MULTIPRODUCT PRODUCTION CHOICES AND PESTICIDE REGULATION IN GEORGIA

An increasing emphasis on surface and groundwater quality and food safety may result in some form of pesticide regulations. A restricted profit function model of Georgia agriculture is used to examine the short-run effects of 2 and 5 percent reductions in all pesticides. Point estimates of short-run impacts, along with their 90 percent confidence intervals are presented.Agricultural and Food Policy,

XSIL: Extensible Scientific Interchange Language

We motivate and define the XSIL language as a flexible, hierarchical, extensible transport language for scientific data objects. The entire object may be represented in the file, or there may be metadata in the XSIL file, with a powerful, fault-tolerant linking mechanism to external data. The language is based on XML, and is designed not only for parsing and processing by machines, but also for presentation to humans through web browsers and web-database technology. There is a natural mapping between the elements of the XSIL language and the object model into which they are translated by the parser. As well as common objects (Parameter, Array, Time, Table), we have extended XSIL to include the IGWDFrame, used by gravitational-wave observatories

Parameter constraints for high-energy models of colliding winds of massive stars: the case WR 147

We explore the ability of high energy observations to constrain orbital parameters of long period massive binary systems by means of an inverse Compton model acting in colliding wind environments. This is particular relevant for (very) long period binaries where orbital parameters are often poorly known from conventional methods, as is the case e.g. for the Wolf-Rayet (WR) star binary system WR 147 where INTEGRAL and MAGIC upper limits on the high-energy emission have recently been presented. We conduct a parameter study of the set of free quantities describing the yet vaguely constrained geometry and respective effects on the non-thermal high-energy radiation from WR 147. The results are confronted with the recently obtained high-energy observations and with sensitivities of contemporaneous high-energy instruments like Fermi-LAT. For binaries with sufficient long periods, like WR 147, gamma-ray attenuation is unlikely to cause any distinctive features in the high-energy spectrum. This leaves the anisotropic inverse Compton scattering as the only process that reacts sensitively on the line-of-sight angle with respect to the orbital plane, and therefore allows the deduction of system parameters even from observations not covering a substantial part of the orbit. Provided that particle acceleration acts sufficiently effectively to allow the production of GeV photons through inverse Compton scattering, our analysis indicates a preference for WR 147 to possess a large inclination angle. Otherwise, for low inclination angles, electron acceleration is constrained to be less efficient as anticipated here.Comment: 33 pages, 9 figures; accepted by Ap

Inconsistency of threat level in soft armour standards, correlation of experimental tests to bullet X-ray 3D images

Fundamental to any ballistic armour standard is the reference projectile that is to be defeated. Typically, for certification, consistency of bullet geometry is assumed. Therefore, practical variations in bullet jacket dimensions can have far reaching consequences. Traditionally, internal dimensions have been analysed by physically sectioning bullets – an approach which rules out any subsequent ballistic assessment. The use of a non-destructive X-ray Computed Tomography (CT) method was demonstrated in [1]. Now, the authors apply this technique to correlate bullet impact response to jacket thickness variations. A set of 20 bullets (9 mm DM 11) was selected to analyse both intra and inter bullet variations using an image based analysis method to map the jacket thickness and measure the centre of gravity. Thickness variations of the order of 200μm were found commonly across all the bullets along the length and an angular variation of up to 50μm was found in a few bullets. The bullets were subsequently impacted against a rigid flat plate and re-scanned. The results of the experiments are shown and compared to the un-deformed bullet jacket thickness variations. The conclusions are relevant for future soft armour standards and provide important data for numerical model correlation and development

A Virtual Data Grid for LIGO

GriPhyN (Grid Physics Network) is a large US collaboration to build grid services for large physics experiments, one of which is LIGO, a gravitational-wave observatory. This paper explains the physics and computing challenges of LIGO, and the tools that GriPhyN will build to address them. A key component needed to implement the data pipeline is a virtual data service; a system to dynamically create data products requested during the various stages. The data could possibly be already processed in a certain way, it may be in a file on a storage system, it may be cached, or it may need to be created through computation. The full elaboration of this system will al-low complex data pipelines to be set up as virtual data objects, with existing data being transformed in diverse ways

