title: Bipolar amplifier bias technique for robust IM3 null tracking independent of internal emitter resistance

authors: Balsom, Toby

abstract: Bipolar amplifiers can be biased to give a deep null in third order non-linearity, with the potential for high IP3 amplifier stages. This requires maintaining a precise voltage drop across a small resistive emitter degeneration resistance, whose value is related to kT/q. To make such a scheme practical, the bias must not only take into account the change in kT/q with temperature, but must compensate for variations in the degeneration resistance. In this paper we present a bias technique for IM3 null tracking that can take account of temperature and resistance tolerances, and is also insensitive to the value of the internal emitter resistance. Simulations using a 27 GHz BiCMOS technology indicate that the bias of an amplifier can be maintained over temperature, representative element tolerances, and mismatch such that the IP3 performance is maintained within ±9.5 dBV of the optimum null condition. The technique is applicable for a range of bipolar BiCMOS technologies and is attractive for amplifiers where high IP3 is required with moderate noise figure.

text: Bipolar amplifier bias technique for robust IM3 null tracking independent of internal emitter resistance Bipolar amplifiers can be biased to give a deep null in third order non-linearity, with the potential for high IP3 amplifier stages. This requires maintaining a precise voltage drop across a small resistive emitter degeneration resistance, whose value is related to kT/q. To make such a scheme practical, the bias must not only take into account the change in kT/q with temperature, but must compensate for variations in the degeneration resistance. In this paper we present a bias technique for IM3 null tracking that can take account of temperature and resistance tolerances, and is also insensitive to the value of the internal emitter resistance. Simulations using a 27 GHz BiCMOS technology indicate that the bias of an amplifier can be maintained over temperature, representative element tolerances, and mismatch such that the IP3 performance is maintained within ±9.5 dBV of the optimum null condition. The technique is applicable for a range of bipolar BiCMOS technologies and is attractive for amplifiers where high IP3 is required with moderate noise figure.

year: 2012

title: Microstructure and mechanical properties of aluminium based nanocomposites strengthened with alumina and silicon carbide

authors: Gazawi, Amro Abdul-Karim

abstract: Al-Al₂O₃ and Al-4wt%Cu-SiC metal matrix nanocomposites were studied because these materials have a potential for offering good ductility, high strength, and high electrical and/or thermal conductivity, which make them ideal for engineering applications such as aerospace and automobile components. In order to achieve these goals the reinforcement phase needs to be in a particulate form, and the size of the particles needs to be small.
Samples of aluminium based nanocomposites were produced with different volume fractions, ranging from 2.5-10 vol.% of alumina (Al₂O₃) and silicon carbide (SiC) nanoparticles. High energy mechanical milling (HEMM) with various milling times ranging from 6-12 hours was used to produce these samples. Optical microscopy, XRD, SEM, TEM and microindentation were used to characterize the milled powder and bulk samples. Bulk solid Al-(2.5-10) vol. % Al₂O₃ and Al-4wt%Cu-(2.5-10) vol. %SiC nanocomposites samples were produced using different powder consolidation techniques such as powder compact forging and powder compact extrusion.
The microstructure of the composite powder/balls/granules produced was studied in details to understand the morphology, macrostructure and microstructural evolution during the HEMM and with changing volume percent of the reinforcements in the matrix. The nano SiC and Al₂O₃ were imbedded into the aluminium matrix due to the high forces and strains affecting particle surfaces during milling and the very small size of the reinforcement relative to the size of the Al particles. The average microhardness was increased with increasing volume fraction of reinforcement within the matrix. HEMM was used to fabricate Ultra-Fine Grained (UFG) and nanostructured Al- (2.5-10) vol. %Al₂O₃ composites with a dispersion of nano alumina within the matrix and Al-4wt%Cu- (2.5-10) vol%SiC with two different sizes of SiC in the micro and nano ranges.
A UFG structure in the Al and Al-(2.5-10)vol.% Al₂O₃ nanocomposites can be synthesized by a combination of high energy mechanical milling and severe plastic deformation used to consolidate the powder compacts into nearly fully dense forged discs and extruded bars. No significant microscopic yielding was found in the Al-2.5 and 10 vol. %Al₂O₃ composites produced by powder compact forging. However, Al-5vol. % Al₂O₃ showed plastic yielding of 8%, and the best fracture strength of 343 MPa. No significant microscopic yielding was noticed for the Al- 10 vol. %Al₂O₃ composite produced by powder compact extrusion. Al-2.5vol. % Al₂O₃ showed plastic yielding of ~1% with the highest tensile strength of 364 MPa while Al-5vol. % Al₂O₃ showed plastic yielding of 8% with a yield strength of 318 MPa.
The average microhardness of the extruded bars for Al-4wt%Cu-(2.5-10)vol.% SiC increased from 104 HV to 205 HV with increasing the volume fraction of SiC nanoparticles from 2.5 to 10%. The ultimate tensile strength increased from 168 MPa to 400 MPa with increasing volume fraction of SiC nanoparticles from 2.5 to 5% while the ductility dropped from 6.8% to 1.2 %. The fracture strength of the Al-4wt%Cu-micro-SiC was increased from 225 MPa for Al-4wt%Cu-2.5vol. %SiC to 412 MPa for Al-4wt%Cu-10vol. % SiC. The Al-4wt%Cu-2.5vol. %SiC forged disc did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol. %SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

