Evidence for moiré excitons in van der Waals heterostructures.

Recent advances in the isolation and stacking of monolayers of van der Waals materials have provided approaches for the preparation of quantum materials in the ultimate two-dimensional limit1,2. In van der Waals heterostructures formed by stacking two monolayer semiconductors, lattice mismatch or rotational misalignment introduces an in-plane moiré superlattice3. It is widely recognized that the moiré superlattice can modulate the electronic band structure of the material and lead to transport properties such as unconventional superconductivity4 and insulating behaviour driven by correlations5-7; however, the influence of the moiré superlattice on optical properties has not been investigated experimentally. Here we report the observation of multiple interlayer exciton resonances with either positive or negative circularly polarized emission in a molybdenum diselenide/tungsten diselenide (MoSe2/WSe2) heterobilayer with a small twist angle. We attribute these resonances to excitonic ground and excited states confined within the moiré potential. This interpretation is supported by recombination dynamics and by the dependence of these interlayer exciton resonances on twist angle and temperature. These results suggest the feasibility of engineering artificial excitonic crystals using van der Waals heterostructures for nanophotonics and quantum information applications.

Perioperative Maternal-Fetal Outcomes in the Setting of Minimally Invasive Fetal Therapy for Complex Monochorionic Pregnancies with Monitored Anesthesia Care.

INTRODUCTION: Fetoscopic selective laser photocoagulation (FSLPC) and selective cord occlusion with radiofrequency ablation (RFA) can improve fetal outcomes when vascular anastomoses between fetuses cause twin-to-twin transfusion syndrome (TTTS) or selective fetal growth restriction (sFGR) in multiple gestation pregnancies with monochorionic placentation. This study analyzed perioperative maternal-fetal complications and anesthetic management in a high-volume fetal therapy center over a 4-year period. METHODS: Included patients received MAC for minimally invasive fetal procedures for complex multiple gestation pregnancies between January 1, 2015, and September 20, 2019. Maternal and fetal complications, intraoperative maternal hemodynamics, medication usage, and reasons for conversion to general anesthesia, if applicable, were analyzed. RESULTS: A total of 203 (59%) patients underwent FSLPC and 141 (41%) had RFA. Four patients (2%; rate 95% CI: 0.00039, 0.03901) undergoing FSLPC had conversion to general anesthesia. No conversions to general anesthesia occurred in the RFA group. The incidence of maternal complications was higher in those who underwent FSLPC. No aspiration or postoperative pneumonia events were observed. Medication usage was similar in FSLPC and RFA groups. CONCLUSION: A low rate of conversion to general anesthesia and no serious adverse maternal events were observed in patients receiving MAC.

Enhanced Spin Coherence of a Self-Assembled Quantum Dot Molecule at the Optimal Electrical Bias.

A pair of coupled dots with one electron in each dot can provide improvements in spin coherence, particularly at an electrical bias called the "sweet spot," but few measurements have been performed on self-assembled dots in this regime. Here, we directly measure the T_{2}^{*} coherence time of the singlet-triplet states in this system as a function of bias and magnetic field, obtaining a maximum T_{2}^{*} of 60 ns, more than an order of magnitude higher than an electron spin in a single quantum dot. Our results uncover two main dephasing mechanisms: electrical noise away from the sweet spot, and a magnetic field dependent interaction with nuclear spins due to a difference in g factors.

Impact of Obesity on Pregnancies Undergoing Laser Therapy for Twin-Twin Transfusion Syndrome.

