Bunching Regions Research Articles

Information acquisition and countervailing incentives

In an agency model, we study how countervailing incentives, which lead to a “bunching” region of the optimal output schedule, are affected by costly information acquisition. We show that, when inducing the agent’s information acquisition, the principal increases the value of information to the agent by squeezing and moving the bunching region toward the expected state, and completely removes the region for sufficiently large information acquisition costs. When deterring information acquisition, the principal reduces the value of information to the agent by distorting the optimal output upward or downward. We also analyze the optimality of inducing or deterring information acquisition in the presence of countervailing incentives.

Experimental and theoretical studies on the surface morphology variation of a Ni substrate by graphene growth

As graphene grows on a metal substrate, step bunching and terrace formation occur due to thermodynamic instability. Variation in the terrace–step bunching morphology is caused by graphene–metal interaction. The mechanism for this morphological variation was elucidated in terms of the crystal lattice matching by the observation of step bunching formation using in situ scanning electron microscopy and analysis of the crystal orientation of the same microscopic field using electron backscatter diffraction. The cross-sectional structure was also observed using transmission electron microscopy (TEM). These combined methods enable a reliable analysis of the step bunching region. The lattice matching was also evaluated according to the 0-lattice theory. From the structural analysis using TEM and the application of the 0-lattice theory, the graphene-covered surface was confirmed to consist of good and poor lattice-matching regions. The steps ejected from the terrace region piled up in the poor lattice-matching region to form a low Miller index plane. It was concluded that step flow occurs on the good lattice-matching region and steps are piled up and arranged very closely on the poor matching region based on the lattice-matching evaluation by the 0-lattice theory.

Scaling characteristics of bunching and no bunching regions of semiconductor mounds

The equilibrations of initial surfaces bounded by envelope functions of the form h(0)-xα and consist of concentric circular monoatomic steps in two dimensions are studied in diffusion limited (DL) regime. Repulsive and attractive step interactions of the form w-2 and w-1, respectively, where w is the step separation are considered. For certain parameter values of repulsive and attractive interactions an initial surface either equilibrates to a flat surface or step bunching occurs on the surface. The bunching - no bunching regions of initial surfaces in a parameter space are investigated and scaling characteristics of bunching/no bunching regions are obtained numerically. The bunching and no bunching regions scales as x0/x0'γN/N'δ for a general surface where x0 is the initial range of the surface and N is the initial number of steps on the surface. For all forms of initial surface (α=1/2,1,2), we find that γ~1/2 and δ~1/6 and these results for scaling can be generalized which takes into account both the size and the slope (and curvature) of the initial surface as provided in the text. Our findings can directly be tested experimentally.

İtici ve Çekici Etkileşimlerin Basamaklı Yüzeyler Üzerinde Oluşan Basamak Gruplaşmaları Üzerindeki Etkileri

A surface which consists concentric circular monoatomic steps in two dimensions and below its roughening temperature is discussed. Repulsive and attractive interactions between steps on the surface are considered. It is supposed that repulsive and attractive interactions vary as and respectively. Here indicates the terrace width between monoatomic steps. The solution of diffusion equation is achieved in two- dimension by using polar coordinates. While the initial surface evolves, it is supposed that the local mass transfer exists because of the surface diffusion only under the step-flow model. In the study initial surfaces bounded by envelope functions which have the form of are dealt. In the case of only repulsive interaction between steps surfaces evolve properly. When both repulsive and attractive interactions between steps are accepted step bunchings separated by large flat terraces occur on the surface. While the surface morphology and the evolution of the height of surface in time are investigated for all surface structures in Diffusion-Limited (DL) regime, a parameter space of bunching and no bunching regions is derived.

