Showing papers by "University of Colorado Boulder published in 1999"

Coupled ocean–atmosphere dynamics in the Indian Ocean during 1997–98

Abstract: Climate variability in the Indian Ocean region seems to be, in some aspects, independent of forcing by external phenomena such as the El Nino/Southern Oscillation1,2,3,4 But the extent to which, and how, internal coupled ocean–atmosphere dynamics determine the state of the Indian Ocean system have not been resolved Here we present a detailed analysis of the strong seasonal anomalies in sea surface temperatures, sea surface heights, precipitation and winds that occurred in the Indian Ocean region in 1997–98, and compare the results with the record of Indian Ocean climate variability over the past 40 years We conclude that the 1997–98 anomalies—in spite of the coincidence with the strong El Nino/Southern Oscillation event—may primarily be an expression of internal dynamics, rather than a direct response to external influences We propose a mechanism of ocean–atmosphere interaction governing the 1997–98 event that may represent a characteristic internal mode of the Indian Ocean climate system In the Pacific Ocean, the identification of such a mode has led to successful predictions of El Nino5; if the proposed Indian Ocean internal mode proves to be robust, there may be a similar potential for predictability of climate in the Indian Ocean region

Interdecadal changes in the ENSO-monsoon system

Abstract: The El Nino–Southern Oscillation (ENSO) and Indian monsoon are shown to have undergone significant interdecadal changes in variance and coherency over the last 125 years. Wavelet analysis is applied to indexes of equatorial Pacific sea surface temperature (Nino3 SST), the Southern Oscillation index, and all-India rainfall. Time series of 2–7-yr variance indicate intervals of high ENSO–monsoon variance (1875–1920 and 1960–90) and an interval of low variance (1920–60). The ENSO–monsoon variance also contains a modulation of ENSO–monsoon amplitudes on a 12–20-yr timescale. The annual-cycle (1 yr) variance time series of Nino3 SST and Indian rainfall is negatively correlated with the interannual ENSO signal. The 1-yr variance is larger during 1935–60, suggesting a negative correlation between annual-cycle variance and ENSO variance on interdecadal timescales. The method of wavelet coherency is applied to the ENSO and monsoon indexes. The Nino3 SST and Indian rainfall are found to be highly coherent, ...

Convectively Coupled Equatorial Waves: Analysis of Clouds and Temperature in the Wavenumber–Frequency Domain

Abstract: A wavenumber-frequency spectrum analysis is performed for all longitudes in the domain 158S‐158N using a long (;18 years) twice-daily record of satellite-observed outgoing longwave radiation (OLR), a good proxy for deep tropical convection. The broad nature of the spectrum is red in both zonal wavenumber and frequency. By removing an estimated background spectrum, numerous statistically significant spectral peaks are isolated. Some of the peaks correspond quite well to the dispersion relations of the equatorially trapped wave modes of shallow water theory with implied equivalent depths in the range of 12‐50 m. Cross-spectrum analysis with the satellite-based microwave sounding unit deep-layer temperature data shows that these spectral peaks in the OLR are ‘‘coupled’’ with this dynamical field. The equivalent depths of the convectively coupled waves are shallower than those typical of equatorial waves uncoupled with convection. Such a small equivalent depth is thought to be a result of the interaction between convection and the dynamics. The convectively coupled equatorial waves identified correspond to the Kelvin, n 5 1 equatorial Rossby, mixed Rossby-gravity, n 5 0 eastward inertiogravity, n 5 1 westward inertio-gravity (WIG), and n 5 2 WIG waves. Additionally, the Madden‐Julian oscillation and tropical depression-type disturbances are present in the OLR spectra. These latter two features are unlike the convectively coupled equatorial waves due to their location away from the equatorial wave dispersion curves in the wavenumber-frequency domain. Extraction of the different convectively coupled disturbances in the time‐longitude domain is performed by filtering the OLR dataset for very specific zonal wavenumbers and frequencies. The geographical distribution of the variance of these filtered data gives further evidence that some of the spectral peaks correspond to particular equatorial wave modes. The results have implications for the cumulus parameterization problem, for the excitation of equatorial waves in the lower stratosphere, and for extended-range forecasting in the Tropics.

