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排序方式: 共有286条查询结果,搜索用时 15 毫秒
1.
Abdul Salam Jarrah Reinhard Laubenbacher Alan Veliz-Cuba 《Bulletin of mathematical biology》2010,72(6):1425-1447
For many biological networks, the topology of the network constrains its dynamics. In particular, feedback loops play a crucial
role. The results in this paper quantify the constraints that (unsigned) feedback loops exert on the dynamics of a class of
discrete models for gene regulatory networks. Conjunctive (resp. disjunctive) Boolean networks, obtained by using only the
AND (resp. OR) operator, comprise a subclass of networks that consist of canalyzing functions, used to describe many published
gene regulation mechanisms. For the study of feedback loops, it is common to decompose the wiring diagram into linked components
each of which is strongly connected. It is shown that for conjunctive Boolean networks with strongly connected wiring diagram,
the feedback loop structure completely determines the long-term dynamics of the network. A formula is established for the
precise number of limit cycles of a given length, and it is determined which limit cycle lengths can appear. For general wiring
diagrams, the situation is much more complicated, as feedback loops in one strongly connected component can influence the
feedback loops in other components. This paper provides a sharp lower bound and an upper bound on the number of limit cycles
of a given length, in terms of properties of the partially ordered set of strongly connected components. 相似文献
2.
David Savage Martin J. Barbetti William J. MacLeod Moin U. Salam Michael Renton 《Diversity & distributions》2010,16(2):288-299
Aim The aim of this study is to determine whether changes to the seasonal and circadian timing of propagule release can a have a significant effect on the area covered by resulting aerial dispersal. Location Western Australia. Methods Using the atmospheric pollution model (TAPM), an existing meso‐scale dispersal model, a range of release patterns was simulated and the resulting deposition compared. Comparisons were based on observations of deposition patterns and the calculated area of deposition. Results Small changes to the timing of propagule release were shown to significantly impact on the area experiencing deposition from the resulting aerial dispersal. Main conclusions Simulations performed in this study show that, for small propagules, changes to the timing of release can lead to alternate, clearly differentiable dispersal events. Small changes in both the seasonal and circadian patterns of release can have significant effects on the area that experiences deposition during the resulting dispersal event. This effect is particularly important at the landscape scale and when there is a need to quantify individual dispersal events. Predictive modelling of aerial dispersal needs to be undertaken with an understanding of the manner in which biological and environmental factors that affect the timing of propagule release can influence results. Results presented highlight the need to characterize the epidemiology of pathogenic organisms of importance to biosecurity as much as possible before they arrive. 相似文献
3.
Uttam Kumer Sarker Md. Romij Uddin Ahmed Khairul Hasan Md. Abdur Rahman Sarkar Md. Abdus Salam Md. Alamgir Hossain Eldessoky S. Dessoky Ismail A. Ismail 《Phyton》2022,91(8):1687-1708
In irrigated agricultural systems, nitrogen (N) and water are the vital resources for sustainability of the crop production in the modern era of climate change. The current study aimed to assess the impact of water and N management on the productivity of irrigated rice cultivars. In the context, a field observation was done at the research
farm of Bangladesh Agricultural University, Mymensingh, during dry seasons in consecutive two years (2018–2019 and 2019–2020). The experiments were set up following split-plot design assigning water management in
the main plots, nitrogen management in the sub-plots, and the cultivars were approved in the split-split plot with
three replications. After two years observation, it was revealed that rice cultivar Binadhan-8 gave the maximum
value of leaf area index, number effective tillers hill-1 and grains panicle-1 which lead to the higher grain yield
(GY). Substantial relationships were observed among the concentration of N, growth, total dry matter (TDM)
and N content, N uptake, N utilization effectiveness, and GY. However, with little exception, the Combined effect
of water and N, cultivars and water management were varied significantly for all parameters. Finally, the results of
the current study concluded that application of irrigation at 8 days after the disappearance of ponded water
and source of 105 kg N ha-1 from PU + Poultry manure are the best management approach for the excellent performance of rice cultivar Binadhan-8. 相似文献
4.
Muhammad T. Salam Pi-Chu Lin Sandrah P. Eckel W. James Gauderman Frank D. Gilliland 《PloS one》2015,10(12)
BackgroundExhaled nitric oxide (FeNO), a biomarker of airway inflammation, predicts asthma risk in children. We previously found that the promoter haplotypes in inducible nitric oxide synthase (NOS2) and exposure to residential traffic independently influence FeNO level. Because NOS2 is inducible by environmental exposures such as traffic-related exposure, we tested the hypothesis that common NOS2 promoter haplotypes modulate the relationship between residential traffic-related exposure and FeNO level in children.MethodsIn a cross-sectional population-based study, subjects (N = 2,457; 7–11 year-old) were Hispanic and non-Hispanic white children who participated in the Southern California Children’s Health Study and had FeNO measurements. For residential traffic, lengths of local roads within circular buffers (50m, 100m and 200m radii around homes) around the subjects’ homes were estimated using geographic information system (GIS) methods. We interrogated the two most common NOS2 promoter haplotypes that were found to affect FeNO level.ResultsThe relationship between local road lengths within 100m and 200m circular buffers and FeNO level varied significantly by one of the NOS2 promoter haplotypes (P-values for interaction between road length and NOS2 promoter haplotype = 0.02 and 0.03, respectively). In children who had ≤250m of local road lengths within 100m buffer around their homes, those with two copies of the haplotype had significantly lower FeNO (adjusted geometric mean = 11.74ppb; 95% confidence intervals (CI): 9.99 to 13.80) than those with no copies (adjusted geometric mean = 15.28ppb; 95% CI: 14.04 to 16.63) with statistically significant trend of lower FeNO level with increasing number of haplotype copy (P-value for trend = 0.002). In contrast, among children who had >250m of local road lengths within 100m buffer, FeNO level did not significantly differ by the haplotype copy-number (P-value for trend = 0.34). Similar interactive effects of this haplotype and local road lengths within 200m buffer on FeNO were also observed.ConclusionsHigher exposure from residential traffic nullifies the protective effect of one common NOS2 promoter haplotype on FeNO level. Regulation of traffic-related pollution may protect children’s respiratory health. 相似文献
5.
