Observational Evidence for Mode Coupling in the Chromospheric Network

Oscillations in network bright points (NBPs) are studied at a variety of chromospheric heights. In particular, the three-dimensional variation of NBP oscillations is studied using image segmentation and cross-correlation analysis between images taken in light of Ca II K3, Ha core, Mg I b2, and Mg I b1-0.4 Å. Wavelet analysis is used to isolate wave packets in time and to search for height-dependent time delays that result from upward- or downward-directed traveling waves. In each NBP studied, we find evidence for kink-mode waves (1.3, 1.9 mHz), traveling up through the chromosphere and coupling with sausage-mode waves (2.6, 3.8 mHz). This provides a means for depositing energy in the upper chromosphere. We also find evidence for other upward- and downward-propagating waves in the 1.3-4.6 mHz range. Some oscillations do not correspond to traveling waves, and we attribute these to waves generated in neighboring regions.

Broken symmetry and pseudogaps in ropes of carbon nanotubes

We investigate the influence of tube-tube interactions in ropes of (10,10) carbon nanotubes, and find that these effects induce a pseudogap in the density of state (DOS) of the rope of width 0.1 eV at the Fermi level. In an isolated (n,n) carbon nanotube there are two bands that cross in a linear fashion at the Fermi level, making the nanotube metallic with a DOS that is constant in a 1.5 eV wide window around the Fermi energy. The presence of the neighbouring tubes causes these two bands to repel, opening up a band gap that can be as large as 0.3 eV. The small dispersion in the plane perpendicular to the rope smears out this gap for a rope with a large cross-sectional area, and we see a pseudogap at the Fermi energy in the DOS where the DOS falls to one third of its value for the isolated tube. This phenomenon should affect many properties of the behavior of ropes of (n,n) nanotubes, which should display a more semimetallic character than expected in transport and doping experiments, with the existence of both hole and electron carriers leading to qualitatively different thermopower and Hall-effect behaviors from those expected for a normal metal. Band repulsion like this can be expected to occur for any tube perturbed by a sufficiently strong interaction, for example, from contact with a surface or with other tubes.

Damage to plasmid DNA induced by low energy carbon ions

The damage induced in supercoiled plasmid DNA molecules by 1-6 keV carbon ions has been investigated as a function of ion exposure, energy and charge state. The production of short linear fragments through multiple double strand breaks has been demonstrated and exponential exposure responses for each of the topoisomers have been found. The cross section for the loss of supercoiling was calculated to be (2.2 +/- 0.5) x 10(-14) cm(2) for 2 keVC(+) ions. For singly charged carbon ions, increased damage was observed with increasing ion energy. In the case of 2 keV doubly charged ions, the damage was greater than for singly charged ions of the same energy. These observations demonstrate that ion induced damage is a function of both the kinetic and potential energies of the ion.

The energetics of huddling in two species of mole-rat (Rodentia: Bathyergidae)

Small rodents with a large surf ace-area-to-volume ratio and a high thermal conductance are likely to experience conditions where they have to expend large: amounts of energy in order to maintain a constant body temperature at low ambient temperatures. The survival of small rodents is thus dependent on their ability to reduce heat loss and increase heat production at low ambient temperatures. Two such animals are the social subterranean rodents Cryptomys damarensis (the Damaraland mole-rat) and Cryptomys hottentotus natalensis (the Natal mole-rat). This study examined the energy savings associated with huddling as a behavioural thermoregulatory mechanism to conserve energy in both these species. Individual oxygen consumption (VO2) was measured in groups ranging in size from one to 15 huddling animals for both species at ambient temperatures of 14, 18, 22, 26 and 30 degrees C. Savings in energy (VO2) were then compared between the two species. Significant differences in VO2 (p

The influence of the relative phase between the driving voltages on electron heating in asymmetric dual frequency capacitive discharges

