Hydrogen Transport and the Spatial Requirements of Renewable Energy

Unlike oil and coal, which are compressed forms of energy, renewable energy requires unusually large land areas. This article calculates the consequences of a switch to hydrogen-cell vehicles powered by electricity from wind turbines. It then re-does the calculation for three other green energy sources : wave power ; biofuels ; solar energy. We argue that policy-makers and social scientists need to understand the significant spatial demands of a move to a carbon-free society.Renewable energy ; wind power ; land use ; energy efficiency ; wind turbines ; transport ; environmental ; solar ; biomass ; wave

Plastid redox state and sugars: Interactive regulators of nuclear-encoded photosynthetic gene expression

Feedback regulation of photosynthesis by carbon metabolites has long been recognized, but the underlying cellular mechanisms that control this process remain unclear. By using an Arabidopsis cell culture, we show that a block in photosynthetic electron flux prevents the increase in transcript levels of chlorophyll a/b-binding protein and the small subunit of Rubisco that typically occurs when intracellular sugar levels are depleted. In contrast, the expression of the nitrate reductase gene, which is induced by sugars, is not affected. These findings were confirmed in planta by using Arabidopsis carrying the firefly luciferase reporter gene fused to the plastocyanin and chlorophyll a/b-binding protein 2 gene promoters. Transcription from both promoters increases on carbohydrate depletion. Blocking photosynthetic electron transport with 3-(3',4'-dichlorophenyl)-1,1'-dimethylurea prevents this increase in transcription. We conclude that plastid-derived redox signaling can override the sugar-regulated expression of nuclear-encoded photosynthetic genes. In the sugar-response mutant, sucrose uncoupled 6 (sun6), plastocyanin-firefly luciferase transcription actually increases in response to exogenous sucrose rather than decreasing as in the wild type. Interestingly, plastid-derived redox signals do not influence this defective pattern of sugar-regulated gene expression in the sun6 mutant. A model, which invokes a positive inducer originating from the photosynthetic electron transport chain, is proposed to explain the nature of the plastid-derived signal

Photoelectron Yield and Photon Reflectivity from Candidate LHC Vacuum Chamber Materials with Implications to the Vacuum Chamber Design

Studies of the photoelectron yield and photon reflectivity at grazing incidence (11 mrad) from candidate LHC vacuum chamber materials have been made on a dedicated beam line on the Electron Positron A ccumulator (EPA) ring at CERN. These measurements provide realistic input toward a better understanding of the electron cloud phenomena expected in the LHC. The measurements were made using synchrotro n radiation with critical photon energies of 194 eV and 45 eV; the latter corresponding to that of the LHC at the design energy of 7 TeV. The test materials are mainly copper, either, i) coated by co- lamination or by electroplating onto stainless steel, or ii) bulk copper prepared by special machining. The key parameters explored were the effect of surface roughness on the reflectivity and the pho toelectron yield at grazing photon incidence, and the effect of magnetic field direction on the yields measured at normal photon incidence. The implications of the results on the electron cloud phenom ena, and thus the LHC vacuum chamber design, is discussed

Electron-spectroscopic investigation of metal-insulator transition in Sr2Ru1-xTixO4 (x=0.0-0.6)

We investigate the nature and origin of the metal-insulator transition in Sr2Ru1-xTixO4 as a function of increasing Ti content (x). Employing detailed core, valence, and conduction band studies with x-ray and ultraviolet photoelectron spectroscopies along with Bremsstrahlung isochromat spectroscopy, it is shown that a hard gap opens up for Ti content greater than equal to 0.2, while compositions with x<0.2 exhibit finite intensity at the Fermi energy. This establishes that the metal-insulator transition in this homovalent substituted series of compounds is driven by Coulomb interaction leading to the formation of a Mott gap, in contrast to transitions driven by disorder effects or band flling.Comment: Accepted for publication in Phys. Rev.

Biomass estimations of invasives Yaupon, Chinese Privet and Chinese Tallow in east Texas Hardwood and Pine Ecosystems

Forest understory fuels can have profound effects on fire behavior and crown fire initiation. Accurate fire behavior prediction in understory fuels is an essential component for estimating fire intensity and severity during wildfire and prescribed fire events. This study focused on estimating temporal and seasonal changes in fuel loading parameters associated with the expansion of invasive yaupon (Ilex vomitoria), Chinese privet (Ligustrum sinense), and Chinese tallow (Triadica sebifera) in East Texas pine and hardwood ecosystems. Fuel loading data of invasive species infested sites indicated significant increases in understory biomass when compared to 1988 estimates, suggesting a clear need to revise regional fuel models. Multiple and simple regression biomass prediction equations were developed for all three-invasive species to facilitate fuel load estimates. These improved prediction equations will enhance fire management efforts as well as invasive species mitigation efforts in east Texas

Universality in the Crossover between Edge Channel and Bulk Transport in the Quantum Hall Regime

We present a new theoretical approach for the integer quantum Hall effect, which is able to describe the inter-plateau transitions as well as the transition to the Hall insulator. We find two regimes (metallic and insulator like) of the top Landau level, in which the dissipative bulk current appears in different directions. The regimes are separated by a temperature invariant point.Comment: 4 page, 2 eps figures included, submitte

Synchrotron radiation studies of the LHC dipole beam screen with COLDEX

The cold bore experiment (COLDEX) installed in a beam line of the electron-positron accumulator (EPA) at CERN, has been used to study the effect of synchrotron radiation onto the LHC dipole beam screen. The ~ 2 m long cryostat, that can be cooled below 3 K, is fitted with an actively cooled beam screen. A 'sawtooth' copper co-laminated type beam screen has been submitted to grazing synchrotron radiation with 194 eV critical energy. Experiments studying the effect of photon dose, gas condensation onto beam screen or cold bore and temperature oscillations is presented. Implications to LHC operation is discussed

Mechanical and Vacuum Stability Design Criteria for the LHC Experimental Vacuum Chambers

Four colliding beam experiments are planned for the Large Hadron Collider (LHC) requiring experimental vacuum chambers in the interaction region. The beam pipe should be as transparent as possible to scattered particles and detectors should be as close as possible to the interaction point, resulting in small diameter beam pipes. This, together with the bunched beam structure, makes ion induced pre ssure bump instability, well known from the Intersecting Storage Rings (ISR) at CERN, a potential problem. Adequate conductance, cleanliness of the beam pipes and efficient pumping are required to avo id this instability. Suppression of electron multipacting requires appropriate surface coatings and cleaning procedures. Small beam pipe diameters must provide the required beam stay clear and still a llow margin for alignment and stability inside detectors. Design criteria to ensure both local and global stability under static and dynamic mechanical loads are defined