4,922 research outputs found
Exploring explicit coarse-grained structure in artificial neural networks
We propose to employ the hierarchical coarse-grained structure in the
artificial neural networks explicitly to improve the interpretability without
degrading performance. The idea has been applied in two situations. One is a
neural network called TaylorNet, which aims to approximate the general mapping
from input data to output result in terms of Taylor series directly, without
resorting to any magic nonlinear activations. The other is a new setup for data
distillation, which can perform multi-level abstraction of the input dataset
and generate new data that possesses the relevant features of the original
dataset and can be used as references for classification. In both cases, the
coarse-grained structure plays an important role in simplifying the network and
improving both the interpretability and efficiency. The validity has been
demonstrated on MNIST and CIFAR-10 datasets. Further improvement and some open
questions related are also discussed
Exclusive decays in the general two-Higgs-doublet models
By employing the QCD factorization approach, we calculated the
next-to-leading order new physics contributions to the branching ratios, CP
asymmetries, isospin and U-spin symmetry breaking of the exclusive decays (), induced by the charged Higgs penguins in the
general two-Higgs-doublet models. Within the considered parameter space, we
found that (a) the new physics corrections to the observables are generally
small in the model I and model III-A, moderate in model II, but large in model
III-B; (b) from the well measured branching ratios and upper limits, a lower
bound of \mhp > 200 GeV in model II was obtained, while the allowed range of
\mhp in model III-B is 226 \leq \mhp \leq 293 GeV; these bounds are
comparable with those from the inclusive decay; (c)the NLO
Wilson coefficient in model III-B is positive and disfavered by the
measured value of isospin symmetry breaking , but still can not be excluded if we take the large errors into
account; (d) the CP asymmetry \acp(B \to \rho \gamma) in model III-B has an
opposite sign with the one in the standard model (SM), which may be used as a
good observable to distinguish the SM from model III-B; (e) the isospin
symmetry breaking is less than 10% in the region of
preferred by the global fit result, but can be
as large as 20 to 40% in the regions of and . The SM and model III-B predictions for are
opposite in sign for small or large values of the CKM angles; (f) the U-spin
symmetry breaking in the SM and the general
two-Higgs-doublet models is generally small in size: .Comment: Revtex, 38 pages with 14 eps figures, minor correction
A single sub-km Kuiper Belt object from a stellar Occultation in archival data
The Kuiper belt is a remnant of the primordial Solar System. Measurements of
its size distribution constrain its accretion and collisional history, and the
importance of material strength of Kuiper belt objects (KBOs). Small, sub-km
sized, KBOs elude direct detection, but the signature of their occultations of
background stars should be detectable. Observations at both optical and X-ray
wavelengths claim to have detected such occultations, but their implied KBO
abundances are inconsistent with each other and far exceed theoretical
expectations. Here, we report an analysis of archival data that reveals an
occultation by a body with a 500 m radius at a distance of 45 AU. The
probability of this event to occur due to random statistical fluctuations
within our data set is about 2%. Our survey yields a surface density of KBOs
with radii larger than 250 m of 2.1^{+4.8}_{-1.7} x 10^7 deg^{-2}, ruling out
inferred surface densities from previous claimed detections by more than 5
sigma. The fact that we detected only one event, firmly shows a deficit of
sub-km sized KBOs compared to a population extrapolated from objects with r>50
km. This implies that sub-km sized KBOs are undergoing collisional erosion,
just like debris disks observed around other stars.Comment: To appear in Nature on December 17, 2009. Under press embargo until
1800 hours London time on 16 December. 19 pages; 7 figure
Solving Nonlinear Parabolic Equations by a Strongly Implicit Finite-Difference Scheme
We discuss the numerical solution of nonlinear parabolic partial differential
equations, exhibiting finite speed of propagation, via a strongly implicit
finite-difference scheme with formal truncation error . Our application of interest is the spreading of
viscous gravity currents in the study of which these type of differential
equations arise. Viscous gravity currents are low Reynolds number (viscous
forces dominate inertial forces) flow phenomena in which a dense, viscous fluid
displaces a lighter (usually immiscible) fluid. The fluids may be confined by
the sidewalls of a channel or propagate in an unconfined two-dimensional (or
axisymmetric three-dimensional) geometry. Under the lubrication approximation,
the mathematical description of the spreading of these fluids reduces to
solving the so-called thin-film equation for the current's shape . To
solve such nonlinear parabolic equations we propose a finite-difference scheme
based on the Crank--Nicolson idea. We implement the scheme for problems
involving a single spatial coordinate (i.e., two-dimensional, axisymmetric or
spherically-symmetric three-dimensional currents) on an equispaced but
staggered grid. We benchmark the scheme against analytical solutions and
highlight its strong numerical stability by specifically considering the
spreading of non-Newtonian power-law fluids in a variable-width confined
channel-like geometry (a "Hele-Shaw cell") subject to a given mass
conservation/balance constraint. We show that this constraint can be
implemented by re-expressing it as nonlinear flux boundary conditions on the
domain's endpoints. Then, we show numerically that the scheme achieves its full
second-order accuracy in space and time. We also highlight through numerical
simulations how the proposed scheme accurately respects the mass
conservation/balance constraint.Comment: 36 pages, 9 figures, Springer book class; v2 includes improvements
and corrections; to appear as a contribution in "Applied Wave Mathematics II
Risk factors for ductal and lobular breast cancer: results from the nurses' health study
