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beecee last won the day on August 5

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About beecee

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  • Birthday 07/18/1944

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  1. 4-D Printing: extract: 4-D printing is conventional 3-D printing combined with the additional element of time as the fourth dimension, where the printed objects can re-shape or self-assemble themselves over time with external stimuli, such as mechanical force, temperature, or a magnetic field. In this research, the team made use of the elastic energy stored in the stretched precursors for shape morphing. When the stretched ceramic precursors are released, they undergo self-reshaping. After heat treatment, the precursors turn into ceramics. :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Origami and 4D printing of elastomer-derived ceramic structures: Abstract: Four-dimensional (4D) printing involves conventional 3D printing followed by a shape-morphing step. It enables more complex shapes to be created than is possible with conventional 3D printing. However, 3D-printed ceramic precursors are usually difficult to be deformed, hindering the development of 4D printing for ceramics. To overcome this limitation, we developed elastomeric poly(dimethylsiloxane) matrix nanocomposites (NCs) that can be printed, deformed, and then transformed into silicon oxycarbide matrix NCs, making the growth of complex ceramic origami and 4D-printed ceramic structures possible. In addition, the printed ceramic precursors are soft and can be stretched beyond three times their initial length. Hierarchical elastomer-derived ceramics (EDCs) could be achieved with programmable architectures spanning three orders of magnitude, from 200 μm to 10 cm. A compressive strength of 547 MPa is achieved on the microlattice at 1.6 g cm−3. This work starts a new chapter of printing high-resolution complex and mechanically robust ceramics, and this origami and 4D printing of ceramics is cost-efficient in terms of time due to geometrical flexibility of precursors. With the versatile shape-morphing capability of elastomers, this work on origami and 4D printing of EDCs could lead to structural applications of autonomous morphing structures, aerospace propulsion components, space exploration, electronic devices, and high-temperature microelectromechanical systems.
  2. How Einstein's equivalence principle extends to the quantum world has been puzzling physicists for decades, but a team including a University of Queensland researcher has found the key to this question. UQ physicist, Dr. Magdalena Zych from the ARC Centre of Excellence for Engineered Quantum Systems, and the University of Vienna's Professor Caslav Brukner have been working to discover if quantum objects interact with gravity only through curved space-time. "Einstein's equivalence principle contends that the total inertial and gravitational mass of any objects are equivalent, meaning all bodies fall in the same way when subject to gravity," Dr. Zych said. "Physicists have been debating whether the principle applies to quantum particles, so to translate it to the quantum world we needed to find out how quantum particles interact with gravity. Read more at: <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> the paper: Quantum formulation of the Einstein equivalence principle: Abstract: The validity of just a few physical conditions comprising the Einstein equivalence principle (EEP) suffices to ensure that gravity can be understood as spacetime geometry. The EEP is therefore subject to ongoing experimental verification, with present-day tests reaching the regime in which quantum mechanics becomes relevant. Here we show that the classical expression of the EEP does not apply in such a regime. The EEP requires equivalence between the rest mass-energy of a system, the mass-energy that constitutes its inertia, and the mass-energy that constitutes its weight. In quantum mechanics, the energy contributing to the mass is given by a Hamiltonian operator of the internal degrees of freedom. Therefore, we introduce a quantum expression of the EEP—equivalence between the rest, inertial and gravitational internal energy operators. Validity of the classical EEP does not imply the validity of its quantum formulation, which thus requires independent experimental verification. We propose new tests as well as re-analysing existing experiments, and we discuss to what extent they allow quantum aspects of the EEP to be tested.
  3. I would 100% agree with charge being neutralised pretty quickly, it was the static solution [zero angular momentum] that had me somewhat disturbed. But as you say, probably never been observed. OK, I believe I can live with that...thanks for the answers and clearing up a couple of misconceptions.
  4. So the Reisner-Norstrom BH is just a theoretical idealised solution, not evidenced? OK this confuses me....I would have thought any BH is defined by some mass, which critically curves the spacetime it is embedded in. I understand that it is a solution to Einstein's field equations with the simplest outcome for convenience. Please alleviate my confusion!! Remember as a lay person I need to be treated a virgin if you will. Ahaa! something I have learnt today!! I have not previously been aware of the " Vaidya" or Vaidya-Bonnor metric.....Thanks. I must say at this stage most of what I do know about BH's was gained a decade or more ago, and I certainly have not done to much brushing up with reputable reading to add to that past knowledge.
  5. Astronomers using the ultraviolet vision of NASA's Hubble Space Telescope have captured one of the largest panoramic views of the fire and fury of star birth in the distant universe. The field features approximately 15,000 galaxies, about 12,000 of which are forming stars. Hubble's ultraviolet vision opens a new window on the evolving universe, tracking the birth of stars over the last 11 billion years back to the cosmos' busiest star-forming period, which happened about 3 billion years after the big bang. Read more at:
  6. Oort clouds around other stars should be visible in the cosmic microwave background August 16, 2018 by Matt Williams, Universe Today For decades, scientists have theorized that beyond the edge of the solar system, at a distance of up to 50,000 AU (0.79 ly) from the sun, there lies a massive cloud of icy planetesimals known as the Oort Cloud. Named in honor of Dutch astronomer Jan Oort, this cloud is believed to be where long-term comets originate from. However, to date, no direct evidence has been provided to confirm the Oort Cloud's existence. Read more at: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: the paper: ABSTRACT: Long-period comets observed in our solar system are believed to originate from the Oort cloud, which is estimated to extend from roughly a few thousand to 105 AU from the Sun. Despite many theoretical arguments for its existence, no direct observations of the cloud have been reported. Here, we explore the possibility of measuring Oort clouds around other stars through their emission at submillimeter wavelengths. Observations with the 545 and 857 GHz bands of the Planck satellite are well matched to the expected temperatures of Oort cloud bodies (on the order of 10 K). By correlating the Planck maps with catalogs of stars observed by the Gaia mission, we are able to constrain interesting regions of the exo-Oort cloud parameter space, placing limits on the total mass and the minimum size of grains in the cloud. We also explore an observed excess around the brightest and nearest stars in our sample as arising from possible exo-Oort clouds or other extended sources of thermal emission. We compare our measurements with known debris disk systems – in the case of Vega and Fomalhaut we find a significant excess that is in agreement with measurements from Herschel. We use the measurements around Fomalhaut to constrain a possible exo-Oort cloud of that system. We argue that future CMB surveys and targeted observations with far-infrared and millimeter wavelength telescopes have the potential to detect exo-Oort clouds or other extended sources of thermal emission beyond ∼ 1000 AU
  7. interpreting hubble data

    You are obviously in the wrong section. Hypothetical and speculative rhetoric should be in speculations. Actually the observable universe/space/time is around 46 L/years distant in all directions. The first step for anyone attempting to invalidate such an overwhelmingly accepted and evidenced theory such as the BB, is to know the model/theory they are trying to invalidate. In actual fact the BB says nothing about any beginning, rather it describes the evolution of space and time from t+10-43 seconds. Firstly C is actually "c"......secondly the recessional velocities of galaxies near the edge of our observable universe are receding at greater then "c". The spacetime expansion is not curtailed by the universal speed limit which only applies to anything with mass. The recessional velocities are evidenced by the cosmological redshift. The BB is overwhelmingly supported because it aligns with four very important pillars of cosmology. [1] The observed expansion: [2] The CMBR [3] The abundance of the lighter elements. [4] Galactic structure and formation.
  8. Because in places of higher mass-energy density, spacetime expansion is negated by gravity. If it was stretching in the manner that you seem to be proposing, it would be stretching everywhere.The BB also describes the evolution of space and time [as we know them] so asking what was before t=0, is like asking what is north of the north pole to quote the late great Stephen Hawking.
  9. I was thinking along the lines of matter falling in, and accretion disk interactions...I would hazard a guess and say depending on trajectory etc, that this could also spped up angular momentum. Hmmm, can you elaborate on that answer a bit? Again, my thoughts are that it would be the natural end state, well into the future [hundreds of billions of years] and prior to BH evaporation via Hawking Radiation process.
  10. The answer is yes to both. Maxwell’s equations can very easily be generalised to curved spacetimes; in fact all you need to do here is write them in terms of the differential forms formalism, which is fully covariant. Likewise, EM fields function as sources of gravity - all you need to do here is insert the stress-energy tensor for the electromagnetic field into the Einstein equations. Ideally one of these (either a metric, or an EM field) will be given, and you can then calculate the other. If you know only a distribution of sources, but neither metric nor EM field, then you will need to solve a system of equations that comprises both the Maxwell and the Einstein equations. This is potentially very challenging, mathematically speaking. But yes, EM fields influence the geometry of spacetime, and the geometry of spacetime influences EM fields. It’s a pretty complex and non-linear “feedback system”. While I understand that charge, mass and angular momentum are the only three properties a BH can have, charge would be quickly negated, would it not? and over far longer periods of time, so to would angular momentum. In other words the Schwarzchild metric while obviously being the simplest, is also the end state of all BH's.
