708 research outputs found
Forecasting Design Day Demand Using Extremal Quantile Regression
Extreme events occur rarely, making them difficult to predict. Extreme cold events strain natural gas systems to their limits. Natural gas distribution companies need to be prepared to satisfy demand on any given day that is at or warmer than an extreme cold threshold. The hypothetical day with temperature at this threshold is called the Design Day. To guarantee Design Day demand is satisfied, distribution companies need to determine the demand that is unlikely to be exceeded on the Design Day.
We approach determining this demand as an extremal quantile regression problem. We review current methods for extremal quantile regression. We implement a quantile forecast to estimate the demand that has a minimal chance of being exceeded on the design day. We show extremal quantile regression to be more reliable than direct quantile estimation. We discuss the difficult task of evaluating a probabilistic forecast on rare events.
Probabilistic forecasting is a quickly growing research topic in the field of energy forecasting. Our paper contributes to this field in three ways. First, we forecast quantiles during extreme cold events where data is sparse. Second, we forecast extremely high quantiles that have a very low probability of being exceeded. Finally, we provide a real world scenario on which to apply these techniques
Experimental f-value and isotopic structure for the Ni I line blended with [OI] at 6300A
We have measured the oscillator strength of the Ni I line at 6300.34 \AA,
which is known to be blended with the forbidden [O I] 6300 line, used
for determination of the oxygen abundance in cool stars. We give also
wavelengths of the two isotopic line components of Ni and Ni
derived from the asymmetric laboratory line profile. These two line components
of Ni I have to be considered when calculating a line profile of the 6300 \AA\
feature observed in stellar and solar spectra. We also discuss the labelling of
the energy levels involved in the Ni I line, as level mixing makes the
theoretical predictions uncertain.Comment: Accepted for publication in ApJLetter
Competition between Magnetic and Structural Transition in CrN
CrN is observed to undergo a paramagnetic to antiferromagnetic transition
accompanied by a shear distortion from cubic NaCl-type to orthorhombic
structure. Our first-principle plane wave and ultrasoft pseudopotential
calculations confirm that the distorted antiferromagnetic phase with spin
configuration arranged in double ferromagnetic sheets along [110] is the most
stable. Antiferromagnetic ordering leads to a large depletion of states around
Fermi level, but it does not open a gap. Simultaneous occurence of structural
distortion and antiferromagnetic order is analyzed.Comment: 10 pages, 10 figure
Family ties: Maternal-offspring attachment and young adult nonmedical prescription opioid use
Background: Nonmedical prescription drug use is prevalent among young adults, yet little is known about modifiable determinants of use. We examined whether maternal-offspring attachment reported at mean age 21 was associated with nonmedical prescription opioid use at mean age 26, and investigated whether a history of depressive symptoms and substance use played a role in associations between maternal-offspring attachment and nonmedical prescription opioid use. Methods: We used data from the Growing Up Today Study, a longitudinal cohort of United States adolescents followed into young adulthood. Maternal-offspring attachment was reported by young adults and their mothers, and defined as mutual low, mutual medium or high, and dissonant. Analyses were carried out in the full sample using generalized estimating equation models, and in a sibling subsample, using conditional fixed effects models to control for stable aspects of the family environment. Results: Analyses with the full sample and the sibling subsample both showed that mutual medium/high maternal-offspring attachment at age 21 was associated with lower odds of nonmedical prescription opioid use at age 26 (RR = 0.74; 95% CI = 0.57–0.97 in full sample). The association was partly mediated by mean age 23 offspring smoking, heavy episodic drinking, and illicit drug use. Conclusions: Promoting reciprocal attachment in the maternal-offspring dyad should be investigated as a strategy to prevent nonmedical prescription opioid use by young adulthood. Even in young adulthood, programs that target both parents and offspring may have greater impact on offspring substance use than programs that target offspring alone
Magnetic stress as a driving force of structural distortions: the case of CrN
We show that the observed transition from rocksalt to orthorhombic P
symmetry in CrN can be understood in terms of stress anisotropy. Using local
spin density functional theory, we find that the imbalance between stress
stored in spin-paired and spin-unpaired Cr nearest neighbors causes the
rocksalt structure to be unstable against distortions and justifies the
observed antiferromagnetic ordering. This stress has a purely magnetic origin,
and may be important in any system where the coupling between spin ordering and
structure is strong.Comment: 4 pages (two columns) 4 figure
The complex TIE between macrophages and angiogenesis
Macrophages are primarily known as phagocytic immune cells, but they also play a role in diverse processes, such as morphogenesis, homeostasis and regeneration. In this review, we discuss the influence of macrophages on angiogenesis, the process of new blood vessel formation from the pre-existing vasculature. Macrophages play crucial roles at each step of the angiogenic cascade, starting from new blood vessel sprouting to the remodelling of the vascular plexus and vessel maturation. Macrophages form promising targets for both pro- and anti-angiogenic treatments. However, to target macrophages, we will first need to understand the mechanisms that control the functional plasticity of macrophages during each of the steps of the angiogenic cascade. Here, we review recent insights in this topic. Special attention will be given to the TIE2-expressing macrophage (TEM), which is a subtype of highly angiogenic macrophages that is able to influence angiogenesis via the angiopoietin-TIE pathway
Compositional variability in a cold-water scleractinian, Lophelia pertusa : new insights into “vital effects”
