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  1. Buch ; Online: Vacuum gas carburizing - fate of hydrocarbons

    Khan, Rafi Ullah

    2008  

    Abstract: This work focuses on gaseous reactive flows in ideal and non-ideal reactors. The objective of this research is the development of models for the numerical simulation of homogeneous reactive flows under vacuum carburizing conditions of steel with propane ... ...

    Abstract This work focuses on gaseous reactive flows in ideal and non-ideal reactors. The objective of this research is the development of models for the numerical simulation of homogeneous reactive flows under vacuum carburizing conditions of steel with propane and acetylene. These models can be used for further investigations of heterogeneous reactions during vacuum carburizing of steel to predict the carbon flux on the complex shaped steel parts to understand and, eventually, optimize the behavior of the whole reactor.arburizing is the case-hardening process in which carbon is added to the surface of low-carbon steels at temperatures generally between 850 and 1050 °C. In the conventional gas carburizing at atmospheric pressure, the carbon potential is controlled by adjusting the flow rate of the carburizing gas.-

    Carbon potential of the furnace atmosphere can be related to partial pressure of CO2 or O2 or vapour pressure of water by equilibrium relationships and a sensor can be used to measure it. This method of carbon-potential control cannot be used for vacuum gas carburizing due to the absence of thermodynamic equilibrium which is one of the main difficulties of the vacuum carburizing process. The formation of soot during carburization isalso undesirable and the process parameters should be selected such that the formation of soot is minimized. The amount of carbon available for carburizing the steel depends on the partial pressure of the carburizing gas, carbon content in the carburizing gas and the pyrolysis reactions of the carburizing gas. The pyrolysis reactions of the carburizing gas are also affected by the contacting pattern or how the gas flows through and contacts with the steel parts being carburized. This work focuses on gaseous reactive flows in ideal and non-ideal reactors.-

    The objective of this research is the development of models for the numerical simulation of homogeneous reactive flows under vacuum carburizing conditions of steel with ropane and acetylene. These models can be used for further investigations of heterogeneous reactions during vacuum carburizing of steel to predict the carbon flux on the complex shaped steel parts to understand and, eventually, optimize the behavior of the whole reactor. Two different approaches have been used to model the pyrolysis of propane and acetylene under vacuum carburizing conditions of steel. One approach is based on formal or global kinetic mechanisms together with the computational fluid dynamics (CFD) tool. The other approach is based on detailed chemistry with simplified or ideal flow models. Two global mechanisms developed at the Engler-Bunte-Institut for pyrolysis of propane and acetylene respectively were used in this work.-
    Schlagwörter Chemical engineering
    Umfang 1 electronic resource (II, 159 p. p.)
    Verlag KIT Scientific Publishing
    Erscheinungsort Verlagsort nicht ermittelbar
    Dokumenttyp Buch ; Online
    Anmerkung ENGLISH ; Open Access
    HBZ-ID HT020197459
    ISBN 9783866442757 ; 3866442750
    Datenquelle ZB MED Katalog Medizin, Gesundheit, Ernährung, Umwelt, Agrar

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  2. Artikel ; Online: Multi-century (635-year) spring season precipitation reconstruction from northern Pakistan revealed increasing extremes

    Nasrullah Khan / Narayan Prasad Gaire / Oimahmad Rahmonov / Rafi Ullah

    Scientific Reports, Vol 14, Iss 1, Pp 1-

    2024  Band 16

    Abstract: Abstract The Hindu Kush Himalaya region is experiencing rapid climate change with adverse impacts in multiple sectors. To put recent climatic changes into a long-term context, here we reconstructed the region’s climate history using tree-ring width ... ...

