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Thermal (Phononic) Memory
Alfredo Pereira Jr
Saturday, 06 September 2008 04:37 UTC
My thanks to Malcolm Dean for calling my attention to the paper and commentary (below).
Some people like me believe something like this occurs in neuron membranes and astrocyte calcium waves.
Alfredo
http://arxiv.org/abs/0808.3311
Cite as: arXiv:0808.3311v1 [cond-mat.stat-mech]
Thermal memory: a storage of phononic information
Lei Wang, Baowen Li
Memory is an indispensable element for computer besides logic gates. In this Letter we report a model of thermal memory. We demonstrate via numerical simulation that thermal (phononic) information stored in the memory can be retained for a long time without being lost and more importantly can be read out without being destroyed. The possibility of experimental realization is also discussed.
http://physicsworld.com/cws/article/news/35579;jsessionid=D1F21F75B64D5407107FAF98C5EF5270
Physics World, Aug 29, 2008, by Michael Banks
Memory device could store data using heat
Heat has long been regarded as useless or even harmful in electronic circuits. But some researchers think that it might be possible to build computers that process phonons — pulses of vibration that carry heat — rather than conventional electrons. Physicists in Singapore and China have now taken a step towards such thermal computation or “phononics” by devising a model for storing thermal information. Although their scheme has yet to be tested experimentally, the researchers claim that bits of information could be read out without destroying the stored data (arXiv:0808.3311v1).
In a conventional electronic circuit, the states “0” and “1” are usually defined by standard voltages. In thermal circuits, however, the states are defined by two arbitrary temperatures. In-line with the second law of thermodynamics, a temperature drop leads to a heat current flowing from a hot to a cold area. Generally, the larger the temperature drop the larger the heat current, which is known as positive differential thermal resistance. These currents are carried by phonons, which are difficult to control because as they are bundles of energy that have no electrical charge and therefore cannot be manipulated using electromagnetic fields.
Missing memories
Researchers have already managed to build a thermal diode and have even shown that it could be possible to build thermal transistors and logic gates — all standard components for functional thermal devices. But memory is required to store the output after performing logical operations.
Now, Baowen Li from the National University of Singapore and Lei Wang from Renmin University of China in Beijing have devised a theoretical model for such thermal memory. Their model takes into account a key element in thermal logic gates — yet to be demonstrated experimentally — by generating a “negative differential thermal resistance” (NDTR). An NDTR means that a large temperature drop leads to a small heat current and a small temperature drop leads to a large heat current.
In their model of thermal memory, Li and Wang considered two heat baths, held at a constant temperature, each sitting at the end of a rod. The other, free ends of the rod do not touch each other, but are nevertheless weakly coupled so that there is an NDTR between them. The final component of their model is a “particle” that sits at the end of one the rods, near the gap between the pair.
Reading and writing
Li and Wang then consider what happens when an object — connected to its own heat bath — cools this particle down to an arbitrary temperature, dubbed “0”. This is what they call the “writing” process. To “read” out the temperature of the particle they use another object — dubbed the “reader” — which is set at a temperature halfway between “0” and another temperature, defined as “1”. The particle then warms up when this reader is brought into contact with it, which causes a large heat current to flow from the particle, down the rod to the heat bath.
However, there is only a small heat flow in the other rod as it is connected via NDTR. In other words, the current in the second rod minus the current in the first rod is negative. This draws heat away from the particle, which cools back down to “0”. As the reader is in contact with the particle, the reader also moves into the “0” state. In other words, it has read out the original “0” state of the particle.
In a similar manner, Li and Weng also showed that if the particle is prepared in the “1” state which is hotter than the reader, then it can also be read out without the state being destroyed. Data cannot be stored for a long time before the heat leaks away. Li calculates that thermal memory will have to be refreshed every 100 μs if the rods were made of carbon nanotubes. This is much more frequent than electronic DRAM currently used in computers today that require refreshing every 64 ms.
Not so instant recall
Another difficulty with thermal memory is the slow access times. “The big difference is between the speed of electromagnetic waves and phonons,” Li told physicsworld.com. Phonons travel at speeds around 1000 ms-1, hundreds of thousands of times slower than electromagnetic waves. “The speed of thermal memory is a key issue that needs further investigation,” he says. Once and if, NTDR is experimentally realized, Li and colleagues are confident that thermal memory will be the next step towards thermal computers.
Updated 06 September 2008 04:37 UTC
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Replies
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A very related discovery (below), although it does not seem to be!
