Thermal stability, mechanical properties, and tribological performance of TiAlXN coatings: Understanding the effects of alloying additions

In tribological applications, the degradation of metallic coatings due to oxidation and thermal softening at high temperatures is an issue of increasing concern. Recently, researchers have focused on the development of durable hard coatings that can perform well under elevated temperatures. The alloying of ternary TiAlN coatings with various elements has received considerable attention due to its ability to improve coating properties at high temperatures by solid solution hardening, grain refinement, formation of new phases, diffusion barriers, and self-lubricious tribo-oxides. This paper reviews the microstructure, thermal stability, oxidation behaviour, and mechanical and tribological properties of resultant quaternary TiAlXN coatings (X = Si, Cr, V, Ta and B). The effects of the deposition parameters, chemical composition, high-temperature annealing, and coating architecture on the coating properties are discussed in depth. The properties of quinary TiAlCrSiN coatings are also reviewed to provide a better understanding of the synergistic effects of Si and Cr additions to TiAlN. The maximum hardness and plastic deformation resistance (H/E and H3/E2) of TiAlXN coatings produced by various deposition techniques are compared. This paper provides useful insights into the challenges and future research perspectives of the reviewed coatings

Saturation and parabolic effects of Langley Calibration at different altitude levels

The performance of the well-known Langley plot technique, used for the calibration of ground-based sunphotometers, has been investigated at three observatory sites of different altitudes. All solar measurements were collected using a portable LED-type sunphotometer programed to a constant measurement protocol to allow direct comparison between different days and sites. Our results show that evaluation on the correlation R-value and slope AOD-value alone is not robust enough to guarantee a good Langley plot. Statistical analysis on global, diffuse and direct component also fails to select a perfect Langley plot within a pool of data available. Instead, examination on the evolution of diffuse component and direct component against global component actually provides a good representation of the performance of Langley plot. Diurnal evolution of diffuse component and direct component was found closely matching to the global component in a similar increasing trend. Our results also highlighted two important effects that greatly govern the performance of Langley plot, which are saturation effect and parabolic effect. Saturation effect occurs for the state when little to no more signal increase can be legibly reflected on Langley plot. It is dominant in low airmass region where the change of airmass is relatively too small for the increase in signal detected by the sunphotometer. Parabolic effect is preceding effect of signal saturation and becomes severely erroneous when high air masses are included in Langley plot

Spectral line survey of the ultracompact HII region Mon R2

Ultracompact (UC) HII regions constitute one of the earliest phases in the formation of a massive star and are characterized by extreme physical conditions (Go>10^5 Habing field and n>10^6 cm^-3). The UC HII Mon R2 is the closest one and therefore an excellent target to study the chemistry in these complex regions. We carried out a 3mm and 1mm spectral survey using the IRAM 30-m telescope towards three positions that represent different physical environments in Mon R2: (i) the ionization front (IF) at (0",0"); two peaks in the molecular cloud (ii) MP1 at the offset (+15",-15") and (iii) MP2 at the farther offset (0",40"). In addition, we carried out extensive modeling to explain the chemical differences between the three observed regions. We detected more than thirty different species. We detected SO+ and C4H suggesting that UV radiation plays an important role in the molecular chemistry of this region. We detected the typical PDR molecules CN, HCN, HCO, C2H, and c-C3H2. While the IF and the MP1 have a chemistry similar to that found in high UV field and dense PDRs like the Orion Bar, the MP2 is more similar to lower UV/density PDRs like the Horsehead nebula. We also detected complex molecules that are not usually found in PDRs (CH3CN, H2CO, HC3N, CH3OH and CH3C2H). Sulfur compounds CS, HCS+, C2S, H2CS, SO and SO2 and the deuterated species DCN and C2D were also identified. [DCN]/[HCN]=0.03 and [C2D]/[C2H]=0.05, are among the highest in warm regions. Our results show that the high UV/dense PDRs present a different chemistry from that of the low UV case. Abundance ratios like [CO+]/[HCO+] or [HCO]/[HCO+] are good diagnostics to differentiate between them. In Mon R2 we have the two classes of PDRs, a high UV PDR towards the IF and the adjacent molecular bar and a low-UV PDR which extends towards the north-west following the border of the cloud.Comment: 31 page

