Inside Vertical-Cavity Surface-Emitting Lasers: Extracting the Refractive Index From Spatial-Spectral Mode Images

We present a method to extract the internal effective refractive index of a vertical-cavity surface-emitting laser (VCSEL) from its transverse mode images. High spatial and spectral resolution mode images of an oxide-guided VCSEL were obtained using an etalon filter and an imaging spectrometer. The refractive index and the oxide radius were extracted from the field intensity distribution and the spectral wavelength of the laser modes. The procedure was repeated at two different currents and both gave a refractive index step of 0.046 plusmn 0.006 with a 14.1-mum oxide diameter. With several degrees of freedom for error available in the refractive index extraction, this method may be extended to ion-implanted, photonic crystal, and noncircular devices     

Next Generation ADC Massive Parallel Testing with Real Time Parameter Evaluation

The paper describes the implementation of a novel Analog-to-Digital-Converter (ADC) test technique for next generation low cost massive parallel ADC testing using a Field Programmable Gate Array (FPGA) on tester load board. The goal is to test the ADC which is embedded in an automotive micro controller with only pure digital tester sources. Therefore, the analog test stimulus for the ADC is generated by using ΔΣ-modulation technique off-line and analog filtering on load board. The digital test response is analyzed by a FPGA in real time by comparing the measured data with a reference signal. The modular concept of FPGA evaluation allows for quick and flexible reaction on changing production test requirements. Simply by reprogramming the FPGA with a new module there is no need of any hardware reconfigurations. Measurements with a high precision reference ADC in laboratory environment show that the method is ready for production.     

Universal Polarization Switching Behavior of Disordered Ferroelectrics

Universal scaling features of polarization switching are established experimentally in rather different classes of disordered ferroelectrics: in well‐studied lead‐zirconate titanate (PZT) ferroelectrics, in recently synthesized Cu‐stabilized 0.94(Bi_1/2Na_1/2)TiO₃–0.06BaTiO₃ (BNT‐BT) relaxor ferroelectrics, and in classical organic ferroelectrics P(VDF‐TrFE). These scaling properties are explained by an extended concept of an inhomogeneous field mechanism (IFM) of polarization dynamics in ferroelectrics. Accordingly, disordered ferroelectrics exhibit a wide spectrum of characteristic switching times due to a statistical distribution of values of the local electric field. How this distribution can be extracted from polarization measurements is demonstrated. Generally, it is shown that the polarization response is primarily controlled by the statistical characteristics of disorder rather than by a temporal law of the local polarization switching.     

Dielectric–Semiconductor Interface Limits Charge Carrier Motion at Elevated Temperatures and Large Carrier Densities in a High‐Mobility Organic Semiconductor

The fundamental nature of charge transport in highly ordered organic semiconductors is under constant debate. At cryogenic temperatures, effects within the semiconductor such as traps or the interaction of charge carriers with the insulating substrate (dipolar disorder or Fröhlich polarons) are known to limit carrier motion. In comparison, at elevated temperatures, where charge carrier mobility often also decreases as function of temperature, phonon scattering or dynamic disorder are frequently discussed mechanisms, but the exact microscopic cause that limits carrier motion is debated. Here, the mobility in the temperature range between 200 and 420 K as function of carrier density is explored in highly ordered perylene‐diimide from 3 to 9 nm thin films. It is observed that above room temperature increasing the gate electric field or decreasing the semiconducting film thickness leads to a suppression of the charge carrier mobility. Via X‐ray diffraction measurements at various temperatures and electric fields, changes of the thin film structure are excluded as cause for the observed mobility decrease. The experimental findings point toward scattering sites or traps at the semiconductor–dielectric interface, or in the dielectric as limiting factor for carrier mobility, whose role is usually neglected at elevated temperatures.     

Pornography and Sexist Attitudes Among Heterosexuals

Using a probability‐based sample of young Danish adults and a randomized experimental design, this study investigated effects of past pornography consumption, experimental exposure to nonviolent pornography, perceived realism of pornography, and personality (i.e., agreeableness) on sexist attitudes (i.e., attitudes toward women, hostile and benevolent sexism). Further, sexual arousal mediation was assessed. Results showed that, among men, an increased past pornography consumption was significantly associated with less egalitarian attitudes toward women and more hostile sexism. Further, lower agreeableness was found to significantly predict higher sexist attitudes. Significant effects of experimental exposure to pornography were found for hostile sexism among low in agreeableness participants and for benevolent sexism among women. These experimental exposure effects were found to be mediated by sexual arousal.     

