538 research outputs found
Enhanced Transmission of Light and Particle Waves through Subwavelength Nanoapertures by Far-Field Interference
Subwavelength aperture arrays in thin metal films can enable enhanced
transmission of light and matter (atom) waves. The phenomenon relies on
resonant excitation and interference of the plasmon or matter waves on the
metal surface. We show a new mechanism that could provide a great resonant and
nonresonant transmission enhancement of the light or de Broglie particle waves
passed through the apertures not by the surface waves, but by the constructive
interference of diffracted waves (beams generated by the apertures) at the
detector placed in the far-field zone. In contrast to other models, the
mechanism depends neither on the nature (light or matter) of the beams
(continuous waves or pulses) nor on material and shape of the multiple-beam
source (arrays of 1-D and 2-D subwavelength apertures, fibers, dipoles or
atoms). The Wood anomalies in transmission spectra of gratings, a long standing
problem in optics, follow naturally from the interference properties of our
model. The new point is the prediction of the Wood anomaly in a classical
Young-type two-source system. The new mechanism could be interpreted as a
non-quantum analog of the superradiance emission of a subwavelength ensemble of
atoms (the light power and energy scales as the number of light-sources
squared, regardless of periodicity) predicted by the well-known Dicke quantum
model.Comment: Revised version of MS presented at the Nanoelectronic Devices for
Defense and Security (NANO-DDS) Conference, 18-21 June, 2007, Washington, US
Influence of the anion potential on the charge ordering in quasi-one dimensional charge transfer salts
We examine the various instabilities of quarter-filled strongly correlated
electronic chains in the presence of a coupling to the underlying lattice. To
mimic the physics of the (TMTTF)X Bechgaard-Fabre salts we also include
electrostatic effects of intercalated anions. We show that small displacements
of the anion can stabilize new mixed Charged Density Wave-Bond Order Wave
phases in which central symmetry centers are suppressed. This finding is
discussed in the context of recent experiments. We suggest that the recently
observed charge ordering is due to a cooperative effect between the Coulomb
interaction and the coupling of the electronic stacks to the anions. On the
other hand, the Spin-Peierls instability at lower temperature requires a
Peierls-like lattice coupling.Comment: Latex, 4 pages, 4 postscript figure
Metamaterial Coatings for Broadband Asymmetric Mirrors
We report on design and fabrication of nano-composite metal-dielectric thin
film coatings with high reflectance asymmetries. Applying basic dispersion
engineering principles to model a broadband and large reflectance asymmetry, we
obtain a model dielectric function for the metamaterial film, closely
resembling the effective permittivity of disordered metal-dielectric
nano-composites. Coatings realized using disordered nanocrystalline silver
films deposited on glass substrates confirm the theoretical predictions,
exhibiting symmetric transmittance, large reflectance asymmetries and a unique
flat reflectance asymmetry.Comment: 4 pages, 4 figures, submitted to Optics Letter
The shape of a moving fluxon in stacked Josephson junctions
We study numerically and analytically the shape of a single fluxon moving in
a double stacked Josephson junctions (SJJ's) for various junction parameters.
We show that the fluxon in a double SJJ's consists of two components, which are
characterized by different Swihart velocities and Josephson penetration depths.
The weight coefficients of the two components depend on the parameters of the
junctions and the velocity of the fluxon. It is shown that the fluxon in SJJ's
may have an unusual shape with an inverted magnetic field in the second
junction when the velocity of the fluxon is approaching the lower Swihart
velocity. Finally, we study the influence of fluxon shape on flux-flow
current-voltage characteristics and analyze the spectrum of Cherenkov radiation
for fluxon velocity above the lower Swihart velocity. Analytic expression for
the wavelength of Cherenkov radiation is derived.Comment: 12 pages, 12 figure
Chiral helix in AdS/CFT with flavor
The D3/D7 holographic model aims at a better approximation to QCD by adding
to N=4 SYM theory N_f of N=2 supersymmetric hypermultiplets in the fundamental
representation of SU(N_c) -- the "flavor fields" representing the quarks.
Motivated by a recent observation of the importance of the Wess-Zumino-like
(WZ) term for realizing the chiral magnetic effect within this model, we
revisit the phase diagram of the finite temperature, massless D3/D7 model in
the presence of external electric/magnetic fields and at finite chemical
potential. We point out that the A-V-V triangle anomaly represented by the WZ
term in the D7 brane probe action implies the existence of new phases that have
been overlooked in the previous studies. In the case of an external magnetic
field and at finite chemical potential, we find a "chiral helix" phase in which
the U(1)_A angle of D7 brane embedding increases monotonically along the
direction of the magnetic field -- this is a geometric realization of the
chiral spiral phase in QCD. We also show that in the case of parallel electric
and magnetic fields (E,B) there exists a phase in which the D7 brane
spontaneously begins to rotate, so that the U(1)_A angle changes as a function
of time -- this may be called the "spontaneous rotation" phase; it is a
geometrical realization of a phase with non-zero chiral chemical potential. Our
results call for a more thorough study of the (T,B,E,\mu) phase diagram of the
massless D3/D7 model taking a complete account of the WZ term.
