Architecture of the hydrophobic and hydrophilic layers as found from crystal structure analysis of N-benzyl-N,N-dimethylalkylammonium bromides.

PubMed

Hodorowicz, Maciej; Stadnicka, Katarzyna; Czapkiewicz, Jan

2005-10-01

The molecular and crystal structures of N-benzyl-N,N-dimethylalkylammonium bromides monohydrates with chain length n=8-10 have been determined. The crystals are isostructural with the N-benzyl-N,N-dimethyldodecylammonium bromide monohydrate. The structures consist of alternated hydrophobic and hydrophilic layers perpendicular to [001]. The attraction between N+ of the cation head-groups and Br- anions is achieved through weak C_H...Br interactions. The water molecules incorporated into ionic layers are donors for two O_H...Br hydrogen bonds and serve as the acceptors in two weak interactions of C_H...O type. The methylene chains, with the slightly curved general shape, have the extended all-trans conformation. The mutual packing of the chains in the hydrophobic layers is governed by weak C_H...pi interactions.

Quantitative study of interactions between oxygen lone pair and aromatic rings: substituent effect and the importance of closeness of contact.

PubMed

Gung, Benjamin W; Zou, Yan; Xu, Zhigang; Amicangelo, Jay C; Irwin, Daniel G; Ma, Shengqian; Zhou, Hong-Cai

2008-01-18

Current models describe aromatic rings as polar groups based on the fact that benzene and hexafluorobenzene are known to have large and permanent quadrupole moments. This report describes a quantitative study of the interactions between oxygen lone pair and aromatic rings. We found that even electron-rich aromatic rings and oxygen lone pairs exhibit attractive interactions. Free energies of interactions are determined using the triptycene scaffold and the equilibrium constants were determined by low-temperature 1H NMR spectroscopy. An X-ray structure analysis for one of the model compounds confirms the close proximity between the oxygen and the center of the aromatic ring. Theoretical calculations at the MP2/aug-cc-pVTZ level corroborate the experimental results. The origin of attractive interactions was explored by using aromatic rings with a wide range of substituents. The interactions between an oxygen lone pair and an aromatic ring are attractive at van der Waals' distance even with electron-donating substituents. Electron-withdrawing groups increase the strength of the attractive interactions. The results from this study can be only partly rationalized by using the current models of aromatic system. Electrostatic-based models are consistent with the fact that stronger electron-withdrawing groups lead to stronger attractions, but fail to predict or rationalize the fact that weak attractions even exist between electron-rich arenes and oxygen lone pairs. The conclusion from this study is that aromatic rings cannot be treated as a simple quadrupolar functional group at van der Waals' distance. Dispersion forces and local dipole should also be considered.

Direction-specific van der Waals attraction between rutile TiO2 nanocrystals

NASA Astrophysics Data System (ADS)

Zhang, Xin; He, Yang; Sushko, Maria L.; Liu, Jia; Luo, Langli; De Yoreo, James J.; Mao, Scott X.; Wang, Chongmin; Rosso, Kevin M.

2017-04-01

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. We report measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation, the attraction is weak and shows no dependence on azimuthal alignment or surface hydration. At separations of approximately one hydration layer, the attraction is strongly dependent on azimuthal alignment and systematically decreases as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces can generate a torque between particles interacting in solution and between grains in materials.

Clustering and phase behaviour of attractive active particles with hydrodynamics.

PubMed

Navarro, Ricard Matas; Fielding, Suzanne M

2015-10-14

We simulate clustering, phase separation and hexatic ordering in a monolayered suspension of active squirming disks subject to an attractive Lennard-Jones-like pairwise interaction potential, taking hydrodynamic interactions between the particles fully into account. By comparing the hydrodynamic case with counterpart simulations for passive and active Brownian particles, we elucidate the relative roles of self-propulsion, interparticle attraction, and hydrodynamic interactions in determining clustering and phase behaviour. Even in the presence of an attractive potential, we find that hydrodynamic interactions strongly suppress the motility induced phase separation that might a priori have been expected in a highly active suspension. Instead, we find only a weak tendency for the particles to form stringlike clusters in this regime. At lower activities we demonstrate phase behaviour that is broadly equivalent to that of the counterpart passive system at low temperatures, characterized by regimes of gas-liquid, gas-solid and liquid-solid phase coexistence. In this way, we suggest that a dimensionless quantity representing the level of activity relative to the strength of attraction plays the role of something like an effective non-equilibrium temperature, counterpart to the (dimensionless) true thermodynamic temperature in the passive system. However there are also some important differences from the equilibrium case, most notably with regards the degree of hexatic ordering, which we discuss carefully.

Structure and effective interactions of comb polymer nanocomposite melts.

PubMed

Xu, Qinzhi; Xu, Mengjin; Feng, Yancong; Chen, Lan

2014-11-28

In this work, the structure and effective interactions of branched comb polymer nanocomposite (PNC) melts are investigated by using the polymer reference interaction site model (PRISM) integral equation theory. It is observed that the nanoparticle contact (bridging) aggregation is formed when the nanoparticle-monomer attraction strength is relatively weak (large) in comb PNCs. The organization states of aggregation for the moderate nanoparticle-monomer attraction strength can be well suppressed by the comb polymer architecture, while the bridging structure for relatively large attraction is obviously promoted. With the increase of the particle volume fraction, the organization states of bridging-type structure become stronger and tighter; however, this effect is weaker than that of the nanoparticle-monomer attraction strength. When the particle volume fraction and moderate nanoparticle-monomer attraction strength are fixed, the effects of degree of polymerization, side chain number, side chain length, and nanoparticle-monomer size ratio on the organization states of PNC melts are not prominent and the nanoparticles can well disperse in comb polymer. All the observations indicate that the present PRISM theory can give a detailed description of the comb PNC melts and assist in future design control of new nanomaterials.

Cross-Cultural Investigation of Male Gait Perception in Relation to Physical Strength and Speed

PubMed Central

Fink, Bernhard; Wübker, Marieke; Ostner, Julia; Butovskaya, Marina L.; Mezentseva, Anna; Muñoz-Reyes, José Antonio; Sela, Yael; Shackelford, Todd K.

2017-01-01

Previous research documents that men and women can accurately judge male physical strength from gait, but also that the sexes differ in attractiveness judgments of strong and weak male walkers. Women’s (but not men’s) attractiveness assessments of strong male walkers are higher than for weak male walkers. Here, we extend this research to assessments of strong and weak male walkers in Chile, Germany, and Russia. Men and women judged videos of virtual characters, animated with the walk movements of motion-captured men, on strength and attractiveness. In two countries (Germany and Russia), these videos were additionally presented at 70% (slower) and 130% (faster) of their original speed. Stronger walkers were judged to be stronger and more attractive than weak walkers, and this effect was independent of country (but not sex). Women tended to provide higher attractiveness judgments to strong walkers, and men tended to provide higher attractiveness judgments to weak walkers. In addition, German and Russian participants rated strong walkers most attractive at slow and fast speed. Thus, across countries men and women can assess male strength from gait, although they tended to differ in attractiveness assessments of strong and weak male walkers. Attractiveness assessments of male gait may be influenced by society-specific emphasis on male physical strength. PMID:28878720

Combined collapse by bridging and self-adhesion in a prototypical polymer model inspired by the bacterial nucleoid

NASA Astrophysics Data System (ADS)

Scolari, Vittore F.; Cosentino Lagomarsino, Marco

Recent experimental results suggest that the E. coli chromosome feels a self-attracting interaction of osmotic origin, and is condensed in foci by bridging interactions. Motivated by these findings, we explore a generic modeling framework combining solely these two ingredients, in order to characterize their joint effects. Specifically, we study a simple polymer physics computational model with weak ubiquitous short-ranged self attraction and stronger sparse bridging interactions. Combining theoretical arguments and simulations, we study the general phenomenology of polymer collapse induced by these dual contributions, in the case of regularly-spaced bridging. Our results distinguish a regime of classical Flory-like coil-globule collapse dictated by the interplay of excluded volume and attractive energy and a switch-like collapse where bridging interaction compete with entropy loss terms from the looped arms of a star-like rosette. Additionally, we show that bridging can induce stable compartmentalized domains. In these configurations, different "cores" of bridging proteins are kept separated by star-like polymer loops in an entropically favorable multi-domain configuration, with a mechanism that parallels micellar polysoaps. Such compartmentalized domains are stable, and do not need any intra-specific interactions driving their segregation. Domains can be stable also in presence of uniform attraction, as long as the uniform collapse is above its theta point.

Quantum droplet of one-dimensional bosons with a three-body attraction

NASA Astrophysics Data System (ADS)

Sekino, Yuta; Nishida, Yusuke

2018-01-01

Ultracold atoms offer valuable opportunities where interparticle interactions can be controlled at will. In particular, by extinguishing the two-body interaction, one can realize unique systems governed by the three-body interaction, which is otherwise hidden behind the two-body interaction. Here we study one-dimensional bosons with a weak three-body attraction and show that they form few-body bound states as well as a many-body droplet stabilized by the quantum mechanical effect. Their binding energies relative to that of three bosons are all universal and the ground-state energy of the dilute droplet is found to grow exponentially as EN/E3→exp(8 N2/√{3 }π ) with increasing particle number N ≫1 . The realization of our system with coupled two-component bosons in an optical lattice is also discussed.

p -wave superconductivity in weakly repulsive 2D Hubbard model with Zeeman splitting and weak Rashba spin-orbit coupling

NASA Astrophysics Data System (ADS)

Hugdal, Henning G.; Sudbø, Asle

2018-01-01

We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the noninteracting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger-type interaction, while the pairing symmetry of the bands is indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction n of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning n . Moreover, n also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral px±i py type state for out-of-plane fields, to a nodal p -wave-type state for purely in-plane fields.

Can biological homochirality result from a phase transition?

PubMed

Figureau, A; Duval, E; Boukenter, A

1995-06-01

The problem of chiral purity in living organisms is still one of the prominent difficulties in the study of the origins of life. In particular the parity non-conservation known to occur in weak interactions could not be related to this lack of symmetry: these physical forces, though universal, are very weak and up to now no amplification process had been proposed. In 1991, A. Salam remarked that, due to the attractive character of the parity violating force in electro-weak interactions, a phase transition at low temperature should exist, leading eventually to enantiomeric purity. We undertook then a series of experimental tests, looking for a sizeable change in the optical activity of cystine molecules. We found no evidence for the phase transition down to 0.01 K. The interpretation of these negative results will be discussed, and future experiments proposed.

Statistical properties and condensate fluctuation of attractive Bose gas with finite number of particles

NASA Astrophysics Data System (ADS)

Bera, Sangita; Lekala, Mantile Leslie; Chakrabarti, Barnali; Bhattacharyya, Satadal; Rampho, Gaotsiwe Joel

2017-09-01

'We study the condensate fluctuation and several statistics of weakly interacting attractive Bose gas of 7 Li atoms in harmonic trap. Using exact recursion relation we calculate canonical ensemble partition function and study the thermal evolution of the condensate. As 7 Li condensate is associated with collapse, the number of condensate atom is truly finite and it facilitates to study the condensate in mesoscopic region. Being highly correlated, we utilize the two-body correlated basis function to get the many-body effective potential which is further used to calculate the energy levels. Taking van der Waals interaction as interatomic interaction we calculate several quantities like condensate fraction N, root-mean-square fluctuation δn0 and different orders of central moments. We observe the effect of finite size on the calculation of condensate fluctuations and the effect of attractive interaction over the noninteracting limit. We observe the depletion of the condensate with increase in temperature. The calculated moments nicely exhibit the mesoscopic effect. The sharp fall in the root-mean-square fluctuation near the critical point signifies the possibility of phase transition.

Direction-specific van der Waals attraction between rutile TiO2 nanocrystals.

PubMed

Zhang, Xin; He, Yang; Sushko, Maria L; Liu, Jia; Luo, Langli; De Yoreo, James J; Mao, Scott X; Wang, Chongmin; Rosso, Kevin M

2017-04-28

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. We report measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation, the attraction is weak and shows no dependence on azimuthal alignment or surface hydration. At separations of approximately one hydration layer, the attraction is strongly dependent on azimuthal alignment and systematically decreases as intervening water density increases. Measured forces closely agree with predictions from Lifshitz theory and show that dispersion forces can generate a torque between particles interacting in solution and between grains in materials. Copyright © 2017, American Association for the Advancement of Science.

Direction-specific van der Waals attraction between rutile TiO 2 nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xin; He, Yang; Sushko, Maria L.

Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. Here we report direct measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation the attraction is weak and shows no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer the attraction is strongly dependent on azimuthal alignment, and systematically decreases as intervening water density increases. Measured forces aremore » in close agreement with predictions from Lifshitz theory, and show that dispersion forces are capable of generating a torque between particles interacting in solution and between grains in materials.« less

X-ray electron density investigation of chemical bonding in van der Waals materials

NASA Astrophysics Data System (ADS)

Kasai, Hidetaka; Tolborg, Kasper; Sist, Mattia; Zhang, Jiawei; Hathwar, Venkatesha R.; Filsø, Mette Ø.; Cenedese, Simone; Sugimoto, Kunihisa; Overgaard, Jacob; Nishibori, Eiji; Iversen, Bo B.

2018-03-01

Van der Waals (vdW) solids have attracted great attention ever since the discovery of graphene, with the essential feature being the weak chemical bonding across the vdW gap. The nature of these weak interactions is decisive for many extraordinary properties, but it is a strong challenge for current theory to accurately model long-range electron correlations. Here we use synchrotron X-ray diffraction data to precisely determine the electron density in the archetypal vdW solid, TiS2, and compare the results with density functional theory calculations. Quantitative agreement is observed for the chemical bonding description in the covalent TiS2 slabs, but significant differences are identified for the interactions across the gap, with experiment revealing more electron deformation than theory. The present data provide an experimental benchmark for testing theoretical models of weak chemical bonding.

Pairing of one-dimensional Bose-Fermi mixtures with unequal masses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rizzi, Matteo; Max Planck Institut fuer QuantenOptik, Hans Kopfermann Strasse 1, D-85748 Garching; Imambekov, Adilet

We have considered one-dimensional Bose-Fermi mixture with equal densities and unequal masses using numerical density matrix renormalization group. For the mass ratio of K-Rb mixture and attraction between bosons and fermions, we determined the phase diagram. For weak boson-boson interactions, there is a direct transition between two-component Luttinger liquid and collapsed phases as the boson-fermion attraction is increased. For strong enough boson-boson interactions, we find an intermediate 'paired' phase, which is a single-component Luttinger liquid of composite particles. We investigated correlation functions of such a 'paired' phase, studied the stability of 'paired' phase to density imbalance, and discussed various experimentalmore » techniques which can be used to detect it.« less

Three-dimensional vortex-bright solitons in a spin-orbit-coupled spin-1 condensate

NASA Astrophysics Data System (ADS)

Gautam, Sandeep; Adhikari, S. K.

2018-01-01

We demonstrate stable and metastable vortex-bright solitons in a three-dimensional spin-orbit-coupled three-component hyperfine spin-1 Bose-Einstein condensate (BEC) using numerical solution and variational approximation of a mean-field model. The spin-orbit coupling provides attraction to form vortex-bright solitons in both attractive and repulsive spinor BECs. The ground state of these vortex-bright solitons is axially symmetric for weak polar interaction. For a sufficiently strong ferromagnetic interaction, we observe the emergence of a fully asymmetric vortex-bright soliton as the ground state. We also numerically investigate moving solitons. The present mean-field model is not Galilean invariant, and we use a Galilean-transformed mean-field model for generating the moving solitons.

Attraction between Opposing Planar Dipolar Polymer Brushes

DOE PAGES

Mahalik, J. P.; Sumpter, Bobby G.; Kumar, Rajeev

2017-08-01

In this paper, we use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on nonadsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration-dependent pairwise interactions, and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the polymer segments can lead to attractive interactions between the brushes at intermediatemore » separation distances. Finally, because classical theory of polymer brushes based on the strong stretching limit (SSL) and the standard self-consistent field theory (SCFT) simulations using the Flory’s χ parameter always predicts repulsive interactions at all separations, our work highlights the importance of dipolar interactions in tailoring and accurately predicting forces between polar polymeric interfaces in contact with each other.« less

Flux quench in a system of interacting spinless fermions in one dimension

NASA Astrophysics Data System (ADS)

Nakagawa, Yuya O.; Misguich, Grégoire; Oshikawa, Masaki

2016-05-01

We study a quantum quench in a one-dimensional spinless fermion model (equivalent to the XXZ spin chain), where a magnetic flux is suddenly switched off. This quench is equivalent to imposing a pulse of electric field and therefore generates an initial particle current. This current is not a conserved quantity in the presence of a lattice and interactions, and we investigate numerically its time evolution after the quench, using the infinite time-evolving block decimation method. For repulsive interactions or large initial flux, we find oscillations that are governed by excitations deep inside the Fermi sea. At long times we observe that the current remains nonvanishing in the gapless cases, whereas it decays to zero in the gapped cases. Although the linear response theory (valid for a weak flux) predicts the same long-time limit of the current for repulsive and attractive interactions (relation with the zero-temperature Drude weight), larger nonlinearities are observed in the case of repulsive interactions compared with that of the attractive case.

Weak competing interactions control assembly of strongly bonded TCNQ ionic acceptor molecules on silver surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Changwon; Rojas, Geoffrey A.; Jeon, Seokmin

2014-09-19

The energy scales of interactions that control molecular adsorption and assembly on surfaces can vary by several orders of magnitude, yet the importance of each contributing interaction is not apparent a priori. Tetracyanoquinodimethane (TCNQ) is an archetypal electron acceptor molecule and it is a key component of organic metals. On metal surfaces, this molecule also acts as an electron acceptor, producing negatively charged adsorbates. It is therefore rather intriguing to observe attractive molecular interactions in this system that were reported previously for copper and silver surfaces. In this paper, our experiments compared TCNQ adsorption on noble metal surfaces of Ag(100)more » and Ag(111). In both cases we found net attractive interactions down to the lowest coverage. However, the morphology of the assemblies was strikingly different, with two-dimensional islands on Ag(100) and one-dimensional chains on Ag(111) surfaces. This observation suggests that the registry effect governed by the molecular interaction with the underlying lattice potential is critical in determining the dimensionality of the molecular assembly. Using first-principles density functional calculations with a van der Waals correction scheme, we revealed that the strengths of major interactions (i.e., lattice potential corrugation, intermolecular attraction, and charge-transfer-induced repulsion) are all similar in energy. The van der Waals interactions, in particular, almost double the strength of attractive interactions, making the intermolecular potential comparable in strength to the diffusion potential and promoting self-assembly. However, it is the anisotropy of local intermolecular interactions that is primarily responsible for the difference in the topology of the molecular islands on Ag(100) and Ag(111) surfaces. Finally, we anticipate that the intermolecular potential will become more attractive and dominant over the diffusion potential with increasing molecular size, providing new design strategies for the structure and charge transfer within molecular layers.« less

Phase separation of a Lennard-Jones fluid interacting with a long, condensed polymer chain: implications for the nuclear body formation near chromosomes.

PubMed

Oh, Inrok; Choi, Saehyun; Jung, YounJoon; Kim, Jun Soo

2015-08-28

Phase separation in a biological cell nucleus occurs in a heterogeneous environment filled with a high density of chromatins and thus it is inevitably influenced by interactions with chromatins. As a model system of nuclear body formation in a cell nucleus filled with chromatins, we simulate the phase separation of a low-density Lennard-Jones (LJ) fluid interacting with a long, condensed polymer chain. The influence of the density variation of LJ particles above and below the phase boundary and the role of attractive interactions between LJ particles and polymer segments are investigated at a fixed value of strong self-interaction between LJ particles. For a density of LJ particles above the phase boundary, phase separation occurs and a dense domain of LJ particles forms irrespective of interactions with the condensed polymer chain whereas its localization relative to the polymer chain is determined by the LJ-polymer attraction strength. Especially, in the case of moderately weak attractions, the domain forms separately from the polymer chain and subsequently associates with the polymer chain. When the density is below the phase boundary, however, the formation of a dense domain is possible only when the LJ-polymer attraction is strong enough, for which the domain grows in direct contact with the interacting polymer chain. In this work, different growth behaviors of LJ particles result from the differences in the density of LJ particles and in the LJ-polymer interaction, and this work suggests that the distinct formation of activity-dependent and activity-independent nuclear bodies (NBs) in a cell nucleus may originate from the differences in the concentrations of body-specific NB components and in their interaction with chromatins.

Effect of interactions for one-dimensional asymmetric exclusion processes under periodic and bath-adapted coupling environment

NASA Astrophysics Data System (ADS)

Midha, Tripti; Kolomeisky, Anatoly B.; Gupta, Arvind Kumar

2018-04-01

Stimulated by the effect of the nearest neighbor interactions in vehicular traffic and motor proteins, we study a 1D driven lattice gas model, in which the nearest neighbor particle interactions are taken in accordance with the thermodynamic concepts. The non-equilibrium steady-state properties of the system are analyzed under both open and periodic boundary conditions using a combination of cluster mean-field analysis and Monte Carlo simulations. Interestingly, the fundamental diagram of current versus density shows a complex behavior with a unimodal dependence for attractions and weak repulsions that turns into the bimodal behavior for stronger repulsive interactions. Specific details of system-reservoir coupling for the open system have a strong effect on the stationary phases. We produce the steady-state phase diagrams for the bulk-adapted coupling to the reservoir using the minimum and maximum current principles. The strength and nature of interaction energy has a striking influence on the number of stationary phases. We observe that interactions lead to correlations having a strong impact on the system dynamical properties. The correlation between any two sites decays exponentially as the distance between the sites increases. Moreover, they are found to be short-range for repulsions and long-range for attractions. Our results also suggest that repulsions and attractions asymmetrically modify the dynamics of interacting particles in exclusion processes.

Conformation-dependent DNA attraction

NASA Astrophysics Data System (ADS)

Li, Weifeng; Nordenskiöld, Lars; Zhou, Ruhong; Mu, Yuguang

2014-05-01

Understanding how DNA molecules interact with other biomolecules is related to how they utilize their functions and is therefore critical for understanding their structure-function relationships. For a long time, the existence of Z-form DNA (a left-handed double helical version of DNA, instead of the common right-handed B-form) has puzzled the scientists, and the definitive biological significance of Z-DNA has not yet been clarified. In this study, the effects of DNA conformation in DNA-DNA interactions are explored by molecular dynamics simulations. Using umbrella sampling, we find that for both B- and Z-form DNA, surrounding Mg2+ ions always exert themselves to screen the Coulomb repulsion between DNA phosphates, resulting in very weak attractive force. On the contrary, a tight and stable bound state is discovered for Z-DNA in the presence of Mg2+ or Na+, benefiting from their hydrophobic nature. Based on the contact surface and a dewetting process analysis, a two-stage binding process of Z-DNA is outlined: two Z-DNA first attract each other through charge screening and Mg2+ bridges to phosphate groups in the same way as that of B-DNA, after which hydrophobic contacts of the deoxyribose groups are formed via a dewetting effect, resulting in stable attraction between two Z-DNA molecules. The highlighted hydrophobic nature of Z-DNA interaction from the current study may help to understand the biological functions of Z-DNA in gene transcription.Understanding how DNA molecules interact with other biomolecules is related to how they utilize their functions and is therefore critical for understanding their structure-function relationships. For a long time, the existence of Z-form DNA (a left-handed double helical version of DNA, instead of the common right-handed B-form) has puzzled the scientists, and the definitive biological significance of Z-DNA has not yet been clarified. In this study, the effects of DNA conformation in DNA-DNA interactions are explored by molecular dynamics simulations. Using umbrella sampling, we find that for both B- and Z-form DNA, surrounding Mg2+ ions always exert themselves to screen the Coulomb repulsion between DNA phosphates, resulting in very weak attractive force. On the contrary, a tight and stable bound state is discovered for Z-DNA in the presence of Mg2+ or Na+, benefiting from their hydrophobic nature. Based on the contact surface and a dewetting process analysis, a two-stage binding process of Z-DNA is outlined: two Z-DNA first attract each other through charge screening and Mg2+ bridges to phosphate groups in the same way as that of B-DNA, after which hydrophobic contacts of the deoxyribose groups are formed via a dewetting effect, resulting in stable attraction between two Z-DNA molecules. The highlighted hydrophobic nature of Z-DNA interaction from the current study may help to understand the biological functions of Z-DNA in gene transcription. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03235c

Nanoparticle engineering of colloidal suspension behavior

NASA Astrophysics Data System (ADS)

Chan, Angel Thanda

We investigate the effects of highly charged nanoparticles on the phase behavior, structure, and assembly of colloidal microsphere suspensions. Specifically, by selectively tuning the electrostatic interactions between silica microspheres and polystyrene nanoparticles, we study the behavior of four key systems: (i) strongly repulsive, (ii) haloing, (iii) weakly attractive, and (iv) strongly attractive systems. In each system, a combination of nanoparticle adsorption, zeta potential, and confocal microscopy measurements are carried out to systematically study the effects of nanoparticle volume fraction, microsphere/nanoparticle size ratios, and interparticle interactions on their behavior. Our observations indicate that minimal adsorption of highly charged nanoparticles occurs on like-charged and negligibly-charged microspheres, whereas their extent of association increases dramatically with increasing microsphere-nanoparticle attraction. A rich phase behavior emerges in these systems based on whether the nanoparticle species serve as depletants, haloing, or bridging species. The phase transitions in the haloing system occur at constant nanoparticle volume fractions, φnano, over a broad range of microsphere volume fractions, φmicro . By contrast, the observed transitions in the weakly and strongly attractive mixtures occur at a constant number ratio of nanoparticles per microsphere, Nnano/Nmicro. Important structural differences emerge, which can be exploited in the assembly of colloidal gels for direct ink writing and colloidal crystals on epitaxially patterned substrates. Finally, for the first time, we explore nanoparticle haloing as a new route for stabilizing hydrophobic colloidal drugs in aqueous suspensions media for preparation of injectable pharmaceuticals. These microsphere suspensions exhibit improved stability relative to their surfactant-stabilized counterparts after autoclaving, a critical processing step for this target applications. This research opens up a new avenue for stabilization of hydrophobic particles, when surfactant additions alone do not provide sufficient stabilization.

Cholera Toxin Inhibitors Studied with High-Performance Liquid Affinity Chromatography: A Robust Method to Evaluate Receptor–Ligand Interactions

PubMed Central

Bergström, Maria; Liu, Shuang; Kiick, Kristi L.; Ohlson, Sten

2009-01-01

Anti-adhesion drugs may be an alternative to antibiotics to control infection of micro-organisms. The well-characterized interaction between cholera toxin and the cellular glycolipid GM1 makes it an attractive model for inhibition studies in general. In this report, we demonstrate a high-performance liquid affinity chromatography approach called weak affinity chromatography to evaluate cholera toxin inhibitors. The cholera toxin B-subunit was covalently coupled to porous silica and a (weak) affinity column was produced. The KD values of galactose and meta-nitrophenyl α-D-galactoside were determined with weak affinity chromatography to be 52 and 1 mM, respectively, which agree well with IC50 values previously reported. To increase inhibition potency multivalent inhibitors have been developed and the interaction with multivalent glycopolypeptides was also evaluated. The affinity of these compounds was found to correlate with the galactoside content but KD values were not obtained because of the inhomogeneous response and slow off-rate from multivalent interactions. Despite the limitations in obtaining direct KD values of the multivalent galactopolypeptides, weak affinity chromatography represents an additional and valuable tool in the evaluation of monovalent as well as multivalent cholera toxin inhibitors. It offers multiple advantages, such as a low sample consumption, high reproducibility and short analysis time, which are often not observed in other methods of analysis. PMID:19152642

Virus assembly occurs following a pH- or Ca2+-triggered switch in the thermodynamic attraction between structural protein capsomeres.

PubMed

Chuan, Yap P; Fan, Yuan Y; Lua, Linda H L; Middelberg, Anton P J

2010-03-06

Viral self-assembly is of tremendous virological and biomedical importance. Although theoretical and crystallographic considerations suggest that controlled conformational change is a fundamental regulatory mechanism in viral assembly, direct proof that switching alters the thermodynamic attraction of self-assembling components has not been provided. Using the VP1 protein of polyomavirus, we report a new method to quantitatively measure molecular interactions under conditions of rapid protein self-assembly. We show, for the first time, that triggering virus capsid assembly through biologically relevant changes in Ca(2+) concentration, or pH, is associated with a dramatic increase in the strength of protein molecular attraction as quantified by the second virial coefficient (B(22)). B(22) decreases from -2.3 x 10(-4) mol ml g(-2) (weak protein-protein attraction) to -2.4 x 10(-3) mol ml g(-2) (strong protein attraction) for metastable and Ca(2+)-triggered self-assembling capsomeres, respectively. An assembly-deficient mutant (VP1CDelta63) is conversely characterized by weak protein-protein repulsion independently of chemical change sufficient to cause VP1 assembly. Concomitant switching of both VP1 assembly and thermodynamic attraction was also achieved by in vitro changes in ammonium sulphate concentration, consistent with protein salting-out behaviour. The methods and findings reported here provide new insight into viral assembly, potentially facilitating the development of new antivirals and vaccines, and will open the way to a more fundamental physico-chemical description of complex protein self-assembly systems.

Nonmonotonic diffusion in crowded environments

PubMed Central

Putzel, Gregory Garbès; Tagliazucchi, Mario; Szleifer, Igal

2015-01-01

We study the diffusive motion of particles among fixed spherical crowders. The diffusers interact with the crowders through a combination of a hard-core repulsion and a short-range attraction. The long-time effective diffusion coefficient of the diffusers is found to depend non-monotonically on the strength of their attraction to the crowders. That is, for a given concentration of crowders, a weak attraction to the crowders enhances diffusion. We show that this counterintuitive fact can be understood in terms of the mesoscopic excess chemical potential landscape experienced by the diffuser. The roughness of this excess chemical potential landscape quantitatively captures the nonmonotonic dependence of the diffusion rate on the strength of crowder-diffuser attraction; thus it is a purely static predictor of dynamic behavior. The mesoscopic view given here provides a unified explanation for enhanced diffusion effects that have been found in various systems of technological and biological interest. PMID:25302920

An optimized full-configuration-interaction nuclear orbital approach to a ``hard-core'' interaction problem: Application to (3He)N-Cl2(B) clusters (N<=4)

NASA Astrophysics Data System (ADS)

de Lara-Castells, M. P.; Villarreal, P.; Delgado-Barrio, G.; Mitrushchenkov, A. O.

2009-11-01

An efficient full-configuration-interaction nuclear orbital treatment has been recently developed as a benchmark quantum-chemistry-like method to calculate ground and excited "solvent" energies and wave functions in small doped ΔEest clusters (N ≤4) [M. P. de Lara-Castells, G. Delgado-Barrio, P. Villarreal, and A. O. Mitrushchenkov, J. Chem. Phys. 125, 221101 (2006)]. Additional methodological and computational details of the implementation, which uses an iterative Jacobi-Davidson diagonalization algorithm to properly address the inherent "hard-core" He-He interaction problem, are described here. The convergence of total energies, average pair He-He interaction energies, and relevant one- and two-body properties upon increasing the angular part of the one-particle basis set (expanded in spherical harmonics) has been analyzed, considering Cl2 as the dopant and a semiempirical model (T-shaped) He-Cl2(B) potential. Converged results are used to analyze global energetic and structural aspects as well as the configuration makeup of the wave functions, associated with the ground and low-lying "solvent" excited states. Our study reveals that besides the fermionic nature of H3e atoms, key roles in determining total binding energies and wave-function structures are played by the strong repulsive core of the He-He potential as well as its very weak attractive region, the most stable arrangement somehow departing from the one of N He atoms equally spaced on equatorial "ring" around the dopant. The present results for N =4 fermions indicates the structural "pairing" of two H3e atoms at opposite sides on a broad "belt" around the dopant, executing a sort of asymmetric umbrella motion. This pairing is a compromise between maximizing the H3e-H3e and the He-dopant attractions, and suppressing at the same time the "hard-core" repulsion. Although the He-He attractive interaction is rather weak, its contribution to the total energy is found to scale as a power of three and it thus increasingly affects the pair density distributions as the cluster grows in size.

Conformation-dependent DNA attraction.

PubMed

Li, Weifeng; Nordenskiöld, Lars; Zhou, Ruhong; Mu, Yuguang

2014-06-21

Understanding how DNA molecules interact with other biomolecules is related to how they utilize their functions and is therefore critical for understanding their structure-function relationships. For a long time, the existence of Z-form DNA (a left-handed double helical version of DNA, instead of the common right-handed B-form) has puzzled the scientists, and the definitive biological significance of Z-DNA has not yet been clarified. In this study, the effects of DNA conformation in DNA-DNA interactions are explored by molecular dynamics simulations. Using umbrella sampling, we find that for both B- and Z-form DNA, surrounding Mg(2+) ions always exert themselves to screen the Coulomb repulsion between DNA phosphates, resulting in very weak attractive force. On the contrary, a tight and stable bound state is discovered for Z-DNA in the presence of Mg(2+) or Na(+), benefiting from their hydrophobic nature. Based on the contact surface and a dewetting process analysis, a two-stage binding process of Z-DNA is outlined: two Z-DNA first attract each other through charge screening and Mg(2+) bridges to phosphate groups in the same way as that of B-DNA, after which hydrophobic contacts of the deoxyribose groups are formed via a dewetting effect, resulting in stable attraction between two Z-DNA molecules. The highlighted hydrophobic nature of Z-DNA interaction from the current study may help to understand the biological functions of Z-DNA in gene transcription.

Sex difference in attractiveness perceptions of strong and weak male walkers.

PubMed

Fink, Bernhard; André, Selina; Mines, Johanna S; Weege, Bettina; Shackelford, Todd K; Butovskaya, Marina L

2016-11-01

Men and women accurately assess male physical strength from facial and body morphology cues. Women's assessments of male facial attractiveness, masculinity, and dominance correlate positively with male physical strength. A positive relationship also has been reported between physical strength and attractiveness of men's dance movements. Here, we investigate men's and women's attractiveness, dominance, and strength assessments from brief samples of male gait. Handgrip strength (HGS) was measured in 70 heterosexual men and their gait was motion-captured. Men and women judged 20 precategorized strong (high HGS) and weak (low HGS) walkers on attractiveness, dominance, and strength, and provided a measure of their own HGS. Both men and women judged strong walkers higher on dominance and strength than weak walkers. Women but not men judged strong walkers more attractive than weak walkers. These effects were independent of observers' physical strength. Male physical strength is conveyed not only through facial and body morphology, but also through body movements. We discuss our findings with reference to studies suggesting that physical strength provides information about male quality in contexts of inter- and intrasexual selection. Am. J. Hum. Biol. 28:913-917, 2016. © 2016Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Antiparallel Self-Association of a γ,α-Hybrid Peptide: More Relevance of Weak Interactions.

PubMed

Venugopalan, Paloth; Kishore, Raghuvansh

2015-08-01

To learn how a preorganized peptide-based molecular template, together with diverse weak non-covalent interactions, leads to an effective self-association, we investigated the conformational characteristics of a simple γ,α-hybrid model peptide, Boc-γ-Abz-Gly-OMe. The single-crystal X-ray diffraction analysis revealed the existence of a fully extended β-strand-like structure stabilized by two non-conventional C-H⋅⋅⋅O=C intramolecular H-bonds. The 2D (1) H NMR ROESY experiment led us to propose that the flat topology of the urethane-γ-Abz-amide moiety is predominantly preserved in a non-polar environment. The self-association of the energetically more favorable antiparallel β-strand-mimic in solid-state engenders an unusual 'flight of stairs' fabricated through face-to-face and edge-to-edge Ar⋅⋅⋅Ar interactions. In conjunction with FT-IR spectroscopic analysis in chloroform, we highlight that conformationally semi-rigid γ-Abz foldamer in appositely designed peptides may encourage unusual β-strand or β-sheet-like self-association and supramolecular organization stabilized via weak attractive forces. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Smart Polymers with Special Wettability.

PubMed

Chang, Baisong; Zhang, Bei; Sun, Taolei

2017-01-01

Surface wettability plays a key role in addressing issues ranging from basic life activities to our daily life, and thus being able to control it is an attractive goal. Learning from nature, both of its structure and function, brings us much inspiration in designing smart polymers to tackle this major challenge. Life functions particularly depend on biomolecular recognition-induced interfacial properties from the aqueous phase onto either "soft" cell and tissue or "hard" inorganic bone and tooth surfaces. The driving force is noncovalent weak interactions rather than strong covalent combinations. An overview is provided of the weak interactions that perform vital actions in mediating biological processes, which serve as a basis for elaborating multi-component polymers with special wettabilities. The role of smart polymers from molecular recognitions to macroscopic properties are highlighted. The rationale is that highly selective weak interactions are capable of creating a dynamic synergetic communication in the building components of polymers. Biomolecules could selectively induce conformational transitions of polymer chains, and then drive a switching of physicochemical properties, e.g., roughness, stiffness and compositions, which are an integrated embodiment of macroscopic surface wettabilities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Flocculation of deformable emulsion droplets. 2: Interaction energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petsev, D.N.; Denkov, N.D.; Kralchevsky, P.A.

1995-12-01

The effect of different factors (drop radius, interfacial tension, Hamaker constant, electrolyte, micellar concentrations, etc.) on the interaction energy of emulsion droplets is studied theoretically. It is demonstrated that the deformation of the colliding droplets considerably affects the interaction energy. The contributions of the electrostatic, van der Waals, depletion, steric, and oscillatory surface forces, as well as for the surface stretching and bending energies, are estimated and discussed. The calculations show that the droplets interact as nondeformed spheres when the attractive interactions are weak. At stronger attractions an equilibrium plane parallel film is formed between the droplets, corresponding to minimummore » interaction energy of the system. For droplets in concentrated micellar surfactant solutions the oscillatory surface forces become operative and one can observe several minima of the energy surface,each corresponding to a metastable state with a different number of micellar layers inside the film formed between the droplets. The present theoretical analysis can find applications in predicting the behavior and stability of miniemulsions (containing micrometer and submicrometer droplets), as well as in interpretation of data obtained by light scattering, phase behavior, rheological and osmotic pressure measurements, etc.« less

Anomalous Protein-Protein Interactions in Multivalent Salt Solution.

PubMed

Pasquier, Coralie; Vazdar, Mario; Forsman, Jan; Jungwirth, Pavel; Lund, Mikael

2017-04-13

The stability of aqueous protein solutions is strongly affected by multivalent ions, which induce ion-ion correlations beyond the scope of classical mean-field theory. Using all-atom molecular dynamics (MD) and coarse grained Monte Carlo (MC) simulations, we investigate the interaction between a pair of protein molecules in 3:1 electrolyte solution. In agreement with available experimental findings of "reentrant protein condensation", we observe an anomalous trend in the protein-protein potential of mean force with increasing electrolyte concentration in the order: (i) double-layer repulsion, (ii) ion-ion correlation attraction, (iii) overcharge repulsion, and in excess of 1:1 salt, (iv) non Coulombic attraction. To efficiently sample configurational space we explore hybrid continuum solvent models, applicable to many-protein systems, where weakly coupled ions are treated implicitly, while strongly coupled ones are treated explicitly. Good agreement is found with the primitive model of electrolytes, as well as with atomic models of protein and solvent.

Exploring the Interaction Natures in Plutonyl (VI) Complexes with Topological Analyses of Electron Density

PubMed Central

Du, Jiguang; Sun, Xiyuan; Jiang, Gang

2016-01-01

The interaction natures between Pu and different ligands in several plutonyl (VI) complexes are investigated by performing topological analyses of electron density. The geometrical structures in both gaseous and aqueous phases are obtained with B3LYP functional, and are generally in agreement with available theoretical and experimental results when combined with all-electron segmented all-electron relativistic contracted (SARC) basis set. The Pu–Oyl bond orders show significant linear dependence on bond length and the charge of oxygen atoms in plutonyl moiety. The closed-shell interactions were identified for Pu-Ligand bonds in most complexes with quantum theory of atoms in molecules (QTAIM) analyses. Meanwhile, we found that some Pu–Ligand bonds, like Pu–OH−, show weak covalent. The interactive nature of Pu–ligand bonds were revealed based on the interaction quantum atom (IQA) energy decomposition approach, and our results indicate that all Pu–Ligand interactions is dominated by the electrostatic attraction interaction as expected. Meanwhile it is also important to note that the quantum mechanical exchange-correlation contributions can not be ignored. By means of the non-covalent interaction (NCI) approach it has been found that some weak and repulsion interactions existed in plutonyl(VI) complexes, which can not be distinguished by QTAIM, can be successfully identified. PMID:27077844

Stability of matter-wave solitons in optical lattices

NASA Astrophysics Data System (ADS)

Ali, Sk. Golam; Roy, S. K.; Talukdar, B.

2010-08-01

We consider localized states of both single- and two-component Bose-Einstein condensates (BECs) confined in a potential resulting from the superposition of linear and nonlinear optical lattices and make use of Vakhitov-Kolokolov criterion to investigate the effect of nonlinear lattice on the stability of the soliton solutions in the linear optical lattice (LOL). For the single-component case we show that a weak nonlinear lattice has very little effect on the stability of such solitons while sufficiently strong nonlinear optical lattice (NOL) squeezes them to produce narrow bound states. For two-component condensates we find that when the strength of the NOL (γ1) is less than that of the LOL (V0) a relatively weak intra-atomic interaction (IAI) has little effect on the stability of the component solitons. This is true for both attractive and repulsive IAI. A strong attractive IAI, however, squeezes the BEC solitons while a similar repulsive IAI makes the component solitons wider. For γ1 > V0, only a strong attractive IAI squeezes the BEC solitons but the squeezing effect is less prominent than that found for γ1 < V0. We make useful checks on the results of our semianalytical stability analysis by solving the appropriate Gross-Pitaevskii equations numerically.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuchinskii, E. Z., E-mail: kuchinsk@iep.uran.ru; Kuleeva, N. A.; Sadovskii, M. V., E-mail: sadovski@iep.uran.ru

We derive a Ginzburg–Landau (GL) expansion in the disordered attractive Hubbard model within the combined Nozieres–Schmitt-Rink and DMFT+Σ approximation. Restricting ourselves to the homogeneous expansion, we analyze the disorder dependence of GL expansion coefficients for a wide range of attractive potentials U, from the weak BCS coupling region to the strong-coupling limit, where superconductivity is described by Bose–Einstein condensation (BEC) of preformed Cooper pairs. We show that for the a semielliptic “bare” density of states of the conduction band, the disorder influence on the GL coefficients A and B before quadratic and quartic terms of the order parameter, as wellmore » as on the specific heat discontinuity at the superconducting transition, is of a universal nature at any strength of the attractive interaction and is related only to the general widening of the conduction band by disorder. In general, disorder growth increases the values of the coefficients A and B, leading either to a suppression of the specific heat discontinuity (in the weak-coupling limit), or to its significant growth (in the strong-coupling region). However, this behavior actually confirms the validity of the generalized Anderson theorem, because the disorder dependence of the superconducting transition temperature T{sub c}, is also controlled only by disorder widening of the conduction band (density of states).« less

Competition between surface adsorption and folding of fibril-forming polypeptides

NASA Astrophysics Data System (ADS)

Ni, Ran; Kleijn, J. Mieke; Abeln, Sanne; Cohen Stuart, Martien A.; Bolhuis, Peter G.

2015-02-01

Self-assembly of polypeptides into fibrillar structures can be initiated by planar surfaces that interact favorably with certain residues. Using a coarse-grained model, we systematically studied the folding and adsorption behavior of a β -roll forming polypeptide. We find that there are two different folding pathways depending on the temperature: (i) at low temperature, the polypeptide folds in solution into a β -roll before adsorbing onto the attractive surface; (ii) at higher temperature, the polypeptide first adsorbs in a disordered state and folds while on the surface. The folding temperature increases with increasing attraction as the folded β -roll is stabilized by the surface. Surprisingly, further increasing the attraction lowers the folding temperature again, as strong attraction also stabilizes the adsorbed disordered state, which competes with folding of the polypeptide. Our results suggest that to enhance the folding, one should use a weakly attractive surface. They also explain the recent experimental observation of the nonmonotonic effect of charge on the fibril formation on an oppositely charged surface [C. Charbonneau et al., ACS Nano 8, 2328 (2014), 10.1021/nn405799t].

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Xiaoning; Wang, Hongli; Liu, Xiaodong

Industrial emissions of anthropogenic aerosols over East Asia have greatly increased in recent decades, and so the interactions between atmospheric aerosols and the East Asian summer monsoon (EASM) have attracted enormous attention. In order to further understand the aerosol-EASM interaction, we investigate the impacts of anthropogenic aerosols on the EASM during the multidecadal strong (1950–1977) and weak (1978–2000) EASM stages using the Community Atmospheric Model 5.1. Numerical experiments are conducted for the whole period, including the two different EASM stages, with present day (PD, year 2000) and preindustrial (PI, year 1850) aerosol emissions, as well as the observed time-varying aerosolmore » emissions. A comparison of the results from PD and PI shows that, with the increase in anthropogenic aerosols, the large-scale EASM intensity is weakened to a greater degree (-9.8%) during the weak EASM stage compared with the strong EASM stage (-4.4%). The increased anthropogenic aerosols also result in a significant reduction in precipitation over North China during the weak EASM stage, as opposed to a statistically insignificant change during the strong EASM stage. Because of greater aerosol loading and the larger sensitivity of the climate system during weak EASM stages, the aerosol effects are more significant during these EASM stages. Moreover, these results suggest that anthropogenic aerosols from the same aerosol emissions have distinct effects on the EASM and the associated precipitation between the multidecadal weak and strong EASM stages.« less

Distinct effects of anthropogenic aerosols on the East Asian summer monsoon between multidecadal strong and weak monsoon stages

DOE PAGES

Xie, Xiaoning; Wang, Hongli; Liu, Xiaodong; ...

2016-06-18

Industrial emissions of anthropogenic aerosols over East Asia have greatly increased in recent decades, and so the interactions between atmospheric aerosols and the East Asian summer monsoon (EASM) have attracted enormous attention. In order to further understand the aerosol-EASM interaction, we investigate the impacts of anthropogenic aerosols on the EASM during the multidecadal strong (1950–1977) and weak (1978–2000) EASM stages using the Community Atmospheric Model 5.1. Numerical experiments are conducted for the whole period, including the two different EASM stages, with present day (PD, year 2000) and preindustrial (PI, year 1850) aerosol emissions, as well as the observed time-varying aerosolmore » emissions. A comparison of the results from PD and PI shows that, with the increase in anthropogenic aerosols, the large-scale EASM intensity is weakened to a greater degree (-9.8%) during the weak EASM stage compared with the strong EASM stage (-4.4%). The increased anthropogenic aerosols also result in a significant reduction in precipitation over North China during the weak EASM stage, as opposed to a statistically insignificant change during the strong EASM stage. Because of greater aerosol loading and the larger sensitivity of the climate system during weak EASM stages, the aerosol effects are more significant during these EASM stages. Moreover, these results suggest that anthropogenic aerosols from the same aerosol emissions have distinct effects on the EASM and the associated precipitation between the multidecadal weak and strong EASM stages.« less

pH-responsive ion transport in polyelectrolyte multilayers of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(4-styrenesulfonic acid-co-maleic acid) (PSS-MA) bearing strong- and weak anionic groups.

PubMed

Maza, Eliana; Tuninetti, Jimena S; Politakos, Nikolaos; Knoll, Wolfgang; Moya, Sergio; Azzaroni, Omar

2015-11-28

The layer-by-layer construction of interfacial architectures displaying stimuli-responsive control of mass transport is attracting increasing interest in materials science. In this work, we describe the creation of interfacial architectures displaying pH-dependent ionic transport properties which until now have not been observed in polyelectrolyte multilayers. We describe a novel approach to create pH-controlled ion-rectifying systems employing polyelectrolyte multilayers assembled from a copolymer containing both weakly and strongly charged pendant groups, poly(4-styrenesulfonic acid-co-maleic acid) (PSS-MA), alternately deposited with poly(diallyldimethylammonium chloride) (PDADMAC). The conceptual framework is based on the very contrasting and differential interactions of PSS and MA units with PDADMAC. In our setting, sulfonate groups play a structural role by conferring stability to the multilayer due to the strong electrostatic interactions with the polycations, while the weakly interacting MA groups remain "silent" within the film and then act as on-demand pH-responsive units. When these multilayers are combined with a strong cationic capping layer that repels the passage of cationic probes, a pH-gateable rectified transport of anions is observed. Concomitantly, we also observed that these functional properties are significantly affected when multilayers are subjected to extensive pH cycling as a consequence of irreversible morphological changes taking place in the film. We envision that the synergy derived from combining weak and strong interactions within the same multilayer will play a key role in the construction of new interfacial architectures displaying tailorable ion transport properties.

Methyl-isoeugenol, a Highly Attractive Male Lure for the Cucurbit Flower Pest Zeugodacus diversus (Coquillett) (syn. Bactrocera diversa) (Diptera: Tephritidae: Dacinae).

PubMed

Royer, Jane E; Khan, Mahfuza; Mayer, David G

2018-05-28

Effective male fruit fly attractants, such as cue lure (CL) and methyl eugenol (ME), are important in the monitoring and management of pest species through lure and kill techniques of trapping and male annihilation. However, some species are only weakly responsive to these lures, making their detection and control difficult. Zeugodacus diversus (Coquillett), a pest of cucurbit flowers in Asia, is weakly attracted to ME. Recently in Australia and Papua New Guinea, the eugenol analogues isoeugenol, methyl-isoeugenol, and dihydroeugenol were found to be effective attractants for species with a weak response to ME and CL, as well as several nonresponsive species. Additionally, studies from the early 1900s indicated that Z. diversus was attracted to isoeugenol. To determine if these eugenol analogues may be more effective attractants for Z. diversus, we field tested them in Bangladesh in comparison to ME, as well as CL and zingerone. Z. diversus was significantly more attracted to all three eugenol analogues than ME, with it most attracted to methyl-isoeugenol. Its attraction to methyl-isoeugenol was 49 times greater than its attraction to ME (respective means 23.58 flies/trap/day (FTD) and 0.48 FTD). Z. diversus was also consistently trapped at methyl-isoeugenol at all trap clearances including when populations were low, whereas it was only trapped at ME at 6 out of the 13 clearances. This study demonstrates that methyl-isoeugenol is a highly attractive lure for Z. diversus and would be a valuable inclusion as an attractant in monitoring and male annihilation programs.

Axions and dark matter

NASA Astrophysics Data System (ADS)

Yang, Qiaoli

2017-05-01

Dark matter constitutes about 23% of the total energy density of the universe, but its properties are still little known besides that it should be composed by cold and weakly interacting particles. Many beyond Standard Model theories can provide proper candidates to serve as dark matter and the axion introduced to solve the strong CP problem turns out to be an attractive one. In this paper, we briefly review several important features of the axion and the axion dark matter.

Quantized orbits in weakly coupled Belousov-Zhabotinsky reactors

NASA Astrophysics Data System (ADS)

Weiss, S.; Deegan, R. D.

2015-06-01

Using numerical and experimental tools, we study the motion of two coupled spiral cores in a light-sensitive variant of the Belousov-Zhabotinsky reaction. Each core resides on a separate two-dimensional domain, and is coupled to the other by light. When both spirals have the same sense of rotation, the cores are attracted to a circular trajectory with a diameter quantized in integer units of the spiral wavelength λ. When the spirals have opposite senses of rotation, the cores are attracted towards different but parallel straight trajectories, separated by an integer multiple of λ/2. We present a model that explains this behavior as the result of a spiral wavefront-core interaction that produces a deterministic displacement of the core and a retardation of its phase.

Enhanced gel formation in binary mixtures of nanocolloids with short-range attraction

NASA Astrophysics Data System (ADS)

Harden, James L.; Guo, Hongyu; Bertrand, Martine; Shendruk, Tyler N.; Ramakrishnan, Subramanian; Leheny, Robert L.

2018-01-01

Colloidal suspensions transform between fluid and disordered solid states as parameters such as the colloid volume fraction and the strength and nature of the colloidal interactions are varied. Seemingly subtle changes in the characteristics of the colloids can markedly alter the mechanical rigidity and flow behavior of these soft composite materials. This sensitivity creates both a scientific challenge and an opportunity for designing suspensions for specific applications. In this paper, we report a novel mechanism of gel formation in mixtures of weakly attractive nanocolloids with modest size ratio. Employing a combination of x-ray photon correlation spectroscopy, rheometry, and molecular dynamics simulations, we find that gels are stable at remarkably weaker attraction in mixtures with size ratio near two than in the corresponding monodisperse suspensions. In contrast with depletion-driven gelation at larger size ratio, gel formation in the mixtures is triggered by microphase demixing of the species into dense regions of immobile smaller colloids surrounded by clusters of mobile larger colloids that is not predicted by mean-field thermodynamic considerations. These results point to a new route for tailoring nanostructured colloidal solids through judicious combination of interparticle interaction and size distribution.

TASEP of interacting particles of arbitrary size

NASA Astrophysics Data System (ADS)

Narasimhan, S. L.; Baumgaertner, A.

2017-10-01

A mean-field description of the stationary state behaviour of interacting k-mers performing totally asymmetric exclusion processes (TASEP) on an open lattice segment is presented employing the discrete Takahashi formalism. It is shown how the maximal current and the phase diagram, including triple-points, depend on the strength of repulsive and attractive interactions. We compare the mean-field results with Monte Carlo simulation of three types interacting k-mers: monomers, dimers and trimers. (a) We find that the Takahashi estimates of the maximal current agree quantitatively with those of the Monte Carlo simulation in the absence of interaction as well as in both the the attractive and the strongly repulsive regimes. However, theory and Monte Carlo results disagree in the range of weak repulsion, where the Takahashi estimates of the maximal current show a monotonic behaviour, whereas the Monte Carlo data show a peaking behaviour. It is argued that the peaking of the maximal current is due to a correlated motion of the particles. In the limit of very strong repulsion the theory predicts a universal behavior: th maximal currents of k-mers correspond to that of non-interacting (k+1) -mers; (b) Monte Carlo estimates of the triple-points for monomers, dimers and trimers show an interesting general behaviour : (i) the phase boundaries α * and β* for entry and exit current, respectively, as function of interaction strengths show maxima for α* whereas β * exhibit minima at the same strength; (ii) in the attractive regime, however, the trend is reversed (β * > α * ). The Takahashi estimates of the triple-point for monomers show a similar trend as the Monte Carlo data except for the peaking of α * ; for dimers and trimers, however, the Takahashi estimates show an opposite trend as compared to the Monte Carlo data.

Explaining financial and prosocial biases in favor of attractive people: Interdisciplinary perspectives from economics, social psychology, and evolutionary psychology.

PubMed

Maestripieri, Dario; Henry, Andrea; Nickels, Nora

2017-01-01

Financial and prosocial biases in favor of attractive adults have been documented in the labor market, in social transactions in everyday life, and in studies involving experimental economic games. According to the taste-based discrimination model developed by economists, attractiveness-related financial and prosocial biases are the result of preferences or prejudices similar to those displayed toward members of a particular sex, racial, ethnic, or religious group. Other explanations proposed by economists and social psychologists maintain that attractiveness is a marker of personality, intelligence, trustworthiness, professional competence, or productivity. Evolutionary psychologists have argued that attractive adults are favored because they are preferred sexual partners. Evidence that stereotypes about attractive people are causally related to financial or prosocial biases toward them is weak or nonexistent. Consistent with evolutionary explanations, biases in favor of attractive women appear to be more consistent or stronger than those in favor of attractive men, and biases are more consistently reported in interactions between opposite-sex than same-sex individuals. Evolutionary explanations also account for increased prosocial behavior in situations in which attractive individuals are simply bystanders. Finally, evolutionary explanations are consistent with the psychological, physiological, and behavioral changes that occur when individuals are exposed to potential mates, which facilitate the expression of courtship behavior and increase the probability of occurrence of mating. Therefore, multiple lines of evidence suggest that mating motives play a more important role in driving financial and prosocial biases toward attractive adults than previously recognized.

A new attraction-disseverance model for explaining landsliding in clay-rich tephras

NASA Astrophysics Data System (ADS)

Kluger, M. O.; Moon, V.; Kreiter, S.; Lowe, D.; Churchman, J.; Hepp, D. A.; Seibel, D.; Jorat, E.; Mörz, T.

2016-12-01

Altered tephras are highly susceptible to landsliding and account for fatalities and property damage every year. The clay mineral halloysite is often associated with landslide-prone layers within weathered tephra successions, especially in deposits with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite on the development of sensitivity and thus sudden and unpredictable landsliding is unknown. Here we show that an abundance of halloysite, dominated by a distinctive ovate mushroom-cap-shaped (MCS) spherical morphology, governs the development of sensitivity, and hence proneness to landsliding, in weathered rhyolitic tephras in eastern North Island, New Zealand. We found that a highly sensitive layer, which was involved in a retrogressive landslide, has an extraordinarily high content of aggregated MCS spheres with imperfectly-closed exterior surfaces, i.e., the MCS spheres have substantial openings on one side. We suggest that short-range electrostatic and van der Waals' interactions enabled the MCS spheres to form interconnected aggregates by attraction between numerous paired silanol and aluminol layers with a weakly positive, or neutral, charge exposed in the openings and the negatively-charged convex silanol faces on the curved exterior surfaces of the spheres. However, if these weak attractions are overcome during slope failure, the prevailing repulsion between two exterior surfaces result in a low remolded shear strength, i.e., a high sensitivity, and thus a high propensity for flow-like landsliding. Our results indicate that this novel electrostatic attraction-disseverance model explains the high sensitivity and therefore contributes to a general understanding of the mechanisms of landsliding in sensitive altered tephras rich in spherical halloysite.

Hydrodynamics in a Degenerate, Strongly Attractive Fermi Gas

NASA Technical Reports Server (NTRS)

Thomas, John E.; Kinast, Joseph; Hemmer, Staci; Turlapov, Andrey; O'Hara, Ken; Gehm, Mike; Granade, Stephen

2004-01-01

In summary, we use all-optical methods with evaporative cooling near a Feshbach resonance to produce a strongly interacting degenerate Fermi gas. We observe hydrodynamic behavior in the expansion dynamics. At low temperatures, collisions may not explain the expansion dynamics. We observe hydrodynamics in the trapped gas. Our observations include collisionally-damped excitation spectra at high temperature which were not discussed above. In addition, we observe weakly damped breathing modes at low temperature. The observed temperature dependence of the damping time and hydrodynamic frequency are not consistent with collisional dynamics nor with collisionless mean field interactions. These observations constitute the first evidence for superfluid hydrodynamics in a Fermi gas.

Quantum Monte Carlo studies of superfluid Fermi gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, S.Y.; Pandharipande, V.R.; Carlson, J.

2004-10-01

We report results of quantum Monte Carlo calculations of the ground state of dilute Fermi gases with attractive short-range two-body interactions. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length and the Fermi wave vector, ak{sub F}. We report results for the ground-state energy, the pairing gap {delta}, and the quasiparticle spectrum. In the weak-coupling regime, 1/ak{sub F}<-1, we obtain Bardeen-Cooper-Schrieffer (BCS) superfluid and the energy gap {delta} is much smaller than the Fermi gas energy E{sub FG}. When a>0, the interaction is strong enough tomore » form bound molecules with energy E{sub mol}. For 1/ak{sub F} > or approx. 0.5, we find that weakly interacting composite bosons are formed in the superfluid gas with {delta} and gas energy per particle approaching E{sub mol}/2. In this region, we seem to have Bose-Einstein condensation (BEC) of molecules. The behavior of the energy and the gap in the BCS-to-BEC transition region, -0.5<1/ak{sub F}<0.5, is discussed.« less

Observation of Spin Polarons in a Tunable Fermi Liquid of Ultracold Atoms

NASA Astrophysics Data System (ADS)

Zwierlein, Martin

2009-05-01

We have observed spin polarons, dressed spin down impurities in a spin up Fermi sea of ultracold atoms via tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom dressed with a spin up cloud constitutes the spin- or Fermi polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The spectra allow us to directly measure the polaron energy and the quasi-particle residue Z. The polarons are found to be only weakly interacting with each other, and can thus be identified with the quasi-particles of Landau's Fermi liquid theory. At a critical interaction strength, we observe a transition from spin one-half polarons to spin zero molecules. At this point the Fermi liquid undergoes a phase transition into a superfluid Bose liquid.

Morphology of clusters of attractive dry and wet self-propelled spherical particle suspensions.

PubMed

Alarcón, Francisco; Valeriani, Chantal; Pagonabarraga, Ignacio

2017-01-25

In order to assess the effect of hydrodynamics in the assembly of active attractive spheres, we simulate a semi-dilute suspension of attractive self-propelled spherical particles in a quasi-two dimensional geometry comparing the case with and without hydrodynamics interactions. To start with, independent of the presence of hydrodynamics, we observe that depending on the ratio between attraction and propulsion, particles either coarsen or aggregate forming finite-size clusters. Focusing on the clustering regime, we characterize two different cluster parameters, i.e. their morphology and orientational order, and compare the case when active particles behave either as pushers or pullers (always in the regime where inter-particle attractions compete with self-propulsion). Studying cluster phases for squirmers with respect to those obtained for active Brownian disks (indicated as ABPs), we have shown that hydrodynamics alone can sustain a cluster phase of active swimmers (pullers), while ABPs form cluster phases due to the competition between attraction and self-propulsion. The structural properties of the cluster phases of squirmers and ABPs are similar, although squirmers show sensitivity to active stresses. Active Brownian disks resemble weakly pusher squirmer suspensions in terms of cluster size distribution, structure of the radius of gyration on the cluster size and degree of cluster polarity.

Electrostatic attraction of weak monoacid anions increases probability for protonation and passage through aquaporins.

PubMed

Rothert, Monja; Rönfeldt, Deike; Beitz, Eric

2017-06-02

A positive electrostatic field emanating from the center of the aquaporin (AQP) water and solute channel is responsible for the repulsion of cations. At the same time, however, a positive field will attract anions. In this regard, l-lactate/lactic acid permeability has been shown for various isoforms of the otherwise highly water and neutral substrate selective AQP family. The structural requirements rendering certain AQPs permeable for weak monoacids and the mechanism of conduction have remained unclear. Here, we show by profiling pH-dependent substrate permeability, measurements of media alkalization, and proton decoupling that AQP9 acts as a channel for the protonated, neutral monocarboxylic acid species. Intriguingly, the obtained permeability rates indicate an up to 10 times higher probability of passage via AQP9 than given by the fraction of the protonated acid substrate at a certain pH. We generated AQP9 point mutants showing that this effect is independent from properties of the channel interior but caused by the protein surface electrostatics. Monocarboxylic acid-conducting AQPs thus employ a mechanism similar to the family of formate-nitrite transporters for weak monoacids. On a more general basis, our data illustrate semiquantitatively the contribution of surface electrostatics to the interaction of charged molecule substrates or ligands with target proteins, such as channels, transporters, enzymes, or receptors. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Quantum liquid droplets in a mixture of Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Cabrera, C. R.; Tanzi, L.; Sanz, J.; Naylor, B.; Thomas, P.; Cheiney, P.; Tarruell, L.

2018-01-01

Quantum droplets are small clusters of atoms self-bound by the balance of attractive and repulsive forces. Here, we report on the observation of droplets solely stabilized by contact interactions in a mixture of two Bose-Einstein condensates. We demonstrate that they are several orders of magnitude more dilute than liquid helium by directly measuring their size and density via in situ imaging. We show that the droplets are stablized against collapse by quantum fluctuations and that they require a minimum atom number to be stable. Below that number, quantum pressure drives a liquid-to-gas transition that we map out as a function of interaction strength. These ultradilute isotropic liquids remain weakly interacting and constitute an ideal platform to benchmark quantum many-body theories.

Social interactions between live and artificial weakly electric fish: Electrocommunication and locomotor behavior of Mormyrus rume proboscirostris towards a mobile dummy fish

PubMed Central

Kirschbaum, Frank; von der Emde, Gerhard

2017-01-01

Mormyrid weakly electric fish produce short, pulse-type electric organ discharges for actively probing their environment and to communicate with conspecifics. Animals emit sequences of pulse-trains that vary in overall frequency and temporal patterning and can lead to time-locked interactions with the discharge activity of other individuals. Both active electrolocation and electrocommunication are additionally accompanied by stereotypical locomotor patterns. However, the concrete roles of electrical and locomotor patterns during social interactions in mormyrids are not well understood. Here we used a mobile fish dummy that was emitting different types of electrical playback sequences to study following behavior and interaction patterns (electrical and locomotor) between individuals of weakly electric fish. We confronted single individuals of Mormyrus rume proboscirostris with a mobile dummy fish designed to attract fish from a shelter and recruit them into an open area by emitting electrical playbacks of natural discharge sequences. We found that fish were reliably recruited by the mobile dummy if it emitted electrical signals and followed it largely independently of the presented playback patterns. While following the dummy, fish interacted with it spatially by displaying stereotypical motor patterns, as well as electrically, e.g. through discharge regularizations and by synchronizing their own discharge activity to the playback. However, the overall emission frequencies of the dummy were not adopted by the following fish. Instead, social signals based on different temporal patterns were emitted depending on the type of playback. In particular, double pulses were displayed in response to electrical signaling of the dummy and their expression was positively correlated with an animals' rank in the dominance hierarchy. Based on additional analysis of swimming trajectories and stereotypical locomotor behavior patterns, we conclude that the reception and emission of electrical communication signals play a crucial role in mediating social interactions in mormyrid weakly electric fish. PMID:28902915

Lipid membrane-assisted condensation and assembly of amphiphilic Janus particles

DOE PAGES

Chambers, Mariah; Mallory, Stewart Anthony; Malone, Heather; ...

2016-01-01

Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs). Janus particles spontaneously concentrated on the inner leaflet of the GUVs. They exhibited biased orientation and heterogeneous rotational dynamics as revealed by single particle rotationalmore » tracking. The combined experimental and simulation results show that Janus particles concentrate on the lipid membranes due to weak particle–lipid attraction, whereas the biased orientation of particles is driven predominantly by inter-particle interactions. Furthermore, this study demonstrates the potential of using lipid membranes to influence the self-assembly of Janus particles.« less

Robust singlet fission in pentacene thin films with tuned charge transfer interactions.

PubMed

Broch, K; Dieterle, J; Branchi, F; Hestand, N J; Olivier, Y; Tamura, H; Cruz, C; Nichols, V M; Hinderhofer, A; Beljonne, D; Spano, F C; Cerullo, G; Bardeen, C J; Schreiber, F

2018-03-05

Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.

Crowding-facilitated macromolecular transport in attractive micropost arrays.

PubMed

Chien, Fan-Tso; Lin, Po-Keng; Chien, Wei; Hung, Cheng-Hsiang; Yu, Ming-Hung; Chou, Chia-Fu; Chen, Yeng-Long

2017-05-02

Our study of DNA dynamics in weakly attractive nanofabricated post arrays revealed crowding enhances polymer transport, contrary to hindered transport in repulsive medium. The coupling of DNA diffusion and adsorption to the microposts results in more frequent cross-post hopping and increased long-term diffusivity with increased crowding density. We performed Langevin dynamics simulations and found maximum long-term diffusivity in post arrays with gap sizes comparable to the polymer radius of gyration. We found that macromolecular transport in weakly attractive post arrays is faster than in non-attractive dense medium. Furthermore, we employed hidden Markov analysis to determine the transition of macromolecular adsorption-desorption on posts and hopping between posts. The apparent free energy barriers are comparable to theoretical estimates determined from polymer conformational fluctuations.

