Showing papers by "Xiaobo Chen published in 2023"

Process-dependent anisotropic thermal conductivity of laser powder bed fusion AlSi10Mg: impact of microstructure and aluminum-silicon interfaces

Abstract: Purpose AlSi10Mg alloy is commonly used in laser powder bed fusion due to its printability, relatively high thermal conductivity, low density and good mechanical properties. However, the thermal conductivity of as-built materials as a function of processing (energy density, laser power, laser scanning speed, support structure) and build orientation, are not well explored in the literature. This study aims to elucidate the relationship between processing, microstructure, and thermal conductivity. Design/methodology/approach The thermal conductivity of laser powder bed fusion (L-PBF) AlSi10Mg samples are investigated by the flash diffusivity and frequency domain thermoreflectance (FDTR) techniques. Thermal conductivities are linked to the microstructure of L-PBF AlSi10Mg, which changes with processing conditions. The through-plane exceeded the in-plane thermal conductivity for all energy densities. A co-located thermal conductivity map by frequency domain thermoreflectance (FDTR) and crystallographic grain orientation map by electron backscattered diffraction (EBSD) was used to investigate the effect of microstructure on thermal conductivity. Findings The highest through-plane thermal conductivity (136 ± 2 W/m-K) was achieved at 59 J/mm3 and exceeded the values reported previously. The in-plane thermal conductivity peaked at 117 ± 2 W/m-K at 50 J/mm3. The trend of thermal conductivity reducing with energy density at similar porosity was primarily due to the reduced grain size producing more Al-Si interfaces that pose thermal resistance. At these interfaces, thermal energy must convert from electrons in the aluminum to phonons in the silicon. The co-located thermal conductivity and crystallographic grain orientation maps confirmed that larger colonies of columnar grains have higher thermal conductivity compared to smaller columnar grains. Practical implications The thermal properties of AlSi10Mg are crucial to heat transfer applications including additively manufactured heatsinks, cold plates, vapor chambers, heat pipes, enclosures and heat exchangers. Additionally, thermal-based nondestructive testing methods require these properties for applications such as defect detection and simulation of L-PBF processes. Industrial standards for L-PBF processes and components can use the data for thermal applications. Originality/value To the best of the authors’ knowledge, this paper is the first to make coupled thermal conductivity maps that were matched to microstructure for L-PBF AlSi10Mg aluminum alloy. This was achieved by a unique in-house thermal conductivity mapping setup and relating the data to local SEM EBSD maps. This provides the first conclusive proof that larger grain sizes can achieve higher thermal conductivity for this processing method and material system. This study also shows that control of the solidification can result in higher thermal conductivity. It was also the first to find that the build substrate (with or without support) has a large effect on thermal conductivity.

In situ anchoring CuS nanoparticles on vertical aligned graphene nanosheets supported on carbon cloth for high-performance supercapacitors

Abstract: In this work, we report the synthesis of copper sulfide/vertically aligned graphene nanosheets nanocomposite on carbon cloth (CC/VAGN/CuS) for asymmetric supercapacitors. CC/VAGN is an excellent conductive backbone with interconnected porous architecture, resulting in fast transportation of electrons and ions, meanwhile improving the utilization of active materials. Impressively, the resulting CC/VAGN/CuS electrode obtains an outstanding specific capacity of 342.6 mAh/g at 1 A/g and demonstrates excellent cyclic performance. Moreover, a solid-state asymmetric supercapacitor (ASC) using two binder-free electrodes, i.e., CC/VAGN/CuS as the positive electrode and CC/VAGN as the negative electrode, exhibits a high specific energy of 76.7 Wh kg−1 at specific power 800.2 W kg−1 with 83.6 % capacity retention over 10,000 cycles at 8 A/g. Our results illustrate the promise of the rational-designed CC/VAGN/CuS as a promising candidate for hybrid supercapacitors.

