Abstract
Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of ...such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe
2
single layer with the 1
T
′ structure that does not exist in the bulk form of WSe
2
. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observe a gap of 129 meV in the 1
T
′ layer and an in-gap edge state located near the layer boundary. The system′s 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator–semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices.
Abstract
Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding ...three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe
2
from the single-layer to the bulk limit. Using angle-resolved photoemission spectroscopy and scanning tunneling microscopy and spectroscopy, we observed the emergence of a (2 × 2) charge density wave order in single-layer TiTe
2
with a transition temperature of 92 ± 3 K. Also observed was a pseudogap of about 28 meV at the Fermi level at 4.2 K. Surprisingly, no charge density wave transitions were observed in two-layer and multi-layer TiTe
2
, despite the quasi-two-dimensional nature of the material in the bulk. The unique charge density wave phenomenon in the single layer raises intriguing questions that challenge the prevailing thinking about the mechanisms of charge density wave formation.
About five to four million years ago, in the early Pliocene epoch, Earth had a warm, temperate climate. The gradual cooling that followed led to the establishment of modern temperature patterns, ...possibly in response to a decrease in atmospheric CO2 concentration, of the order of 100 parts per million, towards preindustrial values. Here we synthesize the available geochemical proxy records of sea surface temperature and show that, compared with that of today, the early Pliocene climate had substantially lower meridional and zonal temperature gradients but similar maximum ocean temperatures. Using an Earth system model, we show that none of the mechanisms currently proposed to explain Pliocene warmth can simultaneously reproduce all three crucial features. We suggest that a combination of several dynamical feedbacks underestimated in the models at present, such as those related to ocean mixing and cloud albedo, may have been responsible for these climate conditions.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene-a strong focus of current research. Such molecular layers are at the quantum ...limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.
This paper presents the results of the simulation of a sewage sludge combustion plant with a productivity of 6 tons per hour using the ASPEN Plus. It is shown that catalytic combustion technology can ...be used for the efficient utilization of mechanically dehydrated sludge with the moisture of ~75% in autothermal mode (without the use of additional fuel). At the same time, the plant for utilization of 6.0 tons of sludge per hour enables us to obtain 3.07 MW of heat energy. It is shown that the sludge moisture and its calorific value significantly affect the combustion process. Thus, at the moisture of less than 72%, additional water supply is necessary to avoid overheating of the catalyst bed. In the case of an increase in sludge moisture of more than 76%, an additional supply of fuel (for example, brown coal) is required. Also, the article discusses the emissions of harmful substances generated during sewage sludge combustion and methods for their utilization.
Display omitted
•The plant for sewage sludge combustion (6 tons/hour) is simulated using ASPEN Plus.•The technology enables to combust of sludge with moisture of 75% in autothermal mode.•The plant for utilization of sludge allows one to obtain 3.07 MW of heat energy.
Single layers of transition metal dichalcogenides (TMDCs) are excellent candidates for electronic applications beyond the graphene platform; many of them exhibit novel properties including charge ...density waves (CDWs) and magnetic ordering. CDWs in these single layers are generally a planar projection of the corresponding bulk CDWs because of the quasi-two-dimensional nature of TMDCs; a different CDW symmetry is unexpected. We report herein the successful creation of pristine single-layer VSe2, which shows a (7×3) CDW in contrast to the (4×4) CDW for the layers in bulk VSe2. Angle-resolved photoemission spectroscopy from the single layer shows a sizable (7×3) CDW gap of ~100 meV at the zone boundary, a 220 K CDW transition temperature twice the bulk value, and no ferromagnetic exchange splitting as predicted by theory. This robust CDW with an exotic broken symmetry as the ground state is explained via a first-principles analysis. The results illustrate a unique CDW phenomenon in the two-dimensional limit.
Anti–CTLA-4 therapy requires an Fc domain for efficacy Ingram, Jessica R.; Blomberg, Olga S.; Rashidian, Mohammad ...
