Showing papers by "University of Utah published in 2001"

Color transfer between images

Abstract: We use a simple statistical analysis to impose one image's color characteristics on another. We can achieve color correction by choosing an appropriate source image and apply its characteristic to another image.

Genotype-Phenotype Correlation in the Long-QT Syndrome Gene-Specific Triggers for Life-Threatening Arrhythmias

Abstract: Background The congenital long-QT syndrome (LQTS) is caused by mutations on several genes, all of which encode cardiac ion channels. The progressive understanding of the electrophysiological consequences of these mutations opens unforeseen possibilities for genotype-phenotype correlation studies. Preliminary observations suggested that the conditions ("triggers") associated with cardiac events may in large part be gene specific. Methods and results We identified 670 LQTS patients of known genotype (LQT1, n=371; LQT2, n=234; LQT3, n=65) who had symptoms (syncope, cardiac arrest, sudden death) and examined whether 3 specific triggers (exercise, emotion, and sleep/rest without arousal) differed according to genotype. LQT1 patients experienced the majority of their events (62%) during exercise, and only 3% occurred during rest/sleep. These percentages were almost reversed among LQT2 and LQT3 patients, who were less likely to have events during exercise (13%) and more likely to have events during rest/sleep (29% and 39%). Lethal and nonlethal events followed the same pattern. Corrected QT interval did not differ among LQT1, LQT2, and LQT3 patients (498, 497, and 506 ms, respectively). The percent of patients who were free of recurrence with ss-blocker therapy was higher and the death rate was lower among LQT1 patients (81% and 4%, respectively) than among LQT2 (59% and 4%, respectively) and LQT3 (50% and 17%, respectively) patients. Conclusions Life-threatening arrhythmias in LQTS patients tend to occur under specific circumstances in a gene-specific manner. These data allow new insights into the mechanisms that relate the electrophysiological consequences of mutations on specific genes to clinical manifestations and offer the possibility of complementing traditional therapy with gene-specific approaches.

Information technology acceptance by individual professionals: a model comparison approach

Abstract: The proliferation of innovative and exciting information technology applications that target individual “professionals” has made the examination or re-examination of existing technology acceptance theories and models in a “professional” setting increasingly important. The current research represents a conceptual replication of several previous model comparison studies. The particular models under investigation are the Technology Acceptance Model (TAM), the Theory of Planned Behavior (TPB), and a decomposed TPB model, potentially adequate in the targeted healthcare professional setting. These models are empirically examined and compared, using the responses to a survey on telemedicine technology acceptance collected from more than 400 physicians practicing in public tertiary hospitals in Hong Kong. Results of the study highlight several plausible limitations of TAM and TPB in explaining or predicting technology acceptance by individual professionals. In addition, findings from the study also suggest that instruments that have been developed and repeatedly tested in previous studies involving end users and business managers in ordinary business settings may not be equally valid in a professional setting. Several implications for technology acceptance/adoption research and technology management practices are discussed.

The evolution of firm networks: from emergence to early growth of the firm

Abstract: This paper addresses whether cohesive networks of socially embedded ties or sparse networks rich in structural holes are more conducive to the success of new firms. We propose that the networks of emerging firms evolve in order to adapt to the firm's changing resource needs and resource challenges. As firms emerge, their networks consist primarily of socially embedded ties drawn from dense, cohesive sets of connections. We label these networks identity based. As firms move into the early growth stage, their networks evolve toward more ties based on a calculation of economic costs and benefits. This shift from identity-based to more calculative networks is manifested in the evolution of the firm networks: (1) from primarily socially embedded ties to a balance of embedded and arm's-length relations; (2) from networks that emphasize cohesion to those that exploit structural holes; and (3) from a more path-dependent to a more intentionally managed network. Thus, this paper suggests that both cohesive and sparse networks are conducive to firm performance when they are aligned with and address firms' evolving resource challenges. Copyright © 2001 John Wiley & Sons, Ltd.

