109 research outputs found
Heterotic String Corrections from the Dual Type II String
We introduce a method of using the a dual type IIA string to compute
alpha'-corrections to the moduli space of heterotic string compactifications.
In particular we study the hypermultiplet moduli space of a heterotic string on
a K3 surface. One application of this machinery shows that type IIB strings
compactified on a Calabi-Yau space suffer from worldsheet instantons, spacetime
instantons and, in addition, "mixed" instantons which in a sense are both
worldsheet and spacetime. As another application we look at the hyperkaehler
limit of the moduli space in which the K3 surface becomes an ALE space. This is
a variant of the "geometric engineering" method used for vector multiplet
moduli space and should be applicable to a wide range of examples. In
particular we reproduce Sen and Witten's result for the heterotic string on an
A1 singularity and a trivial bundle and generalize this to a collection of E8
point-like instantons on an ALE space.Comment: 21 pages, 5 figures, refs adde
D-branes, Discrete Torsion and the McKay Correspondence
We analyze the D-branes of a type IIB string theory on an orbifold
singularity including the possibility of discrete torsion following the work of
Douglas et al. First we prove some general results about the moduli space of a
point associated to the "regular representation" of the orbifold group. This
includes some analysis of the "wrapped branes" which necessarily appear when
the orbifold singularity is not isolated. Next we analyze the stringy homology
of the orbifold using the McKay correspondence and the relationship between
K-theory and homology. We find that discrete torsion and torsion in this
stringy homology are closely-related concepts but that they differ in general.
Lastly we question to what extent the D-1 brane may be thought of as being dual
to a string.Comment: 27 pages, 5 figures, LaTeX2e, minor change
The New House of the Region of Hannover - Building Energy Efficient in a Public Private Partnership
Public Private Partnerships are an increasingly popular approach to carry out public infra-structure projects. PPPs aim at reducing costs and risk and improving service and quality by using private expertise and management potential
Doppler Effect of Nonlinear Waves and Superspirals in Oscillatory Media
Nonlinear waves emitted from a moving source are studied. A meandering spiral
in a reaction-diffusion medium provides an example, where waves originate from
a source exhibiting a back-and-forth movement in radial direction. The periodic
motion of the source induces a Doppler effect that causes a modulation in
wavelength and amplitude of the waves (``superspiral''). Using the complex
Ginzburg-Landau equation, we show that waves subject to a convective Eckhaus
instability can exhibit monotonous growth or decay as well as saturation of
these modulations away from the source depending on the perturbation frequency.
Our findings allow a consistent interpretation of recent experimental
observations concerning superspirals and their decay to spatio-temporal chaos.Comment: 4 pages, 4 figure
Evaluation and Optimization of Underground Thermal Energy Storage Systems of Energy Efficient Buildings (WKSP)- A Project within the new German R&D- Framework EnBop
Until 2003 the research on buildings in operation in Germany focused mainly on demonstration buildings. Starting with the EVA project managed by IGS the attention is shifting towards performance in operation. The paper gives a general review of these research projects and presents detailed results of project WKSP. The performance of buildings with systems for underground thermal energy storage is analysed in this project. As the analyses show several systems work worse than expected. Within the project most of the systems could be significantly improved in operation. The scientific work on building performance in operation will be broadened within the new R&D framework EnBop. IGS will coordinate the framework funded by the German Ministry of Economics and Technology
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