Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide

The metabolic consequence of suboptimal (400 μmol mol⁻¹ or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO₂] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO₂]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO₂] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO₂] and physiological age. In general, plants grown under high [CO₂] exhibited a metabolite profile characteristic of older plants under ambient CO₂. Elevated [CO₂] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO₂] to a much greater extent at 10,000 ppm CO₂ than at 1500 ppm CO₂. The percentage increase of starch content resulting from CO₂ enrichment declined as plants develope. In contrast, elevated [CO₂] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO₂] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO₂] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO₂-grown plants, both elevated CO₂ levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO₂] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO₂ on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO₂ levels.     

Electronically Variable Time-Delay Network for Broad-Band Phased-Array Steering

This paper describes an electronically variable time-elay network that has been developed specffically for time-delay steering of a phased-array antenna. The network consists of microwave dispersive delay lines and two broad-band mixers; its delay is a function of the mixers' local oscillator frequency. The particularly advantageous feature of this network is that its phase is invariant with delay. It can, therefore, be used on a subarray basis, and at IF, without affecting the phase progression across the array. Alternative techniques, such as electron-beam delay lines and digitally switched line lengths, require external phase correction. A breadboard model of the network has been built and tested. Low-loss folded-tape meader lines provide the dispersive delay. The center frequency of the model is 3 GHz; it handles an instantaneous bandwidth of 300 MHz. Delay variation of 25 ns is provided. The spurious responses of the network are 30 dB down.     

Some features of solar cosmic ray penetration into the Earth’s magnetosphere

We compared fluxes of the 1–100 MeV solar energetic particles (SEP) measured in the interplanetary medium (ACE) and in the magnetosphere (Universitetsky-Tatiana, POES—in polar caps, and GOES-11—at geosynchronous orbit) during several SEP events of 2005–2006. Peak intensities of the SEP fluxes inside and outside the magnetosphere were compared for each event. It is shown that observed inside-outside difference depends mainly on direction of interplanetary magnetic field (IMF), on degree of the SEP anisotropy (pitch-angle distribution) in IMF, and on distance of the dayside magnetopause from the Earth.     

Haze aerosols in the atmosphere of early Earth: manna from heaven

An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under early Earth conditions when both CO(2) and CH(4) may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH(4)/CO(2) ratios. Here, we show that haze aerosols are able to form at CH(4) mixing ratios of 1,000 ppmv, a level likely to be present on early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After life arose, the haze may thus have provided food for biota.     

Geophysical Constraints on the Evolution of Mars

The evolution of Mars is discussed using results from the recent Mars Global Surveyor (MGS) and Mars Pathfinder missions together with results from mantle convection and thermal history models and the chemistry of Martian meteorites. The new MGS topography and gravity data and the data on the rotation of Mars from Mars Pathfinder constrain models of the present interior structure and allow estimates of present crust thickness and thickness variations. The data also allow estimates of lithosphere thickness variation and heat flow assuming that the base of the lithosphere is an isotherm. Although the interpretation is not unambiguous, it can be concluded that Mars has a substantial crust. It may be about 50 km thick on average with thickness variations of another ±50 km. Alternatively, the crust may be substantially thicker with smaller thickness variations. The former estimate of crust thickness can be shown to be in agreement with estimates of volcanic production rates from geologic mapping using data from the camera on MGS and previous missions. According to these estimates most of the crust was produced in the Noachian, roughly the first Gyr of evolution. A substantial part of the lava generated during this time apparently poured onto the surface to produce the Tharsis bulge, the largest tectonic unit in the solar system and the major volcanic center of Mars. Models of crust growth that couple crust growth to mantle convection and thermal evolution are consistent with an early 1 Gyr long phase of vigorous volcanic activity. The simplest explanation for the remnant magnetization of crustal units of mostly the southern hemisphere calls for an active dynamo in the Noachian, again consistent with thermal history calculations that predict the core to become stably stratified after some hundred Myr of convective cooling and dynamo action. The isotope record of the Martian meteorites suggest that the core formed early and rapidly within a few tens of Myr. These data also suggest that the silicate rock component of the planet was partially molten during that time. The isotope data suggest that heterogeneity resulted from core formation and early differentiation and persisted to the recent past. This is often taken as evidence against vigorous mantle convection and early plate tectonics on Mars although the latter assumption can most easily explain the early magnetic field. The physics of mantle convection suggests that there may be a few hundred km thick stagnant, near surface layer in the mantle that would have formed rapidly and may have provided the reservoirs required to explain the isotope data. The relation between the planform of mantle convection and the tectonic features on the surface is difficult to entangle. Models call for long wavelength forms of flow and possibly a few strong plumes in the very early evolution. These plumes may have dissolved with time as the core cooled and may have died off by the end of the Noachian.     

Human locomotion and workload for simulated lunar and Martian environments

Human locomotion in simulated lunar and Martian environments is investigated. A unique human-rated underwater treadmill and an adjustable ballasting harness simulate partial gravity in order to better understand how gravity determines the biomechanics and energetics of human locomotion. This study has two research aspects, biomechanics and energetics. The fundamental biomechanics measurements are continuously recorded vertical forces as exerted by subjects of the treadmill which is instrumented with a force platform. Experimental results indicate that peak vertical force and stride frequency decrease as the gravity level is reduced. Foot contact time is independent of gravity level. Oxygen uptake measurements, VO2, constitute the energetics, or workload, data for this study. As theory predicts, locomotion energy requirements for lunar (1/6-g) and Martian (3/8-g) gravity levels are significantly less than at 1-g. The observed variation in workload with gravity level is nonmonotonic, however, in over half the subject population. The hypothesis is offered that energy expenditure increases for lunar, as compared with Martian, locomotion due to the subject "wasting energy" for stability and posture control in simulated lunar gravity. Biomechanics data could influence advanced spacesuit design and planetary habitat design, while workload data will help define oxygen requirements for planetary life support systems.     

The Juno Radiation Monitoring (RM) Investigation

The Radiation Monitoring Investigation of the Juno Mission will actively retrieve and analyze the noise signatures from penetrating radiation in the images of Juno’s star cameras and science instruments at Jupiter. The investigation’s objective is to profile Jupiter’s \(>10\mbox{-MeV}\) electron environment in regions of the Jovian magnetosphere which today are still largely unexplored. This paper discusses the primary instruments on Juno which contribute to the investigation’s data suite, the measurements of camera noise from penetrating particles, spectral sensitivities and measurement ranges of the instruments, calibrations performed prior to Juno’s first science orbit, and how the measurements may be used to infer the external relativistic electron environment.     

Mass loading of planetary atmospheres by rocky satellites—II: Transport and enhanced lifetimes of satellite ejecta in planetary magnetospheres

Extensive studies have been conducted concerning individual mass, temporal and positional distribution of submicron rocky ejecta existing in the satellite-planetary gravitational sphere of influence. The transit time of the major portion of the ejecta that is transported from the satellite's gravitational sphere of influence to the planetary magnetopause is about one week and represents a mass loading pulse occurring each satellite orbit. The mass-flux distributions of lunar ejecta at the surface of the magnetopause for a complete lunar orbit are presented. Spatial mass densities of lunar ejecta in specific zones of the magnetosphere provide a means to compare sporadic interplanetary dust spatial mass densities in the same zones.     

X-rays from the first massive black holes

X-ray studies of high-redshift (z > 4) active galaxies have advanced substantially over the past few years, largely due to results from the new generation of X-ray observatories. As of this writing X-ray emission has been detected from nearly 60 high-redshift active galaxies. This paper reviews the observational results and their implications for models of the first massive black holes, and it discusses future prospects for the field.