Fe/(0.4-2 wt.%) SiO2/polymer composite materials based on irregularly and/or spherically shaped iron powder particles coated with sol-gel SiO2 layer or with an addition of SiO2 nano-powder were prepared in two ways. O...
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ISBN:
(纸本)9781899072446
Fe/(0.4-2 wt.%) SiO2/polymer composite materials based on irregularly and/or spherically shaped iron powder particles coated with sol-gel SiO2 layer or with an addition of SiO2 nano-powder were prepared in two ways. One method is based on a vacuum/pressure impregnation (VPI) of low-temperature sintered Fe/SiO2 compacts with shellac dissolved in ethanol as well as with thermoplast SL450 and the second method is using a conventional procedure - by mixing the Fe/SiO2 powder with shellac dissolved in ethanol. The influence of the iron particles shape, the way of adding SiO2 and the effect of polymer type used on the properties of electro-insulating layer was microscopically evaluated and correlated with electrical resistivity and magnetic coercivity. It was found that the thickness and continuity of insulating phase is strongly controlled by the shape of iron particles. The use of the shellac polymer is more advantageous than the thermoset SL450. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles with smooth surface are well covered with insulating phase.
Despite the recent progress in physical control and manipulation of various condensed matter, atomic, and particle systems, including individual atoms and photons, our ability to control topological defects remains li...
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Despite the recent progress in physical control and manipulation of various condensed matter, atomic, and particle systems, including individual atoms and photons, our ability to control topological defects remains limited. Recently, controlled generation, spatial translation, and stretching of topological point and line defects have been achieved using laser tweezers and liquid crystals as model defect-hosting systems. However, many modes of manipulation remain hindered by limitations inherent to optical trapping. To overcome some of these limitations, we integrate holographic optical tweezers with a magnetic manipulation system, which enables fully holonomic manipulation of defects by means of optically and magnetically controllable colloids used as “handles” to transfer forces and torques to various liquid crystal defects. These colloidal handles are magnetically rotated around determined axes and are optically translated along three-dimensional pathways while mechanically attached to defects, which, combined with inducing spatially localized nematic-isotropic phase transitions, allow for geometrically unrestricted control of defects, including previously unrealized modes of noncontact manipulation, such as the twisting of disclination clusters. These manipulation capabilities may allow for probing topological constraints and the nature of defects in unprecedented ways, providing the foundation for a tabletop laboratory to expand our understanding of the role defects play in fields ranging from subatomic particle physics to early-universe cosmology.
Scanning tunneling microscopy (STM) provides real-space electronic state information at the atomic scale that is most commonly used to study materials surfaces. An intriguing extension of the method is to attempt to s...
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Scanning tunneling microscopy (STM) provides real-space electronic state information at the atomic scale that is most commonly used to study materials surfaces. An intriguing extension of the method is to attempt to study the electronic structure at an insulator/conductor interface by performing low-bias imaging above the surface of an ultrathin insulating layer on the conducting substrate. We use first-principles theory to examine the physical mechanisms giving rise to the formation of low-bias STM images in the MgO/Ag system. We show that the main features of the low-bias STM contrast are completely determined by the atoms on the surface of MgO which overcomes prior ambiguities in assigning observed STM features to atomic positions of the substrate or thin film in such an epitaxial thin film system. Hence, the low-bias contrast is formed by states at the Fermi level in the Ag that propagate evanescently through the lattice and atomic orbitals of the MgO on their way to the surface. We develop a number of analysis techniques based on an ab initio tight-binding representation that allows identification of the origin of the STM contrast in cases where previous approaches have proven ambiguous.
In this paper, we report on the observation of a gyroscope response in the absence of drive oscillator circuitry in a single ended quartz piezoelectric tuning fork. The tuning fork gyroscope was fabricated by conventi...
In this paper, we report on the observation of a gyroscope response in the absence of drive oscillator circuitry in a single ended quartz piezoelectric tuning fork. The tuning fork gyroscope was fabricated by conventional photolithography and wet etching techniques. The tuning fork length is 4 mm and the stem length is 2 mm; the tuning fork width and thickness are 0.4 mm and 0.35 mm, respectively. The measured gyroscope sensitivity and signal to noise ratio were 0.22 mV/°/s and 40, respectively, at a rotational rate of 60 °/s.
