2,910 research outputs found
Classical Solutions for a Class of Burgers Equation
In this paper we consider a class of Burgers equation. We propose a new
method of investigation for existence of classical solutions.Comment: arXiv admin note: substantial text overlap with arXiv:1806.1008
Existence and Smoothness of Navier-Stokes Equations
In this paper we propose new method for proving of global solutions for 3D
Navier-Stokes equations. This complies an application to the Clay Institute
Millennium Prize Navier Stokes Problem. The proposed method can be applied for
investigation of global solutions for other classes of PDEs
Variable stars in the field of open cluster NGC 6939
The results of CCD photometric survey performed with the 90/180 cm
Schmidt-Cassegrain Telescope of the Nicolaus Copernicus University Astronomical
Observatory in Piwnice (Poland) and the 70/172 cm Schmidt Telescope of the
National Astronomical Observatory (NAO) at Rozhen (Bulgaria) of the field of 1
Gyr old open cluster NGC 6939 are presented. Twenty two variable stars were
detected, four of them previously known. Four eclipsing systems (3 detached and
1 contact binary) were found to be members of the cluster. Analysis of the
brightness of the contact binary V20 strongly supports the distance to the
cluster of 1.74 +/- 0.20 kpc. The small population of contact binaries in NGC
6939 confirms also the relatively young age of the cluster.Comment: 9 pages, 3 figures, accepted for publication in A
The PADME Tracking System
The Positron Annihilation into Dark Matter Experiment (PADME) at LNF-INFN
Linac aims to perform a search for dark photons in positron-on-target
annihilation process. A key component of the setup is the tracking system which
allows vetoing the bremsstrahlung-induced background. Different solutions for
the detector will be shown and will be discussed. Attention will be paid to the
possibility to construct a hybrid tracker based on plastic scintillator fibers
read out by CCD matrices.Comment: presented at RAD 2016 Conferenc
Microscopic structure of metal whiskers
We present TEM images of the interior of metal whiskers (MW) grown on
electroplated Sn films. Along with earlier published information, our
observations focus on a number of questions, such as why MWs' diameters are in
the micron range (significantly exceeding the typical nano-sizes of nuclei in
solids), why the diameters remain practically unchanged in the course of MW
growth, what is the nature of MW diameter stochasticity, and what is the origin
of the well-known striation structure of MW side surfaces. In an attempt to
address such questions we performed an in-depth study of MW structure at the
nanoscale by detaching a MW from its original film, reducing its size to a thin
slice by cutting its sides by a focused ion beam, and performing TEM on that
structure. Our observations revealed a rich nontrivial morphology suggesting
that MW may consist of many side by side grown filaments. This structure
appears to extend to the outside whisker surface and be the reason for the
striation. In addition, we put forward a theory where nucleation of multiple
thin metal needles results into micron-scale and larger MW diameters. This
theory is developed in the average field approximation similar to the
roughening transitions of metal surfaces. The theory also predicts MW
nucleation barriers and other observed features.Comment: 8 pages, 7 figure
Variational band theory of vibronic polarons in crystals. III. Numerical calculations
In the preceding Part II, we derived variational equations for the phonon
Fourier amplitudes and for the Fourier amplitudes of the fractional
contribution of the electronic bands to the trial variational state. These
equations are now solved by means of iterations for each value of the total
momentum in order to obtain the energy vs. momentum relation for the ground
state. Another result is mapping out the phonon and band Fourier amplitudes in
the parameter space of the mixing constant and the electron hopping energy.Comment: 9 pages and 23 figures pdf format, paper based on a Ph.D. thesis by
A.G.
