首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
A compressed full-text self-index for a text T, of size u, is a data structure used to search for patterns P, of size m, in T, that requires reduced space, i.e. space that depends on the empirical entropy (H k or H 0) of T, and is, furthermore, able to reproduce any substring of T. In this paper we present a new compressed self-index able to locate the occurrences of P in O((m + occ)log u) time, where occ is the number of occurrences. The fundamental improvement over previous LZ78 based indexes is the reduction of the search time dependency on m from O(m 2) to O(m). To achieve this result we point out the main obstacle to linear time algorithms based on LZ78 data compression and expose and explore the nature of a recurrent structure in LZ-indexes, the suffix tree. We show that our method is very competitive in practice by comparing it against other state of the art compressed indexes.
Arlindo L. OliveiraEmail:
  相似文献   

2.
Findings indicated that the mass media exposure significantly associated with body image dissatisfaction [Chen & Jackson, 2012. Gender and age group differences in mass media and interpersonal influences on body dissatisfaction among Chinese adolescents. Sex Roles, 66(1-2), 3–20; Field et al., 2005. Exposure to the mass media, body shape concerns, and use of supplements to improve weight and shape among male and female adolescents. Pediatrics, 116(2), e214–e220]. However, limited studies have examined the effect of social media on body image concerns. In regard to this, this paper aims to explore how appearance presentation and appearance interaction on social networking sites influence young adults’ body image dissatisfaction in the Chinese patriarchal society. It proposes that internalization, social comparison and body surveillance may be potential mediators of SNS influences from appearance presentation and appearance interaction on female’s and male’s body dissatisfaction. A survey of 181 males and 203 females indicated that online appearance interaction was significantly associated with female’s body dissatisfaction. In addition, its effect was partially mediated by body surveillance. Besides, body surveillance also mediated the effect of appearance presentation on female’s body dissatisfaction. In male’s case, the influence of online appearance interaction on body dissatisfaction was mediated by internalization and social comparison.  相似文献   

3.
Five ratios RH, RT, SH, ST and SZ derived from the three-part division of a set of sources in h-core, h-tail and uncited sources are defined. Dynamic changes in the three independent ratios RH, SH and SZ are studied for six selected topics. Data about these topics are obtained from the Web of Science for scientific papers and Derwent Innovations Index for technical patents. It is observed that all RH- and SH-values decrease when the time span widens, while SZ stays the same or increases; and that all RH- and SH-values for papers are larger than the corresponding values for patents. The shifted Lotka distribution is used in a theoretical interpretation of these empirical phenomena.  相似文献   

4.
《文物保护研究》2013,58(1):49-58
Abstract

Black weathering layers on stone often contain iron. This is particularly true for the Turonian sandstones which were used extensively in architecture and sculpture in Saxony. In order to obtain more knowledge about the oxidic iron phases, samples were collected in the city of Dresden. Mineralogical and analytical characterization was provided for the black layers and the supporting stone. Material originating from Cotta and Posta stone was submitted to Mössbauer spectroscopy. After ample comparisons of Mössbauer parameters and evaluation of infrared spectra it was concluded that the predominant neogenic iron phase is not iron(III) oxide hydrite (ferrihydrite) Fe2O3·1·8H2O or jarosite KFe3(SO4)2(OH)6 or goethite α-FeO(OH) but a defectively ordered precursor of this last compound, characterized by different environments of the iron(III) ions. By the reducing action of organic matter, magnetite Fe4O4 is formed and this contains up to 45% of the iron present in a black layer.  相似文献   

5.
We consider text retrieval applications that assign query-specific relevance scores to documents drawn from particular collections. Such applications represent a primary focus of the annual Text Retrieval Conference (TREC), where the participants compare the empirical performance of different approaches. P(K), the proportion of the top K documents that are relevant, is a popular measure of retrieval effectiveness. Participants in the TREC Very Large Corpus track have observed that when the target is a random sample from a collection, P(K) is substantially smaller than when the target is the entire collection. Hawking and Robertson (2003) confirmed this finding in a number of experimental settings. Hawking et al. (1999) posed as an open research question the cause of this phenomenon and proposed five possible explanatory hypotheses. In this paper, we present a mathematical analysis that sheds some light on these hypotheses and complements the experimental work of Hawking and Robertson (2003). We will also introduce C(L), contamination at L, the number of irrelevant documents amongst the top L relevant documents, and describe its properties. Our analysis shows that while P(K) typically will increase with collection size, the phenomenon is not universal. That is, the asymptotic behavior of P(K) and C(L) depends on the score distributions and relative proportions of relevant and irrelevant documents in the collection. While this article went to press, Yehuda Vardi passed away. We dedicate the paper to his memory.  相似文献   

