A virtual learning community (VLC) is a learning-based integrated platform based on a network sharing mechanism. In a VLC, users are not only the extractors of knowledge results but also the source of the platform knowledge base. The continuous knowledge sharing and communication of VLC users promote the sustainable development of the community. Studying the continuous use behavior of users in the VLC for the sustainable development of the community is of great importance. This study introduces the perceptual normativeness, perceptual enjoyment, perceptual interactivity, and perceptual value variables on the basis of the extended expectation confirmation model of the information system continuance model. After checking and correcting the prediction questionnaire twice, we adopted the "Questionnaire Star" network system to distribute the questionnaire and conducted offline questionnaire surveys of borrowers of Shandong University Library, University of Jinan Library, and Shandong Library. A theoretical model of the continuous use behavior of users in the VLC is constructed using the structural equation model. The survey data were empirically analyzed to explore the influencing factors and mechanism of the continuous use behavior of users in the VLC. Interaction perception, value perception, and perceptual normativeness exerted a significant positive impact on user-perceived usefulness and expectation confirmation, whereas perceptual enjoyment had little effect on perceived usefulness. This study also summarized the relationship between users’ continuous use behavior, continuous willingness and perceived usefulness, expectation confirmation, satisfaction, self-efficacy, and contributing factors in the VLC on the basis of the data results. Suggestions for solving the identified problems are put forward. The Virtual Learning Community (VLC) is an online community based on interest and knowledge sharing –2. ThereAt present, the society is rapidly advancing into a new era of information. The awareness of lifelong learning has been deeply rooted in the hearts of the people. The effective flow of social resources has increased people’s desire for new knowledge as China’s openness continues to increase . As a kiVLCs feature user autonomy, through which users can choose the knowledge they need. This kind of autonomous and selective learning communication refers only to users’ initial decision-making choices, and whether a learner can complete the whole process remains to be verified. The outstanding problems in the actual development of VLCs include high user churn rate, low user dependence, low user stickiness, and withdrawal of community members . This phThe research on continuous use behavior mainly uses the technology acceptance model (TAM), the theory of planned behavior (TPB), and the expectation confirmation model of information system continuance (ECM-ISC) as the theoretical framework.The TAM was proposed by Davis to study users’ theory of the adoption and acceptance of information systems (ISs) . BhattacThe TPB was first proposed by Ajzen as an extension of rational behavior theory to explain behaviors that are not completely controlled by individual will. Meanwhlie, TPB believes that human behavior is the result of thoughtful planning. Ajzen’s publication of the theory of “Planned Behavior” in 1991 is a sign of the maturity of the theory. The theory of planned behavior includes five elements: Attitude, Subjective Norm, Perceived Behavioral Control, Behavior Intention, and Behavior. The application of TPB can be divided into three categories: predicting individual behavior, expanding into the field of new media, and cross-cultural application of TPB. Of course, TPB also has certain limitations, such as the object of TPB must be individual rational behavior; the elements of the TPB model must be aimed at the same object and belong to the same level.The ECM-ISC was proposed by Bhattacherjee (2001) on the basis of the expectation confirmation theory (ECT)  to explaThe expanded ECM-ISC introduces two variables, namely, computer self-efficacy and contributing factors in perceptual behavior control theory. The perceived usefulness in the original model significantly affects users’ satisfaction. Perceived usefulness is a correct reflection of users’ cognition. It also exerts a certain impact on users’ initial choice and continuous use. Users’ willingness to continue to use has a positive impact. The extended model can provide a more detailed explanation and prediction of the continuous willingness and behavior of IS or IT users compared with the original ECM-ISC.VLCs are inevitable outcomes of the development of educational technology to a certain extent. VLCs are used to solve the common needs of learners from different fields and regions, and share network space through certain technical means and network standards. Many scholars have conducted relevant research on this. However, they are now more focused on the development and construction resource creation, learning evaluation, and the impact factors of user composition . The resThe research on user behavior toward ISs in the current academic field is sorted from the perspective of development, and the research on users’ continuous use behavior is mostly based on the basic theoretical model. The research variables in the original model are refined and modified according to the different research objects so that the constructed model can conform to specific situations. The research field has no established evaluation index system for VLCs. Hence, this work combines the domestic and foreign literature on evaluation index systems for VLCs –33. RefePerceptual normativeness is mainly used to test the operability, stability, security, human–computer interaction, and interface friendliness of a VLC support system or platform. Perceived value includes the perception of users’ self-contribution and the value of the community’s knowledge. The purpose of users in participating in VLCs is to acquire knowledge to enhance themselves. The contribution of users to community knowledge is the basis of community development. Perceived enjoyment is the degree of enjoyment of a user during use and is not related to the results of the use. Perceptual interactivity is mainly used to test interactions in a VLC. In communication interaction, users in a VLC freely exchange views and opinions. Moreover, users acquire the required knowledge through effective communication and collaborative learning, and they integrate such knowledge into their own knowledge structure. In addition, the interactivity in a VLC includes the interaction between users and the platform. This kind of interaction refers to whether the user can get timely feedback from the platform when the user faces problems in the process of using it. Perceptual normativeness, perceptual enjoyment, perceptual interactivity, and perceptual value exert an important influence on users’ expectation degree of recognition, perceived usefulness, and continuous use intention in the VLC. Therefore, the following hypotheses are made:Hypothesis 1 (H1). The perceptual normativeness of the VLC positively affects users’ expectations.Hypothesis 2 (H2). The perceived enjoyment of the VLC positively affects the perceived usefulness of users after use.Hypothesis 3 (H3). The perceived interactivity of the VLC positively affects the perceived usefulness of users after use.Hypothesis 4 (H4). The perceived interactivity of the VLC positively affects users’ continued use intention.Hypothesis 5 (H5). The perceived value of the VLC positively affects the perceived usefulness of users after use.perceived usefulness in the extended ECM-ISC is a reflection of users’ cognitive beliefs and is thus different from the perceived usefulness of a single initial contact IS or IT in the TAM. User satisfaction is the degree to which users are satisfied. Users’ satisfaction with a VLC mainly comes from the comparison between their pre-use expectations and their post-use cognition. Moreover, users’ satisfaction significantly affects their willingness to use and their continuous use behavior. Therefore, the following hypotheses are made:Expectation confirmation theory reflects users’ cognitive level to a certain extent. Users will have certain expectations for a VLC before using it. After using the VLC, the users will have certain knowledge of the VLC. Users will compare their expectation with their knowledge of the VLC after use to form a confirmed behavior. The degree of expectation and confirmation can determine the degree of user satisfaction. If the expectation of community users is high, then the satisfaction is high, and the willingness to use is strong. For the VLC, perceived usefulness is the prediction of the degree to which a user’s learning objectives are completed in the VLC. The Hypothesis 6 (H6). The degree of Expectation confirmation in the VLC is positively correlated with perceived usefulness.Hypothesis 7 (H7). The degree of Expectation confirmation in the VLC is positively correlated with user satisfaction.Hypothesis 8 (H8). The perceived usefulness of users in the VLC positively affects their continued use intention.Hypothesis 9 (H9). Users’ satisfaction in the VLC is positively correlated with their continued use intention.Rational behavior theory holds that users’ subjective behavior intention in the IS has a direct impact on their actual behavior. Behavioral intention is a user’s willingness to perform certain behaviors and is a measure of behavioral tendencies. The continuous use behavior of users in a VLC refers to their initial acceptance and adoption of the VLC for a period of time to use it for their own learning or teaching activities. In many cases, users’ behavioral intentions and behaviors lack a one-to-one correspondence. However, multiple behavioral intents can lead to certain behaviors. To effectively explain the individual differences of system users and the influence of external factors on learners’ behavioral intentions and individual behaviors, Bhattacherjee incorporated the variables of self-efficacy and contributing factors in the theory of perceived behavioral control under social psychology . Self-efHypothesis 10 (H10). The continued use intention of users in the VLC positively affects their continuous use behavior.Hypothesis 11(H11). The self-efficacy of users in the VLC positively affects their continued use intention.Hypothesis 12 (H12). The enabling factors of users in the VLC positively affect their continuous use behavior.We used a questionnaire to collect the data needed for this study. First, the related variable scales from the domestic and foreign literature were reviewed on the basis of the research content of this study. The scale is shown in Moreover, the structure, problems, and options of the questionnaire were determined. The questionnaire was divided into three parts: the explanation of the questionnaire, the test questions and options, and the main information about the respondents. The questionnaire description included the explanations of the questions and related concepts. The test questions were aimed at identifying the scale required by the research from the relevant variable scales collected in the review process. The contents and items of this initial scale were then modified and adjusted on the basis of discussions with tutors and classmates to form a predictive questionnaire. A five-level Likert scale was adopted to design the topic options for the questionnaire. The respondents rated their knowledge and usage of the VLC as follows: strongly agree = 5 points, consent = 4 points, generally agree = 3 points, disagree = 2 points, strongly disagree = 1 point. The last part of the questionnaire covered the personal information of the respondents, including their gender, age, education, and specific occupation.We carried out a small-scale test of the prediction questionnaire prior to the formal survey to test whether the questions and options in the questionnaire suffer from ambiguity or semantic problems, as well as to ensure the rationality and comprehensiveness of the questionnaire. First, we invited 10 experts in pedagogy research to explain the meanings of the questions in the questionnaires to the pretesters. We corrected the questionnaire on the basis of their questions and potential problems. Second, we randomly selected 35 college students to answer our questionnaire to ensure the reliability and validity of the test scale. We formed our final questionnaire on the basis of the improvements identified.After the completion of the questionnaire, we conducted the survey using two major methods. The first method was to distribute the questionnaire through the “Questionnaire