Showing papers by "Lund University published in 1995"

A new model for control of systems with friction

Abstract: In this paper we propose a new dynamic model for friction. The model captures most of the friction behavior that has been observed experimentally. This includes the Stribeck effect, hysteresis, spring-like characteristics for stiction, and varying break-away force. Properties of the model that are relevant to control design are investigated by analysis and simulation. New control strategies, including a friction observer, are explored, and stability results are presented. >

Human Aging, Muscle Mass, and Fiber Type Composition

Abstract: To assess the age-related loss of muscle mass and to determine the mechanisms behind this aging atrophy, the muscle structure and fiber type composition have been estimated, using invasive and noninvasive techniques. Limb muscles from older men and women are 25-35% smaller and have significantly more fat and connective tissue than limb muscles from younger individuals. Comparisons of muscle biopsies from younger and older individuals reveal that type 2 (fast-twitch) fibers are smaller in the old, while the size of type 1 (slow-twitch) fibers is much less affected. Studies of whole muscle cross sections also show a significantly smaller number of muscle fibers, a significantly lower relative type 2 fiber area, and a significant increase in fiber type grouping with increasing age. These results indicate a gradual decrease in size/volume with advancing age, accompanied by a replacement by fat and connective tissue. This aging atrophy seems to be due to a reduction in both number and size of muscle fibers, mainly of type 2, and is to some extent caused by a slowly progressive neurogenic process.

Forelimb akinesia in the rat Parkinson model: differential effects of dopamine agonists and nigral transplants as assessed by a new stepping test

Abstract: Methods for the assessment of akinesia in the unilateral rat Parkinson model have so far been lacking. The experiments reported here evaluate the usefulness of a new "stepping test" to monitor forelimb akinesia in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesencephalic dopamine (DA) system, and to assess the ability of DA-receptor agonists and fetal DA neuron transplants to reverse these deficits. The 6-OHDA lesion induced marked and long-lasting impairments in the initiation of stepping movements with the contralateral paw. Systemic injections of low doses (chosen to be subthreshold for induction of rotation) of the mixed D1 and D2 receptor agonist apomorphine, the D1-selective agonist SKF 38393, and to a lesser extent also the D2-selective agonist quinpirole were effective in reversing these deficits. Similar effects was seen after a subrotational dose of L-dopa, whereas amphetamine had no effect. Fetal nigral transplants, implanted as multiple deposits in the ipsilateral caudate-putamen and substantia nigra, restored initiation of stepping to a similar degree as the DA agonists. Nigral grafts placed in substantia nigra alone were also effective, although the improvement was less pronounced. Apomorphine, at a dose effective in the lesion-only animals, had no additive effect in the grafted rats, whereas amphetamine appeared to further improve stepping in the rats with intranigral transplants. Identical experiments were performed on skilled forelimb use in the so-called staircase test. Interestingly, neither the DA agonist drugs nor the nigral transplants had any effects on the lesion induced deficits in this more complex task. The results show that forelimb stepping is a highly useful test to monitor lesion-/and transplant-induced changes in forelimb akinesia, a behavioral parameter that may be analogous to limb akinesia and gait problems seen in patients with Parkinson's disease.

Association of a polymorphism in the β3-adrenergic receptor gene with features of the insulin resistance syndrome in Finns

Abstract: Background Because visceral obesity predicts insulin resistance, we studied whether alterations in the gene encoding for the β3-adrenergic receptor in visceral fat are associated with insulin resistance. Methods We studied the frequency of a cytosine-to-thymidine mutation that results in the replacement of tryptophan by arginine at position 64 (Trp64Arg) of the β3-adrenergic receptor by restriction-enzyme digestion with BstOI in 335 subjects from western Finland, 207 of whom were nondiabetic and 128 of whom had non-insulin-dependent diabetes mellitus (NIDDM). We also determined the frequency of the mutation in 156 subjects from southern Finland. Sensitivity to insulin was measured by the hyperinsulinemic–euglycemic clamp technique in 66 randomly selected nondiabetic subjects. Results In the subjects from western Finland, the frequency of the mutated allele was similar in the nondiabetic subjects and the subjects with NIDDM (12 vs. 11 percent). The mean age of the subjects at the onset of diabetes was lowe...

