13,600 research outputs found
Ultrasonography of the reticulum in 30 healthy Saanen goats
Background: The reticulum plays a crucial role in the ruminant digestive tract because the primary cycle of rumen motility always starts with a reticular contraction. In contrast to cattle, there are only few results on the ultrasonographic examination of the reticulum in goats. Therefore, it was the goal of the present study, to describe the results of ultrasonography of the reticulum of 30 healthy Saanen goats. Methods: Ultrasonography was carried out on standing, non-sedated animals using a 5.0 MHz linear transducer. The shape, contour and motility of the reticulum were investigated. A nine-minute video recording of the reticulum was made for each goat and the frequency, duration and amplitude of reticular contractions were calculated as described for cattle. Results: The reticulum appeared as a crescent-shaped structure with a smooth contour located immediately adjacent to the diaphragm. 0.8 to 2.1 (1.41 ± 0.31) reticular contractions were seen per minute. In all goats, biphasic reticular contractions were observed. 90% of the goats also had monophasic reticular contractions, and two had triphasic contractions. During the nine-minute observation periods, there were 0 to 6 monophasic reticular contractions and 6 to 15 biphasic contractions per goat. The duration of the biphasic contractions was 6.56 ± 0.74 s, which was significantly longer than the monophasic contractions at 4.31 ± 0.81 s. The average interval between two reticular contractions was 45.06 ± 12.57 s. Conclusion: Ultrasonography of the reticulum in goats is a valuable tool to characterise the appearance and motility of this organ. In addition to the biphasic motility pattern seen in cattle the reticular motility of goats is characterized by monophasic reticular contractions. The results of the present study are an important contribution for better understanding of the reticular motility in goats
Decoherence in a system of many two--level atoms
I show that the decoherence in a system of degenerate two--level atoms
interacting with a bosonic heat bath is for any number of atoms governed by
a generalized Hamming distance (called ``decoherence metric'') between the
superposed quantum states, with a time--dependent metric tensor that is
specific for the heat bath.The decoherence metric allows for the complete
characterization of the decoherence of all possible superpositions of
many-particle states, and can be applied to minimize the over-all decoherence
in a quantum memory. For qubits which are far apart, the decoherence is given
by a function describing single-qubit decoherence times the standard Hamming
distance. I apply the theory to cold atoms in an optical lattice interacting
with black body radiation.Comment: replaced with published versio
Periodically driven stochastic un- and refolding transitions of biopolymers
Mechanical single molecule experiments probe the energy profile of
biomolecules. We show that in the case of a profile with two minima (like
folded/unfolded) periodic driving leads to a stochastic resonance-like
phenomenon. We demonstrate that the analysis of such data can be used to
extract four basic parameters of such a transition and discuss the statistical
requirements of the data acquisition. As advantages of the proposed scheme, a
polymeric linker is explicitly included and thermal fluctuations within each
well need not to be resolved.Comment: 7 pages, 5 figures, submitted to EP
Magnetization Switching in Nanowires: Monte Carlo Study with Fast Fourier Transformation for Dipolar Fields
For the investigations of thermally activated magnetization reversal in
systems of classical magnetic moments numerical methods are desirable. We
present numerical studies which base on time quantified Monte Carlo methods
where the long-range dipole-dipole interaction is calculated with the aid of
fast Fourier transformation. As an example, we study models for ferromagnetic
nanowires comparing our numerical results for the characteristic time of the
reversal process also with numerical data from Langevin dynamics simulations
where the fast Fourier transformation method is well established. Depending on
the system geometry different reversal mechanism occur like coherent rotation,
nucleation, and curling.Comment: 7 pages, 5 figures, submitted to J. Magn. Magn. Ma
Oidium longipes, a new powdery mildew fungus on petunia in the USA: A potential threat to ornamental and vegetable solanaceous crops
This is the first North American report of Oidium longipes, an anamorphic powdery mildew species described recently in Europe. It was found on vegetatively propagated petunia grown in a commercial greenhouse in New Jersey, USA, where it caused a rapidly spreading disease. The pathogen might have originated offshore and may have already been distributed in the United States through horticultural trade. During field surveys in Europe, it was found on petunia in Hungary and Austria as well; this is the first report of O. longipes from these two countries. A detailed light microscopy study of American and European specimens of O. longipes, including freshly collected samples and authentic herbarium specimens, revealed that its conidiophore morphology is more variable than illustrated in the original species description or in subsequent works. Microcycle conidiation, a process not yet known to occur in powdery mildews, was repeatedly observed in O. longipes. The rDNA internal transcribed spacer (ITS) sequences were identical in colonies containing different conidiophore types as well as in a total of five specimens collected from petunia in the United States, Austria, Hungary, Germany, and Switzerland. A phylogenetic analysis of the ITS sequences revealed that the closest known relative of O. longipes is