Introduction: On March 11, 2020, the World Health Organization (WHO) declared that the entire World was overrun by a pandemic. Science has managed, in a short time, to characterize a new disease, sequence a new viral ...Introduction: On March 11, 2020, the World Health Organization (WHO) declared that the entire World was overrun by a pandemic. Science has managed, in a short time, to characterize a new disease, sequence a new viral genome, develop diagnostics, produce treatment protocols and establish the efficacy of drugs and vaccines in randomized controlled trials. In this paper we have dealt with different topics regarding the pandemic linked to COVID-19. Objectives: Aim of this paper is to compare the number of deaths attributable to COVID-19, that occurred in the different Italian macro-areas, in the different pandemic waves;we studied the trend of the curves relating to the proportion of deaths to the number of infected in the Italian macro-areas for the pandemic waves and analysed the mortality data, focusing on the Italian context and comparing it with other foreign countries. We examined the data regarding swabs, hospitalizations, home isolation, admissions to intensive care and deaths registered in pandemic period. Results: Geographically, Italy was differently affected by the pandemic. Northern Italy was the most affected area. In comparison with some foreign countries, Italy is one of the nations that paid the most in terms of deaths, due to: delays in understanding the seriousness of the emergency;the slow management in the tracking systems of contagions;the high number of hospitalizations;a corporate organizational system poorly planned. Conclusion: The years 2020 and 2021 have been dramatic and unprecedented. The year 2021 was the year of redemption, where, despite social, economic and health difficulties, thanks to mass vaccination, we were able to give a real strong response to the pandemic. Trust in science has led to a drastic decrease in mortality throughout the world.展开更多
This study explores the complex relationship between climate change and human development. The aim is to understand how climate change affects human development across countries, regions, and the global population. Vi...This study explores the complex relationship between climate change and human development. The aim is to understand how climate change affects human development across countries, regions, and the global population. Visual analytics were used to examine the impact of various climate change indicators on different aspects of human development. The study highlights the urgent need for climate change action and encourages policymakers to make decisive moves. Climate change adversely affects numerous aspects of daily life, leading to significant consequences that must be addressed through policy changes and global governance recommendations. Key findings include that regions with higher CO2 emissions experience a significantly higher incidence of life-threatening diseases compared to regions with lower emissions. Additionally, higher CO2 emissions correlate with consistent death rates. Increased pollution exposure is associated with a higher prevalence of life-threatening diseases and higher rates of malnutrition. Moreover, greater mineral depletion is linked to more frequent life-threatening diseases, suggesting that industrialization contributes to adverse health effects. These results provide valuable insights for policy and decision-making aimed at mitigating the impact of climate change on human development.展开更多
Grey system analysis method was used to study the correlation between water pollution in D Lake area and death rate of malignancy with death rate of malignancy as effect sequence and a variety of water pollution index...Grey system analysis method was used to study the correlation between water pollution in D Lake area and death rate of malignancy with death rate of malignancy as effect sequence and a variety of water pollution index as factor sequence. On the basis of grey correlation analysis, grey system predication model was established for death rate of malignancy in population in D Lake area including GM (1, N) model for death rate of malignancy [ MR (t+1) =(9.9987E 1+5.0001E 2 +10.8994E 3+1.1114E 4+165.1029) ·e -0.0070t -9.9987E 1-5.0001E 2-10.8994E 3-1.1114E 4 ] and GM (1, 1) model for related factors [ E 1(t+1) =52.1214-46.9468e -0.0058t , E 2(t+1) =4.6114-4.5664e 0.0015t, E 3(t+1) =1.1389-1.1212e 0.0065t , E 4(t+1) = 554.5867-549.8006e 0.0016t ], and the trend of death rate of malignancy from 2000 to 2010 was predicted.展开更多
