Subsequent Time Periods Research Articles

Quantifying successional changes in response to forest disturbances

Question: Can dissimilarity measures of individual plots be used to forecast the driving factors among various anthropogenic disturbances influencing understorey successional changes?Location: Yambulla State Forest, south‐eastern Australia (37°14'S, 149°38'E).Methods: Assessments of understorey vegetation communities were taken prior to anthropogenic disturbances and at three subsequent time periods representing a period of 15 years post‐disturbance. Dissimilarities were calculated from the original assessment and modelled in a Bayesian framework to examine the influence of logging, number of prescribed burns and time.Results: All sites underwent significant changes over time independently of the imposed management regimes. Logging resulted in an immediate change in vegetation assemblage which decreased in the subsequent assessments. The number of prescribed fires brought greater change in the shrub vegetation assemblages, but less change in the ground species vegetation assemblages.Conclusions: The anthropogenic disturbances did have some role in the changes of vegetation assemblages but these were minimal. The ongoing changes appear to be a natural response to the last wildfire, which passed through the study area in 1973 (13 years prior to the study). Forest management practices should consider the influence of wildfire succession when planning for the conservation of biodiversity.

Genetic parameters for traits evaluated at field tests of 3- and 4-year-old Swedish Warmblood horses

There are two types of 1-day field tests available for young Swedish Warmblood sport horses; one test for 3-year olds and one more advanced test for 4-year olds. Conformation, gaits and jumping ability are evaluated at both tests. Studies on various genetic parameters were based on about 20 000 tested horses. The data for 4-year olds consisted of 30 years of testing. The aims of the study were to estimate genetic parameters for results from different time periods, and to estimate heritabilities for, and genetic correlations between, traits scored in the two tests. The judgement of traits was shown to have been changed during the 30 years of testing, resulting in changes in higher heritabilities in, and stronger genetic correlations between, later time periods. In the first time period, records showed higher residual and lower genetic variances than in the subsequent time periods. Genetic correlations between traits recorded in the first and last time period deviated considerably from unity. Further studies are needed to investigate how to treat data from the early period in genetic evaluations. Heritabilities were moderate to high for conformation traits (0.24 to 0.58) at both types of tests, except for correctness of legs (0.08). The heritabilities for gait traits were also moderate to high (0.37 to 0.53). For jumping traits, the heritabilities ranged between 0.17 and 0.33. The highly positive genetic correlations (0.82 to 0.99) between corresponding traits tested at the simpler test for 3-year olds and at the ridden test of 4-year olds implied that it would be desirable to include the test results of 3-year olds into the genetic evaluation as breeding values for Swedish Warmbloods for many years has only been based on results from 4-year olds.

Monitoring antibiotic usage: an update

Within a hospital, antibiotic usage can be affected by clustering of infections. In addition, pharmacy imprest systems may deliver stock in one time period that are used in a subsequent time period. As a result, hospital antibiotic usage data can be unpredictable and highly variable.Usage of an antibiotic can be conveniently displayed in a time-series chart with monthly defined daily doses (DDDs) per 1000 bed-days on the vertical axis and months on the horizontal axis. To account for random variation, the chart should ideally have control limits, for example a Shewhart chart. However, conventional Shewhart control charts rely on the availability of a run of predictable data values so that the average and its variability can be determined. Since this may be difficult to achieve with hospital antibiotic usage data, a conventional control chart may give misleading information. A modified control chart based on a generalised additive model can overcome the difficulty in the analysis of these data. This chart is not difficult to employ or interpret.

The Efficacy of a Multicultural Prevention Intervention among Urban American Indian Youth in the Southwest U.S.

