Low Bulk Modulus Research Articles

NOx Emissions of Alternative Diesel Fuels: A Comparative Analysis of Biodiesel and FT Diesel

This study explores the diesel injection and combustion processes in an effort to better understand the differences in NOx emissions between biodiesel, Fischer−Tropsch (FT) diesel, and their blends with a conventional diesel fuel. Emissions studies were performed with each fuel at a variety of static fuel injection timing conditions in a single-cylinder DI diesel engine with a mechanically controlled, in-line, pump-line-nozzle fuel injection system. The dynamic start of injection (SOI) timing correlated well with bulk modulus measurements made on the fuel blends. The high bulk modulus of soy-derived biodiesel blends produced an advance in SOI timing compared to conventional diesel fuel of up to 1.1 crank angle degrees, and the lower bulk modulus of the FT diesel produced a delay in SOI timing of up to 2.4 crank angle degrees. Compared to conventional diesel fuel at high load, biodiesel fuel blends produced increases in NOx emissions of 6−9% while FT fuels caused NOx emissions to decrease 21−22%. Shifts in fuel injection timing, caused by bulk modulus differences, were largely responsible for the NOx increases, but pure FT diesel produced lower NOx emissions than expected on the basis of SOI alone. Further analysis showed that no trends were seen between NOx and either ignition delay or maximum cylinder temperature, and only weak, or fuel-specific, relationships were seen between NOx and maximum heat release rate and the timing of maximum heat release rate. The timing of the maximum cylinder temperature, however, did produce a relationship with NOx emissions that was not dependent on fuel type.

The Impact of the Bulk Modulus of Diesel Fuels on Fuel Injection Timing

In this paper, we examine the interaction between the bulk modulus of compressibility of various fuel samples and its effect on fuel injection timing. The fuels considered range from soy oil-derived biodiesel, unrefined soybean oil, and paraffinic solvents to ultralow-sulfur and conventional diesel fuels. Both the impact on injection timing and the variation in the bulk modulus of compressibility are measured. The present work confirms that the higher bulk modulus of compressibility of vegetable oils and their methyl esters leads to advanced injection timing with in-line pump−line−nozzle fuel injection systems. This has been shown in the literature to contribute to the well-documented increase in NOx emissions with the use of biodiesel fuel. An opposite trend, a retarding of injection timing, is observed with paraffinic fuels, because they have a lower bulk modulus of compressibility than conventional diesel fuels. This supports the observation that paraffinic fuels such as Fischer−Tropsch diesel yield lower NOx emissions.

Structure anomaly and electronic transition inRNiO3(R=La,Pr,…,Gd)

With the increasing size of the rare-earth ion in the $R{\mathrm{NiO}}_{3}$ perovskites, the room-temperature (RT) orthorhombic distortion shows an unusual collapse and restoration before transforming to the rhombohedral structure. We have studied the orthorhombic distortions under pressure of the RT structure of $R{\mathrm{NiO}}_{3}$ for $R=\mathrm{La},\mathrm{Pr},\dots{},\mathrm{Gd}$. The pressure dependence of the orthorhombic distortion reflects a component that opposes the influence of a cooperative rotation of the octahedra. An unusually low bulk modulus has been interpreted with a model at the crossover from localized to itinerant electronic behavior.

Structural and electronic properties ofSi3P4

Structural and electronic properties of ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ were investigated using first-principles total-energy method based on density-functional theory and the local-density approximation (LDA). It was found that pseudocubic-${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ is energetically favored relative to other phases of ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ considered in this study. All phases of ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ have low bulk moduli, with the \ensuremath{\gamma} phase being the hardest (110 GPa). Furthermore, band-structure and density-of-states calculations reveal that \ensuremath{\alpha}, ${\ensuremath{\beta}}_{1},$ pseudocubic, and graphitic phases of ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ are semiconducting while ${\ensuremath{\beta}}_{2},$ cubic, and \ensuremath{\gamma} phases are metallic within LDA. Correction of LDA energy band gap by a more accurate method will likely result in ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ being a narrow gap semiconductor. The structural and electronic properties of ${\mathrm{Si}}_{3}{\mathrm{P}}_{4}$ are compared with those of similar compounds, i.e., ${\mathrm{C}}_{3}{\mathrm{N}}_{4},$ ${\mathrm{Si}}_{3}{\mathrm{N}}_{4},$ ${\mathrm{Ge}}_{3}{\mathrm{N}}_{4},$ and ${\mathrm{C}}_{3}{\mathrm{P}}_{4}.$

