A phase-space approach to directional switching in semiconductor ring lasers

We show that a topological investigation of the phase space of a Semiconductor Ring Laser can be used to devise switching schemes which are alternative to optical pulse injection of counter-propagating light. To provide physical insight in these switching mechanisms, a full bifurcation analysis and an investigation of the topology is performed on a two-dimensional asymptotic model. Numerical simulations confirm the topological predictions.Comment: 9 pages, 7 figure

Probing Protein-protein Interactions Among Proteins of a Nonaggregated Fatty Acid Synthetase From Euglena Gracilis Variety Bacillaris

Enoyl-acyl carrier protein (ACP) reductase from chloroplast nonaggregated fatty acid synthetase (FAS) of Euglena gracilis variety bacillaris was purified to a single band on a denaturing polyacrylamide gel. The enzyme was partially characterized with respect to substrate specificity, reduced nucleotide requirement, and the effect of ACP and Ca\sp{++} on enzyme activity. Antibodies against the purified protein were raised in hens and isolated from eggs. ACP was purified from Euglena in yields of about 1mg/100g (wet weight) of cells. Antibodies were raised against the purified protein. ACP antibodies inhibited the Euglena chloroplast FAS using Euglena or E. coli ACP as a substrate. Comparisons with other ACPs included the following items: biological activity, pI, behavior in size exclusion media, and amino acid sequence of the N-terminal portion of the molecule. ACPs from E. coli and Euglena have been shown to interact with melittin, a cationic peptide from bee venom. E. coli ACP is a small (Mr, 8847), acidic, Ca\sp{++}-binding protein which possesses some characteristics resembling those of regulatory Ca\sp{++}-binding proteins including interaction with melittin. Melittin inhibited activity of the nonaggregated FAS from Euglena using either E. coli or Euglena ACP as a substrate. The peptide also inhibited activity of the aggregated FAS from Euglena. Antibodies against melittin were raised. Anti-melittin inhibited activity of both the nonaggregated and aggregated FAS enzyme systems from Euglena relative to nonimmune antibody. Investigation of inhibition of the nonaggregated FAS enzyme system demonstrated that acetyl-CoA-ACP transacylase, malonyl-CoA-ACP transacylase, and keto-acyl-ACP synthetase activities were inhibited to different degrees by anti-melittin antibodies, while keto-acyl-ACP reductase and enoyl-ACP reductase enzyme activities were not inhibited

Exploring multi-stability in semiconductor ring lasers: theory and experiment

We report the first experimental observation of multi-stable states in a single-longitudinal mode semiconductor ring laser. We show how the operation of the device can be steered to either monostable, bistable or multi-stable dynamical regimes in a controlled way. We observe that the dynamical regimes are organized in well reproducible sequences that match the bifurcation diagrams of a two-dimensional model. By analyzing the phase space in this model, we predict how the stochastic transitions between multi-stable states take place and confirm it experimentally.Comment: 4 pages, 5 figure

Convergence of Discretized Light Cone Quantization in the small mass limit

I discuss the slow convergence of Discretized Light Cone Quantization (DLCQ) in the small mass limit and suggest a solution.Comment: 8 pages, 5 Postscript figures, uses boxedeps.te

Excitability in semiconductor microring lasers: Experimental and theoretical pulse characterization

We characterize the operation of semiconductor microring lasers in an excitable regime. Our experiments reveal a statistical distribution of the characteristics of noise-triggered optical pulses that is not observed in other excitable systems. In particular, an inverse correlation exists between the pulse amplitude and duration. Numerical simulations and an interpretation in an asymptotic phase space confirm and explain these experimentally observed pulse characteristics.Comment: 9 pages, 10 figure

Topological insight into the non-Arrhenius mode hopping of semiconductor ring lasers

We investigate both theoretically and experimentally the stochastic switching between two counter-propagating lasing modes of a semiconductor ring laser. Experimentally, the residence time distribution cannot be described by a simple one parameter Arrhenius exponential law and reveals the presence of two different mode-hop scenarios with distinct time scales. In order to elucidate the origin of these two time scales, we propose a topological approach based on a two-dimensional dynamical system.Comment: 4 pages, 3 figure

An evaluation of solutions to the problem of boundary change when analyzing long-term relationships on aggregate data

