Rayleigh Waves Generated by a Thermal Source: A Three-Dimensional Transient Thermoelasticity Solution

A three-dimensional transient thermoelastic solution is obtained for Rayleigh-type disturbances propagating on the surface of a half-space. These surface waves are generated by either a buried or surface thermal source, which has the form of a concentrated heat flux applied impulsively. In an effort to model this problem as realistically as possible, the half-space material is taken to respond according to Biot’s fully coupled thermoelasticity. The problem has relevance to situations involving heat generation due to: (i) laser action (impulsive electromagnetic radiation) on a surface target, (ii) underground nuclear activity, and (iii) friction developed during underground fault motions related to seismic activity. The problem was attacked with unilateral and double bilateral Laplace transforms, which suppress, respectively, the time variable and two of the space variables. The Rayleigh wave contribution is obtained as a closed-form expression by utilizing asymptotics, complex-variable theory and certain results for Bessel functions. The dependence of the normal displacement associated with the Rayleigh wave upon the distance from the source epicenter and the distance from the wavefront is also determined

A Fractional Viscoelastic Model Of The Axon In Brain White Matter

Traumatic axonal injury occurs when loads experienced on the tissue-scale are transferred to the individual axons. Mechanical characterization of axon deformation especially under dynamic loads however is extremely difficult owing to their viscoelastic properties. The viscoelastic characterization of axon properties that are based on interpretation of results from in-vivo brain Magnetic Resonance Elastography (MRE) are dependent on the specific frequencies used to generate shear waves with which measurements are made. In this study, we aim to develop a fractional viscoelastic model to characterize the time dependent behavior of the properties of the axons in a composite white matter (WM) model. The viscoelastic powerlaw behavior observed at the tissue level is assumed to exist across scales, from the continuum macroscopic level to that of the microstructural realm of the axons. The material parameters of the axons and glia are fitted to a springpot model. The 3D fractional viscoelastic springpot model is implemented within a finite element framework. The constitutive equations defining the fractional model are coded using a vectorized user defined material (VUMAT) subroutine in ABAQUS finite element software. Using this material characterization, representative volume elements (RVE) of axons embedded in glia with periodic boundary conditions are developed and subjected to a relaxation displacement boundary condition. The homogenized orthotropic fractional material properties of the axon-matrix system as a function of the volume fraction of axons in the ECM are extracted by solving the inverse problem.Comment: Accepted for publication at the 12th International Conference on Mathematical Modeling in Physical Science

Consecutive non-natural PZ nucleobase pairs in DNA impact helical structure as seen in 50 μs molecular dynamics simulations

Little is known about the influence of multiple consecutive ‘non-standard’ (Z, 6-amino-5-nitro-2(1H)-pyridone, and P, 2-amino-imidazo[1,2-a]-1,3,5-triazin-4(8H)-one) nucleobase pairs on the structural parameters of duplex DNA. P:Z nucleobase pairs follow standard rules for Watson–Crick base pairing but have rearranged hydrogen bonding donor and acceptor groups. Using the X-ray crystal structure as a starting point, we have modeled the motions of a DNA duplex built from a self-complementary oligonucleotide (5΄-CTTATPPPZZZATAAG-3΄) in water over a period of 50 μs and calculated DNA local parameters, step parameters, helix parameters, and major/minor groove widths to examine how the presence of multiple, consecutive P:Z nucleobase pairs might impact helical structure. In these simulations, the PZ-containing DNA duplex exhibits a significantly wider major groove and greater average values of stagger, slide, rise, twist and h-rise than observed for a ‘control’ oligonucleotide in which P:Z nucleobase pairs are replaced by G:C. The molecular origins of these structural changes are likely associated with at least two differences between P:Z and G:C. First, the electrostatic properties of P:Z differ from G:C in terms of density distribution and dipole moment. Second, differences are seen in the base stacking of P:Z pairs in dinucleotide steps, arising from energetically favorable stacking of the nitro group in Z with π–electrons of the adjacent base