An Interior Point Algorithm for Large-Scale Nonlinear Programming

Abstract: The design and implementation of a new algorithm for solving large nonlinear programming problems is described. It follows a barrier approach that employs sequential quadratic programming and trust regions to solve the subproblems occurring in the iteration. Both primal and primal-dual versions of the algorithm are developed, and their performance is illustrated in a set of numerical tests.

New Ideas In Optimization

Abstract: Optimization is a pivotal aspect of software design. The techniques treated in this text represent research as elucidated by the leaders in the field. The optimization methods are applied to real problems, such as hilllclimbing, simulated annealing, and tabu search.

On the fate of gas accreting at a low rate on to a black hole

Abstract: Gas supplied conservatively to a black hole at rates well below the Eddington rate may not be able to radiate effectively and the net energy flux, including the energy transported by the viscous torque, is likely to be close to zero at all radii. This has the consequence that the gas accretes with positive energy so that it may escape. Accordingly, we propose that only a small fraction of the gas supplied actually falls on to the black hole, and that the binding energy it releases is transported radially outward by the torque so as to drive away the remainder in the form of a wind. This is a generalization of and an alternative to an `ADAF' solution. Some observational implications and possible ways to distinguish these two types of flow are briefly discussed.

Identifying DNA and protein patterns with statistically significant alignments of multiple sequences.

Abstract: Motivation: Molecular biologists frequently can obtain interesting insight by aligning a set of related DNA, RNA or protein sequences. Such alignments can be used to determine either evolutionary or functional relationships. Our interest is in identifying functional relationships. Unless the sequences are very similar, it is necessary to have a specific strategy for measuring-or scoring-the relatedness of the aligned sequences. If the alignment is not known, one can be determined by finding an alignment that optimizes the scoring scheme. Results: We describe four components to our approach for determining alignments of multiple sequences. First, we review a log-likelihood scoring scheme we call information content. Second, we describe two methods for estimating the P value of an individual information content score: (i) a method that combines a technique from large-deviation statistics with numerical calculations; (ii) a method that is exclusively numerical. Third, we describe how we count the number of possible alignments given the overall amount of sequence data. This count is multiplied by the P value to determine the expected frequency of an information content score and, thus, the statistical significance of the corresponding alignment. Statistical significance can be used to compare alignments having differing widths and containing differing numbers of sequences. Fourth, we describe a greedy algorithm for determining alignments of functionally related sequences. Finally, we test the accuracy of our P value calculations, and give an example of using our algorithm to identify binding sites for the Escherichia coli CRP protein.

Mutual Fund Herding and the Impact on Stock Prices

Abstract: We analyze the trading activity of the mutual fund industry from 1975 through 1994 to determine whether funds “herd” when they trade stocks and to investigate the impact of herding on stock prices. Although we find little herding by mutual funds in the average stock, we find much higher levels in trades of small stocks and in trading by growth-oriented funds. Stocks that herds buy outperform stocks that they sell by 4 percent during the following six months; this return difference is much more pronounced among small stocks. Our results are consistent with mutual fund herding speeding the price-adjustment process. DO INSTITUTIONAL INVESTORS “F LOCK TOGETHER” ~or “herd,” as it is often called! when they trade securities? Do some investors follow the lead of others when they trade? Such questions have interested researchers for some time, and are central to understanding the impact of institutional trading on securities markets and to understanding the way in which information becomes incorporated into market prices. 1

Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes

Abstract: The sensitivity of oceanic thermohaline circulation to freshwater perturbations is a critical issue for understanding abrupt climate change1 Abrupt climate fluctuations that occurred during both Holocene and Late Pleistocene times have been linked to changes in ocean circulation2,3,4,5,6, but their causes remain uncertain One of the largest such events in the Holocene occurred between 8,400 and 8,000 calendar years ago2,7,8 (7,650–7,200 14C years ago), when the temperature dropped by 4–8 °C in central Greenland2 and 15–3 °C at marine4,7 and terrestrial7,8 sites around the northeastern North Atlantic Ocean The pattern of cooling implies that heat transfer from the ocean to the atmosphere was reduced in the North Atlantic Here we argue that this cooling event was forced by a massive outflow of fresh water from the Hudson Strait This conclusion is based on our estimates of the marine 14C reservoir for Hudson Bay which, in combination with other regional data, indicate that the glacial lakes Agassiz and Ojibway9,10,11,12, (originally dammed by a remnant of the Laurentide ice sheet) drained catastrophically ∼8,470 calendar years ago; this would have released >1014 m3 of fresh water into the Labrador Sea This finding supports the hypothesis2,7,8 that a sudden increase in freshwater flux from the waning Laurentide ice sheet reduced sea surface salinity and altered ocean circulation, thereby initiating the most abrupt and widespread cold event to have occurred in the past 10,000 years

Communication Theory as a Field

Abstract: This essay reconstructs communication theory as a dialogical-dialectical field according to two principles: the constitutive model of communication as a metamode1 and theory as metadiscursive practice. The essay argues that all communication theories are mutually relevant when addressed to a practical lifeworld in which “communication” is already a richly meaningful term. Each tradition of communication theory derives from and appeals rhetorically to certain commonplace beliefs about communication while challenging other beliefs. The complementarities and tensions among traditions generate a theoretical metadiscourse that intersects with and potentially informs the ongoing practical metadiscourse in society. In a tentative scheme of the field, rhetorical, semiotic, phenomenological, cybernetic, sociopsychological, sociocultural, and critical traditions of communication theory are distinguished by characteristic ways of defining communication and problems of communication, metadiscursive vocabularies, and metadiscursive commonplaces that they appeal to and challenge. Topoi for argumentation across traditions are suggested and implications for theoretical work and disciplinary practice in the field are considered. Communication theory is enormously rich in the range of ideas that fall within its nominal scope, and new theoretical work on communication has recently been flourishing.’ Nevertheless, despite the ancient roots and growing profusion of theories about communication, I argue that communication theory as an identifiable field of study does not yet exist.2 Rather than addressing a field of theory, we appear to be operating primarily in separate domains. Books and articles on communication theory seldom mention other works on communication theory except within narrow (inter)disciplinary specialties and schools of thought.’ Except within these little groups, communication theorists apparently neither agree nor disagree about much of anything. There is no canon of general theory to which they all refer. There are no common goals that

Differential Galaxy Evolution in Cluster and Field Galaxies at z ≈ 0.3

Abstract: We measure spectral indexes for 1823 galaxies in the Canadian Network for Observational Cosmology 1 (CNOC1) sample of 15 X-ray luminous clusters at 0.18 5 A] but no [O II] emission [W0(O ) < 5 A], perhaps indicative of recently terminated star formation. The observed fraction of 4.4% ± 0.7% in the cluster sample is an overestimate due to a systematic effect that results from the large uncertainties on individual spectral index measurements. Corrected for this bias, we estimate that K+A galaxies make up only 2.1% ± 0.7% of the cluster sample and 0.1% ± 0.7% of the field. From the subsample of galaxies more luminous than Mr = -18.8 + 5 log h, which is statistically representative of a complete sample to this limit, the corrected fraction of K+A galaxies is 1.5% ± 0.8% in the cluster and 1.2% ± 0.8% in the field. Compared with the z ≈ 0.1 fraction of 0.30%, the fraction of K+A galaxies in the CNOC1 field sample is greater by perhaps a factor of 4, but with only 1 σ significance; no further evolution of this fraction is detectable over our redshift range. We compare our data with the results of PEGASE and GISSEL96 spectrophotometric models and conclude, from the relative fractions of red and blue galaxies with no [O II] λ3727 emission and strong Hδ absorption, that up to 1.9% ± 0.8% of the cluster population may have had its star formation recently truncated without a starburst. However, this is still not significantly greater than the fraction of such galaxies in the field, 3.1% ± 1.0%. Furthermore, we do not detect an excess of cluster galaxies that have unambiguously undergone starbursts within the last 1 Gyr. In fact, at 6.3% ± 2.1%, the A+em galaxies that Poggianti et al. have recently suggested are dusty starbursts are twice as common in the field as in the cluster environment. Our results imply that these cluster environments are not responsible for inducing starbursts; thus, the increase in cluster blue galaxy fraction with redshift may not be a strictly cluster-specific phenomenon. We suggest that the truncation of star formation in clusters may largely be a gradual process, perhaps due to the exhaustion of gas in the galactic disks over fairly long timescales; in this case differential evolution may result because field galaxies can refuel their disks with gas from extended halos, thus regenerating star formation, while cluster galaxies may not have such halos and so continue to evolve passively.

