ABSTRACT We present key results from the Herschel Orion Protostar Survey: spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion ...molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2-870 m and sample the peak of the protostellar envelope emission at ∼100 m. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.
Turbine types suit specific ranges of head, flow rate and shaft speed and are usually categorised by specific speed. In the pico range, under 5 kW, the requirements are often different to that of ...larger scale turbines and qualitative requirements become more influential in selection. Pico hydro turbines can be applied beyond these conventional application domains, for example at reduced heads, by using non-traditional components such as low speed generators. This paper describes a method to select which turbine architecture is most appropriate for a low-head pico hydro specification using quantitative and qualitative analyses of 13 turbine system architectures found in the literature. Quantitative and qualitative selection criteria are determined from the particular requirements of the end user. The individual scores from this analysis are weighted based on the perceived relative importance of each of the criteria against the original specification and selects a turbine variant based on the total weighted score. This methodology is applied to an example of a remote site, low head and variable flow requirement, leading to the selection of a propeller turbine variant or single-jet Turgo turbine for this specification.
► Limitations with specific speed selection methodology at pico hydro level discussed. ► Method to select a pico hydro turbine for a low head site is presented. ► Quantitative and qualitative criteria developed from the specification. ► These criteria are used to give tangible evidence for the design choice of turbine. ► Propeller or single-jet Turgo design shown suitable for low head pico specification.
Manufacturing Process Selection Handbook provides engineers and designers with process knowledge and the essential technological and cost data to guide the selection of manufacturing processes early ...in the product development cycle. Building on content from the authors' earlier introductory Process Selection guide, this expanded handbook begins with the challenges and benefits of identifying manufacturing processes in the design phase and appropriate strategies for process selection. The bulk of the book is then dedicated to concise coverage of different manufacturing processes, providing a quick reference guide for easy comparison and informed decision making. For each process examined, the book considers key factors driving selection decisions, including: * Basic process descriptions with simple diagrams to illustrate * Notes on material suitability * Notes on available process variations * Economic considerations such as costs and production rates * Typical applications and product examples * Notes on design aspects and quality issues Providing a quick and effective reference for the informed selection of manufacturing processes with suitable characteristics and capabilities, Manufacturing Process Selection Handbook is intended to quickly develop or refresh your experience of selecting optimal processes and costing design alternatives in the context of concurrent engineering. It is an ideal reference for those working in mechanical design across a variety of industries and a valuable learning resource for advanced students undertaking design modules and projects as part of broader engineering programs. * Provides manufacturing process information maps (PRIMAs) provide detailed information on the characteristics and capabilities of 65 processes in a standard format * Includes process capability charts detailing the processing tolerance ranges for key material types * Offers detailed methods for estimating costs, both at the component and assembly level
Aims.
We aim to characterize the outflow properties of a sample of early Class 0 phase low-mass protostars in Orion, which were first identified by the
Herschel
Space Observatory. We also look for ...signatures of infall in key molecular lines.
Methods.
Maps of CO
J
= 3–2 and
J
= 4–3 toward 16 very young Class 0 protostars were obtained using the Atacama Pathfinder EXperiment (APEX) telescope. We searched the data for line wings indicative of outflows and calculated masses, velocities, and dynamical times for the outflows. We used additional HCO
+
, H
13
CO
+
, and NH
3
lines to look for infall signatures toward the protostars.
Results.
We estimate the outflow masses, forces, and mass-loss rates based on the CO
J
= 3–2 and
J
= 4–3 line intensities for eight sources with detected outflows. We derive upper limits for the outflow masses and forces of sources without clear outflow detections. The total outflow masses for the sources with clear outflow detections are in the range between 0.03 and 0.16
M
⊙
for CO
J
= 3–2 and between 0.02 and 0.10
M
⊙
for CO
J
= 4–3. The outflow forces are in the range between 1.57 × 10
−4
and 1.16 × 10
−3
M
⊙
km s
−1
yr
−1
for CO
J
= 3–2 and between 1.14 × 10
−4
and 6.92 × 10
−4
M
⊙
km s
−1
yr
−1
for CO
J
= 4–3. Nine protostars in our sample show asymmetric line profiles indicative of infall in HCO
+
, compared to H
13
CO
+
or NH
3
.
Conclusions.
The outflow forces of the protostars in our sample show no correlation with the bolometric luminosity, unlike those found by some earlier studies for other Class 0 protostars. The derived outflow forces for the sources with detected outflows are similar to those found for other, more evolved, Class 0 protostars, suggesting that outflows develop quickly in the Class 0 phase.
The Herschel Orion Protostar Survey obtained well-sampled 1.2-870 m spectral energy distributions (SEDs) of over 300 protostars in the Orion molecular clouds, home to most of the young stellar ...objects (YSOs) in the nearest 500 pc. We plot the bolometric luminosities and temperatures for 330 Orion YSOs, 315 of which have bolometric temperatures characteristic of protostars. The histogram of the bolometric temperature is roughly flat; 29% of the protostars are in Class 0. The median luminosity decreases by a factor of four with increasing bolometric temperature; consequently, the Class 0 protostars are systematically brighter than the Class I protostars, with a median luminosity of 2.3 as opposed to 0.87 . At a given bolometric temperature, the scatter in luminosities is three orders of magnitude. Using fits to the SEDs, we analyze how the luminosities corrected for inclination and foreground reddening relate to the mass in the inner 2500 au of the best-fit model envelopes. The histogram of the envelope mass is roughly flat, while the median-corrected luminosity peaks at 15 for young envelopes and falls to 1.7 for late-stage protostars with remnant envelopes. The spread in luminosity at each envelope mass is three orders of magnitude. Envelope masses that decline exponentially with time explain the flat mass histogram and the decrease in luminosity, while the formation of a range of stellar masses explains the dispersion in luminosity.
Numerous post-transcriptional modifications of transfer RNAs have vital roles in translation. The 2-methylthio-N
-isopentenyladenosine (ms
i
A) modification occurs at position 37 (A37) in transfer ...RNAs that contain adenine in position 36 of the anticodon, and serves to promote efficient A:U codon-anticodon base-pairing and to prevent unintended base pairing by near cognates, thus enhancing translational fidelity
. The ms
i
A modification is installed onto isopentenyladenosine (i
A) by MiaB, a radical S-adenosylmethionine (SAM) methylthiotransferase. As a radical SAM protein, MiaB contains one Fe
S
cluster used in the reductive cleavage of SAM to form a 5'-deoxyadenosyl 5'-radical, which is responsible for removing the C
hydrogen of the substrate
. MiaB also contains an auxiliary Fe
S
cluster, which has been implicated
in sulfur transfer to C
of i
A37. How this transfer takes place is largely unknown. Here we present several structures of MiaB from Bacteroides uniformis. These structures are consistent with a two-step mechanism, in which one molecule of SAM is first used to methylate a bridging µ-sulfido ion of the auxiliary cluster. In the second step, a second SAM molecule is cleaved to a 5'-deoxyadenosyl 5'-radical, which abstracts the C
hydrogen of the substrate but only after C
has undergone rehybridization from sp
to sp
. This work advances our understanding of how enzymes functionalize inert C-H bonds with sulfur.
Lipoyl synthase (LipA) catalyzes the insertion of two sulfur atoms at the unactivated C6 and C8 positions of a protein-bound octanoyl chain to produce the lipoyl cofactor. To activate its substrate ...for sulfur insertion, LipA uses a 4Fe-4S cluster and S-adenosylmethionine (AdoMet) radical chemistry; the remainder of the reaction mechanism, especially the source of the sulfur, has been less clear. One controversial proposal involves the removal of sulfur from a second (auxiliary) 4Fe-4S cluster on the enzyme, resulting in destruction of the cluster during each round of catalysis. Here, we present two high-resolution crystal structures of LipA from Mycobacterium tuberculosis: one in its resting state and one at an intermediate state during turnover. In the resting state, an auxiliary 4Fe-4S cluster has an unusual serine ligation to one of the irons. After reaction with an octanoyllysine-containing 8-mer peptide substrate and 1 eq AdoMet, conditions that allow for the first sulfur insertion but not the second insertion, the serine ligand dissociates from the cluster, the iron ion is lost, and a sulfur atom that is still part of the cluster becomes covalently attached to C6 of the octanoyl substrate. This intermediate structure provides a clear picture of iron–sulfur cluster destruction in action, supporting the role of the auxiliary cluster as the sulfur source in the LipA reaction and describing a radical strategy for sulfur incorporation into completely unactivated substrates.
► Turgo turbine performance model and volume efficiency model developed. ► Experimental equipment for Turgo turbine designed and built. ► Model and experimental results compare well at specific ...conditions. ► Sensitivity study conducted over set-up parameters showing best performance region. ► Turbine optimisation tests find 91% efficiency at 3.5m head and 87% at 1.0m head.
Turgo turbines are reported to be reliable, robust and able to operate efficiently over a range of flow rates. They are typically used in medium- to high-head applications. In this paper, the operation of a single-jet Turgo turbine outside of this typical application domain is investigated, at low heads of 3.5m down to 1m, a typical head range available for remote communities. A 2D quasi-steady-state mathematical model with low computational requirements is developed, to arrive at a base-line design. Experimental results from this base-line design show the model to predict torque within 5% at the peak power point across the investigated head range. The model requires no calibration and is therefore suitable for rapid performance estimation of first designs. As the head decreases and the jet diameter increases, 3D effects become more significant, reducing the accuracy of the model. Therefore, the model is used to identify important parameters for a further experimental study: Here, these parameters are varied from the base-line design to provide the sensitivity of the efficiency to each parameter. This study improves the turbine’s performance by 5% relative the base-line design to 91% peak jet-to-mechanical power efficiency at 3.5m head, and at 1.0m head provides a 20% improvement in the efficiency to 87%.
Habitat modification and introduced mammalian predators are linked to global species extinctions and declines, but their relative influences can be uncertain, often making conservation management ...difficult. Using landscape-scale models, we quantified the relative impacts of habitat modification and mammalian predation on the range contraction of a threatened New Zealand riverine duck. We combined 38 years of whio (Hymenolaimus malacorhynchos) observations with national-scale environmental data to predict relative likelihood of occurrence (RLO) under two scenarios using bootstrapped boosted regression trees (BRT). Our models used training data from contemporary environments to predict the potential contemporary whio distribution across New Zealand riverscapes in the absence of introduced mammalian predators. Then, using estimates of environments prior to human arrival, we used the same models to hindcast potential pre-human whio distribution prior to widespread land clearance. Comparing RLO differences between potential pre-human, potential contemporary and observed contemporary distributions allowed us to assess the relative impacts of the two main drivers of decline; habitat modification and mammalian predation. Whio have undergone widespread catastrophic declines most likely linked to mammalian predation, with smaller declines due to habitat modification (range contractions of 95% and 37%, respectively). We also identified areas of potential contemporary habitat outside their current range that would be suitable for whio conservation if mammalian predator control could be implemented. Our approach presents a practical technique for estimating the relative importance of global change drivers in species declines and extinctions, as well as providing valuable information to improve conservation planning.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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