The rock breaking mechanism is significantly affected by the joints in the rock mass. With the purpose to study the influence of joint characteristic parameters on cutting force and penetration, ...experimental explorations that contain miniature cutter head with double cutters are conducted in this paper on the basis of Rolling Indentation Abrasion Test (RIAT). In the present research, prefabricated joints of different forms are made in the rock samples. The experimental conclusions indicate that the optimal angle between horizontal and joint plane is equal to 30° for rock breaking process. In detail, the minimum thrust and the maximum penetration, which are related to the rock chipping angle for different joint orientations, are obtained at the optimal angle. Meanwhile, the improved theoretical formulas which are suitable for both intact and jointed rock are proposed. Besides, the change of thrust with penetration can be divided into four stages, which are the loading, starting, boring and stripping stages. Through simulating the rock breaking process by the rock rolling boring experimental method, this study measures the thrust, torque, penetration on the disc cutter, and reveals the influences of joint orientation and spacing on cutting forces and penetration. Furthermore, the penetration variation is summarized and the results are in good agreement with the field observation and numerical simulation results.
The relationship between Mechanical Specific Energy (MSE) and the Rate of Penetration (ROP), or equivalently the depth of cut per revolution, provides an important measure for strategizing a drilling ...operation. This study explores how MSE evolves with depth of cut, and presents a concerted effort that encompasses analytical, computational and experimental approaches. A simple model for the relationship between MSE and cutting depth is first derived with consideration of the wear progression of a circular cutter. This is an extension of Detournay and Defourny's phenomenological cutting model. Wear is modeled as a flat contact area at the bottom of a cutter referred to as a wear flat, and that wear flat in the past is often considered to be fixed during cutting. But during a drilling operation by a full bit that consists of multiple circular cutters, the wear flat length may increase because of various wear mechanisms involved. The wear progression of cutters generally results in reduced efficiency with either increased MSE or decreased ROP. Also, an accurate estimate of removed rock volume is found important for the evaluation of MSE. The derived model is compared with experiment results from a single circular cutter, for cutting soft rock under ambient pressure with actual depth measured through a micrometer, and for cutting high strength rock under high pressure with actual cutting area measured by a confocal microscope. Finally, the model is employed to interpret the evolution of MSE with depth of cut for a full drilling bit under confining pressure. The general form of equation of the developed model is found to describe well the experiment data and can be applied to interpret the drilling data for a full bit.
Kerfing on the working face of tunnel boring machine (TBM) can reduce the integrity of intact rock mass, it's one of feasible methods to improve the TBM performance. When the TBM cutter cut along the ...midline of two kerfs, the chipping mechanism changed to the interaction between the cutter and adjacent kerfs, the lateral cracks generated from the cutter tip could propagate to the bottom of adjacent kerfs. To study the effects of kerf depth on the cracks pattern and the cutting performance of the TBM cutter, a series of full-scale linear rock cutting tests were conducted. In addition, conventional cutting tests without kerfs were also performed to make a comparison. The cutter force and rock muck were collected, and the rock samples were sectioned after the tests. The cracks patterns beneath the cutter tip were observed by fluorescent dye. The results show that the dip angle of the lateral cracks increase with the increasing kerf depth, the vertical cracks become shorter and less. Besides, the area of the crushed zone decreases. The required normal force and rolling force are much reduced even for the large cutter penetration compared with the conventional cutting. The cutter forces decrease, while the characteristic grain diameter and coarseness index of the rock muck increase with the increasing kerf depth. The specific energy of kerf-assisted cutting is lower than that of the conventional cutting, and it declines as the kerf depth increases. A critical kerf spacing to depth ratio is found to efficiently reduce the specific energy. The results are useful for the rational parameter design of the kerfing system installed on the new generation TBM. The kerf spacing could be enlarged to save energy if the kerfs are deeper than 12 mm. However, it's still a challenging task to create deep kerfs on site.
