Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission

The Gamma-Ray Large Area Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within a huge energy range of 100 MeV - 300 GeV. Background cosmic radiation interferes with such detection resulting in confusion over distinguishing cosmic from gamma rays encountered. This quandary is resolved by encasing GLAST's Large Area Telescope (LAT) with an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged particles. The ACD accomplishes this through plastic scintillator tiles; when cosmic rays strike, photons produced induce currents in Photomultiplier Tubes (PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes {approx}550km and latitudes between -26 degree and 26 degree, it will confront the South Atlantic Anomaly (SAA), a region of high particle flux caused by trapped radiation in the geomagnetic field. Since the SAA flux would degrade the sensitivity of the ACD's PMTs over time, a determined boundary enclosing this region need be attained, signaling when to lower the voltage on the PMTs as a protective measure. The operational constraints on such a boundary require a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST has maximum observation time. The AP8 and PSB97 models describing the behavior of trapped radiation were used in analyzing the SAA and defining a convex SAA boundary of twelve sides. The smallest possible boundary was found to cover 14.58% of GLAST's observation time. Further analysis of defining a boundary safety margin to account for inaccuracies in the models reveals if the total SAA hull area is increased by {approx}20%, the loss of total observational area is < 5%. These twelve coordinates defining the SAA flux region are ready for implementation by the GLAST satellite

Age-Related Adaptation of Bone-PDL-Tooth Complex: Rattus-Norvegicus as a Model System

Functional loads on an organ induce tissue adaptations by converting mechanical energy into chemical energy at a cell-level. The transducing capacity of cells alters physico-chemical properties of tissues, developing a positive feedback commonly recognized as the form-function relationship. In this study, organ and tissue adaptations were mapped in the bone-tooth complex by identifying and correlating biomolecular expressions to physico-chemical properties in rats from 1.5 to 15 months. However, future research using hard and soft chow over relevant age groups would decouple the function related effects from aging affects. Progressive curvature in the distal root with increased root resorption was observed using micro X-ray computed tomography. Resorption was correlated to the increased activity of multinucleated osteoclasts on the distal side of the molars until 6 months using tartrate resistant acid phosphatase (TRAP). Interestingly, mononucleated TRAP positive cells within PDL vasculature were observed in older rats. Higher levels of glycosaminoglycans were identified at PDL-bone and PDL-cementum entheses using alcian blue stain. Decreasing biochemical gradients from coronal to apical zones, specifically biomolecules that can induce osteogenic (biglycan) and fibrogenic (fibromodulin, decorin) phenotypes, and PDL-specific negative regulator of mineralization (asporin) were observed using immunohistochemistry. Heterogeneous distribution of Ca and P in alveolar bone, and relatively lower contents at the entheses, were observed using energy dispersive X-ray analysis. No correlation between age and microhardness of alveolar bone (0.7±0.1 to 0.9±0.2 GPa) and cementum (0.6±0.1 to 0.8±0.3 GPa) was observed using a microindenter. However, hardness of cementum and alveolar bone at any given age were significantly different (P<0.05). These observations should be taken into account as baseline parameters, during development (1.5 to 4 months), growth (4 to 10 months), followed by a senescent phase (10 to 15 months), from which deviations due to experimentally induced perturbations can be effectively investigated

Age-related adaptation of bone-PDL-tooth complex: Rattus-Norvegicus as a model system.

Functional loads on an organ induce tissue adaptations by converting mechanical energy into chemical energy at a cell-level. The transducing capacity of cells alters physico-chemical properties of tissues, developing a positive feedback commonly recognized as the form-function relationship. In this study, organ and tissue adaptations were mapped in the bone-tooth complex by identifying and correlating biomolecular expressions to physico-chemical properties in rats from 1.5 to 15 months. However, future research using hard and soft chow over relevant age groups would decouple the function related effects from aging affects. Progressive curvature in the distal root with increased root resorption was observed using micro X-ray computed tomography. Resorption was correlated to the increased activity of multinucleated osteoclasts on the distal side of the molars until 6 months using tartrate resistant acid phosphatase (TRAP). Interestingly, mononucleated TRAP positive cells within PDL vasculature were observed in older rats. Higher levels of glycosaminoglycans were identified at PDL-bone and PDL-cementum entheses using alcian blue stain. Decreasing biochemical gradients from coronal to apical zones, specifically biomolecules that can induce osteogenic (biglycan) and fibrogenic (fibromodulin, decorin) phenotypes, and PDL-specific negative regulator of mineralization (asporin) were observed using immunohistochemistry. Heterogeneous distribution of Ca and P in alveolar bone, and relatively lower contents at the entheses, were observed using energy dispersive X-ray analysis. No correlation between age and microhardness of alveolar bone (0.7 ± 0.1 to 0.9 ± 0.2 GPa) and cementum (0.6 ± 0.1 to 0.8 ± 0.3 GPa) was observed using a microindenter. However, hardness of cementum and alveolar bone at any given age were significantly different (P&lt;0.05). These observations should be taken into account as baseline parameters, during development (1.5 to 4 months), growth (4 to 10 months), followed by a senescent phase (10 to 15 months), from which deviations due to experimentally induced perturbations can be effectively investigated

