Measurement of T1 and T2 relaxation times of the pancreas at 7 T using a multi-transmit system

Objective

To determine T₁ and T₂ relaxation times of healthy pancreas parenchyma at 7 T using a multi-transmit system.

Materials and methods

Twenty-six healthy subjects were scanned with a 7 T MR system using eight parallel transceiver antennas, each with two additional receive loops. A Look-Locker sequence was used to obtain images for T₁ determination, while T₂ was obtained from spin-echo images and magnetic resonance spectroscopy measurements with different echo times. T₁ and T₂ times were calculated using a mono-exponential fit of the average magnitude signal from a region of interest in the pancreas and were tested for correlation with age.

Results

The age range of the included subjects was 21–72 years. Average T₁ and T₂ relaxation times in healthy pancreas were 896 ± 149 ms, and 26.7 ± 5.3 ms, respectively. No correlation with age was found.

Conclusion

T₁ and T₂ relaxation times of the healthy pancreas were reported for 7 T, which can be used for image acquisition optimization. No significant correlations were found between age and T₁ or T₂ relaxation times of the pancreas. Considering their low standard deviation and no observable age dependence, these values may be used as a baseline to study potentially pancreatic tissue affected by disease.

     

A note on large-scale logistic prediction: using an approximate graphical model to deal with collinearity and missing data

Large-scale prediction problems are often plagued by correlated predictor variables and missing observations. We consider prediction settings in which logistic regression models are used and propose a novel approach to make accurate predictions even when predictor variables are highly correlated and only partly observed. Our approach comprises three steps: first, to overcome the collinearity issue, we propose to model the joint distribution of the outcome variable and the predictor variables using the Ising network model. Second, to render the application of Ising networks feasible, we use a latent variable representation to apply a low-rank approximation to the network’s connectivity matrix. Finally, we propose an approximation to the latent variable distribution that is used in the representation to handle missing observations. We demonstrate our approach with numerical illustrations.

     

A Facet‐Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics

Colloidal nanocrystals combine size‐ and facet‐dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size‐ and facet‐tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger‐diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small‐diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short‐wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow‐bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (≈47 meV) and Urbach tail (≈29 meV). This approach provides a ≈50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a ≈70% external quantum efficiency at their excitonic peak.     

Depth‐Resolved Modulation of Metal–Oxygen Hybridization and Orbital Polarization across Correlated Oxide Interfaces

Interface‐induced modifications of the electronic, magnetic, and lattice degrees of freedom drive an array of novel physical properties in oxide heterostructures. Here, large changes in metal–oxygen band hybridization, as measured in the oxygen ligand hole density, are induced as a result of interfacing two isovalent correlated oxides. Using resonant X‐ray reflectivity, a superlattice of SrFeO₃ and CaFeO₃ is shown to exhibit an electronic character that spatially evolves from strongly O‐like in SrFeO₃ to strongly Fe‐like in CaFeO₃. This alternating degree of Fe electronic character is correlated with a modulation of an Fe 3d orbital polarization, giving rise to an orbital superstructure. At the SrFeO₃/CaFeO₃ interfaces, the ligand hole density and orbital polarization reconstruct in a single unit cell of CaFeO₃, demonstrating how the mismatch in these electronic parameters is accommodated at the interface. These results provide new insight into how the orbital character of electrons is altered by correlated oxide interfaces and lays out a broadly applicable approach for depth‐resolving band hybridization.     

Medical surveillance of the lead exposed worker. Current guidelines

1. The "lead standards" established by OSHA for general industry in 1978 and the construction industry in 1993 require employers and clinicians to follow very specific guidelines for protecting lead exposed workers. Depending on the level of exposure, medical surveillance may be legally required. 2. Lead affects multiple body systems and can cause permanent damage. Low level exposures that in the past were thought safe are now considered hazardous as new information emerges about the toxicity of lead. 3. Lead poisoning, if undetected, often results in misdiagnosis and costly care. Adults are exposed to lead in many different workplace settings. All clinicians caring for lead exposed workers need to be informed about the health effects of lead, employer and physician responsibilities, and worker rights. 4. Occupational and environmental health nurses can help identify workers at risk and prevent lead poisoning by education and early intervention through collaboration with the workers, the employer, the company physician, and other health and safety professionals.     

