Excessive utilization of petroleum diesel has led to severe environmental pollution. Biodiesel, which is greener and renewable, can be a potential alternative fuel. Biodiesel is produced through ...transesterification reaction between vegetable oil, animal fat or even waste cooking oil (WCO) and alcohol in the presence of catalyst. Under process intensification, ultrasonic irradiation is employed in the transesterification reaction to enhance the agitation between immiscible reactants. Besides providing intensive mixing, it also offers uniform heating due to the localized temperature increase and formation of micro jets from the transient collapse of cavitation bubbles, thus reducing the energy consumption. The focus of this paper is to review the recent research progress on the ultrasound-assisted catalytic transesterification of non-edible vegetable oils using homogeneous and heterogeneous catalysts. The primary factors that affect the operation and efficiency of ultrasound-assisted transesterification such as alcohol to oil molar ratio, catalyst loading, reaction time, reaction temperature, energy consumption, phase separation time, ultrasonic pulse mode and biodiesel conversion or yield have been reviewed. The highlights of this review paper are the provisions on the mechanism of ultrasonic reactive extraction (RE) in the biodiesel production, kinetic study and the existing pilot reactors on the ultrasound-assisted transesterification which are still rarely reviewed in the current literature. Lastly, the challenges and feasibility for future development in the process intensification of biodiesel production are also addressed.
Three-dimensional food printing (3DFP) leads to advances in digital gastronomy by targeting consumers’ specific requirements for nutrition customization and visual appeal. Dysphagia, or difficulty ...swallowing, is prevalent in elderly people and patients suffering from debilitating illnesses. Dysphagic diets require textural modifications to render them soft and safe to swallow. Diets must be visually pleasing to enable a greater food uptake to prevent malnutrition in patients. 3DFP so far has mainly utilized freeze-dried vegetable powders for shaping 3D designs. Our work focuses on fresh and frozen vegetables having better nutritional profile and low costs. Three different categories of vegetables are identified based on the number of hydrocolloids required to render them printable. Garden pea, carrot and bok choy are chosen as representatives in each category, which requires no HC, one type of HC and two types of HCs, respectively. Food inks are prepared by the addition of HCs i.e. xanthan gum (XG), kappa carrageenan (KC) and locust bean gum (LBG) for texture modification. Rheological, textural, microstructural and syneresis properties of the inks are examined. International dysphagia diet standardisation initiative (IDDSI) tests are done to assess the potential of the inks for dysphagic diets. Optimized ink formulations display excellent 3D printability, minimal water seepage, and dense microstructures with minimal amount of HCs. Using fresh vegetables instead of freeze-dried foods serves the purpose of preserving flavour and nutrition like real food. This in turn may bring 3DFP closer to the hospital and nursing home kitchens.
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•Three-dimensional food printing of fresh vegetables for dysphagic patients.•Three vegetable categories defined according to the number of hydrocolloids required to prepare food inks.•Extensive characterization of food ink properties and its suitability for dysphagic patients.•3D-Printable food inks with no more than 2% hydrocolloids.•A method of quantifying syneresis in food inks.
•Moving heat sources generate heat and thermal cycles as heat rate and cooling rate in fusion welding processes which affect the resistance of materials.•Numerical simulation of welding can ...efficiently predict the thermal cycles and then optimize the welding process.•Element-free Galerkin method (EFGM) is a meshfree method in which nodes are used for approximation rather than elements as in the finite element method (FEM).•EFGM parameters have important influence on the precision of the method.
A three-dimensional unsteady heat transfer model based on the meshless Element-Free Galerkin (EFG) method was developed to predict the temperature field generated by a moving heat source. Numerical results obtained from the EFG method were compared with those from the finite element method (FEM) and then validated with robotic arc welding experimental results. Good agreements were found between the numerical and experimental results. An EFG parametric study was also carried out to investigate the effects of (i) the size and shape of the support domain, (ii) the ratio of quadrature points to field nodes, and (iii) the different weight functions.
Disclosed here is the first geminal (gem‐) hydroborative cyclization of enynes. Different from known hydroborative cyclizations, this process adds hydrogen and boron to the same position, leading to ...a new reaction mode. With Cp*RuCl4 as catalyst, a range of gem‐hydroborated bicyclic products bearing a cyclopropane unit could be rapidly assembled from simple enyne substrates. Control experiments and density functional theory (DFT) calculations provided important insights into the reaction mechanism. Notably, two major competing pathways may operate with substrate‐dependence. 1,6‐Enynes favor initial oxidative cyclometalation to form a ruthenacyclopentene intermediate prior to engaging hydroborane, while other enynes (e.g., 1,7‐enynes) that lack strong propensity toward cyclization prefer initial alkyne gem‐(H,B)‐addition to form an α‐boryl ruthenium carbene followed by intramolecular olefin cyclopropanation. This process also represents the first ruthenium‐catalyzed enyne hydroborative cyclization.
Different from the previously known hydroborative cyclizations that add hydrogen and boron to opposite sides of an enyne, the proper choice of a ruthenium catalyst alters this propensity to a new addition mode, geminal hydroborative cyclopropanation. Two possible mechanisms are operative, which are substrate‐dependent based on DFT studies.
