Formation Of Intrusions Research Articles

Short crack growth and internal stresses

Short crack growth behavior has been examined using the two parametric approach developed earlier by the authors. It is commonly accepted that there is a lack of similitude in the description of the short crack growth behavior. Contrary to this understanding, it is shown that there is no anomaly in the short crack growth behavior. The apparent anomaly arises because of ignoring: (1) the second parameter associated with the threshold K∗max; and (2) the existence of internal stresses in the crack tip field where the short cracks nucleate and grow. In the case of short cracks nucleating from notches the internal stresses can be pre-existing or can be generated in situ if they form at a free surface. In the latter case, formation of intrusions and extrusions at the persistent slip bands are the precursors for the crack nucleation providing the necessary internal stresses. Thus short cracks grow under a total force, consisting of both internal and applied stresses, satisfying the same two thresholds for long cracks. Examples are provided from the literature to illustrate the concepts. It is shown that the internal stresses decrease as a short crack grows out of the existing stress field. These internal stresses can be predicted using elastic or elastic-plastic continuum approximations. Application of this concept is extended to understand the role of: (1) residual stresses; and (2) the transformation induced internal stresses on the crack growth. Based on the analysis, we restate the similitude concept as: equal crack tip forces result in equal crack growth rates for the same crack growth mechanism, provided all the contributing forces are taken into consideration.

The Art of Inaccuracy: Why Pianists' Errors Are Difficult to Hear

Pianists' pitch errors were identified in a MIDI data base comprising more than 90,000 notes. Ten graduate student pianists had played four pieces (Schumann's Träumerei, Debussy's La fille aux cheveux de lin, Chopin's Prelude in D-flat Major, and Grieg's Erotik) three times from the score, after only a brief rehearsal. Pitch errors were classified exhaustively as substitutions, omissions, or intrusions. (A frequent form of intrusion was the "untying" of tied notes.) Nearly all errors occurred in nonmelody voices, often inside chords. The majority of the intrusions and nearly all substitutions seemed contextually appropriate. The repeated performances made it possible to distinguish consistent from unique errors. Consistent errors were more often omissions than intrusions, and consistent intrusions were more contextually appropriate than unique intrusions. Most errors seemed likely to be perceptually inconspicuous. This was confirmed in an error-detection experiment, in which eight pianists, some of whom had recently studied the test piece (the Chopin prelude), collectively detected only 38% of all objectively registered errors. Pitch errors, rather than being a categorical phenomenon (as a scorebased analysis might suggest), vary in the degree to which they violate the music, and their perceptibility is context-, listener-, and situation dependent. Members of a typical concert audience are likely to notice only a small fraction of a pianist's inaccuracies, which is in part due to the contextual appropriateness of most errors.

Evolution of the Snow Lake portion of the Palaeoproterozoic Flin Flon and Kisseynew belts, Trans-Hudson Orogen, Manitoba, Canada

Understanding growth of early Precambrian crust requires knowledge of the evolution of granite-greenstone and metasedimentary belts, two of the fundamental building blocks of early Precambrian cratons. UPb geochronologic data from the Snow Lake area, which straddles the Flin Flon granite-greenstone and Kisseynew metasedimentary belts of the Trans-Hudson Orogen, documents a 60–70 Ma period of Palaeoproterozoic crust formation from inception of these belts in ocean basins through their eventual structural telescoping during ocean basin consumption and collision with bounding Archaean cratons. Earliest volcanic and plutonic rocks of the Flin Flon granite-greenstone terrane at Snow Lake formed ∼1.89 Ga, mainly in a juvenile oceanic arc tectonic setting. Sedimentary rocks of the Kisseynew belt, previously thought to be contemporaneous with Snow Lake area arc volcanism, are up to 30–50 Ma younger (∼1.86-1.84 Ga) and postdate deformation associated with ∼1.88-1.87 Ga arc-arc collisions and ∼1.87-1.84 Ga calc-alkaline plutonism that affected much of the western Flin Flon belt. Deformation at Snow Lake occurred during two widely spaced episodes, both of which effect the post 1.86-1.84 Ga turbidite sequence and, thus, postdate 1.88-1.87 Ga intraoceanic accretion in the western Flin Flon Belt. The older deformational episode involved isoclinal folding formed during ∼1.84 Ga convergence of the Kisseynew and Flin Flon belts and thrusting of Kisseynew sedimentary lithologies southwards onto the Flin Flon volcanic rocks. The younger deformational episode occurred 15–25 Ma later and involved further folding and southwest thrusting, accompanied by a ∼1.81 Ga high grade thermal metamorphic episode, centred in the Kisseynew Belt. Only minor increase of crustal material, in the form of late intrusions, were added following this episode.

