On Shelf-Slope Water Mass Exchanges Near Washington Canyon and Norfolk Canyon in the Mid-Atlantic Bight

The physical exchanges between shelf and slope water masses are important drivers of biological productivity in the shelfbreak region of the Mid-Atlantic Bight (MAB). Based on two ocean glider surveys that were conducted in Autumn 2013, and concurrent wind and satellite based sea surface height observations, this study investigates the dynamic mechanisms of wind, surface height variation, water column hydrographic structure, and canyon topography in driving shelf-slope water mass exchanges across the shelfbreak near Norfolk Canyon and Washington Canyon in the MAB. Over the outer shelf, sea surface height variation and wind are important drivers of cross-shelfbreak transport through geostrophic and Ekman mechanisms. Opposing flow in the different layers of the water column leads to shelf-slope water mass exchange. Over submarine canyons, strong upwelling favorable wind in combination with flat sea surface can cause reversed flow along the MAB shelfbreak and thereby induce canyon upwelling of slope water. In addition, the interfaces of shelf and slope water masses are expected to be conducive to double diffusion, which in turn can drive thermohaline intrusions and further enhance shelf-slope exchanges. These shelf-slope exchange processes can contribute to a net salt flux onto the shelf and support enhanced sub-surface primary production in the shelfbreak regio

Sensitivity of intracavity filtering schemes for detecting gravitational waves

We consider enhancing the sensitivity of future gravitational-wave detectors by adding optical filters inside the signal-recycling cavity -- an intracavity filtering scheme, which coherently feeds the sideband signal back to the interferometer with a proper frequency-dependent phase. We study three cases of such a scheme with different motivations: (i) the case of backaction noise evasion, trying to cancel radiation-pressure noise with only one filter cavity for a signal-recycled interferometer; (ii) the speed-meter case, similar to the speed-meter scheme proposed by Purdue and Chen [Phys. Rev. D 66, 122004 (2002)] but without the resonant-sideband-extraction mirror, and also relieves the optical requirement on the sloshing mirror; (iii) the broadband detection case with squeezed-light input, numerically optimized for a broadband sensitivity.Comment: 10 pages, 10 figure

Impact Of Canyon Upwelling And Downwelling In The Mid-Atlantic Bight

Submarine canyons can impact regional oceanography and provide a conduit for shelf-slope exchanges via topographically induced processes such as canyon upwelling and downwelling. Between Virginia and New York in the Mid-Atlantic Bight (MAB), there are five major shelf-incising canyons (Norfolk, Washington, Baltimore, Wilmington, and Hudson canyons) and four sizable slope-confined canyons (Accomac, Spencer, Lindenkhol, and Toms canyons). Canyon upwelling and downwelling at these canyons have not been well studied. Consequently, the associated hydrographic variability and dynamics inside the canyons and on the adjacent shelf are largely unknown, and the integrated impact of submarine canyons on MAB shelf hydrography and shelf-slope exchanges is poorly understood. This dissertation was inspired by a glider-based survey at Wilmington Canyon, and mainly used numerical modeling simulations for the MAB with an unstructured-grid three-dimensional ocean model to answer these questions. Using glider observations and realistic numerical modeling for February 25–March 7, 2016, Chapter 2 investigated the hydrographic variability associated with the Wilmington Canyon and adjacent outer shelf and shelf-break amid two consecutive events of upwelling and downwelling. Then focusing on the same Wilmington Canyon upwelling and downwelling events and using a realistically forced numerical modeling simulation as well as one without tidal forcing, Chapter 3 tested the dynamical drivers of winds and tides in canyon upwelling and downwelling events, also compared the differences in dynamics between the canyon and adjacent shelf-break. Chapter 4 presented the occurrences and integrated impact of 12 cycles of spatially coherent upwelling and downwelling through nine canyons between Virginia and New York, based on a realistic numerical modeling experiment and a No-Canyon experiment for January 1–April 14, 2016. Chapter 4 also analyzed the frequency of canyon upwelling and downwelling based on a 22-year record (1994–2015) of sea surface elevation. This dissertation found that the submarine canyons in the MAB induced significant spatial and temporal hydrographic variabilities on the shelf and enhanced shelf-slope water exchange. Due to favorable winds, sea surface tilts, and shelf-scale background ocean currents, as well as canyon topography, cycles of spatially coherent multi-canyon upwelling and downwelling frequently occurred in the MAB. Plumes of upwelled slope water from the canyons intruded the outer and mid shelf during the upwelling episodes, and dense water from the shelf retreated into the canyons during the downwelling episodes. For each cycle of upwelling and downwelling, upwelled water from the canyons caused shelf-scale anomalies of low temperature, high density, and northeastward velocity on the MAB outer shelf that were significant when averaged over the course of the season. This thesis suggests that submarine canyons are an integral part of MAB oceanography and deserve further investigations

On the noise effect of test mass surface roughness in spaceborne gravitational wave detectors

Spaceborne gravitational wave detection mission has a demanding requirement for the precision of displacement sensing, which is conducted by the interaction between the laser field and test mass. However, due to the roughness of the reflecting surface of the test mass, the displacement measurement along the sensitive axis suffers a coupling error caused by the residue motion of other degrees of freedom. In this article, we model the coupling of the test mass residue random motion to the displacement sensing along the sensitive axis and derived an analytical formula of the required precision of the surface error for the spaceborne gravitational wave detectors. Our result shows that this coupling error will not contaminate the picometer displacement sensing for the test masses in the LISA pathfinder.Comment: 8 page

