955 research outputs found
Structural studies of novel bismuth containing piezoelectric ceramics
Get PDFPerovskite-based materials are in the focus of research not only because of their excellent
physical properties, but also because their relatively simple structure facilitates
the understanding of structure-property relationships, which is crucial for developing
novel materials with improved qualities. Recent research in the field of ferroelectric
and piezoelectric materials is concerned with the development of eco-friendly lead-free
materials. To achieve this goal, it is important to understand the fundamental correlation
between the ‘Structure’ and the ‘Property’. In this work, the primary focus has
been to elucidate the structural changes occurring as a function of doping in three different
systems: (1) BiScO3-PbTiO3 (BS-PT), a recently developed system which has
already attracted much interest because of its superior physical properties near the morphotropic
phase boundary (MPB); (2) BiScO3-BaTiO3 (BS-BT), which can be considered
as a lead-free analogue of the BS-PT family and lastly, (3) Na0.5Bi0.5TiO3-BaTiO3
(NBT-BT), which is a well-known lead-free material at the NBT-rich side of the phase
diagram.
Powder samples with a range of compositions for each system were prepared following
the solid-state synthesis route and were investigated utilizing both neutron and
x-ray powder diffraction and dielectric measurements. Detailed crystallographic information
was obtained by Rietveld refinement against the neutron powder diffraction
data. Structural phase transitions as a function of temperature were determined by nonambient
x-ray powder diffraction and compared with the physical properties of the ceramics
using high-temperature dielectric measurements. The significant outcomes are:
1. The best model to represent the so-called MPB of xBS-(1-x)PT system is found to
be a mixture of a tetragonal and a monoclinic phases from the powder diffraction
data. The structure beyond the MPB compositions is in better agreement for a
single monoclinic model with the space group Cm than the accepted space group
R3m. By contrast, single crystals with compositions around the MPB provide
evidence for a model consisting of two primitive monoclinic cells.
2. The lead-free BS-BT system exhibits an extended phase boundary between tetragonal
and pseudocubic phases, which can be modelled by a combination of tetragonal
and rhombohedral phases. The incorporation of BS into BT also results in
the suppression of the two low-temperature phase transitions of BT.
3. Samples with new compositions synthesized in the xNBT-(1-x)BT system demonstrate
a rare enhancement in the tetragonality of the unit cell and an increase in
the Curie temperature for compositions where x <= 0.40
Characterization of Mtg2p, a mitochondrial member of the Obg family of GTP -binding protein in <italic>Saccharomyces cerevisiae</italic>.
No full textThe Obg subfamily of GTPases is a novel family of GTP-binding proteins that are universally conserved and predicted to play a role in translation. Interestingly, all Obg proteins studied to date are involved in some aspect of ribosome function. In Chapters 2 and 3 of this study I demonstrate that the Saccharomyces cerevisiae GTPase, Mtg2p (Yhr168wp), is essential for mitochondrial ribosome function. Cells lacking MTG2 lose their mitochondrial DNA, giving rise to respiratory incompetent cells. In addition, cells expressing a temperature sensitive mgt2-1 allele are defective in mitochondrial protein synthesis and contain lower levels of mitochondrial ribosomal subunits. Significantly, elevated levels of Mtg2p partially suppress the thermosensitive loss of mitochondrial DNA in a 21S rRNA methyltransferase mutant, mrm2. Consistent with a role for Mtg2p in mitochondrial ribosome biogenesis, I show that Mtg2p is peripherally localized to the mitochondrial inner membrane and associates with the 54S large ribosomal subunit in a salt-dependent manner. The Obg subfamily of bacterial GTP-binding proteins are biochemically distinct from Ras-like proteins raising the possibility that they are not controlled by conventional guanine nucleotide exchange factors (GEFs) and/or guanine nucleotide activating proteins (GAPs). To test this hypothesis, in Chapter 4 we generated mutations in the Caulobacter crescentus obg gene, (cgtAC) which, in Ras-like proteins, would result in either activating or dominant negative phenotypes. I purified CgtACS173N (analogous to RasS17N) and CgtACP168V (analogous to RasG12V) protein and measured their guanine nucleotide affinities, exchange rates and half life of hydrolysis. In C. crescentus, a P168V mutant is not activating in vivo, although in vitro, the P168V protein showed a modest reduction in the affinity for GDP. Neither the S173N nor N280Y mutations resulted in a dominant negative phenotype. Further, the S173N was significantly impaired for GTP binding, consistent with a critical role of this residue in GTP binding. In general, conserved amino acids in the GTP-binding pocket were, however, important for function.PhDBiological SciencesCellular biologyMicrobiologyMolecular biologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125055/2/3186608.pd
Automating the construction of jet observables with machine learning
Get PDFISSN:1550-7998ISSN:0556-2821ISSN:1550-2368ISSN:0556-2821ISSN:1550-236
How much information is in a jet?