6.
Database searching permits the user to conduct certain types of research beyond the mere gathering of information. An example is provided by conducting a study of geographic bias in the print media using Magazine Index. Though there are limitations in conducting such research the potential exists for using on-line databases as a powerful research tool.  相似文献   

7.
This study tested the double-edged desirability hypothesis to investigate whether a lack of reduction in desirability perceptions signified failure of a media literacy intervention to reduce the appeal of sexual portrayals or whether it instead represented an improved awareness of message-design techniques and, therefore, a successful intervention. Data from two media literacy curriculum evaluations, both pretest–posttest quasi-experiments with control groups (N1 = 922, M = 14.13, SD = 1.07; N2 = 1,098, M = 14.26, SD = 1.06) showed that the media literacy treatment in both studies eliminated the effect of desirability on participants’ attitudes, reduced the effect of message desirability on participants’ expectancies, and reduced the effect of message desirability on participants’ efficacy in one of the evaluations. The results supported the double-edged desirability hypothesis, which holds that media literacy education can diminish the influence of desirable but unrealistic sexual media messages on adolescents’ decision making concerning sex, regardless of whether it decreases their affinity for the messages. This approach appears to represent a more effective alternative to demonizing media messages teens find desirable.  相似文献   

8.
Although traditional mood management theory suggests we use media to deflect sad moods and maintain good moods, various research findings reflect a more complex picture. The present study took a mixed-method, nuanced approach to basic mood management questions and investigated both open and close-ended media preferences among college students (N = 157) immediately following a positive or negative mood induction. Results show that sad (vs. happy) participants showed a preference for viewing a dark comedy or a social drama, whereas happy (vs. sad) participants showed a preference for viewing a slapstick comedy or an action adventure. Women (vs. men) showed an increased preference for romantic genres regardless of mood, whereas men showed a preference for action, suspense, and dark comedy genres. An interaction between gender and mood also emerged; sad men in particular showed a preference for dark comedies. Results are discussed in light of the emotional gratifications that mood-reflecting media may afford men and women.  相似文献   

9.
《文物保护研究》2013,58(2):83-88
Abstract

By using X-ray powder diffraction to identify the crystalline constituents of ceramics, especially porcelains, a considerable amount of information can be obtained from a very small sample. The characteristic mineral in hard-paste porcelains, stonewares and highfired earthenwares is shown to be mullite, an aluminium silicate, 3Al2O3. 2SiO2, (A.S:T.M. 15–776); where there is a high calcium content aluminium silicates may occur e.g. anorthite, CaO. Al2O3. 2SiO2, (A.S.T.M.10–379) and gehlenite 2CaO. Al2O3. SiO2, (A.S.T.M.9–216). Among the soft-paste porcelains, whitlockite, β calcium orthophosphate, Ca3(PO4)2, (A.S.T.M. 9–169), is typical of those containing bone-ash, and enstatite, magnesium meta silicate, MgO. SiO2 (A.S.T.M.7–216) is typical of those containing soapstone. The glassy-frit porcelains generally contain a calcium silicate, wollastonite or pseudowol1astonite, CaO. SiO2, (A.S.T.M.10–487 and 10–486). In addition, silica–either as α quartz or cristobalite–may occur in varying proportions in all these bodies.  相似文献   

