scholarly journals Small-scale permeability heterogeneity has negligible effects on nutrient cycling in streambeds

2013 ◽  
Vol 40 (6) ◽  
pp. 1118-1122 ◽  
Author(s):  
L. Bardini ◽  
F. Boano ◽  
M.B. Cardenas ◽  
A.H. Sawyer ◽  
R. Revelli ◽  
...  
Keyword(s):  
Nutrient Cycling ◽  
Small Scale ◽  
Permeability Heterogeneity

RELATING SMALL-SCALE PERMEABILITY HETEROGENEITY TO LITHOFACIES DISTRIBUTION

2004 ◽  
pp. 55-66 ◽  
Author(s):  
MICHAEL N. GAUD ◽  
GARY A. SMITH ◽  
SEAN A. MCKENNA
Keyword(s):  
Small Scale ◽  
Permeability Heterogeneity

scholarly journals Influence of small-scale patchiness on resilience of nutrient cycling to extended hypoxia in estuarine sediments

2012 ◽  
Vol 453 ◽  
pp. 49-62 ◽  
Author(s):  
JL Banks ◽  
DJ Ross ◽  
MJ Keough ◽  
CK Macleod ◽  
BD Eyre
Keyword(s):  
Nutrient Cycling ◽  
Estuarine Sediments ◽  
Small Scale

scholarly journals Decomposition and stabilization of the organic matter in an old-growth tropical riparian forest: effects of soil properties and vegetation structure

2020 ◽  
Author(s):  
Pedro Fernandes ◽  
Andrea Teixeira Souza ◽  
Marcel Tanaka ◽  
Renata Sebastiani
Keyword(s):  
Organic Matter ◽  
Nutrient Cycling ◽  
Soil Properties ◽  
Forest Structure ◽  
Riparian Forest ◽  
Clay Content ◽  
Small Scale ◽  
Decomposition Rates ◽  
Old Growth ◽  
Decomposition Processes

Abstract Background: Nutrient cycling in tropical forests has large importance for primary productivity, and decomposition of litterfall is a major process influencing nutrient balance in forest soils. Although large-scale factors strongly influence decomposition patterns, small-scale factors can have major influences, especially in old-growth forests that have high structural complexity and strong plant-soil correlations. Methods: We evaluated decomposition rates and stabilization of soil organic matter using the Tea Bag Index in an old-growth riparian forest in southeastern Brazil. We buried 50 pairs of green and red tea at two distances from the watercourse to evaluate the effects of forest structure and soil properties on decomposition processes. Forest structure and soil properties were described using Principal Components Analysis (PCA). The main axes for each analysis were considered predictors of decomposition processes using a structural equations model.Results: Decomposition rates presented a large variation among tea bags and were positively correlated with forest structure, as characterized by higher basal area, larger trees, and tree density. Higher decomposition rates were probably correlated with higher litter production and microbial activity. On the other hand, stabilization factor was related mainly to soil chemical properties, with higher values with increased soil fertility as indicated by the PCA axes. Further analyses evaluated the effects of clay content, soil moisture, soil organic matter, soil base saturation, and soil fertility as predictors of the stabilization factor. These predictors were highly correlated, but clay content was the best predictor, explaining 79% of the variation among plots. Conclusions: These results showed that this old-growth forest presented high heterogeneity in both forest structure and soil properties at small spatial scales, that influenced decomposition processes and contributed to small-scale variation in nutrient cycling. Heterogeneity in ecological processes can contribute to the resilience of old-growth forests, strengthening ecosystem functions such as nutrient cycling and carbon fixation, and highlighting the importance of restoration strategies focused in the recovery of ecosystem processes

The Small-Drillhole Minipermeameter Probe for In-Situ Permeability Measurement

2005 ◽  
Vol 8 (06) ◽  
pp. 491-501 ◽  
Author(s):  
Cynthia L. Dinwiddie
Keyword(s):  
Gas Flow ◽  
Small Scale ◽  
Laboratory Setting ◽  
Permeability Measurement ◽  
Analytical Technique ◽  
Size And Shape ◽  
Permeability Heterogeneity ◽  
Surface Sealing ◽  
Flow Through