Background: COVID-19 has had a major impact on all facets of life in the United States. Its devastating effects have resulted in the mobilization of major resources, both at the national, state, and individu...Background: COVID-19 has had a major impact on all facets of life in the United States. Its devastating effects have resulted in the mobilization of major resources, both at the national, state, and individual levels. This mobilization has resulted in vaccination, personal preventive measures, and new therapies to combat this illness. As a result, the rates of new infections, hospitalizations, and deaths have greatly diminished, minimizing the associated morbidity and mortality. Purpose: What has not been appreciated is that a more serious epidemic has continued unabated in the United States and the Western world. This article emphasizes the importance of a national effort to eradicate cardiovascular disease. Methods: Cardiovascular disease has caused more deaths than COVID-19 in almost all months since the COVID-19 epidemic was first recognized in December 2020. In fact, cardiovascular disease has caused more deaths than either all cancers combined or infections for the last two decades. The tragedy of this truth is that effective therapy is currently available for preventing and reversing cardiovascular disease at a very low cost. What is required is a concerted effort and commitment by all legislative and medical organizations to allocate the resources to abolish asymptomatic cardiovascular disease. Results: Recognition and mobilization of resources to combat this epidemic are much overdue with the resultant savings of lives and billions of dollars. It is past time for the medical establishment to support the national identification of asymptomatic cardiovascular disease and initiate treatment before patients become symptomatic with this deadly disease. Conclusion: The national experience with COVID-19 has demonstrated what can be accomplished when a national concerted effort is made to address a devastating medical epidemic. This commitment is not only feasible for cardiovascular disease, but is also necessary for the benefit of all people in the world.展开更多
Coal mine safety supervision system plays an important role in the coal mine safety management in China.However,the current supervision system is established on the basis of learning the advanced experience from other...Coal mine safety supervision system plays an important role in the coal mine safety management in China.However,the current supervision system is established on the basis of learning the advanced experience from other developed countries.It needs to be further improved according to national conditions.Therefore,the effectiveness of coal mine safety supervision system reform on three types of collieries are assessed by using time series analysis method based on comparative analysis of the supervision system before and after the reform in this paper.The regression results show that the structural reform is not conductive to the improvement of coal mine safety situation in the short term,but conductive significantly in the long term.Specifically,the effects in township coal mines are more significant than stateowned key coal mines in the long run,but negative effects also exist in the short term.The negative effects in state-owned key coal mines are non-significant compared with township coal mines.Moreover,the regression results are analyzed from the aspects of the closure policy of illegal small township coal mines at the end of 1998 and shortage of the new supervision system.Finally,the suggestions on improving the new supervision system are put forward based on the above analysis.展开更多
Abstract [Objective] The study was aimed to screen some Chinese medicines with good inhibitory effects on Neospora [Method] The crude extracts of the tested Chinese medicines were added to the Vero cells that were in...Abstract [Objective] The study was aimed to screen some Chinese medicines with good inhibitory effects on Neospora [Method] The crude extracts of the tested Chinese medicines were added to the Vero cells that were infected by Neospora canium. Then, cell growth was ob- served. The death rate and relative suppression rate of Neospora canium were determined by trypan blue staining. [ Result] The extracts of Scutel- laria baicalensis, Stemona japonica, Rhizoma gastrodiae, Coptis chinensis, Areca catechu and Brucea javanica had better inhibitory and killing effects on Neospora canium in vitro. [ Conclusion ] The study serves the treatment of neosporosis in clinic.展开更多
