12,710 research outputs found
Who Knows What is Best for Children? Honoring Agreements and Contracts Between Parents Who Live Apart
The differing magnitude distributions of the two Jupiter Trojan color populations
The Jupiter Trojans are a significant population of minor bodies in the
middle Solar System that have garnered substantial interest in recent years.
Several spectroscopic studies of these objects have revealed notable
bimodalities with respect to near-infrared spectra, infrared albedo, and color,
which suggest the existence of two distinct groups among the Trojan population.
In this paper, we analyze the magnitude distributions of these two groups,
which we refer to as the red and less red color populations. By compiling
spectral and photometric data from several previous works, we show that the
observed bimodalities are self-consistent and categorize 221 of the 842 Trojans
with absolute magnitudes in the range H<12.3 into the two color populations. We
demonstrate that the magnitude distributions of the two color populations are
distinct to a high confidence level (>95%) and fit them individually to a
broken power law, with special attention given to evaluating and correcting for
incompleteness in the Trojan catalog as well as incompleteness in our
categorization of objects. A comparison of the best-fit curves shows that the
faint-end power-law slopes are markedly different for the two color
populations, which indicates that the red and less red Trojans likely formed in
different locations. We propose a few hypotheses for the origin and evolution
of the Trojan population based on the analyzed data.Comment: Published in AJ; 26 pages, 7 figure
Exact Transformation for Spin-Charge Separation of Spin-half Fermions without Constraints
We demonstrate an exact local transformation which maps a purely Fermionic
manybody system to a system of spinfull Bosons and spinless Fermions,
demonstrating a possible path to a non-Fermi liquid state. We apply this to the
half-filled Hubbard model and show how the transformation maps the ordinary
spin half Fermionic degrees of freedom exactly and without introducing Hilbert
space constraints to a charge-like ``quasicharge'' fermion and a spin-like
``quasispin'' Boson while preserving all the symmetries of the model. We
present approximate solutions with localized charge which emerge naturally from
the Hubbard model in this form. Our results strongly suggest that charge tends
to remain localized for large values of the Hubbard U
Science materials for the gifted in grades two and three
Thesis (Ed.M.)--Boston Universit
Detection of early osteogenic commitment in primary cells using Raman spectroscopy
Major challenges in the development of novel implant surfaces for artificial joints include osteoblast heterogeneity and the lack of a simple and sensitive in vitro assay to measure early osteogenic responses. Raman spectroscopy is a label-free, non-invasive and non-destructive vibrational fingerprinting optical technique that is increasingly being applied to detect biochemical changes in cells. In this study Raman spectroscopy has been used to obtain bone cell-specific spectral signatures and to identify any changes therein during osteoblast commitment and differentiation of primary cells in culture. Murine calvarial osteoblasts (COBs) were extracted and cultured and studied by Raman spectroscopy over a 14 day culture period. Distinct osteogenic Raman spectra were identified after 3 days of culture with strong bands detected for mineral: phosphate ν3 (1030 cm−1) and B-type carbonate (1072 cm−1), DNA (782 cm−1) and collagen matrix (CH2 deformation at 1450 cm−1) and weaker phosphate bands (948 and 970 cm−1). Early changes were detected by Raman spectroscopy compared to a standard enzymatic alkaline phosphatase (ALP) assay and gene expression analyses over this period. Proliferation of COBs was confirmed by fluorescence intensity measurements using the Picogreen dsDNA reagent. Changes in ALP levels were evident only after 14 days of culture and mRNA expression levels for ALP, Col1a1 and Sclerostin remained constant during the culture period. Sirius red staining for collagen deposition also revealed little change until day 14. In contrast Raman spectroscopy revealed the presence of amorphous calcium phosphate (945–952 cm−1) and carbonated apatite (957–962 cm−1) after only 3 days in culture and octacalcium phosphate (970 cm−1) considered a transient mineral phase, was detected after 5 days of COBs culture. PCA analysis confirmed clear separation between time-points. This study highlights the potential of Raman spectroscopy to be utilised for the early and specific detection of proliferation and differentiation changes in primary cultures of bone cells
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