Roton-type mode softening in a quantum gas with cavity-mediated long-range interactions

Long-range interactions in quantum gases are predicted to give rise to an excitation spectrum of roton character, similar to that observed in superfluid helium. We investigated the excitation spectrum of a Bose-Einstein condensate with cavity-mediated long-range interactions, which couple all particles to each other. Increasing the strength of the interaction leads to a softening of an excitation mode at a finite momentum, preceding a superfluid-to-supersolid phase transition. We used a variant of Bragg spectroscopy to study the mode softening across the phase transition. The measured spectrum was in very good agreement with ab initio calculations and, at the phase transition, a diverging susceptibility was observed. The work paves the way toward quantum simulation of long-range interacting many-body systems.     

Modelling and mapping soil erosion potential in China

Soil erosion is an important environmental threat in China.However,quantitative estimates of soil erosion in China have rarely been reported in the literature.In this study,soil loss potential in China was estimated by integrating satellite images,field samples,and ground observations based on the Revised Universal Soil Loss Equation(RUSLE).The rainfall erosivity factor was estimated from merged rainfall data using Collocated CoKriging(ColCOK)and downscaled by geographically weighted regression(GWR).The Random Forest(RF)regression approach was used as a tool for understanding and predicting the relationship between the soil erodibility factor and a set of environment factors.Our results show that the average erosion rate in China is 1.44 t ha~(–1) yr~(–1).More than 60%of the territory in China is influenced by soil erosion limitedly,with an average potential erosion rate less than 0.1 t ha~(–1) yr~(–1).Other unused land and other forested woodlands showed the highest erosion risk.Our estimates are comparable to those of runoff plot studies.Our results provide a useful tool for soil loss assessments and ecological environment protections.     

Galactic X-rays: Variable Sources in Hydromagnetic Waves

Galactic sources of x-rays fluctuating in intensity are explained as being small regions, of enhanced gas density and temperature, emitting thermal Coulomb bremsstrahlung of kiloelectron-volt energies. Hydromagnetic wave motions, of the magnetic fields in the galactic spiral arms, produce the enhanced regions by compressing the clouds of ionized gas to which they are tied by their high electrical conductivity. From the observed periods of fluctuation of a few months, together with the hydromagnetic velocity, it is estimated that the average size of sources does not exceed 10(16) centimeters. By using the formula for Coulomb bremsstrahlung and requiring that the sources shall produce the observed x-ray fluxes, one finds a second estimate of size of sources in agreement at about 1016 centimeters. Such regions are too small to be observable radio sources with current radio telescopes.     

Laser-EXAFS: Fast Extended X-ray Absorption Fine Structure Spectroscopy with a Single Pulse of Laser-Produced X-rays

The extended x-ray absorption fine structure (EXAFS) spectrum of aluminum has been measured with a nanosecond pulse of soft x-rays generated by a laser-produced plasma. This technique provides a practical alternative to synchrotorn radiation for the acquisition of EXAFS data. It also provides a unique capability for the analysis of molecular structure in highly transient chemical species.     

Ambient-temperature isolation of a compound with a boron-boron triple bond

Homoatomic triple bonds between main-group elements have been restricted to alkynes, dinitrogen, and a handful of reactive compounds featuring trans-bent heavier elements of groups 13 and 14. Previous attempts to prepare a compound with a boron-boron triple bond that is stable at ambient temperature have been unsuccessful, despite numerous computational studies predicting their viability. We found that reduction of a bis(N-heterocyclic carbene)-stabilized tetrabromodiborane with either two or four equivalents of sodium naphthalenide, a one-electron reducing agent, yields isolable diborene and diboryne compounds. Crystallographic and spectroscopic characterization confirm that the latter is a halide-free linear system containing a boron-boron triple bond.     

