Process Maps for Laser Deposition of Thin-Walled Structures

In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent deposition conditions and in limiting residual stress-induced warping of parts. In this research, nondimensionalized plots (termed process maps) are developedJrom numerical models of laser-based material deposition of thin-walled structures that.map out the effects of changes in laser power, deposition speed and part preheating on process parameters. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the approach taken is applicable to any solid freeform fabrication process involving. a moving heat source. Similarly, although thinwalled structures treated in the current work, the same approach could be applied to other commonly fabricated geometries. A process map for predicting and controlling melt pool size is presented .and numerically determined results are compared against experimentally measured melt poollengthsfor stainless steel deposition in the LENS process.Mechanical Engineerin

Some Financial Implications of Divestiture Legislation

Those critical of divestiture legislation emphasize both the relative lack of concentration and the advantages of grouping the development of two or more energy materials under the management of one corporate business. Many of these arguments are extremely difficult to evaluate without harder evidence than appears to be available at present. This paper purports to deal with some of the financial and legal consequences of different possible methods of accomplishing divestiture

Economic Issues in the Management of Plants Invading Natural Environments: Scotch Broom in Barrington Tops National Park

Scotch broom (Cytisus scoparius, L.), is an exotic leguminous shrub, native to Europe, which invades pastoral and woodland ecosystems and adjoining river systems in cool, high rainfall regions of southeastern Australia. Broom has invaded 10,000 hectares of eucalypt woodland at Barrington Tops National Park in New South Wales, and is having a major impact on the natural ecology of the sub-alpine environment. It is extremely competitive with the native flora, retarding their growth and in many areas blanketing the ground and preventing growth of many understorey species in open forest areas. An active program to manage this invasion is being implemented by the National Parks and Wildlife Service. The management issues include whether eradication or containment is economically desirable, and when biological control is economically desirable. Management choices depend on the marginal costs of increments of government intervention, effects of uncertain budgets on the control of broom, choice of control measures and effects of uncertain values of biodiversity. These issues are addressed through the application of a detailed bioeconomic model of broom management.Scotch broom, economic issues, management issues, natural environments, bioeconomic model, Environmental Economics and Policy,

Clio: Digital Transformation of Legal Practice - At COVID-19 Speed

Professional services firms face evolving client needs and can better meet these needs through digital transformation. We offer the case of Clio, a leading provider of cloud-based legal technology for law firms to better serve their clients. In this role, Clio provides an example of how digital transformation happens – both before and after the dramatic transformation triggered by the COVID-19 shutdowns. With the onset of COVID-19, the company recognized that remote client access and services, previously embraced by early adopters, would now become essential for all law firms’ survival. The company’s response resulted in dramatic growth and the transition from a customer base of early adopters to customers spanning most of the innovation adoption curve. Clio’s success throughout this period is attributable to three core elements of the company’s strategy: (1) Deep, culturally-rooted commitment to customer success, (2) Research-based understanding of the needs of both law firms and their clients, and (3) Industry thought leadership and assistance. These elements generalize beyond Clio and the pandemic and will help guide any organization seeking to become not just a vendor but an essential partner to its customers

Process Maps for Controlling Residual Stress and Melt Pool Size in Laser-Based SFF Processes 200

Thermal control of solid freeform fabrication processes is critical for obtaining consistent build conditions and in limiting residual stress-induced tolerance losses. In this paper, thermomechanical models are presented for the building of thin-walled structures by laser-based SFF processes. The simulations are used to develop two non-dimensional plots (termed process maps) that quantify the effects of changes in wall height, laser power, deposition speed and part preheating on melt pool size (for consistent build conditions) and thermal gradients (for limiting residual stresses). Mechanical simulations are used to demonstrate the link between thermal gradients and maximum final residual stresses. Models are applied to the Laser Engineered Net Shaping (LENS) process; however, the general approach, insights and conclusions are applicable to most SFF processes involving a moving heat source. The two process maps described herein can be used together to determine optimal process variables for obtaining consistent melt pool length while limiting residual stress in the part. Results from the residual stress simulations also identify two important mechanisms for reducing residual stresses and quantify maximum stress reductions that can be achieved through manipulation of all process variables.This research has been supported by the National Science Foundation under grant DMI9700320 and by Sandia National Laboratories under grant BE-0792.Mechanical Engineerin

Residual Stress Control Issues for Thermal Deposition of Polymers in SFF Processes 209

