Making sense of senseless murders: The who, what, when, and where?

The phenomenon of "senseless" or "motiveless" homicide refers to homicides that lack an objective external motivation. Despite the unique challenges these homicides pose to police, few empirical studies have been conducted on the topic and existing studies are limited to clinical studies using small samples. To overcome existing empirical shortcomings, the current study used a sample of 319 homicide cases where no motive was established during the investigation to describe the "who" (offender and victim characteristics), "what" (modus operandi, crime characteristics), "where" (encounter, crime, and body recovery associated locations), and "when" (time of the crime) of the entire criminal event. Findings provide insight into the entire crime-commission process and suggest a different dynamic to "senseless" homicide from what has been described in previous literature. Implications for police investigative practice are discussed.

Colourimetric plastic film indicator for the detection of the volatile basic nitrogen compounds associated with fish spoilage.

The first example of an extruded polymer film containing the pH sensitive dye bromophenol blue (BPB) is described in which the polymer encapsulated dye changes colour from yellow to blue upon exposure to basic volatile nitrogen compounds, such as those given off by fish as it spoils. The latter include: trimethylamine (TMA), dimethylamine (DMA) and ammonia (NH3), and are collectively known as total volatile basic nitrogen (TVB-N). The films' colourimetric response to specific levels of TMA, as measured using absorbance spectroscopy and digital photography coupled with RGB colour analysis, is reported. The indicator is then used as a fish spoilage indicator at 22 and 4 °C, whilst at the same time a microbiological study is carried out, and in both cases the results reveal a strong correlation between the change in colour of the indicator with the concentration of bacterial colony forming units on the fish; the latter is often used as a measure of fish freshness. The correlation arises because the increase in TVB-N in head space of the package is due to the gradual bacteria-induced decomposition of the fish. The colourimetric TVB-N plastic film indicator's potential as a spoilage indicator for packaged fresh fish is discussed briefly.

Reductive photocatalysis and smart inks.

Semiconductor-sensitised photocatalysis is a well-established and growing area of research, innovation and commercialisation; the latter being mostly limited to the use of TiO2 as the semiconductor. Most of the work on semiconductor photocatalytic systems uses oxygen as the electron acceptor and explores a wide range of electron donors; such systems can be considered to be examples of oxidative photocatalysis, OP. OP underpins most current examples of commercial self-cleaning materials, such as: glass, tiles, concrete, paint and fabrics. OP, and its myriad of applications, have been reviewed extensively over the years both in this journal and elsewhere. However, the ability of TiO2, and other semiconductor sensitisers, to promote reductive photocatalysis, RP, especially of dyes, is significant and, although less well-known, is of growing importance. In such systems, the source of the electrons is some easily oxidised species, such as glycerol. One recent, significant example of a RP process is with respect to photocatalyst activity indicator inks. paiis, which provide a measure of the activity of a photocatalytic film under test via the rate of change of colour of the dye in the ink coating due to irreversible RP. In contrast, by incorporating the semiconductor sensitiser in the ink, rather than outside it, it is possible to create an effective UV dosimeter, based on RP, which can be used as a sun-burn warning indicator. In the above examples the dye is reduced irreversibly, but when the photocatalyst in an ink is used to reversibly photoreduce a dye, a novel, colourimetric oxygen-sensitive indicator ink can be created, which has commercial potential in the food packaging industry. Finally, if no dye is present in the ink, and the semiconductor photocatalyst-loaded ink film coats an easily reduced substrate, such as a metal oxide film, then it can be used to reduce the latter and so, for example, clean up tarnished steel. The above are examples of smart inks, i.e. inks that are active and provide either dynamic information (such as UV dose or O2 level) or a useful function (such as tarnish removal), and all work via a RP process and are reviewed here.

A smart ink for the assessment of low activity photocatalytic surfaces.

The azo dye, basic blue 66 (BB66) is used in a photocatalyst activity indicator ink (paii) to assess the activity of low activity photocatalytic surfaces, such as commercial photocatalytic tiles and silicone contaminated self-cleaning glass. The BB66 paii is shown to respond much faster than a previously reported, resazurin (Rz) based paii, i.e. the use of a BB66 paii on low activity self-cleaning tiles was found to be >6 times faster than the Rz paii. The BB66 paii is also shown to be effective at assessing the activity of piece of commercial self-cleaning glass contaminated with a coating of silicone, on which the Rz ink, in contrast, failed to show any significant change in colour over the same time period.

Prospects for ultracold carbon via charge exchange reactions and laser cooled carbides.

