Resonant amplification of magnetic domain-wall motion by a train of current pulses

The current-induced motion of magnetic domain walls confined to nanostructures is of interest for applications in magnetoelectronic devices in which the domain wall serves as the logic gate or memory element. The injection of spin-polarized current below a threshold value through a domain wall confined to a pinning potential results in its precessional motion within the potential well. We show that by using a short train of current pulses, whose length and spacing are tuned to this precession frequency, the domain wall's oscillations can be resonantly amplified. This makes possible the motion of domain walls with much reduced currents, more than five times smaller than in the absence of resonant amplification.     

A route to the brightest possible neutron source?

We review the potential to develop sources for neutron scattering science and propose that a merger with the rapidly developing field of inertial fusion energy could provide a major step-change in performance. In stark contrast to developments in synchrotron and laser science, the past 40 years have seen only a factor of 10 increase in neutron source brightness. With the advent of thermonuclear ignition in the laboratory, coupled to innovative approaches in how this may be achieved, we calculate that a neutron source three orders of magnitude more powerful than any existing facility can be envisaged on a 20- to 30-year time scale. Such a leap in source power would transform neutron scattering science.     

Molecular borromean rings

The realization of the Borromean link in a wholly synthetic molecular form is reported. The self-assembly of this link, which is topologically achiral, from 18 components by the template-directed formation of 12 imine and 30 dative bonds, associated with the coordination of three interlocked macrocycles, each tetranucleating and decadentate overall, to a total of six zinc(II) ions, is near quantitative. Three macrocycles present diagonally in pairs, six exo-bidentate bipyridyl and six endo-diiminopyridyl ligands to the six zinc(II) ions. The use, in concert, of coordination, supramolecular, and dynamic covalent chemistry allowed the highly efficient construction, by multiple cooperative self-assembly processes, of a nanoscale dodecacation with an approximate diameter of 2.5 nanometers and an inner chamber of volume 250 A(3), lined with 12 oxygen atoms.     

Allosteric mechanisms of signal transduction

Forty years ago, a simple model of allosteric mechanisms (indirect interactions between distinct sites), used initially to explain feedback-inhibited enzymes, was presented by Monod, Wyman, and Changeux. We review the MWC theory and its applications for the understanding of signal transduction in biology, and also identify remaining issues that deserve theoretical and experimental substantiation.     

Status and trends of amphibian declines and extinctions worldwide

The first global assessment of amphibians provides new context for the well-publicized phenomenon of amphibian declines. Amphibians are more threatened and are declining more rapidly than either birds or mammals. Although many declines are due to habitat loss and overutilization, other, unidentified processes threaten 48% of rapidly declining species and are driving species most quickly to extinction. Declines are nonrandom in terms of species' ecological preferences, geographic ranges, and taxonomic associations and are most prevalent among Neotropical montane, stream-associated species. The lack of conservation remedies for these poorly understood declines means that hundreds of amphibian species now face extinction.     

The status of the world's land and marine mammals: diversity, threat, and knowledge

Knowledge of mammalian diversity is still surprisingly disparate, both regionally and taxonomically. Here, we present a comprehensive assessment of the conservation status and distribution of the world's mammals. Data, compiled by 1700+ experts, cover all 5487 species, including marine mammals. Global macroecological patterns are very different for land and marine species but suggest common mechanisms driving diversity and endemism across systems. Compared with land species, threat levels are higher among marine mammals, driven by different processes (accidental mortality and pollution, rather than habitat loss), and are spatially distinct (peaking in northern oceans, rather than in Southeast Asia). Marine mammals are also disproportionately poorly known. These data are made freely available to support further scientific developments and conservation action.     

Vibrationally quantum-state-specific reaction dynamics of H atom abstraction by CN radical in solution

Solvent collisions can often mask initial disposition of energy to the products of solution-phase chemical reactions. Here, we show with transient infrared absorption spectra obtained with picosecond time resolution that the nascent HCN products of reaction of CN radicals with cyclohexane in chlorinated organic solvents exhibit preferential excitation of one quantum of the C-H stretching mode and up to two quanta of the bending mode. On time scales of approximately 100 to 300 picoseconds, the HCN products undergo relaxation to the vibrational ground state by coupling to the solvent bath. Comparison with reactions of CN radicals with alkanes in the gas phase, known to produce HCN with greater C-H stretch and bending mode excitation (up to two and approximately six quanta, respectively), indicates partial damping of the nascent product vibrational motion by the solvent. The transient infrared spectra therefore probe solvent-induced modifications to the reaction free energy surface and chemical dynamics.     

Effects of form of effluent,season and urease inhibitor on ammonia volatilization from dairy farm effluent applied to pasture

Purpose

With land application of farm effluents from cows during housing or milking as an accepted practice, there are increasing concerns over its effect on nitrogen (N) loss through ammonia (NH₃) volatilization. Understanding the relative extent and seasonal variation of NH₃ volatilization from dairy effluent is important for the development of management practices for reducing NH₃ losses. The objectives of this study were to determine potential NH₃ losses from application of different types of dairy effluent (including both liquid farm dairy effluent (FDE) and semi-solid dairy farm manure) to a pasture soil during several contrasting seasons and to evaluate the potential of the urease inhibitor (UI)—N-(n-butyl) thiophosphoric triamide (NBTPT, commercially named Agrotain^®) to reduce gaseous NH₃ losses.

Material and methods

Field plot trials were conducted in New Zealand on an established grazed pasture consisting of a mixed perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) sward. An enclosure method, with continuous air flow, was used to compare the effects of treatments on potential NH₃ volatilization losses from plots on a free-draining volcanic parent material soil which received either 0 (control) or 100 kg N ha^?1 as FDE or manure (about 2 and 15 % of dry matter (DM) contents in FDE or manure, respectively) with or without NBTPT (0.25 g NBTPT kg^?1 effluent N). The experiment was conducted in the spring of 2012 and summer and autumn of 2013.

Results and discussion

Results showed that application of manure and FDE, both in fresh and stored forms, potentially led to NH₃ volatilization, ranging from 0.6 to 19 % of applied N. Difference in NH₃ losses depended on the season and effluent type. Higher NH₃ volatilization was observed from both fresh and stored manure, compared to fresh and stored FDE. The difference was mainly due to solid contents. The losses of NH₃ were closely related to NH₄ ⁺-N content in the two types of manure. However, there was no relationship between NH₃ losses and NH₄ ⁺-N content in either type of FDE. There was no consistent seasonal pattern, although lower NH₃ losses from fresh FDE and stored FDE applied in spring compared to summer were observed. Potential NH₃ losses from application of fresh FDE or manure were significantly (P?<?0.05) reduced by 27 to 58 % when NBTPT was added, but the UI did not significantly reduce potential NH₃ volatilization from stored FDE or manure.

Conclusions

This study demonstrated that NH₃ losses from application of FDE were lower than from manure and that UIs can be effective in mitigating NH₃ emissions from land application of fresh FDE and manure. Additionally, reducing the application of FDE in summer can also potentially reduce NH₃ volatilization from pasture soil.