2,128 research outputs found
Atmospheric mercury inputs in montane soils increase with elevation: evidence from mercury isotope signatures
The influence of topography on the biogeochemical cycle of mercury (Hg) has received relatively little attention. Here, we report the measurement of Hg species and their corresponding isotope composition in soil sampled along an elevational gradient transect on Mt. Leigong in subtropical southwestern China. The data are used to explain orography-related effects on the fate and behaviour of Hg species in montane environments. The total- and methyl-Hg concentrations in topsoil samples show a positive correlation with elevation. However, a negative elevation dependence was observed in the mass- ependent fractionation (MDF) and mass-independent fractionation (MIF) signatures of Hg isotopes. Both a MIF (D199Hg) binary mixing approach and the traditional inert element method indicate that the content of Hg derived from the atmosphere distinctly increases with altitude.publishedVersio
High-Redshift SDSS Quasars with Weak Emission Lines
We identify a sample of 74 high-redshift quasars (z>3) with weak emission
lines from the Fifth Data Release of the Sloan Digital Sky Survey and present
infrared, optical, and radio observations of a subsample of four objects at
z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the
Lya+NV equivalent width distribution, and we compare them to quasars with more
typical emission-line properties and to low-redshift active galactic nuclei
with weak/absent emission lines, namely BL Lac objects. We find that WLQs
exhibit hot (T~1000 K) thermal dust emission and have rest-frame 0.1-5 micron
spectral energy distributions that are quite similar to those of normal
quasars. The variability, polarization, and radio properties of WLQs are also
different from those of BL Lacs, making continuum boosting by a relativistic
jet an unlikely physical interpretation. The most probable scenario for WLQs
involves broad-line region properties that are physically distinct from those
of normal quasars.Comment: Updated to match version published in ApJ. 20 pages, 12 figure
A Strategy for Finding Near Earth Objects with the SDSS Telescope
We present a detailed observational strategy for finding Near Earth Objects
(NEOs) with the Sloan Digital Sky Survey (SDSS) telescope. We investigate
strategies in normal, unbinned mode as well as binning the CCDs 2x2 or 3x3,
which affects the sky coverage rate and the limiting apparent magnitude. We
present results from 1 month, 3 year and 10 year simulations of such surveys.
For each cadence and binning mode, we evaluate the possibility of achieving the
Spaceguard goal of detecting 90% of 1 km NEOs (absolute magnitude H <= 18 for
an albedo of 0.1). We find that an unbinned survey is most effective at
detecting H <= 20 NEOs in our sample. However, a 3x3 binned survey reaches the
Spaceguard Goal after only seven years of operation. As the proposed large
survey telescopes (PanStarss; LSST) are at least 5-10 years from operation, an
SDSS NEO survey could make a significant contribution to the detection and
photometric characterization of the NEO population.Comment: Accepted by AJ -- 12 pages, 11 figure
Separation of Spin and Charge Quantum Numbers in Strongly Correlated Systems
In this paper we reexamine the problem of the separation of spin and charge
degrees of freedom in two dimensional strongly correlated systems. We establish
a set of sufficient conditions for the occurence of spin and charge separation.
Specifically, we discuss this issue in the context of the Heisenberg model for
spin-1/2 on a square lattice with nearest () and next-nearest ()
neighbor antiferromagnetic couplings. Our formulation makes explicit the
existence of a local SU(2) gauge symmetry once the spin-1/2 operators are
replaced by bound states of spinons. The mean-field theory for the spinons is
solved numerically as a function of the ratio for the so-called s-RVB
Ansatz. A second order phase transition exists into a novel flux state for
. We identify the range as the s-RVB phase. It is characterized by the existence of a finite gap
to the elementary excitations (spinons) and the breakdown of all the continuous
gauge symmetries. An effective continuum theory for the spinons and the gauge
degrees of freedom is constructed just below the onset of the flux phase. We
argue that this effective theory is consistent with the deconfinement of the
spinons carrying the fundamental charge of the gauge group. We contrast this
result with the study of the one dimensional quantum antiferromagnet within the
same approach. We show that in the one dimensional model, the spinons of the
gauge picture are always confined and thus cannot be identified with the
gapless spin-1/2 excitations of the quantum antiferromagnet Heisenberg model.Comment: 56 pages, RevteX 3.
Crossover from the chiral to the standard universality classes in the conductance of a quantum wire with random hopping only
The conductance of a quantum wire with off-diagonal disorder that preserves a
sublattice symmetry (the random hopping problem with chiral symmetry) is
considered. Transport at the band center is anomalous relative to the standard
problem of Anderson localization both in the diffusive and localized regimes.
