120 research outputs found
Use of a post-production fractionation process improves the nutritional value of wheat distillers grains with solubles for young broiler chicks
BACKGROUND: Post-production fractionation of wheat distillers grains with solubles (DDGS) increases their crude protein content and reduces their fiber content. This experiment was conducted to determine the effects of fractionation of wheat DDGS on apparent total tract digestibility (ATTD) and performance when fed to broiler chicks (0–21 d). METHODS: A total of 150, day-old, male broiler chicks (Ross-308 line; Lilydale Hatchery, Wynyard, Saskatchewan) weighing an average of 49.6 ± 0.8 g were assigned to one of five dietary treatments in a completely randomized design. The control diet was based on wheat and soybean meal and contained 20% regular wheat DDGS. The experimental diets contained 5, 10, 15 or 20% fractionated wheat DDGS added at the expense of regular wheat DDGS. RESULTS: The ATTD of dry matter and gross energy were linearly increased (P < 0.01) as the level of fractionated wheat DDGS in the diet increased. Nitrogen retention was unaffected by level of fractionated wheat DDGS (P > 0.05). Weight gain increased linearly (P = 0.05) as the level of fractionated wheat DDGS in the diet increased. Feed intake, feed conversion and mortality were unaffected by level of fractionated wheat DDGS in the diet (P > 0.05). CONCLUSIONS: Post-production fractionation of wheat DDGS improves their nutritional value by lowering their fiber content and increasing their content of crude protein and energy. These changes in chemical composition supported increased weight gain of broilers fed wheat DDGS
Looking ahead: forecasting and planning for the longer-range future, April 1, 2, and 3, 2005
This repository item contains a single issue of the Pardee Conference Series, a publication series that began publishing in 2006 by the Boston University Frederick S. Pardee Center for the Study of the Longer-Range Future. This was the Center's spring Conference that took place during April 1, 2, and 3, 2005.The conference allowed for many highly esteemed scholars and professionals from a broad range of fields to come together to discuss strategies designed for the 21st century and beyond. The speakers and discussants covered a broad range of subjects including: long-term policy analysis, forecasting for business and investment, the National Intelligence Council Global Trends 2020 report, Europe’s transition from the Marshal plan to the EU, forecasting global transitions, foreign policy planning, and forecasting for defense
How Do Disks Survive Mergers?
We develop a physical model for how galactic disks survive and/or are
destroyed in interactions. Based on dynamical arguments, we show gas primarily
loses angular momentum to internal torques in a merger. Gas within some
characteristic radius (a function of the orbital parameters, mass ratio, and
gas fraction of the merging galaxies), will quickly lose angular momentum to
the stars sharing the perturbed disk, fall to the center and be consumed in a
starburst. A similar analysis predicts where violent relaxation of the stellar
disks is efficient. Our model allows us to predict the stellar and gas content
that will survive to re-form a disk in the remnant, versus being violently
relaxed or contributing to a starburst. We test this in hydrodynamic
simulations and find good agreement as a function of mass ratio, orbital
parameters, and gas fraction, in simulations spanning a wide range in these
properties and others, including different prescriptions for gas physics and
feedback. In an immediate sense, the amount of disk that re-forms can be
understood in terms of well-understood gravitational physics, independent of
details of ISM gas physics or feedback. This allows us to explicitly quantify
the requirements for such feedback to (indirectly) enable disk survival, by
changing the pre-merger gas content and distribution. The efficiency of disk
destruction is a strong function of gas content: we show how and why
sufficiently gas-rich major mergers can, under general conditions, yield
systems with small bulges (B/T<0.2). We provide prescriptions for inclusion of
our results in semi-analytic models.Comment: 32 pages, 16 figures, accepted to ApJ (minor revisions to match
accepted version
The Structure of the Interstellar Medium of Star Forming Galaxies
We present numerical methods for including stellar feedback in galaxy-scale
simulations. We include heating by SNe (I & II), gas recycling and
shock-heating from O-star & AGB winds, HII photoionization, and radiation
pressure from stellar photons. The energetics and time-dependence are taken
directly from stellar evolution models. We implement these in simulations with
pc-scale resolution, modeling galaxies from SMC-like dwarfs and MW analogues to
massive z~2 starburst disks. Absent feedback, gas cools and collapses without
limit. With feedback, the ISM reaches a multi-phase steady state in which GMCs
continuously form, disperse, and re-form. Our primary results include: (1) Star
forming galaxies generically self-regulate at Toomre Q~1. Most of the volume is
in diffuse hot gas with most of the mass in dense GMC complexes. The phase
structure and gas mass at high densities are much more sensitive probes of
stellar feedback physics than integrated quantities (Toomre Q or gas velocity
dispersion). (2) Different feedback mechanisms act on different scales:
radiation & HII pressure are critical to prevent runaway collapse of dense gas
in GMCs. SNe and stellar winds dominate the dynamics of volume-filling hot gas;
however this primarily vents out of the disk. (3) The galaxy-averaged SFR is
determined by feedback. For given feedback efficiency, restricting star
formation to molecular gas or modifying the cooling function has little effect;
but changing feedback mechanisms directly translates to shifts off the
Kennicutt-Schmidt relation. (4) Self-gravity leads to marginally-bound GMCs
with an ~M^-2 mass function with a cutoff at the Jeans mass; they live a few
dynamical times before being disrupted by stellar feedback and turn ~1-10% of
their mass into stars (increasing from dwarfs through starburst galaxies).