LATE-AND POST-ALPINE TECTONIC EVOLUTION OF THE SOUTHERN PART OF THE ATHOS PENINSULA, NORTHERN GREECE

To όριο μεταξύ των εσωτερικών Ελληνίδων και της Ελληνικής ενδοχώρας αποκαλύπτεται στο νότιο τμήμα της χερσονήσου του Άθω ως μια επαφή ΒΑ-ΝΔ παράταξης μεταξύ της Σέρβο μακεδόνικης μάζας και της Περιροδοπικής Ζώνης. Μελετήθηκαν τα κύρια τεκτονικά χαρακτηριστικά και η παραμόρφωση της περιοχής κατά τη διάρκεια της τελική αλπικής ορογένεσης όσο και μετά από αυτήν με σκοπό την καλύτερη κατανόηση των τελικών ορογενετικών διεργασιών που οδήγησαν στην σημερινή διαμόρφωση αυτού του ορίου. Η υπαίθρια έρευνα έδειξε ότι οι κυρίαρχες δομές στο νότιο τμήμα της χερσονήσου του Αθω είναι ένα ασύμμετρο, βυθιζόμενο προς τα ΝΑ, με φορά προς τα ΒΑ μέγα-αντίμορφο και μια ΒΑ-ΝΔ διεύθυνσης αριστερόστροφη διατρητική ζώνη. Αυτές οι δομές είναι αποτέλεσμα μιας transpressional παραμόρφωσης που άρχισε τουλάχιστον από το Ηώκαινο σε πλαστικές, συμμεταμορφικές (χαμηλή πρασινοσχιστολιθική φάση) συνθήκες και σταδιακά άλλαξε κατά το Ολιγόκαινο - Κάτω Μειόκαινο σε θραυσιγενείς συνθήκες με Α-Δ διεύθυνσης ανάστροφα ρήγματα-επωθήσεις και ΒΒΑ-ΝΝΑ διεύθυνσης δεξιόστροφα και ΒΑ-ΝΑ διεύθυνσης αριστερόστροφα ρήγματα οριζόντιας μετατόπισης. Αυτή η παραμόρφωση σβήνει κατά το Μέσο Μειόκαινο και αλλάζει σε transtension με Α-Δ διεύθυνσης αριστερόστροφα ρήγματα οριζόντιας μετατόπισης και ΒΑ-ΝΑ δεξιόστροφα πλάγια έως κανονικά ρήγματα. Από το Ανω Μειόκαινο ένα εφελκυστικό καθεστώς κυριαρχεί στην περιοχή με τον ελάχιστο κύριο άξονα τάσης (σ3) σε ΒΑ-ΝΔ διεύθυνση κατά το Άνω Μειόκαινο - Πλειόκαινο και σε Β-Ν διεύθυνση από το Κάτω Πλειστόκαινο — σήμερα.The boundary between Internal Hellenides and the Hellenic hinterland is exposed in the southern part of the Athos peninsula as a NE-SW trending contact between the Serbomacedonian massif and the Circum-Rhodope Belt. The main tectonic features and deformation of the area during late- and post-alpine times have been investigated in order to understand better the late orogenic processes that led to the present arrangement of this boundary. The field study showed that the prevailing structures in the southern Athos peninsula are an asymmetric, SW-plunging, NWverging mega-scale antiform and a NE-SW striking left-lateral shear zone. These structures are the result of a transpressional deformation that initiated at least since the Eocene under ductile, syn-metamorphic (low-greenschist fades) conditions and progressively changed during the Oligocene-Early Miocene to brittle conditions with E-W striking reverse faults-thrusts and NNW-SSE striking right-lateral and NESW striking left-lateral strike-slip faults. This deformation waned in Middle Miocene changing to transtension with E- W striking, left-lateral strike-slip and NW-SE rightlateral oblique to normal faults. Since the Late Miocene an extensional regime dominates the area with the least principal stress axis (σ3) orientated NE-SW during Late Miocene - Pliocene andN-Sfrom Early Pleistocene -presen