Background: As the prognosis of lung cancer (LC) patients improves, subcutaneously implanted central venous access device ports (CV-ports) have frequently been used for continuing chemotherapy (CC) or palliative care ...Background: As the prognosis of lung cancer (LC) patients improves, subcutaneously implanted central venous access device ports (CV-ports) have frequently been used for continuing chemotherapy (CC) or palliative care (PC). In this study, we examined the clinical course of LC patients with subcutaneously implanted CV-ports from the time of receiving chemotherapy to the endpoint of cancer. Materials and Methods: We retrospectively reviewed the clinical data and treatment history of LC patients with subcutaneously implanted CV-ports between June 2008 and November 2013 using clinical records and a pharmacy database. Results: Of the 132 LC patients with subcutaneously implanted CV-ports, 79 (59.8%) had CV-ports for CC (the CC group) and 53 (40.2%) had CV-ports for PC (the PC group). After CV-port implantation, LC patients in the CC group received a median of two regimens with a median of 6 cycles. The median survival time of patients in the CC and PC groups was 457 and 44 days, respectively. In the CC group, the median survival time of small cell and non-small cell LC patients was 342 (95% confidence interval, 235 - 627) and 563 (95% confidence interval, 368 - 728) days, respectively. Nine patients (6.8%) had their CV-ports removed due to complications. Forty (30.3%) of the 132 enrolled patients were referred for at-home PC. The at-home death rate observed among these 40 patients was 30.0% (N = 12). Conclusion: CV-ports may contribute to seamless oncological care.展开更多
Trophic properties of hematopoietic stem cells can influence the malignant growth alternatively to immune control. The annual growth of the body mass by age in adult populations of welfare countries used as the most c...Trophic properties of hematopoietic stem cells can influence the malignant growth alternatively to immune control. The annual growth of the body mass by age in adult populations of welfare countries used as the most common criterion of metabolic and proliferative tissue activity, and these data compared with death’ rate for malignant and somatic diseases in different age-groups of the same countries. The rate of physiologic involution of different cell populations in the lymphoid lineage by age also involved in correlations between the above parameters. A decrease in death rate for cancer and increase it’s for non-malignant diseases found in 60+ populations, which have the lowest physiological temp of renewal of lymphocytes number and mass of the body. The lack of both the thymus gland volume and proliferative activity of naive lymphocytes reduces physiological body mass renewal as well as the cancer death rate but enhances somatic death rate, opposing to anticancer immunity at large. A protumor character of the lymphopoietic system’s relation with malignancy seems more realistic than defending one.展开更多
本刊曾经多次刊登文章盛赞百年老药阿斯匹林。去年第10期就载文称阿斯匹林能抗前列腺癌,今又消息文称,阿斯匹林能减少心脏病人的死亡率。百年老药.青春犹在,至今仍能让人们不断发现其新的功效!本文除了传递了有关阿斯匹林的新信息之外...本刊曾经多次刊登文章盛赞百年老药阿斯匹林。去年第10期就载文称阿斯匹林能抗前列腺癌,今又消息文称,阿斯匹林能减少心脏病人的死亡率。百年老药.青春犹在,至今仍能让人们不断发现其新的功效!本文除了传递了有关阿斯匹林的新信息之外,以下观点,也让我们耳目一新: Even as we live and practice medicine in an era of high technology,we mustalways remember that widespread application of relatively low technology,efficacious(有效的;灵验的),and cost-effective(有成本效益的,值得花费的)therapies is often the way we help most of our patients and provide the greatestaggregate(集合的;聚合的)benefit for the broader population. 上句是否可以这样译: 即使我们生活、就医在一个高科技的时代,但是,我们仍必须一直牢记:科技含量相对较低却又广为应用的东西,其灵验而又具有成本效益的治疗常常是我们帮助大多数患者,为广大群众提供最大利益的途径。 上句的难点在于:如何理解provide the greatest aggregate benefit for thebroader population的主语。展开更多
