Prediction of inter packet arrival times for enhanced NR-V2X sidelink scheduling

A significant limitation of the LTE-V2X and NR-V2X sidelink scheduling mechanisms is their difficulty coping with variations in inter packet arrival times, also known as aperiodic packets. This conflicts with the fundamental characteristics of most V2X services which are triggered based on an event. e.g. ETSI Cooperative Awareness Messages (CAMs) - vehicle kinematics, Cooperative Perception Messages (CPMs) - object sensing and Decentralised Event Notification Messages (DENMs) - event occurrences. Furthermore, network management techniques such as congestion control mechanisms can result in varied inter packet arrival times. To combat this, NR-V2X introduced a dynamic grant mechanism, which we show is ineffective unless there is background periodic traffic to stabilise the sensing history upon which the scheduler makes it decisions. The characteristics of V2X services make it implausible that such periodic application traffic will exist. To overcome this significant drawback, we demonstrate that the standardised scheduling algorithms can be made effective if the event triggered arrival rate of packets can be accurately predicted. These predictions can be used to tune the Resource Reservation Interval (RRI) parameter of the MAC scheduler to negate the negative impact of aperiodicity. Such an approach allows the scheduler to achieve comparable performance to a scenario where packets arrive periodically. To demonstrate the effectiveness of our approach, an ML model has been devised for the prediction of cooperative awareness messages, but the same principle can be abstracted to other V2X service types.Comment: 9 pages, 10 figure

Lateral variations in the Unit 7-8 boundary zone of the Rum Eastern Layered Intrusion, NW Scotland: implications for the origin and timing of Cr-spinel seam formation

The Rum Layered Suite, NW Scotland, hosts Cr-spinel seams at the bases of peridotite-troctolite macro-rhythmic units in the eastern portion of the intrusion. Here, we present detailed field observations together with microstructural and mineral chemical analyses for the Unit 7-8 Cr-spinel seam and associated cumulates in the Eastern Layered Intrusion. Detailed mapping and sampling reveal significant lateral variations in the structural characteristics and mineral compositions of the Unit 7-8 boundary zone rocks. Although the Cr-spinel seam is laterally continuous over similar to 3 km, it is absent towards the centre and the margins of the intrusion. The compositional characteristics of Cr-spinel and plagioclase vary systematically along strike, exhibiting a chemical evolution towards more differentiated compositions with increasing distance from the main feeder conduit of the Rum intrusion; the Long Loch Fault. On the basis of our combined datasets, we propose that the upper part of the troctolite, the anorthosite layer underlying the Cr-spinel seam and the seam itself formed during a multi-stage magma replenishment event. The stages can be summarised as follows: (1) peridotite schlieren and anorthosite autoliths formed following melt infiltration and cumulate assimilation in the crystal mush of the Unit 7 troctolite. (2) The anorthosite layer then formed from the Unit 7 troctolite crystal mush by thermal erosion and dissolution due to infiltrating magma. (3) Subsequent dissolution of the anorthosite layer by new replenishing magma led to peritectic in situ crystallisation of the Unit 7-8 Cr-spinel seam, with (4) continued magma input eventually producing the overlying Unit 8 peridotite. In the central part of the Rum Layered Suite, the aforementioned assimilation of the troctolitic footwall formed the anorthosite layer. However, the absence of anorthosite in close proximity to the Long Loch Fault can be explained by enhanced thermochemical erosion close to the feeder zone, and its absence close to the margins of the intrusion, at maximum distance from the Long Loch Fault, may be due to cooling of the magma and loss of erosion potential. In line with other recent studies on PGE-bearing chromitites in layered intrusions, we highlight the importance of multi-stage intrusive magma replenishment to the formation of spatially coupled anorthosite and Cr-spinel seams, as well as the lateral mineral chemical variations observed in the Unit 7-8 boundary zone cumulates

Chromitite petrogenesis in the mantle section of the Ballantrae Ophiolite Complex (Scotland)

5siPodiform chromitites from the Ballantrae Ophiolite Complex (BOC), NW Scotland, are examined to investigate their petrogenesis and elucidate the nature of melt percolation in the supra-subduction zone oceanic mantle more generally. The mantle portion of the BOC comprises two petrologically distinct serpentinite belts, whose differences have previously been attributed to contrasting degrees of melt extraction. Chromitite occurs in each of the northern and southern serpentinite belts, at Pinbain Bridge and Poundland Burn, respectively. Field relationships suggest that chromitites were formed by melt-rock reaction in channel-like conduits in the upper mantle. Chromitite Cr-spinel compositions from the two localities show marked differences to one another, with the Pinbain Bridge chromitite Cr-spinels being characterised by relatively high Cr# [Cr/(Cr+Al); 0.62-0.65] and lower abundances of certain trace elements (e.g., Ti, Ga, V), whereas the Poundland Burn chromitite Cr-spinels exhibit relatively low Cr# (0.44-0.46) and higher concentrations of these trace elements. The contrasting Cr-spinel compositions are used to estimate parental magma compositions for the chromitites; the Pinbain Bridge chromitites crystallised from magmas resembling arc tholeiites whereas MORB-like magmas were involved in formation of the Poundland Burn chromitites. While it is possible that this dichotomy points to early derivation of the BOC at a MORB spreading centre, with subsequent processing in a supra-subduction zone, we suggest that the differences reflect melt extraction from different parts of an evolving subduction zone, such that the MORB-like magmas were generated in a back-arc setting. This interpretation finds support in the Ti/Fe3# versus Ga/Fe3# systematics of peridotite-hosted accessory Cr-spinel that we present here, as well as previously published trace element data and geochronological constraints on the basalt lava sequences associated with the BOC, which collectively favour formation of the Poundland Burn chromitites in subduction zone mantle.partially_openembargoed_20210616Derbyshire, EJ, O’Driscoll, B, Lenaz, D, Zanetti, A, Gertisser, RDerbyshire, Ej; O’Driscoll, B; Lenaz, D; Zanetti, A; Gertisser,

Platinum-group element remobilisation and concentration in the Cliff chromitites of the Shetland Ophiolite Complex, Scotland

ABSTRACTThe ~492 Ma Shetland Ophiolite Complex contains an extensive mantle section, within which numerous podiform chromitite bodies formed during melt percolation in a supra-subduction zone setting. One of the Shetland ophiolite chromitite localities has an unusual style of platinum-group element (PGE) mineralization. Specifically, the Cliff chromitite suite has relatively high (&gt;250 ppm) Pt plus Pd, compared to other chromitites in the Shetland Ophiolite Complex. In this study, we apply petrographic observation, mineral chemistry and novel X-ray microtomography data to elucidate the petrogenesis of PGE-bearing phases at Cliff. The combined datasets reveal that the PGE at Cliff have probably been fractionated by an As-rich fluid, concentrating Pt and Ir into visible (0.1–1 µm) platinum-group minerals (PGM) such as sperrylite and irarsite, respectively. The high (&gt;1 ppm) bulk-rock concentrations of the other PGE (e.g. Os) in the Cliff chromitites suggests the presence of abundant fine-grained unidentified PGM in the serpentinized groundmass. The spatial association of arsenide phases and PGM with alteration rims on Cr-spinel grains suggests that the high Pt and Pd abundances at Cliff result from a late-stage low-temperature (e.g. 200–300°C) hydrothermal event. This conclusion highlights the potential effects that secondary alteration processes can have on modifying and upgrading the tenor of PGE deposits.</jats:p

Phase dynamics of InAs/GaAs quantum dot semiconductor optical amplifiers

The gain and phase dynamics of InAs/GaAs quantum dot amplifiers are studied using single and two-color heterodyne pump probe spectroscopy. The relaxation of the wetting layer carrier density is shown to have a strong effect on the phase dynamics of both ground and excited state transients, while having a much weaker effect on the gain dynamics. In addition, the dynamical alpha factor may also display a constant value after an initial transient. Such behavior is strongly encouraging for reduced pattern effect operation in high speed optical networks. (c) 2007 American Institute of Physics.(DOI: 10.1063/1.2823589

Linking in situ Crystallisation and Magma Replenishment via Sill Intrusion in the Rum Western Layered Intrusion, NW Scotland

The construction of layered mafic-ultramafic intrusions has traditionally been attributed to gravity driven accumulation, involving the mechanical settling of crystals onto the magma chamber floor, at the interface between the crystal mush at the base and overlying replenishing magma, such that the layered sequence of cumulates (i.e., the crystal mush) at the floor aggrades upwards. The Rum Western Layered Intrusion (WLI) is a ~250 m sequence of layered peridotite cumulates comprising the structurally lowest portion of the Rum Layered Suite (RLS). As such, it is taken to represent the oldest sequence in the RLS and has been assumed to young upwards. The WLI hosts the largest proportion of harrisite, a cumulate composed of skeletal olivine that formed by in situ crystallisation, in the Rum layered intrusion. Harrisite layers in the WLI ubiquitously exhibit extremely irregular upward-oriented apophyses, up to several metres high and metres across, alongside laterally extensive dome-like structures; features consistent with intrusive, sill-like emplacement of harrisite. The distribution and abundance of harrisite therefore points to chaotic sill-like emplacement of the magmas that produced at least half of the WLI cumulate. This probably occurred various ambient crystal mush temperatures and punctuated intervals during cumulate formation. The harrisite layers are associated with numerous Cr-spinel seams occurring along the tops, bases, and interiors of these layers, suggesting they formed in situ alongside harrisite sills within the crystal mush. Detailed quantitative textural and mineral chemical analysis of Cr-spinel seams support a simple in situ crystallisation process for their formation. It is suggested the Cr-spinel seams form within melt channels that develop along the same hot tears that allowed the harrisite parental melts to enter the crystal mush. The chemistry and texture of Cr-spinel is controlled by the volume of through-flow of melt through the melt channel. Where melt flux through channels was high, sulphide and platinumgroup minerals are more abundant, highlighting the key economic implications of this model for the platinum-group element enrichment of chromitite horizons in layered intrusions. We also highlight the role of infiltration metasomatism at multiple levels of the WLI, where porous percolation of interstitial melt and reactive liquid flow played a key role in cumulate formation, supporting the notion of layered intrusion growth by incremental sill emplacement

Textural characterization, major and volatile element quantification and Ar-Ar systematics of spherulites in the Rocche Rosse obsidian flow, Lipari, Aeolian Islands:A temperature continuum growth model.

Spherulitic textures in the Rocche Rosse obsidian flow (Lipari, Aeolian Islands, Italy) have been characterized through petrographic, crystal size distribution (CSD) and in situ major and volatile elemental analyses to assess the mode, temperature and timescales of spherulite formation. Bulk glass chemistry and spherulite chemistry analyzed along transects across the spherulite growth front/glass boundary reveal major-oxide and volatile (H2O, CO2, F, Cl and S) chemical variations and heterogeneities at a ≤5 μm scale. Numerous bulk volatile data in non-vesicular glass (spatially removed from spherulitic textures) reveal homogenous distributions of volatile concentrations: H2O (0.089 ± 0.012 wt%), F (950 ± 40 ppm) and Cl (4,100 ± 330 ppm), with CO2 and S consistently below detection limits suggesting either complete degassing of these volatiles or an originally volatile-poor melt. Volatile concentrations across the spherulite boundary and within the spherulitic textures are highly variable. These observations are consistent with diffusive expulsion of volatiles into melt, leaving a volatile-poor rim advancing ahead of anhydrous crystallite growth, which is envisaged to have had a pronounced effect on spherulite crystallization dynamics. Argon concentrations dissolved in the glass and spherulites differ by a factor of ~20, with Ar sequestered preferentially in the glass phase. Petrographic observation, CSD analysis, volatile and Ar data as well as diffusion modeling support continuous spherulite nucleation and growth starting at magmatic (emplacement) temperatures of ~790–825 °C and progressing through the glass transition temperature range (T g ~ 750–620 °C), being further modified in the solid state. We propose that nucleation and growth rate are isothermally constant, but vary between differing stages of spherulite growth with continued cooling from magmatic temperatures, such that there is an evolution from a high to a low rate of crystallization and low to high crystal nucleation. Based on the diffusion of H2O across these temperature ranges (~800–300 °C), timescales of spherulite crystallization occur on a timescale of ~4 days with further modification up to ~400 years (growth is prohibitively slow <400 °C and would become diffusion reliant). Selective deformation of spherulites supports a down-temperature continuum of spherulite formation in the Rocche Rosse obsidian; indeed, petrographic evidence suggests that high-strain zones may have catalyzed progressive nucleation and growth of further generations of spherulites during syn- and post-emplacement cooling