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Maintenance and degradation of proteins in intact and severed axons: Implications for the mechanism of long-term survival of anucleate crayfish axons
Protein maintenance and degradation are examined in the
severed distal (anucleate) portions of crayfish medial giant
axons (MGAs), which remain viable for over 7 months following
axotomy. On polyacrylamide gels, the silver-stained
protein banding pattern of anucleate MGAs severed from
their cell bodies for up to 4 months remains remarkably similar
to that of intact MGAs. At 7 months postseverance, some
(but not all) proteins are decreased in anucleate MGAs compared
to intact MGAs. To determine the half-life of axonally
transported proteins, we radiolabeled MGA cell bodies and
monitored the degradation of newly synthesized transported
proteins. Assuming exponential decay, proteins in the fast
component of axonal transport have an average half-life of
14 d in anucleate MGAs and proteins in the slow component
have an average half-life of 17 d. Such half-lives are very
unlikely to account for the ability of anucleate MGAs to survive
for over 7 months after axotomy.This work was supported by an ATP grant to G.D.B.Neuroscienc
Transient dynamics and structure of optimal excitations in thermocapillary spreading: Precursor film model
Linearized modal stability theory has shown that the thermocapillary spreading of a liquid film on a homogeneous, completely wetting surface can produce a rivulet instability at the advancing front due to formation of a capillary ridge. Mechanisms that drain fluid from the ridge can stabilize the flow against rivulet formation. Numerical predictions from this analysis for the film speed, shape, and most unstable wavelength agree remarkably well with experimental measurements even though the linearized disturbance operator is non-normal, which allows transient growth of perturbations. Our previous studies using a more generalized nonmodal stability analysis for contact lines models describing partially wetting liquids (i.e., either boundary slip or van der Waals interactions) have shown that the transient amplification is not sufficient to affect the predictions of eigenvalue analysis. In this work we complete examination of the various contact line models by studying the influence of an infinite and flat precursor film, which is the most commonly employed contact line model for completely wetting films. The maximum amplification of arbitrary disturbances and the optimal initial excitations that elicit the maximum growth over a specified time, which quantify the sensitivity of the film to perturbations of different structure, are presented. While the modal results for the three different contact line models are essentially indistinguishable, the transient dynamics and maximum possible amplification differ, which suggests different transient dynamics for completely and partially wetting films. These differences are explained by the structure of the computed optimal excitations, which provides further basis for understanding the agreement between experiment and predictions of conventional modal analysis
Infusing Service-Learning into Academic ABC\u27s: Awareness, Behavior, Community Collaboration
As part of a Science, Technology, Engineering, and Mathematics (STEM) Service-Learning grant, a service-learning project was integrated into two college programs. The overall purpose of this project was to address identified community needs concerning nutrition, health-related issues, food security, and food sustainability. First-year college students developed and implemented a community nutrition survey, and created a list of community resources. These students then shared their survey results and overall impressions of the experience with public health nursing students, who then addressed community needs through a variety of service-learning interventions. Some of these interventions included mobilizing church volunteers to increase the availability of fresh produce to the local food shelf, and providing sweat equity to upgrade and maintain community gardens. Student reflections illustrated an increased awareness of food issues, particularly for low-income families. After the service-learning experience, students expressed a greater interest in serving their community and making a difference. Students strengthened the communityâs commitment to meet mutual food needs by bringing in additional collaborators to work with their partnering agencies. Students learned not only about foodâthey learned about themselves, the community, and the results that collaboration can bring
Bioactive ceramic-reinforced composites for bone augmentation
Biomaterials have been used to repair the human body for millennia, but it is only since the 1970s that man-made composites have been used. Hydroxyapatite (HA)-reinforced polyethylene (PE) is the first of the âsecond-generationâ biomaterials that have been developed to be bioactive rather than bioinert. The mechanical properties have been characterized using quasi-static, fatigue, creep and fracture toughness testing, and these studies have allowed optimization of the production method. The in vitro and in vivo biological properties have been investigated with a range of filler content and have shown that the presence of sufficient bioactive filler leads to a bioactive composite. Finally, the material has been applied clinically, initially in the orbital floor and later in the middle ear. From this initial combination of HA in PE other bioactive ceramic polymer composites have been developed
