Ideal Symmetry Research Articles

Development of a freely available simulator with graphical interface for modeling nonlinear focused ultrasound fields with shocks

Measurement-based modeling is gaining acceptance as a standard tool for characterizing the nonlinear fields of existing therapeutic ultrasound devices and designing new ones. Here, a freely available simulation tool is presented for modeling axially symmetric, strongly nonlinear HIFU beams with shocks in a layered propagation medium such as water and different types of tissue. Two nonlinear wave equations are included in the simulator: the KZK equation generalized to include an equivalent source boundary condition for strongly focused beams and the Westervelt equation in a nonlinear wide-angle parabolic representation. Both equations are solved in the frequency domain and permit definition of the HIFU transducer as an annular array. The geometrical parameters and power output of the array, electronic focus steering along the beam axis, and acoustic properties of the layered propagation medium can be configured via graphical interface. Visualization and output of various acoustic field parameters such as peak positive and negative pressures, shock amplitude, intensity, heat deposition rate, and total power of a beam are also provided. The simulator can be used for transducers without ideal symmetry through definition of an equivalent radially symmetric source. Widespread availability of such simulation tools will help advance standardized utilization of measurement-based modeling and facilitate the adoption of such approaches for HIFU treatment planning. [Work supported by NIH R01EB7643, R01EB025187, and RSF №14-12-00974.]

Plasmon coupled super- and sub- radiance from dye shells

Coupled super- and sub- radiant emission of dye fluorescence near the plasmonic surface is shown to be an intrinsic property of the hybrid system. The bi-exponential decay is demonstrated for Au\\SiO2\\ATTO655 core-shell nanoparticles, which persists even when averaging over a broad range of the coupling parameter. The superradiant and subradiant states are distinct and exclusive by the identical permutational symmetry of the atom-field interaction Hamiltonian of the two-level system. Our analytical approach shows that starting from two emitters, coupled for example via the plasmon modes, the symmetry breaking occurs, making detectable the simultaneous existence of the fast super-radiance and the slow sub-radiance. The relaxation in the sub-radiant system occurs mainly due to the interaction with the plasmon modes. Our theory shows that the relaxation leads to the population of the sub-radiant states by dephasing the super-radiant Dicke states giving rise to the bi-exponential decay in agreement with the experiments. Even if we have a group of many coupled emitters or many groups of coupled emitters with different coupling parameters, the averaging will affect the emission among the super-radiant fast transitions and the sub-radiant slow transitions and keep these two group distinct.

Conformation and Structure of Dichlorophosphoryl Isocyanate in the Gaseous and Solid Phases

The conformational properties and the molecular structure of dichlorophosphoryl isocyanate, Cl2P(O)NCO, were studied by combining vibrational spectroscopy (IR and Raman), gas‐phase electron diffraction (GED), X‐ray crystallography (XRD), and quantum‐chemical calculations. Computationally, two conformers of Cs symmetry with the P=O bond being in syn or anti configuration relative to the NCO group are predicted to be close in energy (ca. 2 kJ mol–1). Experimentally, both gas‐phase and matrix‐isolation IR spectra of Cl2P(O)NCO suggest the presence of a single conformer, which was determined to be the energetically more favorable syn‐conformer. This was also found to exist in the solid state by low‐temperature XRD. However, the molecule in the solid state is significantly distorted from ideal Cs symmetry with an O–P–N–C dihedral angle of 38.1(1)° due to intermolecular C···O contacts [2.881(4) Å]. In the gas phase, the GED analysis suggests that the molecule exists predominantly as syn‐conformer but with dynamic behavior about the two minimum structures (syn and anti).

