bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preliminary reconstructions of spring precipitation in southwestern Turkey from tree‐ring width
Authors: Touchan Ramzi , Garfin Gregg M. , Meko David M. , Funkhouser Gary , Erkan Nesat , Hughes Malcolm K. , Wallin Brian S. 
Published: January 2003

AbstractTwo reconstructions of spring (May–June) precipitation have been developed for southwestern Turkey. The first reconstruction (1776–1998) was developed from principal components of nine chronologies of Cedrus libani, Juniperus excelsa, Pinus brutia, and Pinus nigra. The second reconstruction (1339–1998) was derived from principal components of three J. excelsa chronologies. Calibration and verification statistics of both reconstructions indicate reasonably accurate reconstruction of spring precipitation for southwestern Turkey, and show clear evidence of multi‐year to decadal variations in spring precipitation. The longest period of reconstructed spring drought, defined as consecutive years with less than 80% of normal May–June precipitation, was 4 years (1476–79). Only one drought event of this duration has occurred during the last six centuries. Monte Carlo analysis indicates a less than 33% probability that southwestern Turkey has experienced spring drought longer than 5 years in the past 660 years. Apart from the 1476–79 extended dry period, spring droughts of 3 years in length have only occurred from 1700 to the present. The longest reconstructed wet period, defined as consecutive years with more than 120% of normal May–June precipitation, was 4 years (1532–35). The absence of extended spring drought during the 16th and 17th centuries and the occurrence of extended wet spring periods during these centuries suggest a possible regime shift in climate. Preliminary analysis of links between large‐scale climatic variation and these climate reconstructions shows that there is a relationship between extremes in spring precipitation and anomalous atmospheric circulation in the region. Copyright © 2003 Royal Meteorological Society.
Relationship between snow cover variability and Arctic oscillation index on a hierarchy of time scales
Authors: Bamzai A. S. 
Published: January 2003

AbstractBased on satellite‐derived global snow cover data on weekly time scales, the climatology and interannual variability of snow onset day‐of‐year, snowmelt day‐of‐year and number of snow‐free days in a year are presented. Trends for snow onset day‐of‐year, snowmelt day‐of‐year and number of snow‐free days in a year indicate that there has been an increase in number of snow‐free days in recent decades. The relationship between snow cover and the Arctic oscillation (AO) index is examined on a hierarchy of time scales using lagged correlation and composite analysis. On weekly time scales, composite snow extent anomalies are maximum when AO leads snow cover by 1 week. These composite differences are maintained several weeks thereafter, particularly in the negative phase of the AO. Maps of composite snow cover anomalies when AO leads snow cover by 1 week delineate the spatial structure of these snow anomalies. On monthly time scales, lead–lag correlation between monthly snow cover and AO index indicates that the AO index during January, February and March is significantly correlated with snow cover in concurrent and subsequent spring months, particularly over Eurasia. Finally, on seasonal time scales, it is shown that winter season AO and winter/spring season snow cover are significantly correlated. Copyright © 2003 Royal Meteorological Society.
Land under pressure: soil conservation concerns and opportunities for Ethiopia
Authors: Sonneveld B. G. J. S. , Keyzer M. A. 
Published: January 2003

AbstractThis paper evaluates the future impact of soil degradation on national food security and land occupation in Ethiopia. It applies a spatial optimization model that maximizes national agricultural revenues under alternative scenarios of soil conservation, land accessibility and technology. The constraints in the model determine whether people remain on their original site, migrate within their ethnically defined areas or are allowed a transregional migration. Key to this model is the combination of a water erosion model with a spatial yield function that gives an estimate of the agricultural yield in its geographical dependence of natural resources and population distribution. A comparison of simulated land productivity values with historical patterns shows that results are interpretable and yield more accurate outcomes than postulating straightforward reductions in yield or land area for each geographic entity. The results of the optimization model show that in absence of soil erosion control, the future agricultural production stagnates and results in distressing food shortages, while rural incomes drop dramatically below the poverty line. Soil conservation and migration support a slow growth, but do not suffice to meet the expected food demand. In a transregional migration scenario, the highly degraded areas are exchanged for less affected sites, whereas cultivation on already substantially degraded soils largely continues when resettlement is confined to the original ethnic–administrative entity. A shift to modern technology offers better prospects and moderates the migration, but soil conservation remains indispensable, especially in the long term. Finally, an accelerated growth of non‐agricultural sectors further alleviates poverty in the countryside, contributing to higher income levels of the total population and, simultaneously, relieving the pressure on the land through rural–urban migration. Copyright © 2002 John Wiley & Sons, Ltd.
An assessment of restoration of biodiversity in degraded high mountain grazing lands in northern Ethiopia
Authors: Asefa D. T. , Oba G. , Weladji R. B. , Colman J. E. 
Published: January 2003

AbstractLoss of biodiversity is the single most important threat to the conservation and sustainable use of drylands in northern Ethiopia due to many centuries of cultivation and heavy livestock grazing pressure. The current study assessed the restoration of biodiversity in highly degraded areas in eastern Tigray, northern Ethiopia using area enclosures (AEs). The study assessed whether the differences in biodiversity between AEs and open management schemes and time of land abandonment influenced diversity of plant life forms (i.e. herbs, shrubs and trees). Changes in biodiversity were compared using the state‐and‐transition model. Management types and time since abandonment (hereafter called age) had a significant effect on herbaceous plant species abundance but not in shrub species, while site factors had a greater effect on diversity of plant life forms in general. Herbaceous species richness increased with age of restoration, reaching a maximum after three years of rest and declined thereafter, most probably as a result of hay harvesting and replacement of annual species by perennial grass species. Tree species richness increased gradually with age of land abandonment up to the maximum age of eight years. Four vegetation states and seven possible transitions that could guide management were identified. The vegetation states differed in terms of diversity of herbs and tree species but not those of shrubs. Promotion of tree species states will require longer periods of rest, while promotion of herbaceous species richness will need shorter periods. The state‐and‐transitional model could, therefore, be used to guide future management by promoting vegetation states that are desired by land users. Copyright © 2002 John Wiley & Sons, Ltd.
Effects of Newbouldia laevis on soil subjected to shifting cultivation in the Ibadan area, southwestern Nigeria
Authors: Aweto A. O. , Iyanda A. O. 
Published: January 2003

AbstractNewbouldia laevis is the most abundant tree in shifting cultivation farms in the Ibadan area of southwestern Nigeria, where shifting cultivation is undergoing intensification. The physical and chemical properties of the soil under and outside the canopies of N. laevis were compared in order to evaluate the effects of the tree on the soil. Thirty Newbouldia trees were studied in 10 plots that measured 25 × 25 m. There was no significant increase in organic matter, total nitrogen, exchangeable calcium, magnesium, potassium and cation exchange capacity and extractable manganese, iron, and zinc in the 0–10 cm layer of soil under the canopy compared to the soil outside the canopy. The minimal accretion of organic matter and nutrients in the soil under the canopy is mainly attributable to site burning prior to cultivation (which destroys plant litter) and to the prolonged cultivation of the farms. Available phosphorus, however, was significantly higher in the soil under the canopy of trees. This is presumably due to the mobilization of inorganic phosphorus from the subsoil and its subsequent recycling to the topsoil by the trees. Soil physical status was improved under the canopy. Soil bulk density was lower and total porosity higher under the canopy due the effects of the concentration of plant roots near the stem of the trees. Copyright © 2002 John Wiley & Sons, Ltd.
Scale‐dependent effects of grazing on rangeland degradation in northern Kenya: a test of equilibrium and non‐equilibrium hypotheses
Authors: Oba G. , Weladji R. B. , Lusigi W. J. , Stenseth N. C. 
Published: January 2003

AbstractThis study employs scale‐dependence as an analytical approach to understanding effects of livestock grazing on rangeland degradation in northern Kenya. It used extensive datasets previously collected from 13 200 km2 rangelands where grazing pressure gradients of livestock (varied from none, light, moderate, heavy and very heavy grazing) in conjunction with seasonality across different ecological scales influenced plant responses and probably contributed to land degradation. The data representing spatial and temporal scales were used to test the equilibrium and non‐equilibrium‐grazing models and to verify scales at which the models appropriately described range degradation. The equilibrium‐grazing models operated at the coarse scales (e.g. range units, km2) and non‐equilibrium‐grazing models at multiple scales (e.g. spatial, temporal and fine scales—plots, landscape patches). The study showed that the equilibrium‐grazing hypothesis, which stated that responses of plant species richness, cover and biomass varied along grazing pressure gradients at the coarse scale, was rejected, while the non‐equilibrium‐grazing hypothesis, which stated that the factors responded to temporal and spatial scales combined with grazing pressure gradients at the fine scale, was accepted. This study emphasized that in future discussions on shifts in the thinking of range science from equilibrium‐ to non‐equilibrium‐grazing models should clarify scales at which land degradation is assessed. In conclusion, the paper suggests that understanding plant species responses to grazing pressure and seasonality needs to consider multiple scale effects and that the dogmatic notions about degradation of the arid zone rangelands at the coarse scales should be reconsidered. Land degradation assessments in the arid zones should focus at the fine scale. Copyright © 2002 John Wiley & Sons, Ltd.
Causes, consequences and control of wind erosion in Sahelian Africa: a review
Authors: Sterk G. 
Published: January 2003

