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Biomedical subjects

K Schwarz

Publications and source records attributed to K Schwarz.

At least 19 recordsLinked to original sources
PubMed2005

The nature of the hydrogen bond in the LaNiSnH2 and NdNiSnH hydrides.

The electronic structure of LaNiSn and NdNiSn compounds and their hydrides has been studied by first principles calculations and variable temperature 119Sn Mossbauer spectroscopy and the nature of the hydrogen-metal bond is discussed. The analysis of the electronic density of states (DOS) in both compounds before and after hydrogenation indicates an hybridization of the Sn, Ni, and H orbitals. The partial Sn-p DOS of LaNiSnH2 gives evidence for a lower symmetry of electron density around tin atoms compared to LaNiSn, according to the larger quadrupole splitting in the corresponding Mossbauer spectrum. Theoretical and experimental Mossbauer parameters agree very well for all samples.

Journal Article↗
PubMed2005

Hepatitis B vaccination rate of homeless children in Baltimore.

OBJECTIVE: To investigate the hepatitis B vaccination rate in homeless children 2 to 18 years old living in Baltimore City. METHODS: During a 21-month period, 250 children from homeless shelters were enrolled. RESULTS: The percent of children who had received 3 or more doses of hepatitis B vaccine was inversely related to age; 90% in 2- to 5-year-olds and 29% in 13- to 18-year-olds (P<0.0001). Seventy percent of 2- to 5-year-olds had at least some of their vaccine history recorded in the Baltimore Immunization Registry Program but the history was complete in only half. Forty-two percent of 13- to 18-year-olds had no hepatitis B vaccine doses recorded in any source; 49 per cent of 10- to 18-year-olds were either not immunized or had received only one hepatitis B vaccine dose. CONCLUSIONS: Hepatitis B vaccine coverage is high in homeless children up to 9 years of age, whereas the majority of homeless children 10 years of age and older are unprotected against hepatitis B virus infection. Tracking the vaccine records in homeless children is labor intensive. Better public health strategies to deliver hepatitis B vaccine to older homeless children are urgently needed.

Adolescent↗
PubMed2004

Geometric frustration, electronic instabilities, and charge singlets in Y2Nb2O7.

Pyrochlore Y2Nb2O7 is studied with density functional calculations. In the ideal pyrochlore structure, no magnetism is found, consistent with experiments, but the band structure is metallic. The phonon dispersions show unstable modes corresponding to charge instabilities. These frustrated instabilities lead to a metal-insulator transition with the formation of "charge singlets". Partial substitution of Ti for Nb results in moment formation due to the occurrence of Ti3+.

Journal Article↗
PubMed2004

Metallic "ferroelectricity" in the pyrochlore Cd2Re2O7.

A class of materials known as "ferroelectric metals" was discussed theoretically by Anderson and Blount in 1965 [Phys. Rev. Lett. 14, 217 (1965)]], but to date no examples of this class of materials have been reported. Here we present measurements of the elastic moduli of Cd2Re2O7 through the 200 K cubic-to-tetragonal phase transition. A Landau analysis of the moduli reveals that the transition is consistent with Cd2Re2O7 being classified as a ferroelectric metal in the weaker sense described by Anderson and Blount (loss of a center of symmetry). First-principles calculations of the lattice instabilities indicate that the dominant lattice instability corresponds to a twofold degenerate mode with E(u) symmetry and that motions of the O ions forming the O octahedra dominate the energetics of the transition.

Journal Article↗
PubMed2004

A novel method to produce hydroxyapatite objects with interconnecting porosity that avoids sintering.

Porous objects of carbonated apatite were prepared by mixing polyvinyl alcohol fibres (PVA) and sodium chloride as porogens with nanocrystalline carbonated apatite powder. After cold isostatic pressing (CIP) and dissolving the porogens, the bioceramic showed an interconnecting porosity with pore diameters in the range of 250-400 microm. The method can be transposed to any material that is insoluble in water (like many polymers). Such objects are promising for bone regeneration because the interconnecting porosity in carbonated apatite provides a good environment for bone attachment and ingrowth.

Biocompatible Materials↗
PubMed2004

Interaction between histamine-induced itch and experimental muscle pain.

