14 research outputs found
The Pioneer Anomaly
Radio-metric Doppler tracking data received from the Pioneer 10 and 11
spacecraft from heliocentric distances of 20-70 AU has consistently indicated
the presence of a small, anomalous, blue-shifted frequency drift uniformly
changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was
interpreted as a constant sunward deceleration of each particular spacecraft at
the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of
the Newton's gravitational inverse-square law has become known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. In this review, we
summarize the current knowledge of the physical properties of the anomaly and
the conditions that led to its detection and characterization. We review
various mechanisms proposed to explain the anomaly and discuss the current
state of efforts to determine its nature. A comprehensive new investigation of
the anomalous behavior of the two Pioneers has begun recently. The new efforts
rely on the much-extended set of radio-metric Doppler data for both spacecraft
in conjunction with the newly available complete record of their telemetry
files and a large archive of original project documentation. As the new study
is yet to report its findings, this review provides the necessary background
for the new results to appear in the near future. In particular, we provide a
significant amount of information on the design, operations and behavior of the
two Pioneers during their entire missions, including descriptions of various
data formats and techniques used for their navigation and radio-science data
analysis. As most of this information was recovered relatively recently, it was
not used in the previous studies of the Pioneer anomaly, but it is critical for
the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living
Reviews in Relativit
Identification and Characterization of a Novel Porin Family Highlights a Major Difference in the Outer Membrane of Chlamydial Symbionts and Pathogens
The Chlamydiae constitute an evolutionary well separated group of intracellular bacteria comprising important pathogens of humans as well as symbionts of protozoa. The amoeba symbiont Protochlamydia amoebophila lacks a homologue of the most abundant outer membrane protein of the Chlamydiaceae, the major outer membrane protein MOMP, highlighting a major difference between environmental chlamydiae and their pathogenic counterparts. We recently identified a novel family of putative porins encoded in the genome of P. amoebophila by in silico analysis. Two of these Protochlamydia outer membrane proteins, PomS (pc1489) and PomT (pc1077), are highly abundant in outer membrane preparations of this organism. Here we show that all four members of this putative porin family are toxic when expressed in the heterologous host Escherichia coli. Immunofluorescence analysis using antibodies against heterologously expressed PomT and PomS purified directly from elementary bodies, respectively, demonstrated the location of both proteins in the outer membrane of P. amoebophila. The location of the most abundant protein PomS was further confirmed by immuno-transmission electron microscopy. We could show that pomS is transcribed, and the corresponding protein is present in the outer membrane throughout the complete developmental cycle, suggesting an essential role for P. amoebophila. Lipid bilayer measurements demonstrated that PomS functions as a porin with anion-selectivity and a pore size similar to the Chlamydiaceae MOMP. Taken together, our results suggest that PomS, possibly in concert with PomT and other members of this porin family, is the functional equivalent of MOMP in P. amoebophila. This work contributes to our understanding of the adaptations of symbiotic and pathogenic chlamydiae to their different eukaryotic hosts
Summit acid crater lakes and flank instability in composite volcanoes
Volcanic landslides, including flank and sector collapses, constitute a major hazard in many parts of the world. While composite volcanoes are innately unstable, the presence of a hydrothermal system maintained by a magmatic source at depth is recognized as a key factor increasing the risk of failure. This relates to the formation of hydrothermally altered rock masses within the core and upper flanks of the volcano which leads to heterogeneous distribution of rock strength properties and pore fluid pressures. Here an emphasis is placed on acid crater lakes perched high on active volcanoes. By acting as a trap for magmatic heat and gas flows, these lakes localize extreme acid attack on their surrounds, thereby creating a source of instability. We outline how acid crater lakes form in relation to magmatic hydrothermal systems hosted within composite volcanoes, and describe the associated hydrothermal alteration and its relationships to flank instability. The sustainability of a volcanic slope is partly governed by the degree of rock alteration, which in turn reflects the time-integrated flux of acidic gases (SO2 and HCl) released from the subsurface magmatic source. Transient or longer-term changes in pore fluid pressure linked to hydrothermal system activity also readily affect the slope stability of composite volcanoes. Such fluctuations can be initiated by both magmatic and external non-magmatic processes such as major rainfall events and regional seismicity. Kawah Ijen hyper-acid crater lake, Indonesia, is used as a case study to illustrate the cascade of effects that may ensue following slope rupture linked to hydrothermal alteration
Identification and Characterization of a Novel Porin Family Highlights a Major Difference in the Outer Membrane of Chlamydial Symbionts and Pathogens
Reconstructing the tephra dispersal pattern from the Bronze Age eruption of Santorini using an advection–diffusion model
Historic hydrovolcanism at Deception Island (Antarctica): implications for eruption hazards
Soil solarization and sustainable agriculture
Pesticide treatments provide an effective control of soilborne pests in
vegetable and fruit crops, but their toxicity to animals and people and residual toxicity in
plants and soil, and high cost make their use hazardous and economically expensive.
