Experimental validation of a numerical model for heat transfer in vacuum glazing

Flat vacuum glazings consisting of a narrow evacuated space between two glass panes separated by an array of small support pillars have been fabricated. A guarded hot box calorimeter was designed and constructed to measure their heat transfer coefficients. Experimental measurements of temperatures and rates of heat transfer were found to be in very good agreement with those predicted using a developed finite element model. A method for determining the heat transfer coefficient of the evacuated gap has been established and comparisons are made between the measured and predicted glass surface temperature profiles of the exposed glass area and the heat transfer coefficients of the total glazing system in order to validated the model.     

Simple modelling of the effects of exploitation on hot springs, Geyser Valley, Wairakei, New Zealand

Many hot springs in Geyser Valley declined and ceased flowing during well testing (1950–1958) or the early stages of development (1958–1964) of the Wairakei field, North Island, New Zealand. A simple model that considers mixing, geothermal reservoir pressure, and Darcy flow is applied to analyse the changes in flow rate and chemistry of spring SP18. The model suggests that prior to the testing the observed flow rate of 3 l/s was comprised of about 2.1 l/s of water from the deep reservoir and about 0.9 l/s from shallow groundwater. As the pressure in the reservoir decreased as a result of exploitation, the reservoir component declined but the groundwater component remained near constant until the spring had nearly ceased flowing. The model reasonably predicts the flow cessation date for four other springs (Group A) but poorly predicts that for seven other springs (Group B). These two groups of springs do not appear to be clustered at the ground surface. The pressure–elevation relationship suggests that the Group A springs feed from within the shallower Waiora Formation and Group B springs from within the deeper Wairakei Ignimbrite Formation. The observation that declines of chloride concentrations in Group A springs occurred at least three years before those in springs of Group B is consistent with the finding that Group A springs have a shallower feeder depth.     

Fiber Optic Intermodulation Distortion

In analog frequency-division multiplexed fiber optic systems, laser nonlinearities transfer energy between the different carriers, resulting in intermodulation distortion and interference. A third-order polynomial without memory is used to model the nonlinearity. The FM frequency-division multiplexed (FM/FDM) signal consists of a set of FM carriers at frequencies.N_{omega 0}, whereN = L, L + 1, L +2, ... , M. The video distortion introduced by the nonlinearity is determined for various types of second- and third-order intermodulation terms. The intermodulation distortion frequency spectrum is determined for FM signals with assumed Gaussian spectra.     

Pacemaker interference by magnetic fields at power line frequencies

Human exposure to external 50/60-Hz electric and magnetic fields induces electric fields within the body. These induced fields can cause interference with implanted pacemakers. In the case of exposure to magnetic fields, the pacemaker leads are subject to induced electromotive forces, with current return paths being provided by the conducting body tissues. Modern computing resources used in conjunction with millimeter-scale human body conductivity models make numerical modeling a viable technique for examining any such interference. In this paper, an existing well-verified scalar-potential finite-difference frequency-domain code is modified to handle thin conducting wires embedded in the body. The effects of each wire can be included numerically by a simple modification to the existing code. Results are computed for two pacemaker lead insertion paths, terminating at either atrial or ventricular electrodes in the heart. Computations are performed for three orthogonal 60-Hz magnetic field orientations. Comparison with simplified estimates from Faraday's law applied directly to extracorporeal loops representing unipolar leads underscores problems associated with this simplified approach. Numerically estimated electromagnetic interference (EMI) levels under the worst case scenarios are about 40 microT for atrial electrodes, and 140 microT for ventricular electrodes. These methods could also be applied to studying EMI with other implanted devices such as cardiac defibrillators.     

Improving the Reliability of MLC NAND Flash Memories Through Adaptive Data Refresh and Error Control Coding

NAND Flash memory has become the most widely used non-volatile memory technology. We focus on multi-level cell (MLC) NAND Flash memories because they have high storage density. Unfortunately MLC NAND Flash memory also has reliability problems due to narrower threshold voltage gap between logical states. Errors in these memories can be classified into data retention (DR) errors and program interference (PI) errors. DR errors are dominant if the data storage time is longer than 1 day and these errors can be reduced by refreshing the data. PI errors are dominant if the data storage time is less than 1 day and these errors can be handled by error control coding (ECC). In this paper we propose a combination of data refresh policies and low cost ECC schemes that are cognizant of application characteristics to address the errors in MLC NAND Flash memories. First, we use Gray code based encoding to reduce the error rates in the four subpages (MSB-even, LSB-even, MSB-odd, LSB-odd) of a 2-bit MLC NAND Flash memory. Next, we apply data refresh techniques where the refresh interval is a function of the program/erase (P/E) frequency of the application. We show that an appropriate choice of refresh interval and BCH based ECC scheme can minimize memory energy while satisfying the reliability constraint.     

An Energy-Efficient OOK Transceiver for Wireless Sensor Networks

A 1-Mb/s 916.5-MHz on-off keying (OOK) transceiver for short-range wireless sensor networks has been designed in a 0.18-mum CMOS process. The receiver has an envelope detection based architecture with a highly scalable RF front-end. Untuned RF circuits are leveraged and optimized in the receiver to achieve superior energy efficiency compared to tuned RF circuits. The receiver power consumption scales from 0.5 mW to 2.6 mW, with an associated sensitivity of -37 dBm to -65 dBm at a BER of 10 ^-3. The transmitter consumes 3.8 mW to 9.1 mW with output power from -11.4 dBm to -2.2 dBm. The receiver achieves a startup time of 2.5 mus, allowing for efficient duty cycling     

PCI Express普及化超乎想象

PCI Express(PCIe)是目前最新的高速串行连接技术之一,短期内将无所不在.由于它继承了全球相当普遍的PCI数据总线,因此这项技术具有快速带动PC及外围配备市场的威力和重大意义,因而受到相当大的重视.因各式各样的需求所致,PCIe足迹已遍布各种应用系统和市场中,未来还会出现在哪些应用上呢?本文将与您共同探讨一二.     

90° SOI optical hybrid for Radio-over-fibre links

Radio-over- fibre (RoF) technology is receiving large attention due to its ability to provide simple antenna front ends, increased capacity and increased wireless access coverage. Coherently detected RoF systems would enable the information to be carried in both the amplitude and phase or in different states of the polarisation of the optical field. Additionally, the selectivity of coherent receiver is very well suited for access networks. We present a 90° optical hybrid built on a silicon-on-insulator planar light-wave circuit, which can be used as the optical front end of the digital coherent receiver in a digitised RoF link and will lead to reduced receiver footprint and cost. The optical hybrid circuit includes 2?×?2 and 4?×?4 multimode interference (MMI) splitters, in a polarisation diversity configuration. The simulation results at vacuum wavelength 1,550 nm show polarisation independence and phase errors between the ports of less than 0.03°. The properties of the prototyped 4?×?4 MMI were measured over a wide range of wavelengths. The 2?×?2 and 4?×?4 MMI showed nearly equal splitting ratios. Measurements of the relative phase relationship between the ports for Transverse Electric mode polarisation are shown to match the simulation results.     

Self‐Assembly of Atomically Thin Chiral Copper Heterostructures Templated by Black Phosphorus

The fabrication of 2D systems for electronic devices is not straightforward, with top‐down low‐yield methods often employed leading to irregular nanostructures and lower quality devices. Here, a simple and reproducible method to trigger self‐assembly of arrays of high aspect‐ratio chiral copper heterostructures templated by the structural anisotropy in black phosphorus (BP) nanosheets is presented. Using quantitative atomic resolution aberration‐corrected scanning transmission electron microscopy imaging, in situ heating transmission electron microscopy and electron energy‐loss spectroscopy arrays of heterostructures forming at speeds exceeding 100 nm s^?1 and displaying long‐range order over micrometers are observed. The controlled instigation of the self‐assembly of the Cu heterostructures embedded in BP is achieved using conventional electron beam lithography combined with site specific placement of Cu nanoparticles. Density functional theory calculations are used to investigate the atomic structure and suggest a metallic nature of the Cu heterostructures grown in BP. The findings of this new hybrid material with unique dimensionality, chirality, and metallic nature and its triggered self‐assembly open new and exciting opportunities for next generation, self‐assembling devices.