Weak Attenuation Research Articles

Heterogeneities of the field of short-period shear wave attenuation in the lithosphere of Central Asia and their relationship with seismicity

The characteristics of the short-period shear wave attenuation field in the lithosphere of the Turanian Plate, West Tien Shan, Pamir, and Hindu Kush have been studied. The method based on analysis of the logarithm of the ratio between maximal amplitudes of Sn and Pn waves (Sn/Pn parameter) has been applied. More than 400 records of earthquakes, obtained at distances of ∼400–1000 km from the AAK digital station, have been processed. It has been found that relatively weak attenuation is observed in the regions of the West Tien Shan and Pamir. The largest area of strong attenuation is located in the region of the Afghan-Tadjik Depression adjacent to Hindu Kush. A wide band of low Sn/Pn parameter values, stretched northeastwards, has been distinguished. Along with the analogous band of strong attenuation, distinguished before in the regions of Central Tien Shan and Dzungaria, it is the continuation of the largest Chaman Fault, which stretches 850 km along the boundary of the Indian Plate. Source zones of strong earthquakes with M ≥ 7.0 that occurred in the first half of 20th century correspond to relatively weak attenuation. Areas of high attenuation, where strong seismic events have not occurred for the last 110 years, are outlined. Analogously to other seismoactive regions, it is supposed that these areas are related to preparation of strong earthquakes.

Numerical analysis of weak shock attenuation resulting from molecular vibrational relaxation

The attenuation of a weak shock wave generated by the explosion of a unit mass of TNT was numerically analyzed. The effects of viscous and thermal conduction losses and of the molecular vibrational relaxation of oxygen and nitrogen molecules were considered. The effect of each diffusion term on wave attenuation and waveform change was investigated in detail. In addition, the characteristics of each attenuation effect were examined by frequency analysis.

Sum frequency generation in chiral carbon nanotubes

The process of Sum Frequency Generation (SFG) in chiral Carbon Nanotubes (CNTs), with the exciting laser beams propagating along the CNT symmetry axis, is here investigated. First the general form of the first hyperpolarizability third rank tensor β for chiral CNTs is determined with group projecto r technique method applied to the Lnp22 line group describing their symmetry. For this purpose, the group natural factorization has been adopted and the associated irreducible representations, parameterized in terms of helical quantum numbers, then used to construct the group projector operator in the relevant vector space. The method demonstrates that second harmonic generation is symmetry forbidden in the collinear geometry while, conversely, SFG is symmetry allowed. Subsequently, the SFG far-field radiation pattern has been modelled with a calculation scheme derived from antenna's theory and already used for simulation of Rayleigh scattering from a CNT. The method has been overhauled for describing the here considered nonlinear optical interaction. The study of the role played by two induced counter-propagating current density retarded waves in shaping the radiation pattern is addressed and simulations are reported in the limit regimes of strong and weak attenuation.

Seismic wave propagation in Kelvin visco-elastic VTI media

In this article, under the assumption of weak anisotropy and weak attenuation, we present approximate solutions of anisotropic complex velocities and quality-factors for Kelvin visco-elastic transverse isotropy (KEL-VTI) media, based on the complex physical parameter matrix. Also, combined with the KEL-VTI media model, the propagation characteristics of the qP-, qSV-, and qSH-wave phases and energies are discussed. Further, we build a typical KEL-VTI media model of the Huainan coal mine to model the wave propagation. The numerical simulation results show that the PP- and PSV-wave theoretical wave-fields are close to the wave-fields of three-component P- and converted-waves acquired in the work area. This result proves that the KEL-VTI media model gives a good approximation to this typical coalfield seismic-geologic conditions and is helpful to the study of attenuation compensation of multi-component seismic data.

Clinical relevance of retrieval cues for attenuating context renewal of fear

The present studies investigated if retrieval cues (reminder objects) can attenuate context renewal of fear. In Study 1, 32 participants completed exposure in one of two contexts; 1-week follow-up testing occurred in a novel or the same context. Results indicated significant renewal of fear for those tested in a novel context. In Study 2, 40 participants completed exposure in one of these contexts; half were presented with cues. One week later, all were tested in a novel context with or without cues. Results indicated weak attenuation of context renewal for participants re-presented with cues. In Study 3, 18 participants completed exposure in one of two maximally distinct contexts; all with cues. One week later, participants were tested in a novel context with or without cues. Results indicated no group differences. These findings suggest that clinical relevance of this set of cues for attenuating context renewal may be limited.

