General test for interaction modification

Journal ArticleHow can measurements of population dynamics be used to deduce the mechanisms of interaction in an assemblage of species? We present a technique to use such measurements to distinguish among assemblages of species with no direct interactions, sets of species influenced predominantly by pairwise interactions, and communities with significant interaction modification

The Arches Cluster: Extended Structure and Tidal Radius

At a projected distance of ~26 pc from Sgr A*, the Arches cluster provides insight to star formation in the extreme Galactic Center (GC) environment. Despite its importance, many key properties such as the cluster's internal structure and orbital history are not well known. We present an astrometric and photometric study of the outer region of the Arches cluster (R > 6.25") using HST WFC3IR. Using proper motions we calculate membership probabilities for stars down to F153M = 20 mag (~2.5 M_sun) over a 120" x 120" field of view, an area 144 times larger than previous astrometric studies of the cluster. We construct the radial profile of the Arches to a radius of 75" (~3 pc at 8 kpc), which can be well described by a single power law. From this profile we place a 3-sigma lower limit of 2.8 pc on the observed tidal radius, which is larger than the predicted tidal radius (1 - 2.5 pc). Evidence of mass segregation is observed throughout the cluster and no tidal tail structures are apparent along the orbital path. The absence of breaks in the profile suggests that the Arches has not likely experienced its closest approach to the GC between ~0.2 - 1 Myr ago. If accurate, this constraint indicates that the cluster is on a prograde orbit and is located front of the sky plane that intersects Sgr A*. However, further simulations of clusters in the GC potential are required to interpret the observed profile with more confidence.Comment: 24 pages (17-page main text, 7-page appendix), 24 figures, accepted to Ap

The Quintuplet Cluster: Extended Structure and Tidal Radius

The Quintuplet star cluster is one of only three known young ($<10$ Myr) massive (M $>10^4$ M$_\odot$) clusters within $\sim100$ pc of the Galactic Center. In order to explore star cluster formation and evolution in this extreme environment, we analyze the Quintuplet's dynamical structure. Using the HST WFC3-IR instrument, we take astrometric and photometric observations of the Quintuplet covering a $120''\times120''$ field-of-view, which is $19$ times larger than those of previous proper motion studies of the Quintuplet. We generate a catalog of the Quintuplet region with multi-band, near-infrared photometry, proper motions, and cluster membership probabilities for $10,543$ stars. We present the radial density profile of $715$ candidate Quintuplet cluster members with $M\gtrsim4.7$ M$_\odot$ out to $3.2$ pc from the cluster center. A $3\sigma$ lower limit of $3$ pc is placed on the tidal radius, indicating the lack of a tidal truncation within this radius range. Only weak evidence for mass segregation is found, in contrast to the strong mass segregation found in the Arches cluster, a second and slightly younger massive cluster near the Galactic Center. It is possible that tidal stripping hampers a mass segregation signature, though we find no evidence of spatial asymmetry. Assuming that the Arches and Quintuplet formed with comparable extent, our measurement of the Quintuplet's comparatively large core radius of $0.62^{+0.10}_{-0.10}$ pc provides strong empirical evidence that young massive clusters in the Galactic Center dissolve on a several Myr timescale.Comment: 25 pages (21-page main text, 4-page appendix), 18 figures, submitted to Ap

The orbital motion of the Quintuplet cluster - a common origin for the Arches and Quintuplet clusters?

We investigate the orbital motion of the Quintuplet cluster near the Galactic center with the aim of constraining formation scenarios of young, massive star clusters in nuclear environments. Three epochs of adaptive optics high-angular resolution imaging with Keck/NIRC2 and VLT/NACO were obtained over a time baseline of 5.8 years, delivering an astrometric accuracy of 0.5-1 mas/yr. Proper motions were derived in the cluster reference frame and were used to distinguish cluster members from the majority of field stars. Fitting the cluster and field proper motion distributions with 2D gaussian models, we derive the orbital motion of the cluster for the first time. The Quintuplet is moving with a 2D velocity of 132 +/- 15 km/s with respect to the field along the Galactic plane, which yields a 3D orbital velocity of 167 +/- 15 km/s when combined with the previously known radial velocity. From a sample of 119 stars measured in three epochs, we derive an upper limit to the velocity dispersion in the core of the Quintuplet cluster of sigma_1D < 10 km/s. Knowledge of the three velocity components of the Quintuplet allows us to model the cluster orbit in the potential of the inner Galaxy. Comparing the Quintuplet's orbit with the Arches orbit, we discuss the possibility that both clusters originated in the same area of the central molecular zone. [abridged]Comment: 40 pages, 12 figures, accepted for publication in Ap

