Megavoltage bremsstrahlung end point voltage diagnostic.

In a material, a beam of x rays is accompanied by various kinds of secondary radiation, including Compton electrons from collisions between the x rays and the material's electrons. For megavoltage bremsstrahlung in air, many of these Compton electrons are forward-directed and fast enough to be deflected outside the beam's edge by a magnetic field perpendicular to the beam. At the beam's edge, the dose from the deflected Compton electrons has a pattern that depends on the radiation's end point energy. Dose patterns measured with radiochromic film on a nominally 1 and 2 MV linear accelerator agree reasonably well with the corresponding Monte Carlo computations. With further development, the dose pattern produced outside the beam by such a sweeper magnet could become a noninvasive way to monitor megavoltage bremsstrahlung, when the end point energies are difficult to determine with other methods.

Mid- and Near-Infrared Spectra, Millimeterwave Spectra, and Global Analysis of (16)O(12)C(80)Se.

We have recorded a total of 12 FTIR spectra of monoisotopic OC(80)Se in different spectral regions with a resolution (1/maximum optical path difference) between 2.7 and 13.2 x 10(-3) cm(-1). These spectra spanned the range from 350 to 7800 cm(-1), many bands being studied with different p x L products in order to also detect weak hot bands. Altogether 18 band systems comprising 81 different bands, mostly of Sigma type, were observed and analyzed by means of polynomial expansions in J(J + 1). New rotational transitions of vibrationally excited states as high as 2200 cm(-1) with J" 17-25 in the 140-210 GHz and J" 53-58 in the 430-470 GHz millimeterwave regions were measured with the assistance of predictions by the global fit. This fit was performed using a weighted least-squares procedure and employing the whole body of data, and about 100 molecular parameters were determined that describe the energy level of (16)O(12)C(80)Se with statistical accuracy. Improved highly accurate ground state parameters up to sextic centrifugal distortion terms were obtained by a merge of ground state combination differences and pure rotational data. The v(1), v(2), v(3) polyad interacts anharmonically with the v(1) - 1, v(2) + p, v(3) + q polyads with p + 2q = 4. Moreover, some local crossings with Coriolis interactions between (v(1), v(2), v(3)) and (v(1) - 1, v(2) + 3, v(3) + 1) levels were observed and treated perturbationally. Copyright 1999 Academic Press.

Diode Laser and FTIR Spectroscopy of BrCN Isotopomers in the Region of the nu3 Band.

The nu3 fundamental band (C-N stretch) and four associated hot bands (01(1)1-01(1)0, 10(0)1-10(0)0, 02(0)1-02(0)0, and 02(2)1-02(2)0) of natural 79/81Br12C14N have been recorded and analyzed in the 4.8-µm region using an FTIR spectrometer. Analyses of the same hot bands, previously recorded using a diode laser spectrometer, are also presented for the 13C and 15N isotopically labeled species. Copyright 1998 Academic Press.

Nuclear DNA fragmentation during postnatal tooth development of mouse and hamster and during dentin repair in the rat.

The TUNEL (transferase-mediated, dUTP-biotin nick end labeling) method for in situ labeling of DNA strands was utilized to localize DNA fragmentation in cells involved in tooth formation in the neonatal mouse and hamster. Positive reactions for the presence of DNA fragments were obtained in some epithelial cells of the cervical loop region of incisors, late secretory, transitional and early maturation stage ameloblasts, stratum intermedium cells and in shortened ameloblasts just before eruption. Also, cells of the periodontal ligament of the continuously erupting incisors stained positive shortly before eruption. Odontoblasts were negative but became strongly positive during the formation of physiological osteodentin at the tip of developing incisors. Osteodentin matrix and the surfaces of unerupted enamel and cementum just prior to eruption stained for DNA fragments as well. DNA fragmentation could be elicited in odontoblasts and underlying pulpal tissues of mature erupted molars after mechanical injury to the odontoblast processes during cavity preparation. We conclude that, in rodents, DNA fragmentation and cell death are biological processes which take place in a variety of cells involved in formation of teeth. The TUNEL staining technique is a simple but powerful tool to examine the fate of cells and tissues undergoing either programmed cell death (apoptosis) or fragmentation of nuclear DNA induced by external factors leading to pathological changes.

Characterization of cellular responses involved in reparative dentinogenesis in rat molars.

During primary dentin formation, differentiating primary odontoblasts secrete an organic matrix, consisting principally of type I collagen and non-collagenous proteins, that is capable of mineralizing at its distal front. In contrast to ameloblasts that form enamel and undergo programmed cell death, primary odontoblasts remain metabolically active in a functional tooth. When dentin is exposed to caries or by operative procedures, and when exposed dentinal tubules are treated with therapeutic dental materials, the original population of odontoblasts is often injured and destroyed. The characteristics of the replacement pool of cells that form reparative dentin and the biologic mechanisms that modulate the formation of this matrix are poorly understood. Based on the hypothesis that events governing primary dentinogenesis are reiterated during dentin repair, the present study was designed to test whether cells that form reparative dentin are odontoblast-like. Cervical cavities were prepared in rat first molars to generate reparative dentin, and animals were killed at various time intervals. In situ hybridization with gene-specific riboprobes for collagen types I and III was used to study de novo synthesis by cells at the injured dentin-pulp interface. Polyclonal antibodies raised against dentin sialoprotein (DSP), a dentin-specific protein that marks the odontoblast phenotype, were used in immunohistochemical experiments. Data from our temporal and spatial analyses indicated that cells forming reparative dentin synthesize type I but not type III collagen and are immunopositive for DSP. Our results suggest that cells that form reparative dentin are odontoblast-like.

Analysis of tooth development in mice bearing a TGF-beta 1 null mutation.

While transforming growth factor-beta 1 (TGF-beta 1) and its related mammalian isoforms TGF-beta 2 and TGF-beta 3 are coexpressed in developing tooth organs, the specific biological role of each isoform is unknown. To delineate the role of TGF-beta 1 in odontogenesis, we have studied tissues from mice that lack a functional TGF-beta 1 gene. Histologic analyses revealed that in TGF-beta 1 (-/-) mice, tooth morphogenesis, cytodifferentiation and histogenesis were unaffected. Using in situ hybridization we studied the patterns of distribution of TGFs-beta 1, beta 2 and beta 3 in the TGF-beta 1 (+/+, +/- and -/-) genotypes. Our results indicate no detectable TGF-beta 1 mRNA in null tissues while TGFs-beta 2 and beta 3 showed normal temporal-spatial patterns of distribution. Using antibodies against TGF-beta 1, we observed immunoreactive TGF-beta 1 in tissues from null mice suggesting that maternally-derived TGF-beta 1 may be involved in the rescue of several developmental events in TGF-beta 1 knockout mice.