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At least 289 records · Page 16Linked to original sources
PubMed2006

Quartz aggregates revisited.

Quartz aggregates that formed by coalescence of quartz crystals in the magma or in hydrothermal solution are considered. If the individuals have rhombohedral faces in contact, there will be two special cases: parallel intergrowths and intergrowths that agree in orientation and contact plane with Esterel twins grown from a twinned nucleus. For all other known cases, i.e. when the relative orientation satisfies the Japan, Sardinian, Tiflis, Zyndel-A or Samshvildo law, both individuals have exactly coinciding short symmetry translations in only one direction in the contact plane (monoperiodic twins). If a rhombohedral face is in contact with a prism face, monoperiodic twins will occur if the relative orientation satisfies the Zinnwald, Disentis or a proposed hypothetic law. The orientation of the two lattices can be expressed by a 180 degrees rotation about an axis with low indices independent of c/a in the case of the Esterel, Japan and Sardinian laws. The same is true for the Tiflis and Zyndel-A laws only if they are redefined, and not at all in the case of the Samshvildo, Zinnwald, Disentis and hypothetic laws. When the two individuals have rhombohedral faces in contact, there will even be exact two-dimensional coincidence (multiplicity sigma) in the contact plane and exact three-dimensional coincidence (multiplicity Sigma) in space if the square of the axial ratio c/a is rational. Indications are found that (despite their high values) these multiplicities may be related to the frequency of occurrence of intergrowths in low- and high-quartz.

Journal Article↗
PubMed2001

Structural changes of quartz-type crystalline and vitreous GeO2 under pressure.

Using a large volume high pressure apparatus, quartz-type crystalline GeO2 and Li2O-4GeO2 glass have been compressed up to 14 GPa at room temperature and their local structural changes have been investigated by an in-situ XAFS method. In quartz-type crystalline GeO2, the change of the coordination number from 4 to 6 begins above 8 GPa and finishes below 12 GPa. On decompression, reversal transition begins below 8 GPa and there is a large hysteresis. Almost no sixfold coordination of Ge is preserved after releasing pressure. Change of coordination number in vitreous Li2O-4GeO2 begins above 6 GPa and is completed below 10 GPa. Reversal transition begins below 10 GPa and the hysteresis is smaller than that of quartz-type GeO2. Change of coordination number in vitreous Li2O-4GeO2 is also reversal.

Journal Article↗
PubMed2001

A new method for continuous monitoring of series resonance frequency and simple determination of motional impedance parameters for loaded quartz-crystal resonators.

A new electronic design for continuous motional series resonant frequency monitoring of loaded quartz crystal resonators is presented. Using this circuit, a low-cost method for a simple determination of equivalent circuit parameters of quartz crystal resonators is described. Measurements made with the proposed system on typical AT cut quartz crystals are in good agreement with those of an Impedance Analyzer.

Letter↗
PubMed2001

Doubly rotated contoured quartz resonators.

Doubly rotated contoured quartz resonators are used in the design of temperature-compensated stable clocks and dual-mode sensors for simultaneous measurements of pressure and temperature. The design of these devices is facilitated by models that can predict frequency spectra associated with the three thickness modes and temperature and stress-induced frequency changes as a function of crystalline orientation. The Stevens-Tiersten technique for the analysis of the C-mode of a doubly rotated contoured quartz resonator is extended to include the other two thickness modes. Computational results for harmonic and anharmonic overtones of all three thickness modes of such resonators help in optimizing the radius of curvature of the contour and electrode shape for suppression of unwanted modes and prevention of activity dips. The temperature and stress-induced changes in thickness-mode resonator frequencies are calculated from a perturbation technique for small dynamic fields superposed on a static bias. The static bias refers to either a temperature or stress-induced static deformation of the resonator plate. Phenomenological models are also used for calculating the temperature and stress-induced changes in resonant frequencies as a function of crystalline orientation. Results for the SBTC-cut quartz plate with a spherical convex contour of 260 mm indicate that normal trapping occurs for the third (n = 3) and fifth (n = 5) harmonic of the A-mode, the fundamental (n = 1) and third (n = 3) harmonic of the B-mode, and the fundamental (n = 1) and fifth (n = 5) harmonic of the C-mode.

Journal Article↗
PubMed2004

Small and low-loss IF SAW filters using zinc oxide film on quartz substrate.

