Cascade Zone Research Articles

Static connectivity of fluvial reservoirs and their temporal evolution: An example from densely drilled subsurface data in the Sanzhao Sag, Songliao Basin

Research on the static connectivity of reservoirs is of great significance for predicting the lateral continuity of sandstone bodies and determining the field development strategy. The main impacts of static connectivity are geometry, stacking pattern and distribution of fluvial sandstone bodies, which are controlled by changes in base level. This study addresses the static connectivity of fluvial sandstones of the Yangdachegnzy reservoir in the Yushulin oilfield with a dense network of wells. The Yangdachengzy reservoir develops a long-term depositional cycle (a third-level sequence) consisting of 3 mid-term depositional cycles (MDC1-MDC3) and 21 short-term depositional cycles (SDC1-21). Sedimentary facies maps of each stratigraphic intervals in the Yangdachengzy reservoir that are constrained to high well density from the Yushulin Oilfield exhibit: (i) as base-level falls, the planform style of sandstone bodies changes from isolated type to amalgamated type; (ii) how static connectivity evolves through base-level fluctuations and show how static connectivity is sensitive to the net-to-gross ratio and well spacing. The analyses show that the relationship between the net-to-gross ratio and static connectivity exhibits a sigmoid curve. Such a curve is sensitive to the well spacing and the planform style of sandstone bodies. When well spacing increases, the S-curve shifts to the right, with a narrow “cascade zone” and a relatively higher percolation threshold of net-to-gross ratio (e.g., 0.2 at 150 m well spacing). When well spacing decreases, the S-curve tends to be linear, with a large range of “cascade zones” and a relatively lower percolation threshold of the net-to-gross ratio (e.g., 0.43 at 450 m well spacing). At a given net-to-gross ratio, amalgamated-type sandstone bodies that developed at the lowest base-level stage are very prone to reach the fully connected status (reservoir connected over 0.8) with a relatively low well density.

Glassy and ballistic dynamics in collision cascades in amorphous TiO2 : Combined molecular dynamics and Monte Carlo based studies across energy scales

Kinetics in amorphous $\mathrm{Ti}{\mathrm{O}}_{2}$ driven by ion irradiation are discussed in the framework computer simulations. Thermal spike like regions along the path of incident ions are identified and their effects on the glassy system are described. Benefiting from the complementary approaches of purely ballistic TRIM (transport in matter) simulations and molecular dynamics simulations, a distinction between characteristic scales for short-range diffusive relocations ($\ensuremath{\lesssim}4.5\phantom{\rule{0.28em}{0ex}}\text{\AA{}}$) and long-range ballistic relocations is achieved. It is found that diffusion dynamics within thermally activated cascade zones sets in at the critical temperature ${T}_{c}$, identified as the critical temperature of the mode coupling theory, while the mean relocation limit for thermal diffusion in the glassy system is attributed to an overlap between the energy regime of purely ballistic and thermally activated relocation processes.

A Survey of the Analytical Methods of Proton-NIEL Calculations in Silicon and Germanium

The nonionizing energy loss (NIEL) concept has been used for many years for qualitative estimation of the damage induced by radiation (particles and gamma rays). Different approaches, based on the physics of radiation interaction with the nuclear and electronic subsystems of the target atoms, are used for calculating NIEL values. The simplest model used is the binary collision approximation (BCA), which is applicable for energies larger than the threshold energy for Frenkel pair creation. In this article, we analyze the dependence of the calculated NIEL values (in silicon and germanium) on the basic interaction characteristics: the differential cross section (DCS) of energy transferred to the recoiling atoms and the partition factor between ionization and ion displacement. We estimate the differences between existing approaches and the possible scatter of the NIEL data for Coulomb, elastic, and inelastic nuclear scatterings. We also present new partition factors based on fits to experimental data. The contribution of low-energy cascade zones of displaced atoms (pockets) to the total damage is estimated using results of molecular dynamics (MD) calculation. We find for silicon a total increase of NIEL by 30%–40% relative to the original (BCA) NIEL value. The role of phonon excitations in the subthreshold cascades on the damage value is discussed.

