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The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH4F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano‐ and sub‐nano scales. At the nano‐scale, the hidden mosaics of zeolite structure predetermine the spatio‐temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub‐nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites. [ABSTRACT FROM AUTHOR]

Background: The atomizers of electronic cigarettes (ECs) contain metals that transfer to the aerosol upon heating and may present health hazards. This study analyzed 4th-generation EC pod atomizer design features and characterized their elemental/metal composition. Methods: Eleven EC pods from six brands/manufacturers were purchased at local shops and online. Pods were dissected and imaged using a Canon EOS Rebel SL2 camera. Elemental analysis and mapping of atomizer components was done using a scanning electron microscope coupled with an energy dispersive x-ray spectrometer. Results: EC pods varied in size and design. The internal atomizer components were similar across brands except for variations occurring mainly in the wicks and filaments of some products. The filaments were either Elinvar (nickel, iron, and chromium) (36.4%), nichrome (36.4%), iron-chromium (18.2%), or nickel (9%). Thick wires present in 55% of the atomizers were mainly nickel and were joined to filaments by brazing. Wire-connector joints were Elinvar. Metal air tubes were made of Elinvar (50%), nickel, zinc, copper, and tin (37.5%), and nickel and copper (12.5%). Most of the wick components were silica, except for two pods (PHIX and Mico), which were mainly ceramic. Connectors contained gold-plated nickel, iron-chromium multiple alloys of nickel, zinc, gold, iron, and copper. Wick chambers were made of Elinvar. Outer casings were either nickel, copper-tin, or nickel-copper alloys. Magnets were nickel with minor iron, copper, and sulfur. Some frequently occurring elements were high in relative abundance in atomizer components. Conclusions: The atomizers of pods are similar to previous generations, with the introduction of ceramic wicks and magnets in the newer generations. The elements in EC atomizers may transfer into aerosols and adversely affect health and accumulate in the environment. [ABSTRACT FROM AUTHOR]

We report colloidal routes to synthesize silicon@carbon composites for the first time. Surface-functionalized Si nanoparticles (SiNPs) dissolved in styrene and hexadecane are used as the dispersed phase in oil-in-water emulsions, from which yolk-shell and dual-shell hollow SiNPs@C composites are produced via polymerization and subsequent carbonization. As anode materials for Li-ion batteries, the SiNPs@C composites demonstrate excellent cycling stability and rate performance, which is ascribed to the uniform distribution of SiNPs within the carbon hosts. The Li-ion anodes composed of 46 wt % of dual-shell SiNPs@C, 46 wt % of graphite, 5 wt % of acetylene black, and 3 wt % of carboxymethyl cellulose with an areal loading higher than 3 mg cm−2 achieve an overall specific capacity higher than 600 mAh g−1, which is an improvement of more than 100 % compared to the pure graphite anode. These new colloidal routes present a promising general method to produce viable Si-C composites for Li-ion batteries. [ABSTRACT FROM AUTHOR]

30-80 nm thick yttrium iron garnet (YIG) films are grown by pulsed laser deposition on a 5 nm thick sputtered Pt atop gadolinium gallium garnet substrate (GGG) (110). Upon post-growth rapid thermal annealing, single crystal YIG(110) emerges as if it were epitaxially grown on GGG(110) despite the presence of the intermediate Pt film. The YIG surface shows atomic steps with the root-mean-square roughness of 0.12 nm on flat terraces. Both Pt/YIG and GGG/Pt interfaces are atomically sharp. The resulting YIG(110) films show clear in-plane uniaxial magnetic anisotropy with a well-defined easy axis along (001) and a peak-to-peak ferromagnetic resonance linewidth of 7.5 Oe at 9.32 GHz, similar to YIG epitaxially grown on GGG. Both spin Hall magnetoresistance and longitudinal spin Seebeck effects in the inverted bilayers indicate excellent Pt/YIG interface quality. [ABSTRACT FROM AUTHOR]

The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels. [ABSTRACT FROM AUTHOR]

