TFMCC versus ASMP: lessons learned from performance evaluation

In this article we present a simulation‐based comparison of one of the best‐known multicast congestion control schemes—TCP‐friendly Multicast Congestion Control (TFMCC)—against our proposed Adaptive Smooth Multicast Protocol (ASMP). ASMP consists of a single‐rate multicast congestion control mechanism which takes advantage of the RTCP Sender (SR) and Receiver Reports (RR) in order to adjust the sender's transmission rate in respect of the network conditions. The innovation in ASMP lays in the ‘smooth’ transmission rate, which is TCP‐friendly and prevents oscillations. We use an integrated simulation environment named Multi‐Evalvid‐RA for the evaluation of the two congestion control schemes. Multi‐Evalvid‐RA provides all the necessary tools to perform simulation studies and assess video quality by using both network‐centric metrics along with video quality measurements. Performance evaluation results show that ASMP is a very efficient solution for rate‐adaptive multimedia applications and a serious competitor to well‐known TFMCC. Copyright © 2012 John Wiley & Sons, Ltd.     

卫星电视干扰器查找经验

卫星干扰器的安装使用严重影响了人民生活、扰乱了空中电波秩序。对此国家明令禁止,但因利益驱动屡禁不止。自2007年5月以来,我分局查处没收5部卫星干扰器,其中3部干扰了县有线电视前端。下面针对其中两起查找案例,总结一下相关经验教训,并对一种非常规查找方法进行探讨。     

Action research: lessons learned from a multi-iteration study of computer-mediated communication in groups

Action research has been presented as a promising approach for academic inquiry because of its focus on real world problems and its ability to provide researchers with a rich body of field data for knowledge building. Published examples of action research, however, are hard to find in business communication literature. What are the reasons for this? I try to provide a basis for answering this question as well as helping other business communication researchers-particularly those interested in computer-mediated communication issues-to decide whether and when to employ action research. I offer a first-person, confessional tale-like account of an action research study of computer-mediated communication in groups. In order to focus on the lessons learned, my focus is on the process of conducting action research and not on empirical results. Some of the situations and related lessons discussed are somewhat surprising and illustrate the complex nature of action research. The doctoral research, conducted over four years in Brazil and New Zealand, highlights the challenges associated with action research's dual goal of serving practitioners and the research community.     

Success factors and future challenges in the management offaster-better-cheaper projects: lessons learned from NASA

In the last few years, NASA has shifted its mode of management of unmanned space missions from “flagship” missions to faster-better-cheaper (FBC) projects with reduced scope, budget and schedule. In order to examine the successful attributes and potential weaknesses of this new management style, the authors prepared four case studies at NASA's Jet Propulsion Laboratory (Pasadena, CA) in 1997 and 1998. Based on these case studies, (Cassini, Mars Pathfinder, Mars Global Surveyor, and Deep Space 1), they identified a number of management features that seem to have contributed to the success of the early FBC projects. These features generally involve simplification, standardization and the use of commercially available components and talents. They also pointed out that most of these features had potential downsides, and they expressed some concerns about the long-term viability of some of these features. The recent failures of two Mars missions have also shown the limitations of this mode of operations. Therefore, in the future, some of these features may have to be revisited to account better for risks and uncertainties. In this paper, the authors describe these management factors, some of the challenges that remain, and a set of recommendations based on their observations, many of which apply to other industries subjected to similar constraints     

Emerging high-speed xDSL access services: architectures, issues,insights, and implications

High-speed asymmetric and symmetric digital subscriber line loop access systems, designed by numerous computer networking and telecommunications equipment companies, are currently the focus of technical trials, market trials, and commercial services deployment around the world. This is to provide millions of residential and business customers worldwide with high-speed always-on connectivity to the Internet, corporate intranets, and various online services. It is estimated that over 460 million copper loops worldwide could potentially be equipped end-to-end with xDSL access systems. Large-scale deployment of broadband access systems offering always-on connectivity to the global Internet and corporate intranets is seen as a key enabler of the bold vision articulated worldwide to utilize open Internet protocols and emerging technologies such as Java to create a unified software-defined (IP) global networking infrastructure. Such a networking platform would serve as a de facto medium for generation and delivery of integrated multimedia content, and revolutionize the way people around the world learn, do business, and interact with each other     

Early experiences and lessons learned from femtocells - [femtocell wireless communications]

There is a continuous pursuit by mobile operators (MOs) to improve indoor coverage in order not only to improve voice quality but also to enable higher data rates in home/office environments. Indoor coverage improvement, in conjunction with inexpensive (voice) offerings, will enable MOs to compete with and take away voice-call-related revenues from fixed network PTTs and/or VoIP operators. Femtocells constitute a promising solution to address all of the above. In this article we present our experience from our extensive study and trials of early (pre-standard) femtocell solutions that were available in the 2007-2008 timeframe.     

Managing knowledge integration in a national health-care crisis: lessons learned from combating SARS in Singapore.

