Ultra-trace Cu isotope ratio measurements via multi-collector ICP-mass spectrometry using Ga as internal standard : an approach applicable to micro-samples

The capabilities of Cu isotope ratio measurements are often restricted by the small volumes of sample available and/or their low Cu concentration. In this work, an analytical approach was developed for performing Cu isotopic analysis via multi-collector ICP-mass spectrometry (MC-ICP-MS) at ultra-trace level using Ga as an internal standard for mass bias correction. The minimum concentration of Cu required for accurate and precise isotope ratio measurements was established to be 20 mu g L-1 with wet plasma conditions and 5 mu g L-1 with dry plasma conditions. The use of Ga as an internal standard for mass bias correction provided several advantages compared to Ni, i.e. improved internal precision on delta Cu-65 values and lower blank levels. Ga can also be used at a 4- fold lower concentration level than Ni. However, in wet plasma conditions, the signals of (ArO2H+)-Ar-36-O-16-H-1 and (ArNO+)-Ar-40-N-15-O-16 interfered with the signals of Ga-69(+) and Ga-71(+), respectively, while in dry plasma conditions, realized by the use of a desolvation unit, Ga-69(+) suffered from spectral interference from (ArN2H+)-Ar-40-N-14-H-1. These interferences were resolved by using medium mass resolution. For validation purposes, the approach was applied to commercially available blood and serum samples. The delta Cu-65 values for the samples measured at a concentration level of 5 mu g L-1 Cu and 5 mu g L-1 Ga using dry plasma conditions were in good agreement with those obtained for isotope ratio measurements at the "standard" concentration level of 200 mu g L-1 Cu and 200 mu g L-1 Ni using wet plasma conditions. In addition, the delta Cu-65 values obtained for micro-samples of serum/blood (volume of 100 mu L) were in good agreement with the corresponding ones obtained using the "standard" volume for isotopic analysis (500 mu L)

Welfare and Pricing of Mail in a Communications Market

We build a model where a postal incumbent offering single piece, transactional and advertising mail competes with postal entrants and with a firm offering an alternative medium. We solve for the optimal prices under various competition assumptions. We calibrate the model and provide numerical simulations in order to shed light on the impact of these assumptions on volumes and welfare levels.

Undocumented and unaccompanied Latino youth who are exposed to violence are more likely to turn to crime to overcome disadvantage

Recent years have seen growing concern over the increasing number of unaccompanied youth arriving at the US-Mexico border. But despite this concern, such undocumented youth have been an understudied group. In new research, Marika Dawkins and Frank A. Rodriguez interviewed undocumented and unaccompanied Latino youth living at the US-Mexico border. They find that members of this group who experience pervasive violence may be more likely to commit crimes in order to overcome personal hardships

Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View

Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications Surveys and Tutorial