No full textAbstract Machine learning techniques are increasingly being applied toward data analyses at the Large Hadron Collider, especially with applications for discrimination of jets with different originating particles. Previous studies of the power of machine learning to jet physics have typically employed image recognition, natural language processing, or other algorithms that have been extensively developed in computer science. While these studies have demonstrated impressive discrimination power, often exceeding that of widely-used observables, they have been formulated in a non-constructive manner and it is not clear what additional information the machines are learning. In this paper, we study machine learning for jet physics constructively, expressing all of the information in a jet onto sets of observables that completely and minimally span N-body phase space. For concreteness, we study the application of machine learning for discrimination of boosted, hadronic decays of Z bosons from jets initiated by QCD processes. Our results demonstrate that the information in a jet that is useful for discrimination power of QCD jets from Z bosons is saturated by only considering observables that are sensitive to 4-body (8 dimensional) phase space
Novel jet observables from machine learning
No full textAbstract Previous studies have demonstrated the utility and applicability of machine learning techniques to jet physics. In this paper, we construct new observables for the discrimination of jets from different originating particles exclusively from information identified by the machine. The approach we propose is to first organize information in the jet by resolved phase space and determine the effective N -body phase space at which discrimination power saturates. This then allows for the construction of a discrimination observable from the N -body phase space coordinates. A general form of this observable can be expressed with numerous parameters that are chosen so that the observable maximizes the signal vs. background likelihood. Here, we illustrate this technique applied to discrimination of H → b b ¯ decays from massive g → b b ¯ splittings. We show that for a simple parametrization, we can construct an observable that has discrimination power comparable to, or better than, widely-used observables motivated from theory considerations. For the case of jets on which modified mass-drop tagger grooming is applied, the observable that the machine learns is essentially the angle of the dominant gluon emission off of the b b ¯ pair
Novel jet observables from machine learning
No full textAbstract
Previous studies have demonstrated the utility and applicability of machine learning techniques to jet physics. In this paper, we construct new observables for the discrimination of jets from different originating particles exclusively from information identified by the machine. The approach we propose is to first organize information in the jet by resolved phase space and determine the effective N -body phase space at which discrimination power saturates. This then allows for the construction of a discrimination observable from the N -body phase space coordinates. A general form of this observable can be expressed with numerous parameters that are chosen so that the observable maximizes the signal vs. background likelihood. Here, we illustrate this technique applied to discrimination of
H
→
b
b
¯
decays from massive
g
→
b
b
¯
splittings. We show that for a simple parametrization, we can construct an observable that has discrimination power comparable to, or better than, widely-used observables motivated from theory considerations. For the case of jets on which modified mass-drop tagger grooming is applied, the observable that the machine learns is essentially the angle of the dominant gluon emission off of the
b
b
¯
pair.</jats:p
Focusing the inverse method for linear logic
No full textexpressed in this document are those of the author, and do not necessarily reflect the policies o
The power of philosophy : thought and redemption
No full textThis book explores the possibility of philosophical praxis by weaving an ontological thread through four principal thinkers: Heidegger, Schelling, Goethe, and Heraclitus. It argues that a special kind of redemptive power awaits the structural understanding of thought that is beyond semantic formations such as concepts and ideational systems. The author claims that the “power” is negative in nature, trans-personal, and derived directly from the understanding of thought as a structural pulse. The book travels backwards in time, encountering successively Heidegger’s critique of calculative thinking, Schelling’s Mind/Nature relation, Goethe’s Delicate Empiricism, and the aphoristic wisdom of Heraclitus in search of a redemptive power that lies in the self-knowledge of thought. This power is ontological and not historical or developmental; it is the same at all times and all points of history. The author refers to the praxis as “philosophical bilingualism
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