Aims The neutral theory of biodiversity provides a powerful framework for modeling macroecological patterns and interpreting species assemblages.However,there remain several unsolved problems,including the effect of r...Aims The neutral theory of biodiversity provides a powerful framework for modeling macroecological patterns and interpreting species assemblages.However,there remain several unsolved problems,including the effect of relaxing the assumption of strict neutrality to allow for empirically observed variation in vital rates and the‘problem of time’—empirically measured coexistence times are much shorter than the prediction of the strictly neutral drift model.Here,we develop a nearly neutral model that allows for differential birth and death rates of species.This model provides an approach to study species coexistence away from strict neutrality.Methods Based on Moran’s neutral model,which assumes all species in a community have the same competitive ability and have identical birth and death rates,we developed a model that includes birth–death trade-off but excludes speciation.This model describes a wide range of asymmetry from strictly neutral to nearly neutral to far from neutral and is useful for analyzing the effect of drift on species coexistence.Specifically,we analyzed the effects of the birth–death trade-off on the time and probability of species coexistence and quantified the loss of biodiversity(as measured by Simpson’s diversity)due to drift by varying species birth and death rates.Important Findings We found(i)a birth–death trade-off operating as an equalizing force driven by demographic stochasticity promotes the coexistence of nearly neutral species.Species near demographic trade-offs(i.e.fitness equivalence)can coexist even longer than that predicted by the strictly neutral model;(ii)the effect of birth rates on species coexistence is very similar to that of death rates,but their compensatory effects are not completely symmetric;(iii)ecological drift over time produces a march to fixation.Trade-off-based neutral communities lose diversity more slowly than the strictly neutral community,while non-neutral communities lose diversity much more rapidly;and(iv)nearly neutral systems have substantially shorter time of coexistence than that of neutral systems.This reduced time provides a promising solution to the problem of time.展开更多
Suppose {X(t); t≥ 0} is a single birth process with birth rate qii+l (i 〉 0) and death rate qij (i 〉 j ≥ 0). It is proved in this paper that (i) if there exists aconstant c≥ 0 such that b(i)-a(i)+ci...Suppose {X(t); t≥ 0} is a single birth process with birth rate qii+l (i 〉 0) and death rate qij (i 〉 j ≥ 0). It is proved in this paper that (i) if there exists aconstant c≥ 0 such that b(i)-a(i)+ci is nondecreasing with respect to i and a(i) + u(i) - ci ≥ 0 (i≥ 0), then VarX(t)-EX(t)≥-X(0)e^-2ct,t≥0,or (ii) if there exists a constant u(i) - c≥ 0 such that b(i)-a(i)+ci is non-increasing with respect to i and a(i)+u(i)-ci≤0(i≥0),then VarX(t) - EX(t) ≤ -X(0)e^-2c,t ≥ 0 Hereb(i) = qii+1, a(0) = 0, a(i) = ∑j=^ijqii-j (i≥ 1), u(0) = u(1) =0 and u(i) = 1/2∑j=^ij(j - 1)qii-j (i ≥ 2) . This result covers the results for birth-death processes obtained in [7].展开更多
文摘Introduction: On March 11, 2020, the World Health Organization (WHO) declared that the entire World was overrun by a pandemic. Science has managed, in a short time, to characterize a new disease, sequence a new viral genome, develop diagnostics, produce treatment protocols and establish the efficacy of drugs and vaccines in randomized controlled trials. In this paper we have dealt with different topics regarding the pandemic linked to COVID-19. Objectives: Aim of this paper is to compare the number of deaths attributable to COVID-19, that occurred in the different Italian macro-areas, in the different pandemic waves;we studied the trend of the curves relating to the proportion of deaths to the number of infected in the Italian macro-areas for the pandemic waves and analysed the mortality data, focusing on the Italian context and comparing it with other foreign countries. We examined the data regarding swabs, hospitalizations, home isolation, admissions to intensive care and deaths registered in pandemic period. Results: Geographically, Italy was differently affected by the pandemic. Northern Italy was the most affected area. In comparison with some foreign countries, Italy is one of the nations that paid the most in terms of deaths, due to: delays in understanding the seriousness of the emergency;the slow management in the tracking systems of contagions;the high number of hospitalizations;a corporate organizational system poorly planned. Conclusion: The years 2020 and 2021 have been dramatic and unprecedented. The year 2021 was the year of redemption, where, despite social, economic and health difficulties, thanks to mass vaccination, we were able to give a real strong response to the pandemic. Trust in science has led to a drastic decrease in mortality throughout the world.
