On solutions of the transport equation in the presence of singularities

We consider the transport equation on $[0,T]\times \R^n$ in the situation where the vector field is $BV$ off a set $S\subset [0,T]\times \R^n$. We demonstrate that solutions exist and are unique provided that the set of singularities has a sufficiently small anisotropic fractal dimension and the normal component of the vector field is sufficiently integrable near the singularities. This result improves upon recent results of Ambrosio who requires the vector field to be of bounded variation everywhere. In addition, we demonstrate that under these conditions almost every trajectory of the associated regular Lagrangian flow does not intersect the set $S$ of singularities. Finally, we consider the particular case of an initial set of singularities that evolve in time so the singularities consists of curves in the phase space, which is typical in applications such as vortex dynamics. We demonstrate that solutions of the transport equation exist and are unique provided that the box-counting dimension of the singularities is bounded in terms of the H\"older exponent of the curves

The efficiency of reverse engineering in the design of the ORCA XI autonomous underwater vehicle by Rachel E. Sharples.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 40).Reverse engineering is the process of determining how a system works to aid duplication, maintenance, or redesign. Applications of reverse engineering include mechanical, electrical, software, and process systems. Although it has been known for centuries in the vernacular as tinkering with things to see how they work, reverse engineering has only recently been recognized as a systematic process valid for study. Reverse engineering can be applied to both simple and complex systems. The MIT ORCA team applied reverse engineering to build ORCA XI, the first autonomous underwater vehicle (AUV) to issue forth from the ORCA Project in several years. In addition to college-level systems, reverse engineering can be applied to navies, aiding in the prototyping of individual vessels as well as the manufacturing of entire fleets. There is evidence that China is using reverse engineering in this manner to develop a regionally-capable navy. The effectiveness of reverse engineering on the ORCA Project is compared to that of the Chinese navy to determine how a reverse engineering method could be expected to scale from a simple system to a more complex one. To quantify the relationship between the complexity of the system and how effective reverse engineering that system is, a reverse engineering efficiency based on the time necessary to complete a project with reverse engineering and the time necessary to complete the same project without reverse engineering was used. The efficiency values obtained from this comparison show that applying reverse engineering to an AUV can be just as effective as applying reverse engineering to a naval vessel, but that designing the production line necessary to manufacture a fleet of vessels decreases the efficiency of reverse engineering. These results suggest that new reverse engineering methodologies can be tested for efficiency on simple prototypes before being applied to time-consuming, complex projects.S.B

Evaluation of the Impact of an Additive Manufacturing Enhanced CubeSat Architecture on the CubeSat Development Process

Additive manufacturing (AM) is a fabrication method ideally suited to low-quantity, highly customized builds, leading to interest in its application to satellite development and manufacturing, where each build is unique. Due to the issues of long development schedules and high development and manufacturing costs, methods are needed in the CubeSat development process to reduce the weight and volume of subsystems and decrease integration time. The work develops an architecture for an AM-augmented CubeSat and examines the AM techniques of embedded electronics, embedded thrusters, and custom radiation-hardened materials can impact the subsystems of a CubeSat. The AM-augmented architecture shows a shift in CubeSat development and manufacturing from a modular approach to an integrated approach where most of the CubeSats internal bus components, such as electronics, thrusters, and propulsion, are integrated directly into the structure. This integrated approach results in decreased time spent in assembly and integration, decreased mass and volume, and also allows for key components to be embedded in materials with improved radiation attenuation characteristics

Generalised Cantor sets and the dimension of products

In this paper we consider the relationship between the Assouad and box-counting dimension and how both behave under the operation of taking products. We introduce the notion of ‘equi-homogeneity’ of a set, which requires a uniformity in the cardinality of local covers at all length-scales and at all points, and we show that a large class of homogeneous Moran sets have this property. We prove that the Assouad and box-counting dimensions coincide for sets that have equal upper and lower box-counting dimensions provided that the set ‘attains’ these dimensions (analogous to ‘s-sets’ when considering the Hausdorff dimension), and the set is equi-homogeneous. Using this fact we show that for any α ∈ (0, 1) and any β, γ ∈ (0, 1) such that β + γ ≥ 1 we can construct two generalised Cantor sets C and D such that dimBC = αβ, dimBD = α γ, and dimAC = dimAD = dimA (C × D) = dimB (C × D) = α

Using mobile phones in pub talk

We present the findings from a study of how people interleave mobile phone use with conversation in pubs. Our findings, informed by ethnomethodology and conversation analysis, unpack the interactional methods through which groups of people in pubs occasioned, sustained, and disengaged from mobile device use during conversation with friends. Fundamentally, the work that is done consists of various methods of accounting for mobile device use, and displaying involvement in social interaction while the device is used. We highlight multiple examples of the nuanced ways in which interleaving is problematic in interaction, and relate our findings to the CSCW and HCI literature on collocated interaction. We conclude by considering avenues for future research, and discuss how we may support or disrupt interleaving practices through design to overcome the highlighted interactional troubles

Recent trends in organic gunshot residue analysis – a review.

