On the causal interpretation of acyclic mixed graphs under multivariate normality

In multivariate statistics, acyclic mixed graphs with directed and bidirected edges are widely used for compact representation of dependence structures that can arise in the presence of hidden (i.e., latent or unobserved) variables. Indeed, under multivariate normality, every mixed graph corresponds to a set of covariance matrices that contains as a full-dimensional subset the covariance matrices associated with a causally interpretable acyclic digraph. This digraph generally has some of its nodes corresponding to hidden variables. We seek to clarify for which mixed graphs there exists an acyclic digraph whose hidden variable model coincides with the mixed graph model. Restricting to the tractable setting of chain graphs and multivariate normality, we show that decomposability of the bidirected part of the chain graph is necessary and sufficient for equality between the mixed graph model and some hidden variable model given by an acyclic digraph

Generalised knot groups distinguish the square and granny knots (with an appendix by David Savitt)

Given a knot K we may construct a group G_n(K) from the fundamental group of K by adjoining an nth root of the meridian that commutes with the corresponding longitude. These "generalised knot groups" were introduced independently by Wada and Kelly, and contain the fundamental group as a subgroup. The square knot SK and the granny knot GK are a well known example of a pair of distinct knots with isomorphic fundamental groups. We show that G_n(SK) and G_n(GK) are non-isomorphic for all n>1. This confirms a conjecture of Lin and Nelson, and shows that the isomorphism type of G_n(K), n>1, carries more information about K than the isomorphism type of the fundamental group. An appendix by David Savitt contains some results on representations of the trefoil group in PSL(2,p) that are needed for the proof.Comment: 25 pages, 5 figures, to appear in JKTR. v3: example of the target groups added; slight correction to the construction of the target groups; references updated; some changes to notation. v2: section 4.2 expanded to give overview of proo

Seeing faces: evidence suggesting cortical disinhibition in the genesis of visual hallucinations.

The neural mechanisms responsible for triggering visual hallucinations are poorly understood. Here, we report a unique patient whose hallucinations consist exclusively of faces, and which could be reliably precipitated by looking at trees. Using functional Magnetic Resonance Imaging (fMRI), we found that, while face hallucinations was associated with increased neural activity in a number of cortical regions, including low-level visual areas, there was significant decreased activity in the right fusiform face area, a region that is empirically defined by increase activity during veridical perception of faces. These findings indicate key differences in how hallucinatory and veridical perceptions lead to the same phenomenological experience of seeing faces, and are consistent with the hypothesis that hallucinations may be generated by decreased inhibitory inputs to key cortical regions, in contrast to the excitatory synaptic inputs underlying veridical perception

EFFECTS OF FOOD ASSISTANCE AND NUTRITION PROGRAMS ON NUTRITION AND HEALTH, VOLUME 2, DATA SOURCES

This is the second of four reports completed by Abt Associates Inc., under the contract "The Nutrition and Health Outcome Study." This report is an evaluation of various data sources for their potential for analyzing the impacts of USDA's food assistance and nutrition programs (FANPs). Data sources are evaluated against three criteria: coverage of both program participants and nonparticipants; identification of participants and determination of eligibility among nonparticipants; and availability of impact measures. Each data source is classified into one of four categories: principal, potential, recognized, and insufficient. Principal and potential sources are discussed and profiled in this report.USDA Food Assistance and Nutrition Programs, data sources, program participation, nutrition outcomes, health outcomes, Food Consumption/Nutrition/Food Safety, Food Security and Poverty,

Deciphering the role of Epstein-Barr virus in the pathogenesis of T and NK cell lymphoproliferations

Epstein-Barr virus (EBV) is a highly successful herpesvirus, colonizing more than 90% of the adult human population worldwide, although it is also associated with various malignant diseases. Primary infection is usually clinically silent, and subsequent establishment of latency in the memory B lymphocyte compartment allows persistence of the virus in the infected host for life. EBV is so markedly B-lymphotropic when exposed to human lymphocytes in vitro that the association of EBV with rare but distinct types of T and NK cell lymphoproliferations was quite unexpected. Whilst relatively rare, these EBV-associated T and NK lymphoproliferations can be therapeutically challenging and prognosis for the majority of patients is dismal. In this review, we summarize the current knowledge on the role of EBV in the pathogenesis of these tumours, and the implications for treatment. \ud \u

A Compact High Velocity Cloud near the Magellanic Stream: Metallicity and Small-Scale Structure

The Magellanic Stream (MS) is a well-resolved gaseous tail originating from the Magellanic Clouds. Studies of its physical properties and chemical composition are needed to understand its role in Galactic evolution. We investigate the properties of a compact HVC (CHVC 224.0-83.4-197) lying close on the sky to the MS to determine whether it is physically connected to the Stream and to examine its internal structure. Our study is based on analysis of HST/COS spectra of three QSOs (Ton S210, B0120-28, and B0117-2837) all of which pass through this single cloud at small angular separation (\lessim 0.72{\deg}), allowing us to compare physical conditions on small spatial scales. No significant variation is detected in the ionization structure from one part of the cloud to the other. Using Cloudy photoionization models, toward Ton S210 we derive elemental abundances of [C/H] = -1.21 +/- 0.11, [Si/H] = -1.16 +/- 0.11, [Al/H] = -1.19 +/- 0.17 and [O/H] = -1.12 +/- 0.22, which agree within 0.09 dex. The CHVC abundances match the 0.1 solar abundances measured along the main body of the Stream. This suggests that the CHVC (and by extension the extended network of filaments to which it belongs) has an origin in the MS. It may represent a fragment that has been removed from the Stream as it interacts with the gaseous Galactic halo.Comment: ApJ, accepted, 13 pages, 12 figures, 4 table