8,830 research outputs found
The partition function of an interacting many body system: beyond the perturbed static path approximation
Based on the path integral representation of the partition function of a many
body system with separable two body interaction we propose a systematic
extension of the perturbed static path approximation (PSPA) to lower
temperatures. Thereby, special attention must be paid to instabilities of the
classical mean field solution in functional space that cause divergencies
within the conventional PSPA. As a result we develop an approximation
applicable from high to very low temperatures. These findings are tested
against exact results for the archetypical cases of a particle moving in a one
dimensional double well and the exactly solvable Lipkin model. In particular,
we obtain a very good approximation to the level density of the Lipkin model
even at low thermal excitations. Our results may have potential applications in
low temperature nuclear physics and mesoscopic systems, e.g. for gap
fluctuations in nanoscale superconducting devices previously studied within a
PSPA type of approximation.
PACS: 5.30.-d, 24.60.-k, 21.10.Ma, 74.25.BtComment: 11 pages, 7 figures, replaced with shortened version accepted for
publication in EPJB, minor changes not affecting any result
Age and gender composition of the workforce, productivity and profits: Evidence from a new type of data for German enterprises
This empirical paper documents the relationship between composition of a firm's workforce (with a special focus on age and gender) and its performance (productivity and profitability) for a large representative sample of enterprises from manufacturing industries in Germany. We use unique newly available data that for the first time combine information from the statistics of employees covered by social security that is aggregated at the enterprise level and information from enterprise level surveys performed by the Statistical Offices. Our microeconometric analysis confirms previous findings of concave age-productivity profiles, which are consistent with human capital theory, and adds a new finding of a rather negative effect of age on firms' profitability, which is consistent with deferred compensation considerations. Moreover, our analysis reveals for the first time that the ceteris paribus lower level of productivity in firms with a higher share of female employees does not go hand in hand with a lower level of profitability in these firms. If anything, profitability is (slightly) higher in firms with a larger share of female employees. This finding might indicate that lower productivity of women is (over)compensated by lower wage costs for women, which might be driven by general labor market discrimination against women.Ageing, firm performance, gender, productivity, profitability, Germany
Survey Evidence on Conditional Norm Enforcement
We discuss survey evidence on individuals' willingness to sanction norm violations – such as evading taxes, drunk driving, fare dodging, or skiving off work – by expressing disapproval or social exclusion. Our data suggest that people condition their sanctioning behavior on their belief about the frequency of norm violations. The more commonly a norm violation is believed to occur, the lower the individuals' inclination to punish it. Based on an instrumental variable approach, we demonstrate that this pattern reflects a causal relationship.Norm Enforcement, Sanctioning, Social Norms, Survey Evidence
Survey Evidence on Conditional Norm Enforcement
We discuss survey evidence on individuals' willingness to sanction norm violations - such as evading taxes, drunk driving, fare dodging, or skiving o work - by expressing disapproval or social exclusion. Our data suggest that people condition their sanctioning behavior on their belief about the frequency of norm violations. The more commonly a norm violation is believed to occur, the lower the individuals' inclination to punish it. Based on an instrumental variable approach, we demonstrate that this pattern reflects a causal relationship.Norm Enforcement; Sanctioning; Social Norms; Survey Evidence
Differential K-theory. A survey
Generalized differential cohomology theories, in particular differential
K-theory (often called "smooth K-theory"), are becoming an important tool in
differential geometry and in mathematical physics. In this survey, we describe
the developments of the recent decades in this area. In particular, we discuss
axiomatic characterizations of differential K-theory (and that these uniquely
characterize differential K-theory). We describe several explicit
constructions, based on vector bundles, on families of differential operators,
or using homotopy theory and classifying spaces. We explain the most important
properties, in particular about the multiplicative structure and push-forward
maps and will state versions of the Riemann-Roch theorem and of Atiyah-Singer
family index theorem for differential K-theory.Comment: 50 pages, report based in particular on work done sponsored the DFG
SSP "Globale Differentialgeometrie". v2: final version (only typos
corrected), to appear in C. B\"ar et al. (eds.), Global Differential
Geometry, Springer Proceedings in Mathematics 17, Springer-Verlag Berlin
Heidelberg 201
Brain rhythms of pain
Pain is an integrative phenomenon that results from dynamic interactions between sensory and contextual (i.e., cognitive, emotional, and motivational) processes. In the brain the experience of pain is associated with neuronal oscillations and synchrony at different frequencies. However, an overarching framework for the significance of oscillations for pain remains lacking. Recent concepts relate oscillations at different frequencies to the routing of information flow in the brain and the signaling of predictions and prediction errors. The application of these concepts to pain promises insights into how flexible routing of information flow coordinates diverse processes that merge into the experience of pain. Such insights might have implications for the understanding and treatment of chronic pain
Compact quantum metric spaces from quantum groups of rapid decay
We present a modified version of the definition of property RD for discrete
quantum groups given by Vergnioux in order to accommodate examples of
non-unimodular quantum groups. Moreover we extend the construction of spectral
triples associated to discrete groups with length functions, originally due to
Connes, to the setting of quantum groups. For quantum groups of rapid decay we
study the resulting spectral triples from the point of view of compact quantum
metric spaces in the sense of Rieffel.Comment: 19 page
Parallel Quantum Circuit in a Tunnel Junction
The spectrum of 1-state and 2-states per line quantum buses is used to
determine the effective electronic coupling between emitter and
receiver states through the bus as a function of the number of parallel
lines in the bus. When the calculation of is spectrally difficult,
an Heisenberg-Rabi time dependent quantum exchange process can be triggered
through the bus by preparing a specific initial non-stationanry state and
identifying a target state to capture the effective oscillation frequency
between those. For (for ), two
different regimes are observed as a function of : linear and more
moderate increases. This state preparation was remplaced by electronically
coupling the quantum bus to two semi-infinite electrodes. The native quantum
transduction process at work in this tunnel junction is not faithfully
following the variations with . Due to normalisation to
unity of the electronic transparency of the quantum bus and to the low pass
filter character of the transduction, large cannot be followed
by the tunnel junction. At low coupling and when is small enough not to
compensate the small through line coupling, an power law is preserved for
. The limitations of the quantum transduction in a tunnel
junction is pointing how the broadly used concept of electrical contact between
a metallic nanopad and a molecular wire can be better described as a quantum
transduction process
Learning Dictionaries with Bounded Self-Coherence
Sparse coding in learned dictionaries has been established as a successful
approach for signal denoising, source separation and solving inverse problems
in general. A dictionary learning method adapts an initial dictionary to a
particular signal class by iteratively computing an approximate factorization
of a training data matrix into a dictionary and a sparse coding matrix. The
learned dictionary is characterized by two properties: the coherence of the
dictionary to observations of the signal class, and the self-coherence of the
dictionary atoms. A high coherence to the signal class enables the sparse
coding of signal observations with a small approximation error, while a low
self-coherence of the atoms guarantees atom recovery and a more rapid residual
error decay rate for the sparse coding algorithm. The two goals of high signal
coherence and low self-coherence are typically in conflict, therefore one seeks
a trade-off between them, depending on the application. We present a dictionary
learning method with an effective control over the self-coherence of the
trained dictionary, enabling a trade-off between maximizing the sparsity of
codings and approximating an equiangular tight frame.Comment: 4 pages, 2 figures; IEEE Signal Processing Letters, vol. 19, no. 12,
201
- …