ライフサイエンスコーパス: clay

1 the binder is composed of an allophane-like clay.

2 an blue pigment was also mixed into the dyed clay.

3 s via the attachment of nanoparticles to the clay.

4 (>7.0) and generally contained >200 mg g(-1) clay.

5 y to examine relatively undiluted authigenic clay.

6 ld a three-dimensional representation of the clay.

7 s with biologically/chemically reduced model clays.

8 cid modification of Na-enriched and pillared clays.

9 es in what may be very rapidly deposited CIE clays.

10 r alone, with illite outperforming the other clays.

11 l) components on the surface compositions of clays.

12 present as exchangeable Fe oxyhydroxide and clay-adsorbed Se(4+), and 39% of Se is present as organo

13 The porosity of clay aggregates is an important property governing chemi

14 rived from in situ weathering, and exogenous clay and silt, which entered the chamber through fractur

15 r many centuries in Xinjiang, as depicted in clay and wooden figurines unearthed in the Astana cemete

16 cess, utilizing porous catalysts composed of clay and zeolite, converts heavy crude-oil fractions int

17 inary wares; (ii) intervalley homogeneity of clays and fabrics for a wide range of decorated wares (e

18 sults show: (i) intervalley heterogeneity of clays and fabrics for ordinary wares; (ii) intervalley h

19 tructure without considering the presence of clays and other minerals in shales.

20 ydrogen bonding between siloxane groups from clays and peptide molecules.

21 ent-free crystals and solids such as silica, clay, and zeolite and water-soluble hosts that can solub

22 s minerals and mineraloids including gypsum, clays, and amorphous silica (opal).

23 ure iron- and manganese-containing minerals, clays, and aquifer solids.

24 Only certain clays are bactericidal; those containing soluble reduced

25 e-scale production of nanosized zeolites and clays are discussed in depth.

26 rious sorbents (e.g., organic carbon, soils, clay) are reliable and well established.

27 anosized microporous materials (zeolites and clays) are addressed.

28 gation of TiO2 nanoparticles with a smectite clay as analogues for natural colloids.

29 he initial shape and dispersion state of the clay as well as the nanoparticle/clay concentration rati

30 ow connectivity of organic matter-hosted and clay-associated pores in these shales.

31 In the presence of the clay, at lower pyrolysis temperatures, the biochar devel

32 Soil components (e.g., clays, bacteria and humic substances) are known to produ

33 olymer, carbonaceous, metal, metal oxide and clay) based modified electrodes for the sensing of NADH.

34 Here we report self-assembled clay-based 2D nanofluidic channels with surface charge-g

35 in low-permeability geologic formations and clay-based engineered barrier systems.

36 Understanding the fundamentals of clay behavior can lead to better environmental impact mi

37 etreated by iron-sulfate-clay slurries (iron-clay biochar), as compared to untreated bamboo biochar.

38 The clay buffered the media pH to approximately 4.6 and Eh v

39 to measure temporal gains/losses of surface clay caused by periodic wind erosion (dust) and rainfall

40 while at higher temperature, the presence of clay causes a reduction in the biochar pore volume.

41 elite=3:4:1 and com II; bentonite: activated clay: celite=3:4:1+1% citric acid) on the physico-chemic

42 QPVPcS-clay composites were characterized by X-ray diffraction,

43 Hybrid polycation-clay composites, based on methylated poly vinylpyridiniu

44 The clay composition map shows how kaolinite has developed o

45 The same clay composition map, in combination with one sensitive

46 tate of the clay as well as the nanoparticle/clay concentration ratio also affected the nature of the

47 variation among mineral soils in soil C and clay concentrations, soil delta(15)N showed no consisten

48 of OC is also related to grain size with the clay containing mostly (immature) plant derived OC and s

49 creases for this reaction in the presence of clay-containing ATPS over clay in buffer alone, with ill

50 The ability of each clay-containing ATPS to catalyze reaction of o-phenylene

51 As OPC clinker-generating mixtures, six clay-containing binary blends were investigated, three w

52 Clay contamination included pre-saturation of clays with

53 es with pre-existing phyllosilicate-bearing (clay content </=3 wt.%) micro-layers weaken faster than

54 ropose that, within calcite gouge, ultra-low clay content (</=3 wt.%) localized along micrometer-thic

55 L kg(-1), n=19), and was correlated with the clay content (relation to log10(Kr, linear), r2=0.40, n=

56 Soil clay content and pH were the most important predictive s

57 Where high clay content had caused retention of soil solution, amou

58 ctivation would be unlikely because the high clay content of caprocks ensures a reduced permeability

59 he soil properties; a high organic matter or clay content was observed to negatively affect the recov

60 to study soil C cycling: metabolic quotient, clay content, and physical fractionation.

