首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
在模型验证和数据库组建基础上,用WinEPIC模型定量模拟研究了黄土高原半湿润区长武、半干旱区固原和半干旱偏旱区海原20~30年内苜蓿草地水分生产潜力、10m土层土壤有效含水量和土壤湿度剖面分布特征的动态变化.结果表明:长武、固原和海原苜蓿草地水分生产潜力模拟值随降水量变化而呈现波动性降低趋势,其平均值分别为8.81、3.83和2.48t.hm-2;长武、固原和海原苜蓿草地10m土层逐月土壤有效含水量模拟值均呈现明显的波动性降低趋势,模拟初期,4~8年生苜蓿草地土壤干燥化趋势十分强烈,此后,随降水量变化长期在较低水平上波动;随着苜蓿生长年限的延长,苜蓿草地土壤干层逐年加深、加厚,长武、固原和海原土壤干层分布深度达到10m所需时间依次为6、6和4年,此后苜蓿草地降水渗深以下土层长期维持较为稳定的干燥化状态;苜蓿草地水分持续利用的合理年限为半湿润区8~10年,半干旱区6~8年,半干旱偏旱区4~6年.  相似文献   

2.
桂林甑皮岩新石器时代遗址2例儿童的年龄问题   总被引:2,自引:0,他引:2  
作者报告2例于桂林甑皮岩新石器时代早期遗址出土的正处于换牙期的儿童乳、恒牙更换及其被磨耗的状况,讨论了从他们的牙磨耗级估计的年龄与从其乳、恒牙更换关系估计的年龄的误差,并提出用现代人牙磨耗级估计史前人类年龄的意见.  相似文献   

3.
1959—2006年长白山地区降水序列的多时间尺度分析   总被引:7,自引:1,他引:7  
基于长白山地区松江、东岗、长白、和龙、临江和天池6个气象站1959—2006年的月均降水量和年降水量数据,采用Morlet小波分析方法,对1959—2006年长白山地区植被生长季(5—9月)降水量、降雪季(11月至次年4月)降水量和年降水量序列进行多尺度特征分析,并运用Daubechies小波系中的db5小波对各降水序列进行不同层次的分解和低频重构,对重构序列进行了趋势识别和分析.结果表明:研究期间,长白山地区植被生长季降水量存在3~6a、10~13a和24~30a的特征周期;降雪季降水量存在1~2a、5~7a和17~20a的特征周期;年降水存在8~10a、16~20a、25~30a的特征周期;研究区年降水量序列呈现整体下降的趋势.  相似文献   

4.
V. C. Wright  M. A. Riopelle 《CMAJ》1982,127(2):127-131
The Walton Report on cervical cancer screening programs recently recommended a new program for screening for cervical cancer based on chronologic age, calling for 3- and 5-year intervals between examinations. It recommended that such examinations be discontinued after 60 years of age. In a group of 232 routinely examined women (aged 18 to 47 years) in whom cervical intraepithelial neoplasia developed the timing of onset of the disease and the implications for screening were studied. The average age at the time of diagnosis was 30 years; in 20% of the patients the diagnosis had been made after age 35. The screening program recommended in the Walton Report would have been effective in diagnosing most cases (80%) in this sample by age 35 and all by age 60. However, when the patients were grouped according to age at the time of first intercourse, the diagnosis had been made after age 35 in only 13% of those who started having intercourse at age 15 to 17 years, 20% of those who started at age 18 to 19 years and 33% of those who started at age 20 years of later. When the times of diagnosis were expressed by number of years of intercourse the distributions became uniform in the same three groups; in 72% of all the patients the diagnosis had been made within the first 15 years of intercourse, in 88% it had been made within 20 years and in 100% it had been made by 30 years. These data suggest that a program based on number of years of intercourse may be more uniform and more efficient than one based on chronologic age, and that cytologic examinations should be concentrated during the time when most cases develop -- 6 to 20 years after the time of first intercourse.  相似文献   