This study investigated the effects of clear‐cutting and the meteorological and physiological factors on forest evapotranspiration (ET), by using the water‐budget method in the Kamabuchi experimental ...watershed (KMB; 38° 56′ 21″ N, 140° 15′ 58″ E) in northern Japan. Meteorological and discharge data collected during no‐snow periods (from June to October) from 1939 were used to compare ET in three sub‐watersheds: No. 1, where the forest had been left undisturbed, and No. 2 and No. 3, where Cryptomeria japonica was planted after clear‐cutting. Paired watershed experiments revealed that clear‐cutting caused ET to decrease by approximately 100 mm yr−1, and this reduction continued for more than 20 years, even after C. japonica was planted. ET fluctuated similarly across all watersheds, regardless of clear‐cutting or planting. This fluctuation is mainly caused by solar radiation and temperature. Intrinsic water‐use efficiency (iWUE) calculated using δ13C of tree‐ring cellulose in C. japonica increased due to elevated atmospheric CO2 concentration. We estimated annual carbon fixation in a single tree as the annual net photosynthesis (A). Subsequently, transpiration (E) was calculated from the relationship between iWUE and A. The results showed that A and E per tree increased as the tree grew older; however, the trees' responses to increasing ca suppress the increase in ET. Moreover, the fluctuation of ET from the watershed was small compared to the fluctuation of P during the observation periods because the increase and decrease in E and interception loss complemented each other.
Clear‐cutting has had a large impact on evapotranspiration in forests. Inter‐annual fluctuation and long‐term trends in evapotranspiration are mainly caused by meteorological factors. CO2‐induced stomatal closure did not cause a basin‐wide reduction in transpiration but has suppressed the increase in evapotranspiration promoted by global warming.
Forest clearance is a pervasive disturbance worldwide, but many of its impacts are regarded as transient, diminishing in intensity as forest recovers. However, forests can take decades to centuries ...to recover after severe disturbances, and temporal lags in recovery of ecosystem properties for different forest habitats are mostly unknown. This includes forest streams, where most studies of the impacts of forest clearance are restricted to the first years of recovery, typically finding that temporary increases in light and nutrient run‐off diminish as forest recovers. Implications of longer term changes remain little investigated.
In a space‐for‐time substitution experiment, we assessed changes in organic matter processing and in the functional and taxonomic composition of litter‐consuming detritivores along a riparian forest age gradient ranging from 1 to 120 years since last timber harvesting.
Variation in organic matter processing and detritivore functional diversity along the forest succession gradient were both expressed as second‐order polynomial relationships (peaking at ~50 years along the forest age gradient). Decomposition rates were lowest in both the more recently clear‐cut and older riparian forest streams.
Variation of litter decomposition rates among litter bags within streams, measured by the coefficient of variation, was lowest in recent clear‐cuts and increased linearly along the succession gradient. This result indicates higher within‐stream heterogeneity in decomposition rates in older forest streams.
Synthesis and applications. We found that the decomposition of leaf litter, a component of carbon cycling in forests, was higher in streams flowing through intermediately aged forest, and that several key attributes of the organisms regulating litter decomposition also varied systematically with forest age. These findings highlight the longer term consequences of forest succession following forest clear‐cutting for stream habitats. Our findings further illustrate complications arising from the use of forested sites as references for newly cleared sites without properly accounting for forest age, given conclusions regarding biotic responses will depend on the age of the reference forests. Finally, our results emphasise the potential of intensive forest management centred on vast, one‐time clear‐cutting events to drive long‐term homogenisation not only in forest age structure but also in the functioning of associated forest stream habitats.
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We found that the decomposition of leaf litter, a component of carbon cycling in forests, was higher in streams flowing through intermediately aged forest, and that several key attributes of the organisms regulating litter decomposition also varied systematically with forest age. These findings highlight the longer term consequences of forest succession following forest clear‐cutting for stream habitats. Our findings further illustrate complications arising from the use of forested sites as references for newly cleared sites without properly accounting for forest age, given conclusions regarding biotic responses will depend on the age of the reference forests. Finally, our results emphasise the potential of intensive forest management centred on vast, one‐time clear‐cutting events to drive long‐term homogenisation not only in forest age structure but also in the functioning of associated forest stream habitats.
Abstract
We study the analytic properties of tree-level wavefunction coefficients in quasi-de Sitter space.
We focus on theories which spontaneously break dS boost symmetries and can produce ...significant non-Gaussianities.
The corresponding inflationary correlators are (approximately) scale invariant, but are not invariant under the full conformal group.
We derive cutting rules and dispersion formulas for the late-time wavefunction coefficients by using factorization and analyticity properties of the dS bulk-to-bulk propagator.
