InSb Heterodyne Receivers For Submillimeter Astronomy

InSb hot electron bolometer mixer receivers have been used for submillimeter line studies of the interstellar medium up to frequencies of about 500 GHz (600u). Detections of new interstellar lines have been made, such as the ground state fine structure transition of atomic carbon at 492 GHz, and various transitions of molecules such as carbon monoxide and water. The bulk of this work has been performed with the NASA Kuiper Airborne Observatory telescope which is transported to an altitude of aboutl2,000 km by a C141 aircraft, so avoiding most of the effects of the Earth's atmosphere. Some observations have also been made at ground observatories with the 5 m Hale telescope at Mount Palomar and the NASA In-frared Telescope Facility at Mauna Kea, Hawaii. The heterodyne bolometer receivers have achieved noise temperatures of less than 400 K at all frequencies up to 500 GHz. Develop-ment work continues to extend the frequency range further into the submillimeter band

Development of the Submillimeter Band

This short article attempts to summarize my contribution to the field of submillimeter spectroscopy in the dense interstellar medium. It is taken mainly from my recollections and as a result some of the dates may be inaccurate. It covers most of the enabling receiver technology from frequencies of about 100 GHz to 2 THz and discusses the development of hot electron bolometers (HEB) and superconducting tunnel junction detectors (SIS). Many new molecular lines and some atomic lines have been revealed. These detectors are in use in the modern major projects such as ALMA and Herschel and will play their part in the many exciting projects of the next decade. Certainly one of the major contributions to the field has been the generation of many students who obtained Ph.D.s (14) and postdocs (25) in my group. The total number of national and international students who have obtained Ph.D.s (75) with use of the Caltech Submillimeter Observatory (CSO) and those who are currently studying using the CSO (44) is even more impressive

The Caltech Submillimeter Observatory

A brief description of the history and technology of the Caltech Submillimeter Observatory (CSO) is presented. The design of the 10.4 m Leighton telescope is discussed and also the methods used for fine adjustments of the surface. The dome design is explained, plus a short description is given of the technology of the detectors

A preconditioned formulation of the Cauchy-Riemann equations

A preconditioning of the Cauchy-Riemann equations which results in a second-order system is described. This system is shown to have a unique solution if the boundary conditions are chosen carefully. This choice of boundary condition enables the solution of the first-order system to be retrieved. A numerical solution of the preconditioned equations is obtained by the multigrid method

Numerical solution of a coupled pair of elliptic equations from solid state electronics

Iterative methods are considered for the solution of a coupled pair of second order elliptic partial differential equations which arise in the field of solid state electronics. A finite difference scheme is used which retains the conservative form of the differential equations. Numerical solutions are obtained in two ways, by multigrid and dynamic alternating direction implicit methods. Numerical results are presented which show the multigrid method to be an efficient way of solving this problem

Reform and Representation: A New Method Applied to Recent Electoral Changes

Can electoral reforms such as an independent redistricting commission and the top-two primary create conditions that lead to better legislative representation? We explore this question by presenting a new method for measuring a key indicator of representation - the congruence between a legislator's ideological position and the average position of her district's voters. Our novel approach combines two methods: the joint classification of voters and political candidates on the same ideological scale, along with multilevel regression and post-stratification to estimate the position of the average voter across many districts in multiple elections. After validating our approach, we use it to study the recent impact of reforms in California, showing that they did not bring their hoped-for effects

The molecular emission-line spectrum of IRC +10216 between 330 and 358 GHz

We have conducted a spectral line survey of IRC + 10216 using the Caltech Submillimeter Observatory to an average sensitivity of ≾95 mK. A deconvolution algorithm has been used to derive the continuous single-sideband spectrum from 330.2 to 358.1 GHz. A total of 56 spectral lines were detected of which 54 have been identified with 8 molecules and a total of 18 isotopomers. The observed lines are used to derive column densities and relative abundances for the detected species. Within this frequency range the spectral lines detected contribute the majority of the total flux emitted by IRC + 10216. We use the derived column densities and excitation temperatures to simulate the molecular line emission (assuming LTE) at frequencies up to 1000 GHz. The observed and simulated flux from line emission is compared to broadband total flux measurements and to dust emission assuming a power-law variation of the dust emissivity. We conclude that significant corrections for the line flux must be made to broadband flux measurements of IRC + 10216 at wavelengths longer than ~750 µm

Random matrix theory of unquenched two-colour QCD with nonzero chemical potential

We solve a random two-matrix model with two real asymmetric matrices whose primary purpose is to describe certain aspects of quantum chromodynamics with two colours and dynamical fermions at nonzero quark chemical potential mu. In this symmetry class the determinant of the Dirac operator is real but not necessarily positive. Despite this sign problem the unquenched matrix model remains completely solvable and provides detailed predictions for the Dirac operator spectrum in two different physical scenarios/limits: (i) the epsilon-regime of chiral perturbation theory at small mu, where mu^2 multiplied by the volume remains fixed in the infinite-volume limit and (ii) the high-density regime where a BCS gap is formed and mu is unscaled. We give explicit examples for the complex, real, and imaginary eigenvalue densities including Nf=2 non-degenerate flavours. Whilst the limit of two degenerate masses has no sign problem and can be tested with standard lattice techniques, we analyse the severity of the sign problem for non-degenerate masses as a function of the mass split and of mu. On the mathematical side our new results include an analytical formula for the spectral density of real Wishart eigenvalues in the limit (i) of weak non-Hermiticity, thus completing the previous solution of the corresponding quenched model of two real asymmetric Wishart matrices.Comment: 45 pages, 31 figures; references added, as published in JHE

After the games are over: life-history trade-offs drive dispersal attenuation following range expansion.

Increased dispersal propensity often evolves on expanding range edges due to the Olympic Village effect, which involves the fastest and fittest finding themselves together in the same place at the same time, mating, and giving rise to like individuals. But what happens after the ranges leading edge has passed and the games are over? Although empirical studies indicate that dispersal propensity attenuates following range expansion, hypotheses about the mechanisms driving this attenuation have not been clearly articulated or tested. Here, we used a simple model of the spatiotemporal dynamics of two phenotypes, one fast and the other slow, to propose that dispersal attenuation beyond preexpansion levels is only possible in the presence of trade-offs between dispersal and life-history traits. The Olympic Village effect ensures that fast dispersers preempt locations far from the ranges previous limits. When trade-offs are absent, this preemptive spatial advantage has a lasting impact, with highly dispersive individuals attaining equilibrium frequencies that are strictly higher than their introduction frequencies. When trade-offs are present, dispersal propensity decays rapidly at all locations. Our models results about the postcolonization trajectory of dispersal evolution are clear and, in principle, should be observable in field studies. We conclude that empirical observations of postcolonization dispersal attenuation offer a novel way to detect the existence of otherwise elusive trade-offs between dispersal and life-history traits