It was previously reported that a Rayleigh wave propagating on a zinc oxide film (ZnO)/ST-cut 35 degrees X propagation quartz substrate structure has the characteristics of an excellent temperature coefficient of frequency (TCF) and a large electromechanical coupling factor k(s). This substrate was applied to various intermediate-frequency (IF) stage filters. During the filter development, it was clarified that a spurious response due to the Love wave was generated. In this study, a new quartz substrate has been developed with a specific cut and propagation angle, that has the same values of the TCF and the coupling factor as the above-mentioned ones. In addition, it does not have the spurious response due to the Love wave. The combination of this specific-cut-angle quartz and ZnO film has been applied to IF filters for wideband code division multiple access (W-CDMA) and narrow-band CDMA (N-CDMA) systems. The insertion losses of their IF filters were 3-5 dB better and their TCF was superior (deltaf/f = 0.37 ppm/degrees C: one-third) compared with the conventional surface acoustic wave (SAW) filters.

Journal Article↗
PubMed2005

The development of the quartz crystal oscillator industry of World War II.

This paper offers a history of a critical episode in military and electronics history-the difficult creation of quartz crystal frequency control units for radio communications during World War II. As a means of controlling the frequencies of radio transmitters and receivers, amateur radio hobbyists quickly accepted the quartz crystal oscillator after its initial development in the late 1920s. The military, however, declined to adopt this technology until just prior to World War II. Due to the small market for crystal oscillators, no mass production industry had ever developed to produce this extremely high precision electronic component. As war engulfed the nation, the U.S. Army Signal Corps found itself in the dangerous position of having gambled the integrity of its communications equipment on a component that could not possibly be produced in the quantities immediately needed. This paper looks at the challenges the United States faced in building a crystal manufacturing capability and in supplying this industry with sufficient supplies of raw quartz. A fairly specialized component of communications technology emerged from spare beginnings in prewar amateur radio to become the very foundation of a wide range of electronic devices today.

Journal Article↗
PubMed2004

Microinfrared reflection spectroscopic mapping: application to the detection of hydrogen-related species in natural quartz.

A new method of microinfrared reflection spectroscopy and mapping analysis is briefly introduced. It was used to detect distributions and structures of hydrogen-related species (e.g. H(2)O, SiOH and SiH) in plastically deformed natural quartz. We used a Fourier transform-infrared spectrometer with a microscopic imaging system fully automated for all microscope functions (e.g. focusing, aperture, stage motion and measurements). Mapping can be made in thin sections with a thickness of 50 microm at room temperature and low temperatures (77 K) using a liquid N(2) cooling system. Infrared reflection spectra were obtained by five scans for each point with a range from 4000 to 400 cm(-1). The spectra were measured five times within about 2.5 s at each position. The scanning interval was 100-150 microm using a 100 x 100 microm(2) aperture. All obtained spectral data were stored in computer memory to construct two-dimensional mappings of infrared absorption. From the comparisons between infrared mapping images and deformation microstructures, in addition to the molecular H(2)O around 3600-3400 cm(-1), the hydrogen-related point defects (i.e. SiOH and SiH) around 970-900 cm(-1) within quartz grains and between grain boundaries increased with decreasing grain sizes (increasing plastic strain). The method can detect the SiOH and SiH along grain boundaries that enhance the hydrolytic weakening of natural quartz.

Journal Article↗
PubMed2005

Retention of xenon in quartz and Earth's missing xenon.

The reactivity of xenon with terrestrial oxides was investigated by in situ synchrotron x-ray diffraction. At high temperature (T > 500 kelvin), some silicon was reduced, and the pressure stability of quartz was expanded, attesting to the substitution of some xenon for silicon. When the quartz was quenched, xenon diffused out and only a few weight percent remained trapped in samples. These results show that xenon can be covalently bonded to oxygen in quartz in the lower continental crust, providing an answer to the missing xenon problem; synthesis paths of rare gas compounds are also opened.

Journal Article↗
PubMed1994

Effect of solution ionic strength and iron coatings on mineral grains on the sorption of bacterial cells to quartz sand.

Understanding the interaction between bacterial cells and solid surfaces is essential to our attempts to quantify and predict the transport of microbes in groundwater aquifers, whether from the point of view of contamination or from that of bioremediation. The sorption of bacterial cells suspended in groundwater to porous medium grains was examined in batch studies. Bacterial sorption to clean quartz sand yielded equilibrium, linear, adsorption isotherms that varied with the bacterial strain used and the ionic strength of the aqueous solution. Values of K(d) (the slope of the linear sorption isotherm) ranged from 0.55 to 6.11 ml g, with the greatest sorption observed for the highest groundwater ionic strength. These findings are consistent with the interpretation that an increasingly compressed electrical double layer results in stronger adsorption between the like-charged mineral surface and the bacterial cells. When iron-oxyhydroxide-coated sand was used, however, all of the added bacteria were adsorbed up to a threshold of 6.93 x 10 cells g of coated sand, beyond which no further adsorption occurred. The irreversible, threshold adsorption is the result of a strong electrostatic attraction between the sesquioxide coating and the bacterial cells. Experimental results of adsorption in mixtures of quartz and Fe(III)-coated sand were successfully predicted by a simple additive model for sorption by the two substrate phases. Even small amounts of Fe(III)-coated sand in a mixture influenced the extent of adsorption of bacterial cells. A quantitative description of adsorption in the mixtures can be realized by using a linear isotherm for reversible adsorption to the quartz grains with a y intercept that represents the number of cells irreversibly adsorbed to the Fe(III)-coated sand.

Journal Article↗
PubMed1988

Comparison of laser and high-intensity quartz arc tubes in the detection of body secretions.

The detection capabilities of both laser and high-intensity quartz arc tubes were evaluated. The Spectra-Physics Model 171-19, 18-W argon ion laser and Laser Sonics Model CS-2, 200-mW air-cooled argon ion laser were compared with Payton Scientific's Luma-Print, high-intensity quartz arc tube. The light sources were evaluated as to their detection limits for various biological stains. The stains that were evaluated had been made during prior research. These stains had been stored at room temperature for approximately two years. The stains were a serial dilution made from semen, saliva, and sweat specimens and were examined using both laser light sources and the high-intensity quartz arc tube. The advantages and disadvantages of each light source in relationship to its initial costs and potential use in forensic serology are discussed.

Body Fluids↗
PubMedDate not supplied

[Water content in thin films of nucleic acid nitrogen bases. Ultramicroquantitative determination by means of a quartz resonator].

A method of quartz resonator is proposed for accurate micro- and ultramicroquantitative analysis of water in various biological systems. Sensitivity of this method may be about 10(-9) g. Some advantages and specific applications of quartz resonator are shown by "weighing" water rigidly bound to homogenous dry films of cytosine at great changes of their mass. It is suggested to use the quartz resonator with a specific sorbent applied to it as an efficient detector of small quantities of gases and microadmixtures of solved substances.

Chemical Phenomena↗
PubMed2001

Fabrication of quartz microchips with optical slit and development of a linear imaging UV detector for microchip electrophoresis systems.

We have developed quartz microchips for electrophoresis and a linear imaging UV detector along with the microchip. The microchips have an optical slit, which cut off the stray light in order to improve the sensitivity of UV absorption detection on the chip, at the bonding interface. They have been successfully fabricated on synthesized quartz glass substrates using the hydrofluoric acid (HF) solution bonding method. The signal level of UV absorption detection was effectively improved by applying microchips with the "on-chip" optical slit. It is also possible to improve the signal-to-noise ratio by repetitive scanning of linear photodiode array located along the separation channel, and signal averaging during elimination of the potential. Furthermore, the analysis may be performed until the separation of the target component is complete, because the real-time migration pattern of each component in the sample can be seen just as in a slab-gel electrophoresis, thus enabling a shorter analysis time.

Electrophoresis↗
PubMed2003

Lung function decrease in relation to pneumoconiosis and exposure to quartz-containing dust in construction workers.

BACKGROUND: Prevalence of exposure related respiratory symptoms and decreases in lung function are unknown among quartz dust exposed construction workers. METHODS: In a cross-sectional study (n = 1335), the occurrence of respiratory symptoms, was recorded and spirometric lung function was measured. Results were associated with exposure data and presence of radiographic abnormalities and compared with a reference population. RESULTS: Pneumoconiosis (profusion category 1/1 or greater) was associated with increased risks of FEV(1) and FVC values in the lowest 5% group, and with group-based decreases of 270 ml/s and 180 ml, respectively. Average lung function of construction workers was somewhat lower compared to a Dutch reference population. Lung function was not associated with exposure, except for a reduction in FVC of 5 ml per year for those with higher exposure. CONCLUSIONS: In quartz dust exposed construction workers obstructive and restrictive lung function loss was detected.

Adult↗
PubMed1978

Ultrastructure of the lung in the rat following exposure to crocidolite asbestos and quartz.

Lung tissue from rats that had inhaled U.I.C.C. crocidolite asbestos or quartz particles showed thickening of the interstitial tissue and the presence of collagen fibres. Aggregates of macrophages in the alveolar spaces were a dominant feature of all the sections examined from asbestos exposed rats. According to the ultrastructural studies described here, all the macrophages were mature cells, indicating that the ingested crocidolite asbestos was non-toxic. Lung sections of rats exposed to quartz particles were significantly different. Single cells were found in the alveolar spaces and many macrophages showed a characteristic pattern of vacuole formation. Other cells contained intracellular membranous lamellated bodies, similar to those found in Type II pneumocytes. Cells containing lamellated bodies were also found in the interstitial tissue. These findings suggest that the two mineral dusts have quite different biological effects on the macrophage and that the development of pulmonary fibrosis may, to some extent, be caused by a different mechanism in each instance.

Animals↗
PubMed2002

Monitoring and kinetic parameter estimation for the binding process of berberine hydrochloride to bovine serum albumin with piezoelectric quartz crystal impedance analysis.

A new method for monitoring, in real time, the drug-binding process to protein with piezoelectric quartz crystal impedance (PQCI) is proposed. The method was used to monitor the binding process of berberine hydrochloride to bovine serum albumin (BSA). BSA was immobilized on the silver electrode surface of a piezoelectric quartz crystal and the optimized experimental conditions were established. The BSA-coated piezoelectric sensor was in contact with berberine solution. The time courses of the resonant frequency and equivalent circuit parameters of the sensor during the protein-drug binding were simultaneously obtained. On the basis of the analysis of the multidimensional information provided by PQCI, it was concluded that the observed frequency decrease was mainly ascribed to the mass increase of the sensor surface resulting from the binding. According to the frequency decrease with time, the kinetics of the binding process were quantitatively studied. A piezoelectric response model for the binding was theoretically derived. Fitting the experimental data to the model, the kinetic parameters, such as the binding and dissociation rate constants (k(1) and k(-1)) and the binding equilibrium constant (K(a)), were determined. The k(1), k(-1), and K(a) values obtained at 25 degrees C were 67.5 (+/-0.1) (mol liter(-1))(-1) s(-1), 1.7 (+/- 0.1) x 10(-3) s(-1), and 3.97 (+/- 0.06) x10(4) (mol liter(-1))(-1), respectively.

Animals↗
PubMed1976

Atypical quartz dust-induced pneumoconiosis in SPF rats. Aspects of the role of the lymphatic system in the pathogenesis of silicosis.

Experimental exposure to quartz dust for 100 days (= 700 h) induces in SPF rats histologic changes of the lungs, which have such striking similarities with human cases of pulmonary alveolar proteinosis that they may represent an animal model of human disease. Conventional stock rats, the standard model of experimental silicosis research, react upon the same dosage of quartz dust by the formation or an increase in size of perivascular lymphatic sheaths, in which epitheloid cell granulomas can arise. In SPF rats such granulomas can only be developed in the sparse pre-existent lymphatic tissue, mostly in hilar lymph nodes. The reaction of SPF rats opens an interesting aspect on the significance of the phenomenon of lymphatic "drainage," as comparable reactions are only known in conventional rats following extreme dosage and in human pathology as so-called acute silicoproteinosis.

Animals↗
PubMed2002

Protein adsorption on surfaces: dynamic contact-angle (DCA) and quartz-crystal microbalance (QCM) measurements.

Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film.

Adsorption↗
PubMed2003

Cell spreading on quartz crystal microbalance elicits positive frequency shifts indicative of viscosity changes.

Cell attachment and spreading on solid surfaces was investigated with a home-made quartz crystal microbalance (QCM), which measures the frequency, the transient decay time constant and the maximal oscillation amplitude. Initial interactions of the adsorbing cells with the QCM mainly induced a decrease of the frequency, coincident with mass adsorption. After about 80 min, the frequency increased continuously and after several hours exceeded the initial frequency measured before cell adsorption. Phase contrast and fluorescence microscopy indicated that the cells were firmly attached to the quartz surface during the frequency increase. The measurements of the maximal oscillation amplitude and the transient decay time constant revealed changes of viscoelastic properties at the QCM surface. An important fraction of these changes was likely due to alterations of cytosolic viscosity, as suggested by treatments of the attached cells with agents affecting the actin and microtubule cytoskeleton. Our results show that viscosity variations of cells can affect the resonance frequency of QCM in the absence of apparent cell desorption. The simultaneous measurements of the maximal oscillation amplitude, the transient decay time constant and the resonance frequency allow an analysis of cell adsorption to solid substratum in real time and complement cell biological methods.

Adsorption↗