bluuebunny/crossref_metadata_2025 huggingface dataset:
Sex Hormones and Risk of Liver Tumor
Authors: GIANNITRAPANI L. , SORESI M. , LA SPADA E. , CERVELLO M. , D'ALESSANDRO N. , MONTALTO G.
Published: February 2007

Abstract:  The liver is morphologically and functionally modulated by sex hormones. Long‐term use of oral contraceptives (OCs) and anabolic androgenic steroids (AASs) can induce both benign (hemangioma, adenoma, and focal nodular hyperplasia [FNH]) and malignant (hepatocellular carcinoma [HCC]) hepatocellular tumors. Hepatic adenomas (HAs) are rare, benign neoplasms usually occurring in young women, the development and the complications of which have been related to the strength of OCs and the duration of their use. HA incidence has fallen since the introduction of pills containing smaller amounts of estrogens. FNH is a benign lesion, most commonly seen in young women, which is thought to represent a local hyperplastic response of hepatocytes to a vascular abnormality. Because of the female predominance and the young age at onset, a role of female hormones has been suggested. Furthermore, a large proportion of women with FNH (50–75%) are OC users. Liver hemangiomas (LHs) are the most common benign liver tumors and are seen more commonly in young adult females. The female predilection and clinical observations of LH growth under conditions of estrogenic exposure suggest a possible role for estrogen in the pathogenesis of LHs. HCC has become one of the most widespread tumors in the world in recent years, representing the sixth leading cancer and the third most common cause of death from cancer. Apart from liver cirrhosis, numerous other factors responsible for its onset have been proposed: hepatitis infections from virus B (HBV) and C (HCV), alcohol, smoking, and aflatoxin. However, regardless of etiology, chronic liver diseases progress at unequal rates in the two sexes, with the major sequelae, such as cirrhosis and HCC, being more frequent in men than in women. These epidemiological data have prompted researchers to investigate the relationship between sex hormones and liver tumors. The human liver expresses estrogen and androgen receptors and experimentally both androgens and estrogens have been implicated in stimulating hepatocyte proliferation and may act as liver tumor inducers or promoters.
Duplex Ultrasound in the Emergency Department for the Diagnostic Management of Clinically Suspected Deep Vein Thrombosis
Authors: Magazzini Simone , Vanni Simone , Toccafondi Simone , Paladini Barbara , Zanobetti Maurizio , Giannazzo Giuseppe , Federico Roberto , Grifoni Stefano
Published: February 2007

Objectives: To evaluate the accuracy and safety of an emergency duplex ultrasound (EDUS) evaluation performed by emergency physicians in the emergency department.

Methods: Consecutive adult patients suspected of having their first episode of deep vein thrombosis (DVT) presenting to the emergency department were included in the study. All examinations were performed by emergency physicians trained with a 30‐hour ultrasound course. Based on EDUS findings, patients were classified into one of three groups: normal, abnormal, and uncertain. Patients with abnormal and uncertain findings were initially treated as having a DVT. Patients with normal EDUS findings were discharged from the emergency department without anticoagulant therapy. A formal duplex ultrasound evaluation was repeated by a radiologist in all patients within 24–48 hours. Patients with normal findings on duplex ultrasound evaluation were followed up for symptomatic venous thromboembolism for up to one month.

Results: A total of 399 patients were studied. The EDUS findings were normal in 301 (75%), abnormal in 90 (23%), and uncertain in eight (2%). All abnormal test results were confirmed by the formal duplex ultrasound evaluation, and three patients (0.8%) with uncertain findings on EDUS examination were subsequently diagnosed as having a distal DVT (positive predictive value, 95% [95% confidence interval, 92% to 95%]; negative predictive value, 100% [95% confidence interval = 99% to 100%]). No patients with normal findings on EDUS examination died or experienced venous thromboembolism at the one‐month follow‐up.

Conclusions: EDUS examination yielded a high negative predictive value and good positive predictive value, allowing rapid discharge and avoiding improper anticoagulant treatment.
TACE release of TNF-α mediates mechanotransduction-induced activation of p38 MAPK and myogenesis
Authors: Zhan Mei , Jin Bingwen , Chen Shuen-Ei , Reecy James M. , Li Yi-Ping
Published: February 2007

Skeletal muscle responds to mechanical stimulation by activating p38 MAPK, a key signal for myogenesis. However, the mechanotransduction mechanism that activates p38 is unknown. Here we show that mechanical stimulation of myoblasts activates p38 and myogenesis through stimulating TNF-α release by TNF-α converting enzyme (TACE). In C2C12 or mouse primary myoblasts cultured in growth medium, static stretch activated p38 along with ERK1/2, JNK and AKT. Disrupting TNF-α signaling by TNF-α-neutralizing antibody or knocking out TNF-α receptors blocked stretch activation of p38, but not ERK1/2, JNK or AKT. Stretch also activated differentiation markers MEF2C, myogenin, p21 and myosin heavy chain in a TNF-α- and p38-dependent manner. Stretch stimulated the cleavage activity of TACE. Conversely, TACE inhibitor TAPI or TACE siRNA abolished stretch activation of p38. In addition, conditioned medium from stretched myoblast cultures activated p38 in unstretched myoblasts, which required TACE activity in the donor myoblasts, and TNF-α receptors in the recipient myoblasts. These results indicate that posttranscriptional activation of TACE mediates the mechanotransduction that activates p38-dependent myogenesis via the release of TNF-α.
A computerized bioskills system for surgical skills training in total knee replacement
Authors: Conditt M A , Noble P C , Thompson M T , Ismaily S K , Moy G J , Mathis K B
Published: February 2007

