Harmonic Generation from Relativistic Plasma Surfaces in Ultrasteep Plasma Density Gradients

Harmonic generation in the limit of ultrasteep density gradients is studied experimentally. Observations reveal that, while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale lengths (L-p/lambda <1), the absolute efficiency of the harmonics declines for the steepest plasma density scale length L-p -> 0, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the relativistic oscillating mirror was estimated to be in the range of 10(-4)-10(-6) of the laser pulse energy for photon energies ranging from 20-40 eV, with the best results being obtained for an intermediate density scale length.

Control of harmonic generation from relativistic mirrors

We demonstrate for the first time that fine varying of the density gradient of a plasma mirror along with laser spatial phase on target allows total control over the harmonic generation mechanisms and harmonic spatial properties. An analytical model is also proposed. © OSA 2013.

High-order harmonic generation from controlled plasma mirrors

Ultrashort, high contrast laser pulses when focused to high intensity and reflected from a steep solid density 'plasma mirror (PM)' contain coherent XUV radiation in the form of high-order harmonics. The emission can either be due to the relativistically driven oscillating PM (ROM) [1] or due to Coherent wake emission (CWE) [2]. Selective control over the mechanisms and the characteristics of these harmonics and understanding the physics is crucial for the development of intense attosecond light sources. © 2013 IEEE.

XUV Emission from Autoionizing Hole States Induced by Intense XUV-FEL at Intensities up to 10(17) W/cm(2)

Aluminium targets were irradiated with 92 eV radiation from FLASH Free Electron Laser at DESY at intensities up to 10(17)W/cm(2) by focussing the beam on target down to a spot size of similar to 1 mu m by means of a parabolic mirror. High resolution XUV spectroscopy was used to identify aluminium emission from complex hole-states. Simulations carried out with the MARIA code show that the emission characterizes the electron heating in the transition phase solid-atomic. The analysis allows constructing a simple model of electron heating via Auger electrons.

Validation of non‑stationary precipitation series for site‑specific impact assessment: comparison of two statistical downscaling techniques

Statistical downscaling (SD) methods have become a popular, low-cost and accessible means of bridging the gap between the coarse spatial resolution at which climate models output climate scenarios and the finer spatial scale at which impact modellers require these scenarios, with various different SD techniques used for a wide range of applications across the world. This paper compares the Generator for Point Climate Change (GPCC) model and the Statistical DownScaling Model (SDSM)—two contrasting SD methods—in terms of their ability to generate precipitation series under non-stationary conditions across ten contrasting global climates. The mean, maximum and a selection of distribution statistics as well as the cumulative frequencies of dry and wet spells for four different temporal resolutions were compared between the models and the observed series for a validation period. Results indicate that both methods can generate daily precipitation series that generally closely mirror observed series for a wide range of non-stationary climates. However, GPCC tends to overestimate higher precipitation amounts, whilst SDSM tends to underestimate these. This infers that GPCC is more likely to overestimate the effects of precipitation on a given impact sector, whilst SDSM is likely to underestimate the effects. GPCC performs better than SDSM in reproducing wet and dry day frequency, which is a key advantage for many impact sectors. Overall, the mixed performance of the two methods illustrates the importance of users performing a thorough validation in order to determine the influence of simulated precipitation on their chosen impact sector.

Living in the Landscape: Essays in Honour of Graeme Barker

This edited volume reflects on the multitude of ways by which humans shape and are shaped by the natural world, and how Archaeology and its cognate disciplines recover this relationship. The structure and content of the book recognize Graeme Barker’s pioneering contribution to the scientific study of human-environment interaction, and form a secondary dialectic between his many colleagues and past students and the academic vista which he has helped define. The volume comprises 22 thematic papers, arranged chronologically, each a presentation of front-line research in their respective fields. They mirror the scope of Barker’s legacy through a focus on transitions in the human-environment relationship, how they are enacted and perceived. The assembled chapters illustrate how climate, demographic, subsistence, social and ecological change have affected cultures from the Palaeolithic to Historical, from North Africa and West-Central Eurasia to Southeast Asia and China. They also chronicle the innovations and renegotiated relations that communities have devised to meet and exploit the many shifting realities involved with Living in the Landscape.

Using dispersive delay lines and time reversal for low contrast tumour detection

On the basis of the technique of time reversal (TR), through adding dispersive delay lines to each element of a TR mirror, a method for low contrast tumour detection is proposed. When compared with a conventional detection method, the proposed method improves refocusing onto a low dielectric contrast tumour. The method does not require an accurate estimate of the position of the tumour. The theoretical basis for the approach is given and numerical simulated results demonstrate the capability of the proposed method.

