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At least 1,099 records · Page 61Linked to original sources
PubMed2006

Reinforced molecular recognition as an alternative to rigid receptors.

In theory, a perfectly rigid receptor will probably be an unbeatable binder. However, rigidity may not be easy to achieve in practice and it is certainly not Nature's method to realise high affinity. In many proteins binding affinity is increased through non-covalent interactions within the protein. Thus there is a considerable incentive to follow Nature's example and start exploring the use of secondary intra-receptor interactions to aid in the binding process. Secondary interactions within a receptor will reinforce host-guest binding when the same conformational rearrangement (or freezing of motion) is required for guest binding as for the formation of the intra-receptor interactions. Introducing secondary interactions will require rather elaborate synthetic receptors to be produced. With the recent developments in dynamic combinatorial chemistry, access to the desired structures should be facilitated. Whether or not this approach will develop into a practical method remains to be established, but even if it does not, efforts along these lines will lead to a better understanding of the complex interplay between molecular recognition, folding and dynamics.

Journal Article↗
PubMed2000

Mental health nurses and qualitative research methods: a mutual attraction?

Mental health nurses and qualitative research methods: a mutual attraction? In response to issues arising out of curriculum developments, the authors wished to examine more closely the potential reasons why psychiatric/mental health (P/MH) nurses appear to gravitate towards certain research methodologies. This paper therefore briefly examines the essential differences between qualitative and quantitative research paradigms, focusing on philosophical, epistemological and methodological issues. It then proceeds to examine some of the essential characteristics and attributes of P/MH nurses and suggests some differences in emphasis between these and other disciplines of nursing. The authors posit that psychiatric/mental health nurses are drawn to the qualitative paradigm as a result of the potential synchronicity and linkage that appears to exist between the practice of mental health nursing and qualitative research. This apparent synchronicity appears to centre around the three themes of: (a) the purposeful use of self; (b) the creation of an interpersonal relationship; and (c) the ability to accept and embrace ambiguity and uncertainty. Given this alleged synchronicity the authors argue that there are implications for nurse education and nursing research. Further it is possible that each nursing situation where the mental health nurse forms a relationship and attempts to gain an empathic sense of the individual's world is akin to an informal phenomenological study, the product of which would be a wealth of qualitative data. However, as this would be a subconscious, implicit process, the data would remain predominantly unprocessed. The authors conclude that perhaps these data are the knowledge that expert practitioners draw upon when making intuition-based clinical judgements.

Attitude of Health Personnel↗
PubMed1997

Certainty, probability and abduction: why we should look to C.S. Peirce rather than Gödel for a theory of clinical reasoning.

This paper argues that Gödel's proof does not provide the appropriate conceptual basis on which to counter the claims of evidence-based medicine. The nature of, and differences between, deductive, inductive and abductive inference are briefly surveyed. The work of the American logician C.S. Peirce is introduced as a possible framework for a theory of clinical reasoning which can ground the claims of both evidence-based medicine and its critics.

Evidence-Based Medicine↗
PubMed2004

Quantum and classical studies of the O(3P) + H2(v = 0-3,j = 0) --> OH + H reaction using benchmark potential surfaces.

We present results of time-dependent quantum mechanics (TDQM) and quasiclassical trajectory (QCT) studies of the excitation function for O(3P) + H2(v = 0-3,j = 0) --> OH + H from threshold to 30 kcal/mol collision energy using benchmark potential energy surfaces [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)]. For H2(v = 0) there is excellent agreement between quantum and classical results. The TDQM results show that the reactive threshold drops from 10 kcal/mol for v = 0 to 6 for v = 1, 5 for v = 2 and 4 for v = 3, suggesting a much slower increase in rate constant with vibrational excitation above v = 1 than below. For H2(v > 0), the classical results are larger than the quantum results by a factor approximately 2 near threshold, but the agreement monotonically improves until they are within approximately 10% near 30 kcal/mol collision energy. We believe these differences arise from stronger vibrational adiabaticity in the quantum dynamics, an effect examined before for this system at lower energies. We have also computed QCT OH(v',j') state-resolved cross sections and angular distributions. The QCT state-resolved OH(v') cross sections peak at the same vibrational quantum number as the H2 reagent. The OH rotational distributions are also quite hot and tend to cluster around high rotational quantum numbers. However, the dynamics seem to dictate a cutoff in the energy going into OH rotation indicating an angular momentum constraint. The state-resolved OH distributions were fit to probability functions based on conventional information theory extended to include an energy gap law for product vibrations.

Journal Article↗
PubMed2006

Optimal transition paths of stochastic chemical kinetic systems.

We present a new framework for finding the optimal transition paths of metastable stochastic chemical kinetic systems with large system sizes. The optimal transition paths are identified, in terms of reaction advancement coordinates, to be the most probable paths according to large deviation theory for the limiting dynamics governed by stochastic differential equations. Dynamical equations for the optimal transition paths are obtained using the variational principle. A multiscale minimum action method is proposed as a numerical scheme to solve the optimal transition paths. Applications to the toggle switch model are presented.

Journal Article↗
PubMedDate not supplied

Health barriers to walking for exercise in elderly primary care.

Health status is acknowledged by nursing theory as a factor in the probability of health behavior changes. Yet few studies have addressed the health-related barriers encountered by chronically ill elderly patients in primary care clinics who are trying to increase their physical activity. This study used self- and interviewer-administered instruments to assess potential barriers to physical activity in a sample of 60- to 80-year-old patients entering a walking program. Pain, fatigue, and mobility and sensory impairments were prevalent and could be significant barriers to participation. The authors present specific suggestions for helping patients overcome these barriers.

