A walk in the PARC: developing and implementing 21st century chemical risk assessment in Europe

Current approaches for the assessment of environmental and human health risks due to exposure to chemical substances have served their purpose reasonably well. Nevertheless, the systems in place for different uses of chemicals are faced with various challenges, ranging from a growing number of chemicals to changes in the types of chemicals and materials produced. This has triggered global awareness of the need for a paradigm shift, which in turn has led to the publication of new concepts for chemical risk assessment and explorations of how to translate these concepts into pragmatic approaches. As a result, next-generation risk assessment (NGRA) is generally seen as the way forward. However, incorporating new scientific insights and innovative approaches into hazard and exposure assessments in such a way that regulatory needs are adequately met has appeared to be challenging. The European Partnership for the Assessment of Risks from Chemicals (PARC) has been designed to address various challenges associated with innovating chemical risk assessment. Its overall goal is to consolidate and strengthen the European research and innovation capacity for chemical risk assessment to protect human health and the environment. With around 200 participating organisations from all over Europe, including three European agencies, and a total budget of over 400 million euro, PARC is one of the largest projects of its kind. It has a duration of seven years and is coordinated by ANSES, the French Agency for Food, Environmental and Occupational Health & Safety.

Topological modes in a laser cavity through exceptional state transfer

Shaping the light emission characteristics of laser systems is of great importance in various areas of science and technology. In a typical lasing arrangement, the transverse spatial profile of a laser mode tends to remain self-similar throughout the entire cavity. Going beyond this paradigm, we demonstrate here how to shape a spatially evolving mode such that it faithfully settles into a pair of bi-orthogonal states at the two opposing facets of a laser cavity. This was achieved by purposely designing a structure that allows the lasing mode to encircle a non-Hermitian exceptional point while deliberately avoiding non-adiabatic jumps. The resulting state transfer reflects the unique topology of the associated Riemann surfaces associated with this singularity. Our approach provides a route to developing versatile mode-selective active devices and sheds light on the interesting topological features of exceptional points.

All-optical adaptive control of quantum cascade random lasers

Spectral fingerprints of molecules are mostly accessible in the terahertz (THz) and mid-infrared ranges, such that efficient molecular-detection technologies rely on broadband coherent light sources at such frequencies. If THz Quantum Cascade Lasers can achieve octave-spanning bandwidth, their tunability and wavelength selectivity are often constrained by the geometry of their cavity. Here we introduce an adaptive control scheme for the generation of THz light in Quantum Cascade Random Lasers, whose emission spectra are reshaped by applying an optical field that restructures the permittivity of the active medium. Using a spatial light modulator combined with an optimization procedure, a beam in the near infrared (NIR) is spatially patterned to transform an initially multi-mode THz random laser into a tunable single-mode source. Moreover, we show that local NIR illumination can be used to spatially sense complex near-field interactions amongst modes. Our approach provides access to new degrees of freedom that can be harnessed to create broadly-tunable sources with interesting potential for applications like self-referenced spectroscopy.

Tunable quantum cascade lasers can enable applications in multiple areas. Here, the authors demonstrate the adaptive control of the modes and emission spectra of quantum cascade random lasers through a spatially-tailored optical modulation of the active region.

Coherent Coupling of Remote Spin Ensembles via a Cavity Bus

We report coherent coupling between two macroscopically separated nitrogen-vacancy electron spin ensembles in a cavity quantum electrodynamics system. The coherent interaction between the distant ensembles is directly detected in the cavity transmission spectrum by observing bright and dark collective multiensemble states and an increase of the coupling strength to the cavity mode. Additionally, in the dispersive limit we show transverse ensemble-ensemble coupling via virtual photons.

Gravity resonance spectroscopy constrains dark energy and dark matter scenarios

We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14  eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant β>5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of λ=20  μm (95% C.L.).