Summary Laboratory measurement of permeability using a Hassler cell is the industry standard; however, consistently removing undisturbed rock samples from friableout crops is difficult. Although various conventional surface-sealing mini-permeameters are developed as an alternative for permeability measurement, these devices generally suffer from difficulties in maintaining optimal forces on the tip seal when dealing with outcrop irregularities in the field; outcrop weathering is also problematic. Because a reliable field method is needed for studies of friable geological units, this paper presents an innovative technique for measuring permeability in situ. The design of the small-drill hole minipermeameter probe is discussed, as well as the accompanying analytical technique and the size and shape of the instrument's averaging volume. Small-diameter holes [i.e., 1.8 cm (0.7 in.)] are drilled into an outcrop with a masonry drill, followed by drillhole vacuuming, probe insertion, sealexpansion, gas injection, and calculation of the intrinsic permeability through measurement of the injection pressure, gas-flow rate, and knowledge of the system geometry. Advantages of this approach include access to a nonweathered surface, an operator-independent sealing mechanism around the air-injection zone, and the potential for permeability measurement at multiple depths below an outcrop surface. To date, data have been collected from four diverse porousmedia: upper and lower shoreface sandstone (Escalante, Utah), saprolitic soils(Clemson, South Carolina), nonwelded and sintered ignimbrite (Bishop, California), and fluvially reworked tuffaceous sedimentary rock (Bishop, California). The probe has proved durable and robust, with a single probe sufficient for making thousands of measurements in a variety of environments. Data quality supports the conclusion that the drillhole probe is a practical field instrument. Introduction Small-scale permeability heterogeneity plays a substantial role in petroleum migration and reservoir performance; this parameter commonly ranges over many orders of magnitude (e.g., 0.01 to more than 10,000 md). Permeability heterogeneities on the meter-to-micrometer scale associated with beds, laminae, internal sedimentary structures, and variations in pore morphology are the source of most retrieval difficulties during enhanced-oil-recovery operations, thus negatively affecting reservoir recovery efficiency. Considerable heterogeneity is evident when permeability measurements are made on small scales, either in the field or on field samples in a laboratory setting. Traditionally, small-scale permeability measurements are made by inducing 1D gas flow through a cylindrical core plug in a Hassler sleeve or cell. Recently, such measurements also are made by inducing multidimensional gas flow through a sample with various configurations of the conventional surface-sealing gas minipermeameter. Cylindrical plugs generally are extracted from continuous core at 30-cmintervals for Hassler-cell permeability measurement, preserving a majority of the core while minimizing associated costs. Except for relatively homogeneous formations, this scale of permeability measurement is in an ill-defined geologic region, falling within the range of laminae and lamina sets. Furthermore, core-plug samples tend to be biased toward the more consolidated, less permeable, and less friable core sections. As an example, the effect of this arbitrary sampling density on Hassler-sleeve measurements for the case of tight gas sands is that magnitudes of permeability less than 100 md frequently result, even when coarser-grained beds that would operate as preferential flow channels or "thief zones" are clearly present. Currently, the scale of sedimentary heterogeneity is best resolved by use of the minipermeameter, which allows investigation of permeability heterogeneity at much greater (and statistically significant) sampling densities and on much smaller scales than is possible with the traditional technique. The literature documents use of the conventional surface-sealing minipermeameter probe for measurements made on outcrop surfaces, core plugs, slabbed cores, or large-cut blocks. One motivation for using cores, plugs, or blocks of rock is that natural weathering processes may greatly affect permeability values obtained from exposed outcrop surfaces. The weathering effect has been shown to extend up to several inches below the rock surface. Beyond the issue of weathering, there are other rationales for discouraging use of the conventional surface-sealing minipermeameter probe in a field setting. When applying this probe geometry to natural rock outcroppings in the field, as opposed to cut specimens in an automated laboratory setting, seal-quality problems are often encountered because of irregular, rough surfaces and difficulties associated with manually holding the probe stationary while applying a uniform normal force of the optimal magnitude on the tip seal. To enable in-situ measurements of friable geologic units and to overcome weathering and seal-quality problems, a new minipermeameter probe has been developed that is specifically intended for application inside a small drilled hole. The design of the small-drillhole minipermeameter probe is discussed in what follows, as well as the accompanying analytical technique and the size and shape of the instrument's averaging volume. This article concludes with brief reviews of data collected using the technique.

Reasons to strike first

2019 ◽  
Vol 42 ◽  
Author(s):  
William Buckner ◽  
Luke Glowacki
Keyword(s):  
Intergroup Conflict ◽  
Small Scale

Abstract De Dreu and Gross predict that attackers will have more difficulty winning conflicts than defenders. As their analysis is presumed to capture the dynamics of decentralized conflict, we consider how their framework compares with ethnographic evidence from small-scale societies, as well as chimpanzee patterns of intergroup conflict. In these contexts, attackers have significantly more success in conflict than predicted by De Dreu and Gross's model. We discuss the possible reasons for this disparity.

Exploring Coronal Structures with SOHO

2000 ◽  
Vol 179 ◽  
pp. 403-406
Author(s):  
M. Karovska ◽  
B. Wood ◽  
J. Chen ◽  
J. Cook ◽  
R. Howard
Keyword(s):  
Solar Corona ◽  
Image Enhancement ◽  
Coronal Mass Ejections ◽  
Dynamical Evolution ◽  
Small Scale ◽  
Low Contrast ◽  
Contrast Structures ◽  
Scale Structures ◽  
Small Scale Structures ◽  
Coronal Structures

AbstractWe applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board SOHO: LASCO and EIT.

