The pinwheel pattern as a suitable and advantageous alternative for the loading implementation of the pallet loading problem （PLP） is identified after a survey on the loading pattern. The definitions, elements, cate...The pinwheel pattern as a suitable and advantageous alternative for the loading implementation of the pallet loading problem （PLP） is identified after a survey on the loading pattern. The definitions, elements, categories, generating algorithms of the pinwheel pattern are discussed and a uniform symmetric pinwheel notation is proposed. Based on the forming geometry of a pinwheel, the pinwheel structure is analyzed in terms of the innate box ratio, the box/block orientation and the box number by combinatorial and geometrical methods. A revised data set for the PLP with an area ratio range from 1 to 76 and a box ratio range from 1 to 10 is proposed. All pinwheel instances with this data set are calculated, and box ratio range is obtained for each possible pinwheel pattern, which can be found for all non-prime numbers of boxes. And a high box ratio makes an optimal pinwheel pattern more likely appear. Results identify the impact of the above pinwheel pattern and the box ratio on the pallet loading problem.展开更多
We have developed a 202-year tree-ring width chronology of Shensi fir(Abies chensiensis) growing in an open canopy forest at the treeline of the eastern Qinling Mountains. Climate response analyses revealed that the r...We have developed a 202-year tree-ring width chronology of Shensi fir(Abies chensiensis) growing in an open canopy forest at the treeline of the eastern Qinling Mountains. Climate response analyses revealed that the ring width of Shensi fir trees is primarily controlled by the range of temperature from February–June. The regression model that we used for statistical temperature reconstruction passed the leave-one-out cross-validation used in dendroclimatology, resulting in a quality-controlled February–June reconstruction for the eastern Qinling Mountains. The model accounts for 36.7% of the instrumental temperature variance during the period of 1960–2012. Warm springs and early summers occurred during AD 1870–1873, 1909–1914, 1927–1958 and 1997–2012, while the periods of AD 1874–1908, 1915–1926 and 1959–1996 were relatively cold. Spatial climate correlation analyses with gridded land surface data revealed that our temperature reconstruction contains a strong regional temperature signal for central China. The linkages of ourtemperature reconstruction with sea surface temperature in the Atlantic and Pacific oceans suggest the connection of regional temperature variations to large-scale ocean–atmosphere–land circulation. Preliminary analysis of links between large-scale climatic variation and the temperature reconstruction also shows that there is a relationship between extremes in spring and early summer temperature and anomalous atmospheric circulation in the Qinling Mountains. Overall, our study provides reliable information for the research of past temperature variability in the Qinling Mountains, China.展开更多
Aboveground net primary productivity(ANPP)of two dominant species, one deciduous tree(Platycarya strobilacea) and one evergreen tree(Machilus cavaleriei),was estimated based on the tree-ring width and the girth increm...Aboveground net primary productivity(ANPP)of two dominant species, one deciduous tree(Platycarya strobilacea) and one evergreen tree(Machilus cavaleriei),was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.展开更多
[Objective] The aim was to analyze the correlation between tree-ring width of Picea crassifolia in the east of Qilian Mountains and the precipitation, temperature and the normalized difference vegetation index (NDVI)....[Objective] The aim was to analyze the correlation between tree-ring width of Picea crassifolia in the east of Qilian Mountains and the precipitation, temperature and the normalized difference vegetation index (NDVI). [Method] The correlation analysis and the regression analysis were used in this study. [Result] The tree-ring width was significantly correlated with the autumn precipitation and the spring average NDVI. The conversion equation between tree-ring width and spring NDVI (R2 = 48.5% , R2adj =46.2% , F =21.627, P <0.001) was developed and NDVI sequence was reconstructed during the period 1915 -2007. The drought in the 1920s was pronounced. Vegetation cover in the Qilian Mountains increased during the period 1922-1934, 1940-1957, 1965-1969, 1984-1988 and 1995-1997, but decreased during 1935 -1939, 1958 -1964, 1970 -1983, 1989 -1994 and 1998 -2005. [Conclusion] The reconstructed NDVI showed the drought evolution in the study area.展开更多
Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three re...Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three reported episodes of massive tree mortality in 1880, 1980, and 2000 were attributed to drought at least as the triggering factor. Our main objective was to reconstruct drought events that could be linked to Atlas cedar tree mortality using tree-ring series. We developed a Cedrus atlantica tree-ring width chronology in Chelia with a reliable period spanning from 1502 to 2008. Based on the relationship between chronology indices and instrumental precipitation data, we reconstructed total October-June precipitation. Dry events were identified using a threshold of 90% of the October-June mean instrumental precipitation. The unique drought event of 3-year period （1877-1879） could explain the tree mortality occurred in 1880. In terms of severity and frequency of droughts, the later half of the twentieth century seems to be the worst and may be responsible for the recent tree mortality.展开更多