The deposition of alkaline earths onto Ge(100) surfaces leads to well-ordered arrays of narrow trenches and elongated plateaus that extend for thousands of angstroms. Using scanning tunneling microscopy (STM) in conju...
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The deposition of alkaline earths onto Ge(100) surfaces leads to well-ordered arrays of narrow trenches and elongated plateaus that extend for thousands of angstroms. Using scanning tunneling microscopy (STM) in conjunction with density functional theory (DFT), the atomic scale details of these nanostructures are revealed and the driving force responsible for their formation is evaluated. The STM data reveal a dramatic contrast reversal when the polarity of the imaging bias is switched. An energetically favorable structure for the plateaus was found using DFT that can reproduce all of the observed features. This structure is based upon a double dimer vacancy model in which Sr atoms displace two Ge dimers from the surface. Interestingly, the ordered plateau-trench structure is unique to Ge(100) despite the structural and chemical similarities to the Si(100) surface.
Measurements of resonant ultrasonic frequencies of multilayer ceramic capacitors (MLCCs) were performed as a function of excitation amplitude to assess the potential of nonlinear acoustic methods for sensing the prese...
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Measurements of resonant ultrasonic frequencies of multilayer ceramic capacitors (MLCCs) were performed as a function of excitation amplitude to assess the potential of nonlinear acoustic methods for sensing the presence of cracks. The ultimate objective of this work is to establish an approach for nondestructively screeningMLCCs for susceptibility to failure that arises from the evolution of structural flaws into electrical pathways during service. Direct ferroelectric tone-burst transduction and time-domain signal analysis were used to measure the frequency of an extensional mode near 1 MHz in BaTiO 3 -based MLCCs with interleaved Ag electrodes. The capacitors were subjected to thermal stress by quenching from 189 °C into ice water, which led to generation of visible surface-breaking cracks in a fraction of the MLCCs. The amplitude dependence of the resonant frequencies was found to be strongly correlated with the presence of visible cracks.
The long-range surface structure of the dichalcogenide MoS2 is probed with nanometer-length spatial resolution using low-energy electron microscopy (LEEM) and microprobe low-energy electron diffraction (μ-LEED). The ...
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The long-range surface structure of the dichalcogenide MoS2 is probed with nanometer-length spatial resolution using low-energy electron microscopy (LEEM) and microprobe low-energy electron diffraction (μ-LEED). The quality of two differently prepared types of MoS2, single-layer and multilayer exfoliated crystals, as well as single-layer chemical-vapor-deposition (CVD)–grown crystals, is examined. The effects induced by a supporting interface are examined by utilizing two different substrates, SiO2 and native-oxide-covered Si. In addition, the role of impurities is also studied by way of in situ deposition of the alkali-metal potassium. Microprobe measurements reveal that, unlike exfoliated MoS2, CVD-grown MoS2 may, in some instances, exhibit large-scale grain-boundary alterations due to the presence of surface strain during growth. However, real-space probing by LEEM in conjunction with k-space probing by μ-LEED shows that the quality of CVD-grown MoS2 can be comparable to that of exfoliated MoS2.
This paper shows results of in-situ X-ray diffraction analysis of VHCF cycles in duplex steel samples measured in reflection geometry at DELTA synchrotron. Due to the grain size a few number of grains inside the illum...
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This paper shows results of in-situ X-ray diffraction analysis of VHCF cycles in duplex steel samples measured in reflection geometry at DELTA synchrotron. Due to the grain size a few number of grains inside the illuminated area fulfill the Bragg condition simultaneously and allow single grain analysis. Rocking curves (RC) recorded after N· 10 7 fatigue cycles (N=0...8) with increasing stress load reveal changes of shape and intensity of selected austenite and ferrite grains as function of N and are interpreted by rotation of diffracting lattice plane due to formation of slip bands.
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