RECOVERY OF HAEMOPHILUS INFLUENZAE FROM ULTRAVIOLET AND X-RAY DAMAGE

Abstract— Results of experiments on reactivation of ultraviolet (u.v.)-irradiated Haemophilus influenzae and cellular reactivation of u.v.-damaged transforming deoxyribonucleic acid (DNA) and bacteriophage are reported. Liquid-holding recovery (LHR) is small for the u.v.-sensitive mutant BC100 which, relative to the wild type, also has greatly reduced host-cell reactivation (HCR) of u.v.-inactivated phage, and competent cultures show reduced competent cell reactivation (CCR) of u.v.-inactivated transforming DNA. BC100 cells can be transformed with DNA isolated from the wild type strain Rd to a u.v. resistance similar to that of Rd, and irradiation of the DNA reduces the transformation frequency for this marker (uvr). The u.v.-resistant mutant BC200 displays very little LHR under the usual conditions where reactivation occurs after plating. The colony-forming ability (cfa) of irradiated BC200 is greater than that of Rd, but HCR and CCR are the same on this mutant as on the wild type. The major difference between Rd and BC200 is the enhanced u.v. survival of cfa of the latter. It was determined that this difference reflects cell lysis of irradiated Rd and lack of lysis in BC200 cultures. That lysis is closely correlated with damage to the bacterial chromosome is suggested by the finding that the lytic response of Rd (as determined turbidimetrically) can be negated by the liquid-holding procedure, but lysis of BC100 (which lacks comparable DNA-repair ability) can be only partially inhibited by this procedure. LHR occurs when post-plating dark recovery is incomplete, is temperature-sensitive, and occurs unimpeded when post-u.v. protein synthesis is inhibited by chloramphenicol. It is suggested that enzymatically catalyzed reactivation of DNA occurs or is initiated during liquid-holding of u.v.-irradiated H. influenzae Rd and that the necessary enzyme(s) exists prior to appearance of u.v. lesions in the DNA. Results are reported for X-ray inactivation of transforming DNA as assayed on BC100, Rd and BC200 and of the cfa of the three strains.     

Long-wavelength thermal convection in a weak shear flow

The problem of thermal convection in an imposed shear flow isexamined for a horizontal layer of fluid between poorly conductingboundaries. The horizontal scale H of the convective motionnear its onset is much greater than the depth h of the fluidlayer, with h/H being proportional to the one-fourth power ofa Biot number appearing in the condition applied to the temperatureat the horizontal boundaries. It is known that an asymptoticexpansion in powers of h/H yields a nonlinear long-wavelengthevolution equation for the depth-averaged temperature fieldthat is spatially isotropic in the absence of an imposed shearflow, but is strongly anisotropic for ‘strong’ shear.We derive in this paper a nonlocal long-wavelength equationthat bridges these two cases, and that contains each case inthe zero-shear and large-shear limits. Using this evolutionequation, we show how the shear flow stabilizes the longitudinalrolls to the zigzag instability, and how a preference for asquare planfonn on a periodic square lattice gives way to apreference for longitudinal rolls near onset. The longitudinalrolls may then become unstable as the Rayleigh number is increased.The analytical work is illustrated by some numerical simulationsof the full three-dimensional Boussinesq Navier-Stokes equations.The problem of pattern selection on a hexagonal lattice is alsodiscussed, and some new results are presented.     

Residues in toric varieties

We study residues on a complete toric variety X, which are defined in terms of the homogeneous coordinate ring of X.We first prove a global transformation law for toric residues. When the fan of the toric variety has a simplicial cone of maximal dimension, we can produce an element with toric residue equal to 1. We also show that in certain situations, the toric residue is an isomorphism on an appropriate graded piece of the quotient ring. When X is simplicial, we prove that the toric residue is a sum of local residues. In the case of equal degrees, we also show how to represent X as a quotient (Y\{0})/C* such that the toric residue becomes the local residue at 0 in Y.     

The Approximation of a Composite B?zier Cubic Curve by a Composite B?zier Quadratic Curve

In the context of the computer representation of textual characters,we describe an algorithm for approximating a composite B?ziercubic curve by a composite B?rier quadratic curve. The knotsor breakpoints of the approximating function are determinedsuch that the error of approximation does not exceed a specifiedvalue. The number of breakpoints, and hence the number of arcsof the approximation, is not in general optimal but can be expectedto be ‘small’. The work is clearly relevant alsoto other application areas.     