Elastostatic simulation of dislocation sources in heterogeneous stress fields and multilayered media having irregular interfaces

We present an extension of the 2D discontinuity method of Crouch (1976) to simulate dislocation sources in multilayered media having irregular interfaces and surface topography. The magnitudes of dislocations on a given line segment are treated as unknowns that are solved for by satisfying stress or displacement boundary conditions at the center of each line segment. The interaction between dislocation sources within a layer is taken into consideration using analytical kernel functions of homogeneous media. The free surface is simulated by placing dislocation source segments on it and demanding the stress to be zero. Layer interfaces are simulated using dislocation source segments on both sides of the interfaces. The magnitudes of these secondary sources are estimated demanding continuity of stress and displacement on one side of each interface segement. Propagator matrices are introduced to relate the source distributions on neighbouring layers. A simulated vertical dike in a layered medium shows that layering is able to alter the intrusion form and the surface uplift above the intrusion.

Does Repeated Human Intrusion Cause Cumulative Declines in Avian Richness and Abundance?

Human intrusion, the mere presence of people in the environment, has become a dominant form of disturbance in many landscapes. Some forms of intrusion from recreationists and other groups occur repeatedly and can seriously alter avian reproduction, survival, and habitat use. Accordingly, repeated intrusion has the potential to cause impacts that accumulate through time and that are manifested as progressive declines in avian richness and abundance. From 1989 to 1993, we experimentally assessed whether or not temporally cumulative impacts occurred in Wyoming bird communities as a result of repeated intrusion by solitary hikers; the intrusions lasted 1‐2 h each week during 10 consecutive weeks of each year's breeding season. We tested a priori hypotheses about declines in overall richness and abundance, relative richness and abundance for sets of common and uncommon species, richness and abundance for six guilds, and separate abundances of four common species. Relative richness and abundance for the set of common species were the only metrices to exhibit significant declines between years during the 5‐yr period. The declines in these variables, however, were not cumulative. At a statistical power level of 0,85, minimum detectable differences for many variables were small enough to have allowed easy detection of substantive declines, had any occurred. The yearly effects we detected for some richness and abundance variables may not have led to cumulative declines because individuals displaced one year may have been replaced in subsequent years, and some individuals each year may have habituated to or learned to tolerate the intrusions. For the avian communities and intrusion levels we studied, managers should focus on trying to preclude or ameliorate short‐term impacts. Attempts to identify the types and intensities of intrusion that actually cause cumulative declines in richness and abundance should continue. Data about intrusions that do not generate cumulative declines, such as those presented here, are just as important as data about intrusions that do cause cumulative declines; managers need both to define the scope of intrusion disturbances that can lead to cumulative impacts in avian communities. Information about the cumulative effects of intrusion should be used by conservation biologists, wildlife managers, and land‐use planners to decide whether or how to control intrusion.