5.
基于长白山地区松江、东岗、长白、和龙、临江和天池6个气象站1959—2006年的月均降水量和年降水量数据,采用Morlet小波分析方法,对1959—2006年长白山地区植被生长季(5—9月)降水量、降雪季(11月至次年4月)降水量和年降水量序列进行多尺度特征分析,并运用Daubechies小波系中的db5小波对各降水序列进行不同层次的分解和低频重构,对重构序列进行了趋势识别和分析.结果表明:研究期间,长白山地区植被生长季降水量存在3~6 a、10~13 a和24~30 a的特征周期;降雪季降水量存在1~2 a、5~7 a和17~20 a的特征周期;年降水存在8~10 a、16~20 a、25~30 a的特征周期;研究区年降水量序列呈现整体下降的趋势.  相似文献   

6.
The objectives of this paper are to predict life years lost associated with obesity-related diseases (ORDs) for U.S. non-smoking adults, and to examine the relationship between those ORDs and mortality. Data from the National Health Interview Survey, 1997–2000, were used. We employed mixed proportional hazard models to estimate the association between those ORDs and mortality and used simulations to project life years lost associated with the ORDs. We found that obesity-attributable comorbidities are associated with large decreases in life years and increases in mortality rates. The life years lost associated with ORDs is more marked for younger adults than older adults, for blacks than whites, for males than females, and for the more obese than the less obese. Using U.S. non-smoking adults aged 40 to 49 years as an example to illustrate percentage of the life years lost associated with ORDs, we found that the mean life years lost associated with ORDs for U.S. non-smoking black males aged 40 to 49 years with a body mass index above 40 kg/m2 was 5.43 years, which translates to a 7.5% reduction in total life years. White males of the same age range and same degree of obesity lost 5.23 life years on average – a 6.8% reduction in total life years, followed by black females (5.04 years, a 6.5% reduction in life years), and white females (4.7 years, a 5.8% reduction in life years). Overall, ORDs increased chances of dying and lessened life years by 0.2 to 11.7 years depending on gender, race, BMI classification, and age.  相似文献   

7.
Distance and velocity curves for height and weight were analyzed in a mixed longitudinal sample of American White, American Negro and Mexican-American deaf children 6 through 17 years of age. The heights of deaf boys and girls are, on the average, consistently below an accepted pediatric standard from six through ten years of age. Between 11 and 17 years, deaf White and Negro boys approximate the standard, while White and Negro girls are at or slightly below the standard. Deaf Mexican-American children are consistently below the height standard. For body weight, deaf boys are at or slightly below the standard from 6 to 11 years, and are at or slightly above the weight standard from 12 to 17 years of age. White and Negro deaf girls generally approximate the weight standard from eight years of age on. Mexican-American deaf girls are consistently below the standard until 13 years of age, while between 14 and 17 years they are at or above the standard. Height and weight velocity curves for deaf children parallel closely the incremental standards of Falkner ('62). The height velocity curve, however, appears to peak, on the average, about one year earlier in deaf children.  相似文献   

8.
分析2014年7-18岁内蒙古汉族、蒙古族和日本学生身高及体质量最大发育年龄差异。汉族和蒙古族数据来自《2014年内蒙古自治区学生体质与健康调查研究》;日本数据来源于"平成26年(2014年)度体育与运动调查统计情报"。结果显示:7-18岁各年龄段汉族男女生身高分别比蒙古族高出1.98 cm和1.54 cm;高出日本2.59 cm和2.91 cm(P<0.05)。汉族男生体质量平均高出蒙古族1.97 kg、高出日本4.01 kg;汉族和蒙古族女生体质量分别比日本高出2.59 kg(P<0.05)和2.67 kg(P<0.05)。2014年内蒙古汉族和蒙古族学生身高和体质量发育水平优于日本学生。汉族男生身高最大发育年龄分别提前蒙古族和日本1.73岁和0.9岁;汉族和蒙古族男生体质量最大发育年龄分别比日本滞后1.17和1.07岁;日本女生身高最大发育年龄比汉族和蒙古族提前0.68岁和0.37岁。  相似文献   