Low-mass GMCs are preferentially unbound.Comment: 34 pages, 24 figures, accepted to MNRAS (matches accepted version).
Movies of the simulations are available at
https://www.cfa.harvard.edu/~phopkins/Site/Movies_sbw.htm
The Effects of Gas on Morphological Transformation in Mergers: Implications for Bulge and Disk Demographics
Transformation of disks into spheroids via mergers is a well-accepted element
of galaxy formation models. However, recent simulations have shown that bulge
formation is suppressed in increasingly gas-rich mergers. We investigate the
global implications of these results in a cosmological framework, using
independent approaches: empirical halo-occupation models (where galaxies are
populated in halos according to observations) and semi-analytic models. In
both, ignoring the effects of gas in mergers leads to the over-production of
spheroids: low and intermediate-mass galaxies are predicted to be
bulge-dominated (B/T~0.5 at <10^10 M_sun), with almost no bulgeless systems),
even if they have avoided major mergers. Including the different physical
behavior of gas in mergers immediately leads to a dramatic change: bulge
formation is suppressed in low-mass galaxies, observed to be gas-rich (giving
B/T~0.1 at <10^10 M_sun, with a number of bulgeless galaxies in good agreement
with observations). Simulations and analytic models which neglect the
similarity-breaking behavior of gas have difficulty reproducing the strong
observed morphology-mass relation. However, the observed dependence of gas
fractions on mass, combined with suppression of bulge formation in gas-rich
mergers, naturally leads to the observed trends. Discrepancies between
observations and models that ignore the role of gas increase with redshift; in
models that treat gas properly, galaxies are predicted to be less
bulge-dominated at high redshifts, in agreement with the observations. We
discuss implications for the global bulge mass density and future observational
tests.Comment: 14 pages, 11 figures, accepted to MNRAS (matched published version).
A routine to return the galaxy merger rates discussed here is available at
http://www.cfa.harvard.edu/~phopkins/Site/mergercalc.htm
Complete Pseudohole and Heavy-Pseudoparticle Operator Representation for the Hubbard Chain
We introduce the pseudohole and heavy-pseudoparticle operator algebra that
generates all Hubbard-chain eigenstates from a single reference vacuum. In
addition to the pseudoholes already introduced for the description of the
low-energy physics, this involves the heavy pseudoparticles associated with
Hamiltonian eigenstates whose energy spectrum has a gap relatively to the
many-electron ground state. We introduce a generalized pseudoparticle
perturbation theory which describes the relevant finite-energy ground state
transitions. In the present basis these excitations refer to a small density of
excited pseudoparticles. Our operator basis goes beyond the Bethe-ansatz
solution and it is the suitable and correct starting point for the study of the
finite-frequency properties, which are of great relevance for the understanding
of the unusual spectral properties detected in low-dimensional novel materials.Comment: LaTeX, 32 pages, no Figures. To be published in Phys. Rev. B (15th of
August 1997
Stellar Feedback in Galaxies and the Origin of Galaxy-scale Winds
Feedback from massive stars is believed to play a critical role in driving
galactic super-winds that enrich the IGM and shape the galaxy mass function and
mass-metallicity relation. In previous papers, we introduced new numerical
methods for implementing stellar feedback on sub-GMC through galactic scales in
galaxy simulations. This includes radiation pressure (UV through IR), SNe
(Type-I & II), stellar winds ('fast' O-star through 'slow' AGB winds), and HII
photoionization. Here, we show that these feedback mechanisms drive galactic
winds with outflow rates as high as ~10-20 times the galaxy SFR. The
mass-loading efficiency (wind mass loss rate divided by SFR) scales inversely
with circular velocity, consistent with momentum-conservation expectations. We
study the contributions of each feedback mechanism to galactic winds in a range
of galaxy models, from SMC-like dwarfs & MW-analogues to z~2 clumpy disks. In
massive, gas-rich systems (local starbursts and high-z galaxies), radiation
pressure dominates the wind generation. For MW-like spirals and dwarf galaxies
the gas densities are much lower, and shock-heated gas from SNe and stellar
winds dominates production of large-scale outflows. In all models, however,
winds have a multi-phase structure that depends on interactions between
multiple feedback mechanisms operating on different spatial & time scales: any
single mechanism fails to reproduce the winds observed. We provide fitting
functions for wind mass-loading and velocities as a function of galaxy
properties, for use in cosmological simulations and semi-analytic models. These
differ from typically-adopted formulae with explicit dependence on gas surface
density that can be very important in both low-density dwarf galaxies and
high-density gas-rich galaxies.Comment: 16 pages, 11 figures, accepted to MNRAS (matches accepted version).
