| 1. |
- Ehrling, Sebastian, et al.
(författare)
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Temperature Driven Transformation of the Flexible Metal–Organic Framework DUT-8(Ni)
- 2022
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 28:55
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Tidskriftsartikel (refereegranskat)abstract
- DUT-8(Ni) metal–organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition.
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| 2. |
- Honma, Masamitsu, et al.
(författare)
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Improvement of quantitative structure-activity relationship (QSAR) tools for predicting Ames mutagenicity : outcomes of the Ames/QSAR International Challenge Project
- 2019
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Ingår i: Mutagenesis. - Oxford : Oxford University Press (OUP). - 0267-8357 .- 1464-3804. ; 34:1, s. 3-16
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Tidskriftsartikel (refereegranskat)abstract
- The International Conference on Harmonization (ICH) M7 guideline allows the use of in silico approaches for predicting Ames mutagenicity for the initial assessment of impurities in pharmaceuticals. This is the first international guideline that addresses the use of quantitative structure-activity relationship (QSAR) models in lieu of actual toxicological studies for human health assessment. Therefore, QSAR models for Ames mutagenicity now require higher predictive power for identifying mutagenic chemicals. To increase the predictive power of QSAR models, larger experimental datasets from reliable sources are required. The Division of Genetics and Mutagenesis, National Institute of Health Sciences (DGM/NIHS) of Japan recently established a unique proprietary Ames mutagenicity database containing 12140 new chemicals that have not been previously used for developing QSAR models. The DGM/NIHS provided this Ames database to QSAR vendors to validate and improve their QSAR tools. The Ames/QSAR International Challenge Project was initiated in 2014 with 12 QSAR vendors testing 17 QSAR tools against these compounds in three phases. We now present the final results. All tools were considerably improved by participation in this project. Most tools achieved >50% sensitivity (positive prediction among all Ames positives) and predictive power (accuracy) was as high as 80%, almost equivalent to the inter-laboratory reproducibility of Ames tests. To further increase the predictive power of QSAR tools, accumulation of additional Ames test data is required as well as re-evaluation of some previous Ames test results. Indeed, some Ames-positive or Ames-negative chemicals may have previously been incorrectly classified because of methodological weakness, resulting in false-positive or false-negative predictions by QSAR tools. These incorrect data hamper prediction and are a source of noise in the development of QSAR models. It is thus essential to establish a large benchmark database consisting only of well-validated Ames test results to build more accurate QSAR models.
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| 3. |
- Huang, Xing, et al.
(författare)
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Semiconducting Conjugated Coordination Polymer with High Charge Mobility Enabled by "4+2" Phenyl Ligands
- 2023
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 145:4, s. 2430-2438
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Tidskriftsartikel (refereegranskat)abstract
- Electrically conductive coordination polymers and metal-organic frameworks are attractive emerging electroactive materials for (opto-)electronics. However, developing semiconducting coordination polymers with high charge carrier mobility for devices remains a major challenge, urgently requiring the rational design of ligands and topological networks with desired electronic structures. Herein, we demonstrate a strategy for synthesizing high-mobility semiconducting conjugated coordination polymers (c-CPs) utilizing novel conjugated ligands with D2h symmetry, namely, "4 + 2" phenyl ligands. Compared with the conventional phenyl ligands with C6h symmetry, the reduced symmetry of the "4 + 2" ligands leads to anisotropic coordination in the formation of c-CPs. Consequently, we successfully achieve a single-crystalline three-dimensional (3D) c-CP Cu4DHTTB (DHTTB = 2,5-dihydroxy-1,3,4,6-tetrathiolbenzene), containing orthogonal ribbon-like pi-d conjugated chains rather than 2D conjugated layers. DFT calculation suggests that the resulting Cu4DHTTB exhibits a small band gap (similar to 0.2 eV), strongly dispersive energy bands near the Fermi level with a low electron-hole reduced effective mass (similar to 0.2m0*). Furthermore, the four-probe method reveals a semiconducting behavior with a decent conductivity of 0.2 S/cm. Thermopower measurement suggests that it is a p-type semiconductor. Ultrafast terahertz photoconductivity measurements confirm Cu4DHTTB's semiconducting nature and demonstrate the Drude-type transport with high charge carrier mobilities up to 88 +/- 15 cm2 V-1 s-1, outperforming the conductive 3D coordination polymers reported till date. This molecular design strategy for constructing high-mobility semiconducting c-CPs lays the foundation for achieving high-performance c-CP-based (opto-)electronics.
