881 resultados para comparative studies
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The electronic and magnetic structures of Nd2Fe17 and Nd2Fe17N3 have been calculated using the first-principle, spin-polarized orthogonalized linear combination of atomic orbitals method. Comparative studies of the two materials reveal important effects of the nitrogen atoms (at 9e site) on the electronic and magnetic structures. Results are presented for the total density of states, site-projected partial density of states and the spin magnetic moments on four nonequivalent Fe sites. The highest magnetic moments are found to be located on the 6c site for Nd2Fe17 and on the 9d site for Nd2Fe17N3, in agreement with the neutron and Mossbauer experiments. The variation trends of the magnetic moments on different Fe sites are discussed in terms of the separation between Fe and N atoms. Compared with Nd2Fe17, an increase in the exchange splitting of the Fe d band is found in Nd2Fe17N3, which accounts for its higher Curie temperature as observed in experiments. The calculated results show that the nitrogen atoms are charge acceptors in these compounds.
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在青藏高原东部的亚高山针叶林区,如何尽快恢复这一生态脆弱地区的植被,改变生态环境恶化的趋势,是一个十分重要的课题。光一直被认为是植物种间相互替代,尤其是森林演替过程中植物相互替代或植被恢复中的关键环境要素之一。植物能否适应林冠下或林窗中异质的、或多变的光照条件,对其在林中的生存、分布、更新以及森林动态都是非常重要的。 本文以青藏高原东部亚高山针叶林的主要森林类型——岷江冷杉林群落的几种树苗为研究对象,采用实验生态学、生理及生物化学等方法,通过模拟针叶林不同大小林窗内光照强度的变化,在中国科学院茂县生态站内采用遮荫处理设置6个光照梯度(100、55、40、25、15与7%全光照),来研究具有不同喜光特性的植物对光强的响应与适应机制,其研究结果可为揭示亚高山针叶林的演替规律、以及人工林下幼苗的存活与定居提供科学依据,也能为苗木的生产与管理提供科学指导,尤其是对针阔树种在不同光强下的响应与适应的比较研究,能为如何将阔叶树种整合到人工针叶林中提供新的思路。 光强对植物生长的影响 光强对植物的生长具有重要作用,不同植物在各自适宜的光强梯度下才能生长良好。通过一个野外盆栽实验,来研究不同光强对植物生长的影响(第三章)。主要研究结果如下,低光强下植物株高/茎生物量增加,说明植物会将生物量更多用于高生长,以便有效地拦截光资源;在强光下,植物将生物量更多地向根部分配,使得植物在强光下能够吸收更多的水分,而避免干旱胁迫。 在第一个生长季节,以相对生长速率(RGR)表示,红桦和青榨槭在100%全光照下RGR最大,粗枝云杉在55%最大,岷江冷杉在25-40%下较好;然而,在第二个生长季节,2种阔叶树的相对生长速率(RGR)的适宜光强则变为25-55%,云杉为55-100%,而冷杉为25-100%。可见,从第一年到第二年,2种阔叶树苗更适宜在部分荫蔽的条件下生长;而2种针叶树苗对光的需求则逐渐增加,这可能是增加对根生物量相对投资的结果,因为以这种方式,强光下生长的针叶树幼苗更能保持其内部水分平衡,其生长不会因干旱胁迫而受到严重影响。另外,严重遮荫会引起冷杉幼苗死亡。 植物对光强的生理适应 植物可以通过自身形态和生理特征的调整,来发展不同的光能利用策略从而能够在林中共存。通过一个野外盆栽实验,研究了不同光强下生长的几种树苗的生理特征(第四章)对不同光强的响应与适应。结果显示:强光下,粗枝云杉和红桦的光合能力增加,而岷江冷杉和青榨槭在中度遮荫(25-55%)的条件下光合能力最大。植物叶氮和叶绿素含量增高,而光补偿点和暗呼吸速率降低,这些都是植物对低光环境的适应性反应;而强光下植物叶片和栅栏组织变厚,是对强光的一种保护性反应。 植物对光的可塑性反应 不同植物会表现出对光适应有利的生理和形态可塑性反应。本文对第三章、第四章的实验数据进行可塑性指数分析,来研究植物对光强的表型可塑性反应(第五章)。结果显示,生理特征调整是植物对不同光环境的主要适应途径。红桦和青榨槭的可塑性指数平均值要大于粗枝云杉和岷江冷杉,充分表明这2种阔叶树在生理和形态上较强的可塑性更有利于对光环境的适应,而具有比耐荫树种更强的适应能力。另外,2种针叶树相比,云杉的适应性更强。本研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。 植物的光抑制与防御 当植物叶片吸收了过多光能,会发生光抑制现象。植物对光抑制的敏感性及防御能力对其生长具有重要意义。本文通过两个野外盆栽实验,研究了生长在强光下(第六章)和变化光强下(第八章)植物的光抑制现象及其防御策略。结果表明,在强光下或从遮荫状态转入强光下,植物都会发生光抑制,其对光抑制的敏感性与植物的耐荫性(或喜光)和演替状态有密切联系。长期生长在强光下的植物受到光抑制是可恢复的,而当处于荫蔽环境的植物突然暴露于强光下时,受到的光抑制不能完全恢复,可能是(部分)光合机构受到破坏的缘故。粗枝云杉和青榨槭防御光抑制伤害的能力较强,热耗散是其防御光抑制的主要途径。长期的强光作用能使岷江冷杉和红桦发生严重光抑制,甚至光伤害,而红桦能够通过“凋落老叶,萌发新叶”的途径来适应新的强光环境。 How to restore the vegetation of subalpine coniferous forest in eastern Qinghai-Tibet Plateau, and change the trend of ecological deterioration is a very important issue. Acclimation of tree seedlings to different and varing light environment affects to a great extent the successful regeneration and establishment of subalpine coniferous forests in southwestern China’s montane forest areas, because the ability to respond to such changing resource are commonly assumed to be critical to plant success, and have a growth advantage than others. In this paper, several species seedlings in Abies faxoniana community were chosed to study the response and adaptation to light intensity and the interspecific differences of adaptability in six shaded sheds (100, 55, 40, 25, 15 and 7% of full sunlight) in the Maoxian Ecological Station of Chinese Academy of Sciences. Our results could provide