Itch sensation can be inhibited by simultaneously applied cutaneous pain at the same skin site via a central mechanism. Deep muscle pain is often associated with sensory changes in the corresponding dermatome. We investigated whether experimentally induced muscle pain has any influence on histamine-induced itch and vice versa in a double blind placebo-controlled study. Experiments were performed in 18 healthy subjects. In nine individuals control iontophoresis of histamine into the forearm produced a distinct itch sensation. Another nine individuals participated in an additional experiment in which histamine and saline were iontophoresed on the forearm in a randomized double-blinded two-way crossover design after intramuscular injection of capsaicin into the ipsilateral brachioradial muscle. Capsaicin-induced muscle pain reduced itch sensation significantly. In contrast, capsaicin-induced muscle pain increased significantly after cutaneous histamine application compared to muscle pain after iontophoresis of saline (placebo). These novel data indicate that muscle pain inhibits itch and histamine increases muscle pain. A bi-directional interaction between cutaneous histamine-sensitive afferents and nociceptive muscle afferents via central mechanisms is suggested.

Adult↗
PubMed2003

Congenital adrenal hypoplasia presenting as a chronic respiratory condition.

We describe two children with oxygen dependence, which resolved when congenital adrenal hypoplasia was diagnosed and treatment initiated. Chronic respiratory distress can be a symptom of adrenal hypoplasia and this should be taken into consideration when investigating a child with unexplained chronic respiratory difficulties. Respiratory symptoms resolve very quickly when the underlying condition is recognised and treated.

Adrenal Gland Diseases↗
PubMed2002

Antioxidant properties of differently processed spinach products.

The effect of variously processed spinach products (whole-leaf, minced and enzymatically liquefied spinach) on lipid oxidation was determined. In an autoxidative methyl linoleate (MeLo) system the inhibition of hydroperoxide formation, measured by HPLC after three days of oxidation, was in descending order: whole-leaf > liquefied > minced spinach. The inhibition of formation of thiobarbituric acid-reactive substances (TBARS) and hexanal by spinach was determined in cooked meatballs with added spinach after two days of storage at 4 degrees C. The formation of TBARS was inhibited by liquefied spinach at 200 g/kg meat; all other spinach products tested at 100 and 200 g/kg were pro-oxidative. The formation of hexanal was inhibited by both minced and liquefied spinach at 100 and 200 g/kg meat. The variously processed spinach products behaved differently when tested for their antioxidant activity (MeLo) or oxidative stability (meatballs). We conclude that the effect of spinach products on lipid oxidation is affected by processing.

Aldehydes↗
PubMed2002

Survey of school children with visual impairment in Bradford.

UNLABELLED: This work was presented as a poster at the Institute of Health Research Conference 2000: Health of Children and Young People: Research Perspectives. University of Bradford 15th of September 2000. AIMS: The aim of this survey was to determine the prevalence and aetiology of visual impairment in school children in Bradford. METHODS: The case notes of school children with predominantly uncomplicated visual impairment were reviewed. Data including age, sex, race and information on visual diagnosis, heredity, degree of visual impairment and additional morbidity were collected. RESULTS: Seventy-two children between the ages of 5 and 16 years were included in this survey. The male: female ratio was 2.1: 1. Twenty-one children were Caucasian, 42 were of Pakistani and nine of other racial origin. The most common diagnoses were congenital nystagmus (19), ocular albinism (6), myopia (4), cataract (4) and microphthalmia (4). Twenty-five children had a genetically linked visual diagnosis and 31 had a family history of the same visual disorder. CONCLUSIONS: This survey showed similar causes of visual impairment as described in other studies on children with uncomplicated visual impairment and confirmed the previously described preponderance of boys. The proportion of Pakistani children in our study population was significantly higher than that in the general Bradford population, indicating a higher prevalence of visual impairment in this group. Children of Pakistani origin were significantly more likely to have genetically linked visual disease and a positive family history of the same visual disorder than children of Caucasian origin. This is probably due to genetic factors and a higher proportion of consanguineous marriages in this population. Information about the prevalence and causes of visual impairment is important for adequate provision of special services and for developing preventive strategies.

Adolescent↗
PubMed2001

Immunoproteasomes largely replace constitutive proteasomes during an antiviral and antibacterial immune response in the liver.

The proteasome is critically involved in the production of MHC class I-restricted T cell epitopes. Proteasome activity and epitope production are altered by IFN-gamma treatment, which leads to a gradual replacement of constitutive proteasomes by immunoproteasomes in vitro. However, a quantitative analysis of changes in the steady state subunit composition of proteasomes during an immune response against viruses or bacteria in vivo has not been reported. Here we show that the infection of mice with lymphocytic choriomeningitis virus or Listeria monocytogenes leads to an almost complete replacement of constitutive proteasomes by immunoproteasomes in the liver within 7 days. Proteasome replacements were markedly reduced in IFN-gamma(-/-) mice, but were only slightly affected in IFN-alphaR(-/-) and perforin(-/-) mice. The proteasome regulator PA28alpha/beta was up-regulated, whereas PA28gamma was reduced in the liver of lymphocytic choriomeningitis virus-infected mice. Proteasome replacements in the liver strongly altered proteasome activity and were unexpected to this extent, since an in vivo half-life of 12 days had been previously assigned to constitutive proteasomes in the liver. Our results suggest that during the peak phase of viral and bacterial elimination the antiviral cytotoxic T lymphocyte response is directed mainly to immunoproteasome-dependent T cell epitopes, which would be a novel parameter for the design of vaccines.