Time Since Contact and Gene Flow May Explain Variation in Hybrid Frequencies Among Three Dendroica Townsendi × D. Occidentalis (Parulidae) Hybrid Zones

AbstractHermit Warblers (Dendroica occidentalis) and Townsend’s Warblers (D. townsendi) meet and hybridize in three replicate zones in Washington and Oregon. Using male specimens, we show that the ratio of hybrid to parental phenotypes varies systematically across these three zones: there were 60.4% hybrids among 96 males from the Olympic zone, 43.3% hybrids among 411 males from the Washington Cascade zone, and 27.8% hybrids among 209 males from the Oregon Cascade zone. We found no evidence of habitat or climatic factors driving these systematic differences in hybrid frequencies, and we argue that they are related to differences among these zones in the immigration of pure parentals and time since contact. Building on earlier hypotheses about massive movement of the coastal zones (Rohwer and Wood 1998), we can infer that the Olympic and Washington Cascade zones are old and of similar age. The Washington Cascade zone, but not the Olympic zone, receives Townsend’s immigrants from the Rocky Mountains through the Okanogan high- lands, as shown by the linkage analyses in Rohwer et al. (2001). This immigration apparently accounts for the lower frequency of hybrids in the Washington Cascades. The Washington Cascade and Oregon Cascade zones are both situated adjacent to forest corridors that connect them to the Rocky Mountains to the east, so both of these zones should receive Townsend’s immigrants from the east (linkage analyses have yet to be done for the Oregon Cascades because the mitochondrial DNA haplo- types for these specimens have not been determined). The Washington Cascade zone, however, is old, whereas the Oregon Cascade zone appears to have been established only recently in response to anthropogenic habitat changes, which accounts for its low frequency of hybrids. We are unaware of any other replicate set of hybrid zones where differences in time since contact and dispersal have been related to variation in hybrid frequencies.El Tiempo Transcurrido desde el Contacto y el Flujo Genético Podrían Explicar la Variación en la Frecuencia de los Híbridos entre Tres Zonas de Hibridación entre Dendroica townsendi y D. occidentalis (Parulidae)

The differentially rotating force-free magnetosphere of an aligned rotator: analytical solutions in the split-monopole approximation

In this paper we consider the stationary force-free magnetosphere of an aligned rotator when the plasma in the open field-line region rotates differentially as a result of the presence of a zone with an accelerating electric field in the polar cap of the pulsar. We study the impact of differential rotation on the current density distribution in the magnetosphere. Using the split-monopole approximation we obtain analytical expressions for the physical parameters of the differentially rotating magnetosphere. We find the range of admitted current density distributions under the requirement that the potential drop in the polar cap is less than the vacuum potential drop. We show that the current density distribution could deviate significantly from the ‘classical’ Michel distribution and could be made almost constant over the polar cap, even when the potential drop in the accelerating zone is of the order of 10 per cent of the vacuum potential drop. We argue that the differential rotation of the open magnetic field lines could play an important role in adjusting the current density between the magnetosphere and the polar-cap cascade zone and could affect the value of the pulsar braking index.

TIME SINCE CONTACT AND GENE FLOW MAY EXPLAIN VARIATION IN HYBRID FREQUENCIES AMONG THREE DENDROICA TOWNSENDI × D. OCCIDENTALIS (PARULIDAE) HYBRID ZONES

