75 research outputs found
Development of a traceability route for areal surface texture measurements
No full textModern manufacturing industry is beginning to benefit from the ability to control the three dimensional, or areal, structure of a surface. To underpin areal surface manufacturing, a traceable measurement infrastructure is necessary. In this thesis a practical realisation of areal surface traceability is presented, which includes the development of: a primary in-strument, methodologies for using the primary instrument to calibrate material measure-ment standards used as standard transfer artefacts, and the process of transferring this traceability to industrial users of stylus and optical instruments.
The design of the primary instrument and its complex measurement uncertainty model are described, including detailed analysis of the input parameters of the uncertainty model and their effect on the co-ordinate measurements of the instrument.
The development of the process of transferring the areal traceability to industrial users lead to a set of metrological characteristics applicable to all areal surface topography measuring instruments. The set of metrological characteristics, now included into international stand-ards, comprise of: measurement noise, flatness deviation, amplification, linearity and squareness, and resolution. Despite the differences in operation of the various types of in-strument, the idea behind this set of metrological characteristics is based on the fact that these instruments produce three dimensional data sets of points, which is a new approach in the field. Metrological characteristics are quantities that can be measured directly, gener-ally using calibrated material measures. The development of standard methodologies for calibrating the metrological characteristics, and the explicit relationship between the metro-logical characteristics and the measurement uncertainty associated with the co-ordinate measurements provided by the instrument is presented. Many of the techniques described in this thesis are now being discussed for inclusion into international standards
Fabrication and functional evaluation of nature-inspired anti-bacterial surfaces
No full textGiusca, Claudiu - Associate Supervisor
Kumar, Vinod - Associate SupervisorThe critical need to develop novel and efficient anti-bacterial strategies,
particularly for biomedical implants, serves as a significant motivation for this
research. The rise in antibiotic resistance continues to pose a threat to
healthcare, making it increasingly important to explore alternative approaches to
combat implant-associated surgical site infections (SSIs). These infections arise
from bacterial attachment and biofilm formation on the surface of implants and
medical devices, leading to costly treatments and high recurrence rates. The
present research was aimed at investigating nature-inspired anti-bacterial
surfaces through a rigorous fabrication and testing campaign.
The study investigated various nanofabrication techniques, such as femtosecond
laser ablation, deep reactive ion etching, focused ion beam lithography and
scanning probe lithography, for creating nature-inspired sub-micron features on
stainless steel and silicon surfaces. The biological response of bacteria (S.
aureus) and osteoblast-like cells (MG-63) was evaluated on these surfaces to
test antibacterial as well as osseointegration response of the surfaces. S. aureus
was chosen due to its high relevance to SSIs and its prevalence in infection and
MG-63 cells served as a model for examining the osteoblast behaviour in
laboratory studies.
The thesis established a novel scale-dependent relationship between surface
topography and biological functionality, characterised by the dominating surface
wavelength and fractal dimension. The anti-biofouling mechanism was influenced
by surface topography, characterised through the fractal dimension, and it was
consistently achieved and deemed more suitable for future applications due to
the high anti-bacterial efficiency achieved compared to the mechano-bactericidal
mechanism. High aspect ratio features (0.056-0.280 µm wavelength, 0.295-
0.765 µm height, 0.045-0.046 µm diameter) did not induce mechano-bactericidal
effects on S. aureus NCTC7791, indicating further research is needed. Moreover,
the thesis demonstrated a predominant attachment of S. aureus and MG-63 cells
on the crystalline silicon surfaces on the (111) orientation.
ii
For feature sizes below 1 µm, the fractal dimension positively correlated with the
anti-bacterial effect and MG-63 cell spreading. For sizes significantly larger than
bacterial size (> 2 µm), no correlation was found with the anti-bacterial effect, but
surface complexity positively correlated with MG-63 cell spreading. For feature
sizes comparable to MG-63 cell size (10-40 µm), cell spreading was inhibited.
