5,250 research outputs found
Construction of a "mutagenesis cartridge" for poliovirus genome-linked viral protein: Isolation and characterization of viable and nonviable mutants
By following a strategy of genetic analysis of poliovirus, we have constructed a synthetic "mutagenesis cartridge" spanning the genome-linked viral protein coding region and flanking cleavage sites in an infectious cDNA clone of the type 1 (Mahoney) genome. The insertion of new restriction sites within the infectious clone has allowed us to replace the wild-type sequences with short complementary pairs of synthetic oligonucleotides containing various mutations. A set of mutations have been made that create methionine codons within the genome-linked viral protein region. The resulting viruses have growth characteristics similar to wild type. Experiments that led to an alteration of the tyrosine residue responsible for the linkage to RNA have resulted in nonviable virus. In one mutant, proteolytic processing assayed in vitro appeared unimpaired by the mutation. We suggest that the position of the tyrosine residue is important for genome-linked viral protein function(s)
Solar cell radiation handbook
The handbook to predict the degradation of solar cell electrical performance in any given space radiation environment is presented. Solar cell theory, cell manufacturing and how they are modeled mathematically are described. The interaction of energetic charged particles radiation with solar cells is discussed and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a FORTRAN listing of the program is included. Data detailing the degradation of solar cell electrical parameters as a function of 1 MeV electron fluence are presented
Learning Melanocytic Cell Masks from Adjacent Stained Tissue
Melanoma is one of the most aggressive forms of skin cancer, causing a large
proportion of skin cancer deaths. However, melanoma diagnoses by pathologists
shows low interrater reliability. As melanoma is a cancer of the melanocyte,
there is a clear need to develop a melanocytic cell segmentation tool that is
agnostic to pathologist variability and automates pixel-level annotation.
Gigapixel-level pathologist labeling, however, is impractical. Herein, we
propose a means to train deep neural networks for melanocytic cell segmentation
from hematoxylin and eosin (H&E) stained slides using paired
immunohistochemical (IHC) slides of adjacent tissue sections, achieving a mean
IOU of 0.64 despite imperfect ground-truth labels.Comment: {Medical Image Learning with Limited & Noisy Data Workshop at MICCAI
202
Theory of nonlinear optical properties of phenyl-substituted polyacetylenes
In this paper we present a theoretical study of the third-order nonlinear
optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the
third-harmonic-generation (THG) process. We study the aforesaid process in
PDPA's using both the independent electron Hueckel model, as well as
correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based
calculations were performed using various configuration interaction (CI)
methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the
quadruples-CI (QCI) methods, and the both longitudinal and the transverse
components of third-order susceptibilities were computed. The Hueckel model
calculations were performed on oligo-PDPA's containing up to fifty repeat
units, while correlated calculations were performed for oligomers containing up
to ten unit cells. At all levels of theory, the material exhibits highly
anisotropic nonlinear optical response, in keeping with its structural
anisotropy. We argue that the aforesaid anisotropy can be divided over two
natural energy scales: (a) the low-energy response is predominantly
longitudinal and is qualitatively similar to that of polyenes, while (b) the
high-energy response is mainly transverse, and is qualitatively similar to that
of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April
15, 2004
Collapse of stamps for soft lithography due to interfacial adhesion
Collapse of elastomeric elements used for pattern transfer in soft lithography is studied through experimental measurements and theoretical modehng. The objective is to identify the driving force for such collapse. Two potential driving forces, the self-weight of the stamp and the interfacial adhesion, are investigated. An idealized configuration of periodic rectangular grooves and flat punches is considered. Experimental observations demonstrate that groove collapse occurs regardless of whether the gravitational force promotes or suppresses such collapse, indicating that self-weight is not the driving force. On the other hand, model predictions based on the postulation that interfacial adhesion is the driving force exhibit excellent agreement with the experimentally measured collapse behavior. The interfacial adhesion energy is also evaluated by matching an adhesion parameter in the model with the experimental data.open546
Rational Theories of 2D Gravity from the Two-Matrix Model
The correspondence claimed by M. Douglas, between the multicritical regimes
of the two-matrix model and 2D gravity coupled to (p,q) rational matter field,
is worked out explicitly. We found the minimal (p,q) multicritical potentials
U(X) and V(Y) which are polynomials of degree p and q, correspondingly. The
loop averages W(X) and \tilde W(Y) are shown to satisfy the Heisenberg
relations {W,X} =1 and {\tilde W,Y}=1 and essentially coincide with the
canonical momenta P and Q. The operators X and Y create the two kinds of
boundaries in the (p,q) model related by the duality (p,q) - (q,p). Finally, we
present a closed expression for the two two-loop correlators and interpret its
scaling limit.Comment: 24 pages, preprint CERN-TH.6834/9
Describing Function Inversion: Theory and Computational Techniques
In the last few years the study of nonlinear mechanics has received the attention of numerous investigators, either under the scope of pure mathematics or from the engineering point of view. Many of the recent developments are based on the early works of H. Poincare [1] and A. Liapunov [2] As examples can be cited the perturbation method, harmonic balance, the second method of Liapunov, etc. An approximate technique developed almost simultaneously by C. Goldfarb [3] in the USSR, A. Tustin [4] in England, R. Kochenburger [5] in the USA, W, Oppelt [6] in Germany and J. Dutilh [7] and C. Ecary [8] in France, known as the describing function technique, can be considered as the graphical solution of the first approximation of the method of the harmonic balance. The describing function technique has reached great popularity, principally because of the relative ease of computation involved and the general usefulness of the method in engineering problems. However, in the past, the describing function technique has been useful only in analysis. More exactly, it is a powerful tool for the investigation of the possible existence of limit cycles and their approximate amplitudes and frequencies. Several extensions have been developed from the original describing