MANY-ELECTRON SCREENING EFFECT ON THE STABILITY CRITERIA OF AN ALL-COUPLING OPTICAL BIPOLARON IN TWO DIMENSIONS

1993 ◽  
Vol 07 (16) ◽  
pp. 1071-1081 ◽  
Author(s):  
ASHOK CHATTERJEE ◽  
SHREEKANTHA SIL

We perform an all-coupling variational calculation to study the many-electron screening effect on the stability criteria of a two-dimensional singlet optical bipolaron. We also show how the effective mass and the size of the bipolaron would depend on the carrier concentration.

1993 ◽  
Vol 07 (28) ◽  
pp. 4763-4781 ◽  
Author(s):  
ASHOK CHATTERJEE ◽  
SHREEKANTHA SIL

A variational calculation is performed to obtain the stability criteria, effective mass and the size of a large optical singlet bipolaron for the entire range of the coupling parameters in both two and three dimensions. It is shown that the bipolaron binding is stronger in thin films than in bulk crystals. It is suggested that Cu 2 O and TiCl in the form of thin films might exhibit bipolaronic effects.


Author(s):  
T. R. Camp ◽  
I. J. Day

This paper presents a study of stall inception mechanisms a in low-speed axial compressor. Previous work has identified two common flow breakdown sequences, the first associated with a short lengthscale disturbance known as a ‘spike’, and the second with a longer lengthscale disturbance known as a ‘modal oscillation’. In this paper the physical differences between these two mechanisms are illustrated with detailed measurements. Experimental results are also presented which relate the occurrence of the two stalling mechanisms to the operating conditions of the compressor. It is shown that the stability criteria for the two disturbances are different: long lengthscale disturbances are related to a two-dimensional instability of the whole compression system, while short lengthscale disturbances indicate a three-dimensional breakdown of the flow-field associated with high rotor incidence angles. Based on the experimental measurements, a simple model is proposed which explains the type of stall inception pattern observed in a particular compressor. Measurements from a single stage low-speed compressor and from a multistage high-speed compressor are presented in support of the model.


Author(s):  
Yakun Xie ◽  
Xiaojian Zhang ◽  
Sijie Yan ◽  
Han Ding

This paper presents an effective method to improve the computational efficiency of stability prediction in milling based on the two-dimensional bisection method. Contrasted with the traditional semi-analytical time-domain methods, the proposed method for stability prediction only checks the eigenvalues of less nodes on the parameter plane with the two-dimensional bisection method, so that, the computational efficiency of stability can be improved. The novel method for milling stability calculation is comprised of the bisection method in two dimensions and the numerical integration method [NIM], its validity is testified by the comparison of the stability diagram and computation time in contrast to the NIM. The computation demonstrates that the calculated stability diagram by using the presented method agrees well with the result of NIM, while the computation time of the stability diagram can reduce to 1/4 to 3/4 compared with the original methods.


2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040018
Author(s):  
Henri Epstein ◽  
Ugo Moschella

We explore the interplay between quantization, local commutativity and the analyticity properties of the two-point functions of a quantum field in a non trivial topological cosmological background in the example of the two-dimensional de Sitter manifold and its double covering. The global topological differences make the many of the well-known features of de Sitter quantum field theory disappear. In particular there is nothing like a Bunch-Davies vacuum and there are no [Formula: see text]-invariant fields whose mass is less than 1/2.


Fractals ◽  
2008 ◽  
Vol 16 (04) ◽  
pp. 367-378 ◽  
Author(s):  
CARLOS E. PUENTE ◽  
ANDREA CORTIS ◽  
BELLIE SIVAKUMAR

The construction of a host of interesting patterns over one and two dimensions, as transformations of multifractal measures via fractal interpolating functions related to simple affine mappings, is reviewed. It is illustrated that, while space-filling fractal functions most commonly yield limiting Gaussian distribution measures (bells), there are also situations (depending on the affine mappings' parameters) in which there is no limit. Specifically, the one-dimensional case may result in oscillations between two bells, whereas the two-dimensional case may give rise to unexpected circle map dynamics of an arbitrary number of two-dimensional circular bells. It is also shown that, despite the multitude of bells over two dimensions, whose means dance making regular polygons or stars inscribed on a circle, the iteration of affine maps yields exotic kaleidoscopes that decompose such an oscillatory pattern in a way that is similar to the many cases that converge to a single bell.


