Showing papers by "Lawrence Berkeley National Laboratory published in 1985"

Complication Probability as Assessed from Dose-Volume Histograms

Abstract: Optimization of a treatment plan for radiation therapy will produce a plan with the highest probability for tumor control without exceeding an acceptable complication rate. To achieve this goal it is necessary to have a means to estimate probabilities of local control and normal tissue complication. In general, good treatment plans deliver a high uniform dose to the target volume and lower doses to the surrounding normal tissues. The tolerance dose values available for various normal tissues are usually assumed to apply to partial or full volumes of the tissue which have been uniformly irradiated. These values are the best guidelines for estimating complication probabilities in tissues that receive a uniform dose to a fraction of the tissue and no dose to the remainder. Dose-volume histograms are one means of evaluating the uniformity of the irradiation on the tissues. Frequently the normal tissues are not uniformly irradiated as is demonstrated by dose-volume histograms for different treatment plans. A recursive algorithm which uses these tolerance dose data has been written and can be applied to arbitrary dose-volume histograms to estimate the complication probability.

A practical method for modeling fluid and heat flow in fractured porous media

Abstract: A Multiple Interacting Continua method (MINC) is presented which is applicable for numerical simulation of heat and multi-phase fluid flow in multidimensional, fractured porous media. This method is a generalization of the double-porosity concept. The partitioning of the flow domain into computational volume elements is based on the criterion of approximate thermodynamic equilibrium at all times within each element. The thermodynamic conditions in the rock matrix are assumed to be primarily controlled by the distance from the fractures, which leads to the use of nested grid blocks. The MINC concept is implemented through the Integral Finite Difference (IFD) method. No analytical approximations are made for the coupling between the fracture and matrix continua. Instead, the transient flow of fluid and heat between matrix and fractures is treated by a numerical method. The geometric parameters needed in a simulation are preprocessed from a specification of fracture spacings and apertures, and the geometry of the matrix blocks. The MINC method is verified by comparison with the analytical solution of Warren and Root. Illustrative applications are given for several geothermal reservoir engineering problems.

The Molecular Basis of Cancer

Abstract: Malignant Transformation Growth and Spread of Cancer Molecular Abnormalities in Specific Malignancies, Molecular Basis of Cancer Therapy.

A Direct Eulerian MUSCL Scheme for Gas Dynamics

Abstract: We present a second order extension of Godunov’s method for gas dynamics in Eulerian coordinates patterned after van Leer’s MUSCL scheme for gas dynamics in Lagrangian coordinates. The present method performs the Eulerian calculation in a single step by solving Riemann problems and characteristic equations for the fluxes in the Eulerian frame. We also make several modifications in the formulation of MUSCL, applicable to both this scheme and to the original Lagrangian scheme, all aimed at making a more robust and accurate scheme. We present the results of test caclulations in one and two space variables.

High-resolution 29Si NMR study of silicate and aluminosilicate glasses: the effect of network-modifying cations

Abstract: Etude de l'effet des cations modificateurs alcalins et alcalinoterreux sur le degre de polymerisation de verres de silicate, par spectrometrie RMN sous angle magique. La largeur de bande RMN augmente en fonction du pouvoir polarisant du cation. Un effet semblable a lieu dans les verres d'aluminosilicate a reseau tridimensionnel

Applications of algebraic reconstruction techniques to crosshole seismic data

Abstract: Tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data. The experiments were carried out at the Retsoff salt mine in New York and at the underground radioactive waste study site at the Stripa mine facility in Sweden. The traveltimes at Restoff were high quality and were obtained over raypaths of up to 500 m in length. The structure was quite complicated with velocity contrasts up to 50 percent. The Stripa site was in granitic rock with velocity contrasts of only a few percent. The dimensions of the experiment were small with maximum ray lengths of just over 10 m. The data at this site were collected with very high accuracy, source and receiver locations were measured to better than 1.0 mm, and traveltimes were read to 0.001 ms. A number of algorithms similar to the algebraic reconstruction techniques (ART) used in medical imaging have been applied to the data. Some modifications of the algorithms, such as the application of weighting schemes, damping parameters, and curved raypaths, were performed. The resulting velocity fields were compared to the known fields and with each other to determine an optimal method. The algorithms were found to be a rapid, reliable means of reconstructing the slowness field of real data. Low-velocity zones were recovered with accuracy in location and value. It was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken; otherwise poor reconstructions will result.

