Effects of urbanization on climate of Nairobi City

Nairobi, Kenya’s capital city, is one of the fastest growing cities in the world. There is necessity to investigate the effects of urbanization on the climate of the city. This study looked into the long-term urban modification of annual weather conditions by studying the relation between the weather elements and urbanization indicators. The results showed that Nairobi city is growing at a high rate as evidenced by a population growth of about 6.9% annually.The temperature was found to have been modified by urbanization such that there is a warming trend; the stations that were more urban recorded a high rate of temperature increase as compared to the less urban stations revealing the formation of an urban heat island. Rainfall trend was similarly found to be increasing with time; however, the change in humidity was found to be insignificant. It further revealed that some of the long term changes in climate over the city were due to changes in surface and atmospheric characteristics of the city such as surface roughness, smoke and destruction of vegetation cover, as a consequence of urbanization. The environmental implications such as urban surface temperature modification on human comfort are significant. It was suggested that in order to control these trends and to obtain more favourable and healthy climatic conditions, the acreage of green areas must be increased. Incorporation of the findings in the future planning of the city is hence recommended

Insecurity for compact surfaces of positive genus

A pair of points in a riemannian manifold $M$ is secure if the geodesics between the points can be blocked by a finite number of point obstacles; otherwise the pair of points is insecure. A manifold is secure if all pairs of points in $M$ are secure. A manifold is insecure if there exists an insecure point pair, and totally insecure if all point pairs are insecure. Compact, flat manifolds are secure. A standing conjecture says that these are the only secure, compact riemannian manifolds. We prove this for surfaces of genus greater than zero. We also prove that a closed surface of genus greater than one with any riemannian metric and a closed surface of genus one with generic metric are totally insecure.Comment: 37 pages, 11 figure

Seasonal rainfall forecasting using the multi - model ensemble technique over the greater Horn of Africa

This study evaluated the skill of forecasting seasonal rainfall over the Greater Horn of Africa (GHA) using Ensemble Model Technique from a cluster of four General Circulation Climate Models (GCMs) from Global Producing Centers (GPCs). The spatial distribution of rainfall anomalies of the observed models output during extreme events showed that the ensemble model was able to simulate El-Niño (1997) and La-Niña (2000) years. The ensemble models did not show good skill in capturing the magnitude of the extreme events. The skill of the ensemble model was higher than that for the member models in terms of its ability to capture the rainfall peaks during the El-Niño Southern Oscillation (ENSO) phenomena. The analysis for the correlation coefficients showed higher values for the ensemble model output than for the individual models over the Equatorial region with the stations in the northern and southern sectors of the GHA comparatively giving low skill. The ensemble modeling technique significantly improved the skill of forecasting, including the sectors where individual models had low skill. In general, the skill of the models was relatively higher during the onset of the ENSO event and became low towards the decaying phase of the ENSO period. Generally, the study has shown that the ensemble seasonal forecasting significantly adds skill to the forecasts especially for October-December (OND) rainy seasons. From the study, ensemble seasonal forecasting significantly adds skill to the forecasts over the region. Blending dynamical ensemble forecasts with statistical forecast currently being produced during Regional Climate Outlook Forums (RCOFs) would add value to seasonal forecasts. This significantly reduces the impacts and damages associated with climate extremes over the region

Potential of harvesting atmospheric water over urban cities in Kenya

Most urban areas in Kenya are facing water crisis due to rapid population growth, industrialization and climate change. This study investigates potential of harvesting water from fog and air humidity over urban cities in Kenya. Daily air temperature, dew point temperature, wind direction and speed were used. Parameters including atmospheric water vapor pressure, saturated vapor pressure and the absolute and relative humidity of the atmosphere were derived. Air temperatures ranged between 18.2 and 27.6°C in urban areas. Mean annual foggy days was higher at Jomo Kenyatta International Airport (JKIA) with a maximum of 17 foggy days compared to other stations. However, mean annual harvesting days was higher at Moi International Airport (MIA) with a maximum of 350 days. Based on device efficiency of 10%, stations in Nairobi city (JKIA/Dagorretti Corner/Wilson Airport) indicated maximum water harvesting potential of 3.2/1.4/2.9 litres/m2/day in direction d6 (225 -270°) while Kisumu station showed highest potential of harvesting water (2.2 litres/m2/day) in direction d5 (180-225°). In Mombasa, the MIA and Lamu stations showed potential of harvesting 4.4 litres/m2/day and 3.9 litres/m2/day in direction d6 and d5 respectively. Based on monthly distribution of potential monthly water, harvesting from fog and air humidity was classified into either coastal or non-coastal/continental regions. The urban cities in Kenya have high potential of water harvesting from fog and air humidity presenting an alternative sustainable low cost approach to augmenting available fresh water sources and alleviating existing water stress. This will enable achievement of Kenya’s long term development footprint (Vision 2030) and Millennium Development Goals

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 A degrees C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 A degrees C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of gamma aEuro(3) phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 A degrees C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the delta-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe