Newer automobiles have evolved from a mechanical system (distributor) to a completely solid state electronic system with no moving parts. These systems are completely controlled by the on-board computer. In place of the distributor, there are multiple coils that each serve one or two spark plugs. A typical 6 cylinder engine has 3 coils that are mounted together in a coil "pack". A spark plug wire comes out of each side of the individual coil and goes to the appropriate spark plug. The coil fires both spark plugs at the same time. One spark plug fires on the compression stroke igniting the fuel-air mixture to produce power, while the other spark plug fires on the exhaust stroke and does nothing. On some vehicles, there is an individual coil for each cylinder mounted directly on top of the spark plug. This design completely eliminates the high tension spark plug wires for even better reliability. Most of these systems use spark plugs that are designed to last over 100,000 miles, which cuts down on maintenance costs.
Ignition System Distributor
The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don't actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder. When you do a tune-up, one of the things you replace on your engine is the cap and rotor -- these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.
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Older distributors with breaker points have another section in the bottom half of the distributor -- this section does the job of breaking the current to the coil. The ground side of the coil is connected to the breaker points.
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A cam in the center of the distributor pushes a lever connected to one of the points. Whenever the cam pushes the lever, it opens the points. This causes the coil to suddenly lose its ground, generating a high-voltage pulse.
The points also control the timing of the spark. They may have a vacuum advance or a centrifugal advance. These mechanisms advance the timing in proportion to engine load or engine speed.
Spark timing is so critical to an engine's performance that most cars don't use points. Instead, they use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil.
In the next section, we'll take a look at an advance in modern ignition systems: the distributorless ignition.
Distributor
A distributor is a device in the ignition system of an internal combustion engine that routes high voltage from the ignition coil to the spark plugs in the correct firing order. The first reliable battery operated ignition was developed by Dayton Engineering Laboratories Co. (Delco) and introduced in the 1910 Cadillac. This ignition was developed by Charles Kettering and was considered a wonder in its day.
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[edit] Description
It consists of a rotating arm or rotor inside the distributor cap, on top of the distributor shaft, but insulated from it and the body of the vehicle (ground). The distributor shaft is driven by a gear on the camshaft. (Usually the distributor shaft extends to also drive the oil pump.) The metal part of the rotor contacts the central high voltage cable from the coil via a spring loaded carbon brush. The metal part of the rotor arm passes close to (but does not touch) the output contacts which connect via high tension cables to the spark plug of each cylinder. As the rotor spins within the distributor, electrical current is able to jump the small gaps created between the rotor arm and the contacts due to the high voltage created by the ignition coil.
The distributor shaft has a cam that operates the contact breaker. Opening the points causes a high induction voltage in the system's ignition coil.
The distributor also houses the centrifugal advance unit: a set of hinged weights attached to the distributor shaft, that cause the breaker points mounting plate to slightly rotate and advance the spark timing with higher engine rpm. In addition, the distributor has a vacuum advance unit that advances the timing even further as a function of the vacuum in the inlet manifold. Usually there is also a capacitor attached to the distributor. The capacitor is connected parallel to the breaker points, to suppress sparking and prevent wear of the points.
Around the 1970s[citation needed] the primary breaker points were largely replaced with Hall effect sensors. As this is a non-contacting device and the primary circuit is controlled by solid state electronics, a great amount of maintenance in point adjustment and replacement was eliminated. This also eliminates any problem with breaker follower or cam wear, and by eliminating a side load extends distributor shaft bearing life. The remaining secondary (high voltage) circuit was as described above, using a single coil and a rotary distributor.
[edit] Distributor cap
A distributor cap is used in an automobile's engine to cover the distributor and its internal rotor.
The distributor cap has one post for each cylinder, and in points ignition systems there is a central post for the current from the ignition coil coming into the distributor. In High energy ignition (HEI) systems there is no central post and the ignition coil sits on top of the distributor. On the inside of the cap there is a terminal that corresponds to each post, and the plug terminals are arranged around the circumference of the cap according to the firing order in order to send the secondary voltage to the proper spark plug at the right time.
The rotor is attached to the top of the distributor shaft which is driven by a gear on the engine's camshaft and thus synchronized to it. Syncronization to the camshaft is required as the rotor must turn at exactly half the speed of the main crankshaft in the 4-stroke cycle. Often, the rotor and distributor are attached directly to the end of the one of (or the only) camshaft, at the opposite end to the timing drive belt. This rotor is pressed against a carbon brush on the center terminal of the distributor cap which connects to the ignition coil either through the top and wired directly to the coil in HEI systems, or via the center terminal in points ignition systems and remotely connected to the coil. The rotor is constructed such that the center tab is electrically connected to its outer edge so the current coming in to the center post travels through the carbon point to the outer edge of the rotor. As the camshaft rotates, the rotor spins and its outer edge passes each of the internal plug terminals to fire each spark plug in sequence.