An hPer2 Phosphorylation Site Mutation in Familial Advanced Sleep Phase Syndrome

Abstract: Familial advanced sleep phase syndrome (FASPS) is an autosomal dominant circadian rhythm variant; affected individuals are "morning larks" with a 4-hour advance of the sleep, temperature, and melatonin rhythms. Here we report localization of the FASPS gene near the telomere of chromosome 2q. A strong candidate gene (hPer2), a human homolog of the period gene in Drosophila, maps to the same locus. Affected individuals have a serine to glycine mutation within the casein kinase Iepsilon (CKIepsilon) binding region of hPER2, which causes hypophosphorylation by CKIepsilon in vitro. Thus, a variant in human sleep behavior can be attributed to a missense mutation in a clock component, hPER2, which alters the circadian period.

Examining Transformational Resistance Through a Critical Race and Latcrit Theory Framework: Chicana and Chicano Students in an Urban Context

Abstract: Using critical race theory and Latina/Latino critical race theory as a framework, this article utilizes the methods of qualitative inquiry and counterstorytelling to examine the construct of student resistance. The authors use two events in Chicana/Chicano student history—the 1968 East Los Angeles school walkouts and the 1993 UCLA student strike for Chicana and Chicano studies. Using these two methods and events, the authors extend the concept of resistance to focus on its transformative potential and its internal and external dimensions. The authors describe and analyze a series of individual and focus group interviews with women who participated in the 1968 East Los Angeles high school walkouts. The article then introduces a counterstory that briefly listens in on a dialogue between two data-driven composite characters, the Professor and an undergraduate student named Gloria. These characters’ experiences further illuminate the concepts of internal and external transformational resistance.

Ownership Structure, Corporate Governance, and Firm Value: Evidence from the East Asian Financial Crisis

Abstract: We study the effect of ownership structure on firm value during the East Asian financial crisis that began in July 1997. The crisis represents a negative shock to the investment opportunities of firms in these markets that raises the incentives of controlling shareholders to expropriate minority shareholders. Moreover, the large separation between cash flow and control rights that often arise from the use of pyramidal ownership structures and cross-holdings in these markets suggests that insiders have both the incentive and the ability to engage in expropriation. Using data from over 800 firms in eight East Asian countries, we find evidence consistent with this view. Tobin's Q ratios of those firms in which minority shareholders are potentially most subject to expropriation decline twelve percent more than Q ratios in other firms during the crisis period. A similar result holds for stock returns - firms in which minority shareholders are most likely to experience expropriation underperform other firms by about nine percent per year during the crisis period. Further, during the pre-crisis period we find no evidence that firms with a separation between cash flow rights and control rights exhibit performance changes different from firms with no such separation. All of these results are robust to controls for country and industry effects, as well as proxies for differences in risk across firms and the strength of the country's legal institutions. The evidence indicates that corporate ownership structure plays an important role in determining the incentives of insiders to expropriate minority shareholders during the times of declining investment opportunities. Our results add to the literature that examines the link between ownership structure and firm performance and provide additional guidance to policymakers engaged in the ongoing debate about the proper role and design of corporate governance features and legal institutions in developing economies.

Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure

Abstract: Wood density (Dt), an excellent predictor of mechanical properties, is typically viewed in relation to support against gravity, wind, snow, and other environ- mental forces. In contrast, we show the surprising extent to which variation in D t and wood structure is linked to support against implosion by negative pressure in the xy- lem pipeline. The more drought-tolerant the plant, the more negative the xylem pressure can become without cavitation, and the greater the internal load on the xylem conduit walls. Accordingly, Dt was correlated with cavi- tation resistance. This trend was consistent with the maintenance of a safety factor from implosion by nega- tive pressure: conduit wall span ( b) and thickness (t) scaled so that (t/b) 2 was proportional to cavitation resis- tance as required to avoid wall collapse. Unexpectedly, trends in Dt may be as much or more related to support of the xylem pipeline as to support of the plant.