Intrinsic Nanoscale Phase Seperation of bulk As2S3 Glass
Raman scattering on bulk AsxS1-x glasses showes that vibrational modes of
As4S4 monomer first appear near x=0.38, and their concentration increases
precipitously with increasing x, suggesting that the stoichiometric glass
(x=0.40) is intrinsically phase seperated into small As-rich(As4S4) and large
S-righ clusters. Support for the Raman-active vibrational modes of the
orpiment-like and realgar-like nanophases is provided by ab-initio density
functional theory calculations on appropriate clusters. Nanoscale phase
seperation provides a basis for understanding the global maximum in the glass
transition temperature Tg near x=0.40, and the departure from Arrhenius
temperature activation of As2S3 melt viscosities
The Intermediate Phase in Ternary GexAsxSe1-2x Glasses
Melt-quenched AsxGexSe1-2x glasses over the composition range, 0 < x < 0.26,
are examined in Raman scattering, T-modulated Differential Scanning Calorimetry
(MDSC), and 119Sn Mossbauer spectroscopy measurements. The non-reversing
enthalpy near Tg, DHnr(x), accessed from MDSC shows a global minimum (~ 0) in
the xc(1) = 0.09 < x < xc(2) = 0.16 range, and increases by an order of
magnitude both at x xc(2). Raman mode frequency of
corner-sharing Ge(Se1/2)4 tetrahedra studied as a function of x, also shows
three distinct regimes (or power-laws, p) that coincide with DHnr(x) trends.
These regimes are identified with mechanically floppy (x < xc(1)), intermediate
(xc(1) xc(2)) phases. The Raman
elasticity power-law in the intermediate phase, p1 = 1.04(3), and in the
stressed rigid phase, p2= 1.52(5), suggest effective dimensionalities of d = 2
and 3 respectively
Diet of the Golden Eagle (Aquila chrysaetos) (Aves: Accipitridae) in Sarnena Sredna Gora Mountains (Bulgaria)
The material of pellets and food remains (as bone and shell fragments, hair, and feathers) was collected after the breeding season from below and within one nest of Golden Eagles on rocks at Sarnena Sredna Gora Mts., north-east of Stara Zagora town. Our study was carried out during a three year period (1999, 2000 and 2002). Total 65 specimens from minimum 10 species of preys were identified among the food remains from which the reptiles dominated. Mostly preyed by the Golden Eagles couple were the tortoises (Testudo sp.) with 55.4% from all registered individual preys. The most common prey from mammals was the hedgehog (Erinaceus roumanicus) with 13.8%. Interesting fact was and the relatively high percentage of the cats with 7.7% (possibly most of them domestic ones)
The Discrepant Kinematics of ORLs and CELs in NGC 7009 as a Function of Ionization Structure
We present spatially- and velocity-resolved echelle spectroscopy for NGC 7009
obtained with the UVES spectrograph at the European Southern Observatory's Very
Large Telescope. Our objective is to analyze the kinematics of emission lines
excited by recombination and collisions with electrons to determine whether
similarities or differences could be useful in elucidating the well-known
abundance discrepancy derived from them. We construct position-velocity maps
for recombination, fluorescence, charge transfer, and collisionally-excited
lines. We find a plasma component emitting in the C II, N II, O II, and Ne II
recombination lines whose kinematics are discrepant: They are incompatible with
the ionization structure derived from all other evidence and the kinematics
derived from all of these lines are unexpectedly very similar. We find direct
evidence for a recombination contribution to [N II] 5755. Once taken into
account, the electron temperatures from [N II], [O III], and [Ne III] agree at
a given position and velocity. The electron densities derived from [O II] and
[Ar IV] are consistent with direct imaging and the distribution of hydrogen
emission. The kinematics of the C II, N II, O II, and Ne II lines does not
coincide with the kinematics of the [O III] and [Ne III] forbidden emission,
indicating that there is an additional plasma component to the recombination
emission that arises from a different volume from that giving rise to the
forbidden emission from the parent ions within NGC 7009. Thus, the chemical
abundances derived from either type of line are correct only for the plasma
component from which they arise. Apart from [N II] 5755, we find no anomaly
with the forbidden lines usually used to determine chemical abundances in
ionized nebulae, so the abundances derived from them should be reliable for the
medium from which they arise.Comment: accepted for publication in The Astrophysical Journa
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