In situ mixing of organic matter decreases hydraulic conductivity of denitrification walls in sand aquifers

In a previous study, a denitrification wall was constructed in a sand aquifer using sawdust as the carbon substrate. Ground water bypassed around this sawdust wall due to reduced hydraulic conductivity. We investigated potential reasons for this by testing two new walls and conducting laboratory studies. The first wall was constructed by mixing aquifer material in situ without substrate addition to investigate the effects of the construction technique (mixed wall). A second, biochip wall, was constructed using coarse wood chips to determine the effect of size of the particles in the amendment on hydraulic conductivity. The aquifer hydraulic conductivity was 35.4 m/d, while in the mixed wall it was 2.8 m/d and in the biochip wall 3.4 m/d. This indicated that the mixing of the aquifer sands below the water table allowed the particles to re-sort themselves into a matrix with a significantly lower hydraulic conductivity than the process that originally formed the aquifer. The addition of a coarser substrate in the biochip wall significantly increased total porosity and decreased bulk density, but hydraulic conductivity remained low compared to the aquifer. Laboratory cores of aquifer sand mixed under dry and wet conditions mimicked the reduction in hydraulic conductivity observed in the field within the mixed wall. The addition of sawdust to the laboratory cores resulted in a significantly higher hydraulic conductivity when mixed dry compared to cores mixed wet. This reduction in the hydraulic conductivity of the sand/sawdust cores mixed under saturated conditions repeated what occurred in the field in the original sawdust wall. This indicated that laboratory investigations can be a useful tool to highlight potential reductions in field hydraulic conductivities that may occur when differing materials are mixed under field conditions

Circumventing the eta problem in building an inflationary model in string theory

The eta problem is one of the most significant obstacles to building a successful inflationary model in string theory. Planck mass suppressed corrections to the inflaton potential generally lead to inflaton masses of order the Hubble scale and generate contributions of order unity to the eta slow roll parameter rendering prolonged slow roll inflation impossible. We demonstrate the severity of this problem in the context of brane anti-brane inflation in a warped throat of a Calabi-Yau flux compactification with all phenomenologically dangerous moduli stabilized. Using exact numerical solutions we show that the eta problem can be avoided in scenarios where the inflaton is non-minimally coupled to gravity and has Dirac-Born-Infeld (DBI) kinetic term. We show that the resulting cosmic microwave background (CMB) observables such as measures of non-gaussianites can, in principle, serve as a probe of scalar-gravity couplings.Comment: 8 pages, 3 figures; title changed and reference added to match published version in PR

Multi-antenna switch control in 5G

A mobile device typically has multiple antenna elements to enable antenna diversity and to accommodate multiple protocols, e.g., 4G, 5G, SRS, etc. When different antenna elements transmit or receive simultaneously, intermodulation products from one can reduce the sensitivity of another. This disclosure describes techniques to allocate antenna elements across protocols and antenna diversity schemes such that intermodulation desensing is minimized and transceiver-antenna connectivity is continuously maintained

Analysis of the radiation flux profile along a PV through concentrator

The primary advantage of a PV concentrator is that concentrating light allows a significant reduction in the area of solar cell coverage, the main cost driver in a flat plate system. PV systems, whether flat plate or concentrating, normally have groups of solar cells connected in series in order to increase voltage and limit current. However, low illumination on a single cell proportionally reduces its current, and hence affects the performance of all other cells in series. Ideally, a reflective PV concentrator system will have high concentration, a uniform flux distribution, and low cost. However, it is difficult to obtain these three conditions simultaneously, as cost tends to increase with better mirror quality, improved tracking accuracy, and the use of secondary flux modifiers. Linear concentrators have the advantage of simpler and cheaper tracking and support structures than dishes; however, achieving a consistent flux profile on every cell along the focal line is challenging. The aim of this paper is to present results of direct measurements of the flux profile along the length of a single axis tracking trough, and to develop simulation techniques that allow the reasons for peaks and troughs in the flux profile to be better understood

The Attlee governments in perspective - commitment and detachment in the writing of contemporary history.

