Preliminary Results of Aerodynamic Heating Studies on the X-15 Airplane

Aerodynamic heating analysis of X-15 aircraft in fligh

X-ray Amorphous Components of Antarctica Dry Valley Soils: Weathering Implications for Mars

The Antarctic Dry Valleys (ADV) comprise the largest ice-free region of Antarctica. Precipitation usually occurs as snow, relative humidity is frequently low, and mean annual temperatures are about -20C [1]. Substantial work has focused on soil formation in the ADVs [2], however, little work has focused on the mineralogy of secondary alteration phases. The dominant weathering process in the ADV region is physical weathering, however, chemical weathering has been well documented [3]. The occurrence of chemical weathering processes are suggested by the presence of clay minerals and iron and titanium oxides in soil. Previously we have investigated soils from two sites in the ADVs and have shown evidence of chemical weathering by the presence of clay minerals (vermiculite, smectite), short-range ordered (SRO) and/or X-ray amorphous materials, and Fe- and Tioxides as well as the presence of discrete calcite crystals [4, 5]. The Chemistry and Mineralogy (CheMin) instrument onboard the Mars Curiosity rover has detected abundant amounts (approx. 25-30 wt. %) of X-ray amorphous materials in a windblown deposit or soil (Rocknest) and in a sedimentary rocks [6,7,8]. The occurrence of large amounts of X-ray amorphous materials in Mars sediments is surprising because these materials are usually present in small quantities in terrestrial environments. The objective of this study is to further characterize the chemistry and mineralogy, specifically the secondary alteration mineralogy and the presence of X-ray amorphous material, of soils from two sites we have previously studied, a subxerous soil in Taylor Valley, and an ultraxerous soil in University Valley. While the chemical alteration processes and mineralogy of the ADV has been documented previously, there has been limited discussion on the occurrence and formation of X-ray amorphous and SRO materials in Antarctica soils. The process of aqueous alteration in the ADVs may have implications for pedogenic processes on Mars, and may lead to a better understanding to the abundance of amorphous material found in sediments in Gale crater

A Micro-level Analysis of Recent Increases in Labor Force Participation among Older Workers

Aggregate data reveal a sizable increase in labor force participation rates since 2000 among workers on the cusp of retirement, reverting back to levels for older men not seen since the 1970s. These aggregate numbers are useful in that they document overall trends, but they lack the ability to identify the reasons behind workers’ decisions. The Health and Retirement Study (HRS) spans the last dozen years from 1992 to 2004, includes two cohorts of retirees, and provides micro-level data regarding these recent trends. Moreover, the HRS contains information on older Americans and the types of jobs they are taking (full-time versus part-time, self-employed versus wage-and-salary, low-paying versus high-paying, blue collar versus white collar, etc.). This study capitalizes on the richness of the HRS data and explores labor force determinants and outcomes of older Americans, with an emphasis on retirees' choices in recent years. We present a cross-sectional and longitudinal description of the financial, health, and employment situation of older Americans. We then explore retirement determinants using a multinomial approach to model gradual retirement and a two-step approach to model the work-leisure and hours intensity decisions of older workers. Evidence suggests that the majority of older Americans retire gradually, in stages, and that younger retirees continue to respond to financial incentives just as their predecessors did. In addition, recent macro-level changes appear to have blurred the distinction between younger and middle-aged retirees.Economics of Aging, Partial Retirement, Gradual Retirement

An Update on Bridge Jobs: The HRS War Babies

Are today’s youngest retirees following in the footsteps of their older peers with respect to gradual retirement? Recent evidence from the Health and Retirement Study (HRS) suggests that most older Americans with full-time career jobs later in life transitioned to another job prior to complete labor force withdrawal. This paper explores the retirement patterns of a younger cohort of individuals from the HRS known as the “War Babies.” These survey respondents were born between 1942 and 1947 and were 57 to 62 years of age at the time of their fourth bi-annual HRS interview in 2004. We compare the War Babies to an older cohort of HRS respondents and find that, for the most part, the War Babies have followed the gradual-retirement trends of their slightly older predecessors. Traditional one-time, permanent retirements appear to be fading, a sign that the impact of changes in the retirement income landscape since the 1980s continues to unfold.Economics of Aging, Partial Retirement, Gradual Retirement

