2,124 research outputs found
Global Aspects of Electric-Magnetic Duality
We show that the partition function of free Maxwell theory on a generic
Euclidean four-manifold transforms in a non-trivial way under electric-magnetic
duality. The classical part of the partition sum can be mapped onto the
genus-one partition function of a 2d toroidal model, without the oscillator
contributions. This map relates electric-magnetic duality to modular invariance
of the toroidal model and, conversely, the duality to the
invariance of Maxwell theory under the 4d mapping class group. These dualities
and the relation between toroidal models and Maxwell theory can be understood
by regarding both theories as dimensional reductions of a self-dual 2-form
theory in six dimensions. Generalizations to more -gauge fields and
reductions from higher dimensions are also discussed. We find indications that
the Abelian gauge theories related to 4d string theories with space-time
supersymmetry are exactly duality invariant.Comment: Latex-file, 16 page
The Influence of the Time Equation on Remote Sensing Data Interpretation
The interpretation of optical Earth observation data (remote sensing data from satellites) requires knowledge of the exact geographic position of each pixel as well as the exact local acquisition time. But these parameters are not available in each case. If a satellite has a sun-synchronous orbit, equator crossing time (ECT) can be used to determine the local crossing time (LCT) and its corresponding solar zenith distance. Relation between local equator crossing time (LECT) and LCT is given by orbit geometry. The calculation is based on ECT of satellite. The method of actual ECT determination for different satellites on basis of the two-line-elements (TLE), available for their full lifetime period and with help of orbit prediction package is well known. For land surface temperature (LST) studies mean solar conditions are commonly used in the relation between ECT given in Coordinated Universal Time (UTC) and LECT given in hours, thus neglecting the difference between mean and real Sun time (MST, RST). Its difference is described by the equation of time (ET). Of particular importance is the variation of LECT during the year within about ±15 minutes. This is in each case the variation of LECT of a satellite, including satellites with stable orbit as LANDSAT (L8 around 10:05 a.m.) or ENVISAT (around 10:00 a.m.). In case of NOAA satellites the variation of LECT is overlaid by a long-term orbital drift. Ignatov et al. (2004) developed a method to describe the drift-based variation of LECT that can be viewed as a formal mathematical approximation of a periodic function with one or two Fourier terms. But, nevertheless, ET is not included in actual studies of LST.
Our paper aims to demonstrate the possible influence of equation of time on simple examples of data interpretation, e.g. NDVI
Context-Aware Technology Mapping in Genetic Design Automation
Genetic design automation (GDA) tools hold promise to
speed-up
circuit design in synthetic biology. Their widespread adoption is
hampered by their limited predictive power, resulting in frequent
deviations between the in silico and in vivo performance of a genetic
circuit. Context effects, i.e., the change in overall circuit functioning,
due to the intracellular environment of the host and due to cross-talk
among circuits components are believed to be a major source for the
aforementioned deviations. Incorporating these effects in computational
models of GDA tools is challenging but is expected to boost their
predictive power and hence their deployment. Using fine-grained thermodynamic
models of promoter activity, we show in this work how to account for
two major components of cellular context effects: (i) crosstalk due
to limited specificity of used regulators and (ii) titration of circuit
regulators to off-target binding sites on the host genome. We show
how we can compensate the incurred increase in computational complexity
through dedicated branch-and-bound techniques during the technology
mapping process. Using the synthesis of several combinational logic
circuits based on Cello’s device library as a case study, we
analyze the effect of different intensities and distributions of crosstalk
on circuit performance and on the usability of a given device library
Learning from Other Community Renewable Energy Projects: Transnational Transfer of Multi-Functional Energy Gardens from the Netherlands to Germany
Citizen energy in general and renewable energy communities (RECs) in particular are becoming key vehicles for decentralisation, but also for the democratisation of the energy system. These initiatives are now more diverse than ever and are likely to continue to act as incubators for significant projects in the transition to a renewable energy system. Beside the legal, regulatory, and financial challenges, there are several socio-economic and regulatory barriers that hinder the implementation of community energy projects. For this reason, policy learning and the dissemination of good/best practices that are transferable also to other contexts are important. This is an aspect that has not yet attracted much investigation, and only a few studies have explored the importance of transfer activities for the implementation of REC initiatives and their motives. This article aimed to address this knowledge gap by focussing on the transfer processes of best practices initiated in a particular region and discusses how these can be adapted and transferred to other contexts. We analysed the transfer case of a community renewable energy initiative, the multifunctional energy gardens, from the Netherlands to the German federal State of Thuringia, and extracted lessons with an overall validity for the transferability of drivers and success factors. We show how examples from other contexts with similar enabling conditions can represent significant foundations on which to build an effective strategy and what framework conditions are necessary to enhance the uptake of pervasive community energy initiatives in regions with low community energy development
Gauge Bundles and Born-Infeld on the Noncommutative Torus
In this paper, we describe non-abelian gauge bundles with magnetic and
electric fluxes on higher dimensional noncommutative tori. We give an explicit
construction of a large class of bundles with nonzero magnetic 't Hooft fluxes.
