Biomedical subjects
Publications and source records attributed to M Bayer.
We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.
Exciton fine structure in InAs/GaAs coupled quantum dots has been studied by photoluminescence spectroscopy in magnetic fields up to 8 T. Pronounced anticrossings and mixings of optically bright and dark states as functions of magnetic field are seen. A theoretical treatment of the mixing of the excitonic states has been developed, and it traces observed features to structural asymmetries. These results provide direct evidence for coherent coupling of excitons in quantum dot molecules.
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Spontaneous emission of quantum dot systems in laterally structured microcavities that exhibit photon confinement in all three directions has been studied by time-resolved photoluminescence spectroscopy. For on-resonance conditions, we find that the dot emission rate is increased substantially over that of the unstructured planar cavity. For off-resonance conditions, we are able to suppress the emission rate by an order of magnitude by using cavities with metal coatings, which we attribute to the suppression of leaky optical modes in these structures.
Isomeric photonic molecules were formed by connecting four identical cavities in different geometries: a chain, a square, and a T shape. The optical mode spectrum in these structures exhibits three-dimensionally confined photonic states, which have been studied by photoluminescence spectroscopy. The energies of the optical modes depend strongly on the molecule geometry. The experimental data are in good agreement with detailed calculations of the fields in the cavities.
We demonstrate coupling and entangling of quantum states in a pair of vertically aligned, self-assembled quantum dots by studying the emission of an interacting electron-hole pair (exciton) in a single dot molecule as a function of the separation between the dots. An interaction-induced energy splitting of the exciton is observed that exceeds 30 millielectron volts for a dot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spin. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.
Osteoporosis is common in patients with anorexia nervosa (AN), but ultrasound has so far been scarcely used to detect it We measured calcaneal broadband ultrasound attenuation (BUA) and velocity of sound (VOS) in 26 AN girls (mean age 15.1+/- 1.5 years) using a Cuba Clinical device (McCue Ultrasonics, UK). Basic anthropometric (body weight, height and body mass index--BMI) and clinical data (mean duration of AN, number of absent cycles, weight loss) were collected. All of the girls reported that they did at least one hour's vigorous exercise a day. BUA was significantly lower (p<0.004) and VOS significantly higher (p<0.0001) in comparison with reference data. Body weight and BMI at the time of the measurements were significantly lower than the reference data (p<0.0001). There were no correlations between body weight or height and BUA or VOS, but there was a slight correlation between BUA and BMI (r=0.4, p<0.05) and a slight inverse correlation between VOS, body weight and BMI (r=-0.48 and r=-0.43, p<0.01). VOS slightly correlated with weight loss (r=0.4, p<0.05), significantly with the weekly number of exercise hours (r=0.48, p<0.01). The duration of AN, the number of missed cycles and the percentage of weight loss did not correlate with BUA, and neither the duration of AN nor the number of missed cycles correlated with VOS. The low BUA value could be attributed to poor nutrition, and substantial physical activity may lead to the increase in VOS. In conclusion, girls with AN have low BUA and high VOS values, neither of which correlate with the duration of AN or the number of missed cycles.
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To detect specific partners of the small Golgi-localized GTPase rab1b we generated rab1b mutants and used them as bait proteins in yeast two-hybrid screens. We isolated several specifically interacting clones. Two of them encode large protein fragments highly homologous to rat GM130 and to human Golgin95. The full-length human GM130 cDNA was cloned and its interaction with rab1b was characterized in detail by yeast two-hybrid and in vitro binding assays. Here we report for the first time that the rab1b protein interacts specifically with GM130 in a GTP-dependent manner and therefore needs the hypervariable regions of the N- and C-termini. We mapped the rab1b binding site of GM130 and provide evidence that it is different to the previously described p115 and Grasp65 binding sites of the GM130 protein.
