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81.
A new slow pulsed positron beam, including a positron source, a moderator, a chopper, a pre-buncher, a main-buncher and a sample chamber, etc, has been installed and tested. It is necessary to simulate the acceleration, transportation and space focusing of positrons to meet the needs of beam debugging and further positron annihilation experiments. The result from SIMION simulations shows that the radius of the focused positron beam is less than 5 mm, which is further confirmed in our practical debugging process. 相似文献
82.
83.
Details of the active ways to suppress Closed Orbit Distortion (COD), including bending magnet sorting and survey and alignment of the magnets, are discussed based on the studies of affections to the COD by the bending magnet field error and the misalignment of quadrupoles. The closed orbit correction and the Slow Orbit Feed Back (SOFB) system for the SSRF storage ring are presented in this paper. With these available methods, better results were obtained during the commissioning period with 3 GeV beam energy. 相似文献
84.
85.
We shall discuss about the scientific motivation and construction of a 7×7 BaF2 crystal array at Variable Energy Cyclotron Centre, Calcutta. This detector would be used to measure high energy γ-ray photons from GDR decay and proton-neutron bremsstrahlung reactions at the present 88″ cyclotron and upcoming superconducting
cyclotron at VECC, Calcutta. This detector can also be used to measure photons from quark-gluon plasma at the relativistic
heavy ion collider (RHIC) in USA. 相似文献
86.
正电子湮没技术是一种研究材料的微观缺陷和相变的灵敏工具,在通常的正电子谱仪中,正电子能量为MeV量级,在样品中注入深度比较学(-100μm),主要研究材料体内的平均缺陷密度,慢正电子束方法把正电子的能量降低为keV量级(而且可以调节),注入比较浅(-μm),所以是研究表面缺陷的探测手段,正电子慢化体是产生慢正电子的关键设备,对其研究有重要意义,文章综述了慢化体研究的历史和现状,从物理概念出发介绍使正电子慢化的四种可能方法和当今慢化体的五种几何排列方法,其中应用最广泛的是钨慢化体和百叶窗式的排列方式,效率最高的是惰性气体固体慢化体,而加电场慢化体是有待开发的高效慢化体。 相似文献
87.
88.
Pot experiments were conducted to study the efficacy of a slow sulfur-releasing fertilizer, sulfur glass fritz (SGF 1), on
growth, photosynthesis, and sulfur, and nitrogen assimilation potentials of brown mustard (Brassica juncea L. Czern. & Coss. cv. Pusa Jaikisan). Growth as indicated by biomass accumulation slowed down in response to the application
of sulfur glass fritz. A similar trend was observed in the case of photosynthesis rate. The activity of two marker enzymes,
ATP-sulfurylase and nitrate reductase, showed very low levels of activity, indicating poor assimilation of sulfur and nitrogen
by the plant under sulfur glass fritz. It is therefore concluded that the release of sulfur by sulfur glass fritz is too slow
and that the initial nonavailability of sulfur to the plants could lead to suboptimization of both sulfur- and nitrogen-assimilating
enzymes. These factors may contribute to low rates of photosynthesis and poor growth. 相似文献
89.
Desynchronization of large scale delayed neural networks 总被引:2,自引:0,他引:2
Yuming Chen Ying Sue Huang Jianhong Wu 《Proceedings of the American Mathematical Society》2000,128(8):2365-2371
We consider a ring of identical neurons with delayed nearest neighborhood inhibitory interaction. Under general conditions, such a network has a slowly oscillatory synchronous periodic solution which is completely characterized by a scalar delay differential equation with negative feedback. Despite the fact that the slowly oscillatory periodic solution of the scalar equation is stable, we show that the associated synchronous solution is unstable if the size of the network is large.
90.
Neurons at rest can exhibit diverse firing activities
patterns in response to various external deterministic and random
stimuli, especially additional currents. In this paper, neuronal
firing patterns from bursting to spiking, induced by additional
direct and stochastic currents, are explored in rest states
corresponding to two values of the parameter $V_{\rm K}$ in the Chay
neuron system. Three cases are considered by numerical simulation
and fast/slow dynamic analysis, in which only the direct current
or the stochastic current exists, or the direct and
stochastic currents coexist. Meanwhile, several important bursting
patterns in neuronal experiments, such as the period-1
``circle/homoclinic" bursting and the integer multiple
``fold/homoclinic" bursting with one spike per burst, as well as
the transition from integer multiple bursting to period-1
``circle/homoclinic" bursting and that from stochastic
``Hopf/homoclinic" bursting to ``Hopf/homoclinic" bursting, are
investigated in detail. 相似文献