The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the ...disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes. This paper addresses these issues mainly based on two lines of evidence. First, we compiled newly collected data from geological indicators of the Cenozoic environment in China as paleoenvironmental maps of ten intervals. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the maps within the Miocene indicate that this change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted to tropical-subtropical regions. The latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalance in evolution of polar ice-sheets between the two hemispheres. Secondly, we examine the relevant depositional and soil forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with emphasis on the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which have been constantly maintained during the past 22 Ma. Grain-size gradients between loess sections indicate northerly dust-carrying winds from northern sources, a clear indication of an Asian winter monsoon system. Meanwhile, well-developed Luvisols show evidence that moisture from the oceans reached northern China. This evidence shows the coexistence of two kinds of circulations, one from the ocean carrying moisture and another from the inland deserts transporting dust. The formation of the early Miocene paleosols resulted from interactive soil forming and dust deposition processes in these two seasonally alternating monsoonal circulations. The much stronger development of the early Miocene soils compared to those in the Quaternary loess indicates that summer monsoons were either significantly stronger, more persistent through the year, or both. These lines of evidence indicate a joint change in circulation and inland aridity by the early Miocene and suggest a dynamic linkage of them. Our recent sensitivity tests with a general circulation model, along with relevant geological data, suggest that the onset of these contrasting wet/dry responses, as well as the change from the "planetary" subtropical aridity pattern to the "inland" aridity pattern, resulted from the combined effects of Tibetan uplift and withdrawal of the Paratethys seaway in central Asia, as suggested by earlier experiments. The spreading of South China Sea also helped to enhance the south-north contrast of humidity. The Miocene loess record provides a vital insight that these tectonic factors had evolved by the early Miocene to a threshold sufficient to cause this major climate reorganization in Asia.
A remarkable manifestation of the quantum character of electrons in matter is offered by graphene, a single atomic layer of graphite. Unlike conventional solids where electrons are described with the ...Schrödinger equation, electronic excitations in graphene are governed by the Dirac hamiltonian. Some of the intriguing electronic properties of graphene, such as massless Dirac quasiparticles with linear energy-momentum dispersion, have been confirmed by recent observations. Here, we report an infrared spectromicroscopy study of charge dynamics in graphene integrated in gated devices. Our measurements verify the expected characteristics of graphene and, owing to the previously unattainable accuracy of infrared experiments, also uncover significant departures of the quasiparticle dynamics from predictions made for Dirac fermions in idealized, free-standing graphene. Several observations reported here indicate the relevance of many-body interactions to the electromagnetic response of graphene.
Aim
Perineal wound complications after abdominoperineal resection (APR) have become a major clinical challenge. Myocutaneous flap closure has been proposed in place of primary closure to improve ...wound healing. We conducted this comprehensive meta‐analysis to evaluate the current scientific evidence of primary closure vs myocutaneous flap closure of perineal defects following APR for colorectal disease.
Methods
We systematically searched the MEDLINE, Embase, PubMed, Web of Science and Cochrane Library databases to identify all relevant studies. After data extraction from the included studies, meta‐analysis was performed to compare perioperative outcomes of primary closure and myocutaneous flap closure.
Results
Eighteen studies with a total of 17 913 patients (16 346 primary closure vs 1567 myocutaneous flap closure) were included. We found that primary closure was significantly associated with higher total perineal wound complications (P = 0.007), major perineal wound complications (P < 0.001) and perineal wound infection (P = 0.001). On the other hand, myocutaneous flap closure takes more operation time (P < 0.001) and increases the risk of perineal wound dehiscence (P = 0.01), deep surgical site infection (P < 0.001), enterocutaneous fistulas (P = 0.03) and return to the operating room (P = 0.0005). There were no significant differences between the two groups for other outcomes.
Conclusions
This is the first systematic review with meta‐analysis comparing primary closure with myocutaneous flap closure of perineal defects after APR for colorectal disease. Although taking more operation time and an increased risk of specific complications, the pooled results have validated the use of myocutaneous flaps for reducing total/major perineal wound complications. More investigations are needed to draw definitive conclusions on this dilemma.
A solar cell based on the n-MoS
2
/i-SiO
2
/p-Si heterojunction is fabricated. The device exhibits a high power-conversion efficiency of 4.5% due to the incorporation of a nano-scale SiO
2
buffer ...into the MoS
2
/Si interface. The present device architectures are envisaged as potentially valuable candidates for high-performance photovoltaic devices.