Hermit Warblers (Dendroica occidentalis) and Townsend’s Warblers (D. townsendi) meet and hybridize in three replicate zones in Washington and Oregon. Using male specimens, we show that the ratio of hybrid to parental phenotypes varies systematically across these three zones: there were 60.4% hybrids among 96 males from the Olympic zone, 43.3% hybrids among 411 males from the Washington Cascade zone, and 27.8% hybrids among 209 males from the Oregon Cascade zone. We found no evidence of habitat or climatic factors driving these systematic differences in hybrid frequencies, and we argue that they are related to differences among these zones in the immigration of pure parentals and time since contact. Building on earlier hypotheses about massive movement of the coastal zones (Rohwer and Wood 1998), we can infer that the Olympic and Washington Cascade zones are old and of similar age. The Washington Cascade zone, but not the Olympic zone, receives Townsend’s immigrants from the Rocky Mountains through the Okanogan high- lands, as shown by the linkage analyses in Rohwer et al. (2001). This immigration apparently accounts for the lower frequency of hybrids in the Washington Cascades. The Washington Cascade and Oregon Cascade zones are both situated adjacent to forest corridors that connect them to the Rocky Mountains to the east, so both of these zones should receive Townsend’s immigrants from the east (linkage analyses have yet to be done for the Oregon Cascades because the mitochondrial DNA haplo- types for these specimens have not been determined). The Washington Cascade zone, however, is old, whereas the Oregon Cascade zone appears to have been established only recently in response to anthropogenic habitat changes, which accounts for its low frequency of hybrids. We are unaware of any other replicate set of hybrid zones where differences in time since contact and dispersal have been related to variation in hybrid frequencies. El Tiempo Transcurrido desde el Contacto y el Flujo Genético Podrían Explicar la Variación en la Frecuencia de los Híbridos entre Tres Zonas de Hibridación entre Dendroica townsendi y D. occidentalis (Parulidae)

Connectivity of channelized reservoirs: a modelling approach

Connectivity represents one of the fundamental properties of a reservoir that directly affects recovery. If a portion of the reservoir is not connected to a well, it cannot be drained. Geobody or sandbody connectivity is defined as the percentage of the reservoir that is connected, and reservoir connectivity is defined as the percentage of the reservoir that is connected to wells. Previous studies have mostly considered mathematical, physical and engineering aspects of connectivity. In the current study, the stratigraphy of connectivity is characterized using simple, 3D geostatistical models. Based on these modelling studies, stratigraphic connectivity is good, usually greater than 90%, if the net: gross ratio, or sand fraction, is greater than about 30%. At net: gross values less than 30%, there is a rapid diminishment of connectivity as a function of net: gross. This behaviour between net: gross and connectivity defines a characteristic ‘S-curve’, in which the connectivity is high for net: gross values above 30%, then diminishes rapidly and approaches 0. Well configuration factors that can influence reservoir connectivity are well density, well orientation (vertical or horizontal; horizontal parallel to channels or perpendicular) and length of completion zones. Reservoir connectivity as a function of net: gross can be improved by several factors: presence of overbank sandy facies, deposition of channels in a channel belt, deposition of channels with high width/thickness ratios, and deposition of channels during variable floodplain aggradation rates. Connectivity can be reduced substantially in two-dimensional reservoirs, in map view or in cross-section, by volume support effects and by stratigraphic heterogeneities. It is well known that in two dimensions, the cascade zone for the ‘S-curve’ of net: gross plotted against connectivity occurs at about 60% net: gross. Generalizing this knowledge, any time that a reservoir can be regarded as ‘two-dimensional’, connectivity should follow the 2D ‘S-curve’. For channelized reservoirs in map view, this occurs with straight, parallel channels. This 2D effect can also occur in layered reservoirs, where thin channelized sheets are separated vertically by sealing mudstone horizons. Evidence of transitional 2D to 3D behaviour is presented in this study. As the gross rock volume of a reservoir is reduced (for example, by fault compartmentalization) relative to the size of the depositional element (for example, the channel body), there are fewer potential connecting pathways. Lack of support volume creates additional uncertainty in connectivity and may substantially reduce connectivity. Connectivity can also be reduced by continuous mudstone drapes along the base of channel surfaces, by mudstone beds that are continuous within channel deposits, or muddy inclined heterolithic stratification. Finally, connectivity can be reduced by ‘compensational’ stacking of channel deposits, in which channels avoid amalgamating with other channel deposits. Other factors have been studied to address impact on connectivity, including modelling program type, presence of shale-filled channels and nested hierarchical modelling. Most of the stratigraphic factors that affect reservoir connectivity can be addressed by careful geological studies of available core, well log and seismic data. Remaining uncertainty can be addressed by constructing 3D geological models.

