bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of portable and stationary x‐ray fluorescence spectrometers in the study of ancient metallic artefacts
Authors: Guilherme A. , Cavaco A. , Pessanha S. , Costa M. , Carvalho M. L. 
Published: March 2008

AbstractThe aim of this work is to compare the performance of two x‐ray fluorescence (XRF) spectrometers, a portable one and a non‐portable one, in order to evaluate the advantages and drawbacks of each system. The used spectrometers are not commercial, and in both cases the excitation beams are produced by x‐ray tubes and the detection systems are based on common detectors. The portable system is a 90° geometry between the incident and the emitted beams, and the stationary spectrometer is based on a triaxial geometry with a secondary target. Detection limits are compared for a metallic Cu alloy reference material. A case study for ancient metallic artefacts of Cu‐based alloys, is used to compare the performance of both spectrometers. With the portable spectrometer several tests were carried out using two modes: an ‘unfiltered’ and a ‘filtered’ one in order to evaluate the best peak/background ratio for the studied samples. The obtained results showed significant differences between the two systems, namely, in what concerns peak shaping and trace elements detection. Copyright © 2008 John Wiley & Sons, Ltd.
Study of origin and composition of coatings in a monument built with granitic rocks, by SEM, XRD, XRF and DTA‐TGA
Authors: Sanjurjo Sánchez J. , Vidal Romaní J. R. , Fernández Mosquera D. , Alves C. A. 
Published: March 2008

AbstractThe Casas de Paredes (A Coruña, Spain) is an example of 18th Century neoclassical architecture built with granitic rocks. There are neoformation coatings on the main façade of one of the buildings, producing a visible soiling. Sixteen samples of coatings were collected and studied by SEM (surface and cross‐sections), including analyses by EDS and cross‐sections by x‐ray maps, in order to know their textural and chemical characteristics and to elucidate their origin. Studies by XRD, XRF and DTA/TGA were carried out in most of the samples. These analytical methods have allowed us to recognise up to six types of coatings. Three of them are gypsum‐rich coatings, derived from ancient protection plasters and also, by migration of solutions from lime mortar joints. Air pollution contributes to the blackening of these gypsum coatings and to the formation of black crusts by deposition of fuel combustion particles (Pb‐ and Fe‐rich aggregates, fly‐ash) and other particles (airborne soil particles) on the surface. One of the coatings is a dust crust (with significant amounts of iron, lead and other metals) originated by deposition of atmospheric pollution on ashlar surfaces (without gypsum aggregates). Also, Si‐rich detritic coatings originated by surface alteration of the granitic rock and particle deposition and accretion have been found. The last group is made by coatings originated by deposition (and alteration) of bird excrement. These results could help to define an appropriate cleaning program for the façade, and highlight the relevance of coatings as evidence of pollution agents affecting heritage buildings. Copyright © 2008 John Wiley & Sons, Ltd.
Pigment identification using x‐ray fluorescence in a polychromated sculpture by Pedro Millán
Authors: Kriznar A. , Muñoz M. V. , de la Paz F. , Respaldiza M. A. , Vega M. 
Published: March 2008

AbstractPedro Millán is considered one of the more important Andalusian sculptors from the medieval period. He worked mainly in Seville, where he is documented between 1485 and 1507. Most of his sculptures were made of terracotta and then polychromated and gilded. Some of his works exhibited at the Museum of Fine Arts in Seville are characterised by relatively well‐preserved polychromation. His sculpture Christ Man of Sorrows (1485–1503) was selected for the non‐destructive x‐ray fluorescence examination. Using this technique, pigments and support were analysed. The predominant elements, Ca and Fe, and a lesser presence of other elements, such as Mg, Si and Mn, demonstrate that the sculpture is indeed of terracotta. A high presence of Pb was detected in all the selected areas, related in part to the preparation/imprimation layer, and in part to a Pb‐based compound used as a pigment or as a dryer. The analysis shows that the red colour is cinnabar (Hg). The blue pigment is azurite (Cu), possibly mixed with vivianite (Fe). The green colour was made using a copper‐based pigment. The brown colour is an earth pigment, probably toasted umbra (Mn, Fe). In particular parts of the sculpture, gold was confirmed for decorative elements. Traces of silver were found in parts of the sculpture, but we do not have a clear answer to account for its presence yet. Copyright © 2008 John Wiley & Sons, Ltd.
Study and analytical investigation of metal threads from Byzantine/Greek ecclesiastical textiles
Authors: Karatzani Anna 
Published: March 2008

