Observation of Light Thermalization to Negative-Temperature Rayleigh-Jeans Equilibrium States in Multimode Optical Fibers.

Although the temperature of a thermodynamic system is usually believed to be a positive quantity, under particular conditions, negative-temperature equilibrium states are also possible. Negative-temperature equilibriums have been observed with spin systems, cold atoms in optical lattices, and two-dimensional quantum superfluids. Here we report the observation of Rayleigh-Jeans thermalization of light waves to negative-temperature equilibrium states. The optical wave relaxes to the equilibrium state through its propagation in a multimode optical fiber-i.e., in a conservative Hamiltonian system. The bounded energy spectrum of the optical fiber enables negative-temperature equilibriums with high energy levels (high-order fiber modes) more populated than low energy levels (low-order modes). Our experiments show that negative-temperature speckle beams are featured, in average, by a nonmonotonic radial intensity profile. The experimental results are in quantitative agreement with the Rayleigh-Jeans theory without free parameters. Bringing negative temperatures to the field of optics opens the door to the investigation of fundamental issues of negative-temperature states in a flexible experimental environment.

Classical Rayleigh-Jeans Condensation of Light Waves: Observation and Thermodynamic Characterization.

Theoretical studies on wave turbulence predict that a purely classical system of random waves can exhibit a process of condensation, which originates in the singularity of the Rayleigh-Jeans equilibrium distribution. We report the experimental observation of the transition to condensation of classical optical waves propagating in a multimode fiber, i.e., in a conservative Hamiltonian system without thermal heat bath. In contrast to conventional self-organization processes featured by the nonequilibrium formation of nonlinear coherent structures (solitons, vortices,…), here the self-organization originates in the equilibrium Rayleigh-Jeans statistics of classical waves. The experimental results show that the chemical potential reaches the lowest energy level at the transition to condensation, which leads to the macroscopic population of the fundamental mode of the optical fiber. The near-field and far-field measurements of the condensate fraction across the transition to condensation are in quantitative agreement with the Rayleigh-Jeans theory. The thermodynamics of classical wave condensation reveals that the heat capacity takes a constant value in the condensed state and tends to vanish above the transition in the normal state. Our experiments provide the first demonstration of a coherent phenomenon of self-organization that is exclusively driven by optical thermalization toward the Rayleigh-Jeans equilibrium.

Depression and glycemic control in adolescent diabetics: evaluating possible association between depression and hemoglobin A1c.

OBJECTIVES: The objective of this study was to test whether glycemic control varies between adolescent patients diagnosed with type 1 or type 2 diabetes who are depressed and those who are not, after controlling for confounding factors. We hypothesized that diabetic children who have depression or a high risk to develop depression will have worse glycemic control, as indicated by higher hemoglobin A1c (HbA1c) values. STUDY DESIGN: This was a retrospective case-control study. METHODS: A chart review was conducted in the Section of Endocrinology at St. Christopher's Hospital for Children in Philadelphia. Multivariate linear regression was used to determine effects of individual variables. RESULTS: A total of 214 records were included out of 263 reviewed. Significant differences were observed in type 1 diabetics (n = 156) between depressed and non-depressed patients in the percentage of females in the group (P = .002), the duration of diabetes (P = .005), age at diagnosis (P = .01), hemoglobin A1c (P = .03), and the percentage of those with a HbA1c greater than 14% (P = .03). Depression was associated with significant increases in HbA1c values in type 1 diabetics (P < .001). An interaction effect (P = .055) was observed between sex and depression. Given the small sample of children with type 2 diabetes, we were unable to perform any meaningful statistical analysis in this subgroup of patients. CONCLUSIONS: We have detected a significant association between depression and glycemic control in adolescent girls with type 1 diabetes. This association appears to be moderated by sex. Depressed patients with type 2 diabetes generally display higher HbA1c values than their non-depressed counterparts.

Polarization chaos and random bit generation in nonlinear fiber optics induced by a time-delayed counter-propagating feedback loop.

