Modelling asset correlations: A nonparametric approach

This article proposes a time-varying nonparametric estimator and a time-varying semiparametric estimator of the correlation matrix. We discuss representation, estimation based on kernel smoothing and inference. An extensive Monte Carlo simulation study is performed to compare the semiparametric and nonparametric models with the DCC speci fication. Our bivariate simulation results show that the semiparametric and nonparametric models are best in DGPs with gradual changes or structural breaks in correlations. However, in DGPs with rapid changes or constancy in correlations the DCC delivers the best outcome. Moreover, in multivariate simulations the semiparametric and nonparametric models fare the best in DGPs with substantial time-variability in correlations, while when allowing for little variability in the correlations the DCC is the dominant speci fication. The methodologies are illustrated by estimating the correlations for two interesting portfolios. The rst portfolio consists of the equity sectors SPDRs and the S&P 500 composite, while the second one contains major currencies that are actively traded in the foreign exchange market. Portfolio evaluation results show that the nonparametric estimator generally dominates its competitors, with a statistically significant lower portfolio variance

Quantitative determination of deformation by sliding wear,

SUMMARY On the basis of a model, equations have been derived to define for true shearing, the effective deformation from the deflection of the grain boundaries and from the change of grain thicknesses. A linear intercept method was developed for the direct measurement of grain thickness. The theory has been checked by sliding OFHC copper against steel SAE 1045 under conditions of true shearing. The theory may be applied to other processes besides wear where substantial deformation occurs

'Beroepsgeheim onder druk'

Effective Protection of Fundamental Rights in a pluralist worl

Structure–function studies of chemokine-derived carboxy-terminal antimicrobial peptides

AbstractRecent reports which show that several chemokines can act as direct microbicidal agents have drawn renewed attention to these chemotactic signalling proteins. Here we present a structure–function analysis of peptides derived from the human chemokines macrophage inflammatory protein-3α (MIP-3α/CCL20), interleukin-8 (IL-8), neutrophil activating protein-2 (NAP-2) and thrombocidin-1 (TC-1). These peptides encompass the C-terminal α-helices of these chemokines, which have been suggested to be important for the direct antimicrobial activities. Far-UV CD spectroscopy showed that the peptides are unstructured in aqueous solution and that a membrane mimetic solvent is required to induce a helical secondary structure. A co-solvent mixture was used to determine solution structures of the peptides by two-dimensional 1H-NMR spectroscopy. The highly cationic peptide, MIP-3α51–70, had the most pronounced antimicrobial activity and displayed an amphipathic structure. A shorter version of this peptide, MIP-3α59–70, remained antimicrobial but its structure and mechanism of action were unlike that of the former peptide. The NAP-2 and TC-1 proteins differ in their sequences only by the deletion of two C-terminal residues in TC-1, but intact TC-1 is a very potent antimicrobial while NAP-2 is inactive. The corresponding C-terminal peptides, NAP-250–70 and TC-150–68, had very limited and no bactericidal activity, respectively. This suggests that other regions of TC-1 contribute to its bactericidal activity. Altogether, this work provides a rational structural basis for the biological activities of these peptides and proteins and highlights the importance of experimental characterization of peptide fragments as distinct entities because their activities and structural properties may differ substantially from their parent proteins

Critical Review Antibacterial Components of Honey

Summary The antibacterial activity of honey has been known since the 19th century. Recently, the potent activity of honey against antibiotic-resistant bacteria has further increased the interest for application of honey, but incomplete knowledge of the antibacterial activity is a major obstacle for clinical applicability. The high sugar concentration, hydrogen peroxide, and the low pH are well-known antibacterial factors in honey and more recently, methylglyoxal and the antimicrobial peptide bee defensin-1 were identified as important antibacterial compounds in honey. The antibacterial activity of honey is highly complex due to the involvement of multiple compounds and due to the large variation in the concentrations of these compounds among honeys. The current review will elaborate on the antibacterial compounds in honey. We discuss the activity of the individual compounds, their contribution to the complex antibacterial activity of honey, a novel approach to identify additional honey antibacterial compounds, and the implications of the novel developments for standardization of honey for medical applications. IUBMB IUBMB Life, 64(1)

POLY(TRIMETHYLENE CARBONATE)AND POLY(D,L-LACTIC ACID) MODIFY HUMAN DENDRITIC CELL RESPONSES TO STAPHYLOCOCCI BUT DO NOT AFFECT Th1 AND Th2 CELL DEVELOPMENT

Biomaterial-associated infections (BAIs) are frequent complications in the use of medical devices (biomaterials) correlated with considerable patient discomfort and high treatment costs. The presence of a biomaterial in the host causes derangement of local immune responses increasing susceptibility to infection. Dendritic cells (DCs) have an important role in directing the nature of immune responses by activating and controlling CD4+ T helper (Th) cell responses. To assess the immunomodulatory effect of the combined presence of biomaterials and Staphylococcus aureus (S. aureus) or Staphylococcus epidermidis (S. epidermidis), DC-mediated T cell proliferation and Th1/Th2 cell development were measured using an in vitro human cell system. Poly(trimethylene carbonate) (PTMC) and poly(D,L-lactic acid) (PDLLA) modified the production of the DC pro-inflammatory cytokines TNF-α, IL-6 and IL-23 in response to S. aureus and S. epidermidis. However, this modified cytokine production did not cause differences in Th1/Th2 cell polarisation, showing a Th1 cell predominance. In the absence of staphylococci, neither of the biomaterials induced DC-mediated T cell proliferation or Th1/Th2 cell polarisation. Moreover, either in the absence or presence of the biomaterials, S. aureus was a more potent inducer of DC cytokine secretion, T cell proliferation and Th1 cell development than S. epidermidis. In conclusion, although PTMC and PDLLA modulated DC cytokine responses to staphylococci, this did not alter the resulting Th cell development. This result suggested that, in this human cell model, Th1/Th2 cell responses were mainly determined by the species of bacteria and that PTMC or PDLLA did not detectably influence these responses

Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes

Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes