Physical Background

2010 ◽  
pp. 3-9 ◽  
Author(s):  
Thorsten R. C. Johnson ◽  
Willi A. Kalender
Keyword(s):  
Physical Background

Formation of laser-induced periodic surface structures on different materials: fundamentals, properties and applications

2020 ◽  
Vol 9 (1-2) ◽  
pp. 11-39 ◽  
Author(s):  
Stephan Gräf
Keyword(s):  
Friction And Wear ◽  
Review Paper ◽  
Laser Wavelength ◽  
Single Step ◽  
Surface Structures ◽  
Direct Writing ◽  
Periodic Surface ◽  
Experimental Approaches ◽  
Ordered Nanostructures ◽  
Physical Background

AbstractThe use of ultra-short pulsed lasers enables the fabrication of laser-induced periodic surface structures (LIPSS) on various materials following a single-step, direct-writing technique. These specific, well-ordered nanostructures with periodicities in the order of the utilised laser wavelength facilitate the engineering of surfaces with functional properties. This review paper discusses the physical background of LIPSS formation on substrates with different material properties. Using the examples of structural colours, specific wetting states and the reduction of friction and wear, this work presents experimental approaches that allow to deliberately influence the LIPSS formation process and thus tailor the surface properties. Finally, the review concludes with some future developments and perspectives related to forthcoming applications of LIPSS-based surfaces are discussed.

scholarly journals The Non-Stationary Metal Vapour Arc

1973 ◽  
Vol 28 (3-4) ◽  
pp. 428-437
Author(s):  
G. Ecker
Keyword(s):  
Residence Time ◽  
Critical Currents ◽  
Theoretical Studies ◽  
Velocity Dependence ◽  
Metal Vapour ◽  
Energy Characteristics ◽  
Upper Limit ◽  
Physical Background ◽  
Experimental And Theoretical Studies ◽  
Spot Motion

AbstractThe motion is depicted as a sequence of steps of a finite residence time.The spot motion affects essentially only the energy characteristics Te which in comparison to the stationary characteristics Tes are shifted to smaller values. Hereby the critical currents I0, I1 are raised in comparison to the corresponding stationary limits I0s, I1s. Particularly attractive are the phenomena found in connection with the dependence of the spot velocity ʋ on the spot current I. If the spot velocity increases with the spot current stronger than ʋ ∞ I1/2 then the E-diagram reveals the existence of an upper limit lu for the spot current. This result can be used to explain qualitatively the experimentally observed phenomena of "spot multiplicity" and “spot extinction”.Quantitative conclusions are obstructed by the lack of knowledge about the velocity dependence on the spot current, ʋ(I). Experimental and theoretical studies to provide a better understanding of the physical background and the analytical laws describing the motion of the cathode spots are urgently needed.

Cobaltites as perspective thermoelectrics

2005 ◽  
Vol 886 ◽  
Author(s):  
Jiri Hejtmánek ◽  
Miroslav Veverka ◽  
Karel Knižek ◽  
Hiroyuki Fujishiro ◽  
Sylvie Hebert ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Phonon Scattering ◽  
Configurational Entropy ◽  
Energy Difference ◽  
Charge Carriers ◽  
Material Research ◽  
Cobalt Ions ◽  
Similar Materials ◽  
Physical Background ◽  
Open Question

AbstractThe recent material research of mixed cobalt oxides is strongly motivated by the potential of some of them to be used as chemically stable high temperature thermoelectric material. This fact together with both the theoretical and experimental ambitions to fulfill the severe criteria needed for efficient thermoelectric conversion intensified both their theoretical and experimental research. Nonetheless, despite the investigations of the prototype materials represented by 3D perovskites Ln1−xAxCoO3 (Ln = La, Y, rare-earth, A = alkaline-earth) and 2D cobaltites of NaxCoO2 type, the concise physical background of their transport and magnetic properties remain still a matter of debate. This is likely due to a fact that cobalt ions can be stabilized either in low-spin state (diamagnetic for “pure” Co3+), with filled t2g levels and empty eg states, or magnetic ones, with filled eg states. As the energy difference between respective states is due to comparable strength of crystal field and Hund's energies rather small, the thermodynamically most stable ground-state, with eventually different character of charge carriers, can be critically influenced by an interplay of additional degrees of freedom - orbital and charge. The challenge for unequivocal theoretical model represents the thermoelectric power of mixed cobaltites where, up to now, somewhat ambiguous models based either on “classical” approach, associated with diffusion of itinerant charge carriers, or more exotic - based on configurational entropy of quasi-itinerant carriers - are often used for similar materials. Simultaneously, the open question remains the assessment of the dominant mechanism of phonon scattering in 2D cobaltites.