In this manuscript, we experimentally and numerically investigate the chaotic dynamics of the state-of-polarization in a nonlinear optical fiber due to the cross-interaction between an incident signal and its intense backward replica generated at the fiber-end through an amplified reflective delayed loop. Thanks to the cross-polarization interaction between the two-delayed counter-propagating waves, the output polarization exhibits fast temporal chaotic dynamics, which enable a powerful scrambling process with moving speeds up to 600-krad/s. The performance of this all-optical scrambler was then evaluated on a 10-Gbit/s On/Off Keying telecom signal achieving an error-free transmission. We also describe how these temporal and chaotic polarization fluctuations can be exploited as an all-optical random number generator. To this aim, a billion-bit sequence was experimentally generated and successfully confronted to the dieharder benchmarking statistic tools. Our experimental analysis are supported by numerical simulations based on the resolution of counter-propagating coupled nonlinear propagation equations that confirm the observed behaviors.

Decoupled polarization dynamics of incoherent waves and bimodal spectral incoherent solitons.

We consider the propagation of strongly incoherent waves in optical fibers in the framework of the vector nonlinear Schrödinger equation (VNLSE) accounting for the Raman effect. On the basis of the wave turbulence theory, we derive a kinetic equation that greatly simplifies the VNLSE and provides deep physical insight into incoherent wave dynamics. When applied to the study of polarization effects, the theory unexpectedly reveals that the linear polarization components of the incoherent wave evolve independently from each other, even in the presence of weak fiber birefringence. When applied to light propagation in bimodal fibers, the theory reveals that the incoherent modal components can be strongly coupled. After a complex transient, the modal components self-organize into a vector spectral incoherent soliton: The two solitons self-trap and propagate with a common velocity in frequency space.

Temporal dynamics of incoherent waves in noninstantaneous response nonlinear Kerr media.

We consider the temporal evolution of an incoherent optical wave that propagates in a noninstantaneous response nonlinear medium, such as single mode optical fibers. In contrast with the expected Raman-like spectral redshift due to a delayed nonlinear response, we show that a highly noninstantaneous response leads to a genuine modulational instability of the incoherent optical wave. We derive a Vlasov-like kinetic equation that provides a detailed description of this process of incoherent modulational instability in the temporal domain.

Manifestation of Hamiltonian monodromy in nonlinear wave systems.

We show that the concept of dynamical monodromy plays a natural fundamental role in the spatiotemporal dynamics of counterpropagating nonlinear wave systems. By means of an adiabatic change of the boundary conditions imposed to the wave system, we show that Hamiltonian monodromy manifests itself through the spontaneous formation of a topological phase singularity (2π- or π-phase defect) in the nonlinear waves. This manifestation of dynamical Hamiltonian monodromy is illustrated by generic nonlinear wave models. In particular, we predict that its measurement can be realized in a direct way in the framework of a nonlinear optics experiment.

Influence of third-order dispersion on the propagation of incoherent light in optical fibers.

We study the influence of third-order dispersion effects on the propagation of an incoherent nonlinear wave in an optical fiber system. The wave spectrum is shown to exhibit a highly asymmetric deformation characterized by a lateral spectral shoulder and the subsequent formation of an unexpected constant spectral pedestal. A kinetic approach to the problem reveals the existence of an invariant that explains in detail the essential properties of such asymmetric spectral evolution of the wave.

Complete nonlinear polarization control in an optical fiber system.

We consider the counterpropagating interaction of a signal and a pump beam in an isotropic optical fiber. On the basis of recently developed mathematical techniques, we show that an arbitrary state of polarization of the signal beam can be converted into any other desired state of polarization. On the other hand, an unpolarized signal beam may be repolarized into two specific states of polarization, without loss of energy. Both processes of repolarization and polarization conversion may be controlled by adjusting the polarization state of the backward pump.

Polarization domain walls in optical fibres as topological bits for data transmission.

Domain walls are topological defects which occur at symmetry-breaking phase transitions. While domain walls have been intensively studied in ferromagnetic materials, where they nucleate at the boundary of neighbouring regions of oppositely aligned magnetic dipoles, their equivalent in optics have not been fully explored so far. Here, we experimentally demonstrate the existence of a universal class of polarization domain walls in the form of localized polarization knots in conventional optical fibres. We exploit their binding properties for optical data transmission beyond the Kerr limits of normally dispersive fibres. In particular, we demonstrate how trapping energy in well-defined train of polarization domain walls allows undistorted propagation of polarization knots at a rate of 28 GHz along a 10 km length of normally dispersive optical fibre. These results constitute the first experimental observation of kink-antikink solitary wave propagation in nonlinear fibre optics.

From coherent shocklets to giant collective incoherent shock waves in nonlocal turbulent flows.

