Dynamic Behaviour of Rotor Roller Bearing System with Bearing Defects

Rotating machinery is becoming faster and light weight due to the advanced technologies made in engineering and materials sciences. It is required to run them for longer periods of time. The detection, location and analysis of faults are highly recommended in highly reliable operations. The high speed rotor bearing system often shows unpredictable dynamic response due to manufacturing defects. As it is not possible to produce perfect surface or contour even with the best available machine tools so imperfection such as surface waviness in the rolling element and races developed during manufacturing process cannot be avoided. The radial and axial clearance provided in the design of bearings to compensate for thermal expansion, can also be a source of vibrations and introduce nonlinearity in the dynamic system. Using vibration analysis, the condition of a machine can be periodically monitored. In this study, dynamic behaviour of rotor roller bearing system with bearing defects, like radial clearance, declining of roller and localized inner race defect. The nonlinear bearing forces of a roller bearing under two dimensional loads and develops 2-DOF dynamics equation of a rotor-roller bearing system. The contacts between the rolling elements and the races are considered as non-linear springs, whose stiffness is obtained by using Hertzian elastic contact deformation theory. The system shows the nonlinear characteristics under dynamic condition. The equation of motion in radial and axial condition is obtained for shaft and rolling elements and they are solving by numerical integration technique Newmark-? method. Vibration of rolling element in the radial direction is analyzed time and frequency domain. Characteristics defects frequency and their components can be seen in the frequency spectrum of roller element vibration. As the clearance increases the dynamic behaviour becomes complicated with the number and the scale of instable region becoming larger

Seed mucilage effect on water uptake and germination in five species from the hyper-arid Arabian desert

© 2016 Elsevier Ltd. The effect of mucilage removal on germination percentages and velocity (Timson\u27s index) was studied for five Arabian desert species (Lavandula subnuda, Lepidium aucheri, Boerhavia elegans, Plantago ciliata and Plantago amplexicaulis) under two photoperiods (0, 12 h of light daily) and three thermoperiods (night/day temperatures of 15/25, 20/30 and 25/35 °C). Mucilage presence increased water uptake in all species, and was associated with higher germination percentages in L. subnuda, B. elegans and P. ciliata, but not L. aucheri and P. amplexicaulis. Germination velocity response to mucilage presence was mixed, being increased in L. aucheri and reduced in L. subnuda. In all species germination was increased by light and affected by temperature, but species\u27 response to temperature varied. Interactions of mucilage presence with temperature were more frequent than with light. Seed mucilage plays a role in germination regulation of these species, but the effects are species-specific. Mucilage presence inhibited germination at lower temperatures in L. subnuda and P. ciliata, at higher temperatures in B. elegans, and increased germination velocity but not percentage in L. aucheri. It had no influence on germination in P. amplexicaulis. The differences detected demonstrate as perhaps mucilage in seeds of some desert species serves also to other ecological purposes

Foliage colour influence on seed germination of Bienertia cycloptera in Arabian deserts

Bienertia cycloptera (Chenopodiaceae) produces two types of leaf foliage colour (reddish and yellowish). In order to determine the role of leaf colour variation in regulating the germination characteristics and salinity tolerance during germination, a study was conducted on seeds collected from plants of both colours. Seeds with and without pulp were germinated under two illumination conditions (12-h light photoperiod and continuous dark), three alternating temperature regimes (15/25°C, 20/30°C and 25/35°C), and several salinity levels at 20/30°C. Germination percentage was significantly higher for seeds without pulp as compared to the seeds with pulp. The response of B. cycloptera seeds to salinity depended on the leaf colour. Thus, the seeds collected from reddish coloured plants were able to tolerate higher salinity compared to those of yellowish coloured plant. The germination recovery results indicate that the seeds from both coloured plants could remain viable in saline condition and they will be able to germinate once the salinity level are decreased by rain. The production of different foliage colours by B. cycloptera seems to be an adaptative strategy which increases the possibility for establishment in unpredictable environments by producing seeds with different germination requirements and salinity tolerance

Intra-plant Inflorescence and Seed Heterogeneity of Deverra triradiata (Apiaceae)

© 2020, The National Academy of Sciences, India. Deverra triradiata is an aromatic perennial shrub distributed in coastal arid regions. In the present study, we tested the effect of umbel order on seed weight, germination, and germination requirements for temperature and light. Germination rate was strongly affected by umbel order and photoperiod but not by thermoperiod. Seed mass also declined substantially with umbel order. Results suggest that resource allocation within the inflorescence enables plants to produce seeds with a range of germination characteristics