a strong theoretical evidence for understanding the forest succession laws of subalpine coniferous forests, and the survival and settlement of seedlings under plantations, and provide scientific direction for the production and management of seedlings, especially the comparative studies of the acclimation to light between the conifer and broadleaf trees could provide new ideas for how to integrate the broad-leaved trees into the artificial coniferous forest. Growth under different light intensity Light intensity plays an important role on plant growth. One field experiments was conducted to study the growth of tree seedlings of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii under different light intensities. The results showed that plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources, while biomass greater allocation to the roots, could make plants under high light environment absorb more water, and avoid drought stress. During the first growing season, the relative growth rates (RGRs) of Betula albo-sinensis and Acer davidii had the greatest values under the 100% of full light, for 55% of Picea asperata, and for 25-40% of Abies faxoniana. However, in the second growing season the the relative growth rates of the two broad-leaved trees changed and were appropriate for 25-55% of full light, for 55-100% of spruce, and for 25-100% of fir. Thus, from the first year to the second year, two broad-leaved seedlings maybe more suitable to partly shading environment, and two coniferous seedlings would have an increase in light demand, which may be an increased root biomass investment. Because in this way, seedlings grown under high light could better maintain their internal water balance, and thus its growth would not be seriously affected by drought stress. In addition, serious shading would cause fir seedlings to die. Acclimation of physiology to light Plants could coexist in forest ecosystem by forming different strategies of light use. One field experiments was conducted to study the acclimation of tree seedlings to different light intensity of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii. The results showed that the photosynthetic capacity of Picea asperata and Betula albo-sinensis exhibited a general tendency of increase with more light availability; but for Abies faxoniana and Acer davidii seedlings, their highest values of the same parameters were found under intermediate light regime (i.e. 25-55% of PFD relative to full sunlight). Plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources. Leaf nitrogen and chlorophyll content increased, while dark respiration rate and light compensation points decreased, all of which were adaptive response to the low light environment. On the contrary, plants under high light environment had the thicken leaves and palisade tissue, which was a protective response to high light. Phenotypic plasticity to light Phenotypic plasticity can be exhibited in morphological and physiological processes. Physiological characteristical adjustment is the main for plant adaptation to different light environment.The means of plasticity indexes for Betula albo-sinensis and Acer davidii seelings were greater than Picea asperata and Abies faxoniana, amplied that the two broad-leaved trees were much more adaptable to the environment. In addition, spruce had the higher adaptablity than fir. The findings supported the hypothesis that the ecological characteristics of the species determined the biological status and its biological habitat selection. Photoinhibition and photoprotection to light Compared with conifer, broad-leaved trees could better change leaf morphology and adjust biomass allocation to adapt to changing light environment. However, excess light can photoinhibit photosynthesis and may lead to photooxidative