211 research outputs found
The transition zone as a host for recycled volatiles: Evidence from nitrogen and carbon isotopes in ultra-deep diamonds from Monastery and Jagersfontein (South Africa)
Sublithospheric (ultra-deep) diamonds provide a unique window into the deepest parts of Earth's mantle, which otherwise remain inaccessible. Here, we report the first combined C- and N-isotopic data for diamonds from the Monastery and Jagersfontein kimberlites that sample the deep asthenosphere and transition zone beneath the Kaapvaal Craton, in the mid Cretaceous, to investigate the nature of mantle fluids at these depths and the constraints they provide on the deep volatile cycle.
Both diamond suites exhibit very light δ13C values (down to − 26‰) and heavy δ15N (up to + 10.3‰), with nitrogen abundances generally below 70 at. ppm but varying up to very high concentrations (2520 at. ppm) in rare cases. Combined, these signatures are consistent with derivation from subducted crustal materials. Both suites exhibit variable nitrogen aggregation states from 25 to 100% B defects. Internal growth structures, revealed in cathodoluminescence (CL) images, vary from faintly layered, through distinct cores to concentric growth patterns with intermittent evidence for dissolution and regular octahedral growth layers in places.
Modelling the internal co-variations in δ13C-δ15N-N revealed that diamonds grew from diverse C-H-O-N fluids involving both oxidised and reduced carbon species. The diversity of the modelled diamond-forming fluids highlights the complexity of the volatile sources and the likely heterogeneity of the deep asthenosphere and transition zone. We propose that the Monastery and Jagersfontein diamonds form in subducted slabs, where carbon is converted into either oxidised or reduced species during fluid-aided dissolution of subducted carbon before being re-precipitated as diamond. The common occurrence of recycled C and N isotopic signatures in super-deep diamonds world-wide indicates that a significant amount of carbon and nitrogen is recycled back to the deep asthenosphere and transition zone via subducting slabs, and that the transition zone may be dominated by recycled C and N
Cosmic Chronometers: Constraining the Equation of State of Dark Energy. I: H(z) Measurements
We present new determinations of the cosmic expansion history from
red-envelope galaxies. We have obtained for this purpose high-quality spectra
with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters
in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with
high-quality, publicly available archival spectra from the SPICES and VVDS
surveys. We improve over our previous expansion history measurements in Simon
et al. (2005) by providing two new determinations of the expansion history:
H(z) = 97 +- 62 km/sec/Mpc at z = 0.5 and H(z) = 90 +- 40 km/sec/Mpc at z =
0.8. We discuss the uncertainty in the expansion history determination that
arises from uncertainties in the synthetic stellar-population models. We then
use these new measurements in concert with cosmic-microwave-background (CMB)
measurements to constrain cosmological parameters, with a special emphasis on
dark-energy parameters and constraints to the curvature. In particular, we
demonstrate the usefulness of direct H(z) measurements by constraining the
dark- energy equation of state parameterized by w0 and wa and allowing for
arbitrary curvature. Further, we also constrain, using only CMB and H(z) data,
the number of relativistic degrees of freedom to be 4 +- 0.5 and their total
mass to be < 0.2 eV, both at 1-sigma.Comment: Submitted to JCA
Quantum-Hall Quantum-Bits
Bilayer quantum Hall systems can form collective states in which electrons
exhibit spontaneous interlayer phase coherence. We discuss the possibility of
using bilayer quantum dot many-electron states with this property to create
two-level systems that have potential advantages as quantum bits.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. B (Rapid
Communications
On the Background Field Method Beyond One Loop: A manifestly covariant derivative expansion in super Yang-Mills theories
There are currently many string inspired conjectures about the structure of
the low-energy effective action for super Yang-Mills theories which require
explicit multi-loop calculations. In this paper, we develop a manifestly
covariant derivative expansion of superspace heat kernels and present a scheme
to evaluate multi-loop contributions to the effective action in the framework
of the background field method. The crucial ingredient of the construction is a
detailed analysis of the properties of the parallel displacement propagators
associated with Yang-Mills supermultiples in N-extended superspace.Comment: 32 pages, latex, 7 EPS figures. v2: references, comments added, typos
corrected, incorrect `skeleton' conjecture in sect. 3 replaced by a more
careful treatment. v3: typos corrected, final version published in JHE
