pinecone/core-2020-05-10-deduplication huggingface dataset:
Astrophysical Black Holes: A Compact Pedagogical Review

Black holes are among the most extreme objects that can be found in the
Universe and an ideal laboratory for testing fundamental physics. This article
will briefly review the basic properties of black holes as expected from
general relativity, the main astronomical observations, and the leading
astrophysical techniques to probe the strong gravity region of these objects.
It is mainly intended to provide a compact introductory overview on
astrophysical black holes to new students entering this research field, as well
as to senior researchers working in general relativity and alternative theories
of gravity and wishing to quickly learn the state of the art of astronomical
observations of black holes.Comment: 17 pages, 8 figures. v3: refereed versio
Electromagnetic propagation in a relativistic electron gas at finite
  temperatures

We describe electromagnetic propagation in a relativistic electron gas at
finite temperatures and carrier densities. Using quantum electrodynamics at
finite temperatures, we obtain electric and magnetic responses and general
constitutive relations. Rewriting the propagator for the electromagnetic field
in terms of the electric and magnetic responses, we identify the modes that
propagate in the gas. As expected, we obtain the usual collective excitations,
i.e., a longitudinal electric and two transverse magnetic plasmonic modes. In
addition, we find a purely photonic mode that satisfies the wave equation in
vacuum, for which the electron gas is transparent. We present dispersion
relations for the plasmon modes at zero and finite temperatures and identify
the intervals of frequency and wavelength where both electric and magnetic
responses are simultaneously negative, a behavior previously thought not to
occur in natural systems
On the formation of a conducting surface channel by ionic liquid gating
  of an insulator

Ionic liquid gating has become a popular tool for tuning the charge carrier
densities of complex oxides. Among these the band insulator SrTiO$_3$ is one of
the most extensively studied materials. While experiments have succeeded in
inducing (super)conductivity, the process by which ionic liquid gating turns
this insulator into a conductor is still under scrutiny. Recent experiments
have suggested an electrochemical rather than electrostatic origin of the
induced charge carriers. Here, we report experiments probing the time evolution
of conduction of SrTiO$_3$ near the glass transition temperature of the ionic
liquid. By cooling down to temperatures near the glass transition of the ionic
liquid the process develops slowly and can be seen to evolve in time. The
experiments reveal a process characterized by waiting times that can be as long
as several minutes preceding a sudden appearance of conduction. For the
conditions applied in our experiments we find a consistent interpretation in
terms of an electrostatic mechanism for the formation of a conducting path at
the surface of SrTiO$_3$. The mechanism by which the conducting surface channel
develops relies on a nearly homogeneous lowering of the surface potential until
the conduction band edge of SrTiO$_3$ reaches the Fermi level of the
electrodes.Comment: 22 pages, 7 figure
Reliability of digitized quantum annealing and the decay of entanglement

We performed a banged-digital-analog simulation of a quantum annealing
protocol in a two-qubit Nuclear Magnetic Resonance (NMR) quantum computer. Our
experimental simulation employed up to 235 Trotter steps, with more than 2000
gates (pulses), and we obtained a protocol success above 80%. Given the
exquisite control of the NMR quantum computer, we performed the simulation with
different noise levels. We thus analyzed the reliability of the quantum
annealing process, and related it to the level of entanglement produced during
the protocol. Although the presence of entanglement is not a sufficient
signature for a better-than-classical simulation, the level of entanglement
achieved relates to the fidelity of the protocol.Comment: 10 pages, 7 figures. V2: Extended version. Comments are welcom
Completely subradiant multi-atom architectures through 2D photonic
  crystals

Inspired by recent advances in the manipulation of atoms trapped near 1D
waveguides and pro- posals to use surface acoustic waves on piezoelectric
substrates for the same purpose, we show the potential of two-dimensional
platforms. We exploit the directional emission of atoms near photonic crystal
slabs with square symmetry to build perfect subradiant states of 2 distant
atoms, possible in 2D only for finite lattices with reflecting boundaries. We
also show how to design massively parallel 1D arrays of atoms above a single
crystal, useful for multi-port output of nonclassical light, by ex- ploiting
destructive interference of guided resonance modes due to finite size effects.
Directionality of the emission is shown to be present whenever a linear
iso-frequency manifold is present in the dispersion relation of the crystal.
Multi-atom radiance properties can be obtained from a simple cross-talk
coefficient of a master equation, which we compare with exact atom-crystal
dynamics, showing its predictive power
The symmetrical foundation of Measure, Probability and Quantum theories

