Quantum structure of the intermolecular proton bond

A proton shared between two closed-shell molecules, [A.H+.B], constitutes a ubiquitous soft binding motif in biological processes. The vibrational transitions associated with the shared proton, which provide a direct probe of this interaction, have been extensively studied in the condensed phase but have yielded only limited detailed information because of their diffuse character. We exploited recent advances in gas-phase ion spectroscopy to identify sharp spectral features that can be assigned to both the shared proton and the two tethered molecules in a survey of 18 cold, isolated [A.H+.B] ions. These data yield a picture of the intermolecular proton bond at a microscopic scale, facilitating analysis of its properties within the context of a floppy polyatomic molecule.     

A high-pressure structure in curium linked to magnetism

Curium lies at the center of the actinide series and has a half-filled shell with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoclinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium's 5f electrons that stabilizes Cm III. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.     

密度依赖口袋常数下奇异夸克物质及奇异星

在有效质量口袋模型(EMBM)下采用密度依赖口袋常数描述奇异夸克物质,研究了口袋常数的密度依赖性对奇异夸克物质的状态方程及奇异星性质的影响.结果表明,密度依赖口袋常数在低密度处较大,随着密度增大而明显变小,很好地体现了低密度处色禁闭、高密度处夸克退紧闭的量子色动力学(QCD)基本精神.与常数口袋常数的情形相比,密度依赖口袋常数下奇异夸克物质的状态方程变硬,奇异星的引力质量和对应的半径均有明显变大,且均在脉冲星的观测值范围内,表明该模型适合于描述质量和半径较大的奇异星内的夸克物质.     

Molecular basis of proton motive force generation: structure of formate dehydrogenase-N

The structure of the membrane protein formate dehydrogenase-N (Fdn-N), a major component of Escherichia coli nitrate respiration, has been determined at 1.6 angstroms. The structure demonstrates 11 redox centers, including molybdopterin-guanine dinucleotides, five [4Fe-4S] clusters, two heme b groups, and a menaquinone analog. These redox centers are aligned in a single chain, which extends almost 90 angstroms through the enzyme. The menaquinone reduction site associated with a possible proton pathway was also characterized. This structure provides critical insights into the proton motive force generation by redox loop, a common mechanism among a wide range of respiratory enzymes.     

Permanent lunar surface magnetism and its deflection of the solar wind

Magnetic compressions intermittently observed outside the lunar wake in the solar wind may be limb shocks caused by the presence of local regions of permanent magnetism on the lunar limb. Observable compression would be due to regions of length scale (radius) at least as great as several tens of kilometers and field strength greater, similar 10 gammas. Thousands of such regions might exist on the lunar surface. The steady magnetic field measured at the Apollo 12 site probably has length scale less, similar 10 kilometers and probably does not produce an observable limb shock.     

A new theory of lunar magnetism

In the hypothesis advanced here it is supposed that the field, in which rocks at the lunar surface acquired the remanent magnetization found through the Apollo project, arose from permanent magnetization of the deep interior of the moon. This theory involves the assumption that the moon, apart from a surface shell, accreted cold and remained below the Curie point of iron until sometime later than 3 x 10(9) years ago. The magnetization was acquired as the moon formed in a gas sphere in the strong magnetic field of the early sun.     

Insight into the mechanism of the influenza A proton channel from a structure in a lipid bilayer

The M2 protein from the influenza A virus, an acid-activated proton-selective channel, has been the subject of numerous conductance, structural, and computational studies. However, little is known at the atomic level about the heart of the functional mechanism for this tetrameric protein, a His(37)-Trp(41) cluster. We report the structure of the M2 conductance domain (residues 22 to 62) in a lipid bilayer, which displays the defining features of the native protein that have not been attainable from structures solubilized by detergents. We propose that the tetrameric His(37)-Trp(41) cluster guides protons through the channel by forming and breaking hydrogen bonds between adjacent pairs of histidines and through specific interactions of the histidines with the tryptophan gate. This mechanism explains the main observations on M2 proton conductance.     

