Synthesis and characterization of photoswitchable fluorescent silica nanoparticles

We have designed and synthesized a new functional (amino reactive) highly efficient fluorescent molecular switch (FMS) with a photochromic diarylethene and a rhodamine fluorescent dye. The reactive group in this FMS -N-hydroxysuccinimide ester- allows selective labeling of amino containing molecules or other materials. In ethanolic solutions, the compound displays a large fluorescent quantum yield of 52 % and a large fluorescence modulation ratio (94 %) between two states that may be interconverted with red and near-UV light. Silica nanoparticles incorporating the new FMS were prepared and characterized, and their spectroscopic and switching properties were also studied. The dye retained its properties after the incorporation into the silica, thereby allowing light-induced reversible high modulation of the fluorescence signal of a single particle for up to 60 cycles, before undergoing irreversible photobleaching. Some applications of these particles in fluorescence microscopy are also demonstrated. In particular, subdiffraction images of nanoparticles were obtained, in the focal plane of a confocal microscope.     

Removal of arsenic from water streams: an overview of available techniques

Arsenic poisoning has become one of the major environmental worries worldwide, as millions of people, which have been exposed to high arsenic concentrations (through contaminated drinking water), developed severe health problems. The high toxicity of this element made necessary the enforcement of stringent maximum allowable limits in drinking water. So, the development of novel techniques for its removal from aqueous streams is a very important issue. This paper offers an overview of geochemistry, distribution, sources, toxicity, regulations and applications of selected techniques for arsenic removal. The contribution briefly summarizes adsorption processes and mechanism of arsenic species removal from water streams by means of iron oxide/oxyhydroxide based materials. Sorption capacities of various sorbents (e.g. akaganeite, goethite, hydrous ferric oxide, iron oxide coated sand, Fe(III) loaded resin, granular ferric hydroxide, Ce(IV) doped iron oxide, natural iron ores, iron oxide coated cement, magnetically modified zeolite, Fe-hydroxide coated alumina) have been compared.     

Recognizing masked threat: Fear betrays, but disgust you can trust.

If emotions guide consciousness, people may recognize degraded objects in center view more accurately if they either fear the objects or are disgusted by them. Therefore, we studied whether recognition of spiders and snakes correlates with individual differences in spider fear, snake fear, and disgust sensitivity. Female students performed a recognition task with pictures of spiders, snakes, flowers, and mushrooms as well as blanks. Pictures were backward masked to reduce picture visibility. Signal detection analyses showed that recognition of spiders and snakes was correlated with disgust sensitivity but not with fear of spiders or snakes. Further, spider fear correlated with the tendency to misinterpret blanks as threatening (response bias). These findings suggest that effects on recognition and response biases to emotional pictures vary for different emotions and emotional traits. Whereas fear may induce response biases, disgust may facilitate recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social support from family and friends as a buffer of low spousal support among mothers of critically ill children: A multilevel modeling approach.

Objective: To investigate whether social support from family and friends (family/friend support) attenuated ("buffered") adverse effects of having low spouse support (spousal support) among mothers of children undergoing hematopoietic stem cell transplantation (HSCT). Design: One hundred sixty-three married mothers who were their child's primary caregiver during treatment completed assessments during the child's hospitalization for HSCT and 3-, 6-, and 12-months post-HSCT. Measures: Family/friend support and spousal support were assessed during hospitalization. Maternal physical and mental health-related functioning (the main outcome measures) were assessed at all timepoints. Results: Multilevel modeling was used to analyze trajectories of maternal functioning. Findings indicated that mothers with low spousal support and low family/friend support demonstrated the worst functioning across all timepoints. Mothers with low spousal support and high family/friend support demonstrated significantly better functioning, supporting the hypothesized buffering effect. Their functioning compared to the functioning of mothers with high spousal support. Moreover, mothers with high family/friend support demonstrated trajectories of physical health-related functioning that were more stable than the trajectories of mothers with low family/friend support. Conclusion: These findings have clinical implications in addition to advancing knowledge of social support processes among couples coping with the shared stressor of a child's life-threatening illness and treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Marginal adaptation of composite resins under two adhesive techniques

