Stochastic stimulated electronic x-ray Raman spectroscopy

Resonant inelastic x-ray scattering (RIXS) is a well-established tool for studying electronic, nuclear and collective dynamics of excited atoms, molecules and solids. An extension of this powerful method to a time-resolved probe technique at x-ray free electron lasers (XFELs) to ultimately unravel ultrafast chemical and structural changes on a femtosecond time scale is often challenging, due to the small signal rate in conventional implementations at XFELs that rely on the usage of a monochromator set up to select a small frequency band of the broadband, spectrally incoherent XFEL radiation. Here, we suggest an alternative approach, based on stochastic spectroscopy, that uses the full bandwidth of the incoming XFEL pulses. Our proposed method is relying on stimulated resonant inelastic x-ray scattering, where in addition to a pump pulse that resonantly excites the system a probe pulse on a specific electronic inelastic transition is provided, that serves as seed in the stimulated scattering process. The limited spectral coherence of the XFEL radiation defines the energy resolution in this process and stimulated RIXS spectra of high resolution can be obtained by covariance analysis of the transmitted spectra. We present a detailed feasibility study and predict signal strengths for realistic XFEL parameters for the CO molecule resonantly pumped at the O1s-{\pi}* transition. Our theoretical model describes the evolution of the spectral and temporal characteristics of the transmitted x-ray radiation, by solving the equation of motion for the electronic and vibrational degrees of freedom of the system self consistently with the propagation by Maxwell's equations

Praktykmodel vir egskeidingsevaluering : 'n sistemiese perspektief op die belange van die minderjarige kind by sorg en kontak (Afrikaans)

In hierdie ondersoek is daar gepoog om die belange van die minderjarige kind in egskeiding te bevorder deur die egskeidingsevalueringsproses waarvolgens die belange van die kind bepaal word, te ondersoek en te beskryf. Die sisteemteoretiese benadering, wat op holisme as uitgangspunt gebaseer is, is gedefinieer en beskryf ten einde die sistemiese perspektief op die gesin-in-egskeiding uit te klaar. Voorts is egskeiding as internasionale fenomeen en die implikasies van egskeidingsdispute vir die minderjarige kind ondersoek en in terme van die juridiese en maatskaplike implikasies asook die beginsel van die “beste belang” van die kind beskryf en verduidelik. Navorser het `n selfontwikkelde praktykmodel vir egskeidingsevaluering ontwikkel en geëvalueer met die doel om die vasstel van die belange van die minderjarige kind in egskeiding te bevorder. Dit is gevolg deur die empiriese resultate, `n algemene opsomming, gevolgtrekkings en aanbevelings. Die volgende navorsingsvraag is geformuleer om die ondersoekende en beskrywende gedeelte van die empiriese navorsing te rig: Wat is die aard en inhoud van die egskeidingsevalueringsproses wat in die praktyk deur die Kantoor van die Gesinsadvokaat toegepas word ten einde die belange van die minderjarige kind te bevorder? Gelei deur die navorsingsvraag is die volgende hipotese geformuleer: Indien die sisteemteoretiese praktykmodel tydens egskeidingsdispute toegepas word, sal die beste belang van die minderjarige kind bevorder word. Vir hierdie ondersoek, waar twee evalueringsprosesse met mekaar vergelyk is, was die kwantitatiewe navorsingsbenadering die aangewese keuse. Intervensienavorsing as tipe navorsing is volgens die Ontwerp- en Ontwikkelingsmodel toegepas. Die kwantitatief-beskrywende opname navorsingsontwerp is benut ten einde die doel van die studie te bereik, naamlik: Om `n praktykmodel vir egskeidingsevaluering te ontwikkel en empiries te evalueer ten einde die beste belang van die minderjarige kind te bevorder. Voortspruitend uit die doel is die volgende doelwitte geformuleer: Om vanuit `n sisteemteoretiese perspektief egskeiding as maatskaplike verskynsel, die gesin as maatskaplike sisteem en die belange van die minderjarige kind, teoreties te konseptualiseer. Om die huidige egskeidingsevalueringsproses, soos deur die Kantoor van die Gesinsadvokaat toegepas, te ondersoek en te beskryf. Om `n praktykmodel vir egskeidingsevaluering vanuit `n sisteemteoretiese perspektief, wat die belange van die minderjarige kind bevorder, te ontwikkel. Om die effektiwiteit van die nuut ontwikkelde praktykmodel vir egskeidingsevaluering empiries te evalueer. Om aanbevelings te maak ten opsigte van die praktykbenutting van die nuut ontwikkelde praktykmodel om die belange van die minderjarige kind in egskeidingsevaluering te bevorder. Ten einde die heersende evalueringsproses wat deur die Kantoor van die Gesinsadvokaat in egskeidingsdispute toegepas word met die evalueringsproses soos deur die nuut ontwikkelde praktykmodel toegepas is, te kon vergelyk, het navorser `n vraelys ontwerp vir evaluering van beide prosesse. Die vraelys het uit die volgende drie afdeling bestaan: (1) die professionele profiel van die deskundige (gesinsraadgewer/navorser); (2) profiel van die gesinsisteem in egskeiding wat geëvalueer is; en (3) die aard en inhoud van die evalueringsproses vir egskeidingsdispute. Voltooiing van die vraelys deur die deskundiges wat die twee egskeidingsevalueringsprosesse toegepas het, het meegebring dat die data vergelykbaar was. Daarvolgens kon die twee evalueringsprosesse dus vergelyk word en die effektiwiteit van die nuut ontwikkelde praktykmodel empiries geëvalueer word. Die empiriese resultate ten opsigte van die toepassing van die twee egskeidingsevalueringsprosesse in die praktyk, het `n wesenlike onderskeid in die aard en inhoud van die twee prosesse met betrekking tot die beste belang van die minderjarige kind aangetoon. Dit het geblyk dat in die toepassing van die egskeidingsevalueringsproses deur die Kantoor van die Gesinsadvokaat die assessering van die behoeftes, wense, ontwikkelingsvlak, verhoudings asook sistemiese verbintenisse van die minderjarige kind nie prioriteit geniet nie. Tydsbesteding aan konsultasies met die minderjarige kind is baie beperk en is slegs op `n ad hoc basis uitgevoer. Kollaterale bronne is ook op `n ad hoc basis betrek sodat dit nie moontlik was om die sistemiese verbintenisse van die minderjarige kind te eksploreer nie. Die evalueringsproses soos deur die nuut ontwikkelde praktykmodel toegepas is, bepaal as `n standaard prosedure individuele konsultasies vir assesseringsdoeleindes met die minderjarige kind ten einde die wense, behoeftes, ontwikkelingsvlak, verhoudings en sistemiese verbintenisse te kan bepaal met die oog op die vasstelling van die beste belang van die minderjarige kind vir die post-egskeidingsfase. Voldoende tydsbesteding aan die assessering van die minderjarige kind het hoë prioriteit volgens die praktykmodel geniet. Die evalueringsproses volgens die nuut ontwikkelde praktykmodel het kollaterale bronne as `n standaard prosedure betrek sodat die sistemiese verbintenisse van die minderjarige kind volledig geëksploreer kon word. Dit het dus uit die empiriese resultate geblyk dat die hipotese wat vir die studie gestel was, bevestig is. ENGLISH The aim of this study was to promote the interests of the minor child in a divorce situation, through an investigation into the process of assessment and evaluation whereby the best interests of the minor child in divorce disputes are determined. The systems theory approach, which sees holism as basic principle, was defined and described to explain the systems perspective of the family system in a divorce situation. Divorce as an international phenomenon and the implications of divorce disputes on the minor child were investigated, described and explained according to the legal and social implications as well as the principle of “the best interests” of the child. The researcher presented a self-developed practice model for divorce evaluation with the aim to promote the best interests of the minor child in divorce disputes. The study was concluded with the empirical results, a general summation, conclusions and recommendations. One research question was formulated to guide the investigative and descriptive part of the study, namely: What is the nature and content of the process of evaluation in divorce disputes to determine the best interests of the minor child which is administered by the Office of the Family Advocate? The following hypothesis was formulated according to the research question: If the practice model in divorce evaluation, based on systems theory, is administered in divorce disputes, the best interests of the minor child will be promoted. The quantitative research approach was selected in this investigation where two processes of evaluation were to be compared and the type of research was identified as Intervention Design and Development. The quantitative-descriptive survey design was selected to achieve the following goal of the study, namely: To develop a practice model for evaluation in divorce and to evaluate the practice model empirical to promote the best interests of the minor child In order to obtain the goal of the study the following objectives were formulated: To conceptualise theoretically divorce as social phenomenon, the family as social system and the interests of the minor child from a systems perspective. To investigate and describe the current process of evaluation in divorce disputes as it is administered by the Office of the Family Advocate. To develop a practice model for evaluation in divorce disputes from a systems perspective to promote the interests of the minor child. To evaluate empirically the effectiveness of the newly developed practice model for evaluation in divorce disputes. To make recommendations regarding the implementation of the newly developed practice model to promote the interests of the minor child in divorce disputes. A questionnaire was developed by the researcher to enable the comparison of the two processes of evaluation in divorce disputes. The questionnaire had three sections, namely: (1) the professional profile of the expert investigator (family counsellor/researcher); (2) profile of the family system who was evaluated; and (3) the nature and content of the process of evaluation. Data from the questionnaires completed by the expert investigators was compared to enable researcher to evaluate the effectiveness of the newly developed practice model to promote the interests of the minor child. The empirical results from the two evaluation processes confirmed a distinct difference in the nature and content of the two processes. The evaluation process in divorce as done by the Office of the Family Advocate did not put emphasis on the assessment of the needs, wishes, developmental status, relationships or systemic bonds of the minor child in a divorce situation. The time allocated to assessment of the minor child is extremely limited and consultations with the minor child was only done on an ad hoc basis. Consultations with collateral sources were also done on an ad hoc basis. It was thus not possible for family counsellors to explore in-depth the systemic relationships of the minor child in a divorce situation. The evaluation process according to the new practice model recognised the importance of individual consultations with the minor child. Individual assessment of the minor child was done as a regular procedure to establish the needs, wishes, developmental status, relationships as well as the systemic associations of the minor child in a divorce situation. The practice model recognised the need for adequate time allocation for assessment of the minor child. Exploring collateral sources was done as a standard procedure according to the practice model to allow opportunity for assessment of the systemic bonds of the minor child. The empirical results confirmed the hypothesis which was developed for this study.Thesis (DPhil)--University of Pretoria, 2008.Social Work and Criminologyunrestricte

