Linear Approximations and Tests of Conditional Pricing Models

We construct a simple reduced-form example of a conditional pricing model with modest intrinsic nonlinearity. The theoretical magnitude of the pricing errors (alphas) induced by the application of standard linear conditioning are derived as a direct consequence of an omitted variables bias. When the model is calibrated to either characteristics sorted or industry portfolios, we find that the alphas generated by approximation-induced specification error are economically large. A Monte Carlo analysis shows that finite-sample alphas are even larger. It also shows that the power to detect omitted nonlinear factors through tests based on estimated risk premiums can sometimes be quite low, even when the effect of misspecification on alphas is large.

Algebraic and combinatorial aspects of sandpile monoids on directed graphs

The sandpile group of a graph is a well-studied object that combines ideas from algebraic graph theory, group theory, dynamical systems, and statistical physics. A graph's sandpile group is part of a larger algebraic structure on the graph, known as its sandpile monoid. Most of the work on sandpiles so far has focused on the sandpile group rather than the sandpile monoid of a graph, and has also assumed the underlying graph to be undirected. A notable exception is the recent work of Babai and Toumpakari, which builds up the theory of sandpile monoids on directed graphs from scratch and provides many connections between the combinatorics of a graph and the algebraic aspects of its sandpile monoid. In this paper we primarily consider sandpile monoids on directed graphs, and we extend the existing theory in four main ways. First, we give a combinatorial classification of the maximal subgroups of a sandpile monoid on a directed graph in terms of the sandpile groups of certain easily-identifiable subgraphs. Second, we point out certain sandpile results for undirected graphs that are really results for sandpile monoids on directed graphs that contain exactly two idempotents. Third, we give a new algebraic constraint that sandpile monoids must satisfy and exhibit two infinite families of monoids that cannot be realized as sandpile monoids on any graph. Finally, we give an explicit combinatorial description of the sandpile group identity for every graph in a family of directed graphs which generalizes the family of (undirected) distance-regular graphs. This family includes many other graphs of interest, including iterated wheels, regular trees, and regular tournaments.Comment: v2: Cleaner presentation, new results in final section. Accepted for publication in J. Combin. Theory Ser. A. 21 pages, 5 figure

Microwave-assisted synthesis and electrochemical evaluation of VO2 (B) nanostructures

Understanding how intercalation materials change during electrochemical operation is paramount to optimizing their behaviour and function and in situ characterization methods allow us to observe these changes without sample destruction. Here we first report the improved intercalation properties of bronze phase vanadium dioxide VO2 (B) prepared by a microwave-assisted route which exhibits a larger electrochemical capacity (232 mAh g-1) compared with VO2 (B) prepared by a solvothermal route (197 mAh g-1). These electrochemical differences have also been followed using in situ X-ray absorption spectroscopy allowing us to follow oxidation state changes as they occur during battery operation

Comparisons of Three Different Investigative Interview Techniques With Young Children

After viewing a film of a mother hitting her son, a film not seen by the college student interviewers, children were misinformed about a detail (via exposure to a misleadingquestion) as well as explicitly coached to disclose 3 false details. The children were then interviewed by interviewers who had previously learned 1 of 3 different interviewing procedures: the Yuille Step-Wise Interview developed by J. C. Yuille, R. Hunter,R. Joffe, & J. Zaparniuk (1993); a doll play interview developed by Action for Child Protection Inc. (1994); or the Modified Structured Interview developed for this study. The Modified Structured Interview yielded more “where” information and was better at detecting if coaching had occurred. However, the interviewers were not very good at discriminating suggested versus coached versus correct witnessed information. The authors found that the deeper one digs for memories, the more one uncovers incorrect versus correct items. They concluded that although the Modified Structured Interview was superior tothe techniques currently in use, cautions are necessary

Orbital Dimer Model for Spin-Glass State in Y2_2Mo2_2O7_7

The formation of a spin glass usually requires both structural disorder and frustrated magnetic interactions. Consequently, the origin of spin-glass behaviour in Y$_2$Mo$_2$O$_7$ $-$ in which magnetic Mo$^{4+}$ ions occupy a frustrated pyrochlore lattice with minimal compositional disorder $-$ has been a longstanding question. Here, we use neutron and X-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously-reported PDF, EXAFS and NMR studies and provides a new and physical mechanism for spin-glass formation. We show that Mo$^{4+}$ ions displace according to a local "2-in/2-out" rule on each Mo$_4$ tetrahedron, driven by orbital dimerisation of Jahn-Teller active Mo$^{4+}$ ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O$^{2-}$ displacements yield a distribution of Mo$-$O$-$Mo angles, which in turn introduces disorder into magnetic interactions. Our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition.Comment: 6 pages, 3 figure