Quantification starts with sum and product rules that express combination and
partition. These rules rest on elementary symmetries that have wide
applicability, which explains why arithmetical adding up and splitting into
proportions are ubiquitous. Specifically, measure theory formalises addition,
and probability theory formalises inference in terms of proportions. Quantum
theory rests on the same simple symmetries, but is formalised in two
dimensions, not just one, in order to track an object through its binary
interactions with other objects. The symmetries still require sum and product
rules (here known as the Feynman rules), but they apply to complex numbers
instead of real scalars, with observable probabilities being modulus-squared
(known as the Born rule). The standard quantum formalism follows. There is no
mystery or weirdness, just ordinary probabilistic inference.Comment: 17 page
Copernicus's Heliograph at Olsztyn -- the 500th Anniversary of a
  Scientific Milestone

Exactly 500 years ago, Nicolaus Copernicus drew a lattice of lines on a panel
above the doorway to his rooms at Olsztyn Castle, then in the Bishopric of
Warmia. Although its design has long been regarded as some kind of reflecting
vertical sundial, the exact astronomical designation of the lines and related
measuring techniques remained unknown. Surprisingly, Copernicus did not refer
to his new observational methods in his principal work, \textit{De
Revolutionibus}. A data analysis of a 3D model of the panel has, at last,
solved the mystery: Copernicus created a new type of measuring device -- a
heliograph with a non-local reference meridian -- to precisely measure ecliptic
longitudes of the Sun around the time of the equinoxes. The data, 3D model and
modeling results of our analysis are open access and available in the form of
digital (Jupyter) notebooks
Coherent light generation in hybrid atomic-nanophotonic integrated
  structures

The integration of neutral atoms with nanophotonic structures offer
significant potential as a versatile platform to explore fundamental
light-matter interactions as well as realizing novel quantum-optical devices.
Here, we investigate the possibility of creating low-threshold micro-scale
lasers in hybrid systems based on integrating room-temperature atomic gases
with both dielectric and metallic nanophotonic systems. We particularly focus
on studying two different devices resulting from incorporating an
optically-pumped Rb-ethane mixture in a dielectric ring resonator and a
plasmonic lattice. We show in both cases the combination of the optical gain
provided by the atomic vapor, along with the unique field-confinement
properties of nanophotonic structures, enables generating of coherent
radiation, i.e. laser light, at low power levels. In addition, we provide
general design guidelines for these hybrid nano-lasers and an efficient density
matrix-based formalism for studying these systems. Our results demonstrate a
unique route towards small foot-print, highly efficient, and fast lasers, which
paves the way towards the development of a whole new class of active
nanophotonic and metamaterial systems.Comment: 19 pages, 5 figure
Brownian motion in fluctuating periodic potentials

This work deals with the overdamped motion of a particle in a fluctuating
one-dimensional periodic potential. If the potential has no inversion symmetry
and its fluctuations are asymmetric and correlated in time, a net flow can be
generated at finite temperatures. We present results for the stationary current
for the case of a piecewise linear potential, especially for potentials being
close to the case with inversion symmetry. The aim is to study the stationary
current as a function of the potential. Depending on the form of the potential,
the current changes sign once or even twice as a function of the correlation
time of the potential fluctuations. To explain these current reversals, several
mechanisms are proposed. Finally, we discuss to what extent the model is useful
to understand the motion of biomolecular motors.Comment: 15 pages, 8 eps-figures, uses epsfig.sty. Accepted for publication in
  Ann. Physik (Leipzig
Frustration of antiferromagnetism in the t-t'-Hubbard model at weak
  coupling

