Augmenting Mask-Based Lithography with Direct Laser Writing to Increase Resolution and Speed

We present combined direct-laser-writing and UV Lithography in SU-8F and S1813 as a fast and flexible lithographic technique for the prototyping of functional polymer devices and pattern transfer applications. Direct laser writing (DLW), which is performed by focusing a laser through a microscope objective, is a useful alternative method for patterning photoresists with sub-micron resolution. DLW however, can be time consuming if the pattern density is high since it is a serial technique. Typically, dense patterns are made using conventional mask-based UV lithography, but these masks can be quite expensive if the resolution is high and the mask cannot be modified once created. Here, we combine UV lithography using inexpensive transparency masks, which have modest resolution of about 20 µm linewidths, with DLW to create smaller features. By using the laser to augment an inexpensive mask, high resolution prototypes can be created, tested, and modified quickly to optimize a design. Here we show that this Laser Augmented Microlithographic Patterning (LAMP) method works with both positive- and negative-tone photoresists, S1813 and SU-8, respectively. The laser written features can be registered to within 2.2 µm of the mask created features and we demonstrate the applicability of LAMP by fabricating an interdigitated electrode and a microfluidic device that can capture an array of dozens of silica beads or living cells

Whither to Regulate?

Book Review: Public Policy Toward Cable Television: The Economics of Rate Controls, by Thomas W. Hazlett and Matthew L. Spitzer, The MIT Press and The AEI Press, 1997, 253 pages

Whither to Regulate?

Book Review: Public Policy Toward Cable Television: The Economics of Rate Controls, by Thomas W. Hazlett and Matthew L. Spitzer, The MIT Press and The AEI Press, 1997, 253 pages

Living with HIV after Release from Prison: An Evaluation of the Long-term Health of Formerly Incarcerated Individuals who used Michigan’s Community Reentry Service

In 2003, Michigan implemented a reentry service to assist HIV-infected people incarcerated in state prisons in linking to HIV medical care immediately upon their release. We examined whether formerly incarcerated people were linked to care successfully, remained in care, and were in good health 3 years after their date of release. In all, 190 people used the service over the 5 years following its inception. Only a minority of those who were alive and not reincarcerated at the time of the evaluation engaged consistently with medical care. Unsurprisingly given low rates of engagement in care, 3 years after their release only 27% had achieved viral suppression. Concerted efforts to support formerly incarcerated HIV-infected individuals’ engagement in care over the long term are urgently needed

Crystallographic properties and elemental migration in two-stage prepared CuIn1−xAlxSe2 thin films for photovoltaic applications

Two-stage fabrication of CuIn1−xAlxSe2 thin films for photovoltaic absorbers using sputtered Cu–In–Al metallic precursors has been investigated. Precursors containing different relative amounts of Al were selenised and their structural and chemical properties characterised. X-ray diffraction (XRD) analyses revealed that the Al was only incorporated into the chalcopyrite structure for precursor composition ratios x = [Al]/([Al] + [In]) ⩾ 0.38, while chemical analysis of the cross-section indicated partial segregation of Al near the back of the film. Precursor films in the range of compositions that yielded no Al incorporation were then selenised at four different temperatures. Glow discharge optical emission spectroscopy, plasma profiling time-of-flight mass spectrometry and XRD analyses provided an insight into the diffusion processes and reactions taking place during the selenisation stage. The effect of post-selenisation annealing without additional Se was also investigated, and led to partial incorporation of the Al into the CuInSe2 lattice but no rediffusion

Contributing evidence of choice and change when using Open Educational Resources

Open Educational Resources (OER) provide a vast array of free course materials. The Open Learning Network (OLnet) is a research project, which started in March 2009 and is funded by the William and Flora Hewlett Foundation. A major technique adopted in OLnet to uncover what has been achieved with OER (by MIT, OpenLearn, OpenER and others) is to undertake a host of facilitative workshops. This particular workshop explores the reuse of content already published on OpenLearn (as part of the CAPITAL project funded by Becta).The workshop will involve the audience in considering how they would reuse OER in their own teaching practic

