Publications by authors named "Ali Arab"

18 Publications

  • Page 1 of 1

Migratory strategy drives species-level variation in bird sensitivity to vegetation green-up.

Nat Ecol Evol 2021 Apr 29. Epub 2021 Apr 29.

Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA.

Animals and plants are shifting the timing of key life events in response to climate change, yet despite recent documentation of escalating phenological change, scientists lack a full understanding of how and why phenological responses vary across space and among species. Here, we used over 7 million community-contributed bird observations to derive species-specific, spatially explicit estimates of annual spring migration phenology for 56 bird species across eastern North America. We show that changes in the spring arrival of migratory birds are coarsely synchronized with fluctuations in vegetation green-up and that the sensitivity of birds to plant phenology varied extensively. Bird arrival responded more synchronously with vegetation green-up at higher latitudes, where phenological shifts over time are also greater. Critically, species' migratory traits explained variation in sensitivity to green-up, with species that migrate more slowly, arrive earlier and overwinter further north showing greater responsiveness to earlier springs. Identifying how and why species vary in their ability to shift phenological events is fundamental to predicting species' vulnerability to climate change. Such variation in sensitivity across taxa, with long-distance neotropical migrants exhibiting reduced synchrony, may help to explain substantial declines in these species over the last several decades.
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http://dx.doi.org/10.1038/s41559-021-01442-yDOI Listing
April 2021

Environmental Correlates of Lyme Disease Emergence in Southwest Virginia, 2005-2014.

J Med Entomol 2021 Apr 7. Epub 2021 Apr 7.

Nicholas School of the Environment, Duke University, Durham, NC.

Lyme disease is the most common tick-borne disease in North America. Though human infection is mostly transmitted in a limited geography, the range has expanded in recent years. One notable area of recent expansion is in the mountainous region of southwestern Virginia. The ecological factors that facilitate or constrain the range of human Lyme disease in this region remain uncertain. To evaluate this further, we obtained ecological data, including remotely sensed data on forest structure and vegetation, weather data, and elevation. These data were aggregated within the census block groups of a 9,153 km2 area around the cities of Blacksburg and Roanoke, VA, an area with heterogeneous Lyme disease transmission. In this geographic area, 755 individuals were reported to have Lyme disease in the 10 yr from 2006 to 2015, and these cases were aggregated by block group. A zero-inflated negative binomial model was used to evaluate which environmental variables influenced the abundance of Lyme disease cases. Higher elevation and higher vegetation density had the greatest effect size on the abundance of Lyme disease. Measures of forest edge, forest integrity, temperature, and humidity were not associated with Lyme disease cases. Future southward expansion of Lyme disease into the southeastern states may be most likely in ecologically similar mountainous areas.
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http://dx.doi.org/10.1093/jme/tjab038DOI Listing
April 2021

A Bayesian approach for estimating age-adjusted rates for low-prevalence diseases over space and time.

Stat Med 2021 Mar 16. Epub 2021 Mar 16.

Department of Mathematics and Statistics, Georgetown University, Washington, District of Columbia, USA.

Age-adjusted rates are frequently used by epidemiologists to compare disease incidence and mortality across populations. In small geographic regions, age-adjusted rates computed directly from the data are subject to considerable variability and are generally unreliable. Therefore, we desire an approach that accounts for the excessive number of zero counts in disease mapping datasets, which are naturally present for low-prevalence diseases and are further innated when stratifying by age group. Bayesian modeling approaches are naturally suited to employ spatial and temporal smoothing to produce more stable estimates of age-adjusted rates for small areas. We propose a Bayesian hierarchical spatio-temporal hurdle model for counts and demonstrate how age-adjusted rates can be estimated from the hurdle model. We perform a simulation study to evaluate the performance of the proposed model vs a traditional Poisson model on datasets with varying characteristics. The approach is illustrated using two applications to cancer mortality at the county level.
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http://dx.doi.org/10.1002/sim.8948DOI Listing
March 2021

A fast and fully-automated deep-learning approach for accurate hemorrhage segmentation and volume quantification in non-contrast whole-head CT.

