1,833 research outputs found
Nonequilibrium quantum fluctuation relations for harmonic systems in nonthermal environments
We formulate exact generalized nonequilibrium fluctuation relations for the
quantum mechanical harmonic oscillator coupled to multiple harmonic baths. Each
of the different baths is prepared in its own individual (in general
nonthermal) state. Starting from the exact solution for the oscillator dynamics
we study fluctuations of the oscillator position as well as of the energy
current through the oscillator under general nonequilibrium conditions. In
particular, we formulate a fluctuation-dissipation relation for the oscillator
position autocorrelation function that generalizes the standard result for the
case of a single bath at thermal equilibrium. Moreover, we show that the
generating function for the position operator fullfills a generalized
Gallavotti-Cohen-like relation. For the energy transfer through the oscillator,
we determine the average energy current together with the current fluctuations.
Finally, we discuss the generalization of the cumulant generating function for
the energy transfer to nonthermal bath preparations.Comment: 21 page
Modeling microbial dormancy in soils
Dormancy is a very effective trait of microorganisms in soil to cope with varying environmental conditions (e.g. substrate availability or moisture) that leads to a graded, switch-like microbial response to fluctuations in environmental parameters. Microbial dormancy strategies vary from rapid to delayed response to environmental change and the activation from dormant to active state is typically faster than the transition to dormant state (Blagodatskaya, E., & Kuzyakov, Y. 2013). Dormancy is typically represented in models by explicitly considering active and dormant biomass pools or by introducing a physiological state variable that describes the active fraction of the total biomass. Existing modeling approaches mainly differ in the description of the transformation process between active and dormant states and disregard the classification into active, potentially active and dormant microbial states. The growth rate, death rates and the transition rate from active to dormant state are represented by generic functions. The question arises of gauging the sensitivity of model predictions for the temporal evolution of active and dormant bacteria not only to perturbations in constants of proportionality (parameter sensitivity), but to perturbations in uncertain or assumed expressions (functional sensitivity). Instead of postulating a particular description, the functional form of the transition function can be tested by fitting a type of free-form function as a linear combination of shape functions to the experimental dataset used in Wang et al. 2014. Depending on the form of the transition function, we observe that simple SOM turnover models show qualitatively different dynamical behavior. We aim to generalize existing modeling approaches to account for diversity in dormancy strategies and to understand which strategies for transiting between dormant and active states are favoured under which environmental conditions
Chemical Properties of Star-Forming Emission Line Galaxies at z=0.1 - 0.5
We measure oxygen and nitrogen abundances for 14 star-forming emission line
galaxies (ELGs) at 0.11<z<0.5 using Keck/LRIS optical spectroscopy. The targets
exhibit a range of metallicities from slightly metal-poor like the LMC to
super-solar. Oxygen abundances of the sample correlate strongly with rest-frame
blue luminosities. The metallicity-luminosity relation based on these 14
objects is indistinguishable from the one obeyed by local galaxies, although
there is marginal evidence (1.1sigma) that the sample is slightly more
metal-deficient than local galaxies of the same luminosity. The observed
galaxies exhibit smaller emission linewidths than local galaxies of similar
metallicity, but proper corrections for inclination angle and other systematic
effects are unknown. For 8 of the 14 objects we measure nitrogen-to-oxygen
ratios. Seven of 8 systems show evidence for secondary nitrogen production,
with log(N/O)> -1.4 like local spirals. These chemical properties are
inconsistent with unevolved objects undergoing a first burst of star formation.
The majority of the ELGs are presently ~4 magnitudes brighter and ~0.5 dex more
metal-rich than the bulk of the stars in well-known metal-poor dwarf
spheroidals such as NGC 205 and NGC 185, making an evolution between some ELGs
and metal-poor dwarf spheroidals improbable. However, the data are consistent
with the hypothesis that more luminous and metal-rich spheroidal galaxies like
NGC 3605 may become the evolutionary endpoints of some ELGs. [abridged]Comment: 41 pages, w/12 figures, uses AASTeX aaspp4.sty, psfig.sty; To appear
in The Astrophysical Journa
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