Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation

We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter Rmfp within 21cmFAST.Comment: 20 pages, 16 figures - Accepted for publication by MNRA

The origins of postmating reproductive isolation: testing hypotheses in the grasshopper Chorthippus parallelus

Although there are several well-established hypotheses for the origins of postmating isolation during allopatric divergence, there have been very few attempts, to determine their relative importance in nature. We have developed an approach based on knowledge of the differing evolutionary histories of populations within species that allows systematic comparison of the predictions of these hypotheses. In previous work, we have applied this methodology to mating signal variation and premating reproductive isolation between populations of the meadow grasshopper Chorthippus parallelus. Here we review the principles behind our approach and report a study measuring postmating isolation in the same set of populations. The populations have known and differing evolutionary histories and relationships resulting from the colonization of northern Europe following the last glaciation. We use a maximum-likelihood analysis to compare the observed pattern of postmating isolation with the predictions of the hypotheses that isolation primarily evolves either as a result of gradual accumulation of mutations in allopatry, or through processes associated with colonization, such as founder events., We also quantify the extent to which degree of postmating isolation can be predicted by genetic distance. Our results suggest that although there is only a weak correlation between genetic distance and postmating isolation, long periods of allopatry do lead to postmating isolation. In contrast to the pattern of premating isolation described in our previous study, colonization does not seem to be associated with increased postmating isolation

Senstitivty analysis and optimization of nodal point placement for vibration reduction

A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location - for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed

Sensitivity derivatives and optimization of nodal point locations for vibration reduction

A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed which uses added lumped masses on the structure as design variables to move the node to a preselected location; for example, where low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed

Participation And performance In 8.02x Electricity And Magnetism: The First Physics MOOC From MITx

Massive Open Online Courses are an exciting new avenue for instruction and research, yet they are full of unknowns. In the Spring of 2013, MITx released its first introductory physics MOOC through the edX platform, generating a total enrollment of 43,000 students from around the world. We describe the population of participants in terms of their age, gender, level of education, and country of origin, highlighting both the diversity of 8.02x enrollees as well as gender gap and retention. Using three midterm exams and the final as waypoints, we highlight performance by different demographic subpopulations and their retention rates. Our work is generally aimed at making a bridge between available MOOC data and topics associated with the Physics Education Research community.Comment: 4 pages, 5 figures, Accepted for publication in the Physics Education Research Conference Proceedings, Portland OR 201

Metaphoric interpretation: Comparison or categorisation?

This paper compares two different theoretical approaches which have been developed to account for metaphoric interpretation: the comparison approach and the categorisation approach. Following a brief review on the history of the two theoretical approaches, the paper points out in part 5 that these two approaches are not fundamentally incompatible. It is further argued in parts 6 and 7 that while the comparison approach can be improved to provide metaphoric interpretations beyond a focus on words and phrases, similar improvement can hardly be made for the categorisation approach, whether by updating the approach itself or by merging it with non-categorisational processes. As a result, the metaphoric cases accountable by the categorisation approach can only be a subset of the cases accountable by the comparison approach

Development of an in Vivo Model to Determine the Biological Value of Microbial Protein

A semi-purified diet (SPD) was fed to 12 wether lambs and one fistulated wether and evaluated for acceptability and ability to support growth. Ruminal pH and NH3 were monitored throughout the diet adaptation period. Treatments included three levels of dry matter intake; low intake (LI) 750 g-hd-l. d-l, medium intake (MI) 1125 g-hd-l..d-l and high intake (HI) 1500 g-hd-l.d-l. Digestibility of dry matter (DM, 70.6%), acid detergent fiber (ADF, 62.8%), nitrogen (N, 72.8%) and percentage digestible nitrogen retained (33.2%) were not different across intake levels. Indigestible ADF of the semi-purified diet appears to be a suitable solid phase marker for estimating DM digestibility if DM intake is accounted for. Regression analysis indicated indigestible ADF recovered in feces was related to indigestible ADF intake and DM intake as described by the equation Indigestible ADF recovered = 80.3824 +.852 (indigestible ADF intake) + .0426 DM intake; (r2 = ,7057; P\u3c .01)

Discourse: Assessment and Therapy

Discourse is essential for interaction and for the expression of ideas, feelings and opinions. Telling personal stories, such as talking about your day or recounting what happened in the playground, is essential for communication and establishing relationships. However, due to their language impairments, people with aphasia (PWA) and children with developmental language disorder (DLD) often have problems with everyday discourse which impact on their lives more widely. While improvement in language skills is supported by speech-language pathology (therapy), it tends to focus on smaller linguistic components, such as single words and sentences. This chapter outlines how speakers construct discourse in everyday situations and focuses on the meanings that people use discourse to convey, as well as the lexical and grammatical resources they use to convey these meanings. Current methods for discourse analysis will be outlined and key developments in narrative discourse production therapy will be reviewed

Atom interferometry with Bose-Einstein condensates in a double-well potential

A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 $\mu$m for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates.Comment: 4 pages, 4 figure