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Phase equilibria involving orientationally disordered (OD) and liquid phases of the two-component system between carbon tetrachloride (CCl 4 ) and 2-methyl-2-bromomethane ((CH 3 ) 3 CBr) have been determined by means of X-ray powder diffraction and thermal analysis techniques from 210 K up to the liquid state. The isomorphism relation between the OD stable face-centered cubic (FCC) phase of (CH 3 ) 3 CBr and the metastable FCC phase of CCl 4 has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition, despite the monotropy of the FCC phase for the CCl 4 component with respect to its OD rhombohedral (R) stable phase. A continuous series of OD R mixed crystals is found, which confirms the R lattice symmetry of the OD phase II of (CH 3 ) 3 CBr, for which the crystallographic results have been long-time misinterpreted. X-ray patterns of such a phase were indexed according to the recent single-crystal results obtained by Rudman (Rudman, R. J. Mol. Struct. 2001, 569, 157). In addition, some experimental evidences are given to confirm the number of molecules per unit cell (Z = 21). The thermodynamic assessment reproduces coherently the phase diagram for the stable [R + L] and [R + FCC] two-phase equilibria as well as for the partially metastable [FCC + L] two-phase equilibrium and provides a set of data for the thermodynamic properties of nonexperimentally available phase transitions of pure components. Surprisingly, the phase equilibrium involving R and FCC OD phases appears as one of the very few showing a solid-solid equilibrium with two extremes.

The strength of molecular orientational correlations in polar liquids is assessed by means of comparison of the diffuse scattering patterns of a liquid composed by molecules devoid of permanent electric dipole but having a weak quadrupole moment and those for a liquid composed by permanent molecular dipoles. The extent of orientational correlations within the liquid phases is in both cases assessed by comparison of the liquid radial distributions to those present in the rotator-phase (plastic) crystal phases of both compounds. For such disordered-crystal phases, information concerning orientational correlations is directly derived from the experimental scattering patterns by means of analysis of the diffuse scattering background present beneath the Bragg peaks. The results show that rather than long-ranged, orientational correlations in polar or polarizable liquids are confined within distances comprising the second coordination sphere.

The polymorphism of bromotrichloromethane (CBrCl 3 ) has been investigated by X-ray powder diffraction and high-pressure density experiments. Phase transitions as a function of temperature and pressure between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p-v-rdiagram (and the denved p-T diagram) the volume variations at the transition points have been calculated and compared with those obtained by means of X-ray powder diffraction characterization. Special attention is given to the lattice symmetry of the orientational disordered phase II, characterized as rhombohedral (a = 14.639(8) A, α = 89.44(1)° at 240.2 K). The existence of a glass transition from the monoclinic low-temperature stable ordered phase (III) to its nonergodic state (associated with the freezing of exchange positions between Cl and Br atoms) is analyzed in terms of the asymmetry of the intermolecular interactions, and a new "fingerprint" for the glass transition is proposed on the basis of the aspherism index. Lattice parameters as a function of temperature were determined in order to build up the thermal expansion tensor.

The orientationally disordered stable and metastable mixed crystals of the two-component system (CH 3 )CCl 3 (1,1,1-trichloroethane) + CBrCl 3 (bromotrichloro-methane) have been characterised by means of X-ray powder diffraction and thermal analysis techniques. The thermodynamic assessment coherently reproduces the melting equilibria (the stable [R + L] and the partially metastable [FCC + L]) and provides a coherent set of data for the thermodynamic properties of non-experimentally available phase transitions of pure compounds which agree perfectly with those properties obtained from the pressure–temperature phase diagrams.

8 págs.; 11 figs. ; PACS number s : 61.43. j, 61.20. p, 61.72. y, The spatial extent of orientational short-range order in liquid and rotationally disordered phases of two halogen-substituted methanes are examined by means of neutron diffraction. The pair distribution functions measured within the liquids are compared to those corresponding to the rotator-phase crytals where the separation between orientational and positional correlations is enabled by the presence of time-averaged fcc lattices. The two condensed systems under scrutiny comprise a material devoid (CCl4) and another [C(CD3)3Cl] having a relatively strong molecular dipole moment. Our results show orientational correlations to be confined below the second coordination sphere. Furthermore, contrary to what could be expected, angular correlations within the nonpolar material are of comparable strength to those present within the polar C(CD3)3Cl. © 2005 The American Physical Society., This work was supported by the Spanish Ministry of Science and Technology Grant Nos. BFM2002-01425, MAT2002-04540-C05-03 and by the catalonian goverment Grant No. SGR2002-00152.

