287 research outputs found
Stability of 1-D Excitons in Carbon Nanotubes under High Laser Excitations
Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide
continuum probe, we show that interband exciton peaks in single-walled carbon
nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates
of the initial densities of excitons from the excitation conditions, combined
with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest
that their positions do not change at all even near the Mott density. In
addition, we found that the presence of lowest-subband excitons broadens all
absorption peaks, including those in the second-subband range, which provides a
consistent explanation for the complex spectral dependence of pump-probe
signals reported for SWNTs.Comment: 4 pages, 4 figure
Production of the Superconducting Matching Quadrupoles for the LHC Insertions
The LHC insertions are equipped with individually powered superconducting quadrupole assemblies comprising several quadrupole magnets and orbit correctors, and range in length from 5.3Â m to 11.3Â m. Following the initial experience in the assembly of the pre-series cold masses, the production has advanced well and about half of the total of 82 units has been produced at CERN. In this paper we present the experience gained in steering the cold mass production, in particular with respect to the alignment requirements. We also report on the field quality and other measurements made for assuring the quality of the quadrupoles
The Construction of the Superconducting Matching Quadrupoles for the LHC Insertions
After several years of effort, the construction of the superconducting matching quadrupoles for the LHC insertions is nearing completion. We retrace the main events of the project from the initial development of the quadrupole magnets of several types to the series production of over 100 complex superconducting magnets, and report on the techniques developed for steering of the production. The main performance parameters for the full series, such as quench training, field quality and magnet geometry are presented. The experience gained in the production of these special superconducting magnets is of considerable value for further development of the LHC insertions
Design Study of a Superconducting Insertion Quadrupole Magnet for the Large Hadron Collider
The conceptual design study of a high gradient super conducting insertion quadrupole magnet has been carried out in collaboration between KEK and CERN for the Large Hadron Collider (LHC) to be built at CERN. A model magnet design has been optimized to provide a nominal design field gradient of 240 T/m with a bore aperture of 70 mm and an operational field gradient of 225 T/m at 1.9 K under radiation environment with a beam energy deposit of several watts per meter in the superconducting coils. The design and its optimization process are discussed
Common data elements to standardize genomics studies in cerebral palsy
Aim
To define clinical common data elements (CDEs) and a mandatory minimum data set (MDS) for genomic studies of cerebral palsy (CP).
Method
Candidate data elements were collated following a review of the literature and existing CDEs. An online, three-round Delphi survey was used to rate each data element as either ‘core’, ‘recommended’, ‘exploratory’, or ‘not required’. Members of the International Cerebral Palsy Genomics Consortium (ICPGC) rated the core CDEs as either mandatory or not, to form the MDS. For both the CDEs and the MDS, a data element was considered to have reached consensus if more than 75% of respondents agreed.
Results
Forty-six individuals from around the world formed the Delphi panel: consumers (n=2), scientists/researchers (n=17), medical (n=19), and allied health professionals (n=8). The CDEs include 107 data elements across six categories: demographics, diagnostics, family history, antenatal and neonatal details, clinical traits, and CP-specific assessments. Of these, 10 are mandatory, 42 core, 41 recommended, and 14 are exploratory.
Interpretation
The ICPGC CDEs provide a foundation for the standardization of phenotype data captured in CP genomic studies and will benefit international collaborations and pooling of data, particularly in rare conditions
Sensitivity of the stress response function to packing preparation
A granular assembly composed of a collection of identical grains may pack
under different microscopic configurations with microscopic features that are
sensitive to the preparation history. A given configuration may also change in
response to external actions such as compression, shearing etc. We show using a
mechanical response function method developed experimentally and numerically,
that the macroscopic stress profiles are strongly dependent on these
preparation procedures. These results were obtained for both two and three
dimensions. The method reveals that, under a given preparation history, the
macroscopic symmetries of the granular material is affected and in most cases
significant departures from isotropy should be observed. This suggests a new
path toward a non-intrusive test of granular material constitutive properties.Comment: 15 pages, 11 figures, some numerical data corrected, to appear in J.
Phys. Cond. Mat. special issue on Granular Materials (M. Nicodemi Editor
Response of a Hexagonal Granular Packing under a Localized External Force: Exact Results
We study the response of a two-dimensional hexagonal packing of massless,
rigid, frictionless spherical grains due to a vertically downward point force
on a single grain at the top layer. We use a statistical approach, where each
mechanically stable configuration of contact forces is equally likely. We show
that this problem is equivalent to a correlated -model. We find that the
response is double-peaked, where the two peaks, sharp and single-grain diameter
wide, lie on the two downward lattice directions emanating from the point of
the application of the external force. For systems of finite size, the
magnitude of these peaks decreases towards the bottom of the packing, while
progressively a broader, central maximum appears between the peaks. The
response behaviour displays a remarkable scaling behaviour with system size
: while the response in the bulk of the packing scales as , on
the boundary it is independent of , so that in the thermodynamic limit only
the peaks on the lattice directions persist. This qualitative behaviour is
extremely robust, as demonstrated by our simulation results with different
boundary conditions. We have obtained expressions of the response and higher
correlations for any system size in terms of integers corresponding to an
underlying discrete structure.Comment: Accepted for publication in JStat; 33 pages, 10 figures; Section 2.2
reorganized and rewritten; Details about the simulation procedure added in
Sec.3.1. ; A new section, summarizing the final results and the calculation
procedure adde
Mechanical Design and Characteristics of a Superconducting Insertion Quadrupole Model Magnet for the Large Hadron Collider
A superconducting insertion quadruple is being developed by KEK in collaboration with CERN for the Large Hadron Collider (LHC) project. The mechanical design of the magnet in which the pre-stress is applied to the coil through thin stainless steel collars inside the yoke, the two halves of which are held together by means of keys, has been validated experimentally by measurements on a short model. The 140 mm long model was assembled from real magnet components in order to simulate the magnet assembly and to evaluate the change in coil pre-stress during assembly and cool-down. A new technique using capacitance pressure transducers was used, which has enabled measurements of the stress distributions in the coil with high accuracy. This paper describes the mechanical design of the quadrupole magnet and results obtained from the short mechanical model
Development and Test Results of a low- Quadrupole Model for the Large Hadron Collider
A 1-m model of the high gradient 70 mm aperture superconducting low-b quadrupoles for the Large Hadron Collider (LHC) has been developed. A field gradient of 250 T/m at 1.9 K has been achieved with a peak field of 10 T in the coil. This paper describes development of the first model magnet and presents the test results
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