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 7 (2006): Q12004, doi:10.1029/2006GC001354.We analyzed Sr/Ca and Mg/Ca ratios in the thecal wall of Lophelia pertusa, a cold-water coral, using SIMS ion microprobe techniques. The wall grows by simultaneous upward extension and outward thickening. Compositional variability displays similar trends along the upward and outward growth axes. Sr/Ca and Mg/Ca ratios oscillate systematically and inversely. The sensitivity of Lophelia Sr/Ca ratios to the annual temperature cycle (−0.18 mmol · mol−1/°C) is twice as strong as that exhibited by tropical reef corals, and four times as strong as the temperature dependence of Sr/Ca ratios of abiogenic aragonites precipitated experimentally from seawater. A comparison of the skeletal composition of Lophelia with results from precipitation calculations carried out using experimentally determined partition coefficients suggests that both temperature-dependent element partitioning and seasonal changes in the mass fraction of aragonite precipitated from the calcifying fluid influence the composition of Lophelia skeleton. Results from calculations that combine these effects reproduce both the exaggerated amplitude of the Sr/Ca and Mg/Ca oscillations and the inverse relationship between Sr/Ca and Mg/Ca ratios.This study was supported in part by a WHOI Ocean Life Institute fellowship to ALC, by NSF grant OCE-0527350 to G.A.G. and A.L.C., and by the EU 6FP project HERMES, EC contract GOCE-CT-2005-511234 to T.L
Impact of generic alendronate cost on the cost-effectiveness of osteoporosis screening and treatment
Introduction: Since alendronate became available in generic form in the Unites States in 2008, its price has been decreasing. The objective of this study was to investigate the impact of alendronate cost on the cost-effectiveness of osteoporosis screening and treatment in postmenopausal women. Methods: Microsimulation cost-effectiveness model of osteoporosis screening and treatment for U.S. women age 65 and older. We assumed screening initiation at age 65 with central dual-energy x-ray absorptiometry (DXA), and alendronate treatment for individuals with osteoporosis; with a comparator of "no screening" and treatment only after fracture occurrence. We evaluated annual alendronate costs of 800; outcome measures included fractures; nursing home admission; medication adverse events; death; costs; quality-adjusted life-years (QALYs); and incremental cost-effectiveness ratios (ICERs) in 2010 U.S. dollars per QALY gained. A lifetime time horizon was used, and direct costs were included. Base-case and sensitivity analyses were performed. Results: Base-case analysis results showed that at annual alendronate costs of 400 through 714 per QALY gained through 50,000/QALY at all alendronate costs evaluated. Conclusions: Osteoporosis screening followed by alendronate treatment is effective and highly cost-effective for postmenopausal women across a range of alendronate costs, and may be cost-saving at annual alendronate costs of $200 or less. © 2012 Nayak et al
Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V_2O_3
Magnetic correlations in all four phases of pure and doped vanadium
sesquioxide V_2O_3 have been examined by magnetic thermal neutron scattering.
While the antiferromagnetic insulator can be accounted for by a Heisenberg
localized spin model, the long range order in the antiferromagnetic metal is an
incommensurate spin-density-wave, resulting from a Fermi surface nesting
instability. Spin dynamics in the strongly correlated metal are dominated by
spin fluctuations in the Stoner electron-hole continuum. Furthermore, our
results in metallic V_2O_3 represent an unprecedentedly complete
characterization of the spin fluctuations near a metallic quantum critical
point, and provide quantitative support for the SCR theory for itinerant
antiferromagnets in the small moment limit. Dynamic magnetic correlations for
energy smaller than k_BT in the paramagnetic insulator carry substantial
magnetic spectral weight. However, the correlation length extends only to the
nearest neighbor distance. The phase transition to the antiferromagnetic
insulator introduces a sudden switching of magnetic correlations to a different
spatial periodicity which indicates a sudden change in the underlying spin
Hamiltonian. To describe this phase transition and also the unusual short range
order in the paramagnetic state, it seems necessary to take into account the
orbital degrees of freedom associated with the degenerate d-orbitals at the
Fermi level in V_2O_3.Comment: Postscript file, 24 pages, 26 figures, 2 tables, accepted by Phys.
Rev.
Measurements of Dihadron Correlations Relative to the Event Plane in Au+Au Collisions at GeV
Dihadron azimuthal correlations containing a high transverse momentum (\pt)
trigger particle are sensitive to the properties of the nuclear medium created
at RHIC through the strong interactions occurring between the traversing parton
and the medium, i.e. jet-quenching. Previous measurements revealed a strong
modification to dihadron azimuthal correlations in Au+Au collisions with
respect to \pp\ and \dAu\ collisions. The modification increases with the
collision centrality, suggesting a path-length dependence to the jet-quenching
effect. This paper reports STAR measurements of dihadron azimuthal correlations
in mid-central (20-60\%) Au+Au collisions at \snn=200~GeV as a function of
the trigger particle's azimuthal angle relative to the event plane,
\phis=|\phit-\psiEP|. The azimuthal correlation is studied as a function of
both the trigger and associated particle \pt. The subtractions of the
combinatorial background and anisotropic flow, assuming Zero Yield At Minimum
(\zyam), are described. The away-side correlation is strongly modified, and the
modification varies with \phis, which is expected to be related to the
path-length that the away-side parton traverses. The pseudo-rapidity (\deta)
dependence of the near-side correlation, sensitive to long range \deta
correlations (the ridge), is also investigated. The ridge and jet-like
components of the near-side correlation are studied as a function of \phis.
The ridge appears to drop with increasing \phis while the jet-like component
remains approximately constant. ...Comment: 50 pages, 39 figures, 6 table
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