Asymmetric Fragmentation Research Articles

Gradient pattern analysis of cosmic structure formation: Norm and phase statistics

This paper presents the preliminary results of the characterization of pattern evolution in the process of cosmic structure formation. We are applying to N -body cosmological simulations data the technique proposed by Rosa et al. [R.R. Rosa, A.S. Sharma, J.A. Valdivia, Int. J. Modern Phys. C 10 (1999) 147] and Ramos et al. [F.M. Ramos, et al., Physica A 283 (2000) 171] to estimate the time behaviour of asymmetries in the gradient field. The gradient pattern analysis is a well tested tool, used to build asymmetrical fragmentation parameters estimated over a gradient field of an image matrix able to quantify a complexity measure of nonlinear extended systems. In this investigation we work with the high resolution cosmological data simulated by the Virgo consortium, in different time steps, in order to obtain a diagnostic of the spatio-temporal disorder in the matter density field. We perform the calculations of the gradient vectors statistics, such as mean, variance, skewness, kurtosis, and correlations on the gradient field. Our main goal is to determine different dynamic regimes through the analysis of complex patterns arising from the evolutionary process of structure formation. The results show that the gradient pattern technique, specially the statistical analysis of second and third gradient moment, may represent a very useful tool to describe the matter clustering in the Universe.

Synthesis and crystal structure of KBi(C6H4O7) · 3.5H2O

A novel compound, KBi(C6H4O7) · 3.5H2O (I), has been synthesized in the Bi(NO3)2-K3(HCit) system (HCit3− is an anion of citric acid C6H8O7) at a component ratio (n) of 8 in a water-glycerol mixture, and its crystal structure has been determined. The crystals are unstable in air. The crystals are triclinic: a = 7.462 A, b = 10.064 A, c = 17.582 A, α = 100.27°, β = 99.31°, γ = 105.48°, V = 1221.2 A3, Z = 2, space group % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqipu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaiqaig% dagaqeaaaa!3775! $$P\bar 1$$ . In the structure of I, asymmetric binuclear fragments [Bi2(Cit4−)2(H2O)2]2− are linked through inversion centers into polymeric chain anions. Ions K+ and crystal water molecules are arranged in channels between the chains. The Bi(1)...Bi(2) distances in the binuclear fragment are 4.62 A, and the Bi(1)...Bi(1) and Bi(2)...Bi(2) distances between bismuth atoms in the chain are 5.83 and 5.95 A, respectively. The chains are linked through bridging oxygen atoms of the ligands Cit to form layers. In the centrosymmetric four-membered chelate ring Bi2O2 formed through Bi-O(Cit) bonds, the distances Bi(1)-Bi(1) are equal to 4.55 A, and Bi(1)-O are 2.66 and 2.84 A. The Bi-O bond lengths in I are in the range 2.12–3.16 A. The Cit ligands act as hexadentate chelating/bridging ligands.

IMF isotopic properties in semi-peripheral collisions at Fermi energies

We study the neutron and proton dynamical behavior along the fragmentation path in semi-peripheral collisions: 58Fe + 58Fe (charge asymmetric, N / Z = 1.23 ) and 58Ni + 58Ni (charge symmetric, N / Z = 1.07 ), at 47 A MeV . We observe that isospin dynamics processes take place also in the charge-symmetric system 58Ni + 58Ni, that may produce more asymmetric fragments. A neutron enrichment of the neck fragments is observed, resulting from the interplay between pre-equilibrium emission and the phenomenon of isospin-migration. Both effects depend on the EoS (equation of state) symmetry term. This point is illustrated by comparing the results obtained with two different choices of the symmetry energy density dependence. New correlation observables are suggested, to study the reaction mechanism and the isospin dynamics.

