Time-Resolved Chiral Vibrational Spectroscopy

Advances in infrared laser technology and detection sensitivity have made time-resolved chiral vibrational spectroscopy experimentally feasible. Here we describe our recent efforts in detecting, for the first time, transient vibrational circular dichroism (VCD) signals with picosecond time resolution. The absorption changes of the cobalt (?)-sparteine complex Co(sp)Cl2 after visible excitation of a d-d excited state was probed in the CH-stretch region by alternating left- and right-handed circular polarized mid IR laser pulses. VCD spectra can be sensitive reporters of peptide and protein secondary structure or the absolute configuration of chiral organic compounds in solution. Recent developments are presented, which may in the future allow us to access this information in the course of fast chemical reactions

Versatile Femtosecond Laser Synchronization for Multiple-Timescale Transient IR Spectroscopy

Several ways to electronically synchronize different types of amplified femtosecond laser systems are presented, based on a single freely programmable electronics hardware: Arbitrary-detuning asynchronous optical sampling, as well as actively locking two femtosecond laser oscillators, albeit not necessarily to the same round-trip frequency. They allow us to rapidly probe a very wide range of timescales, from picoseconds to potentially seconds, in a single transient absorption experiment without the need to move any delay stage. Experiments become possible that address a largely unexplored aspect of many photochemical reactions, in particular in the context of photo-catalysis as well as photoactive proteins, where an initial femtosecond trigger very often initiates a long-lasting cascade of follow-up processes. The approach is very versatile, and allows us to synchronize very different lasers, such as a Ti:Sa amplifier and a 100~kHz Yb-laser system. The jitter of the synchronisation, and therewith the time-resolution in the transient experiment, lies in the range from 1~ps to 3~ps, depending on the method. For illustration, transient IR measurements of the excited state solvation and decay of a metal carbonyl complex as well as the full reaction cycle of bacteriorhodopsin are shown. The pros and cons of the various methods are discussed, with regard to the scientific question one might want to address, and also with regard to the laser systems that might be already existent in a laser lab

A radio air shower surface detector as an extension for IceCube and IceTop

The IceCube neutrino detector is built into the Antarctic ice sheet at the South Pole to measure high energy neutrinos. For this, 4800 photomultiplier tubes (PMTs) are being deployed at depths between 1450 and 2450 meters into the ice to measure neutrino induced charged particles like muons. IceTop is a surface air shower detector consisting of 160 Cherenkov ice tanks located on top of IceCube. To extend IceTop, a radio air shower detector could be built to significantly increase the sensitivity at higher shower energies and for inclined showers. As air showers induced by cosmic rays are a major part of the muonic background in IceCube, IceTop is not only an air shower detector, but also a veto to reduce the background in IceCube. Air showers are detectable by radio signals with a radio surface detector. The major emission process is the coherent synchrotron radiation emitted by e+ e- shower particles in the Earths magnetic field (geosynchrotron effect). Simulations of the expected radio signals of air showers are shown. The sensitivity and the energy threshold of different antenna field configurations are estimated.Comment: 4 pages, 6 figures, to be published in Proceedings of the 30th International Cosmic Ray Conferenc

Charge-transfer and impulsive electronic-to-vibrational energy conversion in ferricyanide: ultrafast photoelectron and transient infrared studies

The photophysics of ferricyanide in H2O, D2O and ethylene glycol was studied upon excitation of ligand-to-metal charge transfer (LMCT) transitions by combining ultrafast photoelectron spectroscopy (PES) of liquids and transient vibrational spectroscopy. Upon 400 nm excitation in water, the PES results show a prompt reduction of the Fe 3+ to Fe 2+ and a back electron transfer in ∼0.5 ps concomitant with the appearance and decay of a strongly broadened infrared absorption at ∼2065 cm -1 . In ethylene glycol, the same IR absorption band decays in ∼1 ps, implying a strong dependence of the back electron transfer on the solvent. Thereafter, the ground state ferric species is left vibrationally hot with significant excitation of up to two quanta of the CN-stretch modes, which completely decay on a 10 ps time scale. Under 265 nm excitation even higher CN-stretch levels are populated. Finally, from a tiny residual transient IR signal, we deduce that less than 2% of the excited species undergo photoaquation, in line with early flash photolysis experiments. The latter is more significant at 265 nm compared to 400 nm excitation, which suggests photodissociation in this system is an unlikely statistical process related to the large excess of vibrational energy

Evaluating the systemic right ventricle by CMR: the importance of consistent and reproducible delineation of the cavity

