Dark Matter with Time-Dependent Mass

We propose a simple model in which the cosmological dark matter consists of particles whose mass increases with the scale factor of the universe. The particle mass is generated by the expectation value of a scalar field which does not have a stable vacuum state, but which is effectively stabilized by the rest energy of the ambient particles. As the universe expands, the density of particles decreases, leading to an increase in the vacuum expectation value of the scalar (and hence the mass of the particle). The energy density of the coupled system of variable-mass particles (``vamps'') redshifts more slowly than that of ordinary matter. Consequently, the age of the universe is larger than in conventional scenarios.Comment: 14 pages, 2 figures; based on a talk by SMC at Cosmo-97, September 1997, Ambleside, England. Important references adde

Predicting the reducing power of organic super electron donors

The utilization of computational methods to predict reactivity is an increasingly useful tool for chemists to save time and materials by screening compounds for desirable reactivity prior to testing in the laboratory. In the field of electron transfer reactions, screening can be performed through the application of Marcus Hush theory to calculate the activation free energy of any potential reaction. This work describes the most accurate and efficient approach for modelling the electron transfer process. In particular, the importance of using an electron transfer complex to model these reactions rather than considering donor and acceptor molecules as separate entities is highlighted. The use of the complex model is found to produce more accurate calculation of the electron transfer energy when the donor and acceptor spin densities are adequately localised

BUSINESS SUCCESS: WHAT FACTORS REALLY MATTER?

This paper provides a comparison of successful and financially distressed producers based on the data from more than 400 individualized financial analyses. These objective variables are combined with subjective observations of management styles and attitudes to provide unique identification of the factors most influential in the success of Texas producers.Production Economics,

Glial cells are functionally impaired in juvenile neuronal ceroid lipofuscinosis and detrimental to neurons.

The neuronal ceroid lipofuscinoses (NCLs or Batten disease) are a group of inherited, fatal neurodegenerative disorders of childhood. In these disorders, glial (microglial and astrocyte) activation typically occurs early in disease progression and predicts where neuron loss subsequently occurs. We have found that in the most common juvenile form of NCL (CLN3 disease or JNCL) this glial response is less pronounced in both mouse models and human autopsy material, with the morphological transformation of both astrocytes and microglia severely attenuated or delayed. To investigate their properties, we isolated glia and neurons from Cln3-deficient mice and studied their basic biology in culture. Upon stimulation, both Cln3-deficient astrocytes and microglia also showed an attenuated ability to transform morphologically, and an altered protein secretion profile. These defects were more pronounced in astrocytes, including the reduced secretion of a range of neuroprotective factors, mitogens, chemokines and cytokines, in addition to impaired calcium signalling and glutamate clearance. Cln3-deficient neurons also displayed an abnormal organization of their neurites. Most importantly, using a co-culture system, Cln3-deficient astrocytes and microglia had a negative impact on the survival and morphology of both Cln3-deficient and wildtype neurons, but these effects were largely reversed by growing mutant neurons with healthy glia. These data provide evidence that CLN3 disease astrocytes are functionally compromised. Together with microglia, they may play an active role in neuron loss in this disorder and can be considered as potential targets for therapeutic interventions

