Instantaneous Density Research Articles

The Unsteady Shock-Boundary Layer Interaction in a Compressor Cascade – Part 1: Measurements With Time-Resolved PIV

Abstract Time-resolved PIV is performed in the transonic cascade to elucidate the shock-boundary layer interaction. Measurements are conducted in the center blade passage of the cascade at a sampling frequency of 20 kHz or 0.18 convective time units (CTU) for the acquisition of multiple time sequences with duration of approx. 2000 CTU. The sampling rate is sufficient to capture fluctuations of the separating region and accompanying movements of the shock system. To align both instantaneous density variations in the shock system and velocity data obtained in spatially separated regions, shadowgraphs are acquired synchronously with TR-PIV recordings at the same sampling rate. An analysis of power spectral densities along near-wall rows in PIV data reveals the chord-wise spatial distribution of specific peaks and bands. The upstream propagation of disturbances beyond the excursion range of the main shock was demonstrated for the dominant buffet frequency as well as for the high-frequency tone and its first harmonic using cross-correlation maps. A spectral proper orthogonal decomposition (SPOD) indicates that upstream of the main shock oblique shock waves occur at higher order harmonics of the fundamental buffet frequency as well for specific high-frequency tones. To locate possible sources of distinct tones at the entrance of the center passage, a SPOD of high-speed schlieren recordings is performed, capturing the shock systems in three neighboring blade passages. Results indicate that with these high-frequency tones opposing vibrations of bow and lip shocks occur for neighboring blades.

Electrolytic conversion of CO2 to proportionally tunable syngas using nickel-nitrogen doped carbon materials derived from Chlorella sp.

Chlorella sp., a common type of algae found in global surface waters, is prone to causing "blooms" and can accumulate significant amounts of nutrients such as nitrogen, phosphorus, and carbon. While carbon materials derived from Chlorella sp. are widely used in the field of adsorption, there are relatively few reports focused on electrocatalysis. This study utilized Chlorella sp. as a raw material to synthesize functional carbon materials, and prepared nitrogen-doped (CN), nickel-doped (CNi), and nitrogen-nickel co-doped (CNNi) carbon-based catalysts with both metal and non-metal elements. The results showed that the CN, CNi and CNNi catalysts possessed certain electrocatalytic properties, among which the CNNi material had the best electrocatalytic activity towards CO2 reduction (CO2RR). In 1.0 M KHCO3, the CNNi catalyst exhibited an instantaneous current density of 15.4 mA/cm2 under the potential of -0.82 V (vs. RHE). In terms of product selectivity, the Faraday efficiency of CO on the CNNi electrode was up to 90 % when the electrode potential was -0.62 V (vs. RHE), while the selectivity of the CN and CNi catalysts for CO was only 59 % under the optimal conditions. The co-doping of nitrogen and nickel significantly enhanced the electrocatalytic activity and the selectivity towards CO of Chlorella-based carbon materials.

Loofah-based self-powered triboelectric nanogenerator-supercapacitor for an integrated self-charging energy system

New urbanization is ushering in a surge in construction and amplifying a substantial demand for urban road development, simultaneously spurring innovation and development of environmentally sustainable power sources. Triboelectric nanogenerator (TENG), a revolutionary technology of energy conversion, efficiently capturing high-entropy energy from the environment and offering the advantages of self-powered and immediacy. Recognizing the critical need to store the energy harvested by TENGs, we present an integrated energy conversion and storage system that combines a loofah-based self-powered rotating TENG (LS-TENG) with a supercapacitor. The maximum instantaneous output power and the corresponding instantaneous power density of the LS-TENG are 0.75 mW and 202.69 mW/m2 at 30 rpm. The supercapacitor, featuring carbon nanotube (CNT) interdigitated electrodes created through microelectronic printing technology, utilizes polyacrylamide (PAM)-lithium chloride (LiCl) as a gel electrolyte (adhesion strength of 16.69 kPa). The supercapacitor is seamlessly integrated onto the back of the LS-TENG’s stator, which effectively simplified the energy conversion and storage system. At a current density of 0.01 mA/cm2, the supercapacitor achieves a high volumetric capacitance of 341.47 mF/cm3, an energy density of 17.07 mWh/cm3, and a power density of 257.07 mW/cm3, with a remarkable capacitance retention rate of 99.12 % after 30,000 cycles at a current density of 0.02 mA/cm2. Furthermore, a concept demonstration of an integrated self-charging energy system is implemented, in which the supercapacitor can be charged at wind speed rate of 3.0 m/s. The proposed integrated energy storage and conversion system makes it ideal for converting and storing wind energy.

