Showing papers by "Hong Kong Polytechnic University published in 2023"
01 Jan 2023
TL;DR: In this paper , the IOR catalytic mechanism of the carbon-based catalyst Pt/C with poor OER activity was revealed and the fabricated ZABs delivered a low charging voltage of 1.68 V, high energy efficiency of 76.5%, and long cycle life of over 80 h at 5 mA cm−2.
Abstract: Rechargeable Zn-air batteries (ZABs) are promising for energy storage and conversion. However, the low energy efficiency caused by the high charging voltage greatly hinders their commercialization. Herein, potassium iodide (KI) is introduced to ZABs to change the oxidation pathway from the sluggish oxygen evolution reaction (OER) to I- oxidation reaction (IOR) with faster kinetics and lower oxidation potential. Unexpectedly, the commercial carbon-based catalyst Pt/C with poor OER activity exhibits remarkable IOR activity. Benefitting from its high oxygen reduction reaction (ORR) activity, the fabricated ZABs deliver a low charging voltage of 1.68 V, high energy efficiency of 76.5%, and long cycle life of over 80 h at 5 mA cm−2. Density functional theory (DFT) calculation is conducted to reveal the IOR catalytic mechanism of the Pt/C catalyst. This work will reverse the traditional mindset on catalyst selection from ORR/OER to ORR/IOR and boost the commercialization of rechargeable ZABs.
14 citations
TL;DR: In this article , an adaptive multi-taper approach with the varying NoT at each frequency point for estimating the power spectral density (PSD) and coherence function of multivariate stationary processes is proposed.
10 citations
01 Jan 2023
TL;DR: In this article , surface and lattice engineered Mo-modified Ru superstructures have been prepared with high performance for bifunctional hydrogen catalysis (HER and HOR) for the first time.
Abstract: Surface and lattice engineered Mo-modified Ru superstructures have been prepared with high performance for bifunctional hydrogen catalysis (HER and HOR).
8 citations
TL;DR: In this article , a bi-objective optimization methodology of EMSD is proposed for the simultaneous maximization of energy harvesting from the damper and the suppression of resonant vibration of a dynamic structure.
4 citations
TL;DR: In this paper , the hydrophilic surfactant/Brij L4 mixture scheme was used for fabrication of highly stable paraffinic nano-emulsions melting at 55 °C by the low-energy phase inversion temperature method.
3 citations
TL;DR: In this article , an experiment was carried out to study the thermal performance of a floor partially irradiated by solar radiation, and the results showed that the solar radiation can promote the heat transfer from the irradiated floor to the room and reduce the heat transferred from the hot water to the floor.
Abstract: In some buildings with radiant floor systems for heating, solar radiation can irradiate the local floor surface, causing overheating and affecting the heating performance of the radiant floor. In this paper, an experiment was carried out to study the thermal performance of radiant floor partially irradiated by solar radiation. Results show that the solar radiation can promote the heat transfer from the irradiated floor to the room and reduce the heat transfer from the hot water to the floor. Compared with the cases without the solar radiation, the heat transfer from the hot water to the floor was reduced from 131.8 W/m 2 to 79.7 W/m 2 and the heating capacity of radiant floor surface was increased from 128.0 W/m 2 to 402.8 W/m 2 with the solar radiation on one third of the floor surface and the absorbed intensity of 456.2 W/m 2 . With the same irradiation area, if the solar radiation irradiated at the centre of the floor, the reduction effect on the heat transfer from the hot water was more obvious. Based on this experiment, these results can be used to evaluate the thermal performance of irradiated radiant floor, and are beneficial to the design of heating systems.
2 citations
TL;DR: In this article , the authors proposed a design strategy by integrating asymmetric oxygen-boron-nitrogen (O-B-N) multi-resonance (MR) unit into traditional N-b-N MR molecules to form a rigid and extended O-BN-B -N MR π-skeleton.
