Differences in Thermal Tolerance Between Two Thermally Isolated and Genetically Indistinct Populations of \u3ci\u3eParagnetina Media\u3c/i\u3e (Walker) (Plecoptera: Perlodidae)

The critical thermal maximum (CTM) of Paragnetina media (Walker) (Plecoptera: Perlodidae) was studied at two sites of the Big Sable River in northwestern Lower Michigan during summer 2013. The sites were separated by ~8 km and differed in temperature by ~1°C in the early spring to ~5°C in mid-summer. Individual P. media specimens from the warm site had consistently higher CTM when acclimated to the mean temperature of the two sites for 3 days prior to experimental trials during May, June, and July. When acclimated for an additional 3 days to a higher or lower temperature, this thermal disadvantage disappeared. Groups of individuals from both sites simultaneously acclimated to both site temperatures for 3 days exhibited similar CTMs, except that cold site specimens acclimated to the cold temperature had a lower CTM than the other treatments. Sequencing of the CO1 gene revealed that nearly 75% of specimens shared a single haplotype, which was found in both warm and cold site individuals. Our results suggest that both long term and short term thermal history can influence thermal tolerance within populations of the same species that do not appear genetically distinct

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Conflicts of interest: None

Convective intensification of magnetic fields in the quiet Sun

Kilogauss-strength magnetic fields are often observed in intergranular lanes at the photosphere in the quiet Sun. Such fields are stronger than the equipartition field B_e, corresponding to a magnetic energy density that matches the kinetic energy density of photospheric convection, and comparable with the field B_p that exerts a magnetic pressure equal to the ambient gas pressure. We present an idealised numerical model of three-dimensional compressible magnetoconvection at the photosphere, for a range of values of the magnetic Reynolds number. In the absence of a magnetic field, the convection is highly supercritical and is characterised by a pattern of vigorous, time-dependent, “granular” motions. When a weak magnetic field is imposed upon the convection, magnetic flux is swept into the convective downflows where it forms localised concentrations. Unless this process is significantly inhibited by magnetic diffusion, the resulting fields are often much greater than B_e, and the high magnetic pressure in these flux elements leads to their being partially evacuated. Some of these flux elements contain ultra-intense magnetic fields that are significantly greater than B_p. Such fields are contained by a combination of the thermal pressure of the gas and the dynamic pressure of the convective motion, and they are constantly evolving. These ultra-intense fields develop owing to nonlinear interactions between magnetic fields and convection; they cannot be explained in terms of “convective collapse” within a thin flux tube that remains in overall pressure equilibrium with its surroundings

Differences in Thermal Tolerance Between Two Thermally Isolated and Genetically Indistinct Populations of \u3ci\u3eParagnetina Media\u3c/i\u3e (Walker) (Plecoptera: Perlodidae)

The critical thermal maximum (CTM) of Paragnetina media (Walker) (Plecoptera: Perlodidae) was studied at two sites of the Big Sable River in northwestern Lower Michigan during summer 2013. The sites were separated by ~8 km and differed in temperature by ~1°C in the early spring to ~5°C in mid-summer. Individual P. media specimens from the warm site had consistently higher CTM when acclimated to the mean temperature of the two sites for 3 days prior to experimental trials during May, June, and July. When acclimated for an additional 3 days to a higher or lower temperature, this thermal disadvantage disappeared. Groups of individuals from both sites simultaneously acclimated to both site temperatures for 3 days exhibited similar CTMs, except that cold site specimens acclimated to the cold temperature had a lower CTM than the other treatments. Sequencing of the CO1 gene revealed that nearly 75% of specimens shared a single haplotype, which was found in both warm and cold site individuals. Our results suggest that both long term and short term thermal history can influence thermal tolerance within populations of the same species that do not appear genetically distinct

