Multipass V-shaped system with a large relative aperture: stages of development

In this review I describe the step-by-step development and update of an optical multipass system with a fixed path length and large relative aperture. The system has been researched off and on for 20 years. Contrary to acknowledged ideas, some of the models were designed using the ratio between the base length of a multipass system and the focal length of an objective equal to 1.5 (compared with 2 for the classical White system). Such an unconventional choice of 1.5f base length between opposite mirrors ensured the development of a cycle of six-pass single-objective systems with a large relative aperture. The described systems were used in various gas analytical equipment. Of special interest is an original scheme with an f-number of 3.7 to be used in high-resolution spectroscopy.     

Prediction of corrosion-induced cover cracking in reinforced concrete structures

Usually, the time of repair/replacement of reinforced concrete structures due to corrosion is controlled by cracking of the concrete cover. Thus, it is important to be able to predict with sufficient accuracy the time from corrosion initiation to crack formation in the concrete cover. The paper presents a critical overview of existing empirical, analytical and numerical models for predicting the time to corrosion-induced cover cracking. A simple nonlinear finite element (FE) is then formulated and validated. The FE model is employed to investigate inaccuracies of analytical models arising due to simplified formulation of the nonlinear behaviour of concrete and inability to account for actual location of corroding reinforcing bars. Recommendations on the applicability of analytical models are provided. Finally, the FE model is used to estimate the amount of corrosion products penetrating into concrete pores and microcracks since this amount is an essential parameter for analytical and numerical models.     

Chitinolytic activity in Chromobacterium violaceum: substrate analysis and regulation by quorum sensing

Quorum sensing control mediated by N-acyl homoserine lactone (AHL) signaling molecules has been established as a key feature of the regulation of exoenzyme production in many gram-negative bacteria. In Chromobacterium violaceum ATCC 31532 a number of phenotypic characteristics, including production of the purple pigment violacein, hydrogen cyanide, antibiotics, and exoproteases are known to be regulated by the endogenous AHL N-hexanoyl-L-homoserine lactone (HHL). In this study we show that C. violaceum produces a set of chitinolytic enzymes whose production is regulated by HHL. The chitinolytic activity was induced in strains grown in the presence of chitin as the sole carbon source and quantitated in the secreted proteins by using p-nitrophenol analogs of disaccharide, trisaccharide, and tetrasaccharide oligomers of N-acetylglucosamine. By using 4-methylumbelliferyl analogs of the same oligomers of N-acetylglucosamine as substrates for proteins separated and renatured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, at least six enzymes were detected: a chitobiase with high specificity to a dimeric substrate of 87 kDa, two N-acetylglucosaminidases with apparent molecular masses of 162 and 133 kDa, two endochitinases of 108 and 67 kDa, and a chitobiosidase of 56 kDa. In addition, two unidentified bands of >205 kDa were found where a tetrameric chitin derivative was used as a substrate. A pleiotropic mini-Tn5 mutant of C. violaceum (CV026) that is defective in HHL production and other quorum-sensing-regulated factors was also found to be completely deficient in chitinolytic activity. Growth of this mutant on minimal medium with chitin supplemented with culture supernatant from the C. violaceum wild-type strain or 10 microM synthetic HHL restored chitinase production to the level shown by the parental strain. These results constitute the most complete evidence so far for regulation of chitinolytic activity by AHL signaling in a gram-negative bacterium.     

Chitinolytic activity of an endophytic strain of Bacillus cereus

Bacillus cereus strain 65, previously isolated as an endophyte of Sinapis, was shown to produce and excrete a chitinase with an apparent molecular mass of 36 kDa. The enzyme was classified as a chitobiosidase because it was able to cleave diacetylchitobiose (GlcNAc)2 from the non-reducing end of trimeric chitin derivatives. The chitinase exhibited activity over the pH range 4.5-7.5 and was stable between pH 4.0 and 8.5. The enzyme had an isoelectric point of 6.4. Application of B. cereus 65 directly to soil significantly protected cotton seedlings from root rot disease caused by Rhizoctonia solani.     

Three-dimensional modeling of AC space charge for large-signal TWT simulation

We describe a new model for calculating the ac space charge in a linear-beam traveling wave tube (TWT) large-signal simulation code when the true three-dimensional (3-D) geometry of the interaction circuit is taken into account. We use the 3-D electromagnetic simulation code CTLSS to characterize the ac space charge fields generated by a set of test currents placed inside the periodic interaction structure. This information, expressed in matrix form, is used by the large-signal simulation codes CHRISTINE-1D and CHRISTINE-3D to compute self-consistently the additional space charge field terms due to the structure in response to the beam evolution during the simulation. We present the formulation, and describe the implementation in both CTLSS and the large-signal codes. We validate the model by comparison with the analytical sheath helix model, and evaluate the importance of including this correction for modeling a number of helix and coupled-cavity TWT devices.     

Molecular cloning, structural analysis, and expression in Escherichia coli of a chitinase gene from Enterobacter agglomerans

The gene chiA, which codes for endochitinase, was cloned from a soilborne Enterobacter agglomerans. Its complete sequence was determined, and the deduced amino acid sequence of the enzyme designated Chia_Entag yielded an open reading frame coding for 562 amino acids of a 61-kDa precursor protein with a putative leader peptide at its N terminus. The nucleotide and polypeptide sequences of Chia_Entag showed 86.8 and 87.7% identity with the corresponding gene and enzyme, Chia_Serma, of Serratia marcescens, respectively. Homology modeling of Chia_Entag's three-dimensional structure demonstrated that most amino acid substitutions are at solvent-accessible sites. Escherichia coli JM109 carrying the E. agglomerans chiA gene produced and secreted Chia_Entag. The antifungal activity of the secreted endochitinase was demonstrated in vitro by inhibition of Fusarium oxysporum spore germination. The transformed strain inhibited Rhizoctonia solani growth on plates and the root rot disease caused by this fungus in cotton seedlings under greenhouse conditions.     

Spurious reflection of space charge fields in TWTAs

The reflection of waves at the termination of a beam loaded traveling wave structure is considered. The presence of a bunched beam in the structure induces additional currents and voltages on the structure, which give rise to an additional reflection at the termination. This effect is first illustrated in a simple transmission line model, and then a formal field-based derivation for the reflection in a periodic structure is presented. Simple estimates for the magnitude of the reflection can be made based on the amplifier's Pierce parameter. Unlike the reflection due to a mismatched load, the spurious reflection due to the beam depends on signal power level. The spurious reflection can be simulated in large signal parametric codes, and examples of this are presented.     

Naturalizing Racial Differences Through Comedy: Asian, Black, and White Views on Racial Stereotypes in Rush Hour 2

In this paper, we examine the ideological implications of racial stereotypes in comedy through a textual and audience analysis of Rush Hour 2 . Although Asian, Black, and White focus group participants differentially engaged with racial stereotypes in the film, most participants, regardless of race, found the film's racial jokes inoffensive. Many Asian and Black participants found a positive source of pleasure in the negative portrayals of their own race and did not produce oppositional discourse. Our study suggests that the generic conventions and textual devices of comedy encourage the audience to naturalize racial differences rather than to challenge racial stereotypes.