Abstract: Developing deep-blue thermally activated delayed fluorescence (TADF) emitters with both high efficiency and color purity remains a formidable challenge. Here, we proposed a design strategy by integrating asymmetric oxygen-boron-nitrogen (O-B-N) multi-resonance (MR) unit into traditional N-B-N MR molecules to form a rigid and extended O-B-N-B-N MR π-skeleton. Three deep-blue MR-TADF emitters of OBN, NBN and ODBN featuring asymmetric O-B-N, symmetric N-B-N and extended O-B-N-B-N MR units were synthesized through the regioselective one-shot electrophilic C-H borylation at different positions of the same precursor. The proof-of-concept emitter ODBN exhibited respectable deep-blue emission with Commission International de l'Eclairage coordinate of (0.16, 0.03), high photoluminescence quantum yield of 93 % and narrow full width at half maximum of 26 nm in toluene. Impressively, the simple trilayer OLED employing ODBN as emitter achieved a high external quantum efficiency up to 24.15 % accompanied by a deep blue emission with the corresponding CIE y coordinate below 0.1.
2 citations
TL;DR: In this paper , an effective strategy to grow robust perovskite film with enlarged grain size, enhanced crystallinity, and preferred orientation in high-humidity air was demonstrated.
2 citations
TL;DR: In this article , the authors derived analytical formulations of the leak-induced wave reflection and phase difference at any measurement point in a leaky viscoelastic pipe and further developed an optimization algorithm to detect the leak.
2 citations
TL;DR: In this article , the authors present a review of the failure probability of water pipes, including physical, statistical, and machine learning (ML)-based models, and identify gaps and future research directions.
Abstract: Failures of water distribution networks (WDNs) are rising at an exponential rate, necessitating immediate attention. An effective way to reduce the failure rate is to develop accurate predictive models for the failure probability of water pipes, which are the most critical assets of WDNs. Despite the fact that researchers have invested efforts to develop various predictive models, the extant literature lacks a complete state-of-the-art review. To fill this gap, this study employs a mixed approach (i.e., quantitative and qualitative) by providing (a) a bibliometric analysis of existing scholarly literature, (b) a systematic review of the techniques used in modeling the failure probability of water pipes, including physical, statistical, and machine-learning (ML)-based models, and (c) identified gaps and future research directions. The bibliometric analysis shows that ML-based models are emerging and, hence understudied as compared to the physical and statistical-based models. Regarding the systematic review, a proper understanding of the development of each model has been provided in addition to their advantages and critiques. Furthermore, failure probability integration methods are discussed. Findings reveal that the social and operation-related predictors have been understudied, thereby suggesting their further exploration. This study adds to the existing body of knowledge by providing water utilities and academics with a comprehensive understanding of the probability of water pipe failure, which will be useful in the decision-making process and network management.
2 citations
TL;DR: In this paper , the Curie brothers who first discovered the piezoelectric effect have introduced C-eigenvalues and C-Eigenvectors for the C-type tensors, which are invariant under orthogonal transformations.
Abstract: <p style="text-indent:20px;">In crystallography, piezoelectric tensors of various crystals play a crucial role in piezoelectric effect and converse piezoelectric effect. Generally, a third order real tensor is called a piezoelectric-type tensor if it is partially symmetric with respect to its last two indices. The piezoelectric tensor is a piezoelectric-type tensor of dimension three. We introduce C-eigenvalues and C-eigenvectors for piezoelectric-type tensors. Here, "C'' names after Curie brothers, who first discovered the piezoelectric effect. We show that C-eigenvalues always exist, they are invariant under orthogonal transformations, and for a piezoelectric-type tensor, the largest C-eigenvalue and its C-eigenvectors form the best rank-one piezoelectric-type approximation of that tensor. This means that for the piezoelectric tensor, its largest C-eigenvalue determines the highest piezoelectric coupling constant. We further show that for the piezoelectric tensor, the largest C-eigenvalue corresponds to the electric displacement vector with the largest 2-norm in the piezoelectric effect under unit uniaxial stress, and the strain tensor with the largest 2-norm in the converse piezoelectric effect under unit electric field vector. Thus, C-eigenvalues and C-eigenvectors have concrete physical meanings in piezoelectric effect and converse piezoelectric effect. Finally, by numerical experiments, we report C-eigenvalues and associated C-eigenvectors for piezoelectric tensors corresponding to several piezoelectric crystals.</p>
TL;DR: In this paper , a two-folder conceptual framework with strategic folder and practical folder is constructed to explore the adoption and performance value of responsible shipping practices. But the authors do not consider the dual role of shipping industry in servicing trade activities of the global economy.
