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1.
We present our results on a newly synthesized bis-phenylazo derivative, namely bisperfluoroalkylsulfonylamino- arylazomethylene-triphenyl-phosphorane
(BAM-TPP). Thin films of BAM-TPP in polymethylmethacrylate (PMMA) matrix were prepared. The films (thickness, d < 60 μm) were exposed to UV-vis light with variable intensity in order to stimulate the photochromic reaction of BAM-TPP.
The resulting absorption changes of the BAM-TPP/PMMA films were investigated by spectrophotometry. The absorption spectra
reveal that BAM-TPP molecules in PMMA undergo photoisomerization with resulting decrease of absorbance in the range 500–700 nm.
Finally, the time response of film transmittance at 514 nm under increasing CW light intensity was recorded, showing that
the reverse photochromic process brings the absorbance back to its pristine value. The obtained films thus proved to be suitable
for optical switching applications.
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2.
The work undertaken investigates the spectral, thermal and surface characteristics of a random styrene butadiene rubber (SBR)
with monomeric graft(s) of acrylic acid (AA), N-vinyl-2-pyrrolidinone (NVP) or N-isopropylacrylamide (NIPAAm) synthesised using UV polymerisation. The grafted materials were characterised by differential
scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), attenuated total reflectance infrared Fourier
transform spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Thermograph analysis has shown an endothermic transition
occurring at ~75 °C for all random SB-g-NVP copolymers, whereas the T
g value for random SB copolymer was found at 60 °C, thus suggesting that a chemical reaction between styrene and NVP had occurred.
Similar thermal profiles to that of random SB-g-NVP copolymers were evident when random SB was UV polymerised with AA. When
NIPAAm was grafted onto random SB, a notable exothermic transition was evident in all samples tested using DSC. It was established
using MDSC that this exothermic transition was caused by the breakdown of crosslinks as a result of UV polymerisation.
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3.
The microstructure of the compound (“white”) layer formed on the surface of Fe–4wt.%V alloy, by nitriding in a gas mixture
of ammonia and hydrogen at 580 °C, has been investigated by employing light and scanning electron microscopy, X-ray diffraction
and electron probe microanalysis. The compound layer is dominantly composed of γ |-Fe 4N nitride. Quantitative analysis of the composition data demonstrated that V is present in the compound layer as VN precipitates,
i.e. V is not taken up significantly in (Fe, V) nitrides. A mechanism for compound-layer formation has been proposed.
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4.
A number of different families of nanowires which self-assemble on semiconductor surfaces have been identified in recent years. They are particularly interesting from the standpoint of nanoelectronics, which seeks non-lithographic ways of creating interconnects at the nm scale (though possibly for carrying signal rather than current), as well as from the standpoint of traditional materials science and surface science. We survey these families and consider their physical and electronic structure, as well as their formation and reactivity. Particular attention is paid to rare earth nanowires and the Bi nanoline, both of which self-assemble on Si(001).Further information within the topic of this review article, including an up-to-date list of relevant publications, can be found on our Website. The address is:
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5.
By dedicated pre-nitriding (at 580 °C in an ammonia/hydrogen gas atmosphere) and de-nitriding (at 470 °C in a hydrogen gas
atmosphere) experiments, performed on Fe-1.04at.%Cr alloy, it could be demonstrated that the uptake of “excess” nitrogen by
the nitrided ferritic matrix is not due to the presence of iron in chromium-nitride precipitates, as it was suggested previously.
The determination of nitrogen-absorption isotherms for these pre-nitrided and de-nitrided Fe-1.04at.%Cr alloy specimens revealed
that the total amount of excess nitrogen in the alloy is composed of two parts: (a) nitrogen adsorbed at the precipitate/matrix
interface, and (b) nitrogen dissolved interstitially in the ferrite matrix strained by the misfit between (coherent) the CrN
precipitates and the matrix.
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6.
Low-temperature sintered Ca 2Zn 4Ti 15O 36 microwave dielectric ceramic was prepared by conventional solid state reaction method. The influences from V 2O 5 addition on the sintering behavior, crystalline phases, microstructures and microwave dielectric properties were investigated.
