High-energy molecular-frame photoelectron angular distributions: a molecular bond-length ruler.

We present a study on molecular-frame photoelectron angular distributions (MFPADs) of small molecules using circularly polarized synchrotron light. We find that the main forward-scattering peaks of the MFPADs are slightly tilted with respect to the molecular axis. This tilt angle is directly connected to the molecular bond length by a simple, universal formula. We apply the derived formula to several examples of MFPADs of C 1s and O 1s photoelectrons of CO, which have been measured experimentally or obtained by means of ab initio modeling. In addition, we discuss the influence of the back-scattering contribution that is superimposed over the analyzed forward-scattering peak in the case of homo-nuclear diatomic molecules such as N2.

Investigating charge-up and fragmentation dynamics of oxygen molecules after interaction with strong X-ray free-electron laser pulses.

During the last decade, X-ray free-electron lasers (XFELs) have enabled the study of light-matter interaction under extreme conditions. Atoms which are subject to XFEL radiation are charged by a complex interplay of (several subsequent) photoionization events and electronic decay processes within a few femtoseconds. The interaction with molecules is even more intriguing, since intricate nuclear dynamics occur as the molecules start to dissociate during the charge-up process. Here, we demonstrate that by analyzing photoelectron angular emission distributions and kinetic energy release of charge states of ionic molecular fragments, we can obtain a detailed understanding of the charge-up and fragmentation dynamics. Our novel approach allows for gathering such information without the need of complex ab initio modeling. As an example, we provide a detailed view on the processes happening on a femtosecond time scale in oxygen molecules exposed to intense XFEL pulses.

Ion and Electron Momentum Distributions from Single and Double Ionization of Helium Induced by Compton Scattering.

We present the momentum distributions of the nucleus and of the electrons from double ionization of the helium atom by Compton scattering of photons with hν=40 keV. We find that the doubly charged ion momentum distribution is very close to the Compton profile of the nucleus in the ground state of the helium atom, and the momentum distribution of the singly charged ion to give a precise image of the electron Compton profile. To reproduce these results, nonrelativistic calculations require the use of highly correlated initial- and final-state wave functions.

Fourfold Differential Photoelectron Circular Dichroism.

We report on a joint experimental and theoretical study of photoelectron circular dichroism (PECD) in methyloxirane. By detecting O 1s photoelectrons in coincidence with fragment ions, we deduce the molecule's orientation and photoelectron emission direction in the laboratory frame. Thereby, we retrieve a fourfold differential PECD clearly beyond 50%. This strong chiral asymmetry is reproduced by ab initio electronic structure calculations. Providing such a pronounced contrast makes PECD of fixed-in-space chiral molecules an even more sensitive tool for chiral recognition in the gas phase.

Strong Differential Photoion Circular Dichroism in Strong-Field Ionization of Chiral Molecules.

We investigate the differential ionization probability of chiral molecules in the strong-field regime as a function of the helicity of the incident light. To this end, we analyze the fourfold ionization of bromochlorofluoromethane (CHBrClF) with subsequent fragmentation into four charged fragments and different dissociation channels of the singly ionized methyloxirane. By resolving for the molecular orientation, we show that the photoion circular dichroism signal strength is increased by 2 orders of magnitude.

Enantioselective fragmentation of an achiral molecule in a strong laser field.

Chirality is omnipresent in living nature. On the single molecule level, the response of a chiral species to a chiral probe depends on their respective handedness. A prominent example is the difference in the interaction of a chiral molecule with left or right circularly polarized light. In the present study, we show by Coulomb explosion imaging that circularly polarized light can also induce a chiral fragmentation of a planar and thus achiral molecule. The observed enantiomer strongly depends on the orientation of the molecule with respect to the light propagation direction and the helicity of the ionizing light. This finding might trigger new approaches to improve laser-driven enantioselective chemical synthesis.

Reorganization of Synaptic Connections and Perineuronal Nets in the Deep Cerebellar Nuclei of Purkinje Cell Degeneration Mutant Mice.

The perineuronal net (PN) is a subtype of extracellular matrix appearing as a net-like structure around distinct neurons throughout the whole CNS. PNs surround the soma, proximal dendrites, and the axonal initial segment embedding synaptic terminals on the neuronal surface. Different functions of the PNs are suggested which include support of synaptic stabilization, inhibition of axonal sprouting, and control of neuronal plasticity. A number of studies provide evidence that removing PNs or PN-components results in renewed neurite growth and synaptogenesis. In a mouse model for Purkinje cell degeneration, we examined the effect of deafferentation on synaptic remodeling and modulation of PNs in the deep cerebellar nuclei. We found reduced GABAergic, enhanced glutamatergic innervations at PN-associated neurons, and altered expression of the PN-components brevican and hapln4. These data refer to a direct interaction between ECM and synapses. The altered brevican expression induced by activated astrocytes could be required for an adequate regeneration by promoting neurite growth and synaptogenesis.

A New Type of ECT Stimuli: Burst Stimulus ECT.

OBJECTIVES: Pulse width in electroconvulsive therapy has significant influence on effectiveness and side effects. While shorter pulses are beneficial for cognitive performance, there is still a debate about a negative impact on ECT efficacy at least for ultra-brief pulse durations. METHODS: We report a first patient treated with burst stimulus ECT, i. e., with 4 consecutive 250-µs pulses, separated by another 250 µs. Within the same patient we compared 6 classical vs. 6 burst stimulus ECT sessions. RESULTS: In all cases a typical tonic-clonic seizure was observed. Seizure parameters like concordance, coherence and mid-ictal amplitude increased numerically, but not significantly with burst ECT. The time needed to show a reorientation was significantly shortened with burst stimuli (30 min vs. 14 min, p=0.007). CONCLUSIONS: In conclusion we present the first case of ECT in a single patient comparing "classical" single stimulus pulses vs. burst stimulus ECT. The new burst stimulus was better tolerated regarding reorientation time after the treatment, while parameters of seizure quality remained basically unchanged. Whether burst stimulus ECT has the potential to improve ECT quality by reducing side effects without losing efficacy has to be investigated in clinical trials.

[Ketamine as anesthetic agent in electroconvulsion therapy]. / Ketamin als Anästhetikum bei der Elektrokrampftherapie.

BACKGROUND: Electroconvulsive therapy (ECT) is a well-established, safe and effective treatment for severe psychiatric disorders. Ketamine is known as a core medication in anesthesiology and has recently gained interest in ECT practice as there are three potential advantages: (1) ketamine has no anticonvulsive actions, (2) according to recent studies ketamine could possess a unique intrinsic antidepressive potential and (3) ketamine may exhibit neuroprotective properties, which again might reduce the risk of cognitive side effects associated with ECT. OBJECTIVES: The use of ketamine in psychiatric patients has been controversially discussed due to its dose-dependent psychotropic and psychotomimetic effects. This study was carried out to test if the occurrence of side effects is comparable and if seizure quality is better with ketamine when compared to thiopental. MATERIAL AND METHODS: This retrospective study analyzed a total of 199 patients who received ketamine anesthesia for a total of 2178 ECT sessions. This cohort was compared to patients who were treated with thiopental for 1004 ECT sessions. RESULTS AND DISCUSSION: A repeated measurement multiple logistic regression analysis revealed significant advantages in the ketamine group for seizure concordance and postictal suppression (both are surrogates for central inhibition). S-ketamin also necessitated the use of a higher dose of urapidil and a higher maximum postictal heart frequency. Clinically relevant psychiatric side effects were rare in both groups. No psychiatric side effects occurred in the subgroup of patients with schizophrenia (ketamine: n = 30). The mean dose of S-ketamine used increased in the first years but stabilized at 63 mg per patient in 2014. From these experiences it can be concluded that S-ketamine can be recommended at least as a safe alternative to barbiturates.

Bispectral index monitoring and seizure quality optimization in electroconvulsive therapy.

In ECT, the relative timing of seizure induction and anesthesia may critically impact on seizure quality when anesthetic agents with anticonvulsive properties such as barbiturates or propofol are used. Measuring the depth of anesthesia by bispectral index (BIS) monitoring and thereby identifying the optimal moment for seizure induction might enhance seizure quality.Seizures from 869 individual ECT -sessions with thiopental anesthetic from 118 patients were examined in this retrospective study. The associations of the BIS value at the moment of seizure induction with 7 established seizure parameters and with a novel model of seizure quality were tested by regression analyses.BIS value at induction correlated positively with seizure duration, central inhibition, coherence and maximal heart rate, but not with midictal amplitude. Higher seizure quality was related with a higher BIS value at the moment of seizure induction.The BIS value at seizure induction serves as an independent predictor of seizure quality, influencing most other established markers. BIS monitoring appears as a simple tool to identify the optimal moment for seizure induction.

Venlafaxin-associated post-ictal asystole during electroconvulsive therapy.

While post-stimulus asystoles occur quite often during electroconvulsive therapy (ECT) post-ictal or post-seizure sinus bradycardias or even asystoles are rare events. We report the case of an 82-year-old female patient with a current major depressive episode, who developed the rare event of a post-ictal asystole of 6 s and 4 ventricular escape beats during ECT. In the past this patient with a bipolar disorder and mild Alzheimer's disease had already been frequently treated with ECT with good success and no adverse events. Relevant comedication was venlafaxin, quetiapine, donepezil and clonidine, anesthesia was performed with ketamine and succinylcholine. Concurrent medication was completely unchanged compared to previous ECT sessions with the exception of venlafaxine, presumably at high serum levels. In summary, in line with some already existing reports, we expect the noradrenergic action of venlafaxin to have contributed substantially to the post-ictal asystole and want to indicate that the combination of ECT and venlafaxin might be harmful--especially in the elderly population.

High-speed asynchronous optical sampling with sub-50fs time resolution.

We report an ultrafast time-domain spectroscopy system based on high-speed asynchronous optical sampling operating without mechanical scanner. The system uses two 1 GHz femtosecond oscillators that are offset-stabilized using high-bandwidth feedback electronics operating at the tenth repetition rate harmonics. Definition of the offset frequency, i.e. the time-delay scan rate, in the range of a few kilohertz is accomplished using direct-digital-synthesis electronics for the first time. The time-resolution of the system over the full available 1 ns time-delay window is determined by the laser pulse duration and is 45 fs. This represents a three-fold improvement compared to previous approaches where timing jitter was the limiting factor. Two showcase experiments are presented to verify the high time-resolution and sensitivity of the system.

Rapid-scanning terahertz precision spectrometer with more than 6 THz spectral coverage.

We report a terahertz time-domain spectrometer with more than 6 THz spectral coverage and 1 GHz resolution based on high-speed asynchronous optical sampling. It operates at 2 kHz scan rate without mechanical delay stage. The frequency error of the system at 60 s acquisition time is determined by comparing a measured water vapor absorption spectrum to data reported in the HITRAN database. The mean error of 87 evaluated absorption lines is 142 MHz.

Self-interstitial in germanium.

Low-temperature radiation damage in n- and p-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.

Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling.

High-speed asynchronous optical sampling (ASOPS) is a novel technique for ultrafast time-domain spectroscopy (TDS). It employs two mode-locked femtosecond oscillators operating at a fixed repetition frequency difference as sources of pump and probe pulses. We present a system where the 1 GHz pulse repetition frequencies of two Ti:sapphire oscillators are linked at an offset of Deltaf(R)=10 kHz. As a result, their relative time delay is repetitively ramped from zero to 1 ns within a scan time of 100 micros. Mechanical delay scanners common to conventional TDS systems are eliminated, thus systematic errors due to beam pointing instabilities and spot size variations are avoided when long time delays are scanned. Owing to the multikilohertz scan-rate, high-speed ASOPS permits data acquisition speeds impossible with conventional schemes. Within only 1 s of data acquisition time, a signal resolution of 6 x 10(-7) is achieved for optical pump-probe spectroscopy over a time-delay window of 1 ns. When applied to terahertz TDS, the same acquisition time yields high-resolution terahertz spectra with 37 dB signal-to-noise ratio under nitrogen purging of the spectrometer. Spectra with 57 dB are obtained within 2 min. A new approach to perform the offset lock between the two femtosecond oscillators in a master-slave configuration using a frequency shifter at the third harmonic of the pulse repetition frequency is employed. This approach permits an unprecedented time-delay resolution of better than 160 fs. High-speed ASOPS provides the functionality of an all-optical oscilloscope with a bandwidth in excess of 3000 GHz and with 1 GHz frequency resolution.

High-resolution THz spectrometer with kHz scan rates.

We demonstrate a rapid scanning high-resolution THz spectrometer capable of acquiring THz field transients with 1 ns duration without mechanical delay line. The THz spectrometer is based on two 1-GHz Ti:sapphire femtosecond lasers which are linked with a fixed repetition rate difference in order to perform high-speed asynchronous optical sampling. One laser drives a high-efficiency large-area GaAs based THz emitter, the other laser is used for electro-optic detection of the emitted THz-field. At a scan rate of 9 kHz a time resolution of 230 fs is accomplished. High-resolution spectra from 50 GHz up to 3 THz are obtained and water absorption lines with a width of 11 GHz are observed. The use of femtosecond lasers with 1 GHz repetition rate is essential to obtain rapid scanning and high time-resolution at the same time.

All-optical switching of the transmission of electromagnetic radiation through subwavelength apertures.

Unprecedented optical control of the surface plasmon polariton assisted transmission of terahertz radiation through subwavelength apertures is rendered possible by carrier-induced changes to the dielectric properties of a semiconductor grating. Although the study presented is static, the extension of our approach to dynamic switching and tuning is deemed straightforward, opening the way for the realization of ultrafast surface plasmon based devices.

Asynchronous optical sampling for high-speed characterization of integrated resonant terahertz sensors.

Two femtosecond Ti:sapphire lasers with slightly different repetition rates near 1 GHz are coupled to implement high-speed asynchronous optical sampling. The application of this technique is successfully demonstrated in the field of terahertz time-domain spectroscopy (TDS). A time delay of 1 ns is scanned at a frequency of 5 kHz without moving mechanical parts. Compared with that of conventional TDS schemes based on lock-in detection and moving mirrors, the readout time of integrated resonant THz sensors is reduced by a factor of 20, opening the way for high-throughput THz sensing in marker-free DNA analysis.

[Anaphylactic cardiocirculatory failure after intraoperative application of dipyrone]. / Anaphylaktisches Herz-Kreislauf-Versagen nach intraoperativer Metamizolapplikation.

CASE REPORT: In our case, a 48-year-old healthy woman undergoing elective tympanoplasty under general anesthesia received an infusion of 2 g dipyrone in 100 ml 0.9% sodium chloride solution for pain prophylaxis. After receiving 1 g dipyrone within 5 min, the patient exhibited a cardiocirculatory failure and cyanosis and had to be resuscitated. After 20 min of cardiopulmonary resuscitation and administration of 3mg epinephrine and 2 mg norepinephrine, a stable circulation was reestablished. After exclusion of a fulminant pulmonary embolism and a primary cardiac event by computer tomography, electrocardiogram and enzyme diagnostics, the patient was transferred to an intensive care unit where she was mechanically ventilated for a period of 6 h. After 2 days of intensive monitoring, she was transferred to a peripheral ward,where she exhibited a normal neurological status and stable cardiocirculatory condition. A postoperatively performed allergy testing revealed a type I sensitization to dipyrone, which was responsible for the intraoperative cardiocirculatory failure due to a massive anaphylactic reaction. However, in this case, the typical symptoms of allergic reactions such as erythema, edema or bronchospasm were missing, which did not allow for an immediate diagnosis. CONCLUSION. Regarding the frequent perioperative use of dipyrone and the severity of anaphylaxis observed in this case, it should be considered that this analgesic should be applied intravenously only if adequate safety measures such as emergency therapy option and patient monitoring are guaranteed as recommended by the German drug regulation authority since 1982.

Differential susceptibility of inbred mouse strains to Helicobacter pylori infection.

BACKGROUND: Host factors play an important part in the pathogenesis of Helicobacter pylori-associated disease. The aim of this study was to screen various inbred strains of mice for genetic differences in susceptibility to H. pylori infection. METHODS: Mice of strains BALB/cJ, C.B-17-Prkdc(scid), C3H/HeJ, C3H/HeN, C57BL/6J, C57BL/6J-I110(tm/Cgn), DBA/2J, and FVB/N were inoculated intragastrically with H. pylori SS1. At 1, 4 and 6 months after inoculation, mice were necropsied, and bacterial cultures and histologic studies of the stomachs were performed. RESULTS: Significant differences in the level of colonization by H. pylori were observed among inbred strains at each time of infection. These differences were most distinct at 4 months after inoculation with highest levels in strains C3H/HeJ and C3H/HeN and lowest in strains FVB/N, C57BL/6J and C57BL/6J-I110(tm/Cgn). Infected mice revealed a mild increase in inflammatory cells compared with controls at 1 and 4 months, but not at 6 months after inoculation. The host strain effect on gastric disease was fairly mild, with two exceptions. Firstly, infected I110(tm/Cgn) mice developed a severe, hyperplastic gastritis, indicating that interleukin-10 is an important regulator of the inflammatory response to H. pylori. Secondly, infected C3H/HeN mice had a propensity to develop lymphoid aggregates in the gastric mucosa. CONCLUSIONS: The strain differences described here will be useful for the design of genetic mapping studies in mice to elucidate the genes controlling gastric infection by H. pylori. Our results further show that genetically altered mice are a valuable tool for identifying candidate genes possibly contributing to susceptibility to H. pylori infection.