Kinds Of Pairs Research Articles

Effect of coupling of forward- and backward-going electron-hole pairs on the static local-field factor of jellium

We investigate the effect of the coupling of the forward- and backward-going electron-hole pairs on the static local-field factor of jellium with and without a gap. We calculate the static local-field factor for the two types of jellium as a function of $\mathbf{q}$ using the Bethe-Salpeter equation. We assume that a particle and a hole interact via a statically screened Coulomb interaction. The polarization diagrams that include this interaction are summed to infinite order, leading to a matrix equation for the inverse of the polarization propagator. Employing a string of manipulations we convert the matrices in convenient forms, and we then invert the resulting matrices iteratively. This allows us to use matrices of very large size, something that would have not been feasible with straightforward inversion, and therefore achieve a very high level of convergence of results with respect to sampling of electron states in the Fermi sea with relative computational ease. For the calculation of the static local-field factor, we find that the coupling of both kinds of pairs gives qualitatively different results compared to the case when there is no coupling, and that the coupling of both kinds of electron-hole pairs is necessary for obtaining the most accurate results. We compare our results with recent calculations and point out the similarities and differences.

Mutual influences of general practitioners in partnerships

The aim of this study was to find out whether or not general practitioners (GPs) within the same partnership show more similarities in attitudes and behaviour than GPs in different partnerships, and what the causes of these similarities might be. Knowledge of the causes of patterns of similarities within medical teams contributes to understanding medical practice variation, which is crucial in developing effective health care policies. Data were used from the Dutch National Survey of General Practice (’87/’88), consisting of a stratified sample of 161 Dutch GPs, who served 335,000 patients in total. To find out whether GPs in the same partnership are indeed more similar than GPs randomly chosen from different partnerships, we constructed two kinds of pairs: all possible pairs of GPs working in the same partnership (actual pairs), and randomly constructed pairs of GPs who are not working in the same partnership (random pairs). For each pair difference scores were computed for a variety of attitudes and behaviour. Difference scores for actual and random pairs were analysed using multi-level analysis. Most differences in attitudes and behaviour were smaller for actual pairs than for random pairs. Furthermore, in the majority of the cases differences were no longer statistically significant after explanatory variables indicating selection, gradual adaptation and rapid adaptation through shared circumstances were taken into account. It was found that Dutch GPs working in the same partnership showed more resemblance in attitudes and behaviour than GPs not working in the same partnership. Most indications point towards circumstances, and to a lesser extent towards adaptation, as an explanation of similarities within partnerships. The implication of this study is that medical practice variations are not merely individual differences in preferred practice style, but are patterned by social processes in partnerships and local circumstances.

2701 関数表現される相対変位拘束を与える多自由度対偶の総合

Aiming to synthesize new mechanisms, new kinematic pairs with multi-DOF were proposed. In the pair, one element moved along a spatial curve with rotations about three axes relative to the other element. Spatial curves were classified with respect to their curvature and twist ratio. The condition that the one element can move along a spatial curve relative to the other element was derived. Consequently only a straight line, a circle and a constant spiral were obtained as a suitable spatial curve. Three kinds of pairs with 1,2 and 4 DOF which were composed of a spiral tube and a block with rectangular or circular closs-section were synthesized and built with a rapid prototyping method.

Selective impairments in rats on an odor-guided continuous delayed nonmatching-to-sample (cDNMS) task after fornix transection

The two experiments reported in this article examined recognition of simple and complex olfactory stimuli. In Experiment 1, three groups of control rats were trained to criterion without delay then, tested with delays on a continuous delayed nonmatching-to-sample (cDNMS) task using one of three kinds of odor pairs: replicates of the same odor (S), different odors that were each common with another pair (O), different odors with no overlap between pairs (NO). Results showed that initial learning and performance with delays were both poorer for O pairs than for S and NO pairs. Experiment 2 used a within-subject design to study the effects of fornix transection on recognition of the same three kinds of odor pairs as those described for Experiment 1. Sham-operated controls and rats (SH) with fornix transection were trained to criterion prior to the test with delays first on S, then on O and, finally, on NO pairs. During training, numbers of sessions to criterion did not differ in lesioned and SH rats on any of the three kinds of pairs. During testing, the level of performance was delay-dependent in both groups. However, lesioned rats were significantly impaired when tested with S and O pairs, but did not differ from sham-operated controls when tested with NO pairs. This selective impairment can be interpreted as evidence that fornix lesions impair recognition memory of stimuli that provide few and/or confusing retrieval cues. It might also suggest that postlesional performance on DNMS procedures depends on task difficulty.