Animals↗
PubMed2001

Histamine-induced itch converts into pain in neuropathic hyperalgesia.

Physiologically, itch and pain are transmitted in separate specific peripheral C-units and central afferent pathways. Some neuropathic pain patients with intact but sensitized (irritable) primary C-nociceptors have spontaneous pain, heat hyperalgesia, static and dynamic mechanical hyperalgesia. The question was whether cutaneous histamine application induces pain in these patients. For comparison histamine was applied into normal skin experimentally sensitized by capsaicin. Histamine application in the capsaicin-induced primary or secondary hyperalgesic skin did not change the intensity and quality of capsaicin pain. Itch was profoundly inhibited. Conversely, histamine application in neuropathic skin induced severe increase in spontaneous burning pain but no itch. In neuropathies irritable nociceptors may express histamine receptors or induce central sensitization to histaminergic stimuli so that itch converts into pain.

Histamine↗
PubMed2001

Electron-density distribution in stishovite, SiO2: a new high-energy synchrotron-radiation study.

The electron-density distribution of the high-pressure polymorph of SiO2, stishovite [a = 4.177 (1), c = 2.6655 (5) A, space group P4(2)/mnm, Z = 2], has been redetermined by single-crystal diffractometry using synchrotron radiation of 100.42 and 30.99 keV, respectively, in order to obtain essentially absorption- and extinction-free data. Room-temperature diffraction experiments on two samples of irregular shape were carried out on two different diffractometers installed at HASYLAB/DESY, Hamburg, Germany. The structure refinement on the high-energy data converged at R(F) = 0.0047, wR(F) = 0.0038, GoF = 0.78, for a multipole model with neutral atoms and multipole expansions up to seventh order. For each atom, the radial expansion coefficients of the multipole orders (l > 0) were constrained to a common value. The absence of extinction was indicated by a refined correction parameter equalling zero within error limit. The excellent quality of the data is also illustrated by a high-order (HO) refinement (s > 0.7 A(-1)) yielding R(F) = 0.0060, wR(F) = 0.0048, GoF = 0.85. Both static deformation electron-density distribution and structure amplitudes compare well with corresponding results obtained from band-structure calculations using the linearized-augmented-plane-wave (LAPW) method. Ensuing topological analysis of the total model electron density distribution revealed bond critical point properties for the two unique Si--O bonds, indicating a predominantly closed-shell interaction mixed with a significant shared interaction contribution that decreases with increasing interatomic distance. Calculation of atomic basins yielded charges of +3.39 e and -1.69 e for Si and O, respectively, in good agreement with the theoretically calculated values of +3.30 e and -1.65 e. The volumina of the Si and O basins are 2.32 and 10.48 A3, corresponding to spheres with radii of 0.82 and 1.36 A, respectively. The results also conform well with correlations between bond length and bond critical point properties reported in the literature for geometry-optimized hydroxyacid molecules. Estimates of the Si cation electronegativity indicate that the change of Si coordination by oxygen from 4 to 6 is accompanied by an increase of the ionicity of the Si--O bond of about 7%.

Journal Article↗
PubMed2001

Differentiation- and stress-dependent nuclear cytoplasmic redistribution of myopodin, a novel actin-bundling protein.

We report the cloning and functional characterization of myopodin, the second member of the synaptopodin gene family. Myopodin shows no significant homology to any known protein except synaptopodin. Northern blot analysis resulted in a 3.6-kb transcript for mouse skeletal and heart muscle. Western blots showed an 80-kD signal for skeletal and a 95-kD signal for heart muscle. Myopodin contains one PPXY motif and multiple PXXP motifs. Myopodin colocalizes with alpha-actinin and is found at the Z-disc as shown by immunogold electron microscopy. In myoblasts, myopodin shows preferential nuclear localization. During myotube differentiation, myopodin binds to stress fibers in a punctuated pattern before incorporation into the Z-disc. Myopodin can directly bind to actin and contains a novel actin binding site in the center of the protein. Myopodin has actin-bundling activity as shown by formation of latrunculin-A-sensitive cytosolic actin bundles and nuclear actin loops in transfected cells expressing green fluorescent protein-myopodin. Under stress conditions, myopodin accumulates in the nucleus and is depleted from the cytoplasm. Nuclear export of myopodin is sensitive to leptomycin B, despite the absence of a classical nuclear export sequence. We propose a dual role for myopodin as a structural protein also participating in signaling pathways between the Z-disc and the nucleus.

