Implementation of controllable universal unital optical channels.

We show that a configuration of four birefringent crystals and wave-plates can emulate almost any arbitrary unital channel for polarization qubits encoded in single photons, where the channel settings are controlled by the wave-plate angles. The scheme is applied to a single spatial mode and its operation is independent of the wavelength and the fine temporal properties of the input light. We implemented the scheme and demonstrated its operation by applying a dephasing environment to classical and quantum single-photon states with different temporal properties. The applied process was characterized by a quantum process tomography procedure, and a high fidelity to the theory was observed.

[Nationwide survey of postgraduate medical training in clinical neurology]. / Deutschlandweite Evaluation der ärztlichen Weiterbildung in der klinischen Neurologie.

BACKGROUND: Currently, no data are available, which reflect the situation of medical doctors specializing in neurology in German hospitals. In order to secure the high standard of neurological patient care it is essential to evaluate the working conditions and the specialty training in neurology. OBJECTIVE: This nationwide survey was conducted throughout Germany with the aim to address problems and to give suggestions for improvements in neurological training curricula. MATERIAL AND METHODS: The survey was online from February to May 2017 and 953 neurologists undergoing further training participated. RESULTS: More than half of the young neurologists were satisfied with their medical training. One of the main problems that complicates clinical training is the workload. In addition, organizational obstacles within the clinic, such as poor structure of education or a lack of mentors, lead to dissatisfaction among participants. The size or type of the department, as well as the prevailing service system, exert only a minor influence on the quality of specialist training, although there were differences especially in the self-assessment of the participants in connection with the type of department (university hospital versus public or private hospital). CONCLUSION: Specialist training in neurology can be improved by simple arrangements, e. g., the introduction of a binding rotation scheme, internal mentoring and structured feedback. In addition, it will be necessary to relieve medical staff of administrative duties in order to create time for training and the learning of competencies.

Super-resolved phase measurements at the shot noise limit by parity measurement.

Classically, the resolution of optical measurements is limited by the Rayleigh limit and their sensitivity by the shot noise limit. However, non-classical measurements can surpass these limits. Measuring the photon number parity using a photon-number resolving detector, super resolved phase measurements up to 144 better than the Rayleigh limit are presented, with coherent states of up to 4,200 photons on average. An additional measurement that can be implemented with standard single-photon detectors is proposed and demonstrated. With this scheme, super resolution at the shot noise limit is demonstrated with coherent states of up to 200 photons on average.

Compact 2D nonlinear photonic crystal source of beamlike path entangled photons.

We demonstrate a method to generate entangled photons with controlled spatial shape by parametric down conversion (PDC) in a 2D nonlinear crystal. A compact and novel crystal source was designed and fabricated, generating directly path entangled photons without the use of additional beam-splitters. This crystal supports two PDC processes, emitting biphotons into two beamlike modes simultaneously. Two coherent path entangled amplitudes of biphotons were created and their interference observed. Our method enables the generation of entangled photons with controlled spatial, spectral and polarization properties.

Entanglement swapping between photons that have never coexisted.

The role of the timing and order of quantum measurements is not just a fundamental question of quantum mechanics, but also a puzzling one. Any part of a quantum system that has finished evolving can be measured immediately or saved for later, without affecting the final results, regardless of the continued evolution of the rest of the system. In addition, the nonlocality of quantum mechanics, as manifested by entanglement, does not apply only to particles with spacelike separation, but also to particles with timelike separation. In order to demonstrate these principles, we generated and fully characterized an entangled pair of photons that have never coexisted. Using entanglement swapping between two temporally separated photon pairs, we entangle one photon from the first pair with another photon from the second pair. The first photon was detected even before the other was created. The observed two-photon state demonstrates that entanglement can be shared between timelike separated quantum systems.

Measurements of the dependence of the photon-number distribution on the number of modes in parametric down-conversion.

Optical parametric down-conversion (PDC) is a central tool in quantum optics experiments. The number of collected down-converted modes greatly affects the quality of the produced photon state. We use Silicon Photomultiplier (SiPM) number-resolving detectors in order to observe the photon-number distribution of a PDC source, and show its dependence on the number of collected modes. Additionally, we show how the stimulated emission of photons and the partition of photons into several modes determine the overall photon number. We present a novel analytical model for the optical crosstalk effect in SiPM detectors, and use it to analyze the results.

Resource efficient source of multiphoton polarization entanglement.

Current photon entangling schemes require resources that grow with the photon number. We present a new approach that generates quantum entanglement between many photons, using only a single source of entangled photon pairs. The different spatial modes, one for each photon as required by other schemes, are replaced by different time slots of only two spatial modes. States of any number of photons are generated with the same setup, solving the scalability problem caused by the previous need for extra resources. Consequently, entangled photon states of larger numbers than before are practically realizable.

The biaxial nonlinear crystal BiB3O6 as a polarization entangled photon source using non-collinear type-II parametric down-conversion.

We describe the full characterization of the biaxial nonlinear crystal BiB3O6 (BiBO) as a polarization entangled photon source using non-collinear type-II parametric down-conversion. We consider the relevant parameters for crystal design, such as cutting angles, polarization of the photons, effective nonlinearity, spatial and temporal walk-offs, crystal thickness and the effect of the pump laser bandwidth. Experimental results showing entanglement generation with high rates and a comparison to the well investigated ß-BaB2O4 (BBO) crystal are presented as well. Changing the down-conversion crystal of a polarization entangled photon source from BBO to BiBO enhances the generation rate as if the pump power was increased by 2.5 times. Such an improvement is currently required for the generation of multiphoton entangled states.

Projection of two biphoton qutrits onto a maximally entangled state.

Bell state measurements, in which two quantum bits are projected onto a maximally entangled state, are an essential component of quantum information science. We propose and experimentally demonstrate the projection of two quantum systems with three states (qutrits) onto a generalized maximally entangled state. Each qutrit is represented by the polarization of a pair of indistinguishable photons-a biphoton. The projection is a joint measurement on both biphotons using standard linear optics elements. This demonstration enables the realization of quantum information protocols with qutrits, such as teleportation and entanglement swapping.

Sequential generation of linear cluster states from a single photon emitter.

Light states composed of multiple entangled photons-such as cluster states-are essential for developing and scaling-up quantum computing networks. Photonic cluster states can be obtained from single-photon sources and entangling gates, but so far this has only been done with probabilistic sources constrained to intrinsically low efficiencies, and an increasing hardware overhead. Here, we report the resource-efficient generation of polarization-encoded, individually-addressable photons in linear cluster states occupying a single spatial mode. We employ a single entangling-gate in a fiber loop configuration to sequentially entangle an ever-growing stream of photons originating from the currently most efficient single-photon source technology-a semiconductor quantum dot. With this apparatus, we demonstrate the generation of linear cluster states up to four photons in a single-mode fiber. The reported architecture can be programmed for linear-cluster states of any number of photons, that are required for photonic one-way quantum computing schemes.

Skin sensory afterglows.

Brief stimulation of the upper lip with the tip of a nylon thread frequently produces an " afterglow" sensation that may persist as long as several minutes after cessation of stimulation. The duration of afterglow is increased by strong suggestion, and decreased by vibration of the skin prior to stimulation. The afterglow may be followed by a period of acute "awareness" of the area, distincty different from the stimulus and afterglow sensations. The afterglows produced by a warm stimulator applied to the back often well up into a painful sting.

Cerebral vessels have the capacity to transport sodium and potassium.

The activity of Na+, K+-activated adenosinetriphosphatase and the uptake of a potassium analog, rubidium, were found to be similar in cerebral microvessels and choroid plexus when measured in vitro. This similarity suggests that sodium and potassium concentrations in the nascent brain extracellular fluid are determined by the same active process that regulates their concentration in nascent cerebrospinal fluid. The brain microvessels may thereby play on active role in brain potassium homeostasis and brain extracellular fluid formation.

Halophilic proteins and the influence of solvent on protein stabilization.

Competition between protein-solvent and protein-protein interactions is arguably the most important contributing factor to polypeptide folding in general. A study of halophilic proteins, correlating their stability and solution structures in different conditions, focuses on the effects of a high salt solvent. A mechanism is proposed to explain how these proteins have adapted to such an extreme environment.

One-Stop Management with Perfusion for Transfer Patients with Stroke due to a Large-Vessel Occlusion: Feasibility and Effects on In-Hospital Times.

BACKGROUND AND PURPOSE: In-hospital time delays lead to a relevant deterioration of neurologic outcomes in patients with stroke with large-vessel occlusions. At the moment, CT perfusion is relevant in the triage of late-window patients with stroke. We conducted this study to determine whether one-stop management with perfusion is feasible and leads to a reduction of in-hospital times. MATERIALS AND METHODS: In this observational study, we report the first 15 consecutive transfer patients with stroke with externally confirmed large-vessel occlusions who underwent flat panel detector CT perfusion and thrombectomy in the same room. Preinterventional imaging consisted of noncontrast flat panel detector CT and flat panel detector CT perfusion, acquired with a biplane angiography system. The flat panel detector CT perfusion was used to reconstruct a flat panel detector CT angiography to confirm the large-vessel occlusions. After confirmation of the large-vessel occlusion, the patient underwent mechanical thrombectomy. We recorded time metrics and safety parameters prospectively and compared them with those of transfer patients whom we treated before the introduction of one-stop management with perfusion. RESULTS: Fifteen transfer patients underwent flat panel detector CT perfusion and were treated with mechanical thrombectomy from June 2017 to January 2019. The median time from symptom onset to admission was 241 minutes. Median door-to-groin time was 24 minutes. Compared with 23 transfer patients imaged with multidetector CT, it was reduced significantly (24 minutes; 95% CI, 19-37 minutes, versus 53 minutes; 95% CI, 44-66 minutes; P < .001). Safety parameters were comparable between groups. CONCLUSIONS: In this small series, one-stop management with perfusion led to a significant reduction of in-hospital times compared with our previous workflow.

Nicotinic receptor activation in human cerebral cortical interneurons: a mechanism for inhibition and disinhibition of neuronal networks.

Cholinergic control of the activity of human cerebral cortical circuits has long been thought to be accounted for by the interaction of acetylcholine (ACh) with muscarinic receptors. Here we report the discovery of functional nicotinic receptors (nAChRs) in interneurons of the human cerebral cortex and discuss the physiological and clinical implications of these findings. The whole-cell mode of the patch-clamp technique was used to record responses triggered by U-tube application of the nonselective agonist ACh and of the alpha7-nAChR-selective agonist choline to interneurons visualized by means of infrared-assisted videomicroscopy in slices of the human cerebral cortex. Choline induced rapidly desensitizing whole-cell currents that, being sensitive to blockade by methyllycaconitine (MLA; 50 nM), were most likely subserved by an alpha7-like nAChR. In contrast, ACh evoked slowly decaying whole-cell currents that, being sensitive to blockade by dihydro-beta-erythroidine (DHbetaE; 10 microM), were most likely subserved by an alpha4beta2-like nAChR. Application of ACh (but not choline) to the slices also triggered GABAergic postsynaptic currents (PSCs). Evidence is provided that ACh-evoked PSCs are the result of activation of alpha4beta2-like nAChRs present in preterminal axon segments and/or in presynaptic terminals of interneurons. Thus, nAChRs can relay inhibitory and/or disinhibitory signals to pyramidal neurons and thereby modulate the activity of neuronal circuits in the human cerebral cortex. These mechanisms, which appear to be retained across species, can account for the involvement of nAChRs in cognitive functions and in certain neuropathological conditions.

Solution structure of halophilic malate dehydrogenase from small-angle neutron and X-ray scattering and ultracentrifugation.

Data from small-angle X-ray and neutron scattering and ultracentrifugation experiments on solutions of malate dehydrogenase from Halobacterium maris mortui are analysed together to yield a model for the enzyme particle formed by the protein and its interactions with water and salt in the solvent. The halophilic enzyme is stable only in high concentrations of salt and the model has structural features that are absent from non-halophilic malate dehydrogenase. The complementarity of the information derived from the three experimental methods is discussed extensively and quantitatively. It derives from the fact that mass density (ultracentrifugation), electron density (X-rays) and neutron scattering density are independent of each other. Each method gives a different "view" of the same particle, and an analysis of the combined data provided thermodynamic and structural parameters with, apart from the chemical composition of the solutions, only one other assumption: a constant partial specific volume for water equal to 1.00 cm3 g-1. Both the insights gained by this novel approach and its limitations are carefully pointed out. In solvents between 1 M and 5 M-NaCl, the enzyme forms a particle of invariant volume, consisting of a protein dimer (87,000 g mol-1) with which are associated 0.87 g of water and 0.35 g of salt per gram of protein. The partial specific volume of the protein calculated from the combined experimental data is 0.753(+/- 0.030) cm3 g-1, in good agreement with the value calculated from the amino acid composition. The particle has a radius of gyration of 32 A and an equivalent Stokes radius of 43 A. By combining the data from the X-ray and neutron scattering studies, the radii of gyration of the protein moiety alone and of the associated water and salt distribution were calculated. They are 28 A and about 40 A, respectively. The large-angle scattering curves show that the shapes of the particle and of the protein moiety alone are similar. At very low resolution they can be approximated by an ellipsoid of axial ratio 1:1:0.6 (or 1:1:1.5). At higher resolution, it becomes apparent that the particle has a significantly larger interface with solvent than an homogeneous ellipsoid or globular protein. The model has a globular protein core similar to non-halophilic malate dehydrogenase, with about 20% of the protein extending loosely out of the core, forming the large interface with solvent. The main interactions with water and salt take place on this outer part.

