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Biomedical subjects

A Madsen

Publications and source records attributed to A Madsen.

At least 19 recordsLinked to original sources
PubMed2004

Surface roughness of supercooled polymer melts.

We report on in situ x-ray reflectivity measurements of the surface roughness of supercooled glass forming polymers in a temperature range from 190 to 330 K. The experimentally determined rms roughness has been found to obey the capillary wave model of a single liquid/vapor interface over the entire temperature range. An expression for the surface roughness below the bulk glass transition (T(G) approximately equal to 200 K) is deduced from the viscoelastic theory of surface fluctuations; however, no indication of a frozen-in surface roughness has been observed in the experiment. Additionally, it is shown that precise values of the surface tension of highly viscous liquids in the supercooled state can be determined by x-ray reflectivity.

Journal Article↗
PubMed2004

Capillary waves at the transition from propagating to overdamped behavior.

We measure the dispersion relation of capillary waves on a liquid surface by heterodyne x-ray photon correlation spectroscopy near the transition from propagating to overdamped dynamic behavior. A strong deviation of the propagation frequency from the small-damping result omega(p) proportional, variant k(3/2) is observed long before the actual transition where ( partial differential omega(p)/ partial differential k)<0 and omega(p) tends to zero. This behavior is successfully described by expressions derived within linear response theory.

Journal Article↗
PubMed2003

Observation of heterodyne mixing in surface x-ray photon correlation spectroscopy experiments.

We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau).

Journal Article↗
PubMed2001

Surface ordering in a concentrated suspension of colloidal particles investigated by x-ray scattering methods.

The spatial arrangement of colloids near the free surface of a concentrated suspension of colloidal silica in water is investigated by means of x-ray scattering. The weakly charged particles are found to organize in layers along the surface normal direction. The degree of layering decreases with increasing distance from the surface and three layers are identified from the scattering profile. In the lateral direction, the scattering profile indicates a random spatial arrangement of particles at the surface. Based on the findings, a simple structural model for the near surface arrangement of colloidal particles in this system is proposed.

Journal Article↗
PubMed2001

The LlaGI restriction and modification system of Lactococcus lactis W10 consists of only one single polypeptide.

The naturally occurring 12.1-kb plasmid, pEW104, in Lactococcus lactis ssp. cremoris W10 was found to confer decreased bacteriophage sensitivity to its host. Plasmid pEW104 encodes a non-classic restriction and modification (R/M) system, named LlaGI, consisting of only one single polypeptide. Analysis of the amino acid sequence revealed the presence of a catalytic motif and seven helicase-like motifs (DEAD-box motifs) characteristic of type I and III endonucleases, followed by four conserved methylase motifs characteristic of adenine-methylases. A comparison between LlaGI and the very similar R/M system, LlaBIII, suggests that the C-terminal region of LlaGI, apparently containing no known motifs, could possibly specify target DNA recognition. Conceivably, the LlaGI gene is included in the operon of the plasmid replication machinery. Finally, it is proposed that LlaGI represents a variant of the type I R/M systems.

Amino Acid Sequence↗
PubMed2000

Characterization of a novel plasmid-encoded HsdS subunit, S.LlaW12I, from Lactococcus lactis W12.

A novel type I restriction-modification specificity subunit, S. LlaW12I, has been identified on the naturally occurring 8.0-kb plasmid pAW122 in the lactic acid bacterium Lactococcus lactis subsp. cremoris W12. Presence of the HsdS protein together with a complete type I restriction-modification system conferred increased phage restriction to the host, indicating exchange of specificity subunits. Sequence analysis showed that the S.LlaW12I subunit is most probably of type IC. Presumably, the hsdS gene is organized together with the repB gene on one transcriptional unit.

Amino Acid Sequence↗
PubMed1999

Cortical brain dysfunction in early schizophrenia: secondary pathogenetic hierarchy of neuroplasticity, psychopathology and social impairment.

Schizophrenia has the quality of a 'top-down' disorder with perturbation of self, and malattuned appraisal of basic experience of the outside world, and of intentionality. There is dissonance between the faculties of consciousness. The neuronal cortical network displays distributed activation of the sensory cortices during perception, and retroactivation during recall. This multimodal organization is sensitive to aberrations of structure and informational content during the metabolically dynamic phases of expansion and pruning in childhood and adolescence. There is substantial evidence of deviant function of the cortical network in schizophrenia. This includes increased neuronal density, reduced prefrontal capacity for activation, impaired fronto-temporal interaction during language production, defect monitoring of inner speech, activation of secondary sensory cortices during hallucinations, reduced cortical and thalamic volume, reduced thalamic activation (filtering) and sensitization of dopaminergic modulation. As a hypothesis the cortical defects lead to secondary causation of abnormalities at the levels of neuroplasticity, symptomatology and social competence. Suggestions for empirical testing are presented for the hypothesis that neocortical defects are primary, thalamic defects secondary and dopaminergic aberrations tertiary in the schizophrenic process. This testing of hypotheses involves prospective studies of patient groups at various ages of onset, as well as comparison of neurobiological measures in remitting vs. treatment-resistant cases.