The early to mid-nineteen eighties saw the publication of several substantial studies of the two immediate post-war Labour governments, studies which - in claiming to meet all the requirements of scholarly history - also made out a strong case for the possibility of a value-free explanation of the recent past. The basis for this assertion is examined in the present account by means of a preliminary survey of the changes through which the literature on the Attlee governments has already passed, drawing attention to the differing attitudes and presuppositions of the main schools of historical and other disciplinary opinion and the extent to which these differing approaches - exhibiting contrasting elements of commitment and detachment, and of insight and distortion - can be shown to have contributed to, or departed from, the notion of an enhanced understanding. Evidence for the growth of a more objectively critical history is then explored in greater detail by tracing the development of some of the central problems and controversies relating to the period after 1945, clarifying the main points at issue, outlining the evolution of evidence and interpretation, and demonstrating the way in which empirically-based explanations have, by scholars working independently together, become recognisably accepted. That these arguments have given rise to a variety of alternative viewpoints, which it is has not proved possible to choose between or account for on empirical grounds alone, also lends support - however - to the continuing influence of personal, partial and evaluative considerations. To this end, a framework of historiographical change is proposed which, in tracing the progress made towards a more dispassionate view of the Attlee years, and the reasons for the persistence of remaining disagreements, throws light upon the wider question of the possibilities and limitations of contemporary historical inquiry

In-situ characterization of sea state with improved navigation on an Autonomous Underwater Glider

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.This thesis presents an Autonomous Underwater Glider (AUG) architecture with improved onboard navigation and acoustics-based sensing intended to enable basin-scale unattended surveys of our Earth’s most remote oceans. Traditional AUGs have long-been an important platform for oceanographic surveys due to their high endurance and autonomy, yet lack the operational flexibility to operate in many regions of scientific interest and the sensing capability to capture scientific data at the air-sea interface. Particularly of interest is the marginal ice zone (MIZ) in the Arctic and the Southern Ocean, as both are vitally important to understanding global climate trends, yet prohibitively expensive to persistently monitor with support vessels. To fill this observational gap, the sensing, navigation, and adaptability of AUGs must be improved. This is possible by employing onboard acoustic sensing for sea state observation and navigation, as well as incorporating vehicle improvements targeting maneuverability and intelligent adaptability to evolving environmental states. To enable persistent monitoring of both the water-column and air-sea interface, this thesis proposes an improved vehicle architecture for a more capable AUG, a real-time DVLaided navigation process that leverages ocean current sensing to limit localization error, and a subsea acoustics-based sea state characterization method capable of analyzing wave spectra under-ice and with zero surface expression. These methods are evaluated with respect to extensive laboratory experiments and field data collected during in-situ implementation.Support for this research was provided through grants from the National Science Foundation (NSF) Navigating the New Arctic Grant (NNA #1839063) and the National Ocean Partnership Program (NOPP) Enhanced Propulsion Integrated Capability - Deep Autonomous Underwater Glider (EPIC-DAUG) grant (NA19OAR0110408)

Quasinormal Modes of Optical Solitons

Quasinormal modes (QNMs) are essential for understanding the stability and resonances of open systems, with increasing prominence in black hole physics. We present here the first study of QNMs of optical potentials. We show that solitons can support QNMs, deriving a soliton perturbation equation and giving exact analytical expressions for the QNMs of fiber solitons. We discuss the boundary conditions in this intrinsically dispersive system and identify novel signatures of dispersion. From here, we discover a new analogy with astrophysical black holes and describe a regime in which the soliton is a robust black hole simulator for light-ring phenomena. Our results invite a range of applications, from the description of optical pulse propagation with QNMs to the use of state-of-the-art technology from fiber optics to address questions in black hole physics, such as QNM spectral instabilities and the role of nonlinearities in ringdown.Comment: 5 pages, 3 figure

Intrusive Images in Psychological Disorders: Characteristics, Neural Mechanisms, and Treatment Implications

Involuntary images and visual memories are prominent in many types of psychopathology. Patients with posttraumatic stress disorder, other anxiety disorders, depression, eating disorders, and psychosis frequently report repeated visual intrusions corresponding to a small number of real or imaginary events, usually extremely vivid, detailed, and with highly distressing content. Both memory and imagery appear to rely on common networks involving medial prefrontal regions, posterior regions in the medial and lateral parietal cortices, the lateral temporal cortex, and the medial temporal lobe. Evidence from cognitive psychology and neuroscience implies distinct neural bases to abstract, flexible, contextualized representations (C-reps) and to inflexible, sensory-bound representations (S-reps). We revise our previous dual representation theory of posttraumatic stress disorder to place it within a neural systems model of healthy memory and imagery. The revised model is used to explain how the different types of distressing visual intrusions associated with clinical disorders arise, in terms of the need for correct interaction between the neural systems supporting S-reps and C-reps via visuospatial working memory. Finally, we discuss the treatment implications of the new model and relate it to existing forms of psychological therapy