Accurate and efficient spin integration for particle accelerators

Accurate spin tracking is a valuable tool for understanding spin dynamics in particle accelerators and can help improve the performance of an accelerator. In this paper, we present a detailed discussion of the integrators in the spin tracking code gpuSpinTrack. We have implemented orbital integrators based on drift-kick, bend-kick, and matrix-kick splits. On top of the orbital integrators, we have implemented various integrators for the spin motion. These integrators use quaternions and Romberg quadratures to accelerate both the computation and the convergence of spin rotations. We evaluate their performance and accuracy in quantitative detail for individual elements as well as for the entire RHIC lattice. We exploit the inherently data-parallel nature of spin tracking to accelerate our algorithms on graphics processing units.Comment: 43 pages, 17 figure

Charakterisierung der Kohärenz ultrakalter Atome mit Methoden der nichtlinearen Materiewellenoptik

In this dissertation we make use of the many analogies between quantum optical and ultra-cold atomic and molecular systems in order to study the coherence properties of the latter with methods of non-linear optics. We adapt the XFROG method that has first been developed for the characterization of ultra-short laser pulses, to the problem of reconstructing both amplitude and phase of the condensate wavefunction of a Bose-Einstein-condensate (BEC). Using the example of a vortex state we study the dependence of the reconstruction quality on the number of measurements and different sources of noise and we find that the method is feasible with available experimental technology. Exploiting the similarity between the coherent formation of ultra-cold molecules and optical sum frequency generation we devise a scheme for measuring second-order correlations of atoms through density measurements of molecules. We use perturbation theory in the cases of weak and strong coupling between atoms and molecules to calculate the momentum distribution of the molecules for the cases where the molecules are formed from a BEC, a normal Fermi gas and a Fermi gas with superfluidity in a Bardeen-Cooper-Schrieffer (BCS) state. These calculations are supplemented by exact integrations of Schroedinger's equation in the single mode approximation for the molecules. Atoms in a BEC are collectively transformed into molecules with a narrow momentum distribution reflecting the long coherence length of atoms in the BEC. For the normal Fermi gas molecules are formed non-collectively and their momentum distribution is much wider. The momentum distribution of molecules from a BCS state looks similar to the BEC case: The superfluid component leads to collectively formed molecules with a very narrow momentum distribution and the unpaired fraction gives rise to non-collectively formed molecules with a much wider momentum distribution similar to the normal Fermi gas case. The counting statistics of the molecules from a BEC is that of a coherent state, from a normal Fermi gas it is that of a thermal state and the BCS case interpolates between the two.In dieser Dissertation benutze ich die zahlreichen Analogien zwischen quantenoptischen Systemen und Systemen aus ultrakalten Atomen und Molekuelen, um die Kohaerenzeigenschaften der letzteren zu charakterisieren. Dazu zeige ich, wie die aus der Physik der ultra-kurzen Laserpulse bekannte XFROG Methode modifiziert werden kann, so dass die Phase von Kondensatwellenfunktionen von atomaren Bose-Einstein-Kondensaten mit ihr bestimmt werden kann. Am Beispiel eines quantisierten Wirbelzustandes untersuche ich, wie die Qualitaet der Rekonstruktion von der Anzahl der Messungen und von verschiedenen Arten von Rauschen abhaengt. Ich zeige, dass diese Rekonstruktionsmethode mit heute verfuegbarer Technologie realisiert werden kann. Desweiteren benutze ich die Aehnlichkeiten zwischen der kohaerenten Bildung ultra-kalter Molekuele und optischer Summenfrequenzerzeugung, um eine Methode zu konstruieren, mit der Korrelationen ultra-kalter atomarer Gase zweiter Ordnung mit Hilfe von Messungen der molekularen Dichte bestimmt werden koennen. In Stoerungstheorie berechne ich die Impulsverteilung der Molekuele fuer die Faelle, dass die Molekuele aus Atomen in einem Bose-Einstein-Kondensat, einem normalen Fermi Gas und einem Fermi Gas mit Superfluiditaet gebildet werden. Diese Rechnungen werden durch exakte numerische Loesungen der Schroedingergleichung der entsprechenden Probleme in der Einmodennaeherung fuer das molekulare Feld ergaenzt. Atome in einem Bose-Einstein-Kondensat werden kollektiv in Molekuele mit einer scharfen Impulsverteilung umgewandelt, was die grosse Kohaerenzlaenge im atomaren Zustand widerspiegelt. Fuer das normale Fermi Gas werden die Atome nichtkollektiv in Molekuele mit einer breiten Impulsverteilung umgewandelt. Der Fall eines BCS-suprafluiden Fermi Gases liegt zwischen diesen beiden Grenzfaellen: Der suprafluide Anteil wird kollektiv in Molekuele mit einer scharfen Impulsverteilung umgewandelt waehrend die ungepaarten Fermionen nichtkollektiv in Molekuele mit breiter Impulsverteilung umgewandelt werden. Die Zaehlstatistik der aus einem Bose-Einstein-Kondensat gebildeten Molekuele ist die eines kohaerenten Zustandes, fuer die aus einem normalen Fermi Gas gebildeten Molekuele ist die Zaehlstatistik thermisch und der BCS-superfluide Fall liegt wieder zwischen diesen beiden Extremen