TL;DR: In this article , the authors proposed a hybrid indirect evaporative cooler (IEC) and a cooling coil unit as a primary air handling unit (PAU) for hot-humid buildings.
TL;DR: In this article , an oxygen-incorporated Ni aerogel is prepared by a facile reduction-oxidation method to achieve high performance non-noble metal-based systems for catalytic CO2 utilization.
Abstract: Photochemical CO2 reduction to CO, acting as a mild and feasible method, holds huge prospects for atmospheric CO2 level diminution. Non-noble metal aerogel has been supposed to be an appealing material in the field of catalysis, yet suffering from low conductivity and poor activity. From the perspective of electronic structure modification, oxygen-incorporated Ni aerogel is prepared by a facile reduction-oxidation method. With the optimized electronic structure in [email protected] aerogel by oxygen incorporation, brilliant photocatalytic activity with CO yield of 39.30 μmol/mg and CO selectivity of 94.4 % could be achieved, taking advantage of the electron-rich Ni and greatly increased conductivity as well as sufficient active sites exposure. This work sheds light on the design and development of high-performance non-noble metal-based systems for catalytic CO2 utilization.
TL;DR: In this paper , an aerodynamic noise prediction model for counter-rotating coaxial rotors is presented, where the aerodynamic interactions due to the flow accelerations and wake flow properties are considered in an efficient blade element and momentum theory method to compute the mean flow variables.
TL;DR: Zhang et al. as mentioned in this paper proposed an effective framework, Stabilized Self-Training (SST), which is applicable to existing GNNs to handle the scarcity of labeled data, and consequently, boost classification accuracy.
01 Jan 2023
TL;DR: In this paper , the thermal effects of a pulsed nanosecond dielectric barrier discharge plasma actuator (NSDBD) with varying pulse voltages and pulse repetitive frequencies under different air pressures ranging from 0.1 to 1 bar are studied experimentally.
Abstract: The thermal effects of a pulsed nanosecond dielectric barrier discharge plasma actuator (NSDBD) with varying pulse voltages and pulse repetitive frequencies under different air pressures ranging from 0.1 to 1 bar are studied experimentally. By observing discharge features with a charge-coupled device camera, the transition from a filamentary discharge mode to a diffuse mode with decreasing air pressure is described. The filamentary streamers extend along the radius direction, forming a thicker yet more stable and uniform plasma region due to the increasing ionized volume yielded by the decreasing air pressure to maintain the high values of the reduced electric field. The spatiotemporal temperature distribution on the surface is captured by an infrared camera, indicating that the heated surface can be divided into three typical regions with different features. Because gas heating is generated in the quenching process of excited molecules, the maximum temperature increase on the surface occurs in the plasma region and attenuates downstream. The surface temperature increase is primarily caused by heat convection from the residual heat in plasma and the heat generated by the dielectric losses. The results of heat flux on the surface suggest that the rising applied voltage may not increase the heat flux in a moderate air pressure ranging from 0.6 to 0.8 bar. Different discharge modes and discharge parameters exhibit markedly different thermal performances. Also, the Schlieren technique and the pressure sensor are used to visualize the induced shock wave, estimate the thermal expansion region, and measure the overpressure strength. The results of the overpressure strength at different air pressures are similar to the thermal features, which highlights the strong influence of the discharge mode on the thermal effect of NSDBD plasma actuators.
TL;DR: In this article , a ternary molten salt-lithium reduction method is designed to create controllable oxygen vacancies (Ovs) as well as to manipulate the surface microstructure of the classic photocatalyst TiO2.
Abstract: The efficiency of photoabsorption, photo-generated charge separation, and surface redox reaction determine the overall efficiency of photocatalysts. Therefore, exploring ways to simultaneously optimize the parameters is key to improving the photocatalytic performance. Herein, a novel low-temperature ternary molten salt-lithium reduction method is designed to create controllable oxygen vacancies (Ovs) as well as to manipulate the surface microstructure of the classic photocatalyst TiO2. The optimized TiO2 exhibits a 10-fold increase in the photocatalytic RhB breakdown rate and H2 generation quantity compared to pristine TiO2. The dual surface defects result in synergistic effects: i) Ovs lower band gap, enhance the charge separation efficiency as capture centers, and facilitate hydrogen adsorption; ii) the enlarged surface area enhances light-harvesting and provides more active sites. This research proposes a novel strategy for manipulating surface defects in a controlled manner and highlights the synergistic optimization of the thermodynamical and kinetical parameters to promote the photocatalytic performance.
