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Exploring tree diversity and stand structure of savanna woodlands in southeastern Sudan

Journal of Arid Land 2020年第4期12卷 609-617页

作者： ahmed m m HASOBA ahmed A H SIDDIG yousif E yAGOUB Faculty of Forest Sciences and Technology University of GeziraMadani 22212Sudan Faculty of Forestry University of KhartoumKhartoum North 13314Sudan Department of Environmental Conservation University of Massachusetts AmherstAmherst 01003USA

Savanna woodlands in Sudan host great biodiversity, provide a plethora of ecosystem goods and services to local communities, and sustain numerous ecological functions. Although the importance of the Acacia trees in these areas is well known, up-to-date information about these woodlands' diversity is limited and changes in their woody vegetation composition, density, diversity and relative frequency are not monitored over time. This study explored tree diversity and stand stage structure in Nuara Reserved Forest, a typical savanna woodland ecosystem in southeastern Sudan. A total of 638 circular sample plots(1000 m^2 for each) were established using a systematic sampling grid method. The distance between plots was 200 m. In each plot, all living trees with diameter at breast height(DBH) ≥5.00 cm were identified and counted, and their DBH values were recorded. From these data, tree composition, diversity, density and stage structure were assessed. There were 12,259 individual trees representing four species(Acacia seyal, Balanites aegyptiaca, Acacia Senegal and Acacia mellifera) that belong to two families. The dominant species was Acacia seyal. Average tree density was 191 trees/hm^2 and the Shannon-Weiner index for trees diversity was 0.204. Overall, young trees comprised 86.30% of the forest. The state of tree richness and density in the study area was low compared to other similar environments in the region and around the world. We recommended adoption of a proper management system that includes monitoring of woody vegetation diversity in this forest, and management actions to enhance tree diversity and sustain ecosystem services to local communities. In addition to care for the dominant Acacia seyal stands, more attention and conservation should be devoted to reestablishing Acacia senegal and Acacia mellifera trees because of their high ecological and economic values for local communities.

关键词： species diversity stand structure savanna woodland ecosystem forest monitoring forest management ecosystem services Nuara Reserved Forest

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Von Kármán rotating flow of maxwell nanofluids featuring the Cattaneo-Christov theory with a Buongiorno model

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Applied mathematics and mechanics(English Edition) 2020年第8期41卷 1195-1208页

作者： A.ahmed m.KHAN J.ahmed A.HAFEEZ Department of mathematics Quaid-i-Azam UniversityIslamabad 44000Pakistan Department of Basic Sciences University of Engineering and TechnologyTaxila 47050Pakistan

This research paper analyzes the transport of thermal and solutal energy in the maxwell nanofluid flow induced above the disk which is rotating with a constant angular *** significant features of thermal and solutal relaxation times of fluids are studied with a Cattaneo-Christov double diffusion theory rather than the classical Fourier’s and Fick’s laws.A novel idea of a Buongiorno nanofluid model together with the Cattaneo-Christov theory is introduced for the first time for the maxwell fluid flow over a rotating ***,the thermal and solutal distributions are controlled with the impacts of heat source and chemical *** classical von Karman similarities are used to acquire the non-linear system of ordinary differential equations(ODEs).The analytical series solution to the governing ODEs is obtained with the well-known homotopy analysis method(HAm).The validation of results is provided with the published results by the comparison *** graphically presented outcomes for the physical problem reveal that the higher values of the stretching strength parameter enhance the radial velocity and decline the circumferential *** increasing trend is noted for the axial velocity profile in the downward direction with the higher values of the stretching strength *** higher values of the relaxation time parameters in the Cattaneo-Christov theory decrease the thermal and solutal energy transport in the flow of maxwell *** higher rate of the heat transport is observed in the case of a larger thermophoretic force.