A quasi-continuous superradiant Raman laser with < 1 intracavity photon

Steady-state collective emission from ensembles of laser cooled atoms has been proposed as a method for generating sub-millihertz linewidth optical lasers, with potential for broad impacts across science and technology. We have built a model system that tests key predictions for such active oscillators using a Raman laser with laser cooled atoms as the gain medium. The laser operates deep in the bad-cavity, or superradiant, regime of laser physics, where the cavity decay rate is much greater than the atomic coherence decay rate. Specifically, we demonstrate that a system of 106 87Rb atoms trapped in a 1D standing wave optical lattice can spontaneously synchronize and collectively emit a quasi-continuous coherent optical output, even when the intracavity field contains on average < 1 photon

Therapist-supported online cognitive therapy for post-traumatic stress disorder (PTSD) in young people: protocol for an early-stage, parallel-group, randomised controlled study (OPTYC trial).

INTRODUCTION: Post-traumatic stress disorder (PTSD) is a disabling psychiatric condition that affects a significant minority of young people exposed to traumatic events. Effective face-to-face psychological treatments for PTSD exist. However, most young people with PTSD do not receive evidence-based treatment. Remotely delivered digital interventions have potential to significantly improve treatment accessibility. Digital interventions have been successfully employed for young people with depression and anxiety, and for adults with PTSD. However, digital interventions to treat PTSD in young people have not been evaluated. The Online PTSD Treatment for Young People & Carers (OPTYC) trial will evaluate the feasibility, acceptability and initial indications of clinical efficacy of a novel internet-delivered Cognitive Therapy for treatment of PTSD in young people (iCT-PTSD-YP). METHODS AND ANALYSIS: This protocol describes a two-arm, parallel-groups, single-blind (outcome assessor), early-stage randomised controlled trial, comparing iCT-PTSD-YP with a waiting list (WL) comparator. N=34 adolescents (12-17 years old), whose primary problem is PTSD after exposure to a single traumatic event, will be recruited from 14 NHS Child and Adolescent Mental Health Services in London and southeast England, from secondary schools and primary care in the same region, or via self-referral from anywhere in the UK using the study website. Individual patient-level randomisation will allocate participants in a 1:1 ratio, randomised using minimisation according to sex and baseline symptom severity. The primary study outcomes are data on feasibility and acceptability, including recruitment, adherence, retention and adverse events (AEs). The primary clinical outcome is PTSD diagnosis 16 weeks post-randomisation. Secondary clinical outcomes include continuous measures of PTSD, anxiety and depression symptoms. Regression analyses will provide preliminary estimates of the effect of iCT-PTSD-YP on PTSD diagnosis, symptoms of PTSD, anxiety and depression relative to WL. Process-outcome evaluation will consider which mechanisms mediate recovery. Qualitative interviews with young people, families and therapists will evaluate acceptability. ETHICS AND DISSEMINATION: The study was approved by a UK Health Research Authority Research Ethics Committee (19/LO/1354). For participants aged under 16, informed consent will be provided by carers and the young person will be asked for their assent; participants aged 16 years or older can provide informed consent without their parent or caregiver's involvement. Findings will be disseminated broadly to participants, healthcare professionals, the public and other relevant groups. Study findings will be published in peer-reviewed journals. TRIAL REGISTRATION NUMBER: ISRCTN16876240

Medication adherence in patients with severe asthma prescribed oral corticosteroids in the U-BIOPRED cohort

Background: Although estimates of suboptimal adherence to oral corticosteroids in asthma range from 30% to 50%, no ideal method for measurement exists; the impact of poor adherence in severe asthma is likely to be particularly high. Research Questions: What is the prevalence of suboptimal adherence detected by self-reporting and direct measures? Is suboptimal adherence associated with disease activity? Study Design and Methods: Data were included from individuals with severe asthma taking part in the U-BIOPRED (Unbiased Biomarkers for the Prediction of Respiratory Disease Outcomes) study and prescribed daily oral corticosteroids. Participants completed the Medication Adherence Report Scale, a five-item questionnaire used to grade adherence on a scale from 1 to 5, and provided a urine sample for analysis of prednisolone and metabolites by liquid chromatography-mass spectrometry. Results: Data from 166 participants were included in this study: mean (SD) age, 54.2 (± 11.9) years; FEV1, 65.1% (± 20.5%) predicted; female, 58%; 37% completing the Medication Adherence Report Scale reported suboptimal adherence; and 43% with urinary corticosteroid data did not have detectable prednisolone or metabolites in their urine. Good adherence by both methods was detected in 49 of the 142 (35%) of participants in whom both methods were performed; adherence detection did not match between methods in 53%. Self-reported high adherers had better asthma control and quality of life, whereas directly measured high adherers had lower blood eosinophil levels. Interpretation: Low adherence is a common problem in severe asthma, whether measured directly or self-reported. We report poor agreement between the two methods, suggesting some disassociation between self-assessment of medication adherence and regular oral corticosteroid use, which suggests that each approach may provide complementary information in clinical practice