Semiclassical theory of transport in a random magnetic field
We study the semiclassical kinetics of 2D fermions in a smoothly varying
magnetic field . The nature of the transport depends crucially on
both the strength of the random component of and its mean
value . For , the governing parameter is ,
where is the correlation length of disorder and is the Larmor radius
in the field . While for the Drude theory applies, at
most particles drift adiabatically along closed contours and are
localized in the adiabatic approximation. The conductivity is then determined
by a special class of trajectories, the "snake states", which percolate by
scattering at the saddle points of where the adiabaticity of their
motion breaks down. The external field also suppresses the diffusion by
creating a percolation network of drifting cyclotron orbits. This kind of
percolation is due only to a weak violation of the adiabaticity of the
cyclotron rotation, yielding an exponential drop of the conductivity at large
. In the regime the crossover between the snake-state
percolation and the percolation of the drift orbits with increasing
has the character of a phase transition (localization of snake states) smeared
exponentially weakly by non-adiabatic effects. The ac conductivity also
reflects the dynamical properties of particles moving on the fractal
percolation network. In particular, it has a sharp kink at zero frequency and
falls off exponentially at higher frequencies. We also discuss the nature of
the quantum magnetooscillations. Detailed numerical studies confirm the
analytical findings. The shape of the magnetoresistivity at is
in good agreement with experimental data in the FQHE regime near .Comment: 22 pages REVTEX, 14 figure
Deriving Non-decoupling Effects of Heavy Fields from the Path Integral: a Heavy Higgs Field in an SU(2) Gauge Theory
We describe a method to remove non-decoupling heavy fields from a quantized
field theory and to construct a low-energy one-loop effective Lagrangian by
integrating out the heavy degrees of freedom in the path integral. We apply
this method to the Higgs boson in a spontaneously broken SU(2) gauge theory
(gauged linear sigma-model). In this context, the background-field method is
generalized to the non-linear representation of the Higgs sector by applying (a
generalization of) the Stueckelberg formalism. The (background) gauge-invariant
renormalization is discussed. At one loop the log M_H-terms of the heavy-Higgs
limit of this model coincide with the UV-divergent terms of the corresponding
gauged non-linear sigma-model, but vertex functions differ in addition by
finite (constant) terms in both models. These terms are also derived by our
method. Diagrammatic calculations of some vertex functions are presented as
consistency check.Comment: 33 Pages LaTeX, 6 figures uuencoded postscrip
Calibrating and adjusting expectations in life: A grounded theory on how elderly persons with somatic health problems maintain control and balance in life and optimize well-being
Aim: This study aims at exploring the main concern for elderly individuals with somatic health problems and what they do to manage this. Method: In total, 14 individuals (mean = 74.2 years; range = 68–86 years) of both gender including hospitalized and outpatient persons participated in the study. Open interviews were conducted and analyzed according to grounded theory, an inductive theory-generating method. Results: The main concern for the elderly individuals with somatic health problems was identified as their striving to maintain control and balance in life. The analysis ended up in a substantive theory explaining how elderly individuals with somatic disease were calibrating and adjusting their expectations in life in order to adapt to their reduced energy level, health problems, and aging. By adjusting the expectations to their actual abilities, the elderly can maintain a sense of that they still have the control over their lives and create stability. The ongoing adjustment process is facilitated by different strategies and result despite lower expectations in subjective well-being. The facilitating strategies are utilizing the network of important others, enjoying cultural heritage, being occupied with interests, having a mission to fulfill, improving the situation by limiting boundaries and, finally, creating meaning in everyday life. Conclusion: The main concern of the elderly with somatic health problems was to maintain control and balance in life. The emerging theory explains how elderly people with somatic health problems calibrate their expectations of life in order to adjust to reduced energy, health problems, and aging. This process is facilitated by different strategies and result despite lower expectation in subjective well-being
Infrastructure for Detector Research and Development towards the International Linear Collider
The EUDET-project was launched to create an infrastructure for developing and