Multilayer Electrode Strategy Shorten Thermal Charging Time and Boost Energy Output in Gelatin‐Based i‐TE Cells

AbstractGel‐based ionic thermoelectric (i‐TE) cells provide alternative thermal energy harvesting from the environment, showing obvious advantages in voltage matching for self‐powered Internet‐of‐Things (IoT) sensors. However, the gel‐based i‐TE cells always suffer a long thermal charging time and poor output power performance. Herein, a multilayer electrode engineering strategy is proposed from the device‐design level, aiming to decrease the ions' diffusion distance, increase the electrode surface area, and facilitate the ions' reaction and recovery process. The thermal charging time is shortened from 27 to 8 min as the electrode layers increase from 2 to 8. An ultrahigh instantaneous power density of 15.8 mW m−2 K−2 and 2 h output energy density (E2h) of 403 J m−2 are achieved in an 8‐layer electrode i‐TE cell. Finally, A flexible and wearable i‐TE device with 20 units is demonstrated to generate a remarkable voltage of 3.8 V and output power of 282 µW by harvesting the human body heat. This work provides a feasible and effective route to design the i‐TE device, hopefully promoting its practical power generation application.

Koopman-inspired data-driven quantification of fluid–structure energy transfers

The linear-time-invariance notion to the Koopman analysis is a recent advance in fluid mechanics [Li et al., “The linear-time-invariance notion to the Koopman analysis: The architecture, pedagogical rendering, and fluid–structure association,” Phys. Fluids 34(12), 125136 (2022c) and Li et al., “The linear-time-invariance notion of the Koopman analysis—Part 2. Dynamic Koopman modes, physics interpretations and phenomenological analysis of the prism wake,” J. Fluid Mech. 959, A15 (2023a)], targeting the long-standing issue of correlating nonlinear excitation and response phenomena in fluid–structure interactions (FSI), or, in the simplified case, flow over rigid obstacles. Continuing the serial research, this work presents a data-driven, Koopman-inspired methodology to decouple nonlinear FSI by establishing cause-and-effect correspondences between structure surface pressure and the flow field. Exploiting unique features of the Koopman operator, the new methodology renders dynamic visualizations of in-sync, fluid–structure-coupled Koopman modes possible, fostering phenomenological analysis and statistical quantifications of FSI energy transfers. Instantaneous contribution contours and densities offer new angles to evaluate pathways of energy amplification and diminution. The methodology enables better descriptions and interpretations of phenomena occurring in the flow and on the boundary (walls) of an FSI domain and readily applies to a broad spectrum of engineering problems given its data-driven nature.

Investigating superior performance by configuring bimetallic electrodes on fabric triboelectric nanogenerators (F-TENGs) for IoT enabled touch sensor applications

Fabric Triboelectric Nanogenerators (F-TENGs) are increasingly becoming more significant in wearable monitoring and beyond. These devices offer autonomous energy generation and sensing capabilities, by replacing conventional batteries in flexible wearables. Despite the substantial effort, however, achieving high output with optimal stability, durability, comfort, and washability poses substantial challenges, so we have yet to see any practical commercial uses of these materials. This study focuses on output and investigates the impacts of mono and bimetallic composite fabric electrode configurations on the output performance of F-TENGs. Our findings showcase the superiority of bimetallic configurations, particularly those incorporating Copper (Cu) with Nickel (Ni), over monometallic (Cu only) electrodes. These configurations demonstrate remarkable results, exhibiting a maximum instantaneous voltage, current, and power density of ∼ 199 V (a twofold increase compared to monometallic configurations), ∼22 μA (a threefold increase compared to monometallic configurations), and 2992 mW/m², respectively. Notably, these bimetallic configurations also exhibit exceptional flexibility, shape adaptability, structural integrity, washability, and mechanical stability. Furthermore, the integration of passive component-based power management circuits significantly enhances the performance capabilities of the F-TENGs, highlighting the essential role of power management circuits and electrode selection in optimizing F-TENGs. In addition, we have developed a complete IoT-enabled touch sensor system using CuNi-BEF EcoFlex layered F-TENGs for precise detection of soft and hard touches. This advanced system enhances robotic functionality, enabling nuanced touch understanding essential for precision tasks and fostering more intuitive human-machine interactions.

