RESUMO
Chickenpox is a common acute and highly contagious disease in childhood; moreover, there is currently no targeted treatment. Carrying out an early warning on chickenpox plays an important role in taking targeted measures in advance as well as preventing the outbreak of the disease. In recent years, the infectious disease dynamic model has been widely used in the research of various infectious diseases. The logistic differential equation model can well demonstrate the epidemic characteristics of epidemic outbreaks, gives the point at which the early epidemic rate changes from slow to fast. Therefore, our study aims to use the logistic differential equation model to explore the epidemic characteristics and early-warning time of varicella. Meanwhile, the data of varicella cases were collected from first week of 2008 to 52nd week of 2017 in Changsha. Finally, our study found that the logistic model can be well fitted with varicella data, besides the model illustrated that there are two peaks of varicella at each year in Changsha City. One is the peak in summer-autumn corresponding to the 8th-38th week; the other is in winter-spring corresponding to the time from the 38th to the seventh week next year. The 'epidemic acceleration week' average value of summer-autumn and winter-spring are about the 16th week (ranging from the 15th to 17th week) and 45th week (ranging from the 44th to 47th week), respectively. What is more, taking warning measures during the acceleration week, the preventive effect will be delayed; thus, we recommend intervene during recommended warning weeks which are the 15th and 44th weeks instead.
Assuntos
Varicela/epidemiologia , Surtos de Doenças , China/epidemiologia , Humanos , Modelos LogísticosRESUMO
The population structure characteristics, natural regeneration, and the influential factors of Haloxylon ammodendron plantations at six different stand ages on the southern edge of the Gurbantunggut Desert were studied. The results showed that H. ammodendron plantation at the stand age of 7 could naturally regenerate. At the stand age of 17, the densities of the seedlings (ï¼30 cm height), saplings (30≤Hï¼50 height), and small trees (≥50 cm height) reached optimal class, and the mean height and base diameter of the small tress reached 1.10 m and 1.91 cm, respectively. The parent trees in H. ammodendron plantation at the stand age of 20 grew best. The height of 35% individuals grew up to 2.50-3.00 m, and the basal stem diameter of 23.1% individuals grew up to 8.00-10.00 cm. The height and diameter growth of the parent trees in H. ammodendron plantation at the stand age of 33 apparently declined, but the regeneration ability by natural seed dispersal was still strong. The regeneration density of natural seed dispersal showed the greatest correlation with the available nitrogen content in 0-100 cm soil layer (0.87), followed by the soil rapidly available phosphorus content (0.84) and the soil water content (0.79). The soils with pH 8.1-8.6 did not limit the nutrient growth of the regeneration layer. In the main stand layer, the individual density of whole regeneration layer showed the greatest correlation with the biomass of the parent trees (0.77), while the density of regeneration layer of the small trees showed the greatest correlation with the planting density (0.71) and the age of the parent trees (0.70).
Assuntos
Chenopodiaceae , Solo , China , ÁrvoresRESUMO
With five temperature gradient treatments, this paper studied the effects of high temperature stress on the photosynthetic parameters and chlorophyll fluorescence characteristics of four Xinjiang hybrid hazels. When the temperature gradually raised from 25 degrees C to 45 degrees C, the net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, water use efficiency and light use efficiency of the hybrid hazels decreased gradually, and the decrement was the largest at 35 degrees C - 45 degrees C. The actual photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient increased slowly with increasing temperature, but decreased sharply when the temperature was raised to >35 degrees C. The water consumption for transpiration and the heat dissipation also increased with increasing temperature. Among the four hybrid hazels, Xinzhen No. 3 had higher tolerance against high temperature in photosynthesis, belonging to heat-resistant cultivar.
