1,585 research outputs found

    Aerothermodynamic radiation studies

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    We have built and made operational a 6 in. electric arc driven shock tube which alloys us to study the non-equilibrium radiation and kinetics of low pressure (0.1 to 1 torr) gases processed by 6 to 12 km/s shock waves. The diagnostic system allows simultaneous monitoring of shock radiation temporal histories by a bank of up to six radiometers, and spectral histories with two optical multi-channel analyzers. A data set of eight shots was assembled, comprising shocks in N2 and air at pressures between 0.1 and 1 torr and velocities of 6 to 12 km/s. Spectrally resolved data was taken in both the non-equilibrium and equilibrium shock regions on all shots. The present data appear to be the first spectrally resolved shock radiation measurements in N2 performed at 12 km/s. The data base was partially analyzed with salient features identified

    Multi-spot ignition in type Ia supernova models

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    We present a systematic survey of the capabilities of type Ia supernova explosion models starting from a number of flame seeds distributed around the center of the white dwarf star. To this end we greatly improved the resolution of the numerical simulations in the initial stages. This novel numerical approach facilitates a detailed study of multi-spot ignition scenarios with up to hundreds of ignition sparks. Two-dimensional simulations are shown to be inappropriate to study the effects of initial flame configurations. Based on a set of three-dimensional models, we conclude that multi-spot ignition scenarios may improve type Ia supernova models towards better agreement with observations. The achievable effect reaches a maximum at a limited number of flame ignition kernels as shown by the numerical models and corroborated by a simple dimensional analysis.Comment: 14 pages, 12 figures with reduced resolution to meet astro-ph file size restriction, full-resolution version available from http://www.mpa-garching.mpg.de/~fritz/publications/astro-ph/multispot.pdf submitted to A&

    Crosstalk between neighbouring channels in multianode PMTs

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    Etablierung der homöopathischen Mastitistherapie in einem biologisch-dynamisch wirtschaftenden Milcherzeugerbetrieb unter Berücksichtigung ökologischer, epidemiologischer und ökonomischer Gesichtspunkte.

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    6 Summary The dairy cow mastitis as a disease with an immense economic impact is widely spread in organic as well as in conventional farms. Due to the lack of alternatives to antibiotic treatment, most therapeutical measures are based on antibiotics even in organic farms and against common regulations. In contrary to these procedures the EU regulations (Council Regulation EC 1804/99)as well as the consumer’s anticipation demand the possibly lowest levels of residual charges of dairy products and environment. A two and a half year study in a bio-dyn dairy herd in Brandenburg (Germany) with 300 dairy cows suffering from udder health problems was conducted to evaluate if clinical mastitis in dairy cows is to control successfully with homeopathic remedies to minimize antibiotic treatment. To assess the efficacy of the homeopathic treatment the investigations are made using a double blind placebo controlled study design (RCCT). Using a predetermined treatment protocol and a certain diagnostic pattern to match right remedies in the sense of the homeopathic remedy pictures, the intention of the chosen treatment schedule was to provide a very transparent concept which can be used also by unexperienced veterinarians. For treatment of acute mastitis the following remedies were used: Phytolacca D6, Bryonia D6 , Echinacea D6 and Belladonna D6. Aconitum D6 was added in case of fever at the beginning of disease. Cases of chronical and subclinical mastitis were treated by Echinacea D6, Phytolacca D6 and Hepar sulfuris D8. In the first part of the study nearly all mastitis cases were treated only with homeopathics avoiding antibiotics strictly. The unsatisfying results in this part lead to a modification in the second part in which in case of certain infections (S.aureus, Sc.spp.) a limited use of antibiotics was admitted. Furthermore, selected udders with subclinical and chronical infections with these kind of bacteria were dried off antibiotically. Simultaneously the farmer was engaged to intensify the efforts to optimize preventive and environmental measures in the herd. In the second part of the study 126 cows (148 quarters) suffered from clinical mastitis (Verum: n=60; Placebo: n=66). The cure rates were nearly identical. In the whole population the clinical cure rate (CCR) immediately after treatment was 95%, 7 to 8 weeks after treatment 65%. The 107 clinically affected quarters which were infected by pathogenic bacteria showed a bacteriological cure rate (BCR) of 55% each and a complete bacterio-cytological cure rate (BCCR) of 35% and 40% after 4-5 weeks and 7-8 weeks after treatment, respectively. During the observation time of 8 weeks a total of 12 cows in each of the treatment groups produced a homologous recurrent infection. 6 cows in the verum group and 4 cows in the placebo group developed a new infection in one of the other quarters. The treatment results seems to be satisfying while the enhanced but still not optimized environmental conditions in the herd are possibly responsible for the high amount of new infections and recurrences. Looking at the results of the study at all, the use of antibiotics could be decreased by 75% due to the therapy management (in spite of the change of it because of unsatisfying results) in combination with preventive measures. Additionally the herd udder health could be increased. So the mean herd somatic cell count decreased by 75.000 somatic cells/ml to 165.000 somatic cells/ml. Furthermore, the milk yield increased by 250 kg to 6.500 kg/cow/year. The count of infections with S. aureus in the herd decreased dramatically. The decreasing input of antibiotics in mastitis therapy in the project farm lead to a decrease of 36.000 kg antibiotically loaded milk compared to a hypothetic conventional mastitis management. Furthermore, the omission of withdrawal times after homeopathic treatment resulted in a benefit of additional production milk of 25.000 kg. The antibiotics minimizing therapy concept of the second part of this investigation which could be evaluated under practice conditions can be recommended for other farms too if simultaneous herd prevention measures can be assured by the farm manager to ensure good preconditions for the convalescence of the cows. The cure rates after placebo are unexpected high. Due to these results it is profoundly debatable whether the strategies of conventional therapy of bovine mastitis are suitable to ensure herd udder health. It should be evaluated which part of the cure rate is amounted by self cure and which other factors have an effect on the healing. The nearly identical cure rates in both treatment groups do not allow the proof of homeopathic efficacy at all. Indeed, comparing the bacteriologically caused mastitis cases (107 quarters), there is a significantly higher cure rate in the verum group (p < 0.05)