This letter presents a new design method for a tunable bandpass filter with independently and widely tunable transmission zeros (TZs). Varactor‐loaded microstrip resonators are introduced to a fixed ...bandpass filter to realize the continuously tunable TZs. Although the tunable resonators have unloaded Q lower than 100, the insertion loss of the filter is not increased. The coupling matrix with the lossy resonators is synthesized and used to analyze the characteristic of the TZ‐tunable filter. A bandpass filter centered at 2 GHz with a 3‐dB bandwidth of 230 MHz is designed to validate the design concept. The measured results show good agreement with the simulated results. The fabricated filter has 2 TZs ranging from 1.4 to 1.8 GHz and from 2.28 to 3.08 GHz, respectively. The TZ‐tunable filter exhibits insertion losses ranging from 1.62 dB to 1.93 dB at the center frequency. The center frequency and bandwidth keep nearly unchanged when the TZs are tuned.
This Letter presents a third-order multilayer substrate integrated waveguide (SIW) filter with broadband stopband. The filter is composed of three vertically stacked square SIW cavities. The ...input/output feeding structure and the coupling slot in the middle metal layer of two cavities are properly designed to just allow the fundamental resonant mode to a couple while other higher spurious resonant modes are isolated. The fabricated filter is at a centre frequency of 6.96 GHz with a stopband suppression of 24 dB up to 2.77f0.
Piezoelectric-driven mechanisms have several advantages like high stiffness, rapid response, and good resolution. Therefore, they are widely used for many micro/nano trajectory-tracking applications. ...However, the existence of the hysteretic nonlinearity behavior makes it challenging to use in practice. In addition, the hysteresis changes with frequency and is dependent on environmental parameters like temperature and load. Finding a method that can track both continuous periodic and nonperiodic motion under wide frequency range with high precision is nontrivial. In this study, a feedforward-feedback control strategy is proposed to bridge this gap, where a direct inverse rate-dependent Prandtl-Ishlinskii model based on radial basis function neural network to compensate rate-dependent hysteresis and a proportional-integral controller with an inner-loop disturbance observer to further attenuate tracking error (caused by the imperfect modeling, unknown lumped disturbance). The proposed method can perform a wide-bandwidth tracking control of periodic and nonperiodic motion of a piezoelectric-driven mechanism. Experiments are then conducted to demonstrate the capability of the proposed controller.
Abstract
Among about 150 identified allenic natural products, the exocyclic allenes constitute a major subclass. Substantial efforts are devoted to the construction of axially chiral allenes, ...however, the strategies to prepare chiral exocyclic allenes are still rare. Herein, we show an efficient strategy for the asymmetric synthesis of chiral exocyclic allenes with the simultaneous control of axial and central chirality through copper(I)-catalyzed asymmetric intramolecular reductive coupling of 1,3-enynes to cyclohexadienones. This tandem reaction exhibits good functional group compatibility and the corresponding optically pure exocyclic allenes bearing
cis
-hydrobenzofuran,
cis
-hydroindole, and
cis
-hydroindene frameworks, are obtained with high yields (up to 99% yield), excellent diastereoselectivities (generally >20:1 dr) and enantioselectivities (mostly >99% ee). Furthermore, a gram-scale experiment and several synthetic transformations of the chiral exocyclic allenes are also presented.
Localization in GPS-denied environments is challenging, and many existing solutions have infrastructural and on-site calibration requirements. This article tackles these challenges by proposing a ...localization system that is infrastructure free and does not require on-site calibration, using a single active pan-tilt-zoom camera to detect, track, and localize a circular LED marker. We propose to use a convolutional neural network (CNN) trained using only synthetic images to detect the LED marker as an ellipse and show that our approach is more robust than using traditional ellipse detection without requiring tuning of parameters for feature extraction. We also propose to leverage the predicted elliptical angle as a measure of uncertainty of the CNN's predictions and show how it can be used in a filter to improve marker range estimation and 3-D localization. We evaluate our system's performance through localization of a unmanned aerial vehicle in real-world flight experiments and show that it can outperform alternative methods for localization in GPS-denied environments. We also demonstrate our system's performance in indoor and outdoor environments.
Parkinson's disease (PD) is a significantly progressive neurodegenerative disease characterised by both motor and nonmotor disorders. The main pathological characteristics of PD consist of the loss ...of dopaminergic neurons and the formation of alpha-synuclein-containing Lewy bodies in the substantia nigra. Currently, the main therapeutic method for PD is anti-Parkinson medications, including levodopa, madopar, sirelin, and so on. However, the effect of pharmacological treatment has its own limitations, the most significant of which is that the therapeutic effect of dopaminergic treatments gradually diminishes with time. Exercise training, as an adjunctive treatment and complementary therapy, can improve the plasticity of cortical striatum and increase the release of dopamine. Exercise training has been proven to effectively improve motor disorders (including balance, gait, risk of falls and physical function) and nonmotor disorders (such as sleep impairments, cognitive function and quality of life) in PD patients. In recent years, various types of exercise training have been used to treat PD. In this review, we summarise the exercise therapy mechanisms and the protective effects of different types of exercise training on PD patients.
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