11,740 research outputs found
Introduction to tailored forming
In recent years, the requirements for technical components have been increasing steadily. This development is intensified by the desire for products with lower weight, smaller size and extended functionality, but at the same time higher resistance against specific loads. Mono-material components manufactured according to established processes reach their limits regarding conflicting requirements. It is, for example, hardly possible to combine excellent mechanical properties with lightweight construction using mono-materials. Thus, a significant increase in production quality, lightweight design, functionality and efficiency can only be reached by combining different materials in one component. The superior aim of the Collaborative Research Centre (CRC) 1153 is to develop novel process chains for the production of hybrid solid components. In contrast to existing process chains in bulk metal forming, in which the joining process takes place during forming or at the end of the process chain, the CRC 1153 uses tailored semi-finished workpieces which are joined before the forming process. This results in a geometric and thermomechanical influence on the joining zone during the forming process which cannot be created by conventional joining techniques. The present work gives an overview of the CRC and the Tailored Forming approach including the applied joining, forming and finishing processes as well as a short summary of the accompanying design and evaluation methods
Microstructure and wear behaviour of high alloyed hot-work tool steels 1.2343 and 1.2367 under thermo-mechanical loading
Tools and their maintenance costs in hot forging processes account for a considerable proportion of the total components' costs. Forging tools undergo extreme heating and subsequent cooling during the forging process and between the forging cycles, respectively. This cyclic heating and cooling of the tool surfaces leads to local changes in the tool microstructure which result in hardening or softening of the material in different regions of the tool and consequently influence the tool strength. Temperature in the tool areas experiencing high thermo-mechanical loadings can exceed the austenitic temperature. Hence, a strong cooling, for example by spraying or lubrication, can lead to formation of a martensitic layer in the boundary zone of the tool. Due to its higher hardness, martensitic layer has greater resistance to wear as compared to the basic or tempered materials. In the scope of this paper, the austenitisation behaviours of two high alloyed hot-work tool steels, 1.2343 and 1.2367, have been characterized by means of dilatometer tests to obtain time-temperature-austenitisation (TTA) diagrams for specimen under thermo-mechanical loads. Moreover, continuous-cooling-transformation (CCT) diagrams were recorded. Metallographic investigations were carried out to gather a detailed understanding of the microstructure behaviour and its resulting hardness. With the results of this works, it is aimed to gather a detailed and accurate insight into the arising hardening and softening effects. This would eventually lead to an optimisation of the numerical modelling for tool wear prediction
A semi-analytical perspective on massive galaxies at
The most massive and luminous galaxies in the Universe serve as powerful
probes to study the formation of structure, the assembly of mass, and
cosmology. However, their detailed formation and evolution is still barely
understood. Here we extract a sample of massive mock galaxies from the
semi-analytical model of galaxy formation (SAM) GALACTICUS from the
MultiDark-Galaxies, by replicating the CMASS photometric selection from the
SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). The comparison of the
GALACTICUS CMASS-mock with BOSS-CMASS data allows us to explore different
aspects of the massive galaxy population at , including the
galaxy-halo connection and the galaxy clustering. We find good agreement
between our modelled galaxies and observations regarding the galaxy-halo
connection, but our CMASS-mock over-estimates the clustering amplitude of the
2-point correlation function, due to a smaller number density compared to BOSS,
a lack of blue objects, and a small intrinsic scatter in stellar mass at fixed
halo mass of dex. To alleviate this problem, we construct an alternative
mock catalogue mimicking the CMASS colour-magnitude distribution by randomly
down-sampling the SAM catalogue. This CMASS-mock reproduces the clustering of
CMASS galaxies within 1 and shows some environmental dependency of star
formation properties that could be connected to the quenching of star formation
and the assembly bias.Comment: 15 pages, 10 figures, 2 tables, submitted to MNRA
Wave conditions in the Baltic Proper and in the Gulf of Finland during windstorm Gudrun
International audienceWave conditions in the northern Baltic Proper during windstorm Erwin/Gudrun (January 2005) are analysed based on in situ measurements in three locations and output of operational wave models from the German Weather Forecast Service, the Danish Meteorological Institute and the Finnish Institute of Marine Research. The measured significant wave height reached 7.2 m in the northern Baltic Proper and 4.5 m in the Gulf of Finland. The roughest wave conditions, estimated from the comparison of the forecast and measured data, occurred remote from the sensors, off the coasts of Saaremaa and Latvia where the significant wave height was about 9.5 m. Peak periods exceeded 12 s in a large part of the northern Baltic Proper and in the central part of the Gulf of Finland
