A Lab Scale Polymer Micro-Embossing Machine for Process Control Research

Micro embossing is the process of fabricating micron-sized features by plastic deformation of a work piece by means of a shaped tool or die. In our work we are concerned with hot embossing of PMMA to produce features in the 1-100 µm range, suited for micro fluidic and photonic product requirements. As with any deformation process, hot micro embossing yields products with dimensional variation. In ideal situations, several products can be manufactured repeatedly with the same machine settings and be expected to be exactly the same in every aspect with each other. In reality, final products from the same process might have variations in dimensions and material properties even if the machine settings are kept constant. These can be natural variations of the process or variations caused by external disturbances. Variations can decrease the yield of a manufacturing process and can also restrict the ultimate level of product precision attainable. Manufacturing process control entails the study of the origins of process variations and the use of this knowledge to reduce this variation under production conditions. Manufacturing process control is thus vital in establishing the ultimate cost, quality, rate and flexibility of any manufacturing process. Thus, we are interested in controlling inputs that have a direct effect on the work piece’s final shape and thus the productivity. For hot embossing of PMMA, we are interested in controlling: (1) the temperature of the die and work piece during the entire forming process (forming & cooling), (2) the rate of cooling of the die and substrate, (3) die and substrate platen displacement and displacement rate, (4) force applied on the platen and distribution of this force. The temperature needs to be controlled as it affects the thermo-mechanical behavior of the PMMA. The forming temperature determines the forming properties of the material, the rate of cooling will affect the amount of shrinkage and thermal stresses that the polymer work piece undergoes. The displacement will affect the flow of the material into the die and this will affect the feature size and depths to be embossed. The displacement rate will affect the non-Newtonian polymeric material flow rate into the cavity. It is imperative to carefully control those inputs to minimize variations in forming behavior and final product dimension and properties. An experimental lab scale micro embossing machine to address the needs was designed and fabricated at the Manufacturing Process Control Lab (MPCL) at MIT. An Instron Model 5869 Table mounted materials testing system of capacity 50KN (11250lb) was chosen as the platform for the apparatus and it was modified to accept the forming platens with temperature controllers which have capability of controlling the temperatures of the substrate and master to +/- 1 degree Celsius accuracy. The controller powers 2 x 200 watt heaters that can heat the platens to 150 Celsius in 8 minutes. The Instron has a test speed range of 1 micron to 500mm/min (0.00004in/min to 20in/min) with a 50KN load cell attached to the platen with an accuracy of +/- 1N. The platen cooling system uses water where flow rate will vary the resulting cooling rate. To ensure even heating of the substrate, shape factor analysis was used in the design of the copper platens. The shape factor analysis reveals the heat flow patterns and regions of isotherm within the platens originating from the cartridge heaters and thus using this information, the platens can be designed to have the cartridge heaters located so as to minimize temperature variation of the surface of the platen. The apparatus has been used so far to study hot embossing of sub-millimeter sized features using a copper master on a 1mm thick PMMA material. This presentation will provide greater details on the design of the machine, its initial performance tests and some preliminary process variation experiments.Singapore-MIT Alliance (SMA

Minkowski Tensors in Two Dimensions - Probing the Morphology and Isotropy of the Matter and Galaxy Density Fields

We apply the Minkowski Tensor statistics to two dimensional slices of the three dimensional density field. The Minkowski Tensors are a set of functions that are sensitive to directionally dependent signals in the data, and furthermore can be used to quantify the mean shape of density peaks. We begin by introducing our algorithm for constructing bounding perimeters around subsets of a two dimensional field, and reviewing the definition of Minkowski Tensors. Focusing on the translational invariant statistic $W^{1,1}_{2}$ - a $2 \times 2$ matrix - we calculate its eigenvalues for both the entire excursion set ($\Lambda_{1},\Lambda_{2}$) and for individual connected regions and holes within the set ($\lambda_{1},\lambda_{2}$). The ratio of eigenvalues $\Lambda_{2}/\Lambda_{1}$ informs us of the presence of global anisotropies in the data, and $\langle \lambda_{2}/\lambda_{1} \rangle$ is a measure of the mean shape of peaks and troughs in the density field. We study these quantities for a Gaussian field, then consider how they are modified by the effect of gravitational collapse using the latest Horizon Run 4 cosmological simulation. We find $\Lambda_{1,2}$ are essentially independent of gravitational collapse, as the process maintains statistical isotropy. However, the mean shape of peaks is modified significantly - overdensities become relatively more circular compared to underdensities of the same area. When applying the statistic to a redshift space distorted density field, we find a significant signal in the eigenvalues $\Lambda_{1,2}$, suggesting that they can be used to probe the large-scale velocity field.Comment: 17 pages, accepted for publication in AP

Incidence, Age at Onset, Clinical Spectrum and Short Term Outcome of Neonatal Hypoglycemia in a Tertiary Care Hospital