Actins↗
PubMed2001

Correlation induced paramagnetic ground state in FeAl.

Experimentally the intermetallic compound FeAl is known to be nonmagnetic, whereas conventional density functional theory calculations within the local density approximation always yield a ferromagnetic ground state with a magnetic moment at the Fe site of about 0.7 mu(B). We show that a correlation correction within the LDA+U scheme yields a nonmagnetic ground state for U>or=3.7 eV using two different implementations. The disappearance of the magnetic ground state occurs since Fe-t(2g) and Fe-e(g) manifolds are affected differently by a common U. For large values of U a magnetic solution reappears as expected for strong correlation.

Journal Article↗
PubMed2001

Transplacentally acquired maternal T lymphocytes in severe combined immunodeficiency: a study of 121 patients.

A study in 121 infants with severe combined immunodeficiency (SCID) was performed to determine the prevalence of an engraftment by transplacentally acquired maternal T cells and to explore clinical and immunological findings related to this abnormality. Each newly diagnosed patient with SCID presenting with circulating T cells was evaluated for chimerism by performing selective HLA typing of T cells and non-T cells. In patients with engraftment, maternal T cells were characterized phenotypically and functionally, and results were correlated with clinical findings in the patients. Maternal T cells were detected in the circulation in 48 patients; these cells ranged from fewer than 100/microL in 14 cases to more than 2000/microL in 4 cases (median, 415/microL). Clinical signs of graft-versus-host disease (GVHD) were absent in 29 patients. In the other cases, manifestations of GVHD were present, involving the skin and in 14 cases also the liver. Skin GVHD was mild in 8 patients. In these patients, as well as in patients with no signs of GVHD, maternal T cells were predominantly CD8(+) and, with one exception, failed to respond to mitogen stimulation. In 9 patients, manifestations of skin GVHD were prominent. T cells in these cases were predominantly CD4(+) and responded, with one exception, to mitogen stimulation. In 8 of the cases with prominent skin GVHD, the underlying SCID variant was characterized by the absence of B cells. In this study, further understanding is provided of a phenomenon that is responsible for the significant heterogeneity of clinical and immunological findings in SCID.

Cells, Cultured↗
PubMed2001

Recovering experimental and theoretical electron densities in corundum using the multipolar model: IUCr Multipole Refinement Project.

This electron-density study on corundum (alpha-Al2O3) is part of the Multipole Refinement Project supported by the IUCr Commission on Charge, Spin and Momentum Densities. For this purpose, eight different data sets (two experimental and six theoretical) were chosen from which the electron density was derived by multipolar refinement (using the MOLLY program). The two experimental data sets were collected on a conventional CAD4 and at ESRF, ID11 with a CCD detector, respectively. The theoretical data sets consist of static, dynamic, static noisy and dynamic noisy moduli of structure factors calculated at the Hartree-Fock (HF) and density functional theory (DFT) levels. Comparisons of deformation and residual densities show that the multipolar analysis works satisfactorily but also indicate some drawbacks in the refinement. Some solutions and improvements during the refinements are proposed like contraction or expansion of the inner atomic shells or increasing the order of the spherical harmonic expansion.

Journal Article↗
PubMed2001

Proton motion and proton transfer in the formamidine-formic acid complex: an Ab initio projector augmented wave molecular dynamics study.

An ab initio molecular dynamics study performed with the projector augmented wave method (PAW) on proton motion and (double) proton transfer in the formamidine-formic acid complex is reported. The PAW trajectories were calculated with a time interval of 0.12 fs, for a total evolution time period of 36ps, and for temperatures in the range 500-600 K. All proton-transfer processes start with a proton transition at the O-H...N group, and are followed by a second proton transition, either at the same group ("single crossing-recrossing transitions") or at the other group, namely the N-H...O group ("double proton transfers"). According to the delay between the two transitions (more or less than 15 fs), one may distinguish between "concerted" (42%) or "successive" (16%) single crossing-recrossing transitions, and between "simultaneous" (7%) or "successive" (35%) double proton transfers. Successive processes take place via a zwitterionic intermediate, which remains stable for up to approximately 120 fs ("ionic regions"). The findings are in excellent agreement with the results of ab initio (HF, MP2) and density functional theory (DFT; B3LYP, B3P86) calculations, according to which the zwitterionic intermediate that results from the first proton transition is a true local minimum. Furthermore, it is shown that the optimized geometries of stationary points (ground state, transition state, and zwitterion) comply well with corresponding average data obtained from the PAW trajectories for normal periods, crossover points, and ionic regions.

Journal Article↗