The Least Squares Solution of Overdetermined Linear Equations Having Band or Augmented Band Structure

Methods for linear least squares problems in which the observationmatrix is banded or takes the form of a band plus several columnsare considered. Algorithms using Givens plane rotations to exploitthese structures are presented and some applications discussed.The level of presentation is predominantly expository.     

Torsion—rotation interactions in monodeuterated acetaldehyde

This paper presents an analysis of previously observed rotational transitions up to J = 17 of the sym and asym rotamers of monodeuterated acetaldehyde using a three-level Hamiltonian incorporating connections between rotational states of the v_sym = 0, v_asym = 0⁺ and v_asym = 0 ^? torsional energy level manifolds. Rotational transitions observed to be significantly perturbed in earlier studies, where the spectrum was fitted using a single-level Hamiltonian for the v_sym = 0 torsional state and a separate two-level Hamiltonian for the non-rigid asym states, are now fitted satisfactorily. It is confirmed that the perturbations detected in the earlier studies and tentatively attributed there to torsion-rotation interactions between the energetically distinct sym and asym manifolds do indeed arise as a consequence of such interactions. Rotational and quartic centrifugal distortion constants are given for each torsional state, together with torsion-rotation coupling constants primarily responsible for the perturbations noted in the earlier studies. Tunnelling between the energetically distinct sym and asym potential wells of the torsional potential energy function is also discussed.     

Curve Fitting with Piecewise Polynomials

Polynomials and splines are frequently used as approximatingfunctions in curve fitting. This paper discusses curve fittingwith the more general piecewise polynomials employed as theapproximating functions. Various representations of piecewisepolynomials are discussed and one particular form is selectedas providing a basis for a well-conditioned formulation of theleast-squares curve-fitting problem. Continuous and discontinuousapproximations with fixed and free knots are considered fromthe points of view of existence, uniqueness and characterizationof solutions. Two general algorithms are suggested for the continuouscase with arbitrary degree and continuity with fixed knots.The imposition of end conditions is shown to be straightforward.Using the principles of dynamic programming a method is proposedthat enables global solutions to be obtained economically inthe case of discontinuous approximating functions with freeknots.     

An Algorithm for Least-Squares Circle Fitting to Data with Specified Uncertainty Ellipses

The problem considered here is that of fitting a circle to aset of measured data points specified in terms of their cartesiancoordinates. It is assumed that the data adequately representsa circle and that associated with each data point there is anuncertainty ellipse describing the measurement error. A weightednonlinear least-squares problem is formulated in order to determineunbiased estimates of the centre and radius of the circle whichbests fits the given data. The resulting problem displays structurewhich is exploited when the Gauss-Newton algorithm is used toobtain a solution. In addition to estimates of the circle parametersthe algorithm produces error ellipses for the centre of thecircle and any point on its circumference.     

Heuristic least-cost computation of discrete classification functions with uncertain argument values

We consider the problem of minimizing the expected cost of computing the correct value of a discrete-valued function when it is costly to determine (inspect) the values of its arguments. This type of problem arises in distributed computing, in the design of interactive expert systems, in reliability analysis of coherent systems, in classification of pattern vectors, and in many other applications. In this paper, we first show that the general problem is NP-hard and then introduce several efficient heuristic sequential inspection procedures for solving it approximately. We obtain theoretical results showing that the heuristics are optimal in important special cases; moreover, their computational structures make them well suited for parallel implementation. Next, for the special case of linear threshold (or discrete linear discriminant) functions, which are widely used in statistical classification procedures, we use Monte Carlo simulation to analyze the performances of the heuristics and to compare the heuristic solutions with the exact (true minimum expected cost) solutions over a wide range of randomly generated test problems. All of the heuristics give average relative errors, compared to the exact optimal solutions, of less than 2%. The best heuristic for this class of functions gives an average relative error of less than 0.05% and runs two to four orders of magnitude faster than the exact solution procedure, for functions with ten arguments.Mr. Warren Kuehner is also Chairman of the Department of Computer and Management Science at Metropolitan State College, 1006 11th Street, Denver, Colorado 80204, U.S.A.