Although all agree that the results of total knee replacement (TKR) are primarily determined by surgical skill, there are few satisfactory alternatives to the ‘apprenticeship’ model of surgical training. A system capable of evaluating errors of instrument alignment in TKR has been developed and demonstrated. This system also makes it possible quantitatively to assess the source of errors in final component position and limb alignment. This study demonstrates the use of a computer-based system to analyse the surgical skills in TKR through detailed quantitative analysis of the technical accuracy of each step of the procedure. Twelve surgeons implanted a posterior-stabilized TKR in 12 fresh cadavers using the same set of surgical instruments. During each procedure, the position and orientation of the femur, tibia, each surgical instrument, and the trial components were measured with an infrared coordinate measurement system. Through analysis of these data, the sources and relative magnitudes of errors in position and alignment of each instrument were determined, as well as its contribution to the final limb alignment, component positioning and ligament balance. Perfect balancing of the flexion and extension gaps was uncommon (0/15). Under standardized loading, the opening of the joint laterally exceeded the opening medially by an average of approximately 4 mm in both extension (4.1 ± 2.1 mm) and flexion (3.8 ± 3.4 mm). In addition, the overall separation of the femur and the tibia was greater in flexion than extension by an average of 4.6 mm. The most significant errors occurred in locating the anterior/posterior position of the entry point in the distal femur (SD = 8.4 mm) and the correct rotational alignment of the tibial tray (SD = 13.2°). On a case-by-case basis, the relative contributions of errors in individual instrument alignments to the final limb alignment and soft tissue balancing were identified. The results indicate that discrete steps in the surgical procedure make the largest contributions to the ultimate alignment and laxity of the prosthetic knee. Utilization of this method of analysis and feedback in orthopaedic training is expected rapidly to enhance surgical skills without the risks of patient exposure.
Stable Farsighted Coalitions in Competitive Markets
Authors: Nagarajan Mahesh , Sošić Greys
Published: February 2007

In this paper, we study dynamic alliance formation among agents in competitive markets. We look at n agents selling substitutable products competing in a market. In this setting, we examine models with deterministic and stochastic demand, and we use a two-stage approach. In Stage 1, agents form alliances (coalitions), and in Stage 2, coalitions make decisions (price and inventory) and compete against one another. To analyze the stability of coalition structures in Stage 1, we use two notions from cooperative games—the largest consistent set (LCS) and the equilibrium process of coalition formation (EPCF)—which allow players to be farsighted. Thus, in forming alliances, players consider two key phenomena: First, players trade off the size of the total profit of the system versus their allocation of this total pie, and second, they weigh the possibility that an immediate beneficial defection can trigger further counter defections that in the end may prove to be worse than the status quo. In particular, one such example is that of the grand coalition—which we show to be stable in the farsighted sense—even though players benefit myopically by defecting from it. We also provide conditions under which a situation of a few lone players competing against a large coalition is stable. We examine the impact of the size of the market (n), the degree of competition, the effect of cost parameters, and the variability of the demand process on the prices, inventory levels, and structure of the market. We discuss the possible strategic implications of our results to firms in a competitive market and for new entrants.
Ambulatory Care: Efficacy and Safety of Oral Phenylephrine: Systematic Review and Meta-Analysis
Authors: Hatton Randy C , Winterstein Almut G , McKelvey Russell P , Shuster Jonathan , Hendeles Leslie
Published: February 2007

Background:

Oral phenylephrine is used as a decongestant, yet there has been no previously published systematic review supporting its efficacy and safety.

Objective:

To assess the efficacy and safety of oral phenylephrine as a nonprescription decongestant.

Methods:

MEDLINE, the Cochrane Central Registry of Controlled Trials, EMBASE International Pharmaceutical Abstracts, and the Federal Register were searched for-English and non–English-language studies published through January 2007 that measured the effects of oral phenylephrine on nasal airway resistance (NAR) in patients with nasal congestion. The retrieved studies were supplemented with information from our personal files and by hand searches of the references in any of the studies. Additionally, a Web of Science Search was conducted using the Cited Reference function for all published clinical trials identified. Studies included in the analysis were randomized, placebo-controlled trials; studies of combination products were excluded. Two investigators independently extracted data on NAR, self-reported decongestant effects, and cardiovascular effects (ie, heart rate, blood pressure) from each of the included studies. Meta-analyses were performed for NAR and cardiovascular effects using a random effects model. Subjective decongestant effects were summarized.

Results:

Based on 8 unpublished studies that included 138 patients, phenylephrine 10 mg did not affect NAR more than placebo; the mean maximal difference in relative change from baseline between phenylephrine and placebo was 10.1% (95% CI −3.8% to 23.9%). Eight unpublished studies on phenylephrine 25 mg showed a significant reduction of maximal NAR compared with placebo of 27.6% (95% CI 17.5% to 37.7%). There was significant heterogeneity among the studies included in this analysis, which was partially attributable to different laboratories and methods used. Patient-re ported decongestion was not consistently better for any phenylephrine dose compared with placebo, and NAR was a more sensitive measurement of efficacy. Phenylephrine showed no consistent effect on heart rate or blood pressure for doses of 25 mg or less.

Conclusions:

There is insufficient evidence that oral phenylephrine is effective for nonprescription use as a decongestant. The Food and Drug Administration should require additional studies to show the safety and efficacy of phenylephrine.
Use of Otolith Microstructure to Discriminate Stocks of Juvenile Central Valley, California, Fall‐Run Chinook Salmon
Authors: Volkoff Martha C. , Titus Robert G.
Published: February 2007

We examined the utility of otolith microstructure analysis as a means of discriminating among stocks and between rearing types of juvenile fall‐run Chinook salmon Oncorhynchus tshawytscha in California's Central Valley. Otolith samples were collected from 11 geographically discrete stocks of fall‐run Chinook salmon of river and hatchery rearing types over 2 years. Six measured otolith attributes and three statistics derived from these measurements served as dependent variables in a multifactor analysis of variance of paired river and hatchery stocks. Morphometrics that demonstrated no significant interaction between year and stock or rearing type were used as predictors in discriminant function analyses; 32% of samples were correctly classified by stock and 80% were correctly classified by rearing type. Measures of otolith size at fry emergence were the best predictors for distinguishing among both stocks and rearing types with discriminant function analysis. We hypothesize that observed differences in otolith size at emergence among stocks and rearing types reflect differential responses in development of Chinook salmon embryos reared under different temperature regimes. Although classification success among stocks was rather limited, results for correctly classifying fall‐run Chinook salmon by rearing type were encouraging. We suggest that observed differences in otolith microstructure between rearing types be augmented with thermal marking in Central Valley hatcheries to provide a fully reliable tool for determining the proportionate contribution of natural and hatchery production to spawner populations. This information alone would greatly advance stock management of Central Valley fall‐run Chinook salmon.
Migration Timing, Growth, and Estimated Parr‐to‐Smolt Survival Rates of Wild Snake River Spring–Summer Chinook Salmon from the Salmon River Basin, Idaho, to the Lower Snake River
Authors: Achord Stephen , Zabel Richard W. , Sandford Benjamin P.
Published: February 2007

Survival, growth, and juvenile migration timing are key life history traits for at‐risk salmon populations. To estimate these traits in threatened wild Snake River spring–summer Chinook salmon Oncorhynchus tshawytscha, we tagged fish as parr in 3–17 natal streams per year from 1991 to 2003. We injected passive integrated transponder tags into parr collected from streams within the Salmon River basin in Idaho. Each spring, after the previous summer's tagging, fish were detected as smolts in the juvenile fish bypass systems of lower Snake River dams. Estimated parr‐to‐smolt survival to Lower Granite Dam (excluding migration year 1992) ranged from 3% to 48% for individual populations and from 8% to 25% (yearly average = 16%) for all streams combined. From 1998 to 2004, estimated parr‐to‐smolt survival declined from 25% to 8%, in part because of parr density‐dependent effects. Overall annual average growth rates from tagging to detection at Little Goose Dam ranged from 39.7 to 43.3 mm during 2001–2004, and significant differences in growth were observed among sites and years. Growth of individuals was positively related to elapsed time between tagging and recapture and negatively related to fork length at tagging. Annual migration timing distributions for fish populations from the different streams varied highly within and between years. Timing of the 10th to 90th percentile passing Lower Granite Dam ranged from 20 to 45 d for the combined wild populations (average = 38 d). Median passage date was negatively related to autumn temperature, spring temperature, and March river flow, and was positively related to elevation of the tagging site. Baseline data generated by this project provide a foundation for understanding the biocomplexity of these populations, which is critical to effective recovery efforts for these threatened wild fish stocks.
Disproportionate Relative Importance of a Terrestrial Beetle Family (Coleoptera: Scarabaeidae) as a Prey Source for Central Appalachian Brook Trout
Authors: Utz Ryan M. , Ratcliffe Brett C. , Moore Brett T. , Hartman Kyle J.
Published: February 2007

