9,066 research outputs found
Knowledge Flows Through Social Networks in a Cluster Interfirm versus University-Industry Contacts
Knowledge spillovers from a university to the local industry play an important role in clusters, but we know little about these spillovers. This paper examines empirically the extent of university-industry informal contacts. Furthermore, it analyses the characteristics of an engineer that acquire knowledge from informal contacts with university researchers. The university-industry contacts are compared with results for interfirm contacts. The research shows that the interfirm informal contacts are more numerous than university informal contacts. Likewise, knowledge is more frequently acquired from other firms than through university-industry contacts. Engineers that have participated in formal projects with university researchers and engineers that are educated at the university have a higher likelihood of acquiring knowledge from informal contacts with university researchers.Knowledge flows; informal contacts
On the convergence of eigenfunctions to threshold energy states
We prove the convergence in certain weighted spaces in momentum space of
eigenfunctions of H = T-lambda*V as the energy goes to an energy threshold. We
do this for three choices of kinetic energy T, namely the non-relativistic
Schr"odinger operator, the pseudorelativistc operator sqrt{-\Delta+m^2}-m, and
the Dirac operator.Comment: 15 pages; references and comments added (e.g., Remark 3
Improved Upper Bounds to the Causal Quadratic Rate-Distortion Function for Gaussian Stationary Sources
We improve the existing achievable rate regions for causal and for zero-delay
source coding of stationary Gaussian sources under an average mean squared
error (MSE) distortion measure. To begin with, we find a closed-form expression
for the information-theoretic causal rate-distortion function (RDF) under such
distortion measure, denoted by , for first-order Gauss-Markov
processes. Rc^{it}(D) is a lower bound to the optimal performance theoretically
attainable (OPTA) by any causal source code, namely Rc^{op}(D). We show that,
for Gaussian sources, the latter can also be upper bounded as Rc^{op}(D)\leq
Rc^{it}(D) + 0.5 log_{2}(2\pi e) bits/sample. In order to analyze
for arbitrary zero-mean Gaussian stationary sources, we
introduce \bar{Rc^{it}}(D), the information-theoretic causal RDF when the
reconstruction error is jointly stationary with the source. Based upon
\bar{Rc^{it}}(D), we derive three closed-form upper bounds to the additive rate
loss defined as \bar{Rc^{it}}(D) - R(D), where R(D) denotes Shannon's RDF. Two
of these bounds are strictly smaller than 0.5 bits/sample at all rates. These
bounds differ from one another in their tightness and ease of evaluation; the
tighter the bound, the more involved its evaluation. We then show that, for any
source spectral density and any positive distortion D\leq \sigma_{x}^{2},
\bar{Rc^{it}}(D) can be realized by an AWGN channel surrounded by a unique set
of causal pre-, post-, and feedback filters. We show that finding such filters
constitutes a convex optimization problem. In order to solve the latter, we
propose an iterative optimization procedure that yields the optimal filters and
is guaranteed to converge to \bar{Rc^{it}}(D). Finally, by establishing a
connection to feedback quantization we design a causal and a zero-delay coding
scheme which, for Gaussian sources, achieves...Comment: 47 pages, revised version submitted to IEEE Trans. Information Theor
The electron densities of pseudorelativistic eigenfunctions are smooth away from the nuclei
We consider a pseudorelativistic model of atoms and molecules, where the
kinetic energy of the electrons is given by . In this model
the eigenfunctions are generally not even bounded, however, we prove that the
corresponding one-electron densities are smooth away from the nuclei.Comment: 16 page
Hartree-Fock theory for pseudorelativistic atoms
We study the Hartree-Fock model for pseudorelativistic atoms, that is, atoms
where the kinetic energy of the electrons is given by the pseudorelativistic
operator \sqrt{(pc)^2+(mc^2)^2}-mc^2. We prove the existence of a Hartree-Fock
minimizer, and prove regularity away from the nucleus and pointwise exponential
decay of the corresponding orbitals
Design and Analysis of LT Codes with Decreasing Ripple Size
In this paper we propose a new design of LT codes, which decreases the amount
of necessary overhead in comparison to existing designs. The design focuses on
a parameter of the LT decoding process called the ripple size. This parameter
was also a key element in the design proposed in the original work by Luby.
Specifically, Luby argued that an LT code should provide a constant ripple size
during decoding. In this work we show that the ripple size should decrease
during decoding, in order to reduce the necessary overhead. Initially we
motivate this claim by analytical results related to the redundancy within an
LT code. We then propose a new design procedure, which can provide any desired
achievable decreasing ripple size. The new design procedure is evaluated and
compared to the current state of the art through simulations. This reveals a
significant increase in performance with respect to both average overhead and
error probability at any fixed overhead
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