61 roperties (such as cation exchange capacity, clay content, bulk density) 24%.

62 organic C (POC, HOC, and ROC, respectively), clay content, cation exchange capacity (CEC), pH, volume

63 e BJH pore volume is positively related with clay content, suggesting N2GA is suitable for describing

64 soil organic carbon (C), soil C:N ratio, and clay content, where Q10 was primarily influenced by the

65 andard deviation while negatively related to clay content.

66 ine-textured soils, and in soils with higher clay contents (>35%) and low pH (<5.5).

67 Badland soils-which have high silt and clay contents, bulk density, and soil electric conductiv

68 s, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transpo

69 ave the potential to host large lithium-rich clay deposits.

70 mas have the potential to host large lithium clay deposits.

71 to organic carbon and organic carbon-coated clays dominate U(IV) speciation in an organic-rich natur

72 linite; therefore, Ca(2+)-bridging of BPS to clay edge sites was assessed by comparing sorption from

73 e to propagate rapidly once initiated at the clay edge.

74 correlated to the reduction potential of the clay (EH,clay, R2=0.95 for both minerals), indicating th

75 Only Al derived from the clay exceeded the minimum inhibitory concentrations for

76 ir microporous nature nanosized zeolites and clays exhibit novel properties, different from those of

77 by added/sorbed Fe(II) (if Fe(II)SORBED > 8% clay Fe(II)LABILE); however, the kinetics of this concep

78 l-bearing jarosite and other minerals (e.g., clays, Fe-(oxy)hydroxides).

79 was caused by different forms of structural clay-Fe(II) in the clay minerals and different reduction

80 logical activity, the reactivity of biogenic clay-Fe(II) toward reducible contaminants is particularl

81 s are ubiquitous in the environment, and the clay-Fe(II)/Fe(III) redox couple plays important roles i

82 with NAu-2 and biogenic uraninite, 16.4% of clay-Fe(III) was reduced in the presence of excess urani

83 ers showing higher abundances in terra firme clay forest.

84 s of sauconite identifying new mechanisms of clay formation in surface environments of rocky planets.

85 esent experimental evidence that shows rapid clay formation under conditions that would have been pre

86 The Opalinus Clay formation will host geological nuclear waste reposi

87 over the Cenozoic reduced marine authigenic clay formation, contributing to the rise in seawater Mg/

88 e and mudstone seals is heavily dependent on clay fraction and can be extremely low even in the prese

89 The clay fraction enhanced the retention of the CeO2 nanopar

90 er component was found in the sand, silt, or clay fraction while the structural component was exclusi

91 roportion of microbial-derived C in the silt-clay fraction, as compared with that in adjacent soils t

92 ctionated into sand, silt, and (if possible) clay fractions as well as hand-picked calcine pebbles.

93 in the antibacterial action of a kaolin-rich clay from the Colombian Amazon (AMZ).

94 This study shows that Opalinus Clay harbours the potential for chemolithoautotrophic-ba

95 Some clays have been shown to kill antibiotic-resistant human

96 In the constrained interlayer regions of the clay, hydrated electrons and co-sorbed PFCs are brought

97 in the presence of clay-containing ATPS over clay in buffer alone, with illite outperforming the othe

98 and the concentrations of organic carbon and clay in soil.

99 Whereas the iron natural to clay in the composite seems to be unaffected by operatio

100 clays in tailings ponds and the behaviors of clays in diverse industrial and natural environments.

