Nitration of primary amines to form primary nitramines (Review)

Poster presentation at 19th Seminar on New Trends in Research of Energetic Materials; Pardubice, Czech Republic; 20/04/2016-22/04/2016The nitration of primary amines to form primary nitramines is a rarely reported synthetic procedure which proceeds through a minimum of two steps. This is in stark contrast to the nitration of alcohols and secondary amines which is readily achievable by a number of methods in a single step. In general the primary amine must initially be activated to nitration as direct exposure to nitrating media tends to result in the formation of an ionic nitrate salt. This activation may be achieved through the use of a multitude of protecting groups that are stable to the nitrating conditions used thereafter. The review presented here is an attempt to bring together the published literature on this often overlooked synthetic procedure in energetic materials chemistry

Compatibility assessment of thermoplastic formulations

Presented at 19th Seminar on new trends in research of energetic materials (NTREM 2016)Prior to the large-scale preparation of any new chemical formulation an assessment of the potential reactivity between the components must be carried out. This practice, which is common to many fields including pharmaceutical science, is particularly essential in the case of energetic formulations whose chemical incompatibility may result in an unexpected and potentially explosive decomposition. The common method used to investigate incompatibility is to heat 1:1 (w/w) formulations and evaluate the variation in their thermal stability with respect to the neat, pristine explosive. The techniques used are: differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vacuum stability and heat flow calorimetry. As trends in energetics move towards safer formulations the components are more commonly selected for their high thermal stability and low sensitivity to initiation. However, recently prepared thermoplastic formulations which incorporate a thermally stable explosive, 2,2’,4,4’,6,6’-hexanitrostilbene (HNS II), and a selection of high-melting-point thermoplastics produced anomalous results during their compatibility assessment leading to the suggestion that historical tests originally devised for less thermally stable materials, such as N,N’,N’’-trinitro-1,3,5-triazacyclohexane (RDX), may not be directly transferable to the newer generations of insensitive explosive formulations

Network oscillations at the boundary of an equatorial coronal hole

We investigate intensity oscillations observed simultaneously in the quiet chromosphere and in the corona, above an enhanced network area at the boundary of an equatorial coronal hole. A Fourier analysis is applied to a sequence of images observed in the 171 A and 1600 A passbands of TRACE. Four interesting features above the magnetic network are further investigated by using a wavelet analysis. Our results reveal that, in both the 171 A and 1600 A passbands, oscillations above the magnetic network show a lack of power at high frequencies (5.0-8.3 mHz), and a significant power at low (1.3-2.0 mHz) and intermediate frequencies (2.6-4.0 mHz). The global 5-min oscillation is clearly present in the 4 analyzed features when seen in the 1600 A passband, and is also found with enhanced power in feature 1 (leg of a large coronal loop) and feature 2 (legs of a coronal bright point loop) when seen in the 171 A passband. Two features above an enhanced network element (feature 3 and feature 4) show repeated propagating behaviors with a dominant period of 10 min and 5 min, respectively. We suggest these oscillations are likely to be slow magneto-acoustic waves propagating along inclined magnetic field lines, from the lower solar atmosphere into the corona. The energy flux carried by these waves is estimated of the order of 40 erg cm\^{-2} s\^{-1} for the 171 A passband and is far lower than the energy required to heat the quiet corona. For the 1600 A passband, the energy flux is about 1.4*10^6 erg cm\^{-2} s\^{-1}, which is about one third of the required energy budget for the chromosphere.Comment: 7 pages, 8 figure

Chromospheric Velocities of a C-class Flare

We use high spatial and temporal resolution observations from the Swedish Solar Telescope to study the chromospheric velocities of a C-class flare originating from active region NOAA 10969. A time-distance analysis is employed to estimate directional velocity components in H-alpha and Ca II K image sequences. Also, imaging spectroscopy has allowed us to determine flare-induced line-of-sight velocities. A wavelet analysis is used to analyse the periodic nature of associated flare bursts. Time-distance analysis reveals velocities as high as 64 km/s along the flare ribbon and 15 km/s perpendicular to it. The velocities are very similar in both the H-alpha and Ca II K time series. Line-of-sight H-alpha velocities are red-shifted with values up to 17 km/s. The high spatial and temporal resolution of the observations have allowed us to detect velocities significantly higher than those found in earlier studies. Flare bursts with a periodicity of approximately 60 s are also detected. These bursts are similar to the quasi-periodic oscillations observed at hard X-ray and radio wavelength data. Some of the highest velocities detected in the solar atmosphere are presented. Line-of-sight velocity maps show considerable mixing of both the magnitude and direction of velocities along the flare path. A change in direction of the velocities at the flare kernel has also been detected which may be a signature of chromospheric evaporation.Comment: Accepted for publication in Astronomy and Astrophysics, 5 figure

An Automated Algorithm to Distinguish and Characterize Solar Flares and Associated Sequential Chromospheric Brightenings

