Calculation of the specific heat in ultra-thin free-standing silicon membranes

The specific heat of ultra-thin free-standing membranes is calculated using the elastic continuum model. We first obtain the dispersion relations of the discrete set of acoustic modes in the system. The specific heat is then calculated by summing over the discrete out-of-plane wavevector component and integrating over the continuous in-plane wavevector of these waves. In the low-temperature regime (T < 4 K), the flexural polarization is seen to have the highest contribution to the total specific heat. This leads to a linear dependence with temperature, resulting in a larger specific heat for the membrane compared to that of the bulk counterpar

Blockchain electricity trading using tokenised power delivery contracts. ESRI Working Paper No. 649 December 2019

This paper proposes a new mechanism for forward selling renewable electricity generation. In this transactive framework, a wind or solar farm may directly sell to consumers a claim on their future power output in the form of nonfungible blockchain tokens. Using the flexibility of smart contract code, which executes irrevocably on a blockchain, the realised generation levels will offset the token holders’ electricity consumption in near real-time. To elucidate the flexibility offered by such smart contracts, two ways of structuring these power delivery instruments are considered: firstly, an exotic tranched system, where more senior tokens holders enjoy priority claims on power, as compared against a simpler pro-rata scheme, where the realised output of a generator is equally apportioned between token holders. A notional market simulation is provided to explore whether, for instance, consumers could exploit the flatter power delivery profiles of more senior tranches to better schedule their responsive demands

Book review: the eagle and the dragon by Serge Gruzinski

This book addresses two episodes from the sixteenth century which shaped the relationship between Europe and the civilisations of China and Mexico. James B. Cuffe writes that while the text is at times a little difficult to read, the book nevertheless offers a highly rewarding account of both European colonialism, and the histories of Central America and China

The effect of payday lending restrictions on liquor sales

We exploit a change in lending laws to estimate the causal effect of restricting access to payday loans on liquor sales. Leveraging lender- and liquor store-level data, we find that the changes reduce sales, with the largest decreases at stores located nearest to lenders. By focusing on states with state-run liquor monopolies, we account for supply side variables that are typically unobserved. Our results are the first to quantify how credit constraints affect spending on liquor, and suggest mechanisms underlying some loan usage. These results illustrate that the benefits of lending restrictions extend beyond personal finance and may be large

Evidence on the Efficacy of School-Based Incentives for Healthy Living

We analyze the effects of a school-based incentive program on children's exercise habits. The program offers children an opportunity to win prizes if they walk or bike to school during prize periods. We use daily child-level data and individual fixed effects models to measure the impact of the prizes by comparing behavior during prize periods with behavior during non-prize periods. Variation in the timing of prize periods across different schools allows us to estimate models with calendardate fixed effects to control for day-specific attributes, such as weather and proximity to holidays. On average, we find that being in a prize period increases riding behavior by sixteen percent, a large impact given that the prize value is just six cents per participating student. We also find that winning a prize lottery has a positive impact on ridership over subsequent weeks; consider heterogeneity across prize type, gender, age, and calendar month; and explore differential effects on the intensive versus extensive margins.health; exercise; children; school; incentives; active commuting

Too Busy for School? The Effect of Athletic Participation on Absenteeism

While existing research supports that participation in high-school athletics is associated with better education and labour-market outcomes, the mechanisms through which these benefits accrue are not well established. We use data from a large public-school district to retrieve an estimate of the causal effect of high-school athletic participation on absenteeism. We show that active competition decreases absences, with most of the effect driven by reductions in unexcused absences truancy among active male athletes declines significantly, with the effects larger in earlier grades and for black and Hispanic boys. Strong game-day effects are also evident, in both boys and girls, as truancy declines on game days are offset with higher rates of absenteeism the following day. Addressing the effects on academic performance, we find significant heterogeneity in the response to active athletic participation by race, gender and family structure, with boys not in dual-parent households exhibiting small academic improvements in semesters in which they experienced greater athletic participation

Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultra-thin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from \sim 4.7 ns to 5 ps with decreasing membrane thickness from \sim 194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures