Nucleation-controlled growth in polyethylene single crystals: Growth and shape of {100} sectors

The nucleation rate and propagation rate of steps on the {100} faces of polyethylene crystals have been determined. For single crystals, under conditions where the width of the {100} sectors remains constant during growth, it is confirmed that the growth is in regime I or the crossover region between regime I and II. In {110} twinned crystals, the {100} sectors are well developed and the width increases linearly with time; therefore, the growth in the twins must be in regime II. It is shown that the differing growth regimes of {100} faces in single crystals and twins allow the independent determination of the nucleation rate and the propagation rate of steps. The nucleation rate and propagation rate of steps on the {100} faces were determined from measurements of the constant width of the {100} faces in single crystals and the growth rate of the {100} faces in single crystals and twins. The observed rates show abnormal dependence on supercooling and concentration. The results are attributed to a weaker dependence of the constant width of {100} sectors on supercooling and concentration than predicted.     

Single-molecule orientations in dyed salt crystals

We present single-molecule confocal microscopy studies of orientational distributions for luminophores isolated in potassium hydrogen phthalate (KAP) crystals. The incorporation of dye molecules that bear no size or shape similarity to the host ions is observed, demonstrating that single-molecule studies on mixed crystals need not be restricted to isomorphous host/guest pairs. Violamine R is oriented and overgrown by the fast vicinal slopes of growth hillocks within the symmetry-related {010} growth sectors and DCM deposits in the {11} growth sectors of KAP. Both mixed crystals exhibit modest absorption dichroism relative to basic pyranine-doped K(2)SO(4). The latter was studied to ensure that a range of orientations was sampled in our experiments. Average orientations determined at the single-molecule level were in close agreement to ensemble-averaged measurements for all three systems, and the chromophore orientational distributions were broader than anticipated, indicating that the crystals incorporate guest molecules in a range of orientations outside the measured ensemble average.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5 μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5?μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Effect of sunset yellow dye on morphological,optical, dielectric,thermal and mechanical properties of KDP crystal

Herein, we describe the growth and morphology of well-defined dyed crystals of KH₂PO₄ (potassium dihydrogen orthophosphate; KDP) containing organic azo (sunset yellow; SSY) dye in the {1 0 1} & {0 0 1} pyramidal growth sectors. An understanding on selective dye inclusion in various growth sector of host crystal is proposed, which will help in designing novel tailor-made dyed photonic crystals. The structural analysis and the identification of various functional groups present in as grown KDP crystals were carried out using powder XRD, FTIR and Raman studies. Solid state transmittance spectra for dyed KDP crystals displayed three absorption peaks at 230 nm, 311 nm and 477 nm, which were blue shifted for SSY dye in KDP crystal relative to neutral aqueous solution of SSY dye. These blue shifts in the absorption maxima confirm the successful incorporation of sunset yellow dye into the pyramidal growth sectors of dyed KDP crystals. The band around 409 nm in the photoluminescence emission spectrum indicates a violet emission. SSY dye doped KDP crystals showed enhanced dielectric properties and thermal stability as compared to pure KDP crystal. The mechanical strength of the KDP crystals estimated using Vickers microhardness test was found to decrease with the increase in SSY dye doping.     

Influence of SiO_3~（2-）Impurity on the Optical Properties of KDP Crystal

In this paper,potassium dihydrogen phosphate(KDP) crystals were grown in the presence of a series of silicate(SiO32-) impurity concentrations via conventional temperature cooling and rapid growth methods,respectively.It revealed that the SiO32-impurity could lead to the decrease of transmittance at the region of ultraviolet band for pyramidal sectors and slightly increased the transmittance for prismatic sectors.SiO32-could enter into the crystal lattice and create lattice defects,which consequently increased the density of light scatter.The decrease of laser damage threshold was attributed to the lattice defects and the redundant electrons brought by the replacement of SiO32-at the PO43-position.     

Study on the Growth and Quality of Potassium Dihydrogen Phosphate Grown from Acid-doped Solution

Potassium dihydrogen phosphate （KDP） single crystals have been grown respectively at the rates of about 1 and 20 mm/day from the pure and acid-added solutions by temperature reduction method. The effects of acid and supersaturation on the shape and size of grown crystals were compared and discussed. Samples were cut from different parts of the as-grown crystals for investigating the optical quality, including transmissibility, scattering centers and laser damage threshold. It is found that the stability of KDP growth solution improves to some extent and the growth rates in x- and z-directions have great difference after adding acid. Moreover, the acid causes remarkable differences in optical quality between prismatic and pyramidal sectors.     

