Anolis cooki

Number of Pages: 2Integrative BiologyGeological Science

New laser materials for laser diode pumping

The potential advantages of laser diode pumped solid state lasers are many with high overall efficiency being the most important. In order to realize these advantages, the solid state laser material needs to be optimized for diode laser pumping and for the particular application. In the case of the Nd laser, materials with a longer upper level radiative lifetime are desirable. This is because the laser diode is fundamentally a cw source, and to obtain high energy storage, a long integration time is necessary. Fluoride crystals are investigated as host materials for the Nd laser and also for IR laser transitions in other rare earths, such as the 2 micron Ho laser and the 3 micron Er laser. The approach is to investigate both known crystals, such as BaY2F8, as well as new crystals such as NaYF8. Emphasis is on the growth and spectroscopy of BaY2F8. These two efforts are parallel efforts. The growth effort is aimed at establishing conditions for obtaining large, high quality boules for laser samples. This requires numerous experimental growth runs; however, from these runs, samples suitable for spectroscopy become available

On the hard sphere model and sphere packings in high dimensions

We prove a lower bound on the entropy of sphere packings of $\mathbb R^d$ of density $\Theta(d \cdot 2^{-d})$. The entropy measures how plentiful such packings are, and our result is significantly stronger than the trivial lower bound that can be obtained from the mere existence of a dense packing. Our method also provides a new, statistical-physics-based proof of the $\Omega(d \cdot 2^{-d})$ lower bound on the maximum sphere packing density by showing that the expected packing density of a random configuration from the hard sphere model is at least $(1+o_d(1)) \log(2/\sqrt{3}) d \cdot 2^{-d}$ when the ratio of the fugacity parameter to the volume covered by a single sphere is at least $3^{-d/2}$. Such a bound on the sphere packing density was first achieved by Rogers, with subsequent improvements to the leading constant by Davenport and Rogers, Ball, Vance, and Venkatesh

What about local climate governance? A review of promise and problems

A large proportion of greenhouse gas emissions is produced in urban areas, particularly in high income countries. Cities are also vulnerable to the impacts of climate change, and particularly so in developing countries. Therefore, local climate policies for mitigation and adaptation have to play an important role in any effective global climate protection strategy. Based upon a systematic literature review, this article gives a comprehensive overview of motivation and challenges for local climate governance. A large part of the literature focuses on mitigation and cities in industrialized countries. The review also includes the smaller and emerging body of literature on adaptation and cities in developing or industrializing countries. Motivations and challenges we find fall into broad categories like ‘economic’, ‘informational’, ‘institutional’, ‘liveability’ or ‘political/cultural’. We conclude that the mix of motivation and challenges is city-specific, and that the national framework conditions are important. It matters, whether cities engage in mitigation or adaptation policies, whether they are located in developing, industrializing or industrialized countries, and at which stage of climate policy-making cities are. For many cities, cost savings are a primary motivation for local mitigation policies, while perceived vulnerability and a commitment to development is the primary motivator for adaptation policies. The collective action problem of climate protection (also known as ‘Tragedy of the Commons’) and inappropriate legal frameworks are key barriers to mitigation policies. Challenges for adaptation include financial constraints, and a lack of expertise, cooperation, leadership and political support. Understanding their specific motivation and challenges may support cities in developing appropriate local climate action plans. Furthermore, the understanding of motivation and challenges can inform other policy levels that want to help realize the local climate protection potential.Climate policy, local authorities, cities, mitigation, adaptation, energy, local climate governance

On kissing numbers and spherical codes in high dimensions

We prove a lower bound of $\Omega (d^{3/2} \cdot (2/\sqrt{3})^d)$ on the kissing number in dimension $d$. This improves the classical lower bound of Chabauty, Shannon, and Wyner by a linear factor in the dimension. We obtain a similar linear factor improvement to the best known lower bound on the maximal size of a spherical code of acute angle $\theta$ in high dimensions