Showing papers by "Colorado State University published in 1990"

Protein secondary structures in water from second-derivative amide I infrared spectra.

Abstract: Infrared spectra have been obtained for 12 globular proteins in aqueous solution at 20 degrees C. The proteins studied, which vary widely in the relative amounts of different secondary structures present, include myoglobin, hemoglobin, immunoglobulin G, concanavalin A, lysozyme, cytochrome c, alpha-chymotrypsin, trypsin, ribonuclease A, alcohol dehydrogenase, beta 2-microglobulin, and human class I major histocompatibility complex antigen A2. Criteria for evaluating how successfully the spectra due to liquid and gaseous water are subtracted from the observed spectrum in the amide I region were developed. Comparisons of second-derivative amide I spectra with available crystal structure data provide both qualitative and quantitative support for assignments of infrared bands to secondary structures. Band frequency assignments assigned to alpha-helix, beta-sheet, unordered, and turn structures are highly consistent among all proteins and agree closely with predictions from theory. alpha-Helix and unordered structures can each be assigned to only one band whereas multiple bands are associated with beta-sheets and turns. These findings demonstrate a method of analysis of second-derivative amide I spectra whereby the frequencies of bands due to different secondary structures can be obtained. Furthermore, the band intensities obtained provide a useful method for estimating the relative amounts of different structures.

Genetic algorithms and neural networks: optimizing connections and connectivity

Abstract: Genetic algorithms are a robust adaptive optimization method based on biological principles. A population of strings representing possible problem solutions is maintained. Search proceeds by recombining strings in the population. The theoretical foundations of genetic algorithms are based on the notion that selective reproduction and recombination of binary strings changes the sampling rate of hyperplanes in the search space so as to reflect the average fitness of strings that reside in any particular hyperplane. Thus, genetic algorithms need not search along the contours of the function being optimized and tend not to become trapped in local minima. This paper is an overview of several different experiments applying genetic algorithms to neural network problems. These problems include 1. (1) optimizing the weighted connections in feed-forward neural networks using both binary and real-valued representations, and 2. (2) using a genetic algorithm to discover novel architectures in the form of connectivity patterns for neural networks that learn using error propagation. Future applications in neural network optimization in which genetic algorithm can perhaps play a significant role are also presented.

The Relevance of the Microphysical and Radiative Properties of Cirrus Clouds to Climate and Climatic Feedback

Abstract: This paper examines the effects of the relationship between cirrus cloud ice water content and cloud temperature on climate change A simple mechanistic climate model is used to study the feedback between ice water content and temperature The central question studied in this paper concerns the extent to which both the radiative and microphysical properties of cirrus cloud influence such a feedback To address this question, a parameterization of the albedo and emissivity of clouds is introduced Observations that relate the ice water content to cloud temperature are incorporated in the parameterization to introduce a temperature dependence to both albedo and emittance The cloud properties relevant to the cloud feedback are expressed as functions of particles size re, asymmetry parameter g and cloud temperature and analyses of aircraft measurements, lidar and ground based radiometer data are used to select re and g It was shown that scattering calculations assuming spherical particles with a di

Physical habitat template of lotic systems: Recovery in the context of historical pattern of spatiotemporal heterogeneity

Abstract: Spatial and temporal environmental heterogeneity in lotic ecosystems can be quantitatively described and identified with characteristic levels of ecological organization. The long-term pattern of physicochemical variability in conjunction with the complexity and stability of the substratum establishes a physical habitat template that theoretically influences which combinations of behavioral, physiological and life history characteristics constitute appropriate “ecological strategies” for persistence in the habitat. The combination of strategies employed will constrain ecological response to and recovery from disturbance. Physical habitat templates and associated ecological attributes differ geographically because of biogeoclimatic processes that constrain lotic habitat structure and stability and that influence physicochemical variability and disturbance patterns (frequency, magnitude, and predictability). Theoretical considerations and empirical studies suggest that recovery from natural and anthropogenic disturbance also will vary among lotic systems, depending on historical temporal variability regime, degree of habitat heterogeneity, and spatial scale of the perturbation. Characterization of physical habitat templates and associated ecological dynamics along gradients of natural disturbance would provide a geographic framework for predicting recovery from anthropogenic disturbance for individual streams. Description of lotic environmental templates at the appropriate spatial and temporal scale is therefore desirable to test theoretical expectations of biotic recovery rate from disturbance and to guide selection of appropriate reference study sites for monitoring impacts of anthropogenic disturbance. Historical streamflow data, coupled with stream-specific thermal and substratum-geomorphologic characteristics, are suggested as minimum elements needed to characterize physical templates of lotic systems.