The influence of the relative phase between the driving voltages on electron heating in asymmetric phase-locked dual frequency capacitively coupled radio frequency plasmas operated at 2 and 14 MHz is investigated. The basis of the analysis is a nonlinear global model with the option to implement a relative phase between the two driving voltages. In recent publications it has been reported that nonlinear electron resonance heating can drastically enhance the power dissipation to electrons at moments of sheath collapse due to the self-excitation of nonlinear plasma series resonance (PSR) oscillations of the radio frequency current. This work shows that depending on the relative phase of the driving voltages, the total number and exact moments of sheath collapse can be influenced. In the case of two consecutive sheath collapses a substantial increase in dissipated power compared with the known increase due to a single PSR excitation event per period is observed. Phase resolved optical emission spectroscopy (PROES) provides access to the excitation dynamics in front of the driven electrode. Via PROES the propagation of beam-like energetic electrons immediately after the sheath collapse is observed. In this work we demonstrate that there is a close relation between moments of sheath collapse, and thus excitation of the PSR, and beam-like electron propagation. A comparison of simulation results to experiments in a single and dual frequency discharge shows good agreement. In particular the observed influence of the relative phase on the dynamics of a dual frequency discharge is described by means of the presented model. Additionally, the analysis demonstrates that the observed gain in dissipation is not accompanied by an increase in the electrode’s dc-bias voltage which directly addresses the issue of separate control of ion flux and ion energy in dual frequency capacitively coupled radio frequency plasmas.

Body mass-abundance relationships are robust to cascading effects in marine food webs

Body mass has been shown to scale negatively with abundance in a wide range of habitats and ecosystems. It is believed that this relationship has important consequences for the distribution and maintenance of energy in natural communities. Some studies have shown that the relationship between body mass and abundance may be robust to major food web perturbations, fuelling the belief that natural processes may preserve the slope of this relationship and the associated cycling of energy and nutrients. Here, we use data from a long-term experimental food web manipulation to examine this issue in a semi-natural environment. Similar communities were developed in large experimental mesocosms over a six month period. Some of the mesocosms were then subjected to species removals, based on the mean strength of their trophic interactions in the communities. In treatments where the strongest interactors were removed, a community-level trophic cascade occurred. The biomass density of invertebrates increased dramatically in these communities, which led to a suppression of primary production. In spite of these widespread changes in ecosystem functioning, the slope of the relationship between body mass and abundance remained unchanged. This was the case whether average species body mass and abundance or individual organism size spectra were considered. An examination of changes in species composition before and after the experimental manipulations revealed an important mechanism for maintaining the body mass-abundance relationship. The manipulated communities all had a higher species turnover than the intact communities, with the highest turnover in communities that experienced cascading effects. As some species increased in body mass and abundance, new species filled the available size-abundance niches that were created. This maintained the overall body mass-abundance relationship and provided a stabilising structure to these experimental communities.

Massive stars exploding in a He-rich circumstellar medium - I. Type Ibn (SN 2006jc-like) events

We present new spectroscopic and photometric data of the Type Ibn supernovae 2006jc, 2000er and 2002ao. We discuss the general properties of this recently proposed supernova family, which also includes SN 1999cq. The early-time monitoring of SN 2000er traces the evolution of this class of objects during the first few days after the shock breakout. An overall similarity in the photometric and spectroscopic evolution is found among the members of this group, which would be unexpected if the energy in these core-collapse events was dominated by the interaction between supernova ejecta and circumstellar medium. Type Ibn supernovae appear to be rather normal Type Ib/c supernova explosions which occur within a He-rich circumstellar environment. SNe Ibn are therefore likely produced by the explosion of Wolf-Rayet progenitors still embedded in the He-rich material lost by the star in recent mass-loss episodes, which resemble known luminous blue variable eruptions. The evolved Wolf-Rayet star could either result from the evolution of a very massive star or be the more evolved member of a massive binary system. We also suggest that there are a number of arguments in favour of a Type Ibn classification for the historical SN 1885A (S-Andromedae), previously considered as an anomalous Type la event with some resemblance to SN 1991bg.

Dependence of laser accelerated protons on laser energy following the interaction of defocused, intense laser pulses with ultra-thin targets

The scaling of the flux and maximum energy of laser-driven sheath-accelerated protons has been investigated as a function of laser pulse energy in the range of 15-380 mJ at intensities of 10(16)-10(18) W/cm(2). The pulse duration and target thickness were fixed at 40 fs and 25 nm, respectively, while the laser focal spot size and drive energy were varied. Our results indicate that while the maximum proton energy is dependent on the laser energy and laser spot diameter, the proton flux is primarily related to the laser pulse energy under the conditions studied here. Our measurements show that increasing the laser energy by an order of magnitude results in a more than 500-fold increase in the observed proton flux. Whereas, an order of magnitude increase in the laser intensity generated by decreasing the laser focal spot size, at constant laser energy, gives rise to less than a tenfold increase in observed proton flux.

