A closely packed system of low-mass, low-density planets transiting Kepler-11

When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47?days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation.     

Can purchasing power parity help forecast the dollar?

This paper examines the information on future exchange rate movements provided by the doctrine of purchasing power parity (PPP). Previous research has studied this issue by analyzing the time-series properties of period-by-period levels of, or changes in, exchange rates. In contrast, the present study focuses on the durations of periods in which exchange rates deviate from their PPP levels. If PPP provides information about future exchange rate movements, these durations should exhibit positive duration dependence. That is, the probability of returning to PPP levels should increase as the period of deviation increases. Parametric hazard functions estimated using data from eighteen countries provide no evidence of positive duration dependence. These results are robust to alternative definitions of PPP and to alternative functional specifications. While exchange rates take prolonged swings away from their PPP levels and then eventually return, these movements apparently constitute Monte Carlo cycles in which, at any point in time, the probability of moving back toward PPP is the same as the probability of moving farther away. Thus, PPP provides no useful information on future exchange rate changes, a result consistent with market efficiency.     

Diode-like behaviour of a mitochondrial electron-transport enzyme.

In mitochondria, electrons derived from the oxidation of succinate by the tricarboxylic acid cycle enzyme succinate-ubiquinone oxido-reductase are transferred directly to the quinone pool. Here we provide evidence that the soluble form of this enzyme (succinate dehydrogenase) behaves as a diode that essentially allows electron flow in one direction only. The gating effect is observed when electrons are exchanged rapidly and directly between fully active succinate dehydrogenase and a graphite electrode. Turnover is therefore measured under conditions of continuously variable electrochemical potential. The otherwise rapid and efficient reduction of fumarate (the reverse reaction) is severely retarded as the driving force (overpotential) is increased. Such behaviour can arise if a rate-limiting chemical step like substrate binding or product release depends on the oxidation state of a redox group on the enzyme. The observation provides, for a biological electron-transport system, a simple demonstration of directionality that is enforced by kinetics as opposed to that which is assumed from thermodynamics.     

Sterility and lethality in crosses involving two translocation heterozygotes of the Germay cockroach, Blatella germanica (L.).

Productivity in crosses involving two independent reciprocal translocations in Blattella germanica are reported. Lethal effects alone could not account for the reductions in hatch since completely unproductive crosses occurred frequently. The latter are attributed to the inability of reduced numbers of viable embryos to force open the egg case. The implications for genetic control of the joint dominant effects from embryonic trapping and translocation semisterility are discussed.     

Sterility and lethality in crosses involving two translocation heterozygotes of the German cockroach,Blattella germanica (L.)

Summary Productivity in crosses involving two independent reciprocal translocations inBlattella germanica are reported. Lethal effects alone could not account for the reductions in hatch since completely unproductive crosses occurred frequently. The latter are attributed to the inability of reduced numbers of viable embryos to force open the egg case. The implications for genetic control of the joint dominant effects from embryonic trapping and translocation semisterility are discussed.Acknowledgment. This research was supported in part by Naval Facilities Engineering Command Contract No. N00025-74-C-0014 and a grant from Johnson's Wax Fund, Inc. The data on the translocation heterozygote and the wild-type matings were obtained byNancy L. Ross, and their use is gratefully acknowledged.     

Evidence of recent volcanic activity on the ultraslow-spreading Gakkel ridge

Seafloor spreading is accommodated by volcanic and tectonic processes along the global mid-ocean ridge system. As spreading rate decreases the influence of volcanism also decreases, and it is unknown whether significant volcanism occurs at all at ultraslow spreading rates (<1.5 cm yr(-1)). Here we present three-dimensional sonar maps of the Gakkel ridge, Earth's slowest-spreading mid-ocean ridge, located in the Arctic basin under the Arctic Ocean ice canopy. We acquired this data using hull-mounted sonars attached to a nuclear-powered submarine, the USS Hawkbill. Sidescan data for the ultraslow-spreading (approximately 1.0 cm yr(-1)) eastern Gakkel ridge depict two young volcanoes covering approximately 720 km2 of an otherwise heavily sedimented axial valley. The western volcano coincides with the average location of epicentres for more than 250 teleseismic events detected in 1999, suggesting that an axial eruption was imaged shortly after its occurrence. These findings demonstrate that eruptions along the ultraslow-spreading Gakkel ridge are focused at discrete locations and appear to be more voluminous and occur more frequently than was previously thought.     

Toxic effects of boric acid on the German cockroach

Boric acid is a slow-acting, inorganic insecticide whose mode of action has not been satisfactorily elucidated. Reported here is evidence which shows that ingested boric acid destroys the cellular lining of the foregut of German cockroaches,Blattella germanica (L.). This effect appears to be sufficient to bring about the death of the insects, perhaps ultimately by starvation. This finding is important because resistance to conventional insectivides may re-establish boric acid as a prominent cockroach control chemical.