Understanding turbulent flows arising from random dispersive waves that interact strongly through nonlinearities is a challenging issue in physics. Here we report the observation of a characteristic transition: strengthening the nonlocal character of the nonlinear response drives the system from a fully turbulent regime, featuring a sea of coherent small-scale dispersive shock waves (shocklets) towards the unexpected emergence of a giant collective incoherent shock wave. The front of such global incoherent shock carries most of the stochastic fluctuations and is responsible for a peculiar folding of the local spectrum. Nonlinear optics experiments performed in a solution of graphene nano-flakes clearly highlight this remarkable transition. Our observations shed new light on the role of long-range interactions in strongly nonlinear wave systems operating far from thermodynamic equilibrium, which reveals analogies with, for example, gravitational systems, and establishes a new scenario that can be common to many turbulent flows in photonic quantum fluids, hydrodynamics and Bose-Einstein condensates.

Examiner standardization for caries studies.

Examiners in clinical control programs customarily undergo an intensive period of training to standardize their interpretation of diagnostic criteria. Data are presented summarizing examiner error rates in calibration examinations and reversal rates in a field study.

Influence of a chlorhexidine and a zinc mouthrinse on gingivitis.

The end point methodology did not indicate a difference between the agents. The prophylaxis effect was only demonstrable through 8 weeks, although the analysis of variance indicated a prophylaxis effect on gingival index throughout the study. An agent effect was not demonstrable in the study. The "positive control," chlorhexidine, did not give the same results in this brushing study as in previous no-brushing studies reported by Loe and by our group. One might conclude that the effectiveness of brushing in reducing gingivitis is greater than the effect of chlorhexidine. Decreasing plaque and gingivitis scores are seen with increasing time, probably reflecting increased subject interest and involvement in the study. Mere involvement in the study apparently produced a beneficial effect on gingival health. This "placebo effect" also has been noted in an earlier study. A similar decrease in plaque scores in a placebo group attributable to a general improvement of oral hygiene was reported by Gjermo and Rolla. The subjects who began the study with no calculus (prophylaxis group) had consistently lower calculus scores than those not given a prophylaxis. This difference became less distinct at later exams, as the treated group developed calculus. The agents, although ineffective under the test regimen produced no adverse effects.

Three-dimensional hybrid solitary waves: transverse vortex solitons stabilized by longitudinal parametric solitary waves.

We show that the parametric process in quadratic nonlinear media supports three-dimensional (3D) hybrid solitary wave solution in which a transverse vortex solitons embedded in an infinite plane-wave background is sustained by a longitudinal parametric solitary wave. The structure of the parametric solitary wave results from the interplay of the quadratic nonlinearity and the temporal walk off (i.e., the velocity mismatch) between the interacting waves. The 3D hybrid solitary wave proved to be robust with respect to modulational instability, a feature that contrasts with previous studies on quadratic vortex solitons that revealed them to be always modulationally unstable. We show that the mechanism of stabilization of the vortex background lies on the temporal walkoff between the interacting waves that is able to drift the modulational instability out of the temporally localized structure that constitutes the 3D hybrid solitary wave.

Influence of walk-off, dispersion, and diffraction on the coherence of parametric fluorescence.

We consider the basic problem of spontaneous parametric generation from quantum noise fluctuations in the presence of a continuous plane-wave pump. We show, both numerically and analytically, that the walk-off between the down-converted fields is the key ingredient that leads to the generation of coherent fields in the parametric process. Along these lines, our theory reveals that, in the absence of walk-off, diffraction and chromatic dispersion in usual quadratically nonlinear materials only lead to incoherent erratic dynamics. Moreover, a two-dimensional study shows that, when the walk-off is exclusively temporal (or spatial), the parametric process is not able to yield the generation of spatially (or temporally) coherent fields. This study sheds light on the problem of coherence in parametric fluorescence and, in particular, allows us to explain various recent experimental observations.

Noise-seeded spatiotemporal modulation instability in normal dispersion.

In optical second-harmonic generation with normal dispersion, the virtually infinite bandwidth of the unbounded, hyperbolic, modulational instability leads to quenching of spatial multisoliton formation and to the occurrence of a catastrophic spatiotemporal breakup when an extended beam is left to interact with an extremely weak external noise with a coherence time much shorter than that of the pump.

Geriatric pharmacology for the dentist. An overview.

