Reverse Gradient Research Articles

Reverse Gradient Distributions of Drug and Polymer Molecules within Electrospun Core-Shell Nanofibers for Sustained Release.

Core-shell nanostructures are powerful platforms for the development of novel nanoscale drug delivery systems with sustained drug release profiles. Coaxial electrospinning is facile and convenient for creating medicated core-shell nanostructures with elaborate designs with which the sustained-release behaviors of drug molecules can be intentionally adjusted. With resveratrol (RES) as a model for a poorly water-soluble drug and cellulose acetate (CA) and PVP as polymeric carriers, a brand-new electrospun core-shell nanostructure was fabricated in this study. The guest RES and the host CA molecules were designed to have a reverse gradient distribution within the core-shell nanostructures. Scanning electron microscope and transmission electron microscope evaluations verified that these nanofibers had linear morphologies, without beads or spindles, and an obvious core-shell double-chamber structure. The X-ray diffraction patterns and Fourier transform infrared spectroscopic results indicated that the involved components were highly compatible and presented in an amorphous molecular distribution state. In vitro dissolution tests verified that the new core-shell structures were able to prevent the initial burst release, extend the continuous-release time period, and reduce the negative tailing-off release effect, thus ensuring a better sustained-release profile than the traditional blended drug-loaded nanofibers. The mechanism underlying the influence of the new core-shell structure with an RES/CA reverse gradient distribution on the behaviors of RES release is proposed. Based on this proof-of-concept demonstration, a series of advanced functional nanomaterials can be similarly developed based on the gradient distributions of functional molecules within electrospun multi-chamber nanostructures.

Evaluating the image quality and local tumor invasion of uterine cancer by MUSE DWI with RPG

Diffusion-weighted imaging (DWI) is widely utilized for evaluating uterine diseases. However, the prevalent technique, single-shot echo planar imaging (ssEPI), is hindered by notable image distortion and low spatial resolution. Therefore, optimizing uterine DWI sequences is vital for improving image quality. To investigate the efficacy of multiplexed sensitivity encoding (MUSE) combined with reverse polarity gradient (RPG) in enhancing uterine DWI quality and assessing local invasion in endometrial and cervical cancer, we included 149 patients. Each patient underwent DWI of the uterus using ssEPI, MUSE, and RPG-MUSE techniques. We compared these three sequences regarding image quality, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), geometric distortion rate (GDR), ADC values, accuracy in determining the extent of cancer invasion, and the Area Under the Curve (AUC) for identifying endometrial cancer and benign endometrial lesions using ADC values. The results indicated that RPG-MUSE DWI had less artifacts than MUSE and ssEPI (P < 0.05). Lesions were more apparent in MUSE and RPG-MUSE sequences compared to ssEPI (P < 0.05), with RPG-MUSE providing clearer lesion edges (P < 0.05). Additionally, RPG-MUSE DWI demonstrated higher SNR and CNR than ssEPI and MUSE (P < 0.05), along with a lower GDR (P < 0.05). The ADC values did not show significant differences among the three sequences (P > 0.05). Furthermore, the AUC of the ROC for detecting endometrial cancer and benign endometrial lesions using ADC values showed no significant differences across the sequences (P = 0.7609, 0.7186, and 0.8706, respectively). When combining each DWI sequence with T2WI for FIGO staging, RPG-MUSE and MUSE exhibited better alignment with pathology findings compared to ssEPI (P < 0.05). Overall, RPG-MUSE DWI showed fewer artifacts, higher SNR and CNR, reduced geometric distortion, and clearer lesion visualization compared to ssEPI and MUSE, leading to a more precise assessment of endometrial and cervical cancer invasion extent.

Thermal Performance of Heat Sink Filled with Double-Porosity Porous Aluminum Skeleton/Paraffin Phase Change Material.