The investigation of the morphology of a decaying conic mound in the presence of repulsive and attractive step interactions

A surface below its roughening temperature consisting of two dimensional concentric circular monoatomic steps is discussed under step-flow model. Both repulsive and attractive interactions between steps are considered where they vary as r-2 and r-1 respectively where r is the terrace width between steps. The diffusion equation is solved in two dimensional polar coordinates with the assumption that the local mass transfer occurs due to surface diffusion only during the evolution of the initial surface. The evolution of an initial surface which has a regular cone shape is considered. The morphology and the evolution of the height of surface as a function of time are analyzed in diffusion limited (DL) regime. While in the case of only repulsive interaction between steps surface evolves properly, when both repulsive and attractive interactions between steps are taken into account step bunchings separated by large flat terraces occur on the surface for some parameter values that depend on the relative strength of attractive and repulsive step interactions and the line tension of circular steps. A phase diagram separating the step bunching and no step bunching regions in parameter space is also obtained.

Doping Fluctuation and Defect Formation in Fast 4H-SiC Crystal Growth Using a High-Temperature Gas Source Method

This paper investigates the quality of 4H-SiC crystals grown at a very fast growth rate (> 2.5 mm/h) using a high-temperature gas source method. Differences in nitrogen doping efficiency were clarified in facet and step-flow regions. In case for growth in the macro-step bunching mode, doping fluctuation and void formation were observed in the macro-step bunching region. Propagation of threading screw dislocations (TSDs) in the grown crystal was also investigated by synchrotron X-ray topography.

Voting over selfishly optimal nonlinear income tax schedules

Majority voting over selfishly optimal nonlinear income tax schedules proposed by a continuum of individuals who have quasilinear-in-consumption preferences is considered. Röell (2012) has shown that individual preferences over these schedules are single-peaked. In this article, a complete characterization of selfishly optimal schedules is provided. Each selfishly optimal schedule has a bunching region in a neighborhood of the proposer's skill type, coincides with the maxi-max schedule below this region, and coincides with the maxi-min schedule above it. Using techniques introduced by Vincent and Mason (1967), the bunching region is identified by solving an unconstrained optimization problem. Information about the optimal schedules is used to provide a relatively simple proof of single-peakedness. The Condorcet-winning tax schedule features marginal tax rates that are negative (resp. positive) on the maxi-max (resp. maxi-min) part of the schedule except at the endpoints of the skill distribution where they are zero.

Temperature-induced transformation of electrochemically formed hydrous RuO2 layers over Ru(0001) model electrodes.

Hydrous RuO2 reveals excellent performance both as a supercapacitor and as a heterogeneous oxidation catalyst. Molecular understanding of these processes needs, however, a model system with preferably low structural and morphological complexity. This goal is partly accomplished here by using single crystalline Ru(0001) as a template on which hydrous RuO2 is electrochemically formed. The hydrous RuO2 layers on Ru(0001) and their temperature induced transformation under ultra high vacuum (UHV) conditions are comprehensively characterized by scanning electron microscopy and X-ray photoemission spectroscopy. The hydrous RuO2 layer grows with an intricate morphology governed by the presence of step bunching regions of the Ru(0001) surface. Upon annealing to 200 °C in UHV the hydrous RuO2 layer transforms mostly into flat metallic Ru islands and occasionally into (100) and (111) oriented RuO2 particles aligned along the high symmetry direction of Ru(0001).

Analysis on Generation of Localized Step-Bunchings on 4H-SiC(0001)Si Face by Synchrotron X-Ray Topography

Surface roughening regions running like scratches are often observed locally after epitaxy film grown on a very flat 4H-SiC wafer surfaces. We investigated generation mechanism of such roughening surface by using X-ray topography and confocal optical microscopy. We found that lattice defects were often introduced during CMP at local regions, and those local regions cannot be recognized by optical microscopy, since very flat surface can be observed. By H2 etching which is preprocess of epitaxy film growth, those lattice defects are almost etched off, but local rough surface consists of pits and step bunching regions appear like scratches, and those local pits and surface roughening regions grew up to step bunching during epitaxy film growth.

