149 research outputs found
Finding the Dynamics of an Integrable Quantum Many-Body System via Machine Learning
We study the dynamics of the Gaudin magnet ("central-spin model") using
machine-learning methods. This model is of practical importance, e.g., for
studying non-Markovian decoherence dynamics of a central spin interacting with
a large bath of environmental spins and for studies of nonequilibrium
superconductivity. The Gaudin magnet is also integrable, admitting many
conserved quantities: For spins, the model Hamiltonian can be written as
the sum of independent commuting operators. Despite this high degree of
symmetry, a general closed-form analytic solution for the dynamics of this
many-body problem remains elusive. Machine-learning methods may be well suited
to exploiting the high degree of symmetry in integrable problems, even when an
explicit analytic solution is not obvious. Motivated in part by this intuition,
we use a neural-network representation (restricted Boltzmann machine) for each
variational eigenstate of the model Hamiltonian. We then obtain accurate
representations of the ground state and of the low-lying excited states of the
Gaudin-magnet Hamiltonian through a variational Monte Carlo calculation. From
the low-lying eigenstates, we find the non-perturbative dynamic transverse spin
susceptibility, describing the linear response of a central spin to a
time-varying transverse magnetic field in the presence of a spin bath. Having
an efficient description of this susceptibility opens the door to improved
characterization and quantum control procedures for qubits interacting with an
environment of quantum two-level systems. These systems include electron-spin
and hole-spin qubits interacting with environmental nuclear spins via hyperfine
interactions or qubits with charge or flux degrees of freedom interacting with
coherent charge or paramagnetic impurities.Comment: 13 pages, 9 figure
Quantification of lentiviral vector copy numbers in individual hematopoietic colony-forming cells shows vector dose-dependent effects on the frequency and level of transduction
Lentiviral vectors are effective tools for gene transfer and integrate variable numbers of proviral DNA copies in variable proportions of cells. The levels of transduction of a cellular population may therefore depend upon experimental parameters affecting the frequency and/or the distribution of vector integration events in this population. Such analysis would require measuring vector copy numbers (VCN) in individual cells. To evaluate the transduction of hematopoietic progenitor cells at the single-cell level, we measured VCN in individual colony-forming cell (CFC) units, using an adapted quantitative PCR (Q-PCR) method. The feasibility, reproducibility and sensitivity of this approach were tested with characterized cell lines carrying known numbers of vector integration. The method was validated by correlating data in CFC with gene expression or with calculated values, and was found to slightly underestimate VCN. In spite of this, such Q-PCR on CFC was useful to compare transduction levels with different infection protocols and different vectors. Increasing the vector concentration and re-iterating the infection were two different strategies that improved transduction by increasing the frequency of transduced progenitor cells. Repeated infection also augmented the number of integrated copies and the magnitude of this effect seemed to depend on the vector preparation. Thus, the distribution of VCN in hematopoietic colonies may depend upon experimental conditions including features of vectors. This should be carefully evaluated in the context of ex vivo hematopoietic gene therapy studies
Universal high work function flexible anode for simplified ITO-free organic and perovskite light-emitting diodes with ultra-high efficiency
Flexible transparent electrode materials such as conducting polymers, silver nanowires, carbon nanotubes and graphenes are being investigated as possible replacements for conventional brittle inorganic electrodes. However, they have critical drawbacks of low work function (WF), resulting in a high hole injection barrier to an overlying semiconducting layer in simplified organic or organic-inorganic hybrid perovskite light-emitting diodes (OLEDs or PeLEDs). Here, we report a new anode material (AnoHIL) that has multifunction of both an anode and a hole injection layer (HIL) as a single layer. The AnoHIL has easy WF tunability up to 5.8 eV and thus makes ohmic contact without any HIL. We applied our anodes to simplified OLEDs, resulting in very high efficiency (62% ph el(-1) for single and 88% ph el(-1) for tandem). The AnoHIL showed a similar tendency in simplified PeLEDs, implying universal applicability to various optoelectronics. We also demonstrated large-area flexible lightings using our anodes. Our results provide a significant step toward the next generation of high-performance simplified indium tin oxide (ITO)-free light-emitting diodes.
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