Femtosecond laser ablation emerged as a promising technique for commercial
applications, while scanning probe lithography proved to be a cost-effective,
flexible tool for prototyping and research-scale investigations.
In conclusion, the development and evaluation of nature-inspired anti-bacterial
surfaces have revealed valuable insights into the scale-dependent relationship
between surface topography and biological functionality. The findings from this
research have the potential to improve the performance and safety of implantable
medical devices by reducing the risk of implant-associated SSIs, ultimately
benefiting patients and healthcare providers.PhD in Manufacturin
Measurement Uncertainty Associated With Profilometry Of Tooth Wear In Vitro.
No full textMeasurement Uncertainty Associated With Profilometry of Tooth Wear In VitroAustin RS 1, Giusca C 2, Leach R 2, Festy F 3, Dunne S 1, Moazzez R 4, Bartlett DW 5.1 Department of Primary Dental Care, King's College London Dental Institute, London Bridge, SE1 9RT 2 Higher Research Scientist, National Physical Laboratory, Hampton Rd, Teddington, Middlesex, UK, TW11 0LW 2 Principal Research Scientist, Mass & Dimensional Group, Engineering Measurement Division, National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW 3 Department of Biomaterials Science, King's College London Dental Institute, London Bridge, SE1 9RT 1 Department of Primary Dental Care, King’s College London Dental Institute, King’s College Hospital Denmark Hill, London. SE5 9RW 4 Department of Conservative Dentistry, King’s College London Dental Institute, London Bridge, SE1 9RT 5 Department of Fixed and Removable Prosthodontics, King’s College London Dental Institute, London Bridge, SE1 9RT.AbstractObjectives: To identify and quantify all possible sources of measurement uncertainty associated with a tooth wear measurement system. To carry out an analysis of uncertainty in accordance with international guidelines. To analyse the relative merits of tooth wear outcome parameters. Methods: An analysis of uncertainty associated with the use of a white light confocal profilometer (XYRIS 4000 WL, TaiCaan Technologies Ltd., Southampton, UK) in combination with custom designed software (ImageJ v1.42q, Rasband, W. S., U. S. National Institutes of Health, Bethesda, Maryland, USA) for measuring tooth wear in vitro, was carried out following the principles outlined in the ISO Guide to the Expression of Uncertainty in Measurement. Uncertainty budgets were compiled by summating the variances of each potential source of uncertainty and the effect of the measurement of tooth wear was considered. The relationship between step height and volume loss of enamel after erosion; erosion-abrasion and erosion-attrition was then examined.Results: The main contribution to the uncertainty budget was from a flatness deviation (max 0.49 µm), whereas the contributions from noise, non-linearity, sample shrinkage during dehydration and software errors were negligible. Despite the flatness error, the overall combined uncertainty was < 6 %, even when measuring a simulated depth of wear of 0.3 µm. Investigation of the use of step height and volume loss outcome parameters suggested that for erosion and erosion-abrasion the preferred outcome measure should be step height loss and for erosion-attrition the preferred outcome measure should be volume loss.Conclusion: The uncertainty analysis quantitatively expressed of the comprehensive effect of the likely degree of uncertainty introduced during tooth wear measurement. This allows users to gauge how ‘fit for purpose’ a measurement system is in order that the results of tooth wear research can be readily understood and properly interpreted.<br/
Influence of Structural Defects on the Electronic Properties of Carbon Nanotubes Examined by Scanning Tunnelling Microscopy
No full textInfluence of Structural Defects on the Electronic Properties of Carbon Nanotubes Examined by Scanning Tunnelling Microscopy
No full textStrain-encoded cardiac magnetic resonance imaging: a new approach for fast estimation of left ventricular function