Mineral density volume gradients in normal and diseased human tissues.

Clinical computed tomography provides a single mineral density (MD) value for heterogeneous calcified tissues containing early and late stage pathologic formations. The novel aspect of this study is that, it extends current quantitative methods of mapping mineral density gradients to three dimensions, discretizes early and late mineralized stages, identifies elemental distribution in discretized volumes, and correlates measured MD with respective calcium (Ca) to phosphorus (P) and Ca to zinc (Zn) elemental ratios. To accomplish this, MD variations identified using polychromatic radiation from a high resolution micro-computed tomography (micro-CT) benchtop unit were correlated with elemental mapping obtained from a microprobe X-ray fluorescence (XRF) using synchrotron monochromatic radiation. Digital segmentation of tomograms from normal and diseased tissues (N=5 per group; 40-60 year old males) contained significant mineral density variations (enamel: 2820-3095 mg/cc, bone: 570-1415 mg/cc, cementum: 1240-1340 mg/cc, dentin: 1480-1590 mg/cc, cementum affected by periodontitis: 1100-1220 mg/cc, hypomineralized carious dentin: 345-1450 mg/cc, hypermineralized carious dentin: 1815-2740 mg/cc, and dental calculus: 1290-1770 mg/cc). A plausible linear correlation between segmented MD volumes and elemental ratios within these volumes was established, and Ca/P ratios for dentin (1.49), hypomineralized dentin (0.32-0.46), cementum (1.51), and bone (1.68) were observed. Furthermore, varying Ca/Zn ratios were distinguished in adapted compared to normal tissues, such as in bone (855-2765) and in cementum (595-990), highlighting Zn as an influential element in prompting observed adaptive properties. Hence, results provide insights on mineral density gradients with elemental concentrations and elemental footprints that in turn could aid in elucidating mechanistic processes for pathologic formations

Immunohistochemical staining for identification of SLRPs.

<p>a) Light micrograph at 10X using immunohistochemical methods shows representative localization of SLRPs (biglycan expression in a 6 month old rat) counterstained with hematoxylin. Black arrows indicate localization at mesial PDL-bone enthesis spanning the root length as well as the coronal predominance. In addition localization was also observed in precementum layers (black arrow heads, in Fig. 5a) and at the CDJ (black arrow in inset, Fig. 5a), predentin, and the transseptal fibers (asterisk, Fig. 5a) between any two molars. Scale bars = 500 µm. b) Serially sectioned 60X light micrographs show immunohistochemical localization of SLRPs: biglycan (BGN), decorin (DCN), fibromodulin (FMOD), asporin (ASP), and negative controls (NC). Localization indicates more intense staining in coronal regions relative to apical regions across all age groups. All micrographs indicate regions where PDL meets primary bone (B) and primary cementum (PC) or secondary cementum (SC), with adjacent dentin (D). All Scale bars = 100 µm.</p

Histomorphometry as a function of age.

<p>a) Representative light micrograph of first molar distal root at 4X magnification illustrates histomorphometric parameters including i) CEJ-ABC distance, radial widths of: ii) primary cementum, iii) secondary cementum (SC), iv) PDL adjoining primary cementum (PDL-PC), and v) PDL adjoining secondary cementum (PDL-SC). Scale bar = 1 millimeter. b) The table illustrates increasing values of CEJ-ABC distance signifying recession with age. c) Plotted histomorphometric parameters as a function of age comparatively demonstrates increasing cementum and decreasing PDL trends with age.</p

Localization of sulfated GAGs using alcian blue stain.