Brook trout Salvelinus fontinalis and other salmonids in Appalachia typically inhabit headwater watersheds, where food resources may limit growth. We monitored the feeding trends of a brook trout population in central Appalachia over the course of 2 years to determine variation in feeding intensity and important prey items. One terrestrial beetle family, Scarabaeidae, provided a disproportionate amount of energy during the only time of year when brook trout were feeding substantially above maintenance ration. Scarab beetles contributed 39.6% of all energy consumed during May and June of both years, though the number of fish with one or more scarabaeids present in the stomach varied by month (22.2–51.7%). The species composition of scarab beetles consumed suggested that four species are of particular importance. Our findings imply that scarabaeids represent a considerably important prey taxon for brook trout in the region. Considering the foraging habits of the scarabaeid species in question, the phenomenon we witnessed probably occurs throughout Appalachia.
Case Histories of Electrical Resistivity and Controlled-Source Magnetotelluric Surveys for the Site Investigation of Tunnel Construction
Authors: Kwon Hyoung-Seok , Song Yoonho , Yi Myeong-Jong , Chung Ho-Joon , Kim Ki-Seog
Published: February 2007

In tunnel construction, the information regarding rock mass quality and the distribution of weak zones is crucial for economical tunnel design and to ensure safety. Usually, the rock mass grade is estimated by observing recovered cores obtained by drilling or by physical parameters calculated in a laboratory using core samples. However, the high drilling cost limits the number of boreholes; furthermore, rough terrains can reduce the access of drilling machines to the survey sites. In such situations, surface geophysical methods such as electrical resistivity or controlled-source magnetotelluric (CSMT) can provide a rough estimate of the rock mass condition over the planned tunnel route. These methods can also map weak zones (faults, fractures, coal bearing zones, and cavities), which are characterized by a lower resistivity than the surrounding fresh rock mass. We present two successful applications of the electrical resistivity and CSMT methods to the site investigation of tunnel construction over a rough terrain. The first example demonstrates that the boundary of the bedrock and weak zones related to the distribution of coaly shale and coal seams were estimated to extend beyond a few hundred meters below the rough surface. The second example shows that the developing direction and depth of cavities, which are mainly related to the weak zones in limestone, were successfully interpreted by a three-dimensional (3-D) electrical resistivity survey with the aid of borehole test results.
The Trianon and On: Reading Mass Social Dancing in the 1930s and 1940s in Alberta, Canada
Authors: Doolittle Lisa
Published: February 2007

Every Friday and Saturday night during the 1930s and 1940s in southern Alberta everybody danced, or so the story goes. And that is about as far as “the story” goes. Serious considerations of popular dancing are largely absent from existing historical records of this time and place, despite the apparent omnipresence of dancing in so many people's lives. Social dancing happened on a large scale at a pivotal time for community formation in Canada's West, when profound social changes occurred as the Depression gave way to World War II. What was going on besides and through and because of all that dancing? And how to investigate such an ephemeral phenomenon?

Today, I can still stand in the Trianon Ballroom in Lethbridge, Alberta's third largest city and the center of the region I will discuss here. The Trianon first opened its doors as a dance hall in 1931 and ceased operating in 1961. In the 1930s and 1940s literally hundreds of little Trianon-like halls graced small Canadian prairie towns, although most of these dance halls have since disappeared. In Lethbridge alone, four major dancing establishments were packed with patrons dancing to live bands on as many as three nights a week, the YMCA offered hostess dances for military personnel, the Kiwanis club gave teen dances every Friday night, and one could dance at the Masonic Hall and in local hotels (Viel 1998, 24).
C'mon to my house: Underground-House Dancing
Authors: Sommer Sally R.
Published: February 2007

The media attention surrounding Raves in the last couple of years has brought the subject of nightlife and dancing to the foreground of American consciousness. Yet even as dancing and nightlife were enjoying renewed popularity, a national crackdown on clubs was taking place. Almost concurrently, and partly in response to the crackdown, a nostalgia movement arose among the new generation of clubbers for the Utopian ethos of the 1970s and 1980s “Underground-House” scene. These new “Househeads” yearned for the carefully cultivated constructs of the “family,” the “vibe,” and the distinctive styles of House music and dancing—all of which they were attempting to recreate in their parties in 2001. Since the September 11 terrorist attack and its devastating aftershocks, the longing for a safer, golden past has intensified. As eloquently demonstrated by the tremendous popularity during the Depression of escapist movies, in hard times people seek good times and the reassurance of nonviolent congregations.
Dancing in the Past, Living in the Present: Nostalgia and Race in Southern California Neo-Swing Dance Culture
Authors: Usner Eric Martin
Published: February 2007

Nostalgia is a revisionary act, emptying history of depth and texture, when having a manageable history is contingent on accumulation of time-trapped stuff. It's what people hold to, release into play, invent from, use for amusement and amazement, it's what and how people define their passage, their commonality and distinctiveness; a faith, a system of belief expressed in accumulated tokens and artifacts; a culture nourished on mythological narratives and seasonal events, by the passing of gods and goddesses, by stacks of packaged time renewed in changing formats; it's generality so resolutely particular to each adherent that often only myth and liturgy can serve as neutral rites of discourse. It's obviously the faith love invents to reassure its durability; a radical theology, a fusion of intensified sacred and secular yearnings and desires.

“Pre-Ramble” to Reading Jazz, David Meltzer (1993, 34)
Performative Power in Native America: Powwow Dancing
Authors: Axtmann Ann
Published: February 2007

Back in 1988, my father had passed away and for a short time I stopped dancing. I lost interest, I lost my heart, you know…' cause I used to dance on stage for my father…Recently,…I just started back dancing…the reason is 'cause…This is me. This is who I am. A dancer. A Fancy dancer at that. And this is where I felt my father was most proud of me. And even now, I still feel that he is most proud of me. Right now, he's with me when I dance and I dance for my father. I dance for him, for my pop, for Gray Fox.

