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At least 271 records · Page 15Linked to original sources

arXiv2014

Is it Possible to Accurately Identify a Shooter's Face as Illuminated by the Muzzle Flash of a 22 LR Pistol?

The science of firearms muzzle flash has been dominated by three perspectives: 1) Does the muzzle flash reveal friendly positions to naked eye observers so as to draw fire from enemy combatants? 2) Can flash signatures be recognized by electronic surveillance with sufficient accuracy to identify source firearms? 3) Is the muzzle flash so bright as to diminish the night vision of friendly forces during a firefight? This paper addresses a fourth question: Does the muzzle flash of a specific cartridge provide sufficient duration and intensity of illumination with visible light to allow observers to positively identify a shooter's face? The experiment used two shooters firing a total of 20 shots from a 22 LR semi-automatic pistol. Shooters fired in randomized order, while eight observers (male US military veterans) attempted to identify the shooter for each trial shot. The firing range was mostly darkened with only enough ambient light to safely conduct firing tests at the direction of a range safety officer. There was not enough ambient light to identify the shooter's face. Observers correctly identified the shooter 54% of the time and failed to correctly identify the shooter 46% of the time. Observers were unanimous that there was no hint of any visible illumination on the shooter's face provided by the muzzle flash. In cases where the shooter was correctly identified, observers reported using visual cues such as the sillhouette of the shooters' hair and slight differences in arm positions when firing the pistol. Other people in the room (including the author) were in unanimous agreement that there was no illumination of the shooters' faces from discharge of a 22 LR pistol.

physics.pop-ph↗

arXiv2014

Performance testing of lead free primers: blast waves, velocity variations, and environmental testing

Results are presented for lead free primers based on diazodinitrophenol (DDNP)compared with tests on lead styphnate based primers. First, barrel friction measurements in 5.56 mm NATO are presented. Second, shot to shot variations in blast waves are presented as determined by detonating primers in a 7.62x51mm rifle chamber with a firing pin, but without any powder or bullet loaded and measuring the blast wave at the muzzle with a high speed pressure transducer. Third, variations in primer blast waves, muzzle velocities, and ignition delay are presented after environmental conditioning (150 days) for two lead based and two DDNP based primers under cold and dry (-25 deg C,0% relative humidity), ambient (20 deg C, 50% relative humidity), and hot & humid (50 deg C, 100% relative humidity) conditions in 5.56 mm NATO. Taken together, these results indicate that DDNP based primers are not sufficiently reliable for service use.

physics.pop-ph↗

arXiv2015

The symmetry and simplicity of the laws of physics and the Higgs boson

We describe the theoretical ideas, developed between the 1950s-1970s, which led to the prediction of the Higgs boson, the particle that was discovered in 2012. The forces of nature are based on symmetry principles. We explain the nature of these symmetries through an economic analogy. We also discuss the Higgs mechanism, which is necessary to avoid some of the naive consequences of these symmetries, and to explain various features of elementary particles.

physics.pop-ph↗

arXiv2014

On the fields due to line segments

The remarkable geometries of ellipsoidal equipotentials and their associated gradient fields, as produced by uniformly charged straight-line segments, are discussed at an elementary level, motivated by recent treatments intended for introductory physics classes. Some effort is made to put the results into a broader conceptual and historical context. The equipotentials and vector fields were first obtained for the electrostatic problem by George Green in his famous 1828 essay. Related problems were commonly found on the Mathematical Tripos examinations given at the University of Cambridge, and their solutions were widely disseminated by William Thomson (Lord Kelvin), Peter Guthrie Tait, and Edward Routh during the last half of the 19th century.

physics.hist-ph↗

arXiv2014

Internalizing Null Extraterrestrial "Signals": An Astrobiological App for a Technological Society

