Transformation of a star into a planet in a millisecond pulsar binary

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.     

Action at a distance along a DNA

A number of ways are known by which an event at one location on a DNA molecule can affect an event at a distant location on the same molecule. Three classes of mechanisms are described for such distal actions: tracking or translocation of a protein along a DNA, the association of two proteins bound at separate sites to form a DNA loop in between, and distal interactions that are affected by the topology of the DNA. The basic characteristics of each type of mechanism are discussed in terms of the known physicochemical properties of DNA. The various modes of action at a distance are often interrelated. Examples include the formation of positively and negatively supercoiled DNA loops by tracking and the strong effects of DNA topology on looping.     

Conversion of a peroxiredoxin into a disulfide reductase by a triplet repeat expansion

Pathways for the reduction of protein disulfide bonds are found in all organisms and are required for the reductive recycling of certain enzymes including the essential protein ribonucleotide reductase. An Escherichia coli strain that lacks both thioredoxin reductase and glutathione reductase grows extremely poorly. Here, we show that a mutation occurring at high frequencies in the gene ahpC, encoding a peroxiredoxin, restores normal growth to this strain. This mutation is the result of a reversible expansion of a triplet nucleotide repeat sequence, leading to the addition of one amino acid that converts the AhpC protein from a peroxidase to a disulfide reductase. The ready mutational interconversion between the two activities could provide an evolutionary advantage to E. coli.     

Development of a receptor on a foreign nerve fiber in a Pacinian corpuscle

When the sensory fiber of a Pacinian corpuscle (in cat mesentery) is transected (at the inferior mesenteric nerve) transduction fails within 30 hours: the nerve ending produces no generator potentials in response to mechanical stimulation. Electrically elicited nerve impulse conduction continues for at least another 18 hours. A transducer mechanism develops on a regenerating nerve fiber when this fiber enters the denervated corpuscle. Such transducer development takes place on myelinated fibers from the inferior mesenteric nerve, which normally supplies corpuscles, as well as on myelinated hypogastric nerve fibers, which normally do not go to corpuscles, including fibers larger than the original corpuscle afferents.     

Methanol as a gasoline extender: a critique

The tests conducted with the three vehicles at different emission control levels suggest that, in the area of fuel economy and emissions, potential benefits with methanol blends are related to carburetion and are only significant in the case of the rich-operating cars built before emission control standards were imposed. Theoretical considerations related to methanol's leaning effect on carburetion support this conclusion. Potential advantages for methanol in these areas are therefore continuously diminishing as the older cars leave the roads. At present, these older cars use only about one-fourth of the totalc motor gasoline consumed and, before methanol could be used on a large scale, this fraction would be much smaller. The use of methanol in gasoline would almost certainly create severe product quality problems. Water contamination could lead to phase separation in the distribution system and possibly in the car tank as well, and this would require additional investment in fuel handling and blending equipment. Excess fuel volatility in hot weather may also have adverse effects on car performance if the methanol blends include typical concentrations of butanes and pentanes. Removal of these light hydrocarbon components would detract from methanol's role as a gasoline extender and if current fuel volatility specifications were maintained, its use could lead to a net loss in the total available energy for use in motor fuels. Car performance problems associated with excessively lean operation would also be expected in the case of a significant proportion of late-model cars which are adjusted to operate on lean fuel-air mixtures. If methanol does become available in large quantities, these factors suggest that it would be more practical to use it for purposes other than those related to the extending of motor gasoline, such as for gas turbines used for electric power generation. In this case, the "pure" methanol would act as a cleanburning fuel, having none of the potentially severe product quality problems associated with its use in motor gasoline, while the fuel oil or natural gas cLirrently burned in these tuLrbines CotLild be diverted to other ulses.     

Identification of a sex pheromone from a spider

The compounds (R)-3-hydroxybutyric acid and its dimer, (R)-3-[(R)-3-hydroxybutyryloxy]-butyric acid, have been identified as sex pheromones of a spider. These compounds elicit web reduction behavior by males of Linyphia triangularis (Clerck) on the webs of unmated adult females.     

Solid-state chemistry: a a rediscovered chemical frontier

Chemical bonding in solids is not completely understood, mainly because of the wide variation in the chemical properties of the elements. Many difficult challenges remain in predicting the composition, structure, and the properties of new materials. Consequently, the synthesis of novel solids is as much an art as a science. Discoveries of new compounds and structure types highlight the versatility that nature has allowed with the relatively small number of elements. This article explores the long-term challenges in solid-state chemistry and then focuses on efforts at Cornell to prepare new solids.     

Capture of a single molecule in a nanocavity

We describe a heptameric protein pore that has been engineered to accommodate two different cyclodextrin adapters simultaneously within the lumen of a transmembrane beta barrel. The volume between the adapters is a cavity of approximately 4400 cubic angstroms. Analysis of single-channel recordings reveals that individual charged organic molecules can be pulled into the cavity by an electrical potential. Once trapped, an organic molecule shuttles back and forth between the adapters for hundreds of milliseconds. Such self-assembling nanostructures are of interest for the fabrication of multianalyte sensors and could provide a means to control chemical reactions.     

离散型三维竞争系统中某群体竞争获胜的条件

研究了离散型三维竞争系统的模型结构与稳定性,得到了这类竞争系统中各类平衡点的坐标及其性质,获得了系统在某些边界上的平衡点渐近稳定的充分条件和不稳定的充分条件,并由此得到了系统中的某群体在竞争过程中竞争获胜淘汰所有对手的条件和参与竞争的各个群体永不和谐的充分条件.     

一个具有非自治性扰动的拟线性椭圆方程非平凡解的存在性

利用变量替换和Ekeland变分原理,在R～N上获得了一类具有非自治扰动的拟线性椭同方程非平凡解的存在性结果.

Abstract：

The existence of a nontrivial solution is obtained for a quasilinear elliptic equations on RN with a non-autonomous perturbation by the change of variable and the Ekeland's variational principle.     

Identification of a juvenile hormone-like compound in a crustacean

Juvenile hormone (JH) has central roles in the regulation of insect development and reproduction but has not previously been identified in other arthropod classes. The hemolymph of a crustacean, Libinia emarginata (Leach), has now been analyzed for JH-like compounds. Samples contained 0.003 to 0.030 nanogram of JH III per milliliter and 10 to 50 nanograms of methyl farnesoate per milliliter; methyl farnesoate is a compound structurally related to JH III that has JH bioactivity. Several tissues were examined for synthesis and secretion of JH-like compounds. Of these tissues, only the mandibular organs produced and secreted JH III and methyl farnesoate. However, microchemical analysis revealed that this JH III was racemic, and thus likely an artifactual oxidation product of methyl farnesoate. Secretion of methyl farnesoate was related to reproduction in females, with the highest rates observed in Libinia near the end of the ovarian cycle when oocyte growth and vitellogenesis are greatest. These results indicate that JH-like compounds such as methyl farnesoate have regulatory roles in crustaceans.     

Allergenic component of a liverwort: a sesquiterpene lactone

Frullania spp. (Hepaticae, Jungermanniales) are agents of allergies. Extraction and fractionation of Frullania tamarisci has given, as the only allergenic component isolated, a levorotatory crystalline sutbstance, the structure of which is demonstrated. It is a sesquiterpene lactone. The racemic (+/-) form is isolated from a mixed sample of Frullania tamarisci and Frullania dilatata; the dextrorotatory form, from Frullania dilatata. The observed allergenic properties are shared by some other-sesquiterpene lactones.