Moreover, actual environmental legislation is imposing severe restrictions on the
use or the total withdrawal of most soil-applied pesticides. Therefore, an increasing
emphasis has been placed on the use of nonchemical or pesticide-reduced control
methods. Soil solarization is a nonpesticidal technique which kills a wide range
of soil pathogens, nematodes, and weed seeds and seedlings through the high soil
temperatures raised by placing plastic sheets on moist soil during periods of high
ambient temperature. Direct thermal inactivation of target organisms was found to be
the most important mechanism of solarization biocidal effect, contributed also by
a heat-induced release of toxic volatile compounds and a shift of soil microflora to
microorganisms antagonist of plant pathogens. Soil temperature and moisture are
critical variables in solarization thermal effect, though the role of plastic film is also
fundamental for the solarizing process, as it should increase soil temperature by
allowing the passage of solar radiation while reducing energetic radiative and convective
losses. Best solarizing properties were shown by low-density or vynilacetate-
coextruded polyethylene formulations, but a wide range of plastic materials
were documented as also suitable to soil solarization. Solar heating was normally
reported to improve soil structure and increase soil content of soluble nutrients, particularly
dissolved organic matter, inorganic nitrogen forms, and available cations,
and shift composition and richness of soil microbial communities, with a marked
increase of plant growth beneficial, plant pathogen antagonistic or root quick recolonizer
microorganisms. As a consequence of these effects, soil solarization was
largely documented to increase plant growth and crop yield and quality along more than two crop cycles. Most important fungal plant pathogenic species were found
strongly suppressed by the solarizing treatment, as several studies documented an
almost complete eradication of economically relevant pathogens, such as Fusarium
spp., Phytophthora spp., Pythium spp., Sclerotium spp., Verticillium spp., and their
related diseases in many vegetable and fruit crops and in different experimental
conditions. Beneficial effects on fungal pathogens were stated to commonly last
for about two growing seasons and also longer. Soil solarization demonstrated to
be effective for the control of bacterial diseases caused by Agrobacterium spp.,
Clavibacter michiganensis and Erwinia amylovora, but failed to reduce incidence
of tomato diseases caused by Pseudomonas solanacearum. Solarization was generally
found less effective on phytoparasitic nematodes than on other organisms, due
to their quicker soil recolonization compared to fungal pathogens and weeds, but
field and greenhouse studies documented consistant reductions of root-knot severity
and population densities of root-knot nematodes, Meloidogyne spp., as well as a
satisfactory control of cyst-nematode species, such as Globodera rostochiensis and
Heterodera carotae, and bulb nematode Ditylenchus dipsaci. Weeds were variously
affected by solar heating, as annual species were generally found almost completely
suppressed and perennial species more difficult to control, due to the occurrence
deep propagules not exposed to lethal temperature. Residual effect of solarization
on weeds was found much more pronounced than on nematodes and most fungal
pathogens. Soil solarization may be perfect fit for all situations in which use of
pesticides is restricted or completely banned, such as in organic production, or in
farms located next to urban areas, or specialty crops with few labeled pesticides.
Advantages of solarization also include economic convenience, as demonstrated
by many comparative benefit/cost analyses, ease of use by growers, adaptability
to many cropping systems, and a full integration with other control tools, which
makes this technique perfectly compatible with principles of integrated pest management
required by sustainable agriculture