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Estimating software project effort using analogies
Accurate project effort prediction is an important goal for the software engineering community. To date most work has focused upon building algorithmic models of effort, for example COCOMO. These can be calibrated to local environments. We describe an alternative approach to estimation based upon the use of analogies. The underlying principle is to characterise projects in terms of features (for example, the number of interfaces, the development method or the size of the functional requirements document). Completed projects are stored and then the problem becomes one of finding the most similar projects to the one for which a prediction is required. Similarity is defined as Euclidean distance in n-dimensional space where n is the number of project features. Each dimension is standardised so all dimensions have equal weight. The known effort values of the nearest neighbours to the new project are then used as the basis for the prediction. The process is automated using a PC based tool known as ANGEL. The method is validated on nine different industrial datasets (a total of 275 projects) and in all cases analogy outperforms algorithmic models based upon stepwise regression. From this work we argue that estimation by analogy is a viable technique that, at the very least, can be used by project managers to complement current estimation techniques
Small-angle scattering in a marginal Fermi-liquid
We study the magnetotransport properties of a model of small-angle scattering
in a marginal Fermi liquid. Such a model has been proposed by Varma and
Abrahams [Phys. Rev. Lett. 86, 4652 (2001)] to account for the anomalous
temperature dependence of in-plane magnetotransport properties of the high-Tc
cuprates. We study the resistivity, Hall angle and magnetoresistance using both
analytical and numerical techniques. We find that small-angle scattering only
generates a new temperature dependence for the Hall angle near particle-hole
symmetric Fermi surfaces where the conventional Hall term vanishes. The
magnetoresistance always shows Kohler's rule behavior.Comment: 4 pages, 3 figures, Revtex
Phase diagram and quasiparticle properties of the Hubbard model within cluster two-site DMFT
We present a cluster dynamical mean-field treatment of the Hubbard model on a
square lattice to study the evolution of magnetism and quasiparticle properties
as the electron filling and interaction strength are varied. Our approach for
solving the dynamical mean-field equations is an extension of Potthoff's
"two-site" method [Phys. Rev. B. 64, 165114 (2001)] where the self-consistent
bath is represented by a highly restricted set of states. As well as the
expected antiferromagnetism close to half filling, we observe distortions of
the Fermi surface. The proximity of a van Hove point and the incipient
antiferromagnetism lead to the evolution from an electron-like Fermi surface
away from the Mott transition, to a hole-like one near half-filling. Our
results also show a gap opening anisotropically around the Fermi surface close
to the Mott transition (reminiscent of the pseudogap phenomenon seen in the
cuprate high-Tc superconductors). This leaves Fermi arcs which are closed into
pockets by lines with very small quasiparticle residue.Comment: 10 pages, 8 figures, latex (revtex4
A H2 PEM fuel cell and high energy dense battery hybrid energy source for an urban electric vehicle
Electric vehicles are set to play a prominent role in addressing the energy and environmental impact of an increasing road transport population by offering a more energy efficient and less polluting drive-train alternative to conventional internal combustion engine (ICE) vehicles. Given the energy (and hence range) and performance limitations of electro-chemical battery storage systems, hybrid systems combining energy and power dense storage technologies have been proposed for vehicle applications. The paper discusses the application of a hydrogen fuel cell as a range extender for an urban electric vehicle for which the primary energy source is provided by a high energy dense battery. A review of fuel cell systems and automotive drive-train application issues are discussed, together with an overview of the battery technology. The prototype fuel cell and battery component simulation models are presented and their performance as a combined energy/power source assessed for typical urban and sub-urban driving scenario
SAW torque transducers for disturbance rejection and tracking control of multi-inertia servo-drive systems