2018 ◽  
Vol 848 ◽  
pp. 256-287 ◽  
Author(s):  
N. C. Hurst ◽  
J. R. Danielson ◽  
D. H. E. Dubin ◽  
C. M. Surko

The dynamics of two-dimensional (2-D) ideal fluid vortices is studied experimentally in the presence of an irrotational strain flow. Laboratory experiments are conducted using strongly magnetized pure electron plasmas, a technique which is made possible by the isomorphism between the drift–Poisson equations describing plasma dynamics transverse to the field and the 2-D Euler equations describing an ideal fluid. The electron plasma system provides an excellent opportunity to study the dynamics of a 2-D Euler fluid due to weak dissipation and weak 3-D effects, simple diagnosis and precise control. The plasma confinement apparatus used here was designed specifically to study vortex dynamics under the influence of external flow by applying boundary conditions in two dimensions. Additionally, vortex-in-cell simulations are carried out to complement the experimental results and to extend the parameter range of the studies. It is shown that the global dynamics of a quasi-flat vorticity profile is in good quantitative agreement with the theory of a piecewise-constant elliptical patch of vorticity, including the equilibria, dynamical orbits and stability properties. Deviations from the elliptical patch theory are observed for non-flat vorticity profiles; they include inviscid damping of the orbits and modified stability limits. The dependence of these phenomena on the flatness of the initial profile is discussed. The relationship of these results to other theoretical, numerical and experimental studies is also discussed.


1989 ◽  
Vol 111 (4) ◽  
pp. 471-478 ◽  
Author(s):  
Xi-Ding Qiu ◽  
Shin-Min Song

The performance of a legged system is closely related to the adopted gait. Among the many available gaits, the wave gait possesses the optimum stability [1–3] and has been applied to walking on perfectly smooth terrain. The follow-the-leader (FTL) gait has the least demands for foothold selection and is the most suitable for walking on rough terrain [14]. In this paper, a strategy of wave gait which enables a hexapod to traverse two-dimensional, rough terrain is developed. This strategy applies a quasi FTL mode in walking and hence it has the advantages of both wave gait (optimum stability) and FTL gait (easy control on rough terrain). During walking, the legs move according to the wave gait and the two forelegs are adjusted to avoid forbidden areas. The maximum foot adjustment is determined by the current foot positions and the foot positions in the following one or two step(s). In order to improve the stability, different methods of foot adjustments and body adjustments are evaluated and integrated into the strategy. Finally, this strategy is verified by using computer graphics simulations.


2019 ◽  
Vol 22 (3) ◽  
pp. 325-346 ◽  
Author(s):  
Swati Srivastava

AbstractThis article presents social construction as a research framework, rather than an explanatory theory in constructivism, to outline different research strategies. Varieties of constructivism thus far conceived in international relations prefer cleavages where scholars are regarded as thin/thick, conventional/critical, or mainstream/radical. In contrast, I introduce a new landscape of social construction to show unique mechanisms for socially constructing international politics. The new landscape varies on two dimensions. The first, source of socialization, asks whether scholars treat social context as fixed in discrete, observable forms or as fluid in indiscrete, shifting arrangements. The second dimension, focus of analysis, asks whether scholars primarily study social structures, social subjects, or some interaction of the two. The dimensions make visible a multitude of research strategies with implications for the stability of social processes and the potential for causal analysis. Moreover, within this landscape, the article focuses on four processes of social construction—aggregating, assembling, internalizing, and performing—as seen inductively through examining prominent constructivist projects. Disaggregating the many processes avoids the misuse of social construction as a catchall mechanism. Finally, the article applies the select processes to the social construction of international norms to better grasp the relative payoffs of constructivist IR scholarship for research and teaching.


2009 ◽  
Vol 23 (20n21) ◽  
pp. 4186-4197
Author(s):  
S. V. KRAVCHENKO

Strong electron-electron interactions in dilute two-dimensional electron systems in silicon lead to Pauli spin susceptibility growing critically at low electron densities. This effect originates from renormalization of the effective mass rather than the g-factor. The relative mass enhancement is system- and disorder-independent, which suggests that it is determined by electron-electron interactions only.


2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Xue-Yang Song ◽  
Chong Wang ◽  
Ashvin Vishwanath ◽  
Yin-Chen He

Abstract Quantum magnets provide the simplest example of strongly interacting quantum matter, yet they continue to resist a comprehensive understanding above one spatial dimension. We explore a promising framework in two dimensions, the Dirac spin liquid (DSL) — quantum electrodynamics (QED3) with 4 Dirac fermions coupled to photons. Importantly, its excitations include magnetic monopoles that drive confinement. We address previously open key questions — the symmetry actions on monopoles on square, honeycomb, triangular and kagome lattices. The stability of the DSL is enhanced on triangular and kagome lattices compared to bipartite (square and honeycomb) lattices. We obtain the universal signatures of the DSL on triangular and kagome lattices, including those of monopole excitations, as a guide to numerics and experiments on existing materials. Even when unstable, the DSL helps unify and organize the plethora of ordered phases in correlated two-dimensional materials.


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