18,684 research outputs found
Magnetic Gradient Survey at the M. S. Roberts (41HE8) Site in Henderson County, Texas
The M. S. Roberts site is located in Henderson County, Texas and it represents one of the few known Caddo mound sites in the upper Neches River Basin in northeast Texas (Figure 1). The site is situated along Caddo Creek – an eastward-flowing tributary of the Neches River (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). The site is located southeast of Athens, Texas. When first recorded, the single mound at the site was approximately 24 m long and 20 m wide and roughly 1.7 m in height (Pearce and Jackson 1931). Directly west of the mound was a large depression, which has since been mostly filled, and likely represents the borrow pit for mound fill. The mound is situated at the southern end of an elevated alluvial landform.
The site was first reported to Dr. J. E. Pearce of the University of Texas in September 1931. In October of the same year, archaeologists from the University of Texas began investigating the mound and defining the extent of the associated settlement (Pearce and Jackson 1931). Researchers obtained a surface collection from the site and excavated an unknown number of trenches in the mound where portions of at least one burned and buried Caddo structure was identified. Their excavation notes document that the mound began as a 25 cm deposit of yellow sand constructed on the undisturbed brown sandy loam that defines the alluvial landform. A structure had been built on the yellow sand and then at some point had been burned. The burned structure was then covered with mound fill at least a meter in depth. Materials collected from the surface as part of the 1931 investigations indicate the presence of a Caddo habitation area surrounding the mound and suggest the site was occupied from the fourteenth to the early fifteenth centuries (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). At that time, the landscape around the mound was a used as a cotton field and subject to extensive plowing. Today, the landscape is part of a residential ranch development where landowners are stewards of the site with a focus on preservation and research.
In January 2015, with the permission of the landowners, renewed interested in the site began with a surface collection and the examination of the artifact collections from the 1931 work held by the Texas Archeological Research Laboratory (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). A series of shovel tests and auger holes were then dug in the mound and surrounding habitation area in mid-2015. Shovel tests and auger holes documented organically-stained and charcoal-rich areas within the mound that were thought to represent the remains of several burned Caddo structures, and also identified non-mound habitation deposits at the site. An initial aerial survey was also conducted to map the landform topography, estimate the extent of the current mound dimensions and borrow pit, and to reconstruct changes in the shape and size of the mound since it was first recorded in 1931 (Perttula et al. 2016). The survey employed a small Unmanned Aerial Vehicle (UAV) to map the roughly 20-acre property surrounding the site at a 2 cm per pixel resolution. The aerial survey of the mound and surrounding landscape and the creation of a high-resolution digital elevation model reveal that the mound dimensions have changed significantly from what was reported in 1931 (Perttula et al. 2016).
For example, aerial data document both the mound and borrow pit features and show that the mound measures 43 m North-South and 26 m East-West, and is roughly 1 meter above the surrounding terrace surface (Perttula et al. 2016). The aerial survey demonstrates that the mound has elongated over the last century since it was first recorded, likely related to historic landscape modification.
In January 2016, the site was again revisited. The purpose of the fieldwork was to better define the spatial extent of archaeological deposits in the non-mounded habitation area and investigate the stratigraphy of mound deposits, identify cultural features in the mound, and hopefully obtain charred plant remains or unburned animal bones from these deposits for AMS dating.
To help evaluate and identify the distribution of cultural features in the mound and the surrounding non-mounded habitation area, an area just over 1 hectare or 2.8 acres was surveyed using magnetic gradient and a second aerial survey was completed to refine the overall landscape topography (Figure 2).
The magnetic gradient results document the subsurface location of at least two interpreted structures within the mound, the possible locations of three 1931 UT trenches, and several possible pit features proximate to the mound. The combination of aerial and geophysical data and the excavation results are revising our understanding of the archaeological remains and preservation conditions of the site
A Damping of the de Haas-van Alphen Oscillations in the superconducting state
Deploying a recently developed semiclassical theory of quasiparticles in the
superconducting state we study the de Haas-van Alphen effect. We find that the
oscillations have the same frequency as in the normal state but their amplitude
is reduced. We find an analytic formulae for this damping which is due to
tunnelling between semiclassical quasiparticle orbits comprising both
particle-like and hole-like segments. The quantitative predictions of the
theory are consistent with the available data.Comment: 7 pages, 5 figure
Discovery of a 270 Hz X-Ray Burst Oscillation in the X-Ray Dipper 4U 1916-053
We report the discovery of a highly coherent oscillation in a type-I X-ray
burst observed from 4U 1916-053 by the Rossi X-ray Timing Explorer (RXTE). The
oscillation was most strongly detected approx. 1 s after the burst onset at a
frequency of 269.3 Hz, and it increased in frequency over the following 4
seconds of the burst decay to a maximum of around 272 Hz. The total measured
drift of 3.58 +/- 0.41 Hz (1 sigma) represents the largest fractional change in
frequency (1.32 +/- 0.15 %) yet observed in any burst oscillation. If the
asymptotic frequency of the oscillation is interpreted in terms of a decoupled
surface burning layer, the implied neutron star spin period is around 3.7 ms.
However, the expansion of the burning layer required to explain frequency drift
during the burst is around 80 m, substantially larger than expected
theoretically (assuming rigid rotation). The oscillation was not present in the
persistent emission before the burst, nor in the initial rise. When detected
its amplitude was 6-12% (RMS) with a roughly sinusoidal profile. The burst
containing the oscillation showed no evidence for photospheric radius
expansion, while at least 5 of the other 9 bursts observed from the source by
RXTE during 1996 and 1998 did. No comparable oscillations were detected in the
other bursts. A pair of kilohertz quasi-periodic oscillations (QPOs) has been
previously reported from this source with a mean separation of 348 +/- 12 Hz.
