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Quanta and fields : the biggest ideas in the universe
\"In the second book of this already internationally acclaimed series, Sean Carroll, the most trusted explainer of the most mind-boggling concepts, digs deep into matter itself. What is the universe made of? In his quest to redefine the \"popular\" treatment of the biggest ideas in the universe, Sean Carroll is creating a profoundly new approach to physics and math as reviewer after reviewer has attested. Adventuring in the math of fields, he now intrepidly guides readers into the fantastic depths of The Standard Model of particle physics illuminating the mysteries of quantum reality. The universe is made of atoms and Sean Carroll explains exactly what that means and how we know it\"-- Provided by publisher.
Book
Techniques for Measuring Parallax and Proper Motion with VLBI
Astrometry at centimeter wavelengths using Very Long Baseline Interferometry is approaching accuracies of ∼1 μas for the angle between a target and a calibrator source separated by ≲1° on the sky. The BeSSeL Survey and the Japanese VERA project are using this to map the spiral structure of the Milky Way by measuring trigonometric parallaxes of hundreds of maser sources associated with massive, young stars. This paper outlines how μas astrometry is done, including details regarding the scheduling of observations, calibration of data, and measuring positions.
Journal Article
A Practical Guide to the Partition Function of Atoms and Ions
The partition function, U, the number of available states in an atom or molecules, is crucial for understanding the physical state of any astrophysical system in thermodynamic equilibrium. There are surprisingly few useful discussions of the partition function’s numerical value. Textbooks often define U; some give tables of representative values, while others do a deep dive into the theory of dense plasma. Most say that it depends on temperature, atomic structure, density, and that it diverges, that is, it goes to infinity, at high temperatures, but few give practical examples. We aim to rectify this. We show that there are two limits, one- and two-electron (or closed-shell) systems like H or He, and species with a complicated electronic structure like C, N, O, and Fe. The high-temperature divergence does not occur for one- and two-electron systems in practical situations because, at high temperatures, species are collisionally ionized to higher-ionization stages and are not abundant. The partition function is then close to the statistical weight of the ground state. There is no such simplification for many-electron species. U is temperature sensitive across the range of temperatures where an ion is abundant but remains finite at even the highest practical temperatures. The actual value depends on highly uncertain truncation theories in highdensity plasmas. We show that there are various theories for continuum lowering but that they are not in good agreement. This remains a long-standing unsolved problem.
Journal Article
Jupiter Observing Velocity Experiment (JOVE)
The Jupiter Observing Velocity Experiment (JOVE) is a solar-powered technology demonstration of rapid flight to outer solar system targets, performing a flyby of Jupiter 30 days after launch. This is achieved using a magnetic drag device to accelerate with the solar wind plasma. This “Wind Rider” propulsion system can potentially also decelerate against the Jovian magnetosphere dawn eddy, to enable Jupiter orbital insertion in future missions. The 16U cubesat bus contains scientific instruments to record the plasma parameters from the vicinity of the spacecraft, with principal measurements coming from a SPAN-I ion velocity sensor. This paper includes a description of the propulsive mechanisms and supporting subsystems and trajectory simulation results derived from solar wind measurements over the past two solar cycles. The objectives of the JOVE technology demonstrator design include: (1) verify Wind Rider stability and control; (2) characterize loss mechanisms in the solar wind, such as resistive losses in the plasma, as well as the magnetic field transient interaction time; (3) operate onboard instruments to measure the velocity and direction of the solar wind (SPAN-Ai) and speed of the spacecraft relative to the Earth (radio Doppler shift), to enable precision navigation on future science missions; and (4) characterize the Lift-to-Drag ratio of the plasma magnetic field. (The lift force enables lateral course control and maneuvering within the solar wind.) Applying existing scientific data from Voyagers and other deep space probes into new engineering models was important for enabling new insights about Wind Rider propulsion. It enables more science to be performed in a shorter amount of time, across the Jovian system.
Journal Article
Estimating Electron Temperatures in Ionized Nebulae
In this paper we examine the Direct Method for measuring electron temperatures in H II regions, and the extent to which such measurements can provide meaningful information on the physical conditions in these regions. We discuss the limits to what can be inferred about electron temperatures from nebular emission line fluxes. We provide a new simplified method for estimating electron temperatures, including parameters that can be used to determine this from UV [O III] and [O II] oxygen lines observable in high-redshift objects using ground-based telescopes. We test this method on published UV high redshift observations and compare the results with reported electron temperatures.