The perfect-nesting instability towards antiferromagnetism of the Hubbard
model is suppressed by next-nearest neighbor hopping t'. The exact asymptotic
behavior of the critical coupling U_c(t') at small t' is calculated in
dimensions d=2,3 and infinity using Hartree theory, and the order of the
transition is determined. A region of stability of a metallic antiferromagnetic
phase in d=3 is identified.Comment: 5 pages revtex, 5 eps figures; typos corrected and a discussion about
  the applicability to two-dimensional organic superconductors adde
On the averaged quantum dynamics by white-noise Hamiltonians with and
  without dissipation

Exact results are derived on the averaged dynamics of a class of random
quantum-dynamical systems in continuous space. Each member of the class is
characterized by a Hamiltonian which is the sum of two parts. While one part is
deterministic, time-independent and quadratic, the Weyl-Wigner symbol of the
other part is a homogeneous Gaussian random field which is delta correlated in
time, but smoothly correlated in position and momentum. The averaged dynamics
of the resulting white-noise system is shown to be a monotone mixing increasing
quantum-dynamical semigroup. Its generator is computed explicitly. Typically,
in the course of time the mean energy of such a system grows linearly to
infinity. In the second part of the paper an extended model is studied, which,
in addition, accounts for dissipation by coupling the white-noise system
linearly to a quantum-mechanical harmonic heat bath. It is demonstrated that,
under suitable assumptions on the spectral density of the heat bath, the mean
energy then saturates for long times.Comment: 44 page
Localization Length Exponent, Critical Conductance Distribution and
  Multifractality in Hierarchical Network Models for the Quantum Hall Effect

We study hierarchical network models which have recently been introduced to
approximate the Chalker-Coddington model for the integer quantum Hall effect
(A.G. Galstyan and M.E. Raikh, PRB 56 1422 (1997); Arovas et al., PRB 56, 4751
(1997)). The hierarchical structure is due to a recursive method starting from
a finite elementary cell. The localization-delocalization transition occurring
in these models is displayed in the flow of the conductance distribution under
increasing system size. We numerically determine this flow, calculate the
critical conductance distribution, the critical exponent of the localization
length, and the multifractal exponents of critical eigenstates.Comment: 6 pages REVTeX, 9 postscript figures and 1 postscript tabl
Spin Flip Torsion Balance

The spin flip of the conduction electrons at the interface of a ferromagnetic
and a nonmagnetic part of a metallic wire, suspended between two electrodes, is
shown to tort the wire when a current is driven through it.
  In order to enhance the effect it is suggested to use an alternating current
in resonance with the torsional oscillations.
  Thereby the magnetic polarization of the conduction electrons in the
ferromagnet can be measured directly, and compared to the total magnetization.
  This may yield new information on the transport properties of the narrow band
electrons in itinerant ferromagnets.Comment: 3 pages, 1 figur
The role of virtual photons in nanoscale photonics

The fundamental theory of processes and properties associated with nanoscale photonics should properly account for the quantum nature of both the matter and the radiation field. A familiar example is the Casimir force, whose significant role in nanoelectromechanical systems is widely recognised; the correct representation invokes the creation of short-lived virtual photons from the vacuum. In fact, there is an extensive range of nanophotonic interactions in which virtual photon exchange plays a vital role, mediating the coupling between particles. This review surveys recent theory and applications, also exhibiting novel insights into key electrodynamic mechanisms. Examples are numerous and include: laser-induced inter-particle forces known as optical binding; non-parametric frequency-conversion processes especially in rare-earth doped materials; light-harvesting polymer materials that involve electronic energy transfer between their constituent chromophores. An assessment of these and the latest prospective applications concludes with a view on future directions of research
Evidence of fluoride transfer from the anion of\ud
[Zr{C5H3[SiMe2(η1-NtBu)]2}]+[RB(C6F5)3]_\ud
complexes to the zirconocenium cation

In summary, we have found experimental evidence to support a reaction pathway involving direct fluoride migration\ud
to the zirconium cation without previous transfer of C6F5.\ud
It is noteworthy that the opening of the silyl–amido bridge was not observed in the course of these activations. Experiments with other donor ligands are in progress to investigate the conditions under which the ion pairs 1 and 2 may follow different decomposition routes and the possible mechanisms of these reactions.Financial support by the Spanish MEC (project MAT2004-02614)\ud
and DGUI/CM (program S/0505/PPQ-0328) is acknowleged
Monitoring Protein Kinases in Cellular Media with Highly Selective Chimeric Reporters

