307,515 research outputs found
Uhlmann phase of coherent states and the Uhlmann-Berry correspondence
No full textWe first compare the geometric frameworks behind the Uhlmann and Berry phases
in a fiber-bundle language and then evaluate the Uhlmann phases of bosonic and
fermionic coherent states. The Uhlmann phases of both coherent states are shown
to carry geometric information and decrease smoothly with temperature.
Importantly, the Uhlmann phases approach the corresponding Berry phases as
temperature decreases. Together with previous examples in the literature, we
propose a correspondence between the Uhlmann and Berry phases in the
zero-temperature limit as a general property except some special cases and
present a conditional proof of the correspondence.Comment: 23 pages, no figur
Caracterização dos solos de experimentos com biossolubilizadores e avaliação das formas e dos teores de fósforo.
No full textRESUMO – A caracterização dos solos é fundamental na compreensão dos processos de aquisição do fósforo (P) no sistema solo/planta e para entender os processos de biodisponibilidade de nutrientes e para se recomendar o uso de bioinsumos. A produção agrícola em fronteiras agrícolas encontra muitos desafios, incluindo a colocação em produção de áreas com solos ainda pouco conhecidos e sem avaliações agronômicas consolidadas, como muitos dos Plintossolos do Tocantins e sul do Pará. Este trabalho visou a caracterização taxonômica, química e mineralógica de solos em Minas Gerais, Tocantins e Mato Grosso do Sul, e alguns perfis adicionais de Plintossolos do Pará. Foi realizada a descrição morfológica e a classificação dos solos, além da coleta de amostras de solo para análises laboratoriais de rotina e para análise mineralógica. Todos os solos apresentam baixo teor de P disponível pelos extratores usados, exceto os das áreas sob cultivo agrícola. Há uma grande variação entre os perfis da capacidade de retenção de P. A mineralogia mostra o grau elevado de intemperismo dos solos, indicando o potencial elevado de adsorção de fósforo, o que também é indicado pela condutividade hidráulica. Os teores totais de fósforo apresentam grande variação entre as amostras analisadas, sem correlação com os valores disponíveis pelos extratores usados. Em alguns dos solos estudados, há um grande estoque de fósforo em formas indisponíveis com potencial para ser biodisponibilizado por biossolubilizadores. ABSTRACT - Soil characterization is essential for understanding the processes of phosphorus (P) acquisition in the soil/plant system and for understanding the processes of nutrient bioavailability and for recommending the use of bioinputs. Agricultural production in agricultural frontiers faces many challenges, including the implementation of areas with soils that are still poorly known and without consolidated agronomic evaluations, such as many of the Plinthosols in the State of Tocantins and southern of the State of Pará. This study aimed to characterize the taxonomic, chemical and mineralogical characteristics of soils in the States of Minas Gerais, Tocantins and Mato Grosso do Sul, and some additional profiles of Plinthosols in Pará. Morphological description and classification of soils were performed, in addition to collecting soil samples for routine laboratory analysis and mineralogical analysis. All soils presented low levels of available P through the extractors used, except for those in areas under agricultural cultivation. There is a large variation between the profiles of P retention capacity. The mineralogy shows the high degree of weathering of the soils, indicating the high potential for phosphorus adsorption, which is also indicated by the hydraulic conductivity. The total phosphorus contents show a large variation between the samples analyzed, without correlation with the values available by the extractors. In some of the soils studied, there is a large stock of phosphorus in unavailable forms with the potential to be made bioavailable by biosolubilizers
Unitary Complexity and the Uhlmann Transformation Problem
No full textState transformation problems such as compressing quantum information or
breaking quantum commitments are fundamental quantum tasks. However, their
computational difficulty cannot easily be characterized using traditional
complexity theory, which focuses on tasks with classical inputs and outputs.
To study the complexity of such state transformation tasks, we introduce a
framework for unitary synthesis problems, including notions of reductions and
unitary complexity classes. We use this framework to study the complexity of
transforming one entangled state into another via local operations. We
formalize this as the Uhlmann Transformation Problem, an algorithmic version of
Uhlmann's theorem. Then, we prove structural results relating the complexity of
the Uhlmann Transformation Problem, polynomial space quantum computation, and
zero knowledge protocols.
