Current methods of chemical vapour deposition (CVD) of graphene on copper are complicated by multiple processing steps and by high temperatures required in both preparing the copper and inducing ...subsequent film growth. Here we demonstrate a plasma-enhanced CVD chemistry that enables the entire process to take place in a single step, at reduced temperatures (<420 °C), and in a matter of minutes. Growth on copper foils is found to nucleate from arrays of well-aligned domains, and the ensuing films possess sub-nanometre smoothness, excellent crystalline quality, low strain, few defects and room-temperature electrical mobility up to (6.0±1.0) × 10(4) cm(2) V(-1) s(-1), better than that of large, single-crystalline graphene derived from thermal CVD growth. These results indicate that elevated temperatures and crystalline substrates are not necessary for synthesizing high-quality graphene.
We experimentally realize a universal set of single-bit and two-bit geometric quantum gates by adiabatically controlling solid-state spins in a diamond defect. Compared with the nonadiabatic ...approach, the adiabatic scheme for geometric quantum computation offers a unique advantage of inherent robustness to parameter variations, which is explicitly demonstrated in our experiment by showing that the single-bit gates remain unchanged when the driving field amplitude varies by a factor of 2 or the detuning fluctuates in a range comparable to the inverse of the gate time. The reported adiabatic control technique and its convenient implementation offer a paradigm for achieving quantum computation through robust geometric quantum gates, which is important for quantum information systems with parameter-fluctuation noise such as those from the inhomogeneous coupling or the spectral diffusion.
Objective
To assess the current prevalence of and risk factors for infertility among couples of reproductive age in China.
Design
Population‐based cross‐sectional study.
Setting
We approached 25 270 ...couples in eight provinces/municipalities, of whom 18 571 (response rate 74%) were interviewed.
Population
Couples living together and married for more than 1 year, of whom the female spouse was 20–49 years old.
Methods
Women were approached via telephone and face‐to‐face conversation to complete the standardised and structured questionnaire by trained interviewers.
Main outcome measures
Prevalence of and risk factors for infertility.
Results
Among women ‘at risk’ of pregnancy, the prevalence of infertility was 15.5% (2680/17 275). Among 10 742 women attempting to become pregnant, the prevalence of infertility was 25.0% (2680/10 742), which increased with age in the second population. Among women who failed to achieve pregnancy in the last 12 months, 3470 finished our questionnaire about fertility care, and 55.2% (1915/3470) of them had sought medical help. Sociodemographic risk factors for infertility included lower educational level adjusted odds ratio (aOR) 3.4, 95% CI 2.0–5.5 and employment (aOR 2.3, 95% CI 1.9–2.9). Clinical risk factors were irregular menstrual cycle (aOR 1.8, 95% CI 1.2–2.5), light menstrual blood volume (aOR 1.6, 95% CI 1.2–2.0), history of cervicitis (aOR 1.5, 95% CI 1.2–2.0) and endometriosis (aOR 3.1, 95% CI 1.1–9.3), previous stillbirth (aOR 2.1, 95% CI 1.3–3.3) and miscarriage (aOR 2.7, 95% CI 2.1–3.5). In addition, history of operation was a significant risk factor of infertility.
Conclusions
Among couples of reproductive age in China, the prevalence of infertility was 25%, and almost half of the couples experiencing infertility had not sought medical help.
Tweetable
In China, 25% of couples actively attempting to become pregnant suffered infertility.
Tweetable
In China, 25% of couples actively attempting to become pregnant suffered infertility.
Leptomeningeal metastases (LM) are more frequent in non-small-cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) mutations. Due to limited access to leptomeningeal lesions, the ...purpose of this study was to explore the potential role of cerebrospinal fluid (CSF) as a source of liquid biopsy in patients with LM.
Primary tumor, CSF, and plasma in NSCLC with LM were tested by next-generation sequencing. In total, 45 patients with suspected LM underwent lumbar puncture, and those with EGFR mutations diagnosed with LM were enrolled.
A total of 28 patients were enrolled in this cohort; CSF and plasma were available in 26 patients, respectively. Driver genes were detected in 100% (26/26), 84.6% (22/26), and 73.1% (19/26) of samples comprising CSF cell-free DNA (cfDNA), CSF precipitates, and plasma, respectively; 92.3% (24/26) of patients had much higher allele fractions in CSF cfDNA than the other two media. Unique genetic profiles were captured in CSF cfDNA compared with those in plasma and primary tissue. Multiple copy number variations (CNVs) were mainly identified in CSF cfDNA, and MET copy number gain identified in 47.8% (11/23) of patients was the most frequent one, while other CNVs included ERBB2, KRAS, ALK, and MYC. Moreover, loss of heterozygosity (LOH) of TP53 was identified in 73.1% (19/26) CSF cfDNA, which was much higher than that in plasma (2/26, 7.7%; P<0.001). There was a trend towards a higher frequency of concomitant resistance mutations in patients with TP53 LOH than those without (70.6% versus 33.3%; P=0.162). EGFR T790M was identified in CSF cfDNA of 30.4% (7/23) of patients who experienced TKI progression.
CSF cfDNA could reveal the unique genetic profiles of LM and should be considered as the most representative liquid biopsy medium for LM in EGFR-mutant NSCLC.
Optical upconversion via sensitized triplet-triplet exciton annihilation converts incoherent low-energy photons to shorter wavelengths under modest excitation intensities. Here, we report a ...solid-state thin film for infrared-to-visible upconversion that employs lead sulphide colloidal nanocrystals as a sensitizer. Upconversion is achieved from pump wavelengths beyond λ = 1 μm to emission at λ = 612 nm. When excited at λ = 808 nm, two excitons in the sensitizer are converted to one higher-energy state in the emitter at a yield of 1.2 ± 0.2%. Peak efficiency is attained at an absorbed intensity equivalent to less than one sun. We demonstrate that colloidal nanocrystals are an attractive alternative to existing molecular sensitizers, given their small exchange splitting, wide wavelength tunability, broadband infrared absorption, and our transient observations of efficient energy transfer. This solid-state architecture for upconversion may prove useful for enhancing the capabilities of solar cells and photodetectors.
High-temperature superconductivity emerges on doping holes or electrons into antiferromagnetic copper oxides. The large energy scale of magnetic excitations, for example, compared with phonon ...energies, is thought to drive superconductivity with high transition temperatures (Tc). Comparing high-energy magnetic excitations of hole- and electron-doped superconductors provides an opportunity to test this hypothesis. Here, we use resonant inelastic X-ray scattering at the Cu L3-edge to reveal collective excitations in the electron-doped cuprate Nd2xCexCuO4. Surprisingly, magnetic excitations harden signicantly across the antiferromagnetic high-temperature superconductivity phase boundary despite short-ranged antiferromagnetic correlations, in contrast to the hole-doped cuprates. Furthermore, we nd an unexpected branch of collective modes in superconducting compounds, absent in hole-doped cuprates. These modes emanate from the zone centre and possess a higher temperature scale than Tc, signalling a distinct quantum phase. Despite their dierences, the persistence of magnetic excitations and the existence of a distinct quantum phase are apparently universal in both hole- and electron-doped cuprates.
Objective
To assess whether vaginal secretions and breast milk of women with coronavirus disease 2019 (COVID‐19) contain severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2).
Design
Single ...centre cohort study.
Setting
Renmin Hospital of Wuhan University, Wuhan, Hubei province, China.
Population
We studied 13 SARS‐CoV‐2‐infected pregnant women diagnosed between 31 January and 9 March 2020.
Methods
We collected clinical data, vaginal secretions, stool specimens and breast milk from SARS‐CoV‐2‐infected women during different stages of pregnancy and collected neonatal throat and anal swabs.
Main outcomes and measures
We assessed viral presence in different biosamples.
Results
Of the 13 women with COVID‐19, five were in their first trimester, three in their second trimester and five in their third trimester. Of the five women in their third trimester who gave birth, all delivered live newborns. Among these five deliveries, the primary adverse perinatal outcomes included premature delivery (n = 2) and neonatal pneumonia (n = 2). One of nine stool samples was positive; all 13 vaginal secretion samples, and five throat swabs and four anal swabs collected from neonates, were negative for the novel coronavirus. However, one of three samples of breast milk was positive by viral nucleic acid testing.
Conclusions
In this case series of 13 pregnant women with COVID‐19, we observed negative viral test results in vaginal secretion specimens, suggesting that a vaginal delivery may be a safe delivery option. However, additional research is urgently needed to examine breast milk and the potential risk for viral contamination.
Tweetable
New evidence for the safety of vaginal delivery and breastfeeding in pregnant women infected with SARS‐CoV‐2, positive viral result in a breast‐milk sample.
New evidence for the safety of vaginal delivery and breastfeeding in pregnant women infected with SARS‐CoV‐2, positive viral result in a breast‐milk sample.
Multistage coupling of laser-wakefield accelerators is essential to overcome laser energy depletion for high-energy applications such as TeV-level electron-positron colliders. Current staging schemes ...feed subsequent laser pulses into stages using plasma mirrors while controlling electron beam focusing with plasma lenses. Here a more compact and efficient scheme is proposed to realize the simultaneous coupling of the electron beam and the laser pulse into a second stage. A partly curved channel, integrating a straight acceleration stage with a curved transition segment, is used to guide a fresh laser pulse into a subsequent straight channel, while the electrons continue straight. This scheme benefits from a shorter coupling distance and continuous guiding of the electrons in plasma while suppressing transverse beam dispersion. Particle-in-cell simulations demonstrate that the electron beam from a previous stage can be efficiently injected into a subsequent stage for further acceleration while maintaining high capture efficiency, stability, and beam quality.
High-efficiency acceleration of charged particle beams at high gradients of energy gain per unit length is necessary to achieve an affordable and compact high-energy collider. The plasma wakefield ...accelerator is one concept being developed for this purpose. In plasma wakefield acceleration, a charge-density wake with high accelerating fields is driven by the passage of an ultra-relativistic bunch of charged particles (the drive bunch) through a plasma. If a second bunch of relativistic electrons (the trailing bunch) with sufficient charge follows in the wake of the drive bunch at an appropriate distance, it can be efficiently accelerated to high energy. Previous experiments using just a single 42-gigaelectronvolt drive bunch have accelerated electrons with a continuous energy spectrum and a maximum energy of up to 85 gigaelectronvolts from the tail of the same bunch in less than a metre of plasma. However, the total charge of these accelerated electrons was insufficient to extract a substantial amount of energy from the wake. Here we report high-efficiency acceleration of a discrete trailing bunch of electrons that contains sufficient charge to extract a substantial amount of energy from the high-gradient, nonlinear plasma wakefield accelerator. Specifically, we show the acceleration of about 74 picocoulombs of charge contained in the core of the trailing bunch in an accelerating gradient of about 4.4 gigavolts per metre. These core particles gain about 1.6 gigaelectronvolts of energy per particle, with a final energy spread as low as 0.7 per cent (2.0 per cent on average), and an energy-transfer efficiency from the wake to the bunch that can exceed 30 per cent (17.7 per cent on average). This acceleration of a distinct bunch of electrons containing a substantial charge and having a small energy spread with both a high accelerating gradient and a high energy-transfer efficiency represents a milestone in the development of plasma wakefield acceleration into a compact and affordable accelerator technology.
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