The larvae and pupae of three Cetoniinae scarab beetles, Gymnetis pantherina Blanchard, 1837; Gymnetis holosericea (Voet, 1779), and Euphoria precaria Janson, 1881 from Colombia are described. Multiple color patterns of adults and key larval characters are illustrated for each species for the first time. The described larvae of Gymnetis MacLeay are included in a key to the larvae of the genus, now with five species; and Euphoria precaria is added to the extant key of the known Euphoria larvae. New distributional records for the country are presented and some comments on the biology of the species in captivity are provided.Se describe la larva y la pupa de tres escarabajos cetoninos: Gymnetis pantherina Blanchard, 1837; Gymnetis holosericea (Voet, 1779), y Euphoria precaria Janson, 1881 de Colombia. Los caracteres larvales estudiados y las multiples formas de coloraci n de los adultos de las especies tratadas son ilustrados por primera vez. Una clave para las larvas de las especies de Gymnetis descritas al momento es elaborada y la clave existente para las larvas de Euphoria es actualizada con la nueva informaci n. El rango distribucional de las especies en Colombia es ampliado con nuevos registros y se presenta informaci n sobre la biolog a de las especies en cautiverio.

–OH) is revealed to be a complexproblem and only two stable solid phases, denoted on cooling from the liquid as phases I and II, are foundusing static ~thermodynamic and x-ray diffraction! as well as dynamic ~dielectric spectroscopy! experimentaltechniques. Both solid phases are known to exhibit glass transitions if they are cooled down fast enough toprevent transition to ordered crystalline states. Although glass transitions corresponding to both phases hadbeen well documented by means of specific heat measurements, x-ray measurements constitute, as far as weknow, the first evidence from the structural point of view. In addition, a great amount of dielectric worksdevoted to phase I and its glass transition, were published in the past but next to nothing relating to thedielectric properties of phase II and its glass transition. The nature of the disorder of phase II will be discussed.DOI: 10.1103/PhysRevB.69.224202 PACS number~s!: 61.43.2j, 64.70.Pf, 65.60.1a, 77.22.2dI. INTRODUCTION

The phase diagram of the two-component system between two halomethanes, carbon tetrachloride (CCl4) and bromotrichloromethane (CBrCl3) has been determined by means of X-ray powder diffraction and thermal analysis techniques from 200 K to the liquid state. From the continuous series of mixed crystals, three relations of isomorphism have been evidenced: (i) between the stable low-temperature monoclinic (M) phases, (ii) between the stable orientationally disordered (OD) rhombohedral (R) phases, and (iii) between the stable OD face-centered cubic (FCC) of CBrCl3 and the metastable FCC phase of CCl4. The existence of such a metastable phase gives rise to the appearance, for a large range of composition, of metastable FCC mixed crystals that behave monotropically with respect to the R mixed crystals accordingly with the well-known monotropic character of the R to FCC phase transition of the CCl4. The isomorphism relationships i and ii enable us to validate the previously proposed structure of the monoclinic ph...

Orientationally disordered (OD) stable and metastable mixed crystals of the two-component system 2,2-dichloropropane ((CH3)2CCl2)+methylchloroform ((CH3)CCl3) have been characterized from crystallographic and thermodynamic points of view. Continuous series of mixed crystals in the stable rhombohedral (R) phase points out an isomorphism relationship. The monotropic behavior of the non-isomorphous OD metastable phases in the pure components (simple cubic, SC, and face-centered cubic, FCC, respectively) with respect to the R stable phase is partially retained by the mixed crystals. In particular, SC mixed crystals were found persistent enough as metastable crystals in the whole composition range with the exception of the pure compound (CH3)CCl3, for which only the FCC metastable phase was experimentally available. On the contrary, samples with compositions greater than X=0.70 in (CH3)CCl3 crystallized into either the FCC or SC, both being metastable with respect to the R phase. Thus, three kinds of OD mixed crystals appear which give rise to three independent OD+Liquid equilibria. The thermodynamic analysis of such non-interfering equilibria, [R+L], [SC+L] and [FCC+L], enables us to infer the stability relationships between the whole of OD phases.

