Study of the Performance of Propulsion Units with Nitrogen-Jet Thrusters for Astronaut Extravehicular Activities’ (EVAs)

The future plans of the space agencies all across the globe, mainly focus on the advance of the Extravehicular Activities (EVAs) that are orientated in the repair and maintenance of the space vehicles. This thesis presents a brief history of the space suits (EMU, Orlan-M) utilized in space applications and the propulsion units (Hand-Held Maneuvering Unit, Manned Maneuvering Unit and the Simplified Aid for Extravehicular Activity Rescue-SAFER which is currently being used for performing self-rescue maneuvers, in the case the EVA crew member becomes untethered from the orbiter) that have been used during the space activities. After introducing the space environment and the critical conditions that surround the astronaut during these activities, the fundamentals of the Cold Gas Propulsion Systems on which the function of the SAFER propulsion unit is based, are presented. The aim of this thesis is to perform a performance analysis of the SAFER propulsion unit, with the extraction of the basic space propulsion concepts, i.e. thrust, specific impulse, etc. and the verification of the produced results with the technical characteristics of the unit. The orbital dynamics applying on the astronaut during an EVA are also being studied in this thesis, starting from the scenario where the crew member becomes untethered and floats freely in the vacuum of space and at the same time, examining the case where the SAFER propulsion unit is being activated for the performance of the self-rescue maneuver, and the return of the astronaut to the orbiter

