Optical Kinetic Theory of Nonlinear Multimode Photonic Networks.

Recent experimental developments in multimode nonlinear photonic circuits (MMNPCs), have motivated the development of an optical thermodynamic theory that describes the equilibrium properties of an initial beam excitation. However, a nonequilibrium transport theory for these systems, when they are in contact with thermal reservoirs, is still terra incognita. Here, by combining Landauer and kinematics formalisms we develop a universal one-parameter scaling theory that describes the whole transport behavior from the ballistic to the diffusive regime, including both positive and negative optical temperature scenarios. We also derive a photonic version of the Wiedemann-Franz law that connects the thermal and power conductivities. Our work paves the way toward a fundamental understanding of the transport properties of MMNPCs and may be useful for the design of all-optical cooling protocols.

Stationary Charge Radiation in Anisotropic Photonic Time Crystals.

Time metamaterials offer a great potential for wave manipulation, drawing increasing attention in recent years. Here, we explore the exotic wave dynamics of an anisotropic photonic time crystal (APTC) formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix formalism, we show that a stationary charge embedded in an APTC emits radiation, in contrast to the case of isotropic photonic time crystals, and its distribution in momentum space is controlled by the APTC band structure. Our approach extends the functionalities of time metamaterials, offering new opportunities for radiation generation and control, with implications for both classical and quantum applications.

Adiabatic Thermal Radiation Pumps for Thermal Photonics.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

Thermal transport in phononic Cayley-tree networks.

We analytically investigate the heat current I and its thermal fluctuations Δ in a branching network without loops (Cayley tree). The network consists of two types of harmonic masses: vertex masses M placed at the branching points where phononic scattering occurs and masses m at the bonds between branching points where phonon propagation takes place. The network is coupled to thermal reservoirs consisting of one-dimensional harmonic chains of coupled masses m. Due to impedance mismatch phenomena, both I and Δ are non-monotonic functions of the mass ratio µ=M/m. Furthermore, we find that in the low-temperature limit the thermal conductance approaches zero faster than linearly due to the small transmittance of the long-wavelength modes.

Reference-free thyroid uptake measurement.

PURPOSE: An easy-to-implement scintigraphic method that enables the assay of thyroid iodine uptake with improved accuracy and without the use of a reference source was developed with an aim to avoid unnecessary high radiation burden to patients undergoing (131)I treatment for benign thyroid disease. MATERIALS AND METHODS: Dual-energy (123)I planar imaging involving simultaneous recording of both the primary (159 keV) and scatter (130 keV) frames was followed by generation of subtraction 'scatter-free' images. A uniform cutoff level of 15% was chosen to delineate the functional thyroid tissue with the help of isocontour regions of interest, which in turn enabled quantitation of the scatter-free thyroid counts. The ratio of the total counts being recorded in each of the above frames, the 'primary-to-Compton' ratio, was determined and compared with the uniform absorption-free ratio ascribed to all of the thyroid images. This enabled determination of the upscaling factor needed to restore the scatter-free counts to their unmoderated level. The corrected count content was subsequently converted to the iodine dose accumulated by the thyroid with the help of the camera-specific net detection efficiency. As a result, the true uptake value could be determined without the need to image a reference source or phantom. RESULTS: Clinical evaluation of the proposed reference-free method was carried out by reviewing the 24-h uptake values obtained for the 32 patients suffering from Graves' disease, multinodular struma, or autonomous nodule. A comparison with concurrently assayed thyroid uptake values derived from the counts of the 24-h urine samples measured by the well-type scintillation counter (direct assay method) revealed very good linear correlation (r > 0.96). Furthermore, a comparison with uptake values determined using the 159 keV images of the patient as well as those of the reference sample in a commonly used so-called 'classic' manner was also carried out. The outcomes of the classic assay were found on average to underestimate the thyroid uptake in absolute terms by ∼ 25% because of unattended scatter and absorption-induced count losses. In contrast, the results of the reference-free method exhibited slight overestimation only, which on average amounted to less than 2%. However, because of the time-related fluctuations of the gamma camera and the dose calibrator as well as uncertainties induced by the scatter and absorption corrections, the average relative error associated with thyroid uptake values as determined by the proposed reference-free method was found to amount to nearly 10%. CONCLUSION: Strong evidence in support of the validity of the reference-free method designed to measure thyroid uptake with improved accuracy and without relating to a reference phantom image was produced in a clinical setting. As a result, the unnecessary high radiation burden to patients undergoing (131)I therapy because of systematic uptake underestimation could be avoided.

Random-matrix-theory approach to mesoscopic fluctuations of heat current.

We consider an ensemble of fully connected networks of N oscillators coupled harmonically with random springs and show, using random-matrix-theory considerations, that both the average phonon heat current and its variance are scale invariant and take universal values in the large N limit. These anomalous mesoscopic fluctuations is the hallmark of strong correlations between normal modes.

Increased superconducting transition temperature of a niobium thin film proximity coupled to gold nanoparticles using linking organic molecules.

The superconducting critical temperature, T(C), of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The T(C) increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below T(C) typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

On the Waring problem for polynomial rings.

In this note we discuss an analog of the classical Waring problem for C[x0,x1,...,x(n)]. Namely, we show that a general homogeneous polynomial p ∈ C[x0,x1,...,x(n)] of degree divisible by k≥2 can be represented as a sum of at most k(n) k-th powers of homogeneous polynomials in C[x0,x1,...,x(n)]. Noticeably, k(n) coincides with the number obtained by naive dimension count.

Thermalization of strongly disordered nonlinear chains.

Thermalization of systems described by the discrete nonlinear Schrödinger equation, in the strong disorder limit, is investigated both theoretically and numerically. We show that introducing correlations in the disorder potential, while keeping the "effective" disorder fixed (as measured by the localization properties of wave-packet dynamics), strongly facilitates the thermalization process and leads to a standard grand canonical distribution of the probability norms associated with each site.

One-parameter scaling theory for stationary states of disordered nonlinear systems.

We show, using detailed numerical analysis and theoretical arguments, that the normalized participation number of the stationary solutions of disordered nonlinear lattices obeys a one-parameter scaling law. Our approach opens a new way to investigate the interplay of Anderson localization and nonlinearity based on the powerful ideas of scaling theory.

Exponentially fragile PT symmetry in lattices with localized eigenmodes.

We study the effect of localized modes in lattices of size N with parity-time (PT) symmetry. Such modes are arranged in pairs of quasidegenerate levels with splitting delta approximately exp(-N/xi) where xi is their localization length. The level "evolution" with respect to the PT breaking parameter gamma shows a cascade of bifurcations during which a pair of real levels becomes complex. The spontaneous PT symmetry breaking occurs at gammaPT approximately min{delta}, thus resulting in an exponentially narrow exact PT phase. As N/xi decreases, it becomes more robust with gammaPT approximately 1/N2 and the distribution P(gammaPT) changes from log-normal to semi-Gaussian. Our theory can be tested in the frame of optical lattices.

Expansion of a Bose-Einstein condensate in the presence of disorder.

Expansion of a Bose-Einstein condensate (BEC) is studied in the presence of a random potential. The expansion is controlled by a single parameter, (microtau(eff)/variant Planck's over 2pi), where micro is the chemical potential, prior to the release of the BEC from the trap, and tau(eff) is a transport relaxation time which characterizes the strength of the disorder. Repulsive interactions (nonlinearity) facilitate transport and can lead to diffusive spreading of the condensate which, in the absence of interactions, would have remained localized in the vicinity of its initial location.