A low-loss and low-crosstalk multimode waveguide bend is proposed and demonstrated for mode-division-multiplexed optical interconnects. The proposed 90°-bend is composed of two identical 45°-bends, ...which are defined as modified Euler curves. For the designed 90° Euler-bend with a core width of 2.36 μm for supporting four TM-polarization modes, it is allowed to achieve an effective radius as small as 45 μm, which is about 1/4 of the radius (~175 μm) for a regular 90° arc-bend. In theory, this proposed 90° Euler-bend has very low excess losses (<0.1 dB) and very low inter-mode crosstalks (<-25 dB) over a broad wavelength-band. A silicon photonic integrated circuit is designed, fabricated and characterized by integrating a pair of mode (de)multiplexers and a multimode bus waveguide with a Euler S-bend consisting of two cascaded 90° Euler-bends. The measurement results show that the fabricated Euler S-bend has low excess losses of <0.5 dB and low inter-mode crosstalks of <-20 dB over a broad band from 1520 nm to 1610 nm for all the 4 mode-channels of TM polarization.
Injectable, long-acting depot formulations based on poly(lactide-co-glycolide) (PLGA) have been used clinically since 1989. Despite 30 years of development, however, there are only 19 different drugs ...in PLGA formulations approved by the U.S. Food and Drug Administration (FDA). The difficulty in developing depot formulations stems in large part from the lack of a clear molecular understanding of PLGA polymers and a mechanistic understanding of PLGA microparticles formation. The difficulty is readily apparent by the absence of approved PLGA-based generic products, limiting access to affordable medicines to all patients.
PLGA has been traditionally characterized by its molecular weight, lactide:glycolide (L:G) ratio, and end group. Characterization of non-linear PLGA, such as star-shaped glucose-PLGA, has been difficult due to the shortcomings in analytical methods typically used for PLGA. In addition, separation of a mixture of different PLGAs has not been previously identified, especially when only their L:G ratios are different while the molecular weights are the same. New analytical methods were developed to determine the branch number of star-shaped PLGAs, and to separate PLGAs based on L:G ratios regardless of the molecular weight. A deeper understanding of complex PLGA formulations can be achieved with these new characterization methods. Such methods are important for further development of not only PLGA depot formulations with controllable drug release kinetics, but also generic formulations of current brand-name products.
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Poly (lactide-co-glycolide) (PLGA) has been used for making injectable, long-acting depot formulations for the last three decades. An in depth understanding of PLGA polymers is critical for ...development of depot formulations as their properties control drug release kinetics. To date, about 20 PLGA-based formulations have been approved by the U.S. Food and Drug Administration (FDA) through new drug applications, and none of them have generic counterparts on the market yet. The lack of generic PLGA products is partly due to difficulties in reverse engineering. A generic injectable PLGA product is required to establish qualitative and quantitative (Q1/Q2) sameness of PLGA to that of a reference listed drug (RLD) to obtain an approval from the FDA. Conventional characterizations of PLGA used in a formulation rely on measuring the molecular weight by gel permeation chromatography (GPC) based on polystyrene molecular weight standards, and determining the lactide:glycolide (L: G) ratio by 1H NMR and the end-group by 13C NMR. These approaches, however, may not be suitable or sufficient, if a formulation has more than one type of PLGA, especially when they have similar molecular weights, but different L:G ratios. Accordingly, there is a need to develop new assay methods for separating PLGAs possessing different L:G ratios when used in a drug product and characterizing individual PLGAs.
The current work identifies a series of semi-solvents which exhibit varying degrees of PLGA solubility depending on the L:G ratio of the polymer. A good solvent dissolves PLGAs with all L:G ratios ranging from 50:50 to 100:0. A semi-solvent dissolves PLGAs with only certain L:G ratios. Almost all semi-solvents identified in this study increase their PLGA solubility as the L:G ratio increases, i.e., the lactide content increases. This lacto-selectivity, favoring higher L:G ratios, has been applied for separating individual PLGAs in a given depot formulation, leading to analysis of each type of PLGA. This semi-solvent method allows a simple, practical bench-top separation of PLGAs of varying L:G ratios. This method enables isolation and identification of individual PLGAs from a complex mixture that is critical for the quality control of PLGA formulations, as well as reverse engineering for generic products to establish the Q1/Q2 sameness.
•Spatiotemporal variation in vegetation on the Loess Plateau was investigated.•Precipitation was the greatest driving factor.•There was a bivariate or nonlinear enhancement between all factors.•Key ...factors' adaptation range or type suitable for vegetation cover was identified.