INTRODUCTION: We sought to determine if maternal obesity, defined by body mass index (BMI) 30-34.9 or BMI ≥35, negatively impacts the technical aspects and pregnancy outcomes in women treated with selective laser photocoagulation of placental communicating vessels for twin-twin transfusion syndrome (TTTS). METHODS: Retrospective review of women undergoing laser for TTTS from January 2010 to December 2021. Outcomes were stratified based on maternal BMI <30, 30-34.9, and ≥35. Data obtained included maternal age, parity, ethnicity, gestational age at laser, placental location, Quintero stage, CHOP cardiovascular score, operative and anesthesia times, procedure-to-delivery interval, gestational age at delivery, survival to birth, survival to discharge, and the presence of residual anastomoses. Statistical analysis included the χ2 or Fisher's exact test for categorical variables and the Mann-Whitney U test for continuous variables with p < 0.05 being significant. RESULTS: A total of 434 women underwent laser for TTTS during the study period. Of those, 274 (63%) had a BMI of <30, 92 (21.2%) had a BMI between 30 and 34.9, and 68 (15.7%) had a BMI ≥ 35. There were no differences in maternal age, parity or ethnicity, Quintero stage, CHOP cardiovascular score, placental location, operative time, laser-to-delivery interval, gestational age at delivery, survival outcomes, or the presence of residual anastomoses between the three groups. Patients with a BMI of 30-34.9 were operated on at a slightly later gestational age, and those with a BMI > 35 had longer operative and anesthesia times. There were no technical failures as a result of BMI ≥ 30 or 35. CONCLUSION: Using appropriate technical adjustments, outcomes for obese women undergoing laser for TTTS are similar to nonobese women, although patients with BMI ≥35 have longer operative and anesthesia times.

Phonon Dephasing Dynamics in MoS2.

A variety of quantum degrees of freedom, e.g., spins, valleys, and localized emitters, in atomically thin van der Waals materials have been proposed for quantum information applications, and they inevitably couple to phonons. Here, we directly measure the intrinsic optical phonon decoherence in monolayer and bulk MoS2 by observing the temporal evolution of the spectral interference of Stokes photons generated by pairs of laser pulses. We find that a prominent optical phonon mode E2g exhibits a room-temperature dephasing time of ∼7 ps in both the monolayer and bulk. This dephasing time extends to ∼20 ps in the bulk crystal at ∼15 K, which is longer than previously thought possible. First-principles calculations suggest that optical phonons decay via two types of three-phonon processes, in which a pair of acoustic phonons with opposite momentum are generated.

Coherent Population Trapping Combined with Cycling Transitions for Quantum Dot Hole Spins Using Triplet Trion States.

Optical spin rotations and cycling transitions for measurement are normally incompatible in quantum dots, presenting a fundamental problem for quantum information applications. Here we show that for a hole spin this problem can be addressed using a trion with one hole in an excited orbital, where strong spin-orbit interaction tilts the spin. Then, a particular trion triplet forms a double Λ system, even in a Faraday magnetic field, which we use to demonstrate fast hole spin initialization and coherent population trapping. The lowest trion transitions still strongly preserve spin, thus combining fast optical spin control with cycling transitions for spin readout.

Phonon-Assisted Intervalley Scattering Determines Ultrafast Exciton Dynamics in MoSe_{2} Bilayers.

While valleys (energy extrema) are present in all band structures of solids, their preeminent role in determining exciton resonances and dynamics in atomically thin transition metal dichalcogenides (TMDC) is unique. Using two-dimensional coherent electronic spectroscopy, we find that exciton decoherence occurs on a much faster timescale in MoSe_{2} bilayers than that in the monolayers. We further identify two population relaxation channels in the bilayer, a coherent and an incoherent one. Our microscopic model reveals that phonon-emission processes facilitate scattering events from the K valley to other lower-energy Γ and Λ valleys in the bilayer. Our combined experimental and theoretical studies unequivocally establish different microscopic mechanisms that determine exciton quantum dynamics in TMDC monolayers and bilayers. Understanding exciton quantum dynamics provides critical guidance to the manipulation of spin-valley degrees of freedom in TMDC bilayers.

Twist Angle-Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures.

In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in MoSe_{2}/WSe_{2} twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1° to 3.5°. Using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moiré potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of "twistronics".

Anesthesia for Maternal-Fetal Interventions: A Consensus Statement From the American Society of Anesthesiologists Committees on Obstetric and Pediatric Anesthesiology and the North American Fetal Therapy Network.