Strange and unconventional isotope effects in ozone formation

The puzzling mass-independent isotopic enrichment in ozone formation contrasts markedly with the more recently observed large unconventional mass-dependent ratios of the individual ozone formation rate constants in certain systems. An RRKM (Rice, Ramsperger, Kassel, Marcus)-based theory is used to treat both effects. Restrictions of symmetry on how energy is shared among the rotational/vibrational states of the ozone isotopomer, together with an analysis of the competition between the transition states of its two exit channels, permit the calculation of isotope effects consistent with a wide array of experimental results.     

Strange floral attractors: pollinator attraction and the evolution of plant sexual systems

Individual plants of hummingbird-pollinated Besleria triflora display two flower morphs: staminate flowers, which have shortened styles and do not produce fruit, and hermaphrodite flowers. Experiments with B. triflora indicate that pollinator attraction can drive the evolution of a dimorphic plant sexual system. In field-manipulated plants, visitation increased at large floral displays; however, pollen receipt increased only when staminate flowers were used to enlarge the display. Laboratory experiments showed that staminate flowers do not remove pollen from visiting pollinators, effectively concentrating outcross pollen onto stigmas of fertile flowers. A dimorphic sexual system is favored because the morphology of staminate flowers enhances their role in pollinator attraction.     

磁化肥对小麦生长和土壤性状的影响

经小麦盆栽试验表明:磁化肥与等量养分常规化肥相比,小麦苗期株高、地上部鲜重都有明显的增加,表明磁化肥对小麦的苗期生长有明显的促进作用.大田试验表明,与等量养分常规化肥相比,磁化肥增产8%～14.1%.在磁化肥用量0～1500kg/hm2范围内,以750kg/hm2磁化肥用量的小麦产量和经济效益最好.     

Is the proton stable

For nearly 50 years there has been a strong belief that the proton is absolutely stable. The current experimental upper bound on its decay rate is less than one proton decay per 3 tons of matter per year, which corresponds to a mean lifetime of more than 10(30) years. Even more sensitive searches for proton decay are now in progress. These are partially motivated by the development of a class of models that combine the presently accepted theories of electromagnetic, weak, and strong inter-actions into an elegant unified form. Some of these theories predict a proton lifetime short enough for the decays to be detectable by the proposed experiments. If the proton is unstable, a plausible explanation can be given for the apparent excess of matter over antimatter in the universe.     

怪味方便复合调味酱的研制

[目的]研究怪味方便调味酱的加工工艺,开发复合型专用调味品。[方法]运用现代食品加工工艺对传统的酱料做适当的改良,采用L9(34)正交试验筛选最佳配方。[结果]L9(34)正交试验表明,对怪味调味酱影响因素的主次顺序为:盐>糖和醋>豆瓣酱和芝麻酱>花椒粉,说明盐的添加量对该制品的品质影响最大。该产品的最佳配方为:盐2%、芝麻酱25%、豆瓣酱25%、醋19%、糖14%、葱1.5%、姜1.5%、蒜2%、花椒粉2%,色拉油8%、山梨酸钾0.5 g/kg、茶多酚0.1 g/kg。然后,经热处理调配采用真空软包装,条件为0.06～0.08 MPa,热封3～5 s,最后趁热封口沸水杀菌5～10 min。[结论]经过37℃下5 d保温检验,产品符合商业无菌要求和相关质量标准,是理想的制作怪味菜肴的复合方便调味品。     

Antiphase domains and reverse thermoremanent magnetism in ilmenite-hematite minerals

Examination of synthetic ilmenite-hematite samples by transmission electron microscopy has for the first time revealed the presence of well-defined antiphase domains and antiphase domain boundaries in this mineral system. Samples quenched from 1300 degrees C have a high density of domain boundaries, whereas samples quenched from 900 degrees C have a much lower density. Only the high-temperature samples acquire reverse thermoremanent magnetism when cooled in an applied magnetic field. The presence of a high density of domain boundaries seems to be a necessary condition for the acquisition of reverse thermoremanent magnetism.