16 fs, 350 nJ pulses at 5 MHz repetition rate delivered by chirped pulse compression in fibers

We demonstrate a simple approach for broadening and compression of intense pulses at megahertz repetition rates by self-phase modulation in nonlinear photonic crystal fibers. In order to avoid damage by self-focusing, we positively chirp the input pulses, which allows coupling of significantly more energy into the fiber, while maintaining the same spectral bandwidth and compression as compared to the Fourier-limited case at lower energy. Using a commercial long-cavity Ti:sapphire oscillator with 55 fs, 400 nJ pulses at 5 MHz, we generate 16 fs, 350 nJ pulses, which is a factor of 4 more energy than possible with unchirped input pulses. Self-phase-modulated spectra supporting 11 fs duration are also shown with 350 nJ pulse energy. Excellent stability is recorded over at least 1 h.     

The A53T mutation is key in defining the differences in the aggregation kinetics of human and mouse α-synuclein

Despite a 95% sequence similarity, the aggregation of human and mouse α-synuclein is remarkably different, as the human form is slower than the mouse form in forming fibrils but is associated with Parkinson's disease in both humans and transgenic mice. Here, the amino acid code underlying these differences is investigated by comparing the lag times, growth rates, and secondary structure propensities of a systematic series of eight human-mouse chimeras. Fluorescence analysis of these variants shows that the A53T substitution dominates the growth kinetics, while the lag phase is affected by a combination of the A53T and S87N substitutions. The secondary structure propensities derived from an NMR chemical shift analysis of the monomeric forms of the human-mouse variants enable us to establish a link between the changes in the conformational properties in the region of position 53 upon mutation and the corresponding changes in growth rates. These results suggest that the presence of an alanine residue at position 53 may be an evolutionary adaptation to minimize Parkinson's disease in humans and indicates that effective drug development efforts may be directed to target this N-terminal region of the sequence.     

Synthesis of Polynitro-2,6-dioxabicyclo[3.3.0]octanes

Polynitro ether, 4,4,8,8-tetranitro-2,6-dioxabicyclo[3.3.0]octane (1), was synthesized in four steps from 1,4:3,6-dianhydromannitol ditosylate.     

Thermally stable polymers based on acetylene-terminated adamantanes

1,3-Diethynyl-5,7-dimethyladamantane, 1,3-diethynyl-5-phenyladamantane, 1,3,5-triethynyladamantane, and 3,3′-diethynyl-1,1′-biadamantane, were synthesized and polymerized thermally at 210°C. The thermoset resins obtained were post-cured at 300°C for 16 h to give materials that exhibited onsets of degradation (TGA) in air at 460–477°C and in helium at 460–485°C. The fully cured materials did not exhibit any detectable DSC transitions between 25 and 400°C. An attempt to thermally polymerize 1-ethynyl-3-phenyladamantane was unsuccessful. © 1992 John Wiley & Sons, Inc.     

The K-Theory of Heegaard-Type Quantum 3-Spheres

We use a Heegaard splitting of the topological 3-sphere as a guiding principle to construct a family of its noncommutative deformations. The main technical point is an identification of the universal C^*-algebras defining our quantum 3-spheres with an appropriate fiber product of crossed-product C^*-algebras. Then we employ this result to show that the K-groups of our family of noncommutative 3-spheres coincide with their classical counterparts. Dedicated to the memory of Olaf Richter An erratum to this article is available at .     

A Product Theorem for Markov Chains with Application to PF-Queueing Networks

Queueing networks in random environments represent more realistic models of computer and telecommunication systems than classical product form networks. This is due to the fact that network behaviour often depends on human activities which may vary according to daytime dependent behavioural patterns as well as physiological and mental indexes. In this paper we establish a product connection theorem for Markov chains which contains some corresponding results for spatial processes as well as for queueing networks in random environment as special cases. We demonstrate how our results can be applied to construct an adequate model for wireless networks with hook up capacity.     

Eigenvalue estimates for Dirac operators coupled to instantons

We prove a sharp lower bound for the first positive eigenvalue of Dirac operators coupled to instantons and discuss the limit case.     

Zur Analytischen Darstellung des Ranges Konvexer Körper Durch Stützhyperboloide

LetK be a convex body in (n+1)-dimensional Euclidean space Eⁿ⁺¹. The set (K) of all support-elements ofK is uniquely determined by the semiaxis-function a(u). First part of this note contains an explicit specification of the support-elements by means of a(u), and in the second part we give necessary and sufficient conditions which characterize a function a(u) as semiaxis-function of a closed convex subset of Eⁿ⁺¹.