text: Microstructure and mechanical properties of aluminium based nanocomposites strengthened with alumina and silicon carbide Al-Al₂O₃ and Al-4wt%Cu-SiC metal matrix nanocomposites were studied because these materials have a potential for offering good ductility, high strength, and high electrical and/or thermal conductivity, which make them ideal for engineering applications such as aerospace and automobile components. In order to achieve these goals the reinforcement phase needs to be in a particulate form, and the size of the particles needs to be small.
Samples of aluminium based nanocomposites were produced with different volume fractions, ranging from 2.5-10 vol.% of alumina (Al₂O₃) and silicon carbide (SiC) nanoparticles. High energy mechanical milling (HEMM) with various milling times ranging from 6-12 hours was used to produce these samples. Optical microscopy, XRD, SEM, TEM and microindentation were used to characterize the milled powder and bulk samples. Bulk solid Al-(2.5-10) vol. % Al₂O₃ and Al-4wt%Cu-(2.5-10) vol. %SiC nanocomposites samples were produced using different powder consolidation techniques such as powder compact forging and powder compact extrusion.
The microstructure of the composite powder/balls/granules produced was studied in details to understand the morphology, macrostructure and microstructural evolution during the HEMM and with changing volume percent of the reinforcements in the matrix. The nano SiC and Al₂O₃ were imbedded into the aluminium matrix due to the high forces and strains affecting particle surfaces during milling and the very small size of the reinforcement relative to the size of the Al particles. The average microhardness was increased with increasing volume fraction of reinforcement within the matrix. HEMM was used to fabricate Ultra-Fine Grained (UFG) and nanostructured Al- (2.5-10) vol. %Al₂O₃ composites with a dispersion of nano alumina within the matrix and Al-4wt%Cu- (2.5-10) vol%SiC with two different sizes of SiC in the micro and nano ranges.
A UFG structure in the Al and Al-(2.5-10)vol.% Al₂O₃ nanocomposites can be synthesized by a combination of high energy mechanical milling and severe plastic deformation used to consolidate the powder compacts into nearly fully dense forged discs and extruded bars. No significant microscopic yielding was found in the Al-2.5 and 10 vol. %Al₂O₃ composites produced by powder compact forging. However, Al-5vol. % Al₂O₃ showed plastic yielding of 8%, and the best fracture strength of 343 MPa. No significant microscopic yielding was noticed for the Al- 10 vol. %Al₂O₃ composite produced by powder compact extrusion. Al-2.5vol. % Al₂O₃ showed plastic yielding of ~1% with the highest tensile strength of 364 MPa while Al-5vol. % Al₂O₃ showed plastic yielding of 8% with a yield strength of 318 MPa.
The average microhardness of the extruded bars for Al-4wt%Cu-(2.5-10)vol.% SiC increased from 104 HV to 205 HV with increasing the volume fraction of SiC nanoparticles from 2.5 to 10%. The ultimate tensile strength increased from 168 MPa to 400 MPa with increasing volume fraction of SiC nanoparticles from 2.5 to 5% while the ductility dropped from 6.8% to 1.2 %. The fracture strength of the Al-4wt%Cu-micro-SiC was increased from 225 MPa for Al-4wt%Cu-2.5vol. %SiC to 412 MPa for Al-4wt%Cu-10vol. % SiC. The Al-4wt%Cu-2.5vol. %SiC forged disc did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol. %SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

