Model for quantitative tip-enhanced spectroscopy and the extraction of nanoscale-resolved optical constants

Near-field infrared spectroscopy by elastic scattering of light from a probe tip resolves optical contrasts in materials at dramatically sub-wavelength scales across a broad energy range, with the demonstrated capacity for chemical identification at the nanoscale. However, current models of probe-sample near-field interactions still cannot provide a sufficiently quantitatively interpretation of measured near-field contrasts, especially in the case of materials supporting strong surface phonons. We present a model of near-field spectroscopy derived from basic principles and verified by finite-element simulations, demonstrating superb predictive agreement both with tunable quantum cascade laser near-field spectroscopy of SiO$_2$ thin films and with newly presented nanoscale Fourier transform infrared (nanoFTIR) spectroscopy of crystalline SiC. We discuss the role of probe geometry, field retardation, and surface mode dispersion in shaping the measured near-field response. This treatment enables a route to quantitatively determine nano-resolved optical constants, as we demonstrate by inverting newly presented nanoFTIR spectra of an SiO$_2$ thin film into the frequency dependent dielectric function of its mid-infrared optical phonon. Our formalism further enables tip-enhanced spectroscopy as a potent diagnostic tool for quantitative nano-scale spectroscopy.Comment: 19 pages, 9 figure

Causal Inference in Epidemiological Studies with Strong Confounding

One of the identifiabilty assumptions of causal effects defined by marginal structural model (MSM) parameters is the experimental treatment assignment (ETA) assumption. Practical violations of this assumption frequently occur in data analysis, when certain exposures are rarely observed within some strata of the population. The inverse probability of treatment weighted (IPTW) estimator is particularly sensitive to violations of this assumption, however, we demonstrate that this is a problem for all estimators of causal effects. This is due to the fact that the ETA assumption is about information (or lack thereof) in the data. A new class of causal models, causal models for realistic individualized exposure rules (CMRIER), introduced in van der Laan and Petersen (2007), is based on dynamic interventions. CMRIER generalize MSM, and their parameters remain fully identifiable from the observed data, even when the ETA assumption is violated, if the dynamic interventions are set to be realistic. Examples of such realistic interventions are provided. We argue that causal effects defined by CMRIER may be more appropriate in many situations, particularly those with policy considerations. Through simulation studies, we examine the performance of the IPTW estimator of the CMRIER parameters in contrast to that of the MSM parameters. We also apply the methodology to a real data analysis in air pollution epidemiology to illustrate the interpretation of the causal effects defined by CMRIER

Nanoscale-length control of the flagellar driveshaft requires hitting the tethered outer membrane

The bacterial flagellum exemplifies a system where even small deviations from the highly regulated flagellar assembly process can abolish motility and cause negative physiological outcomes. Consequently, bacteria have evolved elegant and robust regulatory mechanisms to ensure that flagellar morphogenesis follows a defined path, with each component self-assembling to predetermined dimensions. The flagellar rod acts as a driveshaft to transmit torque from the cytoplasmic rotor to the external filament. The rod self-assembles to a defined length of ~25 nanometers. Here, we provide evidence that rod length is limited by the width of the periplasmic space between the inner and outer membranes. The length of Braun's lipoprotein determines periplasmic width by tethering the outer membrane to the peptidoglycan layer

Interviewer: 'Are women and girls ever responsible for the domestic violence they encounter?' Student: 'No, well, unless they did something really, really bad …'

Research shows the ‘gendered nature’ of domestic violence, with Women’s Aid (a UK-based charity) estimating that 1 in 4 women are affected (2014). This paper reports on a project - funded by Comic Relief, completed by Nottinghamshire Domestic Violence Forum (now known as Equation) and evaluated by Nottingham Trent University. The project adopts a Whole School Approach in seeking to prevent domestic violence. Students at three secondary schools attended between one and five blocks of work, and special events. There is evidence of positive developments - with young people showing understanding of domestic violence as well as the margins between healthy and unhealthy relationships. However, not all students could reply ‘never’ to the question of ‘are women and girls to blame for the domestic violence they experience?’, remarking that if the woman had done something ‘really, really bad’ then violence might be justified. We argue that young people’s uncertainties need to be situated within the gender-unequal socio-contexts of contemporary society, and further call for a WSA to domestic violence prevention to be a compulsory part of the UK national curriculum