One of the beneficial outcomes of searching for life in the Universe is that it grants greater awareness of our own problems here on Earth. Lack of contact with alien beings to date might actually comprise a null "signal" pointing humankind toward a viable future. Astrobiology has surprising practical applications to human society; within the larger cosmological context of cosmic evolution, astrobiology clarifies the energetic essence of complex systems throughout the Universe, including technological intelligence that is intimately dependent on energy and likely will be for as long as it endures. The "message" contained within the "signal" with which today's society needs to cope is reasonably this: Only solar energy can power our civilization going forward without soiling the environment with increased heat yet robustly driving the economy with increased per capita energy usage. The null "signals" from extraterrestrials also offer a rational solution to the Fermi paradox as a principle of cosmic selection likely limits galactic civilizations in time as well as in space: Those advanced life-forms anywhere in the Universe that wisely adopt, and quickly too, the energy of their parent star probably survive, and those that don't, don't.

physics.pop-ph↗

arXiv2014

Worlds beyond our own

We give a popular account of the present state of the research in the field of extra-solar planetary systems, popularly termed as exoplanets, with a brief overview of the techniques employed. We also discuss the question of habitability and the possibility of finding intelligent life elsewhere in the Milky Way. We conclude with a brief exposition on the less explored territory of exomoons.

physics.pop-ph↗

arXiv2014

Can Collimated Extraterrestrial Signals be Intercepted?

The Optical Search for Extraterrestrial Intelligence (OSETI) attempts to detect collimated, narrowband pulses of electromagnetic radiation. These pulses may either consist of signals intentionally directed at the Earth, or signals between two star systems with a vector that unintentionally intersects the Solar System, allowing Earth to intercept the communication. But should we expect to be able to intercept these unintentional signals? And what constraints can we place upon the frequency of intelligent civilisations if we do? We carry out Monte Carlo Realisation simulations of interstellar communications between civilisations in the Galactic Habitable Zone (GHZ) using collimated beams. We measure the frequency with which beams between two stars are intercepted by a third. The interception rate increases linearly with the fraction of communicating civilisations, and as the cube of the beam opening angle, which is somewhat stronger than theoretical expectations, which we argue is due to the geometry of the GHZ. We find that for an annular GHZ containing 10,000 civilisations, intersections are unlikely unless the beams are relatively uncollimated. These results indicate that optical SETI is more likely to find signals deliberately directed at the Earth than accidentally intercepting collimated communications. Equally, civilisations wishing to establish a network of communicating species may use weakly collimated beams to build up the network through interception, if they are willing to pay a cost penalty that is lower than that meted by fully isotropic beacons. Future SETI searches should consider the possibility that communicating civilisations will attempt to strike a balance between optimising costs and encouraging contact between civilisations, and look for weakly collimated pulses as well as narrow-beam pulses directed deliberately at the Earth.

physics.pop-ph↗

arXiv2014

Astonishing Judo, first contact tactics: A Biomechanical evaluation of tactics at start of high level competitions

This paper is focalized on the limit application of judo throws, by tactics at first contact time, with some astonishing information at a first seeing, but biomechanically grounded, not often applied or because against the sound common sense or out the old oral judo tradition. To do so we provide an appraisal of the grips concept and his consequences in the Olympic sport judo from a biomechanics perspective, we will try to deeper both the concept and the function of grips and define the potential application of some throws without grips. Broadening this situation we try to underline some specific throwing situation in which grips are or not at all applied or applied in non conventional way. We describe at first the problem from the theoretical point of view. And as second point we try to find practical application, original or already developed in high level competitions. The provocative words Judo without grips or throw without grips are connected to the limit application of some biomechanical tricks, grounded on two well known physical principles: the time advance in the attack, in Japanese Sen no Sen (already applied in real competitions), and the utilization of the own inertia connected to high attack speed to apply in totally original way one of the two biomechanical tools utilized to throw the human body.

physics.pop-ph↗

arXiv2014

Diversification versus specialization -- lessons from a noise driven linear dynamical system

Specialization and diversification are two major strategies that complex systems might exploit. Given a fixed amount of resources, the question is whether to invest this in elements that respond in a correlated manner to external perturbations, or to build a diversified system with groups of elements that respond in a not necessarily correlated manner. This general dilemma is investigated here using a high dimensional discrete dynamical system subject to an external noise, analyzing the statistical properties of an order parameter that quantifies growth. Our analytical solution suggests that diversification is a good strategy once the system has a fair amount of resources. For systems with small or extremely large supplies, we argue that specialization might be a more successful strategy. We discuss the results also from the perspective of economic and biologic systems.