Nucleosome core particle stability and conformational change. Effect of temperature, particle and NaCl concentrations, and crosslinking of histone H3 sulfhydryl groups.

We have studied the reversible dissociation of core size DNA from chicken erythrocyte nucleosome core particles in solutions containing 0 X 1 M to 0 X 6 M-NaCl. Dissociation increases with increasing NaCl concentration, increasing temperature and decreasing particle concentration. At high particle concentrations, no free DNA is observed below 0 X 3 M-NaCl, whereas above 0 X 3 M-NaCl a lower limit of dissociation is reached. A theoretical analysis based on the migrating-octamer mechanism of Stein is in disagreement with his conclusions concerning dependence of core particle dissociation on particle concentration, but provides a good explanation for our observations, and those of others, using salt concentrations up to 1 M-NaCl. It appears that the core particle is not stabilized primarily by electrostatic interactions. DNA length is not critical for core particle stabilization. The conformation of remaining intact nucleosome core particles changes only moderately within the range of NaCl concentrations studied. Crosslinking by copper phenanthroline of the Cys110 histone H3 single sulfhydryl groups in the intact nucleosome core particle leads to a decrease in stability, yet essentially unchanged hydrodynamic properties are maintained at 0 X 6 M-NaCl, confirming conclusions derived from the behavior of the native core particles. Values for density increments of nucleosome core particles over a range of NaCl concentrations are also given. A method is described for studying binding of histones to nucleosome core particles in the ultracentrifuge by scanning at 230 and 260 nm.

Interaction of chromatin with NaCl and MgCl2. Solubility and binding studies, transition to and characterization of the higher-order structure.

Chicken erythrocyte chromatin containing histones H1 and H5 was carefully separated into a number of well-characterized fractions. A distinction could be made between chromatin insoluble in NaCl above about 80 mM, and chromatin soluble at all NaCl concentrations. Both chromatin forms were indistinguishable electrophoretically and both underwent the transition from the low salt "10 nm" coil to the "30 nm" higher-order structure solenoid by either raising the MgCl2 concentration to about 0.3 mM or the NaCl concentration to about 75 mM. The transitions were examined in detail by elastic light-scattering procedures. It could be shown that the 10 nm form is a flexible coil. For the 30 nm solenoid, the assumption of a rigid cylindrical structure was in good agreement with 5.7 nucleosomes per helical turn. However, disagreement of calculated frictional parameters with values derived from quasielastic light-scattering and sedimentation introduced the possibility that the higher-order structure, under these conditions, is more extended, flexible, or perhaps a mixture of structures. Values for density and refractive index increments of chromatin are also given. To understand the interaction of chromatin with NaCl and with MgCl2, a number of experiments were undertaken to study solubility, precipitation, conformational transitions and binding of ions over a wide range of experimental conditions, including chromatin concentration.

Denaturation of a halophilic enzyme monitored by small-angle neutron scattering.

Malate dehydrogenase from Halobacterium maris mortui exists in 4 M-NaCl as a stable protein dimer, with which are associated unusually large amounts of salt and water. In 1 M-NaCl at 25 degrees C, it denatures with a time-constant of about 0.5 h-1. Small-angle neutron scattering data from the protein under these conditions were monitored regularly over more than 12 hours during denaturation. They are quantitatively consistent with a model in which the protein dimer loses its exceptional salt and water-binding properties, and dissociates into monomers that partially unfold and have the interactions with solvent expected from their relatively charged amino acid composition. The exceptional salt and water-binding by the native enzyme, therefore, is associated with the native structure of the dimer.

Nucleosome core particle structure and structural changes in solution.

The radius of gyration, Rg, of chicken erythrocyte nucleosome core particles, was found to be 4.56 (+/- 0.07) nm by small-angle X-ray scattering, independent of particle concentration and of NaCl concentration between 0.1 M and 0.6 M-NaCl. The large, positive, second virial coefficient, A2, from particle concentration dependence (but independent of NaCl concentration) in small-angle X-ray scattering may indicate non-electrostatic repulsive ordering over large distances. Density contrast variation in equilibrium sedimentation with a small probe (sucrose) and a larger probe (gamma-cyclodextrin) yields good results for core particle hydration in the first instance, and for an estimate of the total particle volume in the second instance.