Pinching an open cylindrical shell: Extended deformation and its persistence

Against external loads, shells with ideal symmetries, such as perfect spheres and cylinders, show enhanced rigidities, whose origin is known to be largely geometric and is often termed “geometric rigidity.” In contrast, shells with free boundaries (i.e., open shells) may respond quite differently to external loads. They may deflect significantly as free boundaries may allow (almost) inextensional bending deformations that are impossible in the case of closed surfaces. Herein, we investigate the smooth deformation of an open cylindrical shell induced by pinching through a combination of experiment, simulations, and theory. To be more specific, we apply a localized pinch at one end of a long semi-cylindrical shell, and investigate the distance at which the shell recovers its undeformed form; we call this distance the persistence length of a pinch. We establish a new scaling law for the persistence length of shallow shells, which is shown to be valid for an arbitrarily deep shell. We show that the persistence length of a sufficiently deep open cylinder exceeds that of a closed cylinder, thereby highlighting the importance of the subtle interplay between the intrinsic curvature and the free edges on shell mechanics. These findings are rationalized by a detailed asymptotic analysis of the shallow shell equations. Our results reveal how the free boundaries essentially alter the balance between bending and stretching in thin shells.

Two tris-(3,5-disubstituted phen-yl)phosphines and their isostructural PV oxides.

The crystal structures of tris-(3,5-di-methyl-phen-yl)phosphine (C24H27P), (I), tris-(3,5-di-methyl-phen-yl)phosphine oxide (C24H27OP), (II), tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine (C27H33O3P), (III), and tris-(4-meth-oxy-3,5-di-methyl-phen-yl)phosphine oxide (C27H33O4P), (IV), are reported. The strucure of (III) has been described before [Romain et al. (2000 ▸). Organometallics, 19, 2047-2050], but it is rereported here on the basis of modern area-detector data and to facilitate comparison with the other structures reported here. Compounds (I) and (II) crystallize isostructurally in P21/c. Similarly, (III) and (IV) crystallize isostructurally in Pbca. The conformations of (I) and (II) in the solid state deviate strongly from helical, whereas those of (III) and (IV) are found to be closer to an ideal threefold rotational symmetry. The pyramidality indices, ∑(C-P-C), are 305.35 (16), 317.23 (15), 307.2 (4) and 318.67 (18)° for (I), (II), (III) and (IV), respectively. Each is found to be more pyramidal than Ph3P or Ph3PO. Hybrid DFT calculations incorporating terms for dispersion provide evidence that the causes of the increased pyramidality, despite the 3,5-dimethyl group substitution, include dispersion inter-actions. The calculated ∑(C-P-C) values are 304.8° for both (I) and (III) and 317.4° for both (II) and (IV), with no difference arising from the substitution at ring position 4.

Non-adiabatic quantum reactive scattering in hyperspherical coordinates.

A new electronically non-adiabatic quantum reactive scattering methodology is presented based on a time-independent coupled channel formalism and the adiabatically adjusting principal axis hyperspherical coordinates of T Pack and Parker [J. Chem. Phys. 87, 3888 (1987)]. The methodology computes the full state-to-state scattering matrix for A + B2(v, j) ↔ AB(v', j') + B and A + AB(v, j) → A + AB(v', j') reactions that involve two coupled electronic states which exhibit a conical intersection. The methodology accurately treats all six degrees of freedom relative to the center-of-mass which includes non-zero total angular momentum J and identical particle exchange symmetry. The new methodology is applied to the ultracold hydrogen exchange reaction for which large geometric phase effects have been recently reported [B. K. Kendrick et al., Phys. Rev. Lett. 115, 153201 (2015)]. Rate coefficients for the H/D + HD(v = 4, j = 0) → H/D + HD(v', j') reactions are reported for collision energies between 1 μK and 100 K (total energy ≈1.9 eV). A new diabatic potential energy matrix is developed based on the Boothroyd, Keogh, Martin, and Peterson (BKMP2) and double many body expansion plus single-polynomial (DSP) adiabatic potential energy surfaces for the ground and first excited electronic states of H3, respectively. The rate coefficients computed using the new non-adiabatic methodology and diabatic potential matrix reproduce the recently reported rates that include the geometric phase and are computed using a single adiabatic ground electronic state potential energy surface (BKMP2). The dramatic enhancement and suppression of the ultracold rates due to the geometric phase are confirmed as well as its effects on several shape resonances near 1 K. The results reported here represent the first fully non-adiabatic quantum reactive scattering calculation for an ultracold reaction and validate the importance of the geometric phase on the Wigner threshold behavior.

