103 research outputs found
Ferroelectric and anomalous quantum Hall states in bare rhombohedral trilayer graphene
Nontrivial interacting phases can emerge in elementary materials. As a prime
example, continuing advances in device quality have facilitated the observation
of a variety of spontaneous quantum Hall-like states, a cascade of Stoner-like
magnets, and an unconventional superconductor in bilayer graphene. Its natural
extension, rhombohedral trilayer graphene is predicted to be even more
susceptible to interactions given its even flatter low-energy bands and larger
winding number. Theoretically, five spontaneous quantum Hall phases have been
proposed to be candidate ground states. Here, we provide transport evidence for
observing four of the five competing ordered states in interaction-maximized,
dually-gated, rhombohedral trilayer graphene. In particular, at vanishing but
finite magnetic fields, two states with Chern numbers 3 and 6 can be stabilized
at elevated and low electric fields, respectively, and both exhibit clear
magnetic hysteresis. We also reveal that the quantum Hall ferromagnets of the
zeroth Landau level are ferroelectrics with spontaneous layer polarizations
even at zero electric field, as evidenced by electric hysteresis. Our findings
exemplify the possible birth of rich interacting electron physics in a simple
elementary material
Interaction-driven (quasi-) insulating ground states of gapped electron-doped bilayer graphene
Bernal bilayer graphene has recently been discovered to exhibit a wide range
of unique ordered phases resulting from interaction-driven effects and
encompassing spin and valley magnetism, correlated insulators, correlated
metals, and superconductivity. This letter reports on a novel family of
correlated phases characterized by spin and valley ordering, observed in
electron-doped bilayer graphene. The novel correlated phases demonstrate an
intriguing non-linear current-bias behavior at ultralow currents that is
sensitive to the onset of the phases and is accompanied by an insulating
temperature dependence, providing strong evidence for the presence of
unconventional charge carrying degrees of freedom originating from ordering.
These characteristics cannot be solely attributed to any of the previously
reported phases, and are qualitatively different from the behavior seen
previously on the hole-doped side. Instead, our observations align with the
presence of charge- or spin-density-waves state that open a gap on a portion of
the Fermi surface or fully gapped Wigner crystals. The resulting new phases,
quasi-insulators in which part of the Fermi surface remains intact or
valley-polarized and valley-unpolarized Wigner crystals, coexist with
previously known Stoner phases, resulting in an exceptionally intricate phase
diagram
A mock circulation loop to test extracorporeal CO2 elimination setups
Background: Extracorporeal carbon dioxide removal (ECCO2R) is a promising yet
limited researched therapy for hypercapnic respiratory failure in acute respiratory
distress syndrome and exacerbated chronic obstructive pulmonary disease. Herein,
we describe a new mock circuit that enables experimental ECCO2R research without
animal models. In a second step, we use this model to investigate three experimental
scenarios of ECCO2R: (I) the influence of hemoglobin concentration on CO2 removal. (II)
a potentially portable ECCO2R that uses air instead of oxygen, (III) a low-flow ECCO2R
that achieves effective CO2 clearance by recirculation and acidification of the limited
blood volume of a small dual lumen cannula (such as a dialysis catheter).
Results: With the presented ECCO2R mock, CO2 removal rates comparable to previous
studies were obtained. The mock works with either fresh porcine blood or diluted
expired human packed red blood cells. However, fresh porcine blood was preferred
because of better handling and availability. In the second step of this work, hemoglobin
concentration was identified as an important factor for CO2 removal. In the second
scenario, an air-driven ECCO2R setup showed only a slightly lower CO2 wash-out than the
same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO2R,
the blood flow at the test membrane lung was successfully raised with a recirculation
channel without the need to increase cannula flow. Low recirculation ratios resulted in
increased efficiency, while high recirculation ratios caused slightly reduced CO2 removal
rates. Acidification of the CO2 depleted blood in the recirculation channel caused an
increase in CO2 removal rate.
