High strength and high ductility together are prime requirements for modern structural metallic materials. Important industrial examples are steels for car components such as body sheets, tubes and ...forgings. The present paper traces two lines of alloy development, stable austenitic stainless steels and intentionally metastable austenitic stainless steels. Although both groups have different advantages and disadvantages, each one exceeds all other presently available structural metallic materials in terms of strength to density ratio at equal ductility.
This paper seeks to refocus the attention of environmentalists on the importance of population trends to environmental sustainability and identifies prevention of unintended pregnancy as potential ...common ground for environmentalists and family planning advocates. The health and other welfare benefits of preventing unintended pregnancy are felt most keenly by individual women, men, and their families. At the same time, however, preventing unwanted pregnancies usually results in smaller family size, an important factor in slowing population growth and, as a result, a source of broader benefits--including environmental benefits--to society.
Past US FDA decisions about emergency contraception (EC) have been subject to undue political influence, and last year s barring of over-the-counter access to Plan B One-Step
for those under the age ...of 17 years is no exception. The US Department of Health and Human Services cited insufficient data on EC use for females aged 11-12 years. These youngest adolescents, however, rarely need EC: data from California (USA) show that in 2009, fewer than one in 10,000 females under the age of 13 years received EC. Maintaining barriers to safe and effective EC is not medically necessary and conflicts with national goals to decrease teenage and unintended pregnancies.
Heterogeneous cellular networks (HetNets), where low-power base-stations are overlaid with conventional macro base-stations, is a promising technique to improve coverage and capacity of the ...macro-only networks. To realize the potential benefits of HetNets, it is crucial to jointly optimize the user association, channel assignment, beamforming and power control to ensure that the inter- and intra-cell interference will not overwhelm the cell-splitting gains. This paper presents an iterative algorithm to solve the joint optimization problem with an objective of maximizing the network sum rate and simultaneously guaranteeing the individual user quality-of-service. The proposed algorithm is built on the so-called convex-concave procedure, and the feasibility issue is handled by L1-norm heuristic. Numerical results demonstrate the large gains over currently used methods for cellular networks.
This paper investigates the performance of the digital symbol timing recovery schemes for 16QAM upstream transmission of the DOCSIS standard. Two forms of nonlinearity are considered: the magnitude ...square operation and the delay multiplication operation, both of which generate the output signal that contains the symbol timing information. The detailed analysis for the magnitude square timing recovery is given in the digital domain, and consequently the symbol timing estimate can be directly obtained by the discrete Fourier transform. The simulation results show that the magnitude square timing recovery and delay multiplication timing recovery algorithms suffer from the same problem that the estimation error is reduced slowly at high signal-to-noise ratios due to the effect of self-noise. To this end, the third scheme, which is the magnitude square timing recovery with prefilter, is examined. This scheme shows a superior performance and a comparison with the results of the other two schemes is made.
In upstream transmission of the DOCSIS (data over cable service interface specification) 1.0/1.1 and the TDMA mode of DOCSIS 2.0 standard, a packet begins with a preamble, the length and value of ...which are programmable by the headend. The acquisition process includes packet detection, symbol timing estimation, carrier frequency offset estimation and carrier phase estimation by means of the preamble so that the following information packet can be correctly demodulated. Methods to solve these tasks are not subject to standardization and are left to the system designer. However, they have a great impact on the system performance and thus are key elements for implementation. We present dedicated algorithms. A specific preamble is created and the corresponding scheme for packet acquisition is described in some detail. The packet detecting algorithm is independent of the carrier and symbol timing. The symbol timing estimate is obtained by using the minimum mean square algorithm regardless of the carrier frequency deviation and carrier phase. Algorithms for estimating the carrier frequency offset and carrier phase are proposed. Computer simulation results are given for all algorithms presented.
We propose and analyze a generalized spatial modulation scheme, where depending on the bits to be transmitted a certain data symbol as well as a certain beamforming vector is chosen. The receiver ...then has to estimate both the used beamforming vector and the transmitted data symbol for being able to reconstruct the originally transmitted bit sequence. We analyze our scheme theoretically by deriving a very tight upper bound on the average bit error rate (BER) for arbitrary symbol constellations and beamforming codebooks in correlated Rayleigh fading channels. Based on this bound, we determine a design criterion for optimizing the used beamforming codebook in presence of spatial correlation at the transmitter-side. Simulation results are shown to be in excellent agreement with our analytical calculated BERs and they illustrate the significant performance gains that can be obtained with our generalized scheme compared to conventional spatial modulation.
MPEG-2 video coding is widely used in broadcasting and increasingly in studio applications. For reasons of limited storage and/or transmission capacity, it may be necessary to reduce the bit rate of ...MPEG-2 video bitstreams. We present an implementation of a frequency domain transcoder (FDTC) on a media processor which reduces the bit rate of an incoming video bitstream in real time. The FDTC has a low complexity and low memory requirements. A rate control with low delay provides a bitstream with constant bit rate (CBR) at the output, independent whether the input bit rate is variable (VBR) or constant (CBR). The FDTC achieves a better or same peak signal-to-noise ratio (PSNR) than a bulky cascade of a complete MPEG-2 video decoder and encoder.
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