destruction of the photosynthetic appatus. Two field experiments were conducted to study the photoinhibition of photosynthesis. The results showed that when plants grown under high light environment or plants transferred from low to high irradiance, the four tree seedlings would undergo a period of photoinhibition. In four species, photoinhibited leaves could recover to initial photosynthetic rates when they were long-term planted under high light environment. However, when plants were suddenly exposed to high irradiance, this photoinhibition could not be reversible, may be the photosynthesis apparatus were (or partly) photooxidatively destructed.
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Post-steam-treatment is a facile and effective method for improving the catalytic performances of Mo/HZSM-5 catalysts in methane dehydroaromatization under nonoxidative conditions. The treatment can enhance the stability of the catalyst and also give a higher methane conversion and a higher yield of light aromatics, as well as a decrease in the formation rate of carbonaceous deposits. (27)Al, (29)Si, and (1)H multinuclear magic angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy, and thermogravimetric analysis measurements as well as catalytic reaction evaluations were employed to conduct comparative studies on the properties of the catalysts before and after the post-steam-treatment. The results revealed that the number of free Bronsted acid sites per unit cell decreased, while more Mo species migrated into the HZSM-5 channels for the 6Mo/HZSM-5 catalysts after the post-steam-treatment. In addition, the average pore diameter was also larger for the post-steam-treated catalysts, and this was advantageous for mass transport of the reaction products. However, a severe post-steam-treatment, i.e., with longer treating time, of the 6Mo/HZSM-5 catalyst will lead to the formation of the Al(2)(MoO(4))(3) phases, which is detrimental to the reaction.
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It is more and more acknowledged that land-use/cover dynamic change has become a key subject urgently to be dealt with in the study of global environmental change. Supported by the Landsat TM digital images, spatial patterns and temporal variation of land-use change during 1995 -2000 are studied in the paper. According to the land-use dynamic degree model, supported by the 1km GRID data of land-use change and the comprehensive characters of physical, economic and social features, a dynamic regionalization of land-use change is designed to disclose the spatial pattern of land-use change processes. Generally speaking, in the traditional agricultural zones, e.g., Huang-Huai-Hai Plains, Yangtze River Delta and Sichuan Basin, the built-up and residential areas occupy a great proportion of arable land, and in the interlock area of farming and pasturing of northern China and the oases agricultural zones, the reclamation I of arable land is conspicuously driven by changes of production conditions, economic benefits and climatic conditions. The implementation of "returning arable land into woodland or grassland" policies has won initial success in some areas, but it is too early to say that the trend of deforestation has been effectively reversed across China. In this paper, the division of dynamic regionalization of land-use change is designed, for the sake of revealing the temporal and spatial features of land-use change and laying the foundation for the study of regional scale land-use changes. Moreover, an integrated study, including studies of spatial pattern and temporal process of land-use change, is carried out in this paper, which is an interesting try on the comparative studies of spatial pattern on change process and the change process of spatial pattern of land-use change.