Star” network system and then promote it using network communication tools such as WeChat and QQ. The second method was through offline visits. The survey subjects were mainly divided into three main categories, namely, the Shandong University Library, the University of Jinan Library, and the Shandong Provincial Library. Highly educated college students are the main users of VLCs. Most of them come from different regions. Their majors are extensive, and they possess a certain understanding of VLCs. In this study, most of the respondents were actual users of VLCs and thus have extensive experience in using these virtual communities. The survey included a wide range of people, with a relatively dispersed age group and certain representativeness. Most of the respondents were public officials working in relevant units, and some were students preparing for career editing, civil service, postgraduate examinations, etc. All of them have the motivation to actively learn. Most of the respondents had experienced online learning and were not new to VLCs. Some of them were even long-term users of VLCs whose needs could be met by these VLCs. The sample selection was critical. Considering the experience of users in using VLCs in the electronic reading rooms of university libraries is important in studying the influencing factors and mechanisms of community user behavior. A total of 380 questionnaires were distributed, and 341 questionnaires were returned; among those returned, 296 questionnaires were deemed valid. The effective recovery rate was 86.8%. The reliability test is a test of the credibility of survey data, and it mainly reflects the continuity and stability of survey results. The validity test relates to the level of a given problem measured by a scale. If validity is high, then the measurement scale meets the measurement requirements. In this work, the collected data were sorted and analyzed, and the reliability and validity of the test scale were measured by SPSS 25.0 and Amos 20.0 data statistics software. The credibility of the survey data was tested using the level of Cronbach’s coefficient according to the principle of statistical correlation. Composite reliability (CR) can effectively evaluate the degree of correlation of measured variables and is a commonly used evaluation variable that can reflect the degree of internal consistency of latent construct. Validity tests include test validity and discriminant validity. The average extracted variance (AVE) value reflects the proportion of measurement error in the variance explained by the latent construct. AVE can effectively check the discriminant validity of the scale, and the aggregate validity can be measured by the standard load. In using structural equations to validate models, the appropriate model fit is the premise of use. The degree of fit of the model is the degree of fit between the research model and the actual sample data. If the covariance matrix implied by the research model is close to the covariance matrix of the sample data, then the fit of the model is satisfactory.In reference to Marsh, we selected the following for testing: chi-square/degree of freedom (CMIN/DF), comparative fit index (CFI), goodness-of-fit index (GFI), incremental fitness index (IFI), normed fit index (NFI), unconventional fitness index (TLI), and root mean square error of approximation (RMSEA). The results of each indicator test of the model meet the requirements of the reference standard. Hence, the covariance matrix of the survey data is consistent with the covariance matrix of the research model, and the fit of the research model is satisfactory. The model assumptions were analyzed using a structural equation model. Therefore, the test results of the hypothesis in this paper can be obtained, as shown in In order to see the influence between different variables, we have drawn a research model diagram. The main relationship between the variables in the structural model path map is discussed as follows.In the VLC, the normativeness of user perception positively affects users’ expectation confirmation, which further affects users’ perceived usefulness; this result is consistent with the interpretation of user acceptance and acceptance behavior in the TAM –58. The In the VLC, the perceptual value of users positively affects their perceived usefulness while their perceptual enjoyment has no significant effect on perceived usefulness. This finding indicates that some of the students surveyed in this study have rich experience and knowledge in using the VLC and that they will make rational choices according to their own needs. The learning community is different from virtual games, shopping, and other communities. The learning community is a collection of learners who share a common learning language and interest in learning. In such community, their beliefs are strengthened when they face a variety of choices. VLC users are mainly concerned about the exchange and sharing of resources and knowledge in the learning process and the improvement of learning and cognitive ability rather than community entertainment. Therefore, the community should focus on improving the quality of resource services and resources to stimulate users’ continuous use behavior. With regard to the perceptual value of community users, users pay more attention to the value of acquiring knowledge than to the value of self-contribution. In the current information-driven society, interpersonal communication and interactive learning rely heavily on network terminal tools. Such dependence is not conducive to the formation of values and sociality, which is achievable through certain offline activities. Therefore, the VLC needs to organize offline activities on a regular basis to improve the core literacy of users. At the same time, it should strengthen external cooperation, use external forces to achieve overall improvement, encourage users to actively participate in meaningful activities, and cultivate users’ sociality and values. The perceptual value of users is closely related to the degree to which their needs are met. In response to the different characteristics and needs of different users, the community should provide diversified, personalized, and multi-level resource sharing and communication services. New modes of construction and development in the era of knowledge fragmentation are also necessary.The perceptual interactivity of the VLC positively affects users’ perceived usefulness, which in turn influences users’ continuous use behavior. The perceptual interactivity of the VLC positively affects the user's perceptual usefulness and continued use intention. The user's perceptual usefulness also positively affects continuous use intent At the same time, perceptual interactivity indirectly affects users' continuous use intentions through their perceptual usefulness. The interaction between users in the VLC creates a number of connections that are intertwined to form an interactive network. If many interactions exist in the network, users’ perception of the interactions and the connection in the network are strengthened. When this connection is strong enough, the perceptual interactivity affects users’ continuous use behavior and positively influences their intended use. In the research, we found that after a user accepts the VLC, the low-quality interaction for a period of time not only reduces users’ attraction and hinders the development of the community but also causes the interactor to become a potential user of community knowledge to a certain extent. The interaction bias has a direct positive impact on users’ continuous use intention. This finding shows that when the perceptual interactivity reaches a certain standard of user requirements, it can directly affect the intention to use regardless of its quality. This finding also shows that the acceptance of the interaction is relatively high after the user accepts the VLC. In the interaction type, the interaction between users (0.82) is almost as important as the interaction between the user and the system (0.79). The communication and sharing of knowledge in the VLC are based on user interaction. Quality user interaction is the premise of community knowledge transfer. However, providing timely feedback on relevant suggestions and questions raised by users is also important. Timely feedback reflects users’ perceived usefulness and enhances their continuous use intention. Hence, high-quality system software services can enhance user experience. Frequent interactions between learners in the VLC can enhance user loyalty and strengthen mutual trust. When the trust degree of people in the VLC is high, the enthusiasm of users to exchange knowledge in the community will be greatly improved. On the contrary, weak perceptual interactivity will have a negative impact on users’ perceived usefulness. When sharing knowledge, users may worry that their content is negatively affected by irresponsible malicious comments. Such issue is not conducive to VLC resource construction and user perception.In the VLC, users’ expectation degree of recognition has a significant impact on and is positively related to perceived usefulness and satisfaction. This finding is in line with expectation confirmation theory, the interpretation of satisfaction, and perceived usefulness in the ECM-ISC. Moreover, the finding verifies the content of the hypothesis. At the same time, this conclusion shows that in the VLC, if the degree of expectation is high, then the satisfaction and perceived usefulness of users is high. The key to improving user satisfaction and perceived usefulness is to increase user expectations.In the VLC, user satisfaction has a significant impact on continuous use intention, and the effect of self-efficacy on users’ continuous use intention is not significant. This finding shows that users’ focus in their use of the VLC is on whether the community can achieve their intended goals, learning resources, and sharing value. Users’ learning willingness and efficacy, value goals, and mental models will be satisfied and developed and they will be willing to continue their use only after experiencing actual learning through the VLC. Self-efficacy is a subjective judgment. After adopting and accepting the VLC, users may change their intention to continue using the learning objectives, learning effects, learning time, and their own knowledge and skills. The probability of such a change is high due to the subjectivity of self-efficacy, resulting in its insignificant impact on user’s continuous use intention.In the VLC, users’ continuous use behavior is significantly affected by contributing factors and users’ continuous use intention. The contributing factor of the impact on users’ continuous use behavior (0.41) is higher than that of continuous use intention (0.33). However, users 'self-efficacy has a significant positive impact on users' intentions of continuous use, which is limited by their own knowledge and learning ability, and has the intention of giving up continuous use. This result shows that users’ perception of external resources can directly affect their behavioral retention; in subjective knowledge, the latter’s influence exceeds that of the former.A practical incentive system should be developed to encourage users’ continuous us of the community. The system should pay attention to user feedback, take feasible and timely measures, and offer a free and open platform application environment. The use conditions of the system should be optimized to create a good atmosphere for users.Aimed at the continuous use behavior of users in VLCs, this study utilizes the ECM-ISC proposed by Bhattacherjee (2008) as the basic framework structure through the analysis of relevant literature and theories. On the basis of a mature research literature scale, a new IS model is introduced. Variables comprise the model of users’ continuous use behavior in the VLC. They could serve as a reference for the subsequent research on the continuous use behavior of VLC users. In the use of a covariance structure model for empirical testing, the model interpretation rate reached 74.1%, which confirmed the research hypothesis. Although the test model is in good condition, the research results are limited to the scope of the Shandong University Library, the University of Jinan Library, and the Shandong Provincial Library. They also involve a limited sample size. In future research, the capacity and randomness of the sample will be increased to obtain superior results. The follow-up research will examine the changes in the willingness and behavior of users in their later use of the VLC. The mechanism of learning motivation on willingness and behavior is also studied.


