Il campo elettrico fuori dal conduttore percorso da corrente

The electric field outside a conductor in which was flowing a current was observed experimentally by  Oleg J. Jefimenko. "He had an ingenious idea of utilizing grass seeds as test particles near current carrying wires. They are electrically neutral in normal state so that they do not induce any charges in the conductor. On the other hand, they are easily polarized in the presence of an electric field, aligning themselves with it. The lines of electric field are then observed in analogy with iron fillings generating the lines of magnetic field." [Assis, A. K. T., Rodrigues, W. A., & Mania, A. J. (1999). The electric field outside a stationary resistive wire carrying a constant current. Foundations of Physics, 29(5), 729-753.]. Jefimenko presented his results in Plate 6 of  his Electricity and Magnetism, Meredith Publishing. 1966. 

Earnshaw's Theorem

Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic fields, but was first applied to electrostatic fields. Earnshaw's theorem applies to classical inverse-square law forces (electric and gravitational).
It means that it is linked to the Gauss Law. And here a proof.

Bernoulli Numbers: from Ada Lovelace to the Debye Functions

Bernoulli Numbers: from Ada Lovelace to the Debye Functions: Jacob Bernoulli owes his fame for the numerous contributions to calculus and for his discoveries in the field of probability. Here we will discuss one of his contributions to the theory of numbers, the Bernoulli numbers. They were proposed as a case study by Ada Lovelace in her analysis of Menabrea's report on Babbage Analytical Engine. It is probable that it was this Lovelace's work, that inspired Hans Thirring in using the Bernoulli numbers in the calculus of the Debye functions.

Mimetic "animal"

The original image is available at the link

https://mars.jpl.nasa.gov/msl-raw-images/msss/01928/mcam/1928MR0100610000900537E01_DXXX.jpg

The image was taken by Mastcam: Right (MAST_RIGHT) onboard NASA's Mars rover Curiosity on Sol 1928 (2018-01-08 04:04:28 UTC). Image Credit: NASA/JPL-Caltech/MSSS 

Some processing of the image is giving this mimetic "animal".

Recurrence Plots of Pulsar Profiles (Philica, 2015)

Recurrence plots of pulsar profiles
Amelia Carolina Sparavigna Polito - Politecnico di Torino [Torino]

Abstract : Pulsars are rotating neutron stars that have an emission of electromagnetic
radiations which is continuous but beamed. Therefore, an observer sees a pulse of
radiation when the beam sweeps across his line-of-sight. Averaging over many pulses,
a pulse profile specific of the observed pulsar is obtained. Here we propose the use of
a recurrence plot for showing it.
This plot can highlight specific behaviours in pulse profiles.


Keywords : Recurrence Plots Pulsars Pulse Profiles
Type de document :
Article dans une revue


Philica, Philica, 2015, pp.533.
  Available at https://hal.archives-ouvertes.fr/hal-01487452/
Domaine :
Planète et Univers [physics] /
Astrophysique [astro-ph] /
Astrophysique stellaire et solaire [astro-ph.SR]

Here the figures of the article





Figure 1: On the left, the plot of 512 ASCII data of the pulse profile
 from PSR J2307+2225 [8].
 On the right, the corresponding recurrence plot.





Figure 2: On the left, the plot of 1024 ASCII data of the pulse profile
 of PSR J2235+1506 [10]. On the right, the corresponding recurrence plot.





Figure 3: On the left, the plot of 1024 ASCII data of the pulse profile
 at high frequency of PSR J1919 [11].
 On the right, the corresponding recurrence plot.





Figure 4: Recurrence plot of Pulsar J2317+1439 [10].
The background is displaying an interesting pattern,
typical of a autoregressive process [7].





Figure 5: PSR J0437-4715 pulse profiles at two different frequencies [14] .
 Note the presence of a double notch.





Figure 6: PSR J2322+2057 pulse profiles at two different frequencies [16].
 Note that we can see two peaks. One is quite faint at the lower frequency,
 but it is visible in the recurrence plot.




References

[1] J.J. Condon and S.M. Ransom, Essential Radio Astronomy, National Radio Astronomy Observatory, retrieved 18 October 2015, http://www.cv.nrao.edu/course/astr534/ERA.shtml

[2] W. Baade and F. Zwicky, On Super-novae, Proceedings of the National Academy of Sciences of the United States of America, vol. 20, no. 5, 1034, p. 254-259.

[3] R. Oppenheimer and G.M. Volkoff, On Massive Neutron Cores, Phys. Rev. 55, 1939, p.374.

