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  • 1
    Electronic Resource
    Electronic Resource
    Small-Angle X-ray and Neutron Scattering from Bulk and Oriented Triblock Copolymer Gels (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 2054-2062 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00110a045
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  • 2
    Electronic Resource
    Electronic Resource
    Ontogeny of proventitious epicormic buds in Quercus petraea. I. In the 5 years following initiation (1998)
    Springer
    Trees 13 (1998), S. 54-62 
    Details
    ISSN: 0931-1890
    Keywords: Key words Epicormic potential ; Meristematic area ; Proventitious bud ; Quercus petraea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The persistence of large epicormic shoots is one of the main factors that reduces timber quality and value in Quercus petraea. The early phases of epicormic shoot formation, i.e. the initiation of the epicormic buds, their survival and their proliferation over the years, are not clearly understood. In the present work, we studied the initiation of the axillary buds giving rise to epicormic buds and shoots, and followed their behaviour during the first 5 years using both scanning electron microscopy and light microscopy. Two types of proventitious epicormic buds have been identified. The first type has small axillary buds associated with the rings of bud-scale scars which are found at the base and tip of each growth unit. These buds are made of a terminal meristem surrounded only by scales; no leaf primordium is detected. During the second and third years of epicormic life, meristematic areas appear in the scale axil. Progressively, the meristematic areas organize into secondary bud primordia composed solely of the terminal meristem surrounded by scales. The second type of epicormic bud has secondary buds produced by a large axillary bud when this large bud either developed into a shoot or partially abscised. The epicormic potential in Q. petraea is characterized by a balance between the epicormic buds in apparent rest, enclosing meristematic areas and secondary bud primordia, and their mortality over the years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009737
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  • 3
    Electronic Resource
    Electronic Resource
    Ontogeny of the proventitious epicormic buds in Quercus petraea. (1999)
    Springer
    Trees 14 (1999), S. 83-90 
    Details
    ISSN: 0931-1890
    Keywords: Key words  Quercus petraea ; Epicormic bud ; Proventitious ; Vascular trace
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia. The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk, but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when epicormic buds develop into shoots.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009755
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  • 4
    Electronic Resource
    Electronic Resource
    Chemical vapor deposition of B-doped polycrystalline diamond films: Growth rate and incorporation efficiency of dopants (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7404-7406 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth rate and the incorporation efficiency of dopants have been studied in the case of chemical vapor deposition of B-doped polycrystalline diamond films. The deposition rate is found to decrease with the addition of diborane in the gas phase. This is correlated with a modification of the plasma chemistry as observed by emission spectroscopy (decrease in the H/H2, CH/H, and C2/H ratios with the addition of diborane). The concentration of boron incorporated in the films is observed to vary with the square of the boron concentration in the gas phase. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360393
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  • 5
    Electronic Resource
    Electronic Resource
    Electrical conduction and deep levels in polycrystalline diamond films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6633-6638 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the dark conductivity (field, temperature, and frequency dependence), and the photoconductivity in undoped polycrystalline diamond films. Detailed analysis reveals that either of two alternative models can be invoked to explain all the observed features of the dark conductivity. The first model is a Hill-type hopping conduction involving the presence of discrete acceptor states located at 0.91 eV above the valence band with a density around 1017 cm−3. The second model involves the presence of a band-tail of acceptor states extending about 1 eV above the valence band. In this case, variable range hopping conduction dominates at low fields with a density of states at the Fermi level around 5×1015 cm−3 eV−1, while space charge limited currents dominate at high fields. The states controlling the dark conductivity give rise to photoconduction with a threshold around 0.85 eV and a peak at 1.1 eV. The shape of the photoconductivity spectrum suggests that lattice relaxation (with a Franck-Condon shift around 0.08 eV) occurs at these states. Peaks in the photoconductivity at 1.4 eV and at 1.9 eV give evidence for the presence of deeper states in these films. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360485
