Core formation during early accretion of the Earth

Recent studies are leading to a better understanding of the formation of the earth's metal core. This new information includes: better knowledge of the physics of metal segregation, improved geochemical data on the abundance of siderophile and chalcophile elements in the silicate part of the earth, and experimental data on the partitioning behavior of siderophile and chalcophile elements. Extensive melting of the earth as a result of giant impacts, accretion, or the presence of a dense blanketing atmosphere is thought to have led to the formation of the core. Collision between a planet-sized body and the earth may have also produced the moon. Near the end of accretion, core formation evidently ceased as upper mantle conditions became oxidizing. The accumulation of the oceans is a consequence of the change to oxidizing conditions.     

cDNA expression cloning of the IL-1 receptor, a member of the immunoglobulin superfamily

Interleukin-1 alpha and -1 beta (IL-1 alpha and IL-1 beta) are cytokines that participate in the regulation of immune responses, inflammatory reactions, and hematopoiesis. A direct expression strategy was used to clone the receptor for IL-1 from mouse T cells. The product of the cloned complementary DNA binds both IL-1 alpha and IL-1 beta in a manner indistinguishable from that of the native T cell IL-1 receptor. The extracellular, IL-1 binding portion of the receptor is 319 amino acids in length and is composed of three immunoglobulin-like domains. The cytoplasmic portion of the receptor is 217 amino acids long.     

The immunological synapse balances T cell receptor signaling and degradation

The immunological synapse is a specialized cell-cell junction between T cell and antigen-presenting cell surfaces. It is characterized by a central cluster of antigen receptors, a ring of integrin family adhesion molecules, and temporal stability over hours. The role of this specific organization in signaling for T cell activation has been controversial. We use in vitro and in silico experiments to determine that the immunological synapse acts as a type of adaptive controller that both boosts T cell receptor triggering and attenuates strong signals.     

Astronomy and Solar Physics: X-ray Gas Scintillation Spectrometer Experiment

The payload complement on Spacelab 1 included a spectrometer for observations of the brighter cosmic x-ray sources. The primary scientific objective was to study the detailed spectral features of cosmic x-ray sources and their associated temporal variations over a wide energy range from about 2 to 80 kiloelectron volts. The instrument, based on the gas scintillation proportional counter, had a geometrical area of some 180 square centimeters with an energy resolution of about 9 percent at 7 kiloelectron volts. The results presented here show new results from two galactic binary x-ray sources, Cygnus X-3 and Centaurus X-3, and from the Perseus cluster of galaxies. The excellent energy resolution of the instrument permits line features to be identified in these sources with unprecedented quality.     

Somatic mutation in genes for the variable portion of the immunoglobulin heavy chain

The size of the gene pool potentially encoding antibodies to p-azophenyl arsonate has been examined. A heavy chain-specific full-length complementary DNA clone has been constructed with the use of messenger RNA from a hybridoma that produces antibodies to the arsonate hapten and bears nearly a full complement of the determinants comprising the cross-reactive idiotype (CRI). The sequences of both the complementary DNA clone and the corresponding immunoglobulin heavy chain have been independently determined. A probe for the variable region gene was prepared from the original heavy chain complementary DNA clone and used to analyze, by Southern filter hybridization, genomic DNA from both A/J (CRI positive) and BALB/c (CRI negative) mice. Approximately 20 to 25 restriction fragments containing "germline" variable region gene segments were detected in both strains, and many are shared by both, Since 35 CRI-positive heavy chains have been partially sequenced thus far and 31 are different, the results of the hybridization analysis suggest that somatic mutation events involving the variable region gene segments of the heavy chain play a role in the origin of the amino acid sequence diversity seen in this system.     

Statistical power and sea turtle nesting beach surveys: How long and when?

Identifying long-term population trends is essential for the conservation of species of concern. With money and personnel often in short supply, the success of a monitoring program to provide an estimate of population trend requires an efficient survey design that can detect biologically important changes within some prescribed budgetary framework. In this paper we illustrate how costs can be reduced while maintaining an efficient design using a nesting beach survey of female hawksbill sea turtles (Eretmochelys imbricata) in the Eastern Caribbean as a specific example. We compared the statistical power of the current, intensive protocol with those of shorter duration and differing start date to generate general guidelines on sampling. Counts of individual turtles from 1987-2003 were analyzed using Poisson log-linear regression and models with both fixed and random effects describing the temporal variability were explored. We estimate that the current 20 week saturation-tagging survey design could detect a 3% per annum growth with acceptable statistical power (>0.8) in less than 14 years. However, by changing the current survey start date and counting for only 10 weeks, it is possible to detect similar trends with little loss of power while reducing monitoring costs by 25-50%. Our analyses indicate that the statistical power of surveys for hawksbills is influenced by the timing and duration of the survey because of their effect on the proportion of the annual number of nesting females that the survey captures. This simplifies estimating the power of a prospective survey program.     

Evaluation of a model for Escherichia coli O157:H7 colonization in streptomycin-treated adult cattle

OBJECTIVE: To develop a repeatable model for studying colonization with streptomycin-resistant Escherichia coli O157:H7 in adult cattle. ANIMALS: 5 adult mixed-breed beef cattle. PROCEDURES: Cattle were surgically cannulated in the duodenum, treated daily with streptomycin (33 mg/kg) via the duodenal cannula prior to and during experimental colonizations, and colonized with 10(10) CFUs of streptomycin-resistant E coli O157:H7 via the duodenal cannula. Colonization of rectal mucus and shedding in feces were monitored. Antimicrobials were administered to eliminate the colonizing strain so that 5 repeated colonization experiments could be performed. A comprehensive analysis of colonization was performed at necropsy. RESULTS: Streptomycin treatment resulted in improved experimental colonization variables, compared with untreated controls, during initiation (days 2 to 6) and early maintenance (days 7 to 12) of colonization. Elimination of the colonizing strain followed by 5 repeated colonizations in the same animals indicated the repeatability of the protocol. Positive results of bacteriologic culture of feces 7 and 12 days after colonization were obtained in 100% and 84% of samples, respectively, across all animals and trials. At necropsy, highest magnitude recovery was in terminal rectal mucus. CONCLUSIONS AND CLINICAL RELEVANCE: The model was highly repeatable and novel with respect to streptomycin treatment, use of duodenal cannulas, and repeated colonizations of the same animals. Its use in adult cattle, from which most bovine-derived food originates, is critical to the study of preharvest food safety. The findings have implications for understanding intermittency of shedding in the field and for proposed vaccine-based interventions.