Browsing by Author "Witte, T."

Applying pump and probe differential reflection (Delta R) and transmission (Delta T) of femtosecond light pulses inr either co- or counterpropagating pump and probe geometries, a direct time of flight method with submicrometer resolution is presented. With this technique we study the density-dependent transport of photogenerated carrier plasmas perpendicular to the surface of GaAs samples for delay times 20 ps less than or equal to tau less than or equal to 1 ns. At a pump fluence of 800 mu J cm(-2) a relatively sharp charge-carrier front was observed, with high velocities of 14 x 10(5) cm/s at a delay time tau approximate to 20 ps, decreasing as v proportional to tau(-2/3) to 2 x 10(5) cm/s at tau approximate to 350 ps. The arrival times tau of the carriers at a fixed sample thickness depend on the fluence of the pump pulses F such as tau proportional to 1/F-0.45. The results are discussed in the framework of diffusive transport with a strongly density-dependent diffusivity D. The data can be described consistently with the assumption of Fermi pressure as the dominating driving force fur plasma expansion.

Pump and probe differential reflection (Delta R) and transmission (Delta T) measurement of subpicosecond light pulses for either co- and counterpropagating pump and probe geometries are performed on thin GaAs samples. With this time of flight (TOF) method we study density dependent electron-hole plasma (EHP) expansion in GaAs perpendicular to the sample surface in the temperature range of 300 K greater than or equal to T-L greater than or equal to 4 K. At a fluence of F = 800 mu Jcm(-2) the expansion velocities increase with decreasing lattice temperature T-L. The expansion velocities v at T-L = 300 K and 4 K show a dependence on the delay time tau like v proportional to tau(-2/3). At low lattice temperatures we find a much stronger dependence of the expansion velocities on the fluence of the pump pulses.

The light-induced (266 nm) ultrafast decarboxylation of two peroxides R-1-C(O)O-OR2, with R-1 = phenyl and R-2 = benzoyl or tert-butyl, in solution has been studied on the picosecond time scale by absorption spectroscopy with a time resolution typically of 100 to 200 fs. The reaction was investigated in various solvents of different polarity and viscosity to elucidate the influence of the solvent environment on the decarboxylation rate. Transient intermediate benzoyloxy radicals, R-1-CO2, were monitored at wavelengths between 300 and 1000 nm. While the primary dissociation of the peroxide is too fast to be resolved, the dissociation of intermediate benzoyloxy radicals is clearly detected on the picosecond time scale. The mechanism of light-induced two-step dissociation is discussed, as is the dependence of reaction dynamics on the type of substituent R-2 as well as the branching ratio between prompt and delayed CO2 formation. A model for the decarboxylation process is presented that is based on molecular structure parameters and energies. The latter quantities, which are obtained from density functional theory calculations, serve as input data for calculations of the specific decomposition rate coefficients of benzoyloxy intermediates via statistical unimolecular rate theory. The predicted benzoyloxy radical decay data are compared with corresponding experimental concentration versus time traces.

