Yohana S - Academia.edu (original) (raw)

Papers by Yohana S

Aquaculture, 2006

To determine the effect of straw size and thawing temperature on cryopreserved sperm quality of y... more To determine the effect of straw size and thawing temperature on cryopreserved sperm quality of yamú (Brycon amazonicus), ovulation and spermiation were induced in sexually mature broodstock using Carp Pituitary Extract. Sperm quality was evaluated by motility, activation time and fertility. Sperm was diluted (1:4) in a solution of glucose, egg yolk and dimethyl sulfoxide (DMSO). Sperm concentration was determined using a Neubauer chamber, and motility evaluated after activation with 1% NaHCO 3 . In the laboratory, four sizes of straw (0.5, 1.8, 2.5 and 4.0 mL) and two thawing temperatures (35°C or 80°C water bath) were evaluated. To assess fertility, 2 g of eggs (ca. 2800) were inseminated with 500 μL of frozen-thawed sperm (ca. 75,000 motile spermatozoa/egg) from each straw thawed at 35°C or 80°C, or 160 μL (ca. 50,000 motile spermatozoa/egg) of fresh sperm. Large scale fertility assays consisted of 40 g eggs inseminated with approximately 5.0 mL (ca. 75,000 motile spermatozoa/egg) of cryopreserved sperm in large straws thawed at 35°C. The fertilization rate was estimated 6 h post-insemination. In all straws, postthaw motility was significantly lower than for fresh sperm (p b 0.05). In laboratory trials, fertility of fresh sperm was higher (67 ± 4%) than frozen-thawed sperm (p b 0.05). For all types of straw, semen thawed at 35°C had a higher percentage of fertility (p b 0.05) than semen thawed at 80°C; sperm cryopreserved in 1.8-, 2.5-and 4.0-mL straws had similar fertility percentages (p N 0.05) to sperm frozen in 0.5-mL straws (48 ± 2%, 51 ± 2%, 52 ± 2% and 54 ± 3%, respectively). In large scale fertilization trials, fresh sperm showed a higher (p b 0.05) fertilization rate (83 ± 1%) than frozen-thawed sperm (68 ± 1%). Although the fertility percentage with fresh sperm was significantly higher than with frozen-thawed sperm in large straws, the fertilization rate of the latter is considered acceptable and profitable in a commercial setting.

Environmental Toxicology and Pharmacology, 2008

To evaluate the toxicity of sodium chloride (NaCl), juveniles and adult Metynnis orinocensis were... more To evaluate the toxicity of sodium chloride (NaCl), juveniles and adult Metynnis orinocensis were exposed for 96 h to 0, 5, 10, 15, 20 or 40 g L −1 of salt. Food intake, behaviour, opercular frequency (OF), mortality, body weight and gill microscopic alterations were evaluated. Behavioural changes were observed in fish exposed to concentrations higher than 10 g L −1 . Juveniles and adults showed a progressive decrease in the OF and body weight. Food intake decreased in concentrations below 15 g L −1 . Juveniles and adults exposed to 15, 20 or 40 g L −1 had 100% mortality. Lamellar congestion, hyperplasia and fusion were the common microscopic alterations at higher concentrations. The gill congestion severity increased with salt concentration. The LC 50 for juveniles and adults were 10.5 g L −1 and 10.8 g L −1 , respectively. These results suggest that salt concentrations lower than 5 g L −1 are safe for preventive and therapeutic practices in Metynnis orinocensis; whereas prolonged exposure higher than 10 g L −1 is deleterious in this species.

Acta Tropica, 2001

In this assessment of cardiovascular risk factors, we examined the prevalence of selected risk fa... more In this assessment of cardiovascular risk factors, we examined the prevalence of selected risk factors according to the World Health Organisation (WHO) CARDIAC Study protocol and compared them with a similar study conducted more than a decade ago. The survey was carried out in Dar es Salaam (D, urban), Handeni (H, rural) and Monduli (Mo, semi-nomadic area). Subjects aged 47-57 were recruited randomly for blood pressure and anthropometrical measurements, 24 h urine collection and blood sampling. A structured questionnaire was used to obtain dietary information. The 1998 survey studied 446 subjects, while the 1987 survey included 496 men and women. The measured weight, body mass index (BMI) and prevalence of obesity (BMI ] 30 kg/m 2 ) increased significantly among women in the 1998 survey in rural Handeni and urban Dar. The overall prevalence of obesity was higher for women in the most recent survey (22.8%, PB 0.0001). Diastolic blood pressure (DBP) was higher in the most recent survey for women in Handeni. The overall prevalence of hypertension (blood pressure \ 160/95 mmHg, or antihypertensive drug use), rose to 41.1% in 1998, (P B0.001) for men and to 38.7% (PB 0.05) for women. The mean total serum cholesterol and prevalence of hypercholesterolaemia increased significantly in the most recent survey in the three studied areas. The overall prevalence of hypercholestrolaemia (serum cholesterol \5.2 mmol/l) was higher in the 1998 survey for both men (21.8%, PB0.0001) and women (54.0%, PB 0.0001). The mean HDL cholesterol increased significantly in the most recent survey, with a significant reduction in the mean atherogenic index, though these were still at higher levels (men 5.8, PB0.0001; women 5.1, PB 0.0001 vs. 1987). A strong positive correlation was observed between blood pressure (SBP and DBP) and body mass index, total serum cholesterol and sodium to potassium ratio. : S 0 0 0 1 -7 0 6 X ( 0 1 ) 0 0 1 3 4 -6 These data suggest that for the past decade there has been an increase in the mean levels and prevalence of selected cardiovascular risk factors in Tanzania.