AlfredoUltrasound shown to exert remote control of brain circuits
In a twist on nontraditional uses of ultrasound, a group of neuroscientists at Arizona State University has developed pulsed ultrasound techniques that can remotely stimulate brain circuit activity. Their findings, published in the Oct. 29 issue of the journal Public Library of Science (PLoS) One, provide insights into how low-power ultrasound can be harnessed for the noninvasive neurostimulation of brain circuits and offers the potential for new treatments of brain disorders and disease.
While it might be hard to imagine the day where doctors could treat post traumatic stress disorders, traumatic brain injury and even Alzheimer’s disease with the flip of a switch, most of us have in fact experienced some of ultrasound’s numerous applications in our daily lives. For example, ultrasound has been used in fetal and other diagnostic medical imaging, ultrasonic teeth cleaning, physiotherapies, or surgical ablation. Ultrasound also provides a multitude of other non-medical uses, including pharmaceutical manufacturing, food processing, nondestructive materials testing, sonar, communications, oceanography and acoustic mapping.
“Studies of ultrasound and its interactions with biological tissues have a rich history dating back to the late 1920s,” lead investigator William “Jamie” Tyler points out. “Several research groups have, for more than a half-century, demonstrated that ultrasound can produce changes in excitable tissues, such as nerve and/or muscle, but detailed studies in neurons at the cellular level have been lacking.”
“We were able to unravel how ultrasound can stimulate the electrical activity of neurons by optically monitoring the activity of neuronal circuits, while we simultaneously propagated low-intensity, low-frequency ultrasound through brain tissues,” says Tyler, assistant professor of neurobiology and bioimaging in the School of Life Sciences in the College of Liberal Arts and Sciences.
Led by Tyler, the ASU research group discovered that remotely delivered low intensity, low frequency ultrasound (LILFU) increased the activity of voltage-gated sodium and calcium channels in a manner sufficient to trigger action potentials and the release of neurotransmitter from synapses. Since these processes are fundamental to the transfer of information among neurons, the authors pose that this type of ultrasound provides a powerful new tool for modulating the activity of neural circuits.
“Many of the stimulation methods used by neuroscientists require the use and implantation of stimulating electrodes, requiring direct contact with nervous tissue or the introduction of exogenous proteins, such as those used for the light-activation of neurons,” Tyler explains.
The search for new types of noninvasive neurostimulation methods led them to revisit ultrasound.
“We were quite surprised to find that ultrasound at power levels lower than those typically used in routine diagnostic medical imaging procedures could produce an increase in the activity of neurons while higher power levels produced very little effect on their activity,” Tyler says.
Other neuroscientists and engineers have also been rapidly developing new neurostimulation methods for controlling nervous system activity and several approaches show promise for the treatment of a wide variety of nervous system disorders. For example, Deep Brain Stimulation (DBS) and Vagal Nerve Stimulation (VNS) have been shown to be effective in the management of psychiatric disorders such as depression, bipolar disorders, post-traumatic stress disorder, and drug addition, as well as for therapies of neurological diseases such as Parkinson’s disease, Alzheimer’s disease, Tourette Syndrome, epilepsy, dystonia, stuttering, tinnitus, recovery of cognitive and motor function following stroke, and chronic pain. Up until now, these two techniques have captured the attention of physicians and scientists; however, these therapies still pose risks to patients because they require the surgical implantation of stimulating electrodes. Thus, these types of therapies are often only available to patients presenting the worst of prognoses.
One prior stumbling block to using ultrasound noninvasively in the brain has been the skull. However, the acoustic frequencies utilized by Tyler and his colleagues to construct their pulsed ultrasound waveforms, overlap with a frequency range where optimal energy gains are achieved between transcranial transmission and brain absorption of ultrasound – which allows the ultrasound to penetrate bone and yet prevent damage to the soft tissues. Their findings are supported by other studies examining the potential of high-intensity focused ultrasound for ablating brain tissues, where it was shown that low-frequency ultrasound could be focused through human skulls.
When asked about the potential of using his groups’ methods to remotely control brain activity, Tyler says: "One might be able to envision potential applications ranging from medical interventions to use in video gaming or the creation of artificial memories along the lines of Arnold Schwarzenegger’s character in ‘Total Recall.’ Imagine taking a vacation without actually going anywhere?
“Obviously, we need to conduct further research and development, but one of the most exhilarating prospects is that low intensity, low frequency ultrasound permit deep-brain stimulation procedures without requiring exogenous proteins or surgically implanted medical devices,” he adds.