Noninvasive MRI thermometry with the proton resonance frequency (PRF) method: in vivo results in human muscle.

Abstract: The noninvasive thermometry method is based on the temperature dependence of the proton resonance frequency (PRF). High-quality temperature images can be obtained from phase information of standard gradient-echo sequences with an accuracy of 0.2 degrees C in phantoms. This work was focused on the in vivo capabilities of this method. An experimental setup was designed that allows a qualitative in vivo verification. The lower-leg muscles of a volunteer were cooled and afterwards reheated with an external water bolus. The temperature of the bolus water varied between 17 degrees C and 37 degrees C. The in vivo temperature images can be used to extract the temperature in muscle tissue. The data in the fat tissue are difficult to interpret because of the predominance of susceptibility effects. The results confirm the method's potential for hyperthermia control.

Roentgen stereophotogrammetric analysis as a predictor of mechanical loosening of knee prostheses

Abstract: The tibial components in 143 patients with total knee replacements performed before 1988 were assessed for micromotion using roentgen stereophotogrammetric analysis (RSA) over a period of 13 years. The fixation of the prostheses remained clinically sound in all cases, although revision had been required for other reasons in seven. In a second group taken from all cases with RSA available on our full database to 1990, 15 tibial components had been followed by RSA from the insertion until, 1 to 11 years after the initial arthroplasty, they were revised for mechanical loosening of the tibial component; 12 of these comprised all the loosenings in the base group, thus making a total of 155 consecutive cases, while an additional three were inserted after the base material had been compiled. The mean migration in the first group was about 1 mm at one year, but subsequent migration was slower, reaching a mean of about 1.5 mm after ten years. About one-third migrated continuously throughout follow-up, while two-thirds ceased to migrate after one to two years. In the revision group, 14 components had migrated continuously and at one year significantly more than those in the first group. One revision case lacked the crucial one-year follow-up and could not be classified. These findings suggest that mechanical loosening begins early in the postoperative period. Clinical symptoms which necessitate revision, seen at this stage in 20% of abnormally migrating tibial components, may not appear until up to ten years after the operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of two csg operons is required for production of fibronectin‐ and Congo red‐binding curli polymers in Escherichia coli K‐12

Abstract: Two divergently transcribed operons in Escherichia coli required for the expression of fibronectin- and Congo red-binding curli polymers were identified and characterized by transposon mutagenesis, sequencing and transcriptional analyses, as well as for their ability to produce the curli subunit protein. The csgBA operon encodes CsgA, the major subunit protein of the fibre, and CsgB, a protein with sequence homology to CsgA. A non-polar csgB mutant is unaffected in its production of CsgA, but the subunit protein is not assembled into insoluble fibre polymers. A third open reading frame, orfC, positioned downstream of csgA may affect some functional property of curli since an insertion in this putative gene abolishes the autoagglutinating ability typical of curliated cells without affecting the production of the fibre. The promoter for the oppositely transcribed csgDEFG operon was identified by primer extension and shown, like the csgBA promoter, to be dependent upon the alternate stationary phase-specific sigma factor sigma s in wild-type cells, but not in mutants lacking the nucleoid associated protein H-NS. Insertions in csgD abolish completely trancription from the csgBA promoter. Therefore, any regulatory effect on the csgBA promoter might be secondary to events controlling the csgDEFG promoter and/or activation of CsgD. Insertions in csgE, csgF and csgG abolish curli formation but allow CsgA expression suggesting that one or more of these gene products are involved in secretion/assembly of the CsgA subunit protein. No amino acid sequence homologies were found between the CsgE, CsgF and CsgG proteins and secretion/assembly proteins for other known bacterial fibres, suggesting that the formation of curli follows a novel pathway.

