Showing papers by "Lawrence Berkeley National Laboratory published in 1991"

Tolerance of normal tissue to therapeutic irradiation.

Abstract: The importance of knowledge on tolerance of normal tissue organs to irradiation by radiation oncologists cannot be overemphasized. Unfortunately, current knowledge is less than adequate. With the increasing use of 3-D treatment planning and dose delivery, this issue, particularly volumetric information, will become even more critical. As a part of the NCI contract N01 CM-47316, a task force, chaired by the primary author, was formed and an extensive literature search was carried out to address this issue. In this issue. In this manuscript we present the updated information on tolerance of normal tissues of concern in the protocols of this contract, based on available data, with a special emphasis on partial volume effects. Due to a lack of precise and comprehensive data base, opinions and experience of the clinicians from four universities involved in the contract have also been contributory. Obviously, this is not and cannot be a comprehensive work, which is beyond the scope of this contract.

Reconciliation of neutron star masses and binding of the lambda in hypernuclei

Abstract: By relating scalar and vector couplings of the hyperons to the inferred empirical binding of the \ensuremath{\Lambda} hyperon in saturated nuclear matter, we obtain compatibility of this binding energy with neutron-star masses. Use of the observational constraint on the lower bound on the maximum neutron-star mass and the upper bound of the couplings that are compatible with hypernuclear levels, places bounds on the reduction in neutron-star mass that hyperons produce. For the best current estimate of nuclear-matter properties, the reduction in mass due to conversion of nucleons to hyperons is (0.71\ifmmode\pm\else\textpm\fi{}0.15)${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$. Neutrons comprise a slight majority population \ensuremath{\sim}${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$ neutron stars with mass \ensuremath{\sim}1.5${\mathit{M}}_{\mathrm{\ensuremath{\bigodot}}}$.

Endogenous mutagens and the causes of aging and cancer.

Abstract: A very large oxidative damage rate to DNA occurs as part of normal metabolism. In each rat cell the steady-state level is estimated to be about 106 oxidative adducts and about 105 new adducts are formed daily. It is argued that this endogenous DNA damage is a major contributor to aging and the degenerative diseases of aging, such as cancer. The oxidative damage rate in mammalian species with a high metabolic rate, short life span, and high age-specific cancer rate is much higher than the rate in humans, a long-lived creature with a lower metabolic rate and a lower age-specific cancer rate. It is argured that deficiency of micronutrients, such as dietary antioxidants or folate, is a major contributor to human cancer and degenerative diseases. Understanding the role of mitogenesis in mutagenesis is critical for clarifying the mechanisms of carcinogenesis and interpreting high-dose animal cancer tests. High-dose animal cancer tests have been done mainly on synthetic industrial chemicals, yet almost all of the chemicals humans are exposed to are natural. About half of natural chemicals tested in high-dose animal cancer tests are rodent carcinogens, a finding that is consistent with the view that high-dose tests frequently increase mitogenesis rates. Animals have numerous defenses against toxins that make them very well buffered against low doses of almost all toxins, whether synthetic or natural.

Control of mammary epithelial differentiation: basement membrane induces tissue-specific gene expression in the absence of cell-cell interaction and morphological polarity.

Abstract: Functional differentiation in mammary epithelia requires specific hormones and local environmental signals. The latter are provided both by extracellular matrix and by communication with adjacent cells, their action being intricately connected in what appears to be a cascade of events leading to milk production. To distinguish between the influence of basement membrane and that of cell-cell contact in this process, we developed a novel suspension culture assay in which mammary epithelial cells were embedded inside physiological substrata. Single cells, separated from each other, were able to assimilate information from a laminin-rich basement membrane substratum and were induced to express beta-casein. In contrast, a stromal environment of collagen I was not sufficient to induce milk synthesis unless accompanied by cell-cell contact. The expression of milk proteins did not depend on morphological polarity since E-cadherin and alpha 6 integrin were distributed evenly around the surface of single cells. In medium containing 5 microM Ca2+, cell-cell interactions were impaired in small clusters and E-cadherin was not detected at the cell surface, yet many cells were still able to produce beta-casein. Within the basement membrane substratum, signal transfer appeared to be mediated through integrins since a function-blocking anti-integrin antibody severely diminished the ability of suspension-cultured cells to synthesize beta-casein. These results provide evidence for a central role of basement membrane in the induction of tissue-specific gene expression.