Conclusions: We demonstrate a simple and cost effective, yet powerful, “in-vitro”
ECCO2R model that can be used as an alternative to animal experiments for many
research scenarios. Moreover, in our approach parameters such as hemoglobin level can
be modified more easily than in animal models
Comparison of Serial and Parallel Connections of Membrane Lungs against Refractory Hypoxemia in a Mock Circuit
Extracorporeal membrane oxygenation (ECMO) is an important rescue therapy method
for the treatment of severe hypoxic lung injury. In some cases, oxygen saturation and oxygen partial
pressure in the arterial blood are low despite ECMO therapy. There are case reports in which patients
with such instances of refractory hypoxemia received a second membrane lung, either in series or in
parallel, to overcome the hypoxemia. It remains unclear whether the parallel or serial connection
is more effective. Therefore, we used an improved version of our full-flow ECMO mock circuit to
test this. The measurements were performed under conditions in which the membrane lungs were
unable to completely oxygenate the blood. As a result, only the photometric pre- and post-oxygenator
saturations, blood flow and hemoglobin concentration were required for the calculation of oxygen
transfer rates. The results showed that for a pre-oxygenator saturation of 45% and a total blood flow of
10 L/min, the serial connection of two identical 5 L rated oxygenators is 17% more effective in terms
of oxygen transfer than the parallel connection. Although the idea of using a second membrane lung
if refractory hypoxia occurs is intriguing from a physiological point of view, due to the invasiveness
of the solution, further investigations are needed before this should be used in a wider clinical setting
Comparison of Circular and Parallel-Plated Membrane Lungs for Extracorporeal Carbon Dioxide Elimination
Extracorporeal carbon dioxide removal (ECCO2R) is an important technique to treat critical lung diseases such as exacerbated chronic obstructive pulmonary disease (COPD) and mild or
moderate acute respiratory distress syndrome (ARDS). This study applies our previously presented
ECCO2R mock circuit to compare the CO2 removal capacity of circular versus parallel-plated membrane lungs at different sweep gas flow rates (0.5, 2, 4, 6 L/min) and blood flow rates (0.3 L/min,
0.9 L/min). For both designs, two low-flow polypropylene membrane lungs (Medos Hilte 1000,
Quadrox-i Neonatal) and two mid-flow polymethylpentene membrane lungs (Novalung Minilung,
Quadrox-iD Pediatric) were compared. While the parallel-plated Quadrox-iD Pediatric achieved the
overall highest CO2 removal rates under medium and high sweep gas flow rates, the two circular
membrane lungs performed relatively better at the lowest gas flow rate of 0.5 L/min. The low-flow
Hilite 1000, although overall better than the Quadrox i-Neonatal, had the most significant advantage
at a gas flow of 0.5 L/min. Moreover, the circular Minilung, despite being significantly less efficient
than the Quadrox-iD Pediatric at medium and high sweep gas flow rates, did not show a significantly
worse CO2 removal rate at a gas flow of 0.5 L/min but rather a slight advantage. We suggest that
circular membrane lungs have an advantage at low sweep gas flow rates due to reduced shunting as
a result of their fiber orientation. Efficiency for such low gas flow scenarios might be relevant for
possible future portable ECCO2R devices
A Novel Mock Circuit to Test Full-Flow Extracorporeal Membrane Oxygenation
Extracorporeal membrane oxygenation (ECMO) has become an important therapeutic
approach in the COVID-19 pandemic. The development and research in this field strongly relies on
animal models; however, efforts are being made to find alternatives. In this work, we present a new
mock circuit for ECMO that allows measurements of the oxygen transfer rate of a membrane lung at
full ECMO blood flow. The mock utilizes a large reservoir of heparinized porcine blood to measure the
oxygen transfer rate of the membrane lung in a single passage. The oxygen transfer rate is calculated
from blood flow, hemoglobin value, venous saturation, and post-membrane arterial oxygen pressure.
Before the next measuring sequence, the blood is regenerated to a venous condition with a sweep
gas of nitrogen and carbon dioxide. The presented mock was applied to investigate the effect of a
recirculation loop on the oxygen transfer rate of an ECMO setup. The recirculation loop caused a
significant increase in post-membrane arterial oxygen pressure (paO2
). The effect was strongest for
the highest recirculation flow. This was attributed to a smaller boundary layer on gas fibers due to
the increased blood velocity. However, the increase in paO2 did not translate to significant increases
in the oxygen transfer rate because of the minor significance of physically dissolved oxygen for gas
transfer. In conclusion, our results regarding a new ECMO mock setup demonstrate that recirculation
loops can improve ECMO performance, but not enough to be clinically relevant
Probing the tunable multi-cone bandstructure in Bernal bilayer graphene
Controlling the bandstructure of Dirac materials is of wide interest in
current research but has remained an outstanding challenge for systems such as
monolayer graphene. In contrast, Bernal bilayer graphene (BLG) offers a highly
flexible platform for tuning the bandstructure, featuring two distinct regimes.
