Assessment of wear resistance of tin and tin alloy coatings

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Tin alloy coatings have traditionally been used as corrosion resistant bamens due to their inert nature and comprehensive coverage, and have seldom been considered in physically demanding applications, such as wear resistant coatings owing to misconceptions associated with the soft nature of tin metal. The alloying of tin with copper has already been shown to significantly increase its mechanical properties, as demonstrated by the adoption of tin-copper alloys for use as bearing materials. Unfortunately, its cyanide plating technology makes tin-copper environmentally unsustainable, whilst the process requires constant regulation and monitoring, and there are disposal costs associated with the cyanide waste products. The tin-nickel alloy, however, can be produced with minimal supervision and its plating process uses less harmful precursors, making it an alternative consideration. The research documented in this thesis assesses this increase by quantifying the resistance of tin, tin-nickel and tin-copper coatings to removal from sliding wear. As tin is a soft material and behaves dissimilarly to conventional coatings in a sliding wear environment, traditional wear assessment techniques are not appropriate. A novel approach is therefore devised and implemented, and this involves the continually monitoring the effect of damage introduced to the surface of the tin and tin alloy coatings, from an abrading ceramic ball. Using an elemental detection tool, it is possible to analyse wear scars that exhibit progressively depleted coating material, by identifying the underlying substrate material as it becomes exposed. In this way, it is possible to quantify the improvements made to tin from alloying with nickel and copper. The large volume of data acquired from this research is presented in a matrix format to enable simultaneous depiction of multiple parameters, and to allow quick and easy interpretation. The tin-nickel coating is found to be comparable to tin-copper in terms of resistance to removal. Despite tin-copper being slightly superior over the range of test conditions used, tin-nickel as been shown to be an environmentally friendly and cost effective alternative coating alloy to tin-copper.Funding was obtained from ITRI Ltd

Challenges to the DGP Model from Horizon-Scale Growth and Geometry

We conduct a Markov Chain Monte Carlo study of the Dvali-Gabadadze-Porrati (DGP) self-accelerating braneworld scenario given the cosmic microwave background (CMB) anisotropy, supernovae and Hubble constant data by implementing an effective dark energy prescription for modified gravity into a standard Einstein-Boltzmann code. We find no way to alleviate the tension between distance measures and horizon scale growth in this model. Growth alterations due to perturbations propagating into the bulk appear as excess CMB anisotropy at the lowest multipoles. In a flat cosmology, the maximum likelihood DGP model is nominally a 5.3 sigma poorer fit than Lambda CDM. Curvature can reduce the tension between distance measures but only at the expense of exacerbating the problem with growth leading to a 4.8 sigma result that is dominated by the low multipole CMB temperature spectrum. While changing the initial conditions to reduce large scale power can flatten the temperature spectrum, this also suppresses the large angle polarization spectrum in violation of recent results from WMAP5. The failure of this model highlights the power of combining growth and distance measures in cosmology as a test of gravity on the largest scales.Comment: 12 pages, 7 figures, 4 tables, minor revisions reflect PRD published versio

Millimeter-wave diode-grid phase shifters

Monolithic diode grids have been fabricated on 2-cm square gallium-arsenide wafers with 1600 Schottky-barrier varactor diodes. Shorted diodes are detected with a liquid-crystal technique, and the bad diodes are removed with an ultrasonic probe. A small-aperture reflectometer that uses wavefront division interference was developed to measure the reflection coefficient of the grids. A Phase shift of 70° with a 7-dB loss was obtained at 93 GHz when the bias on the diode grid was changed from -3 V to 1 V. A simple transmission-line grid model, together with the measured low-frequency parameters for the diodes, was shown to predict the measured performance over the entire capacitive bias range of the diodes, as well as over the complete reactive tuning range provided by a reflector behind the grid, and over a wide range of frequencies form 33 GHz to 141 GHz. This shows that the transmission-line model and the measured low-frequency diode parameters can be used to design an electronic beam-steering array and to predict its performance. An electronic beam-steering array made of a pair of grids using state-of-the-art diodes with 5-Ω series resistances would have a loss of 1.4 dB at 90 GHz

Millimeter-Wave Diode-Grid Frequency Doubler

Monolithic diode grid were fabricated on 2-cm^2 gallium-arsenide wafers in a proof-of-principle test of a quasi-optical varactor millimeter-wave frequency multiplier array concept. An equivalent circuit model based on a transmission-line analysis of plane wave illumination was applied to predict the array performance. The doubler experiments were performed under far-field illumination conditions. A second-harmonic conversion efficiency of 9.5% and output powers of 0.5 W were achieved at 66 GHz when the diode grid was pumped with a pulsed source at 33 GHz. This grid had 760 Schottky-barrier varactor diodes. The average series resistance was 27 Ω, the minimum capacitance was 18 fF at a reverse breakdown voltage of -3 V. The measurements indicate that the diode grid is a feasible device for generating watt-level powers at millimeter frequencies and that substantial improvement is possible by improving the diode breakdown voltage