A comprehensive review of the literature concerning all aspects of sampling and analytical techniques used for the determination of organic gunshot residue (OGSR) compounds is presented. Currently, 136 compounds associated with OGSR have been identified in the literature. Despite this area gaining increasing attention and recognition in recent years, there is still an absence of a set combination of sample collection, extraction and analysis methods that are universally optimal for the treatment of any given OGSR sample. Moreover, there are no generally accepted guidelines for selecting the compounds of interest that will inform sampling and analysis protocols. We highlight recent developments in both extraction and analytical methods employed for their detection. The main advantages and disadvantages of the sampling and analysis methods are critically discussed

Organic compositional analysis of propellant powders using monolithic material sorption extraction ( MSSE) - a feasibility study

The application of monolithic material sorption extraction, specifi cally MonoTrapTM, to the extraction of organic gunshot residue (OGSR) compounds from unburnt propellant powders is described. Four different MonoTraps were assessed for their capability to extract OGSR compounds from two different ammunition types. Extracts were analysed using gas chromatography-mass spectrometry. Results indicated that the carbon disc was suitable for the extraction of OGSR compounds from unburnt propellant powders. Quantities for major compounds were comparable to methanol extractions. The method was successfully used to detect a wide range of OGSR compounds, including nitrotoluenes, nitroglycerin, diphenylamines and centralites and is expected to be applicable to a wide range of ammunition types

Preliminary classification of characteristic organic gunshot residue compounds.

For the first time, a classification system for organic gunshot residue (OGSR) compounds with respect to the confirmation of OGSR materials is presented. There are 136 compounds considered to be associated with OGSR that have been highlighted in the literature. Many of these compounds could be classified as being ubiquitous in the environment and thus their detection as characteristic components of OGSR could cause issues with the interpretation of chemical ballistic evidence. The proposed system aims to address this problem by classifying OGSR compounds based on their forensic relevance with respect to the confirmation of GSR materials. To increase the forensic relevance of such a system, the large number of OGSR compounds reported in the literature has been decreased to 20 OGSR compounds based on the organic chemical composition of over 200 propellant powders. Occupational and environmental materials also associated with OGSR compounds have been considered

Seasonality in the cross-shelf physical structure of a temperate shelf sea and the implications for nitrate supply

We address a long-standing problem of how nutrients are transported from the shelf edge and from rivers to support regular, seasonal primary production in the interior of a wide, temperate, shelf sea. Cross-shelf sections of hydrography and nutrients, from a series of cruises between March 2014 and August 2015, along with time series of river discharge and river nutrient load are used to assess the seasonality of cross-shelf transports. Riverine nitrogen inputs are estimated to account for 30% of the nitrate available for the spring bloom on the inner shelf, and 10% in the mid- to outer-shelf. In the bottom layer in summer, high salinity, nutrient-rich waters are transported on-shelf as a result of wind-driven Ekman transport, cross-shelf pressure gradients and/or internal tidal wave Stoke’s drift. In the centre of the shelf this advection is responsible for 25% of the increase in bottom water nitrate seen between April and November 2014. The remaining nitrate increase suggests that about 50–62% of the nitrogen fixed into organic material during spring, summer and autumn phytoplankton growth is recycled in the bottom water over the 12 months between March 2014 and March 2015. In winter, when the water column is vertically mixed, there is a weak net off-shelf transport of about 1 m2 s−1, possibly driven by a reversal of the horizontal density gradient caused by excess cooling of shallower shelf waters. Overall, shelf nitrate concentrations are maintained by a combination of riverine supply, recycling of organic material, and summer on-shelf transports. We suggest that the main driver of inter-annual variability in pre-spring nitrate concentrations is variability in the depth of the winter mixed layer over the shelf slope

“Do animals have accents?”: talking with agents in multi-party conversation

In this paper we unpack the use of conversational agents, or so-called intelligent personal assistants (IPAs), in multi- party conversation amongst a group of friends while they are socialising in a café. IPAs such as Siri or Google Now can be found on a large proportion of personal smartphones and tablets, and are promoted as ‘natural language’ interfaces. The question we pursue here is how they are actually drawn upon in conversational practice? In our work we examine the use of these IPAs in a mundane and common-place setting and employ an ethnomethodological perspective to draw out the character of the IPA-use in conversation. Additionally, we highlight a number of nuanced practicalities of their use in multi-party settings. By providing a depiction of the nature and methodical practice of their use, we are able to contribute our findings to the design of IPAs