Exchange Rate Speculation and Heterogeneous Expectations in a Small Open Economy.

We consider a standard macroeconomic model of a small open economy in which the flow of capital on the international foreign exchange market crucially depends on the expected exchange rate. These expectations about the exchange rate are modelled to be either homogeneous or heterogeneous, i.e., all agents may form naive expectations, or they may switch between different simple linear extrapolative or regressive predictors with respect to changing market circumstances. Using a mixture of analytical and numerical tools, we attempt to describe the characteristics of our model's dynamical systems we obtain with these different assumptions and analyse the impact of exchange rate expectations on short-term business cycle fluctuations. Our results suggest that fluctuations in both national income and the exchange rate are crucially driven by speculators' expectations. With respect to these expectations, our numerical results additionally show an ambiguous effect of extrapolative expectations on stability. Due to coexisting attractors, an increase in the strength of extrapolative expectations may have both a destabilising and a stabilising impact on dynamics. I n contrast, regressive expectations have a stabilising effect on the business cycle.

Continuously tunable polymer membrane laser.

Thin-film organic distributed feedback (DFB) lasers processed with elastomeric polymers allow fabrication of flexible and continuously tunable coherent light sources. So far, the realized laser devices fall short on broad continuous tuning range. We demonstrate that the addition of plasticizers to the polymer matrix and the minimization of the thickness of the laser can reduce mechanical impact and, thus, extend the wavelength tuning range to the full gain range of the active medium. A contact-transfer method is used to transfer gently the ultra-thin membrane DFB laser to a silicone support. A continuous tuning of the laser wavelength up to 77 nm in the orange-red spectral range of a single laser dye was achieved by mechanical stretching of the supporting film with a DFB membrane laser on top.

Photocontrol of Antibacterial Activity: Shifting from UV to Red Light Activation.

The field of photopharmacology aims to introduce smart drugs that, through the incorporation of molecular photoswitches, allow for the remote spatial and temporal control of bioactivity by light. This concept could be particularly beneficial in the treatment of bacterial infections, by reducing the systemic and environmental side effects of antibiotics. A major concern in the realization of such light-responsive drugs is the wavelength of the light that is applied. Studies on the photocontrol of biologically active agents mostly rely on UV light, which is cytotoxic and poorly suited for tissue penetration. In our efforts to develop photoswitchable antibiotics, we introduce here antibacterial agents whose activity can be controlled by visible light, while getting into the therapeutic window. For that purpose, a UV-light-responsive core structure based on diaminopyrimidines with suitable antibacterial properties was identified. Subsequent modification of an azobenzene photoswitch moiety led to structures that allowed us to control their activity against Escherichia coli in both directions with light in the visible region. For the first time, full in situ photocontrol of antibacterial activity in the presence of bacteria was attained with green and violet light. Most remarkably, one of the diaminopyrimidines revealed an at least 8-fold difference in activity before and after irradiation with red light at 652 nm, showcasing the effective "activation" of a biological agent otherwise inactive within the investigated concentration range, and doing so with red light in the therapeutic window.

Silver-free activation of ligated gold(I) chlorides: the use of [Me3NB12Cl11]- as a weakly coordinating anion in homogeneous gold catalysis.

Phosphane and N-heterocyclic carbene ligated gold(I) chlorides can be effectively activated by Na[Me3NB12Cl11] (1) under silver-free conditions. This activation method with a weakly coordinating closo-dodecaborate anion was shown to be suitable for a large variety of reactions known to be catalyzed by homogeneous gold species, ranging from carbocyclizations to heterocyclizations. Additionally, the capability of 1 in a previously unknown conversion of 5-silyloxy-1,6-allenynes was demonstrated.

Inkjet printed solar cell active layers based on a novel, amorphous polymer.

Organic solar cells are a favorable alternative to their inorganic counterparts because the functional layers of these devices can be processed with printing or coating on a large scale. In this study, a novel polymer was synthesized, blended with fullerene and deposited with inkjet printing for solar cell applications. Devices with printed layers were compared to those with spin coated films in order to evaluate inkjet printing as a thin film deposition method. Efficiency values of 3.7% were found for devices with inkjet printed or spin coated layers. Inkjet printing can be used to successfully process the active layers of organic solar cells consisting of novel polymers without sacrificing device performance.

Mechanism of Resistance Development in E. coli against TCAT, a Trimethoprim-Based Photoswitchable Antibiotic.

