9,117 research outputs found
Enhanced uptake of water by oxidatively processed oleic acid
International audienceA quartz crystal microbalance apparatus has been used to measure the room temperature uptake of water vapour by thin films of oleic acid as a function of relative humidity, both before and following exposure of the films to various partial pressures of gas phase ozone. A rapid increase in the water-sorbing ability of the film is observed as its exposure to ozone is increased, followed by a plateau region in which additional water is taken up more gradually. In this fully-processed region the mass of water taken up by the film is about 4 times that of the unprocessed film. Infrared spectra of the films, measured after variable exposures to ozone, show dramatic increases in both the "free" and hydrogen-bonded O-H stretching regions, and a decrease in the intensity of olefinic features. These results are consistent with the formation of an oxygenated polymeric product or products, as well as the gas phase products previously identified
Hydroxyl radical reactivity at the air-ice interface
Hydroxyl radicals are important oxidants in the atmosphere and in natural waters. They are also expected to be important in snow and ice, but their reactivity has not been widely studied in frozen aqueous solution. We have developed a spectroscopic probe to monitor the formation and reactions of hydroxyl radicals in situ. Hydroxyl radicals are produced in aqueous solution via the photolysis of nitrite, nitrate, and hydrogen peroxide, and react rapidly with benzene to form phenol. Similar phenol formation rates were observed in aqueous solution and bulk ice. However, no reaction was observed at air-ice interfaces, or when bulk ice samples were crushed prior to photolysis to increase their surface area. We also monitored the heterogeneous reaction between benzene present at air-water and air-ice interfaces with gas-phase OH produced from HONO photolysis. Rapid phenol formation was observed on water surfaces, but no reaction was observed at the surface of ice. Under the same conditions, we observed rapid loss of the polycyclic aromatic hydrocarbon (PAH) anthracene at air-water interfaces, but no loss was observed at air-ice interfaces. Our results suggest that the reactivity of hydroxyl radicals toward aromatic organics is similar in bulk ice samples and in aqueous solution, but is significantly suppressed in the quasi-liquid layer (QLL) that exists at air-ice interfaces
Euler number of Instanton Moduli space and Seiberg-Witten invariants
We show that a partition function of topological twisted N=4 Yang-Mills
theory is given by Seiberg-Witten invariants on a Riemannian four manifolds
under the condition that the sum of Euler number and signature of the four
manifolds vanish. The partition function is the sum of Euler number of
instanton moduli space when it is possible to apply the vanishing theorem. And
we get a relation of Euler number labeled by the instanton number with
Seiberg-Witten invariants, too. All calculation in this paper is done without
assuming duality.Comment: LaTeX, 34 page
The analysis of TRICARE Navy obstetric delivery costs within continental United States military treatment facilities
MBA Professional ReportNavy medicine spends approximately $75 million on purchased obstetric (OB) care for Navy personnel and their dependents, a sum that continues to increase each year. The purpose of this research is to compare the cost of Navy OB medical care under TRICARE Prime (civilian sector) with similar care provided in four representative Navy Medical Treatment Facilities (MTF). Specifically, the study will examine (1) the quantity of selected deliveries in TRICARE and four specific MTF catchment areas; (2) the average delivery cost for the different types of Purchased Care (PC) deliveries, and (3) best practice techniques to increase the amount of Direct Care (DC) deliveries care in Navy Medicine. The goal of this study is to compare the benefits and drawbacks of each system to gain insights for providing better and more cost-effective OB care in the Navy.http://archive.org/details/thenalysisoftric1094510397Approved for public release; distribution is unlimited
Hamiltonian 2-forms in Kahler geometry, III Extremal metrics and stability
This paper concerns the explicit construction of extremal Kaehler metrics on
total spaces of projective bundles, which have been studied in many places. We
present a unified approach, motivated by the theory of hamiltonian 2-forms (as
introduced and studied in previous papers in the series) but this paper is
largely independent of that theory.
We obtain a characterization, on a large family of projective bundles, of
those `admissible' Kaehler classes (i.e., the ones compatible with the bundle
structure in a way we make precise) which contain an extremal Kaehler metric.