文摘This study explores the complex relationship between climate change and human development. The aim is to understand how climate change affects human development across countries, regions, and the global population. Visual analytics were used to examine the impact of various climate change indicators on different aspects of human development. The study highlights the urgent need for climate change action and encourages policymakers to make decisive moves. Climate change adversely affects numerous aspects of daily life, leading to significant consequences that must be addressed through policy changes and global governance recommendations. Key findings include that regions with higher CO2 emissions experience a significantly higher incidence of life-threatening diseases compared to regions with lower emissions. Additionally, higher CO2 emissions correlate with consistent death rates. Increased pollution exposure is associated with a higher prevalence of life-threatening diseases and higher rates of malnutrition. Moreover, greater mineral depletion is linked to more frequent life-threatening diseases, suggesting that industrialization contributes to adverse health effects. These results provide valuable insights for policy and decision-making aimed at mitigating the impact of climate change on human development.
基金ThisprojectwassupportedbyagrantfromtheNational"TheNinthFive YearPlan"ScienceandTechnologyKeyProjectofChina (No .96 9110 70 2 0 4 )
文摘Grey system analysis method was used to study the correlation between water pollution in D Lake area and death rate of malignancy with death rate of malignancy as effect sequence and a variety of water pollution index as factor sequence. On the basis of grey correlation analysis, grey system predication model was established for death rate of malignancy in population in D Lake area including GM (1, N) model for death rate of malignancy [ MR (t+1) =(9.9987E 1+5.0001E 2 +10.8994E 3+1.1114E 4+165.1029) ·e -0.0070t -9.9987E 1-5.0001E 2-10.8994E 3-1.1114E 4 ] and GM (1, 1) model for related factors [ E 1(t+1) =52.1214-46.9468e -0.0058t , E 2(t+1) =4.6114-4.5664e 0.0015t, E 3(t+1) =1.1389-1.1212e 0.0065t , E 4(t+1) = 554.5867-549.8006e 0.0016t ], and the trend of death rate of malignancy from 2000 to 2010 was predicted.
文摘Background: COVID-19 has had a major impact on all facets of life in the United States. Its devastating effects have resulted in the mobilization of major resources, both at the national, state, and individual levels. This mobilization has resulted in vaccination, personal preventive measures, and new therapies to combat this illness. As a result, the rates of new infections, hospitalizations, and deaths have greatly diminished, minimizing the associated morbidity and mortality. Purpose: What has not been appreciated is that a more serious epidemic has continued unabated in the United States and the Western world. This article emphasizes the importance of a national effort to eradicate cardiovascular disease. Methods: Cardiovascular disease has caused more deaths than COVID-19 in almost all months since the COVID-19 epidemic was first recognized in December 2020. In fact, cardiovascular disease has caused more deaths than either all cancers combined or infections for the last two decades. The tragedy of this truth is that effective therapy is currently available for preventing and reversing cardiovascular disease at a very low cost. What is required is a concerted effort and commitment by all legislative and medical organizations to allocate the resources to abolish asymptomatic cardiovascular disease. Results: Recognition and mobilization of resources to combat this epidemic are much overdue with the resultant savings of lives and billions of dollars. It is past time for the medical establishment to support the national identification of asymptomatic cardiovascular disease and initiate treatment before patients become symptomatic with this deadly disease. Conclusion: The national experience with COVID-19 has demonstrated what can be accomplished when a national concerted effort is made to address a devastating medical epidemic. This commitment is not only feasible for cardiovascular disease, but is also necessary for the benefit of all people in the world.
基金supported by the National Nat-ural Science Foundation Projects of China under Grant 71271206Innovation Project of Graduate Education for Jiangsu Province under Grant KYZZ_0377.