    Abstract Abstract The Hindu Kush Himalaya region is experiencing rapid climate change with adverse impacts in multiple sectors. To put recent climatic changes into a long-term context, here we reconstructed the region’s climate history using tree-ring width chronologies of climate-sensitive Cedrus deodara and Pinus gerardiana. Growth-climate analysis reveals that the species tree-growth is primarily limited by moisture stress during or preceding the growing season, as indicated by a positive relationship between the chronology and precipitation and scPDSI, and a negative one with temperature. We have reconstructed 635 years (1384–2018 CE) of February–June precipitation using a robust climate reconstruction model that explains about 53% variance of the measured precipitation data. Our reconstruction shows several dry and wet episodes over the reconstruction period along with an increase in extreme precipitation events during recent centuries or years. Long, very wet periods were observed during the following years: 1392–1393, 1430–1433, 1456–1461, 1523–1526, 1685–1690, 1715–1719, 1744–1748, 1763–1767, 1803–1806, 1843–1846, 1850–1855, 1874–1876, 1885–1887, 1907–1909, 1921–1925, 1939–1944, and 1990–1992, while long dry periods were observed during the following years: 1398–1399, 1464–1472, 1480–1484, 1645–1649, 1724–1727, 1782–1786, 1810–1814, 1831–1835, 1879–1881, 1912–1918, 1981–1986, 1998–2003, and 2016–2018 CE. We found predominantly short-term periodicity cycles of 2.0, 2.2, 2.3, 2.4, 2.6–2.7, 2.9, 3.3, 4.8, 8.1–8.3, and 9.4–9.6 years in our reconstruction. Spatial correlation analyses reveal that our reconstruction is an effective representation of the precipitation variability in the westerly climate-dominated areas of Pakistan and adjacent regions. In addition to the influence of regional circulation systems like western disturbances, we found possible teleconnections between the precipitation variability in northern Pakistan and broader-scale climate modes or phases like AMO and ENSO. The study also highlights the ...
    Schlagwörter Medicine ; R ; Science ; Q
    Thema/Rubrik (Code) 550
    Sprache Englisch
    Erscheinungsdatum 2024-01-01T00:00:00Z
    Verlag Nature Portfolio
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  3. Artikel ; Online: Stand Structure and Dynamics of the Naturally Managed Oak-Dominated Forests and Their Relation to Environmental Variables in Swat Hindu Kush Range of Pakistan

    Ataur Rahman / Nasrullah Khan / Rafi Ullah / Kishwar Ali

    Sustainability, Vol 15, Iss 4002, p

    2023  Band 4002

    Abstract: Although oak woodlands are a characteristic landscape component in the Swat Hindukush Mountain ranges, little is known about their current or historical stand population structure and regeneration dynamics related to environmental variables. Therefore, ... ...

    Abstract Although oak woodlands are a characteristic landscape component in the Swat Hindukush Mountain ranges, little is known about their current or historical stand population structure and regeneration dynamics related to environmental variables. Therefore, the present study assessed the stand structure, regeneration status, and relationship of oak communities with environmental variables. The study assessed 30 oak-dominated forest sites using the quadrates method, sampling 300 quadrates for evaluating the phytosociological and environmental variables. The stand structures of forests were dominated by four oak species, i.e., Quercus incana , Quercus baloot , Quercus dilatata , and Quercus semecarpifolia , distributed along with the elevation. The lower elevation stand structures were most diverse and dominated by Q. incana , having higher stand parameters, i.e., importance value index, basal area, and density. In contrast, the higher-elevation stand structures were dominated by Q. semecarpifolia , having stand parameters in moderate measures, while those at intermediate elevations have lower stand parameters. The environmental variables were negatively correlated with the stand structures, i.e., elevation ( r = −0.51), precipitation ( r = −0.47), and relative humidity ( r = −0.77), whereas soil nutrients such as Potassium concentration have a significant negative relation with stands structure ( r = −0.66) indicating their vital role in sustaining the oak communities. The communities were fairly regenerated, with an age structure between 12–36 years, indicating young communities. These results concluded that the observed wide range of variability in stand characteristics reflects the mechanisms that have shaped them. The recent anthropogenic factors, i.e., military operations and natural hazards such as the flood of 2010, have deliberately affected the communities under natural restoration.
    Schlagwörter stand structure ; environmental variables ; elevation gradients ; anthropogenic factors ; natural hazards ; Environmental effects of industries and plants ; TD194-195 ; Renewable energy sources ; TJ807-830 ; Environmental sciences ; GE1-350
    Thema/Rubrik (Code) 710
    Sprache Englisch
    Erscheinungsdatum 2023-02-01T00:00:00Z
    Verlag MDPI AG
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  4. Artikel ; Online: Symptomatic Interarterial Course Of Coronary Arteries In Middle Aged Patients.

    Nasir, Abdul / Ullah, Abid / Masoud, Maryum / Jan, Rafi Ullah

    Journal of Ayub Medical College, Abbottabad : JAMC

    2024  Band 35Suppl 1, Heft 4, Seite(n) S793–S796

    Abstract: Anomalous aortic origin of a coronary artery (AAOCA) is the most common congenital abnormality and is sometimes associated with various life-threatening conditions. We present the cases of a 35-year-old male and a 50-year-old female with complaints of ... ...

