Model selection via Bayesian information capacity designs for generalised linear models

The first investigation is made of designs for screening experiments where the response variable is approximated by a generalised linear model. A Bayesian information capacity criterion is defined for the selection of designs that are robust to the form of the linear predictor. For binomial data and logistic regression, the effectiveness of these designs for screening is assessed through simulation studies using all-subsets regression and model selection via maximum penalised likelihood and a generalised information criterion. For Poisson data and log-linear regression, similar assessments are made using maximum likelihood and the Akaike information criterion for minimally-supported designs that are constructed analytically. The results show that effective screening, that is, high power with moderate type I error rate and false discovery rate, can be achieved through suitable choices for the number of design support points and experiment size. Logistic regression is shown to present a more challenging problem than log-linear regression. Some areas for future work are also indicated

Quitting in Protest: A Theory of Presidential Policy Making and Agency Response

This paper examines the effects of centralized presidential policy-making, implemented through unilateral executive action, on the willingness of bureaucrats to exert effort and stay in the government. Extending models in organizational economics, we show that policy initiative by the president is a substitute for initiative by civil servants. Yet, total effort is enhanced when both work. Presidential centralization of policy often impels policy-oriented bureaucrats ( zealots ) to quit rather than implement presidential policies they dislike. Those most likely to quit are a range of moderate bureaucrats. More extreme bureaucrats may be willing to wait out an opposition president in the hope of tempering future policy when an allied president is elected. As control of the White House alternates between ideologically opposed extreme presidents, policy-minded moderates are stripped from bureaucratic agencies leaving only policy extremists or poorly performing slackers. These departures degrade policy initiative in moderate agencies

Spin-dependent charge recombination along para-phenylene molecular wires

We have used an efficient new quantum mechanical method for radical pair recombination reactions to study the spin-dependent charge recombination along PTZ$^{\bullet+}$--Ph$_n$--PDI$^{\bullet-}$ molecular wires. By comparing our results to the experimental data of E. Weiss {\em et al.} [J. Am. Chem. Soc. {\bf 126}, 5577 (2004)], we are able to extract the spin-dependent (singlet and triplet) charge recombination rate constants for wires with $n=2-5$. These spin-dependent rate constants have not been extracted previously from the experimental data because they require fitting its magnetic field-dependence to the results of quantum spin dynamics simulations. We find that the triplet recombination rate constant decreases exponentially with the length of the wire, consistent with the superexchange mechanism of charge recombination. However, the singlet recombination rate constant is nearly independent of the length of the wire, suggesting that the singlet pathway is dominated by an incoherent hopping mechanism. A simple qualitative explanation for the different behaviours of the two spin-selective charge recombination pathways is provided in terms of Marcus theory. We also find evidence for a magnetic field-independent background contribution to the triplet yield of the charge recombination reaction, and suggest several possible explanations for it. Since none of these explanations is especially compelling given the available experimental evidence, and since the result appears to apply more generally to other molecular wires, we hope that this aspect of our study will stimulate further experimental work.Comment: 12 pages, 10 figure

Public Sector Personnel Economics: Wages, Promotions, and the Competence-Control Trade-off

We model personnel policies in public agencies, examining how wages and promotion standards can partially offset a fundamental contracting problem: the inability of public sector workers to contract on performance, and the inability of political masters to contract on forbearance from meddling. Despite the dual contracting problem, properly constructed personnel policies can encourage intrinsically motivated public sector employees to invest in expertise, seek promotion, remain in the public sector, and develop policy projects. However, doing so requires internal personnel policies that sort slackers from zealots. Personnel policies that accomplish this task are quite different in agencies where acquired expertise has little value in the private sector, and agencies where acquired expertise commands a premium in the private sector. Finally, even with well-designed personnel policies, there remains an inescapable trade-off between political control and expertise acquisition

Polarized synchrotron emission in quiescent black hole X-ray transients

We present near-infrared polarimetric observations of the black hole X-ray binaries Swift J1357.2-0933 and A0620-00. In both sources, recent studies have demonstrated the presence of variable infrared synchrotron emission in quiescence, most likely from weak compact jets. For Swift J1357.2-0933 we find that the synchrotron emission is polarized at a level of 8.0 +- 2.5 per cent (a 3.2 sigma detection of intrinsic polarization). The mean magnitude and rms variability of the flux (fractional rms of 19-24 per cent in K_s-band) agree with previous observations. These properties imply a continuously launched (stable on long timescales), highly variable (on short timescales) jet in the Swift J1357.2-0933 system in quiescence, which has a moderately tangled magnetic field close to the base of the jet. We find that for A0620-00, there are likely to be three components to the optical-infrared polarization; interstellar dust along the line of sight, scattering within the system, and an additional source that changes the polarization position angle in the reddest (H and K_s) wave-bands. We interpret this as a stronger contribution of synchrotron emission, and by subtracting the line-of-sight polarization, we measure an excess of ~ 1.25 +- 0.28 per cent polarization and a position angle of the magnetic field vector that is consistent with being parallel with the axis of the resolved radio jet. These results imply that weak jets in low luminosity accreting systems have magnetic fields which possess similarly tangled fields compared to the more luminous, hard state jets in X-ray binaries.Comment: Accepted to MNRA

Asymmetric recombination and electron spin relaxation in the semiclassical theory of radical pair reactions

We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nuclear spins which has recently been used to establish a 'proof of principle' for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C+PF- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical

Occupational Therapy and Accessibility in the Outdoors and Summer Camps

Opportunities for positive youth development (PYD) are promoted through both outdoor and camp experiences. The experiences provided by the outdoors and camps are ideal for developing physically, cognitively, socially, emotionally, and spiritually. These areas of PYD are further generalizable to several aspects of occupational performance and participation, while continuing to have benefits throughout the lifespan. While the outdoors and camps provide these valuable opportunities for development, the environments and contexts of these opportunities are often limiting factors for individuals with disabilities. Utilizing an occupational therapy approach allows for further understanding of how to promote inclusion and accessibility practices in these settings and further support occupational performance and participation for individuals of all abilities. The application of an occupational therapy perspective combined with research, review, and collaboration within these communities determined appropriate project objectives to address these areas of need. Further development based on project objectives led to the creation of Access Outdoors Occupational Therapy and the associated website www.accessoutdoorsot.com. Access Outdoors Occupational Therapy is a cumulative result of fulfilling project objectives and aims to promote and advocate for inclusion and accessibility in the outdoors and camp programs while also expanding available knowledge. Areas of growth for Access Outdoors Occupational Therapy include expanding occupational therapy roles, community partnerships, on the ground advocacy and outreach, and individualized consulting for outdoors and camp programs