101 anced applications of nanosized zeolites and clays in free (suspension and powder forms) and fixed (f

102 itative insights underlying the stability of clays in tailings ponds and the behaviors of clays in di

103 ago, John Desmond Bernal proposed a role for clays in the origin of life.

104 cium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments.

105 f solution of as-received and "contaminated" clays, in as-received and "contaminated" organic solvent

106 ely mediated by cation exchange in micaceous clays, in particular Illite-a non-swelling clay mineral

107 Clays, in tailings, are a significant ongoing environmen

108 Pore spaces in clays include interlayer and interparticle pores.

109 -indole-acetic-acid within an organomodified clay induce the reductive defluorination of co-sorbed PF

110 , suggesting N2GA is suitable for describing clay inter-crystalline pores in tight sandstones.

111 s loop is consistent with SEM observation on clay inter-crystalline pores while BJH pore volume is po

112 wn to dominate the energetics of the solvent-clay interaction, and organic liquids as solvents or as

113 Water diffusion within smectite clay interlayers is reduced by confinement and hence is

114 The affinity of TiO2 nanoparticles for clay is driven by electrostatic interactions.

115 Illite has been widely studied, because this clay is especially relevant for Cs migration-retention i

116 in the environment is greater where percent clay is less than 18% and soil pH is greater than 6.6.

117 evolution model; we find that the primordial clay is locally disrupted by impacts and buried by impac

118 We compared the three main types of natural clay: kaolinite, montmorillonite and illite, all of whic

119 d octahedral (structural) Fe(III) within the clay lattice, as well as between aqueous Fe(II) and stru

120 teristics of these nanocomposites, including clay-layer spacings, out-of-plane clay-sheet bending ene

121 ince been dedicated to the study of silicate clays, layered double hydroxides, believed to be common

122 y are discussed in this review with focus on clays, layered transition metal oxides, silicates, layer

123 sand into and subsequently out of kaolinite clay layers of vertical thickness 15 mm, 20 mm, and 60 m

124 ases with rapid solute diffusion and/or thin clay layers.

125 method to construct a complex and realistic clay-like nanoparticle aggregate with interparticle pore

126 for a given soil especially for the two high clay low OC soils, BPS sorbed much more than expected re

127 i sequestration is in close proximity to the clay matrix.

128 molecules that were removed from solution by clay-mediated processes.

129 Based on these measurements polymer-clay micro- and nanostructures, as a function of polymer

130 sequestration by a lanthanum (La) exchanged clay mineral (La-Bentonite), which is extensively used i

131 A Na-smectite clay mineral (Na-Mt) was exchanged with various amounts

132 reverse tricarboxylic acid (rTCA) cycle and clay mineral catalysts coevolved remains a mystery in th

133 increase in reduction potential results from clay mineral dissolution resulting in increased Fe(III)

134 iments motivated by the hypothesis that some clay mineral formation may have occurred under oxidized

135 arly Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian

136 Microdiffraction imaging identified the clay mineral kaolinite to play a key role in the immobil

137 ditions are needed to synthesize the Fe-rich clay mineral nontronite at low temperatures.

138 Here we explore the distribution of natural clay mineral particles in poly(ethylene glycol) (PEG)/de

139 to electron equivalents retained within the clay mineral structure.

140 Adsorption and redox transformations on clay mineral surfaces are prevalent in surface environme

141 /precipitation), and surface complexation on clay mineral surfaces.

142 approach is applied to study collections of clay mineral tactoids interacting with two synthetic pol

143 s clays, in particular Illite-a non-swelling clay mineral that naturally contains interlayer K(+) and

144 Using experimental data on an iron-bearing clay mineral, we illustrate how mediated electrochemical

145 Clay mineral-bearing locations have been targeted for ma

146 e is a degree of site masking in the ternary clay mineral-humic acid-bacteria composite.

147 nts and to be poorly adsorbed onto untreated clay mineral.

148 distinct microbial communities more so than clay mineralogy, where microbial-derived SOM accumulatio

149 NIR) spectrometer to measure iron oxides and clay mineralogy.

150 th (13)C-labelled amino acids and two common clay minerals (kaolinite and montmorillonite).