Interest in graphene as a two-dimensional quantum-well material for energy applications and nanoelectronics has increased exponentially in the last few years. The recent advances in large-area single-sheet fabrication of pristine graphene have opened unexplored avenues for expanding from nano- to meso-scale applications. The relatively low level of absorptivity and the short lifetimes of excitons of single-sheet graphene suggest that it needs to be coupled with light sensitizers in order to explore its feasibility for photonic applications, such as solar-energy conversion. Red-emitting CdSe quantum dots are employed for photosensitizing single-sheet graphene with areas of several square centimeters. Pyridine coating of the quantum dots not only enhances their adhesion to the graphene surface, but also provides good electronic coupling between the CdSe and the two-dimensional carbon allotrope. Illumination of the quantum dots led to injection of n-carrier in the graphene phase. Time-resolved spectroscopy reveals three modes of photoinduced electron transfer between the quantum dots and the graphene occurring in the femtosecond and picosecond time-domains. Transient absorption spectra provide evidence for photoinduced hole-shift from the CdSe to the pyridine ligands, thereby polarizing the surface of the quantum dots. That is, photoinduced electrical polarization, which favors the simultaneous electron transfer from the CdSe to the graphene phase. These mechanistic insights into the photoinduced interfacial charge transfer have a promising potential to serve as guidelines for the design and development of composites of graphene and inorganic nanomaterials for solar-energy conversion applications. [ABSTRACT FROM AUTHOR]

During mineralization, the hard outer magnetite-containing shell of the radular teeth of Cryptochiton stelleri undergoes four distinct stages of structural and phase transformations: (i) the formation of a crystalline α-chitin organic matrix that forms the structural framework of the non-mineralized teeth, (ii) the templated synthesis of ferrihydrite crystal aggregates along these organic fibers, (iii) subsequent solid state phase transformation from ferrihydrite to magnetite, and (iv) progressive magnetite crystal growth to form continuous parallel rods within the mature teeth. The underlying α-chitin organic matrix appears to influence magnetite crystal aggregate density and the diameter and curvature of the resulting rods, both of which likely play critical roles in determining the local mechanical properties of the mature radular teeth. [ABSTRACT FROM AUTHOR]

The growth of crystalline copper sulfide using a viral template was investigated using sequential incubation in CuCl2 and Na2S precursors. Non-specific electrostatic attraction between a genetically-modified M13 bacteriophage and copper cations in the CuCl2precursor caused phage agglomeration and bundle formation. Following the addition of Na2S, polydisperse nanocrystals 2-7 nm in size were found along the length of the viral scaffold. The structure of the copper sulfide material was identified as cubic anti-fluorite type Cu1.8S, space group FmN3m. Strong interband absorption was observed within the ultraviolet to visible range with an onset near 800 nm. Furthermore, free carrier absorption, associated with the localized surface plasmon resonance of the copper sulfide nanocrystals, was seen in the near infrared with absorbance maxima at 1060 nm and 3000 nm, respectively. [ABSTRACT FROM AUTHOR]

A series of experiments with and without sample retreatment was performed on a starting mixture of dolomite plus quartz at 0.5 GPa and 600 °C in a CO2-H2O fluid with a mole fraction of CO2 of 0.2 for durations up to 582 h. The initial reaction of dolomite and quartz led to rapid formation of talc and calcite instead of tremolite and calcite by the intended reaction: 5 dolomite + 8 quartz + H2O = tremolite + 3 calcite + 7 CO2. With continued treatment, the talc + calcite + quartz assemblage gradually reacts to form increasing amounts of tremolite and diopside with the eventual loss of quartz and nearly complete loss of talc. The detailed structure of the amphibole and the nature of the Mg enrichment were revealed using AEM analysis of individual amphibole crystals. The most abundant defects are triple-chain chain multiplicity faults (CMFs), which appear as isolated lamellae with single periodicity in short-duration experiments and increasingly as groups of lamellae with variable multiplicity and periodicity in longer duration experiments and especially in a long-duration experiment without retreatment. In this latter experiment, a calcian clinojimthompsonite domain extending 15 unit cells along the b axis was observed. The sample after 582 h and five retreatments shows, on average, 3.5% true solid solution with Mg expressed as the Mg-cummingtonite (MC) component after correction for the presence of CMFs. This sample is thought to most closely approach the equilibrium composition for the amphibole. The sample after 250 h with three retreatments has about 10%, whereas that after 582 h without retreatment has 0.6% MC component, the latter having a relatively high density of CMFs. This study affirms the importance that precursor non-amphibole biopyriboles play in the formation of tremolitic amphibole. [ABSTRACT FROM AUTHOR]