TL;DR: In this article , a new type of two-dimensional (2D) Janus electrenes with different cation layers was reported, and the phonon spectra demonstrate the dynamical stability of ZrScCl2, ZrYCl2 and ZrCaCl2.
TL;DR: In this article , the sound absorption performance of a wavy micro-perforated panel absorber (WMPPA) is investigated and compared with those of flat and corrugated FMPPAs.
TL;DR: In this paper , a relational approach to examine the rationalisation of purchases of cosmetic surgery as an embodied good is presented, and participants stress their resignation and powerlessness in being forced to adopt this instrumental reconceptualisation as a response to intensifying economic hardships in contemporary capitalist South Korea.
Abstract: Embodied goods like cosmetic surgery comprise a unique and growing consumer industry, most of all in the Asia-Pacific, yet the rationalisation processes motivating their purchase are less understood. Addressing this lacuna, this article builds upon open-ended surveys and semi-structured interviews of consumers in Seoul, South Korea to articulate a relational approach to examine the rationalisation of purchases of cosmetic surgery as an embodied good. Theorised through the conceptual lens of Bourdieusian capital, participant accounts point to macro-level economic anxieties that inform a micro-level cognitive logic of competition through which consumers rationalise the purchase of embodied goods as a form of aesthetic capital. When performed, this capital is believed to offer actors social distinction that provides workplace and social networking advantages by impressing gatekeepers and alters. Participants are shown to reconceptualise their bodies in a means-end orientation for upward mobility but stress their resignation and powerlessness in being forced to adopt this instrumental reconceptualisation as a response to intensifying economic hardships in contemporary capitalist South Korea.
TL;DR: A textile-based wearable sensor monitored each participant's HRV after they completed 60 min of bar bending and fixing tasks as mentioned in this paper , indicating a change in the relative activity of cardiac autonomic functions as a result of fatigue.
Abstract: Several studies have analyzed heart rate variability (HRV) using nonlinear methods, such as approximate entropy, the largest Lyapunov exponent, and correlation dimension in patients with cardiovascular disorders. However, few studies have used nonlinear methods to analyze HRV in order to determine the level of physical fatigue experienced by construction workers. As a result, to identify and categorize physical fatigue in construction workers, the current study examined the linear and nonlinear approaches of HRV analysis. Fifteen healthy construction workers (mean age, 33.2±6.9 years) were selected for this study. A textile-based wearable sensor monitored each participant’s HRV after they completed 60 min of bar bending and fixing tasks. At baseline, 15, 30, 45, and 60 min into the task, participants were given the Borg-20 to measure their subjective levels of physical fatigue. Nonlinear [e.g., R-R interval (RRI) variability, entropy, detrended fluctuation analysis] and linear (e.g., time- and frequency-domain) HRV parameters were extracted. Five machine learning classifiers were used to identify and discern different physical fatigue levels. The accuracy and validity of the classifier models were evaluated using 10-fold cross-validation. The classification models were developed by either combining or individualized HRV features derived from linear and nonlinear HRV analyses. In the individualized feature sets, time-domain features had the highest classification accuracy (92%) based on the random forest (RF) classifier. The combined feature (i.e., the time-domain and nonlinear features) sets showed the highest classification accuracy (93.5%) using the RF classifier. In conclusion, this study showed that both linear and nonlinear HRV analyses can be used to detect and classify physical fatigue in construction workers. This research offers important contributions to the industry by analyzing the variations in linear and nonlinear HRV parameters in response to construction tasks. This study demonstrates that HRV values changed significantly in response to physical work, indicating a change in the relative activity of cardiac autonomic functions as a result of fatigue. Using the ways in which HRV parameters vary in response to increased workloads provides a sensitive marker for contrasting construction workers with and without cardiovascular disease. It also allows the site manager to track how quickly workers fatigue, so that they can switch up their workload to reduce the likelihood that any one worker would get severely exhausted, or to suggest that workers who are already severely fatigued take a break to prevent further injury.
TL;DR: In this article , the authors present the emerging conversion routes for plastic wastes and highlight the advantages of artificial photosynthesis for processing plastic wastes, including plastic photodegradation, tandem decomposition of plastic and CO2 reduction, selective plastic oxidation, as well as photoreforming of plastic.
Abstract: The accumulation of plastic wastes in landfills and the environment threatens our environment and public health, while leading to the loss of potential carbon resources. The urgent necessary lies in developing an energy-saving and environmentally benign approach to upgrade plastic into value-added chemicals. Artificial photosynthesis holds the ability to realize plastic upcycling by using endless solar energy under mild conditions, but remains in the initial stage for plastic upgrading. In this review, we aim to look critically at the photocatalytic conversion of plastic wastes from the perspective of resource reutilization. To begin with, we present the emerging conversion routes for plastic wastes and highlight the advantages of artificial photosynthesis for processing plastic wastes. By parsing photocatalytic plastic conversion process, we demonstrate the currently available routes for processing plastic, including plastic photodegradation, tandem decomposition of plastic and CO2 reduction, selective plastic oxidation, as well as photoreforming of plastic. This review concludes with a personal perspective for potential advances and emerging challenges in photocatalytic plastic conversion.
TL;DR: Wang et al. as mentioned in this paper used a descriptive phenomenological approach to capture and explore family caregivers' lived experience of caring for hospitalised patients with cancer during the lockdown, including feeling scared for the patient, living a life feeling trapped under COVID-19 surveillance, feeling neglected and unseen, growing resilience and appreciation.
Abstract: Aims This study aimed to capture and explore family caregivers' lived experience of caring for hospitalised patients with cancer during the lockdown. Background The unprecedented lockdown episodes due to COVID-19 have brought significant changes in the hospital visiting policies and caregiving practices. As part of the precautionary measures for hospital visits, the bedside companion was restricted to one caregiver for patients with cancer in Shanghai hospitals. Design This study adopted a descriptive phenomenological approach. Methods Data were collected among 20 family caregivers recruited from the Oncology department of a tertiary hospital in Shanghai in May 2022, using purposive sampling method and followed by unstructured, open-ended interviews. Colaizzi's seven-step data analysis method was used to analyse the data to reveal the emergent themes and subthemes of the phenomenon. Results Four themes were generated on family caregivers' lived experience of caring for hospitalised patients with cancer during the lockdown, including (1) Feeling scared for the patient; (2) Living a life feeling trapped under COVID-19 surveillance; (3) Feeling neglected and unseen; (4) Growing resilience and appreciation. Conclusions The lockdown exacerbated the burden of family caregivers when they cared for the hospitalised patients with cancer during the lockdown period. However, positive reframing of the lived experience facilitated their coping with the challenging situation. Relevance to Clinical Practice Findings from this study highlighted the potential proactive roles the healthcare providers could play in improving family caregivers' health and supporting them during and beyond the COVID-19 pandemic. Reporting Method The study adhered to relevant EQUATOR guidelines; the study was reported according to the COREQ checklist. Patient or Public Contribution Family caregivers of patients with cancer were involved in data collection and member-checking of the transcripts and interpretations of their experiences.
TL;DR: In this paper , the authors proposed a novel ductile machining model for ultra-precision fly cutting (UPFC) to efficiently fabricate deep micro-structures on brittle materials.
Abstract: Due to its extremely low fracture toughness of brittle materials, it is difficult to obtain deep micro-structures on brittle materials with ultra-smooth surface quality using previous ductile machining models based on plunge cutting, diamond milling, and grinding. Current methods to enhance the machinability of silicon include laser-assisted machining, ion implantation modification, and vibration-assisted machining. However, the increase of the ductile machining depth using these methods is still very small in the fabrication of deep micro-structures with a depth over tens of micrometers on silicon. This chapter proposes a novel ductile machining model for ultra-precision fly cutting (UPFC) to efficiently fabricate deep micro-structures on brittle materials. The modeling results show that through configuring a large swing radius, much deeper ductile machining depth can be reached by UPFC. To confirm this proposed model, micro-grooves with different depths were machined, and the surface micro-topographies, form error, tool wear patterns, and material phase transformation were analyzed and compared with that acquired by diamond sculpturing method. The experimental results demonstrated that much deeper micro-grooves (over tens of micrometers) with better surface quality were acquired by UPFC. Moreover, compared with the sculpturing method, UPFC prolonged the tool life and generated less amorphous silicon on the machined surface.
