信息搜索中用户学习行为内在机理研究

阐述了信息搜索用户学习行为的核心概念,梳理了信息搜索和学习行为的研究进展.以意义建构理论、认知风格理论和行为科学理论为切入点,将信息搜索中用户的学习行为过程抽象为"学习搜索需求-学习搜索认知-学习搜索思考"的用户认知结构改变和行为调整过程,并以此揭示用户搜索决策行为的外在表现特征和内在心智特征,剖析信息搜索中学习行为的...     

二维视觉搜索的计算机模拟

视觉搜索的模拟算法考虑两个交互作用的过程:覆盖过程(“看”)和视觉过程(“看见”)。搜索场景包含有靶,假目标和背景噪声;一个视力角模型按一定的搜索策略去覆盖场景。对模拟程序的输入是场景和靶的空间大小,随机分布的靶和假目标的数目。靶探测几率和识别几率均为物体在场景中对比度和物体离视力角中心的距离的函数。本模拟程序的目的是比较系统搜索和随机搜索的性能,验证关于计算最佳视窗宽度的公式,进而鉴别影响靶探测和识别能力的覆盖过程和视觉过程的参数,阐明它们之间的相互作用。     

Assessment of Granger Causality by Nonlinear Model Identification: Application to Short-term Cardiovascular Variability

A method for assessing Granger causal relationships in bivariate time series, based on nonlinear autoregressive (NAR) and nonlinear autoregressive exogenous (NARX) models is presented. The method evaluates bilateral interactions between two time series by quantifying the predictability improvement (PI) of the output time series when the dynamics associated with the input time series are included, i.e., moving from NAR to NARX prediction. The NARX model identification was performed by the optimal parameter search (OPS) algorithm, and its results were compared to the least-squares method to determine the most appropriate method to be used for experimental data. The statistical significance of the PI was assessed using a surrogate data technique. The proposed method was tested with simulation examples involving short realizations of linear stochastic processes and nonlinear deterministic signals in which either unidirectional or bidirectional coupling and varying strengths of interactions were imposed. It was found that the OPS-based NARX model was accurate and sensitive in detecting imposed Granger causality conditions. In addition, the OPS-based NARX model was more accurate than the least squares method. Application to the systolic blood pressure and heart rate variability signals demonstrated the feasibility of the method. In particular, we found a bilateral causal relationship between the two signals as evidenced by the significant reduction in the PI values with the NARX model prediction compared to the NAR model prediction, which was also confirmed by the surrogate data analysis. Furthermore, we found significant reduction in the complexity of the dynamics of the two causal pathways of the two signals as the body position was changed from the supine to upright. The proposed is a general method, thus, it can be applied to a wide variety of physiological signals to better understand causality and coupling that may be different between normal and diseased conditions.     

Modulation by mexiletine of action potentials, L-type Ca current and delayed rectifier K current recorded from isolated rabbit atrioventricular nodal myocytes

 Using whole-cell patch clamp recordings at 37°C, we have examined the effects of externally applied mexiletine (a class 1b antiarrhythmic agent) on action potentials, L-type Ca current (I_Ca,L) and delayed rectifier K current (I_K) in single isolated rabbit atrioventricular nodal (AVN) myocytes. In spontaneously active AVN cells, 30–100 μM mexiletine depolarised the maximum diastolic potential and slowed both action potential upstroke and repolarisation. Under selective recording conditions for I_Ca,L, mexiletine reduced peak I_Ca,L (at +10 mV) amplitude in a dose-dependent fashion (41.8 ± 3.0% inhibition by 100 μM and 16.4 ± 1.8% at 30 μM). The voltage dependence of I_Ca,L activation was unaffected by both concentrations of the drug. Under selective recording conditions, I_K amplitude was measured as the peak of the deactivating tail current following a depolarising voltage pulse to +20 mV. 30 μM mexiletine inhibited I_K by 34.3 ± 5.8%, whilst 100 μM mexiletine reduced the current by 52.7 ± 6.1%. The effects of mexiletine on I_Ca,L and I_K are likely to contribute significantly to the changes in action potentials observed in spontaneously active cells. These findings are also suggestive of key roles for I_Ca,L and I_K in determining the shape and rate of action potentials in this region of the heart. Received: 21 May 1997 / Received after revision: 25 July 1997 / Accepted: 19 August 1997     

Electrophysiology reveals semantic priming at a short SOA irrespective of depth of prime processing