The entire sequence of crystallization events, starting with formation of the initial organic-cation- free gel, proceeding through the zeolite nucleation stage, and finishing with complete transformation into LTA-type zeolite crystals, has been monitored by means of high-resolution transmission electron microscopy. Formation and development of voids, containing highly hydrated material transformed later into negative crystals, has been discovered in the solid part of the system. The evolution of these areas has been found to be an integral and noteworthy part of the chemical transformation of the gel that preceded the nucleation in the system. These void structures and, in particular, their solid-liquid interfaces have been identified as the specific locations where the formation of protozeolite nuclei took place. Further development of the system followed the classical for zeolite-yielding systems of crystallization that could be described by the autocatalytic model. [ABSTRACT FROM AUTHOR]

A series of low-Ca (1.8-1.65 atoms Ca per formula unit) actinolites were synthesized in the system CaO-FeO-MgO-SiO2-H2O with bulk compositions of 0, 10, 20, and 30 mol% ferro-actinolite when projected onto the tremolite--ferro-actinolite join for the purpose of determining the cation site occupancies as a function of bulk composition. Syntheses were done by multiple treatments of the oxide-metal mixtures in internally heated gas vessels at 600-800 °C, 6 kbar, fO2 near the Co-CoO buffer, which is sufficiently low to prevent the appearance of Fe3+ in this study, and-for total durations up to 774 hours. Bulk compositions of the synthesis products were assessed by electron microprobe analysis (EMPA), analytical transmission electron microscopy (AEM), and by using unit-cell dimensions (CD method), whereas the site occupancies were assessed using powder X-ray diffraction (XRD) Rietveld refinements, Fourier-transform infrared (FTIR) spectroscopy, and Mössbauer spectroscopy. Selected-area electron-diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images were obtained to study the structure and defects of the samples. A maximum of about 2% non-amphibole chain-multiplicity faults (CMFs) were observed in the sample with 10 mol% ferro-actinolite component, indicating the strong reduction in CMFs that occurs with only a small addition of ferro-actinolite to tremolitic amphiboles. This study, as with earlier studies, found no significant preferential partitioning of Fe and Mg relative to the bulk Fe content of the sample at the M1 and M3 sites, weak partitioning of Mg relative to Fe into the M2 site, and strong partitioning of Fe relative to Mg at the M4 site. No ferric iron was detected. The partitioning of Fe and Mg at the M4 site was modeled by a simple ideal-activity, two-site exchange reaction using the actinolites from this study and those of previous studies with bulk Fe/(Fe + Mg) ≤ 0.3 and with low Al, Mn, and Na contents using 1 bar and 298K values of ΔG° = 62 kJ and ΔS° = 54 J/K. The FTIR data were analyzed for the presence of short-range order of Fe and Mg at the M1 and M3 sites but none was found. [ABSTRACT FROM AUTHOR]

