Chris Fenton has written about building a strictly mechanical computer with 3D-printed parts, which he calls the Turbo-Entabulator: see http://www.chrisfenton.com/the-turbo-entabulator/, plus writeups eslewhere. (See other entries on his very interesting site, including the FIBIAC electromechanical computer.)
This makes me wonder whether non-electric computing may actually benefit from 3D printing. It may be possible eventually to 'print' very fine components like microtubes with minimal friction that could be used in nonE systems. Granted such systems would then still be at best semi-electric, since you can't 3D-manufacture the parts without electricity. But again, it may give us analogies of how to proceed in a genuinely nonE manner, if this seems like a good idea.
However, there is also the usual reservation that 3D printing or 'additive manufacturing' as the industry calls it, is an unevaluated technology, commercialized in the usual disregard of the Precautionary Principle, or any accounting of social, political, or ecological costs. This approach in the long-term will probably turn lots of people away from technological progress in general. Borrowing from Dune, we may eventually face the equivalent of the 'Butlerian Jihad' against computing systems, which would be a silly shame.
Proponents of tech must become hard-core proponents of rigorous full-cost accounting of the tech, or they risk the future of technology itself. They must insist upon fully funded adversarial science to investigate the downside of all big tech ventures before we OK them as a society. Even if we then go ahead with the tech, we need such research in order to come up with methods of mitigation.
Tuesday, 27 August 2013
Monday, 19 August 2013
Light-speed functions in non-electric computers? (with a perhaps laughable aside on 'faster-than-light' processes)
Of course, historically the mechanical computers like Zuse's Z1 (c1939) and electromechanical computers like the first differential analyzer at MIT (c1930) could nowhere near approach the calculating speeds of even primitive electronic computers like ENIAC (1945) or EDVAC.
Can non-electric computing achieve such speeds?
How do we achieve this? Light run along fiberoptic cables is the obvious way, perhaps with short-term memory on a photosensitive medium (eg. a fluorescent substance).
Murad (2000) (see below), writes, '...pseudo-fluid dynamic processes interestingly approach near steady-state conditions at light speed.' [I haven't applied for permission to quote this.] Has this got any implications for the use of light in computing -- eg. is there an analogue of solid-state systems here? Using microfluidics? [The blogger (me) clearly knows nothing about pseudo-fluid processes, and just thinks there's a similarity with microfluidics because of the name!]
A note on faster-than-light processes (that's a laugh):
There seem to be a number of observations in nature, as well as inferences in theory, suggesting the possibility of faster-than-light processes. If so, can we harness any of them in an eco-benign and equitable fashion, for use in nonE computing, and elsewhere? Some such processes may include:
Can non-electric computing achieve such speeds?
How do we achieve this? Light run along fiberoptic cables is the obvious way, perhaps with short-term memory on a photosensitive medium (eg. a fluorescent substance).
Murad (2000) (see below), writes, '...pseudo-fluid dynamic processes interestingly approach near steady-state conditions at light speed.' [I haven't applied for permission to quote this.] Has this got any implications for the use of light in computing -- eg. is there an analogue of solid-state systems here? Using microfluidics? [The blogger (me) clearly knows nothing about pseudo-fluid processes, and just thinks there's a similarity with microfluidics because of the name!]
A note on faster-than-light processes (that's a laugh):
There seem to be a number of observations in nature, as well as inferences in theory, suggesting the possibility of faster-than-light processes. If so, can we harness any of them in an eco-benign and equitable fashion, for use in nonE computing, and elsewhere? Some such processes may include:
- radio jets from quasars (Sams, Bruce J., Andreas Eckart, and Rashid Sunyaev. "Near-infrared jets in the Galactic microquasar GRS1915+ 105." Nature 382, 47 - 49 (04 July 1996).);
- the motion of electromagnetic solitons (Bugay, A. N., & Sazonov, S. V. (2004). Faster-than-light propagation of electromagnetic solitons in nonequilibrium medium taking account of diffraction. Journal of Optics B: Quantum and Semiclassical Optics, 6(7), 328.);
- superluminal (=faster-than-light) tunnelling of light pulses observed in photonic barrier experiments (Winful, H. G. (2003). Optics (communication arising): Mechanism for 'superluminal' tunnelling. Nature, 424(6949), 638-638.)
But of course some of these are electric or EM processes, if they exist. How can we 'catch' a hypothetical faster-than-light particle at the quantum level and translate its action into >125-nm-scale work, without running into problems of the use of artificial substances built at the quantum level? Or of artificially-organized light-speed particles getting into material where we don't want them and toxifying it (a superluminal version of the 'grey goo' or 'green goo' problem of nanotechnology and synthetic biology).
Can we get superluminal tunnelling through a fiberoptic cable that functions as a logic gate, etc.?
See also Murad, P. A. (2000). Hyper-light dynamics and the effects of relativity, gravity, electricity and magnetism. Acta Astronautica, 47(2), 575-587. Various claims exist for superluminal devices -- just go to GoogleScholar or other academic search engine and search for 'superluminal devices.'
See also Murad, P. A. (2000). Hyper-light dynamics and the effects of relativity, gravity, electricity and magnetism. Acta Astronautica, 47(2), 575-587. Various claims exist for superluminal devices -- just go to GoogleScholar or other academic search engine and search for 'superluminal devices.'
Friday, 16 August 2013
Non-Electronic Logic Gates
Logic gates for computation can be constructed of various materials; they don't have to be made of silicon chips with electronic transistors. Some examples:
1. Blikstein's simple water gates: see
http://www.techrepublic.com/blog/geekend/the-mit-water-computer-see-ya-electrons/540.
2. An elaboration of this: a form of microfluidics(not nanofluidics): the running of water or steam through micrometre-scale tubes.
3. Use of light along fiberoptic cables, with mechanical switching, or switching using miniaturized (125-200 nm thick) solar sails (if that's possible) made of CP1 or aluminum-reinforced Mylar. The sails would have to be extremely small and light for the minute amount of light coming along the cable to move them into their 'output' position. (See http://science.howstuffworks.com/solar-sail.htm.) Extremely difficult, but may be something here. (Of course, too, light is an electromagnetic material, but since it's neither electronic nor electric precisely we might allow it.)
General reservation re quantum nanotechnology: Since below the 50-nanometre scale the quantum size effect enters, and nanotechnology is often defined as working with matter on the scale of 100 nm or smaller, it would be best to keep to the >125 nm scale, so we continue to work with micro- not nano (quantum)-tech. This is because of the ethical and ecological problems with quantum nanotech, as well as it not having been evaluated before being commercialized -- an egregious error that endangers technological progress generally. For more that's critical of nanotech, see the ETC Group: www.etcgroup.org. You can find celebrations of nanotech anywhere, but for some degree of thoughtfulness in supporting the technology, see the Foresight Institute: www.foresight.org.
1. Blikstein's simple water gates: see
http://www.techrepublic.com/blog/geekend/the-mit-water-computer-see-ya-electrons/540.
2. An elaboration of this: a form of microfluidics(not nanofluidics): the running of water or steam through micrometre-scale tubes.
3. Use of light along fiberoptic cables, with mechanical switching, or switching using miniaturized (125-200 nm thick) solar sails (if that's possible) made of CP1 or aluminum-reinforced Mylar. The sails would have to be extremely small and light for the minute amount of light coming along the cable to move them into their 'output' position. (See http://science.howstuffworks.com/solar-sail.htm.) Extremely difficult, but may be something here. (Of course, too, light is an electromagnetic material, but since it's neither electronic nor electric precisely we might allow it.)
General reservation re quantum nanotechnology: Since below the 50-nanometre scale the quantum size effect enters, and nanotechnology is often defined as working with matter on the scale of 100 nm or smaller, it would be best to keep to the >125 nm scale, so we continue to work with micro- not nano (quantum)-tech. This is because of the ethical and ecological problems with quantum nanotech, as well as it not having been evaluated before being commercialized -- an egregious error that endangers technological progress generally. For more that's critical of nanotech, see the ETC Group: www.etcgroup.org. You can find celebrations of nanotech anywhere, but for some degree of thoughtfulness in supporting the technology, see the Foresight Institute: www.foresight.org.
Wednesday, 14 August 2013
Mechanical or Non-Electric Computer Memory / 非电计算机内存
Non-electromagnetic computer memory? There's a challenge!
Mechanical memory. Pioneered by Charles Babbage in the 19th century, who called the memory in his mechanical calculator a 'store,' and by Konrad Zuse in 1938 and after, whose Z1 computer had a memory in the form of thin metal plates with slots. This model used sliding metal bars that could move only forward or backward (hence suitable for a binary device.) His Z2 and Z4 also included mechanical memory. (Not sure about the Z3.) The Z4 had a 64-word memory (32 bits each for a total of 2048 bits), which could be accessed in half a second. (Zuse also built a form of pseudo-memory which helped speed up the operations.)
High-precision forms of milling today, as well as the potential of 3D printing or 'additive manufacturing' may allow the creation of useable metal components for mechanical memory. However, here we would be using electrical and electronic processes to produce non-electric computers; so perhaps we should call such computers 'semi-electric' or 'electric-engendered' devices. They're not hard-core non-electric. (Also, as usual, there are reservations about the use of new technologies like 3D printing because so many of them have not been adequately evaluated before being commercialized, and have in-built harmful biases. There is no precautionary principle at work in the development of new technologies today, despite a half-century of environmental activism. Partly this seems a pricing issue: damaging technologies are 'cheaper' because subsidized at various levels, while more eco-benign ones are less so.)
What kind of device might we be able to build that's mechanical, on the foundation of these mechanical memories? Worth thinking about.
Thermal memory. Binary digits retained as heat in heat-retaining packets.
Biological memory. Memory involving mold and other non-genetically-engineered and non-cyborg forms of biological computation. (But these are electric or semi-electric systems, though not electronic.)
Solar or light memory. Incorporating concepts of photography, and the making of an impression by light on a medium, which then affects the pattern of light or other signal that is sent back through that medium. Or fluorescent light memory, in which the incoming light imprints itself in a pattern on a fluorescent substance. This, being relatively evanescent, might be suitable for such functions as the pseudo-memory (short-term) built by Zuse in his Z4.
Some shortcomings:
Laughably primitive ideas! He has no clue what he's talking about.
Give sources and links.
Sources:
Stan Augarten (1984), An Illustrated History of Computers.
Mechanical memory. Pioneered by Charles Babbage in the 19th century, who called the memory in his mechanical calculator a 'store,' and by Konrad Zuse in 1938 and after, whose Z1 computer had a memory in the form of thin metal plates with slots. This model used sliding metal bars that could move only forward or backward (hence suitable for a binary device.) His Z2 and Z4 also included mechanical memory. (Not sure about the Z3.) The Z4 had a 64-word memory (32 bits each for a total of 2048 bits), which could be accessed in half a second. (Zuse also built a form of pseudo-memory which helped speed up the operations.)
High-precision forms of milling today, as well as the potential of 3D printing or 'additive manufacturing' may allow the creation of useable metal components for mechanical memory. However, here we would be using electrical and electronic processes to produce non-electric computers; so perhaps we should call such computers 'semi-electric' or 'electric-engendered' devices. They're not hard-core non-electric. (Also, as usual, there are reservations about the use of new technologies like 3D printing because so many of them have not been adequately evaluated before being commercialized, and have in-built harmful biases. There is no precautionary principle at work in the development of new technologies today, despite a half-century of environmental activism. Partly this seems a pricing issue: damaging technologies are 'cheaper' because subsidized at various levels, while more eco-benign ones are less so.)
What kind of device might we be able to build that's mechanical, on the foundation of these mechanical memories? Worth thinking about.
Thermal memory. Binary digits retained as heat in heat-retaining packets.
Biological memory. Memory involving mold and other non-genetically-engineered and non-cyborg forms of biological computation. (But these are electric or semi-electric systems, though not electronic.)
Solar or light memory. Incorporating concepts of photography, and the making of an impression by light on a medium, which then affects the pattern of light or other signal that is sent back through that medium. Or fluorescent light memory, in which the incoming light imprints itself in a pattern on a fluorescent substance. This, being relatively evanescent, might be suitable for such functions as the pseudo-memory (short-term) built by Zuse in his Z4.
Some shortcomings:
Laughably primitive ideas! He has no clue what he's talking about.
Give sources and links.
Sources:
Stan Augarten (1984), An Illustrated History of Computers.
Rojas, R. (2000, July). The architecture of Konrad Zuse's early computing machines. In Rojas, R., & Hashagen, U. (eds.), (2002) The first computers: history and architectures. The MIT Press. Pp. 237-261.
Speiser, A. P. (2000, July). Konrad Zuse's Z4: architecture, programming, and modifications at the ETH Zurich. In Rojas, R. and Hashagen, U. eds., The first computers (pp. 263-276). MIT Press.
Below is a (probably funny) attempt at a Chinese translation, thanks to Google (whose translation program I do appreciate).
无电磁电脑内存？还有一个挑战！
机械记忆。由查尔斯·巴贝奇在19世纪，谁在叫他的机械计算器内存中的“店”，并通过康拉德·楚泽于1938年，之后，他的Z1计算机曾在薄金属板与插槽的形式存储首创。该模型用于滑动金属条，可以只移动向前或向后（因此适用于二进制设备）。他Z2和Z4还包括机械记忆。 （不知道的Z3）Z4的有64个字的内存（每个32位，总共2048位），这可能会在半秒进行访问。 （楚泽还内置伪内存，这有助于加快行动的一种形式。）
高精度形式的铣削今天的，以及三维印刷或“添加制造'的电势可以允许创建可用的金属部件的机械存储器。不过，在这里我们将使用的电气和电子流程来生产非电电脑;所以也许我们应该把这种计算机的半电动“或”电动主义及其“设备。他们不是硬核无电。 （另外，像往常一样，大概有利用新技术，如3D打印的保留，因为这么多的人没有得到充分商业化之前进行评估，并内置有害的偏见。没有预防原则在工作中的发展新技术的今天，尽管环保主义的一个半世纪的部分原因似乎是一个定价的问题：损坏的技术是“便宜”，因为补贴各级，同时更加环保的良性的人要少一些）。
也许我们是什么样的设备能够构建的机械，在这些机械记忆的基础？值得深思。
热记忆。二进制位保留作为热在保温的数据包。
生物记忆。存储器包括模具和生物计算的其他非基因工程改造的和非半机械的形式。 （但是，这些电或半电系统，虽然没有电子。）
太阳能或浅的记忆。的培养基中，然后影响到光或发送回通过该介质的其他信号的模式上装有摄影的概念以及印象的制作由光。或荧光灯存储器，其中，所述入射光的印记本身的图案上的荧光物质。此，作为相对渐逝，也可能是合适的功能，例如通过足色在他Z4内置伪存储器（短期）。
一些不足之处：
可笑的原始想法！他不知道他在说什么。
提供来源和链接。
来源：
斯坦奥加唐（1984），计算机图录。
罗哈斯，R.（2000年7月）。康拉德·楚泽的早期计算机器的体系结构。在罗哈斯，河，与Hashagen，U（合编），（2002年）的第一台电脑：历史和架构。麻省理工学院出版社。 PP。 237-261。
Speiser，A P.（2000年7月）。康拉德·楚泽的Z4 M：架构，编程，并在苏黎世联邦理工学院的修改。在罗哈斯河和Hashagen，U编，第一台计算机（页263-276）。麻省理工学院出版社。
Speiser, A. P. (2000, July). Konrad Zuse's Z4: architecture, programming, and modifications at the ETH Zurich. In Rojas, R. and Hashagen, U. eds., The first computers (pp. 263-276). MIT Press.
Below is a (probably funny) attempt at a Chinese translation, thanks to Google (whose translation program I do appreciate).
无电磁电脑内存？还有一个挑战！
机械记忆。由查尔斯·巴贝奇在19世纪，谁在叫他的机械计算器内存中的“店”，并通过康拉德·楚泽于1938年，之后，他的Z1计算机曾在薄金属板与插槽的形式存储首创。该模型用于滑动金属条，可以只移动向前或向后（因此适用于二进制设备）。他Z2和Z4还包括机械记忆。 （不知道的Z3）Z4的有64个字的内存（每个32位，总共2048位），这可能会在半秒进行访问。 （楚泽还内置伪内存，这有助于加快行动的一种形式。）
高精度形式的铣削今天的，以及三维印刷或“添加制造'的电势可以允许创建可用的金属部件的机械存储器。不过，在这里我们将使用的电气和电子流程来生产非电电脑;所以也许我们应该把这种计算机的半电动“或”电动主义及其“设备。他们不是硬核无电。 （另外，像往常一样，大概有利用新技术，如3D打印的保留，因为这么多的人没有得到充分商业化之前进行评估，并内置有害的偏见。没有预防原则在工作中的发展新技术的今天，尽管环保主义的一个半世纪的部分原因似乎是一个定价的问题：损坏的技术是“便宜”，因为补贴各级，同时更加环保的良性的人要少一些）。
也许我们是什么样的设备能够构建的机械，在这些机械记忆的基础？值得深思。
热记忆。二进制位保留作为热在保温的数据包。
生物记忆。存储器包括模具和生物计算的其他非基因工程改造的和非半机械的形式。 （但是，这些电或半电系统，虽然没有电子。）
太阳能或浅的记忆。的培养基中，然后影响到光或发送回通过该介质的其他信号的模式上装有摄影的概念以及印象的制作由光。或荧光灯存储器，其中，所述入射光的印记本身的图案上的荧光物质。此，作为相对渐逝，也可能是合适的功能，例如通过足色在他Z4内置伪存储器（短期）。
一些不足之处：
可笑的原始想法！他不知道他在说什么。
提供来源和链接。
来源：
斯坦奥加唐（1984），计算机图录。
罗哈斯，R.（2000年7月）。康拉德·楚泽的早期计算机器的体系结构。在罗哈斯，河，与Hashagen，U（合编），（2002年）的第一台电脑：历史和架构。麻省理工学院出版社。 PP。 237-261。
Speiser，A P.（2000年7月）。康拉德·楚泽的Z4 M：架构，编程，并在苏黎世联邦理工学院的修改。在罗哈斯河和Hashagen，U编，第一台计算机（页263-276）。麻省理工学院出版社。
If you get any invention ideas from this blog
If you get any ideas for inventions from this blog, please say so in your desciptions of how you developed your inventions. Thank you!
Some Principles of Mechanical/Non-Electric Computer Design: Electronic and Electric Analogies and Their Limitations
Obviously a huge source of ideas for the design and building of mechanical computers and a mech computer network is in the area of electronic digital computers and electric-mechanical ones (not to mention quantum mechanical ones). For instance, we can improve on Zuse's 1938/1945 mechanical memory (and Babbage's 19th-century 'store' or memory) by looking at electric and electromagnetic memory. Also, we can copy electronic chip logic gates and construct logic gates that use water instead of current, or use sunlight, or heat, or steam. It might be possible to construct a primitive type of microprocessor using fluidics or air currents in micrometre-scale tubes; or sunlight sent along micro-fiberoptic cables. The latter by the way would have the advantage of light-speed contact, as well as being a type of (semi-) 'solid state' device (few or no moving parts, which of course is one of the great strengths of the integrated circuit that contemporary electronic computers are based on).
But there also do need to be fast mechanical or non-electric analogues of relays and basic electric-mechanical motors, as well as chips.
But it would be a mistake to think of mechanical computation as simply a series of copies of electronic methods, and poor copies at that. Mechanical computation has its own forms governed by the nature of the forces involved in it. It is a plum, and digital electronic computing is an orange.
As a sort of heuristic device, we can assume that non-electric computation has the potential to be every bit as powerful as digital electronic computing -- it's just up to us to find out how. But we cannot forget that it will be a powerful plum, not an orange.
To add:
Give sources, links.
But there also do need to be fast mechanical or non-electric analogues of relays and basic electric-mechanical motors, as well as chips.
But it would be a mistake to think of mechanical computation as simply a series of copies of electronic methods, and poor copies at that. Mechanical computation has its own forms governed by the nature of the forces involved in it. It is a plum, and digital electronic computing is an orange.
As a sort of heuristic device, we can assume that non-electric computation has the potential to be every bit as powerful as digital electronic computing -- it's just up to us to find out how. But we cannot forget that it will be a powerful plum, not an orange.
To add:
Give sources, links.
Toward a Non-Electric Computer Network 4: Analog Vitality, and Problems
Some possible elements of a Non-Electro/Petrochemical/
Obviously one of the difficulties for strictly mechanical or micromechanical computing -- or rather calculating -- is to be able to solve differential and linear equations accurately. (Remember that we are only at about a 1930 level in this field (problematic quantum mechanicals systems aside).) Vannevar Bush's differential analyzer in the '20s was no better than 98% accurate at solving differential equtions, and it was electromechanical. Zuse's Z1 (1938) was strictly mechanical, and he had the vital approach that a calculator/computer should be able to solve all equations, ie. be a general-purpose device, and should use binary math. Also he and Schreyer built a memory. (So perhaps it's not stretching it too much to call the Z1 a computer.) But the Z1 didn't work very well, despite its brilliance.
So there needs to be work on accurate and rapid solution of differential and linear equations by strictly mechanical analog and binary/digital calculators. What a laugh!
So there needs to be work on accurate and rapid solution of differential and linear equations by strictly mechanical analog and binary/digital calculators. What a laugh!
Some sources:
Augarten, Stan (1984), Bit by Bit: An Illustrated History of Computers (New York: Ticknor and Fields).
Augarten, Stan (1984), Bit by Bit: An Illustrated History of Computers (New York: Ticknor and Fields).
Some Shortcomings:
Cite more sources for these historical statements, please!
Armchair stuff; little practical experience.
Toward a Non-Electric Computer Network 3: Microfluidic Microprocessor Musings
MICROFLUIDIC MICROPROCESSOR MUSINGS........Since an MIT student created a computer that uses water-flows for its logic gates, it should be not inordinately difficult to create microfluidic logic gates for computers -- which could be a significant step toward the development of a non-electrical computer network. Such a network is a great idea for many reasons. Check it out at: http://www.techrepublic.com/
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Toward a Non-Electric Computer Network 2: Microfluidics
Some steps toward the development of a useful non-electronic computer network lie in the field of fluidics and microfluidics. However, nanofluidics remains ecologically highly problematic: better to stay above the 150 nanometre scale. Such a computer network would be useful due to the fragility of electronic systems in an environment of solar storms, shifts in Earth's magnetic field, human-caused disruptions, etc. See fluidics references in Wikipedia, and elsewhere.
Toward a Non-Electric Computer Network 1: The 10 Weirdest Computers
A non-electronic computer network.......Some possible elements can be found in 'The 10 Weirdest Computers' at http://www.newscientist.com/article/dn13656-ten-weirdest-computers.html?page=1. But some of the entries are ecologically or politically problematic -- like quantum (nanotech) or DNA computing; and nuclear magnetic resonance (NMR) computing is obviously a type of electromagnetic computing. What would be useful is a genuine NECST (Non-Electromagnetic Computer System Technology).
Tuesday, 13 August 2013
Why do we need a Non-Electric Computer Network?
Why do we
need a Non-Electric Computer Network?
1. Electronic and electric devices are
vulnerable to many things. For instance, to solar storms, to changes in the
Earth’s magnetosphere, to nuclear detonations, to human or natural destruction
of power plants and hubs in computer networks. All of these things are
possible, and most of them are likely.
2. There are health risks of electronic
devices, particularly in the present climate in which the Precautionary
Principle is wanting (ie. there is little or no evaluation of new technologies
before they’re commercialized; nor pricing constraints on the proliferation of
harmful tech).
3. Non-Electric systems are likely to be
more ecologically sensible, esp. if developed through fair-trade practices.
Genuine non-EPNN (non-Electric/Petrochem/Nuclear/Nano) would be the greenest.
4. A Non-Electronic Computer System
technology (NECST) has applications in harsh environments where EM systems may
not work, eg. space or other-planetary environments. (Cf. the Globus device.)
5. NECST thinking will help keep
innovation lively because it’s outside of the transistor/chip box. (Granted
there’s a lot of innovation within the transistor/chip world as well.) New NECS
Technologies will also be able to be fed back into electronic tech development,
which will benefit.
6. NECST helps keep people more aware of
the nature of computation and various different physical approaches to carrying
it out. This can only benefit education, computer engineering, public policy, and
tech generally.
What this blog is about
This blog is devoted to info about non-electric computing and computers, and also to promoting them. So it is NOT about our standard electronic digital computers, nor about electronic analog computers, except tangentially. There will be some info about electromechanical computers and about biological computers (eg. molds, esp. non-genetically-engineered ones). But it is primarily devoted to mechanical computers and to any other kinds of non-electric systems. (Remember that bio-computers are often still a form of electric system.) I am trying to explore the notion and construction of genuinely non-EPNN devices. (This means Non-Electric/Petroleum/Nuclear/Nano.) So quantum (nano) mechanical computing will be treated only insofar as it may have implications for macro and micro-scale mechanical systems.
Welcome!!!
I hope you have a good time here.
Welcome!!!
I hope you have a good time here.
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