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At least 595 records · Page 33Linked to original sources

arXiv2020

Hate multiverse spreads malicious COVID-19 content online beyond individual platform control

We show that malicious COVID-19 content, including hate speech, disinformation, and misinformation, exploits the multiverse of online hate to spread quickly beyond the control of any individual social media platform. Machine learning topic analysis shows quantitatively how online hate communities are weaponizing COVID-19, with topics evolving rapidly and content becoming increasingly coherent. Our mathematical analysis provides a generalized form of the public health R0 predicting the tipping point for multiverse-wide viral spreading, which suggests new policy options to mitigate the global spread of malicious COVID-19 content without relying on future coordination between all online platforms.

physics.soc-ph↗

arXiv2020

Shielded dumbbell L5 settlement

We present a two-sphere dumbbell configuration of a rotating settlement at Earth-Moon L5. The two-sphere configuration is chosen to minimize the radiation shielding mass which dominates the mass budget. The settlement has max 20 mSv/year radiation conditions and 1 g artificial gravity. If made for 200 people, it weighs 89000 tonnes and provides 60 m$^2$ of floorspace per person. The radiation shield is made of asteroid rock, augmented by a water layer with 2 % of the mass for neutron moderation, and a thin boron-10 layer for capturing the thermalized neutrons. We analyze the propulsion options for moving the material from asteroids to L5. The FFC Cambridge process can be used to extract oxygen from asteroid regolith. The oxygen is then used as Electric Propulsion propellant. One can also find a water-bearing asteroid and use water for the same purpose. If one wants to avoid propellant extraction, one can use a fleet of electric sails. The settlers fund their project by producing and selling new settlements by zero-delay teleoperation in the nearby robotic factory which they own. The economic case looks promising if LEO launch costs drop below $\sim$ \$300/kg.

physics.pop-ph↗

arXiv2020

Diamagnetic Levitation Using High-Temperature Superconducting Wires for Microgravity Research and Mitigation in Human Spaceflight Applications

A novel use of high temperature superconducting (HTS) electromagnets for human sized microgravity research and mitigation is outlined. Recent advances in HTS technology have resulted in electromagnets that potentially could levitate large diamagnetic targets, such as human organs, for additive manufacturing or entire humans for microgravity training. These applications are then used as a springboard to discuss the possibility of active microgravity compensation and inertial dampeners for future space travel applications. Finite element simulations are used to check the validity of the designs and motivate future research.

physics.pop-ph↗

arXiv2020

Radiation conditions in relativistic interstellar flight

Radiation hazard on board of a relativistic rocket can be of internal and external origin. Because of its highest specific energy density, antimatter is considered to be the preferred rocket fuel for accelerating a multi-ton rocket up to relativistic speed. High-energy products of matter-antimatter annihilation (gamma-photons and meson radiation) can produce a severe radiation hazard for crew and electronics. Another factor that can stand against our pursuit to the stars is intense nucleons radiation produced by the oncoming relativistic headwind of interstellar gas and cosmic rays with their intensity increasing with rocket velocity. When a rocket accelerates to a relativistic speed, the rarefied interstellar gas of neutral and ionized atoms and molecules transforms into the oncoming flux of high-energy nucleons irradiating the rocket body and creating the severe radiation hazard. The oncoming flux of relativistic dust granules imposes a threat of mechanical damage to the rocket body.

physics.pop-ph↗

arXiv2020

On modelling bicycle power-meter measurements: Part II. Relations between rates of change of model quantities

Power-meter measurements are used to study a model that accounts for the use of power by a cyclist. The focus is on relations between rates of change of model quantities, such as power and speed, both in the context of partial derivatives, where other quantities are constant, and Lagrange multipliers, where other quantities vary to maintain the imposed constraints.

physics.pop-ph↗

arXiv2020

On modelling bicycle power for velodromes: Part I: Formulation for individual pursuits

For a moving bicycle, the power can be modelled as a response to the propulsion of the centre of mass of the bicycle-cyclist system. On a velodrome, an accurate modelling of power requires a distinction between the trajectory of the wheels and the trajectory of the centre of mass. We formulate and examine an individual-pursuit model that takes into account the aforementioned distinction. In doing so, we provide details of the invoked physical principles and mathematical derivations, with an emphasis on their limitations. We assume that a velodrome consists of two parallel straights and two semicircular arcs. We neglect the effects of the track inclination along the straights and assume the track inclination along the curves to be constant. For either segment, we consider two distinct black-line speeds. For the latter, the lean-angle expression is derived based on a noninertial frame of the cyclist. Among conclusions quantified by this model is the fact that a constant-cadence approach to an individual pursuit does not minimize the required power.

