A variety of organisms, such as bacteria, fungi, and plants, produce secondary metabolites, also known as natural products. Natural products have been a prolific source and an inspiration for ...numerous medical agents with widely divergent chemical structures and biological activities, including antimicrobial, immunosuppressive, anticancer, and anti-inflammatory activities, many of which have been developed as treatments and have potential therapeutic applications for human diseases. Aside from natural products, the recent development of recombinant DNA technology has sparked the development of a wide array of biopharmaceutical products, such as recombinant proteins, offering significant advances in treating a broad spectrum of medical illnesses and conditions. Herein, we will introduce the structures and diverse biological activities of natural products and recombinant proteins that have been exploited as valuable molecules in medicine, agriculture and insect control. In addition, we will explore past and ongoing efforts along with achievements in the development of robust and promising microorganisms as cell factories to produce biologically active molecules. Furthermore, we will review multi-disciplinary and comprehensive engineering approaches directed at improving yields of microbial production of natural products and proteins and generating novel molecules. Throughout this article, we will suggest ways in which microbial-derived biologically active molecular entities and their analogs could continue to inspire the development of new therapeutic agents in academia and industry.
The stress-strain-strength response of soils is of significant interest to development and calibration of realistic constitutive models that can be used in numerical simulation of geotechnical ...engineering problems. An extensive characterization of Ottawa F65 sand along with various monotonic and cyclic tests conducted during the course of the Liquefaction Experiments and Analysis Projects (LEAP) are presented here. The specimens in these tests were prepared using a meticulous sample preparation technique to facilitate their consistency and repeatability. Monotonic drained and undrained triaxial tests shed light on the steady-state (critical state) of Ottawa sand, while stress-controlled and strain-controlled cyclic triaxial and direct simple shear tests provide key information on the cyclic stress-strain behavior and liquefaction strength of this soil. The triaxial tests identify the liquefaction strength of the soil at different densities, while the direct simple shear tests evaluate the effect of overburden pressure on the cyclic response. The results of these experiments are also compared to the experimental results available in the literature. The data obtained from the cyclic triaxial and direct simple shear tests were further analyzed by plotting the computed shear modulus degradation and damping curves. The results show how the soil stiffness degrades as cyclic shear stress is applied for soil at different densities and confining stresses. It can be seen that the rate of shear modulus degradation increases with the increase of confining stress and decreases with the increase of soil density. The damping curves consistently show an increasing in damping ratio until a shear strain of about 0.05%, followed by a plateau at about 20–25% damping ratio for shear strain between 0.05 and 0.5%, and ending with a decrease in damping until reaching a final damping ratio of about 10%.
•An experimental study was presented on the stress-strain response and liquefaction strength of Ottawa F65 sand.•23 stress-controlled cyclic triaxial tests were performed on samples of different relative densities (71.5, 87.5 and 97.5%).•37 strain-controlled cyclic triaxial tests were performed on samples of different relative densities (40, 63.8 and 75.6%).•11 cyclic direct shear tests were conducted on samples under 100 and 40 kPa overburden stress.•Results showed consistency and repeatability, and shear modulus degradation and damping curves were computed for each test.
Hourly wind speed time series data of two meteorological stations in Malaysia have been used for stochastic generation of wind speed data using the transition matrix approach of the Markov chain ...process. The transition probability matrices have been formed using two different approaches: the first approach involves the use of the first order transition probability matrix of a Markov chain, and the second involves the use of a second order transition probability matrix that uses the current and preceding values to describe the next wind speed value. The algorithm to generate the wind speed time series from the transition probability matrices is described. Uniform random number generators have been used for transition between successive time states and within state wind speed values. The ability of each approach to retain the statistical properties of the generated speed is compared with the observed ones. The main statistical properties used for this purpose are mean, standard deviation, median, percentiles, Weibull distribution parameters, autocorrelations and spectral density of wind speed values. The comparison of the observed wind speed and the synthetically generated ones shows that the statistical characteristics are satisfactorily preserved.
