8,688 research outputs found
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Learning to teach : the development of teaching knowledge in trained and untrained physical education teachers.
The primary purpose of this study was to further the understanding of how people learn to teach. The central research question focused on differences in teaching knowledge that may be associated with training and experience. Eight teachers were selected to participate in this study. They represented a wide range of teaching experience, formal training, professional certification and sport participation. The common criterion for selection was previous experience in the teaching of volleyball. Data were collected from both questionnaires and transcribed interviews which followed the viewing of a twenty-minute videotaped volleyball lesson. Results indicated differences among the participating teachers in content knowledge (the skills of playing volleyball), pedagogical knowledge (general teaching principles), and pedagogical content knowledge (content-specific teaching knowledge). The comments of trained teachers displayed a greater awareness of and concern for general teaching principles. In contrast, untrained teachers devoted most of their comments to lesson content. Experienced teachers, whether trained or untrained, demonstrated a superior understanding of the relationship between the nature of content and the needs of learners at different levels of skill development. In that regard, they had a more elaborately developed sense of pedagogical content knowledge. Untrained teachers cited their experience as students and athletes as major sources of information about teaching, while trained teachers pointed to experiences associated with their formal training. Members from both group indicated that they had learned from role models and early teaching experiences. Among trained and untrained teachers the sources for the differences in knowledge, and how that knowledge was processed, included the following: varied teaching contexts such as public high schools and university classes, the extent of teaching experience which ranged from one to eighteen years, and views about teaching that were influenced by previous experience in either coaching or teaching roles. Implications for teacher education and staff development include a need for training experiences that will integrate various forms of teaching knowledge. In addition, it is clear that teacher preparation programs must deal much more explicitly with the differences between coaching and teaching contexts
ADZE: a rarefaction approach for counting alleles private to combinations of populations
Motivation: Analysis of the distribution of alleles across populations is a useful tool for examining population diversity and relationships. However, sample sizes often differ across populations, sometimes making it difficult to assess allelic distributions across groups
Levinson's theorem for the Schr\"{o}dinger equation in two dimensions
Levinson's theorem for the Schr\"{o}dinger equation with a cylindrically
symmetric potential in two dimensions is re-established by the Sturm-Liouville
theorem. The critical case, where the Schr\"{o}dinger equation has a finite
zero-energy solution, is analyzed in detail. It is shown that, in comparison
with Levinson's theorem in non-critical case, the half bound state for
wave, in which the wave function for the zero-energy solution does not decay
fast enough at infinity to be square integrable, will cause the phase shift of
wave at zero energy to increase an additional .Comment: Latex 11 pages, no figure and accepted by P.R.A (in August); Email:
[email protected], [email protected]
Ultralow threshold graded-index separate-confinement heterostructure single quantum well (Al,Ga)As lasers
Broad area graded‐index separate‐confinement heterostructure single quantum well lasers grown by molecular‐beam epitaxy (MBE) with threshold current density as low as 93 A/cm^2 (520 μm long) have been fabricated. Buried lasers formed from similarly structured MBE material with liquid phase epitaxy regrowth had threshold currents at submilliampere levels when high reflectivity coatings were applied to the end facets. A cw threshold current of 0.55 mA was obtained for a laser with facet reflectivities of ∼80%, a cavity length of 120 μm, and an active region stripe width of 1 μm. These devices driven directly with logic level signals have switch‐on delays <50 ps without any current prebias. Such lasers permit fully on–off switching while at the same time obviating the need for bias monitoring and feedback control
Contribution of Matrix Metalloproteinase-9 to Cerebral Edema and Functional Outcome following Experimental Subarachnoid Hemorrhage
Background: Cerebral edema is an important risk factor for death and poor outcome following subarachnoid hemorrhage (SAH). However, underlying mechanisms are still poorly understood. Matrix metalloproteinase (MMP)-9 is held responsible for the degradation of microvascular basal lamina proteins leading to blood-brain barrier dysfunction and, thus, formation of vasogenic cerebral edema. The current study was conducted to clarify the role of MMP-9 for the development of cerebral edema and for functional outcome after SAH. Methods: SAH was induced in FVB/N wild-type (WT) or MMP-9 knockout (MMP-9(-/-)) mice by endovascular puncture. Intracranial pressure (ICP), regional cerebral blood flow (rCBF), and mean arterial blood pressure (MABP) were continuously monitored up to 30 min after SAH. Mortality was quantified for 7 days after SAH. In an additional series neurological function and body weight were assessed for 3 days after SAH. Subsequently, ICP and brain water content were quantified. Results: Acute ICP, rCBF, and MABP did not differ between WT and MMP-9(-/-) mice, while 7 days' mortality was lower in MMP-9(-/-) mice (p = 0.03; 20 vs. 60%). MMP-9(-/-) mice also exhibited better neurological recovery, less brain edema formation, and lower chronic ICP. Conclusions: The results of the current study suggest that MMP-9 contributes to the development of early brain damage after SAH by promoting cerebral edema formation. Hence, MMP-9 may represent a novel molecular target for the treatment of SAH. Copyright (C) 2011 S. Karger AG, Base
The Relativistic Levinson Theorem in Two Dimensions
In the light of the generalized Sturm-Liouville theorem, the Levinson theorem
for the Dirac equation in two dimensions is established as a relation between
the total number of the bound states and the sum of the phase shifts
of the scattering states with the angular momentum :
\noindent The critical case, where the Dirac equation has a finite
zero-momentum solution, is analyzed in detail. A zero-momentum solution is
called a half bound state if its wave function is finite but does not decay
fast enough at infinity to be square integrable.Comment: Latex 14 pages, no figure, submitted to Phys.Rev.A; Email:
[email protected], [email protected]
Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons
We propose an efficient phase-encoding quantum secret key generation scheme
with heralded narrow-band single photons. The key information is carried by the
phase modulation directly on the single-photon temporal waveform without using
any passive beam splitters or optical switches. We show that, when the
technique is applied to the conventional fiber-based phase-encoding BB84 and
differential phase shift (DPS) quantum key distribution schemes, the key
generation efficiencies can be improved by a factor of 2 and 3, respectively.
For N(>3)-period DPS systems, the key generation efficiency can be improved by
a factor of N. The technique is suitable for quantum memory-based long-distance
fiber communication system.Comment: 5 pages, 5 figure
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A conserved morphogenetic mechanism for epidermal ensheathment of nociceptive sensory neurites.
Interactions between epithelial cells and neurons influence a range of sensory modalities including taste, touch, and smell. Vertebrate and invertebrate epidermal cells ensheath peripheral arbors of somatosensory neurons, including nociceptors, yet the developmental origins and functional roles of this ensheathment are largely unknown. Here, we describe an evolutionarily conserved morphogenetic mechanism for epidermal ensheathment of somatosensory neurites. We found that somatosensory neurons in Drosophila and zebrafish induce formation of epidermal sheaths, which wrap neurites of different types of neurons to different extents. Neurites induce formation of plasma membrane phosphatidylinositol 4,5-bisphosphate microdomains at nascent sheaths, followed by a filamentous actin network, and recruitment of junctional proteins that likely form autotypic junctions to seal sheaths. Finally, blocking epidermal sheath formation destabilized dendrite branches and reduced nociceptive sensitivity in Drosophila. Epidermal somatosensory neurite ensheathment is thus a deeply conserved cellular process that contributes to the morphogenesis and function of nociceptive sensory neurons
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