Emergent flat band and topological Kondo semimetal driven by orbital-selective correlations

Flat electronic bands are expected to show proportionally enhanced electron correlations, which may generate a plethora of novel quantum phases and unusual low-energy excitations. They are increasingly being pursued in d-electron-based systems with crystalline lattices that feature destructive electronic interference, where they are often topological. Such flat bands, though, are generically located far away from the Fermi energy, which limits their capacity to partake in the low-energy physics. Here we show that electron correlations produce emergent flat bands that are pinned to the Fermi energy. We demonstrate this effect within a Hubbard model, in the regime described by Wannier orbitals where an effective Kondo description arises through orbital-selective Mott correlations. Moreover, the correlation effect cooperates with symmetry constraints to produce a topological Kondo semimetal. Our results motivate a novel design principle for Weyl Kondo semimetals in a new setting, viz. d-electron-based materials on suitable crystal lattices, and uncover interconnections among seemingly disparate systems that may inspire fresh understandings and realizations of correlated topological effects in quantum materials and beyond.

Field-Induced Non-BEC Transitions in Frustrated Magnets

Frustrated spin systems have traditionally proven challenging to understand, owing to a scarcity of controlled methods for their analyses. By contrast, under strong magnetic fields, certain aspects of spin systems admit simpler and universal description in terms of hardcore bosons. The bosonic formalism is anchored by the phenomenon of Bose-Einstein condensation (BEC), which has helped explain the behaviors of a wide range of magnetic compounds under applied magnetic fields. Here, we focus on the interplay between frustration and externally applied magnetic field to identify instances where the BEC paradigm is no longer applicable. As a representative example, we consider the antiferromagnetic J_{1}-J_{2}-J_{3} model on the square lattice in the presence of a uniform external magnetic field, and demonstrate that the frustration-driven suppression of the Néel order leads to a Lifshitz transition for the hardcore bosons. In the vicinity of the Lifshitz point, the physics becomes unmoored from the BEC paradigm, and the behavior of the system, both at and below the saturation field, is controlled by a Lifshitz multicritical point. We obtain the resultant universal scaling behaviors, and provide strong evidence for the existence of a frustration and magnetic-field driven correlated bosonic liquid state along the entire phase boundary separating the Néel phase from other magnetically ordered states.

Shot noise in a strange metal

Strange-metal behavior has been observed in materials ranging from high-temperature superconductors to heavy fermion metals. In conventional metals, current is carried by quasiparticles; although it has been suggested that quasiparticles are absent in strange metals, direct experimental evidence is lacking. We measured shot noise to probe the granularity of the current-carrying excitations in nanowires of the heavy fermion strange metal YbRh2Si2. When compared with conventional metals, shot noise in these nanowires is strongly suppressed. This suppression cannot be attributed to either electron-phonon or electron-electron interactions in a Fermi liquid, which suggests that the current is not carried by well-defined quasiparticles in the strange-metal regime that we probed. Our work sets the stage for similar studies of other strange metals.

Ultrasound characteristics, serum biochemistry and outcome of ectopic pregnancies presenting during COVID-19 pandemic

OBJECTIVE

To describe and compare the characteristics of ectopic pregnancies (EPs) in the year prior to vs during the coronavirus disease 2019 (COVID-19) pandemic.

METHODS

This was a retrospective analysis of women diagnosed with an EP on transvaginal sonography conducted at a center in London, UK, providing early-pregnancy assessment, between 1 January 2019 and 31 December 2020. Women were identified via the Astraia ultrasound reporting system using coded and non-coded outcomes of EP or pregnancy outside the uterine cavity. Data related to predefined outcomes were collected using Astraia and Cerner electronic reporting systems. Main outcome measures included clinical, ultrasound and biochemical features of EP, in addition to reported complications and management.

RESULTS

There were 22 683 consultations over the 2-year period. Following consultation, a similar number and proportion of EPs were diagnosed in 2019 (141/12 657 (1%)) and 2020 (134/10 026 (1%)). Both cohorts were comparable in age, ethnicity, weight and method of conception. Gestational age at the first transvaginal sonography scan and at diagnosis were similar, and no difference in location, size or morphology of EP was found between the two cohorts. Serum human chorionic gonadotropin (hCG) levels at the time of EP diagnosis were higher in 2020 than in 2019 (1005 IU/L vs 665 IU/L; P = 0.03). The proportions of women according to type of final EP management were similar, but the rate of failed first-line management was higher during vs before the pandemic (16% vs 6%; P = 0.01). The rates of blood detected in the pelvis (hemoperitoneum) on ultrasound (23% vs 26%; P = 0.58) and of ruptured EP confirmed surgically (9% vs 3%; P = 0.07) were similar in 2019 vs 2020.

