QSO number counts to B < 24.5 from hubble space telescope WFPC2 images

We have conducted a survey for faint quasars to B < 24.5, z < 2.1 based on archival high-latitude Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) images covering 0.04 deg² of the sky in three filters spanning 2300–9600 Å. Taking advantage of the superb 0.1″ resolution of WFPC2, we have developed an approach to select quasar candidates based on their morphology and position in multicolor space. We derive cumulative surface densities and compare them with our previous survey in the Groth–Westphal Strip and other faint quasar surveys that utilize very different selection approaches. In most cases the agreement with these surveys is good, however, we find approximately twice as many quasar candidates to B = 24.5 as the COMBO-17 survey. Although we are confident that our approach eliminates most contaminating stars and galaxies, spectroscopic follow-up will be required to determine the level of residual contamination and confirm or refute this excess.     

Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet 9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters could indicate unusually low density (< 0.3 g cm⁻³) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying DI flyby instruments should provide critical data that will further resolve ambiguities.     

The Magnetometer Instrument on MESSENGER

The Magnetometer (MAG) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission is a low-noise, tri-axial, fluxgate instrument with its sensor mounted on a 3.6-m-long boom. The boom was deployed on March 8, 2005. The primary MAG science objectives are to determine the structure of Mercury’s intrinsic magnetic field and infer its origin. Mariner 10 observations indicate a planetary moment in the range 170 to 350 nT R _M³ (where R _M is Mercury’s mean radius). The uncertainties in the dipole moment are associated with the Mariner 10 trajectory and variability of the measured field. By orbiting Mercury, MESSENGER will significantly improve the determination of dipole and higher-order moments. The latter are essential to understanding the thermal history of the planet. MAG has a coarse range, ±51,300 nT full scale (1.6-nT resolution), for pre-flight testing, and a fine range, ±1,530 nT full scale (0.047-nT resolution), for Mercury operation. A magnetic cleanliness program was followed to minimize variable and static spacecraft-generated fields at the sensor. Observations during and after boom deployment indicate that the fixed residual field is less than a few nT at the location of the sensor, and initial observations indicate that the variable field is below 0.05 nT at least above about 3 Hz. Analog signals from the three axes are low-pass filtered (10-Hz cutoff) and sampled simultaneously by three 20-bit analog-to-digital converters every 50 ms. To accommodate variable telemetry rates, MAG provides 11 output rates from 0.01 s⁻¹ to 20 s⁻¹. Continuous measurement of fluctuations is provided with a digital 1–10 Hz bandpass filter. This fluctuation level is used to trigger high-time-resolution sampling in eight-minute segments to record events of interest when continuous high-rate sampling is not possible. The MAG instrument will provide accurate characterization of the intrinsic planetary field, magnetospheric structure, and dynamics of Mercury’s solar wind interaction.     

Stochastic-constraints method in nonstationary hot-cluttercancellation. I. Fundamentals and supervised training applications

This paper considers the use of spatio-temporal adaptive array processing in over-the-horizon radar (OTHR) and airborne radar applications in order to remove nonstationary multipath interference, known as “hot clutter”. Since the spatio-temporal properties of hot clutter cannot be assumed constant over the coherent processing interval (CPI), conventional adaptive techniques fail to provide effective hot-clutter mitigation without simultaneously degrading the properties of the backscattered radar signals, known as “cold clutter”. The approach presented incorporates multiple “stochastic” (data-dependent) constraints to achieve effective hot-clutter suppression, while maintaining distortionless output cold-clutter post-processing stationarity     

Continuous Measurement of Shock and Contact Discontinuities Velocity

An experimental method applying microwave techniques to obtain continuous measurement of both the shock and contact discontinuities bounding an air plasma generated in a cylindrical hypersonic shock tube is developed. X-band microwave signals excited in the TE11 mode reflect from the moving shock and contact surfaces. The resulting FM interference pattern is demodulated, yielding continuous velocity versus time data. Results depicting subtle detail of velocity behavior, particularly of the shock front, were obtained over a shock Mach number range of 9 to 13.     

