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Graphene-polyelectrolyte multilayer membranes with tunable structure and internal charge
One great advantage of graphene-polyelectrolyte multilayer (GPM) membranes is their tunable structure and internal charge for improved separation performance. In this study, we synthesized GO-dominant GPM membrane with internal negatively-charged domains, polyethyleneimine (PEI)-dominant GPM membrane with internal positively-charged domains and charge-balanced dense/loose GPM membranes by simply adjusting the ionic strength and pH of the GO and PEI solutions used in layer-by-layer membrane synthesis. A combined system of quartz crystal microbalance with dissipation (QCM-D) and ellipsometry was used to analyze the mass deposition, film thickness, and layer density of the GPM membranes. The performance of the GPM membranes were compared in terms of both permeability and selectivity to determine the optimal membrane structure and synthesis strategy. One effective strategy to improve the GPM membrane permeability-selectivity tradeoff is to assemble charge-balanced dense membranes under weak electrostatic interactions. This balanced membrane exhibits the highest MgCl2 selectivity (∼86%). Another effective strategy for improved cation removal is to create PEI-dominant membranes that provide internal positively-charged barrier to enhance cation selectivity without sacrificing water permeability. These findings shine lights on the development of a systematic approach to push the boundary of permeability-selectivity tradeoff for GPM membranes
Threshold Dynamics of a Semiconductor Single Atom Maser
We demonstrate a single-atom maser consisting of a semiconductor double
quantum dot (DQD) that is embedded in a high quality factor microwave cavity. A
finite bias drives the DQD out of equilibrium, resulting in sequential single
electron tunneling and masing. We develop a dynamic tuning protocol that allows
us to controllably increase the time-averaged repumping rate of the DQD at a
fixed level detuning, and quantitatively study the transition through the
masing threshold. We further examine the crossover from incoherent to coherent
emission by measuring the photon statistics across the masing transition. The
observed threshold behavior is in agreement with an existing single atom maser
theory when small corrections from lead emission are taken into account
Double Quantum Dot Floquet Gain Medium
Strongly driving a two-level quantum system with light leads to a ladder of
Floquet states separated by the photon energy. Nanoscale quantum devices allow
the interplay of confined electrons, phonons, and photons to be studied under
strong driving conditions. Here we show that a single electron in a
periodically driven DQD functions as a "Floquet gain medium," where population
imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern
of gain and loss features in the cavity response. We further measure a large
intra-cavity photon number n_c in the absence of a cavity drive field, due to
equilibration in the Floquet picture. Our device operates in the absence of a
dc current -- one and the same electron is repeatedly driven to the excited
state to generate population inversion. These results pave the way to future
studies of non-classical light and thermalization of driven quantum systems
The Patient Health Questionnaire-9 for detection of major depressive disorder in primary care: consequences of current thresholds in a crosssectional study
Background: There is a need for brief instruments to ascertain the diagnosis of major depressive disorder. In this study, we present the reliability, construct validity and accuracy of the PHQ-9 and PHQ-2 to detect major depressive disorder in primary care.Methods: Cross-sectional analyses within a large prospective cohort study (PREDICT-NL). Data was collected in seven large general practices in the centre of the Netherlands. 1338 subjects were recruited in the general practice waiting room, irrespective of their presenting complaint. The diagnostic accuracy (the area under the ROC curve and sensitivities and specificities for various thresholds) was calculated against a diagnosis of major depressive disorder determined with the Composite International Diagnostic Interview (CIDI).Results: The PHQ-9 showed a high degree of internal consistency (ICC = 0.88) and test-retest reliability (correlation = 0.94). With respect to construct validity, it showed a clear association with functional status measurements, sick days and number of consultations. The discriminative ability was good for the PHQ-9 (area under the ROC curve = 0.87, 95% CI: 0.84-0.90) and the PHQ-2 (ROC area = 0.83, 95% CI 0.80-0.87). Sensitivities at the recommended thresholds were 0.49 for the PHQ-9 at a score of 10 and 0.28 for a categorical algorithm. Adjustment of the threshold and the algorithm improved sensitivities to 0.82 and 0.84 respectively but the specificity decreased from 0.95 to 0.82 (threshold) and from 0.98 to 0.81 (algorithm). Similar results were found for the PHQ-2: the recommended threshold of 3 had a sensitivity of 0.42 and lowering the threshold resulted in an improved sensitivity of 0.81.Conclusion: The PHQ-9 and the PHQ-2 are useful instruments to detect major depressive disorder in primary care, provided a high score is followed by an additional diagnostic work-up. However, often recommended thresholds for the PHQ-9 and the PHQ-2 resulted in many undetected major depressive disorders
Label-Dependencies Aware Recurrent Neural Networks
In the last few years, Recurrent Neural Networks (RNNs) have proved effective
on several NLP tasks. Despite such great success, their ability to model
\emph{sequence labeling} is still limited. This lead research toward solutions
where RNNs are combined with models which already proved effective in this
domain, such as CRFs. In this work we propose a solution far simpler but very
effective: an evolution of the simple Jordan RNN, where labels are re-injected
as input into the network, and converted into embeddings, in the same way as
words. We compare this RNN variant to all the other RNN models, Elman and
Jordan RNN, LSTM and GRU, on two well-known tasks of Spoken Language
Understanding (SLU). Thanks to label embeddings and their combination at the
hidden layer, the proposed variant, which uses more parameters than Elman and
Jordan RNNs, but far fewer than LSTM and GRU, is more effective than other
RNNs, but also outperforms sophisticated CRF models.Comment: 22 pages, 3 figures. Accepted at CICling 2017 conference. Best
Verifiability, Reproducibility, and Working Description awar
Simple Metals at High Pressure
In this lecture we review high-pressure phase transition sequences exhibited
