Semiparametric Quantile Regression Estimation in Dynamic Models with Partially Varying Coefficients

We study quantile regression estimation for dynamic models with partially varying coefficients so that the values of some coefficients may be functions of informative covariates. Estimation of both parametric and nonparametric functional coefficients are proposed. In particular, we propose a three stage semiparametric procedure. Both consistency and asymptotic normality of the proposed estimators are derived. We demonstrate that the parametric estimators are root-n consistent and the estimation of the functional coefficients is oracle. In addition, efficiency of parameter estimation is discussed and a simple efficient estimator is proposed. A simple and easily implemented test for the hypothesis of varying-coefficient is proposed. A Monte Carlo experiment is conducted to evaluate the performance of the proposed estimators.  This paper is forthcoming in Journal of Econometrics

Procurement with Reverse Auction and Flexible Noncompetitive Contracts

This article investigates a hybrid procurement mechanism that combines a reverse auction with flexible noncompetitive contracts. A buyer adopts such mechanism to procure multiple units of a product from a group of potential suppliers. Specifically, the buyer first offers contracts to some suppliers who, if accepting the contract, do not participate in the auction while committing to selling a unit to the buyer at the price of the subsequent auction. For the suppliers rejecting the offers, they can join the subsequent auction with the other suppliers to compete on the remaining units. When the buyer offers only one flexible noncompetitive contract, we find that the selected supplier may accept the offer regardless of whether he knows his exact cost information. Meanwhile, the buyer can benefit from offering such a contract, as opposed to solely conducting a regular reverse auction or offering a noncompetitive contract that does not allow suppliers declining offers to join the subsequent auction. Moreover, we find that the suppliers\u27 information about their own costs has a significant impact on the buyer\u27s decision. When the buyer makes multiple offers, we analyze the resulting game behavior of the selected suppliers and demonstrate that the buyer can benefit more than just offering one such contract. Therefore, the hybrid procurement mechanism can be mutually beneficial for both the buyer and the selected suppliers

Enhanced electrochemical performance of CuCo2S4/carbon nanotubes composite as electrode material for supercapacitors

CuCo2S4 is regarded as a promising electrode material for supercapacitor, but has inferior conductivity and poor cycle stability which restrict its wide-range applications. In this work, hierarchically hybrid composite of CuCo2S4/carbon nanotubes (CNTs) was synthesized using a facile hydrothermal and sulfuration process. The embedded CNTs in the CuCo2S4 matrix provided numerous effective paths for electron transfer and ion diffusion, and thus promoted the faradaic reactions of the CuCo2S4 electrode in the energy storage processes. The CuCo2S4/CNTs-3.2% electrode exhibited a significantly increased specific capacitance of 557.5 F g-1 compared with those of the pristine CuCo2S4 electrode (373.4 F g-1) and CuO/Co3O4/CNTs-3.2% electrode (356.5 F g-1) at a current density of 1 A g-1. An asymmetric supercapacitor (ASC) was assembled using the CuCo2S4/CNTs-3.2% as the positive electrode and the active carbon as the negative electrode, which exhibited an energy density of 23.2 Wh kg-1 at a power density of 402.7 W kg-1. Moreover, the residual specific capacitance of this ASC device retained 85.7 % of its original value after tested for 10000 cycles, indicating its excellent cycle stability

Association of magnesium depletion score with serum anti-aging protein Klotho in the middle-aged and older populations

BackgroundMagnesium deficiency and low levels of the anti-aging protein Klotho have been independently associated with various age-related diseases. The Magnesium Depletion Score (MDS) is recognized as a more valuable and reliable predictor of body magnesium status than traditional clinical markers such as serum and urine magnesium. However, the relationship between magnesium status and serum Klotho levels remains unexplored. This study aimed to investigate the association between magnesium depletion, as quantified by MDS, and serum Klotho levels in US adults.MethodsWe analyzed data from 11,387 participants aged 40–79 years in the National Health and Nutrition Examination Survey (NHANES) 2007–2016. Participants were divided into three groups based on MDS: low (0–1 points), middle (2 points), and high (3–5 points), reflecting cumulative risks of magnesium depletion derived from diuretic use, proton pump inhibitors, renal function, and alcohol intake. Serum Klotho levels were measured using a validated ELISA assay. Sample-weighted multivariable linear regression models were used to examine the association between MDS and serum Klotho levels, adjusting for age, sex, race, socioeconomic status, lifestyle factors (smoking, alcohol use), clinical parameters (body mass index, blood pressure, lipid levels), and energy intake.ResultsThe weighted average serum Klotho concentrations decreased significantly across MDS groups (low: 864.50, middle: 805.67, high: 755.02 pg./mL; p < 0.0001). After full adjustment, compared to the low MDS group, participants in the middle and high groups had significantly lower serum Klotho levels (β = −35.49, 95% CI: −62.29 to −8.69; β = −64.82, 95% CI: −115.30 to −14.34, respectively; p for trend = 0.003). This inverse association remained consistent across various subgroups, with particularly strong relationships observed in individuals with BMI <25, current smokers, and those with low income.ConclusionThis study provides novel evidence of an inverse association between MDS, a new valuable indicator of magnesium status, and serum Klotho levels in a large, representative sample of US adults. These findings suggest that monitoring magnesium status via MDS could help identify individuals at risk of accelerated aging, prompting interventions such as dietary adjustments or magnesium supplementation in high-risk populations. Further research is warranted to elucidate the mechanisms underlying this association and its implications for age-related diseases