Regions of the skeletal muscle dihydropyridine receptor critical for excitation-contraction coupling.

Abstract: IT is thought that in skeletal muscle excitation–contraction (EC) coupling, the release of Ca2+ from the sarcoplasmic reticulum is controlled by the dihydropyridine (DHP) receptor in the transverse tubular membrane, where it serves as the voltage sensor1–3. We have shown previously4 that injection of an expression plasmid carrying the skeletal muscle DHP receptor complementary DNA3 restores EC coupling and L-type calcium current that are missing in skeletal muscle myotubes from mutant mice with muscular dysgenesis5–9. This restored coupling resembles normal skeletal muscle EC coupling4, which does not require entry of extracellular Ca2+ (refs 10, 11). By contrast, injection into dysgenic myotubes of an expression plasmid carrying the cardiac DHP receptor cDNA12 produces L-type calcium current and cardiac-type EC coupling13, which does require entry of extracellular Ca2+ (refs 14–16). To identify the regions responsible for this important functional difference between the two structurally similar DHP receptors, we have expressed various chimaeric DHP receptor cDNAs in dysgenic myotubes. The results obtained indicate that the putative cytoplasmic region between repeats II and III of the skeletal muscle DHP receptor3 is an important determinant of skeletal-type EC coupling.

A new mode of communication between man and his surroundings

Abstract: The feasibility of establishing an alternative mode of communication between man and his surroundings was studied. The form of communication proposed uses only the subject's brain waves, with no overt physical action required. The subject's electroencephalograms (EEG) were recorded while various mental tasks designed to elicit hemispheric responses were performed. Features formed from the EEG recording were then used as inputs into a Bayes quadratic classifier to test classification accuracy between the various tasks. The results obtained indicate that it is possible to accurately distinguish between any two of the five tasks investigated. A comparison between three different methods for creating the feature sets is also presented. >

Adolescent drug use: findings of national and local surveys.

Abstract: Adolescent drug use increased until about 1981, but since then it has steadily declined. Current data show some drug use in the 4th and 5th grades and considerable increases from the 6th to the 9th grades. For drugs such as marijuana, cocaine, and stimulants, lifetime prevalence continues to increase through high school; for drugs such as inhalants and heroin, lifetime prevalence may decline for Grades 10, 11, and 12, suggesting that students who use these drugs early may drop out. Drug use of rural youth is similar to that of other youth. Barrio, ghetto, and Native-American reservation youth may have high rates of use, but use of Black and Hispanic seniors may be equivalent to or less than that of White seniors. National data and broadly defined ethnic data, however, may cover up important subgroup differences. For example, Western Mexican-American girls have lower use than Western Spanish-American girls, possibly because of the greater influence of "marianisma." Different locations may also have very different patterns of adolescent drug use, calling for different types of local intervention.

Plant Response to Herbivory and Belowground Nitrogen Cycling

Abstract: Plant responses to herbivory and links to belowground nitrogen cycling were investigated at Wind Cave National Park, South Dakota. Laboratory estimates of net nitrogen mineralization were highest in soils from the more altered areas of prairie dog colonies (Cynomys ludovicianus) and lowest in the adjacent, lightly grazed, uncolonized grassland. The ratio of CO2: net nitrogen mineralized, an index of immobilization, was highest in the uncolonized grassland and lowest in the altered core areas. Soil moisture was an important modifier of in situ field estimates of net nitrogen mineralization. Root biomass, an important carbon source for decomposers in perennial grasslands, was lowest in the altered core area and highest in the adjacent uncolonized grassland. Decreased nitrogen immobilization and increased net nitrogen mineralization in the laboratory in- cubations likely resulted from decreased root carbon inputs in grazed areas, which limited carbon availability to decomposers. Such increases in plant-available nitrogen may partially explain the frequently reported grazing-induced increases in shoot nitrogen concentrations. These studies suggest that carbon allocation to roots is a key link determining nitrogen- cycling responses to herbivory.

A review of synchronization of estrus in postpartum cattle.

