In this study, we consider a summarization method using the document level similarity based on embeddings, or distributed representations of words, where we assume that an embedding of each word can represent its "meaning." We formalize our task as the problem of maximizing a submodular function defined by the negative summation of the nearest neighbors' distances on embedding distributions, each of which represents a set of word embeddings in a document. We proved the submodularity of our objective function and that our problem is asymptotically related to the KL-divergence between the probability density functions that correspond to a document and its summary in a continuous space. An experiment using a real dataset demonstrated that our method performed better than the existing method based on sentence-level similarity.
RAS and BRAF-mutated colorectal cancers are associated with resistance to chemotherapy and poor prognosis, highlighting the need for new therapeutic strategies. Although these cancers sometimes respond to mitogen activated protein kinase kinase (MEK) inhibitor treatment, they often acquire resistance via mechanisms, which are poorly understood. Here, we investigated the mechanism of MEK inhibitor resistance in primary- and acquired-resistant cells. Cell viability was examined using the trypan blue dye exclusion assay. Protein expression was analyzed by western blotting. Somatic mutations in colorectal cancer cells were investigated using the polymerase chain reaction array. PD0325901 and trametinib induced cell death in LoVo and Colo-205 cells but not in DLD-1 and HT-29 cells, which have a PIK3CA mutation constitutively activating Akt and NF-κB. Treatment with PD0325901 and trametinib suppressed ERK1/2 activation in all four cell lines but only induced Akt and NF-κB activation in DLD-1 and HT-29 cells. Inhibition of Akt but not NF-κB, overcame MEK inhibitor resistance in DLD-1 and HT-29 cells. Acquired-resistant LoVo/PR, Colo-205/PR and LoVo/TR cells have constitutively active Akt due to a M1043V mutation in the kinase activation loop of PIK3CA and Akt inhibitor resensitized these cells to MEK inhibitor. These results demonstrate that the overactivation of Akt plays a critical role in MEK inhibitor primary and acquired resistance and implicate combined Akt/MEK inhibition as a potentially useful treatment for RAS/BRAF-mutated colorectal cancer.
In Taiwan Mandarin, retroflex [ʂ] is allegedly merging with dental [s], reducing the traditional three-way contrast between sibilant fricatives (i.e., dental [s]–retroflex [ʂ]–alveopalatal [ɕ]) to a two-way contrast. Most of the literature on the observed merging focuses on the acoustic properties and perceptual identification of the sibilants, whereas much less attention has been drawn to the articulatory evidence accounting for the aforementioned sibilant merging. The current study employed ultrasound imaging techniques to uncover the tongue postures for the three sibilant fricatives [s, ʂ, ɕ] in Taiwan Mandarin occurring before vowels [a], [ɨ], and [o]. Results revealed varying classes of the [s–ʂ] merger: complete merging ( overlap), no merging ( non-overlap), and context-dependent merging ( context-dependent overlap, which only occurred before [a]). The observed [s–ʂ] merger was also confirmed by the perceptual identification by trained phoneticians. Center of gravity (CoG), a reliable spectral moment of identifying different sibilant fricatives, was also measured to reflect the articulatory–acoustic correspondence. Results showed that the [s–ʂ] merger varies across speakers and may also be conditioned by vowel contexts and that articulatory mergers may not be entirely reflected in CoG values, suggesting that auxiliary articulatory gestures may be employed to maintain the acoustic contrast.
In human languages, different speech sounds can be contextual variants of a single phoneme, called allophones. Learning which sounds are allophones is an integral part of the acquisition of phonemes. Whether given sounds are separate phonemes or allophones in a listener's language affects speech perception. Listeners tend to be less sensitive to acoustic differences between sounds that are allophones. This study investigated the mechanisms behind the learning of allophones by looking at adults' sensitivity to acoustic differences between two unfamiliar sounds when they were exposed to input in which the sounds behave like separate phonemes versus allophones in terms of their contextual distribution. The results of two experiments showed that adults became less sensitive to acoustic differences between two unfamiliar sounds after being exposed to input in which the sounds were in complementary distribution and that the emergence of allophonic perception was constrained by the phonetic naturalness of complementary distribution.Keywords allophone perception; distributional learning; constraints; language learning; phonetic naturalness Introduction Sound systems are a basic building block of any human language, and a major component of sound systems is the inventory of phonemes or sounds that are used to make lexical contrasts (e.g., Trubetzkoy, 1969;Twaddell, 1935 Phonemes often have contextually conditioned variants called allophones (e.g., Hall, 2009;Jones, 1950). In order to acquire sound systems, learners need to know whether given sounds are separate phonemes or allophones of the same phoneme. There is growing interest in the learning of allophones (see Seidl & Cristia, 2012, for a review of the learning of allophones by infants). However, the mechanisms supporting allophone learning are not yet understood. In this study, we investigated whether adults would perceive two unfamiliar sounds as being allophone-like after exposure to input in which these sounds were presented in mutually exclusive contexts, their occurrences being thus predictable from the contexts. We also investigated whether the emergence of allophonic perception is constrained by linguistic factors, specifically the phonetic naturalness of the patterns in the contextual distribution. BackgroundWhether given sounds are separate phonemes or the allophones of the same phoneme is determined by their function and distribution. In terms of function, sounds that are separate phonemes are used to create lexical contrasts. This means that replacing one sound with a different one can change the meaning of a word. Sounds that are allophones, by contrast, are not used to create lexical contrasts. In terms of distribution, sounds that are separate phonemes can occur in the same phonological environment, and thus their occurrences are not contextually predictable. Sounds that are allophones, by contrast, do not occur in the same phonological environment. They occur in mutually exclusive contexts, that is, they are in complementary distribution, and thus the...
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