During the last decades, a continuous rise of multi-drug resistant pathogens has threatened antibiotic efficacy. To tackle this key challenge, novel antimicrobial therapies are needed with increased specificity for the site of infection. Photopharmacology could enable such specificity by allowing for the control of antibiotic activity with light, as exemplified by trans/cis-tetra-ortho-chloroazobenzene-trimethoprim (TCAT) conjugates. Resistance development against the on (irradiated, TCATa) and off (thermally adapted, TCATd) states of TCAT were compared to that of trimethoprim (TMP) in Escherichia coli mutant strain CS1562. Genomics and transcriptomics were used to explore the acquired resistance. Although TCAT shows TMP-like dihydrofolate reductase (DHFR) inhibition in vitro, transcriptome analyses show different responses in acquired resistance. Resistance against TCATa (on) relies on the production of exopolysaccharides and overexpression of TolC. While resistance against TCATd (off) follows a slightly different gene expression profile, both indicate hampering the entrance of the molecule into the cell. Conversely, resistance against TMP is based on alterations in cell metabolism towards a more persister-like phenotype, as well as alteration of expression levels of enzymes involved in the folate biosynthesis. This study provides a deeper understanding of the development of new therapeutic strategies and the consequences on resistance development against photopharmacological drugs.

Endogenous Business Cycle Dynamics within Metzlers Inventory Model: Adding an Inventory Floor.

Metzlers inventory model may produce dampened fluctuations in economic activity, thus contributing to our understanding of business cycle dynamics. For some parameter combinations, however, the model generates oscillations with increasing amplitude, implying that the inventory stock of firms eventually turns negative. Taking this observation into account, we reformulate Metzlers model by simply putting a floor to the inventory level. Within the new piecewise linear model, endogenous business cycle dynamics may now be triggered via a center bifurcation, i.e. for certain parameter combinations production changes are (quasi-)periodic.

Micro-CT imaging as a method for comparing perfusion in graduated-height and single-height surgical staple lines.

BACKGROUND: Wound healing is a goal for advanced technology in the surgical space to benefit clinical outcomes. Surgical staplers are commonly used in a variety of open and minimally invasive abdominal and thoracic procedures. Assessment of wound healing traits, such as perfusion, has been challenging due to technical limitations. A novel technique that utilizes micro-computed tomography methodology to measure perfusion was designed to compare the micro-perfusion of staple lines between commercial stapler reloads that employ different staple height strategies. MATERIALS AND METHODS: Following an Institutional Animal Care and Use Committee-approved protocol, rats were euthanized and immediately heparinized prior to a subtotal gastrectomy with either graduated-height or single-height staples. Rats were then perfused with barium, following which stomachs were removed and immediately fixed in formalin to prevent degradation. Stomachs were then imaged using micro-computed tomography and subsequent analysis was utilized to quantify fluid volume and patent vasculature proximity to staples within the staple line region for each group. RESULTS: Average perfusion volume was significantly higher with graduated-height staples (0.33% ± 0.18%) compared to single-height staples (0.16% ± 0.09%, P=0.011). Average vessel-to-staple line distance was not significant but trended lower with graduated-height staples (0.35±0.02 mm) compared to single-height staples (0.36±0.03 mm, P=0.18). DISCUSSION: Graduated-height staples had significantly higher perfusion volume than single-height staples, which likely has a downstream benefit on wound healing and clinical outcomes. CONCLUSION: This study shows a higher perfusion volume around the staple lines using graduated-height staples as compared to single-height staples and this may contribute to better wound healing in patients.

Holographic Structuring of Elastomer Actuator: First True Monolithic Tunable Elastomer Optics.

Volume diffraction gratings (VDGs) are inscribed selectively by diffusive introduction of benzophenone and subsequent UV-holographic structuring into an electroactive dielectric elastomer actuator (DEA), to afford a continuous voltage-controlled grating shift of 17%. The internal stress coupling of DEA and optical domain allows for a new generation of true monolithic tunable elastomer optics with voltage controlled properties.

Versatile process for the stereodiverse construction of 1,3-polyols: iterative chain elongation with chiral building blocks.

A versatile process for the construction of 1,3-polyols, a key structural element of polyketide-type natural products, is presented. The modular synthesis strategy involves the iterative chain elongation with novel four-carbon building blocks to access all possible stereoisomers of a growing 1,3-polyol chain. These chiral building blocks are designed to install four carbon atoms with two stereogenic centres by performing only four experimentally simple steps per elongation cycle, thus making these building blocks attractive for the realization of a universal platform from which to access a diverse range of polyketidic molecules.

