Magneto-optical conductivity in graphene including electron-phonon coupling

We show how coupling to an Einstein phonon $\omega_E$ affects the absorption peaks seen in the optical conductivity of graphene under a magnetic field $B$. The energies and widths of the various lines are shifted, and additional peaks arise in the spectrum. Some of these peaks are Holstein sidebands, resulting from the transfer of spectral weight in each Landau level (LL) into phonon-assisted peaks in the spectral function. Other additional absorption peaks result from transitions involving split LLs, which occur when a LL falls sufficiently close to a peak in the self-energy. We establish the selection rules for the additional transitions and characterize the additional absorption peaks. For finite chemical potential, spectral weight is asymmetrically distributed about the Dirac point; we discuss how this causes an asymmetry in the transitions due to left- and right-handed circularly polarized light and therefore oscillatory behavior in the imaginary part of the off-diagonal Hall conductivity. We also find that the semiclassical cyclotron resonance region is renormalized by an effective-mass factor but is not directly affected by the additional transitions. Last, we discuss how the additional transitions can manifest in broadened, rather than split, absorption peaks due to large scattering rates seen in experiment.Comment: 24 pages, 21 figure

Phonon structures in the electronic density of states of graphene in magnetic field

Unlike in ordinary metals, in graphene, phonon structure can be seen in the quasiparticle electronic density of states, because the latter varies on the scale of the phonon energy. In a magnetic field, quantization into Landau levels creates even more significant variations. We calculate the density of states incorporating electron-phonon coupling in this case and find that the coupling has pronounced new effects: shifting and broadening of Landau levels, creation of new peaks, and splitting of any Landau levels falling near one of the new peaks. Comparing our calculations with a recent experiment, we find evidence for a phonon with energy similar to but somewhat greater than the optical $E_{2g}$ mode and a coupling corresponding to a mass enhancement parameter $\lambda \simeq 0.07$.Comment: 6 pages, 4 figures, final version to be published in EP

Speculative Behavior of Institutional Investors

A survey compared speculative behavior in two groups of institutional investors. The "experimental" group held stocks that had shown extraordinary price increases over the preceding year that also had high price earnings ratios. The control group held randomly selected stocks. In Shiller and Pound [1986] we argued that the survey results gave some support to some diffusion or epidemic models for interest in the stocks in the experimental group. Here, we show that the two groups are similar in describing their investment strategy as relating to a theory about fundamental value rather than about the kind of stocks that are becoming attractive to investors. However, the experimental group is less likely to make explicit comparisons of price with measures of fundamental value, and differs from the control group in their attitudes toward timing, price changes, and short-term earnings disappointment. Overall, these results appear consistent with the notion that price changes unrelated to fundamentals may be caused by contagious enthusiasm about fundamentals amongst institutional investors. The holding patterns of those experimental group investors who said that they were unsystematic in their stock choice are studied. These investors tended to show gradually increasing holdings over the period of stock price increase. Reasons respondents gave for the gradual increase are discussed.