Proceedings of the National Academy of Sciences - PNAS,
04/2018, Letnik:
115, Številka:
15
Journal Article
Recenzirano
Odprti dostop
Ipilimumab, a monoclonal antibody that recognizes cytotoxic T lymphocyte antigen (CTLA)-4, was the first approved “checkpoint”-blocking anticancer therapy. In mouse tumor models, the response to ...antibodies against CTLA-4 depends entirely on expression of the Fcγ receptor (FcγR), which may facilitate antibody-dependent cellular phagocytosis, but the contribution of simple CTLA-4 blockade remains unknown. To understand the role of CTLA-4 blockade in the complete absence of Fc-dependent functions, we developed H11, a high-affinity alpaca heavy chain-only antibody fragment (VHH) against CTLA-4. The VHH H11 lacks an Fc portion, binds monovalently to CTLA-4, and inhibits interactions between CTLA-4 and its ligand by occluding the ligand-binding motif on CTLA-4 as shown crystallographically. We used H11 to visualize CTLA-4 expression in vivo using whole-animal immuno-PET, finding that surface-accessible CTLA-4 is largely confined to the tumor microenvironment. Despite this, H11-mediated CTLA-4 blockade has minimal effects on antitumor responses. Installation of the murine IgG2a constant region on H11 dramatically enhances its antitumor response. Coadministration of the monovalent H11 VHH blocks the efficacy of a full-sized therapeutic antibody. We were thus able to demonstrate that CTLA-4–binding antibodies require an Fc domain for antitumor effect.
Helical Dirac fermions-charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum-are proposed to be the key to ...realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose-Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators-materials with a bulk insulating gap of spin-orbit origin and surface states protected against scattering by time-reversal symmetry-and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuth-based class of material by combining spin-imaging and momentum-resolved spectroscopies, bulk charge compensation, Hall transport measurements and surface quantum control. Our results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry's phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime. The observed topological nodal state is shown to be protected even up to 300 K. Our demonstration of room-temperature topological order and non-trivial spin-texture in stoichiometric Bi2Se3.Mx (Mx indicates surface doping or gating control) paves the way for future graphene-like studies of topological insulators, and applications of the observed spin-polarized edge channels in spintronic and computing technologies possibly at room temperature.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Many members of the mechanistically diverse enolase superfamily have unknown functions. In this report we use both genome (operon) context and screening of a library of acid sugars to assign the ...l-fuconate dehydratase (FucD) function to a member of the mandelate racemase (MR) subgroup of the superfamily encoded by the Xanthomonas campestris pv. campestris str. ATCC 33913 genome (GI:21233491). Orthologues of FucD are found in both bacteria and eukaryotes, the latter including the rTS beta protein in Homo sapiens that has been implicated in regulating thymidylate synthase activity. As suggested by sequence alignments and confirmed by high-resolution structures in the presence of active site ligands, FucD and MR share the same active site motif of functional groups: three carboxylate ligands for the essential Mg2+ located at the ends of the third, fourth, and fifth β-strands in the (β/α)7β-barrel domain (Asp 248, Glu 274, and Glu 301, respectively), a Lys-x-Lys motif at the end of the second β-strand (Lys 218 and Lys 220), a His-Asp dyad at the end of the seventh and sixth β-strands (His 351 and Asp 324, respectively), and a Glu at the end of the eighth β-strand (Glu 382). The mechanism of the FucD reaction involves initial abstraction of the 2-proton by Lys 220, acid catalysis of the vinylogous β-elimination of the 3-OH group by His 351, and stereospecific ketonization of the resulting enol, likely by the conjugate acid of Lys 220, to yield the 2-keto-3-deoxy-l-fuconate product. Screening of the library of acid sugars revealed substrate and functional promiscuity: In addition to l-fuconate, FucD also catalyzes the dehydration of l-galactonate, d-arabinonate, d-altronate, l-talonate, and d-ribonate. The dehydrations of l-fuconate, l-galactonate, and d-arabinonate are initiated by abstraction of the 2-protons by Lys 220. The dehydrations of l-talonate and d-ribonate are initiated by abstraction of the 2-protons by His 351; however, protonation of the enediolate intermediates by the conjugate acid of Lys 220 yields l-galactonate and d-arabinonate in competition with dehydration. The functional promiscuity discovered for FucD highlights possible structural mechanisms for evolution of function in the enolase superfamily.
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