Development of the fast neutron imaging telescope

We report on the development of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV energy range. The Fast Neutron Imaging Telescope (FNIT) was initially conceived to study solar neutrons as a candidate instrument for the Inner Heliosphere Sentinels (IHS) program under formulation at NASA. This detector is now being adapted to locate Special Nuclear Material (SNM) for homeland security purposes by detecting fission neutrons and reconstructing the image of their source. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing the scattering coordinates and measuring the recoil proton energy, the direction and energy of each neutron can be determined and discrete neutron sources identified. We describe the performance of the FNIT prototype, report on the current status of R&D efforts and present the results of recent laboratory measurements

Advanced characterization and simulation of SONNE: a fast neutron spectrometer for Solar Probe Plus

SONNE, the SOlar NeutroN Experiment proposed for Solar Probe Plus, is designed to measure solar neutrons from 1-20 MeV and solar gammas from 0.5-10 MeV. SONNE is a double scatter instrument that employs imaging to maximize its signal-to-noise ratio by rejecting neutral particles from non-solar directions. Under the assumption of quiescent or episodic small-flare activity, one can constrain the energy content and power dissipation by fast ions in the low corona. Although the spectrum of protons and ions produced by nanoflaring activity is unknown, we estimate the signal in neutrons and γ−rays that would be present within thirty solar radii, constrained by earlier measurements at 1 AU. Laboratory results and simulations will be presented illustrating the instrument sensitivity and resolving power

Design optimization and performance capabilities of the fast neutron imaging telescope (FNIT)

We describe the design optimization process and performance characterization of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 1-20 MeV energy range. The response of the Fast Neutron Imaging Telescope (FNIT), its efficiency in neutron detection, energy resolution and imaging capabilities were characterized through a combination of lab tests and Monte Carlo simulations. Monte Carlo simulations, together with experimental data, are also being used in the development and testing of the image reconstruction algorithm. FNIT was initially conceived to study solar neutrons as a candidate instrument for the Inner Heliosphere Sentinel (IHS) spacecraft. However, the design of this detector was eventually adapted to locate Special Nuclear Material (SNM) sources for homeland security purposes, by detecting fission neutrons. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing event locations and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. This paper presents the most recent results arising from our efforts and outlines the performance of the FNIT detector

Evolutionarily Conserved Transcriptional Co-Expression Guiding Embryonic Stem Cell Differentiation

Understanding the molecular mechanisms controlling pluripotency in embryonic stem cells (ESCs) is of central importance towards realizing their potentials in medicine and science. Cross-species examination of transcriptional co-expression allows elucidation of fundamental and species-specific mechanisms regulating ESC self-renewal or differentiation.We examined transcriptional co-expression of ESCs from pathways to global networks under the framework of human-mouse comparisons. Using generalized singular value decomposition and comparative partition around medoids algorithms, evolutionarily conserved and divergent transcriptional co-expression regulating pluripotency were identified from ESC-critical pathways including ACTIVIN/NODAL, ATK/PTEN, BMP, CELL CYCLE, JAK/STAT, PI3K, TGFbeta and WNT. A set of transcription factors, including FOX, GATA, MYB, NANOG, OCT, PAX, SOX and STAT, and the FGF response element were identified that represent key regulators underlying the transcriptional co-expression. By transcriptional intervention conducted in silico, dynamic behavior of pathways was examined, which demonstrate how much and in which specific ways each gene or gene combination effects the behavior transition of a pathway in response to ESC differentiation or pluripotency induction. The global co-expression networks of ESCs were dominated by highly connected hub genes such as IGF2, JARID2, LCK, MYCN, NASP, OCT4, ORC1L, PHC1 and RUVBL1, which are possibly critical in determining the fate of ESCs.Through these studies, evolutionary conservation at genomic, transcriptomic, and network levels is shown to be an effective predictor of molecular factors and mechanisms controlling ESC development. Various hypotheses regarding mechanisms controlling ESC development were generated, which could be further validated by in vitro experiments. Our findings shed light on the systems-level understanding of how ESC differentiation or pluripotency arises from the connectivity or networks of genes, and provide a "road-map" for further experimental investigation

