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The EUV/X-ray photoevaporation and core-powered mass-loss models are both capable of reproducing the bimodality in the sizes of small, close-in exoplanets observed by the \textit{Kepler} space mission, often referred to as the "radius gap". However, it is unclear which of these two mechanisms dominates the atmospheric mass-loss which is likely sculpting the radius gap. In this work, we propose a new method of differentiating between the two models, which relies on analysing the radius gap in 3D parameter space. Using models for both mechanisms, and by performing synthetic transit surveys we predict the size and characteristics of a survey capable of discriminating between the two models. We find that a survey of $\gtrsim 5000$ planets, with a wide range in stellar mass and measurement uncertainties at a $\lesssim 5\%$ level is sufficient. Our methodology is robust against moderate false positive contamination of $\lesssim 10\%$. We perform our analysis on two surveys (which do not satisfy our requirements): the \textit{California Kepler Survey} and the \textit{Gaia-Kepler Survey} and find, unsurprisingly, that both data-sets are consistent with either model. We propose a hypothesis test to be performed on future surveys which can robustly ascertain which of the two mechanisms formed the radius gap, provided one dominates over the other., 17 pages, 11 figures. Accepted for publication in MNRAS

The radius distribution of small, close-in exoplanets has recently been shown to be bimodal. The photoevaporation model predicted this bimodality. In the photoevaporation scenario, some planets are completely stripped of their primordial H/He atmospheres, whereas others retain them. Comparisons between the photoevaporation model and observed planetary populations have the power to unveil details of the planet population inaccessible by standard observations, such as the core mass distribution and core composition. In this work, we present a hierarchical inference analysis on the distribution of close-in exoplanets using forward-models of photoevaporation evolution. We use this model to constrain the planetary distributions for core composition, core mass and initial atmospheric mass fraction. We find that the core-mass distribution is peaked, with a peak-mass of $\sim 4$M$_\oplus$. The bulk core-composition is consistent with a rock/iron mixture that is ice-poor and ``Earth-like''; the spread in core-composition is found to be narrow ($\lesssim 16\%$ variation in iron-mass fraction at the 2$\sigma$ level) and consistent with zero. This result favours core formation in a water/ice poor environment. We find the majority of planets accreted a H/He envelope with a typical mass fraction of $\sim 4\%$; only a small fraction did not accrete large amounts of H/He and were ``born-rocky''. We find four-times as many super-Earths were formed through photoevaporation, as formed without a large H/He atmosphere. Finally, we find core-accretion theory over-predicts the amount of H/He cores would have accreted by a factor of $\sim 5$, pointing to additional mass-loss mechanisms (e.g. ``boil-off'') or modifications to core-accretion theory., Comment: 18 pages, 16 figures. Accepted for publication in MNRAS. Supplementary material can be found at https://doi.org/10.5281/zenodo.4554210

Atmospheric mass-loss is known to play a leading role in sculpting the demographics of small, close-in exoplanets. Knowledge of how such planets evolve allows one to ``rewind the clock'' to infer the conditions in which they formed. Here, we explore the relationship between a planet's core mass and their atmospheric mass after protoplanetary disc dispersal by exploiting XUV photoevaporation as an evolutionary process. Historically, this style of inference problem would be computationally infeasible due to the large number of planet models required; however, we make use of a novel atmospheric evolution emulator which utilises neural networks to provide three orders of magnitude in speedup. First, we provide proof-of-concept for this emulator on a real problem, by inferring the initial atmospheric conditions to the TOI-270 multi-planet system. Using the emulator we find near-indistinguishable results when compared to original model. We then apply the emulator to the more complex inference problem, which aims to find the initial conditions for a sample of \textit{Kepler}, \textit{K2} and \textit{TESS} planets with well-constrained masses and radii. We demonstrate there is a relationship between core masses and the atmospheric mass that they retain after disc dispersal, and this trend is consistent with the `boil-off' scenario, in which close-in planets undergo dramatic atmospheric escape during disc dispersal. Thus, it appears the exoplanet population is consistent with the idea that close-in exoplanets initially acquired large massive atmospheres, the majority of which is lost during disc dispersal; before the final population is sculpted by atmospheric loss over 100~Myr to Gyr timescales., Comment: 16 pages, 10 figures. Accepted for publication in MNRAS

Large surface areas (tens of square centimeters to square meters) covered with high-aspect-ratio microstructures (HARMs) have potential applications in a wide range of fields including heat transfer, adaptive aerodynamics, acoustics, catalysts, seal and bearing design, and composite materials. HARMs are typically hundreds of micrometers in height, with widths ranging from a few micrometers to tens of micrometers, and they can be manufactured from a variety of materials such as metals, polymers, and ceramics. Three of the barriers to extensive use of large HARM-covered surfaces are cost, nonplanarity of typical surfaces, and adhesion of the microstructures to the surface. A starting point for inexpensive reproduction of large arrays of HARMs is the plastic molding step of the LIGA micromanufacturing process. In order to address the latter two problems, the standard LIGA process was modified/extended. Free-standing polymer sheets, perforated with a pattern of high-aspect-ratio throughholes, were clamped to conductive substrates. The sheets provide a template for electrodeposition of nickel microstructures onto the target surface. This process makes it economically feasible to electroform metal microstructures directly onto large planar and nonplanar metal surfaces (cylinders).