Our experimental simulations of the exhumation path of mantle peridotites show that high-temperature (1400 °C) decompression of lherzolite from 14 to 13 and 12 GPa results in exsolution of interstitial blebs of diopside and Mg2SiO4 (wadsleyite) lamellae from majoritic garnet. At lower pressures (from 8 to 5 GPa, atT = 1400 °C) only enstatite exsolves as blebs at garnet boundaries. Continuous high-temperature decompression from 14 to 7 GPa produces zoned majoritic garnet containing blebs of exsolved pyroxenes inside garnet rims. No intracrystalline precipitation of pyroxene was observed in garnet, although such lamellae are found in some natural garnet peridotites. The explanation appears to be the three orders of magnitude difference in grain size between experimental and natural specimens. Our data suggest that Mg2SiO4 and diopside exsolutions reflect the deepest point of the exhumation path of garnet peridotites, whereas enstatite precipitation may be restricted to garnets with less majoritic component at shallower depths.Terra Nova, 16, 325–330, 2004 [ABSTRACT FROM AUTHOR]

The formation mechanisms of tremolite in a time series of hydrothermal experiments at 850 °C and 6.1 kbar were studied using transmission electron microscopy (TEM), analytical TEM, and X-ray diffraction. The starting materials were unseeded mixtures of reagent-grade oxides. After the first 8 min of reaction, the synthesis products were diopside, enstatite, clinoenstatite, quartz, and minor C-centered and primitive monoclinic amphibole (13 wt% total). The compositions of the first-formed amphiboles vary considerably, from essentially pure cummingtonite (Ca/Mg = 0) to nearly ideal tremolite (Ca/Mg = 0.4). Three groupings of amphiboles with successively higher Ca/Mg ratios were identified, respectively 0.1, 0.22, and 0.35. Over a period of 97 h, the proportions of Mg-rich amphibole gradually decrease, and the average Ca/Mg ratios of all amphiboles steadily increase from about 0.22 to 0.35. Other changes include: (1) a decrease in the aspect ratio of amphibole crystals with increasing time; (2) a decrease in the number of non-amphibole chain multiplicity faults (CMFs), from early A'(2) values as low as 0.81 to a final value of 0.94; and (3) a distinct change in the rate of amphibole growth after 1 h of synthesis. These observations suggest that two mechanisms of amphibole formation are dominant: (1) formation of pyroxene modules with subsequent hydration and arrangement into the double-chain amphibole structure and (2) direct nucleation and growth of amphibole from hydrothermal solution. A third mechanism involving formation of talc-like modules, followed by their breakdown into double-chain modules, incorporation of Ca, and ordering into the amphibole structure, may also occur but probably only at the lamellar or unit-cell scale, because these syntheses were performed outside the stability field of talc. [ABSTRACT FROM AUTHOR]

A re-investigation of the synthesis, characterization, and upper-thermal stability of ferro-actinolite has been performed in the system CaO-FeO-SiO[sub 2]-H[sub 2]O. Synthesis experiments were done over the range of 2 to 10 kbar and 420° to 600°C for several bulk compositions along the join Ca[sub 2]Fe[sub 5]Si[sub 8]O[sub 22](OH)[sub 2] - Fe[sub 7]Si[sub 8]O[sub 22](OH)[sub 2] and at oxygen fugacities (f[sub O[sub 2]]) defined by the vessel (∼Ni-NiO), Co-CoO, and iron-magnetite (IM) buffers. The highest yields of actinolite were obtained at 2 kbar, 420°C, and at the relatively oxidizing conditions of the Ni-NiO buffer. Grinding and retreatment of the sample was found to be important for increasing the yield of amphibole up to a maximum of about 70 weight percent; however, complete yields of actinolite were never obtained indicating some physical barrier or incorrect chemical (f[sub O[sub 2]]) conditions preventing complete reaction. The highest-yield actinolite syntheses were characterized using a high-resolution transmission electron microscope (TEM) equipped with an energy-dispersive spectrometer. A survey of representative grains using the TEM revealed the presence of very few chain-multiplicity faults (A'(2) = 0.98 - 0.99); however, a rather large spread of compositions was observed, with crystals having Ca contents that range from as little as 0.5 up to 2.0 Ca atoms per formula unit (apfu). There was no clear correlation between actinolite crystal composition and the bulk composition of the starting material. By combining these analyses with three other techniques for determining the composition of the synthetic actinolite (that is, volume-composition relationships, Rietveld refinement of Ca and Fe on the M4 site, and mass balancing involving bulk-composition and mineral-proportions), the average composition of the synthetic actinolite was determined to be Ca[sub 1.67]Fe[sub 5.33]Si[sub 8]O[sub 22](OH)[sub 2]. Experimental reversals were obtained on reaction (1): 2 ferro-actinolite = 4 hedenbergite + 3 fayalite + 5 quartz + 2 water over the range of 1 to 5 kbar and 500° to 525°C with the f[sub O[sub 2]] defined by the Co-CoO buffer. A parallel set of experiments on reaction (1) was done in the presence of grunerite and the iron-magnetite/wüstite-magnetite (IM/WM) buffers. These latter experiments allowed the direct comparison of the upper-thermal stability of actinolite via reaction (1) and of Ca-saturated grunerite via reaction (2): 2 grunerite = 7 fayalite + 9 quartz + 2 water. Reaction (2) was found to lie 20° to 60°C above reaction (1). Modeling the miscibility gap between actinolite and grunerite as a regular solution with W = 15.3 kJ, a thermodynamic analysis of the internal consistency of the experimental reversals for reaction (1) was performed, from which the best-lit values of 696.4 J/K · mol and -10,518.2 kJ/mol were derived for the S° and Δ[sup o, sub f] of pure ferro-actinolite, respectively. Calculation of the invariant array of curves involving the phases ferro-actinolite, grunerite, hedenbergite, fayalite, quartz, and water indicate that reaction (1) is metastable at all geologically relevant pressures and that the stable reaction defining the stability limit of ferro-actinolite is 7 ferro-actinolite = 14 hedenbergite + 3 grunerite + 4 quartz + 4 water. [ABSTRACT FROM AUTHOR]

Reports the results of high-resolution transmission electron microscopy analysis of amphiboles synthesized near the tremolite-pargasite join in the ternary system tremolite-pargasite-cummingtonite. Materials and methods; Results; Discussion.

Presents a study that determined the three-dimensional distribution of ilmenite in olivine from Alpe Arami, Switzerland using confocal laser scanning microscopy. Background of confocal laser scanning microscopy; Comparison of the ilmenite distribution determined by wavelength dispersive x-ray spectroscopy and energy dispersive x-ray spectroscopy; Determination of the volumetric abundance of ilmenite.

Presents a transmission electron microscopy study which revealed the microstructure of polysynthetically twinned near end-member grunerite from Rockport, Massachusetts. Structure of amphiboles; Details of electron microprobe analysis; Implication of the clear difference in the microstructures of grunerite from Rockfort and protoferroanthophyllite from Cheyenne.

Two new polymorphs of niobium trisulfide are established by single crystal x-ray diffraction. NbS3-iv crystallizes in the monoclinic space group P21/c with lattice parameters a = 6.7515(5) Å, b = 4.9736(4) Å, c = 18.1315(13) Å, and β = 90.116(2)°. Its structure is based on chains of [NbS6] trigonal prisms containing Nb–Nb pairs with a bond length of 3.0448(8) Å; this pairing causes the chains to corrugate slightly along their axis, a feature also present in triclinic NbS3-i that leads to semiconductor properties. The stacking arrangement of chains is different in these polymorphs, however, with NbS3-i having an ABCDE repeating sequence of chain bilayers and NbS3-iv having an AB repeating sequence. HRTEM studies show the presence of topotactically-oriented intergrown zones and numerous dislocations, which result in mosaic structuring. A second new polymorph, NbS3-v, crystallizes in the monoclinic space group P21/m with lattice parameters a = 4.950(5) Å, b = 3.358(4) Å, c = 9.079(10) Å, β = 97.35(2)°. In contrast to NbS3-iv, NbS3-v maintains fixed a Nb–Nb bond distance of 3.358(4) Å along the chains, and it has an ABCDE repeating sequence of chain bilayers similar to NbS3-i. High resolution scanning transmission electron microscopy (HR-STEM) imaging of an exfoliated NbS3-v nanoribbon shows the continuous [NbS6] chains oriented along the b-axis. These results provide the first firmly established structural data for monoclinic NbS3. In addition, SEM images show the formation of NbS3 rings and cylinders, and a combination of powder x-ray diffraction and Raman spectroscopy provides a way to distinguish between NbS3 polymorphs. [ABSTRACT FROM AUTHOR]

A correction to the article "3D Study of the Morphology and Dynamics of Zeolite Nucleation" that was published in a 2015 is presented.

Many biological materials are known for their remarkable structural complexity as well as their impressive mechanical properties. The ultrahard abrasion‐resistant radular teeth of the chitons are one such example and members of this group of mollusks, studied by David Kisailus and co‐workers on page 2908, have the surprising capacity to erode away the rocky substrates on which they graze for algae. The foreground image depicts the anterior end of the conveyor belt‐like radula that contains the magnetite‐rich teeth and the background image depicts the oriented rod‐like aggregates of magnetic nanoparticles that comprise the material. [ABSTRACT FROM AUTHOR]

Among various ways to produce nanowires, anodic alumina membrane- (AAM-) based synthesis has constantly received much attention, because AAM has a uniform and parallel porous nanostructure which makes it an ideal template material for fabricating highly ordered nanostructures. In this paper, we report fabrication of InSb nanowire arrays with diameter of 200nm and 30nm by direct current electrodeposition inside the nanochannels of anodic alumina membranes without subsequent annealing. The nanowires have four major growth directions, (220) being the most dominant with structure defects such as twins. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results demonstrate that these InSb nanowires are uniform with diameters about 200nm and 30 nm, corresponding to the pore diameter of the AAMs. The I-V measurement of a single nanowire is also reported with encouraging preliminary results. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the rheology of hot-pressed polycrystalline omphacite (Di58Jd42, space group C2/c) at strain rates of 10−4–10−5/s, temperatures of 1300–1500K and a pressure of 3GPa, using a 5GPa Griggs-type deformation apparatus. The rheological constitutive equation of omphacite is determined with a stress exponent of 3.5±0.2 and an activation energy of 310±50kJ/mol. Our study shows that: (1) the creep strength of omphacite falls between those of diopside and jadeite; (2) experimental omphacite microfabrics are indistinguishable from natural ones: S-type fabric and its mesoscopic foliation develop under conditions of axially symmetric shortening, whereas L-type fabric and its mesoscopic lineation develop under conditions of general strain, with L parallel to the greatest elongation; (3) as in naturally deformed omphacite, the deformation substructure is characterized by the dominant slip systems {110}1/2〈110〉, {110}[001] and (100)[001]. We conclude that both S- and L-type omphacite fabrics are produced by these slip systems; fabric differences arise solely from variation of the geometry and orientation of the finite strain ellipsoid. We also confirm the previous suggestion that Na-bearing pyroxenes are significantly weaker than Na-free pyroxenes. [Copyright &y& Elsevier]

The first direct transmission electron microscopic (TEM) observation has been carried out on the continuous monocrystal-thick b-oriented pure silica zeolite MFI films produced by in situ crystallization. The self-supporting film samples for TEM study were fabricated by dissolving the steel substrate with acid. This TEM study is free of those artifacts that are typically associated with TEM sample preparations, and allows us to investigate the "true" structure and texture of a very large area of the film and at the same time to focus at will on each individual zeolite crystal in the film. Abundant TEM information including crystallographic orientation relationships among crystals in the film (both out-of-plane and in-plane), grain boundaries, and each crystal grain was obtained. This TEM investigation provides direct unambiguous new evidence to support the homogeneous nucleation mechanism, by which the films form through homogeneous nucleation and crystal growth in the bulk to form equal-sized disk-shape crystals, followed by self-assembly of these crystals onto the substrate to produce a two-dimensional close-packed structure. The last stage of the film formation involves simultaneous space-limited growth and rotation of the individual crystals to realize the in-plane crystallographic control within the film. [ABSTRACT FROM AUTHOR]