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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Deformation monitoring (also referred to as deformation survey) is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stresses induced by applied loads. Deformation monitoring is a major component of logging measured values that may be used for further computation, deformation analysis, predictive maintenance, and alarming.[1]
Deformation monitoring is primarily associated with the field of applied surveying but may also be relevant to civil engineering, mechanical engineering, construction, and geology. The measurement devices utilized for deformation monitoring depend on the application, the chosen method, and the preferred measurement interval.
Measuring devices (or sensors) can be sorted in two main groups: geodetic and geotechnical sensors. Both measuring devices can be seamlessly combined in modern deformation monitoring.
Deformation monitoring can be required for the following applications:
Deformation monitoring can be manual or automatic. Manual deformation monitoring is the operation of sensors or instruments by hand or manual downloading of collected data from deformation monitoring instruments. Automatic deformation monitoring operation of a group of software and hardware elements for deformation monitoring that, once set up, does not require human input to function.
Note that deformation analysis and interpretation of the data collected by the monitoring system is not included in this definition.
Automated deformation monitoring requires instruments to communicate with a base station. Communication methods used include:
The monitoring regularity and time interval of the measurements must be considered depending on the application and object to be monitored. Objects can undergo both rapid, high frequency movement and slow, gradual movement. For example, a bridge might oscillates with a period of a few seconds due to the influence of traffic and wind and also be shifting gradually due to tectonic changes.
Deformation analysis is concerned with determining if a measured displacement is significant enough to warrant a response. Deformation data must be checked for statistical significance, and then checked against specified limits, and reviewed to see if movements below specified limits imply potential risks.
The software acquires data from sensors, computes meaningful values from the measurements, records results, and can notify responsible persons should threshold value be exceeded. However, a human operator must make considered decisions on the appropriate response to the movement, e.g. independent verification though on-site inspections, re-active controls such as structural repairs and emergency responses such as shut down processes, containment processes and site evacuation.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Deformation monitoring (also referred to as deformation survey) is the systematic measurement and tracking of the alteration in the shape or dimensions of an object as a result of stresses induced by applied loads. Deformation monitoring is a major component of logging measured values that may be used for further computation, deformation analysis, predictive maintenance, and alarming. Deformation monitoring is primarily associated with the field of applied surveying but may also be relevant to civil engineering, mechanical engineering, construction, and geology. The measurement devices utilized for deformation monitoring depend on the application, the chosen method, and the preferred measurement interval.
Tidal triggering of earthquakes is the idea that tidal forces may induce seismicity. In connection with earthquakes, syzygy refers to the idea that the combined tidal effects of the sun and moon – either directly as earth tides in the crust itself, or indirectly by hydrostatic loading due to ocean tides – should be able to trigger earthquakes in rock that is already stressed to the point of fracturing, and therefore a higher proportion of earthquakes should occur at times of maximal tidal stress, such as at the new and full moons. Scientists have searched for such a correlation for over a century, but with the exception of volcanic areas (including mid-ocean spreading ridges) the results have been mixed. It has been suggested that some negative results are due to failure to account for tidal phase and fault orientation (dip), while "many studies reporting positive correlations suffer from a lack of statistical rigor." One systematic investigation found "no evidence for an increase in seismicity during intervals of large tidal range but there is clear evidence for small but significant increase in earthquake rates near low tide"; it did not find an increase of earthquakes near peak spring tides. Seismicity is favored at low tides, particularly for reverse faults, because unloading unclamps the fault, reducing friction. Ocean loading has no effect at all on strike-slip faults. Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor activity. Volcanologists use the regular, predictable Earth tide movements to calibrate and test sensitive volcano deformation monitoring instruments. The tides may also trigger volcanic events.
In volcanology, deformation refers to the change in the shape of a volcano or the surrounding landscape due to the movement of magma. This can be in the form of inflation, which is a response to pressurization, or deflation, which is a response to depressurization. Inflation is represented by swelling of the ground surface, a volcanic edifice, or a subsurface magma body. It can be caused by magma accumulation, exsolution of volatiles, geothermal processes, heating, and tectonic compression. Deflation is represented by shrinking of the ground surface, a volcanic edifice, or a subsurface magma body. It can be caused by magma withdrawal (related to intrusion or eruption), volatile escape, thermal contraction, phase changes during crystallization, and tectonic extension. Deformation is a key indicator of pre-eruptive unrest at many active volcanoes, but deformation signals must be used in combination with other eruption indicators for forecasting reliability.
In engineering, deformation is the change in size or shape of an object when subjected to force, and may be elastic or plastic depending on whether the deformation is reversible when the actuating force is removed. An object's intrinsic resistance to deformation is known as its stiffness or rigidity. If the deformation is negligible under stress, the object is said to be rigid; conversely, it is said to be flexible or pliable.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