The outbreak of Severe Acute Respiratory Syndrome is the first severe and readily transmissible disease to emerge in the 21st century. Often one new infection meant tracing of several people to monitor their health conditions as well. In Singapore, several agencies coordinated their efforts to quickly bring the outbreak under control. The current breed of health-care information systems (HCIS) was not sufficient to handle new information-sharing needs during the crisis. In this paper, we take a look at the measures taken during the crisis in Singapore through a knowledge integration perspective. This perspective reveals interesting implications for HCIS.     

XMPP: lessons learned from ten years of XML messaging - [topics in design & implementation]

Can an entire technology ecosystem be designed? Although we usually think of design and implementation in relation to particular features or applications, overall technologies ? such as the Session Initiation Protocol for Voice over IP or the Hypertext Transfer Protocol for the World Wide Web ? can constrain the set of possible solutions to more well-bounded problems. Given the large scope of a technology ecosystem (including protocols, software implementations, application types, service deployments, and various stakeholders), we would expect to find that some of its aspects can be designed, some aspects can be guided in an approximate fashion, and other aspects exhibit an emergent order or no order whatsoever. To investigate such issues, this article summarizes some of the challenges faced, and lessons learned, by the Extensible Messaging and Presence Protocol developer community since 1999.     

A case study for micro‐grid PV: lessons learned from a rural electrification project in India

Micro‐grids in developing countries present a significant application opportunity for photovoltaics (PV) as an energy‐enabling technology. The authors project 10 GW for this application in the next decade. The growth of this sector will be enhanced by shared learning of the best practices. The authors are part of a team that successfully installed 1/3 MW in micro‐grids and presented the lessons learned and a useful methodology for determining key metrics. The PV is part of the rural electrification in India and is representative of current global PV micro‐grids. This project provides basic lighting and electricity for 57 villages in Visakhapatnam in India. The project was carried out with a goal of optimizing power against cost. Various metrics are presented: costs, time, operations and maintenance, and performance. Also discussed are implementation strategies for cost containment, stakeholder considerations, and post‐install support and user payment collection. Learning points are presented on project execution, engagement of local people, and challenges addressed. The aspect of demand capacity level (hours of availability) is examined in more detail, with modeling being performed to identify an optimal approach to increasing the level given the cost constraints. The combination of real data and modeling is a useful approach for PV and micro‐grid optimization. This case study quantitatively supports the value of the use of PV for rural electrification. Beyond this example in India, where the federal government is planning an increase to more than 2000 sites, there is a significant opportunity for PV in the global micro‐grid electrification context. Copyright © 2013 John Wiley & Sons, Ltd.     

Parathyroid hormone 1 receptor: insights into structure and function

The parathyroid hormone (PTH) and parathyroid hormone type 1 receptor (PTH1-Rc) are major players in regulating blood calcium homeostasis. PTH1-Rc is a G protein-coupled receptor (GPCR) and it is also activated by PTH-related protein (PTHrP), which has potent effects in several target tissues including bone, via endocrine, paracrine, and autocrine mechanisms in prenatal and adult stages of life, and in several diseases. Another layer of complexity is added by the recently discovered PTH2-Rc subtype displaying unique tissue distribution and ligand specificity, and the potential presence in mammals of a third receptor subtype. Understanding of the mechanisms regulating PTH1-Rc gene expression, receptor desensitization, endocytosis, recycling, and intracellular signaling is advancing and provides insights to understand PTH1-Rc's role in both normal and pathophysiology. In addition, development of an experimentally based model of the PTH-PTH1-Rc complex by combining photoaffinity crosslinking, mutagenesis, conformational analysis, and molecular modeling sheds light, at the atomic resolution, on the molecular mechanisms involved in ligand binding, receptor activation, and coupling to intracellular effectors. Taken together, these lines of investigation offer not only a better understanding of GPCR mechanisms of action in general, but also contribute to the treatment of PTH/PTHrP-PTH1-Rc-related disease states and to the rational development of novel mechanism-based drugs to treat them.     

60 GHz indoor WLANs: insights into performance and power consumption

This paper presents a feasibility study of 60 GHz indoor WLANs. We evaluate 60 GHz performance in a typical academic office building under the primary assumption that 60 GHz WLAN APs and clients will be equipped with relatively wide-beam antennas to cope with client mobility. In contrast to previous works which measured performance at a single layer using custom, non-standard compliant hardware, we investigate performance across multiple layers using primarily 802.11ad-compliant wide-beam COTS devices. Our study shows that the large number of reflective surfaces in typical indoor WLAN environments combined with wider beams makes performance highly unpredictable and invalidates several assumptions that hold true in static, narrow-beam, Line-Of-Sight scenarios. Additionally, we present the first measurements, to our best knowledge, of power consumption of an 802.11ad NIC and examine the impact of a number of factors on power consumption.     

Physical insights regarding design and performance of independent-gate FinFETs

Important physical insights regarding the design and performance of independent-gate FinFETs, e.g., the MIGFET , are gained from measured data and predictions from our process/physics-based double-gate (DG) MOSFET model (UFDG) in Spice3. Inversion charge-centroid shifting, modulated by gate biases as well as by quantum-confinement and short-channel effects, underlies the sensitivity of the MIGFET (front-gate) threshold voltage to the back-gate bias. MIGFET design and operation-mode options are examined for optimizing circuit applications. Further, novel design of a single-device RF mixer and a double-balanced counterpart using MIGFETs is studied with UFDG/Spice3. Reasonably good MIGFET mixers, with regard to conversion gain and linearity with small-size/low-voltage/low-power requirements, can be achieved with optimal biases on the two gates and good design of the MIGFET structure.     

Characteristics, structure, and performance of a diffused-base germanium oscillator transistor

The diffused-base transistor structure affords a degree of design flexibility not found in previous structures. This is true because it has a larger number of independently adjustable design parameters than the previous structures. Its flexibility has been exploited in an oscillator transistor for 200-mc service. Design analysis shows that low ohmic base resistance, low collector body resistance, and operation at about 0.3 of the collector breakdown voltage are desirable in the present application. The methods of Lee have been used in making this germaniump-n-pdiffused-base unit. Alloyed emitter and base electrodes are parallel stripes approximately 0.5-mil apart, each measuring 1 × 6 mils. The collector is about 4.5 × 8 mils. Typical parameters at Vc= -10 volts and 1E= 10 ma are: fα= 600 mc,r'_{b}= 35 ohms, and Cc= 1.0 mmf. Median 200-mc oscillator efficiency of 50 per cent is obtained at the design bias point of -20 volts, 10 ma; this exceeds the performance objective. The unit withstands 20,000-gaccelerations in any direction, an additional demand imposed by the specific application for which it was developed.     

Language generation: Applications, issues, and approaches

As computer systems become more sophisticated they must be able to communicate their results successfully to their users. Natural language generation is the area of research concerned with developing methods that will allow a computer system to respond to its user in human language. In this paper, the need for natural language generation is first motivated by showing how it is used in several applications. Given that language generation is necessary for such systems, the paper also focuses on the issues that must be taken into account in developing a system that can generate language. Finally, techniques that have been used in two question-answering systems, the TEXT system [21] and TAILOR [22], are discussed.     

DC-to-RF dispersion effects in GaAs- and GaN-based heterostructure FETs: performance and reliability issues

The performance and reliability implications of DC-to-RF dispersion effects are addressed. The proposed physical explanations and technological counteractions are reviewed. GaAs- and GaN-based FET technologies are considered, trying to point out both similar and peculiar aspects.     

Some results and insights on the performance gains of MIMO systems

Multiple-input-multiple-output (MIMO) systems generally fall into two categories, depending on the kind of gain they provide: spatial multiplexing (SM) methods yield capacity gain and diversity methods yield link quality gain [measured here by the post-processing signal-to-noise ratio (SNR)]. We consider a set of systems from each category, quantify their gains analytically or via simulations, and show how these gains vary with the receiver input SNR and the numbers of antennas. The contribution of this work resides in both the closed-form analytical results and the numerical comparisons. We both highlight the benefits of using additional transmit antennas and provide comparisons among diversity-based and SM-based MIMO schemes. The analytical results are for a diversity-based scheme that combines selection diversity at the transmit side with maximum ratio combining (MRC) at the receive side, which we show to upper bound the SNR performance of other diversity-based schemes. We find that, for practical system parameters, the relevant SNR metric is 6-12 dB higher for the diversity-based schemes than for SM-based schemes. At the same time, SM-based schemes yield capacity metrics which range from 30% higher to double that of diversity-based schemes.     

HI hydrolysis-derived intermediate as booster for CsPbI3 perovskite: from crystal structure,film fabrication to device performance

Nowadays,inorganic CsPbI3 perovskite solar cells(PSCs)have become one of the most attractive research hotspots in photovoltaic field for its superior chemical stability and excellent photo-electronic properties.Since the first independent report in 2015,the power conversion efficiency(PCE)of CsPbI3 based PSCs has sharply increased from 3.9%to 19.03%.Importantly,during the developing process of CsPbI3 PSCs,HI hydrolysis-derived intermediate plays an important role:from stabilizing the crystal structure,optimizing the fabricated film to boosting the device performance.In this review,the different crystal and electronic structures of CsPbI3 are introduced.We then trace the history and disputes of HI hydrolysis-derived intermediate to make this review more logical.Meanwhile,we highlight the functions of HI hydrolysis-derived intermediate,and systematically summarize the advanced works on CsPbI3 PSCs.Finally,the bottlenecks and prospects are revealed to further increase the CsPbI3 PSCs performance.     

蔗糖热解碳对LiFePO4材料结构和性能的影响

应用微波法制备了锂离子电池正极材料LiFePO4,通过预加在前驱体中的蔗糖受热分解产生的碳来改善材料的结构和性能。XRD和SEM分析发现,这种方式引进的碳对材料的晶体结构影响不大,但可抑制由于加热时间增加而引起的晶体长大。添加蔗糖材料的高倍率循环性能比纯LiFePO4大大提高。电化学阻抗谱显示,添加蔗糖的材料所装电池的阻抗可达123?,远小于纯LiFePO4材料的1110?。