Molecular simulation of a concentrated aqueous KCl solution

A 1.0 M aqueous KCl solution was studied by molecular dynamics simulations at 293 K in order to study the influence of the ionic concentration on the hydration structure of the ions as well as the formation of ion clusters. The hydration structures of the ions are almost independent of the ionic concentration unless in respect to the perturbation that appears due to ionic clustering. Fractions equal to 31.9% of the anions and 37.8% of the cations are associated. Clusters constituted by two, three and four ions were detected. Their mean lifetimes are always affected by thermal effects, reorientational relaxation while the longest lifetimes are a consequence of ionic cloud relaxations. The pairs constituted by two anions or two cations are stabilized by water molecules belonging to the solvation shells of both ions. The neutral K +Cl − pairs are formed under the influence of the electrostatic attraction that, however, is small due to the ionic radii of these ions. Consequently, this kind of pairs contains only 8.8% of the ions while the fraction of ions in the negative and positive pairs are equal to 29.2 and 39.3%, respectively, when the same ion can pertain to more than one pair.

Categorical perception of happiness and fear facial expressions: an ERP study.

Behavioral studies have shown that two different morphed faces perceived as reflecting the same emotional expression are harder to discriminate than two faces considered as two different ones. This advantage of between-categorical differences compared with within-categorical ones is classically referred as the categorical perception effect. The temporal course of this effect on fear and happiness facial expressions has been explored through event-related potentials (ERPs). Three kinds of pairs were presented in a delayed same-different matching task: (1) two different morphed faces perceived as the same emotional expression (within-categorical differences), (2) two other ones reflecting two different emotions (between-categorical differences), and (3) two identical morphed faces (same faces for methodological purpose). Following the second face onset in the pair, the amplitude of the bilateral occipito-temporal negativities (N170) and of the vertex positive potential (P150 or VPP) was reduced for within and same pairs relative to between pairs. This suggests a repetition priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for the between pairs was higher than for the within and same pairs. These results indicate that the categorical perception of human facial emotional expressions has a perceptual origin in the bilateral occipito-temporal regions, while typical prior studies found emotion-modulated ERP components considerably later.

Two Wrongs May Make a Right ... If They Argue Together!

Several studies have investigated the cognitive development of interacting peers. This study focuses on a phenomenon that has not yet been studied: the cognitive gains of 2 children with low levels of competence who fail to solve a task individually but who improve when working in peer interaction. We show that this phenomenon (which we call the two-wrongs-make-a-right phenomenon) may occur when (a) the 2 wrongs disagree, (b) they have different strategies, and (c) active hypothesis testing is made possible. In a preliminary study, 30 Grade 10 low-achieving students were tested about the rules they use to compare 2 decimal fractions in a questionnaire. The students who were diagnosed as wrongs were invited to solve a task (the 6-cards task) with peers. Three kinds of pairs were formed: 7 W1-W2 pairs in which the 2 wrongs have different conceptual bugs; 4 W1-W1 pairs in which the 2 wrongs have the same conceptual bugs; 4 R-W pairs in which a wrong interacted with a right student. The 6-cards task was designed to create conflicts between students with different conceptual bugs and between wrong and right students. Two days after solving the 6-cards task, the students were asked to answer a similar questionnaire individually. The preliminary study revealed the two-wrongs-make-a-right phenomenon: Among the 7 W1-W2 pairs, at least 1 wrong became right. In contrast, in the 4 R-W pairs, only 1 wrong became right, and in the 3 W1-W1 pairs, no change was detected. In a case study that replicated the phases of the preliminary study, disagreement, argumentative operations (such as challenge and concession), hypothesis testing (with a calculator), and the internalization of social interactions mediated the change of peers from wrongs to rights. We then replicated the initial study with 72 low-achieving Grade 10 and 11 students, confirming the two-wrongs-make-a-right effect.

