Nearly a century ago it was recognized that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models. A particular problem arose when refined photosphere spectral analysis led to reductions of 30-50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9-2.3 million kelvin and electron densities of (0.7-4.0) × 10(22) per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30-400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

We present two-dimensional inviscid hydrodynamic simulations of a protoplanetary disk with an embedded planet, emphasizing the evolution of potential vorticity (the ratio of vorticity to density) and its dependence on numerical resolutions. By analyzing the structure of spiral shocks made by the planet, we show that progressive changes of the potential vorticity caused by spiral shocks ultimately lead to the excitation of a secondary instability. We also demonstrate that very high numerical resolution is required to both follow the potential vorticity changes and identify the location where the secondary instability is first excited. Low-resolution results are shown to give the wrong location. We establish the robustness of a secondary instability and its impact on the planet's torque. After the saturation of the instability, the disk shows large-scale nonaxisymmetry, causing the torque on the planet to oscillate with large amplitude. The impact of the oscillating torque on the protoplanet's migration remains to be investigated.

The paucity of observed dwarf galaxies in the Local Group relative to the abundance of predicted dark matter halos remains one of the greatest puzzles of the ΛCDM paradigm. Solving this puzzle now requires not only matching the numbers of objects but also understanding the details of their star formation histories. We present a summary of such histories derived from the HST data using the color-magnitude diagram fitting method. To reduce observational uncertainties, we condense the data into five cumulative parameters -the fractions of stellar mass formed in the last 1, 2, 5, and 10 Gyr, and the mean stellar age. We interpret the new data with a phenomenological model based on the mass assembly histories of dark matter halos and the Schmidt law of star formation. The model correctly predicts the radial distribution of the dwarfs and the fractions of stars formed in the last 5 and 10 Gyr. However, in order to be consistent with the observations, the model requires a significant amount of recent star formation in the last 2 Gyr. Within the framework of our model, this prolonged star formation can be achieved by adding a stochastic variation in the density threshold of the star formation law. The model results are not sensitive to late gas accretion, the slope of the Schmidt law, or the details of cosmic reionization. A few discrepancies still remain: our model typically predicts too large stellar masses, only a modest population of ultra-faint dwarfs, and a small number of dwarfs with anomalously young stellar populations. Nevertheless, the observed star formation histories of Local Group dwarfs are generally consistent the expected star formation in cold dark matter halos.

We regret overlooking two important citations relevant to the current work, and wish to add these [1, 2]. We also cite [3], which reports crucial experimental parameters pertaining to [1], e.g. chamber pressure during water target experiment. To correct the oversight of missing references, the 4th paragraph of the introduction follows with modified and additional text underlined:Liquid targets have a number of attractive features for meeting these needs. Liquid targets can be rapidly delivered into the interaction region, and mitigate debris [31,[34][35][36]. This is well illustrated by the pioneering research in [1, 3], who, for the first time combined a kHz, femtosecond laser and liquid jet targets with a long-term vision of developing integrated sources of energetic radiation and particles for future applications. They reported the production of 9.25 keV x-rays from the interaction of a kHz, 50 fs pulsed laser interacting with a liquid Ga jet target. They also reported the use of CR39 film to record the production of 500 keV protons from the interaction of the kHz laser with an intensity of 3×10 16 W cm −2 focused on a 10-30μm diameter water jet, with a background chamber pressure of 0.7-3 mbar. The proton production efficiency of 10 −5 % was reported. Prior to switching to the liquid sheet target described in our current work, we attempted to obtain protons from the interaction of 15-30μm diameter water jets with a 40 fs pulsed laser focused to an intensity of 1×10 18 W cm −2 . We recorded many tracks on the CR39 film but, when a magnetic spectrometer was used, all of the tracks were shown to be due to electrons. As noted in this paper, we later discovered that the chamber background pressure required to produce a significant flux of protons was below the freeze point pressure of water.Skip to the end of the last sentence of the paragraph and add as the last sentence of the paragraph: the ability to generate a well collimated proton beam with proton energies greater than 500 keV has recently been demonstrated [2], using a high repetition rate 0.5 kHz, 3 mJ, 55 fs laser interacting with a solid target. The focus intensity was 2×10 18 W cm −2 . A proton beam was generated at the front surface of a rotating optical quality glass disk at a chamber pressure of 3×10 −3 mbar. AbstractLaser acceleration of ions to MeV energies has been achieved on a variety of Petawatt laser systems, raising the prospect of ion beam applications using compact ultra-intense laser technology. However, translation from proof-of-concept laser experiment into real-world application requires MeV-scale ion energies and an appreciable repetition rate (>Hz). We demonstrate, for the first time, proton acceleration up to 2 MeV energies at a kHz repetition rate using a milli-joule-class short-pulse laser system. In these experiments, 5 mJ of ultrashort-pulse laser energy is delivered at an intensity neaŕ -5 10 W cm 18 2 onto a thin-sheet, liquid-density target. Key to this effort is a flowing liquid ethylene glycol target formed i...

Motivated by cosmological surveys that demand accurate theoretical modeling of the baryon acoustic oscillation (BAO) feature in galaxy clustering, we analyze N-body simulations in which a BAO-like gaussian bump modulates the linear theory correlation function ξL(r) = (r0/r) n+3 of an underlying self-similar model with initial power spectrum P (k) = Ak n . These simulations test physical and analytic descriptions of BAO evolution far beyond the range of most studies, since we consider a range of underlying power spectra (n = −0.5, −1, −1.5) and evolve simulations to large effective correlation amplitudes (equivalent to σ8 = 4 − 12 for r bao = 100h −1 Mpc). In all cases, non-linear evolution flattens and broadens the BAO bump in ξ(r) while approximately preserving its area. This evolution resembles a "diffusion" process in which the bump width σ bao is the quadrature sum of the linear theory width and a length proportional to the rms relative displacement Σpair(r bao ) of particle pairs separated by r bao . For n = −0.5 and n = −1, we find no detectable shift of the location of the BAO peak, but the peak in the n = −1.5 model shifts steadily to smaller scales, following r peak /r bao = 1 − 1.08(r0/r bao )1.5 . The perturbation theory scheme of McDonald (2007) [1] and, to a lesser extent, standard 1-loop perturbation theory are fairly successful at explaining the non-linear evolution of the fourier power spectrum of our models. Analytic models also explain why the ξ(r) peak shifts much more for n = −1.5 than for n ≥ −1, though no ab initio model we have examined reproduces all of our numerical results. Simulations with L box = 10r bao and L box = 20r bao yield consistent results for ξ(r) at the BAO scale, provided one corrects for the integral constraint imposed by the uniform density box.