function technique. Among these can be cited the dual-input describing function, J. C. Douce et al. [9]; the Gaussian-input describing function, R. C, Booton [10]; and the root-mean-square describing function, J. E. Gibson and K. S. Prasanna-Kumar [11]. In a recent work which employs the describing function, C. M„ Shen [12] gives one example of stabilization of a nonlinear system by introducing a saturable feedback. However, Shen’s work cannot be qualified as a synthesis method since he fixes a priori the nonlinearity to be introduced in the feedback loop. A refinement of the same principle used by Shen has been proposed by R. Haussler [13] The goal of this new method of synthesis is to find the describing function of the element being synthesized. Therefore, for Haussler’s method to be useful, a way must be found to reconstruct the nonlinearity from its describing function. This is called the inverse-describing-function-problem and is essentially a synthesis problem. This is not the only ease in which the inverse-describing-function-problem can be useful. Sometimes, in order to find the input-output characteristic of a physical nonlinear element, a harmonic test can be easier to perform rather than a static one (which also may be insufficient). The purpose of this report is to present the results of research on a question which may then be concisely stated as; If the describing function of a nonlinear element is known, what is the nonlinearity? The question may be divided into two parts, the first part being the determination of the restrictions on the nonlinearity (or its describing function) necessary to insure that the question has an answer, and the second part the practical determination of that answer when it exists. Accordingly, the material in this report is presented in two parts. Part I is concerned with determining what types of nonlinearities are (and what types are not) uniquely determined by their conventional (fundamental) describing function. This is done by first showing the non-uniqueness in general of the describing function, and then constructing a class of null functions with respect to the describing function integral, i.e., a class of nonlinearities not identically zero whose describing functions are identically zero. The defining equations of the describing function are transformed in such a manner as to reduce the inverse describing function problem to the problem of solving a Volterra integral equation, an approach similar to that used by Zadeh [18]. The remainder of Part I presents the solution of the integral equations and studies the effect of including higher order harmonics in the description of the output ware shape. The point of interest here is that inclusion of the second harmonic may cause the describing function to become uniquely invertible in some cases. Part II presents practical numerical techniques for effecting the inversion of types of describing functions resulting from various engineering assumptions as to the probable form of the nonlinearities from which said describing functions were determined. The most general method is numerical evaluation of the solution to the Volterra integral equations developed in Part I, A second method, which is perhaps the easiest to apply, requires a least squares curve fit to the given describing function data. Then use is made of the fact that the describing function of a polynomial nonlinearity is itself a polynomial to calculate the coefficients in a polynomial approximation to the nonlinearity. This approach is indicated when one expects that the nonlinearity is a smooth curve, such as a cubic characteristic. The third method presented assumes that the nonlinearity can be approximated by a piecewise linear discontinuous function, and the slopes and y-axis intercepts of each linear segment are computed. This approach is indicated when one expects a nonlinearity with relatively sharp corners. It may toe remarked that the polynomial approximation and the piecewise linear approximation are derived independently of the material in Part I. All three methods presented in Part II are suited for use with experimental data as well as with analytic expressions for the describing functions involved. Indeed, an analytical expression must toe reduced to discrete data for the machine methods to the of use. To the best of the authors® knowledge, research in the area of describing function inversion has been nonexistent with the exception of Zadeh’s paper [18] in 1956. It seems that a larger effort in this area would toe desirable in the light of recent extensions of the describing function itself to signal stabilization of nonlinear control systems by Oldentourger and Sridhar [19] and Boyer [20] and the less restrictive study of dual-input describing functions for nonautonomous systems by Gibson and Sridhar [21]. There presently exist techniques for determining a desired describing function for use in avoiding limit cycle oscillations in an already nonlinear system (Haussler [13]), and the methods presented in this report now allow the exact synthesis of the nonlinear element from the describing function data
Perturbative approach to the critical behaviour of two-matrix models in the limit N -> infinity
We construct representations of the Heisenberg algebra by pushing the
perturbation expansion to high orders. If the multiplication operators
tend to differential operators of order , respectively, the
singularity is characterized by . Let . Then
the two cases A : `` does not divide '' and B : `` divides
'' need a different treatment. The universality classes are labelled
where =[,] in case A and
=[,] in case B.Comment: 23 pages, Late
On the Canonical Reduction of Spherically Symmetric Gravity
In a thorough paper Kuchar has examined the canonical reduction of the most
general action functional describing the geometrodynamics of the maximally
extended Schwarzschild geometry. This reduction yields the true degrees of
freedom for (vacuum) spherically symmetric general relativity. The essential
technical ingredient in Kuchar's analysis is a canonical transformation to a
certain chart on the gravitational phase space which features the Schwarzschild
mass parameter , expressed in terms of what are essentially
Arnowitt-Deser-Misner variables, as a canonical coordinate. In this paper we
discuss the geometric interpretation of Kuchar's canonical transformation in
terms of the theory of quasilocal energy-momentum in general relativity given
by Brown and York. We find Kuchar's transformation to be a ``sphere-dependent
boost to the rest frame," where the ``rest frame'' is defined by vanishing
quasilocal momentum. Furthermore, our formalism is general enough to cover the
case of (vacuum) two-dimensional dilaton gravity. Therefore, besides reviewing
Kucha\v{r}'s original work for Schwarzschild black holes from the framework of
hyperbolic geometry, we present new results concerning the canonical reduction
of Witten-black-hole geometrodynamics.Comment: Revtex, 35 pages, no figure
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