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of heavily B-doped polycrystalline diamond films using Raman spectroscopy and electron spin resonance (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7059-7062 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Heavily B-doped polycrystalline diamond films ([B](approximately-greater-than)1019 cm−3) are studied by Raman spectroscopy and electron spin resonance. The formation of an impurity band is accompanied by a Fano-type interference for the one-phonon scattering. Bands at 1200 and 500 cm−1 are observed in Raman spectroscopy for concentrations above 1020 cm−3. They are related to maxima in the phonon density of states, and are ascribed to disordered regions or crystalline regions of very small size. The concentration of defects associated with the paramagnetic signal observed around g=2.0030 increases drastically above 1021 B cm−3. The Mott insulator-metal transition is accompanied by the presence of a new paramagnetic signal (g=2.0007 for 2×1020 B cm−3, g=1.9990 for 1021 B cm−3) ascribed to free holes in the impurity band. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360410
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  • 7
    Electronic Resource
    Electronic Resource
    Boron implantation/in situ annealing procedure for optimal p -type properties of diamond (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2264-2266 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Record values for high Hall mobility and for low compensation ratio of boron doped diamond by ion implantation are reported. These are achieved, following the suggestion by Prins, by low dose Boron implantation into cold diamond (−97 °C) and in situ rapid heating (1050 °C for 10 min) and by a further anneal at higher temperature (1450 °C for 10 min). Detailed evaluation of Hall effect data and of the temperature dependence of the resistivity over a wide temperature range (200 to 700 K) prove that this implantation/annealing scheme yields p-type behavior of the implanted layer with the highest hole mobility (385 cm2/V s, at room temperature) and the lowest compensation ratio (0.05) ever reported for diamond doped by ion implantation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115879
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of Hexagonal and Lamellar Mesoporous Silicas, Aluminosilicates and Gallosilicates by Small-Angle X-ray Scattering (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 1065-1074 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Various mesoporous silicas and the corresponding aluminosilicates or gallosilicates have been synthesized using a series of literature or `home made' recipes. The efficiency of Al or Ga incorporation in the siliceous walls of these materials depends markedly on the trivalent source and the evolution (ageing) of the so-formed Si-MIII gel-type phases at different starting pH values and temperatures, after adding the surfactant-structuring compounds. Crystallization at low temperature (e.g. 〈 373 K) yielded mesoporous compounds with hexagonal topology (MCM-41 type), involving double-layered Si walls possibly partly substituted by Al or Ga. Such structures remain stable after calcination in air at 873 K. When the same gels are crystallized at 423 K for 2 d, lamellar frameworks (MCM-50 type) are preferentially stabilized. They readily collapse on heating. The ultra-small-angle X-ray scattering (USAXS) data and the first part of the SAXS data show a power behaviour that indicates a fractal interface before calcination. After calcination, in the case of MCM-50 type materials, the fractal dimension significantly increases, the fractality region being larger than in the precursor. By contrast, in the case of MCM-41 type materials, the fractal region tends to disappear after calcination. The second part of the SAXS curve reflects the hexagonal or lamellar structure. Some precursors simultaneously exhibit both structures. The hexagonal parameter ranges from 4.6 to 5.8 nm, while the thickness of the wall is estimated to be of the order of 0.7 nm from observations of the satellite peaks in the vicinity of the successive peaks characterizing the hexagonal array. The successive peaks relative to the lamellar structure are consistent with the superposition of two or three layers, the thickness of which are of the order of 3.3, 2.85 and 2.5 nm. Predominant hexagonal structures are maintained after calcination while lamellar structures collapse during calcination. In the case of hexagonal structure, the hexagonal array is slightly contracted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897001350
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  • 9
    Electronic Resource
    Electronic Resource
    Small-Angle X-ray Scattering and Small-Angle Neutron Scattering Studies of Liquid-Crystalline Halato(semi)telechelic Polymers (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 1075-1083 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Model liquid-crystalline ionomers have been synthesized, which consist of low molecular weight (700–49 000) linear ω- and α,ω-sodium sulfonato- and carboxylato-poly(styrenes or isoprenes) selectively end-capped at one or both end(s) with an ionic mesogenic group. These compounds are referred to as liquid-crystalline halato(semi)telechelic polymers [LC H(S)TPs]. A combination of small-angle X-ray scattering and small-angle neutron scattering studies on these LC H(S)TPs clearly shows the usual ionic peak related to interparticle interference between the ionic aggregates and a peak which can be related to the organization of a smectic mesophase. This mesogenic peak is generally masked by the foot of the broad ionic peak. The ionic peak Bragg spacing is much larger in the LC H(S)TP than in the H(S)TP precursor. This increased interaggregate distance results from the hindrance due to the mesogenic organization and from the restricted mobility experienced by the chains closely attached to the mesogen layers. As a rule, the lower the glass transition temperature of the polymeric matrix, the better the definition of the ionic peak. The ionic peak is well defined as long as the temperature is lower than the temperature of transition from solid to smectic phase (323 K). At higher temperatures, the ionic peak intensity decreases with increasing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889897001544
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