194 research outputs found
A methodology for the concurrent design of products and their assembly sequence
No full textThis thesis reports on the development of a Two-Tier methodology that provides
support for assembly sequence construction, validation and evaluation in parallel with
the design. This facilitates the production of products that are optimised for
assemblability. The proposed approach diverges significantly from many of the
sequence generation methods developed to date, which assume that assembly
planning starts at the conclusion of the design process. It is believed that the latter
approach misses an important opportunity to concurrently implement design and
sequence improvements that would result in products inherently suited to assembly.
The industrial assembly planning process was found to be completely different from
the automatic sequence generation approach. The Two-Tier methodology has its
foundations in this manual process, which uses a breadth-first, depth-second search. A
constraint-based method is used to interactively validate the sequence. In direct
contrast to traditional sequence generators, the hard and soft constraints are invoked
throughout the process. A novel approach to sequence evaluation allows the user to
quantitatively determine the suitability of the sequence at any time during the
construction process.
However, designers are rarely assembly experts and it is unreasonable to expect
practical sequences to be generated without assistance. Thus, a set of generic
assembly planning rules was identified from industrial surveys by the author. These
were collaboratively implemented into an Expert Assembler, which currently consists
of two mini advisors. Support is available to identify the most suitable base
component and the most appropriate component to add next.
The Two-Tier methodology has been implemented into a computer-based system
called SPADE (Sequence Planning And Design Environment). A four-layer model
holds the product data that underpins this implementation. The methodology and
SPADE have been successfully tested using representative case studies and the results
are reported as part of this thesis
Comprehensive assessment of the management of acute cholecystitis in Scotland: population-wide cohort study
No full textFunding The study was funded by an NHS Grampian endowment fund (NER 11062). © The Author(s) 2023. Published by Oxford University Press on behalf of BJS Society Ltd. Elements of this paper were presented as an oral presentation at the Surgical Research Society in Nottingham, UK on 25 March 2023. Data from this paper have also been presented in the Moynihan prize presentation section of the Association of Surgeons of Great Britain and Ireland, Harrogate, UK on 18 May 2023Peer reviewe
Trauma recidivism in England and Wales: an epidemiological study
No full textBackground: Trauma recidivism refers to patients who are injured repeatedly. There has been no evaluation of trauma recidivism in England and Wales. We hypothesize that, because population demographics and predominant trauma mechanism differ from other studied populations, the typical demographics of patients suffering repeated trauma would differ. Our aim was to determine the demographic and injury characteristics, and outcomes of patients suffering repeated trauma.
Methods: This was a national, retrospective, population-based cohort study of patients included in the prospectively collected Trauma Audit & Research Network’s (TARN) National Trauma Registry for England and Wales between 2019 and 2020. We defined recidivism as a second admission, with different injuries, within 1 year of the initial admission. Analysis was descriptive.
Results: 2517 patients (5136 admissions) were included. Median age at first admission was 81 years, and 1888 (75%) were ≥65 years. 1301 (52%) were female. The most common mechanism of injury at first and second admission was a fall ≤2 m (2159 86%, 2237 89%). 2035 (81%) suffered a fall ≤2 m on both admissions. Patients with severe injury increased from 838 (33%) to 982 (39%) from first to second admission. Patients discharged home decreased from 1776 (71%) to 1449 (58%) from first to second admission. Mortality on 2nd admission was 10.2%.
Conclusions: In England and Wales, trauma recidivism consists primarily of elderly patients who repeatedly suffer low-energy falls. It follows that prevention strategies should consist of greater and earlier involvement of multidisciplinary team input including geriatric physicians and allied health professionals, for anyone ≥65 who fulfills the criteria for TARN inclusion.
Level of evidence: Level III
On the questions of local and global well-posedness for the hyperbolic PDEs occurring in some relativistic theories of gravity and electromagnetism
No full textThe two hyperbolic systems of PDEs we consider in this work are the source-free Maxwell-Born-Infeld (MBI) field equations and the Euler-Nordstr??m system for gravitationally self-interacting fluids. The former system plays a central role in Kiessling's recently proposed self-consistent model of classical
electrodynamics with point charges, a model that does not suffer from the infinities found in the classical Maxwell-Maxwell model with point charges. The latter system is a scalar gravity caricature of the incredibly more complex Euler-Einstein system. The primary original contributions of the thesis can be summarized as follows:
1) We give a sharp non-local criterion for the formation of singularities in plane-symmetric solutions to the source-free MBI field equations. We also use a domain of dependence argument to show that 3-d initial data agreeing with certain plane-symmetric data on a large enough ball lead to solutions that form singularities in finite time. This work is an extension of a theorem of Brenier, who studied singularity formation in periodic plane-symmetric solutions.
2) We prove well-posedness for the Euler-Nordstr??m system with a cosmological constant k (EN_k) for initial data that are an H^N perturbation (not necessarily small) of a uniform, quiet fluid, for N [greater than]= 3. The method of proof relies on the framework of energy currents that has been recently developed by Christodoulou. We turn to this method out of necessity: two common frameworks for showing well-posedness in H^N, namely symmetric hyperbolicity and strict hyperbolicity, do not apply to the EN_k system, while Christodoulou's techniques apply to all hyperbolic systems derivable from a Lagrangian, of which the EN_k system is an example.
