Magnetic field controlled reversal of ferroelectric polarization in conical spin ordered multiferroics : Monte Carlo simulation

Author name used in this publication: 姚晓燕Author name used in this publication: 羅永祥Author name used in this publication: 刘俊明2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Monte Carlo simulation on ferroelectric response to magnetic field in an elastic lsing spin chain

Author name used in this publication: 姚晓燕Author name used in this publication: Veng Cheong Lo, 羅永祥Author name used in this publication: 刘俊明2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Magnetoelectric coupling induced by exchange striction in frustrated Ising spin chain : Monte Carlo simulation

Author name used in this publication: Veng Cheong Lo2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

The influence of magnetic anisotropy on magnetoelectric behavior in conical spin ordered multiferroic state

2009-2010 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

A novel soft-switching inverter using resonant inductor freewheeling

A novel topology of the voltage-source soft-switching inverter for induction motor drives is presented. The key of this topology is to employ two fractional-duty auxiliary switches and one resonant inductor per phase to provide a favorable zero-voltage turn-on condition for those main switches. By fully utilizing the inherent natural freewheeling of the inverter, the auxiliary switches need to operate in the resonant inductor freewheeling only in a fractional duty. Apart from providing a soft-switching environment with minimum voltage and current stresses, the distinct advantage of this topology is its capability to control the operation of each phase individually. Therefore, this inverter can readily adopt the well-established PWM techniques while possessing the advantages of soft switching-namely PWM-oriented soft switching. Moreover, a new concept of the zero-voltage soft-switching vector is introduced to determine whether the auxiliary circuit needs to operate to achieving soft switching. A theoretical analysis has been conducted and then verified by using both computer simulation and experimental results.published_or_final_versio

PGC-1 family coactivators and cell fate: roles in cancer, neurodegeneration, cardiovascular disease and retrograde mitochondria-nucleus signalling.

Over the past two decades, a complex nuclear transcriptional machinery controlling mitochondrial biogenesis and function has been described. Central to this network are the PGC-1 family coactivators, characterised as master regulators of mitochondrial biogenesis. Recent literature has identified a broader role for PGC-1 coactivators in both cell death and cellular adaptation under conditions of stress, here reviewed in the context of the pathology associated with cancer, neurodegeneration and cardiovascular disease. Moreover, we propose that these studies also imply a novel conceptual framework on the general role of mitochondrial dysfunction in disease. It is now well established that the complex nuclear transcriptional control of mitochondrial biogenesis allows for adaptation of mitochondrial mass and function to environmental conditions. On the other hand, it has also been suggested that mitochondria alter their function according to prevailing cellular energetic requirements and thus function as sensors that generate signals to adjust fundamental cellular processes through a retrograde mitochondria-nucleus signalling pathway. Therefore, altered mitochondrial function can affect cell fate not only directly by modifying cellular energy levels or redox state, but also indirectly, by altering nuclear transcriptional patterns. The current literature on such retrograde signalling in both yeast and mammalian cells is thus reviewed, with an outlook on its potential contribution to disease through the regulation of PGC-1 family coactivators. We propose that further investigation of these pathways will lead to the identification of novel pharmacological targets and treatment strategies to combat disease

Spanning Properties of Theta-Theta Graphs

We study the spanning properties of Theta-Theta graphs. Similar in spirit with the Yao-Yao graphs, Theta-Theta graphs partition the space around each vertex into a set of k cones, for some fixed integer k > 1, and select at most one edge per cone. The difference is in the way edges are selected. Yao-Yao graphs select an edge of minimum length, whereas Theta-Theta graphs select an edge of minimum orthogonal projection onto the cone bisector. It has been established that the Yao-Yao graphs with parameter k = 6k' have spanning ratio 11.67, for k' >= 6. In this paper we establish a first spanning ratio of $7.82$ for Theta-Theta graphs, for the same values of $k$. We also extend the class of Theta-Theta spanners with parameter 6k', and establish a spanning ratio of $16.76$ for k' >= 5. We surmise that these stronger results are mainly due to a tighter analysis in this paper, rather than Theta-Theta being superior to Yao-Yao as a spanner. We also show that the spanning ratio of Theta-Theta graphs decreases to 4.64 as k' increases to 8. These are the first results on the spanning properties of Theta-Theta graphs.Comment: 20 pages, 6 figures, 3 table

