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

Elections, Ideology, and Turnover in the U.S. Federal Government

A defining feature of public sector employment is the regular change in elected leadership. Yet, we know little about how elections influence public sector careers. We describe how elections alter policy outputs and disrupt the influence of civil servants over agency decisions. These changes shape the career choices of employees motivated by policy, influence, and wages. Using new Office of Personnel Management data on the careers of millions of federal employees between 1988 and 2011, we evaluate how elections influence employee turnover decisions. We find that presidential elections increase departure rates of career senior employees, particularly in agencies with divergent views relative to the new president and at the start of presidential terms. We also find suggestive evidence that vacancies in high-level positions after elections may induce lower-level executives to stay longer in hopes of advancing. We conclude with implications of our findings for public policy, presidential politics, and public management

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

Decentralization and Health: Case Studies of Kenya, Pakistan, and the Philippines

Decentralization, defined by the World Bank (2001) as, “the transfer of authority and responsibility for public functions from the central government to intermediate and local governments or quasi-­‐independent government organizations and/or the private sector,” is a movement that has gained much traction in recent history. For many countries undergoing decentralization, a major driver has been a desire to increase the role and participation of local governments in the decision-­‐making space. In doing this, it is hoped to create governance structures that are more accountable and responsive to the people. For health, decentralization has been touted as a potential way to improve responsiveness to local needs, improve service delivery, and improve equitability. In light of these goals, many countries as part of their political decentralization have also opted to decentralize healthcare.https://jdc.jefferson.edu/cwicposters/1020/thumbnail.jp

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

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

Magnetic Actuators and Suspension for Space Vibration Control

The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals

The Office of Ordnance and the Parliamentarian land forces, 1642-1648

An investigation into the means by which the Parliament carried on the War during the years 1642 to 1648 must take into consideration the role of the Office of Ordnance at the Tower of London. A study of the financial and administrative aspects of the Civil Wars would be incomplete without an examination of the ways in which the parties supplied their respective forces with arms, ammunition, clothing and equipment of all kinds. The extent to which they were successful in this sphere has a bearing on other aspects of the conflict. In monetary terms, the resources allocated by Parliament to the procurement of munitions, clothing and equipment for its forces on land appear small in comparison with some other items of military expenditure such as soldiers' pay. Lack of pay had an adverse effect on the strength and effectiveness of an army, and indeed it might have political as well as military repercussions, yet the consequences of a deficiency of munitions could obviously be significant too. The Ordnance Office had since the fifteenth century assumed a central position in the procurement, storage and distribution of munitions to English armies and garrisons, even though it had not acquired a monopoly of those tasks. This fact alone makes it worthwhile to investigate the effect of the outbreak of the Civil Wars upon the personnel and routines of the Office and then the way in which it functioned during the years of conflict that ensued. The Ordnance Office has been the subject of study during the period of its history stretching from the time of its inception to the early eighteenth century, but there has so far been no account of the institution as it was maintained by the Parliament during the Civil War years

Sequence analysis of the cis-regulatory regions of the bithorax complex of Drosophila

The bithorax complex (BX-C) of Drosophila, one of two complexes that act as master regulators of the body plan of the fly, has now been entirely sequenced and comprises approximate to 315,000 bp, only 1.4% of which codes for protein. Analysis of this sequence reveals significantly overrepresented DNA motifs of unknown, as well as known, functions in the nonprotein-coding portion of the sequence. The following types of motifs in that portion are analyzed: (i) concatamers of mono-, di-, and trinucleotides; (ii) tightly clustered hexanucleotides (spaced less than or equal to 5 bases apart); (iii) direct and reverse repeats longer than 20 bp; and (iv) a number of motifs known from biochemical studies to play a role in the regulation of the BX-C. The hexanucleotide AGATAC is remarkably overrepresented and is surmised to play a role in chromosome pairing. The positions of sites of highly overrepresented motifs are plotted for those that occur at more than five sites in the sequence, when <0.5 case is expected. Expected values are based on a third-order Markov chain, which is the optimal order for representing the BXCALL sequence