Finite-difference time-domain simulations of the effects of air gaps in double-shell extended hemispherical lenses

The effects of parasitic air gaps on the input impedance and radiation characteristics of dense double-shell integrated lens antennas are studied numerically at millimetre waves using the finite-difference time-domain method. The lens core is made up of Macor or silicon, and is coated with a quarter wavelength matching layer. Two kinds of gaps are compared: they are located either (i) between both shells of the lens, or (ii) between the lens base and the feed substrate. We show that their impact is much more critical in the second case, and that it becomes dramatic for silicon lenses, even with very thin gaps (smaller than ? ₀/100); the three major observed effects are the following: (i) strong shift of the resonant frequency, (ii) beam broadening and directivity loss, (iii) increase of the side lobe level.     

Hydrocarbon Signatures of Egg Maternity, Caste Membership and Reproductive Status in the Common Wasp

In most ants, bees, and wasps, the workers are capable of challenging the reproductive monopoly of the queen by laying unfertilized, male eggs. An important mechanism that can resolve this conflict is policing, whereby the queen or workers prevent successful worker reproduction by selectively eating worker-laid eggs or by attacking egg-laying workers. Egg policing by workers has been shown to occur in several social wasp species, but the information used by worker wasps to discriminate between queen-laid and worker-laid eggs has never been investigated. Our aim, therefore, was to investigate if hydrocarbons might be used in egg policing by workers in the common wasp, Vespula vulgaris, where worker policing previously has been shown to be effective. Our results show that 51 different hydrocarbons are present on the surface of newly-laid eggs, and that there are pronounced quantitative differences in the hydrocarbon profiles of queen-laid and worker-laid eggs, with longer-chained alkenes and methylated alkanes (C₂₈–C₃₁) in particular being more abundant on the surface of queen-laid eggs. We further show that the hydrocarbon profiles on the surface of queen-laid and worker-laid eggs resemble those found on the mother queen’s and workers’ cuticles. Interestingly, longer-chained methylated alkanes also were more abundant on the cuticle of both mother queens and reproductive workers, suggesting that these compounds are linked to fertility, as has also been found to be the case in several ant species.     

Do Cuticular Hydrocarbons Provide Sufficient Information for Optimal Sex Allocation in the Ant <Emphasis Type="Italic">Formica exsecta</Emphasis>?

Split sex ratio theory predicts that when kin structure varies among colonies of social insects, in order to maximize the inclusive fitness, colonies with relatively high sister-sister relatedness should specialize in producing reproductive females, whereas in those with relatively low sister-sister relatedness workers should bias their sex ratio towards males. However, in order to achieve this, workers need to be able to reliably assess the type of colony in which they live. The information on colony kin structure may be encoded in cuticular hydrocarbons (CHCs), assuming that genetic variability translates accurately into chemical variability. However, in genetically heterogeneous colonies, too accurate information may encourage the pursuit of individual interests through nepotistic behavior and reduce colony efficiency or cause social disruption. In this study, we estimated how well variability of CHC recognition cues reflects colony kin structure in the ant Formica exsecta. Our results show that CHC variability does not covary with kin structure or the overall genetic diversity of the colony, and that patrilines and matrilines can have distinct CHC profiles in some but not all colonies. However, within-colony relatedness remains the key determinant of colony sex ratios. Based on our results, CHC variability cannot serve as accurate information on within-colony relatedness, kin structure, or full-sib affiliation, nor do workers seem to use colony CHC variability as a proxy for sex-ratio adjustment. The use of this type of information thus could lead workers to make mistakes, and it remains unclear how colonies of Formica exsecta adjust offspring sex ratio to their optimal value.     

Bis(ethynyl)-polymers

Poly(2,5-thiophenediyl)ethynylene and poly[ethynylene(2,5-thiophenediyl)ethynylene], synthesized in our laboratory, have been investigated in order to characterize their physicochemical properties. The optical and infrared spectra of the two polymers were studied as well as their thermal properties by means of differential scanning calorimetry and thermogravimetric analysis. The electrical conductivity of the two polymers in the pristine state and in the I₂-doped one has been measured and the effects due to the doping on the spectroscopic and thermal properties have been studied.     

Leaky-Wave Slot Array Antenna Fed by a Dual Reflector System

A leaky-wave slot array antenna fed by a dual offset Gregorian reflector system is realized by pins in a parallel plate waveguide. The radiating part of the antenna is composed by parallel slots etched on one side of the same parallel plate waveguide. The dual offset Gregorian reflector system is fed by an arrangement constituted by two vias and a grid, also constituted by pins. Also this feed arrangement realizes a leaky type of radiation, this time inside the parallel plate waveguide. A prototype of the antenna has been designed, manufactured and successfully tested. The low profile, low cost and high efficiency of the antenna render it suited for a variety of radar or telecom applications.     

alpha,alpha-Cyclopentaneglycine dipeptides capped with biaryls as tachykinin NK(2) receptor antagonists

The NK(2) receptor belongs to the family of tachykinin neurotransmitters. It has been reported to be involved in several pathological conditions, and selective antagonists are potentially useful drugs for the treatment of asthma, irritable bowel syndrome, cystitis, and depression. Starting from in-house capped dipeptide libraries, we were able to identify a number of molecules with sub-nanomolar binding affinity for the hNK(2) receptor. All were characterized by a rigid core structure with a strong constraint induced by an alpha,alpha-cyclopentaneglycine fragment. Herein we report the further elaboration of three initial basic structures. The planar benzothiophene group was substituted with a series of biphenyl and heterobiphenyl moieties that are well tolerated in terms of receptor affinity. The new compounds also maintained good antagonist potency in an in vitro functional assay, and a number of them showed significant in vivo activity after intravenous administration in our guinea pig model.     

Chemical Signature and Reproductive Status in the Facultatively Polygynous ant Pachycondyla Verenae

In insects, cuticular hydrocarbons (CHCs) generally are used as cues and signals for within colony processes, such as signaling reproductive status, and between colony processes, such as colony membership. We examined CHC profiles of the facultatively polygynous ant Pachycondyla verenae in order to identify chemical signals of reproductive queens within colonies containing many gynes. Colonies of P. verenae, belonging to two different members of a complex of morphospecies, were collected from three geographic localities within South America. We also tested whether CHC profiles differed between geographic localities and morphospecies. We found three alkenes, two isomers of pentacosene and heptacosene, which were more abundant in CHC profiles of reproductive queens of this morphospecies complex. When we tested whether these differences were consistent across geographic localities, we found the abundance of these alkenes differed according to morphospecies, with the isomers of pentacosene being more abundant in queens from morph one, and heptacosene being more abundant in queens from morph two. Our study has given further insight into the mechanisms behind maintenance of reproductive dominance, and has demonstrated that chemical signatures associated with reproductive status in Pachycondyla verenae are not conserved within this species complex.