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Abstract. The open internet is plagued by congestion that restricts the development of sophisticated internet-based services, as was predicted in early work on priority pricing. Broadband and edge providers have [...]

This paper examines the effects of providing broadband to schools on students' performance. We use a rich panel of data on broadband use and students' grades from all middle schools in Portugal. Employing a first-differences specification to control for school-specific unobserved effects and instrumenting the quality of broadband to account for unobserved time-varying effects, we show that high levels of broadband use in schools were detrimental for grades on the ninth-grade national exams in Portugal. For the average broadband use in schools, grades reduced 0.78 of a standard deviation from 2005 to 2009. We also show that broadband has a negative impact on exam scores regardless of gender, subject, or school quality and that the way schools allow students to use the Internet affects their performance. In particular, students in schools that block access to websites such as YouTube perform relatively better. Data, as supplemental material, are available at http://dx.doi.org/10.1287/mnsc.2013.1770. Keywords: broadband; school; education; instrumental variables History: Received February 3, 2012; accepted January 27, 2013, by Lorin Hitt, information systems. Published online in Articles in Advance October 23, 2013., 1. Introduction The role of information and communication technologies (ICTs) in our economy can hardly be overemphasized. There is a great amount of literature in both information technology (IT) and [...]

A study was conducted to present potential architectural and technological solutions for broadband services. A scalable architecture which reduces complexity as far as possible by shifting packet processing to the edges of the network is described. The implementation of high leverage transport networks is also discussed.

A flourishing digital economy needs broadband access and content relevant to people's lives. This paper describes how Electronic Resources Australia (ERA: http://era.nla.gov.au/) was established to deliver digital content, Through national [...]

The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth's climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem C[O.sub.2] uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both C[O.sub.2] uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle--climate models. nitrogen cycle | climate change | foliar nitrogen | ecosystem-climate feedback | remote sensing

In this article, an inversion-based feedforward control approach to achieve broadband active-noise control is investigated. Broadband active-noise control is needed in many areas, from heating, ventilation and air conditioning (HVAC) ducts to aircraft cabins. Achieving broadband active-noise control, however, is very challenging due to issues such as the complexity of acoustic dynamics (which has no natural roll-off at high frequency, and is often nonminimum phase), the wide frequency spectrum of the acoustic noise, and the critical requirement to overcome the delay of the control input relative to the noise signal. These issues have limited the success of existing feedforward control techniques to the low-frequency range of [0, 1] kHz. The modeling issues in capturing the complex acoustic dynamics coupled with its nonminimum-phase characteristic also prevent the use of high-gain feedback methods, making the design of an effective controller to combat broadband noises challenging. In this article, we explore, through experiments, the potential of inversion-based feedforward control approach for noise control over the 1 kHz low-frequency range limit. Then we account for the effect of modeling errors on the feedforward input by a recently developed inversion-based iterative control technique. Experimental results presented show that noise reduction of over 10-15 dB can be achieved in a broad frequency range of 5 kHz by using the inversion-based feedforward control technique. [DOI: 10.1115/1.2948411]

A broad-band fiber mirror (BFM) and a tunable fiber Bragg grating (TFBG) at either end of laser cavity were used for developing a linear-cavity tunable erbium-doped fiber laser (TEDFL). Results suggest the achievement of a side-mode suppression ratio of 57.9 dB, wavelength tuning range up to 30 nm with step resolution of 0.2 nm and power variation less than +1.0 dB.

A scanning method is developed to obtain the broadband ultrasound attenuation (BUA) map in the calcaneal region. The method provides results that could be used to screen patients before referring them for Dual Energy X-ray Absorptiometry (DEXA).

Broadband optical monitoring for thin-film filter manufacturing is more and more developed thanks to better performances of spectrometers with array detectors. We compare this optical monitoring with turning point monitoring and quartz monitoring of different designs. The sensitivity to thickness errors and to refractive index errors is evaluated. We show that real time determination of deposited thickness is a valuable criterion. We also present our experimental setup of transmittance and reflectance broadband optical monitoring. The use of a 400-1000 nm range combined with a signal-to-noise ratio of ~2500 in transmittance and 1000 in reflectance permits us to expect the manufacturing of high-performance non-quarter-wave designs. A first manufacturing of an 18-layer non-quarter-wave high-pass filter is provided. OCIS codes: 310.0310, 310.1860, 310.1620, 310.6860.

A converged broadcast and telecommunication service platform is presented that is able to create, deliver, and manage interactive, multimedia content and services for consumption on three different terminal types. The motivations of service providers for designing converged interactive multimedia services, which are crafted for their individual requirements, are investigated. The overall design of the system is presented with particular emphasis placed on the operational features of each of the sub-systems, the flows of media and metadata through the sub-systems and the formats and protocols required for inter-communication between them. The key features of tools required for creating converged interactive multimedia content for a range of different end-user terminal types are examined. Finally possible enhancements to this system are discussed. This study is of particular interest to those organizations currently conducting trials and commercial launches of DVB-H services because it provides them with an insight of the various additional functions required in the service provisioning platforms to provide fully interactive services to a range of different mobile terminal types. Index Terms--Broadcasting, multimedia communication, service platform, terrestrial mobile cellular radio systems.

We replace the traditional grating used in a dispersive spectrometer with a multiplex holographic grating to increase the spectral range sensed by the instrument. The multiplexed grating allows us to measure three different, overlapping spectral bands on a color digital focal plane. The detector's broadband color filters, along with a computational inversion algorithm, let us disambiguate measurements made from the three bands. The overlapping spectral bands allow us to measure a greater spectral bandwidth than a traditional spectrometer with the same sized detector. Additionally, our spectrometer uses a static coded aperture mask in the place of a slit. The aperture mask allows increased light throughput, offsetting the photon loss at the broadband filters. We present our proof-of-concept dispersion multiplexing spectrometer design with experimental measurements to verify its operation. OCIS codes: 120.620, 090.1970.

A single-stage equivalent circuit is proposed to model microwave bandpass filters (BPFs) fabricated in low-temperature co-fired ceramic (LTCC) technology up to several times its passband frequency. The equivalent circuit adopts a modified T topology with the expandable multilayer resonators to achieve an extremely large bandwidth. It can be efficiently established from the measured S-parameters using direct extraction or rational approximation. As a result, the modeled S-parameters for a 2.45-GHz wideband local area network (WLAN) LTCC BPF show good agreement with the measured results over a wide frequency range up to 8.5 GHz. Such a broadband model can be used to accurately predict the suppression of harmonics and interferences in system simulation of the WLAN front-end modules. Index Terms--Equivalent-circuit model, low-temperature co-fired ceramic (LTCC) bandpass filter (BPF), wideband local area network (WLAN) BPF.

Gradient index coatings and optical filters are a challenge for fabrication. In a round-robin experiment, basically the same hybrid antireflection coating for the visible spectral region, combining homogeneous refractive index layers of pure materials and linear gradient refractive index layers of material mixtures, has been deposited. The experiment involved three different deposition techniques: electron-beam evaporation, ion-beam sputtering, and radio frequency magnetron sputtering. The material combinations used by these techniques were [Nb.sub.2][O.sub.5]Si[O.sub.2], Ti[O.sub.2]/Si[O.sub.2], and [Ta.sub.2][O.sub.5]Si[O.sub.2], respectively. The spectral performances of samples coated on one side and on both sides have been compared to the corresponding theoretical spectra of the designed profile. Also, the reproducibility of results for each process is verified. Finally, it is shown that ion-beam sputtering gave the best results in terms of deviation from the theoretical performance and reproducibility. OCIS codes: 310.1210, 310.1620, 310.1860.

Broadband communications for indoor power-line networks with impulsive noise using orthogonal frequency division multiplexing (OFDM) is considered. From earlier investigations, it is known that this channel suffers from multipath fading and frequency selectivity along with man-made impulsive bursty noise. Nevertheless, the calculated channel capacity limit promises very high data rates over this channel. Enhancement techniques, such as coding can help an OFDM system to tackle impulsive noise burst. In this paper, the bit error rate (BER) performance of the OFDM system under impulsive noise and frequency fading is theoretically analyzed and closed form expression for the performance is derived. Two different impulsive noise environment models are studied and it is confirmed that both models represent the same environment. Furthermore, a theoretical upper bound on the performance of coded OFDM system is obtained, given perfect interleaving. The effect of the interleaver length on coding performance is also studied. Simulations show that the upper bound is quite tight for the case of employing a longer interleaver. The effect of interleaver size on the system performance is studied, as well. Index Terms--Error control coding, impulsive noise, low voltage, orthogonal frequency division multiplexing (OFDM), power-line communications, union upper bound.

Transmission properties of the power-line channels play a very important role in the reliability of signal propagations. This paper discusses the physical signal transmission property on the broadband power-line channels based on transmission-line theory, mode propagation theory and electromagnetic-field radiation theory. It also examines the carrier signal propagating through the multi-path line channel by empirical data. The correlations among the channel attenuation and frequency, length of the path, loads and branches are analyzed, respectively, and the path loss is calculated based on empirical data and linear regressive analysis. In the end, the impact of the radiation from carrier signals on the channel characteristic measurement is concluded. Index Terms--Power-line communication, signal propagation, transmission properties.

Electromagnetic coupling between a broadband over power line (BPL) system and an HF communication system is discussed in this paper. Numerical analyses using the method of moments were performed to determine the near-field coupling between the BPL and communication systems at 3.5, 7, 14, and 28 MHz. Half-wave dipole and quarter-wave vertical antennas were positioned at 1-m intervals along the power line to find the maximum and minimum signal levels caused by the BPL system. Signal levels induced into the BPL system by a 100-W HF transmitter are also presented. Index Terms--Broadband over power lines (BPL), electromagnetic compatibility, electromagnetic interference (EMI), HF communications, radiation.

This paper describes the application of finite elements for the modeling and simulation of overhead power-line structures in the high-frequency range, using existing computing tools and software. This paper treats specifically non-uniform wire arrangements common in overhead power networks, including line junctions, bends, neutral grounding, etc., which disturb the transmission of signals, especially at high frequencies, increasing reflections, radiation, and mode conversion. The proposed models could be used in applications associated with broadband communication over power lines providing a reliable representation for assessing the capability of the overhead network to carry high-frequency signals and estimate the resulting electromagnetic emissions. Index Terms--Broadband over power lines (BPL), electromagnetic (EM) emissions, finite elements, high-frequency line models.

The problem of discontinuities in broadband multisection coupled-stripline 3-dB directional couplers, phase shifters, high-pass tapered-line 3-dB directional couplers, and magic-T's, regarding the connections of coupled and terminating signal lines, is comprehensively investigated in this paper for the first time. The equivalent circuit of these discontinuities proposed in Part I has been used for accurate modeling of the broadband multisection and ultra-broadband high-pass coupled-stripline circuits. It has been shown that parasitic reactances, which result from the connections of signal and coupled lines, severely deteriorate the return losses and the isolation of such circuits and also--in case of tapered-line directional couplers--the coupling responses. Moreover, it has been proven theoretically and experimentally that these discontinuity effects can be substantially reduced by introducing compensating shunt capacitances in a number of cross sections of coupled and signal lines. Results of measurements carried out for various designed and manufactured coupled-line circuits have been very promising and have proven the efficiency of the proposed broadband compensation technique. The theoretical and measured data are given for the following coupled-stripline circuits: a decade-bandwidth asymmetric three-section 3-dB directional coupler, a decade-bandwidth three-section phase-shifter compensator, and a high-pass asymmetric tapered-line 3-dB coupler. Index Terms--Asymmetric multisection coupled-line directional couplers, asymmetric tapered-line directional couplers, broadband magic-T's, discontinuities, multisection coupled-line phase shifters and compensators, technique of capacitive compensation.

This paper studies the impact of the data-over-cable service interface specification (DOCSIS) media-access control (MAC) protocol on the performance of the transmission control protocol (TCP) in hybrid fiber coax (HFC) broadband access networks. We find that the asymmetry ratio expressed in existing work cannot adequately explain the behavior of TCP in DOCSIS-based networks. To better capture the effect of DOCSIS on TCP, we express the asymmetry ratio (denoted by [eta]) in another way (denoted by k), considering the time-division multiple-access-like MAC layer operation of DOCSIS. When [eta] > 1, TCP behaves as in a symmetric network, and when [eta] [less than or equal to] 1, the system acts as in an asymmetric network, and the performance of TCP degrades. We find that the number of simultaneous TCP transfers significantly affects the asymmetry ratio. When the number of active transfers is below two times the maximum number of pending requests in a transmission period, the value of [eta] is larger than one, regardless of the value of k. However, when the number of active transfers becomes very large, the effect of DOCSIS on TCP becomes negligible, and the asymmetry ratio is determined by the bandwidth ratio of the channels times the length ratio of data and acknowledgement packets. Based on [eta], we develop the round-trip delay of sending a data packet for both one-way and two-way transfers, and discuss the buffer requirement at the head end. The accuracy of the analytical model is validated by ns-2 simulations. The analytical result can provide useful guidelines in the design of slot allocation or scheduling mechanisms for any DOCSIS-based broadband access networks, including the emerging IEEE 802.16 WiMAX networks. Index Terms--Broadband access networks, community antenna television (CATV), data-over-cable service interface specification (DOCSIS), transmission control protocol (TCP).

Experimental demonstration of small angle (0.8[degrees]-5[degrees]) direct UV-written X couplers in silica-on-silicon is presented. Maximum and minimum coupling ratios of 95% ([+ or -] 0.8%) and 1.9% ([+ or -]1%), respectively, were recorded. The structures also display very low polarization and wavelength dependence. A typical excess loss of 1.0 dB ([+ or -]0.5 dB) was recorded. Device modeling using the beam propagation method and an analytical model showed good agreement with experimental results over a broad crossing angle and wavelength range. OCIS codes: 130.0130, 130.1750, 220.0220, 220.4610.