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At least 145 records · Page 8Linked to original sources
arXiv2012

Criticality and self-organization in branching processes: application to natural hazards

The statistics of natural catastrophes contains very counter-intuitive results. Using earthquakes as a working example, we show that the energy radiated by such events follows a power-law or Pareto distribution. This means, in theory, that the expected value of the energy does not exist (is infinite), and in practice, that the mean of a finite set of data in not representative of the full population. Also, the distribution presents scale invariance, which implies that it is not possible to define a characteristic scale for the energy. A simple model to account for this peculiar statistics is a branching process: the activation or slip of a fault segment can trigger other segments to slip, with a certain probability, and so on. Although not recognized initially by seismologists, this is a particular case of the stochastic process studied by Galton and Watson one hundred years in advance, in order to model the extinction of (prominent) families. Using the formalism of probability generating functions we will be able to derive, in an accessible way, the main properties of these models. Remarkably, a power-law distribution of energies is only recovered in a very special case, when the branching process is at the onset of attenuation and intensification, i.e., at criticality. In order to account for this fact, we introduce the self-organized critical models, in which, by means of some feedback mechanism, the critical state becomes an attractor in the evolution of such systems. Analogies with statistical physics are drawn. The bulk of the material presented here is self-contained, as only elementary probability and mathematics are needed to start to read.

cond-mat.stat-mech↗
arXiv2012

Harvesting and storing laser energy with graphene-cu compound structure

Graphene-metal compound structure has been reported as a novel and outstanding component used in electrical and optical devices. We report on a first-principles study of graphene-cu compound structure, showing its capacity of converting laser energy into electrical power and storing the harvested energy for a long time. A real-time and real-space time-dependent density functional method (TDDFT) is applied for the simulation of electrons dynamics and energy absorption. The laser-induced charge transfer from copper layer to graphene layer is observed and represented by plane-averaged electron difference and dipoles. The effects of laser frequency on the excitation energy and charge transfer are studied as well. The enhancement of C-C σ-bond and decreasing of electron density corresponding to π-bond within graphene layer indicate the way in which the transferred-charges are stored. In addition, the shift and oscillations of dipole along z-direction after the application of laser pulse offer a concept that the compound structure has the ability of storing the harvested energy for a long time.

physics.pop-ph↗
arXiv2012

Virtual experiments about a walker fly: beyond the Neumann`s solution

We extend the traditional problem of calculating the traveled distance of a fly that is moving with constant speed on a straight path between two trains that are approaching one another, we found two analytical solutions for the traditional problem and we propose a generalization to the accelerated motion of the trains through a simulation. With this problem the teachers can teach some topics of basic physics as the relations between mathematical and physics, the graphical analysis and various situations on kinematics in one dimension. We show an analogy between the move of the fly and a ultrasonic wave pulse in a sensor of velocity, this show the pedagogical power of this problem.

physics.ed-ph↗
arXiv2012

Quantum view of Mass

The classical view of mass is that it quantifies the amount of substance and is a kinematical parameter. All matter has an attribute of mass and is a conserved quantity in any interaction. With the advent of special relativity, mass became no longer a conserved quantity, since energy and momenta had the status of conserved variables. Nevertheless, the expression for relativistic mass gives a Poincare invariant measure that can be associated as the mass, a useful attribute of the body or system. In the quantum regime, mass becomes truly dynamical. Higgs field is said to provide mass to all the species of elementary constituents - as widely popularized by the media in connection with the recent (most likely) discovery of the Higgs meson at CERN. However, we emphasize that the most abundant component of matter - Nucleons - derives its mass largely as a consequence of quantum effects of (color gluonic QCD) radiation. Further, interestingly this arises out of literally nothing, save the QCD scale determined experimentally, through a self consistent perturbative analysis of nucleon structure.

physics.pop-ph↗
arXiv2013

A Fractal Comparison of Escher and Koch Tessellations

M.C. Eschers tessellations have captured the imaginations of both artists and mathematicians. Circle Limit III is the most intricate of his tessellations, featuring patterns that repeat at increasingly fine scales. Although his patterns follow a scaling law determined by hyperbolic geometry, his work is often mistakenly described as following fractal geometry. Here, we perform a 'box counting' scaling analysis on Circle Limit III and an equivalent monofractal pattern based on a Koch Snowflake. Whereas our analysis highlights the expected visual differences between Eschers hyperbolic patterns and the simple monofractal, the analysis also identifies unexpected similarities between Eschers work and the bifractal poured paintings of Jackson Pollock.

physics.pop-ph↗
arXiv2013

The logical clarinet: numerical optimization of the geometry of woodwind instruments

The tone hole geometry of a clarinet is optimized numerically. The instrument is modeled as a network of one dimensional transmission line elements. For each (non-fork) fingering, we first calculate the resonance frequencies of the input impedance peaks, and compare them with the frequencies of a mathematically even chromatic scale (equal temperament). A least square algorithm is then used to minimize the differences and to derive the geometry of the instrument. Various situations are studied, with and without dedicated register hole and/or enlargement of the bore. With a dedicated register hole, the differences can remain less than 10 musical cents throughout the whole usual range of a clarinet. The positions, diameters and lengths of the chimneys vary regularly over the whole length of the instrument, in contrast with usual clarinets. Nevertheless, we recover one usual feature of instruments, namely that gradually larger tone holes occur when the distance to the reed increases. A fully chromatic prototype instrument has been built to check these calculations, and tested experimentally with an artificial blowing machine, providing good agreement with the numerical predictions.