Neutrino and antineutrino charge-exchange reactions on 12C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. Explicit
violation of CVC hypothesis by the Coulomb field, as well as development of a
sum rule approach for the inclusive cross sections have been worked out. We
have done a thorough study of exclusive (ground state) properties of B
and N within the projected quasiparticle random phase approximation
(PQRPA). Good agreement with experimental data achieved in this way put in
evidence the limitations of standard RPA and the QRPA models, which come from
the inability of the RPA in opening the shell, and from the
non-conservation of the number of particles in the QRPA. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin. The quasi-elastic C(N cross section recently
measured in the MiniBooNE experiment is briefly discussed. We study the
decomposition of the inclusive cross-section based on the degree of
forbiddenness of different multipoles. A few words are dedicated to the
-C charge-exchange reactions related with astrophysical
applications.Comment: 21 pages, 13 figures, 1 table, submitted to Physical Review
Particle size effect in methane activation over supported palladium nanoparticles
A synthesis method for producing MgAl oxide supported uniform palladium nanoparticles with varying diameters has been developed. The method consists of reductive-thermal decomposition of a PdMgAl hydrotalcite-like compound, formed via co-precipitation of metal nitrate salts and sodium carbonate. The hydrotalcite–like precursors were characterized by XRD, TG-MS and SEM, and were found to contain a well-defined crystalline structure and a uniform distribution of all constituent elements. The resulting catalysts were characterized by XRD, TEM, Chemisorption of CO and in situ IR measurements of CO, and were found to consist of partially oxide-embedded Pd nanoparticles with diameters ranging from d = 1.7 to 3.3 nm and correspond dispersions of 67–14%. Furthermore, the particle size was found to be inversely related to Pd loading. The palladium catalysts were studied for methane activation via chemisorption at 200 and 400 °C followed by a temperature programmed surface hydrogenation. The most disperse catalyst (d = 1.7 nm) possessed an intrinsic methane adsorption capacity, which was an order of magnitude larger than that of other catalysts in the series, indicating a strong structure sensitivity in this reaction. Additionally, the methane adsorption capacity of the hydrotalcite-derived Pd catalysts was nearly two orders of magnitude higher than that of catalysts derived through other synthesis pathways such as colloidal deposition or sonochemical reduction
-Decay Spectrum, Response Function and Statistical Model for Neutrino Mass Measurements with the KATRIN Experiment
The objective of the Karlsruhe Tritium Neutrino (KATRIN) experiment is to
determine the effective electron neutrino mass with an
unprecedented sensitivity of (90\% C.L.) by precision electron
spectroscopy close to the endpoint of the decay of tritium. We present
a consistent theoretical description of the electron energy spectrum in
the endpoint region, an accurate model of the apparatus response function, and
the statistical approaches suited to interpret and analyze tritium
decay data observed with KATRIN with the envisaged precision. In addition to
providing detailed analytical expressions for all formulae used in the
presented model framework with the necessary detail of derivation, we discuss
and quantify the impact of theoretical and experimental corrections on the
measured . Finally, we outline the statistical methods for
parameter inference and the construction of confidence intervals that are
appropriate for a neutrino mass measurement with KATRIN. In this context, we
briefly discuss the choice of the energy analysis interval and the
distribution of measuring time within that range.Comment: 27 pages, 22 figures, 2 table
Technical design and commissioning of the KATRIN large-volume air coil system
The KATRIN experiment is a next-generation direct neutrino mass experiment
with a sensitivity of 0.2 eV (90% C.L.) to the effective mass of the electron
neutrino. It measures the tritium -decay spectrum close to its endpoint
with a spectrometer based on the MAC-E filter technique. The -decay
electrons are guided by a magnetic field that operates in the mT range in the
central spectrometer volume; it is fine-tuned by a large-volume air coil system
surrounding the spectrometer vessel. The purpose of the system is to provide
optimal transmission properties for signal electrons and to achieve efficient
magnetic shielding against background. In this paper we describe the technical
design of the air coil system, including its mechanical and electrical
properties. We outline the importance of its versatile operation modes in
background investigation and suppression techniques. We compare magnetic field
measurements in the inner spectrometer volume during system commissioning with
corresponding simulations, which allows to verify the system's functionality in
fine-tuning the magnetic field configuration. This is of major importance for a
successful neutrino mass measurement at KATRIN.Comment: 32 pages, 16 figure
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