Cutting carbon-carbon composites by the diamond drills variable cyclic feed

Аннотация. У статті представлено оригінальне вирішення актуальної проблеми підвищення ефективності свердління композиційних матеріалів вуглецевої групи алмазними свердлами за рахунок використання динамічної робочої подачі. Показано, що накладання циклічного низькочастотного навантаження алмазного свердла дозволяє підвищити ефективність і якість обробки, без деструкції та руйнування композиту. На основі аналізу поведінки початкового структурного елементу було оцінено напружений стан зони різання у вуглецевих композиційних матеріалах, при цьому показано, що їх обробка за допомогою алмазних кільцевих свердел є дієвою і ефективною. Застосування змінного циклічного навантаження дозволяє значно зменшити товщину еструктованого шару, який формується самим свердлом, а також зменшити силу різання, особливо при тривалій роботі. Оскільки пило- та шламоутворення грають важливу роль під час свердління, подальші дослідження повинні бути спрямовані на встановлення раціональних параметрів робочого шару інструменту, наявності на ньому порожнин для видалення мікрошламу і пилу за зону обробки.Purpose. The article presents an original solution to the actuality problem of increasing the efficiency of drilling composite materials of the carbon group with diamond drills through the use of a dynamic working feed. It is shown that the application of a cyclic lowfrequency load to a diamond drill makes it possible to increase the efficiency and quality of processing without destroying the composite. Methodology. To solve the problems of determining the rational dynamic load of the drill during the operation, the approach of micro- and macroanalysis of the behavior of the processed material was used. The material itself was represented by an inhomogeneous finite medium, the properties of which are described using the concept of the initial structural element of the material. Results. Based on the analysis of the behavior of the primary structural element, the stress state of the cutting zone in carbon composite materials was estimated, and it was shown that their processing using diamond ring drills is effective and efficient. Originality. The construction of models based on the primary structural element and the establishment of patterns of crack development in an inhomogeneous medium allowed us to obtain an expression for estimating the sizes of sludge particles formed during processing and determined rational processing conditions. Practical value. The use of variable cyclic loading can significantly reduce the thickness of the destructive layer formed by the drill, as well as reduce the cutting force, especially during prolonged use. Since dust and sludge formation play an important role in drilling, further research should be aimed at establishing rational parameters of the working layer of the tool, the presence of cavities on it to remove microsludge and dust from the treatment zone.Аннотация. В статье представлено оригинальное решение актуальной проблемы повышения эффективности сверления композиционных материалов углеродной группы алмазными сверлами за счет использования динамической рабочей подачи. Показано, что приложение циклической низкочастотной нагрузки к алмазному сверлу позволяет повысить эффективность и качество обработки, не разрушая композит. Для решения задач определения рациоанльной динамической нагрузки сверла при выполнении операции использовался подход микро- и макроанализа поведения обрабатываемого материала. Сам материал представляли неоднородной конечной средой, свойства которой описаны с применением понятия начального структурного элемента материала. На основе анализа поведения начального структурного элемента было оценено напряженное состояние зоны резания в углеродных композиционных материалах, при этом показано, что их обработка с помощью алмазных кольцевых сверл является действенной и эффективной. Построение моделей на основе начального структурного элемента и установление закономерностей развития трещин в неоднородной среде позволила получить выражение для оценки размеров образующихся в процессе обработки частиц шлама и установить рациональные условия обработки. Применение изменяемого циклического нагружения позволяет значительно уменьшить толщину разрушающего слоя, формируемого самим свердом, а также уменьшить силу резания, особенно при длительной работе. Поскольку пыле- и шламообразование играют важную роль при сверлении, дальнейшие исследования должны быть направлены на установление рациональных параметров рабочего слоя инструмента, наличия на нем плостей для удаления микрошлама и пыли из зоны обработки

Transformation and analysis of tobacco plant var Petit havana with T-urf13 gene under anther-specific TA29 promoter