Mono- and bivalent ligands bearing mannose 6-phosphate (M6P) surrogates: targeting the M6P/insulin-like growth factor II receptor

[reaction: see text] Mannose 6-phosphate mimics locked into the alpha-configuration and bearing hydrolase-resistant phosphate surrogates were synthesized and evaluated for binding affinity to the mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R). Affinity increases as the phosphate surrogate is varied in the order malonyl ether < malonate < phosphonate. An alkene cross-metathesis approach to sought-after bivalent M6P-bearing ligands is also described. These compounds were designed to map onto biantennary sectors of high-mannose-type oligosaccharides carried by glycoprotein M6P/IGF2R ligands.     

Enzymatic degradation of poly(octamethylene suberate) lamellar crystals

Enzymatic degradation of poly(octamethylene suberate) single crystals was investigated by electron microscopy. Different lamellar morphologies were obtained using 2.5-hexanediol as a solvent and at a temperature between 42 and 51 °C. Crystals with a different degree of truncation and with monolayer or bilayer organization were analyzed. Lipases from Rhizopus oryzae were found to be highly effective in degrading crystalline domains and showed different attack mechanisms. Thus, enzymes preferentially attacked the lateral crystal growth faces or the lamellar fold surfaces depending on the crystallization conditions. Temperature and indeed its fluctuation during the crystallization process were crucial to determine how degradation started and progressed. The most interesting results were obtained for single crystals characterized by a low degree of truncation and formed in crystallization baths with a small temperature oscillation. In this case, it was shown that degradation started on the folding surface of specific sectors and progressed along a preferred crystal direction.     

Accelerated Approach to the Synthesis of Fluoriated Polyether Dendrimers

Fluorine-containinglinear0rcascadepolymersexhibitexcellentthermalstabilityandoxidativeresistance,g00delectricalpropertiesands0lventresistance,andareexcellentcandidatesf0radvancedmaterialsI'2.Replacementofhydr0genwithfluorineyieldsanoxidativelyandthermallystablepolymer,anobservationattributedtotheC-Fb0nd3.However,litterattentionhasbeenpaidt0theflu0rine-c0ntainingdendrimersf0ralongtime.Theworkrep0rtedhereinc0ncernsthesynthesisofpolyetherdendrimersupt0thethirdgeneration,inwhichtheoutertier0fphen…     

Influence of solid solution formation on polarity: molecular modeling investigation of the system 4-chloro-4'-nitrostilbene/4,4'-dinitrostilbene

Growth-induced polarity formation in solid solutions composed of dipolar 4-chloro-4'-nitrostilbene molecules and nonpolar 4,4'-dinitrostilbene molecules was investigated by means of two molecular modeling procedures. Calculation of the mixing energy in the bulk structures predicted solid solution formation within the whole composition range. Computation of the interaction energies present at growing surfaces allowed the distribution coefficient as well as the fraction of dipoles in either the up or down orientation to be calculated by a mean-field model. Miscibility and polarity were found to vary for the faces (hkl) investigated, leading to crystals composed of sectors with different compositions and polarities. The present study highlights the fact that a solid solution crystal may not be a homogeneous entity and that surface effects arising during slow growth can have an impact on solid state properties.     

Deformation morphology of polyester single crystals

Truncated, six-sided single crystals of a 10–16 linear polyester were grown from dilute solution in hexanol, deposited onto Mylar film, and uniaxially deformed at room temperature. For elongations below 10%, the crystals deform uniformly; however, above 20% elongation many cracks spanned by fibrils of 300 Å diameter develop approximately normal to the applied stress direction. Depending on the position of the crystal relative to the draw direction, lateral buckling pleats and cleavage cracks can also occur. Collapse of the nonplanar crystals onto the substrate with a resulting nonuniform adherence of the crystal influences the deformation. The deformation morphology is compared to that of truncated sixfold sector polyethylene crystals. Most notably, in contrast to polyethylene, {010} fold sectors do not deform differently from {110} fold sectors and phase boundaries between {110} and {010} fold sectors do not fracture easily.     

