Shock waves in solids represent a critical area of high-strain-rate mechanics, encompassing elastic-plastic deformation, phase transitions, spallation, and high-pressure equation-of-state (EOS) studies. This review synthesizes fundamental physics, theoretical models, experimental techniques, and engineering applications of shock wave propagation in condensed matter. Key concepts such as the Hugoniot Elastic Limit (HEL), Rankine-Hugoniot relations, and elastic-plastic wave structure are discussed. Experimental methods (plate impact, explosive loading) and numerical approaches are evaluated. The review highlights the influence of material microstructure, viscosity, and strength on shock structure and decay. Applications in armor design, planetary impact cratering, and material synthesis are summarized.
The forward problem here is the Cauchy problem for a 1D hyperbolic PDE with a variable coefficient in the principal part of the operator. That coefficient is the spatially distributed dielectric constant. The inverse problem consists of the recovery of that dielectric constant from backscattering boundary measurements. The data depend on one variable, which is time. To address this problem, a new version of the convexification method is analytically developed. The theory guarantees the global convergence of this method. Numerical testing is conducted for both computationally simulated and experimental data. Experimental data, which are collected in the field, mimic the problem of the recovery of the spatially distributed dielectric constants of antipersonnel land mines and improvised explosive devices.
International Ocean Discovery program (IODP) Site U1438 is located within the Amami‐Sankaku Basin, ~50 km SW of the Kyushu‐Palau Ridge and ~500 km SE of the present‐day volcanic front of the Kyushu‐Ryukyu arc. Thirty‐eight rhyolitic tephra layers (1–15 cm thick) deposited over the last 4 Myr were recovered at this site. Representative ash layers dominated by unaltered, colorless glass shards reaching 100–300 μm in size, in association with rare pyroxene, amphibole, biotite, and zircon, were sampled for isotopic analysis. The isotopic compositions of the tephra have a narrow range in 87Sr/86Sr (0.704 to 0.706), 206Pb/204Pb (18.32 to 18.46), 207Pb/204Pb (15.57 to 15.62), and 208Pb/204Pb (38.46 to 38.75) and are more variable in εNd (−3.5 to +4.8) and εHf (+2.0 to +13.3). This record indicates the tephra were not sourced from the Izu‐Bonin‐Mariana arc or from Central Japan but derived from felsic volcanism from the Kyushu‐Ryukyu arc. The 4.8‐km‐deep Amami‐Sankaku Basin was located up to 600–900 km from the Kyushu‐Ryukyu arc over the last 4 Ma, which is significantly more distal than other drill sites from which extensive tephra layers sourced from SW Japan have been recovered. Site U1438 tephra are thus likely related to widely distributed (M > 6) rhyolitic eruptions. We propose the unique tephra record and high‐precision isotope analysis of recovered tephra from Site U1438 can be used as an important marker to identify submerged calderas within the Ryukyu arc and/or constrain the history of activity (>1 Ma) of major calderas‐forming eruptions within the Kyushu‐Ryukyu arc.
A. Jerkstrand, Francis Timmes, Francis Timmes
et al.
Measurements of explosive nucleosynthesis yields in core-collapse supernovae provide tests for explosion models. We investigate constraints on explosive conditions derivable from measured amounts of nickel and iron after radioactive decays using nucleosynthesis networks with parameterized thermodynamic trajectories. The Ni/Fe ratio is for most regimes dominated by the production ratio of 58Ni/(54Fe + 56Ni), which tends to grow with higher neutron excess and with higher entropy. For SN 2012ec, a supernova (SN) that produced a Ni/Fe ratio of 3.4 ± 1.2 times solar, we find that burning of a fuel with neutron excess &eegr; ≈ 6 × 10 − 3 ?> is required. Unless the progenitor metallicity is over five times solar, the only layer in the progenitor with such a neutron excess is the silicon shell. SNe producing large amounts of stable nickel thus suggest that this deep-lying layer can be, at least partially, ejected in the explosion. We find that common spherically symmetric models of M ZAMS ≲ 13 ?> M ⊙ ?> stars exploding with a delay time of less than one second ( M cut M ⊙ ?> ) are able to achieve such silicon-shell ejection. SNe that produce solar or subsolar Ni/Fe ratios, such as SN 1987A, must instead have burnt and ejected only oxygen-shell material, which allows a lower limit to the mass cut to be set. Finally, we find that the extreme Ni/Fe value of 60–75 times solar derived for the Crab cannot be reproduced by any realistic entropy burning outside the iron core, and neutrino-neutronization obtained in electron capture models remains the only viable explanation.
ABSTRACT The selective forces that played a role in the evolution of the musculoskeletal system of the genus Homo have long been debated and remain poorly understood. In this investigation, we introduce a new approach for testing alternative hypotheses. Our analysis is based on the premise that natural selection can be expected to have resulted in muscles that are large enough to achieve necessary levels of maximum performance in essential behaviors, but not larger. We used surface electromyography in male subjects to identify maximum activation levels in 13 muscles of the back and leg during eight behaviors that have been suggested to have been important to foraging, hunting and fighting performance in early humans. We asked two questions: (1) what behaviors produce maximum activation in each of the investigated muscles and (2) are there specific behaviors that elicit maximum recruitment from all or most of the muscles? We found that in eight of the 13 muscles, the highest activity occurred during maximal effort vertical jumping (i.e. whole-body acceleration). Punching produced the highest median activity in the other five muscles. Together, jumping and punching accounted for 73% of the incidences of maximum activity among all of the muscles and from all of the subjects. Thus, the size of the muscles of the back and leg appear to be more related to the demands of explosive behaviors rather than those of high speed sprinting or sustained endurance running. These results are consistent with the hypothesis that selection on aggressive behavior played an important role in the evolution of the genus Homo. Summary: In this study, we identified behaviors that produce maximum activation of muscles to test hypotheses of the specific behaviors that influenced the evolution of the human musculoskeletal system.
