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Liquid Crystals and Electro-Optic Modulation

Introduction Liquid crystals are a class of organic compounds with particular liquid-crystalline properties, discovered in 1888 by the Austrian botanist Friedrich Reinitzer. Reinitzer noticed that by heating cholesterol benzoate this first became opaque, and then cleared up as the temperature gradually increased. Once cooled, the liquid turned bluish and then …

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Observing Quantized Conductance in a Normal Relay

Introduction Relatively recent experiments (1988) have allowed to experimentally observe the phenomenon of quantization of conductance which occurs in a one-dimensional conductor in which the transport takes place in a so-called “ballistic” mode. This phenomenon occurs when the conductor has very small transverse dimensions, of the order of nanometers, in …

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LED – SPAD Detector Characterization

In the previous post Using LED as Single Photon Detector we described how a simple LED can be used as a single photon detector (SPAD), now let’s try to make its technical characterization. Instrumentation To verify the operation of the LED as a single photon detector we used a “dark …

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Using LED as a Single Photon Detector

Single Photon Detector : the SPAD device The SPAD (single photon avalanche detector) is a photodiode-like device that works in an operating area that is usually avoided : the breakdown region. A conventional photodiode is usually realized with a reverse-biased p-n junction (a diode) where the photons can interact with silicon and …

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Measuring Action Potential in Plants

Action Potential In physiology, an action potential occurs when the membrane potential of a specific cell location rapidly rises and falls : this depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, endocrine cells, glomus cells, and in some plant cells. (from Wikipedia) Although plants don’t have …

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Low Light Detection with PMT

There is no shortage of photomultipliers in the PhysicsOpenLab laboratory ! For this reason, we decided to use one of these instruments to measure physical phenomena characterized by low intensity light emission such as phosphorescence and bioluminescence. We have already made measurements of this type, but with different instruments, based …

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Cosmic Ray Energies

Introduction In our experimental physics website, cosmic rays are an “unmissable” appointment : this physical phenomenon always offers new possibilities for experimentation and always gives many satisfactions. Over time we have used different experimental detection techniques : geiger tubes, scintillation detectors coupled to both PMT and SiPM, Cherenkov detectors. We …

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Biosignal Amplifier

Introduction The electrical signal deriving from biological activity is characterized by very low voltage values, just above the noise level, and spread over a frequency band that extends from fractions of Hz to a few hundred Hz. The amplifiers used for these applications represent an interesting challenge for designers and, …

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Muography DIY

Introduction Our friend Antonio Zanardo has carried out an interesting experiment with cosmic rays : “muography”. In this post we will describe its realization. MUOGRAPHY what is it? It is a radiographic technique used to obtain images of objects, generally of large dimensions, otherwise unattainable with other procedures (X-Rays). The …

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Raspberry Pi Sense HAT

The Sense HAT Expansion Card (Reference La Scienza con il Raspberry pi – Marco Casolino) One of the most interesting features of the Raspberry – which differentiates it from a simple low-cost computer – is that it can be connected to a series of sensors and actuators via the digital ports …

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