<p>a) Light micrographs at 10X of alcian blue with nuclear fast red counterstain indicates more sulfated GAGs on the mesial aspect as indicated by black arrows (shown here in a 1.5 month old rat), as well as around osteocytes in the alveolar bone, precementum (white arrows) and cementum dentin junction (white asterisks). We also observed staining to occur in dentin. Scale bars = 500 µm. b) Corresponding age-related changes at interradicular, coronal-apical, and mesial-distal entheses regions showed decreased alcian blue staining and lost mesial specificity with age (black arrows). Scale bars = 100 µm.</p

Elemental mapping using BSE and EDS.

<p>a) SEM in BSE mode indicated distribution of high and low Z elements of the periodontium. Scale Bar = 0.5 mm. b) Using SEM-BSE greatest heterogeneity is observed in the different layers of bone owing to different chemical compositions of bone during its turnover (i.e. remodeling or modeling). Scale Bar = 100 µm. Representative point shoot EDS demonstrate varying counts of Ca and P (Kα1, Kα2, and Kβ1 lines) within adjacent regions. SE mode indicates at length scales c) the enthesis region of PDL-bone with scale bar = 100 µm, d) the site of a resorption pit, which indicate the digested layers of bone with scale bar = 5 µm, and e) the exposed collagen fibers that help compose a mineralized matrix with scale bar = 4 µm.</p

Morphological changes and anatomical locations within TRAP positive cells.

<p>Morphological changes were observed in histological sections and confirmed in three dimensional space using a MicroXCT (shown in insets comparing occlusal, distal, and mesial surfaces). The distal preference of TRAP positive cells and progressive mesial curving were observed. Anatomical structures include enamel space (ES), dentin (D), periodontal ligament (PDL), alveolar bone (AB), and secondary cementum (SC). TRAP stained micrographs at 4X magnification show first molar distal roots decreasing in osteoclast intensity and frequency with age. Representative coronal and apical TRAP positive areas in the encircled regions are enlarged in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035980#pone-0035980-g003" target="_blank">Figure 3</a>. With age, a transition from CEJ to DGJ (demarcated by white asterisk) and increasing recession (CEJ-ABC distance represented by distance between dashed red lines) were observed. Scale bar = 1 millimeter. CEJ: cementoenamel junction; DGJ: dentin gingival junction; ABC: alveolar bone crest.</p

Biomechanics of a bone–periodontal ligament–tooth fibrous joint

This study investigates bone-tooth association under compression to identify strain amplified sites within the bone-periodontal ligament (PDL)-tooth fibrous joint. Our results indicate that the biomechanical response of the joint is due to a combinatorial response of the constitutive properties of organic, inorganic, and fluid components. Second maxillary molars within intact maxillae (N=8) of 5-month-old rats were loaded with a μ-XCT-compatible in situ loading device at various permutations of displacement rates (0.2, 0.5, 1.0, 1.5, 2.0 mm/min) and peak reactionary load responses (5, 10, 15, 20 N). Results indicated a nonlinear biomechanical response of the joint, in which the observed reactionary load rates were directly proportional to displacement rates (velocities). No significant differences in peak reactionary load rates at a displacement rate of 0.2mm/min were observed. However, for displacement rates greater than 0.2mm/min, an increasing trend in reactionary rate was observed for every peak reactionary load with significant increases at 2.0mm/min. Regardless of displacement rates, two distinct behaviors were identified with stiffness (S) and reactionary load rate (LR) values at a peak load of 5 N (S(5 N)=290-523 N/mm) being significantly lower than those at 10 N (LR(5 N)=1-10 N/s) and higher (S(10 N-20 N)=380-684 N/mm; LR(10 N-20 N)=1-19 N/s). Digital image correlation revealed the possibility of a screw-like motion of the tooth into the PDL-space, i.e., predominant vertical displacement of 35 μm at 5 N, followed by a slight increase to 40 μm at 10 N and 50 μm at 20 N of the tooth and potential tooth rotation at loads above 10 N. Narrowed and widened PDL spaces as a result of tooth displacement indicated areas of increased apparent strains within the complex. We propose that such highly strained regions are "hot spots" that can potentiate local tissue adaptation under physiological loading and adverse tissue adaptation under pathological loading conditions