3,571 research outputs found
A mathematical model for jet engine combustor pollutant emissions
Mathematical modeling for the description of the origin and disposition of combustion-generated pollutants in gas turbines is presented. A unified model in modular form is proposed which includes kinetics, recirculation, turbulent mixing, multiphase flow effects, swirl and secondary air injection. Subelements of the overall model were applied to data relevant to laboratory reactors and practical combustor configurations. Comparisons between the theory and available data show excellent agreement for basic CO/H2/Air chemical systems. For hydrocarbons the trends are predicted well including higher-than-equilibrium NO levels within the fuel rich regime. Although the need for improved accuracy in fuel rich combustion is indicated, comparisons with actual jet engine data in terms of the effect of combustor-inlet temperature is excellent. In addition, excellent agreement with data is obtained regarding reduced NO emissions with water droplet and steam injection
Schubert Polynomials for the affine Grassmannian of the symplectic group
We study the Schubert calculus of the affine Grassmannian Gr of the
symplectic group. The integral homology and cohomology rings of Gr are
identified with dual Hopf algebras of symmetric functions, defined in terms of
Schur's P and Q-functions. An explicit combinatorial description is obtained
for the Schubert basis of the cohomology of Gr, and this is extended to a
definition of the affine type C Stanley symmetric functions. A homology Pieri
rule is also given for the product of a special Schubert class with an
arbitrary one.Comment: 45 page
The Combinatorial World (of Auctions) According to GARP
Revealed preference techniques are used to test whether a data set is
compatible with rational behaviour. They are also incorporated as constraints
in mechanism design to encourage truthful behaviour in applications such as
combinatorial auctions. In the auction setting, we present an efficient
combinatorial algorithm to find a virtual valuation function with the optimal
(additive) rationality guarantee. Moreover, we show that there exists such a
valuation function that both is individually rational and is minimum (that is,
it is component-wise dominated by any other individually rational, virtual
valuation function that approximately fits the data). Similarly, given upper
bound constraints on the valuation function, we show how to fit the maximum
virtual valuation function with the optimal additive rationality guarantee. In
practice, revealed preference bidding constraints are very demanding. We
explain how approximate rationality can be used to create relaxed revealed
preference constraints in an auction. We then show how combinatorial methods
can be used to implement these relaxed constraints. Worst/best-case welfare
guarantees that result from the use of such mechanisms can be quantified via
the minimum/maximum virtual valuation function
Phase I Trial of an Alhydrogel Adjuvanted Hepatitis B Core Virus-Like Particle Containing Epitopes of Plasmodium falciparum Circumsporozoite Protein
The objectives of this non-randomized, non-blinded, dose-escalating Phase I clinical trial were to assess the safety, reactogenicity and immunogenicity of ICC-1132 formulated with Alhydrogel (aluminum hydroxide) in 51 healthy, malaria-naive adults aged 18 to 45 years. ICC-1132 (Malariavax) is a recombinant, virus-like particle malaria vaccine comprised of hepatitis core antigen engineered to express the central repeat regions from Plasmodium falciparum circumsporozoite protein containing an immunodominant B [(NANP)3] epitope, an HLA-restricted CD4 (NANPNVDPNANP) epitope and a universal T cell epitope (T*) (amino acids 326—345, NF54 isolate). We assessed an Alhydrogel (aluminum hydroxide)-adjuvanted vaccine formulation at three ICC-1132 dose levels, each injected intramuscularly (1.0 mL) on study days 0, 56 and 168. A saline vaccine formulation was found to be unstable after prolonged storage and this formulation was subsequently removed from the study. Thirty-two volunteers were followed for one year. Local and systemic adverse clinical events were measured and immune responses to P. falciparum and hepatitis B virus core antigens were determined utilizing the following assays: IgG and IgM ELISA, indirect immunofluorescence against P. falciparum sporozoites, circumsporozoite precipitin (CSP) and transgenic sporozoite neutralization assays. Cellular responses were measured by proliferation and IL-2 assays. Local and systemic reactions were similarly mild and well tolerated between dose cohorts. Depending on the ICC-1132 vaccine concentration, 95 to 100% of volunteers developed antibody responses to the ICC-1132 immunogen and HBc after two injections; however, only 29—75% and 29—63% of volunteers, respectively, developed malaria-specific responses measured by the malaria repeat synthetic peptide ELISA and IFA; 2 of 8 volunteers had positive reactions in the CSP assay. Maximal transgenic sporozoite neutralization assay inhibition was 54%. Forty-seven to seventy-five percent demonstrated T cell proliferation in response to ICC-1132 or to recombinant circumsporozoite protein (rCS) NF-54 isolate. This candidate malaria vaccine was well tolerated, but the vaccine formulation was poorly immunogenic. The vaccine may benefit from a more powerful adjuvant to improve immunogenicity
Correlations between zeros of a random polynomial
We obtain exact analytical expressions for correlations between real zeros of
the Kac random polynomial. We show that the zeros in the interval are
asymptotically independent of the zeros outside of this interval, and that the
straightened zeros have the same limit translation invariant correlations. Then
we calculate the correlations between the straightened zeros of the SO(2)
random polynomial.Comment: 31 pages, 2 figures; a revised version of the J. Stat. Phys. pape
Supersymmetric Vacua in Random Supergravity
We determine the spectrum of scalar masses in a supersymmetric vacuum of a
general N=1 supergravity theory, with the Kahler potential and superpotential
taken to be random functions of N complex scalar fields. We derive a random
matrix model for the Hessian matrix and compute the eigenvalue spectrum.