Protein kinases are important regulators of cellular function, and the dynamics of their activities are critical indicators of the health or pathology of living systems.[1, 2] In particular, extracellular-signal regulated kinases 1 and 2 (ERK1/2) play a pivotal role in the mitogen-activated protein kinase (MAPK) signaling pathway responsible for regulated cell survival and proliferation.[3] The centrality of these enzymes in normal and diseased cell states underscores the need for high throughput, selective, and sensitive methods that accurately and directly diagnose kinase activities. The benchmark phosphorylation assays for ERK1/2 rely on transfer of radioactive γ-phosphate of [γ-32P]ATP to peptide or protein substrates.[4] While broadly employed, this approach has limitations, including the discontinuous nature of the radioactive assay and the non-native ATP concentrations that are utilized. Alternatively, for cellular imaging, genetically-encoded sensors that rely on phosphorylation-based changes in fluorescence resonance energy transfer (FRET) between fluorescent protein pairs[5, 6] have been constructed for several kinases, including ERK1/2.[7-10] These sensors are powerful because they can be expressed in cells, however, they cannot be used for high throuput screening of recombinant enzymes and unfractionated cell lysates due to the very limited fluorescence changes that accompany phosphorylation. As a complementary approach, probes based on small, organic fluorophores with direct readouts[6, 11] can give sensitive and robust signals under physiogical conditions and are thus amenable to high throughput applications. For example, we have incorporated a sulfonamido-oxine (Sox) chromophore into peptides[12, 13] to report phosphorylation via chelation-enhanced fluorescence (CHEF) (Figure 1a). The weak binding affinity of the unphosphorylated substrate for Mg2+ increases significantly upon phosphorylation, resulting in robust (2- to 12-fold) fluorescence enhancements. This versatile peptide-based sensor design has been applied to monitor the activity of numerous Ser/Thr and Tyr kinases both in vitro[13] and in cell lysates.National Institutes of Health (U.S.) (NIH Cell Migration Consortium (GM064346)
Using Explosions to Power a Soft Robot

This manuscript describes the use of explosions to power a soft robot—one composed solely of organic elastomers (e.g., silicones). The robot has three pneumatic actuators (pneu-nets) in a tripedal configuration. Explosion of a stoichiometric mixture of methane and oxygen within the microchannels making up the actuators produced hot gas that rapidly inflated the pneu-nets, and caused the robot to launch itself vertically from a flat surface (e.g., to jump). A soft flap embedded in the pneu-net acted as the valve of a passive exhaust system, and allowed multiple sequential actuations. The flame and temperature increase from the explosions are short-lived, and do not noticeably damage the robots over dozens of actuation cycles.Chemistry and Chemical Biolog
Photonenergy-Controlled Symmetry Breaking with Circularly Polarized Light

International audienceCircularly polarized light (CPL) is known to be a true chiral entity capable of generating absolute molecular asymmetry. However, the degree of inducible optical activity depends on the λ of the incident CPL. Exposure of amorphous films of rac-alanine to tunable CPL led to enantiomeric excesses (ee) which not only follow the helicity but also the energy of driving electromagnetic radiation. Postirradiation analyses using enantioselective multidimensional GC revealed energy-controlled ee values of up to 4.2 %, which correlate with theoretical predictions based on newly recorded anisotropy spectra g(λ). The tunability of asymmetric photochemical induction implies that both magnitude and sign can be fully controlled by CPL. Such stereocontrol provides novel insights into the wavelength and polarization dependence of asymmetric photochemical reactions and are highly relevant for absolute asymmetric molecular synthesis and for understanding the origins of homochirality in living matter
Boron Clusters as Highly Stable Magnesium‐Battery Electrolytes

