Base Diameter (base + diameter)

Distribution by Scientific Domains

Selected Abstracts

Effects of composition distribution on electronic structures of self-assembled InGaN/GaN quantum dots

Wei-Yi Tsai
Abstract In this study, we investigate the influences of different composition distributions on the electronic structures of truncated cone-shaped InGaN quantum dots (QDs). A varying parameter, , is defined as , in which w1 and w2 are the top and base diameter of QD, respectively. This factor is set to study the role of similar truncated cones with the same base diameter and height on electronic structures of QD. Three indium composition distributions are considered: ellipsoid, uniform, and linear. The single-band effective-mass equation and six-band kp theory are used to calculate the transition energies of electrons and holes, respectively. The numerical results reveal that the parameter plays an important role in changing the piezoelectric potential. In addition, an InGaN quantum dot with a linear distribution of indium has the maximum transition energy, whereas one with an ellipsoidal distribution has the minimum value. It is noteworthy that the binding energy greatly decreases as increases for different indium distributions. [source]

Extended defects in ion assisted MBE grown SiGe/Si-nanostructures

P. I. Gaiduk
Abstract MBE-grown SiGe nano-structures assisted with in situ implantation of 1 keV Ge+ ions are investigated by transmission electron (TEM) and atomic force microscopy (AFM). Self-assembled Ge islands of small size and no extended defects are observed by TEM after low ion fluence pre-implantation at high temperature. Implanted SiGe nano-structures of larger size produce threading dislocations. High dose implantation at low temperature results in formation of semi-spherical SiGe/Si nanostructures of a twin-related type. Epitaxial islands of 30-40 nm in base diameter and 11 nm in height, and a density of about 6x1010 cm,2 are produced in this case. It is evidenced by XTEM that the islands have a complicated inner structure and consist of micro-twin nucleus and semi-spherical nano-layers of a various SiGe composition. The results are discussed in terms of strain relaxation through implantation induced defects. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Millimetre-scale bubble-like dielectric elastomer actuators

Federico Carpi
Abstract Hydrostatic coupling has recently been reported as a means to improve the versatility and safety of electromechanical actuators based on dielectric elastomers (DEs). Hydrostatically coupled DE actuators rely on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load. The work reported here was aimed at developing millimetre-scale bubble-like versions of such transducers. Silicone-made oil-filled actuators were manufactured as both single units and arrays of parallel elements. Bubbles had a base diameter of 6 mm and were driven up to a voltage of 2.25 kV, applied across a silicone film with a thickness of 42 m. Active relative displacements and stresses up to 18% and 2.2 kPa, respectively, were recorded with static driving. Dynamic investigations reported a ,3 dB bandwidth of the order of 100 Hz and a resonance frequency of about 250 Hz. Millimetre-scale hydrostatically coupled DE actuators might play a useful role in several fields of application. Among them, we are currently exploring novel tactile displays and cutaneous stimulators, made of wearable, distributed and flexible devices. Although further miniaturization is required for high-resolution uses, this technology holds promise to properly combine performance with safe and compliant interfaces with users, low specific weight, no acoustic noise and low cost. Copyright 2009 Society of Chemical Industry [source]

4365: The role of transpupillary thermotherapy in combined treatment of retinoblastoma

Purpose Retinoblastoma (RB) is one of the most serious ophthalmic pathology in childhood. Treatment options that provide eye preservation include chemotherapy, brachytherapy, external beam radiation, cryotherapy and laser treatment. The aim of our study is to evaluate efficiency of transpupillary thermotherapy (TTT) as a part of combined treatment of RB. Methods Our group consists of 30 RB patients (34 eyes). All patients received systemic chemotherapy (Carboplatin and Vincristine). Tumor thickness before TTT varied from 0.9 to 2.6 mm, tumor base diameter varied from 2 to 10 mm. Seven patients had monolateral RB, others had bilateral lesion. Five patients were treated with brachytherapy before TTT. TTT was performed using infrared diode laser Nidec DC 3300. Exposure time was 60 seconds. Width of laser beam was from 1000 to 2000 nm. TTT power setting varied from 600 to 900 mW. Eleven patients had TTT more then once. Follow-up period after TTT was up to 24 months. Results Control examination after TTT showed good response to the treatment in 27 eyes (79.4%). After TTT we saw hyperpigmented scar on the eye fundus at the place of previous tumor location, on OCT it looked like hyper-reflective stripe replacing all layers of a retina. Seven eyes (20.6%) were resistant to TTT, five of them were successfully treated by additional brachytherapy. Two eyes were enucleated because of uncontrolled tumor growth. Evaluation of metastatic disease in all patients revealed no signs of metastasis at the time of treatment or during follow-up. Conclusion TTT can be used in combined treatment of RB for small multifocal lesions. The method is rather simple and uncomplicated. Patients treated with TTT have better visual prognosis in comparison with brachytherapy. [source]