RETRACTED: A droplet-based electricity generator with high instantaneous power density, high efficiency, and reliable long-term stability

Droplet-based electricity generators (DEGs) have recently revolutionized the prospects for energy harvesting from raindrops. However, achieving high instantaneous power density, high efficiency, and reliable long-term stability remains challenging. Here, we propose a DEG with an intermediate metal electrode underneath the dielectric layer (IM-DEG) for substantial instantaneous outputs, high efficiency, and improved long-term stability. This intermediate metal layer not only plays a vital role as additional charge storage but also opens up a new route to inject negative charges into the dielectric layer from below to further increase the surface charge density. Unlike other ion injection techniques that inject negative charges from the top of the dielectric materials, in our case, the negative charges injected from below tend to remain in the dielectric layer without leaking to the upper electrode or droplets, resulting in elevated electrical performance and improved long-term stability. The IM-DEG's instantaneous peak voltage, power density, and energy conversion efficiency reach 836 V, 6.92 kW/m2, and 32.69%, respectively, while the instantaneous peak voltage drops less than 3% after 1000 h of a continuous flow of droplets. This method offers substantial electrical outputs with high efficiency and reliable long-term stability, paving the way for the future of raindrop energy harvesting.

High performance flexible green triboelectric nanogenerator with polyethylene oxide/mica tribo-positive composite material

Innovating novel, green, biodegradable, and recyclable polymers are critical for the development of environmentally sustainable solutions, eliminating concerns of pollution and microplastic accumulation. Herin, this study presents remarkably enhanced tribo-positive polyethylene oxide (PEO) polarity, by incorporating for the first time, a clay inorganic filler, creating a novel biodegradable composite triboelectric material. The low-cost composite comprised a biodegradable polymeric PEO matrix, an abundant naturally sourced muscovite mica micro-platelet filler, and integrated simple material fabrication methods. A 4 cm2 PEO/Mica film was paired with polytetrafluoroethylene (PTFE), generating a peak-to-peak voltage, current density, and transferred charge density of respectfully, 296 V, 24.2 mA m−2, and 110.3 µC m−2. Reducing the film thickness to 40 µm dramatically enhanced the electrical output, resulting in a peak-to-peak voltage and instantaneous power density of respectfully, 424 V and 12.1 W m−2. The addition of mica greatly improved the dielectric permittivity, promoting the outstanding triboelectric performance. The composite material's long-term stability and flexibility demonstrated significant advantages for self-powering small electronic systems. Furthermore, PEOs facile water solubility allowed mica separation, recovery, recyclability, and integration within new PEO/Mica films, resulted in preserved triboelectric outputs. The PEO/Mica composite delivers exceptional sustainable, recyclable, and tribo-positive attributes, serving as an excellent energy harvesting solution.

From natural abundant silk to TENG; from biowaste to carbon supercap: A natural sustainable approach of active energy storage

Integrating an energy harvester and energy storage into a single unit, without connecting any external source, has gathered substantial attention for its ability to convert and store energy in a single device. This study introduces an innovative, self-sustaining power cell called the self-power supercapacitor (SPSC). The SPSC consists of two triboelectric nanogenerators (TENG) and a carbon based supercapacitor cell sandwiched between two TENGs. The SPSC utilizes the energy produced by two TENGs and stores it directly in the supercapacitor, bypassing the requirement of power management circuits. This energy storage process is achieved using tribo-electrochemical methodology. The supercapacitor consists of activated porous carbon obtained from natural biowaste, infused with an ionic liquid electrolyte gel. Each TENG is constructed using a blend of naturally abundant Silk with PVA and PVDF as triboelectric components and exhibit a maximum voltage of 800 V with an instantaneous output power density of 598 mW/cm2. In addition, the self-power supercapacitor effectively gets charged to a voltage of 0.8 V after continuous tapping of 100 s Due to the huge active surface area of the activated carbon electrodes, the device attains a specific capacitance of 43.75 mF/cm2. The assessed specific energy and specific power of the assembled SPSC device were 3.89 mWh/cm2 and 666.67 mW/cm2, respectively when subjected to tapping operations. The self-power supercapacitor cell also has the ability to power a range of portable electronics, such as LED. This research evidences the competence of charging the supercapacitor of SPSC system using TENGs without the need for an external parameter.

