scholarly journals Models of the interaction between electrons and polar optical phonons in nanostructures

2016 ◽  
Vol 55 (4) ◽  
Author(s):  
Brian K. Ridley
Keyword(s):  
Boundary Conditions ◽  
Linear Combination ◽  
Optical Phonons ◽  
Coupled Mode ◽  
Electrical Boundary Conditions ◽  
Optical Modes ◽  
Simple Models

A brief summary is made of the models used to describe the interaction between electrons and polar optical phonons in nanostructures. Simpler models are compared with the model that describes optical modes that satisfy both mechanical and electrical boundary conditions. Satisfaction of these boundary conditions requires modes to be a linear combination (LC) of longitudinal (LO), transverse (TO) and interface (IF) modes. The role of lattice dispersion turns out to be crucial. If accuracy is not essential, the simple models can provide adequate results, provided that coupled-mode and hot-phonon effects are absent.

Examining the Role of Free Carrier Concentration on the Phonon Lifetimes in GaN Using Raman Spectroscopy

2007 ◽  
Author(s):  
Thomas Beechem ◽  
Samuel Graham
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Performance ◽  
Uncertainty Relation ◽  
Free Carrier ◽  
Optical Phonons ◽  
Time Uncertainty ◽  
Longitudinal Phonon ◽  
Optical Modes ◽  
Carrier Interaction

The lifetimes of polar optical phonons are known to affect the electrical and thermal performance of gallium nitride (GaN) based devices. Utilizing the energy-time uncertainty relation, this study investigates these lifetimes using Raman spectroscopy for a series of samples having free carrier concentrations ranging from 1.24e18 to 3e17 cm−3. By measuring across the typical operating temperatures of these devices, the mechanisms responsible for scattering of 5 separate optical modes are elucidated. It is found that phonon-carrier interaction directly determines the lifetime of the polar optical A1(LO) mode while indirectly influencing the modes into which this longitudinal phonon decays, namely, E1 and A1(TO). Thus understanding the entire phonon energy cascade is vital both for management of the so called “hot phonon” effect as well as modeling of carrier-phonon interactions.

Determining preference for potential: The role of perceived economic mobility

2019 ◽  
Vol 47 (6) ◽  
pp. 1-8 ◽  
Author(s):  
Chen Yang ◽  
Shaochen Zhao
Keyword(s):  
Boundary Conditions ◽  
Economic Mobility ◽  
Individual Perceptions ◽  
Future Success ◽  
The Future

Although previous researchers have demonstrated that people often prefer potential rather than achievement when evaluating other people or products, few have focused on the boundary conditions on this effect. We proposed that the preference for potential would emerge when individuals’ perception of economic mobility was high, but the preference for achievement would emerge among individuals with low perceptions of economic mobility. Our results showed that people paid more attention to the future (vs. the present) when their perception of economic mobility was high; this, in turn, promoted more favorable reactions toward potential (vs. achievement). Thus, we suggested circumstances under which highlighting a person’s potential for future success is effective and those when it is not effective. Moreover, we revealed the important role of individual perceptions regarding economic mobility in driving this effect.

scholarly journals Charge algebra in Al(A)dSn spacetimes

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Adrien Fiorucci ◽  
Romain Ruzziconi
Keyword(s):  
Boundary Conditions ◽  
Dirichlet Boundary ◽  
Three Dimensional ◽  
Dirichlet Boundary Conditions ◽  
Boundary Structure ◽  
Asymptotic Symmetry ◽  
Renormalization Procedure ◽  
Field Dependent ◽  
Odd Dimensions

Abstract The gravitational charge algebra of generic asymptotically locally (A)dS spacetimes is derived in n dimensions. The analysis is performed in the Starobinsky/Fefferman-Graham gauge, without assuming any further boundary condition than the minimal falloffs for conformal compactification. In particular, the boundary structure is allowed to fluctuate and plays the role of source yielding some symplectic flux at the boundary. Using the holographic renormalization procedure, the divergences are removed from the symplectic structure, which leads to finite expressions. The charges associated with boundary diffeomorphisms are generically non-vanishing, non-integrable and not conserved, while those associated with boundary Weyl rescalings are non-vanishing only in odd dimensions due to the presence of Weyl anomalies in the dual theory. The charge algebra exhibits a field-dependent 2-cocycle in odd dimensions. When the general framework is restricted to three-dimensional asymptotically AdS spacetimes with Dirichlet boundary conditions, the 2-cocycle reduces to the Brown-Henneaux central extension. The analysis is also specified to leaky boundary conditions in asymptotically locally (A)dS spacetimes that lead to the Λ-BMS asymptotic symmetry group. In the flat limit, the latter contracts into the BMS group in n dimensions.

