9 research outputs found
Transport coefficients from the lattice?
The prospects of extracting transport coefficients from euclidean lattice
simulations are discussed. Some general comments on the reconstruction of
spectral functions using the Maximal Entropy Method are given as well.Comment: Lattice2002(nonzerot), 3 pages with 2 eps figure
Transport coefficients and quantum fields
Various aspects of transport coefficients in quantum field theory are
reviewed. We describe recent progress in the calculation of transport
coefficients in hot gauge theories using Kubo formulas, paying attention to the
fulfillment of Ward identities. We comment on why the color conductivity in hot
QCD is much simpler to compute than the electrical conductivity. The
nonperturbative extraction of transport coefficients from lattice QCD
calculations is briefly discussed.Comment: 15 pages with 9 eps figures. Combined invited talk by G.A. and poster
by J.M.M.R. presented at Strong and Electroweak Matter (SEWM 2002),
Heidelberg, Germany, 2-5 Oct 200
Transport coefficients and the 2PI effective action in the large N limit
We discuss the computation of transport coefficients in large N_f QCD and the
O(N) model for massive particles. The calculation is organized using the 1/N
expansion of the 2PI effective action to next-to-leading order. For the gauge
theory, we verify gauge fixing independence and consistency with the Ward
identity. In the gauge theory, we find a nontrivial dependence on the fermion
mass.Comment: 10 pages, based on presentations at Strong and Electroweak Matter
(SEWM04), Helsinki, Finland, June 16-19 2004, and the Workshop on QCD in
Extreme Environments, Argonne National Laboratory, USA, June 29-July 3 200
Shear Viscosity in the O(N) Model
We compute the shear viscosity in the O(N) model at first nontrivial order in
the large N expansion. The calculation is organized using the 1/N expansion of
the 2PI effective action (2PI-1/N expansion) to next-to-leading order, which
leads to an integral equation summing ladder and bubble diagrams. We also
consider the weakly coupled theory for arbitrary N, using the three-loop
expansion of the 2PI effective action. In the limit of weak coupling and
vanishing mass, we find an approximate analytical solution of the integral
equation. For general coupling and mass, the integral equation is solved
numerically using a variational approach. The shear viscosity turns out to be
close to the result obtained in the weak-coupling analysis.Comment: 37 pages, few typos corrected; to appear in JHE
Climate change induced declines in fuel moisture may turn currently fire-free Pyrenean mountain forests into fire-prone ecosystems
Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6–15 °C and 395–933 mm, respectively. We observed significant spatial variation in live (78–162%) and dead (10–15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|–|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006–2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the “safety margin” for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response
TRY plant trait database - enhanced coverage and open access
10.1111/gcb.14904GLOBAL CHANGE BIOLOGY261119-18