Magnetic properties of materials ranging from conventional ferromagnetic metals to strongly correlated materials such as cuprates originate from Coulomb exchange interactions. The existence of alternate mechanisms for magnetism that could naturally facilitate electrical control has been discussed theoretically<sup>1-7</sup>, but an experimental demonstration<sup>8</sup> in an extended system has been missing. Here we investigate MoSe<sub>2</sub>/WS<sub>2</sub> van der Waals heterostructures in the vicinity of Mott insulator states of electrons forming a frustrated triangular lattice and observe direct evidence of magnetic correlations originating from a kinetic mechanism. By directly measuring electronic magnetization through the strength of the polarization-selective attractive polaron resonance<sup>9,10</sup>, we find that when the Mott state is electron-doped, the system exhibits ferromagnetic correlations in agreement with the Nagaoka mechanism.
The interactions between charges and excitons involve complex many-body interactions at high densities. The exciton-polaron model has been adopted to understand the Fermi sea screening of charged excitons in monolayer transition metal dichalcogenides. The results provide good agreement with absorption measurements, which are dominated by dilute bright exciton responses. Here we investigate the Fermi sea dressing of spin-forbidden dark excitons in monolayer WSe<sub>2</sub>. With a Zeeman field, the valley-polarized dark excitons show distinct p-doping dependence in photoluminescence when the carriers reach a critical density. This density can be interpreted as the onset of strongly modified Fermi sea interactions and shifts with increasing exciton density. Through valley-selective excitation and dynamics measurements, we also infer an intervalley coupling between the dark trions and exciton-polarons mediated by the many-body interactions. Our results reveal the evolution of Fermi sea screening with increasing exciton density and the impacts of polaron-polaron interactions, which lay the foundation for understanding electronic correlations and many-body interactions in 2D systems.
Janus transition-metal dichalcogenide monolayers are artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>18 meV) spectra obfuscating their specific excitonic origin. Here, we identify the neutral and the negatively charged inter- and intravalley exciton transitions in Janus W<sub>Se</sub><sup>S</sup> monolayers with ∼6 meV optical line widths. We integrate Janus monolayers into vertical heterostructures, allowing doping control. Magneto-optic measurements indicate that monolayer W<sub>Se</sub><sup>S</sup> has a direct bandgap at the K points. Our results pave the way for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and the development of Janus-based optoelectronic devices, which requires charge-state control and integration into vertical heterostructures.
The characteristics and outcome of acute respiratory distress syndrome (ARDS) may have changed with time. Some studies have reported that mortality is more commonly related to the development of sepsis/multiple organ failure (MOF), and others that it is related to the severity of acute respiratory failure (ARF). The present study evaluates the relative importance of the two phenomena in a large series of patients. The clinical and biological data of all patients who developed ARDS during a 26 month period (January 1993 until February 1995) in our intensive care unit (ICU) were reviewed retrospectively. A total of 129 patients developed ARDS during the study period, representing an incidence of 2.4% of all ICU admissions. The mortality rate was 52%. The primary cause of death was sepsis/MOF (49%), followed by respiratory failure (16%), cardiac failure or arrhythmias (15%), neurological failure (10%), and other causes (8%). The mortality rate was related to age and degree of organ failure. MOF was not always a cause of late death, since half the deaths occurred within 5 days after admission. In addition, mortality was higher in septic than in nonseptic patients, and lower in trauma and surgical than in medical patients. We conclude that sepsis/multiple organ failure is still the most common cause of death in acute respiratory distress syndrome. Improvements in outcome of acute respiratory distress syndrome may depend more on treatment of sepsis and multiple organ failure than on oxygenation measures.
In Response: We do agree with Dr. Celebioglu that the patient's death was due to clip malposition and not to coagulation abnormalities. Figure 1of our original article [1] shows that death occurred after coagulopathy had resolved. Stephane Baldassarre, MD Jean-Louis Vincent, MD, PhD Department of Intensive Care; Universite Libre de Bruxelles; B-1070 Brusells, Belgium
Delivery of DNA mixed with a degradable matrix carrier was supposed to improve transgene expression. Using a rabbit hind-limb ischemia model, we tested the angiogenic potency of plasmid encoding human vascular endothelial growth factor (pSG5-VEGF165) entrapped in fibrin sealant. Animals were injected intramuscularly with 500 μg of pSG5-VEGF165 or control plasmid, dissolved in saline (PBS) or fibrin glue. After 14 days, presence of delivered constructs and expression of transgene was confirmed in injected muscles of all animals. There were no significant differences in the levels of human VEGF mRNA and protein between VEGF-PBS and VEGF-fibrin groups (Mann-Whitney test). Accordingly, pSG5-VEGF165 regardless of the way of delivery, induced similar increases in capillary density within treated muscles (ANOVA). Control plasmid did not show any effects. In conclusion, injection of pSG5-VEGF165 into ischemic adductor muscle leads to synthesis of human VEGF and increases the number of capillaries. Fibrin carrier does not influence its angiogenic potential.
Exfoliated flakes of layered materials, such as hexagonal boron nitride (hBN) and graphite with a thickness of several tens of nanometers, are used to construct van der Waals heterostructures. A flake with a desirable thickness, size, and shape is often selected from many exfoliated flakes placed randomly on a substrate using an optical microscope. This study examined the visualization of thick hBN and graphite flakes on SiO<sub>2</sub>/Si substrates through calculations and experiments. In particular, the study analyzed areas with different atomic layer thicknesses in a flake. For visualization, the SiO<sub>2</sub>thickness was optimized based on the calculation. As an experimental result, the area with different thicknesses in a hBN flake showed different brightness in the image obtained using an optical microscope with a narrow band-pass filter. The maximum contrast was 12% with respect to the difference of monolayer thickness. In addition, hBN and graphite flakes were observed by differential interference contrast (DIC) microscopy. In the observation, the area with different thicknesses exhibited different brightnesses and colors. Adjusting the DIC bias had a similar effect to selecting a wavelength using a narrow band-pass filter.
