9,274 research outputs found
Supporting the active learning of collaborative database browsing techniques
We describe the implications of a study of database browsing behaviour for the development of a system to support more effective browsing. In particular we consider the importance of collaborative working, both in learning browsing skills and in coâoperating on a shared informationâretrieval task. From our study, we believe that an interface to support collaboration should promote the awareness of the activities of others, better visualization of the information data structures being browsed, and effective communication of the browsing process
Signatures of spin in the n=1/3 Fractional Quantum Hall Effect
The activation gap Delta of the fractional quantum Hall state at constant
filling n =1/3 is measured in wide range of perpendicular magnetic field B.
Despite the full spin polarization of the incompressible ground state, we
observe a sharp crossover between a low-field linear dependence of Delta on B
associated to spin texture excitations and a Coulomb-like behavior at large B.
From the global gap-reduction we get information about the mobility edges in
the fractional quantum Hall regime.Comment: 4 pages, 3 figure
Self-adjoint Momentum Operator for a Particle Confined in a Multi-Dimensional Cavity
Based on the recent construction of a self-adjoint momentum operator for a
particle confined in a one-dimensional interval, we extend the construction to
arbitrarily shaped regions in any number of dimensions. Different components of
the momentum vector do not commute with each other unless very special
conditions are met. As such, momentum measurements should be considered one
direction at a time. We also extend other results, such as the Ehrenfest
theorem and the interpretation of the Heisenberg uncertainty relation to higher
dimensions.Comment: 22 pages, 2 figure
A perspective on the role of anions in highly concentrated aqueous electrolytes
Highly concentrated aqueous electrolytes enable a wider electrochemical stability window and, thus, higher energy batteries compared to conventional dilute aqueous solutions. Multiple properties of the electrolyte, e.g., ionic interactions, solvation structure, ion transport, tendency to hydrolyze, and capability to form a solid electrolyte interphase, distinctly change when the salt concentration is increased and highly depend on the salt anion. This work aims at reviewing, discussing and rationalizing the role of the salt anion in these physical and chemical properties in order to provide perspective guidelines for future developments
Macroscopic fluctuations theory of aerogel dynamics
We consider the thermodynamic potential describing the macroscopic
fluctuation of the current and local energy of a general class of Hamiltonian
models including aerogels. We argue that this potential is neither analytic nor
strictly convex, a property that should be expected in general but missing from
models studied in the literature. This opens the possibility of describing in
terms of a thermodynamic potential non-equilibrium phase transitions in a
concrete physical context. This special behaviour of the thermodynamic
potential is caused by the fact that the energy current is carried by particles
which may have arbitrary low speed with sufficiently large probability.Comment: final versio
Interplanetary flow systems associated with cosmic ray modulation in 1977 - 1980
The hydromagnetic flow configurations associated with cosmic ray modulation in 1977 to 1980 were determined using solar wind plasma and magnetic field data from Voyagers 1 and 2 and Helios 1. The modulation was related to two types of large scale systems of flows: one containing a number of transients such as shocks, post shock flows and magnetic clouds; the other consisting primarily of a series of quasi-stationary flows following interaction regions containing a stream interface and often bounded by a forward reverse shock pair. Each of the three major episodes of cosmic ray modulation was characterized by the passage of the system of transient flows. Plateaus in the cosmic ray intensity time profile were associated with the passage of systems of corotating streams
Finite-size effects on the dynamic susceptibility of CoPhOMe single-chain molecular magnets in presence of a static magnetic field
The static and dynamic properties of the single-chain molecular magnet
[Co(hfac)NITPhOMe] are investigated in the framework of the Ising model
with Glauber dynamics, in order to take into account both the effect of an
applied magnetic field and a finite size of the chains. For static fields of
moderate intensity and short chain lengths, the approximation of a
mono-exponential decay of the magnetization fluctuations is found to be valid
at low temperatures; for strong fields and long chains, a multi-exponential
decay should rather be assumed. The effect of an oscillating magnetic field,
with intensity much smaller than that of the static one, is included in the
theory in order to obtain the dynamic susceptibility . We find
that, for an open chain with spins, can be written as a
weighted sum of frequency contributions, with a sum rule relating the
frequency weights to the static susceptibility of the chain. Very good
agreement is found between the theoretical dynamic susceptibility and the ac
susceptibility measured in moderate static fields ( kOe),
where the approximation of a single dominating frequency turns out to be valid.
For static fields in this range, new data for the relaxation time,
versus , of the magnetization of CoPhOMe at low temperature are
also well reproduced by theory, provided that finite-size effects are included.Comment: 16 pages, 9 figure
Bouncing wave packets, Ehrenfest theorem, and uncertainty relation based upon a new concept for the momentum of a particle in a box
For a particle in a box, the operator
is not self-adjoint and thus does not qualify as the physical momentum. As a result, in general the Ehrenfest theorem is violated. Based upon a recently developed new concept for a self-adjoint momentum operator, we reconsider the theorem and find that it is now indeed satisfied for all physically admissible boundary conditions. We illustrate these results for bouncing wave packets which first spread, then shrink, and return to their original form after a certain revival time. We derive a very simple form of the general HeisenbergâRobertsonâSchrödinger uncertainty relation and show that our construction also provides a physical interpretation for it
Attention Mechanism-Driven Sensor Placement Strategy for Structural Health Monitoring
Automated vibration-based structural health monitoring (SHM) strategies have been
recently proven to be promising in the presence of aging and material deterioration threatening the
safety of civil structures. Within such a framework, ensuring high-quality and informative data is
a critical aspect that is highly dependent on the deployment of the sensors in the network and on
their capability to provide damage-sensitive features to be exploited. This paper presents a novel
data-driven approach to the optimal sensor placement devised to identify sensor locations that
maximize the information effectiveness for SHM purposes. The optimization of the sensor network
is addressed by means of a deep neural network (DNN) equipped with an attention mechanism, a
state-of-the-art technique in natural language processing (NLP) that is useful in focusing on a limited
number of important components in the information stream. The trained attention mechanism
eventually allows for quantifying the relevance of each sensor in terms of the so-called attention
scores, thereby enabling to identify the most useful input channels to solve the relevant downstream
SHM task. With reference to the damage localization task, framed here as a classification problem
handling a set of predefined damage scenarios, the DNN is trained to locate damage on labeled data
that had been simulated to emulate the effects of damage under different operational conditions. The
capabilities of the proposed method are demonstrated by referring to an eight-story shear building,
characterized by damage states possibly located at any story and of unknown severity
Confined Charged Particles in C-periodic Volumes
Charged particles in an Abelian Coulomb phase are non-local infraparticles
that are surrounded by a cloud of soft photons which extends to infinity.
Gauss' law prevents the existence of charged particles in a periodic volume. In
a -periodic volume, which is periodic up to charge conjugation, on the other
hand, charged particles can exist. This includes vortices in the -d
XY-model, magnetic monopoles in -d gauge theory, as well as
protons and other charged particles in QCD coupled to QED. In four dimensions
non-Abelian charges are confined. Hence, in an infinite volume non-Abelian
infraparticles cost an infinite amount of energy. However, in a -periodic
volume non-Abelian infraparticles (whose energy increases linearly with the box
size) can indeed exist. Investigating these states holds the promise of
deepening our understanding of confinement.Comment: Proceedings for the 39th International Symposium on Lattice Field
Theory, LATTICE202
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