Right N170 modulation in a face discrimination task: An account for categorical perception of familiar faces

Behavioral studies have shown that two different morphed faces belonging to the same identity are harder to discriminate than two faces stemming from two different identities. The temporal course of this categorical perception effect has been explored through event-related potentials. Three kinds of pairs were presented in a matching task: (1) two different morphed faces representing the same identity (within), (2) two other faces representing two different identities (between), and (3) two identical morphed faces (same). Following the second face onset in the pair, the amplitude of the right occipitotemporal negativity (N170) was reduced for within and same pairs as compared with between pairs, suggesting an identity priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for within pairs was higher than for between and same pairs, suggesting a higher complexity of the task for within pairs. These results indicate that categorical perception of human faces has a perceptual origin in the right occipitotemporal hemisphere.

Global Block-Similarity and Pole Assignment of Class Cp

Starting from the existence of a Cp-basis for any Cp-family of subspaces having constant dimension, we construct a Brunovsky basis of class Cp for a Cp-family of pairs of matrices having constant Brunovsky type. We derive a global pole assignment theorem for such kinds of pairs. In all the cases we assume that the manifold of parameters is contractible.

Absence of superconducting long-range order in low-dimensional Hubbard models

Using Bogoliubov's inequality we rigorously show that the one- and two-dimensional Hubbard model with narrow bands does not exhibit long-range order for different kinds of pairing, e.g. s-wave Cooper pairing and generalized η pairing. This result holds at any finite temperature for both repulsive and attractive Coulomb interactions. At zero temperature there will be no on-site electron pairing long-range order if a gap in the charge excitation spectrum exists. The present results do not cover the case of d x 2− y 2 pairing of electrons.

Neutron-proton correlations in an exactly solvable model

We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double $\ensuremath{\beta}$ decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller ${\ensuremath{\beta}}^{+}$ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an $N=Z$ core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes $T=0$ and $T=1$ pairing, but only on the isoscalar side of the phase transition.

A proposed complementary pairing mode between single‐stranded nucleic acids and β‐stranded peptides: A possible pathway for generating complex biological molecules

AbstractA structure for a heterologous double‐stranded molecule consisting of an oligoribonucleotide and a β‐stranded oligopeptide, paired through complementary Watson‐Crick‐type hydrogen bonding, is proposed. The basis for such complementary pairings between oligoribonucleotides and oligopeptides is the close correspondence of the distances between the side‐chains attached to the backbones of the two molecules. Both inter‐nucleotide spacing and inter‐amino acid side‐chain spacing are approximately 3.4 Å. These kinds of interactions may have implications in protein‐mediated‐RNA splicing. Formation of a heterologous duplex through such a pairing mode could provide a simple coding mechanism for a reciprocal information transfer between oligonucleotides and oligopeptides. Because of its simplicity and versatility, allowing both specific and nonspecific coding, interactions via these kinds of pairing may have been relevant for prebiotic molecular evolution and for generating complex biological molecules.

Pseudopotential plane-wave study of alpha -YHx.

The solid-solution phase of hydrogen in hexagonal close-packed yttrium (\ensuremath{\alpha}-${\mathrm{YH}}_{\mathit{x}}$) is studied using the pseudopotential method within the local-density-functional approximation with a plane-wave basis. The binding energies associated with different interstitial sites are evaluated for several ordered structures: ${\mathrm{YH}}_{0.5}$, ${\mathrm{YH}}_{0.25}$, and ${\mathrm{YH}}_{0.167}$. It is found that the occupation of the tetrahedral site is always energetically favorable. The hydrogen potential-energy curves around the tetrahedral sites along the c axis and along the path connecting the adjacent octahedral sites are also calculated for ${\mathrm{YH}}_{0.25}$. In particular, the local vibrational mode along the c axis is estimated to be 100 meV, in excellent agreement with that measured in neutron-scattering experiments. Finally, the intriguing pairing phenomenon is investigated by calculating the total energy for various pairing configurations. The possibility of pairing between nearest-neighbor tetrahedral sites is excluded due to the high energy. It is found that the pairing of hydrogen across a metal atom is indeed energetically favorable compared with other kinds of pairs considered and also with isolated tetrahedral hydrogen atoms. The connection with the electronic structure of the system is also examined.