Piezoelectric two-layer stacks of cellular polypropylene ferroelectrets: transducer response at audio and ultrasound frequencies.

Piezoelectric cellular polypropylene films, so-called ferroelectrets, are assembled in a stack with two active transducer layers. The stack is characterized with respect to its linear and quadratic response in a frequency range from 1 kHz to 80 kHz. A relatively smooth frequency response in the sound-pressure level is found for the individual layers as well as for both layers driven in phase. The piezoelectric response of the two-layer stack is twice the response of an individual layer over a rather broad frequency range. Furthermore, the influence of the preparation conditions on the resonance frequency and the effect of the quadratic distortion on the radiated sound are investigated both for the individual transducer films in the stack and for the stack system as a whole.

The reactivity of 4-hydroxy- and 4-silyloxy-1,5-allenynes with homogeneous gold(I) catalysts.

Two new gold(I)-catalyzed cascade reactions of 4-hydroxy- and 4-silyloxy-1,5-allenynes are disclosed, offering access to a variety of mono- and bicyclic, polyunsaturated carbonyl compounds. The diverse reactivity observed for the investigated allenyne system is controlled by the nature of the unsaturated substrate: Allenynes bearing a free hydroxyl group engage in what is likely an oxycyclization/allene-ene carbocyclization cascade, while their silylated analogues are converted through a carbocyclization/pinacol-type rearrangement process.

Electric poling and electromechanical characterization of 0.1-mm-thick sensor films and 0.2-mm-thick cable layers from piezoelectric poly(vinylidene fluoride-trifluoroethylene).

Piezoelectric polymers have been proposed for many sensor and actuator applications. Among these, piezoelectric polymer films with thicknesses between several tens and a few hundreds of micrometers as well as coaxial cables with piezoelectric polymer layers are highly suitable and attractive for the detection of mechanical loads. In addition to good piezoelectric properties, materials for such sensors should have high mechanical strength. Therefore, the most common materials are nonporous piezoelectric polymers, such as polyvinylidene fluoride (PVDF) or its copolymer with trifluoroethylene (P(VDF-TrFE)). Here, P(VDF-TrFE) polymer films as well as the operating principle and the geometry of piezoelectric polymer cables are described. As active piezoelectric cable layer, P(VDF-TrFE) (76/24) was employed. After electrical poling with one or more point-to-cable corona discharges, the polarization in the P(VDF-TrFE) layer was investigated. Poling parameters, such as electric field and poling time, were varied. The resulting polarization was characterized with measurements of polarization profiles across the film or the cable-layer thickness as well as with the determination of other electromechanical quantities. The optimized poling process yields good piezoelectric properties in the piezoelectric polymer layers as well as useful sensor properties of the piezoelectric polymer cable, which are assessed and discussed.

Note: Piezoelectric polymers as transducers for the ultrasonic-reflection method and the application in mechanical property-screening of coatings.

In the last years, non-destructive ultrasonic testing methods are more and more frequently employed in order to investigate the drying and curing processes of different coatings. Among them an ultrasonic reflection method was developed allowing the simultaneous measurement with longitudinal and transversal waves. In order to generate the ultrasonic pulse, piezoelectric ceramics or oxides are usually used as transducer materials which are connected to a delay line. Here, we demonstrate a similar approach for the ultrasonic reflection method installing piezoelectric polymers as ultrasonic transducer materials. In detail, poly(vinylidene fluoride and trifluoroethylene) [P(VDF-TrFE)] copolymers were prepared as piezoelectric transducer layers directly onto the metallization of glass delay lines avoiding additional bonding processes. The film preparation was carried out by solvent casting the polymer onto an area with a diameter of 12 mm and is optimized so that relatively homogeneous polymer layers with thicknesses between 14 and 35 µm are adjusted by the deposited amount of the polymer. Electrical poling renders the polymer piezoelectric. The ultrasonic properties of the P(VDF-TrFE) transducer and their usability for the ultrasonic reflection method are described also in comparison to previous measurements using LiNbO(3) transducer.

Soft Polymers for Building up Small and Smallest Blood Supplying Systems by Stereolithography.

