Calculation of spectrometric ratings of new scintillators

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 53–55, May, 1990.     

Fourteen ways to say nothing with scientific visualization

In “Twelve Ways to Fool the Masses When Giving Performance Results on Parallel Computers,” (see Supercomputer Rev., vol.4, no.8, p.54-5, 1991) David Bailey ends with the admonition, “Conclude your technical presentation and roll the videotape. Audiences love razzle-dazzle color graphics, and this material often helps deflect attention from the substantive technical issues.” Unfortunately, Bailey gives no guidance in the means and methods for producing such a result. This article seeks to fill this void. There are numerous time-tested scientific visualization techniques for producing pretty pictures while avoiding unnecessary illumination of the data. Our collection has been culled from the scientific visualization literature and numerous presentations we have given and attended     

THz Characterization of All-Trans and 9-cis Retinal, Experiment, and Modeling

Two conformations of the retinal molecule have been studied in order to characterize the molecule's THz transmission spectra in both the ground and metastable states. When subjected to an adequate external excitation the retinal molecule can experience a change in conformation and associated THz transmission spectra. In an attempt to accomplish this characterization, the FTIR system was modified to include a simple off axis excitation source inside of the systems sample chamber. Measurements were made of the retinal molecule's THz spectra both with and without external excitation of the molecule. The results gathered were then compared with the results obtained from simulation. Data obtained from two retinal isomers reveal more spectral features at frequencies ~11 - 15 cm^-1 than were predicted for these conformations. The most likely explanation for this is that the material is actually a mixture of several metastable conformations. There is correlation between simulated and measured THz spectra in the ground state at a frequency of 14 cm^-1 for all-trans retinal. The strongest vibrational mode frequency predicted for the 9-cis conformation through modeling was 22 cm^-1, which correlates quite well with the experimental line at 21.3 cm^-1 in the ground state. When the 9-cis samples were exposed to UV illumination there was a noticeable change in the absorption spectra and this line at 21.3 cm^-1 almost disappeared which can be related to the transformation of a 9-cis into a more stable all-trans retinal. The absorption spectra of all-trans retinal that is the most stable conformation showed very weak features in experimental spectra, with some of them changing under illumination.     

Effects of differential experience on dendritic spine counts in rat cerebral cortex.

Measured the effects of 30 days experience in enriched conditions (EC) or impoverished conditions (IC) on pyramids in the occipital cortex of 40 male Berkeley S1 strain littermate pairs in 4 replication experiments. Using the rapid Golgi method, counts were made of dendritic spines, and the lateral width of basal dendrites was measured. The density of spines was greater in EC than in IC Ss on basal dendrites (9.7%, p     

Optoelectronic Signatures of Biomolecules Including Hybrid Nanostructure-DNA Ensembles

Biological macromolecules such as DNA, proteins, and polysaccharides often display unique absorptive signatures in the THz region, useful in their identification and imaging through Raman and Fourier transform transmission spectroscopy. The optoelectronic properties of nanostructure-DNA complexes immobilized on transparent, semi-rigid substrates such as polymethyl methacrylate (PMMA) have been studied. By chemically modifying the PMMA substrates with amine terminal groups and using suitable linking agents, amine terminated DNA can be localized on these substrates. THz Fourier transform transmission spectroscopy was used to detect low-frequency vibrational modes (10-25 cm^-1) within single- and double-stranded DNA molecules immobilized on PMMA attached to TiO₂ nanoparticles. Additionally, DNA strands end terminated with TiO₂ nanoparticles are used in this study to cleave the DNA at guanine (G) rich sites due to trapping of photo-induced charge carriers from the TiO₂ at these sites. Theoretical modeling of charge transport through DNA via polaron transport is discussed in detail. By examining the vibrational modes of DNA, as well as the transport of charge in DNA this study underlies potential applications involving DNA micro-arrays, DNA-based sensors, and DNA-based THz devices.     