In one regime, which is well established and widely used, a tunable bandgap is
induced by a large enough transverse displacement field. Another is a gapless
metallic band occurring near charge neutrality and at not too strong fields,
featuring rich 'fine structure' consisting of four linearly-dispersing Dirac
cones with opposite chiralities in each valley and van Hove singularities. Even
though BLG was extensively studied experimentally in the last two decades, the
evidence of this exotic bandstructure is still elusive, likely due to
insufficient energy resolution. Here, rather than probing the bandstructure by
direct spectroscopy, we use Landau levels as markers of the energy dispersion
and carefully analyze the Landau level spectrum in a regime where the cyclotron
orbits of electrons or holes in momentum space are small enough to resolve the
distinct mini Dirac cones. We identify the presence of four distinct Dirac
cones and map out complex topological transitions induced by electric
displacement field. These findings introduce a valuable addition to the toolkit
for graphene electronics
Towards coherent O-band data center interconnects
Upcoming generations of coherent intra/inter data center interconnects currently lack a clear path toward a reduction of cost and power consumption, which are the driving factors for these data links. In this work, the tradeoffs associated with a transition from coherent C-band to O-band silicon photonics are addressed and evaluated. The discussion includes the fundamental components of coherent data links, namely the optical components, fiber link and transceivers. As a major component of these links, a monolithic silicon photonic BiCMOS O-band coherent receiver is evaluated for its potential performance and compared to an analogous C-band device.TU Berlin, Open-Access-Mittel - 2021BMBF, 13N14932, Verbundprojekt: Photonic Embedding of Active Region LASER Chips on Silicon (PEARLS) - Teilvorhaben: Entwurf und Charakterisierung von eingebetteten, horizontal-gekoppelten Laser-Strukturen auf SiliziumEC/H2020/822002/EU/Lasercom-on-chip for next generation, high-speed satellite constelation interconnectivity/ORIONA
Selektivno određivanje Fe(III) u uzorcima Fe(II) UV-spektrofotometrijom pomoću kvercetina i morina
Selective UV-spectrophotometric methods for determination of iron(III) in iron(II) samples have been developed. The methods are based on the interaction of Fe(III) with quercetin and morin, compounds of the flavonoid group. Redox reactions occurring between Fe(III) ions and the reagents used make the basis for the detection. Iron(II) does not react with quercetin and morin under the conditions applied [aqueous-methanolic (3 : 2) solutions, 0.3 mol L1 HCl, and 1.2 × 10-4 mol L1 quercetin (morin)] and does not interfere with the determination of Fe(III). Iron(III) can be determined up to 15 μg mL1 using both the examined systems. The detection limits are 0.06 and 0.38 μg mL1 when using quercetin or morin, respectively. The method with quercetin was applied to the determination of Fe(III) (ca. 0.2%) in a Fe(II) pharmaceutical product.U radu je opisan razvoj selektivnih UV-spektrofotometrijskih metoda za određivanje željeza(III) u uzorku željeza(II). Metode se temelje na redoks reakciji Fe(III) sa spojevima iz skupine flavonoida kvercetinom i morinom u reakcijskim uvjetima u kojima željezo(II) ne reagira (vodeno/metanolna otopina 3:2, 0,3 mol L1 HCl, 1,2 x 104 mol L1 kvercetin ili morin). Najniža koncentracija željeza(III) koja se može odrediti je 15 μg mL1 u oba ispitivana sustava. Granice detekcije su 0,06 i 0,38 μg mL1 ako se koristi kvercetin, odnosno morfin. Metoda s kvercetinom primijenjena je za određivanje Fe(III (približno 0,2%) u farmaceutskom produktu Fe(II)
Hexokinase 3 enhances myeloid cell survival via non-glycolytic functions.
The family of hexokinases (HKs) catalyzes the first step of glycolysis, the ATP-dependent phosphorylation of glucose to glucose-6-phosphate. While HK1 and HK2 are ubiquitously expressed, the less well-studied HK3 is primarily expressed in hematopoietic cells and tissues and is highly upregulated during terminal differentiation of some acute myeloid leukemia (AML) cell line models. Here we show that expression of HK3 is predominantly originating from myeloid cells and that the upregulation of this glycolytic enzyme is not restricted to differentiation of leukemic cells but also occurs during ex vivo myeloid differentiation of healthy CD34+ hematopoietic stem and progenitor cells. Within the hematopoietic system, we show that HK3 is predominantly expressed in cells of myeloid origin. CRISPR/Cas9 mediated gene disruption revealed that loss of HK3 has no effect on glycolytic activity in AML cell lines while knocking out HK2 significantly reduced basal glycolysis and glycolytic capacity. Instead, loss of HK3 but not HK2 led to increased sensitivity to ATRA-induced cell death in AML cell lines. We found that HK3 knockout (HK3-null) AML cells showed an accumulation of reactive oxygen species (ROS) as well as DNA damage during ATRA-induced differentiation. RNA sequencing analysis confirmed pathway enrichment for programmed cell death, oxidative stress, and DNA damage response in HK3-null AML cells. These signatures were confirmed in ATAC sequencing, showing that loss of HK3 leads to changes in chromatin configuration and increases the accessibility of genes involved in apoptosis and stress response. Through isoform-specific pulldowns, we furthermore identified a direct interaction between HK3 and the proapoptotic BCL-2 family member BIM, which has previously been shown to shorten myeloid life span. Our findings provide evidence that HK3 is dispensable for glycolytic activity in AML cells while promoting cell survival, possibly through direct interaction with the BH3-only protein BIM during ATRA-induced neutrophil differentiation
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