Phase change materials (PCMs) are used to cool high-power-density electronic devices because of their high latent heat and chemical stability. However, their low thermal conductivity limits the application of PCMs. To solve this problem, a double-porosity porous aluminum skeleton/paraffin phase change materials (DPAS/PCM) was prepared via additive manufacturing and the water-bath method. The thermal performance of the DPAS/PCM heat sink (HS) was experimentally investigated to examine the effects of the positive- and reverse-gradient porosity structures of the DPAS/PCM. The results show that a positive-gradient porosity arrangement is more conducive to achieving a low-temperature cooling target for LED operation. In particular, the temperature control time for the positive gradient porosity structure increased by 4.6-13.7% compared with the reverse gradient porosity structure. Additionally, the thermal performances of uniform porous aluminum skeleton/paraffin (UAS) and DPAS/PCMs were investigated. The temperature control effect of the DPAS/PCM was better than that of the UAS/PCM HS at high critical temperatures. Compared with the UAS/PCM HS, the temperature control time of the DPAS/PCM HS is increased by 7.8-12.5%. The results of this work show that the prepared DPAS/PCM is a high-potential hybrid system for thermal management of high-power electronic devices.

Investigation on the flow and thermal properties of fibrous insulation used in thermal batteries at alternative atmosphere and pressure gradient

The accurate prediction of behavior for insulations within thermal battery can be impeded due to the fact that the thermal properties of insulations have not been thoroughly characterized under the complex conditions in which they operate. In this study, an effective and extendible model is developed based on fractal theory and finite element method to predict the flow and thermal properties for fibrous insulations within thermal batteries. Two common fibrous insulations are tested and verified with this model under the operating gas atmosphere of thermal battery. It is found that the predictive permeability and effective thermal conductivity agree well with the existing experimental data. Verification under various gas atmosphere shows that present model can reduce the relative error of existing model by 5.21–17.2 %. The gas contributed thermal conductivity for insulations filled with high thermal conductivity gas is always significant. In addition, under the tested pressure gradients, the deviations of temperature are generally greater than 1.42 % for air, methane and carbon dioxide atmosphere, but less than 0.7 % for hydrogen atmosphere. The high porosity of material, the large or reverse pressure gradient may strongly promote the influence of the energy migration within insulations.

Investigation of GaAs-Based Laser Diode Adopting an Al Composition Gradient Double Waveguide Structure and its Photoelectric Properties

The double waveguide structure of a 1060 nm laser diode with different Al composition linear gradient was designed for achieving high output power. In contrast to the single waveguide layer with Al-free composition gradient structure, the double waveguide layer with a reverse Al composition gradient from n side to p side showed excellent optoelectronic properties. We found that the reverse Al composition gradient double waveguide layer could decrease injection potential barrier for electrons and holes, as well as has a high block leakage potential barrier, which can be help to increase carrier transport and optical confined factor. Meanwhile, it can improve sheet carrier concentration in order to decrease non-radiative recombination. When the injection current is 6 A, the maximal output power and peak wall-plug conversion efficiency are 6.12 W and 81.1%, respectively. The influencing mechanism of these photoelectric parameters on power and wall-plug conversion efficiency was discussed. The novel waveguide structure will be favorable for designing epitaxial structure and providing a theoretical basis for high-power laser diode.

Investigation on formation mechanism of cavitation channel vortex in the runner of Francis turbine

Abstract Cavitation channel vortices generally cause flow state more complex in the runner, leading to the work efficiency is reduced and the cavitation erosion on flow components is enhanced. In this paper, simulation of cavitation flow is carried out for a Francis turbine model, and the evolution of vortices in the runner during cavitation development is analyzed under partial load conditions. The results show that cavitation has a great influence on the morphology and distribution of attached vortices between blades, trailing vortices at the outlet edge of the blades, and vortex near the cone in the runner. With the gradual development of cavitation, the invasion effect of vortex rope in draft tube on the runner is enhanced, and the vortex near runner cone is gradually connected as a whole. Under the effect of the downstream reverse pressure gradient in local low-pressure area, the flow separation area gradually expands to the blade and upstream, and more singular points evolve on flow separation lines, which leads to more trailing vortices at the outlet of the blade and cavitation channel vortices are formed in serious cavitation stage.

A Dynamic Gradient Stiffness Material Platform to Manipulate Cardiac Fibroblasts' Spatio‐Temporal Behavior

AbstractAfter myocardial infarction, there exists a spatiotemporal variation of cardiac tissue stiffness across the infarcted border region outward to remote regions, influencing adverse remodeling and cardiac fibrosis, and this stiffness gradient changes over time. Here, a platform with dynamic, tunable, and reversible gradient stiffness can recapitulate in vitro the time‐dependent stiffness range across the infarction border that occurs as part of the remodeling process is presented. This platform enables the observation of time‐dependent interaction between cardiac fibroblasts and their mechanical microenvironment in a spatiotemporal manner. Specifically, the competition and cooperation of a chemical cue (antifibrotic drug) and mechanical cue (gradient softening) in tandem to attenuate the fibrotic responses of cardiac fibroblasts is examined. Applying a combined intervention showed either additive or antagonistic effects on fibrosis‐related gene regulation compared to separate interventions of drug or softening. This work reveals the spatiotemporal variation of fibrotic response in cardiac fibroblasts as well as the complexity of antifibrotic drug dosing with stiffness changes and their combinatory effect on cardiac fibroblasts. This platform provides a unique in vitro tool to study disease progression mechanisms in a more clinically relevant microenvironment and also serves as a cost‐effective model for potential therapeutic screening.

Fabrication of cemented carbides with bidirectional gradient structure via graphene deposition to simultaneously enhance surface hardness and toughness

The adoption of a continuous gradient in Co content stands as the foremost strategy for attaining heightened surface hardness and improved core toughness in cemented carbides. Nevertheless, the reduction in surface toughness stemming from a decreased Co content often precipitates premature surface failure of components. In this paper, WC-11Co powders was utilized as the precursor materials for fabricating a bidirectional gradient cemented carbide using the combined approach of low-temperature presintering and ultrasonic treatment techniques. The resultant cemented carbide exhibited a distinct gradient distribution, characterized by a forward gradient of graphene content, a reverse gradient of Co content, a forward gradient of WC grain size, and a forward gradient of residual compressive stress. The hardening and toughening mechanisms of the fabricated bidirectional gradient cemented carbides were comprehensively characterized and quantitatively discussed. The results provide compelling evidence that the gradient distribution of Co content plays a crucial role in attaining an impressive surface hardness of 1820 kgf/mm2. By utilizing the crack bridging mechanism of graphene, which efficiently exploits its strain transfer capabilities across a semi-coherent interface, in conjunction with the toughening effects of crack deflection and residual compressive stress, an exceptional surface fracture toughness of 17.62 MPa m1/2 is achieved. Additionally, the gradient layer exhibited a higher critical load for cracking. The present findings presents a novel strategy for the fabrication of high-performance ceramic-based composites.

Improving RF characteristic and suppress gate leakage in normally-off GaN-HEMTs using negative polarization effect and floating gate for millimeter-wave systems

This article demonstrates the effect of reverse gradient barrier layer and floating gate structure on DC and RF performance of GaN-based HEMTs. In terms of power characteristics, using reverse gradient barrier and floating gate, the GaN-HEMTs with Lg of 240 nm and S-D spacing of 8.4 μm demonstrated the maximum drain current and peak transconductance are increased by 70 % and 15 % respectively, and the linearity of GaN based HEMT is greatly improved. Meanwhile, using the reverse gradient barrier layer, the gate leakage current is significantly reduced by nearly 1 to 5 orders of magnitude, and it is proved that the negative polarization effect has a certain effect on increasing the threshold voltage and breakdown voltage. In terms of RF characteristics, due to the existence of the floating gate, the parasitic capacitance is reduced and the frequency performance is improved. In addition, for both conventional and proposed HEMTs, this article proposes two equivalent capacitance models to optimize RF performance. As a result, the optimal structure offers approximately 10 and 7 times improvement in the current gain cutoff frequency (ft) and unilateral power gain cutoff frequency (fmax) (from 5.3 and 9.8 to 52 and 73.8 GHz, respectively). Additionally, the optimal structure exhibits outstanding scaling factors of 12.48 GHz·μm.

