How to centralize and normalize quandle extensions

We show that quandle coverings in the sense of Eisermann form a (regular epi)-reflective subcategory of the category of surjective quandle homomorphisms, both by using arguments coming from categorical Galois theory and by constructing concretely a centralization congruence. Moreover, we show that a similar result holds for normal quandle extensions.Comment: 17 page

When Will the Gender Gap in Retirement Income Narrow?

Among recent retirees, women receive substantially less retirement income from Social Security and private pensions than men. Increases in women's labor market attachment and earnings relative to men over the past 50 years provide some optimism for an improvement in female retirement income, particularly for married women. This study shows that women's income from Social Security and private pensions has improved only slightly relative to men over the past 25 years. Using data on people approaching retirement age over the next 20 years, prospects for future improvement are investigated. One of the main conclusions is that pension income among women (particularly married women) will rise sharply relative to men's over the next few decades, but a substantial gap could remain even if women close the gap in experience and salaries.

The Impact of Rising 401(k) Pension Coverage on Future Pension Income

Using data from the 1992 Health and Retirement Survey and the 1992 Survey of Consumer Finances, this study compares the level of benefits in 401(k), non-401(k) defined contribution (DC), and defined benefit (DB) plans. Based on current pension information regarding pension contribution rates or benefit formulas, it is shown that a shift to 401(k) plans will reduce the average level of pension benefits for low income workers but have relatively small effects on middle and high income workers. A shift to 401(k) plans would also increase the variance of benefits among low income workers, though the effect would be negligible for middle and high income workers.pension plan; defined benefit; defined contribution

The Growth of Participant Direction in Defined Contribution Plans

Since 1990, most pension plans have shifted the responsibility for directing pension assets to the employee. This study summarizes some of the possible explanations for this rapid shift toward participant direction and uses IRS Form 5500 data to investigate the effect of worker and plan characteristics on the likelihood of making a switch. The study also estimates the effect of a switch to participant direction on employee contribution and asset allocation behavior. The analysis reveals that collective bargaining and pension investments in employer stock reduce the chance of a switch to participant direction, whereas below average return performance increases the chance. Also, a switch to participant direction increases employee contributions to the pension and reduces the share of assets invested in employer securities.participant direction, pensions, employer stock

Is Bigger Still Better? The Decline of the Wage Premium at Large Firms

This study shows that the wage premium paid by large firms fell over the past 20 years and that the decline in the size premium has been most pronounced among the least educated work force. Empirical evidence supports several explanations for the decline in the size premium. First, there has been a convergence in the returns to worker characteristics at large and small firms over time. Second, there has been a convergence in the types of workers employed at small and large firms. Particularly important have been changes in the distribution of workers across industries and the greater rate of decline in unionism at large firms.firm size, wages, fringe benefits

When Will the Gender Gap in Retirement Income Narrow?

Among recent retirees, women receive substantially less retirement income from Social Security and private pensions than men. Increases in women’s labor market attachment and earnings relative to men over the past 50 years provide some optimism for an improvement in female retirement income, particularly for married women. This study shows that women’s income from Social Security and private pensions has improved only slightly relative to men over the past 25 years. Using data on people approaching retirement age over the next 20 years, prospects for future improvement are investigated. One of the main conclusions is that pension income among women (particularly married women) will rise sharply relative to men’s over the next few decades, but a substantial gap could remain even if women close the gap in experience and salaries.

Determinants and Effects of Employer Matching Contributions in 401(k) Plans

This paper uses data from the April 1993 Pension Supplements to the Current Population Survey to investigate the impact of employer matching and employee tenure on participation levels in 401(k) plans. While earlier studies examine similar issues, this study makes several advances. First, consistent with the theory that employers may use matching contributions to satisfy nondiscrimination rules, the study shows that correcting for the endogeneity of employer matching substantially increases the estimated effect of matching on participation levels. Second, the study provides evidence that the large positive association between employee tenure and 401(k) participation is because 'stayers' tend to be 'savers'.

Functionally Specified Distributed Transactions in Co-operative Scenarios

Addresses the problem of specifying co-operative, distributed transactions in a manner that can be subject to verification and testing. Our approach combines the process-algebraic language LOTOS and the object-oriented database modelling language TM to obtain a clear and formal protocol for distributed database transactions meant to describe co-operation scenarios. We argue that a separation of concerns, namely the interaction of database applications on the one hand and data modelling on the other, results in a practical, modular approach that is formally well-founded. An advantage of this is that we may vary over transaction models to support the language combinatio

Dynamic Approximate All-Pairs Shortest Paths: Breaking the O(mn) Barrier and Derandomization

We study dynamic $(1+\epsilon)$-approximation algorithms for the all-pairs shortest paths problem in unweighted undirected $n$-node $m$-edge graphs under edge deletions. The fastest algorithm for this problem is a randomized algorithm with a total update time of $\tilde O(mn/\epsilon)$ and constant query time by Roditty and Zwick [FOCS 2004]. The fastest deterministic algorithm is from a 1981 paper by Even and Shiloach [JACM 1981]; it has a total update time of $O(mn^2)$ and constant query time. We improve these results as follows: (1) We present an algorithm with a total update time of $\tilde O(n^{5/2}/\epsilon)$ and constant query time that has an additive error of $2$ in addition to the $1+\epsilon$ multiplicative error. This beats the previous $\tilde O(mn/\epsilon)$ time when $m=\Omega(n^{3/2})$. Note that the additive error is unavoidable since, even in the static case, an $O(n^{3-\delta})$-time (a so-called truly subcubic) combinatorial algorithm with $1+\epsilon$ multiplicative error cannot have an additive error less than $2-\epsilon$, unless we make a major breakthrough for Boolean matrix multiplication [Dor et al. FOCS 1996] and many other long-standing problems [Vassilevska Williams and Williams FOCS 2010]. The algorithm can also be turned into a $(2+\epsilon)$-approximation algorithm (without an additive error) with the same time guarantees, improving the recent $(3+\epsilon)$-approximation algorithm with $\tilde O(n^{5/2+O(\sqrt{\log{(1/\epsilon)}/\log n})})$ running time of Bernstein and Roditty [SODA 2011] in terms of both approximation and time guarantees. (2) We present a deterministic algorithm with a total update time of $\tilde O(mn/\epsilon)$ and a query time of $O(\log\log n)$. The algorithm has a multiplicative error of $1+\epsilon$ and gives the first improved deterministic algorithm since 1981. It also answers an open question raised by Bernstein [STOC 2013].Comment: A preliminary version was presented at the 2013 IEEE 54th Annual Symposium on Foundations of Computer Science (FOCS 2013

An electronic model for self-assembled hybrid organic/perovskite semiconductors: reverse band edge electronic states ordering and spin-orbit coupling

Based on density functional theory, the electronic and optical properties of hybrid organic/perovskite crystals are thoroughly investigated. We consider the mono-crystalline 4FPEPI as material model and demonstrate the optical process is governed by three active Bloch states at the {\Gamma} point of the reduced Brillouin zone with a reverse ordering compared to tetrahedrally bonded semiconductors. Giant spin-orbit coupling effects and optical activities are subsequently inferred from symmetry analysis.Comment: 17 pages, 6 figure