The otherwise robust behavioral semantic priming effect is reduced to the point of being absent when a letter search has to be performed on the prime word. As a result the automaticity of semantic activation has been called into question. It is unclear, however, in how far automatic processes are even measurable in the letter search priming paradigm as the prime task necessitates a long prime–probe stimulus-onset asynchrony (SOA). In a modified procedure, a short SOA can be realized by delaying the prime task response until after participants have made a lexical decision on the probe. While the absence of lexical decision priming has already been demonstrated in this design it seems premature to draw any definite conclusions from this purely behavioral result since event related potential (ERP) measures have been shown to be a more sensitive index of semantic activation. Using the modified paradigm we thus recorded ERP in addition to lexical decision times. Stimuli were presented at two different SOAs (240 ms vs. 840 ms) and participants performed either a grammatical discrimination (Experiment 1) or a letter search (Experiment 2) on the prime. Irrespective of prime task, the modulation of the N400, the ERP correlate of semantic activation, provided clear-cut evidence of semantic processing at the short SOA. Implications for theories of semantic activation as well as the constraints of the delayed prime task procedure are discussed.     

Characteristics of the delayed rectifier K current compared in myocytes isolated from the atrioventricular node and ventricle of the rabbit heart

The delayed rectifier potassium current (I _K) is known to be important in action potential repolarisation and may contribute to the diastolic pacemaker depolarisation in pacemaker cells from the heart. In this study, using whole-cell patch clamp, we investigated the characteristics of I _K in morphologically normal cells from the atrioventricular node (AVN) and ventricle of the rabbit heart. Cells were held at −40 mV and 5 μM external nifedipine was used to block L-type calcium current (I _Ca,L). Significant I _K was observed with pulses to potentials more positive than −30 mV. The steady-state activation curve in both cell types showed maximal activation at between + 10 and + 20 mV. Half-maximal activation of I _K occurred at −4.9 and −4.1 mV with slope factors of 8.3 and 12.4 mV in ventricular and AVN cells, respectively. Using pulses of increasing duration, significant I _K tails after repolarisation from + 40 mV were observed with pulses of 20 ms and increased with pulses up to 100–120 ms in both cell types. Pulses of longer duration did not activate further I _K and this suggested that only the rapid component of I _K, called I _Kr, was present in either cell type. Moreover, I _K tails after pulses to all potentials were blocked completely by E-4031, a selective blocker of I _Kr. The reversal potential of I _K varied with the concentration of external K. Superfusion of AVN cells with medium containing 4, 15 and 40 mM [K⁺]_o resulted in reversal potentials of −81, −56 and −32 mV, respectively, which are close to values predicted if the I _K channel were highly selective for K. The time constants for deactivation of I _K in ventricle and AVN on return to −40 mV after a 500-ms activating pulse to + 60 mV were 480 ms and 230 ms, respectively. The faster deactivation of I _K in AVN cells was a distinguishing feature and suggests that there may be differences in the I _Kr channel protein between ventricular and AVN cells. Received: 24 July 1995 /Received after revision: 20 October 1995 /Accepted: 23 October 1995     

Using Internet search engines to obtain medical information: a comparative study

Background

The Internet has become one of the most important means to obtain health and medical information. It is often the first step in checking for basic information about a disease and its treatment. The search results are often useful to general users. Various search engines such as Google, Yahoo!, Bing, and Ask.com can play an important role in obtaining medical information for both medical professionals and lay people. However, the usability and effectiveness of various search engines for medical information have not been comprehensively compared and evaluated.

Objective

To compare major Internet search engines in their usability of obtaining medical and health information.

Methods

We applied usability testing as a software engineering technique and a standard industry practice to compare the four major search engines (Google, Yahoo!, Bing, and Ask.com) in obtaining health and medical information. For this purpose, we searched the keyword breast cancer in Google, Yahoo!, Bing, and Ask.com and saved the results of the top 200 links from each search engine. We combined nonredundant links from the four search engines and gave them to volunteer users in an alphabetical order. The volunteer users evaluated the websites and scored each website from 0 to 10 (lowest to highest) based on the usefulness of the content relevant to breast cancer. A medical expert identified six well-known websites related to breast cancer in advance as standards. We also used five keywords associated with breast cancer defined in the latest release of Systematized Nomenclature of Medicine-Clinical Terms (SNOMED CT) and analyzed their occurrence in the websites.

Results

Each search engine provided rich information related to breast cancer in the search results. All six standard websites were among the top 30 in search results of all four search engines. Google had the best search validity (in terms of whether a website could be opened), followed by Bing, Ask.com, and Yahoo!. The search results highly overlapped between the search engines, and the overlap between any two search engines was about half or more. On the other hand, each search engine emphasized various types of content differently. In terms of user satisfaction analysis, volunteer users scored Bing the highest for its usefulness, followed by Yahoo!, Google, and Ask.com.

Conclusions

Google, Yahoo!, Bing, and Ask.com are by and large effective search engines for helping lay users get health and medical information. Nevertheless, the current ranking methods have some pitfalls and there is room for improvement to help users get more accurate and useful information. We suggest that search engine users explore multiple search engines to search different types of health information and medical knowledge for their own needs and get a professional consultation if necessary.     

