Quantitative LEED I-V and ab initio study of the Si(111)-3x2-Sm surface structure and the missing half order spots in the 3x1 diffraction pattern

We have used Low Energy Electron Diffraction (LEED) I-V analysis and ab initio calculations to quantitatively determine the honeycomb chain model structure for the Si(111)-3x2-Sm surface. This structure and a similar 3x1 recontruction have been observed for many Alkali-Earth and Rare-Earth metals on the Si(111) surface. Our ab initio calculations show that there are two almost degenerate sites for the Sm atom in the unit cell and the LEED I-V analysis reveals that an admixture of the two in a ratio that slightly favours the site with the lower energy is the best match to experiment. We show that the I-V curves are insensitive to the presence of the Sm atom and that this results in a very low intensity for the half order spots which might explain the appearance of a 3x1 LEED pattern produced by all of the structures with a 3x2 unit cell.Comment: 10 pages, 13 figures. Preliminary work presented at the the APS March meeting, Baltimore MD, 2006. To be published in Phys. Rev. B. April/May 200

Structurally Embedded Electrical Systems Using Ultrasonic Consolidation (UC)

Current research has demonstrated the use of Ultrasonic Consolidation (UC) to embed several USB-based sensors into aluminum, and is working toward embedding suites of sensors, heaters and other devices, connected via USB hubs, which can be monitored and controlled using an embedded USB capable processor. Additionally, the research has shown that electronics can be embedded at room temperature, but with some inter-layer delamination between the ultrasonically bonded aluminum layers. Embedding sensors and electronics at 300o F to overcome the delamination issues resulted in optimal bonding, and the sensors used thus far have functioned normally. Future investigation will explore other UC parameter combinations to ascertain the quality of embedding at lower temperatures.Mechanical Engineerin

STM and ab initio study of holmium nanowires on a Ge(111) Surface

A nanorod structure has been observed on the Ho/Ge(111) surface using scanning tunneling microscopy (STM). The rods do not require patterning of the surface or defects such as step edges in order to grow as is the case for nanorods on Si(111). At low holmium coverage the nanorods exist as isolated nanostructures while at high coverage they form a periodic 5x1 structure. We propose a structural model for the 5x1 unit cell and show using an ab initio calculation that the STM profile of our model structure compares favorably to that obtained experimentally for both filled and empty states sampling. The calculated local density of states shows that the nanorod is metallic in character.Comment: 4 pages, 12 figures (inc. subfigures). Presented at the the APS March meeting, Baltimore MD, 200

Towards a Framework for Alignment Between Automotive Safety and Security Standards

Modern automotive systems increasingly rely on software and network connectivity for new functions and features. Security of the software and communications of the on-board system of systems becomes a critical concern for the safety of new generation vehicles. Besides methods and tools, safety and security of automotive systems requires frameworks of standards for holistic process and assurance. As a part of our ongoing work, this paper investigates the possibility of a combined safety and security approach to standards in the automotive domain. We examine existing approaches in the railway and avionics domain with similar challenges and identify speci c requirements for the automotive domain. We evaluate ISO 15408 as a potential candidate for a combined safety and security approach for complementing automotive safety standard ISO 26262, and discuss their points of alignment

Energy efficient vacuum glazed window: A system design and investigations on hermetic sealing materials

Predictions by Fang et al (2010) indicate that triple vacuum glazing can theoretically achieve a centre of pane thermal transmittance of less than 0.26 W/(m2.K). To date two materials indium and solder glass have been used for sealing the edges the glass sheets in a vacuum glazing. Indium is a low temperature sealing material (157C) but is very expensive. Solder glass is a high temperature sealing material (around 450 C). One of the main hindrance to the manufacture of vacuum glazing at the industrial level is the cost. In this poster presentation, a vacuum glazing system for production at a laboratory scale using a modified evacuation pump-out sealing technique is presented. A number of samples have been fabricated using existing and new sealing materials that achieve a vacuum pressure less than 0.001Pa in the cavity of the vacuum glazing samples. An experimental performance verification of samples using new cost effective sealing materials will be executed in a hot box calorimeter to measure thermal transmittance performance of the samples. Issues associated with degradation of the vacuum pressure inside the cavity can be addressed by introducing non-evaporable getters

Heat load and solar gain prediction for solid wall dwellings retrofitted with triple vacuum glazing for selected window to wall area ratios

