Comment on "Interface state recombination in organic solar cells"

In a recent paper, Street et al. [Phys. Rev. B 81, 205307 (2010)] propose first order recombination due to interface states to be the dominant loss mechanism in organic bulk heterojunction solar cells, based on steady-state current--voltage characteristics. By applying macroscopic simulations, we found that under typical solar cell conditions, monomolecular or bimolecular recombination cannot be inferred from the slope of the light intensity dependent photocurrent. In addition, we discuss the validity of calculating a mobility--lifetime product from steady-state measurements. We conclude that the experimental technique applied by Street et al. is not sufficient to unambiguously determine the loss mechanism.Comment: 4 pages, 2 figures. Corrected Eqns. (2) and (4): 1/... was missin

Exploring neutralino dark matter resonance annihilation via bA,bH -> b mu^+ mu^- at the LHC

One of the main channels which allows for a large rate of neutralino dark matter annihilation in the early Universe is via the pseudoscalar Higgs A-resonance. In this case, the measured dark matter abundance can be obtained in the minimal supergravity (mSUGRA) model when tan(beta)\sim 50 and 2m_{\tz_1}\sim m_A. We investigate the reaction pp\to b\phi\to b\mu^+\mu^- +X (where \phi =A or H) at the CERN LHC where requiring the tag of a single b-jet allows for amplification of the signal-to-background ratio. The rare but observable Higgs decay to muon pairs allows for a precise measurement of the Higgs boson mass and decay width. We evaluate signal and background using CalcHEP, with muon energy smearing according to the CMS detector. We find that the Higgs width (\Gamma_A) can typically be determined with the accuracy up to \sim 8% (\sim 17%) for m_A\sim 400 (600) GeV assuming 10^3 fb^{-1} of integrated luminosity. Therefore, the pp\to b\phi\to b\mu^+\mu^- +X process provides a unique possibility for direct \Gamma_A measurement at the LHC. While the Higgs width is correlated with the parameter \tan\beta for a given value of m_A, extracting \tan\beta is complicated by an overlap of the A and H peaks, radiative corrections to the b and \tau Yukawa couplings, and the possibility that SUSY decay modes of the Higgs may be open. In the case where a dilepton mass edge from \tz_2\to\ell^+\ell^-\tz_1 is visible, it should be possible to test the relation that 2m_{\tz_1}\sim m_A.Comment: 19 pages with 25 .eps figure

Spatial Mechanical Behaviour of Skin

PhDSkin is a complex biological composite system that serves as the outermost barrier to the environment and is mechanically robust. Understanding the mechanical properties of skin is important to improve and compare current in vitro experiments to the physiological conditions as the mechanical properties have a crucial role in determining cell behaviour. The mechanical behaviour of skin at the cellular level is expected to be dominated by the collagen fibre network within the dermis, which displays an anisotropic mechanical response to macroscopic loading. However, the three dimensional mechanical properties of skin at the nanoscale are not well understood. The aim of this work is to examine the mechanical properties of skin at the nanoscale in three dimensions and explore the links between the nanoscale and the macroscopic behaviour. Multiple sample preparation techniques are employed to expose the different layers of skin for mechanical testing and the elastic modulus of skin is evaluated by using atomic force microscopy (AFM) nanoindentation. The effect of freezing skin to cryogenic temperatures on the mechanical properties is evaluated and found to have no impact on the mechanical response of skin, indicating that the composition and structure of skin are robust enough to withstand the cryosectioning sample preparation methods used to expose the transverse layers of skin. AFM indentation was used to evaluate the elastic modulus of the dermis depending on the orientation of the sample and found to have an isotropic mechanical response. This result is opposite to anisotropy observed in macroscopic skin due to small scale mechanical testing ignoring collagen fibril orientation during strain. The variations in the elastic modulus of skin are also evaluated by AFM indentation at high spatial resolution to construct a composite model of the mechanical behaviour of skin at the nanoscale to predict the macroscopic response. The AFM nanoindentation technique was extended to evaluate the mechanical properties of a cell derived matrix deposited on an electrospun nanofibre scaffold, where the results indicate increasing the nanofibre diameter produces a cell derived matrix with an increased elastic modulus for more effective scaffolds. This work highlights the use of AFM mechanical testing to evaluate the nanoscale mechanical behaviour of skin, treated as a composite biological system, and determine the influence of the length scale and sample orientation on the observed mechanical response.Queen Mary, University of Londo

PULL: Reactive Log Anomaly Detection Based On Iterative PU Learning

Due to the complexity of modern IT services, failures can be manifold, occur at any stage, and are hard to detect. For this reason, anomaly detection applied to monitoring data such as logs allows gaining relevant insights to improve IT services steadily and eradicate failures. However, existing anomaly detection methods that provide high accuracy often rely on labeled training data, which are time-consuming to obtain in practice. Therefore, we propose PULL, an iterative log analysis method for reactive anomaly detection based on estimated failure time windows provided by monitoring systems instead of labeled data. Our attention-based model uses a novel objective function for weak supervision deep learning that accounts for imbalanced data and applies an iterative learning strategy for positive and unknown samples (PU learning) to identify anomalous logs. Our evaluation shows that PULL consistently outperforms ten benchmark baselines across three different datasets and detects anomalous log messages with an F1-score of more than 0.99 even within imprecise failure time windows

CryoEM structure of the human SLC4A4 sodium-coupled acid-base transporter NBCe1.

Na+-coupled acid-base transporters play essential roles in human biology. Their dysfunction has been linked to cancer, heart, and brain disease. High-resolution structures of mammalian Na+-coupled acid-base transporters are not available. The sodium-bicarbonate cotransporter NBCe1 functions in multiple organs and its mutations cause blindness, abnormal growth and blood chemistry, migraines, and impaired cognitive function. Here, we have determined the structure of the membrane domain dimer of human NBCe1 at 3.9 Å resolution by cryo electron microscopy. Our atomic model and functional mutagenesis revealed the ion accessibility pathway and the ion coordination site, the latter containing residues involved in human disease-causing mutations. We identified a small number of residues within the ion coordination site whose modification transformed NBCe1 into an anion exchanger. Our data suggest that symporters and exchangers utilize comparable transport machinery and that subtle differences in their substrate-binding regions have very significant effects on their transport mode

Fluorescent silica manoparticles with well-separated intensity distributions from batch reactions

Silica chemistry provides pathways to uniquely tunable nanoparticle platforms for biological imaging. It has been a long-standing problem to synthesize fluorescent silica nanoparticles (SNPs) in batch reactions with high and low fluorescence intensity levels for reliable use as an intensity barcode, which would greatly increase the number of molecular species that could be tagged intracellularly and simultaneously observed in conventional fluorescence microscopy. Here, employing an amino-acid catalyzed growth, highly fluorescent SNP probes were synthesized with sizes <40 nm and well-separated intensity distributions, as mapped by single-particle imaging techniques. A seeded growth approach was used to minimize the rate of secondary particle formation. Organic fluorescent dye affinity for the SNP during shell growth was tuned using specifics of the organosilane linker chemistry. This work highlights design considerations in the development of fluorescent probes with well-separated intensity distributions synthesized in batch reactions for single-particle imaging and sensing applications, where heterogeneities across the nanoparticle ensemble are critical factors in probe performance