Shocked water in the Cep E protostellar outflow

Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30m telescope, we searched for and detected the para-water line emission at 183 GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2" resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the water emission arises from warm (\sim 200\K), dense ((1-2)\times 10^6\cmmt) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel.Comment: To appear in Astronomy and Astrophysics, section 1. Letters to the Editor. 4 pages; 4 figures. Fig.3 available on-lin

Reduced Ordered Binary Decision Diagram with Implied Literals: A New knowledge Compilation Approach

Knowledge compilation is an approach to tackle the computational intractability of general reasoning problems. According to this approach, knowledge bases are converted off-line into a target compilation language which is tractable for on-line querying. Reduced ordered binary decision diagram (ROBDD) is one of the most influential target languages. We generalize ROBDD by associating some implied literals in each node and the new language is called reduced ordered binary decision diagram with implied literals (ROBDD-L). Then we discuss a kind of subsets of ROBDD-L called ROBDD-i with precisely i implied literals (0 \leq i \leq \infty). In particular, ROBDD-0 is isomorphic to ROBDD; ROBDD-\infty requires that each node should be associated by the implied literals as many as possible. We show that ROBDD-i has uniqueness over some specific variables order, and ROBDD-\infty is the most succinct subset in ROBDD-L and can meet most of the querying requirements involved in the knowledge compilation map. Finally, we propose an ROBDD-i compilation algorithm for any i and a ROBDD-\infty compilation algorithm. Based on them, we implement a ROBDD-L package called BDDjLu and then get some conclusions from preliminary experimental results: ROBDD-\infty is obviously smaller than ROBDD for all benchmarks; ROBDD-\infty is smaller than the d-DNNF the benchmarks whose compilation results are relatively small; it seems that it is better to transform ROBDDs-\infty into FBDDs and ROBDDs rather than straight compile the benchmarks.Comment: 18 pages, 13 figure

A line confusion limited millimeter survey of Orion KL. II: Silicon-bearing species

We present a study of the Silicon-bearing species detected in a line confusion limited survey towards Orion KL performed with the IRAM 30-m telescope, which ranges from 80 to 280 GHz. Our aim is to derive physical and chemical conditions for each family taking into account all observed lines from all isotopologues of each species. We have modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between LVG and LTE approximations depending on the physical conditions of the gas. We have used appropriate collisional rates for the LVG calculations. For the v=1 state of SiO we have detected the J=2-1 line and, for the first time in this source, emission in the J=4-3 transition, both of them showing strong masering effect. For SiO v=0, we have detected 28SiO, 29SiO, and 30SiO; in addition, we have mapped the J = 5-4 SiO line. For SiS, we have detected the main species, 29SiS, and SiS v=1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of ~15.5 km s-1; a study of the 5-4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive a SiO/SiS column density ratio of ~13 in the plateau component. Besides, we provide upper limits to the column density of several non-detected Silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of S with Si.Comment: Astronomy and Astrophysics, in pres

Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes

We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re

BASECOL2012: A collisional database repository and web service within the Virtual Atomic and Molecular Data Centre (VAMDC)

The BASECOL2012 database is a repository of collisional data and a web service within the Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu). It contains rate coefficients for the collisional excitation of rotational, ro-vibrational, vibrational, fine, and hyperfine levels of molecules by atoms, molecules, and electrons, as well as fine-structure excitation of some atoms that are relevant to interstellar and circumstellar astrophysical applications. Submissions of new published collisional rate coefficients sets are welcome, and they will be critically evaluated before inclusion in the database. In addition, BASECOL2012 provides spectroscopic data queried dynamically from various spectroscopic databases using the VAMDC technology. These spectroscopic data are conveniently matched to the in-house collisional excitation rate coefficients using the SPECTCOL sofware package (http:// vamdc.eu/software), and the combined sets of data can be downloaded from the BASECOL2012 website. As a partner of the VAMDC, BASECOL2012 is accessible from the general VAMDC portal (http://portal.vamdc.eu) and from user tools such as SPECTCOL

Global control of flexural vibration of a one dimensional structure using tuneable vibration neutralisers

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN032560 / BLDSC - British Library Document Supply CentreGBUnited Kingdo