1,851 research outputs found
A Multi-scale Analysis of Disturbance Dynamics in Hardwood Forest Communities on the Cumberland Plateau, U.S.A.
The purpose of this research was to quantify forest disturbance processes and evaluate the influence of these processes on secondary hardwood forest communities on a section of the Cumberland Plateau in Tennessee. The specific objectives of this study were to: (1) reconstruct the disturbance history of a secondary hardwood forest using species composition, stand structure, tree-ring data, and soil charcoal analyses, (2) quantify canopy gap formation mechanisms, (3) document canopy gap characteristics, and (4) determine the forest response to small-scale disturbance events. This information is useful to understand the importance of localized disturbances on stand development and forest successional patterns.
With the exception of one stand-wide disturbance in the early 1980s, the disturbance regime of the forest was characterized by localized, asynchronous events that occurred at variable spatial and temporal scales. Gap-scale disturbance events became frequent after about 40 years of forest development. The presence of soil charcoal indicated that fire had occurred in the Pogue Creek Natural Area in the past, but species composition and a lack of fire-scarred trees indicated that fire had not occurred during the development of the current stand.
The majority of canopy gaps were caused by treefall (either windthrow or basal-shear) and half of all gaps were caused by the death of a Quercus individual. Gap ages ranged from 1 to 17 years with a mean of 7 years. Seasonality of death could be accurately determined for 17 gap makers and all but one of these trees died during the growing season. Strong wind associated with convective storms is the most probable disturbance agent in the forest.
The fraction of land area in expanded gaps and true canopy gaps was 15% and 6%, respectively. The amount of land area in canopy gaps was highest for younger gaps and generally decreased with increased gap age. Most expanded and true canopy gaps had elliptical shapes and the majority of gaps were oriented perpendicular to slope contours.
Significant positive relationships were documented between expanded gap size and the density of saplings, trees, and total stems. Only weak relationships existed between stem diversity and expanded gap size. Most of the canopy gaps documented were projected to close by lateral crown expansion rather than height growth of subcanopy individuals, but gaps still provided a means for understory trees to recruit to larger size classes. Over half of all trees located in true canopy gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron tulipifera. Because the gaps documented were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. This study indicated that gap-scale disturbance processes have an influence on stand development and successional patterns of secondary hardwood forests in the absence of large-scale events
Iatrogenic Spinal Cord Injury Resulting From Cervical Spine Surgery.
STUDY DESIGN: Retrospective cohort study of prospectively collected data.
OBJECTIVE: To examine the incidence of iatrogenic spinal cord injury following elective cervical spine surgery.
METHODS: A retrospective multicenter case series study involving 21 high-volume surgical centers from the AOSpine North America Clinical Research Network was conducted. Medical records for 17 625 patients who received cervical spine surgery (levels from C2 to C7) between January 1, 2005, and December 31, 2011, were reviewed to identify occurrence of iatrogenic spinal cord injury.
RESULTS: In total, 3 cases of iatrogenic spinal cord injury following cervical spine surgery were identified. Institutional incidence rates ranged from 0.0% to 0.24%. Of the 3 patients with quadriplegia, one underwent anterior-only surgery with 2-level cervical corpectomy, one underwent anterior surgery with corpectomy in addition to posterior surgery, and one underwent posterior decompression and fusion surgery alone. One patient had complete neurologic recovery, one partially recovered, and one did not recover motor function.
CONCLUSION: Iatrogenic spinal cord injury following cervical spine surgery is a rare and devastating adverse event. No standard protocol exists that can guarantee prevention of this complication, and there is a lack of consensus regarding evaluation and treatment when it does occur. Emergent imaging with magnetic resonance imaging or computed tomography myelography to evaluate for compressive etiology or malpositioned instrumentation and avoidance of hypotension should be performed in cases of intraoperative and postoperative spinal cord injury
Changes in Sexual Roles and Quality of Life for Gay Men after Prostate Cancer: Challenges for Sexual Health Providers
Introduction Gay men with prostate cancer ( GMPCa ) may have differential health‐related quality of life ( HRQOL ) and sexual health outcomes than heterosexual men with prostate cancer ( PCa ), but existing information is based on clinical experience and small studies. Aims Our goals were to: (i) describe HRQOL and examine changes in sexual functioning and bother; (ii) explore the psychosocial aspects of sexual health after PCa ; and (iii) examine whether there were significant differences on HRQOL and sexual behavior between GMPCa and published norms. Methods A convenience sample of GMPCa completed validated disease‐specific and general measures of HRQOL , ejaculatory function and bother, fear of cancer recurrence, and satisfaction with prostate cancer care. Measures of self‐efficacy for PCa management, illness intrusiveness, and disclosure of sexual orientation were also completed. Where possible, scores were compared against published norms. Main Outcome Measures Main outcome measures were self‐reported sexual functioning and bother on the E xpanded P rostate C ancer I ndex. Results Compared with norms, GMPCa reported significantly worse functioning and more severe bother scores on urinary, bowel, hormonal symptom scales ( P s < 0.015–0.0001), worse mental health functioning ( P < 0.0001), greater fear of cancer recurrence ( P < 0.0001), and were more dissatisfied with their PCa medical