Abstract: Estrus has been synchronized in cattle with progestogens, prostaglandins (prostaglandin F2 alpha and its analogues), progestogen-estrogen combinations and progestogen-prostaglandin combinations. Progestogens administered for 14 to 20 d are effective in synchronizing estrus; however, fertility at the synchronized estrus is subnormal. Duration of progestogen treatment can be reduced by combining it with an estrogen. Syncro-Mate B is a progestogen-estrogen combination that results in a tightly synchronized estrous response. Prostaglandins can be used in double- or single-injection programs. Fertility of the estrus after prostaglandin treatment is similar to that of controls. Estrus also has been synchronized effectively by combining a 5- to 9-d progestogen treatment with prostaglandin at or near the end of treatment. When prostaglandin is used alone, cattle in the late stages of the luteal phase (d 11 to 15 of the estrous cycle) at the time of prostaglandin injection have a higher estrous response and may be more fertile than those injected with prostaglandin in the early part (d 6 to 9) of the luteal phase. More recently, a 14-d progestogen treatment has been combined with a prostaglandin injection given 16 to 18 d after progestogen withdrawal. This system places cattle in the late luteal phase of the estrous cycle at the time of prostaglandin injection and has resulted in an estrus with greater fertility than that immediately following progestogen treatment.

Influence of landscape structure on local and regional climate

Abstract: This paper discusses the physical linkage between the surface and the atmosphere, and demonstrates how even slight changes in surface conditions can have a pronounced effect on weather and climate. Observational and modeling evidence are presented to demonstrate the influence of landscape type on the overlying atmospheric conditions. The albedo, and the fractional partitioning of atmospheric turbulent heat flux into sensible and latent fluxes is shown to be particularly important in directly affecting local and regional weather and climate. It is concluded that adequate assessment of global climate and climate change cannot be achieved unless mesoscale landscape characteristics and their changes over time can be accurately determined.

GENITOR II.: a distributed genetic algorithm

Abstract: GENITOR is a genetic algorithm which employs one-at-a-time reproduction and allocates reproductive opportunities according to rank to achieve selective pressure. Theoretical arguments and empirical evidence suggest that GENITOR is less vulnerable to some of the biases that degrade performance in standard genetic algorithms. A distributed version of GENITOR which uses many smaller distributed populations in place of a single large population is introduced. GENITOR II is able to optimize a broad range of sample problems more accurately and more consistently than GENITOR with a single population. GENITOR II also appears to be more robust than a single population genetic algorithm, yielding better performance without parameter tuning. We present some preliminary analyses to explain the performance advantage of the distributed algorithm. A distributed search is shown to yield improved search on several classes of problems, including binary encoded feedforward neural networks, the Traveling Salesman Pr...

An Examination of Propagation Effects in Rainfall on Radar Measurements at Microwave Frequencies

Abstract: Propagation effects in rainfall are examined at three microwave frequencies corresponding to S (3.0 GHz), C (5.5 GHz), and X ( 10.0 GHz) bands. Attenuation at horizontal polarization, as well a s differential attenuation and differential propagation phase between horizontal (HI and vertical ( V ) polarizations are considered. It is shown that at the three frequencies both attenuation and differential attenuation are nearly linearly related to differential propagation phase ( cbDP). This is shown through simulation using ( a ) gamma raindrop size distributions (RSD) with three parameters (No, DO. m ) that are varied over a very wide range representing a variety of rainfall types, and ( b ) measured raindrop size distributions at a single location using a disdrometer. Measurements of X-band specific attenuation and S-band specific differential phase in convective rainshafts using the National Center for Atmospheric Research CP-2 radar are presented in order to experimentally demonstrate the linear relationship between attenuation and differential propagation phase. Correction procedures for reflectivity and differential reflectivity (&) are developed assuming that differential propagation phase is measured using a radar that alternately transmits H and V polarized waves with copolar reception through the same receiver and processor system. The correction procedures are not dependent on the actual rainrate profile between the radar and the range location of interest. The accuracy of the procedure depends on, (a) RSD fluctuations, (b) variability in the estimate of differential propagation phase due to measurement fluctuations, and ( c ) nonzero values of the backscatter differential phase ( & ) between H and V polarizations. Simulations are used to gauge the accuracy of correction procedures at S- and C-bands assuming 6 is negligible. The correction accuracy for attenuation at S-band is estimated to be -0.05 dB while at C-band it is estimated to be within I dB if (IDP G 60 deg). Simulations further indicate that C-band differential attenuations effects can be corrected to within -35% of the mean value.