6-Deoxyhexoses froml-Rhamnose in the Search for Inducers of the Rhamnose Operon: Synergy of Chemistry and Biotechnology

In the search for alternative non‐metabolizable inducers in the l ‐rhamnose promoter system, the synthesis of fifteen 6‐deoxyhexoses from l ‐rhamnose demonstrates the value of synergy between biotechnology and chemistry. The readily available 2,3‐acetonide of rhamnonolactone allows inversion of configuration at C4 and/or C5 of rhamnose to give 6‐deoxy‐d ‐allose, 6‐deoxy‐d ‐gulose and 6‐deoxy‐l ‐talose. Highly crystalline 3,5‐benzylidene rhamnonolactone gives easy access to l ‐quinovose (6‐deoxy‐l ‐glucose), l ‐olivose and rhamnose analogue with C2 azido, amino and acetamido substituents. Electrophilic fluorination of rhamnal gives a mixture of 2‐deoxy‐2‐fluoro‐l ‐rhamnose and 2‐deoxy‐2‐fluoro‐l ‐quinovose. Biotechnology provides access to 6‐deoxy‐l ‐altrose and 1‐deoxy‐l ‐fructose

Activation of Transfer RNA-Guanine Ribosyltransferase by Protein Kinase C

Transfer RNA-guanine ribosyltransferase (TGRase) irreversibly incorporates queuine into the first position in the anticodon of four tRNA isoacceptors. Rat brain protein kinase C (PKC) was shown to stimulate rat liver TG Rase activity, TGRase preparations derived from rat liver have been observed to decrease in activity over time in storage at -20 or -70°C, Contamination of the samples by phosphatases was indicated by a p-nitrophenylphosphate conversion test, The addition of micromolar concentrations of the phosphatase inhibitors sodium pyrophosphate and sodium fluoride into TGRase isolation buffers resulted in a greater return of TGRase activity than without these inhibitors, Inactive TGRase preparations were reactivated to their original activity with the addition of PKC, In assays combining both TGRase and PKC enzymes, inhibitors of protein kinase C (sphingosine, staurosporine, H-7 and calphostin C) all blocked the reactivation of TGRase, whereas activators of protein kinase C (calcium, diacylglycerol and phosphatidyl serine) increased the activity of TGRase, None of the PKC modulators affected TGRase activity directly, Alkaline phosphatase, when added to assays, decreased the activity of TGRase and also blocked the reactivation of TGRase with PKC, Denaturing PAGE and autoradiography was performed on TGRase isolates that had been labelled with 32P by PKC, The resulting strong 60 kDa band (containing the major site for phosphorylation) and weak 34.5 kDa band (containing the TGRase activity) are suggested to associate to make up a 104 kDa heterodimer that comprises the TGRase enzyme, This was corroberated by native and denaturing size-exclusion chromatography These results suggest that PKC-dependent phosphorylation of TGRase is tied to efficient enzymatic function and therefore control of the queuine modification of tRNA

The potential role of hybridization in diversification and speciation in an insular plant lineage: insights from synthetic interspecific hybrids

Hybridization is recognized as an important process in plant evolution, and this may be particularly true for island plants where several biotic and abiotic factors facilitate interspecific hybridization. Although rarely done, experimental studies could provide insights into the potential of natural hybridization to generate diversity when species come into contact in the dynamic island setting. The potential of hybridization to generate morphological variation was analysed within and among 12 families (inbred lines) of an F4 hybrid generation between two species of Tolpis endemic to the Canary Islands. Combinations of characters not seen in the parents were present in hybrids. Several floral and vegetative characters were transgressive relative to their parents. Morphometric studies of floral, vegetative and fruit characters revealed that several F4 families were phenotypically distinct from other families, and from their parents. The study demonstrates that morphologically distinct pollen-fertile lines, potentially worthy of taxonomic recognition if occurring in nature, can be generated in four generations. The ability of the hybrid lines to set self-seed would reduce gene flow among the lines, and among the hybrids and their parental species. Selfing would also facilitate the fixation of characters within each of the lines. Overall, the results show the considerable potential of hybridization for generating diversity and distinct phenotypes in island lineages

Threat of Hantavirus Pulmonary Syndrome to Field Biologists Working with Small Mammals

Field biologists should use personal protective equipment appropriate for their activities