4,663 research outputs found
Hierarchical elimination-by-aspects and nested logit models of stated preferences for alternative fuel vehicles
1. INTRODUCTION
Since the late 1960s, transport demand analysis has been the context for significant developments in model forms for the representation of discrete choice behaviour. Such developments have adhered almost exclusively to
the behavioural paradigm of Random Utility Maximisation (RUM), first proposed by Marschak (1960) and Block and Marschak (1960). A common argument for the allegiance to RUM is that it ensures consistency with the fundamental axioms of microeconomic consumer theory and, it follows,
permits interface between the demand model and the concepts of welfare economics (e.g. Koppelman and Wen, 2001). The desire to better represent observed choice, which has driven developments in RUM models, has been somewhat at odds, however, with the frequent assault on the utility maximisation paradigm, and by implication
RUM, from a range of literatures. This critique has challenged the empirical validity of the fundamental axioms (e.g. Kahneman and Tversky, 2000; Mclntosh and Ryan, 2002; Saelensmide, 1999) and, more generally, the
realism of the notion of instrumental rationality inherent in utility maximisation (e.g. Hargreaves-Heap, 1992; McFadden, 1999; Camerer, 1998). Emanating from these literatures has been an alternative family of so-called
non-RUM models, which seek to offer greater realism in the representation of how individuals actually process choice tasks. The workshop on Methodological Developments at the 2000 Conference of the International Association for Travel Behaviour Research concluded: 'Non-RUM models
deserve to be evaluated side-by-side with RUM models to determine their practicality, ability to describe behaviour, and usefulness for transportation policy. The research agenda should include tests of these models' (Bolduc and McFadden, 2001 p326). The present paper, together with a companion paper, Batley and Daly (2003), offer a timely contribution to this research
priority. Batley and Daly (2003) present a detailed account of the theoretical derivation of RUM, and consider the relationships of two specific RUM forms;
nested logit [NL] (Ben-Akiva, 1974; Williams, 1977; Daly and Zachary, 1976; McFadden, 1978) and recursive nested extreme value [RNEV] (Daly, 2001 ; Bierlaire, 2002; Daly and Bierlaire, 2003); to two specific non-RUM forms;
elimination-by-aspects [EBA] (Tversky, 1972a, 1972b) and hierarchical EBA [HEBA] (Tversky and Sattath, 1979). In particular, Batley and Daly (2003) establish conditions under which NL and RNEV derive equivalent choice
probabilities to HEBA and EBA, respectively. These findings would seem to ameliorate the concern that the application of RUM models to data generated by non-RUM choice processes could introduce significant biases. That
aside, substantive issues remain as to how non-RUM models can best be specified so as to yield useful and robust information in both estimation and forecasting contexts, and how their empirical performance compares with
RUM models. Such issues are the focus of the present paper, which applies non-RUM models to a real empirical context
Recent results from the NA48 experiment at CERN: CP violation and CKM parameter Vus
Several recent results from the NA48 experiment are presented: a measurement
, search for CP violating phenomena in decays, and
a measurement of .Comment: A talk given at the 2007 Europhysics Conference on High Energy
Physics. 3 page
Radiative corrections to neutral pion-pair production
We calculate the one-photon loop radiative corrections to the neutral
pion-pair photoproduction process . At leading
order this reaction is governed by the chiral pion-pion interaction. Since the
chiral contact-vertex depends only on the final-state
invariant-mass it factors out of all photon-loop diagrams. We give analytical
expressions for the multiplicative correction factor
arising from eight classes of contributing one-photon loop diagrams. An
electromagnetic counterterm has to be included in order to cancel the
ultraviolet divergences generated by the photon-loops. Infrared finiteness of
the virtual radiative corrections is achieved (in the standard way) by
including soft photon radiation below an energy cut-off . The
radiative corrections to the total cross section vary between and
for center-of-mass energies from threshold up to . The finite part of
the electromagnetic counterterm gives an additional constant contribution of
about , however with a large uncertainty.Comment: 10 pages, 6 figures, submitted to Eur. Phys. J.