Algebraic study of chiral anomalies

Abstract: The algebraic structure of chiral anomalies is made globally valid on non-trivial bundles by the introduction of a fixed background connection. Some of the techniques used in the study of the anomaly are improved or generalized, including a systematic way of generating towers of “descent equations”.

MEIOTIC GENE CONVERSION MUTANTS IN SACCHAROMYCES CEREVISIAE. I. ISOLATION AND CHARACTERIZATION OF pms1-1 AND pms1-2

Abstract: The pms1 mutants, isolated on the basis of sharply elevated meiotic prototroph frequencies for two closely linked his4 alleles, display pleiotropic phenotypes in meiotic and mitotic cells. Two isolates carrying recessive mutations in PMS1 were characterized. They identify a function required to maintain low postmeiotic segregation (PMS) frequencies at many heterozygous sites. In addition, they are mitotic mutators. In mutant diploids, spore viability is reduced, and among survivors, gene conversion and postmeiotic segregation frequencies are increased, but reciprocal exchange frequencies are not affected. The conversion event pattern is also dramatically changed in multiply marked regions in pms1 homozygotes. The PMS1 locus maps near MET4 on chromosome XIV. The PMS1 gene may identify an excision-resynthesis long patch mismatch correction function or a function that facilitates correction tract elongation. The PMS1 gene product may also play an important role in spontaneous mitotic mutation avoidance and correction of mismatches in heteroduplex DNA formed during spontaneous and UV-induced mitotic recombination. Based on meiotic recombination models emphasizing mismatch correction in heteroduplex DNA intermediates, this interpretation is favored, but alternative interpretations involving longer recombination intermediates in the mutants are also considered.

Microwave radiation from a high-gain free-electron laser amplifier.

Abstract: A high-gain, high--extraction-efficiency, linearly polarized free-electron laser amplifier has been operated at 34.6 GHz. At low signal levels, exponential gain of 13.4 dB/m has been measured. With a 3-=kW input signal, saturation was observed with an 80-MW output and a 5% extraction efficiency. The results are in good agreement with linear models at small signal levels and nonlinear models at large signal levels.

Molecular models for DNA damaged by photoreaction

Abstract: Structural models of a DNA molecule containing a radiation-induced psoralen cross-link and of a DNA containing a thymine photodimer were constructed by applying energy-minimization techniques and model-building procedures to data from x-ray crystallographic studies. The helical axes of the models show substantial kinking and unwinding at the sites of the damage, which may have long-range as well as local effects arising from the concomitant changes in the supercoiling and overall structure of the DNA. The damaged areas may also serve as recognition sites for repair enzymes. These results should help in understanding the biologic effects of radiation-induced damage on cells.

Superconductivity in high-pressure metallic phases of Si.

Abstract: Superconductivity in the simple hexagonal phase of silicon is predicted on the basis of an electron-phonon-coupling calculation and measured experimentally up to a pressure of 25 GPa in a Bridgman-type opposed-anvil device. The highest measured superconducting transition temperature is 8.2 K at 15 GPa for the simple hexagonal phase.

Optical guiding in a free-electron laser.

Abstract: By use of two-dimensional approximations for the equations that describe a high-gain free-electron laser (FEL) amplifier, and the properties of optical fibers, it is shown that the coherent interaction between the light and the electron beam in a FEL can optically guide the light. In the exponential-gain regime, the FEL performance in the presence of strong diffraction can be simply described by a cubic equation for the complex gain and the dispersion relation for an optical fiber. The phenomenon of optical guiding is illustrated with two-dimensional numerical simulations. The phenomenon has applications to short-wavelength FEL's, to directing of intense light, and to bending of x-rays.

Calculations for cosmic axion detection.

Abstract: Calculations are presented, using properly nomalized couplings and masses for Dine-Fischler-Srednicki axions, of power rates and signal temperatures for axion-photon conversion in microwave cavities. The importance of the galactic-halo axion line shape is emphasized. Spin-coupled detection as an alternative to magnetic-field-coupled detection is mentioned.

A double-blind test of astrology

Abstract: Two double-blind tests were made of the thesis that astrological ‘natal charts’ can be used to describe accurately personality traits of test subjects.

