5,505 research outputs found
The contact angle in inviscid fluid mechanics
We show that in general, the specification of a contact angle condition at
the contact line in inviscid fluid motions is incompatible with the classical
field equations and boundary conditions generally applicable to them. The
limited conditions under which such a specification is permissible are derived;
however, these include cases where the static meniscus is not flat. In view of
this situation, the status of the many `solutions' in the literature which
prescribe a contact angle in potential flows comes into question. We suggest
that these solutions which attempt to incorporate a phenomenological, but
incompatible, condition are in some, imprecise sense `weak-type solutions';
they satisfy or are likely to satisfy, at least in the limit, the governing
equations and boundary conditions everywhere except in the neighbourhood of the
contact line. We discuss the implications of the result for the analysis of
inviscid flows with free surfaces.Comment: 13 pages, no figures, no table
The motion of bubbles inside drops in containerless processing
A theoretical model of thermocapillary bubble motion inside a drop, located in a space laboratory, due to an arbitrary axisymmetric temperature distribution on the drop surface was constructed. Typical results for the stream function and temperature fields as well as the migration velocity of the bubble were obtained in the quasistatic limit. The motion of bubbles in a rotating body of liquid was studied experimentally, and an approximate theoretical model was developed. Comparison of the experimental observations of the bubble trajectories and centering times with theoretical predictions lends qualified support to the theory
Random sampling of an AC source: A tool to teach probabilistic observations
An undergraduate level experiment is described to demonstrate the role of
probabilistic observations in physics. A capacitor and a DC voltmeter are used
to randomly sample an AC voltage source. The resulting probability distribution
is analyzed to extract information about the AC source. Different
characteristic probability distributions arising from various AC waveforms are
calculated and experimentally measured. The reconstruction of the AC waveform
is demonstrated from the measured probability distribution under certain
restricted circumstances. The results are also compared with a simulated data
sample. We propose this as a pedagogical tool to teach probabilistic
measurements and their manipulations.Comment: Revtex4 file, 10 pages with 8 figure
Quality of Service in bandwidth adapted hybrid UMTS/WLAN interworking network
Integration of Universal Mobile Telecommunications System (UMTS) and Wireless Local Area Network (WLAN) result in ubiquitous connection for end users. In the integrated network, ensuring the quality of service to users and enhancing capacity of network are prominent issues. Bandwidth adaptation technique is one of the solutions to overcome these issues. Bandwidth adaptation based on per flow and per class schemes were proposed for loosely coupled interworking network. In this paper, hybrid coupled UMTS and WLAN interworking network is analyzed with bandwidth adaptation based on per flow and per class schemes and the performances have been compared. Simulation result shows that the proposed hybrid coupled interworking network with bandwidth adaptation based on per class scheme performs better with enhanced quality of service and network capacity
A stable Algebraic Spin Liquid in a Hubbard model
We show the existence of a stable Algebraic Spin Liquid (ASL) phase in a
Hubbard model defined on a honeycomb lattice with spin-dependent hopping that
breaks time-reversal symmetry. The effective spin model is the Kitaev model for
large on-site repulsion. The gaplessness of the emergent Majorana fermions is
protected by the time reversal (TR) invariance of this model. We prove that the
effective spin model is TR invariant in the entire Mott phase thus ensuring the
stability of the ASL. The model can be physically realized in cold atom systems
and we propose experimental signals of the ASL.Comment: Published in PR
Internal and external axial corner flows
The inviscid, internal, and external axial corner flows generated by two intersecting wedges traveling supersonically are obtained by use of a second-order shock-capturing, finite-difference approach. The governing equations are solved iteratively in conical coordinates to yield the complicated wave structure of the internal corner and the simple peripheral shock of the external corner. The numerical results for the internal flows compare favorably with existing experimental data
Parity Measurement is Sufficient for Phase Estimation at the Quantum Cramer-Rao Bound for Path-Symmetric States
In this letter, we show that for all the so-called path-symmetric states, the
measurement of parity of photon number at the output of an optical
interferometer achieves maximal phase sensitivity at the quantum Cramer-Rao
bound. Such optimal phase sensitivity with parity is attained at a suitable
bias phase, which can be determined a priori. Our scheme is applicable for
local phase estimation
Spin Bose-Metal phase in a spin-1/2 model with ring exchange on a two-leg triangular strip
Recent experiments on triangular lattice organic Mott insulators have found
evidence for a 2D spin liquid in proximity to the metal-insulator transition. A
Gutzwiller wavefunction study of the triangular lattice Heisenberg model with
appropriate four-spin ring exchanges has found that the projected spinon Fermi
sea state has a low variational energy. This wavefunction, together with a
slave particle gauge theory, suggests that such spin liquid possesses spin
correlations that are singular along surfaces in momentum space ("Bose
surfaces"). Signatures of this state, which we refer to as a "Spin Bose-Metal"
(SBM), are expected to be manifest in quasi-1D ladder systems: The discrete
transverse momenta cut through the 2D Bose surface leading to a distinct
pattern of 1D gapless modes. Here we search for a quasi-1D descendant of the
triangular lattice SBM state by exploring the Heisenberg plus ring model on a
two-leg strip (zigzag chain). Using DMRG, variational wavefunctions, and a
Bosonization analysis, we map out the full phase diagram. Without ring exchange
the model is equivalent to the J_1 - J_2 Heisenberg chain, and we find the
expected Bethe-chain and dimerized phases. Remarkably, moderate ring exchange
reveals a new gapless phase over a large swath of the phase diagram. Spin and
dimer correlations possess particular singular wavevectors and allow us to
identify this phase as the hoped for quasi-1D descendant SBM state. We derive a
low energy theory and find three gapless modes and one Luttinger parameter
controlling all power laws. Potential instabilities out of the zigzag SBM give
rise to other interesting phases such as a period-3 VBS or a period-4 Chirality
order, which we discover in the DMRG; we also find an interesting SBM state
with partial ferromagnetism.Comment: 30 pages, 23 figure
Physical phenomena in containerless glass processing
Experiments were conducted on bubble migration in rotating liquid bodies contained in a sphere. Experiments were initiated on the migration of a drop in a slightly less dense continuous phase contained in a rotating sphere. A refined apparatus for the study of thermocapillar flow in a glass melt was built, and data were acquired on surface velocities in the melt. Similar data also were obtained from an ambient temperature fluid model. The data were analyzed and correlated with the aid of theory. Data were obtained on flow velocities in a pendant drop heated from above. The motion in this system was driven principally by thermocapillarity. An apparatus was designed for the study of volatilization from a glass melt
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