The Integrative Approach to Study of the Structure and Functions of Cardiac Voltage-Dependent Ion Channels

Crystallography Reports - Membrane proteins, including ion channels, became the focus of structural proteomics midway through the 20th century. Methods for studying ion channels are diverse and...     

Investigation of fill factor losses on 20.2% efficient n‐type mono‐like silicon solar cells with laser contact opening

Large area (243.36 cm²) back‐junction passivated emitter, rear totally diffused (PERT) solar cells with laser contact opening (LCO) on n‐type mono‐like crystalline Si with efficiencies of 20.2% are presented. Boron emitters with high electrical quality (implied open circuit voltage iV_OC up to 700 mV) are formed during a co‐diffusion step using SiO_x:B layers. Increasing the rear metal contact coverage, we observed a decrease in fill factor (FF) instead of the expected increase due to the decrease of the back side series resistance. We show that it can be attributed to recombination centers (RCs) in the space charge region underneath the contact spots inducing an increasing second diode contribution. The presented empirical model for the RCs implemented in Synopsys Sentaurus TCAD allows for a successful reproduction of the FF, pseudo FF and V_OC behaviour with contact coverage. According to this model, the RCs induced by laser ablation and subsequently evaporation of Al have a shallow exponential distribution with a characteristic length of L_T = 0.2 µm and an effective surface density of N *_T0 = 25 cm^–1. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Spatial and temporal resolution effects on dynamic contrast-enhanced magnetic resonance mammography

We tested the hypothesis that partial volume effects due to poor in-plane resolution and/or low temporal resolution used in clinical dynamic contrast-enhanced magnetic resonance imaging results in erroneous diagnostic information based on inaccurate estimates of tumor contrast agent extravasation and tested whether reduced encoding techniques can correct for dynamic data volume averaging. Image spatial resolution was reduced from 469 x 469 microm2 to those reported below by selecting a subset of k-space data. We then compared the top five K(trans)/V(T) "hot spots" obtained from the original data set, 469 x 469-microm in-plane spatial resolution and an 18-s temporal resolution processed by fast Fourier transform (FFT), with values obtained from data sets having in-plane spatial resolutions of 938 x 938, 1875 x 1875 and 2500 x 2500 microm2 and a temporal resolution of 18 s, or data sets with temporal resolutions of 36, 54 and 72 and a spatial resolution of 469 x 469 microm2, and found them to statistically differ from the parent data sets. We then tested four different post processing methods for improving the spatial resolution without sacrificing temporal resolution: zero-filled FFT, keyhole, reduced-encoding imaging by generalized-series reconstruction (RIGR) and two-reference RIGR (TRIGR). The top five values of K(trans)/V(T) obtained from data sets, the in-plane spatial resolutions of which were improved to 469 x 469 microm2 by zero-filling FFT, Keyhole and RIGR, statistically differed from those obtained from the original 469 x 469 microm2 FFT parent image data set. Only the 938 x 938 and 1875 x 1875 microm2 data sets reconstructed to 469 x 469 microm2 with TRIGR reconstruction method yielded values of the top five K(trans)/V(T) hot spots statistically the same as the original parent data set, 469 x 469 microm2 in-plane spatial and 18-s temporal-resolution FFT. That is, partial volume effects from data sets of different in-plane spatial resolution resulted in statistically different values of the top five K(trans)/V(T) hot spots relative to a high spatial and temporal resolution data set, and TRIGR reconstruction of these low resolution data sets to high resolution images provided statistically similar values with a savings in temporal resolution of 2 to 4 times.     