Chronic Achilles tendinopathy. A survey of surgical and histopathologic findings

Abstract: The surgical findings and the histopathology are reported for 163 patients (134 males, 29 females; mean age, 38 years; range, 13-72 years; 75% athletes) with chronic Achilles tendinopathy. Biopsy specimens from symptomatic (155 cases) and nonsymptomatic (90 cases) parts of the tendon and from the paratenon (97 cases) were obtained. Surgical reports were reviewed and histopathology was evaluated according to a standardized protocol. Eighteen tendons also were analyzed by immunofluorescence for fibrinogen, immunoglobulins, and complement. Degenerative changes (tendinosis) characterized by abnormal fiber structure, focal hypercellularity, and vascular proliferation were noted in 90% of biopsy specimens from symptomatic parts of the tendons and, to a lesser degree, in 20% from nonsymptomatic parts. Fibrinogen could be identified in most lesion biopsy specimens. Partial tendon ruptures were present in 19% of the patients and always occurred in areas afflicted with tendinosis. The paratenon was mostly normal or revealed only slight changes. Increasing age and male gender were associated with more pronounced histopathologic changes. Tendinosis, sometimes complicated by partial rupture, appears to be the major lesion in chronic Achilles tendinopathy; the paratenon is rarely involved. Important features are a lack of inflammatory cells and a poor healing response.

Microbial community structure and pH response in relation to soil organic matter quality in wood-ash fertilized, clear-cut or burned coniferous forest soils

Abstract: Humus phospholipid fatty acid (PLFA) analysis was used in clear-cut, wood-ash fertilized (amounts applied: 1000, 2500, and 5000 kg ha−1), or prescribed burned (both in standing and clear-cut) coniferous forests to study the effects of treatments on microbial biomass and community structure. The microbial biomass (total PLFAs) decreased significantly due to the highest rate of wood-ash fertilization, clear-cutting, and the two different fire treatments when compared to control amounts. Fungi appeared more seriously reduced by these treatments than bacteria, as revealed by a decreased index of fungal:bacterial PLFAs when compared to the controls. The community structure was evaluated using the PLFA pattern. The largest treatment effect was due to burning in both areas studied, which resulted in increases in 16:1ω5 and proportional decreases in 18:2ω6. Clear-cutting and the different amounts of ash application resulted in similar changes in the PLFA pattern to the burning treatments, but these were less pronounced. Attempts to correlate the changes in the PLFA pattern to soil pH, bacterial pH response patterns (measured using thymidine incorporation), or substrate quality (measured using IR spectroscopy) were only partly successful. Instead, we hypothesize that the changes in the PLFA pattern of the soil organisms were related to an altered substrate quantity, that is the availability of substrates after the treatments.

Carbon paste electrodes modified with enzymes, tissues, and cells

Abstract: A review is presented dealing with the use of carbon paste amperometric electrodes for electroanalytical purposes, with either the surface or the bulk being modified with biologically derived material such as enzymes, tissues, and cells It covers virtually all the publications which have appeared from the very first enzyme-modified carbon paste electrode up to early 1994 and includes 220 references

An Epidemiologic Study of Lyme Disease in Southern Sweden

Abstract: Background Lyme disease is the most common vector-borne infection in some temperate regions of the Northern Hemisphere. However, for most areas of endemic disease reliable epidemiologic data are sparse. Methods Over a one-year period, we conducted a prospective, population-based survey of cases of Lyme disease in southern Sweden. The diagnosis was made on the basis of the presence of erythema migrans at least 5 cm in diameter or characteristic clinical manifestations such as arthritis, neuroborreliosis, and carditis. Results We identified 1471 patients with Lyme disease, for an overall annual incidence of 69 cases per 100,000 inhabitants. The incidence varied markedly according to geographic region, and there were several areas where disease was widely prevalent. The incidence varied according to age, with the highest rates among people 5 to 9 and 60 to 74 years of age, but not according to sex. The most frequent clinical manifestation was erythema migrans (seen in 77 percent of all cases), followed by ne...

