The Effect of Anelasticity on Periods of the Earth's Free Oscillations (Toroidal Modes)

It is known that the anelastic properties of the Earth characterized by a ‘Q’ structure will affect the periods of free oscillation. It is generally considered that the effect is negligible compared to the other perturbing effects due to rotation, ellipticity, and lateral inhomogeneities. Nevertheless, it is of some interest to investigate the precise magnitude of this effect for the observed free oscillation modes since it could provide us with another constraint in the determination of the Q structure of the Earth. An application of perturbation theory provides us with a good estimate of the magnitude of the changes in the periods of an elastic model due to inclusion of anelastic effects. Calculations based on currently accepted mean elastic and anelastic models for the Earth show that the shift in period due to anelasticity is at most 0·023 per cent for the toroidal modes from _0T_2 to _0T_(99), the maximum occurring near _0T_(60). For more extreme Q models, which may be locally applicable, period shifts of the order 0·1 per cent occur, with the maximum again near _0T_(60), corresponding to a period of approximately 150 s. Observational accuracy for the toroidal oscillations is around 0·1 per cent so that anelastic shifts in toroidal oscillation periods are at the present limit of observational accuracy. Viewed in terms of propagating surface waves, the dispersion due to anelasticity results in at most 0·005-0·01 km s^(−1) variations in the phase and group velocities. Such shifts are within the observational resolution of surface dispersion measurements using narrow band filtering techniques. Compared to other perturbing effects, anelasticity is significant for the toroidal oscillation only in the 50- to 300-s period range. In this range, lateral variations in structure generally cause larger perturbations. However, when viewed in terms of propagating surface waves in selected homogeneous regions, anelasticity becomes the dominating effect. Further, the frequency shift due to anelasticity is scaled by (1/Q)^2, so that the anelastic effect can be well within observational accuracy and comparable to any perturbing effect for more extreme, yet acceptable, Q models. In particular, when applied to surface waves propagating across a tectonic region with a strong low velocity zone in the upper mantle, the anelasticity induced dispersion on frequency shift can be significant and measurable. In such cases a joint inversion of elastic and anelastic properties is appropriate

Dilatancy and precursory bulging along incipient fracture zones in uniaxially compressed westerly granite

The existence of precursory bulge along an incipient fracture zone in a uniaxially compressed Westerly granite sample has been investigated by two optical methods. The first method is the method of slit diffraction. The cross section of a cylindrical rock sample is monitored by bringing two straightedges next to the rock sample to form two slits (each slit being formed between one straightedge and one side of the rock sample) and by illuminating alternately the two slits with a collimated laser beam. The Fraunhofer diffraction pattern is recorded on film in the direction perpendicular to the straightedge and can be interpreted as the absolute value squared of the one-dimensional spatial Fourier transform of the slit under certain conditions, thereby providing a simple method of magnification of the rock surface geometry. The conditions under which the Fraunhofer diffraction pattern can be interpreted as the absolute value squared of a one-dimensional Fourier transform are related to the radius of the rock sample, width of the slit, position of the recording film plane, and nature of deformation of the rock surface and are presented in this paper. The films are digitized by a microdensitometer. The data are analyzed by digital filtering and interpolation techniques to give a strain resolution of 10^(−5). During a test with the slit diffraction method, strain inhomogeneities in terms of local bulges indicative of incipient failure zones were found to develop at ∼92% of the uniaxial compressive strength, and their propagation is traced at 2.66-s intervals until failure. Local strains in the incipient failure zones are of the order of 10^(−2) before failure takes place. Because of the large amplitude of the strain inhomogeneity prior to failure recorded by the slit diffraction method, we then tried the faster method of recording without magnification by a motion picture camera. In the second test a precursory bulge in the middle of the sample first appeared at ∼3.75 s prior to failure at a load of >99.7% of the uniaxial compressive strength. The bulge developed rapidly in successive frames until eventually a failure plane passed through this sharp bulge. The results from both tests demonstrate the formation of a concentrated weak zone as a result of the interaction and coalescence among the microcracks in the final stage of the test, which then develop into fracture zones. The bulging is the result of accentuated deformation in the weak zone because of its reduced deformation moduli. It is considered that the local bulge and orientation of the fracture zones in the first test were controlled by the stress concentration at the sample-load block interface, whereas those in the second test were controlled mainly by the inhomogeneity in the material properties within the sample. The precursor times of both tests do not fit into the empirical relationship between precursor time and fault dimension as derived from earthquakes and mine rock bursts. The precursor times of these tests are too long by 3 orders of magnitude in comparison with those given by the empirical relationship