We present a new automated algorithm to identify, track, and characterize small-scale brightening associated with solar eruptive phenomena observed in H{\alpha}. The temporal spatially-localized changes in chromospheric intensities can be separated into two categories: flare ribbons and sequential chromospheric brightenings (SCBs). Within each category of brightening we determine the smallest resolvable locus of pixels, a kernel, and track the temporal evolution of the position and intensity of each kernel. This tracking is accomplished by isolating the eruptive features, identifying kernels, and linking detections between frames into trajectories of kernels. We fully characterize the evolving intensity and morphology of the flare ribbons by observing the tracked flare kernels in aggregate. With the location of SCB and flare kernels identified, they can easily be overlaid on top of complementary data sets to extract Doppler velocities and magnetic field intensities underlying the kernels. This algorithm is adaptable to any dataset to identify and track solar features.Comment: 22 pages, 9 figure

Tissue multifractality and Born approximation in analysis of light scattering: a novel approach for precancers detection

Multifractal, a special class of complex self-affine processes, are under recent intensive investigations because of their fundamental nature and potential applications in diverse physical systems. Here, we report on a novel light scattering-based inverse method for extraction/quantification of multifractality in the spatial distribution of refractive index of biological tissues. The method is based on Fourier domain pre-processing via the Born approximation, followed by the Multifractal Detrended Fluctuation Analysis. The approach is experimentally validated in synthetic multifractal scattering phantoms, and tested on biopsy tissue slices. The derived multifractal properties appear sensitive in detecting cervical precancerous alterations through an increase of multifractality with pathology progression, demonstrating the potential of the developed methodology for novel precancer biomarker identification and tissue diagnostic tool. The novel ability to delineate the multifractal optical properties from light scattering signals may also prove useful for characterizing a wide variety of complex scattering media of non-biological origin

Improved methods for determining the kinematics of coronal mass ejections and coronal waves

The study of solar eruptive events and associated phenomena is of great importance in the context of solar and heliophysics. Coronal mass ejections (CMEs) and coronal waves are energetic manifestations of the restructuring of the solar magnetic field and mass motion of the plasma. Characterising this motion is vital for deriving the dynamics of these events and thus understanding the physics driving their initiation and propagation. The development and use of appropriate methods for measuring event kinematics is therefore imperative. Traditional approaches to the study of CME and coronal wave kinematics do not return wholly accurate nor robust estimates of the true event kinematics and associated uncertainties. We highlight the drawbacks of these approaches, and demonstrate improved methods for accurate and reliable determination of the kinematics. The Savitzky-Golay filter is demonstrated as a more appropriate fitting technique for CME and coronal wave studies, and a residual resampling bootstrap technique is demonstrated as a statistically rigorous method for the determination of kinematic error estimates and goodness-of-fit tests. It is shown that the scatter on distance-time measurements of small sample size can significantly limit the ability to derive accurate and reliable kinematics. This may be overcome by (i) increasing measurement precision and sampling cadence, and (ii) applying robust methods for deriving the kinematics and reliably determining their associated uncertainties. If a priori knowledge exists and a pre-determined model form for the kinematics is available (or indeed any justified fitting-form to be tested against the data), then its precision can be examined using a bootstrapping technique to determine the confidence interval associated with the model/fitting parameters.Comment: 12 pages, 12 figure

Revisiting the symptom iceberg in today's primary care: results from a UK population survey

Peer reviewedPublisher PD

Horizontal supergranule-scale motions inferred from TRACE ultraviolet observations of the chromosphere

We study horizontal supergranule-scale motions revealed by TRACE observation of the chromospheric emission, and investigate the coupling between the chromosphere and the underlying photosphere. A highly efficient feature-tracking technique called balltracking has been applied for the first time to the image sequences obtained by TRACE (Transition Region and Coronal Explorer) in the passband of white light and the three ultraviolet passbands centered at 1700 {\AA}, 1600 {\AA}, and 1550 {\AA}. The resulting velocity fields have been spatially smoothed and temporally averaged in order to reveal horizontal supergranule-scale motions that may exist at the emission heights of these passbands. We find indeed a high correlation between the horizontal velocities derived in the white-light and ultraviolet passbands. The horizontal velocities derived from the chromospheric and photospheric emission are comparable in magnitude. The horizontal motions derived in the UV passbands might indicate the existence of a supergranule-scale magnetoconvection in the chromosphere, which may shed new light on the study of mass and energy supply to the corona and solar wind at the height of the chromosphere. However, it is also possible that the apparent motions reflect the chromospheric brightness evolution as produced by acoustic shocks which might be modulated by the photospheric granular motions in their excitation process, or advected partly by the supergranule-scale flow towards the network while propagating upward from the photosphere. To reach a firm conclusion, it is necessary to investigate the role of granular motions in the excitation of shocks through numerical modeling, and future high-cadence chromospheric magnetograms must be scrutinized.Comment: 5 figures, accepted by Astronomy & Astrophysic