The measurement of alpha particle emissions from semiconductor memory materials

With the increasing concern for the affects of alpha particles on the reliability of semiconductor memories, an interest has arisen in characterizing semiconductor manufacturing materials for extremely low-level alpha-emitting contaminants. It is shown that four elements are of primary concern: uranium, thorium, radium, and polonium. Measurement of contamination levels are given relevance by first correlating them with alpha flux emission levels and then corre1ating these flux values with device soft error rates. Measurement techniques involve either measurements of elemental concentrations-applicable to only uranium and thorium - or direct measurements of alpha emission fluxes. Alpha fluxes are most usefully measured by means of ZnS scintillation counting, practical details of which are discussed. Materials measurements are reported for ceramics, solder, silicon, quartz, and various metals and organic materials. Ceramics and most metals have contamination levels of concern, but the high temperature processing normally used in semiconductor manufacturing and low total amounts reduce problems, at least for metals. Silicon, silicon compounds, and organic materials have been found to have no detectable alpha emitters. Finally, a brief discussion of the calibration of alpha sources for accelerated device testing is given, including practical details on the affects of source/chip separation and alignment variations.     

Dense crowd counting from still images with convolutional neural networks

For reasons of public security, modeling large crowd distributions for counting or density estimation has attracted significant research interests in recent years. Existing crowd counting algorithms rely on predefined features and regression to estimate the crowd size. However, most of them are constrained by such limitations: (1) they can handle crowds with a few tens individuals, but for crowds of hundreds or thousands, they can only be used to estimate the crowd density rather than the crowd count; (2) they usually rely on temporal sequence in crowd videos which is not applicable to still images. Addressing these problems, in this paper, we investigate the use of a deep-learning approach to estimate the number of individuals presented in a mid-level or high-level crowd visible in a single image. Firstly, a ConvNet structure is used to extract crowd features. Then two supervisory signals, i.e., crowd count and crowd density, are employed to learn crowd features and estimate the specific counting. We test our approach on a dataset containing 107 crowd images with 45,000 annotated humans inside, and each with head counts ranging from 58 to 2201. The efficacy of the proposed approach is demonstrated in extensive experiments by quantifying the counting performance through multiple evaluation criteria.     

Multi‐pronged analysis of degradation rates of photovoltaic modules and arrays deployed in Florida

The long‐term performance and reliability of photovoltaic (PV) modules and systems are critical metrics for the economic viability of PV as a power source. In this study, the power degradation rates of two identical PV systems deployed in Florida are quantified using the Performance Ratio analytical technique and the translation of power output to an alternative reporting condition of 1000 W m⁻² irradiance and cell temperature of 50 °C. We introduce a multi‐pronged strategy for quantifying the degradation rates of PV modules and arrays using archived data. This multi‐pronged approach utilizes nearby weather stations to validate and, if needed, correct suspect environmental data that can be a problem when sensor calibrations may have drifted. Recent field measurements, including I‐V curve measurements of the arrays, visual inspection, and infrared imaging, are then used to further investigate the performance of these systems. Finally, the degradation rates and calculated uncertainties are reported for both systems using the methods described previously. Copyright © 2012 John Wiley & Sons, Ltd.     

Clean galena, contaminated lead, and soft errors in memory chips

Lead (Pb) disks were exposed to a radon (Rn)-rich atmosphere and surface alpha particle emissions were detected over time. Cumulative ²¹⁰Po alpha emission increased nearly linearly with time. Conversely, cumulative emission for each of ²¹⁸Po and ²¹⁴Po was constant after one and two hours, respectively. Processing of radiation-free Pb ore (galena) in inert atmospheres was compared with processing in ambient air. Galena processed within a flux heated in a graphite crucible while exposed to an inert atmosphere, resulted in lead contaminated with ²¹⁰Po (Trial 1). A glove box was next used to prepare a baseline radiation-free flux sample in an alumina crucible that was heated in an oven with an inert atmosphere (Trials 2 and 3). Ambient air was thereafter introduced, in place of the inert atmosphere, to the radiation-free flux mixture during processing (Trial 4). Ambient air introduced Rn and its progeny (RAD) into the flux during processing so that the processed Pb contained Po isotopes. A typical coke used in lead smelting also emitted numerous alpha particles. We postulate that alpha particles from tin/lead solder bumps, a cause of computer chip memory soft errors, may originate from Rn and RAD in the ambient air and/or coke used as a reducing agent in the standard galena smelting procedure. Author’s Note: No-alpha lead (NAL) as used in this article is a misnomer. What is meant is lead in which the alpha particle (α) emission is so low that it cam not be detected with current instrumentation and t memory chips are not affected by α emission from lead solder bumps.     

C2C电子商务交易的信用及风险评估方法研究

提出了一种改进的信用计分方法,该方法采用商品价格的区间分布来对成功交易进行加分,采用信用等级的扣分系数来对不同信用等级的失败交易进行扣分,可以解决信用炒作和周期欺骗问题.通过对信用风险的分析,在改进的信用计分模型的基础上,设计了一种网上交易的风险计算方法,该方法可以根据历史交易的情况以及当前交易的价格来对当前交易的风险进行评估.模拟实验结果表明,改进的信用计分方法具有较好的抗信用炒作和周期欺骗效果,所给出的风险评估方法对电子商务交易中的风险分析和预测是比较准确和有效的.     

Multi‐“Color” Delineation of Bone Microdamages Using Ligand‐Directed Sub‐5 nm Hafnia Nanodots and Photon Counting CT Imaging

The early detection of bone microdamages is crucial to make informed decisions about the therapy and taking precautionary treatments to avoid catastrophic fractures. Conventional computed tomography (CT) imaging faces obstacles in detecting bone microdamages due to the strong self‐attenuation of photons from bone and poor spatial resolution. Recent advances in CT technology as well as novel imaging probes can address this problem effectively. Herein, the bone microdamage imaging is demonstrated using ligand‐directed nanoparticles in conjunction with photon counting spectral CT. For the first time, Gram‐scale synthesis of hafnia (HfO₂) nanoparticles is reported with surface modification by a chelator moiety. The feasibility of delineating these nanoparticles from bone and soft tissue of muscle is demonstrated with photon counting spectral CT equipped with advanced detector technology. The ex vivo and in vivo studies point to the accumulation of hafnia nanoparticles at microdamage site featuring distinct spectral signal. Due to their small sub‐5 nm size, hafnia nanoparticles are excreted through reticuloendothelial system organs without noticeable aggregation while not triggering any adverse side effects based on histological and liver enzyme function assessments. These preclinical studies highlight the potential of HfO₂‐based nanoparticle contrast agents for skeletal system diseases due to their well‐placed K‐edge binding energy.     

Avoiding Counting to Infinity in Distance Vector Routing

The Routing Information Protocol (RIP) may introduce misleading routing information into the routing table, due to network topology changes such as link or router failures. This is known as the counting to infinity problem. In the past, the distance metric had to be below 16 hops in order to keep this counting within reasonable limits. In this paper a more elaborate approach is presented in order to recognize those router interfaces which might have received misleading routing messages. This is accomplished by evaluating routing updates more carefully than is done by the well known split horizon approach. This new approach gets by without any additional message exchange between the RIP-protocol partners. In contrast to other approaches, the router interfaces are examined in pairs to determine if a loop exists between them. The algorithm locally extracts all the information it needs from the normal update messages that are exchanged between RIP neighbors and is thus executed in constant time. Only some minor calculations have to be carried out to gain the knowledge that is necessary to recognize those interfaces which may have received misleading routing information. Hence, this new distance vector routing without counting to infinity can be used in complex networking environments.     

Automatic counting of etch Pits in InP

A computer algorithm for automatic EPD-counting (etch-pit density) with an optical microscope is presented. Several dislocation etchants proposed in the literature to reveal structural defects on InP were employed and improved. Their reliability for automatic counting was proven. For a considerable number of samples exhibiting an EPD between 10⁴ and 10⁶ cm⁻² it is shown that the automatically counted number of etch pits agrees with the visually determined value within less than ±30%. Using a modified H₃PO₄:HBr etchant good results for automatically determined EPDs beyond 10⁷ cm⁻² were obtained on InP layers epitaxially grown on Si substrates.     

光子计数用光电倍增管的外围工作电路

光电倍增管是光子计数系统经常采用的一种典型探测器,是整＋~-t-计数系统的基础。光子计数系统中光电倍增管的外围工作电路设计得是否舍理,对光子计数系统的性能有很大影响。文中介绍了光电倍增管常采用的一些工作电路,分析了这些工作电路的特点,并给出了适合光子计数用光电倍增管的外围工作电路。     

Interband scattering effects on secondary ionization coefficients in GaAs

The ionization rates of holes and electrons in GaAs were measured experimentally over a wide doping range covering field values from 2.2×10⁵ V/cm to 4.7×10⁵ V/cm. As opposed to most experimemental measurements in GaAs, no assumption of equal ionization rates of the two carriers has been made. By using the conventional theoretical relationship between carrier ionization coefficients and multiplication data, the effective α is observed to be larger than β in lightly doped diodes while β is larger than α in heavily doped diodes. Previous theories of ionization rates utilizing just the normal conduction and valence bands do not show any possibility of such a crossover. It is suggested that electron transitions to higher conduction bands, which effectively increase the equilibration time of the electron distribution function, offer a resolution of this difficulty. The dependence of the effective electron ionization rate on doping can be explained by the requirement that electrons must make an interband transition before reaching the ionization threshold energy. This interband transition time estimated by this experiment is of the order of 10^?13 sec and is comparable to the transit time of electrons in the avalanching region. The breakdown voltages extrapolated from the measured α and β are consistent with those observed experimentally.     

