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51.
Best V Gallun FJ Ihlefeld A Shinn-Cunningham BG 《The Journal of the Acoustical Society of America》2006,120(3):1506-1516
If spatial attention acts like a "spotlight," focusing on one location and excluding others, it may be advantageous to have all targets of interest within the same spatial region. This hypothesis was explored using a task where listeners reported keywords from two simultaneous talkers. In Experiment 1, the two talkers were placed symmetrically about the frontal midline with various angular separations. While there was a small performance improvement for moderate separations, the improvement decreased for larger separations. However, the dependency of the relative talker intensities on spatial configuration accounted for these effects. Experiment 2 tested whether spatial separation improved the intelligibility of each source, an effect that could counteract any degradation in performance as sources fell outside the spatial spotlight of attention. In this experiment, intelligibility of individual sources was equalized across configurations by adding masking noise. Under these conditions, the cost of divided listening (the drop in performance when reporting both messages compared to reporting just one) was smaller when the spatial separation was small. These results suggest that spatial separation enhances the intelligibility of individual sources in a competing pair but increases the cost associated with having to process both sources simultaneously, consistent with the attentional spotlight hypothesis. 相似文献
52.
A microfluidic biosensor with electrochemical detection for the quantification of nucleic acid sequences was developed. In contrast to most microbiosensors that are based on fluorescence for signal generation, it takes advantage of the simplicity and high sensitivity provided by an amperometric and coulorimetric detection system. An interdigitated ultramicroelectrode array (IDUA) was fabricated in a glass chip and integrated directly with microchannels made of poly(dimethylsiloxane) (PDMS). The assembly was packaged into a Plexiglas housing providing fluid and electrical connections. IDUAs were characterized amperometrically and using cyclic voltammetry with respect to static and dynamic responses for the presence of a reversible redox couple-potassium hexacyanoferrate (ii)/hexacyanoferrate (iii) (ferri/ferrocyanide). A combined concentration of 0.5 microM of ferro/ferricyanide was determined as lower limit of detection with a dynamic range of 5 orders of magnitude. Background signals were negligible and the IDUA responded in a highly reversible manner to the injection of various volumes and various concentrations of the electrochemical marker. For the detection of nucleic acid sequences, liposomes entrapping the electrochemical marker were tagged with a DNA probe, and superparamagnetic beads were coated with a second DNA probe. A single stranded DNA target sequence hybridized with both probes. The sandwich was captured in the microfluidic channel just upstream of the IDUA via a magnet located in the outside housing. Liposomes were lysed using a detergent and the amount of released ferro/ferricyanide was quantified while passing by the IDUA. Optimal location of the magnet with respect to the IDUA was investigated, the effect of dextran sulfate on the hybridization reaction was studied and the amount of magnetic beads used in the assay was optimized. A dose response curve using varying concentrations of target DNA molecules was carried out demonstrating a limit of detection at 1 fmol assay(-1) and a dynamic range between 1 and 50 fmol. The overall assay took 6 min to complete, plus 15-20 min of pre-incubation and required only a simple potentiostat for signal recording and interpretation. 相似文献
53.
A novel protocol for the synthesis of dye-encapsulating liposomes tagged with DNA oligonucleotides at their outer surface
was developed. These liposomes were optimized for use as signal enhancement agents in lateral-flow sandwich-hybridization
assays for the detection of single-stranded RNA and DNA sequences. Liposomes were synthesized using the reverse-phase evaporation
method and tagged with oligonucleotides by adding cholesteryl-modified DNA probes to the initial lipid mixture. This resulted
in a greatly simplified protocol that provided excellent control of the probe coverage on the liposomes and cut the preparation
time from 16 hours to just 6 hours. Liposomes were prepared using probe concentrations ranging from 0.00077 to 0.152 mol%
of the total lipid, several hydrophobic and polyethylene glycol-based spacers between the cholesteryl anchor and the probe,
and liposome diameters ranging from 208 nm to 365 nm. The liposomes were characterized by dynamic light scattering, visible
spectroscopy, and fluorescence spectroscopy. Their signal enhancement functionality was compared by using them in lateral-flow
optical biosensors for the detection of single-stranded DNA sequences. In these assays, an optimal reporter probe concentration
of 0.013 mol%, liposome diameter of 315 nm, and liposome optical density of 0.4–0.6 at 532 nm were found. The spacer length
between the cholesteryl anchor and the probe showed no significant effect on the signals in the lateral-flow assays. The results
presented here provide important data for the general use of liposomes as labels in analytical assays, with specific emphasis
on nucleic acid detection via lateral flow assays. 相似文献
54.
