Vivaldi Antennas for Microwave Imaging: Theoretical Analysis and Design Considerations

The geometrical and electrical features of the Vivaldi antenna are studied in the light of the frequency-independent antenna theory. A scaling principle is derived for the exponential tapering of the antenna, and a closed-form model for the current distribution is provided. Such theoretical results are in good agreement with several numerical simulations performed by using the NEC2 code. Furthermore, a practical feeding system, based on a double-Y balun, is developed and tested to obtain a more systematic approach to the design of the aforesaid antennas     

A Perturbation Expansion Method to Study Highly Correlated Spins

This paper proposes a new numerical algorithm to study dynamical spin dependent properties of local highly correlated structures. The method consists in diagonalizing a finite cluster containing the many-body terms of the Hamiltonian and embedding it into the rest of the system, the Embedding Cluster Approximation (ECA), combined with Wilson’s ideas of logarithmic discretization of the representation of the Hamiltonian, the Logarithm Discretization Embedded Cluster Approximation (LDECA). The physics associated to a dot and a side-coupled double dot connected to leads are discussed in detail.     

A situated approach to the acquisition of shared SA in team contexts

Theories of team situation awareness (SA) differ in the information they require operators to have for effective coordination. Endsley stresses shared SA, whereas distributed SA argues that coordination involves transactive and compatible SA. We distinguish between weak and strong shared SA, and argue the latter enhances communication and increases team cohesion. Although we agree with Endsley on the importance of shared SA, we argue her account of how it is acquired exceeds the working memory capacity of individual team members. We offer an account consistent with our situated SA perspective that claims individuals off-load information to their environment whenever possible to minimise effortful internal processing. We argue that our approach, in conjunction with Pickering and Garrod's (2004, Towards a mechanistic psychology of dialogue. Behavioral and Brain Sciences, 27, pp. 169–226) interactive-alignment model, can explain how shared SA is acquired, relying on automatic processes enacted when individuals interact in conversations. This approach can be used to study team SA in many complex and distributed systems.     

In vitro activity of Δ6 and Δ9 desaturases in hepatomas of different growth rates

The in vitro activity of Δ9- and Δ6-desaturases was determined in the microsomal fraction of C3H/S normal mouse liver, SS1K fast growing hepatoma, and SS1H slow growing hepatoma. These tumors are two different sublines of a spontaneous hepatoma transplanted in 1949 by J.W. Wilson, Brown University, Providence, R.I., into C3H/ST W: strain. The activity of the two enzymes showed a parallel decrease in the two studied hepatomas. These alterations could be attributed to a fundamental change in structure or function in the tumors. The fatty acid desaturase activity seems to be independent of cell division in malignant tissues.     

In vitro desaturation of 1-14C linoleic acid in Novikoff hepatoma

The lipid fatty acid pattern of normal liver, host liver, and Novikoff hepatoma was determined by gas liquid chromatography, and Δ6-desaturase activity for linoleic acid was measured in the microsomal fractions. The results showed that, in Novikoff hepatoma, there is a correlation between the low content of arachidonic acid and the low activity of Δ6-desaturase, a key enzyme in the biosynthetic pathway of this acid.     

Clinical approach to the analysis of causes of death in the first two years of life of very-low-birthweight infants in a multicentre setting

Mortality in the first 2 years of 634 very-low-birthweight infants admitted to eight neonatal intensive care units in Italy, and the factors associated with the net probability of death from each cause, were studied by means of the Cox proportional hazard model. A clinical classification of the causes of death was used. Overall mortality was 33.7% (intercentre range 12.6-52.9%). The highest cause-specific mortality rates were observed for respiratory problems, intra-ventricular haemorrhage (IVH) and infections (14.5%, 6.3% and 5.7% respectively). The leading causes of death were respiratory problems and IVH in the first week of life, infections from the second week up to the end of the first month, and bronchopulmonary dysplasia (BPD) afterwards. Birthweight < 1000 g, gestational age < 30 weeks, absence of spontaneous respiratory activity, unknown body temperature and pH < 7.20 at admission were associated with death from respiratory problems and IVH. Male sex, birthweight < 1000 g and unknown body temperature at admission were associated with death from BPD. Mortality from infections was higher in one centre; no other differences emerged among the eight NICUs. The classification of the causes of death employed and the use of the net probabilities of death appear as practical and useful instruments to study the relationship between specific aspects of medical care and mortality, and to investigate the reasons for differences in performance between neonatal units.     

Transparent Plasmonic Nanowire Electrodes via Self‐Organised Ion Beam Nanopatterning

A self‐organised approach for the synthesis of transparent metal nanowire arrays is based on defocused ion beam sputtering. The nanowire arrays, supported on low‐cost dielectric substrates (glass slides), feature a dual functionality: they exhibit anisotropic conductivity, with sheet resistances which are reduced in comparison to those of transparent conductive oxides, and additionally they support localised plasmon resonances. The latter represents an attractive feature in view of plasmon enhanced photon harvesting applications, in which the nanostructured metal electrodes are employed as an alternative to conventional transparent conductive oxides.     

Sugar-derived ionic liquids

Ionic liquids (ILs) are special molten salts with melting points below 100 degrees C that are typically constituted of organic cations (imidazolium, pyridinium, sulfonium, phosphonium, etc.) and inorganic anions. Due to their ionic nature, they are endowed with high chemical and thermal stability, good solvent properties, and non-measurable vapor pressure. Although the recycling of ILs partly compensate their rather high cost, it is important to develop new synthetic approaches to less expensive and environmentally sustainable ILs based on renewable raw materials. In fact, most of these alternative solvents are still prepared starting from fossil feedstocks. Until now, only a limited number of ionic liquids have been prepared from renewable sources (e.g., hydroxy acids, amino acids, terpenes), and even less from naturally occurring carbohydrates. This short review describes the synthesis and applications of chiral and achiral ILs obtained from inexpensive sugars.