CONCLUSIONS

No difference was observed in the location, size, morphology or gestational age at the first ultrasound examination or at diagnosis of EP between women diagnosed before vs during the COVID-19 pandemic. Complication rates and final management strategy were also unchanged. However, hCG levels and the failure rate of first-line conservative management measures were higher during the pandemic. Our findings suggest that women continued to access appropriate care for EP during the COVID-19 pandemic, with no evidence of diagnostic delay or an increase in adverse outcome in our population. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

First-trimester intrauterine hematoma and pregnancy complications

OBJECTIVE

To assess whether sonographic diagnosis of intrauterine hematoma (IUH) in the first trimester of pregnancy is associated with first-trimester miscarriage and antenatal, delivery and neonatal complications.

METHODS

This was a prospective observational cohort study of women with an intrauterine singleton pregnancy between 5 and 14 weeks' gestation recruited at Queen Charlotte's and Chelsea Hospital, London, UK, between March 2014 and March 2016. Participants underwent serial ultrasound examinations in the first trimester, and the presence, location, size and persistence of any IUH was evaluated. First-trimester miscarriage was defined as pregnancy loss before 14 weeks' gestation. Clinical symptoms, including pelvic pain and vaginal bleeding, were recorded at each visit using validated symptom scores. Antenatal, delivery and neonatal outcomes were obtained from hospital records. Logistic regression analysis and the chi-square test were used to assess the association between the presence and features of IUH and the incidence of adverse pregnancy outcome. Odds ratios (OR) were first adjusted for maternal age (aOR) and then further adjusted for the presence of vaginal bleeding or pelvic pain in the first trimester.

RESULTS

Of 1003 women recruited to the study, 946 were included in the final analysis and of these, 268 (28.3%) were diagnosed with an IUH in the first trimester. The presence of IUH was associated with the incidence of preterm birth (aOR, 1.94 (95% CI, 1.07-3.52)), but no other individual or overall antenatal, delivery or neonatal complications. No association was found between the presence of IUH in the first trimester and first-trimester miscarriage (aOR, 0.81 (95% CI, 0.44-1.50)). These findings were independent of the absolute size of the hematoma and the presence of vaginal bleeding or pelvic pain in the first trimester. When IUH was present in the first trimester, there was no association between its size, content or position in relation to the gestational sac and overall antenatal, delivery and neonatal complications. Diagnosis of a retroplacental IUH was associated with an increased risk of overall antenatal complications (P = 0.04).

CONCLUSIONS

Our findings demonstrate that there is no association between the presence of IUH in the first trimester and first-trimester miscarriage. However, an association with preterm birth, independently of the presence of symptoms of pelvic pain and/or vaginal bleeding, is evident. Women diagnosed with IUH in the first trimester should be counseled about their increased risk of preterm birth and possibly be offered increased surveillance during the course of their pregnancy. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Unifying Interacting Nodal Semimetals: A New Route to Strong Coupling

We propose a general framework for constructing a large set of nodal-point semimetals by tuning the number of linearly (d_{L}) and (at most) quadratically (d_{Q}) dispersing directions. By virtue of such a unifying scheme, we identify a new perturbative route to access various strongly interacting non-Dirac semimetals with d_{Q}>0. As a demonstrative example, we relate a two-dimensional anisotropic semimetal with d_{L}=d_{Q}=1, describing the topological transition between a Dirac semimetal and a normal insulator, and its three-dimensional counterparts with d_{L}=1, d_{Q}=2. We address the quantum critical phenomena and emergence of non-Fermi liquid states with unusual dynamical structures within the framework of an ε expansion, where ε=2-d_{Q}, when these systems reside at the brink of charge- or spin-density-wave orderings, or an s-wave pairing. Our results can be germane to two-dimensional uniaxially strained optical honeymcomb lattice, α-(BEDT-TTF)_{2}I_{3}.

Managing pregnancy of unknown location based on initial serum progesterone and serial serum hCG levels: development and validation of a two-step triage protocol

OBJECTIVES

A uniform rationalized management protocol for pregnancies of unknown location (PUL) is lacking. We developed a two-step triage protocol to select PUL at high risk of ectopic pregnancy (EP), based on serum progesterone level at presentation (step 1) and the serum human chorionic gonadotropin (hCG) ratio, defined as the ratio of hCG at 48 h to hCG at presentation (step 2).