The Uhlmann Transformation Problem allows us to characterize the complexity
of a variety of tasks in quantum information processing, including decoding
noisy quantum channels, breaking falsifiable quantum cryptographic assumptions,
implementing optimal prover strategies in quantum interactive proofs, and
decoding the Hawking radiation of black holes. Our framework for unitary
complexity thus provides new avenues for studying the computational complexity
of many natural quantum information processing tasks.Comment: 126 pages, comments welcome. updated some references in v
New species, reports, observations and taxonomical changes of southern African rust fungi (Uredinales)
No full textThis work presents research on the diversity of the southern African rust mycobiota (Uredinales). It describes new species, lists new reports and adds new information on several rust fungi. Puccinia cornurediata, Puccinia dioscoreae-mundtii, Puccinia horti-kirstenboschi, Puccinia othonnoides, Puccinia rapipes, Puccinia subindumentana, Uredo otholobii and Uromyces lotononidicola are described as new; Puccinia verwoerdiana is assigned to Puccinia lycii as a synonym, and Uredo lotononi to U. lotononidicola. Comprehensive accounts and keys are presented for Puccinia species on Lycium (Solanaceae), Helichrysum and Othonna (Asteraceae). Puccinia butleri and Uromyces bidenticola are new reports for South Africa, and Puccinia spinulosa is new for Namibia. So far, the latter species has only been known from Madagascar, and P. butleri from the Indian subcontinent. Taxonomical novelties are P. cornurediata R. Berndt; P. dioscoreae-mundtii R. Berndt, A.R. Wood & E. Uhlmann; P. horti-kirstenboschi R. Berndt & E. Uhlmann; P. othonnoides R. Berndt, A.R. Wood & E. Uhlmann; P. rapipes R. Berndt & E. Uhlmann; P. subindumentana R. Berndt; U. otholobii R. Berndt, A.R. Wood & E. Uhlmann and U. lotononidicola R. Bernd
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Uhlmann quench and geometric dynamic quantum phase transition of mixed states
No full textDynamic quantum phase transitions (DQPT) following quantum quenches exhibit
singular behavior of the overlap between the initial and evolved states. Here
we present a formalism to incorporate a geometric phase into quench dynamics of
mixed quantum states, a process named the Uhlmann quench, based on the Uhlmann
parallel transport. To overcome the incompatibility between the Uhlmann
parallel-transport condition and Hamiltonian dynamics, we formulate the
evolution of purification of the density matrix in a form which not only
respects the dynamics according to the density matrix but also follows the
Uhlmann parallel-transport condition to generate a geometric phase after a
quantum quench. For cyclic processes exemplified by a spin-1/2 system,
geometric DQPTs (GDQPTs) can emerge with both singular behavior in the dynamic
analogue of the free energy and jumps of the geometric phase. Moreover, the
Uhlmann phase reflecting the holonomy is generated at the end of each cycle.
The Uhlmann quench thus paves the way for investigating the interplay between
quantum dynamics and geometric processes in mixed states.Comment: 10 pages, 1 figur
Thermal Uhlmann phase in a locally driven two-spin system
No full textWe study the geometric Uhlmann phase of mixed states at finite temperature in
a system of two coupled spin- particles driven by a magnetic field
applied to one of the spins. In the parameter space of temperature and
coupling, we show the emergence of two topological Uhlmann phase transitions
when the magnetic field evolves around the equator, where a winding number can
characterize each temperature range. For small couplings, the width of the
temperature gap of the non-trivial phase is roughly the critical temperature
of one-dimensional fermion systems with two-band Hamiltonians. The first
phase transition in the low-temperature regime and small values of the coupling
corresponds to the peak of the \textit{Schottky anomaly} of the heat capacity,
typical of a two-level system in solid-state physics involving the ground and
first excited states. The second phase transition occurs at temperatures very
close to the second maximum of the heat capacity associated with a multilevel
system. We also derive analytical expressions for the thermal Uhlmann phase for
both subsystems, showing that they exhibit phase transitions. In the driven
subsystem, for minimal , a topological phase transition phase appears at
again. However, for larger values of , the transitions occur at lower
temperature values, and they disappear when the coupling reaches a critical
value . The latter is not the case for the undriven subsystem, where at
low temperatures, a single phase transition occurs at . Nevertheless, as
the temperature rises, we demonstrate the emergence of two phase transitions
defining a coupling gap, where the phase is non-trivial and vanishes as the
temperature reaches a critical value.Comment: 11 pages, 13 figure
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
On numerics and inverse problems
No full textThesis (Ph.D.)--University of Washington, 2015In this thesis, two projects in inverse problems are described. The first concerns a simple mathematical model of synthetic aperture radar with undirected beam, modeled as a 2D circular Radon transform with centers restricted to a plane curve \gamma. From the work of Stefanov and Uhlmann (2013), it is known that this operator is microlocally non-injective locally, but microlocally injective globally if \gamma is closed. The problem for non-closed \gamma is examined; it is shown that the Radon transform R_\gamma is microlocally non-injective to leading order if a certain geometric condition is satisfied. Known examples where this condition holds are given. Numerical simulations demonstrate R_\gamma's microlocal non-injectivity for a single curve, and for a four-curve setup satisfying the geometric condition. The second project involves the implementation of an algorithm by de Hoop, Uhlmann, Vasy, and Wendt (2013), with refinements, for computing generic Fourier integral operators (FIOs) associated with canonical graphs, possibly involving caustics. The algorithm can be divided into two parts: a local component that approximately evaluates an FIO A: C^\infty_0(X)\to \mathcal D'(Y) expressed in the oscillatory integral form Af(y)=\int e^{i\phi(y,\xi)} a(y,\xi)\,\hat f(\xi)\,d\xi, modulo an error operator of order 1/2 less than the order of A, and a global component that expresses an arbitrary FIO associated with a canonical graph as a finite sum of these local oscillatory integrals composed with appropriate coordinate changes. A numerical implementation of their algorithm is demonstrated and successfully applied to a variety of FIOs associated with canonical graphs. This algorithm is designed to be easy-to-use for future researchers and the code is freely available from the author
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