Same Neighbourhood … Different Views? A Confrontation of Internal and External Neighbourhood Reputations

Residents and non-residents are likely to think differently about a neighbourhood's reputation. Relatively little is known about the similarities and differences between these internal and external types of neighbourhood reputation or the relationship between reputations and ‘real’ or ‘objective’ neighbourhood characteristics. This paper addresses two points: first, the extent to which neighbourhood reputations differ between and within groups; second, the extent to which these neighbourhood reputations are associated with measured neighbourhood characteristics. Data from a specially designed survey carried out in 24 neighbourhoods in Utrecht, the fourth largest city in the Netherlands, are used. Analysis of the data showed that neighbourhood reputations are rated higher by residents and estate agents than by other city residents. Within the group of other city residents, differences were found in how neighbourhood reputations are rated by socio-economic status, ethnicity and educational background. Further, it was found that neighbourhood reputations are correlated with measured social characteristics of the neighbourhood, while physical and functional neighbourhood characteristics are of less importance.     

Transcending binary logic by gating three coupled quantum dots

Physical considerations supported by numerical solution of the quantum dynamics including electron repulsion show that three weakly coupled quantum dots can robustly execute a complete set of logic gates for computing using three valued inputs and outputs. Input is coded as gating (up, unchanged, or down) of the terminal dots. A nanosecond time scale switching of the gate voltage requires careful numerical propagation of the dynamics. Readout is the charge (0, 1, or 2 electrons) on the central dot.     

Jasmonic Acid and Herbivory Differentially Induce Carnivore-Attracting Plant Volatiles in Lima Bean Plants

Lima bean plants respond to feeding damage of two-spotted spider mites (Tetranychus urticae) with the emission of a complex blend of volatiles that are products of several different biosynthetic pathways. These volatiles attract the carnivorous mite Phytoseiulus persimilis, a specialist predator of the spider mites that exterminates entire prey populations, and thus the volatiles contribute indirectly to plant defense. The volatile blend constitutes information to the carnivores, and blend composition is an important factor in this. Jasmonic acid (JA) is involved in the signal transduction of this induced defense. Application of JA through the petiole of Lima bean plants induces a volatile blend that is similar, but not identical, to that emitted by spider mite-infested plants. The induced volatiles originate from the lipoxygenase pathway, the shikimic acid pathway, and the isoprenoid pathway. Among the induced bean plant volatiles are nitriles and oximes. Of a total of 61 components, 10 are emitted at significantly different rates. Among these are the terpene (E)-4,8-dimethyl-1,3,7-nonatriene and the phenolic methyl salicylate, two compounds that are known to attract P. persimilis. A crucial test for comparing the effect of spider mite damage and JA application on volatile induction is the response of P. persimilis. The carnivore is attracted by volatiles from JA-treated plants. Moreover, even treatment of Lima bean plants with methyl jasmonate vapor made the plants attractive to the carnivorous mites. However, the predators prefer the volatiles from spider-mite-infested Lima bean plants over those from JA-treated plants. Thus, chemical as well as behavioral analyses demonstrate that spider mite damage and JA treatment have similar, although not identical, effects on volatile induction in Lima bean plants.     

Directed evolution: From a staphylococcal lipase to a phospholipase

The lipase of Staphylococcus aureus (SAL) is able to degrade lipids and p‐nitrophenylesters but is not active on phospholipid substrates. Interestingly, the homologous lipase from Staphylococcus hyicus is highly active on phospholipids. In order to investigate the molecular basis for this difference in substrate specificity, phospholipase activity was introduced into SAL by directed evolution strategy. In this approach, sequential rounds of error‐prone PCR were performed in combination with a screening of the resulting mutant libraries. The screening was based on a high‐throughput plate assay and a subsequent chromogenic assay in 96‐well plate format to accurately determine the enzymatic activities in cell lysates of a selected number of clones. After 4 rounds of error‐prone PCR, two products were obtained, displaying a 7.8‐ and 9.2‐fold increase in absolute phospholipase activity and a 5.9‐ and 6.9‐fold increase in phospholipase/ lipase activity ratio. A final round of DNA shuffling with these two products and wildtype (WT)‐SAL was performed to combine beneficial mutations and to eliminate neutral or deleterious mutations. This procedure yielded a best variant containing 6 amino acid mutations displaying a 11.6‐fold increase in absolute phospholipase activity and a 11.5‐fold increase in phospholipase/lipase ratio as compared to the starting point. The character of the mutations and their possible effects on substrate specificity are discussed.