Ionospheric Electron Density During Solar Eclipse of 20 July 1963

Ionospheric electron density during solar eclips

Body shape preferences: Associations with rater body shape and sociosexuality

Copyright @ 2013 Price et al.This article has been made available through the Brunel Open Access Publishing Fund.There is accumulating evidence of condition-dependent mate choice in many species, that is, individual preferences varying in strength according to the condition of the chooser. In humans, for example, people with more attractive faces/bodies, and who are higher in sociosexuality, exhibit stronger preferences for attractive traits in opposite-sex faces/bodies. However, previous studies have tended to use only relatively simple, isolated measures of rater attractiveness. Here we use 3D body scanning technology to examine associations between strength of rater preferences for attractive traits in opposite-sex bodies, and raters' body shape, self-perceived attractiveness, and sociosexuality. For 118 raters and 80 stimuli models, we used a 3D scanner to extract body measurements associated with attractiveness (male waist-chest ratio [WCR], female waist-hip ratio [WHR], and volume-height index [VHI] in both sexes) and also measured rater self-perceived attractiveness and sociosexuality. As expected, WHR and VHI were important predictors of female body attractiveness, while WCR and VHI were important predictors of male body attractiveness. Results indicated that male rater sociosexuality scores were positively associated with strength of preference for attractive (low) VHI and attractive (low) WHR in female bodies. Moreover, male rater self-perceived attractiveness was positively associated with strength of preference for low VHI in female bodies. The only evidence of condition-dependent preferences in females was a positive association between attractive VHI in female raters and preferences for attractive (low) WCR in male bodies. No other significant associations were observed in either sex between aspects of rater body shape and strength of preferences for attractive opposite-sex body traits. These results suggest that among male raters, rater self-perceived attractiveness and sociosexuality are important predictors of preference strength for attractive opposite-sex body shapes, and that rater body traits -with the exception of VHI in female raters- may not be good predictors of these preferences in either sex.This study is funded by the Brunel University School of Social Sciences and made available through the Brunel Open Access Publishing Fund

AC impedance study of degradation of porous nickel battery electrodes

AC impedance spectra of porous nickel battery electrodes were recorded periodically during charge/discharge cycling in concentrated KOH solution at various temperatures. A transmission line model (TLM) was adopted to represent the impedance of the porous electrodes, and various model parameters were adjusted in a curve fitting routine to reproduce the experimental impedances. Degradation processes were deduced from changes in model parameters with electrode cycling time. In developing the TLM, impedance spectra of planar (nonporous) electrodes were used to represent the pore wall and backing plate interfacial impedances. These data were measured over a range of potentials and temperatures, and an equivalent circuit model was adopted to represent the planar electrode data. Cyclic voltammetry was used to study the characteristics of the oxygen evolution reaction on planar nickel electrodes during charging, since oxygen evolution can affect battery electrode charging efficiency and ultimately electrode cycle life if the overpotential for oxygen evolution is sufficiently low

Survey Evidence on Diffusion of Interest Among Institutional Investors

Contagion or epidemic models of financial markets are proposed in which interest in or attention to individual stocks is spread by word of mouth. The models give alternative interpretations of the random walk character of stock prices. A questionnaire survey of institutional investors was undertaken to ascertain the relevance of such models. Questions elicited what fraction of these investors were unsystematic and allowed themselves to be influenced by word-of-mouth communications or other salient stimuli. Rough indications of the infection rate and removal rate were produced. Investors in stocks whose price had recently increased dramatically to a high P/E ratio were contrasted with a control group of investors

Effects of electron-phonon coupling on Landau levels in graphene

We calculate the density of states (DOS) in graphene for electrons coupled to a phonon in an external magnetic field. We find that coupling to an Einstein mode of frequency $\omega_E$ not only shifts and broadens the Landau levels (LLs), but radically alters the DOS by introducing a new set of peaks at energies $E_n\pm\omega_E$, where $E_n$ is the energy of the $n$th LL. If one of these new peaks lies sufficiently close to a LL, it causes the LL to split in two; if the system contains an energy gap, a LL may be split in three. The new peaks occur outside the interval $(-\omega_E,\omega_E)$, leaving the LLs in that interval largely unaffected. If the chemical potential is greater than the phonon frequency, the zeroth LL lies outside the interval and can be split, eliminating its association with a single Dirac point. We find that coupling to an extended phonon distribution such as a Lorentzian or Debye spectrum does not qualitatively alter these results.Comment: 16 pages, 17 figures, 1 table. Accepted for publication in PR

