Purification and characterization of an endopeptidase from Lactobacillus delbrueckii subsp. bulgaricus B14

An intracellular endopeptidase was purified from cell-free extracts of Lactobacillus delbrueckii subsp. bulgaricus B14 by anion exchange chromatography on DEAE-Sepharose, hydroxyapatite chromatography, second anion exchange chromatography on Mono-Q, and metal-chelating affinity chromatography. The endopeptidase was a monomer with a molecular mass of approximately 70 kDa determined by SDS-PAGE and gel filtration. Various oligopeptides (e.g. Met-enkephalin, bradykinin) were hydrolysed by the endopeptidase. Exopeptidase activity and cleavage of dipeptides or tripeptides was not observed. The K_M value for the cleavage of Metenkephalin was 1.2 mM. Temperature and pH optima were 47 °C and pH 7.7, respectively. The endopeptidase was inhibited by the classical agents for metal-dependent (EDTA) and serine (DFP) enzymes. Activity was increased by Co²⁺ and Mg²⁺, no effect was observed with Ca²⁺. After inhibition with EDTA, enzyme activity could be restored fully by Co²⁺. Activity was inhibited by Zn²⁺, Mn²⁺, Fe²⁺, Cu²⁺, Cd²⁺ and Hg²⁺. The N-terminal sequence of the endopeptidase was determined as: H₂N-Val-Arg-Gly-Gly-Ser-Gly-Asp-Thr-Thr-Val-0H.     

MRI-compatible intensity-modulated force sensor for cardiac catheterization procedures

This paper presents a novel, magnetic resonance imaging (MRI)-compatible, force sensor suitable for cardiac catheterization procedures. The miniature, fiber-optic sensor is integrated with the tip of a catheter to allow the detection of interaction forces with the cardiac walls. The optical fiber light intensity is modulated when a force acting at the catheter tip deforms an elastic element, which, in turn, varies the distance between a reflector and the optical fiber. The tip sensor has an external diameter of 9 Fr (3?mm) and can be used during cardiac catheterization procedures. The sensor is able to measure forces in the range of 0-0.85?N, with relatively small hysteresis. A nonlinear method for calibration is used and real-time MRI in vivo experiments are carried out, to prove the feasibility of this low-cost sensor, enabling the detection of catheter-tip contact forces under dynamic conditions.     

Charge transfer in thin films of donor–acceptor complexes studied by infrared spectroscopy

The degree of charge transfer in thin films of organic charge transfer (CT)-complexes, which are deposited via thermal evaporation, is examined via infrared-spectroscopy. We demonstrate a linear relationship between the shift in the excitation energy of the CN-stretching mode of CT-complexes with the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the charge transfer. The measured correlation corresponds very well with DFT calculations. For Na-TCNQ we observe a splitting in the peak of the CN-stretching mode, which can be explained by the coupling of two modes and was confirmed by the calculations. In CT-complexes with partial charge transfer the appearance of an electronic excitation is demonstrated.     

The Effect of Ageing on Exciton Dynamics,Charge Separation,and Recombination in P3HT/PCBM Photovoltaic Blends

A study of how light‐induced degradation influences the fundamental photophysical processes in the active layer of poly(3‐hexylthiophene)/[6,6]‐phenyl C₆₁‐butyric acid methyl ester (P3HT/PCBM) solar cells is presented. Non‐encapsulated samples are systematically aged by exposure to AM 1.5 illumination in the presence of dry air for different periods of time. The extent of degradation is quantified by the relative loss in the absorption maximum of the P3HT, which is varied in the range 0% to 20%. For degraded samples an increasing loss in the number of excitons within the P3HT domains is observed with longer ageing periods. This loss occurs rapidly, within the first 15 ps after photoexcitation. A more pronounced decrease in the population of polarons than excitons is observed, which also occurs on a timescale of a few picoseconds. These observations, complemented by a quantitative analysis of the polaron and exciton population dynamics, unravel two primary loss mechanisms for the performances of aged P3HT/PCBM solar cells. One is an initial ultrafast decrease in the polaron generation, apparently not related to the exciton diffusion to the polymer/fullerene interface; the second, less significant, is a loss in the exciton population within the photoexcited P3HT domains. The steady‐state photoinduced absorption spectra of degraded samples exhibits the appearance of a signal ascribed to triplet excitons, which is absent for non‐degraded samples. This latter observation is interpreted considering the formation of degraded sites where intersystem crossing and triplet exciton formation is more effective. The photovoltaic characteristics of same blends are also studied and discussed by comparing the decrease in the overall power conversion efficiency of solar cells.     