01 Jan 2023
TL;DR: In this paper , a series of laboratory seepage-erosion tests on soil specimens with different Talbot indexes and initial porosities were conducted to evaluate the applicability of existing k-φ models in this problem.
Abstract: During the construction of tunnelling in soil ground, erosion-induced water inrush is one of the most serious geohazards, during which the migration of soil particles can substantially alter soil porosity and permeability. Understanding the permeability-porosity (k-φ) relation is crucial for predicting the rate of water inflow and the possibility of water inrush. The applicability of existing k-φ models in this problem has not been evaluated. In this study, the k-φ relation was investigated by a series of laboratory seepage-erosion tests on soil specimens with different Talbot indexes and initial porosities. Based on the experimental results, an evaluation was made on the performance of four popular k-φ models, including the Kozeny-Carman (K-C), Kruger, Ives-Pienvichitr (I-P), and Verma and Pruess (V-P) models. Two types of seepage-erosion processes were observed, including the common erosion and mutation erosion processes (CEP and MEP). CEP and MEP mean the processes with and without the occurrence of water inrush, respectively. During the CEP associated with low Talbot index and porosity, the permeability of soil was significantly overestimated by the V-P model and slightly underestimated by the other three models. During the MEP associated with high Talbot index and porosity, the erosion led to water inrush through three stages: slow and rapid evolution as well as stable stages. Significant underestimates of soil permeability were caused by all the models, thereby leading to high risk. None of these models was able to well capture the k-φ relation during different erosion-flow processes for both CEP and MEP. To address this problem, a power function with one adjustable exponent for the k-φ relation was proposed and verified.
TL;DR: In this paper , the authors investigated how baseline quadriceps passive stiffness predicts the incidence of clinical knee OA at the 12-month follow-up, and they found that higher passive stiffness of the quadrices at baseline was associated with a higher risk of clinical OA.
Abstract: Quadriceps weakness is a known risk factor for the onset of knee osteoarthritis (OA). In addition to muscle weakness, increased passive stiffness of the quadriceps may affect knee biomechanics and hence contribute to the pathogenesis of knee OA. However, the association between quadriceps stiffness and the risk of knee OA development has not been prospectively investigated.The aim of this study was to investigate how baseline quadriceps passive stiffness predicts the incidence of clinical knee OA at the 12-month follow-up.Prospective cohort study.University laboratory.Community-dwelling adults aged 60-80 years were recruited. We excluded participants with: 1) knee pain or known arthritis; 2) knee injury; 3) knee or hip joint replacement, 4) cognitive impairment; or 5) neurological conditions.At baseline, passive stiffness of the three superficial quadriceps muscle heads (rectus femoris [RF], vastus lateralis [VL], and vastus medialis oblique [VMO]) was evaluated using shear-wave ultrasound elastography. Knee muscle (quadriceps and hamstrings) strength was tested using a Cybex dynamometer. Knee OA was defined based on clinical criteria 12 months after baseline measurements. Generalized estimating equations were used to examine the associations of quadriceps stiffness and knee muscle strength with the risk of knee OA, controlling for age, sex, Body Mass Index, comorbidities, and activity level.The analyses included 158 knees (58.2% females, age: 65.6±4.1 years). Twenty-eight knees (17.7%) were classified as having clinical OA at 12 months. Compared with the lowest stiffness tertiles, the highest stiffness tertiles of the RF (relative risk =5.31, 95% CI: 1.34-21.0), VMO (4.15, 1.04-16.6), and total superficial quadriceps (6.35, 1.48-27.3) at baseline were significantly associated with a higher risk of knee OA at the follow-up. The highest strength tertile of quadriceps has a trend of association with a lower risk of knee OA than the lowest tertile (0.18, 0.03-1.25, P=0.083).Greater passive stiffness of the quadriceps at baseline was associated with a higher risk of clinical knee OA incidence at the 12-month follow-up.Interventions for reducing the passive stiffness of the quadriceps should be included in preventative training programs for older adults.
