How to restrain Auger recombination predominance in the threshold of asymmetric bi-quantum-well lasers

Both radiative and nonradiative processes which occur in the active region of GaInAs–GaInAsP–InP asymmetric multiple quantum-well (AMQW) heterolasers with two quantum wells of different width (4 and 9 nm) are described. Several possible processes of non-radiative Auger recombination which affect the temperature sensitivity of the lasing threshold are analyzed and the temperature dependencies of the investigated processes are presented. For the above-mentioned AMQW heterostructure, it is shown that the influence of the Auger recombination processes on the temperature behaviour of the lasing threshold can be restrained by operation at temperatures lower than 340 K and the cavity losses which do not exceed 60 cm-1

Optoelectronics – Devices and Applications

Optoelectronics - Devices and Applications is the second part of an edited anthology on the multifaced areas of optoelectronics by a selected group of authors including promising novices to experts in the field. Photonics and optoelectronics are making an impact multiple times as the semiconductor revolution made on the quality of our life. In telecommunication, entertainment devices, computational techniques, clean energy harvesting, medical instrumentation, materials and device characterization and scores of other areas of R&D the science of optics and electronics get coupled by fine technology advances to make incredibly large strides. The technology of light has advanced to a stage where disciplines sans boundaries are finding it indispensable. New design concepts are fast emerging and being tested and applications developed in an unimaginable pace and speed. The wide spectrum of topics related to optoelectronics and photonics presented here is sure to make this collection of essays extremely useful to students and other stake holders in the field such as researchers and device designers

How to restrain Auger recombination predominance in the threshold of asymmetric bi-quantum-well lasers

Both radiative and nonradiative processes which occur in the active region of GaInAs–GaInAsP–InP asymmetric multiple quantum-well (AMQW) heterolasers with two quantum wells of different width (4 and 9 nm) are described. Several possible processes of non-radiative Auger recombination which affect the temperature sensitivity of the lasing threshold are analyzed and the temperature dependencies of the investigated processes are presented. For the above-mentioned AMQW heterostructure, it is shown that the influence of the Auger recombination processes on the temperature behaviour of the lasing threshold can be restrained by operation at temperatures lower than 340 K and the cavity losses which do not exceed 60 cm-1

A comprehensive multi-scale modeling of defective CdSe colloidal nanocrystals through advanced X-ray scattering techniques

The dissertation includes a comprehensive multi-scale modeling of defective CdSe colloidal nanocrystals through advanced X-ray scattering techniques. Chapter 1 introduces the reader to the entire work of the Ph. D. thesis and to its main topic of research, which is focused on structural and microstructural characterization of colloidal quantum-dots. The following Chapter is dedicated to the description of conventional and unconventional characterization methods at the nanoscale, discussing their limits and potentiality in characterizing real nano-systems. Chapter 3 serves as a mathematical description of the DSE, and its implementation in the DebUsSy suite for the characterization of real ensembles of nanosized samples. Therein, the data collection and reduction procedures are also reported, together with a brief section in which the DSE to PDF approaches are compared. The need of introducing strains and defects in the complex atomistic model of CdSe nanocrystals makes it necessary to describe these defects, with a brief state of the art of their characterization methods (Chapter 4). Chapter 5 is completely dedicated to describing the computational model used for the characterization of cQDs and its use as a part of the overall data analysis strategy. The final Chapters focus on the application of the model to real systems in which its potentiality and sensitivity are tested on different materials, disclosing new size-dependent fault driven relaxation and faceting features in CdSe cQDs. An additional section presents an alternative method for the characterization of metallic NPs with larger sizes, but (much) lower stacking fault probabilities

A comprehensive multi-scale modeling of defective CdSe colloidal nanocrystals through advanced X-ray scattering techniques

