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Showing posts with label nodal. Show all posts
Showing posts with label nodal. Show all posts

Monday, July 01, 2013

Songs of the Stars: the Real Music of the Spheres



Songs of the Stars: the Real Music of the Spheres

Recording Details Speaker(s): Donald Kurtz
Collection/Series: Perimeter Institute Public Lecture Series
Perimeter Institute Recorded Seminar Archive (PIRSA).


Different oscillation modes penetrate to different depths inside a star.


Asteroseismology (from Greek ἀστήρ, astēr, "star"; σεισμός, seismos, "earthquake"; and -λογία, -logia) also known as stellar seismology[1][2] is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra. Different oscillation modes penetrate to different depths inside the star. These oscillations provide information about the otherwise unobservable interiors of stars in a manner similar to how seismologists study the interior of Earth and other solid planets through the use of earthquake oscillations.[2]

Asteroseismology provides the tool to find the internal structure of stars. The pulsation frequencies give the information about the density profile of the region where the waves originate and travel. The spectrum gives the information about its chemical constituents. Both can be used to give information about the internal structure. Astroseismology effectively turns tiny variations in the star's light into sounds.[3]


Contents

Oscillations

The oscillations studied by asteroseismologists are driven by thermal energy converted into kinetic energy of pulsation. This process is similar to what goes on with any heat engine, in which heat is absorbed in the high temperature phase of oscillation and emitted when the temperature is low. The main mechanism for stars is the net conversion of radiation energy into pulsational energy in the surface layers of some classes of stars. The resulting oscillations are usually studied under the assumption that they are small, and that the star is isolated and spherically symmetric. In binary star systems, stellar tides can also have a significant influence on the star's oscillations. One application of asteroseismology is neutron stars, whose inner structure cannot be directly observed, but may be possible to infer through studies of neutron-star oscillations.[citation needed]


Wave types


Waves in sun-like stars can be divided into three different types;[4]
  • p-mode: Acoustic or pressure (p) modes,[2] driven by internal pressure fluctuations within a star; their dynamics being determined by the local speed of sound.
  • g-mode: Gravity (g) modes, driven by buoyancy,[5]
  • f-mode: Surface gravity (f) modes, akin to ocean waves along the stellar surface.[6]
Within a sun-like star, such as Alpha Centauri, the p-modes are the most prominent as the g-modes are essentially confined to the core by the convection zone. However, g-modes have been observed in white dwarf stars.[5]


Solar seismology


Helioseismology, also known as Solar seismology, is the closely related field of study focused on the Sun. Oscillations in the Sun are excited by convection in its outer layers, and observing solar-like oscillations in other stars is a new and expanding area of asteroseismology.

Space missions


A number of active spacecraft have asteroseismology studies as a significant part of their mission.
  • MOST – A Canadian satellite launched in 2003. The first spacecraft dedicated to asteroseismology.
  • COROT – A French led ESA planet-finder and asteroseismology satellite launched in 2006
  • WIRE – A NASA satellite launched in 1999. A failed infrared telescope now used for asteroseismology.
  • SOHO – A joint ESA / NASA spacecraft launched in 1995 to study the Sun.
  • Kepler – A NASA planet-finder spacecraft launched in 2009 that is currently making asteroseismology studies of over a thousand stars in its field, including the now well-studied subgiant KIC 11026764.[7][8]

Red giants and asteroseismology


Red giants are a later stage of evolution of sun-like stars after the core hydrogen fusion ceases as the fuel runs out. The outer layers of the star expand by about 200 times and the core contracts. However, there are two different stages, first one when there is fusion of hydrogen in a layer outside the core, but none of helium in the core, and then a later stage when the core is hot enough to fuse helium. Previously, these two stages could not be directly distinguished by observing the star's spectrum, and the details of these stages were incompletely understood. With the Kepler mission, asteroseismology of hundreds of relatively nearby red giants[9] enabled these two types of red giant to be distinguished. The hydrogen-shell-burning stars have gravity-mode period spacing mostly ~50 seconds and those that are also burning helium have period spacing ~100 to 300 seconds. It was assumed that, by conservation of angular momentum, the expansion of the outer layers and contraction of the core as the red giant forms would result in the core rotating faster and the outer layers slower. Asteroseismology showed this to indeed be the case[10] with the core rotating at least ten times as fast as the surface. Further asteroseismological observations could help fill in some of the remaining unknown details of star evolution.


