Showing papers on "Crossover published in 1984"

Crossover and Self-Controlled Designs in Clinical Research

Abstract: Crossover studies (clinical trials in which each patient receives two or more treatments in sequence) and self-controlled studies (in which each patient serves as his or her own control) can produce results that are statistically and clinically valid with far fewer patients than would otherwise be required. We investigated the use of the crossover design in the 13 crossover studies that appeared in the Journal during 1978 and 1979. We considered the following important features of design and analysis as they applied to these studies: the method by which patients were assigned to initial treatment (only 7 of 13 studies used random assignment); the determination of when to switch treatments (10 of the 13 used a time-dependent rule, and 3 a less appropriate disease-state-dependent rule); blinding of the crossover point (in only 3 of the 13 studies was the crossover point concealed, but in 4 of the remaining 10 concealment was impossible); assessment of the effects of the order of treatments (included in only 1 of the 13 studies); and the use of at least minimally acceptable statistical analysis (11 of the 13 studies had such an analysis). We also report briefly on 28 additional studies of a single treatment each, in which each patient served as his or her own control before or after treatment or both. The scientific issues were much the same as in crossover studies except that self-controlled comparisons of treatments tended to be less precisely designed and conducted and to focus on clinical problems and patient groups that are especially difficult to study.

Crossover Phenomenon in Dynamical Scaling of Phase Separation in Fe-Cr Alloy

Abstract: A neutron-scattering study of phase separation in the Fe-Cr alloy system clearly indicates dynamical scaling. The results are compared with the predictions of recent scaling theories. Both the time evolution of the characteristic wave vector and the scaling function of the structure factor show crossover phenomenon. The crossover is attributed to a transition from a coagulation to a condensation process at a late stage of phase separation in alloy systems.

Three-period crossover designs for two treatments.

Abstract: The use of three periods in the two-treatment crossover design for clinical trials is considered. It is proposed that a series of such trials in a particular therapeutic area may establish the relevance of the crossover design in that area. Treatment sequences to be used in three-period two-treatment trials are discussed. Two possible designs which allow carryover effects to be tested against the within-subject variability are compared. A design involving four treatment sequences is recommended.

A crossover integral equation for the structure of simple liquids

Abstract: We propose here a new choice of bridge function appearing in the modified hypernetted chain approximation for determining the structure and thermodynamic functions of simple classical fluids. It takes the form of a crossover between the bridge function for a hard sphere system, which is known to give a satisfactory short‐range description of correlations in such systems, and the mean spherical model result which is more suitable for long‐range behavior. We derive a thermodynamic consistency requirement which is entirely local in its implementation. The results of the method are compared with simulation studies of the Lennard‐Jones fluid, the one‐component plasma, and models of simple liquid metals.

A simple objective method for minimizing crossover errors in marine gravity data

Abstract: A method is presented which does not require a model for the source of crossover errors in marine gravity data in order to minimize them. The cruises are divided up into straight line segments and the assumption is made that whatever the sources of error, their net effect will be constant over the length of the track segment. A least‐squares approach is used where the crossover differences in the original data are the observations which it is desired to match. The desired set of constant corrections, one for each segment, is that which will minimize the sum of the squares of the residual crossover errors. This method has the advantage of reducing the crossover errors while simultaneously preserving the relative gravity anomalies along individual ship’s profiles. A data set consisting of gravity measurements made on nine cruises in the region of the Vema fracture zone in the equatorial Atlantic is used as a case study. The resulting least squares solution reduces the root mean square (rms) of 298 crossover...