physics.soc-ph↗

arXiv2014

Comets in ancient India

The Indo-aryans of ancient India observed stars and constellations for ascertaining auspicious times in order to conduct sacrificial rites ordained by vedas. It is but natural that they would have recounted in the vedic texts about comets. In Rigveda ($\sim $ 1700 - 1500 BC) and Atharvaveda ($\sim $ 1150 BC), there are references to dhumaketus and ketus, which stand for comets in Sanskrit. Rigveda mentions a fig tree with roots held up in the sky (Parpola 2009, 2010). Could it have been inspired by the hirsute appearance of a comet's tail? Similarly, could `Ketu' (the torso or the tail part of Rahu) be a Dravidian loan word, since `kottu', an old Tamil word, is associated with scorpion's sting and top tuft of hair? Varahamihira in 550 AD and Ballal Sena ($\sim $ 1100 - 1200 AD) have described a large number of comets recorded by ancient seers such as Parashara, Vriddha Garga, Narada, Garga, etc. In this article, I conjecture that an episode narrated in Mahabharata of a radiant king, Nahusha, ruling the heavens, and later turning into a serpent after he had kicked the seer Agastya (also the star Canopus), is a mythological retelling of a cometary event.

physics.pop-ph↗

arXiv2015

Hubble's Law Implies Benford's Law for Distances to Galaxies

A recent article by Alexopoulos and Leontsinis presented empirical evidence that the first digits of the distances to galaxies are a reasonably good fit to the probabilities predicted by Benford's law, the well known logarithmic statistical distribution of significant digits. The purpose of the present article is to give a theoretical explanation, based on Hubble's law and mathematical properties of Benford's law, why galaxy distances might be expected to follow Benford's law. The new galaxy-distance law derived here, which is robust with respect to change of scale and base, to additive and multiplicative computational or observational errors, and to variability of the Hubble constant in both time and space, predicts that conformity to Benford's law will improve as more data on distances to galaxies becomes available. Conversely, with the logical derivation of this law presented here, the recent empirical observations may be viewed as independent evidence of the validity of Hubble's law.

physics.data-an↗

arXiv2015

A LEGO Watt Balance: An apparatus to determine a mass based on the new SI

A global effort to redefine our International System of Units (SI) is underway and the change to the new system is expected to occur in 2018. Within the newly redefined SI, the present base units will still exist but be derived from fixed numerical values of seven reference constants. More specifically, the unit of mass, the kilogram, will be realized through a fixed value of the Planck constant $h$. For instance, a watt balance can be used to realize the kilogram unit of mass within a few parts in $10^8$. Such a balance has been designed and constructed at the National Institute of Standards and Technology. For educational outreach and to demonstrate the principle, we have constructed a LEGO tabletop watt balance capable of measuring a gram size mass to 1 % relative uncertainty. This article presents the design, construction, and performance of the LEGO watt balance and its ability to determine $h$

physics.ins-det↗

arXiv2014

Galactic-scale macro-engineering: Looking for signs of other intelligent species, as an exercise in hope for our own

If we consider Big History as simply 'our' example of the process of cosmic evolution playing out, then we can seek to broaden our view of our possible fate as a species by asking questions about what paths or trajectories other species' own versions of Big History might take or have taken. This paper explores the broad outlines of possible scenarios for the evolution of long-lived intelligent engineering species---scenarios which might have been part of another species' own Big History story, or which may yet lie ahead in our own distant future. A sufficiently long-lived engineering-oriented species may decide to undertake a program of macro-engineering projects that might eventually lead to a re-engineered galaxy so altered that its artificiality may be detectable from Earth. We consider activities that lead ultimately to a galactic structure consisting of a central inner core surrounded by a more distant ring of stars separated by a relatively sparser 'gap', where star systems and stellar materials may have been removed, 'lifted' or turned into Dyson Spheres. When one looks to the sky, one finds that such galaxies do indeed exist---including the beautiful ringed galaxy known as 'Hoag's Object' (PGC 54559) in the constellation Serpens. This leads us to pose the question: Is Hoag's Object an example of galaxy-scale macro-engineering? And this suggests a program of possible observational activities and theoretical explorations, several of which are presented here, that could be carried out in order to begin to investigate this beguiling question.

