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Topic: Critical frequency

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	Thermoset heating composition including high efficiency heating agents and methods of use - US Patent 6677559 (Site not responding. Last check: 2007-10-22)
		The reference depth is dependent on the frequency of the alternating current through the coil, and the electrical resistivity and relative magnetic permeability of the workpiece or heating agent.
		Thus for a round bar the critical frequency is that at which the ratio of workpiece diameter to reference depth is approximately 4+/1.
		Frequently the carbon fiber reinforced substrates are either closer to the coil and/or between the coil and the heating agent.
	www.patentstorm.us /patents/6677559.html (18010 words)

	ipedia.com: Ionosphere Article (Site not responding. Last check: 2007-10-22)
		The critical frequency determines the limiting frequency at or below which a wave component is reflected by, and above which it penetrates through, an ionospheric layer.
		The cutoff frequency is the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by reflection from the layer.
		Maximum usable frequency (MUF) describes, in radio transmission, using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time.
	www.ipedia.com /ionosphere.html (1582 words)

	HF Radiation - Choosing the right frequency (Site not responding. Last check: 2007-10-22)
		The MUF is proportional to the critical frequency and the secant (equal to 1/cosine) of the incident angle.
		Therefore the MUF is higher with a higher critical frequency and with a larger angle from vertical.
		The critical frequency depends on the time of day, the latitude, season and space weather (the latter to be discussed later).
	www.weather.nps.navy.mil /~psguest/EMEO_online/module3/module_3_2b.html (3108 words)

	OzDASL: Eye Colour and Flicker Frequency (Site not responding. Last check: 2007-10-22)
		An individual's critical flicker frequency is the highest frequency at which the flicker in a flickering light source can be detected.
		At frequencies above the critical frequency, the light source appears to be continuous even though it is actually flickering.
		This investigation recorded critical flicker frequency and iris colour of the eye for 19 subjects.
	www.statsci.org /data/general/flicker.html (87 words)

	Calcium electrogenesis in distal apical dendrites of layer 5 pyramidal cells at a critical frequency of ...
		At the critical frequency, 100 Hz (middle trace), the integral increased to 1.28 mV·s.
		The voltage-time integral at this frequency was 1.52 mV·s
		The mechanism underlying the frequency sensitivity is related to summation of back-propagating APs in the distal dendrite.
	www.pnas.org /cgi/content/full/96/25/14600 (4218 words)

	Facilities Engineering Journal (Site not responding. Last check: 2007-10-22)
		It is believed that this reduction went largely undetected for years until the critical system frequency dropped to near the 980 rpm operating speed of the fan.
		The 16% increase in critical frequency and the increased damping have reduced the bearing vibration displacements by a factor of four at the normal operating speed of 890 rpm (Figure 1) with the same imbalance.
		If the critical system frequency was to have remained at 914 rpm, then a one-pound imbalance at a radius of 60 inches will result in a vibration load of 19,500 pounds for a fan speed of 890 rpm.
	www.afe.org /members/journal/july_august2003/Fans703.html (1394 words)

	Near-Real-Time E-Layer Critical Frequency Map
		This corresponds to the maximum radio frequency that can be reflected by E-region of the ionosphere at vertical incidence (that is, when the signal is transmitted straight up into the ionosphere).
		The E-region critical frequency corresponds to the highest frequency of a signal is transmitted straight upward (vertically incident) that can be returned back to the Earth by the E-region alone.
		Signals that exceed the E-layer critical frequency (and are vertically incident) will penetrate the E-region and travel toward the F-regions.
	www.spacew.com /www/foe.html (747 words)

	Radio-Electronics.Com :: Critical Frequency, LUF, and MUF
		As the frequency is increased a point is reached where the signal will pass right through the layer, and on to the next one, or into outer space.
		As the frequency of a transmission is reduced further reflections from the ionosphere may be needed, and the losses from the D layer increase.
		It is generally three to five times the critical frequency, dependent upon the layer being used and the angle of incidence.
	www.radio-electronics.com /info/propagation/HF/critical.php (930 words)

	Observations of Internal Waves on an Oceanic Boundary
		He argued that the lack of critical frequency enhancement was due either to the concavity of the local topography at many sites (such as at the base of the slope) or to the fact that when the slope was weak, such that the critical frequency was close to
		To date we have found that the near-bottom enhancement, relative to the canonical GM spectrum, of the internal wave energy at the critical frequency spans a large range from being almost nothing to being equal to that found at Fieberling Guyot (Eriksen, 1998) which is the largest enhancement that has ever been observed.
		The stability of the orientation of the current ellipse as frequency varies across the critical frequency bands suggests that Rhines' (1970) trapped modes are not present.
	www.soest.hawaii.edu /oceanography/dluther/LIWI/POlds.htm (1596 words)