Maternal-fetal surgery is a rapidly evolving specialty, and significant progress has been made over the last 3 decades. A wide range of maternal-fetal interventions are being performed at different stages of pregnancy across multiple fetal therapy centers worldwide, and the anesthetic technique has evolved over the years. The American Society of Anesthesiologists (ASA) recognizes the important role of the anesthesiologist in the multidisciplinary approach to these maternal-fetal interventions and convened a collaborative workgroup with representatives from the ASA Committees of Obstetric and Pediatric Anesthesia and the Board of Directors of the North American Fetal Therapy Network. This consensus statement describes the comprehensive preoperative evaluation, intraoperative anesthetic management, and postoperative care for the different types of maternal-fetal interventions.

Management of neonatal difficult airway emergencies in the delivery room.

Neonatal airway emergencies in the delivery room are associated with significant morbidity and mortality. Etiologies vary, but often predispose the neonate to life threatening airway obstruction. With the recent expansion of fetal medicine programs, pediatric anesthesiologists are increasingly being asked to care for these patients. In this review, we discuss common etiologies of difficult airway at delivery, management tools and techniques, and surgical approaches.

Fetal anesthesia: intrauterine therapies and immediate postnatal anesthesia for noncardiac surgical interventions.

PURPOSE OF REVIEW: This review describes maternal and fetal anesthetic management for noncardiac fetal surgical procedures, including the management of lower urinary tract obstruction, congenital diaphragmatic hernia (CDH), myelomeningocele, sacrococcygeal teratoma, prenatally anticipated difficult airway and congenital lung lesions. RECENT FINDINGS: Fetal interventions range from minimally invasive fetoscopic procedures to mid-gestation open surgery, to ex-utero intrapartum treatment procedure. Anesthetic management depends on the fetal intervention and patient characteristics. Anesthesia for most minimally invasive procedures can consist of intravenous sedation and local anesthetic infiltration in clinically appropriate maternal patients. Open fetal and ex-utero intrapartum treatment procedures require maternal general anesthesia with volatile anesthetic and other medications to maintain uterine relaxation. Tracheal balloons are a promising therapy for CDH and can be inserted via minimally invasive techniques. Management of the prenatally anticipated difficult airway during delivery and removal of tracheal balloons from patients with CDH during delivery can be clinically dynamic and require flexibility, seamless communication and a high-functioning, multidisciplinary care team. SUMMARY: Maternal and fetal anesthetic management is tailored to the fetal intervention and the underlying health of the fetus and mother.

Microsecond Valley Lifetime of Defect-Bound Excitons in Monolayer WSe_{2}.

In atomically thin two-dimensional semiconductors such as transition metal dichalcogenides (TMDs), controlling the density and type of defects promises to be an effective approach for engineering light-matter interactions. We demonstrate that electron-beam irradiation is a simple tool for selectively introducing defect-bound exciton states associated with chalcogen vacancies in TMDs. Our first-principles calculations and time-resolved spectroscopy measurements of monolayer WSe_{2} reveal that these defect-bound excitons exhibit exceptional optical properties including a recombination lifetime approaching 200 ns and a valley lifetime longer than 1 µs. The ability to engineer the crystal lattice through electron irradiation provides a new approach for tailoring the optical response of TMDs for photonics, quantum optics, and valleytronics applications.

A Synthetic Binder of Breast Cancer Stem Cells.

Cancer stem cells (CSCs) are associated with drug resistance, metastasis and recurrence of cancer. A synthetic binder of CSCs can provide a valuable tool to study the biology of CSCs and a lead to develop imaging, diagnostic and therapeutic agents targeting CSCs. Herein, a synthetic ligand (1) that specifically binds to CSCs over non-CSCs of breast cancer cells was identified for the first time via a cell-binding screening of a chemical library. The ligand 1 showed specific binding to CD24- /CD44+ /ALDH+ CSC population of MCF-7 and MDA-MB-231. We have demonstrated that 1-immobilized beads can be used as matrices for affinity isolation of 1-binding CSC population from breast cancer cells. The 1-binding population showed significantly increased expressions of stemness-associated transcription factors. Importantly, the 1-binding population demonstrated accelerated tumor growth in vivo, and the resulting tumor displayed an increased migratory activity and high expressions of CSC markers.

