Tracking the l_2 Norm with Constant Update Time

The l_2 tracking problem is the task of obtaining a streaming algorithm that, given access to a stream of items a_1,a_2,a_3,... from a universe [n], outputs at each time t an estimate to the l_2 norm of the frequency vector f^{(t)}in R^n (where f^{(t)}_i is the number of occurrences of item i in the stream up to time t). The previous work [Braverman-Chestnut-Ivkin-Nelson-Wang-Woodruff, PODS 2017] gave a streaming algorithm with (the optimal) space using O(epsilon^{-2}log(1/delta)) words and O(epsilon^{-2}log(1/delta)) update time to obtain an epsilon-accurate estimate with probability at least 1-delta. We give the first algorithm that achieves update time of O(log 1/delta) which is independent of the accuracy parameter epsilon, together with the nearly optimal space using O(epsilon^{-2}log(1/delta)) words. Our algorithm is obtained using the Count Sketch of [Charilkar-Chen-Farach-Colton, ICALP 2002]

The trading volume trend, investor sentiment, and stock returns

This dissertation relates the information contained in past trading volume to investor sentiment, and investigates its ability in predicting stock returns. Investor sentiment here refers to the enthusiasm of irrational investors on an asset, relative to that of rational investors. Motivated by Baker and Stein (2004) that an increase in trading volume reflects a rise in investor sentiment, I use the change in trading volume per unit of time, referring it as the trading volume trend, as a measure of investor sentiment on individual stocks. I document a negative and significant cross-sectional relation between the trading volume trend and stock returns, both in the short term and in the long run. This relation is dynamic and holds after controlling for several liquidity measures and other possible determinants of expected returns. It also holds for various volume measures and momentum portfolios. Specifically, both winner and loser portfolios show the effect of the trading volume trend. The effect exists in stocks of small and large firms, and in optioned and non-optioned stocks. These findings suggest that the negative effect of the trading volume trend on stocks returns is robust. Moreover, a composite trading volume trend, formed on the trading volume trends of individual stocks, can predict both the equally-weighted and the value-weighted market returns in the expected direction, after controlling for other possible determinants of market returns. The composite trading volume trend also explains closed-end fund discounts. Collectively these findings support that the trading volume trend contains information on investor sentiment, and that investor sentiment has a valuation effect on stocks

Special Libraries, January 1926

Volume 17, Issue 1https://scholarworks.sjsu.edu/sla_sl_1926/1000/thumbnail.jp

Terahertz Time-Domain Magnetospectroscopy of a High-Mobility Two-Dimensional Electron Gas

We have observed cyclotron resonance in a high-mobility GaAs/AlGaAs two-dimensional electron gas by using the techniques of terahertz time-domain spectroscopy combined with magnetic fields. From this, we calculate the real and imaginary parts of the diagonal elements of the magnetoconductivity tensor, which in turn allows us to extract the concentration, effective mass, and scattering time of the electrons in the sample. We demonstrate the utility of ultrafast terahertz spectroscopy, which can recover the true linewidth of cyclotron resonance in a high-mobility ($>{10}^{6} \mathrm{cm^{2} V^{-1} s^{-1}}$) sample without being affected by the saturation effect.Comment: 4 pages, 3 figure

Competition between ferromagnetism and antiferromagnetism in the rutile Cr1-xVxO2 system

We present a comprehensive computational and experimental examination of the Cr1−xVxO2 (0 ≤ x ≤ 0.5) system. The entire series crystallizes in the rutile structure, but the compounds exhibit significantly different magnetic properties depending on x. Lattice parameter a increases linearly with x, but the c parameter is slightly reduced due to vanadium-vanadium bonding. The V-for-Cr substitution creates Cr3+-V5+ pairs; this leads to competition between ferromagnetic (Cr4+-Cr4+) and antiferromagnetic (Cr3+-Cr3+) interactions such that the materials change from ferromagnetic to antiferromagnetic with increasing x. Weak ferromagnetic interactions arising from Cr4+ are observed even in the seemingly antiferromagnetic phases with the exception of x = 0.5, which contains only Cr3+. Density functional theory calculations are performed, but they incorrectly predict the x = 0.5 phase to be a half-metal. This is caused by an incorrect prediction of the oxidation states of chromium and vanadium.Peer reviewe