Soil quality evaluation of organically cultivated fields

Τhe subject of this thesis concerns the organically and conventionally cultivated soils and the study of the possible differences of their physical, biochemical and morphometric parameters. We compared soil variables among fields with different duration of organic cultivation (2 (O2), 3(O3), 5 (O5) and 6 (O6) yrs) and between these fields and a conventional one (Σ). All fields were planted with a common perennial plant (Asparagus officinalis (L.)) and they were subject to the same seasonal management practices (fertilizing, crop harvest, incorporation of aboveground residues etc). All sampling fields were located in the same area (Kria Vrisi, Giannitsa) in order to ensure similar climatic conditions. Soil samples were collected four times throughout a year (September, March, May, December) corresponding to management practices applied on asparagus cultivation. Samples were also collected from the close to the cultivations (organic-conventional) hedgerows. Τhe thesis is divided in four chapters and their content is briefly presented in the following paragraphs. In the first chapter the questions that were explored were the following: (a) which factor exerts the greatest influence on soil variables; management type (organic vs conventional) –regarding as long-term disturbances- or management practices- considering as short-term disturbances- (b) do fields with different duration of organic cultivation were distinguishable in terms of their soil biochemical status and (c) the importance of variables in fields’ distinction relates to the specific management practice applied or not? The effect of seasonal management practices on soil biochemical status was much more pronounced than of management type. Among the sampling periods, December was characterized by greater heterogeneity on samples’ soil variables. A fact that could be attributed to laying of aboveground biomass on soil surface which stimulated the microbial community (MBC and MBN) with consequent changes in NH4, NO3, N-mineralization and C-mineralization rate. The importance of soil variables in fields distinction was related to the specific practice applied. The differences among fields, even in the cases of extractable P and N organic that were important classification factors across all samplings, were not systematic. In addition, 10% of samples of the oldest organic field (O6), shared common soil features with samples belonging to the newest organically cultivated field (O2). This high intra-variability showed that none of the examined fields has developed systematically different soil characteristics. Therefore, the idea that soil quality improves as the duration of organic cultivation increases was not supported by our data. In the second chapter was analyzed the data only from the December sampling as it was shown that in this period many soil parameters differ among the cultivations. Data referring to the bacterial functional diversity (Biolog) and the activity of enzymes of the N and P nutrient cycles were also analyzed. The general objectives of this chapter were: a) to see which of the tested soil parameters could be used as indicators reflecting differences in soil quality between organically and conventionally managed asparagus fields, b) how the duration of organic management affects soil parameters.Το αντικείμενο της συγκεκριμένης διδακτορικής διατριβής αφορά στη μελέτη των φυσικών, βιοχημικών και μορφομετρικών εδαφικών παραμέτρων σε οργανικά και συμβατικά καλλιεργούμενα εδάφη σπαραγγιού. Συγκρίναμε εδαφικές παραμέτρους σε καλλιέργειες με διαφορετικό χρόνο ένταξης σε καθεστώς οργανικής καλλιέργειας (δυο (ο2), τριών (ο3), πέντε (ο5) και έξι (ο6) ετών) όπως επίσης έγινε και σύγκριση μεταξύ αυτών των καλλιεργειών και μιας συμβατικής καλλιέργειας (Σ) του ιδίου είδους. Σε όλες τις δειγματοληπτικές θέσεις καλλιεργούνταν το είδος Asparagus officinalis (L.) (σπαράγγι) και όλες οι καλλιέργειες υπόκειντο στις ίδιες εποχιακές καλλιεργητικές πρακτικές (λίπανση, συλλογή σοδειάς,προσθήκη οργανικού υλικού). Οι καλλιέργειες βρίσκονταν στη περιοχή της Κρύας Βρύσης, Γιαννιτσών, πολύ κοντά η μία στην άλλη προκειμένου να χαρακτηρίζονται από τις ίδιες κλιματικές συνθήκες και να ανήκουν στον ίδιο εδαφικό τύπο. Εδαφικά δείγματα συλλέχθηκαν τέσσερις φορές κατά τη διάρκεια ενός έτους (Σεπτέμβριο, Μάρτιο, Μάϊο και #εκέμβριο) που αντιστοιχούν σε καλλιεργητικές πρακτικές που εφαρμόζονται στις καλλιέργιες σπαραγγιών. Επιπρόσθετα, συλλέχθηκαν δείγματα και από τους φυτοφράκτες, που συνιστούν εναπομείνανατα τμήματα φυσικής βλάστησης, που γειτνίαζαν με κάποιες οργανικές καθώς και με την συμβατική καλλιέργεια.συγκεκριμένη διατριβή αποτελείται απο τέσσερα κεφάλαια, το περιεχόμενο των οποίων παρουσιάζεται εν συντομία ακολούθως. Στο πρώτο κεφάλαιο διερευνώνται τα ακόλουθα ερωτήματα: α) ποιός παράγοντας ασκεί μεγαλύτερη επίδραση στις εδαφικές παραμέτρους, ο τρόπος καλλιέργειας (οργανική – συμβατική) ή οι εποχιακές καλλιεργητικές πρακτικές, β) οι περιοχές με διαφορετική διάρκεια ένταξης σε καθεστώς οργανικής καλλιέργειας ήταν διακριτές με βάση το επίπεδο των βιοχημικών τους παραμέτρων ώστε να αποτελούν έναν διαβαθμητή ποιότητας εδάφους και γ) η σημαντικότητα των παραμέτρων στη διάκριση των καλλιεργειών σχετίζεται με τη συγκεκριμένη πρακτική που εφαρμόζεται ή όχι? Οπως προέκυψε η επίδραση των εποχιακών καλλιεργητικών πρακτικών στις βιοχημικές παραμέτρους ήταν πολύ πιο έντονη σε σχέση με αυτό του τρόπου καλλιέργειας. Μεταξύ των δειγματοληπτικών περιόδων, τα δείγματα του #εκεμβρίου εμφάνισαν τη μεγαλύτερη διασπορά. Τον #εκέμβριο εναποτίθεται η υπέργεια βιομάζα στην επιφάνεια του εδάφους μετά το κόψιμό της, γεγονός που ενεργοποιεί τη μικροβιακή βιομάζα (μικροβιακό άνθρακα και μικροβιακό άζωτο) με αποτέλεσμα αλλαγές στις συγκεντρώσεις των αμμωνιακών και νιτρικών ιόντων, στους ρυθμούς ανοργανοποίησης του άνθρακα και του αζώτου. Η σημαντικότητατων εδαφικών παραμέτρων στη διάκριση των καλλιεργειών σχετίστηκε με τη συγκεκριμένη πρακτική που εφαρμόστηκε δηλαδή διαφοροποιήθηκε στις επιμέρους δειγματοληψίες. Οι διαφορές μεταξύ των καλλιεργειών ακόμα και στην περίπτωση του εκχυλίσιμου φωσφόρου και του οργανικού αζώτου που λειτούργησαν ως σημαντικοί παράμετροι διάκρισης στο σύνολο των δειγματοληψιών, δεν ήταν συστηματικές. Επιπρόσθετα, το 10% των δειγμάτων που προέρχονταν από την παλαιότερη οργανική καλλιέργεια ο6, εμφάνισαν κοινά εδαφικά χαρακτηριστικά με δείγματα της νεότερης οργανικής καλλιέργειας ο2. Αυτή η υψηλή εσωτερική ποικιλότητα έδειξε πως καμία από τις εξεταζόμενες καλλιέργειες δεν έχει αναπτύξει συστηματικά διαφορετικά εδαφικά χαρακτηριστικά. Επομένως η ιδέα πως η ποιότητα του εδάφους βελτιώνεται καθώς η διάρκεια της οργανικής καλλιέργειας αυξάνει δε φαίνεται να ενισχύεται από τα δεδομένα αυτά

