The optimization of bi-objective vehicle routing problem has become a research hotspot in recent years. In this paper, a time-dependent and biobjective vehicle routing problem with time windows ...(TD-BO-VRPTW) is proposed, which is a new extension of classical vehicle routing problem. Time-dependency is presented for the situation that vehicle's travel speed is affected by its departure time and the distance between two customers. The total transportation costs and time costs are two objectives optimized simultaneously through constructing a bi-objective mixed integer linear programming model. To deal with this problem, the non-dominated sorting genetic algorithm II (NSGA-II) is adopted to obtain the Pareto optimal solution set. In the numerical examples, the RC108 from Solomon's benchmark set is employed and the results in the Pareto front show the efficiency of NSGA-II for the TD-BO-VRPTW. To further test the performance of this algorithm, two objectives are optimized separately and then the sum of two objectives is also optimized. Through comparing these results with solutions in the Pareto front, it can be concluded that the algorithm is reliable, and the results in Pareto front are competitive because there is a trade-off between two objectives.
Lifestyle interventions are an important and viable approach for preventing cognitive deficits. However, the results of studies on alcohol, coffee and tea consumption in relation to cognitive decline ...have been divergent, likely due to confounds from dose-response effects. This meta-analysis aimed to find the dose-response relationship between alcohol, coffee or tea consumption and cognitive deficits.
Prospective cohort studies or nested case-control studies in a cohort investigating the risk factors of cognitive deficits were searched in PubMed, Embase, the Cochrane and Web of Science up to 4th June 2020. Two authors searched the databases and extracted the data independently. We also assessed the quality of the studies with the Newcastle-Ottawa scale. Stata 15.0 software was used to perform model estimation and plot the linear or nonlinear dose-response relationship graphs.
The search identified 29 prospective studies from America, Japan, China and some European countries. The dose-response relationships showed that compared to non-drinkers, low consumption (<11 g/day) of alcohol could reduce the risk of cognitive deficits or only dementias, but there was no significant effect of heavier drinking (>11 g/day). Low consumption of coffee reduced the risk of any cognitive deficit (<2.8 cups/day) or dementia (<2.3 cups/day). Green tea consumption was a significant protective factor for cognitive health (relative risk, 0.94; 95% confidence intervals, 0.92-0.97), with one cup of tea per day brings a 6% reduction in risk of cognitive deficits.
Light consumption of alcohol (<11 g/day) and coffee (<2.8 cups/day) was associated with reduced risk of cognitive deficits. Cognitive benefits of green tea consumption increased with the daily consumption.
Selective laser melting (SLM) of NiTi shape memory alloys (SMAs) was studied systematically for the resulting density and surface roughness. It was found that high laser energy density could not ...guarantee dense SLM NiTi SMAs. Furthermore, the phase composition and transformation temperatures varied remarkably with delicate change of laser power and scanning speed. Mechanical tests suggested that the SLM NiTi alloys made under the optimal process parameters (70 W in laser power and 105 mm/s in laser scanning speed) had an ultimate tensile strength of 788 MPa, an elongation of 7.43% in austenite state. Bending shape memory test revealed that 100% recovery rate was obtained in a sequent bending test (45°→90°→180°→270°→360°), and the bending deformation was fully recovered in ten-time cycle bending test at 180°, and recovery rate was 97% after ten-time cycle bending test at 360°. The excellent bending shape memory properties was attributed to high-density dislocations and Ti2Ni nanoprecipitates which impeded the occurrence of plastic deformation effectively. The findings in this study demonstrated that SLM NiTi parts had excellent shape memory properties and was promising for industrial applications.
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•The effect of process parameters on the density, surface roughness, and transformation behaviors for SLM NiTi were studied.•High laser energy density could not guarantee dense SLM NiTi SMAs.•Fully recovered bending deformation in ten-time cycle at 180°, and 97% recovery rate after ten-time cycle at 360°.
Bright-field TEM image showing martensitic transformation of a retained austenite grain subjected to nanoindentation (α′: martensite, γ: austenite).
The mechanical stability of individual retained ...austenite grains is studied by nanoindentation combined with electron backscattered diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy and transmission electron microscopy. The average hardness of retained austenite and ferrite is 7.7 and 3.4GPa, respectively. The large scatter of hardness distribution in retained austenite may be due to the varied stability and boundary structure of different austenite grains. The mechanical stability of retained austenite increases with Mn content.
beta decay of proton-rich nuclei plays an important role in exploring isospin mixing. The beta decay of P-26 at the proton drip line is studied using double-sided silicon strip detectors operating in ...conjunction with high-purity germanium detectors. The T = 2 isobaric analog state (IAS) at 13 055 keV and two new high-lying states at 13 380 and 11 912 keV in Si-26 are unambiguously identified through beta-delayed two-proton emission (beta 2p). Angular correlations of two protons emitted from Si-26 excited states populated by P-26 beta decay are measured, which suggests that the two protons are emitted mainly sequentially. We report the first observation of a strongly isospin-mixed doublet that deexcites mainly via two-proton decay. The isospin mixing matrix element between the Si-26 IAS and the nearby 13 380-keV state is determined to be 130(21) keV, and this result represents the strongest mixing, highest excitation energy, and largest level spacing of a doublet ever observed in beta-decay experiments.
