Hopping transport on a fractal: ac conductivity of porous silicon

We have measured the frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz-100 kHz at different temperatures. The conductivity data exhibit a strong frequency dependence. When normalized to the dc conductivity, our data obey a universal scaling law, with a well-defined crossover, in which the real part of the conductivity sigma' changes from an sqrt(omega) dependence to being proportional to omega. We explain this in terms of activated hopping in a fractal network. The low-frequency regime is governed by the fractal properties of porous Si, whereas the high-frequency dispersion comes from a broad distribution of activation energies. Calculations using the effective-medium approximation for activated hopping on a percolating lattice give fair agreement with the data.

Statnote 27: Principal components analysis (PCA)

In Statnotes 24 and 25, multiple linear regression, a statistical method that examines the relationship between a single dependent variable (Y) and two or more independent variables (X), was described. The principle objective of such an analysis was to determine which of the X variables had a significant influence on Y and to construct an equation that predicts Y from the X variables. ‘Principal components analysis’ (PCA) and ‘factor analysis’ (FA) are also methods of examining the relationships between different variables but they differ from multiple regression in that no distinction is made between the dependent and independent variables, all variables being essentially treated the same. Originally, PCA and FA were regarded as distinct methods but in recent times they have been combined into a single analysis, PCA often being the first stage of a FA. The basic objective of a PCA/FA is to examine the relationships between the variables or the ‘structure’ of the variables and to determine whether these relationships can be explained by a smaller number of ‘factors’. This statnote describes the use of PCA/FA in the analysis of the differences between the DNA profiles of different MRSA strains introduced in Statnote 26.

Novel tear film supplements:a potential application for synthetic protein-phospholipid complexes

Purpose: Surfactant proteins A, B, C and D complex with (phospho)lipids to produce surfactants which provide low interfacial tensions. It is likely that similar complexation occurs in the tear film and contributes to its low surface tension. Synthetic protein-phospholipid complexes, with styrene maleic anhydrides (SMAs) as the protein analogue, have been shown to have similarly low surface tensions. This study investigates the potential of modified SMAs and/or SMA-phospholipid complexes, which form under physiological conditions, to supplement natural tear film surfactants. Method: SMAs were modified to provide structural variants which can form complexes under varying conditions. Infrared spectroscopy and Nuclear Magnetic Resonance were used to confirm SMA structure. Interfacial behaviour of the SMA and SMA-phospholipid complexes was studied using Langmuir trough, du Nûoy ring and pulsating bubblemethods. Factors which affect SMA-phospholipid complex formation, such as temperature and pH, were also investigated. Results: Structural manipulation of SMAs allows control over complex formation, including under physiological conditions (e.g. partial SMAesterfication allowed complexation with dimyristoylphosphatidylcholine, at pH7). The low surface tensions of the SMAs (42mN/m for static (du Nûoy ring) and 34mN/m for dynamic (Langmuir) techniques) demonstrate their surface activity at the air-aqueous interface. SMA-phospholipid complexes provide even lower surface tensions (~2 mN/m), approaching that of lung surfactant, as measured by the pulsating bubblemethod. Conclusions: Design of the molecular architecture of SMAs allows control over their surfactant properties. These SMAs could be used as novel tear films supplements, either alone to complex with native tear film phospholipids or delivered as synthetic protein-phospholipid complexes.

Contrast integration over area is extensive: a three-stage model of spatial summation

Classical studies of area summation measure contrast detection thresholds as a function of grating diameter. Unfortunately, (i) this approach is compromised by retinal inhomogeneity and (ii) it potentially confounds summation of signal with summation of internal noise. The Swiss cheese stimulus of T. S. Meese and R. J. Summers (2007) and the closely related Battenberg stimulus of T. S. Meese (2010) were designed to avoid these problems by keeping target diameter constant and modulating interdigitated checks of first-order carrier contrast within the stimulus region. This approach has revealed a contrast integration process with greater potency than the classical model of spatial probability summation. Here, we used Swiss cheese stimuli to investigate the spatial limits of contrast integration over a range of carrier frequencies (1–16 c/deg) and raised plaid modulator frequencies (0.25–32 cycles/check). Subthreshold summation for interdigitated carrier pairs remained strong (~4 to 6 dB) up to 4 to 8 cycles/check. Our computational analysis of these results implied linear signal combination (following square-law transduction) over either (i) 12 carrier cycles or more or (ii) 1.27 deg or more. Our model has three stages of summation: short-range summation within linear receptive fields, medium-range integration to compute contrast energy for multiple patches of the image, and long-range pooling of the contrast integrators by probability summation. Our analysis legitimizes the inclusion of widespread integration of signal (and noise) within hierarchical image processing models. It also confirms the individual differences in the spatial extent of integration that emerge from our approach.

Community pharmacy in a commissioning-led NHS:can pharmacy compete effectively?

