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The ability of the Space Surveillance Telescope (SST) to find small (2-15m diameter) NEAs suitable for the NASA asteroid retrieval mission is investigated. Orbits from a simulated population of targetable small asteroids were propagated and observations with the SST were simulated. Different search patterns and telescope time allocation cases were considered, as well as losses due to FOV gaps and weather. It is concluded that a full-time, dedicated survey at the SST is likely necessary to find a useful population of these NEAs within the mission launch timeframe, especially if an object must be observed on >1 night at SST to qualify as a detection. The simulations were also performed for an identical telescope in the southern hemisphere, which is found to produce results very similar to the SST in New Mexico due to significant (~80%) overlap in the population of objects detected at each site. In addition to considering the SST's ability to detect small NEAs, a parallel study was performed focusing on >100m diameter objects. This work shows that even with limited telescope time (3 nights per month) a substantial number of these larger objects would be detected. [ABSTRACT FROM AUTHOR]

Utilizing the largest available data sets for the observed taxonomic (Binzel et al., 2004, Icarus 170, 259–294) and albedo (Delbo et al., 2003, Icarus 166, 116–130) distributions of the near-Earth object population, we model the bias-corrected population. Diameter-limited fractional abundances of the taxonomic complexes are A-0.2%; C-10%, D-17%, O-0.5%, Q-14%, R-0.1%, S-22%, U-0.4%, V-1%, X-34%. In a diameter-limited sample, ∼30% of the NEO population has jovian Tisserand parameter less than 3, where the D-types and X-types dominate. The large contribution from the X-types is surprising and highlights the need to better understand this group with more albedo measurements. Combining the C, D, and X complexes into a “dark” group and the others into a “bright” group yields a debiased dark-to-bright ratio of ∼1.6. Overall, the bias-corrected mean albedo for the NEO population is 0.14±0.02, for which an H magnitude of 17.8±0.1 translates to a diameter of 1 km, in close agreement with Morbidelli et al. (2002, Icarus 158 (2), 329–342). Coupling this bias corrected taxonomic and albedo model with the H magnitude dependent size distribution of (Stuart, 2001, Science 294, 1691–1693) yields a diameter distribution with 1090±180 NEOs with diameters larger than 1 km. As of 2004 June, the Spaceguard Survey has discovered 56% of the NEOs larger than 1 km. Using our size distribution model, and orbital distribution of (Stuart, 2001, Science 294, 1691–1693) we calculate the frequency of impacts into the Earth and the Moon. Globally destructive collisions (∼1021 J) of asteroids 1 km or larger strike the Earth once every 0.60±0.1 Myr on average. Regionally destructive collisions with impact energy greater than 4×1018 J (∼200 m diameter) strike the Earth every 56,000±6000 yr. Collisions in the range of the Tunguska event (4–8×1016 J) occur every 2000–3000 yr. These values represent the average time between randomly spaced impacts; actual impacts could occur more or less closely spaced solely by chance. As a verification of these impact rates, the crater production function of Shoemaker et al. (1990, Geological Society of American Special Paper 247) has been updated by combining this new population model with a crater formation model to find that the observed crater production function on both the Earth and Moon agrees with the rate of crater production expected from the current population of NEOs. [Copyright &y& Elsevier]

Estimates the size and shape of the near-Earth asteroid (NEA) population. Significance of LINEAR survey in the estimation process; Importance of simulation of detection probabilities for difference values of orbital parameters; Inclination of NEA population from previous estimates.

We present new visible and near-infrared spectroscopic measurements for 252 near-Earth (NEO) and Mars-crossing (MC) objects observed from 1994 through 2002 as a complement to the Small Main-Belt Asteroid Spectroscopic Survey (SMASS, ). Combined with previously published SMASS results, we have an internally consistent data set of more than 400 of these objects for investigating trends related to size, orbits, and dynamical history. These data also provide the basis for producing a bias-corrected estimate for the total NEO population (Stuart and Binzel, 2004, Icarus 170, 295–311). We find 25 of the 26 Bus (1999, PhD thesis) taxonomic types are represented, with nearly 90% of the objects falling within the broad S-, Q-, X-, and C-complexes. Rare A- and E-types are more common in the MC than NEO population (about 5% compared to <1%) and may be direct evidence of slow diffusion into MC orbits from the Flora and Hungaria regions, respectively. A possible family of MC objects (C-types) may reside at the edge of the 5:2 jovian resonance. Distinct signatures are revealed for the relative contributions of different taxonomic types to the NEO population through different source regions. E-types show an origin signature from the inner belt, C-types from the mid to outer belt, and P-types from the outer belt. S- and Q-types have effectively identical main-belt source region profiles, as would be expected if they have related origins. A lack of V-types among Mars-crossers suggests entry into NEO space via rapid transport through the ν6 and 3:1 resonances from low eccentricity main-belt orbits, consistent with a Vesta origin. D-types show the strongest signature from Jupiter family comets (JFC), with a strong JFC component also seen among the X-types. A distinct taxonomic difference is found with respect to the jovian Tisserand parameter T, where C-, D-, and X-type (most likely low albedo P-class) objects predominate for T⩽3. These objects, which may be extinct comets, comprise 4% of our observed sample, but their low albedos makes this magnitude limited fraction under-representative of the true value. With our taxonomy statistics providing a strong component to the diameter limited bias correction analysis of Stuart (2003, PhD thesis), we estimate 10–18% of the NEO population above any given diameter may be extinct comets, taking into account asteroids scattered into T<3 orbits and comets scattered into T>3 orbits. In terms of possible space weathering effects, we see a size-dependent transition from ordinary chondrite-like (Q-type) objects to S-type asteroids over the size range of 0.1 to 5 km, where the transition is effectively complete at 5 km. A match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes. However, space weathering may proceed at a very rapid rate compared with collisional timescales. In this case, the presence or absence of a regolith may be the determining factor for whether or not an object appears “space weathered.” Thus 0.1 to 5 km appears to be a critical size range for understanding the processes, timescales, and conditions under which a regolith conducive to space weathering is generated, retained, and refreshed. [Copyright &y& Elsevier]

The water gas shift (WGS) reaction was conducted in the presence of two natural and two synthetic CaO-based sorbents. It was shown that such sorbents can affect the WGS in two ways: (i) by catalysis of the reaction and (ii) by altering the equilibrium position by abstraction of CO2from the gas phase. It was shown that CaO can significantly enhance the production of H2during the WGS reaction; however, a trade-off between the production of H2and contamination of the product gas with CO2(the “CO2slip”) has to be made. It was found that CaO catalyzes the WGS reaction. The carbonation reaction was very close to thermodynamic equilibrium, even at small contact times at 650 °C. However, the concentration of H2was significantly below that predicted from equilibrium considerations. In our experiments, once the sorbent had been fully carbonated, it was regenerated by heating to release the CO2so that it could be reused. In such a cyclic experiment, calcium magnesium acetate, a synthetic sorbent, was the best sorbent tested, albeit only over five cycles of reaction, with respect to the amount of H2produced. The other sorbents, especially limestone, revealed a decrease in the production of hydrogen with the number of cycles. [ABSTRACT FROM AUTHOR]

A chemical looping process, which uses a packed bed of the various oxides of iron, has been formulated to produce separate, pure streams of H 2and CO 2from syngas. The process has the following stages: (1) Reduction of Fe 2O 3to Fe 0.947O in the syngas from gasifying coal or biomass. This stage generates pure CO 2, once the water has been condensed. (2) Subsequent oxidation of Fe 0.947O to Fe 3O 4using steam, to simultaneously produce H 2. (3) Further oxidation of Fe 3O 4to Fe 2O 3using air to return the oxide to step 1. Step 1 was studied here using a mixture of CO + CO 2+ N 2as the feed to a packed bed of iron oxide particles, while measuring the concentrations of CO and CO 2in the off-gas; step 2 was investigated by passing steam in N 2through the packed bed and measuring the quantity of H 2produced. The third step simply involved passing air through the bed. Reduction to Fe, rather than Fe 0.947O, in step 1 gave low levels of H 2in step 2 after 10 cycles of reduction and oxidation and led to the deposition of carbon at lower temperature. Step 3, i.e. reoxidizing the particles in air to Fe 2O 3, led to no deterioration of the hydrogen yield in step 2 and benefited the process by (i) increasing the heat produced in each redox cycle and (ii) preventing the slip of CO from the bed in step 1. The proposed process is exothermic overall and very usefully generates separate streams of very pure H 2and CO 2without complicated separation units. [ABSTRACT FROM AUTHOR]

Background: The incidence of tricuspid annuloplasty (TR) observed early after cardiac biatrial implantation is unpredictable and in our experience not infrequently problematic. Although the bicaval method of implant may reduce the incidence of TR, its benefit has not been conclusively documented.Methods: In an attempt to reduce the incidence of TR observed early after cardiac transplantation, 25 consecutive patients undergoing cardiac transplantation received donor heart tricuspid annuloplasty (TA) with either a DeVega or Ring technique. Early transthoracic echocardiograms were analyzed and compared with an immediately prior and consecutive cohort of 25 patients undergoing transplantation without TA. The biatrial technique of cardiac transplantation with a Cabrol modification was used for donor heart implant in both groups. Echocardiograms obtained 5 days after cardiac transplantation were reviewed in blinded fashion. TR was scored 0 = none, 1 = mild, 2 = moderate, and 3 = severe.Results: Donor and recipient characteristics were not different between groups. No hospital deaths occurred in either group. Patients undergoing transplantation without TA had a higher TR score, 1.3 (range 0–3), than did patients with TA, 0.7 (range 0–1.5, p = 0.002). Moderate or severe TR was present in 8 of 25 patients without TA compared with 0 of 25 patients with TA (p = 0.004). No patients required permanent pacemaker.Conclusions: TA can significantly reduce the incidence of early postoperative TR after biatrial cardiac transplant without adding to the complexity of operation. [Copyright &y& Elsevier]

We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ∼30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales . Imposing cuts on minimum τ and allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ⩾ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8′. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ∼3 years in the rest frame of the jet, in contrast with the ∼320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics. [ABSTRACT FROM AUTHOR]