Constraining fault constitutive behavior with slip and stress heterogeneity

We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional finite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m^2, which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M^2

Reply to Comment by J. Zhang and N. Makris on “Estimates of the Ground Accelerations at Point Reyes Station during the 1906 San Francisco Earthquake” by A. Anooshehpoor, T. H. Heaton, B. Shi, and J. N. Brune

Contrary to the comments by Zhang and Makris (hereafter, ZM), our equations of motion governing the rocking response of a rectangular block subjected to a full-sine acceleration pulse are correct. Therefore, the first part of ZM's discussion, which is based primarily upon the assumption that the equations of motion in our article were incorrect, is inappropriate. In the second part of the discussion, ZM present new results for mode 2, toppling without impact. We did not consider this mode because it was not relevant to the Point Reyes train, which by eyewitness accounts, had overturned after experiencing one impact. However, as explained in this reply, toppling with no impact is never the minimum condition for overturning, and would in general involve very large horizontal accelerations, especially at frequencies where mode 2 is the only overturning mode

Grasses and Legumes for Cellulosic Bioenergy

Human life has depended on renewable sources of bioenergy for many thousands of years, since the time humans fi rst learned to control fi re and utilize wood as the earliest source of bioenergy. The exploitation of forage crops constituted the next major technological breakthrough in renewable bioenergy, when our ancestors began to domesticate livestock about 6000 years ago. Horses, cattle, oxen, water buffalo, and camels have long been used as sources of mechanical and chemical energy. They perform tillage for crop production, provide leverage to collect and transport construction materials, supply transportation for trade and migratory routes, and create manure that is used to cook meals and heat homes. Forage crops—many of which form the basis of Grass: The 1948 Yearbook of Agriculture (Stefferud, 1948), as well as the other chapters of this volume—have composed the principal or only diet of these draft animals since the dawn of agriculture

Frequency of neurolopsychological deficits after traumatic brain injury

El traumatismo craneoencefálico (TCE) puede conllevar impactantes cambios en la vida cotidiana, que incluyen alteraciones a nivel social, profesional, comunicativo y cognitivo (dificultades atencionales, mnemónicas y ejecutivas). Este estudio tuvo por objeto caracterizar la ocurrencia de déficits neuropsicológicos post-TCE y constatar el impacto ocasionado por el nivel de severidad del trauma en el desempeño cognitivo de los pacientes. Participaron 96 adultos en la muestra total, que fue dividida en dos grupos para evaluar el nivel de severidad del trauma: TCE leve (n=39) y TCE grave (n=77). La gravedad de la lesión se clasificó por medio de la Escala de Coma de Glasgow, por la duración de la pérdida de consciencia, o por la amnesia post-traumática. No había diferencias entre la edad y la escolaridad de los participantes. Para la comparación entre los grupos en cuanto a la distribución de ocurrencia de déficits neuropsicológicos, se utilizó el Chi-cuadrado. Se utilizó una batería de evaluación neuropsicológica flexible conformada por tareas verbales y visoespaciales de habilidades lingüísticas, mnemónicas y ejecutivas. Los grupos no se diferenciaron en cuanto a las variables sociodemográficas. Los pacientes con TCE leve tuvieron mejores puntajes comparados con los de TCE grave (número de errores y categorías completadas del Test de clasificación de tarjetas de Wisconsin- [WCST, por sus siglas en inglés]; errores en la parte B del Test de Hayling; y en la interferencia retro y proactiva del Test de aprendizaje auditivo verbal de Rey [RAVLT, por sus siglas en inglés]. El nivel de severidad del trauma parece mostrar diferencias en los individuos en cuanto al desempeño en memoria episódica de información nueva y en el control de interferencia entre los recuerdos; lo mismo se aplica a las funciones de flexibilidad e inhibición. Estos resultados sugieren que es necesaria una mayor inversión en acciones de políticas públicas, priorizando intervenciones neurocognitivas reeducativas y métodos de prevención de accidentes relacionados con lesiones traumáticas que tengan alta incidencia de secuelas.El traumatismo craneoencefálico (TCE) puede conllevar impactantes cambios en la vida cotidiana, que incluyen alteraciones a nivel social, profesional, comunicativo y cognitivo (dificultades atencionales, mnemónicas y ejecutivas). Este estudio tuvo por objeto caracterizar la ocurrencia de déficits neuropsicológicos post-TCE y constatar el impacto ocasionado por el nivel de severidad del trauma en el desempeño cognitivo de los pacientes. Participaron 96 adultos en la muestra total, que fue dividida en dos grupos para evaluar el nivel de severidad del trauma: TCE leve (n=39) y TCE grave (n=77). La gravedad de la lesión se clasificó por medio de la Escala de Coma de Glasgow, por la duración de la pérdida de consciencia, o por la amnesia post-traumática. No había diferencias entre la edad y la escolaridad de los participantes. Para la comparación entre los grupos en cuanto a la distribución de ocurrencia de déficits neuropsicológicos, se utilizó el Chi-cuadrado. Se utilizó una batería de evaluación neuropsicológica flexible conformada por tareas verbales y visoespaciales de habilidades lingüísticas, mnemónicas y ejecutivas. Los grupos no se diferenciaron en cuanto a las variables sociodemográficas. Los pacientes con TCE leve tuvieron mejores puntajes comparados con los de TCE grave (número de errores y categorías completadas del Test de clasificación de tarjetas de Wisconsin- [WCST, por sus siglas en inglés]; errores en la parte B del Test de Hayling; y en la interferencia retro y proactiva del Test de aprendizaje auditivo verbal de Rey [RAVLT, por sus siglas en inglés]. El nivel de severidad del trauma parece mostrar diferencias en los individuos en cuanto al desempeño en memoria episódica de información nueva y en el control de interferencia entre los recuerdos; lo mismo se aplica a las funciones de flexibilidad e inhibición. Estos resultados sugieren que es necesaria una mayor inversión en acciones de políticas públicas, priorizando intervenciones neurocognitivas reeducativas y métodos de prevención de accidentes relacionados con lesiones traumáticas que tengan alta incidencia de secuelas.Traumatic brain injury (TBI) can lead to significant changes in daily life, as well as in social, labor, communicative, and cognitive domains (attention, memory and executive functions). This study aimed to characterize the occurrence of post-TBI neuropsychological deficits as well as to determine whether there is an impact related to the level of severity of the trauma on the patient's performance. Ninety-six adults participated in the study, who were divided in two groups to assess the trauma's level of severity: mild TBI (n=39) and severe TBI (n=57). This severity was classified by the Glasgow Coma Scale, by the duration of consciousness loss, or by post-traumatic amnesia. There were no differences between the groups regarding variables of age and years of schooling. A Chi- square test was used to do a comparison between the two groups in terms of occurrence of neuropsychological deficits. Verbal, visuospatial, mnemonic, linguistic and executive tests composed a flexible neuropsychological battery. Patients with mild TBI had better scores compared to those with severe TBI (number of errors and in completed categories of the Modified Wisconsin Card Sorting Test (MWCST); errors in Part B of The Hayling Test; and proactive and retroactive interference in the Rey Auditory Verbal Learning Test (RAVLT). The severity of the trauma seems to differentiate individual's performance on episodic memory of new information and in the control of interference between memories; the same is applied to flexibility and inhibition functions. These results suggest the need for more investments in public health policy actions, prioritizing neurocognitive remedial intervention and prevention methods for such condition with high incidence of sequelae