151 on rate constants by bioreduced iron-bearing clay minerals (montmorillonite SWy-2 and nontronite NAu-

152 erent forms of structural clay-Fe(II) in the clay minerals and different reduction potentials (Eh) of

153 These results suggest the coevolution of clay minerals and early metabolites in our planet could

154 between aqueous Fe(II) and structural Fe in clay minerals and electron conduction in octahedral shee

155 cs of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) beha

156 for further studies on the sorption of Tl to clay minerals and Mn-oxides and its impact on Tl solubil

157 m, oxytetracycline) with two aluminosilicate clay minerals and one soil.

158 tals can be associated with soil components (clay minerals and organic matter), biosolid application

159 the high capacity for binding of arsenic to clay minerals and oxides of iron and aluminum in subsoil

160 the fossils are composed of aluminosilicate clay minerals and some carbon, a composition comparable

161 In contrast, Fe-(hydr)oxides associated with clay minerals are dispersed by both extractants.

162 ics and pathways of Cr(VI) reduction by such clay minerals are poorly understood.

163 Clay minerals are principally Fe-Mg illite, mixed layers

164 idence that Fe(II) uptake characteristics on clay minerals are strongly correlated to the redox prope

165 Iron-bearing clay minerals are ubiquitous in the environment, and the

166 ity toward reductive dissolution, Fe-bearing clay minerals are viewed as a renewable source of Fe red

167 On Mars, clay minerals are widespread in terrains that date back

168 Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(

169 biologically formed structural Fe(II) in the clay minerals became increasingly important.

170 This work shows that clay minerals can provide an exceptionally high fidelity

171 r reaction controlling its mobilization, and clay minerals could mitigate As mobilization with surfac

172 pidly than biologically reduced iron-bearing clay minerals despite the minerals having similar struct

173 Authigenic clay minerals formed on or in the seafloor occur in ever

174 Fe(II)-rich clay minerals found in subsurface redox transition zones

175 E distinguishes Fe(III) reduction of layered clay minerals from that of Fe oxyhydroxides, where accum

176 redox interactions between sorbed Fe(II) and clay minerals gained in this study is essential for futu

177 e of simple oxide surfaces: edge surfaces of clay minerals have a variable proton surface charge aris

178 Iron occurs in clay minerals in both ferric and ferrous forms.

179 Our finding of 5-20% Fe atom exchange in clay minerals indicates that we need to rethink how Fe m

180 Clay minerals inter-finger with calcium phosphate that c

181 Herein, the crystallization of clay minerals is catalyzed by succinate, an example of a

182 ise the question whether Fe interaction with clay minerals is more dynamic than previously thought.

183 that: (1) As desorption/adsorption from/onto clay minerals is the major reaction controlling its mobi

184 electron donor, we found that the Fe-bearing clay minerals montmorillonite SWy-2 and nontronite NAu-2

185 We calculated that 5-20% of structural Fe in clay minerals NAu-1, NAu-2, and SWa-1 exchanged with aqu

186 s arsenate) adsorption to the phyllosilicate clay minerals of the aquifer.

187 demonstrated the rapid formation of Fe-rich clay minerals of variable crystallinity from aqueous Fe(

188 We investigated the role of Fe-bearing clay minerals on the bioreduction of nitrobenzene.

189 chemically reduced (dithionite) iron-bearing clay minerals reduced nitrobenzene more rapidly than bio

190 The surface reactivity of clay minerals remains challenging to characterize becaus

191 Our results suggest that Fe-rich clay minerals such as nontronite can form rapidly under

192 aining soluble reduced metals and expandable clay minerals that absorb cations, providing a capacity

193 ematic oscillations of various evaporite and clay minerals that can be linked to the variation of reg

194 study, the retention mechanism of Fe(II) on clay minerals was investigated using macroscopic sorptio

195 uction on soil surrogates composed of HA and clay minerals was studied by use of a coated-wall flow r

196 Clay minerals were co-located with P only to a lesser ex

197 Water in clay minerals, ammoniated phyllosilicates, or a mixture

198 n surface areas and equilibrium constants of clay minerals, and cation exchange capacity.

199 mentally relevant surfaces (Fe (hydr)oxides, clay minerals, and soil from Arizona and the Saharan Des

200 -toxic ionic aluminium (Al(3+)) species from clay minerals, driving the evolution of counteractive ad

201 In addition to clay minerals, Fe(III) oxides particles have recently be

202 (hydr)oxides were dominantly associated with clay minerals, suggesting that their dispersion as free

203 ffect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction var

204 many inter-crystalline pores are produced in clay minerals, this type of pores is not the most import

205 nect the synthesis of sauconite, a model for clay minerals, to prebiotic photochemistry.

206 luence the sorption processes at surfaces of clay minerals.

207 in barite, sphene, chalcedony, apatite, and clay minerals.

208 d in the U(VI) sorption curves for the three clay minerals.

209 by bioreduced (and pasteurized) iron-bearing clay minerals.

210 mechanism for Fe atom exchange in Fe-bearing clay minerals.

211 d different reduction potentials (Eh) of the clay minerals.

212 quid water during this time to form hydrated clay minerals.

213 o study directly due to dilution by detrital clay minerals.

214 mmediately that initiates release of As from clay minerals.

215 aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich

216 , degradable, layered double hydroxide (LDH) clay nanosheets.

217 s of atmospheric CO2 on amine-functionalized clay nanotubes followed the fractional-order kinetic mod

218 pheric CO2 entrapped in aminosilane-modified clay nanotubes.

219 ing nanoparticles occurred at a nanoparticle/clay number ratio of greater than 0.5.

220 we suggest that most of the magnetite in the clay occurs as isolated, near-equidimensional nanopartic

221 hydroxylated silicates, including ammoniated clays of endogenous origin.

222 can explain the present distribution of many clays on Mars, and the anomalously low density of the Ma

223 avior in two different clay stones, Opalinus Clay (OPA) and Helvetic Marl (HM), was studied using a w

224 e oxidized forms of Pu(V,VI) within Opalinus Clay (OPA) rock, a heterogeneous, natural argillaceous r

225 long oceanic subduction zones, where pelagic clays participate in seismic slip propagation.

226 candidates for the "active sites" that make clay particles effective nucleants for ice in the atmosp

227 Natural clay particles have been hypothesized as catalysts on th

228 chemical and physical properties of silt and clay particles that occlude organic matter from microbia

229 The addition of 2 wt % clay particles to sand greatly retarded the transport of

230 Association of clay particles with droplets formed by liquid-liquid pha

231 a finite Fe(III) pool along the edges of the clay particles, accompanied by a limited release to solu

232 In soil clay particles, the pervasive C forms were aromatic C, c

233 tural Fe sites located near the edges of the clay particles.

234 Cutting across these clay patterns are sandy deserts that developed <10 Ma an

235 With dispersed clay platelets (10(-3) M NaCl), secondary heteroaggregat

236 This model of clay-polymer interactions is based on a three-level appr

237 -matrix composites--such as nacre, silk, and clay-polymer-exhibit a remarkable balance of strength, t

238 We also show that the clay-poor location includes an abundant sulfate supply a

239 NMR cryoporosimetry, is altered by the iron-clay pretreatment.

240 troscopy shows that the presence of the iron clay prevents degradation of the cellulosic fraction at

241 m chloride salt crystals and Montmorillonite clay, previously proposed to promote polymerization.

242 higher temperatures (350-550 degrees C), the clay promotes biomass degradation, resulting in an incre

243 The organomontmorillonite clay promotes the formation of highly reactive hydrated

244 lite with spectral bands designed to measure clays, quartz and other minerals were released in 2012 f

245 d to the reduction potential of the clay (EH,clay, R2=0.95 for both minerals), indicating that the cl

246 0.95 for both minerals), indicating that the clay reduction potential also influences its reactivity.

247 ning and oilsands production industries, and clay rehabilitation following contamination poses challe

248 water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of t

249 hermore, we explore the fate of a primordial clay-rich layer with the help of a parameterized crustal

250 are exclusively H. naledi, and occur within clay-rich sediments derived from in situ weathering, and

251 ndrite Khatyrka recovered from fine-grained, clay-rich sediments in the Koryak Mountains, Chukotka (R

252 ia magnetosome chains, have been reported in clay-rich sediments in the New Jersey Atlantic Coastal P

253 ding forms in aggregates taken from a high-P clay-rich soil and a low-P sandy soil by combining advan

254 igher fullerol mineralization in an organic, clay-rich soil versus a silty, low C soil ( approximatel

255 ment images of a cesium-infiltrated Opalinus clay rock were recorded using LA with a laser-spot diame

256 om heterogeneous materials, such as Opalinus clay rock, will remain a challenge for 3D LA-ICPMS imagi

257 major and minor constituents in an Opalinus clay-rock sample at a 1.5 mum laser-spot diameter and qu

258 e to study the iron-rich minerals within the clay sediment in their bulk state.

259 including clay-layer spacings, out-of-plane clay-sheet bending energies, X-ray diffractograms, and m

260 ctericidal mechanism demonstrated by natural clays should guide designs of new mineral-based antibact

261 Characterization of the clay size fraction of a fine-grained unit from the RTZ i

262 Here we report the clay-sized (<2 mum) Hf-Nd isotope data from Asian dust s

263 ia-mineral aggregates and biofilms formed on clay-sized minerals.

264 60 cm were from SOM associated with silt and clay-sized particles.

265 bamboo biomass is pretreated by iron-sulfate-clay slurries (iron-clay biochar), as compared to untrea

266 s: a sandy soil poor in organic matter and a clay soil rich in organic matter, both contaminated with

267 ganic matter (OM)-rich peat soil, an OM-poor clay soil, a hydrophilic Aldrich humic acid salt, and wa

268 Phenol uptake by peat and clay soils was also associated with a significant enhanc

269 increased with rainfall and on nutrient-rich clay soils.

270 (corrosion inhibitor), tetramethylammonium (clay stabilizer), biocides or strong oxidants.

271 by using a set of storage jar handles (fired clay) stamped by royal seals as part of the ancient admi

272 In this latter case, a nanoparticle to clay sticking efficiency could be determined.

273 uivalent pores are small pores in compressed clay stones that are small enough to have, because of ov

274 he anion exclusion behavior in two different clay stones, Opalinus Clay (OPA) and Helvetic Marl (HM),

275 Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI).

276 ntration that correlated to the nanoparticle/clay surface area ratio.

277 red interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in

278 this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for

279 available in the outermost few nanometers of clay surfaces.

280 are shown to displace water from as-received clay surfaces.

281 Notably slower Fe(II) precipitation in the clay suspensions compared to gamma-Al2O3 and SiO2 is att

282 amical process of polymer intercalation into clay tactoids and the ensuing aggregation of polymer-ent

283 iscrimination of illite from montmorillonite clays that typically develop in large depositional envir

284 Colloids, such as clays, that are present in soil may interact with PPCPs

285 In the case of Opalinus Clay, the anion accessible porosity increases from 3% at

286 eactivity studies are based on reduced model clays, the reactivity of naturally reduced field samples

287 Two factors were varied: sawdust size and clay-to-sawdust ratio.

288 such as carbon-based 2D materials, silicate clays, transition metal dichalcogenides (TMDs), and tran

289 including framework (zeolites) and layered (clays) type materials.

290 The three clay types differ in particle size, crystal structure, a

291 In 10(-1) M NaCl, the clay was preaggregated into larger and more spherical un

292 on semiconductor minerals, the synthesis of clays was demonstrated at low temperature and ambient pr

293 ever, that a substantial proportion of these clays was formed when Mars' primary crust reacted with a

294 th previous rock magnetic studies on the CIE clay, we suggest that most of the magnetite in the clay

295 Natural antibacterial clays, when hydrated and applied topically, kill human p

296 Amazonian rain forest, including terra firme clay, white-sand and seasonally flooded forests in Peru

297 Halloysite is an alumosilicate tubular clay with a diameter of 50 nm, an inner lumen of 15 nm a

298 r all compounds across the various homoionic clays with sorption coefficients (Kd) decreasing as foll

299 lay contamination included pre-saturation of clays with water and organic liquids.

300 int and quantify the abundance of authigenic clay within SPG sediment.

301 hydrothermal fluids becomes concentrated in clays within caldera lake sediments to potentially econo