The paper proposes a resonance ratio control (RRC) technique for the coordinated motion control of multi-inertia mechanical systems, based on the measurement of shaft torque via a SAW-based torque sensor. Furthermore, a new controller structure, RRC plus disturbance feedback is proposed, which enables the controller to be designed to independently satisfy tracking and regulation performance. A tuning method for the RRC structure is given based on the ITAE index, normalized as a function of the mechanical parameters enabling a direct performance comparison between a basic proportional and integral (PI) controller. The use of a reduced-order state observer is presented to provide a dynamic estimate of the load-side disturbance torque for a multi-inertia mechanical system, with an appraisal of the composite closed-loop dynamics. It is shown that the integrated formulation of the tuning criteria enables lower bandwidth observers to be implemented with a corresponding reduction in noise and computational load. The control structures are experimentally validated via a purpose designed test facility and demonstrate significant improvement in dynamic tracking performance, whilst additionally rejecting periodic load side disturbances, a feature previously unrealisable except by other, high-gain control schemes that impose small stability margins
Structural determination of archaeal UDP-N-acetylglucosamine 4-epimerase from Methanobrevibacter ruminantium M1 in complex with the bacterial cell wall intermediate UDP-N-acetylmuramic acid
The crystal structure of UDP-N-acetylglucosamine 4-epimerase (UDP-GlcNAc 4-epimerase; WbpP; EC 5.1.3.7), from the archaeal methanogen Methanobrevibacter ruminantium strain M1, was determined to a resolution of 1.65 Å. The structure, with a single monomer in the crystallographic asymmetric unit, contained a conserved N-terminal Rossmann fold for nucleotide binding and an active site positioned in the C-terminus. UDP-GlcNAc 4-epimerase is a member of the short-chain dehydrogenase/reductase superfamily, sharing sequence motifs and structural elements characteristic of this family of oxidoreductases and bacterial 4-epimerases. The protein was co-crystallized with coenzyme NADH and UDP-N-acetylmuramic acid, the latter an unintended inclusion and well known product of the bacterial enzyme MurB and a critical intermediate for bacterial cell wall synthesis. This is a non-native UDP sugar amongst archaea and was most likely incorporated from the Eschericha coli expression host during purification of the recombinant enzyme
Mapping Nuclear Fallout Using the Weather Research & Forecasting (WRF) Model
There are many models that attempt to predict transport & dispersion (T&D) of particulate matter in the sensible atmosphere. The majority of these existing models are unable to incorporate atmospheric processes such wet deposition through scavenging and cloud condensation nuclei (CCN) formation. To this end, the numerical weather prediction (NWP) model known as the Weather Research & Forecasting with Chemistry (WRF/Chem) Model is studied to determine its suitability as a potential tool for predicting particulate T&D following an atmospheric nuclear detonation. This is done by modifying relevant modules, originally designed to predict the settling of volcanic ash, such that a stabilized cloud of nuclear particulate is initialized within the model. This modified code is then executed for various atmospheric test explosions and the results are qualitatively and quantitatively compared to historical dose-rate contour data contained in DNA-1251-EX. The same simulations were also performed using the offline (NWP wind flow separately applied) Hazard Predication Assessment & Capability (HPAC) Model and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. By comparison, using WRF/Chem for particulate tracking allows for the incorporation of important meteorological processes inline with dispersion processes and leads to more realistic fallout pattern with effects of the fallout coupled back into the numerical weather forecast
Investigating the mediation effects of student-teacher relationships between extracurricular activities and students\u27 academic achievement in high school
While there is evidence to support the notion that extracurricular activities have a positive impact on student success and development, the reasons why students participate in these activities, why they continue to participate in these activities, and why these activities lead to better educational outcomes are unclear. This study was conducted at three high schools in a county in northeast Florida with a total n of 131 students. This study used three theories as lenses to examine how student-teacher relationships impacted student engagement in extracurricular activities and in turn student achievement: Self-Systems Processing (Connell & Wellborn, 1991), Attachment Theory (Bowlby, 1969), and School Belonging (Goodenow & Grady, 1993) to analyze the data collected from the surveys. This data collection for this study included both quantitative survey questions and open-ended qualitative survey questions that produced three main findings. First, overall, students involved in extracurricular activities had slightly higher mean-level perceptions about their student-teacher relationships (i.e., caring, trust, and help) than those not involved in extracurricular activities, but this difference was not statistically significant. Second, for students involved in extracurricular activities their perceptions of the student-teacher relationship were slightly higher for their extracurricular teachers than their general teachers, but again, not significantly so. Finally, there were no effects of extracurricular activity on academic achievement within this sample
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