The LIGA process is being further developed to fabricate large surfaces covered with high aspect ratio microstructures (HARMs). A HARM is defined as a structure hundreds of micrometers in height and with a height and with a height/characteristic lateral dimension which is five or greater. The molding step of the LIGA process provides one method to rapidly and inexpensively fabricate HARM-covered sheets. Molding experiments were performed to determine combinations of processing parameters which produce high quality, high density polyethylene HARMs. In addition to developing an inexpensive process to manufacture HARMs, uses for HARM-covered sheets are being investigated. One example is heat transfer enhancement. Microfins were added to the surface of a cylinder and experiments quantified their effect on the rate of convective heat transfer for a cylinder in crossflow.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The MicroSystems Engineering Team ((mu) SET) at Louisiana State University, in close collaboration with the Center for Advanced Microstructures and Devices, has successfully completed the lithography and electroplating steps of the LIGA process sequence using cyanoacrylate to bond a PMMA resist layer to a nickel surface. Nickel microstructures 300 micrometers in height have been electroplated. Tests were performed which indicate that the bond between cyanoacrylate and nickel is much stronger than the bond between PMMA and nickel.

Four major display variables, luminance adaptation level, symbol contrast ratio, symbol visual size and off-axis viewing angle, were related, in a rotatable central composite design, to an observer's ability to identify symbols shown on a large screen display (LSD). The results show the nature and significance of all main effects as well as delineate the important interactions among these variables. The results can be used as an LSD design and evaluation tool permitting tradeoffs to be made among the important features of display equipment, projection screens and viewing facilities.

Field maintenance actions reported in a deployed air defense system were reviewed to determine and quantify (1) the nature of operator and maintainer influences on system malfunctions, and (2) the nature of man-machine problems being encountered by system personnel in actual diagnosis and repair activities. Maintenance events described in 213 problem reports from the field were categorized according to three probable sources of malfunction: primarily human, combination human and equipment, and primarily equipment. Human involvement in system malfunctions was clearly established in 25% of the events reported. Additional information contained in 21 documents analyzing system maintenance was examined. The nature of human influence on system malfunction is described by examples of “unfortunate” field maintenance, “ordinary” field maintenance, and troubleshooting deficiencies. The nature of reported man-machine problems highlighted the fact that human engineering participation in establishing maintainability design requirements can serve to make equipment that will be suitable to the presence and actions of human users.

Advances in the design of radar data processing and display systems have resulted in certain nonlinearities in the response of the displayed cursor to a manual input. This paper examines the effects upon target acquisition time, in a simulated air defense environment, of (1) a low-velocity “dead zone” for which no cursor movement occurs, and (2) quantization of control velocity into a small number of discrete cursor velocities. Resulting decrements in acquisition latencies are given as functions of tracking distance and direction. A rolling ball control is used.

Perceptual enhancement for image motion in the visual periphery was evaluated by threshold measurements with a moving-bar stimulus. Lowered peripheral thresholds were found for both forward and backward image movement with no significant elevation of the contrast threshold for an image in motion out to 55° eccentricity from the fovea. Either real or phi-phenomenon movement is recommended for the display of emergency or mission-critical signals.

Modern manual tracking and display systems transmit velocity, rather than position, of the rolling hall control into the display computer; in this manner, the necessity of continually updating control position is avoided, and a signal is transmitted to the computer only when the ball is moved. This presents difficulties to the system designer, however, insofar as the expected range of velocities for the rolling ball control has not been experimentally determined. In the present study, the maximum rate of surface travel for a 3-in.-diameter track ball is elicited for subjects tracking randomly-positioned stationary targets at varying distances and directions. Maximum ball velocities, presented in graphical and tabular form, are found to be functions of both target distance and direction, increasing almost linearly with distance.

An illumination system is described which utilizes for display, portions of the visible spectrum which have been excluded from the ambient light. The resulting tinted illumination is matched in brightness to a standard white light by experimental subjects, and stimulus threshold measurements made as a function of display intensity for various stimulus and ambient spectra. Certain combinations are found to lower the threshold of detection, indicating enhanced stimulus brightness, whereas others are found to raise the threshold. A close relationship is found between experimental data and results predicted on the basis of previously published increment-threshold measurements.