We have developed and implemented an iterative algorithm of flux calibration for the LAMOST Spectroscopic Survey of the Galactic anticentre (LSS-GAC). For a given LSS-GAC plate, the spectra are first ...processed with a set of nominal spectral response curves (SRCs) and used to derive initial stellar atmospheric parameters (effective temperature T
eff, surface gravity log g and metallicity Fe/H) as well as dust reddening E(B − V) of all targeted stars. For each of the 16 spectrographs, several F-type stars with good signal-to-noise ratios are selected as flux standard stars for further, iterative spectral flux calibration. Comparison of spectrophotometric colours, deduced from the flux-calibrated spectra, with the photometric measurements yield average differences of 0.02 ± 0.07 and −0.04 ± 0.09 mag for (g − r) and (g − i), respectively. The relatively large negative offset in (g − i) is because we have opted not to correct for the telluric bands, most notably the atmospheric A band in the wavelength range of the i band. Comparison of LSS-GAC multi-epoch observations of duplicate targets indicates that the algorithm has achieved an accuracy of about 10 per cent in relative flux calibration for the wavelength range 4000–9000 Å. The shapes of SRCs deduced for individual LAMOST spectrographs vary by up to 30 per cent for a given night, and larger for different nights, indicating that the derivation of SRCs for the individual plates is essential to achieve accurate flux calibration for the LAMOST spectra.
The cumulative atmospheric nitrogen deposition has been found to profoundly impact the nutrient stoichiometry of the eastern China seas (ECSs: the Yellow Sea and East China Sea) and the northwestern ...Pacific Ocean (NWPO). In spite of the potential significance of dry deposition in those regions, shipboard observations of atmospheric aerosols remain insufficient, particularly regarding the compositions of water-soluble nitrogen species (nitrate, ammonium and water-soluble organic nitrogen – WSON). We conducted a cruise covering the ECSs and the NWPO during the spring of 2014 and observed three types of atmospheric aerosols. Aluminum content, air mass backward trajectories, weather conditions, and ion stoichiometry allowed us to discern dust aerosol patches and sea-fog-modified aerosols (widespread over the ECSs) from background aerosols (open ocean). Among the three types, sea-fog-modified aerosols contained the highest concentrations of nitrate (536 ± 300 nmol N m−3), ammonium (442 ± 194 nmol N m−3) and WSON (147 ± 171 nmol N m−3); furthermore, ammonium and nitrate together occupied ∼ 65 % of the molar fraction of total ions. The dust aerosols also contained significant amounts of nitrate (100 ± 23 nmol N m−3) and ammonium (138 ± 24 nmol N m−3) which were obviously larger than those in the background aerosols (26 ± 32 for nitrate and 54 ± 45 nmol N m−3 for ammonium), yet this was not the case for WSON. It appeared that dust aerosols had less of a chance to come in contact with WSON during their transport. In the open ocean, we found that sea salt (e.g., Na+, Cl−, Mg2+), as well as WSON, correlated positively with wind speed. Apparently, marine dissolved organic nitrogen (DON) was emitted from breaking waves. Regardless of the variable wind speeds from 0.8 to as high as 18 m s−1, nitrate and ammonium, by contrast, remained in narrow ranges, implying that some supply and consumption processes of nitrate and ammonium were required to maintain such a quasi-static condition. Mean dry deposition of total dissolved nitrogen (TDN) for sea-fog-modified aerosols (1090 ± 671 µmol N m−2 d−1) was 5 times higher than that for dust aerosols (190 ± 41.6 µmol N m−2 d−1) and around 20 times higher than that for background aerosols (56.8 ± 59.1 µmol N m−2 d−1). Apparently, spring sea fog on the ECSs played an important role in removing atmospheric reactive nitrogen from the Chinese mainland and depositing it into the ECSs, thus effectively preventing its seaward export to the NWPO.
It is challenging to simultaneously achieve nearly full density and high strength in refractory alloys using selective laser melting (SLM). In this study, the achievement of ultrahigh-strength ...resulting from nearly full density has been reported in beta-type titanium alloy by controlling the melt pool mode in SLM. The melt pool mode was divided into the conduction and keyhole modes, which were determined from the macroscopic morphology of the melt pool in the SLMed Ti-34.2Nb-6.8Zr-4.9Ta-2.3Si (wt%) (TNZTS) alloy single tracks in combination with the keyhole threshold (P·V−0.5 = 251.3 W (m⋅s−1)−0.5) calculated theoretically. Compared with condition mode, the keyhole mode has higher porosity and inevitably causes poor mechanical property. Fortunately, by optimizing the SLM process parameters predicted via the keyhole threshold, an ultrahigh-strength and nearly full density (99.7%) TNZTS alloy with conduction mode was obtained by SLM. The alloy exhibited an ultrahigh compressive yield strength of 1286 MPa, which was higher than the majority of the beta-type titanium alloys reported so far. The microstructural analyses indicated that the ultrahigh-strength TNZTS alloy consisted of a thin shell-shaped (Ti, Nb, Zr)2Si (S2) phase (20–50 nm) around the columnar β-Ti grain boundaries together with an ultrafine dot shaped (Ti, Nb, Zr)5Si3 (S1) phase (50–300 nm) in the β-Ti matrix. The ultrahigh strength resulted from high-density dislocations and the effective dislocation blockage by the semi-coherent S1 and coherent S2 phases, thereby leading to the dislocation-strengthening and hardening effect. The strategy utilized in this study provides the fundamental guidelines for generating refractory metallic alloys with high density and excellent performance.
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