油菜种子硫苷含量QTL定位和低硫等位基因的发掘与应用

以中、高硫苷油菜品种‘Sollux’与‘高油605’选系‘Gaoyou’杂交F1产生的DH（doubled haploid）群体（SG,n=282）为材料,在中国和德国4种环境下对其硫苷含量进行QTL定位分析,旨在解析高硫双亲背景下的超亲分离现象,发现新的低硫苷等位基因为育种服务;并在QTL水平上通过分析硫苷含量的上位性和环境互作,揭示硫苷遗传较预期复杂的可能原因。研究结果表明,定位的8个主效QTL加性效应值在22～34 μmol·g-1,纯合并存时可影响硫苷表型44 μmol·g-1,可解释群体内遗传变异的约50%。其中3个主效QTL（GSLqA9\|1,GSLqC2和GSLqC9）可能与前人在低硫×高硫分离群体中检测到的属同位点。GSLqA9\|2,GSLqA8和GSLqC1是SG群体中新检测到的控制种子硫苷含量的QTL。通过育种手段将低硫等位基因引入目前的双低油菜品种,有望进一步降低其硫苷含量至15 μmol·g-1以下,进一步提高其饼粕饲用价值;另检测到8对上位性QTL,效应值在050～185 μmol·g-1,累计总效应2062 μmol·g-1,约为加性总效应的1/2,可能是造成该性状复杂遗传机理的原因之一;5个QTL的8个连锁标记,其标记基因型和性状表现型的符合率在60%～85%,可作为辅助手段应用于低硫苷育种材料筛选。     

三七根腐病研究进展

\t\t\t\t\t目的\t\t\t\t\t明确臭氧处理连作土壤后对三七出苗和生长的影响,以及对三七自毒皂苷的降解和对根腐病菌的抑制作用。\t\t\t\t\t\t\t\t\t\t\t\t\t方法\t\t\t\t\t用不同质量浓度的臭氧水处理三七连作土壤,调查不同处理对三七种子出苗和农艺性状的影响;用高效液相色谱法研究臭氧对自毒皂苷R₁、Rg₁、Re、Rd和Rg₂的降解作用;用平板计数法研究臭氧对主要根腐病菌茄腐镰刀菌(Fusarium solani)和毁灭柱孢菌(Cylindrocarpon destructans)的杀灭作用。\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t结果\t\t\t\t\t利用0.3~0.6 mg/L臭氧水处理连作土可显著提高三七种子的出苗率和生长势,但不同质量浓度及水量的处理间三七幼苗的株高、整株鲜重和地下部干重等农艺性状指标不存在显著差异。臭氧可以降解三七连作土壤中主要的皂苷类自毒物质,抑制引起三七根腐病的主要病原菌茄腐镰刀菌和毁灭柱孢菌的生长。\t\t\t\t\t\t\t\t\t\t\t\t\t结论\t\t\t\t\t臭氧处理可以通过降解自毒皂苷抑制三七主要根腐病菌,从而促进连作土壤中三七的出苗和生长。\t\t\t\t     

Decamethyldizincocene, a stable compound of Zn(I) with a Zn-Zn bond

Unlike mercury, which has an extensive +1 oxidation state chemistry, zinc usually adopts the +2 oxidation state. Decamethyldizincocene, Zn2(eta5-C5Me5)2, an organometallic compound of Zn(I) formally derived from the dimetallic [Zn-Zn]2+ unit, has been isolated from the low-temperature (-10 degrees C) reaction of Zn(C5Me5)2 and Zn(C2H5)2 in diethyl ether. X-ray studies show that it contains two eclipsed Zn(eta5-C5Me5) fragments with a Zn-Zn distance (+/- standard deviation) of 2.305(+/-3) angstroms, indicative of a metal-metal bonding interaction.     

Polyamine metabolism: a potential therapeutic target in trypanosomes

alpha-Difluoromethylornithine (RMI 71,782), a specific irreversible inhibitor of the first step in polyamine biosynthesis, that is, the formation of putrescine from ornithine by ornithine decarboxylase, cures mice infected with a virulent, rodent-passaged strain of Trypanosoma brucei brucei. This parasite is closely related to the trypanosomes that cause human sleeping sickness. The drug, which is remarkably nontoxic, was effective when administered in drinking water or by intubation. The ability of the compound to inhibit ornithine decarboxylase in vitro was demonstrated by the reduced amounts of putrescine synthesized from tritiated ornithine in Trypanosoma brucei suspensions. These observations direct attention to polyamine metabolism as a target for chemotherapy of parasitic diseases.     

Science centers: a potential for learning

The past decade has witnessed a proliferation of science-technology centers, or public places for informal learning about science and technology. Science centers are the only institutions that can provide the general public with participatory exhibits and experiences, together with an accurate scientific interpretation of the materials that are involved. The dramatic rise in attendance and the enthusiasm of repeat visitors to science centers reflect a strong public demand for exhibits designed to help the visitor develop a better understanding of the contemporary scientific issues of society.     