Contains fulltext : 70334.pdf (publisher's version ) (Open Access)BACKGROUND: The method used to delineate the boundary of the right ventricle (RV), relative to the trabeculations and papillary muscles in cardiovascular magnetic resonance (CMR) ventricular volume analysis, may matter more when these structures are hypertrophied than in individuals with normal cardiovascular anatomy. This study aimed to compare two methods of cavity delineation in patients with systemic RV. METHODS: Twenty-nine patients (mean age 34.7 +/- 12.4 years) with a systemic RV (12 with congenitally corrected transposition of the great arteries (ccTGA) and 17 with atrially switched (TGA) underwent CMR. We compared measurements of systemic RV volumes and function using two analysis protocols. The RV trabeculations and papillary muscles were either included in the calculated blood volume, the boundary drawn immediately within the apparently compacted myocardial layer, or they were manually outlined and excluded. RV stroke volume (SV) calculated using each method was compared with corresponding left ventricular (LV) SV. Additionally, we compared the differences in analysis time, and in intra- and inter-observer variability between the two methods. Paired samples t-test was used to test for differences in volumes, function and analysis time between the two methods. Differences in intra- and inter-observer reproducibility were tested using an extension of the Bland-Altman method. RESULTS: The inclusion of trabeculations and papillary muscles in the ventricular volume resulted in higher values for systemic RV end diastolic volume (mean difference 28.7 +/- 10.6 ml, p < 0.001) and for end systolic volume (mean difference 31.0 +/- 11.5 ml, p < 0.001). Values for ejection fraction were significantly lower (mean difference -7.4 +/- 3.9%, p < 0.001) if structures were included. LV SV did not differ significantly from RV SV for both analysis methods (p = NS). Including structures resulted in shorter analysis time (p < 0.001), and showed better inter-observer reproducibility for ejection fraction (p < 0.01). CONCLUSION: The choice of method for systemic RV cavity delineation significantly affected volume measurements, given the CMR acquisition and analysis systems used. We recommend delineation outside the trabeculations for routine clinical measurements of systemic RV volumes as this approach took less time and gave more reproducible measurements

Validation of Real-time Transthoracic 3D echocardiography in Children with Congenital Heart Disease

Aims: Assessment of feasibility, accuracy and applicability in clinical practice of real-time three-dimensional echocardiography (RT-3DE) in children with congenital heart defects. Methods and results: From September 2004 to June 2005, 100 consecutive children (57 infants, 43 children &gt; 1 year of age), who were scheduled for corrective intracardiac surgery, were enrolled in this study. RT-3DE was performed with Philips Sonos 7500 echo-system and off-line analysis with TomTec Echoview© software. Quantitative and qualitative assessments of the region of interest were performed on the 3D reconstruction, comparing these results with the anatomic findings and measurements performed during intracardiac surgery. Acquisition of RT-3DE datasets was feasible in 92 of the 100 (92%) patients and acquisition time was 6 ± 3 minutes. The overall quantitative analyses showed an excellent correlation (r &lt; 0.90) between RT-3De and surgery. Also the qualitative analyses were accurate compared with surgical findings, in all patients in which RT-3DE was feasible. Conclusion: This study shows that RT-3DE can be used in the clinical practice for the assessment of intracardiac anatomy in children with congenital heart disease. The information derived from the 3D reconstructions can be taken into consideration in the preoperative planning and management regarding interventional or surgical therapy

Ultrafast broadband circular dichroism in the deep ultraviolet

The measurement of chirality and its temporal evolution are crucial for the understanding of a large range of biological functions and chemical reactions. Steady-state circular dichroism (CD) is a standard analytical tool for measuring chirality in chemistry and biology. Nevertheless, its push into the ultrafast time domain and in the deep-ultraviolet has remained a challenge, with only some isolated reports of subnanosecond CD. Here, we present a broadband time-resolved CD spectrometer in the deep ultraviolet (UV) spectral range with femtosecond time resolution. The setup employs a photo-elastic modulator to achieve shot-to-shot polarization switching of a 20 kHz pulse train of broadband femtosecond deep-UV pulses (250-370 nm). The resulting sequence of alternating left- and right-circularly polarized probe pulses is employed in a pump-probe scheme with shot-to-shot dispersive detection and thus allows for the acquisition of broadband CD spectra of ground- and excited-state species. Through polarization scrambling of the probe pulses prior to detection, artifact-free static and transient CD spectra of enantiopure [Ru(bpy)(3)](2+) are successfully recorded with a sensitivity of <2 x 10(-5) OD (approximate to 0.7 mdeg). Due to its broadband deep-UV detection with unprecedented sensitivity, the measurement of ultrafast chirality changes in biological systems with amino-acid residues and peptides and of DNA oligomers is now feasible. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

A comparative study of Macroscopic Fundamental Diagrams of arterial road networks governed by adaptive traffic signal systems

Using a stochastic cellular automaton model for urban traffic flow, we study and compare Macroscopic Fundamental Diagrams (MFDs) of arterial road networks governed by different types of adaptive traffic signal systems, under various boundary conditions. In particular, we simulate realistic signal systems that include signal linking and adaptive cycle times, and compare their performance against a highly adaptive system of self-organizing traffic signals which is designed to uniformly distribute the network density. We find that for networks with time-independent boundary conditions, well-defined stationary MFDs are observed, whose shape depends on the particular signal system used, and also on the level of heterogeneity in the system. We find that the spatial heterogeneity of both density and flow provide important indicators of network performance. We also study networks with time-dependent boundary conditions, containing morning and afternoon peaks. In this case, intricate hysteresis loops are observed in the MFDs which are strongly correlated with the density heterogeneity. Our results show that the MFD of the self-organizing traffic signals lies above the MFD for the realistic systems, suggesting that by adaptively homogenizing the network density, overall better performance and higher capacity can be achieved.Comment: 35 pages, 14 figure