The Secondary Alkaline Zinc Electrode

Abstract: Zinc is the most commonly used battery electrode, and zinc primary batteries have found numerous applications. The zinc electrode is electrochemically reversible in alkaline electrolytes, and there is a strong incentive to develop a practical secondary battery based on this metal. However, secondary batteries that use zinc electrodes typically exhibit short lifetimes, because of problems with zinc material redistribution and undesirable zinc morphologies that form during recharge. There has been a worldwide effort to develop a long‐lived secondary alkaline zinc electrode, and marked improvements in cell lifetimes have resulted. This article reviews these efforts, paying particular attention to research and development during the period 1975–1990.

Connections with multiple congested gateways in packet-switched networks part 1: one-way traffic

Abstract: In this paper we explore the bias in TCP/IP networks against connections with multiple congested gateways. We consider the interaction between the bias against connections with multiple congested gateways, the bias of the TCP window modification algorithm against connections with longer roundtrip times, and the bias of Drop Tail and Random Drop gateways against bursty traffic. Using simulations and a heuristic analysis, we show that in a network with the window modification algorithm in 4.3 tahoe BSD TCP and with Random Drop or Drop Tail gateways, a longer connection with multiple congested gateways can receive unacceptably low throughput. We show that in a network with no bias against connections with longer roundtrip times and with no bias against bursty traffic, a connection with multiple congested gateways can receive an acceptable level of throughput.We discuss the application of several current measures of fairness to networks with multiple congested gateways, and show that different measures of fairness have quite different implications. One view is that each connection should receive the same throughput in bytes/second, regardless of roundtrip times or numbers of congested gateways. Another view is that each connection should receive the same share of the network's scarce congested resources. In general, we believe that the fairness criteria for connections with multiple congested gateways requires further consideration.

Traffic phase effects in packet-switched gateways

Abstract: Much of the traffic in existing packet networks is highly periodic, either because of periodic sources (e.g., real time speech or video, rate control) or because window flow control protocols have a periodic cycle equal to the connection roundtrip time (e.g., a network-bandwidth limited TCP bulk data transfer). Control theory suggests that this periodicity can resonate (i.e., have a strong, non-linear interaction) with deterministic estimation or control algorithms in network gateways.1 In this paper we define the notion of traffic phase in a packet-switched network and describe how phase differences between competing traffic streams can be the dominant factor in relative throughput. Drop Tail gateways in a TCP/IP network with strongly periodic traffic can result in systematic discrimination against some connections. We demonstrate this behavior with both simulations and theoretical analysis. This discrimination can be eliminated with the addition of appropriate randomization to the network. In particular, analysis suggests that simply coding a gateway to drop a random packet from its queue (rather than the tail) on overflow is often sufficient.We do not claim that Random Drop gateways solve all of the problems of Drop Tail gateways. Biases against bursty traffic and long roundtrip time connections are shared by both Drop Tail and Random Drop gateways. Correcting the bursty traffic bias has led us to investigate a different kind of randomized gateway algorithm that operates on the traffic stream, rather than on the queue. Preliminary results show that the Random Early Detection gateway, a newly developed gateway congestion avoidance algorithm, corrects this bias against bursty traffic. The roundtrip time bias (at least in TCP/IP networks) results from the TCP window increase algorithm, not from the gateway dropping policy, and we briefly discuss changes to the window increase algorithm that could eliminate this bias.

Energy loss of a heavy quark in the quark-gluon plasma.

Abstract: The energy loss {ital dE}/{ital dx} for a heavy quark propagating through a quark-gluon plasma is calculated to leading order in the QCD coupling constant. Simple formulas for {ital dE}/{ital dx} are obtained in the regions {ital E}{much lt}{ital M}{sub {ital Q}}{sup 2}/{ital T} and {ital E}{much gt}{ital M}{sub {ital Q}}{sup 2}/{ital T}, where {ital M}{sub {ital Q}} is the mass of the heavy quark and {ital T} is the temperature. The crossover energy between the two regions is determined to be approximately 1.8{ital M}{sub {ital Q}}{sup 2}/{ital T}. Under conditions relevant to ultrarelativistic heavy-ion collisions, charm quarks and bottom quarks lie on opposite sides of the crossover energy and therefore experience significantly different energy losses.

Energy loss of a heavy fermion in a hot QED plasma.

Abstract: The energy loss $\frac{\mathrm{dE}}{\mathrm{dx}}$ for a heavy lepton propagating through a high-temperature QED plasma is calculated to leading order in the QED coupling constant. The screening effects of the plasma are computed consistently using a resummation of perturbation theory in the small-momentum-transfer region. At large momentum transfer, recoil effects are properly taken into account. Our complete leading-order calculation differs significantly from previous calculations.

Radiation injury of the brain.

Abstract: The clinical, radiologic, and pathologic findings in radiation injury of the brain are reviewed. Late radiation injury is the major, dose-limiting complication of brain irradiation and occurs in two forms, focal and diffuse, which differ significantly in clinical and radiologic features. Focal and diffuse injuries both include a wide spectrum of abnormalities, from subclinical changes detectable only by MR imaging to overt brain necrosis. Asymptomatic focal edema is commonly seen on CT and MR following focal or large-volume irradiation. Focal necrosis has the CT and MR characteristics of a mass lesion, with clinical evidence of focal neurologic abnormality and raised intracranial pressure. Microscopically, the lesion shows characteristic vascular changes and white matter pathology ranging from demyelination to coagulative necrosis. Diffuse radiation injury is characterized by periventricular decrease in attenuation of CT and increased signal on proton-density and T2-weighted MR images. Most patients are asymptomatic. When clinical manifestations occur, impairment of mental function is the most prominent feature. Pathologic findings in focal and diffuse radiation necrosis are similar. Necrotizing leukoencephalopathy is the form of diffuse white matter injury that follows chemotherapy, with or without irradiation. Vascular disease is less prominent and the latent period is shorter than in diffuse radiation injury; radiologic findings and clinical manifestations are similar. Late radiation injury of large arteries is an occasional cause of postradiation cerebral injury, and cerebral atrophy and mineralizing microangiopathy are common radiologic findings of uncertain clinical significance. Functional imaging by positron emission tomography can differentiate recurrent tumor from focal radiation necrosis with positive and negative predictive values for tumor of 80-90%. Positron emission tomography of the blood-brain barrier, glucose metabolism, and blood flow, together with MR imaging, have demonstrated some of the pathophsiology of late radiation necrosis. Focal glucose hypometabolism on positron emissin tomography in irradiated patients may have prognostic significance for subsequent development of clinically evident radiation necrosis.

Vacuum arc ion charge-state distributions

Abstract: Vacuum arc ion charge-state spectra have been measured for a wide range of metallic cathode materials. The charge-state distributions were measured using a time-of-flight diagnostic to monitor the energetic ion beam produced by a metal vapor vacuum arc ion source. Data were obtained for 48 metallic cathode elements: Li, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn Fe, Co, Ni, Cu, Zn, Ge, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er Yb, Hf, Ta, W, Ir, Pt, Au Pb, Bi, Th, and U. The arc was operated in a pulsed mode with pulse length 0.25 ms: arc current was 100 A throughout. The measured distributions are cataloged and compared with earlier results. Some observations about the performance of the various elements as suitable vacuum arc cathode materials are also presented. >

Proteinases of the mammary gland: developmental regulation in vivo and vectorial secretion in culture

Abstract: The extracellular matrix (ECM) is an important regulator of mammary epithelial cell function both in vivo and in culture. Substantial remodeling of ECM accompanies the structural changes in the mammary gland during gestation, lactation and involution. However, little is known about the nature of the enzymes and the processes involved. We have characterized and studied the regulation of cell-associated and secreted mammary gland proteinases active at neutral pH that may be involved in degradation of the ECM during the different stages of mammary development. Mammary tissue extracts from virgin and pregnant CD-1 mice resolved by zymography contained three major proteinases of 60K (K = 10(3) Mr), 68K and 70K that degraded denatured collagen. These three gelatinases were completely inhibited by the tissue inhibitor of metalloproteinases. Proteolytic activity was lowest during lactation especially for the 60K gelatinase which was shown to be the activated form of the 68K gelatinase. The activated 60K form decreased prior to parturition but increased markedly after the first two days of involution. An additional gelatin-degrading proteinase of 130K was expressed during the first three days of involution and differed from the other gelatinases by its lack of inhibition by the tissue inhibitor of metalloproteinases. The activity of the casein-degrading proteinases was lowest during lactation. Three caseinolytic activities were detected in mammary tissue extracts. A novel 26K cell-associated caseinase--a serine arginine-esterase--was modulated at different stages of mammary development. The other caseinases, at 92K and a larger than 100K, were not developmentally regulated. To find out which cell type produced the proteinases in the mammary gland, we isolated and cultured mouse mammary epithelial cells. Cells cultured on different substrata produced the full spectrum of gelatinases and caseinases seen in the whole gland thus implicating the epithelial cells as a major source of these enzymes. Analysis of proteinases secreted by cells grown on a reconstituted basement membrane showed that gelatinases were secreted preferentially in the direction of the basement membrane. The temporal pattern of expression of these proteinases and the basal secretion of gelatinases by epithelial cells suggest their involvement in the remodelling of the extracellular matrix during the different stages of mammary development and thus modulation of mammary cell function.

Identification and characterization of zinc binding sites in protein kinase C.

Abstract: Metal ion coordination in the regulatory domain of protein kinase C (PKC) is suggested by the conservation of six cysteines and two histidines in two homologous regions found therein. By monitoring x-ray fluorescence from a purified sample of rat PKC beta I overexpressed in insect cells, direct evidence has been obtained that PKC beta I tightly binds four zinc ions (Zn2+) per molecule. Extended x-ray absorption fine structure (EXAFS) data are best fit by an average Zn2+ coordination of one nitrogen and three sulfur atoms. Of the plausible Zn2+ coordination models, only those featuring nonbridged Zn2+ sites accommodate the EXAFS data and all of the conserved potential ligands.

Measurement of the Lamb shift in lithiumlike uranium (U89

Abstract: The 2{sup 2}{ital P}{sub 1/2}-2{sup 2}{ital S}{sub 1/2} (lowest-excited-state to ground-state) energy splitting in lithiumlike uranium, which has large quantum-electrodynamic corrections, has been measured using Doppler-tuned spectrometry. Our result, 280.59{plus minus}0.10 eV, is more precise than current theory and is an 80-fold improvement over the previous most precise measurement of the Lamb shift in (heliumlike) uranium.

Nonlinear optical studies of the pure liquid/vapor interface: Vibrational spectra and polar ordering

Abstract: Using infrared-visible sum-frequency generation we have obtained the vibrational spectra of CH stretches of methanol molecules at the interface between methanol vapor and liquid. This is the first vibrational spectrum ever observed from a neat liquid surface. The measured polarization dependence and phase of the nonlinear susceptibility allow us to conclude that the surface methanol molecules are polar oriented with the ${\mathrm{CH}}_{3}$ group pointing away from the liquid with a very broad orientational distribution.

Quasiparticle band structure of thirteen semiconductors and insulators.

Abstract: By using a model dielectric matrix in electron self-energy evaluations the computational effort of a quasiparticle band-structure calculation for a semiconductor is greatly reduced. Applications to various systems with or without inversion symmetry, having narrow or wide band gaps, and semiconductor alloys demonstrate the reliability and accuracy of the method. Calculations have been performed for thirteen semiconducting or insulating materials: Si, LiCl, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, and the Al{sub 0.5}Ga{sub 0.5}As and In{sub 0.53}Ga{sub 0.47}As alloys. Excellent agreement with experimental results is obtained for the quasiparticle energies for these materials. The only three exceptions, {ital E}({Gamma}{sub 1{ital c}}) of AlP, {ital E}({ital L}{sub 1{ital c}}) of AlAs, and {ital E}({ital L}{sub 1{ital c}}) of AlSb are discussed and attributed to various experimental uncertainties. Several other quasiparticle-excitation-related properties are also examined in this work. The many-body corrections to the eigenvalues of the valence-band-maximum states obtained from the local-density approximation are calculated for the zinc-blende-structure semiconductors, which are widely used in semiconductor-interface studies. In the present approach, the static screening of the Coulomb interaction between two electrons in a crystal is determined using a model that depends only on the local charge densities at these two points.more » Since a direct quantitative modeling of the electron self-energy operator has proven difficult, the successful application of the present model-dielectric-function scheme in self-energy calculations makes possible detailed studies of the quasiparticle properties of rather complex systems, which would be otherwise computationally too demanding.« less

Human electroretinogram responses to video displays, fluorescent lighting, and other high frequency sources.

Abstract: Time-averaged human electroretinogram (ERG) responses were determined for several workplace visual stimuli which are temporally modulated at rates exceeding the perceptual critical fusion frequency (CFF). A clearly identifiable synchronous response was in evidence for a video display terminal (VDT) stimulus operating with a refresh rate as high as 76 Hz. A directly viewed fluorescent luminaire with controllable driving frequency elicited a synchronous response at rates as high as 145 Hz. In addition, an intense stimulus created by modulating the light from a slide projector produced responses at least as high as 162 Hz. The implications of these high-frequency responses are representing a potential basis for visual symptoms are discussed.