Predicting mode‐1, internal‐tide signals in the Philippine Sea using tidal analysis of satellite altimeter data.

Tidal analysis of satellite altimeter data has demonstrated that mode‐1 internal tides near Hawaii have considerable predictability. Temporally incoherent contributions to mode‐1 internal tides appear to be minimal, and very weak attenuation is evident. The internal‐tide modes are associated functions of displacement, temperature, sound speed, current, etc. Sea‐surface height is determined by the displacement mode. Whether derived from thermistors, altimetry, or acoustic tomography, the mode amplitude implies specific profiles of temperature, current, etc. The tidal analysis of altimeter data for the region of the Philippine Sea will be discussed, leading to predictions of in situ variability. These predictions will be compared to thermistor and tomographic data acquired in the Philippine Sea during the ONR‐sponsored, PhilSea09 test experiment in March 2009. These data consist of month‐long measurements of temperature acquired by thermistors on two moorings, affording excellent resolution of the internal‐...

Simulation of ground motion in the Moscow region using the empirical Green’s function

Historically, the Moscow region regularly experienced rather weak but quite perceptible seismic vibrations produced by intermediate-depth earthquakes of the Vrancea zone (Romania), located at a distance of 1400 km from Moscow. The coincidence of a number of unique factors such as a slowly varying focal depth, predominant source mechanisms, weak attenuation of seismic radiation in the north-northeast direction provide favorable conditions for application of the empirical Green’s function method. Using the digital seismogram of the Vrancea Mw-5.8 earthquake recorded at the Moscow seismic station, we simulated synthetic seismograms of a scenario (expected maximum) earthquake with Mw = 8.0, by application of the empirical Green’s function method adjusted for the given conditions. The calculation procedure was verified using analog records of strong earthquakes available at the Moscow seismic station. Digital records of the Obninsk seismic station included in the Incorporated Research Institutions for Seismology (IRIS) system were used for additional control. Here, the scenario earthquake was modeled using the data on a much stronger earthquake of 1990 (MW = 6.9). It is shown that, despite a certain scatter (quite adequately assessed in the scope of the method), the ultimate estimates of expected seismic impacts are quite reliable and can be recommended for practical use.

Roles of cutaneous versus spinal TRPA1 channels in mechanical hypersensitivity in the diabetic or mustard oil-treated non-diabetic rat

Previous results indicate that intaperitoneal administration of a TRPA1 channel antagonist attenuates diabetic hypersensitivity. We studied whether the antihypersensitivity effect induced by a TRPA1 channel antagonist in diabetic animals is explained by action on the TRPA1 channel in the skin, the spinal cord, or both. For comparison, we determined the contribution of cutaneous and spinal TRPA1 channels to development of hypersensitivity induced by topical administration of mustard oil in healthy controls. Diabetes mellitus was induced by streptozotocin in the rat. Hypersensitivity was assessed by the monofilament- and paw pressure-induced limb withdrawal response. Intrathecal (i.t.) administration of Chembridge-5861528 (CHEM, a TRPA1 channel antagonist) at doses 2.5-5.0 microg/rat markedly attenuated diabetic hypersensitivity, whereas 20 microg of CHEM was needed to produce a weak attenuation of diabetic hypersensitivity with intraplantar (i.pl.) administrations. In controls, i.pl. administration of CHEM (20 microg) produced a weak antihypersensitivity effect at the mustard oil-treated site. I.t. administration of CHEM (10 microg) in controls produced a strong antihypersensitivity effect adjacent to the mustard oil-treated area (site of secondary hyperalgesia), while it failed to influence hypersensitivity at the mustard oil-treated area (site of primary hyperalgesia). A reversible antagonism of the rat TRPA1 channel by CHEM was verified using in vitro patch clamp recordings. The results suggest that while cutaneous TRPA1 channels contribute to mechanical hypersensitivity induced by diabetes or topical mustard oil, spinal TRPA1 channels, probably on central terminals of primary afferent nerve fibers, play an important role in maintenance of mechanical hypersensitivity in these conditions.