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| 4. |
- Kleijn, W. Bastiaan, et al.
(författare)
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Optimizing Speech Intelligibility in a Noisy Environment
- 2015
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Ingår i: IEEE signal processing magazine (Print). - 1053-5888 .- 1558-0792. ; 32:2, s. 43-54
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Tidskriftsartikel (refereegranskat)abstract
- Modern communication technology facilitates communication from anywhere to anywhere. As a result, low speech intelligibility has become a common problem, which is exacerbated by the lack of feedback to the talker about the rendering environment. In recent years, a range of algorithms has been developed to enhance the intelligibility of speech rendered in a noisy environment. We describe methods for intelligibility enhancement from a unified vantage point. Before one defines a measure of intelligibility, the level of abstraction of the representation must be selected. For example, intelligibility can be measured on the message, the sequence of words spoken, the sequence of sounds, or a sequence of states of the auditory system. Natural measures of intelligibility defined at the message level are mutual information and the hit-or-miss criterion. The direct evaluation of high-level measures requires quantitative knowledge of human cognitive processing. Lower-level measures can be derived from higher-level measures by making restrictive assumptions. We discuss the implementation and performance of some specific enhancement systems in detail, including speech intelligibility index (SII)-based systems and systems aimed at enhancing the sound-field where it is perceived by the listener. We conclude with a discussion of the current state of the field and open problems.
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| 5. |
- Maliuta, Mariia, et al.
(författare)
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Flexibility in DUT-8(Cu) Metal–Organic Framework : Impact of Cluster, Stress, History, and Hierarchical Texture
- 2023
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Ingår i: CCS Chemistry. - 2096-5745. ; 5:10, s. 2225-2236
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Tidskriftsartikel (refereegranskat)abstract
- The flexibility of metal–organic frameworks (MOFs) featuring stimuli-responsive structural transitions is often governed not only by the chemical composition and topology but also by orthogonal factors such as particle size, desolvation method, and history of the sample. A precise understanding of the mechanism behind such observations has been lacking up to now, and there are still substantial open questions concerning the impact of sample treatment history. The DUT-8(M) family ([M2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), encompasses isostructural compounds based on Ni, Zn, Co, and Cu in the cluster node and is representative of pillared layer MOFs, often showing flexible behavior. In this contribution, we discuss a possible explanation for the differences in flexibility observed in desolvated phases of DUT-8(Cu). Theoretical calculations and crystallographic data shed light on the preferred formation of interpenetrated confined closed pore phases in DUT-8(Cu) in contrast to DUT-8(Ni, Co, Zn) where the closed pore phases are formed.
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| 6. |
- Mossavat, Iman, et al.
(författare)
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A Hierarchical Bayesian Approach to Modeling Heterogeneity in Speech Quality Assessment
- 2012
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Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - 1558-7916 .- 1558-7924. ; 20:1, s. 136-146
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Tidskriftsartikel (refereegranskat)abstract
- The development of objective speech quality measures generally involves fitting a model to subjective rating data. A typical data set comprises ratings generated by listening tests performed in different languages and across different laboratories. These factors as well as others, such as the sex and age of the talker, influence the subjective ratings and result in data heterogeneity. We use a linear hierarchical Bayes (HB) structure to account for heterogeneity. To make the structure effective, we develop a variational Bayesian inference for the linear HB structure that approximates not only the posterior over the model parameters, but also the model evidence. Using the approximate model evidence we are able to study and exploit the heterogeneity inducing factors in the Bayesian framework. The new approach yields a simple linear predictor with state-of-the-art predictive performance. Our experiments show that the new method compares favorably with systems based on more complex predictor structures such as ITU-T recommendation P.563, Bayesian MARS, and Gaussian processes.