Nematicidal Amendments and Soil Remediation

The intensification of agriculture has created concerns about soil degradation and toxicity of agricultural chemicals to non-target organisms. As a result, there is great urgency for discovering new ecofriendly tools for pest management and plant nutrition. Botanical matrices and their extracts and purified secondary metabolites have received much research interest, but time-consuming registration issues have slowed their adoption. In contrast, cultural practices such as use of plant matrices as soil amendments could be immediately used as plant protectants or organic fertilizers. Herein, we focus on some types of soil amendments of botanical origin and their utilization for nematicidal activity and enhancement of plant nutrition. The mode of action is discussed in terms of parasite control as well as plant growth stimulation

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In this study we investigated the effects of management regime (organic vs conventional) and the duration of organic farming on soil microbial and chemical variables (C-and N-microbial, Cand N-organic, N-inorganic, P-extractable, C-and N-mineralization rate) and on enzymes involved in N-and P-cycle. To meet this goal, sites cultivated organically with Phaseolus vulgaris (L.) for 2, 5, and 14 yrs as well as a conventional one were investigated. Samples were collected at two occasions coinciding to different stages of plant development. Both management regime and the duration of organic farming did not affect significantly the chemical and microbiological soil variables such as microbial C and N, rates of C-and N-mineralization, N-inorganic, P-extractable and C-organic. It seems that, for bean cultivations (bean is an annual plant), the mechanical disturbance of the soil induced yearly by plowing and tillage masked the effects of the repeated addition of organic amendments. On the contrary, enzymatic activities increased with increasing duration of organic farming (from 2 to 14 yrs) and they were higher in the oldest organic site compared to the conventional one. However, although most soil variables did not exhibit significant quantitative differences in various sites, these latter differed in respect to the temporal changes in these variables. The magnitude of temporal changes increased from conventional to the oldest organic site

The Crucial Role of Soil Organic Matter in Satisfying the Phosphorus Requirements of Olive Trees (Olea europaea L.)

Under high organic matter content, even under low extractable soil P concentrations, sufficient or over-sufficient foliar P levels may be found. This multi-year study aimed at examining the effects of organic matter content and irrigation management on (a) soil fertility, (b) P-cycle related soil enzymes (acid and alkaline phosphatase, pyrophosphatase) and (c) foliar nutrient concentrations. Irrigated and non-irrigated groves of fully productive trees of the cultivar “Chondrolia Chalkidikis” with low organic matter (LOM < 1.5%), medium organic matter (1.5% < MOM < 2.5%) and high organic matter (HOM > 2.5%) were selected for the experimentation. It was hypothesized that olive groves receiving high inorganic fertilization and irrigation inputs (usually with medium to relatively low organic matter content) would show higher soil and foliar P concentrations compared to the non-irrigated groves with higher organic matter content receiving manure applications. Most of the soil variables (including the three enzymes’ activities) were affected by differences in organic matter content. However, organic matter content did not show a significant influence on foliar nutrient concentrations. Olive trees, especially those cultivated in soils with high organic matter content (receiving organic fertilization), can over-satisfy their P nutritional needs, even though soil analyses show low soil extractable P concentrations, probably due to the high enzymatic activity of acid and alkaline phosphatases. The practical conclusion of this study is that P fertilizer recommendations should be primarily based on foliar P rather than on extractable soil P

The Role of Microbial Inoculants on Plant Protection, Growth Stimulation, and Crop Productivity of the Olive Tree (Olea europea L.)

The olive tree (Olea europaea L.) is an emblematic, long-living fruit tree species of profound economic and environmental importance. This study is a literature review of articles published during the last 10 years about the role of beneficial microbes [Arbuscular Mycorrhizal Fungi (AMF), Plant Growth Promoting Rhizobacteria (PGPR), Plant Growth Promoting Fungi (PGPF), and Endophytes] on olive tree plant growth and productivity, pathogen control, and alleviation from abiotic stress. The majority of the studies examined the AMF effect using mostly Rhizophagus irregularis and Glomus mosseae species. These AMF species stimulate the root growth improving the resistance of olive plants to environmental and transplantation stresses. Among the PGPR, the nitrogen-fixing bacteria Azospirillum sp. and potassium- and phosphorous-solubilizing Bacillus sp. species were studied extensively. These PGPR species were combined with proper cultural practices and improved considerably olive plant’s growth. The endophytic bacterial species Pseudomonas fluorescens and Bacillus sp., as well as the fungal species Trichoderma sp. were identified as the most effective biocontrol agents against olive tree diseases (e.g., Verticillium wilt, root rot, and anthracnose)

The Free-Living Nematodes as Indicators of the Soil Quality in Relation to the Clay Content, When Coffee Waste Is Applied

