Edge selective gas detection using Langmuir films of graphene platelets

Recent advances in large-scale production of graphene have led to the availability of solution processable platelets at the commercial scale. Langmuir-Schaefer (L-S) deposition is a scalable process for forming a percolating film of graphene platelets which can be used for electronic gas sensing. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from commercially-available graphene dispersions. The sensitivity of the devices and repeatability of the electrical response upon gas exposure has been characterized. Raman spectroscopy and Kelvin probe force microscopy (KPFM) show doping of the basal plane using ammonia (n-dopant) and acetone (p-dopant). The resistive signal is increased upon exposure to both gases showing that sensing originates from the change in contact resistance between nanosheets. We demonstrate that Arrhenius fitting of the desorption response potentially allows measurements of the desorption process activation energies for gas molecules adsorbed onto the graphene nanosheets

Can Automated Smoothing Significantly Improve Benchmark Time Series Classification Algorithms?

tl;dr: no, it cannot, at least not on average on the standard archive problems. We assess whether using six smoothing algorithms (moving average, exponential smoothing, Gaussian filter, Savitzky-Golay filter, Fourier approximation and a recursive median sieve) could be automatically applied to time series classification problems as a preprocessing step to improve the performance of three benchmark classifiers (1-Nearest Neighbour with Euclidean and Dynamic Time Warping distances, and Rotation Forest). We found no significant improvement over unsmoothed data even when we set the smoothing parameter through cross validation. We are not claiming smoothing has no worth. It has an important role in exploratory analysis and helps with specific classification problems where domain knowledge can be exploited. What we observe is that the automatic application does not help and that we cannot explain the improvement of other time series classification algorithms over the baseline classifiers simply as a function of the absence of smoothing

[Letter] Size selection of liquid-exfoliated 2D nanosheets

Here we present a size selection model for liquid-exfoliated two-dimensional nanosheets. The ability to consistently select exfoliated nanosheets with desired properties is important for development of applications in all areas. The model presented facilitates determination of centrifugation parameters for production of dispersions with controlled size and thickness for different materials, solvents and exfoliation processes. Importantly, after accounting for the influence of viscosity on exfoliation, comparisons of different solvents are shown to be well described by the surface tension and Hansen parameter matching. This suggests that previous analyses may have overestimated the relative performance of more viscous solvents. This understanding can be extended to develop a model based on the force balance of nanosheets falling under viscous drag during centrifugation. By considering the microscopic aspect ratio relationships, this model can be both calibrated for size selection of nanosheets and compare the exfoliation processes themselves

Selective mechanical transfer deposition of Langmuir graphene films for high-performance silver nanowire hybrid electrodes

In this work we present silver nanowire hybrid electrodes, prepared through the addition of small quantities of pristine graphene by mechanical transfer deposition from surface-assembled Langmuir films. This technique is a fast, efficient, and facile method for modifying the opto-electronic performance of AgNW films. We demonstrate that it is possible to use this technique to perform two-step device production by selective patterning of the stamp used, leading to controlled variation in the local sheet resistance across a device. This is particularly attractive for producing extremely low-cost sensors on arbitrarily large scales. Our aim is to address some of the concerns surrounding the use of AgNW films as replacements for indium tin oxide (ITO); namely the use of scarce materials and poor stability of AgNWs against flexural and environmental degradation

Sequestration of Zn into mixed pyrite-zinc sulfide framboids: A key to Zn cycling in the ocean?

Zinc (Zn) is an important micronutrient in the ocean, and fixation of Zn into organic, trace element-rich sediments is an important contributor to Zn cycling in the ocean. Framboidal sulfides are considered to be the major host for Zn in such settings. The sequestration of Zn into framboids via biotic or abiotic processes is not fully understood, which presents difficulties for interpretation of Zn isotope values in sediments. In this work, we describe a novel type of framboid with mixed pyrite and zinc sulfide (sphalerite or wurtzite) microcrystals from meta-pelites of the Otago Schist, New Zealand. A combination of optical microscopy, scanning electron microscopy (SEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) were utilized to assess the association between Zn, pyrite and organic matter in framboids. The distribution of Zn in framboids is variable. Most pyrite microcrystals include minor amounts of Zn. Trace Zn is also observed to co-locate with organic matter, which occurs on the boundaries of pyrite microcrystals. Finally, Zn is found as single zinc sulfide microcrystals or zinc sulfide rims around pyrite microcrystals within individual framboids. These textures have not been recorded before, to our knowledge. The sequence of events that sequesters Zn into framboids may affect Zn isotope fractionation from seawater to continental margin sediments

A multi-site service evaluation of silver diamine fluoride use for children

Introduction: The use of silver diamine fluoride (SDF) is relatively new to the UK. It is unknown how it is being used and for what indications in UK paediatric dental services. // Aim To: 1) establish how SDF is being used across different paediatric dental settings in the UK; and 2) consider parental and patient views on the treatment experience and side effect of discolouration. // Method: A multi-site service evaluation was carried out across six paediatric dentistry units covering hospital and community services. Data were collected prospectively from 17/02/2020 to 02/03/2022. Simple descriptive statistics were used to analyse the data. // Results: Data were collected for 54 patients. The included patients had an age range of 2-13 years, with a mean of 4.9 years. The reason SDF was chosen was reported as: to avoid general anaesthetic (n = 25); to avoid extractions (n = 8); stabilisation (n = 25); acclimatisation (n = 24); and insufficient cooperation for other treatment (n = 17). In total, 42 cases had SDF applied to the primary dentition. This was in the anterior dentition for 18 patients and the posterior dentition for 15, with nine patients having SDF applied both anteriorly and posteriorly. The majority of children and parents were accepting of the technique and immediate aesthetic outcome. // Conclusion: In the services involved in this multi-site service evaluation, SDF is used for young patients in the primary dentition for the purpose of caries arrest. The technique was viewed positively by the majority of parents and children

b→sb \to s Transitions in Family-dependent U(1)′U(1)^\prime Models

We analyze flavor-changing-neutral-current (FCNC) effects in the $b\to s$ transitions that are induced by family non-universal $U(1)'$ gauge symmetries. After systematically developing the necessary formalism, we present a correlated analysis for the $\Delta B =1, 2$ processes. We adopt a model-independent approach in which we only require family-universal charges for the first and second generations and small fermion mixing angles. We analyze the constraints on the resulting parameter space from $B_s - \bar B_s$ mixing and the time-dependent CP asymmetries of the penguin-dominated $B_d \to (\pi, \phi, \eta', \rho, \omega, f_0)K_S$ decays. Our results indicate that the currently observed discrepancies in some of these modes with respect to the Standard Model predictions can be consistently accommodated within this general class of models.Comment: 36 pages, 11 figure

Pristine carbon nanotube scaffolds for the growth of chondrocytes

The effective growth of chondrocytes and the formation of cartilage is demonstrated on scaffolds of aligned carbon nanotubes; as two dimensional sheets and on three dimensional textiles. Raman spectroscopy is used to confirm the presence of chondroitin sulfate, which is critical in light of the unreliability of traditional dye based assays for carbon nanomaterial substrates. The textile exhibits a very high affinity for chondrocyte growth and could present a route to implantable, flexible cartilage scaffolds with tuneable mechanical properties