Gear drives are one of the most common parts in many rotating machinery. If the gear drive runs under lower torque load, nonlinear effects like gear mesh interruption can occur and vibration is accompanied by impact m...Gear drives are one of the most common parts in many rotating machinery. If the gear drive runs under lower torque load, nonlinear effects like gear mesh interruption can occur and vibration is accompanied by impact motions of the gears, This paper presents an original method of the mathematical modelling of gear drive nonlinear vibrations by using the modal synthesis method with degrees of freedom number reduction. The model respects nonlinearities caused by gear mesh interruption, parametric gearing excitation caused by time-varying meshing stiffness and nonlinear contact forces acting between journals of the rolling-element bearings and the outer housing. The nonlinear model is then used for investigation of gear drive vibration, especially for constant gear mesh determination. The theoretical method is applied for investigating of test gear drive nonlinear vibration.展开更多
The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chr...The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chronology and climatic conditions based on tree-ring width samples from three sites on the northeast slopes of Yangming Mountain. This data is used to study the relationship between the tree-ring width of a young tree and climatic conditions in a moist hilly region of southern China and to understand the general pattern of climate variation and its effects on tree growth in the past in this region. The results indicate that changes in tree-ring widths in these sites are closely related to local climatic conditions. There is a significant positive correlation between the radial growth of Pinus massoniana and the mean temperature of the current year from January to May（coefficient of correlation, R, is 0.596, P〈0.01） and the mean temperature of the previous year from June to July（R is 0.639, P〈0.01）. The radial growth of Pinus massoniana is negatively correlated with the total precipitation of the previous year from January to March and November to December（R is-0.46, P〈0.05） and negatively correlated with the total precipitation of the previous year from June to July（R is-0.582, P〈0.05）. The effect of precipitation on the radial growth of Pinus massoniana is known as the ＂hysteresis effect＂.展开更多
A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River,Shanxi Province,China.Based on the tree-ring-width indices,a 157-year long Palmer Drought ...A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River,Shanxi Province,China.Based on the tree-ring-width indices,a 157-year long Palmer Drought Severity Index(PDSI) was reconstructed,which explains 53.7% of the variance of the modeled PDSI over the common period 1957-2008.The drought periods in the study area include 1914-1931 and 1970 to the present,whereas the wet periods were 1866-1892 and 1932-1969.The drought of 1914-1931 was a severe long-lasting drought with a low inter-annual variability,and the drought of 1970-2009 was an overall long-term drought with a high inter-annual variability.The period of 1866-1892 is a continuously wet period with a low inter-annual variability and the period of 1932-1969 is an overall long-term wet period with a high inter-annual variability.The reconstructed PDSI series in the source of the Fenhe River shows synchronous variations with the regional drought/wetness indices.Spatial correlation analyses indicate that the higher correlations lie exclusively in the Fenhe River Basin.This indicates that the reconstructed PDSI has regional representativeness and can represent the drought history of the entire Fenhe River Basin to some extent.Furthermore,the reconstructed PDSI matches with the variability of the per unit yield of summer grain crops in Shanxi Province very well and they have significant correlation.From a long-term perspective the reconstructed PDSI series could supply scientific and valuable information to the water resources management and then help the sustainable development in agricultural production,economic development,and ecosystem balance.展开更多
The ring-width chronology of a Juniperus przewalskii tree from the middle of the Qilian Mountain was constructed to estimate the annual precipitation (from previous August to current July) since AD 1480.The reconstruc...The ring-width chronology of a Juniperus przewalskii tree from the middle of the Qilian Mountain was constructed to estimate the annual precipitation (from previous August to current July) since AD 1480.The reconstruction showed four major alternations of drying and wetting over the past 521 years.The rainy 16th century was followed by persistent drought in the 17th century.Moreover,relatively wet conditions persisted from the 18th to the beginning of 20th century until the recurrence of a drought during the 1920s and 1930s.Based on the Empirical Mode Decomposition method,eight Intrinsic Mode Functions (IMFs) were extracted,each representing unique fluctuations of the reconstructed precipitation in the time-frequency domain.The high amplitudes of IMFs on different timescales were often consistent with the high amount of precipitation,and vice versa.The IMF of the lowest frequency indicated that the precipitation has undergone a slow increasing trend