Physics

Super-Earths are one of the most common types of extrasolar planets currently known. Hundreds of these planets have been discovered by the Kepler spacecraft and other surveys, with masses up to 10 M ⊕ and consequently higher surface gravity than Earth. These planets would have greater escape velocities than Earth, reaching as high as 27 km s −1 for the largest super-Earths. To launch a spacecraft from the surface of such a world with chemical rockets would be cost-prohibitive or nearly so, while another commonly proposed launch system, the space elevator, would lack the necessary tensile strength to support its weight. However, we find that a hybrid launch system combining chemical rockets and a space-based momentum-exchange tether could reduce the Δv to be provided by chemical rockets to reach escape velocity by 40\%, bringing it back into the realm of feasibility. Such a system could also function on Earth with considerably less exotic materials.

We describe a hands-on accurate demonstrator for cosmic rays realized by six high school students, whose main aim is to show the relevance and the functioning of the principal parts of a cosmic rays telescope (muon detector), with the help of two large size wooden artifacts. The first one points out how cosmic rays can be tracked in a muon telescope, while the other one shows the key avalanche process of electronic ionization that effectively allows muon detection through a photomultiplier. Incoming cosmic rays are visualized in terms of laser beams, whose 3D trajectory is highlighted by the turning on of LEDs on two orthogonal matrices. Instead the avalanche ionization process is demonstrated through the avalanche falling of glass marbles on an inclined plane, finally turning on a LED. A pictured poster accompanying the demonstrator is as well effective in assisting cosmic rays demonstration and its detection. The success of the demonstrator has been fully proven by general public during a Science Festival, the corresponding project winning the Honorable Mention in a dedicated competition.

Whether we are alone in the universe is one of the greatest mysteries facing humankind. Given the >100 billion stars in our galaxy, many have argued that it is statistically unlikely that life, including intelligent life, has not emerged anywhere else. The lack of any sign of extraterrestrial intelligence, even though on a cosmic timescale extraterrestrial civilizations would have enough time to cross the galaxy, is known as Fermi's Paradox. One possible explanation for Fermi's Paradox is the Zoo Hypothesis which states that one or more extraterrestrial civilizations know of our existence and can reach us, but have chosen not to disturb us or even make their existence known to us. I propose here a proactive test of the Zoo Hypothesis. Specifically, I propose to send a message using television and radio channels to any extraterrestrial civilization(s) that might be listening and inviting them to respond. Even though I accept this is unlikely to be successful in the sense of resulting in a response from extraterrestrial intelligences, the possibility that extraterrestrial civilizations are monitoring us cannot be dismissed and my proposal is consistent with current scientific knowledge. Besides, issuing an invitation is technically feasible, cheap and safe, and few would deny the profound importance of establishing contact with one or more extraterrestrial intelligences. A website has been set up (this http URL) to encourage discussion of this proposal and for drafting the invitation message.

In order to quickly study quantum devices in transient problems, this work demonstrates an analytical algorithm to solve the Hartree potential associated with charge fluctuations in the time-dependent non-equilibrium green function (TDNEGF) method. We implement the calculations in the heterojunction system of gold metals and silicon quantum dots for applications of photoelectric semiconductors in the future. Numerical results for the transient solutions are shown to be valid by comparing with the steady solutions calculated by the standard time-independent density functional method.

We propose to develop a full-accuracy flight test environment for the Mars helicopter and related Mars-atmospheric vehicles. The experiment would use reduced-g atmospheric flights with an aircraft that houses a properly sized vacuum chamber.

