4,409 research outputs found
Refactoring Legacy JavaScript Code to Use Classes: The Good, The Bad and The Ugly
JavaScript systems are becoming increasingly complex and large. To tackle the
challenges involved in implementing these systems, the language is evolving to
include several constructions for programming- in-the-large. For example,
although the language is prototype-based, the latest JavaScript standard, named
ECMAScript 6 (ES6), provides native support for implementing classes. Even
though most modern web browsers support ES6, only a very few applications use
the class syntax. In this paper, we analyze the process of migrating structures
that emulate classes in legacy JavaScript code to adopt the new syntax for
classes introduced by ES6. We apply a set of migration rules on eight legacy
JavaScript systems. In our study, we document: (a) cases that are
straightforward to migrate (the good parts); (b) cases that require manual and
ad-hoc migration (the bad parts); and (c) cases that cannot be migrated due to
limitations and restrictions of ES6 (the ugly parts). Six out of eight systems
(75%) contain instances of bad and/or ugly cases. We also collect the
perceptions of JavaScript developers about migrating their code to use the new
syntax for classes.Comment: Paper accepted at 16th International Conference on Software Reuse
(ICSR), 2017; 16 page
Renormalization-group analysis of the one-dimensional extended Hubbard model with a single impurity
We analyze the one-dimensional extended Hubbard model with a single static
impurity by using a computational technique based on the functional
renormalization group. This extends previous work for spinless fermions to
spin-1/2 fermions. The underlying approximations are devised for weak
interactions and arbitrary impurity strengths, and have been checked by
comparing with density-matrix renormalization-group data. We present results
for the density of states, the density profile and the linear conductance.
Two-particle backscattering leads to striking effects, which are not captured
if the bulk system is approximated by its low-energy fixed point, the Luttinger
model. In particular, the expected decrease of spectral weight near the
impurity and of the conductance at low energy scales is often preceded by a
pronounced increase, and the asymptotic power laws are modified by logarithmic
corrections.Comment: 36 pages, 13 figures, revised version as publishe
Comment on "Spin relaxation in quantum Hall systems"
W. Apel and Yu.A. Bychkov have recently considered the spin relaxation in a
2D quantum Hall system for the filling factor close to unity [PRL v.82, 3324
(1999)]. The authors considered only one spin flip mechanism (direct
spin-phonon coupling) among several possible spin-orbit related ones and came
to the conclusion that the spin relaxation time due to this mechanism is quite
short: around s at B=10 T (for GaAs). This time is much shorter than
the typical time ( s) obtained earlier by D. Frenkel while considering
the spin relaxation of 2D electrons in a quantizing magnetic field without the
Coulomb interaction and for the same spin-phonon coupling. I show that the
authors' conclusion about the value of the spin-flip time is wrong and have
deduced the correct time which is by several orders of magnitude longer. I also
discuss the admixture mechanism of the spin-orbit interaction.Comment: 1 pag
Nuclear Spin Relaxation for Higher Spin
We study the relaxation of a spin I that is weakly coupled to a quantum
mechanical environment. Starting from the microscopic description, we derive a
system of coupled relaxation equations within the adiabatic approximation.
These are valid for arbitrary I and also for a general stationary
non--equilibrium state of the environment. In the case of equilibrium, the
stationary solution of the equations becomes the correct Boltzmannian
equilibrium distribution for given spin I. The relaxation towards the
stationary solution is characterized by a set of relaxation times, the longest
of which can be shorter, by a factor of up to 2I, than the relaxation time in
the corresponding Bloch equations calculated in the standard perturbative way.Comment: 4 pages, Latex, 2 figure
The muonic longitudinal shower profiles at production
In this paper the longitudinal profile of muon production along the shower
axis is studied. The characteristics of this distribution is investigated for
different primary masses, zenith angles, primary energies, and different high
energy hadronic models. It is found that the shape of this distribution
displays universal features similarly to what is known for the electromagnetic
profile. The relation between the muon production distribution and the
longitudinal electromagnetic evolution is also discussed
Quantum Hall Ferromagnets: Induced Topological term and electromagnetic interactions
The quantum Hall ground state in materials like GaAs is well known
to be ferromagnetic in nature. The exchange part of the Coulomb interaction
provides the necessary attractive force to align the electron spins
spontaneously. The gapless Goldstone modes are the angular deviations of the
magnetisation vector from its fixed ground state orientation. Furthermore, the
system is known to support electrically charged spin skyrmion configurations.
It has been claimed in the literature that these skyrmions are fermionic owing
to an induced topological Hopf term in the effective action governing the
Goldstone modes. However, objections have been raised against the method by
which this term has been obtained from the microscopics of the system. In this
article, we use the technique of the derivative expansion to derive, in an
unambiguous manner, the effective action of the angular degrees of freedom,
including the Hopf term. Furthermore, we have coupled perturbative
electromagnetic fields to the microscopic fermionic system in order to study
their effect on the spin excitations. We have obtained an elegant expression
for the electromagnetic coupling of the angular variables describing these spin
excitations.Comment: 23 pages, Plain TeX, no figure
Constructive factorization of LPDO in two variables
We study conditions under which a partial differential operator of arbitrary
order in two variables or ordinary linear differential operator admits a
factorization with a first-order factor on the left. The factorization process
consists of solving, recursively, systems of linear equations, subject to
certain differential compatibility conditions. In the generic case of partial
differential operators one does not have to solve a differential equation. In
special degenerate cases, such as ordinary differential, the problem is finally
reduced to the solution of some Riccati equation(s). The conditions of
factorization are given explicitly for second- and, and an outline is given for
the higher-order case.Comment: 16 pages, to be published in Journal "Theor. Math. Phys." (2005
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