The Politics of Service Delivery Reform
This article identifies the leaders, the supporters and the resisters of public service reform. It adopts a principal–agent framework, comparing reality with an ‘ideal’ situation in which citizens are the principals over political policy-makers as their agents, and policy-makers are the principals over public service officials as their agents. Reform in most developing countries is complicated by an additional set of external actors — international financial institutions and donors. In practice, international agencies and core government officials usually act as the ‘principals’ in the determination of reforms. The analysis identifies the interests involved in reform, indicating how the balance between them is affected by institutional and sectoral factors. Organizational reforms, particularly in the social sectors, present greater difficulties than first generation economic policy reforms
Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking
Dispersive representations of the pi-pi scattering amplitudes and pion form
factors, valid at two-loop accuracy in the low-energy expansion, are
constructed in the presence of isospin-breaking effects induced by the
difference between the charged and neutral pion masses. Analytical expressions
for the corresponding phases of the scalar and vector pion form factors are
computed. It is shown that each of these phases consists of the sum of a
"universal" part and a form-factor dependent contribution. The first one is
entirely determined in terms of the pi-pi scattering amplitudes alone, and
reduces to the phase satisfying Watson's theorem in the isospin limit. The
second one can be sizeable, although it vanishes in the same limit. The
dependence of these isospin corrections with respect to the parameters of the
subthreshold expansion of the pi-pi amplitude is studied, and an equivalent
representation in terms of the S-wave scattering lengths is also briefly
presented and discussed. In addition, partially analytical expressions for the
two-loop form factors and pi-pi scattering amplitudes in the presence of
isospin breaking are provided.Comment: 57 pages, 12 figure
Direct CP violation in neutral kaon decays
The final result is presented of the NA48 Experiment performed at CERN SPS
neutral kaon beams on the direct CP violation parameter Re(epsilon'/epsilon),
as maesured from the decay rates of neutral kaons into two pions. The data
collected in years 1997-2001 yield the evidence for direct CP violation with
Re(epsilon'/epsilon)=(14.7+-2.2)10^-4. Description of expermental method and
systematics, comparison with world data and some discussion of implications for
theory are given.Comment: 5 pp., 3 figs, presented on behalf of NA48 Collaboration at PASCOS
2003 Conference, Mumbai, India, 2-8 Jan 2003, to appear in Praman
Genome analysis identified novel candidate genes for ascochyta blight resistance in chickpea using whole genome re-sequencing data
Ascochyta blight (AB) is a fungal disease that can significantly reduce chickpea production in Australia and other regions of the world. In this study, 69 chickpea genotypes were sequenced using whole genome re-sequencing (WGRS) methods. They included 48 Australian varieties differing in their resistance ranking to AB, 16 advanced breeding lines from the Australian chickpea breeding program, four landraces, and one accession representing the wild chickpea species Cicer reticulatum. More than 800,000 single nucleotide polymorphisms (SNPs) were identified. Population structure analysis revealed relatively narrow genetic diversity amongst recently released Australian varieties and two groups of varieties separated by the level of AB resistance. Several regions of the chickpea genome were under positive selection based on Tajima’s D test. Both Fst genome- scan and genome-wide association studies (GWAS) identified a 100 kb region (AB4.1) on chromosome 4 that was significantly associated with AB resistance. The AB4.1 region co-located to a large QTL interval of 7 Mb∼30 Mb identified previously in three different mapping populations which were genotyped at relatively low density with SSR or SNP markers. The AB4.1 region was validated by GWAS in an additional collection of 132 advanced breeding lines from the Australian chickpea breeding program, genotyped with approximately 144,000 SNPs. The reduced level of nucleotide diversity and long extent of linkage disequilibrium also suggested the AB4.1 region may have gone through selective sweeps probably caused by selection of the AB resistance trait in breeding. In total, 12 predicted genes were located in the AB4.1 QTL region, including those annotated as: NBS-LRR receptor-like kinase, wall-associated kinase, zinc finger protein, and serine/threonine protein kinases. One significant SNP located in the conserved catalytic domain of a NBS-LRR receptor-like kinase led to amino acid substitution. Transcriptional analysis using qPCR showed that some predicted genes were significantly induced in resistant lines after inoculation compared to non-inoculated plants. This study demonstrates the power of combining WGRS data with relatively simple traits to rapidly develop “functional makers” for marker-assisted selection and genomic selection.Yongle Li, Pradeep Ruperao, Jacqueline Batley, David Edwards, Jenny Davidson, Kristy Hobson and Tim Sutto
Radiative corrections in K --> 3 pi decays
We investigate radiative corrections to K --> 3 pi decays. In particular, we
extend the non-relativistic framework developed recently to include real and
virtual photons and show that, in a well-defined power counting scheme, the
results reproduce corrections obtained in the relativistic calculation. Real
photons are included exactly, beyond the soft-photon approximation, and we
compare the result with the latter. The singularities generated by pionium near
threshold are investigated, and a region is identified where standard
perturbation theory in the fine structure constant alpha may be applied. We
expect that the formulae provided allow one to extract S-wave pi pi scattering
lengths from the cusp effect in these decays with high precision.Comment: 57 pages, 17 figure
AutoSNPdb: an annotated single nucleotide polymorphism database for crop plants
Single nucleotide polymorphisms (SNPs) may be considered the ultimate genetic marker as they represent the finest resolution of a DNA sequence (a single nucleotide), are generally abundant in populations and have a low mutation rate. Analysis of assembled EST sequence data provides a cost-effective means to identify large numbers of SNPs associated with functional genes. We have developed an integrated SNP discovery pipeline, which identifies SNPs from assembled EST sequences. The results are maintained in a custom relational database along with EST source and annotation information. The current database hosts data for the important crops rice, barley and Brassica. Users may rapidly identify polymorphic sequences of interest through BLAST sequence comparison, keyword searches of annotations derived from UniRef90 and GenBank comparisons, GO annotations or in genes corresponding to syntenic regions of reference genomes. In addition, SNPs between specific varieties may be identified for targeted mapping and association studies. SNPs are viewed using a user-friendly graphical interface. The database is freely accessible at http://autosnpdb.qfab.org.au/
The isospin symmetry breaking effects in decays
The Fermi-Watson theorem is generalized to the case of two coupled channels
with different masses and applied to final state interaction in
decays. The impact of considered effect on the phase of the scattering
is estimated and shown that it can be crucial for scattering lengths extraction
from experimental data on decays
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