Direct evidence for charge stripes in a layered cobalt oxide

Recent experiments indicate that static stripe-like charge order is generic to the hole-doped copper oxide superconductors and competes with superconductivity. Here we show that a similar type of charge order is present in La5/3 Sr1/3 CoO4 , an insulating analogue of the copper oxide superconductors containing cobalt in place of copper. The stripe phase we have detected is accompanied by short-range, quasi-one-dimensional, antiferromagnetic order, and provides a natural explanation for the distinctive hour- glass shape of the magnetic spectrum previously observed in neutron scattering mea- surements of La2−xSrx CoO4 and many hole-doped copper oxide superconductors. The results establish a solid empirical basis for theories of the hourglass spectrum built on short-range, quasi-static, stripe correlations

Hour-glass magnetic spectrum in an insulating, hole-doped antiferromagnet

Superconductivity in layered copper-oxide compounds emerges when charge carriers are added to antiferromagnetically-ordered CuO2 layers. The carriers destroy the antiferromagnetic order, but strong spin fluctuations persist throughout the superconducting phase and are intimately linked to super-conductivity. Neutron scattering measurements of spin fluctuations in hole-doped copper oxides have revealed an unusual `hour-glass' feature in the momentum-resolved magnetic spectrum, present in a wide range of superconducting and non-superconducting materials. There is no widely-accepted explanation for this feature. One possibility is that it derives from a pattern of alternating spin and charge stripes, an idea supported by measurements on stripe-ordered La1.875Ba0.125CuO4. However, many copper oxides without stripe order also exhibit an hour-glass spectrum$. Here we report the observation of an hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the family of superconducting copper oxides. Our system has stripe correlations and is an insulator, which means its magnetic dynamics can conclusively be ascribed to stripes. The results provide compelling evidence that the hour-glass spectrum in the copper-oxide superconductors arises from fluctuating stripes.Comment: 13 pages, 4 figures, to appear in Natur

Serotonin and corticosterone rhythms in mice exposed to cigarette smoke and in patients with COPD:implication for COPD-associated neuropathogenesis

The circadian timing system controls daily rhythms of physiology and behavior, and disruption of clock function can trigger stressful life events. Daily exposure to cigarette smoke (CS) can lead to alteration in diverse biological and physiological processes. Smoking is associated with mood disorders, including depression and anxiety. Patients with chronic obstructive pulmonary disease (COPD) have abnormal circadian rhythms, reflected by daily changes in respiratory symptoms and lung function. Corticosterone (CORT) is an adrenal steroid that plays a considerable role in stress and anti-inflammatory responses. Serotonin (5-hydroxytryptamine; 5HT) is a neurohormone, which plays a role in sleep/wake regulation and affective disorders. Secretion of stress hormones (CORT and 5HT) is under the control of the circadian clock in the suprachiasmatic nucleus. Since smoking is a contributing factor in the development of COPD, we hypothesize that CS can affect circadian rhythms of CORT and 5HT secretion leading to sleep and mood disorders in smokers and patients with COPD. We measured the daily rhythms of plasma CORT and 5HT in mice following acute (3 d), sub-chronic (10 d) or chronic (6 mo) CS exposure and in plasma from non-smokers, smokers and patients with COPD. Acute and chronic CS exposure affected both the timing (peak phase) and amplitude of the daily rhythm of plasma CORT and 5HT in mice. Acute CS appeared to have subtle time-dependent effects on CORT levels but more pronounced effects on 5HT. As compared with CORT, plasma 5HT was slightly elevated in smokers but was reduced in patients with COPD. Thus, the effects of CS on plasma 5HT were consistent between mice and patients with COPD. Together, these data reveal a significant impact of CS exposure on rhythms of stress hormone secretion and subsequent detrimental effects on cognitive function, depression-like behavior, mood/anxiety and sleep quality in smokers and patients with COPD