Showing papers by "Texas A&M University published in 1989"

Common amino acid sequence domains among the LEA proteins of higher plants.

Abstract: LEA proteins are late embryogenesis abundant in the seeds of many higher plants and are probably universal in occurrence in plant seeds. LEA mRNAs and proteins can be induced to appear at other stages in the plant's life by desiccation stress and/or treatment with the plant hormone abscisic acid (ABA). A role in protecting plant structures during water loss is likely for these proteins, with ABA functioning in the stress transduction process. Presented here are conserved tracts of amino acid sequence among LEA proteins from several species that may represent domains functionally important in desiccation protection. Curiously, an 11 amino acid sequence motif is found tandemly repeated in a group of LEA proteins of vastly different sizes. Analysis of this motif suggests that it exists as an amphiphilic α helix which may serve as the basis for higher order structure.

A survey of preventive maintenance models for stochastically deteriorating single-unit systems

Abstract: A survey of the research done on preventive maintenance is presented. The scope of the present survey is on the research published after the 1976 paper by Pierskalla and Voelker [98]. This article includes optimization models for repair, replacement, and inspection of systems subject to stochastic deterioration. A classification scheme is used that categorizes recent research into inspection models, minimal repair models, shock models, or miscellaneous replacement models.

Long‐Term Recurrence Rates in Previously Untreated (Primary) Basal Cell Carcinoma: Implications for Patient Follow‐Up

Abstract: We reviewed all studies (since 1947) reporting recurrence rates for treatment of primary (previously untreated) basal cell carcinomas using surgical excision, radiotherapy, cryotherapy, curettage and electrodesiccation, and Mohs micrographic surgery. Our findings indicate that recurrences following treatment of primary basal cell carcinoma appear later than is generally acknowledged in the literature. We found that less than one-third of all recurrences appear in the first year following treatment; only 50% appear within the first 2 years following treatment; and only 66%, or nearly two-thirds, appear within the first 3 years following treatment. A good rule of thumb is that the 10-year recurrence rate is double, or 2 times, that of the 2-year recurrence rate. Furthermore, 18% of recurrences appear between the fifth and tenth year following treatment. These results held true, irrespective of treatment modality examined. Seventy-two studies reporting short-term recurrence rates (follow-up less than 5 years) had a weighted average recurrence rate of 4.2%, whereas 34 long-term studies (follow-up of 5 years) had a weighted average recurrence rate of 8.7%, or more than 2 times the short-term rate. Five-year recurrence rates by treatment modality are as follows: Mohs micrographic surgery 1.0%, surgical excision 10.1%, curettage and electrodesiccation 7.7%, radiation therapy 8.7%, and cryosurgery 7.5%. We conclude that the reporting of recurrence rate data for basal cell carcinoma should be standardized using 5-year life table analysis, and even more important is our conclusion that lifetime follow-up is necessary after treatment of primary basal cell carcinoma in order both recurrences and new primaries.

Strategic Adaptability and Firm Performance: A Market-Contingent Perspective:

Abstract: The authors test the proposition that the effectiveness of a particular strategic orientation—reactor, defender, analyzer, and prospector—is contingent upon the dynamics of the market. In mildly vo...

Diversification Strategy and R&D Intensity in Multiproduct Firms

Abstract: This study provides empirical evidence that choice of diversification strategy systematically affects R&D intensity in large multiproduct firms. Research and development intensity in dominant-busin...

Have southern Texas savannas been converted to woodlands in recent history

Abstract: At savanna woodland sites in southern Texas, discrete clusters of woody plants form in herbaceous clearings following the invasion of mesquite (Prosopis glandulosa var. glandulosa), an arborescent ...

Principles of mental imagery

Abstract: Imagery can be used to improve memory, perceptual skills, even creativity. Numerous experiments carried out over the past 20 years have probed the nature of mental imagery and unlocked its powers. "Principles of Mental Imagery "offers a broad, balanced, and up to date introduction to the major findings of this research and identifies 5 general principles that can account for most of them. It considers the development of experimental techniques that have solved many of the challenging methodological problems inherent in imagery research and includes recent experimental findings not covered in other imagery books."Principles of Mental Imagery "brings together work by all of the key imagery researchers, among them Roger Shepard, Stephen Kosslyn, Allen Paivio, Lynn Cooper, Steven Pinker and the author. Chapters present new research on the role that imagery plays in human memory, new findings on how mental imagery influences perception (one of the dominant issues in modern imagery research), recent studies on "representational momentum" experimental demonstrations of how imagery can be used to make creative, visual discoveries, and recent work on imagery deficits in brain damaged patients. And, a new argument is made for why the study of mental imagery should be motivated by general principles, rather than formal models. Each chapter concludes with convenient summaries and suggestions for further exploration.Ronald A. Fluke is Associate Professor of Psychology at Texas A & M University. A Bradford Book

Mohs surgery is the treatment of choice for recurrent (previously treated) basal cell carcinoma

Abstract: We reviewed all studies (since 1945) reporting recurrence rates for treatment of recurrent (previously treated) basal cell carcinomas (BCC) using surgical excision, radiotherapy, cryotherapy, curettage and electrodesiccation, and Mohs micrographic surgery. The 5-year recurrence rate for Mohs micrographic surgery is 5.6%. The recurrence rate for non-Mohs modalities of 19.9% is nearly four times higher. Individual recurrence rates for the non-Mohs modalities are 17.4% for surgical excision, 40.0% for curettage and electrodesiccation, and 9.8% for radiation therapy. There are no studies reporting 5-year data for cryotherapy. However, the recurrence rate is 13.0% for cryotherapy when the follow-up period is less than five years. The data support the following conclusions: (1) Mohs surgery is the treatment of choice for recurrent BCC; (2) if the patient is not a surgical candidate and the lesion is small, radiation therapy is an alternative that offers a better chance for cure than the other non-Mohs modalities; and (3) curettage and electrodesiccation should not be used to treat recurrent basal cell carcinoma.

Design complexity measurement and testing

Abstract: System designers can quantify the complexity of a software design by using a trio of finely tuned design metrics.

Sex Differences in Positive Well-Being: A Consideration of Emotional Style and Marital Status

Abstract: This article reviews all published studies reporting tests for sex differences in well-being. Women were found to report greater happiness and life satisfaction than men. This sex difference was explained in terms of men's and women's social roles: The female (vs. male) gender role specifies greater emotional responsiveness. Furthermore, past role-related experiences provide women with appropriate skills and attitudes. Women's (vs. men's) greater well-being was also found to hold for married but not unmarried Ss: For both sexes the married state (vs. unmarried) was associated with favorable well-being, but the favorable outcomes proved stronger for women than men. Given that most Ss were married, the overall sex difference in well-being can be attributed to Ss' marital status. These findings were discussed in the context of prior research on sex differences in negative well-being. Research on subjective social indicators has demonstrated that one's objective life circumstances do not necessarily correspond to one's personal experience of well-being. The fact, then, that men and women in our society differ in terms of a variety of biological, personality, and situational factors may or may not result in sex differences in subjective quality of life. This article examines whether men and women do differ in evaluations of their life as a whole. The inquiry is limited to consideration of data on positive welbbeing and excludes findings on negative affect and psychological symptomatology. This is because positive and negative affect appem; under some circumstances, to be uncorrelated (Diener, Larson, Levine, & Emmons, 1985; Wart, Barter, & Brownbridge, 1983). I Reports of positive wen-being are best interpreted as indicators of positive domains of experience, separate from negative aspects of one's life circumstances. Prior research on sex differences in subjective life quality has focused almost exclusively on negative affect and psychological symptomatology. Consequently, most theories in this area are tailored to explain the occurrence of men's and women's poor well-being. This work, and the data on which it is based, is presented as a frame of reference for interpreting sex differences in positive well-being. First, we consider what is represented by judgments of wellbeing. Philosophers and psychologists have debated this question at length (see, e.g., Diener's, 1984, impressive review of the

Gulf of Mexico hydrocarbon seep communities

Abstract: Sediment and water samples were collected by submersible in September 1986 at 16 locations on the carbonate cap overlying a conical diapir, which was formed by the upward migration of oil and gas through a subsurface fault on the continental slope off Louisiana, USA (27°47′N; 91°30.4′W). The biological community at the site was photographed quantitatively with still and video cameras. Rigorous spatial sampling indices were maintained so that variation in chemical parameters and in the abundance of photographed organisms could be estimated within the bounds of the study site. Concentrations of extractable organic material (EOM) ranged from 0.24 to 119.26‰ in the sediment samples, while methane concentrations in the water samples were from 0.037 to 66.474 μM. The visible biological community was predominantly composed of the chemosynthetic tube worms (Vestimentifera) Lamellibrachia sp. and Escarpia sp., and an undescribed, methane-oxidizing mussel (Mytilidae: Bathymodiolus-like), as well as diverse non-chemosynthetic organisms. The ranked abundance of tube worms was significantly correlated (p<0.05) with the concentration of EOM in the sediment samples, while the abundance of mussels was significantly correlated (p<0.05) with the concentration of methane in the water samples. Tube worms and mussels both occurred in dense clusters; however, the clusters of mussels had a more restricted distribution within the study site than did clusters of tube worms. Both organisms were most abundant in the vicinity of the subsurface fault.

A second proteinase encoded by a plant potyvirus genome.

Abstract: The RNA genome of tobacco etch virus (TEV) encodes a large polyprotein precursor that is processed to mature proteins by virus-specific proteinases. Cleavage sites located within the carboxyl-terminal two-thirds of the polyprotein are processed by a TEV-encoded 49 kd proteinase, while the enzyme(s) responsible for cleaving the remaining sites has not been found. In this study, a second TEV-encoded proteinase has been identified based on cell-free expression of defined RNA transcripts. The boundaries of this proteinase have been delineated by deletion analysis and site-directed mutagenesis. The proteolytically active domain has been localized to the carboxyl-terminal half of the 56 kd aphid-transmission helper component. A cleavage site that is recognized by this proteinase has been identified in the polyprotein adjacent to the carboxyl-terminus of the enzyme, and the proteinase appears to cleave by an autocatalytic mechanism. Proteolysis in vitro occurs between a Gly-Gly dipeptide as determined by radiochemical sequencing at the amino-terminus of the proteolytic product.

A generalization of Kharitonov's theorem; Robust stability of interval plants

Abstract: The robust stability problem is considered for interval plants, in the case of single input (multioutput) or single output (multi-input) systems. A necessary and sufficient condition for the robust stabilization of such plants is developed, using a generalization of V. L. Kharitonov's theorem (1978). The generalization given provides necessary and sufficient conditions for the stability of a family of polynomials delta (s)=Q/sub 1/(s)P/sub 1/(s)+ . . . +Q/sub m/(s)P/sub m/(s), where the Q/sub i/ are fixed and the P/sub i/ are interval polynomials, the coefficients of which are regarded as a point in parameter space which varies within a prescribed box. This generalization, called the box theorem, reduces the question of the stability of the box, in parameter space to the equivalent problem of the stability of a prescribed set of line segments. It is shown that for special classes of polynomials Q/sub i/(s) the set of line segments collapses to a set of points, and this version of the box theorem in turn reduces to Kharitonov's original theorem. >

Regulation of beta-glucuronidase expression in transgenic tobacco plants by an A/T-rich, cis-acting sequence found upstream of a French bean beta-phaseolin gene.

Abstract: A 0.8-kilobase fragment from the 5'-flanking region of a French bean beta-phaseolin gene yielded strong, temporally regulated, and embryo-specific expression of beta-glucuronidase (GUS) in transgenic tobacco plants, paralleling that found for the seed protein phaseolin [Sengupta-Gopalan, C., Reichert, N.A., Barker, R.F., Hall. T.C., and Kemp, J.D. (1985) Proc. Natl. Acad. Sci. USA 82, 3320-3324]. Gel retardation and footprinting assays using nuclear extracts from immature bean cotyledons revealed strong binding of nuclear proteins to an upstream region (-628 to -682) that contains two inverted A/T-rich motifs. Fusion of a 103-base pair fragment or a 55-base pair synthetic oligonucleotide containing these motifs to a minimal 35S promoter/GUS cassette yielded strong GUS expression in several tissues. A different pattern of GUS expression was obtained in immature embryos and germinating seedlings from the nominally constitutive, full-length, 35S promoter. Whereas GUS expression under the control of the 0.8-kilobase beta-phaseolin regulatory region is limited to immature embryos, expression from constructs containing the A/T-rich motifs is strongest in roots. These data, combined with S1 mapping, provide direct evidence that a plant upstream A/T-rich sequence that binds nuclear proteins can activate transcription in vivo. They also indicate that additional regulatory elements in the beta-phaseolin 5'-flanking region are required for embryo-specific gene expression.

Glycosylation and secretion of human tissue plasminogen activator in recombinant baculovirus-infected insect cells.

Abstract: Cell lines established from the lepidopteran insect Spodoptera frugiperda (fall armyworm; Sf9) are used routinely as hosts for the expression of foreign proteins by recombinant baculovirus vectors. We have examined the pathway of protein glycosylation and secretion in these cells, using human tissue plasminogen activator (t-PA) as a model. t-PA expressed in Sf9 cells was both N glycosylated and secreted. At least a subset of the N-linked oligosaccharides in extracellular t-PA was resistant to endo-beta-N-acetyl-D-glucosaminidase H, which removes immature, high-mannose-type oligosaccharides. This refutes the general conclusion from previous studies that Sf9 cells cannot process immature N-linked oligosaccharides to an endo-beta-N-acetyl-D-glucosaminidase H-resistant form. A nonglycosylated t-PA precursor was not detected in Sf9 cells, even with very short pulse-labeling times. This suggests that the mammalian signal sequence of t-PA is efficiently recognized in Sf9 cells and that it can mediate rapid translocation across the membrane of the rough endoplasmic reticulum, where cotranslational N glycosylation takes place. However, t-PA was secreted rather slowly, with a half-time of about 1.6 h. Thus, a rate-limiting step(s) in secretion occurs subsequent to translocation and N glycosylation of the t-PA polypeptide. Treatment of Sf9 cells with tunicamycin, but not with inhibitors of oligosaccharide processing, prevented the appearance of t-PA in the extracellular medium. This suggests that N glycosylation per se, but not processing of the N-linked oligosaccharides, is required directly or indirectly in baculovirus-infected Sf9 cells for the secretion of t-PA. Finally, the relative efficiency of secretion decreased dramatically with time of infection, suggesting that the Sf9 host cell secretory pathway is compromised during the later stages of baculovirus infection.

Coronal positioning of existing gingiva: short term results in the treatment of shallow marginal tissue recession.

Abstract: Although not a new procedure, coronal positioning of existing gingiva may be used to enhance esthetics and reduce sensitivity. Unfortunately when recession is minimal and the marginal tissue is healthy, many periodontists do not suggest treatment. This article outlines a simple surgical technique with the criteria for its use which results in a high degree of predictability and patient satisfaction.

Woody plant invasion of grasslands: establishment of honey mesquite (Prosopis glandulosa var.glandulosa) on sites differing in herbaceous biomass and grazing history