The single-channel regime of transport through random media

The propagation of light through samples with random inhomogeneities can be described by way of transmission eigenchannels, which connect incoming and outgoing external propagating modes. Although the detailed structure of a disordered sample can generally not be fully specified, these transmission eigenchannels can nonetheless be successfully controlled and used for focusing and imaging light through random media. Here we demonstrate that in deeply localized quasi-1D systems, the single dominant transmission eigenchannel is formed by an individual Anderson-localized mode or by a 'necklace state'. In this single-channel regime, the disordered sample can be treated as an effective 1D system with a renormalized localization length, coupled through all the external modes to its surroundings. Using statistical criteria of the single-channel regime and pulsed excitations of the disordered samples allows us to identify long-lived localized modes and short-lived necklace states at long and short time delays, respectively.

Vectorial velocity filter for ultracold neutrons based on a surface-disordered mirror system

We perform classical three-dimensional Monte Carlo simulations of ultracold neutrons scattering through an absorbing-reflecting mirror system in the Earth's gravitational field. We show that the underlying mixed phase space of regular skipping motion and random motion due to disorder scattering can be exploited to realize a vectorial velocity filter for ultracold neutrons. The absorbing-reflecting mirror system proposed allows beams of ultracold neutrons with low angular divergence to be formed. The range of velocity components can be controlled by adjusting the geometric parameters of the system. First experimental tests of its performance are presented. One potential future application is the investigation of transport and scattering dynamics in confined systems downstream of the filter.

Pump-induced exceptional points in lasers

We demonstrate that the above-threshold behavior of a laser can be strongly affected by exceptional points which are induced by pumping the laser nonuniformly. At these singularities, the eigenstates of the non-Hermitian operator which describes the lasing modes coalesce. In their vicinity, the laser may turn off even when the overall pump power deposited in the system is increased. Such signatures of a pump-induced exceptional point can be experimentally probed with coupled ridge or microdisk lasers.

Cavity QED with magnetically coupled collective spin states

We report strong coupling between an ensemble of nitrogen-vacancy center electron spins in diamond and a superconducting microwave coplanar waveguide resonator. The characteristic scaling of the collective coupling strength with the square root of the number of emitters is observed directly. Additionally, we measure hyperfine coupling to (13)C nuclear spins, which is a first step towards a nuclear ensemble quantum memory. Using the dispersive shift of the cavity resonance frequency, we measure the relaxation time of the NV center at millikelvin temperatures in a nondestructive way.

Nanowires with surface disorder: giant localization lengths and quantum-to-classical crossover

We investigate electronic quantum transport through nanowires with one-sided surface roughness. A magnetic field perpendicular to the scattering region is shown to lead to exponentially diverging localization lengths in the quantum-to-classical crossover regime. This effect can be quantitatively accounted for by tunneling between the regular and the chaotic components of the underlying mixed classical phase space.

Tunable Fano resonances in transport through microwave billiards

We present a tunable microwave scattering device that allows the controlled variation of Fano line shape parameters in transmission through quantum billiards. Transport in this device is nearly fully coherent. By comparison with quantum calculations, employing the modular recursive Green's-function method, the scattering wave function and the degree of residual decoherence can be determined. The parametric variation of Fano line shapes in terms of interacting resonances is analyzed.

Analysis of higher-order neuronal interactions based on conditional inference

Higher-order neural interactions, i.e., interactions that cannot be reduced to interactions between pairs of cells, have received increasing attention in the context of recent attempts to understand the cooperative dynamics in cortical neural networks. Typically, likelihood-ratio tests of log-linear models are being employed for statistical inference. The parameter estimation of these models for simultaneously recorded single-neuron spiking activities is a crucial ingredient of this approach. Extending a previous investigation of a two-neuron system, we present here the general formulation of an exact test suited for the detection of positive higher-order interactions between m neurons. This procedure does not require the estimation of any interaction parameters and additionally optimizes the test power of the statistical inference. We apply the approach to a three-neuron system and show how second-order and third-order interactions can be reliably distinguished. We study the performance of the method as a function of the interaction strength.

