Spectrophotometry for cerebrospinal fluid pigment analysis

The use of spectrophotometry for the analysis of the cerebrospinal fluid (CSF) is reviewed. The clinically relevant CSF pigments--oxyhemoglobin and bilirubin--are introduced and discussed with regard to clinical differential diagnosis and potentially confounding variables (the four T's: traumatic tap, timing, total protein, and total bilirubin). The practical laboratory aspects of spectrophotometry and automated techniques are presented in the context of analytical and clinical specificity and sensitivity. The perceptual limitations of human color vision are highlighted and the use of visual assessment of the CSF is discouraged in light of recent evidence from a national audit in the United Kingdom. Finally, future perspectives including the need for longitudinal CSF profiling and routine spectrophotometric calibration are outlined

Sex-related differences in chromatic sensitivity

Generally women are believed to be more discriminating than men in the use of colour names and this is often taken to imply superior colour vision. However, if both X-chromosome linked colour deficient males (~8%) and females (<1%) as well as heterozygote female carriers (~15%) are excluded from comparisons, then differences between men and women in red-green colour discrimination have been reported as not being significant (e.g., Pickford, 1944; Hood et al., 2006). We re-examined this question by assessing the performance of 150 males and 150 females on the Colour Assessment and Diagnosis (CAD) test (Rodriguez-Carmona, 2005). This is a sensitive test that yields small colour detection thresholds. The test employs direction-specific, moving, chromatic stimuli embedded in a background of random, dynamic, luminance contrast noise. A four-alternative, forced-choice procedure is employed to measure the subject’s thresholds for detection of colour signals in 16 directions in colour space, while ensuring that the subject cannot make use of any residual luminance contrast signals. In addition, we measured the Rayleigh anomaloscope matches in a subgroup of 111 males and 114 females. All the age-matched males (30.8 ± 9.7) and females (26.7 ± 8.8) had normal colour vision as diagnosed by a battery of conventional colour vision tests. Females with known colour deficient relatives were excluded from the study. Comparisons between the male and female groups revealed no significant differences in anomaloscope midpoints (p=0.709), but a significant difference in matching ranges (p=0.040); females on average tended to have a larger mean range (4.11) than males (3.75). Females also had significantly higher CAD thresholds than males along the red-green (p=0.0004), but not along the yellow-blue discrimination axis. The differences between males and females in red-green discrimination may be related to the heterozygosity in X-linked cone photopigment expression common among females

The loss of the PDE6 deactivating enzyme, RGS9, results in precocious light adaptation at low light levels

The GTPase activating protein, RGS9-1, is vital for the deactivation and regulation of the phototransduction cascade (C. K. Chen et al., 2000; C. W. Cowan, R. N. Fariss, I. Sokal, K. Palczewski, & T. G. Wensel, 1998; W. He, C. W. Cowan, & T. G. Wensel, 1998; A. L. Lyubarsky et al., 2001). Its loss through genetic defects in humans has been linked to a slow recovery to changes in illumination (K. M. Nishiguchi et al., 2004). Such a deficit is to be expected because RGS9-1 normally speeds up the deactivation of the activated phosphodiesterase effector molecule, PDE6*, and thus accelerates the turning off of the visual response. Paradoxically, however, we find that the cone response in an observer lacking RGS9-1 is faster at lower light levels than it is in a normal observer. Though surprising, this result is nonetheless consistent with molecular models of light adaptation (e.g., E. N. Pugh, S. Nikonov, & T. D. Lamb, 1999), which predict that the excess of PDE6* resulting from the loss of RGS9-1 will shorten the visual integration time and speed up the visual response at inappropriately low light levels. The gain in speed caused by the superfluity of PDE6* at lower light levels compensates for the loss caused by its slow deactivation; thus quickening the response relative to that in the normal. As the light level is increased and the PDE6* concentration in the normal rises relative to that in the observer lacking RGS9-1, the temporal advantage of the latter is soon lost, leaving only the deficit due to delayed deactivation

Marshall Grazing Incidence X-ray Spectrometer Slitjaw Imager Implementation and Performance

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a slit spectrograph designed to fly on a sounding-rocket and to observe the Sun in soft X-rays (SXRs) to determine the frequency of coronal heating events. The MaGIXS wavelength range (≈ 0.6 – 2.5 nm) has a significant number of diagnostic lines formed at coronal temperatures, but developing SXR instrumentation presents several challenges, including how to efficiently perform context imaging. A slitjaw image is required for pointing the instrument during flight and for co-alignment with coordinated data sets after flight, but operating in the SXR regime implies that a simple normal-incidence optical system could not be employed to image the same wavelength range as the spectrograph. Therefore, to avoid the complexity of additional grazing-incidence optics, the MaGIXS slitjaw system is designed to image in the extreme ultraviolet (EUV) between roughly 20 – 80 nm. The temperature sensitivity of this EUV bandpass will observe complementary features visible to the MaGIXS instrument. The image on the slitjaw is then converted, via a phosphor coating, to readily detectable visible light. Presented here is the design, implementation, and characterization of the MaGIXS slitjaw imaging system. The slitjaw instrument is equipped with an entrance filter that passes EUV light, along with X-rays, onto the slit, exciting a fluorescent coating and causing it to emit in the visible. This visible light can then be imaged by a simple implementation of commercial off-the-shelf (COTS) optics and low-light camera. Such a design greatly reduces the complexity of implementing and testing the slitjaw imager for an X-ray instrument system and will accomplish the pointing and co-alignment requirements for MaGIXS

The two-fund separation theorem revisited

Portfolio choice, CAPM, Risk aversion, Equilibrium, Market participation, C62, D11, G11, G12,