多项式xn-bx-a的二次不可约因式

设n>4,fb(x)=xn-bx-a∈Z[x],其中a,b≠0,n∈N,a,b∈Z.讨论b=±1时fb(x)的二次不可约因式.证明x6-x-a在Z[x]中没有二次不可约因式;若f-1(x)在Z[x]中有二次不可约因式,除了n≡2(mod 3),a=-1,g(x)=x2+x+1情况外,必有n=5,a=±6或n=13,a=±90,且g(x)=x2±x+2.     

Progress in the study of mercury methylation and demethylation in aquatic environments

Mercury(Hg) and its compounds are a class of highly toxic and pervasive pollutants.During the biogeochemical cycling of Hg,methylmercury(MeHg),a potent neurotoxin,can be produced and subsequently bioaccumulated along the food chain in aquatic ecosystems.MeHg is among the most widespread contaminants that pose severe health risks to humans and wildlife.Methylation of inorganic mercury to MeHg and demethylation of MeHg are the two most important processes in the cycling of MeHg,determining the levels of MeHg in aquatic ecosystems.This paper reviews recent progress on the study of Hg methylation and demethylation in aquatic environments,focusing on the following three areas:(1) sites and pathways of Hg methylation and demethylation,(2) bioavailability of Hg species for methylation and demethylation,and(3) application of isotope addition techniques in quantitatively estimating the net production of MeHg.     

Cloning and functional analysis of chloroplast division gene NtFtsZ2-l in Nicotiana tabacum

FtsZ protein plays an important role in the division of chloroplasts. With the finding and functional analysis of higher plant FtsZ proteins, people have deepened the understanding in the molecular mechanism of chloroplast division. Multiple ftsZ genes are diversified into two families in higher plants, ftsZ1 and ftsZ2 . On the basis of the research on ftsZl family, we analyzed the function of NtFtsZ2-l gene in Nicotiana tabacum . Microscopic analysis of the sense and antisense NtFtsZ2-l transgenic tobacco plants revealed that the chloroplasts were abnormal in size and also in number when compared with wild-type tobacco chloroplasts. Our investigations confirmed that the NtFtsZ2-l gene is involved in plant chloroplast division.     

Debating about the climate warming

Debating about the climate warming is reviewed. Discussions have focused on the validity of the temperature reconstruction for the last millennium made by Mann et al. Arguments against and for the reconstruction are introduced. Temperature reconstructions by other authors are examined, including the one carried out by Wang et al. in 1996. It is concluded that: (1) Ability of reproducing temperature variability of time scale less than 10 a is limited, so no sufficient evidence proves that the 1990s was the warmest decade, and 1998 was the warmest year over the last millennium. (2) All of the temperature reconstructions by different authors demonstrate the occurrence of the MWP (Medieval Warm Period) and LIA (Little Ice Age) in low frequency band of temperature variations, though the peak in the MWP and trough in LIA varies from one reconstruction to the others. Therefore, terms of MWP and LIA can be used in studies of climate change. (3) The warming from 1975 to 2000 was significant, but we do not know if it was the strongest for the last millennium, which needs to be proved by more evidence.     

Experimental Study on the Feasibility of Methane Drainage i n Coal Seams with Compound Technique of Perforating and Fracturin g

Compound technique of perforating and fracturing can effectively control the perforating direction and the fracturing expansion．The feasibility of this technique used in fracturing coal seams is analyzed．In this paper,the experiments of perforating and fracturing are carried out on samples of coal and the experimental effects are satisfactory．Compound technique of perforating and fracturing is promising in coal seams．     

Correlation of burial organic carbon and paleoproductivity in the Mesoproterozoic Hongshuizhuang Formation, northern North China

In general, total organic carbon (TOC) is directly used as a proxy for paleoproductivity, however, it is not only affected by paleoproductivity, but also controlled by redox conditions and terrigenous detrital matter influx. Major and trace elements were analysed with the purpose of investigating the redox potential and paleoproductivity during deposition of the Hongshuizhuang Formation. In the present study, C-S relationship, V/Cr ratio and Mo concentration indicate that the dolomites were deposited in oxic environments, however, most of the black shales were accumulated in euxinic environments. P/Ti values in the Hongshuizhuang samples can be compared with those in the Japanese Ubara Permian-Triassic section which were regarded to be deposited under a moderate to high paleoproductivity. Ba/Al values are slightly lower than that of the laminated sediments from the continental margins of Central California (CCAL) which were thought to be accumulated under a high paleoproductivity. These results indicate that the paleoproductivity was moderate to high during deposition of the Hongshuizhuang Formation. Burial organic carbon shows positive correlations with V/Cr and Mo, but shows only weakly or no correlation with P/Ti and Ba/Al, respectively, suggesting that although the paleoproductivity was moderate to high during deposition of the Hongshuizhuang Formation, its organic-rich sediments were predominantly controlled by redox conditions and had no direct relationship with paleoproductivity.     

SDBS辅助制备的花状ZnO微结构的生长机理及光催化性能评价

Flower-like ZnO microstructures were successfully produced using a hydrothermal method employing ZnSO₄/(NH₄)₂SO₄ as a raw material. The effect of the operating parameters of the hydrothermal temperature, OH?/Zn2+ molar ratio, time, and amount of dispersant on the phase structure and micromorphology of the ZnO particles were investigated. The synthesis conditions of the flower-like ZnO microstructures were: hydrothermal temperature of 160°C, OH?/Zn2+ molar ratio of 5:1, reaction time of 4 h, and 4 mL of dispersant. The flower-like ZnO microstructures were comprised of hexagon-shaped ZnO rods arranged in a radiatively. Degradation experiments of Rhodamine B with the flower-like ZnO microstructures demonstrated a degradation efficiency of 97.6% after 4 h of exposure to sunshine, indicating excellent photocatalytic capacity. The growth mechanism of the flower-like ZnO microstructures was presented.