675 research outputs found
Field induced ordering in highly frustrated antiferromagnets
We predict that an external field can induce a spin order in highly
frustrated classical Heisenberg magnets. We find analytically stabilization of
collinear states by thermal fluctuations at a one-third of the saturation field
for kagome and garnet lattices and at a half of the saturation field for
pyrochlore and frustrated square lattices. This effect is studied numerically
for the frustrated square-lattice antiferromagnet by Monte Carlo simulations
for classical spins and by exact diagonalization for . The field induced
collinear states have a spin gap and produce magnetization plateaus.Comment: 4 pages, new analytical proof the order by disorder by thermal
fluctuations is adde
Locating bugs without looking back
Bug localisation is a core program comprehension task in software maintenance: given the observation of a bug, e.g. via a bug report, where is it located in the source code? Information retrieval (IR) approaches see the bug report as the query, and the source code files as the documents to be retrieved, ranked by relevance. Such approaches have the advantage of not requiring expensive static or dynamic analysis of the code. However, current state-of-the-art IR approaches rely on project history, in particular previously fixed bugs or previous versions of the source code. We present a novel approach that directly scores each current file against the given report, thus not requiring past code and reports. The scoring method is based on heuristics identified through manual inspection of a small sample of bug reports. We compare our approach to eight others, using their own five metrics on their own six open source projects. Out of 30 performance indicators, we improve 27 and equal 2. Over the projects analysed, on average we find one or more affected files in the top 10 ranked files for 76% of the bug reports. These results show the applicability of our approach to software projects without history
Orientational Defects in Ice Ih: An Interpretation of Electrical Conductivity Measurements
We present a first-principles study of the structure and energetics of
Bjerrum defects in ice Ih and compare the results to experimental electrical
conductivity data. While the DFT result for the activation energy is in good
agreement with experiment, we find that its two components have quite different
values. Aside from providing new insight into the fundamental parameters of the
microscopic electrical theory of ice, our results suggest the activity of traps
in doped ice in the temperature regime typically assumed to be controlled by
the free migration of L defects.Comment: 4 pages, 4 Figures, 1 Tabl
Photon Shot Noise Dephasing in the Strong-Dispersive Limit of Circuit QED
We study the photon shot noise dephasing of a superconducting transmon qubit
in the strong-dispersive limit, due to the coupling of the qubit to its readout
cavity. As each random arrival or departure of a photon is expected to
completely dephase the qubit, we can control the rate at which the qubit
experiences dephasing events by varying \textit{in situ} the cavity mode
population and decay rate. This allows us to verify a pure dephasing mechanism
that matches theoretical predictions, and in fact explains the increased
dephasing seen in recent transmon experiments as a function of cryostat
temperature. We investigate photon dynamics in this limit and observe large
increases in coherence times as the cavity is decoupled from the environment.
Our experiments suggest that the intrinsic coherence of small Josephson
junctions, when corrected with a single Hahn echo, is greater than several
hundred microseconds.Comment: 5 pages, 4 figures; includes Supporting Online Material of 6 pages
with 5 figure
Transition to Long Range Magnetic Order in the Highly Frustrated Insulating Pyrochlore Antiferromagnet Gd_2Ti_2O_7
Experimental evidence from measurements of the a.c. and d.c. susceptibility,
and heat capacity data show that the pyrochlore structure oxide, Gd_2Ti_2O_7,
exhibits short range order that starts developing at 30K, as well as long range
magnetic order at K. The Curie-Weiss temperature, =
-9.6K, is largely due to exchange interactions. Deviations from the Curie-Weiss
law occur below 10K while magnetic heat capacity contributions are found
at temperatures above 20K. A sharp maximum in the heat capacity at K
signals a transition to a long range ordered state, with the magnetic specific
accounting for only 50% of the magnetic entropy. The heat capacity above
the phase transition can be modeled by assuming that a distribution of random
fields acts on the ground state for Gd. There is no
frequency dependence to the a.c. susceptibility in either the short range or
long range ordered regimes, hence suggesting the absence of any spin-glassy
behavior. Mean field theoretical calculations show that no long range ordered
ground state exists for the conditions of nearest-neighbor antiferromagnetic
exchange and long range dipolar couplings. At the mean-field level, long range
order at various commensurate or incommensurate wave vectors is found only upon
inclusion of exchange interactions beyond nearest-neighbor exchange and dipolar
coupling. The properties of Gd$_2Ti_2O_7 are compared with other geometrically
frustrated antiferromagnets such as the Gd_3Ga_5O_{12} gadolinium gallium
