关于一类二次哈密尔顿系统在二次扰动下的极限环个数问题

本文研究了一类具有两个鞍点和一个中心的通用二次哈密尔顿向量场在二次扰动下的三参数开折，证明极限环的最小上界为２。     

A High Efficiency,High Throughput Unipolar Aerosol Charger for Nanoparticles

A novel aerosol charger has been developed, which has high efficiency and high throughput especially for nanometer particles in the size range of 3–50nm. Unipolar charging with high ion concentration and long charging time is used to obtain the high charging efficiency. High throughput is achieved by reducing particle loss within the charger. This is accomplished by directing ion flow and aerosol flow in the same direction and by the use of sheath air flow. The charger configuration is of a longitudinal design – the direction of aerosol stream and ion stream are flowing parallel along the longitudinal axis of the charger. The charger consists of four sections: the inlet zone, the ion production zone, the unipolar charging zone, and the exit zone. In the inlet and ion production zones, unipolar ions are generated using Po²¹⁰ radioactive sources with an electric field designed to separate the positive and negative ions, and to focus the selected unipolar ions into the core region of the charger. The ions with the selected polarity is then attracted to the charging zone by an uniform electric field created by a series of ring electrodes applied with a linear ramped voltage. Aerosol entering the charger is sheathed with clean gas flow in order to keep the aerosol in the core region. A novel exit design with a reversed electric field is incorporated in order to minimize the charged particles loss. The performance of the charger is first evaluated using computer simulation and then constructed for experimental validation. Experiment data have demonstrated that the charger achieves 90% and 95% charged-particles penetration efficiency and with 22% and 48% extrinsic charging efficiency at 3 and 5nm particle sizes, respectively. These performance data represent significant improvement, over a factor of 10, compared with the existing chargers.     

The Pfaffian Calabi–Yau, its Mirror, and their Link to the Grassmannian G(2,7)

The rank 4 locus of a general skew-symmetric 7 × 7 matrix gives the Pfaffian variety in P ²⁰ which is not defined as a complete intersection. Intersecting this with a general P ⁶ gives a Calabi–Yau manifold. An orbifold construction seems to give the 1-parameter mirror-family of this. However, corresponding to two points in the 1-parameter family of complex structures, both with maximally unipotent monodromy, are two different mirror-maps: one corresponding to the general Pfaffian section, the other to a general intersection of G(2,7) P ²⁰ with a P ¹³. Apparently, the Pfaffian and G(2,7) sections constitute different parts of the A-model (Kähler structure related) moduli space, and, thus, represent different parts of the same conformal field theory moduli space.     

低能He原子与Li_2分子碰撞散射截面理论计算

利用Fuchs势模型和密耦方法对He-Li2碰撞体系低能散射截面进行理论计算,研究了He-Li2碰撞体系的散射总截面随能量的变化、微分截面随角度的变化、分波截面随总角动量的变化以及与入射能量之间的关系,并总结了量子效应随入射能量的变化规律.     

The Paternity of the H-Bombs: Soviet-American Perspectives

There are major problems in the history of the American and Soviet hydrogen bombs. They are associated with the Teller-Ulam and Teller-Oppenheimer controversies, and the question of whether the design of the Soviet H-bomb was an independent conception. Because of the scarcity of documentary evidence, these problems have little chance of being settled if the histories of the two are considered separately within their national frameworks. Considered comparatively, however, they can help clarify these problems separately and convert them into different facets of this most important segment in the history of the thermonuclear age.The recently disclosed evidence on the history of the Soviet H-bomb, in particular, on Klaus Fuchs’s key idea of radiation implosion, validates Edward Teller’s view on the invention of the H-bomb, including his understatement of his own accomplishment and his concern about the benefits and head start that the Soviet H-bomb program could have gotten from Fuchs’s espionage. In addition, the Russian perspective on the realities of illusory worlds during the Cold War helps us see these illusory worldviews as largely responsible for the intensity of the H-bomb debate in the United States. Gennady Gorelik is a research fellow in the Center for Philosophy and History of Science at Boston University and is the author of biographies of Matvei Bronstein and Andrei Sakharov.     

On a generalization of a theorem of Erdős and Fuchs

Let A={a₁,a₂,…}(a₁<a₂<) be an infinite sequence of nonnegative integers, let k≥2 be a fixed integer and denote by r_k(A,n) the number of solutions of a_i1+a_i2++a_ik≤n. Montgomery and Vaughan proved that r₂(A,n)=cn+o(n^1/4) cannot hold for any constant c>0. In this paper, we extend this result to k>2.     

On the period function of a class of reversible quadratic centers

This paper is devoted to the study of the period function for a class of reversible quadratic system