Giant Piezoelectric Effects in Monolayer Group-V Binary Compounds with Honeycomb Phases: A First-Principles Prediction

Two-dimensional (2D) piezoelectric materials have gained considerable attention since they could play important roles in the nanoelectromechanical systems. Herein, we report a first-principles study on the piezoelectric properties of monolayer group-V binary compounds with theoretically stable honeycomb phases (α-phase and β-phase). Our calculations for the first time reveal that a majority of the monolayers possess extremely high piezoelectric coefficients d11, i.e., 118.29, 142.44, and 243.45 pm/V for α-SbN, α-SbP, and α-SbAs, respectively, comparable to those of recently reported group-IV monochalcogenides (d11 = 75–250 pm/V) with an identical mm2 symmetry. It is found that the giant piezoelectric responses of α-phase monolayers as compared to those of β-phase monolayers are induced by their flexible structures and special symmetry. Meanwhile, the piezoelectric coefficients of α-phase monolayers are found to be surprisingly anisotropic and obey a unique periodic trend which is not exactly identical to ...

Efficient Energy Transfer (EnT) in Pyrene- and Porphyrin-Based Mixed-Ligand Metal–Organic Frameworks

Designing and synthesizing the ordered light-harvesting systems, possessing complementary absorption and energy-transfer process between the chromophores, are essential steps to accomplish successful mimicking of the natural photosynthetic systems. Metal-organic frameworks (MOFs) can be considered as an ideal system to achieve this due to their highly ordered structure, superior synthetic versatility, and tailorable functionality. Herein, we have synthesized the new light-harvesting mixed-ligand MOFs (MLMs, MLM-1-3) via solvothermal reactions between a Zr6 cluster and a mixture of appropriate ratio of 1,3,6,8-tetrakis(p-benzoic acid)pyrene and [5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrinato]-Zn(II) ligands. The identical symmetry and connectivity of the two ligands of the MLMs was the key parameter of successful synthesis as a single MOF form, and the ample overlap between the emission spectrum of pyrene and the absorption spectrum of porphyrin provided the ideal platform to design an efficient-energy transfer (EnT) process within the MLMs. We obtained the nanoscale maps of the fluorescence intensities and lifetimes of microsize MLM grains for unambiguous visualization of EnT phenomena occurring between two ligands in MLMs. Moreover, due to complementary absorption and energy transfer between the two ligands in the MLMs, our MLMs performed as superior photoinduced singlet-oxygen generators, verifying the enhanced light-harvesting properties of the pyrene- and porphyrin-based MLMs.

Open-Framework Manganese(II) and Cobalt(II) Borophosphates with Helical Chains: Structures, Magnetic, and Luminescent Properties.

Two borophosphates, (NH4)1-2xM1+x(H2O)2(BP2O8)·yH2O with M = Mn (I) and Co (II), synthesized hydrothermally crystallize in enantiomorphous space groups P6522 and P6122 with a = 9.6559(3) and 9.501(3) Å, c = 15.7939(6) and 15.582(4) Å, and V = 1275.3(1) and 1218.2(8) Å3 for I and II, respectively. Both compounds feature helical chains composed of vertex-sharing tetrahedral PO4 and BO4 groups that are connected through O atoms to transition-metal cations, Mn2+ and Co2+, respectively. For the two crystallographically distinct transition-metal cation sites present in the structure, this results in octahedral coordination with different degrees of distortion from the ideal symmetry. The crystal-field parameters, calculated from the corresponding absorption spectra, indicate that Mn2+ and Co2+ ions are located in a weak octahedral-like crystal field and suggest that the Co-ligand interactions are more covalent than the Mn-ligand ones. Luminescence measurements at room temperature reveal an orange emission that red-shifts upon lowering of the temperature to 77 K for I, while II is not luminescent. The luminescence lifetimes of I are 33.4 μs at room temperature and 1.87 ms at 77 K. Both compounds are Curie-Weiss paramagnets with negative Weiss constants and effective magnetic moments expected for noninteracting Mn2+ and Co2+ cations but no clear long-range magnetic order above 2 K.

