Nano-Hertz Gravitational Waves Searches with Interferometric Pulsar Timing Experiments

We estimate the sensitivity to nano-Hertz gravitational waves of pulsar timing experiments in which two highly-stable millisecond pulsars are tracked simultaneously with two neighboring radio telescopes that are referenced to the same time-keeping subsystem (i.e. "the clock"). By taking the difference of the two time-of-arrival residual data streams we can exactly cancel the clock noise in the combined data set, thereby enhancing the sensitivity to gravitational waves. We estimate that, in the band ($10^{-9} - 10^{-8}$) Hz, this "interferometric" pulsar timing technique can potentially improve the sensitivity to gravitational radiation by almost two orders of magnitude over that of single-telescopes. Interferometric pulsar timing experiments could be performed with neighboring pairs of antennas of the forthcoming large arraying projects.Comment: Paper submitted to Phys. Rev. Letters. It is 9 pages long, and includes 2 figure

JointZone: users' view of an adaptive online learning resource for rheumatology

This paper describes an online learning resource for rheumatology that was designed for a wide constituency of users including primarily undergraduate medical students and health professionals. Although the online resources afford an informal learning environment, the site was pedagogically designed to comply with the general recommendations of the Standing Committee on Training and Education of EULAR (European League Against Rheumatism) for a rheumatology core curriculum. Any Internet user may freely browse the site content with optional registration providing access to adaptive features that personalize the user’s view, for example, providing a reading history and targeted support based on scores from completed case studies. The site has now been available since early 2003, and an online survey of site registrants indicates that well structured pedagogical materials that reflect a learners’ dominant ‘community of practice’ appear to be a successful aid to informal learning

Approximate density-effect correction for the ionization loss of charged particles

Approximate density-effect correction for ionization loss of charged particle

An estimate of the prompt photon spectrum arising from cosmic-ray bombardment of the moon

Calculation method for estimating photon leakage spectrum arising from cosmic ray bombardment of moo

Monte Carlo calculations of high energy nucleon meson cascades and applications to galactic cosmic ray transport

Results obtained using a recently developed calculational method for determining the nucleon-meson cascade induced in thick materials by high-energy nucleons and charged pions are presented. The calculational method uses the intranuclear-cascade-evaporation model to treat nonelastic collisions by particles with energies approximately or smaller than GeV and an extrapolation model at higher energies. The following configurations are considered: (1) 19.2-GeV/c protons incident on iron; (2) 30.3-GeV/c protons incident on iron; (3) solar and galactic protons incident on the moon, and (4) galactic protons incident on tissue. For the first three configurations, experimental results are available and comparisons between the experimental and calculated results are given

Elimination of Clock Jitter Noise in Spaceborn Laser Interferometers

Space gravitational wave detectors employing laser interferometry between free-flying spacecraft differ in many ways from their laboratory counterparts. Among these differences is the fact that, in space, the end-masses will be moving relative to each other. This creates a problem by inducing a Doppler shift between the incoming and outgoing frequencies. The resulting beat frequency is so high that its phase cannot be read to sufficient accuracy when referenced to state-of-the-art space-qualified clocks. This is the problem that is addressed in this paper. We introduce a set of time-domain algorithms in which the effects of clock jitter are exactly canceled. The method employs the two-color laser approach that has been previously proposed, but avoids the singularities that arise in the previous frequency-domain algorithms. In addition, several practical aspects of the laser and clock noise cancellation schemes are addressed.Comment: 20 pages, 5 figure

Scattering of Pruppacher-Pitter raindrops at 30 GHz

Optimum design of modern ground-satellite communication systems requires the knowledge of rain-induced differential attenuation, differential phase shift, and cross polarization factors. Different available analytical techniques for raindrop scattering problems were assessed. These include: (1) geometrical theory of diffraction; (2) method of moment; (3) perturbation method; (4) point matching methods; (5) extended boundary condition method; and (6) global-local finite element method. The advantages and disadvantages of each are listed. The extended boundary condition method, which was determined to yield the most scattering results, is summarized. The scattered fields for Pruppacher-Pitter raindrops with sizes ranging from 0.5 mm to 3.5 mm at 20 C and at 30 GHz for several incidence angles are tabulated

IMPLICATIONS OF A MARKET FOR CARBON ON TIMBER AND NON-TIMBER VALUES IN AN UNCERTAIN WORLD

Despite considerable interest in the potential for forests to sequester carbon, the impact of carbon management on the provision of timber and non-timber resources has received relatively little attention in the literature. The introduction of value for stored carbon may result in modifications to traditional forest management objectives, generating trade-offs with other forest resources depending on the incentives provided by carbon markets. This paper investigates these issues by examining the impact of a particular form of carbon market on timber and non-timber values in a managed forest. An integrated modeling framework, developed for the incorporation of carbon management into operational timber management modeling tools, is also described. There is still substantial debate over how to properly credit carbon sequestered in forests. To date, there has been little research on how the form of a carbon market will impact the operations and objectives of forestry firms. Alternative market structures could produce very different responses in terms of rotation age, net present value and harvest policy. Here, a specific form of carbon market, the specified level contract, is investigated. Forestry firms are assumed to reach contracts with carbon-seeking agents which "guarantee" that a specified level of carbon stock will be maintained over a defined time period. Optimal forest management decisions are examined by implementing an optimization model for a specific land base in Alberta. The Woodstock forest modeling package is used for optimization. Analysis of trade-offs is based on the work of Armstrong et al. (1999, 2003) which assess non-timber resources using the natural disturbance approach to forest management. The analysis is then expanded to include a more rigorous, and realistic, depiction of carbon and carbon stock changes. Using the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3), carbon yield curves are developed which are integrated directly into the Woodstock forest management ii model. These carbon yields capture dynamics specific to separate biomass and dead organic matter (DOM) carbon pools and are represented for individual forest cover types. Interestingly, the inclusion of DOM carbon generates unexpected relationships between non-timber resources and incentives to sequester carbon. Results show that the presence of co-benefits will depend upon forest cover type, the harvest flow regulation faced by the managing firm and the incentives for timber supply provided by the market. Furthermore, firms that agree to enter contracts for carbon sequestration appear to do so at the expense of a decline in timber supply, with estimates of the opportunity cost of carbon management falling within the range of those found in recent literature.Resource /Energy Economics and Policy,

Rigorous QCD Predictions for Decays of P-Wave Quarkonia

Rigorous QCD predictions for decay rates of the P-wave states of heavy quarkonia are presented. They are based on a new factorization theorem which is valid to leading order in the heavy quark velocity and to all orders in the running coupling constant of QCD. The decay rates for all four P states into light hadronic or electromagnetic final states are expressed in terms of two phenomenological parameters, whose coefficients are perturbatively calculable. Logarithms of the binding energy encountered in previous perturbative calculations of P-wave decays are factored into a phenomenological parameter that is related to the probability for the heavy quark-antiquark pair to be in a color-octet S-wave state. Applying these predictions to charmonium, we use measured decay rates for the \chione and \chitwo to predict the decay rates of the \chizero and $h_c$.Comment: 13 page