References

  1. ^ Ghosh, Pallab (23 October 2008). "Team records 'music' from stars". BBC News. Retrieved 2008-10-24.
  2. ^ a b c Guenther, David. "Solar and Stellar Seismology". Saint Mary's University. Retrieved 2008-10-24.
  3. ^ Palmer, Jason (20 February 2013). "Exoplanet Kepler 37b is tiniest yet - smaller than Mercury". BBC News. Retrieved 2013-02-20.
  4. ^ Unno W, Osaki Y, Ando H, Saio H, Shibahashi H (1989). Nonradial Oscillations of Stars (2nd ed.). Tokyo, Japan: University of Tokyo Press.
  5. ^ a b Christensen-Dalsgaard, Jørgen (June 2003). "Chapter 1" (PDF). Lecture Notes on Stellar Oscillations (5th ed.). p. 3. Retrieved 2008-10-24.
  6. ^ Christensen-Dalsgaard, Jørgen (June 2003). "Chapter 2" (PDF). Lecture Notes on Stellar Oscillations (5th ed.). p. 23. Retrieved 2008-10-24.
  7. ^ Metcalfe, T. S.; et al (2010-10-25). "A Precise Asteroseismic Age and Radius for the Evolved Sun-like Star KIC 11026764". The Astrophysical Journal 723 (2): 1583. arXiv:1010.4329. Bibcode:2010ApJ...723.1583M. doi:10.1088/0004-637X/723/2/1583.
  8. ^ "Graphics for 2010 Oct 26 webcast – Images from the Kepler Asteroseismology Science Consortium (KASC) webcast of 2010 Oct 26". NASA. 2010-10-26. Retrieved 3 November 2010.
  9. ^ Bedding TR, Mosser B, Huber D, Montalbaan J, et al. (Mar 2011). "Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars". Nature 471 (7340): 608–611. arXiv:1103.5805. Bibcode:2011Natur.471..608B. doi:10.1038/nature09935. PMID 21455175.
  10. ^ Beck, Paul G.; Montalban, Josefina; Kallinger, Thomas; De Ridder, Joris; et al. (Jan 2012). "Fast core rotation in red-giant stars revealed by gravity-dominated mixed modes". Nature 481 (7379): 55–57. arXiv:1112.2825. Bibcode:2012Natur.481...55B. doi:10.1038/nature10612. PMID 22158105.

 

External links






See Also:


Wednesday, December 19, 2012

Binaural beats by Wiki

Binaural beats or binaural tones are auditory processing artifacts, or apparent sounds, the perception of which arises in the brain for specific physical stimuli. This effect was discovered in 1839 by Heinrich Wilhelm Dove, and earned greater public awareness in the late 20th century based on claims that binaural beats could help induce relaxation, meditation, creativity and other desirable mental states. The effect on the brainwaves depends on the difference in frequencies of each tone: for example, if 300 Hz was played in one ear and 310 in the other, then the binaural beat would have a frequency of 10 Hz.[1][2]
The brain produces a phenomenon resulting in low-frequency pulsations in the amplitude and sound localization of a perceived sound when two tones at slightly different frequencies are presented separately, one to each of a subject's ears, using stereo headphones. A beating tone will be perceived, as if the two tones mixed naturally, out of the brain. The frequencies of the tones must be below 1,000 hertz for the beating to be noticeable.[3] The difference between the two frequencies must be small (less than or equal to 30 Hz) for the effect to occur; otherwise, the two tones will be heard separately and no beat will be perceived.