Protein P19 encoded by the conjugative resistance plasmid R1 has been identified as being one member of a large family of muramidases encoded by bacteriophages and by type III and type IV secretion systems. We carried out a mutational analysis to investigate the function of protein P19 and used in vivo complementation assays to test those of several P19 mutants. The results indicated that conserved residues present in the presumed catalytic center of P19 are absolutely essential for its function in conjugation of plasmid R1 and infection by the RNA phage R17. Overexpression of protein P19 in an early growth phase resulted in a massive lysis of Escherichia coli cells in liquid culture, as indicated by a rapid and distinct decrease in cell culture densities after induction. Change of the proposed catalytic glutamate at position 44 to glutamine completely abolished this effect. P19-induced cell lysis was directly shown by transmission and scanning electron microscopy. Typically, P19-overexpressing cells showed bulges protruding from the cell surfaces. Our interpretation is that these protrusions arose from a localized and spatially confined disruption of the bacterial cell wall. To our knowledge such an effect has not previously been documented for any member of the lytic transglycosylase family. From the data presented here, we conclude that protein P19 possesses the proposed localized peptidoglycan-hydrolyzing activity. This activity would be a prerequisite for efficient penetration of the cell envelope by the DNA translocation complex encoded by the conjugative plasmid.
A simulator for testing finger joint replacements was developed. Movement intervals of 15 degrees at flexion and extension plain can be set using an adjustable crank drive. The maximum range of motion is 105 degrees, 90 degrees being the maximum flexion and 15 degrees the extension. Thus, the simulator is also suitable for impingement tests. A constant joint load is infinitely variable from 20 N to 500 N. Test frequency is also infinitely variable from 0.2 Hz to 2 Hz. A modular assembly of the components of the prosthesis means that these can be positioned as required, and that any type of prosthesis may be tested. The design and the material allow for an all-round lubrication at a heat up to 37 degrees C. The equipment is designed for permanent operation. Pre-clinical quality assurance for finger joint replacements can be considerably improved by the implementation of the present simulator.
The excitonic absorption spectrum of a single quantum dot is investigated theoretically and experimentally. The spectrum is determined by an interacting electron-valence-hole complex. We show that the mixing of quantum configurations by two-body interactions leads to distinct absorption spectra controlled by the number of confined electronic shells. The theoretical results are compared with results of photoluminescence excitation spectroscopy on a series of single self-assembled In0.60Ga0.40As quantum dots.
Quantum dots or 'artificial atoms' are of fundamental and technological interest--for example, quantum dots may form the basis of new generations of lasers. The emission in quantum-dot lasers originates from the recombination of excitonic complexes, so it is important to understand the dot's internal electronic structure (and of fundamental interest to compare this to real atomic structure). Here we investigate artificial electronic structure by injecting optically a controlled number of electrons and holes into an isolated single quantum dot. The charge carriers form complexes that are artificial analogues of hydrogen, helium, lithium, beryllium, boron and carbon excitonic atoms. We observe that electrons and holes occupy the confined electronic shells in characteristic numbers according to the Pauli exclusion principle. In each degenerate shell, collective condensation of the electrons and holes into coherent many-exciton ground states takes place; this phenomenon results from hidden symmetries (the analogue of Hund's rules for real atoms) in the energy function that describes the multi-particle system. Breaking of the hidden symmetries leads to unusual quantum interferences in emission involving excited states.
Protein P19 encoded by the conjugative resistance plasmid R1, is essential for efficient conjugative DNA transfer and infection by the pilus-specific RNA phage R17. Based on sequence homologies P19 belongs to a family of lysozyme-like virulence factors which are found in type III and type IV secretion systems. In this report we describe the processing and subcellular localization of P19. Pulse-chase experiments were used to demonstrate the processing of P19 by the signal peptidase I of Escherichia coli. Translocation of P19 across the inner membrane was shown by gene 19-phoA fusions. Cell fractionation studies of P19 expressing cells showed the presence of P19 in the membrane compartment. P19 was solubilized with the detergent Sarkosyl indicating an inner membrane localization. Using sucrose density gradient centrifugation to separate inner and outer membranes, P19 was found in both membrane fractions. Taken together, our data suggest that mature P19 is a periplasmic protein which may be attached to the proposed membrane-spanning DNA transport complex.