T-urf13, a well-documented cms-associated gene from maize, has been shown to render methomyl sensitivity to heterologous systems like rice, yeast and bacteria when expressed constitutively. Since these transgenic plants were fertile, it was hypothesized that T-urf13 gene if expressed in anthers may result in male sterility that could be used for hybrid seed production. Hence, this work was aimed at analysing whether T-urf13 gene when expressed in anthers can result in male sterile plants or requires methomyl treatment to cause male sterility (controllable). This is the first report of transformation of tobacco with T-urf13 gene under anther-specific promoter (TA29) with or without mitochondrial targeting sequence. Most of the transgenic plants obtained were fertile; this was surprising as many male sterile plants were expected as T-urf13 gene is a cms associated gene. Our results suggest that it may not be possible to obtain male sterility by expressing URF13 in the anther by itself or by methomyl application

PPR proteins - orchestrators of organelle RNA metabolism.

Pentatricopeptide repeat (PPR) proteins are important RNA regulators in chloroplasts and mitochondria, aiding in RNA editing, maturation, stabilisation or intron splicing, and in transcription and translation of organellar genes. In this review, we summarise all PPR proteins documented so far in plants and the green alga Chlamydomonas. By further analysis of the known target RNAs from Arabidopsis thaliana PPR proteins, we find that all organellar-encoded complexes are regulated by these proteins, although to differing extents. In particular, the orthologous complexes of NADH dehydrogenase (Complex I) in the mitochondria and NADH dehydrogenase-like (NDH) complex in the chloroplast were the most regulated, with respectively 60 and 28% of all characterised A. thaliana PPR proteins targeting their genes

The steady-state level of mRNA from the Ogura cytoplasmic male sterility locus in Brassica cybrids is determined post-transcriptionally by its 3' region.

We have investigated the control of the expression of three different configurations of the mitochondrial gene orf138, whose expression is correlated with Ogura cytoplasmic male-sterility in rapeseed cybrids. These configurations, termed Nco2.5/13S, Nco2.7/13F and Bam4.8/18S, specific to the 13S (sterile), 13F (fertile) and 18S (sterile) cybrids respectively, have the same 5' regions but different 3' regions. The orf138 transcript from Bam4.8/18S is 10-fold more abundant than the one from Nco2.5/13S, while no orf138 transcript from Nco2.7/13F accumulates. However, transcriptional activity measurements show that the rate of transcription is equivalent for the three configurations. These results strongly suggest that the steady-state level of mRNA from the orf138 locus is determined post-transcriptionally, most likely by its 3' region. To determine the role of these 3' regions, we have established an in vitro decay and processing system. In the presence of rapeseed mitochondrial lysate, synthetic RNAs corresponding to the 3' region of the Nco2.7/13F transcript are, as expected, less stable than RNAs corresponding to the 3' regions of the Nco2.5/13S and Bam4.8/18S transcripts. We have also observed in vitro processing of synthetic RNAs at the sites corresponding to the 3' ends of the natural mRNAs from Nco2.5/13S and Bam4.8/18S. Further analysis of the role of these 3' regions in in vitro RNA stability should help us to better understand post-transcriptional control in plant mitochondria

Agrobacterium-Mediated Gene Transfer Results Mainly in Transgenic Plants Transmitting T-DNA as a Single Mendelian Factor

Forty-four independent transformed tobacco plants were obtained from a cocultivation experiment with Agrobacterium tumefaciens strains carrying modified Ti-plasmids. The transformed plants were either self-fertilized or crossed with nontransformed plants or with other transformed plants. The segregation of a phenotypic marker (kanamycin resistance) in the progenies of these plants was determined. In 40 cases out of 44, the segregation of the kanamycin resistance marker is consistent with Mendelian genetics. Among these 40 clones, 35 contain a single kanamycin resistance locus. The five others segregate two independent resistance loci. In two of the single insert clones, the segregation ratio after selfing indicates that the T-DNA insertion may have caused a recessive lethal mutation