physics.pop-ph↗
arXiv2025

Who cares about physics today? A marketing strategy for the survival of fundamental science and the benefit of society

It would seem that the present dry economic times impose a very precise focus for science in general and physics in particular: research, possibly of applied type. However in doing so two basic pillars of a healthy future for science are being undermined: fundamental research and public engagement. The first is what makes applications possible in the first place, many times with a path from inception to implementation that is as long and indirect as poorly advertised. The second pillar, public engagement, is mostly regarded as a commodity: if there is good level of funding scientists can consider spending money for public relations otherwise this is the first thing scientists cut because it is the least necessary. On the contrary, public engagement in science is very much needed, at the very least because the public is either an enemy or an ally, as testified respectively by the climate change denial and the 2009 Shuttle mission that people wanted in order to service the Hubble Space Telescope for the last time. In this article I will make the case for why popularizing science should be a funding priority, instead of a commodity, for both nation-wide organizations and local research institutions. I will take examples from my personal background with the hope that they will serve to enlighten a more general picture and to frame the discussion around concrete issues and practical avenues to be pursued immediately.

physics.pop-ph↗
arXiv2012

The United Nations Human Space Technology Initiative (HSTI): Activity Status in 2012

In 2010, the Human Space Technology Initiative (HSTI) was launched by the United Nations Office for Outer Space Affairs (UNOOSA) within the United Nations Programme on Space Applications. The Initiative aims at promoting international cooperation in human spaceflight and space exploration-related activities, creating awareness among countries on the benefits of utilizing human space technology and its applications, and building capacity in microgravity education and research. HSTI has conducted a series of outreach activities and expert meetings bringing together participants from around the world. HSTI will also be implementing science and educational activities in relevant areas to raise the capacities, particularly in developing countries, in pursuit of the development goals of the United Nations, thus contributing to promoting the peaceful uses of outer space.

physics.pop-ph↗
arXiv2012

The United Nations Human Space Technology Initiative (HSTI): Science Activities

The United Nations Human Space Technology Initiative (HSTI) aims at promoting international cooperation in human spaceflight and space exploration-related activities; creating awareness among countries on the benefits of utilizing human space technology and its applications; and building capacity in microgravity education and research. HSTI has been conducting various scientific activities to promote microgravity education and research. The primary science activity is called 'Zero-gravity Instrument Distribution Project', in which one-axis clinostats will be distributed worldwide. The distribution project will provide unique opportunities for students and researchers to observe the growth of indigenous plants in their countries in a simulated microgravity condition and is expected to create a huge dataset of plant species with their responses to gravity.

physics.pop-ph↗
arXiv2012

The Zeeman Effect in Finance: Libor Spectroscopy and Basis Risk Management

Once upon a time there was a classical financial world in which all the Libors were equal. Standard textbooks taught that simple relations held, such that, for example, a 6 months Libor Deposit was replicable with a 3 months Libor Deposits plus a 3x6 months Forward Rate Agreement (FRA), and that Libor was a good proxy of the risk free rate required as basic building block of no-arbitrage pricing theory. Nowadays, in the modern financial world after the credit crunch, some Libors are more equal than others, depending on their rate tenor, and classical formulas are history. Banks are not anymore too "big to fail", Libors are fixed by panels of risky banks, and they are risky rates themselves. These simple empirical facts carry very important consequences in derivative's trading and risk management, such as, for example, basis risk, collateralization and regulatory pressure in favour of Central Counterparties. Something that should be carefully considered by anyone managing even a single plain vanilla Swap. In this qualitative note we review the problem trying to shed some light on this modern animal farm, recurring to an analogy with quantum physics, the Zeeman effect.

q-fin.PR↗
arXiv2012

The Quantum Zeno Effect -- Watched Pots in the Quantum World

In the 5th century B.C.,the philosopher and logician Zeno of Elea posed several paradoxes which remained unresolved for over two thousand five hundred years. The $20^{th}$ century saw some resolutions to Zeno's mind boggling problems. This long journey saw many significant milestones in the form of discoveries like the tools of converging series and theories on infinite sets in mathematics. In recent times, the Zeno effect made an intriguing appearance in a rather unlikely place - a situation involving the time evolution of a quantum system, which is subject to "observations" over a period of time. Leonid Khalfin working in the former USSR in the 1960s and ECG Sudarshan and B. Misra at the University of Texas, Austin, first drew attention to this problem. In 1977, ECG Sudarshan and B. Misra published a paper on the quantum Zeno effect, called "The Zeno's paradox in quantum theory". Their fascinating result revealed the bizarre workings of the quantum world. Misra and Sudarshan's 1977 paper activated over two decades of theoretical and experimental explorations into the subject and still continues to evoke a lot of interest. In the following, the quantum Zeno effect is described and a brief outline of some of the work following Misra and Sudarshan's paper is given. The quantum Zeno effect is yet another example of the myriad unimaginable possibilities that lie waiting in the magical world of the quantum.

