1,075 research outputs found
A simple rocker-induced mechanical stimulus upregulates mineralization by human osteoprogenitor cells in fibrous scaffolds
Biodegradable electrospun polycaprolactone scaffolds can be used to support bone-forming cells and could fill a thin bony defect, such as in cleft palate. Oscillatory fluid flow has been shown to stimulate bone production in human progenitor cells in monolayer culture. The aim of this study was to examine whether bone matrix production by primary human mesenchymal stem cells from bone marrow or jaw periosteal tissue could be stimulated using oscillatory fluid flow supplied by a standard see-saw rocker. This was investigated for cells in two-dimensional culture and within electrospun polycaprolactone scaffolds. From day 4 of culture onwards, samples were rocked at 45 cycles/min for 1 h/day, 5 days/week (rocking group). Cell viability, calcium deposition, collagen production, alkaline phosphatase activity and vascular endothelial growth factor secretion were evaluated to assess the ability of the cells to undergo bone differentiation and induce vascularisation. Both cell types produced more mineralized tissue when subjected to rocking and supplemented with dexamethasone. Mesenchymal progenitors and primary human mesenchymal stem cells from bone marrow in three-dimensional scaffolds upregulated mineral deposition after rocking culture as assessed by micro-computed tomography and alizarin red staining. Interestingly, vascular endothelial growth factor secretion, which has previously been shown to be mechanically sensitive, was not altered by rocking in this system and was inhibited by dexamethasone. Rocker culture may be a cost effective, simple pretreatment for bone tissue engineering for small defects such as cleft palate
Reproducibility of quantitative indices of lung function and microstructure from 129Xe chemical shift saturation recovery (CSSR) MR spectroscopy
Purpose
To evaluate the reproducibility of indices of lung microstructure and function derived from 129Xe chemical shift saturation recovery (CSSR) spectroscopy in healthy volunteers and patients with chronic obstructive pulmonary disease (COPD), and to study the sensitivity of CSSR-derived parameters to pulse sequence design and lung inflation level.
Methods
Preliminary data were collected from five volunteers on three occasions, using two implementations of the CSSR sequence. Separately, three volunteers each underwent CSSR at three different lung inflation levels. After analysis of these preliminary data, five COPD patients were scanned on three separate days, and nine age-matched volunteers were scanned three times on one day, to assess reproducibility.
Results
CSSR-derived alveolar septal thickness (ST) and surface-area-to-volume (S/V) ratio values decreased with lung inflation level (P < 0.001; P = 0.057, respectively). Intra-subject standard deviations of ST were lower than the previously measured differences between volunteers and subjects with interstitial lung disease. The mean coefficient of variation (CV) values of ST were 3.9 ± 1.9% and 6.0 ± 4.5% in volunteers and COPD patients, respectively, similar to CV values for whole-lung carbon monoxide diffusing capacity. The mean CV of S/V in volunteers and patients was 14.1 ± 8.0% and 18.0 ± 19.3%, respectively.
Conclusion
129Xe CSSR presents a reproducible method for estimation of alveolar septal thickness
A hetero-multimeric chitinase-containing plasmodium falciparum and plasmodium gallinaceum ookinete-secreted protein complex involved in mosquito midgut invasion
Malaria parasites are transmitted by Anopheles mosquitoes. During its life cycle in the mosquito vector the Plasmodium ookinete escapes the proteolytic milieu of the post-blood meal midgut by traversing the midgut wall. This process requires penetration of the chitin-containing peritrophic matrix lining the midgut epithelium, which depends in part on ookinete-secreted chitinases. Plasmodium falciparum ookinetes have one chitinase (PfCHT1), whereas ookinetes of the avian-infecting parasite, P. gallinaceum, have two, a long and a short form, PgCHT1 and PgCHT2, respectively. Published data indicates that PgCHT2 forms a high molecular weight (HMW) reduction-sensitive complex; and one binding partner is the ookinete-produced von Willebrand A-domain-containing protein, WARP. Size exclusion chromatography data reported here show that P. gallinaceum PgCHT2 and its ortholog, P. falciparum PfCHT1 are covalently-linked components of a HMW chitinase-containing complex (> 1,300 kDa). Mass spectrometry of ookinete-secreted proteins isolated using a new chitin bead pull-down method identified chitinase-associated proteins in P. falciparum and P. gallinaceum ookinete-conditioned culture media. Mass spectrometry of this complex showed the presence of several micronemal proteins including von Willebrand factor A domain-related protein (WARP), ookinete surface enolase, and secreted ookinete adhesive protein (SOAP). To test the hypothesis that ookinete-produced PfCHT1 can form a high molecular homo-multimer or, alternatively, interacts with P. berghei ookinete-produced proteins to produce an HMW hetero-multimer, we created chimeric P. berghei parasites expressing PfCHT1 to replace PbCHT1, enabling the production of large numbers of PfCHT1-expressing ookinetes. We show that chimeric P. berghei ookinetes express monomeric PfCHT1, but a HMW complex containing PfCHT1 is not present. A better understanding of the chitinase-containing HMW complex may enhance development of next-generation vaccines or drugs that target malaria transmission stages.Host-parasite interactio
Comparison of 3He and129Xe MRI for evaluation of lung microstructure and ventilation at 1.5T
BACKGROUND: To support translational lung MRI research with hyperpolarized129Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from3He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of129Xe functional metrics have not been reported. PURPOSE/HYPOTHESIS: To compare hyperpolarized129Xe and3He MRI-derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.5T. STUDY TYPE: Retrospective. POPULATION: Fourteen healthy nonsmokers (HN), five exsmokers (ES), five patients with chronic obstructive pulmonary disease (COPD), and 16 patients with nonsmall-cell lung cancer (NSCLC). FIELD STRENGTH/SEQUENCE: 1.5T. NSCLC, COPD patients and selected HN subjects underwent 3D balanced steady-state free-precession lung ventilation MRI using both3He and129Xe. Selected HN, all ES, and COPD patients underwent 2D multislice spoiled gradient-echo diffusion-weighted lung MRI using both hyperpolarized gas nuclei. ASSESSMENT: Ventilated volume percentages (VV%) and mean apparent diffusion coefficients (ADC) were derived from imaging. COPD patients performed the whole MR protocol in four separate scan sessions to assess repeatability. Same-day pulmonary function tests were performed. STATISTICAL TESTS: Intermetric correlations: Spearman's coefficient. Intergroup/internuclei differences: analysis of variance / Wilcoxon's signed rank. Repeatability: coefficient of variation (CV), intraclass correlation (ICC) coefficient. RESULTS: A significant positive correlation between3He and129Xe VV% was observed (r = 0.860, P < 0.001). VV% was larger for3He than129Xe (P = 0.001); average bias, 8.79%. A strong correlation between mean3He and129Xe ADC was obtained (r = 0.922, P < 0.001). MR parameters exhibited good correlations with pulmonary function tests. In COPD patients, mean CV of3He and129Xe VV% was 4.08% and 13.01%, respectively, with ICC coefficients of 0.541 (P = 0.061) and 0.458 (P = 0.095). Mean3He and129Xe ADC values were highly repeatable (mean CV: 2.98%, 2.77%, respectively; ICC: 0.995, P < 0.001; 0.936, P < 0.001). DATA CONCLUSION:129Xe lung MRI provides near-equivalent information to3He for quantitative lung ventilation and microstructural MRI at 1.5T. LEVEL OF EVIDENCE: 3 Technical Efficacy Stage
Superscaling of Inclusive Electron Scattering from Nuclei
We investigate the degree to which the concept of superscaling, initially
developed within the framework of the relativistic Fermi gas model, applies to
inclusive electron scattering from nuclei. We find that data obtained from the
low energy loss side of the quasielastic peak exhibit the superscaling
property, i.e., the scaling functions f(\psi') are not only independent of
momentum transfer (the usual type of scaling: scaling of the first kind), but
coincide for A \geq 4 when plotted versus a dimensionless scaling variable
\psi' (scaling of the second kind). We use this behavior to study as yet poorly
understood properties of the inclusive response at large electron energy loss.Comment: 33 pages, 12 color EPS figures, LaTeX2e using BoxedEPSF macros; email
to [email protected]
Nonequilibrium Evolution of Correlation Functions: A Canonical Approach
We study nonequilibrium evolution in a self-interacting quantum field theory
invariant under space translation only by using a canonical approach based on
the recently developed Liouville-von Neumann formalism. The method is first
used to obtain the correlation functions both in and beyond the Hartree
approximation, for the quantum mechanical analog of the model. The
technique involves representing the Hamiltonian in a Fock basis of annihilation
and creation operators. By separating it into a solvable Gaussian part
involving quadratic terms and a perturbation of quartic terms, it is possible
to find the improved vacuum state to any desired order. The correlation
functions for the field theory are then investigated in the Hartree
approximation and those beyond the Hartree approximation are obtained by
finding the improved vacuum state corrected up to . These
correlation functions take into account next-to-leading and