AbstractSahelian Africa is one of the poorest regions of the world, where approximately 90 per cent of the population depends on subsistence agriculture. Due to the high population growth, with annual growth rates of about 3 per cent during recent decades, farmers have expanded their cropping areas to increase production. At the same time the traditional bush fallow system collapsed and more land became subject to soil degradation processes. Wind erosion is one of the main degradation processes that has received much scientific attention since the 1980s. The objective of this paper is to review the latest research results on wind‐erosion causes, consequences, perceptions and control in the Sahel. First the main processes involved in wind erosion (creep, saltation and suspension) are described and related to the Sahelian climate, soils and farming systems. Then the agricultural consequences of wind erosion are evaluated. Three types of damage are distinguished: undesired sedimentation, crop damage and soil degradation. Several studies were done to determine farmers knowledge and perceptions of wind erosion. In general the Sahelian farmers have a good qualitative understanding of wind‐erosion processes, and they are concerned about the consequences, especially about crop damage and soil productivity decline. Finally, the possibilities and constraints for wind‐erosion control are evaluated. The most widely applied control measure is mulching with crop residues, but the quantity of residue is insufficient due to low biomass yields and multiple uses. It is concluded that regeneration and exploitation of natural, scattered vegetation is a promising control strategy that needs more research. Copyright © 2002 John Wiley & Sons, Ltd.
Molecular determinants of tumor differentiation in papillary serous ovarian carcinoma
Authors: Jazaeri Amir A. , Lu Karen , Schmandt Rosemarie , Harris Charles P. , Rao Pulivarthi H. , Sotiriou Christos , Chandramouli G. V. R. , Gershenson David M. , Liu Edison T. 
Published: January 2003

AbstractIn epithelial ovarian cancer, tumor grade is an independent prognosticator whose molecular determinants remain unknown. We investigated patterns of gene expression in well‐ and poorly differentiated serous papillary ovarian and peritoneal carcinomas with cDNA microarrays. A 6500‐feature cDNA microarray was used for comparison of the molecular profiles of eight grade III and four grade I stage III serous papillary adenocarcinomas. With a modified F‐test in conjunction with random permutations, 99 genes whose expression was significantly different between grade I and grade III tumors were identified (P < 0.01). A disproportionate number of these differentially expressed genes were located on the chromosomal regions 20q13 and all exhibited higher expression in grade III tumors. Interphase fluorescent in situ hybridization demonstrated 20q13 amplification in two of the four grade III and none of the three grade I tumors available for evaluation. Several centrosome‐related genes also showed higher expression in grade III tumors. We propose a model in which tumor differentiation is inversely correlated with the overexpression of several oncogenes located on 20q13, a common amplicon in ovarian and numerous other cancers. Dysregulation of centrosome function is one potential mechanistic link between genetic/epigenetic changes and the poorly differentiated phenotype in ovarian cancer. Published 2003 Wiley‐Liss, Inc.
Alterations in the Fhit gene in pancreatic duct adenocarcinomas induced by N‐nitrosobis(2‐oxopropyl)amine in hamsters
Authors: Tsujiuchi Toshifumi , Sasaki Yasutaka , Kubozoe Tadahiko , Konishi Yoichi , Tsutsumi Masahiro 
Published: January 2003

AbstractAlteration of the Fhit gene was investigated in pancreatic duct adenocarcinomas induced by N‐nitrosobis(2‐oxopropyl)amine (BOP) in Syrian golden hamsters. The animals received 70 mg/kg BOP, followed by repeated exposure to an augmentation pressure regimen consisting of a choline‐deficient diet combined with DL‐ethionine and then L‐methionine and administration of 20 mg/kg BOP. A total of 15 pancreatic duct adenocarcinomas were obtained 10 wk after the beginning of the experiment, and total RNAs were extracted from each for assessment of aberrant transcription of the Fhit gene by reverse transcription–polymerase chain reaction analysis. Aberrant transcripts lacking nucleotides in the regions of nt −75 to 348, nt −15 to 348, or nt −75 to 178 were detected in 11 adenocarcinomas (73.3%). Southern blot analysis of eight tumors did not show any evidence of gross rearrangement or deletion. These results indicated that changes in the Fhit gene occurred frequently and thus may have played a role in the development of pancreatic duct adenocarcinomas induced by BOP in hamsters. © 2003 Wiley‐Liss, Inc.
On the nature of genetic changes required for the development of esophageal cancer
Authors: Uys Pieter , van Helden Paul D. 
Published: January 2003