关键词： maxwell fluid nanoparticle Cattaneo-Christov theory rotating disk homotopy analysis method(HAm)

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Ultralow-Vertical-Current magnetization Switching Effect in an All Van Der Waals 2D Heterostructure

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Chinese Physics Letters 2025年第2期42卷 239-248页

作者： Hao Wu Li yang Gaojie Zhang Wen Jin Jie yu Bichen Xiao ahmed Annas Wenfeng Zhang Haixin Chang Center for Joining and Electronic Packaging State Key Laboratory of Material Processing and Die&Mold TechnologySchool of Materials Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China Wuhan National High magnetic Field Center and Institute for Quantum Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China Shenzhen R&D Center of Huazhong University of Science and Technology Shenzhen 518000China

The manipulation of magnetization and spin polarization using electrical currents represents a fundamental breakthrough in *** has formed the foundation for data storage and next-generation computing ***-transfer torque(STT)and spin-orbit torque(SOT)have emerged as prominent mechanisms in current-driven magnetization ***,these approaches typically require critical current densities in the range of 10^(6) to 10^(9) A·cm^(-2),resulting in significant heat generation during data writing ***,we report the discovery of an ultralow-vertical-current magnetization switching effect in a van der Waals ferromagnetic/ferroelectric heterostructure based on the modulation of the critical magnetic field(H_(C))using small vertical currents,with a critical current density as low as 1.81A·cm^(-2) and an average effective field(H_(eff)/J_(C))as high as 150.3mT·A^(-1)·cm^(2).This unique magnetization switching effect with ultralow-critical-vertical-current densities typically six to nine orders of magnitude lower than those of the STT and SOT provides a new transformative and viable pathway for developing next-generation spintronic and quantum technologies.

关键词： magnetization critical typically

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Assessment of clay stiffness and strength parameters using index properties

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Journal of Rock mechanics and Geotechnical Engineering 2018年第3期10卷 579-593页

作者： Sayed m.ahmed Structural Engineering Department Ain Shams University

A new approach is developed to determine the shear wave velocity in saturated soft to firm clays using measurements of the liquid limit, plastic limit, and natural water content with depth. The shear wave velocity is assessed using the site-specific variation of the natural water content with the effective mean stress. Subsequently, an iterative process is envisaged to obtain the clay stiffness and strength *** at-rest earth pressure coefficient, as well as bearing capacity factor and rigidity index related to the cone penetration test, is also acquired from the analyses. Comparisons are presented between the measured clay parameters and the results of corresponding analyses in five different case studies. It is demonstrated that the presented approach can provide acceptable estimates of saturated clay stiffness and strength parameters. One of the main privileges of the presented methodology is the site-specific procedure developed based on the relationships between clay strength and stiffness parameters, rather than adopting direct correlations. Despite of the utilized iterative processes, the presented approach can be easily implemented using a simple spreadsheet, benefiting both geotechnical researchers and practitioners.

关键词： Soft to firm clays Atterberg limits Shear wave velocity Small-strain shear modulus Constrained modulus Undrained shear strength Effective friction angle Cone penetration test

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An Integrated Framework for Cloud Service Selection Based on BOm and TOPSIS

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Computers, materials & Continua 2022年第8期72卷 4125-4142页

作者： ahmed m.mostafa Computer and Systems Engineering Department Faculty of Engineering at HelwanHelwan UniversityCairo11795Egypt

many businesses have experienced difficulties in selecting a cloud service provider(CSP)due to the rapid advancement of cloud computing services and the proliferation of *** independent criteria should be considered when evaluating the services provided by different *** is a case of multi-criteria decision-making(mCDm).This paper presents an integrated mCDm cloud service selection framework for determining the most appropriate service provider based on the best only method(BOm)and technique for order of preference by similarity to ideal solution(TOPSIS).To obtain the weights of criteria and the relative importance of CSPs based on each criterion,BOm performs pairwise comparisons of criteria and also for alternatives on each criterion,and TOPSIS uses these weights to rank cloud *** evaluation and validation of the proposed framework have been carried out through a use-case model to prove its efficiency and ***,the developed framework was compared with the analytical hierarchical process(AHP),a popular mCDm approach,based on two perspectives:efficiency and *** to the research results,the proposed framework only requires 25%of the comparisons needed for the AHP ***,the proposed framework has a CR of 0%,whereas AHP has 38%.Thus,the proposed framework performs better than AHPwhen it comes to computation complexity and consistency,implying that it is more efficient and trustworthy.