Atomic scale insights into the initial oxidation of Ru(0001) using atomic oxygen

With scanning tunneling microscopy (STM) we studied the initial oxidation of Ru(0001) using atomic oxygen (O′) as oxidizing agent at various sample temperatures and exposures. In contrast to the oxidation of Ru(0001) by molecular oxygen, exposure of atomic oxygen is remarkably corrosive even at temperatures as low as 300K. The initial oxidation process is accompanied by the formation of small three-dimensional Ru-oxide domains (clusters) primarily formed at single steps and the formation of larger clusters in the step bunching regions. With increasing O′ exposure both the corrosion at the step edges and the size of the produced clusters progress. The corrosion of the steps leads to the formation of a mobile Ru–O precursor species preceding the actual nucleation and growth of Ru–O clusters. From this study we conclude that the activation of molecular oxygen is the true bottleneck in the initial oxidation of Ru(0001) by O2 exposure. Applying a fixed O′ exposure in the oxidation of Ru(0001), the size of clusters at single steps depends critically on the preparation temperature: For lower temperatures the clusters are small, while the cluster size increases with increasing sample temperature up to 700K. At 700K the Ru-oxide cluster growth accelerated drastically. Anneal of Ru-oxide clusters to 700K for 30min in vacuum leads to thermal decomposition of the Ru-oxide clusters so that this process may modify also the oxidation process at 700K. Flat precursor domains of RuO2 are found to grow at 600K and 700K. At higher O′ exposures (80L of O′) small RuO2(110) domains are observed on a densely with clusters covered Ru(0001) surface. At a sample temperature of 800K corrosion of the Ru(0001) surface is substantial but almost no clusters are observed with STM.

Atomic Scale Insights into the Initial Oxidation of Ru(0001) Using Molecular Oxygen: A Scanning Tunneling Microscopy Study

The initial oxidation of Ru(0001) has been studied by scanning tunneling microscopy (STM) using molecular oxygen as the oxidizing agent. The initial oxidation process reveals a complex behavior in which three-dimensional RuO2 domains (clusters) are exclusively formed at multiple steps, and only few of these clusters are able to initiate the growth of flat RuO2 domains with its (110) orientation along the (0001) direction of the Ru substrate. The oxide formation requires a minimum temperature of 500 K and a minimum pressure of about 1 × 10–5 mbar of oxygen. Below 1 × 10–5 mbar, oxide growth is very slow, although even at pressure of 10–6 mbar oxidation in step bunching regions is occasionally observed. The modified nucleation and growth mode of Ru(0001) oxidation is corroborated by growing the oxide in two separate steps: Starting with oxygen exposure of 1.5 × 10–5 mbar of O2 for 960 s at a sample temperature of 680 K, RuO2 nuclei are preferably formed. Subsequently, the further growth of flat oxide domain...

A realistic cellular automata model of bus route system based on open boundary

In this article, a cellular automata model under opening boundary condition is proposed to simulate the characteristics of bus route. Through massive numerical simulations, phase diagram is obtained, which consists of four regions, including uniform region, insufficient capability region, bunching region, and serious congestion region. By studying the characteristics of each phase region and comparing the average speed and utilization, it is found that the position in uniform region or bunching region but near to the border of insufficient capability region is the best. Furthermore, phenomena of inhomogeneous bus stop situations are simulated, and resolution of driving shuttle buses is discussed. Comparing the simulation results with the real-life bus route investigation, some similarities are found.

Regular step arrays on silicon

Highly regular arrays of steps are produced on vicinal Si(111)7×7. The step edges are atomically straight for up to 2×104 lattice sites. The terraces are single domain, which produces a minimum kink width of 2.3 nm (half a 7×7 unit cell) and thus a high barrier for creating kinks. Criteria for obtaining optimum step arrays are established, such as the miscut [≈1° towards (1̄1̄2)] and an annealing sequence which passes through step bunching regions quickly.

Modified self-consistent nonlinear simulation of cyclotron autoresonance maser amplifiers

Since the electron cyclotron auto-resonance maser (CARM) is operated with the wave refractive index being very close to unity, a little variation of the refractive index in the CARM calculations might be crucial. Therefore, a modified self-consistent one-dimensional nonlinear model was developed by exactly setting the evolving wave refractive index and keeping all second-order terms to examine the inadequacy induced by the simplification of the earlier one-dimensional models. Comparisons of the numerical results obtained by the earlier models and the modified model for a CARM amplifier reveal that the inadequate relaxation of the limited azimuthal and axial bunching region for electrons to lose energy in the earlier models was the main reason for the overestimate of the linear gain and the saturated efficiency for the fast (the slow) wave branch with initial refractive index n0<1 (n0>1). However, the earlier model with fixed n0=1 is an excellent approximation whatever linear or saturated state is considered. The efficiency dependence of a CARM amplifier on some basic operating parameters was reexamined by the modified formulations.

