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21.
Termite soldiers are the most specialized caste of social insects in terms of their morphology and function. Soldier development
requires increased juvenile hormone (JH) titer and the two molts via a presoldier stage. These molts are accompanied by dramatic
morphological changes, including the exaggeration and regression of certain organs. Soldiers of the most apical termitid subfamily
Nasutitermitinae possess not only a horn-like frontal tube, called the nasus, for the projection of defensive chemicals from
the frontal gland reservoir but also regressed mandibles. Although candidate genes regulating soldier mandibular growth were
reported in a relatively basal termite species, the regulatory mechanisms of mandibular regression remain unknown. To clarify
these mechanisms, we performed morphological and histological examinations of the mandibles during soldier differentiation
in Nasutitermes takasagoensis. Mandibular size reduced dramatically during soldier differentiation, and mandibular regression occurred just prior to the
presoldier molt. Spotted TUNEL signals were observed in regressing mandibles of presoldiers, suggesting that the regression
involved programmed cell death. Because soldiers of N. takasagoensis possess exaggerated organs (nasus and frontal gland), the present results suggest that JH-dependent regressive mechanisms
exist in the mandibles without interfering with the formation of the exaggerated organs. 相似文献
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Masahiro Funabashi Fumi Ninomiya Masao Kunioka 《Journal of Polymers and the Environment》2007,15(4):245-250
Returnable cups made of poly(lactic acid) (PLA) are employed as an example of products made of biodegradable plastics. Two
kinds of PLA samples plates and powders with different shapes were prepared from PLA cups. The plates were cut from a cup
using nippers. Powders were prepared using a rotation mechanical mixer for 45 min. PLA powders were separated by sieves with
60 meshes (250 μm) into a size ranging from 0 to 250 μm. An average diameter of powders separated by a sieve is 169 μm. Biodegradation
tests of PLA plates, PLA powders and cellulose powders in controlled compost at 58 °C were performed using a Microbial Oxidative
Degradation Analyzer (MODA) instrument according to ISO 14855-2. PLA powders showed almost the same biodegradation curve as
that of cellulose powders. PLA plates biodegraded at a slower rate than PLA powders. 相似文献
24.
Ammonia removal from pretreated methane fermentation effluent through a soil trench system: a column experiment 总被引:1,自引:0,他引:1
In order to find the optimal running conditions and mechanisms of ammonia removal through a soil trench system that is designed for treating pretreated methane fermentation effluent, a soil column whose structure was similar to the soil trench system was prepared, and irrigated with wastewater below 30 °C. At the beginning, ammonia was mainly adsorbed by the soils, and the ammonia adsorption capacity of soils gradually saturated. After the 12th day, nitrification began in the soil column; the ammonia in the soil column decreased sharply, and the nitrite and nitrate peak appeared sequentially as the wastewater application rate decreased from 0.74 to 0.37 l h−1. When the nitrification in the soil column reached a steady-state, 98% of all the ammonia in the influent was transformed into nitrate.
By changing the running conditions such as temperature, aeration, and wastewater application rate, it was found that the ammonia removal efficiency can be improved by aeration and impeded by low temperature. In these three variables, wastewater application rate has much greater affect on the ammonia removal efficiency; a lower wastewater application rate can increase the ammonia removal efficiency substantially because of the longer travel time. 相似文献