Sensitivity and predictive value of 15 PubMed search strategies to answer clinical questions rated against full systematic reviews

Background

Clinicians perform searches in PubMed daily, but retrieving relevant studies is challenging due to the rapid expansion of medical knowledge. Little is known about the performance of search strategies when they are applied to answer specific clinical questions.

Objective

To compare the performance of 15 PubMed search strategies in retrieving relevant clinical trials on therapeutic interventions.

Methods

We used Cochrane systematic reviews to identify relevant trials for 30 clinical questions. Search terms were extracted from the abstract using a predefined procedure based on the population, interventions, comparison, outcomes (PICO) framework and combined into queries. We tested 15 search strategies that varied in their query (PIC or PICO), use of PubMed’s Clinical Queries therapeutic filters (broad or narrow), search limits, and PubMed links to related articles. We assessed sensitivity (recall) and positive predictive value (precision) of each strategy on the first 2 PubMed pages (40 articles) and on the complete search output.

Results

The performance of the search strategies varied widely according to the clinical question. Unfiltered searches and those using the broad filter of Clinical Queries produced large outputs and retrieved few relevant articles within the first 2 pages, resulting in a median sensitivity of only 10%–25%. In contrast, all searches using the narrow filter performed significantly better, with a median sensitivity of about 50% (all P < .001 compared with unfiltered queries) and positive predictive values of 20%–30% (P < .001 compared with unfiltered queries). This benefit was consistent for most clinical questions. Searches based on related articles retrieved about a third of the relevant studies.

Conclusions

The Clinical Queries narrow filter, along with well-formulated queries based on the PICO framework, provided the greatest aid in retrieving relevant clinical trials within the 2 first PubMed pages. These results can help clinicians apply effective strategies to answer their questions at the point of care.     

Phylogenetic and developmental study of CD4, CD8 α and β T cell co-receptor homologs in two amphibian species, Xenopus tropicalis and Xenopus laevis

CD4 and CD8 co-receptors play critical roles in T cell development and activation by interacting both with T cell receptors and MHC molecules. Although homologs of these genes have been identified in many jawed vertebrates, there are still unresolved gaps concerning their evolution and specialization in MHC interaction and T cell function. Using experimental and computational procedures we identified CD4, CD8α and CD8β gene homologs both in Xenopus tropicalis, whose full genome has been sequenced, and its sister species Xenopus laevis. Multiple alignments of deduced amino acid sequences reveal a poor conservation of the residues involved in binding of CD4 to MHC class II, and CD8α to class I in non-mammalian species, presumably related to the co-evolutionary pressure of MHC I and II genes. Phylogenetic study suggests that Xenopodinae co-receptor genes are more closely related to their homologs in other tetrapods than those of bony fish. Furthermore, the developmental and cell-specific expression patterns of these genes in X. laevis are very similar to that of mammals. X. laevis CD4 is mainly expressed by peripheral non-CD8 T cells and detected in the thymus as early as four days post-fertilization (dpf) at the onset of thymic organogenesis. CD8β expression is specific to adult surface CD8⁺ T cells and thymocytes, and is first detected in the thymus at 5 dpf in parallel with productive TCRγ transrcipts, whereas productive TCRβ and α rearrangements are not detected before 7-9 dpf.     

Genome-wide association scan allowing for epistasis in type 2 diabetes

In the presence of epistasis multilocus association tests of human complex traits can provide powerful methods to detect susceptibility variants. We undertook multilocus analyses in 1924 type 2 diabetes cases and 2938 controls from the Wellcome Trust Case Control Consortium (WTCCC). We performed a two‐dimensional genome‐wide association (GWA) scan using joint two‐locus tests of association including main and epistatic effects in 70,236 markers tagging common variants. We found two‐locus association at 79 SNP‐pairs at a Bonferroni‐corrected P‐value = 0.05 (uncorrected P‐value = 2.14 × 10^?11). The 79 pair‐wise results always contained rs11196205 in TCF7L2 paired with 79 variants including confirmed variants in FTO, TSPAN8, and CDKAL1, which are associated in the absence of epistasis. However, the majority (82%) of the 79 variants did not have compelling single‐locus association signals (P‐value = 5 × 10^?4). Analyses conditional on the single‐locus effects at TCF7L2 established that the joint two‐locus results could be attributed to single‐locus association at TCF7L2 alone. Interaction analyses among the peak 80 regions and among 23 previously established diabetes candidate genes identified five SNP‐pairs with case‐control and case‐only epistatic signals. Our results demonstrate the feasibility of systematic scans in GWA data, but confirm that single‐locus association can underlie and obscure multilocus findings.