Statistical and Scientific Database Issues

Abstract: The purpose of this paper is to summarize the research issues of statistical and scientific databases (SSDB's). It organizes the issues into four major groups: physical organization and access methods, operators, logical organization and user interfaces, and miscellaneous issues. It emphasizes the differences between SSDB's and traditional database applications, and motivates the need for new and innovative techniques for the support of SSDB's. In addition to describing current work in this field, it discusses open research areas and proposes possible approaches to their solution.

A numerical study of oblique shock-wave reflections with experimental comparisons

Abstract: A direct comparison is made for several occurrences of oblique shock-wave reflections between interferometric results obtained at the University of Toronto Institute for Aerospace Studies (UTIAS) 10 cm x 18 cm hypervelocity shock tube and numerical results obtained by using a current computational method for solving the Euler equations. Very good qualitative agreement is obtained for equilibrium and frozen flow fields except in small regions where the experiments were dominated by viscous flow. The quantitative agreement is very close in some cases but can be out by 10-15% in cases with non-equilibrium flow or viscous structures or both. Additional parametrized sequences of calculations are presented to assess the utility of the present numerical method in constructing the various reflection- transition lines for perfect inviscid flows in the shock-wave Mach number, wedge-angle ($M\_s, \theta\_w$)-plane, and the validity of the `boundary- layer defect' theory.

Solid-solid phase transitions and soft phonon modes in highly condensed Si.

Abstract: The pseudopotential method is used to examine the structural transitions of Si from \ensuremath{\beta}-Sn to simple hexagonal (sh) to hexagonal close packed (hcp). The calculated transition pressures, transition volumes, and c/a ratios are in good agreement with the measured values. Furthermore, the phase-transition pressure from hexagonal close packed to face-centered cubic is predicted to be 1.2 Mbar. The phonon frequencies are also calculated with use of the frozen-phonon approximation for the \ensuremath{\beta}-Sn, sh, and hcp phases. For both the \ensuremath{\beta}-Sn and sh phases, pressure-sensitive soft phonon modes exist. These are the longitudinal optic mode at the Brillouin-zone center for \ensuremath{\beta}-Sn and the transverse acoustic mode at the Brillouin-zone boundary for sh in the [001] direction. These soft modes are most likely associated with the phase transformations from \ensuremath{\beta}-Sn to sh to hcp. The metallic sh phase has strong covalent interlayer bonding. This is opposite to the case for the graphite structure. The weak bonding in the hexagonal plane of the sh phase causes the soft transverse mode for this phase.

Heavy-ion effects on mammalian cells: inactivation measurements with different cell lines.

Abstract: In track segment experiments, the inactivation of different mammalian cells by heavy charged particles between helium and uranium in the energy range between 1 and 1000 MeV/u has been measured at the heavy ion accelerator Unilac, Darmstadt, the Tandem Van de Graaf, Heidelberg, and the Bevalac, Berkeley. The inactivation cross sections calculated from the final slope of the dose-effect curves are given as a function of the particle energy and the linear energy transfer.

Tunable Coherent X-rays

Abstract: A modern 1- to 2-billion-electron-volt synchrotron radiation facility (based on high-brightness electron beams and magnetic undulators) would generate coherent (laser-like) soft x-rays of wavelengths as short as 10 angstroms. The radiation would also be broadly tunable and subject to full polarization control. Radiation with these properties could be used for phase- and element-sensitive microprobing of biological assemblies and material interfaces as well as reserch on the production of electronic microstructures with features smaller than 1000 angstroms. These short wavelength capabilities, which extend to the K-absorption edges of carbon, nitrogen, and oxygen, are neither available nor projected for laboratory XUV lasers. Higher energy storage rings (5 to 6 billion electron volts) would generate significantly less coherent radiation and would be further compromised by additional x-ray thermal loading of optical components.

DC SQUIDs as radiofrequency amplifiers

Abstract: The optimization of radiofrequency amplifiers involving dc SQUIDs is discussed for both tuned and untuned input circuits. For a given frequency and input coil coupled to the SQUID, expressions are obtained for the optimum source resistance, gain, and noise temperature. The performance of two amplifiers designed according to these predictions is described. The gain of an untuned amplifier operated at 100 MHz and 4.2 K was 16.5±0.5 dB with a noise temperature of 3.8±0.9K; at 1.5 K the gain increased to 19.5±0.5 dB, while the noise temperature decreased to 0.9±0.4 K. A tuned amplifier operated at 93 MHz and 4.2 K had a gain of 18.6±0.5 dB and a noise temperature of 1.7±0.5 K. These results were in good agreement with predicted values.

