Radiation from a Charge Uniformly Accelerated for All Time

A recent paper of Singal [Gen. Rel. Grav. 27 (1995), 953-967] argues that a uniformly accelerated particle does not radiate, in contradiction to the consensus of the research literature over the past 30 years. This note points out some questionable aspects of Singal's argument and shows how similar calculations can lead to the opposite conclusion.Comment: LaTeX, 9 pages, to appear in General Relativity and Gravitatio

Validation of an Acoustic Impedance Prediction Model for Skewed Resonators

An impedance prediction model was validated experimentally to determine the composite impedance of a series of high-aspect ratio slot resonators incorporating channel skew and sharp bends. Such structures are useful for packaging acoustic liners into constrained spaces for turbofan noise control applications. A formulation of the Zwikker-Kosten Transmission Line (ZKTL) model, incorporating the Richards correction for rectangular channels, is used to calculate the composite normalized impedance of a series of six multi-slot resonator arrays with constant channel length. Experimentally, acoustic data was acquired in the NASA Langley Normal Incidence Tube over the frequency range of 500 to 3500 Hz at 120 and 140 dB OASPL. Normalized impedance was reduced using the Two-Microphone Method for the various combinations of channel skew and sharp 90o and 180o bends. Results show that the presence of skew and/or sharp bends does not significantly alter the impedance of a slot resonator as compared to a straight resonator of the same total channel length. ZKTL predicts the impedance of such resonators very well over the frequency range of interest. The model can be used to design arrays of slot resonators that can be packaged into complex geometries heretofore unsuitable for effective acoustic treatment

Intergenerational conflicts about social equity, expectations and obligations: lessons from the United States

"Justice across generations" has become a policy issue throughout the Western-industrial world during the past decade. Debate about intergenerational equity involves the distribution of resources and obligations across age groups and generations. Our analysis suggests that debate centres around five specific issues: (1) Conceptual confusions between age groups and family generations; (2) disagreements over the meaning of "equity"; (3) arguments about whether supporting the old is an unbearable public cost; (4) differing opinions about familial expectations, obligations and burdens; and (5) discrepancies between media coverage and empirical evidence on intergenerational relations. While these issues first surfaced in the United States, it can be expected that such disputes will arise in many other nations with similar economic environments, demographic profiles, and public sentiment regarding welfare and entitlement spending. We conclude by examining the potential for increased intergenerational solidarity as an outcome of discussions about equity

Dishwashing and Water Conservation: An Opportunity for Environmental Education

Technological advances have continued to improve the cleaning and water efficiency of automatic dishwashers. However, research indicates consumers waste water and energy during the dishwashing process through their actions and decisions. To gain more current information on consumer dishwasher usage, a major university conducted a kitchen usage study that asked questions about dishwashing. The study found that consumers use water unnecessarily by pre-rinsing dishes at the sink before placing them into the dishwasher. Numerous factors underlie this behavior. It seems clear that consumer education about proper dishwashing procedures is needed

The evolution and consequences of snaR family transposition in primates

The small NF90 associated RNA (snaR) family of small noncoding RNAs (ncRNA) appears to have evolved from retrotransposon ancestors at or soon after pivotal stages in primate evolution. snaRs are thought to be derived from a FLAM C-like (free left Alu monomer) element through multiple short insertion/deletion (indel) and nucleotide (nt) substitution events. Tracing snaR’s complex evolutionary history through primate genomes led to the recent discovery of two novel retrotransposons: the Alu/snaR related (ASR) and catarrhine ancestor of snaR (CAS) elements. ASR elements are present in the genomes of Simiiformes, CAS elements are present in Old World Monkeys and apes, and snaRs are restricted to the African Great Apes (Homininae, including human, gorilla, chimpanzee and bonobo). Unlike their ancestors, snaRs have disseminated by multiple rounds of segmental duplication of a larger encompassing element. This process has produced large tandem gene arrays in humans and possibly precipitated the accelerated evolution of snaR. Furthermore, snaR segmental duplication created a new form of chorionic gonadotropin β subunit (CGβ) gene, recently classified as Type II CGβ, which has altered mRNA tissue expression and can generate a novel short peptide

Expression and Action of Kit Ligand/Stem Cell Factor in Normal Human and Bovine Ovarian Surface Epithelium and Ovarian Cancer

Greater than 95% of ovarian cancers originate from the epithelial cells on the surface of the ovary termed ovarian surface epithelium (OSE). A normal aspect of OSE function is repeated proliferation after ovulation, and this is postulated to be involved in part in the onset of ovarian cancer. The hypothesis tested is that locally produced growth factors have an important role in controlling OSE proliferation. The current study investigates the potential role of the growth factor kit ligand (KL)/stem cell growth factor and its receptor c-kit in normal OSE biology and ovarian cancer. Human tumors from borderline, stage I, and stage III cases of ovarian cancer were found to express KL and c-kit protein in the epithelial cell component by ICC analysis. The stromal cell component of human ovarian tumors contained little immunostaining. Bovine ovarian physiology and endocrinology are similar to the human such that cow ovaries were used as a model system to investigate normal OSE functions. KL and c-kit proteins were detected in the OSE from both normal human and bovine ovaries. Adjacent ovarian stromal tissue contained less intense but positive KL and c-kit immunostaining. To extend the ICC results, RNA was collected from normal bovine OSE and ovarian stromal cells to examine KL gene expression. KL transcripts were detected in cultured OSE and stromal cells by Northern blot analysis. KL gene expression was found to be high in freshly isolated OSE but low in freshly isolated stroma using a quantitative polymerase chain reaction procedure. Levels of KL gene expression in cultured OSE and stroma increased to high levels. Observations indicate that normal OSE expresses high levels of KL in vivo and in vitro. The actions of KL on the growth of both normal OSE cells and ovarian cancer cells was investigated. KL was found to stimulate the growth of normal OSE cells in a similar manner to epidermal growth factor. Observations demonstrate the production and action of KL by normal OSE cells and ovarian cancer cells. Coexpression of KL and c-kit by normal OSE suggests that KL can act as an autocrine factor for OSE. The local production and action of KL on OSE provides insight into normal OSE biology, and a factor that may be involved in the onset and progression of ovarian cancer