10.
We develop efficient dynamic programming algorithms for pattern matching with general gaps and character classes. We consider patterns of the form p 0 g(a 0,b 0)p 1 g(a 1,b 1)…p m−1, where p i ⊂ Σ, Σ is some finite alphabet, and g(a i ,b i ) denotes a gap of length a i …b i between symbols p i and p i+1. The text symbol t j matches p i iff t j  ∈ p i . Moreover, we require that if p i matches t j , then p i+1 should match one of the text symbols Either or both of a i and b i can be negative. We also consider transposition invariant matching, i.e., the matching condition becomes t j  ∈ p i + τ, for some constant τ determined by the algorithms. We give algorithms that have efficient average and worst case running times. The algorithms have important applications in music information retrieval and computational biology. We give experimental results showing that the algorithms work well in practice.  相似文献   

11.
《文物保护研究》2013,58(3):199-210
Abstract

Descente des vaches (1836) by Théodore Rousseau in the Mesdag Collection in The Hague is barely readable and its paint layers are in poor condition. The surface of the painting is strongly deformed and cracked, the whole painting has darkened and especially the greens have lost all or most of their colour resulting in brown passages. Large passages of the painting that were painted with multiple thick and medium-rich layers have darkened dramatically. This paper proposes that the degradation of Emerald green (Cu(C2H3O2)2·3Cu(AsO2)2, copperacetoarsenite) – the main green pigment used in this painting – is a significant factor in the cause of the darkening. Electron backscatter images reveal that the Emerald green particles are shown different degrees of degradation: from partially to completely disintegrated. Elemental maps show that arsenic is distributed throughout the paint cross section, with relatively higher concentrations around iron- and aluminium-containing particles, and in the varnish layer. Imaging-Fourier-transform infrared microscopy detects copper soaps in the degraded Emerald green-containing layers. Analytical data from four paint cross sections strongly suggest that Emerald green reacts with free fatty acids derived from the binding medium forming copper soaps and mobile arsenic-based species. Chemical laboratory experiments fully support this hypothesis. Emerald green and palmitic acid in chloroform form copper palmitate and arsenic trioxide (arsenolite, cubic) under room temperature and normal light conditions. The degradation of Emerald green particles in Descente des vaches has resulted in a loss of light-reflecting surfaces and in newly formed compounds in the paint, both contribute to the colour change from green to brown.  相似文献   

12.
Much research has been published on cellular phone only households and the challenges posed by cellular phones to traditional survey methodologies that attempt to generate representative samples using only landline telecommunications. This study reports analyses comparing two separate survey strata (N landline = 152, N cellular = 153) collected simultaneously and nested within a single-frame survey of a state in the American Midwest for differences in demographics, political orientations, individual differences, and a variety of political media consumption variables. Focus is also given to differences among audience variables that predict various forms of political media use across the two survey strata.  相似文献   

13.
《文物保护研究》2013,58(4):284-286
Abstract

The widespread occurrence of thecotrichite, Ca3(CH3COO)3Cl(NO3)2·7H2O, in the museum environment is explained theoretically by construction and examination of its phase diagram. Thecotrichite formation was simulated in the laboratory to identify the key factors involved in its production. This efflorescence occurs on porous limestone or calcareous artefacts such as pottery, stored in wooden cabinets that generate acetic acid vapour. Salt production depends on the moisture content of the object and the concentration of acetic acid in its surroundings. Furthermore, for thecotrichite to form the artefact must contain soluble chloride and nitrate salts.  相似文献   

14.
Sleep experts have raised concern over the effects of electronic media use on sleep. To date, few studies have looked beyond the effects of duration and frequency of media exposure or examined the underlying mechanisms of this association. As procrastinatory media use has been related to lower well-being, we used data from two survey studies (N1 = 821, N2 = 584) to investigate (a) predictors of procrastinatory TV viewing and (b) the link between procrastinatory TV viewing and sleep quality. Findings from both studies indicate that those with a stronger viewing habit, higher TV involvement, and an eveningness preference reported more procrastinatory TV viewing. Procrastinatory TV viewing was related to subjective sleep quality, sleep latency, sleep efficiency, and daytime dysfunction. This association was fully mediated by perceived stress. As sleep is key for the replenishment of self-control, procrastinators may be setting themselves up to fail at self-regulating, a situation exacerbated by the omnipresence of media in today’s society.  相似文献   

