Showing papers by "Michigan Technological University published in 1991"
TL;DR: This paper presents a time-efficient algorithm that produces k best ''non-intersecting'' local alignments for any chosen k that needs only O(M + N + K) space.
1,015 citations
TL;DR: In this paper, a generalized plasticity model with higher-order spatial gradients of the equivalent plastic strain in the yield condition was proposed and it was shown how these gradients affect the critical condition for the onset of localization and allow for a wavelength selection analysis leading to estimates for the width and or spacing of shear bands.
779 citations
TL;DR: The results demonstrate that closely related species of mobile terrestrial vertebrates have the potential for extensive genetic exchange when ecological conditions change suddenly.
Abstract: Mitochondrial DNA (mtDNA) genotypes of gray wolves and coyotes from localities throughout North America were determined using restriction fragment length polymorphisms. Of the 13 genotypes found among the wolves, 7 are clearly of coyote origin, indicating that genetic transfer of coyote mtDNA into wolf populations has occurred through hybridization. The transfer of mtDNA appears unidirectional from coyotes into wolves because no coyotes sampled have a wolf-derived mtDNA genotype. Wolves possessing coyote-derived genotypes are confined to a contiguous geographic region in Minnesota, Ontario, and Quebec, and the frequency of coyote-type mtDNA in these wolf populations is high (>50%). The ecological history of the hybrid zone suggests that hybridization is taking place in regions where coyotes have only recently become abundant following conversion of forests to farmlands. Dispersing male wolves unable to find conspecific mates may be pairing with female coyotes in deforested areas bordering wolf territories. Our results demonstrate that closely related species of mobile terrestrial vertebrates have the potential for extensive genetic exchange when ecological conditions change suddenly.
304 citations
TL;DR: In this article, single-grain laser-fusion analyses of individual sanidine phenocrysts from the two youngest Toba (Indonesia) tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka.
Abstract: Single-grain laser-fusion {sup 40}Ar/{sup 39}Ar analyses of individual sanidine phenocrysts from the two youngest Toba (Indonesia) tuffs yield mean ages of 73{plus minus}4 and 501{plus minus}5 ka. In addition, glass shards from Toba ash deposited in Malaysia were dated at 68{plus minus}7 ka by the isothermal plateau fission-track technique. These new determinations, in conjunction with previous ages for the two oldest tuffs at Toba, establish the chronology of four eruptive events from the Toba caldera complex over the past 1.2 m.y. Ash-flow tuffs were erupted from the complex every 0.34 to 0.43 m.y., culminating with the enormous (2500-3000 km{sup 3}) Youngest Toba tuff eruption, caldera formation, and subsequent resurgence of Samosir Island. Timing of this last eruption at Toba is coincident with the early Wisconsin glacial advance. The high-precision {sup 40}Ar/{sup 39}Ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions.
297 citations
TL;DR: A flow theory of plasticity for pressure-sensitive, dilatant materials incorporating second order gradients into the flow-rule and yield condition is suggested in this article, where the appropriate extra boundary conditions are obtained with the aid of the principle of virtual work.
Abstract: A flow theory of plasticity for pressure-sensitive, dilatant materials incorporating second order gradients into the flow-rule and yield condition is suggested. The appropriate extra boundary conditions are obtained with the aid of the principle of virtual work. The implications of the theory into shear-band analysis are examined. The determination of the shear-band thickness and the persistence of ellipticity in the governing equations are discussed.
255 citations
TL;DR: In this model, nitrate is a signal for developmental changes in the physiology of the plant, which are expressed in a hierarchy and the primary responses include induction of genes for nitrate and nitrite reductases,Nitrate uptake and translocation systems, and DNA regulatory proteins required for expression of the secondary response gene systems.
Abstract: Nitrate is the most common N source used by higher plants and is the ‘substrate inducer’ of nitrate and nitrite reductase activities. However, environmental nitrate also has other effects on higher plants, which include the induction of a high affinity nitrate transport system. changes in root morphology, and increased root respiration. Nitrate induces nitrate and nitrite reductase activities by altering gene expression, mainly by enhancing transcription of the respective genes. We have begun to view these responses of higher plant tissues to environmental nitrate in the context of a model for signal transduction. In our model, nitrate is a signal for developmental changes in the physiology of the plant, which are expressed in a hierarchy. The primary responses include induction of genes for nitrate and nitrite reductases, nitrate uptake and translocation systems, and DNA regulatory proteins required for expression of the secondary response gene systems. The secondary responses include more complex phenomena such as proliferation of the root system, enhancement of respiration and other changes in the physiology of the plant.
182 citations
TL;DR: In this article, the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting) were addressed.
Abstract: The small group of wolves on Isle Royale has been studiedfor over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to asfew as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population; a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale Correspondence s/ould be a44ressed to this autbor Paper submitted May 7, 1990; revised manuscript accepted October 10, 1990. See table of contents for order of author's names for citation purposes. Resumen: El pequeno grupo de lobos de la Isla Royale ha sido estudiado por mas de tres decadas como un modelo de las relaciones entre grandes carni'voros y su presa Durante los ultimos diez anios la poblacion disminuyo de 50 individuos a tan solo 12 individuos. La causa de esta disminucion puede ser debida a la escasez de comida a las enfermedades o a la reducida variabilidad genetica Nosotros tratamos el aspecto de la variabilidad genetica y las relaciones con los lobos de la Isla Royale utilizando la electroforesis con aloenzimas, el ana'lisis restringido a mtDNA y el analisis de hipervariable multilocus minisatelite DNA (huellas geneticas). Nuestros resultados indican que aproximadamente el 50% de la heterozigosis de la aloenzima ha sidoperdida en lapoblacion de la isla esta es una disminucion similar a la que se esperari'a si no hubiese habido inmigracion de la tierrafirme. Los datos de las huellas geneticas indican que los siete lobos muestreados en la Isla Royale son tan parecidos entresi como las poblaciones de bermanos en cautiverio. Sorprendentemente los lobos de la Isla Royale tienen un genotipo mtDNA que es muy raro en tierrafirme habiendo sido encontrado en solamente uno de
172 citations
TL;DR: Spectroscopic properties of pure and impurity-activated alkaline-earth sulfides as studied by optical and magnetic resonance techniques are reviewed in this paper, where the authors propose a spectral model of the sulfide.
165 citations
TL;DR: A biphasic pattern of gene expression and enzyme activity for OMT was observed fromxylem samples of aspen during the growing season which suggests linkage between gene expression for a monolignol biosynthetic enzyme and seasonal regulation of xylem differentiation in woody plants.
Abstract: A cDNA clone (Ptomt 1) encoding a lignin-bispecific O-methyltransferase (OMT) was isolated by immunological screening of a lambda gt11 expression library prepared from mRNA of developing secondary xylem of aspen (Populus tremuloides). Nucleotide sequence analysis of Ptomt1 revealed an open reading frame of 1095 bp which encodes a polypeptide with a predicted molecular weight of 39,802, corresponding well with the size of the OMT polypeptide estimated by SDS-PAGE. Authenticity of Ptomt1 was demonstrated in part by detection of OMT activity and protein in extracts of Escherichia coli cultures transformed with a plasmid construct containing Ptomt1. In addition, peptides produced from a proteolytic digest of purified OMT and sequenced by automated Edman degradation matched to portions of the deduced amino acid sequence of Ptomt1. Comparison of this sequence to amino acid sequences of OMTs of diverse species identified regions of similarity which probably contribute to the binding site of S-adenosyl-L-methionine. Tissue-specific expression was demonstrated by northern analysis which showed that Ptomt1 hybridized to a 1.7 kb transcript from aspen developing secondary xylem and by tissue printing of aspen stems in which only the outer layer of xylem bound the antibody. A biphasic pattern of gene expression and enzyme activity for OMT was observed from xylem samples of aspen during the growing season which suggests linkage between gene expression for a monolignol biosynthetic enzyme and seasonal regulation of xylem differentiation in woody plants.
163 citations
TL;DR: Gene transfer and plant regeneration systems have been developed for European larch by demonstrating agrobacteria attached to larch cells by examination of scanning electron micrographs and calli derived from symptomatic tissues exhibited phytohormone autotrophic growth.
Abstract: Gene transfer and plant regeneration systems have been developed for European larch (Larix decidua Mill.) in our laboratory. Aseptically germinated young seedlings were hypocotyl wound-inoculated withAgrobacterium rhizogenes strains 11325 containing a wild-type Ri (root-inducing) plasmid. Swollen stems appeared at infected wounds followed by either abundant hairy roots or adventitious shoot buds that developed within 3 to 4 wk after inoculation. No symptoms were seen on wounded but uninoculated seedlings. We demonstrated agrobacteria attached to larch cells by examination of scanning electron micrographs. Subsequently, calli derived from symptomatic tissues exhibited phytohormone autotrophic growth. Adventitious buds were elongated and rooted in vitro before being transferred to the greenhouse where the transformed whole plants grew normally. Transformants tested positive for opine production and transformation was further confirmed by Southern blot analysis with larch genomic DNAs isolated from both proliferated calli and needle tissue of transgenic plants.
141 citations
TL;DR: On-line computer conferences have been of increasing interest to teachers of composition who hope to provide alternative forums for student-centered, collaborative writing that involve all members of the community.
Abstract: On-line computer conferences have been of increasing interest to teachers of composition who hope to provide alternative forums for student-centered, collaborative writing that involve all members ...
TL;DR: A band-structure calculation for CdO is presented, which is believed to be more accurate than any in the literature and to be a consequence of the hybridization of oxygen 2p-derived orbitals with Zn 3d or Cd 4d states, combined with octahedral point symmetry.
Abstract: ZnO, which normally occurs in the hexagonal wurtzite structure, can be transformed to the cubic rocksalt (NaCl) structure by the application of high pressure; this cubic phase has been reported to be metastable at atmospheric pressure. The band structure of this phase is calculated by the ab initio correlated Hartree-Fock method. Not surprisingly, the band structure of rocksalt ZnO is very similar to that of CdO, which has the same crystal structure; we present a band-structure calculation for CdO, which we believe is more accurate than any in the literature. A hallmark of these band structures is that the valence-band maximum is not at the center of the Brillouin zone, in contrast to the situation in tetrahedrally coordinated II-VI semiconductors. We confirm by direct calculation that this peculiarity of the band structure is a consequence of the hybridization of oxygen 2p-derived orbitals with Zn 3d or Cd 4d states, combined with octahedral point symmetry.
TL;DR: The electronic structure of the oxides and sulfides of Mg, Ca, and Sr is computed with use of the self-consistent Hartree-Fock method including correlation, predicting that these materials (except MgS) are direct-band-gap materials.
Abstract: The electronic structure of the oxides and sulfides of Mg, Ca, and Sr is computed with use of the self-consistent Hartree-Fock method including correlation. Energy-band structure and density of states are presented and discussed in context with the available experimental and theoretical studies. Our results predict that these materials (except MgS) are direct-band-gap materials.
TL;DR: In the past 1.2 m.y. as discussed by the authors, four separate eruptions have occurred from vents within the present collapse structure, which formed from eruption of the 2800 km3 Youngest Toba Tuff (YTT) at 74 ka.
Abstract: During the past 1.2 m.y., a magma chamber of batholithic proportions has developed under the 100 by 30 km Toba Caldera Complex. Four separate eruptions have occurred from vents within the present collapse structure, which formed from eruption of the 2800 km3 Youngest Toba Tuff (YTT) at 74 ka. Eruption of the three older Toba Tuffs alternated from calderas situated in northern and southern portions of the present caldera. The northern caldera apparently developed upon a large andesitic stratovolcano. The calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the YTT. Samosir Island and the Uluan Block are two sides of a single resurgent dome that has resurged since eruption of the YTT. Samosir Island is composed of thick YTT caldera fill, whereas the Uluan Block consists mainly of the Oldest Toba Tuff (OTT). In the past 74000 years lava domes have been extruded on Samosir Island and along the caldera's western ring fracture. This part of the ring fracture is the site of the only current activity at Toba: updoming and fumarolic activity. The Toba eruptions document the growth of the laterally continuous magma body which eventually erupted the YTT. Repose periods between the four Toba Tuffs range between 0.34 and 0.43 m.y. and give insights into pluton emplacement and magmatic evolution at Toba.
TL;DR: In this paper, a numerical method is presented which generates the rotovibrational (free-free) collision-induced absorption (RV CIA) spectra of H 2 -H 2 pairs in the fundamental band of hydrogen, at temperatures from 20 to 300 K.
TL;DR: The investigation shows that there is a marked dichotomy between certain large-bodied freshwater microcrustaceans in how they respond to small particles, and suggests that the degree of taste discrimination is often related to particle size.
Abstract: We used the Rassoulzadegan-DeMott bead bioassay to evaluate the ability of various pelagic microcrustaceans to discriminate between particles on the basis of taste and size. The test examined zooplankton reactions to fresh algal exudates adsorbed onto polystyrene microspheres. The investigation shows that there is a marked dichotomy between certain large-bodied freshwater microcrustaceans in how they respond to small particles; it confirms that large daphnid cladocerans exhibit no taste discrimination for small beads, whereas calanoid copepods continually appraise resource quality of both small and large particles with a fine degree of discrimination. In contrast, smaller bodied daphnids and other cladocerans show some degree of taste and acute size discrimination, the former presumably related to processing large particles one at a time and to the individual peculiarities of the filtering mechanisms. Based on the findings from taste discrimination tests, we suggest that the degree of taste discrimination is often related to particle size. Moreover, we assert that many cladocerans are categorized more appropriately as detritivores than as herbivores, although they exhibit modest, size-related taste discrimination.
TL;DR: It is suggested that phenotypic response to food supply may account for most variation in body size of coyotes, and northward and eastward expansion of the range of coyote in North America has been associated with an increase in body Size.
Abstract: Northward and eastward expansion of the range of coyote ( Canis latrans ) in North America has been associated with an increase in body size, although documentation is limited. In this study, published weights of coyotes from various geographic areas and new data from the Kenai Peninsula, Alaska, were found to differ by sex ( P < 0.001) and longitude (females, P = 0.036; males, P = 0.017), but not latitude (females, P = 0.861; males, P = 0.302). Significant longitudinal variation was attributable to the large size of coyotes in New Hampshire. We suggest that phenotypic response to food supply may account for most variation in body size of coyotes.
TL;DR: The canopies of northern hardwood forests dominated by sugar maple were examined at five locations spanning 800 km along an acid deposition and climatic gradient in the Great Lakes region and similarity among the sites in allometric relationships, maximum LAI, canopy transmittance, and patterns of SLA suggests these characteristics were controlled primarily by the similar nutrient and moisture availability at the sites.
Abstract: The canopies of northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.) were examined at five locations spanning 800 km along an acid deposition and climatic gradient in the Great Lakes region. Leaf area index (LAI) calculated from litterfall ranged from 6.0 to 8.0 in 1988, from 4.9 to 7.9 in 1989, and from 5.3 to 7.8 in 1990. The data suggest that maximum LAI for the sites is between 7 and 8. Insect defoliation and the allocation of assimilates to reproductive parts in large seed years reduced LAI by up to 34%. Allometric equations for leaf area and foliar biomass were not significantly different among sites. They predicted higher LAI values than were estimated from litterfall and could not account for the influences of defoliation and seed production. Canopy transmittance was a viable alternative for estimating LAI. Extinction coefficients (K) of 0.49 to 0.65 were appropriate for solar elevations of 63{degree} to 41{degree}. Patterns of specific leaf area (SLA) were similar for the sites. Average sugar maple SLA increased from 147 cm{sup 2}g{sup {minus}1} in the upper 5 m of the canopy to 389 cm{sup 2}g{sup {minus}1} in the seeding layer. Litterfall SLA averaged 196 cm{sup 2}g{sup {minus}1} more » for all species and 192 cm{sup 2}g{sup {minus}1} for sugar maple. Similarity among the sites in allometric relationships, maximum LAI, canopy transmittance, and patterns of SLA suggests these characteristics were controlled primarily by the similar nutrient and moisture availability at the sites. A general increasing trend in litter production along the gradient could not be attributed to N deposition or length of growing season due to year to year variability resulting from insect defoliation and seed production. « less
TL;DR: In this paper, the effect of corona discharge on forced-convection heat transfer in a tube is studied experimentally, and it is found that heat transfer enhancements are significant only in the laminar and transitional flow regimes when using a single electrode.
TL;DR: In this paper, the authors studied deformation microstructures in PWA 1480 nickel-base superalloy single crystals in the range of 20 °C to 1100 °C.
Abstract: Deformation microstructures in PWA 1480 nickel-base superalloy single crystals were studied in the range of 20 °C to 1100 °C Similar to previous investigations, superlattice stacking faults were observed after slow strain rate deformation at temperatures between 700 °C and 950 °C Unlike previous studies, a high density of superlattice stacking faults was observed after deformation at 200 °C and below The mechanisms of fault formation in the two temperature regimes were different In the range of 700 °C to 950 °C, single isolated superlattice-intrinsic stacking faults (SISFs) were produced by the decomposition of an a/2(110) matrix dislocation in the γ/γ′ interface The a/3(112) partial shears the particle, while the a/6(112) Shockley remains in the interface At 200 °C and below, a high density of faults was produced on closely spaced parallel planes The most common feature after deformation in this range is the faulted loop, which is most often observed to be a superlattice-extrinsic stacking fault (SESF) These low-temperature faults, along with their temperature dependence, were quite similar to those observed in single-phase Ll22 materials The available evidence suggests that the low-temperature faults were produced by the dissociation of an a unit superdislocation into a pair of a/3 partials The temperature dependence of the faulting (at low temperatures) was modeled by linear isotropic elasticity, and the results suggest that the SISF energy increases significantly from 20 °C to 400 °C Multiplanar, overlapping superlattice faults were analyzed with respect to bond violations This analysis suggested that an antiphase boundary (APB) on top of an SISF has a very high fault energy, similar to that of the complex stacking fault Therefore, the presence of SISF loops on glide planes promotes further dissociation by the SISF scheme instead of the APB scheme and explains the high density of SESFs and microtwins observed in the deformation structures
TL;DR: In this article, the authors used a multispectral processing technique to distinguish ash-bearing eruption plumes from ordinary clouds from a wavelength-dependent variable emission of silicate ash or reflect a spectral role of sulfuric acid aerosol in the plume.
Abstract: Eighteen digital AVHRR (advanced very high resolution radiometer) data sets from NOAA-6 and NOAA-9 polar-orbiting satellites recorded between 27 March and 7 April 1986 depict the eruptive activity of Augustine volcano, located 280 km SW of Anchorage, Alaska. The synoptic view (resolution of either 1.1 or 4.4 km), frequent coverage (often twice a day), and multispectral coverage (five bands: 0.58–0.68; 0.72–1.1; 3.55–3.93; 10.5–11.3; and 11.5–12.5 μm) makes the AVHRR broadly applicable to analyzing explosive eruption clouds. The small scale of the Augustine activity (column heights of 2–13 km and eruption rates of 2x106–8x107 metric tonnes/day) facilitated intensive multispectral study because the plumes generally covered areas within the 550x550 km area of one easily manipulated image field. Hourly ground weather data and twice-daily radiosonde measurements from stations surrounding the volcano plus numerous volcanological observations were made throughout the eruption, providing important ground truth with which to calibrate the satellite data. The total erupted volume is estimated to be at least 0.102 km3. The pattern of changing eruption rates determined by satellite observations generally correlate with more detailed estimates of explosion magnitudes. Multispectral processing techniques were used to distinguish eruption clouds from meteorological clouds. Variable weather during the Augustine eruption offered an opportunity to test various trial algorithms. A ratio between thermal IR channels four and five, served to delineate the ashbearing eruption plumes from ordinary clouds. Future work is needed to determine whether the successful multispectral discrimination is caused by wavelength-dependent variable emission of silicate ash or reflects a spectral role of sulfuric acid aerosol in the plume.
TL;DR: In this paper, the crumpling mechanisms of thin-walled octagonal steel tubes subjected to axial static compression and their efficiency as energy absorbing components under impact conditions are investigated and compared with the equivalent circular and square tubes of same material.
Abstract: The crumpling mechanisms of thin-walled octagonal steel tubes subjected to axial static compression and their efficiency as energy absorbing components under impact conditions are investigated and compared with the equivalent circular and square tubes of same material. Both inextensional and extensible collapse mechanisms are theoretically analysed. Theoretically predicted values based on the deformation modes encountered, as well as experimentally obtained ones, are compared and found to be in good agreement.
TL;DR: In this article, a spin-dependent enhancement of free-carrier capture processes can occur directly at a paramagnetic deep defect without the need for other defects nearby, which is consistent with new experimental results which indicate the absence of any adjacent trapping centers.
Abstract: This paper presents a new model for spin-dependent recombination and generation processes based on the electrical detection of magnetic resonance in semiconductor p - n junction diodes. Based on a modified Shockley-Read recombination statistics, this model differs from those models previously proposed in that the spin-dependent enhancement of free-carrier capture processes can occur directly at a paramagnetic deep defect without the need for other defects nearby. This model incorporates singlet-triplet mechanisms of existing models, but is shown to be consistent with new experimental results which indicate the absence of any adjacent trapping centers.
TL;DR: In this paper, a generalization of the conventional constitutive models of viscoplasticity is proposed, which is accomplished by the inclusion of spatial gradients of the equivalent stress and strain in the evolution equation for the equivalent plastic strain rate.
Abstract: We suggest here a generalization of the conventional constitutive models of viscoplasticity. This is accomplished by the inclusion of spatial gradients of the equivalent stress and strain in the evolution equation for the equivalent plastic strain rate. We restrict attention to plane deformation and elastic effects are neglected for simplicity. The implications of the new terms in the constitutive model are discussed for the case of a general eigenvalue problem of an initially homogeneous and stationary viscous flow. It turns out that the nonclassical material parameters can be chosen in such a way that the governing differential equations are always strongly elliptic irrespective of whether the mateiral is strain softening. As it is well known, the latter typically leads to loss of ellipticity in the conventional theories. Explicit results are presented for the case of a shear band instability. Within the framework of the present theory, and in contrast to conventional models, the shear band kinematics have a well defined geometrical structure.
TL;DR: It is suggested that this family of flavoenzymes, nearly all of which reduce a hemoprotein, be called "flavoprotein pyridine nucleotide cytochrome reductases."
TL;DR: In this paper, a convenient description of the geometry of slip and the associated kinematics of finite deformation in an elastic-plastic crystal is presented, and the physical meaning of the plastic spin is discussed in detail.
TL;DR: The Earth Observing System (EOS) is scheduled for launch in 1997 and 1999, and the EOS volcanology investigation objectives are discussed in this article, including long and short-term monitoring of selected volcanoes, the detection of precursor activity associated with unanticipated eruptions, and a detailed study of on-going eruptions.