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

Radiation reaction in the 2.5PN waveform from inspiralling binaries in circular orbits

In this Comment we compute the contributions of the radiation reaction force in the 2.5 post-Newtonian (PN) gravitational wave polarizations for compact binaries in circular orbits. (i) We point out and correct an inconsistency in the derivation of Arun, Blanchet, Iyer, and Qusailah. (ii) We prove that all contributions from radiation reaction in the 2.5PN waveform are actually negligible since they can be absorbed into a modification of the orbital phase at the 5PN order.Comment: 7 pages, no figures, submitted to CQ

High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects

A large magnetoresistance effect is obtained at room-temperature by using p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is the virtual elimination of thermal currents due to the presence of band gaps in the contacts. The current at B=0T is greatly decreased while the current at B>0T is relatively large due to the band-to-band tunneling effects, resulting in a high magnetoresistance ratio, even at room-temperature. Moreover, we explore the effects of edge-roughness, length, and width of GNR channels on device performance. An increase in edge-roughness and channel length enhances the magnetoresistance ratio while increased channel width can reduce the operating bias.Comment: http://dx.doi.org/10.1063/1.362445

Marketing of Library and Information Products and Services During Covid -19 Pandemic: A Study

The Social networking sites play a major role in promoting library services and products to its user community. In this Covid-19 Pandemic and lockdown period, physical communication was locked and online web communication technology proved a powerful tool to bridge the gap between the library and users. The users were unable to reach the libraries during this pandemic period. The librarians used social networking tools to provide information during this pandemic period. The libraries provided a variety of services to its user community. The purpose of this paper is to show how effectively the libraries used Social Networking Sites for marketing & promoting the library and information products & services to their users during this pandemic and lockdown period. A structured online questionnaire was used for data collection. The targeted population was academic librarians working in colleges in Goa, India. From the study, it was found that Social networking sites play a major role in marketing and promoting library and information products and services during this pandemic period. Maximum librarians are using the Library website, Facebook and WhatsApp tool for marketing and promoting the library services and products to reach their users

Assessment Of Groundwater Potentials Of The Crystalline Aquifers Using Hydraulic Propertiesfor Gidanwaya Town And Its Environs, Southern Parts Of Kaduna State, North Western Nigeria

Pumping test data for 25 boreholes were used to evaluate the hydraulic properties of the aquifers derived from the crystalline Basement rocks of Gidan Waya in southern part of Kaduna State Sheet 188 Jema’a NE and NW North Western Nigeria using the Cooper – Jacobs’s non equilibrium graphical procedures. The transmissivity values for the 25 boreholes in the area have a range of between 1.16x10-1 and 9.76x10-3.The hydraulic conductivity values are between 1.12x10-2m/s and 9.24x10-3m/s. The specific capacity values in the studied area ranges between 1.00x10-1 and 9.95x10-2. The maximum drawdown recorded for the boreholes is between 4.24 to 22.9 m while the drawdown per log cycle ranges from 0.28 to 4.40 m.  The above range of aquifer properties has revealed the area to be of high to very high groundwater potentials. Lithological borehole logs revealed the aquifers in the area to comprise of clay, silt, sand, gravels and fractured basement rocks aquifer materials. This is further supported by the values of hydraulic conductivity obtained. Generally the result of the pumping test analysis shows that the boreholes on the average have high groundwater potentials with capacity to sustain withdrawals for regional importance in most cases and in fewer situations the supply can only be local and limited. Keywords:  Basement Complex, Aquifers, Groundwater potentials, Hydraulic Properties

IMPACT OF ACADEMIC LIBRARY SERVICES ON STUDENTS SUCCESS AND PERFORMANCE

Libraries play an important role as a reliable and beneficial information provider in the students academic success and performance. The aim of this study is to investigate the students satisfaction with library resources and services provided by the academic library. Random surveying was conducted to find out the problem and difficulties faced by the students in accessing the library resources and its impact on their academic success and performance. The finding in the study showed that there is a significant and remarkable relationship between the library usage and the students’ academic performance and success. the major finding of the study is to conduct the information literacy programme for the students to promote awareness about the resources, services and facilities available in the library so that the students can take maximum advantage of the benefits provided by the library . One way to overcome this problem is to encourage the students to embrace using the library in their academic studies and explain its benefits

Efficacy of Sakacin on Selected Food Pathogenic Microorganisms Isolated from Fermented Milk Products

The efficacy of sakacin on selected food pathogenic microorganisms isolated from fermented milk products  was investigated. The L .sake was isolated using the pour plate technique and was characterized based on it colony, cell morphology and some biochemical tests. This isolate was identified using standard scheme. The L .sake FCF 33 was propagated in De Man Rogosa Sharpe (MRS) broth for bacteriocin (sakacin) production. The sakacin had inhibitory effects on all test microorganisms (ranging from +5mm to +6mm) except Shigella dysenteriae N11, Salmonella typhimurium N8, Klebsiella ozaenae W24 and Proteus mirabilisN16a). Bacteriocins are antimicrobial substances of lactic acid bacteria (LAB) have gained tremendous attention as potential bio preservatives in the food and dairy industries. The LAB can serve as probiotics, which are products aimed at delivering living, potentially beneficial bacterial cells to the gut ecosystem of humans and other animals. © JASEMKeywords: Inhibition, sakacin, De Man Rogosa Sharpe, broth, morpholog

Paper-based electroanalytical devices with an integrated, stable reference electrode

This paper describes the development of a referenced Electrochemical Paper-based Analytical Device (rEPAD) comprising a sample zone, a reference zone, and a connecting microfluidic channel that includes a central contact zone. We demonstrated that the rEPADs provide a simple system for direct and accurate voltammetric measurements that are referenced by an electrode with a constant, well-defined potential. The performance of the rEPADs is comparable to commercial electrochemical cells, and the layout can be easily integrated into systems that permit multiplexed analysis and pipette-free sampling. The cost of this portable device is sufficiently low that it could be for single-use, disposable applications, and its method of fabrication is compatible with that used for other paper-based systems.Chemistry and Chemical Biolog

Early outcome of interlocking intramedullary nailing of infected tibia fracture nonunions: A report of 2 cases

Background: Eradication of infection and fracture union are the two major objectives of treatment of infected non unions. Recent studies indicate that locked intramedullary nailing of tibia fracture non unions provide a  mechanical environment which enhances fracture healing even in the presence of infection. It also allows early weight-bearing without the burden of an external frame making it more acceptable to patients than external fixators.The Cases: The authors present 2 cases of infected tibia non unions. The first case had segmental fibulectomy, fracture debridement, deep tissue sampling, locked intramedullary nailing, cancellous bone grafting and antibiotic therapy. The second case had segmental fibulectomy, wound and fracture debridement, deep tissue sampling, locked intramedullary nailing, cancellous bone grafting, fasciocutaneous flap wound cover and antibiotic therapy.Results: The first case had a satisfactory (early) outcome having achieved full weight bearing at 12 weeks with no clinical evidence of infection.  Similarly, the second case had a good outcome having achieved full weight bearing without clinical signs of infection at 12 weeks (although immediate post-op period was complicated by surgical site infection which was effectively managed). Based on these two cases, the importantguiding principles were identified and discussed.Conclusion: With appropriate surgical technique and strict adherence to surgical principles, the outcome of interlocking intramedullary nailing for infected tibia non unions are satisfactory.Keywords: Early Outcome, Intramedullary Nailing, Tibia, Fracture Non  union