Binaural beats are of interest to neurophysiologists investigating the sense of hearing.[4][5][6][7]

Binaural beats reportedly influence the brain in more subtle ways through the entrainment of brainwaves[3][8][9] and have been claimed to reduce anxiety[10] and to provide other health benefits such as control over pain.[11]

Contents

 

 

Acoustical background

 


Interaural time differences (ITD) of binaural beats
For sound localization the human auditory system analyses interaural time differences between both ears inside small frequency ranges, called critical bands. For frequencies below 1000 to 1500 Hz interaural time differences are evaluated from interaural phase differences between both ear signals.[12] The perceived sound is also evaluated from the analysis of both ear signals.

If different pure tones (sinusoidal signals with different frequencies) are presented to each ear, there will be time dependent phase and time differences between both ears (see figure). The perceived sound depends on the frequency difference between both ear signals:

  • If the frequency difference between the ear signals is lower than some hertz, the auditory system can follow the changes in the interaural time differences. As a result an auditory event is perceived, which is moving through the head. The perceived direction corresponds to the instantaneous interaural time difference.
  • For slightly bigger frequency differences between the ear signals (more than 10 Hz) the auditory system can no longer follow the changes in the interaural parameters. A diffuse auditory event appears. The sound corresponds to an overlay of both ear signals, which means amplitude and loudness are changing rapidly (see figure in the chapter above).
  • For frequency differences between the ear signals of above 30 Hz the cocktail party effect begins to work, and the auditory system is able to analyze the presented ear signals in terms of two different sound sources at two different locations, and two distinct signals are perceived.

Binaural beats can also be experienced without headphones, they appear when playing two different pure tones through loudspeakers. The sound perceived is quite similar: with auditory events which move through the room, at low frequency differences, and diffuse sound at slightly bigger frequency differences. At bigger frequency differences apparent localized sound sources appear.[13] However, it is more effective to use headphones than loudspeakers.

History

Heinrich Wilhelm Dove discovered binaural beats in 1839. While research about them continued after that, the subject remained something of a scientific curiosity until 134 years later, with the publishing of Gerald Oster's article "Auditory Beats in the Brain" (Scientific American, 1973). Oster's article identified and assembled the scattered islands of relevant research since Dove, offering fresh insight (and new laboratory findings) to research on binaural beats.

In particular,Oster saw binaural beats as a powerful tool for cognitive and neurological research, addressing questions such as how animals locate sounds in their three-dimensional environment, and also the remarkable ability of animals to pick out and focus on specific sounds in a sea of noise (which is known as the "cocktail party effect").
Oster also considered binaural beats to be a potentially useful medical diagnostic tool, not merely for finding and assessing auditory impairments, but also for more general neurological conditions. (Binaural beats involve different neurological pathways than ordinary auditory processing.) For example, Oster found that a number of his subjects that could not perceive binaural beats, suffered from Parkinson's disease. In one particular case, Oster was able to follow the subject through a week-long treatment of Parkinson's disease; at the outset the patient could not perceive binaural beats; but by the end of the week of treatment, the patient was able to hear them.

In corroborating an earlier study, Oster also reported gender differences in the perception of beats. Specifically, women seemed to experience two separate peaks in their ability to perceive binaural beats—peaks possibly correlating with specific points in the menstrual cycle, onset of menstruation and during the luteal phase. This data led Oster to wonder if binaural beats could be used as a tool for measuring relative levels of estrogen.[3]

The effects of binaural beats on consciousness were first examined by physicist Thomas Warren Campbell and electrical engineer Dennis Mennerich, who under the direction of Robert Monroe sought to reproduce a subjective impression of 4 Hz oscillation that they associated with out-of-body experience.[14] On the strength of their findings, Monroe created the binaural-beat technology self-development industry by forming The Monroe Institute, now a charitable binaural research and education organization.

