A cheap and simple pre-earthquake warning system. Watch those frogs !
Cracks in Earth's Magnetic Shield
Immense cracks in our planet's magnetic field can remain open for hours, allowing the solar wind to gush through and power stormy space weather.
"that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux".
But a changing magnetic flux produces a varying current through the coil which itself will produce its own magnetic field as we saw in the Electromagnets tutorial. This self-induced emf opposes the change that is causing it and the faster the rate of change of current the greater is the opposing emf. This self-induced emf will, by Lenz’s law oppose the change in current in the coil and because of its direction this self-induced emf is generally called a back-emf.
"the direction of an induced emf is such that it will always opposes the change that is causing it". In other words, an induced current will always OPPOSE the motion or change which started the induced current in the first place. Likewise, if the magnetic flux is decreased then the induced emf will oppose this decrease by generating and induced magnetic flux that adds to the original flux.
Nerve Conductivity
Rapid echo planar imaging and high-performance MRI gradient systems create fast-switching magnetic fields that can stimulate muscle and nerve tissues produced by either changing the electrical resistance or the potential of the excitation. There are apparently no effects on the conduction of impulses in the nerve fiber up to field strength of 0.1 T. A preliminary study has indicated neurological effects by exposition to a whole body imager at 4.0 T. Theoretical examinations argue that field strengths of 24 T are required to produce a 10% reduction of nerve impulse conduction velocity.
Nerve stimulations during MRI scans can be induced by very rapid changes of the magnetic field. This stimulation may occur for example during diffusion weighted sequences or diffusion tensor imaging and can result in muscle contractions caused by effecting motor nerves. The so-called magnetic phosphenes are attributed to magnetic field variations and may occur in a threshold field change of between 2 and 5 T/s. Phosphenes are stimulations of the optic nerve or the retina, producing a flashing light sensation in the eyes. They seem not to cause any damage in the eye or the nerve.
Varying magnetic fields are also used to stimulate bone-healing in non-unions and pseudarthroses. The reasons why pulsed magnetic fields support bone-healing are not completely understood. The mean threshold levels for various stimulations are 3 600 T/s for the heart, 900 T/s for the respiratory system, and 60 T/s for the peripheral nerves.
Guidelines in the United States limit switching rates at a factor of three below the mean threshold for peripheral nerve stimulation. In the event that changes in nerve conductivity happens, the MRI scan parameters should be adjusted to reduce dB/dt for nerve stimulation.
Scientists trace origin of shark’s electric sense
February 6, 2006
Sharks are known for their almost uncanny ability to detect electrical signals while hunting and navigating. Now researchers have traced the origin of those electrosensory powers to the same type of embryonic cells that gives rise to many head and facial features in humans.
Rescaled earthquake recurrence time statistics: application to microrepeaters
Christian Goltz 1,2 , Donald L. Turcotte 2 , Sergey G. Abaimov 2 , Robert M. Nadeau 3 , Naoki Uchida 4 and Toru Matsuzawa 4
1 Kiel University, Germany. ABSTRACT
Slip on major faults primarily occurs during 'characteristic' earthquakes. The recurrence statistics of characteristic earthquakes play an important role in seismic hazard assessment. A major problem in determining applicable statistics is the short sequences of characteristic earthquakes that are available worldwide. In this paper, we introduce a rescaling technique in which sequences can be superimposed to establish larger numbers of data points. We consider the Weibull and log-normal distributions, in both cases we rescale the data using means and standard deviations. We test our approach utilizing sequences of microrepeaters, micro-earthquakes which recur in the same location on a fault. It seems plausible to regard these earthquakes as a miniature version of the classic characteristic earthquakes. Microrepeaters are much more frequent than major earthquakes, leading to longer sequences for analysis. In this paper, we present results for the analysis of recurrence times for several microrepeater sequences from Parkfield, CA as well as NE Japan. We find that, once the respective sequence can be considered to be of sufficient stationarity, the statistics can be well fitted by either a Weibull or a log-normal distribution. We clearly demonstrate this fact by our technique of rescaled combination. We conclude that the recurrence statistics of the microrepeater sequences we consider are similar to the recurrence statistics of characteristic earthquakes on major faults.
:Product: Geophysical Alert Message wwv.txt
:Issued: 2010 Apr 05 1200 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
#
# Geophysical Alert Message
#
Solar-terrestrial indices for 04 April follow.
Solar flux 79 and mid-latitude A-index 12.
The mid-latitude K-index at 1200 UTC on 05 April was 7 (257 nT).
Official Space Weather Advisory issued by NOAA Space Weather Prediction Center
Boulder, Colorado, USA
SPACE WEATHER ADVISORY BULLETIN #10- 1
2010 April 05 at 12:13 p.m. MST (2010 April 05 1213 UTC)
**** STRONG GEOMAGNETIC STORM IN PROGRESS ****
A geomagnetic storm began at 05:55 AM EST Monday, April 5, 2010. Space
weather storm levels reached Strong (G3) levels on the Geomagnetic
Storms Space Weather Scale. The source of the storming is an
Earth-directed Coronal Mass Ejection associated with a weak solar flare
that occurred in Active Region 1059 on April 3 at 05:54 AM EST. This
is expected to be an isolated storm that should subside quickly. Other
than the flare and CME erupting on April 3, this active region has not
produced any significant activity. Systems that can be affected
include electric power systems, spacecraft operations, high-frequency
communications, GPS, and other navigation systems.
Data used to provide space weather services are contributed by NOAA,
USAF, NASA, NSF, USGS, the International Space Environment Services
and other observatories, universities, and institutions. More
information is available at SWPC's Web site http://swpc.noaa.gov
This alert is from the Rice Space Institute issued on Mon Apr 5 13:00:01 GMT 2010
ACE Solar Wind observations warrant condition RED
Trigger Boyle index (kV): 201.410000
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