2,148 research outputs found
La Vie En Robot
School of Art and Design: Integrative Project ThesisArt and Design, School ofUniversity of MichiganUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/60494/1/IPThesis_Stolz.pd
Synthesis of allylic and homoallylic alcohols via organometallic ring-opening of vinylic epoxides and oxetanes
Additions of organometallic reagents to vinylic epoxides have become useful synthetic reactions for preparing allylic alcohols when the regio- and stereochemistry of the product can be controlled. Analogous organometallic processes employing vinylic oxetanes have never been reported in the literature. The results presented in this dissertation are the first observed examples of vinylic oxetanes reacting with organometallic reagents to afford homoallylic alcohols. The scope and limitations of these reactions will be discussed;The reactions of aryl- and vinylpalladium compounds with vinylic oxetanes provide a high yielding route to functionally substituted homoallylic alcohols. The homoallylic alcohols are isolated as mixtures of E- and Z-isomers. The E/Z ratio, however, is generally greater than 80:20. Catalytic amounts of palladium can be employed in the reaction if cupric chloride and oxygen are used to reoxidize the palladium;Vinylic oxetanes have also been observed to react with various nucleophiles in the presence of a catalytic amount of palladium(0) to produce the corresponding di- or trisubstituted homoallylic alcohols. These reactions proceed in high yield and are both regio- and stereoselective. It has also been shown that trisubstituted allylic alcohols can be produced in high yields, via palladium(0)-catalyzed nucleophilic ring-opening of substituted vinylic epoxides. Conditions have been found for this reaction where either the E- or Z-isomer of the trisubstituted allylic alcohol can be formed preferentially;The reactions of vinylic oxetanes with organolithium, -copper and -boron reagents have been explored. The corresponding homoallylic alcohols are isolated as mixtures of stereoisomers in good yields
A quantitative central limit theorem for linear statistics of random matrix eigenvalues
It is known that the fluctuations of suitable linear statistics of Haar
distributed elements of the compact classical groups satisfy a central limit
theorem. We show that if the corresponding test functions are sufficiently
smooth, a rate of convergence of order almost can be obtained using a
quantitative multivariate CLT for traces of powers that was recently proven
using Stein's method of exchangeable pairs.Comment: Title modified; main result stated under slightly weaker conditions;
accepted for publication in the Journal of Theoretical Probabilit
Numerical simulation of exciton dynamics in Cu2O at ultra low temperatures within a potential trap
We have studied theoretically the relaxation behaviour of excitons in cuprous
oxide (Cu2O) at ultra low temperatures when excitons are confined within a
potential trap by solving numerically the Boltzmann equation. As relaxation
processes, we have included in this paper deformation potential phonon
scattering, radiative and non-radiative decay and Auger decay. The relaxation
kinetics has been analysed for temperatures in the range between 0.3K and 5K.
Under the action of deformation potential phonon scattering only, we find for
temperatures above 0.5K that the excitons reach local equilibrium with the
lattice i.e. that the effective local temperature is coming down to bath
temperature, while below 0.5K a non-thermal energy distribution remains.
Interestingly, for all temperatures the global spatial distribution of excitons
does not reach the equilibrium distribution, but stays at a much higher
effective temperature. If we include further a finite lifetime of the excitons
and the two-particle Auger decay, we find that both the local and the global
effective temperature are not coming down to bath temperature. In the first
case we find a Bose-Einstein condensation (BEC) to occur for all temperatures
in the investigated range. Comparing our results with the thermal equilibrium
case, we find that BEC occurs for a significantly higher number of excitons in
the trap. This effect could be related to the higher global temperature, which
requires an increased number of excitons within the trap to observe the BEC. In
case of Auger decay, we do not find at any temperature a BEC due to the heating
of the exciton gas
Towards Environmental Sustainability in Marine Finfish Aquaculture
Aquaculture is one of the fastest growing food production sectors and has great potential for food security and livelihoods. However, it generates concerning consequences for the environment, including chemical and biological pollution, disease outbreaks, unsustainable feeds and competition for coastal space. Recent investigations are focusing on sustainable techniques (e.g., polyculture, offshore facilities) to improve the relationship between the industry, environment and society. This review provides an overview of the main factors of ecological concern within marine finfish aquaculture, their interactions with the environment, and highlights sustainable alternatives that are currently in use or development. Adequate environmental monitoring and location of farms, the reduction and exploitation of wastes and chemicals being used is crucial to ensure the growth and continuity of aquaculture production
Comparison of Simulator Wear Measured by Gravimetric vs Optical Surface Methods for Two Million Cycles
Understanding wear mechanisms are key for better implants
Critical to the success of the simulation
Small amount of metal wear can have catastrophic effects in the patient such as heavy metal poisoning or deterioration of the bone/implant interface leading to implant failure
Difficult to measure in heavy hard-on-hard implants (metal-on-metal or ceramic-on-ceramic)
May have only fractions of a milligram of wear on a 200 g component
At the limit of detection of even high-end balances when the component is 200 g and the change in weight is on the order of 0.000 1 grams
Here we compare the standard gravimetric wear estimate with
A non-contact 3D optical profiling method at each weighing stop
A coordinate measuring machine (CMM) at the beginning and end of the ru
Bacterial Respiration of Arsenate and Its Significance in the Environment
Although arsenic is a trace element in terms of its natural abundance, it nonetheless
has a common presence within the earth's crust. Because it is classified as a
group VB element in the periodic table, it shares many chemical and biochemical
properties in common with its neighbors phosphorus and nitrogen. Indeed, in the
case of this element's most oxidized (+5) oxidation state, arsenate [HAsO_4^(2-) or
As (V)], its toxicity is based on its action as an analog of phosphate. Hence,
arsenate ions uncouple the oxidative phosphorylation normally associated with
the enzyme glyceraldehyde 3-phosphate dehydrogenase, thereby preventing the
formation ofphosphoglyceroyl phosphate, a key high-energy intermediate in glycolysis.
To guard against this, a number of bacteria possess a detoxifying arsenate
reductase pathway (the arsC system) whereby cytoplasmic enzymes remove internal
pools of arsenate by achieving its reduction to arsenite [H_2AsO_3- or As
(III)]. However, because the arsenite product binds with internal sulfhydryl
groups that render it even more toxic than the original arsenate, efficient arsenite
efflux from the cell is also required and is achieved by an active ion ''pumping'' system (1). The details of this bacterial arsenic detoxification phenomenon have
been well established in the literature, and Chapter 10 in this volume provided
a thorough review. Here, we discuss bacterial respiration of arsenate and its significance
in the environment. As a biological phenomenon, respiratory growth
on arsenate is quite remarkable, given the toxicity of the element. Moreover, the
consequences of microbial arsenate respiration may, at times, have a significant
impact on environmental chemistry
On the Coulomb-dipole transition in mesoscopic classical and quantum electron-hole bilayers
We study the Coulomb-to-dipole transition which occurs when the separation
of an electron-hole bilayer system is varied with respect to the
characteristic in-layer distances. An analysis of the classical ground state
configurations for harmonically confined clusters with reveals that
the energetically most favorable state can differ from that of two-dimensional
pure dipole or Coulomb systems. Performing a normal mode analysis for the N=19
cluster it is found that the lowest mode frequencies exhibit drastic changes
when is varied. Furthermore, we present quantum-mechanical ground states
for N=6, 10 and 12 spin-polarized electrons and holes. We compute the
single-particle energies and orbitals in self-consistent Hartree-Fock
approximation over a broad range of layer separations and coupling strengths
between the limits of the ideal Fermi gas and the Wigner crystal
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