Probing graphene’s nonlocality with singular metasurfaces

Singular graphene metasurfaces, conductivity gratings realized by periodically suppressing the local doping level of a graphene sheet, were recently proposed to efficiently harvest THz light and couple it to surface plasmons over broad absorption bands, thereby achieving remarkably high field enhancement. However, the large momentum wavevectors thus attained are sensitive to the nonlocal behavior of the underlying electron liquid. Here, we extend the theory of singular graphene metasurfaces to account for the full nonlocal optical response of graphene and discuss the resulting impact on the plasmon resonance spectrum. Finally, we propose a simple local-analogue model that is able to reproduce the effect of nonlocality in local-response calculations by introducing a constant conductivity offset, which could prove a valuable tool in the modeling of more complex experimental graphene-based platforms

Purifying single photon emission from a CdSe/CdS colloidal quantum dot

Colloidal quantum dots are robust and flexible single photon emitters for room-temperature applications, but their purity is strongly reduced at high pump powers, due to multiexcitonic emission which cannot be easily filtered due to the photo-luminescence spectral broadening at room temperature. Giant-shell quantum dots feature a large blueshift of the biexciton spectrum due to electron-hole wave function engineering and piezoelectric charge separation, which can be exploited for spectral separation of the single exciton from the multiexciton emission. Here, by spectral filtering, we show that we can recover an excellent single-photon emission, with $g_2{(0)} < 0.05$ (resolution limited), even at high pump powers above saturation of the exciton emission. The bright and pure single-photon generation shown here has important applications in quantum information technology and random-number generation

Liquid-infiltrated photonic crystals - enhanced light-matter interactions for lab-on-a-chip applications

Optical techniques are finding widespread use in analytical chemistry for chemical and bio-chemical analysis. During the past decade, there has been an increasing emphasis on miniaturization of chemical analysis systems and naturally this has stimulated a large effort in integrating microfluidics and optics in lab-on-a-chip microsystems. This development is partly defining the emerging field of optofluidics. Scaling analysis and experiments have demonstrated the advantage of micro-scale devices over their macroscopic counterparts for a number of chemical applications. However, from an optical point of view, miniaturized devices suffer dramatically from the reduced optical path compared to macroscale experiments, e.g. in a cuvette. Obviously, the reduced optical path complicates the application of optical techniques in lab-on-a-chip systems. In this paper we theoretically discuss how a strongly dispersive photonic crystal environment may be used to enhance the light-matter interactions, thus potentially compensating for the reduced optical path in lab-on-a-chip systems. Combining electromagnetic perturbation theory with full-wave electromagnetic simulations we address the prospects for achieving slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap based refractometry, and high-Q cavity sensing.Comment: Invited paper accepted for the "Optofluidics" special issue to appear in Microfluidics and Nanofluidics (ed. Prof. David Erickson). 11 pages including 8 figure

Drivers and barriers to acceptance of human-papillomavirus vaccination among young women: a qualitative and quantitative study

<p>Abstract</p> <p>Background</p> <p>Human papillomavirus (HPV) is a necessary cause of cervical dysplasia and cancer, and of genital warts. Few studies have examined attitudes to HPV vaccination since the introduction of HPV vaccines. We aimed to investigate the reasons for young women's acceptance or rejection of the quadrivalent HPV vaccine after its general availability in Denmark.</p> <p>Method</p> <p>A literature review assessed attitudes towards HPV vaccination and the information was used to identify relevant questions for telephone and focus group interviews with women aged 16-26 who had decided to receive or reject HPV vaccination. 435 women across Denmark were interviewed by telephone. Qualitative interviews were undertaken in focus groups with 33 women living in Odense who had completed the telephone survey. Four focus groups were set up according to age (16-20 and 21-26 years of age) and acceptance/rejection of the vaccine.</p> <p>Results</p> <p>Of 839 women initially contacted by telephone, 794 were included, 411 (49%) said they accepted vaccination but only 201 (24%) had actually received the vaccine and these latter were interviewed. 242 women said they refused vaccination of which 234 were interviewed. Women who were undecided were excluded from the study. Prevention of cervical cancer was the main driver for acceptance of the vaccine, followed by parental encouragement and financial support, personal experience of someone with cancer and recommendation by health-care professionals. The greatest barrier to vaccination was its cost. A lack of information about the benefits of vaccination for sexually active women was also an important barrier and the older participants in particular considered that they were too old to be vaccinated. Knowledge about HPV and its role in the development of cervical cancer and genital warts was poor.</p> <p>Conclusions</p> <p>The difference between intention to be vaccinated and starting vaccination was considerable, and a large proportion of women aged 16-26 did not wish to be vaccinated. If the most important barriers to vaccination were addressed (cost and a lack of information about vaccination benefits), it is likely that the uptake of vaccination in Denmark would increase substantially.</p

Numerical investigation of nanostructured silica PCFs for sensing applications.

