18,365 research outputs found
Three-dimensional cell to tissue assembly process
The present invention relates a 3-dimensional cell to tissue and maintenance process, more particularly to methods of culturing cells in a culture environment, either in space or in a gravity field, with minimum fluid shear stress, freedom for 3-dimensional spatial orientation of the suspended particles and localization of particles with differing or similar sedimentation properties in a similar spatial region
Bulk and contact-sensitized photocarrier generation in single layer TPD devices
In this paper, we report on the photoelectronic properties of TPD studied in
sandwich geometry. In particular, we have obtained from both forward and
reverse bias measurements the "mew-tau" product for holes in TPD. "mew" is the
hole mobility and "tau" the carrier trapping time. The "mew-tau" product is a
measure of the electronic quality of the material and allows a quantitative
comparison of different samples. We have carried out numerical simulations to
understand the photocurrent in these structures. We show that in reverse bias,
the photocurrent (PC) is due to bulk. The carrier generation is governed by
field assisted exciton dissociation at electric fields greater than 10^6 V/cm.
At lower fields the generation of carriers occurs spontaneously in the bulk of
the sample. In forward bias, the photocurrent is due to exciton dissociation at
the ITO contact. We also obtain a "mew-tau" product for holes from forward bias
PC measurements which is in agreement with the value obtained from reverse bias
measurements. Based on our experiments, we demonstrate that TPD in a sandwich
structure is a good candidate for cheap large area solar blind UV detector
arrays.Comment: Submitted to J. Appl. Phy
Accretion Disks around Young Stars: Lifetimes, Disk Locking and Variability
We report the findings of a comprehensive study of disk accretion and related
phenomena in four of the nearest young stellar associations spanning 6-30
million years in age, an epoch that may coincide with the late stages of planet
formation. We have obtained ~650 multi-epoch high-resolution optical spectra of
100 low-mass stars that are likely members of the eta Chamaeleontis (~6 Myr),
TW Hydrae (~8 Myr), beta Pictoris (~12 Myr) and Tucanae-Horologium (~30 Myr)
groups. Our data were collected over 12 nights between 2004 December - 2005
July on the Magellan Clay 6.5m telescope. Based on H line profiles,
along with a variety of other emission lines, we find clear evidence of
on-going accretion in three out of 11 eta Cha stars and two out of 32 TW Hydrae
members. None of the 57 beta Pic or Tuc-Hor members shows measurable signs of
accretion. Together, these results imply significant evolution of the disk
accretion process within the first several Myr of a low-mass star's life. While
a few disks can continue to accrete for up to ~10 Myr, our findings suggest
that disks accreting for beyond that timescale are rather rare. This result
provides an indirect constraint on the timescale for gas dissipation in inner
disks and, in turn, on gas giant planet formation. All accretors in our sample
are slow rotators, whereas non-accretors cover a large range in rotational
velocities. This may hint at rotational braking by disks at ages up to ~8 Myr.