Seed maturation time influences the germination requirements of perennial grasses in desert climate of Arabian Gulf

AbstractQatar has a dry, subtropical desert climate, with minimum annual rainfall and intensely hot and humid summers. Using indigenous grass, those adapted to local conditions have the potential to be used for fodder and can also be used for restoration or rehabilitation of degraded rangelands. Chloris virgata, Coelachyrum brevifolium and Cenchrus ciliaris bloom twice a year from April to May (summer) and September to October (winter) under the nursery condition. Therefore, it is important to understand, how seeds produced in different seasons affect the dormancy as well as germination of these species. Seeds of C. virgata, C. brevifolium and C. ciliaris, three desert grasses, were collected from the plants growing on Shahniya nursery in two different seasons, summer (May) and winter (October). The seeds collected in May (summer) were stored up to winter. However seeds collected in October (winter) were immediately used for experiment. We compared the germination potential of seeds that matured in different season at different alternating temperatures at 15/25, 20/30 and 25/35°C. Lower temperatures correspond to the dark period, while higher temperatures reflect the light period. Seeds collected in summer season (old seeds) were heavier as compared to seeds collected in winter season (new seeds). Winter seeds of C. virgata seem to be dormant, while summer seeds, germinated well in all the tested temperature regimes. However, C. ciliaris seeds showed opposite trends

Dimorphic fruit colour is associated with differences in germination of calligonum comosum

© 2019, Canadian Science Publishing. Calligonum comosum L’Hér is a perennial evergreen shrub that produces dimorphic fruits of distinctly yellow or red colour. The species is found on sand dunes of the Middle East, is valued as a highly palatable livestock feed that survives extreme drought, and is suitable for desert restoration of non-saline sandy soils. The association of fruit colour with germination was assessed in laboratory conditions under two temperature (15/20 and 20/30 °C) and two light (0 and 12 h per day) treatments. Additionally, the association of fruit colour with emergence and seedling growth up to 90 days from sowing was assessed in shade house conditions. Germination percentage in the laboratory was the only variable that exhibited significant variation by seed colour. Germination was highest for red seeds grown in the dark at the higher temperature but the influence of seed colour on germination was not repeated in the shade house study. The dimorphic fruit colour of C. comosum is thus associated with differing germination rates, but further study is needed to determine whether morphs employ differing recruitment strategies

Perianth colour dimorphism is related to germination properties and salinity tolerance in Salsola vermiculata in the Arabian deserts

© 2017 The Authors We investigated the dimorphic perianth colour of Salsola vermiculata and its association with seed germination percentage, interactions with temperature, light, salinity and recovery from prior salinity exposure. Seeds with and without pink and yellow perianth were incubated at three thermal regimes, two photoperiods, and five salinity levels. Germination recovery after salinity exposure was observed on seeds that failed to germinate during the salinity study. The germination percentage and rate were significantly related to the perianth colour, the presence of perianth wings, thermal regimes and photoperiod. The presence of a perianth wing significantly reduced germination percentage and germination rate in both the pink and the yellow morph, but the yellow morph exhibited a higher germination percentage. Perianth wing removal increased germination in saline conditions. With the perianth removed, germination recovery was higher for the pink morph than for the yellow one. We suggest that by providing two different strategies for balancing germination with dormancy during favourable conditions, the presence of two morphs makes S. vermiculata more successful in highly unpredictable desert environments

Multicultural, Heritage and Learner Identities in Complementary Schools

In this paper we look at three identity positions salient in research of young people studying in complementary schools in Leicester, a large linguistically and ethnically diverse city in the East Midlands, England. Our discussion of identity focuses on three identity positions: multicultural, heritage and learner. The first two of these are linked to discussions on ethnicity as a social category. We explore the fluidity and stability of ethnicity as a social description in interview transcripts of young people at complementary schools. In addition, the paper explores another, more emergent identity salient in the two schools, that of ‘learner identity’. The research can be characterised as adopting a linguistic ethnographic approach using a team of ethnographers. Data was collected for 20 weeks by four researchers and consists of fieldnotes, interviews and audio recordings of classroom interactions. We consider the importance of ambiguity and certainty in students’ conceptualisation of themselves around ethnicity and linguistic diversity and look at the institutional role complementary schools play in the production of these and successful learner identities. We explore how complementary schools privilege and encourage these particular identity positionings in their endorsement of flexible bilingualism. Overall, we argue that complementary schools allowed the children a safe haven for exploring ethnic and linguistic identities while producing opportunities for performing successful learner identity