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Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1)(More)
Multiple-input-multiple-output (MIMO) techniques have been actively pursued recently in underwater acoustic communications to increase the data rate over the bandwidth-limited channels. In this communication, we present a MIMO system design, where spatial multiplexing is applied with orthogonal-frequency-division-multiplexing (OFDM) signals. The proposed(More)
To determine whether myocyte death and angiotensin II (AT II) formation are implicated in the development of diabetic cardiomyopathy, rats were injected with streptozotocin, and apoptosis and necrosis were measured at 3, 10, and 28 days. Expression of the components of the renin-angiotensin system (RAS) and AT II levels were assessed at 3 days. The(More)
Underwater acoustic channels are wideband in nature due to the fact that the signal bandwidth is not negligible with respect to the center frequency. OFDM transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among OFDM subcarriers. In this paper, we propose a two-step approach to mitigating the(More)
The success of multicarrier modulation in the form of OFDM in radio channels illuminates a path one could take towards high-rate underwater acoustic communications, and recently there are intensive investigations on underwater OFDM. In this paper, we implement the acoustic OFDM transmitter and receiver design of [4,5] on a TMS320C6713 DSP board. We analyze(More)
Recent studies have shown strong temporal correlations between past climate changes and societal crises. However, the specific causal mechanisms underlying this relation have not been addressed. We explored quantitative responses of 14 fine-grained agro-ecological, socioeconomic, and demographic variables to climate fluctuations from A.D. 1500-1800 in(More)
Multicarrier modulation in the form of OFDM facilitates high-rate transmission over long dispersive channels, while multiple-input multiple-output (MIMO) techniques increase the system capacity. In this paper, we report on the design of a MIMO-OFDM with two transmitters and test it using experimental data recorded during the AUV Fest, Panama City, FL, June(More)
Multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has prevailed in recent broadband wireless radio applications due to the low complexity of receivers required to deal with highly dispersive channels. This fact motivates the use of OFDM in underwater environments. However, underwater acoustic (UWA) channels are far(More)
Using acoustic measurement interfaced with a large volume multi-anvil apparatus in conjunction with in situ X-radiation techniques, we are able to measure the density and elastic wave velocities (VP and VS) for both orthoand high-pressure clino-MgSiO3 polymorphs in the same experimental run. The elastic bulk and shear moduli of the unquenchable(More)