Reversing microcrystalline tests: an analytical approach to recycling of microcrystals from drugs of abuse

A combined analysis of microcrystalline tests followed by LC-MS or GC-MS analysis is described. Microcrystalline tests are shown to be non-destructive as addition products formed were easily dissociated after the application of an appropriate solvent. Subsequent analysis of the sample was done to quantify the recovery of the drug. Examples were performed using the date rape drug γ-hydroxybutyrate (GHB) and the synthetic opioid methadone

Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?

Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted by their own melt at the triple point. We present extensive simulations for NaCl, followed by calculations of the solid-vapor, solid-liquid, and liquid-vapor free energies showing that solid NaCl(100) is a nonmelting surface, and that its full behavior can quantitatively be accounted for within a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting is traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface. The latter is pursued in detail, and it is shown that surface short-range charge order acts to raise the surface tension because incipient NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl much below that of solid NaCl(100).Comment: 4 pages, 3 figure

Terahertz response of dipolar impurities in polar liquids: On anomalous dielectric absorption of protein solutions

A theory of radiation absorption by dielectric mixtures is presented. The coarse-grained formulation is based on the wavevector-dependent correlation functions of molecular dipoles of the host polar liquid and a density-density structure factor of the positions of the solutes. A nonlinear dependence of the absorption coefficient on the solute concentration is predicted and originates from the mutual polarization of the liquid surrounding the solutes by the collective field of the solute dipoles aligned along the radiation field. The theory is applied to terahertz absorption of hydrated saccharides and proteins. While the theory gives an excellent account of the observations for saccharides without additional assumptions and fitting parameters, experimental absorption coefficient of protein solutions significantly exceeds theoretical calculations within standard dielectric models and shows a peak against the protein concentration. A substantial polarization of protein's hydration shell is required to explain the differences between standard theories and experiment. When the correlation function of the total dipole moment of the protein with its hydration shell from numerical simulations is used in the present analytical model an absorption peak similar to that seen is experiment is obtained. The result is sensitive to the specifics of protein-protein interactions in solution. Numerical testing of the theory requires the combination of terahertz dielectric and small-angle scattering measurements.Comment: 11 p

Anomalous temperature dependence of surface tension and capillary waves at liquid gallium

The temperature dependence of surface tension \gamma(T) at liquid gallium is studied theoretically and experimentally using light scattering from capillary waves. The theoretical model based on the Gibbs thermodynamics relates the temperature derivative of \gamma to the surface excess entropy -\Delta S. Although capillary waves contribute to the surface entropy with a positive sign the effect of dipole layer on \Delta S is negative. Experimental data collected at a free Ga surface in the temperature range from 30 to 160 C show that the temperature derivative of the tension changes sign near 100 C.Comment: 11 pages, 1 Postscript figure, submitted to J. Phys.

Does Young's equation hold on the nanoscale? A Monte Carlo test for the binary Lennard-Jones fluid

When a phase-separated binary ($A+B$) mixture is exposed to a wall, that preferentially attracts one of the components, interfaces between A-rich and B-rich domains in general meet the wall making a contact angle $\theta$. Young's equation describes this angle in terms of a balance between the $A-B$ interfacial tension $\gamma_{AB}$ and the surface tensions $\gamma_{wA}$, $\gamma_{wB}$ between, respectively, the $A$- and $B$-rich phases and the wall, $\gamma _{AB} \cos \theta =\gamma_{wA}-\gamma_{wB}$. By Monte Carlo simulations of bridges, formed by one of the components in a binary Lennard-Jones liquid, connecting the two walls of a nanoscopic slit pore, $\theta$ is estimated from the inclination of the interfaces, as a function of the wall-fluid interaction strength. The information on the surface tensions $\gamma_{wA}$, $\gamma_{wB}$ are obtained independently from a new thermodynamic integration method, while $\gamma_{AB}$ is found from the finite-size scaling analysis of the concentration distribution function. We show that Young's equation describes the contact angles of the actual nanoscale interfaces for this model rather accurately and location of the (first order) wetting transition is estimated.Comment: 6 pages, 6 figure