    Abstract Anomalous aortic origin of a coronary artery (AAOCA) is the most common congenital abnormality and is sometimes associated with various life-threatening conditions. We present the cases of a 35-year-old male and a 50-year-old female with complaints of chest pain. Patients had anomalous aortic origin of coronary arteries with the interarterial course and were treated surgically. By literature review, we came to know that the approach to treat patients with anomalous aortic origin of coronary arteries should be largely individualized and there is no ample scientific data to support any specific diagnostic modality and treatment option.
    Mesh-Begriff(e) Male ; Female ; Humans ; Middle Aged ; Adult ; Coronary Vessel Anomalies/diagnostic imaging ; Coronary Vessel Anomalies/surgery ; Aorta
    Sprache Englisch
    Erscheinungsdatum 2024-02-26
    Erscheinungsland Pakistan
    Dokumenttyp Case Reports ; Journal Article
    ZDB-ID 2192473-9
    ISSN 1819-2718 ; 1025-9589
    ISSN (online) 1819-2718
    ISSN 1025-9589
    DOI 10.55519/JAMC-S4-12086
    Datenquelle MEDical Literature Analysis and Retrieval System OnLINE

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  5. Artikel ; Online: Eco-Friendly Valorization and Utilization of Plant Waste as a Source of Tannin for Leather Tanning

    Shahid Rehman Khan / Shahzad Maqsood Khan / Rafi Ullah Khan

    Sustainability, Vol 15, Iss 3884, p

    2023  Band 3884

    Abstract: In the present study, bark, which is the waste part of a tree, was utilized as a source of tannin for leather tanning after its value addition. The barks of Acacia nilotica L. and Eucalyptus globulus , which are abundantly available in Pakistan, were ... ...

    Abstract In the present study, bark, which is the waste part of a tree, was utilized as a source of tannin for leather tanning after its value addition. The barks of Acacia nilotica L. and Eucalyptus globulus , which are abundantly available in Pakistan, were selected in this study. Different extraction techniques including mechanical, soxhlet, reflux and ultrasonic extraction were used for the extraction of tannin from the selected barks. The medium of extraction included aqueous as well as different solvent mixtures in different ratios. The solvent mixtures used in this study were methanol-water and acetone–water. The methanol–water ratio was kept (50:50) and the acetone–water ratio was maintained at (50:50 and 70:30). In the first step, the process of extraction was optimized for solvent mixtures and extraction time by taking a fixed dose (5 g) of each bark and a fixed volume of each extracting solvent mixture (150 mL). The total phenolic contents (TPC) of the bark extracts were determined by colorimetric assay (as mg GAE/g bark), taking gallic acid as the reference standard. The tannin contents (TC) of the bark extracts were determined by using the standard hide powder method (SLC 117). It was concluded that among the different extraction techniques, and among the solvent mixtures acetone–water in ratio (70:30), ultrasonic extraction resulted in maximum extraction of tannin (196.1 and 125.2 mg/g), respectively for A. nilotica and E. globulus . FTIR analyses of the dried extracts obtained from both barks were compared with FTIR of the most commonly used commercial vegetable tanning agent in the leather industry, i.e., mimosa. Results were comparable, which confirmed the presence of condensed tannin in both barks. The extracted tannin was applied on a pickle and wet blue leather to evaluate its tanning and re-tanning capability. Mimosa, the most abundantly used vegetable tanning material in the leather industry, was applied as a reference standard on the same pickle and wet blue leather for comparison. Different ...
    Schlagwörter bark waste ; eco-friendly extraction ; FTIR ; tannin ; UV–Visible spectroscopy ; Environmental effects of industries and plants ; TD194-195 ; Renewable energy sources ; TJ807-830 ; Environmental sciences ; GE1-350
    Thema/Rubrik (Code) 660
    Sprache Englisch
    Erscheinungsdatum 2023-02-01T00:00:00Z
    Verlag MDPI AG
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  6. Artikel ; Online: Scheduling management and optimization analysis of intermediate products transfer in a shipyard for cruise ships.

    Jiajie Liu / Jingbo Yin / Rafi Ullah Khan

    PLoS ONE, Vol 17, Iss 3, p e

    2022  Band 0265047

    Abstract: Shipbuilding is a complex and large-scale operation involving many intermediate products (blocks) and the frequent transfer of blocks among workshops and stockyards. The reasonable use of methods to complete the transfer scheduling of intermediate ... ...