Our multi-epoch spectra confirm that emission-line variability is common even
in somewhat older T Tauri stars, among which accretors tend to show
particularly strong variations. Thus, our results indicate that accretion and
wind activity undergo significant and sustained variations throughout the
lifetime of accretion disks.Comment: to appear in The Astrophysical Journa
The psychophysics of absolute threshold and signal duration: A probabilistic approach
The absolute threshold for a tone depends on its duration; longer tones have lower thresholds. This effect has traditionally been explained in terms of ?temporal integration? involving the summation of energy or perceptual information over time. An alternative probabilistic explanation of the process is formulated in terms of simple equations that predict not only the time=duration dependence but also the shape of the psychometric function at absolute threshold. It also predicts a tight relationship between these two functions. Measurements made using listeners with either normal or impaired hearing show that the probabilistic equations adequately fit observed threshold-duration functions and psychometric functions. The mathematical formulation implies that absolute threshold can be construed as a two-valued function: (a) gain and (b) sensory threshold, and both parameters can be estimated from threshold-duration data. Sensorineural hearing impairment is sometimes associated with a smaller threshold=duration effect and sometimes with steeper psychometric functions. The equations explain why these two effects are expected to be linked. The probabilistic approach has the potential to discriminate between hearing deficits involving gain reduction and those resulting from a raised sensory threshold
Signaling local non-credibility in an automatic segmentation pipeline
The advancing technology for automatic segmentation of medical images should be accompanied by techniques to inform the user of the local credibility of results. To the extent that this technology produces clinically acceptable segmentations for a significant fraction of cases, there is a risk that the clinician will assume every result is acceptable. In the less frequent case where segmentation fails, we are concerned that unless the user is alerted by the computer, she would still put the result to clinical use. By alerting the user to the location of a likely segmentation failure, we allow her to apply limited validation and editing resources where they are most needed. We propose an automated method to signal suspected non-credible regions of the segmentation, triggered by statistical outliers of the local image match function. We apply this test to m-rep segmentations of the bladder and prostate in CT images using a local image match computed by PCA on regional intensity quantile functions. We validate these results by correlating the non-credible regions with regions that have surface distance greater than 5.5mm to a reference segmentation for the bladder. A 6mm surface distance was used to validate the prostate results. Varying the outlier threshold level produced a receiver operating characteristic with area under the curve of 0.89 for the bladder and 0.92 for the prostate. Based on this preliminary result, our method has been able to predict local segmentation failures and shows potential for validation in an automatic segmentation pipeline
A survey of snellen acuity sizes and linance contrasts of letters on signs visible from the front of the college of optometry building at PU
A survey of snellen acuity sizes and linance contrasts of letters on signs visible from the front of the college of optometry building at P
Recrystallization of epitaxial GaN under indentation
We report recrystallization of epitaxial (epi-) GaN(0001) film under
indentation.Hardness value is measured close to 10 GPa, using a Berkovich
indenter. Pop-in burst in the loading line indicates nucleation of dislocations
setting in plastic motion of lattice atoms under stress field for the
recrystallization process. Micro-Raman studies are used to identify the
recrystallization process. Raman area mapping indicates the crystallized
region. Phonon mode corresponding to E2(high) close to 570 cm-1 in the as-grown
epi-GaN is redshifted to stress free value close to 567 cm-1 in the indented
region. Evolution of A1(TO) and E1(TO) phonon modes are also reported to
signify the recrystallization process.Comment: 10 pages, 3 figures
Developing Career Development Profiles of Student-Athletes: A Comparison with Non-Athletes
Student-athletes' and non-athletes' scores on several career-related assessments were compared. During the 1990-91 academic year at a medium-sized, state-supported university in the South, a sample of 41 student-athletes (83% males and 17% females) and 178 non-athletes (29% males and 71% females) completed the Values Scale (Super & Nevill, 1985b), Career Development Inventory (Super, Thompson, Lindeman, Jordaan, & Myers, 1981), and Salience Inventory (Super & Nevill, 1985a). Completion of these instruments was required for a semester-long, three-credit course in career/life planning. The student-athletes were non-revenue scholarship athletes representing a NCAA Division II institution in soccer, basketball, and tennis. Both groups contained students representing all class ranks, with a majority in both groups being white (93% of the student-athlete group and 69% of the non-athlete group. Results of two-way ANOVAs indicated that student-athletes highly value physical activity and spend more time in leisure activities than non-athletes. Only one significant gender effect was found: females had a higher score on the combined knowledge scale (M = 100.29) than males (M = 85.16) (F(1, 138) = 8.43, p < .006). The combined knowledge scale score is a linear combination of scores in decision-making and world-of-work information. This result indicates that females may be better able to apply career development principles to decision-making scenarios as well as demonstrate more knowledge of what it takes to get a job and succeed. No differences in career maturity scores were found. Implications for programming to accommodate the special needs of student-athletes are discussed
- …