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Interactive influence of rainfall manipulation and livestock grazing on species diversity of the herbaceous layer community in a humid savannah in Kenya

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Plant Diversity 2019年第3期41卷 198-205页

作者： Joseph O.Ondier Daniel O.Okach john c.onyango Dennis O.Otieno Department of Botany Maseno University Private Bag Maseno Kenya Department of Biological Sciences Jaramogi Oginga Odinga University of Science and Technology P.O Box 210-40601 Bondo Kenya Department of Plant Ecology University of Bayreuth D-95440 Bayreuth Germany

changes in rainfall regime and grazing pressure affect vegetation composition and diversity with ecological implications for savannahs. The savannah in East Africa has experienced increased livestock grazing and rainfall variability but the impacts associated with those changes on the herbaceous layer have rarely been documented. We investigated the effect of livestock grazing, rainfall manipulation and their interaction on the composition and diversity of the herbaceous community in the savannah for two years in Lambwe, Kenya. Rainfall manipulation plots were set up for vegetation sampling;these plots received either 50% more or 50% less rainfall than control plots. Simpson’s diversity and Bergere Parker indices were used to determine diversity changes and dominance respectively. The frequency of species was used to compute their abundance and their life forms as determined from the literature. Grazing significantly increased species diversity through suppression of dominant species. Rainfall manipulation had no significant impact on plant diversity in fenced plots, but rainfall reduction significantly reduced diversity in grazed plots. In contrast, rainfall manipulation had no impact on dominance in either fenced or grazed plots. The interaction of grazing and rainfall manipulation is complex and will require additional survey campaigns to create a complete picture of the implications for savannah structure and composition.

关键词： Plant diversity Grazing Rainfall Moist savannah

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Targeting TrkB–PSD-95 coupling to mitigate neurological disorders

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Neural Regeneration Research 2025年第3期20卷 715-724页

作者： Xin Yang Yu-Wen Alvin Huang john Marshall Department of Molecular Biology Cell Biology and BiochemistryBrown UniversityProvidenceRIUSA Department of Neurology Warren Alpert Medical School of Brown UniversityProvidenceRIUSA center for Translational Neuroscience Robert J.and Nancy D.Carney Institute for Brain Science and Brown Institute for Translational ScienceBrown UniversityProvidenceRIUSA

Tropomyosin receptor kinase B(TrkB)signaling plays a pivotal role in dendritic growth and dendritic spine formation to promote learning and *** activity-dependent release of brain-derived neurotrophic factor at synapses binds to pre-or postsynaptic TrkB resulting in the strengthening of synapses,reflected by long-term ***,the association of postsynaptic density protein-95 with TrkB enhances phospholipase cγ-ca^(2+)/calmodulin-dependent protein kinaseⅡand phosphatidylinositol 3-kinase-mechanistic target of rapamycin signaling required for long-term *** this review,we discuss TrkB-postsynaptic density protein-95 coupling as a promising strategy to magnify brain-derived neurotrophic factor signaling towards the development of novel therapeutics for specific neurological disorders.A reduction of TrkB signaling has been observed in neurodegenerative disorders,such as Alzheimer's disease and Huntington's disease,and enhancement of postsynaptic density protein-95 association with TrkB signaling could mitigate the observed deficiency of neuronal connectivity in schizophrenia and *** with brain-derived neurotrophic factor is problematic,due to poor pharmacokinetics,low brain penetration,and side effects resulting from activation of the p75 neurotrophin receptor or the truncated TrkB.T1 *** TrkB agonists and antibodies that activate TrkB are being intensively investigated,they cannot distinguish the multiple human TrkB splicing isoforms or cell type-specific *** TrkB–postsynaptic density protein-95 coupling provides an alternative approach to specifically boost TrkB signaling at localized synaptic sites versus global stimulation that risks many adverse side effects.