We discuss Morita equivalence between these bundles. The action of the duality
is worked out in detail for the four-torus. As an application, we discuss
Born-Infeld on this torus, as a description of compactified string theory. We
show that the resulting theory, including the fluctuations, is manifestly
invariant under the T-duality group SO(4,4;Z). The U-duality invariant BPS
mass-formula is discussed shortly. We comment on a discrepancy of this result
with that of a recent calculation.Comment: 22 pages, LaTeX2e. Small errors correcte
Does polycentrism deliver? A case study of energy community governance in Europe
The European Union's Clean Energy Package (CEP) plans to transform ‘passive consumers’ into ‘active citizens’ to support the transition to a carbon-neutral energy system by 2050. By stimulating the growth of renewable energy communities, the CEP works towards the redefinition of renewable energy as an economic commodity to a common good. In this paper, we approach the implementation of the CEP through the notion of polycentricity. Building on previous literature, we identified seven variables for effective polycentric energy governance: equity and co-benefits; inclusivity and local involvement; information, demonstration and innovation; ownership and accountability; organizational multiplicity; experimentation and flexibility; and clear goals set and enforced by a higher-level authority. To compare a variety of polycentric institutional configurations, we analyze Norway, the Netherlands, and Germany. Our findings indicate that, in general, some degree of polycentricity appears to be beneficial for the energy transition. This is the foundation for building local ownership and inclusivity and thus the emphasis is rightly placed there and could be expanded. Secondly, issues of ownership and accountability stand out as key enablers of renewable energy communities and the additional common goods that they bring to the energy system. These communities need to be enabled in financial terms to deploy a sufficient amount of projects, e.g., by giving them access to risk capital in the early development stages. In turn, this requires clear regulations and accountability mechanisms being installed on what precisely falls under the definition of a renewable energy community. Finally, we found that even as polycentricity is a promising approach, it does need to be anchored with a significant role for higher level government in order to function effectively
Fast Mapping of Terahertz Bursting Thresholds and Characteristics at Synchrotron Light Sources
Dedicated optics with extremely short electron bunches enable synchrotron
light sources to generate intense coherent THz radiation. The high degree of
spatial compression in this so-called low-alpha optics entails a complex
longitudinal dynamics of the electron bunches, which can be probed studying the
fluctuations in the emitted terahertz radiation caused by the micro-bunching
instability ("bursting"). This article presents a "quasi-instantaneous" method
for measuring the bursting characteristics by simultaneously collecting and
evaluating the information from all bunches in a multi-bunch fill, reducing the
measurement time from hours to seconds. This speed-up allows systematic studies
of the bursting characteristics for various accelerator settings within a
single fill of the machine, enabling a comprehensive comparison of the measured
bursting thresholds with theoretical predictions by the bunched-beam theory.
This paper introduces the method and presents first results obtained at the
ANKA synchrotron radiation facility.Comment: 7 pages, 7 figures, to be published in Physical Review Accelerators
and Beam
Computational modeling identifies key gene regulatory interactions underlying phenobarbital-mediated tumor promotion
Gene regulatory interactions underlying the early stages of non-genotoxic carcinogenesis are poorly understood. Here, we have identified key candidate regulators of phenobarbital (PB)-mediated mouse liver tumorigenesis, a well-characterized model of non-genotoxic carcinogenesis, by applying a new computational modeling approach to a comprehensive collection of in vivo gene expression studies. We have combined our previously developed motif activity response analysis (MARA), which models gene expression patterns in terms of computationally predicted transcription factor binding sites with singular value decomposition (SVD) of the inferred motif activities, to disentangle the roles that different transcriptional regulators play in specific biological pathways of tumor promotion. Furthermore, transgenic mouse models enabled us to identify which of these regulatory activities was downstream of constitutive androstane receptor and β-catenin signaling, both crucial components of PB-mediated liver tumorigenesis. We propose novel roles for E2F and ZFP161 in PB-mediated hepatocyte proliferation and suggest that PB-mediated suppression of ESR1 activity contributes to the development of a tumor-prone environment. Our study shows that combining MARA with SVD allows for automated identification of independent transcription regulatory programs within a complex in vivo tissue environment and provides novel mechanistic insights into PB-mediated hepatocarcinogenesi
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