160 research outputs found
A description of the ratio between electric and magnetic proton form factors by using space-like, time-like data and dispersion relations
We use the available information on the ratio between the electric and
magnetic proton form factors coming from recently published space-like data and
from the few available time-like data. We apply a dispersive procedure on these
data to evaluate the behaviour of this ratio, as a complex function, for all
values of q^2.Comment: 12 pages, 7 Encapsulated Postscript figures, uses epsfig, rotating,
exscale, amsmath, cite, latexsym, graphics, color packages, added reference
Comparative performances of machine learning methods for classifying Crohn Disease patients using genome-wide genotyping data
© 2019, The Author(s). Crohn Disease (CD) is a complex genetic disorder for which more than 140 genes have been identified using genome wide association studies (GWAS). However, the genetic architecture of the trait remains largely unknown. The recent development of machine learning (ML) approaches incited us to apply them to classify healthy and diseased people according to their genomic information. The Immunochip dataset containing 18,227 CD patients and 34,050 healthy controls enrolled and genotyped by the international Inflammatory Bowel Disease genetic consortium (IIBDGC) has been re-analyzed using a set of ML methods: penalized logistic regression (LR), gradient boosted trees (GBT) and artificial neural networks (NN). The main score used to compare the methods was the Area Under the ROC Curve (AUC) statistics. The impact of quality control (QC), imputing and coding methods on LR results showed that QC methods and imputation of missing genotypes may artificially increase the scores. At the opposite, neither the patient/control ratio nor marker preselection or coding strategies significantly affected the results. LR methods, including Lasso, Ridge and ElasticNet provided similar results with a maximum AUC of 0.80. GBT methods like XGBoost, LightGBM and CatBoost, together with dense NN with one or more hidden layers, provided similar AUC values, suggesting limited epistatic effects in the genetic architecture of the trait. ML methods detected near all the genetic variants previously identified by GWAS among the best predictors plus additional predictors with lower effects. The robustness and complementarity of the different methods are also studied. Compared to LR, non-linear models such as GBT or NN may provide robust complementary approaches to identify and classify genetic markers
Time domain deBroglie wave interferometry along a magnetic guide
Time domain deBroglie wave interferometry [Cahn et al, Phys. Rev. Lett. 79,
784] is applied to Rb87 atoms in a magnetic guide. A standing wave light field
is carefully aligned along the guiding direction of the magnetic trapping
potential from a soft-ferromagnetic 4-foil structure. A sequence of two
standing wave pulses is applied to the magnetically trapped atoms. The
backscattered light at the atomic density grating revival time is collected and
detected via a heterodyning technique. In addition to the observed recoil
oscillations that fit the interferometer theory for atoms in free space, we
observe a decay of the interferometer contrast on a millisecond time scale with
unexpected millisecond-scale oscillations. We find that the oscillating decay
is explained by a residual variation of the linear trapping potential along the
standing wave direction.Comment: 22 pages, 7 figure
Fast matrix computations for pair-wise and column-wise commute times and Katz scores
We first explore methods for approximating the commute time and Katz score
between a pair of nodes. These methods are based on the approach of matrices,
moments, and quadrature developed in the numerical linear algebra community.
They rely on the Lanczos process and provide upper and lower bounds on an
estimate of the pair-wise scores. We also explore methods to approximate the
commute times and Katz scores from a node to all other nodes in the graph.