by simple elements, looking at the examples of the main group I, II, IV, V, and
VI elements. General trends are established by analyzing the changes in
coordination number on compression. Experimentally found phase transitions and
crystal structures are discussed with a brief description of the present
theoretical picture.Comment: 22 pages, 4 figures, lecture notes for the lecture given at the Erice
course on High-Pressure Crystallography in June 2009, Sicily, Ital
Phase reconstruction of strong-field excited systems by transient-absorption spectroscopy
We study the evolution of a V-type three-level system, whose two resonances
are coherently excited and coupled by two ultrashort laser pump and probe
pulses, separated by a varying time delay. We relate the quantum dynamics of
the excited multi-level system to the absorption spectrum of the transmitted
probe pulse. In particular, by analyzing the quantum evolution of the system,
we interpret how atomic phases are differently encoded in the
time-delay-dependent spectral absorption profiles when the pump pulse either
precedes or follows the probe pulse. We experimentally apply this scheme to
atomic Rb, whose fine-structure-split 5s\,^2S_{1/2}\rightarrow 5p\,^2P_{1/2}
and 5s\,^2S_{1/2}\rightarrow 5p\,^2P_{3/2} transitions are driven by the
combined action of a pump pulse of variable intensity and a delayed probe
pulse. The provided understanding of the relationship between quantum phases
and absorption spectra represents an important step towards full time-dependent
phase reconstruction (quantum holography) of bound-state wave-packets in
strong-field light-matter interactions with atoms, molecules and solids.Comment: 5 pages, 4 figure
Assessing the policy impacts on non-ferrous metals industry's CO2 reduction: Evidence from China
The nonferrous metals industry (NMI) consumes a great amount of energy, and is a typical high CO2 emission sector. The NMI is one of the eight most concerning industries in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report. In this study, we summarized policies that impact Chinese NMI's development and grouped them into three types: energy structure policies, energy efficiency improving policies and production-scale policies. Based on those quantitative policy goals, a bottom-up model has been developed to study the CO2 emissions of five NMI's major sub-sectors from 2010 to 2030. The results showed that if China's central government could stick to the CO2 reduction policy strength of 13th Five-Year Plan (2016–2020), then the copper, lead and zinc industries can reach their emissions peak before 2030. Furthermore, if the Chinese government restricts the production of primary aluminum of 46.2 million tons in 2025, then the CO2 emissions of China's non-ferrous industry could reach the peak in that year, when the CO2 emissions peak is 297 million tons. Having benefited from the effective CO2 reduction policies of NMI, China may reach its ambitious CO2 peaking goals more easily
Assessment on the research trend of low-carbon energy technology investment: A bibliometric analysis
Based on databases of Science Citation Index Expanded (1981-present) and Social Sciences Citation Index (2002-present), this paper applies the bibliometric method to analyze the scientific publications of low-carbon energy technology investment. By characterizing the basic information of the publications, we found: the historical development process is clearly divided into two stages; the field of low-carbon energy technology investment has entered a stage of rapid development; the strength of developed countries is far greater than that of developing countries; the comprehensive strength of the United States ranks the first in the field, followed by UK and Denmark and only China and Turkey are developing countries among the top 15 countries; the auctorial collaboration degree in this field shows a clear upward trend, but institutional and national collaboration degrees are steady and relatively low. In addition, distributions of geography, journals and subjects, productive authors and institutions, frequently cited articles, etc. are obtained: articles in this area are mainly distributed in the USA, several countries in Europe and China; the most productive journal, author and institution are Energy Policy, Lund H from Denmark and National Technical University of Athens in Greece; Energy Fuel is the most popular subject among all the outcomes; the most frequently cited article is written by Demirbas published in Energy Policy in 2007. According to the frequency analysis of keywords, it reveals that: “renewable energy” is a kind of keyword used most frequently; “carbon capture and storage technology” is an emerging keyword which is increasingly concerned about; scholars pay widespread attention to electricity issues, especially the feed-in tariff; the policy mainly includes energy policy and climate policy; the real option theory is the most widely used theory; the existing uncertainty is summarized as the cost uncertainty and policy uncertainty. In the end, several suggestions for the future research are given
Direct electronic measurement of the spin Hall effect
The generation, manipulation and detection of spin-polarized electrons in
nanostructures define the main challenges of spin-based electronics[1]. Amongst
the different approaches for spin generation and manipulation, spin-orbit
coupling, which couples the spin of an electron to its momentum, is attracting
considerable interest. In a spin-orbit-coupled system, a nonzero spin-current
is predicted in a direction perpendicular to the applied electric field, giving
rise to a "spin Hall effect"[2-4]. Consistent with this effect,
electrically-induced spin polarization was recently detected by optical
techniques at the edges of a semiconductor channel[5] and in two-dimensional
electron gases in semiconductor heterostructures[6,7]. Here we report
electrical measurements of the spin-Hall effect in a diffusive metallic
conductor, using a ferromagnetic electrode in combination with a tunnel barrier
to inject a spin-polarized current. In our devices, we observe an induced
voltage that results exclusively from the conversion of the injected spin
current into charge imbalance through the spin Hall effect. Such a voltage is
proportional to the component of the injected spins that is perpendicular to
the plane defined by the spin current direction and the voltage probes. These
experiments reveal opportunities for efficient spin detection without the need
for magnetic materials, which could lead to useful spintronics devices that
integrate information processing and data storage.Comment: 5 pages, 4 figures. Accepted for publication in Nature (pending
format approval
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