Effective Dielectric Function of Porous Silicon: the Transverse Component

1994 ◽  
Vol 358 ◽  
Author(s):  
G. Gumbs
Keyword(s):  
Absorption Spectrum ◽  
Absorption Coefficient ◽  
Electron Density ◽  
Quantum Wires ◽  
Interband Transition ◽  
Incident Light ◽  
Transverse Component ◽  
Effect Of Temperature ◽  
High Electron ◽  
Confining Potential

ABSTRACTA self-consistent many-body theory is developed to study the effect of temperature and electron density on the interband absorption coefficient and the frequency-dependent refractive index for an array of isolated quantum wires. The peaks in the absorption coefficient correspond to interband transitions resulting in the resonant absorption of light. The oscillations in the derivative spectrum are due to the quantization of the energy levels related to the in-plane confining potential for such reduced dimensional systems. There are appreciable changes in the absorption spectrum when the electron density or temperature is increased. One interband transition peak is suppressed in the high electron density limit and the thermal depopulation effect on the electron subbands can be easily seen when the temperature is high. We also find that the exciton coupling weakens the shoulder features in the absorption spectrum. This study is relevant to optical characterization of the confining potential and the areal density of electrons using photoreflectance. By using incident light with tunable frequencies in the interband excitation regime, contactless photoreflectance measurements may be carried out and the data compared with our calculations. By fitting the numerical results to the peak positions of the photoreflectance spectrum, the number of electrons in each wire may be extracted.

scholarly journals Estudo das propriedades ópticas em pontos quânticos de CdTe carregados

2020 ◽  
Vol 41 (2) ◽  
pp. 205
Author(s):  
Silvio José Prado
Keyword(s):  
Optical Properties ◽  
Absorption Spectrum ◽  
Optical Absorption ◽  
Quantum Dot ◽  
Absorption Coefficient ◽  
Optical Absorption Spectrum ◽  
Incident Light ◽  
Charge Carriers ◽  
The Right ◽  
Cdte Quantum Dot

In this article we theoretically study how the presence of charge carriers added to the conduction and valence band of a spherical CdTe quantum dot affects the optical properties, especially the absorption coefficient. For this study, we simulated the interband optical absorption spectrum for incident light with circular polarizations on the left (ê-), on the right (ê+) and linear (êz). We also consider Coulomb's interaction between optically excited and added carriers.

Electron microscope study of the secretory activity of epithelial cells in embryonic thymus

1990 ◽  
Vol 48 (3) ◽  
pp. 382-383
Author(s):  
H. Alasam
Keyword(s):  
Cell Differentiation ◽  
T Cell ◽  
Epithelial Cells ◽  
Electron Density ◽  
Secretory Activity ◽  
T Cell Differentiation ◽  
High Electron ◽  
Transmission Electron ◽  
Medullary Epithelial Cells ◽  
Thymic Factor

The possibility that intrathymic T-cell differentiation involves stem cell-lymphoid interactions in embryos led us to study the ultrastructure of epithelial cell in normal embryonic thymus. Studies in adult thymus showed that it produces several peptides that induce T-cell differentiation. Several of them have been chemically characterized, such as thymosin α 1, thymopoietin, thymic humoral factor or the serum thymic factor. It was suggested that most of these factors are secreted by populations of A and B-epithelial cells.Embryonic materials were obtained from inbred matings of Swiss Albino mice. Thymuses were disected from embryos 17 days old and prepared for transmission electron microscopy. Our studies showed that embryonic thymus at this stage contains undifferentiated and differentiated epithelial cells, large lymphoblasts, medium and few small lymphocytes (Fig. 5). No differences were found between cortical and medullary epithelial cells, in contrast to the findings of Van Vliet et al,. Epithelial cells were mostly of the A-type with low electron density in both cytoplasm and nucleus. However few B-type with high electron density were also found (Fig. 7).

Unusually high electron density in an intermolecular non-bonding region: Role of metal substrate

2017 ◽  
Vol 28 (4) ◽  
pp. 759-764 ◽  
Author(s):  
Chen-Guang Wang ◽  
Zhi-Hai Cheng ◽  
Xiao-Hui Qiu ◽  
Wei Ji
Keyword(s):  
Electron Density ◽  
Metal Substrate ◽  
High Electron ◽  
High Electron Density

scholarly journals The scattering of light by turbid media.–Part II

1931 ◽  
Vol 131 (817) ◽  
pp. 464-475 ◽  
Keyword(s):  
Refractive Index ◽  
Absorption Coefficient ◽  
Spherical Shell ◽  
Direct Observation ◽  
Single Particle ◽  
Unit Volume ◽  
Incident Light ◽  
Parallel Beam ◽  
Photometric Observations ◽  
Transmission And Reflection

In Part I it was shown how the values of the transmission and reflection of a sheet of a medium containing particles in suspension can he calculated. First the amounts of light scattered in the forward and forward directions from a single particle were determined; from these results the transmission 1 and rejection R for diffuse incident light were found for a layer of the disusing medium, when the effects of boundary reflections are negligible. At this stage, the expressions developed apply to a mist or fog consisting of particles suspended in air. Finally it was shown how, if the particles are suspended in some other medium, having a different refractive index from that of air, the transmission and reflection ז and p can be expressed in terms of T and R and the surface rejection coefficients. The more general expressions, for the case when the incident light is a parallel beam, were also developed. We shall now show how the absorption coefficient μ can be determined from photometric observations. As a check on the theory, we shall deduce the diameter D of the particles and the number N present per unit volume and compare these calculated values with those found by direct observation, Finally, the necessary modifications of the theory will be made to cover the case when the diffusing medium is in the form of a spherical shell.