Here, our approach for the commute times is based on a variation of the
conjugate gradient algorithm, and it provides an estimate of all the diagonals
of the inverse of a matrix. Our technique for the Katz scores is based on
exploiting an empirical localization property of the Katz matrix. We adopt
algorithms used for personalized PageRank computing to these Katz scores and
theoretically show that this approach is convergent. We evaluate these methods
on 17 real world graphs ranging in size from 1000 to 1,000,000 nodes. Our
results show that our pair-wise commute time method and column-wise Katz
algorithm both have attractive theoretical properties and empirical
performance.Comment: 35 pages, journal version of
http://dx.doi.org/10.1007/978-3-642-18009-5_13 which has been submitted for
publication. Please see
http://www.cs.purdue.edu/homes/dgleich/publications/2011/codes/fast-katz/ for
supplemental code
Coherence length of an elongated condensate: a study by matter-wave interferometry
We measure the spatial correlation function of Bose-Einstein condensates in
the cross-over region between phase-coherent and strongly phase-fluctuating
condensates. We observe the continuous path from a gaussian-like shape to an
exponential-like shape characteristic of one-dimensional phase-fluctuations.
The width of the spatial correlation function as a function of the temperature
shows that the condensate coherence length undergoes no sharp transition
between these two regimes.Comment: 8 pages, 6 figure, submitted to EPJ
Eikonal representation in the momentum-transfer space
By means of empirical fits to the differential cross section data on pp and
p(bar)p elastic scattering, above 10 GeV (center-of-mass energy), we determine
the eikonal in the momentum - transfer space (q^2- space). We make use of a
numerical method and a novel semi-analytical method, through which the
uncertainties from the fit parameters can be propagated up to the eikonal in
the - space. A systematic study of the effect of the experimental
information at large values of the momentum transfer is developed and discussed
in detail. We present statistical evidence that the imaginary part of the
eikonal changes sign in the q^2- space and that the position of the zero
decreases as the energy increases; after the position of the zero, the eikonal
presents a minimum and then goes to zero through negative values. We discuss
the applicability of our results in the phenomenological context, outlining
some connections with nonperturbative QCD. A short review and a critical
discussion on the main results concerning "model-independent" analyses are also
presented.Comment: 18 pages, 17 figures, 4 tables, svjour.cls. Revised discussion on the
proton's electromagnetic form factor and references added. To appear in Eur.
Phys. J.
Understanding edge-connectivity in the Internet through core-decomposition
Internet is a complex network composed by several networks: the Autonomous
Systems, each one designed to transport information efficiently. Routing
protocols aim to find paths between nodes whenever it is possible (i.e., the
network is not partitioned), or to find paths verifying specific constraints
(e.g., a certain QoS is required). As connectivity is a measure related to both
of them (partitions and selected paths) this work provides a formal lower bound
to it based on core-decomposition, under certain conditions, and low complexity
algorithms to find it. We apply them to analyze maps obtained from the
prominent Internet mapping projects, using the LaNet-vi open-source software
for its visualization
Triangulations and Severi varieties
We consider the problem of constructing triangulations of projective planes
over Hurwitz algebras with minimal numbers of vertices. We observe that the
numbers of faces of each dimension must be equal to the dimensions of certain
representations of the automorphism groups of the corresponding Severi
varieties. We construct a complex involving these representations, which should
be considered as a geometric version of the (putative) triangulations
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Comprehensive testing of NedWind 12-meter wind turbine blades at NREL
This paper describes the structural testing of two NedWind 25, 12-m blades at the National Renewable Energy Laboratory (NREL). The tests were conducted under the Standards, Measurement and Testing (SMT) Program in conjunction with tests conducted by four European laboratories to develop a common database of blade testing methods. All of the laboratories tested duplicate copies of blades taken from series production. Blade properties, including weight, center of gravity, natural frequencies, and damping were determined. Static load tests were performed at 110% of the extreme design load for strain verification. NREL performed single-axis and two-axis fatigue tests using business-as-usual testing practices. The single-axis test combined equivalent life loading for the edge and flap spectra into a single resultant load. The two-axis test applied the edge and flap components independently at a phase angle of 90°. Damage areas were observed at (1) the trailing edge, which cracked near the maximum chord; (2) between the steel root collar and the composite, where circumferential cracking was noted; and (3) along the top of the spar between the 2500-mm and 4200-mm stations, where a notable increase in acoustic emissions was detected. NREL observed that the onset of visible damage occurred earlier in the single-axis test
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