- Proceedings of the National Academy of Sciences of the United States of America
- Published over 2 years ago
Archaeological accounts of cultural change reveal a fundamental conflict: Some suggest that change is gradual, accelerating over time, whereas others indicate that it is punctuated, with long periods of stasis interspersed by sudden gains or losses of multiple traits. Existing models of cultural evolution, inspired by models of genetic evolution, lend support to the former and do not generate trajectories that include large-scale punctuated change. We propose a simple model that can give rise to both exponential and punctuated patterns of gain and loss of cultural traits. In it, cultural innovation comprises several realistic interdependent processes that occur at different rates. The model also takes into account two properties intrinsic to cultural evolution: the differential distribution of traits among social groups and the impact of environmental change. In our model, a population may be subdivided into groups with different cultural repertoires leading to increased susceptibility to cultural loss, whereas environmental change may lead to rapid loss of traits that are not useful in a new environment. Taken together, our results suggest the usefulness of a concept of an effective cultural population size.
Raman amplification arising from the excitation of a density echelon in plasma could lead to amplifiers that significantly exceed current power limits of conventional laser media. Here we show that 1-100 J pump pulses can amplify picojoule seed pulses to nearly joule level. The extremely high gain also leads to significant amplification of backscattered radiation from “noise”, arising from stochastic plasma fluctuations that competes with externally injected seed pulses, which are amplified to similar levels at the highest pump energies. The pump energy is scattered into the seed at an oblique angle with 14 J sr(-1), and net gains of more than eight orders of magnitude. The maximum gain coefficient, of 180 cm(-1), exceeds high-power solid-state amplifying media by orders of magnitude. The observation of a minimum of 640 J sr(-1) directly backscattered from noise, corresponding to ≈10% of the pump energy in the observation solid angle, implies potential overall efficiencies greater than 10%.
A growing body of literature describes how the Affordable Care Act (ACA) has expanded health insurance coverage. What is less well known is how these coverage gains have affected populations that are at risk for high health spending. To investigate this issue, we used prescription transaction data for a panel of 6.7 million prescription drug users to compare changes in coverage, prescription fills, plan spending, and out-of-pocket spending before and after the implementation of the ACA’s coverage expansion. We found a 30 percent reduction in the proportion of this population that was uninsured in 2014 compared to 2013. Uninsured people who gained private coverage filled, on average, 28 percent more prescriptions and had 29 percent less out-of-pocket spending per prescription in 2014 compared to 2013. Those who gained Medicaid coverage had larger increases in fill rates (79 percent) and reductions in out-of-pocket spending per prescription (58 percent). People who gained coverage who had at least one of the chronic conditions detailed in our study saw larger decreases in out-of-pocket spending compared to those who did not have at least one condition. These results demonstrate that by reducing financial barriers to care, the ACA has increased treatment rates while reducing out-of-pocket spending, particularly for people with chronic conditions.
NMR studies with hyperpolarized xenon as functionalized sensor or contrast agent recently made notable progress in developing a new approach for detecting molecular markers and parameters of biomedical interest. Combining spin polarization enhancement with novel indirect detection schemes easily enables a 10(7)-fold signal gain, thus having promising potential to solve the NMR sensitivity problem in many applications. Though an inert element, (129)Xe has exquisite NMR properties to sense molecular environments. This review summarizes recent developments in the production of hyperpolarized xenon and the design and detection schemes of xenon biosensors.
- Prevention science : the official journal of the Society for Prevention Research
- Published about 5 years ago
This cost-effectiveness study analyzes the cost per quality-adjusted life year (QALY) gained in a randomized controlled trial that tested school support as a structural intervention to prevent HIV risk factors among Zimbabwe orphan girl adolescents. The intervention significantly reduced early marriage, increased years of schooling completed, and increased health-related quality of life. By reducing early marriage, the literature suggests the intervention reduced HIV infection. The intervention yielded an estimated US$1,472 in societal benefits and an estimated gain of 0.36 QALYs per orphan supported. It cost an estimated US$6/QALY gained, about 1 % of annual per capita income in Zimbabwe. That is well below the maximum price that the World Health Organization (WHO) Commission on Macroeconomics and Health recommends paying for health gains in low and middle income countries. About half the girls in the intervention condition were boarded when they reached high school. For non-boarders, the intervention’s financial benefits exceeded its costs, yielding an estimated net cost savings of $502 per pupil. Without boarding, the intervention would yield net savings even if it were 34 % less effective in replication. Boarding was not cost-effective. It cost an additional $1,234 per girl boarded (over the 3 years of the study, discounted to present value at a 3 % discount rate) but had no effect on any of the outcome measures relative to girls in the treatment group who did not board. For girls who did not board, the average cost of approximately 3 years of school support was US$973.
