4,971 research outputs found
STM imaging of electronic waves on the surface of BiTe: topologically protected surface states and hexagonal warping effects
Scanning tunneling spectroscopy studies on high-quality BiTe crystals
exhibit perfect correspondence to ARPES data, hence enabling identification of
different regimes measured in the local density of states (LDOS). Oscillations
of LDOS near a step are analyzed. Within the main part of the surface band
oscillations are strongly damped, supporting the hypothesis of topological
protection. At higher energies, as the surface band becomes concave,
oscillations appear which disperse with a particular wave-vector that may
result from an unconventional hexagonal warping term.Comment: 4 pages, 4 figures. Revised manuscript with improved analysis and
figure
The emergency observation and assessment ward
A recent development to reduce ED crowding and increase urgent patient admissions is the opening of an Emergency Observation and Assessment Ward (EOA Ward). At these wards urgent patients are temporarily hospitalized until they can be transferred to an inpatient bed. In this paper we present an overflow model to evaluate the effect of employing an EOA Ward on elective and urgent patient admissions
Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11
We report the discovery of a galaxy overdensity at z=1.11 associated with the
z=1.110 high-redshift radio galaxy MG0442+0202. The group, CL0442+0202, was
found in a near-infrared survey of z>1 radio galaxies undertaken to identify
spatially-coincident regions with a high density of objects red in I-K' color,
typical of z>1 elliptical galaxies. Spectroscopic observations from the Keck
telescope reveal five galaxies within 35" of MG0442+0202 at 1.10<z<1.11. These
member galaxies have broad-band colors and optical spectra consistent with
passively-evolving elliptical galaxies formed at high redshift. A 45ks Chandra
X-Ray Observatory observation detects the radio galaxy and four point sources
within 15" of the radio galaxy, corresponding to a surface density two orders
of magnitude higher than average for X-ray sources at these flux levels,
S(0.5-2keV) > 5e-16 erg/cm2/s. One of these point sources is identified with a
radio-quiet, typeII quasar at z=1.863, akin to sources recently reported in
deep Chandra surveys. The limit on an extended hot intracluster medium in the
Chandra data is S(1-6keV) < 1.9e-15 erg/cm2/s (3-sigma, 30" radius aperture).
Though the X-ray observations do not confirm the existence of a massive, bound
cluster at z>1, the success of the optical/near-infrared targeting of
early-type systems near the radio galaxy validates searches using radio
galaxies as beacons for high-redshift large-scale structure. We interpret
CL0442+0202 to be a massive cluster in the process of formation.Comment: 23 pages, 7 figure
Discovery of a Color-Selected Quasar at z=5.50
We present observations of RD J030117+002025, a quasar at z=5.50 discovered
from deep, multi-color, ground-based observations covering 74 square arcmin.
This is the most distant quasar or AGN currently known. The object was targeted
as an R-band dropout, with R(AB)>26.3 (3-sigma limit in a 3 arcsec diameter
region), I(AB)=23.8, and z(AB)=23.4. The Keck/LRIS spectrum shows broad
Lyman-alpha/NV emission and sharp absorption decrements from the
highly-redshifted hydrogen forests. The fractional continuum depression due to
the Lyman-alpha forest is D(A)=0.90. RD J030117+002025 is the least luminous,
high-redshift quasar known (M(B)~-22.7).Comment: 9 pages, 2 figures; to appear in the The Astrophysical Journal
Letter
Spectroscopic confirmation of a galaxy cluster associated with 7C1756+6520 at z=1.416
We present spectroscopic follow-up of an overdensity of galaxies
photometrically selected to be at 1.4<z<2.5 found in the vicinity of the radio
galaxy 7C1756+6520 at z=1.4156. Using the DEIMOS optical multi-object
spectrograph on the Keck 2 telescope, we observed a total of 129 BzK-selected
sources, comprising 82 blue, star-forming galaxy candidates (sBzK) and 47 red,
passively-evolving galaxy candidates (pBzK*), as well as 11 mid-infrared
selected AGN candidates. We obtain robust spectroscopic redshifts for 36 blue
galaxies, 7 red galaxies and 9 AGN candidates. Assuming all foreground
interlopers were identified, we find that only 16% (9%) of the sBzK (pBzK*)
galaxies are at z<1.4. Therefore, the BzK criteria are shown to be relatively
robust at identifying galaxies at moderate redshifts. Twenty-one galaxies,
including the radio galaxy, four additional AGN candidates and three red galaxy
candidates are found with 1.4156 +/- 0.025, forming a large scale structure at
the redshift of the radio galaxy. Of these, eight have projected offsets <2Mpc
relative to the radio galaxy position and have velocity offsets <1000km/s
relative to the radio galaxy redshift. This confirms that 7C1756+6520 is
associated with a high-redshift galaxy cluster. A second compact group of four
galaxies is found at z~1.437, forming a sub-group offset by Dv~3000km/s and
approximately 1.5' east of the radio galaxy.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in A&A
Solutrean hypothesis: genetics, the mammoth in the room
© 2014 Taylor & Francis. This is an Accepted Manuscript of an article published by Taylor & Francis Group in World Archaeology on 31/10/2014, available online: http://www.tandfonline.com/10.1080/00438243.2014.966273.The Solutrean Hypothesis for the origin of the Clovis archaeological culture has received numerous challenges and critiques. Oft-repeated contra-assertions, predominantly from archaeologists, range from: “NO genetic evidence”, to: it must have been either a sole Beringian or European origin, so Beringia wins, to: the troublesome fifth American mtDNA lineage “X2a” overlanded from West-Eurasia to Beringia, leaving no trace en-route, to: there is no evidence from the rest of the genome to parallel X2a. We refute these contra-assertions, detailing published contrary evidence, supporting a West-Eurasian origin for some Native American ancestors, mainly found in north-eastern America, in parallel to the majority arriving from Beringia. Specifically this includes mtDNA-X2a found in ancient and modern Native American populations, with no evidence to support migration of X2a through Siberia. Prima facie (i.e. under-researched) published evidence also exists for equivalent levels of West-Eurasian Y-chromosomes and autosomal markers in the same regions
Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey
We present the galaxy cluster autocorrelation function of 277 galaxy cluster
candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow
Cluster Survey. We find strong clustering throughout our galaxy cluster sample,
as expected for these massive structures. Specifically, at = 0.5 we find a
correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent
agreement with the Las Campanas Distant Cluster Survey, the only other
non-local measurement. At higher redshift, = 1, we find that strong
clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56}
h^-1 Mpc. A comparison with high resolution cosmological simulations indicates
these are clusters with halo masses of \sim 10^{14} Msun, a result supported by
estimates of dynamical mass for a subset of the sample. In a stable clustering
picture, these clusters will evolve into massive (10^{15} Msun) clusters by the
present day.Comment: 4 pages, 4 figures, 1 table. ApJ Letters, in pres
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