20,357 research outputs found
Effects of age, sex, context, and lexicality on hyperarticulation of Korean fricatives
Seoul Korean is known for a rare three-way laryngeal contrast among lenis, fortis, and aspirated voiceless stops, which has recently undergone a change in phonetic implementation: whereas older speakers rely more on voice onset time (VOT) to distinguish lenis and aspirated stops, younger speakers rely more on onset fundamental frequency (f 0) in the following vowel. This production difference is reflected in disparate strategies for enhancing the contrast in clear speech, supporting the view that younger and older speakers represent the three laryngeal categories differently in terms of VOT and f 0 targets (Kang & Guion, 2008). In the current study, we used the clear speech paradigm to test for change in the representation of the two-way contrast between fortis (/s*/) and non-fortis (/s/) fricatives. Native Seoul Korean speakers (n = 32), representing two generations and both sexes, were recorded producing the coronal stops and fricatives in different vowel contexts, item types (real vs. nonce words), and speech registers (plain citation vs. clear). We report acoustic data on how the above factors influence production of the fricative contrast and discuss implications for the phonological categorization of non-fortis /s/ as lenis, aspirated, or a hybrid lenis-aspirated category.https://drive.google.com/open?id=0B1_NoAiLQlnkZ2RtdEtuYTlaMkkOthe
Polymer Release out of a Spherical Vesicle through a Pore
Translocation of a polymer out of curved surface or membrane is studied via
mean first passage time approach. Membrane curvature gives rise to a constraint
on polymer conformation, which effectively drives the polymer to the outside of
membrane where the available volume of polymer conformational fluctuation is
larger. Considering a polymer release out of spherical vesicle, polymer
translocation time is changed to the scaling behavior for
, from for , where is the polymer contour
length and , are vesicle radius and polymer radius of gyration
respectively. Also the polymer capture into a spherical budd is studied and
possible apparatus for easy capture is suggested.Comment: 14 pages RevTeX, 6 postscript figures, published in Phys. Rev. E 57,
730 (1998
Diverse Inflammatory Response After Cerebral Microbleeds Includes Coordinated Microglial Migration and Proliferation.
BACKGROUND AND PURPOSE:Cerebral microbleeds are linked to cognitive decline, but it remains unclear how they impair neuronal function. Infarction is not typically observed near microbleeds, suggesting more subtle mechanisms, such as inflammation, may play a role. Because of their small size and largely asymptomatic nature, real-time detection and study of spontaneous cerebral microbleeds in humans and animal models are difficult. METHODS:We used in vivo 2-photon microscopy through a chronic cranial window in adult mice to follow the inflammatory response after a cortical microhemorrhage of ≈100 µm diameter, induced by rupturing a targeted cortical arteriole with a laser. RESULTS:The inflammatory response included the invasion of blood-borne leukocytes, the migration and proliferation of brain-resident microglia, and the activation of astrocytes. Nearly all inflammatory cells responding to the microhemorrhage were brain-resident microglia, but a small number of CX3CR1+ and CCR2+ macrophages, ultimately originating from the invasion of blood-borne monocytes, were also found near the lesion. We found a coordinated pattern of microglia migration and proliferation, where microglia within 200 µm of the microhemorrhage migrated toward the lesion over hours to days. In contrast, microglia proliferation was not observed until ≈40 hours after the lesion and occurred primarily in a shell-shaped region where the migration of microglia decreased their local density. These data suggest that local microglia density changes may trigger proliferation. Astrocytes activated in a similar region as microglia but delayed by a few days. By 2 weeks, this inflammatory response had largely resolved. CONCLUSIONS:Although microhemorrhages are small in size, the brain responds to a single bleed with an inflammatory response that involves brain-resident and blood-derived cells, persists for weeks, and may impact the adjacent brain microenvironment
Reduced chemistry for butanol isomers at engine-relevant conditions
Butanol has received significant research attention as a second-generation
biofuel in the past few years. In the present study, skeletal mechanisms for
four butanol isomers were generated from two widely accepted, well-validated
detailed chemical kinetic models for the butanol isomers. The detailed models
were reduced using a two-stage approach consisting of the directed relation
graph with error propagation and sensitivity analysis. During the reduction
process, issues were encountered with pressure-dependent reactions formulated
using the logarithmic pressure interpolation approach; these issues are
discussed and recommendations made to avoid ambiguity in its future
implementation in mechanism development. The performance of the skeletal
mechanisms generated here was compared with that of detailed mechanisms in
simulations of autoignition delay times, laminar flame speeds, and perfectly
stirred reactor temperature response curves and extinction residence times,
over a wide range of pressures, temperatures, and equivalence ratios. The
detailed and skeletal mechanisms agreed well, demonstrating the adequacy of the
resulting reduced chemistry for all the butanol isomers in predicting global
combustion phenomena. In addition, the skeletal mechanisms closely predicted
the time-histories of fuel mass fractions in homogeneous compression-ignition
engine simulations. The performance of each butanol isomer was additionally
compared with that of a gasoline surrogate with an antiknock index of 87 in a
homogeneous compression-ignition engine simulation. The gasoline surrogate was
consumed faster than any of the butanol isomers, with tert-butanol exhibiting
the slowest fuel consumption rate. While n-butanol and isobutanol displayed the
most similar consumption profiles relative to the gasoline surrogate, the two
literature chemical kinetic models predicted different orderings.Comment: 39 pages, 16 figures. Supporting information available via
https://doi.org/10.1021/acs.energyfuels.6b0185
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