care. However, GMPCa reported better sexual functioning scores ( P < 0.002) compared with norms. Many of the observed differences met criteria for clinical significance. Physical functioning HRQOL and sexual bother scores were similar to that of published samples. GMPCa tended to be more “out” about their sexual orientation than other samples of gay men. Conclusions GMPCa reported substantial changes in sexual functioning after PCa treatment. They also reported significantly worse disease‐specific and general HRQOL , fear of recurrence, and were less satisfied with their medical care than other published PCa samples. Sexual health providers must have an awareness of the unique functional and HRQOL differences between gay and heterosexual men with PCa. Hart TL, Coon DW, Kowalkowski MA, Zhang K, Hersom JI, Goltz HH, Wittmann DA, and Latini DM. Changes in sexual roles and quality of life for gay men after prostate cancer: Challenges for sexual health providers. J Sex Med 2014;11:2308–2317.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108360/1/jsm12598.pd
Gauge dependence of effective gravitational field
The problem of gauge independent definition of effective gravitational field
is considered from the point of view of the process of measurement. Under
assumption that dynamics of the measuring apparatus can be described by the
ordinary classical action, effective Slavnov identities for the generating
functionals of Green functions corresponding to a system of arbitrary
gravitational field measured by means of scalar particles are obtained. With
the help of these identities, the total gauge dependence of the non-local part
of the one-loop effective apparatus action, describing the long-range quantum
corrections, is calculated. The value of effective gravitational field inferred
from the effective apparatus action is found to be gauge-dependent. A probable
explanation of this result, referring to a peculiarity of the gravitational
interaction, is given.Comment: Revised version as publishe
Sellers on the street: the human infrastructure of the mobile phone network in Kigali, Rwanda
This paper looks in detail at the social and economic background of mobile airtime sellers on the streets of Kigali. While informal networks have proved to be an invaluable resource for large multinational telecommunication companies seeking to penetrate African markets, changing technological capabilities may soon displace them. As Rwanda develops its Internet and payment systems, companies and institutions hope to provide airtime and services directly. The paper draws on interviews with airtime sellers in three neighbourhoods of Kigali to ask what this temporary source of employment has done to their long-term career prospects. While the Rwandan government information and communication technology (ICT) strategy has hereto focused on high-end ICT and business process outsourcing, this paper uses the experiences of airtime sellers to advocate for a more bottom-up approach to entrepreneurship and economic development in Rwanda. We stress that planners and researchers need to think more critically about value chains at the bottom of the pyramid, not just in terms of how informal networks can be used as temporary appendages to further the reach of formal multinational corporations, but how these new kinds of chains and networks can be re-engineered to provide permanent and sustainable livelihoods to workers and business owners at the base of the economy
Incomplete Contracts with Asymmetric Information: Exclusive v. Optional Remedies
Law and economics scholars have always had a strong interest in contract remedies. Perhaps the most explored issue in contract law has been the desirability of various contract remedies, such as expectation damages, specific performance, or liquidated damages, to name the most common. Scholars have been debating for years, from various perspectives, the comparative advantage of these remedies. Yet, most scholars have assumed that each of these remedies is exclusive, and their work has compared a single remedy contract to another single remedy contract. Interestingly, an analysis that assumes these remedies are optional (or cumulative) has not yet been explored, in spite of the fact that contract law provides the non-breaching party with a variety of optional remedies to choose from in case of a breach, and in spite of the fact that parties themselves write contracts which provide such an option. In this paper we attempt to start filling in this gap by studying the relationship between these remedies. Specifically, we study the conditions at which a contract that grants the non-breaching party an option to choose from optional remedies is superior to an exclusive remedy contract. We show that under conditions of double-sided uncertainty and asymmetric information between a seller (who might breach) and a buyer (who never breaches) the interaction of the parties\u27 distributions should determine whether a contract provides for exclusive or optional remedies. Specifically, if the buyer\u27s conditional expected valuation is larger than the seller\u27s conditional expected valuation (in both cases - conditional that their expected valuation is above the buyer\u27s mean valuation), then a contract which provides the buyer an option to choose between liquidated damages or specific performance (or actual damages) is superior. Our analysis in this paper informs transactional lawyers of the relevant economic factors they should consider when deciding the optimal composition of remedies in a given context. Moreover, our analysis is relevant for courts that interpret contracts because it will help them to better understand whether rational parties would have agreed that a particular remedy would be an exclusive remedy or an optional remedy when the language of the contract is ambiguous. Lastly, our analysis provides yet another economic rationale for why courts should enforce parties\u27 liquidated damages clauses even if it seems ex-post over, or under, compensatory. We present a model which shows when parties will agree on a non-exclusive liquidated damages clause. Under such a contract the parties stipulate ex-ante that the buyer will have the option to choose