关键词： Angelman syndrome autism brain-derived neurotrophic factor depression neurodegenerative disorder neurodevelopmental disorder postsynaptic density protein-95 synaptic plasticity TrkB

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cold plasma redistribution throughout geospace

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Science china(Technological Sciences) 2016年第9期59卷 1340-1345页

作者： Foster john c. Massachusetts Institute of Technology Haystack Observatory

The redistribution of the electrically charged cold plasma of ionospheric origin involves the equatorial,low,mid,auroral,and polar-latitude regions in a multi-step,system-wide process linking the regions of *** with ground and space-based instruments characterize the geospace plume-regularly occurring channels of enhanced plasma density flowing at both ionospheric and magnetospheric *** in the SAPS channel transports the eroded material to the noontime cusp in the ionosphere and to the dayside magnetopause at high *** the fluxes of cold plume plasma traverse the cusp and enter the polar cap,they form the polar tongue of *** the cusp the plume plasma provides a rich source of heavy ions for the magnetospheric injection and acceleration via the mechanisms operative on those field lines.

关键词： plasmasphere ionosphere geospace GPS TEc ionospheric electric field plume

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Urinary Tract Infection among Pregnant Women at Pumwani Maternity Hospital, Nairobi, Kenya: Bacterial Etiologic Agents, Antimicrobial Susceptibility Profiles and Associated Risk Factors

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Advances in Microbiology 2018年第3期8卷 175-187页

作者： Hellen A. onyango carolyne Ngugi john Maina john Kiiru Department of Medical Microbiology Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya Department of Medical Microbiology College of Health Sciences Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya centre of Microbiology Research Kenya Medical Research Institute Nairobi Kenya

Urinary Tract Infections (UTIs) during pregnancy are among the most common infections worldwide and can lead to poor perinatal and maternal outcomes. This study determined the prevalence of UTIs during pregnancy, associated risk factors and antimicrobial susceptibility profiles of associated bacterial pathogens. A cross-sectional study was conducted among 210 pregnant women attending antenatal clinic at Pumwani Maternity hospital. Their social-demographic profiles were obtained using a structured questionnaire. cultures were done from midstream urine and antimicrobial susceptibility testing determined using the disc diffusion test. The overall prevalence of UTI was 15.7% regardless of the women’s age, parity and stage of gestation. Prevalence of asymptomatic and symptomatic bacteriuria was 4.3% and 11.4% respectively. Material of undergarment and frequency of changing the undergarments were found to contribute significantly to the acquisition of UTI (P coli was the most predominant UTI organism at (44.5%) followed by K. pneumoniae (21.2%) and S. aureus (15.1%). Almost a half (over 49%) of all Gram-negative organisms showed resistance prevalence against third generation cephalosporins, fluoroquinolones, Sulfamethoxazole-Trimethoprim, cefoxitin, Nitrofurantoin and Amoxicillin-clavulanic acid. Gram-positive strains were susceptible to Amoxicillin-clavulanic acid, Nitrofurantoin, Linezolid and Ofloxacin. The prevalence of multi-drug resistance (MDR) in all study isolates was 96%. Our data suggest a serious resistance trend among UTI strains and more should be done to slow down this trend. Pregnant women should be screened by urine culture and treatment be guided by the antimicrobial susceptibility data.

关键词： Urinary Tract Infection Pregnancy Risk Factors Antimicrobial Resistance ESBL MRSA MDR

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Estimating a Finite Population Mean under Random Non-Response in Two Stage cluster Sampling with Replacement

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Open Journal of Statistics 2017年第5期7卷 834-848页

作者： Nelson Kiprono Bii christopher Ouma onyango john Odhiambo Institute of Mathematical Sciences Strathmore University Nairobi Kenya Department of Statistics Kenyatta University Nairobi Kenya

Non-response is a regular occurrence in Sample Surveys. Developing estimators when non-response exists may result in large biases when estimating population parameters. In this paper, a finite population mean is estimated when non-response exists randomly under two stage cluster sampling with replacement. It is assumed that non-response arises in the survey variable in the second stage of cluster sampling. Weighting method of compensating for non-response is applied. Asymptotic properties of the proposed estimator of the population mean are derived. Under mild assumptions, the estimator is shown to be asymptotically consistent.