9.
荒漠生态系统对大气CO2浓度升高响应的干湿年差异   总被引:1,自引:0,他引:1  
利用一个基于详细生理学过程的生态系统模型PALS-FT,通过模拟实验分析了美国亚利桑那州(Arizona)首府凤凰城(Phoenix)市西郊的Larreatridentata荒漠生态系统在干湿年份(1988-2002年)对大气CO2浓度升高响应的差别。结果表明,生态系统地上净初级生产力(ANPP)和土壤有机质年累积速率(SOM)均随大气CO2浓度升高而呈非线性(湿年)或线性(正常年和干年)增加;所有年份的土壤N含量(Nsoil)则呈非线性显著下降。ANPP与SOM的绝对变化量总是湿年大于正常年和干年,相对变化量则与所分析的CO2处理水平有关;Nsoil的绝对变化量和相对变化量均为湿年大于正常年和干年。不同功能型的植物ANPP对大气CO2浓度升高的绝对变化量均为湿年大于正常年和干年;相对变化量则因具体植物功能型而异,灌木和亚灌木为干年大于正常年和湿年,一年生C3和C4草本均为湿年大于正常年和干年。因此,无论是生态系统水平还是植物功能型(或物种)水平,荒漠生态系统对未来大气CO2浓度升高的响应都将受降水格局的显著影响。  相似文献   

10.
The aims were to determine the benefit of bilateral cochlear implantation in a 20 years old patient implanted in Croatia on hearing and speech development. The male patient, after 10 years of deafness, got cochlear implants Med-EL Combi 40+ on both sides in one-stage surgery. The etiology of his deafness was posttraumatic meningitis. Auditory capacity and speech recognition tests were performed for both ears separately and together Average hearing level on the right ear with right cochlear implant switched on started at 62 dB 1 month after the cochlear implantation and was on 55 dB after 10 years. Average hearing level on the left ear with left cochlear implant switched on started at 55 dB 1 month after the cochlear implantation and was on 32 dB after 10 years. Average hearing level on the both ears with 2 cochlear implants switched on started at 35 dB 1 month after the cochlear implantation and was on 27 dB after 10 years. Long-term functional outcomes with bilateral cochlear implantation provides advantages over unilateral implantation including improved hearing level, speech perception in noise and improved sound localization.  相似文献   

11.
郭二辉  方晓  马丽  杨小燕  杨喜田 《生态学报》2020,40(11):3785-3794
弃耕地撂荒是土壤与植被向自然方向进行的次生演替,研究河岸带土壤撂荒后碳氮磷生态化学计量特征,是恢复和重建由农田干扰导致的退化河岸带生态系统的重要科学基础之一。以河岸带农地为对照,不同撂荒年限(撂荒2年、撂荒8年、撂荒10年)的土壤为研究对象,探索不同撂荒年限对土壤碳、氮、磷含量及相互关系的影响。结果表明:(1)土壤有机碳、氮的含量均呈现撂荒10年撂荒8年农田撂荒2年;土壤中磷含量呈现撂荒10年撂荒8年撂荒2年农田;农田和各撂荒年限的土壤碳、氮、磷含量,均随着土层深度的增加而呈降低的规律,但土壤碳和氮差异的显著性比磷明显。(2)河岸带土壤中C/N、C/P的均值均呈现:撂荒10年农田撂荒8年撂荒2年趋势。N/P的均值呈现:撂荒10年(0.78)农田(0.77)撂荒8年(0.77)撂荒2年(0.67),表明N是本研究区河岸带植被恢复的限制性营养元素。(3)河岸带农田和不同撂荒年限土壤碳、氮含量均存在极显著的耦合线性关系,而碳与磷、氮与磷之间的线性拟合程度相对较低。(4)在农田撂荒演替的初期阶段(2年),土壤的容重没有显著的变化,而随着撂荒时间的增加(8年和10年),土壤容重均有显著的降低,土壤结构得到改善。  相似文献   

12.
There is evidence of Holocene emergence on several of the Cook Islands. On Suwarrow Atoll there are extensive outcrops of emergent, but truncated, reef on the northern atoll rim, radiocarbon-dated 4680–4310 years B. P., overlain by younger cemented boulder conglomerates. On the northeast of the atoll there are fossil algal ridges indicating up to 1 m of emergence; the landwardmost has been dated 4220 years B. P., the intermediate one 3420 years B. P. and the present one 1250 years B. P. On Mitiaro, a makatea island in the Southern Cooks, there are emergent reefal deposits in the centre of the reef flat dated 5140–3620 years B. P. Similar thought poorly preserved deposits occur on Mauke, and an erosional bench and notch occurs on Atiu. Emergence on all islands appears synchronous with that reported on Mangaia, where a relative fall of sea level of at least 1.7 m in the last 3400 years has been reported. The evidence for emergence is broadly similar to that described from French Polynesia, though timing of emergence appears to differ.  相似文献   