Cerebral Cortex↗
PubMed1998

Cloning and characterization of the lactococcal plasmid-encoded type II restriction/modification system, LlaDII.

The LlaDII restriction/modification (R/M) system was found on the naturally occurring 8.9-kb plasmid pHW393 in Lactococcus lactis subsp. cremoris W39. A 2.4-kb PstI-EcoRI fragment inserted into the Escherichia coli-L. lactis shuttle vector pCI3340 conferred to L. lactis LM2301 and L. lactis SMQ86 resistance against representatives of the three most common lactococcal phage species: 936, P335, and c2. The LlaDII endonuclease was partially purified and found to recognize and cleave the sequence 5'-GC decreases NGC-3', where the arrow indicates the cleavage site. It is thus an isoschizomer of the commercially available restriction endonuclease Fnu4HI. Sequencing of the 2.4-kb PstI-EcoRI fragment revealed two open reading frames arranged tandemly and separated by a 105-bp intergenic region. The endonuclease gene of 543 bp preceded the methylase gene of 954 bp. The deduced amino acid sequence of the LlaDII R/M system showed high homology to that of its only sequenced isoschizomer, Bsp6I from Bacillus sp. strain RFL6, with 41% identity between the endonucleases and 60% identity between the methylases. The genetic organizations of the LlaDII and Bsp6I R/M systems are identical. Both methylases have two recognition sites (5'-GCGGC-3' and 5'-GCCGC-3') forming a putative stemloop structure spanning part of the presumed -35 sequence and part of the intervening region between the -35 and -10 sequences. Alignment of the LlaDII and Bsp6I methylases with other m5C methylases showed that the protein primary structures possessed the same organization.

Amino Acid Sequence↗
PubMed1986

Immunohistochemical colocalization of GABA and insulin in beta-cells of rat islet.

gamma-Aminobutyric acid (GABA) is found in high concentrations in the pancreatic islet. In addition, enzymes regulating the level of GABA (L-glutamate decarboxylase and GABA-alpha-ketoglutarate transaminase) have been immunohistochemically localized in the medullary cells of the islet. In this study, an immunofluorescence and elution/restaining protocol is used to determine the distribution of GABA and either insulin, glucagon, or somatostatin in a tissue section. GABA was not detected within the islet alpha- or delta-cells but was determined to be localized within the insulin-containing beta-cells.

Animals↗
PubMed1985

Thyroxine concentrations and secretion rates in relation to pregnancy, lactation and energy balance in goats.

Plasma thyroxine (T4) concentrations were measured during pregnancy and lactation in goats on diets with different energy concentrations to study the role of T4 secretion in metabolic adaptation to pregnancy and lactation. Thyroxine distribution space (the volume of fluid required to dissolve the total pool of circulating T4 at a concentration equal to that in the plasma) and secretion rates were determined by using 125I-labelled T4 at different stages of lactation and pregnancy. Plasma concentrations of T4 increased during lactation and reached maximum levels 4-5 months after giving birth. They then remained fairly constant for the following 2-3 months until the goats became pregnant again. Thyroxine concentrations decreased slightly during pregnancy and showed a sudden drop at the onset of lactation. Minimum concentrations were observed during the first 2-3 weeks of lactation after which time concentrations increased slowly. Average concentrations for goats on a low-energy diet were consistently lower than those in goats on a high-energy consistently lower than those in goats on a high-energy diet. The mean secretion rate was 10.4 nmol day-1 kg body wt-0.75. The distribution spaces were much lower than the total extracellular space. The average distribution space in non-pregnant and pregnant goats was 11 and 5.3% of the body weight respectively. The decrease in T4 secretion rate and T4 distribution space during pregnancy is considered to be part of a homeorhetic adaptation to the condition. The drop in T4 secretion rate at the onset of lactation appears to be a homeostatic adaptation to a decreased fuel supply, similar to the situation with fasting or energy malnutrition.

Animals↗
PubMed1979

Porcine nephropathy induced by long-term ingestion of ochratoxin A.

Nine pigs were fed crystalline ochratoxin A in their feed at a concentration of about 1 mg/kg. Three pigs and their controls were killed after 3 months and 6 pigs and controls were killed after 2 years. A decrease of the ratio TmPAH/CIn, increased urinary glucose excretion and decreased ability to concentrate urine, occurred within a few weeks and aggravated slightly during the 2-year period. Changes in renal structure, characterized by degeneration and atrophy of proximal tubules, interstitial fibrosis and hyalinization of glomeruli, were progressive during time of exposure, but terminal renal failure was not reached. The kidney, liver, muscular and adipose tissue contained 3 to 27 microgram ochratoxin A/kg after 3 months of exposure. No further accumulation of ochratoxin A residue was found after 2 years of exposure.

Animals↗