Modeling Crack Propagation in Bituminous Binders under a Rotational Shear Fatigue Load using Pseudo J-Integral Paris’ Law

Fatigue resistance of bituminous binders plays a critical role in determining the fatigue performance of asphalt pavements. It is reported in the literature that, under a rotational shear fatigue load like a dynamic shear rheometer (DSR) test, the crack grows in the cylindrical bitumen sample as a circumferential crack that is initiated at the periphery of the sample and propagates toward the center of the sample. This study aims to model this crack propagation in bituminous binders under rotational shear fatigue load by time sweep (TS) fatigue test using the DSR. The crack length in the TS test is determined using a damage mechanics-based DSR-C model which is a function of the shear moduli and phase angles under undamaged and damaged conditions. The crack evolution is modeled by a pseudo J-integral based Paris’ law. Samples of virgin bitumen 40/60 and polymer-modified bitumen X-70 under unaged and aged conditions are tested by the TS tests at different temperatures, frequencies, and strain levels. Results show that the pseudo J-integral Paris’ law is able to predict accurately the crack propagation in bituminous binders under the rotational shear fatigue load. The crack grows faster in aged bitumen or at lower temperatures. The Paris’ law model parameters (A and n) are independent of loading frequency or load amplitude. They are fundamental material properties and can be determined at one loading frequency and amplitude, then can be implemented to predict the growth of cracks in bituminous binders at different loading frequencies or amplitudes

Characterizing stress-dependent complex and relaxation moduli of dense graded asphalt mixtures

The objective of this paper is to investigate the stress-dependence of the complex and relaxation moduli of dense graded asphalt mixtures. Complex modulus tests at four different confining pressures were conducted. Then, the stress dependence of the long-term equilibrium modulus of asphalt mixture based on Prony series model was modeled by Uzan model. The Maxwell components of the relaxation modulus were determined by a two-step method. Finally, the stress dependence of the relaxation modulus was quantified by relaxation spectrum of the material. The results show that for the selected dense-graded asphalt mixtures, the dynamic modulus increases, and phase angle decreases with the increasing confining pressures at relatively low reduced loading frequency. However, the stress dependence is insignificant in a relatively high-reduced loading frequency. The Uzan model coefficient of the long-term equilibrium modulus of the relaxation modulus can be determined effectively by the proposed deviatoric stress master curves. To obtain reliable and accurate Maxwell component coefficients, it is recommended that: (a) the measured loss moduli rather than the storage moduli should be used to calculate Maxwell component coefficients if collocation method is utilized, and (b) a log-scaled least squared regression minimization objective should be used as the regression objective for the coefficient determination. The relaxation spectrum of asphalt mixture can be modeled by Gaussian function, where the size of the relaxation spectrum increases but the shape and position of the relaxation spectrum remain unchanged when the confining pressure increases

Failure mechanism analysis of asphalt–aggregate systems subjected to direct shear loading

In order to investigate the mechanical behavior of asphalt–aggregate systems subjected to direct shear loading and reveal the shear failure mechanism, four groups of direct shear tests were conducted on composite specimens under different experimental conditions with a self-manufactured direct shear test apparatus at 25 °C. Comparative studies were conducted to evaluate the effects of stone surface treatment, asphalt film thickness and loading rate on the shear mechanical behavior of asphalt–aggregate specimens. Results showed that two kinds of the complete stress–displacement curves, including the general single-peak curve and the first-known double-peak curve, were clearly observed for each condition. In addition, the internal failure mechanisms were analyzed based on qualitative and quantitative methods. It can be concluded that the potential failure modes of the direct shear test include adhesive failure at the asphalt–aggregate interface and cohesive failure within the asphalt film. The research results enhance understanding of the shear mechanical behavior and failure mechanism of asphalt mixture, and also provide a reference for the interfacial failure

Research on unsteady performance of a two-stage self-priming centrifugal pump

In order to study the unsteady performance of a two-stage self-priming centrifugal pump, the unsteady numerical calculation in a two-stage self-priming centrifugal pump was performed and energy characteristics experiments and self-priming experiments were carried out. The pressure pulsation and radial force in the pump were then analyzed. The results show that numerical calculation values are close to the experiment values. Head deviation of the pump is less than 3 %, and efficiency deviation of the pump is less than 2 percentage points. Compared with monitoring point P1, the pressure fluctuation coefficient of monitoring point P3 at the design flow rate is reduced by 61 %. Compared with monitoring point P8, the pressure fluctuation coefficient of monitoring point P5 is reduced by 70 %. The radial force on the radial guide-vane is obviously smaller than that on the volute. Under the same flow rate, radial force on the volute of second-stage pump is almost 20 times larger than that on the radial guide-van of first-stage pump

A Review of Vegetation Phenological Metrics Extraction Using Time-Series, Multispectral Satellite Data