A simple stress-ratio controlled, critical state compatible, sand plasticity model is presented, first in the triaxial and then in generalized stress space. The model builds upon previous work of the ...writers, albeit the presentation here is made with extreme simplicity in mind, and three novel aspects are introduced. The first is a fabric-dilatancy related quantity, scalar valued in the triaxial and tensor valued in generalized stress space, which is instrumental in modeling macroscopically the effect of fabric changes during the dilatant phase of deformation on the subsequent contractant response upon load increment reversals, and the ensuing realistic simulation of the sand behavior under undrained cyclic loading. The second aspect is the dependence of the plastic strain rate direction on a modified Lode angle in the multiaxial generalization, a feature necessary to produce realistic stress-strain simulations in nontriaxial conditions. The third aspect is a very systematic connection between the simple triaxial and the general multiaxial formulation, in order to use correctly the model parameters of the former in the implementation of the latter. The simulative ability of the model is illustrated by comparison with data over a very wide range of pressures and densities.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Global transportation has shifted toward electromobility to achieve net-zero emission, and in the next few decades, commercial electric aircraft is likely to become a reality. This transition has ...embarked on through the existing more electric aircraft (MEA), and the ultimate goal will be potentially achieved by hybrid-electric and all-electric airliners, along with green fuels, such as green hydrogen or supercritical CO2 (sCO2) and its potential Gg CO2 equivalent elimination-with or without combustion. Electric propulsion replaces conventional jet propulsors with electric fans powered by electric generators rotated by an engine, a combination of generators and energy storage, or just energy storage. An appealing idea is to distribute the electric fans along the aircraft wings or tails to improve aerodynamics, boost energy efficiency, and reduce carbon emissions and acoustic noise. Focusing on distributed electric propulsion (DEP) systems, this article reviews the state-of-the-art advancements in aircraft electrification. Three major DEP categories, i.e., turboelectric, hybrid-electric, and all-electric propulsion technologies, are investigated. Although all of them utilize electric fans as propulsors, their system structures and power generation stages are different. Hence, comprehensive considerations are required to optimize the DEP system designs. Starting with the multifarious electrical system architectures proposed in the literature, a thorough review is conducted including the system parametric specifications, design considerations of power converters, the power electronics devices' characteristics in cryogenic conditions, and various energy storage systems. This review aims to provide a reference to researchers, engineers, and policy-makers in aviation to accelerate the progress toward future net-zero emissions.
During an earthquake, soil deposits are often subjected to complex stress/strain time histories that are quite different from the simplified ones used in laboratory tests for evaluation of the ...stress-strain-strength of these soils. To mimic the stress/strain time histories experienced at different depths of a mildly sloping soil deposit, a series of direct simple shear tests were conducted on Ottawa F65 sand specimens. The trends observed in these experiments were then used to estimate the lateral spreading of mildly sloping saturated deposits of the same sand subjected to various base motion time histories measured in the centrifuge tests conducted as part of an international research project (Liquefaction Experiment and Analysis Project, LEAP-2015 and LEAP-2017).
In each CDSS test, after imposing the initial stress state, the specimen was subjected to non-uniform stress waves that resembled the shear stress time histories likely to develop in the LEAP-2015 and LEAP-2017 centrifuge specimens. A total of 17 CDSS tests were performed on specimens with relative densities of approximately 66%. Initial vertical and shear stresses were imposed on each soil specimen to correspond to the state of stress in a mildly sloping soil layer at two depths of about 4 m and 3 m. A ramped sinusoidal shear stress wave similar to the ramped sinusoidal base motion used in the LEAP centrifuge experiments was employed. The test results displayed a consistent trend between the peak cyclic stress ratio and the permanent shear strain that developed in the soil. The effects of overburden stress on the magnitude of permanent deformations were observed. Smaller initial vertical stress resulted in a more dilative response and smaller permanent shear strain. The observed permanent shear strain vs. peak cyclic stress ratio curves were then used to predict the lateral spreading of mildly sloping deposits tested in the LEAP-2015 and LEAP-2017 centrifuge experiments. Reasonably close correlation between the predicted and measured displacements were obtained. The developed dataset, made publicly available on DesignSafe-CI, can be used for calibration, evaluation, and further development of constitutive models for liquefiable soils.
