2,348 research outputs found
Constructing Numerical Semigroups of a Given Genus
Let n_g denote the number of numerical semigroups of genus g. Bras-Amoros
conjectured that n_g possesses certain Fibonacci-like properties. Almost all
previous attempts at proving this conjecture were based on analyzing the
semigroup tree. We offer a new, simpler approach to counting numerical
semigroups of a given genus. Our method gives direct constructions of families
of numerical semigroups, without referring to the generators or the semigroup
tree. In particular, we give an improved asymptotic lower bound for n_g.Comment: 11 pages, 3 figures, 2 tables; accepted by Semigroup Foru
Herstructurering industrieel erfgoed in plattelandsgebieden
Het onderzoek van de afstudeergroep [email protected] is een poging tot aanvulling en verdieping van onderzoek van DAAD. Het architectenbureau verricht research naar een reeks industriële erfgoederen (in plattelandsgebieden) met de bedoeling een nieuwe ontwerpmethodiek te formuleren. Het bureau probeert op deze wijze de structurele leegstand van industriepanden tegen te gaan. De nieuwe ontwerpmethodiek moet het (financieel) aantrekkelijker moeten maken om de oude silo’s te herstructureren, en daarmee de dikwijls gebiedseigen panden behouden van sloop. DAAD heeft daartoe een aantal vragen opgesteld die als weegfactor kunnen dienen voor de verlenging van de levensduur van het erfgoed
Recent experiments on a small-angle/wide-angle X-ray scattering beam line at the ESRF
Recent results using a new combined small-angle/wide-angle X-ray scattering (SAXS/WAXS) beam line at the European Synchrotron Radiation Source (ESRF) will be presented. This beam line is specifically designed to be able to handle complicated sample environments required to perform time-resolved experiments mimicking processing conditions used in material science. Besides the attention that has been given to the interfacing of these sample environments to the beam line data acquisition system also the developments in detector technology will be discussed. The influence that a high count rate and low noise WAXS detector can have on the accuracy of experimental results in polymer crystallisation will be shown. It is shown that it is feasible to detect crystalline volume fractions as low as 10(-3)-10(-4) in polymeric systems
Patterns on the numerical duplication by their admissibility degree
We develop the theory of patterns on numerical semigroups in terms of the
admissibility degree. We prove that the Arf pattern induces every strongly
admissible pattern, and determine all patterns equivalent to the Arf pattern.
We study patterns on the numerical duplication when . We
also provide a definition of patterns on rings
Effect of hydrogen addition on the consumption speed of lean premixed laminar methane flames exposed to combined strain and heat loss
This study presents a numerical analysis of the impact of hydrogen addition
on the consumption speed of premixed lean methane-air laminar flames exposed to
combined strain and heat loss. Equivalence ratios of 0.9, 0.7, and 0.5 with
fuel mixture composition ranging from pure methane to pure hydrogen are
considered to cover a wide range of conditions in the lean region. The 1-D
asymmetric counter-flow premixed laminar flame aCFPF with heat loss on the
product side is considered as a flamelet configuration that represents an
elementary unit of a turbulent flame and the consumption speed is used to
characterize the effect of strain and heat loss. Due to the ambiguity in the
definition of the consumption speed of multi-component mixtures, two
definitions are compared. The definition of the consumption speed based on the
heat release results in lower values of the stretched flame speed and even an
opposite response to strain rate for some methane-hydrogen-air mixtures
compared to the definition based on the fuel consumption. Strain rate leads to
an increase in the flame speed for the lean methane-hydrogen mixtures, reaching
a maximum value after which the flame speed decreases with strain rate. Heat
loss decreases the stretched flame speed and leads to a sooner extinction of
the flamelet due to combined strain and heat loss. Hydrogen addition and
equivalence ratio significantly impact the maximum consumption speed and the
flame response to combined strain rate and heat loss. The effect of hydrogen on
the thermo-diffusive properties of the mixture, characterized by the Zel'dovich
number and the effective Lewis number, are also analyzed and related to the
effect on the consumption speed. Two definitions of the Lewis number of the
multi-component fuel mixture are evaluated against the results from the aCFPF.Comment: Submitted to journal Combustion Theory and Modelling - Manuscript ID
TCTM-2022-06-6
On the ordeal of quinolone preparation via cyclisation of aryl-enamines; synthesis and structure of ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)-quinoline-3-carboxylate
