310 research outputs found
A New Methodology for the Selective Measurement of building Performance and Safety
This paper evaluates the present evidence of smoke spread due to problems in compartmentation and also reviews different test methods which can be employed to identify these problems during construction stages. Since 2010, evidence has emerged that the rapid spread of smoke occurs in and between UK buildings, including where accredited construction details and/or robust details are specified [1, 2]. It is considered that this rapid smoke spread could be due to incorrect installation, missing, inappropriate or defective components, that make up compartmentation and fire stopping within concealed spaces [1, 2, 3]. These defects can compromise the ability of compartmentation to resist fire and smoke spread between dwellings and also into any means of escape. The impact of the defects could ultimately be detrimental to occupant safety, care staff with the occupants and also fire fighters, in the event of a real fire. In 2016, fire risk assessments undertaken in buildings before occupancy (that ascertain the performance of the building with respect to fire and smoke spread in accordance with Approved Document B) of the UK Building Regulations are based upon a visual review of building design details and documentation, and also visual inspection of as-built details. However, this approach is inadequate to identify defects in the components that make up compartmentation and fire stopping details in concealed spaces [3] since, it is impossible to determine with the naked eye whether these details have been installed as designed. Littlewood and Smallwood [1, 2] have identified an urgent need to investigate the extent of these smoke spread problems within new dwellings being constructed in the UK and also the development for an appropriate compliance test which can identify issues in fire compartmentation and fire stopping and used before buildings are occupied - such as the in-construction testing (iCT) process. The paper also reviews different tests that can be employed as part of iCT methodology to identify the potential defects in fire compartmentation, and fire stops such as cavity barriers in buildings
A Geometric Approach to Modeling Microstructurally Small Fatigue Crack Formation
The objective of this paper is to develop further a framework for computationally modeling microstructurally small fatigue crack growth in AA 7075-T651 [1]. The focus is on the nucleation event, when a crack extends from within a second-phase particle into a surrounding grain, since this has been observed to be an initiating mechanism for fatigue crack growth in this alloy. It is hypothesized that nucleation can be predicted by computing a non-local nucleation metric near the crack front. The hypothesis is tested by employing a combination of experimentation and nite element modeling in which various slip-based and energy-based nucleation metrics are tested for validity, where each metric is derived from a continuum crystal plasticity formulation. To investigate each metric, a non-local procedure is developed for the calculation of nucleation metrics in the neighborhood of a crack front. Initially, an idealized baseline model consisting of a single grain containing a semi-ellipsoidal surface particle is studied to investigate the dependence of each nucleation metric on lattice orientation, number of load cycles, and non-local regularization method. This is followed by a comparison of experimental observations and computational results for microstructural models constructed by replicating the observed microstructural geometry near second-phase particles in fatigue specimens. It is found that orientation strongly influences the direction of slip localization and, as a result, in uences the nucleation mechanism. Also, the baseline models, replication models, and past experimental observation consistently suggest that a set of particular grain orientations is most likely to nucleate fatigue cracks. It is found that a continuum crystal plasticity model and a non-local nucleation metric can be used to predict the nucleation event in AA 7075-T651. However, nucleation metric threshold values that correspond to various nucleation governing mechanisms must be calibrated
Neutron scattering in a d_{x^2-y^2}-wave superconductor with strong impurity scattering and Coulomb correlations
We calculate the spin susceptibility at and below T_c for a d_{x^2-y^2}-wave
superconductor with resonant impurity scattering and Coulomb correlations. Both
the impurity scattering and the Coulomb correlations act to maintain peaks in
the spin susceptibility, as a function of momentum, at the Brillouin zone edge.
These peaks would otherwise be suppressed by the superconducting gap. The
predicted amount of suppression of the spin susceptibility in the
superconducting state compared to the normal state is in qualitative agreement
with results from recent magnetic neutron scattering experiments on
La_{1.86}Sr_{0.14}CuO_4 for momentum values at the zone edge and along the zone
diagonal. The predicted peak widths in the superconducting state, however, are
narrower than those in the normal state, a narrowing which has not been
observed experimentally.Comment: 24 pages (12 tarred-compressed-uuencoded Postscript figures), REVTeX
3.0 with epsf macros, UCSBTH-94-1
Quantum Pair Creation of Soliton Domain Walls
A large body of experimental evidence suggests that the decay of the false
vacuum, accompanied by quantum pair creation of soliton domain walls, can occur
in a variety of condensed matter systems. Examples include nucleation of charge
soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett.
