梅花开花物候期及加长观赏期的研究

根据１８１个梅花品种开花物候期观察记载,在南京地区拟定２月２０日以前进入开花最佳观赏期的为早花品种;２月２０日～３月１０日进入开花最佳观赏期的为中花品种;３月１０日以后进入开花最佳观赏期的为晚花品种．早花品种最佳观赏期最长为２８ｄ,最短为１３５ｄ,平均１７４ｄ;中花品种最佳观赏期最长为１５ｄ,最短为８５ｄ,平均为１１５ｄ;晚花品种花期最长为９６ｄ,最短５ｄ,平均７８ｄ．选取５０个左右的代表品种组成梅花园景品种组合,其中早、中、晚花品种植株数量按３５∶３５∶３的比例配植,可使梅园在正常气候年景梅花最佳观赏期达到５０～５６ｄ,较目前一般梅园观赏期可加长２０～２５ｄ左右,从而大大提高梅园的观赏效益．     

Gas-phase polymerization: ultraslow chemistry

The mechanism of formation of polymer molecules in the gas phase is difficult to study because the involatile polymers tend to condense out of that phase. However, new techniques, involving the use of cloud chambers, have enabled workers to use the nucleation of liquid drops in supersaturated monomer vapors to detect single polymer molecules and therefore to work with so few simultaneously growing polymers that aggregation and condensation are avoided. Chain polymerization in which the chain carriers are either radicals or ions can therefore be studied in the vapor. Furthermore, the ability to work with such small concentrations of growing polymeric radicals, for example, makes it possible to avoid encounters between them that lead to recombination and the formation of "dead" polymers that are incapable of further growth. Many aspects of gas-phase polymerization can be studied including, besides radical and ion chains, ring-opening polymerization, initiation, radiation-induced polymerization, and especially "ultraslow" chemistry.     

梅花不同品种幼树期及开花物候期研究

在长沙地区,对65个梅花品种的幼树期及开花物候期进行了观察记载。梅花不同品种其幼树期不同,丰后、美人梅、小骨里红等品种的幼树期短,嫁接当年就能开花。三轮玉蝶、桃红朱砂、南京红等品种嫁接后3~4 a才可开花。不同品种开花时期及花期长短也不同。早花品种的最佳观赏期最长为25 d,最短为18 d。中花品种的最佳观赏期最长为24 d,最短为8 d。晚花品种的最佳观赏期最长为10 d,最短为7 d。     

The dependence of electron transfer efficiency on the conformational order in organic monolayers

The electron transfer through an organized organic monolayer of alkyl chains adsorbed on a silicon wafer has been studied. The silicon was used as an electrode in a three-electrode electrochemical cell, and the current versus voltage response was measured. The results show that when the chains in the monolayer are in the "all trans" configuration, the charge transfer efficiency is higher than when the chains have a "gauche" configuration. A mechanism rationalizing all the observations is suggested.     

人工合成甘蓝型油菜特长果突变系选育初报

从 16 9份人工合成甘蓝型油菜新材料中 ,鉴定出了 2 1份特长果株系 ,其主花序中部角果长度一般在 12cm以上 ,果身长度在 10cm以上。其中 ,最长角果系为“H2 18” ,其平均角果长度达到了 18 12cm ,果身长达到了 15 2 5cm ,最长果单株角果长度达到了 19 34cm ,果身长达到了 16 2 0cm。并在该系中一个折断了主花序的单株上 ,得到了一个极端最长达 30 5cm ,果身长达 2 5cm的超长角果。本研究中所获得的特长果材料与现已报导的特长果材料有着完全不同的遗传来源 ,其角果和果身的长度也大大超过了现有特长角突变系的相应长度。它们在油菜育种及遗传研究中将具有重要的利用价值。在它们的亲本中 ,却未曾见到长角特性 ,所获得的特长果性状都是在杂种后代分离和选育过程中发生的 ,其形成机制和遗传规律有待进一步研究     

三个优质水稻不育系生育特性的比较

观测结果表明 :在供试的 3个优质不育系中 ,以“IR580 2 5A”的播始历期最长( 76～ 99d) ,“东B1 1A”次之 ( 69～ 97d) ,“金 2 3A”最短 ( 50～78d) ;“东B1 1A”和“金 2 3A”的柱头活力及柱头外露率均高于“IR580 2 5A” ;“东B1 1A”的开花最高峰最明显 ,但其始花期比另 2个不育系迟 1d;“金 2 3A”和“IR580 2 5A”的花粉典败率达 1 0 0 % ,“东B1 1A”的典败率为98.0 8% ,圆败率为 1 .92 %。     