physics.pop-ph↗

arXiv2020

Hierarchical Eclipses

The obscuration of a celestial body that covers another one in the background will be called a ``hierarchical eclipse''. The most obvious case is that a star or a planet will be hidden from sight by the moon during a lunar eclipse. Four objects of the solar system will line up then. We investigate this phenomenon with respect to the region of visibility and periodicity. There exists a parallax field constraining the chances for observation. A historic account from the Middle Ages is preserved that we analyse from different viewing angles. Furthermore, we provide a list of events from 0 to 4000 AD. From this, it is apparent that Jupiter is most often involved in such spectacles because its orbit inclination is small. High-inclination orbits reduce the probability to have a coincidence of an occultation of that object with a lunar eclipse.

physics.pop-ph↗

arXiv2020

Teaching quantum information science to high-school and early undergraduate students

We present a simple, accessible, yet rigorous outreach/educational program focused on quantum information science and technology for high-school and early undergraduate students. This program allows students to perform meaningful hands-on calculations with quantum circuits and algorithms, without requiring knowledge of advanced mathematics. A combination of pen-and-paper exercises and IBM Q simulations helps students understand the structure of quantum gates and circuits, as well as the principles of superposition, entanglement, and measurement in quantum mechanics.

physics.ed-ph↗

arXiv2020

Reworking the SETI Paradox: METI's Place on the Continuum of Astrobiological Signaling

The Search for Extraterrestrial Intelligence (SETI) has heretofore been a largely passive exercise, reliant on the pursuit of technosignatures. Still, there are those that advocate a more active approach. Messaging Extraterrestrial Intelligence (METI) has had a controversial history within the larger SETI project; it is claimed that the risks involved outweigh any potential benefits. These arguments are ultimately not compelling, result in absurd policy recommendations, and rest on a faulty appreciation of the nature of technosignatures, whose detectability implies intent to signal. Present technology is advancing quickly such that we will soon have great observational reach, to the point of reliably detecting such technosignatures and biosignatures: a capability that can be matched or exceeded elsewhere. To escape the SETI Paradox properly defined, at least one technological civilization must choose not to suppress its own continuum of astrobiological signals, of which METI is merely the most effective endmember. Passive SETI's low likelihood of success in the short-term is a serious obstacle to sustainable funding, alongside a 'giggle factor' enhanced by a pernicious fear of contact. The scientific community must integrate an active approach to better ensure both the continuity and eventual success of the SETI project.

physics.pop-ph↗

arXiv2020

The Solar Eclipse of the Xia Dynasty: A Review

We present a review on the renowned solar eclipse in the Chinese book "Shujing" describing the oldest account of this kind. After balancing the arguments on the time, place, and the celestial stage, we offer a new scenario. The path of totality on 15 September 1903 BCE traversed Anyi, the assumed capital of the Xia dynasty. The date matches remarkably well the chronological order of two other incidents of mythological rank: the closest-ever agglomeration of the naked-eye planets and the Great Flood under Emperor Yu. Still, this eclipse does not remove all questions about the historical circumstances given in the account.

physics.hist-ph↗

arXiv2021

On maximizing VAM for a given power: Slope, cadence, force and gear-ratio considerations

The velocità ascensionale media (VAM) is measurement that quantifies a cyclist's climbing ability. It depends on both the ground speed of a bicycle-cyclist system and the slope of an incline. To maximize the ascent speed, the solution to the brachistochrone problem determines that the optimal curve for the incline is a straight line, which is a hill with a constant slope. The maximum obtainable VAM value by a cyclist increases monotonically with the slope of the incline, but is limited by the maximum sustainable power. These properties -- which are theorems stemming from a standard mathematical model to account for the power required to propel a bicycle -- constitute a mathematical-physics background upon which various strategies for the VAM maximization can be examined in the context of the maximum sustainable power as a function of both the gear ratio and cadence. Recently established records provide an empirical support for these analytical results, which are based on theoretical considerations.

physics.pop-ph↗

arXiv2020

Low--Temperature Plasma Technology: Impact on Indian Rural Life

The low temperature plasma technology has been emerged as an alternative environmental friendly technology that has a potential to replace the traditional technologies in various sectors such as textile industries, agriculture, food industries and waste water treatment. The future prospective of the low temperature plasma technology on the life of rural Indians has been discussed in this brief report.

