695915 research outputs found
Sort by
The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime
No full textWe describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly-commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain (∼ 2.8 K/Jy) low-system temperature (∼ 18 K at 20cm) radio array that currently operates from 580–1670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar J0737−3039A, pulse profiles from 34 millisecond pulsars from a single 2.5 h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR J0540−6919, and nulling identified in the slow pulsar PSR J0633–2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright millisecond pulsars confirm that MeerKAT delivers exceptional timing. PSR J2241−5236 exhibits a jitter limit of < 4 ns per hour whilst timing of PSR J1909−3744 over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1000 pulsars per day and the future deployment of S-band (1750–3500 MHz) receivers will further enhance its capabilities
Novel eco-efficient process for dimethyl carbonate production by indirect alcoholysis of urea
No full textDimethyl carbonate (DMC) is a valuable eco-friendly compound which can be sustainable produced from CO2. Its rapid increase in demand is driven by the fast growth of its wide ranging end-use industries (e.g. polycarbonates, solvent, pharmaceutical, and the lithium-ion battery industries). DMC can be produced in different ways, but the indirect alcoholysis of urea with ethylene- or propylene glycol is a very promising route. The trans-esterification of the ethylene- or propylene carbonate with methanol, leading to DMC, plays a key role in the energy efficiency of the process, being the main hurdle when it is performed using an excess of methanol due to the DMC-methanol azeotrope that requires expensive separation steps. This work proposes a new process in which the trans-esterification reaction takes place at an excess of propylene carbonate instead of methanol, such that the costly separation of DMC methanol azeotrope is avoided and high purity DMC (>99.8 %wt) can be produced. The newly proposed process is optimally designed. After heat integration, the energy requirement is only 2.64 kWh/kg DMC, which is about 35% lower than best reported figure for the classic process. The dynamics and control of the new process is also provided, and the stability of the process is proven for production changes of ±10% from the nominal rate of 32 ktpy DMC
A Uranium(VI)-Oxo-Imido Dimer Complex Derived from a Sterically Demanding Triamidoamine
No full textReaction of [UO2(µ-Cl)4{K(18-crown-6)}2] with [{N(CH2CH2NSiPri 3)3}Li3] gives [{UO(µNCH2CH2N[CH2CH2NSiPri 3]2)}2] (1), [{(LiCl)(KCl)(18-crown-6)}2] (2), and [LiOSiPri 3] (3) in a 1:2:2 ratio. The formation of the oxo-imido 1 involves cleavage of a N-Si bond, and activation of one of the usually robust U=O bonds of uranyl(VI), resulting in formation of uranium(VI)-imido and siloxide linkages. Notably, the uranium oxidation state remains unchanged at +6 in starting material and product. Structural characterization suggests the dominance of a core RN=U=O group, and the dimeric formulation of 1 is supported by bridging imido linkages in a highly asymmetric U2N2 ring. DFT analysis finds s > p orbital energy ordering for the U=N and U=O bonds in 1, which is uranyllike in nature. Complexes 1-3 were characterized variously by single crystal X-ray diffraction, multinuclear NMR, IR, Raman, and optical spectroscopies, cyclic voltammetry, and density functional theory
Attracting and repelling 2-body problems on a family of surfaces of constant curvature
No full textWe first provide a classification of the pure rotational motion of 2 particles on a sphere interacting via a repelling potential. This is achieved by providing a simple geometric equivalence between repelling particles and attracting particles, and relying on previous work on the similar classification for attracting particles. The second theme of the paper is to study the 2-body problem on a surface of constant curvature treating the curvature as a parameter, and with particular interest in how families of relative equilibria and their stability behave as the curvature passes through zero and changes sign. We consider two cases: firstly one where the particles are always attracting throughout the family, and secondly where they are attracting for negative curvature and repelling for positive curvature, interpolated by no interaction when the curvature vanishes. Our analysis clarifies the role of curvature in the existence and stability of relative equilibria
Predictors of health behaviours among Indian college students: An exploratory study
No full textObjectives: To understand the association between health behaviours of diet, physical activity, smoking cigarettes, alcohol consumption, safe sex, and sleep quality with demographic (e.g., age, gender) and psychological (i.e., stress, self-esteem and sense of coherence) factors in Indian residential college students. Methods: Students studying for Bachelor of Technology at residential colleges in India were invited to complete an online questionnaire regarding their health behaviours, demographics and psychological variables. Each health behaviour was regressed onto demographic and psychological factors to determine which of them were associated with performing each behaviour. Results: There was no clear pattern of predictors for the health behaviours overall. Self-esteem was related to healthy diet, being single was related to adequate sleep, higher parental income was related to safer sex and being older was related to more alcohol use and safer sex. Conclusions: This study revealed that health education efforts may need to be designed for specific behaviours and correlates among Indian college students. Interventions regarding (i) healthy eating should target students with lower self-esteem, (ii) sleep should target students in a relationship, and (iii) safer sex should target younger students and those from less affluent backgrounds
Construction professionals' commitment to the organisation, work-life balance and well-being
No full textThis theory-driven literature review aims to examine how work-life balance and emerging research in positive psychology may inform our understanding of the underlying mechanisms that affect the organisational commitment of construction professionals. Based on the review, we propose that work-life balance, well-being (i.e., sense of purpose and positive emotions) are linked to construction professionals’ organisational commitment. From this we offer a research model and eight research propositions postulating that work-life balance directly affects organisational commitment via promoting sense of purpose and positive emotions. Furthermore, we propose two additional paths where positive emotions mediate the relationship between work-life balance and organisational commitment, and between sense of purpose and organisational commitment
The Gardner correlation length scale in glasses
No full textThe Gardner length scale ξ is the correlation length in the vicinity of the Gardner transition, which is a transition in glasses where the phase space of the glassy phase fractures into smaller sub-basins on experimental time scales. We argue that ξ grows like p B∞/G∞, where B∞ is the bulk modulus and G∞ is the shear modulus, both measured in the high-frequency limit of the glassy state. We suggest that ξ might be inferred from stress-stress correlation functions, which is more practical for experimental investigation than studying two copies of the system, which can only be done in numerical simulations. Our arguments are illustrated by explicit calculations for a system of disks moving in a narrow channel, which is solved exactly by transfer matrix techniques
Sound C Code Decompilation for a subset of x86-64 Binaries
No full textWe present FoxDec: an approach to C code decompilation that aims at producing sound and recompilable code. Formal methods are used during three phases of the decompilation process: control flow recovery, symbolic execution, and variable analysis. The use of formal methods minimizes the trusted code base and ensures soundness: the extracted C code behaves the same as the original binary. Soundness and recompilablity enable C code decompilation to be used in the contexts of binary patching, binary porting, binary analysis and binary improvement, with confidence that the recompiled code’s behavior is consistent with the original program. We demonstrate that FoxDec can be used to improve execution speed by recompiling a binary with different compiler options, to patch a memory leak with a code transformation tool, and to port a binary to a different architecture. FoxDec can also be leveraged to port a binary to run as a unikernel, a minimal and secure virtual machine usually requiring source access for porting
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
No full textThe 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 ~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 multistage 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 insitu crystallisation of the Unit 7-8 Cr-spinel seam, with (4) continued magma input eventuallyproducing 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