Global patterns of terrestrial biological nitrogen (N2) fixation in natural ecosystems

Abstract: Human activities have clearly caused dramatic alterations of the terrestrial nitrogen cycle, and analyses of the extent and effects of such changes are now common in the scientific literature. However, any attempt to evaluate N cycling processes within ecosystems, as well as anthropogenic influences on the N cycle, requires an understanding of the magnitude of inputs via biological nitrogen fixation (BNF). Although there have been many studies addressing the microbiology, physiology, and magnitude of N fixation at local scales, there are very few estimates of BNF over large scales. We utilized >100 preexisting published estimates of BNF to generate biome- and global-level estimates of biological N fixation. We also used net primary productivity (NPP) and evapotranspiration (ET) estimates from the Century terrestrial ecosystem model to examine global relationships between these variables and BNF as well as to compare observed and Century-modeled BNF. Our data-based estimates showed a strong positive relationship between ecosystem ET and BNF, and our analyses suggest that while the model's simple relationships for BNF predict broad scale patterns, they do not capture much of the variability or magnitude of published rates. Patterns of BNF were also similar to patterns of ecosystem NPP. Our “best estimate” of potential nitrogen fixation by natural ecosystems is ∼195 Tg N yr−1, with a range of 100–290 Tg N yr−1. Although these estimates do not account for the decrease in natural N fixation due to cultivation, this would not dramatically alter our estimate, as the greatest reductions in area have occurred in systems characterized by relatively low rates of N fixation (e.g., grasslands). Although our estimate of BNF in natural ecosystems is similar to previously published estimates of terrestrial BNF, we believe that this study provides a more documented, constrained estimate of this important flux.

Matrices, Vector Spaces, and Information Retrieval

Abstract: The evolution of digital libraries and the Internet has dramatically transformed the processing, storage, and retrieval of information. Efforts to digitize text, images, video, and audio now consume a substantial portion of both academic and industrial activity. Even when there is no shortage of textual materials on a particular topic, procedures for indexing or extracting the knowledge or conceptual information contained in them can be lacking. Recently developed information retrieval technologies are based on the concept of a vector space. Data are modeled as a matrix, and a user's query of the database is represented as a vector. Relevant documents in the database are then identified via simple vector operations. Orthogonal factorizations of the matrix provide mechanisms for handling uncertainty in the database itself. The purpose of this paper is to show how such fundamental mathematical concepts from linear algebra can be used to manage and index large text collections.

Differential roles for cyclin-dependent kinase inhibitors p21 and p16 in the mechanisms of senescence and differentiation in human fibroblasts.

Abstract: The irreversible G1 arrest in senescent human diploid fibroblasts is probably caused by inactivation of the G1 cyclin–cyclin-dependent kinase (Cdk) complexes responsible for phosphorylation of the retinoblastoma protein (pRb). We show that the Cdk inhibitor p21Sdi1,Cip1,Waf1, which accumulates progressively in aging cells, binds to and inactivates all cyclin E-Cdk2 complexes in senescent cells, whereas in young cells only p21-free Cdk2 complexes are active. Furthermore, the senescent-cell-cycle arrest occurs prior to the accumulation of the Cdk4-Cdk6 inhibitor p16Ink4a, suggesting that p21 may be sufficient for this event. Accordingly, cyclin D1-associated phosphorylation of pRb at Ser-780 is lacking even in newly senescent fibroblasts that have a low amount of p16. Instead, the cyclin D1-Cdk4 and cyclin D1-Cdk6 complexes in these cells are associated with an increased amount of p21, suggesting that p21 may be responsible for inactivation of both cyclin E- and cyclin D1-associated kinase activity at the early stage of senescence. Moreover, even in the late stage of senescence when p16 is high, cyclin D1-Cdk4 complexes are persistent, albeit reduced by ≤50% compared to young cells. We also provide new evidence that p21 may play a role in inactivation of the DNA replication factor proliferating cell nuclear antigen during early senescence. Finally, because p16 accumulates in parallel with the increases in senescence-associated β-Gal activity and cell volume that characterize the senescent phenotype, we suggest that p16 upregulation may be part of a differentiation program that is turned on in senescent cells. Since p21 decreases after senescence is achieved, this upregulation of p16 may be essential for maintenance of the senescent-cell-cycle arrest.