Abstract: Emergence and survival of honey mesquite (Prosopis glandulosa var.glandulosa Torr.) seedlings was quantified on sites with contrasting grazing histories: long-term continuous grazing (LTG) and long-term protection (LTP) from grazing by cattle. On each site, different levels of heroaceous defoliation were imposed at monthly intervals (no defoliation=ND, moderate=MD and heavy=HD). The two weeks following seed dissemination appeared to be the most critical toProsopis establishment on LTP-ND plots. Openings in the herbaceous layer created by moderate defoliation of grasses on the LTP site increased germination and/or survival 7-to 8-fold during this period. However, increasing the degree of defoliation from moderate to heavy did not stimulate additional emergence on either the LTP or LTG site. Emergence from scarified seed placed in cattle dung (17 to 30%) was lower than that of bare seed placements in various microhabitats (43–60%). However, deposition of scarifiedProsopis seed in dung in conjunction with graminoid defoliation may be the most likely combination of events when livestock are present. Emergence from seeds transported into grasslands by other fauna likely would be low, unless seeds were deposited in areas where grasses had been defoliated.Prosopis survival was comparably high in dung and bare seed placements after one growing season. survival of seedlings present two weeks after seed dissemination ranged from 74 to 97% at the end of the second growing season. Seedling survival and shoot development (biomass, leaf area and height) were similar on LTP and LTG sites, regardless of the level of herbaceous defoliation or seed placement. In addition, the magnitude and patterns of net photosynthesis, stomatal conductance and xylem water potential were comparable among one-year-old seedtings on ND, MD and HD plots, even though differences in herbaceous species composition and above- and below-ground biomass between these treatments were substantial. Such data suggest competition for soil resources between grasses andProsopis may be minimal early in the life cycle ofProsopis. High rates ofProsopis emergence and establishment on LTP-MD plots are counter to the widespread assumption that long-term and/or heavy grazing is requisite forProsopis encroachment into grasslands. Results are discussed with regard to factors contributing to the recent, widespread invasion of this woody legume into grasslands of southwestern North America.

Design for a practical laboratory detector for solar axions.

Abstract: We present a practical design for a detector sensitive to axions and other light particles with a two-photon interaction vertex. Such particles would be produced in the solar interior by Primakoff conversion of blackbody photons and could be detected by their reconversion into x rays (average energy about 4 keV) in a strong laboratory magnetic field. An existing large superconducting magnet would be suitable for this purpose. The transition rate is enhanced by filling the conversion region with a buffer gas (${\mathrm{H}}_{2}$ or He). This induces an effective photon mass (plasma frequency) which can be adjusted to equal the axion mass being searched for. Axion-photon conversion is then coherent throughout the detector volume for all axion energies. Axions with mass in the range 0.1 eV\ensuremath{\lesssim}${m}_{a}$\ensuremath{\lesssim}5 eV can be detected using gas pressures of 0.1--300 atm. Axions with the standard coupling strength to photons would give counting rates of ${10}^{\mathrm{\ensuremath{-}}5}$--10 ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ over this mass range. The search would definitively test one of the only two regions of axion parameters not excluded by astrophysical constraints.

Structure-activity relationships in the hydrolysis of substrates by the phosphotriesterase from Pseudomonas diminuta.

Abstract: The mechanism and substrate specificity of the phosphotriesterase from Pseudomonas diminuta have been examined. The enzyme hydrolyzes a large number of phosphotriester substrates in addition to paraoxon (diethyl p-nitrophenyl phosphate) and its thiophosphate analogue, parathion. The two ethyl groups in paraoxon can be changed to propyl and butyl groups, but the maximal velocity and Km values decrease substantially. The enzyme will not hydrolyze phosphomonoesters or -diesters. There is a linear correlation between enzymatic activity and the pKa of the phenolic leaving group for 16 paraoxon analogues. The beta value in the corresponding Bronsted plot is -0.8. No effect on either Vmax or Vmax/Km is observed when sucrose is used to increase the relative solvent viscosity by 3-fold. These results are consistent with rate-limiting phosphorus-oxygen bond cleavage. A plot of log V versus pH for the hydrolysis of paraoxon shows one enzymatic group that must be unprotonated for activity with a pKa of 6.1. The deuterium isotope effect by D2O on Vmax and Vmax/Km is 2.4 and 1.2, respectively, and the proton inventory is linear, which indicates that only one proton is "in flight" during the transition state. The inhibition patterns by the products are consistent with a random kinetic mechanism.