35,564 research outputs found
An Equivalent Circuit Model for Predicting the Core Loss in a Claw-Pole Permanent Magnet Motor with Soft Magnetic Composite Core
© 1965-2012 IEEE. Soft magnetic composite (SMC) materials and SMC electromagnetic devices have attracted strong research interest in the past decades. However, SMC devices have large core loss that needs to be put into consideration even at the design stage. Effective and accurate prediction of the core loss becomes crucial for the design and optimization of high-performance motors with these materials. Equivalent circuit model is a widely used method for machine analysis, due to the advantages in the fast calculation with a clear physical mechanism. This paper presents an equivalent circuit model to predict the core loss of a claw-pole permanent magnet motor with SMC stator core. All the parameters including the equivalent core-loss resistance in the equivalent circuit model are identified based on the finite-element method to achieve high accuracy, and the effectiveness of the parameters identification methods is experimentally verified. The proposed equivalent circuit model can predict the core loss and motor's performance efficiently both under no-load and loading conditions
Super-resolution, Extremal Functions and the Condition Number of Vandermonde Matrices
Super-resolution is a fundamental task in imaging, where the goal is to
extract fine-grained structure from coarse-grained measurements. Here we are
interested in a popular mathematical abstraction of this problem that has been
widely studied in the statistics, signal processing and machine learning
communities. We exactly resolve the threshold at which noisy super-resolution
is possible. In particular, we establish a sharp phase transition for the
relationship between the cutoff frequency () and the separation ().
If , our estimator converges to the true values at an inverse
polynomial rate in terms of the magnitude of the noise. And when no estimator can distinguish between a particular pair of
-separated signals even if the magnitude of the noise is exponentially
small.
Our results involve making novel connections between {\em extremal functions}
and the spectral properties of Vandermonde matrices. We establish a sharp phase
transition for their condition number which in turn allows us to give the first
noise tolerance bounds for the matrix pencil method. Moreover we show that our
methods can be interpreted as giving preconditioners for Vandermonde matrices,
and we use this observation to design faster algorithms for super-resolution.
We believe that these ideas may have other applications in designing faster
algorithms for other basic tasks in signal processing.Comment: 19 page
Norovirus Infection and Disease in an Ecuadorian Birth Cohort: Association of Certain Norovirus Genotypes With Host FUT2 Secretor Status.
BACKGROUND: Although norovirus is the most common cause of gastroenteritis, there are few data on the community incidence of infection/disease or the patterns of acquired immunity or innate resistance to norovirus. METHODS: We followed a community-based birth cohort of 194 children in Ecuador with the aim to estimate (1) the incidence of norovirus gastroenteritis from birth to age 3 years, (2) the protective effect of norovirus infection against subsequent infection/disease, and (3) the association of infection and disease with FUT2 secretor status. RESULTS: Over the 3-year period, we detected a mean of 2.26 diarrheal episodes per child (range, 0-12 episodes). Norovirus was detected in 260 samples (18%) but was not found more frequently in diarrheal samples (79 of 438 [18%]), compared with diarrhea-free samples (181 of 1016 [18%]; P = .919). A total of 66% of children had at least 1 norovirus infection during the first 3 years of life, and 40% of children had 2 infections. Previous norovirus infections were not associated with the risk of subsequent infection. All genogroup II, genotype 4 (GII.4) infections were among secretor-positive children (P < .001), but higher rates of non-GII.4 infections were found in secretor-negative children (relative risk, 0.56; P = .029). CONCLUSIONS: GII.4 infections were uniquely detected in secretor-positive children, while non-GII.4 infections were more often found in secretor-negative children
Inert gas clearance from tissue by co-currently and counter-currently arranged microvessels
To elucidate the clearance of dissolved inert gas from tissues, we have developed numerical models of gas transport in a cylindrical block of tissue supplied by one or two capillaries. With two capillaries, attention is given to the effects of co-current and counter-current flow on tissue gas clearance. Clearance by counter-current flow is compared with clearance by a single capillary or by two co-currently arranged capillaries. Effects of the blood velocity, solubility, and diffusivity of the gas in the tissue are investigated using parameters with physiological values. It is found that under the conditions investigated, almost identical clearances are achieved by a single capillary as by a co-current pair when the total flow per tissue volume in each unit is the same (i.e., flow velocity in the single capillary is twice that in each co-current vessel). For both co-current and counter-current arrangements, approximate linear relations exist between the tissue gas clearance rate and tissue blood perfusion rate. However, the counter-current arrangement of capillaries results in less-efficient clearance of the inert gas from tissues. Furthermore, this difference in efficiency increases at higher blood flow rates. At a given blood flow, the simple conduction-capacitance model, which has been used to estimate tissue blood perfusion rate from inert gas clearance, underestimates gas clearance rates predicted by the numerical models for single vessel or for two vessels with co-current flow. This difference is accounted for in discussion, which also considers the choice of parameters and possible effects of microvascular architecture on the interpretation of tissue inert gas clearance
Collider Phenomenology with Split-UED
We investigate the collider implications of Split Universal Extra Dimensions.
The non-vanishing fermion mass in the bulk, which is consistent with the
KK-parity, largely modifies the phenomenology of Minimal Universal Exta
Dimensions. We scrutinize the behavior of couplings and study the discovery
reach of the Tevatron and the LHC for level-2 Kaluza-Klein modes in the
dilepton channel, which would indicates the presence of the extra dimensions.
