Discrete Multitone Modulation for Maximizing Transmission Rate in Step-Index Plastic Optical Fibres

The use of standard 1-mm core-diameter step-index plastic optical fiber (SI-POF) has so far been mainly limited to distances of up to 100 m and bit-rates in the order of 100 Mbit/s. By use of digital signal processing, transmission performance of such optical links can be improved. Among the different technical solutions proposed, a promising one is based on the use of discrete multitone (DMT) modulation, directly applied to intensity-modulated, direct detection (IM/DD) SI-POF links. This paper presents an overview of DMT over SI-POF and demonstrates how DMT can be used to improve transmission rate in such IM/DD systems. The achievable capacity of an SI-POF channel is first analyzed theoretically and then validated by experimental results. Additionally, first experimental demonstrations of a real-time DMT over SI-POF system are presented and discusse

A Superconducting Instability in the Infinite-U Anderson Lattice in the Presence of Crystal Electric Fields

We report evidence of a superconducting instability (of $T_{1g}$ symmetry) in the infinite-U Anderson lattice in the presence of crystal fields of cubic symmetry. We assume a lattice of $4f$ sites, each with a total angular momentum of $J=5/2$ that is split by crystal fields into a low-lying doublet of $\Gamma_7$ symmetry and an excited quartet of $\Gamma_8$ symmetry. Slave Bosons on the $4f$ sites create and destroy $4f^0$ configurations and Lagrange multipliers at each $4f$ site enforce the occupancy constraint due to the infinite Coulomb repulsion. Quasiparticle interactions are due to exchange of $4f$ density fluctuations, which are represented by fluctuations in the slave Bosons and Lagrange multipliers. We use the so-called analytic tetrahedron method to calculate the dressed (to order 1/N) Boson Green functions. In weak couping, the exchange of the dressed Bosons gives rise to a superconducting instability of $T_{1g}$, $xy(x^2-y^2)$, symmetry. The $A_{1g}$, ``s-wave'', channel has strongly repulsive interactions and hence no pairing instability. The $T_{2g}$ channel exhibits weakly repulsive interactions. Average quasiparticle interactions in the $E_g$, $x^2-y^2$, $3z^2-r^2$, channel fluctuate strongly as a function of the number of tetrahedra used to calculate the Bosonic Green functions,Comment: 66 pages+ 17 postscript figures, LATE

Modeling Legal Requirements

Ever increasing complexity is one of the key challenges for software-intensive systems. All phases of the system engineering lifecycle are affected; thus, appropriate methods, techniques, and tools must be provided to manage this increasing complexity. Another challenge arises from the fact that requirements are traditionally documented in natural language. This is especially true for legal artifacts such as laws or standards, since organizations are required to consider these kinds of legal requirements when bringing products to the market. Applying model-based engineering approaches is one possibility to address these problems, but methodical uncertainties caused by a lack of method support have so far prevented their widespread use in early project phases. This paper addresses these uncertainties by introducing a systematic approach for modeling legal artifacts such as laws or standards. The method is assessed in the context of emission legislation in the automotive domain

Upper critical magnetic fields of the heavy fermion superconductors CeCu₂Si₂, UPt₃, and UBe₁₃: Comparison between experiment and theory

We report measurements of the upper critical magnetic field,B c2 (T), on single crystal and polycrystalline samples of the heavy-fermion superconductors CeCu2Si2, UPt3 and UBe13. Comparison is made with experimental results for a “conventional” superconductor (CeRu3Si2) and with results of the weak-coupling theory applied to both ans-wave superconductor in the “dirty-limit” and ap-wave superconductor. New anomalies are discovered to add to the unusualB c2 (T) behavior

CeCu₂Si₂ and UPt₃: Two different cases of heavy fermion superconductivity

Specific heat and thermal conductivity in the superconducting state of the Kondo-lattice system CeCu2Si2 and the paramagnon system UPt3 point to substantial mass anisotropies at the Fermi surface (FS): while in CeCu2Si2 bare band electrons at certain portions of the FS seem to remain normal, in UPt3 heavier fermions seem to stay normal and Cooper pairs are formed by somewhat less heavy ones. The upper critical field of UPt3 shows no influence of Pauli limiting and can reasonably well be explained with S = 0 as well as S = 1 pairing. CeCu2Si2 is strongly Pauli limited, independent of orientation. This substantiates recent Josephson experiments which show that CeCu2Si2 is a singlet superconductor