Banning Tobacco Billboards

In 1994, Baltimore, Md, became the first city to generally prohibit billboards from displaying alcohol and tobacco advertisements. The owner of most of Baltimore's billboards, Penn Advertising, sued, but the federal district court rejected the billboard company's complaint and ruled that the First Amendment had not been violated and that the federal cigarette labeling acts had not preempted the ability of Baltimore to regulate and prohibit billboard cigarette advertising. In the fall of 1995, the federal district court's judgment was unanimously affirmed by the Fourth Circuit Court of Appeals in Richmond, Va. This article analyzes the constitutional and preemption issues and concludes that states and municipalities are on firm legal ground when they restrict the location or placement of publicly visible cigarette advertisements without attempting to regulate the advertisement's content or message. States and municipalities command broad authority to protect children and to shield the public from intrusive forms of advertisement that inflict their messages on a captive audience. A billboard ban thus offers local communities a legal avenue to help curb the rising tide of juvenile smoking without raising taxes, creating bureaucracy, or angering smokers. (<i>JAMA</i>. 1996;275:1263-1269)

Banning tobacco billboards: The case for municipal action.

In 1994, Baltimore, Md, became the first city to generally prohibit billboards from displaying alcohol and tobacco advertisements. The owner of most of Baltimore's billboards, Penn Advertising, sued, but the federal district court rejected the billboard company's complaint and ruled that the First Amendment had not been violated and that the federal cigarette labeling acts had not preempted the ability of Baltimore to regulate and prohibit billboard cigarette advertising. In the fall of 1995, the federal district court's judgment was unanimously affirmed by the Fourth Circuit Court of Appeals in Richmond, Va. This article analyzes the constitutional and preemption issues and concludes that states and municipalities are on firm legal ground when they restrict the location or placement of publicly visible cigarette advertisements without attempting to regulate the advertisement's content or message. States and municipalities command broad authority to protect children and to shield the public from intrusive forms of advertisement that inflict their messages on a captive audience. A billboard ban thus offers local communities a legal avenue to help curb the rising tide of juvenile smoking without raising taxes, creating bureaucracy or angering smokers.

Experiments on gas-ash separation processes in volcanic umbrella plumes

We present a series of analogue laboratory experiments which simulate the separation of ash and gas and the formation of secondary intrusions from finite volcanic umbrella plumes. We examined the lateral spreading of mixtures of freshwater and particles released into a laboratory tank containing a uniformly stratified aqueous solution. For times smaller than the sedimentation time of particles through the intrusion, the current remains coherent and intrudes laterally. As some of the particles settle into the underlying ambient fluid, a layer of particle-depleted fluid develops below the upper surface of the current and the density of the residual fluid is reduced. Over longer times, the intrusion ceases to be coherent, with small fingers of relatively buoyant, particle-depleted fluid rising from the upper part of the intrusion into the overlying fluid. Meanwhile, the lateral motion of the injected solution induces a return flow in the ambient fluid which sweeps some of the particles sedimenting from the lower surface of the intrusion inwards. As a result, relatively dense particle-laden fluid collects below the intrusion and then sinks into the underlying fluid. Eventually this fluid reaches a new neutral buoyancy height, where it intrudes to form a second laterally spreading current below the original intrusion. The process then repeats to form further weaker intrusions below. These results of the separation of the ash and volcanic gas in an umbrella plume are consistent with field observations at Sakurajima volcano where positively charged plumes, thought to consist of volcanic gas, have been observed above negatively charged plumes of ash. This work also suggests that volcanic aerosols may form up to a kilometer above the original injection height of the ash. In a strong wind shear, this could result in very different trajectories of the ash and gas and so be important for evaluating the impact of ash plumes on both aviation safety and volcanic aerosol formation. The separation of the ash from the umbrella plume, after a time of order 10 3−10 4 s, corroborates recent models of the May 18, 1980 eruption at Mount St. Helens that, after a few hours, the motion of the ash was simply controlled by wind dispersal and gravitational settling. The complex motion of the sedimenting ash may also explain some of the observations of multiple intrusions in short-lived umbrella plumes such as observed at Redoubt, Alaska in April 1990.

