347 research outputs found
Probing finite size effects in MonteCarlo calculations
The Constrained Effective Potential (CEP) is known to be equivalent to the
usual Effective Potential (EP) in the infinite volume limit. We have carried
out MonteCarlo calculations based on the two different definitions to get
informations on finite size effects. We also compared these calculations with
those based on an Improved CEP (ICEP) which takes into account the finite size
of the lattice. It turns out that ICEP actually reduces the finite size effects
which are more visible near the vanishing of the external source.Comment: LATTICE98(Gauge, Higgs and Yukawa Models
Mass Determination from Constraint Effective Potential
The Constraint Effective Potential (CEP) allows a determination of the mass
and other quantities directly, without relying upon asymptotic correlator
decays. We report and discuss the results of some mass calculations in
, obtained from CEP and our improved version of CEP (ICEP).Comment: LATTICE99(Higgs, Yukawa, SUSY
A Geometrical Interpretation of Hyperscaling Breaking in the Ising Model
In random percolation one finds that the mean field regime above the upper
critical dimension can simply be explained through the coexistence of infinite
percolating clusters at the critical point. Because of the mapping between
percolation and critical behaviour in the Ising model, one might check whether
the breakdown of hyperscaling in the Ising model can also be intepreted as due
to an infinite multiplicity of percolating Fortuin-Kasteleyn clusters at the
critical temperature T_c. Preliminary results suggest that the scenario is much
more involved than expected due to the fact that the percolation variables
behave differently on the two sides of T_c.Comment: Lattice2002(spin
A lattice test of alternative interpretations of ``triviality'' in theory
There are two physically different interpretations of ``triviality'' in
theories. The conventional description predicts a
second-order phase transition and that the Higgs mass must vanish in the
continuum limit if , the physical v.e.v, is held fixed. An alternative
interpretation, based on the effective potential obtained in
``triviality-compatible'' approximations (in which the shifted `Higgs' field
is governed by an effective quadratic Hamiltonian)
predicts a phase transition that is very weakly first-order and that and
are both finite, cutoff-independent quantities. To test these two
alternatives, we have numerically computed the effective potential on the
lattice. Three different methods were used to determine the critical bare mass
for the chosen bare coupling value. All give excellent agreement with the
literature value. Two different methods for obtaining the effective potential
were used, as a control on the results. Our lattice data are fitted very well
by the predictions of the unconventional picture, but poorly by the
conventional picture.Comment: 16 pages, LaTeX, 2 eps figures (acknowledgements added in the
replaced version
Characterizing high energy explosive eruptions at Stromboli volcano using multidisciplinary data: An example from the 9 January 2005 explosion
Stromboli is well known for its persistent, normal explosive activity, consisting of intermittent, mild to
moderate, Strombolian explosions that typically occur every 10â20 min. All tephras erupted during this
activity usually fall back into the crater terrace, and consist of volatile-poor scoriae fed by Highly Porphyritic
(HP) magma. More occasionally, large explosions or âparoxysmsâ eject a greater quantity of tephra, mainly
consisting of HP scoriae and pumice clasts of Low Porphyritic (LP) magma, but also including large lithic
blocks. In addition to this activity, between 2004 and 2006 high energy explosions, displaying an
intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height,
duration and tephra dispersal, were observed to occur at a frequency of one to eight events per year. While
many volcanological, geochemical and geophysical studies have focused in the last few years on the two endmembers
of activity, i.e. normal or paroxysmal, a detailed investigation on these intermediate types of events
has not been carried out yet. Here we report of a study on the 9 January 2005 explosion, one of the high
energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse
bombs up to a height of 120 m, and of ash and lapilli to N200 m. An accompanying ash plume rose up to
500 m at the end of the explosion. We present a multidisciplinary approach that integrates the results from
analysis of live-camera images with compositional and textural characterization of the erupted products.
Major element composition of glassy groundmass and 3D views of textures in the erupted scoriae support
the hypothesis based on volcanological observations that this explosion falls between normal and
paroxysmal activity, for which we use the term âintermediateâ. By comparing the video-camera images of
the 9 January 2005 explosion with volcanological features of other high energy explosions that occurred at
Stromboli between June 2004 and October 2006, we find that three additional events can be considered
intermediate explosions, suggesting that this type of activity may be fairly common on this volcano. The
results of this study, although preliminary given our limited dataset, clearly indicate that the methodology
used here can be successfully applied to better define the range of eruptive styles typifying the normal
explosive activity, potentially improving our capability of eruption forecasting and assessing volcanic hazard
at Stromboli
The 2nd to 4th century explosive activity of Vesuvius: new data on the timing of the upward migration of the post-A.D. 79 magma chamber
ber
(SMM), the eruption cycle occurred at Vesuvius (Italy) in the period
between the A.D. 79 plinian and the A.D. 472 subplinan eruptions. Historical
accounts report only sporadic, poorly reliable descriptions of the
volcanic activity in this period, during which a stratified sequence of ash
and lapilli beds, up to 150 cm thick, with a total volume estimated around
0.15 km3, was widely dispersed on the outer slopes of the volcano. Stratigraphic
studies and component analyses suggest that activity was characterized
by mixed hydromagmatic and magmatic processes. The
eruption style has been interpreted as repeated alternations of continuous
and prolonged ash emission activity intercalated with short-lived, violent
strombolian phases. Analyses of the bulk rock composition reveal that
during the entire eruption cycle, magma maintained an homogeneous
phonotephritic composition. In addition, the general trends of major and
trace elements depicted by the products of the A.D. 79 and A.D. 472 eruptions
converge to the SMM composition, suggesting a common mafic endmember
for these eruptions. The volatile content measured in
pyroxene-hosted melt inclusions indicates two main values of crystallization
pressures, around 220 and 70 MPa, roughly corresponding to the
previously estimated depth of the magma reservoirs of the A.D. 79 and
A.D. 472 eruptions, respectively. The study of SMM eruption cycle may
thus contribute to understand the processes governing the volcano reawakening
immediately after a plinian event, and the timing and modalities
which govern the migration of the magma reservoir
Comment on "Feynman Effective Classical Potential in the Schrodinger Formulation"
We comment on the paper "Feynman Effective Classical Potential in the
Schrodinger Formulation"[Phys. Rev. Lett. 81, 3303 (1998)]. We show that the
results in this paper about the time evolution of a wave packet in a double
well potential can be properly explained by resorting to a variational
principle for the effective action. A way to improve on these results is also
discussed.Comment: 1 page, 2eps figures, Revte
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