Genetic Structure of Chum Salmon (Oncorhynchus keta) Populations in the Lower Columbia River: Are Chum Salmon in Cascade Tributaries Remnant Populations?

The lower Columbia River drainage once supported a run of over a million chum salmon. By the late 1950s, the run had decreased to often a few hundred fish. With the exception of Grays River near the coast and an aggregation of chum salmon spawning in creeks and the main stem near Bonneville Dam in the Columbia Gorge, most populations were thought to be extinct. However, chum salmon consistently return in low numbers to tributaries originating in the Cascade Range: the Cowlitz, Lewis, and Washougal rivers. To assess whether Cascade spawners were strays or remnants of former populations, chum salmon from the Coastal, Cascade and Gorge ecoregional zones were characterized at 17 microsatellite loci. Significant heterogeneity in genotype distributions was detected between zones and collections formed regional groups in a neighbor-joining tree. Cascade collections had higher allelic richness and private alleles, and the Cowlitz River supported genetically divergent fall and summer runs, the only summer chum salmon run extant in the Columbia River drainage. We propose that chum salmon in the Cascade zone are remnants of original populations. We attribute the divergence between zonal groups to diverse ecological conditions in each zone, which promoted regional genetic adaptation, and to genetic drift experienced in small populations.

Reallocation of impurity atoms in a supersaturated solid solution by thermodiffusion in collision cascades

We consider a weak supersaturated binary solid solution under continuous irradiation. Irradiation produces collision cascades in the media. Local energy deposition within a cascade zone, as is known, causes relaxation of the excess temperature to an ambient level. A simple model, that is taking into account the effect of temperature relaxation to a clustering formation of alloying atoms, is presented. The model is based on general principles of irreversible non-equilibrium thermodynamics. It is shown that the relaxation and thermodiffusion processes in supersaturated alloys may result in spatial redistribution of solute atoms in the media.

Mechanism of surface influence on dislocation loop yield in copper andCu3Au

A recently developed hybrid binary-collision/continuum model [V. G. Kapinos and D. J. Bacon, Phys. Rev. B 52, 4029 (1995)] of temperature and defect evolution in displacement cascades has been used to investigate the influence of a nearby surface on vacancy defect formation in cascade events. The shape, vacancy, and thermal conditions in cascade zones that melt and intersect the surface during the thermal spike phase have been analyzed. Simplified geometries of such zones have been simulated by molecular dynamics on the basis of these data and the mechanisms of vacancy generation in the melt zone analyzed. It has been demonstrated that additional vacancies are formed in the resolidified zone under the surface through a combination of thermal sputtering and viscous flow of atoms from the cascade core. Quantitative relationships between the geometry and size of the melt zone and number of additional vacancies have been considered, and used in the hybrid model to calculate the depth, yield, and size distribution of vacancy dislocation loops in Cu and ${\mathrm{Cu}}_{3}\mathrm{Au}$ irradiated with 50-keV ${\mathrm{Ni}}^{+}$ ions. The results are in good agreement with experimental data obtained by transmission electron microscopy of ion-irradiated thin foils.

Nucleation and growth of dislocation loops in austenitic stainless steels irradiated by fission and fusion neutrons

Nucleation and growth of interstitial type dislocation loops were investigated by fusion and fission neutron irradiations with improved temperature control. The density of loops formed by both irradiations increased linearly with fluence. The average size of loops also increased. It was concluded that the loops were nucleated directly by the defect processes in the cascade zone, and not by the reaction among the freely migrating point defects in the matrix. If the efficiency of loop formation is assumed to be directly proportional to the energy of the primary knock-on atom (PKA) produced by the neutron, the threshold energy of 20 keV and the efficiency of loop formation of 0.4% at this energy were obtained.