Online College Education For Computer-Savvy Students: A Study Of Perceptions And Needs

With new technologies and cyberspace-literate students, distance education has been in high demand and more schools are getting into online education. As such, understanding the needs of current and prospective learners has become especially important for success in the new millennium. Based on the learners’ needs and current technology status, this study provides a review on the feasibility of online education for modern students in a developed nation. Based on the survey of 203 undergraduate students, this research provides an assessment of their views, needs, and wants for the feasibility of offering online courses and programs. Such demographic variables as gender, ethnicity and education demonstrated statistically significant results. Recommendations are provided for administrators to enhance their online offerings as a result of the feedback from students. The document further explores online education, online operation, and other such variables that impact the success of students in higher education.&nbsp

Mathematical principles for the design of isostatic mount systems for dynamic structures

Isostatic mounts are used in applications like telescopes and robotics to move and hold part of a structure in a desired pose relative to the rest, by driving some controls rather than driving the subsystem directly. To achieve this successfully requires an understanding of the structure of the coupled space of configurations and controls, and of the singularities of the mapping from the coupled space to the space of controls. It is crucial to avoid such singularities because generically they lead to large constraint forces and internal stresses which can cause distortion. In this paper we outline design principles for isostatic mount systems for dynamic structures, with particular emphasis on robots

Simulation, modelling and development of the metris RCA

In partnership with Metris UK we discuss the utilisation of modelling and simulation methods in the development of a revolutionary 7-axis Robot CMM Arm (RCA). An offline virtual model is described, facilitating pre-emptive collision avoidance and assessment of optimal placement of the RCA relative to scan specimens. Workspace accessibility of the RCA is examined under a range of geometrical assumptions and we discuss the effects of arbitrary offsets resulting from manufacturing tolerances. Degeneracy is identified in the number of ways a given pose may be attained and it is demonstrated how a simplified model may be exploited to solve the inverse kinematics problem of finding the “correct” set of joint angles. We demonstrate how the seventh axis may be utilised to avoid obstacles or otherwise awkward poses, giving the unit greater dexterity than traditional CMMs. The results of finite element analysis and static force modelling on the RCA are presented which provide an estimate of the forces exerted on the internal measurement arm in a range of poses

Characteristics, accuracy and reverification of robotised articulated arm CMMs

VDI article 2617 specifies characteristics to describe the accuracy of articulated arm coordinate measuring machines (AACMMs) and outlines procedures for checking them. However the VDI prescription was written with a former generation of machines in mind: manual arms exploiting traditional touch probe technologies. Recent advances in metrology have given rise to noncontact laser scanning tools and robotic automation of articulated arms – technologies which are not adequately characterised using the VDI specification. In this paper we examine the “guidelines” presented in VDI 2617, finding many of them to be ambiguous and open to interpretation, with some tests appearing even to be optional. The engineer is left significant flexibility in the execution of the test procedures and the manufacturer is free to specify many of the test parameters. Such flexibility renders the VDI tests of limited value and the results can be misleading. We illustrate, with examples using the Nikon RCA, how a liberal interpretation of the VDI guidelines can significantly improve accuracy characterisation and suggest ways in which to mitigate this problem. We propose a series of stringent tests and revised definitions, in the same vein as VDI 2617 and similar US standards, to clarify the accuracy characterisation process. The revised methodology includes modified acceptance and reverification tests which aim to accommodate emerging technologies, laser scanning devices in particular, while maintaining the spirit of the existing and established standards. We seek to supply robust re-definitions for the accepted terms “zero point” and “useful arm length”, pre-supposing nothing about the geometry of the measuring device. We also identify a source of error unique to robotised AACMMs employing laser scanners – the forward-reverse pass error. We show how eliminating this error significantly improves the repeatability of a device and propose a novel approach to the testing of probing error based on statistical uncertainty