Two-dimensional metal–organic framework nanocomposite membranes with shortened ion pathways for enhanced salinity gradient power harvesting

Harnessing energy through the reverse electrodialysis-based salinity gradient power conversion is an exciting and promising technological endeavor. The key to its success lies in developing the advanced ion-selective membrane capable of enhancing ion flux and accelerating ion transport at confined nanospaces. Traditional two-dimensional (2D) membranes typically employ a layer-by-layer arrangement of nanosheets with an extremely narrow layer separation, limiting ion flux and creating elongated 2D ion pathways. In response to this limitation, our study introduces an innovative design of the 2D metal–organic framework (MOF)-based nanocomposite membrane (named as Cu-TCPP@SNF), which is composed of the 2D Cu-TCPP and natural-based silk nanofibers (SNFs). We show that the introduction of the space-charged SNFs can significantly enhance the stability of the 2D MOF nanocomposite membrane in electrolyte solutions, and this unique framework facilitates a multitude of abundant one-dimensional ion pathways across the membrane while maintaining the advantage of minimal layer separation. Our results demonstrate that the Cu-TCPP@SNF exhibits low resistance, thus facilitating ion transport. Furthermore, numerical simulations elucidate the impacts of the SNF content and membrane thickness on power performance. Remarkably, our membrane achieves a notable power density of ∼6.48 W/m2 by mixing artificial seawater and river water. Impressively, an ultrahigh performance of ∼29.5 W/m2 can be achieved under a 5 M/0.01 M NaCl gradient, surpassing the existing advanced membranes. These findings hold significant promise for the future of composite 2D membrane development, paving the way for scalable applications in salinity-based energy harvesting.

SRG: Energy-Efficient Localized Routing to Bypass Void in Wireless Sensor Networks

The Shift Reverse Gradient (SRG) approach presents a void-size-independent hole bypassing scheme for wireless sensor networks. It does not require establishing any chain or hierarchical tree structure to ensure reliable delivery. The proposed Shift Reverse Gradient (SRG) offers an energy-efficient solution with minimal overhead and consumes minimum power. It has a communication overhead equivalent to greedy forwarding. We have shown through the simulation that SRG energy consumption is minimal and is not much affected by an increase in the void size like other existing void bypassing methods.

SLANG.D: Fast, Modular and Differentiable Shader Programming

We introduce SLANG.D, an extension to the Slang shading language that incorporates first-class automatic differentiation support. The new shading language allows us to transform a Direct3D-based path tracer to be fully differentiable with minor modifications to existing code. SLANG.D enables a shared ecosystem between machine learning frameworks and pre-existing graphics hardware API-based rendering systems, promoting the interchange of components and ideas across these two domains. Our contributions include a differentiable type system designed to ensure type safety and semantic clarity in codebases that blend differentiable and non-differentiable code, language primitives that automatically generate both forward and reverse gradient propagation methods, and a compiler architecture that generates efficient derivative propagation shader code for graphics pipelines. Our compiler supports differentiating code that involves arbitrary control-flow, dynamic dispatch, generics and higher-order differentiation, while providing developers flexible control of checkpointing and gradient aggregation strategies for best performance. Our system allows us to differentiate an existing real-time path tracer, Falcor, with minimal change to its shader code. We show that the compiler-generated derivative kernels perform as efficiently as handwritten ones. In several benchmarks, the SLANG.D code achieves significant speedup when compared to prior automatic differentiation systems.

Electrospun gas diffusion layers with reverse gradient pore structures for proton exchange membrane fuel cells under low humidity

For proton exchange membrane fuel cell (PEMFC) systems, the parasitic power loss can be decreased by removing the external humidifier. However, when the PEMFC system does not have an external humidifier, the maintenance of the PEMFC performance requires the use of gas diffusion layers (GDLs) with a good water-retention capacity. In this study, a reverse-gradient GDL suitable for PEMFC operation under nonhumidification conditions is fabricated using the electrospinning method. The reverse-gradient GDL is characterized by a decrease in the pore size from the catalyst layer to the flow-field plate. The breakthrough pressure and water saturation are tested using custom-made experimental apparatus, and the fluid transport mechanism is theoretically analyzed and simulated at the mesoscale. In addition, the single-fuel cell performance is tested to verify the effectiveness of the designed reverse-gradient structure. The theoretical analyses and mesoscale simulations show that the reverse-gradient GDL can retain more water in the fuel cell than the positive-gradient and uniform GDLs, and the PEMFC performance tests show that the reverse-gradient GDL can improve the water retention capacity and provide a higher power density under low-humidity conditions.