Since radio frequency interference (RFI) seriously degrades the performance of a global navigation satellite system (GNSS) receiver, interference detection becomes very important for GNSS receivers. In this paper, a novel rearranged wavelet–Hough transform (RWHT) method is proposed in GNSS interference detection, which is obtained by the combination of rearranged wavelet transform and Hough transform (HT). The proposed RWHT method is tested for detecting sweep interference and continuous wave (CW) interference, the major types of GNSS interfering signals generated by a GNSS jammer in a controlled test bench experiment. The performance of the proposed RWHT method is compared with the conventional techniques such as Wigner–Ville distribution (WVD) and Wigner–Hough transform (WHT). The analysis results show that the proposed RWHT method reduces the influence of cross-item problem and improves the energy aggregation property in GNSS interference detection. When compared with the WHT approach, this proposed RWHT method presents about 90.3% and 30.8% performance improvement in the initial frequency and chirp rate estimation of the GNSS sweep interfering signal, respectively. These results can be further considered to be the proof of the validity and effectiveness of the developed GNSS interference detection method using RWHT. With the increasing global navigation satellite system (GNSS) applications in various civil and military fields, reliable navigation and positioning performance has become a key and important requirement for GNSS receivers ,2,3,4. TThe commonly used methods in GNSS interference detection mainly include automatic gain control (AGC) method, time domain methods, and frequency domain methods. AGC adjusts the GNSS input signal level to the range of the analog-to-digital converter (ADC), which performs interference detection by monitoring the AGC level ,18,19; hPresently, the research topic on time-frequency (TF) transforms in GNSS interference detection has obtained increasing attention ,11,12,13To deal with the TF resolution trade-off problem with the spectrogram and the cross-term problem with the WVD, the Wigner–Hough transform (WHT) has been adopted ,26,27. IThe rearrangement operation can be combined with the TF representations for signal detection applications ,9,28,29.In this paper, first, the cross-term problem with the conventional TF analyses such as WVD used in GNSS interference detection has been discussed and then the Hough transform has been adopted to overcome this tough cross-term problem; second, the rearranged wavelet transform has been developed to improve the TF resolution in the TF plane; finally, the rearranged wavelet transform has been further combined with the Hough transform obtaining the novel RWHT which is expected to improve the interference detection performance for GNSS receivers. To prove the validity and effectiveness of the proposed RWHT-based GNSS interference detection method, the interference detection experiment has been performed by using the real GPS L1-C/A signal collected in the presence of sweep interference or continuous wave (CW) interference. The analysis results have shown that the proposed RWHT technique effectively suppress the cross-terms in the bilinear TF distributions and greatly enhances the TF localization property in the TF plane, which significantly improves the interference detection performance for GNSS receivers particularly working in the difficult jamming scenarios.This paper is organized as follows: ith GNSS signal jRFt=The input signal essed as ,12,13,15To avoid the cross-terms caused by the interaction between the positive and negative frequency parts of the spectrum, an analytic form of the received GNSS signal has been proposed ,12,13,15WVD is a commonly used TF distribution for analyzing non-stationary time-varying signals, which belongs to a typical quadratic or bilinear TF representation since the analyzed signal is used twice in the calculation. The WVD can be defined as the Fourier transform of the time-dependent instantaneous auto-correlation function Although WVD has many nice properties and provides nearly the best TF resolution among all the TF analysis techniques, its main drawback comes from cross-term problem due to its bilinearity nature ,31. ConsTaking Fourier transforms of Equation (9) with respect to From Equation (11), it is easy to know that the WVD of the sum of two signals is not only the sum of their corresponding WVDs, but also of their XWVD. This means that the spectrum energy density of the sum of two signals does not reduce to the sum of the individual densities . If As a result, if a signal contains more than one component in the TF plane, its WVD suffers from spurious features containing cross-terms that occur halfway between each pair of auto-terms. As an example, the LFM signal in the presence of AWGN is analyzed, where the SNR is set to be 3 dB. The WVD of the noisy LFM signal is provided in The WVD is a quadratic transformation, although it shows satisfactory TF aggregation property, the WVD of multi-component signal inevitably presents cross-term problem due to its bilinearity nature ,31. To dCWT is a linear transform which does not suffer from the tough cross-term problem with the quadratic TF representation, and it can be expressed as :(13)Wya,Since the integral of the squared amplitude of the CWT is proportional to the energy of the analyzed signal, the squared modulus of the CWT can be defined as scalogram, written as follows: In this paper, Morlet wavelet is chosen to extract linear frequency modulation feature of the sweep interfering signal. The Morlet wavelet kernel is given as ,34:(15) By substituting Equation (15) to Equation (13), the Morlet wavelet transform can be obtained, which is expressed as:In Since the concept of rearrangement or reassignment can be used to improve the TF energy aggregation property in the signal detection applications ,12, simical area ,12. One possible way to solve this problem is to reallocate the signal average energy density value to the gravity center ibutions ,12. The Furthermore, the rearrangement operator is given as:In Hough transform can be used to detect the line of frequency modulation law for a given signal in the TF image space. The principle of Hough transform can be explained in  follows :(20)xcosIf a single point in the TF image is considered, then all the straight lines passing through this point definitely correspond to a unique sinusoidal curve in the When considering the detection of the LFM interfering signal (sweep interference) by using the WVD, if the undesired cross-term is not considered, the auto-term’s energy distribution is concentrated on a straight line representing the signal’s frequency modulation law in the TF plane . If the -θ plane . Therefo-θ plane ,27:(21)WIn The characteristic parameters of the LFM signal can be further determined by using the Hough transform. In According to the geometric relationship shown in When the WHT is used in sweep interference detection for GNSS applications, the colinear points The observed straight line denoting the frequency modulation law of the sweep interfering signal performed by using rearranged wavelet transform is usually described with the Cartesian coordinates From Cartesian coordinates to polar coordinates, the point-line duality has been converted to the point-sinusoidal curve duality through Hough transform; in this way, the detection of linear lines in the TF image space can be converted to detect intersection points of sinusoidal curves in the Equation (25) can be also rewritten in the form of polar coordinates , provideIt can be seen from Equation (26) that through Hough transform, the original straight line denoting the sweep interring signal’s frequency modulation law which is represented by the rearranged wavelet scalogram in the TF plane can be mapped to the concurrent sinusoidal curves which are concentrated in a particular point in the form of polar coordinates within the When dealing with the sweep interference present in the received GNSS signal, since the concurrent sinusoidal curves which represent the collinear points on the sweep interference frequency modulation line are intersected in the same point within the The proposed GNSS interference detection method based on RWHT is clearly explained in When the RWHT is used in the detection of sweep interference present in the received GNSS signal, a sharp energy peak definitely appears in a specific point domain within the parameter space, presenting all the information of the frequency modulation law of the linear chirp interference. By searching for the local RWHT peak and determining this particular point position within the parameter space where the RWHT peak energy concentrates, the sweep interfering signal can be effectively detected, and furthermore the initial frequency and chirp rate of the linear chirp interference present in the received GNSS signal can be precisely estimated by the peak detection process.In this section, the performance of GNSS interference detection based on rearranged wavelet–Hough transform was analyzed in comparison with the traditional interference detection techniques such as WVD and WHT. The scheme of the GNSS interference detection test is illustrated in 4 MHz/s.To demonstrate the validity and effectiveness of the proposed RWHT-based interference detection method for GNSS receivers, several tests were performed, which were characterized by the corresponding parameters provided in In To mitigate the cross-term interference with the WVD, the rearranged wavelet scalogram of the interfered GPS L1-C/A signal is shown The Hough transform can be used to mitigate the cross-terms present in the TF energy distributions. In When the JNR of the sweep interference is set to be −2 dB, the WHT of the interfered GNSS signal is presented in To further improve the interference detection performance for GNSS receivers, the RWHT of the interfered GPS L1-C/A signal is provided in 4 MHz/s.In case of JNR equal to −2 dB, the RWHT of the interfered GNSS signal is provided in To comprehensively evaluate the GNSS detection performance of the proposed RWHT method, root mean square error (RMSE) has been used in the analysis for the estimates of the initial frequency and chirp rate of the sweep interference in comparison to the WHT approach. In different JNR scenarios, the RMSE results for the estimated initial frequency and chirp rate values of the sweep interference present in the received GPS L1-C/A signal are provided in In details, in Moreover, the proposed RWHT method is expected to be also valid in the detection of CW interference since it can be considered to be a special case of LFM interfering signal with a fixed carrier center frequency . In the In In summary, it is known that the proposed RWHT method is not only effective for sweep interference detection, but also suitable for CW interference detection for GNSS receivers.From the GNSS sweep interference detection results, the proposed RWHT method can be used to detect the GNSS sweep (linear chirp) interference effectively since it successfully deals with the cross-term problem and presents much improved energy localization property. The estimation of the characteristic parameters such as the initial frequency and chirp rate of the sweep interfering signal has been performed, and the corresponding quantitative metric RMSE results have been compared between the proposed RWHT method and the WHT approach. The RWHT method shows much improved precision in the estimation of the characteristic parameters of the sweep interference present in the received GPS-L1 C/A signal. Furthermore, in this paper, this proposed RWHT method has been experimentally verified to be valid and effective in the detection of CW interference for GNSS receivers. The RMSE analysis of this proposed RWHT method in dealing with the CW interference for GNSS applications will be evaluated in the future research works.In addition, since both Beidou and GPS signals use spread spectrum communication and code division multiple access (CDMA) technologies , the proIn this paper, a novel GNSS interference detection method based on rearranged wavelet–Hough transform has been proposed. To prove the validity and effectiveness of the developed technique, a comprehensive interference detection performance evaluation has been performed in comparison to the existed TF analysis approaches such as WVD, WHT, and rearranged wavelet scalogram. The interference detection tests have been performed on the real GPS L1-C/A signal in the presence of sweep interference or CW interference to verify the theoretical analyses.From the experimental results, the traditional WVD approach shows unsatisfactory interference detection performance since it is suffered from the serious cross-term problem; the rearranged scalogram can partially suppress cross-terms, but it presents TF energy distribution discontinuity problem in the TF plane due to the rearrangement operation, which degrades the GNSS interference detection performance; when the WVD is combined with the Hough transform, the obtained WHT can partially alleviate the cross-terms present in the TF plane; when the Hough transform is combined with the rearranged scalogram, it is of vital importance that the developed RWHT method effectively suppresses the undesired cross-terms since the RWHT energy distributions are greatly strengthened and mainly concentrated in a particular limited point domain within the parameter space, and at the same time, the RWHT method presents satisfactory energy aggregation property since the rearrangement operation is made, this can be considered to be the main novelty of this paper. It is clear to know that the proposed RWHT method provides significant performance improvement in GNSS interference detection when compared with the existed TF analysis approaches.The proposed interference detection method by using RWHT has been proven to be very effective to remove the cross-terms within the traditional bilinear TF distributions and improve the TF energy aggregation property at the same time, which is critically important to the GNSS interference detection performance enhancement. Based on these achieved technical improvements, the RWHT-based GNSS interference detection method provides much improved performance over the WVD, rearranged wavelet scalogram, and WHT techniques.In summary, by using the developed efficient RWHT algorithm, the proposed GNSS interference detection method is not only effective in GNSS sweep interference detection, but also valid in dealing with GNSS CW interference, which is very promising to be used in anti-interference design for GNSS receivers particularly working in the difficult and challenging interfering environments.


Soft sensors are essential for robotic systems to safely interact with humans and the environment. Although significant research has been carried out in the field of soft tactile sensing, most of these sensors are restricted to a predefined geometry and a fixed measurement range, hence limiting their application. This paper introduces a novel approach to soft sensing by proposing a soft load-sensing unit with an adjustable mechanical compliance achieved using an elastically inflatable fluidic dome. The sensor consists of a three-dimensional Hall-effect sensor, above which is a magnet whose movement is modulated by an intermediate elastomeric dome structure. Sensor configurations were designed and fabricated using three different silicone rubbers to cover ‘00–10’ and ‘20A’ durometer shore hardness scales. We demonstrated that the compliance of the sensor could be dynamically tuned by changing the internal pressure of the inflatable fluidic dome in all configurations. We performed finite element simulations to determine the reaction force of the sensor under load as well as the stresses within the internal structural behavior, which are not possible to capture experimentally. The proposed soft sensor has the potential to be readily adapted for use in various soft robotic applications of differing size, compliance range, and safety requirements. In recent years, soft robotics have been developed with reduced complexity, greater adaptability, and for a safer interaction with delicate objects, humans, or unstructured environments owing to their intrinsic material compliance ,2,3. HowExisting soft tactile sensors are limited by their complicated fabrication, fragile materials, structural complexity, and insufficient performance on measurement range and sensitivity. To address above disadvantages, researchers have fabricated magnetic-based tactile sensors by embedding magnet(s) in a deformable matrix  featurinControllable compliance is also essential for functional soft robots to facilitate multi-task movement, adaptable locomotion, and dexterous manipulation of various objects. The deformable nature of soft sensors and their fixed stiffness makes it difficult to build a controllable and dynamic measurement system for soft tactile sensors ,22,23. TIn this paper, we demonstrate a novel variable compliance load-sensing unit in which the sensing and the controllable compliance are provided by a single system, thus the robotic structure is drastically simplified. The sensor can adjust its compliance by changing the pressure inside its elastically inflatable fluidic dome. This can be harnessed to alter the dome’s load-carrying capacity as well as the sensing range. 5–107 Pa). Moreover, by controlling the internal fluidic pressure level within the dome, this study aims to develop a soft load-sensing unit for tactile sensing in which the compound stiffness of the dome, and therefore its measurement range, can be adjusted in real-time.The proposed soft load-sensing unit for tactile sensing, described herein as a soft sensor, consists of three main components: a Hall-effect sensor, a magnetic source, and an anisotropic flexible dome-structure that is elastically inflated by pressurized air, as shown in For this purpose, a hollow silicone dome was created by fabricating a compliant wall consisting of a strain-limiting layer sandwiched between two elastomeric layers. A permanent magnet is embedded into the upper part of the dome. This inflatable dome was then fixed above a 3D Hall-effect sensor, as illustrated in hS is the sensitivity of the 3D Hall-effect sensor, B is the magnetic field, and When an external normal force is applied to the dome, the magnet is displaced, causing a variation in the magnetic field detected by the 3D Hall-effect sensor. The change in the magnetic field is related to the displacement of the magnet by:The mechanical behavior of the proposed soft sensor is linked to both the selected elastomeric material and the manufacturing process used to fabricate the inflatable dome, since they affect the produced compliance levels required for the sensing application. In addition, compliance and stiffness determine the robustness of the structure to leaks in pressure or structural failure. The stiffness of the chosen material also affects the adjustable measurement range as stiffer material create a larger range with a higher measuring start.We used silicone rubber at three durometer shore hardness values  to produce different mechanical properties for the elastomeric layers. An isotropic and inextensible non-woven embroidery fabric  was selected as a strain-limiting layer sandwiched between two layers of silicone rubber to constrain the circumferential strain. This fabric is highly permeable, allowing integration with the pre-polymer liquid silicone rubber, thus helping ensure mechanical integrity of the sandwiched layers.The fabrication process for the inflatable dome consists of three main steps, as shown in The addition of the strain-limiting layer aims to minimize deformation of the fluidic dome under different internal pressures such that deformation of the dome, and resultant movement of the magnet, is dominated by the action of external loads. This facilitates characterization and calibration and reduces the risk of mechanical failure from over-strain of the elastomeric dome. A comparison is shown in A Finite Element (FE) model of the sensor’s inflatable dome was developed using commercial FE software  to characterize the representative reaction force on the sensor during indentation as well as observing the deformation mechanisms within the structure, which is not possible to capture in an experimental setting. The strain and stress distribution contours within the sensor obtained from the simulations can then be used as a design tool for modification of the sensor to suit different applications.The simulation is performed in two steps: (1) a pressurizing step in which a uniform pressure as boundary condition is applied into the interior of the inflatable dome and (2) the indentation step, in which the pressurized dome was indented by the vertical displacement of a 22 mm diameter rigid indenter onto the top exterior surface of the structure .