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1.
Nature ; 600(7887): 59-63, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34666339

RESUMO

Mare volcanics on the Moon are the key record of thermo-chemical evolution throughout most of lunar history1-3. Young mare basalts-mainly distributed in a region rich in potassium, rare-earth elements and phosphorus (KREEP) in Oceanus Procellarum, called the Procellarum KREEP Terrane (PKT)4-were thought to be formed from KREEP-rich sources at depth5-7. However, this hypothesis has not been tested with young basalts from the PKT. Here we present a petrological and geochemical study of the basalt clasts from the PKT returned by the Chang'e-5 mission8. These two-billion-year-old basalts are the youngest lunar samples reported so far9. Bulk rock compositions have moderate titanium and high iron contents  with KREEP-like rare-earth-element and high thorium concentrations. However, strontium-neodymium isotopes indicate that these basalts were derived from a non-KREEP mantle source. To produce the high abundances of rare-earth elements and thorium, low-degree partial melting and extensive fractional crystallization are required. Our results indicate that the KREEP association may not be a prerequisite for young mare volcanism. Absolving the need to invoke heat-producing elements in their source implies a more sustained cooling history of the lunar interior to generate the Moon's youngest melts.

2.
Materials (Basel) ; 14(9)2021 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-33946389

RESUMO

This study aimed to establish the minimum radiant exposure and irradiance to trigger an adequate polymerization of a photo-polymerized resin cement. In total, 220 disc-shaped specimens (diameter of 10 mm and thickness of 0.1 mm) were fabricated using a photo-polymerized resin cement (Variolink N-transparent, Ivoclar Vivadent). To investigate the minimum radiant exposure, the specimens were polymerized with radiant exposures of 1, 2, 3, 4, 5, 6, and 18 J/cm2 (n = 20). During polymerization, the irradiance was maintained at 200 mW/cm2. To investigate the minimum irradiance, the specimens were polymerized with irradiances of 50, 100, 150, and 200 mW/cm2 (n = 20). During polymerization, the radiant exposure was maintained at the previously determined minimum radiant exposure. The Vickers microhardness (HV) and degree of conversion (DC) of the carbon double bond of the specimens were measured to determine the degree of polymerization of the specimens. The results were analyzed using one-way analysis of variance (ANOVA) and Tukey's test (p < 0.05). In the investigation of the minimum radiant exposure, the HV and DC of the specimens polymerized with a radiant exposure from 1 to 5 J/cm2 were significantly lower than those with 18 J/cm2 (all p < 0.05). However, no significant difference in HV and DC was found between the specimens polymerized with 6 J/cm2 and 18 J/cm2 (p > 0.05). In the investigation of the minimum irradiance, the specimens polymerized with an irradiance of 50 mW/cm2 had significantly lower HV and DC than the specimens polymerized with an irradiance of 200 mW/cm2 (p < 0.05). However, no significant difference in the HV and DC was found among the specimens cured with irradiances of 100, 150, and 200 mW/cm2 (p > 0.05). In conclusion, the minimum radiant exposure and irradiance to trigger an adequate polymerization of the light-cured resin cement were 6 J/cm2 and 100 mW/cm2, respectively.

3.
Ying Yong Sheng Tai Xue Bao ; 31(9): 3227-3240, 2020 Sep 15.
Artigo em Chinês | MEDLINE | ID: mdl-33345524

RESUMO

We summarized research progress of forest fire occurrence prediction model in China based on the literature review, from the prospects of forest fire drivers, models of forest fire occurrence probability, models of forest fire occurrence frequency and model validation methods. The main conclusions are: 1) Meteorology, terrain, vegetation, fuel and human activities were the main driving factors of forest fire occurrence and model prediction accuracy. 2) In the models of forest fire occurrence probability, the geographically weighted logistic regression model considered the spatial correlation between model variables, the Gompit regression model could fit the asymmetric structure fire data. The random forest algorithm had a high prediction accuracy without the requirement of multicollinearity test and excessive fitting, which made it as one of the optimal methods of forest fire occurrence probability prediction. 3) Among all the forest fire occurrence frequency models, the negative binomial regression model was suitable for fitting the over discrete data, the zero-inflated model and hurdle model could deal with fire data that contained a large number of zeros. 4) ROC test, AIC test, likelihood ratio test, and Wald test were the most common methods for evaluating the accuracy of fire occurrence probability and frequency models. The study of forest fire occurrence prediction model should be the main focus of the forest fire management. Model selection should base on fire data structure of different forests. More influencing factors should be taken into account to improve the prediction accuracy of model. In addition, it was necessary to further explore the application of other mathematical methods in forest fire prediction, to improve the accuracy of the models.


