3,781 research outputs found
Influence of the Polarity of the Electric Field on Electrorheometry
Uniaxial extensional flow is a canonical flow typically used in rheological characterization to provide complementary information to that obtained by imposing simple shear flow. In spite of the importance of having a full rheological characterization of complex fluids, publications on the rheological characterization of mobile liquids under extensional flow have increased significantly only in the last 20 years. In the case of the rheological characterization of electrorheological fluids, the situation is even more dramatic, as the ERFs have been exclusively determined under simple shear flow, where an electrorheological cell is attached to the rotational rheometer generating an electric field perpendicular to the flow direction and that does not allow for inverting the polarity. The very recent work published by Sadek et al., who developed a new electrorheological cell to be used with the commercial Capillary Breakup Extensional Rheometer (CaBER), allows for the very first time performing electrorheometry under extensional flow. By means of the same experimental setup, this study investigates the influence of the polarity of the imposed electric field on the filament thinning process of a Newtonian and an electrorheological fluid. Results show that a polarity against the gravity results in filament thinning processes that live longer or reach a stable configuration at lower intensities of the applied electric field
Knot Groups of Torus Knots
For this project, an expository approach was taking insofar as examining knots groups goes, specifically for torus knots. As such, the first set of materials examined covered the concept of knot groups and the general tenets of knot theory itself. The rest of the time was spent gaining acquaintance with group theory, specifically relating to free groups, and the basics of abstract algebra. The last portion of work spent on the project was examining how all of these theories work together to define the knot groups of torus knots
Entropy, fidelity, and double orthogonality for resonance states in two-electron quantum dots
Resonance states of a two-electron quantum dot are studied using a
variational expansion with both real basis-set functions and complex scaling
methods. The two-electron entanglement (linear entropy) is calculated as a
function of the electron repulsion at both sides of the critical value, where
the ground (bound) state becomes a resonance (unbound) state. The linear
entropy and fidelity and double orthogonality functions are compared as methods
for the determination of the real part of the energy of a resonance. The
complex linear entropy of a resonance state is introduced using complex scaling
formalism
Quantum nonlocality in the presence of superselection rules and data hiding protocols
We consider a quantum system subject to superselection rules, for which
certain restrictions apply to the quantum operations that can be implemented.
It is shown how the notion of quantum-nonlocality has to be redefined in the
presence of superselection rules: there exist separable states that cannot be
prepared locally and exhibit some form of nonlocality. Moreover, the notion of
local distinguishability in the presence of classical communication has to be
altered. This can be used to perform quantum information tasks that are
otherwise impossible. In particular, this leads to the introduction of perfect
quantum data hiding protocols, for which quantum communication (eventually in
the form of a separable but nonlocal state) is needed to unlock the secret.Comment: 4 page
The H=xp model revisited and the Riemann zeros
Berry and Keating conjectured that the classical Hamiltonian H = xp is
related to the Riemann zeros. A regularization of this model yields
semiclassical energies that behave, in average, as the non trivial zeros of the
Riemann zeta function. However, the classical trajectories are not closed,
rendering the model incomplete. In this paper, we show that the Hamiltonian H =
x (p + l_p^2/p) contains closed periodic orbits, and that its spectrum
coincides with the average Riemann zeros. This result is generalized to
Dirichlet L-functions using different self-adjoint extensions of H. We discuss
the relation of our work to Polya's fake zeta function and suggest an
experimental realization in terms of the Landau model.Comment: 5 pages, 3 figure
Superconvergent Perturbation Method in Quantum Mechanics
An analogue of Kolmogorov's superconvergent perturbation theory in classical
mechanics is constructed for self adjoint operators. It is different from the
usual Rayleigh--Schr\"odinger perturbation theory and yields expansions for
eigenvalues and eigenvectors in terms of functions of the perturbation
parameter.Comment: 11 pages, LaTe
Scintillation light produced by low-energy beams of highly-charged ions
Measurements have been performed of scintillation light intensities emitted
from various inorganic scintillators irradiated with low-energy beams of
highly-charged ions from an electron beam ion source (EBIS) and an electron
cyclotron resonance ion source (ECRIS). Beams of xenon ions Xe with
various charge states between =2 and =18 have been used at energies
between 5 keV and 17.5 keV per charge generated by the ECRIS. The intensity of
the beam was typically varied between 1 and 100 nA. Beams of highly charged
residual gas ions have been produced by the EBIS at 4.5 keV per charge and with
low intensities down to 100 pA. The scintillator materials used are flat
screens of P46 YAG and P43 phosphor. In all cases, scintillation light emitted
from the screen surface was detected by a CCD camera. The scintillation light
intensity has been found to depend linearly on the kinetic ion energy per time
deposited into the scintillator, while up to =18 no significant contribution
from the ions' potential energy was found. We discuss the results on the
background of a possible use as beam diagnostics e.g. for the new HITRAP
facility at GSI, Germany.Comment: 6 pages, 8 figure
The narrative potential of the British Birth Cohort Studies
This paper draws attention to the narrative potential of longitudinal studies such as the British Birth Cohort Studies (BBCS), and explores the possibility of creating narrative case histories and conducting narrative analysis based on information available from the studies. The BBCS have historically adopted a quantitative research design and used structured interviews and questionnaires to collect data from large samples of individuals born in specific years. However, the longitudinal nature of these studies means that they follow the same sample of individuals from birth through childhood into adult life, and this leads to the creation of data that can be understood as a quantitative auto/biography
Quantum thermodynamics: thermodynamics at the nanoscale
A short introduction on quantum thermodynamics is given and three new topics
are discussed: 1) Maximal work extraction from a finite quantum system. The
thermodynamic prediction fails and a new, general result is derived, the
``ergotropy''. 2) In work extraction from two-temperature setups, the presence
of correlations can push the effective efficiency beyond the Carnot bound. 3)
In the presence of level crossing, non-slow changes may be more optimal than
slow ones.Comment: 5 pages. Talk given at Physics of Quantum Electronics (PQE2004),
Snowbird, by Th.M. Nieuwenhuize
- …