Wavefront sensing of atmospheric phase distortions at the Palomar 200-in. telescope and implications for adaptive optics

Major efforts in astronomical instrumentation are now being made to apply the techniques of adaptive optics to the correction of phase distortions induced by the turbulent atmosphere and by quasi-static aberrations in telescopes themselves. Despite decades of study, the problem of atmospheric turbulence is still only partially understood. We have obtained video-rate (30 Hz) imaging of stellar clusters and of single-star phase distortions over the pupil of the 200" Hale telescope on Palomar Mountain. These data show complex temporal and spatial behavior, with multiple components arising at a number of scale heights in the atmosphere; we hope to quantify this behavior to ensure the feasibility of adaptive optics at the Observatory. We have implemented different wavefront sensing techniques to measure aperture phase in wavefronts from single stars, including the classical Foucault test, which measures the local gradient of phase, and the recently-devised curvature sensing technique, which measures the second derivative of pupil phase and has formed the real-time wavefront sensor for some very productive astronomical adaptive optics. Our data, though not fast enough to capture all details of atmospheric phase fluctuations, provide important information regarding the capabilities that must be met by the adaptive optics system now being built for the 200" telescope by a team at the Jet Propulsion Lab. We describe our data acquisition techniques, initial results from efforts to characterize the properties of the turbulent atmosphere at Palomar Mountain, and future plans to extract additional quantitative parameters of use for adaptive optics performance predictions

A Brief Outline of the Growth of Philippine Law

The Philippine Constitution was adopted pursuant to the mandate of the Tydings-McDuffie Law that it should be republican in form and contain a bill of rights. It contains a declaration of principles which includes five major items. These are: the Philippines are a republican state and sovereignty resides in, and all government authority emanates from, the people; national defense is the prime duty of government and all citizens may be required by law to render personal military or civil service; war is renounced as an instrument of national policy and the generally accepted principles of international law are adopted as part of the nation\u27s law; aid and support should be given by the government to parents in rearing youth for civic efficiency; and that the promotion of social justice to insure the well-being and economic security of all the people should be the concern of the state

Predicting the Deforestation–Trend Under Different Carbon–Prices

Background: Global carbon stocks in forest biomass are decreasing by 1.1 Gt of carbon annually, owing to continued deforestation and forest degradation. Deforestation emissions are partly offset by forest expansion and increases in growing stock primarily in the extra-tropical north. Innovative financial mechanisms would be required to help reducing deforestation. Using a spatially explicit integrated biophysical and socio-economic land use model we estimated the impact of carbon price incentive schemes and payment modalities on deforestation. One payment modality is adding costs for carbon emission, the other is to pay incentives for keeping the forest carbon stock intact. Results, Baseline scenario calculations show that close to 200mil ha or around 5% of today’s forest area will be lost between 2006 and 2025, resulting in a release of additional 17.5 GtC. Today’s forest cover will shrink by around 500 million hectares, which is 1/8 of the current forest cover, within the next 100 years. The accumulated carbon release during the next 100 years amounts to 45 GtC, which is 15% of the total carbon stored in forests today. Incentives of 6 US$/tC for the standing biomass paid every 5 years will bring deforestation down by 50$/year. On the other hand a carbon tax of 12$/tC harvested forest biomass will also cut deforestation by half. The tax income will decrease from 6 billion US$ in 2005 to 4.3 billion US$in 2025 and 0.7 billion US$ in 2100 due to decreasing deforestation speed. Conclusions, Avoiding deforestation requires financial mechanisms that make retention of forests economically competitive with the currently often preferred option to seek profits from other land uses. Incentive payments need to be at a very high level to be effective against deforestation. Taxes on the other hand will generate budgetary revenues by the regions which are already poor. A combination of incentives and taxes could turn out to be a viable solution for this dilemma. Increasing the value of forest land and thereby make it less easily prone to deforestation would act as a strong incentive to increase productivity of agricultural and fuelwood production, which could be supported by revenues generated by the deforestation tax.Deforestation, Carbon Prices

