2,822 research outputs found
Functionalisation of colloidal transition metal sulphides nanocrystals: A fascinating and challenging playground for the chemist
Metal sulphides, and in particular transition metal sulphide colloids, are a broad, versatile and exciting class of inorganic compounds which deserve growing interest and attention ascribable to the functional properties that many of them display. With respect to their oxide homologues, however, they are characterised by noticeably different chemical, structural and hence functional features. Their potential applications span several fields, and in many of the foreseen applications (e.g., in bioimaging and related fields), the achievement of stable colloidal suspensions of metal sulphides is highly desirable or either an unavoidable requirement to be met. To this aim, robust functionalisation strategies should be devised, which however are, with respect to metal or metal oxides colloids, much more challenging. This has to be ascribed, inter alia, also to the still limited knowledge of the sulphides surface chemistry, particularly when comparing it to the better established, though multifaceted, oxide surface chemistry. A ground-breaking endeavour in this field is hence the detailed understanding of the nature of the complex surface chemistry of transition metal sulphides, which ideally requires an integrated experimental and modelling approach. In this review, an overview of the state-of-the-art on the existing examples of functionalisation of transition metal sulphides is provided, also by focusing on selected case studies, exemplifying the manifold nature of this class of binary inorganic compounds
Cadmium transport in sediments by tubificid bioturbation: An assessment of model complexity
Biogeochemistry of metals in aquatic sediments is strongly influenced by bioturbation. To determine the effects of biological transport on cadmium distribution in freshwater sediments, a bioturbation model is explored that describes the conveyor-belt feeding of tubificid oligochaetes. A stepwise modelling strategy was adopted to constrain the many parameters of the model: (i) the tubificid transport model was first calibrated on four sets of microspheres (inert solid tracer) profiles to constrain tubificid transport; (ii) the resulting transport coefficients were subsequently applied to simulate the distribution of both particulate and dissolved cadmium. Firstly, these simulations provide quantitative insight into the mechanism of tubificid bioturbation. Values of transport coefficients compare very well with the literature, and based on this, a generic model of tubificid bioturbation is proposed. Secondly, the application of the model to cadmium dataset sheds a light on the behaviour of cadmium under tubificid bioturbation. Cadmium enters the sediment in two ways. In one pathway, cadmium enters the sediment in the dissolved phase, is rapidly absorbed onto solid particles, which are then rapidly transported to depth by the tubificids. In the other pathway, cadmium is adsorbed to particles in suspension in the overlying water, which then settle on the sediment surface, and are transported downwards by bioturbation. In a final step, we assessed the optimal model complexity for the present dataset. To this end, the two-phase conveyor-belt model was compared to two simplified versions. A solid phase-only conveyorbelt model also provides good results: the dissolved phase should not be explicitly incorporated because cadmium adsorption is fast and bioirrigation is weak. Yet, a solid phase-only biodiffusive model does not perform adequately, as it does not mechanistically capture the conveyor-belt transport at short time-scales
CEPC Technical Design Report -- Accelerator (v2)
The Circular Electron Positron Collider (CEPC) is a large scientific project
initiated and hosted by China, fostered through extensive collaboration with
international partners. The complex comprises four accelerators: a 30 GeV
Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to
180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar).
The Linac and Damping Ring are situated on the surface, while the Booster and
Collider are housed in a 100 km circumference underground tunnel, strategically
accommodating future expansion with provisions for a Super Proton Proton
Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline
design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve
a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab
for two interaction points over a decade, producing 2.6 million Higgs bosons.
Increasing the SR power to 50 MW per beam expands the CEPC's capability to
generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs
coupling at sub-percent levels, exceeding the precision expected from the
HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the
Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design
Report (CDR, 2018), comprehensively detailing the machine's layout and
performance, physical design and analysis, technical systems design, R&D and
prototyping efforts, and associated civil engineering aspects. Additionally, it
includes a cost estimate and a preliminary construction timeline, establishing
a framework for forthcoming engineering design phase and site selection
procedures. Construction is anticipated to begin around 2027-2028, pending
government approval, with an estimated duration of 8 years. The commencement of
experiments could potentially initiate in the mid-2030s.Comment: 1106 page
Technologies to develop technology: the impact of new technologies on the organisation of the innovation process.
Companies are under increasing pressure to develop new product more effectively and efficiently. In order to meet this challenge, the organisation of the new product development process has received ample attention both in the academic literature and in the practitioner literature. As a consequence, a myriad of methods to design new products has been developed. These methods aim at facilitating concurrent product design and engineering. However, it is only recently, through the advent of families of new design technologies, that concurrency really becomes possible. In this paper, research on the impact of new design technologies on the product development process is reported and discussed. It is demonstrated that these technologies can have a significant impact on the organisation of innovation processes.Processes;
From ligands to binding motifs and beyond; the enhanced versatility of nanocrystal surfaces
Surface chemistry bridges the gap between nanocrystal synthesis and their applications. In this respect, the discovery of complex ligand binding motifs on semiconductor quantum dots and metal oxide nanocrystals opens a gateway to new areas of research. The implications are far-reaching, from catalytic model systems to the performance of solar cells
Correlative Microscopy of Morphology and Luminescence of Cu porphyrin aggregates
Transfer of energy and information through molecule aggregates requires as
one important building block anisotropic, cable-like structures. Knowledge on
the spatial correlation of luminescence and morphology represents a
prerequisite in the understanding of internal processes and will be important
for architecting suitable landscapes. In this context we study the morphology,
fluorescence and phosphorescence of molecule aggregate structures on surfaces
in a spatially correlative way. We consider as two morphologies, lengthy
strands and isotropic islands. It turns out that phosphorescence is quite
strong compared to fluorescence and the spatial variation of the observed
intensities is largely in line with the amount of dye. However in proportion,
the strands exhibit more fluorescence than the isotropic islands suggesting
weaker non-radiative channels. The ratio fluorescence to phosphorescence
appears to be correlated with the degree of aggregation or internal order. The
heights at which luminescence saturates is explained in the context of
attenuation and emission multireflection, inside the dye. This is supported by
correlative photoemission electron microscopy which is more sensitive to the
surface region. The lengthy structures exhibit a pronounced polarization
dependence of the luminescence with a relative dichroism up to about 60%,
revealing substantial perpendicular orientation preference of the molecules
with respect to the substrate and parallel with respect to the strands
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Rich Chemistry in Inorganic Halide Perovskite Nanostructures.
Halide perovskites have emerged as a class of promising semiconductor materials owing to their remarkable optoelectronic properties exhibiting in solar cells, light-emitting diodes, semiconductor lasers, etc. Inorganic halide perovskites are attracting increasing attention because of the higher stability toward moisture, light, and heat as compared with their organic-inorganic hybrid counterparts. In particular, inorganic halide perovskite nanomaterials provide controllable morphology, tunable optoelectronic properties, and improved quantum efficiency. Here, the development controlled synthesis of desired inorganic halide perovskite nanostructures by various chemical approaches is described. Utilizing these nanostructures as platforms, anion exchange chemistry for wide compositional and optical tunabilities is described, and the rich structural phase transition phenomenon and mechanism investigated systematically. Furthermore, these nanostructures and extracted knowledge are applied to design photonic, photovoltaic, and thermoelectric devices. Finally, future directions and challenges toward improvement of the optical, electrical, and optoelectronic properties, exploration of the anion and cation exchange kinetics, and alleviation of the stability and toxicity issues in inorganic lead based halide perovskites are discussed to provide an outlook on this promising field
GW quasiparticle band structures of stibnite, antimonselite, bismuthinite, and guanajuatite
We present first-principles calculations of the quasiparticle band structures
of four isostructural semiconducting metal chalcogenides AB (with A =
Sb, Bi and B = S, Se) of the stibnite family within the GW approach. We
perform extensive convergence tests and identify a sensitivity of the
quasiparticle corrections to the structural parameters and to the semicore
electrons. Our calculations indicate that all four chalcogenides exhibit direct
band gaps, if we exclude some indirect transitions marginally below the direct
gap. Relativistic spin-orbit effects are evaluated for the Kohn-Sham band
structures, and included as scissor corrections in the quasiparticle band gaps.
Our calculated band gaps are 1.5 eV (SbS), 1.3 eV (SbSe), 1.4
eV (BiS) and 0.9 eV (BiSe). By comparing our calculated gaps
with the ideal Shockley-Queisser value we find that all four chalcogenides are
promising as light sensitizers for nanostructured photovoltaics.Comment: 11 pages, 5 figures. Revised manuscript - includes spin-orbit
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Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals
Cu2-xTe nanocubes were used as starting seeds to access metal telluride
nanocrystals by cation exchanges at room temperature. The coordination number
of the entering cations was found to play an important role in dictating the
reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e.
with coordination number 4), such as Cd2+ or Hg2+, yielded monocrystalline CdTe
or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like
heterostructures as intermediates. The formation of Janus-like architectures
was attributed to the high diffusion rate of the relatively small tetrahedrally
coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and
nucleate the CdTe (or HgTe) phase in a preferred region of the host structure.
Also, with both Cd2+ and Hg2+ ions the exchange led to wurtzite CdTe and HgTe
phases rather than the more stable zinc-blende ones, indicating that the anion
framework of the starting Cu2- xTe particles could be more easily deformed to
match the anion framework of the metastable wurtzite structures. As hexagonal
HgTe had never been reported to date, this represents another case of
metastable new phases that can only be accessed by cation exchange. On the
other hand, the exchanges involving octahedrally coordinated ions (i.e. with
coordination number 6), such as Pb2+ or Sn2+, yielded rock-salt polycrystalline
PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell
architectures at the early stages of the exchange process. In this case, the
octahedrally coordinated ions are probably too large to diffuse easily through
the Cu2-xTe structure: their limited diffusion rate restricts their initial
reaction to the surface of the nanocrystals, where cation exchange is initiated
unselectively, leading to core@shell architectures.Comment: 11 pages, 7 figures in J. Am. Chem. Soc, 13 May 201
FIXES, a system for automatic selection of set-ups and design of fixtures
This paper reports on the development of a computer aided planning system for the selection of set-ups and the design of fixtures in part manufacturing. First, the bottlenecks in the present planning methods are indicated. A brief description is given of the CAPP environment PART, in which FIXES is incorporated. The planning procedure of FIXES consists of two parts: the selection of set-ups and the design of a fixture for each set-up. The automatic selection of set-ups is based on the comparison of the tolerances of the relations between the different shape elements of the part. A tolerance factor has been developed to be able to compare the different tolerances. The system automatically selects the positioning faces and supports the selection of tools for positioning, clamping and supporting the part. A prototype implementation of FIXES is discussed
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