    Abstract Shipbuilding is a complex and large-scale operation involving many intermediate products (blocks) and the frequent transfer of blocks among workshops and stockyards. The reasonable use of methods to complete the transfer scheduling of intermediate products is of great importance. In this paper, the blocks and the flat transporters are the research objects. Based on organizing the various logistical processes for blocks and the circulation process in the shipyard, we established a model that takes the task time window and other factors as constraints, and minimizes the sum of delay time and no-load time of flat transporters while satisfying the punctuality of scheduling tasks. Three conclusions are reached: (1)The flat transporter utilization rate is inversely related to the value of the objective function. The smaller the value of the objective function, the more the usage rate of a particular one (2) loading is the biggest obstacle to the overall working time of flat transporters, and a simple optimization model cannot solve this problem; and (3) based on the optimization model, the load efficiency of flat transporters can be improved, and the delivery time can be reduced.
    Schlagwörter Medicine ; R ; Science ; Q
    Thema/Rubrik (Code) 600
    Sprache Englisch
    Erscheinungsdatum 2022-01-01T00:00:00Z
    Verlag Public Library of Science (PLoS)
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  7. Artikel ; Online: Scheduling management and optimization analysis of intermediate products transfer in a shipyard for cruise ships

    Jiajie Liu / Jingbo Yin / Rafi Ullah Khan

    PLoS ONE, Vol 17, Iss

    2022  Band 3

    Abstract: Shipbuilding is a complex and large-scale operation involving many intermediate products (blocks) and the frequent transfer of blocks among workshops and stockyards. The reasonable use of methods to complete the transfer scheduling of intermediate ... ...

    Abstract Shipbuilding is a complex and large-scale operation involving many intermediate products (blocks) and the frequent transfer of blocks among workshops and stockyards. The reasonable use of methods to complete the transfer scheduling of intermediate products is of great importance. In this paper, the blocks and the flat transporters are the research objects. Based on organizing the various logistical processes for blocks and the circulation process in the shipyard, we established a model that takes the task time window and other factors as constraints, and minimizes the sum of delay time and no-load time of flat transporters while satisfying the punctuality of scheduling tasks. Three conclusions are reached: (1)The flat transporter utilization rate is inversely related to the value of the objective function. The smaller the value of the objective function, the more the usage rate of a particular one (2) loading is the biggest obstacle to the overall working time of flat transporters, and a simple optimization model cannot solve this problem; and (3) based on the optimization model, the load efficiency of flat transporters can be improved, and the delivery time can be reduced.
    Schlagwörter Medicine ; R ; Science ; Q
    Thema/Rubrik (Code) 600
    Sprache Englisch
    Erscheinungsdatum 2022-01-01T00:00:00Z
    Verlag Public Library of Science (PLoS)
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  8. Artikel ; Online: Agriculture communities’ perception and willingness to pay for eradicating Xanthium strumarium L

    Rafi Ullah / Nasrullah Khan / Zoya Baig / Nabila

    Taiwania, Vol 67, Iss 3, Pp 341-

    A step towards the progressive decrease of economic and biodiversity loss

    2022  Band 350

    Abstract: Xanthium strumarium L. is native to North America and rapidly spreading in Khyber Pakhtunkhwa (KP) Pakistan as an alien invasive plant species (AIPs) and possess a severe threat to crops. Hence this study was conducted to assess socioeconomic impacts on ... ...

    Abstract Xanthium strumarium L. is native to North America and rapidly spreading in Khyber Pakhtunkhwa (KP) Pakistan as an alien invasive plant species (AIPs) and possess a severe threat to crops. Hence this study was conducted to assess socioeconomic impacts on agriculture, livestock, and biodiversity along with the mode of invasion, spread, and willingness to pay for its eradication in selected areas of KP Pakistan. Methods: Three divisions of Khyber Pakhtunkhwa province , i.e. Malakand, Peshawar, and Hazara, were selected for the study. The respondents were divided into two categories, i.e., agricultural and non-agricultural. The respondent's information was collected using a closed-ended questionnaire and semi-structured interview. The data were analyzed and interpreted by tabulation in excel 2010, and variation was tested using online chi-square tests. Results: Most respondents believed that the plant preferred to grow on the roadside and wasteland, affecting crops, especially maize, and infesting the areas for more than 20 years with regular and timely increased infestation. Livestock animals are affected severely in health and products. The chi-square test results indicated that the agricultural communities were affected more than non-agricultural communities. The invasion of the species has affected people's livelihood to the extent that they would spend money on its eradication/control. Biodiversity effects were severe in all the areas, as revealed by decreased species richness index in invaded sites. Conclusions: We concluded that cash crops and communities' economic value suffered severely from the invasion of X. strumarium, and therefore integrated management is needed for its control and eradication.
    Schlagwörter agriculture ; live-stock ; invasive alien species ; xanthium strumarium ; respondents ; Biology (General) ; QH301-705.5
    Sprache Englisch
    Erscheinungsdatum 2022-06-01T00:00:00Z
    Verlag National Taiwan University
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  9. Artikel ; Online: Accident and pollution risk assessment for hazardous cargo in a port environment.