Quetiapine blocks cocaine-induced enhancement of brain stimulation reward

Quetiapine is an effective atypical antipsychotic medication that was reported to reduce substance use and craving in patients with schizophrenia. This clinical effect of quetiapine is hypothesized to be due to its low affinity for dopamine receptors and its weak attenuation of central reward functions. The present study was designed to determine the magnitude of the reward attenuation induced by different doses of quetiapine and its effectiveness at reducing the effect of cocaine. Experiments were performed on male Sprague–Dawley rats that were trained to produce operant responses to receive rewarding stimulations to the medial forebrain bundle. In a first study, we tested the effects of three doses of quetiapine (5, 10, 20mg/kg) on brain stimulation reward using a within-subject design and the curve-shift method. In a second study, we tested the effectiveness of a low and high dose of quetiapine (5 and 20mg/kg) at blocking the reward enhancing effect of cocaine (4mg/kg) in different groups of animals. Quetiapine produced a weak (20%) but significant attenuation of reward. Cocaine enhanced reward by 20% and the combination of cocaine with the high dose of quetiapine lead to cancellation of each drug effect. The low dose of quetiapine did not alter baseline reward but completely blocked the effect of cocaine. The magnitude of the reward attenuation induced by quetiapine is consistent with its low affinity for dopamine receptors. Its actions on dopamine and non-dopamine neurotransmission are likely to account for its effectiveness at blocking the enhancement of reward by cocaine.

Activity-Dependent Control of Neuronal Output by Local and Global Dendritic Spike Attenuation

Neurons possess elaborate dendritic arbors which receive and integrate excitatory synaptic signals. Individual dendritic subbranches exhibit local membrane potential supralinearities, termed dendritic spikes, which control transfer of local synaptic input to the soma. Here, we show that dendritic spikes in CA1 pyramidal cells are strongly regulated by specific types of prior input. While input in the linear range is without effect, supralinear input inhibits subsequent spikes, causing them to attenuate and ultimately fail due to dendritic Na(+) channel inactivation. This mechanism acts locally within the boundaries of the input branch. If an input is sufficiently strong to trigger axonal action potentials, their back-propagation into the dendritic tree causes a widespread global reduction in dendritic excitability which is prominent after firing patterns occurring in vivo. Together, these mechanisms control the capability of individual dendritic branches to trigger somatic action potential output. They are invoked at frequencies encountered during learning, and impose limits on the storage and retrieval rates of information encoded as branch excitability.

Study of Sediment Nonlinearity Using Explosion Data in the Mississippi Embayment

Strong and weak motion data from the Mississippi Embayment Seismic Excitation Experiment (ESEE) were analyzed for signatures of nonlinear site responses. This experiment was performed jointly by the University of Memphis and U. S. Geological Survey in October 2002, by detonating two explosions of 2500 and 5000 lbs. Intrinsic and scattering Q estimates (QI and QS) from the coda of the strong motion data were found to be very low compared to previously determined Q values of P- and Rayleigh waves of weak motion data from the same explosions. The QI estimates from P-wave late coda of the strong motion data are less by more than 100 at 3 Hz and by more than 200 at 10 Hz, compared to the P-wave Q values determined from the weak motion data by Langston et al (2005). Also, QI determined from the late coda of strong motion Rayleigh-wave data is less by more than 200 at 0.5 Hz and by more than 50 at 3.0 Hz, compared to Q values determined from Rayleigh-wave weak motion data. A resonance peak spectral amplitude of the early part of a strong motion seismogram is shifted to lower frequencies compared to that from a later part of the same seismogram. Spectral amplitude ratios between transverse and vertical components of the strong motion data are degraded between frequencies 2 and 10 Hz for P waves, and less than 4 Hz for Rayleigh waves compared to the weak motion transverse to vertical spectral ratio. All these are signatures of nonlinear site responses during strong ground motion. This study proves the non-transportability of weak motion attenuation results to estimate ground motion from a future large earthquake that may take place in areas like the New Madrid Seismic zone.

Identification of Salmonella enterica serovar Dublin-specific sequences by subtractive hybridization and analysis of their role in intestinal colonization and systemic translocation in cattle.

