4,083 research outputs found
Supersonic Deflagrations in Cosmological Phase Transitions
The classification of the hydrodynamical growth mechanisms for the spherical
bubbles of the low-temperature phase in cosmological phase transitions is
completed by showing that the bubbles can grow as supersonic deflagrations.
Such deflagrations consist of a Jouguet deflagration, followed by a rarefaction
wave. Depending on the amount of supercooling, the maximal velocity of
supersonic deflagrations varies between the sound and the light velocities. The
solutions faster than supersonic deflagrations are weak detonations.Comment: 8 pages, RevTeX, 6 figures. Complete paper appended as uuencoded
postscript and at http://www.physics.helsinki.fi/tft/tft_preprints.htm
A quantum jump description for the non-Markovian dynamics of the spin-boson model
We derive a time-convolutionless master equation for the spin-boson model in
the weak coupling limit. The temporarily negative decay rates in the master
equation indicate short time memory effects in the dynamics which is explicitly
revealed when the dynamics is studied using the non-Markovian jump description.
The approach gives new insight into the memory effects influencing the spin
dynamics and demonstrates, how for the spin-boson model the the co-operative
action of different channels complicates the detection of memory effects in the
dynamics.Comment: 9 pages, 6 figures, submitted to Proceedings of CEWQO200
No-till cultivation suppresses broad-leaved weeds but favours grasses
When shifting from traditional ploughing to no-till cultivation there will be new possibilities to weeds. However, the changes in weed population are more dependent on each field than on cultivation method.
We had two field trials in southern Finland (Jokioinen and Mietoinen) on heavy clay for four years (2001-2004). The main treatment was direct seeding or conventional sowing after autumn ploughing combined with spring rotary hoeing
Mesonic screening masses at high temperature and finite density
We compute the first perturbative correction to the static correlation
lengths of light quark bilinears in hot QCD with finite quark chemical
potentials. The correction is small and positive, with mu-dependence depending
on the relative sign of chemical potentials and the number of dynamical
flavors. The computation is carried out using a three-dimensional effective
theory for the lowest fermionic Matsubara mode. We also compute the full
correlator in free theory and find a rather complicated general mu-dependence
at shorter distances. Finally, rough comparisons with lattice simulations are
discussed.Comment: 24 pages, 5 figures, JHEP style. Minor corrections and
clarifications, version to appear in JHE
A non-perturbative estimate of the heavy quark momentum diffusion coefficient
We estimate the momentum diffusion coefficient of a heavy quark within a pure
SU(3) plasma at a temperature of about 1.5Tc. Large-scale Monte Carlo
simulations on a series of lattices extending up to 192^3*48 permit us to carry
out a continuum extrapolation of the so-called colour-electric imaginary-time
correlator. The extrapolated correlator is analyzed with the help of
theoretically motivated models for the corresponding spectral function.
Evidence for a non-zero transport coefficient is found and, incorporating
systematic uncertainties reflecting model assumptions, we obtain kappa = (1.8 -
3.4)T^3. This implies that the "drag coefficient", characterizing the time
scale at which heavy quarks adjust to hydrodynamic flow, is (1.8 - 3.4)
(Tc/T)^2 (M/1.5GeV) fm/c, where M is the heavy quark kinetic mass. The results
apply to bottom and, with somewhat larger systematic uncertainties, to charm
quarks.Comment: 18 pages. v2: clarifications adde
Vector screening masses in the quark-gluon plasma and their physical significance
Static and non-static thermal screening states that couple to the conserved
vector current are investigated in the high-temperature phase of QCD. Their
masses and couplings to the current are determined at weak coupling, as well as
using two-flavor lattice QCD simulations. A consistent picture emerges from the
comparison, providing evidence that non-static Matsubara modes can indeed be
treated perturbatively. We elaborate on the physical significance of the
screening masses.Comment: 4 pages, 3 figures. Submitted as a contribution to the proceedings of
the Quark Matter 2014 conference (talk given by H. Meyer
Critical point and scale setting in SU(3) plasma: An update
We explore a method developed in statistical physics which has been argued to
have exponentially small finite-volume effects, in order to determine the
critical temperature Tc of pure SU(3) gauge theory close to the continuum
limit. The method allows us to estimate the critical coupling betac of the
Wilson action for temporal extents up to Nt ~ 20 with < 0.1% uncertainties.
Making use of the scale setting parameters r0 and sqrt{t0} in the same range of
beta-values, these results lead to the independent continuum extrapolations Tc
r0 = 0.7457(45) and Tc sqrt{t0} = 0.2489(14), with the latter originating from
a more convincing fit. Inserting a conversion of r0 from literature
(unfortunately with much larger errors) yields Tc / LambdaMSbar = 1.24(10).Comment: 12 pages. v2: clarifications and references added, published versio
A relation between screening masses and real-time rates
Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.Comment: 32 pages. v2: clarifications added, typos corrected; published
versio
Dental attendance after fear treatment in primary oral health care:data-based 10 year follow-up study
Abstract. Background: Dental fear or dental anxiety is one of the most common fears in the society today. It may be treated effectively e.g. with cognitive-behavioural therapy or CBT.
Aim: The scope of this practise-based study was to investigate dental attendance of patients having received treatment for dental fear, based on CBT, in 10–15-year span following their fear treatment.
Materials and methods: Study participants had received treatment, mainly CBT, for dental fear by primary health care dentists interested and trained in the era, during 2000–2006 in the City of Oulu, Finland. The number of dental examinations, emergency visits and no shows were collected from the patient records if the City of Oulu; the organization or register keeper gave permission for this retrospective study. Data were analysed with IBM SPSS statistics processor.
Patient files of a total of 152 patients out of the original 163 were found with sufficient data, and comprised the study population. These data were quantified and cross-tabled with age, gender and perceived initial dental fear treatment success.
Results: Patients receiving dental fear treatment at the age of 2–10 years had significantly more dental examinations on average than those treated at later age. When treatment for a patient <10 years of age was initially considered successful, the number of emergency visits was significantly reduced. Gender did not seem to be a significant factor in later dental attendance.
Conclusions: Administering CBT at early age (2–10y) and successful outcome by CBT seem to be associated with more regular dental attendance and need for less emergency care than in the opposite case
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