In the diffusive regime, there is no weak-localization correction to the
conductance and universal conductance fluctuations are twice as large as in the
standard cases. Exponential localization occurs only for an even number of
transmission channels in which case the localization length does not depend on
whether time-reversal and spin rotation symmetry are present or not. For an odd
number of channels the conductance decays algebraically. Upon moving away from
the band center transport characteristics undergo a crossover to those of the
standard universality classes of Anderson localization. This crossover is
calculated in the diffusive regime.Comment: 22 pages, 9 figure
The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview
The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a
dedicated multi-object RM experiment that has spectroscopically monitored a
sample of 849 broad-line quasars in a single 7 deg field with the SDSS-III
BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and
covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during
2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more
than 30 epochs. Supporting photometric monitoring in the g and i bands was
conducted at multiple facilities including the CFHT and the Steward Observatory
Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar
phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS
W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07,
with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month
baseline program aims to detect time lags between the quasar continuum and
broad line region (BLR) variability on timescales of up to several months (in
the observed frame) for ~10% of the sample, and to anchor the time baseline for
continued monitoring in the future to detect lags on longer timescales and at
higher redshift. SDSS-RM is the first major program to systematically explore
the potential of RM for broad-line quasars at z>0.3, and will investigate the
prospects of RM with all major broad lines covered in optical spectroscopy.
SDSS-RM will provide guidance on future multi-object RM campaigns on larger
scales, and is aiming to deliver more than tens of BLR lag detections for a
homogeneous sample of quasars. We describe the motivation, design and
implementation of this program, and outline the science impact expected from
the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or
"It is what it is": masculinity, homosexuality, and inclusive discourse in mixed martial arts
In this paper we make use of inclusive masculinity theory to explore online media representations of male homosexuality and masculinity within the increasingly popular combat sport of mixed martial arts MMA). Adopting a case-study approach, we discuss narratives constructed around one aspirational male MMA fighter, Dakota Cochrane, whose history of having participated in gay pornography became a major talking point on a number of MMA 'fanzine'/'community' websites during early 2012. While these narratives attempted to discursively 'rescue' Cochrane's supposedly threatened masculinity, highlighting both his 'true' heterosexuality and his prodigious fighting abilities, they also simultaneously celebrated the acceptance of homosexual men within the sport which Cochrane's case implied. Thus, we suggest that these media representations of homosexuality and masculinity within MMA are indicative of declining cultural homophobia and homohysteria, and an inclusive vision of masculinity, as previously described by proponents of inclusive masculinity theory
The mechanism of spin and charge separation in one dimensional quantum antiferromagnets
We reconsider the problem of separation of spin and charge in one dimensional
quantum antiferromagnets. We show that spin and charge separation in one
dimensional strongly correlated systems cannot be described by the slave boson
or fermion representation within any perturbative treatment of the interactions
between the slave holons and slave spinons. The constraint of single occupancy
must be implemented exactly. As a result the slave fermions and bosons are not
part of the physical spectrum. Instead, the excitations which carry the
separate spin and charge quantum numbers are solitons. To prove this {\it
no-go} result, it is sufficient to study the pure spinon sector in the slave
boson representation. We start with a short-range RVB spin liquid mean-field
theory for the frustrated antiferromagnetic spin- chain. We derive
an effective theory for the fluctuations of the Affleck-Marston and Anderson
order parameters. We show how to recover the phase diagram as a function of the
frustration by treating the fluctuations non-perturbatively.Comment: 53 pages; Revtex 3.
Inequality, Fiscal Capacity and the Political Regime: Lessons from the Post-Communist Transition
Using panel data for twenty-seven post-communist economies between 1987-2003, we examine the nexus of relationships between inequality, fiscal capacity (defined as the ability to raise taxes efficiently) and the political regime. Investigating the impact of political reform we find that full political freedom is associated with lower levels of income inequality. Under more oligarchic (authoritarian) regimes, the level of inequality is conditioned by the stateâs fiscal capacity. Specifically, oligarchic regimes with more developed fiscal systems are able to defend the prevailing vested interests at a lower cost in terms of social injustice. This empirical finding is consistent with the model developed by Acemoglu (2006). We also find that transition countries undertaking early macroeconomic stabilisation now enjoy lower levels of inequality; we confirm that education fosters equality and the suggestion of Commander et al (1999) that larger countries are prone to higher levels of inequality.http://deepblue.lib.umich.edu/bitstream/2027.42/57211/1/wp831 .pd
Intravital FRAP imaging using an E-cadherin-GFP mouse reveals disease- and drug-dependent dynamic regulation of cell-cell junctions in live tissue
E-cadherin-mediated cell-cell junctions play a prominent role in maintaining the epithelial architecture. The disruption or deregulation of these adhesions in cancer can lead to the collapse of tumor epithelia that precedes invasion and subsequent metastasis. Here we generated an E-cadherin-GFP mouse that enables intravital photobleaching and
quantification of E-cadherin mobility in live tissue without affecting normal biology. We demonstrate the broad applications of this mouse by examining
E-cadherin regulation in multiple tissues, including mammary, brain, liver, and kidney tissue, while specifically monitoring E-cadherin mobility during
disease progression in the pancreas. We assess E-cadherin stability in native pancreatic tissue upon genetic manipulation involving Kras and p53
or in response to anti-invasive drug treatment and gain insights into the dynamic remodeling of E-cadherin during in situ cancer progression. FRAP in the E-cadherin-GFP mouse, therefore, promises to be a valuable tool to fundamentally expand our understanding of E-cadherin-mediated events in native microenvironments
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