Driven to Distraction: Dual-Task Studies of Simulated Driving and Conversing on a Cellular Telephone

Abstract: Dual-task studies assessed the effects of cellular-phone conversations on performance of a simulated driving task. Perfor- mance was not disrupted by listening to radio broadcasts or listening to a book on tape. Nor was it disrupted by a continuous shadowing task using a handheld phone, ruling out, in this case, dual-task inter- pretations associated with holding the phone, listening, or speaking. However, significant interference was observed in a word-generation variant of the shadowing task, and this deficit increased with the diffi- culty of driving. Moreover, unconstrained conversations using either a handheld or a hands-free cell phone resulted in a twofold increase in the failure to detect simulated traffic signals and slower reactions to those signals that were detected. We suggest that cellular-phone use disrupts performance by diverting attention to an engaging cognitive context other than the one immediately associated with driving. crease in the likelihood of getting into an accident, and that this increased risk was comparable to that found for driving with a blood alcohol level above the legal limit. In addition, these authors found no reliable safety advantages for those individuals who used a hands-free cellular device. The authors concluded that the interference associated with cell-phone use was due to attentional factors rather than to pe- ripheral factors such as holding the phone. The field studies of Redelmeier and Tibshirani (1997) establish a correlation between cell-phone use and motor-vehicle accidents, but they do not necessarily imply that use of cell phones causes an increase in accident rates. There may be self-selection factors creating an asso- ciation between cell-phone use and accidents. For example, people who drive and use their cell phone may be more likely to engage in risky behavior, and this increase in risk taking may underlie the corre- lation. Similarly, being in a highly emotional state may increase one's likelihood of driving erratically and may also increase one's likelihood of talking on the cell phone. In order to assess the possible causal rela- tionship between cell-phone use and automobile accidents, carefully controlled experiments, such as the ones described in this report, are needed.

The Impact of Psoriasis on Quality of Life: Results of a 1998 National Psoriasis Foundation Patient-Membership Survey

Abstract: Background Psoriasis can have a profound impact on a patient's quality of life. Objectives To assess patients' perspectives on the impact of psoriasis on their lifestyle and emotional well-being and the social ramifications of living with the disease; to determine the range of therapies available; and to ascertain patients' satisfaction with the management of their disease. Design A 4-page, self-administered questionnaire was mailed on July 13 and 14, 1998, to the entire membership of the National Psoriasis Foundation (N = 40 350), and followed by a telephone survey of responders with severe psoriasis. Main Outcome Measures Patients' perspectives on the psychosocial impact of psoriasis and the effectiveness of the management of their disease. Results Of the 40 350 questionnaires mailed out, a response rate of 43% was realized. The most frequent symptoms experienced by the mail-survey respondents were scaling (94%), itching (79%), and skin redness (71%); 39% reported that psoriasis covered 10% or more of their bodies. A total of 6194 patients with severe psoriasis were entered into the database for the telephone survey. Of these, 79% reported that psoriasis had a negative impact on their lives, 40% felt frustrated with the ineffectiveness of their current therapies, and 32% reported that treatment was not aggressive enough. Conclusions The unprecedented response to the survey provides compelling evidence that individuals with psoriasis believe that the disease has a profound emotional and social as well as physical impact on their quality of life. Many patients with psoriasis, particularly those with severe disease, are frustrated with the management of their disease and by the perceived ineffectiveness of their therapies. Physicians may need to improve communication with their patients and should reevaluate their management of psoriasis.

Modification of the integral isoconversional method to account for variation in the activation energy

Abstract: Integral isoconversional methods may give rise to noticeable systematic error in the activation energy when the latter strongly varies with the extent of conversion. This error is eliminated by using an integration technique that properly accounts for the variation in the activation energy. The technique is implemented as a modification of the earlier proposed advanced isoconversional method [Vyazovkin, S. J Comput Chem 1997, 18, 393]. The applications of the modified method are illustrated by simulations as well as by processing of data on the thermal decomposition of calcium oxalate monohydrate and ammonium nitrate. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 178–183, 2001

Solar 8B and hep Neutrino Measurements from 1258 Days of Super-Kamiokande Data

Abstract: Solar neutrino measurements from 1258days of data from the Super-Kamiokande detector are presented. The measurements are based on recoil electrons in the energy range 5.0{endash}20.0MeV. The measured solar neutrino flux is 2.32{+-}0.03(stat){sup +0.08}{sub {minus}0.07}(syst){times}10{sup 6} cm{sup {minus}2}s{sup {minus}1} , which is 45.1{+-}0.5(stat ){sup +1.6}{sub {minus}1.4}(syst) % of that predicted by the BP2000 SSM. The day vs night flux asymmetry ({Phi}{sub n}{minus}{Phi}{sub d})/ {Phi}{sub average} is 0.033{+-}0.022(stat){sup +0.013}{sub {minus}0.012}(syst) . The recoil electron energy spectrum is consistent with no spectral distortion. For the hep neutrino flux, we set a 90% C.L.upper limit of 40{times}10{sup 3} cm{sup {minus}2}s{sup {minus}1} , which is 4.3times the BP2000 SSM prediction.

Synthesizing natural textures

Abstract: We present a simple texture synthesis algorithm that is well-suited for a specific class of naturally occurring textures. This class includes quasi-repeating patterns consisting of small objects of familiar but irregular size, such as flower fields, pebbles, forest undergrowth, bushes and tree branches. The algorithm starts from a sample image and generates a new image of arbitrary size the appearance of which is similar to that of the original image. This new image does not change the basic spatial frequencies the original image; instead it creates an image that is a visually similar, and is of a size set by the user. This method is fast and its implementation is straightforward. We extend the algorithm to allow direct user input for interactive control over the texture synthesis process. This allows the user to indicate large-scale properties of the texture appearance using a standard painting-style interface, and to choose among various candidate textures the algorithm can create by performing different number of iterations.

Compulsory averaging of crowded orientation signals in human vision

Abstract: A shape can be more difficult to identify when other shapes are near it. For example, when several grating patches are viewed parafoveally, observers are unable to report the orientation of the central patch. This phenomenon, known as 'crowding,' has historically been confused with lateral masking, in which one stimulus attenuates signals generated by another stimulus. Here we show that despite their inability to report the orientation of an individual patch, observers can reliably estimate the average orientation, demonstrating that the local orientation signals are combined rather than lost. Our results imply that crowding is distinct from ordinary masking, and is perhaps related to texture perception. Under crowded conditions, the orientation signals in primary visual cortex are pooled before they reach consciousness.

Asian Dust Events of April 1998

Abstract: On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia. The April 19 dust cloud crossed the Pacific Ocean in 5 days, subsided to the surface along the mountain ranges between British Columbia and California, and impacted severely the optical and the concentration environments of the region. In east Asia the dust clouds increased the albedo over the cloudless ocean and land by up to 10–20%, but it reduced the near-UV cloud reflectance, causing a yellow coloration of all surfaces. The yellow colored backscattering by the dust eludes a plausible explanation using simple Mie theory with constant refractive index. Over the West Coast the dust layer has increased the spectrally uniform optical depth to about 0.4, reduced the direct solar radiation by 30–40%, doubled the diffuse radiation, and caused a whitish discoloration of the blue sky. On April 29 the average excess surface-level dust aerosol concentration over the valleys of the West Coast was about 20–50 μg/m3 with local peaks >100 μg/m3. The dust mass mean diameter was 2–3 μm, and the dust chemical fingerprints were evident throughout the West Coast and extended to Minnesota. The April 1998 dust event has impacted the surface aerosol concentration 2–4 times more than any other dust event since 1988. The dust events were observed and interpreted by an ad hoc international web-based virtual community. It would be useful to set up a community-supported web-based infrastructure to monitor the global aerosol pattern for such extreme aerosol events, to alert and to inform the interested communities, and to facilitate collaborative analysis for improved air quality and disaster management.

