Continuum theory for the piezoelectric response of chiral nanotubes under uniaxial and torsional stresses

We develop and solve a continuum theory for the piezoelectric response of nanotubes under applied uniaxial and torsional stresses. We find that the piezoelectric response is controlled by the chiral angle, the aspect ratio, and two dimensionless parameters specifying the ratio of the strengths of the electrostatic and elastic energies. The model is solved in two limiting cases and the solutions are discussed. These systems are found to have several unexpected physical effects not seen in conventional bulk systems, including a strong stretch-twist coupling and the development of a significant bound charge density in addition to a surface charge density. The model is applied to estimate the piezoelectric response of a boron-nitride nanotube under uniform tensile stress.Comment: 8 pages, 4 figures. Submitted to Physical Review

An Application of the Computer to Planning

This paper discusses a simulation model which was developed to provide the National Range Division with a method for planning the National fleet of instrumented ships to support a wide variety of tests of many missile and space vehicle programs. The model simulates in a realistic way the manner and frequency with which missiles with their associated support requirements appear on a launch schedule. Then it uses the launch schedule to impose a loading upon the range ships on a simulated real-time basis. Finally the model schedules the ships against this simulated workload, and both qualitative and quantitative estimates are obtained of the future need for the given range resource. The purpose of this paper is to discuss a planning methodology used by the U.S. Air Force National Range Division. It is a simulation model wh ich generates launch schedules, schedules ships against the simulated launches, and determines the arnount of support that can be expected with a given ship pool. This model has been used to determine the number of instrumented ships needed in support of a forecasted global workload of launched missiles and space vehicles and more recently in a trade-off study between instrumented ships and aircraft. The trade-off study was done by Mr. M.J. Cleveland and others in the Operations Analysis Office within the Directorate of Operations Management of the National Range Division

Carbon Nanotubes in Helically Modulated Potentials

We calculate effects of an applied helically symmetric potential on the low energy electronic spectrum of a carbon nanotube in the continuum approximation. The spectrum depends on the strength of this potential and on a dimensionless geometrical parameter, P, which is the ratio of the circumference of the nanotube to the pitch of the helix. We find that the minimum band gap of a semiconducting nanotube is reduced by an arbitrarily weak helical potential, and for a given field strength there is an optimal P which produces the biggest change in the band gap. For metallic nanotubes the Fermi velocity is reduced by this potential and for strong fields two small gaps appear at the Fermi surface in addition to the gapless Dirac point. A simple model is developed to estimate the magnitude of the field strength and its effect on DNA-CNT complexes in an aqueous solution. We find that under typical experimental conditions the predicted effects of a helical potential are likely to be small and we discuss several methods for increasing the size of these effects.Comment: 12 pages, 10 figures. Accepted for publication in Physical Review B. Image quality reduced to comply with arxiv size limitation

Continuum Theory for Piezoelectricity in Nanotubes and Nanowires

We develop and solve a continuum theory for the piezoelectric response of one dimensional nanotubes and nanowires, and apply the theory to study electromechanical effects in BN nanotubes. We find that the polarization of a nanotube depends on its aspect ratio, and a dimensionless constant specifying the ratio of the strengths of the elastic and electrostatic interactions. The solutions of the model as these two parameters are varied are discussed. The theory is applied to estimate the electric potential induced along the length of a BN nanotube in response to a uniaxial stress.Comment: 4 pages in RevTex4, 2 epsf figure

Evolution of CO2 and H2O on Mars: A cold Early History?

The martian climate has long been thought to have evolved substantially through history from a warm and wet period to the current cold and dry conditions on the martian surface. This view has been challenged based primarily on evidence that the early Sun had a substantially reduced luminosity and that a greenhouse atmosphere would be difficult to sustain on Mars for long periods of time. In addition, the evidence for a warm, wet period of martian history is far from conclusive with many of the salient features capable of being explained by an early cold climate. An important test of the warm, wet early Mars hypothesis is the abundance of carbonates in the crust [1]. Recent high precision isotopic measurements of the martian atmosphere and discoveries of carbonates on the martian surface provide new constraints on the evolution of the martian atmosphere. This work seeks to apply these constraints to test the feasibility of the cold early scenari

Can conventional forces really explain the anomalous acceleration of Pioneer 10/11 ?