Gas-phase ion chemistry and organic chemistry-the story of a hybrid six sector mass spectrometer--the "AutoSpec 6F"

The AutoSpec 6F mass spectrometer is a large, floor standing instrument comprising a pair of commercial EBE geometry (AutoSpec) mass spectrometers coupled in series to provide an hybrid EBE-EBE configuration, (E and B being respectively electrostatic and magnetic sectors.) It was designed in close collaboration between Professor R. Flammang and VG Analytical in Manchester, UK. It was equipped with five collision cells and allowed the recording of high energy CID (collision induced dissociation), MIKES (mass analyzed ion kinetic energy spectrometry) and NRMS (neutralization re-ionization mass spectrometry) data as well as consecutive MSn analyses. The field-free regions between sectors allowed the study of unimolecular decomposition products from long-lived metastable ions. The mass spectrometer became even more versatile when an RF-only quadrupole collision cell was installed between the second and the third electric sector. This allowed the study of associative ion/molecule reactions in the low kinetic energy regime. Bimolecular chemical reactions were performed inside the quadrupole cell when a neutral reagent was introduced and the reaction products were analyzed by high energy CID in the downstream sectors. This paper tells the history and summarizes the capabilities of this versatile instrument.     

Polymer decoration study in chain folding behavior of solution-grown poly(ethylene oxide) crystals

The polymer decoration method based on the vaporization and condensation-crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution-grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c-axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.     

工艺参数对TSMTG法制备单畴YBCO样品的影响

用顶部籽晶熔融织构法(TSMTG)制备了30min直径的YBCO超导块，研究了不同的工艺条件对样品宏观形貌、织构取向和磁浮力的影响，比较了3种样品在零场冷条件下的排斥力和场冷条件下的吸引力。结果发现：由籽晶控制取向生长的单畴YBCO样品宏观形貌是以顶部籽晶为中心的4个结晶扇区，有单一的c轴取向，零场冷条件下的排斥力和场冷条件下的吸引力最大；籽晶成核但没有控制取向生长的YB-CO样品宏观形貌是以顶部籽晶为中心的多个(大于4个)扇区，相邻扇区间夹角不等，c轴取向不一致，磁浮力性能居中；非籽晶成核生长的多畴YBCO样品，上表面是以籽晶为中心的一个边长约1cm的四方结晶区，其余部分是自发成核的多晶，样品c轴取向杂乱，磁浮力很低。     

Dyeing uric acid crystals with methylene blue

The growth of anhydrous uric acid (UA) and uric acid dihydrate (UAD) crystals from supersaturated aqueous solutions containing methylene blue, a cationic organic dye, has been investigated. Low concentrations of dye molecules were found to be included in both types of crystal matrixes during the growth process. Incorporation of dye into UA crystals occurs with high specificity, affecting primarily [001] and [201] growth sectors, while UAD crystals grown from solutions of similar dye concentration show inclusion but little specificity. The orientation of the UA-trapped species was determined from polarization data obtained from visible light microspectrometry. To achieve charge neutrality, a second anionic species must also be included with the methylene blue into UA and UAD crystal matrices. Under high pH conditions, crystallization of 1:1 stoichiometric mixtures of methylene blue and urate yields methylene blue hexahydrate (MBU.6(H2O). The crystal structure of MBU.6(H2O) reveals continuous pi-pi stacks of planes of dye cations and urate anions mediated by water molecules. This structure provides an optimal geometry for methylene blue-urate pairs and additional support for the incorporation of these dimers in uric acid single-crystal matrices. The strikingly different inclusion patterns in UA and UAD demonstrate that subtle changes in the crystal surfaces and/or growth dynamics can greatly affect recognition events.     

Beiträge zur mikrochemischen analyse langlebiger uranspaltprodukte in staubproben

A microchemical qualitative and quantitative separation process for long-lived radionuclides from uranium fission (Cs, Sr, Ce, Zr, Ru) in dust samples is described. The loaded dust filter is moistened with carrier solution and with borax-sodium carbonate, and ashed in an electrically heated platinum spiral; the dust is thus decomposed, forming beads. The solution of the bead in dilute acid is concentrated in a ring with the ring oven ; the paper bearing the radioactive ring is cut into sectors and a specific precipitation reaction is applied for each nuclide in separate sectors. Identification and determination are carried out by autoradiography of the sectors. Practical testing was done with a 2.5-year old dust sample originating from nuclear studies in 1961–62 ; radioactive Cs, Sr and Ru were detected in 1.7 mg of dust ash. The quantitative evaluation of strontium-90 of the order of 10^-12 C showed the sensitivity of the method. The range of application of the method is indicated.     

