56 research outputs found
A new reduced network to simulate detonations in superbursts from mixed H/He accretors
We construct a new reduced nuclear reaction network able to reproduce the
energy production due to the photo-disintegration of heavy elements such as Ru,
which are believed to occur during superbursts in mixed H/He accreting systems.
We use this network to simulate a detonation propagation, inside a mixture of
C/Ru. As our reference, we use a full nuclear reaction network, including 14758
reactions on 1381 nuclides. Until the reduced and full networks converge to a
good level of accuracy in the energy production rate, we iterate between the
hydrodynamical simulation, with a given reduced network, and the readjustment
of a new reduced network, on the basis of previously derived hydrodynamical
profiles. We obtain the thermodynamic state of the material after the passage
of the detonation, and the final products of the combustion. Interestingly, we
find that all reaction lengths can be resolved in the same simulation. This
will enable C/Ru detonations to be more easily studied in future
multi-dimensional simulations, than pure carbon ones. We underline the
dependence of the combustion products on the initial mass fraction of Ru. In
some cases, a large fraction of heavy nuclei, such as Mo, remains after the
passage of the detonation front. In other cases, the ashes are principally
composed of iron group elements.Comment: 6 pages, 12 figure
Height growth of sprouts emerged from small stumps and seed origin saplings under shade, in low elevation Fagus sylvatica L. s.l. stands in Greece
The objectives of this study were a) to analyze the growth of seed origin saplings and young
stump sprouts, emerged from small dimension stumps that were established and grew under different
shade and site conditions in low elevation Fagus sylvatica L. s.l. stands, which are located in northeastern
Greece, and b) to examine whether those stump sprouts can be incorporated in the regeneration process
of beech stands growing in analogous marginal, for the species conservation conditions. Fifty-six seed and
sprout origin saplings were cut. The sprouts had emerged from stumps having a basal diameter lower than
7 cm. For each of the 56 saplings, the mean annual height increment was calculated, dividing the height
of the sapling by the age of its base. The different shade regimes were determined using hemispherical
photography. Sprouts, which grew in deep shade in both site types, and in the moderate shade in medium
productivity sites, exhibited height growth analogous to seed origin plants growing under moderate and
deep shade in good productivity sites, and under moderate shade in medium productivity sites. Moreover,
even though it is of no practical significance, stump sprouts that were established and grew under mod-
erate shade in good productivity sites, showed higher height growth rates than all the other (compared)
categories of seed and sprout origin saplings. Consequently, sprouts can be used in various types and forms
of shelterwood silvicultural systems where regeneration plants are established and grow under shade con-
ditions. A few years after the emergence of sprouts, as regeneration cuttings proceed through the gradual
removal of the mother trees, sprouts will probably exhibit high growth rates as a result of the improved
light conditions and their pre-existing root syste
Calculation of diffraction effects on the average phase of an optical field
We report on algorithms for the computation of the average phase of a beam over a detector in the near field. The basic idea is to reconstruct the optical field numerically and then use a quadrature algorithm to evaluate the quantity of interest. The various algorithms that employ discrete Fourier transform techniques for the computation of the field are described, and numerical tests that assess the accuracy of these algorithms are presented. No particular algorithm delivers the desired accuracy over the entire range of Fresnel numbers of interest, but each can produce satisfactory results within a particular range. Finally, new methods to evaluate the average phase are introduced, and their efficiency is assessed
Average-phase calculations with near-field diffraction algorithms for the Space Interferometry Mission
This work reports on the computation of the average phase of a beam over an optical element via discrete
Fourier transform techniques. The objective is to develop accurate diffraction models for the Space Interferometry
Mission (SIM). Applications related to SIM include calibration of metrology measurements,
evaluation of cornercube diffraction effects, and others. The algorithms that are used to compute the field
are described and numerical tests that assess their accuracy are presented
Structural characteristics of detonation expansion from a small channel to a larger one
We report on numerical simulations of the evolution of two-dimensional detonation waves that are expanded from a small channel to a larger one. In accordance with experimental data, the simulations predict three different types of evolution, namely, supercritical, critical and subcritical detonations. In a supercritical detonation, the reaction zone remains always attached to the precursor shock, whereas in a critical one it temporarily detaches and then re-attaches to the front. In the subcritical type, the extinction is permanent, i.e., the detonation quenches. The effects of the fuel's activation energy and the channel-width ratio are studied via a parametric study. It is found that sufficiently large values of these two parameters can result to flows of the critical and even the subcritical type. Finally, three-dimensional simulations have also been performed and are briefly discussed herein. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved
Odonats Of Beypazarı (Ankara)
Ülkemiz farklı sulak alanların çok olduğu bir coğrafyadadır. Odonatlar bulundukları habitatların çevre sağlığının göstergesi olması yanında, besin zincirinde de önemli bir yere sahiptir ve ekolojik dengenin korunmasında önemli rol oynarlar. Bundan dolayı odonatlar biyoçeşitlilik çalışmalarında da önemli böcek gruplarındandır. Sulak alan çeşitliliğinin yüksek olduğu Beypazarı ilçesinde yapılmış olan araştırmalar bölgenin tamamını temsil etmemektedir. Bundan dolayı Beypazarı odonatlarının biyolojik çeşitliliğinin daha detaylı olarak ortaya çıkarılması amaçlanmıştır. Bu çalışma ile Ankara ili Beypazarı ilçesinde, 2014 yılı mayıs-eylül ayları arasında yapılan arazi çalışmaları sonucunda 192 erkek ve 91 dişi olmak üzere 283 ergin birey atrap yardımıyla toplanmıştır. Örneklerin sistematik olarak değerlendirmesi yapıldığında 9 familya ve 18 cinse ait 24 tür ve 3 alttür belirlenmiştir. Araştırma alanında tespit edilen tür ve alttürlerin morfolojik özellikleri, habitatları, fenolojileri ve araştırma alanında yayılış bilgileri verilmiştir. Faunistin değerlendirmeler sonucunda ise tespit edilen türlerden Erythromma lindenii ve alttürlerden Aeschna isosceles antehumeralis Ankara ili faunası için ilk kez kaydedilmiştir. Ayrıca tespit edilen taksonların teşhis anahtarları, Dünya ve Türkiye yayılışları ile erkek ve dişi fotoğrafları da verilmiştir.Our country is a geographical region where a lot of different wetlands. Odonats; besides being indicators of environmental health of the habitat, because of have an important part in the food chain, they play a critical role in preserving the ecological balance. Therefore Odonats are one of the major insect groups in biodiversity studies. The researchs in the Beypazarı where the diversity of the wetlands is high, do not represent the complete section. Therefore it is intended to reveal the biological diversity of Odonats of Beypazari in more details. In this study, including 192 male and 91 female totally 461 adult Odonata samples which are collected around Beypazarı province of Ankara in May- September 2014 were collected by using sweep net. At the end of the systematic evaluations, 24 species and 3 subspecies belonging to 18 genus of 9 family were identified. Morphological characteristics, habitat, phenology and distribution in the study area of the identified species and subspecies were given. Also, as a result of the faunistic evaluations of the identified species Erythromma lindenii and subspecies Aeschna isosceles antehumeralis was recorded for the first time in Ankara's fauna. Besides, identification keys, distribution in Turkey and world, male and female photos belonging to the identified species were supplied
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