Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “FRUSTRATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed2006

Anomalous excitation spectra of frustrated quantum antiferromagnets.

We use series expansions to study the excitation spectra of spin-1/2 antiferromagnets on anisotropic triangular lattices. For the isotropic triangular lattice model (TLM), the high-energy spectra show several anomalous features that differ strongly from linear spin-wave theory (LSWT). Even in the Néel phase, the deviations from LSWT increase sharply with frustration, leading to rotonlike minima at special wave vectors. We argue that these results can be interpreted naturally in a spinon language and provide an explanation for the previously observed anomalous finite-temperature properties of the TLM. In the coupled-chains limit, quantum renormalizations strongly enhance the one-dimensionality of the spectra, in agreement with experiments on Cs2CuCl4.

Journal Article↗
PubMed2006

Metallic spin-liquid behavior of the geometrically frustrated Kondo lattice.

Strongly frustrated magnetism of the metallic pyrochlore oxide Pr2Ir2O7 has been revealed by single crystal study. While Pr 4f moments have an antiferromagnetic RKKY interaction energy scale of /T*/ = 20 K mediated by Ir 5d-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a lnT dependence in the resistivity, emerges and leads to a partial screening of the moments below /T*/. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K.

Journal Article↗
PubMed2006

Spin dynamics and magnetic order in magnetically frustrated Tb2Sn2O7.

We report a study of the geometrically frustrated magnetic material Tb2Sn2O7 by the positive muon-spin relaxation technique. No signature of a static magnetically ordered state is detected while neutron magnetic reflections are observed in agreement with a published report. This is explained by the dynamical nature of the ground state of Tb2Sn2O7: the Tb3+ magnetic moment characteristic fluctuation time is approximately 10(-10) s. The strong effect of the magnetic field on the muon-spin-lattice relaxation rate at low fields indicates a large field-induced increase of the magnetic density of states of the collective excitations at low energy.

Journal Article↗
PubMed2006

Frustration of tilts and A-site driven ferroelectricity in KNbO3-LiNbO3 alloys.

Density functional calculations for K(0.5)Li(0.5)NbO(3) show strong A-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no stereochemically active A-site ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling.

Journal Article↗
PubMed2006

Frustrated polyelectrolyte bundles and T= 0 Josephson-junction arrays.

We establish a one-to-one mapping between a model for hexagonal polyelectrolyte bundles and a model for two-dimensional, frustrated Josephson-junction arrays. We find that the T = 0 insulator-to-superconductor transition of the quantum system corresponds to a continuous liquid-to-solid transition of the condensed charge in the finite-temperature classical system. We find that the role of the vector potential in the quantum system is played by elastic strain in the classical system. Exploiting this correspondence we show that the transition is accompanied by a spontaneous breaking of a discrete symmetry associated with the chiral patterning of the array and that at the transition the polyelectrolyte bundle adopts a universal response to shear.

Journal Article↗
PubMed2004

Haemophilia in the developing world: successes, frustrations and opportunities.

There is a need to bridge key gaps between high- and low-income countries and individuals; between health policy and clinical practice; and between producers and users of healthcare technology and scientific evidence. The objective of this report was to perform a diagnosis of the situation in the developing world through a survey. This survey was conducted to gather specific information on various aspects related to haemophilia. Countries were chosen by their comparability in infant and adult mortality rates according to the regionalization proposed by the World Health Organization. These indicators are very sensitive to socioeconomic conditions, and have been widely used to study health inequalities. All regions, except Africa and the East Mediterranean, were represented. Africa was excluded because its indicators were not comparable. The East Mediterranean was not represented because of difficulties in contacting investigators. Twenty-one country representatives were contacted, and 11 answered the questionnaire. Successes obtained by developing countries are based more on the skills and creativity of the local professionals than on the availability of state-of-the-art technology. Frustrations were related to disease underregistration and the limited availability of treatment products. Haemophilia care in the developing world is not as fair as we would like it to be. Governments do not always cover treatment costs, and a very small percentage of the national health budgets is allotted to haemophilia care. The role of the World Federation of Hemophilia was considered crucial by all the investigators surveyed. Training programmes and supply of factor concentrates were the main contributions identified by the respondents.

Adult↗
PubMed1993

Influence of staphylococcal lipoteichoic acid on the frustrated phagocytosis of neutrophils against opsonized corneocytes.

