Primary Growth Process Research Articles

A low-cost approach for recycling large GdBCO bulk superconductors using an infiltration technique with different liquid sources

The high-temperature superconductor has become a research hotspot, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. Single-domain REBa2Cu3O7−δ (REBCO) superconductors, where RE is a rare-earth element such as Y, Gd, Sm or Nd, have wide and potential applications in high-tech fields, such as micro-magnet superconducting maglev trains, superconducting motors and superconducting magnetic separation systems. However, a large number of multi-domain samples are easily produced in the preparation process, resulting in a significantly lower success rate and a significant increase in cost, which restricts their practical applications. Thus, we successfully recycle a series of GdBCO samples by re-supplementing the liquid phase lost in the primary growth process and pre-treating the failed sample as solid-phase source billets, which was proposed by Shi. The growth morphology and superconducting properties of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the key superconductivity properties have been significantly improved, which provides the scientific basis and new ideas for the development of low-cost and highly efficient fabrication yields of REBCO bulk superconductors.

Fabrication process and superconducting properties of recycling multi-domain GdBCO bulk superconductors using improved infiltration technique

High temperature superconductor has become one of the hotspots of research, because of its high critical temperature, strong trapped flux density, stable suspension characteristics and large magnet levitation force. The single domain REBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–<i>δ</i></sub> (REBCO) superconductors have the wide and potential applications in the high-tech fields, such as micro-magnet superconducting maglev train, superconducting motor and superconducting magnetic separation system. However, a large number of multi-domain samples are easy to produce in the preparation process, which leads the success rate to decrease significantly and the cost to increase considerably, which restricts its practical application process. Inspired by the top seeded infiltration growth method, we develop a reliable method of recycling failed GdBCO sample by re-supplementing the liquid phase lost in the primary growth process and pretreating the failed sample as solid phase source billets. We recycle a series of GdBCO samples by using this new technique successfully. The growth morphology, superconducting properties, and microstructures of the recycled GdBCO bulk superconductors are investigated in detail in this study. The results show that the magnetic levitation forces of the recycled GdBCO samples are all greater than 30 N, their magnetic flux densities are all above 0.3 T, and their capture efficiencies are above 60%. These results provide the scientific basis and new ideas for developing the low cost and high efficient yield of fabrication of the REBCO bulk superconductors.

非对称Fe 3 O 4 -SiO 2 介孔纳米粒子的合成与性质

采用高温水解法合成了具有超顺磁性且表面修饰的Fe 3 O 4 纳米粒子, 将该Fe 3 O 4 纳米粒子作为种子, 采用非经典控核生长方法在其表面生长SiO 2 棒状结构, 获得了非对称Fe 3 O 4 -SiO 2 介孔纳米粒子, 通过调节硅源加入量调控非对称粒子棒状部分的长度. 由于一次生长出的结构尺寸有限, 使用二次生长法进一步增加纳米棒部分的长度, 最后对该非对称粒子进行了药物的装载与释放实验, 表明其对阿霉素具有缓释作用.

Distribution and Substitution Mechanism of Ge in a Ge-(Fe)-Bearing Sphalerite

The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on zones, could be the result of either a primary growth process, or alternatively, polystage crystallization, in which early Fe-Ge-rich sphalerite is partially replaced by Fe-Ge-poor wurtzite. FIB-SEM imaging shows evidence for replacement supporting the latter. Transformation of sphalerite into wurtzite is promoted by (111)* twinning or lattice-scale defects, leading to a heterogeneous ZnS sample, in which the dominant component, sphalerite, can host up to ~20% wurtzite. Ge K-edge XANES spectra for this sphalerite are identical to those of the germanite and argyrodite standards and the synthetic chalcogenide glasses GeS2 and GeSe2, indicating the Ge formally exists in the tetravalent form in this sphalerite. Fe K-edge XANES spectra for the same sample indicate that Fe is present mainly as Fe2+, and Cu K-edge XANES spectra are characteristic for Cu+. Since there is no evidence for coupled substitution involving a monovalent element, we propose that Ge4+ substitutes for (Zn2+, Fe2+) with vacancies in the structure to compensate for charge balance. This study shows the utility of synchrotron radiation combined with electron beam micro-analysis in investigating low-level concentrations of minor metals in common sulfides.