Enhancing interference rejection of preamplified electrodes by automated gain adaption

The use of preamplified electrodes in electrocardiography (ECG) or electroencephalography (EEG) has a numbe of benefits, most importantly, the noise reduction through preamplification and the interference reduction through buffering (Fernandez and Pallas-Areny, 1997). Normally, preamplified electrodes are not used because the mismatch in amplification due to component tolerances leads to a reduced common mode rejection ration (CMRR) (Pallas-Areny and Webster, 1991). In this paper, we introduce a new technique to restore the CMRR. We do this by adapting the gain of the differential amplifier (DA) following the preamplified electrodes. The technique is based on measuring the transfer function of a chosen common mode signal. The gain of the DA is adjusted by a closed loop controller to maximize the CMRR. With this technique, there is no adverse effect on the ECG or EEG. In this way, the control loop can be operated continuously if needed.     

Simplified Large‐Area Manufacturing of Organic Electrochemical Transistors Combining Printing and a Self‐Aligning Laser Ablation Step

A hybrid manufacturing approach for organic electrochemical transistors (OECTs) on flexible substrates is reported. The technology is based on conventional and digital printing (screen and inkjet printing), laser processing, and post‐press technologies. A careful selection of the conductive, dielectric, and semiconductor materials with respect to their optical properties enables a self‐aligning pattern formation which results in a significant reduction of the usual registration problems during manufacturing. For the prototype OECTs, based on this technology, on/off ratios up to 600 and switching times of 100 milliseconds at gate voltages in the range of 1 V were obtained.     

Development of Synthetic Platelet‐Activating Hydrogel Matrices to Induce Local Hemostasis

Several hemostatic strategies rely on the use of blood components such as fibrinogen and thrombin, which suffer from high cost and short shelf‐life. Here, a cost‐effective synthetic biomaterial is developed for rapid local hemostasis. Instead of using thrombin, thrombin‐receptor‐agonist‐peptide‐6 (TRAP6) is covalently engineered in polyvinyl alcohol (PVA) hydrogels. Soluble PVA‐TRAP6 is first prepared by covalent attachment of cysteine‐containing TRAP6 onto the backbone of PVA‐norbornenes (PVA‐NB) through photoconjugation. Cytotoxicity studies using C2C12 myoblasts indicate that PVA‐NB and PVA‐TRAP6 are nontoxic. Thromboelastography reveals that hemostatic activity of TRAP6 is retained in conjugated form, which is comparable to free TRAP6 solutions with equal concentrations. A 0.1% PVA‐TRAP6 solution can shorten the clotting time (CT) to ca. 45% of the physiological CT. High platelet‐activating efficiency is further confirmed by platelet aggregation assay and flow cytometry (FACS). For potential clinical applications, TRAP6‐presenting hydrogel particulates (PVA‐TRAP6‐P) are developed for local platelet activation and hemostasis. PVA‐TRAP6‐P is prepared by biofunctionalization of photopolymerized PVA‐NB hydrogel particulates (PVA‐NB‐P) with TRAP6. It is demonstrated that PVA‐TRAP6‐P can effectively shorten the CT to ca. 50%. FACS shows that PVA‐TRAP6‐P can activate platelets to a comparable extent as soluble TRAP6 control. Altogether, PVA‐TRAP6‐P represents a promising class of biomaterials for safe hemostasis and wound healing.     

Overcoming selective ensemble averaging: unsupervised identification of event-related brain potentials

We present a novel approach to the problem of event-related potential (ERP) identification, based on a competitive artificial neural network (ANN) structure. Our method uses ensembled electroencephalogram (EEG) data just as used in conventional averaging, however without the need for a priori data subgrouping into distinct categories (e.g., stimulus- or event-related), and thus avoids conventional assumptions on response invariability. The competitive ANN, often described as a winner takes all neural structure, is based on dynamic competition among the net neurons where learning takes place only with the winning neuron. Using a simple single-layered structure, the proposed scheme results in convergence of the actual neural weights to the embedded ERP patterns. The method is applied to real event-related potential data recorded during a common odd-ball type paradigm. For the first time, within-session variable signal patterns are automatically identified, dismissing the strong and limiting requirement of a priori stimulus-related selective grouping of the recorded data. The results present new possibilities in ERP research.     

Multimodal Bioactivation of Hydrophilic Electrospun Nanofibers Enables Simultaneous Tuning of Cell Adhesivity and Immunomodulatory Effects

Biomaterials research usually focuses on functional and structural mimicry of the extracellular matrix or tissue hierarchy and morphology. Most recently, material‐induced modulatory effects on the immune system to arouse a healing response is another upcoming strategy. Approaches, however, that integrate both aspects to induce healing and facilitate specific cell adhesion are so far little explored. This study exploits manifold but chemical crosslinker free functionalization of hydrophilic and nonadhesive electrospun fiber surfaces with peptides for controlled cell adhesion, and with neutra­lizing antibodies targeting the master cytokine tumor necrosis factor (TNF) to dampen proinflammatory reactions by the fiber adherent cells. It is demonstrated that cell attachment and immunomodulatory properties of a textile can be tailored at the same time to generate meshes that combine immunosuppressive activity with specific cell adhesion properties.