Sci Rep 2020 11 9;10(1):19389. Epub 2020 Nov 9.

Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.

This project aimed to develop and evaluate a fast and fully-automated deep-learning method applying convolutional neural networks with deep supervision (CNN-DS) for accurate hematoma segmentation and volume quantification in computed tomography (CT) scans. Non-contrast whole-head CT scans of 55 patients with hemorrhagic stroke were used. Individual scans were standardized to 64 axial slices of 128 × 128 voxels. Each voxel was annotated independently by experienced raters, generating a binary label of hematoma versus normal brain tissue based on majority voting. The dataset was split randomly into training (n = 45) and testing (n = 10) subsets. A CNN-DS model was built applying the training data and examined using the testing data. Performance of the CNN-DS solution was compared with three previously established methods. The CNN-DS achieved a Dice coefficient score of 0.84 ± 0.06 and recall of 0.83 ± 0.07, higher than patch-wise U-Net (< 0.76). CNN-DS average running time of 0.74 ± 0.07 s was faster than PItcHPERFeCT (> 1412 s) and slice-based U-Net (> 12 s). Comparable interrater agreement rates were observed between "method-human" vs. "human-human" (Cohen's kappa coefficients > 0.82). The fully automated CNN-DS approach demonstrated expert-level accuracy in fast segmentation and quantification of hematoma, substantially improving over previous methods. Further research is warranted to test the CNN-DS solution as a software tool in clinical settings for effective stroke management.
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http://dx.doi.org/10.1038/s41598-020-76459-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7652921PMC
November 2020

Finite-Element analysis of a lateral femoro-tibial impact on the total knee arthroplasty.

Comput Methods Programs Biomed 2020 Aug 12;192:105446. Epub 2020 Mar 12.

Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506, United States.

Background And Objective: Total knee arthroplasty (TKA) is a routine surgery performed to treat patients with severe knee osteoarthritis. The success of a TKA depends strongly on the initial stability of the prosthetic components and its long-term osseointegration due to the optimal distribution of mechanical stresses in the surrounding bones under the effect of the different biomechanical loads applied to the Femur-TKA-Tibia system. The purpose of this study is to analyze the level and the distribution of the induced stresses in a Femur-TKA-Tibia system subjected to combined triaxial forces, which mimic a femoral mechanical shock.

Methods: In this study, complex TKA system implanted in both femoral and tibial bones has been analyzed numerically with a three-dimensional finite-element method. A virtual model is designed to examine in silico the effect of the combined triaxial forces acting on this prosthesis in femoral region. Anatomical three-dimensional finite-element models of both femoral and tibial bones were constructed to calculate the interfacial stresses around the TKA components. The 3D finite-element processing program ABAQUS was used to perform the analysis.

Results: The stresses propagated in the bone regions adjacent to the TKA osseointegrated components, and the decreased in their magnitude to the outer region. These stresses reached the highest level in the cortical bone areas that are right next to the proximal upper attachment portions of the TKA osseointegrated components. The magnitude of the stresses in the tibial component is higher than that in the femoral component. Finally, it is very important to emphasize the role of the polyethylene articulating spacer in the shock absorption of bone support sections. Thus, this component should be preserved mechanically from the impact of high shocks in order to maintain healthy TKA systems.

Conclusions: Optimizing TKA model by controlling the biomechanical stresses distributed within its both components and supporting bones is a valid approach to achieving favorable long-term outcomes. The 3D finite-element analysis provides an effective pre-operative method for planning patient-specific TKA prostheses, and for designing future models that preserves the biomechanical function of the Femur-TKA-Tibia system.
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http://dx.doi.org/10.1016/j.cmpb.2020.105446DOI Listing
August 2020

Effect of MgO Addition on the Mechanical and Dynamic Properties of Zirconia Toughened Alumina (ZTA) Ceramics.

Materials (Basel) 2019 Jul 31;12(15). Epub 2019 Jul 31.

State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China.