Pinus halepensis Mill. crown development and fruiting declined with repeated drought in Mediterranean France

The objectives of this study were to describe and quantify Aleppo pine aerial primary growth processes and to assess their relationships with climate. Primary growth (branch length growth, branching rate, polycyclism, needle number and size, fruiting), i.e. crown development and reproduction, was reconstructed for the last 16 years in Mediterranean France. From 1998 to 2007, climate has been far hotter and drier than normal in South-eastern France. All variables related to crown development and fruiting, as well as radial growth, significantly declined after 2003 heat wave and during repeated droughts from 2004 to 2007. A partial recovery of most parameters occurred from 2008 to 2010 on vigorous branches while frail branches showed less improvement. The limited crown development during unfavourable years may significantly hold back tree potential photosynthetic biomass for several following years and contribute to a slower than expected recovery of tree growth or to delayed die-back.

Synoptic and Topographic Variability of Northern California Precipitation Characteristics in Landfalling Winter Storms Observed during CALJET

Abstract Observations from northern California during the California Landfalling Jets (CALJET) experiment are used to examine the mean characteristics of precipitation and their variances as functions of synoptic and topographic regimes. Ten cases involving the landfall of extratropical cyclones are analyzed with radar and rain gauge data collected at two sites: one in the coastal mountains north of San Francisco (CZD) and the other in the Central Valley just west of Sacramento (KDAX). Aside from the melting-layer bright band, the most striking feature in the 10-case composite vertical profile of radar reflectivity at CZD was a distinct change in slope about 2.5 km above the bright band. This “shoulder” is thought to represent a change in the growth rate of hydrometeors. Although the bright band was quite distinct, about one-third of the profiles in the composite did not exhibit this feature. These nonbrightband (NBB) profiles had a low-level slope where reflectivity increased with decreasing altitude, a structure suggesting that collision–coalescence was the primary growth process. The relationship between surface rainfall rate and low-level radar reflectivity implies that all profiles were composed of larger numbers of small drops than expected from a Marshall–Palmer drop size distribution, a trend that was especially apparent for NBB profiles. Synoptic variability of precipitation characteristics at CZD were examined by identifying five distinct regimes (cold sector, warm front, warm sector, cold front, and cool sector) based on a simplified conceptual model. The shoulder remained approximately 2.5 km above the bright band in each regime. Rainfall intensity was highest during the cold-frontal regime and NBB rainfall was most common during the warm-frontal, warm-sector, and cool-sector regimes. Topographic variability of precipitation characteristics was investigated by comparing results at CZD and KDAX. A shoulder structure located about 2.5 km above the bright band was also evident in the KDAX profiles, suggesting that this feature is related to large-scale dynamic, thermodynamic, and microphysical processes rather than orographic effects. The relationship between surface rainfall rate and low-level radar reflectivity near KDAX closely followed a trend expected for a Marshall–Palmer drop size distribution, implying the presence of relatively larger raindrops than observed at CZD and indicating that NBB rainfall occurs less frequently near KDAX.

