41 research outputs found
Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry
Transmission spectra of metallic films or membranes perforated by arrays of
subwavelength slits or holes have been widely interpreted as resonance
absorption by surface plasmon polaritons (SPPs). Alternative interpretations
involving evanescent waves diffracted on the surface have also been proposed.
These two approaches lead to divergent predictions for some surface wave
properties. Using far-field interferometry, we have carried out a series of
measurements on elementary one-dimensional (1-D) subwavelength structures with
the aim of testing key properties of the surface waves and comparing them to
predictions of these two points of view
Periodic Chiral Structures
The electromagnetic properties of a structure that is both chiral and periodic are investigated using coupled-mode equations. The chirality is characterized by the constitutive relations D = εE + iXicB and H = iXicE+B/µ, where Xic is the chiral admittance. The periodicity is described by a sinusoidal perturbation of the permittivity, permeability and chiral admittance. The coupled-mode equations are derived from physical considerations. The coupled-mode equations are used to examine bandgap structure and reflected and transmitted fields. Chirality is observed predominantly in transmission while periodicity is present in both reflection and transmission
The RNA chaperone Hfq is essential for the virulence of Salmonella typhimurium
The RNA chaperone, Hfq, plays a diverse role in bacterial physiology beyond its original role as a host factor required for replication of Qβ RNA bacteriophage. In this study, we show that Hfq is involved in the expression and secretion of virulence factors in the facultative intracellular pathogen, Salmonella typhimurium. A Salmonella hfq deletion strain is highly attenuated in mice after both oral and intraperitoneal infection, and shows a severe defect in invasion of epithelial cells and a growth defect in both epithelial cells and macrophages in vitro. Surprisingly, we find that these phenotypes are largely independent of the previously reported requirement of Hfq for expression of the stationary phase sigma factor, RpoS. Our results implicate Hfq as a key regulator of multiple aspects of virulence including regulation of motility and outer membrane protein (OmpD) expression in addition to invasion and intracellular growth. These pleiotropic effects are suggested to involve a network of regulatory small non-coding RNAs, placing Hfq at the centre of post-transcriptional regulation of virulence gene expression in Salmonella. In addition, the hfq mutation appears to cause a chronic activation of the RpoE-mediated envelope stress response which is likely due to a misregulation of membrane protein expression
Live Recombinant Salmonella Typhi Vaccines Constructed to Investigate the Role of rpoS in Eliciting Immunity to a Heterologous Antigen
We hypothesized that the immunogenicity of live Salmonella enterica serovar Typhi vaccines expressing heterologous antigens depends, at least in part, on its rpoS status. As part of our project to develop a recombinant attenuated S. Typhi vaccine (RASTyV) to prevent pneumococcal diseases in infants and children, we constructed three RASTyV strains synthesizing the Streptococcus pneumoniae surface protein PspA to test this hypothesis. Each vector strain carried ten engineered mutations designed to optimize safety and immunogenicity. Two S. Typhi vector strains (χ9639 and χ9640) were derived from the rpoS mutant strain Ty2 and one (χ9633) from the RpoS+ strain ISP1820. In χ9640, the nonfunctional rpoS gene was replaced with the functional rpoS gene from ISP1820. Plasmid pYA4088, encoding a secreted form of PspA, was moved into the three vector strains. The resulting RASTyV strains were evaluated for safety in vitro and for immunogenicity in mice. All three RASTyV strains were similar to the live attenuated typhoid vaccine Ty21a in their ability to survive in human blood and human monocytes. They were more sensitive to complement and were less able to survive and persist in sewage and surface water than their wild-type counterparts. Adult mice intranasally immunized with any of the RASTyV strains developed immune responses against PspA and Salmonella antigens. The RpoS+ vaccines induced a balanced Th1/Th2 immune response while the RpoS− strain χ9639(pYA4088) induced a strong Th2 immune response. Immunization with any RASTyV provided protection against S. pneumoniae challenge; the RpoS+ strain χ9640(pYA4088) provided significantly greater protection than the ISP1820 derivative, χ9633(pYA4088). In the pre-clinical setting, these strains exhibited a desirable balance between safety and immunogenicity and are currently being evaluated in a Phase 1 clinical trial to determine which of the three RASTyVs has the optimal safety and immunogenicity profile in human hosts
Foundations of the composite diffracted evanescent wave model
1 page, 1 figure.To the Editor — In the paper by Gay et al. in the
April 2006 issue of Nature Physics, an experimental
investigation of the light transmission through a
two-dimensional system composed of one slit and
one indentation drilled on a silver film is carried
out. The results were analysed within the composite
diff racted evanescent wave (CDEW) model. This
comment demonstrates that the mathematical
foundation of the CDEW model is flawed.Peer reviewe