15.
《文物保护研究》2013,58(3):148-152
Abstract

Mineralogical changes which occur during the reaction of copper(II) chloride with carbonate in aqueous solution have been investigated, and compared with those involving copper(I) chloride, nantokite, CuCI, and copper artifacts coated with malachite, CU2CO3(OH)2 The reactions observed and the products obtained are seen to have implications with respect to the use of aqueous sodium carbonate solutions to stabilize archaeological copper objects. The frequent observation of the mineralogically rare species chalconatronite, Na2Cu(CO3)2·3H2O, on the surface of treated objects is readily explained by known reaction chemistry. Its formation can be minimized by washing the object after treatment.  相似文献   

16.
The paper proposes a Vector Space Model over the Cayley-Klein Hyperbolic Geometry (referred to as Hyperbolic Information Retrieval = HIR) using a similarity measure derived from the hyperbolic distance. It is shown that the proposed model is equivalent with the classical Vector Space Model using Cosine measure with normalized weighting scheme. It is also shown that the categoricity of the new retrieval system can be varied by only modifying the radius of the hyperbolic space and without using a different weighting scheme and similarity measure, which is not the case in the VSM, where the same effect can only be obtained by both changing the weighting scheme and similarity measure at the expense of a more costly computation. Experiments are also reported to demonstrate and support the ideas, and they show that categoricity in HIR can be varied more than O(n) faster, where n is the number of index terms, than in the VSM.  相似文献   

17.
Lead white is widely used as a white pigment in the history of Persian painting. This paper focuses on three Persian treatises dated between the twelfth and the sixteenth century, which explained different manufacturing methods of lead white or sefidāb-i-sorb. Experimental reconstruction of each recipe to access the comprehensive meaning of the text and analytical studies with X-ray powder diffraction on products of recipes revealed white compounds other than the previously known products of hydrocerussite (Pb(OH)2?·?PbCO3) and cerussite (PbCO3) in samples. Chlorine-containing raw materials mentioned in these recipes lead to the chemical products of laurionite (Pb(OH)Cl), blixite (Pb8O5(OH)2Cl4), and phosgenite (Pb2Cl2(CO)3) in the final products. These data lead to the hypothesis of the discrepancy of the lead white pigment between Iran and Europe and a marked probability of other compounds in historic Persian lead white samples.  相似文献   

18.
Social media activism has become very relevant for many student activist groups. How can political use of social media be motivated? The concept of Social Media Political Efficacy was proposed to resolve inconsistencies in prior theories of social media activism. A survey (n = 222) of members of 3 student activist groups showed that social media political efficacy was positively related to successful experiences using social media for activism. The relationship between social media political efficacy and social media activism was stronger than that between the concept of political efficacy employed in prior research and social media activism. Theory and social media activism implications are discussed.  相似文献   

19.
This study used a survey design (N = 168) to examine how parent and child demographics, parental media-use motives, parental subjective norms, and parental attitudes toward preschool media use (PMU) are all related to actual media exposure among children 6 months to 5 years in age. Results indicate that, in accordance with the theory of reasoned action, parents’ perceived subjective norms regarding various categories of media were significantly related to actual child consumption. Further, positive attitudes toward media were significantly related to higher rates of child consumption. Interestingly, parental worries about media were only negatively related to television consumption and unrelated to child exposure to other kinds of media.  相似文献   

20.
《文物保护研究》2013,58(3):183-186
Abstract

A yellowish copper vanadate mineral has been found in Swedish mural paintings from the fifteenth century. Small patches occur in malachite-green paint. Thirteen samples from five churches have been analyzed by optical and scanning electron microscopy with energy–dispersive X-ray spectrometry, transmission electron microscopy, X-ray powder diffraction, and polarized light microscopy. The substance is evidently the rather uncommon mineral volborthite, with the chemical formula Cu3V2O7(OH)2.2H2O. Very small quantities have also been noted for another mineral, presumably calcio-volborthite, CaCu(VO4)(OH), also named tangeite. The results show that the conservator should always be observant for pigments not earlier noticed or reported. There are some old mines in Central Europe, e.g. in Germany, which contain malachite as well as copper vanadate minerals, and this is probably the origin of the yellow patches in the paintings.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号