Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis

This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low‐cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07, and 0.2 mm. It was found that changes in magnetic properties are sensitive to microstructural changes taking place at the surface of the material throughout the fatigue life. The changes in the Barkhausen signals have been attributed to distribution of dislocations in stage I and stage II of fatigue life and the formation of a macrocrack in the final stage of fatigue

Study of relativistic electron beam production and transport in high-intensity laser interaction with a wire target by integrated LSP modeling

The results of a numerical study of high-intensity short-pulse laser interaction with wire targets are presented. Fast electron production and transport in solid density plasma is modeled using the implicit hybrid particle-in-cell code LSP [D. R. Welch et al., Phys. Plasmas 13, 063105 (2006)]. These simulations were performed with realistic target size and laser parameters and over times much longer than the laser pulse. Nonlinear interaction processes, i.e., microchanneling and density steepening, have been observed. The spectrum of the relativistic electrons produced has a reduced slope temperature compared to that predicted by ponderomotive scaling. Preformed underdense plasma has been found to bottleneck fast electrons due to the intense magnetic fields generated near the critical surface. In a thin long wire target, the overall propagation length of the fast electrons is about 160 mu m; however, surface fields guide a small fraction of electrons to longer distances. These results are in good agreement with the experiments and have demonstrated that the modeling of electron transport relevant to fast ignition can be pursued in an integrated manner. (C) 2008 American Institute of Physics

Generation of a strong reverse shock wave in the interaction of a high-contrast high-intensity femtosecond laser pulse with a silicon target

We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high “plasma-mirror” phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (ne 10^23 cm^-3 and Te ~10eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior

A Single-Arm, Proof-Of-Concept Trial of Lopimune (Lopinavir/Ritonavir) as a Treatment for HPV-Related Pre-Invasive Cervical Disease

BACKGROUND: Cervical cancer is the most common female malignancy in the developing nations and the third most common cancer in women globally. An effective, inexpensive and self-applied topical treatment would be an ideal solution for treatment of screen-detected, pre-invasive cervical disease in low resource settings. METHODS: Between 01/03/2013 and 01/08/2013, women attending Kenyatta National Hospital's Family Planning and Gynaecology Outpatients clinics were tested for HIV, HPV (Cervista®) and liquid based cervical cytology (LBC -ThinPrep®). HIV negative women diagnosed as high-risk HPV positive with high grade squamous intraepithelial lesions (HSIL) were examined by colposcopy and given a 2 week course of 1 capsule of Lopimune (CIPLA) twice daily, to be self-applied as a vaginal pessary. Colposcopy, HPV testing and LBC were repeated at 4 and 12 weeks post-start of treatment with a final punch biopsy at 3 months for histology. Primary outcome measures were acceptability of treatment with efficacy as a secondary consideration. RESULTS: A total of 23 women with HSIL were treated with Lopimune during which time no adverse reactions were reported. A maximum concentration of 10 ng/ml of lopinavir was detected in patient plasma 1 week after starting treatment. HPV was no longer detected in 12/23 (52.2%, 95%CI: 30.6-73.2%). Post-treatment cytology at 12 weeks on women with HSIL, showed 14/22 (63.6%, 95%CI: 40.6-82.8%) had no dysplasia and 4/22 (18.2%, 95%CI: 9.9-65.1%) were now low grade demonstrating a combined positive response in 81.8% of women of which 77.8% was confirmed by histology. These data are supported by colposcopic images, which show regression of cervical lesions. CONCLUSIONS: These results demonstrate the potential of Lopimune as a self-applied therapy for HPV infection and related cervical lesions. Since there were no serious adverse events or detectable post-treatment morbidity, this study indicates that further trials are clearly justified to define optimal regimes and the overall benefit of this therapy. TRIAL REGISTRATION: ISRCTN Registry 48776874

Efficient ion acceleration and dense electron-positron plasma creation in ultra-high intensity laser-solid interactions

The radiation pressure of next generation ultra-high intensity ($>10^{23}$ W/cm$^{2}$) lasers could efficiently accelerate ions to GeV energies. However, nonlinear quantum-electrodynamic effects play an important role in the interaction of these laser pulses with matter. Here we show that these effects may lead to the production of an extremely dense ($\sim10^{24}$ cm$^{-3}$) pair-plasma which absorbs the laser pulse consequently reducing the accelerated ion energy and energy conversion efficiency by up to 30-50\%