Construction of Ti3C2Tx MXene wrapped urchin-like CuCo2S4 microspheres for high-performance asymmetric supercapacitors.

Abstract: Copper cobalt sulfide (CuCo2S4) nanomaterials are regarded as promising electrode materials for high-performance supercapacitors due to their abundant redox states and considerable theoretical capacities. However, the intrinsic poor electrical conductivity, sluggish reaction kinetics and insufficient number of electroactive sites of these materials are huge barriers to realize their practical applications. In this study, a facile two-step strategy to engineer a hierarchical 3D porous CuCo2S4/MXene composite electrode is presented for enhanced storage properties. This well-constructed CuCo2S4/MXene composite not only provides abundant active sites for the faradaic reaction, but also offers more efficient pathways for rapid electron/ion transport and restricts the volumetric expansion during the charge/discharge process. When evaluated in a 3 M KOH electrolyte, the CuCo2S4/MXene-3 electrode exhibits a specific capacity of 1351.6 C g-1 at 1 A g-1 while retaining excellent cycling stability (95.2% capacity retention at 6 A g-1 after 10 000 cycles). Additionally, the solid-state asymmetric supercapacitor (ASC) CuCo2S4/MXene//AC device displays an energy density of 78.1 W h kg-1 and a power density of 800.7 W kg-1. Two ASC devices connected in series can illuminate a blue LED indicator for more than 20 min, demonstrating promising prospects for practical applications. These electrochemical properties indicate that the high-performance CuCo2S4/MXene composites are promising electrode materials for advanced asymmetric supercapacitors.

Association of Critical Value With 28-Day Mortality After Cardiac Surgery.

Abstract: OBJECTIVE The emergence of critical values gives a warning to the medical safety of hospitalized patients, especially Cardiosurgery Intensive Care Unit (CSICU) patients. The aim of this study was to investigate the association between early postoperative critical values and the prognosis of patients after cardiac surgery. METHODS Clinical data of the patients were obtained from the Cardiac Critical Care Clinical Database of the Cardiovascular Intensive Care Unit of Nanjing First Hospital. A total of 1,598 consecutive patients undergoing cardiac surgery were enrolled in this retrospective cohort study, during the period from July 2019 to December 2020. According to whether critical value occurred within 7 days after cardiac surgery, patients were divided into two groups: the critical value group and control group. COX regression and survival analysis were performed to analyze the clinical data of the two groups. The area under the receiver operating characteristic curve (ROC) was used to assess the critical value's predictive value and determine the optimal cutoff value. RESULTS With patients in the critical value group, the 28-day mortality after cardiac surgery was 21.98%, significantly higher than that of the control group (P < 0.05). Logistic regression analysis revealed the APACHE II score (Adjusted HR-1.11, 95% CI-1.043-1.185) and critical value group (Adjusted HR-13.57, 95% CI-6.714-27.435 ) were independent predictors of 28-day mortality after cardiac surgery. The ROC curve showed that the critical value case model (AUC = 0.748 ± 0.052, P < 0.05) could effectively predict the 28-day mortality, and the optimum cutoff was 1 case (sensitivity 52.63%, specificity 95.70%). CONCLUSIONS One or more reported cases of critical values in the early postoperative period could be an independent risk factor for 28-day mortality in patients undergoing cardiac surgery. The predictive model based on critical value might be effective in clinical therapy and risk stratification.

Edge Engineering of Carbon Nitride Nanodots with Pocket-like Sites for Effective Photoreduction of Bicarbonate to CO under Visible Light