关键词： Non-Response Nadaraya-Watson Estimation Two Stage cluster Sampling

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construction of Non-Symmetric Balanced Incomplete Block Design through combination of Symmetric Disjoint Balanced Incomplete Block Designs

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Open Journal of Statistics 2023年第6期13卷 789-802页

作者： Troon john Benedict onyango Fredrick Karanjah Anthony Njuguna Edward Department of Economics Maasai Mara University Narok Kenya Department of Mathematics and Actuarial Science Maseno University Luanda Kenya Department of Mathematics Multimedia University Nairobi Kenya Department of Mathematics and Physical Science Maasai Mara University Narok Kenya

The existence of several non-symmetric balanced incomplete block designs (BIBDs) is still unknown. This is because the non-existence property for non-symmetric BIBDs is still not known and also the existing construction methods have not been able to construct these designs despite their design parameters satisfying the necessary conditions for the existence of BIBD. The study aimed to bridge this gap by introducing a new class of non-symmetric BIBDs. The proposed class of BIBDs is constructed through the combination of disjoint symmetric BIBDs. The study was able to determine that the total number of disjoint symmetric BIBDs (n) with parameters (v = b, r = k, λ) that can be obtained from an un-reduced BIBD with parameters (v, k) is given by n = r - λ. When the n symmetric disjoint BIBDs are combined, then a new class of symmetric BIBDs is formed with parameters v* = v, b* = nb, r* = nr, k* = k, λ* = λ, where 2≤ n ≤ r - λ. The study established that the non-existence property of this class of BIBD was that when is not a perfect square then v should be even and when v* is odd then the equation should not have a solution in integers x, y, z which are not all simultaneously zero. In conclusion, the study showed that this construction technique can be used to construct some non-symmetric BIBDs. However, one must first construct the disjoint symmetric BIBDs before one can construct the non-symmetric BIBD. Thus, the disjoint symmetric BIBDs must exist first before the non-symmetric BIBDs exist.

关键词： Disjoint Symmetric BIBD Un-Reduced BIBD combination Symmetric BIBD Non-Symmetric BIBD Non-Existence of BIBD

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Spatial Modelling of Weather Variables for Plant Disease Applications in Mwea Region

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Journal of Geoscience and Environment Protection 2016年第5期4卷 127-136页

作者： Paul onyango Ouma Patroba Achola Odera john Bosco Mukundi Department of Geomatic Engineering and Geospatial Information Systems Jomo Kenyatta University of Agriculture and Technology Juja Kenya Department of Horticulture and Food Sciences Jomo Kenyatta University of Agriculture and Technology Juja Kenya

climate change is expected to affect the agricultural systems, such as crop yield and plant disease occurrence and spread. To be able to mitigate against the negative impacts of climate change, there is a need to use early warning systems that account for expected changes in weather variables such as temperature and rainfall. Moreover, providing such information at high spatial and temporal resolutions can be useful in improving the accuracy of an early warning system. This paper describes a methodology that can be used to produce high spatial and temporal resolutions of minimum temperature, maximum temperature and rainfall in an agricultural area. We utilize MarkSim GcM, a weather file generator that incorporates IPcc based climate change models to downscale the weather variables at monthly intervals. An ensemble of 17 GcM models is used within the RcP 8.0 emission scenario within the latest model based cMIP5. We first assess the usability of the model, by comparing results produced to what has been recorded at weather station level over a vast region. Then, we estimate the correction factors for model results by implementing a linear regression that is used to assess the relationship between the variables and the deviation of model outputs to the weather station data. Finally, we use kriging geostatistical technique to interpolate the weather data, for the year 2010. Results indicated that the model overestimated the results of maximum temperature, while underestimating the result of minimum temperature. Variability in the recorded weather variables was also evident, indicating that the response variables such as plant disease severity dependent on such weather information could vary in the area. These datasets can be useful especially in predicting the occurrence of plant diseases, which are affected by either rainfall or temperature.