13.
Fluctuating asymmetry (FA) is small deviations from perfect symmetry which reflect one component of fitness, i.e. developmental stability. There is accumulating evidence that low FA is important in inter- and intra-sexual selection in humans. However, there is little information on the pattern of FA in children. Data from cross-sectional studies of 680 participants from 2–18 years suggests that (1) both absolute and relative FA reduces with age until 10 years (2) there is an increase in FA in adolescents (11–15 years) with a peak at 13 years for males and 14 years for females (3) after 15 years there is reduction in FA which is maintained until 18 years. The importance of growth rate, metabolic maintenance and sex steroids on developmental stability is discussed.  相似文献   

14.
Age-related changes in characteristics of saccadic eye movements (latency, duration and percentage of multistep saccades) in healthy subjects and patients with Parkinson's disease were evaluated. Healthy volunteers were divided into 6 age groups (17-20 years, 21-30 years, 31-40 years, 41-50 years, 51-60 years, 61-75 years), parkinsonian patients into 3 age groups (41-50 years, 51-60 years, 61-75 years). According to our data, saccade characteristics depend upon age in both healthy subjects and parkinsonian patients. In healthy volunteers the percentage of multistep saccades and the mean saccade latency increase significantly after the age of 60. Values of these characteristics in patients with Parkinson's disease significantly exceed the values in the corresponding age groups of healthy subjects. The "disease" factor (MANOVA) has a greater influence on saccade latency and percentage of multistep saccades then the "age" factor. The duration of single saccades depends on age to a smaller extent and does not change in patients with Parkinson's disease. The peculiarities of neurodegenerative processes during normal aging and aging with Parkinson's disease are discussed.  相似文献   

15.
Heritability studies of BMI, based upon twin samples, have identified genetic and shared environmental components of BMI, but have been largely silent about the nonshared environmental factors. Intrauterine factors have been identified as having significant long‐term effects on BMI and may be a critical source of nonshared environmental influence. Extant studies based on samples of either unrelated individuals or twins cannot separate the effects of genetics, shared environments, and nonshared intrauterine conditions because the one lacks variation in the degree of relatedness and the other has insufficient variation in intrauterine conditions. This study improves upon these prior studies by using a large, sibling‐based sample to examine heritability, shared environmental, and nonshared intrauterine influences on BMI during two age periods in childhood (6–8 years; 12–14 years). The primary interest was in determining the effects of the intrauterine environment on BMI as a component of the nonshared environment and in determining whether there were sex‐specific differences in heritability and/or in the intrauterine factors. These were estimated using regression‐based techniques introduced by DeFries and Fulker. Heritability of BMI was estimated to be 0.20–0.28 at 6–8 years and 0.46–0.61 at 12–14 years. Differences in heritability were found at 12–14 years between same‐sex as compared to mixed‐sex pairs. The shared environmental effect was significant at 6–8 years but insignificant at 12–14 years. Differences in birth weight were significant in all groups at 6–8 years suggesting long‐term effects of the nonshared intrauterine environment; at 12–14 years, birth weight was no longer significant for girls.  相似文献   

16.
用太阳黑子和自相关因子预测杉木生长   总被引:4,自引:0,他引:4  
以太阳黑子和自相关因子为预测因子,采用逐步回归分析方法,建立杉木〔Cunninghamialanceolata(Lamb.)Hook.〕胸径生长的预测模型,结果表明前3年和8年的太阳黑子相对数及前5年杉木胸径生长的年轮指数值对杉木胸径生长存在正相关,前1年和4年的太阳黑子相对数及前6年和7年杉木胸径生长的年轮指数值对杉木胸径生长存在负相关,该模型的模拟精度和预测精度分别为9895%和9845%,且可提前5年进行预测,为林木生长预测提供了新的系统分析方法  相似文献   

