1,383 research outputs found
Electronic Education at the Faculty of Nuclear Sciences and Physical Engineering
This paper deals with the current issue of electronic education, and is based on a study of Internet support for education at the Faculty of Nuclear Sciences and Physical Engineering at the Czech Technical University in Prague.The goal of the study was to establish to what extent and in what ways electronic support for education is utilized at FNSPE CTU. In order to answer these questions, a questionnaire was conducted at the faculty. We will present the outcomes here.
Edge Effects Are Important in Supporting Beetle Biodiversity in a Gravel-Bed River Floodplain
Understanding complex, dynamic, and diverse ecosystems is essential for
developing sound management and conservation strategies. Gravel-bed river
floodplains are composed of an interlinked mosaic of aquatic and terrestrial
habitats hosting a diverse, specialized, and endangered fauna. Therefore, they
serve as excellent models to investigate the biodiversity of multiple ecotones
and related edge effects. In this study, we investigated the abundance,
composition, richness, and conservation status of beetle assemblages at
varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1,
5, 20, and 60–100 m, and 5 m within the riparian forest), and time of the year
(February–November) across a 200 m-wide gravel bar at the near-natural
Tagliamento River (Italy), to detect edge effects in four floodplain ecotones:
aquatic-terrestrial, forest-active floodplain, sediment-air, and sediment-
groundwater. We used conventional pitfall traps and novel tube traps to sample
beetles comparably on the sediment surface and within the unsaturated
sediments. We found a total of 308 beetle species (including 87 of
conservation concern) that showed multiple, significant positive edge effects
across the floodplain ecotones, mainly driven by spatial heterogeneity: Total
and red list beetle abundance and richness peaked on the sediment surface, at
channel margins, and at the edge of the riparian forest. All ecotones
possessed edge/habitat specialists. Most red list species occurred on the
sediment surface, including five species previously considered extinct – yet
two of these species occurred in higher densities in the unsaturated
sediments. Conservation and management efforts along gravel-bed rivers must
therefore promote a dynamic flow and sediment regime to create and maintain
habitat heterogeneity and ecotone diversity, which support a unique and high
biodiversity
Is the unsaturated sediment a neglected habitat for riparian arthropods? Evidence from a large gravel-bed river
AbstractDespite exposed surface sediments of braided, gravel-bed rivers host a diverse and endangered arthropod fauna, the ecology of the unsaturated layers below the surface but above the groundwater is mostly unexplored. Even if only parts of this zone are accessible to arthropods, this could be the most extensive habitat along braided rivers with likely important functions for arthropods’ population dynamics. Across a 200 m-wide gravel bar at the Tagliamento River (Italy), we investigated the abundance, taxon richness, and composition of arthropods at varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1, 5, 20, and 60–100 m), and time of the year (February–November). We used conventional pitfall traps and novel tube traps to sample surface and subsurface sediments comparably. Although abundance and diversity hotspots were located at the sediment surface at the edge of the gravel bar, the subsurface sediments supported an abundant arthropod fauna with similar richness to the sediment surface. We demonstrate that arthropods inhabit unsaturated sediments throughout the year, and speculate on the zone’s role as refugium and/or partial habitat. To ensure the future of this dynamic and diverse habitat we urge science, conservation, and management to include it in future programmes
Coupling of growth rate and developmental tempo reduces body size heterogeneity in C. elegans.
Animals increase by orders of magnitude in volume during development. Therefore, small variations in growth rates among individuals could amplify to a large heterogeneity in size. By live imaging of C. elegans, we show that amplification of size heterogeneity is prevented by an inverse coupling of the volume growth rate to the duration of larval stages and does not involve strict size thresholds for larval moulting. We perturb this coupling by changing the developmental tempo through manipulation of a transcriptional oscillator that controls the duration of larval development. As predicted by a mathematical model, this perturbation alters the body volume. Model analysis shows that an inverse relation between the period length and the growth rate is an intrinsic property of genetic oscillators and can occur independently of additional complex regulation. This property of genetic oscillators suggests a parsimonious mechanism that counteracts the amplification of size differences among individuals during development
Western Wheatgrass Recovery From Drought
Native grasses are predictably taller in wet years than in dry years and their density also increases with favorable precipitation. These responses of western wheatgrass are more dramatic on mechanically treated rangeland when precipitation is adequate. Measurements taken in July 1991 confirmed that western wheatgrass was slightly taller and density at least two times greater on mechanically treated claypan soils compared with untreated soils 13 and 18 years following treatment. Increases of this magnitude constitute a potentially greater carrying capacity which livestock producers should be prepared to utilize. This report briefly summarizes the effects of mechanical treatment on height and density of western wheatgrass 13 and 18 years following treatment and in a wet year following several dry years
Inclusion of ionic interactions in force field calculations of charged biomolecules – DNA structural transitions.
