Robust regularized singular value decomposition with application to mortality data

We develop a robust regularized singular value decomposition (RobRSVD) method for analyzing two-way functional data. The research is motivated by the application of modeling human mortality as a smooth two-way function of age group and year. The RobRSVD is formulated as a penalized loss minimization problem where a robust loss function is used to measure the reconstruction error of a low-rank matrix approximation of the data, and an appropriately defined two-way roughness penalty function is used to ensure smoothness along each of the two functional domains. By viewing the minimization problem as two conditional regularized robust regressions, we develop a fast iterative reweighted least squares algorithm to implement the method. Our implementation naturally incorporates missing values. Furthermore, our formulation allows rigorous derivation of leave-one-row/column-out cross-validation and generalized cross-validation criteria, which enable computationally efficient data-driven penalty parameter selection. The advantages of the new robust method over nonrobust ones are shown via extensive simulation studies and the mortality rate application.Comment: Published in at http://dx.doi.org/10.1214/13-AOAS649 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Coupled Reversible and Irreversible Bistable Switches Underlying TGF-\beta-induced Epithelial to Mesenchymal Transition

Epithelial to mesenchymal transition (EMT) plays important roles in embryonic development, tissue regeneration and cancer metastasis. While several feedback loops have been shown to regulate EMT, it remains elusive how they coordinately modulate EMT response to TGF-\beta treatment. We construct a mathematical model for the core regulatory network controlling TGF-\beta-induced EMT. Through deterministic analyses and stochastic simulations, we show that EMT is a sequential two-step program that an epithelial cell first transits to partial EMT then to the mesenchymal state, depending on the strength and duration of TGF-\beta stimulation. Mechanistically the system is governed by coupled reversible and irreversible bistable switches. The SNAIL1/miR-34 double negative feedback loop is responsible for the reversible switch and regulates the initiation of EMT, while the ZEB/miR-200 feedback loop is accountable for the irreversible switch and controls the establishment of the mesenchymal state. Furthermore, an autocrine TGF-\beta/miR-200 feedback loop makes the second switch irreversible, modulating the maintenance of EMT. Such coupled bistable switches are robust to parameter variation and molecular noise. We provide a mechanistic explanation on multiple experimental observations. The model makes several explicit predictions on hysteretic dynamic behaviors, system response to pulsed stimulation and various perturbations, which can be straightforwardly tested.Comment: 32 pages, 8 figures, accepted by Biophysical Journa

How to Avoid Compensating CEO for Luck: The Case of Microeconomic Fluctuations

Incentive effects of performance-based compensation schemes for management may be weakened or biased by macroeconomic influences on remuneration. These influences can be seen as reflecting luck from the CEO’s perspective. In this chapter we present a model for how to avoid compensating CEO for luck by filtering out the macroeconomic influences. In the empirical section we analyze the impact of macroeconomic, industry and firm-specific factors on the compensations (salary, bonus, options, and pensions) of CEOs in 127 Swedish corporations during the period 2001-2007. We find macroeconomic influences on Swedish CEOs’ compensation to be substantial. Distinguishing between favorable and unfavorable macroeconomic developments, we find compensation to be more responsive to favorable than to unfavorable developments in macroeconomic variables.Executive compensation; Salary; Bonus; Option; Pension; Macroeconomic uncertainty; Macroeconomic factors; Performance; Luck

Population Ecology Of Panicum Virgatum L And Agropyron Psammophilum Gillett & Senn On The Dune System Along Lake Erie

Panicum virgatum and Agropyron psammophilum are the two dominant sand-binding grasses on the sand dunes along Lake Erie at Port Burwell Provincial Park. In this thesis, results on some aspects of seed and seedling ecology are presented.;Seeds of P. virgatum possess innate dormancy. Pretreatment for two weeks at constant or alternating temperatures ranging from 5 to 15{dollar}\sp\circ{dollar}C under either dark or light/dark conditions significantly improved seed germination. Injury to the seed embryo also significantly increased seed germination. After ripening of seeds in dry storage at room temperature did not alter their germinability significantly during the first 26 weeks. Seeds of A. psammophilum did not exhibit any seed dormancy.;Seed size of P. virgatum and A. psammophilum showed considerable variability. Seed size had significant effect on seedling size at early stages of development in both species. This effect disappeared with time in P. virgatum. However, the seedling size fluctuated in A. psammophilum because the relative growth rate had a negative correlation with seed size for young seedlings but a positive correlation with seed size for older seedlings.;Greenhouse experiments indicated that seedling size was mainly dependent on weight of the endosperm rather than the embryo size in both species. Removal of a part of the endosperm resulted in seedlings of smaller sizes with more proportion of dry matter allocated to the root and less to the leaf of resulting seedlings in comparison with the control.;The maximum depth of emergence of P. virgatum and A. psammophilum seedlings was 11 and 7 cm in the field and 16 and 8 cm in a greenhouse, respectively. Sand burial stimulated the growth in height of P. virgatum seedlings. In A. psammophilum burial of seedlings resulted in an increase in height, number of green leaves and tillers, and dry weight. Seedlings of P. virgatum that emerged from shallow burial depths had fewer surviving individuals. In contrast, seedlings emerging from deep burial depths had more individuals surviving than random expectation. Seedlings emerging from shallow depths could withstand greater post-emergence sand burial than those emerging from deep sand burial