Recognition of a peptide antigen by heat shock--reactive gamma delta T lymphocytes.

Abstract: Small synthetic peptides that correspond to different portions of the 65-kilodalton mycobacterial heat shock protein (Hsp65) were used to identify a putative antigenic epitope for gamma delta cells. Weaker gamma delta responses to the equivalent portion of the autologous homolog, mouse Hsp63, were also seen. The stimulatory epitope overlaps with an epitope recognized by arthritogenic alpha beta T cell clones. The data suggest that gamma delta cells have a role in autoimmune disorders and imply that these cells recognize ligands by a mechanism similar to that of alpha beta T lymphocytes, that is, in the form of small processed protein fragments bound to antigen-presenting molecules.

Intramembrane charge movement restored in dysgenic skeletal muscle by injection of dihydropyridine receptor cDNAs.

Abstract: THE skeletal muscle dihydropyridine (DHP) receptor is essential in excitation–contraction (EC) coupling1–4. The receptor is postulated to be the voltage sensor giving rise to the intramembrane current, termed charge movement5. We have now tested this hypothesis using myotubes from mice with the muscular dysgenesis mutation, which alters the skeletal muscle DHP receptor gene and prevents its expression3,4,6. Our results indicate that charge movement is deficient in dysgenic myotubes but is fully restored following injection of an expression plasmid carrying the rabbit skeletal muscle DHP receptor complementary DNA, strongly supporting the hypothesis that the DHP receptor is the voltage sensor for EC coupling in skeletal muscle. Additionally, our data obtained for normal and chimaeric DHP receptor constructs demonstrate that DHP receptors with widely differing abilities to function as calcium channels and to mediate EC coupling produce very similar charge movements

Savanna tree influence on understory vegetation and soil nutrients in northwestern Kenya

Abstract: Contrary to observations and models in which trees and herbaceous plants are viewed as competitors, we found that trees in an African savanna have positive impacts on herbaceous biomass production and compo- sition, and on soil nutrient status. In the Turkana District of northwestem Kenya, we investigated vegetation and soil gradients along equi-angular transects radiating from the boles of individual Acacia tortilis trees. Total herba- ceous biomass averaged 260 ? 17(se) g/m2 at the bole and declined to 95 ? 8 g/m2 in the tree interspaces. Soil organic carbon and total nitrogen concentrations were greatest (0.72 % and 0.083 %, respectively) in shallow soils near the bole and declined rapidly toward the inter- spaces and with increasing depth. Transects were also established between tree pairs to assess effects of differ- ential canopy proximities. Grass production averaged 220 + 21 g / m2 below overlapping canopies, 150 ? 15 g / m2 under individual canopies, and 95 ? 8 g / m2 in interstitial areas. Detrended correspondence analysis revealed that shifts in species composition were correlat- ed with distance from tree bole out to the edge of the canopy. Species response, in terms of relative cover, to increasing distance from the bole, seemed to fall into five general classes: 1) greatest at the bole, 2) increasing with distance from the bole, 3) greatest in the mid canopy zone, 4) least at the bole and 5) no response. Trees did not influence herbaceous composition beyond tree canopies. It is assumed that shade cast by the tree canopy with subsequent reductions of understory water stress and temperature and increased nutrient concentrations may be the most important factors affecting understory soil and vegetation.

Cardiac-type excitation-contraction coupling in dysgenic skeletal muscle injected with cardiac dihydropyridine receptor cDNA

Abstract: There are dihydropyridine (DHP)-sensitive calcium currents in both skeletal and cardiac muscle cells, although the properties of these currents are very different in the two cell types (for simplicity, we refer to currents in both tissues as L-type). The mechanisms of depolarization-contraction coupling also differ. As the predominant voltage-dependent calcium current of cardiac cells, the L-type current represents a major pathway for entry of extracellular calcium. This entry triggers the subsequent large release of calcium from the sarcoplasmic reticulum (SR). In contrast, depolarization of skeletal muscle releases calcium from the SR without the requirement for entry of extracellular calcium through L-type calcium channels. To investigate the molecular basis for these differences in calcium currents and in excitation-contraction (E-C) coupling, we expressed complementary DNAs for the DHP receptors from skeletal and cardiac muscle in dysgenic skeletal muscle. We compared the properties of the L-type channels produced and showed that expression of a cardiac calcium channel in skeletal muscle cells results in E-C coupling resembling that of cardiac muscle.