New insights into electrolyte-component biased and transfer- and transport-limited charge recombination in dye-sensitized solar cells

RSC Advances ◽  
2015 ◽  
Vol 5 (103) ◽  
pp. 84959-84966 ◽  
Author(s):  
Dong-Li Gao ◽  
Yi Wang ◽  
Ping Zhang ◽  
Li-Min Fu ◽  
Xi-Cheng Ai ◽  
...  
Keyword(s):  
Solar Cells ◽  
Electron Density ◽  
Dye Sensitized Solar Cells ◽  
Charge Recombination ◽  
High Electron ◽  
High Electron Density ◽  
Dye Sensitized ◽  
Electrolyte Component ◽  
Sensitized Solar Cells

Charge recombination takes place, respectively, within the frameworks of transfer- and transport-limited recombination mechanisms, at low and high electron density.

Absorption and Emission of Light in Quantum Structures

2020 ◽  
pp. 343-418
Author(s):  
Vurgaftman Igor
Keyword(s):  
Quantum Wells ◽  
Radiative Recombination ◽  
Quantum Wires ◽  
Incident Light ◽  
Optical Gain ◽  
Two Dimensional ◽  
Intersubband Transitions ◽  
Recombination Rates ◽  
Zinc Blende ◽  
Two Dimensional Materials

This chapter shows how to calculate the absorption coefficient, optical gain, and radiative recombination rates in quantum wells and superlattices. A detailed treatment of both interband and intersubband transitions is presented, and their differences and similarities are considered in detail. The optical properties of wurtzite quantum wells and zinc-blende quantum wires and dots are also discussed. Finally, the interaction of excitonic transitions with incident light in quantum wells is considered as a model for other two-dimensional materials.

Interaction of Epididymal Epithelia and their Secretions with Spermatozoa Supports Functional and Morphological Changes During Long-Term Storage in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

2020 ◽  
Vol 26 (3) ◽  
pp. 542-550
Author(s):  
Imran Tarique ◽  
Mansoor Tariq ◽  
Xuebing Bai ◽  
Qu Wenjia ◽  
Ping Yang ◽  
...  
Keyword(s):  
Electron Density ◽  
Morphological Changes ◽  
Storage Period ◽  
Sperm Storage ◽  
Synthetic Activity ◽  
High Electron ◽  
Pelodiscus Sinensis ◽  
Clear Cells ◽  
Long Term Storage

AbstractPost-testicular maturation of spermatozoa is crucial for attaining the morphological and functional capabilities needed for successful fertilization. Epididymal epithelia offer a favorable environment for spermatozoa that are stored long term in the turtle epididymis; however, sperm–epithelial interactions during storage, which are enormously important for sperm functional and morphological maturation, are still largely unknown in turtles. The present study examined the epididymis during the sperm-storage period (November–April) in the Chinese soft-shelled turtle (Pelodiscus sinensis). Light and transmission electron microscopy were used to determine the cellular features of each epididymal segment (caput, corpus, and cauda) and their epithelial interactions with the spermatozoa. Spermatozoa were mainly located in the lumena of caput, corpus, and cauda epididymides. Numerous spermatozoa were bound to apical surfaces of the epithelia, and several were even embedded in the epithelial cytoplasm of the caput and corpus epididymides. No embedded spermatozoa were found in the cauda epididymis. In all epididymal segments, principal and clear cells showed the synthetic activity, evidenced by a well-developed endoplasmic reticulum network and high and low electron-dense secretory materials, respectively. Principal and clear cells in the caput and corpus segments showed embedded spermatozoa in electron-dense secretions and in the lipid droplets within the cytoplasm. No lysosomes were observed around the embedded spermatozoa. The lumena of the caput and corpus segments showed few apocrine and low electron density secretions. In the lumen of the cauda epididymidis, different secretions, such as holocrine with low and high electron density and their fragmentation, apocrine, and dictyosome, were found and are summarized. Altogether, sperm physical interactions with secretions either in the cytoplasm of epithelium or in the lumen may support the viability, morphological maintenance, and transfer of various proteins involved in long-term sperm storage in the turtle. This interaction could help us to understand the mechanisms of long-term sperm storage and provide more insights into the reproductive strategies of turtle sperm preservation.

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