6th Lone Star Regional Native Plant Conference

https://scholarworks.sfasu.edu/sfa_gardens_lonestar/1003/thumbnail.jp

The White Dwarf Cooling Sequence of NGC6397

We present the results of a deep Hubble Space Telescope (HST) exposure of the nearby globular cluster NGC6397, focussing attention on the cluster's white dwarf cooling sequence. This sequence is shown to extend over 5 magnitudes in depth, with an apparent cutoff at magnitude F814W=27.6. We demonstrate, using both artificial star tests and the detectability of background galaxies at fainter magnitudes, that the cutoff is real and represents the truncation of the white dwarf luminosity function in this cluster. We perform a detailed comparison between cooling models and the observed distribution of white dwarfs in colour and magnitude, taking into account uncertainties in distance, extinction, white dwarf mass, progenitor lifetimes, binarity and cooling model uncertainties. After marginalising over these variables, we obtain values for the cluster distance modulus and age of \mu_0 = 12.02 \pm 0.06 and T_c = 11.47 \pm 0.47Gyr (95% confidence limits). Our inferred distance and white dwarf initial-final mass relations are in good agreement with other independent determinations, and the cluster age is consistent with, but more precise than, prior determinations made using the main sequence turnoff method. In particular, within the context of the currently accepted \Lambda CDM cosmological model, this age places the formation of NGC6397 at a redshift z=3, at a time when the cosmological star formation rate was approaching its peak.Comment: 56 pages, 30 figure

The Attrition of Young Physician-Scientists: Problems and Potential Solutions

Physician-scientists have played a prominent role as thought leaders in American medicine over the past century. This group has produced many basic scientific advances and pioneered the translation of these advances into clinical practice. Now that we are in the post-genomic era, there is a greater need than ever for the continued participation of this group because of their unique ability to bridge the "bench to bedside." However, the number of physicians pursuing this career is static and their average age is rising. Recent data indicate that the many benefits of this career path are seen as being outweighed by so many negative factors, as to prompt the question, "Is this a career that a reasonable person should undertake in 2007 and beyond?" The following analysis suggests that the current answer is "no." We have identified the lack of professional security as a major factor that prompts young physicians to abandon the physician-scientist track. Because this problem has not been sufficiently emphasized, we believe current efforts are unlikely to reverse this disturbing trend. We propose strategies that seek to address this problem and help sustain young physician-scientists at career transition points at which they are most vulnerable to give up

A novel ruthenium-silver based antimicrobial potentiates aminoglycoside activity against Pseudomonas aeruginosa

The rapid dissemination of antibiotic resistance combined with the decline in the discovery of novel antibiotics represents a major challenge for infectious disease control that can only be mitigated by investments in novel treatment strategies. Alternative antimicrobials, including silver, have regained interest due to their diverse mechanisms of inhibiting microbial growth. One such example is AGXX, a broad-spec­trum antimicrobial that produces highly cytotoxic reactive oxygen species (ROS) to inflict extensive macromolecular damage. Due to the connections identified between ROS production and antibiotic lethality, we hypothesized that AGXX could potentially increase the activity of conventional antibiotics. Using the gram-negative pathogen Pseudomonas aeruginosa, we screened possible synergistic effects of AGXX on several antibiotic classes. We found that the combination of AGXX and aminoglycosides tested at sublethal concentrations led to a rapid exponential decrease in bacterial survival and restored the sensitivity of a kanamycin-resistant strain. ROS production contributes significantly to the bactericidal effects of AGXX/aminoglycoside treatments, which is dependent on oxygen availability and can be reduced by the addition of ROS scaveng­ers. Additionally, P. aeruginosa strains deficient in ROS detoxifying/repair genes were more susceptible to AGXX/aminoglycoside treatment. We further demonstrate that this synergistic interaction was associated with a significant increase in outer and inner membrane permeability, resulting in increased antibiotic influx. Our study also revealed that AGXX/aminoglycoside-mediated killing requires an active proton motive force across the bacterial membrane. Overall, our findings provide an understanding of cellular targets that could be inhibited to increase the activity of conventional antimicrobial

Optimized Merger of Ocean Chlorophyll Algorithms of MODIS-Aqua and VIIRS

Standard ocean chlorophyll-a (Chla) products from currently operational satellite sensors Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Visible Infrared Imager Radiometer Suite (VIIRS) underestimate medium and high in situ Chla concentrations and have approximately 9% bias between each other in the California Current. By using the regional optimization approach of Kahru et al., we minimized the differences between satellite estimates and in situ match-ups as well as between estimates of the two satellite sensors and created improved empirical algorithms for both sensors. The regionally optimized Chla estimates from MODIS-Aqua and VIIRS have no bias between each other, have improved retrievals at medium to high in situ Chla, and can be merged to improve temporal frequency and spatial coverage and to extend the merged time series