Abstract: Abundant pocket-like defects are engineered on the edge of carbon nitride nanodots (CN1.9), using hydrazine groups to attack carbon atoms which results in CN heterocycle opening of porous graphitic C3N4. These edge defects on CN1.9 not only modulate the electronic structure, extend light absorption, and promote photoexcited electron transfer but also lead to c(HCO3–)/c(CO2, aq)-dependent photocatalytic CO evolution in CO2 bubbling HCO3– aqueous solution (pH ≈ 7.1∼7.5). Even in the N2/HCO3– system (pH ≈ 8.17), wherein c(HCO3–) is about 67 times higher than c(CO2, aq), the CO production also attains 48.6 μmol g–1 h–1 on CN1.9. In the same experimental condition, almost no CO produces except for H2 on graphitic carbon nitride (GCN). DFT theoretical calculation reveals that edge defects prefer to contact with HCO3– and proton to orient a special reaction pathway of HCO3* → H2CO3* → CO on CN1.9 with a relatively low-energy barrier rather than HCO3* → H2O–CO2* → CO on GCN.

What affects the risks of fintech lending enterprises?

Abstract: Five main risk factors of fintech lending enterprises are empirically analysed by using the duration analysis model. The main findings are: Technology does not cause a significant increase in enterprise risk, the main reason is that although technology brings new types of risk, namely, technical risk, but it eliminates the human errors and moral hazards in a certain extent. There is debate on the role of regulatory policy on corporate risk, ‘market failure theory’ and ‘regulatory failure theory’, the empirical results show that the institutionalization of regulatory is more conducive to reducing risk than the frequently issuing ‘new regulatory policies’. As for the debate about whether large or small enterprises carry greater risks, the empirical evidence shows that the failure risks of large enterprises are only 79% of the risks of small enterprise. Another important finding is that the risks of listed companies or venture capital-controlled enterprises are far less than that of private enterprises, which suggests that the institution is very important to reduce risk.

Atomistic Origins of Reversible Noncatalytic Gas-Solid Interfacial Reactions.

Abstract: Noncatalytic gas-solid reactions are a large group of heterogeneous reactions that are usually assumed to occur irreversibly because of the strong driving force to favor the forward direction toward the product formation. Using the example of Ni oxidation into NiO with CO2, herein, we demonstrate the existence of the reverse element that results in the NiO reduction from the countering effect of the gaseous product of CO. Using in situ electron microscopy observations and atomistic modeling, we show that the oxidation process occurs via preferential CO2 adsorption along step edges that results in step-flow growth of NiO layers, and the presence of Ni atoms on the flat NiO surface promotes the nucleation of NiO layers. Simultaneously, the NiO reduction happens via preferential step-edge adsorption of CO that leads to the receding motion of atomic steps, and the presence of Ni vacancies in the NiO surface facilitates the CO-adsorption-induced surface pitting. Temperature and CO2 pressure effect maps are constructed to illustrate the spatiotemporal dynamics of the competing NiO redox reactions. These results demonstrate the rich gas-solid surface reaction dynamics induced by the coexisting forward and reverse reaction elements and have practical applicability in manipulating gas-solid reactions via controlling the gas environment or atomic structure of the solid surface to steer the reaction toward the desired direction.

Antimony nanobelt asymmetric membranes for sodium ion battery

Abstract: In this study, composite asymmetric membranes containing antimony (Sb) nanobelts are prepared via a straightforward phase inversion method in combination with post-pyrolysis treatment. Sb nanobelt asymmetric membranes demonstrate improved cyclability and specific capacity as the alloy anode of sodium ion battery compared to Sb nanobelt thin films without asymmetric porous structure. The unique structure can effectively accommodate the large volume expansion of Sb-based alloy anodes, prohibit the loss of fractured active materials, and aid in the formation of stable artificial solid electrolyte interphases as evidenced by an outstanding capacity retention of ∼98% in 130 cycles at 60 mA g−1. A specific capacity of ∼600 mAh g−1 is obtained at 15 mA g−1 (1/40C). When the current density is increased to 240 mA g−1, ∼80% capacity can be maintained (∼480 mAh g−1). The relations among phase inversion conditions, structures, compositions, and resultant electrochemical properties are revealed through comprehensive characterization.

Experiences of maintaining awake prone positioning in non-intubated patients with COVID-19: A qualitative study.