Zirconia toughened alumina (ZTA) is a promising advanced ceramic material for a wide range of applications that are subjected to dynamic loading. Therefore, the investigation of dynamic compressive strength, fracture toughness and hardness is essential for ZTA ceramics. However, the relationship between these mechanical properties in ZTA has not yet been established. An example of this relationship is demonstrated using ZTA samples added with MgO prepared through conventional sintering. The microstructure and mechanical properties of ZTA composites were characterized. The hardness of ZTA composites increased for ≤0.7 wt.% MgO due to the pinning effect of MgO and decrease of the porosity in the microstructure. Oppositely, the fracture toughness of ZTA composites continuously decreased due to the size reduction of AlO grains. This is the main reason of deteriorate of dynamic compressive strength more than 0.2 wt.% of MgO addition. Therefore, the SHPB test shows the improvement of the dynamic compressive strength only up to a tiny amount (0.2 wt.% of MgO addition) into ZTA ceramics.
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http://dx.doi.org/10.3390/ma12152440DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6696285PMC
July 2019

Automation of CT-based haemorrhagic stroke assessment for improved clinical outcomes: study protocol and design.

BMJ Open 2018 04 19;8(4):e020260. Epub 2018 Apr 19.

Health Sciences and Innovation, Fraser Health Authority, Surrey, British Columbia, Canada.

Introduction: Haemorrhagic stroke is of significant healthcare concern due to its association with high mortality and lasting impact on the survivors' quality of life. Treatment decisions and clinical outcomes depend strongly on the size, spread and location of the haematoma. Non-contrast CT (NCCT) is the primary neuroimaging modality for haematoma assessment in haemorrhagic stroke diagnosis. Current procedures do not allow convenient NCCT-based haemorrhage volume calculation in clinical settings, while research-based approaches are yet to be tested for clinical utility; there is a demonstrated need for developing effective solutions. The project under review investigates the development of an automatic NCCT-based haematoma computation tool in support of accurate quantification of haematoma volumes.

Methods And Analysis: Several existing research methods for haematoma volume estimation are studied. Selected methods are tested using NCCT images of patients diagnosed with acute haemorrhagic stroke. For inter-rater and intrarater reliability evaluation, different raters will analyse haemorrhage volumes independently. The efficiency with respect to time of haematoma volume assessments will be examined to compare with the results from routine clinical evaluations and planimetry assessment that are known to be more accurate. The project will target the development of an enhanced solution by adapting existing methods and integrating machine learning algorithms. NCCT-based information of brain haemorrhage (eg, size, volume, location) and other relevant information (eg, age, sex, risk factor, comorbidities) will be used in relation to clinical outcomes with future project development. Validity and reliability of the solution will be examined for potential clinical utility.

Ethics And Dissemination: The project including procedures for deidentification of NCCT data has been ethically approved. The study involves secondary use of existing data and does not require new consent of participation. The team consists of clinical neuroimaging scientists, computing scientists and clinical professionals in neurology and neuroradiology and includes patient representatives. Research outputs will be disseminated following knowledge translation plans towards improving stroke patient care. Significant findings will be published in scientific journals. Anticipated deliverables include computer solutions for improved clinical assessment of haematoma using NCCT.
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http://dx.doi.org/10.1136/bmjopen-2017-020260DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5914893PMC
April 2018

Deploying digital health data to optimize influenza surveillance at national and local scales.

PLoS Comput Biol 2018 03 7;14(3):e1006020. Epub 2018 Mar 7.

Department of Biology, Georgetown University, Washington, DC, United States of America.

The surveillance of influenza activity is critical to early detection of epidemics and pandemics and the design of disease control strategies. Case reporting through a voluntary network of sentinel physicians is a commonly used method of passive surveillance for monitoring rates of influenza-like illness (ILI) worldwide. Despite its ubiquity, little attention has been given to the processes underlying the observation, collection, and spatial aggregation of sentinel surveillance data, and its subsequent effects on epidemiological understanding. We harnessed the high specificity of diagnosis codes in medical claims from a database that represented 2.5 billion visits from upwards of 120,000 United States healthcare providers each year. Among influenza seasons from 2002-2009 and the 2009 pandemic, we simulated limitations of sentinel surveillance systems such as low coverage and coarse spatial resolution, and performed Bayesian inference to probe the robustness of ecological inference and spatial prediction of disease burden. Our models suggest that a number of socio-environmental factors, in addition to local population interactions, state-specific health policies, as well as sampling effort may be responsible for the spatial patterns in U.S. sentinel ILI surveillance. In addition, we find that biases related to spatial aggregation were accentuated among areas with more heterogeneous disease risk, and sentinel systems designed with fixed reporting locations across seasons provided robust inference and prediction. With the growing availability of health-associated big data worldwide, our results suggest mechanisms for optimizing digital data streams to complement traditional surveillance in developed settings and enhance surveillance opportunities in developing countries.
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http://dx.doi.org/10.1371/journal.pcbi.1006020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858836PMC
March 2018