Photonic crystal fibers (PCFs) developed using nanostructured composite materials provide special optical properties. PCF light propagation and modal characteristics can be tailored by modifying their structural and material parameters. Structuring and infusion of liquid crystal materials enhances the capabilities of all silica PCFs, facilitating their operation in different spectral regimes. The wavelength tunability feature of nanostructured PCFs can be utilized for many advanced sensing applications. This paper discusses a new approach to modify the optical properties of PCFs by periodic nanostructuring and composite material (liquid crystal-silica) infiltration. PCF characteristics like confinement wavelength, confinement loss, mode field diameter (MFD) and bandwidth are investigated by varying the structural parameters and material infiltrations. Theoretical study revealed that composite material infusion resulted in a spectral band shift accompanied by an improvement in PCF bandwidth. Moreover, nanostructured PCFs also achieved reduced confinement losses and improved MFD which is very important in long-distance remote sensing applications

Observation of the exceptional-point-enhanced Sagnac effect

Exceptional points (EPs) are special spectral degeneracies of non-Hermitian Hamiltonians that govern the dynamics of open systems. At an EP, two or more eigenvalues, and the corresponding eigenstates, coalesce. Recently, it was predicted that operation of an optical gyroscope near an EP results in improved response to rotations. However, the performance of such a system has not been examined experimentally. Here we introduce a precisely controllable physical system for the study of non-Hermitian physics and nonlinear optics in high-quality-factor microresonators. Because this system dissipatively couples counter-propagating lightwaves within the resonator, it also functions as a sensitive gyroscope for the measurement of rotations. We use our system to investigate the predicted EP-enhanced Sagnac effect and observe a four-fold increase in the Sagnac scale factor by directly measuring rotations applied to the resonator. The level of enhancement can be controlled by adjusting the system bias relative to the EP, and modelling results confirm the observed enhancement. Moreover, we characterize the sensitivity of the gyroscope near the EP. Besides verifying EP physics, this work is important for the understanding of optical gyroscopes

Signal Detection on the Battlefield: Priming Self-Protection vs. Revenge-Mindedness Differentially Modulates the Detection of Enemies and Allies

Detecting signs that someone is a member of a hostile outgroup can depend on very subtle cues. How do ecology-relevant motivational states affect such detections? This research investigated the detection of briefly-presented enemy (versus friend) insignias after participants were primed to be self-protective or revenge-minded. Despite being told to ignore the objectively nondiagnostic cues of ethnicity (Arab vs. Western/European), gender, and facial expressions of the targets, both priming manipulations enhanced biases to see Arab males as enemies. They also reduced the ability to detect ingroup enemies, even when these faces displayed angry expressions. These motivations had very different effects on accuracy, however, with self-protection enhancing overall accuracy and revenge-mindedness reducing it. These methods demonstrate the importance of considering how signal detection tasks that occur in motivationally-charged environments depart from results obtained in conventionally motivationally-inert laboratory settings.National Institute of Mental Health (U.S.) (Grant MH64734)U.S. Army Research Institute for the Behavioral and Social Sciences (Grant W74V8H-05-K-0003)National Science Foundation (U.S.) (Grant BCS-0642873

Protocol for Work place adjusted Intelligent physical exercise reducing Musculoskeletal pain in Shoulder and neck (VIMS): a cluster randomized controlled trial

<p>Abstract</p> <p>Background</p> <p>Neck and shoulder complaints are common among employees in sedentary occupations characterized by intensive computer use. Specific strength training is a promising type of physical exercise for relieving neck and shoulder pain in office workers. However, the optimal combination of frequency and exercise duration, as well as the importance of exercise supervision, is unknown. The VIMS study investigates in a cluster randomized controlled design the effectiveness of different time wise combinations of specific strength training with identical accumulated volume, and the relevance of training supervision for safe and effective training.</p> <p>Methods/design</p> <p>A cluster randomized controlled trial of 20 weeks duration where employed office workers are randomized to 1 × 60 min, 3 × 20 min, 9 × 7 min per week of specific strength training with training supervision, to 3 × 20 min per week of specific strength training with a minimal amount of training supervision, or to a reference group without training. A questionnaire will be sent to 2000 employees in jobs characterized by intensive computer work. Employees with cardiovascular disease, trauma, hypertension, or serious chronic disease will be excluded. The main outcome measure is pain in the neck and shoulders at week 20.</p> <p>Trial Registration</p> <p>The trial is registered at ClinicalTrials.gov, number NCT01027390.</p

Streamwise-travelling viscous waves in channel flows

The unsteady viscous flow induced by streamwise-travelling waves of spanwise wall velocity in an incompressible laminar channel flow is investigated. Wall waves belonging to this category have found important practical applications, such as microfluidic flow manipulation via electro-osmosis and surface acoustic forcing and reduction of wall friction in turbulent wall-bounded flows. An analytical solution composed of the classical streamwise Poiseuille flow and a spanwise velocity profile described by the parabolic cylinder function is found. The solution depends on the bulk Reynolds number R, the scaled streamwise wavelength (Formula presented.), and the scaled wave phase speed U. Numerical solutions are discussed for various combinations of these parameters. The flow is studied by the boundary-layer theory, thereby revealing the dominant physical balances and quantifying the thickness of the near-wall spanwise flow. The Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) theory is also employed to obtain an analytical solution, which is valid across the whole channel. For positive wave speeds which are smaller than or equal to the maximum streamwise velocity, a turning-point behaviour emerges through the WKBJ analysis. Between the wall and the turning point, the wall-normal viscous effects are balanced solely by the convection driven by the wall forcing, while between the turning point and the centreline, the Poiseuille convection balances the wall-normal diffusion. At the turning point, the Poiseuille convection and the convection from the wall forcing cancel each other out, which leads to a constant viscous stress and to the break down of the WKBJ solution. This flow regime is analysed through a WKBJ composite expansion and the Langer method. The Langer solution is simpler and more accurate than the WKBJ composite solution, while the latter quantifies the thickness of the turning-point region. We also discuss how these waves can be generated via surface acoustic forcing and electro-osmosis and propose their use as microfluidic flow mixing devices. For the electro-osmosis case, the Helmholtz–Smoluchowski velocity at the edge of the Debye–Hückel layer, which drives the bulk electrically neutral flow, is obtained by matched asymptotic expansion

Bacterial Surface Appendages Strongly Impact Nanomechanical and Electrokinetic Properties of Escherichia coli Cells Subjected to Osmotic Stress

The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO3, cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700–900 kPa and ∼100–300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions