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#3700 by rq3 on 09 Jul, 2016 14:24
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It generates splatter because it's an AM (amplitude modulated) oscillator being driven to 100% modulation depth with an approximation of a square wave. The Fourier frequencies extend (theoretically) to infinity. You get the fundamental carrier of the magnetron, +/- all of the Fourier frequencies.
If you are still talking about 60 Hz then no that is incorrect. The Fourier coefficients of a square wave do not all have the same amplitude. They fall off very rapidly. To get a sideband 1 MHz away from the nominal magnetron center frequency (choose any frequency +/- 10 MHz) there would have to be an harmonic 17,000 times the 60 Hz. Anyway there is no square wave. The half-wave rectified AC is half a sine wave, not a square wave. Define "splatter". What is the mechanism according to the established physics of RF energy that creates this "splatter"? Also AM modulation does not create phase noise or a broadband signal.
I think most of what is seen in rfmwguy's spectral plot is from the magnetron RF overdriving the spectrum analyzer he is using. You were right in your earlier post. He needs to put more attenuators on the input and maybe put the unit in a well shielded box.
All non-linear devices exhibit AM/PM conversion. Magnetrons are particularly notorious for this, and a major reason they are rarely used in RADAR applications. -
#3701 by X_RaY on 09 Jul, 2016 14:33
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Quote from: rfmwguy
..snip..
Rather than the expense of phase locking a fundamental to the molecular resonance of H2O, designers chose to fire a broad-band signal around 2.45 GHz that would contain multiple "spikes" so when thermal drifting, there would always be a component at or near molecular resonance of water, which heats the food.
...
There is no fundamental molecular resonance of H2O in this frequency spectrum. Heating of water also works at frequencies like 900MHz or any other. The Heating effect is related to the dipolemoment and the reorientation of the molecules in the electric field. Its simply heating by moving the molecules:
https://de.wikipedia.org/wiki/Orientierungspolarisation
Sorry couldn't find a english version of the site.Quote from: wikipediaNevertheless, the primary heating effect of all types of electromagnetic fields at both radio and microwave frequencies occurs via the dielectric heating effect, as polarized molecules are affected by a rapidly alternating electric field.
...
https://en.wikipedia.org/wiki/Microwave_oven
http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html
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#3702 by Rodal on 09 Jul, 2016 15:38
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...
There is no fundamental molecular resonance of H2O in this frequency spectrum. Heating of water also works at frequencies like 900MHz or any other. The Heating effect is related to the dipolemoment and the orientation of the molecules in the electric field. Its simply heating by moving the molecules:
....
You are correct, X_Ray, here is another chart showing further information, courtesy of London South Bank University, notice the upper horizontal axis, going from less than 1 GHz at the right hand end to more than 1000 GHz at the left end.
Notice the very important influence of temperature (different curves for different temperatures).
Notice the vertical bar at 2.45 GHz, showing how wrong is the statement that...
Rather than the expense of phase locking a fundamental to the molecular resonance of H2O, designers chose to fire a broad-band signal around 2.45 GHz that would contain multiple "spikes" so when thermal drifting, there would always be a component at or near molecular resonance of water, which heats the food.
...
Water has a huge number of resonance peaks in the spectrum, but looking just at the frequencies of interest (GHz):
The local resonance peak (shown by the dielectric loss, in the blue curves) at 20 deg C is at around 20 GHz instead of at 2.45 GHz
At 100 deg C (the boiling point of water) the dielectric loss (blue curves) exceeds 100GHz. There is nothing much at around 2.45 GHz
There was nothing at 2.45 GHz to "lock in"
Here is a chart showing attenuation for atmosphere constituents such as water vapour (H2O) and molecular oxygen (O2). Notice that the axis is logarithmic
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation. Microwaves are strongly absorbed at wavelengths shorter than about 1.5 cm (above 20 GHz) by water and other molecules in the air.
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#3703 by Monomorphic on 09 Jul, 2016 17:18
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Another quick dampening test. First bump is a light tap, afterwards there is some movement from me walking around in the room. But when I am still, it is surprisingly stable.
Will work on proper labeling/annotation next.
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#3704 by rfmwguy on 09 Jul, 2016 18:21
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Still always there to correct me I see. I have removed my incorrect assumption to Shell as I have just googled the same info the way you did and found it to be fairly accurate although you did not explain why exactly 2.45 GHz was utilized in cooking....
There is no fundamental molecular resonance of H2O in this frequency spectrum. Heating of water also works at frequencies like 900MHz or any other. The Heating effect is related to the dipolemoment and the orientation of the molecules in the electric field. Its simply heating by moving the molecules:
....
You are correct, X_Ray, here is another chart showing further information, courtesy of London South Bank University, notice the upper horizontal axis, going from less than 1 GHz at the right hand end to more than 1000 GHz at the left end.
Notice the very important influence of temperature (different curves for different temperatures).
Notice the vertical bar at 2.45 GHz, showing how wrong is the statement that...
Rather than the expense of phase locking a fundamental to the molecular resonance of H2O, designers chose to fire a broad-band signal around 2.45 GHz that would contain multiple "spikes" so when thermal drifting, there would always be a component at or near molecular resonance of water, which heats the food.
...
Water has a huge number of resonance peaks in the spectrum, but looking just at the frequencies of interest (GHz):
The local resonance peak (shown by the dielectric loss, in the blue curves) at 20 deg C is at around 20 GHz instead of at 2.45 GHz
At 100 deg C (the boiling point of water) the dielectric loss (blue curves) exceeds 100GHz. There is nothing much at around 2.45 GHz
There was nothing at 2.45 GHz to "lock in"
Here is a chart showing attenuation for atmosphere constituents such as water vapour (H2O) and molecular oxygen (O2). Notice that the axis is logarithmic
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation. Microwaves are strongly absorbed at wavelengths shorter than about 1.5 cm (above 20 GHz) by water and other molecules in the air. -
#3705 by X_RaY on 09 Jul, 2016 19:04
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...I have removed my incorrect assumption to Shell as I have just googled the same info the way you did and found it to be fairly accurate although you did not explain why exactly 2.45 GHz was utilized in cooking...
There are historical and technical reasons to use this frequency but the the most important is that 2.4GHz-2.5GHz is worldwide defined as ISM band (free for Industrial, Scientific and Medical use). Also the size of the required components is good to handle and can be easy and cheap manufactured.
Over this the penetration depth of the EM field is fine for cooking food and safety issues are good to handle (wavelength in comparison with the door gaps and so on).Quote from: wikipedia...
Microwave ovens use frequencies in one of the ISM (industrial, scientific, medical) bands, which are reserved for this use, so they do not interfere with other vital radio services. Consumer ovens usually use 2.45 gigahertz (GHz)—a wavelength of 12.2 centimetres (4.80 in)—while large industrial/commercial ovens often use 915 megahertz (MHz)—32.8 centimetres (12.9 in)
...
The microwave frequencies used in microwave ovens are chosen based on regulatory and cost constraints. The first is that they should be in one of the industrial, scientific, and medical (ISM) frequency bands set aside for non-communication purposes. For household purposes, 2.45 GHz has the advantage over 915 MHz in that 915 MHz is only an ISM band in the ITU Region 2 while 2.45 GHz is available worldwide. Three additional ISM bands exist in the microwave frequencies, but are not used for microwave cooking. Two of them are centered on 5.8 GHz and 24.125 GHz, but are not used for microwave cooking because of the very high cost of power generation at these frequencies. The third, centered on 433.92 MHz, is a narrow band that would require expensive equipment to generate sufficient power without creating interference outside the band, and is only available in some countries.
... -
#3706 by rfmwguy on 09 Jul, 2016 19:32
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This is very correct. Somewhere along the line, someone told me it was ideal for moving water molecules around. Turns out, lots of MW freqs are, especially 22 GHz. Guess I'll leave molecular chemistry alone for a while...back to the shop...Still always there to correct me I see. I have removed my incorrect assumption to Shell as I have just googled the same info the way you did and found it to be fairly accurate although you did not explain why exactly 2.45 GHz was utilized in cooking. Feel free to report this post to the Mods as has been your habit over the past several months.
There are historical and technical reasons to use this frequency but the the most important is that 2.4GHz-2.5GHz is worldwide defined as ISM band (free for Industrial, Scientific and Medical use). Also the size of the required components is good to handle and can be easy and cheap manufactured. -
#3707 by dustinthewind on 09 Jul, 2016 19:34
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Its difficult to describe without a chalkboard. I'll check back from time to time, but have put in a lot of long hours...time is a precious commodity. Thanks again.
I wanted to suggest a possibly simple improvement for Dave's experiment. There is talk about the thermal thrust displacement of his pendulum/frustum. I would think the displacement of air over time could be fairly long in period as opposed to an EM thrust. The idea is to let the frustum develop its thermal displacement of the pendulum which should be a fairly constant displacement. This is if the thermal equilibrium and gradient can be kept about constant and the magnetron can be kept in lock
The EM thrust (if there is any) should be pulsed at the period of osculation for the pendulum. Under-dampening of the pendulum may be desirable in this situation. Basically, he won't be interested in the constant displacement of the pendulum but rather the period and amplitude of osculation for the pendulum. What would be needed is to take into account a dampened harmonic oscillator to derive the amount of force being applied. The nature of a harmonic oscillator should amplify the observation of any force if there is any.
If a test pulse of force is needed it may be possible to do this by winding a coil or solenoid and placing it near an aluminum/copper plate hanging from the pendulum. When the coil is turned on at a known number of turns and current a change in the magnetic field should develop counter-currents in the plate pushing the plate away. The solenoid could be pulsed at the frequency of the pendulum to test the system.
I felt like I should provide a solution of a pendulum with this suggestion. Below is attached the solution for a damped pendulum worked out in wxMaxima. Amplitude max is A/(2*c*w) where A= force magnitude, c= damping constant, w=sqrt(g/L)=sqrt(m*g*L/I)-see paper-=radians/second of pendulum. f=w/(2*pi)=frequency of pendulum=cycles/second. I have attached a paper "notes13a.pdf" on a damped pendulum and the link to this paper is located here: https://www.physast.uga.edu/uploads/phys1111_stancil/notes13a.pdf The solution I present assumes small displacement theta<25 degrees. The force applied is in one direction to simulate a force from the EM drive. A test force can be used to test the system. From the test force and the known frequency of the pendulum one can get the damping constant.
In the image plot the pendulum starts out displaced and the force is applied in opposition to the swing. The pendulum slows down and then speeds back up till it reaches maximum amplitude. The extra constant term of the solution is a symptom of applying a force in only one direction and isn't really needed. the force applied is in the form of a sin wave that sits above zero.
The y(t) is a displacement along the curved path for the pendulum. This should be approximately straight for small angles/long pendulums. A long pendulum being seemingly more desirable for the increased displacement.
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#3708 by zen-in on 09 Jul, 2016 21:49
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To be fair, the rectified signal must contain a square wave component as it can be mathematically expressed with such. Although, I have a bit of confusion how a half wave rectified AC signal turns into 60Hz. I suspect we might be discussing a full wave rectified signal. That said, I must agree with zen-in that the harmonics aren't causing the signal seen.
For a full wave signal, we can express that signal as a sine wave multiplied by a square wave of the same period. Negative components of both multiply to become positive.
The Fourier transform of such is then given by the convolution of the transforms of each individually
Likewise, a half wave signal can be expressed as a multiplication of a sine wave with a square wave containing a DC offset (to bring the wave from 2V to 0 instead of V to -V).
Re-normalizing the amplitude, this transform looks similar:
What's important is the summation terms in both. As the cosine terms necessarily cannot become greater than 1, we see that the amplitude of each harmonic falls off as the power of that harmonic squared. The 10,000th harmonic of 60Hz (even less for 17k) at best contributes one part in 400 million to the overall energy of the signal. This corresponds to a -86db drop from peak; and although I can't read the spectrum analyzer display very clearly, I suspect it broadens far earlier than that.
I asked a friend today who has many years experience as an RF engineer what his opinion was about magnetron "splatter". He said the microwave oven supplies drive the magnetron with time-varying power. During each cycle the current and voltage vary, due to the half wave rectification so that causes the output frequency to vary. If someone used a spectrum analyzer that had a line sweep and if they varied the synch level they would the see the output frequency move up and down and also increase/decrease in amplitude with the changes in synch level (the same as phase of the AC). So I stand corrected. There is splatter due to the way microwave oven power supplies are made. But this has nothing to do with the harmonic content of the half wave power. It is just because the operating point (voltage, current) is constantly changing. I was also told that a lot of filtering is required to achieve a stable output. High voltage power inductors and voltage regulation are needed. Just adding more diodes and caps is not enough. -
#3709 by Monomorphic on 10 Jul, 2016 00:01
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Looking forward to the future, including a completely battery-powered build, I think it is feasible for a DIYer to build a spherical air bearing. This system would allow the emdrive to accelerate on its own. I am in the early stages of designing such a system. This would be a separate test-stand augmenting the current torsional pendulum.
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#3710 by otlski on 10 Jul, 2016 00:41
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Looking forward to the future, including a completely battery-powered build, I think it is feasible for a DIYer to build a spherical air bearing. Such a system would allow the emdrive to accelerate on its own. I am in the early stages of designing such a system. This would be a separate test-stand augmenting the current torsional pendulum.
Given the issues that our intrepid experimenters are running in to now, a hemispherical air bearing would definitely be a step up. However, as someone who has made hundreds of air bearings, my guess is that a DIY one suitable of doing what the one in your video does, would take you more hours than you have invested already. The overall surface profile is +/- 50 millionths inch from a true sphere. The shiny finish isn't just pretty, it is there to limit self-motoring of the rotor. The jeweled orifices are machined to breach the surface exactly at the right angle to further reduce the chance of motoring. The difference in spherical radius between the rotor and stator is 500 millionths inch. The one in your video, is a high pressure, low flow bearing running at about 50% efficiency. Yes, one can build a lesser version where a low pressure high flow source (vacuum cleaner) can power it, but then high flow disturbances will corrupt the measurement. It can be done but is not that easy. BTW - The one in your video is diamond turned to shape by a machine made with air bearings.
When you get to the point of strongly indicated positive results with your existing experiments, PM me. -
#3711 by dustinthewind on 10 Jul, 2016 02:03
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... a DIYer to build a spherical air bearing. This system would allow the emdrive to accelerate on its own. ...
It would be nice to let it accelerate on its own. One issue is separating thermal air flow from the actual thrust if there is any. One of the reasons for suggesting boosting at resonance on an osculating pendulum is to separate the thermal thrust from any useful thrust it may have. That is, if thermal thrust can be made not to osculate, while the useful thrust can. Now that I think of it the pendulum approach does allow it to freely accelerate.
I was just thinking that if you tilt the air bearing it also can be used as a pendulum. Good point from Swallow below is that it wouldn't work in a vacuum test. ... Maybe a magnetic bearing then? -
#3712 by A_M_Swallow on 10 Jul, 2016 07:14
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... a DIYer to build a spherical air bearing. This system would allow the emdrive to accelerate on its own. ...
It would be nice to let it accelerate on its own. One issue is separating thermal air flow from the actual thrust if there is any. One of the reasons for suggesting boosting at resonance on an osculating pendulum is to separate the thermal thrust from any useful thrust it may have. That is, if thermal thrust can be made not to osculate, while the useful thrust can. Now that I think of it the pendulum approach does allow it to freely accelerate.
I suspect that an air bearing does not work in a vacuum. People plan to perform some Emdrive testing in a vacuum to simulate outer space and eliminate hot air effects. -
#3713 by RERT on 10 Jul, 2016 09:22
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Frobnicat -
You have discussed the period of motion of rfmwguy's test setup with reference to the periods of undamped pendulums, arguing that some end up with implausible dimensions.
A damped pendulum follows an equation
d˛x/dt˛+2a(dx/dt)+ω˛=C
where a is a damping constant, omega is the natural frequency, and C is an externally applied acceleration.
In the underdamped case, kernel solutions are A*exp(λt), where
λ = -a±i*√(ω˛-a˛)
In other words, the frequency is modified by the damping constant, and can be arbitrarily small, i.e. the period arbitrarily long.
I make no comment on your conclusions, which might be valid, but unless I've misread something the logic is in this way flawed.
regards,
R. -
#3714 by frobnicat on 10 Jul, 2016 11:15
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@RERT
Yes the observed (pseudo)period of a damped harmonic oscillator is longer than the natural (undamped) period, but if there is significant observed oscillation at all (which is the case, clearly with the pen side tap) meaning we are significantly less than critically damped case then the pseudo-period can't be much larger than the natural period (undamped, that I calculated above) :
While pulsation ω1 can indeed be made arbitrarily small (pseudo-period arbitrarily large) relative to ω0 this means ζ<1 very close to one and no perceptible oscillations (back and forth) to speak of. For instance at ζ=0.5 behavior is barely oscillating, one overshoot, one very attenuated undershoot and that's it. See green curve below. Is it the kind of "oscillations" that you consider attributing to other axis than yaw to the minute long swings in rfmwguy's plots ?
ζ=0.5 gives pseudo period T1 ≈ 1.15 T0, not significantly longer while already barely oscillating. Why I wrote "If it oscillates at all then we know that the period of such damped oscillations can't be far from un-damped ones, as calculated above."
Now if you wan't we could (should ?) discuss 2 other aspects :
- Sampling period (data acquisition) can indeed make spurious apparent periods >> period of a signal and period of sampling, depending on filtering input analog data. I don't think so in the plots we see (for reasons I have no time to substantiate right now)
- Oscillations for the recorded decays after frustum/magnetron power off have an amplitude that is not clearly decaying, are not really regular, and appear more like a perturbed (forced) chaotic motion that the natural slightly underdamped decay (in Yaw) after side tap : air flows ?
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#3715 by Star One on 10 Jul, 2016 13:47
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Does anyone know the status of the new paper by White and March?
No
I just received the paper Dr. White published in September. A Discussion on Characteristics of the Quantum Vacuum, published in Physics Essays, Sept. 2015. http://physicsessays.org/browse-journal-2/product/1396-11-harold-sonny-white-a-discussion-on-characteristics-of-the-quantum-vacuum.html
It's not what you're looking for but I found it to be a very inspiring read. I'm currently working on a response to this discussion.
Last I heard, after several re-writes of their copper frustum in-vacuum paper, there is no hope in sight of getting it past the peer reviewers for the Journal in question. Not much else going on, due to budget cuts. It sounds like any work being done is on their own time.
So are you saying that funding for their work has been cut? -
#3716 by otlski on 10 Jul, 2016 13:54
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... a DIYer to build a spherical air bearing. This system would allow the emdrive to accelerate on its own. ...
It would be nice to let it accelerate on its own. One issue is separating thermal air flow from the actual thrust if there is any. One of the reasons for suggesting boosting at resonance on an osculating pendulum is to separate the thermal thrust from any useful thrust it may have. That is, if thermal thrust can be made not to osculate, while the useful thrust can. Now that I think of it the pendulum approach does allow it to freely accelerate.
I was just thinking that if you tilt the air bearing it also can be used as a pendulum. Good point from Swallow below is that it wouldn't work in a vacuum test. ... Maybe a magnetic bearing then?
An air bearing would work in a vacuum but would only have a max working pressure of 14.7 p.s.i. In this configuration the bearing's pressure input would be ported through the chamber wall to "suck" normal air in. Of course, the pumps would have to run continuously to maintain a less than ideal vacuum but it would be good enough to get the data. For a 6 inch bearing, 14.7 psi delta would allow for a 50 lb payload.
In a different configuration, we have had customers go as far to supply 60 p.s.i. to the input while in the chamber and let the pumps take care of the increased parasitic air flow. The high efficiency versions of air bearings have low flow demands to make this possible to do.
Alternatively, in the absence of a vacuum chamber, other gasses can be used to pressure the bearing and a tent used to surround the test, and the results compared and extrapolated to a vacuum environment.
I don't know much about magnetic bearings but thoughts of electromagnetic field interactions with the EM drive leaves me fraught with questions. -
#3717 by mharney on 10 Jul, 2016 15:11
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Has anybody tried filling a cavity with ammonia or hydrogen and using stimulated emissions to increase the number of photons (which increases the power)? If we can increase the number of photons in the cavity without increasing the weight we may increase the measurable thrust out of micronewtons and into 100 milinewtons which will eliminate thermal and other effects as false positives. Plus, the battery required to generate high power levels is smaller if the design uses stimulated emissions. http://vixra.org/abs/1604.0024
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#3718 by TheTraveller on 10 Jul, 2016 15:12
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I asked Roger to check Dave's Q, freq & likely mode. His reply:Quote
Hi Phil
Thanks for the update.
I have run Dave’s design through our software for D1=254mm D2=158.75mm L=205.74mm
Then for TM013 mode, Fo=2462.5MHz Df= 0.4886
Theoretical Q = 88,500 but even with high precision machining and spherical endplates, max practical Q would be around 60,000. With flat end plates 10,000 is probably the max achievable, but is compatible with a commercial magnetron.
Direct injection without any circulator and load to absorb reflected power is very hard on the magnetron and I would not expect a very long life.
From the displacement data it looks like Dave is measuring a reaction force and acceleration. To obtain a true value of thrust, the dynamics of the measurement apparatus would need to be modelled and Newton’s laws applied.
Best regards
Roger.
Roger's resonant freq & mode match my spreadsheet calcs. Calcs based on standard microwave enginerring equations for the calculation of guide wavelength at 65,000 points along the frustum's varying diameter length axis & then numerically integerated to obtain the average guide wavelength and from that the excitation freq that allows 3 x 1/2 averaged guide waves to fit between the end plates in TM013 mode. Yes I know many here will not accept this but hey guys, Dave's VNA S11 rtn loss scan finds resonance at 2.44GHz or 20MHz lower (< 1% error). Which says to me Roger's calcs & theory regarding how guide wavelength varies inside a resonant frustum is correct.
Using Roger's force equation we get (2 × 10,000Qu x 0.4886Df x 900Pwr) / 299,700,000c = 29mN. Dave's best result 18.4mN. -
#3719 by Chrochne on 10 Jul, 2016 17:08
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Does anyone know the status of the new paper by White and March?
No
I just received the paper Dr. White published in September. A Discussion on Characteristics of the Quantum Vacuum, published in Physics Essays, Sept. 2015. http://physicsessays.org/browse-journal-2/product/1396-11-harold-sonny-white-a-discussion-on-characteristics-of-the-quantum-vacuum.html
It's not what you're looking for but I found it to be a very inspiring read. I'm currently working on a response to this discussion.
Last I heard, after several re-writes of their copper frustum in-vacuum paper, there is no hope in sight of getting it past the peer reviewers for the Journal in question. Not much else going on, due to budget cuts. It sounds like any work being done is on their own time.
So are you saying that funding for their work has been cut?
So there is no desire to publish it. Easy as that. Only thing they can do is try to publish it without official approaval, which they will of course will not do.
