On the critical slowing down exponents of mode coupling theory

A method is provided to compute the parameter exponent $\lambda$ yielding the dynamic exponents of critical slowing down in mode coupling theory. It is independent from the dynamic approach and based on the formulation of an effective static field theory. Expressions of $\lambda$ in terms of third order coefficients of the action expansion or, equivalently, in term of six point cumulants are provided. Applications are reported to a number of mean-field models: with hard and soft variables and both fully-connected and dilute interactions. Comparisons with existing results for Potts glass model, ROM, hard and soft-spin Sherrington-Kirkpatrick and p-spin models are presented.Comment: 4 pages, 1 figur

Low EUV Luminosities Impinging on Protoplanetary Disks

The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the EUV luminosity impinging on 14 disks around young (~2-10Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10$^{42}$ photons/s for all sources without jets and lower than $5 \times 10^{40}$ photons/s for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [NeII] 12.81 micron luminosities from three disks with slow [NeII]-detected winds. This indicates that the [NeII] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.Comment: Accepted for publication to The Astrophysical Journa

Finite size corrections to disordered systems on Erd\"{o}s-R\'enyi random graphs

We study the finite size corrections to the free energy density in disorder spin systems on sparse random graphs, using both replica theory and cavity method. We derive an analytical expressions for the $O(1/N)$ corrections in the replica symmetric phase as a linear combination of the free energies of open and closed chains. We perform a numerical check of the formulae on the Random Field Ising Model at zero temperature, by computing finite size corrections to the ground state energy density.Comment: Submitted to PR

Re: Management of women with low-grade cytology: How reassuring is a normal colposcopy examination?

The debate over best management of low-grade smear results is still open. The Italian Society of Colposcopy and Cervico-Vaginal Pathology, in the Guidelines on the Management of Women with Abnormal Cervical Cytology stated that women with low-grade cytological abnormalities should be immediately referred for colposcopic examination in an outpatient clinic.This option was criticised because it may lead to overtreatment, complications and later adverse effects in young women, without clear psychological benefit. One suggestion that we could make is to restrict the use of a see-and-treat approach since the two-step approach, requiring a colposcopically obtained direct biopsy, as recently recommended by the Society of Obstetricians and Gynecologists of Canada, is, in our opinion, preferable and favours a better training for colposcopist

Influence of the Lower Hybrid Drift Instability on the onset of Magnetic Reconnection

Two-dimensional and three-dimensional kinetic simulation results reveal the importance of the Lower-Hybrid Drift Instability LHDI to the onset of magnetic reconnection. Both explicit and implicit kinetic simulations show that the LHDI heats electrons anisotropically and increases the peak current density. Linear theory predicts these modifications can increase the growth rate of the tearing instability by almost two orders of magnitude and shift the fastest growing modes to significantly shorter wavelengths. These predictions are confirmed by nonlinear kinetic simulations in which the growth and coalescence of small scale magnetic islands leads to a rapid onset of large scale reconnection

Plasma sheet structure in the magnetotail: kinetic simulation and comparison with satellite observations

We use the results of a three-dimensional kinetic simulation of an Harris current sheet to propose an explanation and to reproduce the ISEE-1/2, Geotail, and Cluster observations of the magnetotail current sheet structure. Current sheet flapping, current density bifurcation, and reconnection are explained as the results of the kink and tearing instabilities, which dominate the current sheet evolution.Comment: Submitted to Geophys. Res. Lett. (2003

Flux profile scanners for scattered high-energy electrons

The paper describes the design and performance of flux integrating Cherenkov scanners with air-core reflecting light guides used in a high-energy, high-flux electron scattering experiment at the Stanford Linear Accelerator Center. The scanners were highly radiation resistant and provided a good signal to background ratio leading to very good spatial resolution of the scattered electron flux profile scans.Comment: 22 pages, 17 figure

The Zeeman effect in the G band

We investigate the possibility of measuring magnetic field strength in G-band bright points through the analysis of Zeeman polarization in molecular CH lines. To this end we solve the equations of polarized radiative transfer in the G band through a standard plane-parallel model of the solar atmosphere with an imposed magnetic field, and through a more realistic snapshot from a simulation of solar magneto-convection. This region of the spectrum is crowded with many atomic and molecular lines. Nevertheless, we find several instances of isolated groups of CH lines that are predicted to produce a measurable Stokes V signal in the presence of magnetic fields. In part this is possible because the effective Land\'{e} factors of lines in the stronger main branch of the CH A$^{2}\Delta$--X$^{2}\Pi$ transition tend to zero rather quickly for increasing total angular momentum $J$, resulting in a Stokes $V$ spectrum of the G band that is less crowded than the corresponding Stokes $I$ spectrum. We indicate that, by contrast, the effective Land\'{e} factors of the $R$ and $P$ satellite sub-branches of this transition tend to $\pm 1$ for increasing $J$. However, these lines are in general considerably weaker, and do not contribute significantly to the polarization signal. In one wavelength location near 430.4 nm the overlap of several magnetically sensitive and non-sensitive CH lines is predicted to result in a single-lobed Stokes $V$ profile, raising the possibility of high spatial-resolution narrow-band polarimetric imaging. In the magneto-convection snapshot we find circular polarization signals of the order of 1% prompting us to conclude that measuring magnetic field strength in small-scale elements through the Zeeman effect in CH lines is a realistic prospect.Comment: 22 pages, 6 figures. To be published in the Astrophysical Journa

Multi instanton tests of holography

Gauge theories living on stacks of D7-branes are holographically related to IIB gravitational backgrounds with a varying axion-dilaton field (F-theory). The axion-dilaton field is generated by D7, O7 and D-instanton sources and can be written in terms of the chiral correlators of the eight dimensional gauge theory living on the D7-branes. Using localization techniques, we prove that the same correlators determine the gauge coupling of the four-dimensional N=2 supersymmetric SU(2) gauge theories living on the elementary D3-brane which probes the F-theory geometries.Comment: 18 page