The role of ambient light level in fatal crashes: inferences from daylight saving time transitions

The purpose of this study was to estimate the size of the influence of ambient light level on fatal pedestrian and vehicle crashes in three scenarios. The scenarios were: fatal pedestrian crashes at intersections, fatal pedestrian crashes on dark rural roads, and fatal single-vehicle run-off-road crashes on dark, curved roads. Each scenario's sensitivity to light level was evaluated by comparing the number of fatal crashes across changes to and from daylight saving time, within daily time periods in which an abrupt change in light level occurs relative to official clock time. The analyses included 11 years of fatal crashes in the United States, between 1987 and 1997. Scenarios involving pedestrians were most sensitive to light level, in some cases showing up to seven times more risk at night over daytime. In contrast, single-vehicle run-off-road crashes showed little difference between light and dark time periods, suggesting factors other than light level play the dominant role in these crashes. These results are discussed in the context of the possible safety improvements offered by new developments in adaptive vehicle headlighting.     

Probability-based validation of protein identifications using a modified SEQUEST algorithm

Database-searching algorithms compatible with shotgun proteomics match a peptide tandem mass spectrum to a predicted mass spectrum for an amino acid sequence within a database. SEQUEST is one of the most common software algorithms used for the analysis of peptide tandem mass spectra by using a cross-correlation (XCorr) scoring routine to match tandem mass spectra to model spectra derived from peptide sequences. To assess a match, SEQUEST uses the difference between the first- and second-ranked sequences (ACn). This value is dependent on the database size, search parameters, and sequence homologies. In this report, we demonstrate the use of a scoring routine (SEQUEST-NORM) that normalizes XCorr values to be independent of peptide size and the database used to perform the search. This new scoring routine is used to objectively calculate the percent confidence of protein identifications and posttranslational modifications based solely on the XCorr value.     

Convergent optical correlator aligment based on frequency filtering

The convergent correlator is widely used but it presents the drawback of the alignment requirements: fine focusing of the input scene Fourier transform on the filter plane, filter centering, scaling the scene Fourier transform to match the filter size, and azimuth matching of the filter with the input scene. We propose a set of tests to obtain a precise alignment of the convergent correlator. These methods are based on frequency filtering properties and they are applicable either for amplitude input or for phase-encoded input. The tests we present allow us to fulfill all the alignment requirements. The theory on which these tests are based is explained. The experimental results obtained during the alignment procedure are presented. We show some additional verifications of the correct alignment of the convergent correlator.     

Detection and identification of aqueous saccharides by using surface-enhanced Raman spectroscopy

The sensitive detection and characterization of carbohydrates by means of a strategy based on surface-enhanced Raman spectroscopy is demonstrated. Spectra are obtained after injecting a small amount of saccharide solution onto a roughened silver substrate, with subsequent deposition of silver colloid. The sensitivity achieved by this two-step approach enables high-quality Raman spectra to be obtained for small amounts of aqueous saccharides (5 microL of a 10(-2) M solution) utilizing minimal laser power and small signal acquisition times (a few seconds). Spectral "fingerprints" obtained for seven structurally similar monosaccharides demonstrate clearly an effective means by which each sugar can be identified. The application to more complex analyses is demonstrated for monosaccharide mixtures and a disaccharide, whereby the SERS fingerprints aid in the determination of components.     

Simulation and optimization of retention in ion chromatography using virtual column 2 software

A new software package, Virtual Column 2, is described for the simulation and optimization of the separation of inorganic anions by ion chromatography (IC). The software uses a limited amount of experimental retention data acquired according to a correct experimental design to predict retention times for analytes over a designated search area of eluent compositions. The experimental retention data are used to solve a new retention model, called the linear solvent strength model, empirical approach (LSSM-EA), which then enables prediction of retention times for all eluent compositions in the search area. The theoretical development of LSSM-EA and the processes used for solving the equations are discussed. Virtual Column 2 can be used for eluents containing one or two competing ions, and the software contains retention databases for up to 33 analytes on the Dionex AS9A-HC, AS4A-SC, and AS14A analytical columns with carbonate-bicarbonate eluents and the Dionex AS10, AS15, and AS16 analytical columns with hydroxide eluents (results for the AS10 and AS15 columns are not discussed in the present study). Virtual Column 2 has been evaluated extensively and is shown to give predicted retention times that in most cases agree with experimentally determined data to within 5%. The software has uses in practical IC method development, education and training in IC, and refinement of existing IC methodology. A free version of this program is available by download at www.virtualcolumn.com.     

A test of metabolically efficient coding in the retina

We tested the hypothesis that aspects of the neural code of retinal ganglion cells are optimized to transmit visual information at minimal metabolic cost. Under a broad ensemble of light patterns, ganglion cell spike trains consisted of sparse, precise bursts of spikes. These bursts were viewed as independent neural symbols. The noise in each burst was measured via repeated presentation of the visual stimulus, and the energy cost was estimated from the total charge flow during ganglion cell spiking. Given these costs and noise, the theory of efficient codes predicts an optimal distribution of symbol usage. Symbols that are either noisy or costly occur less frequently in this optimal code. We found good qualitative and quantitative agreement with the measured distribution of burst sizes for ganglion cells in the tiger salamander retina.     

Classic annulenes,nonclassical applications

This Account details the application of [n]annulenes as functional building blocks for electromechanical actuators, double-helical ladder polymers, and protecting groups for supramolecular interactions. Specifically, redox-induced conformational changes occurring in [8]annulenes are utilized as the transducing element in polymeric electromechanical actuators. Conversely, rigid [8]annulenes are utilized as double-helical fragments for the synthesis of double-helical octaaryl macromolecules. Last, Dewar benzenes are prepared from [4 + 2] cycloadditions (where the 4pi component is a [4]annulene). The potential of using Dewar benzenes as protecting groups for [6]annulne-[6]annulene supramolecular interactions is exemplified by demonstration of photolithographic crystallization (amorphous [4]annulene --> crystalline [6]annulene) on a surface, followed by subsequent X-ray analysis of the resulting [6]annulene crystals.     

Tight binding of the antitumor drug ditercalinium to quadruplex DNA

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was found to bind to double-stranded DNA with a preference for GC-rich species but can in addition form stable complexes with triplex and quadruplex structures. The preferential interaction of the drug with four-stranded DNA structures was independently confirmed by electrospray mass spectrometry and a detailed analysis of the binding reaction was performed by surface plasmon resonance (SPR) spectroscopy. The BIAcore SPR study showed that the kinetic parameters for the interaction of ditercalinium with the human telomeric quadruplex sequence are comparable to those measured with a duplex sequence. Slow association and dissociation were observed with both the quadruplex and duplex structures. The newly discovered preferential binding of ditercalinium to the antiparallel quadruplex sequence d(AG(3)[T(2)AG(3)](3)) provides new perspectives for the design of drugs that can bind to human telomeres.