Research requirements to reduce maintenance costs of civil helicopters

The maintenance problems faced by the operators of civil helicopters that result in high costs are documented. Existing technology that can be applied to reduce maintenance costs and research that should be carried out were identified. Good design practice and application of existing technology were described as having a significant impact on reducing maintenance costs immediately. The research and development that have potential for long range reduction of maintenance costs are presented

Genotype x environment interaction and stability analysis for yield and yield related traits of Kabuli-type Chickpea (Cicer arietinum L.) in Ethiopia

Chickpea is the major pulse crop cultivated in Ethiopia. However, its production is constrained due to genotype instability and environmental variability. This research was carried out to examine the magnitude of environmental effect on yield of chickpea genotypes and to investigate the stability and adaptability of genotypes under different agro-ecologies. Seventeen (17) genotypes were evaluated in randomized complete block design (RCBD) with four replications in five locations. Various stability indices were used to assess stability and genotype by environment performances. Combined analysis of variance (ANOVA) for yield and yield components revealed highly significant (P≤0.01) differences for genotypes, environments and their interaction. The significant interaction showed genotypes respond differently across environments. At Akaki, Chefe Donsa, Debre Zeit, Dembia and Haramaya, top performing genotype were DZ-2012-CK-0001 (2933 kg/ha), Arerti (3219 kg/ha), Arerti (3560 kg/ha) DZ-2012-CK-0013 (2675 kg/ha) and Arerti (2019 kg/ha), respectively. The first two PCs explained 74.45% of the variance. Based on ASV value, DZ-2012-CK-0002 were most stable genotypes. As per AMMI biplot, Arerti and DZ-10-4 were most widely adapted genotypes. Dembia and Haramaya were most discriminative environments for genotypes. Debre Zeit and Chefe Donsa were favorable environment for genotype. Genotypes DZ-2012-CK-0004, DZ-2012-CK-0010, DZ-2012-CK-0013, DZ-2012-CK-0007 and DZ-10-4 are recommendable to Akaki, Chefe Donsa, Debre Zeit, Dembia and Haramya, respectively.Keywords: AMMI, ASV, clustering, phenologic traits, Kabuli, univariate statistics.Abbreviation: E, Environments; G, genotypes; RCBD, randomized complete block design.

Computer simulation results for PCM/PM/NRZ receivers in nonideal channels

This article studies, by computer simulations, the performance of deep-space telemetry signals that employ the pulse code modulation/phase modulation (PCM/PM) technique, using nonreturn-to-zero data, under the separate and combined effects of unbalanced data, data asymmetry, and a band-limited channel. The study is based on measuring the symbol error rate performance and comparing the results to the theoretical results presented in previous articles. Only the effects of imperfect carrier tracking due to an imperfect data stream are considered. The presence of an imperfect data stream (unbalanced and/or asymmetric) produces undesirable spectral components at the carrier frequency, creating an imperfect carrier reference that will degrade the performance of the telemetry system. Further disturbance to the carrier reference is caused by the intersymbol interference created by the band-limited channel

Ram pressure stripping of the cool core of the Ophiuchus Cluster

(abridged) We report results from a Chandra study of the central regions of the nearby, X-ray bright, Ophiuchus Cluster (z = 0.03), the second-brightest cluster in the sky. Our study reveals a dramatic, close-up view of the stripping and potential destruction of a cool core within a rich cluster. The X-ray emission from the Ophiuchus Cluster core exhibits a comet-like morphology extending to the north, driven by merging activity, indicative of ram-pressure stripping caused by rapid motion through the ambient cluster gas. A cold front at the southern edge implies a velocity of 1000$\pm$200 km/s (M~0.6). The X-ray emission from the cluster core is sharply peaked. As previously noted, the peak is offset by 4 arcsec (~2 kpc) from the optical center of the associated cD galaxy, indicating that ram pressure has slowed the core, allowing the relatively collisionless stars and dark matter to carry on ahead. The cluster exhibits the strongest central temperature gradient of any massive cluster observed to date: the temperature rises from 0.7 keV within 1 kpc of the brightness peak, to 10 keV by 30 kpc. A strong metallicity gradient is also observed within the same region. This supports a picture in which the outer parts of the cool core have been stripped by ram-pressure due to its rapid motion. The cooling time of the innermost gas is very short, ~5$\times10^7$ yrs. Within the central 10 kpc radius, multiple small-scale fronts and a complex thermodynamic structure are observed, indicating significant motions. Beyond the central 50 kpc, and out to a radius ~150 kpc, the cluster appears relatively isothermal and has near constant metallicity. The exception is a large, coherent ridge of enhanced metallicity observed to trail the cool core, and which is likely to have been stripped from it.Comment: Accepted to MNRAS. 11 pages, 9 figure