Performance Improvement and Application of Degradable Poly-l-lactide and Yttrium-Doped Zinc Oxide Hybrid Films for Energy Harvesting.

Piezoelectric nanogenerators (PENGs) are booming for energy collection and wearable energy supply as one of the next generations of green energy-harvesting devices. Balancing the output, safety, degradation, and cost is the key to solving the bottleneck of PENG application. In this regard, yttrium (Y)-doped zinc oxide (ZnO) (Y-ZnO) was synthesized and embedded into polylactide (PLLA) for developing degradable piezoelectric composite films with an enhanced energy-harvesting performance. The synthesized Y-ZnO exhibits high piezoelectric properties benefiting from the stronger polarity of the Y-O bond and regulation of oxygen vacancy concentration, which improve the output performance of the composite film with Y-ZnO and PLLA (Y-Z-PLLA). The obtained open-circuit voltage (Voc), short-circuit current (Isc), and instantaneous power density of the optimized Y-Z-PLLA PENG reach 17.52 V, 2.45 μA, and 1.76 μW/cm2, respectively. The proposed PENG also shows good degradability. In addition, practical applications of the proposed PENG were demonstrated by converting biomechanical energy, such as walking, running, and jumping, into electricity.

A triboelectric nanogenerator based on a spiral rotating shaft for efficient marine energy harvesting of the hydrostatic pressure differential

Equipment used in underwater sensing and exploration typically relies on cables or batteries for energy supply, resulting in a limited and inconvenient energy supply and marine environmental pollution that hinder the sustainable development of distributed ocean sensing networks. Here, we design a deep-sea differential-pressure triboelectric nanogenerator (DP-TENG) based on a spiral shaft drive using modified polymer materials to harness the hydrostatic pressure gradient energy at varying ocean depths to power underwater equipment. The spiral shaft structure converts a single compression into multiple rotations of the TENG rotor, achieving efficient conversion of differential pressure energy. The multi-pair electrode design enables the DP-TENG to generate a peak current of 61.7 μA, the instantaneous current density can reach 0.69 μA cm−2, and the output performance can be improved by optimizing the spiral angle of the shaft. The DP-TENG can charge a 33 μF capacitor to 17.5 V within five working cycles. It can also power a digital calculator and light up 116 commercial power light-emitting diodes, demonstrating excellent output capability. With its simple structure, low production cost, and small form factor, the DP-TENG can be seamlessly integrated with underwater vehicles. The results hold broad prospects for underwater blue energy harvesting and are expected to contribute to the development of self-powered equipment toward emerging “smart ocean” and blue economy applications.

Synergy between gelatin hydrogels and electrodes for adjustable and thermally stable ionic thermoelectric supercapacitors

Gelatin-based ionic hydrogels are flexible, bio-compatible, and abundant materials, showing immense potential as quasi-solid-state electrolytes in energy conversion and storage applications. Recent studies highlighted the critical synergy between hydrogel electrolytes and electrodes on the thermopower and energy density in emerging ionic thermoelectric (i-TE) devices. In this work, the significant impact from electrodes to the thermoelectric response of gelatin hydrogels is explored and explained at the molecular level. A universal negative offset in the thermopower is observed when substituting the conventional Cu foil by carbon-based paper (CBP) electrodes. This is attributed to the electrolyte infiltration and strong cation restriction on the CBP electrodes, which facilitates anion thermodiffusion. The thermopowers of Gelatin-CsCl change from p- (0.1–0.5 mV K−1) to n-type (up to −2.89 ± 0.34 mV K−1) and remain thermally stable at a large temperature difference of −36.8 K. The power factor and average power density in the ionic thermoelectric supercapacitors (ITESCs) made from Gelatin-0.02 M CsCl and CBP electrodes reach 2.13 ± 0.50 μW m−1 K−2 and 145.37 μW m−2 at a small temperature difference of −7.7 K. Furthermore, the highest normalized instantaneous power density achieved during the quasi-continuous charge–discharge cycles is 39.42 μW m−2 K−2, among the best ITESCs. This work provides fundamental insights into the previously overlooked synergy between gelatin hydrogels and electrodes for adjustable and thermally stable i-TE conversion and energy storage devices.