- IEEE transactions on ultrasonics, ferroelectrics, and frequency control
- Published over 5 years ago
Understanding amplifier phase noise is a critical issue in many fields of engineering and physics, such as oscillators, frequency synthesis, telecommunication, radar, and spectroscopy; in the emerging domain of microwave photonics; and in exotic fields, such as radio astronomy, particle accelerators, etc. Focusing on the two main types of base noise in amplifiers, white and flicker, the power spectral density of the random phase ��(t) is S��( f ) = b(0) + b(���1)/f. White phase noise results from adding white noise to the RF spectrum in the carrier region. For a given RF noise level, b(0) is proportional to the reciprocal of the carrier power P(0). By contrast, flicker results from a near-dc 1/f noise-present in all electronic devices-which modulates the carrier through some parametric effect in the semiconductor. Thus, b(-1) is a parameter of the amplifier, constant in a wide range of P(0). The consequences are the following: Connecting m equal amplifiers in parallel, b(-1) is 1/m times that of one device. Cascading m equal amplifiers, b(-1) is m times that of one amplifier. Recirculating the signal in an amplifier so that the gain increases by a power of m (a factor of m in decibels) as a result of positive feedback (regeneration), we find that b(���1) is m(2) times that of the amplifier alone. The feedforward amplifier exhibits extremely low b(-1) because the carrier is ideally nulled at the input of its internal error amplifier. Starting with an extensive review of the literature, this article introduces a system-oriented model which describes the phase flickering. Several amplifier architectures (cascaded, parallel, etc.) are analyzed systematically, deriving the phase noise from the general model. There follow numerous measurements of amplifiers using different technologies, including some old samples, and in a wide frequency range (HF to microwaves), which validate the theory. In turn, theory and results provide design guidelines and give suggestions for CAD and simulation. To conclude, this article is intended as a tutorial, a review, and a systematic treatise on the subject, supported by extensive experiments.
Neuromorphic systems are gaining increasing importance in an era where CMOS digital computing techniques are reaching physical limits. These silicon systems mimic extremely energy efficient neural computing structures, potentially both for solving engineering applications as well as understanding neural computation. Toward this end, the authors provide a glimpse at what the technology evolution roadmap looks like for these systems so that Neuromorphic engineers may gain the same benefit of anticipation and foresight that IC designers gained from Moore’s law many years ago. Scaling of energy efficiency, performance, and size will be discussed as well as how the implementation and application space of Neuromorphic systems are expected to evolve over time.
Understanding differences between summer vs. school obesogenic behaviors of children: the structured days hypothesis
- The international journal of behavioral nutrition and physical activity
- Published 8 months ago
Although the scientific community has acknowledged modest improvements can be made to weight status and obesogenic behaviors (i.e., physical activity, sedentary/screen time, diet, and sleep) during the school year, studies suggests improvements are erased as elementary-age children are released to summer vacation. Emerging evidence shows children return to school after summer vacation displaying accelerated weight gain compared to the weight gained occurring during the school year. Understanding how summer days differ from when children are in school is, therefore, essential.
- Proceedings of the National Academy of Sciences of the United States of America
- Published 7 months ago
Recent research by Chetty and colleagues finds that children’s chances of upward mobility are affected by the communities in which they grow up [Chetty R, Hendren N (2016) Working paper 23002]. However, the developmental pathways through which communities of origin translate into future economic gain are not well understood. In this paper we examine the association between Chetty and Hendren’s county-level measure of intergenerational mobility and children’s cognitive and behavioral development. Focusing on children from low-income families, we find that growing up in a county with high upward mobility is associated with fewer externalizing behavioral problems by age 3 years and with substantial gains in cognitive test scores between ages 3 and 9 years. Growing up in a county with 1 SD better intergenerational mobility accounts for ∼20% of the gap in developmental outcomes between children from low- and high-income families. Collectively, our findings suggest that the developmental processes through which residential contexts promote upward mobility begin early in childhood and involve the enrichment of both cognitive and social-emotional development.
CMOS platforms operating at the telecommunications wavelength either reside within the highly dissipative two-photon regime in silicon-based optical devices, or possess small nonlinearities. Bandgap engineering of non-stoichiometric silicon nitride using state-of-the-art fabrication techniques has led to our development of USRN (ultra-silicon-rich nitride) in the form of Si7N3, that possesses a high Kerr nonlinearity (2.8 × 10(-13) cm(2) W(-1)), an order of magnitude larger than that in stoichiometric silicon nitride. Here we experimentally demonstrate high-gain optical parametric amplification using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities. Optical parametric gain of 42.5 dB, as well as cascaded four-wave mixing with gain down to the third idler is observed and attributed to the high photon efficiency achieved through operating above the two-photon absorption edge, representing one of the largest optical parametric gains to date on a CMOS platform.