Apoptosis induced by a human milk protein

Abstract: To the breast-fed infant, human milk is more than a source of nutrients; it furnishes a wide array of molecules that restrict microbes, such as antibodies, bactericidins, and inhibitors of bacterial adherence. However, it has rarely been considered that human milk may also contain substances bioactive toward host cells. While investigating the effect of human milk on bacterial adherence to a human lung cancer cell line, we were surprised to discover that the milk killed the cells. Analysis of this effect revealed that a component of milk in a particular physical state--multimeric alpha-lact-albumin--is a potent Ca(2+)-elevating and apoptosis-inducing agent with broad, yet selective, cytotoxic activity. Multimeric alpha-lactalbumin killed all transformed, embryonic, and lymphoid cells tested but spared mature epithelial elements. These findings raise the possibility that milk contributes to mucosal immunity not only by furnishing antimicrobial molecules but also by policing the function of lymphocytes and epithelium. Finally, analysis of the mechanism by which multimeric alpha-lactalbumin induces apoptosis in transformed epithelial cells could lead to the design of antitumor agents.

Glial cell line-derived neurotrophic factor but not transforming growth factor beta 3 prevents delayed degeneration of nigral dopaminergic neurons following striatal 6-hydroxydopamine lesion.

Abstract: Glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor beta 3 (TGF-beta 3) are members of the TGF-beta superfamily with high neurotrophic activity on cultured nigral dopamine neurons. We investigated the effects of intracerebral administration of GDNF and TGF-beta 3 on the delayed cell death of the dopamine neurons in the rat substantia nigra following 6-hydroxydopamine lesions of dopaminergic terminals in the striatum. Fluorescent retrograde tracer injections and tyrosine hydroxylase immunocytochemistry demonstrated nigral degeneration with an onset 1 week after lesion, leading to extensive death of nigral neurons 4 weeks postlesion. Administration of recombinant human GDNF for 4 weeks over the substantia nigra at a cumulative dose of 140 micrograms, starting on the day of lesion, completely prevented nigral cell death and atrophy, while a single injection of 10 micrograms 1 week postlesion had a partially protective effect. Continuous administration of TGF-beta 3, starting on the day of lesion surgery, did not affect nigral cell death or atrophy. These findings support the notion that GDNF, but not TGF-beta 3, is a potent neurotrophic factor for nigral dopamine neurons in vivo.

Xylose-metabolizing Saccharomyces cerevisiae strains overexpressing the TKL1 and TAL1 genes encoding the pentose phosphate pathway enzymes transketolase and transaldolase

Abstract: Saccharomyces cerevisiae was metabolically engineered for xylose utilization. The Pichia stipitis CBS 6054 genes XYL1 and XYL2 encoding xylose reductase and xylitol dehydrogenase were cloned into S. cerevisiae. The gene products catalyze the two initial steps in xylose utilization which S. cerevisiae lacks. In order to increase the flux through the pentose phosphate pathway, the S. cerevisiae TKL1 and TAL1 genes encoding transketolase and transaldolase were overexpressed. A XYL1- and XYL2-containing S. cerevisiae strain overexpressing TAL1 (S104-TAL) showed considerably enhanced growth on xylose compared with a strain containing only XYL1 and XYL2. Overexpression of only TKL1 did not influence growth. The results indicate that the transaldolase level in S. cerevisiae is insufficient for the efficient utilization of pentose phosphate pathway metabolites. Mixtures of xylose and glucose were simultaneously consumed with the recombinant strain S104-TAL. The rate of xylose consumption was higher in the presence of glucose. Xylose was used for growth and xylitol formation, but not for ethanol production. Decreased oxygenation resulted in impaired growth and increased xylitol formation. Fermentation with strain S103-TAL, having a xylose reductase/xylitol dehydrogenase ratio of 0.5:30 compared with 4.2:5.8 for S104-TAL, did not prevent xylitol formation.

Enhanced bacterial growth in response to photochemical transformation of dissolved organic matter

Abstract: We tested the hypothesis that light, especially UV-B radiation, increases the availability of dissolved organic matter (DOM) to pelagic bacteria in lake water. Filtered (0.2 μm) and autoclaved humic lake water (water color 70 mg Pt liter −1 , 12 mg dissolved organic C liter −1 ) was exposed to simulated sunlight (UV-B, 1.14 W m −2 ; UV-A, 3.87 W m −2 ; and PAR, 20 W m −2 ) for various periods of time (0-100 h). Irradiated water was then inoculated with a natural bacterial assemblage (0.6-μm filtered water) and bacterial yield was measured in the stationary phase of the resulting batch cultures. Both bacterial numbers and cell volumes increased (numbers by 65% and volumes as much as 360%) with increasing UV radiation, resulting in an almost sixfold increase in bacterial biomass. Our experiment shows that light exposure can enhance availability of natural lake DOM to bacteria, possibly through cleavage of macromolecules into smaller units, and may influence both carbon cycling and food webs in lake water