Dye-encapsulating unilamellar DNA oligonucleotide-tagged liposomes were prepared and characterized for use as signal-enhancing
reagents in a microtiter plate sandwich-hybridization analyses of single-stranded RNA or DNA sequences. The liposomes were
synthesized using the reversed-phase evaporation method and tagged with DNA oligonucleotides by adding cholesteryl-modified
DNA reporter probes to the initial lipid mixture. Liposomes were prepared using probe coverages of 0.0013–0.103 mol% of the
total lipid input, several hydrophobic and poly(ethylene glycol)-based spacers between the cholesteryl anchor and the probe,
and liposome diameters ranging from 200 nm to 335 nm. Their signal enhancement functionality was compared by using them in
microtiter plate sandwich-hybridization assays for the detection of single-stranded DNA sequences. In these assays, an optimal
reporter probe concentration of 0.103 mol%, a liposome diameter of 274 nm, and a phospholipid concentration of 0.3 mM were
found. The length between the cholesteryl anchor and the probe was optimal when a spacer composed of TEG+(CH2O)3 was used. Under optimal conditions, a detection limit of 0.5 nM for a truncated synthetic DNA sequence was found with a coefficient
of variation of 4.4%. A 500-fold lower limit of detection using fluorescence was found using lysed dye-encapsulating liposomes
versus a single fluorescein-labeled probe. Finally, when this method was applied to the detection of atxA RNA extracted from E.coli SG12036-pIu121 and amplified using NASBA, a minimum extracted concentration of RNA of 1.1×10−7 μg/μL was found. 相似文献
55.
Ihlefeld A Shinn-Cunningham B 《The Journal of the Acoustical Society of America》2008,123(6):4380-4392
When listening selectively to one talker in a two-talker environment, performance generally improves with spatial separation of the sources. The current study explores the role of spatial separation in divided listening, when listeners reported both of two simultaneous messages processed to have little spectral overlap (limiting "energetic masking" between the messages). One message was presented at a fixed level, while the other message level varied from equal to 40 dB less than that of the fixed-level message. Results demonstrate that spatial separation of the competing messages improved divided-listening performance. Most errors occurred because listeners failed to report the content of the less-intense talker. Moreover, performance generally improved as the broadband energy ratio of the variable-level to the fixed-level talker increased. The error patterns suggest that spatial separation improves the intelligibility of the less-intense talker by improving the ability to (1) hear portions of the signal that would otherwise be masked, (2) segregate the two talkers properly into separate perceptual streams, and (3) selectively focus attention on the less-intense talker. Spatial configuration did not noticeably affect the ability to report the more-intense talker, suggesting that it was processed differently than the less-intense talker, which was actively attended. 相似文献
56.
57.
Johanna M. Spörl Antje Ota Ronald Beyer Thomas Lehr Alexandra Müller Frank Hermanutz Michael R. Buchmeiser 《Journal of polymer science. Part A, Polymer chemistry》2014,52(9):1322-1333
Reversible‐addition fragmentation‐transfer (RAFT) polymerization of acrylonitrile (AN) was performed with 2‐(2‐cyano‐2‐propyl‐dodecyl)trithiocarbonate as RAFT agent and azobis(isobutyronitrile) as initiator. Linear polyacrylonitrile (Mn = 133,000 g/mol, PDI = 1.34) was prepared within 7 h in 86% isolated yield. High‐yield copolymerization with methyl methacrylate (MMA) was performed and copolymerization parameters were determined according to Kelen and Tüdös at 90 °C in ethylene carbonate yielding rAN = 0.2 and rMMA = 0.42. The molecular weights, polydispersity indices (PDIs), and MMA content of the copolymer were adjusted in a way that precursor fibers could be prepared via wet spinning. These precursor fibers had round cross‐sections and a dense morphology, showing tenacities of 40–50 cN/tex and elastic moduli of 900–1000 cN/tex at a fineness of 1 dtex and an elongation of 13–17%. Precursor fibers were oxidatively stabilized and then carbonized at different temperatures. A maximum tensile strength of 2.5 GPa was reached at 1350 °C. Thermal analysis, infrared and Raman spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and tensile testing were used to characterize the resulting carbon fibers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1322–1333 相似文献
58.
