3,244 research outputs found
Degenerate mixing of plasma waves on cold, magnetized single-species plasmas
In the cold-fluid dispersion relation ω = ω_p/[1+(k_⊥/k_z)^(2]1/2) for Trivelpiece-Gould waves on an infinitely long magnetized plasma cylinder, the transverse and axial wavenumbers appear only in the combination k_⊥/k_z. As a result, for any frequency ω<ω_p, there are infinitely many degenerate waves, all having the same value of k_⊥/k_z. On a cold finite-length plasma column, these degenerate waves reflect into one another at the ends; thus, each standing-wave normal mode of the bounded plasma is a mixture of many degenerate waves, not a single standing wave as is often assumed. A striking feature of the many-wave modes is that the short-wavelength waves often add constructively along resonance cones given by dz/dr = ±(ω_p^2/ω^2-1)^(1/2). Also, the presence of short wavelengths in the admixture for a predominantly long-wavelength mode enhances the viscous damping beyond what the single-wave approximation would predict. Here, numerical solutions are obtained for modes of a cylindrical plasma column with rounded ends. Exploiting the fact that the modes of a spheroidal plasma are known analytically (the Dubin modes), a perturbation analysis is used to investigate the mixing of low-order, nearly degenerate Dubin modes caused by small deformations of a plasma spheroid
Murine cytomegalovirus genomic material in marrow cells; relation to altered leukocyte counts during sublethal infection of mice
A search for Low Surface Brightness galaxies in the near-infrared I. Selection of the sample
A sample of about 3,800 Low Surface Brightness (LSB) galaxies was selected
using the all-sky near-infrared (J, H and K_s-band) 2MASS survey. The selected
objects have a mean central surface brightness within a 5 arcsec radius around
their centre fainter than 18 mag/sq.arcsec in the K_s band, making them the
lowest surface brightness galaxies detected by 2MASS. A description is given of
the relevant properties of the 2MASS survey and the LSB galaxy selection
procedure, as well as of basic photometric properties of the selected objects.
The latter properties are compared to those of other samples of galaxies, of
both LSBs and `classical' high surface brightness (HSB) objects, which were
selected in the optical. The 2MASS LSBs have a (B_T_c)-(K_T) colour which is on
average 0.9 mag bluer than that of HSBs from the NGC. The 2MASS sample does not
appear to contain a significant population of red objects.Comment: accepted for publication in Astronomy and Astrophysics on 24/2/2003;
62 page
Phase transition in the collisionless regime for wave-particle interaction
Gibbs statistical mechanics is derived for the Hamiltonian system coupling
self-consistently a wave to N particles. This identifies Landau damping with a
regime where a second order phase transition occurs. For nonequilibrium initial
data with warm particles, a critical initial wave intensity is found: above it,
thermodynamics predicts a finite wave amplitude in the limit of infinite N;
below it, the equilibrium amplitude vanishes. Simulations support these
predictions providing new insight on the long-time nonlinear fate of the wave
due to Landau damping in plasmas.Comment: 12 pages (RevTeX), 2 figures (PostScript
The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies
Although numerous simulations have been done to understand the effects of
intense bursts of star formation on high surface brightness galaxies, few
attempts have been made to understand how localized starbursts would affect
both the color and surface brightness of low surface brightness (LSB) galaxies.
To remedy this, we have run 53 simulations involving bursts of star formation
activity on LSB galaxies, varying both the underlying galaxy properties and the
parameters describing the starbursts. We discovered that although changing the
total color of a galaxy was fairly straightforward, it was virtually impossible
to alter a galaxy's central surface brightness and thereby remove it from the
LSB galaxy classification without placing a high (and fairly artificial)
threshold for the underlying gas density. The primary effect of large amounts
of induced star formation was to produce a centralized core (bulge) component
which is generally not observed in LSB galaxies. The noisy morphological
appearance of LSB galaxies as well as their noisy surface brightness profiles
can be reproduced by considering small bursts of star formation that are
localized within the disk. The trigger mechanism for such bursts is likely
distant/weak tidal encounters. The stability of disk central surface brightness
to these periods of star formation argues that the large space density of LSB
galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available
on http://guernsey.uoregon.edu/~kare
Family Caregiving Challenges in Advanced Colorectal Cancer: Patient and Caregiver Perspectives
Purpose
Family caregivers of advanced colorectal cancer patients may be at increased risk for psychological distress. Yet their key challenges in coping with the patient’s illness are not well understood. Soliciting both patient and caregiver perspectives on these challenges would broaden our understanding of the caregiving experience. Thus, the purpose of this research was to identify caregivers’ key challenges in coping with their family member’s advanced colorectal cancer from the perspective of patients and caregivers.
Methods
Individual, semi-structured qualitative interviews were conducted with 23 advanced colorectal cancer patients and 23 primary family caregivers. Interview data were analyzed via thematic analysis.
Results
In nearly all cases, patient and caregiver reports of the caregiver’s key challenge were discrepant. Across patient and caregiver reports, caregivers’ key challenges included processing emotions surrounding the patient’s initial diagnosis or recurrence and addressing the patient’s practical and emotional needs. Other challenges included coping with continual uncertainty regarding the patient’s potential functional decline and prognosis and observing the patient suffer from various physical symptoms.
Conclusions
Findings suggest that eliciting the perspectives of both patients and caregivers regarding caregivers’ challenges provides a more comprehensive understanding of their experience. Results also point to the need to assist caregivers with the emotional and practical aspects of caregiving
Positive changes among patients with advanced colorectal cancer and their family caregivers: a qualitative analysis
OBJECTIVE:
This study assessed positive changes in patients with advanced colorectal cancer and their family caregivers following diagnosis. We compared self-reported positive changes within patient-caregiver dyads as well as self-reports and patient reports of positive changes in caregivers.
DESIGN:
Individual, semi-structured qualitative interviews were conducted with 23 patients with advanced colorectal cancer and 23 caregivers. A theoretical thematic analysis of interview transcripts was framed by posttraumatic growth theory.
RESULTS:
Patients and caregivers described five positive changes: closer relationships with others, greater appreciation of life, clarifying life priorities, increased faith, and more empathy for others. Additionally, only caregivers reported better health habits following the cancer diagnosis, and a minority of patients and caregivers reported no positive changes. In about half of cases, patients reported at least one positive change that was identical to that of their caregiver. However, in most cases, patient and caregiver reports of the caregiver's positive change were discrepant.
CONCLUSION:
Findings suggest that positive changes are a shared experience for many patient-caregiver dyads and obtaining both patient and caregiver reports of caregiver positive changes provides a more comprehensive understanding of their experience. Interventions may capitalise on positive changes to promote meaningful living in the context of advanced cancer
Star Cluster Formation and Evolution in Nearby Starburst Galaxies: II. Initial Conditions
We use the ages, masses and metallicities of the rich young star cluster
systems in the nearby starburst galaxies NGC 3310 and NGC 6745 to derive their
cluster formation histories and subsequent evolution. We further expand our
analysis of the systematic uncertainties involved in the use of broad-band
observations to derive these parameters by examining the effects of a priori
assumptions on the individual cluster metallicities. The age (and metallicity)
distributions of both the clusters in the circumnuclear ring in NGC 3310 and of
those outside the ring are statistically indistinguishable, but there is a
clear and significant excess of higher-mass clusters IN the ring compared to
the non-ring cluster sample; it is likely that the physical conditions in the
starburst ring may be conducive for the formation of higher-mass star clusters,
on average, than in the relatively more quiescent environment of the main
galactic disc. For the NGC 6745 cluster system we derive a median age of ~10
Myr. NGC 6745 contains a significant population of high-mass "super star
clusters", with masses in the range 6.5 <= log(M_cl/M_sun) <= 8.0. This
detection supports the scenario that such objects form preferentially in the
extreme environments of interacting galaxies. The age of the cluster
populations in both NGC 3310 and NGC 6745 is significantly lower than their
respective characteristic cluster disruption time-scales. This allows us to
obtain an independent estimate of the INITIAL cluster mass function slope,
alpha = 2.04(+- 0.23)(+0.13)(-0.43) for NGC 3310, and 1.96(+- 0.15)(+- 0.19)
for NGC 6745, respectively, for masses M_cl >= 10^5 M_sun and M_cl >= 4 x 10^5
M_sun. These mass function slopes are consistent with those of other young star
cluster systems in interacting and starburst galaxies.Comment: 17 pages LaTeX, incl. 11 postscript figures, accepted for publication
in MNRA
Nuclear Disks of Gas and Dust in Early Type Galaxies and the Hunt for Massive Black Holes: Hubble Space Telescope Observations of NGC 6251
We discuss Hubble Space Telescope optical images and spectra of NGC 6251, a
giant E2 galaxy and powerful radio source at a distance of 106 Mpc (for H_0 =
70 km/s/Mpc). The galaxy is known to host a very well defined dust disk (O'Neil
et al. 1994); the exceptional resolution of our V and I images allows a
detailed study of the disk structure. Furthermore, narrow band images centered
on the Halpha+[NII] emission lines, reveal the presence of ionized gas in the
inner 0.3 arcsec of the disk. We used the HST/Faint Object Spectrograph with
the 0.09 arcsec aperture to study the velocity structure of the disk. Dynamical
models were constructed for two extreme (in terms of central concentration)
analytical representations of the stellar surface brightness profile, from
which the mass density and corresponding rotational velocity are derived
assuming a constant mass-to-light ratio (M/L)_V ~ 8.5 M_solar/L_solar. For both
representations of the stellar component, the models show that the gas is in
Keplerian motion around a central mass ~ 4 - 8 X 10^8 solar masses, and that
the contribution of radial flows to the velocity field is negligible.Comment: 45 pages, submitted to Ap
Social correlates of mental health in gastrointestinal cancer patients and their family caregivers: Exploring the role of loneliness
Purpose
The present study examined the degree to which loneliness mediated the influence of negative (social constraints) and positive (emotional support) relationship qualities on the global mental health of advanced gastrointestinal (GI) cancer patients and their family caregivers.
Methods
Fifty patient-caregiver dyads completed measures assessing social constraints (e.g., avoidance, criticism) from the other dyad members, emotional support from others, loneliness, and global mental health. Structural equation modeling was used to examine individual models, and Actor-Partner Interdependence Mediation Modeling was used to examine dyadic associations.
Results
Individual path analyses for patients and caregivers demonstrated that emotional support had a significant indirect effect on mental health through loneliness (Bs = 0.32 and 0.30, respectively), but no associations were found between social constraints and mental health. In dyadic analyses, participants’ loneliness and mental health were not significantly related to their partner’s emotional support, loneliness, or mental health (Bs = − 0.18 to 0.18).
Conclusions
Findings suggest that for advanced GI cancer patients and caregivers, emotional support from others alleviates feelings of loneliness, which may lead to better mental health. However, the benefits of emotional support appear to be primarily intrapersonal rather than interpersonal in nature. Additionally, participants endorsed low levels of social constraints, which might explain their lack of relation to loneliness and mental health. Continued examination of interdependence in social processes between cancer patients and caregivers will inform intervention development
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