A Computational Study of Vertical Partial Gate Carbon Nanotube FETs

A vertical partial gate carbon nanotube (CNT) field-effect transistor (FET), which is amenable to the vertical CNT growth process and offers the potential for a parallel CNT array channel, is simulated using a self-consistent atomistic approach. We show that the underlap between the gate and the bottom electrode (required for isolation between electrodes) is advantageous for transistor operation because it suppresses ambipolar conduction. A vertical CNTFET with a gate length that covers only 1/6 of the channel length has a much smaller minimum leakage current than one without underlap, while maintaining comparable on current. Both n-type and p-type transistor operations with balanced performance metrics can be achieved on a single partial gate FET by using proper bias schemes. Even with a gate underlap, it is demonstrated that increasing the CNT diameter still leads to a simultaneous increase of on current and minimum leakage current. Along with a partial gate, the simulated transistor features a significant amount of air between the surface of the channel CNT and the gate insulator, as is caused by the vertical CNT growth process. Filing this pore with a high-k insulator is shown to have the potential to decrease the on current, due to electrostatic phenomena at the source-channel contact

Optimal waste stream discharge temperature selection for dryer operations using thermo-economic assessment

A typical drying process that has liquid and gas discharge streams has been analysed and the impact of selecting various combinations of soft temperatures on heat recovery, utility targets, area targets, capital cost and total cost is reported. The method is based on the plus-minus principle and traditional pinch analysis methods for utility, area and capital cost targeting with the modification of using a ΔT contribution. Results show that there is significant benefit from optimising discharge temperatures for total cost. To achieve minimum energy consumption and total cost, heat recovery from the dryer exhaust air is necessary. Heat recovery from liquid heat sources is shown to be preferable over gas streams due to a higher film coefficient resulting in less heat exchanger area and capital cost. There is also value in making process modifications, such as combining streams or removing small streams to be solely heated by utility, to reduce the number of network heat exchangers. For the best case, the discharge temperatures of the leaving streams are 18.0 °C for water condensate (liquid stream) and 52.4 °C for the exhaust air (gas stream)

Minimising energy use in milk powder production using process integration techniques

Spray drying of milk powder is an energy intensive process and there remains a significant opportunity to reduce energy consumption by applying process integration principles. The ability to optimally integrate the drying process with the other processing steps has the potential to improve the overall efficiency of the entire process, especially when exhaust heat recovery is considered. However, achieving the minimum energy targets established using pinch analysis results in heat exchanger networks that, while theoretically feasible, are impracticable, unrealistic, contain large number of units, and ultimately uneconomic. Integration schemes that are acceptable from an operational point of view are examined in this paper. The use of evaporated water is an important factor to achieve both energy and water reductions. The economics of additional heat recovery seem favourable and exhaust heat recovery is economically justifiable on its own merits, although milk powder deposition should be minimised by selecting an appropriate target temperature for the exhaust air. This will restrict the amount of heat recovery but minimise operational risk from heat exchanger fouling. The thermodynamic constraints caused by the operating temperatures of the dryer and the poor economics exclude the use of heat pumps for exhaust heat recovery in the short to medium term

Optimal stream discharge temperatures for a dryer operation using a thermo-economic assessment

The application of traditional pinch analysis to processes involving waste streams require the discharge temperatures of the waste streams to be estimated prior to performing the pinch analysis

The modifier effect and property mutability

The modifier effect is the reduction in perceived likelihood of a generic property sentence, when the head noun is modified. We investigated the prediction that the modifier effect would be stronger for mutable than for central properties, without finding evidence for this predicted interaction over the course of five experiments. However Experiment 6, which provided a brief context for the modified concepts to lend them greater credibility, did reveal the predicted interaction. It is argued that the modifier effect arises primarily from a general lack of confidence in generic statements about the typical properties of unfamiliar concepts. Neither prototype nor classical models of concept combination receive support from the phenomenon

Co-designing food waste services in the catering sector

© 2018, Emerald Publishing Limited. Purpose: The purpose of this paper is to present results from the action research project, where sustainability professionals, local businesses and academic researchers collaborated on exploring barriers for food waste recycling in SMEs food outlets in order to inform local policy and business practices in Bristol, UK. Design/methodology/approach: The researchers conducted face-to-face, qualitative surveys of 79 catering businesses in three diverse areas of the city. The action research methodology was applied, where a range of co-researchers contributed towards study design and review. Findings: The research reveals the main barriers to recycling and how such perceptions differ depending on whether the respondents do or do not recycle, with “convenience” and “cost” being the main issue according to the already recycling participants. On the other hand, participants who do not recycle state that their main reason is “not enough waste” and “lack of space”. Practical implications: Participants recommended a range of measures, which could improve the current food waste services in Bristol. For example, they suggest that business engagement should address the barriers voiced by the participants applying the framings used by them, rather than assuming restaurants and cafes are not aware of the issue. By inviting a variety of non-academic stakeholders into the process of research design and analysis, the project addressed the imbalances in knowledge production and policy design. Originality/value: Despite the local and qualitative focus of this paper, the results and research methodology could act as a useful guide for conducting food waste action research in the policy context

Dilaton EFT framework for lattice data

We develop an effective-field-theory (EFT) framework to analyze the spectra emerging from lattice simulations of a large class of confining gauge theories. Simulations of these theories, for which the light-fermion count is not far below the critical value for transition to infrared conformal behavior, have indicated the presence of a remarkably light singlet scalar particle. We incorporate this particle by including a scalar field in the EFT along with the Nambu-Goldstone bosons (NGB's), and discuss the application of this EFT to lattice data. We highlight the feature that data on the NGB's alone can tightly restrict the form of the scalar interactions. As an example, we apply the framework to lattice data for an SU(3) gauge theory with eight fermion flavors, concluding that the EFT can describe the data well

Resummation in Hot Field Theories

There has been significant progress in our understanding of finite-temperature field theory over the past decade. In this paper, we review the progress in perturbative thermal field theory focusing on thermodynamic quantities. We first discuss the breakdown of naive perturbation theory at finite temperature and the need for an effective expansion that resums an infinite class of diagrams in the perturbative expansion. This effective expansion which is due to Braaten and Pisarski, can be used to systematically calculate various static and dynamical quantities as a weak-coupling expansion in powers of g. However, it turns that the weak-coupling expansion for thermodynamic quantities are useless unless the coupling constant is very small. We critically discuss various ways of reorganizing the perturbative series for thermal field theories in order to improve its convergence. These include screened perturbation theory (SPT), hard-thermal-loop perturbation theory (HTLPT), the Phi-derivable approach, dimensionally reduced (DR) SPT, and the DR Phi-derivable approach.Comment: 82 pages, 20 figures; v2 - typos corrected, references adde