Geographic Data Mining and Knowledge Discovery

Abstract: Introduction Harvey J. Miller and Jiawei Han Spatiotemporal Data Mining Paradigms and Methodologies John F. Roddick and Brian G. Lees Fundamentals of Spatial Data Warehousing for Geographic Knowledge Discovery Yvan Bedard and Jiawei Han Analysis of Spatial Data with Map Cubes: Highway Traffic Data Chang-Tien Lu, Arnold P. Boedihardjo, and Shashi Shekhar NEW! Data Quality Issues and Geographic Knowledge Discovery Marc Gervais, Yvan Bedard, Marie-Andree Levesque, Eveline Bernier, and Rodolphe Devillers Spatial Classification and Prediction Models for Geospatial Data Mining Shashi Shekhar, Ranga Raju Vatsavai, and Sanjay Chawla An Overview of Clustering Methods in Geographic Data Analysis Jiawei Han, Jae-Gil Lee, and Micheline Kamber NEW! Computing Medoids in Large Spatial Datasets Kyriakos Mouratidis, Dimitris Papadias, Spiros Papadimitriou NEW! Looking for a Relationship? Try GWR A. Stewart Fotheringham, Martin Charlton, and Urska Demsar Leveraging the Power of Spatial Data Mining to Enhance the Applicability of GIS Technology Donato Malerba, Antonietta Lanza, and Annalisa Appice Visual Exploration and Explanation in Geography: Analysis with Light Mark Gahegan NEW! Multivariate Spatial Clustering and Geovisualization Diansheng Guo NEW! Toward Knowledge Discovery about Geographic Dynamics in Spatiotemporal Databases} May Yuan NEW! The Role of a Multitier Ontological Framework in Reasoning to Discover Meaningful Patterns of Sustainable Mobility Monica Wachowicz, Jose Macedo, Chiara Renso, and Arend Ligtenberg NEW! Periodic Pattern Discovery from Trajectories of Moving Objects Huiping Cao, Nikos Mamoulis, and David W. Cheung NEW! Decentralized Spatial Data Mining for Geosensor Networks Patrick Laube and Matt Duckham NEW! Beyond Exploratory Visualization of Space-Time Paths Menno-Jan Kraak and Otto Huisman

Creep, Hysteresis, and Vibration Compensation for Piezoactuators: Atomic Force Microscopy Application

Abstract: Structural vibrations and hysteresis nonlinearities in piezoactuators have been fundamental limitations when using these actuators for high-speed precision-positioning applications. Positioning speed (bandwidth) is limited by structural vibrations, typically, to about one-tenth the fundamental vibrational frequency of the piezoprobe. Further, precision in positioning is limited by hysteresis nonlinearities, which can result in signie cant errors for large-range positioning applications. This paper shows that signie cant improvements in precision and bandwidth can be achieved by using an inversion-based approach to compensate for hysteresis and vibrations in the piezodynamics. Theapproach decouplestheinversion into 1 )inversion of thehysteresisnonlinearity and 2 )inversion ofthe structuraldynamics,toe ndaninputvoltageproe lethatachievesprecisiontracking ofa desiredpositiontrajectory. Theapproachisappliedtoapiezoactuator,andexperimentalresultsshowthatanorderofmagnitudeimprovement in positioning speed is achieved, while maintaining precision tracking of the desired position trajectory. I. Introduction P IEZOACTUATORS can achieve nanometer resolution positioning and are hence increasingly being used for ultraprecision positioning in aerospace applications, 1;2 vibration control, scanning probe microscopy for surface characterization, and nanofabrication. 3i5 Two major limitations of present positioning techniquesusing piezoactuatorsare 1 )lowoperating bandwidthdue to positioning errors caused by structural vibrations at high speeds and 2) low precision for relatively large-range displacements (due to errors caused by hysteresis nonlinearities ), resulting in restricted positioning range. This paper presents a method to improve both the accuracy and the speed of piezoactuators by using an inversionbased approach to e nd the voltage input to the piezoactuators that compensates for the hysteresis nonlinearities and the structural vibrations. This approach e rst decouples the system dynamics into two separate subsystems that model 1 ) the hysteresis nonlinearity

Signaling by toll-like receptor 2 and 4 agonists results in differential gene expression in murine macrophages.