Recent studies directed to the design of compounds targeting the bc(1) protein complex of Plasmodium falciparum, the parasite responsible for most lethal cases of malaria, identified quinolones (4-oxo-quinolines) with low nanomolar inhibitory activity against both the enzyme and infected erythrocytes. The 4-oxo-quinoline 3-ester chemotype emerged as a possible source of potent bc(1) inhibitors, prompting us to expand the library of available analogs for SAR studies and subsequent lead optimization. We now report the synthesis and structural characterization of unexpected ethyl 6-methyl-7-iodo-4-(3-iodo-4-methylphenoxy)quinoline-3-carboxylate, a 4-aryloxy-quinoline 3-ester formed during attempted preparation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate (4-oxo-quinoline 3-ester). We propose that the 4-aryloxy-quinoline 3-ester derives from 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate (4-hydroxy-quinoline 3-ester), the enol form of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate. Formation of the 4-aryloxy-quinoline 3-ester confirms the impact of quinolone/hydroxyquinoline tautomerism, both on the efficiency of synthetic routes to quinolones and on pharmacologic profiles. Tautomers exhibit different cLogP values and interact differently with the enzyme active site. A structural investigation of 6-methyl-7-iodo-4-oxo-quinoline-3-carboxylate and 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, using matrix isolation coupled to FTIR spectroscopy and theoretical calculations, revealed that the lowest energy conformers of 6-methyl-7-iodo-4-hydroxy-quinoline-3-carboxylate, lower in energy than their most stable 4-oxo-quinoline tautomer by about 27 kJ mol(-1), are solely present in the matrix, while the most stable 4-oxo-quinoline tautomer is solely present in the crystalline phase.Fundacao para a Ciencia e Tecnologia (FCT - Portugal) [UID/Multi/04326/2013]; QREN-COMPETE-UE; CCMAR; FCT [SFRH/BD/81821/2011, RECI/BBB-BQB/0230/2012, UI0313/QUI/2013, UID/FIS/04564/2016]; FEDER/COMPETE-UE; [PTDC/QEQ-QFI/3284/2014 - POCI-01-0145-FEDER-016617]info:eu-repo/semantics/publishedVersio
Tracking Labrador Sea Water property signals along the Deep Western Boundary Current
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 5348–5366, doi:10.1002/2017JC012921.Observations of the Deep Western Boundary Current (DWBC) at Line W on the western North Atlantic continental slope southeast of Cape Cod from 1995 to 2014 reveal water mass changes that are consistent with changes in source water properties upstream in the Labrador Sea. This is most evident in the cold, dense, and deep class of Labrador Sea Water (dLSW) that was created and progressively replenished and deepened by recurring winter convection during the severe winters of 1987–1994. The arrival of this record cold, fresh, and low potential vorticity anomaly at Line W lags its formation in the Labrador Sea by 3–7 years. Complementary observations along the path of the DWBC provide further evidence that this anomaly is advected along the boundary and indicate that stirring between the boundary and the interior intensifies south of the Flemish Cap. Finally, the consistency of the data with realistic advective and mixing time scales is assessed using the Waugh and Hall (2005) model framework. The data are found to be best represented by a mean transit time of 5 years from the Labrador Sea to Line W, with a leading order role for both advection by the DWBC and mixing between the boundary flow and interior waters.NSF Grant Numbers: OCE-0726720 , 1332667 , 13328342018-01-0
Investigating the interstellar dust through the Fe K-edge
The chemical and physical properties of interstellar dust in the densest
regions of the Galaxy are still not well understood. X-rays provide a powerful
probe since they can penetrate gas and dust over a wide range of column
densities (up to ). The interaction (scattering and
absorption) with the medium imprints spectral signatures that reflect the
individual atoms which constitute the gas, molecule, or solid. In this work we
investigate the ability of high resolution X-ray spectroscopy to probe the
properties of cosmic grains containing iron. Although iron is heavily depleted
into interstellar dust, the nature of the Fe-bearing grains is still largely
uncertain. In our analysis we use iron K-edge synchrotron data of minerals
likely present in the ISM dust taken at the European Synchrotron Radiation
Facility. We explore the prospects of determining the chemical composition and
the size of astrophysical dust in the Galactic centre and in molecular clouds
with future X-ray missions. The energy resolution and the effective area of the
present X-ray telescopes are not sufficient to detect and study the Fe K-edge,
even for bright X-ray sources. From the analysis of the extinction cross
sections of our dust models implemented in the spectral fitting program SPEX,
the Fe K-edge is promising for investigating both the chemistry and the size
distribution of the interstellar dust. We find that the chemical composition
regulates the X-ray absorption fine structures in the post edge region, whereas
the scattering feature in the pre-edge is sensitive to the mean grain size.
Finally, we note that the Fe K-edge is insensitive to other dust properties,
such as the porosity and the geometry of the dust.Comment: 11 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
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