A conventional explanation of the correlation between the Pioneer 10/11 anomalous acceleration and spin-rate change is given. First, the rotational Doppler shift analysis is improved. Finally, a relation between the radio beam reaction force and the spin-rate change is established. Computations are found in good agreement with observational data. The relevance of our result to the main Pioneer 10/11 anomalous acceleration is emphasized. Our analysis leads us to conclude that the latter may not be merely artificial.Comment: 9 pages, no figur

Techno-economic feasibility assessment of calcium looping combustion using commercial technology appraisal tools

Calcium looping combustion (CaLC) is a new class of lowCO2emission technologies for thermochemical conversion of carbonaceous fuels that can help achieve the emissions reduction targets set out in the Paris Agreement. Compared to mature CO2 capture technologies, which cause net efficiency penalties higher than 7% points, CaLC results in a net efficiency penalty of 2.9% points. However, a thorough economic assessment of CaLC needs to be undertaken to evaluate its economic viability. The levelised cost of electricity is commonly used to assess the economic performance of clean energy systems. However, this method does not account for commercially important parameters, such as tax, interest, and depreciation charges. This study aimed to improve the reliability and accuracy of economic assessments of clean energy systems by implementing the net present value (NPV) approach. This approach was applied to assess the economic performance of two concepts of the CaLC-based power plant with either the conventional steam cycle (SC) or the supercritical CO2 cycle (s-CO2) for heat utilisation along with the bottom-up approach to total capital cost estimation. A parametric study for both concepts was also conducted to assess the impact of the key thermodynamic parameters on the economic performance. Although the s-CO2 case with revised assumptions was shown to result in a 1%-point lower net efficiency compared to the SC case, its break-even cost of electricity was lower by 0.81 €/MWh. Further improvements of the techno-economic performance can be sought by optimisation of the s-CO2 cycle structure

From post-combustion carbon capture to sorption-enhanced hydrogen production: A state-of-the-art review of carbonate looping process feasibility

Carbon capture and storage is expected to play a pivotal role in achieving the emission reduction targets established by the Paris Agreement. However, the most mature technologies have been shown to reduce the net efficiency of fossil fuel-fired power plants by at least 7% points, increasing the electricity cost. Carbonate looping is a technology that may reduce these efficiency and economic penalties. Its maturity has increased significantly over the past twenty years, mostly due to development of novel process configurations and sorbents for improved process performance. This review provides a comprehensive overview of the calcium looping concepts and statistically evaluates their techno-economic feasibility. It has been shown that the most commonly reported figures for the efficiency penalty associated with calcium looping retrofits were between 6 and 8% points. Furthermore, the calcium-looping-based coal-fired power plants and sorption-enhanced hydrogen production systems integrated with combined cycles and/or fuel cells have been shown to achieve net efficiencies as high as 40% and 50–60%, respectively. Importantly, the performance of both retrofit and greenfield scenarios can be further improved by increasing the degree of heat integration, as well as using advanced power cycles and enhanced sorbents. The assessment of the economic feasibility of calcium looping concepts has indicated that the cost of carbon dioxide avoided will be between 10 and 30 € per tonne of carbon dioxide and 10–50 € per tonne of carbon dioxide in the retrofit and greenfield scenarios, respectively. However, limited economic data have been presented in the current literature for the thermodynamic performance of calcium looping concepts

Water Temperature and Harmful Algal Bloom Rate

Harmful algal blooms, made up of cyanobacteria, is an increasing problem in Midwestern lakes. Nitrogen and phosphorus fertilizers used in crops such as corn and soybeans run off into streams and eventually lakes. Nitrogen and phosphorus in the form of nitrate and phosphate respectively is then used by cyanobacteria as a food source, allowing them to bloom at an alarming rate. Massive bloom events can be hazardous to both human health and the natural environment because of the release of neurotoxins, hepatotoxins and others into the air and drinking water. We set out to find if different water temperature can affect the rate at which cyanobacteria can use nitrate. Six different species of cyanobacteria were analyzed. For each species, two solutions with known amounts of nitrate and excess phosphate were mixed, with one solution kept at 31 degrees Celsius and the other kept at room temperature. Overtime, the concentration of nitrate was measured. We found that, on average, the species kept at a higher temperature were able to use nitrate faster than their colder counterpart

Exploring the Cloud Icy Early Mars Hypothesis Through Geochemistry and Mineralogy

While ancient fluvial channels have long been considered strong evidence for early surface water on Mars, many aspects of the fluvial morphology and occurrence suggest that they formed in relatively water limited conditions (com-pared to Earth) and that climatic excursions allowing for surface water might have been short-lived. Updated results mapping valley networks at higher resolution have changed this paradigm, showing that channels are much more abundant and wide-spread, and of higher order than was previously recognized, suggesting that Mars had a dense enough atmosphere and warm enough climate to allow channel formation up to 3.6-3.8 Ga. This revised view of the ancient martian climate might be broadly consistent with a climate history of Mars devised from infrared remote sensing of surface minerals, suggesting that widespread clay minerals formed in the Noachian, giving way to a sulfur-dominated surface weathering system by approx. 3.7 Ga