Cell Differentiation Is a Primary Growth Process in Developing Limbs of Artemia

The limb of the brine shrimp Artemia develops over a four-instar period when the protopod, endite, exopod, endopod, and epipod are defined and cell differentiation (change in cell shape) occurs. To understand the importance of cell differentiation in limb growth, development of the epidermis was studied in the first thoracopod of instar V-VIII larvae. Each region was established by instar V, and the larval epidermal cells developed into general epidermal (GEC), tendinal, setal, or transport cells by instar VI. Basal extensions of the GECs formed pillar structures. The epidermal cells decreased in height from 10 to 4 microm by instar VI. Increase in length and width resulted from both cell replication and expansion of the apical cell surface in differentiating cells. Growth occurred mainly by cell replication in instar V, whereas expansion of the cell surface in GEC and setae was the major growth process in instar VII. Increase in apical cell surface area occurred primarily by change in cell shape from columnar to squamous during instar V and by increase in total cell surface in subsequent instars. The results demonstrated that cell differentiation is a significant component of growth during limb development.

Fusicoccin-induced cell elongation and endogenous fusicoccin-like ligands in germinating seeds

As cell elongation is the primary growth process at early seed germination, we studied the influence of fusicoccin A (FC A) on growth initiation in axial organs in parallel with endogenous fusicoccin-like ligands (FLL) in germinating seeds in which initial and subsequent growth of axes occurs only by cell elongation. In quiescent broad beans ( Vicia faba var. minor L.), exogenous 20 μM FC A promoted radicle emergence by inducing earlier initiation of cell elongation first in the hypocotyl, then in the radicle. Prior to initiation of elongation, FLL appeared in the axes and acidification of cell walls sharply increased. In nondormant horse chestnut ( Aesculus hippocastanum L.) seeds, treatment with 100 μM FC A promoted radicle protrusion and further growth of axial organs by cell elongation. FLL were absent from the axes at dormancy, but appeared when the seeds acquired germinability and remained during germination. Their presence was also accompanied by enhanced cell wall acidification which was sensitive to diethylstilbestrol (DES) and attributed to plasmalemma H +-ATPase. Endogenous FCs or FC-like compounds are presumed to participate in the regulation of cell preparation for elongation and then axis elongation. Therefore, the system of cell elongation response comprises not only FC receptors and H +-ATPase, but previously unreported endogenous FC-like compounds as well.

A scaling growth model for bubbles in basaltic lava flows

Pahoehoe, an and massive lavas from Mount Etna show common statistical properties from one sample to another which are independent of scale/size over certain ranges. The gas vesicle distribution shows two scale-invariant regimes with number density n(V) α V −B−1 where V is the volume and empirically B ≈ 0 for small bubbles and B ≈ 1 for medium to large bubbles. We introduce a bubble growth model which explains the B > 1 range by a strongly non-linear cascading growth regime dominated by a quasi-steady-state coalescence process. The small bubble region is dominated by diffusion; its role is to supply small bubbles to the coalescence regime. The presence of measured dissolved gas in the matrix glass is consistent with the notion that bubbles generally grow in quasi-steady-state conditions. The basic model assumptions are quite robust with respect to the action of a wide variety of processes, since we only require that the dynamics are scaled over the relevant range of scales, and that during the coalescence process, bubble volumes are (approximately) conserved. The model also predicts a decaying coalescence regime (with B > 1) associated with a depletion of the gas source or, alternatively, a loss of large vesicles through the surface of the flow. Our model thus explains the empirical evidence pointing to the coexistence of two different growth mechanisms in subsurface lava flows, but acting over distinct ranges of scale, with non-linear coalescence as the primary growth process. The total vesicularity of each sample can then be well estimated from the partial vesicularity of each growth regime without any outlier problems.

An approach to the formation and growth of new phases with application to polymer crystallization: effect of finite size, metastability, and Ostwald's rule of stages