Car engines that use a mechanical distributor may fail if they run into deep puddles because any water that leaks into the distributor can short out the electric current that should go through the spark plug, rerouting it directly to the body of the vehicle. This in turn causes the engine to stop as the fuel is not ignited in the cylinders. This problem can be fixed by removing the distributor's cap and drying the cap, cam, rotor and the contacts by: wiping with tissue paper or a clean rag, by blowing hot air on them, or using a moisture displacement spray ie. WD 40 or similar. Oil, dirt or other contaminants can cause similar problems, so the distributor should be kept clean inside and outside to ensure reliable operation.
The distributor cap is a prime example of a component that eventually succumbs to heat and vibration. It is a relatively easy and inexpensive part to replace if its bakelite housing does not break or crack first. Carbon deposit accumulation or erosion of its metal terminals may also cause distributor-cap failure.
[edit] Direct ignition
Modern engine designs have abandoned the distributor and coil, instead performing the distribution function in the primary circuit electronically and applying the primary (low-voltage) pulse to individual coils for each spark plug. In some cars, the coils are mounted together in a 'coil pack'; others utilize a coil located very near to or directly on top of each spark plug (Direct Ignition or coil-on-plug). This avoids the need to switch very high voltages, which is very often a source of trouble, especially in damp conditions. These systems also allow finer levels of ignition control by the engine computer, which assists in increasing power output, decreasing fuel consumption and emissions, and implementing features such as Active Fuel Management.
2-cylinder engines can be built without a distributor, as in Citroen 2CV of about 1975 and BMW boxer twin motorcycles. Both spark plugs of the boxer twin are fired simultaneously, resulting in a waste spark on the cylinder currently on its exhaust stroke.
US Patent 5073882 - Servo-controlled actuator with two-peak flux density distribution
The present invention relates generally to servo-controlled actuators, and more specifically to a lens actuator which is servo-controlled to keep the optical axis of a tracking following device on the right track of a recording disk such as optical disks.
Conventional track following devices include a permanent magnet mounted on a base, and at least one pair of tracking coils and a focusing coil which are mounted on a resiliently movable support. These coils cooperate with the magnet to produce force components in a direction transverse to the direction of tracks to keep the optical axis of a lens system on a desired track and in an orthogonal direction to focus a light beam on the track. Magnetic flux density distribution generated by the permanent magnet has only one peak. As the tracking coils are moved in a focusing direction, flux densities at the upper and lower portions of the tracking coils tend to differ from each other, causing a rotary moment to occur in the movable support. The optical axis of the lens is thus tilted with respect to the vertical.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an actuator which eliminates the tilting of a major axis of a movable support by the provision of a magnetic flux density distribution having two peaks.
According to a broader aspect of the present invention, a magnetic flux density distribution having two peaks of equal magnitudes are generated, the two peaks being located symmetrically on opposite sides of a center axis of the distribution and arranged in a first direction perpendicular to the center axis. A pair of first coils and a second coil are mounted on a resiliently movable support. The first coils have first coil sections which cooperate with the magnetic flux to generate force components contributing to movement of the support in a second direction perpendicular to the first direction and second coil sections which cooperate with the magnetic flux to generate force components not contributing to the movement of the support in the second direction. The second coil sections of the first coils are located respectively at the peaks of the magnetic flux density distribution. The second coil cooperates with the magnetic flux to produce a force component that moves the support in the first direction. Because of the two peaks, flux densities do not substantially differ between upper and lower sections of the first coils when they are moved in a focusing direction. Specifically, the magnetic flux density distribution is generated by a permanent magnetic having opposite pole faces on major surfaces thereof and a groove formed on one of the pole faces, the groove extending in the second direction.
According to a second aspect, the actuator of the present invention is provided for optical disk and comprises a magnetic flux generator mounted on a base to generate a magnetic flux density distribution having two peaks of equal magnitudes, the two peaks being located symmetrically on opposite sides of a center axis of the distribution and arranged in a first direction perpendicular to the center axis. A pair of tracking coils and a focusing coil are mounted on a support resiliently movable with respect to the base. The tracking coils have first coil sections which cooperate with the magnetic flux to generate force components contributing to movement of the support in a second direction perpendicular to the first direction and second coil sections which cooperate with the magnetic flux to generate force components not contributing to the movement of the support in the second direction. The second coil sections of the tracking coils are located respectively at the peaks of the magnetic flux density distribution. The focusing coil cooperates with the magnetic flux to produce a force component that moves the support in the first direction. An optical lens is mounted on the movable support so that an optical axis thereof extends in the first direction to form a light spot on the recording disk
Distribution of surface peaks in 1+1 and 2+1 ballistic growth models
Laboratoire de Physique Théorique et Modèles Statistiques, Université Paris-Sud, Bâtiment 100, F-91405 Orsay Cedex, France
Abstract. We present analytical calculations for the average value and the variance of the number of peaks developing at the surface of 1+1 and 2+1 growing ballistic deposits. Our results are compared with numerical simulations.