Massive stars live fast and die young. They shine furiously for a few million years, during which time they synthesize most of the heavy elements in the universe in their cores. They end by blowing themselves up in a powerful explosion known as a supernova (SN). During this process, the core collapses to a neutron star or a black hole, while the outer layers are expelled with velocities of thousands of kilometers per second. The resulting fireworks often outshine the entire host galaxy for many weeks. The explosion energy is eventually radiated away, but powering of the newborn nebula continues by radioactive isotopes synthesized in the explosion. The ejecta are now quite transparent, and we can see the material produced in the deep interiors of the star. To interpret the observations, detailed spectral modeling is needed. This thesis aims to develop and apply state-of-the-art computational tools for interpreting and modeling SN observations in the nebular phase. This requires calculation of the physical conditions throughout the nebula, including non-thermal processes from the radioactivity, thermal and statistical equilibrium, as well as radiative transport. The inclusion of multiline radiative transfer, which we compute with a Monte Carlo technique, represents one of the major advancements presented in this thesis. On February 23 1987, the first SN observable by the naked eye since 1604 exploded, SN 1987A. Its proximity has allowed unprecedented observations, which in turn have lead to significant advancements in our understanding of SN explosions. As a first application of our model, we analyze the 44Tipowered phase (t & 5 years) of SN 1987A. We find that a magnetic field is present in the nebula, trapping the positrons that provide the energy input, and resulting in strong iron lines in the spectrum. We determine the 44Ti mass to 1.5(+0.5−0.5)*10−4 M⊙. From the near-infrared spectrum at an age of 19 years, we identify strong emission lines from explosively synthesized metals such as silicon, calcium, and iron. We use integral-field spectroscopy to construct three-dimensional maps of the ejecta, showing a morphology suggesting an asymmetric explosion. The model is then applied to the close-by and well-observed Type IIP SN 2004et, analyzing its ultraviolet to mid-infrared evolution. Based on its Mg I] 4571 A, Na I 5890, 5896 A, [O I] 6300, 6364 A, and [Ne II] 12.81 mm nebular emission lines, we determine its progenitor mass to be around 15 M⊙. We confirm that silicate dust, SiO, and CO have formed in the ejecta. Finally, the major optical emission lines in a sample of Type IIP SNe areanalyzed.We find that most spectral regions in Type IIP SNe are dominated by emission from the massive hydrogen envelope, which explains the relatively small variation seen in the sample. We also show that the similar line profiles seen from all elements suggest extensive mixing occurring in most hydrogenrich SNe.
Context. Observing the inner ejecta of a supernova is possible only in a handful of nearby supernova remnants. The core-collapse explosion mechanism has been extensively explored in recent models and predict large asymmetries. SN 1987A is the first modern stellar explosion that has been continuously observed from its beginning to the supernova remnant phase. Twenty years after the explosion, we are now able to observe the three-dimensional spatially resolved inner ejecta of this supernova. Aims. Detailed mapping of newly synthesised material and its radioactive decay daughter products sheds light on the explosion mechanism. This may reveal the geometry of the explosion and its connection to the equatorial ring and the outer rings around SN 1987A. Methods. We have used integral field spectroscopy to image the supernova ejecta and the equatorial ring in the emission lines of [Si I] + [Fe II] (λ1.64 μm) and He I (λ2.058 μm). The spectral information can be mapped into a radial velocity image revealing the expansion of the ejecta both as projected onto the sky and perpendicular to the sky plane. Results. The inner ejecta are spatially resolved in a North-South direction and are clearly asymmetric. Like the ring emission, the northern parts of the ejecta are blueshifted, while the material projected to the South of the supernova centre is moving away from us. We argue that the bulk of the ejecta is situated in the same plane as defined by the equatorial ring and does not form a bipolar structure as has been suggested. The exact shape of the ejecta is modelled and we find that an elongated triaxial ellipsoid fits the observations best. The velocity measured in the [Si I] + [Fe II] line corresponds to ∼3000 km s −1 and is the same as the width of the IR [Fe II] line profiles during the first years. From our spectral analyses of the ejecta spectrum we find that most of the He I, [Si I] and [Fe I-II] emission originates in the core material which has undergone explosive nucleosynthesis. The He I emission may be the result of α-rich freeze-out if the positron energy is deposited locally. Conclusions. Our observations clearly indicate a non-symmetric explosion mechanism for SN 1987A. The elongation and velocity asymmetries point towards a large-scale spatial non-spherical distribution as predicted in recent explosion models. The orientation of the ejecta in the plane of the equatorial ring argues against a jet-induced explosion through the poles due to stellar rotation.