—Calvin Burns (Cherokee) (Traveling the Distance)

Throughout the United States and Canada people go to Native American intertribal powwows. At powwows women, men, and children execute rhythmic movement, drumming, and song as they experience and express sensory stimuli. The aroma of sage incense pervades as Indians and non-Indians socialize, share fry bread, and sell, buy, or “window shop” at concession stands. Vendors display T-shirts, fur, turquoise, silver, and beaded jewelry as well as artwork, CDs, and Ecuadorian and Peruvian items. All participants enjoy storytelling, comedy skits, Indian rap and country music performances, and Mexican “Aztec” dance presentations alongside rituals such as giveaways, the Eagle ceremony, or the Veterans dance. These social and spiritual celebrations occur in increasing numbers across North America. In the tristate region of New York, New Jersey, and Connecticut alone, from 1995 to 2001, the number of powwow events has tripled.
Dialogue in Dance Studies Research
Authors: Dils Ann , Crosby Jill Flanders
Published: February 2007

In writing this paper, we—Jill Crosby and Ann Dils—render into text six years of sporadic dialogues. Through our explanation and examination of the 1994 movement analysis and description project that began our exchanges and discussion of subsequent readings, we hope to explore important aspects of dance studies research. Our use and understanding of Laban-based movement analysis as a tool for understanding movement as it is felt and observed, awareness of concepts of dialogue and the dialogical process as potential frameworks, critical lenses, and theoretical bases for dance studies research, and adaptation of the interpretive paradigm to suit dance research are especially important to this exploration. Little of our text is written in dialogue form (Crosby:, Dils:); rather, we hope, by drawing examples from our project, Crosby's dissertation, and the works of other researchers, to capture the bubbling-up of understanding that stems from the cooperative and confrontational exchanges of dance studies research.

Over a three-month period in 1994, we conducted a movement analysis and description project as part of Crosby's work for her doctoral dissertation, “Will the Real Jazz Dance Please Stand Up? A Critical Examination of the Roots and Essence of Jazz Dance with Implications for Education.” Crosby investigated the aesthetic shapings of jazz expression inclusive of its West African roots from a cross-disciplinary perspective, using ethnographic methods as tools for understanding artistic form (Crosby 1995). An arts educator and dancer, Crosby wanted to establish a pool of descriptive and potentially inherent characteristics for music-based jazz dance. These characteristics would comprise a personal definition for the form and provide Crosby with a point of departure for a discussion of jazz as a movement tradition.
Transgressive character expression in a hybrid sunflower species
Authors: Schwarzbach Andrea E. , Donovan Lisa A. , Rieseberg Loren H.
Published: February 2007

Diploid hybrid lineages often are ecologically distinct from their parental species. However, it is unclear whether this niche divergence is typically achieved via hybrid intermediacy, a mixture of parental traits, and/or the evolution of extreme (transgressive) morphological and ecophysiological features. Here we compare an extensively studied hybrid sunflower species,Helianthus anomalus, with its putative parents,H. annuusandH. petiolaris, for 41 morphological and 12 ecophysiological traits.Helianthus anomaluswas morphologically intermediate for one trait (2.4%), parental‐like for 23 traits (56.1%), and transgressive for 17 traits (41.5%). For ecophysiological traits,H. anomaluswas not significantly different from one or both parents for nine traits (75%), and was transgressive for the remaining three (25%). Thus,H. anomalusappears to be a mosaic of parental‐like and transgressive phenotypes. Although the fitness effects of the transgressive characters are not yet known, many of these characters are consistent with adaptations reported for other sand dune plants. Genetic studies are currently underway to ascertain whether these extreme characters arose as a direct byproduct of hybridization or whether they evolved via mutational divergence.
Reconstruction ofPseudomariopteris busquetii, a vine‐like Late Carboniferous–Early Permian pteridosperm
Authors: Krings Michael , Kerp Hans , Taylor Edith L. , Taylor Thomas N.
Published: February 2007

The growth habit of the Late Carboniferous–Early Permian pteridospermPseudomariopteris busquetiiis reconstructed based on compression material from the upper Stephanian of the Blanzy‐Montceau and Commentry Basins (Massif Central, France), and the upper Rotliegend of the Saar‐Nahe Basin (Nahe Group, N 4, Rheinland Pfalz, Germany).Pseudomariopteris busquetiiwas a medium‐sized, vine‐ to liana‐like plant with slender stems to which small bipartite fronds were attached. What is most interesting is that the species used at least two different strategies to both anchor and support the plant body. Most specimens possess specialized climber hooks developed from apical extensions of the pinna axes, indicating that the fronds were used to attach the plant. A few specimens suggest that the stem may also have had some capacity for attachment. In the absence of suitable supports, however,P. busquetiiwas apparently able to grow in dense stands or thickets in which the individual plants supported each other.
Anatomically preserved Woodwardia virginica (Blechnaceae) and a new filicalean fern from the middle Miocene Yakima Canyon flora of central Washington, USA
Authors: Pigg Kathleen B. , Rothwell Gar W.
Published: February 2007

