New Routes and Airport Connectivity

This paper shows how module identification techniques can help airports evaluate the impact of new routes on their network connectivity. Although only carriers can choose whether to open a new route, this research is also of interest to airports and regional governments, who can offer incentives for new connections to desirable destinations. The analysis employs simulated annealing to verify the existence of highly interconnected subsystems, or modules, within the European aviation network. A module is a group of airports with very strong internal links in terms of exchanged seats, but weak connections to the rest of the network. From the standpoint of improving connectivity, we expect that new routes towards large airports belonging to other modules are the most desirable. We also find that the lower the interchange between the modules to be connected, the higher the connectivity gain. We test this hypothesis on all 467 European airports with at least one scheduled flight in autumn 2007.     

Integrators’ Air Transport Networks in Europe

Integrators are shipping carriers that control complete air and road delivery networks and offer a wide range of package delivery services. Despite the increasing relevance of small package delivery services in the European air transport market, very little has been written on integrated carriers’ air transport networks on the Old Continent. In this paper we examine the network configurations of DHL, FedEx, TNT, and UPS in terms of hubs, spokes, and market shares. Our results show that integrators operate hub-and-spoke networks. Network indices and centrality measures confirm that their network structures are more similar to those of full-service passenger carriers rather than those of low-cost carriers. However, the nature of their hub-and-spoke systems is different because freight tons, as compared to passengers, are more easily flown along multiple-stop and circular routes. As a consequence, FedEx, TNT, and UPS operate non-pure star networks with a dominant central hub and a set of intermediate airports acting as stops between the central hub and (usually) one “external airport”. DHL operates a multi-hub architecture, with a main dominant hub in Leipzig and a set of “secondary hubs” that provide several connections to other network nodes. Furthermore, we provide evidence of the most important intra-Europe and long-haul routes for each integrator, showing that DHL seems to have a more developed Europe-Asia connection, and is the only integrator to connect Europe to Sub-Saharan Africa. Finally, we show the high degree of complementarity existing between FedEx and TNT networks and that such complementarity is confirmed also by an analysis of their market shares in the different European sub-markets. Despite the significant level of market concentration, our analysis shows that the recent merger between FedEx and TNT is not expected to significantly modify market equilibrium in Europe.

     

Candida albicans morphotypes and in vitro adhesivity to cells of the human oral mucosa in HIV-positive and AIDS patients after exposure of blastospores to fluconazole. II

BACKGROUND: Oro-pharyngeal candidosis is a frequently initial clinical manifestation of HIV infection and the adhesive properties of Candida spp. represent a very important pathogenicity factor. METHODS: In this study the adhesivity rate of Candida albicans to the oral epithelial cells of 33 HIV-positive patients and 12 healthy volunteers, have been assessed before and after the exposure of blastospores to inhibitory concentrations of fluconazole, in relation to 11 morphotypes obtained from 13 C. albicans strains. RESULTS: Results can be summarized as follows: 1) the number of blastospores adhering to the HIV-positive donor' cells is higher than that of blastospores adhering to the healthy donors' cells (rate is 2.7:1); 2) blastospores from strains producing rough or very coarse fringes show adhesive properties higher than those of strains with different morphology; 3) in the group of HIV-positive patients the adhesivity inhibition of blastospores from strains producing rough or very coarse fringes was higher (38.3%) than that of strains with different morphology (33.8%); 4) overall, adhesivity inhibition due to exposure to fluconazole is higher for epithelial cells from healthy donors. CONCLUSIONS: These results can suggest the validity of an antimycotic pretreatment of persons at risk of oro-pharyngeal candidiasis.     

Evidence for an inhibitory effect of physiological levels of insulin on the growth hormone (GH) response to GH-releasing hormone in healthy subjects

It has been previously reported that in healthy subjects, the acute reduction of free fatty acids (FFA) levels by acipimox enhances the GH response to GHRH. In the present study, the GH response to GHRH was evaluated during acute blockade of lipolysis obtained either by acipimox or by insulin at different infusion rates. Six healthy subjects (four men and two women, 25.8 +/- 1.9 yrs old, mean +/- SE) underwent three GHRH tests (50 micrograms iv, at 1300 h) during: 1) iv 0.9% NaCl infusion (1200-1500 h) after oral acipimox administration (250 mg) at 0700 h and at 1100 h; 2) 0.1 mU.kg-1.min-1 euglycemic insulin clamp (1200-1500 h) after oral acipimox administration (250 mg at 0700 h and at 1100 h); 3) 0.4 mU.kg-1.min-1 euglycemic insulin clamp (1200-1500 h) after oral placebo administration (at 0700 and 1100 h). Serum insulin (immunoreactive insulin) levels were significantly different in the three tests (12 +/- 2, 100 +/- 10, 194 +/- 19 pmol/L, P < 0.06), plasma FFA were low and similar (0.04 +/- 0.003, 0.02 +/- 0.005, 0.02 +/- 0.003, not significant), and the GH response to GHRH was progressively lower (4871 +/- 1286, 2414 +/- 626, 1076 +/- 207 micrograms/L 120 min), although only test 3 was significantly different from test 1 (P < 0.05). Pooling the three tests together, a significant negative regression was observed between mean serum immunoreactive insulin levels and the GH response to GHRH (r = -0.629, P < 0.01). Our results indicate that in healthy subjects, acipimox and hyperinsulinemia produce a similar decrease in FFA levels and that at similar low FFA, the GH response to GHRH is lower during insulin infusion than after acipimox. These data suggest that insulin exerts a negative effect on GH release. Because the insulin levels able to reduce the GH response to GHRH are commonly observed during the day, for instance during the postprandial period, we conclude that the insulin negative effect on GH release may have physiological relevance.