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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 11 (1988), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The crack tip cyclic heat generation rate, fatigue crack growth rate, and the crack closure stress were measured in a β-annealed Ti-6Al-4V for R ratios of -0.1, 0.1 and 0.2. The R= -0.1 and 0.1 cases exhibited macroscopic crack closure and the R = 0.2 case exhibited no macroscopic crack closure as measured by strain gage techniques. There was a transition in the slope of the da/dN vs ΔK curve for the closure cases and no transition for the no-closure case. The crack tip heat generation rate above the transition for the closure cases was an order of magnitude greater than for the no-closure case. Also the crack tip heat generation rate below the transition was greater for the closure cases than for the no-closure case. The transition in the heat generation rate and the crack growth rate was attributed to a transition from static frictional locking of shear branch cracks to sliding of the branch crack surfaces. Below the transition the crack faces are locked open creating a large roughness-induced closure component. When the branch cracks are allowed to undergo reverse shear, the amount of roughness-induced closure markedly decreases and the fracture surface becomes less tortuous. The relative sliding generates the increased heat.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 22 (1969), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The absorption of H2O and D2O was studied in seeds with different reserve food materials represented by barley and rice (starch), linseed and mustard (fat) and mung, and kidney beans (protein). Respiration rate and respiratory quotient during absorption were also measured. The results indicate that the water absorption profiles of the starchy and fatty seeds are essentially similar but differ from that of The proteinaceous type. Initial hydration is relatively incomplete in D2O in all The seeds to varying degrees the latter being maximum in The proteinaceous and minimum in The starchy seeds. The respiration rate is lower in D2O while The R.Q. values are higher for The first hour but lower later on. The results, in part, help explain The varying effects of D2O on The germination of different types of seeds. These studies also support The earlier reported preference (Cope et al. 1965) by the higher plant systems for protium.
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  • 3
    Publication Date: 2015-08-08
    Description: The detection of planar structures within the satellite systems of both the Milky Way (MW) and Andromeda (M31) has been reported as being in stark contradiction to the predictions of the standard cosmological model ( cold dark matter – CDM). Given the ambiguity in defining a planar configuration, it is unclear how to interpret the low incidence of the MW and M31 planes in CDM. We investigate the prevalence of satellite planes around galactic mass haloes identified in high-resolution cosmological simulations. We find that planar structures are very common, and that ~10 per cent of CDM haloes have even more prominent planes than those present in the Local Group. While ubiquitous, the planes of satellite galaxies show a large diversity in their properties. This precludes using one or two systems as small-scale probes of cosmology, since a large sample of satellite systems is needed to obtain a good measure of the object-to-object variation. This very diversity has been misinterpreted as a discrepancy between the satellite planes observed in the Local Group and CDM predictions. In fact, ~10 per cent of CDM galactic haloes have planes of satellites that are as infrequent as the MW and M31 planes. The look-elsewhere effect plays an important role in assessing the detection significance of satellite planes and accounting for it leads to overestimating the significance level by a factor of 30 and 100 for the MW and M31 systems, respectively.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 4
    Publication Date: 2015-05-08
    Description: We present densely sampled ultraviolet/optical photometric and low-resolution optical spectroscopic observations of the Type IIP supernova 2013ab in the nearby (~24 Mpc) galaxy NGC 5669, from 2 to 190 d after explosion. Continuous photometric observations, with the cadence of typically a day to one week, were acquired with the 1–2 m class telescopes in the Las Cumbres Observatory Global Telescope network, ARIES telescopes in India and various other telescopes around the globe. The light curve and spectra suggest that the supernova (SN) is a normal Type IIP event with a plateau duration of ~80 d with mid-plateau absolute visual magnitude of –16.7, although with a steeper decline during the plateau (0.92 mag 100 d –1 in V band) relative to other archetypal SNe of similar brightness. The velocity profile of SN 2013ab shows striking resemblance with those of SNe 1999em and 2012aw. Following the Rabinak & Waxman prescription, the initial temperature evolution of the SN emission allows us to estimate the progenitor radius to be ~800 R , indicating that the SN originated from a red supergiant star. The distance to the SN host galaxy is estimated to be 24.3 Mpc from expanding photosphere method. From our observations, we estimate that 0.064 M of 56 Ni was synthesized in the explosion. General relativistic, radiation hydrodynamical modelling of the SN infers an explosion energy of 0.35  x 10 51  erg, a progenitor mass (at the time of explosion) of ~9 M and an initial radius of ~600 R .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 5