The habitable zone is the circumstellar region in which a terrestrial-mass planet with an atmosphere can sustain liquid water on its surface. However, despite the usefulness of this concept, it is being found to be increasingly limiting in a number of ways. The following is known: (i) Liquid water can exist on worlds for reasons unrelated to its specific distance from a star. (ii) Energy sources can exist for reasons unrelated to the distance to a star. Furthermore, the habitable zone is based on both astronomy: the distance and stellar energy, and chemistry: liquid water and the right temperature. However, these factors are only part of the consideration. Thus, discussions of habitability and the possibility for the emergence of life on a world must consider the evolutionary principles that govern life as well as the laws that govern stellar and planetary science. This is important because the following is also known: (iii) The time window for the emergence of life is within 600 million years. (iv) The Earth was an extreme environment overall in the period when this window existed. (v) The first life was necessarily fragile. Therefore, chemical evolution must have taken place in a relatively protected and restricted environment. Thus, rather than as in the Goldilocks zone, which focuses too narrowly on the world as a whole, this paper suggests that it is better to focus on a particular region and time period on a world, in which fitting conditions for habitability exist. Thus, the following is suggested: The Goldilocks Edge is a spatial and temporal window on an astronomical body or planemo, where liquid solvents, SPONCH elements, and energy sources exist. Furthermore, since the mere presence of these do not in themselves necessarily lead to the emergence of life, this possibility only arises when these interact. Thus, the prebiotic spot will be suggested.

Phys and Math are two colleagues at the University of Sa{\c c}enbon (Crefan Kingdom), dialoguing about the remarkable efficiency of mathematics for physics. They talk about the notches on the Ishango bone, the various uses of psi in maths and physics, they arrive at dessins d'enfants, moonshine concepts, Rademacher sums and their significance in the quantum world. You should not miss their eccentric proposal of relating Bell's theorem to the Baby Monster group. Their hyperbolic polygons show a considerable singularity/cusp structure that our modern age of computers is able to capture. Henri Poincar{é} would have been happy to see it.

Egyptian faience is a non-clay ceramic semi-transparent material, formed of a quartz core and alkali lime glaze with some cases exhibiting an interaction layer between them. Several possible glazing methods have been identified. Previous investigations have tried to identify the glazing technique by using the microstructure images obtained from polished sections using scanning electron microscope(SEM). Such techniques require sampling which is not feasible on museum collections. Optical Coherence Tomography (OCT) is a non-invasive 3D imaging technique, that produces virtual cross sections of transparent and semi-transparent materials. Liang et al. (2012a) investigated the feasibility of using OCT to non-invasively investigate microstructures of Egyptian faience, but the limited probing depth of the 930nm OCT prevented viewing down to the core of the objects, where the presence of glass was thought to be a distinguishing feature between some of the manufacturing techniques, and where the particle size of the quartz may indicate the difference in the raw material. In this paper, a unique longer wavelength OCT at 2um is used to scan a number of ancient Egyptian faience objects including ring and shabti fragments. It was found that the core of the faience could be imaged at this longer wavelength, allowing comparisons in all the layers within the microstructure, and leading to discussions about the possible glazing methods. The 2um OCT offers the possibilities of rapid, non invasive imaging of faience microstructure down to the core, allowing comprehensive studies of intact objects and large museum collections.

This paper investigates the use of Optical Coherence Tomography (OCT) and Short-wave Infrared (SWIR) spectral imaging to study the deterioration of a Limoges enamel panel. Limoges enamels are formed of glass layers applied on a metal substrate and are prone to glass disease. However, the level of deterioration in Limoges enamels is generally difficult to assess visually. In this study, SWIR was used to produce a hydration level map of the enamel, which was coupled with virtual OCT cross-sections. The study shows a good correlation between levels of hydration and structural damage over the enamel panel. Hydration mapping allows visualisation of structural damage across the entire enamel in one image.

It is well-known that the straight gravity tunnel between any two different positions on a non-rotating Earth, which has uniform density, is traversable, i.e., an object initially at rest will reach its destination through the gravity tunnel in both directions. Moreover, the time taken to fall is always constant. These facts are no longer true if rotation is allowed. The aim of this note is to derive the necessary and sufficient condition for traversability of straight gravity tunnels through a rotating physical body with spherically symmetric gravitational field. Fall-through times are expressed in a closed form for linear and constant gravitational fields. In conclusion, these models are compared to numerically obtained data using the internal structure of the Earth.