High-Mass Proto-Stellar Candidates - II : Density structure from dust continuum and CS emission

We present a detailed 1.2 mm continuum and CS spectral line study of a large sample of 69 massive star forming regions in very early stages of evolution, most of them prior to building up an ultracompact HII region. The continuum data show a zoo of different morphologies and give detailed information on the spatial distributions, the masses, column densities and average densities of the whole sample. Fitting the radial intensity profiles shows that three parameters are needed to describe the spatial distribution of the sources: constant emission from the center out to a few arcsec radius followed by a first power law intensity distribution which steepens further outside into a second power law distribution. The mean inner power law intensity index mi (I~r^(-mi)) is 1.2 corresponding to density indices p (n~r^(-p)) of 1.6. In total the density distribution of our massive star formations sites seem to be not too different from their low-mass counterparts, but we show that setting tight constrains on the density indices is very difficult and subject to many possible errors. The local densities we derive from CS calculations are higher (up to one order of magnitude) than the mean densities we find via the mm-continuum. Such inhomogeneous density distribution reflects most likely the ubiquitous phenomenon of clumping and fragmentation in molecular clouds. Linewidth-mass relations show a departure from virial equilibrium in the stages of strongly collapsing cores.Comment: 15 pages, 13 jpeg-figures. Astrophysical Journal, in pres

Dynamic effect of phase conjugation on wave localization

We investigate what would happen to the time dependence of a pulse reflected by a disordered single-mode waveguide, if it is closed at one end not by an ordinary mirror but by a phase-conjugating mirror. We find that the waveguide acts like a virtual cavity with resonance frequency equal to the working frequency omega_0 of the phase-conjugating mirror. The decay in time of the average power spectrum of the reflected pulse is delayed for frequencies near omega_0. In the presence of localization the resonance width is tau_s^{-1}exp(-L/l), with L the length of the waveguide, l the mean free path, and tau_s the scattering time. Inside this frequency range the decay of the average power spectrum is delayed up to times t simeq tau_s exp(L/l).Comment: 10 pages including 2 figure

Traveling wave solutions in the Burridge-Knopoff model

The slider-block Burridge-Knopoff model with the Coulomb friction law is studied as an excitable medium. It is shown that in the continuum limit the system admits solutions in the form of the self-sustained shock waves traveling with constant speed which depends only on the amount of the accumulated stress in front of the wave. For a wide class of initial conditions the behavior of the system is determined by these shock waves and the dynamics of the system can be expressed in terms of their motion. The solutions in the form of the periodic wave trains and sources of counter-propagating waves are analyzed. It is argued that depending on the initial conditions the system will either tend to synchronize or exhibit chaotic spatiotemporal behavior.Comment: 12 pages (ReVTeX), 7 figures (Postscript) to be published in Phys. Rev.