Risk factors for perioperative mortality and transfusion in sacrococcygeal teratoma resections.

BACKGROUND: Sacrococcygeal teratomas are a common congenital tumor. Surgical resection can occur in utero, in the neonatal period, or in the postneonatal period. AIMS: We describe patient and tumor factors associated with mortality and transfusion in this population. METHODS: We did a retrospective chart review of patients who underwent sacrococcygeal teratoma resection between January 1998 and March 2016. Demographic data, transfusion data, and tumor characteristics were collected. Descriptive statistics were calculated, and univariate comparisons were performed with chi-square test and Fisher's exact test. Variables significant at univariate level were used in multivariate logistic regression and negative binomial regression. RESULTS: Of the 112 cases, 6 were in utero repairs, 73 were neonatal repairs, and 33 were repairs at >30 days of life. There was 17%, 1%, and 0% intraoperative mortality and 33%, 5%, and 0% 30-day mortality in the in utero, neonatal, and >30 days of life repairs, respectively. All six patients who died within the first 30 days of life had a postmenstrual age of <32 weeks at time of surgery. All six patients who died had noncystic tumors. Patients with noncystic tumors were more likely to be born prior to 30-week gestation (23/65 vs 6/47; χ2 = 7.3; P = 0.007). Gestational age >30 weeks was associated with decreased intraoperative death (0% vs 10%; modified maximum likelihood estimate of OR 0.05; 95% CI 0.002-0.96; P = 0.02). Gestational age >30 weeks (2.4% vs 13.8%; OR 0.15; 95% CI 0.03-0.89; P = 0.04) and cystic morphology (0% vs 9.2%; modified maximum likelihood estimate of OR 0.1; CI 0.01-1.75; P = 0.04) were associated with decreased 30-day mortality and emergent surgery (17.9% vs 1.2%; OR 18; 95% CI 2-162.2; P = 0.004) was associated with increased 30-day mortality. Gestational age >30 weeks (33.7% vs 62.1%; OR 0.27; 95% CI 0.09-0.79; P = 0.02) and Altman class 3-4 (12.1% vs 52.7%; OR 0.1; 95% CI 0.03-0.34; P = 0.0002) were associated with decreased need for transfusion and noncystic tumor was associated with increased transfusion volume (131.6 ml·kg-1 [95% CI 94-184] vs 63 ml·kg-1 [95% CI 40-100.1]; P = 0.01). CONCLUSIONS: Prematurity is associated with increased intraoperative and 30-day mortality. Noncystic tumor morphology was the only significant factor associated with transfusion volume and all six patients who died had transfusion volumes of 240 ml·kg-1 or greater. In these patients at high risk of mortality due to blood loss, the anesthesia team should be prepared to manage massive transfusion and coagulopathy with blood components and pharmacologic measures.

Coherent and Incoherent Coupling Dynamics between Neutral and Charged Excitons in Monolayer MoSe2.

The optical properties of semiconducting transition metal dichalcogenides are dominated by both neutral excitons (electron-hole pairs) and charged excitons (trions) that are stable even at room temperature. While trions directly influence charge transport properties in optoelectronic devices, excitons may be relevant through exciton-trion coupling and conversion phenomena. In this work, we reveal the coherent and incoherent nature of exciton-trion coupling and the relevant time scales in monolayer MoSe2 using optical two-dimensional coherent spectroscopy. Coherent interaction between excitons and trions is definitively identified as quantum beating of cross peaks in the spectra that persists for a few hundred femtoseconds. For longer times up to 10 ps, surprisingly, the relative intensity of the cross peaks increases, which is attributed to incoherent energy transfer likely due to phonon-assisted up-conversion and down-conversion processes that are efficient even at cryogenic temperature.