Vegetation dynamics and phenology play an important role in inter-annual vegetation changes in terrestrial ecosystems and are key indicators of climate-vegetation interactions, land use/land cover changes, and variation in year-to-year vegetation productivity. Satellite remote sensing data have been widely used for vegetation phenology monitoring over large geographic domains using various types of observations and methods over the past several decades. The goal of this paper is to present a detailed review of existing methods for phenology detection and emerging new techniques based on the analysis of time-series, multispectral remote sensing imagery. This paper summarizes the objective and applications of detecting general vegetation phenology stages (e.g., green onset, time or peak greenness, and growing season length) often termed “land surface phenology,” as well as more advanced methods that estimate species-specific phenological stages (e.g., silking stage of maize). Common data-processing methods, such as data smoothing, applied to prepare the time-series remote sensing observations to be applied to phenological detection methods are presented. Specific land surface phenology detection methods as well as species-specific phenology detection methods based on multispectral satellite data are then discussed. The impact of different error sources in the data on remote-sensing based phenology detection are also discussed in detail, as well as ways to reduce these uncertainties and errors. Joint analysis of multiscale observations ranging from satellite to more recent ground-based sensors is helpful for us to understand satellite-based phenology detection mechanism and extent phenology detection to regional scale in the future. Finally, emerging opportunities to further advance remote sensing of phenology is presented that includes observations from Cubesats, near-surface observations such as PhenoCams, and image data fusion techniques to improve the spatial resolution of time-series image data sets needed for phenological characterization

Modelling crack initiation in bituminous binders under a rotational shear fatigue load

This study aims to model fatigue crack initiation in bituminous binders. An energy-based crack initiation criterion is developed for bitumen under a rotational shear fatigue load. Based on a damage mechanics analysis of fatigue cracking process, the crack initiation is defined and local energy redistribution around crack tips due to ‘factory-roof’ cracking is quantified. A quantitative energy criterion is proposed for the fatigue crack initiation in the bitumen using viscoelastic Griffith’s theory. The crack initiation criterion is validated through comparing the predicted and measured surface energy of the bitumen. The results show that bitumen fatigue cracking under the rotational shear fatigue load can be divided into two stages: the edge flow damage and the ‘factory-roof’ cracking. The crack initiation is dependent of the shear modulus and surface energy of bituminous binders, critical crack size, and loading amplitude. The energy-based crack initiation criterion along with the DSR fatigue tests can be potentially used to determine the material surface energy

Paliperidone long-acting injection in the treatment of an adolescent with schizophrenia with fluctuating mental symptoms during menstrual period: a case report

BackgroundThe treatment of schizophrenia, a chronic disabling psychiatric disorder, mainly relies on antipsychotics to control the disease and improve clinical symptoms. Various medication options are available, and differences in treatment effects, even for the same medication, have been noted. Treatment efficacy is correlated with the patient’s sex, age, and physical condition. When a drug fails to achieve the desired effect or the symptoms are unstable, the drug dose is often increased or a change in medication is advised according to the patient’s situation.Case presentationWe report the case of a 16 years-old girl with schizophrenia and apparent psychotic symptoms. According to the genetic testing results, the symptoms were effectively controlled, and she was discharged from the hospital with the prescription of paliperidone sustained-release tablets. During the follow-up, her symptoms fluctuated during menstrual period, causing her great distress. Furthermore, her compliance gradually declined during the following 2 years of treatment, and the medication was often discontinued. We changed the drug from an oral tablet to an injection preparation while maintaining the active ingredients of the drug. The patient’s symptoms were significantly controlled, and no fluctuation of symptoms occurred during the menstrual cycle.ConclusionLong-acting antipsychotic injections can be administered to female adolescents with schizophrenia who experience fluctuating psychotic symptoms during menstruation. This technique can ensure both consistency of medication and improvement in clinical symptoms

Methyl eucomate

The crystal structure of the title compound [systematic name: methyl 3-carboxy-3-hydr­oxy-3-(4-hydroxy­benz­yl)propanoate], C12H14O6, is stabilized by inter­molecular O—H⋯O and C—H⋯O hydrogen bonds. The mol­ecules are arranged in layers, parallel to (001), which are inter­connected by the O—H⋯O hydrogen bonds

Flavonoid Ampelopsin Inhibits the Growth and Metastasis of Prostate Cancer In Vitro and in Mice

The objective of this study was to evaluate the chemopreventive effect of a novel flavonoid, ampelopsin (AMP) on the growth and metastasis of prostate cancer cells. AMP showed the more potent activity in inhibiting the proliferation of androgen-sensitive LNCaP and, to less extent, androgen-independent PC-3 human prostate cancer cell lines in vitro, primarily by induction of apoptosis associated with down-regulation of bcl-2. On the other hand, AMP showed much less activity in inhibiting the proliferation of normal prostate epithelial cells than that of prostate cancer cell lines. AMP also inhibited the migration and invasion of PC-3 cells in vitro associated with down-regulation of CXCR4 expression. In the animal study using an orthotopic prostate tumor model, AMP (150 and 300 mg/kg body weight) inhibited the growth of PC-3 tumors and lymph node and lung metastases in a dose-dependent manner. Compared to the control mice, mice treated with AMP at 300 mg/kg BW had reduced final tumor weight by 49.2% (P<0.05), lymph node metastases by 54.5% (P = 0.3) and lung metastases by 93% (P<0.05), but had no apparent alteration on food intake or body weight. The in vivo anti-growth and anti-metastasis activities of AMP were associated with induction of apoptosis and inhibition of proliferation of prostate cancer cells, reduction of prostate tumor angiogenesis, and reduction of CXCR4 expression. Our results provide supporting evidence to warrant further investigation to develop AMP as a novel efficacious and safe candidate agent against progression and metastasis of prostate cancer