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| 7. |
- Mossavat, S. I., et al.
(författare)
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A Bayesian hierarchical mixture of experts approach to estimate speech quality
- 2010
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Ingår i: 2010 2nd International Workshop on Quality of Multimedia Experience. - 9781424469604 ; , s. 200-205
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Konferensbidrag (refereegranskat)abstract
- This paper demonstrates the potential of theoretically motivated learning methods in solving the problem of non-intrusive quality estimation for which the state-of-the-art is represented by ITU-T P.563 standard. To construct our estimator, we adopt the speech features from P.563, while we use a different mapping of features to form quality estimates. In contrast to P.563 which assumes distortion-classes to divide the feature space, our approach divides the feature space based on a clustering which is learned from the data using Bayesian inference. Despite using weaker modeling assumptions, we are still able to achieve comparable accuracy on predicting mean-opinion-scores with P.563. Our work suggests Bayesian model-evidence as an alternative metric to correlation-coefficient for determining the necessary number of experts for modeling the data.
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| 8. |
- Petkov, Petko N., et al.
(författare)
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A Bayesian Approach to Non-Intrusive Quality Assessment of Speech
- 2009
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Ingår i: INTERSPEECH 2009. - BAIXAS : ISCA-INST SPEECH COMMUNICATION ASSOC. ; , s. 2875-2878
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Konferensbidrag (refereegranskat)abstract
- A Bayesian approach to non-intrusive quality assessment of narrow-band speech is presented. The speech features used to assess quality are the sample mean and variance of band-powers evaluated from the temporal envelope in the channels of an auditory filter-bank. Bayesian multivariate adaptive regression splines (BMARS) is used to map features into quality ratings. The proposed combination of features and regression method leads to a high performance quality assessment algorithm that learns efficiently from a small amount of training data and avoids overfitting. Use of the Bayesian approach also allows the derivation of credible intervals on the model predictions, which provide a quantitative measure of model confidence and can be used to identify the need for complementing the training databases.
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| 9. |
- Petkov, Petko N., et al.
(författare)
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Discrete Choice Models for Non-Intrusive Quality Assessment
- 2011
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Ingår i: 12th Annual Conference Of The International Speech Communication Association 2011 (INTERSPEECH 2011), Vols 1-5. - : ISCA. - 9781618392701 ; , s. 200-203
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Konferensbidrag (refereegranskat)abstract
- Non-intrusive signal quality assessment in general, and its application to speech signal processing, in particular, builds extensively upon statistical regression models. Commonly, the raw preference scores used for fitting these models belong to a categorical scale. Averaging the scores over a number of test subjects results in smooth, close-to-continuous ratings, thus justifying the use of regression as opposed to classification models. A form of marginalization, averaging subjective ratings takes away useful information about the reliability of individual test points. Using a model tailored to the raw data achieves highly competitive performance in terms of conventional performance measures while providing the additional advantage of identifying the usability of individual test points. In this paper, we consider the application of discrete choice models to non-intrusive quality assessment of speech.
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| 10. |
- Petkov, Petko N., et al.
(författare)
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Enhancing Subjective Speech Intelligibility Using a Statistical Model of Speech
- 2012
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Ingår i: 13th Annual Conference of the International Speech Communication Association 2012, INTERSPEECH 2012, Vol 1. - 9781622767595 ; , s. 166-169
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Konferensbidrag (refereegranskat)abstract
- The intelligibility of speech in adverse noise conditions can be improved by modifying the characteristics of the clean speech prior to its presentation. An effective and flexible paradigm is to select the modification by optimizing a measure of objective intelligibility. Here we apply this paradigm at the text level and optimize a measure related to the classification error probability in an automatic speech recognition system. The proposed method was applied to a simple but powerful band-energy modification mechanism under an energy preservation constraint. Subjective evaluation results provide a clear indication of a significant gain in subjective intelligibility. In contrast to existing methods, the proposed approach is not restricted to a particular modification strategy and treats the notion of optimality at a level closer to that of subjective intelligibility. The computational complexity of the method is sufficiently low to enable its use in on-line applications.
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