λ1, λ2, λ3) and 2·n material constants, where n is the number of polynomials that constitute the strain energy density function defined as:The dome sensor and indenter were modeled as axisymmetric deformable geometries and meshed using four-node bilinear axisymmetric quadrilateral elements with hybrid formulation (CAX4RH) within ABAQUS software. A linear elastic model with 1.6 GPa elastic modulus was used in simulations for the indenter, which was 3D-printed using Formlab Clear Standard material . It shouExperiments were conducted to validate the FE model of the sensor and then to calibrate and evaluate the mechanical and sensing performance of the proposed sensor under normal indentation, using 6 and 22 mm indenters. The experimental apparatus used in this study was similar to the one used in our previous work . A lineaThe soft sensor was calibrated to correlate the change in the magnetic field output signal with the applied force across a range of pressures within the elastomeric dome. Each elastomeric dome (three different durometers) was calibrated for five different air pressure conditions, from 0 to 4 psi in 1 psi increments (five repeats at each condition). For each pressure condition, the sensor was cyclically indented vertically between 0 and 7 mm in 0.1 mm increments at a constant speed of 2 mm/s. The measurement of contact force and air pressure are both taken at the end of 0.1 mm increments. The applied external force was recorded by the load cell while displacement was recorded by the linear stage connected to the PC. The data sampling rate is 200 Hz. The air pressure was recorded by the pressure sensor and the magnetic field is recorded by the Hall-effect sensor.As shown in K is specified by recording the relations between As defined in Equation (2), external force K in the Z-axis is calculated by:As the fluidic pressure inside the chamber is increased, there is a small effect of inflation in the elastomeric dome, which in turn reduces the gap to the indenter. This is shown in the schematics of A, force, F, and The structural modulus is defined by the contact section area, zK reduce significantly due to the buckling of the vertical walls. In the final phase, with further indentation of the dome, the horizontal and vertical walls contact and compress each other, which results in the rise of the gradient again until the end of the indentation.During the process of indentation, the sensor’s structural stiffness changes due to the deformation of the dome. The first phase of indentation begins when the indenter hits the exterior surface of the elastomeric dome. This phase continues until there is a discernible change in gradient of the force-displacement data. This signifies the start of the second phase, in which the gradient and A, by Equation (5).The results shown in zK, as well as the structural modulus in the Z-axis, zE. An approximate phase division on a prototype of the fluidic dome is shown in Using the phases defined in Bz, and pressure, P, in the fluidic dome:A calibration process was undertaken to find the relationship of the force Z direction, This was achieved using a modified Genetic Programming (GP) approach ,38, traiThe experimental data for indentation at 0, 1, 2, 3, and 4 psi were used as inputs to train the GP program and obtain a general formulation in the form of Equation (6). Then, a reconstruction of force, magnetic field, and fluidic pressure were conducted. This work demonstrates a conceptual soft sensor with adjustable variable compliance. Our work here has shown the feasibility of an elastically inflatable fluidic dome by pneumatic control. It also demonstrates the potential of a proposed fabrication method of constrained silicone rubber. The simulation results showed a good coherence with the experimental results and revealed the deformations of the sensor structure that could not be captured in the experiments. The experimental and simulation results show the potential of the proposed design as an adjustable soft sensor, which can be used in various soft robotics applications. While the dome was at a low air pressure condition, there was a larger discrepancy in the force measurement range between simulation and experiment. This is likely due to small imperfections or inconsistencies in the fabrication process (related to adding the dome constraint layer) that are more significant in this low pressure sensor state, but become negligible as the sensor pressure increases.The proposed soft sensor achieved variable and controllable stiffness and compliance. Compared to the previous soft sensor , the elaThe sensor showed a variable compliance for different air pressure inside the inflatable dome as the required force for displacing the dome changed from 1.01 to 8.99 N for a 6 mm indenter. This force was also variable from 7.19 to 34.77 N for the 22 mm indenter. The force-displacement data of the sensor represented a three-phase reaction of the sensor with a linear behavior in the second phase. We also measured a variable structural modulus for the sensor in the range of 0.05 to 1.01 MPa for different domes’ material and pressure. The measurement range is potentially further expanded by applying softer or stiffer material of the inflatable dome to achieve lower measurement range but more sensitive measurement.The limitation of the proposed sensor is that its structure is not fully soft. The substrate board and transducer are still rigid. But with the technologies of stretchable electronics, the soft sensor can be developed to the fully soft sensor. For example, a flexible and stretchable Hall-effect sensor will help to cancel the substrate board . Its meaPotential applications of the proposed sensor are aimed at complex occasions of robots, where their contacting objects are often shifted. Adaptive and variable stiffness of this sensor helps, for example, home-caring robots to evaluate their contacting force between holding a hand and holding an iron. Sorting and logistics robots will also be more capable with the help of the variable stiffness of the proposed sensor when they are dealing with various goods. The proposed sensor could also be integrated in pneumatic robotic manipulators ,42 systeFuture work on the proposed sensor will aim to optimize the sensor’s inflatable fluidic dome, which is the key component of the sensor. With improved design of the dome, it will provide a more linear and reliable measurement. This will largely increase its adaptivity and practical potential. Another direction is to apply new material and a new fabrication method to the inflatable fluidic dome to enable more air pressure, inside which will also help to increase its measuring range.We have demonstrated a soft sensor platform whose structural compliance can be dynamically altered to modulate the sensor’s measurement range and sensitivity. The concept allows for safe interaction in which the sensor can change stiffness relative to applied load and the environment. The sensor consists of an elastomeric inflatable dome with an internal air cavity in which the pressure could be adjusted, resulting in a varying compliance for the dome. The relative displacement of the dome is detected by measuring the magnetic field of a permanent magnet, adhered to the dome, using a Hall-effect transducer. We found the optimized structural stiffness using different elastomeric materials and evaluated these in an experimental setup in which an indenter applied force on top of the sensor and measured the corresponding displacement for different air pressures inside the dome. FEM simulations were used to evaluate the characteristics of structural deformation under different load regimes to enable optimization of the concept. A Genetic Programming approach was then used to determine a relationship between the applied force, magnetic field, and air pressure, and this was shown to provide a robust calibration for the sensor. This novel sensor concept has relevance in a range of fields, notably the development of soft robotic manipulators. The proposed sensor potentially extends the sensibility of soft robotic manipulators in multiple applications.This study demonstrated a new soft sensor with adjustable stiffness, compliance, and controllable measurement range. The concept of the soft sensor with a strain-limiting layer-imbedded silicone dome was validly proven. The fabrication method of the new soft sensor for tactile sensing provided a concise casting technology for rapid manufacture. Simulation and experimental results showed the performance of controllability, sensitivity, and repeatability.