    Rafi Ullah Khan / Jingbo Yin / Faluk Shair Mustafa

    PLoS ONE, Vol 16, Iss 6, p e

    2021  Band 0252732

    Abstract: The catastrophic environmental, life and monetary losses concomitant to the hazardous cargo accidents have remained a matter of critical concern for the maritime transportation officials. The factors that instigate these accidents while dealing with ... ...

    Abstract The catastrophic environmental, life and monetary losses concomitant to the hazardous cargo accidents have remained a matter of critical concern for the maritime transportation officials. The factors that instigate these accidents while dealing with hazardous cargo in a port environment requires rigorous analysis and evaluation, which still remains in its infancy. In accord to these prevailing issues, this study focusses on the assessment of multifactor risks associated with the dealing of hazardous cargos inside a port. The methodology adopted is the amalgamation of expert judgment and literature review for the identification of factors and developing their causal relationship, while Bayesian Network (BN) for the inference, which was based on 348 past accident reports from the year 1990 to 2018. The results indicate that under normal circumstances, the probability of an accident with considerable consequences is 59.8, where human and management were found to be the highest contributing factors. Setting evidence at the environment and pollution accident to occur, the incidence probability of the "management" is raised by 7.06%. A sensitivity analysis was conducted to determine the most critical factors for the hazardous cargo accident. This study reveals that in order to evade the hazardous cargo accidents and curtail severity of the consequences, the port authorities, concerned government departments and other related institutions should pay specific attention to the qualification, training and attitude of the involved workforce. Moreover, the development and implementation of stringent safety protocols was also revealed to have critical prominence. This study holds practical vitality for enhancing safety and mitigating risks associated to hazardous cargo dealing in a port.
    Schlagwörter Medicine ; R ; Science ; Q
    Thema/Rubrik (Code) 380
    Sprache Englisch
    Erscheinungsdatum 2021-01-01T00:00:00Z
    Verlag Public Library of Science (PLoS)
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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  10. Artikel ; Online: Evaluating the Effect of Plastomer Modified Asphalt Mixture on High/Low Temperature Performance

    Rafi Ullah / Imran Hafeez / Waqas Haroon / Safeer Haider

    Mehran University Research Journal of Engineering and Technology, Vol 40, Iss 3, Pp 680-

    2021  Band 691

    Abstract: Asphalt pavement’s surfaces deteriorate over time due to combined effect of traffic and surrounding environment. Fatigue and rutting are the major distresses which cause failures in flexible pavements. Different temperature control computer operated ... ...

    Abstract Asphalt pavement’s surfaces deteriorate over time due to combined effect of traffic and surrounding environment. Fatigue and rutting are the major distresses which cause failures in flexible pavements. Different temperature control computer operated equipment’s are being used worldwide to predict the performance of asphalt mixtures at approximately same condition to those in-service pavements. Similarly, different types of polymers such as elastomer and thermoplastic have been used all over the world in Hot Mix Asphalt (HMA) for the improvement of asphalt mixtures. But little attention has been taken to evaluate the effect of plastomer on hot mix asphalt performance. Moreover, the initial cost of elastomer is higher than other types of polymers such as plastomer. The aim of this research study is to check the effect of various plastomers on high/low temperature performance of asphalt mixture. Four performance tests like Cooper wheel tracker, dynamic modulus, uniaxial repeated load and four-point bending beam test are used to evaluate the effect of different type of plastomers such as polyethylene terephthalate, high density and low density polyethylene with limestone aggregate quarry and 60/70 pen grade asphalt binder. This research study concludes that plastomer increases flexibility and hardness of asphalt mixtures and improves the rut resistance, dynamic modulus and fatigue life of asphalt mixtures. Plastomer modification shows significant benefits as compared to neat binder for high/low temperature performance. Moreover, it can be concluded that plastomer provides an efficient and economical blend of asphalt mixture.
    Schlagwörter Technology ; T ; Engineering (General). Civil engineering (General) ; TA1-2040 ; Science ; Q
    Thema/Rubrik (Code) 621
    Sprache Englisch
    Erscheinungsdatum 2021-07-01T00:00:00Z
    Verlag Mehran University of Engineering and Technology
    Dokumenttyp Artikel ; Online
    Datenquelle BASE - Bielefeld Academic Search Engine (Lebenswissenschaftliche Auswahl)

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