Asharaf Abdul Salam Ibrahim Elsegaey Rshood Khraif Abdullah AlMutairi Ali Aldosari 《PloS one》2015,10(5)
The Arab world, which consists of the 22 member states of the Arab League, is undergoing a rapid transition in demographics, including fertility, mortality, and migration. Comprising a distinctive geographic region spread across West Asia and North East Africa and unified by the Arabic language, these states share common values and characteristics despite having diverse economic and political conditions. The demographic lag (high fertility and low mortality) that characterizes the Arab world is unique, but the present trend of declining fertility, combined with the relatively low mortality, brings about significant changes in its population size. This research aimed to: (i) assess the population growth in the Arab world over 3 time periods, (ii) explore its components, and (iii) understand its public health impact. Data from the International Data Base (IDB) of the U.S. Census Bureau for 3 time periods (1992, 2002, and 2012) in 21 countries of the Arab world were analyzed by dividing them into four geographic sectors, namely, the Gulf Cooperation Council (GCC), West Asia, Maghreb, and the Nile Valley African Horn. The population of the Arab world has grown considerably due to both natural growth and migration. The immigration is pronounced, especially into resource-intensive GCC nations, not only from East Asian and Central African countries but also from resource-thrifty (limited-resource) Arab nations. The migrations within, as well as outside, the Arab world reveal an interesting demographic phenomenon that requires further research: migration flows and trends. However, the transformations in public health statistics related to mortality—the impact of demographic changes—depict a new era in the Arab world. 相似文献
6.
7.
8.
Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δεext/εmax) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)3(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)3(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)3(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)3(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δεext/εmax) corresponding to the 7F1 → 5D0 transition at 590 nm is 0.091 for [Eu(TFN)3(S-BINAPO)] and for [Yb(hfa)3(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the 2F7/2 → 2F5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)3(S-BINAPO)] and [Eu(TFN)3(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on. 相似文献
9.
Sumon Kumar Das Shahnawaz Ahmed Farzana Ferdous Fahmida Dil Farzana Mohammod Jobayer Chisti Daniel T. Leung Mohammad Abdul Malek Kaisar Ali Talukder Pradip Kumar Bardhan Mohammed Abdus Salam Abu Syed Golam Faruque Rubhana Raqib 《PloS one》2013,8(4)
Background
Shigellosis continues to be a public health challenge for developing countries, including Bangladesh. The aim of the study is to demonstrate recent changes in Shigella sero-groups and their geographical diversity.Methods
Data were extracted from data archive of four diarrheal disease surveillance systems. A 2% sub sample from urban Dhaka Hospital (2008–2011; n = 10,650), and 10% from urban Mirpur Treatment Centre (2009–2011; n = 3,585), were enrolled systematically; whereas, all patients coming from the Health and Demographic Surveillance System area in rural Matlab (2008–2011; n = 6,399) and rural Mirzapur (2010–2011; n = 2,812) were included irrespective of age, sex, and disease severity. A fresh stool specimen was collected for identification of Shigella spp. Of them, 315 (3%) were positive for Shigella in Dhaka, 490 (8%) from Matlab, 109 (3%) from Mirpur and 369 (13%) from Mirzapur and considered as analyzable sample size.Results
Among all Shigella isolates regardless of age, significant decreases in percentage of S. flexneri over time was observed in Mirpur (55→29%; p value of χ2-for trend = 0.019) and Mirzapur (59→47%; p = 0.025). A non-significant decrease was also seen in Dhaka (58→48%), while in Matlab there was a non-significant increase (73→81%). Similar patterns were observed among under-5 children at all sites. Emergence of S. sonnei was found in Dhaka (8→25%; p<0.001) and Mirpur (10→33%; p = 0.015), whereas it decreased in Mirzapur (32→23%; p = 0.056). The emergence of S. boydii was seen in all ages in Mirzapur [(3→28%; p<0.001); (3→27%; p<0.001)]. On the other hand, we saw non-significant percent reductions in S. boydii in Dhaka [overall (25→16%); under-5 (16→9%)]. Decreasing rates of Shigella dysenteriae were observed in Matlab, Mirpur and Mirzapur; whereas, in Dhaka it remained unchanged.Conclusion and Significance
Emergence of S. sonnei and S. boydii as important infectious diarrhea etiologies and variations in geographical diversity underscore the need for monitoring, with possible implications for vaccine development. 相似文献10.
Sumon Kumar Das Mohammod Jobayer Chisti Sayeeda Huq Mohammad Abdul Malek Lana Vanderlee Guddu Kaur Mohammed Abdus Salam Tahmeed Ahmed Abu Syed Golam Faruque Abdullah Al Mamun 《PloS one》2013,8(8)