Large Porphyrin Squares from the Self‐Assembly of meso‐Triazole‐Appended L‐Shaped meso–meso‐Linked ZnII–Triporphyrins: Synthesis and Efficient Energy Transfer

meso‐Triazolyl‐appended Zn^II–porphyrins were readily prepared by Cu^I‐catalyzed 1,3‐dipolar cycloaddition of benzyl azide to meso‐ethynylated Zn^II–porphyrin (click chemistry). In noncoordinating CHCl₃ solvent, spontaneous assembly occurred to form tetrameric array ( 3 )₂ from meso–meso‐linked diporphyrins 3 , and dodecameric porphyrin squares ( 4 )₄ and ( 5 )₄ from the L ‐shaped meso–meso‐linked triporphyrins 4 and 5 . The structures of these assemblies were examined by ¹H NMR spectra, absorption spectra, and their gel permeation chromatography (GPC) retention time. Furthermore, the structures of the dodecameric porphyrin squares ( 4 )₄ and ( 5 )₄ were probed by small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) measurements in solution using a synchrotron source. Excitation‐energy migration processes in these assemblies were also investigated in detail by using both steady‐state and time‐resolved spectroscopic methods, which revealed efficient excited‐energy transfer (EET) between the meso–meso‐linked Zn^II–porphyrin units that occurred with time constants of 1.5 ps^?1 for ( 3 )₂ and 8.8 ps^?1 for ( 5 )₄.     

Queues in tandem with customer deadlines and retrials

We study queues in tandem with customer deadlines and retrials. We first consider a 2-queue Markovian system with blocking at the second queue, analyze it, and derive its stability condition. We then study a non-Markovian setting and derive the stability condition for an approximating diffusion, showing its similarity to the former condition. In the Markovian setting, we use probability generating functions and matrix analytic techniques. In the diffusion setting, we consider expectations of the first hitting times of compact sets.     

Spectroscopic and DFT investigation of [M{HB(3,5-iPr2pz)3}(SC6F5)] (M = Mn, Fe, Co, Ni, Cu, and Zn) model complexes: periodic trends in metal-thiolate bonding

A series of metal-varied [ML(SC6F5)] model complexes (where L = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate and M = Mn, Fe, Co, Ni, Cu, and Zn) related to blue copper proteins has been studied by a combination of absorption, MCD, resonance Raman, and S K-edge X-ray absorption spectroscopies. Density functional calculations have been used to characterize these complexes and calculate their spectra. The observed variations in geometry, spectra, and bond energies are interpreted in terms of changes in the nature of metal-ligand bonding interactions. The metal 3d-ligand orbital interaction, which contributes to covalent bonding in these complexes, becomes stronger going from Mn(II) to Co(II) (the sigma contribution) and to Cu(II) (the pi contribution). This change in the covalency results from the increased effective nuclear charge of the metal atom in going from Mn(II) to Zn(II) and the change in the 3d orbital populations (d5-->d10). Ionic bonding also plays an important role in determining the overall strength of the ML(+)-SC6F5(-) interaction. However, there is a compensating effect: as the covalent contribution to the metal-ligand bonding increases, the ionic contribution decreases. These results provide insight into the Irving-Williams series, where it is found that the bonding of the ligand being replaced by the thiolate makes a major contribution to the observed order of the stability constants over the series of metal ions.     

Decoding neural events from fMRI BOLD signal: A comparison of existing approaches and development of a new algorithm

Neuroimaging methodology predominantly relies on the blood oxygenation level dependent (BOLD) signal. While the BOLD signal is a valid measure of neuronal activity, variances in fluctuations of the BOLD signal are not only due to fluctuations in neural activity. Thus, a remaining problem in neuroimaging analyses is developing methods that ensure specific inferences about neural activity that are not confounded by unrelated sources of noise in the BOLD signal. Here, we develop and test a new algorithm for performing semiblind (i.e., no knowledge of stimulus timings) deconvolution of the BOLD signal that treats the neural event as an observable, but intermediate, probabilistic representation of the system's state. We test and compare this new algorithm against three other recent deconvolution algorithms under varied levels of autocorrelated and Gaussian noise, hemodynamic response function (HRF) misspecification and observation sampling rate. Further, we compare the algorithms' performance using two models to simulate BOLD data: a convolution of neural events with a known (or misspecified) HRF versus a biophysically accurate balloon model of hemodynamics. We also examine the algorithms' performance on real task data. The results demonstrated good performance of all algorithms, though the new algorithm generally outperformed the others (3.0% improvement) under simulated resting-state experimental conditions exhibiting multiple, realistic confounding factors (as well as 10.3% improvement on a real Stroop task). The simulations also demonstrate that the greatest negative influence on deconvolution accuracy is observation sampling rate. Practical and theoretical implications of these results for improving inferences about neural activity from fMRI BOLD signal are discussed.     