Tachyons consistent with the Breitenlohner-Freedman bound are generically
present, and although these tachyons cannot destabilize the supersymmetric
vacuum, they do influence the likelihood of the existence of an `uplift' to a
metastable vacuum with positive cosmological constant. We show that the
probability that a supersymmetric AdS vacuum has no tachyons is formally
equivalent to the probability of a large fluctuation of the smallest eigenvalue
of a certain real Wishart matrix. For normally-distributed matrix entries and
any N, this probability is given exactly by P = exp(-2N^2|W|^2/m_{susy}^2),
with W denoting the superpotential and m_{susy} the supersymmetric mass scale;
for more general distributions of the entries, our result is accurate when N >>
1. We conclude that for |W| \gtrsim m_{susy}/N, tachyonic instabilities are
ubiquitous in configurations obtained by uplifting supersymmetric vacua.Comment: 26 pages, 6 figure
Respiratory Inductance Plethysmography to Assess Fatigability during Repetitive Work
publishersversionPeer reviewe
Histopathological evaluation of placentas after diagnosis of maternal SARS-CoV-2 infection.
Background:The impact of maternal SARS-CoV-2 infection on placental histopathology is not well known. Objectives:To determine if significant placental histopathological changes occur after diagnosis of SARS-CoV-2 infection in pregnancy and whether these changes are correlated with the presence or absence of symptoms associated with infection. Study Design:Retrospective cohort study of women diagnosed with SARS-CoV-2 infection who delivered at a single center from April 9th to April 27th, 2020, and had placental specimens reviewed by pathology. Women with singleton gestations and laboratory-confirmed SARS-CoV-2 infection were eligible for inclusion. Historical controls selected from a cohort of women who delivered 6 months prior to the study period were matched in a 1:1 fashion by week of gestation at delivery. Histopathological characteristics were evaluated in each placenta and the incidence of these findings were compared between placentas after diagnosis of maternal SARS-CoV-2 infection and historical controls, as well as between placentas from patients with or without typical symptoms related to infection. Statistical analysis included use of Wilcoxon rank sum test and Fisher\u27s exact test for comparison of categorical and continuous variables. Statistical significance was defined as P value \u3c 0.05. Results:A total of 50 placentas after diagnosis of maternal SARS-CoV-2 infection and 50 historical controls were analyzed. Among placentas from patients diagnosed with SARS-CoV-2 infection, 3 (6%) were preterm (33 3/7, 34 6/7 and 36 6/7 weeks of gestation), 16 (32%) were from patients with typical symptoms related to infection and 34 (68%) were from patients without typical symptoms related to the infection. All patients had diagnosis of SARS-CoV-2 infection in the third trimester. Decidual vasculopathy was not visualized in any of the placentas from patients diagnosed with SARS-CoV-2 infection. There was no statistically significant difference in placental histopathological characteristics between the groups. SARS-CoV-2 testing for all neonates at 24 hours of life was negative. Conclusions:Based on our data, there are no significant placental histopathological changes that occur after diagnosis of SARS-CoV-2 infection in the third trimester of pregnancy compared to a gestational age-matched historical control group. Similar incidences of histopathological findings were also discovered when comparing placentas from patients with SARS-CoV-2 infection with or without the presence of symptoms typically related to infection
Phase diagram of bismuth in the extreme quantum limit
Elemental bismuth provides a rare opportunity to explore the fate of a
three-dimensional gas of highly mobile electrons confined to their lowest
Landau level. Coulomb interaction, neglected in the band picture, is expected
to become significant in this extreme quantum limit with poorly understood
consequences. Here, we present a study of the angular-dependent Nernst effect
in bismuth, which establishes the existence of ultraquantum field scales on top
of its complex single-particle spectrum. Each time a Landau level crosses the
Fermi level, the Nernst response sharply peaks. All such peaks are resolved by
the experiment and their complex angular-dependence is in very good agreement
with the theory. Beyond the quantum limit, we resolve additional Nernst peaks
signaling a cascade of additional Landau sub-levels caused by electron
interaction
Random matrix ensembles with an effective extensive external charge
Recent theoretical studies of chaotic scattering have encounted ensembles of
random matrices in which the eigenvalue probability density function contains a
one-body factor with an exponent proportional to the number of eigenvalues. Two
such ensembles have been encounted: an ensemble of unitary matrices specified
by the so-called Poisson kernel, and the Laguerre ensemble of positive definite
matrices. Here we consider various properties of these ensembles. Jack
polynomial theory is used to prove a reproducing property of the Poisson
kernel, and a certain unimodular mapping is used to demonstrate that the
variance of a linear statistic is the same as in the Dyson circular ensemble.
For the Laguerre ensemble, the scaled global density is calculated exactly for
all even values of the parameter , while for (random
matrices with unitary symmetry), the neighbourhood of the smallest eigenvalue
is shown to be in the soft edge universality class.Comment: LaTeX209, 17 page
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