scholarly journals Mechanics of tubular helical assemblies: ensemble response to axial compression and extension

2021 ◽  
Author(s):  
Jacopo Quaglierini ◽  
Alessandro Lucantonio ◽  
Antonio DeSimone
Keyword(s):  
Boundary Conditions ◽  
Elastic Properties ◽  
Central Region ◽  
Mechanical Response ◽  
Different Boundary Conditions ◽  
Kirchhoff Rods ◽  
Model Versus ◽  
The Individual ◽  
Opposite Chirality

Abstract Nature and technology often adopt structures that can be described as tubular helical assemblies. However, the role and mechanisms of these structures remain elusive. In this paper, we study the mechanical response under compression and extension of a tubular assembly composed of 8 helical Kirchhoff rods, arranged in pairs with opposite chirality and connected by pin joints, both analytically and numerically. We first focus on compression and find that, whereas a single helical rod would buckle, the rods of the assembly deform coherently as stable helical shapes wound around a common axis. Moreover, we investigate the response of the assembly under different boundary conditions, highlighting the emergence of a central region where rods remain circular helices. Secondly, we study the effects of different hypotheses on the elastic properties of rods, i.e., stress-free rods when straight versus when circular helices, Kirchhoff’s rod model versus Sadowsky’s ribbon model. Summing up, our findings highlight the key role of mutual interactions in generating a stable ensemble response that preserves the helical shape of the individual rods, as well as some interesting features, and they shed some light on the reasons why helical shapes in tubular assemblies are so common and persistent in nature and technology. Graphic Abstract We study the mechanical response under compression/extension of an assembly composed of 8 helical rods, pin-jointed and arranged in pairs with opposite chirality. In compression we find that, whereas a single rod buckles (a), the rods of the assembly deform as stable helical shapes (b). We investigate the effect of different boundary conditions and elastic properties on the mechanical response, and find that the deformed geometries exhibit a common central region where rods remain circular helices. Our findings highlight the key role of mutual interactions in the ensemble response and shed some light on the reasons why tubular helical assemblies are so common and persistent.

scholarly journals Retrospectives Whatever Happened to the Cambridge Capital Theory Controversies?

2003 ◽  
Vol 17 (1) ◽  
pp. 199-214 ◽  
Author(s):  
Avi J Cohen ◽  
G. C Harcourt
Keyword(s):  
Business Cycle ◽  
Endogenous Growth ◽  
Path Dependence ◽  
Real Business Cycle ◽  
Capital Theory ◽  
Economic Process ◽  
The 1950S ◽  
Simple Models

We argue that the Cambridge capital theory controversies of the 1950s to 1970s were the latest in a series of still-unresolved controversies over three deep issues: explaining and justifying the return to capital; Joan Robinson's complaint that, due to path dependence, equilibrium is not an outcome of an economic process and therefore an inadequate tool for analyzing accumulation and growth; and the role of ideology and vision in fuelling controversy when results of simple models are not robust. We predict these important and relevant issues, latent in endogenous growth and real business cycle theories, will erupt in future controversy.

Rayleigh-Ritz Analysis of Vibrating Plates Based on a Class of Eigenfunctions

2009 ◽  
Author(s):  
Giuseppe Catania ◽  
Silvio Sorrentino
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Boundary Conditions ◽  
Linear Combination ◽  
Equation Of Motion ◽  
Extensive Literature ◽  
Shape Functions ◽  
Element Analysis ◽  
Vibrating Plates ◽  
General Basis

In the Rayleigh-Ritz condensation method the solution of the equation of motion is approximated by a linear combination of shape-functions selected among appropriate sets. Extensive literature dealing with the choice of appropriate basis of shape functions exists, the selection depending on the particular boundary conditions of the structure considered. This paper is aimed at investigating the possibility of adopting a set of eigenfunctions evaluated from a simple stucture as a general basis for the analysis of arbitrary-shaped plates. The results are compared to those available in the literature and using standard finite element analysis.

scholarly journals A first intercomparison of the simulated LGM carbon results within PMIP-carbon: role of the ocean boundary conditions

2021 ◽  
Author(s):  
Fanny Lhardy ◽  
Nathaelle Bouttes ◽  
Didier M. Roche ◽  
Ayako Abe-Ouchi ◽  
Zanna Chase ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ocean Boundary
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