Coupled Spin-Phonon Excitations in Helical Multiferroics

Both the Dzyaloshiskii-Moriya interaction and the exchange-striction are shown to affect dynamically the magnetoelectric excitations in the perovskite multiferroic RMnO3. The exchange-striction results in a biquadratic interaction between the spins and the transverse phonons, giving rise to quantum fluctuations of the ferroelectric polarization P. This leads to low-lying phonon modes that are perpendicular to P and to the helical spins at small wave vector but are parallel to P at a wave vector close to the magnetic modulation vector. For spin-1/2 helimagnet, the local polarization can be completely reversed by the spin fluctuation, and so does the direction of the on-site spin chirality, which allows for a finite differential scattering intensity of polarized neutrons from a cycloidal magnet.Comment: 7 page

Improved Noisy Student Training for Automatic Speech Recognition

Recently, a semi-supervised learning method known as "noisy student training" has been shown to improve image classification performance of deep networks significantly. Noisy student training is an iterative self-training method that leverages augmentation to improve network performance. In this work, we adapt and improve noisy student training for automatic speech recognition, employing (adaptive) SpecAugment as the augmentation method. We find effective methods to filter, balance and augment the data generated in between self-training iterations. By doing so, we are able to obtain word error rates (WERs) 4.2%/8.6% on the clean/noisy LibriSpeech test sets by only using the clean 100h subset of LibriSpeech as the supervised set and the rest (860h) as the unlabeled set. Furthermore, we are able to achieve WERs 1.7%/3.4% on the clean/noisy LibriSpeech test sets by using the unlab-60k subset of LibriLight as the unlabeled set for LibriSpeech 960h. We are thus able to improve upon the previous state-of-the-art clean/noisy test WERs achieved on LibriSpeech 100h (4.74%/12.20%) and LibriSpeech (1.9%/4.1%).Comment: 5 pages, 5 figures, 4 tables; v2: minor revisions, reference adde

Lentiviral vector design using alternative RNA export elements

<p>Abstract</p> <p>Background</p> <p>Lentiviral vectors have been designed with complex RNA export sequences in both the integrating and packaging plasmids in order to co-ordinate efficient vector production. Recent studies have attempted to replace the existing complex rev/RRE system with a more simplistic RNA export system from simple retroviruses to make these vectors in a rev-independent manner.</p> <p>Results</p> <p>Towards this end, lentiviral transfer plasmids were modified with various cis-acting DNA elements that co-ordinate RNA export during viral production to determine their ability to affect the efficiency of vector titer and transduction in different immortalized cell lines in vitro. It was found that multiple copies of the constitutive transport element (CTE) originating from different simian retroviruses, including simian retrovirus type 1 (SRV-1) and type-2 (SRV-2) and Mason-Pfizer (MPV) could be used to eliminate the requirement for the rev responsive element (RRE) in the transfer and packaging plasmids with titers >10⁶T.U./mL (n = 4–8 preparations). The addition of multiple copies of the murine intracisternal type A particle, the woodchuck post-regulatory element (WPRE), or single and dual copies of the simian CTE had minimal effect on viral titer. Immortalized cell lines from different species were found to be readily transduced by VSV-G pseudotyped lentiviral vectors containing the multiple copies of the CTE similar to the findings in HeLa cells, although the simian-derived CTE were found to have a lower infectivity into murine cell lines compared to the other species.</p> <p>Conclusion</p> <p>These studies demonstrated that the rev-responsive element (RRE) could be replaced with other constitutive transport elements to produce equivalent titers using lentivectors containing the RRE sequence <it>in vitro</it>, but that concatemerization of the CTE or the close proximity of RNA export sequences was needed to enhance vector production.</p

Quantifying and monitoring functional Photosystem II and the stoichiometry of the two photosystems in leaf segments: Approaches and approximations

Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus of studies of photosynthetic structure and function, particularly in environmental stress conditions. Here we review four approaches for quantifying or monitoring PS II functionality or the stoichiometry of the two photosystems in leaf segments, scrutinizing the approximations in each approach. (1) Chlorophyll fluorescence parameters are convenient to derive, but the information-rich signal suffers from the localized nature of its detection in leaf tissue. (2) The gross O2 yield per single-turnover flash in CO2-enriched air is a more direct measurement of the functional content, assuming that each functional PS II evolves one O2 molecule after four flashes. However, the gross O2 yield per single-turnover flash (multiplied by four) could overestimate the content of functional PS II if mitochondrial respiration is lower in flash illumination than in darkness. (3) The cumulative delivery of electrons from PS II to P700? (oxidized primary donor in PS I) after a flash is added to steady background far-red light is a whole-tissue measurement, such that a single linear correlation with functional PS II applies to leaves of all plant species investigated so far. However, the magnitude obtained in a simple analysis (with the signal normalized to the maximum photo-oxidizable P700 signal), which should equal the ratio of PS II to PS I centers, was too small to match the independently-obtained photosystem stoichiometry. Further, an under-estimation of functional PS II content could occur if some electrons were intercepted before reaching PS I. (4) The electrochromic signal from leaf segments appears to reliably quantify the photosystem stoichiometry, either by progressively photoinactivating PS II or suppressing PS I via photo-oxidation of a known fraction of the P700 with steady far-red light. Together, these approaches have the potential for quantitatively probing PS II in vivo in leaf segments, with prospects for application of the latter two approaches in the field