Anatomically preserved Woodwardia virginica (Blechnaceae) and a newly recognized onocleoid fern are described from the middle Miocene Yakima Canyon flora of central Washington State, USA. Identification of the W. virginica fossils is based on a combination of vegetative pinnules, rhizome and stipe anatomy, and fertile pinnules with indusiate sori and sporangia like those of extant W. virginica. Fronds are isomorphic. Vegetative pinnae are elongated and pinnatifid, with a secondary vein paralleling the midvein. Secondary veins of the pinnule lobe anastomose to form primary areoles and are either simple or dichotomize toward the margin. Rhizomes have a simple dictyostele with 3–5 cauline vascular bundles and often a sclerotic hypodermis. Leaf traces contain two large adaxial vascular bundles that occur laterally and adaxially, flanking an arc of 4–6 smaller bundles. Fertile pinnules have linear sori that are somewhat embedded in the laminae and are enclosed by a thin indusium. Leptosporangia display a vertical annulus and an elongated stalk. A second fern, Wessiea yakimaensis gen. et sp. nov., is represented by anatomically preserved branching rhizomes and attached frond bases that conform to the Onoclea‐type pattern of rhizome and frond‐base vasculature. Rhizomes have a simple dictyostele of 4–5 cauline meristeles. Leaf divergence is helical, with paired hippocampiform rachial traces. These two ferns occur in the same matrix with specimens of Osmunda wehrii. They demonstrate that filicalean fern assemblages similar to those of extant temperate floras were well established in western North America by the middle Miocene and further emphasize the exceptional species longevity of some homosporous pteridophytes.
Mediterranean climate effects. I. Conifer water use across a Sierra Nevada ecotone
Authors: Royce E. B. , Barbour M. G.
Published: February 2007

Xylem water potential of the midelevation conifersPinus jeffreyi, Pinus lambertiana, Abies concolor, andCalocedrus decurrens, the higher elevationPinus monticolaandAbies magnifica, and co‐occurring evergreen angiosperm shrubs, together with soil moisture under these plants, were monitored at three sites on the Kern Plateau in the southernmost Sierra Nevada Range of California. Site locations spanned the ecotone between the mid‐ and upper montane forests at elevations of 2230–2820 m. Measurements were made through a low‐snowfall year and a heavy‐snowfall year.

In the Mediterranean climate of the Sierra Nevada, the heavy winter snowpack persists into late spring, after precipitation has effectively stopped. We found the subsequent depletion of soil moisture due to plant water uptake to result in predawn xylem water potentials for conifers more negative by 0.6–1.4 MPa than those for shrubs or inferred soil potentials. Shrubs generally depleted soil moisture more rapidly and ultimately extracted a greater fraction of the available soil moisture than did the conifers. This depletion of soil moisture by shrubs, particularlyArctostaphylos patula, may limit conifer growth and regeneration by prematurely terminating growth on the shallow soils studied. The conifers all generally showed similar patterns of soil moisture use, except thatA. magnificaextracted moisture more rapidly early in the season.
Seed size variation and predation of seeds produced by wild and crop–wild sunflowers
Authors: Alexander Helen M. , Cummings Charity L. , Kahn Lisa , Snow Allison A.
Published: February 2007

The movement of pollen between crop and wild sunflowers (both Helianthus annuus) has led to concerns about the possible introduction of crop transgenes into wild populations. The persistence of crop traits in wild populations will depend in part on the relative fitness of crop–wild hybrid vs. wild plants. Using seeds from two large experimental field plots, we found that seeds produced by crop–wild plants were twice the size of wild seeds and differed in coloration. Head diameter, date of flowering, identity of mother plant, and levels of predispersal predation explained some variation in mean seed size. We hypothesized that postdispersal vertebrate seed predation would be affected by seed size, with hybrid seeds preferentially eaten. In each of three field trials, significantly more hybrid seeds were eaten (62% of hybrid seed; 42% of wild seed). Within the category of wild seeds, larger seeds were preferentially eaten; however among hybrid seeds, predation was not significantly related to seed size. In this study, differential predation thus reduces hybrid fitness and would presumably slow the spread of transgenes into wild populations.
Ontogenetic derivation and cell differentiation in photosynthetic tissues of C3and C4Cyperaceae
Authors: Soros Connie L. , Dengler Nancy G.
Published: February 2007

Four variants of Kranz anatomy occur in the Cyperaceae. Three of these anatomical types (fimbristyloid, chlorocyperoid, and eleocharoid) are unique among taxa with C4photosynthesis in that the photosynthetic carbon reduction tissue (PCR, functional equivalent of bundle sheath) is located within the vascular strand and is separated from the primary carbon assimilation tissue (PCA, positional equivalent of mesophyll) by the mestome sheath layer. In the fourth anatomical type, rhynchosporoid, PCR tissue is located in the position of the mestome sheath. In this study, we compared two aspects of development of PCR and PCA tissues in representatives of the C3and C4types: (1) ontogenetic derivation and (2) cellular differentiation. Analysis of the planes of cell division associated with procambial strand formation indicated that PCR tissue is always derived from the procambium, while PCA tissue is derived from the ground meristem. These cell lineages remain distinct after the initial organization of vascular strands. Analysis of cell differentiation using accumulation of cell‐type‐specific photosynthetic enzymes as markers of differentiation indicated that, with one exception, a low level of non‐cell‐specific enzyme accumulation preceded abundant and cell‐specific accumulation of photosynthetic enzymes at the distal end of the leaf elongation zone. Enzyme accumulation coincided spatially (and temporally) with structural aspects of cell differentiation. Previous cladistic analyses have indicated that these anatomical types represent separate evolutionary origins of the C4pathway, and the differences in developmental pathways observed here reflect these independent origins from C3ancestors.
Phylogenetic relationships and evolution of Crassulaceae inferred from matK sequence data
Authors: Mort Mark E. , Soltis Douglas E. , Soltis Pamela S. , Francisco‐Ortega Javier , Santos‐Guerra Arnoldo
Published: February 2007

Chloroplast gene matK sequence data were used to estimate the phylogeny of 112 species of Crassulaceae sampled from 33 genera and all six recognized subfamilies. Our analyses suggest that five of six subfamilies recognized in the most recent comprehensive classification of the family are not monophyletic. Instead, we recovered a basal split in Crassulaceae between the southern African Crassula clade (Crassuloideae) and the rest of the family (Sedoideae). These results are compatible with recent studies of cpDNA restriction site analyses. Within Sedoideae, four subclades were also recovered: Kalanchoe, Leucosedum, Acre, and Aeonium; evidence also exists for a Telephium clade and Sempervivum clade. The genus Sedum is highly polyphyletic with representatives spread throughout the large Sedoideae clade. Sympetaly and polymerous flowers have arisen multiple times in Crassulaceae and thus are not appropriate characters upon which to base subfamilial limits, as has been done in the past. One floral character, haplostemy, appears to be confined to the well‐supported Crassula clade. Our analyses suggest a southern African origin of the family, with subsequent dispersal northward into the Mediterranean region. From there, the family spread to Asia/eastern Europe and northern Europe; two separate lineages of European Crassulaceae subsequently dispersed to North America and underwent substantial diversification. Our analyses also suggest that the original base chromosome number in Crassulaceae is x = 8 and that polyploidy has played an important role in seven clades. Three of these clades are exclusively polyploid (Sempervivum clade and two subclades within the Kalanchoe and Aeonium clades), whereas four (Crassula, Telephium, Leucosedum, and Acre clades) comprise both diploid and polyploid taxa. Polyploidy is particularly rampant and cytological evolution especially complex in the Acre clade.
Getting by with the Advice of Their Friends: CEOs' Advice Networks and Firms' Strategic Responses to Poor Performance
Authors: McDonald Michael L. , Westphal James D.
Published: February 2007

This paper theorizes that relatively poor firm performance can prompt chief executive officers (CEOs) to seek more advice from executives of other firms who are their friends or similar to them and less advice from acquaintances or dissimilar others and suggests how and why this pattern of advice seeking could reduce firms' propensity to change corporate strategy in response to poor performance. We test our hypotheses with large-sample survey data on the identities of CEOs' advice contacts and archival data on firm performance and corporate strategy. The results confirm our hypotheses and show that executives' social network ties can influence firms' responses to economic adversity, in particular by inhibiting strategic change in response to relatively poor firm performance. Additional findings indicate that CEOs' advice seeking in response to low performance may ultimately have negative consequences for subsequent performance, suggesting how CEOs' social network ties could play an indirect role in organizational decline and downward spirals in firm performance.
Liquidity Events and the Geographic Distribution of Entrepreneurial Activity
Authors: Stuart Toby E. , Sorenson Olav
Published: February 2007

In this paper, we examine the ecological consequences of initial public offerings (IPOs) and acquisitions, specifically how the spatial distribution of these events influences the location-specific founding rates of new companies. We explore whether relatively small spatial units (metropolitan statistical areas) in close geographic proximity to firms that recently have been acquired or experienced an IPO exhibit high new venture creation rates and whether the magnitudes of these effects depend on regional differences in statutes governing the freedom of employees to move between employers. Count models of biotechnology firm foundings establish three findings: (1) IPOs of organizations located contiguous to or within an MSA accelerate the founding rate within that MSA, (2) acquisitions of biotech firms situated near to or within an MSA accelerate the founding rate within the MSA, but only when the acquirer enters from outside of the biotech industry, and (3) the enforceability of post-employment non-compete covenants, which is determined at the state level, strongly moderates these effects.
Keeping Directors in Line: Social Distancing as a Control Mechanism in the Corporate Elite
Authors: Westphal James D. , Khanna Poonam
Published: February 2007

