1,714 research outputs found
A Model for the Propagation of Sound in Granular Materials
This paper presents a simple ball-and-spring model for the propagation of
small amplitude vibrations in a granular material. In this model, the
positional disorder in the sample is ignored and the particles are placed on
the vertices of a square lattice. The inter-particle forces are modeled as
linear springs, with the only disorder in the system coming from a random
distribution of spring constants. Despite its apparent simplicity, this model
is able to reproduce the complex frequency response seen in measurements of
sound propagation in a granular system. In order to understand this behavior,
the role of the resonance modes of the system is investigated. Finally, this
simple model is generalized to include relaxation behavior in the force network
-- a behavior which is also seen in real granular materials. This model gives
quantitative agreement with experimental observations of relaxation.Comment: 21 pages, requires Harvard macros (9/91), 12 postscript figures not
included, HLRZ preprint 6/93, (replacement has proper references included
Instability Analysis of Pressure- Loaded Thin Arches of Arbitrary Shape
Introduction Although basic theoretical principles for the inclusion of pressure-load effects in finite element, elastic instability analysis have been established for some time now [1], there is considerable interest in and need for relationships for specific cases of interest and for the study of the basic properties of these relationships. Thus, Hibbitt [2], Loganathan, et al. Because the finite element method owes its significance to its potentiality for the treatment of structures of rather arbitrary geometry, it is desirable to have available the theoretical basis for formulation of arch elements of any shape. Thus, the purpose of this paper is to derive geometrically nonlinear formulations for arches of arbitrary shape acted on by pressure loads. Both the governing differential equations and the associated virtual work expressions are presented. Generalized stress vectors are defined which are consistent with the definitions of the strains. The interaction of membrane and bending deformations is taken into account. The governing differential equations derived herein are more general than those that have appeared previously. gives basic nonlinear equations for arches of arbitrary shape, but neglects the interaction of bending and membrane deformations. Wang [8] presents a linear static analysis for a class of ring segments. The equilibrium equations, however, are established for the undeforme
A Multi-resolution Model for Histopathology Image Classification and Localization with Multiple Instance Learning
Histopathological images provide rich information for disease diagnosis.
Large numbers of histopathological images have been digitized into high
resolution whole slide images, opening opportunities in developing
computational image analysis tools to reduce pathologists' workload and
potentially improve inter- and intra- observer agreement. Most previous work on
whole slide image analysis has focused on classification or segmentation of
small pre-selected regions-of-interest, which requires fine-grained annotation
and is non-trivial to extend for large-scale whole slide analysis. In this
paper, we proposed a multi-resolution multiple instance learning model that
leverages saliency maps to detect suspicious regions for fine-grained grade
prediction. Instead of relying on expensive region- or pixel-level annotations,
our model can be trained end-to-end with only slide-level labels. The model is
developed on a large-scale prostate biopsy dataset containing 20,229 slides
from 830 patients. The model achieved 92.7% accuracy, 81.8% Cohen's Kappa for
benign, low grade (i.e. Grade group 1) and high grade (i.e. Grade group >= 2)
prediction, an area under the receiver operating characteristic curve (AUROC)
of 98.2% and an average precision (AP) of 97.4% for differentiating malignant
and benign slides. The model obtained an AUROC of 99.4% and an AP of 99.8% for
cancer detection on an external dataset.Comment: 9 pages, 6 figure
On Conceptually Simple Algorithms for Variants of Online Bipartite Matching
We present a series of results regarding conceptually simple algorithms for
bipartite matching in various online and related models. We first consider a
deterministic adversarial model. The best approximation ratio possible for a
one-pass deterministic online algorithm is , which is achieved by any
greedy algorithm. D\"urr et al. recently presented a -pass algorithm called
Category-Advice that achieves approximation ratio . We extend their
algorithm to multiple passes. We prove the exact approximation ratio for the
-pass Category-Advice algorithm for all , and show that the
approximation ratio converges to the inverse of the golden ratio
as goes to infinity. The convergence is
extremely fast --- the -pass Category-Advice algorithm is already within
of the inverse of the golden ratio.
We then consider a natural greedy algorithm in the online stochastic IID
model---MinDegree. This algorithm is an online version of a well-known and
extensively studied offline algorithm MinGreedy. We show that MinDegree cannot
achieve an approximation ratio better than , which is guaranteed by any
consistent greedy algorithm in the known IID model.
Finally, following the work in Besser and Poloczek, we depart from an
adversarial or stochastic ordering and investigate a natural randomized
algorithm (MinRanking) in the priority model. Although the priority model
allows the algorithm to choose the input ordering in a general but well defined
way, this natural algorithm cannot obtain the approximation of the Ranking
algorithm in the ROM model
Coarse-grained entanglement classification through orthogonal arrays
Classification of entanglement in multipartite quantum systems is an open
problem solved so far only for bipartite systems and for systems composed of
three and four qubits. We propose here a coarse-grained classification of
entanglement in systems consisting of subsystems with an arbitrary number
of internal levels each, based on properties of orthogonal arrays with
columns. In particular, we investigate in detail a subset of highly entangled
pure states which contains all states defining maximum distance separable
codes. To illustrate the methods presented, we analyze systems of four and five
qubits, as well as heterogeneous tripartite systems consisting of two qubits
and one qutrit or one qubit and two qutrits.Comment: 38 pages, 1 figur
Epitope Characterization of an Aromatase Monoclonal Antibody Suitable for the Assessment of Intratumoral Aromatase Activity
Immunohistochemistry is one of the most suitable methods for the detection of intratumoral aromatase in order to identify patients who may respond to aromatase inhibitor therapy in hormone-dependent breast cancer. Previous studies showed statistically significant correlation between results of immnuohistochemistry and biochemical analysis in carcinoma components stained by aromatase monoclonal antibody 677. In this study, determination of the antigenic peptides recognized by aromatase antibodies through epitope mapping, combined with the new knowledge on aromatase-reductase interaction, provide insights for understanding various immunostaining patterns using different aromatase antibodies. Our studies on aromatase-reductase interaction also provided critical information on how aromatase and reductase interact with each other on the endoplasmic reticulum membrane, and identified key residues, including K108 of aromatase, that are involved in the interaction with reductase. Through epitope mapping and taking into consideration the interference with aromatase immunohistochemical staining by NADPH-cytochrome P450 reductase, we demonstrated that monoclonal antibody 677 is a suitable antibody for an assessment of intratumoral aromatase activity in breast cancer patients for making clinical management decisions. These results also provide valuable information to identify new aromatase antibodies for immunohistochemical diagnosis of hormone-dependent breast cancer in future
Interface-tuned epoxy/clay nanocomposites
Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modifiers: ethanolamine (denoted ETH), Jeffamine� M2070 (M27) and Jeffamine� XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an interme-diate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magnification show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Young’s modulus, fracture toughness and glass transition temperature (Tg) of matrix. With w1.3 wt% clay, the critical strain energy release rate G1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and Tg enhanced from 93.7 to 99.
Charge photogeneration in few-layer MoS2
The two-dimensional semiconductor MoS2 in its mono- and few-layer form is
expected to have a significant exciton binding energy of several 100 meV,
leading to the consensus that excitons are the primary photoexcited species.
Nevertheless, even single layers show a strong photovoltaic effect and work as
the active material in high sensitivity photodetectors, thus indicating
efficient charge carrier photogeneration (CPG). Here we use continuous wave
photomodulation spectroscopy to identify the optical signature of long-lived
charge carriers and femtosecond pump-probe spectroscopy to follow the CPG
dynamics. We find that intitial photoexcitation yields a branching between
excitons and charge carriers, followed by excitation energy dependent hot
exciton dissociation as an additional CPG mechanism. Based on these findings,
we make simple suggestions for the design of more efficient MoS2 photovoltaic
and photodetector devices
Wigner Crystallization in a Quasi-3D Electronic System
When a strong magnetic field is applied perpendicularly (along z) to a sheet
confining electrons to two dimensions (x-y), highly correlated states emerge as
a result of the interplay between electron-electron interactions, confinement
and disorder. These so-called fractional quantum Hall (FQH) liquids form a
series of states which ultimately give way to a periodic electron solid that
crystallizes at high magnetic fields. This quantum phase of electrons has been
identified previously as a disorder-pinned two-dimensional Wigner crystal with
broken translational symmetry in the x-y plane. Here, we report our discovery
of a new insulating quantum phase of electrons when a very high magnetic field,
up to 45T, is applied in a geometry parallel (y-direction) to the
two-dimensional electron sheet. Our data point towards this new quantum phase
being an electron solid in a "quasi-3D" configuration induced by orbital
coupling with the parallel field
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