    Publication Date: 2016-06-30
    Description: The sterile neutrino is a viable dark matter candidate that can be produced in the early Universe via non-equilibrium processes, and would therefore possess a highly non-thermal spectrum of primordial velocities. In this paper we analyse the process of structure formation with this class of dark matter particles. To this end we construct primordial dark matter power spectra as a function of the lepton asymmetry, L 6 , that is present in the primordial plasma and leads to resonant sterile neutrino production. We compare these power spectra with those of thermally produced dark matter particles and show that resonantly produced sterile neutrinos are much colder than their thermal relic counterparts. We also demonstrate that the shape of these power spectra is not determined by the free-streaming scale alone. We then use the power spectra as an input for semi-analytic models of galaxy formation in order to predict the number of luminous satellite galaxies in a Milky Way-like halo. By assuming that the mass of the Milky Way halo must be no more than 2 x 10 12 M (the adopted upper bound based on current astronomical observations) we are able to constrain the value of L 6 for M s ≤ 8 keV. We also show that the range of L 6 that is in best agreement with the 3.5 keV line (if produced by decays of 7 keV sterile neutrino) requires that the Milky Way halo has a mass no smaller than 1.5 x 10 12 M . Finally, we compare the power spectra obtained by direct integration of the Boltzmann equations for a non-resonantly produced sterile neutrino with the fitting formula of Viel et al. and find that the latter significantly underestimates the power amplitude on scales relevant to satellite galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 6
    Publication Date: 2016-06-01
    Description: We use a suite of cosmological simulations to study the mass–concentration–redshift relation, c ( M, z ), of dark matter haloes. Our simulations include standard -cold dark matter (CDM) models, and additional runs with truncated power spectra, consistent with a thermal warm dark matter (WDM) scenario. We find that the mass profiles of CDM and WDM haloes are self-similar and well approximated by the Einasto profile. The c ( M, z ) relation of CDM haloes is monotonic: concentrations decrease with increasing virial mass at fixed redshift, and decrease with increasing redshift at fixed mass. The mass accretion histories (MAHs) of CDM haloes are also scale-free, and can be used to infer concentrations directly. These results do not apply to WDM haloes: their MAHs are not scale-free because of the characteristic scale imposed by the power spectrum suppression. Further, the WDM c ( M, z ) relation is non-monotonic: concentrations peak at a mass scale dictated by the truncation scale, and decrease at higher and lower masses. We show that the assembly history of a halo can still be used to infer its concentration, provided that the total mass of its progenitors is considered (the ‘collapsed mass history’; CMH), rather than just that of its main ancestor. This exploits the scale-free nature of CMHs to derive a simple scaling that reproduces the mass–concentration–redshift relation of both CDM and WDM haloes over a vast range of halo masses and redshifts. Our model therefore provides a robust account of the mass, redshift, cosmology and power spectrum dependence of dark matter halo concentrations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
    Publication Date: 2016-02-27
    Description: We introduce Copernicus Complexio ( coco ), a high-resolution cosmological N -body simulation of structure formation in the CDM model. coco follows an approximately spherical region of radius ~17.4 h –1 Mpc embedded in a much larger periodic cube that is followed at lower resolution. The high-resolution volume has a particle mass of 1.135  x  10 5 h –1 M (60 times higher than the Millennium-II simulation). coco gives the dark matter halo mass function over eight orders of magnitude in halo mass; it forms ~60 haloes of galactic size, each resolved with about 10 million particles. We confirm the power-law character of the subhalo mass function, $\overline{N}( 〉 \mu )\propto \mu ^{-s}$ , down to a reduced subhalo mass M sub / M 200 μ = 10 –6 , with a best-fitting power-law index, s  = 0.94, for hosts of mass 〈 M 200 〉 = 10 12 h –1 M . The concentration–mass relation of coco haloes deviates from a single power law for masses M 200  〈 afew  x  10 8 h –1 M , where it flattens, in agreement with results by Sanchez-Conde et al. The host mass invariance of the reduced maximum circular velocity function of subhaloes, V max / V 200 , hinted at in previous simulations, is clearly demonstrated over five orders of magnitude in host mass. Similarly, we find that the average, normalized radial distribution of subhaloes is approximately universal (i.e. independent of subhalo mass), as previously suggested by the Aquarius simulations of individual haloes. Finally, we find that at fixed physical subhalo size, subhaloes in lower mass hosts typically have lower central densities than those in higher mass hosts.