Salmonella enterica serovar Dublin is a host-restricted serovar associated with typhoidal disease in cattle. In contrast, the fowl-associated serovar S. enterica serovar Gallinarum is avirulent in calves, yet it invades ileal mucosa and induces enteritis at levels comparable to those induced by S. enterica serovar Dublin. Suppression subtractive hybridization was employed to identify S. enterica serovar Dublin strain SD3246 genes absent from S. enterica serovar Gallinarum strain SG9. Forty-one S. enterica serovar Dublin fragments were cloned and sequenced. Among these, 24 mobile-element-associated genes were identified, and 12 clones exhibited similarity with sequences of known or predicted function in other serovars. Three S. enterica serovar Dublin-specific regions were homologous to regions from the genome of Enterobacter sp. strain 638. Sequencing of fragments adjacent to these three sequences revealed the presence of a 21-kb genomic island, designated S. enterica serovar Dublin island 1 (SDI-1). PCR analysis and Southern blotting showed that SDI-1 is highly conserved within S. enterica serovar Dublin isolates but rarely found in other serovars. To probe the role of genes identified by subtractive hybridization in vivo, 24 signature-tagged S. enterica serovar Dublin SD3246 mutants lacking loci not present in Salmonella serovar Gallinarum SG9 were created and screened by oral challenge of cattle. Though attenuation of tagged SG9 and SD3246 Salmonella pathogenicity island-1 (SPI-1) and SPI-2 mutant strains was detected, no obvious defects of these 24 mutants were detected. Subsequently, a DeltaSDI-1 mutant was found to exhibit weak but significant attenuation compared with the parent strain in coinfection of calves. SDI-1 mutation did not impair invasion, intramacrophage survival, or virulence in mice, implying that SDI-1 does not influence fitness per se and may act in a host-specific manner.

Evolution of bulk strain solitons in long polymeric waveguides

We have studied the propagation of longitudinal strain solitons in waveguides made of polystyrene and plexiglas (polymethyl methacrylate) and long enough to provide noticeable changes in the wave shape and amplitude. The decay rate for nonlinear waves in these materials is estimated from the experimental data. An anomalously weak attenuation of strain solitons in polymers featuring a high dissipation of linear waves is discovered for the first time.

Functional Structure of the Mitral Cell Dendritic Tuft in the Rat Olfactory Bulb

The input-output transform performed by mitral cells, the principal projection neurons of the olfactory bulb, is one of the key factors in understanding olfaction. We used combined calcium and voltage imaging from the same neuron and computer modeling to investigate signal processing in the mitral cells, focusing on the glomerular dendritic tuft. The main finding was that the dendritic tuft functions as a single electrical compartment for subthreshold signals within the range of amplitudes detectable by voltage-sensitive dye recording. These evoked EPSPs had uniform characteristics throughout the glomerular tuft. The Ca(2+) transients associated with spatially uniform subthreshold synaptic potentials were comparable but not equal in amplitude in all regions. The average range of normalized amplitudes of the EPSP-driven Ca(2+) signals from different locations on dendritic branches in the glomerular tuft was relatively narrow and appeared to be independent of the dendritic surface-to-volume ratio. The computer simulations constrained by the imaging data indicated that a synchronized activation of approximately 100 synapses randomly distributed on tuft branches was sufficient to generate spatially homogenous EPSPs. This number of activated synapses is consistent with the data from anatomical studies. Furthermore, voltage attenuation of the EPSP along the primary dendrite at physiological temperature was weak compared with other cell types. In the model, weak attenuation of the EPSP along the primary dendrite could be accounted for by passive electrical properties of the mitral cell.

Preliminary study of a phase-contrast cone-beam computed tomography system: the edge-enhancement effect in the tomographic reconstruction of in-line holographic images

A phase-contrast cone-beam computed tomography (PC CBCT) system is proposed for small-animal imaging that incorporates the in-line holography technique into CBCT system. Theoretical analysis shows that the in-line holographic image can be approximately transformed into line integrals of an object function composed of an attenuation term and a phase term. The Fresnel diffraction theory is applied to generate in-line holographic images along a circular orbit, and the Feldkamp-Davis-Kress algorithm is applied to reconstruct the object function. The proposed system was investigated using a numerical phantom, and the reconstruction was evaluated using the edge-enhancement factor and the relative reconstruction error. The reconstruction results show that all the structures in the numerical phantom are bounded with enhanced edges with negligible artifacts. These enhanced edges make the reconstruction visually sharper and clearer. The results show that while the relative reconstruction errors are very close to that of the conventional CBCT reconstruction, having a small cone angle, weak attenuation, small focal spot size, and high-resolution detector are preferred for a greater edge-enhancement effect.

