Analysis of injection locking in pulsed dye laser systems

A pulsed dye laser system with a narrow-band signal injected into the cavity is considered. The injection starts prior to the excitation pulse. It is shown that during a transient period, injection locking can be achieved for a much wider range of parameters than under conventional CW conditions. The analysis is based on a set of coupled rate equations for the population densities and photon fluxes at all wavelengths. These are solved numerically with appropriate initial and boundary conditions. Analytical approximations, which are helpful for understanding the behavior of such systems, are presented. Both straight, two-mirror cavities, and ring laser cavities are discussed. The temporal evolution of the spectral components at all wavelengths is described. The range of tunability in this mode of operation and its dependence on various parameters, such as pulse length, cavity dimensions, and injection intensity are discussed.     

Role of soil freezing events in interannual patterns of stream chemistry at the Hubbard Brook Experimental Forest,New Hampshire

Soil freezing is a disturbance of the below ground environment, potentially resulting in increased losses of NO3- and surface water acidification. Here, we report the effects of soil freezing on interannual variation in stream chemistry at the Hubbard Brook Experimental Forest, New Hampshire. Data from 1970 to 1997 of soil frost depth, snow cover, precipitation, air temperature, and stream discharge and chemistry were used in a stepwise linear regression model to select the variables that best predicted deviations of annual stream concentrations from 4-year running averages. Variables quantifying soil freezing severity were selected as significant predictors of short-term fluctuations in stream K+, NO3-, Ca2+, and Mg2+ concentrations from 1970 to 1989, explaining 59 and 47% of the short-term variability in K+ and NO3-, respectively. Fine-root mortality and disturbance of root-soil-microbe interactions, with subsequent effects on decomposition and nutrient uptake, likely contributed to the mobilization of K+ and NO3- to streamwater following severe soil freezing events. The relationship between soil freezing and stream chemistry, however, weakened during the period 1990-1997. Because soil freezing has had inconsistent effects on stream chemistry during the period 1970-1997, it is unclear whether future changes in the frequency, duration, and depth of soil freezing events as the result of changes in the snow cover regime under a warmer climate will have significant impacts on the losses of NO3- and nutrient-base cations from temperate northern ecosystems.     

Finance, Policy and Industrial Dynamics—The Rise of Co-productions in the Film Industry

This paper explores the growing phenomenon of international co-productions in the film industry. We argue that the rise of co-productions is part of a wider narrative of financial and institutional innovation shaping industrial organization in the film industry. This narrative centres on film finance as a central risk distribution mechanism, and discusses how changes in film support policy, increased tax competition, the search for finance and an abundance of inflowing capital are increasingly driving industrial dynamics in the film industry.     

Applications of real number theorem proving in PVS

Real number theorem proving has many uses, particularly for verification of safety critical systems and systems for which design errors may be costly. We discuss a chain of developments building on real number theorem proving in PVS. This leads from the verification of aspects of an air traffic control system, through work on the integration of computer algebra and automated theorem proving to a new tool, NRV, first presented here that builds on the capabilities of Maple and PVS to provide a verified and automatic analysis of Nichols plots. This automates a standard technique used by control engineers and greatly improves assurance compared with the traditional method of visual inspection of the Nichols plots.     

A coupled-mode analysis of twin-stripe index-guided lasers

An approximated coupled-mode solution to the problem of lateral mode behavior in twin-stripe index-guided injection lasers near threshold is presented. The optical properties are determined by the coupling coefficients between the two waveguides, taking into account the external current-dependent perturbation to the dielectric constant. In the calculations of the external perturbation, a simple model of current spreading under the contacts and carrier diffusion in the active layer is given for a multistripe structure. Emphasis is on the influence of the current ratio on the lateral field shape and modal gain. It is shown that for symmetrical current injection, the fundamental supermode has a slight advantage (higher gain) over the second 180° phase-shifted mode. As the injected current ratio is driven away from the symmetrical point, the second supermode is favored with increasing modal gain difference. The coupled-mode approach is relatively simple and can describe rather accurately this already-known behavior     