Boron clusters are proposed as a new concept for the design of magnesium‐battery electrolytes that are magnesium‐battery‐compatible, highly stable, and noncorrosive. A novel carborane‐based electrolyte incorporating an unprecedented magnesium‐centered complex anion is reported and shown to perform well as a magnesium‐battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium‐battery electrolytes is very high.     Ein b(o)rillantes Konzept : Ein Elektrolyt mit einem Magnesium‐zentrierten Komplexanion wurde für den Einsatz in wiederaufladbaren Magnesiumbatterien entwickelt. Das Carboranylmagnesiumhalogenid (siehe Struktur; B lila, C weiß, Cl grün, O rot, Mg orange) war mit Magnesiummetall‐Anoden kompatibel und zeigte an verschiedenen Nichtedelmetall‐Elektroden eine bemerkenswerte oxidative Stabilität (3.2 V gegen Mg)
Chemically Orthogonal Three‐Patch Microparticles

Compared to two‐dimensional substrates, only a few methodologies exist for the spatially controlled decoration of three‐dimensional objects, such as microparticles. Combining electrohydrodynamic co‐jetting with synthetic polymer chemistry, we were able to create two‐ and three‐patch microparticles displaying chemically orthogonal anchor groups on three distinct surface patches of the same particle. This approach takes advantage of a combination of novel chemically orthogonal polylactide‐based polymers and their processing by electrohydrodynamic co‐jetting to yield unprecedented multifunctional microparticles. Several micropatterned particles were fabricated displaying orthogonal click functionalities. Specifically, we demonstrate novel two‐ and three‐patch particles. Multi‐patch particles are highly sought after for their potential to present multiple distinct ligands in a directional manner. This work clearly establishes a viable route towards orthogonal reaction strategies on multivalent micropatterned particles.     Patchwork‐Familie : Mikropartikel aus drei Patches (siehe Schema) mit funktionalisierten Poly(lactid)‐Derivaten in ausgewählten Kompartimenten wurden durch elektrohydrodynamisches (EHD) Co‐Sprühen hergestellt. Die Mikropartikel wurden durch konfokale Raman‐Mikrospektroskopie charakterisiert, und die bioorthogonale Oberflächenmodifikation eines jedes Patches wurde belegt
Substrate Activity Screening with Kinases: Discovery of Small‐Molecule Substrate‐Competitive c‐Src Inhibitors

Substrate‐competitive kinase inhibitors represent a promising class of kinase inhibitors, however, there is no methodology to selectively identify this type of inhibitor. Substrate activity screening was applied to tyrosine kinases. By using this methodology, the first small‐molecule substrates for any protein kinase were discovered, as well as the first substrate‐competitive inhibitors of c‐Src with activity in both biochemical and cellular assays. Characterization of the lead inhibitor demonstrates that substrate‐competitive kinase inhibitors possess unique properties, including cellular efficacy that matches biochemical potency and synergy with ATP‐competitive inhibitors.     Mit dem Substrat konkurrierende  niedermolekulare Inhibitoren der Tyrosinkinase c‐Src wurden mithilfe eines Substrataktivitäts‐Screenings (SAS) entdeckt. Die Charakterisierung des Leit‐Inhibitors zeigt, dass substratkompetitive Kinaseinhibitoren einzigartige Eigenschaften haben, einschließlich einer zellulären Effizienz, die ihrer biochemischen Wirksamkeit entspricht, und einer Synergie mit ATP‐kompetitiven Inhibitoren
The Assembly-Disassembly-Organization-Reassembly mechanism for 3D-2D-3D transformation of germanosilicate IWW zeolite

This research was part funded by EPSRC grant number EP/K025112/1. The article processing charge for this article was funded through the RCUK open access block grant.Hydrolysis of germanosilicate zeolites with the IWW structure shows two different outcomes depending on the composition of the starting materials. Ge-rich IWW (Si/Ge=3.1) is disassembled into a layered material (IPC-5P), which can be reassembled into an almost pure silica IWW on treatment with diethoxydimethylsilane. Ge-poor IWW (Si/Ge=6.4) is not completely disassembled on hydrolysis, but retains some 3D connectivity. This structure can be reassembled into IWW by incorporation of Al to fill the defects left when the Ge is removed.Publisher PDFPeer reviewe