Orally Disintegrating Tablets (ODTs) are used to restore the nutritional status of people suffering from swallowing pathologies such as dysphagia. ODTs are consumed without water intake and are easily swallowed. The main active compounds of ODTs are vitamins and minerals. These nutrients can have a bad taste or aftertaste, which can be masked by sweetening or flavoring. To ensure the effectiveness of masking strategies and to prescribe a product to patients with acceptable sensory qualities, it is essential to perform a precise and complete sensory characterization of these ODTs. Temporal dominance of sensations (TDS) and temporal check-all-that-apply (TCATA) methods were chosen to characterize the temporal sensory perceptions during the consumption of four ODTs varying in galenic forms and flavoring because of their particularly acute temporality in flavor perception. The ODTs presented common and individual sensory properties, mainly related to their galenic form and to the nature of the active ingredients. The use of a nose-clip to stop retro-nasal airflow showed that flavoring had a minimal impact on the sensory taste qualities of the ODTs. A comparison between the TDS and TCATA results indicates that these tests are capable of providing complementary information on the dynamic sensory qualities of the products studied. Although results were generally similar for both methods, TDS showed a greater number of differences in sensory taste attribute, whereas TCATA was more discriminating. These methods allowed for a better understanding of the evolution of sensory perceptions of these ODTs during their consumption, which could help to optimize masking strategies and develop new products with acceptable sensory properties. Nutrients such as vitamins and minerals are essential for correct body function. As nutrients are mainly provided by a healthy and balanced diet, nutrient deficiencies can appear during certain pathologies such as cancers or gastrointestinal disease ,2. NutriThe purpose of the current research was to study the dynamics of perception of the taste and retro-nasal odor of ODTs to better control and limit their off flavors. Two temporal sensory analytical methods were used to study the sensory qualities of these products with particular characteristics. We assumed that the use of certain aromas contributed to increasing taste perception with negative valences such as bitterness; therefore, the contribution of aroma to savoring perception was evaluated. Although widely used with products other than ODTs, we determined whether these temporal analytical methods provided accurate and similar sensory information for these ODTs considering the dynamic aspect of sensory perception ,26,27,28Four ODTs, available in drugstores, of various galenic and aromatized forms were evaluated: two ODTs in the form of powders called sticks due to their cylindrical packaging, ODT_exotic and ODT_cola, and two ODTs in the form of tablets called fizzy tabs due to the tingling sensation felt on the tongue when the tablet disintegrates in the mouth, ODT_red and ODT_citrus. These ODTs are comprised of different active ingredients such as vitamins and minerals as well as sweeteners and many excipients including flavor compounds . The ODTFifteen panelists  were recruited from Dijon (France) and surrounding areas. The selection was based on their availability, their interest in the study, and their sensory ability such as taste and olfactory capacity (sensitivity and recognition tests). All panelists were naïve to classical descriptive sensory analytical techniques such as quantitative descriptive analysis profiles and descriptive temporal analytical methods ,30. An eBased on the results obtained in a previous sensory profile on similar nutritional supplements (data not shown), 10 attributes were selected based on their relatively high perception intensity, discriminating power, and relevance to provide an answer to the objective of the study ,31,32. TOrganization of the sessions: The panelists were randomly divided into two groups. The first group started with TDS and then moved to the TCATA session, and the other group started with TCATA followed by the TDS sessions. All panelists performed four repetitions of each test under two conditions: with nose clips (WNC) and without nose clips (WoNC).Training sessions: Before performing the measurement sessions, two training sessions were provided in the same week to familiarize the panelists with the attribute list, sensory tests used, and the signal acquisition software. The first training session was devoted to the presentation of the two dynamic sensory tests, irrespective of the method by which the panelists would start. The temporal and dynamic aspects of a tasting was debated and exemplified. For the TDS, the concept of “dominant attribute” was defined as an attribute that attracts the most attention, but is not the most intense ,16. For Measure sessions: Four samples, randomly coded by three-digit codes and placed in white cups, were distributed to each panelist. The instructions were to consume the whole sample  were given to all panelists. Since manufacture recommendations recommend an oral dose of two ODTs per day, four products could be tested during the same sensory analysis sessions. The order of product presentation was balanced for each repetition and for all panelists using Williams Latin Squares. The panelists were asked to rinse their mouths with pure water and wait a minimum of two minutes between each sample. To evaluate the impact of aromatization on taste perceptions, the evaluations were also performed with a nose-clip (WNC) by each panelist for each sensory method and for each product, according to the protocol established previously. A total number of eighteen sessions was conducted including training and measure sessions.X-axis of the TDS and TCATA curves did not represent the real time of the OFD, but the period from first scoring (x = 0) to last scoring (x = 1) [Data collection and analysis were similarly performed for both tests using the statistical models available in TimeSens. TDS and TCATA data were acquired by the software every 250 ms. First, the product curves for the TDS and TCATA methods were constructed by plotting the dominance (TDS) and citation frequency (TCATA) of each attribute by standardized time ,33. Time (x = 1) . The TDSAn overview of the dynamic sensory characteristics of the studied products was observed through a product map generated by performing canonical variate analysis (CVA) on the perception duration of each attribute of the sample by the panelists’ means evaluation. The product map was generated by using a statistical test available in TimeSens (CVApack R-package) applied to data from TDS and TCATA . In thisA trajectory map representing the oral disintegration path of each sample was established by performing principal component analysis (PCA) on the standardized data of TDS and TCATA (tempR package of TimeSens) . This grp < 0.05 was performed to check the samples that differed significantly from one another.To examine the impact of the galenic form on the sensory perception duration in the mouth, oral flavor duration (in seconds) was determined, and ANOVA with repeated measurements that included the main effect of the product was performed (model: OFD ~ product + err) . Tukey’sp < 0.05 was performed to find means that were significantly different from each other.To investigate the flavoring effect on dynamic taste perceptions, difference curves between a given pair of products , based on a Fisher test (95% significance), were generated using XLSTAT 2020.2.3 software. A no-displayed curve corresponding to an attribute for a given time period meant that no difference could be observed between samples for this attribute. One-way ANOVAs (tempR package) that included the main effect of the evaluation condition (with nose-clip and without nose-clip) were separately performed on TDS and TCATA data to study the flavoring effect on dominance and citation duration of all attributes (model: dominance or citation duration ~ product + err). The dependent variables were the dominance duration (TDS) and the citation proportion (TCATA) of all attributes for each product. Post-hoc Tukey’s honest significant difference (HSD) test with a significance level of Dynamic product curves were generated for both sensory tests to perform a product sensory characterization and to evaluate the evolution of their sensory qualities during tasting. A comparison, although exclusively visual, was carried out to establish similarities or differences between these two dynamic sensory methods. These curves were generated in a standardized format, where the x-axis represents the percentage of oral treatment time and the Y-axis represents the dominance rate in TDS and the citation proportion in TCATA.The TDS curves are presented in The dynamic TCATA curves for the four products are shown in An overview of the dynamic sensory characteristics of the studied products was observed through a product map generated by performing CVA on the perception duration of each attribute of the sample by the panelists’ means evaluation. This graphical representation allowed us to determine whether the products had been differentiated from each other by the dominance durations of each attribute. The proximity degree of the ellipses provided information on the similarity degree between products. A vector that indicated the direction and whose length was proportional to the product discrimination provided by this attribute represented each attribute. The F-statistic gave information regarding product discrimination and allowed for a comparison of the discriminating power of both methods.p < 0.001 and an F-statistic of 6.96 for TDS (As shown in  for TDS A and an  for TDS B. The fiThe sensory trajectories of the dominance rates for the TDS data are plotted in a PCA biplot . The twoThe observation of the PCA biplot generated with the TCATA data indicated that the first two dimensions explained 74.08% of the variance . Althougp < 0.001) and an F-statistic of 28.69 (p < 0.001), respectively , which corresponds to the perception duration of the different attributes in the mouth, was analyzed to determine whether the dosage form used had an effect on the process time of the products. Significant differences were found