North American Journal of Aquaculture, 2007

Osmolality, the concentrations of glucose, total cholesterol, and triglyceride, and the concentra... more Osmolality, the concentrations of glucose, total cholesterol, and triglyceride, and the concentrations of ions such as Na þ , Cl À , K þ , and Mg 2þ in the seminal plasma of yamú Brycon amazonicus were evaluated during one reproductive season. Semen quality and the relationship between spermatocrit and sperm concentration were examined over two reproductive seasons. Activation time, spermatocrit, and sperm concentration were significantly higher in 2003 than in 2004. Spermatocrit and sperm concentration showed a significant positive relationship (r 2 ¼ 0.79). During the 2004 reproductive season, a significant variation was observed for spermatocrit and sperm concentration between the initial period (February 15th to March 14th) and the middle and final periods (March 15th to April 14th and April 15th to May 14th, respectively). Neither the ion concentrations nor the glucose and cholesterol concentrations varied between any periods of the reproductive season. Osmolality and triglyceride concentrations showed significant variations between periods during the reproductive season.

Chemosphere, 2004

Residues of five pesticides in surface water were surveyed during 2001 and 2003 in the Traiguén r... more Residues of five pesticides in surface water were surveyed during 2001 and 2003 in the Traiguén river basin in Southern Chile. Simazine, hexazinone, 2,4-D, picloram herbicides and carbendazim fungicide were selected through a pesticide risk classification index. Six sampling stations along the river were set up based on agricultural and forestry land use. The water sampling was carried out before and after the pesticide application periods and in correspondence to some rain events. Pesticides were analyzed by HPLC with DAD detection in a multiresidue analysis. During 2001, in the first sampling campaign (March), the highest concentrations of pesticides were 3.0 lg l À1 for simazine and hexazinone and 1.8 lg l À1 for carbendazim. In the second sampling (September), the highest concentration were 9.7 lg l À1 for 2,4-D, 0.3 lg l À1 for picloram and 0.4 lg l À1 for carbendazim. In the last sampling period (December), samples indicated contamination with carbendazim fungicide at levels of up to 1.2 lg l À1 . In sampling carried out on May 2003, no pesticides were detected. In October 2003, the highest concentrations of pesticides were 4.5 lg l À1 for carbendazim and 2.9 lg l À1 for 2,4-D. Data are discussed in function of land use and application periods of the products, showing a clear seasonal pattern pollution in the Traiguén river. Risk assessment for these pesticides was calculated by using a risk quotient (RQ = PNEC/PEC). For picloram the calculated RQ < was 0, which indicates that no adverse effects may occur due to the exposure to this herbicide in the Traiguén river basin. For 2,4-D, simazine, hexazinone, carbendazim RQ > 1, meaning that adverse effects could occur and it is necessary to reduce pesticide exposure in surface waters. It is recommended to continue with a pesticide monitoring program and the implementation of ecotoxicological testing with local and standardized species in order to consider the probability of effects occurrence, with less uncertainty. Thus, it will be more feasible to make some recommendations to regulatory agencies regarding the pesticide use.

Comparative Biochemistry and Physiology C-toxicology & Pharmacology, 2011

Adult zebrafish (Danio rerio) were exposed to 0 (control), 0.16 or 0.48 μg/L of the insecticide, ... more Adult zebrafish (Danio rerio) were exposed to 0 (control), 0.16 or 0.48 μg/L of the insecticide, endosulfan, for 28 days. Haematology, whole body ions, thiobarbituric acid reactive substances (TBARS), Na + K + -ATPase, organ histology and reproduction were assessed in adults. The resulting offspring were examined for latent effects on development (heart rate and morphometrics). On day 14, adult fish exposed to 0.16 μg/L endosulfan showed significantly lower red blood cell counts than those exposed to 0.48 μg/L endosulfan; adult fish exposed to 0.16 ug/L also showed elevated TBARS compared to controls. Both concentrations of endosulfan caused a 4.0 fold increase in Na + K + -ATPase activity compared to controls (ANOVA, p b 0.05). On day 14, the livers of fish exposed to endosulfan had fewer, enlarged hepatocytes, with cell diameters greater than the controls (ANOVA, p b 0.05). Morphological alterations in the progeny of fish exposed to endosulfan were observed. Heart beat frequency was significantly lower in larvae from exposed adults to 0.16 μg/L compared to the control (ANOVA, p b 0.05). These findings show that sublethal exposure to endosulfan causes adverse sublethal effects in adult D. rerio, and effects on the development of their offspring.