A solar cell based on the n-MoS
2
/i-SiO
2
/p-Si heterojunction is fabricated.
A novel partitioned stator (PS) hybrid excited (HE) switched flux (SF) (PS-HESF) machine is proposed in this paper. In the PS-HESF machine, the permanent magnets (PMs) and field windings are ...allocated on one stator while the armature windings are placed on the other. The iron-piece-rotor is sandwiched between the two stators. Consequently, compared with the conventional HESF machine having PMs, field windings as well as armature windings all on one stator, the available space of the novel machine is greatly boosted and therefore the performance is enhanced. Based on 2-D finite-element analysis, the electromagnetic performance of the PS-HESF machine is evaluated and the results reveal that it can exhibit not only better flux regulation capability but also higher torque than the conventional HESF machine. Moreover, the influences of the key design parameters on the hybridization ratio in the PS-HESF machines are investigated. A prototype machine is manufactured and tested to validate the predictions.
A partitioned stator hybrid excited machine is proposed, in which the permanent magnets and field windings are alternately placed on an inner stator separated from the outer stator having armature ...windings. This machine inherits the features of brushless machines and benefits from better space utilization. The operating principle and the effects of slot/pole combinations are investigated in detail. Further, based on 2-D finite-element analysis, the electromagnetic performances of the proposed machines, including back-electromotive force, cogging torque, flux regulation range, torque capability, power factor and torque-speed curve, are evaluated. The results reveal that the proposed machines can exhibit wide flux regulation range as well as good torque density. The prototype is manufactured and tested to validate the predictions.
Hybrid excited (HE) machines combine the advantages of both high torque density and excellent flux regulation capability, while also having extensive applications. A novel partitioned stator HE ...machine employing two stators to allocate armature windings and excitations separately, is proposed in this paper. The permanent magnet (PM) pole-pair and wound field pole-pair are alternately placed on one stator to exhibit parallel magnetic paths, while the armature windings are located on the other stator. The iron-piece-rotor is sandwiched between the two stators. This machine inherits the advantages of stator-PM machine and further benefits from attractive flux regulation capability due to parallel topology. The operating principle and the slot/pole combination rule that are different from the conventional PM machine are illustrated. The two-dimensional finite element technique is used to evaluate the electromagnetic performance, confirming the mentioned advantages. A prototype is manufactured and tested to validate the predictions.
The initial desertification in the Asian interior is thought to be one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic era. But the dating of this transition is ...uncertain, partly because desert sediments are usually scattered, discontinuous and difficult to date. Here we report nearly continuous aeolian deposits covering the interval from 22 to 6.2 million years ago, on the basis of palaeomagnetic measurements and fossil evidence. A total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils. This new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch, at least 14 million years earlier than previously thought. Regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in Asia.
Variable flux memory (VFM) permanent magnet (PM) machines exhibit an additional degree of freedom for control, i.e., PM magnetization state, and thus excellent flux controllability. Moreover, the ...hybrid PM topologies having variable PM (VPM) with low coercive force and constant PM (CPM) with high coercive force at the same time are employed to improve the torque density and the flux controllability. The parallel and series connections between the two different kinds of PMs are both feasible. Based on equivalent magnetic circuits, two-dimensional finite element analyses and experiments, the VFM machines with these two connection types are investigated and compared in this paper. The results reveal that the VPM with series-connected CPM is beneficial for more stable working point and higher torque density. A pair of VFM prototypes with parallel and series hybrid PMs are manufactured and tested to validate the analyses.
Abstract
Electric-field control of magnetism requires deterministic control of the magnetic order and understanding of the magnetoelectric coupling in multiferroics like BiFeO
3
and EuTiO
3
. Despite ...this critical need, there are few studies on the strain evolution of magnetic order in BiFeO
3
films. Here, in (110)-oriented BiFeO
3
films, we reveal that while the polarization structure remains relatively unaffected, strain can continuously tune the orientation of the antiferromagnetic-spin axis across a wide angular space, resulting in an unexpected deviation of the classical perpendicular relationship between the antiferromagnetic axis and the polarization. Calculations suggest that this evolution arises from a competition between the Dzyaloshinskii–Moriya interaction and single-ion anisotropy wherein the former dominates at small strains and the two are comparable at large strains. Finally, strong coupling between the BiFeO
3
and the ferromagnet Co
0.9
Fe
0.1
exists such that the magnetic anisotropy of the ferromagnet can be effectively controlled by engineering the orientation of the antiferromagnetic-spin axis.
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