On the cloud absorption anomaly

Abstract: This paper provides an overview of the subject of absorption of solar radiation by water clouds in the earth's atmosphere. the paper summarizes the available evidence which points to disagreements between theoretical and observed values of both cloud absorption and reflection. the importance of these discrepancies, particularly to remote sensing of clouds as well as to studies of cloud physics and earth radiation budgets, is emphasized. Existing cloud absorption and reflection measurements are reviewed and the persistent differences that exist between calculated and measured near-infrared cloud albedos are highlighted. Various explanations for these reflection and absorption discrepancies are discussed and a simple outline of the theory of cloud absorption is provided. This outline is used to examine the large-droplet hypothesis as well as the effects of absorbing aerosol and enhanced water vapour continuum absorption. A further hypothesis regarding the effects of cloud inhomogeneities is also examined. While the theory of cloud absorption is not completely understood, especially with regard to inhomogeneous clouds, the underlying conclusion of this paper points to the need for better measurements of solar radiation in clouds, water vapour absorption and microphysics properties of clouds.

Strong association between west african rainfall and u.s. Landfall of intense hurricanes.

Abstract: Intense hurricanes occurred much more frequently during the period spanning the late 1940s through the late 1960s than during the 1970s and 1980s, except for 1988 and 1989. Seasonal and multidecadal variations of intense hurricane activity are closely linked to seasonal and multidecadal variations of summer rainfall amounts in the Western Sahel region of West Africa. The multidecadal nature of West African precipitation variations and their association with variations of intense Atlantic hurricane activity can be observed in data going back nearly a century. The apparent recent breaking of the 18-year Sahel drought during 1988 and 1989 suggests that the incidence of intense hurricanes making landfall on the U.S. coast and in the Caribbean basin will likely increase during the 1990s and early years of the 21st century to levels of activity notably greater than were observed during the 1970s and 1980s.

Network resilience: a measure of network fault tolerance

Abstract: A probabilistic measure of network fault tolerance expressed as the probability of a disconnection is proposed. Qualitative evaluation of this measure is presented. As expected, the single-node disconnection probability is the dominant factor irrespective of the topology under consideration. The authors derive an analytical approximation to the disconnection probability and verify it with a Monte Carlo simulation. On the basis of this model, the measures of network resilience and relative network resilience are proposed as probabilistic measures of network fault tolerance. These are used to evaluate the effects of the disconnection probability on the reliability of the system. >

The effect of conformation on the CD of interacting helices: A theoretical study of tropomyosin

Abstract: A recent report [M. E. Holtzer, et al. (1988) Biophysics Journal, 53, 96a] of the anomalous CD spectrum of the tropomyosin (TM) fragment 11TM127 motivated us to model the system as two 21-residue alpha-helices distorted to a coiled-coil conformation. We used strong-coupling exciton theory to model the optical properties of the system. Two backbone amide excited states (n pi* and pi pi*) were considered, as well as four excited states (Lb, La, Bb, Ba) for the phenolic side chain. We calculated the effect of superhelix formation on the backbone CD spectrum. The decrease in molar ellipticity of the alpha-helix parallel-polarized transition at 208 nm was found to be a simple function of superhelix tilt angle. We then modeled a coiled coil (radius = 5.5 A, pitch = -140 A) with one aromatic ring per superhelix. Steric interactions between aromatic side chains in a coiled coil were calculated as a function of side-chain conformation and heptet position. Steric interactions between phenolic rings will be significant for heptet positions a and d, but not for positions b, c, e, f, or g. We calculated the phenolic Lb transition rotational strength as a function of position within the heptet repeats, and of all possible side-chain dihedral angles, chi 1 and chi 2. When tyrosines were placed at heptet positions b, c, e, f, or g, the rotational-strength surface was nearly identical to that of a single tyrosine in an undistorted helix. In contrast, the rotational-strength surface for tyrosines in heptet positions a or d showed substantial intertyrosine coupling components. The rotational-strength surfaces for the three types of heptet positions (position a, position d, and the others) allowed an interpretation of the aromatic CD spectra of TM and its fragments. It was predicted that the three types of heptet positions will be spectroscopically distinguishable.