Learning input correlations through nonlinear temporally asymmetric Hebbian plasticity

Triggered by recent experimental results, temporally asymmetric Hebbian (TAH) plasticity is considered as a candidate model for the biological implementation of competitive synaptic learning, a key concept for the experience-based development of cortical circuitry. However, because of the well known positive feedback instability of correlation-based plasticity, the stability of the resulting learning process has remained a central problem. Plagued by either a runaway of the synaptic efficacies or a greatly reduced sensitivity to input correlations, the learning performance of current models is limited. Here we introduce a novel generalized nonlinear TAH learning rule that allows a balance between stability and sensitivity of learning. Using this rule, we study the capacity of the system to learn patterns of correlations between afferent spike trains. Specifically, we address the question of under which conditions learning induces spontaneous symmetry breaking and leads to inhomogeneous synaptic distributions that capture the structure of the input correlations. To study the efficiency of learning temporal relationships between afferent spike trains through TAH plasticity, we introduce a novel sensitivity measure that quantifies the amount of information about the correlation structure in the input, a learning rule capable of storing in the synaptic weights. We demonstrate that by adjusting the weight dependence of the synaptic changes in TAH plasticity, it is possible to enhance the synaptic representation of temporal input correlations while maintaining the system in a stable learning regime. Indeed, for a given distribution of inputs, the learning efficiency can be optimized.

MEA-Tools: an open source toolbox for the analysis of multi-electrode data with MATLAB

Recent advances in electrophysiological techniques have created new tools for the acquisition and storage of neuronal activity recorded simultaneously with numerous electrodes. These techniques support the analysis of the function as well as the structure of individual electrogenic cells in the context of surrounding neuronal or cardiac network. Commercially available tools for the analysis of such data, however, cannot be easily adapted to newly emerging requirements for data analysis and visualization, and cross compatibility between them is limited. In this report we introduce a free open source toolbox called microelectrode array tools (MEA-Tools) for the analysis of multi-electrode data based on the common data analysis environment MATLAB (version 5.3-6.1, The Mathworks, Natick, MA). The toolbox itself is platform independent. The file interface currently supports files recorded with MCRack (Multi Channel Systems, Reutlingen, Germany) under Microsoft Windows 95, 98, NT, and 2000, but can be adapted to other data acquisition systems. Functions are controlled via command line input and graphical user interfaces, and support common requirements for the analysis of local field potentials, extracellular spike activity, and continuous recordings, in addition to supplementary data acquired by additional instruments, e.g. intracellular amplifiers. Data may be processed as continuous recordings or time windows triggered to some event.

Neural dynamics in cortical networks--precision of joint-spiking events

Electrophysiological studies of cortical function on the basis of multiple single-neuron recordings reveal neuronal interactions which depend on stimulus context and behavioural events. These interactions exhibit dynamics on different time scales, with time constants down to the millisecond range. Mechanisms underlying such dynamic organization of the cortical network were investigated by experimental and theoretical approaches. We review some recent results from these studies, concentrating on the occurrence of precise joint-spiking events in cortical activity, both in physiological and in model neural networks. These findings suggest that a combinatorial neural code, based on rapid associations of groups of neurons co-ordinating their activity at the single spike level, is biologically feasible.

Single-trial estimation of neuronal firing rates: from single-neuron spike trains to population activity

We present a method to estimate the neuronal firing rate from single-trial spike trains. The method, based on convolution of the spike train with a fixed kernel function, is calibrated by means of simulated spike trains for a representative selection of realistic dynamic rate functions. We derive rules for the optimized use and performance of the kernel method, specifically with respect to an effective choice of the shape and width of the kernel functions. An application of our technique to the on-line, single-trial reconstruction of arm movement trajectories from multiple single-unit spike trains using dynamic population vectors illustrates a possible use of the proposed method.

Exact digital simulation of time-invariant linear systems with applications to neuronal modeling

An efficient new method for the exact digital simulation of time-invariant linear systems is presented. Such systems are frequently encountered as models for neuronal systems, or as submodules of such systems. The matrix exponential is used to construct a matrix iteration, which propagates the dynamic state of the system step by step on a regular time grid. A large and general class of dynamic inputs to the system, including trains of delta-pulses, can be incorporated into the exact simulation scheme. An extension of the proposed scheme presents an attractive alternative for the approximate simulation of networks of integrate-and-fire neurons with linear sub-threshold integration and non-linear spike generation. The performance of the proposed method is analyzed in comparison with a number of multi-purpose solvers. In simulations of integrate-and-fire neurons, Exact Integration systematically generates the smallest error with respect to both sub-threshold dynamics and spike timing. For the simulation of systems where precise spike timing is important, this results in a practical advantage in particular at moderate integration step sizes.