	Consonance and Dissonance
		For sounds with frequency greater than 1,000 Hz, the critical bandwidth is a fixed fraction (roughly 15%) of the central frequency of the band.
		A lower frequency critical band is centered at 2,000 Hz and has a bandwidth of ~280 Hz.
		Why the notion of critical bands is relevant, is that when two sounds have their frequencies within the same critical band, the physiological response results in a perception of "roughness" for the resulting sounds, and we identify the two sounds played together as being dissonant.
	needmore.physics.indiana.edu /~rickv/consonance_and_dissonance.html (1309 words)

	Webvision: Temporal Resolution
		This point is called the critical flicker frequency and is influenced by a number of factors.
		Critical duration is shorter for stimulus of high luminance as threshold is reached faster and slower for stimulus of low luminance as a longer period of time is required to sum the quanta to reach threshold.
		Critical flicker frequency (CFF) is the transition point of an intermittent light source where the flickering light ceases and appears as a continuous light.
	webvision.med.utah.edu /temporal.html (2650 words)

	SOLUTIONS TO CRITICAL FREQUENCY DISTURBANCES
		All turbo equipment and variable frequency driven equipment operate at certain speeds where the forcing or self-exciting frequencies are sympathetic (at synchronous or harmonic frequencies) to the resonance’s of a rotor, bearing or support structure.
		If all the above and possibly more corrective measures are taken and the critical frequency's are not eliminated then proceed to variable frequency drive's program for the rejection of critical frequencies.
		After the critical frequency or frequencies are pinpointed, proceed with Critical Frequency Rejection Program to ensure safe operation.
	www.idssproactive.com /scf.htm (807 words)

	Refraction in the ionosphere
		Radio waves transmitted at frequencies higher than the critical frequency of a given layer will pass through the layer and be lost in space; but if these same waves enter an upper layer with a higher critical frequency, they will be refracted back to Earth.
		The rate at which a wave of a given frequency is refracted by an ionized layer depends on the angle at which the wave enters the layer.
		As the frequency of the radio wave is increased, the critical angle must be reduced for refraction to occur.
	www.tpub.com /neets/book10/40e.htm (845 words)

	A Frequency Response Laboratory Problem
		Compute the critical frequency for the circuit (otherwise known as the corner frequency or bandwidth).
		The critical frequency occurs when the squared term is 1.
		If it is not true, determine where the critical frequency really is for your filter by determining where the output is 0.707 times the input.
	www.facstaff.bucknell.edu /mastascu/eLessonsHTML/Labs/Freq/LabRCFreqResp.html (972 words)

	Critical_Band
		As the frequency difference increases, roughness in the tones appears, indicating that both frequencies are activating the same part of the basilar membrane.
		With complex tones, frequency discrimination is improved but the critical bandwidth remains the same for each of the component partials.
		Schematic representation of the frequency (shown in heavy lines) corresponding to the tone sensations evoked by the superposition of two pure tones of nearby frequencies (from Roederer, Introduction to the Physics and Psychophysics of Music, Springer, 1975, p.
	www.sfu.ca /sonic-studio/handbook/Critical_Band.html (431 words)

	Near-Real-Time F2-Layer Critical Frequency Map
		This corresponds to the maximum radio frequency that can be reflected by the F2-region of the ionosphere at vertical incidence (that is, when the signal is transmitted straight up into the ionosphere).
		Critical F2 layer frequencies in excess of about 8 MHz correspond to regions of the ionosphere that are relatively strong and capable of reflecting high-frequency signals over longer distances.
		Critical frequencies below about 4 MHz are weaker and will result in greater signal loss to space, lower MUFs and greater signal instability.
	www.spacew.com /www/fof2.html (731 words)

	Biot's sigmoid velocity versus frequency curves
		For a sand of 40% porosity and 10 Darcy permeability, critical frequency is in the sonic-ultrasonic range (10-100 kHz).
		For a silt of 60% porosity and 10 mD permeability, critical frequency is in the high ultrasonic frequency range (10 MHz).
		The shape of these curves is sigmoid: the velocity is constant for low frequencies until it reaches a transitional region where it strongly increases to reach eventually another constant-velocity level corresponding to the high frequencies.
	sepwww.stanford.edu /public/docs/sep77/patrick2/paper_html/node9.html (270 words)

	HF Propagation tutorial (Site not responding. Last check: 2007-10-22)
		Also, we got into comparing the effective vertical frequency of a signal with the critical frequency of the E-region to determine whether the signal would be blocked or go up into the F-region.
		The ionization in the E-region is under solar control and was shown by the critical frequency depending on solar zenith angle (Z).
		Such critical frequency maps demonstrate that the ionosphere is controlled by the geomagnetic field at great heights but down lower, the distribution of ionization is under solar control.
	www.astrosurf.com /lombry/qsl-hf-tutorial-nm7m4.htm (3961 words)

	Dooling, R (Site not responding. Last check: 2007-10-22)
		Avoidance conditioning and the method of limits were used to measure absolute auditory thresholds, masked thresholds, and critical ratios in 4 parakeets.
		The power spectrum and "constancy of intonation" of the parakeet call were also measured and related to the absolute and differential frequency sensitivity.
		The mechanism of frequency analysis in the parakeet ear was considered in relation to the present results and to the anatomical and functional differences between the avian and mammalian auditory systems.
	www.bsos.umd.edu /psyc/dooling/1975he.htm (119 words)

