Multisymplecticity and wave action conservation

This paper discuses some novel results concerning the wave action conservation law for multisymplectic partial differential equations and their discretizations. We provide a method for deriving this conservation law in Fourier spectral space. A discrete wave action conservation law for a multisymplectic box scheme and for the midpoint time-discretization of a spectral method is also derived.     

The femR315 gene from Staphylococcus aureus, the interruption of which results in reduced methicillin resistance, encodes a phosphoglucosamine mutase

The femR315 gene was recently identified by Tn551 insertional mutagenesis as one of the new auxiliary genes, the alteration of which resulted in a drastically reduced methicillin resistance of the Staphylococcus aureus strain COL. femR315 (also known as femD) theoretically encoded a protein of 451 amino acids showing significant amino acid sequence homology with phosphoglucomutases and similar enzymes catalyzing the isomerization of hexoses and hexosamine phosphates (S. Wu, H. de Lencastre, A. Sali, and A. Tomasz, Microb. Drug Resist. 2:277-286, 1996). We describe here the overproduction and purification of the FemR315 protein as well as its identification as the phosphoglucosamine mutase which catalyzes the formation of glucosamine-1-phosphate from glucosamine-6-phosphate, the first step in the reaction sequence leading to the essential peptidoglycan precursor UDP-N-acetylglucosamine. On the basis of these findings, we propose to change the names femR315 and femD to the functionally more appropriate name glmM.     

An incremental analysis of plane strain fully plastic crack growth in strain-hardening materials under extension

Analyses of inelastic fracture have mainly followed two directions. One is crack-tip-field analysis in strain-hardening materials (e.g., the HRR solution). The other is whole field analysis in non-hardening materials (e.g., McClintock's slip-line approach). In this paper, a theoretical approach that combines the two directions is presented to account for large crack growth. As an example, plane strain mode I fully plastic crack growth in a single-edge-cracked-specimen under extension is analyzed. The incremental analysis based on the deformed configuration is developed for large crack growth in strain-hardening materials. A kinematically admissible displacement increment field with crack-tip singularity is first constructed in a presumed symmetrical triangular deformation zone extending from the crack tip to the back flank of the ligament (whole field). Then the size of the deformation zone is determined by minimizing the total force in each incremental step. The strain histories of all material points in the ligament are traced and a fracture criterion based on the hole growth theory is applied. The comparisons between the present study and the experiments existing in the literature show the validity of the present approach.     

Structure and properties of nitrocarburized diffusion layers generated on high-speed steels

This work analyzes the structure and properties of nitrocarburized diffusion cases generated on M2 type high-speed and 321 stainless steels in a thermochemical. Application of variable process temperatures in the range of 450–600 °C and a variable process duration (2–6 h) enabled observation of growth kinetics of the layers on tested steel grades. Evaluation of properties of the cases obtained comprised hardness measurements and wear tests, carried out by the 3 cylinder-cone method. The evaluation showed that the nitrocarburizing process developed for high-speed and stainless steels yields hard surface layers with beneficial functional properties.     

Nature of Linear Spectral Properties and Fast Electronic Relaxations in Green Fluorescent Pyrrolo[3,4-c]Pyridine Derivative

The electronic nature of 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-trione (HPPT) was comprehensively investigated in liquid media at room temperature using steady-state and time-resolved femtosecond transient absorption spectroscopic techniques. The analysis of the linear photophysical and photochemical parameters of HPPT, including steady-state absorption, fluorescence and excitation anisotropy spectra, along with the lifetimes of fluorescence emission and photodecomposition quantum yields, revealed the nature of its large Stokes shift, specific changes in the permanent dipole moments under electronic excitation, weak dipole transitions with partially anisotropic character, and high photostability. Transient absorption spectra of HPPT were obtained with femtosecond resolution and no characteristic solvate relaxation processes in protic (methanol) solvent were revealed. Efficient light amplification (gain) was observed in the fluorescence spectral range of HPPT, but no super-luminescence and lasing phenomena were detected. The electronic structure of HPPT was also analyzed with quantum-chemical calculations using a DFT/B3LYP method and good agreement with experimental data was shown. The development and investigation of new pyrrolo[3,4-c]pyridine derivatives are important due to their promising fluorescent properties and potential for use in physiological applications.     