•An experimental study was presented on liquefaction-induced permanent strain on sloping grounds.•17 CDSS tests were conducted to model the stress-strain response of liquefiable sloping ground soil at different depths.•Non-uniform cyclic shear stress was subject to the soil to mimic the stresses induced by an earthquake.•A close agreement was observed between the results and previously conducted centrifuge experiments.•The results obtained from the element tests were used to predict the lateral spreading observed by LEAP centrifuge tests.
Experimental investigations were performed to evaluate the effect of waste Polyethylene Terephthalate (PET) fibres on the mechanical properties of Green Ultra-High Performance Cementitious Composites ...(GUHPCCs). Ultra-fine Palm Oil Fuel Ash (UPOFA) and Silica Fume (SF) were utilised to produce GUHPCCs that consist of up to 50% UPOFA and 20% SF as a partial replacement binder with cement. PET fibres were added to the GUHPCCs at a proportion of 1% of the total mixed volume, to produce Green Ultra-High Performance PET reinforced Cementitious Composites (GUHPPCCs). The mechanical properties and flexural performance of the resulting beams and slabs, including their stress-strain behaviour and ductility, were investigated. Results showed that addition of PET fibres increases the flexural strength of GUHPPCCs beams by approximately 63.24% compared with that of the ultra-high performance concrete control at the age of 90 days. Moreover, significant improvements in the flexural capacity and ductility index of the GUHPPCCs slabs were obtained. These findings may due to the bridging effects of PET fibres. Thus, the combination of UPOFA and SF with PET fibres can produce GUHPPCCs with superior mechanical properties and enhanced ductility.
Seismic performance of bridge abutments founded in potentially liquefiable soils is of significant interest to researcher and practitioners in geotechnical earthquake engineering. Piles are typically ...a key element of these geo-structures and may undergo large deformations and rotations when their lateral support is significantly reduced or momentarily lost due to the occurrence of earthquake-induced soil liquefaction. Observations from the past earthquakes show that in addition to material nonlinearity, geometric nonlinearity of the pile may also play an important role in the overall response of the foundation. In this work, a series of finite element analyses are carried out to assess the effects of material and geometric nonlinearities on the response of a pile embedded in liquefiable soil. The results of these numerical simulations are compared with the responses observed in the centrifuge experiments, performed at Kyoto University, modeling the same boundary value problem in Toyoura sand. The constitutive model used in the simulations is calibrated against a series of cyclic direct simple shear (CDSS) tests conducted at the George Washington University on Toyoura sand. The simulation results demonstrate that in addition to material nonlinearity of the pile material, geometric nonlinearity plays a critical role in modeling of the pile response, and without proper consideration of these effect, the overall response of the pile will not be accurately represented by the numerical simulations.