Control of multi-scroll attractors in a memristor-coupled resonator via time-delayed feedback

2018 ◽  
Vol 32 (32) ◽  
pp. 1850399 ◽  
Author(s):  
Zhilong Liu ◽  
Fuqiang Wu ◽  
Faris Alzahrani ◽  
Jun Ma
Keyword(s):  
Dynamical System ◽  
Time Delay ◽  
Magnetic Flux ◽  
Memory Effect ◽  
Delayed Feedback ◽  
Feedback Gain ◽  
Initial Setting ◽  
Physical Background ◽  
Time Delayed Feedback ◽  
With Memory

A four-variable dynamical system composed of memristor is proposed to investigate the dependence of multi-scroll attractor on initial setting for one variable with memory, and the description for physical background is supplied. It is found that appropriate setting of initial values for the memory variable can induce different numbers of attractor, as a result, resetting initials can change the profile of attractors which is also dependent on the calculating period. Time-delayed feedback is used to stabilize the dynamical system thus the effect of initial dependence is suppressed and multi-scroll attractors are controlled by applying appropriate time delay and feedback gain in the controller. Furthermore, the system is verified on FPGA circuit platform and memristor is used to describe the memory effect of variable related to magnetic flux. It is confirmed that multi-scroll attractors can be stabilized and the dependence of initials setting is suppressed in experiment way.

The Physical Background of Perception. E. D. Adrian

1948 ◽  
Vol 23 (2) ◽  
pp. 170-171
Author(s):  
A. Chapanis
Keyword(s):  
Physical Background

scholarly journals Three-Method Hybrid Numerical Simulation for Surface-Plasmon-Enhanced GaInN-Based Light-Emitting Diodes with Metal-Embedded Nanostructures

2021 ◽  
Vol 9 ◽  
Author(s):  
Ryoya Hiramatsu ◽  
Ryo Takahashi ◽  
Ryoto Fujiki ◽  
Keisuke Hozo ◽  
Kanato Sawai ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Light Emitting Diodes ◽  
Simulation Tool ◽  
Wave Analysis ◽  
Light Emitting ◽  
Rigorous Coupled Wave Analysis ◽  
Physical Background ◽  
Simulation Results ◽  
Rigorous Coupled Wave ◽  
Difference Time

In this paper, a hybrid numerical simulation tool is introduced and performed for GaInN-based light-emitting diodes (LEDs) with metal-embedded nanostructure to theoretically predict external quantum efficiency (EQE), which composed of finite-difference time-domain, rigorous coupled wave analysis, and ray tracing. The advantage is that the proposed method provides results supported by sufficient physical background within a reasonable calculation time. From the simulation results, the EQE of LED with Ag-nanoparticles embedded nanostructure is expected to be enhanced by as high as ∼1.6 times the conventional LED device in theory.

scholarly journals The Step-Drawdown Test and Non-Darcian Flow: A Critical Review of Theory, Methods and Practice

1982 ◽  
Vol 13 (4) ◽  
pp. 247-256 ◽  
Author(s):  
Henrik Kærgaard
Keyword(s):  
Critical Review ◽  
Equal Duration ◽  
Physical Background

Step-drawdown tests are usually carried out with succeeding steps of increased pumping yield, each step of equal duration of 1 hour. The background for this procedure is reviewed, and it is shown, that very often much shorter duration of steps is adequate. The analysis of step-tests is usually based on the formulas of Jacob or Rorabaugh. The physical background for these formulas is reviewed, and the latter is shown to be unsatisfactory. However, the formula is used in cases where the data do not fit the Jacob formula, some typical deviations are shown. Reasons for these problems, trivial and non-trivial, are discussed, and some reasonably sound pshysical explanations for the various systematic deviations from the Jacob formula are given.

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