Author's Reply

In response to Luchini's comments, we recalculate the small-signal gain in planar-wiggler free-electron lasers. When all first-order contributions are included, the standard gain formula is obtained, as required by the Madey theorem.     

TAPER: query-aware,partition-enhancement for large,heterogenous graphs

Graph partitioning has long been seen as a viable approach to addressing Graph DBMS scalability. A partitioning, however, may introduce extra query processing latency unless it is sensitive to a specific query workload, and optimised to minimise inter-partition traversals for that workload. Additionally, it should also be possible to incrementally adjust the partitioning in reaction to changes in the graph topology, the query workload, or both. Because of their complexity, current partitioning algorithms fall short of one or both of these requirements, as they are designed for offline use and as one-off operations. The TAPER system aims to address both requirements, whilst leveraging existing partitioning algorithms. TAPER takes any given initial partitioning as a starting point, and iteratively adjusts it by swapping chosen vertices across partitions, heuristically reducing the probability of inter-partition traversals for a given path queries workload. Iterations are inexpensive thanks to time and space optimisations in the underlying support data structures. We evaluate TAPER on two different large test graphs and over realistic query workloads. Our results indicate that, given a hash-based partitioning, TAPER reduces the number of inter-partition traversals by \(\sim \)80%; given an unweighted Metis partitioning, by \(\sim \)30%. These reductions are achieved within eight iterations and with the additional advantage of being workload-aware and usable online.     

A Monte Carlo approach to the theoretical prediction of temperature noise in LMFBR sub-assemblies

A candidate technique for detecting incipient blockages in the fuel sub-assemblies of liquid-metal-cooled fast-breeder reactors is the measurement of coolant outlet temperature fluctuations caused by turbulence. A theoretical basis for the method is required, and one model is discussed in this paper.

The model requires the paths of individual fluid particles to be traced, allowing their motions to vary randomly, subject to certain constraints of the turbulent motion. It is a Monte Carlo method, already used successfully in predicting the transport of scalar fluctuations. Its advantage is that it allows actual time-dependent temperatures to be computed, and so various methods of analysis (power spectral density, amplitude probability distribution, for example) can be examined. The effect of heat conduction is neglected at present.

Computed results show the way in which mean temperature and rms temperature-noise profiles develop in a turbulent flow in a pipe downstream of a plane at which a steady mean profile is maintained. Power spectral densities and amplitude-probability densitiesare presented, and it is shown how an amplitude-probability density plot distinguishes between a temperature-gradient input profile and a gaussian input profile.

Comparisons are given with experimental measurements made in representative heated pin rigs in sodium, with good agreement. Some of the problems associated with extrapolation to real sub-assemblies are discussed.     

User-friendly algorithms for estimating completeness and diversity in randomized protein-encoding libraries

Directed evolution of proteins depends on the production ofmolecular diversity by random mutagenesis. While a number ofmethods have been developed for introducing this diversity,the best ways to sample it are not always clear. Here we usedsimple statistics to analyse completeness and diversity in randomizedlibraries generated by oligonucleotide-directed mutagenesis,error-prone polymerase chain reaction (epPCR) and in vitro recombinationof highly homologous sequences. For oligonucleotide-directedmutagenesis, we derive equations to estimate how complete agiven library is expected to be and also to predict the sizeof library required to give a fixed probability of being 100%complete. We describe the statistical bases for computer programswhich estimate the number of distinct variants represented inepPCR and shuffled libraries, dubbed PEDEL and DRIVeR, respectively.These programs allow the user to calculate (rather than guess)the diversity represented in a given library and also provideempirical guidelines for maximizing this diversity. PEDEL andDRIVeR are available at www.bio.cam.ac.uk/     

Spin saturation and pump depletion in continuous spin-flip Raman oscillation

A saturation model of stimulated Raman scattering, of general applicability, is put forward. The model is developed with reference to spin-flip electronic Raman scattering in InSb, where the number of excitations available for Raman scattering may be small by comparison with the incident photon numbers. A rate equation technique is used to evaluate the steady-state Stokes intensity and output powers for a Gaussian pump beam. The model is extended to take account of pump depletion and the relative importance of depletion, and saturation in limiting the conversion efficiency under different conditions is brought out. By comparison with continuous wave spin-flip measurements, values are obtained for the spin-relaxation time (τs) associated with spin reversal in InSb. For 10¹⁶free carriers per cubic centimeter at 36 kG,tau_{s} sim 12ns and for 10¹⁵cm^-3at 16.9 kG,tau_{s} sim 1.3ns.     