Shapes and shells in nuclear structure

Abstract: Preface 1. Introduction 2. Charge and matter distribution in nuclei 3. The semi-empirical mass formula and nuclear stability 4. Nuclear fission and the liquid-drop model 5. Shell structure and magic numbers 6. The nuclear one-particle potential in the spherical case 7. The magnetic dipole moment and electric quadrupole moment for nuclei with closed shells +/- one nucleon 8. Single-particle orbitals in deformed nuclei 9. The shell correction method and the nuclear deformation energy 10. The barrier penetration problem - fission and alpha-decay 11. Rotational bands - the particle-rotor model 12. Fast nuclear rotation - the cranking model 13. The nucleon-nucleon two-body interaction 14. The pairing interaction Solutions to exercises.

Molecular Cloning and Functional Expression of the Gene Encoding the Human Proteinase‐Activated Receptor 2

Abstract: We previously reported the molecular cloning of a mouse guanosine-nucleotide-binding-protein-coupled receptor similar to the thrombin receptor. Since the physiological agonist was unknown, the receptor was named proteinase-activated receptor 2. We describe here the cloning and functional expression of the gene encoding the corresponding human receptor. The gene is divided into two exons separated by about 14 kb intronic DNA. The deduced protein sequence is 397 amino acids long and 83% identical to the mouse receptor sequence. Within the extracellular amino terminus, the residues predicted to form the tethered agonist ligand differ between the two receptors; of the first six residues only four are conserved. At positions five and six, a lysine residue and a valine residue, respectively, have replaced arginine and leucine residues found in the mouse sequence. When the human receptor is expressed in Chinese hamster ovary cells, it can be activated by low nanomolar concentrations of the serine proteinase trypsin and by peptides made from the receptor sequence. Northern-blot analysis of receptor expression showed that the receptor transcript is widely expressed in human tissues with especially high levels in pancreas, liver, kidney, small intestine and colon. Moderate expression was detected in many organs but none in brain or skeletal muscle. By fluorescence in situ hybridization, the human proteinase-activated receptor 2 gene was mapped to chromosomal region 5q13, where, previously, the related thrombin receptor gene has been located.

Environment Influences Functional Outcome of Cerebral Infarction in Rats

Abstract: Background and Purpose The purpose of this study was to determine whether preoperative and postoperative enrichment of the environment can enhance the functional outcome after cerebral infarction in rats. Methods The right middle cerebral artery was ligated in adult spontaneously hypertensive male rats, and the functional outcome was studied for 12 weeks after the operation. Three groups were compared: A, rats kept in individual cages before and after the operation (n=9); B, rats kept in individual cages before the operation but transferred to an enriched environment after the operation (n=10); and C, rats kept in an enriched environment all the time (n=12). The enriched environment consisted of a large cage with opportunities for various activities, but rats were not forced to do any particular tasks. Results Rats kept in an enriched environment (groups B and C) performed significantly better than rats in group A in a leg-placement test, beam walking, walking on a rotating pole, and climbing. The infarct...

Neurological complications after anaesthesia. A follow-up of 18,000 spinal and epidural anaesthetics performed over three years.

Abstract: 17 733 consecutive central blocks (8501 spinal and 9232 epidural anaesthetics) performed during a three-year period were analyzed for alleged complications. Neurological complications related to anaesthesia were reported in 17 cases of which 13 patients had persisting lesions after three spinal and ten epidural blocks. In two patients given spinal anaesthesia, the technique was inadequate. In seven epidural blocks, the connection between neurological lesion and the anaesthetic technique could be argued. In five of these cases, polyneuropathy or nonspecific neurological symptoms were present. Three complications after epidural blocks were paraplegias caused by spinal haematomas in patients with deranged haemostatic capacity.