Strategies to produce an ultracold sample of carbon atoms are explored and assessed with the help of quantum chemistry. After a brief discussion of the experimental difficulties using conventional methods, two strategies are investigated. The first attempts to exploit charge exchange reactions between ultracold metal atoms and sympathetically cooled C(+) ions. Ab initio calculations including electron correlation have been conducted on the molecular ions [LiC](+) and [BeC](+) to determine whether alkali or alkaline earth metals are a suitable buffer gas for the formation of C atoms but strong spontaneous radiative charge exchange ensure they are not ideal. The second technique involves the stimulated production of ultracold C atoms from a gas of laser cooled carbides. Calculations on LiC suggest that the alkali carbides are not suitable but the CH radical is a possible laser cooling candidate thanks to very favourable Frank-Condon factors. A scheme based on a four pulse STIRAP excitation pathway to a Feshbach resonance is outlined for the production of atomic fragments with near zero centre of mass velocity.

Electronic states and spin-forbidden cooling transitions of AlH and AlF.

The feasibility of laser cooling AlH and AlF is investigated using ab initio quantum chemistry. All the electronic states corresponding to the ground and lowest two excited states of the Al atom are calculated using multi-reference configuration interaction (MRCI) and the large AV6Z basis set for AlH. The smaller AVQZ basis set is used to calculate the valence electronic states of AlF. Theoretical Franck-Condon factors are determined for the A(1)Π→ X(1)Σ(+) transitions in both radicals and found to agree with the highly diagonal factors found experimentally, suggesting computational chemistry is an effective method for screening suitable laser cooling candidates. AlH does not appear to have a transition quite as diagonal as that in SrF (which has been laser cooled) but the A(1)Π→ X(1)Σ(+) transition transition of AlF is a strong candidate for cooling with just a single laser, though the cooling frequency is deep in the UV. Furthermore, the a(3)Π→ X(1)Σ(+) transitions are also strongly diagonal and in AlF is a practical method for obtaining very low final temperatures around 3 µK.

Time-resolved three-dimensional molecular tracking in live cells.

We report a method for tracking individual quantum dot (QD) labeled proteins inside of live cells that uses four overlapping confocal volume elements and active feedback once every 5 ms to follow three-dimensional molecular motion. This method has substantial advantages over three-dimensional molecular tracking methods based upon charge-coupled device cameras, including increased Z-tracking range (10 µm demonstrated here), substantially lower excitation powers (15 µW used here), and the ability to perform time-resolved spectroscopy (such as fluorescence lifetime measurements or fluorescence correlation spectroscopy) on the molecules being tracked. In particular, we show for the first time fluorescence photon antibunching of individual QD labeled proteins in live cells and demonstrate the ability to track individual dye-labeled nucleotides (Cy5-dUTP) at biologically relevant transport rates. To demonstrate the power of these methods for exploring the spatiotemporal dynamics of live cells, we follow individual QD-labeled IgE-FcεRI receptors both on and inside rat mast cells. Trajectories of receptors on the plasma membrane reveal three-dimensional, nanoscale features of the cell surface topology. During later stages of the signal transduction cascade, clusters of QD labeled IgE-FcεRI were captured in the act of ligand-mediated endocytosis and tracked during rapid (~950 nm/s) vesicular transit through the cell.

Effect of shell thickness and composition on blinking suppression and the blinking mechanism in 'giant' CdSe/CdS nanocrystal quantum dots.

We recently developed an inorganic shell approach for suppressing blinking in nanocrystal quantum dots (NQDs) that has the potential to dramatically improve the utility of these fluorophores for single-NQD tracking of individual molecules in cell biology. Here, we consider in detail the effect of shell thickness and composition on blinking suppression, focusing on the CdSe/CdS core/shell system. We also discuss the blinking mechanism as understood through profoundly altered blinking statistics. We clarify the dependence of blinking behavior and photostability on shell thickness, as well as on interrogation times. We show that, while the thickest-shell systems afford the greatest advantages in terms of enhanced optical properties, thinner-shell NQDs may be adequate for certain applications requiring relatively shorter interrogation times. Shell thickness also determines the sensitivity of the NQD optical properties to aqueous-phase transfer, a critical step in rendering NQDs compatible with bioimaging applications. Lastly, we provide a proof-of-concept demonstration of the utility of these unique NQDs for fluorescent particle tracking.

Going beyond 2D: Following membrane diffusion and topography in the IgE-Fc[Epsilon]RI system using 3-dimensional tracking microscopy.

The ability to follow and observe single molecules as they function in live cells represents a major milestone for molecular-cellular biology. Here we present a tracking microscope that is able to track quantum dots in three dimensions and simultaneously record time-resolved emission statistics from a single dot. This innovative microscopy approach is based on four spatial filters and closed loop feedback to constantly keep a single quantum dot in the focal spot. Using this microscope, we demonstrate the ability to follow quantum dot labeled IgE antibodies bound to FcεRI membrane receptors in live RBL-2H3 cells. The results are consistent with prior studies of two dimensional membrane diffusion (Andrews et al., Nat. Cell Biol., 10, 955, 2008). In addition, the microscope captures motion in the axial (Z) direction, which permits tracking of diffusing receptors relative to the "hills and valleys" of the dynamically changing membrane landscape. This approach is uniquely capable of following single molecule dynamics on live cells with three dimensional spatial resolution.

