In this study Digital Image Correlation (DIC) was adopted to evaluate the mechanical properties of bovine hoof horn. Using specific process, tensile specimens comprised of Zones 4 and 5 of the sole were excised from t...In this study Digital Image Correlation (DIC) was adopted to evaluate the mechanical properties of bovine hoof horn. Using specific process, tensile specimens comprised of Zones 4 and 5 of the sole were excised from the claws of the front and rear hooves of a mature Black Angus cow. After extraction the specimens were conditioned to obtain horn with relative moisture content of either 0% (dry) or 100% (wet) and then subjected to uniaxial tension to failure. The average elastic modulus (E) of all "dry" and "wet" hoof horn was 2870 ± 460 MPa and 102 ± 34 MPa respectively. Similarly, the average proportional limit stress (σ) was 29.0 ± 4.8 MPa and 1.4 ± 0.3 MPa respectively. Although the mechanical properties were dependent on distance from the dermal-epidermal junction, the influence of moisture on mechanical behavior was far greater.展开更多
A mathematical model and finite element model for analysis of temperature rise of the hoisting machine brake sys- tem was constructed, limit conditions were defined, and the law of temperature rise of brake shoes duri...A mathematical model and finite element model for analysis of temperature rise of the hoisting machine brake sys- tem was constructed, limit conditions were defined, and the law of temperature rise of brake shoes during emergent brake course was analyzed and calculated by using finite element software. By analyzing the calculation results, the law of tempera- ture change of surface of brake disk and shoes during the braking process was found. The law of brake shoes surface tempera- ture distribution and the law of temperature change along with thickness of brake shoes at brake time 0.5 s, 1.0 s and 1.5 s was analyzed. A hoisting machine emergent braking test was carried out. Finally, the author concluded that velocity rebound in the process of hoisting machine emergent brake is due to decreased friction coefficient caused by the temperature rise of the brake shoes surface.展开更多
In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodivers...In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as 'Heitutan'. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.展开更多
A three-dimensional autonomous chaotic system is discussed in this paper. Some basic dynamical properties of the system, including phase portrait, Poincar′e map, power spectrum, Kaplan–Yorke dimension, Lyapunov expo...A three-dimensional autonomous chaotic system is discussed in this paper. Some basic dynamical properties of the system, including phase portrait, Poincar′e map, power spectrum, Kaplan–Yorke dimension, Lyapunov exponent spectra, signal amplitude and topological horseshoe are studied theoretically and numerically. The main finding by analysis is that the signal amplitude can be modulated via controlling the coefficients of the linear term, cross-product term and squared term simultaneously or respectively, and the phase of x3 can be modulated by the product of the coefficients of the linear term and cross-product term. Furthermore, scaling chaotic attractors of this system are achieved by modified projective synchronization with an optimization-based linear coupling method, which is safer for secure communications than the existed synchronization scheme since the scaling factors can be regarded as the security encoding key.展开更多
基金This work was partially sponsored by the National Science Foundation 0238237(USA)Shanghai Leading Academic Discipline Project, No. Y0103, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of China.
文摘In this study Digital Image Correlation (DIC) was adopted to evaluate the mechanical properties of bovine hoof horn. Using specific process, tensile specimens comprised of Zones 4 and 5 of the sole were excised from the claws of the front and rear hooves of a mature Black Angus cow. After extraction the specimens were conditioned to obtain horn with relative moisture content of either 0% (dry) or 100% (wet) and then subjected to uniaxial tension to failure. The average elastic modulus (E) of all "dry" and "wet" hoof horn was 2870 ± 460 MPa and 102 ± 34 MPa respectively. Similarly, the average proportional limit stress (σ) was 29.0 ± 4.8 MPa and 1.4 ± 0.3 MPa respectively. Although the mechanical properties were dependent on distance from the dermal-epidermal junction, the influence of moisture on mechanical behavior was far greater.
基金Supported by the National Natural Science Foundation of China (50875252)
文摘A mathematical model and finite element model for analysis of temperature rise of the hoisting machine brake sys- tem was constructed, limit conditions were defined, and the law of temperature rise of brake shoes during emergent brake course was analyzed and calculated by using finite element software. By analyzing the calculation results, the law of tempera- ture change of surface of brake disk and shoes during the braking process was found. The law of brake shoes surface tempera- ture distribution and the law of temperature change along with thickness of brake shoes at brake time 0.5 s, 1.0 s and 1.5 s was analyzed. A hoisting machine emergent braking test was carried out. Finally, the author concluded that velocity rebound in the process of hoisting machine emergent brake is due to decreased friction coefficient caused by the temperature rise of the brake shoes surface.
基金supported by Special Fund for Agroscientific Research in the Public Interest(201203041)the National Natural Sciences Foundation of China(41161084)International Science & Technology Cooperation Program of China(2011DFG93160,2011DFA20820)
文摘In many ecosystems ungulates have coexisted with grasslands over long periods of time. However, high densities of grazing animals may change the floristic and structural characteristics of vegetation, reduce biodiversity, and increase soil erosion, potentially triggering abrupt and rapid changes in ecosystem condition. Alternate stable state theory provides a framework for understanding this type of dynamic. In the Sanjiangyuan atop the Qinghai-Tibetan plateau (QTP), grassland degradation has been accompanied by irruptions of native burrowing animals, which has accentuated the loss of ground cover. Severely degraded areas of alpine meadows are referred to as 'Heitutan'. Here, using the framework of alternate stable state theory, we describe the proximate and ultimate drivers of the formation of Heitutan on the QTP, and we assess prospects for recovery, in relation to the degree of biophysical alteration, of these alpine meadows. Effective rehabilitation measures must address the underlying causes of degradation rather than their symptoms. Heitutan degradation is not uni-causal. Rather it reflects different mechanisms operating at different spatio-temporal scales across this vast region. Underlying causes include overly aggressive exploitation of the grasslands (e.g. overgrazing), amplification of grazing and erosion damage by small mammals when outbreaks occur, and/or climate change. Given marked variability in environmental conditions and stressors, restorative efforts must vary across the region. Restoration efforts are likely toyield greatest success if moderately and severely degraded areas are targeted as the first priority in management programmes, before these areas are transformed into extreme Heitutan.
基金Supported by Hunan Provincial Natural Science Foundation of China under Grant No.2016JJ4036University Natural Science Foundation of Jiangsu Province under Grant No.14KJB120007the National Natural Science Foundation of China under Grant Nos.11504176and 11602084
文摘A three-dimensional autonomous chaotic system is discussed in this paper. Some basic dynamical properties of the system, including phase portrait, Poincar′e map, power spectrum, Kaplan–Yorke dimension, Lyapunov exponent spectra, signal amplitude and topological horseshoe are studied theoretically and numerically. The main finding by analysis is that the signal amplitude can be modulated via controlling the coefficients of the linear term, cross-product term and squared term simultaneously or respectively, and the phase of x3 can be modulated by the product of the coefficients of the linear term and cross-product term. Furthermore, scaling chaotic attractors of this system are achieved by modified projective synchronization with an optimization-based linear coupling method, which is safer for secure communications than the existed synchronization scheme since the scaling factors can be regarded as the security encoding key.