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.

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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

Damage Threshold as a Function of Pulse Duration in Biological Tissue.

Switching of high voltage pulses (of the order of 10 kV) of durations from about 10μs (microseconds) to 10ms (milliseconds) with picosecond accuracy is accomplished by a laser activated semiconductor switch made up of a body (18) of high resistivity semiconductor material, such as nearly intrinsic silicon, integrated into a wide band (10GHz) geometry, which is part of a transmission line (28). The high bias voltage pulses are obtained by charging the line in synchronism with the generation of the laser pulse. The high voltage bias pulse width can be typically in the range of 10μs- 10ms, and the length of the body (18) is selected so as to prevent thermal breakdown of the semiconductor with such pulse widths. The energy of the laser pulse switches the high voltage to produce a multikilovolt output pulse suitable for driving devices, such as streak cameras or Pockels cells, by the same laser, which need to be synchronized with picosecond accuracy to the laser pulse. The length of the transmission line may be varied to adjust the width of the multikilovolt output pulse.

Apparatus for switching high voltage pulses with picosecond accuracy

To evaluate transscleral glaucoma surgery techniques using ultrashort pulsed lasers, we attempted to produce photodisruption on the inner surface of the sclera without damaging the overlying tissue. We identified two methods, using pulses centered at 1700 nm and a transparency inducing drug, to produce the spatial and temporal confinement of the pulse necessary to produce photodisruption in the highly scattering sclera. When fully developed these concepts may help address the longstanding limitations of current glaucoma surgical techniques.

Transscleral photodisruption for the treatment of glaucoma

In order to avoid problems associated with thermal distortion, loss of energy, and destruction of system components, the invention provides a means for producing, for the first time, high repetition rate, high power pulses while avoiding thermal distortion and its attendant difficulties. The invention provides the ability to remove heat generated from the gain media (lasant material) and to repeatedly extract energy from the media without the accumulation of heat in the media which causes thermal distortions. The invention avoids thermal distortions by pumping an unheated gain region every time an optical pulse is incident thereon. In one aspect, the gain media is essentially uniformly pumped using an essentially instantaneous uniform spatial profile provided by a multi-mode oscillator. The resulting instantaneous uniform temperature profile does not create thermal gradients, thus, no thermal distortions occur. In the invention, the total time duration of pumping and lasing or amplification takes place while the thermal profile remains uniform in the region of the media in the beam path. Thus, no thermal distortions occur during the time of pumping and lasing or amplification. Heat is preferably extracted at about the same rate it is generated in the lasant material (media).

Optical pumping method and apparatus

Since the inception of the laser, pulse duration has been continuously decreased by the use of a variety of techniques: Q-switching, mode-locking, and pulse compression. We would like to present a new technique based on the addition of laser sub-harmonic, ALS, that allows the production of a single-cycle pulse with single-femtosecond pulse duration. This simple technique takes advantage of the recent progress made in the generation of a few optical cycles and in optical parametric amplification.

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Gerard Mourou

Papers

Damage Threshold as a Function of Pulse Duration in Biological Tissue.

Apparatus for switching high voltage pulses with picosecond accuracy

Transscleral photodisruption for the treatment of glaucoma

Optical pumping method and apparatus

Single optical cycle laser pulse in the visible and near-infrared spectral range