Drop break-up in turbulent pipe flow downstream of a restriction

This work addresses the drop fragmentation process induced by a cross-sectional restriction in a pipe. An experimental device of an upward co-current oil-in-water dispersed flow (viscosity ratio λ ≈ 0.5 ) in a vertical column equipped with a concentric orifice has been designed. Drop break-up downstream of the restriction has been studied using a high-speed trajectography. The first objective of this work deals with a global analysis of the fragmentation process for a dilute dispersion. In this context, the operating parameters of the study are the orifice restriction ratio β , the flow Reynolds number, Re and the interfacial tension, σ . The break-up domain has been first mapped on a β ( Re ) graph and drop size distributions have been measured for different flow Reynolds numbers. It was observed that the mean drop diameter downstream of the restriction linearly increases as a function of the inverse of the square root of the pressure drop. This behaviour is in agreement with the observations previously made by Percy and Sleicher [A.I.Ch.E. Journal, 1983, 29(1), 161–164]. In addition, experiments based on the observation of single drop break-up downstream of the orifice have allowed the identification of different break-up mechanisms, and the determination of statistical quantities such as the break-up probability, the mean number of fragments and the daughter drop distribution. The drop break-up probability was found to be a monotonous increasing function of the Weber number based on the maximal pressure drop through the orifice. The mean number of fragments is also an increasing function of the Weber number and the reduced mean daughter drop diameter decreases as the Weber number increases. The daughter drop distributions are multimodal at low and moderate Weber numbers as a result of asymmetrical fragmentation processes. The statistical analysis of single drop break-up experiments was implemented in a simple global population balance model in order to predict the evolution of the size distribution across the restriction at different Reynolds numbers, in the limit of dilute dispersions.

Near-site far-site charge asymmetry in diatomic Coulomb fragmentation with slow highly charged ions

The three-center Coulombic over-barrier model is developed for charge asymmetric Coulomb fragmentations of a diatomic molecule following multiple electron transfer to a slow highly charged ion. The near-site far-site asymmetry is calculated in a coplanar geometry through a ratio of phase space volumes at the nuclear configuration where the electron gets localized in the dissociating molecular ion. The model explains the experimental observation in collisions of Kr8++N2 that the fragment pair of N3+N+ shows considerably larger asymmetry than N2+N+ and N3+N2+.

APLICAÇÃO DO OPERADOR DE FRAGMENTAÇÃO ASSIMÉTRICA (FA) NA CARACTERIZAÇÃO DE CONTROLES GEOMORFOLÓGICOS EM RESERVATÓRIOS HIDROELÉTRICOS

This paper proposes the use of the Asymmetrical Fragmentation Operator (FA) to characterize geomorphologic controls affecting hydroelectrical reservoirs. Landsat-TM images were used to map reservoirs flooded surface. The FA operator was applied to vector files describing reservoirs shape to compute the average FA for each reservoir. The reservoir database was then classified according to reservoirs hydrographic basin and reservoirs size. The FA values were compared to the Shoreline Development Index (D) and to the reservoirs primary productivity data available in the literature. Results show that the FA is able to detect high-resolution geomorphologic features, which are not detected by D. Preliminary results show also that there is a significant relationship between FA and the primary productivity. This fact, however, does not hold for D. Moreover, FA showed no sensitivity to reservoirs size, being more responsive to their position in the cascade system, and therefore to the hydrographic basin geomorphology.

APLICAÇÃO DO OPERADOR DE FRAGMENTAÇÃO ASSIMÉTRICA (FA) NA CARACTERIZAÇÃO DE CONTROLES GEOMORFOLÓGICOS EM RESERVATÓRIOS HIDROELÉTRICOS

This paper proposes the use of the Asymmetrical Fragmentation Operator (FA) to characterize geomorphologic controls affecting hydroelectrical reservoirs. Landsat-TM images were used to map reservoirs flooded surface. The FA operator was applied to vector files describing reservoirs shape to compute the average FA for each reservoir. The reservoir database was then classified according to reservoirs hydrographic basin and reservoirs size. The FA values were compared to the Shoreline Development Index (D) and to the reservoirs primary productivity data available in the literature. Results show that the FA is able to detect high-resolution geomorphologic features, which are not detected by D. Preliminary results show also that there is a significant relationship between FA and the primary productivity. This fact, however, does not hold for D. Moreover, FA showed no sensitivity to reservoirs size, being more responsive to their position in the cascade system, and therefore to the hydrographic basin geomorphology.

