1,022 research outputs found
Doing Well by Doing Good: A Study of the Effects of a Service-Learning Experience on Student Success
This study explored the effects of service learning on student success in college. The study consisted of 286 students enrolled in six paired community college courses in various disciplines. One section of each pair was taught using traditional subject matter and course materials,while the other section of each pair was required to participate in a 20-hourservice learning activity in addition to the regular course curriculum.Participating faculty completed questionnaires and interviews regarding the courses, and students completed end-of-course evaluations. The results indicated that, overall, students who participated in the sections with a service learning requirement achieved higher final course grades and reported greater satisfaction with the course. In addition, faculty members who taught the service learning sections reported that class discussions were more stimulating, the sections seemed more vital in terms of student involvement,and the students seemed more challenged academically than in the traditional instruction sections
Extended morphometric analysis of neuronal cells with Minkowski valuations
Minkowski valuations provide a systematic framework for quantifying different
aspects of morphology. In this paper we apply vector- and tensor-valued
Minkowski valuations to neuronal cells from the cat's retina in order to
describe their morphological structure in a comprehensive way. We introduce the
framework of Minkowski valuations, discuss their implementation for neuronal
cells and show how they can discriminate between cells of different types.Comment: 14 pages, 18 postscript figure
Proprotein convertase cleavage liberates a fibrillogenic fragment of a resident glycoprotein to initiate melanosome biogenesis
Lysosome-related organelles are cell typeāspecific intracellular compartments with distinct morphologies and functions. The molecular mechanisms governing the formation of their unique structural features are not known. Melanosomes and their precursors are lysosome-related organelles that are characterized morphologically by intralumenal fibrous striations upon which melanins are polymerized. The integral membrane protein Pmel17 is a component of the fibrils and can nucleate their formation in the absence of other pigment cellāspecific proteins. Here, we show that formation of intralumenal fibrils requires cleavage of Pmel17 by a furin-like proprotein convertase (PC). As in the generation of amyloid, proper cleavage of Pmel17 liberates a lumenal domain fragment that becomes incorporated into the fibrils; longer Pmel17 fragments generated in the absence of PC activity are unable to form organized fibrils. Our results demonstrate that PC-dependent cleavage regulates melanosome biogenesis by controlling the fibrillogenic activity of a resident protein. Like the pathologic process of amyloidogenesis, the formation of other tissue-specific organelle structures may be similarly dependent on proteolytic activation of physiological fibrillogenic substrates
Enhanced inverse bremsstrahlung heating rates in a strong laser field
Test particle studies of electron scattering on ions, in an oscillatory
electromagnetic field have shown that standard theoretical assumptions of small
angle collisions and phase independent orbits are incorrect for electron
trajectories with drift velocities smaller than quiver velocity amplitude. This
leads to significant enhancement of the electron energy gain and the inverse
bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as
Coulomb focusing and correlated collisions of electrons being brought back to
the same ion by the oscillatory field are responsible for large angle, head-on
scattering processes. The statistical importance of these trajectories has been
examined for mono-energetic beam-like, Maxwellian and highly anisotropic
electron distribution functions. A new scaling of the inverse bremsstrahlung
heating rate with drift velocity and laser intensity is discussed.Comment: 12 pages, 12 figure
Markbooks
A collection of carefully left traces ā and their occasionally accompanying thoughts ā Markbooks is the result of āan ongoing conversation about attention, its ecologies, its forms, and the markings of its passage.ā āFor many of the authors included here, the practice of making ā and then reading ā their little book located them in timeā¦ [T]here is paper, and there are pencils, and there are bodies to mark their own motion.
Multiphoton Ionization as Time-Dependent Tunneling
A new semiclassical approach to ionization by an oscillating field is
presented. For a delta-function atom, an asymptotic analysis is performed with
respect to a quantity h, defined as the ratio of photon energy to ponderomotive
energy. This h appears formally equivalent to Planck's constant in a suitably
transformed Schroedinger equation and allows semiclassical methods to be
applicable. Systematically, a picture of tunneling wave packets in complex time
is developped, which by interference account for the typical ponderomotive
features of ionization curves. These analytical results are then compared to
numerical simulations and are shown to be in good agreement.Comment: 36 pages (also printable half size), uuencoded compressed tarred
Latex file with 9 Postscript figures included automaticall
Stem cells as a therapeutic tool for the blind: biology and future prospects
Retinal degeneration due to genetic, diabetic and age-related disease is the most common cause of blindness in the developed world. Blindness occurs through the loss of the light-sensing photoreceptors; to restore vision, it would be necessary to introduce alternative photosensitive components into the eye. The recent development of an electronic prosthesis placed beneath the severely diseased retina has shown that subretinal stimulation may restore some visual function in blind patients. This proves that residual retinal circuits can be reawakened after photoreceptor loss and defines a goal for stem-cell-based therapy to replace photoreceptors. Advances in reprogramming adult cells have shown how it may be possible to generate autologous stem cells for transplantation without the need for an embryo donor. The recent success in culturing a whole optic cup in vitro has shown how large numbers of photoreceptors might be generated from embryonic stem cells. Taken together, these threads of discovery provide the basis for optimism for the development of a stem-cell-based strategy for the treatment of retinal blindness
Recognition of Facial Expressions by Cortical Multi-scale Line and Edge Coding
Face-to-face communications between humans involve emotions, which often are unconsciously conveyed by facial expressions and body gestures. Intelligent human-machine interfaces, for example in cognitive robotics, need to recognize emotions. This paper addresses facial expressions and their neural correlates on the basis of a model of the visual cortex: the multi-scale line and edge coding. The recognition model links the cortical representation with Paul Ekman's Action Units which are related to the different facial muscles. The model applies a top-down categorization with trends and magnitudes of displacements of the mouth and eyebrows based on expected displacements relative to a neutral expression. The happy vs. not-happy categorization yielded a. correct recognition rate of 91%, whereas final recognition of the six expressions happy, anger, disgust, fear, sadness and surprise resulted in a. rate of 78%
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