physics.hist-ph↗
arXiv2013

A simple symmetry as a guide toward new physics beyond the Standard Model

There exists one experimental result that cannot be explained by the Standard Model (SM), the current theoretical framework for particle physics: non-zero masses for the neutrinos (elementary particles travelling close to light speed, electrically neutral and weakly interacting). The SM assumes that they are massless. Therefore, particle physicists are now exploring new physics beyond the SM. There is strong anticipation that we are about to unravel it, in the form of new matter and/or forces, at the Large Hadron Collider (LHC), presently running at CERN. We discuss a minimal extension of the SM, based on a somewhat larger version of its symmetry structure and particle content, that can naturally explain the existence of neutrino masses while also predicting novel signals accessible at the LHC, including a light Higgs boson, as evidenced by current data.

physics.pop-ph↗
arXiv2013

Domino Magnification

The conditions are investigated under which a row of increasing dominoes is able to keep tumbling over. The analysis is restricted to the simplest case of frictionless dominoes that only can topple not slide. The model is scale invariant, i.e. dominoes and distance grow in size at a fixed rate, while keeping the aspect ratios of the dominoes constant. The maximal growth rate for which a domino effect exist is determined as a function of the mutual separation.

physics.pop-ph↗
arXiv2016

Binocular disparity as an explanation for the moon illusion

We present another explanation for the moon illusion, the phenomenon in which the moon looks larger near the horizon than near the zenith. In our model of the moon illusion, the sky is considered a spatially-contiguous and geometrically-smooth surface. When an object such as the moon breaks the contiguity of the surface, instead of perceiving the object as appearing through a hole in the surface, humans perceive an occlusion of the surface. Binocular vision dictates that the moon is distant, but this perception model contradicts our binocular vision, dictating that the moon is closer than the sky. To resolve the contradiction, the brain distorts the projections of the moon to increase the binocular disparity, which results in an increase in the perceived size of the moon. The degree of distortion depends upon the apparent distance to the sky, which is influenced by the surrounding objects and the condition of the sky. As the apparent distance to the sky decreases, the illusion becomes stronger. At the horizon, apparent distance to the sky is minimal, whereas at the zenith, few distance cues are present, causing difficulty with distance estimation and weakening the illusion.

cs.CV↗
arXiv2013

Study of some parameters interstellar transport using of magnetic umbrella

Interstellar transport is an object of interest in many sci-fi stories. In history a lot of sci-fi predictions have turned into reality, such as communications satellites, deep-sea submarines and journies to the moon. In this work we study some physical parameters of a space ship which uses a magnetic umbrella. Our spaceship generates a magnetic field in its neighborhood and captures charged protons into a magnetic trap. These particles are taken into a fusion reactor. The obtained energy and waste in form of helium are used as a fuel in an ion engine. With the help of elementary physics we can work out the basic physical parameters of the ship, e.g. maximal velocity, acceleration of the ship or acceleration time period.

physics.gen-ph↗
arXiv2013

First Steps into Physics in the Winery

Physics is introduced as a basic matter in the curricula of professional schools (i.e. schools for agriculture, electronic or chemistry experts). Students meet physics in the early years of their training and then continue in vocational subjects where many physics' topics can be useful. Rarely, however, the connection between physics and professional matters is quite explicit. Students often feel physics as boring and useless, i.e. very far from their interests. In these schools it is almost always required the physics lab, but it does not always exist. The physics teachers of a local Agricultural Technical Institute asked us to realize a learning path in laboratory for their students, since in their school the physics lab was missing. This institute is the only public school in the Chianti area specializing in Viticulture and Enology, and attending a further year post diploma, allows the achievement of the qualification of Enologist. We report a learning path realized starting from thermal equilibrium to a full understanding of the measures made with the Malligand's ebulliometer, used for determining the alcoholic strength (alcohol concentration by volume) of an alcoholic beverage and water/alcohol solutions in general. The aim was to make interesting measures of physical quantities, calorimetry and state transitions connecting them to the functioning of an instrument that students use in their professional career. The feedback of students and the interests of their teachers convinced us to go further in this way. We intend in the next future to involve teachers of physics and vocational subjects in the design of a physics curriculum spread over two years in which the main physics topics will be introduced to explain the functioning of tools and equipment used, normally, in the winery.

physics.ed-ph↗
arXiv2014

On the Title of Moriarty's 'Dynamics of an Asteroid'

We propose an explanation of the title of Prof. James Moriarty's treatise_Dynamics of an Asteroid_, a scientific work mentioned by Sherlock Holmes in_The Valley of Fear_ and prominently featured in Guy Ritchie's 2011 film_Sherlock Holmes: A Game of Shadows_. Our views on the subject differ from those expressed in Isaac Asimov's "The Ultimate Crime".

physics.pop-ph↗