284 research outputs found
Teacher education accreditation in Turkey: The creation of a culture of quality
Cataloged from PDF version of article.Turkeyâs experience in developing and piloting accreditation criteria and national standards for teacher
education is examined. The full implementation of an accreditation process for teacher education
programs was not completed within the time of the development project. However, the effort to do so
encouraged the formation of a âquality cultureâ in the faculties of education. The paper discusses what
took place and analyses the later response of teacher educators to the introduction of accreditation
criteria and the way in which they were introduced. Educators largely welcomed national standards and
accreditation, but wished to have flexible means of implementation
Wildlife Damage to Agricultural Crops in Pennsylvania: The Farmers\u27 Perspective
Agricultural damage by wildlife is a major concern for both agricultural and wildlife agencies at the state and federal level. Our objective was to estimate wildlife damage to agricultural crops on a statewide basis. We sent questionnaires to 4,958 farmers and 1,003 were returned after 2 mailings. Twenty-five percent of farmers responding to our survey rated the level of wildlife damage to their crops as severe or very severe, 46% as moderate, and 29% had none or very little. Mean levels of crop loss to wildlife ranged from 6% for wheat to 10% for corn grain, and white-tailed deer (Odocoileus virginianus) were the most commonly reported cause of damage for all crops except soybeans. Farmers estimated the economic value of damage caused by wildlife to 6 crops (corn grain, silage, alfalfa, soybeans, oats, and wheat) as \u3e $70 million. Ninety-one percent of Pennsylvania farmers allowed deer hunting on their farms, but 62% of the farms were bordered at least partially by land that was posted (no hunting or limited hunting). Fifty-six percent of farmers whose land was bordered by posted land believed adjacent posted land made it difficult for them to control deer numbers and damage on the land they farmed. Thirty-one percent of farmers responding to the questionnaire reported that they had changed farming practices (i.e., no longer farmed a particular field or raised a particular crop) as a consequence of deer damage. Additional methods used to control deer damage included shooting (28%), chasing (13%), fencing (9.3%), repellents (7%), and noise devices (5%). Fencing and shooting were the only methods rated as being at least moderately effective
Photon localization barrier can be overcome
In contradistinction to a widespread belief that the spatial localization of
photons is restricted by a power-law falloff of the photon energy density,
I.Bialynicki-Birula [Phys. Rev. Lett. 80, 5247 (1998)] has proved that any
stronger -- up to an almost exponential -- falloff is allowed. We are showing
that for certain specifically designed cylindrical one-photon states the
localization is even better in lateral directions. If the photon state is built
from the so-called focus wave mode, the falloff in the waist cross-section
plane turns out to be quadratically exponential (Gaussian) and such strong
localization persists in the course of propagation.Comment: Short communication -- 4 pages, 2 figure
Terrestrial Liming As a Restoration Technique for Acidified Forest Ecosystems
We studied the effects of liming on soils and forest songbirds as well as vegetation and calcium-rich invertebrate prey variables that were predicted to link birds to changes in soil conditions. We observed increases in soil pH, calcium, and magnesium, as well as in songbird abundances in response to lime application, with continuing increases through five years after liming. We observed an overall increase in snail abundance on limed sites, but an initial peak of a 23 fold increase three years after liming was reduced to an 11 fold increase five years after liming. We observed an increase in forb ground cover on limed sites, but liming had no effect on millipede abundance or other vegetation measures. Of the variables we measured, snail abundance was the most likely mechanism for the response in bird abundances. Because we observed continued benefits of liming up to five years post treatment, we concluded that liming is a very promising technique for restoring forest ecosystems impacted by acidic deposition
Superluminal X-shaped beams propagating without distortion along a coaxial guide
In a previous paper [Phys. Rev. E64 (2001) 066603; e-print physics/0001039],
we showed that localized Superluminal solutions to the Maxwell equations exist,
which propagate down (non-evanescence) regions of a metallic cylindrical
waveguide. In this paper we construct analogous non-dispersive waves
propagating along coaxial cables. Such new solutions, in general, consist in
trains of (undistorted) Superluminal "X-shaped" pulses. Particular attention is
paid to the construction of finite total energy solutions. Any results of this
kind may find application in the other fields in which an essential role is
played by a wave-equation (like acoustics, geophysics, etc.). [PACS nos.:
03.50.De; 41.20;Jb; 83.50.Vr; 62.30.+d; 43.60.+d; 91.30.Fn; 04.30.Nk; 42.25.Bs;
46.40.Cd; 52.35.Lv. Keywords: Wave equations; Wave propagation; Localized
beams; Superluminal waves; Coaxial cables; Bidirectional decomposition; Bessel
beams; X-shaped waves; Maxwell equations; Microwaves; Optics; Special
relativity; Coaxial metallic waveguides; Acoustics; Seismology; Mechanical
waves; Elastic waves; Guided gravitational waves.]Comment: plain LaTeX file (22 pages), plus 15 figures; in press in Phys. Rev.