This gives a unitarity method which is valid at tree-level for general
n
-point functions and for fields of arbitrary mass.
Using the cutting rules and dispersion formulas, we are able to compute
n
-point functions by gluing together lower-point functions.
As an application, we study general four-point, scalar exchange diagrams in the EFT of inflation.
We show that exchange diagrams constructed from boost-breaking interactions can be written as a finite sum over residues.
Finally, we explain how the dS identities used in this work are related by analytic continuation to analogous identities in Anti-de Sitter space.
Questions
Sod cutting has been used extensively as an effective measure in removing excess N and restoring dwarf shrub dominance in heathlands affected by increased nitrogen deposition. However, ...recovery of other plant species is often very limited. One barrier is high soil acidity following sod cutting, which results in soil aluminium (Al3+) and ammonium (NH4+) reaching toxic concentrations. Sod‐cutting management also removes most of the major nutrients from the system, so intensified nutrient limitation could be an additional barrier to the recovery of species‐rich communities. Soil phosphorus (P) is of special interest as research indicates sod‐cutting management can shift the system to P limitation.
Location
Hoge Veluwe National Park, The Netherlands.
Methods
We set up a full‐factorial experiment in sod‐cut heathland formerly encroached by Molinia caerulea, adding phosphate (P+) and lime (Ca+) and over the next three growing seasons, we recorded soil chemistry and plant responses.
Results
Soil inorganic N, especially soil NH4+, strongly declined after liming compared to the control situation, confirming that liming alleviates NH4+ toxicity. Addition of P resulted in a similar decline, also suggesting a role for soil phosphate availability in this process. Acid‐sensitive plant species richness increased significantly in both Ca+ and P+ treatment, whereas acid‐insensitive plant species richness only increased significantly as a result of P+ treatment. Mean vegetation relative growth rate increased significantly in both Ca+ and P+ treatments.
Conclusions
Excessive P removal due to sod cutting constitutes a second barrier to restoration in addition to soil acidity. We discourage the large‐scale use of sod cutting to reduce soil N availability in heathlands and propose to use interventions that leave the soil nutrient balance intact, such as burning and grazing, mowing or litter removal, in combination with measures that restore the soil buffer capacity.
Sod cutting is used as measure in heathlands affected by increased nitrogen deposition, but species recovery is often limited. This paper provides experimental evidence for barriers to successful restoration introduced by sod cutting: soil acidity and P limitation. Having important implications for managing ecosystems under high nitrogen load, this advocates a sound N emission reduction instead of N removal policy.
Even-aged management (rotation forestry, RF) involves ditch network maintenance (DNM) operations in peatlands. Although the DNM operations contribute tree growth, they have negative environmental ...effects on watercources. To avoid DNM, a strip cutting (SC) management has been proposed. SC management in peatlands relies on natural regeneration by trees growing on the edge stand next to a clear-cut strip. The width of a cut strip varies, and here 20, 35 and 50 m strip width were applied in three locations in Finland: Akaa (southern), Kuopio (central), and Oulu (northern Finland). Tree growth of an edge stand and sapling stand was modeled with a stand-level model which accounted for the effect of dominant height of the edge stand and variation of shading among alternative strip widths. In southern location, RF financially outperformed SC management with interest rates 2-4%, but with a 5% interest rate and strip with of 35 or 50 m SC management was more beneficial than RF. In central and northern locations RF was better only with a 2% interest rate and with a 20 m strip width. Our results demonstrate that SC management is a financially valid option to apply in pine-dominated peatlands, particularly in northern regions.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A scaled rock cutting test is presented. It is designed as an attachment for hydraulic presses commonly available in rock mechanics laboratories. Rotating disc cutters are used to cut rock samples ...several times with the possibility to adjust indentation depth and spacing. Standard sample sizes, which are available in early phases of a tunnelling project, are used in order to enable this test to be used for tunnel boring machine (TBM) performance prediction. The results are compared to geotechnical standard tests (uniaxial compression, Brazilian tension), full-scale linear cutting tests and TBM operational data. It is shown that scaled rock cutting tests are superior input parameters for TBM performance prediction compared to commonly used geotechnical standard tests.
•A new scaled rock cutting rig was developed at very low cost with high accuracy.•Results are compared with TBM data and full scale cutting tests.•Scaled rock cutting tests are well-suited for TBM performance prediction.
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