10 × 10 Gb/s DWDM Transmission Through 2.2-km Multimode Fiber Using Adaptive Optics

Transmitter-based adaptive optics and receiver-based single-mode filtering are combined to compensate modal dispersion in multimode fiber (MMF). A liquid-crystal spatial light modulator controls the launched field pattern for ten 10-Gb/s nonreturn-to-zero channels, wavelength-division multiplexed on a 200-GHz grid in the C-band. Error-free transmission through 2.2 km of 50-mum graded-index MMF is achieved for launch offsets up to 10 mum and for worst-case launched polarization. A ten-channel transceiver based on parallel integration of electronics and photonics is employed.     

Analysis of Current–Voltage Measurements on Long-Wavelength HgCdTe Photodiodes Fabricated on Si Composite Substrates

We have performed a detailed study of dark current versus voltage to understand existing limitations in dark current and address the nonuniformity of dark current in devices fabricated on HgCdTe grown on silicon substrates. One interesting observation is that trap-assisted tunneling, g-r currents, are not found close to zero bias in certain devices. Devices from the low end of the R ₀ A distribution show heavy shunting paths close to zero bias. We believe that these shunting paths may be the limiting cause of tail distributions in fabricated focal plane array tail distributions. Possible causes for these shunting paths are surface charges associated with dislocation cores and impurity gettering at dislocation cores. The measured non-anti-reflection (AR)-coated quantum efficiency (QE) was 0.576 at 78 K and displays the classical response versus wavelength. The measured QE on isolated single devices is consistent with the 256 × 256 focal-plane array mean QE. Obtained average dark currents are on the order of mid 10⁻⁵ A cm^–2, which is one order of magnitude higher than dark currents obtained from arrays on lattice-matched substrates. On average, arrays on lattice-mismatched substrates show performance characteristics inferior to those of arrays fabricated on lattice-matched substrates. This inferior performance is due to array pixel operability, as can be seen from the tail of the distribution and the average dark currents, which are one order of magnitude higher than those obtained on lattice-matched substrates.     

Robustness of quantitative compressive sensing MRI: the effect of random undersampling patterns on derived parameters for DCE- and DSC-MRI

Compressive sensing (CS) in Cartesian magnetic resonance imaging (MRI) involves random partial Fourier acquisitions. The random nature of these acquisitions can lead to variance in reconstruction errors. In quantitative MRI, variance in the reconstructed images translates to an uncertainty in the derived quantitative maps. We show that for a spatially regularized 2 ×-accelerated human breast CS DCE-MRI acquisition with a 192 (2) matrix size, the coefficients of variation (CoVs) in voxel-level parameters due to the random acquisition are 1.1%, 0.96%, and 1.5% for the tissue parameters K(trans), v(e), and v(p), with an average error in the mean of -2.5%, -2.0%, and -3.7%, respectively. Only 5% of the acquisition schemes had a systematic underestimation larger than than 4.2%, 3.7%, and 6.1%, respectively. For a 2 × -accelerated rat brain CS DSC-MRI study with a 64(2) matrix size, the CoVs due to the random acquisition were 19%, 9.5%, and 15% for the cerebral blood flow and blood volume and mean transit time, respectively, and the average errors in the tumor mean were 9.2%, 0.49%, and -7.0%, respectively. Across 11 000 different CS reconstructions, we saw no outliers in the distribution of parameters, suggesting that, despite the random undersampling schemes, CS accelerated quantitative MRI may have a predictable level of performance.     

The effect of a post processing thermal anneal on pre-existing and stress induced electrically active defects in ultra-thin SiON dielectric layers

In this work we demonstrate the effects of a post processing high temperature anneal on the reliability of ultra-thin SiON layers fabricated into both nmos and pmos devices in terms of the initial gate leakage current, stress induced leakage current (SILC), and the time dependent dielectric breakdown behaviour. The devices under consideration were annealed at several temperatures up to 500 °C. We show that different mechanisms dominate the leakage behaviour at different temperatures by examining the relative leakage in the low voltage range. In particular for pmos devices, the emptying of electron traps induced by temperature and subsequent annealing of these traps alters the leakage current profiles significantly, dependent on anneal temperature. We show that annealing improves the time dependent dielectric breakdown (TDDB) lifetimes of nmos devices and examine the reasons for this.     

Automatic control of lesion size in a simulated model of the eye

A multiple-layer phantom consisting of a thin absorbing layer sandwiched between two nonabsorbing layers was created to simulate laser-induced thermal lesions in the eye. The nonabsorbing layers consisted of clear egg white, and the thin (20-40-μm) absorbing layer was created with black spray paint. Heat generated in the absorbing layer during 0.5-10-s argon irradiation was conducted to the adjacent egg white. Sufficient heat produced a region of coagulation that was graphically evidenced by the characteristic whiteness of cooked egg white. Light reflected from the lesion was monitored with a video camera and used as a feedback signal to control irradiation time. The laser irradiation was automatically ended when the diameter of the reflectance parameter related to coagulation thickness reached a preselected value     

Performance characteristics of high power CW, 1 cm wide monolithic AlGaAs laser diode arrays with a 2 mm total aperture width

One cm wide monolithic laser diode arrays emitting around 810 nm with a 2 mm total aperture width have been characterised under CW conditions. CW operation up to 16 W has been achieved at a heatsink temperature of 70 degrees C. Several arrays have been lifetested at 10 W CW at a 20 degrees C heatsink temperature for a few thousand hours and have projected lifetimes of between 5000 and 17000 hours. The temperature dependence of the degradation rate was characterised, from which data an activation energy of 0.2 eV was obtained.<>     

Deconstructing the Effects of Matrix Elasticity and Geometry in Mesenchymal Stem Cell Lineage Commitment

A wide variety of environmental factors including physical and biochemical signals are responsible for stem cell behavior and function. In particular, matrix elasticity and cell shape have been shown to determine stem cell function, yet little is known about the interplay between how these physical cues control cell differentiation. For the first time, by using ultraviolet (UV) lithography to pattern poly(ethylene) glycol (PEG) hydrogels, it is possible to manufacture microenvironments capable of parsing the effects of matrix elasticity, cell shape, and cell size in order to explore the relationship between matrix elasticity and cell shape in mesenchymal stem cell (MSC) lineage commitment. These data show that cells cultured on 1000 μm² circles, squares, and rectangles are primarily adipogenic lineage regardless of matrix elasticity, while cells cultured on 2500 and 5000 μm² shapes more heavily depend on shape and elasticity for lineage specification. It is further characterized how modifying the cell cytoskeleton through pharmacological inhibitors can modify cell behavior. By showing MSC lineage commitment relationships due to physical signals, this study highlights the importance of cell shape and matrix elasticity in further understanding stem cell behavior for future tissue engineering strategies.     

探讨降低电磁干扰之道

电磁干扰是电子设备和系统设计当中不能回避的问题.电源是把电子设备和电源网络联系起来的部分,因此电源引起的电磁干扰值得认真关注.随着开关稳压器的广泛使用,它越来越多地存在于电子设备中.目前,减轻电磁干扰的方法很多,包括接地、屏蔽和滤波等方式,本文将着重介绍用多相同步和扩展频谱频率调制(SSFM)的方式来降低电磁干扰.