Tyler and the other ASU researchers will now focus on further characterization of the influence of ultrasound on intact brain circuits and translational research, taking low intensity ultrasound from the lab into pre-clinical trials and treatment of neurological diseases.
Source: Arizona State University
http://www.physorg.com/news144495604.htmlPosted by Robert Karl Stonjek in MindBrain Yahoogroup
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I arrived here from a random link and was surprised to come across this as it is basically what I’m doing my PhD on! Very interesting articles, thanks Alfredo, they will be going into my references. I have a few additional papers that you may or may not already know about.
As you are interested in thermodynamic models of neurons, you may find some of the articles by Thomas Heimburg of the Niels Bohr Institute interesting – the latest in vol. 88, issue 2 of Progress in neurobiology – http://www.sciencedirect.com/science/journal/03010082
He hinted at one point that neuron dynamics possibly could be modelled in terms of ultrasound, but has not mentioned that for a while.Also a very interesting new journal (I’ve only just come across it) called Physics of Life has a large number of “very-related-yet-not-seeming-so” articles including one on the development and evolution of life (and one may extend to the sustaining of life) through the interactions of gravity (i.e. mechanical compression) and thermodynamics.
http://www.sciencedirect.com/science/journal/15710645 – vol. 5, Issue 4, Egan et al.Personally, I’m attempting to extend the ultrasound idea down to molecular mechanisms with an eye on its connection to consciousness and emotions (e.g. music), but I’m sure somebody well-known will probably have done it better by the time I’ve finished my PhD!
Michael
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Welcome here, Michael!
Just a hint how to put a link in a clickable form: type the text you want like this “text”: and let the link follow directly. You can always test how it looks by using the preview function. Unfortunately editing a post is not possible.
Yours friendly
Hans -
Hi Hans,
Thanks for the welcome, I’ll try my hand at better formatting next time!
I’d be very interested to see if anyone else is working in this area, I definitely feel that acoustics (and phononics in solid-state) is a bit of a black art in terms of its molecular foundations and will eventually need to catch up with modern photonics research, but that in itself may require a radical rethink. I’ve come across so many people who feel intuitively that acoustics has more to say about life, especially since it interacts to produce structures in the macro-scale (and is itself a product of patterned structures), much like particles are structured by the flux of waves at the quantum scale – indeed the founders of quantum physics were intrigued by the connection with life at the beginning of the last century… I, at least, would like to suggest that we’ve been missing a whole lot of nature’s tricks – hopefully others will have ideas about this too.
Thanks,
Michael -
Dear Michael,
I found something about your work on academia.edu and really like it. First of all I like the very fundamental approach you try there.
I am interested and while working on Jonathan Edwards’ model of single cell consciousness I came unto methodological difficulties that caused me to give up that line.
I think though, it is very worth while to consider acustical effects that do not follow the typical paradigm that follows receptor, nerve, neural network, brain etc. This typical approach has been very fruitful and it may lead us to neglect other physiological pathways that are also relevant.
Monocausal approaches are more and more being enriched by multifactorial approaches. Not sure if this is on the line of your work and of course poets may not have the best scientific intuitions, but I am reminded of a song by Herbert Grönemayer about a deaf girl who loves rock music and thus the suggestion is that she will love the bass player, because she feels the vibration of the bass in her belly.
“Der Mann ihrer Träume muss ein Bassmann sein, das Kribbeln im Bauch macht sie verrückt”, sang Herbert Grönemeyer einst in dem Lied “Musik, nur wenn sie laut ist” über ein taubes Mädchen." Quoted from Die Welt -
Dear all,
Some interesting responses! Hans, I’m glad you enjoyed my research, I wish more people were interested in the fundamentals.I actually cut out a section of my post which mentioned how I always prefer to think about tissue, cell and sub-cellular aspects of the body rather than concentrate on neurons, as I agree with you that we can often get carried away by their speedy communication and forget they are no more special than organs, glia, muscle cells, mitchondria, ECM, hormones etc etc.
It’s funny you mention the song about the deaf girl who loves rock music – the mechano-receptors found in the cochlea are from the same evolutionary line as those which are involved in touch. Indeed, “love-songs” in flies (drosophila) are “sung” by feeling vibrations with their antennae (I’ll add a link later).I had come across the single cell consciousness model in the past, but I’d already decided that there is no difference between ‘organic’ and ‘inorganic’ (contentious I know) and thus the basis of consciousness may need to be based upon some more fundamental property and perhaps should not be attached to any particular system, however big or small – If you go down to a cell, why not down to a molecule or particle or up to the world and universe? I personally do not think this requires any epi-phenomenal or dualist thinking to explain feeling (and awareness of feeling) but in the end, who knows?