Spatial and Spatio-Temporal Models for Modeling Epidemiological Data with Excess Zeros.

Authors:
Ali Arab

Int J Environ Res Public Health 2015 Aug 28;12(9):10536-48. Epub 2015 Aug 28.

Department of Mathematics and Statistics, Georgetown University, 37th and O streets, Washington, DC 20057, USA.

Epidemiological data often include excess zeros. This is particularly the case for data on rare conditions, diseases that are not common in specific areas or specific time periods, and conditions and diseases that are hard to detect or on the rise. In this paper, we provide a review of methods for modeling data with excess zeros with focus on count data, namely hurdle and zero-inflated models, and discuss extensions of these models to data with spatial and spatio-temporal dependence structures. We consider a Bayesian hierarchical framework to implement spatial and spatio-temporal models for data with excess zeros. We further review current implementation methods and computational tools. Finally, we provide a case study on five-year counts of confirmed cases of Lyme disease in Illinois at the county level.
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http://dx.doi.org/10.3390/ijerph120910536DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586626PMC
August 2015

Characterizing Influenza surveillance systems performance: application of a Bayesian hierarchical statistical model to Hong Kong surveillance data.

BMC Public Health 2014 Aug 15;14:850. Epub 2014 Aug 15.

Department of Health Systems Administration, School of Nursing and Health Studies, Georgetown University, Washington, DC, USA.

Background: Infectious disease surveillance is a process the product of which reflects both actual disease trends and public awareness of the disease. Decisions made by patients, health care providers, and public health professionals about seeking and providing health care and about reporting cases to health authorities are all influenced by the information environment, which changes constantly. Biases are therefore imbedded in surveillance systems; these biases need to be characterized to provide better situational awareness for decision-making purposes. Our goal is to develop a statistical framework to characterize influenza surveillance systems, particularly their correlation with the information environment.

Methods: We identified Hong Kong influenza surveillance data systems covering healthcare providers, laboratories, daycare centers and residential care homes for the elderly. A Bayesian hierarchical statistical model was developed to examine the statistical relationships between the influenza surveillance data and the information environment represented by alerts from HealthMap and web queries from Google. Different models were fitted for non-pandemic and pandemic periods and model goodness-of-fit was assessed using common model selection procedures.

Results: Some surveillance systems - especially ad hoc systems developed in response to the pandemic flu outbreak - are more correlated with the information environment than others. General practitioner (percentage of influenza-like-illness related patient visits among all patient visits) and laboratory (percentage of specimen tested positive) seem to proportionally reflect the actual disease trends and are less representative of the information environment. Surveillance systems using influenza-specific code for reporting tend to reflect biases of both healthcare seekers and providers.

Conclusions: This study shows certain influenza surveillance systems are less correlated with the information environment than others, and therefore, might represent more reliable indicators of disease activity in future outbreaks. Although the patterns identified in this study might change in future outbreaks, the potential susceptibility of surveillance data is likely to persist in the future, and should be considered when interpreting surveillance data.
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http://dx.doi.org/10.1186/1471-2458-14-850DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4246552PMC
August 2014

A novel iron complex containing an N,O-type bidentate oxazoline ligand: Synthesis, X-ray studies, DFT calculations and catalytic activity.

Spectrochim Acta A Mol Biomol Spectrosc 2014 Dec 14;133:432-8. Epub 2014 Jun 14.