Scanning tunneling microscopy and atomic force microscopy: New tools for biology

1989 ◽  
Vol 47 ◽  
pp. 778-779
Author(s):  
CE Bracker ◽  
P. K. Hansma
Keyword(s):  
Physical Property ◽  
Scanning Probe ◽  
Scanning Tunneling ◽  
Small Scale ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
New Family ◽  
Small Probe ◽  
Atomic Force ◽  
Transmission Electron

A new family of scanning probe microscopes has emerged that is opening new horizons for investigating the fine structure of matter. The earliest and best known of these instruments is the scanning tunneling microscope (STM). First published in 1982, the STM earned the 1986 Nobel Prize in Physics for two of its inventors, G. Binnig and H. Rohrer. They shared the prize with E. Ruska for his work that had led to the development of the transmission electron microscope half a century earlier. It seems appropriate that the award embodied this particular blend of the old and the new because it demonstrated to the world a long overdue respect for the enormous contributions electron microscopy has made to the understanding of matter, and at the same time it signalled the dawn of a new age in microscopy. What we are seeing is a revolution in microscopy and a redefinition of the concept of a microscope.Several kinds of scanning probe microscopes now exist, and the number is increasing. What they share in common is a small probe that is scanned over the surface of a specimen and measures a physical property on a very small scale, at or near the surface. Scanning probes can measure temperature, magnetic fields, tunneling currents, voltage, force, and ion currents, among others.

Superstructures and ordering phenomena in ceramic superconductors

1996 ◽  
Vol 54 ◽  
pp. 710-711
Author(s):  
R. Gronsky
Keyword(s):  
Domain Growth ◽  
Small Displacement ◽  
Small Scale ◽  
Ceramic Superconductors ◽  
Oxygen Sublattices ◽  
Tweed Contrast ◽  
Diffraction Patterns ◽  
Representative Image ◽  
Static Lattice ◽  
Modulation Wavelength

It is now well established that the phase transformation behavior of YBa2Cu3O6+δ is significantly influenced by matrix strain effects, as evidenced by the formation of accommodation twins, the occurrence of diffuse scattering in diffraction patterns, the appearance of tweed contrast in electron micrographs, and the generation of displacive modulation superstructures, all of which have been successfully modeled via simple Monte Carlo simulations. The model is based upon a static lattice formulation with two types of excitations, one of which is a change in oxygen occupancy, and the other a small displacement of both the copper and oxygen sublattices. Results of these simulations show that a displacive superstructure forms very rapidly in a morphology of finely textured domains, followed by domain growth and a more sharply defined modulation wavelength, ultimately evolving into a strong <110> tweed with 5 nm to 7 nm period. What is new about these findings is the revelation that both the small-scale deformation superstructures and coarser tweed morphologies can result from displacive modulations in ordered YBa2Cu3O6+δ and need not be restricted to domain coarsening of the disordered phase. Figures 1 and 2 show a representative image and diffraction pattern for fully-ordered (δ = 1) YBa2Cu3O6+δ associated with a long-period <110> modulation.

Indirect Assessment of Attitudes with Response-Time-Based Measures

2006 ◽  
Vol 37 (3) ◽  
pp. 131-139 ◽  
Author(s):  
Juliane Degner ◽  
Dirk Wentura ◽  
Klaus Rothermund
Keyword(s):  
Social Cognitive ◽  
Incremental Validity ◽  
Self Report ◽  
Small Scale ◽  
Implicit Measures ◽  
Scale Theory ◽  
Starting Point ◽  
Self Reports ◽  
Predicting Behavior ◽  
Social Cognitive Theories

Abstract: We review research on response-latency based (“implicit”) measures of attitudes by examining what hopes and intentions researchers have associated with their usage. We identified the hopes of (1) gaining better measures of interindividual differences in attitudes as compared to self-report measures (quality hope); (2) better predicting behavior, or predicting other behaviors, as compared to self-reports (incremental validity hope); (3) linking social-cognitive theories more adequately to empirical research (theory-link hope). We argue that the third hope should be the starting point for using these measures. Any attempt to improve these measures should include the search for a small-scale theory that adequately explains the basic effects found with such a measure. To date, small-scale theories for different measures are not equally well developed.

Small-Scale Science to Large-Scale Profession

2000 ◽  
Vol 45 (4) ◽  
pp. 396-398
Author(s):  
Roger Smith
Keyword(s):  
Large Scale ◽  
Small Scale
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