High-pressure synthesis and study of low-compressibility molybdenum nitride (MoN andMoN1−x)phases

We report the compressibility of the stoichiometric hexagonal \ensuremath{\delta} phase of MoN that is a well-known hard material that becomes superconducting below ${T}_{c}=12\mathrm{K}.$ The measured bulk modulus is ${K}_{0}=345(9)\mathrm{GPa}$ and ${K}_{0}^{\ensuremath{'}}=3.5(3).$ We also report the compressibility of the non-stoichiometric cubic $B1$ structured $\ensuremath{\gamma}\ensuremath{-}{\mathrm{Mo}}_{2}\mathrm{N}$ phase, that has a lower bulk modulus $[{K}_{0}=301(7)\mathrm{GPa},$ assuming ${K}_{0}^{\ensuremath{'}}=4].$ The difference in bulk modulus is due to the difference in structure and the cohesive energy between the two phases.

The Morphology and Dynamics of the Viscoelastic Microphase Separation of Diblock Copolymers

In this paper, the kinetics and morphology of viscoelastic microphase separation of diblock copolymers are investigated in detail. It is found that for a symmetric system (f = 0.5), taking into account the bulk modulus differences between the two blocks, the classical randomly oriented lamellar morphology is not observed. Instead, we find that droplets of the lower bulk modulus soft block disperse in a matrix of higher bulk modulus hard block. In the case of off-critical system (f = 0.4), since an inherent composition asymmetry exists between the two blocks, the viscoelastic microphase separated morphology is also different from that normally observed, whether there is an apparent difference in the bulk moduli between two blocks. However, when a bulk modulus difference exists between the two blocks, the morphology is further altered. Addition of random thermal noise to both the critical (f = 0.5) and the off-critical system (f = 0.4) weakens the suppression of concentration fluctuations, but no fundamenta...

Leaf water relations of Eucalyptus cloeziana and Eucalyptus argophloia in response to water deficit.

Leaf water relations responses to limited water supply were determined in 7-month-old plants of a dry inland provenance of Eucalyptus argophloia Blakely and in a humid coastal provenance (Gympie) and a dry inland provenance (Hungry Hills) of Eucalyptus cloeziana F. Muell. Each provenance of E. cloeziana exhibited a lower relative water content at the turgor loss point, a lower apoplastic water content, a smaller ratio of dry mass to turgid mass and a lower bulk modulus of elasticity than the single provenance of E. argophloia. Osmotic potential at full turgor and water potential at the turgor loss point were significantly lower in E. argophloia and the inland provenance of E. cloeziana than in the coastal provenance of E. cloeziana. There was limited osmotic adjustment in response to soil drying in E. cloeziana, but not in E. argophloia. Between-species differences in water relations parameters were larger than those between the E. cloeziana provenances. Both E. cloeziana provenances maintained turgor under moderate water stress through a combination of osmotic and elastic adjustments. Eucalyptus argophloia had more rigid cell walls and reached lower water potentials with less reduction in relative water content than either of the E. cloeziana provenances, thereby enabling it to extract water from dryer soils.

Quantitative evaluation of stress distribution in bulk polymer samples through the comparison of mechanical behaviors between giant single‐crystal and semicrystalline samples of poly(trans‐1,4‐diethyl muconate)

AbstractThe Raman shift and crystallite modulus were measured under the application of tensile force for a giant single crystal and a series of uniaxially oriented semicrystalline samples of poly(trans‐1,4‐diethyl muconate) (polyEMU). The apparent Raman shift factor αapp or a vibrational frequency shift per 1 GPa tensile stress was higher for the semicrystalline samples with lower crystallinity or lower bulk modulus. The apparent crystallite modulus E or Young's modulus along the chain axis in the crystalline region was not constant but varied remarkably between the giant single crystal and semicrystalline samples. A systematic change in αapp and E among the polyEMU samples with different preparation history could be interpreted quantitatively on the basis of a mechanical series parallel model consisting of crystalline and amorphous phases. The origin of different E and αapp was speculated to be a stress concentration on the taut‐tie chain contained as a parallel crystalline component in the mechanical model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 444–453, 2003

Modeling of aging in plutonium by molecular dynamics

The origin of aging in plutonium lies in the extra formation of defects due to self-decay of 239Pu. The modeling of the formation of these defects is achieved by molecular dynamics (MD). In this work a simple EAM potential has been used to study defects formation in fcc plutonium and a 2 keV cascade is analyzed. A large pressure wave is generated around the cascade core. In the used MD code the pressure wave is not absorbed at the box boundaries and due to the periodic boundary conditions, the use of a very large box is crucial in order to avoid interaction of the cascade with itself. More than 800 000 atoms are needed to deal with this small 2 keV cascade without any artifacts. This effect comes from the very low bulk modulus of fcc Pu. The relative long time to achieve the annealing is also connected to the bulk modulus. These results are discussed in terms of large pressure wave: alloying effects are predicted using that viewpoint.

Density-functional investigation of magnetism inδ-Pu

We present density-functional results of $\ensuremath{\delta}$-Pu obtained from three electronic-structure methods. These methods have their individual strengths and are used in combination to investigate the magnetic and crystal stability of $\ensuremath{\delta}$-Pu. An all-electron, full potential linear muffin-tin orbitals (FPLMTO) method, that includes corrections for spin-orbit coupling and orbital-polarization effects, predicts $\ensuremath{\delta}$-Pu to be an antiferromagnet at zero temperature with a volume and a bulk modulus in very good agreement with experiment. The site-projected magnetic moment is smaller than expected $(\ensuremath{\sim}1.5{\ensuremath{\mu}}_{B})$ due to large cancellation of spin and orbital moments. These calculations also predict a mechanical instability of antiferromagnetic (AF) $\ensuremath{\delta}$-Pu. In addition, techniques based on the Korringa-Kohn-Rostoker (KKR) method within a Green's-function formalism and a projector augmented wave (PAW) method predict the same behavior of $\ensuremath{\delta}$-Pu. In order to study disordered magnetism in $\ensuremath{\delta}$-Pu, the KKR Green's-function technique was used in conjunction with the disordered local-moment model, whereas for the FPLMTO and PAW methods this was accomplished within the special quasirandom structure model. While AF $\ensuremath{\delta}$-Pu remains mechanically unstable at lower temperatures, paramagnetic $\ensuremath{\delta}$-Pu is stabilized at higher temperatures where disordered magnetic moments are present and responsible for the crystal structure, the low density, and the low bulk modulus of this phase.

Dynamic measurement of sediment grain compressibility at atmospheric pressure: acoustic applications

Under certain conditions, Wood's equation can be used to predict sound speed in fluid/solid-grain suspensions if the bulk moduli and densities of the grains and fluid are known. In this paper, that relationship is used to estimate grain-bulk moduli in suspensions where sound speed, fluid density, fluid bulk modulus, grain density, and particle concentrations are known or accurately measured. Measured values of grain-bulk moduli for polystyrene beads suspended in water (mean = 4.15 /spl times/ 10/sup 9/ Pa) and soda-lime glass beads suspended in a heavy liquid (mean = 3.8 /spl times/ 10/sup 10/ Pa) are consistent with the values of bulk moduli for polystyrene beads and soda-lime glass beads found in the literature (3.6 to 4.2 /spl times/ 10/sup 9/ Pa and 3.4 to 4.0 /spl times/ 10/sup 10/ Pa, respectively). These measurements thus provide controls, which demonstrate the validity of the suspension technique to estimate values of particle bulk modulus. The values of bulk modulus, measured using the same suspension techniques, for Ottawa sand and quartz sand grains collected from the coastal sediments of the northeast Gulf of Mexico ranged between 3.8 and 4.7 /spl times/ 10/sup 10/ Pa, with 95% confidence limits between 3.0-5.7 /spl times/ 10/sup 10/ Pa. These measured values of bulk modulus are consistent with the range of handbook values for polycrystalline quartz (3.6 to 4.0 /spl times/ 10/sup 10/ Pa). The use of the lower bulk modulus (i.e., 7.0 /spl times/ 10/sup 9/ Pa) recently suggested by Chotiros is therefore inappropriate and traditional handbook values of sediment grain-bulk moduli should be used as inputs for sediment acoustic modeling.

Electronic and elastic properties of the light actinide tellurides

The elastic constants c 11, c 12 and c 44 of U, Np, Pu, and Am telluride single crystals have been obtained by Brillouin scattering from the measured sound velocities in prominent crystallographic directions. In case of the U chalcogenides also by ultrasound techniques. The Cauchy pressure, the Poisson ratio, the anisotropy ratio, the bulk modulus and the Debye temperature have been derived from these data. U and Pu telluride have a negative c 12, implying intermediate valence. AmTe has a very low bulk modulus, but a positive c 12. It is extremely soft, with a very low sound velocity. For AmTe also the LO and TO phonon frequencies could be determined. The elastic data point to a divalent Am state. The optical reflectivity of the light actinide tellurides (and sometimes of all chalcogenides) has been measured between UV and infrared wavelengths, in the case of AmTe down to the far infrared. The plasma edge of the free carriers has been determined, which yields the ratio of n/ m*. Together with the γ value of the specific heat and magnetic data a consistent proposal for the electronic structure of the light actinide chalcogenides can be given. Thus, the Pu chalcogenides are intermediate valent and represent the high-pressure phase of the corresponding Sm chalcogenides. AmTe, as judged by the electronic, optic and magnetic properties seems to be in the 5f 7 configuration, i.e. divalent Am, but with a narrow, half-filled (24 meV) wide 5f band, about 0.1 eV below the bottom of the 6d conduction band. We thus propose a new kind of unhybridized heavy fermion. Also AmTe seems to represent a high-pressure phase of EuTe.

Equations of state for Fe32+Fe23+Si3O12“skiagite” garnet and Fe2SiO4‐Fe3O4spinel solid solutions

The equations of state of Fe32+Fe23+Si3O12, or “skiagite” garnet, and two Fe2SiO4‐Fe3O4spinel solid solutions were determined from room temperature hydrostatic compression experiments up to 11 GPa performed at the European Synchrotron Radiation Facility. These data indicate that there are no first‐order phase transitions or changes in compression mechanism in skiagite garnet or Fe3+‐bearing silicate spinel solid solutions up to 11 GPa at room temperature. Skiagite garnet has an isothermal bulk modulusK0T= 157.4(3.0) GPa and a pressure derivative of the isothermal bulk modulusK0T= 6.7(8), where numbers in parentheses represent 1 estimated standard deviation of these values. Combination of this result with those for other silicate garnets reveals an inverse linear relationship between the octahedral cation‐oxygen (Y‐O) bond length and the bulk modulus. The dominating effect of the octahedral site on the bulk compression of garnet can be understood by considering that the octahedral‐tetrahedral network has no rigid unit modes and that no cation substitution occurs on the tetrahedral sites in these garnets. It is apparent that the incorporation of Fe3+and Cr acts to lower the bulk modulus of aluminosilicate garnets. Consideration of the effect of compression on the molar volume results in nonsystematic changes in calculated oxygen fugacity for garnet‐bearing mantle peridotites that equilibrated at high pressures. The pressure‐volume data obtained from two Fe3+‐bearing silicate spinel solid solutions with compositions Xfay= 0.45 and Xfay= 0.57 (fay, fayalite component) yielded similar enough values ofK0TandK′0Tto warrant a combined refinement with the data points scaled to the appropriate zero‐pressure volumes. This gaveK0T= 168.9(1.2) GPa andK′0T= 5.7(1.2) with χW2= 4.6 (weighted χ2) andK0T= 175.5(1.4) GPa whenK0Tis fixed equal to 4 (χW2= 4.9). Our solid solutions have significantly lower bulk moduli than either magnetite or Fe2SiO4spinel end‐members or indeed many other spinels.

Theoretical study of a three-dimensional all-sp2structure

We present a study of a highly symmetric crystal made of exclusively ${\mathrm{sp}}^{2}$ bonded atoms. Calculations of the structural and electronic properties are performed within the pseudopotential-density-functional approach for two different compositions made of (i) pure carbon and (ii) carbon and nitrogen compound. In both solids, one of the carbon-carbon bond lengths is found to be 1.35 \AA{}, which is considerably smaller than any carbon-carbon bond length found in other carbon solids. The bulk moduli are calculated to be 241 and 286 GPa for the pure carbon and the carbon-nitride compounds, respectively. We demonstrate that the relatively low bulk moduli, considering the short bond lengths found in the structure, is due to the disruption of the carbon \ensuremath{\pi} bonding states. This is probably unavoidable when trying to form a three-dimensional structure out of a planar configuration like the ${\mathrm{sp}}^{2}$ bonds. The calculated density of states and band structures show that the pure carbon form is metallic whereas the carbon nitride is semiconducting. When carbon atoms are added to the interstitial regions, the carbon solid becomes insulating and the bulk modulus increases to 282 GPa.

Neutron powder diffraction study of hydrogarnet to 9.0 GPa

Other| October 01, 1996 Neutron powder diffraction study of hydrogarnet to 9.0 GPa George A. Lager; George A. Lager University of Louisville, Department of Geography and Geosciences, Louisville, KY, United States Search for other works by this author on: GSW Google Scholar Robert B. Von Dreele Robert B. Von Dreele Los Alamos National Laboratory, United States Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (9-10): 1097–1104. https://doi.org/10.2138/am-1996-9-1006 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation George A. Lager, Robert B. Von Dreele; Neutron powder diffraction study of hydrogarnet to 9.0 GPa. American Mineralogist 1996;; 81 (9-10): 1097–1104. doi: https://doi.org/10.2138/am-1996-9-1006 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The crystal structure of synthetic, deuterated katoite [Ca3Al2(O4D4)3] has been refined at 0.0001, 0.78, 3.6, 6.1, 7.9, and 9.0 GPa using the opposed-anvil Paris-Edinburgh cell and the POLARIS powder diffractometer at the U.K. pulsed spallation source, ISIS. A constrained Birch-Mumaghan fit to the unit-cell volume yields K0 = 52(1) GPa for K0´⁠, = 4.0. The lower bulk modulus of katoite relative to anhydrous Ca-bearing garnets (K0 = 159-179 GPa) is due to the greater compressibility of the Ca dodecahedron and O4D4 tetrahedron. At high pressure, corner-sharing tetrahedra and octahedra undergo a rigid-body rotation, which causes a shift in the O position. This rotation, coupled with the large compression of the two tetrahedral edges shared with the dodecahedron, changes the relative lengths of the Ca-O bonds at high pressure, such that Ca2-0 < Cal-O for P > 6 GPa. With increasing pressure, the O-D· · ·O angles widen slightly, as the O-D vector rotates toward the tetrahedral face. Both O-D and O· · ·D bond lengths decrease as a function of pressure, which was unexpected in view of the results of recent high-pressure studies. Comparison of crystallographic and spectroscopic data collected at high pressure for hydrogamets suggests that empirical relationships derived for hydrogen-bond systems at ambient conditions, where a relaxed, equilibrium state is attained, may not always apply to O-D · · · O hydrogen bonds under compression. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

SOME ASPECTS OF THE WATER RELATIONS OF THE LICHEN PARMOTREMA TINCTORUMMEASURED USING THERMOCOUPLE PSYCHROMETRY

The thermocouple psychrometer was used to determine water potential, υ , and its components in the lichenParmotrema tinctorum. Data suggested that using conventional pressure–volume curves to study the water relations of lichens may give anomalous results, possibly because lichens may contain appreciable amounts of intercellular water. A way of correcting pressure–volume curves to remove the effect of intercellular water is discussed. Parmotrema tinctorumhad a very low osmotic potential at full turgor ( c. −2·5 MPa), and a low bulk modulus of elasticity ( c. 2·1 MPa). As a result, P. tinctorumlost turgor only when the relative water content dropped below 0·47. Likely benefits of this for the lichen are discussed.

Some Aspects of the Water Relations of the Lichen Parmotrema Tinctorum Measured Using Thermocouple Psychrometry

The thermocouple psychrometer was used to determine water potential, Ψ and its components in the lichen Parmotrema tinctorum. Data suggested that using conventional pressure-volume curves to study the water relations of lichens may give anomalous results, possibly because lichens may contain appreciable amounts of intercellular water. A way of correcting pressure-volume curves to remove the effect of intercellular water is discussed. Parmotrema tinctorum had a very low osmotic potential at full turgor (c. −2.5 MPa), and a low bulk modulus of elasticit (c. 2.1 MPa). As a result, P. tinctorum lost turgor only when the relative water content dropped below 0.47. Likely benefits of this for the lichen are discussed.

Solvent crazing as a stress‐induced surface adsorption and bulk plasticization effect

AbstractIn solids with low bulk modulus, like polymer glasses, concentration of stress due to surface defects and other kinds of inhomogeneities can induce substantial surface tension reduction and bulk plasticization in extremely localized regions. This effect becomes important in the presence of organic liquids. As a liquid comes into contact with the polymer surface and as stress is applied, a point is reached when the work to draw new surface area becomes minimal. In addition, at least up to a diffusion limited extent, bulk solvation can also take place locally. At this point, solvent crazing initiates in the presence of a triaxial stress field, and craze fibrils are easily drawn with additional deformation. For van der Waals (WL) interactions between polymer and solvent, two different expressions for solvent craze initiation have been derived. The first is derived assuming interfacial tension reduction (ITR) is the dominant mechanism for solvent craze initiation. The second is derived assuming that flaw tip bulk plasticization (BP) is the main mechanism for solvent craze initiation. Existing experimental data on six different glassy polymers was also examined with respect to the above two expressions. A relatively good functional relation (straight line passing near the origin) was found for a wide spectrum of glassy polymers and apolar (WL) liquids, for both the (ITR) and (BP) cases. Additional assumptions made in this analysis, especially about the stress concentration factor and the bulk modulus of the materials, indicate a better correlation with interfacial tension reduction data, in the case of (WL) liquids. However, better controlled experiments would be necessary to properly identify the mechanisms of environmental crazing, even in the case of (WL) liquids. © 1995 John Wiley &amp; Sons, Inc.

Fiber-embedded mandrel-stiffened planar acoustic sensor

A plastic mandrel-based, embedded planar fiber-optic acoustic sensor has been developed by wrapping a single mode fiber around solid plastic mandrels which are embedded in an elastomeric encapsulant forming a planar device. The acoustic sensitivity of the sensor was found to be high and frequency independent. The high sensitivity is a result of the effective utilization of the low bulk modulus encapsulant (elastomer), while the frequency-independent sensitivity is a result of the low acceleration sensitivity of the sensor due to the out-of-plane fiber coil geometry and the presence of the mandrels. A comparison is made between this sensor and other large area fiber-optic sensor designs.

The low-temperature phase sequence gamma - delta - epsilon in halide perovskite tetramethylammonium trichlorogermanate(II) studied by X-ray diffraction

The halide perovskite tetramethylammonium trichlorogermanate(II), N(CH3)4GeCl3, undergoes a structural phase transition at 200 K from an orthorhombic room-temperature phase to an incommensurately modulated orthorhombic phase and at 170 K a further transition to a phase characterized by the coexistence of a monoclinic and an orthorhombic Bravais lattice. It is proposed that the superposition of the two Bravais lattices results from the low bulk modulus (9 GPa) in conjunction with the formation of ferroelastic domains. Local stresses implied by adjacent monoclinic domains allow the soft material to form orthorhombic domain boundaries. Two order parameters xi and eta governing the phase transition at 170 K can be related to a translational and a rotational part of the displacive modulation of the rigid GeCl3 and tetramethylammonium molecules. Experimental evidence suggests that the displacive modulation in the incommensurate phase is related to short-range disorder observed in the room-temperature phase.