文摘Coal mine safety supervision system plays an important role in the coal mine safety management in China.However,the current supervision system is established on the basis of learning the advanced experience from other developed countries.It needs to be further improved according to national conditions.Therefore,the effectiveness of coal mine safety supervision system reform on three types of collieries are assessed by using time series analysis method based on comparative analysis of the supervision system before and after the reform in this paper.The regression results show that the structural reform is not conductive to the improvement of coal mine safety situation in the short term,but conductive significantly in the long term.Specifically,the effects in township coal mines are more significant than stateowned key coal mines in the long run,but negative effects also exist in the short term.The negative effects in state-owned key coal mines are non-significant compared with township coal mines.Moreover,the regression results are analyzed from the aspects of the closure policy of illegal small township coal mines at the end of 1998 and shortage of the new supervision system.Finally,the suggestions on improving the new supervision system are put forward based on the above analysis.
文摘Abstract [Objective] The study was aimed to screen some Chinese medicines with good inhibitory effects on Neospora [Method] The crude extracts of the tested Chinese medicines were added to the Vero cells that were infected by Neospora canium. Then, cell growth was ob- served. The death rate and relative suppression rate of Neospora canium were determined by trypan blue staining. [ Result] The extracts of Scutel- laria baicalensis, Stemona japonica, Rhizoma gastrodiae, Coptis chinensis, Areca catechu and Brucea javanica had better inhibitory and killing effects on Neospora canium in vitro. [ Conclusion ] The study serves the treatment of neosporosis in clinic.
文摘Background: As the prognosis of lung cancer (LC) patients improves, subcutaneously implanted central venous access device ports (CV-ports) have frequently been used for continuing chemotherapy (CC) or palliative care (PC). In this study, we examined the clinical course of LC patients with subcutaneously implanted CV-ports from the time of receiving chemotherapy to the endpoint of cancer. Materials and Methods: We retrospectively reviewed the clinical data and treatment history of LC patients with subcutaneously implanted CV-ports between June 2008 and November 2013 using clinical records and a pharmacy database. Results: Of the 132 LC patients with subcutaneously implanted CV-ports, 79 (59.8%) had CV-ports for CC (the CC group) and 53 (40.2%) had CV-ports for PC (the PC group). After CV-port implantation, LC patients in the CC group received a median of two regimens with a median of 6 cycles. The median survival time of patients in the CC and PC groups was 457 and 44 days, respectively. In the CC group, the median survival time of small cell and non-small cell LC patients was 342 (95% confidence interval, 235 - 627) and 563 (95% confidence interval, 368 - 728) days, respectively. Nine patients (6.8%) had their CV-ports removed due to complications. Forty (30.3%) of the 132 enrolled patients were referred for at-home PC. The at-home death rate observed among these 40 patients was 30.0% (N = 12). Conclusion: CV-ports may contribute to seamless oncological care.
文摘Trophic properties of hematopoietic stem cells can influence the malignant growth alternatively to immune control. The annual growth of the body mass by age in adult populations of welfare countries used as the most common criterion of metabolic and proliferative tissue activity, and these data compared with death’ rate for malignant and somatic diseases in different age-groups of the same countries. The rate of physiologic involution of different cell populations in the lymphoid lineage by age also involved in correlations between the above parameters. A decrease in death rate for cancer and increase it’s for non-malignant diseases found in 60+ populations, which have the lowest physiological temp of renewal of lymphocytes number and mass of the body. The lack of both the thymus gland volume and proliferative activity of naive lymphocytes reduces physiological body mass renewal as well as the cancer death rate but enhances somatic death rate, opposing to anticancer immunity at large. A protumor character of the lymphopoietic system’s relation with malignancy seems more realistic than defending one.