Observation of large event rates for dilepton resonances can result from a
nontrivial fermion mass profile along the extra dimensions, which, in turn, may
corroborate extra dimensional explanation for the observation of the positron
excess in cosmic rays.Comment: 23 pages, 15 figure
Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature
We calculate the heavy quarkonium energy levels and decay widths in a
quark-gluon plasma, whose temperature T and screening mass m_D satisfy the
hierarchy m alpha_s >> T >> m alpha_s^2 >> m_D (m being the heavy-quark mass),
at order m alpha_s^5. We first sequentially integrate out the scales m, m
alpha_s and T, and, next, we carry out the calculations in the resulting
effective theory using techniques of integration by regions. A collinear region
is identified, which contributes at this order. We also discuss the
implications of our results concerning heavy quarkonium suppression in heavy
ion collisions.Comment: 25 pages, 2 figure
On the Theory of Evolution Versus the Concept of Evolution: Three Observations
Here we address three misconceptions stated by Rice et al. in their observations of our article Paz-y-Miño and Espinosa (Evo Edu Outreach 2:655–675, 2009), published in this journal. The five authors titled their note “The Theory of Evolution is Not an Explanation for the Origin of Life.” First, we argue that it is fallacious to believe that because the formulation of the theory of evolution, as conceived in the 1800s, did not include an explanation for the origin of life, nor of the universe, the concept of evolution would not allow us to hypothesize the possible beginnings of life and its connections to the cosmos. Not only Stanley Miller’s experiments of 1953 led scientists to envision a continuum from the inorganic world to the origin and diversification of life, but also Darwin’s own writings of 1871. Second, to dismiss the notion of Rice et al. that evolution does not provide explanations concerning the universe or the cosmos, we identify compelling scientific discussions on the topics: Zaikowski et al. (Evo Edu Outreach 1:65–73, 2008), Krauss (Evo Edu Outreach 3:193–197, 2010), Peretó et al. (Orig Life Evol Biosph 39:395–406, 2009) and Follmann and Brownson (Naturwissenschaften 96:1265–1292, 2009). Third, although we acknowledge that the term Darwinism may not be inclusive of all new discoveries in evolution, and also that creationists and Intelligent Designers hijack the term to portray evolution as ideology, we demonstrate that there is no statistical evidence suggesting that the word Darwinism interferes with public acceptance of evolution, nor does the inclusion of the origin of life or the universe within the concept of evolution. We examine the epistemological and empirical distinction between the theory of evolution and the concept of evolution and conclude that, although the distinction is important, it should not compromise scientific logic
Ultracompact quantum splitter of degenerate photon pairs
Integrated sources of indistinguishable photons have attracted a lot of
attention because of their applications in quantum communication and optical
quantum computing. Here, we demonstrate an ultra-compact quantum splitter for
degenerate single photons based on a monolithic chip incorporating Sagnac loop
and a micro-ring resonator with a footprint of 0.011 mm2, generating and
deterministically splitting indistinguishable photon pairs using time-reversed
Hong-Ou-Mandel interference. The ring resonator provides enhanced photon
generation rate, and the Sagnac loop ensures the photons travel through equal
path lengths and interfere with the correct phase to enable the reversed HOM
effect to take place. In the experiment, we observed a HOM dip visibility of
94.5 +- 3.3 %, indicating the photons generated by the degenerate single photon
source are in a suitable state for further integration with other components
for quantum applications, such as controlled-NOT gates
3D flow in the venom channel of a spitting cobra: do the ridges in the fangs act as fluid guide vanes?
The spitting cobra Naja pallida can eject its venom towards an offender from a distance of up to two meters. The aim of this study was to understand the mechanisms responsible for the relatively large distance covered by the venom jet although the venom channel is only of micro-scale. Therefore, we analysed factors that influence secondary flow and pressure drop in the venom channel, which include the physical-chemical properties of venom liquid and the morphology of the venom channel. The cobra venom showed shear-reducing properties and the venom channel had paired ridges that span from the last third of the channel to its distal end, terminating laterally and in close proximity to the discharge orifice. To analyze the functional significance of these ridges we generated a numerical and an experimental model of the venom channel. Computational fluid dynamics (CFD) and Particle-Image Velocimetry (PIV) revealed that the paired interior ridges shape the flow structure upstream of the sharp 90° bend at the distal end. The occurrence of secondary flow structures resembling Dean-type vortical structures in the venom channel can be observed, which induce additional pressure loss. Comparing a venom channel featuring ridges with an identical channel featuring no ridges, one can observe a reduction of pressure loss of about 30%. Therefore it is concluded that the function of the ridges is similar to guide vanes used by engineers to reduce pressure loss in curved flow channels
Effects of experimental Neisseria meningitis W135 infection on serotoninergic parameters in mice
This study investigated the effects of Neisseria menigitidis W135 infection via intraperitoneal route on plasma free tryptophan concentration, brain serotonin and 5-hydroxyindole acetic acid (5-HIAA) levels in albino mice fed normal and tryptophan-enriched diets. The kinetics of appearance of viable bacteria in the blood, brain and liver following infection were also investigated. The serotoninergic parameters were determined by colorimetric and HPLC methods while colony counts were measured by plate count technique. Compared to normal diet, the tryptophan-enriched diet resulted in significantly (
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