Velocity acquired by an electron in a finite electric field in a polar crystal

The expectation value of the steady-state velocity acquired by an electron interacting with the longitudinal, optical phonons of a polar crystal in a finite electric field is analyzed quantum mechanically for arbitrary coupling strength, field strength, and temperature. The rate of loss of momentum by an electron drifting through the crystal in the applied field is expressed in a form in which the lattice coordinates (the phonons) have been eliminated exactly by path-integral methods. This expression is then evaluated by a path-integral approach similar to that used to calculate the impedance of electrons in polar crystals. We present numerical calculations of field (loss of energy per unit distance) versus velocity for three coupling strengths using the Fröhlich polaron model. In a single curve, all the expected phenomena appear, including a threshold field for producing hot electrons and a decreasing rate of energy loss with velocity for very fast electrons. Using only the experimentally measured values of the reststrahlen energy and the static and optical dielectric constants, we find an energy loss of 0.025 eV/Å for electrons near the threshold in Al2O3, which compares favorably with the experimental value of about 0.03 eV/Å. We conclude that optical-phonon scattering can indeed produce the high rate of energy loss that is present in tunnel-cathode structures

Inelastic Quantum Transport

We solve a Schrodinger equation for inelastic quantum transport that retains full quantum coherence, in contrast to previous rate or Boltzmann equation approaches. The model Hamiltonian is the zero temperature 1d Holstein model for an electron coupled to optical phonons (polaron), in a strong electric field. The Hilbert space grows exponentially with electron position, forming a non-standard Bethe lattice. We calculate nonperturbatively the transport current, electron-phonon correlations, and quantum diffusion. This system is a toy model for the constantly branching ``wavefunction of the universe''.Comment: revtex, 13 pages, 4 figure

The Tunneling Time of an Electron

There is a widely spread misconception regarding the physical significance of the various tunneling times currently used to describe metal-insulator-metal tunneling phenomena. Using quantum mechanics, the transition time of an electron tunneling from a state on one side of the barrier to a state on the other side can be determined. This time is the period of interaction between the electron and the barrier, since before and after the transition, the electron is in a quantum state of one of the metals. Furthermore, the RC time constant of the sandwich-like device and the electron transition or interaction time are equivalent representations of the same physical parameter. But none of these times is the quasiclassical "transmission time" analyzed by Hartman, which has become widely accepted as the electron-barrier interaction time, although this was clearly not his intention. In this communication we wish to point out that it is the (quantum mechanical) transition time which is the characteristic time of tunneling phenomena

Scanning optical pyrometer for measuring temperatures in hollow cathodes

Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed

Hardwiring antimicrobial resistance mitigation into global policy

This is the final version. Available on open access from Oxford University Press via the DOI in this recordIn the wake of COVID-19, antimicrobial resistance (AMR) has become termed the 'silent pandemic', with a growing number of editorials warning that international momentum for AMR mitigation is being lost amidst the global turmoil of COVID-19, economic crises and the climate emergency. Yet, is it sufficient to now simply turn the volume of the pre-existing AMR policy discourse back up? Although existing AMR initiatives have previously achieved high levels of international attention, their impact remains limited. We believe it is time to critically reflect on the achievements of the past 7 years and adapt our AMR policies based on the substantial literature and evidence base that exists on the socioecological drivers of AMR. We argue that developing a more sustainable and impactful response requires a shift away from framing AMR as a unique threat in competition with other global challenges. Instead, we need to move towards an approach that emphasizes AMR as inherently interlinked and consciously hardwires upstream interventions into broader global developmental agendas.University of ExeterWellcome TrustNorwegian Research Counci

An assessment of lessons learned in the communication and dissemination of emerging scientific issues to environmental policymakers. Part 1: Comprehensive Report

The relationship between science and policy is often seen as difficult. Yet from climate change to food security, many of the biggest challenges facing the world today rely upon effective policy making, based upon the best science and evidence. We need to make sure that we have established the right level of communication and relationship between these two groups. This research project sets out to look at that communication process: to examine closely the communications involved in real-life science-to-policy case studies and to identify the lessons from the past that can help us deal with scientific issues that are emerging now and those that will emerge in the future

Communicating antimicrobial resistance: the need to go beyond human health

This is the final version. Available on open access from Oxford University Press via the DOI in this recor

Evaluating antimicrobial resistance in the global shrimp industry

This is the final version. Available on open access from Wiley via the DOI in this recordData availability statement: The research data supporting this publication are provided within this paper.Antimicrobial resistance (AMR) is a growing threat to global public health, and the overuse of antibiotics in animals has been identified as a major risk factor. With high levels of international trade and direct connectivity to the aquatic environment, shrimp aquaculture may play a role in global AMR dissemination. The vast majority of shrimp production occurs in low- and middle-income countries, where antibiotic quality and usage is widely unregulated, and where the integration of aquaculture with family livelihoods offers many opportunities for human, animal and environmental bacteria to come into close contact. Furthermore, in shrimp growing areas, untreated waste is often directly eliminated into local water sources. These risks are very different to many other major internationally-traded aquaculture commodities, such as salmon, which is produced in higher income countries where there are greater levels of regulation and well-established management practices. Assessing the true scale of the risk of AMR dissemination in the shrimp industry is a considerable challenge, not least because obtaining reliable data on antibiotic usage is very difficult. Combating the risks associated with AMR dissemination is also challenging due to the increasing trend towards intensification and its associated disease burden, and because many farmers currently have no alternatives to antibiotics for preventing crop failure. In this review, we critically assess the potential risks the shrimp industry poses to AMR dissemination. We also discuss some of the possible risk mitigation strategies that could be considered by the shrimp industry as it strives for a more sustainable future in production.CGIAR Research Program on Fish Agri‐food Systems (FISH)Biotechnology and Biological Sciences Research Council (BBSRC)Economic and Social Research Council (ESRC

Raising awareness of antimicrobial resistance in rural aquaculture practice in Bangladesh through digital communications: a pilot study

This is the final version. Available on open access from Taylor & Francis Group via the DOI in this recordOne of the key strategic objectives of the World Health Organisation's global antimicrobial resistance (AMR) action plan is to improve public awareness and understanding of this issue. Very few AMR awareness campaigns have targeted the animal production sector, particularly in low- and middle-income countries (LMICs) where rural communities can be geographically difficult to access via traditional face-to-face community engagement methods. Aquaculture is a major food production industry in Bangladesh and across Asia, an area which poses a significant risk to global AMR dissemination. In this pilot study, we sought to investigate the potential for digital communication materials to rapidly and effectively communicate AMR messages to rural aquaculture farmers in Bangladesh. Working with stakeholders from the Bangladesh aquaculture industry, we developed a 4-minute digital animation designed specifically for this audience and assessed its capacity to engage and communicate AMR messages to farmers. We then conducted a small-scale social media campaign, to determine the potential for rapidly disseminating AMR awareness materials to a large audience across Bangladesh, where there is an extensive 4 G internet network and an ever-increasing proportion of the population (57% as of December 2019) have mobile internet access. Thirty-six farmers were surveyed: all of them liked this method of communication and 97% said it would change the way they use antibiotics in the future. Through the social media campaign, the animation received 9,100 views in the first 2 weeks alone. Although preliminary, these results demonstrate the huge potential for digital communication methods for the rapid and widespread communication of AMR awareness materials to rural aquaculture communities in Bangladesh and across Asia. Our results support the need for more research into the most appropriate and effective content of AMR awareness campaigns for aquaculture communities and question the need for explaining the science underlying AMR in such communication materials