Z_2 Symmetry Prediction for the Leptonic Dirac CP Phase

Model-independent consequences of applying a generalized hidden horizontal Z_2 symmetry to the neutrino mass matrix are explored. The Dirac CP phase delta_D can be expressed in terms of the three mixing angles as 4 c_a s_a c_s s_s s_x cos delta_D = (s^2_s - c^2_s s^2_x) (c^2_a - s^2_a) where the s_i, c_i are sines and cosines of the atmospheric, solar, and reactor angles. This relation is independent of neutrino masses and whether neutrinos are Dirac- or Majorana-type. Given the present constraints on the angles, delta_D is constrained to be almost maximal, a result which can be explored in experiments such as NOvA and T2K. The Majorana CP phases do not receive any constraint and are thus model-dependent. Also a distribution of theta_x with a lower limit is obtained without specifying delta_D.Comment: 5 pages, 4 figures; Condensed version or PLB with references added; for more details see the previous versio

Outcomes of patients with Juvenile Polyposis-Hereditary Haemorrhagic Telangiectasia caused by pathogenic SMAD4 variants in a pan-Scotland cohort

Constitutional loss of SMAD4 function results in Juvenile Polyposis-Hereditary Haemorrhagic Telangiectasia Overlap Syndrome (JP-HHT). A retrospective multi-centre case-note review identified 28 patients with a pathogenic SMAD4 variant from 13 families across all Scottish Clinical Genetics Centres. This provided a complete clinical picture of the Scottish JP-HHT cohort. Colonic polyps were identified in 87% (23/28) and gastric polyps in 67% (12/18) of screened patients. Complication rates were high: 43% (10/23) of patients with polyps required a colectomy and 42% (5/12) required a gastrectomy. Colorectal cancer occurred in 25% (7/28) of patients, at a median age of 33 years. Pulmonary arteriovenous malformations were identified in 42% (8/19) of screened patients. 88% (23/26) and 81% (17/21) of patients exhibited JP and HHT features respectively, with 70% (14/20) demonstrating features of both conditions. We have shown that individuals with a pathogenic SMAD4 variant are all at high risk of both gastrointestinal neoplasia and HHT-related vascular complications, requiring a comprehensive screening programme.</p

Outcomes of patients with Juvenile Polyposis-Hereditary Haemorrhagic Telangiectasia caused by pathogenic SMAD4 variants in a pan-Scotland cohort

Constitutional loss of SMAD4 function results in Juvenile Polyposis-Hereditary Haemorrhagic Telangiectasia Overlap Syndrome (JP-HHT). A retrospective multi-centre case-note review identified 28 patients with a pathogenic SMAD4 variant from 13 families across all Scottish Clinical Genetics Centres. This provided a complete clinical picture of the Scottish JP-HHT cohort. Colonic polyps were identified in 87% (23/28) and gastric polyps in 67% (12/18) of screened patients. Complication rates were high: 43% (10/23) of patients with polyps required a colectomy and 42% (5/12) required a gastrectomy. Colorectal cancer occurred in 25% (7/28) of patients, at a median age of 33 years. Pulmonary arteriovenous malformations were identified in 42% (8/19) of screened patients. 88% (23/26) and 81% (17/21) of patients exhibited JP and HHT features respectively, with 70% (14/20) demonstrating features of both conditions. We have shown that individuals with a pathogenic SMAD4 variant are all at high risk of both gastrointestinal neoplasia and HHT-related vascular complications, requiring a comprehensive screening programme.</p

Challenging situations in partial nephrectomy

© 2016 IJS Publishing Group Ltd Although most partial nephrectomies are performed as primary procedures in the elective or semi-imperative setting on kidneys with relatively normal anatomy, this is not always the case. The indications for partial nephrectomy continue to expand and it is becoming particularly relevant in patients with single functioning kidneys, poor kidney function, anatomical anomalies and hereditary syndromes predisposing to multiple kidney cancers, such as Von Hippel-Lindau syndrome. These, along with previous abdominal su rgery, pose surgical challenges. In this article we offer advice as to how to tackle these unusual situations. An ability to master the whole range of indications will allow the modern upper renal tract surgeon to offer partial nephrectomy to a wider range of patients.Link_to_subscribed_fulltex