next-to-next-to-leading order effects in the coupling constant. We also use the
Heisenberg formalism to obtain the time evolution equations for the equal-time,
connected correlation functions beyond the leading order. These equations are
derived by including the connected 4-point functions in the hierarchy. The
resulting coupled set of equations form a part of infinite hierarchy of coupled
equations relating the various connected n-point functions. The connection with
other approaches based on the path integral formalism is established and the
physical implications of the set of equations are discussed with particular
emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with
non-equilibrium evolution beyond Hartree approx. based on the LvN formalism,
has been adde
The Dependence of the Superconducting Transition Temperature of Organic Molecular Crystals on Intrinsically Non-Magnetic Disorder: a Signature of either Unconventional Superconductivity or Novel Local Magnetic Moment Formation
We give a theoretical analysis of published experimental studies of the
effects of impurities and disorder on the superconducting transition
temperature, T_c, of the organic molecular crystals kappa-ET_2X and beta-ET_2X
(where ET is bis(ethylenedithio)tetrathiafulvalene and X is an anion eg I_3).
The Abrikosov-Gorkov (AG) formula describes the suppression of T_c both by
magnetic impurities in singlet superconductors, including s-wave
superconductors and by non-magnetic impurities in a non-s-wave superconductor.
We show that various sources of disorder lead to the suppression of T_c as
described by the AG formula. This is confirmed by the excellent fit to the
data, the fact that these materials are in the clean limit and the excellent
agreement between the value of the interlayer hopping integral, t_perp,
calculated from this fit and the value of t_perp found from angular-dependant
magnetoresistance and quantum oscillation experiments. If the disorder is, as
seems most likely, non-magnetic then the pairing state cannot be s-wave. We
show that the cooling rate dependence of the magnetisation is inconsistent with
paramagnetic impurities. Triplet pairing is ruled out by several experiments.
If the disorder is non-magnetic then this implies that l>=2, in which case
Occam's razor suggests that d-wave pairing is realised. Given the proximity of
these materials to an antiferromagnetic Mott transition, it is possible that
the disorder leads to the formation of local magnetic moments via some novel
mechanism. Thus we conclude that either kappa-ET_2X and beta-ET_2X are d-wave
superconductors or else they display a novel mechanism for the formation of
localised moments. We suggest systematic experiments to differentiate between
these scenarios.Comment: 18 pages, 5 figure
Two-proton correlations from 158 AGeV Pb+Pb central collisions
The two-proton correlation function at midrapidity from Pb+Pb central
collisions at 158 AGeV has been measured by the NA49 experiment. The results
are compared to model predictions from static thermal Gaussian proton source
distributions and transport models RQMD and VENUS. An effective proton source
size is determined by minimizing CHI-square/ndf between the correlation
functions of the data and those calculated for the Gaussian sources, yielding
3.85 +-0.15(stat.) +0.60-0.25(syst.) fm. Both the RQMD and the VENUS model are
consistent with the data within the error in the correlation peak region.Comment: RevTeX style, 6 pages, 4 figures, 1 table. More discussion are added
about the structure on the tail of the correlation function. The systematic
error is revised. To appear in Phys. Lett.
Event-by-event fluctuations of average transverse momentum in central Pb+Pb collisions at 158 GeV per nucleon
We present first data on event-by-event fluctuations in the average
transverse momentum of charged particles produced in Pb+Pb collisions at the
CERN SPS. This measurement provides previously unavailable information allowing
sensitive tests of microscopic and thermodynamic collision models and to search
for fluctuations expected to occur in the vicinity of the predicted QCD phase
transition. We find that the observed variance of the event-by-event average
transverse momentum is consistent with independent particle production modified
by the known two-particle correlations due to quantum statistics and final
state interactions and folded with the resolution of the NA49 apparatus. For
two specific models of non-statistical fluctuations in transverse momentum
limits are derived in terms of fluctuation amplitude. We show that a
significant part of the parameter space for a model of isospin fluctuations
predicted as a consequence of chiral symmetry restoration in a non-equilibrium
scenario is excluded by our measurement.Comment: 6 pages, 2 figures, submitted to Phys. Lett.
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
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