Abstract: BACKGROUND Patient compliance is crucial to maintaining the awake prone position, which has been found to be intolerable by several patients. Addressing patients' compliance while being treated with awake prone positioning and prolonging its duration may be prerequisites for further research. AIMS This study was conducted to explore the personal experiences of non-intubated patients during the implementation of awake prone positioning. STUDY DESIGN We conducted a qualitative study recruiting a purposive sample of twelve adult patients diagnosed with COVID-19 who were previously treated with awake prone positioning. They were recruited from an intermediate care unit (that provides pre- and post-intensive care) in a COVID-19-designated hospital in Nanjing, China from July 15, 2021, to September 20, 2021. Data were collected through individual in-depth interviews and then analysed using Colaizzi's phenomenological method. RESULTS Content analysis of the interviews revealed two main themes, each containing three and four sub-themes, respectively, as follows: (1) barriers to the implementation of awake prone positioning, including (i) generalised discomfort, (ii) a lack of both understanding and trust, and (iii) low satisfaction with the implementation plan; (2) factors promoting the implementation of awake prone positioning, including (i) health education and supervision, (ii) self-motivation and support from healthcare staff and family members, (iii) finding a comfortable position and having access to entertainment, and (iv) symptom improvement. CONCLUSIONS Healthcare staff should clarify the mechanism underlying the effectiveness of the awake prone position to patients to eliminate any doubts that they may have. Psychological support and appropriate supervision should be emphasised. Pain relief programmes should also be established, including the use of a comfortable prone posture in conjunction with access to entertainment. Finally, individualised awake prone positioning protocols should be formulated according to patients' living habits and attempted in combination with out-of-bed activities. These measures may help to enhance the experience and compliance of patients undergoing the treatment. RELEVANCE TO CLINICAL PRACTICE For future instances involving the implementation of awake prone positioning, several measures should be established and implemented alongside it, including a health education programme, supervision programme, support system, and pain relief programme. Personalisation should also be considered during its implementation. These measures may help to enhance the compliance of patients and prolong the duration of the awake prone position.

Reconstruction of Highly-Defective MgO and Exceptional Photochemical Activity on CO2 Upgrade in Aqueous Solution.

Abstract: Defects on metal oxide have attracted extensive attention in photo-/electrocatalytic CO2 reduction. Herein, porous MgO nanosheets with abundant oxygen vacancies (Vo s) and three-coordinated oxygen atoms (O3c ) at corners are reported, which reconstruct into defective MgCO3 ·3H2 O exposing rich surface unsaturated -OH groups and vacancies to initiate photocatalytic CO2 reduction to CO and CH4 . In consecutive 7-cycle tests (each run for 6 h) in pure water, CO2 conversion keeps stable. The total production of CH4 and CO attains ≈367 µmol gcata -1 h-1 . The selectivity of CH4 gradually increases from ≈3.1% (1st run) to ≈24.5% (4th run) and then remains unchanged under UV-light irradiation. With triethanolamine (3.3 vol.%) as the sacrificial agent, the total production of CO and CH4 production rapidly increases to ≈28 000 µmol gcata -1 in 2 h reaction. Photoluminescence spectra reveal that Vo s induces the formation of donor bands to promote charge carrier seperation. A series of trace spectra and theoretical analysis indicate Mg-Vo sites in the derived MgCO3 ·3H2 O are active centers, which play a crucial role in modulating CO2 adsorption and triggering photoreduction reactions. These intriguing results on defective alkaline earth oxides as potential photocatalysts in CO2 conversion may spur some exciting and novel findings in this field.