Clock Synchronization in IoT Network Using Cloud Computing

The Internet of Things is a trending future technological revolution that emerging distributed computing and real-time based application and its development depends on dynamic technical innovation in a number of important fields from wireless sensors to nanotechnology. Cloud integration with IoT made things more convenient and easy. Clock synchronization between systems in a distributed network is the complex and tedious job. It is mandatory to get sync with other and source as well. There are many proposed ways of data synchronization protocols like NTP, global position system to maintain sync process between Systems or IoT devices network. In this paper, we are proposing a clock synchronization approach to sync clocks between IoTs and Cloud which are connected with each other in distributed network. Here we have used cloud service Software as a Service to collect the information to analysis and trigger the results action to IoTs. In this paper, we present the Clock Synchronization based on precision time protocol between IoTs simulation model for Omnet++ with INET framework, which allows us to check clock sync accuracy with a different network configured topologies. We have tried to minimize the clock drift with clock offset updating and with master–slave phenomena also minimize the master–slave delay. To show our simulation results we have used chunks nodes of IoTs in distributed manner placed in different places with different clock values. The simulation result shows that proposed approach works in the desired manner within ideal and network delay symmetry.

Electronic‐Structure Calculations of Cation‐Ordered II‐III Layered Double Hydroxides: Origin of the Distortion of the Metal‐Coordination Symmetry

Cation ordering brings down the crystal symmetry and introduces distortion into the coordination polyhedra around the divalent cations. In particular, edge sharing of the differently sized [M(OH)6] polyhedra causes a non‐uniform distension of the array of hydroxy ions. The question arises as to whether this distortion has its origin in the Jahn–Teller distortion of metal coordination or a 2D “Peierls”‐type distortion of the array of hydroxy ions. To address this question, DFT calculations were performed on the sulfate‐intercalated [Cu–Cr], [Zn–Cr], and [Zn–Al] layered double hydroxides (LDHs). An analysis of the density of states shows that the distortion of the Cu2+ coordination polyhedron is due to the Jahn–Teller effect, whereas the Zn2+ coordination polyhedron in [Zn–Al] LDH likely suffers a “Peierls”‐type distortion. In the [Zn–Cr] LDH, electronic‐structure calculations do not predict any distortion in the metal coordination, which is in agreement with experimental results that show only a slight departure from ideal symmetry.

Crystal structures and new perspectives on Y3Au4 and Y14Au51.

Y3Au4 (triyttrium tetragold) and Y14Au51 (tetradecayttrium henpentacontagold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R-3 and P6/m, adopting the Pu3Pd4 and Gd14Ag51 structure types, respectively (Pearson symbols hR42 and hP65). A variety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu3Pd4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca3Au4, Pr3Au4, Nd3Au4, Gd3Au4, and Th3Au4. Sm6Au7 is suspected to be Sm3Au4 due to identical symmetry and close unit-cell parameters. The Pu3Pd4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd14Ag51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y3Au4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y14Au51, this structure is more complex and is best described in terms of polyhedral `pinwheels' around the tunnel forming polyhedra along the c axis.

CsSc3F6[SeO3]2: A New Rare‐Earth Metal(III) Fluoride Oxoselenate(IV) With Sections Of The ReO3‐Type Structure

A new representative of rare‐earth metal(III) fluoride oxoselenates(IV) derivatized with alkali metals could be synthesized via solid‐state reactions. Colorless single crystals of CsSc3F6[SeO3]2 were obtained through the reaction of Sc2O3, ScF3, and SeO2 (molar ratio 1:1:3) with CsBr as reactant and fluxing agent. For this purpose, corundum crucibles embedded as liners into evacuated silica ampoules were applied as containers for these reactions at 700 °C for seven days. The new quintenary compound crystallizes in the trigonal space group P3m1 with a = 565.34(4) and c = 1069.87(8) pm (c/a = 1.892) for Z = 1. The crystal structure of CsSc3F6[SeO3]2 contains two crystallographically different Sc3+ cations. Each (Sc1)3+ is surrounded by six fluoride anions as octahedron, while the octahedra about (Sc2)3+ are formed by three fluoride anions and three oxygen atoms from three terminal [SeO3]2– anions. The [(Sc1)F6]3– octahedra link via common F– vertices to six fac‐[(Sc2)F3O3]6– octahedra forming 2∞{[Sc3F6O6]9–} layers parallel to (001). These layers are separated by oxygen‐coordinated Cs+ cations (C.N. = 12), arranging for the charge compensation, while Se4+ cations within the layers surrounded by three oxygen atoms as ψ1‐tetrahedral [SeO3]2– units complete the structure. EDX measurements confirmed the composition of the title compound and single‐crystal Raman studies showed the typical vibrational modes of isolated [SeO3]2– anions with ideal C3v symmetry.

Hydroxykenoelsmoreite, the first new mineral from the Republic of Burundi

We report thenewmineralhydroxykenoelsmoreite,whichhas beenapprovedbytheIMAasIMA2016-056.Themineraloccurs at the Masaka gold mine, Burundi, as rosettes up to 150mm across of platy crystals up to 20μm wide but <2μm thick, associated with goethite and galena. Crystals are canary yellow, transparent with a vitreous lustre, and have a pale yellow streak. Hydroxykenoelsmoreite is uniaxial (-) and non-pleochroic. The refractive indices were too high to measure, but the Gladstone-Dale compatibility index predicts n = 2.065. Crystals are brittle with an irregular fracture, but have perfect cleavage on {0 0 1}. TheMohs hardness is ∼3 by analogy with hydrokenoelsmoreite. The mineral is a member of the elsmoreite group of the pyrochlore supergroup, but deviates from the ideal cubic symmetry due mainly to ordering of Fe onto one of two W sites. Its structure is trigonal, space group R3, with unit-cell parameters a = 7.313(2), c = 17.863(7) A, V = 827(1)A3 and Z = 6. The empirical formula (based on 7 (O+OH) per formula unit (pfu)) is: (□PbCa NaKBa)(W Fe Al)(O(OH))(OH). Raman spectroscopy and bond- valence sums showed that molecular HO was absent or nearly so. The calculated density is 5.806 g cm.

Thermal behavior of stilbite and stellerite revisited and dehydration of their Na-exchanged forms: Considerations on the memory effect of the STI framework type

The thermal behavior of Na-exchanged stellerite and stilbite was investigated by in-situ single crystal X-ray diffraction. For comparison with the exchanged forms new data were collected on natural stellerite and stilbite under the same experimental conditions. With the increase of temperature, strong disorder at T and O sites of the tetrahedra of the four-membered ring developed in natural forms. Such disorder was associated with the rupture of T-O-T connections and transition from the A to the B phase. Differently from previous studies, stellerite B at T > 300 °C was found to be monoclinic (space group A2/m). In addition, at 400 °C, a new T-O-T connection occurred, analogous to that in the B phase of barrerite.Na-stellerite and Na-stilbite were at RT monoclinic, space group F2/m. Upon heating, they also displayed the same structural modifications as observed in natural barrerite and Na-barrerite and adopted space group A2/m. Compared to natural stellerite and stilbite different T-O-T connections ruptured leading to a different topology of the B phase. The total volume contraction was −16% at 350 °C compared to −8% of pristine materials. The highly-condensed D phase, which does not form in natural stellerite and stilbite, was obtained by heating a Na-stellerite crystal ex-situ at 525 °C. The structure corresponded to the D phase of natural barrerite and Na-barrerite.All investigated STI members, after being exchanged with Na, have identical symmetry and demonstrate corresponding behavior upon heating and associated dehydration. Thus, a previously assumed memory effect of the symmetry of the natural parent structure, is not confirmed.

Benchmarking a computational design method for the incorporation of metal ion-binding sites at symmetric protein interfaces.

The design of novel metal-ion binding sites along symmetric axes in protein oligomers could provide new avenues for metalloenzyme design, construction of protein-based nanomaterials and novel ion transport systems. Here, we describe a computational design method, symmetric protein recursive ion-cofactor sampling (SyPRIS), for locating constellations of backbone positions within oligomeric protein structures that are capable of supporting desired symmetrically coordinated metal ion(s) chelated by sidechains (chelant model). Using SyPRIS on a curated benchmark set of protein structures with symmetric metal binding sites, we found high recovery of native metal coordinating rotamers: in 65 of the 67 (97.0%) cases, native rotamers featured in the best scoring model while in the remaining cases native rotamers were found within the top three scoring models. In a second test, chelant models were crossmatched against protein structures with identical cyclic symmetry. In addition to recovering all native placements, 10.4% (8939/86013) of the non-native placements, had acceptable geometric compatibility scores. Discrimination between native and non-native metal site placements was further enhanced upon constrained energy minimization using the Rosetta energy function. Upon sequence design of the surrounding first-shell residues, we found further stabilization of native placements and a small but significant (1.7%) number of non-native placement-based sites with favorable Rosetta energies, indicating their designability in existing protein interfaces. The generality of the SyPRIS approach allows design of novel symmetric metal sites including with non-natural amino acid sidechains, and should enable the predictive incorporation of a variety of metal-containing cofactors at symmetric protein interfaces.

Magnetic structure of DyN: A Dy161 Mössbauer study

Conventional magnetometry yields a low temperature bulk magnetic moment of about $4\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\phantom{{\ensuremath{\mu}}_{\mathrm{B}}\mathrm{D}{\mathrm{y}}^{3+}}\phantom{\rule{0.0pt}{0ex}}\mathrm{D}{\mathrm{y}}^{3+}$ in an applied field of ${\ensuremath{\mu}}_{0}H=9\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.28em}{0ex}}\mathrm{T}$ for thin and thick dysprosium nitride (DyN) films. This is significantly lower than the maximum possible value of $10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}/\phantom{10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}\mathrm{D}{\mathrm{y}}^{3+}}\phantom{\rule{0.0pt}{0ex}}\mathrm{D}{\mathrm{y}}^{3+}.$ Ion-assisted deposition was used to grow 5.7-\ensuremath{\mu}m-thick rare earth nitride DyN films on organic Kapton\textregistered{} substrates. $^{161}\mathrm{Dy}$ M\ossbauer spectroscopy (with its time scale on the order of nanoseconds) indicates thermal relaxation between fully stretched $\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ levels of a low-lying Kramers doublet, which is inconsistent with the $\mathrm{D}{\mathrm{y}}^{3+}$ site's ideal cubic symmetry. However, a small tetragonal distortion $[\ensuremath{\epsilon}\ensuremath{\approx}\ensuremath{-}0.024(10)]$ observed using x-ray powder diffraction is compatible with an additional rank 2 crystal field term, ${B}_{2}^{0}\ensuremath{\approx}\ensuremath{-}1.0(4)\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, approaching the magnitude estimated to bring this about. The observed magnetic behavior can then be described using a two-level, molecular field model with ${\ensuremath{\theta}}_{\mathrm{C}}$ set to $\ensuremath{\approx}6--8\phantom{\rule{0.16em}{0ex}}\mathrm{K},$ which is substantially smaller than the accepted ordering temperature of ${T}_{\mathrm{C}}\ensuremath{\approx}17--26\phantom{\rule{0.16em}{0ex}}\mathrm{K}$.

Exposure to heavy metal stress does not increase fluctuating asymmetry in populations of isopod and hardwood trees

Fluctuating asymmetry (FA) refers to random, small and non-directional deviations from ideal bilateral symmetry is proposed as a bio-indicator of abiotic stress in both animals and plants. We investigated the effect of heavy metal stress on FA levels of morphological traits in a terrestrial isopod (Philoscia muscorum) as well as in the leaves of two hardwood tree species: Gray birch (Betula populifolia) and eastern cottonwood (Populus deltoides), in an urban brownfield in New Jersey. FA levels measured for five traits (length of two segments of antennae and three segments of the seventh legs) were compared in male and female populations of P. muscorum sampled from three low and three high soil metal load sites within the brownfield. FA levels measured for leaf width (perpendicular distance from a midpoint on midrib to the widest point of the lamina in right and left half in a leaf) were compared for both gray birch and eastern cottonwood leaves collected from the same low and high soil metal load sites. Contrary to the hypothesis that FA increases with higher heavy metal stress in isopods and trees, our results revealed that true asymmetry in gray birch and for some isopod traits (2nd antenna article, 3rd antenna article and merus of males and females, carpus and prodopus in females) did not differ between low and high metal contaminated sites. Furthermore, FAs measured in eastern cottonwood leaves and other isopod traits (carpus and prodopus in males) were found to be even lower at high metal contaminated sites than the low metal load sites. The overall effect of metal stress was shown as reduction in growth (measured as body size for a given head width in an individual) of isopods at high metal load sites as compared to the low metal load sites. Various hypotheses including induction of detoxification mechanisms in response to metal stress, selection against individuals with presumably lower fitness (high FA), difference in sensitivity of traits to stress, and plasticity are discussed to explain the observed lack of a significant association between FA and heavy metal stress in isopods and trees.

Finite element modelling of woven composite failure modes at the mesoscopic scale: deterministic versus stochastic approaches

Textile composites are composed of 3D complex architecture. To assess the durability of such engineering structures, the failure mechanisms must be highlighted. Examinations of the degradation have been carried out thanks to tomography. The present work addresses a numerical damage model dedicated to the simulation of the crack initiation and propagation at the scale of the warp yarns. For the 3D woven composites under study, loadings in tension and combined tension and bending were considered. Based on an erosion procedure of broken elements, the failure mechanisms have been modelled on 3D periodic cells by finite element calculations. The breakage of one element was determined using a failure criterion at the mesoscopic scale based on the yarn stress at failure. The results were found to be in good agreement with the experimental data for the two kinds of macroscopic loadings. The deterministic approach assumed a homogeneously distributed stress at failure all over the integration points in the meshes of woven composites. A stochastic approach was applied to a simple representative elementary periodic cell. The distribution of the Weibull stress at failure was assigned to the integration points using a Monte Carlo simulation. It was shown that this stochastic approach allowed more realistic failure simulations avoiding the idealised symmetry due to the deterministic modelling. In particular, the stochastic simulations performed have shown several variations of the stress as well as strain at failure and the failure modes of the yarn.

Imposing high-symmetry and tuneable geometry on lanthanide centres with chelating Pt and Pd metalloligands.

Exploitation of HSAB preferences allows for high-yield, one-pot syntheses of lanthanide complexes chelated by two Pd or Pt metalloligands, [MII(SAc)4]2- (SAc- = thioacetate, M = Pd, Pt). The resulting complexes with 8 oxygen donors surrounding the lanthanides can be isolated in crystallographically tetragonal environments as either [NEt4]+ (space group: P4/mcc) or [PPh4]+ (space group: P4/n) salts. In the case of M = Pt, the complete series of lanthanide complexes has been structurally characterized as the [NEt4]+ salts (except for Ln = Pm), while the [PPh4]+ salts have been structurally characterized for Ln = Gd-Er, Y. For M = Pd, selected lanthanide complexes have been structurally characterized as both salts. The only significant structural difference between salts of the two counter ions is the resulting twist angle connecting tetragonal prismatic and tetragonal anti-prismatic configurations, with the [PPh4]+ salts approaching ideal D4d symmetry very closely (φ = 44.52-44.61°) while the [NEt4]+ salts exhibit intermediate twist angles in the interval φ = 17.28-27.41°, the twist increasing as the complete 4f series is traversed. Static magnetic properties for the latter half of the lanthanide series are found to agree well in the high temperature limit with the expected Curie behavior. Perpendicular and parallel mode EPR spectroscopy on randomly oriented powder samples and single crystals of the Gd complexes with respectively Pd- and Pt-based metalloligands demonstrate the nature of the platinum metal to strongly affect the spectra. Consistent parametrization of all of the EPR spectra reveals the main difference to stem from a large difference in the magnitude of the leading axial term, B02, this being almost four times larger for the Pt-based complexes as compared to the Pd analogues, indicating a direct Pt(5d z2 )-Ln interaction and an arguable coordination number of 10 rather than 8. The parametrization of the EPR spectra also confirms that off-diagonal operators are associated with non-zero parameters for the [NEt4]+ salts, while only contributing minimally for the [PPh4]+ salts in which lanthanide coordination approximates D4d point group symmetry closely.