Waveguide mode imaging and dispersion analysis with terahertz near-field microscopy

Propagation of terahertz waves in hollow metallic waveguides depends on the waveguide mode. Near-field scanning probe terahertz microscopy is applied to identify the mode structure and composition in dielectric-lined hollow metallic waveguides. Spatial profiles, relative amplitudes, and group velocities of three main waveguide modes are experimentally measured and matched to the HE11, HE12, and TE11 modes. The combination of near-field microscopy with terahertz time-resolved spectroscopy opens the possibility of waveguide mode characterization in the terahertz band

A steady-state Bi-substrate technique for measurement of the thermal conductivity of ceramic coatings

This paper presents a steady-state, bi-substrate technique for measurement of the through-thickness thermal conductivity of ceramic coatings, with a range of specimen thickness and porosity content. The technique is based on establishing unidirectional steady-state heat flow through the sample, sandwiched between a pair of (metallic) substrates with known thermal properties. Comparison between the heat fluxes passing through the two substrates allows a check to be made about the accuracy of the assumption of unidirectional heat flow. The interfacial conductances must be known and these can be estimated by testing samples of different thickness. Measured conductivities are likely to be more accurate if the interfacial conductance is relatively high. This is assisted by the introduction of a thin interfacial layer of a viscous, thermally conductive compound, or thermal pads of some sort, and by maintaining a suitable pressure across the setup. However, if such compounds (pastes) are used, then care must be taken to ensure that it does not enter the specimen via surface-connected pores, since this could significantly affect the measured conductivity. The reliability of the technique has been confirmed by testing fused silica samples of known thermal conductivity. It has also been applied to sprayed zirconia and plasma electrolytic oxide (PEO) alumina coatings. The values obtained were 1.05±0.10 W m?1 K?1 and 1.63±0.35 W m?1 K?1, respectively

Thin-Film Metamaterials called Sculptured Thin Films

Morphology and performance are conjointed attributes of metamaterials, of which sculptured thin films (STFs) are examples. STFs are assemblies of nanowires that can be fabricated from many different materials, typically via physical vapor deposition onto rotating substrates. The curvilinear--nanowire morphology of STFs is determined by the substrate motions during fabrication. The optical properties, especially, can be tailored by varying the morphology of STFs. In many cases prototype devices have been fabricated for various optical, thermal, chemical, and biological applications.Comment: to be published in Proc. ICTP School on Metamaterials (Augsut 2009, Sibiu, Romania

Strong Discontinuities in the Complex Photonic Band Structure of Transmission Metallic Gratings

Complex photonic band structures (CPBS) of transmission metallic gratings with rectangular slits are shown to exhibit strong discontinuities that are not evidenced in the usual energetic band structures. These discontinuities are located on Wood's anomalies and reveal unambiguously two different types of resonances, which are identified as horizontal and vertical surface-plasmon resonances. Spectral position and width of peaks in the transmission spectrum can be directly extracted from CPBS for both kinds of resonances.Comment: 4 pages, 4 figures, REVTeX version

Evaluation of the implementation of the sigmoid take-off landmark in the Netherlands

Aim: The sigmoid take-off (STO), the point on imaging where the sigmoid sweeps ventral from the sacrum, was chosen as the definition of the rectum during an international Delphi consensus meeting and has been incorporated into the Dutch guidelines since October 2019. The aim of this study was to evaluate the implementation of this landmark 1 year after the guideline implementation and to perform a quality assessment of the STO training. Method: Dutch radiologists, surgeons, surgical residents, interns, PhD students and physician assistants were asked to complete a survey and classify 20 tumours on MRI as ‘below’, ‘on’ or ‘above’ the STO. Outcomes were agreement with the expert reference, inter-rater variability and accuracy before and after the training. Results: Eighty-six collaborators participated. Six radiologists (32%) and 11 surgeons (73%) used the STO as the standard landmark to distinguish between rectal and sigmoidal tumours during multidisciplinary meetings. Overall agreement with the expert reference improved from 53% to 70% (p &lt; 0.001) after the training. The positive predictive value for diagnosing rectal tumours was high before and after the training (92% vs. 90%); the negative predictive value for diagnosing sigmoidal tumours improved from 39% to 63%. Conclusion: Approximately half of the represented hospitals have implemented the new definition of rectal cancer 1 year after the implementation of the Dutch national guidelines. Overall baseline agreement with the expert reference and accuracy for the tumours around the STO was low, but improved significantly after training. These results highlight the added value of training in implementation of radiological landmarks to ensure unambiguous assessment.</p