In the present research, different adhesive techniques were used to set up fillings with composite resins. After the application of etch and rinse or self etch adhesive technique, marginal adaptation of composite fillings was estimated by the length of margins without gaps, and by the microretention of resin in enamel and dentin. The study material consisted of 40 extracted teeth. Twenty Class V cavities were treated with 35% phosphorous acid and restored after rinsing by Adper Single Bond 2 and Filtek Ultimate‐ASB/FU 3M ESPE composite system. The remaining 20 cavities were restored by Adper Easy One‐AEO/FU 3M ESPE composite system. Marginal adaptation of composite fillings was examined using a scanning electron microscope (SEM). The etch and rinse adhesive technique showed a significantly higher percentage of margin length without gaps (in enamel: 92.5%, in dentin: 57.3%), compared with the self‐etch technique with lower percentage of margin length without gaps, in enamel 70.4% (p < .001), and in dentin‐22.6% (p < .05). In the first technique, microretention was composed of adhesive and hybrid layers as well as resin tugs in interprismatic spaces of enamel, while the dentin microretention was composed of adhesive and hybrid layers with resin tugs in dentin canals. In the second technique, resin tugs were rarely seen and a microgap was dominant along the border of restoration margins. The SEM analysis showed a better marginal adaptation of composite resin to enamel and dentin with better microretention when the etch and rinse adhesive procedure was applied.     

ZnPd/ZnO Aerogels as Potential Catalytic Materials

Many different aerogel materials are known to be accessible via the controlled destabilization of the respective nanoparticle suspensions. Especially for applications in heterogeneous catalysis such materials with high specific surface areas are highly desirable. Here, a facile method to obtain a mixed ZnPd/ZnO aerogel via a reductive treatment of a preformed Pd/ZnO aerogel is presented. Different morphologies of the Pd/ZnO aerogels could be achieved by controlling the destabilization of the ZnO sol. All aerogels show a high CO₂ selectivity of up to 96% and a very good activity in methanol steam reforming that delivers hydrogen, which is one of the most important fuels for future energy concepts. The method presented is promising for different transition metal/metal oxide systems and hence opens a path to a huge variety of materials.     

Catalytically Doped Semiconductors for Chemical Gas Sensing: Aerogel‐Like Aluminum‐Containing Zinc Oxide Materials Prepared in the Gas Phase

Atmospheric contamination with organic compounds is undesired in industry and in society because of odor nuisance or potential toxicity. Resistive gas sensors made of semiconducting metal oxides are effective in the detection of gases even at low concentration. Major drawbacks are low selectivity and missing sensitivity toward a targeted compound. Acetaldehyde is selected due to its high relevance in chemical industry and its toxic character. Considering the similarity between gas‐sensing and heterogeneous catalysis (surface reactions, activity, selectivity), it is tempting to transfer concepts. A question of importance is how doping and the resulting change in electronic properties of a metal‐oxide support with semiconducting properties alters reactivity of the surfaces and the functionality in gas‐sensing and in heterogeneous catalysis. A gas‐phase synthesis method is employed for aerogel‐like zinc oxide materials with a defined content of aluminum (n‐doping), which were then used for the assembly of gas sensors. It is shown that only Al‐doped ZnO represents an effective sensor material that is sensitive down to very low concentrations (<350 ppb). The advance in properties relates to a catalytic effect for the doped semiconductor nanomaterial.     

Physical Mechanisms behind the Field‐Cycling Behavior of HfO2‐Based Ferroelectric Capacitors

Novel hafnium oxide (HfO₂)‐based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite‐based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake‐up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake‐up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake‐up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.     

Ozone Differentially Affects Perception of Plant Volatiles in Western Honey Bees

Floral scents play a key role in mediating plant-pollinator interactions. Volatile organic compounds (VOCs) emitted by flowers are used by flower visitors as olfactory cues to locate flowers, both from a distance and at close range. More recently it has been demonstrated that reactive molecules such as ozone can modify or degrade VOCs, and this may impair the communication between plants and their pollinators. However, it is not known whether such reactive molecules also may affect the olfactory system of pollinators, and thus not only influence signal transmission but perception of the signal. In this study, we used electroantennographic measurements to determine the effect of increased levels of ozone on antennal responses in western honey bees (Apis mellifera L.). Linalool and 2-phenylethanol, both known to be involved in location of flowers by the bees, and (Z)-3-hexenyl acetate, a widespread green leaf volatile also detected by bees, were used. The results showed that ozone affected antennal responses to the different substances differently. Ozone decreased antennal responses to (Z)-3-hexenyl acetate, whereas responses to linalool and 2-phenylethanol were not influenced by ozone. Overall, the study does not provide evidence that pollination by honey bees is impaired by damage in the olfactory system of the bees caused by increased levels of ozone, at least when linalool and 2-phenylethanol are the attractive signals. However, the results also suggest that ozone can change the overall perception of an odor blend. This might have negative effects in pollination systems and other organismic interactions mediated by specific ratios of compounds.