3,357 research outputs found
Entropy of unimodular Lattice Triangulations
Triangulations are important objects of study in combinatorics, finite
element simulations and quantum gravity, where its entropy is crucial for many
physical properties. Due to their inherent complex topological structure even
the number of possible triangulations is unknown for large systems. We present
a novel algorithm for an approximate enumeration which is based on calculations
of the density of states using the Wang-Landau flat histogram sampling. For
triangulations on two-dimensional integer lattices we achive excellent
agreement with known exact numbers of small triangulations as well as an
improvement of analytical calculated asymptotics. The entropy density is
consistent with rigorous upper and lower bounds. The presented
numerical scheme can easily be applied to other counting and optimization
problems.Comment: 6 pages, 7 figure
Human Capital Externalities and the Urban Wage Premium: Two Literatures and their Interrelations
In this paper we survey the recent developments in two empirical literatures at the crossroads of labor and urban economics: Studies about localized human capital externalities (HCE) and about the urban wage premium (UWP). After surveying the methods and main results of each of these two literatures separately, we highlight several interrelations between them. In particular we ask if HCE can be interpreted as one fundamental cause of the UWP, and we discuss if one literature can conceptually learn from the methods that are used by the other one.local labor markets, agglomeration, human capital externalities, urban wage premium
How motifs condition critical thresholds for tipping cascades in complex networks: Linking Micro- to Macro-scales
In this study, we investigate how specific micro interaction structures
(motifs) affect the occurrence of tipping cascades on networks of stylized
tipping elements. We compare the properties of cascades in Erd\"os-R\'enyi
networks and an exemplary moisture recycling network of the Amazon rainforest.
Within these networks, decisive small-scale motifs are the feed forward loop,
the secondary feed forward loop, the zero loop and the neighboring loop.
Of all motifs, the feed forward loop motif stands out in tipping cascades
since it decreases the critical coupling strength necessary to initiate a
cascade more than the other motifs. We find that for this motif, the reduction
of critical coupling strength is 11% less than the critical coupling of a pair
of tipping elements. For highly connected networks, our analysis reveals that
coupled feed forward loops coincide with a strong 90% decrease of the critical
coupling strength.
For the highly clustered moisture recycling network in the Amazon, we observe
regions of very high motif occurrence for each of the four investigated motifs
suggesting that these regions are more vulnerable. The occurrence of motifs is
found to be one order of magnitude higher than in a random Erd\"os-R\'enyi
network.
This emphasizes the importance of local interaction structures for the
emergence of global cascades and the stability of the network as a whole
Optimierung des Anbaus von Sojabohnen: Bestimmung des Vorfruchtwertes und der N2-Fixierleistung sowie Reduzierung der Bodenbearbeitung
Bisher sind die N2-Fixierung aus der Luft, die N-Salden (N2-Fixierung minus N-Abfuhr) und die Vorfruchtwirkung von Soja für Deutschland nicht beschrieben. Diese wurde in Feldversuchen auf einem konventionell und zwei ökologisch bewirtschafteten Standorten im Vergleich zu Körnererbsen untersucht. Die N2-Fixierung von Soja fiel um knapp 100 (ökologisch) und 40 (konventionell) kg ha-1 höher aus als die der Erbsen. Die N-Bilanz war zwischen Soja und Erbsen vergleichbar. Die Vorfruchtwirkung von Erbsen ist aufgrund eines höheren Ertrages in der Nachfrucht Weizen im ökologischen Landbau höher als die von Soja einzuschätzen. Im konventionellen Anbau unterschied sich dagegen die Leistung des nachfolgenden Weizens nicht. Soja passt auch aufgrund einer hohen Wirtschaftlichkeit sehr gut in die Fruchtfolgen. Im ökologischen Anbau erwirtschaftet sie im Fruchtfolgeausschnitt Körnerleguminose – Weizen einen um etwa ein Drittel höheren Deckungsbeitrag als Erbsen, im konventionellen konnte sie mit der Leistung von Körnermais mithalten.