physics.pop-ph↗

arXiv2020

El Modelo Estandar de la Cosmologia Moderna en Jaque

The standard model of modern cosmology provides a description of a wide range of astrophysical and astronomical data. However, despite this impressive success, several discrepancies have have persisted. Most strikingly, the emerging tension in the observed and inferred values of the Hubble constant. This constant parameterizes the rate of expansion of the cosmos and thus provides clues about its energy content. In this article we examine the origin of this discrepancy and we explore possible solutions to overcome the problem.

physics.pop-ph↗

arXiv2020

On a spectral pattern of the Von-Neumann probes

In this paper we have extended our previous work \citep{probe1} and considered spectral characteristics of interstellar non-relativistic Type-II and Type-III Von-Neumann probes. It has been shown that by means of the proton capture, required for replication, strong bremstrahlung emission will be generated. We have found that for both types of civilizations the probes might be visible mainly in the infrared spectral band, but as it has been found the probes might be visible in the ultraviolet as well. For both cases it was shown that differential power has dips for equally spaced frequencies, which might be a significant fingerprint to identify such exotic interstellar objects.

physics.pop-ph↗

arXiv2020

Soft matter science and the COVID-19 pandemic

Much of the science underpinning the global response to the COVID-19 pandemic lies in the soft matter domain. Coronaviruses are composite particles with a core of nucleic acids complexed to proteins surrounded by a protein-studded lipid bilayer shell. A dominant route for transmission is via air-borne aerosols and droplets. Viral interaction with polymeric body fluids, particularly mucus, and cell membranes control their infectivity, while their interaction with skin and artificial surfaces underpins cleaning and disinfection and the efficacy of masks and other personal protective equipment. The global response to COVID-19 has highlighted gaps in the soft matter knowledge base. We survey these gaps, especially as pertaining to the transmission of the disease, and suggest questions that can (and need to) be tackled, both in response to COVID-19 and to better prepare for future viral pandemics.

cond-mat.soft↗

arXiv2020

Monte Carlo estimation of the probability of causal contacts between communicating civilisations

In this work we address the problem of estimating the probabilities of causal contacts between civilisations in the Galaxy. We make no assumptions regarding the origin and evolution of intelligent life. We simply assume a network of causally connected nodes. These nodes refer somehow to intelligent agents with the capacity of receiving and emitting electromagnetic signals. Here we present a three-parametric statistical Monte Carlo model of the network in a simplified sketch of the Galaxy. Our goal, using Monte Carlo simulations, is to explore the parameter space and analyse the probabilities of causal contacts. We find that the odds to make a contact over decades of monitoring are low for most models, except for those of a galaxy densely populated with long-standing civilisations. We also find that the probability of causal contacts increases with the lifetime of civilisations more significantly than with the number of active civilisations. We show that the maximum probability of making a contact occurs when a civilisation discovers the required communication technology.

physics.pop-ph↗

arXiv2020

Solar One: A Proposal for The First Crewed Interstellar Spacecraft

In this paper it is presented the concept and design of a new type of spacecraft that could be used to make the first manned interstellar travel. Solar one would integrate three near-term technologies, namely: compact nuclear fusion reactors, extremely large light sails, and high-energy laser arrays. A system of lenses or mirrors to propel the sail with sunlight is suggested as an alternative to laser propulsion. With a mile-long light sail, Solar One could reach an average of 22% the speed of light, arriving to the closest potentially habitable exoplanet in less than 19 years with the help of a Bussard scoop producing reverse electromagnetic propulsion. Key challenges are reducing the weight of continuous-wave lasers and compact fusion reactors as well as achieving cryo-sleep and artificial gravity.

physics.pop-ph↗

arXiv2020

Exploring Connections Between Cosmos & Mind Through Six Interactive Art Installations in "As Above As Below"

Are there parallels between the furthest reaches of our universe, and the foundations of thought, awareness, perception, and emotion? What are the connections between the webs and structures that define both? What are the differences? "As Above As Below" was an exhibition that examined these questions. It consisted of six artworks, each of them the product of a collaboration that included at least one artist, astrophysicist, and neuroscientist. The installations explored new parallels between intergalactic and neuronal networks through media such as digital projection, virtual reality, and interactive multimedia, and served to illustrate diverse collaboration practices and ways to communicate across very different fields.

physics.pop-ph↗