Journal Article
Common statistical errors in systematic reviews: A tutorial
The aim of this article is to present the most common statistical errors in meta‐analyses included in systematic reviews; these are confusing standard deviation and standard error, using heterogeneity estimators for choosing between a common‐effect and random‐effects model, improper handling of multiarm trials, and unnecessary and misinterpreted subgroup analyses. We introduce some useful terminology and explain what authors can do to avoid these errors and how peer reviewers can spot them. We have also developed a micro‐learning module to provide practical hands‐on tutorial. The aim of this article is to present the most common statistical errors in meta‐analyses included in systematic reviews; these are confusing standard deviation and standard error, using heterogeneity estimators for choosing between a common‐effect and random‐effects model, improper handling of multiarm trials, and unnecessary and misinterpreted subgroup analyses. We introduce some useful terminology and explain what authors can do to avoid these errors and how peer reviewers can spot them. We have also developed a micro‐learning module to provide practical hands‐on tutorial. Common Statistical Errors micro learning module
Journal Article
Stochastic Modeling Handbook for Optical AGN Variability
This work develops application techniques for stochastic modeling of Active Galactic Nuclei (AGNs) variability as a probe of accretion disk physics. Stochastic models, specifically Continuous Auto-Regressive Moving Average (CARMA) models, characterize light curves with a perturbation spectrum and an Impulse-Response function, which crucially provides an interpretation for variability timescales. CARMA timescales are not physical but rather, they describe correlation structure and ordered information in stochastic processes. We begin this tutorial by reviewing discrete auto-regressive and moving-average processes, we bridge these components to their continuous analogs, and lastly we investigate the significance of CARMA timescales, obtained by modeling a light curve in the time domain, in relation to the shape of the power spectrum (PSD) and structure function. We determine that higher order CARMA models, for example the Damped Harmonic Oscillator (DHO or CARMA(2, 1)) are more sensitive to deviations from a single-slope power-law description of AGN variability; unlike Damped Random Walks (DRW or CAR(1)) where the PSD slope is fixed, the DHO slope is not. Higher complexity stochastic models than the DRW capture additional covariance in data and output additional characteristic timescales that probe the driving mechanisms of variability. We provide code using Kali software to generate simulations of diverse complexity stochastic light curves. We also provide a heuristic discussion of aliasing effects in ground-based cadences and the importance of light curve length in regards to uncertainty and limitations in timescale estimation.
Journal Article
How to present an informative summary of findings table for systematic reviews of interventions: A tutorial
This tutorial provides guidance on creating clear and informative summary of findings tables for systematic reviews of interventions. This tutorial provides guidance on creating clear and informative summary of findings tables for systematic reviews of interventions. We will explain what information is required in the different sections of the table. In the accompanying micro‐learning module, you can test your knowledge of the key components of a summary of findings table and practice calculating absolute risks. Summary of findings table micro learning module
Journal Article
Intention‐to‐treat analyses and missing outcome data: A tutorial
This tutorial focuses on “intention‐to‐treat” analyses and missing outcome data in systematic reviews. There is a lack of consensus on the definition of the ITT approach. We will explain the principles of an intention‐to‐treat analysis, and outline the key issues you need to consider when planning, conducting and writing up your systematic review. ITT micro learning module
Journal Article
Formation of the Electronic Spectrum in Relativistic Jets of Gamma-Ray Blazars
We describe the theory of Fermi-type acceleration, including first-order Fermi acceleration at a parallel shock front and second-order Fermi acceleration in a test particle limit. Including the theory of the turbulent acceleration and the derivation of the general Fokker–Planck equation, we take into account the basic particle-transport equation and the Fokker–Planck equation with spatially homogeneous isotropic distribution. In the cases of some special physical processes, we construct the particle-transport equations, and compile the analytical or semi-analytical solutions in 11 different cases. Even though, traditionally, one of the electron energy distributions for these different cases can be used to reproduce the multi-wavelength emission of a blazar, due to very long integration times of high-energy observations, a time-integrated electron energy distribution should be introduced in approaches to modeling the multi-wavelength spectral energy distribution of blazars, especially in modeling the flaring state.
Journal Article