Hot dense matter creation in short-pulse laser interaction with tamped foils

The possibility of producing hot dense matter has important applications for the understanding of transport processes in inertial confinement fusion (ICF) [1] and laboratory astrophysics experiments [2]. While the success of ICF requires the correct solution of a complex interaction between laser coupling, equation-of-state, and particle transport problems, the possibility of experimentally recreating conditions found during the ignition phase in a simplified geometry is extremely appealing. In this paper we will show that hot dense plasma conditions found during ICF ignition experiments can be reproduced by illuminating a tamped foil with a high intensity laser. We will show that temperatures on the order of kiloelectronvolts at solid densities can be achieved under controlled conditions during the experiment. Hydrodynamic tamping by surface coatings allows to reach higher density regimes by enabling the diagnosis of matter that has not yet begun to decompress, thus opening the possibility of directly investigating strongly coupled systems [3]. Our experimental diagnostics is based on K-shell spectroscopy coupled to x-ray imaging techniques. Such techniques have recently become prevalent in the diagnosis of hot dense matter [4]. By looking at the presence, and relative strengths, of lines associated with different ionization states, spectroscopy provides considerable insight into plasma conditions. At the same time, curved crystal imaging techniques allow for the spatial resolution of different regions of the target, both allowing for comparison of heating processes with the results of Particle-In-Cell (PIC) and hybrid simulation codes

Investigating behavioural and computational approaches for defining imprecise regions

People often communicate with reference to informally agreedplaces, such as “the city centre”. However, views of the spatial extent of such areas may vary, resulting in imprecise regions. We compare perceptions of Sheffield’s City Centre from a street survey to extents derived from various web-based sources. Such automated approaches have advantages of speed, cost and repeatability. We show that footprints from web sources are often in concordance with models derived from more labour-intensive methods. Notable exceptions however were found with sources advertising or selling residential property. Agreement between sources was measured by aggregating them to identify locations of consensus

Studying the Role of Human Parietal Cortex in Visuospatial Attention with Concurrent TMS–fMRI

Combining transcranial magnetic stimulation (TMS) with concurrent functional magnetic resonance imaging (fMRI) allows study of how local brain stimulation may causally affect activity in remote brain regions. Here, we applied bursts of high- or low-intensity TMS over right posterior parietal cortex, during a task requiring sustained covert visuospatial attention to either the left or right hemifield, or in a neutral control condition, while recording blood oxygenation-level–dependent signal with a posterior MR surface coil. As expected, the active attention conditions activated components of the well-described “attention network,” as compared with the neutral baseline. Also as expected, when comparing left minus right attention, or vice versa, contralateral occipital visual cortex was activated. The critical new finding was that the impact of high- minus low-intensity parietal TMS upon these visual regions depended on the currently attended side. High- minus low-intensity parietal TMS increased the difference between contralateral versus ipsilateral attention in right extrastriate visual cortex. A related albeit less pronounced pattern was found for left extrastriate visual cortex. Our results confirm that right human parietal cortex can exert attention-dependent influences on occipital visual cortex and provide a proof of concept for the use of concurrent TMS–fMRI in studying how remote influences can vary in a purely top–down manner with attentional demands

Experimental observations of transport of picosecond laser generated electrons in a nail-like target

The transport of relativistic electrons, generated by the interaction of a high intensity (2 x 10(20) W/cm(2)) laser, has been studied in a nail-like target comprised of a 20 mu m diameter solid copper wire, coated with similar to 2 mu m of titanium, with an 80 mu m diameter hemispherical termination. A similar to 500 fs, similar to 200 J pulse of 1.053 mu m laser light produced by the Titan Laser at Lawrence Livermore National Laboratory was focused to a similar to 20 mu m diameter spot centered on the flat face of the hemisphere. K-alpha fluorescence from the Cu and Ti regions was imaged together with extreme ultraviolet (XUV) emission at 68 and 256 eV. Results showed a quasiexponential decline in K-alpha emission along the wire over a distance of a few hundred microns from the laser focus, consistent with bulk Ohmic inhibition of the relativistic electron transport. Weaker K-alpha and XUV emission on a longer scale length showed limb brightening suggesting a transition to enhanced transport at the surface of the wire. (C) 2007 American Institute of Physics