397 research outputs found
On the development of a dynamic cutting force model with application to regenerative chatter in turning
Turning is one of the most widely used processes in machining and is characterized by a cutting tool moving along the axis of a rotating workpiece as it removes material. A detrimental phenomenon to productivity in turning operations is unstable cutting or chatter. This can reduce the life of tooling, dimensional accuracy, and the quality of a part's surface finish because of severe levels of vibration. Ideally, cutting conditions are chosen such that material removal is performed in a stable manner. However, it is sometimes unavoidable because of the geometry of the cutting tool or workpiece. This work seeks to develop a dynamic cutting force model that can be used to predict both the point of chatter instability as well as its amplitude growth over time. Previous chatter models fail to capture the physics of the process from a first-principles point of view because they are oversimplified and rely on various "cutting force coefficients" that must be tuned in order to get a desired correlation with experimental results. The proposed approach models the process in a geometrically rigorous fashion, also giving treatment to the strain, strain rate, and temperature effects encountered in machining. It derives the forces encountered during a turning operation from two sources: forces due to chip formation and forces due to plowing and flank interference. This study consists of a detailed derivation of two new cutting force models. One relies on careful approximations in order to obtain a closed-form solution; the other is more explicit and obtains a solution through numerical methods. The models are validated experimentally by comparing their prediction of the point of instability, the magnitude of vibration in the time and frequency domains, as well as the machined surface topography during chatter.Ph.D.Committee Co-Chair: Bement, Matt; Committee Co-Chair: Liang, Steven; Committee Member: Griffin, Paul; Committee Member: Mayor, Rhett; Committee Member: Melkote, Shreyes; Committee Member: Zhou, Che
Hong-Ou-Mandel interference between independent III-V on silicon waveguide integrated lasers
The versatility of silicon photonic integrated circuits has led to a
widespread usage of this platform for quantum information based applications,
including Quantum Key Distribution (QKD). However, the integration of simple
high repetition rate photon sources is yet to be achieved. The use of
weak-coherent pulses (WCPs) could represent a viable solution. For example,
Measurement Device Independent QKD (MDI-QKD) envisions the use of WCPs to
distill a secret key immune to detector side channel attacks at large
distances. Thus, the integration of III-V lasers on silicon waveguides is an
interesting prospect for quantum photonics. Here, we report the experimental
observation of Hong-Ou-Mandel interference with 46\pm 2% visibility between
WCPs generated by two independent III-V on silicon waveguide integrated lasers.
This quantum interference effect is at the heart of many applications,
including MDI-QKD. Our work represents a substantial first step towards an
implementation of MDI-QKD fully integrated in silicon, and could be beneficial
for other applications such as standard QKD and novel quantum communication
protocols.Comment: 5 pages, 3 figure
Traditional banana diversity in Oceania: an endangered heritage
This study aims to understand the genetic diversity of traditional Oceanian starchy bananas in order to propose an efficient conservation strategy for these endangered varieties. SSR and DArT molecular markers are used to characterize a large sample of Pacific accessions, from New Guinea to Tahiti and Hawaii. All Pacific starchy bananas are shown of New Guinea origin, by interspecific hybridization between Musa acuminata (AA genome), more precisely its local subspecies M. acuminata ssp. banksii, and M. balbisiana (BB genome) generating triploid AAB Pacific starchy bananas. These AAB genotypes do not form a subgroup sensu stricto and genetic markers differentiate two subgroups across the three morphotypes usually identified: Iholena versus Popoulu and Maoli. The Popoulu/Maoli accessions, even if morphologically diverse throughout the Pacific, cluster in the same genetic subgroup. However, the subgroup is not strictly monophyletic and several close, but different genotypes are linked to the dominant genotype. One of the related genotypes is specific to New Caledonia (NC), with morphotypes close to Maoli, but with some primitive characters. It is concluded that the diffusion of Pacific starchy AAB bananas results from a series of introductions of triploids originating in New Guinea area from several sexual recombination events implying different genotypes of M. acuminata ssp. banksii. This scheme of multiple waves from the New Guinea zone is consistent with the archaeological data for peopling of the Pacific. The present geographic distribution suggests that a greater diversity must have existed in the past. Its erosion finds parallels with the erosion of cultural traditions, inexorably declining in most of the Polynesian or Melanesian Islands. Symmetrically, diversity hot spots appear linked to the local persistence of traditions: Maoli in New Caledonian Kanak traditions or Iholena in a few Polynesian islands. These results will contribute to optimizing the conservation strategy for the ex-situ Pacific Banana Collection supported collectively by the Pacific countries
Transplastomic tobacco plants expressing a fatty acid desaturase gene exhibit altered fatty acid profiles and improved cold tolerance
The possibility of altering the unsaturation
level of fatty acids in plant lipids by genetic transformation
has implications for the stress tolerance of
higher plants as well as for their nutritional value and
industrial utilisation. While the integration and expression
of transgenes in the plastome has several potential
advantages over nuclear transformation, very few
attempts have been made to manipulate fatty acid
biosynthesis using plastid transformation. We produced
transplastomic tobacco plants that express a Delta9
desaturase gene from either the wild potato species
Solanum commersonii or the cyanobacterium Anacystis
nidulans, using PEG-mediated DNA uptake by protoplasts. Incorporation of chloroplast antibioticinsensitive
point mutations in the transforming DNA
was used to select transformants. The presence of the
transcript and the Delta9 desaturase protein in transplastomic
plants was confirmed by northern and western
blot analyses. In comparison with control plants,
transplastomic plants showed altered fatty acid profiles
and an increase in their unsaturation level both in leaves
and seeds. The two transgenes produced comparable
results. The results obtained demonstrate the feasibility
of using plastid transformation to engineer lipid
metabolic pathways in both vegetative and reproductive
tissues and suggest an increase of cold tolerance in
transplastomic plants showing altered leaf fatty acid
profiles. This is the first example of transplastomic
plants expressing an agronomically relevant gene
produced with the ‘‘binding-type’’ vectors, which do
not contain a heterologous marker gene. In fact, the
transplastomic plants expressing the S. commersonii
gene contain only plant-derived sequences, a clear
attraction from a public acceptability perspective
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