Accurate spike synchronization in cortex

In view of the enormous capacity and complexity of mammalian brains it is evident that a detailed account of their anatomy and physiology alone cannot lead to a complete understanding of their function. Computer simulation and mathematical analysis of abstract, yet biologically realistic models for neurons and networks yield additional and useful information about the interplay of the underlying anatomical structures, the physiological processes operating on the neuronal substrate, and the resulting brain functions during the performance of behavioral tasks. We discuss some contributions of such experiment-guided theory to the issue of accurate spike synchronization.

Electrophoretic separation of multiprotein complexes from blood platelets and cell lines: technique for the analysis of diseases with defects in oxidative phosphorylation

A two-dimensional electrophoretic technique combining blue native polyacrylamide gel electrophoresis (BN-PAGE) with Tricine sodium dodecyl sulfate (SDS)-PAGE was previously used for the localization of oxidative phosphorylation (OXPHOS) defects in human diseases starting from biopsy or autopsy tissues (Schägger, H., Electrophoresis 1995, 16, 763-770). In the present work the technique was extended for the resolution of OXPHOS enzymes from platelets and tissue-cultured cells. Silver staining is required to detect the protein subunits of OXPHOS complexes in two-dimensional gels. However, the use of cultured cells has major implications for patients with mitochondrial encephalomyopathies since it will reduce the number of invasive muscle biopsies. The ease of isolating the platelet membrane glycoprotein complex from a few milliliters of blood makes it possible to analyze this complex and its protein subunits in bleeding disorders like Glanzmann's thrombasthenia.

Connectional topography in the zebrafish olfactory system: random positions but regular spacing of sensory neurons projecting to an individual glomerulus

It is unknown how neuronal connections are specified in the olfactory system. To define rules of connectivity in this system, we investigated whether the projection of sensory neurons from the olfactory epithelium to the olfactory bulb is topographically ordered. By backtracking with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), we find that neurons projecting into a single identified glomerulus are widely dispersed over the olfactory epithelium. Their positions in the sensory surface do not predict their glomerulus specificity and are probably random. A statistical analysis reveals that neurons connected to the same glomerulus are spaced at distances of several cell diameters from each other. The convergence of projections to one point in the target area from neurons that are widely and evenly distributed in the sensory surface constitutes an unusual type of connectional topography that contrasts with the precise topological (neighborhood-preserving) maps found in other sensory systems. It may maximize the probability to detect odorants that activate a single glomerular unit.

Autografting and PUVA. A combination therapy for vitiligo

A novel approach to the management of vitiligo is described using a combination of epidermal autografts transplanted into the depigmented areas and psoralen-ultraviolet-A (PUVA) therapy. Epidermal autografts can be obtained rapidly and in large numbers using a device that combines the synergistic effects of suction and heat on the skin. Subsequent exposure to PUVA therapy promotes spread of pigmentation out of the grafts resulting in even and complete pigmentation. In certain situations, the combination therapy appears to offer the potential for avoiding the disadvantages of both of the two treatments when they are used alone. This article presents our preliminary work in the development of the methodology for this combined approach.

The use of tissue expanders in immediate breast reconstruction following mastectomy for cancer

From April 1985 to March 1987, 50 women had 56 mastectomies for documented cancer. A tissue expander was used for immediate reconstruction in each case. The patient records were used to determine morbidity and mortality, as well as to examine the effect of reconstruction on adjuvant therapy, cancer surveillance, adequacy of cancer surgery and patient satisfaction. The patients were followed up for an average of 13 months. Fifty-two of 56 expanders were successfully replaced with a permanent prosthesis. Forty-seven women remain alive. Local or regional recurrence did not occur in any women within the study period. Complications, of which superficial skin necrosis was most common, occurred in 35% of reconstructions and were investigated critically. Patient satisfaction was high. Dissatisfaction was not related to the incidence of complications but rather appeared to reflect the success of the patient's cancer treatment.