INTRODUCTION: Neonatal hypoglycemia is common during the hours and days following birth. It may be transitory and asymptomatic but can result in a range of acute symptoms. If sufficiently prolonged, the condition is associated with risk of irreversible neurological (brain) damage. OBJECTIVE: To study incidence, age at onset, clinical spectrum and short term outcome of neonatal hypoglycemia. MATERIALS AND METHODS: Study Design: Prospective cohort study. Setting: Neonatal Intensive Care Unit (NICU), Coimbatore Medical College & Hospital, Coimbatore, From March 2018 to February 2019. Participants: Newborns who admitted with high risk for neonatal hypoglycemia. Main outcome measures: Incidence of hypoglycemia, different clinical spectrum in specific birth weight and maturity categories and short term neuro developmental outcome after hypoglycemia at 3 and 8 months. RESULTS: Incidence were 3.6% in high risk newborn in our study and more common in term SGA neonates .55% (n=73) babies between 1000 -2000gms. Mean age of onset of hypoglycemia is 41 hours. 63.4% (n=83) babies had asymptomatic hypoglycaemia identified in routine screening. Sepsis associated with high mortality of 30% as well as increased duration of treatment and NICU stay. Neurodevelopment was delayed in prolonged hypoglycemia. At 8 months of corrected age 42 babies had gross motor, 26 had language, 52 had fine motor and 34 had personal social milestones delay. CONCLUSION: Neonatal hypoglycemia is a serious issue with under diagnosed and poorly follow up neonatal morbidity in paediatric population. Neurodevelopment beyond infancy to be addressed

Nano-mechanical properties and structural of a 3D-printed biodegradable biomimetic micro air vehicle wing

The biomimetic micro air vehicles (BMAV) are unmanned, micro-scaled aircraft that are bio-inspired from flying organisms to achieve the lift and thrust by flapping their wings. The main objectives of this study are to design a BMAV wing (inspired from the dragonfly) and analyse its nano-mechanical properties. In order to gain insights into the flight mechanics of dragonfly, reverse engineering methods were used to establish three-dimensional geometrical models of the dragonfly wings, so we can make a comparative analysis. Then mechanical test of the real dragonfly wings was performed to provide experimental parameter values for mechanical models in terms of nano-hardness and elastic modulus. The mechanical properties of wings were measured by nanoindentre. Finally, a simplified model was designed and the dragonfly-like wing frame structure was bio-mimicked and fabricated using a 3D printer. Then mechanical test of the BMAV wings was performed to analyse and compare the wings under a variety of simplified load regimes that are concentrated force, uniform line-load and a torque. This work opened up the possibility towards developing an engineering basis for the biomimetic design of BMAV wings

Process Control in Micro-Embossing: A Review

Abstract— A promising technique for the large-scale manufacture of micro-fluidic devices and photonic devices is hot embossing of polymers such as PMMA. Micro-embossing is a deformation process where the workpiece material is heated to permit easier material flow and then forced over a planar patterned tool. In this work we review the basic process and the state of research with respect to manufacturing process control, where the latter is defined as methods for minimizing variation in the product while maximizing production rate. From this review we conclude the following: Several investigators have reported success at creating micron scale features using this process, but none have performed a formal characterization or optimization of the process.Singapore-MIT Alliance (SMA

Childhood infections and trauma as risk factors for stroke

Stroke is as common as brain tumor in children. The etiology of childhood arterial ischemic stroke (AIS) appears to be multifactorial, resulting from the interaction between genetic predisposition and environmental triggers. The risk factors for AIS in children are markedly different from the atherosclerotic risk factors in adults. Trauma and infections have been identified as associations in previous studies and are exposures of particular interest because of their increased prevalence in the children. The aim of this review article is to provide an overview of the research studies that have addressed the role of infections and trauma in pediatric AIS

Process Variability in Micro-Embossing

A promising technique for the large-scale manufacture of micro-fluidic devices and photonic devices is hot embossing of polymers such as PMMA. Micro-embossing is a deformation process where the workpiece material is heated to permit easier material flow and then forced over a planar patterned tool. While there has been considerable, attention paid to process feasibility very little effort has been put into production issues such as process capability and eventual process control. In this paper, we present initial studies aimed at identifying the origins and magnitude of variability for embossing features at the micron scale in PMMA. Test parts with features ranging from 3.5- 630 µm wide and 0.9 µm deep were formed. Measurements at this scale proved very difficult, and only atomic force microscopy was able to provide resolution sufficient to identify process variations. It was found that standard deviations of widths at the 3-4 µm scale were on the order of 0.5 µm leading to a coefficient of variation as high as 13%. Clearly, the transition from test to manufacturing for this process will require understanding the causes of this variation and devising control methods to minimize its magnitude over all types of parts.Singapore-MIT Alliance (SMA