    Delayed detonations in full-star models of Type Ia supernova explosions

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    Aims: We present the first full-star three-dimensional explosion simulations of thermonuclear supernovae including parameterized deflagration-to-detonation transitions that occur once the flame enters the distributed burning regime. Methods: Treating the propagation of both the deflagration and the detonation waves in a common front-tracking approach, the detonation is prevented from crossing ash regions. Results: Our criterion triggers the detonation wave at the outer edge of the deflagration flame and consequently it has to sweep around the complex structure and to compete with expansion. Despite the impeded detonation propagation, the obtained explosions show reasonable agreement with global quantities of observed type Ia supernovae. By igniting the flame in different numbers of kernels around the center of the exploding white dwarf, we set up three different models shifting the emphasis from the deflagration phase to the detonation phase. The resulting explosion energies and iron group element productions cover a large part of the diversity of type Ia supernovae. Conclusions: Flame-driven deflagration-to-detonation transitions, if hypothetical, remain a possibility deserving further investigation.Comment: 4 pages, 1 figur

    On the small-scale stability of thermonuclear flames in Type Ia supernovae

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    We present a numerical model which allows us to investigate thermonuclear flames in Type Ia supernova explosions. The model is based on a finite-volume explicit hydrodynamics solver employing PPM. Using the level-set technique combined with in-cell reconstruction and flux-splitting schemes we are able to describe the flame in the discontinuity approximation. We apply our implementation to flame propagation in Chandrasekhar-mass Type Ia supernova models. In particular we concentrate on intermediate scales between the flame width and the Gibson-scale, where the burning front is subject to the Landau-Darrieus instability. We are able to reproduce the theoretical prediction on the growth rates of perturbations in the linear regime and observe the stabilization of the flame in a cellular shape. The increase of the mean burning velocity due to the enlarged flame surface is measured. Results of our simulation are in agreement with semianalytical studies.Comment: 9 pages, 7 figures, Uses AASTEX, emulateapj5.sty, onecolfloat.sty. Replaced with accepted version (ApJ), Figures 1 and 3 are ne

    Three-dimensional modeling of Type Ia supernovae - The power of late time spectra

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    Late time synthetic spectra of Type Ia supernovae, based on three-dimensional deflagration models, are presented. We mainly focus on one model,"c3_3d_256_10s", for which the hydrodynamics (Roepke 2005) and nucleosynthesis (Travaglio et al. 2004) was calculated up to the homologous phase of the explosion. Other models with different ignition conditions and different resolution are also briefly discussed. The synthetic spectra are compared to observed late time spectra. We find that while the model spectra after 300 to 500 days show a good agreement with the observed Fe II-III features, they also show too strong O I and C I lines compared to the observed late time spectra. The oxygen and carbon emission originates from the low-velocity unburned material in the central regions of these models. To get agreement between the models and observations we find that only a small mass of unburned material may be left in the center after the explosion. This may be a problem for pure deflagration models, although improved initial conditions, as well as higher resolution decrease the discrepancy. The relative intensity from the different ionization stages of iron is sensitive to the density of the emitting iron-rich material. We find that clumping, with the presence of low density regions, is needed to reproduce the observed iron emission, especially in the range between 4000 and 6000 AA. Both temperature and ionization depend sensitively on density, abundances and radioactive content. This work therefore illustrates the importance of including the inhomogeneous nature of realistic three-dimensional explosion models. We briefly discuss the implications of the spectral modeling for the nature of the explosion.Comment: 20 pages, 9 figures, resolution of Fig 1 is reduced to meet astro-ph file size restriction, submitted to A&

    Free fatty acids link metabolism and regulation of the insulin-sensitizing fibroblast growth factor-21

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    OBJECTIVE—Fibroblast growth factor (FGF)-21 improves insulin sensitivity and lipid metabolism in obese or diabetic animal models, while human studies revealed increased FGF-21 levels in obesity and type 2 diabetes. Given that FGF-21 has been suggested to be a peroxisome proliferator–activator receptor (PPAR) –dependent regulator of fasting metabolism, we hypothesized that free fatty acids (FFAs), natural agonists of PPAR, might modify FGF-21 levels. RESEARCH DESIGN AND METHODS—The effect of fatty acids on FGF-21 was investigated in vitro in HepG2 cells. Within a randomized controlled trial, the effects of elevated FFAs were studied in 21 healthy subjects (13 women and 8 men). Within a clinical trial including 17 individuals, the effect of insulin was analyzed using an hyperinsulinemic-euglycemic clamp and the effect of PPAR activation was studied subsequently in a rosiglitazone treatment trial over 8 weeks. RESULTS—Oleate and linoleate increased FGF-21 expression and secretion in a PPAR-dependent fashion, as demonstrated by small-interfering RNA–induced PPAR knockdown, while palmitate had no effect. In vivo, lipid infusion induced an increase of circulating FGF-21 in humans, and a strong correlation between the change in FGF-21 levels and the change in FFAs was observed. An artificial hyperinsulinemia, which was induced to delineate the potential interaction between elevated FFAs and hyperinsulinemia, revealed that hyperinsulinemia also increased FGF-21 levels in vivo, while rosiglitazone treatment had no effect. CONCLUSIONS—The results presented here offer a mechanism explaining the induction of the metabolic regulator FGF-21 in the fasting situation but also in type 2 diabetes and obesity
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