Assuntos
Incêndios Florestais , China , Humanos , Modelos Logísticos , Meteorologia , Modelos Estatísticos
4.
Shanghai Kou Qiang Yi Xue ; 29(1): 13-18, 2020 Feb.
Artigo em Chinês | MEDLINE | ID: mdl-32524114

RESUMO

PURPOSE: To study the optical properties of two common dental light curing units and the optical properties of the transmitted light after transmitting glass ceramics. METHODS: Two types of glass-ceramic disc named IPS e.max CAD and IPS Empress CAD were produced by CAD/CAM technology, and the colors of A2 and A3 were chosen for each type of glass ceramic, then divided into 4 groups. Eight discs were made 0.5 mm to 4.0 mm thick in each group, the total number was 32. Spectra irradiance meter and power meter were used to measure the central wavelengths and irradiance of 3 power modes of 2 new LED light curing units before and after transmitting glass-ceramic discs. Statistical analysis was performed using SPSS 25.0 software package. RESULTS: Under different power modes of light curing units, different types and colors of glass ceramics, the central wavelengths of transmitted light were significantly different (P<0.05). Under different power modes of light curing units, different types, colors and thicknesses of glass ceramics, the irradiance of transmitted light was significantly different (P<0.05). CONCLUSIONS: The power mode of light curing unit, the type and color of the glass ceramic have influence on the central wavelength of the transmitted light, but the thickness of the glass ceramic has no influence on the central wavelength of the transmitted light. The power mode of the light curing unit, the type, color, and thickness of the glass ceramic have influence on the irradiance of the transmitted light, in which glass ceramic thickness has the most significant effect on the attenuation of the irradiance of the transmitted light.


Assuntos
Cerâmica , Luzes de Cura Dentária , Cor , Desenho Assistido por Computador , Porcelana Dentária , Teste de Materiais , Cimentos de Resina , Propriedades de Superfície
5.
Shanghai Kou Qiang Yi Xue ; 26(3): 246-250, 2017 Jun.
Artigo em Chinês | MEDLINE | ID: mdl-29098238

RESUMO

PURPOSE: To evaluate the cytocompatibility of Co-Cr ceramic alloys after recasting. METHODS: Cobalt-chromium (Co-Cr) ceramic alloys were recasted for 1-3 times. Samples of Co-Cr ceramic alloys were immersed in DMEM culture medium. The concentration of ions of leaching liquor was determined by ICP-MS total quantization method. L-929 cells were cultured with leaching liquor, flow cytometry was used to test cell cycle progression, Annexin-V-FITC/PI apoptosis staining kit was used to quantitatively detect cell death patterns. SPSS 13.0 software package was used for statistical analysis. RESULTS: After casting for 1-3 times, no significant increase in the concentration of ions of Co-Cr ceramic alloys was noted (P>0.05) except Ga (P<0.05) . No significant differences in L-929 cell cycle were found in Co-Cr ceramic alloys between the samples cast for 1 time and for 2~3 times (P>0.05). No significant difference in the rates of apoptosis and necrosis was found (P>0.05). CONCLUSIONS: The biocompatibility of Co-Cr ceramic alloys casted for 1-3 times is not changed.


Assuntos
Ligas de Cromo , Técnica de Fundição Odontológica , Cerâmica , Porcelana Dentária , Teste de Materiais
6.
Guang Pu Xue Yu Guang Pu Fen Xi ; 36(12): 3996-4000, 2016 Dec.
Artigo em Chinês | MEDLINE | ID: mdl-30235508

RESUMO

Phyllosilicate belongs to hydrated silica, which is a principal form of hydrous minerals on the martian surface. It's also an indicator in comparing different sediments and degree of aqueous alteration. Therefore, it's essential to establish its recognition model for studying the geologic evolution of the Mars. Short-wave infrared (SWIR) spectral bands and thermal infrared (TIR) spectral bands have distinct spectral response to the mineral groups and ions, so they have distinctive advantages in detecting minerals. However the method of combining SWIR and TIR to recognize phyllosilicate is rarely studied. Based on the USGS spectral library, facing Compact Reconnaissance Imaging Spectrometer for Mars(CRISM) and Thermal Emission Imaging System(THEMIS),we conducted the research on the mechanism of the spectral response of phyllosilicate, and established the SWIR and TIR identification model respectively, then combined the SWIR and TIR spectral features to build the combined recognition model of phyllosilicate with Fisher discriminant analysis. The results of cross validation show that the identification accuracy of combined model is the highest, which can correctly classify 90.6% of the mineral samples and improve the identification precision of phyllosilicate effectively.

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