Coffee waste is an organic material that can potentially be used in agricultural systems as an organic amendment. This study investigated the effects of the application of three concentrations of coffee waste (1%, 2%, and 4% w/v), used as an organic amendment, on soil free-living nematode communities, and in two different soil types (clay and sandy loam). Coffee waste incorporation did not appear to be toxic to the soil’s free-living nematodes; on the contrary, it favored the nematode populations; this increase was greater in the sandy loam soil type. Our results show that the abundance of the cp-1 bacteria-feeding nematodes can be used as an indicator of the soil’s enrichment or depletion phase. Panagrolaimus was the most promising genus to describe quality differentiations that occur in the soil system. Three months after coffee waste application, Panagrolaimus was found to be dominant in all coffee waste applications, indicating that the soil was in a phase of enrichment. Six months after the application, nematode community structure indices (enrichment and structure) showed that coffee waste was decomposed in the 1 and 2% treatments and that these systems were in a stage of nutrient depletion. In terms of agricultural practices, when a coffee waste dose is lesser than 4%, a second application is recommended before 6 months to avoid soil degradation

The Differentiations in the Soil Nematode Community in an Agricultural Field after Soil Amendment Using Composted Coffee Waste in Various Concentrations

In a field experiment, composted coffee waste (CW) was used as soil amendment at three different rates (2%, 4%, and 8%) in plots cultivated with wheat; the effects on the soil nematode community and plant growth were studied. By sampling twice, i.e., three and six months after the application of treatments (3MAA and 6MAA), the duration of these effects was also evaluated. Treatment using composted coffee waste (CW) led to an increased abundance of all soil nematodes, especially of bacterivores and fungivores, probably via a bottom-up effect of CW on the soil community. The most-affected genera were the enrichment opportunists Panagrolaimus and Rhabditis, which increased after CW addition in a dosage-dependent way at 3MAA, while at 6MAA they were replaced by general opportunists, mainly bacterivorous and fungivorous genera; a nematotoxic effect of CW was also observed in the 6MAA condition. The nematode indices and the metabolic footprint indicated an enriched and vigorous soil three months after CW addition and a lower enrichment status of the soil together with a higher fungal participation in the decomposition pathway six months after treatments. However, in the 6 MAA condition, the soil nutrient values were higher in the CW-treated plots. None of our treatments inhibited or enhanced plant growth

Different Contribution of Olive Groves and Citrus Orchards to Soil Organic Carbon Sequestration: A Field Study in Four Sites in Crete, Greece

In this work, we evaluated the effects of cultivation practices and sites (representing four locations in Crete, Greece) on soil organic carbon sequestration in established citrus orchards, olive groves, and uncultivated fields (used as a control). Soil pH, soil texture, soil organic matter (SOM), Permanganate Oxidizable Carbon (POXC), Total Kjeldahl Nitrogen (TKN), Carbon and Nitrogen ratio (C:N), as well as soil CO2 respiration rates, and specific enzymes’ activity (i.e., N-Acetyl Glutamate (NAG), Beta Glucosidase (BG), Dehydrogenase) were determined in the upper soil layer (0–20 cm). It was shown that citrus and olive orchards under the South Mediterranean conditions could substantially increase C storage in the soil. However, soils planted with orange trees showed lower capacity than olive trees, which was related to litter chemistry (i.e., leaf C:N ratio). Sites had no significant impact on SOM. In our study, SOM had a positive relationship with TKN (and less with POXC) and the C:N ratio of the tree crop species litter. Our findings have implications for designing soil conservation practices in Mediterranean conditions and developing initiatives describing achievable targets of SOM restoration depending on soil properties and cropping systems

Use of Microbially Treated Olive Mill Wastewaters as Soil Organic Amendments; Their Short-Term Effects on the Soil Nematode Community

Managing olive mill wastewater (OMW) is a major environmental problem. We followed two methods for OMW bioremediation: one with the white-rot fungus Pleurotus ostreatus alone and one with the fungus plus the microalga Chlorella vulgaris. To evaluate the potential use of both final products as soil amendments, in a pot experiment, we applied treated OMW to soil cultivated with Lactuca sativa, and we studied their short-term effects on the soil nematode community in terms of trophic and functional structure, metabolic footprint, genera composition, and interaction networks. We also applied non-treated OMW and simply water (control). The addition of non-treated OMW significantly reduced the abundance of all nematodes, and the network of interactions was the most fragmented and the least robust against future disturbance. The effect on trophic group abundances was similar but less pronounced when OMW was previously detoxified either by the fungus alone or by its combination with the alga. In the latter case, the phytoparasites were suppressed but the bacterivorous nematodes were not affected. However, the most cohesive and robust nematode network was formed in the soil that received the fungal-treated OMW. None of our OMW applications significantly changed community composition, none improved the already degraded status of the soil food web—which is attributed to the sandy texture of our soil—and none affected the growth of lettuce plants, perhaps because of the short duration of the experiment (30 days). Thus, our future research will aim to estimate the long-term impact of OMW