6,289 research outputs found
Modeling and Validation of Temperature and Concentration for Rapid Freeze Prototyping
Rapid Freeze Prototyping is a solid freeform fabrication process that uses water as the main build
material in a cold environment to create three-dimensional parts. A eutectic sugar-water solution
(C6H12O6 – H2O) has been used as a sacrificial material in order to create complex 3D parts with
features such as overhangs. A study of the interaction of the build and support materials is
presented in this paper. The temperature of both materials during deposition and subsequent
cooling is modeled using a semi-empirical model and a theoretical model. A concentration
model is used to predict the concentration in the fabricated parts around the interface of the two
materials with predicted temperatures as input. Experiments are conducted to validate both the
temperature and concentration models.Mechanical Engineerin
Recommended from our members
Water governance and poverty: a framework for analysis
YesIn this paper we present a framework for understanding water governance, through which we
critique some of the assumptions underlying the current consensus on good governance.
Specifically, we suggest that current approaches are based on incomplete or partial
understandings of the concepts of governance. We question the idea that governance can be
identified as an abstract set of principles, without the need for contextualisation and localisation.
In particular, we suggest that there is a general lack of understanding of the way local
interactions shape and influence governance processes. Finally, and with specific reference to
the MDGs and the water sector, we question the implicit assumption that `good¿ governance is
necessarily pro-poor governance.
The paper addresses these issues through a critical discussion of governance, from which we
develop a framework for conceptualising water governance. The framework draws on theories of
governance, institutions and structuration, but is also informed by recent empirical research and
experiences from the field. We apply the framework to a specific case in Southwestern Tanzania
and raise a number of issues and challenges for further research
Recommended from our members
Study on Incorporating Support Material in Rapid Freeze Prototyping
Rapid Freeze Prototyping (RFP) is a rapid prototyping method that uses water freezing
into ice to make three-dimensional parts. Each layer of a geometry is deposited and allowed to
freeze before the next layer is added. Using a support material in RFP is a relatively new
addition to the process. Validating the successful use of a support material in conjunction with
the main build material of water is presented in this paper. The support material selected for use
is a eutectic sugar solution. The selection criteria, properties, and characteristics of the support
material are discussed. Of particular interest is the diffusion between the support and main build
material, which must be minimized to an acceptable level for producing good quality,
reproducible, complex parts.Mechanical Engineerin
Recommended from our members
How institutions elude design: river basin management and sustainable livelihoods.
YesThis paper challenges ideas that it is possible to `get the institutions right¿ in the management of natural resources. It engages with the literature and policy specifying `design principles¿ for robust institutions and uses data from a river basin management project in Usangu, Tanzania, to illustrate the complexity of institutional evolution. The paper draws on emerging `post-institutionalist¿ perspectives to reject over-formalised managerial approaches in favour of those that accept the dynamic nature of institutional formation, and accommodate a variety of partial and contingent solutions. Data from Usangu suggests that external `crafting¿ is inevitably problematic because, to a certain extent, institutions elude design
An item analysis of Nason phonics test in grades one and two
Thesis (Ed.M.)--Boston Universit
Fine Structure of Changes Produced in Cultured Cells Sampled at Specified Intervals During a Single Growth Cycle of Polio Virus
Primary suspended cultures of rhesus monkey kidney cells were infected with poliomyelitis virus, type 1 (Brunhilde strain). The release of virus from these cells over a one-step growth curve was correlated with their change in fine structure, as seen in the electron microscope. Most of the cells were infected nearly simultaneously, and morphological changes developed in the cells were sufficiently synchronous to be classified into three stages. The earliest change (stage I) became visible at a time when virus release into the culture fluid begins, some 3 hours after adsorption. Accentuation of the abnormal characteristics soon occurs, at 4 to 7 hours after adsorption, and results in stage II. Stage III represents the appearance of cells after their rate of virus release had passed its maximum, and probably the abnormal morphology of these cells reflects non-specific physiological damage. There seems to be consistency between the previously described cellular changes as seen under the light microscope and the finer scale changes reported here.
Cytoplasmic bodies, called U bodies, were seen in large number at the time when the virus release was the most rapid (stage II). While these bodies are not of proper size to be considered polio virus, they seem to be specifically related to the infection. No evidence was found for the presence of particles that could even be presumptively identified with those of polio virus
Community building and virtual teamwork in an online learning environment
In the world of OTIS, an online Internet School for occupational therapists, students from four European countries were encouraged to work collaboratively through problem based learning by interacting with each other in a virtual semi-immersive environment. This paper aims to explore the issues that there was little interaction between students from different tutorial groups and virtual teamwork developed in each of the cross cultural tutorial groups. Synchronous data from European students was captured during tutorial sessions and peer booked meetings and evidence suggests that communities of interest were established. It is possible to conclude that collaborative systems can be designed, which encourage students to build trust and teamwork in a cross cultural online learning environment. </p
Neutral genetic drift can aid functional protein evolution
BACKGROUND: Many of the mutations accumulated by naturally evolving proteins
are neutral in the sense that they do not significantly alter a protein's
ability to perform its primary biological function. However, new protein
functions evolve when selection begins to favor other, "promiscuous" functions
that are incidental to a protein's biological role. If mutations that are
neutral with respect to a protein's primary biological function cause
substantial changes in promiscuous functions, these mutations could enable
future functional evolution.
RESULTS: Here we investigate this possibility experimentally by examining how
cytochrome P450 enzymes that have evolved neutrally with respect to activity on
a single substrate have changed in their abilities to catalyze reactions on
five other substrates. We find that the enzymes have sometimes changed as much
as four-fold in the promiscuous activities. The changes in promiscuous
activities tend to increase with the number of mutations, and can be largely
rationalized in terms of the chemical structures of the substrates. The
activities on chemically similar substrates tend to change in a coordinated
fashion, potentially providing a route for systematically predicting the change
in one function based on the measurement of several others.
CONCLUSIONS: Our work suggests that initially neutral genetic drift can lead
to substantial changes in protein functions that are not currently under
selection, in effect poising the proteins to more readily undergo functional
evolution should selection "ask new questions" in the future
Seven Strategies for Successfully Marketing and Stabilizing the Occupancy of Mixed-Income/Mixed-Race Properties - Summary Report
Mixed-Income rental properties that include extremely low-income households (below 30 percent of AMI) are a valuable strategy for community health. They simultaneously address two critical challenges: housing for those most in need and desegregating poverty. Understanding how to operate mixed-income apartments profitably is important to increase the development and underwriting of these properties.With the generous support of the Ford Foundation, NeighborWorks America undertook this study of management and marketing practices of successful mixed-income properties that have served extremely low-income families while maintaining positive cash flow for at least five years.This report describes seven strategies used by these properties to stabilize and maintain high occupancy rates with healthy operating budgets. For each strategy, we provide concrete implementation examples
- …