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Biomedical subjects

J J Rasmussen

Publications and source records attributed to J J Rasmussen.

9 recordsLinked to original sources
PubMed2006

Superdiffusion and viscoelastic vortex flows in a two-dimensional complex plasma.

Viscoelastic vortical fluid motion in a strongly coupled particle system has been observed experimentally. Optical tracking of particle motion in a complex plasma monolayer reveals high grain mobility and large scale vortex flows coexistent with partial preservation of the global hexagonal lattice structure. The transport of particles is superdiffusive and ascribed to Lévy statistics on short time scales and to memory effects on the longer scales influenced by cooperative motion. At these longer time scales, the transport is governed by vortex flows covering a wide spectrum of temporal and spatial scales.

Journal Article↗
PubMed2003

Congruence on medication between patients and physicians involved in patient course.

OBJECTIVE: To analyse congruence on medication throughout patient courses, including an acute admission to a medical department. DESIGN: A prospective, observational study. Data were collected from patient records in primary health care, hospital departments, from the Health Insurance database and through patient interviews. SETTING: Departments of internal medicine, general practice and patients' homes. MAIN OUTCOME MEASURES: Number, type and character of discrepancies between paired sources of information on patient medication at predefined time points throughout the complete patient course. Assessment of likelihood and severity of potential untoward effects of discrepancies. RESULTS: Data were obtained for 75 of 99 consecutive patients included. Patients stated use of four drugs (median, range 0-17) at admission, five (0-16) at discharge and four (0-15) 1 month after discharge. At admission, 11 patients used no drugs. A median of one (0-20) to three (0-16) discrepancies per patient were identified in seven paired source comparisons with no improvement along patient course. Full agreement throughout the course was found in six patients (8%; 95% confidence interval: 3-17%). No association was found among source discrepancies and number of drugs and age. Of discrepancies, 4-13% were considered serious and likely to cause untoward effects. Discrepancies due to synonymous and analogous drugs accounted for 2-7% of the discrepancies. CONCLUSION: Congruence between sources of information on medication throughout patient courses cannot be obtained with separate medication charts. Discrepancies among patient, general practitioner and hospital give rise to a definitive risk of serious untoward effects.

Adult↗
PubMed2001

Dynamics of solitons and quasisolitons of the cubic third-order nonlinear Schrödinger equation.

The dynamics of soliton and quasisoliton solutions of the cubic third-order nonlinear Schrödinger equation is studied. Regular solitons exist due to a balance between the nonlinear terms and (linear) third-order dispersion; they are not important at small alpha(3) (alpha(3) is the coefficient in the third derivative term) and vanish at alpha(3)-->0. The most essential, at small alpha(3), is a quasisoliton emitting resonant radiation (resonantly radiating soliton). Its relationship with the other (steady) quasisoliton, called embedded soliton, is studied analytically and also in numerical experiments. It is demonstrated that the resonantly radiating solitons emerge in the course of nonlinear evolution, which shows their physical significance.

Journal Article↗
PubMed2001

Modulational instability in nonlocal nonlinear Kerr media.

We study modulational instability (MI) of plane waves in nonlocal nonlinear Kerr media. For a focusing nonlinearity we show that, although the nonlocality tends to suppress MI, it can never remove it completely, irrespective of the particular profile of the nonlocal response function. For a defocusing nonlinearity the stability properties depend sensitively on the response function profile: for a smooth profile (e.g., a Gaussian) plane waves are always stable, but MI may occur for a rectangular response. We also find that the reduced model for a weak nonlocality predicts MI in defocusing media for arbitrary response profiles, as long as the intensity exceeds a certain critical value. However, it appears that this regime of MI is beyond the validity of the reduced model, if it is to represent the weakly nonlocal limit of a general nonlocal nonlinearity, as in optics and the theory of Bose-Einstein condensates.

Journal Article↗
PubMed2001

Finite time singularities in a class of hydrodynamic models.

