Inspired by the developments in photonic metamaterials, the concept of thermal metamaterials has promised new avenues for manipulating the flow of heat. In photonics, the existence of natural ...materials with both positive and negative permittivities has enabled the creation of metamaterials with a very wide range of effective parameters. In contrast, in conductive heat transfer, the available range of thermal conductivities in natural materials is far narrower, strongly restricting the effective parameters of thermal metamaterials and limiting possible applications in extreme environments. Here, we identify a rigorous correspondence between zero index in Maxwell's equations and infinite thermal conductivity in Fourier's law. We also propose a conductive system with an integrated convective element that creates an extreme effective thermal conductivity, and hence by correspondence a thermal analogue of photonic near-zero-index metamaterials, a class of metamaterials with crucial importance in controlling light. Synergizing the general properties of zero-index metamaterials and the specific diffusive nature of thermal conduction, we theoretically and experimentally demonstrate a thermal zero-index cloak. In contrast with conventional thermal cloaks, this meta-device can operate in a highly conductive background and the cloaked object preserves great sensitivity to external temperature changes. Our work demonstrates a thermal metamaterial which greatly enhances the capability for molding the flow of heat.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Particle trapping and binding in optical potential wells provide a versatile platform for various biomedical applications. However, implementation systems to study multi-particle contact interactions ...in an optical lattice remain rare. By configuring an optofluidic lattice, we demonstrate the precise control of particle interactions and functions such as controlling aggregation and multi-hopping. The mean residence time of a single particle is found considerably reduced from 7 s, as predicted by Kramer's theory, to 0.6 s, owing to the mechanical interactions among aggregated particles. The optofluidic lattice also enables single-bacteria-level screening of biological binding agents such as antibodies through particle-enabled bacteria hopping. The binding efficiency of antibodies could be determined directly, selectively, quantitatively and efficiently. This work enriches the fundamental mechanisms of particle kinetics and offers new possibilities for probing and utilising unprecedented biomolecule interactions at single-bacteria level.
Despite considerable efforts over the past decade, only 34 fast radio bursts-intense bursts of radio emission from beyond our Galaxy-have been reported
. Attempts to understand the population as a ...whole have been hindered by the highly heterogeneous nature of the searches, which have been conducted with telescopes of different sensitivities, at a range of radio frequencies, and in environments corrupted by different levels of radio-frequency interference from human activity. Searches have been further complicated by uncertain burst positions and brightnesses-a consequence of the transient nature of the sources and the poor angular resolution of the detecting instruments. The discovery of repeating bursts from one source
, and its subsequent localization
to a dwarf galaxy at a distance of 3.7 billion light years, confirmed that the population of fast radio bursts is located at cosmological distances. However, the nature of the emission remains elusive. Here we report a well controlled, wide-field radio survey for these bursts. We found 20, none of which repeated during follow-up observations between 185-1,097 hours after the initial detections. The sample includes both the nearest and the most energetic bursts detected so far. The survey demonstrates that there is a relationship between burst dispersion and brightness and that the high-fluence bursts are the nearby analogues of the more distant events found in higher-sensitivity, narrower-field surveys
.
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KISLJ, NUK, SBMB, UL, UM, UPUK
Which bright fast radio bursts repeat? James, C W; Osłowski, S; Flynn, C ...
Monthly notices of the Royal Astronomical Society,
06/2020, Volume:
495, Issue:
2
Journal Article
Peer reviewed
Open access
ABSTRACT
A handful of fast radio bursts (FRBs) are now known to repeat. However, the question remains – do they all? We report on an extensive observational campaign with the Australian Square ...Kilometre Array Pathfinder (ASKAP), Parkes, and Robert C. Byrd Green Bank Telescope, searching for repeat bursts from FRBs detected by the Commensal Real-time ASKAP Fast Transients survey. In 383.2 h of follow-up observations covering 27 FRBs initially detected as single bursts, only two repeat bursts from a single FRB, FRB 171019, were detected, which have been previously reported by Kumar et al. We use simulations of repeating FRBs that allow for clustering in burst arrival times to calculate new estimates for the repetition rate of FRB 171019, finding only slight evidence for incompatibility with the properties of FRB 121102. Our lack of repeat bursts from the remaining FRBs set limits on the model of all bursts being attributable to repeating FRBs. Assuming a reasonable range of repetition behaviour, at most 60 per cent (90 per cent confidence limit) of these FRBs have an intrinsic burst distribution similar to FRB 121102. This result is shown to be robust against different assumptions on the nature of repeating FRB behaviour, and indicates that if indeed all FRBs repeat, the majority must do so very rarely.
Currently, sludge pyrolysis has been considered as a promising technology to solve disposal problem of municipal sewage sludge, recover sludge heating value, sequester carbon and replenish nutrients ...in farmland soils. The resultant sludge-derived biochar (SDBC) is potentially an excellent stabilizing agent for metal species. This study applied the SDBC into four soils that had been contaminated in field with cationic Pb(II) and Cd(II)/Ni(II), and anionic Cr(VI) and As(III), respectively. The performance of metal stabilization under various operational and environmental conditions was evaluated with acid batch extraction and column leaching tests. Results indicated the SDBC could effectively stabilize these metals, which was favored by elevated temperature and longer aging. Periodic temperature decrease from 45 to 4 °C resulted in the release of immobilized Cr(VI) and As(III) but not Pb(II). However, a longer aging time offset such metal remobilization. This was possibly because more Pb was strongly bound and even formed stable precipitates, as shown by XRD and sequential extraction results. With increasing time, Cr(VI) was sorbed and partly reduced to Cr(III), while immobilized As(III) was co-oxidized to As(V) as indicated by XPS spectra. Column tests revealed that adding SDBC as a separate layer was unfavorable because the concentrated Cd(II) and Ni(II) in localized positions increased the peak levels of metal release under continuous acid leaching. In contrast, uniformly mixed SDBC could effectively delay the metal breakthrough and reduce their released amounts. Yet, a long-term monitoring may be required for evaluating the potential leaching risks and bioavailability/toxicity of these immobilized and transformed species in the SDBC-amended soils.
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•SDBC can effectively stabilize Pb, Cd, Ni, Cr and As in soils.•A higher temperature and a longer aging favor the stabilization process.•Sharp temperature drop may release the immobilized As(III) and Cr(VI) species.•SDBC can enhance Cr(VI) reduction and As(III) oxidation in soil for a long term.•Adding SDBC as a separate layer is unfavorable as it raises metal release peak.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Fast actuation speed, large-shape deformation and robust responsiveness are critical to synthetic soft actuators. A simultaneous optimization of all these aspects without trade-offs remains ...unresolved. Here we describe porous polymer actuators that bend in response to acetone vapour (24 kPa, 20 °C) at a speed of an order of magnitude faster than the state-of-the-art, coupled with a large-scale locomotion. They are meanwhile multi-responsive towards a variety of organic vapours in both the dry and wet states, thus distinctive from the traditional gel actuation systems that become inactive when dried. The actuator is easy-to-make and survives even after hydrothermal processing (200 °C, 24 h) and pressing-pressure (100 MPa) treatments. In addition, the beneficial responsiveness is transferable, being able to turn 'inert' objects into actuators through surface coating. This advanced actuator arises from the unique combination of porous morphology, gradient structure and the interaction between solvent molecules and actuator materials.
Electron transfer mediated by iron minerals is considered as a critical redox step for the dynamics of pollutants in soil. Herein, we explored the reduction process of Cr(VI) with different ...crystalline ferric oxyhydroxides in the presence of pyrogenic carbon (biochar). Both low- and high-crystallinity ferric oxyhydroxides induced Cr(VI) immobilization mainly via the sorption process, with a limited reduction process. However, the Cr(VI) reduction immobilization was inspired by the copresence of biochar. Low-crystallinity ferric oxyhydroxide had an intense chemical combination with biochar and strong sorption for Cr(VI) via inner-sphere complexation, leading to the indirect electron transfer route for Cr(VI) reduction, that is, the electron first transferred from biochar to iron mineral through C–O–Fe binding and then to Cr(VI) with Fe(III)/Fe(II) transformation on ferric oxyhydroxides. With increasing crystallinity of ferric oxyhydroxides, the direct electron transfer between biochar and Cr(VI) became the main electron transfer avenue for Cr(VI) reduction. The indirect electron transfer was suppressed in the high-crystallinity ferric oxyhydroxides due to less sorption of Cr(VI), limited combination with biochar, and higher iron stability. This study demonstrates that electron transfer mechanisms involving iron minerals change with the mineral crystallization process, which would affect the geochemical process of contaminants with pyrogenic carbon.
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IJS, KILJ, NUK, PNG, UL, UM
Summary
Propofol is used both for induction and maintenance of anaesthesia. Recent evidence shows that propofol has analgesic properties. This meta‐analysis evaluated differences in postoperative ...analgesia between general anaesthetic maintenance with intravenous propofol and inhalational anaesthetics. Fourteen trials met inclusion criteria and were included. Our outcomes were pain scores 2 and 24 h after surgery. No significant difference in pain scores was found at 2 h after surgery (Hedge's g (95% CI) −0.120 (−0.415–0.175) (p = 0.425). Propofol was associated with a statistically significant, albeit marginal, reduction in pain scores 24 h after surgery (Hedge's g (95% CI) −0.134 (−0.248 to −0.021) (p = 0.021). Data were insufficient to allow a meaningful analysis regarding 24‐h morphine‐equivalent consumption. Propofol was associated with reduced postoperative nausea and vomiting (relative risk (95%CI) 0.446 (0.304–0.656) (p < 0.0001). In conclusion, this meta‐analysis suggests that propofol improves postoperative analgesia compared with inhalational anaesthesia 24 h after surgery, with a lower incidence of nausea and vomiting.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The adsorption of Cr(VI) on biochars can be suppressed by coexisting anions, but the roles of O-containing functional groups and in particular N-containing functional groups are unclear. In this ...study, we combined spectroscopic and molecular simulation approaches to investigate the selective adsorption of Cr(VI) on the O-rich (PB, UB1) and N-rich (UB3, UB5) biochars under strong competition of anions. The elemental analysis and pyrolysis-gas chromatography/mass spectrometry indicated that the structures of PB and UB1 were similar, and so were the UB3 and UB5. Quantification of functional groups showed that for UB1, 75.3% of Cr(VI) removal was attributed to O-containing groups, while 53.3–72.7% of that was mediated by N-containing groups in UB3 and UB5. X-ray photoelectron spectra and density functional theory calculations confirmed that for O-rich biochars, surface complexation and strong H-bonds between carboxyl/hydroxyl and HCrO4– improved Cr(VI) removal in the presence of anions, while for N-rich biochars, Cr(VI) adsorption was depressed by coexisting anions in the order of Cl–>NO3– >SO42– because of the weaker H-bond between protonated amino groups and HCrO4–. This study presents a novel approach for quantitative, molecular-level evaluation of the roles of biochar functional groups in the Cr(VI) removal from complex environmental systems.
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•O-rich biochar presented a better selectivity for Cr(VI) than N-rich biochar.•XPS analysis and DFT calculation were used to study selective adsorption of Cr(VI).•For O-rich biochars, complexation and H-bond between COOH/OH and Cr(VI) were formed.•The weaker H-bond was formed between NH2+ of N-rich biochars and HCrO4–.•Principal component analysis showed UB5 was the most superior for Cr(VI) removal.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
This investigation reports on anisotropy in the magnetic interaction, lattice-orbital coupling and degree of phonon softening in single crystal Ni
3
TeO
6
(NTO) using temperature- and ...polarization-dependent X-ray absorption spectroscopic techniques. The magnetic field-cooled and zero-field-cooled measurements and temperature-dependent Ni
L
3,2
-edge X-ray magnetic circular dichroism spectra of NTO reveal a weak Ni-Ni ferromagnetic interaction close to ~60 K (
T
SO
: temperature of the onset of spin ordering) with a net alignment of Ni spins (the uncompensated components of the Ni moments) along the crystallographic
c
-axis, which is absent from the
ab
-plane. Below the Néel temperature,
T
N
~ 52 K, NTO is stable in the antiferromagnetic state with its spin axis parallel to the
c
-axis. The Ni
L
3,2
-edge X-ray linear dichroism results indicate that above
T
SO
, the Ni 3
d e
g
electrons preferentially occupy the out-of-plane 3
d
3z
2
−r
2
orbitals and switch to the in-plane 3
d
x
2
−y
2
orbitals below
T
SO
. The inherent distortion of the NiO
6
octahedra and anisotropic nearest-neighbor Ni-O bond lengths between the
c
-axis and the
ab
-plane of NTO, followed by anomalous Debye-Waller factors and orbital-lattice in conjunction with spin-phonon couplings, stabilize the occupied out-of-plane (3
d
3z
2
−r
2
) and in-plane (3
d
x
2
−y
2
) Ni
e
g
orbitals above and below
T
SO
, respectively.
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