Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells

Well‐defined small molecule (SM) donors can be used as alternatives to π‐conjugated polymers in bulk‐heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC₆₁/₇₁BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self‐assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π‐extended backbone of benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin‐films, and (iii) charge transport in BHJ solar cells. In these systems ( SM1‐3 ), it is found that 6,7‐difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2‐b:4,5‐b′]dithiophene (BDT) unit yield a lower‐bandgap analogue ( SM1 ) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. ¹H‐¹H DQ‐SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end‐group SM3 possess distinct self‐assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively).     

Saddle point MPC approach to nonlinear robust sampled-data control problem

This paper presents a robust nonlinear model predictive control strategy to consider the control of systems described by nonlinear ordinary differential equation in a sampled-data framework. The optimal couple controldisturbances is calculated as a time continuous function at each sampling instant by solving a saddle point problem. Using this controller, it is proved that the system is ultimately bounded and satisfies an exponential stability property at each sampling instants. To validate the efficiency of our approach, the presented methodology is illustrated on a cart, spring and damper example.     

An observer looks at the cell temperature in automotive battery packs

The internal temperature of Li-ion batteries for electric or hybrid vehicles is an important factor influencing their ageing. Generally not measured, it can be reconstructed from an external measurement and a model. This paper presents the simplified modelling of heat transfers in a battery module, leading to a Linear Parameter-Varying (LPV) model. Then, a polytopic observer is proposed to estimate the cell temperature and internal resistance, ensuring a tradeoff between the convergence speed and the noise of the estimated states. Experimental results show the good quality of the estimation and the diagnosis potential offered by internal resistance reconstruction.     

Single quantum dot tracking based on perceptual grouping using minimal paths in a spatiotemporal volume.

Semiconductor quantum dots (QDs) are new fluorescent probes with great promise for ultrasensitive biological imaging. When detected at the single-molecule level, QD-tagged molecules can be observed and tracked in the membrane of live cells over unprecedented durations. The motion of these individual molecules, recorded in sequences of fluorescence images, can reveal aspects of the dynamics of cellular processes that remain hidden in conventional ensemble imaging. Due to QD complex optical properties, such as fluorescence intermittency, the quantitative analysis of these sequences is, however, challenging and requires advanced algorithms. We present here a novel approach, which, instead of a frame by frame analysis, is based on perceptual grouping in a spatiotemporal volume. By applying a detection process based on an image fluorescence model, we first obtain an unstructured set of points. Individual molecular trajectories are then considered as minimal paths in a Riemannian metric derived from the fluorescence image stack. These paths are computed with a variant of the fast marching method and few parameters are required. We demonstrate the ability of our algorithm to track intermittent objects both in sequences of synthetic data and in experimental measurements obtained with individual QD-tagged receptors in the membrane of live neurons. While developed for tracking QDs, this method can, however, be used with any fluorescent probes.     

Graph theoretical analysis of structural and functional connectivity MRI in normal and pathological brain networks

Graph theoretical analysis of structural and functional connectivity MRI data (ie. diffusion tractography or cortical volume correlation and resting-state or task-related (effective) fMRI, respectively) has provided new measures of human brain organization in vivo. The most striking discovery is that the whole-brain network exhibits “small-world” properties shared with many other complex systems (social, technological, information, biological). This topology allows a high efficiency at different spatial and temporal scale with a very low wiring and energy cost. Its modular organization also allows for a high level of adaptation. In addition, degree distribution of brain networks demonstrates highly connected hubs that are crucial for the whole-network functioning. Many of these hubs have been identified in regions previously defined as belonging to the default-mode network (potentially explaining the high basal metabolism of this network) and the attentional networks. This could explain the crucial role of these hub regions in physiology (task-related fMRI data) as well as in pathophysiology. Indeed, such topological definition provides a reliable framework for predicting behavioral consequences of focal or multifocal lesions such as stroke, tumors or multiple sclerosis. It also brings new insights into a better understanding of pathophysiology of many neurological or psychiatric diseases affecting specific local or global brain networks such as epilepsy, Alzheimer’s disease or schizophrenia. Graph theoretical analysis of connectivity MRI data provides an outstanding framework to merge anatomical and functional data in order to better understand brain pathologies.     

Optimal prefix and suffix queries on texts

In this paper, we study a restricted version of the position restricted pattern matching problem introduced and studied by Mäkinen and Navarro [V. Mäkinen, G. Navarro, Position-restricted substring searching, in: J.R. Correa, A. Hevia, M.A. Kiwi (Eds.), LATIN, in: Lecture Notes in Computer Science, vol. 3887, Springer, 2006, pp. 703-714]. In the problem handled in this paper, we are interested in those occurrences of the pattern that lies in a suffix or in a prefix of the given text. We achieve optimal query time for our problem against a data structure which is an extension of the classic suffix tree data structure. The time and space complexity of the data structure is dominated by that of the suffix tree. Notably, the (best) algorithm by Mäkinen and Navarro, if applied to our problem, gives sub-optimal query time and the corresponding data structure also requires more time and space.     

Charge Density Wave and Superconducting Properties in Single Crystals of Lu5Ir4Si10

We measured the electrical resistivity from 2 K up to 900 K on high quality single crystals of Lu₅Ir₄Si₁₀. A clear thermal hysteresis was found at the onset of the Charge Density Wave (CDW), evidencing the first-order nature of the transition. When tantalum is included in the compound, the CDW is destroyed and the superconducting critical temperature is enhanced. Finally, we present specific heat and magnetic penetration depth in the Meissner state. We show that the superconducting properties are very close to a weak coupling BCS superconductor.     

Grid-free interactive and automated data processing for MR chemical shift imaging data

Purpose  

Today’s available chemical shift imaging (CSI) analysis tools are based on Fourier transform of the entire data set prior to interactive display. This strategy is associated with limitations particularly when arbitrary voxel positions within a 3D spatial volume are needed by the user. In this work, we propose and demonstrate a processing-resource-efficient alternative strategy for both interactive and automated CSI data processing up to three spatial dimensions.     

White-light ellipsometer with geometric phase shifter

We describe a simple spectroscopic ellipsometer that uses a geometric phase shifter and a white-light source to generate a small number of phase-stepped intensities I(λ), which are recorded by a spectrometer. The ellipsometric angles ψ and Δ are easily calculated from these intensities at each wavelength simultaneously. We show that errors in Δ due to the nonideal behavior of the achromatic quarter-wave plate in the phase shifter can be made small by suitably adjusting the azimuth of the linearly polarized light incident on the sample. Two silicon dioxide films were measured with this instrument between 450 and 850?nm and yielded best fit film thicknesses of 1000.6±0.1 ? and 20.6±0.1 ?, in excellent agreement with those obtained using a commercial ellipsometer.     

Embedded Doppler system for industrial in-line rheometry

Rheological fluid behavior characterization is crucial for the industrial production of cosmetics, food, pharmaceutics, adhesive, sealants, etc. For example, the measurement of specific rheological features at every step of the production chain is critical for product quality control. Such measurements are often limited to laboratory tests on product specimens because of technical difficulties. In this work, we present an embedded system suitable for in-line rheometric evaluation of highly filled polyurethane-based adhesives. This system includes an ultrasound front-end and a digital signal processing section integrated in a low-cost field-programmable gate array. The system measures the real-time velocity profile developed in the pipe by the fluid, employing a Doppler multigate technique. The high-resolution velocity profile, combined with a pressure drop measurement, allows an accurate evaluation of the flow consistency index, K, and the flow behavior index, n, of the interrogated fluid.