Mobility management approaches for SDN-enabled mobile networks

The evolving network technologies aim at meeting the envisioned communication demands of future smart cities and applications. Although software-defined networking (SDN) enables flexible network control, its applicability to mobile networks is still in its infancy. When it comes to introducing the SDN vision to mobile networks, handling of wireless events and mobility management operations stand out as major challenges. In this paper, we study the scalability issues of SDNized wireless networks, specifically those relevant to mobility management. We design and implement different mobility management approaches in SDNized wireless networks and investigate the impact of various system variables on the overall handover delays. We also study the improvements in handover delays: (i) when a proposed proactive mobility management algorithm is implemented; (ii) when the controller delegates partial control of mobility management to the forwarding entities. For the implementation of the proposed approaches on the OpenFlow network, the paper also suggests potential extensions to the OpenFlow protocol. The contributed approaches are validated on a full-scale demonstrator, with results showing that proactive outperforms reactive and that the delegated control approach performs better than proactive for smaller topology sizes. Furthermore, a proposal for LTE X2-specific control delegation is discussed as a use case.     

Superoleophilic Magnetic Iron Oxide Nanoparticles for Effective Hydrocarbon Removal from Water

Various hydrocarbons are efficiently extracted from water by using a new sorbent material based on covalently functionalized magnetic nanoparticles. The functionalization of the magnetite nanoparticles with a self‐assembled monolayer of hexadecylphosphonic acid renders the nanoparticles oleophilic and the magnetic nature of magnetite allows for simple extraction of the hydrocarbon‐soaked sorbent. The sorbent material is capable of extracting single contaminants such as alkanes and aromatics and complex hydrocarbon mixtures such as crude oils in high extraction rates of up to 14 times the sorbent volume. Experimental results are explained by molecular dynamics simulations on the adsorption of single components from a hydrocarbon‐water mixture to the alkylphosphonic acid layer on the nanoparticles. The core–shell sorbent material is highly stable and therefore, reusable over several successive extraction cycles without degradation. The extraction performance is determined at different water temperatures, different water sources, and different magnetic core materials and evaluated compared to heptadecanoic acid functionalized magnetite. The new sorbent material provides the opportunity for an efficient, reliable, inexpensive, and environmental friendly removal of hydrocarbons from water.     

Statistical modeling of reliability in logic devices

Due to continuous technology scaling VLSI circuits feature an increasing susceptibility to transient faults. While complete elimination of errors cannot be guaranteed, current mitigation techniques based on circuit improvement or architectural measures cause a large overhead in terms of area and energy consumption. A more efficient possibility to cope with transient faults can be to tolerate hardware errors at low physical levels and handle them at higher system levels. This can be achieved by reusing error handling capabilities – such as channel decoders – or introducing specialized error correction blocks that take advantage of the system characteristics by concentrating the effort on the components and bits most crucial for system operation. To enable this approach the influence of hardware errors on system performance needs to be evaluated, requiring spatial and temporal models of error propagation in the system. Since Monte Carlo simulation of complex systems is not feasible, a statistical modeling technique of logic gates and circuits is introduced. This approach allows modeling of noise and variability influences on logic gates as well as correlation due to reconvergent fan-out with an error of 5% compared to Monte Carlo simulation but with considerably less runtime.     

Bottom-contact small-molecule n-type organic field effect transistors achieved via simultaneous modification of electrode and dielectric surfaces

Low-voltage, n-type organic field effect transistors (OFETs) with simultaneously modified bottom-contact (BC) electrodes and dielectric were compared to their top-contact (TC) counterparts. The devices modified with 6-phenoxyhexylphosphonic acid (Ph6PA) self-assembled monolayer (SAM) showed similar performance, morphology, and contact resistance. Electron mobility of C₆₀ devices were 0.212 and 0.320 cm² V⁻¹ s⁻¹ and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) devices were 0.04 and 0.06 cm² V⁻¹ s⁻¹ for TC and BC devices, respectively. Low contact resistance between 11 and 45 kΩ cm was found regardless of device architecture or n-type semiconductor used. This work shows it is possible to fabricate solution processable low-voltage bottom-contact devices with performance that is similar or better than their top-contact counterparts without the addition of complex and time-consuming processing steps.     

Enhancing the efficiency of alternating current driven organic light-emitting devices by optimizing the operation frequency

We report efficient and bright organic light-emitting devices operated by capacitive energy coupling. In this approach, the organic layers are enclosed between sputter-deposited hafnium dioxide layers to prevent charge carrier injection. When a sinusoidal voltage signal is applied to the electrodes, the devices emit bright green light whereas no detectable emission is generated upon application of a constant voltage. The efficiency of the process depends heavily on the frequency of the applied voltage signal. By optimizing the driving scheme, a record luminous efficacy for AC driven OLEDs of 2.7 lm/W at 500 cd/m² is achieved.