Dipole polarizability of onion-like carbons and electromagnetic properties of theircomposites

Onion-like carbons (OLC) obtained by thermal transformation of nanodiamonds areagglomerates of multi-shell fullerenes, often covered by an external graphitic mantle. Forthe present work, elemental OLC units were constructed on the computer by coalescence ofseveral two-layer fullerenes, in a structure similar to carbon peapods with a corrugatedexternal wall. The electrical polarizability of such pod-of-peas fullerenes has beencomputed by a classical monopole–dipole atomistic theory. The description ofpod-of-peas fullerenes was further simplified by representing them as linear arrays ofpoint-like objects, whose polarizability matches that of the starting molecules.Calculations demonstrated that the static polarizability of spherically shapedassemblies of these arrays, modeling real OLC materials, is weakly dependent on thegeometry of its constituent molecules and is chiefly proportional to the volume ofthe whole cluster. It increases with increasing filling fraction of the pod-of-peasfullerenes in the OLC aggregate. The polarizability so obtained can be used inMaxwell–Garnett theory to predict the permittivity of OLC-based composites, atleast for static excitations. Experimental results obtained at GHz frequenciesreveal a weak attenuation for OLC- and nanodiamond-based polydimethylsiloxanecomposites. In these silicone composites, we did not find long chains of coupledOLCs. Quite separated clusters were found instead, which contribute little to thepolarizability and to the dielectric properties, in good agreement with our theoreticalpredictions.

Morphine and ABT-594 (a Nicotinic Acetylcholine Agonist) Exert Centrally Mediated Antinociception in the Rat Cyclophosphamide Cystitis Model of Visceral Pain

A visceral pain model incorporating use of cyclophosphamide (CP) to induce bladder inflammation has been described. CP treatment in rats produces changes in behavior (abnormal postures and eye closure) and respiration rate indicative of visceral pain. We characterized the dose-dependency and progression of CP-induced cystitis pain after intraperitoneal (i.p.) CP. The behavioral and respiration rate changes were ameliorated by systemic morphine and ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine], a neuronal nicotinic acetylcholine receptor agonist, in a manner reversible by naloxone and mecamylamine, respectively. Sites of antinociceptive actions of morphine and ABT-594 were investigated using systemic, intrathecal (i.t.), or intracerebroventricular (i.c.v.) administration of blood-brain barrier impenetrant antagonists. Naloxone methiodide produced a complete antagonism of morphine antinociception after i.c.v. but not i.p. or i.t. administration. Chlorisondamine blocked ABT-594 antinociception after i.c.v. but not i.p. administration. Further pharmacological characterization of behavioral and respiration changes in CP-cystitis was performed using standard analgesics. The alpha(2)-adrenoceptor agonist clonidine produced a weak attenuation of CP-pain behavior. NSAIDs (ibuprofen, acetaminophen, and celecoxib) and anticonvulsants (gabapentin and lamotrigine) were without effect. These results demonstrate that morphine and ABT-594 produce antinociception in CP-cystitis by a predominantly supraspinal site of action, and that mechanisms producing robust centrally-mediated antinociception could be beneficial in cystitis pain. In this article, potential antinociceptive effects of a variety of pharmacological agents were evaluated in a rat cystitis pain model. Morphine and a nicotinic acetylcholine receptor agonist ABT-594 were found to exert potent antinociception in this model. Findings presented here aid identification of agents to treat cystitis pain in the clinic.