Homozygosity mapping: a way to map human recessive traits with the DNA of inbred children

An efficient strategy for mapping human genes that cause recessive traits has been devised that uses mapped restriction fragment length polymorphisms (RFLPs) and the DNA of affected children from consanguineous marriages. The method involves detection of the disease locus by virtue of the fact that the adjacent region will preferentially be homozygous by descent in such inbred children. A single affected child of a first-cousin marriage is shown to contain the same total information about linkage as a nuclear family with three affected children. Calculations show that it should be practical to map a recessive disease gene by studying DNA from fewer than a dozen unrelated, affected inbred children, given a complete RFLP linkage map. The method should make it possible to map many recessive diseases for which it is impractical or impossible to collect adequate numbers of families with multiple affected offspring.     

Word learning in a domestic dog: evidence for "fast mapping"

During speech acquisition, children form quick and rough hypotheses about the meaning of a new word after only a single exposure-a process dubbed "fast mapping." Here we provide evidence that a border collie, Rico, is able to fast map. Rico knew the labels of over 200 different items. He inferred the names of novel items by exclusion learning and correctly retrieved those items right away as well as 4 weeks after the initial exposure. Fast mapping thus appears to be mediated by general learning and memory mechanisms also found in other animals and not by a language acquisition device that is special to humans.     

分蘖角度动态型水稻的特征与基因定位研究

利用一份从贵州引进的分蘖角度在分蘖期半散生、成熟后生长紧凑的水稻特异材料N360,全生育期直立型材料9308和对照材料蜀恢527为研究对象,调查3份材料全生育期分蘖角度的变化,结果表明:从分蘖盛期到成熟期,N360、蜀恢527和9308分蘖角度减小度数分别为30、14和7,°N360具有典型的分蘖角度动态变化特点;将N360与9308杂交,构建F2代定位群体,测量亲本和F2代定位群体分蘖角度的动态变化,采用极端集团-隐性群法,并利用SSR分子标记,初步定位了控制分蘖角度动态型变化的一个主效基因于第9染色体上SSR分子标记RM201和RM215之间,遗传距离分别为21.6和19.0 cM。此外,讨论了这种水稻分蘖角度动态变化性状在育种上的应用。     

Physical mapping of a translocation breakpoint in neurofibromatosis

The gene for von Recklinghausen neurofibromatosis (NF1), one of the most common autosomal-dominant disorders of humans, was recently mapped to chromosome 17 by linkage analysis. The identification of two NF1 patients with balanced translocations that involved chromosome 17q11.2 suggests that the disease can arise by gross rearrangement of the NF1 locus, and that the NF1 gene might be identified by cloning the region around these translocation breakpoints. To further define the region of these translocations, a series of chromosome 17 Not I-linking clones has been mapped to proximal 17q and studied by pulsed-field gel electrophoresis. One clone, 17L1 (D17S133), clearly identifies the breakpoint in an NF1 patient with a t(1;17) translocation. A 2.3-megabase pulsed-field map of this region was constructed and indicates that the NF1 breakpoint is only 10 to 240 kilobases away from 17L1. This finding prepares the way for the cloning of NF1.     

Evidence for coherent proton tunneling in a hydrogen bond network

We observed coherent proton tunneling in the cyclic network of four hydrogen bonds in calix[4]arene. The tunneling frequency of 35 megahertz was revealed by a peak in the magnetic field dependence of the proton spin-lattice relaxation rate measured with field-cycling nuclear magnetic resonance in the solid state at temperatures below 80 kelvin. The amplitude of the coherent tunneling peak grows with temperature according to a Boltzmann law with energy D/kB = (125 +/- 10) kelvin (where kB is Boltzmann's constant). The tunneling peak can be interpreted in the context of level crossings in the region where the tunneling frequency matches the proton Larmor frequency. The tunneling spectrum reveals fine structure that we attribute to coupling between the hydrogen bonds in the network. The characteristics of the tunneling peak are interpreted in the context of the potential energy surface experienced by the hydrogen atoms in the network.     

Covariance mapping: a correlation method applied to multiphoton multiple ionization

In some cases there are hidden correlations in a highly fluctuating signal, but these are lost in a conventional averaging procedure. Covariance mapping allows these correlations to be revealed unambiguously. As an example of the applicability of this technique, the dynamics of fragmentation of molecules ionized by an intense picosecond laser are analyzed.     

A stable silicon(0) compound with a Si=Si double bond

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.     

大豆再生相关性状QTL定位

文章采用子叶节法,利用高再生率大豆品种合丰25与低再生率大豆品系L-28及其衍生的重组自交系群体(RIL)100个家系,评价不定芽诱导率、伸长率、生根率和成苗率等指标,比较不同大豆基因型之间再生率差异,并利用简化基因组测序技术作QTL定位分析.结果表明,在大豆RIL群体4个再生性状中,诱导率与伸长率、生根率和成苗率之间...