Structural flyby characterization of nanoporosity

Recently, Ferreira da Silva et al. [3] have performed a gradient pattern analysis of a canonical sample set (CSS) of scanning force microscopy (SFM) images of p-Si. They applied the so-called Gradient Pattern Analysis to images of three typical p-Si samples distinguished by different absorption energy levels and aspect ratios. Taking into account the measures of spatial asymmetric fluctuations they interpreted the global porosity not only in terms of the amount of roughness, but rather in terms of the structural complexity (e.g., walls and fine structures as slots). This analysis has been adapted in order to operate in a OpenGL flyby environment (the StrFB code), whose application give the numerical characterization of the structure during the flyby real time. Using this analysis we compare the levels of asymmetric fragmentation of active porosity related to different materials as p-Si and "porous diamond-like" carbon. In summary we have shown that the gradient pattern analysis technique in a flyby environment is a reliable sensitive method to investigate, qualitatively and quantitatively, the complex morphology of active nanostructures.

Current Distribution and Random Matrix Ensembles for an Integrable Asymmetric Fragmentation Process

We calculate the time-evolution of a discrete-time fragmentation process in which clusters of particles break up and reassemble and move stochastically with size-dependent rates. In the continuous-time limit the process turns into the totally asymmetric simple exclusion process (only pieces of size 1 break off a given cluster). We express the exact solution of master equation for the process in terms of a determinant which can be derived using the Bethe ansatz. From this determinant we compute the distribution of the current across an arbitrary bond which after appropriate scaling is given by the distribution of the largest eigenvalue of the Gaussian unitary ensemble of random matrices. This result confirms universality of the scaling form of the current distribution in the KPZ universality class and suggests that there is a link between integrable particle systems and random matrix ensembles.

Asymmetric nuclear motion of theF1s–ionized state inBF3probed by quadruple-ion-coincidence momentum imaging

Using the quadruple-ion-coincidence momentum imaging technique, we find that the momentum correlation of the four atomic ions departed from one ${\mathrm{BF}}_{3}^{4+}$ parent molecular ion produced via multiple Auger decay after $\mathrm{F}1s$ ionization exhibits asymmetric fragmentation in which the ${\mathrm{B}}^{+}$ ion is ejected in the direction opposite to one of the ${\mathrm{F}}^{+}$ ions. This observation provides evidence of symmetry lowering, from ${D}_{3h}$ to ${C}_{3v}$ in the $\mathrm{F}1s$--ionized state.

Impact dynamics of molecular clusters on surfaces: Fragmentation patterns and anisotropic effects

The fragmentation dynamics of (H2O)1032 clusters colliding with a repulsive surface at incident velocities of 1753 m/s and 2909 m/s, corresponding to kinetic energies of 0.5 and 1.5 times the cluster binding energy, has been examined in a classical molecular dynamics simulations study. The results show a large anisotropy in the energy redistribution inside the cluster upon impact, which leads to asymmetric fragmentation, starting in the leading part of the cluster. The low-mass region of the fragment size distribution can be described by a power law with an exponent close to −1.6, and the range of this region increases with increasing incident velocity. The formed fragments have rather uniform internal temperatures close to the standard boiling point of water, but the translational energy of the monomers formed upon collision is much larger, pointing at the asymmetric energy distribution inside the cluster. The angular distributions of fragment mass and fragment kinetic energy peak at grazing exit angles. For the investigated conditions, the dynamics is insensitive to the details of the initial structure of the cluster.

Isotopic invariance of fission fragment charge distributions for actinide nuclei at excitation energies above 10 MeV

The fragment mass and energy distributions from the proton-induced fission of compound nuclei 233Pa, 234,236,237,239Np, 239,240,241,243Am, and 245Bk at proton energy Ep=10.3 and 22.0 MeV have been experimentally studied. It was revealed that the shapes of the asymmetric fission mass distributions are mainly defined by the proton numbers of compound nuclei and demonstrate only a weak dependence on the neutron ones. The detailed study of the fission fragment mass yields for compound nuclei Np and Am isotopic chains has shown that the asymmetric fission fragment charge distributions calculated within the unchanged charge density hypothesis for nuclei with equal ZC practically coincide.

Transverse single spin asymmetries in Drell-Yan processes

Recently, it has been shown, contrary to previous beliefs, that the k_T distribution of quarks in a transversely polarized proton can be asymmetric. This ``Sivers effect'' had already been used to explain transverse single spin asymmetries (SSA) observed in inclusive pion production, p(transv. polarized) p --> pion + X and p-bar(transv. polarized) p --> pion + X. In such channels, however, other mechanisms, like the ``Collins effect'' (a k_T asymmetric fragmentation of a transversely polarized quark into pions), may generate SSA. The Sivers asymmetry is used here to compute SSA in Drell-Yan processes; in this case, by considering the differential cross-section in the lepton-pair invariant mass, rapidity and transverse momentum, other mechanisms which may originate SSA cannot contribute. Estimates for RHIC experiments are given.

Dihapto coordination of carboxylic acid derivatives with an asymmetric rhenium pi-base: a new mechanism for amide isomerization?

The asymmetric pi basic metal fragment [TpRe(CO)(MeIm)] (Tp = hydridotris(pyrazolyl)borate, MeIm = 1-methylimidazole) forms thermally stable complexes with ethyl acetate, acetic anhydride, N-methylsuccinimide, N-acetylpyrrole, and N-methylmaleimide in which the metal binds a carbonyl group in a pi fashion. In all cases a single diastereomer is observed, indicating that one enantioface of the carbonyl is selectively coordinated. X-ray and NMR data for the compound TpRe(CO)(MeIm)(eta(2)-N-methylsuccinimide) indicate that metal coordination effectively removes the pi interaction between the bound carbonyl and the nitrogen of the succinimide ring.

Gradient pattern analysis of short nonstationary time series: an application to Lagrangian data from satellite tracked drifters

Based on the gradient pattern analysis (GPA) technique we introduce a new methodology for analyzing short nonstationary time series. Using the asymmetric amplitude fragmentation (AAF) operator from GPA we analyze Lagrangian data observed as velocity time series for ocean flow. The results show that quasi-periodic, chaotic and turbulent regimes can be well characterized by means of this new geometrical approach.

The Structure of DMF · HCl and DMF · (HCl)2 Complexes according to ab initio Calculations

Based on ab initio calculation at the 6-31G level, the differences in the structures of isolated complexes of DMF with HCl with compositions 1 : 1 and 1 : 2 are analyzed. The interaction of HCl with DMF results in the formation of the molecular complex. When HCl is added to this complex, a proton transfers to the DMF molecule and the asymmetric fragment Cl···HCl is formed. Calculated data are compared with the structures of DMF complexes with HCl in the condensed phase.

Phenylantimony(III) derivatives of tetraphenyldichalcogenoimidodiphosphinic acids. Crystal and molecular structure of PhSb[(XPPh 2)(SPPh 2)N] 2 (X=O, S)

The reactions between PhSbCl 2 and M[(XPPh 2)(YPPh 2)N] (M=Na, K; X, Y=O, S), using 1:1 and 1:2 molar ratios, have been investigated. PhSbCl[(XPPh 2)(YPPh 2)N] and PhSb[(XPPh 2)(YPPh 2)N] 2 were isolated as microcrystalline powders and were characterized using IR and NMR ( 1H, 31P) spectroscopy. On standing in chloroform solution the chloro derivative PhSbCl[(SPPh 2) 2N] was found to rearrange to PhSb[(SPPh 2) 2N] 2. The molecular structures of PhSb[(XPPh 2)(SPPh 2)N] 2 (X=O, S) were investigated by X-ray diffraction. The crystals of both compounds contain monomeric units with asymmetric chelating ligand fragments, resulting in a square pyramidal CSbX 2S 2 core with an apical phenyl group. The antimony lone pair of electrons appears to be stereochemically active and is located trans to the phenyl group, as suggested by the displacement of the metal atom from the best basal plane formed by the chalcogens in the opposite direction with respect to the apical carbon. For the monothio derivative, the molecule displays different ligand behaviour, i.e. O- and S-primary coordinations, respectively.

Low energy radioactive ion beams in Dubna

The Dubna radioactive beam factory (DRIBs) [1] will make use of two possibilities for producing secondary beams of radioactive nuclei. During the first phase of the project (Phase I) the possibility for obtaining radioactive nuclei in fragmentation reactions of stable nuclei, accelerated by the cyclotron U400M to intermediate energies (∼ 50 MeVA−1), will be realized. The fragmentation products, obtained in a special ion source, will be converted into single-charged ions, which after transportation to the second cyclotron (U400) will be accelerated up to energies of ∼ 20–25 MeVA−1. This method will allow obtaining mainly beams of light radioactive nuclei with Z 30 with intensities up to 108 pps (e.g., nuclei such as 6He). In the second phase of the project (Phase II) it is supposed to produce and accelerate radioactive neutron-rich nuclei in the mass region 80 A 140. This mass region corresponds to the fragments of low-energy fission of heavy nuclei. For this reason use will be made of the photofission of 238U. The γ -quanta will be produced by the electron accelerator (the microtron MT-25), where the electron beam with an intensity of about 20 μA has an energy of 25 MeV. With the help of a special converter the electron beam is transformed into a beam of γ -quanta with up to 25 MeV energy and a flux of 1014 s−1. This beam, focused into a narrow angle, will fall onto a 238U-target weighing 100 g. It is wellknown that the photofission cross section has a maximum corresponding to the giant dipole resonance at an energy of the γ -quanta equal to Eγ = 13.5–14 MeV [2]. This brings forth an increase of the photofission probability. The yield of the fission fragments will increase as a result of the interactions of the secondary neutrons (γ n and fission neutrons) with the U-target. When the mentioned above parameters of the beam and target are realized, one can get as much as 1011 fission fragments/second. Taking into account the widths of the mass and charge distributions of the fragments, the yields of definite fission fragments can be estimated. When the efficiency of the ion source and the transport system amounts to some 20–30% it is possible to obtain beams of fission fragments in the region of Kr and Xe with an intensity of up to 109 s−1. Simultaneously with the fragments situated close to the maxima of the mass distribution (A = 90 and 130), asymmetric fission fragments are formed with a rather high yield. For the isotopes situated at the “tails” of the fragment

Phosphorylation-dependent regulation is absent in a nonmuscle heavy meromyosin construct with one complete head and one head lacking the motor domain.

To understand the domain requirements of phosphorylation-dependent regulation, we prepared three recombinant constructs of nonmuscle heavy meromyosin IIB containing 1) two complete heads, 2) one complete head and one head lacking the motor domain, and 3) one complete head and one head lacking both motor and regulatory domains. Steady-state ATPase measurements showed that phosphorylation did not alter the affinity for actin by more than a factor of 2 for any construct. Phosphorylation increased V(max) by a factor of 10 for construct 1 and 1.5-3 for construct 2 but had no effect for construct 3. Single turnover measurements, a better measure of slow rates inherent to unphosphorylated regulated myosins, showed that the single-headed construct 2, like construct 3 retains less than 1% of the regulatory properties of the double-headed construct 1 (300-fold activation). Therefore, a complete head cannot be down-regulated by a regulatory domain (without the motor domain) on the partner head. Two motor domains are required for regulation. This result is predicted by a structural model (Wendt, T., Taylor, D., Messier, T., Trybus, K. M., and Taylor, K. A. (1999) J. Cell Biol. 147, 1385-1390) showing interaction between the motor domains for unphosphorylated smooth muscle myosin, if motor-motor interaction is the basis for down-regulation.

Dynamical fragmentation processes ofC605+ions inAr8+−C60collisions

Asymmetric fragmentation dynamics of ${\mathrm{C}}_{60}$ is studied with ${\mathrm{C}}_{60}^{5+}$ in ${\mathrm{Ar}}^{8+}{\ensuremath{-}\mathrm{C}}_{60}$ collisions. A sequential ``unzipping'' emission of light fragments is found to be the principal mechanism in the fullerene to fullerene conversion process. Unstable fullerenes ${\mathrm{C}}_{59}^{4+}$ and ${\mathrm{C}}_{57}^{4+}$ are produced in delayed-then-fast sequential emission of ${\mathrm{C}}^{+}$ and ${\mathrm{C}}_{3}^{+}.$ Fragmentation of a light fragment is observed for ${\mathrm{C}}_{10}^{2+}$ issued from a previous binary fission of the ${\mathrm{C}}_{60}^{5+}.$