In much of the developed world there is a large stock of solid wall dwellings that require intervention to improve their energy performance. Heat loss through the windows of solid wall buildings is one of the factors contributing to high energy consumption for space heating resulting in excessive carbon emissions which lead to climate change. In this paper the heat load and solar gain are analysed for a room in a solid wall dwelling with single, double air filled, triple air filled, double vacuum and triple vacuum glazings at 5.49%, 12.36%, 13.19%, 20.6%, 24.72% and 32.96% window to wall area ratios (WWR’s). Simulated results are presented and the influence on energy required for space heating and solar energy gain in winter months (Dec, Jan and Feb) are analysed. The costs for space heating energy are calculated and show that replacing single glazed windows with triple vacuum glazed windows in the simulated room of a solid wall dwelling could save £36.07 annually. Assuming a dwelling consists of 6 simulated rooms, considerable energy and cost savings could be realised. It was also shown that for low heat loss glazings it is possible to significantly increase the window to wall area ratios with little increase in room heat load

A motif-based approach to network epidemics

Networks have become an indispensable tool in modelling infectious diseases, with the structure of epidemiologically relevant contacts known to affect both the dynamics of the infection process and the efficacy of intervention strategies. One of the key reasons for this is the presence of clustering in contact networks, which is typically analysed in terms of prevalence of triangles in the network. We present a more general approach, based on the prevalence of different four-motifs, in the context of ODE approximations to network dynamics. This is shown to outperform existing models for a range of small world networks

Predicting the Solar Energy and Space-heating Energy Performance for Solid-wall Detached House Retrofitted with the Composite Edge-sealed Triple Vacuum Glazing

Existing UK solid-wall houses, which have both heritage values and historic fabric, are being improved but yet they tend to have preventable heat loss through windows. Triple Vacuum Glazing is regarded as evolutionary step in minimising the space-heating loss. This paper takes a comparative analysis approach to envisage space-heating supply required for achieving thermal comfort temperatures and attainable solar energy gains to households with the retrofit of the thermal transmittance (U-value) of a new composite edge-sealed triple vacuum glazing i.e. 0.33 Wm-2K-1. 3D dynamic thermal models (timely regimes of heating, occupancy, ventilation and internal heat gains) of an externally-insulated solid-wall detached house with a range of existing glazing types along with triple vacuum glazing with frame areas are modelled. The predictions of varying window-to-wall ratios on space-heating energy and solar energy gains for winter months are analysed. The notable winter and annual space-heating energy savings of 14.58% (EUR 49.2) and 15.31% (EUR 105.4), respectively, were obtained with a solid-wall detached house retrofitted with triple vacuum glazed windows compared to single glazed windows. The heat loss calculations show a prominent reduction from 12.92% to 2.69% when replacing single glazed windows to triple vacuum glazed windows

An investigation on edge sealing materials for the fabrication of vacuum glazing

This study aims at experimental durability investigation of low-temperature edge sealing material for the fabrication of vacuum glazing. A new technique offers a number of advantages in terms of cost for direct glass to metal sealing over conventional methods such as indium based vacuum glazing. The present study shows the results of three samples that were fabricated with different techniques and sizes. Sample A-170mmx170mm achieved a vacuum pressure of less than 0.001Pa. Sample B-400mmx400mm achieved a vacuum pressure of down to 0.1Pa. Sample C-300mmx300mm achieved a vacuum pressure of 0.088Pa. The edge seal bond was proven to be rigid; the small leakage around the edge can be avoided by improving the seal material uniformity around the periphery. A crack at one of the sides of the glass occurred due to the intense tensile stress resulting from the hot plate surface temperature of 120°C

Design and fabrication of vacuum glazing units using a new low temperature hermetic glass edge sealing method

This poster aims at presenting experimental investigations for the fabrication of vacuum glazing using a new low temperature (less than 200C) based hermetic edge sealing method, as shown in Fig. 1. To date two materials indium and solder glass have been used for sealing the edges of the glass sheets in a vacuum glazing. Indium is a low temperature sealing material, melts at 157C, but is very expensive. Solder glass is a high temperature sealing material, melts at around 450C, but has limitation of using low-e coatings and a tempered glass. One of the main hindrances to the manufacture of vacuum glazing at the industrial level is the cost. In this poster presentation, a vacuum glazing system for production at a laboratory scale using a modified evacuation pump-out sealing technique is presented. The vacuum pressure measurements are performed using a combined transducer consists of Micro Pirani and miniaturised hot cathode ionisation gauge. The vacuum pressure of less than 0.046Pa in the cavity of the vacuum glazing samples was recorded. An experimental performance verification of samples can be executed in a hot box calorimeter to measure thermal transmittance performance of the samples