Listening to young people’s views of the coast:Living Coast Youth Voice

We have summarised the knowledge that was co-created with young people here. However, we would like to encourage those adults who planned to read just this summary to also hear directly form the young people by reading Chapter 3. Introduction Living Coast was a national partnership pilot project developed by Natural England1 (an organisation that looks after nature and landscapes in England). Natural England wants to help people from all walks-of-life enjoy the benefits of a new long distance path around England: the England Coast Path. By 2020, the path will stretch for approximately 2,700 miles around our beautiful English coastline and open up new stretches of the coastline. Natural England wants to understand how and why young people already use and enjoy the coast, and why others do not (or cannot). They want to know what can be done to help as many young people as possible benefit from the spectacular views, sea air, exercise and nature that the path and surrounding areas offer. In this research, we worked with young people aged 11 – 18 to create new knowledge about what makes it easy or hard for them to make the most of the coast, and what they suggest would help. This is important because there is little other evidence about this, nationally. This research took place in Barrow-in-Furness in Cumbria – a place with a high quality natural environment and areas that fall in the bottom 10% and 3% nationally on measures of deprivation. Cumbria was one of three Living Coast pilot areas in 2018/19. The other two are on the Durham Heritage Coast and the Solent. All three will inform how Natural England and its partners develop work at the coast.2 Research focus The study asked the following research questions: Q What do you think of the coast? Q How do you use the coast? Q How do you benefit from the coast? Q What makes it easy to go to, and enjoy, the coast? Q What makes it hard to go to, and enjoy, the coast? Q What would help you to go more often? Q What suggestions would you make to Natural England about how they can help? Methods used Our methods mixed and blended methods, techniques and principles from participation practice and social science. To do this we: 2 1. In total, we met 59 young people from a mix of ages, genders, ethnicities, and distances from the coast, prioritising those who live in areas that fall in the lowest 3% or 10% in the Indices of Multiple Deprivation. 2. Set up a Participatory Advisory Group (PAG) of eight young people, aged 14, to be our research advisors, comment on our methods and help us interpret and analyse our findings. 3. Met with 47 young people in six groups, from a range of community and educational settings, for 90-minutes each. During these sessions, we worked with young people to create maps, discuss their good and bad experiences, ease of getting to the coast, and the influence of money, jobs, belonging and culture to their views of the coast. 4. Summarised what young people said in this first round in pictures. 5. Ran two ‘Creative Horizons’ events a fortnight later, in two sessions when 22 young people (of those who had taken part in the mapping sessions) were joined by 4 new young people. In these sessions young people took charge of which topics to explore and how to create new knowledge through art, story, rap, music, poems, drama, or discussion. 6. Faithfully reported what young people said in this report and in a film. Findings We found that young people have a mix of attitudes towards the coast, with some finding it a place of enjoyment, peace, and adventure and others finding it boring, uncomfortable and a place of natural and human dangers. Young people go to a mix of places. Some are familiar beaches, which are closer to home and easier to get to, and others are destinations young people enjoy with friends and family but require transport to get to. Walking and dog walking were most often mentioned as activities to do at the coast, with some saying they swam in the sea but many others not mentioning swimming at all or saying they couldn’t swim. For a few, cycling was a key part of enjoying the coast and a couple of young people mentioned anglin g and water sports. Young people in all groups described psychological, physical and social wellbeing benefits of being by the sea. They said that it helped them cope with stress, be fitter and enjoy time with family and friends. The things that made it easier to go included: their own attitudes and confidence, being able to get there, having someone available to go with, feeling safe and belonging and also the time of year and the weather. The barriers to going to the seaside were numerous and interconnected and particularly hard for young people living with multiple pressures and disadvantages. Negative personal attitudes and fears included boredom and anxiety, such as about risks or body shaming. A range of issues around social barriers included not feeling safe from attack, feeling they didn’t belong, that adults and peers were judging them badly as well as outright racism, sexism and homophobia. Young people also said they lacked information about where to go, how to get there, what to do once there, natural risks such as tides, quick sands and rock falls. Getting there and affording to go were practical barriers, as was having someone available to go with them. Litter and dirty beaches deter young people. At this exposed location, bad weather with fierce winds and driving rain can make it too unpleasant to go. Young peoples’ messages to the Natural England and its partners about enjoying the coast: Help make it safe (from attack and by changing adult attitudes toward us) 3 Help us get there Give us information Provide affordable events and activities Run nature trips Provide shelter