Mineralogical, petrological and geochemical aspects of alkaline and alkaline-carbonatite associations from Brazil

A general description of Mesozoic and Tertiary (Fortaleza) Brazilian alkaline and alkaline-carbonatite districts is presented with reference to mineralogy, petrology, geochemistry and geochronology. It mainly refers to scientific results obtained during the last decade by an Italo-Brazilian research team. Alkaline occurrences are distributed across Brazilian territory from the southern (Piratini, Rio Grande do Sul State) to the northeastern (Fortaleza, Ceará State) regions and are mainly concentrated along the borders of the Paraná Basin generally coinciding with important tectonic lineaments. The most noteworthy characteristics of these alkaline and alkaline-carbonatite suites are: (i) prevalence of intrusive forms; (ii) abundance of cumulate assemblages (minor dunites, frequent clinopyroxenites and members of the ijolite series) and (iii) abundance of evolved rock-types. Many data demonstrate that crystal fractionation was the main process responsible for magma evolution of all Brazilian alkaline rocks. A hypothesis is proposed for the genesis of carbonatite liquids by immiscibility processes. The incidence of REE and trace elements for different major groups of lithotypes, belonging both to carbonatite-bearing and carbonatite-free districts, are documented. Sr and preliminary Nd isotopic data are indicative of a mantle origin for the least evolved magmas of all the studied occurrences. Mantle source material and melting models for the generation of the Brazilian alkaline magma types are also discussed.

Fatigue damage in aluminum single crystals—I. On the surface containing the slip burgers vector

An aluminum single crystal with the axial direction of [211̄0 was fatigued in push-pull at the constant resolved shear stress amplitude 4 MPa, frequency 20 Hz room temperature. Microcracks, microvoids, macrobands, extrusions and intrusions were observed on the side-surface containing the Burgers vector b. Most microcracks were opened, and were within, but approximately perpendicular to, PSBs. Slip steps were found in the extrusions and intrusions. There was net irreversible slip in one direction in most PSBs. Some short cracks along the PSBs on the side-surface were also observed at 5 × 10 6 cycles. These observations indicate that, without the aid of the surface roughness of PSBs, cracks can still be nucleated, and that, apart from the notch effect of a PSB, there are other factors controlling crack initiation in single crystal aluminium. There may be an internal tensile stress existing in a PSB in the direction of b, and a shear stress applied by the specimen grips in the specimen due to the irreversible slip in one direction in PSBs. These stresses and the applied stress are responsible for the formation of microcracks, microvoids, extrusions, intrusions and macrobands on the side-surface.

Flux Droplet Formation in NbSe2Single Crystals Observed by Decoration

A potential barrier of geometrical origin, characterized by a barrier field ${H}_{p}$, governs vortex penetration in thin superconducting samples. We observed this effect by the decoration of crystals of NbS${\mathrm{e}}_{2}$. Upon zero field cooling and applying a field ${H}_{a}l{H}_{p}\ensuremath{\approx}5\mathrm{mT}$, vortices form a belt at the sample edges. At ${H}_{a}\ensuremath{\approx}{H}_{p}$ flux begins to penetrate in the form of dropletlike intrusions. The orientational correlation length for the vortex pattern inside the ``droplets'' is much larger than for the field-cooled patterns. This we interpret as recrystallization of the moving flux line lattice.

Mesoscale aspects of a dry intrusion within a vigorous cyclone

AbstractThe results of a diagnostic study using radar and satellite imagery, together with surface reports and output from regional and mesoscale models, are presented for an occasion of a rapidly deepening cyclone that crossed the British Isles. The study shows how air descended from near‐tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front. One of the dry intrusions is analysed in detail, because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band: in some places the precipitation was entirely suppressed, whilst in other places the precipitation became convective, with a tornadic squall line developing. Although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar, the approach of the dry intrusion was also clearly detected in the satellite water‐vapour imagery, and foreshadowed in the model forecasts.The mesoscale model, despite some limitations, reproduced many of the observed mesoscale features. It also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line. It showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity (PV) which was extruded from the lower part of a large region of high PV near a low tropopause. The extruded PV anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt. The dry intrusion was also characterized by relatively low wet‐bulb potential temperature, θw, and it led to potential instability where it overran the warm air. The warm conveyor belt itself was characterized not only by a high θw but also by a separate strip of high PV generated locally, mainly by condensation. The quality of the mesoscale‐model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when, as in this case, they are orchestrated by resolved larger‐scale dynamics.