The information presented in this article suggests that the drug responses of the elderly may be greater than those in the young or essentially the same. We have presented evidence that the pharmacokinetics in the elderly would probably tend toward prolonging the half-life and delaying the clearance of many drugs. Pharmacodynamic changes are more ambiguous, increasing sensitivity to some drugs and decreasing sensitivity to others. Compliance errors, from whatever cause, lead to unpredictable intake of drugs. Psychosocioeconomic factors contribute to compliance errors and no doubt also lead to increased intake of combination of drugs. Multiple diseases are common among the elderly, but it is not clear how disease states, per se, affect drug responses unless the specifically diseased organ is focally important in the handling of drugs. Alterations in perception of pain and in reflex and immune competence will produce changes in all directions. Use of multiple drugs almost certainly will create an environment favorable to drug interactions and adverse reactions. What is the dentist to do with these conflicting effects of aging in drug therapy? There are a few, and only a few, rules that can be said to have a solid basis in fact. Elderly patients seem to be more sensitive to the depressant effects of drugs. It is wise, therefore, to reduce the dosage of such drugs as the benzodiazepines, general anesthetics, analgesics, and sedative-hypnotics in the elderly. Old people are apparently more sensitive to certain drugs, for example, the neuromuscular blocking drugs. It would be wise to reduce the dosage of these for the older patient. The geriatric person appears to be less sensitive to pain; it would be wise to prescribe analgesics for such patients in lower doses. Elderly patients are known to have lost some of their reflex ability to maintain homeostasis. This should be taken into consideration when drugs that affect blood pressure, heart rate, and smooth muscle tone are used. Elderly patients are almost certain to be taking multiple medications. Drug interactions, as well as adverse drug reactions (which are exaggerated in the elderly), are likely to occur in this polypharmaceutical setting. It is critical that the dentist be continually informed of the pharmacologic status of each patient and be aware of the likelihood of interactions between drugs prescribed by the dentist, drugs-prescribed by the physician, and drugs that are self-administered.

A survey of dentists' drug prescribing practices.

The drug prescribing practices of dentists should be of interest to the dental profession, drug manufacturers, the medical profession and dental educators. This article presents an update on an earlier similar survey reported by the authors as well as information on current infection control procedures, the treatment of hepatitis and AIDS patients, and generic drug substitution. The classes of drugs that are important to the practitioner and the level of prescribing activity have not changed appreciably since the earlier study. There has been, however, a significant change in nonopioid analgesic drug preference with ibuprofen overtaking aspirin and acetaminophen by a wide margin. That age affects the character of practice was confirmed: far fewer older practitioners report prescribing drugs than do their younger counterparts. A very gratifying finding was the high level of compliance with ADA recommendations regarding infectious diseases although fears over treating AIDS patients remain high.

Temporal spying and concealing process in fibre-optic data transmission systems through polarization bypass.

Recent research has been focused on the ability to manipulate a light beam in such a way to hide, namely to cloak, an event over a finite time or localization in space. The main idea is to create a hole or a gap in the spatial or time domain so as to allow for an object or data to be kept hidden for a while and then to be restored. By enlarging the field of applications of this concept to telecommunications, researchers have recently reported the possibility to hide transmitted data in an optical fibre. Here we report the first experimental demonstration of perpetual temporal spying and blinding process of optical data in fibre-optic transmission line based on polarization bypass. We successfully characterize the performance of our system by alternatively copying and then concealing 100% of a 10-Gb s(-1) transmitted signal.

A universal optical all-fiber Omnipolarizer.

Wherever the polarization properties of a light beam are of concern, polarizers and polarizing beamsplitters (PBS) are indispensable devices in linear-, nonlinear- and quantum-optical schemes. By the very nature of their operation principle, transformation of incoming unpolarized or partially polarized beams through these devices introduces large intensity variations in the fully polarized outcoming beam(s). Such intensity fluctuations are often detrimental, particularly when light is post-processed by nonlinear crystals or other polarization-sensitive optic elements. Here we demonstrate the unexpected capability of light to self-organize its own state-of-polarization, upon propagation in optical fibers, into universal and environmentally robust states, namely right and left circular polarizations. We experimentally validate a novel polarizing device - the Omnipolarizer, which is understood as a nonlinear dual-mode polarizing optical element capable of operating in two modes - as a digital PBS and as an ideal polarizer. Switching between the two modes of operation requires changing beam's intensity.