AbstractIt is clear that genetic mutations are necessary for the development of cancer, but the exact number required is not clear, with estimates ranging from one critical hit (e.g., p53) to dozens or perhaps even hundreds of expression changes (by microarray analysis) or chromosomal aberrations. We have used a mathematical model to estimate the critical number of mutations required for the development of esophageal cancer (EC) and to test for the likelihood of an EC major susceptibility gene. Our results suggest that six or seven mutations are required for the development of EC and that there is no evidence of a major susceptibility gene. This does not exclude the possibility that gene‐environment interactions may not confer susceptibility or risk. The gradual accumulation of aberrant gene function also can explain the progression of pathologic states seen in the esophagus, from early dysplasia through mild to severe dysplasia and, finally, to cancer, as illustrated in our model. © 2003 Wiley‐Liss, Inc.
The expression of the tumor suppressor gene connexin 26 is not mediated by methylation in human esophageal cancer cells
Authors: Loncarek Jadranka , Yamasaki Hiroshi , Levillain Pierre , Milinkevitch Serge , Mesnil Marc 
Published: January 2003

AbstractGap junctional intercellular communication is thought to play an important role in cell differentiation and tissue homeostasis. Gap junctional intercellular communication is mediated by intercellular channels connecting adjacent cells and composed of connexin (Cx) proteins. Until now, approximately 20 different Cx have been characterized in mammals, and they are expressed in a tissue‐specific manner. The downregulation of Cx expression is often observed in tumors and transformed cell lines and is believed to contribute to the loss of proliferating control. Connexin 26 (Cx26) is a Cx constitutively expressed in the normal epithelial esophageal tissue. In the majority of esophageal tumors, Cx26 expression is low or totally absent. CpG island hypermethylation is known to be associated with gene silencing in cancer. Because the promoter and exon 1 region of Cx26 are rich in CpG dinucleotides, we examined whether the loss of Cx26 expression in human esophageal TE cell lines was related to the hypermethylation of this region. We analyzed several TE cell lines derived from different human esophageal carcinomas and exhibiting different levels of Cx26 expression by using methylation‐sensitive restriction digestion and Southern blot analysis. We did not find any correlation between the Cx26 expression and the methylation level of the promoter region of the Cx26 gene. Our results suggest that methylation was probably not involved as a primary mechanism of Cx26 regulation in human esophageal cancer cell lines. © 2003 Wiley‐Liss, Inc.
Design of “Smart” polymers that can ­direct intracellular drug delivery
Authors: Hoffman Allan S. , Stayton Patrick S. , Press Oliver , Murthy Niren , Lackey Chantal A. , Cheung Charles , Black Fiona , Campbell Jean , Fausto Nelson , Kyriakides Themis R. , Bornstein Paul 
Published: January 2003

AbstractOne of the important characteristics of biological systems is their ability to change important properties in response to small environmental signals. The molecular mechanisms that biological molecules utilize to sense and respond provide interesting models for the development of “smart” polymeric biomaterials with biomimetic properties. An important example of this is the protein coat of viruses, which contains peptide units that facilitate the trafficking of the virus into the cell via endocytosis, followed by delivery of the genetic material out of the endosome into the cytoplasm, and from there into the nucleus. We have designed several new types of synthetic polymers to facilitate intracellular trafficking of drugs. One of these has been designed to mimic the specific peptides on viral coats that facilitate endosomal escape. Another has been designed to contain pH‐degradable bonds, facilitating endosomal escape of the drug only after the bonds are degraded at the acidic pHs of the endosomes. Both types of polymer are responsive to the lowered pH within endosomes, leading to disruption of the endosomal membrane and release of important biomolecular drugs such as DNA, RNA, peptides and proteins to the cytoplasm before they are trafficked to lysosomes and degraded by lysosomal enzymes. In this article, we review our work on the design, synthesis and action of such smart, pH‐sensitive polymers. Copyright © 2003 John Wiley & Sons, Ltd.
Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties
Authors: Breitenbach A. , Jung T. , Kamm W. , Kissel T. 
Published: January 2003

AbstractA major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three‐dimensional architecture, increased hydrophilicity of poly(lactic‐co‐glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2‐sulfobutyl‐vinyl alcohol) and poly(diethylaminoethyl‐vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge‐containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three‐dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core–corona‐like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged‐groups‐containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic–hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley & Sons, Ltd.