•A significant reduction of the tolerable stress amplitude occurs if 107 cycles are exceeded.•Under VHCF conditions a change from surface to subsurface cracks is observed in Ti6Al4V.•Inhomogeneities ...in the α- and β-phase distribution were identified at the crack initiation site.•Grain refinement, twinning and micro cracks occur in Ti6Al4V specimens loaded to 1010 cycles.
High frequency fatigue tests were carried out with a 20kHz ultrasonic testing facility to investigate the cyclic deformation behavior of Ti6Al4V in the Very High Cycle Fatigue (VHCF) regime in detail. The S,Nf-curve at the stress ratio R=−1 shows a significant decrease of the tolerable stress amplitude and a change from surface to subsurface failures in the VHCF regime for more than 107 cycles. Quantitative microscopic investigations of the distribution of the α- and β-phase of Ti6Al4V show that inhomogeneities in the phase distribution exist at subsurface crack initiation sites. This could be proven in scanning electron microscopic as well as light microscopic investigations. Beside the primary fatigue crack additional defects like micro cracks and crack clusters were observed in fatigued specimens. SEM-investigations of specimens loaded up to 1010 cycles without macroscopic failure show irreversible microstructural changes and defects in the subsurface volume. Two step tests were performed to evaluate the influence of fatigue induced defects observed in specimens which did not fail within 1010 cycles.
How to extend the chart of nuclides? Adamian, G. G.; Antonenko, N. V.; Diaz-Torres, A. ...
The European physical journal. A, Hadrons and nuclei,
02/2020, Letnik:
56, Številka:
2
Journal Article
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In the past 85 years the number of known nuclides increased by more than a factor of ten, resulting in 4000 presently known isotopes of 118 elements. This considerable progress we owe to the ...discovery of new reaction types along with the development of powerful accelerators and experimental techniques for separation and identification of reaction products. Model predictions indicate that still about 4000 further nuclides are waiting for their discovery. The vastest unexplored territory is located on the neutron-rich side in the upper half of the chart of nuclides and hides the answers to some of the most fundamental questions of nuclear physics like the limits of nuclear stability, element synthesis in the universe or stellar evolution. The access to these nuclei is presently limited by available beam intensities and/or the lack of appropriate methods for their production and identification. The latter concerns particularly new neutron-rich isotopes of transuranium and superheavy elements. To extend this area, the hope is presently based on multinucleon transfer reactions and on the application of fusion reactions with radioactive ion beams. But how promising are these approaches? Based on a survey of present-day knowledge, we will treat the questions where we currently are on our journey towards new territory on the chart of nuclides, how the chances are to gain new territory in the future and which challenges we will have to face.
The mechanisms by which genetic variation affects transcription regulation and phenotypes at the nucleotide level are incompletely understood. Here we use natural genetic variation as an in vivo ...mutagenesis screen to assess the genome-wide effects of sequence variation on lineage-determining and signal-specific transcription factor binding, epigenomics and transcriptional outcomes in primary macrophages from different mouse strains. We find substantial genetic evidence to support the concept that lineage-determining transcription factors define epigenetic and transcriptomic states by selecting enhancer-like regions in the genome in a collaborative fashion and facilitating binding of signal-dependent factors. This hierarchical model of transcription factor function suggests that limited sets of genomic data for lineage-determining transcription factors and informative histone modifications can be used for the prioritization of disease-associated regulatory variants.
The alignment of liquid crystals on surfaces plays a central role in optimizing their performances. In this work, a cutting-edge nano-lithography-based method to control the local orientation of a ...thermotropic liquid crystal is applied to easily available commercial standard materials and evaluated. Parallel nanogrooves on a substrate, created through 3D nanoprinting in a negative-tone photoresin optimized for two-photon polymerization are used for this purpose. Azimuthal anchoring energies of the order from 10 −6 J/m 2 to 10 −5 J/m 2 are found, depending on the spacing, width and depth of the grooves. In part, these values are larger than those reported previously for another photopolymer. Both uniform alignment and spatial patterns of different alignment directions can be realized. Electro-optic studies confirm the suitability of the method for electrically addressable photonic applications and indicate strong polar anchoring.
Chemically and thermally robust liquid crystal silane‐functionalized gold nanoparticles (i.e. AuNP1–AuNP3) were synthesized through silane conjugation. Colloidal dispersions of these particles with ...mesogenic ligands that are structurally identical (as in AuNP1, AuNP2) or compatible (as in AuNP3) with molecules of the nematic liquid crystal (N‐LC) host showed superior colloidal stability and dispersibility. The thermal, optical, and electro‐optic behaviors of the N‐LC composites at different concentrations of each gold nanoparticle were investigated. All dispersions showed lower values for the rotational viscosity and elastic constant, but only AuNP3 with a dissimilar structure between the nanoparticle ligand and the host displayed the most drastic thermal effects and overall strongest impact on the electro‐optic properties of the host. The observed results were explained considering both the structure and the density of the surface ligands of each gold nanoparticle.
Stable silane shell to the rescue: Thermally and chemically robust gold nanoparticles (NPs) capped with mesogenic groups through silane conjugation show very distinct optical and electro‐optic effects in a nematic liquid crystal. Surprisingly, capping a NP with a mesogen that is structurally dissimilar to that of the host has the most drastic effect on the electro‐optic properties of the host.