This study explored how a non-targeted group of ethnic minority youth might or might not benefit from a prevention intervention focused on other cultural groups. The study specifically evaluated the effects of an evidence-based drug prevention curriculum with a sample of urban American Indian youth in the southwest U.S., most of whom self-reported multi-ethnic heritages. Using growth curve modeling, this research examined the developmental trajectory of drug use for these youth, and compared it with the trajectory of youth from other racial/ethnic groups at pre-intervention, post-intervention, and two follow up time periods. Results indicate that alcohol and marijuana use increased from pre-intervention across subsequent time periods for all youth. The drug use of the American Indian youth in the treatment group increased on some measures. Specifically, they reported a steeper trajectory in the amount and frequency of alcohol and marijuana use compared to the youths in the treatment groups with other racial/ethnic identifications. The implications of these findings for the development of culturally grounded prevention programs for multi-ethnic, urban American Indian youth are discussed. EDITORS' STRATEGIC IMPLICATIONS: This research provides a specific example, but also makes a strong global argument, for the need to develop and evaluate prevention programs that are culturally grounded in the worldview of the target group.

A dynamic look-ahead Monte Carlo algorithm for pricing Bermudan options

Under the assumption of no-arbitrage, the pricing of American and Bermudan options can be casted into optimal stopping problems. We propose a new adaptive simulation based algorithm for the numerical solution of optimal stopping problems in discrete time. Our approach is to recursively compute the so-called continuation values. They are defined as regression functions of the cash flow, which would occur over a series of subsequent time periods, if the approximated optimal exercise strategy is applied. We use nonparametric least squares regression estimates to approximate the continuation values from a set of sample paths which we simulate from the underlying stochastic process. The parameters of the regression estimates and the regression problems are chosen in a data-dependent manner. We present results concerning the consistency and rate of convergence of the new algorithm. Finally, we illustrate its performance by pricing high-dimensional Bermudan basket options with strangle-spread payoff based on the average of the underlying assets.

Effects of additional telemedicine care on mortality and cardiac morbidity in patients with coronary artery disease — The TeleGuard-RCT

Background: The aim of this study was to assess the mortality rates of IHD in subjects with and without diabetes during two subsequent time periods in both genders and to see if the rate ratio between them had changed over time. Material and methods: In 1984–86 (HUNT1) and 1995–97 (HUNT2) two health surveys were conducted in Nord-Trondelag county, Norway. All inhabitants=20 years were invited. 74977 persons attended HUNT1 and 66140 HUNT2. The two cohorts were followed nine years from baseline according to cause specific mortality (ICD codes). Age and sex specific rates of death due to IHD were calculated and compared between the two follow-up periods among persons with and without diabetes. Mantel–Cox comparison was used to calculate rate ratios with 95% confidence intervals as an estimate of the difference in mortality between the two time periods. Results: During follow-up 1822 men/1095 women (HUNT1) and 801 men/488 women (HUNT2) died from IHD. Death rates decreased in all age groups from HUNT1 to HUNT2 in both genders irrespective of diabetes status. Rate ratio for fatal IHD in diabetics compared to nondiabetics is demonstrated in the table: Conclusions: Mortality rates of IHD decreased in all age groups irrespective of diabetes status and gender. In the age groups b70 years the rate ratio for fatal IHD in diabetics compared to nondiabetics decreased substantially between the two periods. In subjects N70 years old a similar decline in rate ratio for fatal IHD was not found.

Mortality rates of ischemic heart disease associated with diabetes has declined. Results from the HUNT1&2 studies

The aim of this study was to assess the mortality rates of IHD in subjects with and without diabetes during two subsequent time periods in both genders and to see if the rate ratio between them had changed over time.

Bone Marrow-Derived Mesenchymal Stem Cells Influence Early Tendon-Healing in a Rabbit Achilles Tendon Model

A repaired tendon needs to be protected for weeks until it has accrued enough strength to handle physiological loads. Tissue-engineering techniques have shown promise in the treatment of tendon and ligament defects. The present study tested the hypothesis that bone marrow-derived mesenchymal stem cells can accelerate tendon-healing after primary repair of a tendon injury in a rabbit model. Fifty-seven New Zealand White rabbits were used as the experimental animals, and seven others were used as the source of bone marrow-derived mesenchymal stem cells. The injury model was a sharp complete transection through the midsubstance of the Achilles tendon. The transected tendon was immediately repaired with use of a modified Kessler suture and a running epitendinous suture. Both limbs were used, and each side was randomized to receive either bone marrow-derived mesenchymal stem cells in a fibrin carrier or fibrin carrier alone (control). Postoperatively, the rabbits were not immobilized. Specimens were harvested at one, three, six, and twelve weeks for analysis, which included evaluation of gross morphology (sixty-two specimens), cell tracing (twelve specimens), histological assessment (forty specimens), immunohistochemistry studies (thirty specimens), morphometric analysis (forty specimens), and mechanical testing (sixty-two specimens). There were no differences between the two groups with regard to the gross morphology of the tendons. The fibrin had degraded by three weeks. Cell tracing showed that labeled bone marrow-derived mesenchymal stem cells remained viable and present in the intratendinous region for at least six weeks, becoming more diffuse at later time-periods. At three weeks, collagen fibers appeared more organized and there were better morphometric nuclear parameters in the treatment group (p < 0.05). At six and twelve weeks, there were no differences between the groups with regard to morphometric nuclear parameters. Biomechanical testing showed improved modulus in the treatment group as compared with the control group at three weeks (p < 0.05) but not at subsequent time-periods. Intratendinous cell therapy with bone marrow-derived mesenchymal stem cells following primary tendon repair can improve histological and biomechanical parameters in the early stages of tendon-healing.

Bone Marrow-Derived Mesenchymal Stem Cells Influence Early Tendon-Healing in a Rabbit Achilles Tendon Model

Background: A repaired tendon needs to be protected for weeks until it has accrued enough strength to handle physiological loads. Tissue-engineering techniques have shown promise in the treatment of tendon and ligament defects. The present study tested the hypothesis that bone marrow-derived mesenchymal stem cells can accelerate tendon-healing after primary repair of a tendon injury in a rabbit model. Methods: Fifty-seven New Zealand White rabbits were used as the experimental animals, and seven others were used as the source of bone marrow-derived mesenchymal stem cells. The injury model was a sharp complete transection through the midsubstance of the Achilles tendon. The transected tendon was immediately repaired with use of a modified Kessler suture and a running epitendinous suture. Both limbs were used, and each side was randomized to receive either bone marrow-derived mesenchymal stem cells in a fibrin carrier or fibrin carrier alone (control). Postoperatively, the rabbits were not immobilized. Specimens were harvested at one, three, six, and twelve weeks for analysis, which included evaluation of gross morphology (sixty-two specimens), cell tracing (twelve specimens), histological assessment (forty specimens), immunohistochemistry studies (thirty specimens), morphometric analysis (forty specimens), and mechanical testing (sixty-two specimens). Results: There were no differences between the two groups with regard to the gross morphology of the tendons. The fibrin had degraded by three weeks. Cell tracing showed that labeled bone marrow-derived mesenchymal stem cells remained viable and present in the intratendinous region for at least six weeks, becoming more diffuse at later time-periods. At three weeks, collagen fibers appeared more organized and there were better morphometric nuclear parameters in the treatment group (p < 0.05). At six and twelve weeks, there were no differences between the groups with regard to morphometric nuclear parameters. Biomechanical testing showed improved modulus in the treatment group as compared with the control group at three weeks (p < 0.05) but not at subsequent time-periods. Conclusions: Intratendinous cell therapy with bone marrow-derived mesenchymal stem cells following primary tendon repair can improve histological and biomechanical parameters in the early stages of tendon-healing. Clinical Relevance: The findings of the present study have clinical importance as the early time-period during tendon-healing is crucial in the treatment of tendon injuries.