We also speculate about the possible phase diagram in the massive case.Comment: 25 pages, 7 figure
Vapour reactive distillation process for hydrogen production by hi decomposition from hi-i2-h2o solutions
In this contribution, a sequential and hierarchical approach for the feasibility analysis and the preliminary design of reactive distillation columns is extended to systems involving vapour phase chemical reaction and is successfully applied to the HI vapour phase decomposition to produce H2.
The complex phase and physico chemical behaviour of the quaternary HI-H2-I2-H2O system is represented by the Neumann’s thermodynamic model and instantaneous vapour phase chemical equilibrium is assumed.
Then, from minimal information concerning the physicochemical properties of the system, three successive steps lead to the design of the unit and the specification of its operating conditions: the feasibility analysis, the synthesis and the design step. First, the analysis of reactive condensation curve map method (rCCM), assuming infinite internal liquid and vapour flow rate and infinite reflux ratio, is used to assess the feasibility of the process. It determines the column structure and estimates the attainable compositions. These results are used as inputs data for the synthesis step. Based on the boundary value design method (BVD), considering finite internal liquid and vapour flow rate and finite reflux ratio while neglecting all thermal effects and assuming a constant heat of vaporisation, the synthesis step provides more precise information about the process configuration (minimum reflux ratio, number of theoretical stages, localisation and number of reactive plates, position of the feed plate). Finally, the BVD method results are used to initialise rigorous simulations, based on an equilibrium stage model with energy balance, to estimate the reflux ratio taking into account thermal effect on the process.
The resulting design configuration consists in a single feed and entirely reactive distillation column. The column operates under a pressure of 22 bars. The feed of the reactive distillation column, coming from the Bunsen reaction section [xHI=0.10; xI2=0.39 xH2O=0.51], is at its boiling temperature. The residue consists in pure iodine. Water and produced hydrogen are recovered at the distillate. The column operates at a reflux ratio of 5 and is composed of 11 theoretical plates including the reboiler and the partial condenser with the feed at the stage 10 (counted downwards). The obtained HI dissociation yield is 99.6%
Impact of A Cargo-Less Liposomal Formulation on Dietary Obesity-Related Metabolic Disorders in Mice.
Current therapeutic options for obesity often require pharmacological intervention with dietary restrictions. Obesity is associated with underlying inflammation due to increased tissue macrophage infiltration, and recent evidence shows that inflammation can drive obesity, creating a feed forward mechanism. Therefore, targeting obesity-induced macrophage infiltration may be an effective way of treating obesity. Here, we developed cargo-less liposomes (UTS-001) using 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC (synthetic phosphatidylcholine) as a single-agent to manage weight gain and related glucose disorders due to high fat diet (HFD) consumption in mice. UTS-001 displayed potent immunomodulatory properties, including reducing resident macrophage number in both fat and liver, downregulating liver markers involved in gluconeogenesis, and increasing marker involved in thermogenesis. As a result, UTS-001 significantly enhanced systemic glucose tolerance in vivo and insulin-stimulated cellular glucose uptake in vitro, as well as reducing fat accumulation upon ad libitum HFD consumption in mice. UTS-001 targets tissue residence macrophages to suppress tissue inflammation during HFD-induced obesity, resulting in improved weight control and glucose metabolism. Thus, UTS-001 represents a promising therapeutic strategy for body weight management and glycaemic control
HIT-COVID, a global database tracking public health interventions to COVID-19
The COVID-19 pandemic has sparked unprecedented public health and social measures (PHSM) by national and local governments, including border restrictions, school closures, mandatory facemask use and stay at home orders. Quantifying the effectiveness of these interventions in reducing disease transmission is key to rational policy making in response to the current and future pandemics. In order to estimate the effectiveness of these interventions, detailed descriptions of their timelines, scale and scope are needed. The Health Intervention Tracking for COVID-19 (HIT-COVID) is a curated and standardized global database that catalogues the implementation and relaxation of COVID-19 related PHSM. With a team of over 200 volunteer contributors, we assembled policy timelines for a range of key PHSM aimed at reducing COVID-19 risk for the national and first administrative levels (e.g. provinces and states) globally, including details such as the degree of implementation and targeted populations. We continue to maintain and adapt this database to the changing COVID-19 landscape so it can serve as a resource for researchers and policymakers alike
Cognitive behaviour therapy versus counselling intervention for anxiety in young people with high-functioning autism spectrum disorders: a pilot randomised controlled trial
The use of cognitive-behavioural therapy (CBT) as a treatment for children and adolescents with autism spectrum disorder (ASD) has been explored in a number of trials. Whilst CBT appears superior to no treatment or treatment as usual, few studies have assessed CBT against a control group receiving an alternative therapy.
Our randomised controlled trial compared use of CBT against person-centred counselling for anxiety in 36 young people with ASD, ages 12–18. Outcome measures included parent- teacher- and self-reports of anxiety and social disability.
Whilst each therapy produced improvements inparticipants, neither therapy was superior to the other to a significant degree on any measure. This is consistent with findings for adults
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