Designer Materials by Self- and Directed Assembly: Photorheological Fluids, Magnetic Microchains and Hemostatic Dressings

Our laboratory seeks to engineer the assembly of “building blocks” such as polymers, surfactants, or colloids into higher-order materials. Such assembly can be induced spontaneously, guided by thermodynamic forces – this is called self-assembly. Alternately, assembly can be directed in specific ways, e.g., by bringing materials into contact at interfaces or around predefined templates – this can be termed directed assembly. Both processes have their analogs in biology and nature, and both are of great technological interest. This talk will provide illustrative examples of our work with self- and directed assembly. We have created assemblies that respond to stimuli such as temperature, pH or light; an example of the latter are photorheological fluids. Also, we have used microfluidic techniques to create magnetic microcapsules of biopolymers, which we have then linked into flexible microchains. We have also developed self-assembling biopolymers that have the ability to gel blood cells and thereby serve as effective hemostatic dressings for both military and civilian use

Electro–Responsive Hydrogel Films And Beads: Using Electric Fields To Break Or Stick Solids

Hydrogels based on water-soluble synthetic or biopolymers are a common class of soft materials. They can be easily prepared either by covalent crosslinking (free-radical polymerization) or by physical crosslinking, e.g., via ionic or hydrogen-bonds. Numerous studies have been published on hydrogels with responsive properties, such as the ability to swell, shrink, or change shape in response to external stimuli such as temperature, pH, light or magnetic fields. Electric fields are another type of stimulus, but hydrogels are not commonly thought to be electrically responsive, unless they can conduct electricity (e.g., if the polymer backbone is a conductive polymer or if the material is a nanocomposite with conductive particles). This talk will present studies from our lab showing a rich variety of behavior induced by electric fields on polyelectrolyte hydrogels, all of which are nonconductive. First, we study ‘electro-adhesion’. When a film or bead of a cationic gel is contacted for just a few seconds with a film or bead of an anionic gel under a DC voltage of about 10 V, the two form a strong adhesive bond. When the polarity is reversed, the phenomenon is reversed, i.e., the gels can be easily detached. Most interestingly, the same phenomenon also works with certain animal tissues. That is, many tissues are anionic, and we show that cationic gels can be electro-adhered to them. We thereby demonstrate that cuts or tears in tissues can be electro-sealed using gels. As an extreme case, two severed pieces of a tube can be stuck back together using a gel strip that spans both cut segments; this is thereby an example of a needleless suture using only hydrogels and an electric field. Next, we study hydrogel beads and capsules made from common biopolymers like alginate and chitosan using ionic complexation. When these beads are placed in aqueous solution and subjected to an electric field of about 10 V/cm, the particles deform within a minute and then burst within about 5 min. Such deformation and rupture can be used to release solutes loaded inside these structures. Alternately, the deformation of the beads can be used to create electrically actuatable valves, where the flow of a liquid occurs only when the bead blocking the flow is deformed, and thereby dislodged. These kinds of electro-responsive phenomena could find application in wearable device technologies. Electric fields are attractive because they can be easily applied even from remote locations, and possibly using wireless signals

Nature-inspired multi-compartment and multi-layered capsules

This talk will describe the design and synthesis of new capsule structures, made from biocompatible polymers through directed assembly in aqueous solution. Our inspiration for creating these structures comes from nature. In one case, the inspiration comes from the architecture of the eukaryotic cell, which has multiple inner compartments (organelles), each with a distinct function. In this vein, we have created biopolymer-based multicompartment capsules (MCCs) using an oil-free microfluidic technique. Our approach exploits the electrostatic complexation (coacervation) of oppositely charged polymers dissolved in aqueous media. We can control the overall size of the MCCs, the sizes of the inner compartments, and the number of inner compartments. More importantly, we can encapsulate different payloads in each of the inner compartments, including colloidal particles, enzymes, and microbial cells. A hallmark of biological cells is the existence of cascade processes, where products created in one organelle are transported and used in another. We will show examples of such cascade processes using our MCCs. A second class of capsules are inspired by natural structures that include eggs, embryos, body parts like blood vessels and the spinal disc, plant seeds, and vegetables like the onion. All these structures have multiple concentric layers, with each layer typically having distinct composition, and thereby function. The creation of multilayered structures in nature typically proceeds by the initial formation of an inner layer or core, followed by a first shell, and a further progression outwards to add more shells. We draw inspiration from natural morphogenesis to create multilayered (onion-like) polymer capsules by an “inside-out” technique. Each polymeric shell grows outward from the surface of the previous shell; thus, the thickness of a given shell steadily increases with time and can be controlled. Using this technique, we can juxtapose different polymers next to each other among the concentric layers in a capsule. We will show that these capsules exhibit a range of interesting properties, including in their ability to release solutes, and in their mechanical strength

