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排序方式: 共有108条查询结果,搜索用时 78 毫秒
1.
Data are presented suggesting that birds have evolved eggs with shells containing different structures (numbers of mammillae per unit of inner eggshell surface area, i.e., mammillary densities) to cope up with different calcium requirements imposed by different growth rates and modes of development. Precocial bird species grow slowly, but have high mammillary density, while altricial bird species grow rapidly, but have low mammillary density. These results suggest an adaptation associated with growth rate and mode of development and show, moreover, that the mammillary layer is indicative of the breeding biology of the bird. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc. 相似文献
2.
Sigbjrn Grini Kostiantyn V. Sopiha Nils Ross Xin Liu Tor S. Bjrheim Charlotte Platzer‐Bjrkman Clas Persson Lasse Vines 《Liver Transplantation》2019,9(27)
Sodium and oxygen are prevalent impurities in kesterite solar cells. Both elements are known to strongly impact performance of the kesterite devices and can be connected to efficiency improvements seen after heat treatments. The sodium distribution in the kesterite absorber is commonly reported, whereas the oxygen distribution has received less attention. Here, a direct relationship between sodium and oxygen in kesterite absorbers is established using secondary ion mass spectrometry and explained by defect analyses within the density functional theory. The calculations reveal a binding energy of 0.76 eV between the substitutional defects NaCu and OS in the nearest neighbor configuration, indicating an abundance of Na? O complexes in kesterite absorbers at relevant temperatures. Oxygen incorporation is studied by introducing isotopic 18O at different stages of the Cu2ZnSnS4/Mo/soda‐lime glass baseline processing. It is observed that oxygen from the Mo back contact and contaminations during the sulfurization are primary contributors to the oxygen distribution. Indeed, unintentional oxygen incorporation leads to immobilization of sodium. This results in a strong correlation between sodium and oxygen, in excellent agreement with the theoretical calculations. Consequently, oxygen availability should be monitored to optimize postdeposition heat treatments to control impurities in kesterite absorbers and ultimately, the solar cell efficiency. 相似文献
3.
Pasture degradation in the central Amazon: linking changes in carbon and nutrient cycling with remote sensing 总被引:3,自引:0,他引:3
Gregory P. Asner † Alan R. Townsend‡ Mercedes M. C. Bustamante§ Gabriela B. Nardoto¶ Lydia P. Olander 《Global Change Biology》2004,10(5):844-862
The majority of deforested land in the Amazon Basin has become cattle pasture, making forest‐to‐pasture conversion an important contributor to the carbon (C) and climate dynamics of the region. However, our understanding of biogeochemical dynamics in pasturelands remains poor, especially when attempting to scale up predictions of C cycle changes. A wide range of pasture ages, soil types, management strategies, and climates make remote sensing the only realistic means to regionalize our understanding of pasture biogeochemistry and C cycling over such an enormous geographic area. However, the use of remote sensing has been impeded by a lack of effective links between variables that can be observed from satellites (e.g. live and senescent biomass) and variables that cannot be observed, but which may drive key changes in C storage and trace gas fluxes (e.g. soil nutrient status). We studied patterns in canopy biophysical–biochemical properties and soil biogeochemical processes along pasture age gradients on two important soil types in the central Amazon. Our goals were to (1) improve our understanding of the plot‐scale biogeochemical dynamics of this land‐use change, (2) evaluate the effects of pasture development on two contrasting soil types (clayey Oxisols and sandy Entisols), and (3) attempt to use remotely sensed variables to scale up the site‐specific variability in biogeochemical conditions of pasturelands. The biogeochemical analyses showed that (1) aboveground and soil C stocks decreased with pasture age on both clayey and sandy soils, (2) declines in plant biomass were well correlated with declines in soil C and with available phosphorus (P) and calcium (Ca), and (3) despite low initial values for total and available soil P, ecosystem P stocks declined further with pasture age, as did a number of other nutrients. Spectral mixture analysis of Landsat imagery provided estimates of photosynthetic vegetation (PV) and non‐photosynthetic vegetation (NPV) that were highly correlated with field measurements of these variables and plant biomass. In turn, the remotely sensed sum PV+NPV was well correlated with the changes in soil organic carbon and nitrogen, and available P and Ca. These results suggest that remote sensing can be an excellent indicator of not only pasture area, but of pasture condition and C storage, thereby greatly improving regional estimates of the environmental consequences of such land‐use change. 相似文献
4.
Cerebrospinal fluid biomarkers as a measure of disease activity and treatment efficacy in relapsing‐remitting multiple sclerosis 下载免费PDF全文
5.
This study investigated beliefs about climate change among Swedish secondary school students at the end of their K-12 education. An embedded mixed method approach was used to analyse 51 secondary school students’ written responses to two questions: (1) What implies climate change? (2) What affects climate? A quantitative analysis of the responses revealed that ‘Earth’, ‘human’ and ‘greenhouse effect’ were frequent topics regarding the first question, and ‘pollution’, ‘atmosphere’ and ‘Earth’ were frequent regarding the second. A qualitative analysis, based on a ‘conceptual elements’ framework, focused on three elements within responses: atmosphere (causes and/or consequences), Earth (causes and consequences) and living beings (humans and/or animals and their impacts on climate change). It revealed a predominantly general or societal, rather than individual, perspective underlying students’ responses to the second question. The ability to connect general/societal issues with individual issues relating to climate change could prompt students to reflect on the contributions of individuals towards climate change mitigation, thereby constituting a basis for decision-making to promote a sustainable environment. Although the students did not discuss climate changes from an individual perspective, their statements revealed their understanding of climate change as a system comprising various components affecting the overall situation. They also revealed an understanding of the difference between weather and climate. 相似文献
6.
7.
Haider MA Olander JE Arnold RF Marous DR McLamb AJ Thompson KC Woodruff WR Haugh JM 《Biomechanics and modeling in mechanobiology》2011,10(6):915-924
A phenomenological mixture model is presented for interactions between biosynthesis of extracellular matrix (ECM) constituents
and ECM linking in a scaffold seeded with chondrocytes. A system of three ordinary differential equations for average apparent
densities of unlinked ECM, linked ECM and scaffold is developed along with associated initial conditions for scaffold material
properties. Equations for unlinked ECM synthesis and ECM linking include an inhibitory mechanism where associated rates decrease
as unlinked ECM concentration in the interstitial fluid increases. Linking rates are proposed to depend on average porosity
in the evolving tissue construct. The resulting initial value problem contains nine independent parameters that account for
scaffold biomaterial properties and interacting mechanisms in the engineered system. Effects of parameter variations on model
variables are analyzed relative to a baseline case with emphasis on the evolution of solid phase apparent density, which is
often correlated with the compressive elastic modulus of the tissue construct. The new model provides an additional quantitative
framework for assessing and optimizing the design of engineered cell-scaffold systems and guiding strategies for articular
cartilage tissue engineering. 相似文献
8.
There are few diagnostic tools for chronic musculoskeletal pain as structural imaging methods seldom reveal pathological alterations. This is especially true for Whiplash Associated Disorder, for which physical signs of persistent injuries to the neck have yet to be established. Here, we sought to visualize inflammatory processes in the neck region by means Positron Emission Tomography using the tracer (11)C-D-deprenyl, a potential marker for inflammation. Twenty-two patients with enduring pain after a rear impact car accident (Whiplash Associated Disorder grade II) and 14 healthy controls were investigated. Patients displayed significantly elevated tracer uptake in the neck, particularly in regions around the spineous process of the second cervical vertebra. This suggests that whiplash patients have signs of local persistent peripheral tissue inflammation, which may potentially serve as a diagnostic biomarker. The present investigation demonstrates that painful processes in the periphery can be objectively visualized and quantified with PET and that (11)C-D-deprenyl is a promising tracer for these purposes. 相似文献
9.
Johansson CB Youssef S Koleckar K Holbrook C Doyonnas R Corbel SY Steinman L Rossi FM Blau HM 《Nature cell biology》2008,10(5):575-583
Transplanted bone marrow-derived cells (BMDCs) have been reported to fuse with cells of diverse tissues, but the extremely low frequency of fusion has led to the view that such events are biologically insignificant. Nonetheless, in mice with a lethal recessive liver disease (tyrosinaemia), transplantation of wild-type BMDCs restored liver function by cell fusion and prevented death, indicating that cell fusion can have beneficial effects. Here we report that chronic inflammation resulting from severe dermatitis or autoimmune encephalitis leads to robust fusion of BMDCs with Purkinje neurons and formation of hundreds of binucleate heterokaryons per cerebellum, a 10-100-fold higher frequency than previously reported. Single haematopoietic stem-cell transplants showed that the fusogenic cell is from the haematopoietic lineage and parabiosis experiments revealed that fusion can occur without irradiation. Transplantation of rat bone marrow into mice led to activation of dormant rat Purkinje neuron-specific genes in BMDC nuclei after fusion with mouse Purkinje neurons, consistent with nuclear reprogramming. The precise neurological role of these heterokaryons awaits elucidation, but their frequency in brain after inflammation is clearly much higher than previously appreciated. 相似文献
10.
Lars B Dahlin Kristina Erichs Charlotte Andersson Catharina Thornqvist Clas Backman Henrik Düppe Pelle Lindqvist Marianne Forslund 《Journal of brachial plexus and peripheral nerve injury》2007,2(1):1-5