Unverified claims


There have been a number of claims regarding binaural beats, among them that they may simulate the effect of recreational drugs, help people memorize and learn, stop smoking, help dieting, tackle erectile dysfunction and improve athletic performance.
Scientific research into binaural beats is very limited. No conclusive studies have been released to support the wilder claims listed above. However, one uncontrolled pilot study[15] of 8 individuals indicates that binaural beats may have a relaxing effect. In absence of positive evidence for a specific effect, however, claimed effects may be attributed to the power of suggestion (the placebo effect).
In a blind study (8 participants) of binaural beats' effects on meditation, 7 Hz frequencies were found to enhance meditative focus while 15 Hz frequencies harmed it.[16]

Physiology


The sensation of binaural beats is believed to originate in the superior olivary nucleus, a part of the brain stem. They appear to be related to the brain's ability to locate the sources of sounds in three dimensions and to track moving sounds, which also involves inferior colliculus (IC) neurons.[17] Regarding entrainment, the study of rhythmicity provides insights into the understanding of temporal information processing in the human brain. Auditory rhythms rapidly entrain motor responses into stable steady synchronization states below and above conscious perception thresholds. Activated regions include primary sensorimotor and cingulate areas, bilateral opercular premotor areas, bilateral SII, ventral prefrontal cortex, and, subcortically, anterior insula, putamen, and thalamus. Within the cerebellum, vermal regions and anterior hemispheres ipsilateral to the movement became significantly activated. Tracking temporal modulations additionally activated predominantly right prefrontal, anterior cingulate, and intraparietal regions as well as posterior cerebellar hemispheres.[18] A study of aphasic subjects who had a severe stroke versus normal subjects showed that the aphasic subject could not hear the binaural beats whereas the normal subjects could.[19]

Hypothetical effects on brain function

 

Overview


Binaural beats may influence functions of the brain in ways besides those related to hearing. This phenomenon is called frequency following response. The concept is that if one receives a stimulus with a frequency in the range of brain waves, the predominant brain wave frequency is said to be likely to move towards the frequency of the stimulus (a process called entrainment).[20] In addition, binaural beats have been credibly documented to relate to both spatial perception & stereo auditory recognition, and, according to the frequency following response, activation of various sites in the brain.[21][22][23][24][25]
The stimulus does not have to be aural; it can also be visual[26] or a combination of aural and visual[27] (one such example would be Dreamachine).

Perceived human hearing is limited to the range of frequencies from 20 Hz to 20,000 Hz, but the frequencies of human brain waves are below about 40 Hz. To account for this lack of perception, binaural beat frequencies are used. Beat frequencies of 40 Hz have been produced in the brain with binaural sound and measured experimentally.[28]
When the perceived beat frequency corresponds to the delta, theta, alpha, beta, or gamma range of brainwave frequencies, the brainwaves entrain to or move towards the beat frequency.[29] For example, if a 315 Hz sine wave is played into the right ear and a 325 Hz one into the left ear, the brain is entrained towards the beat frequency 10 Hz, in the alpha range. Since alpha range is associated with relaxation, this has a relaxing effect or if in the beta range, more alertness. An experiment with binaural sound stimulation using beat frequencies in the Beta range on some participants and Delta/Theta range in other participants, found better vigilance performance and mood in those on the awake alert state of Beta range stimulation.[30][31]

Binaural beat stimulation has been used fairly extensively to induce a variety of states of consciousness, and there has been some work done in regards to the effects of these stimuli on relaxation, focus, attention, and states of consciousness.[8] Studies have shown that with repeated training to distinguish close frequency sounds that a plastic reorganization of the brain occurs for the trained frequencies[32] and is capable of asymmetric hemispheric balancing.[33]

 