SYSPOINT: Unit of Measure for IT Infrastructure Project Sizing

What can be done to improve the success rate of IT infrastructure projects? The Standish group considers an IT project successful when it is completed on time and on budget, with all the features and functions originally specified. Thus, time, cost, and scope – the triple constraint of project management is measured for success. The initial project estimation directly results in constructing the baseline for the two success parameters – time and cost. The traditional software estimation models uses lines of code and function points as sizing unit of measure. The IT infrastructure projects are significantly different from software development projects to use the software sizing techniques. This paper defines the concept of size for IT infrastructure projects. Specifically, the project size for IT infrastructure projects are measured in terms of the eight factors (server, workstation, printer, LAN, WAN, handheld, server applications, and client applications), infrastructure related software components, and the complexities defined based on the physical and functional categories of those factors

Semi-supervised and Active-learning Scenarios: Efficient Acoustic Model Refinement for a Low Resource Indian Language

We address the problem of efficient acoustic-model refinement (continuous retraining) using semi-supervised and active learning for a low resource Indian language, wherein the low resource constraints are having i) a small labeled corpus from which to train a baseline `seed' acoustic model and ii) a large training corpus without orthographic labeling or from which to perform a data selection for manual labeling at low costs. The proposed semi-supervised learning decodes the unlabeled large training corpus using the seed model and through various protocols, selects the decoded utterances with high reliability using confidence levels (that correlate to the WER of the decoded utterances) and iterative bootstrapping. The proposed active learning protocol uses confidence level based metric to select the decoded utterances from the large unlabeled corpus for further labeling. The semi-supervised learning protocols can offer a WER reduction, from a poorly trained seed model, by as much as 50% of the best WER-reduction realizable from the seed model's WER, if the large corpus were labeled and used for acoustic-model training. The active learning protocols allow that only 60% of the entire training corpus be manually labeled, to reach the same performance as the entire data

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Improving support for generic programming in C# with associated types and constraint propagation

Generics has recently been adopted to many mainstream object oriented languages, such as C# and Java. As a particular design choice, generics in C# and Java use a sub-typing relation to constraint type parameters. Failing to encapsulate type parameters within generic interfaces and inability to encapsulate type constraints as part of an interface definition have been identified as deficiencies in the way this design choice has been implemented in these languages. These deficiencies can lead to verbose and redundant code. In particular, they have been reported to affect the development of highly generic libraries. To address these issues, extending object oriented interfaces and sub-typing with associated types and constraint propagation has been proposed and studied in an idealized small-scale formal setting. This thesis builds on this previous work and provides a design and implementation of the extensions in full C#. We also present a proof of soundness of the Featherweight Generic Java (FGJ) formalism extended with interfaces. This property was assumed in a proof of type safety of associated types and constraint propagation, but no proof for the property was provided

Banded matrices with banded inverses

Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 99).We discuss the conditions that are necessary for a given banded matrix to have a banded inverse. Although a generic requirement is known from previous studies, we tend to focus on the ranks of the block matrices that are present in the banded matrix. We consider mainly the two factor 2-by- 2 block matrix and the three factor 2-by-2 block matrix cases. We prove that the ranks of the blocks in the larger banded matrix need to necessarily conform to a particular order. We show that for other orders, the banded matrix in question may not even be invertible. We are then concerned with the factorization of the banded matrix into simpler factors. Simpler factors that we consider are those that are purely block diagonal. We show how we can obtain the different factors and develop algorithms and codes to solve for them. We do this for the two factor 2-by-2 and the three factor 2-by-2 matrices. We perform this factorization on both the Toeplitz and non-Toeplitz case for the two factor case, while we do it only for the Toeplitz case in the three factor case. We then look at extending our results when the banded matrix has elements at its corners. We show that this case is not very different from the ones analyzed before. We end our discussion with the solution for the factors of the circulant case. Appendix A deals with a conjecture about the minimum possible rank of a permutation matrix. Appendices B & C deal with some of the miscellaneous properties that we obtain for larger block matrices and from extending some of the previous work done by Strang in this field.by Venugopalan Srinivasa Gopala Raghavan.S.M

सीप गठन की प्रेरणा के लिए समुद्री द्विकपाटी मोलस्क के मैन्टिल ऊतक के पात्रेन संवर्धन का प्रयोग

In vivo culture of mantle tissue of bivalve molluscs for induced pearl productio