upon breach whether she prefers an optional remedy, such as actual damages or specific performance, to the pre-determined liquidated damages. We focus on the ex-ante design of the contract in light of the new information that the parties anticipate they will gain after they draft the contract. Therefore, we assume that no renegotiation or investments are involved. We demonstrate the optimal way to design contract clauses which takes advantage of the information that the seller and the buyer receive between the time they enter into the contract and the time of the actual breach. We further suggest that parties indeed use such clauses and that courts honor them. After laying out the basic model we provide some extensions to it. As is well known, an exclusive liquidated damages contract is equivalent to granting the seller a call option to breach and pay, where the exercise price is equal to the amount of the agreed liquidated damages. What is perhaps less known is that a non-exclusive, or optional, contract, where the buyer can choose performance, is equivalent to giving the buyer a consecutive call option with the same exercise price. Yet, the consecutive call option to the buyer does not have to have the same exercise price but can rather have a higher one. We call this new contract a two-price contract and show that it is even more efficient than the basic contract we have explored before. Next, we introduce more rounds of sequential options and show that while the regular ex-ante contract can achieve on average about 4 Indeed, in an environment of asymmetric information renegotiation costs are high. More on this below. 90% of the first-best allocative efficiency, an n-rounds contract approaches the first best, as n goes to infinity. We show numerically that within just 4 rounds, 96% of the allocative efficiency can be achieved. Section two describes the legal background against which we have designed our model. Section three surveys the literature that evaluates contract remedies from an economic perspective. Section four presents a simple model with two-sided incomplete information and with a liquidated damages clause. In section four we compare the performance of a regime with optional remedies with a regime of exclusive remedy and then determine the conditions at which each regime should be applied. Section five discusses some interesting extensions meant to approach the first-best allocative efficiency. The appendix provides a more rigorous mathematical demonstration of the model
Sellers on the street: the human infrastructure of the mobile phone network in Kigali, Rwanda
PCSK6 and Survival in Idiopathic Pulmonary Fibrosis
Rationale: Idiopathic pulmonary fibrosis (IPF) is a devastating disease characterized by limited treatment options and high mortality. A better understanding of the molecular drivers of IPF progression is needed. Objectives: To identify and validate molecular determinants of IPF survival. Methods: A staged genome-wide association study was performed using paired genomic and survival data. Stage I cases were drawn from centers across the United States and Europe and stage II cases from Vanderbilt University. Cox proportional hazards regression was used to identify gene variants associated with differential transplantation-free survival (TFS). Stage I variants with nominal significance (P < 5 x 10(-5)) were advanced for stage II testing and meta-analyzed to identify those reaching genome-wide significance (P < 5 x 10(-8)). Downstream analyses were performed for genes and proteins associated with variants reaching genome-wide significance. Measurements and Main Results: After quality controls, 1,481 stage I cases and 397 stage II cases were included in the analysis. After filtering, 9,075,629 variants were tested in stage I, with 158 meeting advancement criteria. Four variants associated with TFS with consistent effect direction were identified in stage II, including one in an intron of PCSK6 (proprotein convertase subtilisin/kexin type 6) reaching genome-wide significance (hazard ratio, 4.11 [95% confidence interval, 2.54-6.67]; P = 9.45 x 10(-9)). PCSK6 protein was highly expressed in IPF lung parenchyma. PCSK6 lung staining intensity, peripheral blood gene expression, and plasma concentration were associated with reduced TFS. Conclusions: We identified four novel variants associated with IPF survival, including one in PCSK6 that reached genome-wide significance. Downstream analyses suggested that PCSK6 protein plays a potentially important role in IPF progression
How Attractive Is the Girl Next Door? An Assessment of Spatial Mate Acquisition and Paternity in the Solitary Cape Dune Mole-Rat, Bathyergus suillus
Behavioural observations of reproduction and mate choice in wild fossorial rodents are extremely limited and consequently indirect methods are typically used to infer mating strategies. We use a combination of morphological, reproductive, spatial, and genetic data to investigate the reproductive strategy of a solitary endemic species, the Cape dune mole-rat Bathyergus suillus. These data provide the first account on the population dynamics of this species. Marked sexual dimorphism was apparent with males being both significantly larger and heavier than females. Of all females sampled 36% had previously reproduced and 12% were pregnant at the time of capture. Post-partum sex ratio was found to be significantly skewed in favour of females. The paternity of fifteen litters (n = 37) was calculated, with sires assigned to progeny using both categorical and full probability methods, and including a distance function. The maximum distance between progeny and a putative sire was determined as 2149 m with males moving between sub-populations. We suggest that above-ground movement should not be ignored in the consideration of mate acquisition behaviour of subterranean mammals. Estimated levels of multiple paternity were shown to be potentially as high as 26%, as determined using sibship and sire assignment methods. Such high levels of multiple paternity have not been found in other solitary mole-rat species. The data therefore suggest polyandry with no evidence as yet for polygyny
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