2,460 research outputs found
Bifurcation curves of subharmonic solutions
We revisit a problem considered by Chow and Hale on the existence of
subharmonic solutions for perturbed systems. In the analytic setting, under
more general (weaker) conditions, we prove their results on the existence of
bifurcation curves from the nonexistence to the existence of subharmonic
solutions. In particular our results apply also when one has degeneracy to
first order -- i.e. when the subharmonic Melnikov function vanishes
identically. Moreover we can deal as well with the case in which degeneracy
persists to arbitrarily high orders, in the sense that suitable generalisations
to higher orders of the subharmonic Melnikov function are also identically
zero. In general the bifurcation curves are not analytic, and even when they
are smooth they can form cusps at the origin: we say in this case that the
curves are degenerate as the corresponding tangent lines coincide. The
technique we use is completely different from that of Chow and Hale, and it is
essentially based on rigorous perturbation theory.Comment: 29 pages, 2 figure
Properties of plasmoids observed in Saturnβs dayside and nightside magnetodisc
Plasmoid is a key structure for transferring magnetic flux and plasma in planetary magnetospheres. At Earth, plasmoids are key media which transfer energy and mass in the "Dungey Cycle". For giant planets, plasmoids are primarily generated by the dynamic processes associated with βVasyliunas Cycleβ. It is generally believed that planetary magnetotails are favorable for producing plasmoids. Nevertheless, recent studies reveal that magnetic field lines could be sufficiently stretched to allow magnetic reconnection in Saturnβs dayside magnetodisc. In the study, we report direct observations of plasmoids in Saturnβs dayside magnetodisc for the first time. Moreover, we perform a statistical investigation on the global plasmoid electron density distribution. The results show an inverse correlation between the nightside plasmoid electron density and local time, and the maximum plasmoid electron density around prenoon local time on the dayside. These results are consistent with the magnetospheric circulation picture associated with the "Vasyliunas Cycle"
THz time-domain spectroscopic ellipsometry with simultaneous measurements of orthogonal polarizations
Long-standing Small-scale Reconnection Processes at Saturn Revealed by Cassini
The internal mass source from the icy moon Enceladus in Saturnβs rapidly rotating magnetosphere drives
electromagnetic dynamics in multiple spatial and temporal scales. The distribution and circulation of the internal
plasma and associated energy are thus crucial in understanding Saturnβs magnetospheric environment. Magnetic
reconnection is one of the key processes in driving plasma and energy transport in the magnetosphere, and also a
fundamental plasma process in energizing charged particles. Recent works suggested that reconnection driven by
Saturnβs rapid rotation might appear as a chain of microscale structures, named drizzle-like reconnection. The
drizzle-like reconnection could exist not only in the nightside magnetodisk, but also in the dayside magnetodisk.
Here, using in situ measurements from the Cassini spacecraft, we report multiple reconnection sites that were
successively detected during a time interval longer than one rotation period. The time separation between two
adjacently detected reconnection sites can be much less than one rotation period, implying that the reconnection
processes are likely small-scale, or frequently repetitive. The spatial distribution of the identified long-standing
multiple small reconnection site sequences shows no significant preference on local times. We propose that the
small reconnection sites discussed in this Letter are rotationally driven and rotate with the magnetosphere.