关键词： Cloud computing(CC) multiple-criteria decision-making(mCDm) cloud service providers(CSPs) analytical hierarchical process(AHP) the best only method(BOm) technique for order of preference by similarity to ideal solution(TOPSIS)

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mosquito autogeny in Aedes caspius （Diptera： Culicidae）： alterations of larval nourishments reservation upon bacterial infection

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Insect Science 2013年第4期20卷 472-484页

作者： Ashraf m. ahmed Zoology Department College of Science King Saud University SaudiArabia Zoology Department College of Science Minia UniversityEl-Minia Egypt

The present study recorded mosquito autogeny for the first time amongst Aedes caspius species in the Eastern region of Saudi Arabia. Laboratory rearing showed an obligatory autogenous species of Ae. caspius since it foregoes blood feeding during its first ovarian cycle, even in the presence of the hosts （CD mouse）, but produces its second egg batch only if ingested a blood meal. Both morphological and molecular identification confirmed that both autogenous and anautogenous strains belong to the same species of Ae. caspius. Data from biochemical analysis showed significant 2, 1.6, and 1.4 folds higher total carbohydrates, proteins, and lipids reserves respectively in the fourth larval instar of the autogenous strain compared to that of the anautogenous ones. In addition, exposing the fourth larval instars of autogenous strain to the infection stress by the mosquito larvicidal bacterium, Bacillus thuringiensis var kurstaki has significantly reduced total carbohydrates, proteins and lipids reserves by 29%, 35%, and 46%, respectively, at 12 h postinfection compared to those of uninfected ones. These reductions in nourishment reserves were more pronounced at 24 h postinfection in the case of proteins and lipids, but not carbohydrates. These results may indicate that bacterial infection is a health stress that significantly reduced nourishments reservation, which may interrupt the success of adult autogeny. However, the impact of infection-induced decline in larval nourishments reservation on successful adult autogeny is still to be investigated.

关键词： Aedes caspius anautogeny autogeny Bacillus thuringiensis nourishmentsreservation

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Unintended changes in ocular biometric parameters during a 6-month follow-up period after FS-LASIK and SmILE

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Eye and Vision 2021年第1期8卷 75-82页

作者： Junjie Wang Bernardo T.Lopes Hechen Li Riccardo Vinciguerra Si Cao Songan Wu Rong Zhu Qinmei Wang Xiaobo Zheng Fangjun Bao ahmed elsheikh Eye Hospital Wenzhou Medical UniversityWenzhou 325027ZhejiangChina The Institution of Ocular Biomechanics Wenzhou Medical UniversityWenzhou 325027ZhejiangChina School of Engineering University of LiverpoolLiverpool L693GHUK Humanitas San Pio X Hospital MilanItaly National Institute for Health Research(NIHR)Biomedical Research Centre for Ophthalmology Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of OphthalmologyLondonUK Beijing Advanced Innovation Center for Biomedical Engineering Beihang UniversityBeijingChina

Background:Corneal refractive surgery has become reliable for correcting refractive errors,but it can induce unintended ocular changes that alter refractive *** study is to evaluate the unintended changes in ocular biometric parameters over a 6-month follow-up period after femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK)and small incision lenticule extraction(SmILE).methods:156 consecutive myopic patients scheduled for FS-LASIK and SmILE were included in this *** corneal thickness(CCT),mean curvature of the corneal posterior surface(K_(pm)),internal anterior chamber depth(IACD)and the length from corneal endothelium to retina(ER)were evaluated before and after surgery over a 6-month ***:Both the FS-LASIK and SmILE groups(closely matched at the pre-surgery stage)experienced flatter Kpm,shallower IACD and decreased ER 1 week post-surgery(PmILE *** the 1 week to 6 months follow up period,K_(pm),IACD and ER remained stable unlike CCT which increased significantly(Pmore in the FS-LASIK ***:During the follow up,the posterior corneal surface became flatter and shifted posteriorly,the anterior chamber depth and the length from the corneal endothelium to retina decreased significantly compared with the pre-surgery *** unintended changes in ocular biometric parameters were greater in patients undergoing FS-LASIK than *** changes present clear challenges for IOL power calculations and should be considered to avoid affecting the outcome of cataract surgery.

关键词： Posterior corneal surface Internal anterior chamber depth The length from corneal endothelium to retina FS-LASIK SmILE

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Crystal Structures, Optical, Electrical and magnetic Properties of Ca0.9Sr0.1mn1−xmoxO3 Perovskites for the Applications of multifunctional Devices

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Journal of Applied mathematics and Physics 2025年第1期13卷 61-86页

作者： Sanjana Afrin Tanvir ahmed mithum Kumar Das mohammad majibur Rahman mohammed Nazrul Islam Khan mohammad J. miah Department of Physics Comilla University Cumilla Bangladesh Department of EEE Bangladesh University of Business and Technology Dhaka Bangladesh Department of Environmental Sciences Jahangirnagar University Dhaka Bangladesh materials Science Division Bangladesh Atomic Energy Commission Dhaka Bangladesh