Asbestiform chain silicates: new minerals and structural groups

The discovery and characterization of structurally ordered and disordered phases that are intermediate between amphiboles and micas have shown that the biopyriboles are a much more complex family of minerals than has previously been recognized. In addition to single-chain, double-chain, and sheet structures, there are also minerals with triple chains and with alternating double and triple chains. Many crystals exhibit disorder in the sequence of double and triple chains, and isolated chains that are wider than triple are common. This structural disorder helps to explain why asbestiform amphiboles are fibrous. The new phases have now been found in several localities, and it is possible that similar phenomena in other minerals could also have been overlooked. In particular, there is no reason to suppose that analogous substances and structures with both single and double chains do not occur between the pyroxenes and the amphiboles. Since the pyroxenes are used extensively by geologists to assess rock histories and formation temperatures and pressures, it is essential that the extent of this type of disorder be evaluated. It is possible that what appears to be only an interesting mineralogical problem may prove to be a petrological nightmare.     

An experimental study of search in global social networks

We report on a global social-search experiment in which more than 60,000 e-mail users attempted to reach one of 18 target persons in 13 countries by forwarding messages to acquaintances. We find that successful social search is conducted primarily through intermediate to weak strength ties, does not require highly connected "hubs" to succeed, and, in contrast to unsuccessful social search, disproportionately relies on professional relationships. By accounting for the attrition of message chains, we estimate that social searches can reach their targets in a median of five to seven steps, depending on the separation of source and target, although small variations in chain lengths and participation rates generate large differences in target reachability. We conclude that although global social networks are, in principle, searchable, actual success depends sensitively on individual incentives.     

椰子叶片气孔特征的品种间比较

采用指甲油涂抹撕取法及石蜡切片法对椰子叶片的气孔进行观察,并比较5个椰子品种的叶片气孔器特征。观察发现,椰子气孔为轮列4细胞型,具有2个侧副卫细胞,2个端副卫细胞;5个椰子品种的气孔器密度、长度、宽度存在显著差异,其中小黄椰的气孔数目、气孔宽度值最大,本地高的气孔长度值最大。研究结果认为椰子叶片的气孔特征能否作为椰子抗性的鉴定指标尚待商榷。     

Hemoglobin adaptation for fast and slow water habitats in sympatric catostomid fishes

The oxygen equilibria of Catostomus insignis hemoglobins are pH dependent. Catostomus clarkii hemoglobins have some components (20 percent) whose oxygen equilibria are independent of pH because the alpha chains have NH(2)-termini that are blocked and the beta chains lack the "usual" COOH-terminal histidine. Since the Bohr effect is normally a beneficial phenomenon, the maintenance of some hemoglobins without a Bohr effect must provide a physiological advantage that is habitat specific. The intrastream ecological preferences of these sympatric catostomids suggest that the hemoglobins without the Bohr effect confer an ecological advantage in a swift water habitat.     

Rabbit hemoglobin biosynthesis: use of human hemoglobin chains to study molecule completion

A cell-free protein-synthesizing system made from rabbit reticulocytes was used to incorporate (14)C-amino acids into hemoglobin. Electrophoretic analyses of the soluble products of this cell-free system revealed a fraction containing rabbit (14)C-alpha chains in addition to the rabbit (14)C-hemoglobin. The addition of isolated human hemoglobin beta chains to this system during active synthesis inhibited the release of newly synthesized rabbit (14)C-beta chains into solution from the ribosome fraction. This inhibition was possibly a result of hybrid hemoglobin formation between rabbit alpha and human beta chains. A model of hemoglobin construction in which soluble alpha chains are intermediates is suggested. These alpha chains may aid in the release of beta chains from the polyribosomes during the completion of the hemoglobin molecule.     

Galactosyl diglycerides: their possible function in Euglena chloroplasts

Illumination of euglenas grown in the dark induces the formation of chloroplasts characterized by the simultaneous appearance of chlorophyll and galactosyl diglycerides in a relatively fixed ratio. The fatty acyl chains of the galactosyl diglycerides are constructed so that they can provide a stable lock-and-key fit with the phytol chains of chlorophyll in such a way as to localize the porphyrin structures of chlorophyll and space them for efficient photoreception. Light-starved photobiotic euglenas show chloroplast shrinkage with a concurrent partial loss of galactosyl diglycerides.     

Supramolecular assembly of amelogenin nanospheres into birefringent microribbons

Although both tooth enamel and bone are composed of organized assemblies of carbonated apatite crystals, enamel is unusual in that it does not contain collagen nor does it remodel. Self-assembly of amelogenin protein into nanospheres has been recognized as a key factor in controlling the oriented and elongated growth of carbonated apatite crystals during dental enamel biomineralization. We report the in vitro formation of birefringent microribbon structures that were generated through the supramolecular assembly of amelogenin nanospheres. These microribbons have diffraction patterns that indicate a periodic structure of crystalline units along the long axis. The growth of apatite crystals orientated along the c axis and parallel to the long axes of the microribbons was observed in vitro. The linear arrays (chains) of nanospheres observed as intermediate states before the microribbon formation give an important indication as to the function of amelogenin in controlling the oriented growth of apatite crystals during enamel mineralization.     

