واحد مشترک کمکی پژوهش و مهندسی «هوش یار-تواندار»     (HT-CSURE)

واحد مشترک کمکی پژوهش و مهندسی «هوش یار-تواندار» (HT-CSURE)

Hooshyar-Tavandar Common Subsidiary Unit for Research & Engineering
واحد مشترک کمکی پژوهش و مهندسی «هوش یار-تواندار»     (HT-CSURE)

واحد مشترک کمکی پژوهش و مهندسی «هوش یار-تواندار» (HT-CSURE)

Hooshyar-Tavandar Common Subsidiary Unit for Research & Engineering

A New And Unusual Force in The Universe Just Got Even Stranger



A New And Unusual Force in The Universe Just Got Even Stranger

The blackbody force is real.

MIKE MCRAE
24    MAY    2017
New research has expanded on the discovery of a strange phenomenon called blackbody force, showing that the effect of radiation on particles surrounding massive objects can be magnified by the space that warps around them.

The find could affect how we model the formation of stars and planets, and even help us finally detect a theoretical form of radiation that allows black holes to evaporate.

In 2013, physicists announced radiation emitted from objects called 'blackbodies' could not only nudge small particles away, but tug them closer. What's more, for hot-enough objects with only a small amount of mass, the pushing force could be stronger than their gravitational pull.

If you've never come across the term, a blackbody is any opaque object that absorbs visible light, but doesn't reflect or transmit it.

Technically, blackbodies describe theoretically perfect objects that cannot reflect any light at all. Physical examples such as the carbon nanotube materials used to make the crazy-looking Vantablack coatings come pretty close.

It'd be a mistake to think of all blackbodies as, well, black - they do emit radiation as their particles jiggle about, making them a useful way to describe an object's thermal properties.

Four years ago, a team of Austrian researchers figured out that the radiation emitted by a blackbody should have a rather curious effect on nearby atoms. 

To understand this effect, it helps to know that atoms can move and change direction when the photons they absorb cause a shift in their momentum. 

Given the right conditions, objects as large as a cell can be nudged around by a beam of light - a phenomenon commonly used in a form of technology called optical tweezers.  

Physicists have known for about a century that electromagnetic radiation can change the properties of nearby atoms through the Stark effect, which changes the positions of its electrons to sit in a lower energy state.

This happens to make them more likely to move towards towards the brighter parts of a beam of light.

The Austrian researchers put two and two together, showing how heat radiation could cause light to not only push particles away, but thanks to the Stark shift, they could also be pulled towards the object.

"The interplay between these two forces - a typically attractive gradient force versus repulsive radiation pressure - is routinely considered in quantum optics laboratories, but it was overlooked that this also shows up with thermal light sources," lead researcher Matthias Sonnleitner from the University of Innsbruck told Phys.org back in 2013.

While force is incredibly weak, they also showed that the radiation's net pulling power could actually be greater than the tiny amount of gravity produced by minuscule, hot objects, having implications for particles smaller than a dust grain.

"These sub-micron-sized grains play an important role in the formation of planets and stars or in astro-chemistry," said Sonnleitner.

"Apparently, there are some open questions on how they interact with surrounding hydrogen gas or with each other. Right now, we are exploring how this additional attractive force affects the dynamics of atoms and dust."

Fast-forward to now, and another team of physicists has taken up where Sonnleitner and his colleagues left off, exploring the effect of both the blackbody's shape and its effect on the curvature of surrounding spacetime on this optical attraction and repulsion.

In particular, they calculated the warping of space - or topology - around a spherical and a cylindrical blackbody, and measured how the differences might affect the blackbody radiation forces.

They found the curvature of the spherical blackbody and the topology of space surrounding it had a magnifying effect on the attractive force due to both the effect of gravity and the angle at which the radiation struck the particles.

This wasn't the case for the cylinder, with its flat surface and surrounding space, where the blackbody effect wasn't magnified.

While the effect wouldn't be detectable in the laboratory, or even for objects the size of our Sun, for massive blackbody objects like neutron stars or more exotic forms of space-bending physics, this effect could make a significant difference.

"We think that the intensification of the blackbody force due to the ultradense sources can influence in a detectable way the phenomena associated with them, such as the emission of very energetic particles, and the formation of accretion discs around black holes," lead researcher Celio Muniz from Ceará State University, Brazil, explained to Phys.org.

The team also applied the previous findings on the blackbody force to a concept called a global monopole - a theoretical point similar to an electric charge, which affects the shape of surrounding space without gravity - as well as another theoretical warping of space called a cosmic string.

"This work puts the blackbody force discovered in 2013 in a wider context, which involves strong gravitational sources and exotic objects like cosmic strings as well as the more prosaic ones found in condensed matter," Muniz said.

This research was published in Europhysics Letters.





 

Plasma Jet Engines Might Soon Take Us From Earth to Space

Plasma Jet Engines Might Soon Take Us From Earth to Space

Fossil fuel-less propulsion.

KARLA LANT, FUTURISM
20 MAY 2017

Imagine a jet engine that could propel an aircraft faster than a traditional engine, taking us all the way to the edge of the atmosphere, all without burning fossil fuels - and for a low cost.

That's exactly what plasma jet engines should be able to do, although thus far they have been confined to research labs, mostly those focusing on using the engines to move satellites and other spacecraft.

Now researchers from the Technical University of Berlin are working to bring them out of the lab and into the sky. 

Instead of burning fuel and compressed air and then shoving the results out of the back of an engine to cause a forward propulsion, a plasma jet engine mimics a fusion reactor or a star.

It creates electricity by exciting and compressing gas into a plasma, and then generating an electromagnetic field.

Led by Berkant Göksel, the research team aims to marry the plasma engine and the passenger jet to come up with something that could fly at very high altitudes but still take off and land.

"We are the first to produce fast and powerful plasma jets at ground level," Göksel told New Scientist.

"These jets of plasma can reach speeds of up to 20 kilometres a second."

Several obstacles are still standing between the plasma jet engine that can carry us to the edge of space and reality. First, Göksel's team was using tiny plasma thrusters - about 80 millimetres in length.

It would take around 10,000 of these little thrusters to propel a standard commercial-size aircraft, so the current design is a non-starter. For now, Göksel's team intends to use 100 to 1,000 thrusters to move a smaller airship or plane, which ought to be feasible.

Like anything else that runs on electricity - especially something that needs so much electricity - the biggest problem that even the tiny version of the plasma thrusters face is the need for batteries.

They need to be lightweight enough to avoid being counterproductive, yet have enough capacity to supply the needed power. The fact that the ultimate goal is making the thrusters bigger only exacerbates the issue.

So far, this problem hasn't been solved:

"An array of thrusters would require a small electrical power plant, which would be impossible to mount on an aircraft with today's technology," the Technion-Israel Institute of Technology's Dan Lev told New Scientist.

Göksel and his team are, thus far, relying on outside power breakthroughs to bridge this gap. Improvements in solar panels or compact fusion reactors for use on aircraft or spacecraft could be exactly what this system needs.

Until something develops on that front, though, the team intends to create a hybrid craft that uses either rockets or pulse detonation combustion engines to fill in the gaps left by the plasma engine.

This article was originally published by Futurism. Read the original article.

راز معمای 400 ساله فیزیک؛ محکمیِ حباب‌های شیشه سرد شده در آب سرد، کشف شد

تیمی از دانشمندان موفق به حل معمای 400 ساله فیزیک شدند.

به گزارش ایسنا به نقل از گیزمگ، قطرات «شاهزاده روپرت» به اندازه‌ای قوی هستند که فقط با چکش می‌توان آن‌ها را در هم شکست. با این حال، چنانچه فردی انتهای این قطرات را با فشار انگشت بشکند،  به شکل پودر در می‌آیند.

حدود 400 سال است که فیزیکدانان به دنبال توضیح این پدیده هستند و به تازگی تیمی از دانشگاه پردو، دانشگاه کمبریج و دانشگاه صنعتی تالین در استونی این معما را حل کرده‌اند.

قطرات شاهزاده روپرت که اشک‌های Batavian نیز خوانده می‌شوند، در قرن هفده کشف شدند. آن‌ها زمانی معروف شدند که شاهزاده روپرت اهل باواریا در آلمان، پنج معما را در دربار چارلز دوم انگلستان مطرح کرد.

انجمن سلطنتی انگلستان در سال 1661 شروع به بررسی این قطرات کرد اما برخلاف چهار قرن تلاش محققان برای حل این معما، راز استحکام فوق‌العاده و همزمان شکنندگی خودتخریبی این قطرات در هاله‌ای از ابهام باقی ماند.

این قطره‌ها با استفاده از حباب‌های داغ و قرمزرنگ شیشه ذوب شده با ضریب انبساط حرارتی بالا و انداختن آن‌ها در ظرفی از آب سرد تولید می‌شوند؛ شیشه ذوب شده بلافاصله به شکل قطره دم‌دار جامد در می‌آید.

دانشمندان حاضر در این مطالعه از فتوالاستیسیته یکپارچه شده برای بررسی این قطرات استفاده کردند. در این تکنیک، یک شی سه بعدی شفاف در نوعی حمام غوطه‌ور معلق می‌شود و نور پلاریزه از میان آن عبور می‌کند. تغییرات حاصل شده در قطبیدگی نور در درون شی، به شکل نوارهای رنگین کمان به نمایش در می‌آید.

فیزیکدانان حاضر در  این مطالعه بر روی سر قطره متمرکز شدند و دریافتند فشارهای کمپرسی (compressive stress) در  شیشه حدود 50 تن در اینچ مربع است و این ویژگی به آن استحکام فولاد را می‌دهد.

به گفته تیم تحقیقاتی، این امر به این خاطر است که سطح بیرونی قطره سریع‌تر از داخل آن سرد می‌شود و این موضوع سطح بیرونی را به لایه‌ای متشکل از نیروهای فشاری قدرتمند تبدیل می‌کند و این نیروها به داخل قطره فشار می‌آورند.

نیروهای کمپرسی توسط نیروهای کششی داخل قطره متعادل می‌شوند و تا زمانی که این نیروها در حال تعادل باقی بمانند، قطره در وضعیت باثبات است و می‌تواند فشار فوق العاده‌ای را تحمل کند.

معمولا چون شیشه نوعی مایع فوق سرده شده است و نه جامد، هر ترکی در سطح آن گسترش یافته و آن را می‌شکند. اما در قطره شاهزاده روپرت، تعامل بین نواحی داخل و خارجی، این نیروها را به حاشیه می‌راند به طوری که ترک‌ها نمی‌توانند گسترش یابند.

با این حال، چنانچه دم قطره شکسته شود، ترک‌های موجود در آن گسترش می‌یابند، به محور قطره نفوذ کرده و وارد سر قطره می‌شوند. آسیب وارده به حدی بزرگ است که نیروهای متعادل شده آزاد می‌شوند و موجب انفجار قطره می‌شوند.

جزئیات این دستاورد علمی در  Applied Physics Letters  منتشر شد.
منبع: ایسنا

Physicists Just Came Up With a Mathematical Model for a Viable Time Machine

Physicists Just Came Up With a Mathematical Model for a Viable Time Machine

"Mathematically, it is possible."

BEC CREW
28 APR 2017

Physicists have come up with what they claim is a mathematical model of a theoretical "time machine" - a box that can move backwards and forwards through time and space.

The trick, they say, is to use the curvature of space-time in the Universe to bend time into a circle for hypothetical passengers sitting in the box, and that circle allows them to skip into the future and the past.

"People think of time travel as something as fiction. And we tend to think it's not possible because we don't actually do it," says theoretical physicist and mathematician, Ben Tippett, from the University of British Columbia in Canada.

"But, mathematically, it is possible."

Together with David Tsang, an astrophysicist at the University of Maryland, Tippett has used Einstein's theory of general relativity to come up with a mathematical model of what they're calling a Traversable Acausal Retrograde Domain in Space-time (yep, the acronym is literally TARDIS).

But before we get into the madness of legit time travel, let's put this into perspective real quick - the researchers aren't claiming to have a blueprint for a Doctor Who-style time machine that can be built tomorrow.

They say the materials we'd need to build this thing are so exotic, we haven't even discovered them yet... but we'll get to that in a minute.

Firstly, let's talk about what Tippett and Tsang are actually proposing. 

The model is based on the idea that instead of looking at the Universe in three spatial dimensions, with the fourth dimension (time) separated, we should be imagining those four dimensions simultaneously.

That allows us to consider the possibility of a space-time continuum, where different directions in space and time are all connected within the curved fabric of the Universe.

Einstein's theory of relativity links gravitational effects in the Universe to a curvature of space-time - the phenomenon thought to be behind the elliptical orbits of planets and stars.

If space-time were 'flat' or uncurved, planets would move in straight lines. But according to relativity, the geometry of space-time becomes curved in the vicinity of high-mass objects, which causes planets to bend their paths and rotate around their star instead.

What Tippett and Tsang argue is that it's not just physical space that can be bent and twisted in the Universe - time itself can also be curved in the vicinity of high-mass objects.

"The time direction of the space-time surface also shows curvature. There is evidence showing the closer to a black hole we get, time moves slower," says Tippett.

"My model of a time machine uses the curved space-time to bend time into a circle for the passengers, not in a straight line. That circle takes us back in time."

In order to harness this theoretical property, the physicists propose creating a kind of 'bubble' of space-time geometry, which carries whatever's inside it through space and time along a large circular path. 

If this bubble can hit speeds greater than the speed of light - something the pair say is mathematically possible - this would allow it to move backwards in time.

"It is a box which travels 'forwards' and then 'backwards' in time along a circular path through spacetime," the researchers explain in their paper.

"Delighted external observers would be able to watch the time travellers within the box evolving backwards in time: un-breaking eggs and separating cream from their coffee."

You can see the basic idea in the image below, with a passenger inside the bubble/time machine (person A), and an external observer standing beside it (person B). 

The arrow of time - which under normal circumstances (in our Universe, at least) always points forward, making the past become the present - is represented by the black arrows:

2419821984 timeB. K. Tippett et. al.

Both person A and person B will experience time in dramatically different ways, the researchers explain:

"Within the bubble, A will see the B's events periodically evolve, and then reverse. Outside the bubble, observer B will see two versions of A emerge from the same location: one's clock hands will turn clockwise, the other counterclockwise."

In other words, the external observer would see two versions of the objects inside the time machine: one version evolving forwards in time, the other backwards.

While Tippett and Tsang say the maths is sound, the problem now is we don't actually have the right materials to build what they're proposing.

"While is it mathematically feasible, it is not yet possible to build a space-time machine because we need materials - which we call exotic matter - to bend space-time in these impossible ways, but they have yet to be discovered," says Tippett.

Their idea recalls another theoretical time machine - the Alcubierre drive, which would also use a shell of exotic matter to transport passengers through time and space (hypothetically).

Both ideas can't go very far without some idea of how to actually produce these space-time-bending materials, but as Tippett points out, we're never going to stop wondering about the possibilities of time travel, and this is just one more direction we can take this mind-bending physics.

"Studying space-time is both fascinating and problematic," he says.

"Experts in my field have been exploring the possibility of mathematical time machines since 1949, and my research presents a new method for doing it."

The research has been published in Classical and Quantum Gravity.

Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum ***


Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum

Nanoparticles can be pushed by pure nothingness.

FIONA MACDONALD
11 APR 2017
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Researchers have discovered a new and unexpected force that acts on nanoparticles in a vacuum, allowing them to be pushed around by pure 'nothingness'.

Of course, quantum physics is beginning to make it clear that 'nothingness', as we like to think of it, doesn't actually exist - even vacuums are filled with tiny electromagnetic fluctuations. This new research is further proof that we're only beginning to understand the strange forces that are at work at the smallest level of the material world, by showing how nothingness can drive lateral motion.

So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects travelling through it.

But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects.

This is called the Casimir effect, and it was first predicted by physicists back in 1948. Now, the new study has shown that this effect is even more powerful than they imagined.

Why does that matter? This Casimir effect might only be measurable on the quantum scale, but as we start engineering smaller and smaller technology, it's becoming clear that these quantum effects can greatly influence the overall products.

"These studies are important because we are developing nanotechnologies where we're getting into distances and sizes that are so small that these types of forces can dominate everything else," said lead researcher Alejandro Manjavacas from the University of New Mexico in the US.

"We know these Casimir forces exist, so, what we're trying to do is figure out the overall impact they have [on] very small particles."

To figure out how else Casimir forces could impact nanoparticles, the team looked at what happened with nanoparticles rotating near a flat surface in a vacuum.

What they found was that the Casimir effect could actually push those nanoparticles laterally - even if they weren't touching the surface.

That's a little strange, but imagine it like this - you have a tiny sphere rotating over a surface that's constantly being bombarded with photons. While the photons slow down the rotation of the sphere, they also cause the sphere to move in a lateral direction.

NanoparticleDiscovery heroUniversity of New Mexico

In the classical physics world, friction would be needed between the sphere and the surface to achieve this lateral motion, but the quantum world doesn't follow the same results, and so it can be pushed across a surface even when it's not touching it.

"The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it," said Manjavacas.

"It's a strange reaction but one that may prove to have significant impact for engineers."

All of this might sound a little obscure, but it could play an important role in figuring out how to develop smaller and smaller technology, as well as devices such as quantum computers.

Intriguingly, the researchers show that they could control the direction of the force by changing the distance between the particle and the surface, which could one day come in handy for engineers and researchers who are constantly looking for better ways to manipulate matter on the nano-scale.

The findings now need to be replicated and verified by other teams. But the fact that we now have evidence of an intriguing new force that could be used to direct nanoparticles within 'nothingness' is pretty exciting - and suggests we're one step closer to understanding the weird forces at work in the quantum world.

The research has been published in Physical Review Letters.