Enhancing the student learning experience through memes

Meme-making is an effective method for engaging students and enhancing the learning environment. Memes are a social media cultural phenomenon that the majority of those in Higher Education are exposed to on an almost daily occurrence. This research examined the use of meme-making within the forensic sciences to allow students to reflect on their knowledge. Students studying modules in forensic science across six universities in the UK and USA participated in the study. At the end of a teaching session, students produced a meme (using Meme Generator) to reflect on what they had learned; memes were then shared with the class anonymously via Padlet. This allowed all class members to see and engage with the memes created. At the end of the activity students were anonymously surveyed on their experience using Microsoft Forms and analysis of the results were undertaken using SPSS software.Meme-making was found to be an inclusive learning activity with no limitations, including age (part-time, distance learning and visually impaired students were not part of the study parameters). Results showed that not only did students find the practice fun, but it also helped with the retention of the class content suggesting that the meme-making process is an effective way to enhance the learning environment while engaging students.Student feedback suggests that to maximise participation the educator should stress reflection and learning as the key purpose of generating a meme, rather than being witty or entertaining. The forensic science educator should be mindful of selecting appropriate subject matter for this often-humorous activity

Variation in amino acid and lipid composition of latent fingerprints

The enhancement of latent fingerprints, both at the crime scene and in the laboratory using an array of chemical, physical and optical techniques, permits their use for identification. Despite the plethora of techniques available, there are occasions when latent fingerprints are not successfully enhanced. An understanding of latent fingerprint chemistry and behaviour will aid the improvement of current techniques and the development of novel ones. In this study the amino acid and fatty acid content of ‘real’ latent fingerprints collected on a non-porous surface was analysed by gas chromatography–mass spectrometry. Squalene was also quantified in addition. Hexadecanoic acid, octadecanoic acid and cis-9- octadecenoic acid were the most abundant fatty acids in all samples. There was, however, wide variation in the relative amounts of each fatty acid in each sample. It was clearly demonstrated that touching sebum-rich areas of the face immediately prior to fingerprint deposition resulted in a significant increase in the amount of fatty acids and squalene deposited in the resulting ‘groomed’ fingerprints. Serine was the most abundant amino acid identified followed by glycine, alanine and aspartic acid. The significant quantitative differences between the ‘natural’ and ‘groomed’ fingerprint samples seen for fatty acids were not observed in the case of the amino acids. This study demonstrates the variation in latent fingerprint composition between individuals and the impact of the sampling protocol on the quantitative analysis of fingerprints

Corrections to scaling in 2--dimensional polymer statistics

Writing $= AN^{2\nu}(1+BN^{-\Delta_1}+CN^{-1}+ ...)$ for the mean square end--to--end length $$ of a self--avoiding polymer chain of $N$ links, we have calculated $\Delta_1$ for the two--dimensional {\em continuum} case from a new {\em finite} perturbation method based on the ground state of Edwards self consistent solution which predicts the (exact) $\nu=3/4$ exponent. This calculation yields $\Delta_1=1/2$. A finite size scaling analysis of data generated for the continuum using a biased sampling Monte Carlo algorithm supports this value, as does a re--analysis of exact data for two--dimensional lattices.Comment: 10 pages of RevTex, 5 Postscript figures. Accepted for publication in Phys. Rev. B. Brief Reports. Also submitted to J. Phys.

Animals can assign novel odours to a known category

The ability to identify a novel stimulus as a member of a known category allows an organism torespond appropriately towards it. Categorisation is thus a fundamental component of cognition andan essential tool for processing and responding to unknown stimuli. Therefore, one might expectto observe it throughout the animal kingdom and across sensory domains. There is much evidenceof visual categorisation in non-human animals, but we currently know little about this process inother modalities. In this experiment, we investigated categorisation in the olfactory domain. Dogswere trained to discriminate between 40 odours; the presence or absence of accelerants formed thecategorical rule. Those in the experimental group were rewarded for responding to substrates withaccelerants (either burnt or un-burnt) and inhibit responses to the same substrates (either burnt or unburnt)without accelerants (S+ counterbalanced). The pseudocategory control group was trained onthe same stimuli without the categorical rule. The experimental group learned the discrimination andanimals were able to generalise to novel stimuli from the same category. None of the control animalswere able to learn the discrimination within the maximum number of trials. This study provides the firstevidence that non-human animals can learn to categorise non-biologically relevant odour information

Melting of Hard Cubes

The melting transition of a system of hard cubes is studied numerically both in the case of freely rotating cubes and when there is a fixed orientation of the particles (parallel cubes). It is shown that freelly rotating cubes melt through a first-order transition, whereas parallel cubes have a continuous transition in which positional order is lost but bond-orientational order remains finite. This is interpreted in terms of a defect-mediated theory of meltingComment: 5 pages, 3 figures included. To appear in Phys. Rev.