over the past 521 years.The 2-3 year and 5-8 year time-scales reflected the characteristics of inter-annual variability in precipitation relevant to regional atmospheric circulation and the El Ni?o-Southern Oscillation (ENSO),respectively.The 10-13 year scale of IMF may be associated with changing solar activity.Specifically,an amalgamation of previous and present data showed that droughts were likely to be a historically persistent feature of the Earth's climate,whereas the probability of intensified rainfall events seemed to increase during the course of the 19th and 20th centuries.These changing characteristics in precipitation indicate an unprecedented alteration of the hydrological cycle,with unknown future amplitude.Our reconstruction complements existing information on past precipitation changes in the Qilian Mountain,and provides additional low-frequency information not previously available.展开更多
To evaluate the applicability of the Standardized Precipitation-Evapotranspiration Index （SPEI） and the self-calibrated Palmer Drought Severity Index （scPDSI） to paleoclimate reconstructions in the east Asian summ...To evaluate the applicability of the Standardized Precipitation-Evapotranspiration Index （SPEI） and the self-calibrated Palmer Drought Severity Index （scPDSI） to paleoclimate reconstructions in the east Asian summer monsoon region, we used a 194-year tree-ring width chronology from Guancen Mountain, Shanxi Province, China, to investigate its correlation with SPEI and scPDSI, respectively. The results indicated scPDSI as a robust drought index that could be reconstructed from tree-ring width on Guancen Mountain other hydroclimate-related Significant correlations with series illustrated that our reconstruction captured common variations of hydroclimate in the surrounding areas. Additionally, our reconstruction showed significant correlation with nearby grid points of the Monsoon Asia Drought Atlas （MADA）. However, while unprecedented drying trend existed during the past several decades in MADA, it was not represented in our reconstruction or in instrumental scPDSI/Dai-PDSI. This may imply that MADA overestimated drought severity during the past several decades in our study area; this overestimation was probably caused by an insufficient spatiotemporal distribution of the tree-ring network used by MADA. Therefore, more drought reconstructions based on individual sampling sites in eastern Asia are necessary to gain a thorough understanding of the Asian Monsoon climate variability.展开更多
基金The National Natural Science Foundation of China(No.70571033,70831002)
文摘The pinwheel pattern as a suitable and advantageous alternative for the loading implementation of the pallet loading problem （PLP） is identified after a survey on the loading pattern. The definitions, elements, categories, generating algorithms of the pinwheel pattern are discussed and a uniform symmetric pinwheel notation is proposed. Based on the forming geometry of a pinwheel, the pinwheel structure is analyzed in terms of the innate box ratio, the box/block orientation and the box number by combinatorial and geometrical methods. A revised data set for the PLP with an area ratio range from 1 to 76 and a box ratio range from 1 to 10 is proposed. All pinwheel instances with this data set are calculated, and box ratio range is obtained for each possible pinwheel pattern, which can be found for all non-prime numbers of boxes. And a high box ratio makes an optimal pinwheel pattern more likely appear. Results identify the impact of the above pinwheel pattern and the box ratio on the pallet loading problem.
基金supported by the Basic Research Operating Expenses of the Central-level Non-profit Research Institutes of China (IDM201105)the Open Foundation of MOE Key Laboratory of Western China's Environmental System, Lanzhou Universitythe Fundamental Research Funds for the Central Universities (lzujbky-2011-t02)
文摘We have developed a 202-year tree-ring width chronology of Shensi fir(Abies chensiensis) growing in an open canopy forest at the treeline of the eastern Qinling Mountains. Climate response analyses revealed that the ring width of Shensi fir trees is primarily controlled by the range of temperature from February–June. The regression model that we used for statistical temperature reconstruction passed the leave-one-out cross-validation used in dendroclimatology, resulting in a quality-controlled February–June reconstruction for the eastern Qinling Mountains. The model accounts for 36.7% of the instrumental temperature variance during the period of 1960–2012. Warm springs and early summers occurred during AD 1870–1873, 1909–1914, 1927–1958 and 1997–2012, while the periods of AD 1874–1908, 1915–1926 and 1959–1996 were relatively cold. Spatial climate correlation analyses with gridded land surface data revealed that our temperature reconstruction contains a strong regional temperature signal for central China. The linkages of ourtemperature reconstruction with sea surface temperature in the Atlantic and Pacific oceans suggest the connection of regional temperature variations to large-scale ocean–atmosphere–land circulation. Preliminary analysis of links between large-scale climatic variation and the temperature reconstruction also shows that there is a relationship between extremes in spring and early summer temperature and anomalous atmospheric circulation in the Qinling Mountains. Overall, our study provides reliable information for the research of past temperature variability in the Qinling Mountains, China.