In Norwegen sind die Gemeinden die kleinste regionale und Verwaltungseinheit. Sie existieren als solche schon seit mehr als 150 Jahren. Deshalb sind die Gemeinden die Hauptverwalter von Daten in den offiziellen Statistiken des Landes. Dies hat zu einer langen Tradition sorgfältig gepflegter Daten auf dieser Ebene geführt. Der norwegische sozialwissenschaftliche Datendienst hat auf Teilen dieser Information eine Datenbank aufgebaut, um die Analysen von regionalen Daten voranzutreiben. Die Daten können gefunden werden für statistische Analysen und/oder kartographische Präsentation. Der Artikel setzt sich mit den Hauptproblemen eines solchen Systems auseinander, nämlich der Veränderung der zugrundeliegenden regionalen Einheiten und den daraus resultierenden Problemen für Analysen des langfristigen Verhältnisses auf einer aggregierten Datenbasis. Wenn die regionalen Einheiten sich verändern, rechnet das Datenbanksystem die Daten für die neuen Einheiten aus. Diese Neuberechnung basiert auf Information über Bevölkerungswanderungen zwischen den betroffenen Einheiten und den betroffenen spezifischen Daten. Die verschiedenen zugrundeliegenden Randbedingungen für dieses Verfahren werden diskutiert, ebenso wie die verschiedenartigen Möglichkeiten, auf diese Weise Verzerrungen in das Datenmaterial hereinzubekommen. Das Verfahren wird einer empirischen Überprüfung unterzogen, auf dessen Grundlage Empfehlungen für den Gebrauch der Daten gegeben werden. Da Datenneuberechung sowohl vorwärts und rückwärts im Zeitablauf vorgenommen werden können, wird empfohlen, daß Datennutzer Daten neu berechnen sollten, in Folge von allgemeinen Aggregationsprozessen im System der regionalen Einheit. Verschiedene Arten von statistischen Daten können allerdings nicht einem gleichartigen Verfahren unterzogen werden. Das Verfahren ist hauptsächlich für variable Größen bestimmt, die Aussagen über die Bevölkerung ermöglichen und basieren auf der Annahme, daß diese Aussagen eine homogene Verteilung in der Bevölkerung der Regionaleinheiten ermöglichen. Das Ergebnis wird beeinträchtigt, sowohl von der gewählten Zeit der abgefragten Daten, d.h. die Anzahl und die Arten der Veränderungen und der Art der abgefragten Daten. Das Hauptergebnis ist, daß Neuberechnungen der Datenbasis, wenn sich die Regionaleinheiten ändern, um Daten vergleichbar zu machen, nicht die Schlußfolgerungen ernsthaft beeinträchtigen, die auf statistischen Analysen aller oder großer Untereinheiten der Regionaleinheiten beruhen. Es wird schwieriger, langfristige Zeitreihen für Einzelfälle zu nutzen. (KWübers.)'In Norway, communes are the smallest regional political and administrative units, and have existed as such for some 150 years. For this reason the communes have been the main datacarrying unit in the offical statistics of the country. This has resulted in a long tradition of well aggregated information at this level. The Norwegian Social Science Data services has built a database containing part of this information, to further the analysis of regional data. Data may be retrieved for statistical analysis and/or cartographic presentation. The present article discusses one of the main problems of such a system, changes in regional units over time, and the problems created for analysis of long-term relationship on aggregated data. When changes occur in the system of regional units, the databse-system recalculates the data values to the new units. These recalculations are based on information about population transfers involved, and the type of data under consideration. Various underlying assumptions for this procedure are discussed, and so are the different types of error that may introduce into the data. The procedure is tested empirically, and based on the empirical results some recommendations for use are advocated. Since it is possible to recalculate data both forwards and backwards in time, it is recommended that users as a general rule should try to recalculate data following general processes of aggregation in the system of regional units. Also various types of data do not lend themselves to the same kind of treatment by this procedure. It is mainly designed for variables that give attributes with the population, and is based on the assumption that these attributes approach a homogeneous distribution across the population of a regional unit. The outcome is effected both by the time-period of the retrieved data, i.e. number and types of changes involved, and kind of data retrieved. The main conclusion is that recalculations of data when units change, to make data comparable, do not seriously affect conclusions based on statistical analyses of all, or large subsets of the regional units. It is more difficult to use long timeseries for just a few cases.' (author's abstract