Concurrent Formation of Metallic Glass During Laser Forward Transfer 3D Printing

In recent years, bulk metallic glasses (BMGs) have drawn much research attention and are shown to be of industrial interest due to their superior mechanical properties and resistance to corrosion. In spite of the interest in harnessing MG for microelectromechanical systems devices, there are limitations in manufacturing such micrometer‐scale structures. A novel approach for the fabrication of 3D MG structures using laser‐induced forward transfer (LIFT) is demonstrated. Inherent tremendous cooling rates associated with the metal LIFT process (≈10¹⁰ k s^?1) make the formation of a variety of BMGs accessible, including also various binary compositions. In this work, it is demonstrated that LIFT printing of ZrPd‐based metallic glass microstructures can also be performed under ambient conditions. X‐ray diffraction analysis of the printed structures reveals > 95% of amorphous metal phase. Taking advantage of the properties of BMG, high quality printing of high aspect ratio BMG pillars, and microbridges are demonstrated. It is also shown how a composite, amorphous‐crystalline metal structure with a required configuration can be fabricated using multimaterial LIFT printing. The inherent high resolution of the method combined with the noncontact and multimaterial printing capacity makes LIFT a valuable additive manufacturing technique to produce metallic glass‐based devices.     

Performance analysis of digital lightwave systems using efficientcomputer simulation techniques

Analytically-based methods for evaluating the performance of digital lightwave systems in terms of bit error rates (BERs) are extremely difficult to develop without making restrictive assumptions. A Monte Carlo simulation approach can offer an attractive alternative. However, for typical optical systems, this approach would require an excessive amount of computer time. Importance sampling (IS) is a variance reduction method which can substantially increase the computational efficiency of Monte Carlo simulations. This paper presents an IS method to efficiently evaluate the BERs of direct-detection optical systems employing avalanche photodiode (APD) receivers. Specifically, using a heuristic argument based on large deviations theory, a large class ℱ of exponentially twisted sampling distributions for the APD-based receiver is developed. It is then demonstrated that when used as a sampling distribution, the “optimized” exponentially twisted distribution of large deviations theory is the most efficient distribution among the sampling distributions in ℱ. Further, it is demonstrated that such a distribution would estimate the performance of optical systems with a high degree of accuracy to warrant its possible use as a powerful and flexible tool in computer-aided design, analysis and modeling of fiber-optic transmission systems     

Design of LDPC-coded BICM using a semi-Gaussian approximation

This paper investigates analysis and design of Low-Density Parity-Check （LDPC） coded Bit Interleaved Coded Modulation （BICM） over Additive White Gaussian Noise （AWGN） channel. It focuses on Gray-labeled 8-ary Phase-Shift-Keying （8PSK） modulation and employs a Maximum A Posteriori （MAP） symbol-to-bit metric calculator at the receiver. An equivalent model of a BICM communication channel with ideal interleaving is presented. The probability distribution function of log-likelihood ratio messages from the MAP receiver can be approximated by a mixture of symmetric Gaussian densities. As a result semi-Gaussian approximation can be used to analyze the decoder. Extrinsic information transfer charts are employed to describe the convergence behavior of LDPC decoder. The design of irregular LDPC codes reduces to a linear programming problem on two-dimensional variable edge-degree distribution. This method allows irregular code design in a wider range of rates without any limit on the maximum node degree and can be used to design irregular codes having rates varying from 0.5275 to 0.9099. The designed convergence thresholds are only a few tenths, even a few hundredths of a decibel from the capacity limits. It is shown by Monte Carlo simulations that, when the block length is 30,000, these codes operate about 0.62-0.75 dB from the capacity limit at a bit error rate of 10s.     

Model of temperature dependence for gain shape of erbium-dopedfiber amplifier

The problem of modeling the temperature dependence of erbium-doped fiber amplifier (EDFAs) is important for multichannel optical WDM systems. A physical model is presented in this paper, which could be used to predict the gain change under temperature variations for such systems. Some of the input parameters for the model are the erbium energy sublevel density, excitation coefficients from lower sublevels to upper sublevels of erbium ions, and electron distribution over energy levels. It is difficult to measure these parameters. In order to use the model for gain shape calculations, some simplifications are demonstrated. These simplifications lead to two numerical models, which are shown to be consistent with experimental data with reasonable accuracy, and are based only on two spectral measurements for different temperatures. Both numerical models were tested for the signal band and the 980 nm pump band of a typical erbium-doped fiber     

激光测高技术的发展趋势

激光测高技术作为一种的先进测量手段,已广泛应用于地形地貌测绘、地球科学研究、航天工程、城市规划、森林资源调查等诸多方面。虽然激光测高技术已相对成熟,但随着激光技术的发展和应用需求的拓展,激光测高技术仍有很大的发展空间。通过对国外近期研制或正在研究的几个具体激光测高设备的介绍和分析,总结了激光测高技术的一些典型技术特点和发展趋势,介绍了多光束发射和接收、单光子探测、多回波测量和多功能集成等技术在激光测高仪的应用。这对开展新型激光测高技术的研究具有一定参考价值。     

Vehicle counting in crowded scenes with multi-channel and multi-task convolutional neural networks

Vehicle counting in crowded urban setting plays a significant role in public security area. Most existing works on vehicle counting focused on video sequence. Though these techniques has achieved significant progress, it has a significant disadvantage: only moving vehicle could be counted. It is not realistic that vehicles are often stopped in most crowded cases, e.g. carpark and traffic-light intersections. To deal with this issue, in this paper, we propose a novel multi-channel and multi-task convolutional neural networks (CNN) to count vehicles from still images. More specially, we present a novel algorithm to produce illumination invariance image and combine it with original gray image as input channels, which could handle more details. And we deem vehicle counting as a local consistency deep regression problem, using a local label supervised deep CNN model to fit it. Moreover, we utilize surveillance camera view classification as a related task to improve the performance of vehicle counting task and the two tasks are trained end-to-end jointly. To evaluate the proposed model, we collect a real-work dataset for research and extensive experimental results show that the proposed method performs better than existing state-of-the-art methods.     

FTIR spectroscopy for the hermeticity assessment of micro-cavities

This paper presents an alternative method for the hermeticity assessment of micro-cavities. The method consists in monitoring the internal gas pressure of a cavity by Fourier Transform Infra Red (FTIR) spectroscopy, and then deducing the cavity’s leak rate from the pressure variations. In order to carry out the IR transmission measurements, nitrous oxide was chosen as bombing gas due to its excellent absorption properties for mid-IR radiations. First FTIR spectroscopy measurements performed on test vehicles have demonstrated the method feasibility on silicon-silicon micro-cavities with internal volumes of 5mm³ or more. These test vehicles were then bombed with nitrous oxide, and standard leak rates of 3.4 × 10⁻⁷ atm.cm³.s⁻¹ were assessed by FTIR spectroscopy. These leak rates have been confirmed by N₂O pressure variation monitoring for a 20 mm³ micro-cavity.     

Counter-based compaction: An analysis for BIST

According to some recently published results, counter-based compaction outperforms compaction by linear feedback shift registers. These results, however, are based on oversimplified assumptions. In this paper, we discuss an error model to describe the behavior of a faulty circuit under test. We study the three most popular counter-based compaction schemes, (i.e., one's counting, transition counting and edge counting). Using Markov processes we derive equations for iterative computations of exact aliasing probability for any test session length and determine the asymptotic probability of aliasing. For one's counting, we also present a closed form expression that, for any test session length, gives the exact aliasing probability. Finally, we present some examples to compare the aliasing in the counter-based compaction and compaction by a linear feedback shift register. These examples indicate that aliasing by LFSRs is more predictable than aliasing by counters.     

Limitations of Equation-Based Congestion Control

We study limitations of an equation-based congestion control protocol, called TCP-friendly rate control (TFRC). It examines how the three main factors that determine TFRC throughput, namely, the TCP-friendly equation, loss event rate estimation, and delay estimation, can influence the long-term throughput imbalance between TFRC and TCP. Especially, we show that different sending rates of competing flows cause these flows to experience different loss event rates. There are several fundamental reasons why TFRC and TCP flows have different average sending rates, from the first place. Earlier work shows that the convexity of the TCP-friendly equation used in TFRC causes the sending rate difference. We report two additional reasons in this paper: 1) the convexity of where is a loss event period and 2) different retransmission timeout period (RTO) estimations of TCP and TFRC. These factors can be the reasons for TCP and TFRC to experience initially different sending rates. But we find that the loss event rate difference due to the differing sending rates greatly amplifies the initial throughput difference; in some extreme cases, TFRC uses around 20 times more, or sometimes 10 times less, bandwidth than TCP. Despite these factors influencing the throughput difference, we also find that simple heuristics can greatly mitigate the problem.     

Effect of ion dose rate on rapid laser annealing of implanted GaAs

Short-duration laser annealing of localized regions on P⁺ ion-implanted GaAs wafers has been examined for various doses and dose rates by micro-Raman scattering and Rutherford backscattering measurements. Time required for complete annealing of ion-induced defects varies from 5 ms to 1 s, corresponding to the implanted dose and rate. It is found that the amount of produced defects is enhanced by implantation with higher dose rates and that defects produced with higher dose rates are more easily annealed by the laser irradiation during short durations within a certain dose range.