Preservation of martian organic and environmental records: final report of the Mars biosignature working group

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.     

Subcritical and supercritical water oxidation of CELSS model wastes.

Controlled-Ecological-Life-Support-System (CELSS) model wastes were wet-oxidized at temperatures from 250 to 500 degrees C, i.e., below and above the critical point of water (374 degrees C and 218 kg/cm2 or 21.4 MPa). A solution of ammonium hydroxide and acetic acid and a slurry of human urine, feces, and wipes were used as model wastes. Almost all of the organic matter in the model wastes was oxidized in the temperature range from 400 to 500 degrees C, i.e., above the critical conditions for water. In contrast, only a small portion of the organic matter was oxidized at subcritical conditions. Although the extent of nitrogen oxidation to nitrous oxide (N2O) and/or nitrogen gas (N2) increased with reaction temperature, most of the nitrogen was retained in solution as ammonia near 400 degrees C. This important finding suggests that most of the nitrogen in the waste feed can be retained in solution as ammonia during oxidation at low supercritical temperatures and be subsequently used as a nitrogen source for plants in a CELSS while at the same time organic matter is almost completely oxidized to carbon dioxide and water. It was also found in this study the Hastelloy C-276 alloy reactor corroded during waste oxidation. The rate of corrosion was lower above than below the critical temperature for water.     

Residual chromatin breaks as biodosimetry for cell killing by carbon ions

We have studied the relationship between cell killing and the induction of residual chromatin breaks on various human cell lines and primary cultured cells obtained by biopsy from patients irradiated with either X-rays or heavy-ion beams to identify potential bio-marker of radiosensitivity for radiation-induced cell killing. The carbon-ion beams were accelerated with the Heavy Ion Medical Accelerator in Chiba (HIMAC). Six primary cultures obtained by biopsy from 6 patients with carcinoma of the cervix were irradiated with two different mono-LET beams (LET= 13 keV/μm, 76 keV/μm) and 200kV X rays. Residual chromatin breaks were measured by counting the number of non-rejoining chromatin fragments detected by the premature chromosome condensation (PCC) technique after a 24 hour postirradiation incubation period. The induction rate of residual chromatin breaks per cell per Gy was the highest for 76 keV/μm beams on all of the cells. Our results indicated that cell which was more sensitive to the cell killing was similarly more susceptible to induction of residual chromatin breaks. Furthermore there is a good correlation between these two end points in various cell lines and primary cultured cells. This suggests that the detection of residual chromatin breaks by the PCC technique may be useful as a predictive assay of tumor response to cancer radiotherapy.     

Angle estimation for two unresolved targets with monopulse radar

Most present-day radar systems use monopulse techniques to extract angular measurements of sunbeam accuracy. The familiar "monopulse ratio" is a very effective means to derive the angle of a single target within a radar beam. For the simultaneous estimation of the angles of two closely-spaced targets, a modification on the monopulse ratio was derived in (Blair and Pearce, 2001), while (Sinha et al., 2002) presented a maximum likelihood (ML) technique via numerical search. In this paper it is shown that the ML solution can in fact be found explicitly, and the numerical search of ((Sinha et al., 2002) is unnecessary. However, the ML solution requires the signal to noise ratio (SNR) for each target to be known, and hence we generalize it so it requires only the relative SNR. Several versions of expectation maximization (EM) joint angle estimators are also derived, these differing in the degree to which prior information on SNR and on beam pattern are assumed. The performances of the different direction-of-arrival (DOA) estimators for unresolved targets are studied via Monte Carlo, and it is found that most have similar performance: this is remarkable since the use of prior information (SNR, relative SNR, beam pattern) varies widely between them. There is, however, considerable performance variability as a function of the two targets' off-boresight angles. A simple combined technique that fuses the results from different approaches is thus proposed, and it performs well uniformly.     

基于CFD技术的鼻腔输药的流动特性研究

鼻腔输药作为一种新颖的输药方式,具有方便可靠的特点,不仅可以适用于局部而且适用于全身用药,已经受到广泛的重视。但由于人类的呼吸道复杂的立体结构使得鼻腔输药成为生物医药研究的一个长期的挑战。利用CFD(计算流体动力学,Computational Fluid Dynamics)技术对鼻腔输药的流动特性进行研究,对一个基于真实的人类鼻腔解剖的3D模型的输药的流动过程进行了分析,着重研究了不同的药物颗粒的流动和沉淀特性。利用CFD的商用软件FLUENT在层流情况下对不同的密度、直径和流动速率的药物颗粒在鼻腔中流动进行了数值模拟,并对计算结果进行了比较分析。CFD研究的结果为鼻腔输药这种新颖的药物输送方式的优化设计提供了依据。     

Muscle atrophy associated with microgravity in rat: basic data for countermeasures

Morphological, contractile properties and myosin heavy chain (MHC) composition of rat soleus muscles were studied after 2 weeks of unloading (HS) and after 2 weeks of HS associated with selective deafferentation (HS + DEAF) at the level L4 and L5. The same significant reductions in muscle mass and tetanic tension were found after HS and HS + DEAF. However, the transformation of the slow-twitch soleus muscle towards a faster type characterized by a decrease in twitch time parameters and an increase in fast-twitch type MHC isoforms in HS did not appear in HS + DEAF conditions. Our results also showed that a pattern similar to firing rate of motoneurones innervating slow-twitch muscles inhibited the slow to fast fiber changes observed during HS. Nevertheless, neither the loss of mass or force output in the HS muscles were prevented by electrostimulation. Immobilization in a stretched position during HS maintained the muscle wet weight, mechanical and electrophoretical characteristics close to control values. We concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command. These basic data suggested that some experimental conditions such as electrostimulation or stretching, could participate in countermeasure programmes.