Controlling residual stress-induced warping and other tolerance losses is important for accurately creating parts by solid freeform fabrication (SFF). In this paper, results are presented from warping experiments on plate-shaped acrylonitrile butadiene styrene (ABS) specimensmcreated by an extrusion process used in Shape Deposition Manufacturing (SDM). Experimental results are compared to predictions from both one- and two-dimensional types of residual stress models. In addition to SDM, methods and results from this study are applicable to a number of other solid freeform fabrication processes involving extrusion of polymers or polymer slurries. Results from polymer extrusion are compared with those from existing work on thermal deposition of metals. Unlike metals, polymer deposition shows essentially no stress reduction due to preheating by the deposition process. Due to a greater number of deposited rows, directionality of warping is also greater than in metals. Polymer deposition experiments show that a preheat temperature near the glass transition temperature is needed for essentially no warping. Comparison of predicted and measured curvatures show that a simple 1-D thermomechanical model does not predict warping magnitudes well, but does provide insight into trends in warping as a function of preheat temperature. The effects of successive material deposition are substantial in this process and a 2-D model that includes the effects of successively deposited rows can provide much more accurate curvature predictions.The authors gratefully acknowledge financial support from the Gintic Institute of Manufacturing Technology and from the National Science Foundation, under grant DMI9700320. A software grant from SDRC allowed use of their software for finite element pre- and post- processing.Mechanical Engineerin

Control of Ca2+ influx and calmodulin activation by SK-channels in dendritic spines (dataset)

A 3-dimensional model of Ca2+ and calmodulin dynamics within an idealised, but biophysically-plausible, dendritic spine, demonstrates that SK-channels regulate calmodulin activation specifically during neurone firing patterns associated with induction of spike timing-dependent plasticity.The journal article associated with this dataset is available at: http://hdl.handle.net/10871/21745.The key trigger for Hebbian synaptic plasticity is influx of Ca2+ into postsynaptic dendritic spines. The magnitude of [Ca2+] increase caused by NMDA-receptor (NMDAR) and voltage-gated Ca2+ -channel (VGCC) activation is thought to determine both the amplitude and direction of synaptic plasticity by differential activation of Ca2+ -sensitive enzymes such as calmodulin. Ca2+ influx is negatively regulated by Ca2+ -activated K+ channels (SK-channels) which are in turn inhibited by neuromodulators such as acetylcholine. However, the precise mechanisms by which SK-channels control the induction of synaptic plasticity remain unclear. Using a 3-dimensional model of Ca2+ and calmodulin dynamics within an idealised, but biophysically-plausible, dendritic spine, we show that SK-channels regulate calmodulin activation specifically during neuron-firing patterns associated with induction of spike timing-dependent plasticity. SK-channel activation and the subsequent reduction in Ca2+ influx through NMDARs and L-type VGCCs results in an order of magnitude decrease in calmodulin (CaM) activation, providing a mechanism for the effective gating of synaptic plasticity induction. This provides a common mechanism for the regulation of synaptic plasticity by neuromodulators

Transcription of telomeric DNA leads to high levels of homologous recombination and t-loops

The formation of DNA loops at chromosome ends (t-loops) and the transcription of telomeres producing G-rich RNA (TERRA) represent two central features of telomeres. To explore a possible link between them we employed artificial human telomeres containing long arrays of TTAGGG repeats flanked by the T7 or T3 promoters. Transcription of these DNAs generates a high frequency of t-loops within individual molecules and homologous recombination events between different DNAs at their telomeric sequences. T-loop formation does not require a single strand overhang, arguing that both terminal strands insert into the preceding duplex. The loops are very stable and some RNase H resistant TERRA remains at the t-loop, likely adding to their stability. Transcription of DNAs containing TTAGTG or TGAGTG repeats showed greatly reduced loop formation. While in the cell multiple pathways may lead to t-loop formation, the pathway revealed here does not depend on the shelterins but rather on the unique character of telomeric DNA when it is opened for transcription. Hence, telomeric sequences may have evolved to facilitate their ability to loop back on themselves

Melt Pool Size and Stress Control for Laser-Based Deposition Near a Free Edge

Thermomechanical models developed in this research address two experimental observations made during the deposition of thin-walled structures by the LENSTM process. The first observation (via thermal imaging) is of substantial increases in melt pool size as a vertical free edge is approached under conditions of constant laser power and velocity. The second observation (via neutron diffraction) is of large tensile stresses in the vertical direction at vertical free edges, after deposition is completed and the wall is allowed to cool to room temperature. At issue is how to best control melt pool size as a free edge is approached and whether such control will also reduce observed free edge stresses. Thermomechanical model results are presented which demonstrate that power reduction curves suggested by process maps for melt pool size under steady-state conditions can be effective in controlling melt pool size as a free edge is approached. However, to achieve optimal results it is important that power reductions be initiated before increases in melt pool size are observed. Stress simulations indicate that control of melt pool size can reduce free-edge stresses; however, the primary cause of these stresses is a constraint effect which is independent of melt pool size.This research was supported by the National Science Foundation Division of Design, Manufacture and Industrial Innovation, through the Materials Processing and Manufacturing Program, award number DMI-0200270.Mechanical Engineerin

Protein Requirements of Dairy Calves: Nitrogen Retention as Related to Live Weight and Age

Dairy Productio