The standard solid-state reaction method was employed to synthesize the polycrystalline Ca0.9Sr0.1mn1−xmoxO3 (CSmmO with x = 0.00, 0.02, 0.04, 0.06, and 0.08) ceramics and each composition was sintered at 1300˚C for 4 hours. The crystal structure, microstructure, optical properties, electrical properties, complex initial permeability, and DC magnetization of the prepared compositions were carried out. The compound exhibited perovskite structure with the transformation of phase from orthorhombic symmetry for x = 0.00 to x = 0.04 samples into a tetragonal symmetry for the samples x = 0.06 and x = 0.08. The lattice constant was found to be enhanced with the doping of mo concentration. The mean grain size was estimated in the micrometer, with values from 1.3045 to 3.0124 µm. Energy band gap (Eg) was determined for each composition and the magnitudes of Eg were lying between 1.85 - 4.00 eV. The Eg values firstly decreased with the doping content up to 2% and, then, increased for 4% to 6% mo contents, where it again very slightly decreased for 8% mo content. The lowest value of Eg was obtained for the x = 0.02 composition. The FTIR spectra revealed the existence of a metal oxide band in each of the prepared samples and supported the formation of a single-phase compound of synthesized material without any impurity, as confirmed by the XRD analysis. The electrical properties, such as resistivity and AC conductivity, were collected using the Impedance analyzer at room temperature. The resistivity and AC conductivity increased with the addition of dopant concentration. The frequency-dependent conductivity spectra showed three distinct regions. The complex initial permeability (μ′) was found to be enhanced with the addition of mo and the highest value was noticed the 6% mo dopant sample. On the other hand, the lowest loss factor was obtained for the samples x ≥ 0.06. The m-H hysteresis loops of various Ca0.9Sr0.1mn1−xmoxO3 ceramics were measured both at room temperature (300 K

关键词： Perovskite Optical Band Gap Conductivity Permeability DC magnetization

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Effect of Colouring Process on Pitting Susceptibility of Austenitic Stainless Steel

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Journal of materials Science & Technology 2008年第3期24卷 400-406页

作者： S.S.mahmoud m.m.ahmed Chemistry Department University College of Girls for ArtsScience and EducationAin Shams University

Colouring of the austenitic stainless steel alloy （20.45% Cr, 8.57% Ni） was carried out in NaNO3-KNO3 eutectic melt without and with additions of Na2O2, NaCl and their mixtures at different temperatures ranging from 400-600℃, under open-circuit and galvanostatic anodic polarization conditions. The produced colours greatly depend on the thickness of oxide films, which in turn depends on the composition of the molten bath and its temperature. The more attractive, bright, adherent and uniform coloured oxide films can be obtained at 400, 450 and 500℃ in molten nitrate bath containing NaCl and Na2O2 mixtures. The pitting corrosion susceptibility of the coloured oxide films was tested in FeCl3 and NaCl as corrosive media. The obtained results indicate that the pitting corrosion susceptibility of the coloured oxide films greatly depends on the previous operating conditions of the colouring process of the stainless steel specimens such as the composition of molten bath, temperature and technique of colouring process.

关键词： Stainless steel alloy Pitting corrosion Colouring processes

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Cutting of nonmetallic materials using Nd:yAG laser beam

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Chinese Physics B 2012年第4期21卷 286-289页

作者： Bashir ahmed Tahir Rashid ahmed m. G. B. Ashiq Afaq ahmed m. A. Saeed Institute of Advanced Photonic Sciences Faculty of Science Universiti Teknologi Malaysia 81310 Skudai Johor Malaysia Physics Department Faculty of Science Universiti Teknologi Malaysia 81310 Skudai Johor Malaysia Centre for Solid State Physics University of the Punjab Lahore Pakistan

This study deals with Nd：yAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd：yAG laser beam power besides work piece scanning speed. For approximate cutting depth, a theoretical study is conducted in terms of material property and cutting speed. Results show a nonlinear relation between the cutting depth and input energy. There is no significant effect of speed on cutting depth with the speed being larger than 30 mm/s. An extra energy is utilized in the deep cutting. It is inferred that as the laser power increases, cutting depth increases. The experimental outcomes are in good agreement with theoretical results. This analysis will provide a guideline for laser-based industry to select a suitable laser for cutting, scribing, trimming, engraving, and marking nonmetallic materials.

关键词： laser power cutting speed depth of cut nonmetallic material Nd:yAG laser

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