Tuning ZnO-based piezoelectric nanogenerator efficiency through n-ZnO/p-NiO bulk interfacing

ZnO based piezoelectric nanogenerators (PENG) hold immense potential for harvesting ambient vibrational mechanical energy into electrical energy, offering sustainable solutions in the field of self-powered sensors, wearable electronics, human–machine interactions etc. In this study, we have developed flexible ZnO-based PENGs by incorporating ZnO microparticles into PDMS matrix, with ZnO concentration ranging from 5 to 25 wt%. Among these, the PENG containing 15 wt% ZnO exhibited the best performance with an open-circuit output voltage/short-circuit current of ~ 42.4 V/2.4 µA. To further enhance the output performance of PENG, p-type NiO was interfaced with ZnO in a bulk hetero-junction geometry. The concentration of NiO was varied from 5 to 20 wt% with respect to ZnO and incorporated into the PDMS matrix to fabricate the PENGs. The PENG containing 10 wt% NiO exhibits the best performance with an open-circuit output voltage/short-circuit current of ~ 65 V/4.1 µA under loading conditions of 30 N and 4 Hz. The PENG exhibiting the best performance demonstrates a maximum instantaneous output power density ~ 37.9 µW/cm2 across a load resistance of 20 MΩ under loading conditions of 30 N and 4 Hz, with a power density per unit force and Hertz of about ~ 0.32 µW/cm2·N·Hz. The enhanced output performance of the PENG is attributed to the reduction in free electron concentration, which suppresses the internal screening effect of the piezopotential. To assess the practical utility of the optimized PENG, we tested the powering capability by charging various commercial capacitors and used the stored energy to illuminate 10 LEDs and to power a stopwatch displays. This work not only presents a straightforward, cost-effective, and scalable technique for enhancing the output performance of ZnO-based PENGs but also sheds light on its underlying mechanism.

Visible-light driven photocatalyzing degradation of antibiotics and dyes enabled by 0D/1D Tb2O3/Er2O3/TiO2@C hybrids

It remains a huge challenge to design a kind of high performance, multifunctional and low cost photocatalysts driven by visible light for the remediation of pollutants from waste water. In this work, the carbon coated Tb2O3/Er2O3/TiO2 nanotubes (Tb2O3/Er2O3/TiO2@C) 0D/1D hybrid photocatalysts were synthesized by a microwave hydrothermal method. Essentially, the Er2O3 nanoparticles can absorb low-energy photons at 800–980 nm and emit high-energy photons to TiO2 through the up-conversion effect, meanwhile, the Tb2O3 act as a redox center to promote the separation of photoinduction charges since the instantaneous photoelectric density was increased by 10 times by compared to TiO2@C. As a result, the photodegradation efficiency of the optimized Tb2O3/Er2O3/TiO2@C photocatalysts is about 15.7 times higher than that of TiO2@C under visible light irradiation for decomposing rhodamine B, respectively. Moreover, the photodegradation efficiency remained above 70 % after reused for 5 times. Thus, the enhanced synergistic effect between Er2O3 and Tb2O3 promises the excellent photodegradation activity and reduce cost.It remains a huge challenge to design a kind of high performance, multifunctional and low cost photocatalysts driven by visible light for the remediation of pollutants from waste water. The carbon coated Tb2O3/Er2O3/TiO2 nanotubes (Tb2O3/Er2O3/TiO2@C) 0D/1D hybrids were synthesized by a microwave hydrothermal method. The Er2O3 nanoparticles can absorb low-energy photons at 800–980 nm and emit high-energy photons to TiO2 through the up-conversion effect, meanwhile, the Tb2O3 act as a redox center to promote the separation of photoinduction charges since the instantaneous photoelectric density was increased by 10 times by compared to TiO2@C. As a result, the photodegradation efficiency of the optimized Tb2O3/Er2O3/TiO2@C photocatalysts is about 15.7 times higher than that of TiO2@C under visible light irradiation for decomposing rhodamine B. Moreover, the photodegradation efficiency remained above 70 % after reused for 5 times. Thus, the enhanced synergistic effect between Er2O3 and Tb2O3 promises the excellent photodegradation activity and reduce cost.