Terahertz (THz) Electromagnetic Field Enhancement in Periodic Subwavelength Structures

In this paper, we show that periodic arrays of rectangular slots with subwavelength width provide for local electromagnetic field enhancements due to edge effects in low-frequency range, 10-25 cm^-1. Periodic structures of Au, doped Si, and InSb with subwavelength thickness were studied. The half power enhancement width is ~500 nm and less around the slot edges in all cases, thereby possibly bringing terahertz (THz) sensing to the nanoscale. InSb is confirmed to offer the best results with the local power enhancements on the order of 1100 at frequency 14 cm^-1. InSb and Si have large skin depths in the frequency range of interest and so the analysis of their structures was done through the Fourier expansion method of field diffracted from gratings. Au, however, has small skin depths at these frequencies compared with the thickness. Surface impedance boundary conditions were employed to model the Au structure, for which the Fourier expansion method was unsuitable owing to the huge magnitude of Au permittivity at these frequencies. The applications possibly include development of novel biosensors, with the strongly enhanced local electromagnetic fields leading to increased detection sensitivity, and monitoring biophysical processes such as DNA denaturation.     

Connection between optical and radiometric characteristics of NaI (T1) scintillator

Conclusions It follows from Table 1 that the resolution of the scintillator worsens and the light collection coefficient decreases with increase of the parameters kD and H/D. The figures of Table 1 give a clear representation of the region of the parameters in which scintillators can be used for spectrometry (outside this region the scintillators have an abnormally large intrinsic resolution or too small light collection coefficient)It follows from the results given in Table 1 that with an optical contact scintillators almost always possess a better intrinsic resolution than without contact with the PEM. However, in several cases the reverse situation holds; in these cases it can prove to be expedient to use the scintillator without an optical contact for spectromety of -radiation of energy from 3 to 5 MeV, when the contribution of the PEM to the resolution is small.Finally we remark that the results of Table 1 enable one to determine the absorption coefficient of packed cylindrical scintillators of arbitrary form from the ratio of the values of or _max at n=1.23 and n=1.85 (this method was first suggested in [4] for scintillators with H/D=1).Translated from Izmeritel'naya Tekhnika, No. 12, pp. 63–66, December, 1968.     

Developmental regulation of early serotonergic neuronal differentiation: the role of brain-derived neurotrophic factor and membrane depolarization

The RN46A cell line was derived from Embryonic Day 13 rat medullary raphe cells by infection with a retrovirus encoding the temperature-sensitive mutant of SV40 large T antigen. This cell line is neuronally restricted and constitutively differentiates following a shift to nonpermissive temperature. Undifferentiated RN46A cells express low levels of tryptophan hydroxylase (TPH), low-affinity neurotrophin receptor (p75NTR), and trkB immunoreactivities, but no detectable levels of serotonin (5HT) immunoreactivity. TrkB, p75NTR, and TPH, but not 5HT, expressions increase with differentiation and treatment with brain-derived neurotrophic factor (BDNF). 5HT synthesis in RN46A cells requires initial treatment with BDNF, followed by growth under partial membrane depolarizing conditions. Embryonic raphe cultures treated similarly with BDNF and partial depolarizing conditions also demonstrate increased 5HT synthesis. The sodium-dependent transporter for 5HT reuptake is present in undifferentiated RN46A cells, and the apparent Km and Bmax are unchanged by differentiation or BDNF treatment and membrane depolarization. The high-affinity 5HT1A receptor is present in both undifferentiated and differentiated RN46A cells, and while the Kd is unaffected by differentiation or BDNF/membrane depolarization, the Bmax increases 20-fold after differentiation and 3.5-fold further with BDNF under depolarizing conditions. The expression of the synaptic vesicular monoamine transporter, as determined by the binding of [125I]iodovinyltetrabenazine, also increases in RN46A cells with differentiation. However, 5HT release is constitutive and is independent of acute membrane depolarization. Collectively these data indicate that distinct aspects of serotonin metabolism are differentially regulated during development and suggest that 5HT may function as a developmental signal in an autocrine loop during early serotonergic differentiation.