The herbaceous lycophyte Haskinsia Grierson and Banks from the Devonian of western Venezuela, with observations on leaf morphology and fertile specimens

The Devonian herbaceous lycophyte genus Haskinsia Grierson and Banks is characterized by narrow dichotomizing stems and helically arranged petiolate leaves with a broad, approximately deltoid, lamina. New specimens are reported from four horizons in the Lower Member of the Campo Chico Formation, Sierra de Perijá, western Venezuela. H. sagittaka Edwards and Benedetto has sagittate leaves, and fertile specimens are reported for the first time; the ellipsoidal/obovoid adaxially-flattened sporangium is attached to unmodified leaves towards the top of the petiole in the adaxial position. H. sp. has sagittate leaves which are larger than any yet attributed to the genus but is represented by only three specimens. H. hastata sp. nov. has hastate leaves; the sporangia are more globose but positioned similarly to those of H. sagittata. The occurrence of the sporangia on unmodified microphylls indicates that Haskinsia is a member of Protolepidodendrales. The status of Haskinsiaceae is discussed. The Venezuelan specimens are compared with other records of Haskimi and Haskinsia -like plants from North America, Kazakhstan, North China, North Africa and Antarctica.     

长管假茉莉的化学成分

从药用植物长管假茉莉（Ｃｌｅｒｏｄｅｎｄｒｕｍｉｎｄｉｃｕｍ）中分离鉴定了８个化合物,通过波谱分析及已知数据对照,分别鉴定为３,４－二羟基苯乙醇（３,４－ｄｉｈｙｄｒｏｘｙｐｈｅｎｙｌｅｔｈａｒｏｌ,１）,粗毛豚草素（ｈｉｓｐｉｄｕｌｉｎ,２）粗毛豚鼠素葡萄糖醛酸苷（ｈｉｓｐｄｕｌｉｎ７－Ｏ－ｇｌｕｃｕｒｏｎｉｄｅ,３）泽兰叶黄素（ｅｕｐａｆｏｌｉｎ,４）黄芩素苷（ｓｅｃｕｔｅｌｌａｒｅｉｎ,５）     

Molecular dynamics simulation of the melting processes of core–shell and pure nanoparticles

Core–shell nanoparticles are nanosized particles that consist of a core and a shell, constructed from different metallic elements. Core–shell nanoparticles have received extensive attention, owing to their various potential applications such as paints, optical films and catalysts. Herein, we investigate the melting behaviours of different core–shell nanoparticles under continuous heating using molecular dynamics simulation. Different metallic elements were examined as core–shell and pure nanoparticles. Five different processes were observed during the melting of core–shell nanoparticles. In contrast, only one process was identified during the melting of pure nanoparticles. These processes were influenced by the nanoparticle size, shell thickness and differences between the lattice constants and melting point temperatures of the metallic elements. Our simulation provides microscopic insights into the melting behaviours of existing and proposed core–shell nanoparticles that would be highly beneficial towards the fabrication of materials with different chemical coatings.     

Responses to selection on male-phase duration in Chamerion angustifolium

Protandry (when male function precedes female) can enhance fitness by reducing selfing and increasing pollen export and outcrossed siring success. However, responses to selection on protandry may be constrained by genetic variation and correlations among floral traits. We examined these potential constraints in protandrous Chamerion angustifolium (Onagraceae) by estimating genetic variation in male-phase duration and associated floral traits using a paternal half-sib design and selection experiment. Narrow-sense heritability of male-phase duration was estimated as 0.23 (SE +/- 0.04) and was positively correlated with floral display. The selection experiment shortened male-phase duration 0.8 SD from the parental average of 17.0 h and lengthened it by 2.0 SD. Furthermore, fixed floral longevity caused a negative association between male- and female-phase durations. These results suggest that selection on male-phase duration is not limited by genetic variation. However, changes in male-phase duration may influence pollinators through correlated changes in floral display and reduced opportunities for pollen receipt during female phase.     

Molecular Dynamics Simulation of Structural Phase Transition of AlPO4 Induced by Pressure

Abstract

The mechanism of pressure-induced phase transition of AlPO₄ has been investigated by means of a molecular dynamics method of constant temperature and pressure. A new crystalline phase with space group C2, which has not yet been experimentally found, appears by an instantaneous compression of 60, 70 and 80 GPa at 300 K. At high temperature (2500 K) and pressure (58 GPa), another new phase of AlPo₄ (y-phase), which is composed of PO₆ and AlO₆ octahedra, has been observed.     

Floral syndrome and insect pollination of the Qinghai-Tibet Plateau endemic Swertia przewalskii（Gentianaceae）

A combination of dichogamy and herkogamy in hermaphroditic plants is an effective mechanism to encourage outcrossing and avoid selfing.In this paper,we studied whether such a mechanism completely avoids geitonogamous selfing in Swertia przewalskii Pissjau     

核桃揪雌雄异熟性的初步研究

对核桃揪开花特性进行了观察。结果表明：核桃揪多数植株为雌雄异熟,有的植株上雌花先开（雌先型）,有的植株上雄花先开（雄先型）。每一植株上雌雄异熟的次序是相当稳定的。并且多数能为雌先型植株提供授粉机会的雄先型群体,其雌花期与雌先型群体的雄花期也能较好的吻合。但是少数花期不同的同一类型（即：雌先型与雌先型或雄先型与雄先型）植株之间也有授粉机会。在坐果率、产量、核果的整齐度、放叶早晚、落叶期、形态差异的调查分析中未发现异熟性与这些性状上有必然的联系。     

Morphology and Phase Behavior of Two-Component Lipid Membranes

The stability and shapes of domains with different bending rigidities in lipid membranes are investigated. These domains can be formed from the inclusion of an impurity in a lipid membrane or from the phase separation within the membrane. We show that, for weak line tensions, surface tensions and finite spontaneous curvatures, an equilibrium phase of protruding circular domains or striped domains may be obtained. We also predict a possible phase transition between the investigated morphologies.     

Simulation of gel phase formation and melting in lipid bilayers using a coarse grained model

The transformation between a gel and a fluid phase in dipalmitoyl-phosphatidylcholine (DPPC) bilayers has been simulated using a coarse grained (CG) model by cooling bilayer patches composed of up to 8000 lipids. The critical step in the transformation process is the nucleation of a gel cluster consisting of 20-80 lipids, spanning both monolayers. After the formation of the critical cluster, a fast growth regime is entered. Growth slows when multiple gel domains start interacting, forming a percolating network. Long-lived fluid domains remain trapped and can be metastable on a microsecond time scale. From the temperature dependence of the rate of cluster growth, the line tension of the fluid-gel interface was estimated to be 3+/-2 pN. The reverse process is observed when heating the gel phase. No evidence is found for a hexatic phase as an intermediate stage of melting. The hysteresis observed in the freezing and melting transformation is found to depend both on the system size and on the time scale of the simulation. Extrapolating to macroscopic length and time scales, the transition temperature for heating and cooling converges to 295+/-5 K, in semi-quantitative agreement with the experimental value for DPPC (315 K). The phase transformation is associated with a drop in lateral mobility of the lipids by two orders of magnitude, and an increase in the rotational correlation time of the same order of magnitude. The lipid headgroups, however, remain fluid. These observations are in agreement with experimental findings, and show that the nature of the ordered phase obtained with the CG model is indeed a gel rather than a crystalline phase. Simulations performed at different levels of hydration furthermore show that the gel phase is stabilized at low hydration. A simulation of a small DPPC vesicle reveals that curvature has the opposite effect.     

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba, Z. mauritiana and Z. spina-christi, with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z. mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba, probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba, the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.     

Evaluation of psychopharmacological effects of Clerodendrum phlomidis Linn. extract

The methanolic extract of Clerodendrum phlomidis Linn. (MECP) leaves was evaluated for its psychopharmacological activities in several experimental models using Swiss albino mice and Wistar albino rats. The MECP was found to cause significant reduction in spontaneous activity, and decreases in exploratory behavioral profiles by the Y-maze and head dip test. It also showed reduction in muscle relaxant activity by rotarod, 30° inclined screen and traction tests, as well as significantly potentiated the phenobarbitone sodium-induced sleeping time in the doses examined (200, 400 and 600 mg/kg body wt.). All the results were compared with respective controls for the evaluation of significance.     

Liquid-Like Behavior in Solids

Abstract

The van der Waals approach to predict liquid-vapor coexistence, becomes exact in the limit of weak, long-ranged attractive forces. However, for shorter ranged attractions, the liquid range shrinks and eventually disappears altogether. When the width of the attractive well becomes very small (less than 7% of the diameter of particles), an iso-structural solid-solid transition, reminiscent of the liquid-vapor transition, appears in the crystalline phase. This transition, that should be experimentally observable in certain colloidal suspensions, ends in a critical point. In quasi-two dimensional systems (e.g. confined colloids), this critical point induces the formation of a stable hexatic phase.     

On the phase transition in a monolayer adsorbed on graphite at temperatures below the 2D-critical temperature

Monte Carlo simulations in the grand ensemble and meso-canonical ensemble in which the adsorbent is connected to a finite reservoir have been used to study adsorption isotherms for monolayer argon adsorption on graphite at temperatures below the 2D-critical temperature in order to elucidate the microscopic details of the 2D-transitions: vapour–solid, vapour–liquid and liquid–solid. An S-shaped van der Waals (vdW) loop was found when a small square surface was used; however, for large square surfaces and rectangular surfaces the isotherms exhibit a vdW-type loop with a vertical segment which indicates the coexistence of two phases separated by a boundary that changes its shape with the loading. This coexistence occurs at the same chemical potential as determined by the mid-density scheme, developed by Do and co-workers (Z. Liu, L. Herrera, V.T. Nguyen, D.D. Do, and D. Nicholson, A Monte Carlo scheme based on mid-density in a hysteresis loop to determine equilibrium phase transition. Mol Simul. 37(11):932–939, 2011; Z. Liu, D.D. Do, and D. Nicholson, A thermodynamic study of the mid-density scheme to determine the equilibrium phase transition in cylindrical pores. Mol Simul. 38(3):189–199, 2011).     

Phosphatidylcholine bilayers A theoretical model which describes the main and the lower transitions

We present a theoretical model which describes both the main and the lower phase transition in phosphatidylcholine bilayers. The main transition involves a melting of the hydrocarbon chains while the lower transition is seen as a nematic to isotropic transition involving entire lipid molecules (which are rod shaped when projected onto the bilayer plane). This latter transition is consistent with experimental data which suggest the presence of long-axis rotation for temperatures below the main melting transtition. The model is extended to mixtures of phosphatidylcholines and compared with experimental data.     

Leaf development of the ostrich fern Matteuccia struthiopteris (L.) Todaro

The timing of emergence of the three different leaf types of Matteuccia struthiopteris is described from plants sampled over the course of a growing season. Vegetative leaves were first to appear, followed five weeks later by sporophylls and cataphylls. Leaf number and type, and total leaf dry weight per plant were assessed in weekly transects. Vegetative fronds contributed the most to total leaf dry weight, which increased during the first four weeks, and then remained constant for the remainder of the season. Cataphylls, although numerous by the end of the season, contributed little weight. Sporophylls occurred on the widest plants with the most vegetative leaves and greatest leaf weight, whereas cataphylls occurred on most plants except the smallest. Experimentally defoliated plants were re-examined in late summer. Following initial harvest, plants often produced a second smaller set of leaves. These were restricted to vegetative leaves and cataphylls. Ability to reissue leaves, especially vegetative fronds, declined very quickly after the first few weeks in the growing season. Defoliated plants draw on the extensive reservoir of developing leaves which are found on the rhizome, thus possibly diminishing the ability of the plant to withstand regular harvesting of the young fronds for food. Individual leaves were tagged and measured over the growing season. Non-linear regression curves fitted to the growth data for the three types of leaves indicate that growth was described best by a monomolecular growth curve for the vegetative and fertile fronds. Cataphyllar growth could be described equally well by either a monomolecular or a logistic function.