Showing papers in "Europhysics News in 2015"

Cosmic Rays, Clouds, and Climate

Abstract: A correlation between a global average of low cloud cover and the flux of cosmic rays incident in the atmosphere has been observed during the last solar cycle. The ionising potential of Earth bound cosmic rays are modulated by the state of the heliosphere, while clouds play an important role in the Earth's radiation budget through trapping outgoing radiation and reflecting incoming radiation. If a physical link between these two features can be established, it would provide a mechanism linking solar activity and Earth's climate. Recent satellite observations have further revealed a correlation between cosmic ray flux and low cloud top temperature. The temperature of a cloud depends on the radiation properties determined by its droplet distribution. Low clouds are warm (>273 K) and therefore consist of liquid water droplets. At typical atmospheric supersaturations (∼1%) a liquid cloud drop will only form in the presence of an aerosol, which acts as a condensation site. The droplet distribution of a cloud will then depend on the number of aerosols activated as cloud condensation nuclei (CCN) and the level of super saturation. Based on observational evidence it is argued that a mechanism to explain the cosmic ray-cloud link might be found through the role of atmospheric ionisation in aerosol production and/or growth. Observations of local aerosol increases in low cloud due to ship exhaust indicate that a small perturbation in atmospheric aerosol can have a major impact on low cloud radiative properties. Thus, a moderate influence on atmospheric aerosol distributions from cosmic ray ionisation would have a strong influence on the Earth's radiation budget. Historical evidence over the past 1000 years indicates that changes in climate have occurred in accord with variability in cosmic ray intensities. Such changes are in agreement with the sign of cloud radiative forcing associated with cosmic ray variability as estimated from satellite observations.

How many gold atoms make gold metal

Abstract: All material supplied via JYX is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. How many gold atoms make gold metal? Häkkinen, Hannu; Malola, Sami

The acoustics of a concert hall -- as a linear problem

Abstract: The main purpose of a concert hall is to convey sound from musicians to listeners and to reverberate the music for more pleasant experience in the audience area. This process is linear and can be represented with impulse responses. However, by studying measured and simulated impulse responses for decades, researchers have not been able to exhaustively explain the success and reputation of certain concert halls.

Extreme light - An intense pursuit of fundamental high energy physics

Abstract: By the compression of petawatt pulses to multi-exawatt, a new route for the generation of Schwinger intensities capable of producing highenergy radiation and particle beams with extremely short time structure down to the attosecond-zeptosecond regime is being presented. Far from the traditional laser investigation in the eV regime, this laser-based approach offers a new paradigm to investigate the structure of vacuum and applications to subatomic physics.

Taking snapshots of atomic motion using electrons

Abstract: 55 years after Richard Feynman’s famous Caltech lecture ‘There is plenty of room at the bottom’ [1], heralding the age of nano science and technology, many of the possibilities he envisaged have come true: Using electron microscopy it is nowadays possible to resolve and even identify individual atoms; STM and AFM not only provide us with similar spatial resolution on surfaces, but also allow dragging individual atoms around in a controlled way; X-ray diffraction has revealed the complicated structures of thousands of proteins, giving invaluable insight into the machinery of life.

Sinking with the Titanic

Abstract: T he occurrence of the sucking is certain. In his memories [1], Tameichi Hara describes his experience of jumping off a sinking boat, and of the resulting sucking vortex. The presence of such a phenomenon is also the subject of a MythBuster episode [2] that negates this effect, but uses a small boat. Searching on Internet, one can generally find three types of explanation. The first one refers to the air contained in the boat, which – while escaping during the sinking – would lower the density of water. The second is that water, entering the void spaces inside the ship, would suck people inside. The third is related to the viscous drag effect that causes a vortex behind a body moving through a fluid. It is the same effect which, in a convertible car /cabriolet, makes long hair whip one’s own face. It is easy to visualize this by blowing at a candle behind a hand (i.e., changing the reference frame), or moving a hand in water containing small floating objects. This effect also depends on the speed of the moving object, at least for small velocities. However, there is a more conspicuous effect due to Archimedes that is generally ignored (somehow related to the “sucking void effect”). If one wants to perform this “show”, I suggest buying the “Tubtanic” bath plug [3], for the initial introduction. One also needs an “iceberg” (to be used for the introduction and the final challenge), a transparent cylinder and a glass with a diameter about half that of the cylinder and a thick bottom (for stability and for displacing more water).