Stratum corneum (SC) exerts a proinflammatory effect in the presence of complement. When Staphylococcus aureus (S. aureus) invades the skin through damaged SC, neutrophils accumulate at the subcorneal portion of epidermis to phagocytize the S. aureus as noted in impetigo. Besides the phagocytosis of bacteria, neutrophils interact with opsonized SC in a form of frustrated phagocytosis, increasing a damage of the surrounding tissues. Based on our previous finding that staphylococcal protein A promotes the interaction between SC and neutrophils, we investigated whether lipoteichoic acid (LTA), another cell wall component of S. aureus, also shows similar properties. We found that LTA significantly promoted the binding of neutrophils to opsonized SC, resulting in an increase in SC-induced respiratory burst of neutrophils assessed by chemiluminescence (CL). The binding of neutrophils to the SC was almost completely inhibited by the blocking of CR3 with anti-CD11b antibody, suggesting that the binding between SC and neutrophils is mediated by interaction between C3bi and CR3 (Mac-1). Such enhanced interaction seems to function in the primary host defence mechanism against the invading S. aureus through the skin such as in impetigo.

Antibodies, Monoclonal↗
PubMed2001

Spin chirality, Berry phase, and anomalous Hall effect in a frustrated ferromagnet.

An electron hopping on non-coplanar spin sites with spin chirality obtains a complex phase factor (Berry phase) in its quantum mechanical amplitude that acts as an internal magnetic field, and is predicted to manifest itself in the Hall effect when it is not cancelled. The present combined work of transport measurement, neutron scattering, and theoretical calculation provides evidence that the gigantic anomalous Hall effect observed in Nd2Mo2O7, a pyrochlore ferromagnet with geometrically frustrated lattice structure, is mostly due to the spin chirality and the associated Berry phase originating from the Mo spin tilting.

Journal Article↗
PubMed2005

Colloidal hard-sphere crystal growth frustrated by large spherical impurities.

Impurities affect the nucleation, growth, and structure of crystals. Here we report the effect of large, spherical, polymethylmethacrylate impurities on the crystal growth of monodisperse, hard, polymethylmethacrylate colloids in a density- and optically matching apolar solvent mixture. Crystal growth, initiated at the bottom of the sample, was studied by imaging sequences of two-dimensional xy slices in the plane of the impurity's center with a laser scanning confocal microscope. Impurities form the center of grain boundaries, and a single fluid particle layer around the impurity persists in all cases. The growth rate sensitively depends on the impurity's size. Crystal growth is inhibited to a greater extent near smaller impurities, pointing to local crystal frustration induced by the curvature of the impurity.

Journal Article↗
PubMed2001

Surface femtochemistry: observation and quantum control of frustrated desorption of alkali atoms from noble metals.

This review presents a case study of the direct, real-time observation of a surface photochemical reaction, namely the frustrated photodesorption of alkali atoms from noble metal surfaces. Charge transfer excitation of an electron from the metal substrate into an unoccupied resonance of the alkali atom instantaneously turns on the repulsive Coulomb force inducing the nuclear motion of both the adsorbate and substrate atoms. The incipient nuclear wave packet dynamics are documented for the case of Cs/Cu(111) through the accompanying change in the surface electronic structure. The intimate view of atoms attempting to escape the surface bond highlights the unique role of the substrate in the electronic and nuclear dynamics that ultimately determine the product yields. Moreover, slow dephasing of the coherent polarization is exploited to demonstrate the control of nuclear wave packets through the phase of the excitation light.

Journal Article↗
PubMed1975

Retest reliability of the Rosenzweig Picture-Frustration Study and similar semiprojective techniques.

Surveys the evidence for the reliability of the Adult, Adolescent and Children's Forms of the Rosenzweig Picture-Frustration (P-F) Study. Analysis of variance and split-half methods, which assume item homogeneity and internal consistency, may be appropriate to psychometric tests, but they are not apposite to projective and semi-projective techniques. The implications of applying such criteria are critically examined, with the P-F Study as an example to demonstrate their nonapplicability. Investigations on retest (total test) reliability from the laboratory of the senior author and from those of other investigators demonstrate statistically significant consistency for the main scoring categories of the P-F, especially those relating to directions of aggression. Implications for other semiprojective techniques are expounded.

Journal Article↗
PubMed1977

Construct validity of the Rosenzweig Picture-Frustration Study.

Projective and semiprojective techniques are both tools and tests. A schema for assessing the validity of projective devices is proposed: (1) Primary, consisting of (a) construct validity i.e., the soundness of the techniques vis-a-vis its underlying concepts; and (b) criterion-related validity, i.e., the concordance between tool results and specified external criteria. (2) Secondary, viz., pragmatic validity, i.e., the usefulness of the instrument in applied fields. Discussion then focuses on the construct validity of the conceptually-based, semiprojective Rosenzweig P-F Study. specifically the evidence on (a) the self-consistency of its conceptual dimensions; (b) the sequential. social development of the Types and Directions of Aggression; (c) levels of behavior elicited; (d) sensitivity to scorable changes after induced frustration: and (e) physiological correlates oft he aggression categories. In each of these areas evidence exists in support of the validity of the P-F Study.

