20,762 research outputs found
Exceptional Field Theory: An Action for F-Theory
Exceptional Field Theory employs an extended spacetime to make supergravity
fully covariant under the U-duality groups of M-theory. The 12-dimensional EFT
associated to the group together with its action is
presented. Demanding the closure of the algebra of local symmetries leads to a
constraint, known as the section condition, that must be imposed on all fields.
This constraint has two inequivalent solutions, one giving rise to
11-dimensional supergravity and the other leading to Type IIB supergravity and
F-theory. Thus Exceptional Field Theory contains both
F-theory and M-theory in a single 12-dimensional formalism.Comment: Proceedings prepared for the "Workshop on Geometry and Physics",
November 2016, Ringberg Castle, Germany, v.2: references added, published in
PoS CORFU2016 (2017
Exoplanet Predictions Based on Harmonic Orbit Resonances
The current exoplanet database includes 5454 confirmed planets and candidate
planets observed with the KEPLER mission. We find 932 planet pairs from which
we extract distance and orbital period ratios. While earlier studies used the
Titius-Bode law or a generalized version with logarithmic spacing, which both
lack a physical model, we employ here the theory of harmonic orbit resonances,
which contains quantized ratios instead, to explain the observed planet
distance ratios and to predict undetected exoplanets. We find that the most
prevailing harmonic ratios are (2:1), (3:2), and (5:3), in 73\% of the cases,
while alternative harmonic ratios of (5:4), (4:3), (5:2), (3:1) occur in 27\%
of the other cases. Our orbital predictions includes 171 exoplanets, 2 Jupiter
moons, one Saturn moon, 3 Uranus moons, and 4 Neptune moons. The accuracy of
the predicted planet distances amounts to a few percent, which fits the data
significantly better than the Titius-Bode law or a logarithmic spacing. This
information may be useful for targeted exoplanet searches with Kepler data and
to estimate the number of live-carrying planets in habitable zones.Comment: 9 pages, 7 Figure
Flow rate of transport network controls uniform metabolite supply to tissue
Life and functioning of higher organisms depends on the continuous supply of
metabolites to tissues and organs. What are the requirements on the transport
network pervading a tissue to provide a uniform supply of nutrients, minerals,
or hormones? To theoretically answer this question, we present an analytical
scaling argument and numerical simulations on how flow dynamics and network
architecture control active spread and uniform supply of metabolites by
studying the example of xylem vessels in plants. We identify the fluid inflow
rate as the key factor for uniform supply. While at low inflow rates
metabolites are already exhausted close to flow inlets, too high inflow flushes
metabolites through the network and deprives tissue close to inlets of supply.
In between these two regimes, there exists an optimal inflow rate that yields a
uniform supply of metabolites. We determine this optimal inflow analytically in
quantitative agreement with numerical results. Optimizing network architecture
by reducing the supply variance over all network tubes, we identify patterns of
tube dilation or contraction that compensate sub-optimal supply for the case of
too low or too high inflow rate.Comment: 11 pages, 4 figures, 8 pages supplemen
HI Observations Towards the Sagittarius Dwarf Spheroidal Galaxy
We have measured the 21-cm line of Galactic HI over more than 50 square
degrees in the direction of the Sagittarius dwarf spheroidal galaxy. The data
show no evidence of HI associated with the dwarf spheroidal which might be
consider analogous to the Magellanic Stream as it is associated in both
position and velocity with the Large Magellanic Cloud. Nor do the HI data show
evidence for any disturbance in the Milky Way disk gas that can be
unambiguously assigned to interaction with the dwarf galaxy. The data shown
here limit the HI mass at the velocity of the Sagittarius dwarf to <7000 solar
masses over some 18 square degrees between Galactic latitudes -13 degrees and
-18 degrees.Comment: 5 pages, 4 figures; accepted for publication in Astronomy &
Astrophysic
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