Negative quantum capacitance in graphene nanoribbons with lateral gates

We present numerical simulations of the capacitive coupling between graphene nanoribbons of various widths and gate electrodes in different configurations. We compare the influence of lateral metallic or graphene side gate structures on the overall back gate capacitive coupling. Most interestingly, we find a complex interplay between quantum capacitance effects in the graphene nanoribbon and the lateral graphene side gates, giving rise to an unconventional negative quantum capacitance. The emerging non-linear capacitive couplings are investigated in detail. The experimentally relevant relative lever arm, the ratio between the coupling of the different gate structures, is discussed.Comment: 8 pages, 6 figure

Using the atmospheric CO2 growth rate to constrain the CO2 flux from land use and land cover change since 1900

We explore the ability of the atmospheric CO2 record since 1900 to constrain the source of CO2 from land use and land cover change (hereafter “land use”), taking account of uncertainties in other terms in the global carbon budget. We find that the atmospheric constraint favors land use CO2 flux estimates with lower decadal variability and can identify potentially erroneous features, such as emission peaks around 1960 and after 2000, in some published estimates. Furthermore, we resolve an offset in the global carbon budget that is most plausibly attributed to the land use flux. This correction shifts the mean land use flux since 1900 across 20 published estimates down by 0.35 PgC year−1 to 1.04 ± 0.57 PgC year−1, which is within the range but at the low end of these estimates. We show that the atmospheric CO2 record can provide insights into the time history of the land use flux that may reduce uncertainty in this term and improve current understanding and projections of the global carbon cycle. © 2022 The Authors. Global Change Biology published by John Wiley Sons Ltd

Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass

We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and observed transport evidence of single anisotropic-mass valley occupancy for the electrons in a 150 \AA wide QW. Our calculations of strain and quantum confinement for these samples predict single anisotropic-mass valley occupancy for well widths $W$ greater than 53 \AA. Below this, double-valley occupation is predicted such that the longitudinal mass axes are collinear. We observed mobility anisotropy in the electronic transport along the crystallographic directions in the ratio of 2.8, attributed to the mass anisotropy as well as anisotropic scattering of the electrons in the X-valley of AlAs

Parachute Swivel Mechanism for planetary entry

A parachute swivel mechanism (PSM) for planetary entry missions such as a Mars probe (MARSNET) or return of cometary material samples (ROSETTA mission) has been developed. The purpose of the PSM is to decouple the spin of the probe from the parachute, with low friction torque, during both the deployment and descent phases. Critical requirements are high shock loads, low friction, low temperatures, and several years of storage in the deep space environment (during the cruise phase of the probe, prior to operation). The design uses a main thrust ball bearing to cope with the load requirement and a smaller thrust ball bearing for guiding of the shaft. Except for use on the Viking and Galileo swivels, it appears that this type of bearing has very rarely been employed in space mechanisms, so that little is known of its friction behavior with dry lubrication. A slip ring assembly allows the transfer of electrical power for post-reefing of the parachute. A test program has been conducted covering the environmental conditions of Mars entry and Earth reentry. This paper describes requirement constraints, model missions of planetary entries, a bearing trade-off, analyses performed, design details, the lubrication system, and test results (friction torque versus load/spin rate). In addition, the design of the test rig is addressed

Security analysis for agroterrorism: applying the threat, vulnerability, consequence framework to developing countries

"We examine access to, use of, and participation in decisions on improved water supply in the Volta basin of Ghana, one of the first countries to introduce a community-based approach to rural water supply on a large scale. While 71 percent of the households interviewed have access to improved water, 43 percent of these continue to use unsafe sources as their main domestic water source. Our results indicate that quality perceptions and opportunity costs play an important role in households' choice of water source. The effect of prices and income levels on this choice differs according to the pricing system used. Given that supply characteristics such as the location and pricing system affect household decisions to use the improved source, households may try to influence these characteristics in their favor during the community decision-making process for the improved source. However, less than 40 percent of the households interviewed participated in decisions on location or technology. We argue that the decision whether to participate depends on three main factors: (i) the household's bargaining power, (ii) the potential benefits from influencing outcomes, and (iii) the cost of participation, (mainly opportunity cost of time). Our results indicate that bargaining power matters In some developing countries the potential exists for agroterrorism to cause widespread disruption through loss of sustenance, income and production. Defense of agriculture may also be problematic because of the lack stability and basic biosecurity infrastructure for the detection and prevention of diseases or invasive species. Currently new methodological approaches for terrorism risk assessments are being actively explored for resource prioritization. One such methodology for risk based allocation of resources is Threat, Vulnerability, and Consequence (TVC) Analysis. A qualitative application of the TVC framework is used to analyze the risk of agroterrorism in developing countries relative to industrialized countries. The analysis suggests that evidence exists to demonstrate general terrorist threats, vulnerability of agriculture and, depending on the country, potentially serious consequences arising from argoterrorism. Where specific threats emerge, action may be needed by the international community to strengthen biosecurity systems in developing countries through: increasing global cooperation, capacity building in monitoring, remediation and risk analysis technologies, and the dissemination of novel technologies for control of pests and diseases." Authors' AbstractCapacity strengthening, Water-supply Management, Agroterrorism, Biosecurity, Risk analysis, resource allocation, Terrorism, Governance,