The Role of Re-entry in the Retirement Process

To what extent do older Americans re-enter the labor force after an initial exit and what drives these “unretirement” decisions? Retirement for most older Americans with full-time career jobs is not a one-time, permanent event. Labor force exit is more likely to be a process. Prior studies have found that between one half and two thirds of career workers take at least one other job before exiting from the labor force completely. The transitional nature of retirement may be even more pronounced when considering the impact of re-entry. This paper examines the extent to which older Americans with career jobs re-entered the labor force. The analysis is based on data from the Health and Retirement Study (HRS), an ongoing, longitudinal survey of older Americans that began in 1992. We examined the retirement patterns of a subset of 5,617 HRS respondents who were on a full-time career job at the time of the first interview. Logistic regression was used to explore determinants of re-entry among those who initially exited the labor force. We found that approximately 15 percent of older Americans with career jobs returned to the labor force after initially exiting. Respondents were more likely to re-enter if they were younger, were in better health, or had a defined-contribution pension plan. This research provides empirical evidence of how older Americans are utilizing bridge jobs as they transition from career employment, and that re-entry may be an important part of the work experience of older Americans.Economics of Aging, Partial Retirement, Bridge Jobs, Gradual Retirement

Self-Employment Transitions among Older American Workers with Career Jobs

What role does self-employment play in the retirement process? Older Americans are staying in the labor force longer than prior trends would have predicted and many change jobs later in life. These job transitions are often within the same occupation or across occupations within wage-and-salary employment. The transition can also be out of wage-and-salary work and into self employment. Indeed, national statistics show that self employment becomes more prevalent with age, partly because self employment provides older workers with opportunities not found in traditional wage-and-salary jobs, such as flexibility in hours worked and independence. This paper analyzes transitions into and out of self employment among older workers who have had career jobs. We utilize the Health and Retirement Study, a nationally-representative dataset of older Americans, to investigate the prevalence of self employment among older workers who made a job transition later in life and to explore the factors that determine the choice of wage-and-salary employment or self employment. We find that post-career transitions into and out of self employment are common and that health status, career occupation, and financial variables are important determinants of these transitions. As older Americans and the country as a whole face financial strains in retirement income in the years ahead, self employment may be a vital part of the pro-work solution.Retirement, Retirement Transitions, Self Employment

Crowding-induced hybridization of single DNA hairpins

It is clear that a crowded environment influences the structure, dynamics, and interactions of biological molecules, but the complexity of this phenomenon demands the development of new experimental and theoretical approaches. Here we use two complementary single-molecule FRET techniques to show that the kinetics of DNA base pairing and unpairing, which are fundamental to both the biological role of DNA and its technological applications, are strongly modulated by a crowded environment. We directly observed single DNA hairpins, which are excellent model systems for studying hybridization, either freely diffusing in solution or immobilized on a surface under crowding conditions. The hairpins followed two-state folding dynamics with a closing rate increasing by 4-fold and the opening rate decreasing 2-fold, for only modest concentrations of crowder [10% (w/w) polyethylene glycol (PEG)]. These experiments serve both to unambiguously highlight the impact of a crowded environment on a fundamental biological process, DNA base pairing, and to illustrate the benefits of single-molecule approaches to probing the structure and dynamics of complex biomolecular systems

Quantum Hall Spherical Systems: the Filling Fraction

Within the newly formulated composite fermion hierarchy the filling fraction of a spherical quantum Hall system is obtained when it can be expressed as an odd or even denominator fraction. A plot of $\nu\frac{2S}{N-1}$ as a function of $2S$ for a constant number of particles (up to N=10001) exhibits structure of the fractional quantum Hall effect. It is confirmed that $\nu_e +\nu_h=1$ for all particle-hole conjugate systems, except systems with $N_e =N_h$, and $N_e=N_h \pm 1$.Comment: 3 pages, Revtex, 7 PostScript figures, submitted to Phys. Rev. B Rapid Communicatio

Extended deterrence dilemmas in the grey zone: transatlantic insights on Baltic security challenges

This is the final version. Available from De Gruyter via the DOI in this record.Should the U.S. respond with military means to a limited Russian incursion in the Baltics? This paper explores Western public and expert attitudes towards such a hypothetical grey zone crisis. Using survey experiments and crisis simulations we find considerable reluctance to use military tools and channels in order to support a Baltic ally, and surprisingly little variation across the audiences. We also find that the understanding of Baltic regional realities in the U.S. and Western Europe, although gradually increasing, remains limited. The underlying reluctance to get the U.S. involved in an armed conflict with Russia in the hopes that such acquiescence may help preserve global stability indicates that the conflict in Ukraine only had a fundamentally limited impact on Western strategic thought vis-à-vis deterring Russia. The study points to young Democrats as the most likely prospective supporters of armed defense of the Baltic region (as opposed to Republicans traditionally approached by Baltic lobbyists), suggesting a due shift in Transatlantic engagement