Introduction – The commissioning of services has been a core responsibility of English Primary Care Trusts (PCTs) since 2002. Primary care organisations (PCOs) in Scotland, Wales and Northern Ireland have also increased their commissioning activities but with, arguably, less fervour than their English counterparts. The commissioning function of English PCTs has been reinforced by the introduction of new contractual frameworks across primary care – for medical services, dentistry and pharmacy. The new pharmaceutical services contract for England and Wales introduced an “enhanced” category of services, the provision of which is dependent on the commissioning decisions of local PCTs. As the NHS, most pertinently in England, continues its transformation from a provider to a commissioner of healthcare, the ability of pharmacy to compete effectively for funding is likely to become increasingly important. Method - After piloting, in August 2006 a self-completion postal questionnaire was sent to a random sample of practising community pharmacists, stratified for country and sex, within Great Britain (n=1998), with a follow-up to non-responders 4 weeks later. Data were analysed using SPSS (v12.0). A final response rate of 51% (n=1023/1998) was achieved. Within the section of the questionnaire relating to service provision, respondents were asked “do you believe that pharmacy will be able to compete effectively with other healthcare providers for access to additional funding to develop services that address a public health need identified by your local Primary Care Organisation (PCO), e.g. PCT/LHB etc.?”. Answers were recorded on a three-point scale; pharmacy “will”, “may”, or “will not” be able to compete effectively for funding. Results - The attitudes of pharmacists showed variation depending on the type of pharmacy they worked in (supermarket, multiple (outlets (n)=200), large chain (200>n>20), small chain (20=n>5), or independent (n=5)) (?2 test with p=0.001). Over a third of survey pharmacists working in small chains and independents (37% (n=21/57) and 33% (n=113/341) respectively) believed that pharmacy would not be able to compete effectively for funding compared to 23% (n=15/65) for supermarket pharmacists, 22% (n=21/97) for pharmacists employed by large chains and just 18% (n=62/353) for pharmacists employed most regularly in multiples. Furthermore, attitudes also varied between the countries of residence of respondents (?2 test with p<0.05). 27% (n=242/893) of pharmacists resident in England and Wales believed that pharmacy would not be able to compete compared to 16% (n=18/116) of pharmacists resident in Scotland. Conclusions – It would appear that community pharmacists believe that the larger pharmacy chains and supermarkets will occupy an advantageous position in terms of attracting finance to develop services. This could have notable implications for service provision across the sector. If corporate pharmacy chains were to monopolise commissioning monies then the proportion of funding available to independents will be diminished; arguably further hastening their demise, as well as stifling the professional development of pharmacists employed within the independent sector. These findings, when combined with the variation observed between UK pharmacists operating under different contractual frameworks, may be a reflection of the divergent policy in the different administrations with developments in England, including the new pharmacy contract, reflecting a market-based approach with Scotland taking a near opposite stance with service integration and a commitment to new public health. However, it should be acknowledged that the questionnaire did not allow for detection of ambiguities in, or misunderstandings of, the survey question and this should be considered as a limitation of the research.

Marc Silberman (ed.),The German Wall. Fallout in Europe, New York: Palgrave Macmillan 2011

Review of: Marc Silberman (ed.),The German Wall. Fallout in Europe, New York: Palgrave Macmillan 2011

Quinols as novel therapeutic agents. 2.1 4-(1-arylsulfonylindol- 2-yl)-4-hydroxycyclohexa-2,5-dien-1-ones and related agents as potent and selective antitumor agents

A series of substituted 4-(1-arylsulfonylindol-2-yl)-4-hydroxycyclohexa-2, 5-dien-1-ones (indolylquinols) has been synthesized on the basis of the discovery of lead compound 1a and screened for antitumor activity. Synthesis of this novel series was accomplished via the "one-pot" addition of lithiated (arylsulfonyl)indoles to 4,4-dimethoxycyclohexa-2,5-dienone followed by deprotection under acidic conditions. Similar methodology gave rise to the related naphtho-, 1H-indole-, and benzimidazole-substituted quinols. A number of compounds in this new series were found to possess in vitro human tumor cell line activity substantially more potent than the recently reported antitumor 4-substituted 4-hydroxycyclohexa-2,5-dien-1-ones1 with similar patterns of selectivity against colon, renal, and breast cell lines. The most potent compound in the series in vitro, 4-(1-benzenesulfonyl-6-fluoro-1H-indol- 2-yl)-4-hydroxycyclohexa-2,5-dienone (1h), exhibits a mean GI50 value of 16 nM and a mean LC50 value of 2.24 μM in the NCI 60-cell-line screen, with LC50 activity in the HCT 116 human colon cancer cell line below 10 nM. The crystal structure of the unsubstituted indolylquinol 1a exhibits two independent molecules, both participating in intermolecular hydrogen bonds from quinol OH to carbonyl O, but one OH group also interacts intramolecularly with a sulfonyl O atom. This interaction, which strengthens upon ab initio optimization, may influence the chemical environment of the bioactive quinol moiety. In vivo, significant antitumor activity was recorded (day 28) in mice bearing subcutaneously implanted MDA-MB-435 xenografts, following intraperitoneal treatment of mice with compound 1a at 50 mg/kg.

Extended reach of 116 Gb/s DP-QPSK transmission using random DFB fiber laser based Raman amplification and bidirectional second-order pumping

We propose a novel random DFB fiber laser based Raman amplification using bidirectional second-order pumping. This extends the reach of 116 Gb/s DP-QPSK WDM transmission up to 7915 km, compared with other Raman amplification techniques.