Problema dinamica

Una persona si trova su una pedana mobile. Tra la pedana ed il pavimento l’attrito è trascurabile. Tra la persona e la pedana c’è attrito statico. La persona tira la fune e nella fune si sviluppa una tensione T di 20 N. La massa M è di 60 kg, la pedana è di 20 kg. Trovate l’accelerazione di persona e pedana.

Pedana M:   M a = T  (verso destra);    M g = N  dove N è l'azione del pavimento

Massa m: ma = mg ─ T (verso il basso) 

La fune  è inestensibile, sommo  equazioni

Ma + ma = T + mg -T = mg

a = mg/(M+m)

Majorana 'zero modes' spotted in superconducting nanowires - physicsworld.com

Majorana 'zero modes' spotted in superconducting nanowires - physicsworld.com

Problema dinamica

Una ragazza di 60 kg sta in piedi su una piattaforma di alluminio di 15 kg per dipingere una casa. Una fune attaccata alla piattaforma e passante su una carrucola fissata al soffitto consente alla ragazza di sollevare se stessa e la piattaforma. (a) Per muoversi la ragazza imprime a se stessa e alla piattaforma un'accelerazione di 0,8 m/s². Con che forza deve tirare la corda? (b) Dopo 1 s la ragazza tira in modo da salire con la piattaforma con la velocità costante di 1 m/s. Che forza deve esercitare sulla corda?
[Ris. (a) 397 N; (b) 367 N.] Vedi anche https://physicstasks.eu/278/boy-on-a-pulley

m _r = 60 kg , m_p = 15 kg , m _tot = 75 kg , a = 0.8 m/s² , g = 9.8 m/s²

A) Sia F la forza applicata F dalla ragazza che tira la fune verso il basso. Sia T la tensione della fune.
Dobbiamo trovare la forza F. Sia la direzione verso l'alto quella positiva. Si ha
F = T (in modulo)

Sulla massa totale: T + F - m_tot g = m_r a 

2 F = m_r (a + g) da cui F = 397 N 

Dove la ragazza applica la forza, si ha in modulo F = T (azione e reazione). La forza F è verso il basso e la reazione è verso l'alto; così la corda agisce sulla ragazza verso l'alto.

B) a=0
F = T
T + F - m_r g = 0
2F = m_r g e quindi: F = 367 N

Problema dinamica

Fate il problema che trovate al link

https://physicstasks.eu/278/boy-on-a-pulley

Gibbs' rule

• Don't stop checking and rechecking evidence until you are satisfied.

Turning "algae from trash into treasure"

Convert harmful algae into Na-ion battery electrodes

http://alternativeenergy.electronicspecifier.com/around-the-industry/convert-harmful-algae-into-na-ion-battery-electrodes

29th October 2015

 Written by : Nat Bowers

• 
  
• 
  
• "A team of researchers, led by Dr. Da Deng, assistant professor of chemical engineering and materials science at Wayne State University, has found that baking algae in a furnace with argon gas at temperatures of 700-1000°C could convert it into a material called 'hard carbon'. This hard carbon can be used as high-capacity, low-cost electrodes for Na-ion batteries."
  "During his commute to work in the summer of 2014, Deng heard several news reports about the harmful algal bloom that poisoned Toledo’s water system and left almost 500,000 people without drinking water. During one of those drives, Deng - who was trained as an environmental engineer - started daydreaming about turning the algae from trash into treasure."
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The Science of Al-Biruni

The Science of Al-Biruni

http://www.ijsciences.com/pub/article/364

Al-Biruni (973-1048) was one of the greatest scientists of all times.

He was an astronomer, mathematician and philosopher, and studied

 physics and natural sciences. In this paper, we will discuss

 some of his experimental methods and some instruments he used. 

On the Role of Tsallis Entropy in Image Processing

International Scientific Research Journal ~ ISSN 2412-026X

Link to the Journal IRJ.Science

On the Role of Tsallis Entropy in Image Processing

In image processing, the maximum entropy principle is generally recognized as having a relevant role in the initial part of image elaboration. The first step of processing in fact, sees the entropy used to determine the segmentation of the image, that is, used to determine objects and background in it. Different entropy formulations are available to this purpose, but the most prominent in recent publications is that of the Tsallis non-extensive entropy. Here, we survey some main methods that are using this entropy and the related literature, in particular that reporting the researches concerning medical image processing.

Keywords: Tsallis Entropy; Image Processing; Image Segmentation; Image Thresholding; Medical Image Processing

DOI: 10.18483/IRJSci.79

Link to the paper http://www.irj.science/pub/article/79

Earth 2.0

An artist's guess of what Kepler 452b could look like.T. Pyle/JPL-Caltech/NASA Ames

Carbon Dioxide Concentration and Emissions in Atmosphere: Trends and Recurrence Plots

The increase of carbon dioxide concentration in atmosphere, due to anthropogenic emissions, is almost generally considered as responsible of global climate changes. We show some data of CO2 concentration and its emission in atmosphere, using the recurrence plots to enhance the visualization of their trends.  See more at: http://www.ijsciences.com/pub/article/582#sthash.L4dBnzsh.dpuf

Data of CO2 concentration in atmosphere, from [1]. The range is from January 1958 to October 2014. In the image we see the recurrence plot. The global annual mean concentration of CO2 in the atmosphere is currently rising at a rate of approximately 2 ppm/year and accelerating [1]. This acceleration is shown by the recurrence plot, where colours are narrowing towards the diagonal line.

[1] Tans, P. & Keeling R. (2014). Trends in atmospheric carbon dioxide, Oceanic & Atmospheric Administration (NOAA). At www.esrl.noaa.gov/ gmd/ ccgg/ trends/

About 1970, the oil production and import of US had a sharp peak (data from Ref.12). Note how the corresponding recurrence plot evidences this peak.

[12] Vv.Aa. (2014). U.S. Energy Information Administration (EIA), at www.eia.gov/petroleum/

 See more at: http://www.ijsciences.com/pub/article/582#sthash.L4dBnzsh.dpuf