A Contact‐Separation Mode Hybrid Generator Based on Magnetic Springs

The emergence of the intelligent society presents a significant challenge with regard to distributed energy. One potential solution is to harvest energy from the environment to power micro/nano systems. Herein, an electric‐triboelectric hybrid generator (ETMHG) supported by magnetic springs is presented that operates in the contact‐separation mode. The traditional mechanical springs in the triboelectric nanogenerators are replaced by magnetic springs, and solenoid coils are added. This structure can achieve electromagnet‐triboelectric hybrid generation without significantly increasing the volume of the generator, and the use of magnetic springs offers a solution to the issues of difficult installation and mechanical wear and tear that are inherent in mechanical spring‐based triboelectric nanogenerators. The proposed hybrid generation ETMHG is shown to increase the output capacity of the generator, improve the efficiency of environmental energy harvesting, and achieve an instantaneous maximum power of 4.75 mW and instantaneous maximum power density of 95 W m−3. The ETMHG can charge a 10 μF capacitor that improves efficiency by 52.6% compared to an electromagnetic generator. The output surface power density of TENG in ETMHG can reach 1.12 W m−2.

Flexible piezoelectric energy-harvesting nanogenerator using supersonically sprayed polyvinylidene fluoride and iron oxide nanocubes

Soft wearable electronics are being applied as state-of-the-art self-powered devices based on piezoelectric nanogenerators (PENGs), which provide flexible energy harvesters and sustainable energy generators. We introduce a composite of poly(vinylidene fluoride) (PVDF) and Fe2O3 nanocube fillers coated via supersonic cold spraying to obtain substrate-free and flexible films for PENGs. The hydrothermally synthesized Fe2O3 nanocubes induce shear stress between Fe2O3 and PVDF during supersonic spraying. An optimized sample having 0.77 g Fe2O3 in 1 g PVDF produces a piezopotential of 25.6 V and a short-circuit current of 70 μA. In addition, a maximum power density of 44.4 μW·cm−2 is achieved at a load resistance of 1 MΩ. Tapping and bending tests for 1800 s confirm the consistent generation of piezopotentials of 25.6 V and 1.5 V, respectively. The developed Fe2O3/PVDF PENG can power several light-emitting diodes, thus showing promise as a device for sustainable power supply.

Unveiling the mechanism of lignin nanofiller in boosting the performance of triboelectric nanogenerators

Lignin has been demonstrated as the tribopositive nanofillers in boosting the triboelectric performances of biopolymer-based triboelectric nanogenerators (TENGs). However, the complex structures of lignin caused the unclear understanding how the molecular structures of lignin affected the output performances of TENGs. Herein, for the first time, five fractionated lignin with different structures were innovatively employed as the tribopositive nanofillers in CMC. Computational simulations and experimental results verified that the lignin with more S units, A-type linkage and large molecular weight give rise to the higher dielectric constant as well as the triboelectric performances. Relying on this principle, the acetone lignin possessed the highest dielectric behavior and the constructed TENG delivered the maximum Voc of 204.34 V, Isc of 6.86 µA, Qsc of 70.27 nC and instantaneous output power density of 836.64 mW/m2 under contact frequency of 1 Hz. Moreover, such biofilm can be dissolved in water and the regenerated film delivered stable output performances at least 5 times. Our findings not only provided the in-depth understanding of the relationship between triboelectrification behaviors and molecular structures of lignin, but also boosted the rational designing high-performance lignin-based tribopositive nanofillers for self-powered sensing or mechanical energy harvesting.

