The Post-Social Turn: Challenges for Housing Research

In an editorial entitled ‘Living Room’ for the journal Urban Geography (Vol. 25, 2004) Susan Smith made reference to the ‘tired state of housing studies’. Smith argued that the ‘post-social turn’ in sociology and cultural geography has largely gone unnoticed by housing researchers and because of this, the radical implications of its epistemology have yet to be explicitly addressed. This post-social turn, elsewhere referred to as Science and Technology Studies, Actor Network theory, feminist technoscience and post-humanism, calls on researchers to decentre the human as the nucleus of social life and in turn recognize the significance of non-human actors (e.g. animals, technology and material artefacts) within social analysis. While in recent years housing scholars have begun to embrace post-structuralist accounts of social life, including discursive and constructionist theories, there has only been limited engagement with post-social assumptions and concepts. In view of this gap, this paper reviews recent developments in post-social theory with a specific focus on the implications of this approach for housing studies.     

Is the use of particle air filtration justified? Costs and benefits of filtration with regard to health effects,building cleaning and occupant productivity

Estimates of costs and the corresponding benefits of particle filtration have been derived for a standard office building. Reduction in occupants’ exposure to particles during their workday is anticipated to reduce their morbidity and mortality. Filtration may also reduce the costs associated with building and HVAC cleaning. Conversely, losses of occupant productivity due to sensory offending pollutants emitted from used ventilation filters can lead to significant economic losses. The results of the present analysis are strongly dependent on several key input parameters; consequently, the sensitivity of the results to these parameters was evaluated as part of this study. The study also acknowledges that the benefits-to-costs ratio depends on the perspective of the stakeholder: the employer renting the building is impacted by occupant performance and building energy costs; the building owner is impacted by maintenance of the building and its HVAC system; society is impacted by the employees’ health and welfare. Regardless of perspective, particle filtration is anticipated to lead to annual savings significantly exceeding the running costs for filtration. However, economic losses resulting from even a small decrease in productivity caused by sensory pollutants emitted from used ventilation filters have the potential to substantially exceed the annual economic benefits of filtration. Further studies are required to determine if meaningful benefits can be obtained from more frequent filter replacement or application of different filtration techniques that limit the emission of offending pollutants into the ventilation air.     

Biocidal polymers (II): Determination of biological activity of novel N-halamine biocidal polymers and evaluation for use in water filters

Novel N-halamine biocidal polymers were prepared by co-polymerizing a heterocyclic ring-based monomer with tolylene-2,6-diisocyanate and toluene-2,4-diisocyanate. The resulting polyurethanes were halogenated; chlorinated, brominated or iodinated. The rate of bacterial killing by the halogenated derivatives was determined both with and without halogen quenching and one of them was evaluated for use in water filters. The effect of these polymers on bacterial growth-rates was also determined.     

Highly potent HIV inhibition: engineering a key anti-HIV structure from PSC-RANTES into MIP-1 beta/CCL4

The HIV coreceptor CCR5 is a validated target for both the prevention and therapy of HIV infection. PSC-RANTES, an N-terminally modified analogue of one of the natural chemokine ligands of CCR5 (RANTES/CCL5), is a potent inhibitor of HIV entry into target cells. Here, we set out to engineer the anti-HIV activity of PSC-RANTES into another natural CCR5 ligand (MIP-1beta/CCL4), by grafting into it the key N-terminal pharmacophore region from PSC-RANTES. We were able to identify MIP-1beta/CCL4 analogues that retain the receptor binding profile of MIP-1beta/CCL4, but acquire the very high anti-HIV potency and characteristic inhibitory mechanism of PSC-RANTES. Unexpectedly, we discovered that in addition to N-terminal structures from PSC-RANTES, the side chain of Lys33 is also necessary for full anti-HIV potency.     

Novel initiators for the synthesis of propylene oxide oligomers by anionic ring opening polymerization

A series of potassium alcoholates was obtained from the reaction between KOH and ethylene glycol, resorcinol, 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol, 4,4′-sulfonyldiphenol. These salts were employed to initiate the anionic ring opening polymerization of propylene oxide (PO). The molecular weight distribution of the propylene oxide oligomers prepared by this method and the initiator structure were correlated. These oligomers were characterized through Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopies and size exclusion chromatography (SEC). It was found that the molecular weight and polydispersity of the synthesized poly(propylene oxide) (PPO) is highly dependant on the initiator structure and solubility in the reactive medium. The oligomers obtained using di-potassium resorcinolate exhibited a molecular weight distribution more polydisperse than that of PO oligomers synthesized by means of di-potassium ethylene glycolate. In the case of the PO polymerizations started by the potassium salts of 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol and 4,4′-sulfonyldiphenol, the oligomer chains showed very broad molecular weight distributions. In general, lower solubility and augmentation of the polymer polydispersity were observed when the number of aromatic rings in the initiator structure increased. The experimental results were contrasted with those obtained from quantum chemical semiempirical calculations at AM1 level. The peculiar behavior exhibited by the initiators with an aromatic structure could be explained in terms of different reactivities of the initiation sites. The theoretical studies revealed that the ring in the aromatic initiators promotes an unsymmetrical growing when the PPO chains are formed. In contrast, the identical reactivity of both initiation sites in the ethylene glycolate produces a symmetrical growing during the PO polymerization.     