Primary knock-on atom energy dependence of cascade damage formation and interaction

Defect production and microstructural evolution in fusion materials should be evaluated based on the primary knock-on atom (PKA) energy spectrum. In this study, formation and interaction of cascade damage are evaluated as a function of PKA energy from irradiation experiments on thin foils of gold irradiated with fission neutrons and 21 MeV self-ions. These results are compared with fusion neutron irradiation data. The interaction of cascades at higher dose is found to result in the appearance of new clusters near the existing groups of vacancy clusters. These are considered to come from the conversion of invisible vacancy rich regions to visible clusters by near-by cascades. The minimum PKA energy to produce new visible clusters by interaction is estimated to be 165 keV, assuming that cascade zone size increases with damage energy.

Family variation for fall cold hardiness in two Washington populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)

In order to assess the genetics of fall cold hardiness in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco), shoot cuttings were collected in October from saplings (9-year-old trees) of open-pollinated families in two progeny tests in each of two breeding zones in Washington, one in the Coast range (80 families) and one on the west slope of the Cascade Mountains (89 families). Samples from over 5500 trees were subjected to artificial freezing and visually evaluated for needle, stem and bud tissue injury. The extent to which cold injury is genetically related to tree height and shoot phenology (timing of bud burst and bud set) was also evaluated.Significant family variation was found for all cold hardiness traits; however, individual heritability estimates were relatively low (ranging from 0.09 to 0.22). Significant family-by-test site interaction was detected for needle injury in the Cascade breeding zone, but not in the coastal zone. Genetic correlations (rA) among needle, stem and bud tissues for cold damage were weak (0.16 ≤ rA ≤ 0.58) indicating that genes controlling fall hardening are somewhat different for different tissues. Timing of bud burst and bud set were only weakly correlated with cold injury (rA ≤ 0.49). Thus, bud phenology is a poor predictor of fall cold hardiness in this species. There was no consistent relationship between tree height and cold injury in the coastal zone. In the Cascade zone, taller trees appeared to be more susceptible to cold injury, but the association was weak (mean rA = 0.38, range 0.20–0.72).

Effect of temperature on the bulk atomic relocation in low-energy collision cascades in silicon: A molecular dynamics study

Abstract The production of damage in a Si lattice by internally starting 100 eV self-recoils has been studied using a MD simulation. Different initial lattice temperatures below the Debye temperature for Si have been considered. The number of stable atomic displacements and the amount of atomic mixing increase with the initial target temperature. The increase with temperature of atomic mixing is nonlinear -appreciable changes take place between 300 and 500 K, while the difference between the amount of mixing corresponding to 0 and 300 K is negligibly small. The size of the cascade zone in which stable atomic displacements occur doubles itself for temperature changes between 0 and 300 K, with a value for 500 K lying in between. This nonmonotonic variation with the initial target temperature of the size of the cascade zone may have its origin in the correlation between the initial direction of motion of the starting recoil and the directions of thermal velocities of the neighbouring atoms around this recoil.

Formation of vacancy clustered defects from cascade collisions during heavy-ion irradiation and their annihilation by freely-migrating interstitial atoms

Heavy-ion irradiation of several fcc metals and their ordered alloys was performed. The behavior of ion-irradiation induced point defect clusters during subsequent electron irradiation indicates that about 90% of the clusters are of vacancy type and 10% of interstitials. For any given ion and energy, a wide variation of the collision cascade zone size was found. In general, the larger zones were associated with a larger number of point-defect clusters. A collision zone of a given size was associated with the same average number of clusters even when they were produced by ions of different energy. The dependence of cluster formation on ion energy, target material, and angle of incidence of the ion beam can be correlated with a unique parameter, the depth in the foil of defect cluster formation. The defect yield increases linearly with irradiation dose for shallow depth distributions but then increases with a square-root relationship for deeper distributions. These results are analyzed in terms of a variation in the role of freely-migrating interstitials for the two cases.