Biosignature detection at an Arctic analog to Europa

The compelling evidence for an ocean beneath the ice shell of Europa makes it a high priority for astrobiological investigations. Future missions to the icy surface of this moon will query the plausibly sulfur-rich materials for potential indications of the presence of life carried to the surface by mobile ice or partial melt. However, the potential for generation and preservation of biosignatures under cold, sulfur-rich conditions has not previously been investigated, as there have not been suitable environments on Earth to study. Here, we describe the characterization of a range of biosignatures within potentially analogous sulfur deposits from the surface of an Arctic glacier at Borup Fiord Pass to evaluate whether evidence for microbial activities is produced and preserved within these deposits. Optical and electron microscopy revealed microorganisms and extracellular materials. Elemental sulfur (S?), the dominant mineralogy within field samples, is present as rhombic and needle-shaped mineral grains and spherical mineral aggregates, commonly observed in association with extracellular polymeric substances. Orthorhombic α-sulfur represents the stable form of S?, whereas the monoclinic (needle-shaped) γ-sulfur form rosickyite is metastable and has previously been associated with sulfide-oxidizing microbial communities. Scanning transmission electron microscopy showed mineral deposition on cellular and extracellular materials in the form of submicron-sized, needle-shaped crystals. X-ray diffraction measurements supply supporting evidence for the presence of a minor component of rosickyite. Infrared spectroscopy revealed parts-per-million level organics in the Borup sulfur deposits and organic functional groups diagnostic of biomolecules such as proteins and fatty acids. Organic components are below the detection limit for Raman spectra, which were dominated by sulfur peaks. These combined investigations indicate that sulfur mineral deposits may contain identifiable biosignatures that can be stabilized and preserved under low-temperature conditions. Borup Fiord Pass represents a useful testing ground for instruments and techniques relevant to future astrobiological exploration at Europa.     

The "gaseous" environment in sealed BRIC-100VC canisters flown on 'Mir' with embryogenic daylily cell cultures.

As part of the "Cellular Mechanisms of Spaceflight-Specific Stress to Plants" experiment, nine BRIC (Biological Research in Canisters) 100VC canisters, each containing four 100 mm dia polycarbonate petri dishes with embryogenic daylily (Hemerocallis sp.) cultures, were launched on 12 Jan 97 (STS-81), transferred to 'Mir' and returned on 24 May 97 (STS-84). Pre-flight, flight and ground control data for temperature, relative humidity, CO2 and ethylene in the BRIC canisters are presented.     

Validating ionospheric models with measured electron density profiles

On behalf of an URSI Working Group 3 initiated study (VIM), three ionospheric models, IRI, PL/PRISM and FLIP, are compared with electron density profiles derived from ionograms Millstone Hill. Four months of data in 1989/90 were analyzed. For most of the time, N(h) profiles were available every 15 minutes providing a good statistical database for the evaluation of the ionospheric models in terms of diurnal and seasonal variations.     

Satellite-derived synoptic climatology in data-sparse regions

Synoptic-scale “moisture bursts” are defined, based on infrared GOES imagery, and their synoptic climatology is developed. Quantitative analysis of satellite-derived individual channel radiance data and vertical eigenfunctions of complete channel data yield rich structural detail; these details do not appear in FGGE analyses in regions void of conventional meteorological data.     

中国航空货运市场分析

全球航空货运市场趋势 全球航空货运市场正面临着富有挑战性的发展趋势。燃油价格上涨、美国经济开始低迷是两个宏观经济导向的趋势。此外,世界范围内的航空货运承运人都面临着日益增加的竞争压力：综合运营商的市场拓展;更为快速、廉价的地面运输方式;客机容量;局部市场能力过剩。