garnet, RE_2Ti_2O_7 pyrochlores where RE = Tb, Ho and Tm, and Heisenberg-type
pyrochlore such as Y_2Mo_2O_7, Tb_2Mo_2O_7, and spinels such as ZnFe_2O_4Comment: Letter, 6 POSTSCRIPT figures included. (NOTE: Figure 5 is not
included --) To appear in Physical Review B. Contact:
[email protected]
ГІГІЄНІЧНА ОЦІНКА НАСЛІДКІВ ХЛОРУВАННЯ ВОДИ ПОВЕРХНЕВИХ ВОДОЙМ УКРАЇНСЬКОГО ПРИДУНАВ’Я
У роботі представлено результати гігієнічної оцінки наслідків хлорування води поверхневих водойм Українського Придунав’я. Встановлено, що хлорування води озер Кагул, Ялпуг, Катлабух супроводжується достовірним (р<0,05) ростом утворення високих рівнів хлороформу залежно від дози введеного хлору, які в 2 (при хлоруванні води озера Кагул дозою хлору 1 мг/дм3) – 20 разів (при хлоруванні води озера Катлабух дозою хлору 7 мг/дм3) перевищують чинний норматив цієї сполуки для питної води. Це створює додатковий ризик канцерогенної захворюванності населення. Висловлено думку, що хлороформ та інші тригалометани (ТГМ) є тільки складовою токсичного та віддалених впливів на стан здоров’я споживачів хлорованої води поверхневих водойм. Обґрунтовано необхідність досліджень хлорвмісних сполук та продуктів трансформації забруднювачів у процесі хлорування та доцільність дослідження і впровадження альтернативних хлоруванню засобів знезараження води, наприклад діоксиду хлору
Chaotic Phenomenon in Nonlinear Gyrotropic Medium
Nonlinear gyrotropic medium is a medium, whose natural optical activity
depends on the intensity of the incident light wave. The Kuhn's model is used
to study nonlinear gyrotropic medium with great success. The Kuhn's model
presents itself a model of nonlinear coupled oscillators. This article is
devoted to the study of the Kuhn's nonlinear model. In the first paragraph of
the paper we study classical dynamics in case of weak as well as strong
nonlinearity. In case of week nonlinearity we have obtained the analytical
solutions, which are in good agreement with the numerical solutions. In case of
strong nonlinearity we have determined the values of those parameters for which
chaos is formed in the system under study. The second paragraph of the paper
refers to the question of the Kuhn's model integrability. It is shown, that at
the certain values of the interaction potential this model is exactly
integrable and under certain conditions it is reduced to so-called universal
Hamiltonian. The third paragraph of the paper is devoted to quantum-mechanical
consideration. It shows the possibility of stochastic absorption of external
field energy by nonlinear gyrotropic medium. The last forth paragraph of the
paper is devoted to generalization of the Kuhn's model for infinite chain of
interacting oscillators
Talking quiescence: a rigorous theory that supports parallel composition, action hiding and determinisation
The notion of quiescence - the absence of outputs - is vital in both
behavioural modelling and testing theory. Although the need for quiescence was
already recognised in the 90s, it has only been treated as a second-class
citizen thus far. This paper moves quiescence into the foreground and
introduces the notion of quiescent transition systems (QTSs): an extension of
regular input-output transition systems (IOTSs) in which quiescence is
represented explicitly, via quiescent transitions. Four carefully crafted rules
on the use of quiescent transitions ensure that our QTSs naturally capture
quiescent behaviour.
We present the building blocks for a comprehensive theory on QTSs supporting
parallel composition, action hiding and determinisation. In particular, we
prove that these operations preserve all the aforementioned rules.
Additionally, we provide a way to transform existing IOTSs into QTSs, allowing
even IOTSs as input that already contain some quiescent transitions. As an
important application, we show how our QTS framework simplifies the fundamental
model-based testing theory formalised around ioco.Comment: In Proceedings MBT 2012, arXiv:1202.582
Spin ice in a field: quasi-phases and pseudo-transitions
Thermodynamics of the short-range model of spin ice magnets in a field is
considered in the Bethe - Peierls approximation. The results obtained for
[111], [100] and [011] fields agrees reasonably well with the existing
Monte-Carlo simulations and some experiments. In this approximation all
extremely sharp field-induced anomalies are described by the analytical
functions of temperature and applied field. In spite of the absence of true
phase transitions the analysis of the entropy and specific heat reliefs over
H-T plane allows to discern the "pseudo-phases" with specific character of spin
fluctuations and define the lines of more or less sharp "pseudo-transitions"
between them.Comment: 18 pages, 16 figure
Field induced transitions in a kagome antiferromagnet
The thermal order by disorder effect in magnetic field is studied for a
classical Heisenberg antiferromagnet on the kagome lattice. Using analytical
arguments we predict a unique H-T phase diagram for this strongly frustrated
magnet: states with a coplanar and a uniaxial triatic order parameters
respectively at low and high magnetic fields and an incompressible collinear
spin-liquid state at a one-third of the saturation field. We also present the
Monte Carlo data which confirm existence of these phases.Comment: 4 pages, 2 figures, accepted versio
- …