84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently,
Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass
of the soliton should be interpreted as a line density and a surface density,
respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair
production rate. As the transverse dimensions are increased and the total mass
(energy) becomes large, thermal activation becomes suppressed, so quantum
processes can dominate even at relatively high temperatures. This paper will
discuss both experimental evidence and theoretical arguments for the existence
of high-temperature collective quantum phenomena
Transformation of spin information into large electrical signals via carbon nanotubes
Spin electronics (spintronics) exploits the magnetic nature of the electron,
and is commercially exploited in the spin valves of disc-drive read heads.
There is currently widespread interest in using industrially relevant
semiconductors in new types of spintronic devices based on the manipulation of
spins injected into a semiconducting channel between a spin-polarized source
and drain. However, the transformation of spin information into large
electrical signals is limited by spin relaxation such that the magnetoresistive
signals are below 1%. We overcome this long standing problem in spintronics by
demonstrating large magnetoresistance effects of 61% at 5 K in devices where
the non-magnetic channel is a multiwall carbon nanotube that spans a 1.5 micron
gap between epitaxial electrodes of the highly spin polarized manganite
La0.7Sr0.3MnO3. This improvement arises because the spin lifetime in nanotubes
is long due the small spin-orbit coupling of carbon, because the high nanotube
Fermi velocity permits the carrier dwell time to not significantly exceed this
spin lifetime, because the manganite remains highly spin polarized up to the
manganite-nanotube interface, and because the interfacial barrier is of an
appropriate height. We support these latter statements regarding the interface
using density functional theory calculations. The success of our experiments
with such chemically and geometrically different materials should inspire
adventure in materials selection for some future spintronicsComment: Content highly modified. New title, text, conclusions, figures and
references. New author include
Topological crystalline insulator states in Pb(1-x)Sn(x)Se
Topological insulators are a novel class of quantum materials in which
time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band
structure result in electronic metallic states on the surfaces of bulk
crystals. These helical states exhibit a Dirac-like energy dispersion across
the bulk bandgap, and they are topologically protected. Recent theoretical
proposals have suggested the existence of topological crystalline insulators, a
novel class of topological insulators in which crystalline symmetry replaces
the role of time-reversal symmetry in topological protection [1,2]. In this
study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a
topological crystalline insulator for x=0.23. Temperature-dependent
magnetotransport measurements and angle-resolved photoelectron spectroscopy
demonstrate that the material undergoes a temperature-driven topological phase
transition from a trivial insulator to a topological crystalline insulator.
These experimental findings add a new class to the family of topological
insulators. We expect these results to be the beginning of both a considerable
body of additional research on topological crystalline insulators as well as
detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and
supplementary information (5 pages, 8 figures
Darbepoetin alfa for treating chemotherapy-induced anemia in patients with a baseline hemoglobin level < 10 g/dL versus ≥10 g/dL: an exploratory analysis from a randomized, double-blind, active-controlled trial