The neural basis of conditional reasoning: An event-related potential study

The spatiotemporal analysis of brain activation during the execution of conditional reasoning tasks (the four inference forms: Modus Ponens (MP), Modus Tollens (MT), affirming the consequent (AC), and denying the antecedent (DA)) and one baseline task (BS) was performed in 12 normal young adult participants using high-density event-related brain potentials (ERPs). Results showed that the early components elicited by the five task types were not significantly different. Reasoning tasks elicited a more negative EPR deflection (N600) than did the BS task in the time window of 500–700 ms after onset of the minor premise. Dipole source analysis of the difference wave (MP − BS) suggested that a generator localized in the left anterior cingulate cortex (BA 24) was involved in the activation and the application of the inference rules. ERP components of the five tasks were similar in the subsequent time period between 700 and 1700 ms. Following that period, a greater negativity in the reasoning tasks, in comparison to the BS task, developed between 1700 and 2000 ms poststimulus over the left fronto-central scalp regions. A generator of this effect was located in the right anterior cingulate cortex (BA 24) and was possibly related to cognitive control. The results indicate that the cingulate cortex was activated by conditional reasoning tasks with purely abstract materials and support the view that human reasoning is not a unified phenomenon but is content-sensitive.

Pesticide Use and Prostate Cancer Incidence in a Prospective Cohort Study

SAA1-O-03 Introduction: Prostate cancer has been observed to occur in excess among farmers and other agricultural workers in a number of countries around the world. Methods: A prospective cohort of 89,658 pesticide applicators and their spouses were followed for cancer incidence for an average of 8.5 years. Members of the cohort completed questionnaires about pesticide use, occupations, lifestyle, and medical history during enrollment (1993–1997) and at 2 subsequent periods of time. A total of 1289 incident prostate cancers cases were identified among the 57,311 male pesticide applicators through December 2003 through linkage with population-based cancer registries. Two exposure metrics were used to estimate exposure. One was an estimate of total days of a specific pesticide use in a life-time; the second, total days of exposure weighted by a published estimate of exposure intensity. Results: Male cohort members experienced a small, but significant, elevated risk of prostate cancer compared with the general populations of the study states (SIR = 1.24; 95% CI, 1.18–1.33). A family history of prostate cancer among first-degree relatives of male cohort members conferred a twofold excess risk of prostate cancer. Significant linear exposure-response trends (P ≤ 0.05) were observed for 6 specific pesticides (fonofos, phorate, coumaphos and chlorpyrifos, which are organothiophosphates; butylate, an herbicide; and permethrin, an insecticide), but only among those with a family history of prostate cancer, confirming a preliminary published report from this study. Discusion/Conclusions: The consistency of our findings with 2 different exposure metrics, in both study sites and with preliminary published results, suggests that genetic susceptibility among pesticide applicators may play an important role in prostate cancer etiology. Shared environmental risk factors for prostate cancer among family members, however, may also explain these results. Planned molecular studies nested within the same cohort to assess genetic and epigenetic modes of action might clarify and explain these associations.

State Psychiatric Hospital Census After the 1999 Olmstead Decision: Evidence of Decelerating Deinstitutionalization

State Psychiatric Hospital Census After the 1999 Olmstead Decision: Evidence of Decelerating Deinstitutionalization

Homocysteine Levels in Patients Undergoing Open-Heart Surgery

Background: The aim of this prospective study was to determine the levels of plasma homocysteine (HCY) in patients who have undergone open-heart surgery for ischemic heart disease (IHD) or nonischemic heart disease (NIHD) and to evaluate whether an association is present between hyperhomocysteinemia and coronary artery disease.Material and Methods: We investigated prospectively 30 patients who underwent open-heart surgery. Of these patients, 15 had IHD, and 15 had NIHD such as mitral and/or aortic valve disease. The 2 groups were well matched for age, sex, body mass index, and blood pressure. In all patients HCY was assayed by high performance liquid chromatography preoperatively and on the first, second, and third day postoperatively.Results: The mean age of the patients was 57.2 years in group IHD and 52.6 years in group NIHD. The male:female ratio was 8:7 in group IHD and 7:8 in group NIHD. Of 15 patients in group IHD, 13 had hyperhomocysteinemia and 2 had normal plasma HCY levels. Of 15 patients in NIHD group, 1 had hyperhomocysteinemia and the others had normal plasma HCY levels. Preoperative plasma HCY levels of all patients in the IHD group were significantly lower during all subsequent time periods, whereas preoperative plasma HCY levels in the NIHD group were lower only on the first day post-surgery (P &lt; .05).Conclusions: Our data suggest that plasma HCY levels in patients with IHD are associated with the development of atherogenesis and coronary artery disease. For this reason, HCY levels should be measured routinely and treated appropriately in patients with risk factors for atherosclerosis.