Momentum Gradient-based Untargeted Attack on Hypergraph Neural Networks

Hypergraph Neural Networks (HGNNs) have been successfully applied in various hypergraph-related tasks due to their excellent higher-order representation capabilities. Recent works have shown that deep learning models are vulnerable to adversarial attacks. Most studies on graph adversarial attacks have focused on Graph Neural Networks (GNNs), and the study of adversarial attacks on HGNNs remains largely unexplored. In this paper, we try to reduce this gap. We design a new HGNNs attack model for the untargeted attack, namely MGHGA, which focuses on modifying node features. We consider the process of HGNNs training and use a surrogate model to implement the attack before hypergraph modeling. Specifically, MGHGA consists of two parts: feature selection and feature modification. We use a momentum gradient mechanism to choose the attack node features in the feature selection module. In the feature modification module, we use two feature generation approaches (direct modification and sign gradient) to enable MGHGA to be employed on discrete and continuous datasets. We conduct extensive experiments on five benchmark datasets to validate the attack performance of MGHGA in the node and the visual object classification tasks. The results show that MGHGA improves performance by an average of 2% compared to the than the baselines

Annual and Seasonal Surface Circulation Over the Mid-Atlantic Bight Continental Shelf Derived From a Decade of High Frequency Radar Observations

A decade (2007–2016) of hourly 6-km-resolution maps of the surface currents across the Mid-Atlantic Bight (MAB) generated by a regional scale High Frequency Radar network are used to reveal new insights into the spatial patterns of the annual and seasonal mean surface flows. Across the 10-year time series, temporal means and interannual and intra-annual variability are used to quantify the variability of spatial surface current patterns. The 10-year annual mean surface flows are weaker and mostly cross-shelf near the coast, increasing in speed and rotating to more alongshore directions near the shelfbreak, and increasing in speed and rotating to flow off-shelf in the southern MAB. The annual mean surface current pattern is relatively stable year to year compared to the hourly variations within a year. The 10-year seasonal means exhibit similar current patterns, with winter and summer more cross-shore while spring and fall transitions are more alongshore. Fall and winter mean speeds are larger and correspond to when mean winds are stronger and cross-shore. Summer mean currents are weakest and correspond to a time when the mean wind opposes the alongshore flow. Again, intra-annual variability is much greater than interannual, with the fall season exhibiting the most interseasonal variability in the surface current patterns. The extreme fall seasons of 2009 and 2011 are related to extremes in the wind and river discharge events caused by different persistent synoptic meteorological conditions, resulting in more or less rapid fall transitions from stratified summer to well-mixed winter conditions

Perspective Chapter: Effect of Laser Key Parameters on the Ignition of Boron Potassium Nitrate with a Changing Working Distance

The need to realize more effective ignition systems and exploit their full potential in aerospace propulsion applications has led to significant developments in laser and power systems. This work aims to investigate experimentally and describe mathematically the effectiveness of laser systems based on varying key parameters and their related effects on the sensitivity, ignition threshold, and combustion performance of boron potassium nitrate, then to define the key variables with the most significant influence on the overall system. Understanding the physics and chemistry behind the combined system of laser power source and optics system, and the considered medium as well as the interaction in between, led to a better apprehension of how an optimal and viable solution can be achieved in terms of ignition delays, burning times, and combustion temperatures, considering laser wavelength, power and energy densities, and the focal length displacement over a changing working distance. This is of paramount importance when operating amid difficult conditions in aerospace propulsion applications or during outer space missions, particularly those involving manned missions, not only in terms of performance and efficiency but also safety, engineering, and economic feasibility

Predicting hyperlinks via hypernetwork loop structure

While links in simple networks describe pairwise interactions between nodes, it is necessary to incorporate hypernetworks for modeling complex systems with arbitrary-sized interactions. In this study, we focus on the hyperlink prediction problem in hypernetworks, for which the current state-of-art methods are latent-feature-based. A practical algorithm via topological features, which can provide understandings of the organizational principles of hypernetworks, is still lacking. For simple networks, local clustering or loop reflects the correlations among nodes; therefore, loop-based link prediction algorithms have achieved accurate performance. Extending the idea to hyperlink prediction faces several challenges. For instance, what is an effective way of defining loops for prediction is not clear yet; besides, directly comparing topological statistics of variable-sized hyperlinks could introduce biases in hyperlink cardinality. In this study, we address the issues and propose a loop-based hyperlink prediction approach. First, we discuss and define the loops in hypernetworks; then, we transfer the loop-features into a hyperlink prediction algorithm via a simple modified logistic regression. Numerical experiments on multiple real-world datasets demonstrate superior performance compared to the state-of-the-art methods

Impact of Water Scarcity on the Fenhe River Basin and Mitigation Strategies

This study produced a drought map for the Fenhe River basin covering the period from 150 BC to 2012 using regional historical drought records. Based on meteorological and hydrological features, the characteristics and causes of water scarcity in the Fenhe River basin were examined, along with their impact on the national economy and ecological environment. The effects of water scarcity in the basin on the national economy were determined from agricultural, industrial, and domestic perspectives. The impact on aquatic ecosystems was ascertained through an evolution trend analysis of surface water systems, including rivers, wetlands, and slope ecosystems, and subterranean water systems, including groundwater and karst springs. As a result of these analyses, strategies are presented for coping with water scarcity in this basin, including engineering countermeasures, such as the construction of a water network in Shanxi, and the non-engineering approach of groundwater resource preservation. These comprehensive coping strategies are proposed with the aim of assisting the prevention and control of water scarcity in the arid and semi-arid areas of China