Establishment of UPLC-Q-TOF-MS Fingerprints and Antioxidant Spectroscopic Relationship of Ethanol-eluting Sites of Tetrastigma hemsleyanum Macroporous Resin

Objective: To study the spectrum-effect relationship between the extracts of Tetrastigma hemsleyanum and its antioxidant activity, and to clarify the quality markers of its antioxidant activity. Methods: The extract was prepared and separated by macroporous resin elution, six different elution sites were obtained using ethanol at concentrations of 10%, 30%, 50%, 70%, 90% and 100%. The fingerprints of the Tetrastigma hemsleyanum extract and each elution site were established by UPLC-Q-TOF-MS and the characteristic peaks were screened. The free radical scavenging rate of 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) was used as an antioxidant index to investigate the antioxidant activity of the extract and each elution site of Tetrastigma hemsleyanum. The Pearson correlation coefficient method and orthogonal partial least squares (OPLS) method were combined to analyze and study the spectrum-effect relationship between the characteristic peaks and the antioxidant activity, to screen the quality markers, and to analyze and identify the chemical compositions. Results: Under the positive and negative ion modes, 57 and 92 characteristic peaks were identified in the extract and each elution site of Tetrastigma hemsleyanum, respectively. The combined results of Pearson correlation coefficient and OPLS analysis showed that 14 ion peaks contributed more to the antioxidant activity, which was vanillin (P2), catechin (P13, N19), rutin (P27, N54), and isoquercitrin (P28), kaempferol-3-O-rutinoside (P33, N61), proanthocyanidin B (N18), proanthocyanidin C (N22), and ion peaks N23, N25, N26, and N29, respectively. Conclusion: UPLC-Q-TOF-MS fingerprints of Tetrastigma hemsleyanum extract and each elution site were established, and the quality markers of Tetrastigma hemsleyanum antioxidant activity were revealed to provide technical support for the formulation of quality standards and resource development and utilization of Tetrastigma hemsleyanum

Research Progress on Protein Additives for Enhancing Gel Properties of Meat Products

Gelation, an important quality attribute of meat products, significantly influences the appearance, flavor, and texture of meat products. Enhancing gelation in meat products holds immense importance in improving the production process and the quality. The gel properties of meat products are influenced by the content and structure of protein aggregates and the aggregation rate during processing. Protein additives have the potential to partially replace myofibrillar proteins in gelation and emulsification properties, leading to cost reduction, and therefore have attracted much research interest for the development of new meat products and the optimization of the processing technology. This paper summarizes recent studies on the gelation mechanism of myofibrillar proteins, and reviews the properties and applications of the major protein additives as well as recent progress in using protein additives combined with polysaccharide colloids, enzymes or phosphates to enhance the gelation of meat products. This review may serve as a valuable reference for enhancing the quality of gel-type meat products

Preparation and Performance Optimization of Two-Component Waterborne Polyurethane Locomotive Coating

This paper reports the effects of different formulas on the performance of waterborne polyurethane (WPU), including two-component WPU and curing agent, wetting dispersant, defoaming agent, and wetting agent. The optimization of rheological additives selection, through the optimization of coating physical properties and chemical properties, can make the film show uniform color and appearance without pinholes, bubbles, or wrinkles, and have a long probation period. Through the analysis of performance after a 1000-h quick ultraviolet (QUV) aging test, the light reduction rate is 23.19%, and the color difference is 1.9. As can be seen from the scanning electron microscope (SEM) image and the three-dimensional stereomicroscope, the film shows relatively uniform dispersion, good compactness, and smooth surface. The two-component WPU topcoat is found to have high gloss 87.1 (60°) and high weather resistance, which provides a positive indication for the modulation and production of waterborne locomotive paint