1,408 research outputs found
On the Concavity of Delivery Games
Delivery games, introduced by Hamers, Borm, van de Leensel and Tijs (1994), are combinatorial optimization games that arise from delivery problems closely related to the Chinese postman problem (CPP). They showed that delivery games are not necessarily balanced. For delivery problems corresponding to the class of bridge-connected Euler graphs they showed that the related games are balanced. This paper focuses on the concavity property for delivery games. A delivery game arising from a delivery model corresponding to a bridge-connected Euler graph needs not to be concave. The main result will be that for delivery problems corresponding to the class of bridge-connected cyclic graphs, which is a subclass of the class of bridge-connected Euler graphs, the related delivery games are concave.
The rate of WD-WD head-on collisions in isolated triples is too low to explain standard type Ia supernovae
Type Ia supernovae (Ia-SNe) are thought to arise from the thermonuclear
explosions of white dwarfs (WDs). The progenitors of such explosions are still
highly debated; in particular the conditions leading to detonations in WDs are
not well understood in most of the suggested progenitor models. Nevertheless,
direct head-on collisions of two WDs were shown to give rise to detonations and
produce Ia-SNe - like explosions, and were suggested as possible progenitors.
The rates of such collisions in dense globular clusters are far below the
observed rates of type Ia SNe, but it was suggested that quasi-secular
evolution of hierarchical triples could produce a high rate of such collisions.
Here we used detailed triple stellar evolution populations synthesis models
coupled with dynamical secular evolution to calculate the rates of WD-WD
collisions in triples and their properties. We explored a range of models with
different realistic initial conditions and derived the expected SNe total mass,
mass-ratio and delay time distributions for each of the models. We find that
the SNe rate from WD-WD collisions is of the order of 0.1% of the observed
Ia-SNe rate across all our models, and the delay-time distribution is almost
uniform in time, and is inconsistent with observations. We conclude that SNe
from WD-WD collisions in isolated triples can at most provide for a small
fraction of Ia-SNe, and can not serve as the main progenitors of such
explosions.Comment: 13 pages, 4 figures, submitted to A&
Профессиональная направленность при обучении английскому языку студентов неязыковых специальностей
Предметом статьи является эффективность использования новой технологии при обучении и изучении английского языка с профессиональной направленностью.Предметом статті є ефективність використання нової технології під час навчання та вивчення англійської мови з професійною направленістю.Subject of the article is the effectiveness of using the new technology when teaching and studying English language for specific purposes
Data reconciliation of immersive heart inspection
IVUS images are complicated medical datasets suffering from some artifacts caused by the data acquisition method of immersive heart inspection. Data reconciliation, which removes tracing and tracking uncertainties of these datasets, is an important step for the medical application of remodeling the arteries in virtual reality to aid diagnosing and treating heart diseases. This paper provides an empirical data reconciliation method, which fuses the features of the coronary longitudinal movement with motion compensation model. It explains the distortion of the data set well and provides a method to analyze and reconcile the dataset
Theoretical study of isolated dangling bonds, dangling bond wires and dangling bond clusters on H:Si(100)-(21) surface
We theoretically study the electronic band structure of isolated unpaired and
paired dangling bonds (DB), DB wires and DB clusters on H:Si(100)-(21)
surface using Extended H\"uckel Theory (EHT) and report their effect on the Si
band gap. An isolated unpaired DB introduces a near-midgap state, whereas a
paired DB leads to and states, similar to those introduced by an
unpassivated asymmetric dimer (AD) Si(100)-(21) surface. Such induced
states have very small dispersion due to their isolation from the other states,
which reside in conduction and valence band. On the other hand, the surface
state induced due to an unpaired DB wire in the direction along the dimer row
(referred to as ), has large dispersion due to the strong coupling
between the adjacent DBs, being 3.84 apart. However, in the direction
perpendicular to the dimer row (referred to as [110]), due to the reduced
coupling between the DBs being 7.68 apart, the dispersion in the surface
state is similar to that of an isolated unpaired DB. Apart from this, a paired
DB wire in direction introduces and states similar
to those of an AD surface and a paired DB wire in [110] direction exhibits
surface states similar to those of an isolated paired DB, as expected. Besides
this, we report the electronic structure of different DB clusters, which
exhibit states inside the band gap that can be interpreted as superpositions of
states due to unpaired and paired DBs.Comment: 7 pages, 10 figure, 1 tabl
The Ge(001) (2 × 1) reconstruction: asymmetric dimers and multilayer relaxation observed by grazing incidence X-ray diffraction
Grazing incidence X-ray diffraction has been used to analyze in detail the atomic structure of the (2 × 1) reconstruction of the Ge(001) surface involving far reaching subsurface relaxations. Two kinds of disorder models, a statistical and a dynamical were taken into account for the data analysis, both indicating substantial disorder along the surface normal. This can only be correlated to asymmetric dimers.
Considering a statistical disorder model assuming randomly oriented dimers the analysis of 13 symmetrically independent in-plane fractional order reflections and of four fractional order reciprocal lattice rods up to the maximum attainable momentum transfer qz = 3c* (c* = 1.77 × 10−1 Å−1) indicates the formation of asymmetric dimers characterized by R>D = 2.46(5) Å as compared to the bulk bonding length of R = 2.45 Å. The dimer height of Δ Z = 0.74(15) Å corresponds to a dimer buckling angle of 17(4)°. The data refinement using anisotropic thermal parameters leads to a bonding length of RD = 2.44(4) Å and to a large anisotropy of the root mean-square vibration amplitudes of the dimer atoms (u112) 1/2 = 0.25 Å, (u222)1/2 = 0.14 Å, (u332)1/2 = 0.50 Å). We have evidence for lateral and vertical disp tenth layer below the surface
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