Some Studies of Bacterial Lysis and of the Bacterial Cell-Wall

Investigations involving the use of the electron microscope have been carried out of the structural changes involved in bacterial autolysis, of the action on bacteria of a cationic detergent (cetyl-trimethyl-ammonium bromide), of the structure of the bacterial cell-wall and of the part played by the bacterial cell-wall in cell division. Spontaneous autolysis was studied in Staph, aureus and in B. subtilis, using both the intact cells and the isolated cell-walls. In both organisms the earliest visible change is a retraction of the cytoplasm from the cell-wall and this is associated with a change to the Gram-negative state. In the case of Staph, aureus this is followed by a slow, irregular disintegration of the cytoplasm within the cell-wall which also undergoes a slow, irregular disintegration but remains undisrupted until a relatively late stage. In B. subtilis the rate of autolysis is very much more rapid and this is due mainly to the early rupture of the cell-wall allowing rapid evacuation and dispersal of the cytoplasm; the cell-wall, itself, also undergoes a more rapid and uniform disintegration than the cell-wall of Staph, aureus. It is suggested that the loss of Gram-positivity during spontaneous autolysis is due not to enzymic activity but to the disruption of cytoplas-mic-cell-wall contact, the latter being associated with loss of soluble cytoplasmic constituents. Certain conditions (cell concentration, age of cells, washing of the cells, pH and temperature) influencing the rate of autolysis of Staph. aureus have also been studied. The action of CTAB on Staph, aureus and B. subtilis. again using both intact cells and isolated cell-walls for the investigation, has been found to follow stoichiometric proportions and to vary with the cell to detergent weight ratio. A high ratio results in a marked stimulation of autolytic disintegration of the cell. A low ratio results in cell fixation. Intermediate ratios cause stripping of the cell-wall but the cytoplasmic body, contrasted and Gram-negative, undergoes no further disintegration. From these results together with a comparison of the effects on autolysis of treatment of the bacterial cell with CTAB and with lipoid solvents an hypothesis has been formulated that detergents cause splitting of lipoprotein complexes throughout the cell: where the concentration of the detergent is relatively low this allows an acceleration of normal autolysis; with higher concentrations of detergent protein denaturation predominates and is responsible for inactivation of autolytic enzymes, cell-wall stripping and cell fixation. The quantitative results obtained show that the active unit of CTAB in producing the above effects is the free ion and not the micelle. The investigation of the intimate structure of the cell-wall of Staph. aureus tends to support the view that the cell-wall of this organism contains a protein, fibrous network. The cell-wall of B. subtilis. on the other hand, seems to consist of a mosaic of small, circular or oval units. The stages of bacterial cell division have been followed by examinations of the isolated cell-walls of Staph. aureus, Strept. faecalis and B. subtilis. In all three organisms a transverse cell-wall septum is formed which originates in and grows centripetally from the cell-wall. The cell-wall septum splits into two layers and division is completed by constriction of the cell-wall through the line of the double septum. Cell-wall septum formation and cell-wall constriction appear to be dissociable phenomena. A cytoplasmic membrane, forming transverse septa before the formation of the cell-wall septum, has been demonstrated in Strept. faecalis

Identifying Challenges to Infusing Ethics into the Development of Engineers at Texas State University

Over the past six years we have worked to integrate ethics education throughout the curriculum of the still-new Ingram School of Engineering. During work on an NSF funded grant, we were able to infuse ethics related modules in 13 different courses, across three colleges and at all levels of undergraduate study. Our goal in participating in the GSW ASEE meeting is to share ideas about addressing challenges that arose during this project. We also hope to learn about faculty resources others have found most helpful in allowing faculty with diverse cultural and professional backgrounds to effectively infuse ethics into technical courses.Cockrell School of Engineerin

On the Size-Dependence of the Inclination Distribution of the Main Kuiper Belt

We present a new analysis of the currently available orbital elements for the known Kuiper belt objects. In the non-resonant, main Kuiper belt we find a statistically significant relationship between an object's absolute magnitude (H) and its inclination (i). Objects with H~170 km for a 4% albedo) have higher inclinations than those with H>6.5 (radii >~ 170 km). We have shown that this relationship is not caused by any obvious observational bias. We argue that the main Kuiper belt consists of the superposition of two distinct distributions. One is dynamically hot with inclinations as large as \~35 deg and absolute magnitudes as bright as 4.5; the other is dynamically cold with i6.5. The dynamically cold population is most likely dynamically primordial. We speculate on the potential causes of this relationship.Comment: 14 pages, 6 postscript figure

Bandpass Sampling – An Opportunity To Stress The Importance Of In-Depth Understanding

Many bandpass signals can be sampled at rates lower than the Nyquist rate, allowing significant practical advantages. Illustrating this phenomenon after discussing (and proving) Shannon’s sampling theorem provides a valuable opportunity for an instructor to reinforce the principle that innovation is possible when students strive to have a complete understanding of physical processes and mathematical models.

The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight

The limiting magnitude of the HST data set used by Cochran et al. (1995) to detect small objects in the Kuiper belt is reevaluated, and the methods used are described in detail. It is shown, by implanting artificial objects in the original HST images, and re-reducing the images using our original algorithm, that the limiting magnitude of our images (as defined by the 50% detectability limit) is $V=28.4$. This value is statistically the same as the value found in the original analysis. We find that $\sim50$ of the moving Kuiper belt objects with $V=27.9$ are detected when trailing losses are included. In the same data in which these faint objects are detected, we find that the number of false detections brighter than $V=28.8$ is less than one per WFPC2 image. We show that, primarily due to a zero-point calibration error, but partly due to inadequacies in modeling the HST'S data noise characteristics and Cochran et al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects in the HST dataset by over a factor of 2, and their conclusions are therefore invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe

Report of the panel on lithospheric structure and evolution, section 3

The panel concluded that NASA can contribute to developing a refined understanding of the compositional, structural, and thermal differences between continental and oceanic lithosphere through a vigorous program in solid Earth science with the following objectives: determine the most fundamental geophysical property of the planet; determine the global gravity field to an accuracy of a few milliGals at wavelengths of 100 km or less; determine the global lithospheric magnetic field to a few nanoTeslas at a wavelength of 100 km; determine how the lithosphere has evolved to its present state via acquiring geologic remote sensing data over all the continents

New Horizons: Long-Range Kuiper Belt Targets Observed by the Hubble Space Telescope

We report on Hubble Space Telescope (HST) observations of three Kuiper Belt Objects (KBOs), discovered in our dedicated ground-based search campaign, that are candidates for long-range observations from the New Horizons spacecraft: 2011 JY31, 2011 HZ102, and 2013 LU35. Astrometry with HST enables both current and future critical accuracy improvements for orbit precision, required for possible New Horizons observations, beyond what can be obtained from the ground. Photometric colors of all three objects are red, typical of the Cold Classical dynamical population within which they reside; they are also the faintest KBOs to have had their colors measured. None are observed to be binary with HST above separations of ~0.02 arcsec (~700 km at 44 AU) and {\Delta}m less than or equal to 0.5.Comment: Pages: 11, Figures: 2, Tables: 3, Icarus, available online May 2014 (http://dx.doi.org/10.1016/j.icarus.2014.04.014

Gray-Matter Degeneration in Presenile Alzheimer's Disease

Previous comparisons between presenile Alzheimer's disease (AD) and senile dementia of the Alzheimer type (SDAT) did not control for disease severity and duration. In the current study, 18 patients with each diagnosis were matched for disease duration, cognitive dysfunction, and behavioral symptoms (using the modified Mini-Mental Status [mMMS] examination and the Blessed Dementia Rating Scale [BDRS]). Regional cerebral blood flow (rCBF) was quantified by the 133xenon inhalation technique, and several indices of tissue perfusion were examined. The two variables of primary interest were relative gray-matter weight and a gray-matter perfusion index, the initial slope index. Presenile onset was associated with loss of gray-matter relative weight (35% in presenile patients versus 39% in senile patients and healthy control subjects, p = 0.006), with neither perfusion nor disease severity differences between the two dementia samples. This loss of gray matter was significantly related to both severity and duration of disease in the patients with presenile AD, but not in patients with SDAT. These findings lend support to previous suggestions of greater degenerative process in presenile AD and confirm the need to examine and control age of onset in future investigations of AD. Further, correlation analysis suggests greater proportion of common variance among clinical and physiological indices in presenile AD