Confocal, three-dimensional tracking of individual quantum dots in high-background environments.

We demonstrate a custom confocal fluorescence-microscope that is capable of tracking individual quantum dots undergoing three-dimensional Brownian motion (diffusion coefficient approximately 0.5 microm(2)/s) in environments with a signal-to-background ratio as low as 2:1, significantly worse than observed in a typical cellular environment. By utilizing a pulsed excitation source and time-correlated single photon counting, the time-resolved photon stream can be used to determine changes in the emission lifetime as a function of position and positively identify single quantum dots via photon-pair correlations. These results indicate that this microscope will be capable of following protein and RNA transport throughout the full three-dimensional volume of a live cell for durations up to 15 s.

Correlated exciton relaxation in Poly(3-hexylthiophene).

Two-color 3 pulse photon echo peak shift (2C-3PEPS) measurements on poly(3-hexylthiophene) (3PHT) demonstrate that spectral regions in the photoluminescence remain correlated with the excitation, despite large differences in energy (>0.5 eV). The observations are explained in terms of exciton-phonon coupling that is dominated by only two motions: one high frequency bond stretch and a low frequency torsional motion. Numerical simulations of the 2C-3PEPS are shown to be consistent with the experimental observations. The results demonstrate that initial intramolecular exciton relaxation in P3HT is not primarily a stochastic process, but is driven by strong, selective exciton-phonon coupling to torsional motions.

Excited state hydrogen bond dynamics: coumarin 102 in acetonitrile-water binary mixtures.

The time dependent change in the intermolecular response of solvent molecules following photoexcitation of Coumarin 102 (C102) has been measured in acetonitrile-water binary mixtures. Experiments were performed on mixtures of composition x(CH3CN) = 0.25, 0.50, 0.75, and 1.00. At low water concentrations (x(H2O) < or = 0.25) the solvent response is consistent with previous measurements probing dipolar solvation. With increasing water concentration (x(H2O) > or = 0.50) an additional response is found subsequent to dipolar solvation, exhibited as a rapid gain in the solvent's polarizability on a approximately 250 fs time scale. Monte Carlo simulations of the C102:binary mixture system were performed to quantify the number of hydrogen-bonding interactions between C102 and water. These simulations indicate that the probability of the C102 solute being hydrogen bound with two water molecules, both as donors at the carbonyl site, increases in a correlated fashion with the amplitude of the additional response in the measurements. We conclude that excitation of C102 simultaneously weakens and strengthens hydrogen bonding in complexes with two inequivalently bound waters.

Consistency of absorbed dose to water measurements using 21 ion-chamber models following the AAPM TG51 and TG21 calibration protocols.

In 1999, the AAPM introduced a reference dosimetry protocol, known as TG51, based on an absorbed dose standard. This replaced the previous protocol, known as TG21, which was based on an air kerma standard. A significant body of literature has emerged discussing the improved accuracy and robustness of the absorbed dose standard, and quantifying the changes in baseline dosimetry with the introduction of the absorbed dose protocol. A significant component playing a role in the overall accuracy of beam output determination is the variability due to the use of different dosimeters. This issue, not adequately addressed in the past, is the focus of the present study. This work provides a comparison of absorbed dose determinations using 21 different makes and models of ion chambers for low- and high-energy photon and electron beams. The study included 13 models of cylindrical ion chambers and eight models of plane-parallel chambers. A high degree of precision (<0.25%) resulted from measurements with all chambers in a single setting, a sufficient number of repeat readings, and the use of high quality ion chambers as external monitors. Cylindrical chambers in photon beams show an improvement in chamber-to-chamber consistency with TG51. For electron dosimetry with plane-parallel chambers, the parameters Ngas and the product ND,w x k(ecal) were each determined in two ways, based on (i) an ADCL calibration, and (ii) a cross comparison with an ADCL-calibrated cylindrical chamber in a high-energy electron beam. Plane-parallel chamber results, therefore, are presented for both methods of chamber calibration. Our electron results with technique (i) show that plane-parallel chambers, as a group, overestimate the beam output relative to cylindrical chambers by 1%-2% with either protocol. Technique (ii), by definition, normalizes the plane-parallel results to the cylindrical results. In all cases, the maximum spread in output from the various cylindrical chambers is <2% implying a standard deviation of less than 0.5%. For plane-parallel chambers, the maximum spread is somewhat larger, up to 3%. A few chambers have been identified as outliers.