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In order to gain an understanding of the diversity and distribution of antimicrobial-resistant bacteria and their resistance genes in maricultural environments, multidrug-resistant bacteria were screened for the rearing waters from a mariculture farm of China. Both abalone Haliotis discus hannai and turbot Scophthalmus maximus rearing waters were populated with abundant chloramphenicol-resistant bacteria. These bacteria were also multidrug resistant, with Vibrio splendidus and Vibrio tasmaniensis being the most predominant species. The chloramphenicol-resistance gene cat II, cat IV or floR could be detected in most of the multidrug-resistant isolates, and the oxytetracycline-resistance gene tet(B), tet(D), tet(E) or tet(M) could also be detected for most of the isolates. Coexistence of chloramphenicol- and oxytetracycline-resistance genes partially explains the molecular mechanism of multidrug resistance in the studied maricultural environments. Comparative studies with different antimicrobial agents as the starting isolation reagents may help detect a wider diversity of the antimicrobial-resistant bacteria and their resistance genes. (C) 2009 Elsevier Ltd. All rights reserved.
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由于局部养殖环境质量恶化和病害频发的困扰,严重影响了我国扇贝养殖产量、质量和出口创汇。针对扇贝养殖面临产品质量不高等问题,系统评估我国扇贝产品质量十分必要。本文以我国北方海域海湾扇贝Argopecten irradians和栉孔扇贝Chlamys farreri为研究对象,较为系统地研究了大连湾、秦皇岛、莱州湾、烟台、威海、胶州湾、胶南等七海域扇贝质量,包括营养品质、重金属富集、麻痹性贝毒污染三个方面。 研究结果表明,栉孔扇贝的蛋白质营养优于海湾扇贝,而脂类营养则低于海湾扇贝,海湾扇贝在不同海域的主成分分析可以看出,地理位置接近的海域营养状况比较相似,各海域的综合营养品质依次为:莱州湾>烟台>大连湾>秦皇岛>威海>胶州湾>胶南; 重金属含量存在组织差异性,贝边的含量总是高于贝柱,取自同一海域的栉孔扇贝的重金属含量高于海湾扇贝,六种重金属的平均含量排序为:Zn>Cu>Cd>As>Pb>Hg,部分海域扇贝Cd和Zn有超标现象,两种重金属分别超标1.41~17.28倍和1.24~1.59倍,Hg、Pb、As和Cu均未超标; 用小白鼠生物测试法对扇贝内脏团、贝柱和其他组织的贝毒含量进行测定,结果仅在秦皇岛和大连湾海湾扇贝的内脏团中检测出麻痹性贝毒,其毒力分别为2.17 Mu•g -1和2.48 Mu•g -1,未超过食用安全标准(4 Mu•g -1),其他海域的样品均未检测到麻痹性贝毒的存在。
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Different one-dimensional nanostructured polyanilines were synthesized in sulfuric acid solutions by conventional polymerization, interfacial polymerization and direct mixed reaction, respectively. The products were characterized with SEM, UV-vis and FTIR and the anticorrosion performance of products on mild steel were studied using electrochemical measurement in 3.5% NaCl aqueous solution. Results showed that the polyaniline nanofibers synthesized by direct mixed reaction have uniform morphology with diameters of 60-100 nm and more excellent protective properties than conventional aggregated polyaniline. Comparative studies revealed that the nanostructure and morphology of polyaniline could influence its anticorrosion performance. (C) 2010 Elsevier B.V. All rights reserved.
