2,416 research outputs found
The Frequency Dependence of Critical-velocity Behavior in Oscillatory Flow of Superfluid Helium-4 Through a 2-micrometer by 2-micrometer Aperture in a Thin Foil
The critical-velocity behavior of oscillatory superfluid Helium-4 flow
through a 2-micrometer by 2-micrometer aperture in a 0.1-micrometer-thick foil
has been studied from 0.36 K to 2.10 K at frequencies from less than 50 Hz up
to above 1880 Hz. The pressure remained less than 0.5 bar. In early runs during
which the frequency remained below 400 Hz, the critical velocity was a
nearly-linearly decreasing function of increasing temperature throughout the
region of temperature studied. In runs at the lowest frequencies, isolated 2 Pi
phase slips could be observed at the onset of dissipation. In runs with
frequencies higher than 400 Hz, downward curvature was observed in the decrease
of critical velocity with increasing temperature. In addition, above 500 Hz an
alteration in supercritical behavior was seen at the lower temperatures,
involving the appearance of large energy-loss events. These irregular events
typically lasted a few tens of half-cycles of oscillation and could involve
hundreds of times more energy loss than would have occurred in a single
complete 2 Pi phase slip at maximum flow. The temperatures at which this
altered behavior was observed rose with frequency, from ~ 0.6 K and below, at
500 Hz, to ~ 1.0 K and below, at 1880 Hz.Comment: 35 pages, 13 figures, prequel to cond-mat/050203
Experiments concerning the low-energy states of the O19 nucleus
Angular distributions have been measured for three groups of protons from the O18(d, p)O19 reaction, those leaving O19 in its states at 0, 0.096, and 1.47 Mev. Deuteron energies of 1.74 and 2.50 Mev in the laboratory system were used. The distributions of protons leaving O19 in its ground state and in its 1.47-Mev state are characteristic of stripping and indicate the formation of the ground state by an l=2 neutron and of the 1.47-Mev state by an l=0 neutron. However, the distribution of protons leaving O19 in its 0.096-Mev state does not lend itself to a stripping interpretation.
It has been found that the γ decay of the 1.47-Mev state of O19, following the formation of this state in the O18(d, p)O19 reaction, proceeds mostly to the 0.096-Mev state. The mean life of the 0.096-Mev state has been measured by observing the decay in flight of recoiling excited O19 nuclei and is found to be 1.75(1±0.16)×10^-9 second. These observations restrict the likely assignments of spin and parity for the 0.096-Mev state to 3/2± or 5/2+
Lifetime of the 0.119-Mev state of the N16 nucleus
The mean life of the 0.119-Mev state of N16 has been measured and is found to be 7.83(1±0.04)×10^-5 second. This state was produced by means of the N15(d, p)N16 reaction with deuterons having a laboratory energy of 1.76 Mev. The experiment involved periodically directing the deuteron beam onto and then away from the target. The lifetime was determined by measuring the decay rate of the 0.119-Mev γ-ray activity during the periods when the beam was off the target
Simulations of Vortex Evolution and Phase Slip in Oscillatory Potential Flow of the Superfluid Component of Helium-4 Through an Aperture
The evolution of semicircular quantum vortex loops in oscillating potential
flow emerging from an aperture is simulated in some highly symmetrical cases.