Kinetic ordering of atoms in sodium chlorate-bromate solid solutions

Kinetic ordering of anions in Na((ClO₃)_1−x(BrO₃)_x) solid solutions with anomalous birefringence was studied by means of single crystal X-ray diffraction. The crystal structures of the two samples (x=0.10 and 0.255) cut out from the {100} growth sectors were refined in the ideal space group P2₁3 and in two of its subgroups—monoclinic P2₁ and triclinic P1 with R=0.030-0.038. The final choice of monoclinic symmetry was confirmed by the analysis of the diffraction pattern and Cl/Br distribution over the halogen crystallographic sites. The Cl/Br ordering reflects the geometrical difference of these sites with respect to the growth front orientation. The observed optical indicatrix was successfully reproduced in the point-dipole approximation. According to our data and the data of Crundwell et al. (Acta Crystallogr. Sect. B 53 (1997) 189), the degree of ordering increases in the middle of the isomorphous series along with the birefringence. The obtained results confirm the hypothesis of growth dissymmetrization.     

Poly-β-hydroxybutyrate and Exopolysaccharide Biosynthesis by Bacterial Isolates from Pigeonpea [<Emphasis Type="Italic">Cajanus cajan</Emphasis> (L.) Millsp] Root Nodules

The bacterial strains that are able to produce biopolymers that are applied in industrial sectors present a source of renewable resources. Some microorganisms are already applied at several industrial sectors, but the prospecting of new microbes must bring microorganisms that are feasible to produce interesting biopolymers more efficiently and in cheaper conditions. Among the biopolymers applied industrially, polyhydroxybutyrate (PHB) and exopolysaccharides (EPS) stand out because of its applications, mainly in biodegradable plastic production and in food industry, respectively. In this context, the capacity of bacteria isolated from pigeonpea root nodules to produce EPS and PHB was evaluated, as well as the cultural characterization of these isolates. Among the 38 isolates evaluated, the majority presented fast growth and ability to acidify the culture media. Regarding the biopolymer production, five isolates produced more than 10 mg PHB per liter of culture medium. Six EPS producing bacteria achieved more than 200 mg EPS per liter of culture medium. Evaluating different carbon sources, the PHB productivity of the isolate 24.6b reached 69% of cell dry weight when cultured with starch as sole carbon source, and the isolate 8.1c synthesized 53% PHB in dry cell biomass and more than 1.3 g L⁻¹ of EPS when grown using xylose as sole carbon source.     

Variation of β-galactosidase expression from Mudlac elements during the development of Escherichia coli colonies

Bacterial colonies reveal the action of systems for multicellular regulation of genetic activity during growth and development. Colonies produced on agar indicator medium by Escherichia coli strains carrying the transposable genetic fusion element Mudlac displayed organized patterns of differential β-galactosidase expression. One feature of these patterns was the presence of phenotypically distinct concenric rings containing cells that were not genetically distinct. A second feature of the patterns was the appearance of sectorial populations with novel phenotypes, frequently displaying coincident variation in several characters, such as enzyme activity, multicellular aggregation and rate of spread over the agar substrate. Subcloning analysis of sectors with more expansive growth phenotypes revealed that they contained bacteria expressing novel developmental sequences on more than one kind of medium. These novel developmental sequences could be transmitted to progeny bacteria but were reversible during growth in liquid medium. More stable clonal variation in patterns of β-galactosidase expression arose during storage in liquid medium. Most of these changes correlated with transpositions or rearrangments of Mudlac sequences. Some changes in β-galactosidase expression involved interactions between Mudlac elements and unlinked Mu derivatives. These results revealed the operation of novel control systems regulating β-galactosidase expression from the lacZ sequences in a chromosomal Mudlac element and demonstrated at least two different kinds of clonal variation events which affected pattern formation in bacterial colonies.