Mechanics of sill emplacement: Comments based on the Tasmanian dolerites

Proposed mechanisms for sill emplacement may be tested by forms of intrusion displayed by Tasmanian dolerites. These intrusions suggest upward, fracture‐controlled, magma passage with local bedding control from an array of feeding centres whose location was determined by basement structures and regional stresses associated with the basin intruded. Many published misconceptions about these intrusions can be resolved in these terms.

Psychosocial perspectives on post-traumatic stress

Although exposure to a traumatic event is a necessary etiological factor in the development of posttraumatic stress disorder, it is not thought to be sufficient and there remains much debate over what other factors may be associated with more severe and chronic distress. The present paper summarizes empirical work with survivors of various traumatic events. Evidence is reviewed for an integrative model of psychosocial factors relating to adjustment following traumatic stressors. The components of this model are stimulus factors, appraisal factors, personality factors, state factors, and activity factors. It is also argued that some forms of intrusion and avoidance constitute normal processes of appraisal and activity that mediate between the traumatic event and symptoms of increased arousal and negative affect. The social context of the traumatic event is also considered to be an important determinant of appraisal and activity. Methodological issues and implications for therapeutic intervention are addressed.

Early Precambrian crustal development: changing styles of mafic magmatism

Abstract The work of Sutton &amp; Watson (1951) was one of the cornerstones in the interpretation of the evolution of early Precambrian (Archaean and early Proterozoic) gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted Archaean cratons. Since then, the concept of geological terranes and terrane accretion has been extended back to the Archaean, and different events can be distinguished by increasingly precise isotopic dating techniques. There is growing evidence that, with certain clear provisos, the principle of uniformitarianism can be applied as equally to the early Precambrian as it can through the rest of the geological record. In terms of mafic magmatism, there are similarities between some ancient and modern suites, both intrusive and extrusive, but there are also some major differences, such as the presence of komatiites in the Archaean and the formation of large-scale layered intrusions and extensive dyke swarms at the end of the late Archaean and in the early Proterozoic. The mantle has evolved continuously with the progressive extraction of mafic magmas but, allowing for this, continental tholeiites appear to have changed little with time. Ancient mid-ocean ridge basalts are elusive because of their poor preservation record. The geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present-day arc systems. The relative abundance of early Precambrian intrusive mafic suites parallels the crustal growth curve, reflecting the global crustal accretion-differentiation superevent towards the close of the Archaean. Bimodal tholeiitic-noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle-mafic crust-continental crust system. This, in turn, gives a possible link between the respective evolutions of Archaean to Recent komatiitic, noritic and boninitic suites.

Two Types of Archaean Grey Gneiss in North China and Their Geological Significance1,2

Abstract Grey gneisses are tonalitic intrusive rocks that have Archaean characteristics and tectonic significance. Archaean grey gneisses in North China may be classified into two types: the Zunhua type and the Hengshan type. Grey gneisses of the Zunhua type alternate with basic granulites, forming a bimodal migmatitic suite. The rock is characterized by complex mineral composition, highly varied REE patterns and positive Eu anomaly and originated from autochthonous or partly autochthonous deep ‐ level migmatization with a high degree (30% ±) of fusion. As the sub ‐ stratum in the root of the early ‐ stage high ‐ grade greenstone belt, they prevented basic rocks from sinking. Grey gneisses of the Hengshan type are characterized by a relatively distinct intrusion form, large ‐ amplitude upward emplacement, rather simple mineral composition, only slight changes of REE patterns and absence of Eu anomaly. The rock is a product of subduction and underthrusting of the high ‐ grade greenstone belt and then fusion and emplacement with a low degree (15% ±) of fusion. In this paper an attempt is made to furnish important information about palaeoplate tectonics and early crustal evolution by means of a study of grey gneisses.