An overview of microbial food safety programs in beef, pork, and poultry from farm to processing in Canada

Canada's vision for the agri-food industry in the 21st century is the establishment of a national food safety system employing hazard analysis and critical control point (HACCP) principles and microbiological verification tools, with traceability throughout the gate-to-plate continuum. Voluntary on-farm food safety (OFFS) programs, based in part on HACCP principles, provide producers with guidelines for good production practices focused on general hygiene and biosecurity. OFFS programs in beef cattle, swine, and poultry are currently being evaluated through a national recognition program of the Canadian Food Inspection Agency. Mandatory HACCP programs in federal meat facilities include microbial testing for generic Escherichia coli to verify effectiveness of the processor's dressing procedure, specific testing of ground meat for E. coli O157:H7, with zero tolerance for this organism in the tested lot, and Salmonella testing of raw products. Health Canada's policy on Listeria monocytogenes divides ready-to-eat products into three risk categories, with products previously implicated as the source of an outbreak receiving the highest priority for inspection and compliance. A national mandatory identification program to track livestock from the herd of origin to carcass inspection has been established. Can-Trace, a data standard for all food commodities, has been designed to facilitate tracking foods from the point of origin to the consumer. Although much work has already been done, a coherent national food safety strategy and concerted efforts by all stakeholders are needed to realize this vision. Cooperation of many government agencies with shared responsibility for food safety and public health will be essential.     

Collagenase-3 (matrix metalloproteinase-13) expression is induced in oral mucosal epithelium during chronic inflammation

Increased proliferation of mucosal epithelium during inflammation is associated with degradation of subepithelial connective tissue matrix and local invasion of the epithelial cells. Here we have studied, whether collagenase-3 (MMP-13), a collagenolytic matrix metalloproteinase with an exceptionally wide substrate specificity, is expressed in the epithelium of chronically inflamed mucosa. Examination of human gingival tissue sections from subjects with chronic adult periodontitis with in situ hybridization revealed marked expression of MMP-13 in basal cells of some epithelial rete ridges expanding into connective tissue. Immunohistochemical staining demonstrated that these cells also expressed strongly laminin-5, suggesting that they are actively migrating cells. A strong signal for MMP-13 mRNA was occasionally also noted in the suprabasal epithelial cells facing the gingival pocket, whereas no collagenase-1 (MMP-1) mRNA was detected in any areas of the epithelium. MMP-13 expression was also detected in fibroblast-like cells associated with collagen fibers of the inflamed subepithelial connective tissue. In organ culture of human oral mucosa, MMP-13 mRNA expression was observed in epithelial cells growing into connective tissue of the specimens. Regulation of MMP-13 expression was examined in cultured normal nonkeratinizing epithelial cells isolated from porcine periodontal ligament. In these cells, MMP-13 expression at the mRNA and protein level was potently enhanced (up to sixfold) by tumor necrosis factor-alpha, transforming growth factor-beta(1), and transforming growth factor-alpha and by keratinocyte growth factor in the presence of heparin. In addition, plating periodontal ligament epithelial cells on type I collagen stimulated MMP-13 expression (sevenfold) as compared with cells grown on tissue culture plastic. The results of this study show, that expression of MMP-13 is specifically induced in undifferentiated epithelial cells during chronic inflammation due to exposure to cytokines and collagen. Thus, it is likely that MMP-13 expression is instrumental in the subepithelial collagenolysis and local invasion of the activated mucosal epithelium into the connective tissue.     

Adaptive Phase Distortion Suppression in a Nonlinear System with Feedback Mirror

Abstract

Kerr nonlinearity, combined with feedback and diffraction, can be used to suppress phase distortions of laser beams and improve their collimation. No reference beam is required, nor need the beam re-traverse the distorting medium.