physics.pop-ph↗

arXiv2014

La teoria de supercuerdas

We discuss superstring theory based on the reader's intuition and her college knowledge of general physics and calculus. Nowadays, superstring theory is considered the best candidate to explain physical phenomena that involve all of the known fundamental interactions: the gravitational, electromagnetic, weak and strong forces. The main purpose of this work is to show and explain some of the concepts and details about superstrings, such as supersymmetry, compactification, dualities and branes.

physics.pop-ph↗

arXiv2014

Lighting up the Christmas tree: high-intensity laser interactions with a nano-structured target

We perform a numerical study of the interaction of a high-intensity laser pulse with a nano-structured target. In particular, we study a target where the nano-structuring increases the absorption rate as compared to the flat target case. The transport of electrons within the target, and in particular in the nano-structure, is analysed. It is shown that it is indeed possible, using a terawatt class laser, to light up a nano-scale Christmas tree. Due to the form of the tree we achieve very strong edge fields, in particular at the top where the star is located. Such edge fields, as here located at ion rich spots, makes strong acceleration gradients possible. It also results in a nice, warm glow suitable for the holiday season.

physics.pop-ph↗

arXiv2014

Measures of the Earth Obliquity during the 1701 Winter Solstice at the Clementine Meridian Line in Rome

The great meridian line in the Basilica of Santa Maria degli Angeli in Rome was built in 1701/1702 with the scope of measuring the obliquity of the Earth's orbit in the following eight centuries, upon the will of Pope Clement XI. During the winter solstice of 1701 the first measurements of the obliquity were taken by Francesco Bianchini. He was the astronomer who designed the meridian line, upgrading the similar instrument realized by Giandomenico Cassini in San Petronio, Bononia. The accuracy of the data is discussed from the point of view of the use of the pinhole.

physics.hist-ph↗

arXiv2014

A physics exhibit to show the effect of the aerosol in the atmosphere on electromagnetic wave propagation

In this paper it is explained the construction and utility of a didactic exhibit about the effect of aerosol in atmosphere on electromagnetic wave propagation. The exhibit is composed by a lamp simulating the Sun, a Plexiglas case (the atmosphere), white or black panels (surface albedo), a combustion chamber to supply aerosol inside the case and other equipments. There are temperature and relative humidity of air sensors and 5 light sensors to measure direct and scattered light. It is possible to measure the cooling effect of aerosol inside the case and the increasing in scattered light.

physics.ed-ph↗

arXiv2017

Musical elements in the discrete-time representation of sound

The representation of basic elements of music in terms of discrete audio signals is often used in software for musical creation and design. Nevertheless, there is no unified approach that relates these elements to the discrete samples of digitized sound. In this article, each musical element is related by equations and algorithms to the discrete-time samples of sounds, and each of these relations are implemented in scripts within a software toolbox, referred to as MASS (Music and Audio in Sample Sequences). The fundamental element, the musical note with duration, volume, pitch and timbre, is related quantitatively to characteristics of the digital signal. Internal variations of a note, such as tremolos, vibratos and spectral fluctuations, are also considered, which enables the synthesis of notes inspired by real instruments and new sonorities. With this representation of notes, resources are provided for the generation of higher scale musical structures, such as rhythmic meter, pitch intervals and cycles. This framework enables precise and trustful scientific experiments, data sonification and is useful for education and art. The efficacy of MASS is confirmed by the synthesis of small musical pieces using basic notes, elaborated notes and notes in music, which reflects the organization of the toolbox and thus of this article. It is possible to synthesize whole albums through collage of the scripts and settings specified by the user. With the open source paradigm, the toolbox can be promptly scrutinized, expanded in co-authorship processes and used with freedom by musicians, engineers and other interested parties. In fact, MASS has already been employed for diverse purposes which include music production, artistic presentations, psychoacoustic experiments and computer language diffusion where the appeal of audiovisual artifacts is exploited for education.

cs.SD↗