PMS—A program to make learning Pascal easier

One of the essential tasks in the teaching of a programming language is the introduction of the main constructs of the language—the syntax and semantics of statements, control, procedures, file handling, and so on. Most teachers present this topic by simulating the operation of the computer on the chalkboard by manual tracing of the execution of sample demonstration programs. Upon closer inspection it becomes clear that this task could be performed by the computer itself. A program implementing this idea would help the teacher in the class and the student (who could use the computer to repeat the instructor's performance at any time and on any problem of his choice) both in the class and in study. This article describes a collection of programs called PMS that performs exactly this function for the teaching of Pascal.PMS is organized as a collection of “mimlanguages” each of which demonstrates, and allows the user to experiment with, a certain category of Pascal features using a particular screen representation. Each of the subsystems contains a syntax-driven, screen-oriented translator associated with an interpreter that controls execution and the appropriate screen representation. This modular structure of PMS reflects the fact that programming is always taught by presenting certain essentially disjoint language features individually. In addition to their logical independence, these disjoint concepts also require different graphical approaches for their visual representation and this reinforces the need for modularization of the package.PMS is written in Pascal and runs on several computers including the IBM PC.     

Mammalian 3-methyladenine DNA glycosylase protects against the toxicity and clastogenicity of certain chemotherapeutic DNA cross-linking agents

DNA repair status is recognized as an important determinant of the clinical efficacy of cancer chemotherapy. To assess the role that a mammalian DNA glycosylase plays in modulating the toxicity and clastogenicity of the chemotherapeutic DNA cross-linking alkylating agents, we compared the sensitivity of wild-type murine cells to that of isogenic cells bearing homozygous null mutations in the 3-methyladenine DNA glycosylase gene (Aag). We show that Aag protects against the toxic and clastogenic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea and mitomycin C (MMC), as measured by cell killing, sister chromatid exchange, and chromosome aberrations. This protection is accompanied by suppression of apoptosis and a slightly reduced p53 response. Our results identify 3-methyladenine DNA glycosylase-initiated base excision repair as a potentially important determinant of the clinical efficacy and, possibly, the carcinogenicity of these widely used chemotherapeutic agents. However, Aag does not contribute significantly to protection against the toxic and clastogenic effects of several chemotherapeutic nitrogen mustards (namely, mechlorethamine, melphalan, and chlorambucil), at least in the mouse embryonic stem cells used here. We also compare the Aag null phenotype with the Fanconi anemia phenotype, a human disorder characterized by cellular hypersensitivity to DNA cross-linking agents, including MMC. Although Aag null cells are sensitive to MMC-induced growth delay and cell cycle arrest, their sensitivity is modest compared to that of Fanconi anemia cells.     

Gate oxide leakage due to temperature accelerated degradation under plasma charging conditions

Plasma-induced gate charging and resulting damage to the gate oxide during fabrication of submicron devices becomes a serious yield and reliability concern, especially when oxide thickness and device dimensions shrink to the nanoscale region. In this paper experimental results from plasma damaged submicron MOS transistors, namely low-level gate leakage and degraded charge-to-breakdown characteristics, are analyzed with respect to conditions of electrical stress. It is demonstrated that wafer temperature is a crucial parameter for charging-induced oxide degradation due to plasma processing. Laboratory experiments simulating plasma charging showed that low-level oxide leakage is the result of oxide breakdown after electrical wear-out under low-level injection conditions. High field stress, performed at 150°C, confirmed that elevated temperature during plasma processing strongly accelerates oxide degradation and even at low-level stress leads to the effects observed in plasma damaged devices.