Models of inviscid incompressible fluid are considered, with the kinetic energy (i.e., the Lagrangian functional) taking the form L approximately integral k(alpha)/vk/2dk in 3D Fourier representation, where alpha is a constant, 0<alpha<1. Unlike the case alpha=0 (the usual Eulerian hydrodynamics), a finite value of alpha results in a finite energy for a singular, frozen-in vortex filament. This property allows us to study the dynamics of such filaments without the necessity of a regularization procedure for short length scales. The linear analysis of small symmetrical deviations from a stationary solution is performed for a pair of antiparallel vortex filaments and an analog of the Crow instability is found at small wave numbers. A local approximate Hamiltonian is obtained for the nonlinear long-scale dynamics of this system. Self-similar solutions of the corresponding equations are found analytically. They describe the formation of a finite time singularity, with all length scales decreasing like (t*-t)(1/(2-alpha)), where t* is the singularity time.

Journal Article↗
PubMed2001

Nonlinearity and disorder: classification and stability of nonlinear impurity modes.

We study the effects produced by competition of two physical mechanisms of energy localization in inhomogeneous nonlinear systems. As an example, we analyze spatially localized modes supported by a nonlinear impurity in the generalized nonlinear Schrödinger equation and describe three types of nonlinear impurity modes, one- and two-hump symmetric localized modes and asymmetric localized modes, for both focusing and defocusing nonlinearity and two different (attractive or repulsive) types of impurity. We obtain an analytical stability criterion for the nonlinear localized modes and consider the case of a power-law nonlinearity in detail. We discuss several scenarios of the instability-induced dynamics of the nonlinear impurity modes, including the mode decay or switching to a new stable state, and collapse at the impurity site.

Journal Article↗
PubMed1999

Investigation of the impact of MIG1 and MIG2 on the physiology of Saccharomyces cerevisiae.

The gene functions of MIG1 and MIG2 are well known for their role in glucose control in Saccharomyces cerevisiae. A prototrophic mig1 disruptant (T468) and mig1mig2 double disruptant (T475) as well as their congenic wild-type strain (CEN.PK 113-7D) were analysed for changes in their peripheral metabolism (batch cultivations on sugar mixtures) and central metabolism (batch and continuous cultivations as well as acceleratostats). Sucrose metabolism was alleviated of glucose control in the mig1 disruptant, and even more so in the mig1mig2 disruptant compared with their wild-type strain. The lag phase in a batch cultivation grown on a glucose-galactose mixture was reduced by 50% in either disruptant, i.e. additional disruption of MIG2 in a mig1 background did not further alleviate galactose metabolism from glucose control. In contrast, both disruptants exhibited a more stringent glucose control of maltose metabolism compared with the wild-type strain. Growing on glucose, the mig1mig2 double disruptant exhibited a 12% higher specific growth rate than the wild-type strain, as well as a significantly higher respiratory capacity.

Culture Media↗
PubMedDate not supplied

Development and evaluation of porous dental implants in miniature swine.

Organized bone ingrowth in endosteal porous implants fabricated from VMC titanium alloy and surgically implanted with a tight interference fit, securely anchored the implants in fresh and healed mandibular premolar sites of miniature swine. This bone-implant union retained its integrity under high as well as slight masticatory stresses up to one-year after implantation. Bone invasion of the alumina porcelain implants was impeded by the lack of adequate interconnecting porosity; when the porosity was increased, insufficient ceramic strength prohibited a tight initial bone-implant fit. As a consequence, inadequate initial implant stability resulted in a soft tissue encapsulation of the majority of the ceramic implants. Histological examination and mechanical testing results were similar for bone-ingrown implants exposed to different experimental stresses for 4, 5, 8, and 12 months. Bone ingrowth and interface shear strengths were also similar in the different VMC pore sizes and shapes investigated. The design of intraoral attachments appeared critical, at least in swine where no postoperative treatment was administered. Gingival inflammation and alveolar bone resorption caused by calculus were severe around truncated cone-shaped devices. Slender transgingival posts, occlusal caps, and crown restorations were less susceptible to calculus accumulation, resulting in a more satisfactory gingival and subgingival response. Excessive epithelial invagination was a problem only in implants with transgingival truncated cones. Good adherence of soft tissue to metal under the gingival mucosa prevented epithelial migration around implants with other transgingival devices. Alveolar bone resportion around the tops of bone-ingrown implants was minimal at the time intervals examined (up to one year); however, a definite conclusion should be delayed until longer-term implants under full occlusion are evaluated.

Aluminum↗