scholarly journals Designing a high-frequency nutrient and biogeochemical monitoring network for the Sacramento–San Joaquin Delta, northern California

2017 ◽  
Author(s):  
Brian A. Bergamaschi ◽  
Bryan D. Downing ◽  
Tamara E.C. Kraus ◽  
Brian A. Pellerin
Keyword(s):  
High Frequency ◽  
Monitoring Network ◽  
Northern California

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

scholarly journals A Methodology for the Characterization of Periodicities in Nonsteady Time Series: Application to Tropospheric Ozone Recharging Cycles in the Western Mediterranean Basin

2012 ◽  
Vol 29 (11) ◽  
pp. 1644-1656 ◽  
Author(s):  
Jose Luis Palau ◽  
Francisco Rovira
Keyword(s):  
Time Series ◽  
Spectral Analysis ◽  
Tropospheric Ozone ◽  
High Frequency ◽  
Monitoring Network ◽  
Western Mediterranean ◽  
Western Mediterranean Basin ◽  
Student’S T ◽  
The Fourier Transform ◽  
Synthetic Time Series

Abstract Environmental measurements often show unsteady variability and background red noise (stochastic component) superimposed on persistent trivial daily, seasonal, and annual variability. In addition to this, environmental time series often present gaps due to a myriad of possible factors, such as malfunction of the sensors, connection loss, etc. As a result, interpreting and identifying periodicities in this type of time series by means of spectral analysis tools, like the Fourier transform, are difficult and lack precision. To overcome these difficulties, a methodology is proposed in the first part of this paper that integrates statistical tools (iterative Student’s t test), parametric reconstruction, and spectral analysis (Lomb periodogram and wavelets). In the second part of the paper, this methodology is tested (i) in the high-frequency part of the spectrum of two (well known) synthetic time series and (ii) to identify nontrivial (e.g., daily cycles) high-frequency periodicities (linked to some mesometeorological processes) in three tropospheric ozone time series recorded by the Valencia regional air quality monitoring network (on the Mediterranean side of Spain) during a 14-yr period. This methodology can determine statistically significant, seasonally dependent recurrences in the high-frequency variability (<15 days) observed in ozone time series measured in a Mediterranean region of Spain under high noise-to-signal ratios.

Infrasonic Signal Observation through the Monitoring Network

2014 ◽  
Vol 643 ◽  
pp. 224-227
Author(s):  
Juan Zhao ◽  
Guo Cheng Hao ◽  
Zuo Xun Zeng
Keyword(s):  
Gravity Wave ◽  
Spectrum Analysis ◽  
High Frequency ◽  
Correlation Method ◽  
Monitoring Network ◽  
Travel Speed ◽  
Calculation Error ◽  
Acoustic Gravity Wave ◽  
Earthquake Sources ◽  
Infrasonic Signal

The methods of observing and processing infrasonic signals from earthquake sources are discussed in this paper. The categories of earthquake infrasound are firstly discussed. Spectrum analysis as well as travel speed calculation are used to distinguish high frequency local infrasound from the acoustic-gravity wave. Monitoring network has been established to capture the signals from the atmosphere. Basing on a simplified correlation method, a triangle array made of three sensors can decide the direction of the coming signal, and locate the earthquake sources. The calculation error and steps of further improvement are also discussed at the end of the paper.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

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