Los bosques de niebla de Tambito (flanco oeste de la Cordillera Occidental, Cauca) albergan un interesante ensamblaje de escarabajos Scarabaeinae saprófagos reconocidos preliminarmente en este trabajo con el propósito de examinar su estructura (composición y abundancia), hábitos alimenticios y hábitats preferidos. Entre los meses de Enero y Julio de 2001 se realizaron cuatro muestreos a través de transectos y trampas en bosque secundario maduro, bosque secundario temprano y pastizal en regeneración. Se acumuló un total de 2578 ejemplares de los géneros Onthophagus, Dichotomius, Ontherus, Uroxys, Canthidium, Oxysternon, Sulcophanaeus, Scybalocanthon, Coprophanaeus, Deltochilum y Canthon; 2271 corresponden a 16 especies atraídas a las coprotrampas y 307 a 11 especies atraídas a las necrotrampas. En ambos casos se observó mayor riqueza en el bosque secundario maduro, anotando que la riqueza del gremio declina desde los ambientes de mayor estructura vegetal a los menos estructurados (23%) y desde la coprofagia a la necrofagia (31%). La abundancia total declinó de manera similar respecto al estado de regeneración del hábitat en ambos tratamientos (coprófagos 69%, necrófagos 91%). El pastizal exhibió una menor colecta explicable por la ausencia de vacunos que en otros casos han ocasionado una notable abundancia de coprófagos. The cloud forests of Tambito (west flank of the Cordillera Occidental, Cauca) harbors an interesting assemblage of saprophagous beetles (Coleoptera: Scarabaeinae) recognized preliminarily in this research with the purpose of presenting their structure (composition and abundance), feeding habits and favorite habitats. During the months of January and September of 2001 we carried out four samplings integrated by transects and traps in mature secondary forest, early secondary forest and pasture. We captured a total of 2578 individuals belonging to the Onthophagus, Dichotomius, Ontherus, Uroxys, Canthidium, Oxysternon, Sulcophanaeus, Scybalocanthon, Coprophanaeus, Deltochilum and Canthon genera; 2271 individuals correspond to 16 species attracted to the coprotraps and 307 to 11 species attracted to the necrotraps. In both cases, higher species richness was observed in the mature secondary forest, the richness of the guild declines by 23% from conserved to intervened environments and 31% from coprophagy to necrophagy. Total abundance declined with respect to the degree of habitat regeneration for both treatments (coprophagous 69%, necrophagous 91%). The pasture exhibited a smaller accountable collection of beetles, explained by the absence of bovines that otherwise would cause a noticeable abundance of coprophagous species.

The polymorphism of 2,2-dichloropropane ((CH3)2CCl2) has been further investigated by both thermal and X-ray powder diffraction experiments. From the former the phase transitions between the different phases have been characterized at normal pressure as well as at high pressures (up to 200 MPa). From the p−T slopes of the two-phase coexistence lines, the volume variations at the transition points have been calculated and compared with those obtained by means of X-ray powder diffraction characterization. The existence of two low-temperature stable ordered phases (III and II), one high-temperature orientationally disordered phase (rhombohedral, Ib) and one additional monotropic orientationally disordered phase Ia, has been confirmed. The structure of the low-temperature ordered phase II has been determined by X-ray powder diffraction and Rietveld profile refinement as monoclinic C2/c, with lattice parameters a =10.6402(3) A, b = 5.4074(2) A, c = 10.7295(3) A, and β = 116.274(3)° at 175.2 K. The strength of ...

The melting phase diagram of the two-component system 2-methyl-2-chloro-propane ((CH3)3CCl) and carbon tetrachloride (CCl4) has been determined by combining X-ray powder diffraction and thermal analysis. The isomorphism relation between the orientationally disordered (OD) stable face-centered cubic (FCC) phase of (CH3)3CCl and the metastable FCC phase of CCl4 has been demonstrated throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition, despite the monotropy of the FCC phase for the CCl4 component. This equilibrium interferes with a rhombohedral plus liquid ([R + L]) equilibrium giving rise to a peritectic invariant. A thermodynamic analysis, in terms of the crossed isodimorphism, has also been performed in order to obtain the excess properties of the FCC and R OD phases.

The motion of phospholipids has previously been studied on many time scales due to the significance for living cells and technological applications. The motions on a pico- to nanosecond time scale were determined by quasielastic neutron scattering (QENS) to be much faster than the ones on the microsecond scale covered by fluorescence recovery after photobleaching (FRAP). This was explained by assuming that the molecules rattle fast in a cage of neighbors (observed with QENS) from which they escape once in a while; this escape was then the primary step of the slower diffusion measured by FRAP. However, nanosecond MD simulation studies could not observe any escape events; recent findings even suggested that the long-range motion in phospholipid membranes on short time scales is not diffusive but has flow-like characteristics. To check this novel view, we have repeated the QENS experiments with today's significantly improved instrumentation. By using the advantage of QENS that allows tuning of the observation time in the pico- to nanosecond range, it was possible to study the evolution of motions in this time frame. Localized motions, e.g., of the head and tail groups, appear separated from the long-range motion and do not obfuscate the analysis as they do in a mean squared displacement plot. The results for the long-range motion are indeed compatible with flow patterns, whereas the localized motions can account for the fast motions interpreted as motions in a cage before. Hereby, we give experimental evidence for a completely different mechanism of long-range motion on short time scales in phospholipid membranes.

International audience; The orientationally disordered stable and metastable mixed crystals of the two-component system methylchloroform ((CH3)CCl3)+carbon tetrachloride (CCl4) have been characterised from a crystallographic and thermodynamic point of view. The monotropic behaviour of the metastable phase in the pure components is maintained for the whole range of composition. The lattice symmetry of the stable orientationally disordered phase of methylchloroform has been found to be isostructural with that of the carbon tetrachloride compound. Continuous series of both stable and metastable mixed crystals give rise to a double isomorphism relationship, one for the stable state and another for the metastable stable of the pure components.

The main objective of this paper is to present a method to fully determine the six degrees of freedom regarding position and orientation of a neighboring molecule around a central one, i.e. the g(rCM,¿) distribution function. This is accomplished by completely determining the short range structure of liquid carbon tetrachloride, while employing results from two different methods, Molecular Dynamics (MD) [1] and Reverse Monte Carlo (RMC) [2]. Exclusively, the structural ordering of the first four molecules will be detailed.

The dynamics of the fully hydrated phospholipid dimyristoylphosphatidylcholine (DMPC) were studied on a time scale of about 60 picoseconds with quasielastic neutron scattering. Three types of samples were employed: multibilayers without solid support, single bilayers in vesicles, and monolayers in emulsions of perdeuterated hexadecane. The vesicles and emulsion droplets had diameters of about 130 nanometres; some of the emulsions also contained sodium glycocholate to enhance the stability. It could be shown that the mobility of the phospholipid molecules in the observed time regime increases from multibilayers over single bilayers to monolayers. Additionally, the high quality of the data of the multibilayer samples allows an evaluation of the molecular mechanism of the motions: while the interpretation in the frame of flow-like motions fits well at temperatures shortly above the main phase transition, the model of diffusive motions fits better at high temperatures of up to 80 °C.

The alpha-relaxation dynamics of 1-cyano-adamantane (CNA) and its mixtures with 1-chloro-adamantane (ClA) has been studied by means of broadband dielectric spectroscopy. The existence of orientationally disordered (OD) face centered cubic mixed crystals (ClA(1-X)CNA(X)) for 0.5or = Xor = 1 has been put in evidence by thermodynamics and structural analyses. In addition to the OD phase of CNA, mixed crystals with compositions higher than the equimolar one exhibit a freezing of the orientational degrees of freedom into a glassy state, which involves also a strong increase of the antiferroelectric order at temperatures higher than the dielectric glass transition temperature. This experimental evidence is revealed by a stairlike effect in the variation of the Kirkwood factor with the temperature as a consequence of a twin effect in the dielectric strength without any anomaly in the temperature-density curves. The characteristic relaxation times are analyzed as a function of temperature and mole fraction. By setting a common temporal origin ("isochronal origin") at tau(T(g)) = 100 s for each mole fraction, it emerges that the substitution of ClA molecules by those of CNA (diminution of X) gives rise to a slow down in the dynamics, despite that the molecular volume of ClA molecules are smaller than those of CNA. This fact goes along and is accompanied by a diminution of the lattice packing with the decrease of composition. It is also shown that the heterogeneities produced by the concentration fluctuations due to the chemical disorder are the main contribution to the non-exponential character of the alpha-relaxation peaks.

The evolution of the primary relaxation time of orientationally disordered (OD) mixed crystals [(CH(3))(2)C(CH(2)OH)(2)](1-X)[(CH(3))C(CH(2)OH)(3)](X), with 0Xor = 0.5, on approaching the glass temperature (T(g)) is discussed. The application of the distortion-sensitive, derivative-based procedure revealed a limited adequacy of the Vogel-Fulcher-Tammann parametrization and a superiority of the critical-like description tau proportional to (T - T(C))(-phi(') ), phi(') = 9-11.5, and T(C) approximately T(g) - 10 K. Basing on these results as well as that of Drozd-Rzoska et al. [J. Chem. Phys. 129, 184509 (2008)] the question arises whether such behavior may be suggested as the optimal universal pattern for dynamics in vitrifying OD crystals (plastic crystals). The obtained behavior is in fair agreement with the dynamic scaling model (DSM) [R. H. Colby, Phys. Rev. E 61, 1783 (2000)], originally proposed for vitrifying molecular liquids and polymers. The application of DSM made it possible to estimate the size of the cooperatively rearranging regions ("heterogeneities") in OD phases near T(g).

We present a thorough dielectric investigation of the relaxation dynamics of plastic crystalline Freon112, which exhibits freezing of the orientational degrees of freedom into a glassy crystal below 90 K. Among other plastic crystals, Freon112 stands out by being relatively fragile within Angell's classification scheme and by showing an unusually strong $\beta$-relaxation. Comparing the results to those on Freon112a, having only a single molecular conformation, points to the importance of the presence of two molecular conformations in Freon112 for the explanation of its unusual properties.

ResumenLos ambientes forestales de zonas de vida secas y muy secas del Caribe colombiano han sido profundamente impactados y a la fecha quedan muy pocos remanentes y rastros de su dinámica biológica original; por ello, en esta investigación se planteó estudiar la estructura y la variación estacional de los escarabajos fitófagos (Coleoptera: Scarabaeidae) en la Reserva Campesina La Montaña. Se realizaron 9 muestreos, desde enero hasta septiembre de 2011, y se instalaron 4 trampas de luz (2 BL y 2 WL) entre las 18:00 y las 24:00h. Se capturaron 3,007 individuos y 18 especies agrupados en 3 subfamilias: Rutelinae (7 especies), Melolonthinae (6 especies) y Dynastinae (5 especies); sobresalió Melolonthinae con la mayor abundancia (2,907 individuos), y Liogenys quadridens fue la especie más abundante (1,667 individuos), reconocida por ser una plaga de cultivos semestrales, de amplia distribución en el Caribe colombiano. La mayor riqueza (16 especies) se observó en mayo y la mayor abundancia (1,421), en abril, lo que coincidió con la época de las primeras lluvias en la región, lo que pone de manifiesto una marcada estacionalidad que quedó demostrada con el análisis de similitud Anosim (R=0.277, p

A new species, Ancognatha veliae, from the Chocó Province, Colombia is described and its morphology and taxonomic position are discussed. The species Ancognatha atacazo Kirsch, A. castanea (Erichson), and A. horrida Endrödi are recorded as new country records for Colombia.

Water is the most important plasticizer of biological and organic hydrophilic materials, which generally exhibit enhanced mechanical softness and molecular mobility upon hydration. The enhancement of the molecular dynamics upon mixing with water, which in glass-forming systems implies a lower glass transition temperature (T g ), is considered a universal result of hydration. In fact, even in the cases where hydration or humidification of an organic glass-forming sample result in stiffer mechanical properties, the molecular mobility of the sample almost always increases with increasing water content, and its T g decreases correspondingly. Here, we present an experimental report of a genuine antiplasticizing effect of water on the molecular dynamics of a small-molecule glass former. In detail, we show that addition of water to prilocaine, an active pharmaceutical ingredient, has the same effect as that of an applied pressure, namely, a decrease in mobility and an increase of T g . We assign the antiplasticizing effect to the formation of prilocaine-H2O dimers or complexes with enhanced hydrogen bonding interactions.

We investigated the dynamics of confined water in different hydrated cement pastes with minimized contributions of capillary water. It was found that the water motions are extremely reduced compared to those of bulk water. The onset of water mobility, which was modified by the local environment, was investigated with elastic temperature scans using the high-resolution neutron backscattering instrument SPHERES. Using a Cauchy-Lorenz distribution, the quasi-elastic signal observed in the spectra obtained by the backscattering spectrometer was analyzed, leading to the identification of rotational motions with relaxation times of 0.3 ns. Additionally, neutron spin echo (NSE) spectroscopy was used to measure the water diffusion over the local network of pores. The motions observed in the NSE time scale were characterized by diffusion constants ranging from 0.6 to 1.1 × 10-9 m2 s-1 most likely related to water molecules removed from the interface. In summary, our results indicate that the local diffusion observed in the gel pores of hardened cement pastes is on the order of that found in deeply supercooled water. Finally, the importance of the magnetic properties of cement pastes were discussed in relation to the observation of a quasi-elastic signal on the dried sample spectra measured using the time-of-flight spectrometer.

The arrangement of water and chloride ions around a model peptide (glycyl-L-prolyl-glycine-NH2) was investigated using Molecular Dynamics (MD) simulations and complementary Empirical Potential Structure Refinement (EPSR) simulations which adapt the modelled structure to reproduce experimentally measured neutron diffraction data. The results are in good qualitative agreement and show a common picture for all hydrogen-containing amine and amide groups: namely that there are two common chloride interactions observed – a direct contact between Cl and peptide backbone and a water-mediated interaction. The geometry of this mediation depends on the distance between chloride and nitrogen and hints towards two distinct modes of interaction between water and the ion, either along one of the O–H bonds or along the water dipole.