AbstractThe study and analytical investigation of metal threads started almost 30 years ago. Several publications exist about the types of threads used for the decoration of textiles as well as about the manufacturing techniques employed for the production of those threads in Western European and Middle Eastern contexts from the medieval period onwards. However, Byzantine/Greek textiles, which are also decorated with metal threads, have mainly been studied from an art historic point of view. Since 2002, a research project about the analytical investigation of Byzantine/Greek metal threads has been conducted at the Institute of Archaeology, University College London. This paper discusses and evaluates the methodology followed during the examination of 290 metal thread samples studied in this project. The main concern was to establish an optimal sequence of scientific methods for obtaining maximum information about the materials and the manufacturing techniques of the metal threads by using as small a sample as possible, and with the least possible damage to the sample. The availability and accessibility of equipment were two other very important issues. Three analytical techniques were chosen as the most appropriate: optical microscopy (OM), scanning electron microscopy coupled with energy dispersive x‐ray spectrometry (SEM/EDS) and electron probe micro‐analysis using a set of wavelength dispersive spectrometers (EPMA/WDS). The two first techniques have routinely been used for the study of metal threads, while EPMA/WDS has not been used before and was chosen to enhance the quality of the data obtained. Copyright © 2008 John Wiley & Sons, Ltd.
Pigment characterization and state of conservation of an 18th century fresco in the Convent of S. António dos Capuchos (Estremoz)
Authors: Gil M. , Carvalho M. L. , Seruya A. , Ribeiro I. , Alves P. , Guilherme A. , Cavaco A. , Mirão J. , Candeias A. 
Published: March 2008

AbstractThis article describes a study carried out on a mural painting in the Convent of Santo António dos Capuchos in the town of Estremoz (southern Portugal). Experimental work was undertaken to identify pigments and to elicit hypothesis about their local origin. Another aim was to ascertain the painting technique (binders, stratigraphy) and to try to investigate the causes that led to the deterioration of the blue and green pigments.Elemental and mineralogical analyses of the pigments were performed by x‐ray diffraction (µ‐XRD), portable energy dispersive x‐ray fluorescence (EDXRF) and scanning electron microscopy (SEM), complemented by microchemical tests and Fourier transform infrared spectroscopy (FTIR). These techniques have shown that a variety of pigments were used, namely earth pigments (red and yellow ochres, green earth and probably black earth and umber), copper pigments (azurite, malachite), probably from the Estremoz region, and smalt, used pure or in mixtures. The results also revealed the presence of salt veils, biological colonization and possibly secco applications with lime (lime painting), which may have contributed to the actual state of conservation of fresco. Copyright © 2008 John Wiley & Sons, Ltd.
Das Lanthaniodidethanid o‐La5I9(C2) – Die orthorhombische Hochtemperaturmodifikation
Authors: Mattausch Hansjürgen , Hoch Constantin , Simon Arndt 
Published: March 2008

AbstractThe Lanthanumiodideethanide o‐La5I9(C2) – The Orthorhombic High Temperature Modificationo‐La5I9(C2) is synthesized by reaction of LaI3, La metal and graphite powder in sealed Ta containers at 850 °C < T < 900 °C. It crystallizes in the orthorhombic space group Pbca with a = 8.0247(16) Å, b = 16.887(3) Å, c = 35.886(7) Å. o‐Ce5I9(C2) is isotypic with the lattice parameters a = 7.9284(4) Å, b = 16.714(1) Å, c = 35.530(3) Å. o‐La5I9(C2) transforms at 800 °C to the triclinic low temperature modification t‐La5I9(C2). The transformation is reversible. The La atoms form trigonal bipyramids centered by C2 groups. These units are connected by iodine atoms above the faces (f), edges (e) and corners according to La5(C2)I(f)iI(e)i−i2/2I(e)i−a7/2I(e)a−i7/2. The C‐C distance in the C2 unit is 1.45(2) Å. The crystals with greenish luster are moisture sensitive.
The Reactions of Sodium Silanethiolates with Benzoyl Chloride. The Crystal Structures of (O‐silyl)thiobenzoates (tBuO)3SiOC(S)Ph, Ph3SiOC(S)Ph, (2,6‐XyO)3SiOC(S)Ph, and of PhC(O)SSSC(O)Ph
Authors: Wojnowski Wiesław , Wojnowska Maria , Grubba Rafał , Konitz Antoni , Pikies Jerzy 
Published: March 2008

