A Lower Bound on the Mixing Time of Uniformly Ergodic Markov Chains in Terms of the Spectral Radius

We give a bound on the mixing time of a uniformly ergodic, reversible Markov chain in terms of the spectral radius of the transition operator. This bound has been established previously in finite state spaces, and is widely believed to hold in general state spaces, but a proof has not been provided to our knowledge

The Habitable Zone Gallery

The Habitable Zone Gallery (www.hzgallery.org) is a new service to the exoplanet community which provides Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table with information on the percentage of orbital phase spent within the HZ, planetary effective temperatures, and other basic planetary properties. In addition to the table, we also plot the period and eccentricity of the planets with respect to their time spent in the HZ. The service includes a gallery of known systems which plot the orbits and the location of the HZ with respect to those orbits. Also provided are animations which aid in orbit visualization and provide the changing effective temperature for those planets in eccentric orbits. Here we describe the science motivation, the under-lying calculations, and the structure of the web site.Comment: 6 pages, 3 figures, accepted for publication in PAS

Elementary Teachers’ Ideologies On The Experience Of A Mixed-Race Student

With bi/multi-racial students existing within a nebulous racial categorization that has been historically defined to support an economic agenda, creating a positive self-identity for students in this group can be challenging. This article examined those challenges by exploring the reflections of elementary level teachers’ classroom practices and perceptions of the collective elementary educational experience of one bi-racial student in a southeastern U.S. public school

The Core of Care Management: The Role of Authentic Relationships in Caring for Patients with Frequent Hospitalizations.

In the movement to improve the health of patients with multiple chronic conditions and vulnerabilities, while reducing the need for hospitalizations, care management programs have garnered wide attention and support. The qualitative data presented in this paper sheds new light on key components of successful chronic care management programs. By going beyond a task- and temporal-based framework, this analysis identifies and defines the importance of authentic healing relationships in driving individual and systemic change. Drawing on the voices of 30 former clients of the Camden Coalition of Healthcare Providers, the investigators use qualitative methods to identify and elaborate the core elements of the authentic healing relationship-security, genuineness, and continuity-a relationship that is linked to patient motivation and active health management. Although not readily found in the traditional health care delivery system, these authentic healing relationships present significant implications for addressing the persistent health-related needs of patients with frequent hospitalizations. (Population Health Management 2016;19:248-256)

Assessment in senior secondary physical education. Questions of judgement

The ways in which various aspects of senior physical education courses should be assessed and whether some can, or indeed should be incorporated in external examinations, are matters of longstanding professional debate across Australia and internationally. Differences in current practice across Australasia reflect an ongoing lack of consensus about how assessment requirements and arrangements and particularly, examinations in senior physical education, can best address concerns to ensure validity, reliability, equity and feasibility. An issue never far from such debates is that of ‘professional judgement’ and more specifically, whether and how professional judgement does and/or should ‘come into play’ in assessment. This paper reports on research that has explored new approaches to examination assessment and marking in senior physical education, using digital technologies. It focuses specifically on the ways in which ‘professional judgement’ can be deemed to be inherent to two contrasting methods of assessment used in the project: ‘analytical standardsbased’ assessment and ‘comparative pairs’ assessment. Details of each method of assessment are presented. Data arising directly from assessors’ comments and from analysis which explored intermarker reliability for each method of assessment and compared results generated by internal teacher assessment, standards-based and comparative pairs assessment, is reported. Discussion explores whether the data arising can be seen as lending weight to arguments for (i) more faith to be placed in professional judgement and (ii) for the comparative pairs methods to be more widely employed in examination assessment in senior physical education

The Secondary School Writing Center: A Place to Build Confident, Competent Writers

The three of us led an International Writing Centers Association-sponsored allday workshop on secondary school writing centers at the NCTE Convention. Writing centers at all levels follow the theoretical background of Bruffee, Murray, Elbow, and North, to name a few. They are not remedial facilities, as some schools would like them to be, or ESL facilities to improve basic writing in English. No, a secondary school writing center is primarily a place where we work with all students, regardless of their innate talent, to build their confidence and competency as writers. Whether we are talking about students who need to fine-tune excellent papers or students who need to discover what they really want to say, a writing center can be a safe harbor within the sometimes stormy seas of the school day. We can think of no better way to reform writing instruction.University Writing Cente

