16 research outputs found
Employment and Disability Policy: the role of the psychologist
Persons with minor or major disabilities represent a significant portion of the U.S. working-age population. Based on the 1993 Survey of Income and Program Participation (SIPP), approximately 30 million (19%) men and women 18 to 64 years of age report some type of physical or mental limitation. For approximately 55% of these individuals (about 10% of those 18 to 64), the limitations are severe
OB Stars & Stellar Bowshocks in Cygnus-X: A Novel Laboratory Estimating Stellar Mass Loss Rates
We use mid-IR images from the Spitzer Cygnus~X Legacy Survey to search for
stellar bowshocks, a signature of early type "runaway" stars with high space
velocities. We identify ten arc-shaped nebulae containing centrally located
stars as candidate bowshocks. New spectroscopic observations of five stars show
that all are late O to early B dwarfs. Our morphologically selected sample of
bowshock candidates encompasses diverse physical phenomena. Three of the stars
appear to be pre-main-sequence objects on the basis of rising SEDs in the
mid-IR, and their nebulae may be photon-dominated regions (PDRs). Four objects
have ambiguous classification. These may be partial dust shells or bubbles. We
conclude that three of the objects are probable bowshocks, based on their
morphological similarity to analytic prescriptions. Their nebular morphologies
reveal no systematic pattern of orientations that might indicate either a
population of stars ejected from or large-scale hydrodynamic outflows from Cyg
OB2. The fraction of runaways among OB stars near Cyg OB2 identified either by
radial velocity or bowshock techniques is ~0.5%, much smaller than the 8%
estimated among field OB stars. We also obtained a heliocentric radial velocity
for the previously known bowshock star, BD+43\degr3654, of -66.2+/-9.4 km/s,
solidifying its runaway status and implying a space velocity of 77+/-10 km/s.
We use the principles of momentum-driven bowshocks to arrive at a novel method
for estimating stellar mass loss rates. Derived mass loss rates range between
10^-7 and few x10^-6 solar masses/yr for the three O5V -- ~B2V stars identified
as generating bowshocks. These values are at the upper range of, but broadly
consistent with, estimates from other methods. (Abridged)Comment: 49 pages, 19 figures; Accepted for publication in ApJ;
full-resolution color figure version available at
http://physics.uwyo.edu/~chip/Papers/CygXBowshocks; comments invite
A Radial Velocity Survey of the Cygnus OB2 Association
We conducted a radial velocity survey of the Cygnus OB2 Association over a 6
year (1999 - 2005) time interval to search for massive close binaries. During
this time we obtained 1139 spectra on 146 OB stars to measure mean systemic
radial velocities and radial velocity variations. We spectroscopically identify
73 new OB stars for the first time, the majority of which are likely to be
Association members. Spectroscopic evidence is also presented for a B3Iae
classification and temperature class variation (B3 - B8) on the order of 1 year
for Cygnus OB2 No. 12. Calculations of the intial mass function with the
current spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars with
the most reliable data, 36 are probable and 9 are possible single-lined
spectroscopic binaries. We also identify 3 new and 8 candidate double-lined
spectroscopic binaries. These data imply a lower limit on the massive binary
fraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is
2.44 +/- km/s, which is typical of open clusters. No runaway OB stars were
found.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the
Astrophysical Journa
At-Risk Individuals, Behavioral Health, and Community Resilience: Preparedness and Response for Vulnerable Communities
Data from: Testing the Münch hypothesis of long distance phloem transport in plants
Long distance transport in plants occurs in sieve tubes of the phloem. The pressure flow hypothesis introduced by Ernst Münch in 1930 describes a mechanism of osmotically generated pressure differentials that are supposed to drive the movement of sugars and other solutes in the phloem, but this hypothesis has long faced major challenges. The key issue is whether the conductance of sieve tubes, including sieve plate pores, is sufficient to allow pressure flow. We show that with increasing distance between source and sink, sieve tube conductivity and turgor increases dramatically in Ipomoea nil. Our results provide strong support for the Münch hypothesis, while providing new tools for the investigation of one of the least understood plant tissues
Figure 3 - source data
phloem geometrical parameters for a large partially defoliated morning glory plan
Figure 5 - source data
phloem geometrical parameters for a large foliated morning glory plan
Figure 1 - source data.xlsx
phloem geometrical parameters for a medium sized foliated morning glory plan