Fallback Rates from Partial Tidal Disruption Events

A tidal disruption event (TDE) occurs when a star plunges through a supermassive black hole's tidal radius, at which point the star's self-gravity is overwhelmed by the tidal gravity of the black hole. In a partial TDE, where the star does not reach the full disruption radius, only a fraction of the star's mass is tidally stripped while the rest remains intact in the form of a surviving core. Analytical arguments have recently suggested that the temporal scaling of the fallback rate of debris to the black hole asymptotes to $t^{-9/4}$ for partial disruptions, effectively independently of the mass of the intact core. We present hydrodynamical simulations that verify the existence of this predicted, $t^{-9/4}$ scaling. We also define a break timescale -- the time at which the fallback rate transitions from a $t^{-5/3}$ scaling to the characteristic $t^{-9/4}$ scaling -- and measure this break timescale as a function of the impact parameter and the surviving core mass. These results deepen our understanding of the properties and breadth of possible fallback curves expected from TDEs and will therefore facilitate more accurate interpretation of data from wide-field surveys.Comment: Accepted for publication in The Astrophysical Journal, 13th June 2020. 11 pages, 8 figure

The persistence of pancakes and the revival of self-gravity in tidal disruption events

The destruction of a star by the tides of a supermassive black hole (SMBH) powers a bright accretion flare, and the theoretical modeling of such tidal disruption events (TDEs) can provide a direct means of inferring SMBH properties from observations. Previously it has been shown that TDEs with $\beta = r_{\rm t}/r_{\rm p} = 1$, where $r_{\rm t}$ is the tidal disruption radius and $r_{\rm p}$ is the pericenter distance of the star, form an in-plane caustic, or ``pancake,'' where the tidally disrupted debris is compressed into a one-dimensional line within the orbital plane of the star. Here we show that this result applies generally to all TDEs for which the star is fully disrupted, i.e., that satisfy $\beta \gtrsim 1$. We show that the location of this caustic is always outside of the tidal disruption radius of the star and the compression of the gas near the caustic is at most mildly supersonic, which results in an adiabatic increase in the gas density above the tidal density of the black hole. As such, this in-plane pancake revitalizes the influence of self-gravity even for large $\beta$, in agreement with recent simulations. This finding suggests that for all TDEs in which the star is fully disrupted, self-gravity is revived post-pericenter, keeps the stream of debris narrowly confined in its transverse directions, and renders the debris prone to gravitational instability.Comment: ApJL Accepte

Data on aeolian sand dune activity in the White River Badlands, South Dakota, northern Great Plains, USA

This data paper reports on optically stimulated luminescence (OSL) data from samples collected in the White River Badlands, South Dakota, northern Great Plains. Sand samples were collected from the crests of parabolic dune heads and arms, as well as blowout exposures, on three tables located on private land in the Buffalo Gap National Grasslands. Using hand augers, samples were collected at depths of 1 and 2m below ground surface to minimize potential effects of bioturbation. An improvised split-spoon sampler was used at selected sites to ensure collection from laminated sediments. At auger and exposure localities, sediment was collected by inserting tubes into a full bucket auger or exposure face. Tubes were tightly packed and taped at both ends to prevent shifting of sediment during shipping. Samples collected from the truck-mounted corer were packed in black plastic liners to ensure samples were not exposed to sunlight. OSL analyses were conducted at the University of Nebraska’s Luminescence and Geochronology Laboratory. Interpretation of OSL data was aided by analyses of aerial photographs from the National Agricultural Imagery Program and from the Aerial Photos Single Frame collection hosted on servers of the United States Geological Survey

Emerald Ash Borer Modeling Methods for Future Forest Projections

Natural Resource Ecology & Mgm