Empirical Distance Attenuation and the Local-Magnitude Scale for the Central United States

Seismic waveform data from the Cooperative New Madrid Seismic Network (CNMSN), the U.S. National Seismograph Network (USNSN), and stations operated by the U.S. Geological Survey and the Incorporated Research Institutions for Seismology (IU) are corrected to the theoretical Wood–Anderson response, and the peak amplitudes are used to determine a local-magnitude scale for the central United States. The distance-correction function can be expressed as ![Graphic][1] , with amplitude A in millimeters and hypocentral distance r in kilometers, showing a weak attenuation with distance. Synthetic seismograms are calculated based on a detailed crustal model obtained from local well log acoustic data in the Mississippi embayment to examine the effect of structure on station factors. The results show that the Mississippi embayment sediment, as a whole, may amplify seismic waves at some specific frequencies, such as 0.5 and 5.0–6.0 Hz, with a factor less than 4.0, and may not amplify seismic waves in the frequency band from 0.5 to 9.9 Hz on average, even though the amplification factors do increase with the source magnitude. Estimations for b -values and magnitudes of earthquakes with a return period of 500 yr in the central United States are performed, based on the original New Madrid catalog ( M D or m bLg ) and the newly created M L catalog. Results show that the b -value is smaller for the M L catalog (0.790) yielding one M 7.5 event every 500 yr, a result that converges with the paleoearthquake estimate for the region. On average, the relation between M L and M D or m bLg (for 1.5≤ M D≤5.0) can be expressed as M L=1.008 M D+0.0714. [1]: /embed/inline-graphic-1.gif

Optically active substances and their contributions to the underwater light climate in Lake Taihu, a large shallow lake in China

There are few data sets on optically active substances and optical conditions to partition the relative contribution of every substance on light attenuation in a lake. To address this need, underwater photosynthetically active radiation (PAR), optical parameters and concentrations of three optically active substances, tripton (non- phytoplankton particulate matter), chlorophyll-a (Chl-a), chromophoric dissolved organic matter (CDOM) were measured at 67 sites in Lake Taihu, a large shallow lake in China in October 2004. The spatial variation of optically active substances and their relative contributions to the underwater light climate were determined. The PAR diffuse attenuation coeffi cient Kd(PAR) at different sites varied between 0.87 and 12.43 m -1 , with a mean of 4.42 m -1 . Sig- nifi cant spatial differences were found for optically active substances and PAR attenuation, with low concentrations and weak light attenuation in macrophyte-dominated bays such as East Lake Taihu, Xukou Bay and Gongshan Bay, and high concentrations and strong light attenuation in the open water and algae-dominated areas such as the center of the lake, southwestern region, and Meiliang Bay. The mean relative contributions of tripton, Chl-a, and CDOM to light attenuation were 82.6 %, 9.7 %, and 6.8 % of Kd(PAR), respectively. Tripton was the dominant constituent of Kd(PAR), and mean of 97.5 % of the variation in Kd(PAR) could be explained by tripton. In autumn, the relative contribution of CDOM to light attenuation was lower than that of phytoplankton. We conclude that suspended par- ticulate matter, rather than dissolved organic matter, is the dominant factor for PAR attenuation in Lake Taihu.

The impact of bio-optical heating on the properties of the upper ocean: A sensitivity study using a 3-D circulation model for the Labrador Sea

Abstract The impact of bio-optical heating on the properties of the upper Labrador Sea water was investigated by considering changes in light attenuation in water associated with the seasonal change of chlorophyll distribution. The time- and depth-dependent attenuation coefficients were obtained from remotely sensed SeaWiFS ocean-colour data. Sea-surface temperature (SST) and mixed-layer depth (MLD) were computed from a three-dimensional ocean circulation model. The model was integrated from 1999 to 2003 with 6-hourly atmospheric forcing. The changes in SST and MLD attributable to bio-optical heating were determined by comparing the model results using the observed attenuation coefficients (chlorophyll) to those using a weak and constant attenuation (clear water). The model results show that bio-optical heating is controlled mainly by chlorophyll concentration and MLD. The increase in SST is around 1 °C in most parts of the Labrador Sea and the shelves, and up to 2.7 °C in areas of shallow MLD and high chlorophyll concentrations (the Grand Banks and Northeastern Newfoundland Shelf). The increase is much higher than that found in previous studies, which was typically a fraction of a degree. Bio-optical heating also can enhance the stratification of the upper ocean and reduce the MLD by 20–50%.