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In this study we examined samples of sandy sediments along the north-south transects crossing the Taklimakan Desert, the Badain Jaran Desert and the Hunshandake Sandy Land respectively. The grain size was measured via dry sieving, and the carbonate content by means of an Eijkelkamp instrument. The analyses of grain size and carbonate contents show: (1) The sand grains of the Badain Jaran Desert are coarsest and best sorted, this should be associated with the strongest usual wind among these three regions. (2) The different desert have its special wind condition in their own regions. The Badain Jaran Desert and the Taklimakan Desert both show that the wind is getting weaker from north towards south, but the Hunshandake Sandy Land have the similar wind stress from north towards south. (3) The frequency curves of the sandy sediments from the Badain Jaran Desert show a kind of distinct double peaks, presumably associated with the alternative transportations of summer and winter monsoons in the north boundaries of the summer monsoon. (4) There are great differences of the carbonate contents among these three regions, this maybe associated with the humidity, the humidity of Hunshandake Sandy Land is the best, and the one of the Taklimakan Desert would be the worst among them. Analyses of The three profiles about grain size and carbonate contents show: (1) From 8ka BP, the winter-monsoon was getting weaker, and the summer-monsoon accordingly became stronger, and about 1 ka later, the winter-monsoon was getting stronger again. (2) In the stage of the profiles, there maybe show two circles of dry and wet climate, and the climate changes in those three regions show the similar trend.
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K. Rasmani and Q. Shen. Subsethood-based fuzzy modelling and classification. Proceedings of the 2004 UK Workshop on Computational Intelligence, pages 181-188.
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The author of the article attempts to present the situation of comparative studies as a field of research and a way of thinking about the contemporary world on the basis of the analyses presented in Comparative Literature at a Crossroads? in the monographic issue of “Comparative Studies” 2006. Much attention is paid to the phenomenon of the crisis of comparative studies connected with a noticeable reluctance towards great theoretical models shared by many researchers, the extensiveness of the topic area and resulting methodological problems but also the fact that comparatists abandon the studies of other languages. This results in a need of searching for a satisfactory definition of this field of study, its scope of research and applicable research methods. Among the specific issues raised in the article there is, e.g. the case of world literature seen in the context of the classical contradiction between cultural hegemony and cultural pluralism. Moreover, an interesting review of the picture of the Polish culture from the perspective of postcolonial theories and intracultural differences is presented.
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Wydział Neofilologii: Instytut Filologii Germańskiej
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For the past fifty years, the interest in issues beyond pure philology has been a watchword in comparative literary studies. Comparative studies, which by default employ a variety of methods, run the major risk – as the experience of American comparative literature shows – of descending into dangerous ‘everythingism’ or losing its identity. However, it performs well when literature remains one of the segments of comparison. In such instances, it proves efficacious in exploring the ‘correspondences of arts’, the problems of identity and multiculturalism as well as contributes to the research into the transfer of ideas. Hence, it delves into phenomena which exist on the borderlines of literature, fine arts and other fields of humanities, employing strategies of interpretation which are typical for each of those fields. This means that in the process there emerges a “borderline methodology”, whose distinctive feature is heterogeneity of conducting research. This, in turn, requires the scholar to be both ingenious and creative while selecting topics as well as to possess competence in literary studies and the related field.