3) We insert the speed of light c as a parameter into the EN_k system (and designate the family of systems EN_k^c) in order to study the non-relativistic limit c to infinity. Taking the formal limit in the equations gives the Euler-Poisson system with a cosmological constant (EP_k). Using energy currents, we prove that for fixed initial data, as c goes to infinity, the solutions to the EN_k^c system converge uniformly on a spacetime slab [0,T] x R^3 to the solution of the EP_k system.Ph.D.Includes bibliographical references (p. 140-143)
The effects of increased midsole bending stiffness of sports shoes on muscle-tendon unit shortening and shortening velocity: a randomized crossover trial in recreational male runners
No full textBackground: Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. It is unknown, however, how these compliances interact with each other when the MBS of a running shoe is increased. The purpose of this study was to investigate how structures of the foot-shoe interface are influenced during running by changes to the MBS of sport shoes.
Methods: A randomised crossover trial was performed, where 13 male, recreational runners ran on an instrumented treadmill at 3.5 m center dot s(-1) while motion capture was used to estimate foot arch, plantar muscle-tendon unit (pMTU), and shank muscle-tendon unit (sMTU) behaviour in two conditions: (1) control shoe and (2) the same shoe with carbon fibre plates inserted to increase the MBS.
Results: Running in a shoe with increased MBS resulted in less deformation of the arch (mean +/- SD; stiff, 7.26 +/- 1.78 degrees; control, 8.84 +/- 2.87 degrees; p <= 0.05), reduced pMTU shortening (stiff, 4.39 +/- 1.59 mm; control, 6.46 +/- 1.42 mm; p <= 0.01), and lower shortening velocities of the pMTU (stiff, - 0.21 +/- 0.03 m center dot s(-1); control, - 0.30 +/- 0.05 m center dot s(-1); p <= 0.01) and sMTU (stiff, - 0.35 +/- 0.08 m center dot s(-1); control, - 0.45 +/- 0.11 m center dot s(-1); p <= 0.001) compared to a control condition. The positive and net work performed at the arch and pMTU, and the net work at the sMTU were significantly lower in the stiff compared to the control condition.
Conclusion: The findings of this study showed that if a compliance of the foot-shoe interface is altered during running (e.g. by increasing the MBS of a shoe), the mechanics of other structures change as well. This could potentially affect long-distance running performance.articl
Impact of load type on microgrid stability
No full textThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.CD-ROM contains PDF of thesis and MDL file.Both MIT Institute Archives and Barker Library copy: with CD-ROM.Cataloged from student submitted PDF version of thesis.Includes bibliographical references.Microgrids show great promise as a means of integrating distributed generation sources into the public grid distribution system. In order to provide uninterrupted,high quality power to local loads, microgrids must have the ability to operate independently of or in parallel with the local utility. Transitioning between independent operation, also called "islanded" operation, and utility connected operation can induce stability problems in the microgrid, especially when islanding is fault induced. Software simulation suggests that induction motor loads on the microgrid significantly decrease stability during fault induced islanding. To validate the software simulations and to investigate the impact of load type on microgrid stability, we have built a hardware system that simulates the operation of a microgrid.by Jared P. Monnin.M.Eng
Knitting with directed graphs
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 67-68).Knitting has historically been communicated by its means of construction. For hand knitting, this is typically a list of instructions or a pictorial grid with knitting symbols. For machine knitting, a similar pictorial grid is used to express needle-level instructions. However, these formats suffer by the nature of their tight coupling with the method used to construct the garments they represent. Alternatively, we use Knit Meshes, which represent knitting structures by their geometry separate from a directed graph description of their topology. This thesis presents an algorithm that can generate a natural, deformed two-dimensional layout of Knit Meshes as well as a conversion pipeline that converts written hand knitting instructions to and from Knit Meshes and an algorithm that converts certain Knit Meshes into knitting machine code.by Jared B. Counts.M. Eng
Impact of deprivation and comorbidity on outcomes in emergency general surgery : an epidemiological study
No full text© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.Peer reviewe
Changes in Achilles tendon stiffness and energy cost following a prolonged run in trained distance runners
No full textDuring prolonged running, the magnitude of Achilles tendon (AT) length change may increase, resulting in increased tendon strain energy return with each step. AT elongation might also affect the magnitude of triceps surae (TS) muscle shortening and shortening velocity, requiring greater activation and increased muscle energy cost. Therefore, we aimed to quantify the tendon strain energy return and muscle energy cost necessary to allow energy storage to occur prior to and following prolonged running. 14 trained male (n = 10) and female (n = 4) distance runners (24 +/- 4 years, 1.72 +/- 0.09 m, 61 +/- 10 kg, (V) over barO(2)max 64.6 +/- 5.8 ml.kg(-1).min(-1)) ran 90 minutes (RUN) at approximately 85% of lactate threshold speed (sLT). Prior to and following RUN, AT stiffness and running energy cost (E-run) at 85% sLT were determined. AT energy return was calculated from AT stiffness, measured with dynamometry and ultrasound and estimated TS force during stance. TS energy cost was estimated on the basis of AT force and assumed crossbridge mechanics and energetics. Following RUN, AT stiffness was reduced from 328 +/- 172 N.mm(-1) to 299 +/- 148 N.mm(-1) (p = 0.022). E-run increased from 4.56 +/- 0.32 J.kg(-1).m-1 to 4.62 +/- 0.32 J.kg(-1).m-1 (p = 0.049). Estimated AT energy return was not different following RUN (p = 0.99). Estimated TS muscle energy cost increased significantly by 11.8 +/- 12.3 J.stride(-1), (p = 0.0034), accounting for much of the post-RUN increase in E-run (8.6 +/- 14.5 J.stride(-1), r(2) = 0.31). These results demonstrate that a prolonged, submaximal run can reduce AT stiffness and increase E-run in trained runners, and that the elevated TS energy cost contributes substantially to the elevated E-run.articl
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