Measurements of pernitric acid at the South Pole during ISCAT 2000
The first measurements of pernitric acid at the South Pole were performed during the second Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT 2000). Observed HO2NO2 concentrations averaged 25 pptv. Simple steady-state calculations constrained by measurements show that the lifetime of pernitric acid was largely controlled by dry deposition, with thermal decomposition becoming increasingly important at warmer temperatures. We determined that the pernitric acid equilibrium constant is less uncertain than indicated in the literature. One consequence of pernitric acid deposition to the snow surface is that it is an important sink for both NOx and HOx. Another is that the photochemistry of HO2NO2 in the Antarctic snowpack may be a NOx source in addition to nitrate photolysis. This might be one of the important differences in snow photochemistry between the South Pole and warmer polar sites
Modeling chemistry in and above snow at Summit, Greenland â Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer
The chemical composition of the boundary layer in snow covered regions is impacted by chemistry in the snowpack via uptake, processing, and emission of atmospheric trace gases. We use the coupled one-dimensional (1-D) snow chemistry and atmospheric boundary layer model MISTRA-SNOW to study the impact of snowpack chemistry on the oxidation capacity of the boundary layer. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. While it is acknowledged that the chemistry occurring at ice surfaces may consist of a true quasi-liquid layer and/or a concentrated brine layer, lack of additional knowledge requires that this chemistry be modeled as primarily aqueous chemistry occurring in a liquid-like layer (LLL) on snow grains. The model has been recently compared with BrO and NO data taken on 10 Juneâ13 June 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). In the present study, we use the same focus period to investigate the influence of snowpack derived chemistry on OH and HOx + RO2 in the boundary layer. We compare model results with chemical ionization mass spectrometry (CIMS) measurements of the hydroxyl radical (OH) and of the hydroperoxyl radical (HO2) plus the sum of all organic peroxy radicals (RO2) taken at Summit during summer 2008. Using sensitivity runs we show that snowpack influenced nitrogen cycling and bromine chemistry both increase the oxidation capacity of the boundary layer and that together they increase the midday OH concentrations. Bromine chemistry increases the OH concentration by 10â18 % (10 % at noon LT), while snow sourced NOx increases OH concentrations by 20â50 % (27 % at noon LT). We show for the first time, using a coupled one dimensional snowpack-boundary layer model, that air-snow interactions impact the oxidation capacity of the boundary layer and that it is not possible to match measured OH levels without snowpack NOx and halogen emissions. Model predicted HONO compared with mistchamber measurements suggests there may be an unknown HONO source at Summit. Other model predicted HOx precursors, H2O2 and HCHO, compare well with measurements taken in summer 2000, which had lower levels than other years. Over 3 days, snow sourced NOx contributes an additional 2 ppb to boundary layer ozone production, while snow sourced bromine has the opposite effect and contributes 1 ppb to boundary layer ozone loss
Planning and managing future space facility projects
To learn how ground-based personnel of a space project plan and organize their work and how such planning and organizing relate to work outcomes, longitudinal study of the management and execution of the Space Lab Mission Development Test 3 (SMD 3) was performed at NASA Ames Research Center. A view of the problems likely to arise in organizations and some methods of coping with these problems are presented as well as the conclusions and recommendations that pertain strictly to SMD 3 management. Emphasis is placed on the broader context of future space facility projects and additional problems that may be anticipated. A model of management that may be used to facilitate problem solving and communication - management by objectives (MBO) is presented. Some problems of communication and emotion management that MBO does not address directly are considered. Models for promoting mature, constructive and satisfying emotional relationships among group members are discussed
A critical review of the life sciences project management at Ames Research Center for the Spacelab Mission development test 3
A management study was initiated by ARC (Ames Research Center) to specify Spacelab Mission Development Test 3 activities and problems. This report documents the problems encountered and provides conclusions and recommendations to project management for current and future ARC life sciences projects. An executive summary of the conclusions and recommendations is provided. The report also addresses broader issues relevant to the conduct of future scientific missions under the constraints imposed by the space environment
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