1,016 research outputs found
Combined aptamer and transcriptome sequencing of single cells.
The transcriptome and proteome encode distinct information that is important for characterizing heterogeneous biological systems. We demonstrate a method to simultaneously characterize the transcriptomes and proteomes of single cells at high throughput using aptamer probes and droplet-based single cell sequencing. With our method, we differentiate distinct cell types based on aptamer surface binding and gene expression patterns. Aptamers provide advantages over antibodies for single cell protein characterization, including rapid, in vitro, and high-purity generation via SELEX, and the ability to amplify and detect them with PCR and sequencing
Questioning the existence of a unique ground state structure for Si clusters
Density functional and quantum Monte Carlo calculations challenge the
existence of a unique ground state structure for certain Si clusters. For Si
clusters with more than a dozen atoms the lowest ten isomers are close in
energy and for some clusters entropic effects can change the energetic ordering
of the configurations. Isotope pure configurations with rotational symmetry and
symmetric configurations containing one additional isotope are disfavored by
these effects. Comparisons with experiment are thus difficult since a mixture
of configurations is to be expected at thermal equilibrium
Systematic computation of crystal field multiplets for X-ray core spectroscopies
We present a new approach to computing multiplets for core spectroscopies,
whereby the crystal field is constructed explicitly from the positions and
charges of surrounding atoms. The simplicity of the input allows the
consideration of crystal fields of any symmetry, and in particular facilitates
the study of spectroscopic effects arising from low symmetry environments. The
interplay between polarization directions and crystal field can also be
conveniently investigated. The determination of the multiplets proceeds from a
Dirac density functional atomic calculation, followed by the exact
diagonalization of the Coulomb, spin-orbit and crystal field interactions for
the electrons in the open shells. The eigenstates are then used to simulate
X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering spectra.
In examples ranging from high symmetry down to low symmetry environment,
comparisons with experiments are done with unadjusted model parameters as well
as with semi-empirically optimized ones. Furthermore, predictions for the RIXS
of low-temperature MnO and for Dy in a molecular complex are proposed.Comment: Accepted for publication in Phys. Rev.
Electronic structure and physical properties of the spinel-type phase of BeP2N4 from all-electron density functional calculations
Using density-functional-theory-based ab initio methods, the electronic structure and physical properties of the newly synthesized nitride BeP2N4 with a phenakite-type structure and the predicted high-pressure spinel phase of BeP2N4 are studied in detail. It is shown that both polymorphs are wide band-gap semiconductors with relatively small electron effective masses at the conduction-band minima. The spinel-type phase is more covalently bonded due to the increased number of P-N bonds for P at the octahedral sites. Calculations of mechanical properties indicate that the spinel-type polymorph is a promising superhard material with notably large bulk, shear, and Young’s moduli. Also calculated are the Be K, P K, P L3, and N K edges of the electron energy-loss near-edge structure for both phases. They show marked differences because of the different local environments of the atoms in the two crystalline polymorphs. These differences will be very useful for the experimental identification of the products of high-pressure syntheses targeting the predicted spinel-type phase of BeP2N4
Non-Adiabatic Potential-Energy Surfaces by Constrained Density-Functional Theory
Non-adiabatic effects play an important role in many chemical processes. In
order to study the underlying non-adiabatic potential-energy surfaces (PESs),
we present a locally-constrained density-functional theory approach, which
enables us to confine electrons to sub-spaces of the Hilbert space, e.g. to
selected atoms or groups of atoms. This allows to calculate non-adiabatic PESs
for defined charge and spin states of the chosen subsystems. The capability of
the method is demonstrated by calculating non-adiabatic PESs for the scattering
of a sodium and a chlorine atom, for the interaction of a chlorine molecule
with a small metal cluster, and for the dissociation of an oxygen molecule at
the Al(111) surface.Comment: 11 pages including 7 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Evolution of the interfacial structure of LaAlO3 on SrTiO3
The evolution of the atomic structure of LaAlO3 grown on SrTiO3 was
investigated using surface x-ray diffraction in conjunction with
model-independent, phase-retrieval algorithms between two and five monolayers
film thickness. A depolarizing buckling is observed between cation and oxygen
positions in response to the electric field of polar LaAlO3, which decreases
with increasing film thickness. We explain this in terms of competition between
elastic strain energy, electrostatic energy, and electronic reconstructions.
The findings are qualitatively reproduced by density-functional theory
calculations. Significant cationic intermixing across the interface extends
approximately three monolayers for all film thicknesses. The interfaces of
films thinner than four monolayers therefore extend to the surface, which might
affect conductivity
Evidence for coupling between collective state and phonons in two-dimensional charge-density-wave systems
We report on a Raman scattering investigation of the charge-density-wave
(CDW), quasi two-dimensional rare-earth tri-tellurides Te (= La, Ce,
Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe and CeTe under
externally applied pressure. The observed phonon peaks can be ascribed to the
Raman active modes for both the undistorted as well as the distorted lattice in
the CDW state by means of a first principles calculation. The latter also
predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition.
The integrated intensity of the two most prominent modes scales as a
characteristic power of the CDW-gap amplitude upon compressing the lattice,
which provides clear evidence for the tight coupling between the CDW condensate
and the vibrational modes
Tunable Conductivity and Conduction Mechanism in a UV light activated electronic conductor
A tunable conductivity has been achieved by controllable substitution of a
novel UV light activated electronic conductor. The transparent conducting oxide
system H-doped Ca12-xMgxAl14O33 (x = 0; 0.1; 0.3; 0.5; 0.8; 1.0) presents a
conductivity that is strongly dependent on the substitution level and
temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x = 0)
to 0.106 S/cm (x = 1) at room temperature. At each composition the conductivity
increases (reversibly with temperature) until a decomposition temperature is
reached; above this value, the conductivity drops dramatically due to hydrogen
recombination and loss. The observed conductivity behavior is consistent with
the predictions of our first principles density functional calculations for the
Mg-substituted system with x=0, 1 and 2. The Seebeck coefficient is essentially
composition- and temperature-independent, the later suggesting the existence of
an activated mobility associated with small polaron conduction. The optical gap
measured remains constant near 2.6 eV while transparency increases with the
substitution level, concomitant with a decrease in carrier content.Comment: Submitted for publicatio
Evidence for SrHo2O4 and SrDy2O4 as model J1-J2 zig-zag chain materials
Neutron diffraction and inelastic spectroscopy is used to characterize the
magnetic Hamiltonian of SrHo2O4 and SrDy2O4. Through a detailed computation of
the crystal-field levels we find site- dependent anisotropic single-ion
magnetism in both materials and diffraction measurements show the presence of
strong one-dimensional spin correlations. Our measurements indicate that
competing interactions of the zig-zag chain, combined with frustrated
interchain interactions, play a crucial role in stabilizing spin-liquid type
correlations in this series.Comment: 5 pages, 5 figure
- …