In many cases, such as on geometrically ruled surfaces, every Kaehler class is
admissible. In particular, our results complete the classification of extremal
Kaehler metrics on geometrically ruled surfaces, answering several
long-standing questions.
We also find that our characterization agrees with a notion of K-stability
for admissible Kaehler classes. Our examples and nonexistence results therefore
provide a fertile testing ground for the rapidly developing theory of stability
for projective varieties, and we discuss some of the ramifications. In
particular we obtain examples of projective varieties which are destabilized by
a non-algebraic degeneration.Comment: 40 pages, sequel to math.DG/0401320 and math.DG/0202280, but largely
self-contained; partially replaces and extends math.DG/050151
Different photolysis kinetics at the surface of frozen freshwater vs. frozen salt solutions
Reactions at air-ice interfaces can proceed at very different rates than those in aqueous solution, due to the unique disordered region at the ice surface known as the quasi-liquid layer (QLL) . The physical and chemical nature of the surfacial region of ice is greatly affected by solutes such as sodium halide salts. In this work, we studied the effects of sodium chloride and sodium bromide on the photolysis kinetics of harmine, an aromatic organic compound, in aqueous solution and at the surface of frozen salt solutions above the eutectic temperature. In common with other aromatic organic compounds we have studied, harmine photolysis is much faster on ice surfaces than in aqueous solution, but the presence of NaCl or NaBr â which does not affect photolysis kinetics in solution â reduces the photolysis rate on ice. The rate decreases monotonically with increasing salt concentration; at the concentrations found in seawater, harmine photolysis at the surface of frozen salt solutions proceeds at the same rate as in aqueous solution. These results suggest that the brine excluded to the surfaces of frozen salt solutions is a true aqueous solution, and so it may be possible to use aqueous-phase kinetics to predict photolysis rates at sea ice surfaces. This is in marked contrast to the result at the surface of frozen freshwater samples, where reaction kinetics are often not well-described by aqueous-phase processes
Pre service primary teachersâ approaches to mathematical generalisation
In our teaching with primary pre-service teachers (PSTs), each of us includes generalising tasks in the context of mathematical reasoning. We set out to explore the value of such activity from the perspective of PSTs and their approaches to generalisation. In this paper, we focus on one PSTâs mathematical reasoning when working on the âflower bedsâ problem. We analyse the ways in which this PST attends to: looking for a relationship; seeing structure within a single figure in a sequence; and seeing sameness and difference between figures in a sequence. We consider what motivates shifts in attention, we reflect on the significance of studentsâ prior experience, and of student collaboration in our teaching sessions
State space c-reductions for concurrent systems in rewriting logic
We present c-reductions, a state space reduction technique.
The rough idea is to exploit some equivalence relation on states (possibly capturing system regularities) that preserves behavioral properties, and explore the induced quotient system. This is done by means of a canonizer
function, which maps each state into a (non necessarily unique) canonical representative of its equivalence class. The approach exploits the expressiveness of rewriting logic and its realization in Maude to enjoy several advantages over similar approaches: exibility and simplicity in
the definition of the reductions (supporting not only traditional symmetry reductions, but also name reuse and name abstraction); reasoning support for checking and proving correctness of the reductions; and automatization
of the reduction infrastructure via Maude's meta-programming
features. The approach has been validated over a set of representative case studies, exhibiting comparable results with respect to other tools
Diffeomorphisms and families of Fourier-Mukai transforms in mirror symmetry
Assuming the standard framework of mirror symmetry, a conjecture is
formulated describing how the diffeomorphism group of a Calabi-Yau manifold Y
should act by families of Fourier-Mukai transforms over the complex moduli
space of the mirror X. The conjecture generalizes a proposal of Kontsevich
relating monodromy transformations and self-equivalences. Supporting evidence
is given in the case of elliptic curves, lattice-polarized K3 surfaces and
Calabi-Yau threefolds. A relation to the global Torelli problem is discussed.Comment: Approx. 20 pages LaTeX. One reference adde
An evidence-based algorithm for the utility of FDG-PET for diagnosing Alzheimer's disease according to presence of medial temporal lobe atrophy
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