Velocity dispersion due to anelasticity; implications for seismology and mantle composition

The concept of a relaxation spectrum is used to compute the absorption and dispersion of a linear anelastic solid. The Boltzmann after-effect equation is solved for a solid having a linear relationship between stress and strain and their first time derivatives, the ‘standard linear solid’, and having a distribution of relaxation times. The distribution function is chosen to give a nearly constant Q over the seismic frequency range. Both discrete and continuous relaxation spectra are considered. The resulting linear solid has a broad absorption band which can be interpreted in terms of a superposition of absorption peaks of individual relaxation mechanisms. The accompanying phase and group velocity dispersion imply that one cannot directly compare body wave, surface wave, and free oscillation data or laboratory and seismic data without correcting for absorption. The necessary formalism for making these corrections is given. In the constant Q regions the correction is the same as that implied in the theories of Futterman, Lomnitz, Strick and Kolsky

Centrifuge modeling of earthquakes

The major problem in scale modeling of crustal tectonic processes, namely, the requirement for a brittle modeling material of extremely low strength (∼0.1 bar) can be overcome by doing model tests under artificial gravity in a centrifuge. When conditions of dynamic similarity are observed, scale modeling, because of its controlled nature, can be an important tool supplementing field investigation, theoretical study, and numerical simulation of crustal tectonic processes. Fracture events by simulated tectonic stress loading in a model thrust fault (model dimensions: 20 cm depth × 25 cm × 27 cm) have been generated when the model is subject to 50 g in a centrifuge of 1.53 m radius. Measurements obtained are: the total loading force, the stress change at one location inside the fault zone, and model seismic signals recorded on the model top surface. With use of a scaled brittle model material, the model scales up to a prototype approximately 2.2 km depth × 2.8 km × 3.0 km in dimensions

Temperature Dependence of Single-Crystal Spinel (MgAl_2O_4) Elastic Constants from 293 to 423°K Measured by Light-Sound Scattering in the Raman-Nath Region

The temperature dependence of single-crystal elastic constants of synthetic stoichiometric MgAl_2O_4 spinel has been measured by the light-sound scattering technique in the Raman-Nath region. The crystal is set into forced vibration by a single crystal LiNbO_3 transducer coupled to one crystal face. A He-Ne Laser beam is diffracted by the stress-induced birefringence inside the crystal. The diffraction angle is determined from the distance between two spots exposed on a photographic plate by the first order diffracted beams as measured by a microdensitometer. The sound wavelength inside the crystal is then inferred from the laser diffraction angle. Combining the sound wavelength with the measured transducer frequency, the velocity inside the crystal is determined typically to a precision of 0·05 per cent. In this method, the measurement of velocity is not dependent on either the determination of sample length or on phase shifts at sample-transducer interface. Velocities of four pure modes, L//[001], T//[001], L//[110], and T//[110](P//[110] are measured in the temperature range between 293 and 423°K. A linear temperature dependence is fit to the data by a least square method

A shock-induced phase change in orthoclase

New shock compression data to 340 kb for single-crystal orthoclase (along (001)) demonstrate the onset of a shock-induced phase change at ∼115 kb. Along the Hugoniot a mixed-phase region extends to ∼300 kb, above which the data are believed to correspond to the properties of a high-pressure phase having the hollandite structure (zero pressure density of 3.84 g/cm^3) reported by Ringwood et al. If the hollandite value for the zero pressure density is used, the zero pressure bulk modulus of this phase is approximately 2.8 ± 0.2 Mb