基金supported by the National Key Basic Research Program(2013CB956704)
文摘Aboveground net primary productivity(ANPP)of two dominant species, one deciduous tree(Platycarya strobilacea) and one evergreen tree(Machilus cavaleriei),was estimated based on the tree-ring width and the girth increment as well as allometric functions in a karst evergreen and deciduous broadleaved mixed forest in central Guizhou Province, southwestern China. Results showed that the ANPP increased from 1961 to 2015, especially during the last 20–30 years, but with strong variations. The deciduous tree had higher ANPP than the evergreen tree according to two kinds of estimates by the tree ring and girth increment. The averaged ANPP for these two mature trees was 2.27 kg/individual/year, ca. 8 t/ha/year considering the normal stand density. Such karst forest productivity was lower than the natural subtropical forests in China and in the world.
基金Supported by the NSFC(41071128 and 40801004)the Key Program of Hebei Education Department(ZH2012035)
文摘[Objective] The aim was to analyze the correlation between tree-ring width of Picea crassifolia in the east of Qilian Mountains and the precipitation, temperature and the normalized difference vegetation index (NDVI). [Method] The correlation analysis and the regression analysis were used in this study. [Result] The tree-ring width was significantly correlated with the autumn precipitation and the spring average NDVI. The conversion equation between tree-ring width and spring NDVI (R2 = 48.5% , R2adj =46.2% , F =21.627, P <0.001) was developed and NDVI sequence was reconstructed during the period 1915 -2007. The drought in the 1920s was pronounced. Vegetation cover in the Qilian Mountains increased during the period 1922-1934, 1940-1957, 1965-1969, 1984-1988 and 1995-1997, but decreased during 1935 -1939, 1958 -1964, 1970 -1983, 1989 -1994 and 1998 -2005. [Conclusion] The reconstructed NDVI showed the drought evolution in the study area.
文摘Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three reported episodes of massive tree mortality in 1880, 1980, and 2000 were attributed to drought at least as the triggering factor. Our main objective was to reconstruct drought events that could be linked to Atlas cedar tree mortality using tree-ring series. We developed a Cedrus atlantica tree-ring width chronology in Chelia with a reliable period spanning from 1502 to 2008. Based on the relationship between chronology indices and instrumental precipitation data, we reconstructed total October-June precipitation. Dry events were identified using a threshold of 90% of the October-June mean instrumental precipitation. The unique drought event of 3-year period （1877-1879） could explain the tree mortality occurred in 1880. In terms of severity and frequency of droughts, the later half of the twentieth century seems to be the worst and may be responsible for the recent tree mortality.
文摘Gear drives are one of the most common parts in many rotating machinery. If the gear drive runs under lower torque load, nonlinear effects like gear mesh interruption can occur and vibration is accompanied by impact motions of the gears, This paper presents an original method of the mathematical modelling of gear drive nonlinear vibrations by using the modal synthesis method with degrees of freedom number reduction. The model respects nonlinearities caused by gear mesh interruption, parametric gearing excitation caused by time-varying meshing stiffness and nonlinear contact forces acting between journals of the rolling-element bearings and the outer housing. The nonlinear model is then used for investigation of gear drive vibration, especially for constant gear mesh determination. The theoretical method is applied for investigating of test gear drive nonlinear vibration.
基金National Natural Science Foundation of China(41571509)
文摘The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chronology and climatic conditions based on tree-ring width samples from three sites on the northeast slopes of Yangming Mountain. This data is used to study the relationship between the tree-ring width of a young tree and climatic conditions in a moist hilly region of southern China and to understand the general pattern of climate variation and its effects on tree growth in the past in this region. The results indicate that changes in tree-ring widths in these sites are closely related to local climatic conditions. There is a significant positive correlation between the radial growth of Pinus massoniana and the mean temperature of the current year from January to May（coefficient of correlation, R, is 0.596, P〈0.01） and the mean temperature of the previous year from June to July（R is 0.639, P〈0.01）. The radial growth of Pinus massoniana is negatively correlated with the total precipitation of the previous year from January to March and November to December（R is-0.46, P〈0.05） and negatively correlated with the total precipitation of the previous year from June to July（R is-0.582, P〈0.05）. The effect of precipitation on the radial growth of Pinus massoniana is known as the ＂hysteresis effect＂.