End states in one-dimensional atom chains

End states--the zero-dimensional analogs of the two-dimensional states that occur at a crystal surface--were observed at the ends of one-dimensional atom chains that were self-assembled by depositing gold on the vicinal Si(553) surface. Scanning tunneling spectroscopy measurements of the differential conductance along the chains revealed quantized states in isolated segments with differentiated states forming over end atoms. A comparison to a tight-binding model demonstrated how the formation of electronic end states transforms the density of states and the energy levels within the chains.     

The use of graft copolymers to bind immiscible blends

Computer simulations and experimental studies were combined to design copolymers that enhance the strength of polymer composites. These copolymers contain side chains that associate across the boundary between phase-separated regions to form a "molecular velcro" that effectively binds the regions together. This behavior significantly improves the structural integrity and mechanical properties of the material. Because the side chains can be fabricated from a large class of compounds, the technique greatly increases the variety of copolymers that can be used in forming high-strength polymer blends.     

Evolution of a protein fold in vitro

A "switch" mutant of the Arc repressor homodimer was constructed by interchanging the sequence positions of a hydrophobic core residue, leucine 12, and an adjacent surface polar residue, asparagine 11, in each strand of an intersubunit beta sheet. The mutant protein adopts a fold in which each beta strand is replaced by a right-handed helix and side chains in this region undergo significant repacking. The observed structural changes allow the protein to maintain solvent exposure of polar side chains and optimal burial of hydrophobic side chains. These results suggest that new protein folds can evolve from existing folds without drastic or large-scale mutagenesis.     

Poverty reduction through the development of inclusive food value chains

Propelled by urbanization, rising incomes, and changing diets, food markets have been expanding in Africa and South Asia, creating the vast potential for job and income opportunities along food supply chains and, hence, for poverty reduction. The novel coronavirus(COVID-19) that spread to a pandemic in early 2020 provokes enormous setbacks to this expansion. This, however, should provide lessons regarding the importance of resilient and inclusive food systems. Emergency responses to COVID-19 should consider interventions towards that end and leverage the opportunities provided by food markets growth as economies recover from the present economic recession. This paper assesses options of how this could be done by facilitating the better functioning and interconnectedness of the many small and medium-sized enterprises that are proliferating along the "hidden middle" of food value chains in storage, logistics, transportation, and wholesale and retail distribution. It also explores how policies can help smallholder farmers connect to this "hidden middle" in more gainful ways and help them climb out of poverty as well.     

Phylogenetic MCMC algorithms are misleading on mixtures of trees

Markov chain Monte Carlo (MCMC) algorithms play a critical role in the Bayesian approach to phylogenetic inference. We present a theoretical analysis of the rate of convergence of many of the widely used Markov chains. For N characters generated from a uniform mixture of two trees, we prove that the Markov chains take an exponentially long (in N) number of iterations to converge to the posterior distribution. Nevertheless, the likelihood plots for sample runs of the Markov chains deceivingly suggest that the chains converge rapidly to a unique tree. Our results rely on novel mathematical understanding of the log-likelihood function on the space of phylogenetic trees. The practical implications of our work are that Bayesian MCMC methods can be misleading when the data are generated from a mixture of trees. Thus, in cases of data containing potentially conflicting phylogenetic signals, phylogenetic reconstruction should be performed separately on each signal.     

Fluorous nanodroplets structurally confined in an organopalladium sphere

The distinct properties of fluorous phases are practically useful for separation, purification, and reaction control in organic synthesis. Here, we report the formation of a liquid-like fluorous droplet, composed of 24 perfluoroalkyl chains confined in the interior of a 5-nanometer-sized, roughly spherical shell that spontaneously assembled in solution from 12 palladium ions and 24 bridging ligands. Crystallographic analysis confirmed the rigid shell framework and amorphous interior. Perfluoroalkanes can dissolve in this well-defined fluorous phase, whereas they can hardly dissolve in a surrounding polar organic solution, and their solubility (up to approximately eight perfluoroalkane molecules per spherical complex) can be finely controlled by tuning the length of perfluoroalkyl chains tethered to the shell.     

短豇豆染色体数目和形态的研究

本文首次研究了短豇豆的染色体数目和形态。短豇豆的染色体数为２ｎ＝２ｘ＝２２,全部为中部着丝粒型,最长的一对染色体长２．４０μｍ,最短的一对长１．５７μｍ,属对称核型,其核型可用下述公式表达：２ｎ＝２ｘ＝２２＝２２ｍ。