33 research outputs found
The Shocking Properties of Supersonic Flows: Dependence of the Thermal Overstability on M, alpha, and T_c/T_0
We investigate the Mach number dependence of the radiative overstability of
shocks. We find that the stability of radiative shocks increases with
decreasing Mach number, with the result that M=2 shocks require cooling
exponents < -1.2 to be overstable. The frequency of oscillation of the
fundamental mode has a strong Mach number dependence. We find that feedback
between the cooling region and the cold dense layer (CDL) further downstream is
a function of Mach number, with stronger feedback and oscillation of the
boundary between the CDL and the cooling region occuring at lower Mach numbers.
This feedback can be quantified in terms of the reflection coefficient of sound
waves. An interesting finding is that the stability properties of low Mach
number shocks can be dramatically altered if the shocked gas is able to cool to
temperatures less than the pre-shock value, and it is probable that low Mach
number astrophysical shocks will be overstable in a variety of situations. The
results of this work are relevant to astrophysical shocks with low Mach
numbers, such as supernova remnants (SNRs) immersed in a hot interstellar
medium (e.g., within a starburst region), and shocks in molecular clouds, where
time-dependent chemistry can lead to overstability. (Abridged)Comment: 12 pages, 12 figures, accepted by A&
The Campbells: lordship, literature and liminality
The Campbells have the potential to offer much to the theme of literature and borders, given that the kindredâs astonishing political success in the late medieval and early modern period depended heavily upon the ability to negotiate multiple frontiers: between Highlands and Lowlands; between Gaelic Scotland and Ireland, and, especially after the Reformation, with England and the matter of Britain. This paper will explore the literary dimension to Campbell expansionism, from the Book of the Dean of Lismore in the earlier sixteenth century, to poetry addressed to dukes of Argyll in the earlier eighteenth century. Particular attention will be paid to the literary proclivities of the household of the Campbells of Glenorchy on either side of what appears to be a major watershed in 1550; and to the agenda of the Campbell protĂ©gĂ© John Carswell, first post-Reformation bishop of the Isles, and author of the first printed book in Gaelic in either Scotland or Ireland, Foirm na n-Urrnuidheadh (âThe Form of Prayersâ), published at Edinburgh in 1567
Interactive effects of cycloheximide and puromycin in altering brain polyribosomes and neural and behavioral responses to electroshock in mice.
A comparison of reaction rate calculations using ENDF/B-VII with critical assembly measurements
We present critical assembly reaction rate data, and modeling of the same using the recently released ENDF/B-VII library. While some of the experimental measurements were performed as long as 50 years ago, the results have not been widely used/available outside of Los Alamos. Over the years, a variety of target foils were fabricated and placed in differing neutron spectrum/fluence environments within critical assemblies. Neutron-induced reactions such as (n,Îł), (n,2n), and (n,f) on these targets were measured, typically referenced to 235U(n,f) or 239Pu(n,f). Because the cross section for the latter reactions are now well known, these experiments provide a rich data set for testing evaluated cross sections. Due to the large variety of critical assemblies that were historically available at Los Alamos, it was possible to make measurements in spectral environments ranging from hard (Pu Jezebel, center of Pu Flattop) through intermediate (Big Ten) to degraded (reflector region of Flattop). This broad range of configurations allows us to test both the cross section magnitudes and their energy dependencies. We will present data, along with reaction rate predictions using primarily MCNP5 in conjunction with ENDF/B-VII, for a number of target nuclei, including iridium, isotopes of uranium (e.g., 233, 235, 237, 238), neptunium (237), plutonium (239), and americium (241)