The emerging field of bioelectronic medicine seeks methods for deciphering and modulating electrophysiological activity in the body to attain therapeutic effects at target organs. Current approaches to interfacing with peripheral nerves and muscles rely heavily on wires, creating problems for chronic use, while emerging wireless approaches lack the size scalability necessary to interrogate small-diameter nerves. Furthermore, conventional electrode-based technologies lack the capability to record from nerves with high spatial resolution or to record independently from many discrete sites within a nerve bundle. Here, we demonstrate neural dust, a wireless and scalable ultrasonic backscatter system for powering and communicating with implanted bioelectronics. We show that ultrasound is effective at delivering power to mm-scale devices in tissue; likewise, passive, battery-less communication using backscatter enables high-fidelity transmission of electromyogram (EMG) and electroneurogram (ENG) signals from anesthetized rats. These results highlight the potential for an ultrasound-based neural interface system for advancing future bioelectronics-based therapies.

Simultaneously measuring the activities of all neurons in a mammalian brain at millisecond resolution is a challenge beyond the limits of existing techniques in neuroscience. Entirely new approaches may be required, motivating an analysis of the fundamental physical constraints on the problem. We outline the physical principles governing brain activity mapping using optical, electrical, magnetic resonance, and molecular modalities of neural recording. Focusing on the mouse brain, we analyze the scalability of each method, concentrating on the limitations imposed by spatiotemporal resolution, energy dissipation, and volume displacement. Based on this analysis, all existing approaches require orders of magnitude improvement in key parameters. Electrical recording is limited by the low multiplexing capacity of electrodes and their lack of intrinsic spatial resolution, optical methods are constrained by the scattering of visible light in brain tissue, magnetic resonance is hindered by the diffusion and relaxation timescales of water protons, and the implementation of molecular recording is complicated by the stochastic kinetics of enzymes. Understanding the physical limits of brain activity mapping may provide insight into opportunities for novel solutions. For example, unconventional methods for delivering electrodes may enable unprecedented numbers of recording sites, embedded optical devices could allow optical detectors to be placed within a few scattering lengths of the measured neurons, and new classes of molecularly engineered sensors might obviate cumbersome hardware architectures. We also study the physics of powering and communicating with microscale devices embedded in brain tissue and find that, while radio-frequency electromagnetic data transmission suffers from a severe power–bandwidth tradeoff, communication via infrared light or ultrasound may allow high data rates due to the possibility of spatial multiplexing. The use of embedded local recording and wireless data transmission would only be viable, however, given major improvements to the power efficiency of microelectronic devices.

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The gas solubility of CO2 has been measured in aqueous mixtures of diethanaolamine and 2-amino-2-methyl-1-propanol at (40, 60, and 80) °C and in the pressure range (10 to 300) kPa. The concentrations of the amine mixtures were 6 mass % diethanolamine (DEA) + 24 mass % 2-amino-2-methyl-1-propanol (AMP), 12 mass % DEA + 18 mass % AMP, and 18 mass % DEA + 12 mass % AMP. The solubilities show a systematic change as the composition of the aqueous mixtures varies.

The primary aim of this study was to investigate the "dilution effect", where dilution of the ionic concentration of the fluid injected into oil wells has been found to enhance oil recovery. We have measured crude oil/brine/carbonate surface (calcite) interactions using a variety of dynamic techniques including contact angles, surface forces apparatus, atomic force microscopy, interfacial tension, X-ray photoelectron spectroscopy, and other physical and chemical surface characterization techniques. The effects due to different brine (ionic electrolyte) solutions and temperatures, as well as the dynamics (timedependence) of these effects, were investigated. Ionic strengths varied from pure water to 350 000 ppm, and temperatures varied from 20 to 75 °C. We found that upon exchanging solutions (as occurs for waterflooding using dilute solutions), three different dynamic processes occur that have very different time scales: (1) the initial, rapid (seconds to minutes) physical ion exchange with the surfaces that locally changes the surface charge/potential and, hence, the double-layer and hydration forces, (2) the local electrochemical dissolution and restructuring of the surfaces (minutes to hours), which is also often accompanied by the desorption of preexisting organic−ionic layers on the mineral surface that come off as visible flakes with the oil, and (3) the largescale, diffusion-rate-controlled restructuring leading to macroscopic changes in rock morphology (months to years). We conclude that the "dilution effect" is in part due to the well-known colloidal interaction forces (electric double-layer, hydrophilic-hydration, and van der Waals). In addition, our experiments reveal (electro)chemical reactions involving dissolution, pitting, adsorption, and restructuring of the calcite surfaces, which increases their roughness (cf. the geological process of "pressure solution"). Both the colloidal forces and surface roughening and restructuring act to reduce the adhesion of the crude oil/brine interface to the calcite/brine interface (across the thin aqueous or "water" film), which in turn reduces the water-side contact angle (increasing the water-wettability and, presumably, oil recovery), with increasing dilution. These two contributionsreduced colloidal forces and surface rougheningappear to be essential for the "dilution effect" to be effective at all solution concentrations from formation water to pure water. We propose a semiquantitative model to explain the "dilution effect" based on a form of the wellestablished extended-Derjaguin−Landau−Verwey−Overbeek theory for the colloidal interactions between the crude oil and carbonate surface across brine of different concentrations and a modified Young−Dupréequation that accounts for the effects of surface roughness. We present the "dilution effect" in terms of "wettability maps" for the calculated (effective) adhesion energy of the crude oil/brine/carbonate system as a function of brine concentration (from formation water down to the infinite-dilution [i.e., pure ...