between the samples for TDS and TCATA, with an F-statistic of 30.78  groups). Obstructing airflow between the nasal and oral cavities minimizes the effect of aromas on dynamic sensory perceptions. Thus, by comparison with open-nose conditions, it was possible to evaluate the impact of flavoring on dominance (TDS) or citation rates (TCATA) and on the dominance or citation duration of taste attributes, considering that the aromas were tasteless at the used concentration.The difference curves show how flavoring can cause differences in the dynamic perception of the taste attributes. The difference curves obtained by difference between the products evaluated with a nose-clip (WNC) and without a nose-clip (WoNC) are presented in The TCATA difference curves showed some discrepancies in comparison to the TDS differences curves. No difference was observable in taste attributes for ODT_exotic, ODT_cola, and ODT_citrus. Only metallic and acid had a higher proportion of citations at particular times of the OFD for ODT_red in the WNC than in the WoNC group. However, the few observed differences were present at a low significance level and for very short periods. These differences in the results obtained were linked to the nature of the test used (selection of a single attribute for TDS and selection of multiple attributes for TCATA).p = 0.032). No significant effect was observed for ODT_exotic , ODT_cola , and ODT_citrus . For TCATA, the analysis of citation duration also revealed a negative significant effect of flavoring for ODT_red  (p = 0.1), ODT_cola , and ODT_citrus .One-way ANOVAs were performed to determine the overall flavoring effect on the dominance duration (TDS) of all attributes for each product followed by Tukey tests . This an= 0.003) . No effep = 0.002). Relative to ODT_red, the evaluation without a nose-clip had a significantly lower domination and citation duration for acid than the evaluation with a nose-clip  as well as a significantly lower dominance duration for bitter . Relative to ODT_citrus evaluated with a nose-clip, ODT_citrus evaluated without a nose-clip had a significantly lower dominance duration for acid  and for astringent .One-way ANOVAs were performed to determine the flavoring impact on dominance or citation duration for each sensory taste attribute . For TDSThe TDS and TCATA methods were used to study the dynamic sensory perception of liquid, semi-solid, or solid products ,21,27,28These ODTs were characterized by omnipresent flavoring during the entire OFD. However, for both odor and taste attributes, different temporal perception patterns were observed according to the particular dosage form of the ODTs, which could be due to various kinetics of release or sensory interaction effects. ODTs in powder form (exotic and cola) showed a faster decrease in dominance and citation rate of the flavoring attributes than ODTs in tablet form (red and citrus). This can be easily explained by a higher surface available for exchange with the liquid and gaseous phase in the mouth as soon as the beginning of the OFD for the powder ODTs. Concerning the tablets, they were progressively fractionated by mastication and salivation, leading to a slower and longer release and perception due to a more progressive increase in the surface exchange of the ODTs .This aromatic persistence in the ODTs in tablet form (red and citrus) would mask the appearance of some taste sensory perceptions in the second half of the OFD. This phenomenon was not observed for ODT_exotic and ODT_cola. The four products had a common sensory characteristic, a pronounced acidity in the first third of the OFD. This acidity was stable during the OFD for ODT_red and ODT_citrus, unlike ODT_exotic and ODT_cola. It is likely that the dosage form used was responsible for this difference. The tingling and effervescent sensation in the mouth, linked to the use of carbonate in the formulation of the ODTs in tablet form, would prolong the feeling of acidity during tasting .In most cases, we observed a more or less important increase in bitterness in the third part of the mastication time. The logical interpretation would be that bitter compounds were released later in the mouth because of their hydrophobic properties, leading to their slower extraction from the matrix by saliva and a higher persistence of this sensation. However, in the case of ODTs, the main bitter compounds are minerals and vitamins. Taking into account their concentration in the products  and theiThe trajectory PCA indicated that the end of product tasting was characterized by an increase in the dominance or citation rate of the bitter attribute. This sensory perception has been linked with the presence of active compounds with bitter potential such as vitamins and minerals . This seAnother component of the study examined the flavoring impact on the sensory perception of taste attributes. It was hypothesized that the flavoring used in the products could boost or attenuate the perception of some taste sensory attributes. Regarding the TDS and TCATA curves of ODT_red and ODT_citrus (with the same formulation but different flavorings), the effects of flavoring on taste sensory perceptions can be suspected. For both methods, ODT_citrus, characterized by the citrus flavoring attribute, was evaluated as slightly more bitter and less sweet than ODT_red, which was flavored with red fruits. Although for TDS, ODT_citrus was significantly more bitter than ODT_red at particular times of tasting, this was not observed for TCATA. This was probably related to the nature of the test . On the other hand, the nose-clip evaluation and the without nose-clip evaluation of each product did not allow us to conclude a potential effect of flavoring on any taste perception. In the same way, no significant effect of flavoring was observed on dominance and citation duration for ODT_exotic, ODT_cola, and ODT_citrus. One explanation could be that the perception time of sapid compounds is greater than or equal to the perception time of flavoring. It is possible that this observation could be linked to the differences in the release kinetics of the various compounds incorporated in the ODTs studied. The same statistical treatment was applied for each taste sensory attribute. The results, in agreement with the results obtained from the difference curves, were coherent with the interpretations of the results reported above. For both methods, few significant differences were observable. Only the flavoring of ODT_red (red fruits) was at the origin of a significant sensory reduction of the acid attribute probably through cross-modal interactions. As described above, the TDS method highlighted a larger number of significant differences that were probably linked to the nature of the test.Finally, the relevance of using these temporal analytical methods to characterize these forms of nutritional supplements as well as whether these two methods gave similar and/or complementary information was examined. These two methods were shown to be suitable for achieving the dynamic sensory profile of these nutritional supplements. For both methods, the product curves showed similarities for all products evaluated. The dominant attributes for a product with TDS were also the most cited attributes with TCATA . The twoAlthough the obtained results were generally similar for both methods, TDS highlighted a greater number of differences in sensory taste attribute perception between the two evaluation conditions. This observation has already been carried out in studies on liquid products . The twoThis work allowed for the sensory characterization of selected ODTs and to study the flavoring impact on taste sensory perceptions. However, some limitations were highlighted. It turned out that nose-clip notation was a difficult exercise for panelists. In all the studied cases, aroma had no or only a low impact on taste perception. Therefore, to avoid the use of a nose-clip in such tests, the use of ODTs formulated without flavoring would have been more suitable for the panelists to obtain more accurate results. The consideration of texture perception aspects such as mouthcoating, grainy, and, indirectly salivation, would allow for examining texture-taste cross-modal interactions and their potential to lower off tastes. Finally, the other limitation was that the subjects performing the test were not the target population for these ODTs. Indeed, these nutritional supplements are prescribed for people suffering from swallowing disorders. Therefore, an added value to this study should be to perform the same analysis with a representative group of the target population.Two temporal sensory analytical methods, TDS and TCATA, allowed for a complete characterization of the taste and flavoring sensory perceptions of ODTs. Both TDS and TCATA highlighted characteristics specific to the two galenic forms studied. These two methods can be used to examine the impact in the formulation on dynamic sensory perceptions. Interactions between tastes were suspected to influence temporal bitterness. However, although some differences could be observed, no major flavoring impact on taste sensory perceptions was found. A more optimized formulation of ODTs, in particular, better use of the sweetness-associated aromas, would make it possible to reduce the use of sweetening molecules and limit off tastes such as bitterness. Another aspect to take into account to improve the formulation of supplements is the flavoring. The main objective of flavoring is to increase the acceptability of ODTs by the users, particularly with the masking of off-flavors. To ensure effective masking of the ODTs, it could be envisaged to use different strategies to modify the release kinetics of the flavoring in the mouth . These improvements could contribute to a better pleasant oral experience by providing the improved and prolonged flavoring that patients have come to expect. TDS and TCATA provided similar, but also complementary, information for the sensory characterization of ODTs, as was already shown for everyday consumed foods. Further studies including temporal taste and aroma compound release and temporal sensory experiments with the same formulations of ODTs but with single and multiple omissions of taste or aroma compounds should allow for a better understanding and control of the flavor perception of ODTs.


