14,127 research outputs found
Resolved shock structure of the Balmer-dominated filaments in Tycho's supernova remnant: Cosmic-ray precursor?
We report on the results from H{\alpha} imaging observations of the eastern
limb of Tycho's supernova remnant (SN1572) using the Wide Field Planetary
Camera 2 on the Hubble Space Telescope. We resolve the detailed structure of
the fast, collisionless shock wave into a delicate structure of nearly edge-on
filaments. We find a gradual increase of H{\alpha} intensity just ahead of the
shock front, which we interpret as emission from the thin (~1") shock
precursor. We find that a significant amount of the H{\alpha} emission comes
from the precursor and that this could affect the amount of temperature
equilibration derived from the observed flux ratio of the broad and narrow
H{\alpha} components. The observed H{\alpha} emission profiles are fit using
simple precursor models, and we discuss the relevant parameters. We suggest
that the precursor is likely due to cosmic rays and discuss the efficiency of
cosmic-ray acceleration at this position.Comment: Prepared with emulateapj.sty (5 pages, 4 figures). Published in ApJL
Constraints on the Heating of High Temperature Active Region Loops: Observations from Hinode and SDO
We present observations of high temperature emission in the core of a solar
active region using instruments on Hinode and SDO. These multi-instrument
observations allow us to determine the distribution of plasma temperatures and
follow the evolution of emission at different temperatures. We find that at the
apex of the high temperature loops the emission measure distribution is
strongly peaked near 4 MK and falls off sharply at both higher and lower
temperatures. Perhaps most significantly, the emission measure at 0.5 MK is
reduced by more than two orders of magnitude from the peak at 4 MK. We also
find that the temporal evolution in broad-band soft X-ray images is relatively
constant over about 6 hours of observing. Observations in the cooler SDO/AIA
bandpasses generally do not show cooling loops in the core of the active
region, consistent with the steady emission observed at high temperatures.
These observations suggest that the high temperature loops observed in the core
of an active region are close to equilibrium. We find that it is possible to
reproduce the relative intensities of high temperature emission lines with a
simple, high-frequency heating scenario where heating events occur on time
scales much less than a cooling time. In contrast, low-frequency heating
scenarios, which are commonly invoked to describe nanoflare models of coronal
heating, do not reproduce the relative intensities of high temperature emission
lines and predict low-temperature emission that is approximately an order of
magnitude too large. We also present an initial look at images from the SDO/AIA
94 A channel, which is sensitive to Fe XVIII.Comment: Movies are available at
http://tcrb.nrl.navy.mil/~hwarren/temp/papers/active_region_core/ Paper has
been refereed and revise
Lease vs. Purchase of Machinery
Leasing or purchasing of machinery and equipment represent alternative ways for farm operators to acquire assets for agricultural production. Leasing has increased in popularity with agricultural producers. Manufacturers and financial institutions view leasing and selling equipment as alternative means to generate business. By comparing the net present value of the after-tax costs, farmers can determine the least expensive way to acquire machinery or other assets in the farmer’s specific situation. Key factors in the lease vs. purchase decision are the interest rate on loans, lease payments, the taxpayer’s marginal tax rate, and the taxpayer’s after-tax discount rate that reflects the time value of money. An important factor in this decision process is the acquisition of new technology and how rapidly that technology may become obsolete or of it is needed for a specific length of time.https://digitalcommons.usu.edu/rural_tax/1018/thumbnail.jp
Global logistics indicators, supply chain metrics, and bilateral trade patterns
Past research into the determinants of international trade highlighted the importance of the basic spatial gravity model augmented by additional variables representing sources of friction. Studies modeled many sources of friction using various proxies, including indices based on expert judgment in some cases. This paper focuses on logistics friction and draws on a data set recently compiled by the World Bank with specific quantitative metrics of logistics performance interms of time, cost, and variability in time. It finds that the new variables that relate directly to logistics performance have a statistically significant relationship with the level of bilateral trade. It also finds that a single logistics index can capture virtually all of the explanatory power of multiple logistics indicators. The findings should spur public and private agencies that have direct or indirect power over logistics performance to focus attention on reducing sources of friction so as to improve their country's ability to compete in today's global economy. Moreover, since the logistics metrics are directly related to operational performance, countries can use these metrics to target actions to improve logistics and monitor their progress.Common Carriers Industry,Transport and Trade Logistics,Economic Theory&Research,Free Trade,Trade Policy
- …