U activity ratios in native thalli sampled during July 2001 were within the natural isotopic ratio in minerals. Uranium/thorium (U/Th) ratios were higher in native thalli towards the NE (average 0.73) than those in the SW (average 0.57). Element signatures in native thalli and transplants suggest U was derived from fossil fuel combustion from Karabash and sources lying further to the east. Systematic and significant U enrichment indicative of a nuclear fuel cycle source was not detected in any sample. Element signatures in epiphytic lichen transplants and native thalli provide a powerful method to evaluate U deposition

Sensing endogenous seasonality in the case of a coffee supply chain

Rogue seasonality, or endogenously generated cyclicality (in variables), is common in supply chains and known to adversely affect performance. This paper explores a technique for sensing rogue seasonality at a supply chain echelon level. A signature and index based on cluster profiles of variables, which are meant to sense echelon-level generation and intensity of rogue seasonality, respectively, are proposed. Their validity is then established on echelons of a downstream coffee supply chain for five stock keeping units (SKUs) with contrasting rogue seasonality generation behaviour. The appropriateness of spectra as the domain for representing variables, data for which is daily sampled, is highlighted. Time-batching cycles which could corrupt the sensing are observed in variables, and the need to therefore filter them out in advance is also highlighted. The knowledge gained about the echelon location, intensity and time of generation of rogue seasonality could enable timely deployment of specific mitigation actions

The floristic changes of Scottish moorland dominated by heather (Calluna vulgaris, Ericaceae) but unburnt for 50 years and kept checked by moderate grazing

Vegetation and herbivore usage have been monitored since 1969/1970 at four moorland sites where heather (Calluna vulgaris) remained the main species under moderate levels of grazing. Much of the annual growth of the heather was regularly consumed by this grazing, but no burning occurred to remove heather biomass. Two sites were on acidic base-poor soils and had only minor cover of grasses and herbs, their vegetation having most affinity to H10 heath in the National Vegetation Classification of British plant communities. The other two sites were on more base-rich soils, and grasses and herbs had substantial cover; their vegetation showed most affinity to NVC CG11a grassland. One of the latter sites lies at 700 m and Calluna grew poorly being close to its altitudinal limit; the other three sites were at lower altitude and Calluna grew strongly creating dense swards. Over the 43–44 years of observation Calluna increased moderately in height but many subordinate higher plants declined in cover, as measured by point-quadrat recording. Bryophytes increased at three sites largely due to substantial gains of Hylocomium splendens, but other pleurocarpous mosses suffered some declines. At the three lower-altitude sites species number fell by 20–35% between the first and last recordings, but at the high-altitude site there was negligible change in species number. The main drivers of change were the grazing received and the performance of Calluna, and no evidence was found of species composition reacting to climate change or nitrogen deposition. To maintain diversity, timely burning is recommended

Radio Frequency Spectra of 388 Bright 74 MHz Sources

As a service to the community, we have compiled radio frequency spectra from the literature for all sources within the VLA Low Frequency Sky Survey (VLSS) that are brighter than 15 Jy at 74 MHz. Over 160 references were used to maximize the amount of spectral data used in the compilation of the spectra, while also taking care to determine the corrections needed to put the flux densities from all reference on the same absolute flux density scale. With the new VLSS data, we are able to vastly improve upon previous efforts to compile spectra of bright radio sources to frequencies below 100 MHz because (1) the VLSS flux densities are more reliable than those from some previous low frequency surveys and (2) the VLSS covers a much larger area of the sky (declination >-30 deg.) than many other low frequency surveys (e.g., the 8C survey). In this paper, we discuss how the spectra were constructed and how parameters quantifying the shapes of the spectra were derived. Both the spectra and the shape parameters are made available here to assist in the calibration of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