year: 2014

title: A core phyllosphere microbiome exists across distant populations of a tree species indigenous to New Zealand

authors: Noble, Anya S.

subjects: Science & Technology

abstract: The phyllosphere microbiome is increasingly recognised as an influential component of plant physiology, yet it remains unclear whether stable host-microbe associations generally exist in the phyllosphere. Leptospermum scoparium (mānuka) is a tea tree indigenous to New Zealand, and honey derived from mānuka is widely known to possess unique antimicrobial properties. However, the host physiological traits associated with these antimicrobial properties vary widely, and the specific cause of such variation has eluded scientists despite decades of research. Notably, the mānuka phyllosphere microbiome remains uncharacterised, and its potential role in mediating host physiology has not been considered. Working within the prevailing core microbiome conceptual framework, we hypothesise that the phyllosphere microbiome of mānuka exhibits specific host association patterns congruent with those of a microbial community under host selective pressure (null hypothesis: the mānuka phyllosphere microbiome is recruited stochastically from the surrounding environment). To examine our hypothesis, we characterised the phyllosphere and associated soil microbiomes of five distinct and geographically distant mānuka populations across the North Island of New Zealand. We identified a habitat-specific and relatively abundant core microbiome in the mānuka phyllosphere, which was persistent across all samples. In contrast, non-core phyllosphere microorganisms exhibited significant variation across individual host trees and populations that was strongly driven by environmental and spatial factors. Our results demonstrate the existence of a dominant and ubiquitous core microbiome in the phyllosphere of mānuka, supporting our hypothesis that phyllosphere microorganisms of mānuka exhibit specific host association and potentially mediate physiological traits of this nationally and culturally treasured indigenous plant. In addition, our results illustrate biogeographical patterns in mānuka phyllosphere microbiomes and offer insight into factors contributing to phyllosphere microbiome assembly.

text: A core phyllosphere microbiome exists across distant populations of a tree species indigenous to New Zealand The phyllosphere microbiome is increasingly recognised as an influential component of plant physiology, yet it remains unclear whether stable host-microbe associations generally exist in the phyllosphere. Leptospermum scoparium (mānuka) is a tea tree indigenous to New Zealand, and honey derived from mānuka is widely known to possess unique antimicrobial properties. However, the host physiological traits associated with these antimicrobial properties vary widely, and the specific cause of such variation has eluded scientists despite decades of research. Notably, the mānuka phyllosphere microbiome remains uncharacterised, and its potential role in mediating host physiology has not been considered. Working within the prevailing core microbiome conceptual framework, we hypothesise that the phyllosphere microbiome of mānuka exhibits specific host association patterns congruent with those of a microbial community under host selective pressure (null hypothesis: the mānuka phyllosphere microbiome is recruited stochastically from the surrounding environment). To examine our hypothesis, we characterised the phyllosphere and associated soil microbiomes of five distinct and geographically distant mānuka populations across the North Island of New Zealand. We identified a habitat-specific and relatively abundant core microbiome in the mānuka phyllosphere, which was persistent across all samples. In contrast, non-core phyllosphere microorganisms exhibited significant variation across individual host trees and populations that was strongly driven by environmental and spatial factors. Our results demonstrate the existence of a dominant and ubiquitous core microbiome in the phyllosphere of mānuka, supporting our hypothesis that phyllosphere microorganisms of mānuka exhibit specific host association and potentially mediate physiological traits of this nationally and culturally treasured indigenous plant. In addition, our results illustrate biogeographical patterns in mānuka phyllosphere microbiomes and offer insight into factors contributing to phyllosphere microbiome assembly.

year: 2020