TL;DR: In this paper , a linear adaptive time-step scheme based on the second-order backward differentiation formulation (BDF2) and using the Fourier spectral method for the spatial discretization is presented and analyzed.
Abstract: In this article, we present and analyze a linear fully discrete second order scheme with variable time steps for the phase field crystal equation. More precisely, we construct a linear adaptive time stepping scheme based on the second order backward differentiation formulation (BDF2) and use the Fourier spectral method for the spatial discretization. The scalar auxiliary variable approach is employed to deal with the nonlinear term, in which we only adopt a first order method to approximate the auxiliary variable. This treatment is extremely important in the derivation of the unconditional energy stability of the proposed adaptive BDF2 scheme. However, we find for the first time that this strategy will not affect the second order accuracy of the unknown phase function ϕ n $$ {\phi}^n $$ by setting the positive constant C 0 $$ {C}_0 $$ large enough such that C 0 ≥ 1 / τ . $$ {C}_0\ge 1/\tau . $$ The energy stability of the adaptive BDF2 scheme is established with a mild constraint on the adjacent time step radio γ n + 1 : = τ n + 1 / τ n ≤ 4 . 8645 $$ {\gamma}_{n+1}:= {\tau}_{n+1}/{\tau}_n\le 4.8645 $$ . Furthermore, a rigorous error estimate of the second order accuracy of ϕ n $$ {\phi}^n $$ is derived for the proposed scheme on the nonuniform mesh by using the uniform H 2 $$ {H}^2 $$ bound of the numerical solutions. Finally, some numerical experiments are carried out to validate the theoretical results and the efficiency of the proposed scheme combined with the time adaptive strategy.
31 Mar 2023
TL;DR: In this article , the authors investigated mechanisms driving resistance and CSC repopulation in hepatocellular carcinoma (HCC) as a cancer model using two drug-resistant, patient-derived tumor xenografts that mimicked the development of acquired resistance to sorafenib or lenvatinib treatment observed in patients with HCC.
Abstract: <div>Abstract<p>Accumulating evidence has demonstrated that drug resistance can be acquired in cancer through the repopulation of tumors by cancer stem cell (CSC) expansion. Here, we investigated mechanisms driving resistance and CSC repopulation in hepatocellular carcinoma (HCC) as a cancer model using two drug-resistant, patient-derived tumor xenografts that mimicked the development of acquired resistance to sorafenib or lenvatinib treatment observed in patients with HCC. RNA sequencing analysis revealed that cholesterol biosynthesis was most commonly enriched in the drug-resistant xenografts. Comparison of the genetic profiles of CD133<sup>+</sup> stem cells and CD133<sup>−</sup> bulk cells from liver regeneration and HCC mouse models showed that the cholesterol pathway was preferentially upregulated in liver CSCs compared with normal liver stem cells. Consistently, SREBP2-mediated cholesterol biosynthesis was crucial for the augmentation of liver CSCs, and loss of SREBP2 conferred sensitivity to tyrosine kinase inhibitors, suggesting a role in regulation of acquired drug resistance in HCC. Similarly, exogenous cholesterol-treated HCC cells showed enhanced cancer stemness abilities and drug resistance. Mechanistically, caspase-3 (CASP3) mediated cleavage of SREBP2 from the endoplasmic reticulum to promote cholesterol biosynthesis, which consequently caused resistance to sorafenib/lenvatinib treatment by driving activation of the sonic hedgehog signaling pathway. Simvastatin, an FDA-approved cholesterol-lowering drug, not only suppressed HCC tumor growth but also sensitized HCC cells to sorafenib. These findings demonstrate that CSC populations in HCC expand via CASP3-dependent, SREBP2-mediated cholesterol biosynthesis in response to tyrosine kinase inhibitor therapy and that targeting cholesterol biosynthesis can overcome acquired drug resistance.</p>Significance:<p>This study finds that cholesterol biosynthesis supports the expansion of cancer stem cell populations to drive resistance to tyrosine kinase inhibitor therapy in hepatocellular carcinoma, identifying potential therapeutic approaches for improving cancer treatment.</p></div>