The potential of mean force (PMF) approach for treating polyion–diffuse ionic cloud interactions [D. M. Soumpasis (1984) Proceedings of the National Academy of Sciences USA81, 5116–5120] has been combined with the AMBER force field describing intramolecular interactions. The resultant generalized AMBER-PMF force field enables one to treat the conformational stabilities and structural transitions of charged biomolecules in aqueous electrolytes more realistically. For example, we have used it to calculate the relative stabilities of the B and Z conformations of d(C-G)6, and the B and heteronomous (H) conformations of dA12 · dT12, as a function of salt concentration. In the case of d(C-G)6, the predicted B–ZI transition occurs at 2.4M and is essentially driven by the phosphate-diffuse ionic cloud interactions alone as suggested by the results of earlier PMF calculations. The ZII conformer is less stable than the B form under all conditions. It is found that the helical parameters of the refined B and Z structures change with salt concentration. For example, the helical rise of B-DNA increases about 10% and the twist angle decreases by the same amount above 1M NaCl. In the range of 0.01–0.3M NaCl, the H form of dA12 · dT12 is found to be more stable than the B form and its stability increases with increasing salt concentration. The computed greater relative stability of the H conformation is likely due to noninclusion of the free energy contribution from the spine of hydration, a feature presumed to stabilize the B form of this sequence
Revealing the structure of the outer disks of Be stars
Context. The structure of the inner parts of Be star disks (20 stellar radii)
is well explained by the viscous decretion disk (VDD) model, which is able to
reproduce the observable properties of most of the objects studied so far. The
outer parts, on the ther hand, are not observationally well-explored, as they
are observable only at radio wavelengths. A steepening of the spectral slope
somewhere between infrared and radio wavelengths was reported for several Be
stars that were previously detected in the radio, but a convincing physical
explanation for this trend has not yet been provided. Aims. We test the VDD
model predictions for the extended parts of a sample of six Be disks that have
been observed in the radio to address the question of whether the observed
turndown in the spectral energy distribution (SED) can be explained in the
framework of the VDD model, including recent theoretical development for
truncated Be disks in binary systems. Methods. We combine new multi-wavelength
radio observations from the Karl. G. Jansky Very Large Array (JVLA) and Atacama
Pathfinder Experiment (APEX) with previously published radio data and archival
SED measurements at ultraviolet, visual, and infrared wavelengths. The density
structure of the disks, including their outer parts, is constrained by
radiative transfer modeling of the observed spectrum using VDD model
predictions. In the VDD model we include the presumed effects of possible tidal
influence from faint binary companions. Results. For 5 out of 6 studied stars,
the observed SED shows strong signs of SED turndown between far-IR and radio
wavelengths. A VDD model that extends to large distances closely reproduces the
observed SEDs up to far IR wavelengths, but fails to reproduce the radio SED.
... (abstract continues but did not fit here)Comment: 20 pages, 8 figure
Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star CMi
The viscous decretion disk (VDD) model is able to explain most of the
currently observable properties of the circumstellar disks of Be stars.
However, more stringent tests, focusing on reproducing multitechnique
observations of individual targets via physical modeling, are needed to study
the predictions of the VDD model under specific circumstances. In the case of
nearby, bright Be star CMi, these circumstances are a very stable
low-density disk and a late-type (B8Ve) central star. The aim is to test the
VDD model thoroughly, exploiting the full diagnostic potential of individual
types of observations, in particular, to constrain the poorly known structure
of the outer disk if possible, and to test truncation effects caused by a
possible binary companion using radio observations. We use the Monte Carlo
radiative transfer code HDUST to produce model observables, which we compare
with a very large set of multitechnique and multiwavelength observations that
include ultraviolet and optical spectra, photometry covering the interval
between optical and radio wavelengths, optical polarimetry, and optical and
near-IR (spectro)interferometry. Due to the absence of large scale variability,
data from different epochs can be combined into a single dataset. A parametric
VDD model with radial density exponent of = 3.5, which is the canonical
value for isothermal flaring disks, is found to explain observables typically
formed in the inner disk, while observables originating in the more extended
parts favor a shallower, = 3.0, density falloff. Modeling of radio
observations allowed for the first determination of the physical extent of a Be
disk (35 stellar radii), which might be caused by a binary
companion. Finally, polarization data allowed for an indirect measurement of
the rotation rate of the star, which was found to be , i.e.,
very close to critical.Comment: 19 pages (35 including online material), 17 figures, 2 online
figures, 2 online tables with dat
Distorted Copulas: Constructions and Tail Dependence
Given a copula C, we examine under which conditions on an order isomorphism ψ of [0, 1] the distortion C ψ: [0, 1]2 → [0, 1], C ψ(x, y) = ψ{C[ψ−1(x), ψ−1(y)]} is again a copula. In particular, when the copula C is totally positive of order 2, we give a sufficient condition on ψ that ensures that any distortion of C by means of ψ is again a copula. The presented results allow us to introduce in a more flexible way families of copulas exhibiting different behavior in the tails
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