Wormhole solutions with a polynomial equation-of-state and minimal violation of the null energy condition

This paper discusses wormholes supported by general equation-of-state , resulting in a significant combination of the linear equation-of-state and some other models. Wormhole with a quadratic equation-of-state is studied as a particular example. It is shown that the violation of null energy condition is restricted to some regions in the vicinity of the throat. The combination of barotropic and polytropic equation-of-state has been studied. We consider fluid near the wormhole throat in an exotic regime which at some $r=r_{1}$, the exotic regime is connected to a distribution of asymptotically dark energy regime with $-1<\omega<-1/3$. We have presented wormhole solutions with small amount of exotic matter. We have shown that using different forms of equation-of-state has a considerable effect on the minimizing violation of the null energy condition. The effect of many parameters such as redshift as detected by a distant observer and energy density at the throat on the $r_1$ is investigated. The solutions are asymptotically flat and compatible with presently available observational data at the large cosmic scale.Comment: 12 pages, 13 figure

Noise vs. News in Equity Returns

What role does noise play in equity markets? Answering this question usually leads immediately to specifying a model of fundamentals and hence the pervasive joint hypothesis quagmire. We avoid this dilemma by measuring noise volatility directly by focusing on the behavior of country closed-end funds (CCEF’s) during foreign (i.e., non-U.S.) holidays – for example, the last days of Ramadan in Islamic countries. These holiday periods are times when the flow of fundamental information relevant to foreign equity markets is substantially reduced and hence trading of CCEF’s in U.S. markets can be responding only weakly, if at all, to fundamental information. We find that, controlling for the effects of industry and global shocks and of the overall U.S. market, there remains a substantial amount of noise in the equity returns of U.S. CCEF’s. In the absence of noise, the noise ratio statistic would be near zero. However, our results indicate statistically significant departures from zero, with values averaged over all U.S. CCEF’s ranging from 76-84% depending on assumptions about the leakage of information during holiday periods and kurtosis. Noise is negatively related to institutional ownership of U.S. CCEF's and is much less important for U.K. CCEF's. The lower levels of noise for matched U.K. and U.S. CCEF’s suggest that the U.K. securities transaction tax is effective in reducing stock market noise.equity market noise, inefficient markets, institutional ownership, securities transaction tax, closed-end funds

One-Bit Precoding and Constellation Range Design for Massive MIMO with QAM Signaling

The use of low-resolution digital-to-analog converters (DACs) for transmit precoding provides crucial energy efficiency advantage for massive multiple-input multiple-output (MIMO) implementation. This paper formulates a quadrature amplitude modulation (QAM) constellation range and one-bit symbol-level precoding design problem for minimizing the average symbol error rate (SER) in downlink massive MIMO transmission. A tight upper-bound for SER with low-resolution DAC precoding is first derived. The derived expression suggests that the performance degradation of one-bit precoding can be interpreted as a decrease in the effective minimum distance of the QAM constellation. Using the obtained SER expression, we propose a QAM constellation range design for the single-user case. It is shown that in the massive MIMO limit, a reasonable choice for constellation range with one-bit precoding is that of the infinite-resolution precoding with per-symbol power constraint, but reduced by a factor of $\sqrt{2/\pi}$ or about $0.8$. The corresponding minimum distance reduction translates to about 2dB gap between the performance of one-bit precoding and infinite-resolution precoding. This paper further proposes a low-complexity heuristic algorithm for one-bit precoder design. Finally, the proposed QAM constellation range and precoder design are generalized to the multi-user downlink. We propose to scale the constellation range for infinite-resolution zero-forcing (ZF) precoding with per-symbol power constraint by the same factor of $\sqrt{2/\pi}$ for one-bit precoding. The proposed one-bit precoding scheme is shown to be within 2dB of infinite-resolution ZF. In term of number of antennas, one-bit precoding requires about 50% more antennas to achieve the same performance as infinite-resolution precoding.Comment: 14 pages, 9 figures, to be published in IEEE Journal on Selected Topics on Signal Processin

Export-Oriented FDI, the Euro, and EU Enlargement

Since 1999, the UK’s share of FDI heading into Europe has declined dramatically, while the Euro-Zone’s share has increased. I argue that the timing of this divergence is not coincidental. The formation of the Euro-Zone has eliminated nominal exchange rate volatility between member-states, increasing export market access intra-union. For source countries outside of Europe, Euro-Zone countries have become more attractive destinations for export-oriented FDI, as operations within the union are insulated from currency fluctuations. As exchange rate volatility between a non-Euro country and local export markets increases, or as the market size of the euro-zone increases, more and more investment will be diverted towards Euro-Zone countries. This theory is tested in two stages using detailed data on the operations of foreign affiliates of US multinationals across seventeen European countries from 1983 – 2004. A host country’s export market access is first estimated with an augmented gravity model. This export series is then included in a dynamic panel with US to host market exchange rate volatility and a range of FDI determinants to explain inflows of FDI from the US to European countries. Potential endogeneity issues are addressed using the Arellano and Bond (1991) GMM procedure. The ability to export from a particular host country has a positive and significant effect on inflows of FDI. Additionally, unobserved features of Euro-Zone membership (beyond the elimination of currency risk) have a positive effect on inflows. A counterfactual experiment sheds light on how much FDI the UK “lost” by not adopting the euro in 1999. Re-estimating the trade and FDI relations under the assumption that the UK had adopted the euro, I estimate that the UK has lost approximately $33 billion (2% of GDP) worth of FDI from the US. Similarly, the flight of FDI to the new EU accession countries has been slowed by these countries staying out of the Euro-Zone.