Non-Markovian dephasing of molecules in solution measured with three-pulse femtosecond photon echoes

Abstract: The electronic dephasing of large molecules in solution is investigated with three-pulse photon echoes generated by 6-fs optical pulses. The observed dephasing behavior, which is analyzed with a model based on a stochastic coupling of the molecules with their heat bath, is clearly shown to be non-Markovian. Moreover, the correlation function of the fluctuations asymptotically approaches an exponential with characteristic times varying from 20 to 80 fs, depending on the solvent environment.

Quasiparticle energies for cubic bn, bp, and bas

Abstract: Electronic excitation energies at the high-symmetry points \ensuremath{\Gamma}, X, and L are obtained for zinc-blende-structure BN, BP, and BAs in the GW approximation using a model dielectric function. A model for the static screening matrix makes use of the ab initio ground-state charge density and either experimental values or empirical estimates for ${\mathrm{\ensuremath{\epsilon}}}_{\mathrm{\ensuremath{\infty}}}$, the electronic contribution to the macroscopic dielectric constant. Wave functions from an ab initio local-density-approximation calculation with norm-conserving pseudopotentials are employed along with the self-consistent quasiparticle spectrum to obtain the energy-dependent one-particle Green function G. The minimum band gaps are found to be 6.3, 1.9, and 1.6 eV for BN, BP, and BAs, respectively, in close agreement with existing measurements of 6.1 and 2.0 eV for BN and BP, respectively. The BN direct band gap is predicted to be 11.4 eV versus the experimental value of 14.5 eV, and the BP direct band gap is predicted to be 4.4 eV versus 5.0 eV from experiment.

Electromagnetic fields of surface coil in vivo NMR at high frequencies.

Abstract: A high frequency solution of the electromagnetic field produced by a circular surface coil adjacend to a homogenous conducting, dielectric sphere is used to predict the attainable signal to noise ratio (S/N) and specific absorption rate (SAR) for in vivo1H NMR spec troscopy experiments from 200 to 430 MHz (47–10T) Above 200 MHz the S/N increases more rapidly with frequency and the SAR increases less rapidly compared with the respective S/N and SAR frequency dependence below 200 MHz The difference in frequency dependence is due to dielectric resonances of the magnetic field inside the sphere at frequencies above 200 MHz It is predicted that surface coil 1H NMR experiments may be performed on a head-sized sphere, having conductivity and relative dielectric constant of brain, at frequencies up to 430 MHz without exceeding 8 W/kg local SAR and 32 W/kg SAR The calculations of the S/N and SAR are used to determine optimum surface coil geometries for NMR experments The power radited by the surface coil in the absence of shielding and asymmetries in the received signal with respect to the plane defined by the surface coil axix and the direction of the static magnetic field are significant at high frequency Experimental measurements of the magnetic field inside a head-sized sphere verfy the presence of dielectric resonances at frequencies above 200 MHz © 1991 Academic Press, Inc

Perioperative thermal insulation.

Abstract: To determine the efficacy of passive insulators advocated for prevention of cutaneous heat loss, we determined heat loss in unanesthetized volunteers covered by one of the following: a cloth "split sheet" surgical drape; a Convertors disposable-paper split sheet; a Thermadrape disposable laparotomy sheet; an unheated Bair Hugger patient-warming blanket; 1.5-mil-thick plastic hamper bags; and a prewarmed, cotton hospital blanket. Cutaneous heat loss was measured using 10 area-weighted thermal flux transducers while volunteers were exposed to a 20.6 degrees C environment for 1 h. Heat loss decreased significantly from 100 +/- 3 W during the control periods to 69 +/- 6 W (average of all covers) after 1 h of treatment. Heat losses from volunteers insulated by the Thermadrape (61 +/- 6 W) and Bair Hugger covers (64 +/- 5 W) were significantly less than losses from those insulated by plastic bags (77 +/- 11 W). The paper drape (67 +/- 7 W) provided slightly, but not significantly, better insulation than the cloth drape (70 +/- 4 W). Coverage by prewarmed cotton blankets initially resulted in the least heat loss (58 +/- 8 W), but after 40 min, resulted in heat loss significantly greater than that for the Thermadrape (71 +/- 7 W). Regional heat loss was roughly proportional to surface area, and the distribution of regional heat loss remained similar with all covers. These data suggest that cost and convenience should be major factors when choosing among passive perioperative insulating covers. It is likely that the amount of skin surface covered is more important than the choice of skin region covered or the choice of insulating material.