SHARP: A Spatially Higher-order, Relativistic Particle-in-Cell Code

Numerical heating in particle-in-cell (PIC) codes currently precludes the accurate simulation of cold, relativistic plasma over long periods, severely limiting their applications in astrophysical environments. We present a spatially higher-order accurate relativistic PIC algorithm in one spatial dimension, which conserves charge and momentum exactly. We utilize the smoothness implied by the usage of higher-order interpolation functions to achieve a spatially higher-order accurate algorithm (up to fifth order). We validate our algorithm against several test problems -- thermal stability of stationary plasma, stability of linear plasma waves, and two-stream instability in the relativistic and non-relativistic regimes. Comparing our simulations to exact solutions of the dispersion relations, we demonstrate that SHARP can quantitatively reproduce important kinetic features of the linear regime. Our simulations have a superior ability to control energy non-conservation and avoid numerical heating in comparison to common second-order schemes. We provide a natural definition for convergence of a general PIC algorithm: the complement of physical modes captured by the simulation, i.e., those that lie above the Poisson noise, must grow commensurately with the resolution. This implies that it is necessary to simultaneously increase the number of particles per cell and decrease the cell size. We demonstrate that traditional ways for testing for convergence fail, leading to plateauing of the energy error. This new PIC code enables us to faithfully study the long-term evolution of plasma problems that require absolute control of the energy and momentum conservation.Comment: 26 pages, 19 figures, discussion about performance is added, published in Ap

Growth of beam-plasma instabilities in the presence of background inhomogeneity

We explore how inhomogeneity in the background plasma number density alters the growth of electrostatic unstable wavemodes of beam plasma systems. This is particularly interesting for blazar-driven beam-plasma instabilities, which may be suppressed by inhomogeneities in the intergalactic medium as was recently claimed in the literature. Using high resolution Particle-In-Cell simulations with the SHARP code, we show that the growth of the instability is local, i.e., regions with almost homogeneous background density will support the growth of the Langmuir waves, even when they are separated by strongly inhomogeneous regions, resulting in an overall slower growth of the instability. We also show that if the background density is continuously varying, the growth rate of the instability is lower; though in all cases, the system remains within the linear regime longer and the instability is not extinguished. In all cases, the beam loses approximately the same fraction of its initial kinetic energy in comparison to the uniform case at non-linear saturation. Thus, inhomogeneities in the intergalactic medium are unlikely to suppress the growth of blazar-driven beam-plasma instabilities.Comment: 10 pages, 6 figures, Accepted by ApJ, comments welcom

Radiation-induced radical formation in solid state sugars: a review of recent EMR and DFT results

Carbohydrates are important constituents of several biological systems, including DNA, and elucidating their radiation chemistry is therefore of general importance. In particular, sugar radicals play a crucial role in radiation-induced single and double strand breaks in DNA, which can lead to mutations and, finally, cancer. Certain sugars such as sucrose (table sugar) are also promising dosimetric materials. An advanced knowledge of the radiation-induced processes in carbohydrates may therefore provide better insight into the DNA radiation chemistry and aid in establishing reliable sugar dosimetry protocols. The first step in acquiring such knowledge is identification of the radical structures. Electron Magnetic Resonance (EMR) experiments on irradiated sugar single crystals allow a very detailed characterisation of the radicals via the g-tensor and the hyperfine interactions between the unpaired electron spin and the nuclear spins in the lattice. Single crystals also offer the advantage of mimicking to some extent the compact structure of chromosomal DNA. Numerous EMR studies on single crystals of sugars and sugar derivatives have been performed the last decades, but radical identification by EMR experiments alone is often ambiguous and sometimes not feasible. The last few years, highly accurate Density Functional Theory (DFT) calculations on extended organic solid state systems have become possible. These provide a powerful tool to help clarify and interpret experimental results and enable unambiguous structural identifications that were not possible before. In this talk, an overview will be given of recently identified radiation-induced radicals in single crystals of sugars (e.g. sucrose,1,2,3 fructose4) and sugar derivatives (e.g. glucose 1-phosphate5,6). The results pertain to primary as well as intermediate and stable species and the identifications are mainly based on the agreement, both in principal values and directions, between experimentally determined and DFT calculated proton hyperfine tensors. Common structural features are highlighted and possible commonly operative formation mechanisms are discussed