Background Disease flares of rheumatoid arthritis (RA) are important stressors for patients (pts) who may use coping for disease management. Some coping styles are thought to be beneficial and may help to improve disease outcome whereas others are thought to be harmful. Objectives We investigate the frequency and intensity of different coping styles in pts with an acute flare of seropositive RA and its impact on disease outcomes after 12 month of therapy. Methods Coping was analysed with the Brief-COPE (1) using a 4 point Likert scale in 222 pts participating in the ERFASS study (2). Coping styles were analysed by confirmatory and exploratory factor analysis (CFA, EFA). Disease activity was measured via DAS28 (CRP), depression and/or anxiety using Hospital Anxiety and Depression Scale (HADS) and Patient Health Questionnaire 9 (PHQ-9). Repeated measures ANOVA was used to identify the effect of different coping strategies on disease activity and Spearman-Rho to identify correlations. Results Factor analysis revealed five dominant coping styles (problem oriented, emotion oriented, dysfunctional, religion, alcohol/drugs) which were consistent during 6 and 12 months follow up. When analysing the relative intensity of each coping strategy over time there was no significant change during treatment (Table 1). The usage of only a single coping style at baseline (“I am doing this a medium amount” or “a lot”) was reported by 70 pts (31,5%). 65 pts (29,3%) reported the use of 2 coping styles simultaneously, 25 pts (11,3%) 3 coping styles and 4 pts (1,8%) four coping styles. Problem oriented coping was used by 125 pts (56,3%), emotional coping by 97 pts (43,7%), dysfunctional coping by 41 pts (18,5%), religion by 24 pts (10,8%) and alcohol/drugs by only 4 pts (1,8%). 58 pts (26,1%) reported not to use any of the coping styles (“I am doing this not at all” or “only a little bit”) and these pts had a lower DAS28 during the course of the study (p=0.036) as compared to pts who use one or more coping strategies. When analysing the group with high disease activity (DAS28 >5.1) at baseline (n=60), pts with medium or high dysfunctional coping had a significantly higher disease activity after 12 months as compared to those with no or little dysfunctional coping (U = 187,00, Z = -2.025, p = 0.043) (Figure 1). The other coping styles did not significantly predict the outcome of disease activity. We observed a strong correlation between dysfunctional coping and depression (PHQ9 r = 0.590; HADS depression r = 0.569) as well as anxiety (HADS anxiety r = 0.639) but not for the other coping strategies at baseline. Figure 1. Table 1. Development of disease activity (DAS28) and coping strategies over time Time Baseline mean (SD) Month 6 mean (SD) Month 12 mean (SD) DAS28 4.32 (1.14) 2.79 (1.23) 2.47 (1.05) Problem oriented 53.10 (14.93) 49.69 (14.10) 47.43 (14.00) Emotion oriented 49.94 (13.00) 50.73 (12.76) 50.46 (13.45) Dysfunctional 40.25 (14.59) 36.44 (11.76) 36.00 (12.26) Religion 36.15 (18.30) 35.53 (17.02) 34.68 (16.64) Alcohol / Drugs 27.03 (7.81) 27.15 (8.75) 26.53 (6.07) Conclusion Different ways of coping may be used simultaneously during an acute flare of seropositive RA. In pts with high disease activity dysfunctional coping is the only coping strategy predicting a worse disease outcome after 12 months and dysfunctional coping correlates with depression and anxiety. References [1]Carver CS (1997) You want to measure coping but your protocol’s too long: consider the brief COPE. Int J Behav Med 4(1):92–100. [2]Hoeper JR, Zeidler J, Meyer SE, et al. Effect of nurse-led care on outcomes in patients with ACPA/RF-positive rheumatoid arthritis with active disease undergoing treat-to-target: a multicentre randomised controlled trial. RMD Open 2021 Disclosure of Interests Juliana Rachel Hoeper: None declared, Ioana Iliadis: None declared, Marianne Richter: None declared, Sara Eileen Meyer: None declared, Kai Kahl: None declared, Torsten Witte: None declared, Kirsten Hoeper Speakers bureau: Abbvie, Novartis, Galapagos, Sandoz Hexal, Chugai, Lilly, Consultant of: Abbvie, Novartis, Galapagos, Sandoz Hexal, Dirk Meyer-Olson Speakers bureau: Bristol Myers Squibb, Celltrion, Chugai, Fresenius Kabi, Galapagos, Lilly, Sandoz Hexal , Consultant of: Abbvie, Amgen, Astra Zeneca, Biogen, Novartis, Viatris

Experimental and theoretical investigations on the ultrafast photoinduced decomposition of three tert-butyl peroxides of general structure R-C(O)O-O-tert-butyl with R = phenyloxy, benzyl, or naphthyloxy in solution are presented. Photoinduced O-O bond scission occurs within the time resolution (200 fs) of the pump-probe experiment. The subsequent dissociation of photochemically excited carbonyloxy radicals, R-CO2, has been monitored on a picosecond time scale by transient absorption at wavelengths between 290 and 1000 nm. The measured decay of R-CO2 is simulated via statistical unimolecular rate theory using molecular energies, geometries, and vibrational frequencies obtained from density functional theory (DFT) calculations. The results are compared with recent data for tert-butyl peroxybenzoate (R = phenyl). While benzoyloxy radicals exhibit nanosecond to microsecond lifetimes at ambient temperature, insertion of an oxygen atom or a methylene group between the phenyl or naphthyl chromophore and the CO2 moiety significantly decreases the stability and thus lowers the lifetime of the carbonyloxy radicals in solution to picoseconds. The reasons behind this structural effect on decomposition rate are discussed in terms of barrier heights for decarboxylation on the ground-state potential energy surface and of a fast reaction channel via electronically excited states of carbonyloxy radicals. Arrhenius parameters are reported for thermal rate constants, k(T), of R-CO2 decarboxylation as deduced from modeling of the time-resolved experimental data in conjunction with the DFT calculations.