Reversible control of hydrogenation of a single molecule

Low-temperature scanning tunneling microscopy was used to selectively break the N-H bond of a methylaminocarbyne (CNHCH3) molecule on a Pt(111) surface at 4.7 kelvin, leaving the C-H bonds intact, to form an adsorbed methylisocyanide molecule (CNCH3). The methylisocyanide product was identified through comparison of its vibrational spectrum with that of directly adsorbed methylisocyanide as measured with inelastic electron tunneling spectroscopy. The CNHCH3 could be regenerated in situ by exposure to hydrogen at room temperature. The combination of tip-induced dehydrogenation with thermodynamically driven hydrogenation allows a completely reversible chemical cycle to be established at the single-molecule level in this system. By tailoring the pulse conditions, irreversible dissociation entailing cleavage of both the C-H and N-H bonds can also be demonstrated.     

Reversible unfolding of single RNA molecules by mechanical force

Here we use mechanical force to induce the unfolding and refolding of single RNA molecules: a simple RNA hairpin, a molecule containing a three-helix junction, and the P5abc domain of the Tetrahymena thermophila ribozyme. All three molecules (P5abc only in the absence of Mg2+) can be mechanically unfolded at equilibrium, and when kept at constant force within a critical force range, are bi-stable and hop between folded and unfolded states. We determine the force-dependent equilibrium constants for folding/unfolding these single RNA molecules and the positions of their transition states along the reaction coordinate.     

The controlled evolution of a polymer single crystal

We present a method for controlling the initiation and kinetics of polymer crystal growth using dip-pen nanolithography and an atomic force microscope tip coated with poly-dl-lysine hydrobromide. Triangular prisms of the polymer epitaxially grow on freshly cleaved mica substrates, and their in-plane and out-of-plane growth rates can be controlled by raster scanning the coated tip across the substrate. Atomic force microscope images were concomitantly recorded, providing a set of photographic images of the process as it spans the nanometer- to micrometer-length scales as a function of environmental conditions.     

高温诱导叶用莴苣抽薹过程中细胞形态的变化

[目的]分析高温处理条件下叶用莴苣抽薹过程中花芽、花茎细胞学和茎的形态变化.[方法]以叶用莴苣(Lactuca sativeL.)“G-B30”,“G-B31”为材料,对两个易抽薹品种的花芽和茎的分化过程进行细胞学观察,并结合茎的快速伸长时期确定叶用莴苣的抽薹期.[结果]随着高温处理时间的延长,两个易抽薹品种的茎尖生长点由尖锐的锐角变为半球形,生长锥逐渐加宽变平,且都是在高温处理第4天时茎尖生长点就开始出现由圆锥形变扁平;花茎高温处理第8天细胞排列出现规律性,与常温8d处理相比差异显著;在8～20 d时花茎伸长迅速.[结论]通过观察花芽和花茎分化的情况,并结合花茎的形态变化判断,综合可知“G-B30”,“G-B31”在高温处理第8天开始抽薹.     

纳米纤维素制备优化及其形貌表征

通过硫酸水解微晶纤维素制备纳米纤维素,分析硫酸浓度、反应温度和水解时间对纳米纤维素得率的影响,采用正交实验优化了实验参数。用场发射环境扫描电镜(ESEM-FEG)和透射电镜(HR-TEM)表征了微晶纤维素与纳米纤维素的形貌,并对其尺寸分布进行了分析。结果表明,当硫酸浓度为56%,反应温度40℃,水解时间90min时,纳米纤维素得率最高,达55.40%;电镜观察纳米纤维素呈棒状,其尺寸较微晶纤维素明显减小,直径2-24nm,长度为50-450nm。     

Reversible Section of the Brain by a Wall of Cold

A fork made up of hollow tubing may be chronically implanted in the cat's brain. When cooling fluid is pumped through this fork a reversible plane lesion is formed. This technique permits analysis of functional parts of the nervous system in unanesthetized animals.     

Mobile point defects and atomic basis for structural transformations of a crystal surface

Structural transformations on elemental semiconductor surfaces typically occur above several hundred degrees Celsius, and the atomic motions involved are extremely rapid and difficult to observe. However, on the (111) surface of germanium, a few lead atoms catalyze atomic motions so that they can be observed with a tunneling microscope at temperatures below 80 degrees C. Mass transport and structural changes are caused by the creation and propagation of both vacancy-like and interstitial-like point defects within the crystal surface. The availability of dangling bonds on the surface is critical. A detailed atomic model for the observed motions has been developed and is used to explain the structural phase transition Ge(111)-c(2x8) <--> 1x1, which occurs near 300 degrees C.     

Observation of metastable structural excitations and concerted atomic motions on a crystal surface

The addition of a small number of lead atoms to a germanium(111) surface reduces the energy barrier for activated processes, and with a tunneling microscope it is possible to observe concerted atomic motions and metastable structures on this surface near room temperature. The formation and annihilation of these metastable structural surface excitations is associated with the shift in position of large numbers of germanium surface atoms along a specific row direction like beads on an abacus. The effect provides a mechanism for understanding the transport of atoms on a semiconductor surface.     

Primaquine-induced changes in morphology of exoerythrocytic stages of malaria

Exposure to primaquine for 48 hours caused lesions in the exoerythrocytic stages of Plasmodium fallax grown in cultivated cells derived from embryonic turkey brain. The lesions appeared in the form of cytoplasmic vacuoles when viewed under the light microscope. The electron microscope revealed these vacuoles as swollen mitochondria readily identifiable by their typical protozoan cristae. Mitochondria of the host cell were unaffected.     

Membrane changes in a single photoreceptor cause associative learning in Hermissenda

Single type B photoreceptors in intact, restrained Hermissenda were impaled with a microelectrode and exposed to either paired or unpaired presentations of light and depolarizing current to simulate natural stimulus effects during conditioning with light and rotation. Paired, but not unpaired, stimulus presentations produced cumulative depolarization and increased input resistance in type B cells. These membrane changes are similar to those observed after pairings of light and rotation are administered to either intact animals or isolated nervous systems or when light is paired with electrical stimulation of the vestibular system in isolated nervous systems. One and two days after treatment, pairing- and light-specific suppression of phototactic behavior was observed in recovered animals. These findings indicate that the membrane changes of type B cells produced by pairing light with current injections cause acquisition of the learned behavior.     

Large magnetic anisotropy of a single atomic spin embedded in a surface molecular network

Magnetic anisotropy allows magnets to maintain their direction of magnetization over time. Using a scanning tunneling microscope to observe spin excitations, we determined the orientation and strength of the anisotropies of individual iron and manganese atoms on a thin layer of copper nitride. The relative intensities of the inelastic tunneling processes are consistent with dipolar interactions, as seen for inelastic neutron scattering. First-principles calculations indicate that the magnetic atoms become incorporated into a polar covalent surface molecular network in the copper nitride. These structures, which provide atom-by-atom accessibility via local probes, have the potential for engineering anisotropies large enough to produce stable magnetization at low temperatures for a single atomic spin.     

Reversible rotation of antimony dimers on the silicon (001) surface with a scanning tunneling microscope

The scanning tunneling microscope (STM) was used to control the configuration of antimony clusters on the (001) surface of silicon. In particular, the STM tip induced a reversible rotation between two orthogonal orientations of individual antimony dimers on the surface. This simple rotation can be explained by an atomic-scale torque exerted on the antimony dimers by the STM tip. The reversibility of this process could provide a basis for making atomic-scale memory cells.     

Importance of surface morphology in interstellar H2 formation

Detailed laboratory experiments on the formation of HD from atom recombination on amorphous solid water films show that this process is extremely efficient in a temperature range of 8 to 20 kelvin, temperatures relevant for H2 formation on dust grain surfaces in the interstellar medium (ISM). The fate of the 4.5 electron volt recombination energy is highly dependent on film morphology. These results suggest that grain morphology, rather than the detailed chemical nature of the grain surface, is most important in determining the energy content of the H2 as it is released from the grain into the ISM.     

Compensation of the birefringence of a polymer by a birefringent crystal

We report a method for compensating the birefringence of optical polymers by doping them with inorganic birefringent crystals. In this method, an inorganic birefringent material is chosen that has the opposite birefringence to that of the polymer and has rod-shaped crystals that are oriented when the polymer chains are oriented. The birefringence of the polymer is thus compensated by the opposing birefringence of the crystal. Birefringence is minimized in various polymer optical devices by adjusting process conditions, because it degrades the performance of devices. This method minimizes it, independent of process conditions, which potentially improves the productivity of devices.     

Detection of radial crossbridge force by lattice spacing changes in intact single muscle fibers

Time-resolved lattice spacing changes were measured (10-millisecond time resolution) by x-ray diffraction of synchrotron radiation in single intact muscle fibers of the frog Rana temporaria undergoing electrically stimulated tension development during application of stretches and releases. Ramp releases, which decreased fiber length at constant speed, caused a lattice expansion. After the ramp, increasing tension during recovery was accompanied by lattice compression. Ramp stretches caused a compression of the lattice. While the fiber was held at a constant length after the stretch, tension decreased and lattice spacing increased. These observations demonstrate the existence of a previously undetected radial component of the force generated by a cycling crossbridge. At sarcomere lengths of 2.05 to 2.2 micrometers, the radial force compresses the myofilament lattice. Hence, the myofilament lattice does not maintain a constant volume during changes in force.     

慈竹植硅体形态及其发育变化研究

【目的】观察植硅体在慈竹(Bambusa emeiensis)竹秆、叶鞘、箨片和叶片等器官中的分布与形态,为硅在丛生竹材中的沉积规律及竹材生物矿化研究提供形态依据。【方法】从2015年7月慈竹发笋开始,在竹秆长到50,100,200,300,500,800,1 000cm高时分别在基部、中部及顶部取竹秆样,在慈竹1年生时从其基部、中部取叶鞘和箨片样,从顶部取叶片样,样品制片后利用光学显微镜和扫描电子显微镜对植硅体在慈竹生长发育期各器官中的形态进行观测。【结果】竹笋时期表皮无植硅体,竹秆表皮植硅体的形成是硅酸在硅质细胞中连续沉积的过程,竹笋-幼竹时期秆高100cm时植硅体始见于表皮内;慈竹秆表皮植硅体为长鞍形和椭圆形,秆内部未见植硅体;幼竹上升期(500cm),同一竹秆不同部位植硅体大小表现为基部中部顶部,成熟竹不同部位植硅体大小无明显差异。慈竹叶植硅体为长椭圆形和哑铃形,成熟叶以哑铃形为主;从新叶到成熟叶,植硅体体积增大。叶鞘植硅体为长椭圆形和鞍形,从内到外长椭圆形的植硅体数量减少,鞍形植硅体数量增多。箨片中植硅体为圆形和椭圆形。【结论】竹笋时期无植硅体,硅质细胞在慈竹发育期形成,同种竹种不同器官植硅体形态有差异。     

表层土壤调控措施对苹果根系形态及活力的影响

针对甘肃省陇东旱塬苹果园缺乏有效的表层土壤管理措施的现状,通过优化表层土壤管理方式,研究了优化化肥施用条件下,不同覆盖材料和不同有机肥对陇东红富士苹果根系形态及活力的影响.对比分析了常规管理(T1)与表层土壤调控措施(T2:覆膜+普通有机肥;T3:覆膜+微生物有机肥;T4:覆草+普通有机肥;T5:覆草+微生物有机肥)对苹果根系形态及根系活力的影响.结果表明,T5比T1的根长、根表面积、根体积和根尖数各增加了766.61cm、118.51cm2、6.64cm3和2216条,T5的根系活力比其他处理高,最高值达364.7μg/(g·h);相同有机肥条件下覆草处理效果优于覆膜处理;相同覆盖方式下微生物有机肥效果优于普通有机肥.