Effects of dilute substitutional solutes on interstitial carbon in α-Fe: Interactions and associated carbon diffusion from first-principles calculations

NASA Astrophysics Data System (ADS)

Liu, Peitao; Xing, Weiwei; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu

2014-07-01

By means of first-principles calculations coupled with the kinetic Monte Carlo simulations, we have systematically investigated the effects of dilute substitutional solutes on the behaviors of carbon in α-Fe. Our results uncover the following. (i) Without the Fe vacancy the interactions between most solutes and carbon are repulsive due to the strain relief, whereas Mn has a weak attractive interaction with its nearest-neighbor carbon due to the local ferromagnetic coupling effect. (ii) The presence of the Fe vacancy results in attractive interactions of all the solutes with carbon. In particular, the Mn-vacancy pair shows an exceptionally large binding energy of -0.81 eV with carbon. (iii) The alloying addition significantly impacts the atomic-scale concentration distributions and chemical potential of carbon in the Fe matrix. Among them, Mn and Cr increase the carbon chemical potential, whereas Al and Si reduce it. (iv) Within the dilute scale of the alloying solution, the solute concentration- and temperature-dependent carbon diffusivities demonstrate that Mn has a little impact on the carbon diffusion, whereas Cr (Al or Si) remarkably retards the carbon diffusion. Our results provide a certain implication for better understanding the experimental observations related with the carbon solubility limit, carbon microsegregation, and carbide precipitations in the ferritic steels.

Magic tilt angle for stabilizing two-dimensional solitons by dipole-dipole interactions

NASA Astrophysics Data System (ADS)

Chen, Xing-You; Chuang, You-Lin; Lin, Chun-Yan; Wu, Chien-Ming; Li, Yongyao; Malomed, Boris A.; Lee, Ray-Kuang

2017-10-01

In the framework of the Gross-Pitaevskii equation, we study the formation and stability of effectively two-dimensional solitons in dipolar Bose-Einstein condensates (BECs), with dipole moments polarized at an arbitrary angle θ relative to the direction normal to the system's plane. Using numerical methods and the variational approximation, we demonstrate that unstable Townes solitons, created by the contact attractive interaction, may be completely stabilized (with an anisotropic shape) by the dipole-dipole interaction (DDI), in the interval θcr<θ ≤π /2 . The stability boundary θcr weakly depends on the relative strength of the DDI, remaining close to the magic angle θm=arccos(1 /√{3 }) . The results suggest that DDIs provide a generic mechanism for the creation of stable BEC solitons in higher dimensions.

Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions

PubMed Central

Hankiewicz, Ewelina M.; Culcer, Dimitrie

2017-01-01

Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless Dirac fermions in topological insulators and massive Dirac fermions in Weyl semimetal thin films, taking into account both intrinsic and extrinsic spin-orbit interactions. The physics is governed by the complex interplay of the chiral spin texture, quasiparticle mass, and scalar and spin-orbit scattering. We demonstrate that terms linear in the extrinsic spin-orbit scattering are generally present in the Bloch and momentum relaxation times in all topological materials, and the correction to the diffusion constant is linear in the strength of the extrinsic spin-orbit. In topological insulators, which have zero quasiparticle mass, the terms linear in the impurity spin-orbit coupling lead to an observable density dependence in the weak antilocalization correction. They produce substantial qualitative modifications to the magnetoconductivity, differing greatly from the conventional Hikami-Larkin-Nagaoka formula traditionally used in experimental fits, which predicts a crossover from weak localization to antilocalization as a function of the extrinsic spin-orbit strength. In contrast, our analysis reveals that topological insulators always exhibit weak antilocalization. In Weyl semimetal thin films having intermediate to large values of the quasiparticle mass, we show that extrinsic spin-orbit scattering strongly affects the boundary of the weak localization to antilocalization transition. We produce a complete phase diagram for this transition as a function of the mass and spin-orbit scattering strength. Throughout the paper, we discuss implications for experimental work, and, at the end, we provide a brief comparison with transition metal dichalcogenides. PMID:28773167

Effects of surfactant micelles on viscosity and conductivity of poly(ethylene glycol) solutions

NASA Astrophysics Data System (ADS)

Wang, Shun-Cheng; Wei, Tzu-Chien; Chen, Wun-Bin; Tsao, Heng-Kwong

2004-03-01

The neutral polymer-micelle interaction is investigated for various surfactants by viscometry and electrical conductometry. In order to exclude the well-known necklace scenario, we consider aqueous solutions of low molecular weight poly(ethylene glycol) (2-20)×103, whose radial size is comparable to or smaller than micelles. The single-tail surfactants consist of anionic, cationic, and nonionic head groups. It is found that the viscosity of the polymer solution may be increased several times by micelles if weak attraction between a polymer segment and a surfactant exists, ɛ

Unattractive, promiscuous and heavy drinkers: perceptions of women with tattoos.

PubMed

Swami, Viren; Furnham, Adrian

2007-12-01

This study examined social and physical perceptions of blonde and brunette women with different degrees of tattooing. Eighty-four female and 76 male undergraduates rated a series of 16 female line drawings that varied in 2 levels of hair colour and 8 levels of tattooing. Ratings were made for physical attractiveness and sexual promiscuity, as well as estimates of the number of alcohol units consumed on a typical night out. Results showed that tattooed women were rated as less physically attractive, more sexually promiscuous and heavier drinkers than untattooed women, with more negative ratings with increasing number of tattoos. There were also weak interactions between body art and hair colour, with blonde women in general rated more negatively than brunettes. Results are discussed in terms of stereotypes about women who have tattoos and the effects of such stereotypes on well-being.

Quantum liquids get thin

NASA Astrophysics Data System (ADS)

Ferrier-Barbut, Igor; Pfau, Tilman

2018-01-01

A liquid exists when interactions that attract its constituent particles to each other are counterbalanced by a repulsion acting at higher densities. Other characteristics of liquids are short-range correlations and the existence of surface tension (1). Ultracold atom experiments provide a privileged platform with which to observe exotic states of matter, but the densities are far too low to obtain a conventional liquid because the atoms are too far apart to create repulsive forces arising from the Pauli exclusion principle of the atoms' internal electrons. The observation of quantum liquid droplets in an ultracold mixture of two quantum fluids is now reported on page 301 of this issue by Cabrera et al. (2) and a recent preprint by Semeghini et al. (3). Unlike conventional liquids, these liquids arise from a weak attraction and repulsive many-body correlations in the mixtures.

Kinetic Assembly of Near-IR Active Gold Nanoclusters using Weakly Adsorbing Polymers to Control Size

PubMed Central

Tam, Jasmine M.; Murthy, Avinash K.; Ingram, Davis R.; Nguyen, Robin; Sokolov, Konstantin V.; Johnston, Keith P.

2013-01-01

Clusters of metal nanoparticles with an overall size less than 100 nm and high metal loadings for strong optical functionality, are of interest in various fields including microelectronics, sensors, optoelectronics and biomedical imaging and therapeutics. Herein we assemble ~5 nm gold particles into clusters with controlled size, as small as 30 nm and up to 100 nm, which contain only small amounts of polymeric stabilizers. The assembly is kinetically controlled with weakly adsorbing polymers, PLA(2K)-b-PEG(10K)-b-PLA(2K) or PEG (MW = 3350), by manipulating electrostatic, van der Waals (VDW), steric, and depletion forces. The cluster size and optical properties are tuned as a function of particle volume fractions and polymer/gold ratios to modulate the interparticle interactions. The close spacing between the constituent gold nanoparticles and high gold loadings (80–85% w/w gold) produce a strong absorbance cross section of ~9×10−15 m2 in the NIR at 700 nm. This morphology results from VDW and depletion attractive interactions that exclude the weakly adsorbed polymeric stabilizer from the cluster interior. The generality of this kinetic assembly platform is demonstrated for gold nanoparticles with a range of surface charges from highly negative to neutral, with the two different polymers. PMID:20361735

A simulation study of sperm motility hydrodynamics near fish eggs and spheres.

PubMed

Ishimoto, Kenta; Cosson, Jacky; Gaffney, Eamonn A

2016-01-21

For teleost fish fertilisation, sperm must proceed through a small opening on the egg surface, referred to as the micropyle. In this paper, we have used boundary element simulations to explore whether the hydrodynamic attraction between sperm and a fish egg can be a sperm guidance cue. Hydrodynamical egg-sperm interactions alone do not increase the chances of an egg encounter, nor do they induce surface swimming for virtual turbot fish sperm across smooth spheres with a diameter of 1mm, which is representative of a turbot fish egg. When a repulsive surface force between the virtual turbot sperm and the egg is introduced, as motivated by surface charge and van-der-Waals interactions for instance, we find that extended surface swimming of the virtual sperm across a model turbot egg occurs, but ultimately the sperm escapes from the egg. This is due to the small exit angle of the scattering associated with the initial sperm-egg interaction at the egg surface, leading to a weak drift away from the egg, in combination with a weak hydrodynamical attraction between both gametes, though the latter is not sufficient to prevent eventual escape. The resulting transience is not observed experimentally but is a detailed quantitative difference between theory and observation in that stable surface swimming is predicted for eggs with radii larger than about 1.8mm. Regardless, the extended sperm swimming trajectory across the egg constitutes a two-dimensional search for the micropyle and thus the egg is consistently predicted to provide a guidance cue for sperm once they are sufficiently close. In addition, the observation that the virtual turbot sperm swims stably next to a flat plane given repulsive surface interactions, but does not swim stably adjacent to a turbot-sized egg, which is extremely large by sperm-lengthscales, also highlights that the stability of sperm swimming near a boundary is very sensitive to geometry. Copyright © 2015 Elsevier Ltd. All rights reserved.

Interpersonal Attraction in Dyads and Groups: Effects of the Hearts of the Beholder and the Beheld.

PubMed

Malloy, Thomas E

2018-04-01

Dyadic interpersonal attraction (IA) was studied within groups of very highly acquainted family members, friends and co-workers. IA was determined by the perceiver (i.e., the heart of the beholder), the target (i.e., the heart of the beheld), and in specific dyads, by the unique combination of the two. The consistency of one's attraction to others and others' attraction to the person across groups were addressed using the key person design . Attraction to a person in one group was independent of attraction to that person in another, although people predicted that members of different groups were similarly attracted to them. A new model (ARRMA) was specified to simultaneously study assumed reciprocity, actual reciprocity, and metaperception accuracy of attraction (i.e., accurate predictions of others' attraction to oneself). Assumed reciprocity of IA was substantial at the individual and dyadic levels. Reciprocity of attraction at the individual level, a heretofore unconfirmed "plausible hypothesis" (Newcomb, 1979), was supported; dyadic reciprocity was weak. Meta-accuracy of IA was observed among individuals but was weak in dyads. Perceived interpersonal similarity predicted IA among individuals and in specific dyads. Considering dyadic attraction within and between groups, and the use of componential analysis permitted the specification of new IA phenomena and resolved a long standing theoretical problem regarding the reciprocity of attraction.

Effects of a hyperonic many-body force on BΛ values of hypernuclei

NASA Astrophysics Data System (ADS)

Isaka, M.; Yamamoto, Y.; Rijken, Th. A.

2017-04-01

The stiff equation of state (EoS) giving the neutron-star mass of 2 M⊙ suggests the existence of strongly repulsive many-body effects (MBE) not only in nucleon channels but also in hyperonic ones. As a specific model for MBE, the repulsive multi-Pomeron exchange potential (MPP) is added to the two-body interaction together with the phenomenological three-body attraction. For various versions of the Nijmegen interaction models, the MBE parts are determined so as to reproduce the observed data of BΛ. The mass dependence of BΛ values is shown to be reproduced well by adding MBE to the strong MPP repulsion, assuring the stiff EoS of hyperon-mixed neutron-star matter, in which P -state components of the adopted interaction model lead to almost vanishing contributions. The nuclear matter Λ N G -matrix interactions are derived and used in Λ hypernuclei on the basis of the averaged-density approximation (ADA). The BΛ values of hypernuclei with 9 ≤A ≤59 are analyzed in the framework of antisymmetrized molecular dynamics with use of the two types of Λ N G -matrix interactions including strong and weak MPP repulsions. The calculated values of BΛ reproduce the experimental data well within a few hundred keV. The values of BΛ in p states also can be reproduced well, when the ADA is modified to be suitable also for weakly bound Λ states.

Long-range magnetic order and interchain interactions in the S = 2 chain system MnCl 3 (bpy)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fishman, Randy S.; Shinozaki, Shin-ichi; Okutani, Akira

Here,more » a compound with very weakly interacting chains, MnCl 3(bpy), has attracted a great deal of attention as a possible S = 2 Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5 K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5 THz and magnetic fields up to 50 T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12 meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3 meV) is significantly stronger than previously reported. The excitation spectrum of this S = 2 compound is well described by a 1/S expansion about the classical limit.« less

Long-range magnetic order and interchain interactions in the S = 2 chain system MnCl 3 (bpy)

DOE PAGES

Fishman, Randy S.; Shinozaki, Shin-ichi; Okutani, Akira; ...

2016-09-28

Here,more » a compound with very weakly interacting chains, MnCl 3(bpy), has attracted a great deal of attention as a possible S = 2 Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5 K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5 THz and magnetic fields up to 50 T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12 meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3 meV) is significantly stronger than previously reported. The excitation spectrum of this S = 2 compound is well described by a 1/S expansion about the classical limit.« less

Quantum chaos and breaking of all anti-unitary symmetries in Rydberg excitons.

PubMed

Aßmann, Marc; Thewes, Johannes; Fröhlich, Dietmar; Bayer, Manfred

2016-07-01

Symmetries are the underlying principles of fundamental interactions in nature. Chaos in a quantum system may emerge from breaking these symmetries. Compared to vacuum, crystals are attractive for studying quantum chaos, as they not only break spatial isotropy, but also lead to novel quasiparticles with modified interactions. Here we study yellow Rydberg excitons in cuprous oxide which couple strongly to the vacuum light field and interact significantly with crystal phonons, leading to inversion symmetry breaking. In a magnetic field, time-reversal symmetry is also broken and the exciton states show a complex splitting pattern, resulting in quadratic level repulsion for small splittings. In contrast to atomic chaotic systems in a magnetic field, which show only a linear level repulsion, this is a signature of a system where all anti-unitary symmetries are broken simultaneously. This behaviour can otherwise be found only for the electro-weak interaction or engineered billiards.

Cell death versus cell survival instructed by supramolecular cohesion of nanostructures

NASA Astrophysics Data System (ADS)

Newcomb, Christina J.; Sur, Shantanu; Ortony, Julia H.; Lee, One-Sun; Matson, John B.; Boekhoven, Job; Yu, Jeong Min; Schatz, George C.; Stupp, Samuel I.

2014-02-01

Many naturally occurring peptides containing cationic and hydrophobic domains have evolved to interact with mammalian cell membranes and have been incorporated into materials for non-viral gene delivery, cancer therapy or treatment of microbial infections. Their electrostatic attraction to the negatively charged cell surface and hydrophobic interactions with the membrane lipids enable intracellular delivery or cell lysis. Although the effects of hydrophobicity and cationic charge of soluble molecules on the cell membrane are well known, the interactions between materials with these molecular features and cells remain poorly understood. Here we report that varying the cohesive forces within nanofibres of supramolecular materials with nearly identical cationic and hydrophobic structure instruct cell death or cell survival. Weak intermolecular bonds promote cell death through disruption of lipid membranes, while materials reinforced by hydrogen bonds support cell viability. These findings provide new strategies to design biomaterials that interact with the cell membrane.

Interaction between water-soluble rhodium complex RhCl(CO)(TPPTS)₂ and surfactants probed by spectroscopic methods.

PubMed

Zhou, Li-Mei; Guo, Cai-Hong; Fu, Hai-Yan; Jiang, Xiao-Hui; Chen, Hua; Li, Rui-Xiang; Li, Xian-Jun

2012-07-01

The interactions of rhodium complex RhCl(CO)(TPPTS)(2) [TPPTS=P(m-C(6)H(4)SO(3)Na)(3)] with cationic, nonionic, and anionic surfactants have been investigated by UV-vis, fluorescence and (1)H NMR measurements. The presence of four different species of RhCl(CO)(TPPTS)(2) in cationic cetyltrimethylammonium (CTAB) solution has been demonstrated: free rhodium complex, rhodium complex bound to CTAB monomer, rhodium complex bound to CTAB premicelles, rhodium complex bound to CTAB micelles. The spectroscopy data show that RhCl(CO)(TPPTS)(2) can adsorb on the interface of cationic CTAB micelles by strong electrostatic attraction, weakly bind to the nonionic polyoxyethylene (20) sorbitan monolaurate (Tween 20) micelles by hydrophobic interaction, and does not interact with anion sodium dodecyl sulfate (SDS) micelles due to the strong electrostatic repulsion. Copyright © 2012 Elsevier B.V. All rights reserved.

Numerical simulations - Some results for the 2- and 3-D Hubbard models and a 2-D electron phonon model

NASA Technical Reports Server (NTRS)

Scalapino, D. J.; Sugar, R. L.; White, S. R.; Bickers, N. E.; Scalettar, R. T.

1989-01-01

Numerical simulations on the half-filled three-dimensional Hubbard model clearly show the onset of Neel order. Simulations of the two-dimensional electron-phonon Holstein model show the competition between the formation of a Peierls-CDW state and a superconducting state. However, the behavior of the partly filled two-dimensional Hubbard model is more difficult to determine. At half-filling, the antiferromagnetic correlations grow as T is reduced. Doping away from half-filling suppresses these correlations, and it is found that there is a weak attractive pairing interaction in the d-wave channel. However, the strength of the pair field susceptibility is weak at the temperatures and lattice sizes that have been simulated, and the nature of the low-temperature state of the nearly half-filled Hubbard model remains open.

Quantum Fluctuations in Quasi-One-Dimensional Dipolar Bose-Einstein Condensates

NASA Astrophysics Data System (ADS)

Edler, D.; Mishra, C.; Wächtler, F.; Nath, R.; Sinha, S.; Santos, L.

2017-08-01

Recent experiments have revealed that beyond-mean-field corrections are much more relevant in weakly interacting dipolar condensates than in their nondipolar counterparts. We show that in quasi-one-dimensional geometries quantum corrections in dipolar and nondipolar condensates are strikingly different due to the peculiar momentum dependence of the dipolar interactions. The energy correction of the condensate presents not only a modified density dependence, but it may even change from attractive to repulsive at a critical density due to the surprising role played by the transversal directions. The anomalous quantum correction translates into a strongly modified physics for quantum-stabilized droplets and dipolar solitons. Moreover, and for similar reasons, quantum corrections of three-body correlations, and hence of three-body losses, are strongly modified by the dipolar interactions. This intriguing physics can be readily probed in current experiments with magnetic atoms.

Quantum Fluctuations in Quasi-One-Dimensional Dipolar Bose-Einstein Condensates.

PubMed

Edler, D; Mishra, C; Wächtler, F; Nath, R; Sinha, S; Santos, L

2017-08-04

Recent experiments have revealed that beyond-mean-field corrections are much more relevant in weakly interacting dipolar condensates than in their nondipolar counterparts. We show that in quasi-one-dimensional geometries quantum corrections in dipolar and nondipolar condensates are strikingly different due to the peculiar momentum dependence of the dipolar interactions. The energy correction of the condensate presents not only a modified density dependence, but it may even change from attractive to repulsive at a critical density due to the surprising role played by the transversal directions. The anomalous quantum correction translates into a strongly modified physics for quantum-stabilized droplets and dipolar solitons. Moreover, and for similar reasons, quantum corrections of three-body correlations, and hence of three-body losses, are strongly modified by the dipolar interactions. This intriguing physics can be readily probed in current experiments with magnetic atoms.

Edible oil structures at low and intermediate concentrations. I. Modeling, computer simulation, and predictions for X ray scattering

NASA Astrophysics Data System (ADS)

Pink, David A.; Quinn, Bonnie; Peyronel, Fernanda; Marangoni, Alejandro G.

2013-12-01

Triacylglycerols (TAGs) are biologically important molecules which form the recently discovered highly anisotropic crystalline nanoplatelets (CNPs) and, ultimately, the large-scale fat crystal networks in edible oils. Identifying the hierarchies of these networks and how they spontaneously self-assemble is important to understanding their functionality and oil binding capacity. We have modelled CNPs and studied how they aggregate under the assumption that all CNPs are present before aggregation begins and that their solubility in the liquid oil is very low. We represented CNPs as rigid planar arrays of spheres with diameter ≈50 nm and defined the interaction between spheres in terms of a Hamaker coefficient, A, and a binding energy, VB. We studied three cases: weak binding, |VB|/kBT ≪ 1, physically realistic binding, VB = Vd(R, Δ), so that |VB|/kBT ≈ 1, and Strong binding with |VB|/kBT ≫ 1. We divided the concentration of CNPs, ϕ, with 0≤ϕ= 10-2 (solid fat content) ≤1, into two regions: Low and intermediate concentrations with 0<ϕ<0.25 and high concentrations with 0.25 < ϕ and considered only the first case. We employed Monte Carlo computer simulation to model CNP aggregation and analyzed them using static structure functions, S(q). We found that strong binding cases formed aggregates with fractal dimension, D, 1.7≤D ≤1.8, in accord with diffusion limited cluster-cluster aggregation (DLCA) and weak binding formed aggregates with D =3, indicating a random distribution of CNPs. We found that models with physically realistic intermediate binding energies formed linear multilayer stacks of CNPs (TAGwoods) with fractal dimension D =1 for ϕ =0.06,0.13, and 0.22. TAGwood lengths were greater at lower ϕ than at higher ϕ, where some of the aggregates appeared as thick CNPs. We increased the spatial scale and modelled the TAGwoods as rigid linear arrays of spheres of diameter ≈500 nm, interacting via the attractive van der Waals interaction. We found that TAGwoods aggregated via DLCA into clusters with fractal dimension D =1.7-1.8. As the simulations were run further, TAGwoods relaxed their positions in order to maximize the attractive interaction making the process look like reaction limited cluster-cluster aggregation with the fractal dimension increasing to D =2.0-2.1. For higher concentrations of CNPs, many TAGwood clusters were formed and, because of their weak interactions, were distributed randomly with D =3.0. We summarize the hierarchy of structures and make predictions for X-ray scattering.

Casimir-Polder shifts on quantum levitation states

NASA Astrophysics Data System (ADS)

Crépin, P.-P.; Dufour, G.; Guérout, R.; Lambrecht, A.; Reynaud, S.

2017-03-01

An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schrödinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall, and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting, respectively, as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose an approximate treatment which is precise enough to discuss spectroscopy experiments aimed at tests of the weak-equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.

Modeling the Interaction between AFM Tips and Pinned Surface Nanobubbles.

PubMed

Guo, Zhenjiang; Liu, Yawei; Xiao, Qianxiang; Schönherr, Holger; Zhang, Xianren

2016-01-26

Although the morphology of surface nanobubbles has been studied widely with different AFM modes, AFM images may not reflect the real shapes of the nanobubbles due to AFM tip-nanobubble interactions. In addition, the interplay between surface nanobubble deformation and induced capillary force has not been well understood in this context. In our work we used constraint lattice density functional theory to investigate the interaction between AFM tips and pinned surface nanobubbles systematically, especially concentrating on the effects of tip hydrophilicity and shape. For a hydrophilic tip contacting a nanobubble, its hydrophilic nature facilitates its departure from the bubble surface, displaying a weak and intermediate-range attraction. However, when the tip squeezes the nanobubble during the approach process, the nanobubble shows an elastic effect that prevents the tip from penetrating the bubble, leading to a strong nanobubble deformation and repulsive interactions. On the contrary, a hydrophobic tip can easily pierce the vapor-liquid interface of the nanobubble during the approach process, leading to the disappearance of the repulsive force. In the retraction process, however, the adhesion between the tip and the nanobubble leads to a much stronger lengthening effect on nanobubble deformation and a strong long-range attractive force. The trends of force evolution from our simulations agree qualitatively well with recent experimental AFM observations. This favorable agreement demonstrates that our model catches the main intergradient of tip-nanobubble interactions for pinned surface nanobubbles and may therefore provide important insight into how to design minimally invasive AFM experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahalik, J. P.; Sumpter, Bobby G.; Kumar, Rajeev

In this paper, we use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on nonadsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration-dependent pairwise interactions, and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the polymer segments can lead to attractive interactions between the brushes at intermediatemore » separation distances. Finally, because classical theory of polymer brushes based on the strong stretching limit (SSL) and the standard self-consistent field theory (SCFT) simulations using the Flory’s χ parameter always predicts repulsive interactions at all separations, our work highlights the importance of dipolar interactions in tailoring and accurately predicting forces between polar polymeric interfaces in contact with each other.« less

Rationalizing Tight Ligand Binding through Cooperative Interaction Networks

PubMed Central

2011-01-01

Small modifications of the molecular structure of a ligand sometimes cause strong gains in binding affinity to a protein target, rendering a weakly active chemical series suddenly attractive for further optimization. Our goal in this study is to better rationalize and predict the occurrence of such interaction hot-spots in receptor binding sites. To this end, we introduce two new concepts into the computational description of molecular recognition. First, we take a broader view of noncovalent interactions and describe protein–ligand binding with a comprehensive set of favorable and unfavorable contact types, including for example halogen bonding and orthogonal multipolar interactions. Second, we go beyond the commonly used pairwise additive treatment of atomic interactions and use a small world network approach to describe how interactions are modulated by their environment. This approach allows us to capture local cooperativity effects and considerably improves the performance of a newly derived empirical scoring function, ScorpionScore. More importantly, however, we demonstrate how an intuitive visualization of key intermolecular interactions, interaction networks, and binding hot-spots supports the identification and rationalization of tight ligand binding. PMID:22087588

Annihilation physics of exotic galactic dark matter particles

NASA Technical Reports Server (NTRS)

Stecker, F. W.

1990-01-01

Various theoretical arguments make exotic heavy neutral weakly interacting fermions, particularly those predicted by supersymmetry theory, attractive candidates for making up the large amount of unseen gravitating mass in galactic halos. Such particles can annihilate with each other, producing secondary particles of cosmic-ray energies, among which are antiprotons, positrons, neutrinos, and gamma-rays. Spectra and fluxes of these annihilation products can be calculated, partly by making use of positron electron collider data and quantum chromodynamic models of particle production derived therefrom. These spectra may provide detectable signatures of exotic particle remnants of the big bang.

On absence of bound states for weakly attractive δ'-interactions supported on non-closed curves in ℝ2

NASA Astrophysics Data System (ADS)

Jex, Michal; Lotoreichik, Vladimir

2016-02-01

Let Λ ⊂ ℝ2 be a non-closed piecewise-C1 curve, which is either bounded with two free endpoints or unbounded with one free endpoint. Let u±|Λ ∈ L2(Λ) be the traces of a function u in the Sobolev space H1(ℝ2∖Λ) onto two faces of Λ. We prove that for a wide class of shapes of Λ the Schrödinger operator Hω Λ with δ'-interaction supported on Λ of strength ω ∈ L∞(Λ; ℝ) associated with the quadratic form H 1 ( R 2 ∖ Λ ) ∋ u ↦ ∫ R 2 |" separators=" ∇ u | 2 d x - ∫ Λ ω |" separators=" u + | Λ - u - | Λ | 2 d s has no negative spectrum provided that ω is pointwise majorized by a strictly positive function explicitly expressed in terms of Λ. If, additionally, the domain ℝ2∖Λ is quasi-conical, we show that σ ( Hω Λ ) = [ 0 , + ∞ ) . For a bounded curve Λ in our class and non-varying interaction strength ω ∈ ℝ, we derive existence of a constant ω∗ > 0 such that σ ( Hω Λ ) = [ 0 , + ∞ ) for all ω ∈ (-∞, ω∗]; informally speaking, bound states are absent in the weak coupling regime.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cada, Glenn F; Bevelhimer, Mark S

The development of hydrokinetic (HK) energy projects is under consideration at over 150 sites in large rivers in the United States, including the Mississippi, Ohio, Tennessee, and Atchafalaya Rivers. These waterbodies support numerous fish species that might interact with the HK projects in a variety of ways, e.g., by attraction to or avoidance of project structures. Although many fish species inhabit these rivers (about 172 species in the Mississippi River alone), not all of them will encounter the HK projects. Some species prefer low-velocity, backwater habitats rather than the high-velocity, main channel areas that would be the best sites formore » HK. Other, riverbank-oriented species are weak swimmers or too small to inhabit the main channel for significant periods of time. Some larger, main channel fish species are not known to be attracted to structures. Based on a consideration of habitat preferences, size/swim speed, and behavior, fish species that are most likely to be attracted to HK structures in the main channel include carps, suckers, catfish, white bass, striped bass, smallmouth bass, spotted bass, and sauger. Proper siting of the project in order to avoid sensitive fish populations, backwater and fish nursery habitat areas, and fish migration corridors will likely minimize concerns about fish attraction to or avoidance of HK structures.« less

Effects of lengthscales and attractions on the collapse of hydrophobic polymers in water

PubMed Central

Athawale, Manoj V.; Goel, Gaurav; Ghosh, Tuhin; Truskett, Thomas M.; Garde, Shekhar

2007-01-01

We present results from extensive molecular dynamics simulations of collapse transitions of hydrophobic polymers in explicit water focused on understanding effects of lengthscale of the hydrophobic surface and of attractive interactions on folding. Hydrophobic polymers display parabolic, protein-like, temperature-dependent free energy of unfolding. Folded states of small attractive polymers are marginally stable at 300 K and can be unfolded by heating or cooling. Increasing the lengthscale or decreasing the polymer–water attractions stabilizes folded states significantly, the former dominated by the hydration contribution. That hydration contribution can be described by the surface tension model, ΔG = γ(T)ΔA, where the surface tension, γ, is lengthscale-dependent and decreases monotonically with temperature. The resulting variation of the hydration entropy with polymer lengthscale is consistent with theoretical predictions of Huang and Chandler [Huang DM, Chandler D (2000) Proc Natl Acad Sci USA 97:8324–8327] that explain the blurring of entropy convergence observed in protein folding thermodynamics. Analysis of water structure shows that the polymer–water hydrophobic interface is soft and weakly dewetted, and is characterized by enhanced interfacial density fluctuations. Formation of this interface, which induces polymer folding, is strongly opposed by enthalpy and favored by entropy, similar to the vapor–liquid interface. PMID:17215352

Glass transition temperature of polymer nano-composites with polymer and filler interactions

NASA Astrophysics Data System (ADS)

Hagita, Katsumi; Takano, Hiroshi; Doi, Masao; Morita, Hiroshi

2012-02-01

We systematically studied versatile coarse-grained model (bead spring model) to describe filled polymer nano-composites for coarse-grained (Kremer-Grest model) molecular dynamics simulations. This model consists of long polymers, crosslink, and fillers. We used the hollow structure as the filler to describe rigid spherical fillers with small computing costs. Our filler model consists of surface particles of icosahedra fullerene structure C320 and a repulsive force from the center of the filler is applied to the surface particles in order to make a sphere and rigid. The filler's diameter is 12 times of beads of the polymers. As the first test of our model, we study temperature dependence of volumes of periodic boundary conditions under constant pressures through NPT constant Andersen algorithm. It is found that Glass transition temperature (Tg) decrease with increasing filler's volume fraction for the case of repulsive interaction between polymer and fillers and Tg weakly increase for attractive interaction.

Some aspects of the scientific significance of high energy gamma ray astrophysics

NASA Technical Reports Server (NTRS)

Fichtel, Carl E.

1991-01-01

The attraction of high energy gamma-ray astronomy lies in this radiation relating directly to those processes in astrophysical situations which deviate most from thermo-dynamic equilibrium. Some examples of these phenomena which are known to or expected to emit gamma rays are cosmic rays as they interact in intergalactic space, the high energy particles in the magnetic fields of neutron stars, the death of a black hole, the explosion and residual of a supernova, lumps of Weakly Interacting Massive Particles, energetic solar particles interacting near the sun, and very high energy particles in the extreme conditions associated with active galaxies. Although the intensities are known to be low as seen near the earth, a partially compensating characteristic is that the very penetrating nature of high energy gamma rays increases the probability that they can escape from their origin and reach the solar system.

The effects of particle shape, size, and interaction on colloidal glasses and gels

NASA Astrophysics Data System (ADS)

Kramb, Ryan C.

Using multiple step seeded emulsion polymerization reactions, colloid particles of tunable shape are synthesized from polystyrene. In all, four particle shapes are studied referred to as spheres (S), heteronuclear dicolloids (hDC), symmetric homonuclear dicolloids (sDC), and tricolloids (TC). Two size ranges of particles are studied with approximate diameters in the range of 200-300nm and 1.1-1.3mum. The solvent ionic strength is varied from 10 -3M to 1M resulting in particle interaction potentials that range from repulsive to attractive. The effect of anisotropic shape is found to increase the glass transition volume fraction (φg) in good agreement with activated naive Mode Coupling Theory (nMCT) calculations. Differences in φg and the linear elastic modulus (G0') due to particle shape can be understood in terms of the Random Close Packed volume fraction (φRCP ) for each shape; φRCP- φg is a constant. In addition, a reentrant phase diagram is found for S and sDC particles with a maximum in the fluid state volume fraction found at weakly attractive interaction potential, in agreement well with theoretical calculations. Nonlinear rheology and yielding behavior of repulsive and attractive spheres and anisotropic particles are examined and understood in terms of barriers constraining motion. The barriers are due to interparticle bonds or cages constraining translational or rotational motion. Yield stress has similar volume fraction dependence as G 0' and a similar framework is used to understand differences due to particle shape and interaction. For larger particles, the effects of shape and interaction are studied with respect to dynamic yielding and shear thickening. The dynamic yield stress is found to increase with volume fraction while the stress at thickening is constant. The intersection of these indicates a possible jamming point below φRCP.

Effect of cation size and charge on the interaction between silica surfaces in 1:1, 2:1, and 3:1 aqueous electrolytes.

PubMed

Dishon, Matan; Zohar, Ohad; Sivan, Uri

2011-11-01

Application of two complementary AFM measurements, force vs separation and adhesion force, reveals the combined effects of cation size and charge (valency) on the interaction between silica surfaces in three 1:1, three 2:1, and three 3:1 metal chloride aqueous solutions of different concentrations. The interaction between the silica surfaces in 1:1 and 2:1 salt solutions is fully accounted for by ion-independent van der Waals (vdW) attraction and electric double-layer repulsion modified by cation specific adsorption to the silica surfaces. The deduced ranking of mono- and divalent cation adsorption capacity (adsorbability) to silica, Mg(2+) < Ca(2+) < Na(+) < Sr(2+) < K(+) < Cs(+), follows cation bare size as well as cation solvation energy but does not correlate with hydrated ionic radius or with volume or surface ionic charge density. In the presence of 3:1 salts, the coarse phenomenology of the force between the silica surfaces as a function of salt concentration resembles that in 1:1 and 2:1 electrolytes. Nevertheless, two fundamental differences should be noticed. First, the attraction between the silica surfaces is too large to be attributed solely to vdW force, hence implying an additional attraction mechanism or gross modification of the conventional vdW attraction. Second, neutralization of the silica surfaces occurs at trivalent cation concentrations that are 3 orders of magnitude smaller than those characterizing surface neutralization by mono- and divalent cations. Consequently, when trivalent cations are added to our cation adsorbability series the correlation with bare ion size breaks down abruptly. The strong adsorbability of trivalent cations to silica contrasts straightforward expectations based on ranking of the cationic solvation energies, thus suggesting a different adsorption mechanism which is inoperative or weak for mono- and divalent cations.

Interactive molecular dynamics

NASA Astrophysics Data System (ADS)

Schroeder, Daniel V.

2015-03-01

Physics students now have access to interactive molecular dynamics simulations that can model and animate the motions of hundreds of particles, such as noble gas atoms, that attract each other weakly at short distances but repel strongly when pressed together. Using these simulations, students can develop an understanding of forces and motions at the molecular scale, nonideal fluids, phases of matter, thermal equilibrium, nonequilibrium states, the Boltzmann distribution, the arrow of time, and much more. This article summarizes the basic features and capabilities of such a simulation, presents a variety of student exercises using it at the introductory and intermediate levels, and describes some enhancements that can further extend its uses. A working simulation code, in html5 and javascript for running within any modern Web browser, is provided as an online supplement.

Diffusion within the cytoplasm: a mesoscale model of interacting macromolecules.

PubMed

Trovato, Fabio; Tozzini, Valentina

2014-12-02

Recent experiments carried out in the dense cytoplasm of living cells have highlighted the importance of proteome composition and nonspecific intermolecular interactions in regulating macromolecule diffusion and organization. Despite this, the dependence of diffusion-interaction on physicochemical properties such as the degree of poly-dispersity and the balance between steric repulsion and nonspecific attraction among macromolecules was not systematically addressed. In this work, we study the problem of diffusion-interaction in the bacterial cytoplasm, combining theory and experimental data to build a minimal coarse-grained representation of the cytoplasm, which also includes, for the first time to our knowledge, the nucleoid. With stochastic molecular-dynamics simulations of a virtual cytoplasm we are able to track the single biomolecule motion, sizing from 3 to 80 nm, on submillisecond-long trajectories. We demonstrate that the size dependence of diffusion coefficients, anomalous exponents, and the effective viscosity experienced by biomolecules in the cytoplasm is fine-tuned by the intermolecular interactions. Accounting only for excluded volume in these potentials gives a weaker size-dependence than that expected from experimental data. On the contrary, adding nonspecific attraction in the range of 1-10 thermal energy units produces a stronger variation of the transport properties at growing biopolymer sizes. Normal and anomalous diffusive regimes emerge straightforwardly from the combination of high macromolecular concentration, poly-dispersity, stochasticity, and weak nonspecific interactions. As a result, small biopolymers experience a viscous cytoplasm, while the motion of big ones is jammed because the entanglements produced by the network of interactions and the entropic effects caused by poly-dispersity are stronger. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Quantum chemical investigation of attractive non-covalent interactions between halomethanes and rare gases.

PubMed

McAllister, Linda J; Bruce, Duncan W; Karadakov, Peter B

2012-11-01

The interaction between rare gas atoms and trifluoromethylhalides and iodomethane is investigated using ab initio and density functional theory (DFT) methods: MP2, CCSD, B3LYP, M06, M06-L, M06-2X, M06-HF, X3LYP, PBE, B97-D, B3LYP-D3, and M06-L-D3, in combination with the aug-cc-pVTZ and aug-cc-pVTZ-PP basis sets. A weakly attractive interaction is observed for all complexes, whose strength increases as the rare gas and halogen bond donor become more polarizable, and as the group bound to the halogen bond donor becomes more electron-withdrawing. The separation between iodine and krypton in the complex CF(3)I···Kr, calculated at the MP2 and B3LYP-D3 levels of theory, agrees very well with recent experimental results (Stephens, S. L.; Walker, N. R.; Legon, A. C. J. Chem. Phys. 2011, 135, 224309). Analysis of the ability of theoretical methods to account for the dispersion interaction present in these complexes leads to the conclusion that MP2 and B3LYP-D3, which produce very similar results, are the better performing methods, followed by B97-D and the M06 suite of functionals; the popular B3LYP as well as X3LYP perform poorly and significantly underestimate the interaction strength. The orbitals responsible for the interaction are identified through Edmiston-Ruedenberg localization; it is shown that, by combining the key orbitals, it is possible to observe a molecular orbital picture of a σ-hole interaction.

Omega-Omega interaction on the Lattice

NASA Astrophysics Data System (ADS)

Yamada, Masanori; Halqcd Collaboration

2014-09-01

We report our results of central potential between two Omega baryons from 2+1 flavor full Lattice QCD simulation. In the past studies, there is a possibility that some decouplet baryons have a bound state. However, almost all decuplet baryons are unstable due to decays via the strong interaction. An exception is the Omega decuplte baryon, which is stable against the strong decays, so its interaction is suitable to be investigated. It is, however, still difficult to investigate the Omega-Omega interaction experimentally due to its short-life time via weak decays. Therefore, the lattice QCD study for the Omega-Omega interaction is necessary and important. We present results obtained by the extension of the HAL QCD method to the system of two decuplet baryons. Our numerical results are obtained from 2+1 flavor full QCD gauge configurations at L ~ 2 . 9 fm mπ ~ 701 MeV and mΩ ~ 1966 MeV, generated by the PACS-CS Collaboration. We find that the Omega-Omega interaction is strong attractive, but it's not strong enough to make a bound state at out simulation set up.

Molecular-scale hydrophobic interactions between hard-sphere reference solutes are attractive and endothermic.

PubMed

Chaudhari, Mangesh I; Holleran, Sinead A; Ashbaugh, Henry S; Pratt, Lawrence R

2013-12-17

The osmotic second virial coefficients, B2, for atomic-sized hard spheres in water are attractive (B2 < 0) and become more attractive with increasing temperature (ΔB2/ΔT < 0) in the temperature range 300 K ≤ T ≤ 360 K. Thus, these hydrophobic interactions are attractive and endothermic at moderate temperatures. Hydrophobic interactions between atomic-sized hard spheres in water are more attractive than predicted by the available statistical mechanical theory. These results constitute an initial step toward detailed molecular theory of additional intermolecular interaction features, specifically, attractive interactions associated with hydrophobic solutes.

Normal modes of weak colloidal gels

NASA Astrophysics Data System (ADS)

Varga, Zsigmond; Swan, James W.

2018-01-01

The normal modes and relaxation rates of weak colloidal gels are investigated in calculations using different models of the hydrodynamic interactions between suspended particles. The relaxation spectrum is computed for freely draining, Rotne-Prager-Yamakawa, and accelerated Stokesian dynamics approximations of the hydrodynamic mobility in a normal mode analysis of a harmonic network representing several colloidal gels. We find that the density of states and spatial structure of the normal modes are fundamentally altered by long-ranged hydrodynamic coupling among the particles. Short-ranged coupling due to hydrodynamic lubrication affects only the relaxation rates of short-wavelength modes. Hydrodynamic models accounting for long-ranged coupling exhibit a microscopic relaxation rate for each normal mode, λ that scales as l-2, where l is the spatial correlation length of the normal mode. For the freely draining approximation, which neglects long-ranged coupling, the microscopic relaxation rate scales as l-γ, where γ varies between three and two with increasing particle volume fraction. A simple phenomenological model of the internal elastic response to normal mode fluctuations is developed, which shows that long-ranged hydrodynamic interactions play a central role in the viscoelasticity of the gel network. Dynamic simulations of hard spheres that gel in response to short-ranged depletion attractions are used to test the applicability of the density of states predictions. For particle concentrations up to 30% by volume, the power law decay of the relaxation modulus in simulations accounting for long-ranged hydrodynamic interactions agrees with predictions generated by the density of states of the corresponding harmonic networks as well as experimental measurements. For higher volume fractions, excluded volume interactions dominate the stress response, and the prediction from the harmonic network density of states fails. Analogous to the Zimm model in polymer physics, our results indicate that long-ranged hydrodynamic interactions play a crucial role in determining the microscopic dynamics and macroscopic properties of weak colloidal gels.

A quasichemical approach for protein-cluster free energies in dilute solution

NASA Astrophysics Data System (ADS)

Young, Teresa M.; Roberts, Christopher J.

2007-10-01

Reversible formation of protein oligomers or small clusters is a key step in processes such as protein polymerization, fibril formation, and protein phase separation from dilute solution. A straightforward, statistical mechanical approach to accurately calculate cluster free energies in solution is presented using a cell-based, quasichemical (QC) approximation for the partition function of proteins in an implicit solvent. The inputs to the model are the protein potential of mean force (PMF) and the corresponding subcell degeneracies up to relatively low particle densities. The approach is tested using simple two and three dimensional lattice models in which proteins interact with either isotropic or anisotropic nearest-neighbor attractions. Comparison with direct Monte Carlo simulation shows that cluster probabilities and free energies of oligomer formation (ΔGi0) are quantitatively predicted by the QC approach for protein volume fractions ˜10-2 (weight/volume concentration ˜10gl-1) and below. For small clusters, ΔGi0 depends weakly on the strength of short-ranged attractive interactions for most experimentally relevant values of the normalized osmotic second virial coefficient (b2*). For larger clusters (i ≫2), there is a small but non-negligible b2* dependence. The results suggest that nonspecific, hydrophobic attractions may not significantly stabilize prenuclei in processes such as non-native aggregation. Biased Monte Carlo methods are shown to accurately provide subcell degeneracies that are intractable to obtain analytically or by direct enumeration, and so offer a means to generalize the approach to mixtures and proteins with more complex PMFs.

Understanding the sorption mechanisms of aflatoxin B1 to kaolinite, illite, and smectite clays via a comparative computational study.

PubMed

Kang, Fuxing; Ge, Yangyang; Hu, Xiaojie; Goikavi, Caspar; Waigi, Michael Gatheru; Gao, Yanzheng; Ling, Wanting

2016-12-15

In current adsorption studies of biotoxins to phyllosilicate clays, multiply weak bonding types regarding these adsorptions are not well known; the major attractive forces, especially for kaolinite and illite, are difficult to be identified as compared to smectite with exchangeable cations. Here, we discriminated the bonding types of aflatoxin B1 (AFB1) contaminant to these clays by combined batch experiment with model computation, expounded their bonding mechanisms which have been not quantitatively described by researchers. The observed adsorbent-to-solution distribution coefficients (K d ) of AFB1 presented in increasing order of 18.5-37.1, 141.6-158.3, and 354.6-484.7L/kg for kaolinite, illite, and smectite, respectively. Normalization of adsorbent-specific surface areas showed that adsorption affinity of AFB1 is mainly dependent on the outside surfaces of clay aggregates. The model computation and test of ionic effect further suggested that weakly electrostatic attractions ((Si/Al-OH) 2 ⋯(OC) 2 ) are responsible for AFB1-kaolinite adsorption (K d , 18.5-37.1L/kg); a moderate electron-donor-acceptor attraction ((CO) 2 ⋯K + ⋯(O-Al) 3 ) is related to AFB1-illite adsorption (K d , 141.6-158.3L/kg); a strong calcium-bridging linkage ((CO) 2 ⋯Ca 2+ ⋯(O-Si) 4 ) is involved in AFB1-smectite adsorption (K d , 354.6-484.7L/kg). Changes in Gibbs free energy (ΔG°) suggested that the computed result is reliable, providing a good reproduction of AFB1-clay interaction. Copyright © 2016 Elsevier B.V. All rights reserved.

Third-order perturbative lattice and complex Langevin analyses of the finite-temperature equation of state of nonrelativistic fermions in one dimension

NASA Astrophysics Data System (ADS)

Loheac, Andrew C.; Drut, Joaquín E.

2017-05-01

We analyze the pressure and density equations of state of unpolarized nonrelativistic fermions at finite temperature in one spatial dimension with contact interactions. For attractively interacting regimes, we perform a third-order lattice perturbation theory calculation, assess its convergence properties by comparing with hybrid Monte Carlo results (there is no sign problem in this regime), and demonstrate agreement with real Langevin calculations. For repulsive interactions, we present lattice perturbation theory results as well as complex Langevin calculations, with a modified action to prevent uncontrolled excursions in the complex plane. Although perturbation theory is a common tool, our implementation of it is unconventional; we use a Hubbard-Stratonovich transformation to decouple the system and automate the application of Wick's theorem, thus generating the diagrammatic expansion, including symmetry factors, at any desired order. We also present an efficient technique to tackle nested Matsubara frequency sums without relying on contour integration, which is independent of dimension and applies to both relativistic and nonrelativistic systems, as well as all energy-independent interactions. We find exceptional agreement between perturbative and nonperturbative results at weak couplings, and furnish predictions based on complex Langevin at strong couplings. We additionally present perturbative calculations of up to the fifth-order virial coefficient for repulsive and attractive couplings. Both the lattice perturbation theory and complex Langevin formalisms can easily be extended to a variety of situations including polarized systems, bosons, and higher dimension.

The shape and dynamics of local attraction

NASA Astrophysics Data System (ADS)

Strömbom, D.; Siljestam, M.; Park, J.; Sumpter, D. J. T.

2015-11-01

Moving animal groups, such as flocks of birds or schools of fish, exhibit a varity of self-organized complex dynamical behaviors and shapes. This kind of flocking behavior has been studied using self-propelled particle models, in which the "particles" interact with their nearest neighbors through repulsion, attraction and alignment responses. In particular, it has been shown that models based on attraction alone can generate a range of dynamic groups in 2D, with periodic boundary conditions, and in the absence of repulsion. Here we investigate the effects of changing these conditions on the type of groups observed in the model. We show that replacing the periodic boundary conditions with a weak global attaction term in 2D, and extending the model to 3D does not significantly change the type of groups observed. We also provide a description of how attraction strength and blind angle determine the groups generated in the 3D version of the model. Finally, we show that adding repulsion do change the type of groups oberved, making them appear and behave more like real moving animal groups. Our results suggest that many biological instances of collective motion may be explained without assuming that animals explicitly align with each other. Instead, complex collective motion is explained by the interplay of attraction and repulsion forces. Supplementary material in the form of four mp4 files available from the Journal web page at http://dx.doi.org/10.1140/epjst/e2015-50093-5

Fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes by protein mixtures: the role of inter-foulant-species interaction.

PubMed

Wang, Yi-Ning; Tang, Chuyang Y

2011-08-01

Protein fouling of nanofiltration (NF), reverse osmosis (RO), and ultrafiltration (UF) membranes by bovine serum albumin (BSA), lysozyme (LYS), and their mixture was investigated under cross-flow conditions. The effect of solution chemistry, membrane properties, and permeate flux level was systematically studied. When the solution pH was within the isoelectric points (IEPs) of the two proteins (i.e., pH 4.7-10.4), the mixed protein system experienced more severe flux decline compared to the respective single protein systems, which may be attributed to the electrostatic attraction between the negatively charged BSA and positively charged LYS molecules. Unlike a typical single protein system, membrane fouling by BSA-LYS mixture was only weakly dependent on solution pH within this pH range, and increased ionic strength was found to enhance the membrane flux as a result of the suppressed BSA-LYS electrostatic attraction. Membrane fouling was likely controlled by foulant-fouled-membrane interaction under severe fouling conditions (elevated flux level and unfavorable solution chemistry that promotes fouling), whereas it was likely dominated by foulant-clean-membrane interaction under mild fouling conditions. Compared to nonporous NF and RO membranes, the porous UF membrane was more susceptible to dramatic flux decline due to the increased risk of membrane pore plugging. This study reveals that membrane fouling by mixed macromolecules may behave very differently from that by typical single foulant system, especially when the inter-foulant-species interaction dominates over the intra-species interaction in the mixed foulant system.

ΛcN interaction from lattice QCD and its application to Λc hypernuclei

NASA Astrophysics Data System (ADS)

Miyamoto, Takaya; Aoki, Sinya; Doi, Takumi; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Iritani, Takumi; Ishii, Noriyoshi; Kawai, Daisuke; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji

2018-03-01

The interaction between Λc and a nucleon (N) is investigated by employing the HAL QCD method in the (2 + 1)-flavor lattice QCD on a (2.9fm) 3 volume at mπ ≃ 410 , 570 , 700 MeV. We study the central potential in S10 channel as well as central and tensor potentials in S31-3D1 channel, and find that the tensor potential for Λc N is negligibly weak and central potentials in both S10 and S31-3D1 channels are almost identical with each other except at short distances. Phase shifts and scattering lengths calculated with these potentials show that the interaction of Λc N system is attractive and has a similar strength in S10 and S31 channels at low energies (i.e. the kinetic energy less than about 40 MeV). While the attractions are not strong enough to form two-body bound states, our results lead to a possibility to form Λc hypernuclei for sufficiently large atomic numbers (A). To demonstrate this, we derive a single-folding potential for Λc hypernuclei from the Λc-nucleon potential obtained in lattice QCD, and find that Λc hypernuclei can exist for A ≥ 12 with the binding energies of a few MeV. We also estimate the Coulomb effect for the Λc hypernuclei.

Self-Organization of Polymer Brush Layers in a Poor Solvent

NASA Astrophysics Data System (ADS)

Karim, A.; Tsukruk, V. V.; Douglas, J. F.; Satija, S. K.; Fetters, L. J.; Reneker, D. H.; Foster, M. D.

1995-10-01

Synthesis of densely grafted polymer brushes from good solvent polymer solutions is difficult when the surface interaction is only weakly attractive because of the strong steric repulsion between the polymer chains. To circumvent this difficulty we graft polymer layers in a poor solvent to exploit attractive polymer-polymer interactions which largely nullify the repulsive steric interactions. This simple strategy gives rise to densely grafted and homogeneous polymer brush layers. Model end-grafted polystyrene chains (M_w = 105,000) are prepared in the poor solvent cyclohexane (9.5 °C) where the chains are chemically attached to the surface utilizing a trichlorosilane end-group. Polished silicon wafers were then exposed to the reactive polymer solutions for a series of “induction times” tau_I and the evolving layer was characterized by X-ray reflectivity and atomic force microscopy. Distinct morphologies were found depending on tau_I. For short tau_I, corresponding to a grafting density less than 5 mg/m^2, the grafted layer forms an inhomogeneous island-like structure. At intermediate tau_I, where the coverage becomes percolating, a surface pattern develops which appears similar to spinodal decomposition in bulk solution. Finally, after sufficiently long tau_I, a dense and nearly homogeneous layer with a sharp interface is formed which does not exhibit surface pattern formation. The stages of brush growth are discussed qualitatively in terms of a random deposition model.

Orientation specific deposition of mesoporous particles

NASA Astrophysics Data System (ADS)

Kjellman, Tomas; Bodén, Niklas; Wennerström, Hâkan; Edler, Karen J.; Alfredsson, Viveka

2014-11-01

We present a protocol for a facile orientation specific deposition of plate-like mesoporous SBA-15 silica particles onto a surface (mesopores oriented normal to surface). A drop of an aqueous dispersion of particles is placed on the surface and water vaporizes under controlled relative humidity. Three requirements are essential for uniform coverage: particle dispersion should not contain aggregates, a weak attraction between particles and surface is needed, and evaporation rate should be low. Aggregates are removed by stirring/sonication. Weak attraction is realized by introducing cationic groups to the surface. Insight into the mechanisms of the so-called coffee stain effect is also provided.

Insight into π-hole interactions containing the inorganic heterocyclic compounds S2N2/SN2P2.

PubMed

Lu, Bo; Zhang, Xueying; Meng, Lingpeng; Zeng, Yanli

2017-08-01

Similar to σ-hole interactions, the π-hole interaction has attracted much attention in recent years. According to the positive electrostatic potentials above and below the surface of inorganic heterocyclic compounds S 2 N 2 and three SN 2 P 2 isomers (heterocyclic compounds 1-4), and the negative electrostatic potential outside the X atom of XH 3 (X = N, P, As), S 2 N 2 /SN 2 P 2 ⋯XH 3 (X = N, P, As) complexes were constructed and optimized at the MP2/aug-cc-pVTZ level. The X atom of XH 3 (X = N, P, As) is almost perpendicular to the ring of the heterocyclic compounds. The π-hole interaction energy becomes greater as the trend goes from 1⋯XH 3 to 4⋯XH 3 . These π-hole interactions are weak and belong to "closed-shell" noncovalent interactions. According to the energy decomposition analysis, of the three attractive terms, the dispersion energy contributes more than the electrostatic energy. The polarization effect also plays an important role in the formation of π-hole complexes, with the contrasting phenomena of decreasing electronic density in the π-hole region and increasing electric density outside the X atom of XH 3 (X = N, P, As). Graphical abstract Computed density difference plots for the complexes 3⋯NH 3 (a 1 ), 3⋯PH 3 (b 1 ), 3⋯AsH 3 (c 1 ) and electron density shifts for the complexes 3⋯NH 3 (a 2 ), 3⋯PH 3 (b 2 ),3⋯AsH 3 (c 2 ) on the 0.001 a.u. contour.

The responsiveness of Bactrocera jarvisi (Diptera: Tephritidae) to two naturally occurring phenylbutaonids, zingerone and raspberry ketone.

PubMed

Wee, Suk-Ling; Peek, Thelma; Clarke, Anthony R

2018-06-08

The males of different species of Bactrocera and Zeugodacus fruit flies are commonly attracted to plant-derived phenylpropanoids (e.g. methyl eugenol (ME)) or phenylbutanoids (e.g. raspberry ketone (RK)) but almost never to both. However, one particular plant-derived phenylbutanoid, zingerone (ZN), which possesses an intermediate chemical structure between ME and RK, weakly attracts both ME- and RK-responding fruit fly species. Bactrocera jarvisi, an Australian fruit fly species, is weakly attracted to cue lure (an analogue of RK) but strongly attracted to ZN. Here, we investigated the minimum olfactory threshold and optimum sensitivity of B. jarvisi males to ZN and RK as a function of dose, time and sexual maturation. Our results show that B. jarvisi males had a marked preferential response to ZN, with a much lower olfactory threshold and faster response time to ZN than RK. Probit analysis demonstrated that ZN was at least >1600× more potent than RK as a male attractant to B. jarvisi. Although fruit fly male attraction to the phytochemicals is generally associated with sexual maturity, in B. jarvisi immature males were also attracted to ZN. Our results suggest that B. jarvisi males have a fine-tuned olfactory response to ZN, which appears to play a central role in the chemical ecology of this species. Copyright © 2018 Elsevier Ltd. All rights reserved.

Chiral Responsive Liquid Quantum Dots.

PubMed

Zhang, Jin; Ma, Junkai; Shi, Fangdan; Tian, Demei; Li, Haibing

2017-08-01

How to convert the weak chiral-interaction into the macroscopic properties of materials remains a huge challenge. Here, this study develops highly fluorescent, selectively chiral-responsive liquid quantum dots (liquid QDs) based on the hydrophobic interaction between the chiral chains and the oleic acid-stabilized QDs, which have been designated as (S)-1810-QDs. The fluorescence spectrum and liquidity of thermal control demonstrate the fluorescence properties and the fluidic behavior of (S)-1810-QDs in the solvent-free state. Especially, (S)-1810-QDs exhibit a highly chiral-selective response toward (1R, 2S)-2-amino-1,2-diphenyl ethanol. It is anticipated that this study will facilitate the construction of smart chiral fluidic sensors. More importantly, (S)-1810-QDs can become an attractive material for chiral separation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

BCS-Bose model of exotic superconductors: Generalized coherence length

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casas, M.; Getino, J.M.; de Llano, M.

1994-12-01

Analytic expressions are derived for the root-mean-square (rms) radius of a pair of fermions in a BCS many-fermion state in one, two, and three dimensions, in terms of the BCS gap energy and the associated chemical potential. These expressions are valid for any coupling strength of [ital any] pair interaction model implying a momentum-independent gap energy. The latter holds, e.g., for an attractive [delta] pair potential examined in the one-dimensional (1D) case (whose [ital N]-fermion ground state can be determined exactly) or for the BCS (electron-phonon) model interaction in any dimension. Weak-coupling and/or high-density limits for the rms radius aremore » identical in 1D, 2D, and 3D, and reduce to the familiar well-known Pippard result to within a factor of order unity. In contrast, strong-coupling and/or low-density limits coincide in 1D and 3D, but differ by a factor of order unity in the 2D limit, and in each case are essentially the size of a single, isolated pair. The 1D [delta] interaction McGuire-Yang-Gaudin many-fermion model is studied in detail. The interaction renormalization scheme of Miyake and of Randeria, Duan, and Shieh, and the BCS interaction model, both in 2D, are employed to analyze cuprate superconductor empirical results. Reasonable agreement between theoretical rms radii with experimental coherence lengths suggests that cuprates can be described moderately well as [ital weakly] [ital coupled] superconductors within the BCS-Bose formalism.« less

Cavitation transition in the energy landscape: Distinct tensile yielding behavior in strongly and weakly attractive systems.

PubMed

Altabet, Y Elia; Fenley, Andreia L; Stillinger, Frank H; Debenedetti, Pablo G

2018-03-21

Particles with cohesive interactions display a tensile instability in the energy landscape at the Sastry density ρ S . The signature of this tensile limit is a minimum in the landscape equation of state, the pressure-density relationship of inherent structures sampled along a liquid isotherm. Our previous work [Y. E. Altabet, F. H. Stillinger, and P. G. Debenedetti, J. Chem. Phys. 145, 211905 (2016)] revisited the phenomenology of Sastry behavior and found that the evolution of the landscape equation of state with system size for particles with interactions typical of molecular liquids indicates the presence of an athermal first-order phase transition between homogeneous and fractured inherent structures, the latter containing several large voids. Here, we study how this tensile limit manifests itself for different interparticle cohesive strengths and identify two distinct regimes. Particles with sufficiently strong cohesion display an athermal first-order phase transition, consistent with our prior characterization. Weak cohesion also displays a tensile instability. However, the landscape equation of state for this regime is independent of system size, suggesting the absence of a first-order phase transition. An analysis of the voids suggests that yielding in the energy landscape of weakly cohesive systems is associated with the emergence of a highly interconnected network of small voids. While strongly cohesive systems transition from exclusively homogeneous to exclusively fractured configurations at ρ S in the thermodynamic limit, this interconnected network develops gradually, starting at ρ S , even at infinite system size.

Cavitation transition in the energy landscape: Distinct tensile yielding behavior in strongly and weakly attractive systems

NASA Astrophysics Data System (ADS)

Altabet, Y. Elia; Fenley, Andreia L.; Stillinger, Frank H.; Debenedetti, Pablo G.

2018-03-01

Particles with cohesive interactions display a tensile instability in the energy landscape at the Sastry density ρS. The signature of this tensile limit is a minimum in the landscape equation of state, the pressure-density relationship of inherent structures sampled along a liquid isotherm. Our previous work [Y. E. Altabet, F. H. Stillinger, and P. G. Debenedetti, J. Chem. Phys. 145, 211905 (2016)] revisited the phenomenology of Sastry behavior and found that the evolution of the landscape equation of state with system size for particles with interactions typical of molecular liquids indicates the presence of an athermal first-order phase transition between homogeneous and fractured inherent structures, the latter containing several large voids. Here, we study how this tensile limit manifests itself for different interparticle cohesive strengths and identify two distinct regimes. Particles with sufficiently strong cohesion display an athermal first-order phase transition, consistent with our prior characterization. Weak cohesion also displays a tensile instability. However, the landscape equation of state for this regime is independent of system size, suggesting the absence of a first-order phase transition. An analysis of the voids suggests that yielding in the energy landscape of weakly cohesive systems is associated with the emergence of a highly interconnected network of small voids. While strongly cohesive systems transition from exclusively homogeneous to exclusively fractured configurations at ρS in the thermodynamic limit, this interconnected network develops gradually, starting at ρS, even at infinite system size.

A new measure of molecular attractions between nanoparticles near kT adhesion energy

NASA Astrophysics Data System (ADS)

Kendall, Kevin; Dhir, Aman; Du, Shangfeng

2009-07-01

The weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e.g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Origin of attraction in p-benzoquinone complexes with benzene and p-hydroquinone.

PubMed

Tsuzuki, Seiji; Uchimaru, Tadafumi; Ono, Taizo

2017-08-30

The origin of the attraction in charge-transfer complexes (a p-hydroquinone-p-benzoquinone complex and benzene complexes with benzoquinone, tetracyanoethylene and Br 2 ) was analyzed using distributed multipole analysis and symmetry-adapted perturbation theory. Both methods show that the dispersion interactions are the primary source of the attraction in these charge-transfer complexes followed by the electrostatic interactions. The natures of the intermolecular interactions in these complexes are close to the π/π interactions of neutral aromatic molecules. The electrostatic interactions play important roles in determining the magnitude of the attraction. The contribution of charge-transfer interactions to the attraction is not large compared with the dispersion interactions in these complexes.

An experimental test of the fluctuation relation in an active camphor boat system

NASA Astrophysics Data System (ADS)

Paroor, H. M.; Nambiar, N.; Bandi, M. M.

The Gallavotti-Cohen fluctuation relation (FR) posits a specific symmetry between positive and negative fluctuations in entropy production, or a related quantity (e.g power) for systems in non-equilibrium stationary state. Successful tests in a variety of systems suggest the FR may be more generally applicable than the conditions under which it was originally derived. Systems where the FR fails are therefore valuable for the insight they provide into the FR's general success. It has recently been suggested that ``active matter'' should not satisfy the fluctuation-dissipation theorem or FR. We experimentally test this possibility in a system of active camphor boats, self-propelled by surface tension gradients at air-water interfaces. The boats interact via short-range capillary attraction which competes with long-range surface tension mediated repulsion. Tuning interaction strength with number density, we test the FR through the statistics of power as one goes from a free non-interacting camphor boat, through a few weakly interacting boats to several, strongly interacting boats. We present preliminary results of our experiments and data analysis.

Various topological Mott insulators and topological bulk charge pumping in strongly-interacting boson system in one-dimensional superlattice

NASA Astrophysics Data System (ADS)

Kuno, Yoshihito; Shimizu, Keita; Ichinose, Ikuo

2017-12-01

In this paper, we study a one-dimensional boson system in a superlattice potential. This system is experimentally feasible by using ultracold atomic gases, and attracts much attention these days. It is expected that the system has a topological phase called a topological Mott insulator (TMI). We show that in strongly-interacting cases, the competition between the superlattice potential and the on-site interaction leads to various TMIs with a non-vanishing integer Chern number. Compared to the hard-core case, the soft-core boson system exhibits rich phase diagrams including various non-trivial TMIs. By using the exact diagonalization, we obtain detailed bulk-global phase diagrams including the TMIs with high Chern numbers and also various non-topological phases. We also show that in adiabatic experimental setups, the strongly-interacting bosonic TMIs exhibit the topological particle transfer, i.e., the topological charge pumping phenomenon, similarly to weakly-interacting systems. The various TMIs are characterized by topological charge pumping as it is closely related to the Chern number, and therefore the Chern number is to be observed in feasible experiments.

Inbreeding alters volatile signalling phenotypes and influences tri-trophic interactions in horsenettle (Solanum carolinense L.).

PubMed

Kariyat, Rupesh R; Mauck, Kerry E; De Moraes, Consuelo M; Stephenson, Andrew G; Mescher, Mark C

2012-04-01

The ecological consequences of inter-individual variation in plant volatile emissions remain largely unexplored. We examined the effects of inbreeding on constitutive and herbivore-induced volatile emissions in horsenettle (Solanum carolinense L.) and on the composition of the insect community attracted to herbivore-damaged and undamaged plants in the field. Inbred plants exhibited higher constitutive emissions, but weaker induction of volatiles following herbivory. Moreover, many individual compounds previously implicated in the recruitment of predators and parasitoids (e.g. terpenes) were induced relatively weakly (or not at all) in inbred plants. In trapping experiments, undamaged inbred plants attracted greater numbers of generalist insect herbivores than undamaged outcrossed plants. But inbred plants recruited fewer herbivore natural enemies (predators and parasitoids) when damaged. Taken together, these findings suggest that inbreeding depression negatively impacts the overall pattern of volatile emissions - increasing the apparency of undamaged plants to herbivores, while reducing the recruitment of predatory insects to herbivore-damaged plants. © 2012 Blackwell Publishing Ltd/CNRS.

Data Mining for New Two- and One-Dimensional Weakly Bonded Solids and Lattice-Commensurate Heterostructures.

PubMed

Cheon, Gowoon; Duerloo, Karel-Alexander N; Sendek, Austin D; Porter, Chase; Chen, Yuan; Reed, Evan J

2017-03-08

Layered materials held together by weak interactions including van der Waals forces, such as graphite, have attracted interest for both technological applications and fundamental physics in their layered form and as an isolated single-layer. Only a few dozen single-layer van der Waals solids have been subject to considerable research focus, although there are likely to be many more that could have superior properties. To identify a broad spectrum of layered materials, we present a novel data mining algorithm that determines the dimensionality of weakly bonded subcomponents based on the atomic positions of bulk, three-dimensional crystal structures. By applying this algorithm to the Materials Project database of over 50,000 inorganic crystals, we identify 1173 two-dimensional layered materials and 487 materials that consist of weakly bonded one-dimensional molecular chains. This is an order of magnitude increase in the number of identified materials with most materials not known as two- or one-dimensional materials. Moreover, we discover 98 weakly bonded heterostructures of two-dimensional and one-dimensional subcomponents that are found within bulk materials, opening new possibilities for much-studied assembly of van der Waals heterostructures. Chemical families of materials, band gaps, and point groups for the materials identified in this work are presented. Point group and piezoelectricity in layered materials are also evaluated in single-layer forms. Three hundred and twenty-five of these materials are expected to have piezoelectric monolayers with a variety of forms of the piezoelectric tensor. This work significantly extends the scope of potential low-dimensional weakly bonded solids to be investigated.

