Heat absorption properties of ground material for solar chimney power plants

One of the major challenges to the widespread application of the solar chimney power plant is its low-power conversion efficiency because of the three technological processes involved. The chimney efficiency is difficult to improve, and thus enhancing the collector or turbine performance can considerably improve the total plant efficiency. This work focused on enhancing the energy conversion efficiency of the collector and also extending the operation time using a heat storage medium. The solar to thermal conversion and thermal storage capabilities of six ground materials that are potentially available in Malaysia were studied experimentally and numerically. The experimental model was designed such that the six materials were exposed to the same operation boundary conditions. The numerical studies were conducted using ANSYS software, where the geometrical models were developed and simulated using FLUENT for the fluid flow and energy/thermal field studies. The selected ground materials were ceramic, black stones, sawdust, dark-green painted wood, sand, and pebbles. The simulation and experimental results are in good agreement in terms of air stream velocity and energy conversion efficiency. The results showed that the different materials have different heat storage capacities, and that ceramics extend the operation with improved efficiency until nighttime. The results also showed that ceramic and black stones have better performance than the other materials. However, black stones are recommended as the absorbing material for solar chimney power plants in Malaysia and regional countries because they are readily available

Transaction Cost and the Small Stock Puzzle: The Impact of Outliers in the NYSE, 1970-2000

In this article we study the effect of transaction costs on asset prices. We examine the characteristics of the actual extreme performers (Outliers), their stock prices, and transactions cost and link them to firm size. The analyses is based on data from the COMPUSTAT tapes with valid data for the bid and ask prices and the CRSP samples of all firms listed in the NYSE, AMEX, and NASDAQ during the period 1970-2000. Once transaction costs are taken into account, no positive abnormal returns are found for small firms. Transaction costs account fully for both the abnormality and the recent size discountability.Outliers, Transaction Costs, Size discount, NYSE, AMEX, NASDAQ

Estimation of Reminant Gold Resources of Old Underground Workings by Indicator Approach – A Case Study

The lack of geological control and old underground development at AngloGold Ashanti (Bibiani mine) in Ghana was a major setback for the conventional methods of resource estimation to produce accurate estimates of the deposit. Consequently, inverse distance weighting of indicator variables were used. This estimation approach, however, overestimated the boundaries of the old underground workings (voids) into inappropriate areas of the resource model and thereby caused significant underestimation of ore tonnage and overestimation of grade. This paper highlights the study that re-evaluated the Bibiani deposit using indicator kriging. The results of re-evaluated reserves compared well with actual production figures in terms of tonnes, grade and stoping volum

Estimation of Gold Resources from Exploration Drilling using Conditional Simulation - A Case Study

Estimation of gold resources from exploration drilling has passed through various phases and methods at the AngloGold Ashanti, Iduapriem Mine Limited, Tarkwa in Ghana. From the use of Inverse Distance Weighting (IDW) to the use of Ordinary Kriging (OK) and currently the use of Uniform Conditioning (UC). This is all with a view of improving the estimations before the grade control drilling is undertaken for mine planning and subsequent mining. This paper compares the estimates obtained from exploration drilling using conditional simulation with the results from ordinary kriging and actual production figures on a block by block basis for areas that have already been mined in the deposit. The results show that estimates using conditional simulation and ordinary kriging are similar; and, both appear to underestimate the resources

Comparison of Ordinary Kriging and Multiple Indicator Kriging Estimates of Asuadai Deposit at Adansi Gold Ghana Limited

Adansi Gold Ghana Ltd has taken over from the then Resolute Amansie Ltd and has three main historical deposits: Nkran, Adubia, Abore, and a new deposit, Asuadai. The company now wants to evaluate the resources at Asuadai which is about 7.5 km from Nkran deposit where Ordinary Kriging (OK) method had been used for estimation. Results of the estimation showed a consistent underestimation of tonnage and grade. Linear estimation models such as OK often produce good estimates but may encounter problems estimating recoverable reserves in cases where the distribution of samples is highly skewed. Multiple Indicator Kriging (MIK) is one of the popular non-linear methods that can handle skewed distribution such as that for gold grades, and addresses some of the deficiencies of the linear methods. This paper compares the estimation results obtained by using MIK and OK for the Asuadai deposit and establishes that MIK presents a better estimate than the OK, and recommends that MIK be used to estimate the gold resources of the Asuadai deposit and other deposits with similar geological settings.Keywords: Indicator Kriging, Ordinary Kriging, Variography, Gold, Outlie

Mycoplasma pneumoniae Pneumonia with Worsening Pleural Effusion Despite Treatment with Appropriate Antimicrobials: Case report