Coexistence of the s wave (on site) pairing and d wave (off site) pairing of high TC superconductors

The energy spectrum of the quasiparticle of high T C superconductors is investigated in the case when the s wave(on site) pairing and the d wave(nearest site) pairing coexists. The bias voltage dependence of the tunneling conductance shows a intermediate shape between U shape and V shape. The anisotropy of the energy gap and the mixture of the two kinds of pairing can be observed by angle resolved photoemission spectroscopy.

Inhibition of oral morphogenesis during conjugation of Tetrahymena thermophila and its resumption after cell separation

During the early stages of the conjugation of Tetrahymena thermophila, the oral apparatus undergoes partial regression: the deep fiber bundle is resorbed and oral membranelies are partially deciliated. However, further progress of the oral replacement is arrested until cell separation. Only then proliferation of basal bodies for a new oral primordium is unblocked and concomitantly the old oral structures are resorbed. This step is followed by the assembly of new oral membranelies and resorption of the old ones. Thus, the cell separation itself may be the source of an important signal for the cortical morphogenesis. To test this hypothesis we have used micronuclearly defective "✴" cells which separate after conjugation about 2.5 h earlier than normal cells and do not undergo postzygotic nuclear divisions. In the "✴" crosses (the crosses of the "✴" × wt cells) the oral primordium appeared before the cell separation (at the stage of hemikarya) following partial regression of the old oral structures, but only in those pairs in which the separation was already advanced in the separation. Consequently onset of conjugational morphogenesis in the "✴" pairs was correlated with the time of the cell separation, in spite of the differences in the course of nuclear events in the two kinds of pairs.

Energy Spectrum of the Quasi Particle of Tl2Ba2CaCu2O8under Coexistence of Interlayer Pairing and Intralayer Pairing

Superconducting properties of Tl 2 Ba 2 CaCu 2 O 8 are investigated taking into consideration the inter- and intralayer pairings. Two kinds of pair potentials are determined self-consistently based on a microscopic energy band calculation. The obtained local tunneling conductance is influenced by the coexistence of two kinds of pairing.

Determination of the type of pairing and the order parameter in high Tc superconductors and heavy fermion systems by sound and microwave absorption experiments

Based on the superconductive (SC) state symmetry classification of heavy fermion systems and high T c superconductors we suggest a method of pairing type determination by using sound and microwave absorption experiments. For both systems the collective excitation spectrum exhibited in these experiments is quite different for different kinds of pairing and even for different SC states for the same pairing. This makes it possible to identify the SC states by these experiments.

The generation effect as an artifact of selective displaced rehearsal

Four experiments on the generation effect of free recall were reported. Experiment 1 used a within-lists design that showed the generation effect with unilingual, but not bilingual, pairs. Experiment 2 had a between-lists design and found no effect with either kind of pairs. Experiment 3 contracted the two design types with unilingual materials, and obtained generation effects only for the mixed-list arrangement. Experiment 4 prevented displaced rehearsal in a mixed-list arrangement, and found no generation effects. It was concluded that the generation effect of recall is an artifact of selective displaced rehearsal that strengthens generated items at the expense of read items. It was also argued that these data render extant theories of the effect untenable.

Bipolarons and superconductivity

Abstract Formation of real-space localised pairs of electrons as observed in many solids are shown to be phonon mediated and resembles in this respect to the mechanism involved in B. C.S. pairing of superconductivity. Profound analogies exist between these two kinds of pairs and will be explored. The localised pair of electrons in a singlet state is the ground state beyond a critical value of the electron-phonon coupling constant. Treating the two-electron scattering problem, one can obtain the expected behavior of the chemical potential in the two limits. Several examples will be given of real-space pairing and of anomalous superconductivity in some systems.

Macromolecular conformations in solutions. I. Model for chains with partial flexibility

Less-than fully flexible polymer chains in solution are considered. Each chain is represented by relatively rigid and with relatively low pervaded volume groupings of monomeric units called compact bundles, intercalated with extended bundles. A partition function for the system is constructed in terms of numbers of possible kinds of pairs of neighboring bundles, and of configurational energies. Results of the extremization of the partition function show an interplay of the interaction forces as decisive for the behavior of the system. The parameters characterizing the system are related to those in the Elory freevolume theory of liquids and solutions. The resulting equations enable evaluation of the relative concentration of compact bundles and of the numbers of pairs of neighboring bundles of different kinds. The model is related to some experimental evidence. Possible connections to structures of polymer-containing phases other than solutions are pointed out.