 Today's global environment has presented some new challenges for project managers. Technical pr... more  Today's global environment has presented some new challenges for project managers. Technical programs today may involve a systems group in Phoenix, a software group in Bombay, and a manufacturer in Beijing. The mixture of cultural, political, and legal issues has added a new level of complexity to the already difficult role of a technical project manager. This paper is aimed at addressing the issues faced by today's global team leaders. It begins with a review of concepts and terms in international organizational behavior. It then explores different scenarios and offers a systematic, practical approach to global project management. The perspectives are taken from engineering leaders across Europe, Asia, and North America. The paper is drawn on the author's personal international business experiences as well as successful practices of other industry professionals. At the conclusion the reader will have a good understanding of how to approach and manage a global project successfully.

Annals of Occupational Hygiene, 2005

Labour-intensive mines are numerous in several developing countries, but dust exposure in such mi... more Labour-intensive mines are numerous in several developing countries, but dust exposure in such mines has not been adequately characterized. The aim of this study was to identify and quantify the determinants of respirable dust and quartz exposure among underground coal mine workers in Tanzania. Personal respirable dust samples (n = 134) were collected from 90 underground workers in June-August 2003 and July-August 2004. The development team had higher exposure to respirable dust and quartz (geometric means 1.80 and 0.073 mg m À3 , respectively) than the mining team (0.47 and 0.013 mg m À3 ), the underground transport team (0.14 and 0.006 mg m À3 ) and the underground maintenance team (0.58 and 0.016 mg m À3 ). The percentages of samples above the threshold limit values (TLVs) of 0.9 mg m À3 for respirable bituminous coal dust and 0.05 mg m À3 for respirable quartz, respectively, were higher in the development team (55 and 47%) than in the mining team (20 and 9%). No sample for the underground transport team exceeded the TLV. Drilling in the development was the work task associated with the highest exposure to respirable dust and quartz (17.37 and 0.611 mg m À3 , respectively). Exposure models were constructed using multiple regression model analysis, with log-transformed data on either respirable dust or quartz as the dependent variable and tasks performed as the independent variables. The models for the development section showed that blasting and pneumatic drilling times were major determinants of respirable dust and quartz, explaining 45.2 and 40.7% of the variance, respectively. In the mining team, only blasting significantly determined respirable dust. Immediate actions for improvements are suggested to include implementing effective dust control together with improved training and education programmes for the workers. Dust and quartz in this underground mine should be controlled by giving priority to workers performing drilling and blasting in the development sections of the mine.

$Research paper thumbnail of Measurements of refractive index sensitivity using long-period grating refractometer$

Optics Communications, 2004

We report the development and demonstration of a long-period grating refractometer. The principle... more We report the development and demonstration of a long-period grating refractometer. The principle of operation is based on the using of a long-period grating that is structurally induced by a CO 2 laser, and where the resonance wavelengths are shifted as the refractive index of medium surrounding the cladding of the long-period grating. The different concentrations for three types of solutions (ethylene glycol, salt, and sugar) were experimentally measured, and results show that, as a refractometer, this fiber-based device not only can differentiate chemicals based on their refractive index, but it can also become a concentration indicator of a particular chemical solution, and applied in the oil and petroleum industry.

Geomicrobiology Journal, 2003

In this study the degree of bacterial attachment of the main microorganisms involved in the biole... more In this study the degree of bacterial attachment of the main microorganisms involved in the bioleaching of metal sulfides and their influence on the dissolution rate and final metal extractions were determined. Three different mineral sulfides were bioleached: chalcopyrite (CuFeS 2 ), sphalerite (ZnS) and pyrite (FeS 2 ). A mixed culture of mesophilic bacteria (Acidithiobacillus and Leptospirillum spp.) was tested at 35 • C and thermophilic bacteria (Sulfolobus spp.) were tested at 68 • C. The results confirmed that a relationship exists between attachment and mineral dissolution rates. The bioleaching process can be divided into three stages. An initial stage with extensive bacterial attachment to the pyritic phase, which is of major importance in order to obtain high dissolution rates (since attached cells liberate Fe 2+ by contact bioleaching and oxidize Fe 2+ to Fe 3+ avoiding iron accumulation at the surface). In a second stage the bacterial attachment diminishes due to the saturation of the surface by the attached cells. This limitation, together with the presence of Fe 2+ in solution, produces an increase in the concentration of free cells, which use Fe 2+ as an energy source. Finally, in a third stage, a balance between free and attached cells is reached, giving rise to a cooperative mechanism. In this case, the attached cells attack the pyrite phase of the mineral generating Fe 2+ . This in turn is oxidized by the free cells in solution, regenerating the oxidizing agent (Fe 3+ ) for the indirect bioleaching of the mineral.