testing new and advanced detector technologies to be used at a future linear
collider. The aim was to make possible experimentation and analysis of data for
institutes, which otherwise could not be realized due to lack of resources. The
infrastructure comprised an analysis and software network, and instrumentation
infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture
Deep carbon through time: Earth’s diamond record and its implications for carbon cycling and fluid speciation in the mantle
Diamonds are unrivalled in their ability to record the mantle carbon cycle and mantle fO2 over a vast portion of Earth’s history. Diamonds’ inertness and antiquity means their carbon isotopic characteristics directly reflect their growth environment within the mantle as far back as ∼3.5 Ga. This paper reports the results of a thorough secondary ion mass spectrometry (SIMS) carbon isotope and nitrogen concentration study, carried out on fragments of 144 diamond samples from various locations, from ∼3.5 to 1.4 Ga for P [peridotitic]-type diamonds and 3.0 to 1.0 Ga for E [eclogitic]-type diamonds. The majority of the studied samples were from diamonds used to establish formation ages and thus provide a direct connection between the carbon isotope values, nitrogen contents and the formation ages. In total, 908 carbon isotope and nitrogen concentration measurements were obtained. The total δ13C data range from −17.1 to −1.9 ‰ (P = −8.4 to −1.9 ‰; E = −17.1 to −2.1‰) and N contents range from 0 to 3073 at. ppm (P = 0 to 3073 at. ppm; E = 1 to 2661 at. ppm). In general, there is no systematic variation with time in the mantle carbon isotope record since > 3 Ga. The mode in δ13C of peridotitic diamonds has been at −5 (±2) ‰ since the earliest diamond growth ∼3.5 Ga, and this mode is also observed in the eclogitic diamond record since ∼3 Ga. The skewness of eclogitic diamonds’ δ13C distributions to more negative values, which the data establishes began around 3 Ga, is also consistent through time, with no global trends apparent.
No isotopic and concentration trends were recorded within individual samples, indicating that, firstly, closed system fractionation trends are rare. This implies that diamonds typically grow in systems with high excess of carbon in the fluid (i.e. relative to the mass of the growing diamond). Any minerals included into diamond during the growth process are more likely to be isotopically reset at the time of diamond formation, meaning inclusion ages would be representative of the diamond growth event irrespective of whether they are syngenetic or protogenetic. Secondly, the lack of significant variation seen in the peridotitic diamonds studied is in keeping with modeling of Rayleigh isotopic fractionation in multicomponent systems (RIFMS) during isochemical diamond precipitation in harzburgitic mantle. The RIFMS model not only showed that in water-maximum fluids at constant depths along a geotherm, fractionation can only account for variations of <1‰, but also that the principal δ13C mode of −5 ± 1‰ in the global harzburgitic diamond record occurs if the variation in fO2 is only 0.4 log units. Due to the wide age distribution of P-type diamonds, this leads to the conclusion that the speciation and oxygen fugacity of diamond forming fluids has been relatively consistent. The deep mantle has therefore generated fluids with near constant carbon speciation for 3.5 Ga
Baseline chest computed tomography as standard of care in high-risk hematology patients
Baseline chest computed tomography (BCT) in high-risk hematology patients allows for the early diagnosis of invasive pulmonary aspergillosis (IPA). The distribution of BCT implementation in hematology departments and impact on outcome is unknown. A web-based questionnaire was designed. International scientific bodies were invited. The estimated numbers of annually treated hematology patients, chest imaging timepoints and techniques, IPA rates, and follow-up imaging were assessed. In total, 142 physicians from 43 countries participated. The specialties included infectious diseases (n = 69; 49%), hematology (n = 68; 48%), and others (n = 41; 29%). BCT was performed in 57% (n = 54) of 92 hospitals. Upon the diagnosis of malignancy or admission, 48% and 24% performed BCT, respectively, and X-ray was performed in 48% and 69%, respectively. BCT was more often used in hematopoietic cell transplantation and in relapsed acute leukemia. European centers performed BCT in 59% and non-European centers in 53%. Median estimated IPA rate was 8% and did not differ between BCT (9%; IQR 5-15%) and non-BCT centers (7%; IQR 5-10%) (p = 0.69). Follow-up computed tomography (CT) for IPA was performed in 98% (n = 90) of centers. In high-risk hematology patients, baseline CT is becoming a standard-of-care. Chest X-ray, while inferior, is still widely used. Randomized, controlled trials are needed to investigate the impact of BCT on patient outcome
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