Vegetation, being a core component of ecosystems, is known to be influenced by natural and anthropogenic factors. Studying vegetation cover dynamics variation and its drivers is critical to understanding the interactions between vegetation and ecosystems. The Loess Plateau (LP) is located in a semi-arid and semi-humid region with severe soil erosion and fragile ecology. This paper used the annual maximum Normalized Difference Vegetation Index (NDVIymax) and growing season mean NDVI (NDVIgsmean) as the vegetation cover indicator. The vegetation cover variation of LP from 2000 to 2020 was analyzed using Sen's slope and Mann-Kendall test. Then the influence of natural and anthropogenic factors on the driving mechanisms of spatial vegetation differentiation was explored by the Geodetector model. The results revealed that the growth trends of NDVIymax and NDVIgsmean were 0.075/10 years and 0.038/10 years, respectively, and the areas with improved vegetation cover accounted for 92.67 % and 88.58 % of the total area. The vegetation cover of the southeastern and northern parts of the LP decreased significantly; however, the central, southwestern, and northeastern parts exhibited a remarkable improvement. Precipitation, vegetation type, soil type, temperature, and land use type were the key driving forces, ranked differently on NDVIymax and NDVIgsmean. However, precipitation was the most critical factor both on NDVIymax and NDVIgsmean. The interaction detection showed non-linear and mutual enhancement, with no independent factor. The findings of our study can assist in identifying the vegetation cover status of the LP, as well as the driving forces, which can provide theoretical support for the formulation of environmental conservation policies.
As an important indicator of terrestrial ecosystems, vegetation plays an important role in the study of global or regional ecological environmental changes. Northern Shaanxi is located in the ...ecologically fragile area of the Loess Plateau, which is affected by interactions between natural and human factors. Here, we used the Normalized Difference Vegetation Index (NDVI) as an indicator to study the temporal and spatial variations of vegetation in Northern Shaanxi from 2000 to 2018. Based on the geographic detector method which can detect spatial differentiation, we analyzed the spatial differentiation characteristics and driving forces of vegetation in Northern Shaanxi, and revealed the most appropriate range or type of influencing factors for promoting vegetation growth. The results showed that the overall vegetation coverage improved in the study area, and NDVI showed an increasing trend with a growth rate of 0.10/10 years from 2000 to 2018. Natural and human factors are crucial driving forces of NDVI change, among which gross domestic product, land-use type, slope, and temperature have the greatest influence. The interaction between natural and human factors on NDVI was dominated by nonlinear and mutual enhancement effects, and the influence of interactions among all factors was significantly higher than that of a single factor. The range or types of factors suitable for vegetation growth were analyzed in the study area, and the joint action of natural and human factors had a more significant impact on vegetation. These findings provide a scientific basis for local governments to intervene in vegetation changes and ecological restoration through natural and human factors within the favorable scope.
•The oxygen concentration errors at each length are 2.46%, 6.16% and 10.36%•The net output power density at 3 atm is 0.403 W∙cm-2 higher than that at 1 atm.•It is more effective when cooling flow ...direction is consistent with oxygen.•Counter-flow facilitates the water hydration level of the membrane.•The non-isothermal thermal condition leads to uneven temperature distribution.
Conventional three-dimensional (3D) computational fluid dynamics (CFD) simulations of proton exchange membrane fuel cell (PEMFC) are limited to the single-channel scale, while the influence of gas distribution zone and complex flow structure with multiple channels is ignored and the role of cooling flow field is not considered. Therefore, a metal bipolar plate structure with “dot matrix” gas distribution zones and a waveform staggered flow field with small cathode size flow channels is proposed. The cooling flow fields are set up to analyze the effect on the output performance of the PEMFC. Firstly, the analysis of the gas and liquid distribution within the flow field reveals a maximum error of 10.36% for the cathode gas concentration, which is much larger than the anode (4.51%). The large pressure drop at the cathode leads to a small value for the liquid saturation. Secondly, the output parameters of the PEMFC are compared at different operating pressures, which results in a high operating pressure that clearly contributes to the improved performance of the fuel cell. Furthermore, when the reaction gas is counter-flow, the electrochemical reaction rate is faster and the water hydration level of the proton exchange membrane (PEM) is higher. The cooling flow field is most effective when it flows in the same direction as the oxygen flow. Finally, the effects of different thermal boundary conditions on the distribution of oxygen within the cathode flow field are compared and the results show that high local temperatures are also a major factor in the uneven distribution of oxygen concentration in the flow field.