Read morevan der Waals (vdW) layered materials have attracted much attention because their physical properties can be controlled by varying the twist angle and layer composition. However, such twisted vdW assemblies are often prepared using mechanically exfoliated monolayer flakes with unintended shapes through a time-consuming search for such materials. Here, we report the rapid and dry fabrication of twisted multilayers using chemical vapor deposition (CVD) grown transition metal chalcogenide (TMDC) monolayers. By improving the adhesion of an acrylic resin stamp to the monolayers, the single crystals of various TMDC monolayers with desired grain size and density on a SiO<sub>2</sub>/Si substrate can be efficiently picked up. The present dry transfer process demonstrates the one-step fabrication of more than 100 twisted bilayers and the sequential stacking of a twisted 10-layer MoS<sub>2</sub> single crystal. Furthermore, we also fabricated hBN-encapsulated TMDC monolayers and various twisted bilayers including MoSe<sub>2</sub>/MoS<sub>2</sub>, MoSe<sub>2</sub>/WSe<sub>2</sub>, and MoSe<sub>2</sub>/WS<sub>2</sub>. The interlayer interaction and quality of dry-transferred, CVD-grown TMDCs were characterized by using photoluminescence (PL), cathodoluminescence (CL) spectroscopy, and cross-sectional electron microscopy. The prominent PL peaks of interlayer excitons can be observed for MoSe<sub>2</sub>/MoS<sub>2</sub> and MoSe<sub>2</sub>/WSe<sub>2</sub> with small twist angles at room temperature. We also found that the optical spectra were locally modulated due to nanosized bubbles, which are formed by the presence of interface carbon impurities. The present findings indicate the widely applicable potential of the present method and enable an efficient search of the emergent optical and electrical properties of TMDC-based vdW heterostructures.
Read moreDuring endotoxic shock, beta-stimulation can improve hepatosplanchnic perfusion and enhance tissue oxygen extraction capabilities, whereas alpha-stimulation does not. In addition, alpha-adrenergic stimulation can increase tumor necrosis factor levels.
Read morePeroxisome proliferator-activated receptor-gamma (PPARgamma) is a ligand-inducible nuclear receptor that functions as a transcription factor involved in lipid metabolism, inflammatory response and angiogenesis. The most potent endogenous PPARgamma activator is 15-deoxy-Delta(12,14)prostaglandin-J(2) (15d-PGJ(2)), whereas synthetic ligands include the oral antidiabetic drugs thiazolidinediones (TZDs). Activation of PPARgamma was reported to decrease the synthesis of matrix metalloproteinases (MMPs) in vascular smooth muscle cells and macrophages. We aimed to investigate the effect of PPARgamma ligands on expression of MMP-1 and urokinase plasminogen activator (uPA) in human microvascular endothelial cells (HMEC-1). We found that treatment of HMEC-1 with 15d-PGJ(2) increased the synthesis of MMP-1 protein up to 168% comparing to untreated cells. TZDs (ciglitazone and troglitazone), more potent activators of PPARgamma in HMEC-1, did not influence MMP-1 production, arguing against the involvement of PPARgamma in this process. Importantly, the stimulatory effect of 15d-PGJ(2) was reversed by the antioxidant N-acetyl-cysteine (NAC), suggesting a contribution of oxidative stress. We demonstrated also that 15d-PGJ(2) did not change the activity of MMP-1 promoter, but increased the stability of MMP-1 mRNA. In contrast, 15d-PGJ(2) very potently inhibited the synthesis of uPA. This effect was in part mimicked by ciglitazone and troglitazone implying an involvement of PPARgamma. Accordingly, NAC did not modify the inhibitory effect of 15d-PGJ(2) on uPA expression. In conclusion, we postulate that 15d-PGJ(2) may differently regulate the synthesis of proteases involved in angiogenesis: it upregulates MMP-1 expression in HMEC-1 through induction of oxidative stress, and inhibits uPA synthesis partly by activation of PPARgamma.
Read moreThe SOFA score is a simple, but effective method to describe organ dysfunction/failure in critically ill patients. Regular, repeated scoring enables patient condition and disease development to be monitored and better understood. The SOFA score may enable comparison between patients that would benefit clinical trials.
Read moreWe have developed a microspectroscopy technique for measuring gate-modulated reflectance to probe excitonic states in two-dimensional transition metal dichalcogenides. Through the use of gate-modulated spectroscopy, we were able to detect excited states of excitons and trions, which would typically have weak optical signals in traditional reflectance spectroscopy. Using a transfer matrix method for spectral analysis, the binding energy of trion 2s was determined to be 26 meV. As observing the Rydberg series of excitonic states provides fruitful information on the strong Coulomb interaction in two-dimensional systems, gate-modulated spectroscopy can be a versatile tool for understanding underlying many-body physics as well as designing next-generation quantum optoelectronics based on two-dimensional materials.
Read moreWe describe a patient who experienced a prolonged episode of hypoglycemia secondary to an acute voluntary intoxication with diphenylhydantoin 20 g and zopiclone 225 mg. This hypoglycemic episode was presumptively attributed to diphenylhydantoin and might be due either to an escape from the inhibitory effects of diphenylhydantoin on insulin secretion or an increased sensitivity of the tissues to insulin. Zopiclone was considered less likely since zopiclone overdoses have been only exceptionally associated with hyperglycemia.
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