No full textAbstract Background Recently introduced fast strain-encoded (SENC) cardiac magnetic resonance (CMR) imaging (fast-SENC) provides real-time acquisition of myocardial performance in a single heartbeat. We aimed to test the ability and accuracy of real-time strain-encoded CMR imaging to estimate left ventricular volumes, ejection fraction and mass. Methods Thirty-five subjects (12 healthy volunteers and 23 patients with known or suspected coronary artery disease) were investigated. All study participants were imaged at 1.5 Tesla MRI scanner (Achieva, Philips) using an advanced CMR study protocol which included conventional cine and fast-SENC imaging. A newly developed real-time free-breathing SENC imaging technique based on the acquisition of two images with different frequency modulation was employed. Results All parameters were successfully derived from fast-SENC images with total study time of 105 s (a 15 s scan time and a 90 s post-processing time). There was no significant difference between fast-SENC and cine imaging in the estimation of LV volumes and EF, whereas fast-SENC underestimated LV end-diastolic mass by 7%. Conclusion The single heartbeat fast-SENC technique can be used as a good alternative to cine imaging for the precise calculation of LV volumes and ejection fraction while the technique significantly underestimates LV end-diastolic mass
INTER-LAYER INTERACTION IN DOUBLE-WALLED CARBON NANOTUBES EVIDENCED BY SCANNING TUNNELING MICROSCOPY AND SPECTROSCOPY
No full textScanning Tunneling Microscopy and Spectroscopy have been used in an attempt to elucidate the electronic structure of nanotube systems containing two constituent shells. Evidence for modified electronic structure due to the inter-layer interaction in double-walled carbon nanotubes is provided by the experimental tunneling spectra and the contribution of the inner tube to the local density of states of the "composite" double-walled system is identified in agreement with previous theoretical calculations. An explicit correlation between the chirality of the two constituent tubes, the inter-wall interaction and the overall electronic structure for double-walled carbon nanotubes, is demonstrated by our experiments, showing that the effect the inner tube has on the overall electronic structure of double-walled nanotubes cannot be neglected, and is key to the opto-electronic properties of the system. We postulate that previous analysis of the opto-electronic properties on multiple-walled carbon nanotubes based purely on the outer layer chirality of the tube needs significant modification based on new understanding brought forth with our analysis
Exploring graphene formation on the C-terminated face of SiC by structural, chemical and electrical methods
No full textThe properties of epitaxial graphene on the C-face of SiC are investigated using comprehensive structural, chemical and electrical analyses. By matching similar nanoscale features on the surface potential and Raman spectroscopy maps, individual domains have been assigned to graphene patches of 1-5 monolayers thick, as well as bare SiC substrate. Furthermore, these studies revealed that the growth proceeds in an island-like fashion, consistent with the Volmer-Weber growth mode, illustrating also the presence of nucleation sites for graphene domain growth. Raman spectroscopy data shows evidence of large area crystallites (up to 620 nm) and high quality graphene on the C-face of SiC. A comprehensive chemical analysis of the sample has been provided by X-ray photoelectron spectroscopy investigations, further supporting surface potential mapping observations on the thickness of graphene layers. It is shown that for the growth conditions used in this study, 5 monolayer thick graphene does not form a continuous layer, so such thickness is not sufficient to completely cover the substrate
CONSIDERATIONS REGARDING INVESTMENTS’ EFFICIENCY IN WINE INDUSTRY IN ROMANIA AND REPUBLIC OF MOLDOVA
No full textCurrently, we believe it will be very interesting and useful to do some investigations on wine industry. It is well known that both Romania and Republic of Moldova have a rich secular tradition in winemaking. Wine sector has a major impact on the national economy of Republic of Moldova. Wine industry in Romania is considered a field with possible future development. Therefore, important investments in this direction have been made until the economic crisis broke out. This paper aims to come out with some considerations regarding the evolution of investments made in wine industry in Romania and Republic of Moldova. In the same time, it focuses on problems they face and on recommendations to increase investments’ efficiency in the field.efficiency, investment, Republic of Moldova, Romania, wine industry.
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