Introduction Ductal and lobular carcinomas are the two most common types of invasive breast cancer. Whether well-established risk factors are differentially associated with risk on the basis of histologic subtype is not clear. We prospectively investigated the association between a number of hormonal and nonhormonal exposures and risk defined by histologic subtype among 4,655 ductal and 659 lobular cases of postmenopausal breast cancer from the Nurses\u27 Health Study. Methods Multivariate Cox proportional hazards regression stratified by histologic subtype and time period was used to examine the association between risk factors and the incidence of ductal and lobular subtypes. For each exposure, we calculated the P value for heterogeneity using a likelihood ratio test comparing models with separate estimates for the two subtypes versus a single estimate across subtypes. Results The associations with age at menarche (P-heterogeneity (het) = 0.03), age at first birth (P-het \u3c 0.001) and postmenopausal hormone use (P-het \u3c 0.001) were more strongly associated with lobular cancers. The associations with age, nulliparity, parity, age at menopause, type of menopause, alcohol intake, adult body mass index (BMI), BMI at age 18, family history of breast cancer and personal history of benign breast disease did not vary by subtype (P-het â„ 0.08). Results were similar when we restricted the analyses to estrogen receptor-positive and progesterone receptor-positive tumors. Conclusions These data indicate that breast cancer is a heterogeneous disease, and the differential association with a number of risk factors is suggestive of etiologically distinct tumors. Epidemiological analyses should continue to take into account a modifying role of histology
Effective and Efficient Similarity Index for Link Prediction of Complex Networks
Predictions of missing links of incomplete networks like protein-protein
interaction networks or very likely but not yet existent links in evolutionary
networks like friendship networks in web society can be considered as a
guideline for further experiments or valuable information for web users. In
this paper, we introduce a local path index to estimate the likelihood of the
existence of a link between two nodes. We propose a network model with
controllable density and noise strength in generating links, as well as collect
data of six real networks. Extensive numerical simulations on both modeled
networks and real networks demonstrated the high effectiveness and efficiency
of the local path index compared with two well-known and widely used indices,
the common neighbors and the Katz index. Indeed, the local path index provides
competitively accurate predictions as the Katz index while requires much less
CPU time and memory space, which is therefore a strong candidate for potential
practical applications in data mining of huge-size networks.Comment: 8 pages, 5 figures, 3 table
Observation of reversible critical current performance under large compressive strain in Sr<sub>0.6</sub>K<sub>0.4</sub>Fe<sub>2</sub>As<sub>2</sub> tapes
Iron-based superconductors have caused great interest regarding high-field applications due to their good properties. A common fabrication route for 122-type wires and tapes is the ex situ powder-in-tube (PIT) process. From the point of application in the high magnetic field, where high electromagnetic forces are present, the conductor strength and its tolerance to the mechanical load are important issues. In order to understand the comparatively integrated critical current characterization of the Sr-122 tape under axial strain, the so-called U-spring setup was used to test a silver-sheathed Sr0.6K0.4Fe2As2 tape sample with a single core over a wide range of applied axial strain (-0.6% ⌠0.3%). It was found that when the sample was compressed, the critical current performance showed reversiblity; meanwhile the irreversible tensile strain limit was quite low. The Sr-122/Ag tape shows very good performance under compression, and a possible conductor design should be considered to make the superconductor work at proper compressive strain states for future applications
Cryo-shocked cancer cells for targeted drug delivery and vaccination
Live cells have been vastly engineered into drug delivery vehicles to leverage their targeting capability and cargo release behavior. Here, we describe a simple method to obtain therapeutics-containing âdead cellsâ by shocking live cancer cells in liquid nitrogen to eliminate pathogenicity while preserving their major structure and chemo-taxis toward the lesion site. In an acute myeloid leukemia (AML) mouse model, we demonstrated that the liquid nitrogenâtreated AML cells (LNT cells) can augment targeted delivery of doxorubicin (DOX) toward the bone marrow. Moreover, LNT cells serve as a cancer vaccine and promote antitumor immune responses that prolong the survival of tumor-bearing mice. Preimmunization with LNT cells along with an adjuvant also protected healthy mice from AML cell challenge
Detectable Changes in The Blood Transcriptome Are Present after Two Weeks of Antituberculosis Therapy
Globally there are approximately 9 million new active tuberculosis cases and 1.4 million deaths annually. Effective antituberculosis treatment monitoring is difficult as there are no existing biomarkers of poor adherence or inadequate treatment earlier than 2 months after treatment initiation. Inadequate treatment leads to worsening disease, disease transmission and drug resistance.To determine if blood transcriptional signatures change in response to antituberculosis treatment and could act as early biomarkers of a successful response.Blood transcriptional profiles of untreated active tuberculosis patients in South Africa were analysed before, during (2 weeks and 2 months), at the end of (6 months) and after (12 months) antituberculosis treatment, and compared to individuals with latent tuberculosis. An active-tuberculosis transcriptional signature and a specific treatment-response transcriptional signature were derived. The specific treatment response transcriptional signature was tested in two independent cohorts. Two quantitative scoring algorithms were applied to measure the changes in the transcriptional response. The most significantly represented pathways were determined using Ingenuity Pathway Analysis.An active tuberculosis 664-transcript signature and a treatment specific 320-transcript signature significantly diminished after 2 weeks of treatment in all cohorts, and continued to diminish until 6 months. The transcriptional response to treatment could be individually measured in each patient.Significant changes in the transcriptional signatures measured by blood tests were readily detectable just 2 weeks after treatment initiation. These findings suggest that blood transcriptional signatures could be used as early surrogate biomarkers of successful treatment response
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