Since the reconnection process on Saturn can be long-durational, the rotational regime can cause these smallscale reconnection sites to spread to all local times, resulting in global release of energy and mass from the
magnetosphere
A Rotating Azimuthally Distributed Auroral Current System on Saturn Revealed by the Cassini Spacecraft
Stunning aurorae are mainly produced when accelerated electrons travel along magnetic field lines to collide with the atmosphere. The motion of electrons often corresponds to the evolution of a magnetic field-aligned current system. In the terrestrial magnetosphere, the current system is formed at the night-side sector, and thus produces an auroral bulge at night. Due to the different energy sources between Saturn and the Earth, it is expected that their auroral current systems are fundamentally different, although the specific auroral driver at Saturn is poorly understood. Using simultaneous measurements of the aurora, particles, magnetic fields, and energetic neutral atoms, we reveal that a chain of paired currents, each of which includes a downward and an upward current branch, is formed in Saturn's magnetosphere, which generates separated auroral patches. These findings inform similar auroral current structures between the Earth and Saturn, while the difference is that Saturn's unique mass and energy sources lead to a rotational characteristic
CK8 phosphorylation induced by compressive loads underlies the downregulation of CK8 in human disc degeneration by activating protein kinase C
Cytokeratin 8 (CK8) is a member of the cytokeratins family with multiple functions on the basis of its unique structural hallmark. The aberrant expression of CK8 and its phosphorylation are pertinent with various diseases. We have previously shown that CK8 exists in normal human nucleus pulposus (NP) cells and decreases as the intervertebral disc degenerates. However, the underlying molecular regulatory machinery of CK8 in intervertebral disc degeneration (IDD) has not been clarified. Here, we collected NP samples from patients with idiopathic scoliosis as control and IDD as degenerate groups. We found that CK8 expression decreased in IDD with an increased phosphorylation in degenerate NP cells. Moreover, NP cells were cultured under different compressive load schemes for diverse time duration. We found that compressive loads resulted in phosphorylation and disassembly of CK8 in a time-dependent and degree-dependent manner in vitro. The activation of protein kinase C was a significant molecular factor contributing to this phenomenon. Taken together, this study is the first to address the molecular mechanisms of CK8 downregulation in NP cells. Importantly, our findings provide clues regarding a molecular link between compressive loads and CK8 alterations, which shed a novel light on the etiology of IDD.published_or_final_versio
Observation of the electromagnetic doubly OZI-suppressed decay
Using a sample of billion events accumulated with the BESIII
detector at the BEPCII collider, we report the observation of the decay , which is the first evidence for a doubly
Okubo-Zweig-Iizuka suppressed electromagnetic decay. A clear structure
is observed in the mass spectrum around 1.02 GeV/, which can
be attributed to interference between and
decays. Due to this interference, two
possible solutions are found. The corresponding measured values of the
branching fraction of are and .Comment: 7 pages, 4 figures, published in Phys. Rev.
An age-period-cohort analysis of female breast cancer mortality from 1990β2009 in China
Disparities and risks of sexually transmissible infections among men who have sex with men in China: a meta-analysis and data synthesis.
BACKGROUND: Sexually transmitted infections (STIs), including Hepatitis B and C virus, are emerging public health risks in China, especially among men who have sex with men (MSM). This study aims to assess the magnitude and risks of STIs among Chinese MSM. METHODS: Chinese and English peer-reviewed articles were searched in five electronic databases from January 2000 to February 2013. Pooled prevalence estimates for each STI infection were calculated using meta-analysis. Infection risks of STIs in MSM, HIV-positive MSM and male sex workers (MSW) were obtained. This review followed the PRISMA guidelines and was registered in PROSPERO. RESULTS: Eighty-eight articles (11 in English and 77 in Chinese) investigating 35,203 MSM in 28 provinces were included in this review. The prevalence levels of STIs among MSM were 6.3% (95% CI: 3.5-11.0%) for chlamydia, 1.5% (0.7-2.9%) for genital wart, 1.9% (1.3-2.7%) for gonorrhoea, 8.9% (7.8-10.2%) for hepatitis B (HBV), 1.2% (1.0-1.6%) for hepatitis C (HCV), 66.3% (57.4-74.1%) for human papillomavirus (HPV), 10.6% (6.2-17.6%) for herpes simplex virus (HSV-2) and 4.3% (3.2-5.8%) for Ureaplasma urealyticum. HIV-positive MSM have consistently higher odds of all these infections than the broader MSM population. As a subgroup of MSM, MSW were 2.5 (1.4-4.7), 5.7 (2.7-12.3), and 2.2 (1.4-3.7) times more likely to be infected with chlamydia, gonorrhoea and HCV than the broader MSM population, respectively. CONCLUSION: Prevalence levels of STIs among MSW were significantly higher than the broader MSM population. Co-infection of HIV and STIs were prevalent among Chinese MSM. Integration of HIV and STIs healthcare and surveillance systems is essential in providing effective HIV/STIs preventive measures and treatments. TRIAL REGISTRATION: PROSPERO NO: CRD42013003721
Influence of GaAs Substrate Orientation on InAs Quantum Dots: Surface Morphology, Critical Thickness, and Optical Properties
InAs/GaAs heterostructures have been simultaneously grown by molecular beam epitaxy on GaAs (100), GaAs (100) with a 2Β° misorientation angle towards [01β1], and GaAs (n11)B (n = 9, 7, 5) substrates. While the substrate misorientation angle increased from 0Β° to 15.8Β°, a clear evolution from quantum dots to quantum well was evident by the surface morphology, the photoluminescence, and the time-resolved photoluminescence, respectively. This evolution revealed an increased critical thickness and a delayed formation of InAs quantum dots as the surface orientation departed from GaAs (100), which was explained by the thermal-equilibrium model due to the less efficient of strain relaxation on misoriented substrate surfaces
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