Otmar, hello! I think your point is quite related to this too! Memory is an important part of our thought processes, but it can also be found in our development and our evolution – science is (sometimes) based upon uncovering the workings of systems by predicting their dynamics, which can be in turn used to predict how certain systems developed (e.g. how they evolved and developed).
I think it is very interesting that we spend so much time looking at the past and future that we forget that we only feel things (as a subject) in the present, whether these feelings relate to things in the present, past or future. Indeed, as one of the basic dimensions in physics is time, how can we possibly explain the genesis of our subjective feelings in biophysical language? We can describe the dynamics of them, but this is merely an abstract model again… In the end, I don’t think scientific models describe reality as it is, they just give us a way to understand and predict it. This may be based upon very false premises (please forgive me if I’m completely out of place) and is very, very difficult to describe accurately, but I just sometimes wish I could find some feeling in physics! -
Here is the link for a paper describing drosophila song.
Michael -
Dear Michael,
Thank you for another interesting article. We are going off topic though. Why don’t we start a new thread that focuses on audition?
Yours friendly
Hans -
Dear all,
Sorry for the slow reply I’ve been away for a while!Hans, thanks for the suggestion and apologies for the rather off-topic article – I think your suggestion for a more related article is very good – von Schilcher, F. (1976) for anyone who is interested.
I believe that the drosophila article and discussion about audition and touch is very related to the original articles posted, but the connection may not be obvious, so I’ll attempt to describe what I mean…
I do not have a solid state physics background, but I think the use of “thermal” in the original article may have confused matters – Phonons, as I understand them, are merely the energy of a mode of vibration in a lattice (i.e. solid) that may be understood as particles in a similar fashion to a photon is the energy of an electromagnetic wave. Phonons can be understood in terms of optic (internal vibrations) and acoustic (centre of mass vibrations) energy – “Thermal” is a classical term based upon the system wide interactions and measurement of these vibrations.
In simpler terms, phononics is a description of vibrations in the particles of solids at such a very small level that the phenomenon of heat (in solids) may be described as emerging from the complex interactions of them. I get the impression that we are still uncovering the basics of the connection between phonons and ultrasound, even though phonons have been around quite a while…So to put this in context of the original articles, researchers have modelled how phononic vibration can be kept in a particular (thermal) energy state, such that it can be used in computer memory. We probably cannot make a direct comparison to brain mechanisms, but I think the second article about acoustic interactions affecting high level neural mechanisms (i.e. neural circuits) is really talking about the same phenomenon at a different level. In between these levels, one could posit that mechanosensation found in the receptors of the ear and touch also work in similar ways.
As you mentioned: “the typical paradigm… may lead us to neglect other physiological pathways that are also relevant.” This may be a case in point, that the typical paradigm of biology (and chemistry/physics for that matter), has ignored acoustic vibration for the past 30 years – that the idea of phonons has become detached from the theory of acoustics is perhaps a symptom?Otmar, I agree that all cells may ‘think’ but this very much depends on your definition – although we shouldn’t underestimate other cells in the body we must also not forget that the nervous system is our most complex and varied organ – there are special things going on at the whole system level of the brain that have allowed us to do such things as science, art and literature and these are based on lower systems (for example mirror neurons, memory etc.) that may also be more varied (at a system level) than other organs. Neural cells also have evolved special architectures and support structures to allow for their various attributes of speedy, networked communication, and yet this does not deny that other cells do still communicate in very similar ways.
I think what I meant by the last comment about feeling in physics is that if we don’t find a way to include consciousness, awareness and feeling into our physical theory, it becomes devoid of meaning for us as human beings. Useful, but meaningless. This is something that we will need to work on in the 21st century as we currently have no way to sort out what is good interdisciplinary research, what is pseudo-science and what is blatant quackery when it comes to the links between basic science and the ‘big questions’ of philosophy and dare I say it, theology – and I don’t think this is something that basic scientists should fear, as it is far better to look into it with a good grounding in science than to let someone else theorise who does not know the basics. As to being destined to achieve failure, I have no doubt that researchers will continue to be culled for asking such outlandish questions, but personally I’m only interested in formulating the questions and expect to be leaving science before I am pushed. Thanks for the support though, I’m sure it’ll work out right in the end!
Apologies for going off-topic a little again, but I hope people will find something interesting in there!
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