Integrating personality research and animal contest theory:Aggressiveness in the green swordtail xiphophorus helleri

Aggression occurs when individuals compete over limiting resources. While theoretical studies have long placed a strong emphasis on context-specificity of aggression, there is increasing recognition that consistent behavioural differences exist among individuals, and that aggressiveness may be an important component of individual personality. Though empirical studies tend to focus on one aspect or the other, we suggest there is merit in modelling both within- and among-individual variation in agonistic behaviour simultaneously. Here, we demonstrate how this can be achieved using multivariate linear mixed effect models. Using data from repeated mirror trials and dyadic interactions of male green swordtails, Xiphophorus helleri, we show repeatable components of (co)variation in a suite of agonistic behaviour that is broadly consistent with a major axis of variation in aggressiveness. We also show that observed focal behaviour is dependent on opponent effects, which can themselves be repeatable but were more generally found to be context specific. In particular, our models show that within-individual variation in agonistic behaviour is explained, at least in part, by the relative size of a live opponent as predicted by contest theory. Finally, we suggest several additional applications of the multivariate models demonstrated here. These include testing the recently queried functional equivalence of alternative experimental approaches, (e.g., mirror trials, dyadic interaction tests) for assaying individual aggressiveness. © 2011 Wilson et al.

Biometric gonioscopy and the effects of age, race, and sex on the anterior chamber angle.

AIM:

To utilise a novel method for making measurements in the anterior chamber in order to compare the anterior chamber angles of people of European, African, and east Asian descent aged 40 years and over.

METHODS:

A cross sectional study on 15 people of each sex from each decade from the 40s to the 70s, from each of three racial groups-black, white, and Chinese Singaporeans. Biometric gonioscopy (BG) utilises a slit lamp mounted reticule to make measurements from the apparent iris insertion to Schwalbe's line through a Goldmann one mirror goniolens. The main outcome measures were BG measurements of the anterior chamber angle as detailed above.

RESULTS:

There was no significant difference in angle measurement between black, white, and Chinese races in this study. However, at younger ages people of Chinese race appeared to have deeper angles than white or black people, whereas the angles of older Chinese were significantly narrower (p = 0.004 for the difference in slope of BG by age between Chinese and both black and white people).

CONCLUSION:

The failure to detect a difference in angle measurements between these groups was surprising, given the much higher prevalence of angle closure among Chinese. It appears that the overall apparent similarity of BG means between Chinese and Western populations may mask very different trends with age. The apparently more rapid decline in angle width measurements with age among Chinese may be due to the higher prevalence of cataract or "creeping angle closure." However, longitudinal inferences from cross sectional data are problematic, and this may represent a cohort phenomenon caused by the increasing prevalence of myopia in the younger Singaporean population.

Age, gender, biometry, refractive error, and the anterior chamber angle among Alaskan Eskimos.

BACKGROUND:

The prevalence of angle-closure glaucoma (ACG) is greater for Eskimos/Inuit than it is for any other ethnic group in the world. Although it has been suggested that this prevalence may be due to a population tendency toward shallower anterior chamber angles, available evidence for other populations such as Chinese with high rates of ACG has not consistently demonstrated such a tendency.

METHODS:

A reticule, slit-lamp, and standard Goldmann one-mirror goniolens were used to make measurements in the anterior chamber (AC) angle according to a previously reported protocol for biometric gonioscopy (BG) (Ophthalmology 1999;106:2161-7). Measurements were made in all four quadrants of one eye among 133 phakic Alaskan Eskimos aged 40 years and older. Automatic refraction, dilated examination of the anterior segment and optic nerve, and A-scan measurements of AC depth, lens thickness, and axial length were also carried out for all subjects.

RESULTS:

Both central and peripheral AC measurements for the Eskimo subjects were significantly lower than those previously reported by us for Chinese, blacks, and whites under the identical protocol. Eskimos also seemed to have somewhat more hyperopia. There were no differences in biometric measurements between men and women in this Eskimo population. Angle measurements by BG seemed to decline more rapidly over life among Eskimos and Chinese than blacks or whites. Although there was a significant apparent decrease in AC depth, increase in lens thickness, and increase in hyperopia with age among Eskimos, all of these trends seemed to reverse in the seventh decade and beyond.

CONCLUSIONS:

Eskimos do seem to have shallower ACs than do other racial groups. Measurements of the AC angle seem to decline more rapidly over life among Eskimos than among blacks or whites, a phenomenon also observed by us among Chinese, another group with high ACG prevalence. This apparent more rapid decline may be due to a cohort effect with higher prevalence of myopia and resulting wider angles among younger Eskimos and Chinese.