The Uncertain Relationship between Board Composition and Firm Performance

Abstract: We survey the evidence on the relationship between board composition and firm performance. Boards of directors of American public companies that have a majority of independent directors behave differently, in a number of ways, than boards without such a majority. Some of these differences appear to increase firm value; others may decrease firm value. Overall, within the range of board compositions present today in large public companies, there is no convincing evidence that greater board independence correlates with greater firm profitability or faster growth. In particular, there is no empirical support for current proposals that firms should have "supermajority-independent boards" with only one or two inside directors. To the contrary, there is some evidence that firms with supermajority-independent boards are less profitable than other firms. This suggests that it may be useful for firms to have a moderate number of inside directors (say three to five on an average-sized eleven member board). We offer some possible explanations for these results, based on board dynamics, the informational advantages possessed by inside (and, often, affiliated) directors, and the value of interaction between different types of directors who bring different strengths to the board. published in 54 Business Lawyer 921-963 (1999) Columbia Law School, Center for Law and Economic Studies Working Paper No. 137 Stanford Law School, John M. Olin Program in Law and Economics Working Paper No. 175 available from the Social Science Research Network Electronic Library at: _______________ * Respectively, Professor of Finance, University of Colorado at Boulder; Professor of Law, Stanford Law School. 1 NATIONAL ASS'N OF CORP. DIRS., REPORT OF THE NACD BLUE RIBBON COMMISSION ON DIRECTOR PROFESSIONALISM 9 (1996). 2 THE BUS. ROUNDTABLE, STATEMENT ON CORPORATE GOVERNANCE 10 (1997). 3 See Adam Bryant, Calpers Draws a Blueprint for its Concept of An Ideal Board, N.Y. TIMES, June 17, 1997, at D5. 2 The Uncertain Relationship Between Board Composition and Firm Performance By Sanjai Bhagat and Bernard Black

Religious involvement and U.S. adult mortality

Abstract: We use recently released, nationally representative data from the National Health Interview Survey—Multiple Cause of Death linked file to model the association of religious attendance and sociodemographic, health, and behavioral correlates with overall and cause-specific mortality Religious attendance is associated with US adult mortality in a graded fashion: People who never attend exhibit 187 times the risk of death in the follow-up period compared with people who attend more than once a week This translates into a seven-year difference in life expectancy at age 20 between those who never attend and those who attend more than once a week Health selectivity is responsible for a portion of the religious attendance effect: People who do not attend church or religious services are also more likely to be unhealthy and, conse-quently, to die However, religious attendance also works through increased social ties and behavioral factors to decrease the risks of death And although the magnitude of the association between religious attendance and mortality varies by cause of death, the direction of the association is consistent across causes

Organizational politics and organizational support as predictors of work attitudes, job performance, and organizational citizenship behavior.

Abstract: This study investigated the relationship of organizational politics and organizational support to various work attitudes and behaviors among a field sample of 128 participants. Consistent with our hypothesis, politics and support were related to job satisfaction, commitment, turnover intentions, and supervisor ratings of organizational citizenship behaviors. However, only support was related to job performance. We also examined whether or not organizational politics and organizational support comprise two distinct constructs or one global factor. The evidence here was ambiguous. Fit indices obtained from confirmatory factor analysis suggested that it is more parsimonious to treat politics and support as opposite ends of the same construct, though the two-factor model did show a slightly better fit. On the other hand, subsequent multiple regression analyses showed that support tended to account for additional criterion variance beyond the effect of politics, implying that there may be some practical utility to retaining politics and support as distinct constructs. Copyright © 1999 John Wiley & Sons, Ltd.

An approach to the formal analysis of user complexity

Abstract: A formal approach to analysing the user complexity of interactive systems or devices is described, based on theoretical results from cognitive psychology. The user's knowledge of how to use a system to accomplish the various tasks is represented in a procedural notation that permits quantification of the amount and complexity of the knowledge required and the cognitive processing load involved in using a system. Making a system more usable can be accomplished by altering its design until the knowledge is adequately simplified. By representing the device behaviour formally as well, it is possible to simulate the user-device interaction to obtain rigorous measures of user complexity.

Applied General Equilibrium Modeling with MPSGE as a GAMS Subsystem: AnOverview of the Modeling Framework and Syntax

Abstract: This paper describes a programming environment for economic equilibrium analysis. The system introduces the Mathematical Programming System for General Equilibrium analysis (MPSGE, Rutherford 1987) within the Generalized Algebraic Modelling System (GAMS, Brooke, Kendrick and Meeraus (1988)). This arrangement exploits GAMS‘ set-oriented algebraic syntax for data manipulation and report writing. The system based on the tabular MPSGE input format provides a compact, non-algebraic representation of a model‘s nonlinear equations. This paper provides an overview of the modelling environment and three worked examples in tax policy analysis.