PACS numbers: 0550, 0510G, 0230J, 0250E
Print publication: Issue 10 (16 March 2001)
Received 6 October 2000, in final form 14 December 2000
Cancers with two peaks in age distribution
To the casual observer, it doesn't make much difference whether a cancer has two peak in its age distribution or one peak. I'm devoting several blog posts to trying to convince readers that the distinction is very important, often implying that what we thought was one type of cancer is actually two different cancers, with similar morphology but with distinctive clinical features and different methods of treatment. Furthermore, several dozen of these cancers with two peaks in their age distribution, would not be discernible without a large cancer data set, such as the public use data files provided by the SEER (the U.S. National Cancer Institutes Surveillance, Epidemiology and End Results) project.
For this discussion, I've uploaded two pdf files
The first file is intended to be a resource for pathologists, epidemiologists and cancer researchers. It contains about 650 neoplasms, each with its age distribution. Details of the graphic represenations of the data are available in the file.
http://www.julesberman.info/seerdist.pdf
Most tumors have a simple, smooth age distribution, with a single peak. The graph of cancer rates (not occurrences), normalized against the age distribution of a standard U.S. population, often produces highest rates at the upper age range (because cancers in the elderly occur within a relatively small population of super-annuated individuals).
A typical cancer with one peak visible on a graph of occurrences (top) and of rates of occurrence normalized against a standard U.S. population (bottom). Click to see larger image.
Not all cancers have a single age-of-occurrence peak. Some have two or more peaks of occurrence.
I've provided a file that lists cancers with multimodal age distributions (i.e., more than one peak in the age distribution for the neoplasm):
http://www.julesberman.info/bimode.pdf
There a about two dozen such cancers (out of about 650 listed in the seerdist.pdf file). Here are two sample pages from the bimode.pdf file:
Cancers with two peaks. Pairs of graphs are 1) occurrences by age and 2) normalized rates. Click to see larger image
By examining these two files and by correlating these observations with known features of the included cancers, we can draw important conclusions about neoplasms in general and the bimodal tumors, in particular.
More to follow on this subject.
Double-peak distribution of electron and ion emission profile during femtosecond laser ablation of metals
a Istituto Nazionale per la Fisica della Materia (INFM), Unità di Napoli, Via Cintia 26, I-80126 Napoli, Italy
b Dipartimento di Ingegneria e Fisica dell’Ambiente, Università della Basilicata, C.da Macchia Romana, I-85100 Potenza, Italy
c Dipartimento di Scienze Fisiche, Università degli Studi di Napoli Federico II, Via Cintia 26, I-80126 Napoli, Italy
d Dipartimento di Chimica, Università della Basilicata, C.da Macchia Romana, I-85100 Potenza, Italy
e Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Via Cintia 26, I-80126 Napoli, Italy
Available online 31 October 2001.
Abstract
Femtosecond laser ablation of metals with a Ti:sapphire laser system has been investigated by a time-of-flight mass spectroscopy technique. Ion mass spectra show a double-peak distribution, evidencing the presence of a high-energy component (up to few keV), even at moderate laser intensities (1012–1013 W cm−2). Two different ablation regimes were identified for the less energetic component, and explained in the framework of the two-temperature modeling of ultrashort laser pulse–solid target interactions. Ambipolar diffusion has been identified as the probable mechanism giving rise to the observed high-energy plasma plume component.
Two-Peak Temporal Distribution of Stroke Onset in Greek Patients A Hospital-Based Study
Konstantinos Spengosa, Kostas N. Vemmosb, Georgios Tsivgoulisa, Andreas Synetosb, Nikolaos A. Zakopoulosb, Vassilios P. Zisa, Demitris Vassilopoulosa
Departments of
aNeurology, University of Athens School of Medicine, 'Eginition' Hospital and
bClinical Therapeutics, University of Athens School of Medicine, 'Alexandra' Hospital, Athens, Greece
Bimodal distribution
From Wikipedia, the free encyclopedia
In statistics, a bimodal distribution is a continuous probability distribution with two different modes. These appear as distinct peaks (local maxima) in the probability density function, as shown in Figure 1.
Examples of variables with bimodal distributions include the time between eruptions of certain geysers, the color of galaxies, the size of worker weaver ants, the age of incidence of Hodgkin's lymphoma, the speed of inactivation of the drug isoniazid in US adults, and the absolute magnitude of novae.
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[hide]Mixture distributions
A bimodal distribution most commonly arises as a mixture of two different unimodal distributions (i.e. distributions having only one mode). In other words, the bimodally distributed random variable X is defined as Y with probability α or Z with probability (1 − α), where Y and Z are unimodal random variables and 0 < α <> is a mixture coefficient. For example, the bimodal distribution of sizes of weaver ant workers shown in Figure 2 arises due to existence of two distinct classes of workers, namely major workers and minor workers[1]. In this case, Y would be the size a random major worker, Z the size of a random minor worker, and α the proportion of worker weaver ants that are major workers.
A mixture of two unimodal distributions with differing means is not necessarily bimodal, however. The combined distribution of heights of men and women is sometimes used as an example of a bimodal distribution, but in fact the difference in mean heights of men and women is too small relative to their standard deviations to produce bimodality[2]. A mixture of two normal distributions with equal standard deviations is bimodal only if their means differ by at least twice the common standard deviation[2].