Position‐Responsive SEI Layer in Bicomponent‐Bidirectional Gradient Current Collector Induces Homogenized Ion Flux for Highly Reversible Li Metal Anode

AbstractA gradient current collector (GCC) can encourage preferential Li metal deposition on the more lithiophilic/conductive bottom of 3D anodes, enhancing the reversibility of the battery. However, as the deposition proceeds, the reduction of lithophilicity/conductivity easily causes the disturbance of Li+ flux. Herein, a brand‐new bicomponent‐bidirectional gradient current collector (BGCC) is proposed. The BGCC constructs slow‐release additives with reverse gradient distribution (SA gradient) based on GCC, allowing it to build a position‐responsive solid electrolyte interface layer. Additionally, as the deposition amount increases, the slow‐release additives will release more and present a stronger ability to regulate Li+ flux, ensuring the anodereversibility under large deposition amounts conditions. Consequently, asymmetric cells can exhibit high reversibility with an average coulomb efficiency (CE) of 97.8% and sustain over 200 cycles using carbonate‐based electrolytes. The Li@BGCC||LiFePO4 full cells hold a capacity retention of 94.8% over 400 cycles with thin Li. Notably, even at low temperatures, the Li@BGCC anodes can exhibit a CE as high as 98.46% and excellent capacity retention of 97.8% after 100 cycles paired with NCM811 cathodes. This strategy opens up a new direction for the development of 3D current collectors.

Anthropause on tardigrade urban communities during COVID-19 pandemic restrictions in Salta, Argentina

Abstract The World Health Organization declared COVID-19 a pandemic on 11 March 2020. The ‘anthropause’ almost emptied our streets of vehicles. In urban areas, automobile traffic is a major environmental factor, and tardigrades can serve as bioindicators of environmental change. During the winter of 2019–2020, samples were taken both before and during the COVID-19 lockdown. In both cases, traffic variables (vehicles per minute), environmental variables, and microhabitats were evaluated. Both before and after the COVID-19 lockdown, the true species diversity and the β-diversity of each habitat and habitat pair were compared. The indicator value method identified species that served as indicators of habitat. Although species richness increased during the anthropause, abundance decreased, as evidenced by the discovery of previously unknown species of Paramacrobiotus and Milnesium in 2020 and by the first record of Mesobiotus in the same year. Different variables were affected in different ways by the decline in vehicular traffic that occurred during the anthropause. Compared to the other examined traffic conditions, the behaviour of the variables was distinct in medium traffic, resulting in more stable conditions. Patterns of nested urban diversity might produce reversible gradients over time. Between habitats with high vehicular traffic and those with medium vehicular traffic, the greatest loss of species occurs.

“Anomalous” diffusion in multi-layer silicide systems

The transition metal silicide coatings have excellent oxidation resistance. In the high-temperature oxidization environment, the “anomalous” diffusion phenomenon of the reverse concentration gradient occurs in the multilayer silicide coating structure, which has a significant impact on the coating degradation. This study is to explore the physical mechanism of “anomalous” diffusion phase transformation in the MoSi2–NbSi2 bilayer silicide coating on the Nb alloy substrate. Through vacuum annealing experiments, combined with micro-Raman spectroscopy and electron probe microanalysis measurements, the diffuisonal phase transformation of multilayer silicide coating in the oxygen-free environment at high temperatures was studied. By decoupling the oxidation and diffusion, the experiments indicate that high-temperature oxidation is not the dominant driving factor for the “anomalous” diffusion of atoms. The thermodynamic analysis reveals that the reduction in the nucleation barrier of the silicide-poor layer due to multicomponent solid solution and the non-uniform distribution of component chemical potential provide the driving force for the “anomalous” diffusion growth. Based on the diffusion kinetic modeling, the simulation of diffusion-controlled phase transformation in multilayer silicide coating was carried out, and the effect of tracer diffusion coefficients on the growth of the silicide-poor phase was analyzed. The research will have guiding significance for the recognition of failure mechanisms of silicide coating systems and performance improvement.

Facile Purification and Use of Tobamoviral Nanocarriers for Antibody-Mediated Display of a Two-Enzyme System.