Sarah J. Reinholt Antje J. Baeumner 《Angewandte Chemie (International ed. in English)》2014,53(51):13988-14001
The detection of nucleic acids (NAs) within micro total analysis systems (μTASs) for point‐of‐care use is a rapidly developing research area. The efficient isolation of NAs from a raw sample is crucial for these systems to be maximally effective. The use of microfluidics assists in reducing sample sizes and reagent consumption, increases speed, avoids contamination, and enables automation. Through miniaturization into microchips, new techniques have been realized that would be unfavorable and inconvenient to use on a macroscopic scale, but provide an excellent platform for the purification of NAs on a microscopic scale. This Review considers the complexities of NA isolation with miniaturized and microfluidic devices, as well as the considerations when choosing a technique for microfluidic NA isolation, along with their advantages, disadvantages, and potential applications. The techniques presented include using silica‐based surfaces, functionalized paramagnetic beads, oligonucleotide‐modified polymer surfaces, pH‐dependent charged surfaces, Al2O3 membranes, and liquid‐phase isolation. This Review provides a basis to develop the chemistry to improve NA isolation and move it toward achieving 100 % efficiencies. 相似文献
59.
Zusammenfassung Es wurde eine Methode angegeben, um eine relativ starke Lösung von Ozon in verdünnten Säuren herzustellen.Die Bedingungen, unter denen sich der Ozongehalt jodometrisch bestimmen läßt, wurden geprüft.Es wurde festgestellt, daß sich bei der Zersetzung des gelösten Ozons kein anderes Endprodukt bildet als Sauerstoff.Bei den Versuchen in saurer Lösung zeigte sich, daß die Zersetzungsgeschwindigkeit unter anscheinend gleichen Bedingungen sehr variabel war; doch waren die Bemühungen, diese Unregelmäßigkeiten auf die Anwesenheit eines Katalysators zurückzuführen, ergebnislos.In alkalischer Lösung waren derartige Unregelmäßigkeiten nicht deutlich bemerkbar.Die Zersetzung des Ozons geht in einigermaßen stark sauren Lösungen langsam vor sich, ihre Geschwindigkeit nimmt mit abnehmender Konzentration des Wasserstoffions zu, aber nicht proportional derselben, sondern langsamer.In den stärksten der untersuchten sauren Lösungen (0·01 normal) verläuft die Reaktion annähernd nach der zweiten Ordnung, in den schwächer sauren und den alkalischen liegt ihre Ordnung zwischen der ersten und zweiten.Macht man die Annahme, daß sich zwei Reaktionen superponieren, von denen die eine mono-, die andere bimolekular ist, so gelangt man zu der Differentialgleichungdx/dt=A(a–x)2+B(a– x), durch welche sich die Versuche gut darstellen lassen.In den sauren Lösungen überwiegt das erste Glied; der Verlauf der Reaktion ist daher annähernd bimolekular, in den schwächer sauren und alkalischen Lösungen kommt die monomolekulare Reaktion mehr zur Geltung. 相似文献
60.
Henschel A Gedrich K Kraehnert R Kaskel S 《Chemical communications (Cambridge, England)》2008,(35):4192-4194
A very high catalytic activity in the cyanosilylation reaction was observed for MIL-101, a chromium based metal-organic framework; moreover, MIL-101 is also a remarkably stable support for palladium in hydrogenation reactions, with significantly higher activity than e.g. palladium on activated carbon. 相似文献