Ninox boobook). Three individual owls were flown at 8 ms−1 in a climatic avian wind tunnel. The velocity field in the wake was sampled at 500 Hz using long-duration high-speed particle image velocimetry (PIV) while the wing kinematics were imaged simultaneously using high speed video. The time series of velocity maps that were acquired over several consecutive wingbeat cycles enabled us to characterize the wake patterns and to associate them with the phases of the wingbeat cycle. We found that the owl wake was dramatically different from other birds measured under the same flow conditions . The near wake of the owl did not exhibit any apparent shedding of organized vortices. Instead, a more chaotic wake pattern was observed, in which the characteristic scales of vorticity (associated with turbulence) are substantially smaller in comparison to other birds. Estimating the pressure field developed in the wake shows that owls reduce the pressure Hessian  to approximately zero. We hypothesize that owls manipulate the near wake to suppress the aeroacoustic signal by controlling the size of vortices generated in the wake, which are associated with noise reduction through suppression of the pressure field. Understanding how specialized feather structures, wing morphology, or flight kinematics of owls contribute to this effect remains a challenge for additional study.The mechanisms associated with the ability of owls to fly silently have been the subject of scientific interest for many decades and may be relevant to bio-inspired design to reduce noise of flapping and non-flapping flying devices. Here, we characterize the near wake dynamics and the associated flow structures produced during flight of the Australian boobook owl ( The formation of the wake flow region stems from the two shear layers moving across the airfoils and interacting beyond it. The velocity field in the near wake region is governed by a streamwise velocity deficit that is formed from the merger of the two-shear layers. The velocity deficit indicates high level of shear in the wake region, as well as vorticity. When the Reynolds number is relatively high, the wake becomes turbulent and vorticity plays a major role in the flow dynamics.Since the pressure is coupled with velocity, it is also coupled with velocity gradients. It is sometimes convenient to express the pressure as a function of the velocity field by taking the divergence of the Navier–Stokes equation and applying the continuity equation. This results in an expression that is similar to the Poisson equation . Re-arraAdvances in technology have allowed for quantitative measurements of wakes using particle image velocimetry (PIV). This method has been applied to a number of flying species i.e., , and meaTyto alba) in a long hallway, where they performed stereo-PIV measurements around the owl during flight. They showed, qualitatively, that a complex vortex flow system was developed in the wake during flapping flight. However, a well-defined topographical characterization of the wake of an owl and a quantitative estimation of the aerodynamic forces exerted on it are lacking, either experimentally or numerically.Recently, Ninox boobook) were performed and the results presented herein provide unique insight into the aerodynamics of owls and the interaction between their unique wing morphology and wake flow dynamics. We compare the wake characterization to two other species that we have measured under the similar conditions: a passerine songbird: European starling (Sturnus vulgaris), and a non-passerine shorebird: western sandpiper . We use wing kinematics from video and wake reconstructions from PIV measurements to compute characteristic spatial flow scales of the wakes. We show that the characteristic spatial scales of the wake relative to chord size of the owl are smaller than those of the other two species and that the owl exhibits the smallest pressure Hessian. Because the near wake flow affects the pressure field within the wake, and the pressure field is related to the aeroacoustic noise  were obtained from the raptor program of the African Lion Safari in Cambridge, Ontario, Canada and brought to the Advanced Facility for Avian Research (AFAR) at the University of Western Ontario, London, Ontario, Canada under animal protocols from the University of Western Ontario Animal Care Committee (UWO #2010-216) and the African Lion Safari (BOP-15-CS). Morphological parameters of the owls, as well as the non-dimensional flow numbers associated with the performed experiments are summarized in Two male and one female captive reared boobook owls  but were not systematically trained in advance of experiments. Rather they flew steadily for several seconds on each attempt, long enough to capture image sequences suitable for PIV and kinematic analysis. Although the flights took place during daytime the wind tunnel was dark so that PIV could be performed. Optoisolators operated by six infrared transceivers were integrated into the PIV system (upstream from the laser sheet location) in order to prevent direct contact between the bird and the laser sheet . The optThe owls were flown in the hypobaric climatic wind tunnel at the AFAR  that is derived from Navier–Stokes equations and play a dominant role in the vorticity equation, allowing to study the relation between pressure and velocity gradients, locally . While tm ±SD =−0.018 ± 0.032, 95% CI −0.022 to −0.013), sandpiper , and the starling , where m is the mean, SD is the standard deviation, and CI is the confidence interval. These statistics show that the distribution of the pressure gradient of the owl’s wake is closer to zero  with little variation. This result indicates that the wake dynamics behind the owl are fundamentally different in comparison to the other two birds—consistent with the results of the other analyses. For the starling and sandpiper, the histogram mean values [right side of Equation (1)] are negative, on average. Here, ω2 corresponds to enstrophy and s2 is proportional to dissipation; thus, these results imply that dissipation is more dominant in the starling and sandpiper wakes behind the wing mid-span location, relative to the enstrophy [based on the relations between them in Equation (1)]. Yet, for the owl, the enstrophy is approximately double the dissipation as both terms counter each other to yield values in the wake that are close to zero. Therefore, we hypothesize that the owl, using its unique wing morphology, generates more vorticity than strain, which essentially is achieved by generating more small scales while destroying, or not generating, large scales in its wake.The difference between the distributions may be attributed to the wake flow patterns, which appear to be meandering for the owl and the sandpiper and less meandering for the starling, for the data cases studied herein. It is noteworthy that the same calculation was performed for the other owls’ datasets and all had similar distributions to the one presented in The near wake flow dynamics of an owl feature unique characteristics that may be associated with its ability to fly silently. Our findings demonstrate significant differences between the wake of an owl and the wake of other birds ; these iS.vulgaris) and America robin (T.migratorius), and a shorebird  exhibit an organized wake where shedding is observed, although these birds are of different size and flight behavior. A detailed comparison between the owl wake and two birds: the western sandpiper and European starling were performed. While they are not comparable in size with the owl, they present broadly similar wake patterns although they differ in their flight behavior: long distance migratory, continuous flapping (sandpiper), and intermediate distance migratory, flap-gliding (starling).The qualitative examination of the reconstructed wakes shows a different topography of the vorticity field in comparison to other birds that have been tested in the AFAR wind tunnel : the neazcω/∞U| > 1). This result is consistent with the notion that owls do not feature high aerodynamic performance  at the mid-span location of the wing and contain smaller areas of large magnitude of vorticity  further supports the results of smaller flow scales in the wake and/or suppression of larger scales. This result implies that in the owl’s wake the strain and vorticity fields interact with each other differently in comparison to the other two birds because the pressure Hessian describes the non-local interaction between vorticity and strain  a strong three-dimensional motion in the spanwise direction (not measured) such that the wake behind the primary remiges is weakened relative to the tip region, or alternatively (ii) experienced a significant degradation of the turbulence level. For the former case it may be that these wake dynamics resulting from flow patterns formed above the wing section are shifted in the spanwise direction toward the wing tip such that the majority of momentum is transferred from the streamwise to the spanwise direction (as suggested originally by The degradation of turbulence may be the result of the unique morphological structure of the leading-edge serrations , velvetyThe owls were brought from the “African Lion Safari” in Cambridge, Ontario, Canada under animal protocol number BOP-15-CS and protocol 2010-216 from the University of Western Ontario Animal Care committee.All relevant data are given within the paper.H.B.-G. and R.G. were responsible for the design of the experimental setup and performed the experiments and analyzed the data. R.G., J.L., and E.E.H. prepared the manuscript. J.L., H.B.-G., and K.K. performed the data analysis and edited the manuscript. G.A.K. assisted in the setup design and edited the manuscript. C.G. assisted with study design and data collection and edited the manuscript. G.M. was responsible for the capture, care, and training of the experimental birds.Supplement_Material_obz001Click here for additional data file.