AbstractBenzoyl chloride reacts with sodium silanothiolates R3SiSNa yielding exclusively silyl derivatives of thionobenzoic acid R3SiOC(S)Ph, R = tBuO (1), R = Ph (2) and R = 2,6‐XyO (3) as orange solids. Compounds 1, 2, and 3 were fully characterized on the basis of X‐ray crystal structure analysis. NMR studies of solutions indicate that the same isomers are present in solutions and in solids.
Variable Bonding Modes of Pyrimidine‐2‐thione in PdII/PtII Complexes [M(η2‐N, S‐pymS)(η1‐S‐pymS)(PPh3)] and [M(η1‐S‐pymS)2(L‐L)] (L‐L = dppm, dppe)
Authors: Lobana Tarlok S. , Kaur Parminderjit , Hundal Geeta , Butcher Ray J. , Castineiras Alfonso 
Published: March 2008

AbstractReactions of pyrimidine‐2‐thione (HpymS) with PdII/PtIV salts in the presence of triphenyl phosphine and bis(diphenylphosphino)alkanes, Ph2P‐(CH2)m‐PPh2 (m = 1, 2) have yielded two types of complexes, viz. a) [M(η2‐N, S‐ pymS)(η1‐S‐ pymS)(PPh3)] (M = Pd, 1; Pt, 2), and (b) [M(η1‐S‐pymS)2(L‐L)] {L‐L, M = dppm (m = 1) Pd, 3; Pt, 4; dppe (m = 2), Pd, 5; Pt, 6}. Complexes have been characterized by elemental analysis (C, H, N), NMR spectroscopy (1H, 13C, 31P), and single crystal X‐ray crystallography (1, 2, 4, and 5). Complexes 1 and 2 have terminal η1‐S and chelating η2‐N, S‐modes of pymS−, while other Pd/Pt complexes have only terminal η1‐S modes. The solution state 31P NMR spectral data reveal dynamic equilibrium for the complexes 3, 5 and 6, whereas the complexes 1, 2 and 4 are static in solution state.
Crystal Structure and Characterization of a Double‐helical‐chain Coordination Polymer Zinc Complex Constructed by Flexible Dicarboxylate Ligand 2‐Nitro‐benzene‐1,4‐di(oxyacetate) and Rigid 2,2′‐Bipyridine Ligand
Authors: Yu Wei , Zhang Tong‐Lai , Zhang Jian‐Guo , Yang Li , Wang Shao‐Zong , Wu Rui‐Feng 
Published: March 2008

AbstractA novel double‐helical‐chain coordination polymer [Zn(nbdoa)(2,2′‐bipy)(H2O)]n constructed by flexible 2‐nitro‐benzene‐1,4‐di(oxyacetate) ligand and rigid 2,2′‐bipyridine ligand was obtained by hydrothermal reaction. The crystal structure demonstrates that there is a double‐helical chain with an inner channel running parallel to the helix axis without any interpenetration, which is connected to network via π‐π stacking and hydrogen bond interactions. The thermal analysis shows that the infinite helical structure is stable up to 536 K. The luminescence property is investigated and the complex shows photoluminescence in the solid state at room temperature.
Ligand Exchange Processes on Solvated Beryllium Cations. II [Be(solvent)(12‐Crown‐4)]2+
Authors: Puchta Ralph , van Eldik Rudi 
Published: March 2008

AbstractThe solvation and solvent exchange mechanism of [Be(12‐crown‐4)]2+ in water and ammonia was studied by DFT calculations (RB3LYP/6‐311+G**). In solution, five‐fold coordinated Be2+ species of quadratic pyramidal [Be(H2O)(12‐crown‐4)]2+ and [Be(NH3)(12‐crown‐4)]2+ exist. The water and ammonia exchange reactions follow an associative interchange mechanism, similar to that found for the pure solvent complexes [Be(H2O)4]2+ and [Be(NH3)4]2+. The activation barriers are clearly smaller than for the pure solvent complexes, viz. [Be(H2O)(12‐crown‐4)]2+: 6.0 kcal/mol and [Be(NH3)(12‐crown‐4)]2+: 15.3 kcal/mol.
Synthesis, Characterization and Explosive Properties of 1,3‐Dimethyl‐5‐amino‐1H‐tetrazolium 5‐Nitrotetrazolate
Authors: Klapötke Thomas M. , Miró Sabaté Carles , Rusan Magdalena 
Published: March 2008