Doping nematic liquid crystals with small amounts of nanoparticles can significantly alter the electro‐optic response of the nematic host. Some of these effects result from nanoparticles influencing ...the liquid crystal/substrate interface, while other effects are caused by nanoparticles in the bulk. So far, little attention has been paid to the influence of surface interactions on the determination of bulk properties. In the present study, these effects are investigated experimentally and confirmed by numerical simulations. The splay‐type Fréedericksz‐transition of the nematic liquid crystal 5CB doped with CdSe quantum dots is investigated, as these dispersions are known from earlier studies to affect the initial alignment layers. In comparison, dispersions of chemically and thermally stable silanized gold nanoparticles in the apolar nematic host FELIX‐2900‐03 are analyzed, which are expected to be bulk‐active only. A data fitting routine is presented which allows a distinction between bulk and surface effects of nanoparticle doping. For the quantum dots, an increase of pretilt angle proportional to the doping concentration is found, as well as a slight decrease of the anchoring energy of molecules at the confining substrates. The silanized gold particles show no influence on the boundary conditions up to doping concentrations of 2.5 % (w). For higher concentrations an increase of pretilt angle is reported.
NPs at the edge: Functionalized nanoparticles can have a great impact on the electro‐optic response of a nematic host, both when dispersed in the bulk and when residing at the LC/substrate interface. Dispersions featuring a combination of both possible effects are studied and a method for distinguishing bulk and surface effects is presented. Experimental data is confirmed by numerical simulations.
M87, the active galaxy at the center of the Virgo cluster, is ideal for studying the interaction of a supermassive black hole (SMBH) with a hot, gas-rich environment. A deep Chandra observation of ...M87 exhibits an approximately circular shock front (13 kpc radius, in projection) driven by the expansion of the central cavity (filled by the SMBH with relativistic radio-emitting plasma) with projected radius ∼1.9 kpc. We combine constraints from X-ray and radio observations of M87 with a shock model to derive the properties of the outburst that created the 13 kpc shock. Principal constraints for the model are (1) the measured Mach number (M ∼ 1.2), (2) the radius of the 13 kpc shock, and (3) the observed size of the central cavity/bubble (the radio-bright cocoon) that serves as the piston to drive the shock. We find that an outburst of ∼5 × 1057 erg that began about 12 Myr ago and lasted ∼2 Myr matches all the constraints. In this model, ∼22% of the energy is carried by the shock as it expands. The remaining ∼80% of the outburst energy is available to heat the core gas. More than half the total outburst energy initially goes into the enthalpy of the central bubble, the radio cocoon. As the buoyant bubble rises, much of its energy is transferred to the ambient thermal gas. For an outburst repetition rate of about 12 Myr (the age of the outburst), 80% of the outburst energy is sufficient to balance the radiative cooling.
We derive the non-linear relation between the core flux Fν of accretion-powered jets at a given frequency and the mass M of the central compact object. For scale-invariant jet models, the ...mathematical structure of the equations describing the synchrotron emission from jets enables us to cancel out the model-dependent complications of jet dynamics, retaining only a simple, model-independent algebraic relation between Fν and M. This approach allows us to derive the Fν–M relation for any accretion disc scenario that provides a set of input boundary conditions for the magnetic field and the relativistic particle pressure in the jet, such as standard and advection-dominated accretion flow (ADAF) disc solutions. Surprisingly, the mass dependence of Fν is very similar in different accretion scenarios. For typical flat-spectrum core-dominated radio jets and standard accretion scenarios, we find Fν∼M17/12. The 7–9 orders of magnitude difference in black hole mass between microquasars and active galactic nuclei (AGN) jets imply that AGN jets must be about 3–4 orders of magnitude more radio-loud than microquasars, i.e. the ratio of radio to bolometric luminosity is much smaller in microquasars than in AGN jets. Because of the generality of these results, measurements of this Fν–M dependence are a powerful probe of jet and accretion physics. We show how our analysis can be extended to derive a similar scaling relation between the accretion rate ṁ and Fν for different accretion disc models. For radiatively inefficient accretion modes, we find that the flat-spectrum emission follows Fν ∝ (M ṁ)17/12.
ABSTRACT We present a combined analysis of the Chandra and Swift observations of the 2015 X-ray echo of V404 Cygni. Using a stacking analysis, we identify eight separate rings in the echo. We ...reconstruct the soft X-ray light curve of the 2015 June outburst using the high-resolution Chandra images and cross-correlations of the radial intensity profiles, indicating that about 70% of the outburst fluence occurred during the bright flare at the end of the outburst on MJD 57199.8. By deconvolving the intensity profiles with the reconstructed outburst light curve, we show that the rings correspond to eight separate dust concentrations with precise distance determinations. We further show that the column density of the clouds varies significantly across the field of view, with the centroid of most of the clouds shifted toward the Galactic plane, relative to the position of V404 Cyg, invalidating the assumption of uniform cloud column typically made in attempts to constrain dust properties from light echoes. We present a new XSPEC spectral dust-scattering model that calculates the differential dust-scattering cross section for a range of commonly used dust distributions and compositions and use it to jointly fit the entire set of Swift echo data. We find that a standard Mathis-Rumpl-Nordsieck model provides an adequate fit to the ensemble of echo data. The fit is improved by allowing steeper dust distributions, and models with simple silicate and graphite grains are preferred over models with more complex composition.
We model the observed size and brightness of the VLBA radio core of the jet in Cygnus X-1 to derive an expression for the jet power as a function of basic jet parameters. We apply this expression to ...recent constraints on the jet power from observations of a large-scale shocked shell around the source by Gallo and coworkers, which leads us to a set of alternative conclusions: either (1) the jet contains large amounts of protons (.2000 protons per radio-emitting electron), (2) it has a very low volume filling factor of f 3 x 10 super(-5), (3) the steady, radio-emitting VLBA jet is not the source of the kinetic energy powering the ISM shell, or (4) its asymptotic behavior differs fundamentally from a broad set of plausible analytic jet models.
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