Solar Neutron Observation at Ground Level and from Space

Neutrinos and Explosive Events in the Universe” brought together experts from diverse disciplines to offer a detailed view of the exciting new work in this part of High Energy Astrophysics. Sponsored by NATO as an Advanced Study Institute, and coordinated under the auspices of the International School of Cosmic Ray Astrophysics (14th biennial course), the ASI featured a full program of lectures and discussion in the ambiance of the Ettore Majorana Centre in Erice, Italy, including visits to the local Dirac and Chalonge museum collections as well as a view of the cultural heritage of southern Sicily. Enri- ment presentations on results from the Spitzer Infrared Space Telescope and the Origin of Complexity complemented the program. This course was the best attended in the almost 30 year history of the School with 121 participants from 22 countries. The program provided a rich ex- rience, both introductory and advanced, to fascinating areas of observational Astrophysics Neutrino Astronomy, High Energy Gamma Ray Astronomy, P- ticle Astrophysics and the objects most likely responsible for the signals - plosions and related phenomena, ranging from Supernovae to Black Holes to the Big Bang. Contained in this NATO Science Series volume is a summative formulation of the physics and astrophysics of this newly emerging research area that already has been, and will continue to be, an important contributor to understanding our high energy universe

Applications of a phoswich-based detector for fast (∼1–10 MeV) solar neutrons for missions to the inner heliosphere

We describe a phoswich-based detector concept for studies of low energy (∼1–10 MeV) solar neutrons in the innermost heliosphere (R \u3c∼ 0.5 AU). The detector has applications both as a very low mass (\u3c∼1 kg), low power (∼1–2 W) stand-alone instrument, and as a component to enhance the capabilities of more sophisticated instruments, for example, the fast neutron imaging telescope instrument described by Moser et al. [Moser, M.R., Flückiger, E.O., Ryan, J.M., et al. A fast neutron imaging telescope for inner heliosphere missions. Adv. Space Res., in press, this issue, doi:10.1016/j.asr.2005.03.037]. In its most basic form, the detector consists of a small volume (∼1 cm3) of fast organic scintillator completely surrounded by a slow inorganic scintillator. The dimensions of the organic scintillator are chosen to minimize multiple n–p scatterings while retaining adequate sensitivity. The inorganic scintillator provides anti-coincidence protection against energetic charged particles. A single PM tube views light from both scintillators. Pulse shape analysis identifies as potential neutrons those events where only the organic scintillator contributes to the signal. The signal size corresponds to the energy of the recoil proton from an n–p elastic scatter, on average half the energy of the incident neutron. An instrument based on this concept would provide measurements of the neutron flux and, through statistical analysis of recoil proton energies, basic information about the neutron spectrum

Lumbosacral transitional vertebrae in dogs: classification, prevalence, and association with sacroiliac morphology

The prevalence of lumbosacral transitional vertebrae (LTV) was determined by reviewing the pelvic radiographs of 4000 medium- and large-breed dogs of 144 breeds routinely screened for canine hip dysplasia. An LTV was seen in 138 (3.5%) dogs. The prevalence was higher in German Shepherd dogs and Greater Swiss Mountain dogs than in the other breeds, suggesting a genetic predisposition. There was no gender predisposition. The transverse processes of the LTV were divided into three types based on their morphological characteristics: lumbar type or type 1; intermediate type or type 2; and sacral type or type 3. In a symmetric LTV, both transverse processes are of the same type, while in an asymmetric LTV they are not. The frequency of occurrence of symmetric and asymmetric LTV was similar. In symmetric LTV, intermediate-type transverse processes predominated. Most of the asymmetric LTV had an intermediate-type transverse process combined with a lumbar or sacral type, respectively. Highly asymmetric LTV were often angled relative to the adjacent vertebrae. We hypothesize that an LTV is not the result of transformation of a lumbar into a sacral vertebra or vice versa, but rather is an autonomous intermediate type of vertebra. It occurs when the point of contact of the pelvis with the vertebral column is slightly cranial or caudal to its normal position. The resulting formative stimulus on the vertebral ossification centers, sagittally still separated, causes the various morphologies seen in LTV including the asymmetric variations