A multiarchitecture parallel-processing development environment

A description is given of the hardware and software of a multiprocessor test bed - the second generation Hypercluster system. The Hypercluster architecture consists of a standard hypercube distributed-memory topology, with multiprocessor shared-memory nodes. By using standard, off-the-shelf hardware, the system can be upgraded to use rapidly improving computer technology. The Hypercluster's multiarchitecture nature makes it suitable for researching parallel algorithms in computational field simulation applications (e.g., computational fluid dynamics). The dedicated test-bed environment of the Hypercluster and its custom-built software allows experiments with various parallel-processing concepts such as message passing algorithms, debugging tools, and computational 'steering'. Such research would be difficult, if not impossible, to achieve on shared, commercial systems

Compiling Irregular Software to Specialized Hardware

High-level synthesis (HLS) has simplified the design process for energy-efficient hardware accelerators: a designer specifies an accelerator’s behavior in a “high-level” language, and a toolchain synthesizes register-transfer level (RTL) code from this specification. Many HLS systems produce efficient hardware designs for regular algorithms (i.e., those with limited conditionals or regular memory access patterns), but most struggle with irregular algorithms that rely on dynamic, data-dependent memory access patterns (e.g., traversing pointer-based structures like lists, trees, or graphs). HLS tools typically provide imperative, side-effectful languages to the designer, which makes it difficult to correctly specify and optimize complex, memory-bound applications. In this dissertation, I present an alternative HLS methodology that leverages properties of functional languages to synthesize hardware for irregular algorithms. The main contribution is an optimizing compiler that translates pure functional programs into modular, parallel dataflow networks in hardware. I give an overview of this compiler, explain how its source and target together enable parallelism in the face of irregularity, and present two specific optimizations that further exploit this parallelism. Taken together, this dissertation verifies my thesis that pure functional programs exhibiting irregular memory access patterns can be compiled into specialized hardware and optimized for parallelism. This work extends the scope of modern HLS toolchains. By relying on properties of pure functional languages, our compiler can synthesize hardware from programs containing constructs that commercial HLS tools prohibit, e.g., recursive functions and dynamic memory allocation. Hardware designers may thus use our compiler in conjunction with existing HLS systems to accelerate a wider class of algorithms than before

Sub-Inertial Gravity Modes in the B8V Star KIC 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing

KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36 consecutive dipole ($\ell=1$) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modelling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass $\sim3.25$ M$_\odot$. By simultaneously matching the slope of the period spacing, and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day$^{-1}$, which is 26\% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than one percent. We succeed to tightly constrain the exponentially-decaying convective core overshooting parameter to $f_{\rm ov}\approx0.024\pm0.001$. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially-decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra diffusive mixing in the radiatively stable envelope is confined to $\log D_{\rm ext}\approx0.75\pm0.25$ (with $D_{\rm ext}$ in cm$^2$ sec$^{-1}$), which is notably smaller than theoretical predictions.Comment: 12 Figures, 2 Tables, all data publicly available for download; accepted for publication in Astrophysical Journa

Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds

We present 2D MHD simulations of the radiatively driven outflow from a rotating hot star with a dipole magnetic field aligned with the star's rotation axis. We focus primarily on a model with moderately rapid rotation (half the critical value), and also a large magnetic confinement parameter, $\eta_{\ast} \equiv B_{\ast}^2 R_{\ast}^{2} / \dot{M} V_{\infty} = 600$. The magnetic field channels and torques the wind outflow into an equatorial, rigidly rotating disk extending from near the Kepler corotation radius outwards. Even with fine-tuning at lower magnetic confinement, none of the MHD models produce a stable Keplerian disk. Instead, material below the Kepler radius falls back on to the stellar surface, while the strong centrifugal force on material beyond the corotation escape radius stretches the magnetic loops outwards, leading to episodic breakout of mass when the field reconnects. The associated dissipation of magnetic energy heats material to temperatures of nearly $10^{8}$K, high enough to emit hard (several keV) X-rays. Such \emph{centrifugal mass ejection} represents a novel mechanism for driving magnetic reconnection, and seems a very promising basis for modeling X-ray flares recently observed in rotating magnetic Bp stars like $\sigma$ Ori E.Comment: 5 pages, 3 figures, accepted by ApJ

Non-radial pulsation of early-type stars

A comprehensive study of pulsation in early-type (O and B) stars is undertaken. Starting with the equations of hydrodynamics, expressions governing adiabatic, non-radial pulsation in such stars are derived, along with complementary formulations of the boundary conditions suitable for solution of the equations. Two types of structure models are presented, one simplistic and the other more physically realistic, and a discussion of various techniques currently used for solution of the pulsation equations is applied to the latter type of models. Such solution demonstrates that early-type main-sequence stars can be expected to be vibrationally unstable towards an opacity-driven excitation mechanism; furthermore, a consideration of the boundary conditions in such stars shows that some types of pulsation will be associated with trans-photospheric wave leakage through the stellar surface, possibly accounting for the wind variability observed in these systems. The interaction between rotation and pulsation is investigated in some depth, with a discussion of two different techniques for approaching the problem. It is demonstrated that rotation leads to the introduction of both convective and quasi-toroidal pulsation, and, furthermore, that it will serve to confine pulsation activity towards equatorial regions. The emphasis throughout the discussion is placed on the numerical implementation of current theories. All theoretical developments are combined in a pair of computer codes which model the line-profile variations of stars undergoing non-radial pulsation. The implementation of these models is discussed, with particular emphasis on the spectral-synthesis approach adopted, and they are compared with similar codes developed by other authors. The models are used to investigate some basic aspects of line-profile variability, with a discussion of the mechanisms behind the phenomenon, and a consideration of a number of issues which have previously been overlooked in the field; in particular, the possibility that a star may exhibit line-profile variability, but no ostensible photometric variability, is demonstrated, and the observational consequences of the trans-photospheric wave leakage previously mentioned are examined

The Ursinus Weekly, October 24, 1955

Editorial: Size of our classes • Alpha Phi Omega outlines its plans and describes its organization • Hottenstein directs Band into 1955-56 school year • Dr. Tait to speak to pre-med group on medicine • Curtain Club plans group productions • Madwoman of Chaillot is chosen as UC\u27s Fall play • YM-YW retreats this weekend to Camp Onas • Spirit Committee reviews activities • Joint commission with Y rejected • Letter to the editor • View at the type of student which Ursinus produces • Quoth the raven • Varied techniques of study used by Ursinus students • Which tree are you in the forest? • Is psychology used in United States relations? • William Yost selected as head basketball coach • Bruins split two close soccer tilts • One-day vacation evades Bears as Criswell leads Garnet in 7-0 upset • Experienced Belles to face rugged West Chester team • Intramural volleyball program begins for girls • I.R.C. questions Alaskan statehood • Sorority row • Chi Alpha hears Mr. Creager speak • Fraternity rowhttps://digitalcommons.ursinus.edu/weekly/1435/thumbnail.jp