Appraisal of reservoir quality for hydrocarbon-bearing deep-water Miocene sandstones incised valley, south-east Asian offshore Indus: An application of seismic attributes and instantaneous spectral porosity quantitative reservoir simulations

Incised marine valleys (IVS) are hot topics in exploring the stratigraphic oil and gas-bearing plays. Multiple channelized sandstone lenses at varying depths [m], thicknesses [m], and porosities [%] constrain seismic impedance. The presence of hydrocarbon-bearing resources affects the seismic impedance (density (g/cc) and velocity (m/s)). Therefore, a quantitative prediction has been carried out for determining the thickness [m], porosity [%], and depths [m] of laterally distributed channelized sandstone lenses (SLS) for IVS, Indus offshore Basin (IOB), Pakistan, using 2-D instantaneous spectral porosity quantitative modelling (2DSSM), continuous wavelet transforms-based (CWT) 2-D instantaneous spectral density modelling (2DSSDM), and spectral decomposition tools. The 2DSSM remained limited in predicting the number of channelized sandstone lenses and their quantitative stratigraphic attributes. The 45-Hz-based processing of conventional 2DSSM has resolved the two channelized sandstone lenses of the stratigraphic trap. The deepest channelized sandstone lens has attained 1–6 m thickness with a lateral extent of 3 km, within the porosity range of 18–33 %. The highest confidence level for predicted petrophysical attributes such as 13 m-thick pay zones, −0.08, −0.067, and −0.07 acoustic impedances [g/c.c.*m/s], and 28 % porosities with R2 > 0.85 have validated interpretations. The response of 45-Hz CWT waveform-based inverted density and thickness simulations has predicted the highest thicknesses and lowest densities of reservoir sandstones within the meandering channel belt of the deepwater depositional system. The predicted densities and thicknesses for the coarse-grained sandstone lenses of point bars were 1.8–1.9 g/cc and 15 m, respectively. In the same way, the quantitative estimates of predicted density and simulated thickness have shown a strong coefficient correlation (R2 > 0.80), which confirms the presence of gas-bearing prospects within the IVS. The facies-controlled migration is thought to be the movement of the reservoir facies of the point bars and channelled sandstone-filled lenses to the side.

A study on the arch mechanism of pedestrian evacuation and congestion alleviation strategies at building exits

The pedestrian flow capacity of building exits has always been a focus of research in evacuation field. This paper focuses on the congestion mechanism of pedestrian flow at exit bottlenecks through simulation and crowd experiments, and tries to propose strategies to alleviate evacuation congestion. Firstly, pedestrian flow evacuation experiments were conducted by setting up scenarios with exits in the middle and corners, and corresponding exit structure models were established using Massmotion software to analyze the congestion mechanisms of pedestrian flow at the exits through simulations coupled with the social force model. Secondly, the severity of congestion in the exit structure was quantified using the example of the middle exit. The width range of the pedestrian evacuation trajectory within 1 m before the exit was defined as the average chord length of the arch structure, and the area enclosed by the semicircular arch with this chord length was defined as the area with a relatively high instantaneous density of pedestrian flow. The results indicate that corner exits are more conducive to evacuation as they reduce the expected velocity of pedestrians near the center of congested areas. Both building width and the inflow rate of pedestrian flow, along with the number of pedestrians, demonstrate significant effects on the average chord length of the arch. The research results can be used to further supplement and improve the dynamic theory of pedestrian flow evacuation in buildings and provide a scientific reference for crowd congestion control at building exits.

Boosting the Piezoelectric Response and Interfacial Compatibility in Flexible Piezoelectric Composites via DET-Doping BT Nanoparticles.

With the advent of the Internet of Things, self-powered wearable sensors have become increasingly prevalent in our daily lives. The utilization of piezoelectric composites to harness and sense surrounding mechanical vibrations has been extensively investigated during the last decades. However, the poor interface compatibility between ceramics nanofillers and polymers matrix, as well as low piezoelectric performance, still serves as a critical challenge. In this work, we employed Di(dioctylpyrophosphato) ethylene titanate (DET) as the coupling agent for modifying barium titanate (BTO) nanofillers. Compared to the BTO/PVDF counterpart, the DET-BTO/PVDF nanofibers exhibit an augmented content of piezoelectric β phase (~85.7%) and significantly enhanced stress transfer capability. The piezoelectric coefficient (d33) is up to ~40 pC/N, which is the highest value among reported BTO/PVDF composites. The piezoelectric energy harvesters (PEHs) present benign durability and attain a high instantaneous power density of 276.7 nW/cm2 at a matched load of 120 MΩ. Furthermore, the PEHs could sense various human activities, with the sensitivity as high as 0.817 V/N ranging from 0.05-0.1 N. This work proposes a new strategy to boosting the piezoelectric performance of PVDF-based composites via DET-doping ceramics nanoparticles, and in turn show significantly improved energy harvesting and sensing capability.