Afshar's Experiment does not show a Violation of Complementarity

A recent experiment performed by S. Afshar [first reported by M. Chown, New Scientist {\bf 183}, 30 (2004)] is analyzed. It was claimed that this experiment could be interpreted as a demonstration of a violation of the principle of complementarity in quantum mechanics. Instead, it is shown here that it can be understood in terms of classical wave optics and the standard interpretation of quantum mechanics. Its performance is quantified and it is concluded that the experiment is suboptimal in the sense that it does not fully exhaust the limits imposed by quantum mechanics.Comment: 6 pages, 6 figure

The significance of the amorphous potential energy landscape for dictating glassy dynamics and driving solid-state crystallisation

Contains fulltext : 180674.pdf (publisher's version ) (Open Access

Multi-timescale Solar Cycles and the Possible Implications

Based on analysis of the annual averaged relative sunspot number (ASN) during 1700 -- 2009, 3 kinds of solar cycles are confirmed: the well-known 11-yr cycle (Schwabe cycle), 103-yr secular cycle (numbered as G1, G2, G3, and G4, respectively since 1700); and 51.5-yr Cycle. From similarities, an extrapolation of forthcoming solar cycles is made, and found that the solar cycle 24 will be a relative long and weak Schwabe cycle, which may reach to its apex around 2012-2014 in the vale between G3 and G4. Additionally, most Schwabe cycles are asymmetric with rapidly rising-phases and slowly decay-phases. The comparisons between ASN and the annual flare numbers with different GOES classes (C-class, M-class, X-class, and super-flare, here super-flare is defined as $\geq$ X10.0) and the annal averaged radio flux at frequency of 2.84 GHz indicate that solar flares have a tendency: the more powerful of the flare, the later it takes place after the onset of the Schwabe cycle, and most powerful flares take place in the decay phase of Schwabe cycle. Some discussions on the origin of solar cycles are presented.Comment: 8 pages, 4 figure

A new urban landscape in East–Southeast Asia, 2000–2010

East–Southeast Asia is currently one of the fastest urbanizing regions in the world, with countries such as China climbing from 20 to 50% urbanized in just a few decades. By 2050, these countries are projected to add 1 billion people, with 90% of that growth occurring in cities. This population shift parallels an equally astounding amount of built-up land expansion. However, spatially-and temporally-detailed information on regional-scale changes in urban land or population distribution do not exist; previous efforts have been either sample-based, focused on one country, or drawn conclusions from datasets with substantial temporal/spatial mismatch and variability in urban definitions. Using consistent methodology, satellite imagery and census data for &gt;1000 agglomerations in the East–Southeast Asian region, we show that urban land increased &gt;22% between 2000 and 2010 (from 155 000 to 189 000 km2), an amount equivalent to the area of Taiwan, while urban populations climbed &gt;31% (from 738 to 969 million). Although urban land expanded at unprecedented rates, urban populations grew more rapidly, resulting in increasing densities for the majority of urban agglomerations, including those in both more developed (Japan, South Korea) and industrializing nations (China, Vietnam, Indonesia). This result contrasts previous sample-based studies, which conclude that cities are universally declining in density. The patterns and rates of change uncovered by these datasets provide a unique record of the massive urban transition currently underway in East–Southeast Asia that is impacting local-regional climate, pollution levels, water quality/availability, arable land, as well as the livelihoods and vulnerability of populations in the regio

Homodyne Bell's inequalities for entangled mesoscopic superpositions

We present a scheme for demonstrating violation of Bell's inequalities using a spin-1/2 system entangled with a pair of classically distinguishable wave packets in a harmonic potential. In the optical domain, such wave packets can be represented by coherent states of a single light mode. The proposed scheme involves standard spin-1/2 projections and measurements of the position and the momentum of the harmonic oscillator system, which for a light mode can be realized by means of homodyne detection. We discuss effects of imperfections, including non-unit efficiency of the homodyne detector, and point out a close link between the visibility of interference and violation of Bell's inequalities in the described scheme.Comment: 6 pages, 3 figures. Extended version, journal reference adde