Abstract: Lipopolysaccharide (LPS) derived from the periodontal pathogen Porphyromonas gingivalis has been reported to differ structurally and functionally from enterobacterial LPS. These studies demonstrate that in contrast to protein-free enterobacterial LPS, a similarly purified preparation of P. gingivalis LPS exhibited potent Toll-like receptor 2 (TLR2), rather than TLR4, agonist activity to elicit gene expression and cytokine secretion in murine macrophages and transfectants. More importantly, TLR2 stimulation by this P. gingivalis LPS preparation resulted in differential expression of a panel of genes that are normally induced in murine macrophages by Escherichia coli LPS. These data suggest that (i) P. gingivalis LPS does not signal through TLR4 and (ii) signaling through TLR2 and through TLR4 differs quantitatively and qualitatively. Our data support the hypothesis that the shared signaling pathways elicited by TLR2 and by TLR4 agonists must diverge in order to account for the distinct patterns of inflammatory gene expression.

Analysis of partial volume effects in diffusion‐tensor MRI

Abstract: The diffusion tensor is currently the accepted model of diffusion in biological tissues. The measured diffusion behavior may be more complex when two or more distinct tissues with different diffusion tensors occupy the same voxel. In this study, a partial volume model of MRI signal behavior for two diffusion-tensor compartments is presented. Simulations using this model demonstrate that the conventional single diffusion tensor model could lead to highly variable and inaccurate measurements of diffusion behavior. The differences between the single and two-tensor models depend on the orientations, fractions, and exchange between the two diffusion tensor compartments, as well as the diffusion-tensor encoding technique and diffusion-weighting that is used in the measurements. The current single compartment model's inaccuracies could cause diffusion-based characterization of cerebral ischemia and white matter connectivity to be incorrect. A diffusion-tensor MRI imaging experiment on a normal human brain revealed significant partial volume effects between oblique white matter regions when using very large voxels and large diffusion-weighting (b ∼ 2.69 × 103 sec/mm2). However, the apparent partial volume effects in white matter decreased significantly when smaller voxel dimensions were used. For diffusion tensor studies obtained using typical diffusion-weighting values (b ∼ 1 × 103 sec/mm2) partial volume effects are much more difficult to detect and resolve. More accurate measurements of multiple diffusion compartments may lead to improved confidence in diffusion measurements for clinical applications. Magn Reson Med 45:770–780, 2001. © 2001 Wiley-Liss, Inc.

Stimulation of homologous recombination through targeted cleavage by chimeric nucleases.

Abstract: Chimeric nucleases that are hybrids between a nonspecific DNA cleavage domain and a zinc finger DNA recognition domain were tested for their ability to find and cleave their target sites in living cells. Both engineered DNA substrates and the nucleases were injected into Xenopus laevis oocyte nuclei, in which DNA cleavage and subsequent homologous recombination were observed. Specific cleavage required two inverted copies of the zinc finger recognition site in close proximity, reflecting the need for dimerization of the cleavage domain. Cleaved DNA molecules were activated for homologous recombination; in optimum conditions, essentially 100% of the substrate recombined, even though the DNA was assembled into chromatin. The original nuclease has an 18-amino-acid linker between the zinc finger and cleavage domains, and this enzyme cleaved in oocytes at paired sites separated by spacers in the range of 6 to 18 bp, with a rather sharp optimum at 8 bp. By shortening the linker, we found that the range of effective site separations could be narrowed significantly. With no intentional linker between the binding and cleavage domains, only binding sites exactly 6 bp apart supported efficient cleavage in oocytes. We also showed that two chimeric enzymes with different binding specificities could collaborate to stimulate recombination when their individual sites were appropriately placed. Because the recognition specificity of zinc fingers can be altered experimentally, this approach holds great promise for inducing targeted recombination in a variety of organisms.

