AuxAg1-x alloy seeds: A way to control growth, morphology and defect formation in Ge nanowires

Germanium (Ge) nanowires are of current research interest for high speed nanoelectronic devices due to the lower band gap and high carrier mobility compatible with high K-dielectrics and larger excitonic Bohr radius ensuing a more pronounced quantum confinement effect [1-6]. A general way for the growth of Ge nanowires is to use liquid or a solid growth promoters in a bottom-up approach which allow control of the aspect ratio, diameter, and structure of 1D crystals via external parameters, such as precursor feedstock, temperature, operating pressure, precursor flow rate etc [3, 7-11]. The Solid-phase seeding is preferred for more control processing of the nanomaterials and potential suppression of the unintentional incorporation of high dopant concentrations in semiconductor nanowires and unrequired compositional tailing of the seed-nanowire interface [2, 5, 9, 12]. There are therefore distinct features of the solid phase seeding mechanism that potentially offer opportunities for the controlled processing of nanomaterials with new physical properties. A superior control over the growth kinetics of nanowires could be achieved by controlling the inherent growth constraints instead of external parameters which always account for instrumental inaccuracy. The high dopant concentrations in semiconductor nanowires can result from unintentional incorporation of atoms from the metal seed material, as described for the Al catalyzed VLS growth of Si nanowires [13] which can in turn be depressed by solid-phase seeding. In addition, the creation of very sharp interfaces between group IV semiconductor segments has been achieved by solid seeds [14], whereas the traditionally used liquid Au particles often leads to compositional tailing of the interface [15] . Korgel et al. also described the superior size retention of metal seeds in a SFSS nanowire growth process, when compared to a SFLS process using Au colloids [12]. Here in this work we have used silver and alloy seed particle with different compositions to manipulate the growth of nanowires in sub-eutectic regime. The solid seeding approach also gives an opportunity to influence the crystallinity of the nanowires independent of the substrate. Taking advantage of the readily formation of stacking faults in metal nanoparticles, lamellar twins in nanowires could be formed.

Dentofacial parameters associated with the unilateral palatally impacted canine

Aims To investigate the relationship between unilateral PIC and specific dentofacial parameters. Materials and methods A sample of 216 subjects, with 108 subjects in the retrospective and prospective samples respectively. Dental parameters: The following dental parameters were assessed: Inter-canine and intermolar width; palatal depth and palatal area; anterior Bolton tooth-size discrepancy (TSD); maxillary arch shape and ratio and maxillary central and lateral incisor shape and ratio. Facial parameters: Three-dimensional (3D) images were taken for subjects in the prospective sample only, and were used to assess the following facial parameters: Face shape; face ratio and 3D distances and angles. Results Dental parameters: Inter-canine width was significantly smaller in the test group compared to the control group in the retrospective (p= 0.0002) and prospective (p= 0.0018) samples respectively. Anterior Bolton TSD was significantly higher in the prospective test group compared to controls (p= 0.0070). Arch ratio was significantly smaller in the test group than the control group for the retrospective sample (p= 0.0029), whereas no significant difference was recorded in the prospective sample (p= 0.1017). Arch shape distribution was significantly different in the retrospective sample (p= 0.009). Tooth shape distribution was significantly different for the maxillary right central incisor in the retrospective sample (p= 0.030). Tooth ratio showed no significant difference for both samples. Facial parameters: Basal width was significantly smaller in the test compared to the control group (p= 0.0001). No significant difference was found in all other 3D distances and angles measured. Conclusion Inter-canine width was significantly smaller in unilateral PIC subjects compared to controls. Anterior Bolton TSD was significantly higher in prospective unilateral PIC compared to controls. Maxillary arch ratio was significantly smaller in retrospective subjects. Square/tapered tooth shape was significantly more common in the retrospective group. Basal width was significantly smaller in subjects with unilateral PIC than controls.

Modelling and predictive control techniques for building heating systems

Model predictive control (MPC) has often been referred to in literature as a potential method for more efficient control of building heating systems. Though a significant performance improvement can be achieved with an MPC strategy, the complexity introduced to the commissioning of the system is often prohibitive. Models are required which can capture the thermodynamic properties of the building with sufficient accuracy for meaningful predictions to be made. Furthermore, a large number of tuning weights may need to be determined to achieve a desired performance. For MPC to become a practicable alternative, these issues must be addressed. Acknowledging the impact of the external environment as well as the interaction of occupants on the thermal behaviour of the building, in this work, techniques have been developed for deriving building models from data in which large, unmeasured disturbances are present. A spatio-temporal filtering process was introduced to determine estimates of the disturbances from measured data, which were then incorporated with metaheuristic search techniques to derive high-order simulation models, capable of replicating the thermal dynamics of a building. While a high-order simulation model allowed for control strategies to be analysed and compared, low-order models were required for use within the MPC strategy itself. The disturbance estimation techniques were adapted for use with system-identification methods to derive such models. MPC formulations were then derived to enable a more straightforward commissioning process and implemented in a validated simulation platform. A prioritised-objective strategy was developed which allowed for the tuning parameters typically associated with an MPC cost function to be omitted from the formulation by separation of the conflicting requirements of comfort satisfaction and energy reduction within a lexicographic framework. The improved ability of the formulation to be set-up and reconfigured in faulted conditions was shown.