Chemistry Department, Iowa State University, Ames, IA 50011-3111, USA.

A five-coordinated Fe(III) complex with the distorted trigonal bipyramidal configuration was synthesized by reactions of FeCl3⋅6H2O and 2-(2'-hydroxyphenyl)oxazoline (Hphox) as a bidentate ON donor oxazoline ligand. Complex [Fe(phox)2Cl] was fully characterized, including by single-crystal X-ray structure analysis. DFT calculations were accompanied with experimental results in order to obtain a deeper insight into the electronic structure and vibrational normal modes of complex. Oxidation of sulfides to sulfoxides in one-step was conducted by this complex as catalyst using urea hydrogen peroxide (UHP) in mixture of CH2Cl2/CH3OH (1:1) under air at room temperature. The results show that using this system in oxidation of sulfides, sulfoxides are obtained as the main products, together with variable amounts of sulfones (≤13%), depending on the nature of the substrate.
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http://dx.doi.org/10.1016/j.saa.2014.06.012DOI Listing
December 2014

Modelling the effects of weather and climate on malaria distributions in West Africa.

Malar J 2014 Mar 28;13:126. Epub 2014 Mar 28.

Department of Mathematics and Statistics, Georgetown University, Washington, DC 20057, USA.

Background: Malaria is a leading cause of mortality worldwide. There is currently conflicting data and interpretation on how variability in climate factors affects the incidence of malaria. This study presents a hierarchical Bayesian modelling framework for the analysis of malaria versus climate factors in West Africa.

Methods: The hierarchical Bayesian framework takes into account spatiotemporal dependencies, and in this paper is applied to annual malaria and climate data from ten West African countries (Benin, Burkina Faso, Côte d'Ivoire, Gambia, Ghana, Liberia, Mali, Senegal, Sierra Leone, and Togo) during the period 1996-2006.

Results: Results show a statistically significant correspondence between malaria rates and the climate variables considered. The two most important climate factors are found to be average annual temperature and total annual precipitation, and they show negative association with malaria incidence.

Conclusions: This modelling framework provides a useful approach for studying the impact of climate variability on the spread of malaria and may help to resolve some conflicting interpretations in the literature.
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http://dx.doi.org/10.1186/1475-2875-13-126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3976358PMC
March 2014

Plant production and alternate prey channels impact the abundance of top predators.

Oecologia 2013 Oct 21;173(2):331-41. Epub 2013 Apr 21.

Mathematics and Statistics Department, Georgetown University, Washington, DC, 20057, USA,

While numerous studies have examined the effects of increased primary production on higher trophic levels, most studies have focused primarily on the grazing food web and have not considered the importance of alternate prey channels. This has happened despite the fact that fertilization not only increases grazing herbivore abundance, but other types of consumers such as detritivores that serve as alternate prey for generalist predators. Alternate prey channels can sustain generalist predators at times when prey abundance in the grazing food web is low, thus increasing predator densities and the potential for trophic cascades. Using arthropod data from a fertilization experiment, we constructed a hierarchical Bayesian model to examine the direct and indirect effects of plant production and alternate prey channels on predators in a salt marsh. We found that increased plant production positively affected the density of top predators via effects on lower trophic level herbivores and mesopredators. Additionally, while the abundance of algivores and detritivores positively affected mesopredators and top predators, respectively, the effects of alternate prey were relatively weak. Because previous studies in the same system have found that mesopredators and top predators rely on alternate prey such as algivores and detritivores, future studies should examine whether fertilization shifts patterns of prey use by predators from alternate channels to the grazing channel. Finally, the hierarchical Bayesian model used in this study provided a useful method for exploring trophic relationships in the salt marsh food web, especially where causal relationships among trophic groups were unknown.
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http://dx.doi.org/10.1007/s00442-013-2618-7DOI Listing
October 2013

Central ventilatory and cardiovascular actions of angiotensin peptides in trout.

Am J Physiol Regul Integr Comp Physiol 2012 Aug 13;303(3):R311-20. Epub 2012 Jun 13.