ESR on adsorbed doubly spin-polarized atomic hydrogen

Studies of the ESR spectrum of spin-polarized atomic hydrogen adsorbed on a liquid helium film are presented. The absorption peaks associated with the surface atoms are displaced relative to that of the gaseous atoms due to the electronic dipole-dipole interaction, which does not average to zero for atoms moving in two dimensions. This phenomenon, first observed by Reynolds et al., allows the surface atom density to be measured directly and, through the lineshape, information on the dynamics of the 2-D gas can in principle be obtained. Here we present a more detailed study, with a better characterized substrate for the helium film.Using only the assumption that the ideal gas approximation is valid for the experimental conditions, we find that the binding energy of hydrogen atoms to the liquid helium surface is 1.03 (2) K. Although these measurements of the binding energy are not the most accurate, they are the most direct.The ESR lineshape of the absorption peak of the bulk atoms is determined by the inhomogeneity of the applied magnetic fields, whereas the resonance lineshape of the adsorbed atoms, which is very asymmetric and much broader than the main resonance, is clearly due to some other mechanism. In spite of a considerable effort to explain the observed lineshapes, we have not reached satisfactory conclusions.     

Molecular characterization of morphologically typical human calicivirus Sapporo

Human calicivirus Sapporo (SV) has typical calicivirus morphology and causes acute gastroenteritis in children. The nucleotide sequence of 3.2 kb of the 3' end of SV was determined from a cloned cDNA. The 3' end of the SV genome is predicted to encode the RNA-dependent RNA polymerase region, the capsid protein and two small open reading frames. The nonstructural and capsid protein coding sequences in the SV genome are fused in a single open reading frame. The organization of these proteins in the SV sequence is similar to that of rabbit hemorrhagic disease virus and the recently described Manchester virus, and distinct from the genome organization of the prototype human calicivirus, Norwalk virus, that lacks typical calicivirus morphology and has been described as a small round structured virus (SRSV). Sequence analysis of the predicted capsid region showed that the SV capsid is longer by approximately 30 amino acids than the capsid of any of the SRSVs, and multiple sequence alignments showed that these additional amino acids are located in the variable region of the capsid protein. Expression of the capsid protein of SV in insect cells resulted in the self-assembly of virus-like particles that have a morphology similar to that of the native virus. This result shows that calicivirus morphology is determined by the primary sequence of the capsid protein.     

A recombinant adenovirus that directs secretion of biologically active kappa-bungarotoxin from mammalian cells

The purpose of this investigation was to develop a method that could be used to estimate how damaging sodium ethoxide is to different antigens with respect to immunolabeling when epoxy sections are deplasticized. If we obtain weak labeling for an antigen on deplasticized epoxy sections, this might be caused by the damaging effect of the ethoxide solution. It is therefore interesting to develop a method to check if this really is the reason. Fibrin clots and tissues of human kidney and thyroid were embedded in LR White resin. Some thin sections from these specimen blocks were exposed to sodium ethoxide in the same way as epoxy sections are when being deplasticized. Other sections from the same blocks were not exposed to sodium ethoxide. Both categories of sections were immunogold-labeled with anti-fibrinogen, anti-thyroglobulin, anti-IgA, anti-IgG, or anti-IgM. The intensity of immunolabeling of sections treated with ethoxide was compared with the immunolabeling of corresponding sections that were not treated with ethoxide. No significant differences were found in immunolabeling for fibrinogen, IgA, IgG, and IgM. For thyroglobulin, the intensity was approximately 30% less in tissues that were exposed to sodium ethoxide. The practical significance of this method is that we easily can examine the degree to which a given antigen is affected by sodium ethoxide, which is the agent used for deplasticizing epoxy sections.     

Amplified spontaneous emission in dye-doped sol-gel amplifiers

Transversely pumped dye doped slab waveguides are investigated. A set of coupled-rate equations for the excited-state population and for the amplified spontaneous emission (ASE) power, at all wavelengths, is presented. The equations are solved numerically for the steady-state case. The results describe the dependence of ASE output power on pumping power, the spectral narrowing process, and the effect of waveguiding. The theoretical calculations are compared with the results of experiments, and good agreement is found