17.
The time of fusion of the sternebrae with one another was studied in sterna obtained from cadavers of 806 male and 212 female adults and 66 male and 29 female children, on whom medicolegal postmortem examinations had been conducted by the senior author. Sterna of 31 neonates were also studied. The bones were X-rayed in an anteroposterior view and later macerated, cleaned, and dried. The sternebrae fused with one another from below upwards. In both sexes, the third and fourth sternebrae showed partial or commencement of fusion in a majority of specimens in the 0-5 years age group. Although the earliest complete fusion was seen in the 6-10 years age group, 100% specimens exhibited complete fusion in the 15-17 years age group. The earliest complete fusion between second and third sternebrae was observed in the 11-14 years age group in both sexes; it was seen in 100% of specimens in males over 25 years and in females over 30 years. The first and second segments showed earliest complete fusion in a boy of 16 years and in a girl of 18 years; 100% of specimens showed complete fusion in the males over 60 years and in the females over 30 years. A mesosternum showing complete fusion of all the sternebrae must be from a subject over 16 years of age if male and over 18 years if female. These observations are at variance with those of workers in Western countries. There has been no other report from India on this subject.  相似文献   

18.

Objectives

To estimate health expectancies based on measures that more fully cover the stages in the disablement process for the older Thais and examine gender differences in these health expectancies.

Methods

Health expectancies by genders using Sullivan’s method were computed from the fourth Thai National Health Examination Survey conducted in 2009. A total of 9,210 participants aged 60 years and older were included in the analysis. Health measures included chronic diseases; cognitive impairment; depression; disability in instrumental activities of daily living (IADL); and disability in activities of daily living (ADL).

Results

The average number of years lived with and without morbidity and disability as measured by multiple dimensions of health varied and gender differences were not consistent across measures. At age 60, males could expect to live the most years on average free of depression (18.6 years) and ADL disability (18.6 years) and the least years free of chronic diseases (9.1 years). Females, on the contrary, could expect to live the most years free of ADL disability (21.7 years) and the least years free of IADL disability (8.1 years), and they consistently spent more years with all forms of morbidity and disability. Finally, and for both genders, years lived with cognitive impairment, depression and ADL disability were almost constant with increasing age.

Conclusion

This study adds knowledge of gender differences in healthy life expectancy in the older Thai population using a wider spectrum of health which provides useful information to diverse policy audiences.  相似文献   

19.
Variation in male lifetime breeding success (LBS) is central to understanding selection, yet it has rarely been measured in natural populations of large mammals. Here, we first describe variation in the opportunity for selection in cohorts of Soay rams (Ovis aries) on the archipelago of St. Kilda, Scotland, that were born during years of varying population density. Variation in LBS is closely coupled with demography, as rams born in years of low density following population crashes enjoy greater LBS than do those born in high-density years. Paradoxically, the opportunity for selection was greatest in the largest cohorts, those born in years of high population density, owing to low juvenile breeding success and overwinter survival. Variation in longevity and the contribution of nonbreeders were the most important components of the total variance in LBS in cohorts born in years of high density, while variation in fecundity was more important in cohorts born in low-density years. The opportunity for sexual selection is thus stronger in cohorts born in low-density years, as many rams in these cohorts survive to compete for mates as adults in subsequent ruts. Variation in population density in the year of birth also influenced the intensity of selection. Individuals born in years of high population density underwent strong natural selection in favor of longer hindlimbs over their first winter. In contrast, in cohorts born in low-density years, there was no natural selection on hindlimb in the first year of life. Longer hindlimbs were associated with increased fecundity over the entire lifetime of individuals born in low-density years. Natural and sexual selection thus act on the same trait in the same direction at different life-history stages in Soay rams, depending on the population density experienced in the year of birth.  相似文献   

20.
Summary Significant correlations have been found between the response of potatoes, spring wheat, and to some extent canary grass to applications of potash and the number of rainless days during the growing period.The influence of applications of potash on the tuber yield of potatoes was higher, on the depression of the under-water-weight of the tubers was less, and on the K2O content of the tubers was lower, in dry years thereby indicating a decreased availability of soil potash in these years.The positive effect of applications of potash on the grain yield of wheat was highest in dry years. Ample applications of potash were found to depress yields in wet years which is also an indication of higher availability of potash in wet years.In the case of canary grass greater increases in the K2O content of the straw after applications of potash were found in wet years.No significant correlations were found in the case of bean crops.The influence of weather conditions on the response to potash is probably greatest during emergence and the early phases of growth. In later periods the influence is slight.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号