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    Electronic ISSN: 1365-2966
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  • 8
    Publication Date: 2015-11-27
    Description: We present broad-band photometric and polarimetric observations of two Type II supernovae (SNe) 2013hj and 2014G. SN 2014G is a spectroscopically classified Type IIL event, which we also confirm photometrically because its light curve shows characteristic features – a plateau slope of 2.55 mag (100 d) –1 in the V band and a duration of ~77 d – of a generic Type IIL SN. However, SN 2013hj also shows a high plateau decline rate of 1.5 mag (100 d) –1 in the V band, similar to SNe IIL, but marginally lower than SNe IIL template light curves. Our high cadence photometric observations of SNe 2013hj and 2014G enables us to cover all characteristic phases up to the radioactive tail of optical light curves. Broad-band polarimetric observations reveal some polarization in SN 2013hj with subtle enhancement as the SN evolves towards the plateau end. However, the polarization angle remains constant throughout the evolution. This characteristic is consistent with the idea that the evolving SN with recombining hydrogen envelope is slowly revealing a more asymmetric central region of explosion. Modelling of the bolometric light curve yields a progenitor mass of ~11 M with a radius of ~700 R for SN 2013hj, while for the SN 2014G model estimated progenitor mass is ~9 M with a radius of ~630 R , both having a typical energy budget of ~2 x 10 51  erg.
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  • 9
    Publication Date: 2016-05-26
    Description: The cold dark matter (CDM) cosmological model unambiguously predicts that a large number of haloes should survive as subhaloes when they are accreted into a larger halo. The CDM model would be ruled out if such substructures were shown not to exist. By contrast, if the dark matter consists of Warm Dark Matter (WDM) particles, then below a threshold mass that depends on the particle mass far fewer substructures would be present. Finding subhaloes below a certain mass would then rule out warm particle masses below some value. Strong gravitational lensing provides a clean method to measure the subhalo mass function through distortions in the structure of Einstein rings and giant arcs. Using mock lensing observations constructed from high-resolution N -body simulations, we show that measurements of approximately 100 strong lens systems with a detection limit of M low  = 10 7 h –1 M would clearly distinguish CDM from WDM in the case where this consists of 7 keV sterile neutrinos such as those that might be responsible for the 3.5 keV X-ray emission line recently detected in galaxies and clusters.
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  • 10
    Publication Date: 2013-04-03
    Description: We present the low-resolution spectroscopic and UBVRI broad-band photometric investigations of the Type IIb supernova (SN) 2011fu, discovered in UGC 01626. The photometric follow-up of this event was initiated a few days after the explosion and covers a period of about 175 d. The early-phase light curve shows a rise, followed by steep decay in all bands, and shares properties very similar to that seen for SN 1993J, with a possible detection of the adiabatic cooling phase. Modelling of the quasi-bolometric light curve suggests that the progenitor had an extended (~1  x 10 13 cm), low-mass (~0.1 M ) H-rich envelope on top of a dense, compact (~2  x 10 11 cm), more massive (~1.1 M ) He-rich core. The nickel mass synthesized during the explosion was found to be ~0.21 M , slightly larger than that seen for other Type IIb SNe. The spectral modelling performed with synow suggests that the early-phase line velocities for H and Fe ii features were ~16 000 and ~14 000 km s –1 , respectively. Then, the velocities declined up to day +40 and became nearly constant at later epochs.
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    Topics: Physics
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