The crystalline phases and microstructures of Ca 2Zn 4Ti 15O 36 ceramic with V 2O 5 addition were investigated by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy
(EDS). V 2O 5 addition lowered the sintering temperature of Ca 2Zn 4Ti 15O 36 ceramics from 1140 °C to 930 °C. Ca 2Zn 4Ti 15O 36 ceramic with 5wt% V 2O 5 addition could be densified well at 930 °C, and showed good microwave dielectric properties of ε r ~ 46, Q × f ~ 13400 GHz, and temperature coefficient of resonant frequency (τ f) ~ 164 ppm/°C.
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7.
Two high-pressure bioassay vessels failed at the Savannah River Site during separate events using a standard procedure for
microwave heating of biosamples. Improper installation of the thermal shield in the first vessel caused the rupture during
microwave heating. The second vessel rupture is attributed to over pressurization during testing. The vessel rupture appeared
to initiate in the mold parting line, the thinnest cross-section of the octagonal vessel. No material flaws were found in
the vessel that would impair structural performance during typical usage. Limits to thermal cycling have been suggested to
avoid premature vessel rupture due to fatigue.
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8.
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Drawing on the transaction costs, strategic capability and the strategic cognition perspectives, our study seeks to examine
whether and how firms’ strategic orientations at the business level influence the entry mode choices that firms make in accessing
foreign markets.
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The study uses a sample of 332 foreign market entries made by 62 U.S. based firms over a period of 6 years to test hypotheses
linking firm business level strategy to the choice of foreign entry modes.
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Findings indicate that Prospectors are more likely to choose equity-based foreign market entry modes than Defenders. In addition,
Prospectors favor full-ownership entry modes, namely, greenfield investments and full acquisitions, over shared-ownership
modes such as joint ventures and partial acquisitions.
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9.
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Drawing on reasoned action and family systems theories, as well as the domestic and international job transfer and relocation,
global assignments, personality and work-life balance research domains, this study examines managers’ willingness to assume
global assignments.
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We propose a multi-factor model and test several hypotheses using survey data collected from 431 global managers and 162 spouses/significant
others that examine the degree to which individual, family, and organizational variables influence managerial willingness
to accept not only the more traditional multi-year, but also the increasingly common traveling and short-term global assignments.
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Results suggest that individual (adventurousness and destination country), family (eldercare, children at home, community
tenure, and spouse/significant other relocation willingness), and organizational (compensatory rewards/benefits and career
fit) factors influence managerial willingness to assume global assignments.
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10.
Melt spinning technique was used to synthesize Ni 2MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis
of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of
Ni 2MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni 2MnGa with a size range of 10–20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel
speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite
and γ (gamma) phases. Amorphous phase, Ni 2MnGa nanoparticles, and the martensite phase are analyzed in detail.
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11.
After 50+ years of research to discover a way of determining the in situ strength of an adhesive bond, a method has been found
to probe this key parameter. The initial testing on composite joints has shown it to be accurate and reliable. While effective,
it is expensive to implement in a production environment and then during the final stages of assembly. A second method of
probing the adherent surface prior to bonding is presented that offers the promise of determining adhesion potential before
final bond consolidation. These new inspection methods should enable significant increases in structural performance for structures
that utilize composite materials. Before examining these two new methods a brief review of past work on adhesive bond strength
determination is presented.
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12.
We propose a quantitative means of characterizing the optical absorption spectrum associated with an amorphous semiconductor.
In particular, for a representative hydrogenated amorphous silicon optical absorption experimental data set, through a series
of least-squares linear fits of an exponential function to this experimental data set, taken over a number of optical absorption
ranges, we determine how the breadth of the optical absorption tail varies along the optical absorption spectrum of hydrogenated
amorphous silicon. We find that the quantitative variations in the breadth of the optical absorption tail that are found provide
for a clear delineation between the different regions of the optical absorption spectrum of hydrogenated amorphous silicon.
We complete this analysis by theoretically determining the form of the optical absorption spectrum using a recently developed
empirical model for the density of states functions corresponding to hydrogenated amorphous silicon, this analysis providing
a theoretical basis for the interpretation of our results.
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13.
We propose that, in large unit cell structures, the operation of local symmetries rather than a coincidence site lattice (CSL), is important for the creation of special, low energy, grain and twin boundaries. We illustrate this with a Dürer tiling, and its monoclinic realization, as well as with crystals with large icosahedral motifs. 相似文献
14.
Weak-beam diffraction-contrast electron microscope images of stacking-fault tetrahedra (SFT) have been simulated by solving numerically the Howie–Basinski equations, which are well suited for studying the dependence of image contrast on experimental parameters. These simulated images are in good qualitative agreement with experimental transmission electron micrographs. The visibility of small SFT and the relationship between measured image sizes and real SFT sizes are discussed. 相似文献
15.
The following case study outlines metallurgical, finite element, and fracture mechanics analyses conducted to determine the
cause of a pipeline rupture that resulted from prior external damage. Metallurgical and fractographic analyses indicated that
the rupture initiated from a shear crack caused by mechanical damage, and that the fracture mode was overload; no indication
of progressive growth was observed. Stress and fracture mechanics analysis indicated that the pipe ruptured at a pressure
below the maximum allowable operating pressure.
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16.
Natural fibers are particularly interesting from a materials point of view since their morphology has been tailored to enable
a wide range of macroscopic level functions and mechanical properties. In this paper, we focus on mussel byssal threads which
possess a morphology specifically designed to provide a hysteretic yet resilient large strain deformation behavior. X-ray
diffraction studies have shown that numerous natural fibers have a multi-domain architecture composed of folded modules which
are linked together in series along a macromolecular chain. This microstructure leads to a strong rate and temperature dependent
mechanical behavior and one which exhibits a stretch-induced softening of the mechanical response as a result of the underlying
morphology evolving with imposed stretched. This paper addresses the development of a constitutive model for the stress–strain
behavior of the distal portion of mussel byssal threads based on the underlying protein network structure and its morphology
evolving with imposed stretched. The model will be shown to capture the major features of the stress–strain behavior, including
the highly nonlinear stress–strain behavior, and its dependence on strain rate and stretch-induced softening.
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17.
In order to synthesize compounds of various Perovskite-related structures, we have utilized a novel “melt synthesis technique”
for phosphors rather than the conventional solid state reaction techniques. The solid state reactions require multi-step processes
of heating/cooling with intermediate grindings to make homogeneous samples. However, for the melt synthesis, it is possible
to make a homogeneous sample in a single step within a short period of time (1–60 s) due to the liquid phase reaction in the
molten samples, which were melted by strong light radiation in an imaging furnace. In this study, we have prepared a red-phosphor
CaLaGaO 4:Eu 3+ which has a perovskite—related layered K 2NiF 4 structure. Well-crystallized CaLa 1−x
Eu
x
GaO 4 samples with the K 2NiF 4 structure have been obtained up to x = 0.25, but there was the formation of an olivine phase when x = 0.5–1.0. The red emission at 618 nm increased with the increasing value of x up to x = 0.25.
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18.
This article reviews designs and materials investigated for various seals in high temperature solid oxide fuel cell “stacks”
and how they might be implemented in solid oxide electrolysis cells that decompose steam into hydrogen and oxygen. Materials
include metals, glasses, glass–ceramics, cements, and composites. Sealing designs include rigid seals, compressive seals,
and compliant seals.
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19.
It is not unusual for decisions in engineering or customer surveys to compare pairs or subsets of alternatives. Surprisingly, this standard, natural approach can cause valued information to be lost: a loss so severe that it can cause demonstrably incorrect decisions. By understanding why these errors occur, we identify an alternative, closely related decision approach that eliminates these problems. Also, we identify the nature of the lost information, and we show how to compute the likelihood that an incorrect outcome will occur. 相似文献
20.
Using the modified-single fiber test developed by Holmes and colleagues (J Appl Polym 2008), a detailed analysis of fibers extracted from soft body armor comprised of polybenzoxazole (PBO) fibers was performed. The
data indicate that hydrolytic degradation of these ballistic fibers is accompanied by degradation associated with folding
(or fatigue-induced degradation) and an undefined degradation mechanism associated with vest use that appears to target the
horizontal yarns of the alternating 0°/90° woven layers. These additional failure mechanisms have the potential to create
localized regions in the PBO soft body armor which are significantly lower than the homogeneous degradation expected from
uniform hydrolysis. Results also indicate that the absence of ballistic penetrations in the initial study conducted at the
National Institute of Standards and Technology may be associated with using the properties of the fibers from the back panel
of a compromised vest as representative of the properties in the front panel that was penetrated. Analysis of a field return
vest showed the front panel to be significantly more degraded than the back panel.
This paper is declared a work of the U.S. government and is not subject to copyright protection in the United States.
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