An Investigation into the Suitability of Sulfate-Reducing Bacteria as Models for Martian Forward Contamination

The NASA Planetary Protection policy requires interplanetary space missions do not compromise the target body for a current or future scientific investigation and do not pose an unacceptable risk to Earth, including biologic materials. Robotic missions to Mars pose a risk to planetary protection in the forms of forward and reverse contamination. To reduce these risks, a firm understanding of microbial response to Mars conditions is required. Sulfate-reducing bacteria are prime candidates for potential forward contamination on Mars. Understanding the potential for forward-contamination of sulfate-reducers on Mars calls for the characterization of sulfate-reducers under Mars atmosphere, temperature, and sulfate-brines. This study investigated the response of several sulfate-reducing bacteria, including spore formers and psychrophiles. The psychrophile Desulfotalea psychrophila was found to inconsistently survive positive control lab conditions, attributed to an issue shipping pure cultures. Desulfotomaculum arcticum, a spore-forming mesophilic sulfate-reducer, and Desulfuromusa ferrireducens, an iron and sulfate-reducer, were metabolically active under positive control lab conditions with complex and minimal growth medium. A wastewater treatment sulfate-reducing bacteria (SRB) isolate was subjected to sulfate + growth-medium solutions of varied concentrations (0.44 & 0.55% wt. SO42-). The wastewater SRB displayed higher cellular light-absorbance levels at delayed rates in 0.55% sulfate solutions, suggesting a greater total culture reproduction, but with increased lag time. Additional SRB were isolated from marine sediments, subjected to a shock pressure of 8.73 GPa, and returned to ideal conditions. The sulfate-concentration patterns in the impacted SRB culture suggests a destruction of culture occurred somewhere during the preparation process. The response of SRB in this investigation to Ca and Na sulfate-brines suggests that Martian sulfate deposits offer a viable energy sink to terrestrial microorganisms, and the studied SRB are capable of replication at reduced water-activity. Further investigation (i.e. sulfate cations and concentrations, temperature, pressure, etc.) may identify Martian locations at risk to forward contamination

Research and education in management of large- scale technical programs Semiannual progress report

Research and education in management of large scale technical programs - education and integration of interdisciplinary tea

Technology and management of large-scale programs Semiannual progress report

Technology and management of large scale program

Formation and decay of electron-hole droplets in diamond

We study the formation and decay of electron-hole droplets in diamonds at both low and high temperatures under different excitations by master equations. The calculation reveals that at low temperature the kinetics of the system behaves as in direct-gap semiconductors, whereas at high temperature it shows metastability as in traditional indirect-gap semiconductors. Our results at low temperature are consistent with the experimental findings by Nagai {\em et al.} [Phys. Rev. B {\bf 68}, 081202 (R) (2003)]. The kinetics of the e-h system in diamonds at high temperature under both low and high excitations is also predicted.Comment: 7 pages, 8 figures, revised with some modifications in physics discussion, to be published in PR

Minipellets: A new and abundant size class of marine fecal pellets

Minipellets, fecal pellets from 3 to 50 μm in diameter, were found on detritus collected by a particle interceptor trap array in the upper 2000 m of the eastern tropical Pacific. The fluxes of minipellets reached 5 × 106 m−2 day−1, and exceeded fluxes of larger (\u3e50 μm diameter) fecal pellets by 3 orders of magnitude. Carbon flux of minipellets was 11–49% that of larger pellets; however, carbon flux of ultrastructurally intact cells (microalgae and bacteria) in minipellets was equal to that of intact cells in the larger pellets. Minipellets also occurred in water samples from similar depths, where they numbered up to 105 m−3, and were usually not associated with particles. Minipellets appear ubiquitous; we have found them in all our samples of particulates from other cruises from surface waters to bathypelagic depths. Minipellet morphologies ranged from Type A, which contained intact, picoplankton-sized cells (cyanobacteria, nitrifying bacteria, morphologically non-descript, Gram-negative bacteria, Chiarella-like cells) in an amorphous matrix surrounded by a boundary, to Type D minipellets, which were identical to previously described olive-green cells. Minipellets are probably wastes of protozoans and small invertebrates that consume marine snow and larger fecal pellets throughout the water column, thereby maintaining the high numbers of minipellets from the surface to 2000 m. We found several sources of minipellets: two groups of sarcodine protozoans (phaeodarian and spumellarian radiolarians) and small hydromedusae. The minipellet producers reprocess a major portion of surface-derived detritus, and represent important biological intermediates that transform particulate matter settling through the ocean

Alternate wet/dry irrigation in rice cultivation: a practical way to save water and control malaria and Japanese encephalitis?

Water management / Water scarcity / Water use efficiency / Water conservation / Irrigated farming / Waterborne diseases / Rice / Malaria / Disease vectors / Productivity / Flood irrigation / Environmental control / Climate / China / East Africa / India / Indonesia / Japan / Philippines / Portugal / USA

An Integrated Model for STEM Teacher Preparation: The Value of a Teaching Cooperative Educational Experience

The purpose of this article is to evaluate an intensive, integrated model for teacher preparation, specifically, a preservice STEM teacher education model which incorporates science or mathematics content with pedagogical content knowledge in an early, intensive classroom immersion program based entirely in a local school. STEM preservice teachers participated in a cooperative teaching experience which placed them at the school site for their university course work and field placements, thus ensuring a more seamless connection between theory and practice. The findings from this comparative study of the STEM preservice students in the teaching co-op and STEM preservice teachers in a traditional preparation model indicate that the STEM preservice teachers in the teaching cooperative model were more confident about their teaching skills, more comfortable with their content knowledge, and prepared to work effectively with high-needs students

Competition Between Antiferromagnetic Order and Spin-Liquid Behavior in the Two-Dimensional Periodic Anderson Model at Half-Filling

We study the two-dimensional periodic Anderson model at half-filling using quantum Monte Carlo (QMC) techniques. The ground state undergoes a magnetic order-disorder transition as a function of the effective exchange coupling between the conduction and localized bands. Low-lying spin and charge excitations are determined using the maximum entropy method to analytically continue the QMC data. At finite temperature we find a competition between the Kondo effect and antiferromagnetic order which develops in the localized band through Ruderman-Kittel-Kasuya-Yosida interactions.Comment: Revtex 3.0, 10 pages + 5 figures, UCSBTH-94-2