The formation of radiation-induced DNA breaks: the ratio of double-strand breaks to single-strand breaks.

Abstract: Ionizing radiation causes the formation of strand breaks in cellular DNA, as well as other types of lesions in the chromatin of cells. Some of the earliest investigations of the molecular basis of radiation-induced damage and the implications of enzymatic repair were done by Dr. H. S. Kaplan. The induction frequency of DNA double-strand breaks is of special importance, and it is of interest to know the relative proportions of single-strand and double-strand breaks. This ratio changes noticeably with the radiation quality (ionization density). Because it is difficult to assay for DNA lesions in the large mammalian genome, we have developed a method of assaying for DNA double-strand breaks in the supercoiled nucleosome-complexed Simian virus 40 (SV40) genome, irradiated intracellularly. In this communication we present our measurements of the DNA double-strand breaks (DSBs) to single-strand breaks (SSBs) ratio obtained from the intracellularly irradiated SV40 genome. After cobalt gamma ray and X ray irradiations, this ratio is about 1/10. Our methods and results are compared with pertinent data in the literature. If the DSBs/SSBs ratio of 1/10 for cellular chromatin is correct, a substantial number of DNA double-strand breaks are formed in a mammalian cell after moderate doses (1 Gy) of radiation. The implications of different types of DNA double-strand breaks are discussed.

Measurements of the dynamic input impedance of a dc SQUID

Abstract: The impedance of a circuit coupled magnetically via a mutual inductanceM i to a dc SQUID of geometric inductanceL is modified by the dynamic input impedance of the SQUID, which can be characterized by the flux-to-current transfer functionJ Ф≡∂J/∂Ф;J is the current circulating in the SQUID loop and Ф is the flux applied to the loop. At the same time, the SQUID is modified by the presence of the input circuit: in the lumped circuit approximation, one expects its inductance to be reduced toL r=(1−α 2 )L, where α e is an effective coupling coefficient. Calculations of JФ using an analog simulator are described and presented in the form of a dynamic inductance ℒ and a dynamic resistance ℛ versus bias currentI and Ф. Experimental measurements of ℒ and ℛ were made on a planar, thin-film SQUID tightly coupled to a spiral input coil that was connected in series with a capacitorC i to form a resonant circuit. Thus,J Ф was determined from the change in the resonant freqency and quality factor of this circuit as a function ofI and Ф. At low bias currents (low Josephson frequencies) the measured values of ℒ were in reasonable agreement with values simulated for the reduced SQUID, while at higher bias currents (higher Josephson frequencies) the measured values were in better agreement with values simulated for the unscreened SQUID. Similar conclusions were reached in the comparison of the experimental and simulated values of the flux-to-voltage transfer functionV Ф. The reduction in the screening at the higher Josephson frequencies is believed to result from the parasitic capacitanceC p between the SQUID and the input coil. In contrast to the behavior of the input inductance, the change in the input resistance ΔR i could not be explained in terms of the dynamic impedance of the SQUID reflected into the input circuit. Instead, ΔR i was dominated by capacitive feedback between the output of the SQUID and the input circuit viaC p . The experimental values of ΔR i were satisfactorily explained by a simplified model that predicts ΔR i ⋍−M iV Ф r (C p /C i ).

A high-temperature high-resolution NMR study of 23 Na, 27 Al and 29 Si in molten silicates

Abstract: Molecular and atomic motions over longer distances, and with much lower frequencies than interatomic vibrations, have a major role in the energetic and dynamic properties of highly structured liquids such as molten aluminosilicates. Rearrangement with increasing temperature of the polymerized anionic network (composed of linked SiO44− and AlO45− tetrahedra) controls viscosity and influences thermal expansion and configurational heat capacity1,2. Diffusive motion of network modifying cations (such as Na+) through the structure allows electrical conductivity and probably also affects entropy. To study such motion directly and to compare liquid and glass structure, we have developed a novel high-temperature high-resolution NMR apparatus. We report here the first data on 23Na, 27Al, and 29Si in liquids in the system Na2O/Al2O3/SiO2 at temperatures to about 1,300 °C. Observed changes in NMR resonant frequencies (chemical shifts) give information on the effects of composition on local structure. Line shapes and widths, and relaxation time measurements, reveal details of the dynamics and of the transition from liquid to glass.