Long-Lived Valley Polarization of Intravalley Trions in Monolayer WSe_{2}.

We investigate valley dynamics associated with trions in monolayer tungsten diselenide (WSe_{2}) using polarization resolved two-color pump-probe spectroscopy. When tuning the pump and probe energy across the trion resonance, distinct trion valley polarization dynamics are observed as a function of energy and attributed to the intravalley and intervalley trions in monolayer WSe_{2}. We observe no decay of a near-unity valley polarization associated with the intravalley trions during ∼ 25 ps, while the valley polarization of the intervalley trions exhibits a fast decay of ∼4 ps. Furthermore, we show that resonant excitation is a prerequisite for observing the long-lived valley polarization associated with the intravalley trion. The exceptionally robust valley polarization associated with resonantly created intravalley trions discovered here may be explored for future valleytronic applications such as valley Hall effects.

Anesthetic Management of 65 Cases of Ex Utero Intrapartum Therapy: A 13-Year Single-Center Experience.

The anesthetic management for open fetal surgery has been described, but many therapeutic tenets have not been supported with data. We present data on the anesthetic management and outcomes of 65 patients undergoing ex utero intrapartum therapy procedures at the Children's Hospital of Philadelphia between 1998 and 2011. Patients were identified, and medical records were retrospectively reviewed. Maternal general anesthesia combined with postoperative epidural analgesia was commonly used. High levels of volatile anesthetic were used for uterine relaxation. Case characteristics such as fetal procedure, operative time, blood loss, transfusion requirements, vasopressor use, and fetal resuscitative measures are described.

The role of echocardiography in the intraoperative management of the fetus undergoing myelomeningocele repair.

INTRODUCTION: Fetal surgery for myelomeningocele (MMC) results in better outcomes compared to postnatal treatment. However, risks are present. We describe our experience with intraoperative fetal echocardiography during repair of MMC and report on the management of serious cardiovascular events. MATERIAL AND METHODS: The subjects included fetuses with intent to repair MMC from January 2011 to February 2014. The protocol involved continuous echocardiography in a looping, sequential manner of systolic function, heart rate and tricuspid and mitral valve regurgitation. RESULTS: A total of 101 cases intended fetal MMC repair; 100 completed surgery. Intraoperative ventricular dysfunction was present in 60% (20 mild, 25 moderate, 15 severe). Heart rate <100 bpm was noted in 11 cases. Tricuspid valve regurgitation was present in 35% (26 mild, 7 moderate, 2 severe); mitral valve regurgitation was present in 19% (15 mild, 4 moderate). Serious cardiovascular events were experienced in 7 cases, which affected the conduct of surgery and/or outcome. In 4 of these, medications were given via the umbilical vein and external cardiac compressions were performed. Fetal echocardiography was used to gauge the efficacy of compressions and to guide resuscitation. DISCUSSION: Cardiovascular compromise is common during fetal surgery for MMC. Intraoperative fetal echocardiography is recommended as a growing number of centers contemplate offering this form of novel, but potentially risky, therapy.

A Prospective Observational Study of EHR-Based Versus Virtual Desktop-Based Access to Pediatric Anesthesia Emergency Algorithms.

When pediatric anesthesia emergencies occur, situations can deteriorate rapidly. At our hospital, the Society for Pediatric Anesthesia's (SPA) emergency algorithms are used as cognitive aids during crises, and nurses are tasked with accessing the algorithms. Operating room nurses' typical workflow includes continuous display of the of the electronic health record (EHR) intraoperative navigator, which can delay navigating to the virtual desktop window and the algorithms' icon. Thus, we implemented a button in the intraoperative navigator's toolbar to access the algorithms with one click. We conducted an observational study of the time required to access and display overhead an algorithm using the new button and old method. We surveyed participants on usability.