  11. Overall I believe popular science articles in the mainstream press, do far more good then any potential misunderstandings due to sensationalism. And while recognising that, any potential misunderstanding/s can be alleviated by further checking out news outlets and asking questions if one is interested in any particular item that is revealed. In fact I will go as far as to say mainstream press popular science outlets are totally necessary if scientific discoveries etc, are to spark any interest in science at the public The recent discoveries of GW's sparked tremendous interest in my country, and were publicised as "ripples in spacetime". With that example, in my opinion at least, not enough information was released at least with regards to what a GW would actually do if it were large enough and should pass our way. Finally I believe any thinking person should know, that journalistic sensationalism is par for the course and exists in near all forms of news item releases. And obviously if any form of personal involvement was to be anticipated [say buying a new car after seeing an advert] then further research into said car is a must. Good idea!
  12. Quest for source of black hole dark matter August 14, 2018 by Anne M Stark, Lawrence Livermore National Laboratory Like a game of "hide and seek," Lawrence Livermore astrophysicists know that there are black holes hiding in the Milky Way, just not where. "If they find them toward the galactic bulge (a tightly packed group of stars) and the Magellanic Clouds, then black holes as massive as 10,000 times the mass of the sun might make up dark matter. If they are only toward the galactic bulge then they are probably just from a few dead stars." Read more at: extract: "We are developing a novel means of microlensing detection that will enable us to detect the parallactic microlensing signature associated with black holes in this mass range," Dawson said. "We will detect and constrain the fraction of dark matter composed of intermediate mass black holes and measure their mass spectrum in the Milky Way." Read more at: """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" Primordial black holes as dark matter: constraints from compact ultra-faint dwarfs: Abstract The ground-breaking detections of gravitational waves from black hole mergers by LIGO have rekindled interest in primordial black holes (PBHs) and the possibility of dark matter being composed of PBHs. It has been suggested that PBHs of tens of solar masses could serve as dark matter candidates. Recent analytical studies demonstrated that compact ultra-faint dwarf galaxies can serve as a sensitive test for the PBH dark matter hypothesis, since stars in such a halo-dominated system would be heated by the more massive PBHs, their present-day distribution can provide strong constraints on PBH mass. In this study, we further explore this scenario with more detailed calculations, using a combination of dynamical simulations and Bayesian inference methods. The joint evolution of stars and PBH dark matter is followed with a Fokker–Planck code PHASEFLOW. We run a large suite of such simulations for different dark matter parameters, then use a Markov chain Monte Carlo approach to constrain the PBH properties with observations of ultra-faint galaxies. We find that two-body relaxation between the stars and PBH drives up the stellar core size, and increases the central stellar velocity dispersion. Using the observed half-light radius and velocity dispersion of stars in the compact ultra-faint dwarf galaxies as joint constraints, we infer that these dwarfs may have a cored dark matter halo with the central density in the range of 1–2 M⊙pc − 3, and that the PBHs may have a mass range of 2–14 M⊙ if they constitute all or a substantial fraction of the dark matter. :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: I see this as interesting research which may lead to the probable answer to one of cosmology's most asked question. But my first thought/s, would be does it or can it, explain the "Bullet Cluster" observation?
  13. So pray tell, what is the electron in an atom of hydrogen pushing against? Leaving that pseudo claim........ Great detailed answer Marcus! This is obviously Pauli's exclusion principle in operation, correct?
  14. Most scientists do accept that we are probably not alone in this universe. Many reasons for that starting with the fact that Earth does not hold any privileged position. Along with the facts that the "near infinite" extent and content of the universe, and the stuff of life being everywhere we look, leads reasonable opinion to conclude that we are not alone. Still the fact remains that so far we do not have any convincing evidence of any life off this Earth, let alone any Alien visitations and anal probing on Earth. Those are the facts at this time, not withstanding the sensational claims of impressionable gullible folk who are so fascinated and in awe of mystique in the world around them, that it clouds any logical judgement on their part.