Conditions for rapid mixing of parallel and simulated tempering on multimodal distributions

We give conditions under which a Markov chain constructed via parallel or simulated tempering is guaranteed to be rapidly mixing, which are applicable to a wide range of multimodal distributions arising in Bayesian statistical inference and statistical mechanics. We provide lower bounds on the spectral gaps of parallel and simulated tempering. These bounds imply a single set of sufficient conditions for rapid mixing of both techniques. A direct consequence of our results is rapid mixing of parallel and simulated tempering for several normal mixture models, and for the mean-field Ising model.Comment: Published in at http://dx.doi.org/10.1214/08-AAP555 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

A Spatio-Temporal Point Process Model for Ambulance Demand

Ambulance demand estimation at fine time and location scales is critical for fleet management and dynamic deployment. We are motivated by the problem of estimating the spatial distribution of ambulance demand in Toronto, Canada, as it changes over discrete 2-hour intervals. This large-scale dataset is sparse at the desired temporal resolutions and exhibits location-specific serial dependence, daily and weekly seasonality. We address these challenges by introducing a novel characterization of time-varying Gaussian mixture models. We fix the mixture component distributions across all time periods to overcome data sparsity and accurately describe Toronto's spatial structure, while representing the complex spatio-temporal dynamics through time-varying mixture weights. We constrain the mixture weights to capture weekly seasonality, and apply a conditionally autoregressive prior on the mixture weights of each component to represent location-specific short-term serial dependence and daily seasonality. While estimation may be performed using a fixed number of mixture components, we also extend to estimate the number of components using birth-and-death Markov chain Monte Carlo. The proposed model is shown to give higher statistical predictive accuracy and to reduce the error in predicting EMS operational performance by as much as two-thirds compared to a typical industry practice

A Window On The Earliest Star Formation: Extreme Photoionization Conditions of a High-Ionization, Low-Metallicity Lensed Galaxy at z~2

We report new observations of SL2SJ021737-051329, a lens system consisting of a bright arc at z=1.84435, magnified ~17x by a massive galaxy at z=0.65. SL2SJ0217 is a low-mass (M <10^9 M*), low-metallicity (Z~1/20 Z*) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for CIV 1548,1550, HeII 1640, OIII] 1661,1666, SiIII] 1883,1892, and CIII] 1907,1909. (2) Double-peaked LyA emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sightline to the lensed galaxy. The relative emission line strengths can be reproduced with a very high-ionization, low-metallicity starburst with binaries, with the exception of He \ii, which indicates an additional ionization source is needed. We rule out large contributions from AGN and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early Universe.Comment: 28 pages, 16 figures, 8 tables, re-submitted to ApJ, comments welcom

Bias in culture-independent assessments of microbial biodiversity in the global ocean

On the basis of 16S rRNA gene sequencing, the SAR11 clade of marine bacteria has almost universal distribution, being detected as abundant sequences in all marine provinces. Yet SAR11 sequences are rarely detected in fosmid libraries, suggesting that the widespread abundance may be an artefact of PCR cloning and that SAR 11 has a relatively low abundance. Here the relative abundance of SAR11 is explored in both a fosmid library and a metagenomic sequence data set from the same biological community taken from fjord surface water from Bergen, Norway. Pyrosequenced data and 16S clone data confirmed an 11-15% relative abundance of SAR11 within the community. In contrast not a single SAR11 fosmid was identified in a pooled shotgun sequenced data set of 100 fosmid clones. This under-representation was evidenced by comparative abundances of SAR11 sequences assessed by taxonomic annotation; functional metabolic profiling and fragment recruitment. Analysis revealed a similar under-representation of low-GC Flavobacteriaceae. We speculate that the fosmid bias may be due to DNA fragmentation during preparation due to the low GC content of SAR11 sequences and other underrepresented taxa. This study suggests that while fosmid libraries can be extremely useful, caution must be used when directly inferring community composition from metagenomic fosmid libraries