2,705 research outputs found
Q^2-Dependence of the Proton's G_1 Structure Function Sum Rule
We study the variation of the first moment of the nucleon's
spin-dependent structure function . As the moment is
determined by the low energy theorem for Compton scattering. In the
deep-inelastic region the moment is calculated using twist expansion to order
. Based on these limits, we construct a formula which smoothly
interpolates between the two regions.Comment: (revised), 8 pages in REVTEX, 1 figure, MIT-CTP-223
Natural Language Processing with Small Feed-Forward Networks
We show that small and shallow feed-forward neural networks can achieve near
state-of-the-art results on a range of unstructured and structured language
processing tasks while being considerably cheaper in memory and computational
requirements than deep recurrent models. Motivated by resource-constrained
environments like mobile phones, we showcase simple techniques for obtaining
such small neural network models, and investigate different tradeoffs when
deciding how to allocate a small memory budget.Comment: EMNLP 2017 short pape
Site-resolved imaging of a fermionic Mott insulator
The complexity of quantum many-body systems originates from the interplay of
strong interactions, quantum statistics, and the large number of
quantum-mechanical degrees of freedom. Probing these systems on a microscopic
level with single-site resolution offers important insights. Here we report
site-resolved imaging of two-component fermionic Mott insulators, metals, and
band insulators using ultracold atoms in a square lattice. For strong repulsive
interactions we observe two-dimensional Mott insulators containing over 400
atoms. For intermediate interactions, we observe a coexistence of phases. From
comparison to theory we find trap-averaged entropies per particle of
. In the band-insulator we find local entropies as low as
. Access to local observables will aid the understanding
of fermionic many-body systems in regimes inaccessible by modern theoretical
methods.Comment: 6+7 page
Universality of the Collins-Soper-Sterman nonperturbative function in gauge boson production
We revise the model for the Collins-Soper-Sterman resummed form factor
to improve description of the leading-power contribution at nearly
nonperturbative impact parameters. This revision leads to excellent agreement
of the transverse momentum resummation with the data in a global analysis of
Drell-Yan lepton pair and Z boson production. The nonperturbative contributions
are found to follow universal quasi-linear dependence on the logarithm of the
heavy boson invariant mass, which closely agrees with an estimate from the
infrared renormalon analysis.Comment: published version; 14 pages, 4 figures, additional discussio
Optimizing Beam Transport in Rapidly Compressing Beams on the Neutralized Drift Compression Experiment - II
The Neutralized Drift Compression Experiment-II (NDCX-II) is an induction
linac that generates intense pulses of 1.2 MeV helium ions for heating matter
to extreme conditions. Here, we present recent results on optimizing beam
transport. The NDCX-II beamline includes a 1-meter-long drift section
downstream of the last transport solenoid, which is filled with
charge-neutralizing plasma that enables rapid longitudinal compression of an
intense ion beam against space-charge forces. The transport section on NDCX-II
consists of 28 solenoids. Finding optimal field settings for a group of
solenoids requires knowledge of the envelope parameters of the beam. Imaging
the beam on scintillator gives the radius of the beam, but the envelope angle
dr/dz is not measured directly. We demonstrate how the parameters of the beam
envelope (r, dr/dz, and emittance) can be reconstructed from a series of images
taken at varying B-field strengths of a solenoid upstream of the scintillator.
We use this technique to evaluate emittance at several points in the NDCX-II
beamline and for optimizing the trajectory of the beam at the entry of the
plasma-filled drift section
Gene expression regulation by the Chromodomain helicase DNA-binding protein 9 (CHD9) chromatin remodeler is dispensable for murine development.
Chromodomain helicase DNA-binding (CHD) chromatin remodelers regulate transcription and DNA repair. They govern cell-fate decisions during embryonic development and are often deregulated in human pathologies. Chd1-8 show upon germline disruption pronounced, often developmental lethal phenotypes. Here we show that contrary to Chd1-8 disruption, Chd9-/-animals are viable, fertile and display no developmental defects or disease predisposition. Germline deletion of Chd9 only moderately affects gene expression in tissues and derived cells, whereas acute depletion in human cancer cells elicits more robust changes suggesting that CHD9 is a highly context-dependent chromatin regulator that, surprisingly, is dispensable for mouse development
- âŠ