Beta-spectrum shapes of forbidden β decays

NASA Astrophysics Data System (ADS)

Kostensalo, Joel; Suhonen, Jouni

2018-03-01

The neutrinoless ββ decay of atomic nuclei continues to attract fervent interest due to its potential to confirm the possible Majorana nature of the neutrino, and thus the nonconservation of the lepton number. At the same time, the direct dark matter experiments are looking for weakly interacting massive particles (WIMPs) through their scattering on nuclei. The neutrino-oscillation experiments on reactor antineutrinos base their analyses on speculations of β-spectrum shapes of nuclear decays, thus leading to the notorious “reactor antineutrino anomaly.” In all these experimental efforts, one encounters the problem of β-spectrum shapes of forbidden β decays, either as unwanted backgrounds or unknown components in the analyses of data. In this work, the problem of spectrum shapes is discussed and illustrated with a set of selected examples. The relation of the β-spectrum shapes to the problem of the effective value of the weak axial-vector coupling strength gA and the enhancement of the axial-charge matrix element is also pointed out.

Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Speck, Thomas; Menzel, Andreas M.; Bialké, Julian

2015-06-14

Recently, we have derived an effective Cahn-Hilliard equation for the phase separation dynamics of active Brownian particles by performing a weakly non-linear analysis of the effective hydrodynamic equations for density and polarization [Speck et al., Phys. Rev. Lett. 112, 218304 (2014)]. Here, we develop and explore this strategy in more detail and show explicitly how to get to such a large-scale, mean-field description starting from the microscopic dynamics. The effective free energy emerging from this approach has the form of a conventional Ginzburg-Landau function. On the coarsest scale, our results thus agree with the mapping of active phase separation ontomore » that of passive fluids with attractive interactions through a global effective free energy (motility-induced phase transition). Particular attention is paid to the square-gradient term necessary for the phase separation kinetics. We finally discuss results from numerical simulations corroborating the analytical results.« less

Concentrated dispersions of equilibrium protein nanoclusters that reversibly dissociate into active monomers

NASA Astrophysics Data System (ADS)

Truskett, Thomas M.; Johnston, Keith; Maynard, Jennifer; Borwankar, Ameya; Miller, Maria; Wilson, Brian; Dinin, Aileen; Khan, Tarik; Kaczorowski, Kevin

2012-02-01

Stabilizing concentrated protein solutions is of wide interest in drug delivery. However, a major challenge is how to reliably formulate concentrated, low viscosity (i.e., syringeable) solutions of biologically active proteins. Unfortunately, proteins typically undergo irreversible aggregation at intermediate concentrations of 100-200 mg/ml. In this talk, I describe how they can effectively avoid these intermediate concentrations by reversibly assembling into nanoclusters. Nanocluster assembly is achieved by balancing short-ranged, cosolute-induced attractions with weak, longer-ranger electrostatic repulsions near the isoelectric point. Theory predicts that native proteins are stabilized by a self-crowding mechanism within the concentrated environment of the nanoclusters, while weak cluster-cluster interactions can result in colloidally-stable dispersions with moderate viscosities. I present experimental results where this strategy is used to create concentrated antibody dispersions (up to 260 mg/ml) comprising nanoclusters of proteins [monoclonal antibody 1B7, polyclonal sheep Immunoglobin G and bovine serum albumin], which upon dilution in vitro or administration in vivo, are conformationally stable and retain activity.

A Pilot Study of the Attractive Features of Active Videogames Among Chinese Primary School Children.

PubMed

Lau, Patrick W C; Lau, Erica Y; Wang, Jing Jing; Choi, Cheong-Rak; Kim, Chang Gyun

2017-04-01

The present study (1) explored the attractive features that affect Chinese primary school children's preferences of active videogames (AVGs) and (2) contrasted these findings with those in the Western literature. A total of 22 Chinese primary school children were recruited and interviewed. Four AVGs (Wii "Boxing," "Wii Fit™ Plus Obstacle Run"; "EyeToy Knockout", "EyeToy Keep ups") from two commercial consoles (Nintendo® Wii™ and Sony PlayStation ® 2 "EyeToy ® ") were employed. Participants used four selected AVGs for 3 minutes each. After each play period, children (1) described the strengths and weaknesses of each game as well as rated the attractive features of each game based on a 16-item questionnaire and (2) rated up to 5 items that were most influential regarding their AVG preferences. Participants indicated that control was the most significant feature, followed by feedback, goal, and graphics. The top five rated features imply that the perception of competence was the most appealing aspect and expected outcome of Chinese children who play AVGs. Compared with the Western findings regarding attractive AVG features, the present study found certain similarities as well as significant differences among Chinese AVG players. Based on the present study, control, feedback, goal, and graphics are the most significant features that attract Chinese children to play AVGs. Physical exertion, social interaction, competition, and learning outcomes, which are valued according to Western studies, were not mentioned as significant features by Chinese children. These findings demonstrate a need to investigate the effect of cultural background in AVG study design.

Local structural ordering in surface-confined liquid crystals

NASA Astrophysics Data System (ADS)

Śliwa, I.; Jeżewski, W.; Zakharov, A. V.

2017-06-01

The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. Extending the McMillan mean field theory to include finite systems, it has been shown that confining surfaces can induce complex orientational and translational ordering of molecules. Typically, local smectic A, nematic, and isotropic phases have been shown to coexist in certain temperature ranges, provided that confining cells are sufficiently thick, albeit finite. Due to the nonlocality of surface interactions, the spatial arrangement of these local phases can display, in general, an unexpected complexity along the surface normal direction. In particular, molecules located in the vicinity of surfaces can still be organized in smectic layers, even though nematic and/or isotropic order can simultaneously appear in the interior of cells. The resulting surface freezing of smectic layers has been confirmed to occur even for rather weak surface interactions. The surface interactions cannot, however, prevent smectic layers from melting relatively close to system boundaries, even when molecules are still arranged in layers within the central region of the system. The internal interfaces, separating individual liquid-crystal phases, are demonstrated here to form fronts of local finite-size transitions that move across cells under temperature changes. Although the complex molecular ordering in surface confined liquid-crystal systems can essentially be controlled by temperature variations, specific thermal properties of these systems, especially the nature of the local transitions, are argued to be strongly conditioned to the degree of molecular packing.

The Challenges of Attracting Asian Students to Study Higher Education in Hong Kong

ERIC Educational Resources Information Center

Ng, Shun Wing

2012-01-01

This article reports a commissioned research project on exploring the emerging issues and challenges of attracting Asian students to study in Hong Kong's higher education institutions. Findings reveal the rapidly growing demand for quality transnational education in Asia and the strengths, weaknesses, opportunities and threats of exporting Hong…

Physical Attractiveness and Health: Comment on Weeden and Sabini

ERIC Educational Resources Information Center

Grammer, Karl; Fink, Bernhard; Moller, Anders P.; Manning, John T.

2005-01-01

Evolutionary behavioral biology suggests that certain characteristics of the human face and body are important for mate preferences and are therefore subject to sexual selection. J. Weeden and J. Sabini identify a number of weaknesses in the association between traits' attractiveness and health. In contrast, the authors argue that (a) studies on…

The Relations among Body Image, Physical Attractiveness, and Body Mass in Adolescence.

ERIC Educational Resources Information Center

Rosenblum, Gianine D.; Lewis, Michael

1999-01-01

Examined body dissatisfaction, physical attractiveness, and body mass index in adolescents at 13, 15, and 18 years of age. Found that sex differences in body dissatisfaction emerged between 13 and 15 years and were maintained. Girls' body dissatisfaction increased, whereas boys' decreased. Body dissatisfaction was weakly related to others' rating…

The structure of ions and zwitterionic lipids regulates the charge of dipolar membranes.

PubMed

Szekely, Or; Steiner, Ariel; Szekely, Pablo; Amit, Einav; Asor, Roi; Tamburu, Carmen; Raviv, Uri

2011-06-21

In pure water, zwitterionic lipids form lamellar phases with an equilibrium water gap on the order of 2 to 3 nm as a result of the dominating van der Waals attraction between dipolar bilayers. Monovalent ions can swell those neutral lamellae by a small amount. Divalent ions can adsorb onto dipolar membranes and charge them. Using solution X-ray scattering, we studied how the structure of ions and zwitterionic lipids regulates the charge of dipolar membranes. We found that unlike monovalent ions that weakly interact with all of the examined dipolar membranes, divalent and trivalent ions adsorb onto membranes containing lipids with saturated tails, with an association constant on the order of ∼10 M(-1). One double bond in the lipid tail is sufficient to prevent divalent ion adsorption. We suggest that this behavior is due to the relatively loose packing of lipids with unsaturated tails that increases the area per lipid headgroup, enabling their free rotation. Divalent ion adsorption links two lipids and limits their free rotation. The ion-dipole interaction gained by the adsorption of the ions onto unsaturated membranes is insufficient to compensate for the loss of headgroup free-rotational entropy. The ion-dipole interaction is stronger for cations with a higher valence. Nevertheless, polyamines behave as monovalent ions near dipolar interfaces in the sense that they interact weakly with the membrane surface, whereas in the bulk their behavior is similar to that of multivalent cations. Advanced data analysis and comparison with theory provide insight into the structure and interactions between ion-induced regulated charged interfaces. This study models biologically relevant interactions between cell membranes and various ions and the manner in which the lipid structure governs those interactions. The ability to monitor these interactions creates a tool for probing systems that are more complex and forms the basis for controlling the interactions between dipolar membranes and charged proteins or biopolymers for encapsulation and delivery applications. © 2011 American Chemical Society

Neutron Measurements and the Weak Nucleon-Nucleon Interaction

PubMed Central

Snow, W. M.

2005-01-01

The weak interaction between nucleons remains one of the most poorly-understood sectors of the Standard Model. A quantitative description of this interaction is needed to understand weak interaction phenomena in atomic, nuclear, and hadronic systems. This paper summarizes briefly what is known about the weak nucleon-nucleon interaction, tries to place this phenomenon in the context of other studies of the weak and strong interactions, and outlines a set of measurements involving low energy neutrons which can lead to significant experimental progress. PMID:27308120

AFM Colloidal Probe Measurements Implicate Capillary Condensation in Punch-Particle Surface Interactions during Tableting.

PubMed

Badal Tejedor, Maria; Nordgren, Niklas; Schuleit, Michael; Millqvist-Fureby, Anna; Rutland, Mark W

2017-11-21

Adhesion of the powders to the punches is a common issue during tableting. This phenomenon is known as sticking and affects the quality of the manufactured tablets. Defective tablets increase the cost of the manufacturing process. Thus, the ability to predict the tableting performance of the formulation blend before the process is scaled-up is important. The adhesive propensity of the powder to the tableting tools is mostly governed by the surface-surface adhesive interactions. Atomic force microscopy (AFM) colloidal probe is a surface characterization technique that allows the measurement of the adhesive interactions between two materials of interest. In this study, AFM steel colloidal probe measurements were performed on ibuprofen, MCC (microcrystalline cellulose), α-lactose monohydrate, and spray-dried lactose particles as an approach to modeling the punch-particle surface interactions during tableting. The excipients (lactose and MCC) showed constant, small, attractive, and adhesive forces toward the steel surface after a repeated number of contacts. In comparison, ibuprofen displayed a much larger attractive and adhesive interaction increasing over time both in magnitude and in jump-in/jump-out separation distance. The type of interaction acting on the excipient-steel interface can be related to a van der Waals force, which is relatively weak and short-ranged. By contrast, the ibuprofen-steel interaction is described by a capillary force profile. Even though ibuprofen is not highly hydrophilic, the relatively smooth surfaces of the crystals allow "contact flooding" upon contact with the steel probe. Capillary forces increase because of the "harvesting" of moisture-due to the fast condensation kinetics-leaving a residual condensate that contributes to increase the interaction force after each consecutive contact. Local asperity contacts on the more hydrophilic surface of the excipients prevent the flooding of the contact zone, and there is no such adhesive effect under the same ambient conditions. The markedly different behavior detected by force measurements clearly shows the sticky and nonsticky propensity of the materials and allows a mechanistic description.

Was Newton right? A search for non-Newtonian behavior of weak-field gravity

NASA Astrophysics Data System (ADS)

Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven

2014-06-01

Empirical tests of Einstein's metric theory of gravitation, even in the non-relativistic, weak-field limit, could play an important role in judging theory-driven extensions of the current Standard Model of fundamental interactions. Guided by Galileo's work and his own experiments, Newton formulated a theory of gravity in which the force of attraction between two bodies is independent of composition and proportional to the inertia of each, thereby transparently satisfying Galileo's empirically informed conjecture regarding the Universality of Free Fall. Similarly, Einstein honored the manifest success of Newton's theory by assuring that the linearized equations of GTR matched the Newtonian formalism under "classical" conditions. Each of these steps, however, was explicitly an approximation raised to the status of principle. Perhaps, at some level, Newtonian gravity does not accurately describe the physical interaction between uncharged, unmagnetized, macroscopic bits of ordinary matter. What if Newton were wrong? Detecting any significant deviation from Newtonian behavior, no matter how small, could provide new insights and possibly reveal new physics. In the context of physics as an empirical science, for us this yet unanswered question constitutes sufficient motivation to attempt precision measurements of the kind described here. In this paper we report the current status of a project to search for violation of the Newtonian inverse square law of gravity.

How important is self-consistency for the dDsC density dependent dispersion correction?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brémond, Éric; Corminboeuf, Clémence, E-mail: clemence.corminboeuf@epfl.ch; Golubev, Nikolay

2014-05-14

The treatment of dispersion interactions is ubiquitous but computationally demanding for seamless ab initio approaches. A highly popular and simple remedy consists in correcting for the missing interactions a posteriori by adding an attractive energy term summed over all atom pairs to standard density functional approximations. These corrections were originally based on atom pairwise parameters and, hence, had a strong touch of empiricism. To overcome such limitations, we recently proposed a robust system-dependent dispersion correction, dDsC, that is computed from the electron density and that provides a balanced description of both weak inter- and intramolecular interactions. From the theoretical pointmore » of view and for the sake of increasing reliability, we here verify if the self-consistent implementation of dDsC impacts ground-state properties such as interaction energies, electron density, dipole moments, geometries, and harmonic frequencies. In addition, we investigate the suitability of the a posteriori scheme for molecular dynamics simulations, for which the analysis of the energy conservation constitutes a challenging tests. Our study demonstrates that the post-SCF approach in an excellent approximation.« less

Conformist-contrarian interactions and amplitude dependence in the Kuramoto model

NASA Astrophysics Data System (ADS)

Lohe, M. A.

2014-11-01

We derive exact formulas for the frequency of synchronized oscillations in Kuramoto models with conformist-contrarian interactions, and determine necessary conditions for synchronization to occur. Numerical computations show that for certain parameters repulsive nodes behave as conformists, and that in other cases attractive nodes can display frustration, being neither conformist nor contrarian. The signs of repulsive couplings can be placed equivalently outside the sum, as proposed in Hong and Strogatz (2011 Phys. Rev. Lett. 106 054102), or inside the sum as in Hong and Strogatz (2012 Phys. Rev. E 85 056210), but the two models have different characteristics for small magnitudes of the coupling constants. In the latter case we show that the distributed coupling constants can be viewed as oscillator amplitudes which are constant in time, with the property that oscillators of small amplitude couple only weakly to connected nodes. Such models provide a means of investigating the effect of amplitude variations on synchronization properties.

Stable swarming using adaptive long-range interactions

NASA Astrophysics Data System (ADS)

Gorbonos, Dan; Gov, Nir S.

2017-04-01

Sensory mechanisms in biology, from cells to humans, have the property of adaptivity, whereby the response produced by the sensor is adapted to the overall amplitude of the signal, reducing the sensitivity in the presence of strong stimulus, while increasing it when it is weak. This property is inherently energy consuming and a manifestation of the nonequilibrium nature of living organisms. We explore here how adaptivity affects the effective forces that organisms feel due to others in the context of a uniform swarm, in both two and three dimensions. The interactions between the individuals are taken to be attractive and long-range and of power-law form. We find that the effects of adaptivity inside the swarm are dramatic, where the effective forces decrease (or remain constant) with increasing swarm density. Linear stability analysis demonstrates how this property prevents collapse (Jeans instability), when the forces are adaptive. Adaptivity therefore endows swarms with a natural mechanism for self-stabilization.

Evaluating the phase diagram of superconductors with asymmetric spin populations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mannarelli, Massimo; Nardulli, Giuseppe; Ruggieri, Marco

2006-09-15

The phase diagram of a nonrelativistic fermionic system with imbalanced state populations interacting via a short-range S-wave attractive interaction is analyzed in the mean-field approximation. We determine the energetically favored state for different values of the mismatch between the two Fermi spheres in the weak- and strong-coupling regimes considering both homogeneous and nonhomogeneous superconductive states. We find that the homogeneous superconductive phase persists for values of the population imbalance that increase with increasing coupling strength. In the strong-coupling regime and for large population differences the energetically stable homogeneous phase is characterized by one gapless mode. We also find that themore » inhomogeneous superconductive phase characterized by the condensate {delta}(x){approx}{delta} exp(iq{center_dot}x) is energetically favored in a range of values of the chemical-potential mismatch that shrinks to zero in the strong-coupling regime.« less

Kosterlitz-Thouless transition and vortex-antivortex lattice melting in two-dimensional Fermi gases with p - or d -wave pairing

NASA Astrophysics Data System (ADS)

Cao, Gaoqing; He, Lianyi; Huang, Xu-Guang

2017-12-01

We present a theoretical study of the finite-temperature Kosterlitz-Thouless (KT) and vortex-antivortex lattice (VAL) melting transitions in two-dimensional Fermi gases with p - or d -wave pairing. For both pairings, when the interaction is tuned from weak to strong attractions, we observe a quantum phase transition from the Bardeen-Cooper-Schrieffer (BCS) superfluidity to the Bose-Einstein condensation (BEC) of difermions. The KT and VAL transition temperatures increase during this BCS-BEC transition and approach constant values in the deep BEC region. The BCS-BEC transition is characterized by the nonanalyticities of the chemical potential, the superfluid order parameter, and the sound velocities as functions of the interaction strength at both zero and finite temperatures; however, the temperature effect tends to weaken the nonanalyticities compared to the zero-temperature case. The effect of mismatched Fermi surfaces on the d -wave pairing is also studied.

On thermal corrections to near-threshold annihilation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Seyong; Laine, M., E-mail: skim@sejong.ac.kr, E-mail: laine@itp.unibe.ch

2017-01-01

We consider non-relativistic ''dark'' particles interacting through gauge boson exchange. At finite temperature, gauge exchange is modified in many ways: virtual corrections lead to Debye screening; real corrections amount to frequent scatterings of the heavy particles on light plasma constituents; mixing angles change. In a certain temperature and energy range, these effects are of order unity. Taking them into account in a resummed form, we estimate the near-threshold spectrum of kinetically equilibrated annihilating TeV scale particles. Weakly bound states are shown to 'melt' below freeze-out, whereas with attractive strong interactions, relevant e.g. for gluinos, bound states boost the annihilation ratemore » by a factor 4 ... 80 with respect to the Sommerfeld estimate, thereby perhaps helping to avoid overclosure of the universe. Modestly non-degenerate dark sector masses and a way to combine the contributions of channels with different gauge and spin structures are also discussed.« less

Sample size requirements for indirect association studies of gene-environment interactions (G x E).

PubMed

Hein, Rebecca; Beckmann, Lars; Chang-Claude, Jenny

2008-04-01

Association studies accounting for gene-environment interactions (G x E) may be useful for detecting genetic effects. Although current technology enables very dense marker spacing in genetic association studies, the true disease variants may not be genotyped. Thus, causal genes are searched for by indirect association using genetic markers in linkage disequilibrium (LD) with the true disease variants. Sample sizes needed to detect G x E effects in indirect case-control association studies depend on the true genetic main effects, disease allele frequencies, whether marker and disease allele frequencies match, LD between loci, main effects and prevalence of environmental exposures, and the magnitude of interactions. We explored variables influencing sample sizes needed to detect G x E, compared these sample sizes with those required to detect genetic marginal effects, and provide an algorithm for power and sample size estimations. Required sample sizes may be heavily inflated if LD between marker and disease loci decreases. More than 10,000 case-control pairs may be required to detect G x E. However, given weak true genetic main effects, moderate prevalence of environmental exposures, as well as strong interactions, G x E effects may be detected with smaller sample sizes than those needed for the detection of genetic marginal effects. Moreover, in this scenario, rare disease variants may only be detectable when G x E is included in the analyses. Thus, the analysis of G x E appears to be an attractive option for the detection of weak genetic main effects of rare variants that may not be detectable in the analysis of genetic marginal effects only.

From the depletion attraction to the bridging attraction: the effect of solvent molecules on the effective colloidal interactions.

PubMed

Chen, Jie; Kline, Steven R; Liu, Yun

2015-02-28

Depletion attraction induced by non-adsorbing polymers or small particles in colloidal solutions has been widely used as a model colloidal interaction to understand aggregation behavior and phase diagrams, such as glass transitions and gelation. However, much less attention has been paid to study the effective colloidal interaction when small particles/molecules can be reversibly attracted to large colloidal particles. At the strong attraction limit, small particles can introduce bridging attraction as it can simultaneously attach to neighbouring large colloidal particles. We use Baxter's multi-component method for sticky hard sphere systems with the Percus-Yevick approximation to study the bridging attraction and its consequence to phase diagrams, which are controlled by the concentration of small particles and their interaction with large particles. When the concentration of small particles is very low, the bridging attraction strength increases very fast with the increase of small particle concentration. The attraction strength eventually reaches a maximum bridging attraction (MBA). Adding more small particles after the MBA concentration keeps decreasing the attraction strength until reaching a concentration above which the net effect of small particles only introduces an effective repulsion between large colloidal particles. These behaviors are qualitatively different from the concentration dependence of the depletion attraction on small particles and make phase diagrams very rich for bridging attraction systems. We calculate the spinodal and binodal regions, the percolation lines, the MBA lines, and the equivalent hard sphere interaction line for bridging attraction systems and have proposed a simple analytic solution to calculate the effective attraction strength using the concentrations of large and small particles. Our theoretical results are found to be consistent with experimental results reported recently.

Dipole interaction of the Quincke rotating particles.

PubMed

Dolinsky, Yu; Elperin, T

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

Dipole interaction of the Quincke rotating particles

NASA Astrophysics Data System (ADS)

Dolinsky, Yu.; Elperin, T.

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

High level theoretical study of benzene-halide adducts: the importance of C-H-anion hydrogen bonding.

PubMed

Coletti, Cecilia; Re, Nazzareno

2009-02-26

High level ab initio calculations were performed on the interaction of halide anions (F(-), Cl(-), Br(-), and I(-)) to benzene. For these systems recent experimental and theoretical data are rather scarce, in spite of their growingly acknowledged importance for binding in complex biological systems. We have thus explored the complete basis set limit and the effect of counterpoise basis set superposition error corrections on the minimum geometries and energies of benzene-halide adducts in their possible interaction modes. The binding energy and enthalpy values (ranging from -15.3 kcal/mol for fluoride to -6.1 kcal/mol for iodide) show that the hydrogen bonding occurring in these complexes cannot be described as a weak interaction. We have furthermore investigated the topology of the minima and of other selected sections of the potential energy surface, so to gain further insight on the nature of the halide-benzene interaction. In particular, the geometry corresponding to the C(6v) symmetry, although being overall repulsive, has displayed the unprecedented presence of a small flex (a minimum in C(6v) symmetry) with interaction energy close to zero or slightly attractive.

A ReaxFF-based molecular dynamics study of the mechanisms of interactions between reactive oxygen plasma species and the Candida albicans cell wall

NASA Astrophysics Data System (ADS)

Zhao, T.; Shi, L.; Zhang, Y. T.; Zou, L.; Zhang, L.

2017-10-01

Atmospheric pressure non-equilibrium plasmas have attracted significant attention and have been widely used to inactivate pathogens, yet the mechanisms underlying the interactions between plasma-generated species and bio-organisms have not been elucidated clearly. In this paper, reactive molecular dynamics simulations are employed to investigate the mechanisms of interactions between reactive oxygen plasma species (O, OH, and O2) and β-1,6-glucan (a model for the C. albicans cell wall) from a microscopic point of view. Our simulations show that O and OH species can break structurally important C-C and C-O bonds, while O2 molecules exhibit only weak, non-bonded interactions with β-1,6-glucan. Hydrogen abstraction from hydroxyl or CH groups occurs first in all bond cleavage mechanisms. This is followed by a cascade of bond cleavage and double bond formation events. These lead to the destruction of the fungal cell wall. O and OH have similar effects related to their bond cleavage mechanisms. Our simulation results provide fundamental insights into the mechanisms underlying the interactions between reactive oxygen plasma species and the fungal cell wall of C. albicans at the atomic level.

Polarity-Dependent Vortex Pinning and Spontaneous Vortex-Antivortex Structures in Superconductor/Ferromagnet Hybrids

NASA Astrophysics Data System (ADS)

Bending, Simon J.; Milošević, Milorad V.; Moshchalkov, Victor V.

Hybrid structures composed of superconducting films that are magnetically coupled to arrays of nanoscale ferromagnetic dots have attracted enormous interest in recent years. Broadly speaking, such systems fall into one of two distinct regimes. Ferromagnetic dots with weak moments pin free vortices, leading to enhanced superconducting critical currents, particularly when the conditions for commensurability are satisfied. Dots with strong moments spontaneously generate one or more vortex-antivortex (V-AV) pairs which lead to a rich variety of pinning, anti-pinning and annihilation phenomena. We describe high resolution Hall probe microscopy of flux structures in various hybrid samples composed of superconducting Pb films deposited on arrays of ferromagnetic Co or Co/Pt dots with both weak and strong moments. We show directly that dots with very weak perpendicular magnetic moments do not induce vortex-antivortex pairs, but still act as strong polarity-dependent vortex pinning centres for free vortices. In contrast, we have directly observed spontaneous V-AV pairs induced by large moment dots with both in-plane and perpendicular magnetic anisotropy, and studied the rich physical phenomena that arise when they interact with added "free" (anti)fluxons in an applied magnetic field. The interpretation of our imaging results is supported by bulk magnetometry measurements and state-of-the-art Ginzburg-Landau and London theory calculations.

Microscopic Description of Thermodynamics of Lipid Membrane at Liquid-Gel Phase Transition

NASA Astrophysics Data System (ADS)

Kheyfets, B.; Galimzyanov, T.; Mukhin, S.

2018-05-01

A microscopic model of the lipid membrane is constructed that provides analytically tractable description of the physical mechanism of the first order liquid-gel phase transition. We demonstrate that liquid-gel phase transition is cooperative effect of the three major interactions: inter-lipid van der Waals attraction, steric repulsion and hydrophobic tension. The model explicitly shows that temperature-dependent inter-lipid steric repulsion switches the system from liquid to gel phase when the temperature decreases. The switching manifests itself in the increase of lateral compressibility of the lipids as the temperature decreases, making phase with smaller area more preferable below the transition temperature. The model gives qualitatively correct picture of abrupt change at transition temperature of the area per lipid, membrane thickness and volume per hydrocarbon group in the lipid chains. The calculated dependence of phase transition temperature on lipid chain length is in quantitative agreement with experimental data. Steric repulsion between the lipid molecules is shown to be the only driver of the phase transition, as van der Waals attraction and hydrophobic tension are weakly temperature dependent.

Multiple dynamic regimes in colloid-polymer dispersions: New insight using X-ray photon correlation spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Sunita; Kishore, Suhasini; Narayanan, Suresh

We present an X-ray photon correlation spectros- copy (XPCS) study of dynamic transitions in an anisotropic colloid-polymer dispersion with multiple arrested states. The results provide insight into the mechanism for formation of repulsive glasses, attractive glasses, and networked gels of col- loids with weakly adsorbing polymer chains. In the presence of adsorbing polymer chains, we observe three distinct regimes: a state with slow dynamics consisting of finite particles and clusters, for which interparticle interactions are predominantly repulsive; a second dynamic regime occurring above the satu- ration concentration of added polymer, in which small clusters of nanoparticles form via a short-rangemore » depletion attraction; and a third regime above the overlap concentration in which dynamics of clusters are independent of polymer chain length. The observed complex dynamic state diagram is primarily gov- erned by the structural reorganization of a nanoparticle cluster and polymer chains at the nanoparticle-polymer surface and in the concentrated medium, which in turn controls the dynamics of the dispersion« less

Repulsive DNA-DNA interactions accelerate viral DNA packaging in phage Phi29.

PubMed

Keller, Nicholas; delToro, Damian; Grimes, Shelley; Jardine, Paul J; Smith, Douglas E

2014-06-20

We use optical tweezers to study the effect of attractive versus repulsive DNA-DNA interactions on motor-driven viral packaging. Screening of repulsive interactions accelerates packaging, but induction of attractive interactions by spermidine(3+) causes heterogeneous dynamics. Acceleration is observed in a fraction of complexes, but most exhibit slowing and stalling, suggesting that attractive interactions promote nonequilibrium DNA conformations that impede the motor. Thus, repulsive interactions facilitate packaging despite increasing the energy of the theoretical optimum spooled DNA conformation.

Investigating the Effects of the Interaction Intensity in a Weak Measurement.

PubMed

Piacentini, Fabrizio; Avella, Alessio; Gramegna, Marco; Lussana, Rudi; Villa, Federica; Tosi, Alberto; Brida, Giorgio; Degiovanni, Ivo Pietro; Genovese, Marco

2018-05-03

Measurements are crucial in quantum mechanics, for fundamental research as well as for applicative fields like quantum metrology, quantum-enhanced measurements and other quantum technologies. In the recent years, weak-interaction-based protocols like Weak Measurements and Protective Measurements have been experimentally realized, showing peculiar features leading to surprising advantages in several different applications. In this work we analyze the validity range for such measurement protocols, that is, how the interaction strength affects the weak value extraction, by measuring different polarization weak values on heralded single photons. We show that, even in the weak interaction regime, the coupling intensity limits the range of weak values achievable, setting a threshold on the signal amplification effect exploited in many weak measurement based experiments.

Molecular Theory and the Effects of Solute Attractive Forces on Hydrophobic Interactions.

PubMed

Chaudhari, Mangesh I; Rempe, Susan B; Asthagiri, D; Tan, L; Pratt, L R

2016-03-03

The role of solute attractive forces on hydrophobic interactions is studied by coordinated development of theory and simulation results for Ar atoms in water. We present a concise derivation of the local molecular field (LMF) theory for the effects of solute attractive forces on hydrophobic interactions, a derivation that clarifies the close relation of LMF theory to the EXP approximation applied to this problem long ago. The simulation results show that change from purely repulsive atomic solute interactions to include realistic attractive interactions diminishes the strength of hydrophobic bonds. For the Ar-Ar rdfs considered pointwise, the numerical results for the effects of solute attractive forces on hydrophobic interactions are opposite in sign and larger in magnitude than predicted by LMF theory. That comparison is discussed from the point of view of quasichemical theory, and it is suggested that the first reason for this difference is the incomplete evaluation within LMF theory of the hydration energy of the Ar pair. With a recent suggestion for the system-size extrapolation of the required correlation function integrals, the Ar-Ar rdfs permit evaluation of osmotic second virial coefficients B2. Those B2's also show that incorporation of attractive interactions leads to more positive (repulsive) values. With attractive interactions in play, B2 can change from positive to negative values with increasing temperatures. This is consistent with the puzzling suggestions of decades ago that B2 ≈ 0 for intermediate cases of temperature or solute size. In all cases here, B2 becomes more attractive with increasing temperature.

Molecular theory and the effects of solute attractive forces on hydrophobic interactions

DOE PAGES

Chaudhari, Mangesh I.; Rempe, Susan B.; Asthagiri, D.; ...

2015-12-22

The role of solute attractive forces on hydrophobic interactions is studied by coordinated development of theory and simulation results for Ar atoms in water. In this paper, we present a concise derivation of the local molecular field (LMF) theory for the effects of solute attractive forces on hydrophobic interactions, a derivation that clarifies the close relation of LMF theory to the EXP approximation applied to this problem long ago. The simulation results show that change from purely repulsive atomic solute interactions to include realistic attractive interactions diminishes the strength of hydrophobic bonds. For the Ar–Ar rdfs considered pointwise, the numericalmore » results for the effects of solute attractive forces on hydrophobic interactions are opposite in sign and larger in magnitude than predicted by LMF theory. That comparison is discussed from the point of view of quasichemical theory, and it is suggested that the first reason for this difference is the incomplete evaluation within LMF theory of the hydration energy of the Ar pair. With a recent suggestion for the system-size extrapolation of the required correlation function integrals, the Ar–Ar rdfs permit evaluation of osmotic second virial coefficients B 2. Those B 2’s also show that incorporation of attractive interactions leads to more positive (repulsive) values. With attractive interactions in play, B 2 can change from positive to negative values with increasing temperatures. Furthermore, this is consistent with the puzzling suggestions of decades ago that B 2 ≈ 0 for intermediate cases of temperature or solute size. In all cases here, B 2 becomes more attractive with increasing temperature.« less

Free energy landscapes of encounter complexes in protein-protein association.

PubMed

Camacho, C J; Weng, Z; Vajda, S; DeLisi, C

1999-03-01

We report the computer generation of a high-density map of the thermodynamic properties of the diffusion-accessible encounter conformations of four receptor-ligand protein pairs, and use it to study the electrostatic and desolvation components of the free energy of association. Encounter complex conformations are generated by sampling the translational/rotational space of the ligand around the receptor, both at 5-A and zero surface-to-surface separations. We find that partial desolvation is always an important effect, and it becomes dominant for complexes in which one of the reactants is neutral or weakly charged. The interaction provides a slowly varying attractive force over a small but significant region of the molecular surface. In complexes with no strong charge complementarity this region surrounds the binding site, and the orientation of the ligand in the encounter conformation with the lowest desolvation free energy is similar to the one observed in the fully formed complex. Complexes with strong opposite charges exhibit two types of behavior. In the first group, represented by barnase/barstar, electrostatics exerts strong orientational steering toward the binding site, and desolvation provides some added adhesion within the local region of low electrostatic energy. In the second group, represented by the complex of kallikrein and pancreatic trypsin inhibitor, the overall stability results from the rather nonspecific electrostatic attraction, whereas the affinity toward the binding region is determined by desolvation interactions.

[Chronic noncancer pain and patient education: a place for e-learning?].

PubMed

Braillard, Olivia; Cedraschi, Christine; Jesaimani, Ameena; Piguet, Valérie

2015-06-24

Chronic non cancerous pain considerably limits the patients' quality of life. Yet, chronic non cancerous pain has a prevalence as high as 25% to 35%, Therapeutic education allows to work on the knowledge and know-how about the disease, the treatment, the management of health resources and health behaviors. E-learning uses new technologies of communication to improve the quality of learning by facilitating access to the resources and favoring the interactivity. It is attractive by its wide accessibility and its limited logistic needs. The level of proof of its efficacy is weak, mainly because of methodological limitations. Some good quality studies are promising, with a positive effect of e-learning programs on pain intensity, disability, autonomy and medication misuse.

Study of Omega-proton correlations in heavy-ion collisions

NASA Astrophysics Data System (ADS)

Han, Yifei; STAR Collaboration

2015-10-01

Recently the STAR experiment at RHIC measured Lambda-Lambda correlations from Au+Au collisions at √{sNN} = 200 GeV to search for the H particle (uuddss). The correlation strength indicated that the Lambda-Lambda interaction is weak and is unlikely to be attractive enough to form a bound state. A recent lattice QCD calculation predicted a possible di-baryon bound state with Omega-nucleon. Thus, we will extend the correlation measurements to Omega-proton, which could potentially be a sensitive approach to search for such a state. We will present the Omega-proton correlations based on data collected by STAR in Au+Au collisions at √{sNN} =200 GeV, and discuss the physics implications. for the STAR collaboration.

Neurofilaments Function as Shock Absorbers: Compression Response Arising from Disordered Proteins.

PubMed

Kornreich, Micha; Malka-Gibor, Eti; Zuker, Ben; Laser-Azogui, Adi; Beck, Roy

2016-09-30

What can cells gain by using disordered, rather than folded, proteins in the architecture of their skeleton? Disordered proteins take multiple coexisting conformations, and often contain segments which act as random-walk-shaped polymers. Using x-ray scattering we measure the compression response of disordered protein hydrogels, which are the main stress-responsive component of neuron cells. We find that at high compression their mechanics are dominated by gaslike steric and ionic repulsions. At low compression, specific attractive interactions dominate. This is demonstrated by the considerable hydrogel expansion induced by the truncation of critical short protein segments. Accordingly, the floppy disordered proteins form a weakly cross-bridged hydrogel, and act as shock absorbers that sustain large deformations without failure.

Neurofilaments Function as Shock Absorbers: Compression Response Arising from Disordered Proteins

NASA Astrophysics Data System (ADS)

Kornreich, Micha; Malka-Gibor, Eti; Zuker, Ben; Laser-Azogui, Adi; Beck, Roy

2016-09-01

What can cells gain by using disordered, rather than folded, proteins in the architecture of their skeleton? Disordered proteins take multiple coexisting conformations, and often contain segments which act as random-walk-shaped polymers. Using x-ray scattering we measure the compression response of disordered protein hydrogels, which are the main stress-responsive component of neuron cells. We find that at high compression their mechanics are dominated by gaslike steric and ionic repulsions. At low compression, specific attractive interactions dominate. This is demonstrated by the considerable hydrogel expansion induced by the truncation of critical short protein segments. Accordingly, the floppy disordered proteins form a weakly cross-bridged hydrogel, and act as shock absorbers that sustain large deformations without failure.

Effect of metal ion intercalation on the structure of MXene and water dynamics on its internal surfaces

DOE PAGES

Osti, Naresh C.; Naguib, Michael; Ostadhossein, Alireza; ...

2016-03-24

MXenes are a recently discovered class of 2D materials with an excellent potential for energy storage applications. Because MXene surfaces are hydrophilic and attractive interaction forces between the layers are relatively weak, water molecules can spontaneously intercalate at ambient humidity and significantly influence the key properties of this 2D material. Using complementary X-ray and neutron scattering techniques, we demonstrate that intercalation with potassium cations significantly improves structural homogeneity and water stability in MXenes. Furthermore, in agreement with molecular dynamics simulations, intercalated potassium ions reduce the water self-diffusion coefficient by 2 orders of magnitude, suggesting greater stability of hydrated MXene againstmore » changing environmental conditions.« less

Multiparticle instability in a spin-imbalanced Fermi gas

NASA Astrophysics Data System (ADS)

Whitehead, T. M.; Conduit, G. J.

2018-01-01

Weak attractive interactions in a spin-imbalanced Fermi gas induce a multiparticle instability, binding multiple fermions together. The maximum binding energy per particle is achieved when the ratio of the number of up- and down-spin particles in the instability is equal to the ratio of the up- and down-spin densities of states in momentum at the Fermi surfaces, to utilize the variational freedom of all available momentum states. We derive this result using an analytical approach, and verify it using exact diagonalization. The multiparticle instability extends the Cooper pairing instability of balanced Fermi gases to the imbalanced case, and could form the basis of a many-body state, analogously to the construction of the Bardeen-Cooper-Schrieffer theory of superconductivity out of Cooper pairs.

Physical attractiveness and reproductive success in humans: Evidence from the late 20 century United States.

PubMed

Jokela, Markus

2009-09-01

Physical attractiveness has been associated with mating behavior, but its role in reproductive success of contemporary humans has received surprisingly little attention. In the Wisconsin Longitudinal Study (1244 women, 997 men born between 1937 and 1940) we examined whether attractiveness assessed from photographs taken at age ~18 predicted the number of biological children at age 53-56. In women, attractiveness predicted higher reproductive success in a nonlinear fashion, so that attractive (second highest quartile) women had 16% and very attractive (highest quartile) women 6% more children than their less attractive counterparts. In men, there was a threshold effect so that men in the lowest attractiveness quartile had 13% fewer children than others who did not differ from each other in the average number of children. These associations were partly but not completely accounted for by attractive participants' increased marriage probability. A linear regression analysis indicated relatively weak directional selection gradient for attractiveness (β=0.06 in women, β=0.07 in men). These findings indicate that physical attractiveness may be associated with reproductive success in humans living in industrialized settings.

Molecular Motions in Functional Self-Assembled Nanostructures

PubMed Central

Dhotel, Alexandre; Chen, Ziguang; Delbreilh, Laurent; Youssef, Boulos; Saiter, Jean-Marc; Tan, Li

2013-01-01

The construction of “smart” materials able to perform specific functions at the molecular scale through the application of various stimuli is highly attractive but still challenging. The most recent applications indicate that the outstanding flexibility of self-assembled architectures can be employed as a powerful tool for the development of innovative molecular devices, functional surfaces and smart nanomaterials. Structural flexibility of these materials is known to be conferred by weak intermolecular forces involved in self-assembly strategies. However, some fundamental mechanisms responsible for conformational lability remain unexplored. Furthermore, the role played by stronger bonds, such as coordination, ionic and covalent bonding, is sometimes neglected while they can be employed readily to produce mechanically robust but also chemically reversible structures. In this review, recent applications of structural flexibility and molecular motions in self-assembled nanostructures are discussed. Special focus is given to advanced materials exhibiting significant performance changes after an external stimulus is applied, such as light exposure, pH variation, heat treatment or electromagnetic field. The crucial role played by strong intra- and weak intermolecular interactions on structural lability and responsiveness is highlighted. PMID:23348927

Pairing from dynamically screened Coulomb repulsion in bismuth

NASA Astrophysics Data System (ADS)

Ruhman, Jonathan; Lee, Patrick A.

2017-12-01

Recently, Prakash et al. have discovered bulk superconductivity in single crystals of bismuth, which is a semimetal with extremely low carrier density. At such low density, we argue that conventional electron-phonon coupling is too weak to be responsible for the binding of electrons into Cooper pairs. We study a dynamically screened Coulomb interaction with effective attraction generated on the scale of the collective plasma modes. We model the electronic states in bismuth to include three Dirac pockets with high velocity and one hole pocket with a significantly smaller velocity. We find a weak-coupling instability, which is greatly enhanced by the presence of the hole pocket. Therefore we argue that bismuth is the first material to exhibit superconductivity driven by retardation effects of Coulomb repulsion alone. By using realistic parameters for bismuth we find that the acoustic plasma mode does not play the central role in pairing. We also discuss a matrix element effect, resulting from the Dirac nature of the conduction band, which may affect Tc in the s -wave channel without breaking time-reversal symmetry.

Effect of attractive interactions between polymers on the effective force acting between colloids immersed in a polymer system: Analytic liquid-state theory.

PubMed

Chervanyov, A I

2016-12-28

By making use of the polymer reference interaction site model, we analytically study the effect of attractive interactions between polymers on the effective forces acting between colloids immersed in a polymer system. The performed theoretical analysis has no restrictions with respect to the polymer density and relative sizes of the colloids and polymers. The polymer mediated (PM) potential acting between colloids is shown to significantly depend on the strength and range of the polymer-polymer interactions. In the nano-particle limit, where the colloid radius is much smaller than the polymer gyration radius, the presence of attractive polymer-polymer interactions causes only quantitative changes to the PM potential. In the opposite limit of relatively large colloids, the polymer-polymer interactions revert the sign of the total effective force acting between colloids so that this force becomes attractive at sufficiently large polymer densities. With the objective to study an intricate interplay between the attractive PM forces and steric repulsion in different polymer density regimes, we calculate the second virial coefficient B of the total effective potential acting between colloids. The dependence of B on the polymer density is discussed in detail, revealing several novel features of the PM interactions caused by the presence of attractive polymer-polymer interactions.

Weak interactions, omnivory and emergent food-web properties.

PubMed

Emmerson, Mark; Yearsley, Jon M

2004-02-22

Empirical studies have shown that, in real ecosystems, species-interaction strengths are generally skewed in their distribution towards weak interactions. Some theoretical work also suggests that weak interactions, especially in omnivorous links, are important for the local stability of a community at equilibrium. However, the majority of theoretical studies use uniform distributions of interaction strengths to generate artificial communities for study. We investigate the effects of the underlying interaction-strength distribution upon the return time, permanence and feasibility of simple Lotka-Volterra equilibrium communities. We show that a skew towards weak interactions promotes local and global stability only when omnivory is present. It is found that skewed interaction strengths are an emergent property of stable omnivorous communities, and that this skew towards weak interactions creates a dynamic constraint maintaining omnivory. Omnivory is more likely to occur when omnivorous interactions are skewed towards weak interactions. However, a skew towards weak interactions increases the return time to equilibrium, delays the recovery of ecosystems and hence decreases the stability of a community. When no skew is imposed, the set of stable omnivorous communities shows an emergent distribution of skewed interaction strengths. Our results apply to both local and global concepts of stability and are robust to the definition of a feasible community. These results are discussed in the light of empirical data and other theoretical studies, in conjunction with their broader implications for community assembly.

Meson-nucleus potentials and the search for meson-nucleus bound states

NASA Astrophysics Data System (ADS)

Metag, V.; Nanova, M.; Paryev, E. Ya.

2017-11-01

Recent experiments studying the meson-nucleus interaction to extract meson-nucleus potentials are reviewed. The real part of the potentials quantifies whether the interaction is attractive or repulsive while the imaginary part describes the meson absorption in nuclei. The review is focused on mesons which are sufficiently long-lived to potentially form meson-nucleus quasi-bound states. The presentation is confined to meson production off nuclei in photon-, pion-, proton-, and light-ion induced reactions and heavy-ion collisions at energies near the production threshold. Tools to extract the potential parameters are presented. In most cases, the real part of the potential is determined by comparing measured meson momentum distributions or excitation functions with collision model or transport model calculations. The imaginary part is extracted from transparency ratio measurements. Results on K+ ,K0 ,K- , η ,η‧ , ω, and ϕ mesons are presented and compared with theoretical predictions. The interaction of K+ and K0 mesons with nuclei is found to be weakly repulsive, while the K- , η ,η‧ , ω and ϕ meson-nucleus potentials are attractive, however, with widely different strengths. Because of meson absorption in the nuclear medium the imaginary parts of the meson-nucleus potentials are all negative, again with a large spread. An outlook on planned experiments in the charm sector is given. In view of the determined potential parameters, the criteria and chances for experimentally observing meson-nucleus quasi-bound states are discussed. The most promising candidates appear to be the η and η‧ mesons.

Localized N, {lambda}, {sigma}, and {xi} single-particle potentials in finite nuclei calculated with SU{sub 6} quark-model baryon-baryon interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohno, M.; Fujiwara, Y.

Localized single-particle potentials for all octet baryons, N, {lambda}, {sigma}, and {xi}, in finite nuclei, {sup 12}C, {sup 16}O, {sup 28}Si, {sup 40}Ca, {sup 56}Fe, and {sup 90}Zr, are calculated using the quark-model baryon-baryon interactions. G matrices evaluated in symmetric nuclear matter in the lowest order Brueckner theory (LOBT) are applied to finite nuclei in local density approximation. Nonlocal potentials are localized by a zero-momentum Wigner transformation. Empirical single-particle properties of the nucleon and the {lambda} hyperon in a nuclear medium have been known to be explained semiquantitatively in the LOBT framework. Attention is focused in the present consideration onmore » predictions for the {sigma} and {xi} hyperons. The unified description for the octet baryon-baryon interactions by the SU{sub 6} quark model enables us to obtain less ambiguous extrapolation to the S=-1 and S=-2 sectors based on the knowledge in the NN sector than other potential models. The {sigma} mean field is shown to be weakly attractive at the surface, but turns out to be repulsive inside, which is consistent with the experimental evidence. The {xi} hyperon s.p. potential is also attractive at the nuclear surface region, and inside it fluctuates around zero. Hence {xi} hypernuclear bound states are unlikely. We also evaluate energy shifts of the {sigma}{sup -} and {xi}{sup -} atomic levels in {sup 28}Si and {sup 56}Fe, using the calculated s.p. potentials.« less

Nanomechanical Contribution of Collagen and von Willebrand Factor A in Marine Underwater Adhesion and Its Implication for Collagen Manipulation.

PubMed

Yoo, Hee Young; Huang, Jun; Li, Lin; Foo, Mathias; Zeng, Hongbo; Hwang, Dong Soo

2016-03-14

Recent works on mussel adhesion have identified a load bearing matrix protein (PTMP1) containing von Willebrand factor (vWF) with collagen binding capability that contributes to the mussel holdfast by manipulating mussel collagens. Using a surface forces apparatus, we investigate for the first time, the nanomechanical properties of vWF-collagen interaction using homologous proteins of mussel byssus, PTMP1 and preCollagens (preCols), as collagen. Mimicking conditions similar to mussel byssus secretion (pH < 5.0) and seawater condition (pH 8.0), PTMP1 and preCol interact weakly in the "positioning" phase based on vWF-collagen binding and strengthen in "locked" phase due to the combined effects of electrostatic attraction, metal binding, and mechanical shearing. The progressive enhancement of binding between PTMP1 with porcine collagen under the aforementioned conditions is also observed. The binding mechanisms of PTMP1-preCols provide insights into the molecular interaction of the mammalian collagen system and the development of an artificial extracellular matrix based on collagens.

Diffusing colloidal probes of protein-carbohydrate interactions.

PubMed

Eichmann, Shannon L; Meric, Gulsum; Swavola, Julia C; Bevan, Michael A

2013-02-19

We present diffusing colloidal probe measurements of weak, multivalent, specific protein-polysaccharide interactions mediated by a competing monosaccharide. Specifically, we used integrated evanescent wave and video microscopy methods to monitor the three-dimensional Brownian excursions of conconavilin A (ConA) decorated colloids interacting with dextran-functionalized surfaces in the presence of glucose. Particle trajectories were interpreted as binding lifetime histograms, binding isotherms, and potentials of mean force. Binding lifetimes and isotherms showed clear trends of decreasing ConA-dextran-specific binding with increasing glucose concentration, consistent with expectations. Net potentials were accurately captured by superposition of a short-range, glucose-independent ConA-dextran repulsion and a longer-range, glucose-dependent dextran bridging attraction modeled as a harmonic potential. For glucose concentrations greater than 100 mM, the net ConA-dextran potential was found to have only a nonspecific repulsion, similar to that of bovine serum albumin (BSA) decorated colloids over dextran determined in control experiments. Our results demonstrate the first use of optical microscopy methods to quantify the connections between potentials of mean force and the binding behavior of ConA-decorated colloids on dextran-functionalized surfaces.

Scanning tunneling microscopy study of graphene on Au(111): Growth mechanisms and substrate interactions

NASA Astrophysics Data System (ADS)

Nie, Shu; Bartelt, Norman C.; Wofford, Joseph M.; Dubon, Oscar D.; McCarty, Kevin F.; Thürmer, Konrad

2012-05-01

We use scanning tunneling microscopy to study the structure of graphene islands on Au(111) grown by deposition of elemental carbon at 950 °C. Consistent with low-energy electron microscopic observations, we find that the graphene islands have dendritic shapes. The islands tend to cover depressed regions of the Au surface, suggesting that Au is displaced as the graphene grows. If small tunneling currents are used, it is possible to image simultaneously the graphene/Au moiré and the Au herringbone reconstruction, which forms underneath the graphene on cooling from the growth temperature. The delicate herringbone structure and its periodicity remain unchanged from the bare Au surface. Using a Frenkel-Kontorova model, we deduce that this striking observation is consistent with an attraction between graphene and Au of less than 13 meV per C atom. Raman spectroscopy supports this weak interaction. However, at the tunneling currents necessary for atomic-resolution imaging of graphene, the Au reconstruction is altered, implying influential tip-sample interactions and a mobile Au surface beneath the graphene.

Fluid-solid interaction: benchmarking of an external coupling of ANSYS with CFX for cardiovascular applications.

PubMed

Hose, D R; Lawford, P V; Narracott, A J; Penrose, J M T; Jones, I P

2003-01-01

Fluid-solid interaction is a primary feature of cardiovascular flows. There is increasing interest in the numerical solution of these systems as the extensive computational resource required for such studies becomes available. One form of coupling is an external weak coupling of separate solid and fluid mechanics codes. Information about the stress tensor and displacement vector at the wetted boundary is passed between the codes, and an iterative scheme is employed to move towards convergence of these parameters at each time step. This approach has the attraction that separate codes with the most extensive functionality for each of the separate phases can be selected, which might be important in the context of the complex rheology and contact mechanics that often feature in cardiovascular systems. Penrose and Staples describe a weak coupling of CFX for computational fluid mechanics to ANSYS for solid mechanics, based on a simple Jacobi iteration scheme. It is important to validate the coupled numerical solutions. An extensive analytical study of flow in elastic-walled tubes was carried out by Womersley in the late 1950s. This paper describes the performance of the coupling software for the straight elastic-walled tube, and compares the results with Womersley's analytical solutions. It also presents preliminary results demonstrating the application of the coupled software in the context of a stented vessel.

Poisson-Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes.

PubMed

Ubbink, Job; Khokhlov, Alexei R

2004-03-15

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson-Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Angstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson-Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)]. (c) 2004 American Institute of Physics.

Indirect Effects of Field Management on Pollination Service and Seed Set in Hybrid Onion Seed Production.

PubMed

Gillespie, Sandra; Long, Rachael; Williams, Neal

2015-12-01

Pollination in crops, as in native ecosystems, is a stepwise process that can be disrupted at any stage. Healthy pollinator populations are critical for adequate visitation, but pollination still might fail if crop management interferes with the attraction and retention of pollinators. Farmers must balance the direct benefits of applying insecticide and managing irrigation rates against their potential to indirectly interfere with the pollination process. We investigated these issues in hybrid onion seed production, where previous research has shown that high insecticide use reduces pollinator attraction. We conducted field surveys of soil moisture, nectar production, pollinator visitation, pollen-stigma interactions, and seed set at multiple commercial fields across 2 yr. We then examined how management actions, such as irrigation rate (approximated by soil moisture), or insecticide use could affect the pollination process. Onions produced maximum nectar at intermediate soil moisture, and high nectar production attracted more pollinators. Insecticide use weakly affected pollinator visitation, but when applied close to bloom reduced pollen germination and pollen tube growth. Ultimately, neither soil moisture nor insecticide use directly affected seed set, but the high correlation between pollinator visitation and seed set suggests that crop management will ultimately affect yields via indirect effects on the pollination process. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Synthetic Superconductivity in Single-Layer Crystals

NASA Astrophysics Data System (ADS)

Levitov, Leonid; Borgnia, Dan; Lee, Patrick

2015-03-01

Electronic states in atomically thin 2D crystals are fully exposed and can couple to extrinsic degrees of freedom via long-range Coulomb interactions. Novel many-body effects in such systems can be engineered by embedding them in a polar environment. Superconducting pairing interaction induced in this way can enhance the intrinsic electron-phonon pairing mechanism. We take on this notion, which was around since the 60's (''excitonic superconductivity''), and consider synthetic superconductivity (SSC) induced in 2D crystals by a polar environment. One interesting aspect of this scenario is that Coulomb repulsion acts as superconductivity friend rather than a foe. Such repulsion-to-attraction transmutation allows to access strong-coupling superconductivity regime even when intrinsic pairing interaction is weak. We analyze pairing interaction in 2D crystals placed atop a highly polarizable dielectric with dispersive permittivity ɛ (ω) and predict that by optimizing system parameters a substantial enhancement can be achieved. We also argue that the SSC mechanism can be responsible, at least in part, for 100 K superconductivity recently observed in FeSe monolayers grown on SrTiO3 substrate, with Tc more than 10 times larger than in bulk 3D FeSe crystals, arxiv:1406.3435.

Nucleation and hysteresis of vapor-liquid phase transitions in confined spaces: effects of fluid-wall interaction.

PubMed

Men, Yumei; Yan, Qingzhao; Jiang, Guangfeng; Zhang, Xianren; Wang, Wenchuan

2009-05-01

In this work, we propose a method to stabilize a nucleus in the framework of lattice density-functional theory (LDFT) by imposing a suitable constraint. Using this method, the shape of critical nucleus and height of the nucleation barrier can be determined without using a predefined nucleus as input. As an application of this method, we study the nucleation behavior of vapor-liquid transition in nanosquare pores with infinite length and relate the observed hysteresis loop on an adsorption isotherm to the nucleation mechanism. According to the dependence of hysteresis and the nucleation mechanism on the fluid-wall interaction, w , in this work, we have classified w into three regions ( w>0.9 , 0.1< or =w< or =0.9 , and w<0.1 ), which are denoted as strongly, moderately, and weakly attractive fluid-wall interaction, respectively. The dependence of hysteresis on the fluid-wall interaction is interpreted by the different nucleation mechanisms. Our constrained LDFT calculations also show that the different transition paths may induce different nucleation behaviors. The transition path dependence should be considered if morphological transition of nuclei exists during a nucleation process.

Dynamics of relaxation to a stationary state for interacting molecular motors

NASA Astrophysics Data System (ADS)

Gomes, Luiza V. F.; Kolomeisky, Anatoly B.

2018-01-01

Motor proteins are active enzymatic molecules that drive a variety of biological processes, including transfer of genetic information, cellular transport, cell motility and muscle contraction. It is known that these biological molecular motors usually perform their cellular tasks by acting collectively, and there are interactions between individual motors that specify the overall collective behavior. One of the fundamental issues related to the collective dynamics of motor proteins is the question if they function at stationary-state conditions. To investigate this problem, we analyze a relaxation to the stationary state for the system of interacting molecular motors. Our approach utilizes a recently developed theoretical framework, which views the collective dynamics of motor proteins as a totally asymmetric simple exclusion process of interacting particles, where interactions are taken into account via a thermodynamically consistent approach. The dynamics of relaxation to the stationary state is analyzed using a domain-wall method that relies on a mean-field description, which takes into account some correlations. It is found that the system quickly relaxes for repulsive interactions, while attractive interactions always slow down reaching the stationary state. It is also predicted that for some range of parameters the fastest relaxation might be achieved for a weak repulsive interaction. Our theoretical predictions are tested with Monte Carlo computer simulations. The implications of our findings for biological systems are briefly discussed.

Viewing time measures of sexual orientation in Samoan cisgender men who engage in sexual interactions with fa'afafine.

PubMed

Petterson, Lanna J; Dixson, Barnaby J; Little, Anthony C; Vasey, Paul L

2015-01-01

Androphilia refers to attraction to adult males, whereas gynephilia refers to attraction to adult females. The current study employed self-report and viewing time (response time latency) measures of sexual attraction to determine the sexual orientation of Samoan cisgender men (i.e., males whose gender presentation and identity is concordant with their biological sex) who engage in sexual interactions with transgender male androphiles (known locally as fa'afafine) compared to: (1) Samoan cisgender men who only engage in sexual interactions with women, and (2) fa'afafine. As expected, both measures indicated that cisgender men who only engaged in sexual interactions with women exhibited a gynephilic pattern of sexual attraction, whereas fa'afafine exhibited an androphilic one. In contrast, both measures indicated that cisgender men who engaged in sexual interactions with fa'afafine demonstrated a bisexual pattern of sexual attraction. Most of the cisgender men who exhibited bisexual viewing times did not engage in sexual activity with both men and women indicating that the manner in which bisexual patterns of sexual attraction manifest behaviorally vary from one culture to the next.

Ontogeny of collective behavior reveals a simple attraction rule.

PubMed

Hinz, Robert C; de Polavieja, Gonzalo G

2017-02-28

The striking patterns of collective animal behavior, including ant trails, bird flocks, and fish schools, can result from local interactions among animals without centralized control. Several of these rules of interaction have been proposed, but it has proven difficult to discriminate which ones are implemented in nature. As a method to better discriminate among interaction rules, we propose to follow the slow birth of a rule of interaction during animal development. Specifically, we followed the development of zebrafish, Danio rerio , and found that larvae turn toward each other from 7 days postfertilization and increase the intensity of interactions until 3 weeks. This developmental dataset allows testing the parameter-free predictions of a simple rule in which animals attract each other part of the time, with attraction defined as turning toward another animal chosen at random. This rule makes each individual likely move to a high density of conspecifics, and moving groups naturally emerge. Development of attraction strength corresponds to an increase in the time spent in attraction behavior. Adults were found to follow the same attraction rule, suggesting a potential significance for adults of other species.

The role of atomic level steric effects and attractive forces in protein folding.

PubMed

Lammert, Heiko; Wolynes, Peter G; Onuchic, José N

2012-02-01

Protein folding into tertiary structures is controlled by an interplay of attractive contact interactions and steric effects. We investigate the balance between these contributions using structure-based models using an all-atom representation of the structure combined with a coarse-grained contact potential. Tertiary contact interactions between atoms are collected into a single broad attractive well between the C(β) atoms between each residue pair in a native contact. Through the width of these contact potentials we control their tolerance for deviations from the ideal structure and the spatial range of attractive interactions. In the compact native state dominant packing constraints limit the effects of a coarse-grained contact potential. During folding, however, the broad attractive potentials allow an early collapse that starts before the native local structure is completely adopted. As a consequence the folding transition is broadened and the free energy barrier is decreased. Eventually two-state folding behavior is lost completely for systems with very broad attractive potentials. The stabilization of native-like residue interactions in non-perfect geometries early in the folding process frequently leads to structural traps. Global mirror images are a notable example. These traps are penalized by the details of the repulsive interactions only after further collapse. Successful folding to the native state requires simultaneous guidance from both attractive and repulsive interactions. Copyright © 2011 Wiley Periodicals, Inc.

Dark-matter particles without weak-scale masses or weak interactions.

PubMed

Feng, Jonathan L; Kumar, Jason

2008-12-05

We propose that dark matter is composed of particles that naturally have the correct thermal relic density, but have neither weak-scale masses nor weak interactions. These models emerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve the dark-matter problem. The framework accommodates single or multiple component dark matter, dark-matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong. These candidates enhance many direct and indirect signals relative to weakly interacting massive particles and have qualitatively new implications for dark-matter searches and cosmological implications for colliders.

Ginzburg-Landau expansion in strongly disordered attractive Anderson-Hubbard model

NASA Astrophysics Data System (ADS)

Kuchinskii, E. Z.; Kuleeva, N. A.; Sadovskii, M. V.

2017-07-01

We have studied disordering effects on the coefficients of Ginzburg-Landau expansion in powers of superconducting order parameter in the attractive Anderson-Hubbard model within the generalized DMFT+Σ approximation. We consider the wide region of attractive potentials U from the weak coupling region, where superconductivity is described by BCS model, to the strong coupling region, where the superconducting transition is related with Bose-Einstein condensation (BEC) of compact Cooper pairs formed at temperatures essentially larger than the temperature of superconducting transition, and a wide range of disorder—from weak to strong, where the system is in the vicinity of Anderson transition. In the case of semielliptic bare density of states, disorder's influence upon the coefficients A and B of the square and the fourth power of the order parameter is universal for any value of electron correlation and is related only to the general disorder widening of the bare band (generalized Anderson theorem). Such universality is absent for the gradient term expansion coefficient C. In the usual theory of "dirty" superconductors, the C coefficient drops with the growth of disorder. In the limit of strong disorder in BCS limit, the coefficient C is very sensitive to the effects of Anderson localization, which lead to its further drop with disorder growth up to the region of the Anderson insulator. In the region of BCS-BEC crossover and in BEC limit, the coefficient C and all related physical properties are weakly dependent on disorder. In particular, this leads to relatively weak disorder dependence of both penetration depth and coherence lengths, as well as of related slope of the upper critical magnetic field at superconducting transition, in the region of very strong coupling.

The attachment of α -synuclein to a fiber: A coarse-grain approach

NASA Astrophysics Data System (ADS)

Ilie, Ioana M.; den Otter, Wouter K.; Briels, Wim J.

2017-03-01

We present simulations of the amyloidogenic core of α-synuclein, the protein causing Parkinson's disease, as a short chain of coarse-grain patchy particles. Each particle represents a sequence of about a dozen amino acids. The fluctuating secondary structure of this intrinsically disordered protein is modelled by dynamic variations of the shape and interaction characteristics of the patchy particles, ranging from spherical with weak isotropic attractions for the disordered state to spherocylindrical with strong directional interactions for a β-sheet. Flexible linkers between the particles enable sampling of the tertiary structure. This novel model is applied here to study the growth of an amyloid fibril, by calculating the free energy profile of a protein attaching to the end of a fibril. The simulation results suggest that the attaching protein readily becomes trapped in a mis-folded state, thereby inhibiting further growth of the fibril until the protein has readjusted to conform to the fibril structure, in line with experimental findings and previous simulations on small fragments of other proteins.

Pairing in a dry Fermi sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maier, Thomas A.; Staar, Peter; Mishra, V.

In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

Pairing in a dry Fermi sea

DOE PAGES

Maier, Thomas A.; Staar, Peter; Mishra, V.; ...

2016-06-17

In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

Crystal structure and Hirshfield analysis of the 4-(di-methyl-amino)-pyridine adduct of 4-meth-oxy-phenyl-borane.

PubMed

Shooter, Jesse; Allen, Caleb J; Tinsley, Colby W K; Zakharov, Lev N; Abbey, Eric R

2017-11-01

The title compound [systematic name: 4-(di-methyl-amino)-pyridine-4-meth-oxy-phenyl-borane (1/1)], C 14 H 19 BN 2 O, contains two independent mol-ecules in the asymmetric unit. Both molecules exhibit coplanar, mostly sp 2 -hybridized meth-oxy and di-methyl-amino substituents on their respective aromatic rings, consistent with π-donation into the aromatic systems. The B-H groups exhibit an intra-molecular close contact with a C-H group of the pyridine ring, which may be evidence of electrostatic attraction between the hydridic B-H and the electropositive aromatic C-H. There appears to be weak C-H⋯π(arene) inter-actions between two of the H atoms of an amino-methyl group and the meth-oxy-substituted benzene ring of the other independent mol-ecule, and another C-H⋯π (arene) inter-action between one of the pyridine ring H atoms and the same benzene ring.

Effect of Fibonacci modulation on superconductivity

NASA Astrophysics Data System (ADS)

Gupta, Sanjay; Sil, Shreekantha; Bhattacharyya, Bibhas

2006-02-01

We have studied finite-sized single band models with short-range pairing interactions between electrons in the presence of diagonal Fibonacci modulation in one dimension. Two models, namely the attractive Hubbard model and the Penson-Kolb model, have been investigated at half-filling at zero temperature by solving the Bogoliubov-de Gennes equations in real space within a mean-field approximation. The competition between 'disorder' and the pairing interaction leads to a suppression of superconductivity (of usual pairs with zero centre-of-mass momenta) in the strong-coupling limit while an enhancement of the pairing correlation is observed in the weak-coupling regime for both models. However, the dissimilarity of the pairing mechanisms in these two models brings about notable differences in the results. The extent to which the bond-ordered wave and the η-paired (of pairs with centre-of-mass momenta = π) phases of the Penson-Kolb model are affected by the disorder has also been studied in the present calculation. Some finite size effects are also identified.

Dimensional control of supramolecular assemblies of diacetylene-derived peptide gemini amphiphile: from spherical micelles to foamlike networks.

PubMed

Jiang, Hao; Ehlers, Martin; Hu, Xiao-Yu; Zellermann, Elio; Schmuck, Carsten

2018-05-22

Peptide amphiphiles capable of assembling into multidimensional nanostructures have attracted much attention over the past decade due to their potential applications in materials science. Herein, a novel diacetylene-derived peptide gemini amphiphile with a fluorenylmethyloxycarbonyl (Fmoc) group at the N-terminus is reported to hierarchically assemble into spherical micelles, one-dimensional nanorods, two-dimensional foamlike networks and lamellae. Solvent polarity shows a remarkable effect on the self-assembled structures by changing the balance of four weak noncovalent interactions (hydrogen-bonding, π-π stacking, hydrophobic interaction, and electrostatic repulsion). We also show the time-evolution not only from spherical micelles to helical nanofibers in aqueous solution, but also from branched wormlike micelles to foamlike networks in methanol solution. In this work, the presence of the Fmoc group plays a key role in the self-assembly process. This work provides an efficient strategy for precise morphological control, aiding the future development in materials science.

Precise Orientation of a Single C60 Molecule on the Tip of a Scanning Probe Microscope

NASA Astrophysics Data System (ADS)

Chiutu, C.; Sweetman, A. M.; Lakin, A. J.; Stannard, A.; Jarvis, S.; Kantorovich, L.; Dunn, J. L.; Moriarty, P.

2012-06-01

We show that the precise orientation of a C60 molecule which terminates the tip of a scanning probe microscope can be determined with atomic precision from submolecular contrast images of the fullerene cage. A comparison of experimental scanning tunneling microscopy data with images simulated using computationally inexpensive Hückel theory provides a robust method of identifying molecular rotation and tilt at the end of the probe microscope tip. Noncontact atomic force microscopy resolves the atoms of the C60 cage closest to the surface for a range of molecular orientations at tip-sample separations where the molecule-substrate interaction potential is weakly attractive. Measurements of the C60C60 pair potential acquired using a fullerene-terminated tip are in excellent agreement with theoretical predictions based on a pairwise summation of the van der Waals interactions between C atoms in each cage, i.e., the Girifalco potential [L. Girifalco, J. Phys. Chem. 95, 5370 (1991)JPCHAX0022-365410.1021/j100167a002].

Z boson mediated dark matter beyond the effective theory

DOE PAGES

Kearney, John; Orlofsky, Nicholas; Pierce, Aaron

2017-02-17

Here, direct detection bounds are beginning to constrain a very simple model of weakly interacting dark matter—a Majorana fermion with a coupling to the Z boson. In a particularly straightforward gauge-invariant realization, this coupling is introduced via a higher-dimensional operator. While attractive in its simplicity, this model generically induces a large ρ parameter. An ultraviolet completion that avoids an overly large contribution to ρ is the singlet-doublet model. We revisit this model, focusing on the Higgs blind spot region of parameter space where spin-independent interactions are absent. This model successfully reproduces dark matter with direct detection mediated by the Zmore » boson but whose cosmology may depend on additional couplings and states. Future direct detection experiments should effectively probe a significant portion of this parameter space, aside from a small coannihilating region. As such, Z-mediated thermal dark matter as realized in the singlet-doublet model represents an interesting target for future searches.« less

Constraints on the dark matter and dark energy interactions from weak lensing bispectrum tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Rui; Feng, Chang; Wang, Bin, E-mail: an_rui@sjtu.edu.cn, E-mail: chang.feng@uci.edu, E-mail: wang_b@sjtu.edu.cn

We estimate uncertainties of cosmological parameters for phenomenological interacting dark energy models using weak lensing convergence power spectrum and bispectrum. We focus on the bispectrum tomography and examine how well the weak lensing bispectrum with tomography can constrain the interactions between dark sectors, as well as other cosmological parameters. Employing the Fisher matrix analysis, we forecast parameter uncertainties derived from weak lensing bispectra with a two-bin tomography and place upper bounds on strength of the interactions between the dark sectors. The cosmic shear will be measured from upcoming weak lensing surveys with high sensitivity, thus it enables us to usemore » the higher order correlation functions of weak lensing to constrain the interaction between dark sectors and will potentially provide more stringent results with other observations combined.« less

Solvophobic and solvophilic contributions in the water-to-aqueous guanidinium chloride transfer free energy of model peptides

NASA Astrophysics Data System (ADS)

Tomar, Dheeraj S.; Ramesh, Niral; Asthagiri, D.

2018-06-01

We study the solvation free energy of two different conformations (helix and extended) of two different peptides (deca-alanine and deca-glycine) in two different solvents (water and aqueous guanidinium chloride, GdmCl). The free energies are obtained using the quasichemical organization of the potential distribution theorem, an approach that naturally provides the repulsive (solvophobic or cavity) and attractive (solvophilic) contributions to solvation. The solvophilic contribution is further parsed into a chemistry contribution arising from solute interaction with the solvent in the first solvation shell and a long-range contribution arising from non-specific interactions between the solute and the solvent beyond the first solvation shell. The cavity contribution is obtained for two different envelopes, ΣS E, which theory helps identify as the solvent excluded volume, and ΣG, a larger envelope beyond which solute-solvent interactions are Gaussian. The ΣS E envelope is independent of the solvent, as expected on the basis of the insensitivity to the solvent type of the distance of closest approach between protein heavy atoms and solvent heavy atoms, but contrary to the intuition based on treating solvent constituents as spheres of some effective radii. For both envelopes, the cavity contribution in water is proportional to the surface area of the envelope. The same does not hold for GdmCl(aq), revealing the limitation of using molecular area to assess solvation energetics. The ΣG-cavity contribution predicts that GdmCl(aq) should favor the more compact state, contrary to the role of GdmCl in unfolding proteins. The chemistry contribution attenuates this effect, but still the net local (chemistry plus ΣG-packing) contribution is inadequate in capturing the role of GdmCl. With the inclusion of the long-range contribution, which is dominated by van der Waals interaction, aqueous GdmCl favors the extended conformation over the compact conformation. Our finding emphasizes the importance of weak, but attractive, long-range dispersion interactions in protein solution thermodynamics.

Solvophobic and solvophilic contributions in the water-to-aqueous guanidinium chloride transfer free energy of model peptides.

PubMed

Tomar, Dheeraj S; Ramesh, Niral; Asthagiri, D

2018-06-14

We study the solvation free energy of two different conformations (helix and extended) of two different peptides (deca-alanine and deca-glycine) in two different solvents (water and aqueous guanidinium chloride, GdmCl). The free energies are obtained using the quasichemical organization of the potential distribution theorem, an approach that naturally provides the repulsive (solvophobic or cavity) and attractive (solvophilic) contributions to solvation. The solvophilic contribution is further parsed into a chemistry contribution arising from solute interaction with the solvent in the first solvation shell and a long-range contribution arising from non-specific interactions between the solute and the solvent beyond the first solvation shell. The cavity contribution is obtained for two different envelopes, Σ SE , which theory helps identify as the solvent excluded volume, and Σ G , a larger envelope beyond which solute-solvent interactions are Gaussian. The Σ SE envelope is independent of the solvent, as expected on the basis of the insensitivity to the solvent type of the distance of closest approach between protein heavy atoms and solvent heavy atoms, but contrary to the intuition based on treating solvent constituents as spheres of some effective radii. For both envelopes, the cavity contribution in water is proportional to the surface area of the envelope. The same does not hold for GdmCl(aq), revealing the limitation of using molecular area to assess solvation energetics. The Σ G -cavity contribution predicts that GdmCl(aq) should favor the more compact state, contrary to the role of GdmCl in unfolding proteins. The chemistry contribution attenuates this effect, but still the net local (chemistry plus Σ G -packing) contribution is inadequate in capturing the role of GdmCl. With the inclusion of the long-range contribution, which is dominated by van der Waals interaction, aqueous GdmCl favors the extended conformation over the compact conformation. Our finding emphasizes the importance of weak, but attractive, long-range dispersion interactions in protein solution thermodynamics.

Ordered phases in the Holstein-Hubbard model: Interplay of strong Coulomb interaction and electron-phonon coupling

NASA Astrophysics Data System (ADS)

Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

2013-09-01

We study the Holstein-Hubbard model at half filling to explore ordered phases including superconductivity (SC), antiferromagnetism (AF), and charge order (CO) in situations where the electron-electron and electron-phonon interactions are strong (comparable to the electronic bandwidth). The model is solved in the dynamical mean-field approximation with a continuous-time quantum Monte Carlo impurity solver. We determine the superconducting transition temperature Tc and the SC order parameter and show that the phonon-induced retardation or the strong Coulomb interaction leads to a significant reduction and shift of the Tc dome against the effective electron-electron interaction Ueff given by the Hubbard U reduced by the phonon-mediated attraction in the static limit. This behavior is analyzed by comparison to an effective static model in the polaron representation with a renormalized bandwidth. In addition, we discuss the superconducting gap Δ and 2Δ/Tc to reveal the effect of the retardation and the Coulomb interaction. We also determine the finite-temperature phase diagram including AF and CO. In the moderate-coupling regime, there is a hysteretic region of AF and CO around Ueff=0, while the two phases are separated by a paramagnetic metal in the weak-coupling regime and a paramagnetic insulator in the strong-coupling regime.

Visualizing an ultra-weak protein-protein interaction in phosphorylation signaling.

PubMed

Xing, Qiong; Huang, Peng; Yang, Ju; Sun, Jian-Qiang; Gong, Zhou; Dong, Xu; Guo, Da-Chuan; Chen, Shao-Min; Yang, Yu-Hong; Wang, Yan; Yang, Ming-Hui; Yi, Ming; Ding, Yi-Ming; Liu, Mai-Li; Zhang, Wei-Ping; Tang, Chun

2014-10-20

Proteins interact with each other to fulfill their functions. The importance of weak protein-protein interactions has been increasingly recognized. However, owing to technical difficulties, ultra-weak interactions remain to be characterized. Phosphorylation can take place via a K(D)≈25 mM interaction between two bacterial enzymes. Using paramagnetic NMR spectroscopy and with the introduction of a novel Gd(III)-based probe, we determined the structure of the resulting complex to atomic resolution. The structure accounts for the mechanism of phosphoryl transfer between the two enzymes and demonstrates the physical basis for their ultra-weak interaction. Further, molecular dynamics (MD) simulations suggest that the complex has a lifetime in the micro- to millisecond regimen. Hence such interaction is termed a fleeting interaction. From mathematical modeling, we propose that an ultra-weak fleeting interaction enables rapid flux of phosphoryl signal, providing a high effective protein concentration. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Familiarity does indeed promote attraction in live interaction.

PubMed

Reis, Harry T; Maniaci, Michael R; Caprariello, Peter A; Eastwick, Paul W; Finkel, Eli J

2011-09-01

Does familiarity promote attraction? Prior research has generally suggested that it does, but a recent set of studies by Norton, Frost, and Ariely (2007) challenged that assumption. Instead, they found that more information about another person, when that information was randomly selected from lists of trait adjectives, using a trait evaluation paradigm, promoted perceptions of dissimilarity and, hence, disliking. The present research began with the assumption that natural social interaction involves contexts and processes not present in Norton et al.'s research or in the typical familiarity experiment. We theorized that these processes imply a favorable impact of familiarity on attraction. Two experiments are reported using a live interaction paradigm in which two previously unacquainted same-sex persons interacted with each other for varying amounts of time. Findings strongly supported the "familiarity leads to attraction" hypothesis: The more participants interacted, the more attracted they were to each other. Mediation analyses identified three processes that contribute to this effect: perceived responsiveness, increased comfort and satisfaction during interaction, and perceived knowledge. PsycINFO Database Record (c) 2011 APA, all rights reserved.

Identification of interfaces involved in weak interactions with application to F-actin-aldolase rafts.

PubMed

Hu, Guiqing; Taylor, Dianne W; Liu, Jun; Taylor, Kenneth A

2018-03-01

Macromolecular interactions occur with widely varying affinities. Strong interactions form well defined interfaces but weak interactions are more dynamic and variable. Weak interactions can collectively lead to large structures such as microvilli via cooperativity and are often the precursors of much stronger interactions, e.g. the initial actin-myosin interaction during muscle contraction. Electron tomography combined with subvolume alignment and classification is an ideal method for the study of weak interactions because a 3-D image is obtained for the individual interactions, which subsequently are characterized collectively. Here we describe a method to characterize heterogeneous F-actin-aldolase interactions in 2-D rafts using electron tomography. By forming separate averages of the two constituents and fitting an atomic structure to each average, together with the alignment information which relates the raw motif to the average, an atomic model of each crosslink is determined and a frequency map of contact residues is computed. The approach should be applicable to any large structure composed of constituents that interact weakly and heterogeneously. Copyright © 2017 Elsevier Inc. All rights reserved.

In-flight food delivery and waste collection service: the passengers’ perspective and potential improvement

NASA Astrophysics Data System (ADS)

Romli, F. I.; Rahman, K. Abdul; Ishak, F. D.

2016-10-01

Increased competition in the commercial air transportation industry has made service quality of the airlines as one of the key competitive measures to attract passengers against their rivals. In-flight services, particularly food delivery and waste collection, have a notable impact on perception of the overall airline's service quality because they are directly and interactively provided to passengers during flight. An online public survey is conducted to explore general passengers' perception of current in-flight food delivery and waste collection services, and to identify potential rooms for improvement. The obtained survey results indicate that in-flight service does have an effect on passengers' choice of airlines. Several weaknesses of the current service method and possible improvements have been established from the collected responses.

Influence of Siphonophore Behavior upon Their Natural Diets: Evidence for Aggressive Mimicry.

PubMed

Purcell, J E

1980-08-29

Collection by divers permitted determination of the natural diets of siphonophore species within II genera. Siphonophores that swim rapidly to spread their tentacles capture small prey, whereas those that swim very weakly capture much larger prey. Nematocyst batteries of two species of weak swimmers closely resemble copepods and fish larvae. Morphology, behavior, and diet suggest that these two species attract large prey by mimicking other zooplankton.

Strong tissue glue with tunable elasticity.

PubMed

Kelmansky, Regina; McAlvin, Brian J; Nyska, Abraham; Dohlman, Jenny C; Chiang, Homer H; Hashimoto, Michinao; Kohane, Daniel S; Mizrahi, Boaz

2017-04-15

Many bio-adhesive materials adhere weakly to tissue due to their high water content and weak structural integrity. Others provide desirable adhesive strength but suffer from rigid structure and lack of elasticity after administration. We have developed two water-free, liquid four-armed PEG pre-polymers modified with NHS or with NH 2 end groups which upon mixing changed from liquids to an elastic solid. The sealant and adhesive properties increased with the amount of the %v/v PEG 4 -NHS pre-polymer, and achieved adhesive properties comparable to those of cyanoacrylate glues. All mixtures showed minimal cytotoxicity in vitro. Mixtures of 90%v/v PEG 4 -NHS were retained in the subcutaneous space in vivo for up to 14days with minimal inflammation. This material's combination of desirable mechanical properties and biocompatibility has potential in numerous biomedical applications. Many bio-adhesive materials adhere weakly to tissue (e.g. hydrogels) due to their high water content and weak structural integrity. Others provide desirable mechanical properties but suffer from poor biocompatibility (e.g. cyanoacrylates). This study proposes a new concept for the formation of super strong and tunable tissue glues. Our bio-materials' enhanced performance is the product of new neat (without water or other solvents) liquid polymers that solidify after administration while allowing interactions with the tissue. Moreover, the elastic modulus of these materials could easily be tuned without compromising biocompatibility. This system could be an attractive alternative to sutures and staples since it can be applied more quickly, causes less pain and may require less equipment while maintaining the desired adhesion strength. Copyright © 2017 Acta Materialia Inc. All rights reserved.

Variation and decomposition of the partial molar volume of small gas molecules in different organic solvents derived from molecular dynamics simulations.

PubMed

Klähn, Marco; Martin, Alistair; Cheong, Daniel W; Garland, Marc V

2013-12-28

The partial molar volumes, V(i), of the gas solutes H2, CO, and CO2, solvated in acetone, methanol, heptane, and diethylether are determined computationally in the limit of infinite dilution and standard conditions. Solutions are described with molecular dynamics simulations in combination with the OPLS-aa force field for solvents and customized force field for solutes. V(i) is determined with the direct method, while the composition of V(i) is studied with Kirkwood-Buff integrals (KBIs). Subsequently, the amount of unoccupied space and size of pre-formed cavities in pure solvents is determined. Additionally, the shape of individual solvent cages is analyzed. Calculated V(i) deviate only 3.4 cm(3) mol(-1) (7.1%) from experimental literature values. Experimental V(i) variations across solutions are reproduced qualitatively and also quantitatively in most cases. The KBI analysis identifies differences in solute induced solvent reorganization in the immediate vicinity of H2 (<0.7 nm) and solvent reorganization up to the third solvation shell of CO and CO2 (<1.6 nm) as the origin of V(i) variations. In all solutions, larger V(i) are found in solvents that exhibit weak internal interactions, low cohesive energy density and large compressibility. Weak internal interactions facilitate solvent displacement by thermal solute movement, which enhances the size of solvent cages and thus V(i). Additionally, attractive electrostatic interactions of CO2 and the solvents, which do not depend on internal solvent interactions only, partially reversed the V(i) trends observed in H2 and CO solutions where electrostatic interactions with the solvents are absent. More empty space and larger pre-formed cavities are found in solvents with weak internal interactions, however, no evidence is found that solutes in any considered solvent are accommodated in pre-formed cavities. Individual solvent cages are found to be elongated in the negative direction of solute movement. This wake behind the moving solute is more pronounced in case of mobile H2 and in solvents with weaker internal interactions. However, deviations from a spherical solvent cage shape do not influence solute-solvent radial distribution functions after averaging over all solvent cage orientations and hence do not change V(i). Overall, the applied methodology reproduces V(i) and its variations reliably and the used V(i) decompositions identify the underlying reasons behind observed V(i) variations.

Variation and decomposition of the partial molar volume of small gas molecules in different organic solvents derived from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Klähn, Marco; Martin, Alistair; Cheong, Daniel W.; Garland, Marc V.

2013-12-01

The partial molar volumes, bar V_i, of the gas solutes H2, CO, and CO2, solvated in acetone, methanol, heptane, and diethylether are determined computationally in the limit of infinite dilution and standard conditions. Solutions are described with molecular dynamics simulations in combination with the OPLS-aa force field for solvents and customized force field for solutes. bar V_i is determined with the direct method, while the composition of bar V_i is studied with Kirkwood-Buff integrals (KBIs). Subsequently, the amount of unoccupied space and size of pre-formed cavities in pure solvents is determined. Additionally, the shape of individual solvent cages is analyzed. Calculated bar V_i deviate only 3.4 cm3 mol-1 (7.1%) from experimental literature values. Experimental bar V_i variations across solutions are reproduced qualitatively and also quantitatively in most cases. The KBI analysis identifies differences in solute induced solvent reorganization in the immediate vicinity of H2 (<0.7 nm) and solvent reorganization up to the third solvation shell of CO and CO2 (<1.6 nm) as the origin of bar V_i variations. In all solutions, larger bar V_i are found in solvents that exhibit weak internal interactions, low cohesive energy density and large compressibility. Weak internal interactions facilitate solvent displacement by thermal solute movement, which enhances the size of solvent cages and thus bar V_i. Additionally, attractive electrostatic interactions of CO2 and the solvents, which do not depend on internal solvent interactions only, partially reversed the bar V_i trends observed in H2 and CO solutions where electrostatic interactions with the solvents are absent. More empty space and larger pre-formed cavities are found in solvents with weak internal interactions, however, no evidence is found that solutes in any considered solvent are accommodated in pre-formed cavities. Individual solvent cages are found to be elongated in the negative direction of solute movement. This wake behind the moving solute is more pronounced in case of mobile H2 and in solvents with weaker internal interactions. However, deviations from a spherical solvent cage shape do not influence solute-solvent radial distribution functions after averaging over all solvent cage orientations and hence do not change bar V_i. Overall, the applied methodology reproduces bar V_i and its variations reliably and the used bar V_i decompositions identify the underlying reasons behind observed bar V_i variations.

History of Weak Interactions

DOE R&D Accomplishments Database

Lee, T. D.

1970-07-01

While the phenomenon of beta-decay was discovered near the end of the last century, the notion that the weak interaction forms a separate field of physical forces evolved rather gradually. This became clear only after the experimental discoveries of other weak reactions such as muon-decay, muon-capture, etc., and the theoretical observation that all these reactions can be described by approximately the same coupling constant, thus giving rise to the notion of a universal weak interaction. Only then did one slowly recognize that the weak interaction force forms an independent field, perhaps on the same footing as the gravitational force, the electromagnetic force, and the strong nuclear and sub-nuclear forces.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaudhari, Mangesh I.; Rempe, Susan B.; Asthagiri, D.

The role of solute attractive forces on hydrophobic interactions is studied by coordinated development of theory and simulation results for Ar atoms in water. In this paper, we present a concise derivation of the local molecular field (LMF) theory for the effects of solute attractive forces on hydrophobic interactions, a derivation that clarifies the close relation of LMF theory to the EXP approximation applied to this problem long ago. The simulation results show that change from purely repulsive atomic solute interactions to include realistic attractive interactions diminishes the strength of hydrophobic bonds. For the Ar–Ar rdfs considered pointwise, the numericalmore » results for the effects of solute attractive forces on hydrophobic interactions are opposite in sign and larger in magnitude than predicted by LMF theory. That comparison is discussed from the point of view of quasichemical theory, and it is suggested that the first reason for this difference is the incomplete evaluation within LMF theory of the hydration energy of the Ar pair. With a recent suggestion for the system-size extrapolation of the required correlation function integrals, the Ar–Ar rdfs permit evaluation of osmotic second virial coefficients B 2. Those B 2’s also show that incorporation of attractive interactions leads to more positive (repulsive) values. With attractive interactions in play, B 2 can change from positive to negative values with increasing temperatures. Furthermore, this is consistent with the puzzling suggestions of decades ago that B 2 ≈ 0 for intermediate cases of temperature or solute size. In all cases here, B 2 becomes more attractive with increasing temperature.« less

Viewing Time Measures of Sexual Orientation in Samoan Cisgender Men Who Engage in Sexual Interactions with Fa’afafine

PubMed Central

Petterson, Lanna J.; Dixson, Barnaby J.; Little, Anthony C.; Vasey, Paul L.

2015-01-01

Androphilia refers to attraction to adult males, whereas gynephilia refers to attraction to adult females. The current study employed self-report and viewing time (response time latency) measures of sexual attraction to determine the sexual orientation of Samoan cisgender men (i.e., males whose gender presentation and identity is concordant with their biological sex) who engage in sexual interactions with transgender male androphiles (known locally as fa’afafine) compared to: (1) Samoan cisgender men who only engage in sexual interactions with women, and (2) fa’afafine. As expected, both measures indicated that cisgender men who only engaged in sexual interactions with women exhibited a gynephilic pattern of sexual attraction, whereas fa’afafine exhibited an androphilic one. In contrast, both measures indicated that cisgender men who engaged in sexual interactions with fa’afafine demonstrated a bisexual pattern of sexual attraction. Most of the cisgender men who exhibited bisexual viewing times did not engage in sexual activity with both men and women indicating that the manner in which bisexual patterns of sexual attraction manifest behaviorally vary from one culture to the next. PMID:25679961

Compressible flow at high pressure with linear equation of state

NASA Astrophysics Data System (ADS)

Sirignano, William A.

2018-05-01

Compressible flow varies from ideal-gas behavior at high pressures where molecular interactions become important. Density is described through a cubic equation of state while enthalpy and sound speed are functions of both temperature and pressure, based on two parameters, A and B, related to intermolecular attraction and repulsion, respectively. Assuming small variations from ideal-gas behavior, a closed-form solution is obtained that is valid over a wide range of conditions. An expansion in these molecular-interaction parameters simplifies relations for flow variables, elucidating the role of molecular repulsion and attraction in variations from ideal-gas behavior. Real-gas modifications in density, enthalpy, and sound speed for a given pressure and temperature lead to variations in many basic compressible flow configurations. Sometimes, the variations can be substantial in quantitative or qualitative terms. The new approach is applied to choked-nozzle flow, isentropic flow, nonlinear-wave propagation, and flow across a shock wave, all for the real gas. Modifications are obtained for allowable mass-flow through a choked nozzle, nozzle thrust, sonic wave speed, Riemann invariants, Prandtl's shock relation, and the Rankine-Hugoniot relations. Forced acoustic oscillations can show substantial augmentation of pressure amplitudes when real-gas effects are taken into account. Shocks at higher temperatures and pressures can have larger pressure jumps with real-gas effects. Weak shocks decay to zero strength at sonic speed. The proposed framework can rely on any cubic equation of state and be applied to multicomponent flows or to more-complex flow configurations.

Experimental investigation and DFT calculation of different amine/ammonium salts adsorption on kaolinite

NASA Astrophysics Data System (ADS)

Chen, Jun; Min, Fan-fei; Liu, Lingyun; Liu, Chunfu; Lu, Fangqin

2017-10-01

The adsorption of four different amine/ammonium salts of DDA (Dodecyl amine), MDA (N-methyldodecyl amine), DMDA (N,N-dimethyldodecyl amine) and DTAC (Dodecyl trimethyl ammonium chloride) on kaolinite particles was investigated in the study through the measurement of contact angles, zeta potentials, aggregation observation, adsorption and sedimentation. The results show that different amine/ammonium salts can adsorb on the kaolinite surface to enhance the hydrophobicity and reduce the electronegativity of kaolinite particle surface, and thus induce a strong hydrophobic aggregation of kaolinite particles which promotes the settlement of kaolinite. To explore the adsorption mechanism of these four amine/ammonium salts on kaolinite surfaces, the adsorptions of DDA+, MDA+, DMDA+ and DTAC+ on kaolinite (001) surface and (00 1 bar) surface are calculated with DFT (Density functional theory). The DFT calculation results indicate that different amine/ammonium cations can strongly adsorbed on kaolinite (001) surface and (00 1 bar) surface by forming Nsbnd H⋯O strong hydrogen bonds or Csbnd H⋯O weak hydrogen bonds, and there are strongly electrostatic attractions between different amine/ammonium cations and kaolinite surfaces. The main adsorption mechanism of amine/ammonium cations on kaolinite is hydrogen-bond interaction and electrostatic attraction.

[Surgery as specialization for female physicians: Results from course evaluations and alumni studies at MHH].

PubMed

Paulmann, V; Fischer, V; Dudzinska, A; Pabst, R

2015-06-01

There is a lack of young surgeons in Germany. In order to provide a successful learning environment in medical education and to attract more physicians, training concepts need to be regularly controlled. Evaluation results compiled over several years from the Hanover Medical School (MHH) were analyzed for gender-related differences. In addition to overall satisfaction with practical training items were included that consider aspects of interaction between students and instructors. Furthermore, alumni studies provided data on the postgraduate specialty choice made by MHH students. Surgical training is integrated into medical education as block training periods of various durations. Against the background of an increased percentage of women in medicine this article analyzed whether surgery is evaluated differently between female and male medical students with respect to their experiences in clinical teaching. Evaluations of clinical training in surgery demonstrated that female and male medical students do not differ substantially with respect to the teaching quality; however, young female physicians choose surgery as a professional option less frequently than men. A systematic review of clinical training evaluations is crucial to identify weaknesses of current curricula. More empirical data from other faculties can induce discussions about the attractiveness of surgery as a profession.

Modified interactions among globular proteins below isoelectric point in the presence of mono-, di- and tri-valent ions: A small angle neutron scattering study

NASA Astrophysics Data System (ADS)

Das, Kaushik; Kundu, Sarathi; Mehan, Sumit; Aswal, V. K.

2016-02-01

Both short range attraction and long range electrostatic repulsion exist among globular protein Bovine Serum Albumin in solution below its isoelectric point (pI ≈ 4.8). At pD ≈ 4.0, below pI, protein has a net positive surface charge although local charge inhomogeneity presents. Small angle neutron scattering study reveals that in the presence of both mono-(Na+) and di-(Ni2+) valent ions attractive interaction increases and repulsive interaction decreases with the increase of salt concentration. However, for tri-valent (Fe3+) ions, both attractive and repulsive interaction increases with increasing salt concentration but the relative strength of repulsion is more than the attraction.

Electrostatic attraction between neutral microdroplets by ion fluctuations

NASA Astrophysics Data System (ADS)

Sheng, Yu-Jane; Tsao, Heng-Kwong

2004-06-01

The interaction between two aqueous droplets containing ions is investigated. The ion-fluctuation correlation gives rise to attraction between two neutral microdroplets, similar to the van der Waals interaction between neutral atoms. Electrostatic attraction consists of contributions from various induced multipole-multipole interactions, including dipole-dipole < P2z >2 r-6 , dipole-quadrupole < P2z > < Q 2zz > r-8 , dipole-octupole < P2z > < O 2zzz > r-10 , and quadrupole-quadrupole interactions < Q 2zz >2 r-10 . The mean-square multipole moments are determined analytically by linear response theory. The fluctuation-driven attraction is so strong at short distance that it may dominate over the Coulomb repulsion between like-charged droplets. These theoretical results are confirmed by Monte Carlo simulations.

Electrostatic attraction between neutral microdroplets by ion fluctuations.

PubMed

Sheng, Yu-Jane; Tsao, Heng-Kwong

2004-06-01

The interaction between two aqueous droplets containing ions is investigated. The ion-fluctuation correlation gives rise to attraction between two neutral microdroplets, similar to the van der Waals interaction between neutral atoms. Electrostatic attraction consists of contributions from various induced multipole-multipole interactions, including dipole-dipole < P(2)(z) >(2) r(-6), dipole-quadrupole < P(2)(z) > < Q (2)(zz ) > r(-8), dipole-octupole < P(2)(z) > < O (2)(zzz ) > r(-10), and quadrupole-quadrupole interactions < Q (2)(zz ) >(2) r(-10). The mean-square multipole moments are determined analytically by linear response theory. The fluctuation-driven attraction is so strong at short distance that it may dominate over the Coulomb repulsion between like-charged droplets. These theoretical results are confirmed by Monte Carlo simulations.

Polymerization Effect of Electrolytes on Hydrogen-Bonding Cryoprotectants: Ion–Dipole Interactions between Metal Ions and Glycerol

PubMed Central

2015-01-01

Protectants which are cell membrane permeable, such as glycerol, have been used effectively in the cryopreservation field for a number of decades, for both slow cooling and vitrification applications. In the latter case, the glass transition temperature (Tg) of the vitrification composition is key to its application, dictating the ultimate storage conditions. It has been observed that the addition of some electrolytes to glycerol, such as MgCl2, could elevate the Tg of the mixture, thus potentially providing more storage condition flexibility. The microscopic mechanisms that give rise to the Tg-enhancing behavior of these electrolytes are not yet well understood. The current study focuses on molecular dynamics simulation of glycerol mixed with a variety of metal chlorides (i.e., NaCl, KCl, MgCl2, and CaCl2), covering a temperature range that spans both the liquid and glassy states. The characteristics of the ion–dipole interactions between metal cations and hydroxyl groups of glycerol were analyzed. The interruption of the original hydrogen-bonding network among glycerol molecules by the addition of ions was also investigated in the context of hydrogen-bonding quantity and lifetime. Divalent metal cations were found to significantly increase the Tg by strengthening the interacting network in the electrolyte/glycerol mixture via strong cation–dipole attractions. In contrast, monovalent cations increased the Tg insignificantly, as the cation–dipole attraction was only slightly stronger than the original hydrogen-bonding network among glycerol molecules. The precursor of crystallization of NaCl and KCl was also observed in these compositions, potentially contributing to weak Tg-enhancing ability. The Tg-enhancing mechanisms elucidated in this study suggest a structure-enhancing role for divalent ions that could be of benefit in the design of protective formulations for biopreservation purposes. PMID:25405831

Separation processes using expulsion from dilute supercritical solutions

DOEpatents

Cochran, Jr., Henry D.

1993-01-01

A process for separating isotopes as well as other mixtures by utilizing the behavior of dilute repulsive or weakly attractive elements of the mixtures as the critical point of the solvent is approached.

Physical Attractiveness: Interactive Effects of Counselor and Client on Counseling Processes.

ERIC Educational Resources Information Center

Vargas, Alice M.; Borkowski, John G.

1983-01-01

Assessed how the physical attractiveness of counselors and clients interacted to build rapport in two experiments involving college students (N=128 and N=64). Results showed the counselor's physical attractiveness had a major impact on her perceived effectiveness and the client's expectation of success irrespective of the client's attractiveness…

Model of human immunodeficiency virus budding and self-assembly: Role of the cell membrane

NASA Astrophysics Data System (ADS)

Zhang, Rui; Nguyen, Toan T.

2008-11-01

Budding from the plasma membrane of the host cell is an indispensable step in the life cycle of the human immunodeficiency virus (HIV), which belongs to a large family of enveloped RNA viruses, retroviruses. Unlike regular enveloped viruses, retrovirus budding happens concurrently with the self-assembly of the main retrovirus protein subunits (called Gag protein after the name of the genetic material that codes for this protein: Group-specific AntiGen) into spherical virus capsids on the cell membrane. Led by this unique budding and assembly mechanism, we study the free energy profile of retrovirus budding, taking into account the Gag-Gag attraction energy and the membrane elastic energy. We find that if the Gag-Gag attraction is strong, budding always proceeds to completion. During early stage of budding, the zenith angle of partial budded capsids, α , increases with time as α∝t1/2 . However, if the Gag-Gag attraction is weak, a metastable state of partial budding appears. The zenith angle of these partially spherical capsids is given by α0≃(τ2/κσ)1/4 in a linear approximation, where κ and σ are the bending modulus and the surface tension of the membrane, and τ is a line tension of the capsid proportional to the strength of Gag-Gag attraction. Numerically, we find α0<0.3π without any approximations. Using experimental parameters, we show that HIV budding and assembly always proceed to completion in normal biological conditions. On the other hand, by changing Gag-Gag interaction strength or membrane rigidity, it is relatively easy to tune it back and forth between complete budding and partial budding. Our model agrees reasonably well with experiments observing partial budding of retroviruses including HIV.

Two-dimensional melting of colloids with long-range attractive interactions.

PubMed

Du, Di; Doxastakis, Manolis; Hilou, Elaa; Biswal, Sibani Lisa

2017-02-22

The solid-liquid melting transition in a two-dimensional (2-D) attractive colloidal system is visualized using superparamagnetic colloids that interact through a long-range isotropic attractive interaction potential, which is induced using a high-frequency rotating magnetic field. Various experiments, supported by Monte Carlo simulations, are carried out over a range of interaction potentials and densities to determine structure factors, Lindermann parameters, and translational and orientational order parameters. The system shows a first-order solid-liquid melting transition. Simulations and experiments suggest that dislocations and disclinations simultaneously unbind during melting. This is in direct contrast with reports of 2-D melting of paramagnetic particles that interact with a repulsive interaction potential.

Dynamics of Entangled Polymers: Role of Attractive Interactions

NASA Astrophysics Data System (ADS)

Grest, Gary S.; Koski, Jason

The coupled dynamics of entangled polymers, which span broad time and length scales, govern their unique viscoelastic properties. Numerical simulations of highly coarse grained models are often used to follow chain mobility from the intermediate Rouse and reptation regimes to the late time diffusive regime. In these models, purely repulsive interactions between monomers are typically used because it is less computationally expensive than including attractive interactions. The effect of including the attractive interaction on the local and macroscopic properties of entangled polymer melts is explored over a wide temperature range using large scale molecular dynamics simulations. Attractive interactions are shown to have little effect on the local packing for all temperatures T and chain mobility for T higher than about twice the glass transition Tg. For lower T, the attractive interactions play a significant role, reducing the chain mobility compared to the repulsive case. As T approaches Tg breakdown of time-temperature superposition for the stress autocorrelation function is observed. Sandia National Labs is a multiprogram laboratory managed and operated by Sandia Corporation, a Lockheed-Martin Company, for the U.S. Dept of Energy under Contract No. DEAC04-94AL85000.

Meeting your match: how attractiveness similarity affects approach behavior in mixed-sex dyads.

PubMed

van Straaten, Ischa; Engels, Rutger C M E; Finkenauer, Catrin; Holland, Rob W

2009-06-01

This experimental study investigated approach behavior toward opposite-sex others of similar versus dissimilar physical attractiveness. Furthermore, it tested the moderating effects of sex. Single participants interacted with confederates of high and low attractiveness. Observers rated their behavior in terms of relational investment (i.e., behavioral efforts related to the improvement of interaction fluency, communication of positive interpersonal affect, and positive self-presentation). As expected, men displayed more relational investment behavior if their own physical attractiveness was similar to that of the confederate. For women, no effects of attractiveness similarity on relational investment behavior were found. Results are discussed in the light of positive assortative mating, preferences for physically attractive mates, and sex differences in attraction-related interpersonal behaviors.

Probing solvation decay length in order to characterize hydrophobicity-induced bead-bead attractive interactions in polymer chains.

PubMed

Das, Siddhartha; Chakraborty, Suman

2011-08-01

In this paper, we quantitatively demonstrate that exponentially decaying attractive potentials can effectively mimic strong hydrophobic interactions between monomer units of a polymer chain dissolved in aqueous solvent. Classical approaches to modeling hydrophobic solvation interactions are based on invariant attractive length scales. However, we demonstrate here that the solvation interaction decay length may need to be posed as a function of the relative separation distances and the sizes of the interacting species (or beads or monomers) to replicate the necessary physical interactions. As an illustrative example, we derive a universal scaling relationship for a given solute-solvent combination between the solvation decay length, the bead radius, and the distance between the interacting beads. With our formalism, the hydrophobic component of the net attractive interaction between monomer units can be synergistically accounted for within the unified framework of a simple exponentially decaying potential law, where the characteristic decay length incorporates the distinctive and critical physical features of the underlying interaction. The present formalism, even in a mesoscopic computational framework, is capable of incorporating the essential physics of the appropriate solute-size dependence and solvent-interaction dependence in the hydrophobic force estimation, without explicitly resolving the underlying molecular level details.

Systematic continuum-discretized coupled-channels calculations of total fusion for 6Li with targets 28Si, 59Co, 96Zr, 198Pt, and 209Bi: Effect of resonance states

NASA Astrophysics Data System (ADS)

Gómez Camacho, A.; Wang, Bing; Zhang, H. Q.

2018-05-01

Continuum discretized coupled-channel (CDCC) calculations of total fusion cross sections for reactions induced by the weakly bound nucleus 6Li with targets 28Si, 59Co, 96Zr, 198Pt, and 209Bi at energies around the Coulomb barrier are presented. In the cluster structure frame of 6Li→α +d , short-range absorption potentials are considered for the interactions between the α and d fragments with the targets. The effect of resonance (l =2 , Jπ=3+,2+,1+ ) and nonresonance states of 6Li on fusion is studied by using two approaches: (1) by omitting the resonance states from the full discretized CDCC breakup space and (2) by considering only the resonance subspace. A systematic analysis of the effect on fusion from resonance breakup couplings is carried out from light to heavy mass targets. Among other things, it is found that resonance breakup states produce strong repulsive polarization potentials that lead to fusion suppression. Couplings from nonresonance states give place to weak repulsive potentials at high energies; however, these become attractive for the heavier targets at low energies.

Application of the Real-Time Time-Dependent Density Functional Theory to Excited-State Dynamics of Molecules and 2D Materials

NASA Astrophysics Data System (ADS)

Miyamoto, Yoshiyuki; Rubio, Angel

2018-04-01

We review our recent developments in the ab initio simulation of excited-state dynamics within the framework of time-dependent density functional theory (TDDFT). Our targets range from molecules to 2D materials, although the methods are general and can be applied to any other finite and periodic systems. We discuss examples of excited-state dynamics obtained by real-time TDDFT coupled with molecular dynamics (MD) and the Ehrenfest approximation, including photoisomerization in molecules, photoenhancement of the weak interatomic attraction of noble gas atoms, photoenhancement of the weak interlayer interaction of 2D materials, pulse-laser-induced local bond breaking of adsorbed atoms on 2D sheets, modulation of UV light intensity by graphene nanoribbons at terahertz frequencies, and collision of high-speed ions with the 2D material to simulate the images taken by He ion microscopy. We illustrate how the real-time TDDFT approach is useful for predicting and understanding non-equilibrium dynamics in condensed matter. We also discuss recent developments that address the excited-state dynamics of systems out of equilibrium and future challenges in this fascinating field of research.

Predictors of facial attractiveness and health in humans.

PubMed

Foo, Yong Zhi; Simmons, Leigh W; Rhodes, Gillian

2017-02-03

Facial attractiveness has been suggested to provide signals of biological quality, particularly health, in humans. The attractive traits that have been implicated as signals of biological quality include sexual dimorphism, symmetry, averageness, adiposity, and carotenoid-based skin colour. In this study, we first provide a comprehensive examination of the traits that predict attractiveness. In men, attractiveness was predicted positively by masculinity, symmetry, averageness, and negatively by adiposity. In women, attractiveness was predicted positively by femininity and negatively by adiposity. Skin colour did not predict attractiveness in either sex, suggesting that, despite recent interest in the literature, colour may play limited role in determining attractiveness. Male perceived health was predicted positively by averageness, symmetry, and skin yellowness, and negatively by adiposity. Female perceived health was predicted by femininity. We then examined whether appearance predicted actual health using measures that have been theoretically linked to sexual selection, including immune function, oxidative stress, and semen quality. In women, there was little evidence that female appearance predicted health. In men, we found support for the phenotype-linked fertility hypothesis that male masculinity signalled semen quality. However, we also found a negative relationship between averageness and semen quality. Overall, these results indicate weak links between attractive facial traits and health.

Predictors of facial attractiveness and health in humans

PubMed Central

Foo, Yong Zhi; Simmons, Leigh W.; Rhodes, Gillian

2017-01-01

Facial attractiveness has been suggested to provide signals of biological quality, particularly health, in humans. The attractive traits that have been implicated as signals of biological quality include sexual dimorphism, symmetry, averageness, adiposity, and carotenoid-based skin colour. In this study, we first provide a comprehensive examination of the traits that predict attractiveness. In men, attractiveness was predicted positively by masculinity, symmetry, averageness, and negatively by adiposity. In women, attractiveness was predicted positively by femininity and negatively by adiposity. Skin colour did not predict attractiveness in either sex, suggesting that, despite recent interest in the literature, colour may play limited role in determining attractiveness. Male perceived health was predicted positively by averageness, symmetry, and skin yellowness, and negatively by adiposity. Female perceived health was predicted by femininity. We then examined whether appearance predicted actual health using measures that have been theoretically linked to sexual selection, including immune function, oxidative stress, and semen quality. In women, there was little evidence that female appearance predicted health. In men, we found support for the phenotype-linked fertility hypothesis that male masculinity signalled semen quality. However, we also found a negative relationship between averageness and semen quality. Overall, these results indicate weak links between attractive facial traits and health. PMID:28155897

Insights into the role of age and social interactions on the sexual attractiveness of queens in an eusocial bee, Melipona flavolineata (Apidae, Meliponini).

PubMed

Veiga, Jamille Costa; Menezes, Cristiano; Contrera, Felipe Andrés León

2017-04-01

The attraction of sexual partners is a vital necessity among insects, and it involves conflict of interests and complex communication systems among male and female. In this study, we investigated the developing of sexual attractiveness in virgin queens (i.e., gynes) of Melipona flavolineata, an eusocial stingless bee. We followed the development of sexual attractiveness in 64 gynes, belonging to seven age classes (0, 3, 6, 9, 15, 18 days post-emergence), and we also evaluated the effect of different social interactions (such as competition between queens and interactions with workers) on the development of attractiveness in other 60 gynes. We used the number of males that tried to mate with a focal gyne as a representative variable of its sexual attractiveness. During the essays, each gyne was individually presented to 10 sexually mature males, and during 3 min, we counted the number of males that everted their genitalia in response to the presence of a gyne. Here, we show that M. flavolineata gynes are capable to (i) maintain their sexual attractiveness for long periods through adult life, (ii) they need a minimum social interaction to trigger the development of sexual attractiveness, and (iii) that gynes express this trait only within a social context. We conclude that the effective occurrence of matings is conditional on potential social interactions that gynes experienced before taking the nuptial flight, when they are still in the nest. These findings bring insights into the factors determining reproductive success in social insects.

Insights into the role of age and social interactions on the sexual attractiveness of queens in an eusocial bee, Melipona flavolineata (Apidae, Meliponini)

NASA Astrophysics Data System (ADS)

Veiga, Jamille Costa; Menezes, Cristiano; Contrera, Felipe Andrés León

2017-04-01

The attraction of sexual partners is a vital necessity among insects, and it involves conflict of interests and complex communication systems among male and female. In this study, we investigated the developing of sexual attractiveness in virgin queens (i.e., gynes) of Melipona flavolineata, an eusocial stingless bee. We followed the development of sexual attractiveness in 64 gynes, belonging to seven age classes (0, 3, 6, 9, 15, 18 days post-emergence), and we also evaluated the effect of different social interactions (such as competition between queens and interactions with workers) on the development of attractiveness in other 60 gynes. We used the number of males that tried to mate with a focal gyne as a representative variable of its sexual attractiveness. During the essays, each gyne was individually presented to 10 sexually mature males, and during 3 min, we counted the number of males that everted their genitalia in response to the presence of a gyne. Here, we show that M. flavolineata gynes are capable to (i) maintain their sexual attractiveness for long periods through adult life, (ii) they need a minimum social interaction to trigger the development of sexual attractiveness, and (iii) that gynes express this trait only within a social context. We conclude that the effective occurrence of matings is conditional on potential social interactions that gynes experienced before taking the nuptial flight, when they are still in the nest. These findings bring insights into the factors determining reproductive success in social insects.

Separation processes using expulsion from dilute supercritical solutions

DOEpatents

Cochran, H.D. Jr.

1993-04-20

A process is described for separating isotopes as well as other mixtures by utilizing the behavior of dilute repulsive or weakly attractive elements of the mixtures as the critical point of the solvent is approached.

Analysis of weak interactions and Eotvos experiments

NASA Technical Reports Server (NTRS)

Hsu, J. P.

1978-01-01

The intermediate-vector-boson model is preferred over the current-current model as a basis for calculating effects due to weak self-energy. Attention is given to a possible violation of the equivalence principle by weak-interaction effects, and it is noted that effects due to weak self-energy are at least an order of magnitude greater than those due to the weak binding energy for typical nuclei. It is assumed that the weak and electromagnetic energies are independent.

Charged nanoparticle attraction in multivalent salt solution: A classical-fluids density functional theory and molecular dynamics study

DOE PAGES

Salerno, K. Michael; Frischknecht, Amalie L.; Stevens, Mark J.

2016-04-08

Here, negatively charged nanoparticles (NPs) in 1:1, 1:2, and 1:3 electrolyte solutions are studied in a primitive ion model using molecular dynamics (MD) simulations and classical density functional theory (DFT). We determine the conditions for attractive interactions between the like-charged NPs. Ion density profiles and NP–NP interaction free energies are compared between the two methods and are found to be in qualitative agreement. The NP interaction free energy is purely repulsive for monovalent counterions, but can be attractive for divalent and trivalent counterions. Using DFT, the NP interaction free energy for different NP diameters and charges is calculated. The depthmore » and location of the minimum in the interaction depend strongly on the NPs’ charge. For certain parameters, the depth of the attractive well can reach 8–10 k BT, indicating that kinetic arrest and aggregation of the NPs due to electrostatic interactions is possible. Rich behavior arises from the geometric constraints of counterion packing at the NP surface. Layering of counterions around the NPs is observed and, as secondary counterion layers form the minimum of the NP–NP interaction free energy shifts to larger separation, and the depth of the free energy minimum varies dramatically. We find that attractive interactions occur with and without NP overcharging.« less

Electrodynamics of Lipid Membrane Interactions in the Presence of Zwitterionic Buffers

PubMed Central

Koerner, Megan M.; Palacio, Luis A.; Wright, Johnnie W.; Schweitzer, Kelly S.; Ray, Bruce D.; Petrache, Horia I.

2011-01-01

Due to thermal motion and molecular polarizability, electrical interactions in biological systems have a dynamic character. Zwitterions are dipolar molecules that typically are highly polarizable and exhibit both a positive and a negative charge depending on the pH of the solution. We use multilamellar structures of common lipids to identify and quantify the effects of zwitterionic buffers that go beyond the control of pH. We use the fact that the repeat spacing of multilamellar lipid bilayers is a sensitive and accurate indicator of the force balance between membranes. We show that common buffers can in fact charge up neutral membranes. However, this electrostatic effect is not immediately recognized because of the concomitant modification of dispersion (van der Waals) forces. We show that although surface charging can be weak, electrostatic forces are significant even at large distances because of reduced ionic screening and reduced van der Waals attraction. The zwitterionic interactions that we identify are expected to be relevant for interfacial biological processes involving lipid bilayers, and for a wide range of biomaterials, including amino acids, detergents, and pharmaceutical drugs. An appreciation of zwitterionic electrodynamic character can lead to a better understanding of molecular interactions in biological systems and in soft materials in general. PMID:21767488

Attractive Interactions between Heteroallenes and the Cucurbituril Portal.

PubMed

Reany, Ofer; Li, Amanda; Yefet, Maayan; Gilson, Michael K; Keinan, Ehud

2017-06-21

In this paper, we report on the noteworthy attractive interaction between organic azides and the portal carbonyls of cucurbiturils. Five homologous bis-α,ω-azidoethylammonium alkanes were prepared, where the number of methylene groups between the ammonium groups ranges from 4 to 8. Their interactions with cucurbit[6]uril were studied by NMR spectroscopy, IR spectroscopy, X-ray crystallography, and computational methods. Remarkably, while the distance between the portal plane and most atoms at the guest end groups increases progressively with the molecular size, the β-nitrogen atoms maintain a constant distance from the portal plane in all homologues, pointing at a strong attractive interaction between the azide group and the portal. Both crystallography and NMR support a specific electrostatic interaction between the carbonyl and the azide β-nitrogen, which stabilizes the canonical resonance form with positive charge on the β-nitrogen and negative charge on the γ-nitrogen. Quantum computational analyses strongly support electrostatics, in the form of orthogonal dipole-dipole interaction, as the main driver for this attraction. The alternative mechanism of n → π* orbital delocalization does not seem to play a significant role in this interaction. The computational studies also indicate that the interaction is not limited to azides, but generalizes to other isoelectronic heteroallene functions, such as isocyanate and isothiocyanate. This essentially unexploited attractive interaction could be more broadly utilized as a tool not only in relation to cucurbituril chemistry, but also for the design of novel supramolecular architectures.

Thermodynamic curvature for attractive and repulsive intermolecular forces

NASA Astrophysics Data System (ADS)

May, Helge-Otmar; Mausbach, Peter; Ruppeiner, George

2013-09-01

The thermodynamic curvature scalar R for the Lennard-Jones system is evaluated in phase space, including vapor, liquid, and solid state. We paid special attention to the investigation of R along vapor-liquid, liquid-solid, and vapor-solid equilibria. Because R is a measure of interaction strength, we traced out the line R=0 dividing the phase space into regions with effectively attractive (R<0) or repulsive (R>0) interactions. Furthermore, we analyzed the dependence of R on the strength of attraction applying a perturbation ansatz proposed by Weeks-Chandler-Anderson. Our results show clearly a transition from R>0 (for poorly repulsive interaction) to R<0 when loading attraction in the intermolecular potential.

Laboratory Evaluation of Synthetic Blends of l-(+)-Lactic Acid, Ammonia, and Ketones As Potential Attractants For Aedes aegypti.

PubMed

Venkatesh, P M; Sen, A

2017-12-01

Attraction of Aedes aegypti to various binary, trinary, and quaternary blends of lactic acid and ketones with or without ammonia was studied using a dual choice olfactometer. A dose dependent attraction was observed in cases of single compounds where cyclopentanone attracted the highest percentage (36.9 ± 1.8%) of Ae. aegypti when tested alone. No significant difference was observed between the attraction levels of trinary and binary blends of lactic acid and acetone or butanone when tested against clear air. However, in competitive bioassays, the trinary blend of lactic acid, acetone, and butanone was significantly preferred over binary blends of individual compounds ( P < 0.05). Acetylacetone was weakly attractive when tested alone but showed additive attraction when blended with lactic acid. However, acetylacetone acted as an attraction inhibitor when blended with other compounds. Cyclopentanone was attractive, but enhancement of attraction was not observed when blended with other components. Addition of ammonia to binary or trinary blends of lactic acid, acetone, and/or butanone did not increase the attraction significantly. In competitive bioassays, the blends containing ammonia were significantly preferred over the blends lacking ammonia ( P < 0.05). This highlights ammonia as an essential component of synthetic blends. A quaternary blend of lactic acid, ammonia, acetone, and butanone was most attractive (65 ± 1.5%) and preferred blend of all other combinations.

Attracting mutualists and antagonists: plant trait variation explains the distribution of specialist floral herbivores and pollinators on crops and wild gourds.

PubMed

Theis, Nina; Barber, Nicholas A; Gillespie, Sandra D; Hazzard, Ruth V; Adler, Lynn S

2014-08-01

• Floral traits play important roles in pollinator attraction and defense against floral herbivory. However, plants may experience trade-offs between conspicuousness to pollinators and herbivore attraction. Comparative studies provide an excellent framework to examine the role of multiple traits shaping mutualist and antagonist interactions.• To assess whether putative defensive and attractive traits predict species interactions, we grew 20 different Cucurbitaceae species and varieties in the field to measure interactions with pollinators and herbivores and in the greenhouse to assess trait variation. Cucurbits are characterized by the production of cucurbitacins, bitter nonvolatile terpenoids that are effective against generalist herbivores but can attract specialist beetles. We determined whether plant traits such as cucurbitacins predict herbivore resistance and pollinator attraction using an information-theoretic approach.• Mutualists and floral antagonists were attracted to the same cucurbit varieties once they flowered. However, rather than cucurbitacin concentration, we found that the size of the flower and volatile emissions of floral sesquiterpenoids explained both pollinator and floral herbivore visitation preference across cucurbit taxa. This pattern held across cucurbit taxa and within the Cucurbita genus.• Surprisingly, floral sesquiterpenoid volatiles, which are associated with direct defense, indirect defense, and attraction, rather than defense traits such as cucurbitacins, appeared to drive interactions with both pollinators and floral herbivores across cucurbit taxa. Identifying the relevant plant traits for attraction and deterrence is important in this economically valuable crop, particularly if pollinators and floral herbivores use the same plant traits as cues. © 2014 Botanical Society of America, Inc.

What Teachers Perceive--Children Receive?

ERIC Educational Resources Information Center

Algozzine, Robert

1976-01-01

Reports a study designed to ascertain the relationship between teacher perceived attractiveness and classroom interactions and suggests that "main effects" such as facial attractiveness of youngsters acts to determine individual potential for interactions with others. (MH)

Spectroscopic investigation of the effect of salt on binding of tartrazine with two homologous serum albumins: quantification by use of the Debye-Hückel limiting law and observation of enthalpy-entropy compensation.

PubMed

Bolel, Priyanka; Datta, Shubhashis; Mahapatra, Niharendu; Halder, Mintu

2012-08-30

Formation of ion pair between charged molecule and protein can lead to interesting biochemical phenomena. We report the evolution of thermodynamics of the binding of tartrazine, a negatively charged azo colorant, and serum albumins with salt. The dye binds predominantly electrostatically in low buffer strengths; however, on increasing salt concentration, affinity decreases considerably. The calculated thermodynamic parameters in high salt indicate manifestation of nonelectrostatic interactions, namely, van der Waals force and hydrogen bonding. Site-marker competitive binding studies and docking simulations indicate that the dye binds with HSA in the warfarin site and with BSA at the interface of warfarin and ibuprofen binding sites. The docked poses indicate nearby amino acid positive side chains, which are possibly responsible for electrostatic interaction. Using the Debye-Hückel interionic attraction theory for binding equilibria, it is shown that, for electrostatic binding the calculated free energy change increases linearly with square root of ionic strength. Also UV-vis, fluorescence, CD data indicate a decrease of interaction with salt concentration. This study quantitatively relates how ionic strength modulates the strength of the protein-ligand electrostatic interaction. The binding enthalpy and entropy have been found to compensate one another. The enthalpy-entropy compensation (EEC), general property of weak intermolecular interactions, has been discussed.

The phenomenology of maverick dark matter

NASA Astrophysics Data System (ADS)

Krusberg, Zosia Anna Celina

Astrophysical observations from galactic to cosmological scales point to a substantial non-baryonic component to the universe's total matter density. Although very little is presently known about the physical properties of dark matter, its existence offers some of the most compelling evidence for physics beyond the standard model (BSM). In the weakly interacting massive particle (WIMP) scenario, the dark matter consists of particles that possess weak-scale interactions with the particles of the standard model, offering a compelling theoretical framework that allows us to understand the relic abundance of dark matter as a natural consequence of the thermal history of the early universe. From the perspective of particle physics phenomenology, the WIMP scenario is appealing for two additional reasons. First, many theories of BSM physics contain attractive WIMP candidates. Second, the weak-scale interactions between WIMPs and standard model particles imply the possibility of detecting scatterings between relic WIMPs and detector nuclei in direct detection experiments, products of WIMP annihilations at locations throughout the galaxy in indirect detection programs, and WIMP production signals at high-energy particle colliders. In this work, we use an effective field theory approach to study model-independent dark matter phenomenology in direct detection and collider experiments. The maverick dark matter scenario is defined by an effective field theory in which the WIMP is the only new particle within the energy range accessible to the Large Hadron Collider (LHC). Although certain assumptions are necessary to keep the problem tractable, we describe our WIMP candidate generically by specifying only its spin and dominant interaction form with standard model particles. Constraints are placed on the masses and coupling constants of the maverick WIMPs using the Wilkinson Microwave Anisotropy Probe (WMAP) relic density measurement and direct detection exclusion data from both spin-independent (XENON100 and SuperCDMS) and spin-dependent (COUPP) experiments. We further study the distinguishability of maverick WIMP production signals at the Tevatron and the LHC---at its early and nominal configurations---using standard simulation packages, place constraints on maverick WIMP properties using existing collider data, and determine projected mass reaches in future data from both colliders. We find ourselves in a unique era of theoretically-motivated, high-precision dark matter searches that hold the potential to give us important insights, not only into the nature of dark matter, but also into the physics that lies beyond the standard model.

Floral scent contributes to interaction specificity in coevolving plants and their insect pollinators.

PubMed

Friberg, Magne; Schwind, Christopher; Roark, Lindsey C; Raguso, Robert A; Thompson, John N

2014-09-01

Chemical defenses, repellents, and attractants are important shapers of species interactions. Chemical attractants could contribute to the divergence of coevolving plant-insect interactions, if pollinators are especially responsive to signals from the local plant species. We experimentally investigated patterns of daily floral scent production in three Lithophragma species (Saxifragaceae) that are geographically isolated and tested how scent divergence affects attraction of their major pollinator-the floral parasitic moth Greya politella (Prodoxidae). These moths oviposit through the corolla while simultaneously pollinating the flower with pollen adhering to the abdomen. The complex and species-specific floral scent profiles were emitted in higher amounts during the day, when these day-flying moths are active. There was minimal divergence found in petal color, which is another potential floral attractant. Female moths responded most strongly to scent from their local host species in olfactometer bioassays, and were more likely to oviposit in, and thereby pollinate, their local host species in no-choice trials. The results suggest that floral scent is an important attractant in this interaction. Local specialization in the pollinator response to a highly specific plant chemistry, thus, has the potential to contribute importantly to patterns of interaction specificity among coevolving plants and highly specialized pollinators.

Coupled electrostatic and material surface stresses yield anomalous particle interactions and deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kemp, B. A., E-mail: bkemp@astate.edu; Nikolayev, I.; Sheppard, C. J.

2016-04-14

Like-charges repel, and opposite charges attract. This fundamental tenet is a result of Coulomb's law. However, the electrostatic interactions between dielectric particles remain topical due to observations of like-charged particle attraction and the self-assembly of colloidal systems. Here, we show, using both an approximate description and an exact solution of Maxwell's equations, that nonlinear charged particle forces result even for linear material systems and can be responsible for anomalous electrostatic interactions such as like-charged particle attraction and oppositely charged particle repulsion. Furthermore, these electrostatic interactions and the deformation of such particles have fundamental implications for our understanding of macroscopic electrodynamics.

Impressions of Counselors as a Function of Counselor Physical Attractiveness

ERIC Educational Resources Information Center

Carter, Jean A.

1978-01-01

Research assessed the effects of counselor physical attractiveness and inter-actions between attractiveness and counselor subject sex. It is suggested that sex of counselor and client may play a more important role independently and in conjunction with attractiveness than does attractiveness alone in influencing impressions and expectations.…

Effect of interactions with the chaperonin cavity on protein folding and misfolding†

PubMed Central

Sirur, Anshul; Knott, Michael; Best, Robert B.

2015-01-01

Recent experimental and computational results have suggested that attractive interactions between a chaperonin and an enclosed substrate can have an important effect on the protein folding rate: it appears that folding may even be slower inside the cavity than under unconfined conditions, in contrast to what we would expect from excluded volume effects on the unfolded state. Here we examine systematically the dependence of the protein stability and folding rate on the strength of such attractive interactions between the chaperonin and substrate, by using molecular simulations of model protein systems in an idealised attractive cavity. Interestingly, we find a maximum in stability, and a rate which indeed slows down at high attraction strengths. We have developed a simple phenomenological model which can explain the variations in folding rate and stability due to differing effects on the free energies of the unfolded state, folded state, and transition state; changes in the diffusion coefficient along the folding coordinate are relatively small, at least for our simplified model. In order to investigate a possible role for these attractive interactions in folding, we have studied a recently developed model for misfolding in multidomain proteins. We find that, while encapsulation in repulsive cavities greatly increases the fraction of misfolded protein, sufficiently strong attractive protein-cavity interactions can strongly reduce the fraction of proteins reaching misfolded traps. PMID:24077053

NMR characterization of weak interactions between RhoGDI2 and fragment screening hits.

PubMed

Liu, Jiuyang; Gao, Jia; Li, Fudong; Ma, Rongsheng; Wei, Qingtao; Wang, Aidong; Wu, Jihui; Ruan, Ke

2017-01-01

The delineation of intrinsically weak interactions between novel targets and fragment screening hits has long limited the pace of hit-to-lead evolution. Rho guanine-nucleotide dissociation inhibitor 2 (RhoGDI2) is a novel target that lacks any chemical probes for the treatment of tumor metastasis. Protein-observed and ligand-observed NMR spectroscopy was used to characterize the weak interactions between RhoGDI2 and fragment screening hits. We identified three hits of RhoGDI2 using streamlined NMR fragment-based screening. The binding site residues were assigned using non-uniformly sampled C α - and H α -based three dimensional NMR spectra. The molecular docking to the proposed geranylgeranyl binding pocket of RhoGDI2 was guided by NMR restraints of chemical shift perturbations and ligand-observed transferred paramagnetic relaxation enhancement. We further validated the weak RhoGDI2-hit interactions using mutagenesis and structure-affinity analysis. Weak interactions between RhoGDI2 and fragment screening hits were delineated using an integrated NMR approach. Binders to RhoGDI2 as a potential anti-cancer target have been first reported, and their weak interactions were depicted using NMR spectroscopy. Our work highlights the powerfulness and the versatility of the integrative NMR techniques to provide valuable structural insight into the intrinsically weak interactions between RhoGDI2 and the fragment screening hits, which could hardly be conceived using other biochemical techniques. Copyright © 2016 Elsevier B.V. All rights reserved.

Universal Features of the Fluid to Solid Transition for Attractive Colloidal Particles

NASA Technical Reports Server (NTRS)

Cipelletti, L.; Prasad, V.; Dinsmore, A.; Segre, P. N.; Weitz, D. A.; Trappe, V.

2002-01-01

Attractive colloidal particles can exhibit a fluid to solid phase transition if the magnitude of the attractive interaction is sufficiently large, if the volume fraction is sufficiently high, and if the applied stress is sufficiently small. The nature of this fluid to solid transition is similar for many different colloid systems, and for many different forms of interaction. The jamming phase transition captures the common features of these fluid to solid translations, by unifying the behavior as a function of the particle volume fraction, the energy of interparticle attractions, and the applied stress. This paper describes the applicability of the jamming state diagram, and highlights those regions where the fluid to solid transition is still poorly understood. It also presents new data for gelation of colloidal particles with an attractive depletion interaction, providing more insight into the origin of the fluid to solid transition.

Hot particles attract in a cold bath

NASA Astrophysics Data System (ADS)

Tanaka, Hidenori; Lee, Alpha A.; Brenner, Michael P.

2017-04-01

Controlling interactions out of thermodynamic equilibrium is crucial for designing addressable and functional self-organizing structures. These active interactions also underpin collective behavior in biological systems. Here we study a general setting of active particles in a bath of passive particles and demonstrate a mechanism for long-range attraction between active particles. The mechanism operates when the translational persistence length of the active particle motion is smaller than the particle diameter. In this limit, the system reduces to particles of higher diffusivity ("hot" particles) in a bath of particles with lower diffusivity ("cold" particles). This attractive interaction arises as a hot particle pushes cold particles away to create a large hole around itself, and the holes interact via a depletion-like attraction. Strikingly, the interaction range is more than an order of magnitude larger than the particle radius, well beyond the range of the conventional depletion force. Although the mechanism occurs outside the parameter regime of typical biological swimmers, the mechanism could be realized in the laboratory.

Molecular Dynamics Simulations of the Permeation of Bisphenol A and Pore Formation in a Lipid Membrane

NASA Astrophysics Data System (ADS)

Chen, Liang; Chen, Junlang; Zhou, Guoquan; Wang, Yu; Xu, Can; Wang, Xiaogang

2016-09-01

Bisphenol A (BPA) is particularly considered as one of the most suspicious endocrine disruptors. Exposure to BPA may bring about possible human toxicities, such as cancerous tumors, birth defects and neoteny. One of the key issues to understand its toxicities is how BPA enters cells. In this paper, we perform molecular dynamics simulations to explore the interactions between BPA and a phospholipid membrane (dipalmitoylphosphatidylcholine, DPPC bilayer). The simulation results show that BPA can easily enter the membrane from the aqueous phase. With the increasing concentrations of BPA in the membrane, BPA tends to aggregate and form into cluster. Meanwhile, several DPPC lipids are pulled out from each leaflet and adsorbed on the cluster surface, leading to pore formation. Detailed observations indicate that the lipid extraction results mainly from the dispersion interactions between BPA cluster and lipid tails, as well as weak electrostatic attractions between lipid headgroups and the two hydroxyl groups on BPA. The lipid extraction and pore formation may cause cell membrane damage and are of great importance to uncover BPA’s cytotoxicity.

New investigations of the guanine trichloro cuprate(II) complex crystal

NASA Astrophysics Data System (ADS)

Fabijanić, Ivana; Matković-Čalogović, Dubravka; Pilepić, Viktor; Ivanišević, Irena; Mohaček-Grošev, Vlasta; Sanković, Krešimir

2017-01-01

Crystals of the guanine trichloro cuprate(II) complex, (HGua)2[Cu2Cl6]·2H2O (HGua = protonated guanine), were prepared and analysed by spectroscopic (IR, Raman) and computational methods. A new single-crystal X-ray diffraction analysis was conducted to obtain data with lower standard uncertainties than those in the previously published structure. Raman and IR spectroscopy and quantum-mechanical analysis gave us new insight into the vibrational states of the (HGua)2[Cu2Cl6]·2H2O crystal. The vibrational spectra of the crystal were assigned by performing a normal coordinate analysis for a free dimer with a centre of inversion as the only symmetry element. The stretching vibration observed at 279 cm-1 in the infrared spectrum corresponds to the N-Cu bond. The noncovalent interaction (NCI) plots and quantum theory of atoms in molecules (QTAIM) analysis of the electron density obtained from periodic DFT calculations elucidated the interactions that exist within the crystal structure. Closed-shell ionic attractions, as well as weak and medium strength hydrogen bonds, prevailed in the crystal packing.

Septins - active GTPases or just GTP-binding proteins?

PubMed

Abbey, Megha; Gaestel, Matthias; Menon, Manoj B

2018-05-10

Septins are conserved cytoskeletal proteins with unique filament forming capabilities and roles in cytokinesis and cell morphogenesis. Septins undergo hetero-oligomerization and assemble into higher order structures including filaments, rings and cages. Hetero- and homotypic interactions of septin isoforms involve alternating GTPase (G)-domain interfaces and those mediated by N- and C-terminal extensions. While most septins bind GTP, display weak GTP-hydrolysis activity and incorporate guanine nucleotides in their interaction interfaces, studies using GTPase-inactivating mutations have failed to conclusively establish a crucial role for GTPase activity in mediating septin functions. In this mini-review, we will critically assess the role of GTP-binding and -hydrolysis on septin assembly and function. The relevance of G-domain activity will also be discussed in the context of human septin mutations as well as the development of specific small-molecules targeting septin polymerization. As structural determinants of septin oligomer interfaces, G-domains are attractive targets for ligand-based inhibition of septin assembly. Whether such an intervention can predictably alter septin function is a major question for future research. This article is protected by copyright. All rights reserved. © 2018 Wiley Periodicals, Inc.

Topological surface states interacting with bulk excitations in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy.

PubMed

Park, Wan Kyu; Sun, Lunan; Noddings, Alexander; Kim, Dae-Jeong; Fisk, Zachary; Greene, Laura H

2016-06-14

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3 Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6 The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6.

Topological surface states interacting with bulk excitations in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy

PubMed Central

Park, Wan Kyu; Sun, Lunan; Noddings, Alexander; Kim, Dae-Jeong; Fisk, Zachary; Greene, Laura H.

2016-01-01

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi2Se3. Here, we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB6. The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveals linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB6. PMID:27233936

Fracture in Kaolinite clay suspensions

NASA Astrophysics Data System (ADS)

Kosgodagan Acharige, Sebastien; Jerolmack, Douglas J.; Arratia, Paulo E.

2017-11-01

Clay minerals are involved in many natural (landslides, river channels) and industrial processes (ceramics, cosmetics, oil recovery). They are plate shaped charged colloids and exhibit different flow properties than simpler colloids when suspended in a liquid such as thixotropy and shear-banding. kaolinite platelets are non-swelling, meaning that the stacks formed by the platelets do not have water layers, and thus the suspension does not have a sol-gel transition. However, it has been shown that kaolinite suspensions possesses a non-zero yield stress even at low concentrations, indicating that the particles arrange themselves in a structure through attractive interactions. Here, we experimentally investigate the sedimentation of kaolinite suspensions in a Hele-Shaw cell. The sedimentation of these dilute suspensions can display solid behavior like fracture, revealed in cross-polarized light, which is linked to the failure of the weakly-bonded structure (typical yield stress 10-2 Pa). By changing the interaction potential of the particles (by sonication or introducing salts), we show through these sedimentation experiments, how the fracture pattern can be avoided. Research was sponsored by the Army Research Laboratory and was accomplished under Grant Number 569074.

Attractive noncovalent interactions in asymmetric catalysis: Links between enzymes and small molecule catalysts

PubMed Central

Knowles, Robert R.; Jacobsen, Eric N.

2010-01-01

Catalysis by neutral, organic, small molecules capable of binding and activating substrates solely via noncovalent interactions—particularly H-bonding—has emerged as an important approach in organocatalysis. The mechanisms by which such small molecule catalysts induce high enantioselectivity may be quite different from those used by catalysts that rely on covalent interactions with substrates. Attractive noncovalent interactions are weaker, less distance dependent, less directional, and more affected by entropy than covalent interactions. However, the conformational constraint required for high stereoinduction may be achieved, in principle, if multiple noncovalent attractive interactions are operating in concert. This perspective will outline some recent efforts to elucidate the cooperative mechanisms responsible for stereoinduction in highly enantioselective reactions promoted by noncovalent catalysts. PMID:20956302

Strategic Sexual Signals: Women's Display versus Avoidance of the Color Red Depends on the Attractiveness of an Anticipated Interaction Partner

PubMed Central

Maner, Jon K.

2016-01-01

The color red has special meaning in mating-relevant contexts. Wearing red can enhance perceptions of women’s attractiveness and desirability as a potential romantic partner. Building on recent findings, the present study examined whether women’s (N = 74) choice to display the color red is influenced by the attractiveness of an expected opposite-sex interaction partner. Results indicated that female participants who expected to interact with an attractive man displayed red (on clothing, accessories, and/or makeup) more often than a baseline consisting of women in a natural environment with no induced expectation. In contrast, when women expected to interact with an unattractive man, they eschewed red, displaying it less often than in the baseline condition. Findings are discussed with respect to evolutionary and cultural perspectives on mate evaluation and selection. PMID:26960135

Evaluating Predators and Competitors in Wisconsin Red Pine Forests for Attraction to Mountain Pine Beetle Pheromones for Anticipatory Biological Control.

PubMed

Pfammatter, Jesse A; Krause, Adam; Raffa, Kenneth F

2015-08-01

Mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is an irruptive tree-killing species native to pine forests of western North America. Two potential pathways of spread to eastern forests have recently been identified. First, warming temperatures have driven range expansion from British Columbia into Albertan jack pine forests that are contiguous with the Great Lakes region. Second, high temperatures and drought have fostered largescale outbreaks within the historical range, creating economic incentives to salvage killed timber by transporting logs to midwestern markets, which risks accidental introduction. We evaluated the extent to which local predators and competitors that exploit bark beetle semiochemicals would respond to D. ponderosae in Wisconsin. We emulated D. ponderosae attack by deploying lures containing synthetic aggregation pheromones with and without host tree compounds and blank control traps in six red pine plantations over 2 yr. Predator populations were high in these stands, as evidenced by catches in positive control traps, baited with pheromones of local bark beetles and were deployed distant from behavioral choice plots. Only one predator, Thanasimus dubius F. (Coleoptera: Cleridae) was attracted to D. ponderosae's aggregation pheromones relative to blank controls, and its attraction was relatively weak. The most common bark beetles attracted to these pheromones were lower stem and root colonizers, which likely would facilitate rather than compete with D. ponderosae. There was some, but weak, attraction of potentially competing Ips species. Other factors that might influence natural enemy impacts on D. ponderosae in midwestern forests, such as phenological synchrony and exploitation of male-produced pheromones, are discussed. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Exploiting attractiveness in persuasion: senders' implicit theories about receivers' processing motivation.

PubMed

Vogel, Tobias; Kutzner, Florian; Fiedler, Klaus; Freytag, Peter

2010-06-01

Previous research suggests a positive correlation between physical attractiveness and the expectation of positive outcomes in social interactions, such as successful persuasion. However, prominent persuasion theories do not imply a general advantage of attractive senders. Instead, the persuasion success should vary with the receivers' processing motivation and processing capacity. Focusing on the perspective of the sender, the authors elaborate on lay theories about how attractiveness affects persuasion success. They propose that lay theories (a) match scientific models in that they also comprise the interaction of senders' attractiveness and receivers' processing characteristics, (b) guide laypersons' anticipation of persuasion success, and (c) translate into strategic behavior. They show that anticipated persuasion success depends on the interplay of perceived attractiveness and expectations about receivers' processing motivation (Experiment 1 and 2). Further experiments show that laypersons strategically attempt to exploit attractiveness in that they approach situations (Experiment 3) and persons (Experiment 4) that promise persuasion success.

Theory of elastic interaction between arbitrary colloidal particles in confined nematic liquid crystals.

PubMed

Tovkach, O M; Chernyshuk, S B; Lev, B I

2012-12-01

We develop the method proposed by Chernyshuk and Lev [Phys. Rev. E 81, 041701 (2010)] for theoretical investigation of elastic interactions between colloidal particles of arbitrary shape and chirality (polar as well as azimuthal anchoring) in the confined nematic liquid crystal (NLC). General expressions for six different types of multipole elastic interactions are obtained in the confined NLC: monopole-monopole (Coulomb type), monopole-dipole, monopole-quadrupole, dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The obtained formulas remain valid in the presence of the external electric or magnetic fields. The exact equations are found for all multipole coefficients for the weak anchoring case. For the strong anchoring coupling, the connection between the symmetry of the shape or director and multipole coefficients is obtained, which enables us to predict which multipole coefficients vanish and which remain nonzero. The particles with azimuthal helicoid anchoring are considered as an example. Dipole-dipole interactions between helicoid cylinders and cones are found in the confined NLC. In addition, the banana-shaped particles in homeotropic and planar nematic cells are considered. It is found that the dipole-dipole interaction between banana-shaped particles differs greatly from the dipole-dipole interaction between the axially symmetrical particles in the nematic cell. There is a crossover from attraction to repulsion between banana particles along some directions in nematic cells. It is shown that monopoles do not "feel" the type of nematic cell: monopole-monopole interaction turns out to be the same in homeotropic and planar nematic cells and converges to the Coulomb law as thickness increases, L→∞.

Molecular Handshake: Recognition through Weak Noncovalent Interactions

ERIC Educational Resources Information Center

Murthy, Parvathi S.

2006-01-01

The weak noncovalent interactions between substances, the handshake in the form of electrostatic interactions, van der Waals' interactions or hydrogen bonding is universal to all living and nonliving matter. They significantly influence the molecular and bulk properties and behavior of matter. Their transient nature affects chemical reactions and…

Simulation of the self-assembly of colloidal droplets in a micro-channel

NASA Astrophysics Data System (ADS)

Ge, Zhouyang; Brandt, Luca

2016-11-01

In colloidal sciences, much progress has been made on the synthesis of complex building blocks mimicking molecular structures to elaborate innovative materials. The basic elements of such colloidal molecules are particles or droplets less than one millimeter in size. Their self-assembly relies on either lengthy brownian motion or careful microfludic designs, on top of typical colloidal interactions, e.g. depletion attraction. Regardless of the approach, however, questions remain why the colloids undergo certain path to organize themselves and how such process can be optimized. Here, we perform direct numerical simulations using a Navier-Stokes solver at low Reynolds number, combined with either the immersed boundary method (IBM) or a newly-proposed level set (LS) method for interface description. In the IBM simulations, the colloids are treated as rigid, spherical particles under a Lennard-Jones-like potential, reproducing attractive depletion force. Results show that, for four particles, a planar diamond is formed under a weak potential while a 3D tetrahedron is formed under a strong potential, which agree qualitatively with experiments. In the next step, LS simulation of colloidal droplets will be performed to investigate the roles of surface tension in the self-assembly. This project has received funding from the European Union's Horizon 2020 research and innovation programme under Grant agreement No 664823.

Real-Time Binding Kinetic Analyses of the Interaction of the Dietary Stain Orange II with Dentin Matrix.

PubMed

Alraies, Amr; Cole, David K; S Rees, Jeremy; Glasse, Carl; Young, Nigel; Waddington, Rachel J; Sloan, Alastair J

2018-06-09

Dietary stains can be adsorbed into the dentin of teeth. Using Orange II as a model dietary stain, this study investigated the strength of its interaction with the mineral and protein components of dentin matrix and how hydrogen peroxide (H 2 O 2 ) treatment influences this interaction. Dentin slices were prepared from human teeth and were either deproteinized (5.6% sodium hypochlorite, 12 days), demineralised (0.5 M EDTA, 3 days) or left as intact control samples. Samples were stained with Orange II for 1-168 h, during which staining intensity was quantified by image analysis. Similarly, uptake of stain by deproteinized / demineralized samples treated with 10 or 30% H 2 O 2 was investigated. Using surface plasmon resonance technology, real-time binding kinetics were determined assessing the interaction of orange II with the dentin matrix protein constituents, collagen type I, biglycan, decorin, dentin sialoprotein and osteopontin. Deproteinization of dentin matrix reduced the uptake of the orange II compared to the intact control. Conversely, demineralization of dentin samples increased the uptake of the dye. Treatment of samples for 48 h with H 2 O 2 reduced subsequent uptake of the orange II. Real-time kinetic analysis indicated moderate strength of binding for Orange II with collagen type I, weak binding with decorin and biglycan and negligible binding with dentine sialoprotein and osteopontin. These results indicate a predominant role for collagen type I, which accounts for 90% of the organic protein matrix of teeth, for attracting dietary stains. Binding analyses indicate that the interaction is highly dissociable, and further binding is reduced following H 2 O 2 treatment. This study provides new information regarding adsorption of dietary stains into tooth dentin, suggesting that they are attracted and moderately bound to the collagen type I matrix. This study also contributes valuable information for discussion for considering the effect of H 2 O 2 on bleaching teeth and its influence on subsequent uptake of dietary stains following whitening treatments. Copyright © 2018. Published by Elsevier Ltd.

RNA and DNA interactions with zwitterionic and charged lipid membranes - a DSC and QCM-D study.

PubMed

Michanek, Agnes; Kristen, Nora; Höök, Fredrik; Nylander, Tommy; Sparr, Emma

2010-04-01

The aim of the present study is to establish under which conditions tRNA associates with phospholipid bilayers, and to explore how this interaction influences the lipid bilayer. For this purpose we have studied the association of tRNA or DNA of different sizes and degrees of base pairing with a set of model membrane systems with varying charge densities, composed of zwitterionic phosphatidylcholines (PC) in mixtures with anionic phosphatidylserine (PS) or cationic dioctadecyl-dimethyl-ammoniumbromide (DODAB), and with fluid or solid acyl-chains (oleoyl, myristoyl and palmitoyl). To prove and quantify the attractive interaction between tRNA and model-lipid membrane we used quartz crystal microbalance with dissipation (QCM-D) monitoring to study the tRNA adsorption to deposit phospholipid bilayers from solutions containing monovalent (Na(+)) or divalent (Ca(2+)) cations. The influence of the adsorbed polynucleic acids on the lipid phase transitions and lipid segregation was studied by means of differential scanning calorimetry (DSC). The basic findings are: i) tRNA adsorbs to zwitterionic liquid-crystalline and gel-phase phospholipid bilayers. The interaction is weak and reversible, and cannot be explained only on the basis of electrostatic attraction. ii) The adsorbed amount of tRNA is higher for liquid-crystalline bilayers compared to gel-phase bilayers, while the presence of divalent cations show no significant effect on the tRNA adsorption. iii) The adsorption of tRNA can lead to segregation in the mixed 1,2-dimyristoyl-sn-glycerol-3-phosphatidylcholine (DMPC)-1,2-dimyristoyl-sn-glycero-3-phosphatidylserine (DMPS) and DMPC-DODAB bilayers, where tRNA is likely excluded from the anionic DMPS-rich domains in the first system, and associated with the cationic DODAB-rich domains in the second system. iv) The addition of shorter polynucleic acids influence the chain melting transition and induce segregation in a mixed DMPC-DMPS system, while larger polynucleic acids do not influence the melting transition in these system. The results in this study on tRNA-phospholipid interactions can have implications for understanding its biological function in, e.g., the cell nuclei, as well as in applications in biotechnology and medicine. Copyright 2010 Elsevier B.V. All rights reserved.

Interplay of Coil–Globule Transition and Surface Adsorption of a Lattice HP Protein Model

PubMed Central

2015-01-01

An end-grafted hydrophobic-polar (HP) model protein chain with alternating H and P monomers is studied to examine interactions between the critical adsorption transition due to surface attraction and the collapse transition due to pairwise attractive H–H interactions. We find that the critical adsorption phenomenon can always be observed; however, the critical adsorption temperature TCAP is influenced by the attractive H–H interactions in some cases. When the collapse temperature Tc is lower than TCAP, the critical adsorption of the HP chain is similar to that of a homopolymer without intrachain attractions and TCAP remains unchanged, whereas the collapse transition is suppressed by the adsorption. In contrast, for cases where Tc is close to or higher than TCAP, TCAP of the HP chain is increased, indicating that a collapsed chain is more easily adsorbed on the surface. The strength of the H–H attraction also influences the statistical size and shape of the polymer, with strong H–H attractions resulting in adsorbed and collapsed chains adopting two-dimensional, circular conformations. PMID:25458556

Using an innovative multiple regression procedure in a cancer population (Part II): fever, depressive affect, and mobility problems clarify an influential symptom pair (pain-fatigue/weakness) and cluster (pain-fatigue/weakness-sleep problems).

PubMed

Francoeur, Richard B

2015-01-01

Most patients with advanced cancer experience symptom pairs or clusters among pain, fatigue, and insomnia. However, only combinations where symptoms are mutually influential hold potential for identifying patient subgroups at greater risk, and in some contexts, interventions with "cross-over" (multisymptom) effects. Improved methods to detect and interpret interactions among symptoms, signs, or biomarkers are needed to reveal these influential pairs and clusters. I recently created sequential residual centering (SRC) to reduce multicollinearity in moderated regression, which enhances sensitivity to detect these interactions. I applied SRC to moderated regressions of single-item symptoms that interact to predict outcomes from 268 palliative radiation outpatients. I investigated: 1) the hypothesis that the interaction, pain × fatigue/weakness × sleep problems, predicts depressive affect only when fever presents, and 2) an exploratory analysis, when fever is absent, that the interaction, pain × fatigue/weakness × sleep problems × depressive affect, predicts mobility problems. In the fever context, three-way interactions (and derivative terms) of the four symptoms (pain, fatigue/weakness, fever, sleep problems) are tested individually and simultaneously; in the non-fever context, a single four-way interaction (and derivative terms) is tested. Fever interacts separately with fatigue/weakness and sleep problems; these comoderators each magnify the pain-depressive affect relationship along the upper or full range of pain values. In non-fever contexts, fatigue/weakness, sleep problems, and depressive affect comagnify the relationship between pain and mobility problems. Different mechanisms contribute to the pain × fatigue/weakness × sleep problems interaction, but all depend on the presence of fever, a sign/biomarker/symptom of proinflammatory sickness behavior. In non-fever contexts, depressive affect is no longer an outcome representing malaise from the physical symptoms of sickness, but becomes a fourth symptom of the interaction. In outpatient subgroups at heightened risk, single interventions could potentially relieve multiple symptoms when fever accompanies sickness malaise and in non-fever contexts with mobility problems. SRC strengthens insights into symptom pairs/clusters.

Water anomalous thermodynamics, attraction, repulsion, and hydrophobic hydration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cerdeiriña, Claudio A., E-mail: calvarez@uvigo.es; Debenedetti, Pablo G., E-mail: pdebene@princeton.edu

A model composed of van der Waals-like and hydrogen bonding contributions that simulates the low-temperature anomalous thermodynamics of pure water while exhibiting a second, liquid-liquid critical point [P. H. Poole et al., Phys. Rev. Lett. 73, 1632 (1994)] is extended to dilute solutions of nonionic species. Critical lines emanating from such second critical point are calculated. While one infers that the smallness of the water molecule may be a relevant factor for those critical lines to move towards experimentally accessible regions, attention is mainly focused on the picture our model draws for the hydration thermodynamics of purely hydrophobic and amphiphilicmore » non-electrolyte solutes. We first focus on differentiating solvation at constant volume from the corresponding isobaric process. Both processes provide the same viewpoint for the low solubility of hydrophobic solutes: it originates from the combination of weak solute-solvent attractive interactions and the specific excluded-volume effects associated with the small molecular size of water. However, a sharp distinction is found when exploring the temperature dependence of hydration phenomena since, in contrast to the situation for the constant-V process, the properties of pure water play a crucial role at isobaric conditions. Specifically, the solubility minimum as well as enthalpy and entropy convergence phenomena, exclusively ascribed to isobaric solvation, are closely related to water’s density maximum. Furthermore, the behavior of the partial molecular volume and the partial molecular isobaric heat capacity highlights the interplay between water anomalies, attraction, and repulsion. The overall picture presented here is supported by experimental observations, simulations, and previous theoretical results.« less

Influence of alkyl chain length and anion species on ionic liquid structure at the graphite interface as a function of applied potential

NASA Astrophysics Data System (ADS)

Li, Hua; Wood, Ross J.; Endres, Frank; Atkin, Rob

2014-07-01

Atomic force microscopy (AFM) force measurements elucidate the effect of cation alkyl chain length and the anion species on ionic liquid (IL) interfacial structure at highly ordered pyrolytic graphite (HOPG) surfaces as a function of potential. Three ILs are examined: 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP), 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] TFSA). The step-wise force-distance profiles indicate the ILs adopt a multilayered morphology near the surface. When the surface is biased positively or negatively versus Pt quasireference electrode, both the number of steps, and the force required to rupture each step increase, indicating stronger interfacial structure. At all potentials, push-through forces for [HMIM] FAP are the highest, because the long alkyl chain results in strong cohesive interactions between cations, leading to well-formed layers that resist the AFM tip. The most layers are observed for [EMIM] FAP, because the C2 chains are relatively rigid and the dimensions of the cation and anion are similar, facilitating neat packing. [EMIM] TFSA has the smallest push-through forces and fewest layers, and thus the weakest interfacial structure. Surface-tip attractive forces are measured for all ILs. At the same potential, the attractions are the strongest for [EMIM] TFSA and the weakest for [HMIM] FAP because the interfacial layers are better formed for the longer alkyl chain cation. This means interfacial forces are stronger, which masks the weak attractive forces.

Hidden multiparticle excitation in a weakly interacting Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Watabe, Shohei

2018-03-01

We investigate multiparticle excitation effect on a collective density excitation as well as a single-particle excitation in a weakly interacting Bose-Einstein condensate (BEC). We find that although the weakly interacting BEC offers weak multiparticle excitation spectrum at low temperatures, this multiparticle excitation effect may not remain hidden, but emerges as bimodality in the density response function through the single-particle excitation. Identification of spectra in the BEC between the single-particle excitation and the density excitation is also assessed at nonzero temperatures, which has been known to be unique nature in the BEC at absolute zero temperature.

Electromagnetic theory of the nuclear interaction. Application to the deuteron {sup 2}H

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaeffer, Bernard

2012-06-20

Bieler of the Rutherford laboratory imagined in 1924 a magnetic attraction equilibrating an electrostatic repulsion between the protons. Since the discovery of the neutron and the magnetic moments of the nucleons proving that the neutron contains electric charges, nobody, as far as I know, has tried to apply electromagnetism to the nuclear interaction. The electrostatic and magnetic interactions are completely neglected except for a mean Coulomb repulsion. As it is well known, there is an attraction between an electric charge and a neutral conductor. In the neutron, the positive charges are repelled and the negative charges attracted by a nearbymore » proton. There is a net attraction explaining quantitatively the so-called strong force as it is shown in this paper. In the deuteron, the magnetic repulsion equilibrates the electrostatically induced neutron-proton attraction. The experimental value (- 2.2 MeV) is surrounded by - 1.6 MeV and - 2.5 MeV, depending on the calculation method. No arbitrary fitting parameter is used, only physical constants: it is a true ab initio calculation. The theoretical ratio between nuclear and chemical energies has been found to be (m{sub p}/m{sub e}{alpha}), proving that the usual assumption that the electromagnetic interaction is too feeble to predict the nuclear interaction is incorrect.« less

Volatile interaction between undamaged plants affects tritrophic interactions through changed plant volatile emission.

PubMed

Vucetic, Andja; Dahlin, Iris; Petrovic-Obradovic, Olivera; Glinwood, Robert; Webster, Ben; Ninkovic, Velemir

2014-01-01

Volatile interactions between unattacked plants can lead to changes in their volatile emissions. Exposure of potato plants to onion plant volatiles results in increased emission of 2 terpenoids, (E)-nerolidol and TMTT. We investigated whether this is detectable by the ladybird Coccinella septempunctata. The odor of onion-exposed potato was significantly more attractive to ladybirds than that of unexposed potato. Further, a synthetic blend mimicking the volatile profile of onion-exposed potato was more attractive than a blend mimicking that of unexposed potato. When presented individually, TMTT was attractive to ladybirds whereas (E)-nerolidol was repellent. Volatile exchange between unattacked plants and consequent increased attractiveness for ladybirds may be a mechanism that contributes to the increased abundance of natural enemies in complex plant habitats.

Collapse and coexistence for a molecular braid with an attractive interaction component subject to mechanical forces.

PubMed

Lee, Dominic J O'

2015-04-15

Dual mechanical braiding experiments provide a useful tool with which to investigate the nature of interactions between rod-like molecules, for instance actin and DNA. In conditions close to molecular condensation, one would expect an appearance of a local minimum in the interaction potential between the two molecules. We investigate this situation, introducing an attractive component into the interaction potential, using a model developed for describing such experiments. We consider both attractive interactions that do not depend on molecular structure and those which depend on a DNA-like helix structure. In braiding experiments, an attractive term may lead to certain effects. A local minimum may cause molecules to collapse from a loosely braided configuration into a tight one, occurring at a critical value of the moment applied about the axis of the braid. For a fixed number of braid pitches, this may lead to coexistence between the two braiding states, tight and loose. Coexistence implies certain proportions of the braid are in each state, their relative size depending on the number of braid pitches. This manifests itself as a linear dependence in numerically calculated quantities as functions of the number of braid pitches. Also, in the collapsed state, the braid radius stays roughly constant. Furthermore, if the attractive interaction is helix dependent, the left-right handed braid symmetry is broken. For a DNA like charge distribution, using the Kornyshev-Leikin interaction model, our results suggest that significant braid collapse and coexistence only occurs for left handed braids. Regardless of the interaction model, the study highlights the possible qualitative physics of braid collapse and coexistence; and the role helix specific forces might play, if important. The model could be used to connect other microscopic theories of interaction with braiding experiments.

Casein micelles and their internal structure.

PubMed

de Kruif, Cornelis G; Huppertz, Thom; Urban, Volker S; Petukhov, Andrei V

2012-01-01

The internal structure of casein micelles was studied by calculating the small-angle neutron and X-ray scattering and static light scattering spectrum (SANS, SAXS, SLS) as a function of the scattering contrast and composition. We predicted experimental SANS, SAXS, SLS spectra self consistently using independently determined parameters for composition size, polydispersity, density and voluminosity. The internal structure of the casein micelles, i.e. how the various components are distributed within the casein micelle, was modeled according to three different models advocated in the literature; i.e. the classical sub-micelle model, the nanocluster model and the dual binding model. In this paper we present the essential features of these models and combine new and old experimental SANS, SAXS, SLS and DLS scattering data with new calculations that predict the spectra. Further evidence on micellar substructure was obtained by internally cross linking the casein micelles using transglutaminase, which led to casein nanogel particles. In contrast to native casein micelles, the nanogel particles were stable in 6M urea and after sequestering the calcium using trisodium citrate. The changed scattering properties were again predicted self consistently. An important result is that the radius of gyration is independent of contrast, indicating that the mass distribution within a casein micelle is homogeneous. Experimental contrast is predicted quite well leading to a match point at a D(2)O volume fraction of 0.41 ratio in SANS. Using SANS and SAXS model calculations it is concluded that only the nanocluster model is capable of accounting for the experimental scattering contrast variation data. All features and trends are predicted self consistently, among which the 'famous' shoulder at a wave vector value Q=0.35 nm(-1) In the nanocluster model, the casein micelle is considered as a (homogeneous) matrix of caseins in which the colloidal calcium phosphate (CCP) nanoclusters are dispersed as very small (about 2 nm) "cherry stones" at an average distance of 18.6 nm. Attached to the surface of the nanoclusters are the centers of phosphorylation (3-5 nearby phosphorylated amino acid residues) of the caseins. The tails of the caseins, much larger than the CCP clusters, then associate to form a protein matrix, which can be viewed as polymer mesh with density fluctuations at the 2 nm scale. The association of the tails is driven by a collection of weak interactions. We explicitly use weak interactions as a collective term for hydrophobic interactions, hydrogen bonding, ion bonding, weak electrostatic Van der Waals attraction and other factors (but not the strong calcium phosphate interaction) leading to self association. The association is highly cooperative and originates in the weak interactions. It is the cooperativety that leads to a stable casein micelle. Invariably, κ-casein is thought to limit the process of self association leading to stabilization of the native casein micelle. Copyright © 2012 Elsevier B.V. All rights reserved.

Casein micelles and their internal structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Kruif, Cornelis G; Huppertz, Thom; Urban, Volker S

2012-01-01

The internal structure of casein micelles was studied by calculating the small-angle neutron and X-ray scattering and static light scattering spectrum (SANS, SAXS, SLS) as a function of the scattering contrast and composition. We predicted experimental SANS, SAXS, SLS spectra self consistently using independently determined parameters for composition size, polydispersity, density and voluminosity. The internal structure of the casein micelles, i.e. how the various components are distributed within the casein micelle, was modeled according to three different models advocated in the literature; i.e. the classical sub-micelle model, the nanocluster model and the dual binding model. In this paper we presentmore » the essential features of these models and combine new and old experimental SANS, SAXS, SLS and DLS scattering data with new calculations that predict the spectra. Further evidence on micellar substructure was obtained by internally cross linking the casein micelles using transglutaminase, which led to casein nanogel particles. In contrast to native casein micelles, the nanogel particles were stable in 6 M urea and after sequestering the calcium using trisodium citrate. The changed scattering properties were again predicted self consistently. An important result is that the radius of gyration is independent of contrast, indicating that the mass distribution within a casein micelle is homogeneous. Experimental contrast is predicted quite well leading to a match point at a D{sub 2}O volume fraction of 0.41 ratio in SANS. Using SANS and SAXS model calculations it is concluded that only the nanocluster model is capable of accounting for the experimental scattering contrast variation data. All features and trends are predicted self consistently, among which the 'famous' shoulder at a wave vector value Q = 0.35 nm{sup -1}. In the nanocluster model, the casein micelle is considered as a (homogeneous) matrix of caseins in which the colloidal calcium phosphate (CCP) nanoclusters are dispersed as very small (about 2 nm) 'cherry stones' at an average distance of 18.6 nm. Attached to the surface of the nanoclusters are the centers of phosphorylation (3-5 nearby phosphorylated amino acid residues) of the caseins. The tails of the caseins, much larger than the CCP clusters, then associate to form a protein matrix, which can be viewed as polymer mesh with density fluctuations at the 2 nm scale. The association of the tails is driven by a collection of weak interactions. We explicitly use weak interactions as a collective term for hydrophobic interactions, hydrogen bonding, ion bonding, weak electrostatic Van der Waals attraction and other factors (but not the strong calcium phosphate interaction) leading to self association. The association is highly cooperative and originates in the weak interactions. It is the cooperativety that leads to a stable casein micelle. Invariably, K-casein is thought to limit the process of self association leading to stabilization of the native casein micelle.« less

Anomalous Ground State of the Electrons in Nano-confined Water

DTIC Science & Technology

2016-06-13

confined water system, Nafion, is so different from that of bulk water that the weakly electrostatically interacting molecule model of water is clearly...assume that water is made up molecules weakly interacting(on the scale of the zero point bond energy~.2eV) electrostatically with its neighbors2-3. In an...not possible for a collection of molecules interacting weakly electrostatically . These changes in the spatial distribution of valence electrons in

Conformational dimorphism of isochroman-1-ones in the solid state

NASA Astrophysics Data System (ADS)

Babjaková, Eva; Hanulíková, Barbora; Dastychová, Lenka; Kuřitka, Ivo; Nečas, Marek; Vícha, Robert

2014-12-01

Isochroman-1-one derivatives, which are relatives of coumarins, display a broad spectrum of biological activity; therefore, these derivatives attract the attention of chemists. A series of new isochroman-1-ones were prepared by the reaction of benzyl-derived Grignard reagents with acyl chlorides. All of the prepared compounds were characterized using single-crystal X-ray diffraction as well as FT-IR, NMR and MS techniques. Single crystal X-ray diffraction analysis revealed that the isochromanones can adopt two distinct conformations in the solid state. For one of the compounds, two polymorphs with unique forms crystallized separately under different temperatures. The packing of all of the examined crystals is stabilized via weak intramolecular C-H⋯π and/or C-H⋯O interactions. Although the closed conformer was predominantly found in the actual crystals, the open conformer is thermochemically more stable for all of the examined compounds according to DFT calculations.

Insight into the microscopic structure of an AdS black hole from a thermodynamical phase transition.

PubMed

Wei, Shao-Wen; Liu, Yu-Xiao

2015-09-11

Comparing with an ordinary thermodynamic system, we investigate the possible microscopic structure of a charged anti-de Sitter black hole completely from the thermodynamic viewpoint. The number density of the black hole molecules is introduced to measure the microscopic degrees of freedom of the black hole. We found that the number density suffers a sudden change accompanied by a latent heat when the black hole system crosses the small-large black hole coexistence curve, while when the system passes the critical point, it encounters a second-order phase transition with a vanishing latent heat due to the continuous change of the number density. Moreover, the thermodynamic scalar curvature suggests that there is a weak attractive interaction between two black hole molecules. These phenomena might cast new insight into the underlying microscopic structure of a charged anti-de Sitter black hole.

Observation of sum-frequency-generation-induced cascaded four-wave mixing using two crossing femtosecond laser pulses in a 0.1 mm beta-barium-borate crystal.

PubMed

Liu, Weimin; Zhu, Liangdong; Fang, Chong

2012-09-15

We demonstrate the simultaneous generation of multicolor femtosecond laser pulses spanning the wavelength range from UV to near IR in a 0.1 mm Type I beta-barium borate crystal from 800 nm fundamental and weak IR super-continuum white light (SCWL) pulses. The multicolor broadband laser pulses observed are attributed to two concomitant cascaded four-wave mixing (CFWM) processes as corroborated by calculation: (1) directly from the two incident laser pulses; (2) by the sum-frequency generation (SFG) induced CFWM process (SFGFWM). The latter signal arises from the interaction between the frequency-doubled fundamental pulse (400 nm) and the SFG pulse generated in between the fundamental and IR-SCWL pulses. The versatility and simplicity of this spatially dispersed multicolor self-compressed laser pulse generation offer compact and attractive methods to conduct femtosecond stimulated Raman spectroscopy and time-resolved multicolor spectroscopy.

City image towards tourist attraction (case in Solo, Central Java) examining city image of solo as tourist attraction

NASA Astrophysics Data System (ADS)

Wiyana, T.; Putranto, T. S.; Zulkarnain, A.; Kusdiana, R. N.

2018-03-01

Affective and cognitive image are two main factors that influence destination in Solo. The purpose of this research is to examine the two main factors of Solo towards tourist attraction. The research method is quantitative. Data collected from observation and survey. A total of 113 respondents obtained from accidental sampling method. The results indicate based on cognitive and affective image. Cognitive consists of culture, batik, city tagline, and community. While, affective consists of tradition, culinary, purposes, climate, and welcoming. The findings show that image has weak correlation towards tourist attraction of Solo. It means most of the tourists are not influenced by city image when they choose Solo as one of their travel destination. The differences between primary and minor image are also examined. Research implication is directed for local government to pursue continuous improvement particularly for the branding of Solo.

Temperature Dependence of the Upper Critical Field in Disordered Hubbard Model with Attraction

NASA Astrophysics Data System (ADS)

Kuchinskii, E. Z.; Kuleeva, N. A.; Sadovskii, M. V.

2017-12-01

We study disorder effects upon the temperature behavior of the upper critical magnetic field in an attractive Hubbard model within the generalized DMFT+Σ approach. We consider the wide range of attraction potentials U—from the weak coupling limit, where superconductivity is described by BCS model, up to the strong coupling limit, where superconducting transition is related to Bose-Einstein condensation (BEC) of compact Cooper pairs, formed at temperatures significantly higher than superconducting transition temperature, as well as the wide range of disorder—from weak to strong, when the system is in the vicinity of Anderson transition. The growth of coupling strength leads to the rapid growth of H c2( T), especially at low temperatures. In BEC limit and in the region of BCS-BEC crossover H c2( T), dependence becomes practically linear. Disordering also leads to the general growth of H c2( T). In BCS limit of weak coupling increasing disorder lead both to the growth of the slope of the upper critical field in the vicinity of the transition point and to the increase of H c2( T) in the low temperature region. In the limit of strong disorder in the vicinity of the Anderson transition localization corrections lead to the additional growth of H c2( T) at low temperatures, so that the H c2( T) dependence becomes concave. In BCS-BEC crossover region and in BEC limit disorder only slightly influences the slope of the upper critical field close to T c . However, in the low temperature region H c2 ( T may significantly grow with disorder in the vicinity of the Anderson transition, where localization corrections notably increase H c2 ( T = 0) also making H c2( T) dependence concave.

Dissipating Step Bunches during Crystallization under Transport Control

NASA Technical Reports Server (NTRS)

Lin, Hong; Yau, S.-T.; Vekilov, Peter, G.

2003-01-01

In studies of crystal formation by the generation and spreading of layers, equidistant step trains are considered unstable---bunches and other spatiotemporal patterns of the growth steps are viewed as ubiquitous. We provide an example to the opposite. We monitor the spatiotemporal dynamics of steps and the resulting step patterns during crystallization of the proteins ferritin and apoferritin using the atomic force microscope. The variations in step velocity and density are not correlated, indicating the lack of a long-range attraction between the steps. We show that (i) because of its coupling to bulk transport, nucleation of new layers is chaotic and occurs at the facet edges, where the interfacial supersaturation is higher; (ii) step bunches self-organize via the competition for supply from the solution; and, (iii) bunches of weakly interacting steps decay as they move along the face. Tests by numerical modeling support the conclusions about the mechanisms underlying our observations. The results from these systems suggest that during crystallization controlled by transport, with weakly or noninteracting growth steps, the stable kinetic state of the surface is an equidistant step train, and step bunches only arise during nucleation of new layers. Since nucleation only occurs at a few sites on the surface, the surface morphology may be controllably patterned or smoothened by locally controlling nucleation.

Hydrogen adatom interaction on graphene: A first principles study

DOE PAGES

Zhang, Wei; Lu, Wen-Cai; Zhang, Hong-Xing; ...

2018-05-01

Interaction between two hydrogen adatoms on graphene was studied by first-principles calculations. We showed that there is an attraction between two H adatoms on graphene. However, the strength of interaction between two hydrogen adatoms and magnetic properties of graphene are strongly dependent on the residence of the two adatoms on the graphene sublattices. Hydrogen adatoms introduce lattice distortion and electron localization in graphene which mediate the attractive interaction between the two H adatoms.

Hydrogen adatom interaction on graphene: A first principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei; Lu, Wen-Cai; Zhang, Hong-Xing

Interaction between two hydrogen adatoms on graphene was studied by first-principles calculations. We showed that there is an attraction between two H adatoms on graphene. However, the strength of interaction between two hydrogen adatoms and magnetic properties of graphene are strongly dependent on the residence of the two adatoms on the graphene sublattices. Hydrogen adatoms introduce lattice distortion and electron localization in graphene which mediate the attractive interaction between the two H adatoms.

Liquid drops attract or repel by the inverted Cheerios effect.

PubMed

Karpitschka, Stefan; Pandey, Anupam; Lubbers, Luuk A; Weijs, Joost H; Botto, Lorenzo; Das, Siddhartha; Andreotti, Bruno; Snoeijer, Jacco H

2016-07-05

Solid particles floating at a liquid interface exhibit a long-ranged attraction mediated by surface tension. In the absence of bulk elasticity, this is the dominant lateral interaction of mechanical origin. Here, we show that an analogous long-range interaction occurs between adjacent droplets on solid substrates, which crucially relies on a combination of capillarity and bulk elasticity. We experimentally observe the interaction between droplets on soft gels and provide a theoretical framework that quantitatively predicts the interaction force between the droplets. Remarkably, we find that, although on thick substrates the interaction is purely attractive and leads to drop-drop coalescence, for relatively thin substrates a short-range repulsion occurs, which prevents the two drops from coming into direct contact. This versatile interaction is the liquid-on-solid analog of the "Cheerios effect." The effect will strongly influence the condensation and coarsening of drops on soft polymer films, and has potential implications for colloidal assembly and mechanobiology.

Molecular dynamics simulations of the adsorption of bone morphogenetic protein-2 on surfaces with medical relevance.

PubMed

Utesch, Tillmann; Daminelli, Grazia; Mroginski, Maria Andrea

2011-11-01

Bone morphogenetic protein-2 (BMP-2) plays a crucial role in osteoblast differentiation and proliferation. Its effective therapeutic use for ectopic bone and cartilage regeneration depends, among other factors, on the interaction with the carrier at the implant site. In this study, we used classical molecular dynamics (MD) and a hybrid approach of steered molecular dynamics (SMD) combined with MD simulations to investigate the initial stages of the adsorption of BMP-2 when approaching two implant surfaces, hydrophobic graphite and hydrophilic titanium dioxide rutile. Surface adsorption was evaluated for six different orientations of the protein, two end-on and four side-on, in explicit water environment. On graphite, we observed a weak but stable adsorption. Depending on the initial orientation, hydrophobic patches as well as flexible loops of the protein were involved in the interaction with graphite. On the contrary, BMP-2 adsorbed only loosely to hydrophilic titanium dioxide. Despite a favorable interaction energy between protein and the TiO(2) surface, the rapid formation of a two-layer water structure prevented the direct interaction between protein and titanium dioxide. The first water adlayer had a strong repulsive effect on the protein, while the second attracted the protein toward the surface. For both surfaces, hydrophobic graphite and hydrophilic titanium dioxide, denaturation of BMP-2 induced by adsorption was not observed on the nanosecond time scale.

The Role of Attractiveness and Aggression in High School Popularity

ERIC Educational Resources Information Center

Borch, Casey; Hyde, Allen; Cillessen, Antonius H. N.

2011-01-01

This study examines the effects of physical attractiveness and aggression on popularity among high school students. Previous work has found positive relationships between aggression and popularity and physical attractiveness and popularity. The current study goes beyond this work by examining the interactive effects of physical attractiveness and…

Interaction of perfluoroalkyl acids with human liver fatty acid-binding protein.

PubMed

Sheng, Nan; Li, Juan; Liu, Hui; Zhang, Aiqian; Dai, Jiayin

2016-01-01

Perfluoroalkyl acids (PFAAs) are highly persistent and bioaccumulative, resulting in their broad distribution in humans and the environment. The liver is an important target for PFAAs, but the mechanisms behind PFAAs interaction with hepatocyte proteins remain poorly understood. We characterized the binding of PFAAs to human liver fatty acid-binding protein (hL-FABP) and identified critical structural features in their interaction. The binding interaction of PFAAs with hL-FABP was determined by fluorescence displacement and isothermal titration calorimetry (ITC) assay. Molecular simulation was conducted to define interactions at the binding sites. ITC measurement revealed that PFOA/PFNA displayed a moderate affinity for hL-FABP at a 1:1 molar ratio, a weak binding affinity for PFHxS and no binding for PFHxA. Moreover, the interaction was mainly mediated by electrostatic attraction and hydrogen bonding. Substitution of Asn111 with Asp caused loss of binding affinity to PFAA, indicating its crucial role for the initial PFAA binding to the outer binding site. Substitution of Arg122 with Gly caused only one molecule of PFAA to bind to hL-FABP. Molecular simulation showed that substitution of Arg122 increased the volume of the outer binding pocket, making it impossible to form intensive hydrophobic stacking and hydrogen bonds with PFOA, and highlighting its crucial role in the binding process. The binding affinity of PFAAs increased significantly with their carbon number. Arg122 and Asn111 played a pivotal role in these interactions. Our findings may help understand the distribution pattern, bioaccumulation, elimination, and toxicity of PFAAs in humans.

In-plane optical anisotropy of layered gallium telluride

DOE PAGES

Huang, Shengxi; Tatsumi, Yuki; Ling, Xi; ...

2016-08-16

Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C 2h 3 space group. Investigating the in-plane optical anisotropy, including the electron–photon and electron–phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropymore » in optical extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. Furthermore, these studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.« less

Binding energy of e^+Li using the Peach model potential.

NASA Astrophysics Data System (ADS)

Shertzer, Janine; Ward, Sandra

2006-05-01

The l-independent, parametric model potential developed by Peach^1 for describing the electron interaction with the alkali ion core yields energy levels that are in excellent agreement with experiment. Because of its relative simplicity, this model potential is an attractive choice for studying e^+- Li collisions;^2,3 the e^+-ion core interaction is obtained by changing the sign of the static term in the interaction. In order to test the usefulness of the potential for describing the physics of an effective three-body system, we calculated the binding energy of e^+Li. This is a stringent test, because the system is very weakly bound. Our results are in excellent agreement with previous calculations,^4 including those using the exact four-body Hamiltonian.^5 This work was funded by NSF under collaborative Grant PHYS-0440714 (JS) and PHYS-0440565 (SJW). ^1G. Peach, H.E. Saraph and M.J. Seaton, J. Phys. B 21, 3669 (1988). ^2M.S.T. Watts and J.W. Humberston, J. Phys. B 25, L491 (1992). ^3S. J. Ward and J. Shertzer, Phys. Rev. A 68, 032720 (2003). ^4J. Mitroy, M.W.J. Bromley, and G.G. Ryzhikh, J. Phys. B 35, R81 (2002). ^5Massimo Mella, Gabriele Morosi, and Dario Bressanini, J. Chem. Phys. 111, 108 (1999).

Removal of diphenhydramine from water by swelling clay minerals.

PubMed

Li, Zhaohui; Chang, Po-Hsiang; Jiang, Wei-Teh; Jean, Jiin-Shuh; Hong, Hanlie; Liao, Libing

2011-08-01

Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK(a) of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK(a) value resulted in a decrease in DPH adsorption by the clay. An increase in d(001) spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities. Copyright © 2011 Elsevier Inc. All rights reserved.

Shakeoff Ionization near the Coulomb Barrier Energy.

PubMed

Sharma, Prashant; Nandi, T

2017-11-17

We measure the projectile K x-ray spectra as a function of the beam energies around the Coulomb barrier in different collision systems. The energy is scanned in small steps around the barrier aiming to explore the nuclear effects on the elastically scattered projectile ions. The variation of the projectile x-ray energy with the ion-beam energies exhibits an unusual increase in between the interaction barrier and fusion barrier energies. This additional contribution to the projectile ionization can be attributed to the shakeoff of outer-shell electrons of the projectile ions due to the sudden nuclear recoil (∼10^{-21}  sec) caused by the attractive nuclear potential, which gets switched on near the interaction barrier energy. In the sudden approximation limit, the theoretical shakeoff probability calculation due to the nuclear recoil explains the observed data well. In addition to its fundamental interest, such processes can play a significant role in dark matter detection through the possible mechanism of x-ray emissions, where the weakly interacting massive particle-nucleus elastic scattering can lead to the nuclear-recoil-induced inner-shell vacancy creations. Furthermore, the present work may provide new prospects for atomic physics research at barrier energies as well as provide a novel technique to perform barrier distribution studies for two-body systems.

Using Pot-Magnets to Enable Stable and Scalable Electromagnetic Tactile Displays.

PubMed

Zarate, Juan Jose; Shea, Herbert

2017-01-01

We present the design, fabrication, characterization, and psychophysical testing of a scalable haptic display based on electromagnetic (EM) actuators. The display consists of a 4 × 4 array of taxels, each of which can be in a raised or a lowered position, thus generating different static configurations. One of the most challenging aspects when designing densely-packed arrays of EM actuators is obtaining large actuation forces while simultaneously generating only weak interactions between neighboring taxels. In this work, we introduce a lightweight and effective magnetic shielding architecture. The moving part of each taxel is a cylindrical permanent magnet embedded in a ferromagnetic pot, forming a pot-magnet. An array of planar microcoils attracts or repels each pot-magnet. This configuration reduces the interaction between neighboring magnets by more than one order of magnitude, while the coil/magnet interaction is only reduced by 10 percent. For 4 mm diameter pins on an 8 mm pitch, we obtained displacements of 0.55 mm and forces of 40 mN using 1.7 W. We measured the accuracy of human perception under two actuation configurations which differed in the force versus displacement curve. We obtained 91 percent of correct answers in pulling configuration and 100 percent in pushing configuration.

Shakeoff Ionization near the Coulomb Barrier Energy

NASA Astrophysics Data System (ADS)

Sharma, Prashant; Nandi, T.

2017-11-01

We measure the projectile K x-ray spectra as a function of the beam energies around the Coulomb barrier in different collision systems. The energy is scanned in small steps around the barrier aiming to explore the nuclear effects on the elastically scattered projectile ions. The variation of the projectile x-ray energy with the ion-beam energies exhibits an unusual increase in between the interaction barrier and fusion barrier energies. This additional contribution to the projectile ionization can be attributed to the shakeoff of outer-shell electrons of the projectile ions due to the sudden nuclear recoil (˜10-21 sec ) caused by the attractive nuclear potential, which gets switched on near the interaction barrier energy. In the sudden approximation limit, the theoretical shakeoff probability calculation due to the nuclear recoil explains the observed data well. In addition to its fundamental interest, such processes can play a significant role in dark matter detection through the possible mechanism of x-ray emissions, where the weakly interacting massive particle-nucleus elastic scattering can lead to the nuclear-recoil-induced inner-shell vacancy creations. Furthermore, the present work may provide new prospects for atomic physics research at barrier energies as well as provide a novel technique to perform barrier distribution studies for two-body systems.

Chemical analysis of human skin emanations: comparison of volatiles from humans that differ in attraction of Aedes aegypti (Diptera: Culicidae).

PubMed

Bernier, Ulrich R; Kline, Daniel L; Schreck, Carl E; Yost, Richard A; Barnard, Donald R

2002-09-01

Host odors are believed to play a major role in the location of blood meals by female mosquitoes. Previous work has shown that female Aedes aegypti (L.) are attracted to a residuum of skin emanations deposited on glass. The attraction of mosquitoes to handled or rubbed glass varies from person to person and from day to day. This variation indicates that mosquito behavior varies over time and that a relative difference exists in the ability of people over time to attract mosquitoes. Volatiles desorbed from glass handled by 2 human subjects that differed markedly in their attraction of Ae. aegypti were examined for differences in compound abundances. The attractive emanations, once deposited onto glass, are known to have a finite lifetime; therefore, compounds that decreased substantially during aging of handled glass also were noted. A study was conducted on the variations in compounds present from a single subject, which were recorded over a 5-day period. Emanations from the subject were transferred to glass, then thermally desorbed from the glass, and compounds present were compared on the 2 consecutive days that showed the largest difference in attraction. Some of the candidate attractants identified by these studies were screened in an olfactometer. A few of these compounds were found to be weak attractants for Ae. aegypti.

n→π* Non-Covalent Interaction is Weak but Strong in Action

NASA Astrophysics Data System (ADS)

Singh, Santosh Kumar; Das, Aloke

2017-06-01

n→π* interaction is a newly discovered non-covalent interaction which involves delocalization of lone pair (n) electrons of an electronegative atom into π* orbital of a carbonyl group or an aromatic ring. It is widely observed in materials, biomolecules (protein, DNA, RNA), amino acids, neurotransmitter and drugs. However, due to its weak strength and counterintuitive nature its existence is debatable. Such weak interactions are often masked by solvent effects in condense phase or physiological conditions thereby, making it difficult to prove the presence of such weak interactions. Therefore, we have used isolated gas phase spectroscopy in combination with quantum chemical calculations to study n→π* interaction in several molecules where, our molecular systems are free from solvent effects or any external forces. Herein I will be discussing two of the molecular systems (phenyl formate and salicin) where, we have observed the significance of n→π* interaction in determining the conformational specificity of the molecules. We have proved the existence of n→π* interaction for the first time through IR spectroscopy by probing the carbonyl stretching frequency of phenyl formate. Our study is further pursued on a drug named salicin where, we have observed that its conformational preferences is ruled by n→π* interaction even though a strong hydrogen bonding interaction is present in the molecule. Our results show that n→π* interaction, in spite of its weak strength, should not be overlooked as it existence can play an important role in governing the structures of molecules like other strong non-covalent interactions do.

Polymer translocation under time-dependent driving forces: resonant activation induced by attractive polymer-pore interactions.

PubMed

Ikonen, Timo; Shin, Jaeoh; Sung, Wokyung; Ala-Nissila, Tapio

2012-05-28

We study the driven translocation of polymers under time-dependent driving forces using N-particle Langevin dynamics simulations. We consider the force to be either sinusoidally oscillating in time or dichotomic noise with exponential correlation time, to mimic both plausible experimental setups and naturally occurring biological conditions. In addition, we consider both the case of purely repulsive polymer-pore interactions and the case with additional attractive polymer-pore interactions, typically occurring inside biological pores. We find that the nature of the interaction fundamentally affects the translocation dynamics. For the non-attractive pore, the translocation time crosses over to a fast translocation regime as the frequency of the driving force decreases. In the attractive pore case, because of a free energy well induced inside the pore, the translocation time can be a minimum at the optimal frequency of the force, the so-called resonant activation. In the latter case, we examine the effect of various physical parameters on the resonant activation, and explain our observations using simple theoretical arguments.

Crystallization tendencies of modelled Lennard-Jones liquids with different attractions

NASA Astrophysics Data System (ADS)

Valdès, L.-C.; Gerges, J.; Mizuguchi, T.; Affouard, F.

2018-01-01

Molecular dynamics simulations are performed on simple models composed of monoatomic Lennard-Jones atoms for which the repulsive interaction is the same but the attractive part is tuned. We investigate the precise role of the attractive part of the interaction potential on different structural, dynamical, and thermodynamical properties of these systems in the liquid and crystalline states. It includes crystallization trends for which the main physical ingredients involved have been computed: the diffusion coefficient, the Gibbs energy difference between the liquid and the crystalline state, and the crystal-liquid interfacial free energy. Results are compared with predictions from the classical nucleation theory including transient and steady-state regimes at moderate and deeper undercooling. The question of the energetic and entropic impact of the repulsive and attractive part of the interaction potential towards crystallization is also addressed.

Collision of impurities with Bose–Einstein condensates

NASA Astrophysics Data System (ADS)

Lingua, F.; Lepori, L.; Minardi, F.; Penna, V.; Salasnich, L.

2018-04-01

Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, plasma, and atomic physics. Recent experimental and theoretical investigations with ultracold atoms have focused on this problem, studying atomic impurities immersed in an atomic Bose–Einstein condensate (BEC) and for various relative coupling strengths tuned by the Fano‑Feshbach resonance technique. Here, we report extensive numerical simulations on a closely related problem: the collision between a bosonic impurity consisting of a few 41K atoms and a BEC of 87Rb atoms in a quasi one-dimensional configuration and under a weak harmonic axial confinement. For small values of the inter-species interaction strength (regardless of its sign), we find that the impurity, which starts from outside the BEC, simply causes the BEC cloud to oscillate back and forth, but the frequency of oscillation depends on the interaction strength. For intermediate couplings, after a few cycles of oscillation the impurity is captured by the BEC, and strongly changes its amplitude of oscillation. In the strong interaction regime, if the inter-species interaction is attractive, a local maximum (bright soliton) in the BEC density occurs where the impurity is trapped; if, instead, the inter-species interaction is repulsive, the impurity is not able to enter the BEC cloud and the reflection coefficient is close to one. However, if the initial displacement of the impurity is increased, the impurity is able to penetrate the cloud, leading to the appearance of a moving hole (dark soliton) in the BEC.

Using an innovative multiple regression procedure in a cancer population (Part 1): detecting and probing relationships of common interacting symptoms (pain, fatigue/weakness, sleep problems) as a strategy to discover influential symptom pairs and clusters.

PubMed

Francoeur, Richard B

2015-01-01

The majority of patients with advanced cancer experience symptom pairs or clusters among pain, fatigue, and insomnia. Improved methods are needed to detect and interpret interactions among symptoms or diesease markers to reveal influential pairs or clusters. In prior work, I developed and validated sequential residual centering (SRC), a method that improves the sensitivity of multiple regression to detect interactions among predictors, by conditioning for multicollinearity (shared variation) among interactions and component predictors. Using a hypothetical three-way interaction among pain, fatigue, and sleep to predict depressive affect, I derive and explain SRC multiple regression. Subsequently, I estimate raw and SRC multiple regressions using real data for these symptoms from 268 palliative radiation outpatients. Unlike raw regression, SRC reveals that the three-way interaction (pain × fatigue/weakness × sleep problems) is statistically significant. In follow-up analyses, the relationship between pain and depressive affect is aggravated (magnified) within two partial ranges: 1) complete-to-some control over fatigue/weakness when there is complete control over sleep problems (ie, a subset of the pain-fatigue/weakness symptom pair), and 2) no control over fatigue/weakness when there is some-to-no control over sleep problems (ie, a subset of the pain-fatigue/weakness-sleep problems symptom cluster). Otherwise, the relationship weakens (buffering) as control over fatigue/weakness or sleep problems diminishes. By reducing the standard error, SRC unmasks a three-way interaction comprising a symptom pair and cluster. Low-to-moderate levels of the moderator variable for fatigue/weakness magnify the relationship between pain and depressive affect. However, when the comoderator variable for sleep problems accompanies fatigue/weakness, only frequent or unrelenting levels of both symptoms magnify the relationship. These findings suggest that a countervailing mechanism involving depressive affect could account for the effectiveness of a cognitive behavioral intervention to reduce the severity of a pain, fatigue, and sleep disturbance cluster in a previous randomized trial.

Hemifield memory for attractiveness.

PubMed

Deblieck, C; Zaidel, D W

2003-07-01

In order to determine whether or not facial attractiveness plays a role in hemispheric facial memory, 35 right-handed participants first assigned attractiveness ratings to faces and then performed a recognition test on those faces in the left visual half-field (LVF) and right visual half-field (RVF). We found significant interactions between the experimental factors and visual half-field. There were significant differences in the extreme ends of the rating scale, that is, the very unattractive versus the very attractive faces: Female participants remembered very attractive faces of both women and men, with memory being superior in the RVF than in the LVF. In contrast, the male participants remembered very unattractive faces of both women and men; RVF memory was better than the LVF for women faces while for men faces memory was superior in the LVF. The interactions with visual half-field suggest that hemispheric biases in remembering faces are influenced by degree of attractiveness.

Size-dependent interaction of silica nanoparticles with lysozyme and bovine serum albumin proteins

NASA Astrophysics Data System (ADS)

Yadav, Indresh; Aswal, Vinod K.; Kohlbrecher, Joachim

2016-05-01

The interaction of three different sized (diameter 10, 18, and 28 nm) anionic silica nanoparticles with two model proteins—cationic lysozyme [molecular weight (MW) 14.7 kDa)] and anionic bovine serum albumin (BSA) (MW 66.4 kDa) has been studied by UV-vis spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The adsorption behavior of proteins on the nanoparticles, measured by UV-vis spectroscopy, is found to be very different for lysozyme and BSA. Lysozyme adsorbs strongly on the nanoparticles and shows exponential behavior as a function of lysozyme concentration irrespective of the nanoparticle size. The total amount of adsorbed lysozyme, as governed by the surface-to-volume ratio, increases on lowering the size of the nanoparticles for a fixed volume fraction of the nanoparticles. On the other hand, BSA does not show any adsorption for all the different sizes of the nanoparticles. Despite having different interactions, both proteins induce similar phase behavior where the nanoparticle-protein system transforms from one phase (clear) to two phase (turbid) as a function of protein concentration. The phase behavior is modified towards the lower concentrations for both proteins with increasing the nanoparticle size. DLS suggests that the phase behavior arises as a result of the nanoparticles' aggregation on the addition of proteins. The size-dependent modifications in the interaction potential, responsible for the phase behavior, have been determined by SANS data as modeled using the two-Yukawa potential accounting for the repulsive and attractive interactions in the systems. The protein-induced interaction between the nanoparticles is found to be short-range attraction for lysozyme and long-range attraction for BSA. The magnitude of attractive interaction irrespective of protein type is enhanced with increase in the size of the nanoparticles. The total (attractive+repulsive) potential leading to two-phase formation is found to be more attractive for larger sized nanoparticles. The nanoparticle aggregates are characterized by mass fractal.

Development of a direct experimental test for any violation of the equivalence principle by the weak interaction

NASA Technical Reports Server (NTRS)

Parker, P. D. M.

1981-01-01

Violation of the equivalence principle by the weak interaction is tested. Any variation of the weak interaction coupling constant with gravitational potential, i.e., a spatial variation of the fundamental constants is investigated. The level of sensitivity required for such a measurement is estimated on the basis of the size of a change in the gravitational potential which is accessible. The alpha particle spectrum is analyzed, and the counting rate was improved by a factor of approximately 100.

Cosmology and the weak interaction

NASA Technical Reports Server (NTRS)

Schramm, David N.

1989-01-01

The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated.

Is Beauty Talent? Sex Interaction in the Attractiveness Halo Effect.

ERIC Educational Resources Information Center

Kaplan, Robert M.

Male and female subjects judged an essay purportedly written by an attractive or an unattractive female author. The attractive author was rated as significantly more talented by male judges. Female judges rated the attractive author less talented although this difference was not statistically significant. A second experiment concerned ratings by…

Effects of Applicant Sex, Physical Attractiveness, and Type of Job on Employment Interviewers' Decisions.

ERIC Educational Resources Information Center

Gilmore, David C.; And Others

Past research on the employment interview has suggested that interviewers are influenced by many variables, including physical attractiveness. To investigate the potential interaction of applicant sex and attractiveness on hiring decisions, the type of job, applicant sex, and applicant physical attractiveness were manipulated to determine the…

Experimental Demonstration of Higher Precision Weak-Value-Based Metrology Using Power Recycling

NASA Astrophysics Data System (ADS)

Wang, Yi-Tao; Tang, Jian-Shun; Hu, Gang; Wang, Jian; Yu, Shang; Zhou, Zong-Quan; Cheng, Ze-Di; Xu, Jin-Shi; Fang, Sen-Zhi; Wu, Qing-Lin; Li, Chuan-Feng; Guo, Guang-Can

2016-12-01

The weak-value-based metrology is very promising and has attracted a lot of attention in recent years because of its remarkable ability in signal amplification. However, it is suggested that the upper limit of the precision of this metrology cannot exceed that of classical metrology because of the low sample size caused by the probe loss during postselection. Nevertheless, a recent proposal shows that this probe loss can be reduced by the power-recycling technique, and thus enhance the precision of weak-value-based metrology. Here we experimentally realize the power-recycled interferometric weak-value-based beam-deflection measurement and obtain the amplitude of the detected signal and white noise by discrete Fourier transform. Our results show that the detected signal can be strengthened by power recycling, and the power-recycled weak-value-based signal-to-noise ratio can surpass the upper limit of the classical scheme, corresponding to the shot-noise limit. This work sheds light on higher precision metrology and explores the real advantage of the weak-value-based metrology over classical metrology.

Carrion mimicry in a South African orchid: flowers attract a narrow subset of the fly assemblage on animal carcasses.

PubMed

van der Niet, Timotheüs; Hansen, Dennis M; Johnson, Steven D

2011-05-01

Although pollination of plants that attract flies by resembling their carrion brood and food sites has been reported in several angiosperm families, there has been very little work done on the level of specificity in carrion mimicry systems and the importance of plant cues in mediating such specialization. Specificity may be expected, as carrion-frequenting flies often exploit different niches, which has been interpreted as avoidance of interspecific competition. Interactions between the orchid Satyrium pumilum and a local assemblage of carrion flies were investigated, and the functional significance of floral traits, especially scent, tested. Pollination success and the incidence of pollinator-mediated self-pollination were measured and these were compared with values for orchids with sexual- and food-deceptive pollination systems. Observations of insect visitation to animal carcasses and to flowers showed that the local assemblage of carrion flies was dominated by blow flies (Calliphoridae), house flies (Muscidae) and flesh flies (Sarcophagidae), but flowers of the orchid were pollinated exclusively by flesh flies, with a strong bias towards females that sometimes deposited live larvae on flowers. A trend towards similar partitioning of fly taxa was found in an experiment that tested the effect of large versus small carrion quantities on fly attraction. GC-MS analysis showed that floral scent is dominated by oligosulfides, 2-heptanone, p-cresol and indole, compounds that also dominate carrion scent. Flesh flies did not distinguish between floral and carrion scent in a choice experiment using olfactory cues only, which also showed that scent alone is responsible for fly attraction. Pollination success was relatively high (31·5 % of flowers), but tracking of stained pollinia also revealed that a relatively high percentage (46 %) of pollen deposited on stigmas originates from the same plant. Satyrium pumilum selectively attracts flesh flies, probably because its relatively weak scent resembles that of the small carrion on which these flies predominate. In this way, the plants exploit a specific subset of the insect assemblage associated with carrion. Pollination rates and levels of self-pollination were high compared with those in other deceptive orchids and it is therefore unlikely that this mimicry system evolved to promote outcrossing.

Developmental changes in perceptions of attractiveness: a role of experience?

PubMed

Cooper, Philip A; Geldart, Sybil S; Mondloch, Catherine J; Maurer, Daphne

2006-09-01

In three experiments, we traced the development of the adult pattern of judgments of attractiveness for faces that have been altered to have internal features in low, average, or high positions. Twelve-year-olds and adults demonstrated identical patterns of results: they rated faces with features in an average location as significantly more attractive than faces with either low or high features. Although both 4-year-olds and 9-year-olds rated faces with high features as least attractive, unlike adults and 12-year-olds, they rated faces with low and average features as equally attractive. Three-year-olds with high levels of peer interaction, but not those with low levels of peer interaction, chose faces with low features as significantly more attractive than those with high-placed features, possibly as a result of their increased experience with the proportions of the faces of peers. Overall, the pattern of results is consistent with the hypothesis that experience influences perceptions of attractiveness, with the proportions of the faces participants see in their everyday lives influencing their perceptions of attractiveness.

Supramolecular features of 2-(chlorophenyl)-3-[(chlorobenzylidene)-amino]-2,3-dihydroquinazolin-4(1H)-ones: A combined experimental and computational study

NASA Astrophysics Data System (ADS)

Mandal, Arkalekha; Patel, Bhisma K.

2018-03-01

The molecular structures of two isomeric 2-(chlorophenyl)-3-[(chlorobenzylidene)-amino] substituted 2,3-dihydroquinazolin-4(1H)-ones have been determined via single crystal XRD. Both isomers contain chloro substitutions on each of the phenyl rings and as a result a broad spectrum of halogen mediated weak interactions are viable in their crystal structures. The crystal packing of these compounds is stabilized by strong N-H⋯O hydrogen bond and various weak, non-classical hydrogen bonds acting synergistically. Both the molecules contain a chiral center and the weak interactions observed in them are either chiral self-discriminatory or chiral self-recognizing in nature. The weak interactions and spectral features of the compounds have been studied through experimental as well as computational methods including DFT, MEP, NBO and Hiresfeld surface analyses. In addition, the effect of different weak interactions to dictate either chiral self-recognition or self-discrimination in crystal packing has been elucidated.

Weak-interaction rates in stellar conditions

NASA Astrophysics Data System (ADS)

Sarriguren, Pedro

2018-05-01

Weak-interaction rates, including β-decay and electron captures, are studied in several mass regions at various densities and temperatures of astrophysical interest. In particular, we study odd-A nuclei in the pf-shell region, which are involved in presupernova formations. Weak rates are relevant to understand the late stages of the stellar evolution, as well as the nucleosynthesis of heavy nuclei. The nuclear structure involved in the weak processes is studied within a quasiparticle proton-neutron random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. First, the energy distributions of the Gamow-Teller strength are discussed and compared with the available experimental information, measured under terrestrial conditions from charge-exchange reactions. Then, the sensitivity of the weak-interaction rates to both astrophysical densities and temperatures is studied. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus and to the electron captures from the degenerate electron plasma.

Argument and Credibility Appeals in Persuasion.

ERIC Educational Resources Information Center

Benoit, William L.

1987-01-01

Indicated that (1) arguments perceived as strong by receivers generated both more favorable, supportive cognitive responses and attitude change than weak message arguments; and (2) perceived source expertise and attractiveness influenced cognitive responses, but not in a coherent fashion or to the extent that they effect attitude change. (JD)

Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

PubMed Central

Wu, Liang; Jackson, George; Müller, Erich A.

2013-01-01

We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids. PMID:23965962

Liquid crystal phase behaviour of attractive disc-like particles.

PubMed

Wu, Liang; Jackson, George; Müller, Erich A

2013-08-08

We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids.

Tunable interactions between paramagnetic colloidal particles driven in a modulated ratchet potential.

PubMed

Straube, Arthur V; Tierno, Pietro

2014-06-14

We study experimentally and theoretically the interactions between paramagnetic particles dispersed in water and driven above the surface of a stripe patterned magnetic garnet film. An external rotating magnetic field modulates the stray field of the garnet film and generates a translating potential landscape which induces directed particle motion. By varying the ellipticity of the rotating field, we tune the inter-particle interactions from net repulsive to net attractive. For attractive interactions, we show that pairs of particles can approach each other and form stable doublets which afterwards travel along the modulated landscape at a constant mean speed. We measure the strength of the attractive force between the moving particles and propose an analytically tractable model that explains the observations and is in quantitative agreement with experiment.

Blow-up behavior of ground states for a nonlinear Schrödinger system with attractive and repulsive interactions

NASA Astrophysics Data System (ADS)

Guo, Yujin; Zeng, Xiaoyu; Zhou, Huan-Song

2018-01-01

We consider a nonlinear Schrödinger system arising in a two-component Bose-Einstein condensate (BEC) with attractive intraspecies interactions and repulsive interspecies interactions in R2. We get ground states of this system by solving a constrained minimization problem. For some kinds of trapping potentials, we prove that the minimization problem has a minimizer if and only if the attractive interaction strength ai (i = 1 , 2) of each component of the BEC system is strictly less than a threshold a*. Furthermore, as (a1 ,a2) ↗ (a* ,a*), the asymptotical behavior for the minimizers of the minimization problem is discussed. Our results show that each component of the BEC system concentrates at a global minimum of the associated trapping potential.

Role of geometrical shape in like-charge attraction of DNA.

PubMed

Kuron, Michael; Arnold, Axel

2015-03-01

While the phenomenon of like-charge attraction of DNA is clearly observed experimentally and in simulations, mean-field theories fail to predict it. Kornyshev et al. argued that like-charge attraction is due to DNA's helical geometry and hydration forces. Strong-coupling (SC) theory shows that attraction of like-charged rods is possible through ion correlations alone at large coupling parameters, usually by multivalent counterions. However for SC theory to be applicable, counterion-counterion correlations perpendicular to the DNA strands need to be sufficiently small, which is not a priori the case for DNA even with trivalent counterions. We study a system containing infinitely long DNA strands and trivalent counterions by computer simulations employing varying degrees of coarse-graining. Our results show that there is always attraction between the strands, but its magnitude is indeed highly dependent on the specific shape of the strand. While discreteness of the charge distribution has little influence on the attractive forces, the role of the helical charge distribution is considerable: charged rods maintain a finite distance in equilibrium, while helices collapse to close contact with a phase shift of π, in full agreement with SC predictions. The SC limit is applicable because counterions strongly bind to the charged sites of the helices, so that helix-counterion interactions dominate over counterion-counterion interactions. Thus DNA's helical geometry is not crucial for like-charge DNA attraction, but strongly enhances it, and electrostatic interactions in the strong-coupling limit are sufficient to explain this attraction.

Catching the role of anisotropic electronic distribution and charge transfer in halogen bonded complexes of noble gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartocci, Alessio; Cappelletti, David; Pirani, Fernando

2015-05-14

The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl{sub 4} and CF{sub 4}. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypicalmore » Ng-CCl{sub 4} and Ng-CF{sub 4} and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF{sub 4}, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl{sub 4}, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the experiments actually reflect two chemically meaningful contributions, namely, a stabilizing interaction arising from the anisotropy of the charge distribution around the Cl atom in CCl{sub 4} and a stereospecific electron transfer that occurs at the intermolecular distances mainly probed by the experiments. Our model calculations suggest that the largest effect is for the vertex geometry of CCl{sub 4} while other geometries appear to play a minor to negligible role.« less

Mechanical Failure in Colloidal Gels

NASA Astrophysics Data System (ADS)

Kodger, Thomas Edward

When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form them.

Unexpected weak interaction

NASA Astrophysics Data System (ADS)

2013-08-01

Stéphane Coen and Miro Erkintalo from the University of Auckland in New Zealand talk to Nature Photonics about their surprising findings regarding a weak long-range interaction they serendipitously stumbled upon while researching temporal cavity solitons.

Long-range interaction between heterogeneously charged membranes.

PubMed

Jho, Y S; Brewster, R; Safran, S A; Pincus, P A

2011-04-19

Despite their neutrality, surfaces or membranes with equal amounts of positive and negative charge can exhibit long-range electrostatic interactions if the surface charge is heterogeneous; this can happen when the surface charges form finite-size domain structures. These domains can be formed in lipid membranes where the balance of the different ranges of strong but short-ranged hydrophobic interactions and longer-ranged electrostatic repulsion result in a finite, stable domain size. If the domain size is large enough, oppositely charged domains in two opposing surfaces or membranes can be strongly correlated by the electrostatic interactions; these correlations give rise to an attractive interaction of the two membranes or surfaces over separations on the order of the domain size. We use numerical simulations to demonstrate the existence of strong attractions at separations of tens of nanometers. Large line tensions result in larger domains but also increase the charge density within the domain. This promotes correlations and, as a result, increases the intermembrane attraction. On the other hand, increasing the salt concentration increases both the domain size and degree of domain anticorrelation, but the interactions are ultimately reduced due to increased screening. The result is a decrease in the net attraction as salt concentration is increased. © 2011 American Chemical Society

Opalescence in monoclonal antibody solutions and its correlation with intermolecular interactions in dilute and concentrated solutions.

PubMed

Raut, Ashlesha S; Kalonia, Devendra S

2015-04-01

Opalescence indicates physical instability of a formulation because of the presence of aggregates or liquid-liquid phase separation in solution and has been reported for monoclonal antibody (mAb) formulations. Increased solution opalescence can be attributed to attractive protein-protein interactions (PPIs). Techniques including light scattering, AUC, or membrane osmometry are routinely employed to measure PPIs in dilute solutions, whereas opalescence is seen at relatively higher concentrations, where both long- and short-range forces contribute to overall PPIs. The mAb molecule studied here shows a unique property of high opalescence because of liquid-liquid phase separation. In this study, opalescence measurements are correlated to PPIs measured in diluted and concentrated solutions using light scattering (kD ) and high-frequency rheology (G'), respectively. Charges on the molecules were calculated using zeta potential measurements. Results indicate that high opalescence and phase separation are a result of the attractive interactions in solution; however, the presence of attractive interactions do not always imply phase separation. Temperature dependence of opalescence suggests that thermodynamic contribution to opalescence is significant and Tcloud can be utilized as a potential tool to assess attractive interactions in solution. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

A novel microfluidics-based method for probing weak protein-protein interactions.

PubMed

Tan, Darren Cherng-wen; Wijaya, I Putu Mahendra; Andreasson-Ochsner, Mirjam; Vasina, Elena Nikolaevna; Nallani, Madhavan; Hunziker, Walter; Sinner, Eva-Kathrin

2012-08-07

We report the use of a novel microfluidics-based method to detect weak protein-protein interactions between membrane proteins. The tight junction protein, claudin-2, synthesised in vitro using a cell-free expression system in the presence of polymer vesicles as membrane scaffolds, was used as a model membrane protein. Individual claudin-2 molecules interact weakly, although the cumulative effect of these interactions is significant. This effect results in a transient decrease of average vesicle dispersivity and reduction in transport speed of claudin-2-functionalised vesicles. Polymer vesicles functionalised with claudin-2 were perfused through a microfluidic channel and the time taken to traverse a defined distance within the channel was measured. Functionalised vesicles took 1.19 to 1.69 times longer to traverse this distance than unfunctionalised ones. Coating the channel walls with protein A and incubating the vesicles with anti-claudin-2 antibodies prior to perfusion resulted in the functionalised vesicles taking 1.75 to 2.5 times longer to traverse this distance compared to the controls. The data show that our system is able to detect weak as well as strong protein-protein interactions. This system offers researchers a portable, easily operated and customizable platform for the study of weak protein-protein interactions, particularly between membrane proteins.

Physical Attractiveness and Counseling Skills.

ERIC Educational Resources Information Center

Vargas, Alice M.; Borkowski, John G.

1982-01-01

Searched for interaction between quality of counseling skills (presence or absence of empathy, genuineness, and positive regard) and physical attractiveness as determinants of counseling effectiveness. Attractiveness influenced perceived effectiveness of counselor's skill. Analyses of expectancy data revealed that only with good skills did…

Attractiveness and Leader Style: Evaluations of Male and Female Leaders by Male and Female Evaluators.

ERIC Educational Resources Information Center

Sopasakis, Maria; Snodgrass, Sara E.

Previous research has suggested that men are stereotypically believed to be better leaders than women; that more physically attractive people are evaluated more positively than less attractive people; and that men and women use different leadership styles. This study examined the interactions of sex, leader style, and physical attractiveness on…

Quantum Phase Transitions in the Bose Hubbard Model and in a Bose-Fermi Mixture

NASA Astrophysics Data System (ADS)

Duchon, Eric Nicholas

Ultracold atomic gases may be the ultimate quantum simulator. These isolated systems have the lowest temperatures in the observable universe, and their properties and interactions can be precisely and accurately tuned across a full spectrum of behaviors, from few-body physics to highly-correlated many-body effects. The ability to impose potentials on and tune interactions within ultracold gases to mimic complex systems mean they could become a theorist's playground. One of their great strengths, however, is also one of the largest obstacles to this dream: isolation. This thesis touches on both of these themes. First, methods to characterize phases and quantum critical points, and to construct finite temperature phase diagrams using experimentally accessible observables in the Bose Hubbard model are discussed. Then, the transition from a weakly to a strongly interacting Bose-Fermi mixture in the continuum is analyzed using zero temperature numerical techniques. Real materials can be emulated by ultracold atomic gases loaded into optical lattice potentials. We discuss the characteristics of a single boson species trapped in an optical lattice (described by the Bose Hubbard model) and the hallmarks of the quantum critical region that separates the superfluid and the Mott insulator ground states. We propose a method to map the quantum critical region using the single, experimentally accessible, local quantity R, the ratio of compressibility to local number fluctuations. The procedure to map a phase diagram with R is easily generalized to inhomogeneous systems and generic many-body Hamiltonians. We illustrate it here using quantum Monte Carlo simulations of the 2D Bose Hubbard model. Secondly, we investigate the transition from a degenerate Fermi gas weakly coupled to a Bose Einstein condensate to the strong coupling limit of composite boson-fermion molecules. We propose a variational wave function to investigate the ground state properties of such a Bose-Fermi mixture with equal population, as a function of increasing attraction between bosons and fermions. The variational wave function captures the weak and the strong coupling limits and at intermediate coupling we make two predictions using zero temperature quantum Monte Carlo methods: (I) a complete destruction of the atomic Fermi surface and emergence of a molecular Fermi sea that coexists with a remnant of the Bose-Einstein condensate, and (II) evidence for enhanced short-ranged fermion-fermion correlations mediated by bosons.

Role of electrostatic interactions in the assembly of empty spherical viral capsids

NASA Astrophysics Data System (ADS)

Šiber, Antonio; Podgornik, Rudolf

2007-12-01

We examine the role of electrostatic interactions in the assembly of empty spherical viral capsids. The charges on the protein subunits that make the viral capsid mutually interact and are expected to yield electrostatic repulsion acting against the assembly of capsids. Thus, attractive protein-protein interactions of nonelectrostatic origin must act to enable the capsid formation. We investigate whether the interplay of repulsive electrostatic and attractive interactions between the protein subunits can result in the formation of spherical viral capsids of a preferred radius. For this to be the case, we find that the attractive interactions must depend on the angle between the neighboring protein subunits (i.e., on the mean curvature of the viral capsid) so that a particular angle(s) is (are) preferred energywise. Our results for the electrostatic contributions to energetics of viral capsids nicely correlate with recent experimental determinations of the energetics of protein-protein contacts in the hepatitis B virus [P. Ceres A. Zlotnick, Biochemistry 41, 11525 (2002)].

Crossing Over from Attractive to Repulsive Interactions in a Tunneling Bosonic Josephson Junction.

PubMed

Spagnolli, G; Semeghini, G; Masi, L; Ferioli, G; Trenkwalder, A; Coop, S; Landini, M; Pezzè, L; Modugno, G; Inguscio, M; Smerzi, A; Fattori, M

2017-06-09

We explore the interplay between tunneling and interatomic interactions in the dynamics of a bosonic Josephson junction. We tune the scattering length of an atomic ^{39}K Bose-Einstein condensate confined in a double-well trap to investigate regimes inaccessible to other superconducting or superfluid systems. In the limit of small-amplitude oscillations, we study the transition from Rabi to plasma oscillations by crossing over from attractive to repulsive interatomic interactions. We observe a critical slowing down in the oscillation frequency by increasing the strength of an attractive interaction up to the point of a quantum phase transition. With sufficiently large initial oscillation amplitude and repulsive interactions, the system enters the macroscopic quantum self-trapping regime, where we observe coherent undamped oscillations with a self-sustained average imbalance of the relative well population. The exquisite agreement between theory and experiments enables the observation of a broad range of many body coherent dynamical regimes driven by tunable tunneling energy, interactions and external forces, with applications spanning from atomtronics to quantum metrology.

Binding affinity of pro-apoptotic BH3 peptides for the anti-apoptotic Mcl-1 and A1 proteins: Molecular dynamics simulations of Mcl-1 and A1 in complex with six different BH3 peptides.

PubMed

Modi, Vivek; Sankararamakrishnan, Ramasubbu

2017-05-01

The anti-apoptotic members of Bcl-2 family of proteins bind to their pro-apoptotic counterparts to induce or prevent cell death.Based on the distinct binding profiles for specific pro-apoptotic BH3 peptides, the anti-apoptotic Bcl-2 proteins can be divided into at least two subclasses. The subclass that includes Bcl-X L binds strongly to Bad BH3 peptide while it has weak binding affinity for the second subclass of Bcl-2 proteins such as Mcl-1 and A1. Anti-apoptotic Bcl-2 proteins are considered to be attractive drug targets for anti-cancer drugs. BH3-mimetic inhibitors such as ABT-737 have been shown to be specific to Bcl-X L subclass while Mcl-1 and A1 show resistance to the same drug. An efficacious inhibitor should target all the anti-apoptotic Bcl-2 proteins. Hence, development of inhibitors selective to Mcl-1 and A1 is of prime importance for targeted cancer therapeutics. The first step to achieve this goal is to understand the molecular basis of high binding affinities of specific pro-apoptotic BH3 peptides for Mcl-1 and A1. To understand the interactions between the BH3 peptides and Mcl-1/A1, we performed multi-nanosecond molecular dynamics (MD) simulations of six complex structures of Mcl-1 and A1. With the exception of Bad, all complex structures were experimentally determined. Bad complex structures were modeled. Our simulation studies identified specific pattern of polar interactions between Mcl-1/A1 and high-affinity binding BH3 peptides. The lack of such polar interactions in Bad peptide complex is attributed to specific basic residues present before and after the highly conserved Leu residue. The close approach of basic residues in Bad and Mcl-1/A1 is hypothesized to be the cause of weak binding affinity. To test this hypothesis, we generated in silico mutants of these basic residues in Bad peptide and Mcl-1/A1 proteins. MD simulations of the mutant systems established the pattern of stable polar interactions observed in high-affinity binding BH3 peptides. We have thus identified specific residue positions in Bad and Mcl-1/A1 responsible for the weak binding affinity. Results from these simulation studies will aid in the development of inhibitors specific to Mcl-1 and A1 proteins. Copyright © 2017 Elsevier Inc. All rights reserved.

Perturbations to trophic interactions and the stability of complex food webs

PubMed Central

O'Gorman, Eoin J.; Emmerson, Mark C.

2009-01-01

The pattern of predator–prey interactions is thought to be a key determinant of ecosystem processes and stability. Complex ecological networks are characterized by distributions of interaction strengths that are highly skewed, with many weak and few strong interactors present. Theory suggests that this pattern promotes stability as weak interactors dampen the destabilizing potential of strong interactors. Here, we present an experimental test of this hypothesis and provide empirical evidence that the loss of weak interactors can destabilize communities in nature. We ranked 10 marine consumer species by the strength of their trophic interactions. We removed the strongest and weakest of these interactors from experimental food webs containing >100 species. Extinction of strong interactors produced a dramatic trophic cascade and reduced the temporal stability of key ecosystem process rates, community diversity and resistance to changes in community composition. Loss of weak interactors also proved damaging for our experimental ecosystems, leading to reductions in the temporal and spatial stability of ecosystem process rates, community diversity, and resistance. These results highlight the importance of conserving species to maintain the stabilizing pattern of trophic interactions in nature, even if they are perceived to have weak effects in the system. PMID:19666606

Dynamic localization and shear-induced hopping of particles: A way to understand the rheology of dense colloidal dispersions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Tianying; Zukoski, Charles F., E-mail: czukoski@illinois.edu

2014-09-01

For decades, attempts have been made to understand the formation of colloidal glasses and gels by linking suspension mechanics to particle properties where details of size, shape, and spatial dependencies of pair potentials present a bewildering array of variables that can be manipulated to achieve observed properties. Despite the range of variables that control suspension properties, one consistent observation is the remarkably similarity of flow properties observed as particle properties are varied. Understanding the underlying origins of the commonality in those behaviors (e.g., shear-thinning with increasing stress, diverging zero shear rate viscosity with increasing volume fraction, development of a dynamicmore » yield stress plateau with increases in volume faction or strength of attraction, development of two characteristic relaxation times probed in linear viscoelasticity, the creation of a rubbery plateau modulus at high strain frequencies, and shear-thickening) remains a challenge. Recently, naïve mode coupling and dynamic localization theories have been developed to capture collective behavior giving rise to formation of colloidal glasses and gels. This approach characterizes suspension mechanics of strongly interacting particles in terms of sluggish long-range particle diffusion modulated by varying particle interactions and volume fraction. These theories capture the scaling of the modulus with the volume fraction and strength of interparticle attraction, the frequency dependence of the moduli at the onset of the gel/glass transition, together with the divergence of the zero shear rate viscosity and cessation of diffusivity for hard sphere systems as close packing is approached. In this study, we explore the generality of the predictions of dynamic localization theory for systems of particles composed of bimodal particle size distributions experiencing weak interactions. We find that the mechanical properties of these suspensions are well captured within the framework of dynamic localization theory and that suspension mechanics can be understood in terms of a dynamical potential barrier, the magnitude of which governs the zero shear rate viscosity, and onset of a dynamic yield stress plateau as volume fraction or strength of interaction is raised.« less

Structure of a tethered polymer under flow using molecular dynamics and hybrid molecular-continuum simulations

NASA Astrophysics Data System (ADS)

Delgado-Buscalioni, Rafael; Coveney, Peter V.

2006-03-01

We analyse the structure of a single polymer tethered to a solid surface undergoing a Couette flow. We study the problem using molecular dynamics (MD) and hybrid MD-continuum simulations, wherein the polymer and the surrounding solvent are treated via standard MD, and the solvent flow farther away from the polymer is solved by continuum fluid dynamics (CFD). The polymer represents a freely jointed chain (FJC) and is modelled by Lennard-Jones (LJ) beads interacting through the FENE potential. The solvent (modelled as a LJ fluid) and a weakly attractive wall are treated at the molecular level. At large shear rates the polymer becomes more elongated than predicted by existing theoretical scaling laws. Also, along the normal-to-wall direction the structure observed for the FJC is, surprisingly, very similar to that predicted for a semiflexible chain. Comparison with previous Brownian dynamics simulations (which exclude both solvent and wall potential) indicates that these effects are due to the polymer-solvent and polymer-wall interactions. The hybrid simulations are in perfect agreement with the MD simulations, showing no trace of finite size effects. Importantly, the extra cost required to couple the MD and CFD domains is negligible.

Graphene/MoS2 heterostructures as templates for growing two-dimensional metals: Predictions from ab initio calculations

NASA Astrophysics Data System (ADS)

Šljivančanin, Željko; Belić, Milivoj

2017-09-01

Preparation of single-atom-thick layers of ordinary metals has been a challenging task since their closely packed atoms lack layered structure with highly anisotropic bonding. Using computational modeling based on density functional theory we showed that graphene/MoS2 heterostructures can be used as suitable templates to grow stable two-dimensional (2D) clusters, as well as extended monoatomic layers of metals with nonlayered structure in the bulk. Considering gold and lithium as two metals with markedly different properties, we found that Li intercalants strengthen coupling between graphene (G) and MoS2, mainly due to electrostatic attraction of 2D materials with positively charged Li atoms. However, intercalation with large Au atoms gives rise to a significant increase in the distance between G and MoS2 and thus, weakens their interaction. In addition to strong preference for 2D growth, we demonstrated that Au intercalants weakly interact with both G and MoS2, and hence G /MoS2 vertical heterostructures could be a promising framework to prepare gold 2D structures with electronic properties closely resembling those of the hypothetical free-standing hexagonal gold monolayer.

Supramolecular organization and chiral resolution of p-terphenyl-m-dicarbonitrile on the Ag(111) surface.

PubMed

Marschall, Matthias; Reichert, Joachim; Seufert, Knud; Auwärter, Willi; Klappenberger, Florian; Weber-Bargioni, Alexander; Klyatskaya, Svetlana; Zoppellaro, Giorgio; Nefedov, Alexei; Strunskus, Thomas; Wöll, Christof; Ruben, Mario; Barth, Johannes V

2010-05-17

The supramolecular organization and layer formation of the non-linear, prochiral molecule [1, 1';4',1'']-terphenyl-3,3"-dicarbonitrile adsorbed on the Ag(111) surface is investigated by scanning tunneling microscopy (STM) and near-edge X-ray absorption fine-structure spectroscopy (NEXAFS). Upon two-dimensional confinement the molecules are deconvoluted in three stereoisomers, that is, two mirror-symmetric trans- and one cis-species. STM measurements reveal large and regular islands following room temperature deposition, whereby NEXAFS confirms a flat adsorption geometry with the electronic pi-system parallel to the surface plane. The ordering within the expressed supramolecular arrays reflects a substrate templating effect, steric constraints and the operation of weak lateral interactions mainly originating from the carbonitrile endgroups. High-resolution data at room temperature reveal enantiormorphic characteristics of the molecular packing schemes in different domains of the arrays, indicative of chiral resolution during the 2D molecular self-assembly process. At submonolayer coverage supramolecular islands coexist with a disordered fluid phase of highly mobile molecules. Following thermal quenching (down to 6 K) we find extended supramolecular ribbons stabilised again by attractive and directional noncovalent interactions, the formation of which reflects a chiral resolution of trans-species.

Polymerase Acidic Protein-Basic Protein 1 (PA-PB1) Protein-Protein Interaction as a Target for Next-Generation Anti-influenza Therapeutics.

PubMed

Massari, Serena; Goracci, Laura; Desantis, Jenny; Tabarrini, Oriana

2016-09-08

The limited therapeutic options against the influenza virus (flu) and increasing challenges in drug resistance make the search for next-generation agents imperative. In this context, heterotrimeric viral PA/PB1/PB2 RNA-dependent RNA polymerase is an attractive target for a challenging but strategic protein-protein interaction (PPI) inhibition approach. Since 2012, the inhibition of the polymerase PA-PB1 subunit interface has become an active field of research following the publication of PA-PB1 crystal structures. In this Perspective, we briefly discuss the validity of flu polymerase as a drug target and its inhibition through a PPI inhibition strategy, including a comprehensive analysis of available PA-PB1 structures. An overview of all of the reported PA-PB1 complex formation inhibitors is provided, and approaches used for identification of the inhibitors, the hit-to-lead studies, and the emerged structure-activity relationship are described. In addition to highlighting the strengths and weaknesses of all of the PA-PB1 heterodimerization inhibitors, we analyze their hypothesized binding modes and alignment with a pharmacophore model that we have developed.

Mesoscale pattern formation of self-propelled rods with velocity reversal

NASA Astrophysics Data System (ADS)

Großmann, Robert; Peruani, Fernando; Bär, Markus

2016-11-01

We study self-propelled particles with velocity reversal interacting by uniaxial (nematic) alignment within a coarse-grained hydrodynamic theory. Combining analytical and numerical continuation techniques, we show that the physics of this active system is essentially controlled by the reversal frequency. In particular, we find that elongated, high-density, ordered patterns, called bands, emerge via subcritical bifurcations from spatially homogeneous states. Our analysis reveals further that the interaction of bands is weakly attractive and, consequently, bands fuse upon collision in analogy with nonequilibrium nucleation processes. Moreover, we demonstrate that a renormalized positive line tension can be assigned to stable bands below a critical reversal rate, beyond which they are transversally unstable. In addition, we discuss the kinetic roughening of bands as well as their nonlinear dynamics close to the threshold of transversal instability. Altogether, the reduction of the multiparticle system onto the dynamics of bands provides a unified framework to understand the emergence and stability of nonequilibrium patterns in this self-propelled particle system. In this regard, our results constitute a proof of principle in favor of the hypothesis in microbiology that velocity reversal of gliding rod-shaped bacteria regulates the transitions between various self-organized patterns observed during the bacterial life cycle.

Evidence for W=0 pairing in repulsive Hubbard square and hexagonal geometries

NASA Astrophysics Data System (ADS)

Perfetto, Enrico; Stefanucci, Gianluca; Callegari, Agnese; Cini, Michele

2004-08-01

Square and hexagonal lattices with purely repulsive on-site interactions on all sites and appropriate fillings show W=0 pairing, and the effective attractive interaction is due to a symmetry driven correlation effect; the W=0 pairs are two-body singlet eigenstates of the Hamiltonian with vanishing on-site repulsion. We can set up gedanken experiments with these bound pairs. Chains of CuO 4 units connected by weak links provide a test case which displays bound pair hopping and superconducting flux quantization (SFQ). Focusing on the low-energy sector, one obtains an accurate description in terms of an effective hard-core boson Hamiltonian which naturally describes itinerant pairs and SFQ in mesoscopic rings. For the numerical calculations, we take advantage of a recently proposed exact spin-disentangled diagonalization technique which can be generally applied to many-fermion problems and drastically reduces the size of the matrices to be handled. Remarkably, the very same pairing mechanism also works neatly with the wrapped honeycomb lattice, suitable for armchair carbon nanotubes; the binding energy of W=0 pairs depends strongly on the filling and decreases towards a small but non-zero value in the graphite limit.

Evidence of C-F-P and aromatic π-F-P weak interactions in imidazolium ionic liquids and its consequences

NASA Astrophysics Data System (ADS)

Panja, Sumit Kumar; Srivastava, Nitin; Srivastava, Jyoti; Prasad, Namburi Eswara; Noothalapati, Hemanth; Shigeto, Shinsuke; Saha, Satyen

2018-04-01

A simple change from alkyl group to alkene in side chain of imidazolium cation with same anion resulted in a drastic impact on physical properties (e.g., melting point) from bmimPF6 IL to cmimPF6 IL. The underlying reasons have been elucidated by structural and interaction studies with the help of DSC, SCXRD, vibrational and multi-nuclear NMR spectroscopic techniques. Experiments reveal existence of new weak interactions involving the carbon and π cloud of the imidazolium aromatic ring with fluoride of PF6 anion (i.e., C2-F-P and π-F-P) in cmimPF6 but are absent in structurally similar prototype IL, bmimPF6. Though weak, these interactions helped to form ladder type supramolecular arrangement, resulting in quite high melting point for cmimPF6 IL compared to bmimPF6 IL. These findings emphasize that an IL system can behave uniquely because of the existence of uncommon weak interactions.

Which is the Ideal Breast Size?: Some Social Clues for Plastic Surgeons.

PubMed

Raposio, Edoardo; Belgrano, Valerio; Santi, PierLuigi; Chiorri, Carlo

2016-03-01

To provide plastic surgeons with more detailed information as to factors affecting the perception of female attractiveness, the present study was aimed to investigate whether the interaction effect of breast and body size on ratings of female attractiveness is moderated by sociodemographic variables and whether ratings of shapeliness diverge from those of attractiveness.A community sample of 958 Italian participants rated the attractiveness and the shapeliness of 15 stimuli (5 breast sizes × 3 body sizes) in which frontal, 3/4, and profile views of the head and torso of a faceless woman were jointly shown.Bigger breast sizes obtained the highest attractiveness ratings, but the breast-by-body size interaction was also significant. Evidence was found of a moderator role of sex, marital status, and age. When the effects of breast and body size and their interaction had been ruled out, sex differences were at best very slight and limited to very specific combinations of breast and body sizes. Ratings of attractiveness and shapeliness were highly correlated and did not significantly differ.Results suggest that to address women's psychological needs, concerns, and expectations about their appearance, plastic surgeons should not simply focus on breast size but should carefully consider the 'big picture': the body in its entirety.

Using an innovative multiple regression procedure in a cancer population (Part 1): detecting and probing relationships of common interacting symptoms (pain, fatigue/weakness, sleep problems) as a strategy to discover influential symptom pairs and clusters

PubMed Central

Francoeur, Richard B

2015-01-01

Background The majority of patients with advanced cancer experience symptom pairs or clusters among pain, fatigue, and insomnia. Improved methods are needed to detect and interpret interactions among symptoms or diesease markers to reveal influential pairs or clusters. In prior work, I developed and validated sequential residual centering (SRC), a method that improves the sensitivity of multiple regression to detect interactions among predictors, by conditioning for multicollinearity (shared variation) among interactions and component predictors. Materials and methods Using a hypothetical three-way interaction among pain, fatigue, and sleep to predict depressive affect, I derive and explain SRC multiple regression. Subsequently, I estimate raw and SRC multiple regressions using real data for these symptoms from 268 palliative radiation outpatients. Results Unlike raw regression, SRC reveals that the three-way interaction (pain × fatigue/weakness × sleep problems) is statistically significant. In follow-up analyses, the relationship between pain and depressive affect is aggravated (magnified) within two partial ranges: 1) complete-to-some control over fatigue/weakness when there is complete control over sleep problems (ie, a subset of the pain–fatigue/weakness symptom pair), and 2) no control over fatigue/weakness when there is some-to-no control over sleep problems (ie, a subset of the pain–fatigue/weakness–sleep problems symptom cluster). Otherwise, the relationship weakens (buffering) as control over fatigue/weakness or sleep problems diminishes. Conclusion By reducing the standard error, SRC unmasks a three-way interaction comprising a symptom pair and cluster. Low-to-moderate levels of the moderator variable for fatigue/weakness magnify the relationship between pain and depressive affect. However, when the comoderator variable for sleep problems accompanies fatigue/weakness, only frequent or unrelenting levels of both symptoms magnify the relationship. These findings suggest that a countervailing mechanism involving depressive affect could account for the effectiveness of a cognitive behavioral intervention to reduce the severity of a pain, fatigue, and sleep disturbance cluster in a previous randomized trial. PMID:25565865

The role of electrostatics in protein-protein interactions of a monoclonal antibody.

PubMed

Roberts, D; Keeling, R; Tracka, M; van der Walle, C F; Uddin, S; Warwicker, J; Curtis, R

2014-07-07

Understanding how protein-protein interactions depend on the choice of buffer, salt, ionic strength, and pH is needed to have better control over protein solution behavior. Here, we have characterized the pH and ionic strength dependence of protein-protein interactions in terms of an interaction parameter kD obtained from dynamic light scattering and the osmotic second virial coefficient B22 measured by static light scattering. A simplified protein-protein interaction model based on a Baxter adhesive potential and an electric double layer force is used to separate out the contributions of longer-ranged electrostatic interactions from short-ranged attractive forces. The ionic strength dependence of protein-protein interactions for solutions at pH 6.5 and below can be accurately captured using a Deryaguin-Landau-Verwey-Overbeek (DLVO) potential to describe the double layer forces. In solutions at pH 9, attractive electrostatics occur over the ionic strength range of 5-275 mM. At intermediate pH values (7.25 to 8.5), there is a crossover effect characterized by a nonmonotonic ionic strength dependence of protein-protein interactions, which can be rationalized by the competing effects of long-ranged repulsive double layer forces at low ionic strength and a shorter ranged electrostatic attraction, which dominates above a critical ionic strength. The change of interactions from repulsive to attractive indicates a concomitant change in the angular dependence of protein-protein interaction from isotropic to anisotropic. In the second part of the paper, we show how the Baxter adhesive potential can be used to predict values of kD from fitting to B22 measurements, thus providing a molecular basis for the linear correlation between the two protein-protein interaction parameters.

Transitions induced by speed in self-propelled particles system with attractive interactions

NASA Astrophysics Data System (ADS)

Cambui, Dorilson. S.; Rosas, Alexandre

2018-05-01

In this work, we consider a system of self-propelled particles with attractive interactions in two dimensions. The model presents an order-disorder transition with the speed playing the role of the control parameter. In order to characterize the transition, we investigate the behavior of the order parameter and the Binder cumulant as a function of the speed. Our main finding is that the transition can be either continuous or discontinuous depending on two parameter of the model: the strength of the noise and the radius of attraction.

Do surfaces of positive electrostatic potential on different halogen derivatives in molecules attract? like attracting like!

PubMed

Varadwaj, Arpita; Varadwaj, Pradeep R; Yamashita, Koichi

2018-03-15

Coulomb's law states that like charges repel, and unlike charges attract. However, it has recently been theoretically revealed that two similarly charged conducting spheres will almost always attract each other when both are in close proximity. Using multiscale first principles calculations, we illustrate practical examples of several intermolecular complexes that are formed by the consequences of attraction between positive atomic sites of similar or dissimilar electrostatic surface potential on interacting molecules. The results of the quantum theory of atoms in molecules and symmetry adapted perturbation theory support the attraction between the positive sites, characterizing the F•••X (X = F, Cl, Br) intermolecular interactions in a series of 20 binary complexes as closed-shell type, although the molecular electrostatic surface potential approach does not (a failure!). Dispersion that has an r -6 dependence, where r is the equilibrium distance of separation, is found to be the sole driving force pushing the two positive sites to attract. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Aggregation in charged nanoparticles solutions induced by different interactions

NASA Astrophysics Data System (ADS)

Abbas, S.; Kumar, Sugam; Aswal, V. K.; Kohlbrecher, J.

2016-05-01

Small-angle neutron scattering (SANS) has been used to study the aggregation of anionic silica nanoparticles as induced through different interactions. The nanoparticle aggregation is induced by addition of salt (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) employing different kind of interactions. The results show that the interaction in presence of salt can be explained using DLVO theory whereas non-DLVO forces play important role for interaction of nanoparticles with protein and surfactant. The presence of salt screens the repulsion between charged nanoparticles giving rise to a net attraction in the DLVO potential. On the other hand, strong electrostatic attraction between nanoparticle and oppositely charged protein leads to protein-mediated nanoparticle aggregation. In case of non-ionic surfactant, the relatively long-range attractive depletion interaction is found to be responsible for the particle aggregation. Interestingly, the completely different interactions lead to similar kind of aggregate morphology. The nanoparticle aggregates formed are found to have mass fractal nature having a fractal dimension (~2.5) consistent with diffusion limited type of fractal morphology in all three cases.

Stacking interactions between nitrogen-containing six-membered heterocyclic aromatic rings and substituted benzene: studies in solution and in the solid state.

PubMed

Gung, Benjamin W; Wekesa, Francis; Barnes, Charles L

2008-03-07

The stacking interactions between an aromatic ring and a pyridine or a pyrimidine ring are studied by using a series of triptycene-derived scaffolds. The indicative ratios of the syn and anti conformers were determined by variable-temperature NMR spectroscopy. The syn conformer aligns the attached aromatic ring and the heterocycle in a parallel-displaced orientation while the anti conformer sets the two rings apart from each other. Comparing to the corresponding control compounds where a benzene ring is in the position of the heterocycle, higher attractive interactions are observed as indicated by the higher syn/anti ratios. In general, the attractive interactions are much less sensitive to the substituent effects than the corresponding nonheterocycles. The greatest attractive interactions were observed between a pyrimidine ring and a N,N-dimethylaminobenzene, consistent with a predominant donor-acceptor interaction. The interactions between a pyridine ring and a substituted benzene ring show that the pyridine is comparable to that of a NO2- or a CN-substituted benzene ring except for the unpredictable substituent effects.

Aggregation in charged nanoparticles solutions induced by different interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbas, S.; Kumar, Sugam; Aswal, V. K., E-mail: vkaswal@barc.gov.in

2016-05-23

Small-angle neutron scattering (SANS) has been used to study the aggregation of anionic silica nanoparticles as induced through different interactions. The nanoparticle aggregation is induced by addition of salt (NaCl), cationic protein (lysozyme) and non-ionic surfactant (C12E10) employing different kind of interactions. The results show that the interaction in presence of salt can be explained using DLVO theory whereas non-DLVO forces play important role for interaction of nanoparticles with protein and surfactant. The presence of salt screens the repulsion between charged nanoparticles giving rise to a net attraction in the DLVO potential. On the other hand, strong electrostatic attraction betweenmore » nanoparticle and oppositely charged protein leads to protein-mediated nanoparticle aggregation. In case of non-ionic surfactant, the relatively long-range attractive depletion interaction is found to be responsible for the particle aggregation. Interestingly, the completely different interactions lead to similar kind of aggregate morphology. The nanoparticle aggregates formed are found to have mass fractal nature having a fractal dimension (~2.5) consistent with diffusion limited type of fractal morphology in all three cases.« less

Investigation on the individual contributions of N-H...O=C and C-H...O=C interactions to the binding energies of beta-sheet models.

PubMed

Wang, Chang-Sheng; Sun, Chang-Liang

2010-04-15

In this article, the binding energies of 16 antiparallel and parallel beta-sheet models are estimated using the analytic potential energy function we proposed recently and the results are compared with those obtained from MP2, AMBER99, OPLSAA/L, and CHARMM27 calculations. The comparisons indicate that the analytic potential energy function can produce reasonable binding energies for beta-sheet models. Further comparisons suggest that the binding energy of the beta-sheet models might come mainly from dipole-dipole attractive and repulsive interactions and VDW interactions between the two strands. The dipole-dipole attractive and repulsive interactions are further obtained in this article. The total of N-H...H-N and C=O...O=C dipole-dipole repulsive interaction (the secondary electrostatic repulsive interaction) in the small ring of the antiparallel beta-sheet models is estimated to be about 6.0 kcal/mol. The individual N-H...O=C dipole-dipole attractive interaction is predicted to be -6.2 +/- 0.2 kcal/mol in the antiparallel beta-sheet models and -5.2 +/- 0.6 kcal/mol in the parallel beta-sheet models. The individual C(alpha)-H...O=C attractive interaction is -1.2 +/- 0.2 kcal/mol in the antiparallel beta-sheet models and -1.5 +/- 0.2 kcal/mol in the parallel beta-sheet models. These values are important in understanding the interactions at protein-protein interfaces and developing a more accurate force field for peptides and proteins. 2009 Wiley Periodicals, Inc.

Expression of Power and Heterosexual Attraction.

ERIC Educational Resources Information Center

DeBlasio, Cynthia L.; Ellyson, Steve L.

Facial attractiveness has been the focus of considerable research in social psychology. Nonverbal behaviors emitted by the face may affect the perceived attractiveness of males and females differently. Visual behavior has particularly important functions in regulating social interaction and in establishing and conveying social power. Power and…

Affiliation of Opposite-Sexed Strangers

ERIC Educational Resources Information Center

Crouse, Bryant Bernhardt; Mehrabian, Albert

1977-01-01

Examines the effects of physical attractiveness on live verbal interactions between males and females. It was assumed that if opposite-sexed individuals primarily base their liking of the other on physical attractiveness, then subjects should be more positive and affiliative with attractive than unattractive others. (Author/RK)

Interactions among the effects of head orientation, emotional expression, and physical attractiveness on face preferences.

PubMed

Main, Julie C; DeBruine, Lisa M; Little, Anthony C; Jones, Benedict C

2010-01-01

Previous studies have shown that preferences for direct versus averted gaze are modulated by emotional expressions and physical attractiveness. For example, preferences for direct gaze are stronger when judging happy or physically attractive faces than when judging disgusted or physically unattractive faces. Here we show that preferences for front versus three-quarter views of faces, in which gaze direction was always congruent with head orientation, are also modulated by emotional expressions and physical attractiveness; participants demonstrated preferences for front views of faces over three-quarter views of faces when judging the attractiveness of happy, physically attractive individuals, but not when judging the attractiveness of relatively unattractive individuals or those with disgusted expressions. Moreover, further analyses indicated that these interactions did not simply reflect differential perceptions of the intensity of the emotional expressions shown in each condition. Collectively, these findings present novel evidence that the effect of the direction of the attention of others on attractiveness judgments is modulated by cues to the physical attractiveness and emotional state of the depicted individual, potentially reflecting psychological adaptations for efficient allocation of social effort. These data also present the first behavioural evidence that the effect of the direction of the attention of others on attractiveness judgments reflects viewer-referenced, rather than face-referenced, coding and/or processing of gaze direction.

Search for a Scalar Component in the Weak Interaction

NASA Astrophysics Data System (ADS)

Zakoucky, Dalibor; Baczyk, Pavel; Ban, Gilles; Beck, Marcus; Breitenfeldt, Martin; Couratin, Claire; Fabian, Xavier; Finlay, Paul; Flechard, Xavier; Friedag, Peter; Glück, Ferenc; Herlert, Alexander; Knecht, Andreas; Kozlov, Valentin; Lienard, Etienne; Porobic, Tomica; Soti, Gergelj; Tandecki, Michael; Vangorp, Simon; Weinheimer, Christian; Wursten, Elise; Severijns, Nathal

Weak interactions are described by the Standard Model which uses the basic assumption of a pure "V(ector)-A(xial vector)" character for the interaction. However, after more than half a century of model development and experimental testing of its fundamental ingredients, experimental limits for possible admixtures of scalar and/or tensor interactions are still as high as 7%. The WITCH project (Weak Interaction Trap for CHarged particles) at the isotope separator ISOLDE at CERN is trying to probe the structure of the weak interaction in specific low energy β-decays in order to look for possible scalar or tensor components or at least significantly improve the current experimental limits. This worldwide unique experimental setup consisting of a combination of two Penning ion traps and a retardation spectrometer allows to catch, trap and cool the radioactive nuclei provided by the ISOLDE separator, form a cooled and scattering-free radioactive source of β-decaying nuclei and let these nuclei decay at rest. The precise measurement of the shape of the energy spectrum of the recoiling nuclei, the shape of which is very sensitive to the character of the weak interaction, enables searching for a possible admixture of a scalar/tensor component in the dominant vector/axial vector mode. First online measurements with the isotope 35Ar were performed in 2011 and 2012. The current status of the experiment, the data analysis and results as well as extensive simulations will be presented and discussed.

An Investigation of Human-Computer Interaction Approaches Beneficial to Weak Learners in Complex Animation Learning

ERIC Educational Resources Information Center

Yeh, Yu-Fang

2016-01-01

Animation is one of the useful contemporary educational technologies in teaching complex subjects. There is a growing interest in proper use of learner-technology interaction to promote learning quality for different groups of learner needs. The purpose of this study is to investigate if an interaction approach supports weak learners, who have…

Alternative method of quantum state tomography toward a typical target via a weak-value measurement

NASA Astrophysics Data System (ADS)

Chen, Xi; Dai, Hong-Yi; Yang, Le; Zhang, Ming

2018-03-01

There is usually a limitation of weak interaction on the application of weak-value measurement. This limitation dominates the performance of the quantum state tomography toward a typical target in the finite and high-dimensional complex-valued superposition of its basis states, especially when the compressive sensing technique is also employed. Here we propose an alternative method of quantum state tomography, presented as a general model, toward such typical target via weak-value measurement to overcome such limitation. In this model the pointer for the weak-value measurement is a qubit, and the target-pointer coupling interaction is no longer needed within the weak interaction limitation, meanwhile this interaction under the compressive sensing can be described with the Taylor series of the unitary evolution operator. The postselection state at the target is the equal superposition of all basis states, and the pointer readouts are gathered under multiple Pauli operator measurements. The reconstructed quantum state is generated from an optimization algorithm of total variation augmented Lagrangian alternating direction algorithm. Furthermore, we demonstrate an example of this general model for the quantum state tomography toward the planar laser-energy distribution and discuss the relations among some parameters at both our general model and the original first-order approximate model for this tomography.

Intergroup perception as a compromise between in-group bias and fair-mindedness.

PubMed

Singh, Ramadhar; Sharmini; Choo, Ivy

2004-08-01

Previously, perceived competence of and attraction toward targets categorized by race showed in-group bias and no bias, respectively. Consequently, previous investigators regarded intergroup perception as a compromise between the norms of in-group bias and fair-mindedness. An alternative hypothesis for such findings is that attraction is not as relevant a dimension for intergroup discrimination as is competence. To test contrasting predictions of these hypotheses, the present authors asked participants from the majority and minority groups in Singapore (ns = 320) to evaluate either competence of or attraction toward one of the five targets. Consistent with the hypothesis that intergroup perception is a compromise, both dimensions yielded a uniform but weak in-group bias. The participants' equating of the in-group with one out-group further illustrated fair-mindedness. The authors discussed implications of the findings.

Protein interactions in concentrated ribonuclease solutions

NASA Astrophysics Data System (ADS)

Boyer, Mireille; Roy, Marie-Odile; Jullien, Magali; Bonneté, Françoise; Tardieu, Annette

1999-01-01

To investigate the protein interactions involved in the crystallization process of ribonuclease A, dynamic light scattering (DLS) and small angle X-ray scattering experiments (SAXS) were performed on concentrated solutions. Whereas the translational diffusion coefficient obtained from DLS is sensitive to thermodynamic and hydrodynamic interactions and permits to calculate an interaction parameter, the shape of the SAXS curves is related to the type of interaction (attractive or repulsive). We compared the effect of pH on protein interactions in the case of two types of crystallizing agents: a mixture of salts (3 M sodium chloride plus 0.2 M ammonium sulfate) and an organic solvent (ethanol). The results show that in the presence of ethanol, as in low salt, protein interactions become more attractive as the pH increases from 4 to 8 and approaches the isoelectric point. In contrast, a reverse effect is observed in high salt conditions: the strength of attractive interactions decreases as the pH increases. The range of the pH effect can be related to ionization of histidine residues, particularly those located in the active site of the protein. The present observations point out the important role played by localized charges in crystallization conditions, whatever the precipitating agent.

Influence of the Location of Attractive Polymer-Pore Interactions on Translocation Dynamics.

PubMed

Ghosh, Bappa; Chaudhury, Srabanti

2018-01-11

We probe the influence of polymer-pore interactions on the translocation dynamics using Langevin dynamics simulations. We investigate the effect of the strength and location of the polymer-pore interaction using nanopores that are partially charged either at the entry or the exit or on both sides of the pore. We study the change in the translocation time as a function of the strength of the polymer-pore interaction for a given chain length and under the effect of an externally applied field. Under a moderate driving force and a chain length longer than the length of the pore, the translocation time shows a nonmonotonic increase with an increase in the attractive interaction. Also, an interaction on the cis side of the pore can increase the translocation probability. In the presence of an external field and a strong attractive force, the translocation time for shorter chains is independent of the polymer-pore interaction at the entry side of the pore, whereas an interaction on the trans side dominates the translocation process. Our simulation results are rationalized by a qualitative analysis of the free energy landscape for polymer translocation.

Attraction and Communicator Style: Perceptual Differences between Friends and Enemies as a Function of Sex and Race.

ERIC Educational Resources Information Center

Miller, Larry D.

Research on attraction in an interpersonal context has strongly suggested that the more attracted two people are to one another, the more they tend to communicate. This study explored attraction and social interaction patterns at the perceptual level. Eighty male and female graduate students, 40 black and 40 white, completed a two part measure of…

Adsorption of weak polyelectrolytes on charged nanoparticles. Impact of salt valency, pH, and nanoparticle charge density. Monte Carlo simulations.

PubMed

Carnal, Fabrice; Stoll, Serge

2011-10-27

Complex formation between a weak flexible polyelectrolyte chain and one positively charged nanoparticle in presence of explicit counterions and salt particles is investigated using Monte Carlo simulations. The influence of parameters such as the nanoparticle surface charge density, salt valency, and solution property such as the pH on the chain protonation/deprotonation process and monomer adsorption at the nanoparticle surface are systematically investigated. It is shown that the nanoparticle presence significantly modifies chain acid/base and polyelectrolyte conformational properties. The importance of the attractive electrostatic interactions between the chain and the nanoparticle clearly promotes the chain deprotonation leading, at high pH and nanoparticle charge density, to fully wrapped polyelectrolyte at the nanoparticle surface. When the nanoparticle bare charge is overcompensated by the polyelectrolyte charges, counterions and salt particles condense at the surface of the polyelectrolyte-nanoparticle complex to compensate for the excess of charges providing from the adsorbed polyelectrolyte chain. It is also shown that the complex formation is significantly affected by the salt valency. Indeed, with the presence of trivalent salt cations, competition is observed between the nanoparticle and the trivalent cations. As a result, the amount of adsorbed monomers is less important than in the monovalent and divalent case and chain conformations are different due to the collapse of polyelectrolyte segments around trivalent cations out of the nanoparticle adsorption layer.

Communication: Polymer entanglement dynamics: Role of attractive interactions

DOE PAGES

Grest, Gary S.

2016-10-10

The coupled dynamics of entangled polymers, which span broad time and length scales, govern their unique viscoelastic properties. To follow chain mobility by numerical simulations from the intermediate Rouse and reptation regimes to the late time diffusive regime, highly coarse grained models with purely repulsive interactions between monomers are widely used since they are computationally the most efficient. In this paper, using large scale molecular dynamics simulations, the effect of including the attractive interaction between monomers on the dynamics of entangled polymer melts is explored for the first time over a wide temperature range. Attractive interactions have little effect onmore » the local packing for all temperatures T and on the chain mobility for T higher than about twice the glass transition T g. Finally, these results, across a broad range of molecular weight, show that to study the dynamics of entangled polymer melts, the interactions can be treated as pure repulsive, confirming a posteriori the validity of previous studies and opening the way to new large scale numerical simulations.« less

Students' Understanding of Boiling Points and Intermolecular Forces

ERIC Educational Resources Information Center

Schmidt, Hans-Jurgen; Kaufmann, Birgit; Treagust, David F.

2009-01-01

In introductory chemistry courses students are presented with the model that matter is composed of particles, and that weak forces of attraction exist between them. This model is used to interpret phenomena such as solubility and melting points, and aids in understanding the changes in states of matter as opposed to chemical reactions. We…

Known and Unknown Weaknesses in Software Animated Demonstrations (Screencasts): A Study in Self-Paced Learning Settings

ERIC Educational Resources Information Center

Palaigeorgiou, George; Despotakis, Theofanis

2010-01-01

Learning about computers continues to be regarded as a rather informal and complex landscape dominated by individual exploratory and opportunistic approaches, even for students and instructors in Computer Science Departments. During the last two decades, software animated demonstrations (SADs), also known as screencasts, have attracted particular…

Neurophysiological Study of Vector Responses to Repellents.

DTIC Science & Technology

1979-08-01

The Al sensilla responded weakly or not at all to oviposition site attractants and the repellent series. Citronellol and geraniol induced a decrease...612 - 0/++ -- ++/0 + + 0 SRI-C6 - 0/-- - /++ ++ 0 0 2504-5 0/- 0 0 0 0 Citronellol 0/++ 0 - 0 Geraniol 0 - - 0 0 Naphthalene 0 0 0 0 Juglone + + +4

Density-functional formulation of the generalized pseudopotential theory. III. Transition-metal interatomic potentials

NASA Astrophysics Data System (ADS)

Moriarty, John A.

1988-08-01

The first-principles, density-functional version of the generalized pseudopotential theory (GPT) developed in papers I and II of this series [Phys. Rev. B 16, 2537 (1977); 26, 1754 (1982)] for empty- and filled-d-band metals is here extended to pure transition metals with partially filled d bands. The present focus is on a rigorous, real-space expansion of the bulk total energy in terms of widely transferable, structure-independent interatomic potentials, including both central-force pair interactions and angular-force triplet and quadruplet interactions. To accomplish this expansion, a specialized set of starting equations is derived from the basic local-density formalism for a pure metal, including refined expansions for the exchange-correlation terms and a simplified yet accurate representation of the cohesive energy. The parent pseudo-Green's-function formalism of the GPT is then used to develop these equations in a plane-wave, localized-d-state basis. In this basis, the cohesive energy divides quite naturally into a large volume component and a smaller structural component. The volume component,which includes all one-ion intra-atomic energy contributions, already gives a good description of the cohesion in lowest order. The structural component is expanded in terms of weak interatomic matrix elements and gives rise to a multi-ion series which establishes the interatomic potentials. Special attention is focused on the dominant d-electron contributions to this series and complete formal results for the two-ion, three-ion, and four-ion d-state potentials (vd2, vd3, and vd4) are derived. In addition, a simplified model is used to demonstrate that while vd3 can be of comparable importance to vd2, vd4 is inherently small and the series is rapidly convergent beyond three-ion interactions. Analytic model forms are also derived for vd2 and vd3 in the case of canonical d bands. In this limit, vd2 is purely attractive and varies with interatomic distance as r-10, while vd3 is weak and attractive for almost empty or filled d bands and maximum in strength and repulsive for half-filled d bands. Full first-principles expressions are then developed for the total two-ion and three-ion potentials and implemented for all 20 3d and 4d transition metals. The first-principles potentials qualitatively display all of the trends predicted by the model results, but they also reflect additional effects, including long-range hybridization tails which must be suitably screened in real-space calculations. Finally, illustrative application of the first-principles potentials is made to the calculation of the [100] phonon spectrum for V and Cr, where the importance of three-ion angular forces is explicitly demonstrated.

Niche construction initiates the evolution of mutualistic interactions.

PubMed

Buser, Claudia C; Newcomb, Richard D; Gaskett, Anne C; Goddard, Matthew R

2014-10-01

Niche construction theory explains how organisms' niche modifications may feed back to affect their evolutionary trajectories. In theory, the evolution of other species accessing the same modified niche may also be affected. We propose that this niche construction may be a general mechanism driving the evolution of mutualisms. Drosophilid flies benefit from accessing yeast-infested fruits, but the consequences of this interaction for yeasts are unknown. We reveal high levels of variation among strains of Saccharomyces cerevisiae in their ability to modify fruits and attract Drosophila simulans. More attractive yeasts are dispersed more frequently, both in the lab and in the field, and flies associated with more attractive yeasts have higher fecundity. Although there may be multiple natural yeast and fly species interactions, our controlled assays in the lab and field provide evidence of a mutualistic interaction, facilitated by the yeast's niche modification. © 2014 John Wiley & Sons Ltd/CNRS.

Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: a Monte Carlo simulation study in the Debye-Hückel approximation.

PubMed

Truzzolillo, D; Bordi, F; Sciortino, F; Sennato, S

2010-07-14

We study the effective interaction between differently charged polyelectrolyte-colloid complexes in electrolyte solutions via Monte Carlo simulations. These complexes are formed when short and flexible polyelectrolyte chains adsorb onto oppositely charged colloidal spheres, dispersed in an electrolyte solution. In our simulations the bending energy between adjacent monomers is small compared to the electrostatic energy, and the chains, once adsorbed, do not exchange with the solution, although they rearrange on the particles surface to accommodate further adsorbing chains or due to the electrostatic interaction with neighbor complexes. Rather unexpectedly, when two interacting particles approach each other, the rearrangement of the surface charge distribution invariably produces antiparallel dipolar doublets that invert their orientation at the isoelectric point. These findings clearly rule out a contribution of dipole-dipole interactions to the observed attractive interaction between the complexes, pointing out that such suspensions cannot be considered dipolar fluids. On varying the ionic strength of the electrolyte, we find that a screening length kappa(-1), short compared with the size of the colloidal particles, is required in order to observe the attraction between like-charged complexes due to the nonuniform distribution of the electric charge on their surface ("patch attraction"). On the other hand, by changing the polyelectrolyte/particle charge ratio xi(s), the interaction between like-charged polyelectrolyte-decorated particles, at short separations, evolves from purely repulsive to strongly attractive. Hence, the effective interaction between the complexes is characterized by a potential barrier, whose height depends on the net charge and on the nonuniformity of their surface charge distribution.

Direct observation of growth and collapse of a Bose-Einstein condensate with attractive interactions

NASA Astrophysics Data System (ADS)

Gerton, Jordan M.; Strekalov, Dmitry; Prodan, Ionut; Hulet, Randall G.

2000-12-01

Quantum theory predicts that Bose-Einstein condensation of a spatially homogeneous gas with attractive interactions is precluded by a conventional phase transition into either a liquid or solid. When confined to a trap, however, such a condensate can form, provided that its occupation number does not exceed a limiting value. The stability limit is determined by a balance between the self-attractive forces and a repulsion that arises from position-momentum uncertainty under conditions of spatial confinement. Near the stability limit, self-attraction can overwhelm the repulsion, causing the condensate to collapse. Growth of the condensate is therefore punctuated by intermittent collapses that are triggered by either macroscopic quantum tunnelling or thermal fluctuation. Previous observations of growth and collapse dynamics have been hampered by the stochastic nature of these mechanisms. Here we report direct observations of the growth and subsequent collapse of a 7Li condensate with attractive interactions, using phase-contrast imaging. The success of the measurement lies in our ability to reduce the stochasticity in the dynamics by controlling the initial number of condensate atoms using a two-photon transition to a diatomic molecular state.

A combined Cyanex-923/HEH[EHP]/Dodecane solvent for recovery of transuranic elements from used nuclear fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, A.; Nash, K.L.

2013-07-01

The separation of minor actinides from fission product lanthanides remains a primary challenge for enabling the recycle of used nuclear fuel. To minimize the complexity of materials handling, combining extractant processes has become an increasingly attractive option. Unfortunately, combined processes sometimes suffer reduced utility due to strong dipole-dipole interactions between the extractants. The results reported here describe a system based on a combination of commercially available extractants Cyanex-923 and HEH[EHP]. In contrast to other combined extractant systems, these extractant molecules exhibit comparatively weak interactions, reducing the impact of secondary interactions. In this process, mixtures containing equal ratios of Cyanex-923 andmore » HEH[EHP] were seen to co-extract americium and the lanthanides from nitric acid solutions. Stripping of An(III) was effectively achieved through contact with an aqueous phase comprised of glycine (for pH control) and a polyamino-poly-carboxylate stripping reagent that selectively removes An(III) from the extractant phase. The lanthanides can then be stripped from the loaded organic phase contacting with high nitric acid concentrations. Extraction of fission products zirconium and molybdenum was also investigated and potential strategies for their management have been identified. The work presented demonstrates the feasibility of combining Cyanex-923 and HEH[EHP] for separating and recovering the transuranic elements from the Ln(III). (authors)« less

Interactions of solitons in Bragg gratings with dispersive reflectivity in a cubic-quintic medium

NASA Astrophysics Data System (ADS)

Dasanayaka, Sahan; Atai, Javid

2011-08-01

Interactions between quiescent solitons in Bragg gratings with cubic-quintic nonlinearity and dispersive reflectivity are systematically investigated. In a previous work two disjoint families of solitons were identified in this model. One family can be viewed as the generalization of the Bragg grating solitons in Kerr nonlinearity with dispersive reflectivity (Type 1). On the other hand, the quintic nonlinearity is dominant in the other family (Type 2). For weak to moderate dispersive reflectivity, two in-phase solitons will attract and collide. Possible collision outcomes include merger to form a quiescent soliton, formation of three solitons including a quiescent one, separation after passing through each other once, asymmetric separation after several quasielastic collisions, and soliton destruction. Type 2 solitons are always destroyed by collisions. Solitons develop sidelobes when dispersive reflectivity is strong. In this case, it is found that the outcome of the interactions is strongly dependent on the initial separation of solitons. Solitons with sidelobes will collide only if they are in-phase and their initial separation is below a certain critical value. For larger separations, both in-phase and π-out-of-phase Type 1 and Type 2 solitons may either repel each other or form a temporary bound state that subsequently splits into two separating solitons. Additionally, in the case of Type 2 solitons, for certain initial separations, the bound state disintegrates into a single moving soliton.

Differences in Expressivity Based on Attractiveness: Target or Perceiver Effects?

PubMed

Rennels, Jennifer L; Kayl, Andrea J

2015-09-01

A significant association exists between adults' expressivity and facial attractiveness, but it is unclear whether the association is linear or significant only at the extremes of attractiveness. It is also unclear whether attractive persons actually display more positive expressivity than unattractive persons (target effects) or whether high and low attractiveness influences expressivity valence judgments (perceiver effects). Experiment 1 demonstrated adult ratings of attractiveness were predictive of expressivity valence only for high and low attractive females and medium attractive males. Experiment 2 showed that low attractive females actually display more negative expressivity than medium and high attractive females, but there were no target effects for males. Also, attractiveness influenced expressivity valence judgments (perceiver effects) for both females and males. Our findings demonstrate that low attractive females are at a particular disadvantage during social interactions due to their low attractiveness, actual displays of negative expressivity, and perceptions of their negative expressivity.

Differences in Expressivity Based on Attractiveness: Target or Perceiver Effects?

PubMed Central

Rennels, Jennifer L.; Kayl, Andrea J.

2015-01-01

A significant association exists between adults’ expressivity and facial attractiveness, but it is unclear whether the association is linear or significant only at the extremes of attractiveness. It is also unclear whether attractive persons actually display more positive expressivity than unattractive persons (target effects) or whether high and low attractiveness influences expressivity valence judgments (perceiver effects). Experiment 1 demonstrated adult ratings of attractiveness were predictive of expressivity valence only for high and low attractive females and medium attractive males. Experiment 2 showed that low attractive females actually display more negative expressivity than medium and high attractive females, but there were no target effects for males. Also, attractiveness influenced expressivity valence judgments (perceiver effects) for both females and males. Our findings demonstrate that low attractive females are at a particular disadvantage during social interactions due to their low attractiveness, actual displays of negative expressivity, and perceptions of their negative expressivity. PMID:26366010

Effects of molecular size and structure on self-diffusion coefficient and viscosity for saturated hydrocarbons having six carbon atoms.

PubMed

Iwahashi, Makio; Kasahara, Yasutoshi

2007-01-01

Self-diffusion coefficients and viscosities for the saturated hydrocarbons having six carbon atoms such as hexane, 2-methylpentane (2MP), 3-methylpentane (3MP), 2,2-dimethylbutane (22DMB), 2,3-dimethylbutane (23DMB), methylcyclopentane (McP) and cyclohexane (cH) were measured at various constant temperatures; obtained results were discussed in connection with their molar volumes, molecular structures and thermodynamic properties. The values of self-diffusion coefficients as the microscopic property were inversely proportional to those of viscosities as the macroscopic property. The order of their viscosities was almost same to those of their melting temperatures and enthalpies of fusion, which reflect the attractive interactions among their molecules. On the other hand, the order of the self-diffusion coefficients inversely related to the order of the melting temperatures and the enthalpies of the fusion. Namely, the compound having the larger attractive interaction mostly shows the less mobility in its liquid state, e.g., cyclohexane (cH), having the largest attractive interaction and the smallest molar volume exhibits an extremely large viscosity and small self-diffusion coefficient comparing with other hydrocarbons. However, a significant exception was 22DMB, being most close to a sphere: In spite of the smallest attractive interaction and the largest molar volume of 22DMB in the all samples, it has the thirdly larger viscosity and the thirdly smaller self-diffusion coefficient. Consequently, the dynamical properties such as self-diffusion and viscosity for the saturated hydrocarbons are determined not only by their attractive interactions but also by their molecular structures.

Electrical percolation in the presence of attractive interactions: An effective medium lattice approach applied to microemulsion systems

NASA Astrophysics Data System (ADS)

Hattori, Y.; Ushiki, H.; Engl, W.; Courbin, L.; Panizza, P.

2005-08-01

Within the framework of an effective medium approach and a mean-field approximation, we present a simple lattice model to treat electrical percolation in the presence of attractive interactions. We show that the percolation line depends on the magnitude of interactions. In 2 dimensions, the percolation line meets the binodal line at the critical point. A good qualitative agreement is observed with experimental results on a ternary AOT-based water-in-oil microemulsion system.

Quantum noise in bright soliton matterwave interferometry

NASA Astrophysics Data System (ADS)

Haine, Simon A.

2018-03-01

There has been considerable recent interest in matterwave interferometry with bright solitons in quantum gases with attractive interactions, for applications such as rotation sensing. We model the quantum dynamics of these systems and find that the attractive interactions required for the presence of bright solitons causes quantum phase-diffusion, which severely impairs the sensitivity. We propose a scheme that partially restores the sensitivity, but find that in the case of rotation sensing, it is still better to work in a regime with minimal interactions if possible.

The relative contribution of profile body shape and weight to judgements of women's physical attractiveness in Britain and Malaysia.

PubMed

Swami, Viren; Tovée, Martin J

2007-12-01

Ninety-six Malaysian and British men rated for physical attractiveness a set of photographs of real women in profile, with known body mass index (BMI) and waist-to-hip ratio (WHR). Results showed that BMI accounted for the greater amount of variance in all settings. There were also significant differences in preferences for body weight, with low resource, low socioeconomic status (SES) raters preferring a significantly heavier partner than high resource, high SES raters. The disparity with previous findings using line drawings of women in profile was discussed in terms of the weaknesses of line-drawn stimuli.

Self-consistent phonon theory of the crystallization and elasticity of attractive hard spheres.

PubMed

Shin, Homin; Schweizer, Kenneth S

2013-02-28

We propose an Einstein-solid, self-consistent phonon theory for the crystal phase of hard spheres that interact via short-range attractions. The approach is first tested against the known behavior of hard spheres, and then applied to homogeneous particles that interact via short-range square well attractions and the Baxter adhesive hard sphere model. Given the crystal symmetry, packing fraction, and strength and range of attractive interactions, an effective harmonic potential experienced by a particle confined to its Wigner-Seitz cell and corresponding mean square vibrational amplitude are self-consistently calculated. The crystal free energy is then computed and, using separate information about the fluid phase free energy, phase diagrams constructed, including a first-order solid-solid phase transition and its associated critical point. The simple theory qualitatively captures all the many distinctive features of the phase diagram (critical and triple point, crystal-fluid re-entrancy, low-density coexistence curve) as a function of attraction range, and overall is in good semi-quantitative agreement with simulation. Knowledge of the particle localization length allows the crystal shear modulus to be estimated based on elementary ideas. Excellent predictions are obtained for the hard sphere crystal. Expanded and condensed face-centered cubic crystals are found to have qualitatively different elastic responses to varying attraction strength or temperature. As temperature increases, the expanded entropic solid stiffens, while the energy-controlled, fully-bonded dense solid softens.

A theoretical approach for estimation of ultimate size of bimetallic nanocomposites synthesized in microemulsion systems

NASA Astrophysics Data System (ADS)

Salabat, Alireza; Saydi, Hassan

2012-12-01

In this research a new idea for prediction of ultimate sizes of bimetallic nanocomposites synthesized in water-in-oil microemulsion system is proposed. In this method, by modifying Tabor Winterton approximation equation, an effective Hamaker constant was introduced. This effective Hamaker constant was applied in the van der Waals attractive interaction energy. The obtained effective van der Waals interaction energy was used as attractive contribution in the total interaction energy. The modified interaction energy was applied successfully to predict some bimetallic nanoparticles, at different mass fraction, synthesized in microemulsion system of dioctyl sodium sulfosuccinate (AOT)/isooctane.

Self-assembly and electrostriction of arrays and chains of hopfion particles in chiral liquid crystals

PubMed Central

Ackerman, Paul J.; van de Lagemaat, Jao; Smalyukh, Ivan I.

2015-01-01

Some of the most exotic condensed matter phases, such as twist grain boundary and blue phases in liquid crystals and Abrikosov phases in superconductors, contain arrays of topological defects in their ground state. Comprised of a triangular lattice of double-twist tubes of magnetization, the so-called ‘A-phase’ in chiral magnets is an example of a thermodynamically stable phase with topologically nontrivial solitonic field configurations referred to as two-dimensional skyrmions, or baby-skyrmions. Here we report that three-dimensional skyrmions in the form of double-twist tori called ‘hopfions’, or ‘torons’ when accompanied by additional self-compensating defects, self-assemble into periodic arrays and linear chains that exhibit electrostriction. In confined chiral nematic liquid crystals, this self-assembly is similar to that of liquid crystal colloids and originates from long-range elastic interactions between particle-like skyrmionic torus knots of molecular alignment field, which can be tuned from isotropic repulsive to weakly or highly anisotropic attractive by low-voltage electric fields. PMID:25607778

A dynamical systems approach for estimating phase interactions between rhythms of different frequencies from experimental data.

PubMed

Onojima, Takayuki; Goto, Takahiro; Mizuhara, Hiroaki; Aoyagi, Toshio

2018-01-01

Synchronization of neural oscillations as a mechanism of brain function is attracting increasing attention. Neural oscillation is a rhythmic neural activity that can be easily observed by noninvasive electroencephalography (EEG). Neural oscillations show the same frequency and cross-frequency synchronization for various cognitive and perceptual functions. However, it is unclear how this neural synchronization is achieved by a dynamical system. If neural oscillations are weakly coupled oscillators, the dynamics of neural synchronization can be described theoretically using a phase oscillator model. We propose an estimation method to identify the phase oscillator model from real data of cross-frequency synchronized activities. The proposed method can estimate the coupling function governing the properties of synchronization. Furthermore, we examine the reliability of the proposed method using time-series data obtained from numerical simulation and an electronic circuit experiment, and show that our method can estimate the coupling function correctly. Finally, we estimate the coupling function between EEG oscillation and the speech sound envelope, and discuss the validity of these results.

Pair aligning improved motility of Quincke rollers.

PubMed

Lu, Shi Qing; Zhang, Bing Yue; Zhang, Zhi Chao; Shi, Yan; Zhang, Tian Hui

2018-06-06

Density-dependent speed is studied in a two-dimensional active colloid in which the colloidal particles are propelled by an external electric field via a Quincke rotation. Above the critcal electric field, dense dynamic clusters form spotaneously, in which the particles are highly aligned in velocity and move much faster than isolated units. Detailed observations on pair collision reveal that the alignment of velocity is induced by the long-ranged hydrodynamic interactions and the improvement of speed in the clusters arises from pair aligning in which two particles are closely paired and rotate synchronically. In the aligning state, the short-range in-plane dipole-dipole attraction enhances the rotation torque and gives rises to a larger rolling speed. The pair aligning becomes difficult and unstable at high electric field where the normal dipole-dipole repulsion becomes dominant. As a consequence, the dependence of speed on density becomes weak increasingly upon the increase of the electric field. This result offers an interpretation for the discrepancy between our and previous observations on Quincke rollers.

Nonlocal van der Waals functionals: The case of rare-gas dimers and solids

NASA Astrophysics Data System (ADS)

Tran, Fabien; Hutter, Jürg

2013-05-01

Recently, the nonlocal van der Waals (vdW) density functionals [M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004), 10.1103/PhysRevLett.92.246401] have attracted considerable attention due to their good performance for systems where weak interactions are important. Since the physics of dispersion is included in these functionals, they are usually more accurate and show less erratic behavior than the semilocal and hybrid methods. In this work, several variants of the vdW functionals have been tested on rare-gas dimers (from He2 to Kr2) and solids (Ne, Ar, and Kr) and their accuracy compared to standard semilocal approximations, supplemented or not by an atom-pairwise dispersion correction [S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010), 10.1063/1.3382344]. An analysis of the results in terms of energy decomposition is also provided.

Understanding the interfacial behavior of lysozyme on Au (111) surfaces with multiscale simulations

NASA Astrophysics Data System (ADS)

Samieegohar, Mohammadreza; Ma, Heng; Sha, Feng; Jahan Sajib, Md Symon; Guerrero-García, G. Iván; Wei, Tao

2017-02-01

The understanding of the adsorption and interfacial behavior of proteins is crucial to the development of novel biosensors and biomaterials. By using bottom-up atomistic multiscale simulations, we study here the adsorption of lysozyme on Au(111) surfaces in an aqueous environment. Atomistic simulations are used to calculate the inhomogeneous polarization of the gold surface, which is induced by the protein adsorption, and by the presence of an interfacial layer of water molecules and monovalent salts. The corresponding potential of mean force between the protein and the gold surface including polarization effects is used in Langevin Dynamics simulations to study the time dependent behavior of proteins at finite concentration. These simulations display a rapid adsorption and formation of a first-layer of proteins at the interface. Proteins are initially adsorbed directly on the gold surface due to the strong protein-surface attractive interaction. A subsequent interfacial weak aggregation of proteins leading to multilayer build-up is also observed at long times.

Polymer diffusion in the interphase between surface and solution.

PubMed

Weger, Lukas; Weidmann, Monika; Ali, Wael; Hildebrandt, Marcus; Gutmann, Jochen Stefan; Hoffmann-Jacobsen, Kerstin

2018-05-22

Total internal reflection fluorescence correlation spectroscopy (TIR-FCS) is applied to study the self-diffusion of polyethylene glycol solutions in the presence of weakly attractive interfaces. Glass coverslips modified with aminopropyl- and propyl-terminated silanes are used to study the influence of solid surfaces on polymer diffusion. A model of three phases of polymer diffusion allows to describe the experimental fluorescence autocorrelation functions. Besides the two-dimensional diffusion of adsorbed polymer on the substrate and three-dimensional free diffusion in bulk solution, a third diffusion time scale is observed with intermediate diffusion times. This retarded three-dimensional diffusion in solution is assigned to long range effects of solid surfaces on diffusional dynamics of polymers. The respective diffusion constants show Rouse scaling (D~N -1 ) indicating a screening of hydrodynamic interactions by the presence of the surface. Hence, the presented TIR-FCS method proves to be a valuable tool to investigate the effect of surfaces on polymer diffusion beyond the first adsorbed polymer layer on the 100 nm length scale.

Direct Immersion Annealing of Thin Block Copolymer Films.

PubMed

Modi, Arvind; Bhaway, Sarang M; Vogt, Bryan D; Douglas, Jack F; Al-Enizi, Abdullah; Elzatahry, Ahmed; Sharma, Ashutosh; Karim, Alamgir

2015-10-07

We demonstrate ordering of thin block copolymer (BCP) films via direct immersion annealing (DIA) at enhanced rate leading to stable morphologies. The BCP films are immersed in carefully selected mixtures of good and marginal solvents that can impart enhanced polymer mobility, while inhibiting film dissolution. DIA is compatible with roll-to-roll assembly manufacturing and has distinct advantages over conventional thermal annealing and batch processing solvent-vapor annealing methods. We identify three solvent composition-dependent BCP film ordering regimes in DIA for the weakly interacting polystyrene-poly(methyl methacrylate) (PS-PMMA) system: rapid short-range order, optimal long-range order, and a film instability regime. Kinetic studies in the "optimal long-range order" processing regime as a function of temperature indicate a significant reduction of activation energy for BCP grain growth compared to oven annealing at conventional temperatures. An attractive feature of DIA is its robustness to ordering other BCP (e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar and cylindrical ordering.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

NASA Astrophysics Data System (ADS)

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-09-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+-[WO4]2--[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

PubMed Central

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-01-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface. PMID:26359212

Hyperspectral imaging in SWIR: from stain-free microscopy to deep tissue imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Berezin, Mikhail Y.

2016-03-01

Recent advances in relatively unexplored short wave infrared (SWIR) range from 800-1600 nm detectors make wide-field imaging in this spectral range attractive to biology. The distinct advantages of SWIR region over the visible and near infrared (NIR) in tissue analysis are two-fold: (i) high abundance endogenous chromophores (i.e. water and lipids) enable tissue component differentiation based on wavelength-dependent absorption properties and (ii) the weak scattering of tissue permits better resolution of imaging in thick specimens. When combined with high spectral resolution, SWIR imaging produces a spectroscopic image, where every pixel corresponds to the entire high-resolution spectrum. This hyperspectral (HS) approach provides rich information about the relative abundance of individual chromophores and their interactions that contribute to the intensity and location of the optical signal. The presentation discusses the challenges in the SWIR-HS instrument design and data analysis and demonstrates some of the promising applications of this technology in life science and medicine.

Using Amphiphilic Copolymers and Nanoparticles to Organize Charged Biopolymers

NASA Astrophysics Data System (ADS)

Park, Jung Hyun; McConnell, Marla; Sun, Yujie; Goldman, Yale; Composto, Russell

2009-03-01

Nanoparticles (NPs) on amphiphilic random copolymers control filamentous actin (F-actin) attachment. 3-aminopropyltriethoxysilane (APTES) coated silica NPs are selectively bonded to acrylic acid groups on the surface of a poly(styrene-r-acrylic acid) (PS-r-PAA) film. By changing the concentration of NPs in the medium, the surface density of positively charged anchors is tuned. Using total internal reflection fluorescence (TIRF) microscopy, immobilization of F-actin is observed via electrostatic interaction with NPs at high NP coverages. Below a critical coverage, F-actin is weakly attached and undergoes thermal fluctuations near the surface. Another method to tune F-actin attachment is to use APTES to cross-link and create positive charge in PAA films. Here, the surface coverage of F-actin decreases as APTES concentration increases. This observation is attributed to an increase in surface roughness and hydrophobicity that reduces the effective surface sites that attract F-actin. In addition, in-situ G-actin polymerization to F-actin is observed on both the NP and cross-linked PAA templates.

Chemistry of the calcite/water interface: Influence of sulfate ions and consequences in terms of cohesion forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pourchet, Sylvie, E-mail: sylvie.pourchet@u-bourgogne.fr; Pochard, Isabelle; Brunel, Fabrice

2013-10-15

Calcite suspensions are used to mimic the behavior of more complex cementitious systems. Therefore the characterization of calcite–water interface in strong alkaline conditions, through ionic adsorption, electrokinetic measurements, static rheology and atomic force microscopy is a prerequisite. Calcium, a potential determining ion for calcite, adsorbs specifically onto the weakly positively charged calcite surface in water. This leads to an increase of the repulsive electric double layer force and thus weakens the particle cohesion. Sulfate adsorption, made at constant calcium concentration and ionic strength, significantly increases the attractive interactions between the calcite particles despite its very low adsorption. This is attributedmore » to a lowering of the electrostatic repulsion in connection with the evolution of the zeta potential. The linear relationship found between the yield stress and ζ{sup 2} proves that the classical DLVO theory applies for these systems, contrary to what was previously observed with C–S–H particles under the same conditions.« less

Direct Immersion Annealing of Thin Block Copolymer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Modi, Arvind; Bhaway, Sarang M.; Vogt, Bryan D.

2015-09-09

We demonstrate ordering of thin block copolymer (BCP) films via direct immersion annealing (DIA) at enhanced rate leading to stable morphologies. The BCP films are immersed in carefully selected mixtures of good and marginal solvents that can impart enhanced polymer mobility, while inhibiting film dissolution. DIA is compatible with roll-to-roll assembly manufacturing and has distinct advantages over conventional thermal annealing and batch processing solvent-vapor annealing methods. We identify three solvent composition-dependent BCP film ordering regimes in DIA for the weakly interacting polystyrene–poly(methyl methacrylate) (PS–PMMA) system: rapid short-range order, optimal long-range order, and a film instability regime. Kinetic studies in themore » “optimal long-range order” processing regime as a function of temperature indicate a significant reduction of activation energy for BCP grain growth compared to oven annealing at conventional temperatures. An attractive feature of DIA is its robustness to ordering other BCP (e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar and cylindrical ordering.« less

Physical controls on directed virus assembly at nanoscale chemical templates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, C L; Chung, S; Chatterji, A

2006-05-10

Viruses are attractive building blocks for nanoscale heterostructures, but little is understood about the physical principles governing their directed assembly. In-situ force microscopy was used to investigate organization of Cowpea Mosaic Virus engineered to bind specifically and reversibly at nanoscale chemical templates with sub-30nm features. Morphological evolution and assembly kinetics were measured as virus flux and inter-viral potential were varied. The resulting morphologies were similar to those of atomic-scale epitaxial systems, but the underlying thermodynamics was analogous to that of colloidal systems in confined geometries. The 1D templates biased the location of initial cluster formation, introduced asymmetric sticking probabilities, andmore » drove 1D and 2D condensation at subcritical volume fractions. The growth kinetics followed a t{sup 1/2} law controlled by the slow diffusion of viruses. The lateral expansion of virus clusters that initially form on the 1D templates following introduction of polyethylene glycol (PEG) into the solution suggests a significant role for weak interaction.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, P. J.; van de Lagemaat, J.; Smalyukh, I. I.

Some of the most exotic condensed matter phases, such as twist grain boundary and blue phases in liquid crystals and Abrikosov phases in superconductors, contain arrays of topological defects in their ground state. Comprised of a triangular lattice of double-twist tubes of magnetization, the so-called ‘A-phase’ in chiral magnets is an example of a thermodynamically stable phase with topologically nontrivial solitonic field configurations referred to as two-dimensional skyrmions, or baby-skyrmions. Here we report that three-dimensional skyrmions in the form of double-twist tori called ‘hopfions’, or ‘torons’ when accompanied by additional self-compensating defects, self-assemble into periodic arrays and linear chains thatmore » exhibit electrostriction. In confined chiral nematic liquid crystals, this self-assembly is similar to that of liquid crystal colloids and originates from long-range elastic interactions between particle-like skyrmionic torus knots of molecular alignment field, which can be tuned from isotropic repulsive to weakly or highly anisotropic attractive by low-voltage electric fields.« less

Weak Interactions Group

Science.gov Websites

Weak Interactions Group UC Berkeley UC Berkeley Physics Lawrence Berkeley Lab Nuclear Science Division at LBL Physics Division at LBL Phonebook A-Z Index Navigation Home Members Research Projects CUORE Design Concept Berkeley Projects People Publications Contact Links KamLAND Physics Impact Neutrino

Turbulence of Weak Gravitational Waves in the Early Universe.

PubMed

Galtier, Sébastien; Nazarenko, Sergey V

2017-12-01

We study the statistical properties of an ensemble of weak gravitational waves interacting nonlinearly in a flat space-time. We show that the resonant three-wave interactions are absent and develop a theory for four-wave interactions in the reduced case of a 2.5+1 diagonal metric tensor. In this limit, where only plus-polarized gravitational waves are present, we derive the interaction Hamiltonian and consider the asymptotic regime of weak gravitational wave turbulence. Both direct and inverse cascades are found for the energy and the wave action, respectively, and the corresponding wave spectra are derived. The inverse cascade is characterized by a finite-time propagation of the metric excitations-a process similar to an explosive nonequilibrium Bose-Einstein condensation, which provides an efficient mechanism to ironing out small-scale inhomogeneities. The direct cascade leads to an accumulation of the radiation energy in the system. These processes might be important for understanding the early Universe where a background of weak nonlinear gravitational waves is expected.

Challenges and dreams: physics of weak interactions essential to life

PubMed Central

Chien, Peter; Gierasch, Lila M.

2014-01-01

Biological systems display stunning capacities to self-organize. Moreover, their subcellular architectures are dynamic and responsive to changing needs and conditions. Key to these properties are manifold weak “quinary” interactions that have evolved to create specific spatial networks of macromolecules. These specific arrangements of molecules enable signals to be propagated over distances much greater than molecular dimensions, create phase separations that define functional regions in cells, and amplify cellular responses to changes in their environments. A major challenge is to develop biochemical tools and physical models to describe the panoply of weak interactions operating in cells. We also need better approaches to measure the biases in the spatial distributions of cellular macromolecules that result from the integrated action of multiple weak interactions. Partnerships between cell biologists, biochemists, and physicists are required to deploy these methods. Together these approaches will help us realize the dream of understanding the biological “glue” that sustains life at a molecular and cellular level. PMID:25368424

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

PubMed Central

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-01-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field. PMID:26459874

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

NASA Astrophysics Data System (ADS)

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-10-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field.

The Effects of Relaxation and Cognitive Expectancy on Attraction in a Social Interaction.

ERIC Educational Resources Information Center

Wilson, Midge

One approach to searching for determinants of interpersonal attraction involves the altering and studying of physiological arousal, psychological stress, and moods. On the basis of the reinforcement-affect model of attraction, it was hypothesized that the positive feelings obtained from undergoing relaxation exercises could serve to enhance…

Long-Range Attractive and Repulsive Interactions between Colloidal Particles at the Air/Water Interface

NASA Astrophysics Data System (ADS)

Gómez-Guzmán, Oscar; Ruiz-García, Jaime

2001-03-01

In the last few years there has been evidence of long-range attractive interactions between colloidal particles trapped between glass plates, where the plates separation is a few particle’s diameter.[1,2,3] In these experiments it is believe that the glass walls play an important role for the observed attractions. Colloidal particles trapped at the air water interface show the formation of different 2-D colloidal patterns such as foams, clusters and chains,[4,5,6,7] whose formation can be taken as an evidence of long range attractive interaction. Here, we present measurements of the pair interaction potential between 0.5 µm colloidal particles at the air/water interface. The potential shows an attractive secondary minimum at about 1.9s, where s is the particle’s diameter, and a secondary repulsive maximum at longer distances. Surprisingly, the position of the secondary well is at a position similar to those found on the colloidal systems trapped between glass plates. It is possible that in our colloidal system the interface plays the role of a glass plate. However, we do not have a clear explanation on the origin of the attractive component of the interaction potential. 1. G. M. Kepler and S. Fraden, Phys. Rev. Lett. 73, 356 (1994) 2. M. D. Carbajal-Tinoco, F. Castro-Roman and J. L. Arauz-Lara, Phys. Rev. E 53, 3745 (1996) 3. J. C. Croker and D. G. Grier, Phys. Rev. Lett. 77, 1897 (1996) 4. J. Ruiz-Garcia, R. Gámez-Corrales and B. I. Ivlev, Physica A 236, 97 (1997) 5. J. Ruiz-Garcia, R. Gámez-Corrales and B. I. Ivlev, Phys. Rev. E 58, 660 (1998) 6. J. Ruiz-Garcia and B. I. Ivlev, Molec. Phys. 95, 371 (1998) 7. S. J. Mejia-Rosales, R. Gamez-Corrales, B. I. Ivlev and J. Ruiz-Garcia, Physica A 276, 30 (2000)

Accurate characterization of weak macromolecular interactions by titration of NMR residual dipolar couplings: application to the CD2AP SH3-C:ubiquitin complex.

PubMed

Ortega-Roldan, Jose Luis; Jensen, Malene Ringkjøbing; Brutscher, Bernhard; Azuaga, Ana I; Blackledge, Martin; van Nuland, Nico A J

2009-05-01

The description of the interactome represents one of key challenges remaining for structural biology. Physiologically important weak interactions, with dissociation constants above 100 muM, are remarkably common, but remain beyond the reach of most of structural biology. NMR spectroscopy, and in particular, residual dipolar couplings (RDCs) provide crucial conformational constraints on intermolecular orientation in molecular complexes, but the combination of free and bound contributions to the measured RDC seriously complicates their exploitation for weakly interacting partners. We develop a robust approach for the determination of weak complexes based on: (i) differential isotopic labeling of the partner proteins facilitating RDC measurement in both partners; (ii) measurement of RDC changes upon titration into different equilibrium mixtures of partially aligned free and complex forms of the proteins; (iii) novel analytical approaches to determine the effective alignment in all equilibrium mixtures; and (iv) extraction of precise RDCs for bound forms of both partner proteins. The approach is demonstrated for the determination of the three-dimensional structure of the weakly interacting CD2AP SH3-C:Ubiquitin complex (K(d) = 132 +/- 13 muM) and is shown, using cross-validation, to be highly precise. We expect this methodology to extend the remarkable and unique ability of NMR to study weak protein-protein complexes.

Accurate characterization of weak macromolecular interactions by titration of NMR residual dipolar couplings: application to the CD2AP SH3-C:ubiquitin complex

PubMed Central

Ortega-Roldan, Jose Luis; Jensen, Malene Ringkjøbing; Brutscher, Bernhard; Azuaga, Ana I.; Blackledge, Martin; van Nuland, Nico A. J.

2009-01-01

The description of the interactome represents one of key challenges remaining for structural biology. Physiologically important weak interactions, with dissociation constants above 100 μM, are remarkably common, but remain beyond the reach of most of structural biology. NMR spectroscopy, and in particular, residual dipolar couplings (RDCs) provide crucial conformational constraints on intermolecular orientation in molecular complexes, but the combination of free and bound contributions to the measured RDC seriously complicates their exploitation for weakly interacting partners. We develop a robust approach for the determination of weak complexes based on: (i) differential isotopic labeling of the partner proteins facilitating RDC measurement in both partners; (ii) measurement of RDC changes upon titration into different equilibrium mixtures of partially aligned free and complex forms of the proteins; (iii) novel analytical approaches to determine the effective alignment in all equilibrium mixtures; and (iv) extraction of precise RDCs for bound forms of both partner proteins. The approach is demonstrated for the determination of the three-dimensional structure of the weakly interacting CD2AP SH3-C:Ubiquitin complex (Kd = 132 ± 13 μM) and is shown, using cross-validation, to be highly precise. We expect this methodology to extend the remarkable and unique ability of NMR to study weak protein–protein complexes. PMID:19359362

The interfacial properties of the peptide Polybia-MP1 and its interaction with DPPC are modulated by lateral electrostatic attractions.

PubMed

Alvares, Dayane S; Fanani, Maria Laura; Ruggiero Neto, João; Wilke, Natalia

2016-02-01

Polybia-MP1 (IDWKKLLDAAKQIL-NH2), extracted from the Brazilian wasp Polybia paulista, exhibits a broad-spectrum bactericidal activity without being hemolytic and cytotoxic. In the present study, we analyzed the surface properties of the peptide and its interaction with DPPC in Langmuir monolayers. Polybia-MP1 formed stable monolayers, with lateral areas and surface potential values suggesting a mostly α-helical structure oriented near perpendicular to the membrane plane. In DPPC-peptide mixed monolayers, MP1 co-crystallized with the lipid forming branched domains only when the subphase was pure water. On subphases with high salt concentrations or at acidic or basic conditions, the peptide formed less densely packed films and was excluded from the domains, indicating the presence of attractive electrostatic interactions between peptides, which allow them to get closer to each other and to interact with DPPC probably as a consequence of a particular peptide arrangement. The residues responsible of the peptide-peptide attraction are suggested to be the anionic aspartic acids and the cationic lysines, which form a salt bridge, leading to oriented interactions in the crystal and thereby to branched domains. For this peptide, the balance between total attractive and repulsive interactions may be finely tuned by the aqueous ionic strength and pH, and since this effect is related with lysines and aspartic acids, similar effects may also occur in other peptides containing these residues in their sequences. Copyright © 2015 Elsevier B.V. All rights reserved.

Quantum controlled-Z gate for weakly interacting qubits

NASA Astrophysics Data System (ADS)

Mičuda, Michal; Stárek, Robert; Straka, Ivo; Miková, Martina; Dušek, Miloslav; Ježek, Miroslav; Filip, Radim; Fiurášek, Jaromír

2015-08-01

We propose and experimentally demonstrate a scheme for the implementation of a maximally entangling quantum controlled-Z gate between two weakly interacting systems. We conditionally enhance the interqubit coupling by quantum interference. Both before and after the interqubit interaction, one of the qubits is coherently coupled to an auxiliary quantum system, and finally it is projected back onto qubit subspace. We experimentally verify the practical feasibility of this technique by using a linear optical setup with weak interferometric coupling between single-photon qubits. Our procedure is universally applicable to a wide range of physical platforms including hybrid systems such as atomic clouds or optomechanical oscillators coupled to light.

Halogen bond: a long overlooked interaction.

PubMed

Cavallo, Gabriella; Metrangolo, Pierangelo; Pilati, Tullio; Resnati, Giuseppe; Terraneo, Giancarlo

2015-01-01

Because of their high electronegativity, halogen atoms are typically considered, in most of their derivatives, as sites of high electron density and it is commonly accepted that they can form attractive interactions by functioning as the electron donor site (nucleophilic site). This is the case when they work as hydrogen bond acceptor sites. However, the electron density in covalently bound halogens is anisotropically distributed. There is a region of higher electron density, accounting for the ability of halogens to function as electron donor sites in attractive interactions, and a region of lower electron density where the electrostatic potential is frequently positive (mainly in the heavier halogens). This latter region is responsible for the ability of halogen atoms to function as the electron-acceptor site (electrophilic site) in attractive interactions formed with a variety of lone pair-possessing atoms, anions, and π-systems. This ability is quite general and is shown by a wide diversity of halogenated compounds (e.g., organohalogen derivatives and dihalogens). According to the definition proposed by the International Union of Pure and Applied Chemistry, any attractive interactions wherein the halogen atom is the electrophile is named halogen bond (XB). In this chapter, it is discussed how the practice and the concept of XB developed and a brief history of the interaction is presented. Papers (either from the primary or secondary literature) which have reported major experimental findings in the field or which have given important theoretical contributions for the development of the concept are recollected in order to trace how a unifying and comprehensive categorization emerged encompassing all interactions wherein halogen atoms function as the electrophilic site.

Investigation of attractive and repulsive interactions associated with ketones in supercritical CO2, based on Raman spectroscopy and theoretical calculations.

PubMed

Kajiya, Daisuke; Saitow, Ken-ichi

2013-08-07

Carbonyl compounds are solutes that are highly soluble in supercritical CO2 (scCO2). Their solubility governs the efficiency of chemical reactions, and is significantly increased by changing a chromophore. To effectively use scCO2 as solvent, it is crucial to understand the high solubility of carbonyl compounds, the solvation structure, and the solute-solvent intermolecular interactions. We report Raman spectroscopic data, for three prototypical ketones dissolved in scCO2, and four theoretical analyses. The vibrational Raman spectra of the C=O stretching modes of ketones (acetone, acetophenone, and benzophenone) were measured in scCO2 along the reduced temperature Tr = T∕Tc = 1.02 isotherm as a function of the reduced density ρr = ρ∕ρc in the range 0.05-1.5. The peak frequencies of the C=O stretching modes shifted toward lower energies as the fluid density increased. The density dependence was analyzed by using perturbed hard-sphere theory, and the shift was decomposed into attractive and repulsive energy components. The attractive energy between the ketones and CO2 was up to nine times higher than the repulsive energy, and its magnitude increased in the following order: acetone < acetophenone < benzophenone. The Mulliken charges of the three solutes and CO2 molecules obtained by using quantum chemistry calculations described the order of the magnitude of the attractive energy and optimized the relative configuration between each solute and CO2. According to theoretical calculations for the dispersion energy, the dipole-induced-dipole interaction energy, and the frequency shift due to their interactions, the experimentally determined attractive energy differences in the three solutes were attributed to the dispersion energies that depended on a chromophore attached to the carbonyl groups. It was found that the major intermolecular interaction with the attractive shift varied from dipole-induced dipole to dispersion depending on the chromophore in the ketones in scCO2. As the common conclusion for the Raman spectral measurements and the four theoretical calculations, solute polarizability, modified by the chromophore, was at the core of the solute-solvent interactions of the ketones in scCO2.

Recent Developments in Computational Techniques for Applied Hydrodynamics.

DTIC Science & Technology

1979-12-07

by block number) Numerical Method Fluids Incompressible Flow Finite Difference Methods Poisson Equation Convective Equations -MABSTRACT (Continue on...weaknesses of the different approaches are analyzed. Finite - difference techniques have particularly attractive properties in this framework. Hence it will...be worthwhile to correct, at least partially, the difficulties from which Eulerian and Lagrangian finite - difference techniques suffer, discussed in

Geographic variation in response of pine engraver, Ips pini, and associated species to pheromone, lanierone

Treesearch

Daniel R. Miller; Kenneth E. Gibson; K.F. Raffa; S.J. Seybold; S.A. Teale; D.L. Wood

1997-01-01

Lanierone strongly synergized the attraction of male and female Ips pini (Say) to ipsdienol in New York and Wisconsin. Synergy was only weakly significant in Montana and British Columbia and not significant in California. Catches of I. pini in ipsdienol-baited traps were increased 0% (i.e., nonsignificant) to 9942% by lanierone,...

Enhanced attraction of Plutella xylostella (Lepidoptera: Plutellidae) to pheromone-baited traps with the addition of green leaf volatiles

USDA-ARS?s Scientific Manuscript database

The GLVs, such as 1-hexanol and (Z)-3-hexen-1-ol, elicited strong electroantennographic responses from unmated male and female P. xylostella, whereas (Z)-3-hexenyl acetate only produced a relative weak response. The behavioral responses of unmated moths to GLVs were further tested in Y-tube olfactom...

Simulation of the weakly interacting Bose gas relaxation for cases of various interaction types

NASA Astrophysics Data System (ADS)

Kartsev, P. F.; Kuznetsov, I. O.

2017-12-01

In this work, we investigate the role of interactions in the process of thermalization of a weakly interacting Bose gas. The system of kinetic equations based on the ‘Fermi’s golden rule’ is solved numerically using special transformation for calculation efficiency. We study the distribution function for particles in various conditions, including interaction with phonon subsystem, i.e. energy exchange with thermal bath. The possibility to achieve the state of Bose-Einstein condensation with specific values of parameters, is also discussed.

Charmed Hadron Spectrum and Interactions

NASA Astrophysics Data System (ADS)

Liu, Liuming

Studying hadrons containing heavy quarks in lattice QCD is challenging mainly due to finite lattice spacing effects. To control the discretization errors, mQa is required to be much less than 1, where mQ is the quark mass and a is the lattice spacing. For currently accessible lattice spacings, the charm quark mass doesn't satisfy this requirement. One approach to simulate heavy quarks on the lattice is non-relativestic QCD, which treats heavy quark as a static source and expand the lattice quark action in powers of 1mQa . Unfortunately, the charm quark is not heavy enough to justify this expansion. An other is Heavy Quark Effective Theory (HQET) matched on QCD. Non-relativestic QCD and HQET are mainly used for bottom quark. Relativistic heavy-quark action, which incorporates both small mass and large mass formulations, is better suited to study the charm quark sector. The discretization errors can be reduced systematically following Symanzik improvement. In this work, we use the relativistic heavy quark action to study the charmed hadron spectrum and interactions in full lattice QCD. For the light quarks we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. The parameters in the heavy quark action are tuned to reduce lattice artifacts and match the charm quark mass and the action is tested by calculating the low-lying charmonium spectrum. We compute the masses of the spin-1/2 singly and doubly charmed baryons. For the singly charmed baryons, our results are in good agreement with experiment within our systematics. For the doubly charmed baryon xicc we find the isospin-averaged mass to be MXcc = 3665 +/- 17 +/- 14+0-78 MeV; the three given uncertainties are statistical, systematic and an estimate of lattice discretization errors, respectively. In addition, we predict the mass splitting of the (isospin-averaged) spin-1/2 O cc with the xicc to be MWcc-MXcc = 98 +/- 9 +/- 22 +/- 13 MeV (in this mass splitting, the leading discretization errors are also suppressed by SU(3) symmetry). Combining this splitting with our determination of MXcc leads to our prediction of the spin-1/2 Occ mass, MWcc = 3763 +/- 19 +/- 26+13-79 MeV. We calculate the scattering lengths of the charmed mesons with the light pseudoscalar mesons. The calculation is performed for four different light quark masses and extrapolated to the physical point using chiral perturbation formulas to next-to-next-to-leading order. The low energy constants are determined and used to make predictions. We find relatively strong attractive interaction in DK channels, which is closely related to the structure of DsJ(2317) state. The scattering of charmonium with light hadrons is also studied. Particularly, we find very weak attractive interaction between J/Psi and nucleon, in this channel the dominate interaction is attractive gluonic van der Walls and it could lead to molecular-like bound states.

Tuning of electrostatic vs. depletion interaction in deciding the phase behavior of nanoparticle-polymer system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sugam, E-mail: sugam@barc.gov.in; Aswal, V. K.; Kohlbrecher, J.

2015-06-24

Nanoparticle-polymer system interestingly show a re-entrant phase behavior where charge stabilized silica nanoparticles (phase I) undergo particle clustering (phase II) and then back to individual particles (phase I) as a function of polymer concentration. Such phase behavior arises as a result of dominance of various interactions (i) nanoparticle-nanoparticle electrostatic repulsion (ii) polymer induced attractive depletion between nanoparticles and (iii) polymer-polymer repulsion, at different concentration regimes. Small-angle neutron scattering (SANS) has been used to study the evolution of interaction during this re-entrant phase behavior of nanoparticles by contrast-marching the polymer. The SANS data have been modeled using a two-Yukawa potential accountingmore » for both attractive and repulsive parts of the interaction between nanoparticles. The degree of both of these parts has been separately tuned by varying the polymer concentration and ionic strength of the solution. Both of these parts are found to have long-range nature. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the strength of depletion leading to re-entrant phase behavior. The clusters formed under depletion attraction are found to have surface fractal morphology.« less

Carrion mimicry in a South African orchid: flowers attract a narrow subset of the fly assemblage on animal carcasses

PubMed Central

van der Niet, Timotheüs; Hansen, Dennis M.; Johnson, Steven D.

2011-01-01

Background and Aims Although pollination of plants that attract flies by resembling their carrion brood and food sites has been reported in several angiosperm families, there has been very little work done on the level of specificity in carrion mimicry systems and the importance of plant cues in mediating such specialization. Specificity may be expected, as carrion-frequenting flies often exploit different niches, which has been interpreted as avoidance of interspecific competition. Interactions between the orchid Satyrium pumilum and a local assemblage of carrion flies were investigated, and the functional significance of floral traits, especially scent, tested. Pollination success and the incidence of pollinator-mediated self-pollination were measured and these were compared with values for orchids with sexual- and food-deceptive pollination systems. Methods and Key Results Observations of insect visitation to animal carcasses and to flowers showed that the local assemblage of carrion flies was dominated by blow flies (Calliphoridae), house flies (Muscidae) and flesh flies (Sarcophagidae), but flowers of the orchid were pollinated exclusively by flesh flies, with a strong bias towards females that sometimes deposited live larvae on flowers. A trend towards similar partitioning of fly taxa was found in an experiment that tested the effect of large versus small carrion quantities on fly attraction. GC-MS analysis showed that floral scent is dominated by oligosulfides, 2-heptanone, p-cresol and indole, compounds that also dominate carrion scent. Flesh flies did not distinguish between floral and carrion scent in a choice experiment using olfactory cues only, which also showed that scent alone is responsible for fly attraction. Pollination success was relatively high (31·5 % of flowers), but tracking of stained pollinia also revealed that a relatively high percentage (46 %) of pollen deposited on stigmas originates from the same plant. Conclusions Satyrium pumilum selectively attracts flesh flies, probably because its relatively weak scent resembles that of the small carrion on which these flies predominate. In this way, the plants exploit a specific subset of the insect assemblage associated with carrion. Pollination rates and levels of self-pollination were high compared with those in other deceptive orchids and it is therefore unlikely that this mimicry system evolved to promote outcrossing. PMID:21402538

Observation of a quadrupole interaction for cubic imperfections exhibiting a dynamic Jahn-Teller effect.

NASA Technical Reports Server (NTRS)

Herrington, J. R.; Estle, T. L.; Boatner, L. A.

1972-01-01

The observation and interpretation of weak EPR transitions, identified as 'forbidden' transitions, establish the existence of a new type of quadrupole interaction for cubic-symmetry imperfections. This interaction is simply a consequence of the ground-vibronic-state degeneracy. The signs as well as the magnitudes of the quadrupole-coupling coefficients are determined experimentally. These data agree well with the predictions of crystal field theory modified to account for a weak-to-moderate vibronic interaction (i.e., a dynamic Jahn-Teller effect).

Interpretation of neutrino-matter interactions at low energies as contraction of gauge group of Electroweak Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gromov, N. A., E-mail: gromov@dm.komisc.ru

The very weak neutrino-matter interactions are explained with the help of the gauge group contraction of the standard Electroweak Model. The mathematical contraction procedure is connected with the energy dependence of the interaction cross section for neutrinos and corresponds to the limiting case of the Electroweak Model at low energies. Contraction parameter is connected with the universal Fermi constant of weak interactions and neutrino energy as j{sup 2}(s) = {radical}(G{sub F} s)

Weak decays of heavy hadrons into dynamically generated resonances

DOE PAGES

Oset, Eulogio; Liang, Wei -Hong; Bayar, Melahat; ...

2016-01-28

In this study, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allowmore » for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.« less

Effect of attractive interactions on the water-like anomalies of a core-softened model potential.

PubMed

Pant, Shashank; Gera, Tarun; Choudhury, Niharendu

2013-12-28

It is now well established that water-like anomalies can be reproduced by a spherically symmetric potential with two length scales, popularly known as core-softened potential. In the present study we aim to investigate the effect of attractive interactions among the particles in a model fluid interacting with core-softened potential on the existence and location of various water-like anomalies in the temperature-pressure plane. We employ extensive molecular dynamic simulations to study anomalous nature of various order parameters and properties under isothermal compression. Order map analyses have also been done for all the potentials. We observe that all the systems with varying depth of attractive wells show structural, dynamic, and thermodynamic anomalies. As many of the previous studies involving model water and a class of core softened potentials have concluded that the structural anomaly region encloses the diffusion anomaly region, which in turn, encloses the density anomaly region, the same pattern has also been observed in the present study for the systems with less depth of attractive well. For the systems with deeper attractive well, we observe that the diffusion anomaly region shifts toward higher densities and is not always enclosed by the structural anomaly region. Also, density anomaly region is not completely enclosed by diffusion anomaly region in this case.

Mapping repulsive to attractive interaction in driven-dissipative quantum systems

NASA Astrophysics Data System (ADS)

Li, Andy C. Y.; Koch, Jens

2017-11-01

Repulsive and attractive interactions usually lead to very different physics. Striking exceptions exist in the dynamics of driven-dissipative quantum systems. For the example of a photonic Bose-Hubbard dimer, we establish a one-to-one mapping relating cases of onsite repulsion and attraction. We prove that the mapping is valid for an entire class of Markovian open quantum systems with a time-reversal-invariant Hamiltonian and physically meaningful inverse-sign Hamiltonian. To underline the broad applicability of the mapping, we illustrate the one-to-one correspondence between the nonequilibrium dynamics in a geometrically frustrated spin lattice and those in a non-frustrated partner lattice.

Chemosignalling effects of human tears revisited: Does exposure to female tears decrease males' perception of female sexual attractiveness?

PubMed

Gračanin, Asmir; van Assen, Marcel A L M; Omrčen, Višnja; Koraj, Ivana; Vingerhoets, Ad J J M

2017-01-01

Gelstein et al. reported the results of three experiments suggesting a dampening influence of inhalation of female emotional tears on males' arousal and perception of female sexual attractiveness, specifically in non-sexual situations. This prompted the hypothesis that crying exerts its influence on others not only via the auditory and visual mode but also via chemosignals. In three studies, we attempted to replicate and extend Gelstein et al.'s findings by including an additional condition with irritant tears, by using pictures of sexually attractive women, and by testing related hypotheses on the pro-social effects of exposure to tears. All three studies, separately or combined in a meta-analysis, failed to replicate the original inhibitory effects of tears. In addition, sniffing tears did not affect measures of connectedness, aggression and pro-social behaviour. It is concluded that the effects of female tears on male arousal and perception of female sexual attractiveness, if any, are very weak at best. Rather, it seems that crying exerts its strong inter-personal effects through the visual and auditory sensory channels.

Evaluating the DLVO Model for Non-Aqueous Colloidal Suspensions

NASA Astrophysics Data System (ADS)

DeCarlo, Keith Joseph

Application of DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory for suspensions utilizing non-aqueous suspension mediums has been tested. Prediction of suspension stability using DLVO theory requires the calculation of the attractive and repulsive forces between the suspended colloids and that the only significant stabilization mechanism present is electrostatic stabilization which was tested. The van der Waals attractive potential was calculated for 12 different colloids in 11 suspending mediums in accord with Lifshitz's treatment and a new approximation proposing that the material bandgap energy can be used to approximate the Hamaker constant was developed. This treatment requires the complete knowledge of the permittivity as a function of frequency for all the components in the respective suspension. The permittivity data was simplified using a damped oscillator model described by Ninham and Parsegian. All permittivity data was compiled from the literature. Microwave data was tabulated by NIST, infrared parameters were determined from FTIR data, and the ultraviolet/visual parameters were determined via Cauchy plots or estimated by the bandgap. Using the bandgap to approximate the ultraviolet/visual parameters proved to be more accurate than other approximations when compared to the accepted values. It was found that the non-oxide and non-stoichiometric colloids tested had the largest associated van der Waals attractive force. The van der Waals potential calculated for oxide particles was found to follow a direct relationship with the ionic character of the bonding. Repulsive forces were calculated for 12 different colloids in 11 suspending mediums. The calculated repulsive potential generated is a function of both the magnitude of charge generated on each colloid (zeta-potential) and the size of the interacting double-layers. zeta-potential was measured for each suspension using a microelectrophoretic technique and the double-layer thickness was calculated. It was demonstrated that as the polarity of the suspending medium increased, the thickness of the double-layer also increased. A large double-layer thickness was found to directly correlate to the suspension stability. A large double-layer thickness results in a decreased slope of the charge degradation from the colloidal surface to the bulk suspension. This coupled with a large magnitude of surface charge increases the probability of dispersion. Through viscosity measurements, the stability mechanism of each suspension was determined by comparison of the viscosity at a shear rate of 1.0s -1 with the shear thinning exponent. It was determined that, of the suspension mediums tested, heptane, octanoic acid, and poly(ethylene glycol) introduce non-electrostatic stabilization mechanisms significant enough to invalidate the DLVO predictions for suspensions made using those mediums. Consistent with DLVO theory, the total interaction potential was calculated by summation of the repulsive and attractive potentials of each suspension (84 suspensions total) as a function of separation distance. Based upon the results of the summation, the suspension stability can be predicted. 64 of the 84 suspensions were determined to be unstable as the colloids agglomerated in the primary minimum, 11 suspensions were determined to be weakly flocculated, and nine suspensions were found to be stable. Viscosity was used to determine the critical value for the thermal energy barrier and to test the DLVO predictions. The critical value of the thermal energy barrier was found to be 2.0 x 10 -6J/m2. Therefore, for suspensions calculated to have a thermal energy barrier less than the critical value, the Brownian motion of the colloids in suspension at 298K were enough to overcome it, resulting in agglomeration at the primary minimum. For suspensions with a thermal barrier larger than 2.0 x 10-6J/m2, the interacting colloids moved into the secondary energy minimum. All suspensions tested in which the thermal energy barrier was less than 2.0 x 10-6J/m 2 had a specific viscosity at a shear rate of 1.0s-1 greater than the cut-off viscosity for stability. If the colloids moved into the secondary minimum, the resulting suspension was characterized as either being weakly flocculated or stable. Weakly flocculated suspensions had an equilibrium separation distance of colloids less than 40nm resulting in a viscosity at a shear rate of 1.0s-1 larger than the determined specific viscosity cut-off (1.1x 104), but a shear thinning exponent greater than 1.0. Stable suspensions were defined by the colloids as having an equilibrium separation distance greater than 40nm, resulting in viscosity values at a shear rate of 1.0s-1 smaller than that of the determined cut-off viscosity value.

The evolution processes of DNA sequences, languages and carols

NASA Astrophysics Data System (ADS)

Hauck, Jürgen; Henkel, Dorothea; Mika, Klaus

2001-04-01

The sequences of bases A, T, C and G of about 100 enolase, secA and cytochrome DNA were analyzed for attractive or repulsive interactions by the numbers T 1,T 2,T 3; r of nearest, next-nearest and third neighbor bases of the same kind and the concentration r=other bases/analyzed base. The area of possible T1, T2 values is limited by the linear borders T 2=2T 1-2, T 2=0 or T1=0 for clustering, attractive or repulsive interactions and the border T2=-2 T1+2(2- r) for a variation from repulsive to attractive interactions at r⩽2. Clustering is preferred by most bases in sequences of enolases and secA’ s. Major deviations with repulsive interactions of some bases are observed for archaea bacteria in secA and for highly developed animals and the human species in enolase sequences. The borders of the structure map for enthalpy stabilized structures with maximum interactions are approached in few cases. Most letters of the natural languages and some music notes are at the borders of the structure map.

Exponentially decaying interaction potential of cavity solitons

NASA Astrophysics Data System (ADS)

Anbardan, Shayesteh Rahmani; Rimoldi, Cristina; Kheradmand, Reza; Tissoni, Giovanna; Prati, Franco

2018-03-01

We analyze the interaction of two cavity solitons in an optically injected vertical cavity surface emitting laser above threshold. We show that they experience an attractive force even when their distance is much larger than their diameter, and eventually they merge. Since the merging time depends exponentially on the initial distance, we suggest that the attraction could be associated with an exponentially decaying interaction potential, similarly to what is found for hydrophobic materials. We also show that the merging time is simply related to the characteristic times of the laser, photon lifetime, and carrier lifetime.

Photogrammetric Analysis of Attractiveness in Indian Faces

PubMed Central

Duggal, Shveta; Kapoor, DN; Verma, Santosh; Sagar, Mahesh; Lee, Yung-Seop; Moon, Hyoungjin

2016-01-01

Background The objective of this study was to assess the attractive facial features of the Indian population. We tried to evaluate subjective ratings of facial attractiveness and identify which facial aesthetic subunits were important for facial attractiveness. Methods A cross-sectional study was conducted of 150 samples (referred to as candidates). Frontal photographs were analyzed. An orthodontist, a prosthodontist, an oral surgeon, a dentist, an artist, a photographer and two laymen (estimators) subjectively evaluated candidates' faces using visual analog scale (VAS) scores. As an objective method for facial analysis, we used balanced angular proportional analysis (BAPA). Using SAS 10.1 (SAS Institute Inc.), the Turkey's studentized range test and Pearson correlation analysis were performed to detect between-group differences in VAS scores (Experiment 1), to identify correlations between VAS scores and BAPA scores (Experiment 2), and to analyze the characteristic features of facial attractiveness and gender differences (Experiment 3); the significance level was set at P=0.05. Results Experiment 1 revealed some differences in VAS scores according to professional characteristics. In Experiment 2, BAPA scores were found to behave similarly to subjective ratings of facial beauty, but showed a relatively weak correlation coefficient with the VAS scores. Experiment 3 found that the decisive factors for facial attractiveness were different for men and women. Composite images of attractive Indian male and female faces were constructed. Conclusions Our photogrammetric study, statistical analysis, and average composite faces of an Indian population provide valuable information about subjective perceptions of facial beauty and attractive facial structures in the Indian population. PMID:27019809

Physical Attractiveness Research. Toward a Developmental Social Psychology of Beauty

ERIC Educational Resources Information Center

Adams, G. R.

1977-01-01

This paper reviews research on physical attractiveness from a dialectical-interactional perspective and attempts to examine the relationship between outer appearance and inner psychological characteristics from a developmental perspective. (BD)

Artificial night light alters nocturnal prey interception outcomes for morphologically variable spiders.

PubMed

Yuen, Suet Wai; Bonebrake, Timothy C

2017-01-01

Artificial night light has the potential to significantly alter visually-dependent species interactions. However, examples of disruptions of species interactions through changes in light remain rare and how artificial night light may alter predator-prey relationships are particularly understudied. In this study, we examined whether artificial night light could impact prey attraction and interception in Nephila pilipes orb weaver spiders, conspicuous predators who make use of yellow color patterns to mimic floral resources and attract prey to their webs. We measured moth prey attraction and interception responses to treatments where we experimentally manipulated the color/contrast of spider individuals in the field (removed yellow markings) and also set up light manipulations. We found that lit webs had lower rates of moth interception than unlit webs. Spider color, however, had no clear impact on moth interception or attraction rates in lit nor unlit webs. The results show that night light can reduce prey interception for spiders. Additionally, this study highlights how environmental and morphological variation can complicate simple predictions of ecological light pollution's disruption of species interactions.

Radiative Energy Loss by Galactic Cosmic Rays

NASA Technical Reports Server (NTRS)

Ahern, Sean C.; Norbury, John W.; Tripathi, R. K.

2002-01-01

Interactions between galactic cosmic rays and matter are a primary focus of the NASA radiation problem. The electromagnetic forces involved are for the most part well documented. Building on previous research, this study investigated the relative importance of the weak forces that occur when a cosmic ray impinges on different types of materials. For the familiar electromagnetic case, it is known that energy lost in the form of radiation is more significant than that lost via contact collisions the rate at which the energy is lost is also well understood. Similar results were derived for the weak force case. It was found that radiation is also the dominant mode of energy loss in weak force interactions and that weak force effects are indeed relatively weak compared to electromagnetic effects.

The physics of pollinator attraction.

PubMed

Moyroud, Edwige; Glover, Beverley J

2017-10-01

Contents 350 I. 350 II. 350 III. 352 IV. 353 V. 353 353 References 354 SUMMARY: This Tansley Insight focuses on recent advances in our understanding of how flowers manipulate physical forces to attract animal pollinators and ensure reproductive success. Research has traditionally explored the role of chemical pigments and volatile organic compounds as cues for pollinators, but recent reports have demonstrated the importance of physical and structural means of pollinator attraction. Here we explore the role of petal microstructure in influencing floral light capture and optics, analysing colour, gloss and polarization effects. We discuss the interaction between flower, pollinator and gravity, and how petal surface structure can influence that interaction. Finally, we consider the role of electrostatic forces in pollen transfer and pollinator attraction. We conclude that this new interdisciplinary field is evolving rapidly. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Cortisol, hedonics, and maternal responsiveness in human mothers.

PubMed

Fleming, A S; Steiner, M; Corter, C

1997-10-01

New mothers are more attracted to the body odor of newborn infants than are nonmothers. In this study we investigated the relation of postpartum hormones and of prior experience with infants to this enhanced maternal attraction to infant odors. New mothers were asked to complete a hedonics task, using a pleasantness scale to provide an attraction score to different odorants presented on a cotton substrate in a 1-pt Baskin-Robbins container. Mothers were "blind" to the contents of the container. Participants also completed an extensive set of 100-item likert scales concerning their attitudes toward infants, care taking, own maternal adequacy, and other interpersonal relations. Mothers were videotaped interacting with their infants and provided salivary samples prior to the interaction. Salivary samples were assayed by radioimmunoassay (RIA) for salivary concentrations of cortisol, progesterone, and testosterone. Results show that first-time mothers with higher cortisol concentrations were more attracted to their own infant's body odor. Mothers with higher cortisol levels were also better able to recognize their own infants' odors. While cortisol was not related to attitudinal measures of maternal responsiveness, mothers with more prior experience interacting with infants exhibited both more attraction to infant odors and more positive maternal attitudes. Together, prior maternal experience and postpartum cortisol explain a significant proportion of the variance in mothers' attraction to newborn infant odors. These relations are discussed in terms of the variety of "meanings" cortisol could have during the postpartum period. Copyright 1997 Academic Press.

Bayesian Variable Selection for Hierarchical Gene-Environment and Gene-Gene Interactions

PubMed Central

Liu, Changlu; Ma, Jianzhong; Amos, Christopher I.

2014-01-01

We propose a Bayesian hierarchical mixture model framework that allows us to investigate the genetic and environmental effects, gene by gene interactions and gene by environment interactions in the same model. Our approach incorporates the natural hierarchical structure between the main effects and interaction effects into a mixture model, such that our methods tend to remove the irrelevant interaction effects more effectively, resulting in more robust and parsimonious models. We consider both strong and weak hierarchical models. For a strong hierarchical model, both of the main effects between interacting factors must be present for the interactions to be considered in the model development, while for a weak hierarchical model, only one of the two main effects is required to be present for the interaction to be evaluated. Our simulation results show that the proposed strong and weak hierarchical mixture models work well in controlling false positive rates and provide a powerful approach for identifying the predisposing effects and interactions in gene-environment interaction studies, in comparison with the naive model that does not impose this hierarchical constraint in most of the scenarios simulated. We illustrated our approach using data for lung cancer and cutaneous melanoma. PMID:25154630

Interaction of lysozyme protein with different sized silica nanoparticles and their resultant structures

NASA Astrophysics Data System (ADS)

Yadav, Indresh; Aswal, V. K.; Kohlbrecher, J.

2016-05-01

The interaction of model protein-lysozyme with three different sized anionic silica nanoparticles has been studied by UV-vis spectroscopy, dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The surface area and curvature of the nanoparticles change with size, which significantly influence their interaction with protein. The lysozyme adsorbs on the surface of the nanoparticles due to electrostatic attraction and leads to the phase transformation from one phase (clear) to two-phase (turbid) of the nanoparticle-protein system. The dominance of lysozyme induced short-range attraction over long-range electrostatic repulsion between nanoparticles is responsible for phase transformation and modeled by the two-Yukawa potential. The magnitude of the attractive interaction increases with the size of the nanoparticles as a result the phase transformation commences relatively at lower concentration of lysozyme. The structure of the nanoparticle-protein system in two-phase is characterized by the diffusion limited aggregate type of mass fractal morphology.

Attractive versus repulsive interactions in the Bose-Einstein condensation dynamics of relativistic field theories

NASA Astrophysics Data System (ADS)

Berges, J.; Boguslavski, K.; Chatrchyan, A.; Jaeckel, J.

2017-10-01

We study the impact of attractive self-interactions on the nonequilibrium dynamics of relativistic quantum fields with large occupancies at low momenta. Our primary focus is on Bose-Einstein condensation and nonthermal fixed points in such systems. For a model system, we consider O (N ) -symmetric scalar field theories. We use classical-statistical real-time simulations as well as a systematic 1 /N expansion of the quantum (two-particle-irreducible) effective action to next-to-leading order. When the mean self-interactions are repulsive, condensation occurs as a consequence of a universal inverse particle cascade to the zero-momentum mode with self-similar scaling behavior. For attractive mean self-interactions, the inverse cascade is absent, and the particle annihilation rate is enhanced compared to the repulsive case, which counteracts the formation of coherent field configurations. For N ≥2 , the presence of a nonvanishing conserved charge can suppress number-changing processes and lead to the formation of stable localized charge clumps, i.e., Q balls.

Interaction of lysozyme protein with different sized silica nanoparticles and their resultant structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Indresh, E-mail: iykumarindresh288@gmail.com; Aswal, V. K.; Kohlbrecher, J.

The interaction of model protein-lysozyme with three different sized anionic silica nanoparticles has been studied by UV-vis spectroscopy, dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The surface area and curvature of the nanoparticles change with size, which significantly influence their interaction with protein. The lysozyme adsorbs on the surface of the nanoparticles due to electrostatic attraction and leads to the phase transformation from one phase (clear) to two-phase (turbid) of the nanoparticle-protein system. The dominance of lysozyme induced short-range attraction over long-range electrostatic repulsion between nanoparticles is responsible for phase transformation and modeled by the two-Yukawa potential. Themore » magnitude of the attractive interaction increases with the size of the nanoparticles as a result the phase transformation commences relatively at lower concentration of lysozyme. The structure of the nanoparticle-protein system in two-phase is characterized by the diffusion limited aggregate type of mass fractal morphology.« less

Measured long-range repulsive Casimir-Lifshitz forces.

PubMed

Munday, J N; Capasso, Federico; Parsegian, V Adrian

2009-01-08

Quantum fluctuations create intermolecular forces that pervade macroscopic bodies. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces. However, as recognized in the theories of Casimir, Polder and Lifshitz, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies. Here we show experimentally that, in accord with theoretical prediction, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir-Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction.

Molecular Self-Assembly Driven by London Dispersion Forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Guo; Cooper, Valentino R; Cho, Jun-Hyung

2011-01-01

The nature and strength of intermolecular interactions are crucial to a variety of kinetic and dynamic processes at surfaces. Whereas strong chemisorption bonds are known to facilitate molecular binding, the importance of the weaker yet ubiquitous van der Waals (vdW) interactions remains elusive in most cases. Here we use first-principles calculations combined with kinetic Monte Carlo simulations to unambiguously demonstrate the vital role that vdW interactions play in molecular self-assembly, using styrene nanowire growth on silicon as a prototypical example. We find that, only when the London dispersion forces are included, accounting for the attractive parts of vdW interactions, canmore » the effective intermolecular interaction be reversed from being repulsive to attractive. Such attractive interactions, in turn, ensure the preferred growth of long wires under physically realistic conditions as observed experimentally. We further propose a cooperative scheme, invoking the application of an electric field and the selective creation of Si dangling bonds, to drastically improve the ordered arrangement of the molecular structures. The present study represents a significant step forward in the fundamental understanding and precise control of molecular self-assembly guided by London dispersion forces.« less

Theoretical studies of weak interactions of formamide with methanol and its derivates

NASA Astrophysics Data System (ADS)

Zheng, Xiao-Wen; Wang, Lu; Han, Shu-Min; Cui, Xiang-Yang; Du, Chong-Yang; Liu, Tao

2015-08-01

Theoretical calculations have been performed for the complexes of formamide (FA) with methanol and its derivates (MAX, X = F, Cl, Br, NO2, H, OH, CH3, and NH2) to study their structures and properties. Substituent effects on the hydrogen bond (H-bond) strength and cooperative effect by using water and its derivatives (HOZ, Z = H, NH2, and Br) as weak interaction probe were also explored. The calculation results show that electron-donating groups strengthen the weak interaction between formamide with methanol whereas electron-withdrawing groups weaken it. The cooperativity is present for the N-HïO H-bond in MAX-FA-HOZ and the cooperative effect increases in a series HONH2, HOH, and HOBr. In addition, we investigated the interaction between FA with hypohalous acids HOY (Y = F, Cl, and Br). It was found that the weak interaction between FA and HOY became stronger with the increase of the size of halogen atom. The nature of the halogen atom has negligible impact on the strength of the H-bond in MAX-FA (X = F, Cl, and Br), whereas it has an obvious influence on the strength of the H-bond in HOY-FA (Y = F, Cl, and Br).

Loss of functionally unique species may gradually undermine ecosystems

PubMed Central

O'Gorman, Eoin J.; Yearsley, Jon M.; Crowe, Tasman P.; Emmerson, Mark C.; Jacob, Ute; Petchey, Owen L.

2011-01-01

Functionally unique species contribute to the functional diversity of natural systems, often enhancing ecosystem functioning. An abundance of weakly interacting species increases stability in natural systems, suggesting that loss of weakly linked species may reduce stability. Any link between the functional uniqueness of a species and the strength of its interactions in a food web could therefore have simultaneous effects on ecosystem functioning and stability. Here, we analyse patterns in 213 real food webs and show that highly unique species consistently tend to have the weakest mean interaction strength per unit biomass in the system. This relationship is not a simple consequence of the interdependence of both measures on body size and appears to be driven by the empirical pattern of size structuring in aquatic systems and the trophic position of each species in the web. Food web resolution also has an important effect, with aggregation of species into higher taxonomic groups producing a much weaker relationship. Food webs with fewer unique and less weakly interacting species also show significantly greater variability in their levels of primary production. Thus, the loss of highly unique, weakly interacting species may eventually lead to dramatic state changes and unpredictable levels of ecosystem functioning. PMID:21106593

Role of Anisotropic Interactions for Proteins and Patchy Nanoparticles

PubMed Central

2015-01-01

Protein–protein interactions are inherently anisotropic to some degree, with orientation-dependent interactions between repulsive and attractive or complementary regions or “patches” on adjacent proteins. In some cases it has been suggested that such patch–patch interactions dominate the thermodynamics of dilute protein solutions, as captured by the osmotic second virial coefficient (B22), but delineating when this will or will not be the case remains an open question. A series of simplified but exactly solvable models are first used to illustrate that a delicate balance exists between the strength of attractive patch–patch interactions and the patch size, and that repulsive patch–patch interactions contribute significantly to B22 for only those conditions where the repulsions are long-ranged. Finally, B22 is reformulated, without approximations, in terms of the density of states for a given interaction energy and particle–particle distance. Doing so illustrates the inherent balance of entropic and energetic contributions to B22. It highlights that simply having strong patch–patch interactions will only cause anisotropic interactions to dominate B22 solution properties if the unavoidable entropic penalties are overcome, which cannot occur if patches are too small. The results also indicate that the temperature dependence of B22 may be a simple experimental means to assess whether a small number of strongly attractive configurations dominate the dilute solution behavior. PMID:25302767

Coalescence of silver clusters by immersion in diluted HF solution

NASA Astrophysics Data System (ADS)

Milazzo, R. G.; Mio, A. M.; D'Arrigo, G.; Grimaldi, M. G.; Spinella, C.; Rimini, E.

2015-07-01

The galvanic displacement deposition of silver on H-terminated Si (100) in the time scale of seconds is instantaneous and characterized by a cluster density of 1011-1012 cm-2. The amount of deposited Ag follows a t1/2 dependence in agreement with a Cottrell diffusion limited mechanism. At the same time, during the deposition, the cluster density reduces by a factor 5. This behavior is in contrast with the assumption of immobile clusters. We show in the present work that coalescence and aggregation occur also in the samples immersed in the diluted hydrofluoric acid (HF) solution without the presence of Ag+. Clusters agglomerate according to a process of dynamic coalescence, typical of colloids, followed by atomic redistribution at the contact regions with the generation of multiple internal twins and stacking-faults. The normalized size distributions in terms of r/rmean follow also the prediction of the Smoluchowski ripening mechanism. No variation of the cluster density occurs for samples immersed in pure H2O solution. The different behavior might be associated to the strong attraction of clusters to oxide-terminated Si surface in presence of water. The silver clusters are instead weakly bound to hydrophobic H-terminated Si in presence of HF. HF causes then the detachment of clusters and a random movement on the silicon surface with mobility of about 10-13 cm2/s. Attractive interaction (probably van der Waals) among particles promotes coarsening.

Destabilization of Titania Nanosheet Suspensions by Inorganic Salts: Hofmeister Series and Schulze-Hardy Rule.

PubMed

Rouster, Paul; Pavlovic, Marko; Szilagyi, Istvan

2017-07-13

Ion specific effects on colloidal stability of titania nanosheets (TNS) were investigated in aqueous suspensions. The charge of the particles was varied by the pH of the solutions, therefore, the influence of mono- and multivalent anions on the charging and aggregation behavior could be studied when they were present either as counter or co-ions in the systems. The aggregation processes in the presence of inorganic salts were mainly driven by interparticle forces of electrostatic origin, however, chemical interactions between more complex ions and the surface led to additional attractive forces. The adsorption of anions significantly changed the surface charge properties and hence, the resistance of the TNS against salt-induced aggregation. On the basis of their ability in destabilization of the dispersions, the monovalent ions could be ordered according to the Hofmeister series in acidic solutions, where they act as counterions. However, the behavior of the biphosphate anion was atypical and its adsorption induced charge reversal of the particles. The multivalent anions destabilized the oppositely charged TNS more effectively and the aggregation processes followed the Schulze-Hardy rule. Only weak or negligible interactions were observed between the anions and the particles in alkaline suspensions, where the TNS possessed negative charge.

Loss of electrostatic cell-surface repulsion mediates myelin membrane adhesion and compaction in the central nervous system.

PubMed

Bakhti, Mostafa; Snaidero, Nicolas; Schneider, David; Aggarwal, Shweta; Möbius, Wiebke; Janshoff, Andreas; Eckhardt, Matthias; Nave, Klaus-Armin; Simons, Mikael

2013-02-19

During the development of the central nervous system (CNS), oligodendrocytes wrap their plasma membrane around axons to form a multilayered stack of tightly attached membranes. Although intracellular myelin compaction and the role of myelin basic protein has been investigated, the forces that mediate the close interaction of myelin membranes at their external surfaces are poorly understood. Such extensive bilayer-bilayer interactions are usually prevented by repulsive forces generated by the glycocalyx, a dense and confluent layer of large and negatively charged oligosaccharides. Here we investigate the molecular mechanisms underlying myelin adhesion and compaction in the CNS. We revisit the role of the proteolipid protein and analyze the contribution of oligosaccharides using cellular assays, biophysical tools, and transgenic mice. We observe that differentiation of oligodendrocytes is accompanied by a striking down-regulation of components of their glycocalyx. Both in vitro and in vivo experiments indicate that the adhesive properties of the proteolipid protein, along with the reduction of sialic acid residues from the cell surface, orchestrate myelin membrane adhesion and compaction in the CNS. We suggest that loss of electrostatic cell-surface repulsion uncovers weak and unspecific attractive forces in the bilayer that bring the extracellular surfaces of a membrane into close contact over long distances.

Tweaking Dendrimers and Dendritic Nanoparticles for Controlled Nano-bio Interactions: Potential Nanocarriers for Improved Cancer Targeting

PubMed Central

Bugno, Jason; Hsu, Hao-Jui; Hong, Seungpyo

2016-01-01

Nanoparticles have shown great promise in the treatment of cancer, with a demonstrated potential in targeted drug delivery. Among a myriad of nanocarriers that have been recently developed, dendrimers have attracted a great deal of scientific interests due to their unique chemical and structural properties that allow for precise engineering of their characteristics. Despite this, the clinical translation of dendrimers has been hindered due to their drawbacks, such as scale-up issues, rapid systemic elimination, inefficient tumor accumulation, and limited drug loading. In order to overcome these limitations, a series of reengineered dendrimers have been recently introduced using various approaches, including: i) modifications of structure and surfaces; ii) integration with linear polymers; and iii) hybridization with other types of nanocarriers. Chemical modifications and surface engineering have tailored dendrimers to improve their pharmacokinetics and tissue permeation. Copolymerization of dendritic polymers with linear polymers has resulted in various amphiphilic copolymers with self-assembly capabilities and improved drug loading efficiencies. Hybridization with other nanocarriers integrates advantageous characteristics of both systems, which includes prolonged plasma circulation times and enhanced tumor targeting. This review provides a comprehensive summary of the newly emerging drug delivery systems that involve reengineering of dendrimers in an effort to precisely control their nano-bio interactions, mitigating their inherent weaknesses. PMID:26453160

The effects of women's age and physical appearance on evaluations of attractiveness and social desirability.

PubMed

Perlini, A H; Bertolissi, S; Lind, D L

1999-06-01

Younger people are perceived as possessing a host of socially desirable attributes, some of which are the same traits attributed to attractive people. In the present study, 160 younger and older White Canadians rated the attractiveness and personality traits of 1 of 4 target women. The results indicated an interaction between the participant's age and gender and the age and attractiveness of the target person. Both younger and older judges showed an attractiveness bias and downrated the social desirability of younger unattractive targets. Younger judges rated younger and older attractive targets as equal in social desirability. Older male judges rated older attractive targets as less socially desirable than younger attractive targets. Results are discussed in terms of cultural expectations of beauty.

Search for a light Higgs boson decaying to long-lived weakly interacting particles in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector.

PubMed

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Stelzer-Chilton, O; Stenzel, H; Stern, S; Stevenson, K; Stewart, G A; Stillings, J A; Stockton, M C; Stoerig, K; Stoicea, G; Stonjek, S; Strachota, P; Stradling, A R; Straessner, A; Strandberg, J; Strandberg, S; Strandlie, A; Strang, M; Strauss, E; Strauss, M; Strizenec, P; Ströhmer, R; Strom, D M; Strong, J A; Stroynowski, R; Strube, J; Stugu, B; Stumer, I; Stupak, J; Sturm, P; Styles, N A; Soh, D A; Su, D; Subramania, Hs; Succurro, A; Sugaya, Y; Sugimoto, T; Suhr, C; Suita, K; Suk, M; Sulin, V V; Sultansoy, S; Sumida, T; Sun, X; Sundermann, J E; Suruliz, K; Sushkov, S; Susinno, G; Sutton, M R; Suzuki, Y; Suzuki, Y; Svatos, M; Sviridov, Yu M; Swedish, S; Sykora, I; Sykora, T; Szeless, B; Sánchez, J; Ta, D; Tackmann, K; Taffard, A; Tafirout, R; Taiblum, N; Takahashi, Y; Takai, H; Takashima, R; Takeda, H; Takeshita, T; Takubo, Y; Talby, M; Talyshev, A; Tamsett, M C; Tanaka, J; Tanaka, R; Tanaka, S; Tanaka, S; Tanaka, Y; Tanasijczuk, A J; Tani, K; Tannoury, N; Tappern, G P; Tapprogge, S; Tardif, D; Tarem, S; Tarrade, F; Tartarelli, G F; Tas, P; Tasevsky, M; Tassi, E; Tatarkhanov, M; Tayalati, Y; Taylor, C; Taylor, F E; Taylor, G N; Taylor, W; Teinturier, M; Teixeira Dias Castanheira, M; Teixeira-Dias, P; Temming, K K; Ten Kate, H; Teng, P K; Terada, S; Terashi, K; Terron, J; Testa, M; Teuscher, R J; Thadome, J; Therhaag, J; Theveneaux-Pelzer, T; Thioye, M; Thoma, S; Thomas, J P; Thompson, E N; Thompson, P D; Thompson, P D; Thompson, A S; Thomson, E; Thomson, M; Thun, R P; Tian, F; Tibbetts, M J; Tic, T; Tikhomirov, V O; Tikhonov, Y A; Timoshenko, S; Tipton, P; Tique Aires Viegas, F J; Tisserant, S; Toczek, B; Todorov, T; Todorova-Nova, S; Toggerson, B; Tojo, J; Tokár, S; Tokunaga, K; Tokushuku, K; Tollefson, K; Tomoto, M; Tompkins, L; Toms, K; Tong, G; Tonoyan, A; Topfel, C; Topilin, N D; Torchiani, I; Torrence, E; Torres, H; Torró Pastor, E; Toth, J; Touchard, F; Tovey, D R; Trefzger, T; Tremblet, L; Tricoli, A; Trigger, I M; Trincaz-Duvoid, S; Trinh, T N; Tripiana, M F; Trischuk, W; Trivedi, A; Trocmé, B; Troncon, C; Trottier-McDonald, M; Trzebinski, M; Trzupek, A; Tsarouchas, C; Tseng, J C-L; Tsiakiris, M; Tsiareshka, P V; Tsionou, D; Tsipolitis, G; Tsiskaridze, V; Tskhadadze, E G; Tsukerman, I I; Tsulaia, V; Tsung, J-W; Tsuno, S; Tsybychev, D; Tua, A; Tudorache, A; Tudorache, V; Tuggle, J M; Turala, M; Turecek, D; Turk Cakir, I; Turlay, E; Turra, R; Tuts, P M; Tykhonov, A; Tylmad, M; Tyndel, M; Tzanakos, G; Uchida, K; Ueda, I; Ueno, R; Ugland, M; Uhlenbrock, M; Uhrmacher, M; Ukegawa, F; Unal, G; Underwood, D G; Undrus, A; Unel, G; Unno, Y; Urbaniec, D; Usai, G; Uslenghi, M; Vacavant, L; Vacek, V; Vachon, B; Vahsen, S; Valenta, J; Valente, P; Valentinetti, S; Valkar, S; Valladolid Gallego, E; Vallecorsa, S; Valls Ferrer, J A; van der Graaf, H; van der Kraaij, E; Van Der Leeuw, R; van der Poel, E; van der Ster, D; van Eldik, N; van Gemmeren, P; van Kesteren, Z; van Vulpen, I; Vanadia, M; Vandelli, W; Vandoni, G; Vaniachine, A; Vankov, P; Vannucci, F; Varela Rodriguez, F; Vari, R; Varnes, E W; Varouchas, D; Vartapetian, A; Varvell, K E; Vassilakopoulos, V I; Vazeille, F; Vegni, G; Veillet, J J; Vellidis, C; Veloso, F; Veness, R; Veneziano, S; Ventura, A; Ventura, D; Venturi, M; Venturi, N; Vercesi, V; Verducci, M; Verkerke, W; Vermeulen, J C; Vest, A; Vetterli, M C; Vichou, I; Vickey, T; Vickey Boeriu, O E; Viehhauser, G H A; Viel, S; Villa, M; Villaplana Perez, M; Vilucchi, E; Vincter, M G; Vinek, E; Vinogradov, V B; Virchaux, M; Virzi, J; Vitells, O; Viti, M; Vivarelli, I; Vives Vaque, F; Vlachos, S; Vladoiu, D; Vlasak, M; Vlasov, N; Vogel, A; Vokac, P; Volpi, G; Volpi, M; Volpini, G; von der Schmitt, H; von Loeben, J; von Radziewski, H; von Toerne, E; Vorobel, V; Vorobiev, A P; Vorwerk, V; Vos, M; Voss, R; Voss, T T; Vossebeld, J H; Vranjes, N; Vranjes Milosavljevic, M; Vrba, V; Vreeswijk, M; Vu Anh, T; Vuillermet, R; Vukotic, I; Wagner, W; Wagner, P; Wahlen, H; Wakabayashi, J; Walbersloh, J; Walch, S; Walder, J; Walker, R; Walkowiak, W; Wall, R; Waller, P; Wang, C; Wang, H; Wang, H; Wang, J; Wang, J; Wang, J C; Wang, R; Wang, S M; Warburton, A; Ward, C P; Warsinsky, M; Watkins, P M; Watson, A T; Watson, I J; Watson, M F; Watts, G; Watts, S; Waugh, A T; Waugh, B M; Weber, M; Weber, M S; Weber, P; Weidberg, A R; Weigell, P; Weingarten, J; Weiser, C; Wellenstein, H; Wells, P S; Wen, M; Wenaus, T; Wendler, S; Weng, Z; Wengler, T; Wenig, S; Wermes, N; Werner, M; Werner, P; Werth, M; Wessels, M; Weydert, C; Whalen, K; Wheeler-Ellis, S J; Whitaker, S P; White, A; White, M J; Whitehead, S R; Whiteson, D; Whittington, D; Wicek, F; Wicke, D; Wickens, F J; Wiedenmann, W; Wielers, M; Wienemann, P; Wiglesworth, C; Wiik-Fuchs, L A M; Wijeratne, P A; Wildauer, A; Wildt, M A; Wilhelm, I; Wilkens, H G; Will, J Z; Williams, E; Williams, H H; Willis, W; Willocq, S; Wilson, J A; Wilson, M G; Wilson, A; Wingerter-Seez, I; Winkelmann, S; Winklmeier, F; Wittgen, M; Wolter, M W; Wolters, H; Wong, W C; Wooden, G; Wosiek, B K; Wotschack, J; Woudstra, M J; Wozniak, K W; Wraight, K; Wright, C; Wright, M; Wrona, B; Wu, S L; Wu, X; Wu, Y; Wulf, E; Wunstorf, R; Wynne, B M; Xella, S; Xiao, M; Xie, S; Xie, Y; Xu, C; Xu, D; Xu, G; Yabsley, B; Yacoob, S; Yamada, M; Yamaguchi, H; Yamamoto, A; Yamamoto, K; Yamamoto, S; Yamamura, T; Yamanaka, T; Yamaoka, J; Yamazaki, T; Yamazaki, Y; Yan, Z; Yang, H; Yang, U K; Yang, Y; Yang, Y; Yang, Z; Yanush, S; Yao, Y; Yasu, Y; Ybeles Smit, G V; Ye, J; Ye, S; Yilmaz, M; Yoosoofmiya, R; Yorita, K; Yoshida, R; Young, C; Youssef, S; Yu, D; Yu, J; Yu, J; Yuan, L; Yurkewicz, A; Zabinski, B; Zaets, V G; Zaidan, R; Zaitsev, A M; Zajacova, Z; Zanello, L; Zarzhitsky, P; Zaytsev, A; Zeitnitz, C; Zeller, M; Zeman, M; Zemla, A; Zendler, C; Zenin, O; Zeniš, T; Zinonos, Z; Zenz, S; Zerwas, D; Zevi Della Porta, G; Zhan, Z; Zhang, D; Zhang, H; Zhang, J; Zhang, X; Zhang, Z; Zhao, L; Zhao, T; Zhao, Z; Zhemchugov, A; Zheng, S; Zhong, J; Zhou, B; Zhou, N; Zhou, Y; Zhu, C G; Zhu, H; Zhu, J; Zhu, Y; Zhuang, X; Zhuravlov, V; Zieminska, D; Zimmermann, R; Zimmermann, S; Zimmermann, S; Ziolkowski, M; Zitoun, R; Zivković, L; Zmouchko, V V; Zobernig, G; Zoccoli, A; Zolnierowski, Y; Zsenei, A; Zur Nedden, M; Zutshi, V; Zwalinski, L

2012-06-22

A search for the decay of a light Higgs boson (120-140 GeV) to a pair of weakly interacting, long-lived particles in 1.94 fb(-1) of proton-proton collisions at sqrt[s] = 7 TeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length.

Photoconductivity study of acid on Zinc phthalocyanine pyridine thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Sukhwinder, E-mail: ss7667@gmail.com; Saini, G. S. S.; Tripathi, S. K.

2016-05-06

The Metal Phthalocyanine (MPc) have attracted much interest because of chemical and high thermal stability. Molecules forming a crystal of MPc are held together by weak attractive Vander Waals forces. Organic semiconductors have π conjugate bonds which allow electrons to move via π-electron cloud overlaps. Conduction mechanisms for organic semiconductor are mainly through tunneling; hopping between localized states, mobility gaps, and phonon assisted hopping. The photo conductivity of thin films of these complexes changes when exposed to oxidizing and reducing gases. Arrhenius plot is used to find the thermal activation energy in the intrinsic region and impurity scattering region. Arrheniusmore » plotsare used to find the thermal activation energy.« less

Face inversion increases attractiveness.

PubMed

Leder, Helmut; Goller, Juergen; Forster, Michael; Schlageter, Lena; Paul, Matthew A

2017-07-01

Assessing facial attractiveness is a ubiquitous, inherent, and hard-wired phenomenon in everyday interactions. As such, it has highly adapted to the default way that faces are typically processed: viewing faces in upright orientation. By inverting faces, we can disrupt this default mode, and study how facial attractiveness is assessed. Faces, rotated at 90 (tilting to either side) and 180°, were rated on attractiveness and distinctiveness scales. For both orientations, we found that faces were rated more attractive and less distinctive than upright faces. Importantly, these effects were more pronounced for faces rated low in upright orientation, and smaller for highly attractive faces. In other words, the less attractive a face was, the more it gained in attractiveness by inversion or rotation. Based on these findings, we argue that facial attractiveness assessments might not rely on the presence of attractive facial characteristics, but on the absence of distinctive, unattractive characteristics. These unattractive characteristics are potentially weighed against an individual, attractive prototype in assessing facial attractiveness. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Attractive interactions between reverse aggregates and phase separation in concentrated malonamide extractant solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erlinger, C.; Belloni, L.; Zemb, T.

1999-03-30

Using small angle X-ray scattering, conductivity, and phase behavior determination, the authors show that concentrated solutions of malonamide extractants, dimethyldibutyltetradecylmalonamide (DMDBTDMA), are organized in reverse oligomeric aggregates which have many features in common with reverse micelles. The aggregation numbers of these reverse globular aggregates as well as their interaction potential are determined from absolute scattering curves. An attractive interaction is responsible for the demixing of the oil phase when in equilibrium with excess oil. Prediction of conductivity as well as the formation conditions for the third phase is possible using standard liquid theory applied to the extractant aggregates. The interactions,more » modeled with the sticky sphere model proposed by Baster, are shown to be due to steric interactions resulting from the hydrophobic tails of the extractant molecule and van der Waals forces between the highly polarizable water core of the reverse micelles. The attractive interaction in the oil phase, equilibrated with water, is determined as a function of temperature, extractant molecule concentration, and proton and neodynium(III) cation concentration. It is shown that van der Waals interactions, with an effective Hamaker constant of 3kT, quantitatively explain the behavior of DMDBTDMA in n-dodecane in terms of scattering as well as phase stability limits.« less

Precision measurement of the weak charge of the proton

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

The weak charge of the proton Q_W^p sets the strength of the proton's interaction with other particles via the neutral electroweak force, just as the electric charge sets the strength of the purely electromagnetic (EM) interaction. The standard model (SM) of electroweak particle physics predicts that Q_W^p is suppressed, due to a near-cancellation between the weak charges of the proton's three constituent quarks. This small SM "background" makes Q_W^p especially sensitive to potential new parity-violating (PV) interactions beyond those of the SM. Parity symmetry (invariance under spatial inversion (x,y,z) --> (-x,-y,-z)) is violated in the weak interaction, but not inmore » the other three forces of nature. Therefore PV provides a unique tool to isolate the weak interaction in order to observe the proton's weak charge1. Earlier experiments2 have measured parity-violating electron-scattering (PVES) asymmetries in kinematic regimes that are more sensitive to the proton's extended structure than to its weak charge. Here we report the most precise measurement of the PV electron-proton scattering asymmetry (A_ep = -226.5 ± 9.3 ppb, 1 ppb=10-9), in a kinematic regime where the theoretical uncertainties involved in determining Q_W^p are small. We use this measurement of A_ep to determine Q_W^p, obtaining consistent results using several methods which vary the degree of experimental and theoretical input. Our result for Q_W^p (0.0719 ± 0.0045) is in excellent agreement with the SM3. We employ energy-scale-dependent quantum corrections to relate Q_W^p to the electroweak mixing angle sin^2 theta_W, a fundamental SM parameter with which we are also in good agreement. In addition, we use our precise Q_W^p result to set TeV-scale constraints on potential new semi-leptonic PV physics not described by the SM.« less

Molecular dynamics simulation of solute diffusion in Lennard-Jones fluids

NASA Astrophysics Data System (ADS)

Yamaguchi, T.; Kimura, Y.; Hirota, N.

We performed a molecular dynamics (MD) simulation for a system of 5 solute molecules in 495 solvent molecules interacting through the Lennard-Jones (LJ) 12-6 potential, in order to study solvent density effects on the diffusion coefficients in supercritical fluids. The effects of the size of the solute and the strength of the solute-solvent attractive interaction on the diffusion coefficient of the solute were examined. The diffusion coefficients of the solute molecules were calculated at T = 1.5 (in the LJ reduced unit), slightly above the critical temperature, from rho = 0.1 to rho = 0.95, where rho is the number density in the LJ reduced unit. The memory function in the generalized Langevin equation was calculated, in order to know the molecular origin of the friction on a solute. The memory function is separated into fast and slow components. The former arises from the solute-solvent repulsive interaction, and is interpreted as collisional Enskog-like friction. The interaction strength dependence of the collisional friction is larger in the low- and medium-density regions, which is consistent with the 'clustering' picture, i.e., the local density enhancement due to the solute-solvent attractive interaction. However, the slow component of the memory function suppresses the effect of the local density on the diffusion coefficients, and as a result the effect of the attractive interaction is smaller on the diffusion coefficients than on the local density. Nonetheless, the solvent density dependence of the effect of the attraction on the diffusion coefficient varies with the local density, and it is concluded that the local density is the principal factor that determines the interaction strength dependence of the diffusion coefficient in the low- and medium-density regions (p < 0.6).

Development of tight-binding based GW algorithm and its computational implementation for graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majidi, Muhammad Aziz; NUSNNI-NanoCore, Department of Physics, National University of Singapore; Singapore Synchrotron Light Source

Graphene has been a hot subject of research in the last decade as it holds a promise for various applications. One interesting issue is whether or not graphene should be classified into a strongly or weakly correlated system, as the optical properties may change upon several factors, such as the substrate, voltage bias, adatoms, etc. As the Coulomb repulsive interactions among electrons can generate the correlation effects that may modify the single-particle spectra (density of states) and the two-particle spectra (optical conductivity) of graphene, we aim to explore such interactions in this study. The understanding of such correlation effects ismore » important because eventually they play an important role in inducing the effective attractive interactions between electrons and holes that bind them into excitons. We do this study theoretically by developing a GW method implemented on the basis of the tight-binding (TB) model Hamiltonian. Unlike the well-known GW method developed within density functional theory (DFT) framework, our TB-based GW implementation may serve as an alternative technique suitable for systems which Hamiltonian is to be constructed through a tight-binding based or similar models. This study includes theoretical formulation of the Green’s function G, the renormalized interaction function W from random phase approximation (RPA), and the corresponding self energy derived from Feynman diagrams, as well as the development of the algorithm to compute those quantities. As an evaluation of the method, we perform calculations of the density of states and the optical conductivity of graphene, and analyze the results.« less

Effects of physical attractiveness on political beliefs.

PubMed

Peterson, Rolfe Daus; Palmer, Carl L

2017-01-01

Physical attractiveness is an important social factor in our daily interactions. Scholars in social psychology provide evidence that attractiveness stereotypes and the "halo effect" are prominent in affecting the traits we attribute to others. However, the interest in attractiveness has not directly filtered down to questions of political behavior beyond candidates and elites. Utilizing measures of attractiveness across multiple surveys, we examine the relationship between attractiveness and political beliefs. Controlling for socioeconomic status, we find that more attractive individuals are more likely to report higher levels of political efficacy, identify as conservative, and identify as Republican. These findings suggest an additional mechanism for political socialization that has further implications for understanding how the body intertwines with the social nature of politics.

Scaling of elongation transition thickness during thin-film growth on weakly interacting substrates

NASA Astrophysics Data System (ADS)

Lü, B.; Souqui, L.; Elofsson, V.; Sarakinos, K.

2017-08-01

The elongation transition thickness ( θElong) is a central concept in the theoretical description of thin-film growth dynamics on weakly interacting substrates via scaling relations of θElong with respect to rates of key atomistic film-forming processes. To date, these scaling laws have only been confirmed quantitatively by simulations, while experimental proof has been left ambiguous as it has not been possible to measure θElong. Here, we present a method for determining experimentally θElong for Ag films growing on amorphous SiO2: an archetypical weakly interacting film/substrate system. Our results confirm the theoretically predicted θElong scaling behavior, which then allow us to calculate the rates of adatom diffusion and island coalescence completion, in good agreement with the literature. The methodology presented herein casts the foundation for studying growth dynamics and cataloging atomistic-process rates for a wide range of weakly interacting film/substrate systems. This may provide insights into directed growth of metal films with a well-controlled morphology and interfacial structure on 2D crystals—including graphene and MoS2—for catalytic and nanoelectronic applications.

Stripes disrupt odour attractiveness to biting horseflies: battle between ammonia, CO₂, and colour pattern for dominance in the sensory systems of host-seeking tabanids.

PubMed

Blahó, Miklós; Egri, Adám; Száz, Dénes; Kriska, György; Akesson, Susanne; Horváth, Gábor

2013-07-02

As with mosquitoes, female tabanid flies search for mammalian hosts by visual and olfactory cues, because they require a blood meal before being able to produce and lay eggs. Polarotactic tabanid flies find striped or spotted patterns with intensity and/or polarisation modulation visually less attractive than homogeneous white, brown or black targets. Thus, this reduced optical attractiveness to tabanids can be one of the functions of striped or spotty coat patterns in ungulates. Ungulates emit CO2 via their breath, while ammonia originates from their decaying urine. As host-seeking female tabanids are strongly attracted to CO2 and ammonia, the question arises whether the poor visual attractiveness of stripes and spots to tabanids is or is not overcome by olfactory attractiveness. To answer this question we performed two field experiments in which the attractiveness to tabanid flies of homogeneous white, black and black-and-white striped three-dimensional targets (spheres and cylinders) and horse models provided with CO2 and ammonia was studied. Since tabanids are positively polarotactic, i.e. attracted to strongly and linearly polarised light, we measured the reflection-polarisation patterns of the test surfaces and demonstrated that these patterns were practically the same as those of real horses and zebras. We show here that striped targets are significantly less attractive to host-seeking female tabanids than homogeneous white or black targets, even when they emit tabanid-luring CO2 and ammonia. Although CO2 and ammonia increased the number of attracted tabanids, these chemicals did not overcome the weak visual attractiveness of stripes to host-seeking female tabanids. This result demonstrates the visual protection of striped coat patterns against attacks from blood-sucking dipterans, such as horseflies, known to transmit lethal diseases to ungulates. © 2013.

Social networks, personal values, and creativity: evidence for curvilinear and interaction effects.

PubMed

Zhou, Jing; Shin, Shung Jae; Brass, Daniel J; Choi, Jaepil; Zhang, Zhi-Xue

2009-11-01

Taking an interactional perspective on creativity, the authors examined the influence of social networks and conformity value on employees' creativity. They theorized and found a curvilinear relationship between number of weak ties and creativity such that employees exhibited greater creativity when their number of weak ties was at intermediate levels rather than at lower or higher levels. In addition, employees' conformity value moderated the curvilinear relationship between number of weak ties and creativity such that employees exhibited greater creativity at intermediate levels of number of weak ties when conformity was low than when it was high. A proper match between personal values and network ties is critical for understanding creativity.

Light-matter interaction in transition metal dichalcogenides and their heterostructures

NASA Astrophysics Data System (ADS)

Wurstbauer, Ursula; Miller, Bastian; Parzinger, Eric; Holleitner, Alexander W.

2017-05-01

The investigation of two-dimensional (2D) van der Waals materials is a vibrant, fast-moving and still growing interdisciplinary area of research. These materials are truly 2D crystals with strong covalent in-plane bonds and weak van der Waals interaction between the layers, and have a variety of different electronic, optical and mechanical properties. Transition metal dichalcogenides are a very prominent class of 2D materials, particularly the semiconducting subclass. Their properties include bandgaps in the near-infrared to the visible range, decent charge carrier mobility together with high (photo-) catalytic and mechanical stability, and exotic many-body phenomena. These characteristics make the materials highly attractive for both fundamental research as well as innovative device applications. Furthermore, the materials exhibit a strong light-matter interaction, providing a high sunlight absorbance of up to 15% in the monolayer limit, strong scattering cross section in Raman experiments, and access to excitonic phenomena in van der Waals heterostructures. This review focuses on the light-matter interaction in MoS2, WS2, MoSe2 and WSe2, which is dictated by the materials’ complex dielectric functions, and on the multiplicity of studying the first-order phonon modes by Raman spectroscopy to gain access to several material properties such as doping, strain, defects and temperature. 2D materials provide an interesting platform for stacking them into van der Waals heterostructures without the limitation of lattice mismatch, resulting in novel devices for applications but also to enable the study of exotic many-body interaction phenomena such as interlayer excitons. Future perspectives of semiconducting transition metal dichalcogenides and their heterostructures for applications in optoelectronic devices will be examined, and routes to study emergent fundamental problems and many-body quantum phenomena under excitations with photons will be discussed.

Nuclei and Fundamental Symmetries

NASA Astrophysics Data System (ADS)

Haxton, Wick

2016-09-01

Nuclei provide marvelous laboratories for testing fundamental interactions, often enhancing weak processes through accidental degeneracies among states, and providing selection rules that can be exploited to isolate selected interactions. I will give an overview of current work, including the use of parity violation to probe unknown aspects of the hadronic weak interaction; nuclear electric dipole moment searches that may shed light on new sources of CP violation; and tests of lepton number violation made possible by the fact that many nuclei can only decay by rare second-order weak interactions. I will point to opportunities in both theory and experiment to advance the field. Based upon work supported in part by the US Department of Energy, Office of Science, Office of Nuclear Physics and SciDAC under Awards DE-SC00046548 (Berkeley), DE-AC02-05CH11231 (LBNL), and KB0301052 (LBNL).

Detection of light-matter interaction in the weak-coupling regime by quantum light

NASA Astrophysics Data System (ADS)

Bin, Qian; Lü, Xin-You; Zheng, Li-Li; Bin, Shang-Wu; Wu, Ying

2018-04-01

"Mollow spectroscopy" is a photon statistics spectroscopy, obtained by scanning the quantum light scattered from a source system. Here, we apply this technique to detect the weak light-matter interaction between the cavity and atom (or a mechanical oscillator) when the strong system dissipation is included. We find that the weak interaction can be measured with high accuracy when exciting the target cavity by quantum light scattered from the source halfway between the central peak and each side peak. This originally comes from the strong correlation of the injected quantum photons. In principle, our proposal can be applied into the normal cavity quantum electrodynamics system described by the Jaynes-Cummings model and an optomechanical system. Furthermore, it is state of the art for experiment even when the interaction strength is reduced to a very small value.

Access to the Albanian VET System: Social, Individual and School-Based Barriers

ERIC Educational Resources Information Center

Xhumari, Merita; Dibra, Sidita

2016-01-01

This article analyses the determinants of access to the VET system in Albania and its impact on the inclusion of young people and vulnerable groups. The VET system often attracts students who have completed the compulsory levels of education with weak academic results. Many come from families with a low level of income and a low education level.…

White Paper Analysis of Human Resource Policy Considerations of Revitalization of Rural America. HRD & ALL Research Series.

ERIC Educational Resources Information Center

Geroy, Gary D.; Williams, Richard A.

The overall economic well-being of U.S. rural communities is on the decline. Rural America is now dependent on a highly diversified economy, and its problems will not be resolved through improved farm income alone. Various weaknesses in rural development policies must be addressed. The narrow policy focus on attracting manufacturing industries to…

Weak encoding of faces predicts socially influenced judgments of facial attractiveness.

PubMed

Schnuerch, Robert; Koppehele-Gossel, Judith; Gibbons, Henning

2015-01-01

Conforming to the majority can be seen as a heuristic type of judgment, as it allows the individual to easily choose the most accurate or most socially acceptable type of behavior. People who process the currently to-be-judged items in a superficial, heuristic way should tend to conform to group judgment more than people processing these items in a systematic and elaborate way. We investigated this hypothesis using electroencephalography (EEG), analyzing whether the strength of neural encoding of faces was related to the tendency to adopt a group's evaluative judgments regarding these faces. As expected, we found that the amplitude of the N170, a specific neural correlate of face encoding, was inversely related to conformity across participants: The weaker the faces were encoded, the more the majority response regarding the faces' attractiveness was adopted instead of relying on the actual qualities of the faces. Applying neurophysiological methodology, we thus provide support for previous claims, based on behavioral data and theorizing, that social conformity is a heuristic type of judgment. We propose that weak encoding of judgment-relevant information is a typical, possibly even necessary, precursor of socially adjusted judgments, irrespective of one's current motivational goal (i.e., to be accurate or accepted).

Inter-DNA Attraction Mediated by Divalent Counterions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qiu Xiangyun; Andresen, Kurt; Kwok, Lisa W.

2007-07-20

Can nonspecifically bound divalent counterions induce attraction between DNA strands? Here, we present experimental evidence demonstrating attraction between short DNA strands mediated by Mg{sup 2+} ions. Solution small angle x-ray scattering data collected as a function of DNA concentration enable model independent extraction of the second virial coefficient. As the [Mg{sup 2+}] increases, this coefficient turns from positive to negative reflecting the transition from repulsive to attractive inter-DNA interaction. This surprising observation is corroborated by independent light scattering experiments. The dependence of the observed attraction on experimental parameters including DNA length provides valuable clues to its origin.

Evolutionary Diversification of Prey and Predator Species Facilitated by Asymmetric Interactions

PubMed Central

Zu, Jian; Wang, Jinliang; Huang, Gang

2016-01-01

We investigate the influence of asymmetric interactions on coevolutionary dynamics of a predator-prey system by using the theory of adaptive dynamics. We assume that the defense ability of prey and the attack ability of predators all can adaptively evolve, either caused by phenotypic plasticity or by behavioral choice, but there are certain costs in terms of their growth rate or death rate. The coevolutionary model is constructed from a deterministic approximation of random mutation-selection process. To sum up, if prey’s trade-off curve is globally weakly concave, then five outcomes of coevolution are demonstrated, which depend on the intensity and shape of asymmetric predator-prey interactions and predator’s trade-off shape. Firstly, we find that if there is a weakly decelerating cost and a weakly accelerating benefit for predator species, then evolutionary branching in the predator species may occur, but after branching further coevolution may lead to extinction of the predator species with a larger trait value. However, if there is a weakly accelerating cost and a weakly accelerating benefit for predator species, then evolutionary branching in the predator species is also possible and after branching the dimorphic predator can evolutionarily stably coexist with a monomorphic prey species. Secondly, if the asymmetric interactions become a little strong, then prey and predators will evolve to an evolutionarily stable equilibrium, at which they can stably coexist on a long-term timescale of evolution. Thirdly, if there is a weakly accelerating cost and a relatively strongly accelerating benefit for prey species, then evolutionary branching in the prey species is possible and the finally coevolutionary outcome contains a dimorphic prey and a monomorphic predator species. Fourthly, if the asymmetric interactions become more stronger, then predator-prey coevolution may lead to cycles in both traits and equilibrium population densities. The Red Queen dynamic is a possible outcome under asymmetric predator-prey interactions. PMID:27685540

Evolutionary Diversification of Prey and Predator Species Facilitated by Asymmetric Interactions.

PubMed

Zu, Jian; Wang, Jinliang; Huang, Gang

We investigate the influence of asymmetric interactions on coevolutionary dynamics of a predator-prey system by using the theory of adaptive dynamics. We assume that the defense ability of prey and the attack ability of predators all can adaptively evolve, either caused by phenotypic plasticity or by behavioral choice, but there are certain costs in terms of their growth rate or death rate. The coevolutionary model is constructed from a deterministic approximation of random mutation-selection process. To sum up, if prey's trade-off curve is globally weakly concave, then five outcomes of coevolution are demonstrated, which depend on the intensity and shape of asymmetric predator-prey interactions and predator's trade-off shape. Firstly, we find that if there is a weakly decelerating cost and a weakly accelerating benefit for predator species, then evolutionary branching in the predator species may occur, but after branching further coevolution may lead to extinction of the predator species with a larger trait value. However, if there is a weakly accelerating cost and a weakly accelerating benefit for predator species, then evolutionary branching in the predator species is also possible and after branching the dimorphic predator can evolutionarily stably coexist with a monomorphic prey species. Secondly, if the asymmetric interactions become a little strong, then prey and predators will evolve to an evolutionarily stable equilibrium, at which they can stably coexist on a long-term timescale of evolution. Thirdly, if there is a weakly accelerating cost and a relatively strongly accelerating benefit for prey species, then evolutionary branching in the prey species is possible and the finally coevolutionary outcome contains a dimorphic prey and a monomorphic predator species. Fourthly, if the asymmetric interactions become more stronger, then predator-prey coevolution may lead to cycles in both traits and equilibrium population densities. The Red Queen dynamic is a possible outcome under asymmetric predator-prey interactions.

Strong FANCA/FANCG but weak FANCA/FANCC interaction in the yeast 2-hybrid system.

PubMed

Reuter, T; Herterich, S; Bernhard, O; Hoehn, H; Gross, H J

2000-01-15

Three of at least 8 Fanconi anemia (FA) genes have been cloned (FANCA, FANCC, FANCG), but their functions remain unknown. Using the yeast 2-hybrid system and full-length cDNA, the authors found a strong interaction between FANCA and FANCG proteins. They also obtained evidence for a weak interaction between FANCA and FANCC. Neither FANCA nor FANCC was found to interact with itself. These results support the notion of a functional association between the FA gene products. (Blood. 2000;95:719-720)

Dispersions of attractive semiflexible fiberlike colloidal particles from bacterial cellulose microfibrils.

PubMed

Kuijk, Anke; Koppert, Remco; Versluis, Peter; van Dalen, Gerard; Remijn, Caroline; Hazekamp, Johan; Nijsse, Jaap; Velikov, Krassimir P

2013-11-26

We prepared dispersions from bacterial cellulose microfibrils (CMF) of a commercial Nata de Coco source. We used an ultra-high-energy mechanical deagglomeration process that is able to disperse the CMFs from the pellicle in which they are organized in an irregular network. Because of the strong attractions between the CMFs, the dispersion remained highly heterogeneous, consisting of fiber bundles, flocs, and voids spanning tens to hundreds of micrometers depending on concentration. The size of these flocs increased with CMF concentration, the size of the bundles stayed constant, and the size of the voids decreased. The observed percolation threshold in MFC dispersions is lower than the theoretical prediction, which is accounted for by the attractive interactions in the system. Because bacterial cellulose is chemically very pure, it can be used to study the interaction of attractive and highly shape-anisotropic, semiflexible fiberlike colloidal particles.

Interactions for pollinator visitation and their consequences for reproduction in a plant community

NASA Astrophysics Data System (ADS)

Hegland, Stein Joar; Totland, Ørjan

2012-08-01

Competition and facilitation in species interactions attract much attention in ecology, but their relative importance has seldom been evaluated in a community context. We assessed competitive and facilitative interactions for pollinator visitation among co-flowering species in a plant community, investigated the subsequent consequences for plant reproduction, and investigated whether effects could be trait-based. We removed the flowers of two species attractive to pollinators, in two separate experiments and assessed the effects on pollinator visitation rates and components of reproductive success in 11 co-flowering focal herb species. Overall, most focal species appear not to interact with the removal species with respect to pollinator visitation and subsequent reproduction (neutral interactions). Three focal species in the community had significantly higher reproductive responses (fruit production and seed weight) in the presence of the attractive removal species (facilitative interactions), but species interaction effects were less pronounced in species' flower visitation rates. A community-wide meta-analysis demonstrated that the two experiments did not have a significant effect on either facilitation or competition, and that there was no overall correlation between effect sizes for visitation and reproduction. Based on species-specific responses, it seems likely that floral traits such as similar flower colors contribute to interspecific facilitation of pollinator visitation and, in particular, that high pollinator dependence for plant reproduction, and associated pollen limitation, may contribute to subsequent interaction effects on reproduction in the focal species.

Adopting a dyadic perspective to better understand the association between physical attractiveness and dieting motivations and behaviors.

PubMed

Reynolds, Tania; Meltzer, Andrea L

2017-09-01

The relationship between women's objective physical attractiveness and their dieting motivations and behaviors may depend upon their social environment-specifically, their romantic partners' attractiveness-such that less attractive women with more attractive partners may be particularly motivated to diet. Theoretically, men's dieting motivations should not depend on their partners' attractiveness. We tested this possibility using a sample of 223 U.S. newlywed spouses. After completing measures assessing dieting motivations, each participant was photographed; we used those photographs to code spouses' objective facial and body attractiveness. Results demonstrated that own and partner attractiveness interacted to predict only women's dieting motivations and behaviors. Less attractive wives married to more (versus less) attractive husbands reported more dieting motivations and behaviors. In contrast, men's dieting motivations were not significantly associated with their own and their partners' attractiveness. These findings highlight the value of adopting a dyadic approach to understanding dieting motivations. Copyright © 2017 Elsevier Ltd. All rights reserved.

Measurement of the Parity-Violating Neutron Spin Rotation in 4He

PubMed Central

Bass, C. D.; Dawkins, J. M.; Luo, D.; Micherdzinska, A.; Sarsour, M.; Snow, W. M.; Mumm, H. P.; Nico, J. S.; Huffman, P. R.; Markoff, D. M.; Heckel, B. R.; Swanson, H. E.

2005-01-01

In the meson exchange model of weak nucleon-nucleon (NN) interactions, the exchange of virtual mesons between the nucleons is parameterized by a set of weak meson exchange amplitudes. The strengths of these amplitudes from theoretical calculations are not well known, and experimental measurements of parity-violating (PV) observables in different nuclear systems have not constrained their values. Transversely polarized cold neutrons traveling through liquid helium experience a PV spin rotation due to the weak interaction with an angle proportional to a linear combination of these weak meson exchange amplitudes. A measurement of the PV neutron spin rotation in helium (φPV (n,α)) would provide information about the relative strengths of the weak meson exchange amplitudes, and with the longitudinal analyzing power measurement in the p + α system, allow the first comparison between isospin mirror systems in weak NN interaction. An earlier experiment performed at NIST obtained a result consistent with zero: φPV (n,α) = (8.0 ±14(stat) ±2.2(syst)) ×10−7 rad / m[1]. We describe a modified apparatus using a superfluid helium target to increase statistics and reduce systematic effects in an effort to reach a sensitivity goal of 10−7 rad/m. PMID:27308122

The effects of facial adiposity on attractiveness and perceived leadership ability.

PubMed

Re, Daniel E; Perrett, David I

2014-01-01

Facial attractiveness has a positive influence on electoral success both in experimental paradigms and in the real world. One parameter that influences facial attractiveness and social judgements is facial adiposity (a facial correlate to body mass index, BMI). Overweight people have high facial adiposity and are perceived to be less attractive and lower in leadership ability. Here, we used an interactive design in order to assess whether the most attractive level of facial adiposity is also perceived as most leader-like. We found that participants reduced facial adiposity more to maximize attractiveness than to maximize perceived leadership ability. These results indicate that facial appearance impacts leadership judgements beyond the effects of attractiveness. We suggest that the disparity between optimal facial adiposity in attractiveness and leadership judgements stems from social trends that have produced thin ideals for attractiveness, while leadership judgements are associated with perception of physical dominance.

Weakly Hydrated Surfaces and the Binding Interactions of Small Biological Solutes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brady, J. W.; Tavagnacco, L.; Ehrlich, L.

2012-04-01

Extended planar hydrophobic surfaces, such as are found in the side chains of the amino acids histidine, phenylalanine, tyrosine, and tryptophan, exhibit an affinity for the weakly hydrated faces of glucopyranose. In addition, molecular species such as these, including indole, caffeine, and imidazole, exhibit a weak tendency to pair together by hydrophobic stacking in aqueous solution. These interactions can be partially understood in terms of recent models for the hydration of extended hydrophobic faces and should provide insight into the architecture of sugar-binding sites in proteins.

Weakly hydrated surfaces and the binding interactions of small biological solutes.

PubMed

Brady, John W; Tavagnacco, Letizia; Ehrlich, Laurent; Chen, Mo; Schnupf, Udo; Himmel, Michael E; Saboungi, Marie-Louise; Cesàro, Attilio

2012-04-01

Extended planar hydrophobic surfaces, such as are found in the side chains of the amino acids histidine, phenylalanine, tyrosine, and tryptophan, exhibit an affinity for the weakly hydrated faces of glucopyranose. In addition, molecular species such as these, including indole, caffeine, and imidazole, exhibit a weak tendency to pair together by hydrophobic stacking in aqueous solution. These interactions can be partially understood in terms of recent models for the hydration of extended hydrophobic faces and should provide insight into the architecture of sugar-binding sites in proteins.

Molecular dynamics simulations study of nano bubble attachment at hydrophobic surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Jiaqi; Dang, Liem X.; Miller, Jan D.

Bubble attachment phenomena are examined using Molecular Dynamics Simulations (MDS) for the first time. The simulation involves a nitrogen nano bubble containing 906 nitrogen molecules in a water phase with 74,000 water molecules at molybdenite surfaces. During a simulation period of 1 ns, film rupture and displacement occurs. The attached nanobubble at the hydrophobic molybdenite face surface results in a contact angle of about 90º. This spontaneous attachment is due to a “water exclusion zone” at the molybdenite face surface and can be explained by a van der Waals (vdW) attractive force, as discussed in the literature. In contrast, themore » film is stable at the hydrophilic quartz (001) surface and the bubble does not attach. Contact angles determined from MD simulations are reported, and these results agree well with experimental and MDS sessile drop results. In this way, film stability and bubble attachment are described with respect to interfacial water structure for surfaces of different polarity. Interfacial water molecules at the hydrophobic molybdenite face surface have relatively weak interactions with the surface when compared to the hydrophilic quartz (001) surface, as revealed by the presence of a 3 Å “water exclusion zone” at the molybdenite/water interface. The molybdenite armchair-edge and zigzag-edge surfaces show a comparably slow process for film rupture and displacement when compared to the molybdenite face surface, which is consistent with their relatively weak hydrophobic character.« less

Effects of muscle dysmorphia, social comparisons and body schema priming on desire for social interaction: an experimental approach.

PubMed

Schneider, Catharina; Agthe, Maria; Yanagida, Takuya; Voracek, Martin; Hennig-Fast, Kristina

2017-06-15

Muscle dysmorphia (MD) is a relatively young diagnosis referring to the desire for a high degree in lean muscle mass, while simultaneously believing that one is insufficiently muscular, mostly found in men. It goes along with a risk for social withdrawal to maintain rigid exercise and dietary regimen. The aim of the current study was thus, to explore differences in men with and without a risk for muscle dysmorphia regarding their desire for social interaction. Furthermore, we investigated potential effects of individual social comparison tendencies (the tendency to compare oneself with persons who are perceived to be superior or inferior to oneself on a certain dimension) and of one's own body schema on the desire for social interaction. One hundred physically active, college aged Austrian men were recruited via social media and flyers at fitness centers and the sports department of the University of Vienna. Participants were randomly assigned to a priming condition evoking their own body schema or a control condition and had to state their desire for social interaction with male or female stimulus persons of high or average attractiveness. We conducted a 2 (group of participant; men with vs. without a risk for MD) × 2 (priming condition; priming vs. non-priming) × 2 (attractiveness of stimulus person; highly attractive vs. less attractive) experimental design with different social comparison tendencies as covariates. Men with a risk for muscle dysmorphia showed lesser desire for social interaction than men without this risk, which can be seen as a risk factor for psychopathological outcomes. Generally, men with and without a risk for muscle dysmorphia did not differ with regard to their preferences for attractive stimulus persons as subjects for social interaction. We confirmed the notion that a tendency for downward social comparisons goes along with a diminished desire for social interaction. This study showed that men with a risk for muscle dysmorphia appeared to be at higher risk for social withdrawal and that this is associated with social comparison tendencies. Future investigations on clinical populations are needed, for this population is highly prone to social isolation and negative outcomes related to it.

Weak Higher-Order Interactions in Macroscopic Functional Networks of the Resting Brain.

PubMed

Huang, Xuhui; Xu, Kaibin; Chu, Congying; Jiang, Tianzi; Yu, Shan

2017-10-25

Interactions among different brain regions are usually examined through functional connectivity (FC) analysis, which is exclusively based on measuring pairwise correlations in activities. However, interactions beyond the pairwise level, that is, higher-order interactions (HOIs), are vital in understanding the behavior of many complex systems. So far, whether HOIs exist among brain regions and how they can affect the brain's activities remains largely elusive. To address these issues, here, we analyzed blood oxygenation level-dependent (BOLD) signals recorded from six typical macroscopic functional networks of the brain in 100 human subjects (46 males and 54 females) during the resting state. Through examining the binarized BOLD signals, we found that HOIs within and across individual networks were both very weak regardless of the network size, topology, degree of spatial proximity, spatial scales, and whether the global signal was regressed. To investigate the potential mechanisms underlying the weak HOIs, we analyzed the dynamics of a network model and also found that HOIs were generally weak within a wide range of key parameters provided that the overall dynamic feature of the model was similar to the empirical data and it was operating close to a linear fluctuation regime. Our results suggest that weak HOI may be a general property of brain's macroscopic functional networks, which implies the dominance of pairwise interactions in shaping brain activities at such a scale and warrants the validity of widely used pairwise-based FC approaches. SIGNIFICANCE STATEMENT To explain how activities of different brain areas are coordinated through interactions is essential to revealing the mechanisms underlying various brain functions. Traditionally, such an interaction structure is commonly studied using pairwise-based functional network analyses. It is unclear whether the interactions beyond the pairwise level (higher-order interactions or HOIs) play any role in this process. Here, we show that HOIs are generally weak in macroscopic brain networks. We also suggest a possible dynamical mechanism that may underlie this phenomenon. These results provide plausible explanation for the effectiveness of widely used pairwise-based approaches in analyzing brain networks. More importantly, it reveals a previously unknown, simple organization of the brain's macroscopic functional systems. Copyright © 2017 the authors 0270-6474/17/3710481-17$15.00/0.

Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors.

PubMed

Wang, Qisi; Park, J T; Feng, Yu; Shen, Yao; Hao, Yiqing; Pan, Bingying; Lynn, J W; Ivanov, A; Chi, Songxue; Matsuda, M; Cao, Huibo; Birgeneau, R J; Efremov, D V; Zhao, Jun

2016-05-13

An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s_{±} or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T_{c} in the S-doped iron selenide superconductors K_{x}Fe_{2-y}(Se_{1-z}S_{z})_{2}. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.

Cooper-pair-condensate fluctuations and plasmons in layered superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cote, R.; Griffin, A.

1993-10-01

Starting from a given attractive potential, we give a systematic analysis of the spin-singlet [ital s]-wave Cooper-pair-condensate fluctuations in a two-dimensional (2D) superconductor. These results are applied to a superlattice of superconducting sheets in which the 2D charge fluctuations are coupled via the Coulomb interaction. Our main interest is how the low-energy Anderson-Bogoliubov (AB) phonon mode in the pair-breaking gap [omega][lt]2[Delta] is modified by the Coulomb interaction. Our formal analysis is valid at arbitrary temperatures. It describes the weakly bound, large-Cooper-pair limit as well as the strongly bound, small-Cooper-pair limit and thus includes both the BCS and Bose-Einstein scenarios (asmore » discussed by Nozieres and Schmitt-Rink as well as Randeira [ital et] [ital al].). A comlete normal-mode analysis is given for a charged BCS superconductor, showing how the repulsive (Coulomb) interaction modifies the collective modes of a neutral superconductor. This complements the recent numerical study carried out by Fertig and Das Sarma. We show that the pair-response function shares the same spectrum as the charge-response function, given by the zero of the longitudinal dielectric function [epsilon]([bold q],[omega]). In 2D and layered superconductors, there is a low-frequency and high-frequency plasmon branch, separated by a relatively narrow particle-hole continuum at around 2[Delta]. The low-frequency ([omega][lt]2[Delta]) plasmon branch is a renormalized version of the AB phonon mode.« less

Study and selection of in vivo protein interactions by coupling bimolecular fluorescence complementation and flow cytometry.

PubMed

Morell, Montse; Espargaro, Alba; Aviles, Francesc Xavier; Ventura, Salvador

2008-01-01

We present a high-throughput approach to study weak protein-protein interactions by coupling bimolecular fluorescent complementation (BiFC) to flow cytometry (FC). In BiFC, the interaction partners (bait and prey) are fused to two rationally designed fragments of a fluorescent protein, which recovers its function upon the binding of the interacting proteins. For weak protein-protein interactions, the detected fluorescence is proportional to the interaction strength, thereby allowing in vivo discrimination between closely related binders with different affinity for the bait protein. FC provides a method for high-speed multiparametric data acquisition and analysis; the assay is simple, thousands of cells can be analyzed in seconds and, if required, selected using fluorescence-activated cell sorting (FACS). The combination of both methods (BiFC-FC) provides a technically straightforward, fast and highly sensitive method to validate weak protein interactions and to screen and identify optimal ligands in biologically synthesized libraries. Once plasmids encoding the protein fusions have been obtained, the evaluation of a specific interaction, the generation of a library and selection of active partners using BiFC-FC can be accomplished in 5 weeks.

Attractiveness, diagnostic ambiguity, and disability cues impact perceptions of women with pain.

PubMed

LaChapelle, Diane L; Lavoie, Susan; Higgins, Nancy C; Hadjistavropoulos, Thomas

2014-05-01

This experimental study investigated how physical attractiveness, disability cue, and diagnostic ambiguity stereotypes impact perceptions of a patient's pain/disability and personality. After viewing photographs of women pictured with or without a cane, accompanied by descriptions of the women's diagnosis (fibromyalgia or rheumatoid arthritis), 147 university students rated the women's pain/disability and personality. Analyses revealed that more attractive women received lower ratings on pain/disability and higher ratings (more positive) on personality. Moreover, those pictured with a disability cue got higher ratings on both pain/disability and personality, and those with medical evidence of pathology (less ambiguity) got higher ratings on pain/disability and lower ratings on personality. Examination of the 3 stereotypes in a single study enabled an evaluation of their interactions. An Attractiveness × Disability Cue × Diagnostic Ambiguity interaction for ratings of pain/disability revealed that the presence of both medical evidence and a disability cue were needed to override the strong "beautiful is healthy" stereotype. Significant 2-way interactions for ratings of personality indicated that the impact of the disability stereotype tends to be overshadowed by the attractiveness stereotype. The results indicate that these stereotypes have a large effect on perceptions of women with chronic pain and that attractiveness, a contextual variable unrelated to the pain experience, exerts an even stronger effect when there is less objective information available. This could have clinical ramifications for assessment and treatment of patients with chronic pain, which often occurs in the absence of "objective" medical evidence or any external cues of disability. (c) 2014 APA, all rights reserved.

Non-equilibrium dynamics of artificial quantum matter

NASA Astrophysics Data System (ADS)

Babadi, Mehrtash

The rapid progress of the field of ultracold atoms during the past two decades has set new milestones in our control over matter. By cooling dilute atomic gases and molecules to nano-Kelvin temperatures, novel quantum mechanical states of matter can be realized and studied on a table-top experimental setup while bulk matter can be tailored to faithfully simulate abstract theoretical models. Two of such models which have witnessed significant experimental and theoretical attention are (1) the two-component Fermi gas with resonant s-wave interactions, and (2) the single-component Fermi gas with dipole-dipole interactions. This thesis is devoted to studying the non-equilibrium collective dynamics of these systems using the general framework of quantum kinetic theory. We present a concise review of the utilized mathematical methods in the first two chapters, including the Schwinger-Keldysh formalism of non-equilibrium quantum fields, two-particle irreducible (2PI) effective actions and the framework of quantum kinetic theory. We study the collective dynamics of the dipolar Fermi gas in a quasi-two-dimensional optical trap in chapter 3 and provide a detailed account of its dynamical crossover from the collisionless to the hydrodynamical regime. Chapter 4 is devoted to studying the dynamics of the attractive Fermi gas in the normal phase. Starting from the self-consistent T-matrix (pairing fluctuation) approximation, we systematically derive a set of quantum kinetic equations and show that they provide a globally valid description of the dynamics of the attractive Fermi gas, ranging from the weak-coupling Fermi liquid phase to the intermediate non-Fermi liquid pairing pseudogap regime and finally the strong-coupling Bose liquid phase. The shortcomings of the self-consistent T-matrix approximation in two spatial dimensions are discussed along with a proposal to overcome its unphysical behaviors. The developed kinetic formalism is finally utilized to reproduce and interpret the findings of a recent experiment done on the collective dynamics of trapped two-dimensional ultracold gases.

Light weakly interacting massive particles

NASA Astrophysics Data System (ADS)

Gelmini, Graciela B.

2017-08-01

Light weakly interacting massive particles (WIMPs) are dark matter particle candidates with weak scale interaction with the known particles, and mass in the GeV to tens of GeV range. Hints of light WIMPs have appeared in several dark matter searches in the last decade. The unprecedented possible coincidence into tantalizingly close regions of mass and cross section of four separate direct detection experimental hints and a potential indirect detection signal in gamma rays from the galactic center, aroused considerable interest in our field. Even if these hints did not so far result in a discovery, they have had a significant impact in our field. Here we review the evidence for and against light WIMPs as dark matter candidates and discuss future relevant experiments and observations.

Highly anisotropic exchange interactions of j eff = 1 2 iridium moments on the fcc lattice in La 2 B IrO 6   ( B = Mg , Zn )

DOE PAGES

Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

2016-06-20

Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $$_2$$ZnIrO$$_6$$ and La$$_2$$MgIrO$$_6$$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

Spinon attraction in spin- 1/2 antiferromagnetic chains.

PubMed

Bernevig, B A; Giuliano, D; Laughlin, R B

2001-04-09

We derive the representation of the two-spinon wave function for the Haldane-Shastry model in terms of the spinon coordinates. This result allows us to rigorously analyze spinon interaction and its physical effects. We show that spinons attract one another. The attraction gets stronger as the size of the system is increased and, in the thermodynamic limit, determines the power law with which the susceptibility diverges.

Mean-field behavior in coupled oscillators with attractive and repulsive interactions.

PubMed

Hong, Hyunsuk; Strogatz, Steven H

2012-05-01

We consider a variant of the Kuramoto model of coupled oscillators in which both attractive and repulsive pairwise interactions are allowed. The sign of the coupling is assumed to be a characteristic of a given oscillator. Specifically, some oscillators repel all the others, thus favoring an antiphase relationship with them. Other oscillators attract all the others, thus favoring an in-phase relationship. The Ott-Antonsen ansatz is used to derive the exact low-dimensional dynamics governing the system's long-term macroscopic behavior. The resulting analytical predictions agree with simulations of the full system. We explore the effects of changing various parameters, such as the width of the distribution of natural frequencies and the relative strengths and proportions of the positive and negative interactions. For the particular model studied here we find, unexpectedly, that the mixed interactions produce no new effects. The system exhibits conventional mean-field behavior and displays a second-order phase transition like that found in the original Kuramoto model. In contrast to our recent study of a different model with mixed interactions [Phys. Rev. Lett. 106, 054102 (2011)], the π state and traveling-wave state do not appear for the coupling type considered here.

Statistical Analyses of Hydrophobic Interactions: A Mini-Review

DOE PAGES

Pratt, Lawrence R.; Chaudhari, Mangesh I.; Rempe, Susan B.

2016-07-14

Here this review focuses on the striking recent progress in solving for hydrophobic interactions between small inert molecules. We discuss several new understandings. First, the inverse temperature phenomenology of hydrophobic interactions, i.e., strengthening of hydrophobic bonds with increasing temperature, is decisively exhibited by hydrophobic interactions between atomic-scale hard sphere solutes in water. Second, inclusion of attractive interactions associated with atomic-size hydrophobic reference cases leads to substantial, nontrivial corrections to reference results for purely repulsive solutes. Hydrophobic bonds are weakened by adding solute dispersion forces to treatment of reference cases. The classic statistical mechanical theory for those corrections is not accuratemore » in this application, but molecular quasi-chemical theory shows promise. Lastly, because of the masking roles of excluded volume and attractive interactions, comparisons that do not discriminate the different possibilities face an interpretive danger.« less

Female parity, maternal kinship, infant age and sex influence natal attraction and infant handling in a wild colobine (Colobus vellerosus).

PubMed

Bădescu, Iulia; Sicotte, Pascale; Ting, Nelson; Wikberg, Eva C

2015-04-01

Primate females often inspect, touch and groom others' infants (natal attraction) and they may hold and carry these infants in a manner resembling maternal care (infant handling). While natal attraction and infant handling occur in most wild colobines, little is known about the factors influencing the expression of these behaviors. We examined the effects of female parity, kinship, and dominance rank, as well as infant age and sex in wild Colobus vellerosus at Boabeng-Fiema Monkey Sanctuary, Ghana. We collected data via focal sampling of females in 2008 and 2009 (N = 61) and of infants in 2010 (N = 12). Accounting for the individuals who interacted with our focal subjects, this study includes 74 females and 66 infants in 8 groups. We recorded female agonistic interactions ad libitum to determine dominance ranks. We used partial pedigree information and genotypes at 17 short tandem repeat loci to determine kinship. We knew female parity, infant age and sex from demographic records. Nulliparous females showed more natal attraction and infant handling than parous females, which may suggest that interactions with infants are more adaptive for nulliparous females because they learn mothering skills through these behaviors. Compared to non-kin, maternal kin were more likely to handle infants. Maternal kin may be permitted greater access to infants because mothers are most familiar with them. Handlers may incur inclusive fitness benefits from infant handling. Dominance rank did not affect female interactions with infants. The youngest infants received the most natal attraction and infant handling, and male infants were handled more than female infants. The potential benefits of learning to mother and inclusive fitness, in combination with the relatively low costs of natal attraction and infant handling, may explain the high rates of these behaviors in many colobines. © 2014 Wiley Periodicals, Inc.

Small-Angle Neutron Scattering Study of Interplay of Attractive and Repulsive Interactions in Nanoparticle-Polymer System.

PubMed

Kumar, Sugam; Aswal, Vinod K; Kohlbrecher, Joachim

2016-02-16

The phase behavior of nanoparticle (silica)-polymer (polyethylene glycol) system without and with an electrolyte (NaCl) has been studied. It is observed that nanoparticle-polymer system behaves very differently in the presence of electrolyte. In the absence of electrolyte, the nanoparticle-polymer system remains in one-phase even at very high polymer concentrations. On the other hand, a re-entrant phase behavior is found in the presence of electrolyte, where one-phase (individual) system undergoes two-phase (nanoparticle aggregation) and then back to one-phase with increasing polymer concentration. The regime of two-phase system has been tuned by varying the electrolyte concentration. The polymer concentration range over which the two-phase system exists is significantly enhanced with the increase in the electrolyte concentration. These systems have been characterized by small-angle neutron scattering (SANS) experiments of contrast-marching the polymer to the solvent. The data are modeled using a two-Yukawa potential accounting for both attractive and repulsive parts of the interaction between nanoparticles. The phase behavior of nanoparticle-polymer system is explained by interplay of attractive (polymer-induced attractive depletion between nanoparticles) and repulsive (nanoparticle-nanoparticle electrostatic repulsion and polymer-polymer repulsion) interactions present in the system. In the absence of electrolyte, the strong electrostatic repulsion between nanoparticles dominates over the polymer-induced depletion attraction and the nanoparticle system remains in one-phase. With addition of electrolyte, depletion attraction overcomes electrostatic repulsion at some polymer concentration, resulting into nanoparticle aggregation and two-phase system. Further addition of polymer increases the polymer-polymer repulsion which eventually reduces the strength of depletion and hence re-entrant phase behavior. The effects of varying electrolyte concentration on the phase behavior of nanoparticle-polymer system are understood in terms of modifications in nanoparticle-nanoparticle and polymer-polymer interactions. The nanoparticle aggregates in two-phase systems are found to have surface fractal morphology.

E2 enzyme inhibition by stabilization of a low affinity interface with ubiquitin

PubMed Central

St-Cyr, Daniel J.; Ziemba, Amy; Garg, Pankaj; Plamondon, Serge; Auer, Manfred; Sidhu, Sachdev; Marinier, Anne; Kleiger, Gary; Tyers, Mike; Sicheri, Frank

2014-01-01

Weak protein interactions between ubiquitin and the ubiquitin-proteasome system (UPS) enzymes that mediate its covalent attachment to substrates serve to position ubiquitin for optimal catalytic transfer. We show that a small molecule inhibitor of the E2 ubiquitin conjugating enzyme Cdc34A, called CC0651, acts by trapping a weak interaction between ubiquitin and the E2 donor ubiquitin binding site. A structure of the ternary CC0651-Cdc34A-ubiquitin complex reveals that the inhibitor engages a composite binding pocket formed from Cdc34A and ubiquitin. CC0651 also suppresses the spontaneous hydrolysis rate of the Cdc34A-ubiquitin thioester, without overtly affecting the interaction between Cdc34A and the RING domain subunit of the E3 enzyme. Stabilization of the numerous other weak interactions between ubiquitin and UPS enzymes by small molecules may be a feasible strategy to selectively inhibit different UPS activities. PMID:24316736

From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

PubMed Central

Kanduč, Matej; Netz, Roland R.

2015-01-01

Using all-atom molecular dynamics (MD) simulations at constant water chemical potential in combination with basic theoretical arguments, we study hydration-induced interactions between two overall charge-neutral yet polar planar surfaces with different wetting properties. Whether the water film between the two surfaces becomes unstable below a threshold separation and cavitation gives rise to long-range attraction, depends on the sum of the two individual surface contact angles. Consequently, cavitation-induced attraction also occurs for a mildly hydrophilic surface interacting with a very hydrophobic surface. If both surfaces are very hydrophilic, hydration repulsion dominates at small separations and direct attractive force contribution can—if strong enough—give rise to wet adhesion in this case. In between the regimes of cavitation-induced attraction and hydration repulsion we find a narrow range of contact angle combinations where the surfaces adhere at contact in the absence of cavitation. This dry adhesion regime is driven by direct surface–surface interactions. We derive simple laws for the cavitation transition as well as for the transition between hydration repulsion and dry adhesion, which favorably compare with simulation results in a generic adhesion state diagram as a function of the two surface contact angles. PMID:26392526

Perceptions of plagiarisers: The influence of target physical attractiveness, transgression severity, and sex on attributions of guilt and punishment.

PubMed

Swami, Viren; Arthey, Elizabeth; Furnham, Adrian

2017-09-01

The attractiveness-leniency effect (ALE) suggests that physically attractive targets are less likely to be perceived as guilty compared to less attractive targets. Here, we tested the ALE in relation to attributions of students who have committed plagiarism. British adults (N=165) were shown one of eight vignette-photograph pairings varying in target sex (female/male), physical attractiveness (high/low), and transgression severity (serious/minor), and provided attributions of guilt and severity of punishment. Analyses of variance revealed significant interactions between attractiveness and transgression severity for both dependent measures. Attractive targets were perceived as guiltier and deserving of more severe punishments in the serious transgression condition, but there was no significant difference between attractive and less attractive targets in the minor transgression condition. These results are discussed in terms of a reverse attribution bias, in which attractive individuals are judged more negatively when they fail to live up to higher standards of conduct. Copyright © 2017 Elsevier Ltd. All rights reserved.

Facial attractiveness is related to women's cortisol and body fat, but not with immune responsiveness.

PubMed

Rantala, Markus J; Coetzee, Vinet; Moore, Fhionna R; Skrinda, Ilona; Kecko, Sanita; Krama, Tatjana; Kivleniece, Inese; Krams, Indrikis

2013-08-23

Recent studies suggest that facial attractiveness indicates immune responsiveness in men and that this relationship is moderated by stress hormones which interact with testosterone levels. However, studies testing whether facial attractiveness in women signals their immune responsiveness are lacking. Here, we photographed young Latvian women, vaccinated them against hepatitis B and measured the amount of specific antibodies produced, cortisol levels and percentage body fat. Latvian men rated the attractiveness of the women's faces. Interestingly, in women, immune responsiveness (amount of antibodies produced) did not predict facial attractiveness. Instead, plasma cortisol level was negatively associated with attractiveness, indicating that stressed women look less attractive. Fat percentage was curvilinearly associated with facial attractiveness, indicating that being too thin or too fat reduces attractiveness. Our study suggests that in contrast to men, facial attractiveness in women does not indicate immune responsiveness against hepatitis B, but is associated with two other aspects of long-term health and fertility: circulating levels of the stress hormone cortisol and percentage body fat.

Expansion or extinction: deterministic and stochastic two-patch models with Allee effects.

PubMed

Kang, Yun; Lanchier, Nicolas

2011-06-01

We investigate the impact of Allee effect and dispersal on the long-term evolution of a population in a patchy environment. Our main focus is on whether a population already established in one patch either successfully invades an adjacent empty patch or undergoes a global extinction. Our study is based on the combination of analytical and numerical results for both a deterministic two-patch model and a stochastic counterpart. The deterministic model has either two, three or four attractors. The existence of a regime with exactly three attractors only appears when patches have distinct Allee thresholds. In the presence of weak dispersal, the analysis of the deterministic model shows that a high-density and a low-density populations can coexist at equilibrium in nearby patches, whereas the analysis of the stochastic model indicates that this equilibrium is metastable, thus leading after a large random time to either a global expansion or a global extinction. Up to some critical dispersal, increasing the intensity of the interactions leads to an increase of both the basin of attraction of the global extinction and the basin of attraction of the global expansion. Above this threshold, for both the deterministic and the stochastic models, the patches tend to synchronize as the intensity of the dispersal increases. This results in either a global expansion or a global extinction. For the deterministic model, there are only two attractors, while the stochastic model no longer exhibits a metastable behavior. In the presence of strong dispersal, the limiting behavior is entirely determined by the value of the Allee thresholds as the global population size in the deterministic and the stochastic models evolves as dictated by their single-patch counterparts. For all values of the dispersal parameter, Allee effects promote global extinction in terms of an expansion of the basin of attraction of the extinction equilibrium for the deterministic model and an increase of the probability of extinction for the stochastic model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pratt, Lawrence R.; Chaudhari, Mangesh I.; Rempe, Susan B.

Here this review focuses on the striking recent progress in solving for hydrophobic interactions between small inert molecules. We discuss several new understandings. First, the inverse temperature phenomenology of hydrophobic interactions, i.e., strengthening of hydrophobic bonds with increasing temperature, is decisively exhibited by hydrophobic interactions between atomic-scale hard sphere solutes in water. Second, inclusion of attractive interactions associated with atomic-size hydrophobic reference cases leads to substantial, nontrivial corrections to reference results for purely repulsive solutes. Hydrophobic bonds are weakened by adding solute dispersion forces to treatment of reference cases. The classic statistical mechanical theory for those corrections is not accuratemore » in this application, but molecular quasi-chemical theory shows promise. Lastly, because of the masking roles of excluded volume and attractive interactions, comparisons that do not discriminate the different possibilities face an interpretive danger.« less

Switching between attractive and repulsive Coulomb-interaction-mediated drag in an ambipolar GaAs/AlGaAs bilayer device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, B.; Croxall, A. F.; Waldie, J., E-mail: jw353@cam.ac.uk

2016-02-08

We present measurements of Coulomb drag in an ambipolar GaAs/AlGaAs double quantum well structure that can be configured as both an electron-hole bilayer and a hole-hole bilayer, with an insulating barrier of only 10 nm between the two quantum wells. Coulomb drag resistivity is a direct measure of the strength of interlayer particle-particle interactions. We explore the strongly interacting regime of low carrier densities (2D interaction parameter r{sub s} up to 14). Our ambipolar device design allows a comparison between the effects of the attractive electron-hole and repulsive hole-hole interactions and also shows the effects of the different effective masses ofmore » electrons and holes in GaAs.« less

Structure-directing weak phosphoryl XH...O=P (X = C, N) hydrogen bonds in cyclic oxazaphospholidines and oxazaphosphinanes.

PubMed

van der Lee, A; Rolland, M; Marat, X; Virieux, D; Volle, J N; Pirat, J L

2008-04-01

The structures of six cyclic oxazaphospholidines and three cyclic oxazaphosphinanes have been determined and their supramolecular structures have been compared. The molecules differ with respect to the functional groups attached to the central five- or six-membered rings, but have one phosphoryl group in common. The predominant feature in the supramolecular structures is the existence of relatively weak intermolecular phosphoryl XH...O=P (X = C, N) hydrogen bonds, creating in nearly all cases linear zigzag or double molecular chains. The molecular chains are in general linked to each other via very weak CH...pi or usual hydrogen-bond interactions. A survey of the Cambridge Structural Database on similar XH...O=P interactions shows a very large flexibility of the XH...O angle, which is in agreement with the DFT calculation reported elsewhere. The strength of the XH...O=P interaction can therefore be considered as relatively weak to moderately strong, and is expected to play at least a role in the formation of secondary substructures.

Effective interactions in lysozyme aqueous solutions: a small-angle neutron scattering and computer simulation study.

PubMed

Abramo, M C; Caccamo, C; Costa, D; Pellicane, G; Ruberto, R; Wanderlingh, U

2012-01-21

We report protein-protein structure factors of aqueous lysozyme solutions at different pH and ionic strengths, as determined by small-angle neutron scattering experiments. The observed upturn of the structure factor at small wavevectors, as the pH increases, marks a crossover between two different regimes, one dominated by repulsive forces, and another one where attractive interactions become prominent, with the ensuing development of enhanced density fluctuations. In order to rationalize such experimental outcome from a microscopic viewpoint, we have carried out extensive simulations of different coarse-grained models. We have first studied a model in which macromolecules are described as soft spheres interacting through an attractive r(-6) potential, plus embedded pH-dependent discrete charges; we show that the uprise undergone by the structure factor is qualitatively predicted. We have then studied a Derjaguin-Landau-Verwey-Overbeek (DLVO) model, in which only central interactions are advocated; we demonstrate that this model leads to a protein-rich/protein-poor coexistence curve that agrees quite well with the experimental counterpart; experimental correlations are instead reproduced only at low pH and ionic strengths. We have finally investigated a third, "mixed" model in which the central attractive term of the DLVO potential is imported within the distributed-charge approach; it turns out that the different balance of interactions, with a much shorter-range attractive contribution, leads in this latter case to an improved agreement with the experimental crossover. We discuss the relationship between experimental correlations, phase coexistence, and features of effective interactions, as well as possible paths toward a quantitative prediction of structural properties of real lysozyme solutions. © 2012 American Institute of Physics

Lipid membrane-mediated attraction between curvature inducing objects

NASA Astrophysics Data System (ADS)

van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.

2016-09-01

The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles.

Measured long-range repulsive Casimir–Lifshitz forces

PubMed Central

Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian

2014-01-01

Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1–3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5–7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8–11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13–15. PMID:19129843

Entire-Dataset Analysis of NMR Fast-Exchange Titration Spectra: A Mg2+ Titration Analysis for HIV-1 Ribonuclease H Domain.

PubMed

Karki, Ichhuk; Christen, Martin T; Spiriti, Justin; Slack, Ryan L; Oda, Masayuki; Kanaori, Kenji; Zuckerman, Daniel M; Ishima, Rieko

2016-12-15

This article communicates our study to elucidate the molecular determinants of weak Mg 2+ interaction with the ribonuclease H (RNH) domain of HIV-1 reverse transcriptase in solution. As the interaction is weak (a ligand-dissociation constant >1 mM), nonspecific Mg 2+ interaction with the protein or interaction of the protein with other solutes that are present in the buffer solution can confound the observed Mg 2+ -titration data. To investigate these indirect effects, we monitored changes in the chemical shifts of backbone amides of RNH by recording NMR 1 H- 15 N heteronuclear single-quantum coherence spectra upon titration of Mg 2+ into an RNH solution. We performed the titration under three different conditions: (1) in the absence of NaCl, (2) in the presence of 50 mM NaCl, and (3) at a constant 160 mM Cl - concentration. Careful analysis of these three sets of titration data, along with molecular dynamics simulation data of RNH with Na + and Cl - ions, demonstrates two characteristic phenomena distinct from the specific Mg 2+ interaction with the active site: (1) weak interaction of Mg 2+ , as a salt, with the substrate-handle region of the protein and (2) overall apparent lower Mg 2+ affinity in the absence of NaCl compared to that in the presence of 50 mM NaCl. A possible explanation may be that the titrated MgCl 2 is consumed as a salt and interacts with RNH in the absence of NaCl. In addition, our data suggest that Na + increases the kinetic rate of the specific Mg 2+ interaction at the active site of RNH. Taken together, our study provides biophysical insight into the mechanism of weak metal interaction on a protein.

Physical Appearance Cues and Interpersonal Attraction in Children

ERIC Educational Resources Information Center

Kleck, Robert E.; And Others

1974-01-01

Two studies are reported which demonstrate a positive relationship between sociometric status (after two weeks of intense social interaction) and social acceptance judged from photographs by an independent group of peers. Acceptance was found to be related to physical attractiveness. (ST)