文摘本刊曾经多次刊登文章盛赞百年老药阿斯匹林。去年第10期就载文称阿斯匹林能抗前列腺癌,今又消息文称,阿斯匹林能减少心脏病人的死亡率。百年老药.青春犹在,至今仍能让人们不断发现其新的功效!本文除了传递了有关阿斯匹林的新信息之外,以下观点,也让我们耳目一新: Even as we live and practice medicine in an era of high technology,we mustalways remember that widespread application of relatively low technology,efficacious(有效的;灵验的),and cost-effective(有成本效益的,值得花费的)therapies is often the way we help most of our patients and provide the greatestaggregate(集合的;聚合的)benefit for the broader population. 上句是否可以这样译: 即使我们生活、就医在一个高科技的时代,但是,我们仍必须一直牢记:科技含量相对较低却又广为应用的东西,其灵验而又具有成本效益的治疗常常是我们帮助大多数患者,为广大群众提供最大利益的途径。 上句的难点在于:如何理解provide the greatest aggregate benefit for thebroader population的主语。
基金National Natural Science Foundation of China(D.Y.Z.and K.L.)Ministry of Science and Technology of China(D.Y.Z.and K.L.)+2 种基金Geomatics for Informed Decisions Network of Canada(F.H.)Natural Sciences and Engineering Research Council of Canada(F.L.)University of Alberta International(the China-UofA Joint Research Lab program).
文摘Aims The neutral theory of biodiversity provides a powerful framework for modeling macroecological patterns and interpreting species assemblages.However,there remain several unsolved problems,including the effect of relaxing the assumption of strict neutrality to allow for empirically observed variation in vital rates and the‘problem of time’—empirically measured coexistence times are much shorter than the prediction of the strictly neutral drift model.Here,we develop a nearly neutral model that allows for differential birth and death rates of species.This model provides an approach to study species coexistence away from strict neutrality.Methods Based on Moran’s neutral model,which assumes all species in a community have the same competitive ability and have identical birth and death rates,we developed a model that includes birth–death trade-off but excludes speciation.This model describes a wide range of asymmetry from strictly neutral to nearly neutral to far from neutral and is useful for analyzing the effect of drift on species coexistence.Specifically,we analyzed the effects of the birth–death trade-off on the time and probability of species coexistence and quantified the loss of biodiversity(as measured by Simpson’s diversity)due to drift by varying species birth and death rates.Important Findings We found(i)a birth–death trade-off operating as an equalizing force driven by demographic stochasticity promotes the coexistence of nearly neutral species.Species near demographic trade-offs(i.e.fitness equivalence)can coexist even longer than that predicted by the strictly neutral model;(ii)the effect of birth rates on species coexistence is very similar to that of death rates,but their compensatory effects are not completely symmetric;(iii)ecological drift over time produces a march to fixation.Trade-off-based neutral communities lose diversity more slowly than the strictly neutral community,while non-neutral communities lose diversity much more rapidly;and(iv)nearly neutral systems have substantially shorter time of coexistence than that of neutral systems.This reduced time provides a promising solution to the problem of time.
基金Supported by the National Natural Science Foundation of China(No.10471130,10371024)
文摘Suppose {X(t); t≥ 0} is a single birth process with birth rate qii+l (i 〉 0) and death rate qij (i 〉 j ≥ 0). It is proved in this paper that (i) if there exists aconstant c≥ 0 such that b(i)-a(i)+ci is nondecreasing with respect to i and a(i) + u(i) - ci ≥ 0 (i≥ 0), then VarX(t)-EX(t)≥-X(0)e^-2ct,t≥0,or (ii) if there exists a constant u(i) - c≥ 0 such that b(i)-a(i)+ci is non-increasing with respect to i and a(i)+u(i)-ci≤0(i≥0),then VarX(t) - EX(t) ≤ -X(0)e^-2c,t ≥ 0 Hereb(i) = qii+1, a(0) = 0, a(i) = ∑j=^ijqii-j (i≥ 1), u(0) = u(1) =0 and u(i) = 1/2∑j=^ij(j - 1)qii-j (i ≥ 2) . This result covers the results for birth-death processes obtained in [7].