Grain Sorghum and Soybean Variety Tests on Reconstructed Prime Land - 1985

Prime farmland disturbed by surface mining must by law be returned to a productivity level equal to that before mining. The coal operator has several test crops that can be selected to determine whether these production standards have been met before final bond release will be made. Grain sorghum and soybeans are two of the crops that may be used. The purposes of this research are (1) to determine the crop yield potential of restored prime farmland from surface mined areas, (2) to determine varietal adaptation on restored prime farmland as compared to non-mined prime farmland, and (3) to provide crop yield data to Kentucky farmers on grain sorghum and soybeans from restored prime farmland

Regulation of seed germination in the close Arabidopsis relative Lepidium sativum : a global tissue-specific transcript analysis

The completion of germination in Lepidium sativum and other endospermic seeds (e.g. Arabidopsis [Arabidopsis thaliana]) is regulated by two opposing forces, the growth potential of the radicle (RAD) and the resistance to this growth from the micropylar endosperm cap (CAP) surrounding it. We show by puncture force measurement that the CAP progressively weakens during germination, and we have conducted a time-course transcript analysis of RAD and CAP tissues throughout this process. We have also used specific inhibitors to investigate the importance of transcription, translation, and posttranslation levels of regulation of endosperm weakening in isolated CAPs. Although the impact of inhibiting translation is greater, both transcription and translation are required for the completion of endosperm weakening in the whole seed population. The majority of genes expressed during this process occur in both tissues, but where they are uniquely expressed, or significantly differentially expressed between tissues, this relates to the functions of the RAD as growing tissue and the CAP as a regulator of germination through weakening. More detailed analysis showed that putative orthologs of cell wall-remodeling genes are expressed in a complex manner during CAP weakening, suggesting distinct roles in the RAD and CAP. Expression patterns are also consistent with the CAP being a receptor for environmental signals influencing germination. Inhibitors of the aspartic, serine, and cysteine proteases reduced the number of isolated CAPs in which weakening developed, and inhibition of the 26S proteasome resulted in its complete cessation. This indicates that targeted protein degradation is a major control point for endosperm weakening

Examining Admission Factors in an MPA Program

This article presents an in-depth examination of the validity of the admission factors employed by a NASPAA-accredited MPA program. Admission factors are examined to determine if particular factors, or a set of factors, are most indicative of an applicant’s potential achievement in the MPA program as measured by a student’s final grade point average (GPA) in the program. The study uses truncated regression techniques to analyze student records in order to determine the relative significance of a set of commonly collected admissions information. We find that the best predictor of success in the MPA program, as measured by final GPA in the program, is the applicant’s undergraduate GPA. This finding brings into question the utility of much of the information collected in a typical MPA program application

LIGAND-INDUCED MOVEMENT OF LYMPHOCYTE MEMBRANE MACROMOLECULES : I. ANALYSIS BY IMMUNOFLUORESCENCE AND ULTRASTRUCTURAL RADIOAUTOGRAPHY

The fate of different complexes on the membrane of thymocytes and spleen lymphocytes was studied with the use of both immunofluorescence and ultrastructural radioautography. The complexes of anti-immunoglobulin (Ig) with the surface Ig of B lymphocytes were present all around the membrane at 4°C; an increase in temperature produced a rapid aggregation of the complex into a cap which was readily interiorized in vesicles. Ultrastructural details of this process were given. The movement of the complexes depended upon the amount of anti-Ig and the temperature. The complexes of anti-lymphocyte antibody with surface antigen(s) did not result in formation of a single large aggregate (or cap) unless an anti-antibody was brought into the reaction. The caps formed by this trilayered complex were not interiorized. Concanavalin A (Con A) bound to cell surface carbohydrate moieties and the complexes of Con A readily formed a cap and were interiorized. Finally, antibodies to H-2 determinants did not form in most instances a single cap aggregate even when anti-antibodies were used. With time the H-2 complexes tended to form several large aggregates with some endocytosis

AN ULTRASTRUCTURAL STUDY OF LYMPHOCYTES WITH SURFACE-BOUND IMMUNOGLOBULIN

This report is on a radioautographic study of lymphocytes exposed to 125I-labeled anti-Ig in an attempt to identify surface-bound Ig molecules. The results as studied by ultrastructural radioautography confirmed the presence of surface-bound Ig on a certain population of lymphocytes. The specificity of the anti-Ig was determined by using appropriate controls that included the use of an absorbed anti-Ig and anti-hemocyanin antibody. The labeling pattern resulting from the interaction of labeled anti-Ig and Ig was found to be specifically associated with the cell surface and random in its distribution. Morphological differences were not apparent between labeled and nonlabeled lymphocytes in the spleen and lymph nodes. In the thymus, most lymphocytes did not exhibit detectable Ig. The few thymic lymphocytes that were labeled had unique morphological characteristics that included fewer ribosomes, many of which were monoribosomes. Relative to the amount in their cytoplasmic organelles, plasma cells had surface Ig but to a lesser degree than lymphocytes. Finally, macrophages were nonspecifically labeled and contained antibody on their membranes as well as intracellularly