	Panic Button (Site not responding. Last check: 2007-10-22)
		At some point in between these two extremes is a frequency range for which neither assumption is reasonable and, in fact, the changing impedance of the capacitor within that frequency range has a significant impact on the behavior of the transfer function within that range.
		To find the lower cutoff frequency, we only need to determine the critical frequency of the capacitor that comes into play at the lower end of the passband - this capacitor is the dominant capacitor (at low frequencies) and the critical frequency of this capacitor serves as an estimate of the actual cutoff frequency.
		The critical frequency is simply the reciprocal of the time constant formed by that capacitor and the resistance seen by that capacitor.
	web.uccs.edu /wbahn/ECE3220/panic.htm (6797 words)

	Critical frequency -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-22)
		In ((often plural) systems used in transmitting messages over a distance electronically) telecommunication, the term critical frequency has the following meanings:
		The existence of the critical frequency is the result of electron limitation, i.e., the inadequacy of the existing number of free electrons to support (The phenomenon of a propagating wave (light or sound) being thrown back from a surface) reflection at higher frequencies.
		In (Click link for more info and facts about signal processing) signal processing the critical frequency it is also another name for the ((telecommunication) twice the maximum frequency occurring in the transmitted signal) Nyquist frequency.
	www.absoluteastronomy.com /encyclopedia/c/cr/critical_frequency.htm (133 words)

	The Subcortical Auditory System: Psychophysics of Binaural Hearing (Site not responding. Last check: 2007-10-22)
		With the noise centred on the frequency of the sine tone the threshold of hearing of the latter is increased.
		However, at lower frequencies, it is apparent that the spike discharges are locked to one phase of the stimulating waveform.
		The frequency of this ringing is equivalent to the characteristic frequency of the cell.
	www.zainea.com /compilationtheory.htm (16414 words)

	Circuit arrangement for detecting a critical frequency of input pulses - Patent 4882545
		It is known to provide a circuit for detection of a critical speed, usually a rotational speed, in an apparatus by arranging that a transducer in the apparatus generates a train of rectangular pulses whose frequency corresponds to the aforesaid speed.
		An indication that the critical speed, for example an upper speed limit, has been reached is provided if the frequency of the input pulses attains a predetermined value.
		It is an object of the present invention to provide a circuit arrangement in which a critical frequency of the input pulses must be sustained over a predetermined number thereof in order to provide an output signal indicative of said critical frequency.
	www.freepatentsonline.com /4882545.html (1136 words)

	Maximum Usable Angle (Site not responding. Last check: 2007-10-22)
		Maximum usable frequency is important for determining the best HF frequency to use in communicating between two locations, for example between Los Angles and Denver.
		is the critical frequency for the F layer of the Ionosphere.
		is the critical frequency as before and varies throughout the day, seasonally, and in accordance with the 11 year solar cycle.
	www.cvarc.org /tech/maxusableangle.html (2026 words)

	Module 5.2: The Bode Diagram (Site not responding. Last check: 2007-10-22)
		The frequency at which 180 degrees PA occurs for a process (and so 360 or 0 degrees for the open loop process + controller) is called the Critical Frequency for the process.
		In this case a sine wave of the critical frequency would emerge from the open loop system with exactly the same amplitude and phase as it entered.
		The AR of the process alone at the critical frequency allows us to determine the gain which can be applied to a proportional controller will result in steady oscillation.
	www.chemeng.ed.ac.uk /~igds/Control/module7/module7-2.html (1420 words)

	HF Propagation tutorial
		The closer a transmitted AM or SSB frequency is to the electron gyro-frequency, the more energy is absorbed by the gyro electrons from that carrier wave frequency.
		Anyway, we know the test which our RF undergoes as it ascends after launch: if its effective vertical frequency is less than the local critical frequency, it will be contained by the ionosphere and if not, it will go past the F-layer peak and be lost.
		Thus, the upper decile value during a month of observation is a frequency which is exceeded only 10% of the time, 3 days, while the lower decile value during a month is a frequency which is exceeded 90% of the time, 27 days.
	www.astrosurf.org /lombry/qsl-hf-tutorial-nm7m5.htm (3657 words)

	Experiment an Interactive Demonstration of the Art of Signal Sampling and Aliasing-MOVIE
		Below this critical sampling aliasing occurs, reaching the zero value if the sampling is an integer times smaller than or equal to the signal frequency (200, 500, 1000).
		The higher sampling frequency than the critical, the more realistic is the sampled signal (5000, 50 000).
		Nyquist frequency defined as maximum signal frequency that could be reliably measured to avoid aliasing, which is solely based on the sampling frequency, i.e.
	www.kostic.niu.edu /aliasing-movie.htm (487 words)

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