Multiphoton ionization of V, Cr, Y, La, and Ir through 0.5-ps ultraviolet laser pulses

The two-photon ionization of the metal atoms V, Cr, Y, La, and Ir sputtered by an Ar-ion gun from solid targets has been investigated using linearly polarized laser pulses of 500- fs duration and 248.6-nm (KrF) wavelength in combination with mass spectroscopy that is free of volume effects. A near-resonant ionization process has to be attributed to all five atoms. By fitting analytical solutions of a rate equation model describing the temporal evolution of the ionization process, we can determine absolute values of the one-photon cross sections and saturation intensities

Analysis of multiphoton ionization of metal atoms in the saturation regime using subpicosecond KrF laser pulses

Singly and multiply charged ion yield curves are reported for resonant and nonresonant two photon- ionization processes for a collection of 31 metal atoms. The atoms are created by sputtering from a solid target using an Ar-ion gun. Single and multiple ionization of these atoms is performed using linearly polarized 248.6-nm (KrF) laser pulses with a full width at half maximum duration of 500 fs, employing intensities between 109 and 1012 W cm-2. A four-grid high-resolution reflecting time-of-flight spectrometer is used for ion detection. This advanced spectrometer has a well-defined and small source volume, enabling absolute measurements of ionization probabilities and saturation intensities. Because our measurements are not affected by the increase of the interaction volume for increasing intensities, we can discriminate between resonant and nonresonant multiphoton ionization processes without varying the laser pulse duration. For many metals, the intensity dependence of the ion yield can be accurately reproduced by rate calculations based on a resonantly enhanced two-photon-ionization scheme. As a result, we can determine absolute values of the one-photon cross sections in the resonant processes and these are compared to theoretical values we calculated. For the nonresonant processes, we give generalized multiphoton-ionization cross sections and compare these to a scaling law of Lambropoulos [J. Opt. Soc. Am. B 4, 821 (1987)]

Laser-induced ultrafast electron emission from a field emission tip

We show that a field emission tip electron source that is triggered with a femtosecond laser pulse can generate electron pulses shorter than the laser pulse duration (~100 fs). The emission process is sensitive to a power law of the laser intensity, which supports an emission mechanism based on multiphoton absorption followed by over-the-barrier emission. Observed continuous transitions between power laws of different orders are indicative of field emission processes. We show that the source can also be operated so that thermionic emission processes become significant. Understanding these different emission processes is relevant for the production of sub-cycle electron pulses

Validity, practical utility, and reliability of the activPAL in preschool children

<p>Purpose: With the increasing global prevalence of childhood obesity, it is important to have appropriate measurement tools for investigating factors (e.g. sedentary time) contributing to positive energy balance in early childhood. For pre-school children, single unit monitors such as the activPALTM are promising. However, validation is required as activity patterns differ from adults.</p> <p>Methods: Thirty pre-school children participated in a validation study. Children were videoed for one hour undertaking usual nursery activity while wearing an activPALTM. Video (criterion method) was analyzed on a second-by-second basis to categorise posture and activity. This was compared with the corresponding activPALTM output. In a subsequent sub-study investigating practical utility and reliability, 20 children wore an activPALTM for seven consecutive 24-hour periods.</p> <p>Results: A total of 97,750 seconds of direct observation from 30 children were categorized as sit/lie (46%), stand (35%), walk (16%); with 3% of time in nonsit/lie/upright postures (e.g. crawl/crouch/kneel-up). Sensitivity for the overall total time matched seconds detected as activPALTM ‘sit/lie’ was 86.7%, specificity 97.1%, and positive predictive value (PPV) 96.3%. For individual children, the median (interquartile range) sensitivity for activPALTM sit/lie was 92.8% (76.1-97.4), specificity 97.3% (94.9-99.2), PPV 97.0% (91.5-99.1). The activPALTM underestimated total time spent sitting (mean difference -4.4%, p<0.01), and overestimated time standing (mean difference 7.1%, p<0.01). There was no difference in overall % time categorised as ‘walk’ (p=0.2). The monitors were well tolerated by children during a seven day period of free-living activity. In the reliability study, at least five days of monitoring were required to obtain an intraclass correlation coefficient of ≥0.8 for time spent sit/lie according to activPALTM output.</p> <p>Conclusion: The activPAL had acceptable validity, practical utility, and reliability for the measurement of posture and activity during freeliving activities in pre-school children.</p&gt

Роль православної церкви у формуванні та функціонуванні політичної системи України в 90-і роки ХХ ст.

У статті зроблено спробу аналізу місця та ролі православної церкви у процесах формування та функціонування політичної системи України у 90-і роки ХХ ст. Доведено, що українські православні церкви відігравали значну роль у політичному житті країни, не тільки агітуючи віруючих за певну політичну силу, а й балотуючи своїх представників до місцевих органів влади. Українські політики використовували церкву заради досягнення власних цілей, що ще більше загострювало міжконфесійні взаємини і посилювало політизацію церковного життя.В статье сделана попытка анализа места и роли православной церкви в процессе формирования и функционирования политической системы Украины в 90-е годы ХХ ст. Доказано, что украинские православные церкви играли значительную роль в политической жизни страны, не только агитируя верующих за определенную политическую силу, но и баллотируя своих представителей в местные органы власти. Украинские политики использовали церковь ради достижения собственных целей, что еще больше обостряло межконфессиональные отношения и усиливало политизацию церковной жизни.In the article the attempt of analysis of place and role of orthodox church in the process of forming and functioning of the political system of Ukraine in the 90 th ys of the XX ct is done. It is proved, that the Ukrainian orthodox churches acted considerable part in the political life of country, not only agitating believers for definite political force, but also voting the representatives in local authorities. The Ukrainian politicians used a church for achievement of own purposes, that yet more intensified the interconfession relations reinforced the political impact on the church life