Dual energy X-ray absorptiometry was performed in 44 patients with phenylketonuria (PKU) aged 6-29 y. The phenylalanine-restricted diet was based on a low-protein diet in combination with phenylalanine-free amino acid mixtures and phenylalanine-low casein hydrolysate in 32 patients. The 10 oldest patients were supplemented only with casein hydrolysate, and the youngest child received only the amino acid mixture. One patient has recently come off the diet. Bone mineral density (BMD) of the lumbar spine and total BMD were measured and expressed as Z-score, i.e. the difference between the BMD of the patient and the average BMD of sex- and age-matched controls divided by the standard deviation of the control group. Normal BMD was found in 24 (54%) patients. Lumbar spine BMD was decreased in 20 patients and total BMD was decreased in 14 patients. Z-scores of -1to 2.5 were found in 14 patients (32%) and Z-scores of <-2.5 in 6 patients (14%). No significant correlation was found between total or lumbar spine BMD and daily intake of phenylalanine from natural sources in the low-protein diet or the amount of phenylalanine-free amino acid mixtures per kg of body weight. A significant negative correlation was observed between both total and lumbar spine BMD Z-scores and the amount of casein hydrolysate supplementation per kg of body weight (r = - 0.45; y = 0.07 - 0.69x; p < 0.01). Long-lasting dietary restriction in patients with PKU may increase the risk of late complications of dietary therapy, such as osteoporosis or trace element deficiency. O Bone mineral density, osteoporosis, phenylalanine-low diet, phenylketonuria
Canadian psychiatric nurses (N = 1,701) participated in a survey in which they-assessed their ability to nurse clients with a history of sexual abuse when cultural differences are present. Thirty-nine percent worked at a facility having a significant number of clients from a different culture. Only 4.6% rated themselves as "very competent." Four themes emerged from nurses' assessment of their ability: culture is not the problem, culture is not an issue, culture influences perspective and responses, and culturally specific competence. Only one cultural group, First Nations, was identified by sufficient numbers of nurses to generate themes concerning the challenge of working with clients from a particular culture. These themes (abuse as a cultural norm, concurrent and related health and social problems, reluctance to talk about problems, a need to learn about First Nations culture, and developing culturally competent caregivers), critical areas of concern, and possible solutions suggested by the nurses are discussed.
BACKGROUND: The objective of this study was to evaluate expenditures and efficacy of osteoporosis treatment in the Czech Republic (CZ) (1.38 million women and 0.99 million men > 55 years of age). METHODS AND RESULTS: Demographic data, incidence of hip fractures and prevalence of osteoporosis and osteopenia in Czech women and men, cost burden to healthcare agencies due to hip fractures and costs of diagnostic procedures, preventive measures and therapies of osteoporosis were obtained from published data and from database of the main health insurance agency (VZP) and the State Institute for Drug Control. The direct costs for treatment of hip fractures in the CZ in 1997 averaged Kc (Czech Crown) 2.5 billion, diagnosis of osteoporosis, Kc 150 million, prevention of osteoporosis using hormone replacement therapy, Kc 66 million, and treatments of osteoporosis which has been applied to less than 5% of osteoporosis patients, 482 million. However, despite the continuously increasing expenditures for treatments of osteoporosis, the incidence of hip fractures doubled in the last 10 years. This is mainly due to increased life expectancy in Czech women and men. CONCLUSIONS: The results of this first economic evaluation of diagnosis, treatment and consequences of osteoporosis in the CZ indicate a need for conceptual decisions in both treatment and prevention of osteoporosis.
Pseudohypoaldosteronism type I (PHA1) is characterized by neonatal renal salt wasting with dehydration, hypotension, hyperkalaemia and metabolic acidosis, despite elevated aldosterone levels. Two forms of PHA1 exist. An autosomal recessive form features severe disease with manifestations persisting into adulthood. This form is caused by loss-of-function mutations in genes encoding subunits of the amiloride-sensitive epithelial sodium channel (ENaC; refs 2,3). Autosomal dominant or sporadic PHA1 is a milder disease that remits with age. Among six dominant and seven sporadic PHA1 kindreds, we have found no ENaC gene mutations, implicating mutations in other genes. As ENaC activity in the kidney is regulated by the steroid hormone aldosterone acting through the mineralocorticoid receptor, we have screened the mineralocorticoid receptor gene (MLR) for variants and have identified heterozygous mutations in one sporadic and four dominant kindreds. These include two frameshift mutations (one a de novo mutation), two premature termination codons and one splice donor mutation. These mutations segregate with PHA1 and are not found in unaffected subjects. These findings demonstrate that heterozygous MLR mutations cause PHA1, underscore the important role of mineralocorticoid receptor function in regulation of salt and blood pressure homeostasis in humans and motivate further study of this gene for a potential role in blood pressure variation.