4U 1916-053 is the first example of a source where the burst oscillation
frequency is significantly smaller than the frequency separation of the kHz
QPOs.Comment: 8 pages, 2 figures, 2 tables; accepted for ApJ Letter
Automorphisms of Partially Commutative Groups II: Combinatorial Subgroups
We define several "standard" subgroups of the automorphism group Aut(G) of a
partially commutative (right-angled Artin) group and use these standard
subgroups to describe decompositions of Aut(G). If C is the commutation graph
of G, we show how Aut(G) decomposes in terms of the connected components of C:
obtaining a particularly clear decomposition theorem in the special case where
C has no isolated vertices.
If C has no vertices of a type we call dominated then we give a semi-direct
decompostion of Aut(G) into a subgroup of locally conjugating automorphisms by
the subgroup stabilising a certain lattice of "admissible subsets" of the
vertices of C. We then characterise those graphs for which Aut(G) is a product
(not necessarily semi-direct) of two such subgroups.Comment: 7 figures, 63 pages. Notation and definitions clarified and typos
corrected. 2 new figures added. Appendix containing details of presentation
and proof of a theorem adde
Limits on the Boron Isotopic Ratio in HD 76932
Data in the 2090 A B region of HD 76932 have been obtained at high S/N using
the HST GHRS echelle at a resolution of 90,000. This wavelength region has been
previously identified as a likely candidate for observing the B11/B10 isotopic
splitting.
The observations do not match a calculated line profile extremely well at any
abundance for any isotopic ratio. If the B abundance previously determined from
observations at 2500 A is assumed, the calculated line profile is too weak,
indicating a possible blending line. Assuming that the absorption at 2090 A is
entirely due to boron, the best-fit total B abundance is higher than but
consistent with that obtained at 2500 A, and the best-fit isotopic ratio
(B11/B10) is in the range ~10:1 to ~4:1. If the absorption is not entirely due
to B and there is an unknown blend, the best-fit isotopic ratio may be closer
to 1:1. Future observations of a similar metal-poor star known to have
unusually low B should allow us to distinguish between these two possibilities.
The constraints that can be placed on the isotopic ratio based on comparisons
with similar observations of HD 102870 and HD 61421 (Procyon) are also
discussed.Comment: Accepted for Nov 1998 Ap
Unquenched QCD with Light Quarks
We present recent results in unquenched lattice QCD with two degenerate light
sea quarks using the truncated determinant approximation (TDA). In the TDA the
infrared modes contributing to the quark determinant are computed exactly up to
some cutoff in quark off-shellness (typically 2). This approach
allows simulations to be performed at much lighter quark masses than possible
with conventional hybrid MonteCarlo techniques. Results for the static energy
and topological charge distributions are presented using a large ensemble
generated on very coarse (6) but physically large lattices. Preliminary
results are also reported for the static energy and meson spectrum on 10x20
lattices (lattice scale =1.15 GeV) at quark masses corresponding to
pions of mass 200 MeV. Using multiboson simulation to compute the
ultraviolet part of the quark determinant the TDA approach becomes an exact
with essentially no increase in computational effort. Some preliminary results
using this fully unquenched algorithm are presented.Comment: LateX, 39 pages, 16 eps figures, 1 ps figur
Generation of frequency sidebands on single photons with indistinguishability from quantum dots
Generation and manipulation of the quantum state of a single photon is at the
heart of many quantum information protocols. There has been growing interest in
using phase modulators as quantum optics devices that preserve coherence. In
this Letter, we have used an electro-optic phase modulator to shape the state
vector of single photons emitted by a quantum dot to generate new frequency
components (modes) and explicitly demonstrate that the phase modulation process
agrees with the theoretical prediction at a single photon level. Through
two-photon interference measurements we show that for an output consisting of
three modes (the original mode and two sidebands), the indistinguishability of
the mode engineered photon, measured through the secondorder intensity
correlation (g2(0)) is preserved. This work demonstrates a robust means to
generate a photonic qubit or more complex state (e.g., a qutrit) for quantum
communication applications by encoding information in the sidebands without the
loss of coherence
Measurement of the SOC State Specific Heat in ^4He
When a heat flux Q is applied downward through a sample of liquid 4He near the lambda transition, the helium self organizes such that the gradient in temperature matches the gravity induced gradient in Tlambda. All the helium in the sample is then at the same reduced temperature tSOC = ((T[sub SOC] - T[sub lambda])/T[sub lambda]) and the helium is said to be in the Self-Organized Critical (SOC) state. We have made preliminary measurements of the 4He SOC state specific heat, C[del]T(T(Q)). Despite having a cell height of 2.54 cm, our results show no difference between C[del]T and the zero-gravity 4He specific heat results of the Lambda Point Experiment (LPE) [J.A. Lipa et al., Phys. Rev. B, 68, 174518 (2003)] over the range 250 to 450 nK below the transition. There is no gravity rounding because the entire sample is at the same reduced temperature tSOC(Q). Closer to Tlambda the SOC specific heat falls slightly below LPE, reaching a maximum at approximately 50 nK below Tlambda, in agreement with theoretical predictions [R. Haussmann, Phys. Rev. B, 60, 12349 (1999)]
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