Race, ethnicity and disasters in the United States: a review of the literature.

Abstract: In this paper we synthesise past disaster research that addresses issues of race and ethnicity in the United States. Using an eight-stage typology to organise the findings, this literature review presents the results from a wide range of studies. The synthesis shows how various racial and ethnic groups perceive natural hazard risks and respond to warnings, how groups may be differentially affected, both physically and psychologically, and how disaster effects vary by race and ethnicity during the periods of emergency response, recovery and reconstruction. We show that studies have important findings, many illustrating that racial and ethnic communities in the US are more vulnerable to natural disasters, due to factors such as language, housing patterns, building construction, community isolation and cultural insensitivities. By presenting these studies together, we are able to witness patterns of racial and ethnic inequalities that may be more difficult to see or interpret in individual studies that take place in one specific time and place. We conclude the review with policy and research recommendations.

Golgi Structure in Three Dimensions: Functional Insights from the Normal Rat Kidney Cell

Abstract: Three-dimensional reconstructions of portions of the Golgi complex from cryofixed, freeze-substituted normal rat kidney cells have been made by dual-axis, high-voltage EM tomography at ∼7-nm resolution The reconstruction shown here (∼1 × 1 × 4 μm3) contains two stacks of seven cisternae separated by a noncompact region across which bridges connect some cisternae at equivalent levels, but none at nonequivalent levels The rest of the noncompact region is filled with both vesicles and polymorphic membranous elements All cisternae are fenestrated and display coated buds They all have about the same surface area, but they differ in volume by as much as 50% The trans-most cisterna produces exclusively clathrin-coated buds, whereas the others display only nonclathrin coated buds This finding challenges traditional views of where sorting occurs within the Golgi complex Tubules with budding profiles extend from the margins of both cis and trans cisternae They pass beyond neighboring cisternae, suggesting that these tubules contribute to traffic to and/or from the Golgi Vesicle-filled “wells” open to both the cis and lateral sides of the stacks The stacks of cisternae are positioned between two types of ER, cis and trans The cis ER lies adjacent to the ER-Golgi intermediate compartment, which consists of discrete polymorphic membranous elements layered in front of the cis-most Golgi cisterna The extensive trans ER forms close contacts with the two trans-most cisternae; this apposition may permit direct transfer of lipids between ER and Golgi membranes Within 02 μm of the cisternae studied, there are 394 vesicles (8 clathrin coated, 190 nonclathrin coated, and 196 noncoated), indicating considerable vesicular traffic in this Golgi region Our data place structural constraints on models of trafficking to, through, and from the Golgi complex

Transdermal photopolymerization for minimally invasive implantation.

Abstract: Photopolymerizations are widely used in medicine to create polymer networks for use in applications such as bone restorations and coatings for artificial implants. These photopolymerizations occur by directly exposing materials to light in “open” environments such as the oral cavity or during invasive procedures such as surgery. We hypothesized that light, which penetrates tissue including skin, could cause a photopolymerization indirectly. Liquid materials then could be injected s.c. and solidified by exposing the exterior surface of the skin to light. To test this hypothesis, the penetration of UVA and visible light through skin was studied. Modeling predicted the feasibility of transdermal polymerization with only 2 min of light exposure required to photopolymerize an implant underneath human skin. To establish the validity of these modeling studies, transdermal photopolymerization first was applied to tissue engineering by using “injectable” cartilage as a model system. Polymer/chondrocyte constructs were injected s.c. and transdermally photopolymerized. Implants harvested at 2, 4, and 7 weeks demonstrated collagen and proteoglycan production and histology with tissue structure comparable to native neocartilage. To further examine this phenomenon and test the applicability of transdermal photopolymerization for drug release devices, albumin, a model protein, was released for 1 week from photopolymerized hydrogels. With further study, transdermal photpolymerization potentially could be used to create a variety of new, minimally invasive surgical procedures in applications ranging from plastic and orthopedic surgery to tissue engineering and drug delivery.