In einem dreijährigen Exaktversuch und in On-Farmversuchen wurde die Eignung von reduzierter Bodenbearbeitung im konventionellen Sojaanbau geprüft. Mit Mulchsaat und Strip-Till konnte Soja agronomisch und ökonomisch erfolgreich angebaut werden. Hingegen war die Direktsaat in gewalzten bzw. abgefahren Grünroggen mit 14,4 dt ha-1 im Ertrag niedriger und hatte einen erheblichen wirtschaftlichen Nachteil. Ferner konnte in Mulchsaat und Strip-Till auf die Applikation von Glyphosat vor der Saat ohne Ertragseinbußen oder einen höheren Unkrautbesatz verzichtet werden
Satisfiability of constraint specifications on XML documents
Jose Meseguer is one of the earliest contributors in the area of Algebraic Specification. In this paper, which we are happy to dedicate to him on the occasion of his 65th birthday, we use ideas and methods coming from that area with the aim of presenting an approach for the specification of the structure of classes of XML documents and for reasoning about them. More precisely, we specify the structure of documents using sets of constraints that are based on XPath and we present inference rules that are shown to define a sound and complete refutation procedure for checking satisfiability of a given specification using tableaux.Peer ReviewedPostprint (author's final draft
The FCC-ee Interaction Region Magnet Design
The design of the region close to the interaction point of the FCC-ee
experiments is especially challenging. The beams collide at an angle (+-15
mrad) in the high-field region of the detector solenoid. Moreover, the very low
vertical beta_y* of the machine necessitates that the final focusing
quadrupoles have a distance from the IP (L*) of around 2 m and therefore are
inside the main detector solenoid. The beams should be screened from the effect
of the detector magnetic field, and the emittance blow-up due to vertical
dispersion in the interaction region should be minimized, while leaving enough
space for detector components. Crosstalk between the two final focus
quadrupoles, only about 6 cm apart at the tip, should also be minimized.Comment: Poster presented at IPAC16, May 8-13, Busan, Kore
Comparison of Options for the Injector of PS2
In its report, the SPC Review Panel has highlighted that the construction of a 4 MW SPL has to be motivated by the needs of a well-defined and approved physics programme, and that it should be compared with a Rapid Cycling Synchrotron (RCS) when considering only the needs of LHC. This report is meant to answer these remarks by describing the version of the SPL that would be built for the needs of LHC alone (the Low Power SPL or LP-SPL) and by making a preliminary comparison with an RCS
Dynamics of Tipping Cascades on Complex Networks
Tipping points occur in diverse systems in various disciplines such as
ecology, climate science, economy or engineering. Tipping points are critical
thresholds in system parameters or state variables at which a tiny perturbation
can lead to a qualitative change of the system. Many systems with tipping
points can be modeled as networks of coupled multistable subsystems, e.g.
coupled patches of vegetation, connected lakes, interacting climate tipping
elements or multiscale infrastructure systems. In such networks, tipping events
in one subsystem are able to induce tipping cascades via domino effects. Here,
we investigate the effects of network topology on the occurrence of such
cascades. Numerical cascade simulations with a conceptual dynamical model for
tipping points are conducted on Erd\H{o}s-R\'enyi, Watts-Strogatz and
Barab\'asi-Albert networks. Additionally, we generate more realistic networks
using data from moisture-recycling simulations of the Amazon rainforest and
compare the results to those obtained for the model networks. We furthermore
use a directed configuration model and a stochastic block model which preserve
certain topological properties of the Amazon network to understand which of
these properties are responsible for its increased vulnerability. We find that
clustering and spatial organization increase the vulnerability of networks and
can lead to tipping of the whole network. These results could be useful to
evaluate which systems are vulnerable or robust due to their network topology
and might help to design or manage systems accordingly.Comment: 22 pages, 12 figure
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