关键词： climate change Rice Blast GIS Geostatistics MarkSim GcM

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Metagenomics: Facts and Artifacts, and computational challenges

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Journal of computer Science & Technology 2010年第1期25卷 71-81页

作者： john c. Wooley 叶玉珍 center for Research on BioSystems Calit2 University of California San Diego School of Informatics and computing Indiana University

Metagenomics is the study of microbial communities sampled directly from their natural environment, without prior culturing. By enabling an analysis of populations including many （so-far） unculturable and often unknown microbes, metagenomics is revolutionizing the field of microbiology, and has excited researchers in many disciplines that could benefit from the study of environmental microbes, including those in ecology, environmental sciences, and biomedicine. Specific computational and statistical tools have been developed for metagenomic data analysis and comparison. New studies, however, have revealed various kinds of artifacts present in metagenomics data caused by limitations in the experimental protocols and/or inadequate data analysis procedures, which often lead to incorrect conclusions about a microbial community. Here, we review some of the artifacts, such as overestimation of species diversity and incorrect estimation of gene family frequencies, and discuss emerging computational approaches to address them. We also review potential challenges that metagenomics may encounter with the extensive application of next-generation sequencing （NGS） techniques.

关键词： metagenomics next-generation sequencing (NGS) taxonomic/functional profiling statistical approaches comparative metagenomics

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Optimization of the Angle of Frog in Mouldboard Tillage Operations in Sandy clay Soil

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Open Journal of Optimization 2015年第4期4卷 131-140页

作者： Angela Hiuhu Ayub Njoroge Gitau Duncan onyango Mbuge john Ndisya Mulwa Department of Biosystems Engineering University of Nairobi Nairobi Kenya

This paper investigated the effect of three independent variables including: tillage speed (ranges of below 2.5 m/s and between 2.5 m/s and 5 m/s), tillage depth (range of 10 cm from 0 cm to 30 cm) and frog angle (30° 40°, and 50°) on draught forces. The experimental work was completed with determination of the draught forces using an analytical method (Saunders Equation). Numerical Simulation: Discrete Element Method (DEM) was used to verify the results obtained analytically. The results indicated that tillage depth has a stronger influence on the draught forces as compared to the tillage speed. Minimal draught forces can then be achieved through operating at shallow tillage depth and maintaining a frog angle of 30°. The results showed a variance of ±15.95% to the calculated values supporting DEM as a numerical method capable of predicting draft forces correctly, tillage power optimization and determination of optimal frog angle for the mouldboard plough.

关键词： DEM EDEM Soil-cut Interactions Modelling Tillage Draught

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Root-Fusion characteristic of Eucalyptus Trees Block Gully Development

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Journal of Environmental Protection 2013年第9期4卷 877-880页

作者： Dalmas O. Sigunga Makoto Kimura Mitsuo Hoshino Shuichi Asanuma john c. onyango Graduate School of Bioagricultural Science Nagoya University Nagoya Japan Maseno University Maseno Kenya

Soil erosion by water resulting in gully formation is a common occurrence in western Kenya. Establishment of local and sustainable countermeasures to prevent gully development/expansion in western Kenya is an urgent issue. This study presents the proposal to prevent gully development/expansion by planting Eucalyptus trees in gully prone regions. A survey study was undertaken in Kenya from 2008 to 2011. Roots of adjacent Eucalyptus citriodora trees fused forming a dense network of closely woven mass of root system holding large amount of soil thereby checking erosion by water and hence gully development. The network of roots among adjacent Eucalyptus trees also supported the standing and normal growth of the other Eucalyptus trees whose root systems were completely free from soil. Recognizable aging and breakdown of root networks were not observed during the survey period.

关键词： Eucalyptus citriodora Gully Erosion Root-Fusion Root System

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