Immunosorbent turnip vein clearing virus (TVCV) particles displaying the IgG-binding domains D and E of Staphylococcus aureus protein A (PA) on every coat protein (CP) subunit (TVCVPA) were purified from plants via optimized and new protocols. The latter used polyethylene glycol (PEG) raw precipitates, from which virions were selectively re-solubilized in reverse PEG concentration gradients. This procedure improved the integrity of both TVCVPA and the wild-type subgroup 3 tobamovirus. TVCVPA could be loaded with more than 500 IgGs per virion, which mediated the immunocapture of fluorescent dyes, GFP, and active enzymes. Bi-enzyme ensembles of cooperating glucose oxidase and horseradish peroxidase were tethered together on the TVCVPA carriers via a single antibody type, with one enzyme conjugated chemically to its Fc region, and the other one bound as a target, yielding synthetic multi-enzyme complexes. In microtiter plates, the TVCVPA-displayed sugar-sensing system possessed a considerably increased reusability upon repeated testing, compared to the IgG-bound enzyme pair in the absence of the virus. A high coverage of the viral adapters was also achieved on Ta2O5 sensor chip surfaces coated with a polyelectrolyte interlayer, as a prerequisite for durable TVCVPA-assisted electrochemical biosensing via modularly IgG-assembled sensor enzymes.

Griddient: a microfluidic array to generate reconfigurable gradients on-demand for spatial biology applications

Biological tissues are highly organized structures where spatial-temporal gradients (e.g., nutrients, hypoxia, cytokines) modulate multiple physiological and pathological processes including inflammation, tissue regeneration, embryogenesis, and cancer progression. Current in vitro technologies struggle to capture the complexity of these transient microenvironmental gradients, do not provide dynamic control over the gradient profile, are complex and poorly suited for high throughput applications. Therefore, we have designed Griddent, a user-friendly platform with the capability of generating controllable and reversible gradients in a 3D microenvironment. Our platform consists of an array of 32 microfluidic chambers connected to a 384 well-array through a diffusion port at the bottom of each reservoir well. The diffusion ports are optimized to ensure gradient stability and facilitate manual micropipette loading. This platform is compatible with molecular and functional spatial biology as well as optical and fluorescence microscopy. In this work, we have used this platform to study cancer progression.

Flight control of a flying wing aircraft based on circulation control using synthetic jet actuators

To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft (FWA), a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders. Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated. Then, flight tests were carried out to verify the control abilities, providing a novel technology for the design of a future rudderless FWA. Results show that synthetic jets could narrow the dead zone area, improve the flow velocity near the trailing edge, and then move the trailing-edge separation point and the leading-edge stagnation point downwards, which make the effective Attack of Angle (AOA) increase, thereby enhancing the pressure envelope area. Circulation control based on synthetic jets could improve the lift, drag and nose-down moment. The variations of lift and nose-down moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency. Finally, synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA, which could realize the roll and pitch control without deflections of rudders during the cruise stage, and the maximum roll and pitch angular velocity are 12.64 (°)/s and 8.51 (°)/s, respectively.

Co-infection with Leucocytozoon and Other Haemosporidian Parasites Increases with Latitude and Altitude in New World Bird Communities.

Establishing how environmental gradients and host ecology drive spatial variation in infection rates and diversity of pathogenic organisms is one of the central goals in disease ecology. Here, we identified the predictors of concomitant infection and lineage richness of blood parasites in New Word bird communities. Our multi-level Bayesian models revealed that higher latitudes and elevations played a determinant role in increasing the probability of a bird being co-infected with Leucocytozoon and other haemosporidian parasites. The heterogeneity in both single and co-infection rates was similarly driven by host attributes and temperature, with higher probabilities of infection in heavier migratory host species and at cooler localities. Latitude, elevation, host body mass, migratory behavior, and climate were also predictors of Leucocytozoon lineage richness across the New World avian communities, with decreasing parasite richness at higher elevations, rainy and warmer localities, and in heavier and resident host species. Increased parasite richness was found farther from the equator, confirming a reverse Latitudinal Diversity Gradient pattern for this parasite group. The increased rates of Leucocytozoon co-infection and lineage richness with increased latitude are in opposition with the pervasive assumption that pathogen infection rates and diversity are higher in tropical host communities.