This article aims to link the mainstream subject of chain-folded polymer crystallization with the rather speciality field of extended-chain crystallization, the latter typified by the crystallization of polyethylene (PE) under pressure. Issues of wider generality are also raised for crystal growth, and beyond for phase transformations. The underlying new experimental material comprises the prominent role of metastable phases, specifically the mobile hexagonal phase in polyethylene which can arise in preference to the orthorhombic phase in the phase regime where the latter is the stable regime, and the recognition of “thickening growth” as a primary growth process, as opposed to the traditionally considered secondary process of thickening. The scheme relies on considerations of crystal size as a thermodynamic variable, namely on melting-point depression, which is, in general, different for different polymorphs. It is shown that under specifiable conditions phase stabilities can invert with size; that is a phase which is metastable for infinite size can become the stable phase when the crystal is sufficiently small. As applied to crystal growth, it follows that a crystal can appear and grow in a phase that is different from that in its state of ultimate stability, maintaining this in a metastable form when it may or may not transform into the ultimate stable state in the course of growth according to circumstances. For polymers this intermediate initial state is one with high-chain mobility capable of “thickening growth” which in turn ceases (or slows down) upon transformation, when and if such occurs, thus “locking in” a finite lamellar thickness. The complete situation can be represented by a P, T, 1/l (l ≡ crystal thickness) phase-stability diagram which, coupled with kinetic considerations, embodies all recognized modes of crystallization including chain-folded and extended-chain type ones. The task that remains is to assess which applies under given conditions of P and T. A numerical assessment of the most widely explored case of crystallization of PE under atmospheric pressure indicates that there is a strong likelihood (critically dependent on the choice of input parameters) that crystallization may proceed via a metastable, mobile, hexagonal phase, which is transiently stable at the smallest size where the crystal first appears, with potentially profound consequences for the current picture of such crystallization. Crystallization of PE from solution, however, would, by such computations, proceed directly into the final stage of stability, upholding the validity of the existing treatments of chain-folded crystallization. The above treatment, in its wider applicability, provides a previously unsuspected thermodynamic foundation of Ostwald's rule of stages by stating that phase transformation will always start with the phase (polymorph) which is stable down to the smallest size, irrespective of whether this is stable or metastable when fully grown. In the case where the phase transformation is nucleation controlled, a ready connection between the kinetic and thermodynamic considerations presents itself, including previously invoked kinetic explanations of the stage rule. To justify the statement that the crystal size can control the transformation between two polymorphs, a recent result on 1 -4-poly-trans-butadiene is invoked. Furthermore, phase-stability conditions for wedge-shaped geometries are considered, as raised by current experimental material on PE. It is found that inversion of phase stabilities (as compared to the conditions pertaining for parallel-sided systems) can arise, with consequences for our scheme of polymer crystallization and with wider implications for phase transformations in tapering spaces in general. In addition, in two of the Appendices two themes of overall generality (arising from present considerations for polymers) are developed analytically; namely, the competition of nucleation-controlled phase growth of polymorphs as a function of input parameters, and the effect of phase size on the triple point in phase diagrams. The latter case leads, inter alia to the recognition of previously unsuspected singularities, with consequences which are yet to be assessed.

Assessment of ice particle growth processes at dye-3, Greenland

As part of the DGASP program on the Greenland Ice Sheet, an investigation was conducted into the nature of ice particle formation processes that result in the formation of snow. Ice particle habits were determined using Formvar replicas of falling snow crystals. From these measurements an assessment of the primary growth process and altitude of formation was made. Results indicate that the scavenging of cloud water by falling ice particles, growth by accretion or riming, rarely occurs. However, when riming does occur, it is usually associated with warmer air masses from the south. The occurrence of riming was also observed to be dependent on the season, with a greater frequency occurring during warmer months. It was estimated that ice particle riming contributes less than 5% of the average annual water mass, but up to 30% of the deposition of some chemical species, deposited to the Greenland Ice Sheet at Dye 3. Ice particle habits indicate that they originate at higher altitudes above the ice cap in summer than in winter. Variations in the magnitude of ice particle riming, the elevation of origin of ice particles, the meteorology and the season of the year are all essential when interpreting snow chemistry and comparing snow and aerosol chemistry at Dye 3.