[4] F. Pacini, Energy Emission from a Neutron Star, Nature, vol. 216, no. 5115, 1967, p. 567, DOI: 10.1038/216567a0

[5] W.R. Burns and B.G. Clark, Pulsar Search Techniques, Astronomy and Astrophysics, vol. 2, 1969, p. 280-287.

[6] N. Marwan and J. Kurths, Cross Recurrence Plots and Their Applications, in Mathematical Physics Research at the Cutting Edge, C.V. Benton Editor, pp.101-139, Nova Science Publishers, 2004.

[7] A.C. Sparavigna, Recurrence Plots of Exchange Rates of Currencies, International Journal of Sciences, vol. 3, no. 7, 2014, p. 87-95. DOI: 10.18483/ijSci.545

[8] F. Camilo and D.J. Nice, Timing parameters of 29 pulsars, Astrophysical Journal, Part 1, vol. 445, no. 2, 1995, p. 756-761.

[9] E. Kononov, Visual Recurrence Analysis, www.visualization-2002.org/

[10] F. Camilo, D.J. Nice and J.H. Taylor, Discovery of Two Fast-Rotating Pulsars, Astrophysical Journal, Part 2 - Letters, vol. 412, no. 1, p. L37-L40.

[11] J.H. Seiradakis, J.A. Gil, D.A. Graham, A. Jessner, M. Kramer, V.M. Malofeev, W. Sieber and R. Wielebinski, Pulsar Profiles at High-frequencies. 1. The Data, Astronomy and Astrophysics Supplement, v.111, 1995, p.205.

[12] S. Johnston, D.R. Lorimer, P.A. Harrison, et al. Discovery of a Very Bright, Nearby Binary Millisecond Pulsar, Nature, vol. 361, no. 6413. 1993, p. 613–615.

[13] Vv. Aa., Wikipedia, https://en.wikipedia.org/wiki/PSR_J0437-4715

[14] J.F. Bell, M. Bailes, R.N. Manchester, A.G. Lyne, F. Camilo and J.S. Sandhu, Timing Measurements and Their Implications for Four Binary Millisecond Pulsars, Monthly Notices of the Royal Astronomical Society, vol. 286, no. 2, 1997, p. 463-469.

[15] J. Navarro, R.N. Manchester, J.S. Sandhu, S.R. Kulkarni and M. Bailes, Mean Pulse Shape and Polarization of PSR J0437-4715, The Astrophysical Journal, vol. 486, 1997, p. 1019-1025.

[16] I.H. Stairs, E.M. Splaver, S.E. Thorsett, D.J. Nice and J.H. Taylor, A Baseband Recorder for Radio Pulsar Observations, Monthly Notices of the Royal Astronomical Society, vol. 314, no. 3, 1999, p. 459-467.

φ-bonacci

phi-bonacci

On "photo-proton” effect

Researchers at Manchester University have discovered that the rate at which graphene conducts protons increases 10 fold when it is illuminated with sunlight.
More at https://www.theengineer.co.uk/graphene-photosynthesis-membranes/

Un trucchetto per i calcoli

C'è un semplice trucchetto per fare i calcoli dei problemi di fisica in modo rapido e senza commettere errori. Per esempio:

Un cilindro con momento d'inerzia I' può ruotare intorno al suo asse. Una corda è avvolta su di esso e passa nella gola di una carrucola. All'estremità della corda è attaccata una massa m. Con quale accelerazione scende la massa m?

Dopo aver fatto i diagrammi di corpo libero, scriviamo le equazioni per m,I ed I'. Mettiamo a sinistra i termini tipo "ma","I alpha". alpha è l'acc. angolare.

ma = mg-T

I alpha= Tr-T'r

I' alpha'=T'R

alpha=a/r; alpha'=a/R

Riscrivo il sistema:

ma = mg - T

I a/r = Tr-T'r

I' a/R= T'R

ma = mg - T

(I/r^2) a = T - T'

(I'/R^2) a = T'

Invece di ricavare e sostituire T' e T,  sommo le equazioni:

a [m+I/r^2+I'/R^2]= mg - T + T - T' + T' = mg

a= mg/[m+I/r^2+I'/R^2]

In questa maniera, l'accelerazione è trovata rapidamente senza ricorrere alle sostituzioni. 

Svolgere esercizio

Fate l'esercizio al link
http://www.edutecnica.it/meccanica/vincolix/29.htm

Sistemi tirante - puntone

Ho trovato un sito con diversi problemi interessanti.
Alcuni riguardano la composizione tirante /fune) e puntone (asta).
Si veda il link
http://www.edutecnica.it/meccanica/decompox/decompox.htm