The output performance of PEMFC (proton exchange membrane fuel cell) is limited by the operating conditions of the fuel cell, including the control temperature, gas concentration distribution and ...working pressure. In order to simplify the calculation process, the existing literatures mostly use single channel to study the output indexes of batteries. Initially, based on 3D (three-dimensional) CFD (computational fluid dynamics) simulation, a method to optimize the gas distribution in the flow field by using the distribution area is proposed for a commercial large-scale PEMFC with an activation area of 107.44 cm2. The uniformity of gas concentration distribution in anode and cathode flow field is taken into consideration to test the influence of flow field. The relationship between liquid saturation and gas velocity in the flow field is also analyzed. Furthermore, the effects of anode and cathode gas flow direction on gas concentration in CL (catalytic layer) and water content in PEM (proton exchange membrane) is studied, and both methods have little effect on PEMFC. Additionally, the performance of PEMFC is obviously improved by increasing operating pressure, and the reactant gas molar concentration and membrane water content are increased significantly. Finally, study proves that it is more beneficial to the performance of PEMFC when cooling flow direction is consistent with oxygen.
•A method to optimize the gas distribution in the flow field by using the distribution area is proposed.•The influence of anode and cathode gas flow direction on gas concentration is studied.•The net power density with high operating pressure is 0.531 (W⋅cm−2) higher than that at 1 atm.•It is more effective when cooling flow direction is consistent with oxygen.
Residual stress plays an important role in controlling the performance of high-precision martensitic steel parts, as it affects the properties of the material in various ways. At present, the dynamic ...evolution of the phase transition mechanism in residual stress generation is not yet fully understood, and there have been few quantitative studies on the effect of phase transitions on the residual stress generated in the micro-grinding process. In this study, flow stress was modeled by considering the specific volume and yield stress in the phase-transition process, and a user-defined constitutive model was developed. A finite-element model that simulates the movement and application of thermo-mechanical loading and phase transitions on the surface and subsurface of the machined material was developed to predict the residual stress generated by micro-grinding. The accuracy of the simulations and the effect of phase transitions on the residual stress were experimentally verified. The results showed that the effect of phase transitions on the residual stress was mainly reflected in the tangential subsurface. This study used a novel approach in the analysis of residual stress induced by micro-grinding and established two process optimization criteria for the reduction of residual stress. The results of this study provide a more comprehensive understanding of the phase transition and residual stress mechanisms governing the grinding process, which could potentially be useful for improving the reliability of high-strength martensitic steel components.
The chemical composition of black tea during tea processing is in a state of flux. However, the dynamic changes of this sophisticated metabolic process are far from clear. GC–MS-based metabolomic ...analyses were performed to examine changes in volatile and non-volatile compounds throughout the five stages of tea processing. The results showed that the most striking differences were observed at the withering and rolling stages, during which 62 non-volatile and 47 volatile compounds were significantly changed. The levels of most monosaccharides decreased at the withering stage and increased in subsequent stages while di-saccharides decreased as the process progressed. Free amino acids increased sharply at the withering stage, and most kept increasing or remained stable afterwards. However, levels of catechin, epicatechin, epigallocatechin, and epigallocatechin gallate decreased after withering and remained at low levels afterwards. Among the 47 volatile compounds with altered levels, phenylpropanoids/benzenoids and carotenoid-derived volatiles, which contribute to the honey-like and rose-like fragrances and quality of Danxia2 tea, kept increasing during the processing, among them eight were newly produced. Furthermore, 19 volatiles with a grassy odor decreased during processing. This study provides a comprehensive profile of metabolic changes during black tea processing, which is potentially important for both quality control and improvement of the flavor of black teas.
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•GC–MS-based metabolic profiling of Camellia sinensis during black tea processing.•Stage-specific dynamic changes of non-volatile/volatile compounds were revealed.•Sixty-two non-volatiles were changed significantly during the processing.•Eight volatiles were newly produced, and 19 were decreased during the processing.•Changes in various metabolites may contribute to black tea unique sensory quality.
Residual stress is a key indicator to measure the forming quality of selective laser melting (SLM) components, and its control method has received extensive attention. As an auxiliary structure for ...forming SLM components, the structural characteristics of the supporting structure will affect the residual stress distribution of the formed parts. Therefore, it is extremely meaningful to explore the influence of the supporting structure design on the residual stress of SLM AlSi10Mg alloy. In this study, an approach is proposed to select and design the supporting structure for forming SLM components with different structural characteristics to achieve the purpose of reducing the residual stress in the overhanging structure of the components. As the result shows, when the contact area of single supporting tooth structure and component overhanging structure is 0.25mm
2
and the X/Y interval of main supporting structure is 2.5mm, the forming effect is relatively good. Furthermore, the block supporting structure is more suitable for the overhanging structure which has small areas and less height, and the contour support is more suitable for the overhanging structure with larger area.
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