A MusD Retrotransposon Insertion in the Mouse Slc6a5 Gene Causes Alterations in Neuromuscular Junction Maturation and Behavioral Phenotypes

Glycine is the major inhibitory neurotransmitter in the spinal cord and some brain regions. The presynaptic glycine transporter, GlyT2, is required for sustained glycinergic transmission through presynaptic reuptake and recycling of glycine. Mutations in SLC6A5, encoding GlyT2, cause hereditary hyperekplexia in humans, and similar phenotypes in knock-out mice, and variants are associated with schizophrenia. We identified a spontaneous mutation in mouse Slc6a5, caused by a MusD retrotransposon insertion. The GlyT2 protein is undetectable in homozygous mutants, indicating a null allele. Homozygous mutant mice are normal at birth, but develop handling-induced spasms at five days of age, and only survive for two weeks, but allow the study of early activity-regulated developmental processes. At the neuromuscular junction, synapse elimination and the switch from embryonic to adult acetylcholine receptor subunits are hastened, consistent with a presumed increase in motor neuron activity, and transcription of acetylcholine receptors is elevated. Heterozygous mice, which show no reduction in lifespan but nonetheless have reduced levels of GlyT2, have a normal thermal sensitivity with the hot-plate test, but differences in repetitive grooming and decreased sleep time with home-cage monitoring. Open-field and elevated plus-maze tests did not detect anxiety-like behaviors; however, the latter showed a hyperactivity phenotype. Importantly, grooming and hyperactivity are observed in mouse schizophrenia models. Thus, mutations in Slc6a5 show changes in neuromuscular junction development as homozygotes, and behavioral phenotypes as heterozygotes, indicating their usefulness for studies related to glycinergic dysfunction

Repository Metadata: Approaches and Challenges

Many institutional repositories have pursued a mixed metadata environment, relying on description by multiple workflows. Strategies may include metadata converted from other systems, metadata elicited from the document creator or manager, and metadata created by library or repository staff. Additional editing or proofing may or may not occur. The mixed environment brings challenges of creation, management, and access. In this article, repository efforts at three major universities are discussed. All three repositories run on the DSpace software package, and the opportunities and limitations of that system will be examined. The authors discuss local strategies in light of current thinking on metadata creation, user behavior, and the aggregation of heterogeneous metadata. The contrasts between the mission of each repository effort will show the importance of local customization, while the experience of all three institutions forms the basis for recommendations on strategies of benefit to a wide range of librarians and repository planners

High-sensitivity cardiac troponin concentrations at presentation in patients with ST-segment elevation myocardial infarction

No abstract available

Utility of interval kidney biopsy in ANCA-associated vasculitis

OBJECTIVES: ANCA-associated vasculitis (AAV) is a rare autoimmune disorder that commonly involves the kidney. Early identification of kidney involvement, assessing treatment-response and predicting outcome are important clinical challenges. Here, we assessed the potential utility of interval kidney biopsy in AAV. METHODS: In a tertiary referral centre with a dedicated vasculitis service, we identified patients with AAV who had undergone interval kidney biopsy, defined as a repeat kidney biopsy (following an initial biopsy showing active AAV) undertaken to determine the histological response in the kidney following induction immunosuppression. We analysed biochemical, histological and outcome data, including times to kidney failure and death for all patients. RESULTS: We identified 57 patients with AAV who underwent at least one interval kidney biopsy (59 interval biopsies in total; median time to interval biopsy ∼130 days). Of the 59 interval biopsies performed, 24 (41%) patients had clinically suspected active disease at time of biopsy which was confirmed histologically in only 42% of cases; 35 (59%) patients were in clinical disease-remission, and this was correct in 97% of cases. The clinician’s impression was incorrect in one in four patients. Hematuria at interval biopsy did not correlate with histological activity. Interval biopsy showed fewer acute lesions and more chronic damage compared with initial biopsy and led to immunosuppressive treatment-change in 75% (44/59) of patients. Clinical risk prediction tools tended to operate better using interval biopsy data. CONCLUSION: Interval kidney biopsy is useful for determining treatment-response and subsequent disease management in AAV. It may provide better prognostic information than initial kidney biopsy and should be considered for inclusion into future clinical trials and treatment protocols for patients with AAV