The Metaphosphite (PO2−) Anion as a Ligand

The utilization of monomeric, lower phosphorous oxides and oxoanions, such as metaphosphite (PO₂⁻), which is the heavier homologue of the common nitrite anion but previously only observed in the gas phase and by matrix isolation, requires new synthetic strategies. Herein, a series of rhenium(I–III) complexes with PO₂⁻ as ligand is reported. Synthetic access was enabled by selective oxygenation of a terminal phosphide complex. Spectroscopic and computational examination revealed slightly stronger σ-donor and comparable π-acceptor properties of PO₂⁻ compared to homologous NO₂⁻, which is one of the archetypal ligands in coordination chemistry.     

A Note On Subloop Lattices

Pálfy and Pudlák (Algebra Universalis 11, 22–27, 1980) posed the question: is every finite lattice isomorphic to an interval sublattice of the lattice of subgroups of a finite group? in this paper we will look at examples of lattices that can be realized as subloop lattices but not as subgroup lattices. This is a first step in answering a new question: is every finite lattice isomorphic to an interval sublattice of the subloop lattice of a finite loop?     

Photochemical and discharge-driven pathways to aromatic products from 1,3-butadiene

A detailed study of the photochemical and discharge-driven pathways taken by gas-phase 1,3-butadiene has been carried out. Photolysis or discharge excitation was initiated inside a short reaction tube attached to the outlet of a pulsed valve. Bath gas temperatures near 100 K were achieved in the reaction tube by the constrained expansion of the gas mixture into the tube, simulating temperatures of relevance in Titan's atmosphere. Photolysis of 1,3-butadiene was initiated at 218 nm with a laser pulse that counter-propagated the reaction tube. Discharge excitation was carried out using discharge electrodes imbedded in the reaction tube walls, enabling the study of the photochemical and discharge products under similar conditions. Products were detected using either single-photon VUV photoionization (118 nm = 10.5 eV) or resonant two-photon ionization (R(2)PI) spectroscopy in a time-of-flight mass spectrometer. Emphasis was placed on characterization of the aromatic products formed, since these may be of particular relevance to Titan's atmosphere, where benzene has been positively identified and 1,3-butadiene is projected as the principle pathway to its formation. Consistent with previous studies of the photodissociation of 1,3-butadiene, C(3)H(3) + CH(3) is the dominant primary product formed. Under the temperature-pressure conditions present in the reaction tube (T approximately 75-100 K, P = 50 mbar), C(6)H(6) is the dominant secondary photochemical product formed. A 1:1 C(4)H(6):C(4)D(6) mixture was used to prove that the C(6)H(6) product was formed by recombination of two C(3)H(3) radicals; however, a careful search for benzene revealed none, indicating that less than 1% of the C(6)H(6) formed in the reaction tube is benzene. This is consistent with expectations for these temperatures and pressures based on previous modeling of propargyl recombination. Two aromatic products were observed from the photochemistry: ethylbenzene and 3-phenylpropyne. Plausible pathways leading to these products are proposed. In the discharge, C(3)H(3) + CH(3) are also identified as significant primary neutral products and C(6)H(6) as a dominant higher-mass product. In this case, the C(6)H(6) was identified as benzene via its R2PI spectrum, appearing with intensity about 10 times larger than any other aromatic formed in the discharge. R2PI spectra of a total of about 15 aromatic products were recorded from the 1,3-butadiene discharge, among them toluene; styrene; phenylacetylene; o-, m-, and p-xylene; ethylbenzene; indane; indene; beta-methylstyrene; and naphthalene. Previously unidentified spectra in the m/z 142 and 144 mass channels were positively identified as the 1,3- and 1,4-isomers of phenylcyclopentadiene and the analogous 1-phenylcyclopentene.