Infrared depth profiling studies of recrystallization in laser-amorphized poly(ethylene terephthalate)

Infrared depth profiling and time-resolved infrared spectroscopy have been used to study recrystallization in laser-amorphized films of poly(ethylene terephthalate) (PET). Laser amorphization of the sample film produces a situation in which both primary and secondary crystallization processes can be independently observed in the subsequent recrystallization of the film. The data are consistent with a model in which recrystallization is nucleated by the interface of laser-amorphized and untreated PET followed by an oriented primary growth process which propagates from this interface toward the surface of the film. Random secondary crystallization processes increase the degree of order in portions of the film which have undergone primary crystallization

Biosynthesis and control of β-lactam antibiotics: The early steps in the “classical” tripeptide pathway

The interaction between growth and secondary metabolism develops from physiological responses of the producer organism to its environment. Nutrients are channelled into primary growth processes or into secondary processes such as antibiotic biosynthesis by a variety of metabolic contols, the nature of which has been extensively studied in organisms producing β-lactam antibiotics via the tripeptide, δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine. In the following article we review the early stages of β-lactam biosynthesis in fungi and actinomycetes, keeping in mind the regulation of primary pathways that provide the amino acid precursors of this group of antibiotics, as well as the regulation of the secondary pathway itself. Of special importance to organisms engaging in secondary metabolism are the control mechanisms that suppress the nonessential process during rapid growth but allow secondary metabolic genes to be expressed and resources to be diverted when environmental factors generate the appropriate biochemical signals.

Shoot morphology and growth pattern in seedlings of Pinusbrutia provenances

The process of primary growth in 2-year-old seedlings of six Pinusbrutia Ten. provenances is described. At the end of the first growing season, two types of shoot morphology were observed: type 1, a terminal winter bud, and type 2, a terminal rosette of primary needles protecting the meristematic apex. During the 2nd year the seedlings exhibited a succession of shoots (varying in number from one to five), each of which was due to the elongation of a new apical bud. Morphological observations along with an anatomical examination of the winter bud led to the conclusion that the growth pattern in juvenile P. brutia is monocyclic with a variable number of summer shoots (using the terminology proposed by Lanner (Lanner, R.M. 1976. In Tree physiology and yield improvement. Editedby M.G.R. Cannell and F.T. Last. Academic Press, London, pp. 223-243)). The provenances studied differed both in growth potential and in seasonal growth pattern (differences in number of shoots, ratio of spring shoot to total growth, growth rate). Two groups could be identified: (i) the provenances of the island of Crete, which had a low growth potential and short growing season, and (ii) the high-altitude provenances of inland Turkey, with high growth potential and a growth rate that peaked in summer.

Relations between apical structure and growth patterns in Pinus halepensis Mill, seedlings

Abstract The process of primary growth in 2-year-old seedlings of 11 populations of Pinus halepensis Mill. is described. At the end of the first growing season one type of apical structure was observed: type-1, a tuft of primary needles placed close together, surrounding and protecting a meristematic apex. At the end of the 2nd growing season, three types of apical structure were observed: type-1; type-2, a terminal winter bud; and type-3; a «bud» with characteristics of both type-1 and type-2. Morphological observation along with an anatomical examination of the winter bud led to the conclusion that the definitive growth pattern in juvenile P. halepensis is monocyclic with a variable number of summer shoots. This growth pattern is reached by some P. halepensis populations in 3–4 years, by contrast, in other pine species two years are usually needed. The populations studied differed both in growth potential (differences in number of cycles, ratio of first cycle to total growth, growth rates) and in the de...

A New Monte-Carlo Simulation Model for the Temporal Development of Cloud Droplet Spectra

Abstract A new Monte-Carlo simulation model for computing the temporal development of cloud droplet spectra is presented. Since the simulation is carried out in probability space, the new model does not need to follow the growth history and position of each and every drop. Additional physical processes, such as turbulence, electrical effects, glaciation, etc., can be added to the primary growth process of gravitational coagulation with relative case. The main features of the model are demonstrated by several numerical examples.