Does Corporate Diversification Destroy Value

Abstract: We analyze several hundred firms that expand via acquisition and/or increase their reported number of business segments. The average combined market reaction to acquisition announcements is positive but, according to the Berger and Ofek (1995) method for valuing conglomerates, the excess values of the acquiring firms decline after the diversifying event. For our sample, half or more of the reduction in excess value occurs because the firms acquire already-discounted business units, and not because combining firms destroys value. We also show that firms that increase their number of business segments due to pure reporting changes do not exhibit reductions in excess value. Our results suggest that the standard assumption that conglomerate divisions can be benchmarked to typical stand-alone firms should be carefully reconsidered.

Functional and ecological xylem anatomy

Abstract: Cohesion-tension transport of water is an energetically efficient way to carry large amounts of water from the roots up to the leaves. However, the cohesion-tension mechanism places the xylem water under negative hydrostatic pressure ( P x ), rendering it susceptible to cavitation. There are conflicts among the structural requirements for minimizing cavitation on the one hand vs maximizing efficiency of transport and construction on the other. Cavitation by freeze-thaw events is triggered by in situ air bubble formation and is much more likely to occur as conduit diameter increases, creating a direct conflict between conducting efficiency and sensitivity to freezing induced xylem failure. Temperate ring-porous trees and vines with wide diameter conduits tend to have a shorter growing season than conifers and diffuse-porous trees with narrow conduits. Cavitation by water stress occurs by air seeding at interconduit pit membranes. Pit membrane structure is at least partially uncoupled from conduit size, leading to a much less pronounced trade-off between conducting efficiency and cavitation by drought than by freezing. Although wider conduits are generally more susceptible to drought-induced cavitation within an organ, across organs or species this trend is very weak. Different trade-offs become apparent at the level of the pit membranes that interconnect neighbouring conduits. Increasing porosity of pit membranes should enhance conductance but also make conduits more susceptible to air seeding. Increasing the size or number of pit membranes would also enhance conductance, but may weaken the strength of the conduit wall against implosion. The need to avoid conduit collapse under negative pressure creates a significant trade-off between cavitation resistance and xylem construction cost, as revealed by relationships between conduit wall strength, wood density and cavitation pressure. Trade-offs involving cavitation resistance may explain the correlations between wood anatomy, cavitation resistance, and the physiological range of negative pressure experienced by species in their native habitats.

Activated platelets mediate inflammatory signaling by regulated interleukin 1β synthesis

Abstract: Platelets release preformed mediators and generate eicosanoids that regulate acute hemostasis and inflammation, but these anucleate cytoplasts are not thought to synthesize proteins or cytokines, or to influence inflammatory responses over time. Interrogation of an arrayed cDNA library demonstrated that quiescent platelets contain many messenger RNAs, one of which codes for interleukin 1β precursor (pro–IL-1β). Unexpectedly, the mRNA for IL-1β and many other transcripts are constitutively present in polysomes, providing a mechanism for rapid synthesis. Platelet activation induces rapid and sustained synthesis of pro–IL-1β protein, a response that is abolished by translational inhibitors. A portion of the IL-1β is shed in its mature form in membrane microvesicles, and induces adhesiveness of human endothelial cells for neutrophils. Signal-dependent synthesis of an active cytokine over several hours indicates that platelets may have previously unrecognized roles in inflammation and vascular injury. Inhibition of β3 integrin engagement markedly attenuated the synthesis of IL-1β, identifying a new link between the coagulation and inflammatory cascades, and suggesting that antithrombotic therapies may also have novel antiinflammatory effects.