Shapes of Stellar Systems and Dark Halos from Simulations of Galaxy Major Mergers

Using a sample of 89 snapshots from 58 hydrodynamic binary galaxy major merger simulations, we find that stellar remnants are mostly oblate while dark matter halos are mostly prolate or triaxial. The stellar minor axis and the halo major axis are almost always nearly perpendicular. This can be understood by considering the influence of angular momentum and dissipation during the merger. If binary mergers of spiral galaxies are responsible for the formation of elliptical galaxies or some subpopulation thereof, these galaxies can be expected to be oblate and inhabit their halos with the predicted shapes and orientations. These predictions are potentially relevant to observational studies of weak gravitational lensing, where one must stack many optically aligned galaxies in order to determine the shape of the resulting stacked mass distribution. The simple relationship between the dark and luminous matter presented here can be used to guide the stacking of galaxies to minimize the information lost.Comment: 4 pages, 5 figures. Minor changes to match published versio

A Two-dimensional Infinte System Density Matrix Renormalization Group Algorithm

It has proved difficult to extend the density matrix renormalization group technique to large two-dimensional systems. In this Communication I present a novel approach where the calculation is done directly in two dimensions. This makes it possible to use an infinite system method, and for the first time the fixed point in two dimensions is studied. By analyzing several related blocking schemes I find that there exists an algorithm for which the local energy decreases monotonically as the system size increases, thereby showing the potential feasibility of this method.Comment: 5 pages, 6 figure

Pengaruh Sabut Kelapa Terhadap Kualitas Nira Aren Dan Palm Wine

Effect of fresh coconut husk on the quality of Arenga pinnata toddy andpalm wineArenga pinnata toddy is the main row material for processing palmsugar and traditional beverage, like palm wine and cap tikus in NorthSulawesi. The quality of product depends on the quality of A. pinnatatoddy before it is processed (fermented). The aim of this research was tostudy the effect of coconut husk to preserve the toddy of A. pinnata and itseffect on the palm wine quality. The research was conducted from Januaryto December 2002, at the Laboratory of Indonesian Coconut and PalmaeResearch Institute (ICOPRI) Manado. Arenga pinnata toddy was obtainedfrom the farmer at Tatengesan Village in Minahasa Regency. The researchconsisted of 2 parts which were done continuously. The first part was theeffect of coconut husk on the quality of Arenga pinnata toddy. Theexperiment was arranged factorially using completely randomized design,with two replications. The first factor was the weight of coconut husk (50g, 100 g and 150 g). The second factor was the period after tapping (1, 2 ,3, and 4 hours). The variables observed were pH, total sucrose and thecolour of toddy. The second part was processing palm wine by using thetoddy of Arenga pinnata. The experiment was arranged factorially using acompletely randomized design, with 3 replications. The first factor waskind of starter/microbial consisted of commercial yeast, pure culture S.cerevisiae and S. ellipsoides. The second factor was aging period consistedof 1 month, 2 months and 3 months. The variables observed were totalsucrose, acidity (pH), alcohol content, total plate count, total acid, volatilacid, colour, flavor and taste. The results on the first part showed that 50gof fresh coconut husk was suitable and efficient to preserve the quality oftoddy up to 3 hours after tapping. The toddy which were produced thatway could be processed for making palm wine. The results of the secondpart showed that the quality of palm wine until 3 months aging period wasgood, especially the palm wine using starter from commercial yeast and S.cerevisiae. The total sucrose and acidity (pH) of the palm wine usingcommercial yeast and pure culture S. cerevisiae are total sugar was asfollows 3.33 – 3.78%, pH 3.94– 4.10 and alcohol content was 6.88%. Byusing S. ellipsoides the total sucrose 10.44%, pH 4.3, and alcohol content1.58%. The total acid of the palm wine using commercial yeast, pureculture S. cerevisiae, and S. ellipsoides: 12.27 meq/100 ml, 10.52meq/100 ml, 9.24 meq/100 ml. Volatil acid content as acetic acid was0.008 – 0.042%. The colour of palm wine was brown redness.Organoleptic test showed that the testers liked the flavor and taste of thepalm wine using S. ellipsoides, better eventhough its alcohol content wasonly 1.58%. In general, the quality of palm wine from A. pinnata toddywas categorized as alcohol beverage group B because its alcohol contentwas low (<2%) and volatile acid content was <0.2%

The initial singularity of ultrastiff perfect fluid spacetimes without symmetries

We consider the Einstein equations coupled to an ultrastiff perfect fluid and prove the existence of a family of solutions with an initial singularity whose structure is that of explicit isotropic models. This family of solutions is `generic' in the sense that it depends on as many free functions as a general solution, i.e., without imposing any symmetry assumptions, of the Einstein-Euler equations. The method we use is a that of a Fuchsian reduction.Comment: 16 pages, journal versio