Abstract1,3‐Dimethyl‐5‐amino‐1H‐tetrazolium 5‐nitrotetrazolate (5b) was synthesized in high yield from 1,4‐dimethyl‐5‐amino‐1H‐tetrazolium iodide (5a) and silver 5‐nitrotetrazolate. Both new compounds (5a and 5b) were characterized using vibrational (IR and Raman) and multinuclear NMR spectroscopy (1H, 13C and 15N), elemental analysis and single‐crystal X‐ray diffraction. 5a crystallizes in an orthorhombic cell: Pbca, a = 11.5016(4), b = 13.7744(5), c = 13.7744(5) Å, V = 1638.2(1) Å3, Z = 8, ρ = 1.955 g cm−3, R1 = 0.0210 (F > 4σ(F)), wR2 (all data) = 0.0542; whereas 5b crystallizes in a monoclinic cell: C1c, a = 14.5228(8), b = 5.0347(2), c = 13.7217(7) Å, β = 112.11(1)°, V = 929.6(2) Å3, Z = 4, ρ = 1.630 g cm−3, R1 = 0.0279 (F > 4σ(F)), wR2 (all data) = 0.0585. The sensitivity of 5b to classical stimuli was determined by using standard BAM tests and its thermal stability was assessed by DSC measurements. In addition, its heat of combustion was determined by bomb calorimetry measurements. The EXPLO5 was used to calculate the detonation pressure (P) and velocity (D) of 5b (P = 13.3 GPa and D = 6379 m s−1), as well as those of its mixtures with ammonium nitrate (P = 23.2 GPa and D = 7862 m s−1) and ammonium dinitramide (P = 29.6 GPa and D = 8594 m s−1). Compound 5b is a hydrolytically stable solid with a high melting point (160 °C) and thermally stable to 190 °C with a very low sensitivity to friction (>360 N) and impact (>30 J) and good performance in combination with an oxidizer making it of interest in new environmentally friendly, insensitive explosive formulations.
Synthese und Metallierung des Diaminosiloxans O(SiiPr2NH2)2
Authors: von Hänisch Carsten 
Published: March 2008

AbstractSynthesis and Metalation of the Diaminosiloxane O(SiiPr2NH2)2The 1,3‐diaminoldisiloxane O(SiiPr2NH2)2 (1) was obtained from the reaction of O(SiiPr2Cl)2 with NH3. The reactions of 1 with AlEt3 or GaEt3 produced the compounds [O{SiiPr2N(H)MEt2}{SiiPr2NMEt}]2 (2: M = Al; 3: M = Ga). The crystal structures of 2 and 3 were determined by single crystal X‐ray diffraction, showing a polycyclic M4N4Si4O2 core structure of these molecules.
The Structures of Methylenebis(dichloroarsane) and Methylenebisarsonic Acid – A Combined Theoretical and Experimental Study
Authors: Betz Richard , Klüfers Peter , Reichvilser Moritz M. , Roeßner Felix W. 
Published: March 2008

AbstractMethylenebisarsonic acid (3) was synthesized according to a published procedure. Its molecular structure and its spectroscopic characteristics were determined by single‐crystal X‐ray diffraction. The first intermediate, methylenebis(dichloroarsane) (1), was structurally and spectroscopically characterized as well. Both molecules were investigated on the B3LYP/6‐31+G(2d,p) level of theory and subsequent NBO analysis.
Synthesis, Structure, Magnetic and Optical Properties of Ternary Thio‐germanates: Ln4(GeS4)3 (Ln = Ce, Nd)
Authors: Choudhury Amitava , Dorhout Peter K. 
Published: March 2008

AbstractSingle crystals of two ternary thio‐germanates containing rare‐earth metals, Ln4(GeS4)3 (Ln = Ce (I), Nd (II)), have been isolated from the reaction of anhydrous rare‐earth trichloride (LnCl3) and ternary sodium thio‐germanate (Na2GeS3) in evacuated quartz ampoules. We have determined the crystal structure of the compounds, which are isostructural to La4(GeS4)3 and crystallize in trigonal system in the space group R3c with the cell dimensions: I, a = b = 19.375(3) Å, c = 8.028(2) Å, Z = 6; II, a = b = 19.250(3) Å, c = 7.949(2) Å, Z = 6. The structure is built with the complex network of two independent tricapped trigonal prisms of CeS9, in which Ge atoms occupy tetrahedral holes of sulfur atoms. The bulk synthesis of the two compounds has also been achieved by the stoichiometric combination of the elements. The magnetic and optical properties of the compounds have been investigated. The magnetic moments of 2.32 and 3.49 μB for I and II, respectively, are in good agreement with the theoretical magnetic moments of Ce and Nd in the +3 oxidation state. The optical band gap of I is found to be located around 2.3 eV, while the optical band gap of II lies around 2.62 eV. In addition, Raman spectroscopic characterizations have also been performed for I, II, and La4(GeS4)3.
The Ylide Adduct SOC2(PPh3)2 as Complex Ligand. Reaction with [Mn2(CO)10] and InCl3; Crystal Structures of [(CO)4Mn(SOC2{PPh3}2)2][Mn(CO)5] and (H2C{PPh3}2)[InCl4]2
Authors: Petz Wolfgang , Fahlbusch Meike , Gromm Enrico , Neumüller Bernhard 
Published: March 2008

AbstractThe betain‐like SOC2(PPh3)2 (1a) reacts with [Mn2(CO)10] in THF to produce the salt‐like complex [(CO)4Mn(SOC2{PPh3}2)2][Mn(CO)5] (2). 1a is bonded via the sulfur atoms which are arranged in trans position in the octahedral environment of the manganese atom. With InCl3 from CH2Cl2 solution the addition product [Cl3In(SOC2{PPh3}2)] (3) is obtained along with the salt (H2C{PPh3}2)[InCl4]2 (4), which is the result of proton abstraction from the solvent. The crystal structures of 2·0.5THF and 4·CH2Cl2 are reported. The compounds are further characterized by IR and 31P NMR spectroscopy.
Indium(I) Heptachlorodigallate(III), InGa2Cl7
Authors: Timofte Tudor , Mudring Anja‐Verena 
Published: March 2008

AbstractIndium(I) heptachlorodigallate(III), InGa2Cl7, has been obtained from a mixture of In, Bi and GaCl3 in a melt of [bmim][Al(nftb)4] under argon at 373 K. The crystal structure of InGa2Cl7 [orthorhombic, Pna21 (no.33), a = 1185.7(2), b = 891.4(4), c = 1071.6(2) pm, V = 1132.6(3)·106 pm3, Z = 4, T = 298 K, R1 for 1994 reflections with I0>2σ(I0): 0.0692] contains discrete indium(I) cations and Ga2Cl7 anions. InGa2Cl7 crystallizes isotypic with Ga3Cl7 and KGa2Cl7. InI is coordinated by ten chloride anions in an irregular (4+6) mode. No evidence was found for the stereochemical activity of the In‐5s2 electron pair.
Synthese und Strukturen der ersten mehrkernigen Mangan‐Guanidin‐Komplexe und der ersten Mangan‐Komplexe mit mono‐protonierten Bis‐Guanidinliganden
Authors: Neuba Adam , Herres‐Pawlis Sonja , Flörke Ulrich , Henkel Gerald 
Published: March 2008

AbstractSyntheses and Structures of the First Polynuclear Manganese Guanidine Complexes and of the First Manganese Complexes Containing Mono‐Protonated Bis‐Guanidine LigandsMetallation of two differently alkylated bis‐guanidine ligands containing a central pyridine functionality, namely N2,N6‐bis(1,3‐dimethylimidazolidin‐2‐ylidene)pyridine‐2,6‐diamine (DMEG2py {N7C15H23}, L1) and N2,N6‐bis(1,1,3,3‐tetramethyl‐guanidine)pyridine‐2,6‐diamine (TMG2py {N7C15H27}, L2), with manganese(II) bromide and chloride leads to the formation of the novel complexes [MnBr3(TMG2pyH)] ([MnBr3(N7C15H28)], (1)), [MnBr2(DMEG2pyH)2]2+ ([MnBr2(N7C15H24)2]2+, (2)), and [Mn2X3(DMEG2py)2]+ ([Mn2X3(N7C15H23)2]+; (3a): X = Cl; (3b): X = Br). 2 and 3 have been isolated as tetrahalomanganate salts. Single crystal X‐ray analyses show that all of them contain the manganese atoms in unusual pseudo‐tetrahedral coordination environments. 3a·1/2[MnCl4] and 3b·1/2[MnBr4] are isostructural and crystallize in the monoclinic space group C2c. The complex cations 3 exhibit a binuclear structure with two terminal and one bridging halide ion, respectively. The compounds 1 and 2 are mononuclear species crystallizing in the orthorhombic space group P212121 in the case of 1 and in the triclinic space group $P{\bar 1}$ in the case of 2·[MnBr4]. The ability of L1 and L2 to bind either two manganese ions naked or only one of them in the mono‐protonated stage is the most remarkable property of these ligands. Further striking features are the spatial arrangements of the pyridine‐to‐manganese bonds which deviate significantly from the situation expected for nitrogen donor functions in sp2 hybridized stages. Moreover, regarding each chelating ligand portion as a component which occupies one coordination site of the metal atom, a pseudo‐tetrahedral metal coordination is identified. To our knowledge, 1 and 2 are the first manganese complexes containing mono‐protonated bis‐guanidine ligands, whereas 3a and 3b are the first polynuclear manganese‐guanidine compounds known so far.
Increasing Access to Surgical Services for the Poor in Rural Haiti: Surgery as a Public Good for Public Health
Authors: Ivers Louise C. , Garfein Evan S. , Augustin Josué , Raymonville Maxi , Yang Alice T. , Sugarbaker David S. , Farmer Paul E. 
Published: March 2008

AbstractAlthough surgical care has not been seen as a priority in the international public health community, surgical disease constitutes a significant portion of the global burden of disease and must urgently be addressed. The experience of the nongovernmental organizations Partners In Health (PIH) and Zanmi Lasante (ZL) in Haiti demonstrates the potential for success of a surgical program in a rural, resource‐poor area when services are provided through the public sector, integrated with primary health care services, and provided free of charge to patients who cannot pay. Providing surgical care in resource‐constrained settings is an issue of global health equity and must be featured in national and international discussions on the improvement of global health. There are numerous training, funding, and programmatic considerations, several of which are raised by considering the data from Haiti presented here.
At the bottom of the differential diagnosis list: unusual causes of pediatric hypertension
Authors: Grinsell Matthew M. , Norwood Victoria F. 
Published: March 2008

AbstractHypertension affects 1–5% of children and adolescents, and the incidence has been increasing in association with obesity. However, secondary causes of hypertension such as renal parenchymal diseases, congenital abnormalities and renovascular disorders still remain the leading cause of pediatric hypertension, particularly in children under 12 years old. Other less common causes of hypertension in children and adolescents, including immobilization, burns, illicit and prescription drugs, dietary supplements, genetic disorders, and tumors will be addressed in this review.
Effects of individual size, local competition and canopy closure on the stem volume growth in a monoclonal Japanese cedar (Cryptomeria japonica D. Don) plantation
Authors: Inoue Sumihiro , Shirota Tetsuoh , Mitsuda Yasushi , Ishii Hiroaki , Gyokusen Koichiro 
Published: March 2008

AbstractWe studied how the dominant factor affecting stem volume growth changes during stand development in a monoclonal stand of Cryptomeria japonica D. Don. Stem analysis was used to compare growth history of trees in an unthinned plot (closed canopy) and a thinned plot (open canopy). In the unthinned plot, the dominant factor affecting stem volume growth was basal area (BA) before canopy closure, whereas neighborhood competition index (CI) was the dominant factor after canopy closure. In contrast, the dominant factor affecting stem volume in the thinned plot was BA throughout stand development. Spearman's rank correlation coefficient between BA and CI continued to increase after canopy closure and size rank among individuals became increasingly fixed. Our results indicated that stem volume growth shifts from size‐dependent to competition‐dependent growth at canopy closure. The apparent correlation between tree size and growth rate observed in many previous studies may be the result of competition‐mediated positive feedback between size and growth.