Ultra high resolution loudspeaker system

Abstract: A speaker system includes crossover networks connected to a low output impedance amplifier through RF chokes The individual outputs of the crossover networks are connected by separate wires to each of the individual speakers RF reducing capacitors are connected across the terminals of each speaker and across the output terminals of the crossover networks Separate back EMF resistors are connected across the speakers for dissipating back EMF signal energy The component values in each of the crossover networks are split and balanced to present a substantially identical electrical configuration to both polarities of signal

Crossover in an exactly solvable dimer model of domain walls with dislocations

Abstract: An exactly solvable generalized dimer model is proposed. In one limit this model is the isotropic Ising model and in another limit it is the anisotropic Kasteleyn model with radically different critical behavior. The value of the crossover exponent $\ensuremath{\varphi}$ near the multicritical point is determined to be \textonehalf{}. The proposed model is isomorphic to a domain-wall model with dislocations, thereby providing an example of dislocation-mediated crossover in uniaxial commensurate-incommensurate transitions.

A Review of Higher Order Crossover Designs

Abstract: (1984). A Review of Higher Order Crossover Designs. Journal of Applied Statistics: Vol. 11, No. 1, pp. 29-50.

Zero phase shift filtering

Abstract: A frequency band filtering circuit and phase shift free crossover network comprising at each crossover frequency range between band pass filters a low-pass filter means characterized by a transfer function that decays at a second or higher order function of frequency and a high-pass filter means characterized by a transfer function that rises as a second or higher order function of frequency and wherein the respective pair of transfer functions sum to unity. By employing circuit filters characterized by high order polynomial transfer functions that sum to unity, the combination of sharp roll-off and excellent frequency separation is achieved without introducing phase distortion when the signals are recombined or summed. Such a filtering system is useful in high fidelity speaker crossover systems, various electronic signal splitting or filtering circuits (whether analog or digital) wherein the information within individual frequency bands are to be isolated and treated independent of an adjacent frequency band yet ultimately recombined and the like.

Loudspeaker system utilizing an equalizer circuit

Abstract: A loudspeaker system includes a low-frequency driver and a high-frequency driver which are connected to a crossover network. The crossover network includes an inductor in series with the low-frequency driver for attenuating high-frequency signals at the crossover frequency and a capacitor in series with the high-frequency driver for attenuating low-frequency signals at the crossover frequency. An equalizer circuit connects between the high- and low-frequency drivers and operates to dampen resonant ringing which is otherwise produced. The equalizer circuit preferably comprises a series LRC circuit having a resonant frequency and a Q factor equal to the resonant frequency and Q factor of the circuit formed by the crossover network and drivers. The equalizer circuit is particularly suited for application in a disclosed loudspeaker system which utilizes a high inductance crossover inductor to enhance system bass response without sacrificing clarity.

Method of fabricating air supported crossovers

Abstract: A method is disclosed for the fabrication of an air supported crossover bridge which consists of a polyimide coating being set over the metalized device. Then, supports are defined for the crossover and the crossover is added. Once the crossover has been added the excess is removed and the polyimide layer is removed leaving the air supported bridge.

Scaling and crossover in the one-dimensional true self-avoiding walk

Abstract: The authors apply scaling and crossover arguments to the one-dimensional true self-avoiding walk, which avoids itself with strength g. The problem is formulated in terms of a grand canonical ensemble, a real-space renormalisation-group analysis shows that for large repulsion, x=e-g is a relevant variable causing crossover from the self-repelling chain (SRC) limit, with crossover exponent phi =1. A physical interpretation of this result is given in terms of competition between the correlation length and the average distance before the walk turns back on itself. The resulting flow suggests the existence of an intermediate attractive fixed point which makes the exponent v different from SRC and random-walk values for all x between 0 and 1, in agreement with recent Monte Carlo results.

Dimensional crossover in directed percolation

Abstract: The authors study the dimensional crossover in directed percolation in three dimensions. Bonds are allowed to have different concentrations along the three cartesian axes of the lattice. Through a position space renormalisation group one obtains the phase diagram where nonpercolating. 1D, 2D and 3D percolating phases are present. The authors find that, contrary to what happens in undirected percolation, the isotropic fixed points are unstable with respect to concentration anisotropy. Numerical estimates are given for the values of critical probabilities and exponents, which are in fairly good agreement with other results, where available.

Quantum crossover behaviour of the X―Y model in a transverse magnetic field

Abstract: The field theoretic renormalization group method, proposed recently as a description of the quantum crossover in the transverse Ising model, is now adopted to the study of the similar effect in the X−Y model in a transverse field. The crossover scaling form of the inverse correlation length and susceptibility has been obtained for the spatial dimension 2

Renormalization-group study of the crossover to classical behavior for an Ising model with vacancies

Abstract: By using Kadanoff's variational renormalization-group method an Ising model with vacancies is investigated for dimensions up to d=4 to study the crossover to classical behavior. Up to a crossover dimension d?3.4, both an optimal critical and tricritical fixed point are located with critical indices that agree well with other data. At d?3.4, both fixed points merge, representing in this way the crossover to classical behavior. At d>3.4, indications are found that the two fixed points do not annihilate but form a "marginal" pair that describes both critical and tricritical behavior.

Requirements for loudspeaker crossover networks

Abstract: After defining terms to be used, the need for a crossover filter in a loudspeaker is explained. Justification of crossover filter functions is based on a listening test first proposed in 1962. The requirements for a crossover filter are: 1. partitioning the audio spectrum, 2. a tolerance on power response, 3. control of intermodulation distortion, 4. a tolerance on phasor magnitude response, 5. a tolerance on system group delay, and 6. a tolerance on adjacent channel group delay difference. The audio fad known as time alignment and several crossover networks will be debunked.

Analysis of Crossover Designs with a Categorical Response

Abstract: In the analysis of two-period crossover designs, one frequently must consider the case of a categorical response with binary as a special case. These circumstances are considered in this paper and the proposed method—an extension of GART'S tests for the binary case—is similar to that of PIKE, CASAGRANDE and SMITH for the analysis of pair-matched case-control studies. The results are illustrated with a numerical example.

Crossover effects induced by lattice compressibility in random magnets

Abstract: Crossover behaviour induced by lattice compressibility in a random magnet is studied using solutions of the renormalization group recursion relations to leading order in e=4−d. An effective exponent of the magnetic susceptibility is introduced and the size of the crossover region is estimated. Crossover scaling functions for the free energy, specific heat, and magnetic susceptibility are also obtained.

Analysis of crossover of dispersion curves of alkali metals in the [ζ00] direction

Abstract: The dispersion curves of alkali metals, deduced on the basis of DAF, CGW, AS and GTF models, are analysed to determine the circumstances under which they crossover along the [ζ00] direction. All these models incorporate the same electron-ion interactions, satisfy the symmetry requirements of the lattice and reproduce the observed crossover in lithium with a positive value for the electron gas constant, C ′. However, none of them produces a crossover in any other alkali metal. It is shown that these dispersion curves are hardly influenced by the nature or range of the ion-ion interactions in a model, but the stronger electron-ion interactions in lithium produces the crossover while the weaker electron-ion interactions in other alkali metals do not. The role played by the umklapp contributions in producing a crossover, apparent differences in the values of C ′ from one model to another and the consequent variation in the wave vector at which the crossover occurs in lithium are discussed.

Criticality and Crossover in Stuctural Phase Transitions

Abstract: Renormalization-group techniques and the exact factorization of the partition function of a particular model in the class of double well Hamiltonians are used to examine the critical behaviour and the high temperature gaussian-Ising crossover behaviour of systems undergoing structural phase transitions. The block probability density function is shown to be consistant with the scaling hypothesis near criticality.

Renormalisation-group study of crossover behaviour in an extended ϕ4 model on a square lattice

Abstract: A real-space renormalisation group transformation is applied to study the order-disorder-displacive crossover in a phi 4 lattice model involving some nearest-neighbour and next-nearest-neighbour interactions. A non-trivial fixed point is found on the crossover surface. It is shown that the point is associated with a 'true' critical behaviour of the system. This critical behaviour is suggested to be a consequence of a continuous phase transition from a phase characterised by the appearance of locally ordered clusters and a long-range order between them to a more disordered high-temperature phase in which the clusters disappear.