Charge transport in disordered graphene-based low dimensional materials

Two-dimensional graphene, carbon nanotubes, and graphene nanoribbons represent a novel class of low dimensional materials that could serve as building blocks for future carbon-based nanoelectronics. Although these systems share a similar underlying electronic structure, whose exact details depend on confinement effects, crucial differences emerge when disorder comes into play. In this review, we consider the transport properties of these materials, with particular emphasis on the case of graphene nanoribbons. After summarizing the electronic and transport properties of defect-free systems, we focus on the effects of a model disorder potential (Anderson-type), and illustrate how transport properties are sensitive to the underlying symmetry. We provide analytical expressions for the elastic mean free path of carbon nanotubes and graphene nanoribbons, and discuss the onset of weak and strong localization regimes, which are genuinely dependent on the transport dimensionality. We also consider the effects of edge disorder and roughness for graphene nanoribbons in relation to their armchair or zigzag orientation. This article is published with open access at Springerlink.com     

Discrimination of isotrigon textures using the Rényi entropy of Allan variances

We present a computational algorithm for isotrigon texture discrimination. The aim of this method consists in discriminating isotrigon textures against a binary random background. The extension of the method to the problem of multitexture discrimination is considered as well. The method relies on the fact that the information content of time or space-frequency representations of signals, including images, can be readily analyzed by means of generalized entropy measures. In such a scenario, the Rényi entropy appears as an effective tool, given that Rényi measures can be used to provide information about a local neighborhood within an image. Localization is essential for comparing images on a pixel-by-pixel basis. Discrimination is performed through a local Rényi entropy measurement applied on a spatially oriented 1-D pseudo-Wigner distribution (PWD) of the test image. The PWD is normalized so that it may be interpreted as a probability distribution. Prior to the calculation of the texture's PWD, a preprocessing filtering step replaces the original texture with its localized spatially oriented Allan variances. The anisotropic structure of the textures, as revealed by the Allan variances, turns out to be crucial later to attain a high discrimination by the extraction of Rényi entropy measures. The method has been empirically evaluated with a family of isotrigon textures embedded in a binary random background. The extension to the case of multiple isotrigon mosaics has also been considered. Discrimination results are compared with other existing methods.     

Building three-dimensional images using a time-reversal chaotic cavity

The design of two-dimensional (2-D) arrays for three-dimensional (3-D) ultrasonic imaging is a major challenge in medical and nondestructive applications. Thousands of transducers are typically needed for focusing and steering in a 3-D volume. In this article, we propose a different concept allowing us to obtain electronic 3-D focusing with a small number of transducers. The basic idea is to couple a small number of transducers to a chaotic reverberating cavity with one face in contact with the body of the patient. The reverberations of the ultrasonic waves inside the cavity create at each reflection virtual transducers. The cavity acts as an ultrasonic kaleidoscope multiplying the small number of transducers and creating a much larger virtual transducer array. By exploiting time-reversal processing, it is possible to use collectively all the virtual transducers to focus a pulse everywhere in a 3-D volume. The reception process is based on a nonlinear pulse-inversion technique in order to ensure a good contrast. The feasibility of this concept for the building of 3-D images was demonstrated using a prototype relying only on 31 emission transducers and a single reception transducer.     

Short and long alteplase dwells in dysfunctional hemodialysis catheters

Background: Hemodialysis catheter dysfunction (CD) is the inability to attain adequate blood pump speeds (BPS) and is attributed to thrombus or catheter malposition; alteplase (TPA) is often given in a variety of dwell times to treat CD. The purpose of this study was to determine if TPA dwell time affects short‐ or long‐term catheter patency rates. Methods: Sixty hemodialysis (HD) patients with CD, as defined by BPS of < 250 mL/min, were randomized to receive either 1‐ or > 48‐hr (to subsequent HD run) TPA dwell. The primary outcomes were catheter patency (BPS of > 250 mL/min) at the subsequent HD run and catheter patency at 2 weeks. The secondary outcome was the time from study entry to the next catheter intervention (including subsequent TPA installation). Results: After TPA installation, a 78% overall catheter patency rate was observed at the subsequent HD run, falling to 48% patency at 2 weeks. There is no statistically significant difference between the short and long TPA dwell groups for catheter patency at the subsequent HD run (76.9% vs. 79.4%) or at 2 weeks (42.3% vs. 52.9%). Multivariate analysis demonstrates that the use of TPA on two or more previous occasions is a predictor of TPA failure both at the subsequent HD run and at 2 weeks. TPA installation achieves a median catheter function time of only 14 days, after which CD reoccurs. Conclusion: This study demonstrates that although patency for the next HD run can be achieved with either short or long TPA dwell, neither is reliable in terms of long‐term patency. Strategies that employ TPA for CD are temporary and allow a 2‐week window during which more definitive therapies for HD access should be sought.     

Capture of water-borne colloids in granular beds using external electric fields: improving removal of Cryptosporidium parvum

Suboptimal coagulation in water treatment plants often results in reduced removal efficiency of Cryptosporidium parvum oocysts by several orders of magnitude (J. AWWA 94(6) (2002) 97, J. AWWA 93(12) (2001) 64). The effect of external electric field on removal of C. parvum oocysts in packed granular beds was studied experimentally. A cylindrical configuration of electrodes, with granular media in the annular space was used. A negative DC potential was applied to the central electrode. No coagulants or flocculants were used and filtration was performed with and without application of an electric field to obtain improvement in removal efficiency. Results indicate that removal of C. parvum increased from 10% to 70% due to application of field in fine sand media and from 30% to 96% in MAGCHEM media. All other test particles (Kaolin and polystyrene latex microspheres) used in the study also exhibited increased removal in the presence of an electric field. Single collector efficiencies were also computed using approximate trajectory analysis, modified to account for the applied external electric field. The results of these calculations were used to qualitatively explain the trends in the experimental observations.