Modeling and calculating the effect of treatment at baseline from panel outcomes

We propose and examine a panel data model for isolating the effect of a treatment, taken once at baseline, from outcomes observed over subsequent time periods. In the model, the treatment intake and outcomes are assumed to be correlated, due to unobserved or unmeasured confounders. Intake is partly determined by a set of instrumental variables and the confounding on unobservables is modeled in a flexible way, varying both by time and treatment state. Covariate effects are assumed to be subject-specific and potentially correlated with other covariates. Estimation and inference is by Bayesian methods that are implemented by tuned Markov chain Monte Carlo methods. Because our analysis is based on the framework developed by Chib [2004. Analysis of treatment response data without the joint distribution of counterfactuals. Journal of Econometrics, in press], the modeling and estimation does not involve either the unknowable joint distribution of the potential outcomes or the missing counterfactuals. The problem of model choice through marginal likelihoods and Bayes factors is also considered. The methods are illustrated in simulation experiments and in an application dealing with the effect of participation in high school athletics on future labor market earnings.

Body Composition and Metabolic Changes Following Bariatric Surgery: Effects on Fat Mass, Lean Mass and Basal Metabolic Rate

Bariatric surgery has become the method of choice for weight loss in severely obese patients. While the incidence of obesity and its co-morbidities have been well-documented, less is known about the outcomes of the surgery as it relates to body composition and metabolic changes. 19 bariatric surgery patients (14 female, 5 male) were assessed for basal metabolic rate (BMR), percent fat, fat mass, and lean body mass (LBM) just prior to surgery and at 1, 3 and 6 months after surgery. Analysis of Variance (ANOVA) using the general linear model indicated significant changes in all measures of body composition for each time period. Linear regression was developed for each of these measures. Of the 39.7-kg weight loss, 26.4 kg (66.5%) was fat mass loss and 13.3 kg (33.5%) was LBM loss. BMR significantly decreased from pre-surgery (2091 kcals) to 1 month post-surgery (1758 kcals), with no significant changes in subsequent time periods. Repeated measures ANOVA for the ratio of BMR/LBM indicated no significant differences for any comparison of time periods (F=2.29, P=.111), suggesting that there is no adaptation of an energy-conserving mechanism in these patients. Bariatric surgery was highly successful in inducing significant changes in body weight (39.7 kg), fat mass (26.4 kg), % body fat (7.9%) but also lean body mass (13.3 kg). The 440 kcal decrease in BMR, while significant, was not greater than expected due to significant decreases in LBM.

Optimal Policies for E-Commerce Sites with Hybrid Revenue Streams: Differentiated Quality Approach

In last few years, several e-commerce organizations have adopted the strategy of providing two web sites that differ in quality, subscription fee and level of advertisements. Most of these organizations charge a subscription fee for better quality web site and provide free service at the low quality web site. We develop an optimal control theory based model to study the pricing and advertising strategy of such e-commerce organizations dynamically. Since the pricing and advertising strategy of one site affects the decision of other site, we optimize the decisions of both the sites simultaneously. Moreover, since the decision at one time period affects the decisions of subsequent time periods, the proposed dynamic model provides a global optimal solution. We consider consumers' sensitivity to quality, price and advertisement for finding the optimal price and advertisement levels over time for both the web sites. In order to present important managerial implications, we conduct several sensitivity analyses and provide different analytical and graphical results.

Optimal Pricing and Advertising Policies for Web Services

The accumulated evidence indicates that pure revenue models, such as free-access models (where the revenue is solely dependent on advertisements) or pure subscription fee based models (where the revenue is solely based on subscription fees, and advertisements are not shown to customers), are not sufficient to support the survival of online information sellers. Hence, hybrid models based on a combination of subscription fees and advertising revenues have replaced the pure revenue models on many web sites including the popular online content provider sites such as Wall Street Journal and Classmates Inc. In response to increasing interest in hybrid models, we study the problem of dynamic pricing of web content on a site where revenue is generated from subscription fee as well as advertisements. Using the optimal control theory, we obtain a dynamic pricing strategy of subscription and the optimal level of advertisements shown to the subscribers. Since the decision in any one time period affects the decisions of all subsequent time periods, the proposed dynamic model provides a globally optimal solution. Our model shows that the subscription fee is reduced initially to attract more customers, and is subsequently increased once a large customer base is obtained. Even when the fee increases in later periods, the number of subscribers increases due to the value associated with the quality of the content. We present several analytical and numerical results which provide some important managerial implications.

Quantitative interpretation of atmospheric carbon records over the last glacial termination

The glacial/interglacial rise in atmospheric pCO2 is one of the best known changes in paleoclimate research, yet the cause for it is still unknown. Forcing the coupled ocean‐atmosphere‐biosphere box model of the global carbon cycle BICYCLE with proxy data over the last glacial termination, we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (δ13C, Δ14C) observed in natural climate archives. The sensitivity of the Box model of the Isotopic Carbon cYCLE (BICYCLE) to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models, respectively. The processes considered here ranked by their contribution to the glacial/interglacial rise in pCO2 in decreasing order are: the rise in Southern Ocean vertical mixing rates (&gt;30 ppmv), decreases in alkalinity and carbon inventories (&gt;30 ppmv), the reduction of the biological pump (∼20 ppmv), the rise in ocean temperatures (15–20 ppmv), the resumption of ocean circulation (15–20 ppmv), and coral reef growth (&lt;5 ppmv). The regrowth of the terrestrial biosphere, sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction, decreasing pCO2 during Termination I by ∼30 ppmv. According to our model the sequence of events during Termination I might have been the following: a reduction of aeolian iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase. After these events the reduced North Atlantic Deep Water (NADW) formation during the Heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the Bølling‐Allerød warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of Termination I. We further deduce that a complete shutdown of the NADW formation during the Younger Dryas was very unlikely. Changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric δ13C after the Bølling‐Allerød warm interval.

Eliminating Inpatient Sliding-Scale Insulin: A Reeducation Project With Medical House Staff

We applaud Baldwin et al.’s (1) efforts to improve the management of inpatient hyperglycemia and to advance resident knowledge about best care practices. However, we would welcome additional data to support the authors’ assertion that the effect on medical house staff education was sustained. The data reported were only from the 8-week study period, when an attending endocrinologist rounded with residents twice each day on all study patients. There are no data from a subsequent time period for comparison. …

Analogical Modeling and morphological change: the case of the adjectival negative prefix in English

This article examines the usefulness of Skousen's Analogical Modeling (AM) for explaining morphological change. In contrast to previous accounts of analogy, AM constitutes a general unified model of language that accounts for both sporadic and systematic changes. AM also provides explicit constraints on analogy that allow explanation of how morphological changes begin, which forms most likely serve as patterns for analogy, and which forms are most likely to change.AM is then tested on the case of the adjectival negative prefix in English (in-, un-, dis-, etc.), using the Middle and Early Modern English portions of the Helsinki corpus as a basis for prediction. AM was given the task of using forms containing negative prefixes for one time period to predict the prefixes that adjectives would take in the subsequent time period. For each of the roughly seventy-year periods in the corpus, AM was able to predict valid prefixes about 90 percent of the time.