基金supported by National Natural Science Foundation of China (Grant Nos. 40901060,41023006,and 40890051)National Basic Research Program of China (Grant No. 2010CB833405)the State Key Laboratory of Loess and Quaternary Geology and the Sino-Swedish Tree-Ring Research Center (SISTRR) Contribution
文摘A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River,Shanxi Province,China.Based on the tree-ring-width indices,a 157-year long Palmer Drought Severity Index(PDSI) was reconstructed,which explains 53.7% of the variance of the modeled PDSI over the common period 1957-2008.The drought periods in the study area include 1914-1931 and 1970 to the present,whereas the wet periods were 1866-1892 and 1932-1969.The drought of 1914-1931 was a severe long-lasting drought with a low inter-annual variability,and the drought of 1970-2009 was an overall long-term drought with a high inter-annual variability.The period of 1866-1892 is a continuously wet period with a low inter-annual variability and the period of 1932-1969 is an overall long-term wet period with a high inter-annual variability.The reconstructed PDSI series in the source of the Fenhe River shows synchronous variations with the regional drought/wetness indices.Spatial correlation analyses indicate that the higher correlations lie exclusively in the Fenhe River Basin.This indicates that the reconstructed PDSI has regional representativeness and can represent the drought history of the entire Fenhe River Basin to some extent.Furthermore,the reconstructed PDSI matches with the variability of the per unit yield of summer grain crops in Shanxi Province very well and they have significant correlation.From a long-term perspective the reconstructed PDSI series could supply scientific and valuable information to the water resources management and then help the sustainable development in agricultural production,economic development,and ecosystem balance.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41001058, 41001009, 40971119 and 40890052)the China Postdoctoral Science Foundation (Grant Nos. 201003194)
文摘The ring-width chronology of a Juniperus przewalskii tree from the middle of the Qilian Mountain was constructed to estimate the annual precipitation (from previous August to current July) since AD 1480.The reconstruction showed four major alternations of drying and wetting over the past 521 years.The rainy 16th century was followed by persistent drought in the 17th century.Moreover,relatively wet conditions persisted from the 18th to the beginning of 20th century until the recurrence of a drought during the 1920s and 1930s.Based on the Empirical Mode Decomposition method,eight Intrinsic Mode Functions (IMFs) were extracted,each representing unique fluctuations of the reconstructed precipitation in the time-frequency domain.The high amplitudes of IMFs on different timescales were often consistent with the high amount of precipitation,and vice versa.The IMF of the lowest frequency indicated that the precipitation has undergone a slow increasing trend over the past 521 years.The 2-3 year and 5-8 year time-scales reflected the characteristics of inter-annual variability in precipitation relevant to regional atmospheric circulation and the El Ni?o-Southern Oscillation (ENSO),respectively.The 10-13 year scale of IMF may be associated with changing solar activity.Specifically,an amalgamation of previous and present data showed that droughts were likely to be a historically persistent feature of the Earth's climate,whereas the probability of intensified rainfall events seemed to increase during the course of the 19th and 20th centuries.These changing characteristics in precipitation indicate an unprecedented alteration of the hydrological cycle,with unknown future amplitude.Our reconstruction complements existing information on past precipitation changes in the Qilian Mountain,and provides additional low-frequency information not previously available.
基金supported by the National Natural Science Foundation of China(41201046,40890051),KZZDEW-04-01the State Key Laboratory of Loess and Quaternary Geology(SKLLQG),and the West Doctoral Foundation of Chinese Academy of Sciences.This is a SISTRR contribution(No.29)
文摘To evaluate the applicability of the Standardized Precipitation-Evapotranspiration Index （SPEI） and the self-calibrated Palmer Drought Severity Index （scPDSI） to paleoclimate reconstructions in the east Asian summer monsoon region, we used a 194-year tree-ring width chronology from Guancen Mountain, Shanxi Province, China, to investigate its correlation with SPEI and scPDSI, respectively. The results indicated scPDSI as a robust drought index that could be reconstructed from tree-ring width on Guancen Mountain other hydroclimate-related Significant correlations with series illustrated that our reconstruction captured common variations of hydroclimate in the surrounding areas. Additionally, our reconstruction showed significant correlation with nearby grid points of the Monsoon Asia Drought Atlas （MADA）. However, while unprecedented drying trend existed during the past several decades in MADA, it was not represented in our reconstruction or in instrumental scPDSI/Dai-PDSI. This may imply that MADA overestimated drought severity during the past several decades in our study area; this overestimation was probably caused by an insufficient spatiotemporal distribution of the tree-ring network used by MADA. Therefore, more drought reconstructions based on individual sampling sites in eastern Asia are necessary to gain a thorough understanding of the Asian Monsoon climate variability.
