4,986 research outputs found
Asymptotically cylindrical Calabi-Yau manifolds
Let be a complete Ricci-flat Kahler manifold with one end and assume that
this end converges at an exponential rate to for some
compact connected Ricci-flat manifold . We begin by proving general
structure theorems for ; in particular we show that there is no loss of
generality in assuming that is simply-connected and irreducible with
Hol SU, where is the complex dimension of . If we
then show that there exists a projective orbifold and a divisor
in with torsion normal bundle such that is
biholomorphic to , thereby settling a long-standing
question of Yau in the asymptotically cylindrical setting. We give examples
where is not smooth: the existence of such examples appears not to
have been noticed previously. Conversely, for any such pair we give a short and self-contained proof of the existence and
uniqueness of exponentially asymptotically cylindrical Calabi-Yau metrics on
.Comment: 33 pages, various updates and minor corrections, final versio
Predicting race performance in triathlon: The role of perfectionism, achievement goals, and personal goal setting
The question of how perfectionism affects performance is highly debated. Because empirical studies examining perfectionism and competitive sport performance are missing, the present research investigated how perfectionism affected race performance and what role athletesâ goals played in this relationship in two prospective studies with competitive triathletes (Study 1: N = 112; Study 2: N = 321). Regression analyses showed that perfectionistic personal standards, high performance-approach goals, low performance-avoidance goals, and high personal goals predicted race performance beyond athletesâ performance level. Moreover, the contrast between performance-avoidance and performance-approach goals mediated the relationship between perfectionistic personal standards and performance, whereas personal goal setting
mediated the relationship between performance-approach goals and performance. The findings indicate that perfectionistic personal standards do not undermine competitive performance, but are associated with goals that help athletes achieve their best possible performance
High energy cosmic ray air showers and small-x QCD
We discuss that hadron-induced atmospheric air showers from ultra-high energy cosmic rays are sensitive to QCD interactions at very small momentum fractions x where nonlinear effects should become important. The leading partons from the projectile acquire large random transverse momenta as they pass through the strong field of the target nucleus, which breaks up their coherence. This leads to a steeper x_F-distribution of leading hadrons as compared to low energy collisions, which in turn reduces the position of the shower maximum Xmax. We argue that high-energy hadronic interaction models should account for this effect, caused by the approach to the black-body limit, which may shift fits of the composition of the cosmic ray spectrum near the GZK cutoff towards lighter elements. We further show that present data on Xmax(E) exclude that the rapid ~ 1/x^0.3 growth of the saturation boundary (which is compatible with RHIC and HERA data) persists up to GZK cutoff energies. Measurements of pA collisions at LHC could further test the small-x regime and advance our understanding of high density QCD significantly
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Benchmarking Utility-Scale PV Operational Expenses and Project Lifetimes: Results from a Survey of U.S. Solar Industry Professionals
This paper draws on a survey of solar industry professionals and other sources to clarify trends in the expected useful life and operational expenditure (OpEx) of utility-scale photovoltaic (PV) plants in the United States.
Solar project developers, sponsors, long-term owners, and consultants have increased project-life assumptions over time, from an average of ~21.5 years in 2007 to ~32.5 years in 2019. Current assumptions range from 25 years to more than 35 years depending on the organization; 17 out of 19 organizations surveyed or reviewed use 30 years or more.
Levelized, lifetime OpEx estimates have declined from an average of ~17/kWDC-yr in 2019. Across 13 sources, the range in average lifetime OpEx for projects built in 2019 is broad, from 25/kWDC-yr. Operations and maintenance (O&M) costsâone component of OpExâhave declined precipitously in recent years, to 305/MWh. Using 2019 values for all parameters yields an average LCOE of 305/MWh to 22/MWh) of the overall decline is due to improvements in project life and OpEx. Project life extensions and OpEx reductions have had similarly sized impacts on LCOE over this period, at 73/MWhâ43% higher.
Given the limited quantity and comparability of previously available data on these cost drivers, the data and trends presented here may inform assumptions used by electric system planners, modelers, and analysts. The results may also provide useful benchmarks to the solar industry, helping developers and assets owners compare their expectations for project life and OpEx with those of their peers
Agriculture, food security, nutrition and the Millennium Development Goals
"...Today, 1.1 billion people live on less than one US dollar per day (the internationally recognized poverty threshold)â430 million in South Asia, 325 million in Sub-Saharan Africa, 260 million in East Asia and the Pacific, and 55 million in Latin America. Too many children live lives characterized by hunger and illness, and all too often succumb to early death. Moreover, another 1.6 billion people live on between one and two dollars per day, often sliding temporarily below the one dollar per day threshold. To enable all these people to live in dignity, the eight goals to achieve by 2015 are: 1. Eradicate extreme poverty and hunger 2. Achieve universal primary education 3. Promote gender equality and empower women 4. Reduce child mortality 5. Improve maternal health 6. Combat HIV/AIDS, malaria, and other diseases 7. Ensure environmental sustainability 8. Develop a global partnership for development." from TextMillenium Development Goals ,HIV/AIDS ,Gender issues ,Equality ,Nutrition ,Impact ,
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