Step bunching induced by 7 × 7 surface reconstruction on vicinal Si(111)

Faceting structure with step bunching and faceting dynamics induced by 7 × 7 surface reconstruction on vicinal Si(111) is studied by Monte Carlo simulation, with the use of the extended TSK (terrace step kink) model to take reconstruction into account. The attractive interaction between neighboring reconstruction units induces the faceting structure in the thermal equilibrium. The calculated local vicinal angle in the step bunching region becomes independent on the global vicinal angle, and it increases as the temperature decreases due to the suppression of the entropy effect. From the simulation of quenching, it is found that the reconstructed (111) facets arise from multiple nucleation of the critical size of reconstruction units and grow via both reducing of the step spacing in step bunches and the rearrangement of a step among step bunches. The calculated results qualitatively explain the observed behavior.

RHEED studies on vicinal Si(111), (100) surfaces.

The analysis of the reflection high energy electron diffraction (RHEED) patterns from the vicinal Si(111) (misoriented 1°-6° from [111] to [112]) and (100) surfaces (misoriented 0.4°-4° from [100] to [011]) clarified the differences in step structures on the two surfaces. On the vicinal Si(111) surface, wide terraces with a 7 7 structure and step bunching regions were observed; whereas on the vicinal Si (100) surface, a regular monolayer or bilayer step array was observed. Terrace width and multilayer step height on the vicinal Si (111) surface were estimated by RHEED, scanning electron microscopy, and transmission electron microscopy. The terrace width and multilayer step height were gathered as functions of misorientation angle.

Emittance studies at the Los Alamos national laboratory free electron laser

Recent emittance studies at the Los Alamos FEL have indicated several areas of concern in the linac and beamline feeding the wiggler. These studies included both experimental measurements and computer simulations. The beamline starts with a 5 A micropulse from the thermionic cathode in the gun. After bunching by velocity modulation and acceleration to 20 MeV in a 1300 MHz standing wave accelerator, the beam current is roughly 250 A. Final bunching to 800 A is performed in the nonisochronous bend that rotates the electrons onto the axis of the wiggler and the optical cavity.Four emittance growth mechanisms of special importance have been studied. First, a rapid growth of the electron beam's emittance immediately after the spherical gridded Pierce gun resulted, in part, from the long time required for our pulsing electronics to ramp the grid voltage up at the start and down at the end of the pulse, which created a pulse with a cosine-like current distribution as a function of time. The growth was compounded by the extremely small radial beam size (almost a waist) leaving the gun. In addition, we saw evidence of electrostatic charging of the insulators in the gun, reducing the quality of the electron beam further. Second the action of the solenoidal focusing fields in the low-voltage bunching region was studied, and criteria for a minimum emittance growth were established. Third, maximum misalignment angles and displacements for various elements of the beamline were calculated for the desired low emittance growth. Finally, emittance growth in the horizontal dimensions through the nonisochronous bend caused by varying energy depression on the particles due to longitudinal wake fields was both calculated and observed. In addition, we measured energy depressions caused by the wake fields generated by various other elements in the beamline. Strategies were developed to relieve the magnitude of these wake-field effects.

Mechanical Analog Computer for Solving the Axial Equations of Motion during Bunching in Linear Electron Accelerators

A mechanical analog computer is described which is suitable for the exploratory study of linear accelerator designs in the bunching region, at least in problems of the kind encountered in electron accelerators, where bunching is accomplished in comparatively short intervals and with relatively few phase oscillations. Particle phase is observed directly from a resolver; and particle momentum, particle velocity, and accelerating wave phase velocity are observed simultaneously as linear magnitudes whose relative change during calculation provides useful intuitive guidance in the choice of accelerator parameters. Some calculations are reported which were made with a rough apparatus capable of ∼5% accuracy.