Prolonged duration of nonequilibrated Dirac fermions in neutral topological insulators

Topological insulators (TIs) possess spin-polarized Dirac fermions on their surface but their unique properties are often masked by residual carriers in the bulk. Recently, (Sb_1−xBi_x)₂Te₃ was introduced as a non-metallic TI whose carrier type can be tuned from n to p across the charge neutrality point. By using time- and angle-resolved photoemission spectroscopy, we investigate the ultrafast carrier dynamics in the series of (Sb_1−xBi_x)₂Te₃. The Dirac electronic recovery of ∼10 ps at most in the bulk-metallic regime elongated to >400 ps when the charge neutrality point was approached. The prolonged nonequilibration is attributed to the closeness of the Fermi level to the Dirac point and to the high insulation of the bulk. We also discuss the feasibility of observing excitonic instability of (Sb_1−xBi_x)₂Te₃.

Distinct Ventral Pallidal Neural Populations Mediate Separate Symptoms of Depression

Major depressive disorder (MDD) patients display a common but often variable set of symptoms making successful, sustained treatment difficult to achieve. Separate depressive symptoms may be encoded by differential changes in distinct circuits in the brain, yet how discrete circuits underlie behavioral subsets of depression and how they adapt in response to stress has not been addressed. We identify two discrete circuits of parvalbumin-positive (PV) neurons in the ventral pallidum (VP) projecting to either the lateral habenula or ventral tegmental area contributing to depression. We find that these populations undergo different electrophysiological adaptations in response to social defeat stress, which are normalized by antidepressant treatment. Furthermore, manipulation of each population mediates either social withdrawal or behavioral despair, but not both. We propose that distinct components of the VP PV circuit can subserve related, yet separate depressive-like phenotypes in mice, which could ultimately provide a platform for symptom-specific treatments of depression.

Characterization of shear stress preventing red blood cells aggregation at the individual cell level: The temperature dependence

BACKGROUND

The novel measure of the red blood cells (RBC) aggregation (RBC-A) - the critical (minimum) shear stress (CSS) to prevent the cells from aggregation was found to be a promising clinically significant parameter. However, the absolute values of this parameter were found to change significantly depending on the shearing geometry (cup-and-bob, cone-plate or microchannel-flow) and have different temperature dependences along with it. The direct confirmation of these dependences aimed to find out the correct values is still pending.

OBJECTIVE

In this work, we aim to assess the absolute values of CSS at different temperatures.

METHODS

The single cell level measurements of CSS were performed using optical tweezers. The measurements were carried out in heavily diluted suspensions of RBCs in plasma.

RESULTS

The temperature dependent changes in CSS were measured at the points (22 and 38°C), in which the cup-and-bob and cone-plate systems yielded about 1.5-fold different values, while the microchannel-flow system yielded a constant value. The single cell CSS were found to be 362±157 mPa (22°C) and 312±57 mPa (38°C).

CONCLUSIONS

Our results prove that the microfluidic-flow approach is reflecting the RBC-A correctly. While the CSS values measured with other systems show the temperature dependent effect of the shearing geometry.

Strong familial association of bone mineral density between parents and offspring: KNHANES 2008-2011

Bone mineral density (BMD) of offspring was significantly associated with their parents' BMD. Parental BMD Z-score ≤-1 was a significant predictor for BMD Z-score ≤-1 in their offspring. Peak bone mass acquisition during early adulthood is more substantially influenced by genetic factors rather than lifestyle or environmental factors.

INTRODUCTION

A person's BMD is affected by both genetic and environmental factors. Family history of osteoporosis or fragility fracture is a well-known risk factor for low bone mass or fracture. The purpose of the present study was to investigate the familial association of BMD between parents and offspring in Korean population.

METHODS

This is a cross-sectional study based on the data from the Korea National Health and Nutrition Examination Surveys (KNHANES) conducted from 2008 to 2011. A total of 5947 subjects (3135 parents and 2812 offspring) were included.

RESULTS

In age-adjusted partial correlation analyses, all BMD values acquired from the lumbar spine, femur neck, total hip, and whole body showed significant associations between parents and offspring. Among these associations, whole-body BMD showed the strongest relationship between offspring and parents. The narrow-sense heritability of BMD ranged from 0.203 to 0.542 in male offspring and from 0.396 to 0.689 in female offspring. Multiple linear regression analyses showed that offspring's BMD was independently associated with BMD of both parents after adjusting for covariates. Lifestyle or environmental factors including dietary calcium intake, serum 25-hydroxyvitamin D level, regular exercise, current smoking, and alcohol intake showed only moderate or no associations with BMD. In multiple logistic regression analyses in offspring aged 19-25 years, the son's risk of having BMD Z-score ≤-1 was associated with both parents' BMD Z-score ≤-1, while the daughter's risk was only associated with maternal BMD Z-score ≤-1.

CONCLUSIONS

Our findings confirm the strong familial association of BMD between parents and offspring in Korean population and suggest that peak bone mass acquisition during early adulthood is more substantially influenced by genetic factors rather than lifestyle or environmental factors.

Topologically Entangled Rashba-Split Shockley States on the Surface of Grey Arsenic

We discover a pair of spin-polarized surface bands on the (111) face of grey arsenic by using angle-resolved photoemission spectroscopy (ARPES). In the occupied side, the pair resembles typical nearly-free-electron Shockley states observed on noble-metal surfaces. However, pump-probe ARPES reveals that the spin-polarized pair traverses the bulk band gap and that the crossing of the pair at Γ[over ¯] is topologically unavoidable. First-principles calculations well reproduce the bands and their nontrivial topology; the calculations also support that the surface states are of Shockley type because they arise from a band inversion caused by crystal field. The results provide compelling evidence that topological Shockley states are realized on As(111).

Bunch-by-bunch position measurement and analysis at PLS-II

A bunch-by-bunch measurement system has been developed at Pohang Light Source II. The system consists of a four-channel button pick-up, 20 GHz sampling oscilloscope and an 800 MHz low-pass digital filter. Upon measuring a bunch-by-bunch spatio-temporal beam motion matrix over many turns, singular-value decomposition analysis is used to reveal the dominant coupled-bunch modes. The system can diagnose injection oscillations due to kicker errors and the effect of resistive-wall impedance that gives rise to instability during operation.

Orbital-Dependent Band Narrowing Revealed in an Extremely Correlated Hund's Metal Emerging on the Topmost Layer of Sr_{2}RuO_{4}

We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr_{2}RuO_{4} crystal, consisting of slightly rotated RuO_{6} octahedrons. The γ band derived from the 4d_{xy} orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the α and β bands derived from the one-dimensional 4d_{xz/yz}. This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the on-site Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr_{2}RuO_{4} is extremely correlated and well isolated from the underlying crystal.

High repetition pump-and-probe photoemission spectroscopy based on a compact fiber laser system

The paper describes a time-resolved photoemission (TRPES) apparatus equipped with a Yb-doped fiber laser system delivering 1.2-eV pump and 5.9-eV probe pulses at the repetition rate of 95 MHz. Time and energy resolutions are 11.3 meV and ∼310 fs, respectively, the latter is estimated by performing TRPES on a highly oriented pyrolytic graphite (HOPG). The high repetition rate is suited for achieving high signal-to-noise ratio in TRPES spectra, thereby facilitating investigations of ultrafast electronic dynamics in the low pump fluence (p) region. TRPES of polycrystalline bismuth (Bi) at p as low as 30 nJ/mm² is demonstrated. The laser source is compact and is docked to an existing TRPES apparatus based on a 250-kHz Ti:sapphire laser system. The 95-MHz system is less prone to space-charge broadening effects compared to the 250-kHz system, which we explicitly show in a systematic probe-power dependency of the Fermi cutoff of polycrystalline gold. We also describe that the TRPES response of an oriented Bi(111)/HOPG sample is useful for fine-tuning the spatial overlap of the pump and probe beams even when p is as low as 30 nJ/mm².

Capacity building for global nursing leaders: challenges and experiences

AIM

The aim of this article is to describe our experience in operating a capacity-building programme, the Korea International Cooperation Project, for global nursing leaders from developing countries, held during the International Council of Nurses (ICN) Conference in 2015 in Seoul, Korea.

BACKGROUND

Globalization points to the importance of global leadership among nursing leaders. In accordance with the theme of 'Global Citizen, Global Nursing' at the ICN conference in 2015, a capacity-building programme for nursing leaders of developing countries was implemented.

INTRODUCTION

The global nursing leadership programme shared experiences during the preparation and operation of the conference. To prepare the programme, this paper describes selecting participants, working with invitation lists from 30 countries, and recruiting and training volunteers. The operation of the programme, orientation, organizing tailored programmes for participant groups, addressing unexpected issues and evaluating the programme are described.

IMPLICATIONS FOR NURSING POLICY

ICN could implement capacity-building programmes for nursing leaders of developing countries during its ICN conference for the nursing society. A programme tailored for each continent with similar sociocultural backgrounds and health issues would provide chances for collaboration and networking. A policy to compile global nursing indicators should be developed. This would allow nursing leaders to learn about the strengths and weaknesses of global nursing and provide evidence for collaboration.

CONCLUSION

The programme was successful in introducing and broadening global perspectives of participants on health and education as well as building a network among leaders and next-generation leaders in participating countries for future cooperation and collaboration.