There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Recent years have witnessed many breakthroughs in research on graphene (the first two-dimensional atomic crystal) as well as a significant advance in the mass production of this material. This one-atom-thick fabric of carbon uniquely combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, as well as many other supreme properties, all of which make it highly attractive for numerous applications. Here we review recent progress in graphene research and in the development of production methods, and critically analyse the feasibility of various graphene applications.

/pdf/a-roadmap-for-graphene-1nstzmbk5x.pdf

A roadmap for graphene

QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ≈ 10−33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ≈ 1017 s which is very long compared to the Planck time ≈ 10−43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (M/M)−3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs. It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.

Black Hole Explosions

Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of a broad range of materials, including semiconductors and biomolecules.

Materials for terahertz science and technology

We have developed a 1-kHz repetition-rate Ti:sapphire laser system that can simultaneously generate high peak and average powers of 0.2 TW and 4 W, respectively. The laser system generates 4-mJ energy pulses with a 20-fs pulse width. We eliminated thermal lensing in the system by cooling the Ti:sapphire crystal to 125 K. The output 20-fs pulses were fully characterized by use of the new technique of transient-grating frequency-resolved optical gating. We demonstrate experimentally that the pulse duration at the output is limited only by fifth-order dispersion.

0.2-TW laser system at 1kHz.

Multi-MeV ion production from the interaction of a short laser pulse with a high-density plasma, accompanied by an underdense preplasma, has been studied with a particle-in- cell simulation and good agreement is found with experiment. The mechanism primarily responsible for the acceleration of ions is identified. Comparison with experiments sheds light on the ion-energy dependence on laser intensity, preplasma scale length, and relative ion energies for a multi-species plasma. Two regimes of maximum ion-energy dependence on laser inten- sity, I, have been identified: subrelativistic, ∝ I; and relativistic, ∝ √ I. Simulations show that the energy of the accelerated ions versus the preplasma scale length increases linearly and then saturates. In contrast, the ion energy decreases with the thick- ness of the solid-density plasma.

/pdf/high-energy-ion-generation-in-interaction-of-short-laser-594vkj8j45.pdf

High-energy ion generation in interaction. of short laser pulse with high-density plasma

Electrical signals are measured (analyzed and displayed) with subpicosecond resolution by electro-optic sampling of the signal in an electro-optic crystal, the index of which changes in response to the electric field produced by the signal, in accordance with the Pockels effect. The crystal is disposed adjacent to a transmission line along which the signals propagate the line may be a coplanar wave guide having a plurality of parallel strips of conductive material on the surface of the crystal. The crystal may be disposed adjacent to and in the fringe field of a line on a substrate, which may be part of an integrated circuit, for measuring signals propagating along the line during the operation of the circuit. A beam of short optical (laser) sampling pulses in the picosecond range is focused so that the region where the beam is confocal is disposed where the field is parallel in the crystal. The confocal region (where the optical wavefront is planar is preferrably close to the surface of the crystal and perpendicular to the optical axis of the crystal. The optical pulses transmitted through the crystal are processed to provide a display affording a measurement of the electrical signal.

Measurement of electrical signals with picosecond resolution

A few years ago, a new type of large-scale laser infrastructure specifically conceived to produce the highest peak power and focused intensity was announced: the Extreme Light Infrastructure, ELI ( 1 ), designed to be the first exawatt-class (1018 W) laser. This gargantuan power will be obtained by cramming a kilojoule of energy into a pulse only 10 fs in duration. Analysis of the history of laser development reveals that the pulse duration and intensity of lasers (or derived coherent radiation bursts) are linearly related over more than 18 orders of magnitude (see the figure). This observation leads us to the conclusion that the shortest coherent pulse should come from such a large-sized laser. If zeptosecond and perhaps yoctosecond pulses can be produced using kilojoule-megajoule systems, it would open a route to time-resolved nuclear physics exploration and the possibility of peeking into the nucleus interior in the same way that chemical reactions or atoms can be probed today.

https://science.sciencemag.org/content/sci/331/6013/41.full.pdf

More Intense, Shorter Pulses

Up to 10 kV have been switched with Si and GaAs laser‐activated switches. We show that in spite of the thermal instability shortcoming experienced in Si, quasi‐dc bias operation can be utilized in a manner which relaxes stringent synchronization requirements. In the case of GaAs the thermal instability is less severe and up to 8 kV dc has been held off and efficiently switched. In both cases, a fast switching time of ∼40 ps is observed. This time is a combination of the laser pulse width, geometry bandwidth, and jitter time. Efficient switching action requires only a few tens of microjoules of laser energy. Electrical pulses ranging from subnanosecond to hundreds of nanoseconds duration have been readily generated.

Gerard Mourou

Papers

0.2-TW laser system at 1kHz.

High-energy ion generation in interaction. of short laser pulse with high-density plasma

Measurement of electrical signals with picosecond resolution

More Intense, Shorter Pulses

High‐power switching with picosecond precision