325 research outputs found
Multiphonon Raman Scattering in Graphene
We report multiphonon Raman scattering in graphene samples. Higher order
combination modes involving 3 phonons and 4 phonons are observed in
single-layer (SLG), bi-layer (BLG), and few layer (FLG) graphene samples
prepared by mechanical exfoliation. The intensity of the higher order phonon
modes (relative to the G peak) is highest in SLG and decreases with increasing
layers. In addition, all higher order modes are observed to upshift in
frequency almost linearly with increasing graphene layers, betraying the
underlying interlayer van der Waals interactions.Comment: Accepted for publication in Phys. Rev.
Cabibbo-suppressed non-leptonic B- and D-decays involving tensor mesons
The Cabibbo-suppressed non-leptonic decays of B (and D) mesons to final
states involving tensor mesons are computed using the non-relativistic quark
model of Isgur-Scora-Grinstein-Wise with the factorization hypothesis. We find
that some of these B decay modes, as B --> (K^*, D^*)D^*_2, can have branching
ratios as large as 6 x 10^{-5} which seems to be at the reach of future B
factories.Comment: Latex, 11 pages, to appear in Phys. Rev.
Non-leptonic B decays involving tensor mesons
Two-body non-leptonic decays of B mesons into PT and VT modes are calculated
using the non-relativistic quark model of Isgur et al.. The predictions
obtained for are a factor of below
present experimental upper limits. Interesting patterns are obtained for ratios
of B decays involving mesons with different spin excitations and their
relevance for additional tests of forms factor models are briefly discussed.Comment: 11 pages, Latex, to appear in Phys. Rev.
Automated Domain Discovery from Multiple Sources to Improve Zero-Shot Generalization
Domain generalization (DG) methods aim to develop models that generalize to
settings where the test distribution is different from the training data. In
this paper, we focus on the challenging problem of multi-source zero shot DG
(MDG), where labeled training data from multiple source domains is available
but with no access to data from the target domain. A wide range of solutions
have been proposed for this problem, including the state-of-the-art
multi-domain ensembling approaches. Despite these advances, the na\"ive ERM
solution of pooling all source data together and training a single classifier
is surprisingly effective on standard benchmarks. In this paper, we hypothesize
that, it is important to elucidate the link between pre-specified domain labels
and MDG performance, in order to explain this behavior. More specifically, we
consider two popular classes of MDG algorithms -- distributional robust
optimization (DRO) and multi-domain ensembles, in order to demonstrate how
inferring custom domain groups can lead to consistent improvements over the
original domain labels that come with the dataset. To this end, we propose (i)
Group-DRO++, which incorporates an explicit clustering step to identify custom
domains in an existing DRO technique; and (ii) DReaME, which produces effective
multi-domain ensembles through implicit domain re-labeling with a novel
meta-optimization algorithm. Using empirical studies on multiple standard
benchmarks, we show that our variants consistently outperform ERM by
significant margins (1.5% - 9%), and produce state-of-the-art MDG performance.
Our code can be found at https://github.com/kowshikthopalli/DREAM
- …