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871.
Langevin equation is widely used to study the stochastic effects in molecular networks, as it often approximates well the
underlying chemical master equation. However, frequently it is not clear when such an approximation is applicable and when
it breaks down. This paper studies the simple Schnakenberg model consisting of three reversible reactions and two molecular
species whose concentrations vary. To reduce the residual errors from the conventional formulation of the Langevin equation,
the authors propose to explicitly model the effective coupling between macroscopic concentrations of different molecular species.
The results show that this formulation is effective in correcting residual errors from the original uncoupled Langevin equation
and can approximate the underlying chemical master equation very accurately. 相似文献
872.
For liquid Ti, it is difficult to achieve high undercooling because of its chemical reactivity; as a result, there is little information available on its properties and structure in the undercooled state. In this study, we investigate the density and structure, using molecular dynamics method, for the undercooling and superheating ranges 0-743 K and 0-457 K. The density increases quadratically for undercooling. At the melting temperature, the density is 4.14 g/cm3, and first and second temperature coefficients are obtained. The pair correlation functions and coordination numbers indicate that the short range degree of order becomes increasingly significant with increasing undercooling. 相似文献
873.
A box model of the interhemispheric thermohaline circulation (THC) in atmosphere-ocean for global climate is considered. By
using the generalized variational iteration method, the approximate solution of a simplified nonlinear model is studied. The
generalized variational iteration method is an analytic method, and the obtained analytic solution can be operated sequentially.
The authors also diversify qualitative and quantitative behaviors for corresponding physical quantities. 相似文献
874.
Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment, but
have rarely been reported in China. In the present study, Lake Sihailongwan in Northeast China was selected for detailed investigation
of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature. This study involved
a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for
both sediment and water at shallow and bottom depths (7 and 49 m below the lake surface, respectively), diatom separation
and purification of the trap sediments, and oxygen isotope measurement for diatom silica and lake water samples. The conditioned
experiment conducted herein demonstrated that the laboratory device, methods and techniques used in this study were capable
of generating reliable data for the typical oxygen isotope composition of diatom frustules. The data obtained revealed a prominent
linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth. The fractionation
coefficient was about −0.185‰/°C−0.238‰/°C in the temperature range of 3.6–24°C, which is consistent with the observations
from various aquatic environments and laboratory culture with different diatom taxa. These findings provide strong support
for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient
water. A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes,
suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples. Another
factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence
on the surface. Overall, the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes
in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions. 相似文献
875.
A surface plasmon resonance (SPR) technique was developed as an online screening method to identify effective adsorbents for the peptide NH2-Cys-Thr-Trp-Trp-COOH (CW-4). To validate the SPR technique, several linear polymers containing amino acid residues were synthesized as models of their corresponding adsorbents. SPR screening of all the linear polymers demonstrated that the linear polymer containing phenylalanine residues (PPhe) exhibited the highest affinity for CW-4 among the polymers tested. In accordance with the screening results from SPR, the adsorbent containing phenylalanine (APhe) exhibited the highest adsorption capacity for CW-4. An interesting observation was that the amounts of CW-4 adsorbed on 3 adsorbents were quite small, even though both SPR and isothermal titration calorimetry (ITC) experiments indicated the presence of interactions between CW-4 and the three polymers. A kinetic analysis performed using SPR technology suggested such a phenomenon was ascribed to the poor stability of the CW-4/polymer complexes; that is, CW-4 associates with the polymers quickly, but it also dissociated quickly. The combined results suggested that SPR was a promising tool to identify the optimal adsorbent for peptides, analyze the interactions contributing to adsorption and explain adsorption phenomena using polymer models. 相似文献
876.
用两种间隙式小型高压釜,在不同条件下考察了究州煤的加氢液化性能,並与联邦德国加氢原料煤Wester holt煤和美国的Illinois 6号煤进行了对比。试验结果表明:兖州煤具有较高的加氢反应活性,它略高于后一种煤,明显高于前一种煤。以循环油为溶剂,拜尔赤泥为催化剂,在氢初压9MPa,435℃和60min条件下,兖州煤的转化率达84%:油产率为46%。 相似文献
877.
本文报导用活性炭盒吸附方法对香港室内氡浓度的测量结果及其浓度分布规律。对室内氡浓度与建筑物表面氡析出率的关系进行了分析研究。证实室内空气中的氡主要来源于建材中的镭,而氡浓度水平只决定于室内建筑物表面氡的析出率及通风状况。 相似文献
878.
Homeobox gene expression correlated with the bifurcation process of limb cartilage development. 总被引:9,自引:0,他引:9
The complex architecture of the limb cartilage pattern probably develops by the sequential segmentation and branching process of precartilaginous cell condensation under the control of positional signalling provided by the zone of polarizing activity (anteroposterior) and the apical ectodermal ridge (proximodistal). This signalling is monitored and interpreted in the mesenchymal cells and induces the position-specific response of subsets of genes. Homeobox genes may be responsible for the interpretation of signalling. A correlation between limb pattern and expression domains of the homeobox genes in the upstream region of Hox/Chox-4 has been proposed. We have analysed the spatial expression pattern of the Chox-1 genes during development of chick limb buds. In contrast to genes in Hox/Chox-4 expressed coordinately along the anteroposterior axis, homeobox genes in Chox-1 have unique and mutually exclusive expression domains along the proximodistal axis. We report here that the expression domains of the Chox-1 genes are closely related to the segmental structure of cartilage along the proximodistal axis, whereas the expression domains of the Chox-4 genes are related to the cartilage branching pattern. 相似文献
879.
CD4+ and CD8+ T cells acquire specific lymphokine secretion potentials during thymic maturation. 总被引:10,自引:0,他引:10
Peripheral CD4+ and CD8+ T lymphocytes carry out different functions during immune reactions, partly as a result of the distinct patterns of lymphokines that they secrete upon stimulation. Using thymic cells from adult and newborn mice as well as from fetal organ cultures, we show here that this functional differentiation occurs inside the thymus and is completed during the single positive stage by the time the T-cell receptor becomes fully coupled to the intracellular activation pathways leading to lymphokine secretion. Surprisingly, CD4+8- thymocytes differ from their immediate progeny, naive peripheral CD4+ cells, in that they secrete a broader range of lymphokines, including interleukins 4, 5 and 10 and gamma-interferon, and more closely resemble immunologically experienced (activated or memory) CD4+ lymphocytes. 相似文献
880.
Type 1 diabetes in mice is linked to the interleukin-1 receptor and Lsh/Ity/Bcg genes on chromosome 1. 总被引:11,自引:0,他引:11
R J Cornall J B Prins J A Todd A Pressey N H DeLarato L S Wicker L B Peterson 《Nature》1991,353(6341):262-265
Human type 1 (insulin-dependent) diabetes is a common auto-immune disease of the insulin-producing beta cells of the pancreas which is caused by both genetic and environmental factors. Several features of the genetics and immunopathology of diabetes in nonobese diabetic (NOD) mice are shared with the human disease. Of the three diabetes-susceptibility genes, Idd-1 -3 and -4 that have been mapped in mice to date, only in the case of Idd-1 is there any evidence for the identity of the gene product: allelic variation within the murine immune response I-A beta gene and its human homologue HLA-DQB1 correlates with susceptibility, implying that I-A beta is a component of Idd-1. We report here the mapping of Idd-5 to the proximal region of mouse chromosome 1. This region contains at least two candidate susceptibility genes, the interleukin-1 receptor gene and Lsh/Ity/Bcg, which encodes resistance to bacterial and parasitic infections and affects the function of macrophages. 相似文献