Hydrophilic modification of polycarbonate using p-phenylenediamine

Abstract: ABSTRACT Polycarbonate is a commonly used plastic, particularly for making glasses lenses. Polycarbonate is prone to fogging, making hydrophilic modification desirable. In this work, polycarbonate is treated with p-phenylenediamine (PPD) to improve its hydrophilicity. The influence of treating conditions, such as solvent, PPD concentration, heating temperature, and heating time, are studied to reveal their impacts on the water contact angle of polycarbonate. For example, the water contact angle of polycarbonate is reduced to 33° from 83° after treated in water with 0.1 wt% PPD at 80°C for 120 minutes. The improvement of the hydrophilicity of polycarbonate by PPD is explained based on the introduction of polar groups by PPD or poly-PPD (p-PPD), in terms of polyurethane, benzyl hydroxyl, or amine centers, which can interact with water to have a better affinity to spread water on the surface due to the like-like principle. The possible mechanisms are supported with infrared spectroscopy measurements. GRAPHICAL ABSTRACT

Temporal correlation in the inverse-gamma polymer

Abstract: Understanding the decay of correlations in time for (1+1)-dimensional polymer models in the KPZ universality class has been a challenging topic. Following numerical studies by physicists, concrete conjectures were formulated by Ferrari and Spohn (Ferrari-Spohn '16) in the context of planar exponential last passage percolation. These have mostly been resolved by various authors. In the context of positive temperature lattice models, however, these questions have remained open. We consider the time correlation problem for the exactly solvable inverse-gamma polymer in $\mathbb{Z}^2$. We establish, up to constant factors, upper and lower bounds on the correlation between free energy functions for two polymers rooted at the origin (droplet initial condition) when the endpoints are either close together or far apart. We find the same exponents as predicted in (Ferrari-Spohn '16). Our arguments rely on the understanding of stationary polymers, coupling, and random walk comparison. We use recently established moderate deviation estimates for the free energy. In particular, we do not require asymptotic analysis of complicated exact formulae.

Modulating oxygen vacancies concentration on Bi4V2O11 nanorods for synergistic photo-driven plastic waste oxidation and CO2 reduction

Abstract: It is a very attractive approach to sunlight-driven CO2 reduction coupled with photo-oxidation of plastic waste to into value-added chemicals towards solving the greenhouse and environmental crisis. Herein, Bi4V2O11 nanorods...

Improving Oxygen Reduction Performance of Surface-Layer-Controlled Pt-Ni Nano-Octahedra via Gaseous Etching.

Abstract: This study demonstrates an atomic composition manipulation on Pt-Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt-Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt-Ni nano-octahedral sample shows a mass activity of 1.50 A/mgPt, exceeding the initial mass activity of the unetched counterpart (1.40 A/mgPt) and outperforming the benchmark Pt/C (0.18 A/mgPt) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features.

Construction of high-performance solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/CuS positive electrode and Fe2O3@rGO negative electrode

Abstract: The reasonable and logical construction of electrode materials along with greater electrochemical features and solid architectural design is an effective strategy for boosting the electrochemical performance of supercapacitors. In this paper, Ti3C2Tx MXene/CuS composites have been synthesized using an electrostatic attraction connection of negatively charged 2D few-layered Ti3C2Tx MXene sheets with positively charged CuS nanoparticles and are investigated as an asymmetric supercapacitor active material. The addition of MXene enhances the conductivity and specific surface area of the MXene/CuS electrode compared to their individual components. The as-prepared MXene/CuS electrode exhibits a high specific capacity (1541.6C g−1 (2569.3 F g−1)) at 1 A g−1 and an excellent cycle performance with 93.5 % capacity retention after 10,000 cycles. Furthermore, Fe2O3 nanoparticles/reduced graphene oxide (rGO) nanosheets (Fe2O3@rGO) composite electrode is also produced. The designed Fe2O3@rGO negative electrode with a wide operation voltage window of 1.1 V can deliver a capacity of 255.6C g−1 at 1 A g−1. Ultimately, the MXene/CuS//Fe2O3@rGO device displays energy density of 74.1 Wh kg−1 and power density of 849.8 W kg−1. In addition, the ASC shows excellent cycling stability of 91.3 % capacity retention after 10,000 cycles.