42,457 research outputs found
The role of stereotactic radiosurgery in the multimodal management of growth hormone–secreting pituitary adenomas
Growth hormone (GH)–secreting pituitary adenomas represent a common source of GH excess in patients with acromegaly. Whereas surgical extirpation of the culprit lesion is considered first-line treatment, as many as 19% of patients develop recurrent symptoms due to regrowth of previously resected adenomatous tissue or to continued growth of the surgically inaccessible tumor. Although medical therapies that suppress GH production can be effective in the management of primary and recurrent acromegaly, these therapies are not curative, and lifelong treatment is required for hormonal control. Stereotactic radiosurgery has emerged as an effective adjunctive treatment modality, and is an appealing alternative to conventional fractionated radiation therapy. The authors reviewed the growing body of literature concerning the role of radiosurgical procedures in the treatment armamentarium of acromegaly, and identified more than 1350 patients across 45 case series. In this review, the authors report that radiosurgery offers true hormonal normalization in 17% to 82% of patients and tumor growth control in 37% to 100% of cases across all series, while minimizing adverse complications. As a result, stereotactic radiosurgery represents a safe and effective treatment option in the multimodal management of primary or recurrent acromegaly secondary to GH-secreting pituitary adenomas
Interface states and anomalous quantum oscillations in graphene hybrid structures
One- and two-layer graphene have recently been shown to feature new physical
phenomena such as unconventional quantum Hall effects and prospects of
supporting a non-silicon technological platform using epitaxial graphene. While
both one- and two-layer graphene have been studied extensively, continuous
sheets of graphene possessing both parts have not yet been explored. Here we
report a study of such graphene hybrid structures. In a bulk hybrid featuring
two large-area one- and two-layer graphene and an interface between them, two
sets of Landau levels and features related to the interface were found. In edge
hybrids featuring a large two-layer graphene with narrow one-layer graphene
edges, we observed an anomalous suppression in quantum oscillation amplitude
due to the locking of one- and two-layer graphene Fermi energies and emergent
chiral interface states. These findings demonstrate the importance of these
hybrid structures whose unique interface states and related phenomena deserve
further studies.Comment: 4 pages, 4 figure
Coupling ideality of integrated planar high-Q microresonators
Chipscale microresonators with integrated planar optical waveguides are
useful building blocks for linear, nonlinear and quantum optical devices. Loss
reduction through improving fabrication processes has resulted in several
integrated micro resonator platforms attaining quality (Q) factors of several
millions. However only few studies have investigated design-dependent losses,
especially with regard to the resonator coupling section. Here we investigate
design-dependent parasitic losses, described by the coupling ideality, of the
commonly employed microresonator design consisting of a microring resonator
waveguide side-coupled to a straight bus waveguide. By systematic
characterization of multi-mode high-Q silicon nitride microresonator devices,
we show that this design can suffer from low coupling ideality. By performing
full 3D simulations to numerically investigate the resonator to bus waveguide
coupling, we identify the coupling to higher-order bus waveguide modes as the
dominant origin of parasitic losses which lead to the low coupling ideality.
Using suitably designed bus waveguides, parasitic losses are mitigated, and a
nearly unity ideality and strong overcoupling (i.e. a ratio of external
coupling to internal resonator loss rate > 9) are demonstrated. Moreover we
find that different resonator modes can exchange power through the coupler,
which therefore constitutes a mechanism that induces modal coupling, a
phenomenon known to distort resonator dispersion properties. Our results
demonstrate the potential for significant performance improvements of
integrated planar microresonators, achievable by optimized coupler designs.Comment: 8 pages, 3 figures, 1 tabl
Integrating China’s Agricultural Economy into the Global Market: Measuring Distortions in China’s Agricultural Sector
International Relations/Trade,
Distortions to Agricultural Incentives in China
Distorted incentives, agricultural and trade policy reforms, national agricultural development, Agricultural and Food Policy, International Relations/Trade, F13, F14, Q17, Q18,
Cross-sectional and plan-view cathodoluminescence of GaN partially coalesced above a nanocolumn array
The optical properties of GaN layers coalesced above an array of nanocolumns have important consequences for advanced optoelectronic devices. GaN nanocolumns coalesced using a nanoscale epitaxial overgrowth technique have been investigated by high resolution cathodoluminescence (CL) hyperspectral imaging. Plan-view microscopy reveals partially coalesced GaN layers with a sub-μm scale domain structure and distinct grain boundaries, which is mapped using CL spectroscopy showing high strain at the grain boundaries. Cross-sectional areas spanning the partially coalesced GaN and underlying nanocolumns are mapped using CL, revealing that the GaN bandedge peak shifts by about 25 meV across the partially coalesced layer of ∼2 μm thick. The GaN above the nanocolumns remains under tensile strain, probably due to Si out-diffusion from the mask or substrate. The cross-sectional data show how this strain is reduced towards the surface of the partially coalesced layer, possibly due to misalignment between adjacent partially coalesced regions
Rotating Superconductors and the Frame-independent London Equation
A frame-independent, thermodynamically exact London equation is presented,
which is especially valid for rotating superconductors. A direct result is the
unexpectedly high accuracy () for the usual expression of the
London moment.Comment: 4 pages, 0 figure
Adhesion, Stiffness and Instability in Atomically Thin MoS2 Bubbles
We measured the work of separation of single and few-layer MoS2 membranes
from a SiOx substrate using a mechanical blister test, and found a value of 220
+- 35 mJ/m^2. Our measurements were also used to determine the 2D Young's
modulus of a single MoS2 layer to be 160 +- 40 N/m. We then studied the
delamination mechanics of pressurized MoS2 bubles, demonstrating both stable
and unstable transitions between the bubbles' laminated and delaminated states
as the bubbles were inflated. When they were deflated, we observed edge pinning
and a snap-in transition which are not accounted for by the previously reported
models. We attribute this result to adhesion hysteresis and use our results to
estimate the work of adhesion of our membranes to be 42 +- 20 mJ/m^2
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