Journal Article↗
PubMed1978

An investigation of the reliability of the Rosenzweig Picture-Frustration (P-F) Study, Children's Form.

Presents data on the retest and split-half reliability of the Rosenzweig Picture-Frustration (P-F) Study, Children's Form, for two groups of subjects (aged 10-11 and 12-13 years, respectively), each group tested twice at an interval of three months. It was found that the retest reliability for all scoring categories (except O-D) were statistically significant (.01 or .05 level). GCR proved stable for the younger group (r = .53) but not for the older group. The difference here may be due to the less comfortable retest conditions prevailing for the older subjects. Reliability by retest was consistently higher than by the less appropriate split-half method, but the latter proved, nevertheless, to be in the main favorable.

Journal Article↗
PubMed1979

Factor and cluster analyses with the Rosenzweig Picture Frustration Study.

The Rosenzweig Picture Frustration (P-F) Study data of 104 psychiatric hospital patients, 56 males and 48 females, were subjected first to a Factor Analysis and then to a Cluster Analysis. In the former, five factors were extracted which showed some similarity to other Factor Analyses reported in the literature. The Cluster Analysis turned up one very large group (42% of the sample) characterized by depression and P-F profiles with elevated i and very low E scores. Seven other clusters are described in the article. The factors and clusters found are clinically meaningful and can provide assistance in interpreting P-F profiles. Recommendations for a revised P-F manual to enhance the usefulness of the test are made.

Adult↗
PubMed1981

The Rorschach EA-ep variable as related to persistence in a task frustration situation under feedback conditions.

Eighty nonpatients, subdivided into four levels based on the Rorschach EA-ep variable, were randomized into two groups and subjected to a frustrating pursuit rotor task. Extrinsic feedback was provided by a noticeable sound that would occur whenever the tracker was off target. Results indicate that where ep is significantly greater than EA a greater persistence occurred even though the extrinsic feedback signaled no substantial improvement in performance. Two of the three elements contributing to the ep, inanimate movement (m) plus the grey-black and shading answers (T, Y, V, C,), and one variable unrelated to ep, white space (S), account for much of the variance in persistence. The findings are discussed in terms of an overload state that interferes with appropriate processing and mediation in a complex situation.

Journal Article↗
PubMed2003

Application of frustrated total internal reflection devices to analytical laser spectroscopy.

Novel implementations of single-fiber laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy systems that gated light switches based on frustrated total internal reflection are described. The switching devices are largely wavelength independent, with full temporal and spatial separation of laser and fluorescence light. Wavelength-independent beam separation or beam combination schemes can be implemented for coaxial optical setups, e.g., in single-fiber or telescopic experimental arrangements. Selected practical examples of schemes for qualitative and quantitative analytical spectroscopy are discussed.

Journal Article↗
PubMed2005

Controlled frustration of total internal reflection by electrophoresis of pigment particles.

A model based on geometrical optics has been developed to describe the photometric observations associated with a novel method to control the reflectance of a surface. In this new reflectance modulation approach, electrophoresis of pigment particles is used to absorb light reflected by total internal reflection (TIR). The pigment particles are sufficiently small that they substantially do not scatter light, but rather they modify the effective refractive index at the reflection interface. An incident light ray interacting with this modified effective index is attenuated in a spectrally selective manner. Although frustrated TIR has been understood and used in various applications for some time, in this case it is used to substantially modify the color of the reflected light, which to our knowledge has not been previously reported. A numerical model of the pigment particle distribution has been developed to describe the observations.

Journal Article↗
PubMed2006

Polarizing properties of embedded symmetric trilayer stacks under conditions of frustrated total internal reflection.

An all-transparent symmetric trilayer structure, which consists of a high-index center layer coated on both sides by a low-index film and embedded in a high-index prism, can function as an efficient polarizer or polarizing beam splitter under conditions of frustrated total internal reflection over a wide range of incidence angles. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of either the p or s polarization at a specified angle, as well as the reflectance of the system for the orthogonal polarization, are determined. A 633 nm design that uses a MgF2-ZnS-MgF2 trilayer embedded in a ZnS prism achieves an extinction ratio (ER) > 40 dB from 50 degrees to 80 degrees in reflection and an ER > 20 dB from 58 degrees to 80 degrees in transmission. IR polarizers that use CaF2-Ge-CaF2 trilayers embedded in a ZnS prism are also considered.

Journal Article↗