81,266 research outputs found
Molecular Gas and Star Formation in the SAURON Early-type Galaxies
We present the results of a survey of CO emission in 43 of the 48
representative E/S0 galaxies observed in the optical with the SAURON
integral-field spectrograph. The CO detection rate is 12/43 or 28%. This is
lower than previous studies of early-types but can probably be attributed to
different sample selection criteria. As expected, earlier type, more luminous
and massive galaxies have a relatively lower molecular gas content. We find
that CO-rich galaxies tend to have higher H\beta but lower Fe5015 and Mgb
absorption indices than CO-poor galaxies. Those trends appear primarily driven
by the age of the stars, an hypothesis supported by the fact that the galaxies
with the strongest evidence of star formation are also the most CO-rich. In
fact, the early-type galaxies from the current sample appear to extend the
well-known correlations between FIR luminosity, dust mass and molecular mass of
other galaxy types. The star formation interpretation is also consistent with
the SAURON galaxies' radio continuum and FIR flux ratios, and their inferred
star formation efficiencies are similar to those in spiral galaxies. It thus
appears that we have identified the material fueling (residual) star formation
in early-type galaxies, and have demonstrated that it is actively being
transformed. Nevertheless, the lack of strong correlations between the CO
content and most stellar parameters is compatible with the idea that, in a
significant number of sample galaxies, the molecular gas has been accreted from
the outside and has properties rather independent from the old, pre-existing
stellar component.Comment: 14 pages, 9 figures, accepted in MNRA
ENVIRONMENTAL AND ECONOMIC IMPACTS OF AGRICULTURAL POLICY REFORM: AN INTERREGIONAL COMPARISON
Mathematical programming results revealed that moving toward more flexible agricultural policies would generate substantial economic and environmental gains in a North Carolina diversified cropping region. But in a Washington-Idaho dryland grains region, only the use of relatively new and sometimes problematic alternative cropping systems permitted environmental and economic gains under policy reform. In both regions, a recoupling policy, which links government payments to resource-conserving farming practices, was needed to protect environmental quality when market prices for program crops were high.Agrichemical leaching, Agricultural policy, Alternative agriculture, Erosion, Mathematical programming, Agricultural and Food Policy,
AN OPERATIONAL APPROACH FOR EVALUATING INVESTMENT RISK: AN APPLICATION TO THE NO-TILL TRANSITION
Roy’s safety-first rule is used to provide measures popular with farmers of short and long term business risk associated with various no-till transition strategies over an investment horizon. The short run rule provided more sensitivity to inter-year financial risk than other commonly used criteria. Results revealed that speed of adoption influenced the probability of successful transition more than did the sequence of drill acquisition methods. Higher equity and larger farms had a greater chance of transition success. Slow acreage expansion with a custom or rental drill reduces risk until a no-till yield penalty is eliminated.Investment risk, Monte Carlo simulation, no-till, rent- purchase, risk, safety-first, technology adoption, transition strategy
Experimental study of an independently deflected wingtip mounted on a semispan wing
The results of a subsonic wind tunnel test of a semispan wing with an independently deflected tip surface are presented and analyzed. The tip surface was deflected about the quarter chord of the rectangular wing and accounted for 17 percent of the wing semispan. The test was conducted to measure the loads on the tip surface and to investigate the nature of aerodynamic interference effects between the wing and the deflected tip. Results are presented for two swept tip surfaces of similar planform but different airfoil distributions. The report contains plots of tip lift, drag, and pitching moment for various Reynolds numbers and tip deflection angles with respect to the inboard wing. Oil flow visualization photographs for a typical Reynolds number are also included. Important aerodynamic parameters such as lift and pitching moment slopes and tip aerodynamic center location are tabulated. A discussion is presented on the relationship between tip experimental data acquired in a steady flow and the prediction of unsteady tip motion at fixed wing angles of attack
An algorithm for a general class of routing problems derived from Huygens' principle
If a set of N points or nodes with a nonnegative cost associated with each ordered pair is known, it is desired to find a path from one given node to another given node which minimizes the cost sum. An algorithm is presented which yields a global minimum solution after at most N - 1 iterations or on a typical large third-generation computer, after 1 hour of computation time for a 10,000-node problem. The rapid-access data storage capacity demanded by the algorithm is approximately 3N words for costs read in from slow-access storage or 2N words for calculable costs. The time-storage requirements of the algorithm known to the authors. When the problem is viewed as a discretized optimal control problem, after N-1 iterations, an optimal control or node transition is established for each of the N nodes or states; thus, the algorithm can be applied to situations were there may be errors in the control that necessitate a closed loop control that necessitate a closed loop control philosophy
Dynamics of merging: Post-merger mixing and relaxation of an Illustris galaxy
During the merger of two galaxies, the resulting system undergoes violent
relaxation and seeks stable equilibrium. However, the details of this evolution
are not fully understood. Using Illustris simulation, we probe two physically
related processes, mixing and relaxation. Though the two are driven by the same
dynamics---global time-varying potential for the energy, and torques caused by
asymmetries for angular momentum---we measure them differently. We define
mixing as the redistribution of energy and angular momentum between particles
of the two merging galaxies. We assess the degree of mixing as the difference
between the shapes of their N(E)s, and their N(L^2)s. We find that the
difference is decreasing with time, indicating mixing. To measure relaxation,
we compare N(E) of the newly merged system to N(E) of a theoretical prediction
for relaxed collisionless systems, DARKexp, and witness the system becoming
more relaxed, in the sense that N(E) approaches DARKexp N(E). Because the
dynamics driving mixing and relaxation are the same, the timescale is similar
for both. We measure two sequential timescales: a rapid, 1 Gyr phase after the
initial merger, during which the difference in N(E) of the two merging halos
decreases by ~80%, followed by a slow phase, when the difference decreases by
~50% over ~8.5 Gyrs. This is a direct measurement of the relaxation timescale.
Our work also draws attention to the fact that when a galaxy has reached Jeans
equilibrium it may not yet have reached a fully relaxed state given by DARKexp,
in that it retains information about its past history. This manifests itself
most strongly in stars being centrally concentrated. We argue that it is
particularly difficult for stars, and other tightly bound particles, to mix
because they have less time to be influenced by the fluctuating potential, even
across multiple merger events.Comment: accepted for publication in JCA
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