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http://www.archive.org/details/christversuskris014648mbp
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Background: Deliberate self-harm (DSH) is common among adolescents in Ireland and internationally. Psychological factors, negative life events and lifestyle factors have been found to be associated with self-harm in this group. However, large scale population-based studies of adolescent selfharm and its correlates have been lacking, and internationally a standardised methodology was needed to facilitate comparative studies. The focus on vulnerability which has been prevalent in this field has meant that research has failed to examine resilient adaptation among at-risk adolescents. Method: Data were obtained from a cross-sectional school-based study conducted in Ireland and in each of the six other centres which participated in the Child and Adolescent Self-harm in Europe (CASE) study. In Ireland, 3,881 adolescents in 39 schools in completing the anonymous questionnaire, while across all 7 centres, over 30,000 young people participated. Data were gathered on health and lifestyle, self-harm thoughts and behaviour, a wide range of life events, psychological characteristics (anxiety and depressive symptoms, self-esteem, impulsivity and coping style), and support available to young people. Results: This thesis reports the findings of the Irish CASE centre as well as one international study. The factors associated with DSH among Irish adolescents differed by gender, but among both genders drug use and knowing a friend who had engaged in self-harm were associated with DSH. Among Irish boys, strong associations were found between bullying and poor mental health and DSH. Among boys who had been bullied, psychological and school factors were associated with DSH, while family support was protective. Links between stressful life events, psychological characteristics and DSH within the international CASE sample were examined. Increased history of self-harm thoughts and acts was associated with greater depression, anxiety and impulsivity, lower self esteem and an increased prevalence of ten different negative life events, supporting the hypothesis of a “dose-response” relationship between these risk factors and the self-harm process. Associations between coping style, mental health factors (depressive symptoms, anxiety and self-esteem) and self-harm were examined among Irish adolescents. Emotion-oriented coping was strongly associated with poorer mental health and self-harm thoughts and acts. A mediating effect of emotion-oriented coping on associations between mental health factors and DSH was found for both genders and between problem-oriented coping and mental health factors for girls. Similar mediating effects of coping style were found when risk of self-harm thoughts was examined. Resilient adaptation among adolescents exposed to suicidal behaviour of others was examined. Self-harm thoughts were common in these adolescents. Among those exposed to suicidal behaviour of others, vulnerability factors were drug use and higher levels of anxiety among boys, while for girls drug use, bullying and abuse were vulnerability factors, while resilience was associated with higher self-esteem and use of problem-oriented coping. Conclusion: These findings can aid in the identification of young people at risk of self-harm in the school setting and highlight the importance of mental health, peer-related and lifestyle factors in the development of DSH. High-risk groups of young people such as bullying victims and those exposed to suicidal behaviour of others have distinctive profiles of risk factors which differ from those of their peers. Findings relating to the importance of positive coping skills can inform positive mental health programmes, many of which aim to enhance life skills and build resilience among young people. Knowledge of the factors associated with positive adaptation among at-risk adolescents can inform prevention efforts among this group.
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This thesis is concentrated on the historical aspects of the elitist field sports of deer stalking and game shooting, as practiced by four Irish landed ascendancy families in the south west of Ireland. Four great estates were selected for study. Two of these were, by Irish standards, very large: the Kenmare estate of over 136,000 acres in the ownership of the Roman Catholic Earls of Kenmare, and the Herbert estate of over 44,000 acres in the ownership of the Protestant Herbert family. The other two were, in relative terms, small: the Grehan estate of c.7,500 acres in the ownership of the Roman Catholic Grehan family, and the Godfrey estate of c.5,000 acres, in the ownership of the Protestant Barons Godfrey. This mixture of contrasting estate size, owner's religions, nobleman, minor aristocrat and untitled gentry should, it is argued, yield a diversity of the field sports and lifestyles of their owners, and go some way to assess the contributions, good or bad, they have bequeathed to modern Ireland. Equally, it should help in assessing what importance, if any, applied to hunting. In this context, hunting is here used in its broadest meaning, and includes deer stalking and game shooting, as well as hunting with dogs and hounds on foot and horseback. Where a specific type of hunting is involved, it is so described; for example, fox hunting, stag hunting, hare hunting. Similarly, the term game is sometimes used in sporting literature to encompass all species of quarry killed, and can include deer, ground game (hares and rabbits), waterfowl, and various species of game birds. Where it refers to specific species, these are so described; for example grouse, pheasants, woodcork, wild duck, etc. Since two of these estates - the Kenmare and Herbert - each created a deer forest, unique in mid-19th century Ireland, they form the core study estates; the two smaller estates serve as comparative studies. And, equally unique, as these two larger estates held the only remnant population of native Irish red deer, the survival of that herd itself forms a concomitant core area of analysis. The numerary descriptions applied to these animals in popular literature are critically reassessed against prime source historical evidence, as are the so-called deer forest 'clearances'. The core period, 1840 to 1970, is selected as the seminal period, spanning 130 years, from the creation of the deer forests to when a fundamental change in policy and administration was introduced by the state. Comparison is made with similar estates elsewhere, in Britain and especially in Scotland. Their influence on the Irish methods and style of hunting is historically examined.