<p>Abstract</p> <p>Background</p> <p>Several studies have shown that darbepoetin alfa, an erythropoiesis-stimulating agent (ESA), can reduce transfusions and increase hemoglobin (Hb) levels in patients with chemotherapy-induced anemia (CIA). Recent safety concerns, however, have prompted changes to ESA product information. In the European Union and United States, ESA therapy initiation for CIA is now recommended at a Hb level ≤10 g/dL. The present exploratory analysis examined how ESA initiation at this Hb level may impact patient care.</p> <p>Methods</p> <p>Data from a phase 3 randomized trial were retrospectively reanalyzed. CIA patients with nonmyeloid malignancies were randomized 1:1 to 500 mcg darbepoetin alfa every three weeks (Q3W) or 2.25 mcg/kg darbepoetin alfa weekly (QW) for 15 weeks. A previously published report from this trial showed Q3W dosing was non-inferior to QW dosing for reducing transfusions from week 5 to end-of-the-treatment period (EOTP). In the present analysis, outcomes were reanalyzed by baseline Hb <10 g/dL and ≥10 g/dL. Endpoints included transfusion rates, Hb outcomes, and safety profiles.</p> <p>Results</p> <p>This study reanalyzed 351 and 354 patients who initiated ESA therapy at a baseline Hb of <10 g/dL or ≥10 g/dL, respectively. From week 5 to EOTP, the estimated Kaplan-Meier transfusion incidence (Q3W vs QW) was lower in the ≥10 g/dL baseline-Hb group (14% vs 21%) compared with the <10 g/dL baseline-Hb group (36% vs 41%). By week 5, the ≥10 g/dL baseline-Hb group, but not the <10 g/dL baseline-Hb group, achieved a mean Hb ≥11 g/dL. The Kaplan-Meier estimate of percentage of patients (Q3W vs QW) who achieved Hb ≥11 g/dL from week 1 to EOTP was 90% vs 85% in the ≥10 g/dL baseline-Hb group and 54% vs 57% in the <10 g/dL baseline-Hb group. Both baseline-Hb groups maintained mean Hb levels <12 g/dL and had similar safety profiles, though more patients in the ≥10 g/dL baseline-Hb group reached the threshold Hb of ≥13 g/dL.</p> <p>Conclusion</p> <p>In this exploratory analysis, darbepoetin alfa Q3W and QW raised Hb levels and maintained mean Hb at <12 g/dL in both baseline-Hb groups. The ≥10 g/dL baseline-Hb group had fewer transfusions and faster anemia correction. Additional studies should prospectively evaluate the relationship between Hb levels at ESA initiation and outcomes.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov Identifier NCT00118638.</p
Experimental realization of a topological crystalline insulator in SnTe
Topological insulators materialize a topological quantum state of matter
where unusual gapless metallic state protected by time-reversal symmetry
appears at the edge or surface. Their discovery stimulated the search for new
topological states protected by other symmetries, and a recent theory predicted
the existence of "topological crystalline insulators" (TCIs) in which the
metallic surface states are protected by mirror symmetry of the crystal.
However, its experimental verification has not yet been reported. Here we show
the first and definitive experimental evidence for the TCI phase in tin
telluride (SnTe) which was recently predicted to be a TCI. Our angle-resolved
photoemission spectroscopy shows clear signature of a metallic Dirac-cone
surface band with its Dirac point slightly away from the edge of the surface
Brillouin zone in SnTe. On the other hand, such a gapless surface state is
absent in a cousin material lead telluride (PbTe), in line with the theoretical
prediction. Our result establishes the presence of a TCI phase, and opens new
avenues for exotic topological phenomena.Comment: 11 pages, 3 figure
Microbiological profiles of sputum and gastric juice aspirates in Cystic Fibrosis patients.
Gastro-Oesophageal Reflux (GOR) is a key problem in Cystic Fibrosis (CF), but the relationship between lung and gastric microbiomes is not well understood. We hypothesised that CF gastric and lung microbiomes are related. Gastric and sputum cultures were obtained from fifteen CF patients receiving percutaneous endoscopic gastrostomy feeding. Non-CF gastric juice data was obtained through endoscopy from 14 patients without lung disease. Bacterial and fungal isolates were identified by culture. Molecular bacterial profiling used next generation sequencing (NGS) of the 16S rRNA gene. Cultures grew bacteria and/or fungi in all CF gastric juice and sputa and in 9/14 non-CF gastric juices. Pseudomonas aeruginosa(Pa) was present in CF sputum in 11 patients, 4 had identical Pa strains in the stomach. NGS data from non-CF gastric juice samples were significantly more diverse compared to CF samples. NGS showed CF gastric juice had markedly lower abundance of normal gut bacteria; Bacteroides and Faecalibacterium, but increased Pseudomonas compared with non-CF. Multivariate partial least squares discriminant analysis demonstrated similar bacterial profiles of CF sputum and gastric juice samples, which were distinct from non-CF gastric juice. We provide novel evidence suggesting the existence of an aerodigestive microbiome in CF, which may have clinical relevance
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