Enhancing Photovoltaic Performance Using an All‐Conjugated Random Copolymer to Tailor Bulk and Interfacial Morphology of the P3HT:ICBA Active Layer

Bulk heterojunction (BHJ) solar cells are fabricated using active material blends of poly(3‐hexylthiophene) (P3HT) donor, indene‐C₆₀ bisadduct (ICBA) acceptor, and an all‐conjugated random copolymer (RCP) additive. By optimizing RCP loading, power conversion efficiencies (PCEs) up to 20% higher than those of a binary P3HT:ICBA mixture are achieved. The improved device characteristics are rationalized in terms of the differences between the photoactive thin film morphologies. Energy‐filtered transmission electron micro­scopy reveals that incorporation of the RCP improves the degree of structural order of the BHJ fibrillar network and increases the extent of microphase separation between P3HT and ICBA. Additionally, a combination of atomic force microscopy and X‐ray photoelectron spectroscopy analysis indicates segregation of the RCP at the free interface, leading to a shift in the surface potentials measured by Kelvin probe force microscopy. These changes, both in the bulk morphology and in the interfacial composition/energetics, are correlated to improved carrier collection efficiency due to a reduction of non‐geminate recombination, which is measured by charge extraction of photo­generated carriers by linearly increasing voltage.     

Optimization of bistable viscoelastic systems

We consider the flow of a viscoelastic fluid in a symmetric cross geometry. For small driving pressures the flow is symmetric, but beyond a certain critical pressure the symmetric flow becomes unstable; two stable asymmetric solutions appear, and forcing of the unstable symmetric flow beyond the critical pressure gives rise to increased hydraulic resistance. We have combined a state-of-the-art implementation for viscoelastic flow modeling with topology optimization in a high level finite element package (COMSOL). We use this framework on the cross geometry with the aim to reduce the critical driving pressure corresponding to the point of bistability, such that the effect is enhanced. The point of bistability is, however, not explicitly contained in the solution, so we opt for a heuristic approach based on the dissipation ratio between the asymmetric and unstable symmetric flow solutions. We find a design that significantly reduces the driving pressure required for bistability, and furthermore is in agreement with the approach followed by experimental researchers. Furthermore, by comparing the two asymmetric solutions, we succesfully apply the same approach to a problem with two fluids meeting in the cross.     

Reproducibility of MRI-based white matter tract estimation using multi-fiber probabilistic tractography: effect of user-defined parameters and regions

Objective

There is a pressing need to assess user-dependent reproducibility of multi-fibre probabilistic tractography in order to encourage clinical implementation of these advanced and relevant approaches. The goal of this study was to evaluate both intrinsic and inter-user reproducibility of corticospinal tract estimation.

Materials and methods

Six clinical datasets including motor functional and diffusion MRI were used. Three users performed an independent tractography analysis following identical instructions. Dice indices were calculated to quantify the reproducibility of seed region, fMRI-based end region, and streamline maps.

Results

The inter-user reproducibility ranged 41–93%, 29–94%, and 50–92%, for seed regions, end regions, and streamline maps, respectively. Differences in streamline maps correlated with differences in seed and end regions. Good inter-user agreement in seed and end regions, yielded inter-user reproducibility close to the intrinsic reproducibility (92–97%) and in most cases higher than 80%.

Discussion

Uncertainties related to user-dependent decisions and the probabilistic nature of the analysis should be considered when interpreting probabilistic tractography data. The standardization of the methods used to define seed and end regions is a necessary step to improve the accuracy and robustness of multi-fiber probabilistic tractography in a clinical setting. Clinical users should choose a feasible compromise between reproducibility and analysis duration.

     

Metallocene QACs: The Incorporation of Ferrocene Moieties into monoQAC and bisQAC Structures

Inspired by the incorporation of metallocene functionalities into a variety of bioactive structures, particularly antimicrobial peptides, we endeavored to broaden the structural variety of quaternary ammonium compounds (QACs) by the incorporation of the ferrocene moiety. Accordingly, 23 ferrocene-containing mono- and bisQACs were prepared in high yields and tested for activity against a variety of bacteria, including Gram-negative strains and a panel of clinically isolated MRSA strains. Ferrocene QACs were shown to be effective antiseptics with some displaying single-digit micromolar activity against all bacteria tested, demonstrating yet another step in the expansion of structural variety of antiseptic QACs.     

Holding State Performance Amelioration by Exploitation of NMOS Body Effect in 1T DRAM Cells

In this study curtailing of idle current in 1T1C and 1T1M DRAM cells by increasing threshold voltage during holding state is analyzed. This is attained by connecting the bulk to source in the active phases and pulling it below source potential throughout the holding phase. The proposed technique leads to body effect which affects the threshold voltage improving leakage current. The 1T1C and 1T1M discussed in this paper are volatile and non-volatile (memristor based) respectively. Memory design is fast becoming the pacemaker in the modern technology design which now requires DRAM cells with prolonged holding period and low idle power hence the need for lowering the leakage current. The dynamic nature of the 1T1C is due to charge leakage and the leakage current flowing through the 1T1M cell affects mem-resistance all this leading to state distortion. Idle current has of-late become one of the major contributors of power in large memory arrays in which in-active periods now dominates active period and by this technique idle power is reduced in both volatile and non-volatile cells. The proposed technique was implemented and simulations were done at different voltage levels at 45 nm technology. The method improved the leakage current, holding time and leakage power but at the expense of area and writing power.