Novel detectors for traceable THz power measurements

Several novel types of detectors for the measurement of electromagnetic radiation in the THz spectral range are described. Firstly, detectors based on pyroelectric foil coated with different absorbers have been developed focusing on the following features: high accuracy due to well-characterized absorption, high sensitivity, large area absorbers and frequency and polarization independence. A three-dimensional design with five absorptions gave an overall absorption of more than 98 %. Secondly, detectors based on pyroelectric foils with thin metal layers were realized. An absorption of 50 % can be obtained if the thickness of the layers is carefully adjusted. According to electromagnetic theory this degree of absorption is independent of the polarization and frequency of the radiation in a wide range from at least 20 GHz to 5 THz. The third type of detector is based on a new type of volume absorber with a polished front surface and a gold-coated back side. It is the absorber of choice of the standard power detector for disseminating the spectral power responsivity scale. This standard detector allows the application of a physical model to calculate its spectral responsivity in the range from 1 THz to 5 THz if the detector has been calibrated at one single frequency. Finally, a THz detector calibration facility was set up and is now in operation at PTB to calibrate detectors from customers with an uncertainty as low as 1.7 %.     

Studying the thermoviscoelastic response of the Redux 312 adhesive—Part 2: Modeling

The aim of this work is to propose a numerical model of a bonded joint that takes into account the thermoviscoelastic response of the adhesive to compute the stress distribution in the adhesive as well as in the adherends. The adhesive is assumed to obey a generalized Maxwell model. The effect of temperature is taken into account by considering that the branches of the model change with temperature. The numerical solution is obtained iteratively. The particular case of the Redux 312 adhesive is then considered as an example. The procedure is applied in various cases exhibiting an increasing complexity. Some significant differences are observed with the usual solution obtained within the framework of elasticity if the effects of both temperature and time are taken into account.     

Auth<Superscript>2</Superscript>(nPA)

Für viele heutige IT-Dienste w?re eine st?rkere Authentifizierung als die mit Nutzername und Passwort wünschenswert. Insbesondere für sicherheitskritische Prozesse, wie das Zurücksetzen von Passw?rtern, sind bestehende L?sungen oft unbefriedigend. Der neue Personalausweis (nPA) stellt mit seiner eID-Funktion die M?glichkeit für eine starke Authentisierung bereit. Jedoch stehen dem erreichbaren Sicherheitsgewinn nicht unerhebliche Kosten gegenüber, die pro Dienstanbieter aufgebracht werden müssen, um die eID-Funktion zu nutzen. Wir zeigen mit dem Konzept Auth²(nPA), wie eine Zweifaktorauthentisierung mit dem nPA von mehreren Einrichtungen gemeinsam genutzt werden kann. Um für diesen Dienst ein Berechtigungszertifikat zu erhalten, realisiert das Auth²(nPA)-Konzept ein vergleichbar hohes Datenschutzniveau wie die generische eID-L?sung mit getrennten Dienstanbietern.     

Rheological studies on PNIPAAm hydrogel synthesis via in situ polymerization and on resulting viscoelastic properties

Bulk poly(N-isopropylacrylamide) hydrogels were prepared via free radical polymerization. Two different initiation methods were studied: redox- and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion (>95%) and adjustable swelling were only obtained by selecting best suited initiation conditions. For redox polymerization, this was achieved by tuning the ratio of accelerator N,N,N′,N′-tetramethylethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoiniated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels, in particular for the integration of smart soft matrices within membrane pores or other microsystems via a rapid reaction. Rheology was also used to investigate the hydrogel after ex situ preparation, revealing “perfect” soft-rubbery behavior. A good correlation between the mesh sizes determined from swelling and rheology was also found. In conclusion, rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character.     

Modulare serielle Roboter

Modular serial robots allow a fast adaption of the robot geometry to changing execution tasks. Thus, a challenge to robot control is to deal with this vast variety of resulting kinematic designs. This contribution discusses the use of a new general method for solving the inverse kinematics problem. Flexibility with respect to the robot geometry, numerical robustness and complexity of this method is analyzed and a comparison with alternative methods is performed.     

Action of andiroba oil (Carapa guianensis) on Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) semi‐engorged females: Morphophysiological evaluation of reproductive system

Because of the increasing medical‐veterinary importance of ticks, the development of alternative control methods, less aggressive to the host and the environment has become the target of several researches. In this sense, the present study analyzed the action of different concentrations (5, 10, and 20%) of andiroba seed oil (Carapa guianensis) on the reproductive system of Rhipicephalus sanguineus females, through histochemical techniques and the quantification of the reproductive efficiency index. The results showed that andiroba oil is a potent natural agent, able to cause several changes in the oocytes of this species, impairing the reproductive success, once this natural product induces great physiological changes in the oocytes in all development stages, such as drastic reduction in proteins, polysaccharides, and lipids in these cells, and these components are essential for the viability of the embryo. In addition, it was observed that this product stimulate the oviposition, mainly at the concentration of 20%. This higher production of eggs represents a defense mechanism developed by the organism in order to ensure the reproductive success of the species, even in the presence of the toxic agent. However, the results obtained suggested that the laid eggs would not be viable, due to the great changes undergone by the oocytes. Thus, the present study showed that the use of this vegetal product would be an alternative way to control the ticks, bringing benefits similar to the ones obtained through the use of synthetic acaricides; however, with less damage to nontarget organisms and the environment as well. Microsc. Res. Tech., 2012. © 2012 Wiley Periodicals, Inc.