829 research outputs found
Deterministic enhancement of coherent photon generation from a nitrogen-vacancy center in ultrapure diamond
The nitrogen-vacancy (NV) center in diamond has an optically addressable,
highly coherent spin. However, an NV center even in high quality
single-crystalline material is a very poor source of single photons: extraction
out of the high-index diamond is inefficient, the emission of coherent photons
represents just a few per cent of the total emission, and the decay time is
large. In principle, all three problems can be addressed with a resonant
microcavity. In practice, it has proved difficult to implement this concept:
photonic engineering hinges on nano-fabrication yet it is notoriously difficult
to process diamond without degrading the NV centers. We present here a
microcavity scheme which uses minimally processed diamond, thereby preserving
the high quality of the starting material, and a tunable microcavity platform.
We demonstrate a clear change in the lifetime for multiple individual NV
centers on tuning both the cavity frequency and anti-node position, a Purcell
effect. The overall Purcell factor translates to a Purcell
factor for the zero phonon line (ZPL) of and an
increase in the ZPL emission probability from to . By
making a step-change in the NV's optical properties in a deterministic way,
these results pave the way for much enhanced spin-photon and spin-spin
entanglement rates.Comment: 6 pages, 4 figure
Question and Answer Test-Train Overlap in Open-Domain Question Answering Datasets
Ideally Open-Domain Question Answering models should exhibit a number of
competencies, ranging from simply memorizing questions seen at training time,
to answering novel question formulations with answers seen during training, to
generalizing to completely novel questions with novel answers. However, single
aggregated test set scores do not show the full picture of what capabilities
models truly have. In this work, we perform a detailed study of the test sets
of three popular open-domain benchmark datasets with respect to these
competencies. We find that 60-70% of test-time answers are also present
somewhere in the training sets. We also find that 30% of test-set questions
have a near-duplicate paraphrase in their corresponding training sets. Using
these findings, we evaluate a variety of popular open-domain models to obtain
greater insight into what extent they can actually generalize, and what drives
their overall performance. We find that all models perform dramatically worse
on questions that cannot be memorized from training sets, with a mean absolute
performance difference of 63% between repeated and non-repeated data. Finally
we show that simple nearest-neighbor models out-perform a BART closed-book QA
model, further highlighting the role that training set memorization plays in
these benchmark
The Rise of Trichlorides Enabling an Improved Chlorine Technology
Chlorine plays a central role for the industrial production of numerous materials with global relevance. More recently, polychlorides have been evolved from an area of academic interest to a research topic with enormous industrial potential. In this minireview, the value of trichlorides for chlorine storage and chlorination reactions are outlined. Particularly, the inexpensive ionic liquid [NEt3Me][Cl3] shows a similar and sometimes even advantageous reactivity compared to chlorine gas, while offering a superior safety profile. Used as a chlorine storage, [NEt3Me][Cl3] could help to overcome the current limitations of storing and transporting chlorine in larger quantities. Thus, trichlorides could become a key technique for the flexibilization of the chlorine production enabling an exploitation of renewable, yet fluctuating, electrical energy. As the loaded storage, [NEt3Me][Cl3], is a proven chlorination reagent, it could directly be employed for downstream processes, paving the path to a more practical and safer chlorine industry
Interpretation of Natural Language Rules in Conversational Machine Reading
Most work in machine reading focuses on question answering problems where the
answer is directly expressed in the text to read. However, many real-world
question answering problems require the reading of text not because it contains
the literal answer, but because it contains a recipe to derive an answer
together with the reader's background knowledge. One example is the task of
interpreting regulations to answer "Can I...?" or "Do I have to...?" questions
such as "I am working in Canada. Do I have to carry on paying UK National
Insurance?" after reading a UK government website about this topic. This task
requires both the interpretation of rules and the application of background
knowledge. It is further complicated due to the fact that, in practice, most
questions are underspecified, and a human assistant will regularly have to ask
clarification questions such as "How long have you been working abroad?" when
the answer cannot be directly derived from the question and text. In this
paper, we formalise this task and develop a crowd-sourcing strategy to collect
32k task instances based on real-world rules and crowd-generated questions and
scenarios. We analyse the challenges of this task and assess its difficulty by
evaluating the performance of rule-based and machine-learning baselines. We
observe promising results when no background knowledge is necessary, and
substantial room for improvement whenever background knowledge is needed.Comment: EMNLP 201
[NEt3Me][O3], Synthesis, Crystal Growth and Crystal Structure Analysis
[NEt3Me][O3] was obtained for the first time by an ion exchange reaction in liquid ammonia. It was thoroughly characterized by X‐Ray diffraction [P21; a=598.51(4) pm, b=1032.03(7) pm, c=723.83(6) pm, β=92.677(3)°, R=0.0384, 15070 reflections] applying non‐spherical and spherical atomic form factors for the refinements. In contrast to previous reported ozonides, [NEt3Me][O3] is the first to adopt the tungsten carbide (WC) motif of cation/ anion arragemnent and shows an untypical hydrogen bond between the central oxygen atom of the ozonide and the cation. Additionally, IR spectroscopy as well as quantum‐chemical calculations were applied to further characterize the compound. The obtained ozonide showed high solubility in ammonia as well as acetonitrile and good properties as a synthon in ozonide chemistry
Cavity-enhanced Raman scattering for in situ alignment and characterization of solid-state microcavities
We report cavity-enhanced Raman scattering from a single-crystal diamond
membrane embedded in a highly miniaturized fully-tunable Fabry-P\'{e}rot
cavity. The Raman intensity is enhanced 58.8-fold compared to the corresponding
confocal measurement. The strong signal amplification results from the Purcell
effect. We show that the cavity-enhanced Raman scattering can be harnessed as a
narrowband, high-intensity, internal light-source. The Raman process can be
triggered in a simple way by using an optical excitation frequency outside the
cavity stopband and is independent of the lateral positioning of the cavity
mode with respect to the diamond membrane. The strong Raman signal emerging
from the cavity output facilitates in situ mode-matching of the cavity mode to
single-mode collection optics; it also represents a simple way of measuring the
dispersion and spatial intensity-profile of the cavity modes. The optimization
of the cavity performance via the strong Raman process is extremely helpful in
achieving efficient cavity-outcoupling of the relatively weak emission of
single color-centers such as nitrogen-vacancy centers in diamond or rare-earth
ions in crystalline hosts with low emitter density
Synthesis and Characterization of Poly(hydrogen halide) Halogenates (–I)
Herein, we report the synthesis and characterization of a variety of novel poly(hydrogen halide) halogenates (−I). The bifluoride ion, which is known to have the highest hydrogen bond energy of ≈160 kJ mol−1, is the most famous among many examples of [X(HX)n]− anions (X=F, Cl) known in the literature. In contrast, little is known about poly(hydrogen halide) halogenates containing two different halogens, ([X(HY)n]−). In this work we present the synthesis of anions of the type [X(HY)n]− (X=Br, I, ClO4; Y=Cl, Br, CN) stabilized by the [PPh4]+ and [PPN]+ cation. The obtained compounds have been characterized by single‐crystal X‐ray diffraction, Raman spectroscopy and quantum‐chemical calculations. In addition, the behavior of halide ions in hydrogen fluoride was investigated by using experimental and quantum‐chemical methods in order to gain knowledge on the acidity of hydrogen halides in HF
Equilibria under Knightian Price Uncertainty
Beißner P, Riedel F. Equilibria under Knightian Price Uncertainty . Center for Mathematical Economics Working Papers. Vol 597. Bielefeld: Center for Mathematical Economics; 2018.We study economies in which agents face Knightian uncertainty
about state prices. Knightian uncertainty leads naturally to nonlinear
expectations. We introduce a corresponding equilibrium concept
with sublinear prices and prove that equilibria exist under weak conditions.
In general, such equilibria lead to Pareto inefficient allocations;
the equilibria coincide with Arrow-Debreu equilibria only if the
values of net trades are ambiguity-free in the mean. In economies
without aggregate uncertainty, inefficiencies are generic. We introduce
a constrained efficiency concept, uncertainty-neutral efficiency;
equilibrium allocations under price uncertainty are efficient in this constrained
sense. Arrow-Debreu equilibria turn out to be non-robust
with respect to the introduction of Knightian uncertainty
- …