The role of prostaglandins in bone in vivo.

Abstract: Prostaglandins of the E series, primarily E2 and E1, have the greatest activity in bone. Following discovery of their potent ability to stimulate bone resorption in vitro, clinical investigations have placed prostaglandins at sites of localized bone resorption associated with inflammatory or space occupying lesions in vivo. These studies have shown that prostaglandin production at such sites may be increased by cytokines such as interleukin-1 but the mechanisms by which prostaglandins stimulate bone resorption are not yet known. Observation of periosteal bone formation in patients given, pharmacological doses of prostaglandin has led to investigation of its bone forming activity. Young, growing rats have increased metaphyseal bone formation and this is accompanied by increased periosteal and endocortical bone formation in older animals. In the mature animals there is a generalized activation of remodelling with increased formation in the remodeling cycle. This is also seen in oophorectomized rats and results in repletion of the lost bone in this model of osteoporosis. In animal models of localized disuse osteopenia, prostaglandins are found to be elevated at the site of bone loss and prostaglandin inhibitors at least partially protect against the exaggerated resorption that occurs. This is also seen in models of orthodontic tooth movement, periodontitis and osteomyelitis. Prostaglandin synthesis inhibitors have been shown to delay healing of bone and this has led to limitations on their use clinically in some situations. Exogenously administered prostaglandins have been found to enhance periosteal callus formation, but healing is not uniformly enhanced. Prostaglandins have also been associated with hypercalcemia in certain animal tumors that model human hypercalcemia of malignancy but are probably most important in this condition as mediators in the localized resorption of bone at tumor sites. These in vivo studies have shown that prostaglandins are involved with increases in both bone formation and bone resorption. In vitro studies have shown that prostaglandins stimulate osteoblasts as well as osteoclastic bone resorption but understanding these effects under in vivo conditions will require further investigation.

Grassland patch dynamics and herbivore grazing preference following urine deposition

Abstract: Field experiments were performed over two growing seasons to investigate the response of Schizachyrium scoparium (C4 photosynthetic pathway) and Poa pratensis (C3) to natural and simulated bison urine deposition in a northern, mixed prairie in South Dakota. We also assessed potential feedbacks of urine deposition on herbivore grazing by monitoring grass response to defoliation and herbivore grazing preference for vegetation occupying urine patches. Total aboveground biomass and root mass were higher and root:shoot ratios were lower on urine patches than in the surrounding plant community. Higher total aboveground biomass on urine patches resulted primarily from increased aboveground P. pratensis production. Urine deposition in May had little effect on aboveground production of S. scoparium except during July when S. scoparium was most active. Urine deposition date and plant phenology appear important in determining changes in species composition. Following urine deposition, aboveground N concentrations of P. pratensis and S. scoparium were higher on patches relative to conspecifics off patches. This increase in N concentration following urine deposition was greater in P. pratensis. We suggest the large increase in P. pratensis biomass following urine deposition is related to its relatively large response to increased soil N availability and its rhizomatous habit. Root N concentrations were higher on urine patches. Poa pratensis on urine patches initiated growth earlier in the season and postponed senescence relative to plants off patches. Aboveground production following clipping was greater on urine patches and N concentrations in regrowth of both species were higher than concentrations in plants not previously clipped. Aboveground herbivore utilization was greater on urine patches than on adjacent vege- tation. Although urine patches covered only 2% of the study site, they provided 7% of the biomass and 14% of the N consumed by aboveground herbivores from June through August. Urine patches probably provided an even greater source of forage and N for herbivores earlier and later in the growing season when surrounding vegetation was mostly quiescent.

Optimization Using Distributed Genetic Algorithms

Abstract: A distributed genetic algorithm is tested on several difficult optimization problems using a variety of different subpopulation sizes. Contrary to our previous results, the more comprehensive tests presented in this paper show the distributed genetic algorithm is often, but not always superior to genetic algorithms using a single large population when the total number of evaluations is held constant. Data collected concerning execution times show that the GENITOR genetic algorithm using multiple subpopulations may execute much faster than the single population version when the cost of the evaluation function is low; thus, total number of evaluations is not always a good metric for making performance comparisons. Finally, our results suggest that "adaptive mutation" may be an important factor in obtaining superior results using a distributed version of GENITOR.