Synthesis of a homologous series of photo-polymerizable α,w-polytetrahydrofuranether-diacrylate (PTHF-DA) resins is described with characterization by NMR, GPC, DSC, soaking and rheometrical measurements. The curing speeds of the resins are determined under UV light exposure. Young's modulus and tensile strength of fully cured resins show flexible to soft material attributes dependent on the molar mass of the used linear PTHF-diacrylates. Structuring the materials by stereo lithography (SL) and multiphoton polymerization (MPP) leads to tubes and bifurcated tube systems with a diameter smaller than 2 mm aimed at small to smallest supplying systems with capillary dimensions. WST-1 biocompatibility tests ofm polymer extracts show nontoxic characteristics of the adapted polymers after a washing process. Some polymers show shape memory effect (SME).

Highly-integrated lab-on-chip system for point-of-care multiparameter analysis.

A novel innovative approach towards a marketable lab-on-chip system for point-of-care in vitro diagnostics is reported. In a consortium of seven Fraunhofer Institutes a lab-on-chip system called "Fraunhofer ivD-platform" has been established which opens up the possibility for an on-site analysis at low costs. The system features a high degree of modularity and integration. Modularity allows the adaption of common and established assay types of various formats. Integration lets the system move from the laboratory to the point-of-need. By making use of the microarray format the lab-on-chip system also addresses new trends in biomedicine. Research topics such as personalized medicine or companion diagnostics show that multiparameter analyses are an added value for diagnostics, therapy as well as therapy control. These goals are addressed with a low-cost and self-contained cartridge, since reagents, microfluidic actuators and various sensors are integrated within the cartridge. In combination with a fully automated instrumentation (read-out and processing unit) a diagnostic assay can be performed in about 15 min. Via a user-friendly interface the read-out unit itself performs the assay protocol, data acquisition and data analysis. So far, example assays for nucleic acids (detection of different pathogens) and protein markers (such as CRP and PSA) have been established using an electrochemical read-out based on redoxcycling or an optical read-out based on total internal reflectance fluorescence (TIRF). It could be shown that the assay performance within the cartridge is similar to that found for the same assay in a microtiter plate. Furthermore, recent developments are the integration of sample preparation and polymerase chain reaction (PCR) on-chip. Hence, the instrument is capable of providing heating-and-cooling cycles necessary for DNA-amplification. In addition to scientific aspects also the production of such a lab-on-chip system was part of the development since this heavily affects the success of a later market launch. In summary, the Fraunhofer ivD-platform covers the whole value chain ranging from microfluidics, material and polymer sciences, assay and sensor development to the production and assembly design. In this consortium the gap between diagnostic needs and available technologies can be closed.

Polarization-electric field hysteresis of ferroelectric PVDF films: comparison of different measurement regimes.

Polarization-electric field hysteresis is an important property of ferroelectric materials. Different experimental procedures and measurement regimes are demonstrated and frequently used in order to determine this hysteresis behavior. For the characterization of the poling behavior of ferroelectric polymers it is common to analyze the poling current and separate current contributions, which are based on charging the sample capacitance as well as on conductivity. Experimentally this can be realized with two different measurement regimes, either poling of the sample with bipolar cycles or with a sequence of bipolar and unipolar cycles of the applied electric field. Here, we demonstrate the comparison of both measurement routines by performing poling experiments on the same ferroelectric PVDF sample.

Microstorms in cellular polymers: a route to soft piezoelectric transducer materials with engineered macroscopic dipoles.

Cellular polymers can be internally charged by "microstorms" (silent or partial discharges) within the voids of the polymer foam. The resulting material, which carries positive and negative charges on the internal void surfaces, is called a ferroelectret. Ferroelectrets behave like typical ferroelectrics, hence they provide a novel class of ferroic materials. The soft foams are strongly piezoelectric and can be used, in a wide range of applications, as transducers for interconverting mechanical and electrical signals. Herein, an overview is provided on the preparation of cellular polymers by physical foaming (extrusion, biaxial stretching, and controlled inflation by pressure treatments), on their charging by "microstorms", on their piezo- and pyroelectricity, and on analogies to ferroelectrics. Finally, a survey of selected applications is presented.

Origin of temperature dependent conductivity of alpha-polyvinylidene fluoride.

The conductivity of alpha-polyvinylidene fluoride is obtained from dielectric measurements performed in the frequency domain at several temperatures. At temperatures above the glass-transition, the conductivity can be interpreted as an ionic conductivity, which confirms earlier results reported in the literature. Our investigation shows that the observed ionic conductivity is closely related to the amorphous phase of the polymer.