Brain waves

Frequency range Name Usually associated with:
> 40 Hz Gamma waves Higher mental activity, including perception, problem solving, fear, and consciousness
13–39 Hz Beta waves Active, busy or anxious thinking and active concentration, arousal, cognition, and or paranoia
7–13 Hz Alpha waves Relaxation (while awake), pre-sleep and pre-wake drowsiness, REM sleep, Dreams
8–12 Hz Mu waves Sensorimotor rhythm Mu_rhythm, Sensorimotor_rhythm
4–7 Hz Theta waves deep meditation/relaxation, NREM sleep
< 4 Hz Delta waves Deep dreamless sleep, loss of body awareness
(The precise boundaries between ranges vary among definitions, and there is no universally accepted standard.)
The dominant frequency determines your current state. For example, if in someone's brain alpha waves are dominating, they are in the alpha state (this happens when one is relaxed but awake). However, other frequencies will also be present, albeit with smaller amplitudes.
The brain entraining is more effective if the entraining frequency is close to the user's starting dominant frequency. Therefore, it is suggested to start with a frequency near to one's current dominant frequency (likely to be about 20 Hz or less for a waking person), and then slowly decreasing/increasing it towards the desired frequency.
Some people find pure sine waves unpleasant, so a pink noise or another background (e.g. natural sounds such as river noises) can also be mixed with them. In addition to that, as long as the beat is audible, increasing the volume should not necessarily improve the effectiveness, therefore using a low volume is usually suggested. One theory is to reduce the volume so low that the beating should not even be clearly audible, but this does not seem to be the case (see the next paragraph).

Other uses

In addition to lowering the brain frequency to relax the listener, there are other controversial, alleged uses for binaural beats. For example, that by using specific frequencies an individual can stimulate certain glands to produce desired hormones. Beta-endorphin has been modulated in studies using alpha-theta brain wave training,[34] and dopamine with binaural beats.[1] Among other alleged uses, there are reducing learning time and sleeping needs (theta waves are thought to improve learning, since children, who have stronger theta waves, and remain in this state for a longer period of time than adults, usually learn faster than adults;[citation needed] and some people find that half an hour in the theta state can reduce sleeping needs up to four hours;[citation needed] similar to another method of achieving a theta state, e.g. meditation;[citation needed]) some use them for lucid dreaming and even for attempting out-of-body experiences, astral projection, telepathy and psychokinesis. However, the role of alpha-wave activity in lucid dreaming is subject to ongoing research).[35][36][37]

Alpha-theta brainwave training has also been used successfully for the treatment of addictions.[34][38][39]

It has been used for the recovery of repressed memories, but as with other techniques this can lead to false memories.[40]

An uncontrolled pilot study of Delta binaural beat technology over 60 days has shown positive effect on self-reported psychologic measures, especially anxiety. There was significant decrease in trait anxiety, an increase in quality of life, and a decrease in insulin-like growth factor-1 and dopamine[1] and has been successfully shown to decrease mild anxiety.[41] A randomised, controlled study concluded that binaural beat audio could lessen hospital acute pre-operative anxiety.[42]

Another claimed effect for sound induced brain synchronization is enhanced learning ability. It was proposed in the 1970s that induced alpha brain waves enabled students to assimilate more information with greater long term retention.[43] In more recent times has come more understanding of the role of theta brain waves in behavioural learning.[44] The presence of theta patterns in the brain has been associated with increased receptivity for learning and decreased filtering by the left hemisphere.[43][45][46] Based on the association between theta activity (4–7 Hz) and working memory performance, biofeedback training suggests that normal healthy individuals can learn to increase a specific component of their EEG activity, and that such enhanced activity may facilitate a working memory task and to a lesser extent focused attention.[47]

A small media controversy was spawned in 2010 by an Oklahoma Bureau of Narcotics official comparing binaural beats to illegal narcotics, and warning that interest in websites offering binaural beats could lead to drug use.[48]

See also

 

 

References

  1. ^ a b c Wahbeh H, Calabrese C, Zwickey H (2007). "Binaural beat technology in humans: a pilot study to assess psychologic and physiologic effects". Journal of alternative and complementary medicine 13 (1): 25–32. doi:10.1089/acm.2006.6196. PMID 17309374.
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