Thermalization of sparse collision cascades in metals: simultaneous relaxation of nonequilibrium electron and ion distributions

Thermalization of ion bombardment induced large and sparse cascades in metals is studied. We introduce a model where nonequilibrium electron and ion distributions relax simultaneously, and coupling between the thermal ions and valence electrons allows heat exchange between electronic and ionic systems. This model takes into account the competing time scales of the relaxation processes and the heat outdiffusion from the cascade zone. Nearly free conduction electron bands are assumed, which restricts the applicability of the model to simple metals only. It is shown that in cascades with an extent of about 10 nm or more, a considerable part of the energy, residing initially in the electronic system, may reappear in the ionic system in the cascade zone. Ions in cascades with radius larger than 20 nm take up nearly all of the energy available in the cascade zone. Due to this energy transfer, the ionic system may experience appreciable additional heating in large cascades.

Correlation of vacancies in α-iron and copper after low temperature neutron irradiation observed by small-angle scattering of synchrotron radiation

Abstract The correlation of vacancies in Fe and Cu, irradiated with fast neutrons at low temperature, was examined by small-angle scattering (SAS) of synchrotron radiation. The scattering curves were analysed in terms of a distribution of depleted zones (DZ) according to the appropriate recoil spectrum. After irradiation and annealing at 90 K single vacancies and small agglomerates were found in Fe. 70% of them were correlated in DZ with an average radius of 12.6 A and a mean vacancy concentration of 1.1%. In Cu we observed larger agglomerates— = 11–15 vacancies—in DZ with an average radius of 8.2 A and a mean vacancy concentration of 5.2%. A strong scattering signal at very low scattering angles is attributed to correlations between the individual cascade zones. During recovery we observed agglomeration of the vacancies in both metals. While in Cu the correlation between individual DZ survived annealing at 430 K, the correlation vanished in Fe samples during annealing in stage III. A computer code wa...

A molecular dynamics study of displacement cascades in α-iron

The mechanisms of defect production in displacement cascades in α-iron have been investigated by computer simulation. Cascades of up to 5 keV in energy have been simulated by molecular dynamics in crystals with atomic interactions described by a many-body potential. The effects of lattice temperature have been studied by using block temperatures of either 100 or 600 K. 80 cascades have been modelled overall. The morphology of cascades during the collisional phase changes at about 1–2 keV, due to the collective nature of atomic displacements at higher energy. This transition is reflected in the relaxation time during the subsequent recombination phase, and it also decreases the efficiency factor for defect production. This factor is similar in size to that obtained from recent modelling of copper, an fcc metal. Although the cascade zone contains a large number of displaced atoms, true melting was not observed in α-Fe, and vacancy clustering did not occur in the thermal spike phase. Interstitial clustering has been analysed, and found to be less pronounced than in copper. One large cluster was observed to grow by interstitial movement during the thermal spike, and visual analysis has shown that it formed a perfect dislocation loop: it was not nucleated by the Eyre-Bullough mechanism, however. Statistics on the cascade parameters are presented, and comparisons with work on other crystal structures are drawn where possible.

Binary collision calculation of subcascade structure and its correspondence to observed subcascade defects in 14 MeV neutron irradiated copper

A model calculation of subcascade structure in copper, based on the binary collision approximation using MARLOWE code, is made. The primary recoil energy spectrum by 14 MeV neutron irradiation and the threshold type subcascade energy of 10 keV are employed. The calculated results of the number of subcascades and the distance between subcascades show good agreement to reported experimental analysis. Distribution of the calculated cascade zone size extends towards larger size much more than that experimentally obtained for thin foil irradiation. This difference is understood as the under estimation in experimental measurement owing to the limitation by the thickness of the microscopically observable specimen foil (< 100 nm). Distribution of subcascade structure produced by monochromatic primary recoil energy is examined by the same calculation model. Primary recoil energy dependence of subcascade structure is also examined. The usefulness and the limitation of the present model calculation is discussed.

Mössbauer spectroscopy of primary knocked-on atoms

In many cases behavior of irradiated alloys is determined by the formation and evolution of the primary damaged zones in the alloys. There are several mechanisms responsible for these processes. One of them is the atomic separation of the alloy species in the cascade zone which can be directly examined by Mossbauers spectroscopy of the primary knocked-on atoms. In this report we summarize some results of measurements on amorphous alloys and intermetallic compounds.