687 research outputs found
Bacillus subtilis regulatory protein GerE
GerE is the latest-acting of a series of factors which regulate gene expression in the mother cell during sporulation in Bacillus. The gene encoding GerE has been cloned from B. subtilis and overexpressed in Escherichia coli. Purified GerE has been crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. The small plate-like crystals belong to the monoclinic space group C2 and diffract beyond 2.2 Angstrom resolution with a synchrotron radiation X-ray source
Material Decomposition in Spectral CT using deep learning: A Sim2Real transfer approach
The state-of-the art for solving the nonlinear material decomposition problem in spectral computed tomography is based on variational methods, but these are computationally slow and critically depend on the particular choice of the regularization functional. Convolutional neural networks have been proposed for addressing these issues. However, learning algorithms require large amounts of experimental data sets. We propose a deep learning strategy for solving the material decomposition problem based on a U-Net architecture and a Sim2Real transfer learning approach where the knowledge that we learn from synthetic data is transferred to a real-world scenario. In order for this approach to work, synthetic data must be realistic and representative of the experimental data. For this purpose, numerical phantoms are generated from human CT volumes of the KiTS19 Challenge dataset, segmented into specific materials (soft tissue and bone). These volumes are projected into sinogram space in order to simulate photon counting data, taking into account the energy response of the scanner. We compared projection- and image-based decomposition approaches where the network is trained to decompose the materials either in the projection or in the image domain. The proposed Sim2Real transfer strategies are compared to a regularized Gauss-Newton (RGN) method on synthetic data, experimental phantom data and human thorax data
Limits on WWgamma and WWZ Couplings from W Boson Pair Production
The results of a search for W boson pair production in pbar-p collisions at
sqrt{s}=1.8 TeV with subsequent decay to emu, ee, and mumu channels are
presented. Five candidate events are observed with an expected background of
3.1+-0.4 events for an integrated luminosity of approximately 97 pb^{-1}.
Limits on the anomalous couplings are obtained from a maximum likelihood fit of
the E_T spectra of the leptons in the candidate events. Assuming identical
WWgamma and WWZ couplings, the 95 % C.L. limits are -0.62<Delta_kappa<0.77
(lambda = 0) and -0.53<lambda<0.56 (Delta_kappa = 0) for a form factor scale
Lambda = 1.5 TeV.Comment: 10 pages, 1 figure, submitted to Physical Review
Probing BFKL Dynamics in the Dijet Cross Section at Large Rapidity Intervals in ppbar Collisions at sqrt{s}=1800 and 630 GeV
Inclusive dijet production at large pseudorapidity intervals (delta_eta)
between the two jets has been suggested as a regime for observing BFKL
dynamics. We have measured the dijet cross section for large delta_eta in ppbar
collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic
cross section increases strongly with the size of delta_eta. The observed
growth is even stronger than expected on the basis of BFKL resummation in the
leading logarithmic approximation. The growth of the partonic cross section can
be accommodated with an effective BFKL intercept of
a_{BFKL}(20GeV)=1.65+/-0.07.Comment: Published in Physical Review Letter
Search for Electroweak Production of Single Top Quarks in ppbar Collisions
We present a search for electroweak production of single top quarks in the
electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of
data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with
the DZero detector between 1992 and 1995. We use events that include a tagging
muon, implying the presence of a b jet, to set an upper limit at the 95%
confidence level on the cross section for the s-channel process ppbar->tb+X of
39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb.Comment: 11 pages, 2 figures. This is the published versio
A Quasi-Model-Independent Search for New Physics at Large Transverse Momentum
We apply a quasi-model-independent strategy ("Sleuth") to search for new high
p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV
collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron.
Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X
exclusive final states are systematically analyzed for hints of physics beyond
the standard model. Simultaneous sensitivity to a variety of models predicting
new phenomena at the electroweak scale is demonstrated by testing the method on
a particular signature in each set of final states. No evidence of new high p_T
physics is observed in the course of this search, and we find that 89% of an
ensemble of hypothetical similar experimental runs would have produced a final
state with a candidate signal more interesting than the most interesting
observed in these data.Comment: 28 pages, 17 figures. Submitted to Physical Review
Search for R-parity Violating Supersymmetry in Dimuon and Four-Jets Channel
We present results of a search for R-parity-violating decay of the neutralino
chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that
this decay proceeds through one of the lepton-number violating couplings
lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data,
collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at
a center of mass energy of 1.8 TeV in 1992-1995.Comment: 10 pages, 3 figure
Search for bottom squarks in pbarp collisions at sqrt(s)=1.8 TeV
We report on a search for bottom squarks produced in pbarp collisions at
sqrt(s) = 1.8 TeV using the D0 detector at Fermilab. Bottom squarks are assumed
to be produced in pairs and to decay to the lightest supersymmetric particle
(LSP) and a b quark with branching fraction of 100%. The LSP is assumed to be
the lightest neutralino and stable. We set limits on the production cross
section as a function of bottom squark mass and LSP mass.Comment: 5 pages, Latex. submitted 3-12-1999 to PRD - Rapid Communicatio
Spin Correlation in tt-bar Production from pp-bar Collisions at sqrt(s)=1.8 TeV
The D0 collaboration has performed a study of spin correlation in tt-bar
production for the process tt-bar to bb-bar W^+W^-, where the W bosons decay to
e-nu or mu-nu. A sample of six events was collected during an exposure of the
D0 detector to an integrated luminosity of approximately 125 pb^-1 of
sqrt{s}=1.8 TeV pp-bar collisions. The standard model (SM) predicts that the
short lifetime of the top quark ensures the transmission of any spin
information at production to the tt-bar decay products.
The degree of spin correlation is characterized by a correlation coefficient
k. We find that k>-0.25 at the 68% confidence level, in agreement with the SM
prediction of k=0.88.Comment: Submitted to PRL, Added references, minor changes to tex
Direct Search for Charged Higgs Bosons in Decays of Top Quarks
We present a search for charged Higgs bosons in decays of pair-produced top
quarks in pbar p collisions at sqrt(s) = 1.8 TeV using 62.2 pb^-1 of data
recorded by the D0 detector at the Fermilab Tevatron collider. No evidence is
found for signal, and we exclude at 95% confidence most regions of the (M
higgs, tan beta) parameter space where the decay t->H b has a branching
fraction greater than 0.36 and B(H -> tau nu) is large.Comment: 11 pages, 4 figures, submitted to Phys. Rev. Let
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