Seismic response of geostructures in liquefiable soils is often quite complex and may involve several factors that contribute to the key mechanisms affecting the overall performance. However, in some ...cases, if critical mechanisms are well understood, it might be possible to estimate the system response by using relatively simple analytical tools. This study investigates the potential use of direct simple shear (DSS) test in estimating the seismic response of sheet-pile retaining structures supporting liquefiable soils. Through a comprehensive analysis of the centrifuge experiments carried out as part of the 2022 Liquefaction Experiments and Analysis Projects (LEAP-2022), coupled with Type-C numerical simulations of the centrifuge experiments, it is observed that the sheet-pile wall response is critically related to the stress-strain response of the soil near the tip of the sheet-pile wall which is embedded in a dense layer of Ottawa F65 sand. An in-depth understanding of such stress-strain response using laboratory-based element tests might provide a means to estimate the wall rotation and its lateral displacements. To this end, simplified numerical analyses were performed to estimate the initial vertical effective stress and time-history of shear stresses caused by the earthquake near the tip of the sheet-pile wall. Then, several specimens of Ottawa F65 sand were prepared at relative densities comparable to the values achieved in the LEAP-2022 centrifuge experiments and were subjected to the estimated shear stress time-histories. By assuming a rigid body motion of the sheet-pile wall during earthquake, the rotation of the wall at the end of earthquake motion was then estimated using the permanent shear strains measured in the DSS tests. It is observed that the estimated rotations of the sheet-pile wall compare well with the rotations observed in the centrifuge tests and those obtained in Type-C numerical simulations. In these cases, DSS tests are shown to provide a relatively simple means for estimating the rotations of the sheet-pile wall.
Centrifuge modeling has been used to observe some key characteristics of liquefiable soils during seismic motions. If carefully conducted, the results of centrifuge tests can be used for validation ...of constitutive models and numerical modeling tools. However, a thorough evaluation of numerical models requires knowledge of the soil properties and the uncertainties associated with these properties. Moreover, the base excitations achieved in centrifuge tests often vary from the target base excitation, and a fair evaluation of the quality of blind prediction of a centrifuge test requires an account of the uncertainties associated with the achieved base motion. This paper presents an analysis of the effects of the inherent variability present in the soil density and base motion on the lateral spreading of mildly sloping ground. The analysis combines fully-coupled non-linear finite element modeling with Monte Carlo simulation. The stochastic analysis is based on the variabilities observed in the density of the soil specimens and in the achieved base motions of the centrifuge tests conducted for the Liquefaction Experiments and Analysis Projects (LEAP): LEAP-GWU-2015 and LEAP-UCD-2017. The two-surface plasticity model for sand is used to model the soil response. The model is calibrated against element tests performed on Ottawa-F65 sand to determine its liquefaction strength. The finite element model is pre-validated through deterministic simulation of the centrifuge experiments conducted during the LEAP project. The sources of variability are identified and their magnitudes are quantified based on the results obtained from the LEAP centrifuge experiments. First, the effects of the soil spatial variability are presented. Then, the effects of the base motion variability are discussed. Finally the combined effects of the variability in the soil density and base motion are evaluated. The results obtained from the stochastic analysis are compared with the variability in the soil response observed in the centrifuge experiments. The results obtained from this study show that by carefully modeling the different sources of variability, the stochastic analysis was able to model the observed variability in the lateral displacement of the centrifuge experiments. The results obtained confirm the observation that the lateral displacement of liquefiable soil is more sensitive to the base excitation variability than the variability in the soil density.
•The effects of the variability in soil density and base motion on lateral spreading of mildly sloping ground is presented.•The analysis combines fully-coupled non-linear finite element modeling with Monte Carlo simulation.•The stochastic analysis is based on the variabilities observed in LEAP-GWU-2015 and LEAP-UCD-2017 centrifuge experiments.•The two-surface plasticity model for sand is used to model the soil response.•The model is calibrated against element tests performed on Ottawa-F65 sand to determine its liquefaction strength.•The finite element model is pre-validated through deterministic simulation of the LEAP centrifuge tests.•The effects of the soil spatial variability are presented including the effects of the sample preparation method.•Synthetic base motions were generated to match the achieved base motion variability are discussed.•The separate and combined effects of the variability in the soil density and base motion are evaluated.•The stochastic analysis results are compared to the soil response observed in the centrifuge experiments.•Close agreement between the variability in the stochastic analysis and the centrifuge experiments was observed.•Results confirm that lateral spreading variability is more sensitive to base motion than to soil density.
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