As the frequency of potential flow oscillation increases, vortex loops that are
evolving so as eventually to cross all of the streamlines of potential flow are
drawn back toward the aperture when the flow reverses. As a result, the escape
size of the vortex loops, and hence the net energy transferred from potential
flow to vortex flow in such 2 Pi phase-slip events, decreases as the
oscillation frequency increases. Above some aperture-dependent and
flow-dependent threshold frequency, vortex loops are drawn back into the
aperture. Simulations are preformed using both radial potential flow and
oblate-spheroidal potential flow.Comment: 18 pages, 6 figures, sequel to cond-mat/050203
Delay Games with WMSO+U Winning Conditions
Delay games are two-player games of infinite duration in which one player may
delay her moves to obtain a lookahead on her opponent's moves. We consider
delay games with winning conditions expressed in weak monadic second order
logic with the unbounding quantifier, which is able to express (un)boundedness
properties. We show that it is decidable whether the delaying player has a
winning strategy using bounded lookahead and give a doubly-exponential upper
bound on the necessary lookahead. In contrast, we show that bounded lookahead
is not always sufficient to win such a game.Comment: A short version appears in the proceedings of CSR 2015. The
definition of the equivalence relation introduced in Section 3 is updated:
the previous one was inadequate, which invalidates the proof of Lemma 2. The
correction presented here suffices to prove Lemma 2 and does not affect our
main theorem. arXiv admin note: text overlap with arXiv:1412.370
A Systematic Extended Iterative Solution for QCD
An outline is given of an extended perturbative solution of Euclidean QCD
which systematically accounts for a class of nonperturbative effects, while
allowing renormalization by the perturbative counterterms. Proper vertices
Gamma are approximated by a double sequence Gamma[r,p], with r the degree of
rational approximation w.r.t. the QCD mass scale Lambda, nonanalytic in the
coupling g, and p the order of perturbative corrections in g-squared,
calculated from Gamma[r,0] - rather than from the perturbative Feynman rules
Gamma(0)(pert) - as a starting point. The mechanism allowing the
nonperturbative terms to reproduce themselves in the Dyson-Schwinger equations
preserves perturbative renormalizability and is tied to the divergence
structure of the theory. As a result, it restricts the self-consistency problem
for the Gamma[r,0] rigorously - i.e. without decoupling approximations - to the
superficially divergent vertices. An interesting aspect of the scheme is that
rational-function sequences for the propagators allow subsequences describing
short-lived excitations. The method is calculational, in that it allows known
techniques of loop computation to be used while dealing with integrands of
truly nonperturbative content.Comment: 48 pages (figures included). Scope of replacement: correction of a
technical defect; no changes in conten
The Sagnac Phase Shift suggested by the Aharonov-Bohm effect for relativistic matter beams
The phase shift due to the Sagnac Effect, for relativistic matter beams
counter-propagating in a rotating interferometer, is deduced on the bases of a
a formal analogy with the the Aharonov-Bohm effect. A procedure outlined by
Sakurai, in which non relativistic quantum mechanics and newtonian physics
appear together with some intrinsically relativistic elements, is generalized
to a fully relativistic context, using the Cattaneo's splitting technique. This
approach leads to an exact derivation, in a self-consistently relativistic way,
of the Sagnac effect. Sakurai's result is recovered in the first order
approximation.Comment: 18 pages, LaTeX, 2 EPS figures. To appear in General Relativity and
Gravitatio
A direct kinematical derivation of the relativistic Sagnac effect for light or matter beams
The Sagnac time delay and the corresponding Sagnac phase shift, for
relativistic matter and electromagnetic beams counter-propagating in a rotating
interferometer, are deduced on the ground of relativistic kinematics. This
purely kinematical approach allows to explain the ''universality'' of the
effect, namely the fact that the Sagnac time difference does not depend on the
physical nature of the interfering beams. The only prime requirement is that
the counter-propagating beams have the same velocity with respect to any
Einstein synchronized local co-moving inertial frame.Comment: 10 pages, 1 EPS figure, to appear in General Relativity and
Gravitatio
Systematic Cu-63 NQR studies of the stripe phase in La(1.6-x)Nd(0.4)Sr(x)CuO(4) for 0.07 <= x <= 0.25
We demonstrate that the integrated intensity of Cu-63 nuclear quadrupole
resonance (NQR) in La(1.6-x)Nd(0.4)Sr(x)CuO(4) decreases dramatically below the
charge-stripe ordering temperature T(charge). Comparison with neutron and X-ray
scattering indicates that the wipeout fraction F(T) (i.e. the missing fraction
of the integrated intensity of the NQR signal) represents the charge-stripe
order parameter. The systematic study reveals bulk charge-stripe order
throughout the superconducting region 0.07 <= x <= 0.25. As a function of the
reduced temperature t = T/T(charge), the temperature dependence of F(t) is
sharpest for the hole concentration x=1/8, indicating that x=1/8 is the optimum
concentration for stripe formation.Comment: 10 pages of text and captions, 11 figures in postscript. Final
version, with new data in Fig.
- …