2,913 research outputs found
Towards the Standard Model spectrum from elliptic Calabi-Yau
We show that it is possible to construct supersymmetric three-generation
models of Standard Model gauge group in the framework of non-simply-connected
elliptically fibered Calabi-Yau, without section but with a bi-section. The
fibrations on a cover Calabi-Yau, where the model has 6 generations of SU(5)
and the bundle is given via the spectral cover description, use a different
description of the elliptic fibre which leads to more than one global section.
We present two examples of a possible cover Calabi-Yau with a free involution:
one is a fibre product of rational elliptic surfaces ; another example is
an elliptic fibration over a Hirzebruch surface. There we give the necessary
amount of chiral matter by turning on in the bundles a further parameter,
related to singularities of the fibration and the branching of the spectral
cover.Comment: 31 pages, 1 eps-figure, reference added, bundle parameters for dP9
model change
Anomalous interaction between vortices and nanomagnets
We study a thin film system consisting of a superconducting and a magnetic
film, where the superconductor contains a vortex and the magnetic film a
nanomagnet. We find that if the magnetic film has planar anisotropy, the vortex
induces a magnetization distribution, and its interaction with the nanomagnet
crosses over from attractive to repulsive at short distances.Comment: 5 page
Quantum geometry of elliptic Calabi-Yau manifolds
We study the quantum geometry of the class of Calabi-Yau threefolds, which
are elliptic fibrations over a two-dimensional toric base. A holomorphic
anomaly equation for the topological string free energy is proposed, which is
iterative in the genus expansion as well as in the curve classes in the base.
T-duality on the fibre implies that the topological string free energy also
captures the BPS-invariants of D4-branes wrapping the elliptic fibre and a
class in the base. We verify this proposal by explicit computation of the BPS
invariants of 3 D4-branes on the rational elliptic surface.Comment: 63 pages, 4 figure
Single-photon emission from Ni-related color centers in CVD diamond
Color centers in diamond are very promising candidates among the possible
realizations for practical single-photon sources because of their long-time
stable emission at room temperature. The popular nitrogen-vacancy center shows
single-photon emission, but within a large, phonon-broadened spectrum (~100nm),
which strongly limits its applicability for quantum communication. By contrast,
Ni-related centers exhibit narrow emission lines at room temperature. We
present investigations on single color centers consisting of Ni and Si created
by ion implantation into single crystalline IIa diamond. We use systematic
variations of ion doses between 10^8/cm^2 and 10^14/cm^2 and energies between
30keV and 1.8MeV. The Ni-related centers show emission in the near infrared
spectral range (~770nm to 787nm) with a small line-width (~3nm FWHM). A
measurement of the intensity correlation function proves single-photon
emission. Saturation measurements yield a rather high saturation count rate of
77.9 kcounts/s. Polarization dependent measurements indicate the presence of
two orthogonal dipoles.Comment: 8 pages, published in conference proceedings of SPIE Photonics Europe
201
A radio air shower surface detector as an extension for IceCube and IceTop
The IceCube neutrino detector is built into the Antarctic ice sheet at the
South Pole to measure high energy neutrinos. For this, 4800 photomultiplier
tubes (PMTs) are being deployed at depths between 1450 and 2450 meters into the
ice to measure neutrino induced charged particles like muons. IceTop is a
surface air shower detector consisting of 160 Cherenkov ice tanks located on
top of IceCube. To extend IceTop, a radio air shower detector could be built to
significantly increase the sensitivity at higher shower energies and for
inclined showers. As air showers induced by cosmic rays are a major part of the
muonic background in IceCube, IceTop is not only an air shower detector, but
also a veto to reduce the background in IceCube. Air showers are detectable by
radio signals with a radio surface detector. The major emission process is the
coherent synchrotron radiation emitted by e+ e- shower particles in the Earths
magnetic field (geosynchrotron effect). Simulations of the expected radio
signals of air showers are shown. The sensitivity and the energy threshold of
different antenna field configurations are estimated.Comment: 4 pages, 6 figures, to be published in Proceedings of the 30th
International Cosmic Ray Conferenc
High-speed Steam Turbine
Předkládaná diplomová práce je zaměřena na konstrukci rychloběžné parní turbíny pro parametry spalovny komunálního odpadu v Brně. V úvodní části diplomové práce je krátce shrnut historický vývoj, transformační proces a pracovní princip parní turbíny. V návaznosti na úvodní kapitoly je detailně rozebráno řešení akčního a reakčního lopatkování, včetně popisu průběhu expanze v i-s diagramu a vyjádření základních vzorců pro výpočet účinnosti. Ve stěžejní části diplomové práce jsou nejprve rozebrány možné koncepční varianty turbosoustrojí pro zadané parametry. Na základě zvolené koncepce je sestaven algoritmus termodynamického výpočtu pro jednotlivá tělesa turbíny. V závěru výpočetní části je uveden zjednodušený výpočet převodovky. Na základě výpočetní části jsou sestaveny konstrukční výkresy převodovek a podélných řezů všech částí turbosoustrojí.Main aim of presented master thesis is focused on construction of high speed steam turbine. Steam turbine is designed based on parameters of waste incineration plant in Brno. First chapters shortly summarized historical development, transformation process and work principal of steam turbine. Consequently on first captures is in depth described impulse and reaction blading including expansion in i-s diagram and basic equations for efficiency calculations. In major part of master thesis is firstly discussed conceptual possibilities of turbine application for given parameters. Based on chosen concept is compiled algorithm for thermodynamic calculation for each turbine module. Simplify calculation of gearbox is included as well. Based on calculations are compiled construction drawings of all parts of steam turbine.
Understanding the Uncertainty Loop of Human-Robot Interaction
Recently the field of Human-Robot Interaction gained popularity, due to the
wide range of possibilities of how robots can support humans during daily
tasks. One form of supportive robots are socially assistive robots which are
specifically built for communicating with humans, e.g., as service robots or
personal companions. As they understand humans through artificial intelligence,
these robots will at some point make wrong assumptions about the humans'
current state and give an unexpected response. In human-human conversations,
unexpected responses happen frequently. However, it is currently unclear how
such robots should act if they understand that the human did not expect their
response, or even showing the uncertainty of their response in the first place.
For this, we explore the different forms of potential uncertainties during
human-robot conversations and how humanoids can, through verbal and non-verbal
cues, communicate these uncertainties
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