Laboratoire de Neurophysiologie, SFR ScInBioS, Faculté de Médecine et des Sciences de la Santé, Université Européenne de Bretagne, Université de Brest, INSERM UMR, CHU de Brest, France.

In the brains of teleosts, angiotensin II (ANG II), one of the main effector peptides of the renin-angiotensin system, is implicated in various physiological functions notably body fluid and electrolyte homeostasis and cardiovascular regulation, but nothing is known regarding the potential action of ANG II and other angiotensin derivatives on ventilation. Consequently, the goal of the present study was to determine possible ventilatory and cardiovascular effects of intracerebroventricular injection of picomole doses (5-100 pmol) of trout [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, ANG IV, and ANG 1-7 into the third ventricle of unanesthetized trout. The central actions of these peptides were also compared with their ventilatory and cardiovascular actions when injected peripherally. Finally, we examined the presence of [Asn(1)]-ANG II, [Asp(1)]-ANG II, ANG III, and ANG IV in the brain and plasma using radioimmunoassay coupled with high-performance liquid chromatography. After intracerebroventricular injection, [Asn(1)]-ANG II and [Asp(1)]-ANG II two ANG IIs, elevated the total ventilation through a selective stimulatory action on the ventilation amplitude. However, the hyperventilatory effect of [Asn(1)]-ANG II was threefold higher than the effect of [Asp(1)]-ANG II at the 50-pmol dose. ANG III, ANG IV, and ANG 1-7 were without effect. In addition, ANG IIs and ANG III increased dorsal aortic blood pressure (P(DA)) and heart rate (HR). After intra-arterial injections, none of the ANG II peptides affected the ventilation but [Asn(1)]-ANG II, [Asp(1)]-ANG II, and ANG III elevated P(DA) (50 pmol: +80%, +58% and +48%, respectively) without significant decrease in HR. In brain tissue, comparable amounts of [Asn(1)]-ANG II and [Asp(1)]-ANG II were detected (ca. 40 fmol/mg brain tissue), but ANG III was not detected, and the amount of ANG IV was about eightfold lower than the content of the ANG IIs. In plasma, ANG IIs were also the major angiotensins (ca. 110 fmol/ml plasma), while significant but lower amounts of ANG III and ANG IV were present in plasma. In conclusion, our study suggests that the two ANG II isoforms produced within the brain may act as a neurotransmitter and/or neuromodulator to regulate the cardioventilatory functions in trout. In the periphery, two ANG IIs and their COOH-terminal peptides may act as a circulating hormone preferentially involved in cardiovascular regulations.
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http://dx.doi.org/10.1152/ajpregu.00145.2012DOI Listing
August 2012

Exposure to polychlorinated biphenyls enhances lipid peroxidation in human normal peritoneal and adhesion fibroblasts: a potential role for myeloperoxidase.

Free Radic Biol Med 2010 Mar 11;48(6):845-50. Epub 2010 Jan 11.

Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, The C.S. Mott Center for Human Growth and Development, Wayne State University School of Medicine, Detroit, MI 48201, USA.

Nitric oxide, superoxide, and lipid peroxidation (LPO) produced under oxidative stress may contribute to the development of postoperative adhesions. The objective of this study was to determine the effects of polychlorinated biphenyls (PCBs) on LPO, superoxide dismutase, myeloperoxidase (MPO), and nitrite/nitrate in human normal peritoneal and adhesion fibroblasts. PCB treatment reduced inducible nitric oxide synthase (iNOS) expression as well as levels of nitrite/nitrate in both cell lines. Although there was no difference in iNOS expression between the two cell lines, adhesion fibroblasts manifested lower basal levels of MPO compared to normal peritoneal fibroblasts. There was a reduction in MPO expression and its activity in response to PCB treatment in normal peritoneal fibroblasts; however, this effect was minimal in adhesion fibroblasts. Moreover, adhesion fibroblasts manifested higher levels of LPO compared to normal peritoneal fibroblasts, whereas PCB treatment increased LPO levels in both cell types. We conclude that PCBs promote the development of the adhesion phenotype by generating an oxidative stress environment. This is evident by lower iNOS, MPO, and nitrite/nitrate and a simultaneous increase in LPO. Loss of MPO activity, possibly through a mechanism involving MPO heme depletion and free iron release, is yet another source of oxidative stress.
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http://dx.doi.org/10.1016/j.freeradbiomed.2010.01.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2834263PMC
March 2010

Restoration of oak forests in soils compacted by human and livestock.

Pak J Biol Sci 2007 May;10(9):1536-9

Department of Forestry, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Iran.

Soil in the oak forests of northern Iran is compacted by human and livestock whereas this problem is resulted to a defect in natural regeneration of tree species. This investigation aims to determine the suitable rehabilitation of these forests using seed sowing of oak in canopy densities of 25-30% (open canopy), 45-55% (semi-closed canopy) and 65-75% (relatively closed canopy). For this purpose, each canopy density specified within the plots of 1000 m2 was chosen in three replicates to plant oak acorn. The experiment was conducted as completely randomized design. The results in the first growing season indicted that seed germination rate as well as root length was greater in open canopy but no significant difference could be detected in terms of collar diameter, shoot growth, flush number and root/shoot ratio. The investigation reveals that for restoration of the soil-compacted oak stands, open canopies are better suited for seed sowing of oak.
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http://dx.doi.org/10.3923/pjbs.2007.1536.1539DOI Listing
May 2007

Effect of sowing depth on performance of Quercus castaneifolia seedling at different levels of canopy cover.

Pak J Biol Sci 2007 Apr;10(7):1020-7

Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran.

Due to failure of oak (Quercus castaneifolia C.A. Meyer) natural regeneration, investigation on the best acorn sowing depth of this species under different levels of canopy cover is an important consideration in the Caspian forests, north of Iran. For this purpose, a study site with north-facing slope, clay-loam soil and 260-280 m a.s.l. was chosen in a mixed oak forest. The experiment was conducted as a Complete Randomized Split Plot Design (CRSPD) and the measurements made in one growing season in nine fenced circular 1000 m2 plots with three canopy densities (25, 50 and 75%) at three soil depths (5, 10 and 15 cm). The results revealed that under all canopy densities the maximum seedling emergence occurred at 5 cm depth. The highest emergence rate was appeared in June and the lowest in October. Neither canopy density nor sowing depth did prominently reduce seedling establishment, but a high quotient of mortality likely could be attributed to rodent populations, particularly Hystrix indica. Under all canopies, ground line diameter decreased with increasing sowing depth, the biggest being at 5 cm depth. Neither canopy density nor sowing depth influenced the seedling height. It can be concluded that the best performance of Q. castaneifolia seedling occurs at 5 cm sowing depth and 25% canopy cover.
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http://dx.doi.org/10.3923/pjbs.2007.1020.1027DOI Listing
April 2007

Vitamin A deficiency among preschool children in a rural area of Egypt: the results of dietary assessment and biochemical assay.

Int J Food Sci Nutr 2002 Nov;53(6):465-74

National Research Center, Department of Nutrition, Giza-Dokki 12311, Egypt.

Vitamin A status was evaluated among a cohort of preschool children (mean age 43 months) pertinent to a traditional society in rural Egypt. The Helen Keller International food frequency questionnaire, the 7-day 24-h dietary recall method and serum vitamin A concentrations were the criteria used for the evaluation. Mean values of 280 and 382 retinol equivalents (RE) were the daily estimates of vitamin A intakes among male and female children, respectively. Animal foods made up 39 and 54% of the total vitamin A intake among male and female children, respectively. The aforementioned estimates of total vitamin A intakes were 58 and 81%, respectively, of the FAO/WHO requirements (35 RE/kg). Children from high socio-economic class had significantly higher (P < 0.05) mean vitamin A intake compared with the respective mean intake obtained with poor children. Serum vitamin A concentrations correlated significantly with the respective vitamin A intakes. A 10-week vitamin A intervention trial using either pharmaceutical vitamin A preparations or a food-based strategy consisting of carrot jam led to significant improvement in the growth velocity of the beneficiaries compared with the control group.
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http://dx.doi.org/10.1080/09637480220164325DOI Listing
November 2002