Parabolic negative magnetoresistance in p-Ge/Ge1-xSix heterostructures

Quantum corrections to the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge1-xSix heterostructures at T = (0.1 - 20.0)K in magnetic field B up to 1.5T. Negative magnetoresistance with logarithmic dependence on T and linear in B^2 is observed for B >= 0.1T. Such a behavior is attributed to the interplay of the classical cyclotron motion and the EEI effect. The Hartree part of the interaction constant is estimated (F_/sigma = 0.44) and the WL and EEI contributions to the total quantum correction /Delta /sigma at B = 0 are separated (/Delta /sigma_{WL} ~ 0.3/Delta /sigma; /Delta /sigma_{EEI} ~ 0.7/Delta /sigma).Comment: 3 pages, 4 figure

Asymptotically exact mean field theory for the Anderson model including double occupancy

The Anderson impurity model for finite values of the Coulomb repulsion $U$ is studied using a slave boson representation for the empty and doubly occupied $f$-level. In order to avoid well known problems with a naive mean field theory for the boson fields, we use the coherent state path integral representation to first integrate out the double occupancy slave bosons. The resulting effective action is linearized using {\bf two-time} auxiliary fields. After integration over the fermionic degrees of freedom one obtains an effective action suitable for a $1/N_f$-expansion. Concerning the constraint the same problem remains as in the infinite $U$ case. For $T \rightarrow 0$ and $N_f \rightarrow \infty$ exact results for the ground state properties are recovered in the saddle point approximation. Numerical solutions of the saddle point equations show that even in the spindegenerate case $N_f = 2$ the results are quite good.Comment: 19, RevTeX, cond-mat/930502

Static Axially Symmetric Einstein-Yang-Mills-Dilaton Solutions: II.Black Hole Solutions

We discuss the new class of static axially symmetric black hole solutions obtained recently in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole solutions are asymptotically flat and they possess a regular event horizon. The event horizon is almost spherically symmetric with a slight elongation along the symmetry axis. The energy density of the matter fields is angle-dependent at the horizon. The static axially symmetric black hole solutions satisfy a simple relation between mass, dilaton charge, entropy and temperature. The black hole solutions are characterized by two integers, the winding number $n$ and the node number $k$ of the purely magnetic gauge field. With increasing node number the magnetically neutral black hole solutions form sequences tending to limiting solutions with magnetic charge $n$, corresponding to Einstein-Maxwell-dilaton black hole solutions for finite dilaton coupling constant and to Reissner-Nordstr\o m black hole solutions for vanishing dilaton coupling constant.Comment: 41 pages including 45 postscript figures, RevTex forma

Cosmological Landscape From Nothing: Some Like It Hot

We suggest a novel picture of the quantum Universe -- its creation is described by the {\em density matrix} defined by the Euclidean path integral. This yields an ensemble of universes -- a cosmological landscape -- in a mixed state which is shown to be dynamically more preferable than the pure quantum state of the Hartle-Hawking type. The latter is dynamically suppressed by the infinitely large positive action of its instanton, generated by the conformal anomaly of quantum fields within the cosmological bootstrap (the self-consistent back reaction of hot matter). This bootstrap suggests a solution to the problem of boundedness of the on-shell cosmological action and eliminates the infrared catastrophe of small cosmological constant in Euclidean quantum gravity. The cosmological landscape turns out to be limited to a bounded range of the cosmological constant $\Lambda_{\rm min}\leq \Lambda \leq \Lambda_{\rm max}$. The domain $\Lambda<\Lambda_{\rm min}$ is ruled out by the back reaction effect which we analyze by solving effective Euclidean equations of motion. The upper cutoff is enforced by the quantum effects of vacuum energy and the conformal anomaly mediated by a special ghost-avoidance renormalization of the effective action. They establish a new quantum scale $\Lambda_{\rm max}$ which is determined by the coefficient of the topological Gauss-Bonnet term in the conformal anomaly. This scale is realized as the upper bound -- the limiting point of an infinite sequence of garland-type instantons which constitute the full cosmological landscape. The dependence of the cosmological constant range on particle phenomenology suggests a possible dynamical selection mechanism for the landscape of string vacua.Comment: Final version, to appear in JCA