Clinical features and outcome of sporadic serogroup W135 disease Taiwan

BACKGROUND: Few published reports have evaluated the clinical features and outcome of serogroup W135 meningococcal disease. In Taiwan, W135 is the second most prevalent meningococcal disease serogroup. METHOD: A nationwide study was conducted to retrospectively analyze epidemiologic data from 115 patients with laboratory confirmed meningococcal disease that occurred from 2001 through 2003. RESULTS: Serogroup W135 accounted for 26% of all cases and most (76.7%) were older than 20 years. There were no cases of serogroup W135 meningococcal disease associated with Hajj pilgrims, and all cases were sporadic. In 88 patients with complete case records, we compared the presenting symptoms, signs, laboratory data, and outcomes between W135 and non-W135 patients. There were no differences in presenting symptoms except for the higher prevalence of pneumonia found in W135 patients (23.8% vs. 1.5%; OR: 20.6; 95%CI: 2.3–189.0; p = 0.003). The distribution of inflammatory cells in CSF in patients with meningitis was also different between W135 and non-W135 patients. W135 patients had a trend toward more intubations and shock but it did not achieve statistical significance. In multivariate analysis of factors associated with death, three independent factors were found: bacteremia without meningitis, altered mental status, and petechiae or purpura on admission. CONCLUSION: Sporadic serogroup W135 meningococcal disease is an important component of the meningococcal disease burden in Taiwan, but it is not directly associated with Hajj pilgrims. Compared with patients infected by other serogroups of meningococci, patients with serogroup W135 were older and more likely to have extrameningeal involvement such as pneumonia

Local Magnetic Field Role in Star Formation

We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions.Comment: 4 pages, 3 figures; to appear in the EAS Proceedings of the 6th Zermatt ISM Symposium "Conditions and Impact of Star Formation from Lab to Space", September 201

Sox2, a stemness gene, regulates tumor-initiating and drug-resistant properties in CD133-positive glioblastoma stem cells

AbstractBackgroundGlioblastoma multiforme (GBM) is the most lethal type of adult brain cancer and performs outrageous growth and resistance regardless of adjuvant chemotherapies, eventually contributing to tumor recurrence and poor outcomes. Considering the common heterogeneity of cancer cells, the imbalanced regulatory mechanism could be switched on/off and contribute to drug resistance. Moreover, the subpopulation of GBM cells was recently discovered to share similar phenotypes with neural stem cells. These cancer stem cells (CSCs) promote the potency of tumor initiation. As a result, targeting of glioma stem cells has become the dominant way of improving the therapeutic outcome against GBM and extending the life span of patients. Among the biomarkers of CSCs, CD-133 (prominin-1) has been known to effectively isolate CSCs from cancer population, including GBM; however, the underlying mechanism of how stemness genes manipulate CSC-associated phenotypes, such as tumor initiation and relapse, is still unclear.MethodsTumorigenicity, drug resistance and embryonic stem cell markers were examined in primary CD133-positive (CD133+) GBM cells and CD133+ subpopulation. Stemness signature of CD133+ GBM cells was identified using microarray analysis. Stem cell potency, tumorigenicity and drug resistance were also tested in differential expression of SOX2 in GBM cells.ResultsIn this study, high tumorigenic and drug resistance was noticed in primary CD-133+ GBM cells; meanwhile, plenty of embryonic stem cell markers were also elevated in the CD-133+ subpopulation. Using microarray analysis, we identified SOX2 as the most enriched gene among the stemness signature in CD133+ GBM cells. Overexpression of SOX2 consistently enhanced the stem cell potency in the GBM cell lines, whereas knockdown of SOX2 dramatically withdrew CD133 expression in CD133+ GBM cells. Additionally, we silenced SOX2 expression using RNAi system, which abrogated the ability of tumor initiation as well as drug resistance of CD133+ GBM cells, suggesting that SOX2 plays a crucial role in regulating tumorigenicity in CD133+ GBM cells.ConclusionSOX2 plays a crucial role in regulating tumorigenicity in CD133+ GBM cells. Our results not only revealed the genetic plasticity contributing to drug resistance and stemness but also demonstrated the dominant role of SOX2 in maintenance of GBM CSCs, which may provide a novel therapeutic target to overcome the conundrum of poor survival of brain cancers