The ability to predict
tandem mass (MS/MS) spectra from peptide sequences can significantly
enhance our understanding of the peptide fragmentation process and
could improve peptide identification in proteomics. However, current
approaches for predicting high-energy collisional dissociation (HCD)
spectra are limited to predict the intensities of expected ion types,
that is, the a/b/c/x/y/z ions and their neutral loss derivatives (referred
to as backbone ions). In practice, backbone ions
only account for <70% of total ion intensities in HCD spectra,
indicating many intense ions are ignored by current predictors. In
this paper, we present a deep learning approach that can predict the complete spectra (both backbone and nonbackbone ions) directly
from peptide sequences. We made no assumptions or expectations on
which kind of ions to predict but instead predicting the intensities
for all possible m/z. Training this
model needs no annotations of fragment ion nor any prior knowledge
of the fragmentation rules. Our analyses show that the predicted 2+
and 3+ HCD spectra are highly similar to the experimental spectra,
with average full-spectrum cosine similarities of 0.820 (±0.088)
and 0.786 (±0.085), respectively, very close to the similarities
between the experimental replicated spectra. In contrast, the best-performed
backbone only models can only achieve an average similarity below
0.75 and 0.70 for 2+ and 3+ spectra, respectively. Furthermore, we
developed a multitask learning (MTL) approach for predicting spectra
of insufficient training samples, which allows our model to make accurate
predictions for electron transfer dissociation (ETD) spectra and HCD
spectra of less abundant charges (1+ and 4+).
Flexoelectricity is an electro-mechanical coupling effect that exists in all dielectrics and has the potential to replace piezoelectric actuating on the microscale. In this letter, a curved flexoelectric actuator with non-polarized polyvinylidene fluoride is presented and shown to exhibit good electro-mechanical properties. This provides experimental support for a body of theoretical research into converse flexoelectricity in polymeric materials. In addition, this work demonstrates the feasibility of lead-free microscale actuating without piezoelectricity.
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