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

Verfahren zum konfigurationsteuern von laserinduziertem zerstören und abtragen

Monte Carlo methods are used to study photoconductive transients in gallium arsenide. It is demonstrated that working with presently established ranges for the Γ‐L coupling coefficient, the existence of a velocity overshoot at moderate fields cannot be exactly predicted. The role of negative velocity electrons in the initial transient for short wavelength excitation is also demonstrated. Details of an actual experiment are described and evaluated against a model which incorporates the Monte Carlo simulation into a transmission line structure with a frequency‐dependent characteristic impedance. The results demonstrate that an appropriately designed experiment can observe subpicosecond carrier transport transients.

Theoretical and experimental investigations of subpicosecond photoconductivity

A new amplifying laser concept based on Coherent Amplification Network (CAN) is proposed to solve the high‐peak high‐average‐power quandary. The amplification network is based on identical telecommunication diode‐pumped fiber lasers. The philosophy behind the approach is to build the amplifying system from numerous small but identical parts as opposed to larger but non‐identical components like in the laser Megajoule in France or NIF in the USA. The basic amplification scheme is in‐fiber Chirped Pulse Amplification. Besides the possibility to simultaneously provide high peak and high average power, the technique gives independent control of the output beam spatial and temporal coherence, as well as the pupilary distribution. In addition to being rugged, CAN offers the additional benefit of being inexpensive and low maintenance. A conceptual design based on CAN is presented that offers an alternative to the next CERN Linear Collider (CLIC).

The Road to High Peak Power and High Average Power Lasers: Coherent‐Amplification‐Network (CAN)

The authors present calculations of the absorption of an ultrashort laser pulse in various plasma density profiles, with density scale lengths less than or comparable to the wavelength, for various angles of incidence, and for both s and p polarizations. This simple model is used to infer submicron plasma-density-gradient scale lengths from measurements of the variation of absorption with angle and polarization, for data obtained with plasmas created by 1-ps, 1.06- mu m laser pulses. These experimental results, obtained with a short pulse (1 ps) incident on solid matter, are analyzed between 5*10/sup 12/ W/cm/sup 2/ and 5*10/sup 14/ W/cm/sup 2/. It is found that in this intensity range, where the interaction is with a plasma of finite but very steep density gradient and where prepulse and nonlinear effects are weak or negligible, 3*10/sup -2/ >

Absorption of an ultrashort laser pulse in very steep plasma density gradients

Bulk Cr:GaAs in a sparkgap‐type arrangement has switched 4 kV pulses into 50 Ω with <1 ns rise time. The required trigger energy from the laser was ⩾ 35 nJ; the timing jitter was ⩽ ±150 ps.

Gerard Mourou

Papers

Verfahren zum konfigurationsteuern von laserinduziertem zerstören und abtragen

Theoretical and experimental investigations of subpicosecond photoconductivity

The Road to High Peak Power and High Average Power Lasers: Coherent‐Amplification‐Network (CAN)

Absorption of an ultrashort laser pulse in very steep plasma density gradients

Laser triggered Cr:GaAs HV sparkgap with high trigger sensitivity