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia. As M. pneumoniae pneumonia is usually a mild and self-limiting disease, complications such as pleural effusion occur only rarely. We report a 22-year-old woman who presented to the Emergency Medicine Department of the Sultan Qaboos University Hospital, Muscat, Oman, in 2017 with an eight-day history of fever associated with coughing, chills and rigors. She was diagnosed with M. pneumoniae pneumonia, but subsequently developed pleural effusion which worsened despite treatment with appropriate antimicrobials. The pleural effusion required drainage, which revealed that it was of the more severe exudative type. Following drainage, the patient improved dramatically. She was discharged and advised to continue taking antibiotics.Keywords: Mycoplasma pneumoniae; Bacterial Pneumonia; Pleural Effusion; Antimicrobial Agents; Drainage; Case Report; Oman

Fertiliser credit and agroecological use of organic soil amendments in northern Ghana

Contemporary African agricultural policy embodies the African Green Revolution’s drive towards modernisation and commercialisation. Agroecologists have criticised this movement on ecological, social and political grounds. Northern Ghanaian fertiliser credit schemes provide a good example through which these critiques can be examined in a context where agricultural policy reflects the African Green Revolution’s ideals. This study aimed to determine the relationship of such credit schemes to farmers’ use of organic amendments, elucidate other factors related to organic amendment use, and comment on the relevance of this modernisation policy and its relationship to agroecology. A first research phase employed semi-structured key informant interviews. Qualitative data from these informed construction of a semi-structured questionnaire that was used in a survey of 205 farmers. Multistage sampling purposively identified five villages and selected farmers within who had joined government and donor-funded fertiliser credit schemes. The use of organic and inorganic amendments was compared to that of peers who had not taken part in such schemes. Quantitative data were used in binomial logistic regression, inferential and descriptive statistics. Qualitative data were content analysed. Credit group membership was associated with higher fertiliser application and yield, but had little influence on the extent of commercialisation. Farmers who applied organic amendments were 40% less likely to belong to a fertiliser credit scheme than not, indicating substitution between organic and inorganic fertilisers. Organic amendments were 40% more likely to be applied to compound farms than outfields and six times more likely to be applied by household heads than other household members. However, household heads also preferentially joined credit groups. This was part of an agroecological soil fertility management strategy. Household heads appreciated the soil moisture retention properties of organic amendments, and applied them to compound farms to reduce risk to their household food supply in a semi-arid environment. They simultaneously accessed fertiliser to enhance this household provisioning strategy. They appreciated the increased yields this achieved, yet complained that the repayment terms of credit schemes were unfair, fertiliser did not enhance yields in dry conditions and fertilisers were supplied late. Farmers’ use of credited fertiliser alongside their existing agroecological strategy is helpful to the extent that it raises yields, yet is problematic in that it conflicts with risk-reduction strategies based on organics. There is some potential for modernised and agroecological management paradigms to coexist. For fertiliser credit to play a role in this, schemes must use fairer repayment terms and involve a focus on simultaneous use of organic amendments.Keywords: Agroecology, compost, Ghana, fertiliser credit, Soil Fertility Management, maiz

Calibrating PIRLS Test in Sultanate of Oman Using Item Response Theory

The study aimed to calibrate Oman data of the PIRLS test using the graded response model and to examine the psychometric properties of it, as well as identify the fit and unfit of its items. PIRLS2011 test booklets were used, which consisted of 146 test items (74 dichotomous and 72 polytomous). Items were divided into 13 booklets; each with two blocks (one literary and one informational). PIRLS test booklets were administered to 13 groups of fourth grade students in Sultanate of Oman with a total sample of 10394 students. Assumptions of IRT (unidimensionality and local independence) were examined and supported. Also, item fit was examined and supported using Samejima’s graded response model. The data was analyzed by Multilog7.03 program to estimate both item and ability parameters. Results indicated that the assumptions of IRT were proved. Also, IRT analysis revealed that 8 items showed unfit which represents only 5% of the test items. So, this result confirms that the test has good psychometric properties under the IRT

The Trajectory of Lost Mercury in Artisanal and Small Scale Gold Extraction in Ghana

AbstractThe Artisanal and Small Scale Mining (ASSM) industry is of great importance to the Ghanaian economy. It provides employment for the teeming youth directly and indirectly and produces gold for the local goldsmiths, among other benefits. Concomitant to their operations, ASSM causes significant environmental pollution with chemicals, predominantly mercury. Mercury is used by small scale miners in the processing of ore mined because it is relatively easy to use and readily available. The laws regulating small scale gold mining in Ghana do not forbid the use of mercury even though there is a loud outcry against the use of mercury in small scale gold mining. The operations have resulted in the discharge of mercury into the environment indiscriminately. No attempt is made by the miners to recover lost mercury hence all of it is lost to the environment. This paper presents the findings of a study that investigated the trajectory of the mercury lost into the environment. The results showed that 2 g of mercury was lost to the environment for every gram of gold recovered through ASSM; 39% of it was lost to the atmosphere due to roasting of the amalgam whilst the remaining 61% was lost into water and spillage onto the ground. Keywords: Mercury, Atmosphere, Pollution, Environment, Socio-economi