Activities of Daily Living↗
PubMed1998

Rapid parapatric speciation on holey adaptive landscapes.

A classical view of speciation is that reproductive isolation arises as a by-product of genetic divergence. Here, individual-based simulations are used to evaluate whether the mechanisms implied by this view may result in rapid speciation if the only source of genetic divergence are mutation and random genetic drift. Distinctive features of the simulations are the consideration of the complete process of speciation (from initiation until completion), and of a large number of loci, which was only one order of magnitude smaller than that of bacteria. It is demonstrated that rapid speciation on the time-scale of hundreds of generations is plausible without the need for extreme founder events, complete geographic isolation, the existence of distinct adaptive peaks or selection for local adaptation. The plausibility of speciation is enhanced by population subdivision. Simultaneous emergence of more than two new species from a subdivided population is highly probable. Numerical examples relevant to the theory of centrifugal speciation and to the conjectures about the fate of 'ring species' and 'sexual continuums' are presented.

Biological Evolution↗
PubMed2000

Branching annihilating random walk on random regular graphs

The branching annihilating random walk is studied on a random graph whose sites have a uniform number of neighbors (z). The Monte Carlo simulations in agreement with the generalized mean-field analysis indicate that the concentration decreases linearly with the branching rate for z>/=4, while the coefficient of the linear term becomes zero if z=3. These properties are described by a modified mean-field theory taking explicitly into consideration the probability of mutual annihilation of the parent and its offspring particles using the returning features of a single walker on the same graph.

Journal Article↗
PubMed2002

Scaling hypothesis leading to generalized extended self-similarity in turbulence.

A scaling hypothesis leading to generalized extended self-similarity (GESS) for velocity structure functions, valid for intermediate scales in isotropic, homogeneous turbulence, is proposed. By introducing an effective scale ŕ, monotonically depending on the physical scale r, with the use of the large deviation theory, the asymptotic forms of the probability densities for the velocity differences u(r) and for the coarse-grained energy-dissipation rate fluctuations epsilon(r), compatible with this GESS, are proposed. The probability density for epsilon(r) is shown to have the form P(r)(epsilon) approximately equal to epsilon(-1)(ŕ/L)(S(ŕ)[z(ŕ)](epsilon))) with z(ŕ)(epsilon)=ln(epsilon/epsilon(L))/ln(L/ŕ), where L and epsilon(L) are the stirring scale and the coarse-grained energy-dissipation rate over the scale L. The concave function S(ŕ)(z), the spectrum, plays the central role of the present approach. Comparing the results with numerical and experimental data, we explicitly obtain the fluctuation spectra S(ŕ)(z).

Journal Article↗
PubMed2004

Statistics of polarization and Stokes parameters of stochastic waves.

Several theories now exist to describe the probability distribution functions (PDFs) for the electric field strength, intensity, and power of signals. In this work, a model is developed for the PDFs of the polarization properties of the superposition of multiple transverse wave populations. The polarization of each transverse wave population is described by a polarization ellipse with fixed axial ratio and polarization angle, and PDFs for the field strength and phase. Wave populations are vectorially added, and expressions found for the Stokes parameters I , U , Q , and V , as well as the degrees of linear and circular polarization, and integral expressions for their statistics. In this work, lognormal distributions are chosen for the electric field, corresponding to stochastic growth, and polarization PDFs are numerically calculated for the superposition of orthonormal mode populations, which might represent the natural modes emitted by a source. Examples are provided of the superposition of linear, circular, and elliptically polarized wave populations in cases where the component field strength PDFs are the same, and where one field strength PDF is dominant.

Journal Article↗
PubMed2006

Adiabatic approximation of the correlation function in the density-functional treatment of ionization processes.

The ionization of a one-dimensional model helium atom in short laser pulses using time-dependent density-functional theory is investigated. We calculate ionization probabilities as a function of laser intensity by approximating the correlation function of the system adiabatically with an explicit dependence on the fractional number of bound electrons. For the correlation potential we take the derivative discontinuity at integer numbers of bound electrons explicitly into account. This approach reproduces ionization probabilities from the solution of the time-dependent Schrödinger equation, in particular, the so-called knee due to nonsequential ionization.

Journal Article↗
PubMed2001

Social understanding in autism: eye gaze as a measure of core insights.

Twenty-eight children with autism and 33 MLD children were given two tasks tapping social understanding and a control task tapping probability understanding. For each task there was a measure of eye gaze (where children looked when anticipating the return of a story character or an object) and a verbal measure (a direct question). We found that eye gaze was better than verbal performance at differentiating children with autism from children with MLD. Children with autism did not look to the correct location in anticipation of the story character's return in the social tasks, but they did look to the correct location in the nonsocial probability task. We also found that within the autistic group, children who looked least to the correct location were rated as having the most severe autistic characteristics. Further, we found that whereas verbal performance correlated with general language ability in the autistic group, eye gaze did not. We argue that: (a) eye gaze probably taps unconscious but core insights into social behavior and as such is better than verbal measures at differentiating children with autism from mentally handicapped controls, (b) eye gaze taps either spontaneous processes of simulation or rudimentary pattern recognition, both of which are less based in language, and (c) the social understanding of children with autism is probably based mostly on verbally mediated theories whereas control children also possess more spontaneous insights indexed by eye gaze.

Adolescent↗