The effect of galaxy mass ratio on merger--driven starbursts

We employ numerical simulations of galaxy mergers to explore the effect of galaxy mass ratio on merger--driven starbursts. Our numerical simulations include radiative cooling of gas, star formation, and stellar feedback to follow the interaction and merger of four disk galaxies. The galaxy models span a factor of 23 in total mass and are designed to be representative of typical galaxies in the local Universe. We find that the merger--driven star formation is a strong function of merger mass ratio, with very little, if any, induced star formation for large mass ratio mergers. We define a burst efficiency that is useful to characterize the merger--driven star formation and test that it is insensitive to uncertainties in the feedback parameterization. In accord with previous work we find that the burst efficiency depends on the structure of the primary galaxy. In particular, the presence of a massive stellar bulge stabilizes the disk and suppresses merger--driven star formation for large mass ratio mergers. Direct, co--planar merging orbits produce the largest tidal disturbance and yield that most intense burst of star formation. Contrary to naive expectations, a more compact distribution of gas or an increased gas fraction both decrease the burst efficiency. Owing to the efficient feedback model and the newer version of SPH employed here, the burst efficiencies of the mergers presented here are smaller than in previous studies.Comment: 26 pages, 21 figures, submitted to MNRA

Simulations of Dust in Interacting Galaxies I: Dust Attenuation

A new Monte-Carlo radiative-transfer code, Sunrise, is used in conjunction with hydrodynamic simulations of major galaxy mergers to calculate the effects of dust in such systems. The simulations are in good agreement with observations of dust absorption in starburst galaxies, and the dust has a profound effect on their appearance. The dust attenuation increases with luminosity such that at peak luminosities ~90% of the bolometric luminosity is absorbed by dust. In general, the detailed appearance of the merging event depends on the stage of the merger and the geometry of the encounter. The fraction of bolometric energy absorbed by the dust, however, is a robust quantity that can be predicted from the intrinsic properties bolometric luminosity, baryonic mass, star-formation rate, and metallicity of the system. This paper presents fitting formulae, valid over a wide range of masses and metallicities, from which the absorbed fraction of luminosity (and consequently also the infrared dust luminosity) can be predicted. The attenuation of the luminosity at specific wavelengths can also be predicted, albeit with a larger scatter due to the variation with viewing angle. These formulae for dust attenuation appear to be valid for both isolated and interacting galaxies, are consistent with earlier studies, and would be suitable for inclusion in theoretical models, e.g. semi-analytic models of galaxy formation.Comment: 12 pages, 10 figures, submitted to Ap

Reduction of the sign problem using the meron-cluster approach

The sign problem in quantum Monte Carlo calculations is analyzed using the meron-cluster solution. The concept of merons can be used to solve the sign problem for a limited class of models. Here we show that the method can be used to \textit{reduce} the sign problem in a wider class of models. We investigate how the meron solution evolves between a point in parameter space where it eliminates the sign problem and a point where it does not affect the sign problem at all. In this intermediate regime the merons can be used to reduce the sign problem. The average sign still decreases exponentially with system size and inverse temperature but with a different prefactor. The sign exhibits the slowest decrease in the vicinity of points where the meron-cluster solution eliminates the sign problem. We have used stochastic series expansion quantum Monte Carlo combined with the concept of directed loops.Comment: 8 pages, 9 figure

Interfaces and Interphases in Ca and Mg Batteries

The development of high energy density battery technologies based on divalent metals as the negative electrode is very appealing. Ca and Mg are especially interesting choices due to their combination of low standard reduction potential and natural abundance. One particular problem stalling the technological development of these batteries is the low efficiency of plating/stripping at the negative electrode, which relates to several factors that have not yet been looked at systematically; the nature/concentration of the electrolyte, which determines the mass transport of electro-active species (cation complexes) toward the electrode; the possible presence of passivation layers, which may hinder ionic transport and hence limit electrodeposition; and the mechanisms behind the charge transfer leading to nucleation/growth of the metal. Different electrolytes are investigated for Mg and Ca, with the presence/absence of chlorides in the formulation playing a crucial role in the cation desolvation. From a R&D point-of-view, proper characterization alongside modeling is crucial to understand the phenomena determining the mechanisms of the plating/stripping processes. The state-of-the-art is here presented together with a short perspective on the influence of the cation solvation also on the positive electrode and finally an attempt to define guidelines for future research in the field

Condensates beyond mean field theory: quantum backreaction as decoherence

We propose an experiment to measure the slow log(N) convergence to mean-field theory (MFT) around a dynamical instability. Using a density matrix formalism, we derive equations of motion which go beyond MFT and provide accurate predictions for the quantum break-time. The leading quantum corrections appear as decoherence of the reduced single-particle quantum state.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let