Structure and spectroscopy of doped helium clusters using quantum Monte Carlo techniques

We present a comparative study of the rotational characteristics of various molecule-doped 4He clusters using quantum Monte Carlo techniques. The theoretical conclusions obtained from both zero and finite temperature Monte Carlo studies confirm the presence of two different dynamical regimes that correlate with the magnitude of the rotational constant of the molecule, i.e., fast or slow rotors. For a slow rotor, the effective rotational constant for the molecule inside the helium droplet can be determined by a microscopic two-fluid model in which helium densities computed by path integral Monte Carlo are used as input, as well as by direct computation of excited energy levels. For a faster rotor, the conditions for application of the two-fluid model for dynamical analysis are usually not fulfilled and the direct determination of excitation energies is then mandatory. Quantitative studies for three molecules are summarized, showing in each case excellent agreement with experimental results

Covenantal Ethics: A Living System for Living Systems

Covenantal ethics is a living system for living systems. We humans are not simple, isolated individuals living stagnant, dead lives. Rather we are immersed in a complex system of living, glowing and developing interpersonal relationships with others. Philosophy in general and ethics in particular are often looked upon as dead or dormant entities. Covenantal ethics is neither. It is a living approach to the philosophy of ethics that recognizes the dynamic system in which we live. Our world recently welcomed a new millennium. We moved forward, leaving behind much of the old and eagerly anticipating what was to come. One of the many things which we left behind was the monopoly held by theistic religion over the world\u27s tradition, philosophy and religion for the last one thousand years. Today the world is much bigger than Europe and North America. The church seems much smaller. For centuries the layman could turn for direction in moral decisions only to the church. In one sense, theism may now be socially antiquated. While it is true that the vast majority of Americans claim to believe in God, it is my observation that the dominant ethical force in our society is not the Church. From what I can tell, our society, by and large, has lost any direct connection between belief in God and normative ethical theory. In its wake, the Church left behind innumerable rivals competing for ethical force in our society. Human ideas like scientific advancement, political correctness, religious pluralism and philosophical relativism have replaced the Church with respect to swaying ethical opinion. However, even within this modern pluralistic society, there are still two dominant ethical forces. They are Kantianism and utilitarianism. Tradition mandates that a respectable ethicist choose between these two schools of thought. And what about the religious ethicist? Must he or she attempt to do ethics only within the confines of existing ethical models? I propose to construct an ethical system that is distinct from Kantian, utilitarian and pluralistic models. I suggest that this system will be a tenable option for the Christian and the non-Christian, for the ethicist and the non-ethicist alike. Furthermore, I propose that this system is internally consistent and that it is useful in the field of medical ethics. I propose to construct this system around the notion of covenant. In this system, we would not be bogged down with many of the philosophical problems that are unavoidable with Kantian, utilitarian or pluralistic rhetoric. Rather, we would be able to discern the right course of action in our lives after we first properly examined the covenantal relationships into which we have entered. For those of us who acknowledge a relationship with God, our primary covenant is with Him. As a couple of contemporary ethicists note, The experience of one\u27s own life as a gift from God becomes an inherent element of one\u27s attitude toward all interventions in life (Pellegrino and Thomasma 1997, 40). In a hypothetical decision, the outcome of which would not affect any other person or thing, this covenant alone is sufficient to discern right from wrong and better from best. In most cases, however, other covenantal relationships need to be evaluated. For instance, as a physician, I may have entered into a covenant with a patient, or as a husband entered a covenant with my wife. How can I, in these particular circumstances, honor this covenant with my patient, or that with my wife, in such a way that I also honor my covenant with God? I propose to begin by arguing that there is a problem with the current discussions of medical ethics and to explain why this problem exists. I will then suggest my proposal concerning covenantal ethics and explain the origins of this idea. Subsequently, I will describe it in greater detail, comparing and contrasting it with other existing ethical systems. I will next describe how covenantal ethics may be used in general. I will close by showing that this system truly will impact real decisions in medical ethics. The question of abortion will provide me with a test case. Throughout this project, I propose to allow historic and current criticism from theology, philosophy and society to raise questions and problems for covenantal ethics. In the end, covenantal ethics will not only survive the challenge, but will grow more vigorous because of it

Cosmic reionization in a dynamic quintessence cosmology

In this paper we investigate the effects that a dynamic dark energy component dominant in the universe at late epochs has on reionization. We follow the evolution of HII regions with the analytic approach of Furlanetto and Oh (2005) in two different universes for which we assume the Peebles and Ratra (2003) and Brax and Martin (2000) quintessence models and we compare our results to the LCDM scenario. We show that, for a fixed ionization efficiency, at the same cosmological epoch the topology of bubbles is dominated by high-mass objects and the characteristic size of the ionized regions is slightly smaller than in the LCDM model, especially at the latest stages of reionization, due to the higher recombination efficiency. As a consequence, the bubbles' `epoch of overlap' happens earlier than in LCDM. Finally, we show how the different evolution of the HII regions affects the transmission of the high-z QSO spectra, reducing the Lyman flux absorption at small optical depths.Comment: 10 pages, minor changes to match the version accepted for publication by MNRA

Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations

We use a large set of cosmological smoothed particle hydrodynamics (SPH) simulations to examine the effect of mass resolution and box size on synthetic Lya forest spectra at 2 \leq z \leq 5. The mass resolution requirements for the convergence of the mean Lya flux and flux power spectrum at z=5 are significantly stricter than at lower redshift. This is because transmission in the high redshift Lya forest is primarily due to underdense regions in the intergalactic medium (IGM), and these are less well resolved compared to the moderately overdense regions which dominate the Lya forest opacity at z~2-3. We further find that the gas density distribution in our simulations differs significantly from previous results in the literature at large overdensities (\Delta>10). We conclude that studies of the Lya forest at z=5 using SPH simulations require a gas particle mass of M_gas \leq 2x10^5 M_sol/h, which is >8 times the value required at z=2. A box size of at least 40 Mpc/h is preferable at all redshifts.Comment: 5 pages, 5 figures, 2 tables, accepted by MNRA

How cold is cold dark matter? Small scales constraints from the flux power spectrum of the high-redshift Lyman-alpha forest

We present constraints on the mass of warm dark matter (WDM) particles derived from the Lyman-alpha flux power spectrum of 55 high- resolution HIRES spectra at 2.0 < z < 6.4. From the HIRES spectra, we obtain a lower limit of mwdm > 1.2 keV 2 sigma if the WDM consists of early decoupled thermal relics and mwdm > 5.6 keV (2 sigma) for sterile neutrinos. Adding the Sloan Digital Sky Survey Lyman-alpha flux power spectrum, we get mwdm > 4 keV and mwdm > 28 keV (2 sigma) for thermal relics and sterile neutrinos. These results improve previous constraints by a factor two.Comment: Some issues clarified (especially resolution related). Conclusions unchanged. Accepted version by PR

Conversion of TeV photons in realistic extragalactic magnetic field

13th Patras Workshop on Axions, WIMPs and WISPs, Patras 2017, Thessaloniki, Greece, 15 May 2017 - 19 May 2017; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC, (2018). doi:10.3204/DESY-PROC-2017-0

Expansion and Collapse in the Cosmic Web

We study the kinematics of the gaseous cosmic web at high redshift with Lyman alpha forest absorption in multiple QSO sightlines. Using a simple analytic model and a cosmological hydrodynamic simulation we constrain the underlying three-dimensional distribution of velocities from the observed line-of-sight distribution of velocity shear across the plane of the sky. The distribution is found to be in good agreement with the intergalactic medium (IGM) undergoing large scale motions dominated by the Hubble flow. Modeling the Lyman alpha clouds analytically and with a hydrodynamics simulation, the average expansion velocity of the gaseous structures causing the Lyman alpha forest in the lower redshift (z = 2) sample appears about 20 percent lower than the local Hubble expansion velocity. We interpret this as tentative evidence for some clouds undergoing gravitational collapse. However, the distribution of velocities is highly skewed, and the majority of clouds at redshifts from 2 to 3.8 expand typically about 5 - 20 percent faster than the Hubble flow. This behavior is explained if most absorbers in the column density range typically detectable are expanding filaments that stretch and drain into more massive nodes. We find no evidence for the observed distribution of velocity shear being significantly influenced by processes other than Hubble expansion and gravitational instability, like galactic winds. To avoid overly disturbing the IGM, winds may be old and/or limp by the time we observe them in the Lyman alpha forest, or they may occupy only an insignificant volume fraction of the IGM. (abridged)Comment: 63 pages, 26 figures, AAS Latex; ApJ, in pres

The association between supervisor mental health training and workplace mental health stigma

Mental health disorders (MHD) are a major cause of human suffering, lost productivity, workplace disability, and economic loss throughout the industrialized world. They can affect people’s thoughts, behaviours, and feelings, as well as disrupt an individual’s life, and create many functional challenges. It is expected that MHD will affect every Canadian at some point in their lifetime, whether directly by personally experiencing a MHD, or indirectly through a family member, friend, or colleague.1 One of the major factors contributing to mental health is the environment that the individual is exposed to, which can precipitate the onset or reoccurrence of a MHD. One of the environments that over 65% of the population interacts with is the workplace,2 and although it should contribute positively to one’s mental health, there are significant workplace challenges experienced by people with MHDs.3 Specifically, stigma toward employees with MHD can increase the effects these disorders have on employees.4 When left unaddressed, MHD can account for high unemployment rates, as well as significant financial impacts to the government, employer, and worker through unemployment benefits, disability insurance, welfare programs, and health care costs.1,5–7 In addition to the high external costs, MHD can have a significant internal effect on productivity within the workplace through both presenteeism and absenteeism

Sterile dark matter and reionization

Sterile neutrinos with masses in the keV range can be the dark matter, and their emission from a supernova can explain the observed velocities of pulsars. The sterile neutrino decays could produce the x-ray radiation in the early universe, which could have an important effect on the formation of the first stars. X-rays could ionize gas and could catalyze the production of molecular hydrogen during the ``dark ages''. The increased fraction of molecular hydrogen could facilitate the cooling and collapse of the primordial gas clouds in which the first stars were formed.Comment: 4 pages, 2 figures, to appear in proceedings of 7th UCLA Symposium on sources and detection of dark matter and dark energy in the universe, 22-24 Feb 2006, Marina de Rey, Californi

First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations.

We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter (FDM) from Lyman-α forest data. Extremely light bosons with a de Broglie wavelength of ∼1  kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time, we use hydrodynamical simulations to model the Lyman-α flux power spectrum in these models and compare it to the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the intergalactic medium (IGM) that allow for jumps in the temperature of up to 5000 K, XQ-100 provides a lower limit of 7.1×10^{-22}  eV, HIRES/MIKE returns a stronger limit of 14.3×10^{-22}  eV, while the combination of both data sets results in a limit of 20×10^{-22}  eV (2σ C.L.). The limits for the analysis of the combined data sets increases to 37.5×10^{-22}  eV (2σ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power law in redshift. Light boson masses in the range 1-10×10^{-22}  eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the "small scale crisis" of the cold dark matter models