Diffraction-free subwavelength-beam optics
Diffraction is a fundamental property of light propagation. Owing to this
phenomenon,light diffracts out in all directions when it passes through a
subwavelength slit.This imposes a fundamental limit on the transverse size of a
light beam at a given distance from the aperture. We show that a
subwavelength-sized beam propagating without diffractive broadening can be
produced in free space by the constructive interference of multiple beams of a
Fresnel source of the respective high-refraction-index waveguide. Moreover, it
is shown that such a source can be constructed not only for continuous waves,
but also for ultra-short (near single-cycle) pulses. The results theoretically
demonstrate the feasibility of completely diffraction-free subwavelength-beam
optics, for both continuous waves and ultra-short pulses. The approach extends
operation of the near-field subwavelength-beam optics, such as near-field
scanning optical microscopy and spectroscopy,to the "not-too-distant" field
regime (0.5 to about 10 wavelengths).Comment: 4 figure
mTORC1 Controls Phase Separation and the Biophysical Properties of the Cytoplasm by Tuning Crowding
International audienceMacromolecular crowding has a profound impact on reaction rates and the physical properties of the cell interior, but the mechanisms that regulate crowding are poorly understood. We developed genetically encoded multimeric nanoparticles (GEMs) to dissect these mechanisms. GEMs are homomultimeric scaffolds fused to a fluorescent protein that self-assemble into bright, stable particles of defined size and shape. By combining tracking of GEMs with genetic and pharmacological approaches, we discovered that the mTORC1 pathway can modulate the effective diffusion coefficient of particles â„20 nm in diameter more than 2-fold by tuning ribosome concentration, without any discernable effect on the motion of molecules â€5 nm. This change in ribosome concentration affected phase separation both in vitro and in vivo. Together, these results establish a role for mTORC1 in controlling both the mesoscale biophysical properties of the cytoplasm and biomolecular condensation
Superluminal Localized Solutions to the wave equation, in (vacuum or) dispersive media, for arbitrary frequencies and with adjustable bandwidth
In this paper we set forth new exact analytical Superluminal localized
solutions to the wave equation for arbitrary frequencies and adjustable
bandwidth. The formulation presented here is rather simple, and its results can
be expressed in terms of the ordinary, so-called "X-shaped waves". Moeover, by
the present formalism we obtain the first analytical localized Superluminal
approximate solutions which represent beams propagating in dispersive media.
Our solutions may find application in different fields, like optics,
microwaves, radio waves, and so on. [PACS nos.: 03.50.De ; 41.20.Jb ; 83.50.Vr
; 62.30.+d ; 43.60.+d ; 91.30.Fn ; 04.30.Nk ; 42.25.Bs ; 46.40.Cd ; 52.35.Lv.
Keywords: Wave equation; Wave propagation; Optics; Localized beams;
Superluminal waves; Bessel beams; X-shaped waves; Acoustics; Mechanical waves;
Dispersion compensation; Seismology; Geophysics; Gravitational Waves;
Elementary particle physics].Comment: plain LaTeX file (16 pages), plus 9 figure
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