High resolution x ray spectra of carbon monoxide reveal ultrafast dynamics induced by long UV pulse

In theoretical simulations of a UV x ray pump probe UVX PP setup, we show that frequency detuning of the pump UV pulse acts as a camera shutter by regulating the duration of the UVX PP process. This two photon absorption with long overlapping UV and x ray pulses, allowing for high spectral resolution, thereby provides information about ultrafast dynamics of the nuclear wave packet without the requirement of ultrashort pulses and controlled delay times. In a case study of carbon monoxide, the calculated UVX PP spectra of the O1s amp; 8722;12 amp; 960;1 and C1s amp; 8722;12 amp; 960;1 core excited states show different vibrational profiles. The interference of intermediate vibrational states reveals details of nuclear dynamics in the UVX PP process related to a variable duration time controlled by the UV detuning. Both O1s amp; 8722;12 amp; 960;1 and C1s amp; 8722;12 amp; 960;1 pump probe channels display a splitting of the spectral profile, which however is associated with different physical mechanisms. At the O1s amp; 8722;12 amp; 960;1 resonance, the observed dispersive and non dispersive spectral bands intersect and result in destructive interferenc

Time resolved study of recoil induced rotation by X ray pump X ray probe spectroscopy

Modern stationary X ray spectroscopy is unable to resolve rotational structure. In the present paper, we propose to use time resolved two color X ray pump probe spectroscopy with picosecond resolution for real time monitoring of the rotational dynamics induced by the recoil effect. The proposed technique consists of two steps. The first short pump X ray pulse ionizes the valence electron, which transfers angular momentum to the molecule. The second time delayed short probe X ray pulse resonantly excites a 1s electron to the created valence hole. Due to the recoil induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X ray absorption as a function of the delay time between the pulses. We developed an accurate theory of the X ray pump probe spectroscopy of the recoil induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time dependent X ray absorption using the CO molecule as a case study. We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamic