776 research outputs found
A Semi-parametric Analysis of Technology, with an Application to U.S. Dairy Farms
This article proposes a semi-parametric stochastic frontier model (SPSF) in which components of the technology and of technical efficiency are represented using semi-parametric methods and estimated in a Bayesian framework. The approach is illustrated in an application to US farm data. The analysis shows important scale economies for small and medium herds and constant return to scale for larger herds. With the exception of labor, estimates of marginal products were close to the value expected under profit maximization. Finally, the results suggest important opportunities to increase productivity through reductions in technical inefficiencies.
Moving Towards Intercultural Communicative Competence and Intercultural Citizenship: Lessons from Second Language Acquisition and Language Pedagogy for the Communication Center
Studies show English language learners (ELLs) experience increased communication apprehension and foreign language anxiety more than primary English speakers. Strategies to better assist ELLs with their public speaking skills are needed, especially within communication centers. One way is to better understand the intercultural aspects of the ELL student population on specific university campuses. Using foreign language pedagogy, this article explores best practices for communication center tutors working with ELL clients. Communication centers can use this information to assess traditional tutoring models and examine how their center meets the needs of this student population. The authors argue for an organizational structure of support and inclusivity, which may be achieved with a stronger emphasis on intercultural competency, including ways to address proficiency levels and practice cultural empathy. With proper support, communication consultants can achieve intercultural communicative competence and intercultural citizenship
Thoughts about disordered thinking: measuring and quantifying the laws of order and disorder
Peer ReviewedPostprint (author's final draft
Large-Scale Structure at z~2.5
We have made a statistically complete, unbiased survey of C IV systems toward
a region of high QSO density near the South Galactic Pole using 25 lines of
sight spanning . Such a survey makes an excellent probe of
large-scale structure at early epochs. We find evidence for structure on the
proper Mpc scale ( km Mpc) as
determined by the two point C IV - C IV absorber correlation function, and
reject the null hypothesis that C IV systems are distributed randomly on such
scales at the level. The structure likely reflects the
distance between two groups of absorbers subtending and Mpc at and respectively. There is also a marginal trend for the association of
high rest equivalent width C IV absorbers and QSOs at similar redshifts but
along different lines of sight. The total number of C IV systems detected is
consistent with that which would be expected based on a survey using many
widely separated lines of sight. Using the same data, we also find 11 Mg II
absorbers in a complete survey toward 24 lines of sight; there is no evidence
for Mg II - Mg II or Mg II - QSO clustering, though the sample size is likely
still small to detect such structure if it exists.Comment: 56 pages including 32 of figures, in gzip-ed uuencoded postscript
format, 1 long table not included, aastex4 package. Accepted for publication
in ApJ Supplement
What Determines the Depth of BALs? Keck HIRES Observations of BALQSO 1603+300
We find that the depth and shape of the broad absorption lines (BALs) in
BALQSO 1603+3002 are determined largely by the fraction of the emitting source
which is covered by the BAL flow. In addition, the observed depth of the BALs
is poorly correlated with their real optical depth. The implication of this
result is that abundance studies based on direct extraction of column densities
from the depth of the absorption troughs are unreliable. Our conclusion is
based on analysis of unblended absorption features of two lines from the same
ion (in this case the Si IV doublet), which allows unambiguous separation of
covering factor and optical depth effects. The complex morphology of the
covering factor as a function of velocity suggests that the BALs are produced
by several physically separated outflows. The covering factor is ion dependent
in both depth and velocity width. We also find evidence that in BALQSO
1603+3002 the flow does not cover the broad emission line region.Comment: 13 pages, 2 figures, accepted for publication in Ap
Physical and kinematical properties of the X-ray absorber in the broad absorption line quasar APM 08279+5255
We have re-analyzed the X-ray spectra of the gravitational lensed
high-redshift BAL QSO APM 08279+5255, observed with the XMM-Newton and Chandra
observatories. Previous studies (Hasinger et al. 2002; Chartas et al. 2002)
detected unusual, highly-ionized iron absorption features, but differed in
their interpretation of these features, regarding the kinematical and
ionization structure. We seek one physical model that can be successfully
applied to both observations. For the first time we have performed detailed
photoionization modeling on the X-ray spectrum of APM 08279+5255. The absorbing
gas in APM 08279+5255 can be represented by a two-absorbers model with column
densities N_H(1)~7x10^{22} cm^-2, N_H(2)~6x10^{22} cm^-2, and ionization
parameters logxi(1)~1.5 and logxi(2)~3, with one of them (the high-ionization
component) outflowing at v~0.18(\pm 0.01)c, carrying large amount of gas out of
the system. We find that the Chandra spectrum of APM 08279+5255 requires the
same Fe/O ratio overabundance (previously) indicated by the XMM-Newton
observation, showing that both absorber components underwent similar chemical
evolution and/or have similar origin.Comment: 12 pages, 7 figures, accepted by A&A at the 13th of June, 200
Probing Broad Absorption Line Quasar Outflows: X-ray Insights
Energetic outflows appear to occur in conjunction with active mass accretion
onto supermassive black holes. These outflows are most readily observed in the
approximately 10% of quasars with broad absorption lines, where the observer's
line of sight passes through the wind. Until fairly recently, the paucity of
X-ray data from these objects was notable, but now sensitive hard-band missions
such as Chandra and XMM-Newton are routinely detecting broad absorption line
quasars. The X-ray regime offers qualitatively new information for the
understanding of these objects, and these new results must be taken into
account in theoretical modeling of quasar winds.Comment: Submitted to Advances in Space Research for New X-ray Results from
Clusters of Galaxies and Black Holes (Oct 2002; Houston, TX), eds. C. Done,
E.M. Puchnarewicz, M.J. Ward. Requires cospar.sty (6 pgs, 5 figs
A new constraint on cosmological variability of the proton-to-electron mass ratio
Exotic cosmologies predict variability of the fundamental physical constants
over the cosmic time. Using the VLT/UVES high resolution spectra of the quasar
Q0347-3819 and unblended electronic - vibrational - rotational lines of the H2
molecule identified at z = 3.025 we test possible changes in the proton - to -
electron mass ratio mu_0 = m_p/m_e over the period of 11 Gyr. We obtained a new
constraint on the time - averaged variation rate of mu_0 of |d mu /d t /mu_0| <
5 10^{-15} yr^{-1} (1 sigma c.l.). The estimated 1 sigma uncertainty interval
of the |Delta mu/mu_0| ratio of about 0.004% implies that since the time when
the H2 spectrum was formed at z = 3.025, mu_0 has not changed by more than a
few thousands of a percent.Comment: 5 pages, 3 figures, a revised version accepted by MNRA
Microlensing induced spectral variability in Q2237+0305
We present both photometry and spectra of the individual images of the
quadruple gravitational lens system Q2237+0305. Comparison of spectra obtained
at two epochs, separated by years, shows evidence for significant
changes in the emission line to continuum ratio of the strong ultraviolet
CIV~1549, CIII]~1909 and MgII~2798 lines. The short,
day, light--travel time differences between the sight lines to the
four individual quasar images rule out any explanation based on intrinsic
variability of the source. The spectroscopic differences thus represent direct
detection of microlensing--induced spectroscopic differences in a quasar. The
observations allow constraints to be placed on the relative spatial scales in
the nucleus of the quasar, with the ultra--violet continuum arising in a region
of \la~0.05~{\rm pc} in extent, while the broad emission line material is
distributed on scales much greater than this.Comment: Accepted for Publication in MNRAS. Paper with 11 figure
Effects of the Spin-Orbit and Tensor Interactions on the and Excitations in Light Nuclei
The effects of varying the spin-orbit and tensor components of a realistic
interaction on excitation rates and are studied on nuclei in the
and shells. Not only the total but also the spin and orbital
parts separately are studied. The single-particle energies are first calculated
with the same interaction that is used between the valence nucleons. Later this
stringent condition is relaxed somewhat and the level is raised relative
to . For nuclei up to , much better results i.e stronger
rates are obtained by increasing the strength of the spin-orbit interaction
relative to the free value. This is probably also true for , but
presents some difficulties. The effects of weakening the tensor
interaction are also studied. On a more subtle level, the optimum spin-orbit
interaction in the lower half of the shell, as far as excitations
are concerned, is substantially larger than the difference
in . A larger spin-orbit splitting
is also needed to destroy the triaxiality in . Also studied are how
much orbital and spin strength lies in an observable region and how much
is buried in the grass at higher energies. It is noted that for many nuclei the
sum is very close to , indicating
that the summed cross terms are very small.Comment: 39 pages, revtex 3.
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