In this study, we consider the social process by which the corporate elite may have resisted pressure from stakeholders to adopt changes in corporate governance that limit managerial autonomy. We examine (1) how directors who participate in corporate governance changes that reflect greater board control over management may be subjected to a kind of informal social sanctioning, which we refer to as social distancing, on other boards; (2) how the tendency for directors to experience social distancing may be moderated by their status in the corporate elite; and (3) how directors who experience such social control could be deterred from participating subsequently in governance changes that threaten the interests of fellow top managers. We test our hypotheses with survey data on processes of social control from a sample of directors and CEOs at Forbes 500 companies and archival data on director participation in four corporate governance changes. The findings show that (1) directors who participate in governance changes that threaten managerial interests experience a higher level of social distancing on other boards, particularly when they have low to medium status in the corporate elite, and (2) directors are less likely to participate in such changes if they have recently experienced social distancing (directly or indirectly). Our theory and empirical tests ultimately address the question of how, or by what social process, boards of directors help maintain the solidarity of the corporate elite and serve the interests of corporate leaders.
Is self‐fertilization an evolutionary dead end? Revisiting an old hypothesis with genetic theories and a macroevolutionary approach
Authors: Takebayashi Naoki , Morrell Peter L.
Published: February 2007

G. Ledyard Stebbins suggested that self‐fertilization (selfing) may be an evolutionary dead end because it may result in the loss of genetic diversity and consequently preclude adaptation to changing environments. While the basic premise of selfing as a dead end is widely accepted, there have been few rigorous evaluations of the hypothesis. We examine the foundations of the dead‐end hypothesis by considering theoretical advances in the study of mating‐system evolution. We discuss theories predicting the irreversibility of self‐fertilization and the extinction of selfing lineages through the loss of adaptive potential and genetic degradation. In the second portion of the review, focusing on the irreversibility of selfing, we summarize the contribution of phylogenetic studies of mating‐system evolution to determine if evolutionary history supports this well‐established hypothesis. Most studies are in accord with the hypothesis; no single study unequivocally demonstrates the transition from highly selfing to outcrossing lineages. Finally, we discuss the problems encountered when phylogenetic studies rely on reconstruction of ancestral mating systems. To avoid some of these problems, we applied likelihood ratio tests of irreversibility of mating‐system evolution to several data sets and found that current data sets are probably too small for this test.
Sexual mass allocation in species with inflorescences as pollination units: a comparison between Arum italicum and Arisaema (Araceae)
Authors: Méndez Marcos
Published: February 2007

Sex allocation models predict that cosexuality is stabilized by high allocation to attractive structures in pollen‐limited species or by high allocation to shared structures that contribute to both genders. High investment in unilateral fixed costs favor the evolution of dioecy or gender change. With these predictions in mind, I studied sexual mass allocation at flowering in the monoecious Arum italicum (Araceae) and compared it with information available for its sex labile relative Arisaema dracontium. In A. italicum, 68% of biomass was allocated to structures believed to be involved in pollinator attraction and capture. This allocation pattern contrasts with that of Arisaema dracontium, in which 70% of biomass was allocated to scape, considered to be a unilateral fixed cost. The importance of attractive structures in A. italicum was further supported by a disproportionate increased allocation, in larger inflorescences, to the appendix (an attractive structure) compared to fertile flowers. In addition, an increase in inflorescence mass involved a disproportionate increase in mass allocation to male, rather than female, flowers. This pattern also contrasts with a size‐related gender change from male to female in Arisaema species. These findings were consistent with sex allocation model predictions and shed light on the evolution of sex lability in Arisaema species.
Occurrence of arbuscular mycorrhizal fungi in a phosphorus‐poor wetland and mycorrhizal response to phosphorus fertilization
Authors: Cornwell William K. , Bedford Barbara L. , Chapin Carmen T.
Published: February 2007

The presence of arbuscular mycorrhizas in fens has received little attention, but because fen plants are often phosphorus limited, the plant–fungus interaction could be an important factor in plant competition for phosphorus. In this field study, we determined mycorrhizal colonization rates for 18 fen plant species. Also in the field, we examined the effect of four different forms of phosphorus on the percentage colonization for one fen plant species, Solidago patula. We found that in a species‐rich, phosphorus‐poor wetland both mycorrhizal and nonmycorrhizal species were common. Nine of ten dicotyledonous species examined formed arbuscular mycorrhizas, while all monocotyledonous species were at most very weakly mycorrhizal. A morphological explanation for this pattern is that the monocots in our study have more extensive aerenchyma, especially in coarse roots. Therefore, monocots are able to transport oxygen to their roots more effectively than dicots. In the organic wetland soil, additional oxygen in the rhizosphere promotes phosphorus mineralization and availability. Two of the monocot species (Typha latifolia and Carex lasiocarpa), which have been described previously as mycorrhizal in other wetland types, are surprisingly nonmycorrhizal in our phosphorus‐poor study site, suggesting that a mycorrhizal association would not offer improved phosphorus nutrition to these species. In contrast, our field phosphorus addition decreased mycorrhizal colonization in S. patula, suggesting that one benefit to S. patula of the mycorrhizas is phosphorus uptake.