Movies of the simulations are available at
https://www.cfa.harvard.edu/~phopkins/Site/Movies_sbw.htm
HDL-transferred microRNA-223 regulates ICAM-1 expression in endothelial cells
High-density lipoproteins (HDL) have many biological functions, including reducing endothelial activation and adhesion molecule expression. We recently reported that HDL transport and deliver functional microRNAs (miRNA). Here we show that HDL suppresses expression of intercellular adhesion molecule 1 (ICAM-1) through the transfer of miR-223 to endothelial cells. After incubation of endothelial cells with HDL, mature miR-223 levels are significantly increased in endothelial cells and decreased on HDL. However, miR-223 is not transcribed in endothelial cells and is not increased in cells treated with HDL from miR-223−/− mice. HDL inhibit ICAM-1 protein levels, but not in cells pretreated with miR-223 inhibitors. ICAM-1 is a direct target of HDL-transferred miR-223 and this is the first example of an extracellular miRNA regulating gene expression in cells where it is not transcribed. Collectively, we demonstrate that HDL’s anti-inflammatory properties are conferred, in part, through HDL-miR-223 delivery and translational repression of ICAM-1 in endothelial cells
Self-Regulated Star Formation in Galaxies via Momentum Input from Massive Stars
Feedback from massive stars is believed to play a critical role in shaping
the galaxy mass function, the structure of the interstellar medium (ISM), and
the low efficiency of star formation, but the exact form of the feedback is
uncertain. In this paper, the first in a series, we present and test a novel
numerical implementation of stellar feedback resulting from momentum imparted
to the ISM by radiation, supernovae, and stellar winds. We employ a realistic
cooling function, and find that a large fraction of the gas cools to <100K, so
that the ISM becomes highly inhomogeneous. Despite this, our simulated galaxies
reach an approximate steady state, in which gas gravitationally collapses to
form giant molecular clouds (GMCs), dense clumps, and stars; subsequently,
stellar feedback disperses the GMCs, repopulating the diffuse ISM. This
collapse and dispersal cycle is seen in models of SMC-like dwarfs, the
Milky-Way, and z~2 clumpy disk analogues. The simulated global star formation
efficiencies are consistent with the observed Kennicutt-Schmidt relation.
Moreover, the star formation rates are nearly independent of the numerically
imposed high-density star formation efficiency, density threshold, and density
scaling. This is a consequence of the fact that, in our simulations, star
formation is regulated by stellar feedback limiting the amount of very dense
gas available for forming stars. In contrast, in simulations without stellar
feedback, i.e. under the action of only gravity and gravitationally-induced
turbulence, the ISM experiences runaway collapse to very high densities. In
these simulations without feedback, the global star formation rates exceed
observed galactic star formation rates by 1-2 orders of magnitude,
demonstrating that stellar feedback is crucial to the regulation of star
formation in galaxies.Comment: 24 pages, 13 figures, accepted to MNRAS (significantly expanded to
match accepted version). Movies of the simulations here can be found at
https://www.cfa.harvard.edu/~phopkins/Site/Movies_sbw.htm
Epidemiologic Responses to Anthrax Outbreaks: A Review of Field Investigations, 1950–2001
We used unpublished reports, published manuscripts, and communication with investigators to identify and summarize 49 anthrax-related epidemiologic field investigations conducted by the Centers for Disease Control and Prevention from 1950 to August 2001. Of 41 investigations in which Bacillus anthracis caused human or animal disease, 24 were in agricultural settings, 11 in textile mills, and 6 in other settings. Among the other investigations, two focused on building decontamination, one was a response to bioterrorism threats, and five involved other causes. Knowledge gained in these investigations helped guide the public health response to the October 2001 intentional release of B. anthracis, especially by addressing the management of anthrax threats, prevention of occupational anthrax, use of antibiotic prophylaxis in exposed persons, use of vaccination, spread of B. anthracis spores in aerosols, clinical diagnostic and laboratory confirmation methods, techniques for environmental sampling of exposed surfaces, and methods for decontaminating buildings
- …