128 research outputs found
The origin of high-resolution IETS-STM images of organic molecules with functionalized tips
Recently, the family of high-resolution scanning probe imaging techniques
using decorated tips has been complimented by a method based on inelastic
electron tunneling spectroscopy (IETS). The new technique resolves the inner
structure of organic molecules by mapping the vibrational energy of a single
carbonmonoxide (CO) molecule positioned at the apex of a scanning tunnelling
microscope (STM) tip. Here, we explain high-resolution IETS imaging by
extending the model developed earlier for STM and atomic force microscopy (AFM)
imaging with decorated tips. In particular, we show that the tip decorated with
CO acts as a nanoscale sensor that changes the energy of the CO frustrated
translation in response to the change of the local curvature of the surface
potential. In addition, we show that high resolution AFM, STM and IETS-STM
images can deliver information about intramolecular charge transfer for
molecules deposited on a~surface. To demonstrate this, we extended our
numerical model by taking into the account the electrostatic force acting
between the decorated tip and surface Hartree potential.Comment: 5 pages, 4 figure
H dissociation over Au-nanowires and the fractional conductance quantum
The dissociation of H molecules on stretched Au nanowires and its effect
on the nanowire conductance are analyzed using a combination of Density
Functional (DFT) total energy calculations and non-equilibrium Keldish-Green
function methods. Our DFT simulations reproduce the characteristic formation of
Au monoatomic chains with a conductance close to % the conductance quantum . These stretched Au nanowires are shown to be better catalysts for
H dissociation than Au surfaces. This is confirmed by the nanowire
conductance evidence: while not affected practically by molecular hydrogen,
atomic hydrogen induces the appearance of fractional conductances () as observed experimentally.Comment: 4 pages, 3 figure
Theoretical analysis of electronic band structure of 2-to-3-nm Si nanocrystals
We introduce a general method which allows reconstruction of electronic band
structure of nanocrystals from ordinary real-space electronic structure
calculations. A comprehensive study of band structure of a realistic
nanocrystal is given including full geometric and electronic relaxation with
the surface passivating groups. In particular, we combine this method with
large scale density functional theory calculations to obtain insight into the
luminescence properties of silicon nanocrystals of up to 3 nm in size depending
on the surface passivation and geometric distortion. We conclude that the band
structure concept is applicable to silicon nanocrystals with diameter larger
than 2 nm with certain limitations. We also show how perturbations
due to polarized surface groups or geometric distortion can lead to
considerable moderation of momentum space selection rules
Design of cutting unit
Tato práce pojednává o konstrukčním řešení řezacího válce, včetně návrhu jeho pohonu a odsávacího systému pro flexotiskový stroj Premia společnosti Soma spol. s r.o.. První část pojednává o technologii flexotisku a obecně o dané problematice ořezu a odsávání materiálu. Další část se zabývá optimalizací těchto systémů, včetně výsledného konstrukčního návrhu. Hlavním výstupem práce jsou výkresy sestavení uvedené v přílohách.This thesis deals with a structural design of a cutting roller including a proposal for its drive and exhaust system of the flexography machine Premia produced by Soma spol. s r.o. company. The first part discusses the technology of flexography and about the issue of cropping and extraction of material in general. Another part discusses the optimization of these systems, including the final engineering design. The main outcome of this thesis are drawings of assemblies listed in the annexes.
On the Beer index of convexity and its variants
Let be a subset of with finite positive Lebesgue measure.
The Beer index of convexity of is the probability
that two points of chosen uniformly independently at random see each other
in . The convexity ratio of is the Lebesgue
measure of the largest convex subset of divided by the Lebesgue measure of
. We investigate the relationship between these two natural measures of
convexity.
We show that every set with simply connected
components satisfies for an
absolute constant , provided is defined. This
implies an affirmative answer to the conjecture of Cabello et al. that this
estimate holds for simple polygons.
We also consider higher-order generalizations of . For
, the -index of convexity of a set
is the probability that the convex hull of a
-tuple of points chosen uniformly independently at random from is
contained in . We show that for every there is a constant
such that every set satisfies
, provided
exists. We provide an almost matching lower bound by
showing that there is a constant such that for every
there is a set of Lebesgue
measure satisfying and
.Comment: Final version, minor revisio
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