Stop-and-Go Movements of Plant Golgi Stacks Are Mediated by the Acto-Myosin System

Abstract: The Golgi apparatus in plant cells consists of a large number of independent Golgi stack/trans-Golgi network/Golgi matrix units that appear to be randomly distributed throughout the cytoplasm. To study the dynamic behavior of these Golgi units in living plant cells, we have cloned a cDNA from soybean (Glycine max), GmMan1, encoding the resident Golgi protein α-1,2 mannosidase I. The predicted protein of approximately 65 kD shows similarity of general structure and sequence (45% identity) to class I animal and fungal α-1,2 mannosidases. Expression of a GmMan1::green fluorescent protein fusion construct in tobacco (Nicotiana tabacum) Bright Yellow 2 suspension-cultured cells revealed the presence of several hundred to thousands of fluorescent spots. Immuno-electron microscopy demonstrates that these spots correspond to individual Golgi stacks and that the fusion protein is largely confined to the cis-side of the stacks. In living cells, the stacks carry out stop-and-go movements, oscillating rapidly between directed movement and random “wiggling.” Directed movement (maximal velocity 4.2 μm/s) is related to cytoplasmic streaming, occurs along straight trajectories, and is dependent upon intact actin microfilaments and myosin motors, since treatment with cytochalasin D or butanedione monoxime blocks the streaming motion. In contrast, microtubule-disrupting drugs appear to have a small but reproducible stimulatory effect on streaming behavior. We present a model that postulates that the stop-and-go motion of Golgi-trans-Golgi network units is regulated by “stop signals” produced by endoplasmic reticulum export sites and locally expanding cell wall domains to optimize endoplasmic reticulum to Golgi and Golgi to cell wall trafficking.

Nitrogen stable isotopic composition of leaves and soil: tropical versus temperate forests

Abstract: Several lines of evidence suggest that nitrogen in most tropical forests is relatively more available than N in most temperate forests, and even that it may function as an excess nutrient in many tropical forests. If this is correct, tropical forests should have more open N cycles than temperate forests, with both inputs and outputs of N large relative to N cycling within systems. Consequent differences in both the magnitude and the pathways of N loss imply that tropical forests should in general be more 15N enriched than are most temperate forests. In order to test this hypothesis, we compared the nitrogen stable isotopic composition of tree leaves and soils from a variety of tropical and temperate forests. Foliar γ15N values from tropical forests averaged 6.5%0 higher than from temperate forests. Within the tropics, ecosystems with relatively low N availability (montane forests, forests on sandy soils) were significantly more depleted in 15N than other tropical forests. The average γ15N values for tropical forest soils, either for surface or for depth samples, were almost 8%o higher than temperate forest soils. These results provide another line of evidence that N is relatively abundant in many tropical forest ecosystems.

The Decolonial Imaginary: Writing Chicanas into History

Abstract: Emma Perez discusses the historical methodology which has created Chicano history. Then borrowing from theorists and philosophers of history, Michel Foucault, Juan Gomez-Quinones, Homi Bhabha, Gayatri Chakravorty Spivak, and Hayden White as well as cultural feminist critics Gloria Anzaldu(accute)a, Teresa de Lauretis, Antonia Castaneda, Deena Gonzalez, Chela Sandoval, the author argues that the Chicano historical narrative has often omitted gender. She poses a theory which rejects the coloniser's methodological assumptions and examines new tools for uncovering the hidden voices of Chicanas who have been relegated to silence.Within that silence, she uncovers what she describes as 'third space feminism'. By traversing political borders and disciplinary boundaries, the text moves from geographic spaces in the Yucatan to California and Texas in and around the Mexican Revolution of 1910. Perez examines Yucatan's socialist revolution, the international revolutionary movement El Partido Liberal Mexicano, and the Club Femenino Chapultepec.In these case studies 'new voices' come into existence to shape knowledge about Chicanas, constructing identities and feminisms which cross borders and boundaries. The last chapter critiques the tale of La Malinche, the translator and alleged lover to Cortes'; a recent film, "Silent Tongue," the story of an Indian woman; Delgadeio, the object of desire in a popular corrido; and Selina, the slain Tex-Mex popular singer who practiced her own cultural feminism in sexualized performances. The historical case studies and contemporary cultural phenomena employ the concept of decolonial imaginary and demonstrate its usefulness as a tool to rewrite Chicana history.