8,860 research outputs found
Graphical Methods in Device-Independent Quantum Cryptography
We introduce a framework for graphical security proofs in device-independent
quantum cryptography using the methods of categorical quantum mechanics. We are
optimistic that this approach will make some of the highly complex proofs in
quantum cryptography more accessible, facilitate the discovery of new proofs,
and enable automated proof verification. As an example of our framework, we
reprove a previous result from device-independent quantum cryptography: any
linear randomness expansion protocol can be converted into an unbounded
randomness expansion protocol. We give a graphical proof of this result, and
implement part of it in the Globular proof assistant.Comment: Publishable version. Diagrams have been polished, minor revisions to
the text, and an appendix added with supplementary proof
Emerging Investigators Series: Pyrolysis Removes Common Microconstituents Triclocarban, Triclosan, and Nonylphenol from Biosolids
Reusing biosolids is vital for the sustainability of wastewater management. Pyrolysis is an anoxic thermal degradation process that can be used to convert biosolids into energy rich py-gas and py-oil, and a beneficial soil amendment, biochar. Batch biosolids pyrolysis (60 minutes) revealed that triclocarban and triclosan were removed (to below quantification limit) at 200 °C and 300 °C, respectively. Substantial removal (\u3e90%) of nonylphenol was achieved at 300 °C as well, but 600 °C was required to remove nonylphenol to below the quantification limit. At 500 °C, the pyrolysis reaction time to remove \u3e90% of microconstituents was less than 5 minutes. Fate studies revealed that microconstituents were both volatilized and thermochemically transformed during pyrolysis; microconstituents with higher vapor pressures were more likely to volatilize and leave the pyrolysis reactor before being transformed than compounds with lower vapor pressures. Reductive dehalogenation products of triclocarban and suspected dehalogenation products of triclosan were identified in py-gas. Application of biosolids-derived biochar to soil in place of biosolids has potential to minimize organic microconstituents discharged to the environment provided appropriate management of py-gas and py-oil
A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model
We present a systematic study of GX 339-4 in both its very high and low hard
states from simultaneous observations made with XMM-Newton and RXTE in 2002 and
2004. The X-ray spectra of both these extreme states exhibit strong reflection
signatures, with a broad, skewed Fe-Kalpha line clearly visible above the
continuum. Using a newly developed, self-consistent reflection model which
implicitly includes the blackbody radiation of the disc as well as the effect
of Comptonisation, blurred with a relativistic line function, we were able to
infer the spin parameter of GX 339-4 to be 0.935 +/- 0.01 (statistical) +/-
0.01 (systematic) at 90 per cent confidence. We find that both states are
consistent with an ionised thin accretion disc extending to the innermost
stable circular orbit around the rapidly spinning black hole.Comment: 10 pages, 10 figures, accepted for publication in MNRAS 17/04/0
X-ray reverberation in 1H0707-495 revisited
The narrow-line Seyfert 1 galaxy 1H0707-495 has previously been identified as
showing time lags between flux variations in the soft- (0.3-1 keV) and
medium-energy (1-4 keV) X-ray bands that oscillate between positive and
negative values as a function of the frequency of the mode of variation. Here
we measure and analyse the lags also between a harder X-ray band (4-7.5 keV)
and the soft and medium bands, using existing XMM-Newton data, and demonstrate
that the entire spectrum of lags, considering both the full energy range,
0.3-7.5 keV, and the full frequency range, 10^-5 < nu < 10^-2 Hz, are
inconsistent with previous claims of arising as reverberation associated with
the inner accretion disk. Instead we demonstrate that a simple reverberation
model, in which scattering or reflection is present in all X-ray bands,
explains the full set of lags without requiring any ad hoc explanation for the
time lag sign changes. The range of time delays required to explain the
observed lags extends up to about 1800 s in the hard band. The results are
consistent with reverberation caused by scattering of X-rays passing through an
absorbing medium whose opacity decreases with increasing energy and that
partially-covers the source. A high covering factor of absorbing and scattering
circumnuclear material is inferred.Comment: Accepted for publication in MNRA
Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and Without a Zero-Torque Inner Boundary Condition
The standard spectral model for analyzing the soft component of thermal
emission from a thin accretion disk around a black hole is the
multi-temperature blackbody (MTB) model. The widely used implementation of this
model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge
of the accretion disk. This assumption is contrary to the classic and current
literature on thin-disk accretion, which advocates the use of a zero-torque
boundary condition. Consequently, we have written code for a zero-torque model,
``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting
RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE
J1550-564, and GRO J1655-40. The chief difference we find is that the
zero-torque model gives a value for the inner disk radius that is about 2.2
times smaller than the value given by diskbb. This result has important
implications, especially for the determination of black-hole angular momentum
and mass accretion rate.Comment: 27 pages, 9 figures, submitted to Ap
Black hole accretion disks in the canonical low-hard state
Stellar-mass black holes in the low-hard state may hold clues to jet
formation and basic accretion disk physics, but the nature of the accretion
flow remains uncertain. A standard thin disk can extend close to the innermost
stable circular orbit, but the inner disk may evaporate when the mass accretion
rate is reduced. Blackbody-like continuum emission and dynamically-broadened
iron emission lines provide independent means of probing the radial extent of
the inner disk. Here, we present an X-ray study of eight black holes in the
low-hard state. A thermal disk continuum with a colour temperature consistent
with is clearly detected in all eight sources, down to
. In six sources, disk models exclude a
truncation radius larger than 10rg. Iron-ka fluorescence line emission is
observed in half of the sample, down to luminosities of
. Detailed fits to the line profiles exclude a
truncated disk in each case. If strong evidence of truncation is defined as (1)
a non-detection of a broad iron line, {\it and} (2) an inner disk temperature
much cooler than expected from the relation, none
of the spectra in this sample offer strong evidence of disk truncation. This
suggests that the inner disk may evaporate at or below
.Comment: Accepted for publication in MNRAS, 20 pages, 18 figure
The absorption-dominated model for the X-ray spectra of type I active galaxies: MCG-6-30-15
MCG-6-30-15 is the archetypal example of a type I active galaxy showing broad
"red-wing" emission in its X-ray spectrum at energies below the 6.4 keV Fe
K-alpha emission line and a continuum excess above 20 keV. Miller et al. (2008)
showed that these spectral features could be caused by clumpy absorbing
material, but Reynolds et al. (2009) have argued that the observed Fe K-alpha
line luminosity is inconsistent with this explanation unless the global
covering factor of the absorber(s) is very low. However, the Reynolds et al.
calculation effectively considers the only source of opacity to be the Fe K
bound-free transition and neglects the opacity at the line energy: correction
to realistic opacity decreases the predicted line flux by a large factor. We
also discuss the interpretation of the covering factor and the possible effect
of occultation by the accretion disk. Finally, we consider a model for
MCG-6-30-15 dominated by clumpy absorption, which is consistent with global
covering factor 0.45, although models that include the effects of Compton
scattering are required to reach a full understanding. Variations in covering
fraction may dominate the observed X-ray spectral variability.Comment: Accepted for publication in MNRAS letter
The Two-Point Correlation of 2QZ Quasars and 2SLAQ LRGs: From a Quasar Fueling Perspective
Public data from the 2dF quasar survey (2QZ) and 2dF/SDSS LRG & QSO (2SLAQ),
with their vast reservoirs of spectroscopically located and identified sources,
afford us the chance to more accurately study their real space correlations in
the hopes of identifying the physical processes that trigger quasar activity.
We have used these two public databases to measure the projected cross
correlation, , between quasars and luminous red galaxies. We find the
projected two-point correlation to have a fitted clustering radius of and a slope, on scales from
0.7-27Mpc.
We attempt to understand this strong correlation by separating the LRG sample
into 2 populations of blue and red galaxies. We measure at the cross
correlation with each population. We find that these quasars have a stronger
correlation amplitude with the bluer, more recently starforming population in
our sample than the redder passively evolving population, which has a
correlation that is much more noisy and seems to flatten on scales Mpc. We compare this result to published work on hierarchical models.
The stronger correlation of bright quasars with LRGs that have undergone a
recent burst of starformation suggests that the physical mechanisms that
produce both activities are related and that minor mergers or tidal effects may
be important triggers of bright quasar activity and/or that bright quasars are
less highly biased than faint quasars.Comment: Accepted for publication in Ap
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