METHODS

This was a cohort study of 2753 PUL (301 EP), involving a secondary analysis of prospectively and consecutively collected PUL data from two London-based university teaching hospitals. Using a chronological split we used 1449 PUL for development and 1304 for validation. We aimed to assign PUL as low risk with high confidence (high negative predictive value (NPV)) while classifying most EP as high risk (high sensitivity). The first triage step assigned PUL as low risk using a threshold of serum progesterone at presentation. The remaining PUL were triaged using a novel logistic regression risk model based on hCG ratio and initial serum progesterone (second step), defining low risk as an estimated EP risk of < 5%.

RESULTS

On validation, initial serum progesterone ≤ 2 nmol/L (step 1) classified 16.1% PUL as low risk. Second-step classification with the risk model selected an additional 46.0% of all PUL as low risk. Overall, the two-step protocol classified 62.1% of PUL as low risk, with an NPV of 98.6% and a sensitivity of 92.0%. When the risk model was used in isolation (i.e. without the first step), 60.5% of PUL were classified as low risk with 99.1% NPV and 94.9% sensitivity.

CONCLUSION

PUL can be classified efficiently into being either high or low risk for complications using a two-step protocol involving initial progesterone and hCG levels and the hCG ratio. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Ultrasound assessment of the peri-implantation uterus: a review

Emerging evidence suggests that early embryo implantation is a more active maternal process than hitherto appreciated, involving active encapsulation of the implanting blastocyst by maternal decidual cells and coordinated changes in the underlying inner myometrium, known as the junctional zone. These concepts raise the possibility that early ultrasound markers predictive of adverse pregnancy outcome could be identified. In this review we assess the role of ultrasound in predicting the likelihood of different pregnancy outcomes and highlight potential novel markers that could be tested.

Prevalence of uterine anomalies and their impact on early pregnancy in women conceiving after assisted reproduction treatment

OBJECTIVE

To estimate the prevalence of congenital uterine anomalies in subfertile women and to evaluate their influence on early pregnancy following assisted reproduction treatment (ART).

METHODS

We prospectively recruited 1402 subjects undergoing ART over a period of 5 years from 2005 to 2009. Three-dimensional transvaginal sonography was performed in the early follicular phase of the menstrual cycle (days 2-5) and repeated in the late follicular phase (days 10-14) if the shape of the uterine cavity could not be assessed at the first scan. All subjects who conceived following ART were followed up to 12 weeks' gestation. Chi-square test was used to compare the pregnancy rates and miscarriage rates between women shown to have uterine anomalies and those with a normal uterus.

RESULTS

One thousand three hundred and eighty-five subjects were included for final analysis after excluding 17 subjects in whom a definitive diagnosis could not be made. While 1201 (86.7%) subjects had a normal uterine cavity, uterine anomalies were demonstrated in 184 (13.3%) subjects. Arcuate uteri represented the commonest anomaly (n = 164 (11.8%)) followed by septate (n = 7 (0.5%)), unicornuate (n = 6 (0.4%)), subseptate (n = 5 (0.4%)), bicornuate (n = 1 (0.1%)) and T-shaped uteri (n = 1 (0.1%)). A total of 440 subjects who underwent ART were followed up. The pregnancy rates in women with arcuate uteri (36/66 (54.5%)) and major uterine anomalies (7/10 (70.0%)) were statistically similar (P = 0.09 and P = 0.11, respectively) to that of the matched controls with normal uteri (158/364 (43.4%)). While first-trimester miscarriage rates were similar (P = 0.81) between the control group (20/158 (12.7%)) and women with arcuate uteri (5/36 (13.9%)), women with major uterine anomalies experienced a higher miscarriage rate (3/7 (42.9%); P = 0.05).

CONCLUSIONS

Women who are referred for ART have a high prevalence of congenital uterine anomalies, the most common anomaly being an arcuate uterus. These anomalies are not associated with a reduction in pregnancy rates following ART. However, while the arcuate uterus was not associated with an increase in first-trimester miscarriage, major uterine anomalies seemed to increase the risk of first-trimester miscarriage.

First rank symptoms: concepts and diagnostic utility

First Rank Symptoms (FRS) were first defined by Schneider as diagnostic of schizophrenia. Since then, there has been an immense debate on their diagnostic and prognostic utility. This review attempts to understand the concepts of FRS as depicted over the years and the diagnostic and prognostic implications of FRS in mental illnesses including schizophrenia. Review of relevant material showed that there are wide variations in the concepts of FRS which may be classified according to broad and narrow definitions. These variations have also led to the differences in the diagnostic systems currently being used. Although the diagnostic utility of FRS in schizophrenia remains, it is not clearly so with other mental illnesses in which these symptoms may also be observed. In addition there is controversy over the prognostic implications with evidence divided between poor and no influence on outcome.