Homological finiteness conditions for groups, monoids and algebras

Recently Alonso and Hermiller introduced a homological finiteness condition\break $bi{-}FP_n$ (here called {\it weak} $bi{-}FP_n$) for monoid rings, and Kobayashi and Otto introduced a different property, also called $bi{-}FP_n$ (we adhere to their terminology). From these and other papers we know that: $bi{-}FP_n \Rightarrow$ left and right $FP_n \Rightarrow$ weak $bi{-}FP_n$; the first implication is not reversible in general; the second implication is reversible for group rings. We show that the second implication is reversible in general, even for arbitrary associative algebras (Theorem 1'), and we show that the first implication {\it is} reversible for group rings (Theorem 2). We also show that the all four properties are equivalent for connected graded algebras (Theorem 4). A result on retractions (Theorem 3') is proved, and some questions are raised.Comment: 10 page

Carbon Fibers and Composites

The basic nature of composite materials is considered. Carbon fiber composites and their area of current and planned application in civil aircraft are discussed, specifically within the framework of the various aspects of risk analysis

Lining Up The P\u27s

This presentation addresses four aspects of marketing and is applicable to academic, special, school and public libraries

Large-scale fiber release and equipment exposure experiments

Outdoor tests were conducted to determine the amount of fiber released in a full scale fire and trace its dissemination away from the fire. Equipment vulnerability to fire released fibers was assessed through shock tests. The greatest fiber release was observed in the shock tube where the composite was burned with a continuous agitation to total consumption. The largest average fiber length obtained outdoors was 5 mm

Environmental effects on composites for aircraft

The influence of the operational environment on the behavior of composite materials and aircraft components fabricated with these composite materials was considered. Structural weight savings, manufacturing cost savings, and long-term environmental durability are among the factors examined. The flight service experience to date of composite components is evaluated. In addition, the influence of a number of worldwide, ground based outdoor exposures on the physical and mechanical properties of six composite materials is discussed. In particular, the current extent of the ultraviolet surface degradation and the moisture gained by diffusion is shown

Molecular bases and role of viruses in the human microbiome.

Viruses are dependent biological entities that interact with the genetic material of most cells on the planet, including the trillions within the human microbiome. Their tremendous diversity renders analysis of human viral communities ("viromes") to be highly complex. Because many of the viruses in humans are bacteriophage, their dynamic interactions with their cellular hosts add greatly to the complexities observed in examining human microbial ecosystems. We are only beginning to be able to study human viral communities on a large scale, mostly as a result of recent and continued advancements in sequencing and bioinformatic technologies. Bacteriophage community diversity in humans not only is inexorably linked to the diversity of their cellular hosts but also is due to their rapid evolution, horizontal gene transfers, and intimate interactions with host nucleic acids. There are vast numbers of observed viral genotypes on many body surfaces studied, including the oral, gastrointestinal, and respiratory tracts, and even in the human bloodstream, which previously was considered a purely sterile environment. The presence of viruses in blood suggests that virome members can traverse mucosal barriers, as indeed these communities are substantially altered when mucosal defenses are weakened. Perhaps the most interesting aspect of human viral communities is the extent to which they can carry gene functions involved in the pathogenesis of their hosts, particularly antibiotic resistance. Persons in close contact with each other have been shown to share a fraction of oral virobiota, which could potentially have important implications for the spread of antibiotic resistance to healthy individuals. Because viruses can have a large impact on ecosystem dynamics through mechanisms such as the transfers of beneficial gene functions or the lysis of certain populations of cellular hosts, they may have both beneficial and detrimental roles that affect human health, including improvements in microbial resilience to disturbances, immune evasion, maintenance of physiologic processes, and altering the microbial community in ways that promote or prevent pathogen colonization

End-to-end testing

The principle objective of the kinds of demonstration tests that are discussed is to try to verify whether or not carbon fibers that are released by burning composite parts in an aircraft-fuel fires can produce failures in electrical equipment. A secondary objective discussed is to experimentally validate the analytical models for some of the key elements in the risk analysis. The approach to this demonstration testing is twofold: limited end-to-end test are to be conducted in a shock tube; and planning for some large outdoor burn tests is being done