Challenges in the Use of Web Technology on Knowledge-sharing Behavior of Academic Staffs: The Case of Ethiopian Higher Education

Universities around the world have faced challenges in maintaining face-to-face knowledge sharing. Knowledge sharing through web technology is an essential solution for all universities. However, web technology-based knowledge-sharing practices in developing countries such as Ethiopia face many challenges. This study examines the factors that challenge the use of web technologies for knowledge-sharing practices by academic staff and presents recommendations to improve the current environment in Ethiopian public universities. The study employed semi-structured interviews with 30 respondents and analyzed the data using Nvivo qualitative data analysis software. The results revealed that lack of technical skill, lack of systems integrated into teaching-learning practice, lack of awareness, lack of an appropriate reward system, lack of commitment from top management, lack of a knowledge-sharing policy, and a lack of knowledge mapping are among the identified challenges hindering the knowledge-sharing practice of academic staff. These findings provide evidence of knowledge-sharing practices and give insights regarding enhancing knowledge-sharing practices within higher education. In addition, this study also contributes to the body of knowledge about the challenges of knowledge sharing. The findings will benefit academic staff, university administrations, and higher education institutions. Future studies could consider replicating this study from a quantitative method perspective with a larger sample size focused on Ethiopian public higher education. This study could also be considered for replication from the perspective of private higher education

A high-frequency study of the Sunyaev-Zel'dovich effect morphology in galaxy clusters

High-frequency, high-resolution imaging of the Sunyaev-Zel'dovich (SZ) effect is an important technique to study the complex structures of the atmospheres of merging galaxy clusters. Such observations are sensitive to the details of the electron spectrum. We show that the morphology of the SZ intensity maps in simulated galaxy clusters observed at 345 GHz, 600 GHz, and 857 GHz are significantly different because of SZ relativistic corrections. These differences can be revealed by high-resolution imaging instruments. We calculate relativistically corrected SZ intensity maps of a simulated, massive, merging galaxy cluster and of the massive, merging clusters 1E0657-558 (the Bullet Cluster) and Abell 2219. The morphologies of the SZ intensity maps are remarkably different between 345 GHz and 857 GHz for each merging cluster. We show that high-resolution imaging observations of the SZ intensity maps at these frequencies, obtainable with the LABOCA and HERSCHEL-SPIRE instruments, allow to fully exploit the astrophysical relevance of the predicted SZ morphological effect.Comment: 9 pages, 14 figures, accepted for publication in MNRA

A high-resolution study of the X-ray emission and Sunyaev–Zel'dovich effect in the Bullet cluster (1E 0657−56)

High-resolution imaging of the Sunyaev–Zel'dovich (SZ) effect opens new possibilities for testing the presence of various high-energy particle populations in clusters of galaxies. A detailed X-ray analysis of the ‘Bullet cluster’ (1E 0657−56) with Chandra has revealed the presence of additional X-ray spectral components beyond a simple, single-temperature plasma in its X-ray spectra. X-ray methods alone are insufficient to elucidate the origins of these spectral components. We show that the morphology and magnitude of the SZ effect at high frequencies are critically dependent upon the mechanism by which the additional X-ray spectra are created. We examine the differences between the predicted SZ effect emission maps at 600 GHz assuming the X-ray spectra are composed of thermal gas with a steep power-law index component and also thermal gas with a significant contribution of strongly heated gas. A two-temperature model with a hot (kT ≃ 30–40 keV) second component is the most consistent with existing SZ data at high frequencies. However, significant morphological differences remain. High-angular-resolution SZ intensity maps at high frequencies in combination with deep X-ray data provide a new window into understanding particle energization processes in the hottest, massive merging galaxy clusters