Energy sustainability indicators for urban environments

Sustainable development comprises of three dimensions. The three dimensions are the environment, the social and the economic. There have been many indicators used to measure the three dimensions of sustainability. For example air pollution, consumption of natural resources, quality of open space, noise, equity and opportunities and economic benefits from transport and land use. Urban areas constitute the most crucial factor in the sustainability. Urban systems affect and are affected by natural systems beyond their physical boundaries and in general the interdependence between the urban system and the regional and global environment is not reflected in urban decision making. The use of energy in the urban system constitutes the major element in the construction and function of urban areas. Energy impacts across the boundaries of the three dimensions of sustainability. The objective of this research is to apply energy-use-indicators to the urban system as a measure of sustainability. This methodology is applied to a case study in the United Kingdom.

Time-dependent density functional theory study of charge transfer in collisions

We study the charge transfer between colliding ions, atoms, or molecules, within time-dependent density functional theory. Two particular cases are presented, the collision between a proton and a Helium atom, and between a gold atom and a butane molecule. In the first case, proton kinetic energies between 16 keV and 1.2 MeV are considered, with impact parameters between 0.31 and 1.9 angstrom. The partial transfer of charge is monitored with time. The total cross-section is obtained as a function of the proton kinetic energy. In the second case, we analyze one trajectory and discuss spin-dependent charge transfer between the different fragments.

Energy: lessons from devolution

Geraint Ellis and Richard Cowell explain the findings of the ‘Delivering renewable energy under devolution’ project, including some reasons for Scotland’s lead.

The UK has seen massive increases in renewable energy since 1998, with installed capacity growing from 2,600 MW to 12,300 MW in 2011. This has coincided with devolution and it is within Northern Ireland, Scotland and Wales that the greatest increases have been seen.

As devolved administrations now host half of the UK’s renewable energy capacity, their policies are critical to achieving the broader UK targets. This also provides a fascinating insight into what sort of approach works best, and why. This has been the focus of a two-year study, funded by the Economic and Social Research Council, involving universities from across the UK, which indicates that Scotland is leading the way on renewable energy.

All devolved governments have offered significant support to renewable energy but have different degrees of powers in relation to energy. Scotland’s success seems to be based on the centrality of energy issues to current political aspirations, particularly the SNP, but also has cross-party support. The research suggests that the consensus on the importance of renewable energy amongst élite interests in Scotland helps to explain why Scottish governments have been empowered and enabled to make robust use of the powers available.

As it has achieved successful growth in the sector, this too helps cultivate credibility among key business interests and gives increased leverage to its position in policy discussions with the UK Government. Scotland has been more consistent over time in presenting the expansion of renewable energy as a national economic agenda, rather than just an environmental or rural development agenda. The availability of larger, windy, but relatively less contested sites for onshore wind in Scotland has meant that more projects went through central consenting procedures rather than local planning authorities. Its enhanced support for wave and tidal power technologies is also notable. These political conditions have been harder to find in the rest of the UK, making progress a little more uncertain.

Northern Ireland has used its powers (which are more extensive than Scotland’s) to facilitate small-scale renewables and bio-fuel processes, with its liberalised planning regime offering an initial boost to expanding capacity.

This has contrasted with the position in Wales, which has least control over energy but the Welsh Government has adopted a more innovative approach to strategic spatial zoning; this appears to have pulled in a larger volume of onshore wind development interest than could be expected in a comparable region of England. A downside of the Welsh approach appears to be the fact that the concentration of these wind projects in these zones has triggered public opposition and political conflict.

It therefore appears that the powers available to the devolved governments do not seem to determine which country has been able to make greatest headway, with broader political commitments being more significant. Despite this, the research does not conclude that the actions and activities undertaken by the devolved governments are necessarily the most important factors in shaping the development of renewable energy in the UK. This is because devolution is still a relatively new dimension of energy governance in the UK and decisions affecting key drivers for renewable energy investment are still made mainly in Westminster, with the Treasury exercising close budgetary control. In all areas of the UK, grid capacity expansion remains slow to achieve. The major growth in offshore wind to date has been driven mainly by Westminster and cross-UK bodies with the most significant capacity growth being in English territorial waters.

An Energy Conserving Finite Difference Scheme for Simulation of Collisions

Nonlinear phenomena play an essential role in the sound production process of many musical instruments. A common source of these effects is object collision, the numerical simulation of which is known to give rise to stability
issues. This paper presents a method to construct numerical schemes that conserve the total energy in simulations of one-mass systems involving collisions, with no conditions imposed on any of the physical or numerical parameters.
This facilitates the adaptation of numerical models to experimental data, and allows a more free parameter adjustment in sound synthesis explorations. The energy preservedness of the proposed method is tested and demonstrated though several examples, including a bouncing ball and a non-linear oscillator, and implications regarding the wider applicability are discussed.