O. lycopersici, known to infect tomato only in Australia. Cross-inoculation tests showed that O. longipes from petunia heavily infected tobacco cv. Xanthi, while the tomato and eggplant cultivars tested were moderately susceptible to this pathogen. These results indicate that its spread represents a potential danger to a number of solanaceous crops. Our ad hoc field surveys conducted in 2006 and 2007 did not detect it outside New Jersey in the United States; all the other powdery mildewâinfected petunias, collected in New York and Indiana, were infected by Podosphaera xanthii. In Europe, most of the powdery mildewâinfected petunias examined in this study were infected by P. xanthii or Golovinomyces orontii. Our multiple inoculation tests revealed that the same petunia plants and even the same leaves can be infected concomitantly by O. longipes, O. neolycopersici, G. orontii, and P. xanthii. Thus, it is at present unclear to what extent O. longipes contributes to the powdery mildew epidemics that develop year after year on solanaceous plants in many parts of the world
Disorder-sensitive superconductivity in the iron silicide LuFeSi studied by the Lu-site substitutions
We studied effect of non-magnetic and magnetic impurities on
superconductivity in LuFeSi by small amount substitution of the Lu
site, which investigated structural, magnetic, and electrical properties of
non-magnetic (LuSc)FeSi,
(LuY)FeSi, and magnetic
(LuDy)FeSi. The rapid depression of by
non-magnetic impurities in accordance with the increase of residual resistivity
reveals the strong pair breaking dominated by disorder. We provide compelling
evidence for the sign reversal of the superconducting order parameter in
LuFeSi.Comment: 4 pages, 5 figure
B-mode and colour Doppler sonographic examination of the milk vein and musculophrenic vein in dry cows and cows with a milk yield of 10 and 20 kg
BACKGROUND: This study investigated the effect of milk yield on blood flow variables in the milk vein and musculophrenic vein in dairy cows. METHODS: Five healthy dry cows, five cows with a daily milk yield of 10 kg and five others with a daily milk yield of 20 kg underwent B-mode and colour Doppler sonographic examination. The diameter of the veins, blood flow velocities and blood flow volumes were measured on both sides in standing, non-sedated cows using a 7.5 MHz linear transducer. RESULTS: Lactating cows had significantly higher blood flow velocities in the milk vein than dry cows; the maximum blood flow velocity of dry cows and those with a daily milk yield of 10 and 20 kg were 14.04, 38.77 and 39.49 cm/s, respectively, the minimum velocities were 0.63, 3.02 and 2.64 cm/s, respectively, and the mean maximum velocities were 8.21, 26.67 und 28.22 cm/s, respectively. Cows producing 20 kg of milk a day had a blood flow volume of 3.09 l/min, which was significantly higher than 0.79 l/min recorded in dry cows. Lactating cows had significantly higher mean maximum blood flow velocities in the musculophrenic vein than dry cows. Blood flow variables of both veins did not differ significantly between the left and right side. CONCLUSION: This study showed that milk yield has a profound effect on blood flow variables in the milk vein and to a lesser extent the musculophrenic vein. This must be taken into consideration in future Doppler sonographic studies of these veins and possibly other vessels. Furthermore, measurements on one side are representative of both sides
Pseudocercospora opuntiae sp. nov., the causal organism of cactus leaf spot in Mexico.
Pseudocercospora opuntiae is newly described from Opuntia spp. from Mexico, where it causes a serious disease of this host. Although P. opuntiae is morphologically similar to other members of the genus with pigmented conidia and conidiophores, and unthickened, not darkened conidiogenous scars, DNA sequence data of the ITS region revealed that it clusters distant from other species of Pseudocercospora within Mycosphaerella. These data support the assumption that Pseudocereospora is paraphyletic within Mycosphaerella
Are Compact High-Velocity Clouds Extragalactic Objects?
Compact high-velocity clouds (CHVCs) are the most distant of the HVCs in the
Local Group model and would have HI volume densities of order 0.0003/cm^3.
Clouds with these volume densities and the observed neutral hydrogen column
densities will be largely ionized, even if exposed only to the extragalactic
ionizing radiation field. Here we examine the implications of this process for
models of CHVCs. We have modeled the ionization structure of spherical clouds
(with and without dark matter halos) for a large range of densities and sizes,
appropriate to CHVCs over the range of suggested distances, exposed to the
extragalactic ionizing photon flux. Constant-density cloud models in which the
CHVCs are at Local Group distances have total (ionized plus neutral) gas masses
roughly 20-30 times larger than the neutral gas masses, implying that the gas
mass alone of the observed population of CHVCs is about 40 billion solar
masses. With a realistic (10:1) dark matter to gas mass ratio, the total mass
in such CHVCs is a significant fraction of the dynamical mass of the Local
Group, and their line widths would exceed the observed FWHM. Models with dark
matter halos fare even more poorly; they must lie within approximately 200 kpc
of the Galaxy. We show that exponential neutral hydrogen column density
profiles are a natural consequence of an external source of ionizing photons,
and argue that these profiles cannot be used to derive model-independent
distances to the CHVCs. These results argue strongly that the CHVCs are not
cosmological objects, and are instead associated with the Galactic halo.Comment: 30 pages, 14 figures; to appear in The Astrophysical Journa
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