Expressions for the "quantum capacitance" are derived, and regimes are discussed in which this concept may be useful in modeling electronic devices. The degree of quantization is discussed for one-and two-dimensional systems, and it is found that two-dimensional (2D) metals, and onedimensional (1D) metallic carbon nanotubes have a truly quantized capacitance over a restricted bias range. For both 1D and 2D semiconductors, a continuous description of the capacitance is necessary. The particular case of carbon nanotube field-effect transistors (CNFETs) is discussed in the context of one-dimensional systems. The bias regime in which the quantum capacitance may be neglected when computing the energy band diagram, in order to assist in the development of compact CNFET models, is found to correspond only to the trivial case where there is essentially no charge, and a solution to Laplace's equation is sufficient for determining a CNFET's energy band diagram. For fully turned-on devices, then, models must include this capacitance in order to properly capture the device behaviour. Finally, the relationship between the transconductance of a CNFET and this capacitance is revealed.

No abstract

No abstract

PURPOSE. To investigate the characteristics of a spectral-domain optical coherence tomography (SD-OCT) image phenomenon known as the mirror artifact, calculate its prevalence, analyze potential risk factors, measure severity, and correlate it to spherical equivalent and central visual acuity (VA). METHODS. OCT macular cube 512 x 128 scans taken between January 2008 and February 2009 at the New England Eye Center were analyzed for the presence of mirror artifacts. Artifact severity was determined by the degree of segmentation breakdown that it caused on the macular map. A retrospective review was conducted of the medical records of patients with artifacts and of a random control group without artifacts. RESULTS. Of 1592 patients, 9.3% (148 patients, 200 eyes) had scans that contained mirror artifacts. A significantly more myopic spherical equivalent (P < 0.001), worse VA (P < 0.001), longer axial lengths (P = 0.004), and higher proportions of moderate to high myopia (P < 0.001) were found in patients with mirror artifacts than in patients without artifacts. Worse VA was associated with increased artifact severity (P = 0.04). CONCLUSIONS. In all scans analyzed, a high prevalence of mirror artifacts was found. This image artifact was often associated with patients with moderate to high myopia. Improvements in instrumentation may be necessary to resolve this problem in moderately and highly myopic eyes. Operators should be advised to properly position the retina when scanning eyes. In cases in which peripheral abnormalities in topographic measurements of retinal thickness are found, corresponding OCT scans should be examined for the presence of mirror artifacts.

Despite postoperative anatomic improvement in many patients and an overall decrease in foveal thickness on OCT, this retrospective series suggests that vitrectomy for lamellar holes may not improve visual acuity.

No abstract

No abstract

Overall, there was a significant improvement in visual acuity and central foveal thickness postoperatively. Eyes with lamellar separation of the inner and outer foveal layers preoperatively had worse visual results, whereas eyes with cystoid macular edema or perifoveal VMT had better visual results.