The dissertation includes a comprehensive multi-scale modeling of defective CdSe colloidal nanocrystals through advanced X-ray scattering techniques. Chapter 1 introduces the reader to the entire work of the Ph. D. thesis and to its main topic of research, which is focused on structural and microstructural characterization of colloidal quantum-dots. The following Chapter is dedicated to the description of conventional and unconventional characterization methods at the nanoscale, discussing their limits and potentiality in characterizing real nano-systems. Chapter 3 serves as a mathematical description of the DSE, and its implementation in the DebUsSy suite for the characterization of real ensembles of nanosized samples. Therein, the data collection and reduction procedures are also reported, together with a brief section in which the DSE to PDF approaches are compared. The need of introducing strains and defects in the complex atomistic model of CdSe nanocrystals makes it necessary to describe these defects, with a brief state of the art of their characterization methods (Chapter 4). Chapter 5 is completely dedicated to describing the computational model used for the characterization of cQDs and its use as a part of the overall data analysis strategy. The final Chapters focus on the application of the model to real systems in which its potentiality and sensitivity are tested on different materials, disclosing new size-dependent fault driven relaxation and faceting features in CdSe cQDs. An additional section presents an alternative method for the characterization of metallic NPs with larger sizes, but (much) lower stacking fault probabilities

Energy. A continuing bibliography with indexes, issue 26, 1 April - 30 June 1980

This bibliography lists 1134 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System from April 1, 1980 through June 30, 1980

Psr1p interacts with SUN/sad1p and EB1/mal3p to establish the bipolar spindle

Regular Abstracts - Sunday Poster Presentations: no. 382During mitosis, interpolar microtubules from two spindle pole bodies (SPBs) interdigitate to create an antiparallel microtubule array for accommodating numerous regulatory proteins. Among these proteins, the kinesin-5 cut7p/Eg5 is the key player responsible for sliding apart antiparallel microtubules and thus helps in establishing the bipolar spindle. At the onset of mitosis, two SPBs are adjacent to one another with most microtubules running nearly parallel toward the nuclear envelope, creating an unfavorable microtubule configuration for the kinesin-5 kinesins. Therefore, how the cell organizes the antiparallel microtubule array in the first place at mitotic onset remains enigmatic. Here, we show that a novel protein psrp1p localizes to the SPB and plays a key role in organizing the antiparallel microtubule array. The absence of psr1+ leads to a transient monopolar spindle and massive chromosome loss. Further functional characterization demonstrates that psr1p is recruited to the SPB through interaction with the conserved SUN protein sad1p and that psr1p physically interacts with the conserved microtubule plus tip protein mal3p/EB1. These results suggest a model that psr1p serves as a linking protein between sad1p/SUN and mal3p/EB1 to allow microtubule plus ends to be coupled to the SPBs for organization of an antiparallel microtubule array. Thus, we conclude that psr1p is involved in organizing the antiparallel microtubule array in the first place at mitosis onset by interaction with SUN/sad1p and EB1/mal3p, thereby establishing the bipolar spindle.postprin

Removal of antagonistic spindle forces can rescue metaphase spindle length and reduce chromosome segregation defects

Regular Abstracts - Tuesday Poster Presentations: no. 1925Metaphase describes a phase of mitosis where chromosomes are attached and oriented on the bipolar spindle for subsequent segregation at anaphase. In diverse cell types, the metaphase spindle is maintained at a relatively constant length. Metaphase spindle length is proposed to be regulated by a balance of pushing and pulling forces generated by distinct sets of spindle microtubules and their interactions with motors and microtubule-associated proteins (MAPs). Spindle length appears important for chromosome segregation fidelity, as cells with shorter or longer than normal metaphase spindles, generated through deletion or inhibition of individual mitotic motors or MAPs, showed chromosome segregation defects. To test the force balance model of spindle length control and its effect on chromosome segregation, we applied fast microfluidic temperature-control with live-cell imaging to monitor the effect of switching off different combinations of antagonistic forces in the fission yeast metaphase spindle. We show that spindle midzone proteins kinesin-5 cut7p and microtubule bundler ase1p contribute to outward pushing forces, and spindle kinetochore proteins kinesin-8 klp5/6p and dam1p contribute to inward pulling forces. Removing these proteins individually led to aberrant metaphase spindle length and chromosome segregation defects. Removing these proteins in antagonistic combination rescued the defective spindle length and, in some combinations, also partially rescued chromosome segregation defects. Our results stress the importance of proper chromosome-to-microtubule attachment over spindle length regulation for proper chromosome segregation.postprin

Reports to the President

A compilation of annual reports for the 1990-1991 academic year, including a report from the President of the Massachusetts Institute of Technology, as well as reports from the academic and administrative units of the Institute. The reports outline the year's goals, accomplishments, honors and awards, and future plans