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261.
Kennedy SM Hodgson M Edgett LD Lamb N Rempel R 《The Journal of the Acoustical Society of America》2006,119(1):299-309
A questionnaire is developed to evaluate perception of the listening environment by university students. The objectives were to develop a questionnaire-based measurement tool, derive a measure of perceived classroom-listening quality, use the questionnaire to investigate factors that enhance, impair, or do not affect perceived listening quality, and consider the implications for classroom design. The questionnaire was administered to over 5700 students in 30 classrooms at one university. Physical and acoustical measurements were also performed in each classroom. The questionnaire included items that recorded aspects of student perception, as well as individual, course-, and instructor-specific factors. Responses to 19 perception items generated a perception of listening ease (PLE) score for each student and a classroom-average score. Decreased PLE was associated with women, English-second-larguage students, those with hearing impairment, students not interested in the course material, and those who found the material difficult. Increased PLE was associated with higher speech transmission index, acceptable lighting, temperature and seating, better instructor voice, increased visual-aid use, and easier course material. Results indicate that PLE is a useful measure of student perception of the classroom-listening environment, and that optimal classroom acoustical design must take into consideration "in-use" conditions, as well as classroom physical characteristics. 相似文献
262.
Representative organic vapors have been introduced into the flowing afterglow of a low power (<5 W) dc-glow discharge, coupled to a quadrupole mass spectrometer. When a positive bias was applied to the ion sampling orifice, the very surprising result was that molecular mass spectra were obtained with a high sensitivity. When a negative bias was applied to the ion sampling orifice, fragmentation of the analyte was observed with an increase in the extent of ion dissociation as the voltage was increased. The breakdown pattern is compound-specific and would be useful in confirming the identity of an unknown sample. When combined with chromatographic separation, the FFGD-MS technique could be used for chemical speciation studies at the sub-picogram level. 相似文献
263.
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265.
Douglas Cenzer Rodney G. Downey Jeffrey B. Remmel Zia Uddin 《Archive for Mathematical Logic》2009,48(1):115-140
We develop a theory of LOGSPACE structures and apply it to construct a number of examples of Abelian Groups which have LOGSPACE presentations. We show that all computable torsion Abelian groups have LOGSPACE presentations and we show that the groups , and the additive group of the rationals have LOGSPACE presentations over a standard universe such as the tally representation and the binary representation of the natural numbers.
We also study the effective categoricity of such groups. For example, we give conditions are given under which two isomorphic
LOGSPACE structures will have a linear space isomorphism.
相似文献
266.
Rodney G. Downey Michael R. Fellows Venkatesh Raman 《Discrete Applied Mathematics》2000,100(3):155-167
An irredundant set of vertices V′V in a graph G=(V,E) has the property that for every vertex uV′, N[V′−{u}] is a proper subset of N[V′]. We investigate the parameterized complexity of determining whether a graph has an irredundant set of size k, where k is the parameter. The interest of this problem is that while most “k-element vertex set” problems are NP-complete, several are known to be fixed-parameter tractable, and others are hard for various levels of the parameterized complexity hierarchy. Complexity classification of vertex set problems in this framework has proved to be both more interesting and more difficult. We prove that the k-element irredundant set problem is complete for W[1], and thus has the same parameterized complexity as the problem of determining whether a graph has a k-clique. We also show that the “parametric dual” problem of determining whether a graph has an irredundant set of size n−k is fixed-parameter tractable. 相似文献
267.
Randy S. Frank Jeffrey S. Downey H. D. H. Stver 《Journal of polymer science. Part A, Polymer chemistry》1998,36(13):2223-2227
Narrow disperse micron-range divinylbenzene-maleic anhydride microspheres have been prepared in near quantitative yields using precipitation polymerization. A variety of solvents were investigated for use as the reaction medium with a 40:60 mixture of methyl ethyl ketone and heptane providing the best results. The effects of solvent composition on particle size and morphology and monomer loading effects were also investigated. Particle size decreased with increasing solvency (increasing MEK fraction) while increases in monomer loading caused larger particle sizes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2223–2227, 1998 相似文献
268.
The effects of hydrostatic pressure (to ~2.4 GPa) on the electrical conductivity of AsTe, AsTeI and AsTeGe bulk semiconducting glasses have been determined. The electrical conductivity σ increases nearly exponentially with increasing pressure P. The Δ 1n σ/ΔP values are dependent upon composition and pressure, and vary from about 2 to 6 GPa?1. This is a narrow range of values considering that the initial conductivies vary over five orders of magnitude for the compositions studied. Many of the glasses exhibited time-dependent conductivity changes both at high pressure and after cycling to high pressure. At high pressure the conductivity drifted to higher values over a period of several hours, initially following a logarithmic time dependence. Generally, the drifts were observed for P ? 0.8 GPa and for . Following the high-pressure experiment, the conductivity (and also the density) of some glasses were above that for the as-prepared material. These same samples had a slightly different conductivity temperature dependence. The conductivity slowly relaxed (over many months) toward the original conductivity state, again initially following a logarithmic time dependence. Much of our data can be interpreted consistently if we assumed that the conductivity changes depend primarily on “expected” volume changes. The kinds of behavior reported here are similar to those observed for a wide variety of glass systems. Any models developed for describing electrical transport under pressure must account for time-dependent as well as pressure-dependent effects. 相似文献
269.
Alexandre Chappard Dr. Craig Leighton Dr. Rebecca S. Saleeb Kiani Jeacock Dr. Sarah R. Ball Katie Morris Owen Kantelberg Dr. Ji-Eun Lee Dr. Elsa Zacco Prof. Dr. Annalisa Pastore Prof. Dr. Margaret Sunde Dr. David J. Clarke Dr. Patrick Downey Prof. Dr. Tilo Kunath Dr. Mathew H. Horrocks 《Angewandte Chemie (International ed. in English)》2023,62(15):e202216771
Protein misfolding and aggregation into oligomeric and fibrillar structures is a common feature of many neurogenerative disorders. Single-molecule techniques have enabled characterization of these lowly abundant, highly heterogeneous protein aggregates, previously inaccessible using ensemble averaging techniques. However, they usually rely on the use of recombinantly-expressed labeled protein, or on the addition of amyloid stains that are not protein-specific. To circumvent these challenges, we have made use of a high affinity antibody labeled with orthogonal fluorophores combined with fast-flow microfluidics and single-molecule confocal microscopy to specifically detect α-synuclein, the protein associated with Parkinson's disease. We used this approach to determine the number and size of α-synuclein aggregates down to picomolar concentrations in biologically relevant samples. 相似文献