The Role of Accumulation in Forming the Nickeliferous Norite-Diorite Intrusions of the Voronezh Crystalline Massif

This paper presents a generalized description of the composition (mineralogy and geochemistry of the rocks and ores) of the nickeliferous norite-diorite intrusions of the Yelan' complex of the Voronezh crystalline massif (European Russia). It is shown that the host norites have features of both ultramafic (substantial contents of MgO, Cr, and Ni; presence of highly magnesian olivine and orthopyroxene and highly chromian spinel) and intermediate rocks (substantial contents of SiO2, K, Rb, Ba, and light rare earth elements; presence of K-feldspar, quartz, and low-calcium plagioclase). The ores have relatively low Cu/Ni and Pd/Ir ratios, are enriched in Mo, Sb, Bi, Se, Te, As, Ag, and Au, and have anomalous sulfur and carbon isotopic compositions. These unique features of the composition are interpreted from the standpoint of an assimilation model proposed by the authors. It is shown that the formation of the norite-diorite intrusions was related to assimilation of silicic rocks of the continental crust by a...

An experimental study on the formation of composite intrusions from zoned magma chambers

We present a model which accounts for the common, but paradoxical arrangement of composite intrusions (i.e. silicic core and mafic margins) on the basis of analogue experiments using gelatin and aqueous solutions. The present model involves simultaneous flow-out of the upper and lower magmas from a longitudinal crack along the chamber wall. Experimental results suggest that the mafic magma from the lower layer leaks from the side-wall of the chamber and travels faster than the silicic magma because of its lower viscosity, so that the mafic magma reaches the tip of the crack first. Once the mafic magma reaches the crack tip, then the rate of dyke propagation becomes determined by the viscosity of the less viscous mafic magma, and so it can advance rapidly. The viscous silicic magma can flow efficiently into the center of the dyke, being lubricated by the mafic magma margins. This model accounts for the common arrangement of composite intrusions and gives an efficient mechanism of flow of viscous silicic magmas.

Early Precambrian crustal development: changing styles of mafic magmatism

The work of Sutton &amp; Watson (1951) was one of the cornerstones in the interpretation of the evolution of early Precambrian (Archaean and early Proterozoic) gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted Archaean cratons. Since then, the concept of geological terranes and terrane accretion has been extended back to the Archaean, and different events can be distinguished by increasingly precise isotopic dating techniques. There is growing evidence that, with certain clear provisos, the principle of uniformitarianism can be applied as equally to the early Precambrian as it can through the rest of the geological record. In terms of mafic magmatism, there are similarities between some ancient and modern suites, both intrusive and extrusive, but there are also some major differences, such as the presence of komatiites in the Archaean and the formation of large-scale layered intrusions and extensive dyke swarms at the end of the late Archaean and in the early Proterozoic. The mantle has evolved continuously with the progressive extraction of mafic magmas but, allowing for this, continental tholeiites appear to have changed little with time. Ancient mid-ocean ridge basalts are elusive because of their poor preservation record. The geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present-day arc systems. The relative abundance of early Precambrian intrusive mafic suites parallels the crustal growth curve, reflecting the global crustal accretion–differentiation superevent towards the close of the Archaean. Bimodal tholeiitic–noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle–mafic crust–continental crust system. This, in turn, gives a possible link between the respective evolutions of Archaean to Recent komatiitic, noritic and boninitic suites.

The Talkative Chair: A Child's Experience of Sexual Abuse Intervention

As part of a special issue of J.S.T. on “Client Voices,” the paper presents an edited transcript of an interview where two clients explain their ideas about their therapy experience to their therapist. The presenting issue was the concern of a mother that her daughter was experiencing aftereffects of childhood sexual abuse. The daughter was concerned that her privacy be respected. The girl had previously experienced an extremely intrusive form of interrogation to determine the veracity of her accusation against her stepbrother. The paper describes the therapy and presents the new understandings that the therapists developed by listening to the clients talk about their experience of therapy.