Bursting money bins, the ice and water structure

Abstract: That water expands when freezing is a well-known fact, and it is at the basis of an experiment that is often involuntary performed with beer bottles in freezers. But why does the water behave this way? And, more difficult, how can one illustrate this phenomenon in simple terms?

On house renovation and coauthoring: Tricks of the trade to boost your h-index

Abstract: Suppose that your house needs some restoration, and that you call a master mason asking for an estimate. If the mason replies at once that he will quote 1000 € for himself, plus 500 € for each helper apprentice, you will likely be puzzled, if not annoyed. Surely you have good reasons to complain, reasoning that the job you ask for should be remunerated with a fixed amount, irrespective of the number of labourers involved. Yet, this is not a criterion that we usually apply when evaluating the CV of an applicant for an academic position or for a grant.

The European Science Foundation; death or mid-life crisis?

Abstract: It was a 40 birthday party with a difference [1]: to celebrate a lively and eventful past (Figs. 1, 2), but with no clearly-defined future. However, what might have been a wistful event turned into a surprisingly lively one. It applauded the achievement of researchers and the great benefits of European collaboration in science. A commemorative booklet was published for the event and a number of associated events held. Highlights from the past were celebrated; but what does the future hold?

The `fire' of opals

Abstract: T he mineral opal, chemically a form of hydrated silica, is found on practically all continents, but mostly as an “opalescent”, milky–white, soft rock. However, in some parts of Australia small pieces of beautifully coloured gemstones, “precious opal”, are to be found embedded in a matrix of ordinary opal. What makes these quintessentially Australian gemstones sparkle with flecks of pure spectral colour (Fig.1)? Oddly enough, the answer to this question was a mystery to mineralogists for a long time until noted CSIRO electron microscopist John Sanders discovered the surprising answer as recently as the 1970s [1],[2]. Because of the spectral colours exhibited, the phenomenon of diffraction from periodic features was suspected to be the cause, but nobody could guess at the nature of such periodic structures until they were revealed by electron microscopy. It was surmised that the optical properties of precious opal, as distinct from the milky-white appearance of common opal that shows no ‘fire’, depends on the existence of orderly, regular arrays of optical discontinuities, spaced at repeat distances of the order of 150 to 350 nanometers, i.e., distances that correspond to half the wavelength of visible light. Chemically, opals are made of pure, transparent, hydrated silica, i.e., hydrated Silicon Dioxide. But what the electron microscope revealed was that the silica is in the form of tiny spheres, of the appropriate range of sizes, stacked in close-packed regular arrays, as may be seen in Fig. 2, just like atoms or molecules in crystalline substances. How are these little spherical objects formed is answered by noting that the solubility of silica in water increases markedly with temperature so that, upon cooling, silica is usually deposited as quartz crystals that are said to grow in what is called a hydrothermal process. Alternatively, in the presence of centres of nucleation, the silica can precipitate from saturated solutions in the form of amorphous clusters. These continue to grow as concentric spheres, which then fall through the solution and end up in interstitial cavities. In most cases, a poly-disperse range of sizes results, which when dried out results in a milky-white solid of ordinary, or so-called ‘potch’ opal. However, in rare cases, where the little spheres have a greater distance through which to fall, a gravitational separation can take place, where the larger spheres fall more quickly than the smaller ones and arrange themselves in layers upon layers of uniformly sized regions of hexagonal close-packed groups, like oranges in a crate. Hence the quasi-crystalline arrangement of precious opal, usually in small pieces consisting of separate small regions, is analogous to crystal grains. The opal ‘grains’ can vary in size, from a few millimeters, known as pin-fire opals, up to quite large ones in what is known as boulder opals. Because the individual silica spheres are completely transparent, pieces of opal show practically no colour when viewed in transmission. However, when viewed in reflection, strong diffraction colours are seen. These diffraction phenomena are not like those from a two-dimensional grating, such as is seen from the surface of a CD or DVD, and erroneously shown in illustrations in some popular articles. On the contrary, 3-dimensional diffraction

Quantum light : The puzzling predictions of entanglement are coming of age

Abstract: Entanglement is the physical property that marks the most striking deviation of the quantum from the classical world. It has been mentioned first by the great Austrian Physicist Erwin Schr¨odinger in 1935 (an introduction to this and other quantum phenomena is given in [1]). Yet, despite this theoretical prediction now being 80 years old, and the famous experimental verifications by Alain Aspect dating back to the early eighties [2], entanglement and its use entered mainstream physics as a key element of quantum information science [3] only in the 1990’s.