Destabilizing resonances of precessing inertia-gravity waves.

Instabilities in stratified precessing fluid are investigated. We extend the study by Mahalov [Phys. Fluids A 5, 891 (1993)0899-821310.1063/1.858635] in the stably stratified Boussinesq framework, with an external Coriolis force (with rate Ω_{p}) altering the base flow through the distortion of the circular streamlines of the unperturbed axially stratified rotating columns (with constant vorticity 2Ω.) It is shown that the inviscid part of the modified velocity flow (0,Ωr,-2ɛΩrsinφ) and buoyancy with gradient N^{2}(-2ɛcosφ,2ɛsinφ,1) are an exact solution of Boussinesq-Euler equations. Here (r,φ,z) is a cylindrical coordinate system, with ɛ=Ω_{p}/Ω being the Poincaré number and N the Brunt-Väisälä frequency. The base flow is transformed into a Cartesian coordinate system, and the stability of a superimposed perturbation is studied in terms of Fourier (or Kelvin) modes. The resulting Floquet system for the Fourier modes has three parameters: ɛ, N=N/Ω, and µ, which is the angle between the wave vector k and the solid-body rotation axis in the limit ɛ=0. In this limit, there are inertia-gravity waves propagating with frequency ±ω and the resonant cases are those for which 2ω=nΩ, n being an integer. We perform an asymptotic analysis to leading order in ɛ and characterize the destabilizing resonant case of order n=1 (i.e., the subharmonic instability) which exists and for 0≤N<Ω/2. In this range, the subharmonic instability remains the strongest with a maximal growth rate σ_{m}=[ɛ(5sqrt[15]/8)sqrt[1-4N^{2}]/(4-N^{2})]. Stable stratification acts in such a way as to make the subharmonic instability less efficient, so as it disappears for N≥0.5Ω. The destabilizing resonant cases of order n=2,3,4,5 are investigated in detail by numerical computations. The effect of viscosity on these instabilities is briefly addressed assuming the diffusive coefficients (kinematic and thermal) are equal. Likewise, we briefly investigate the case where N^{2}<0 and show that the instability associated to the mode with k_{3}=0 is the strongest.

Altering the Optical Properties of GaAsSb-Capped InAs Quantum Dots by Means of InAlAs Interlayers.

In this work, we investigate the optical properties of InAs quantum dots (QDs) capped with composite In0.15Al0.85As/GaAs0.85Sb0.15 strain-reducing layers (SRLs) by means of high-resolution X-ray diffraction (HRXRD) and photoluminescence (PL) spectroscopy at 77 K. Thin In0.15Al0.85As layers with thickness t = 20 Å, 40 Å, and 60 Å were inserted between the QDs and a 60-Å-thick GaAs0.85Sb0.15 layer. The type II emissions observed for GaAs0.85Sb0.15-capped InAs QDs were suppressed by the insertion of the In0.15Al0.85As interlayer. Moreover, the emission wavelength was blueshifted for t = 20 Å and redshifted for t ≥ 40 Å resulting from the increased confinement potential and increased strain, respectively. The ground state and excited state energy separation is increased reaching 106 meV for t = 60 Å compared to 64 meV for the QDs capped with only GaAsSb SRL. In addition, the use of the In0.15Al0.85As layers narrows significantly the QD spectral linewidth from 52 to 35 meV for the samples with 40- and 60-Å-thick In0.15Al0.85As interlayers.

Spectral energy scaling in precessing turbulence.

We study precessing turbulence, which appears in several geophysical and astrophysical systems, by direct numerical simulations of homogeneous turbulence where precessional instability is triggered due to the imposed background flow. We show that the time development of kinetic energy K occurs in two main phases associated with different flow topologies: (i) an exponential growth characterizing three-dimensional turbulence dynamics and (ii) nonlinear saturation during which K remains almost time independent, the flow becoming quasi-two-dimensional. The latter stage, wherein the development of K remains insensitive to the initial state, shares an important common feature with other quasi-two-dimensional rotating flows such as rotating Rayleigh-Bénard convection, or the large atmospheric scales: in the plane k_{∥}=0, i.e., the plane associated to an infinite wavelength in the direction parallel to the principal rotation axis, the kinetic energy spectrum scales as k_{⊥}^{-3}. We show that this power law is observed for wave numbers ranging between the Zeman "precessional" and "rotational" scales, k_{S}^{-1} and k_{Ω}^{-1}, respectively, at which the associated background shear or inertial timescales are equal to the eddy turnover time. In addition, an inverse cascade develops for (k_{⊥},k)

Energy partition, scale by scale, in magnetic Archimedes Coriolis weak wave turbulence.

Magnetic Archimedes Coriolis (MAC) waves are omnipresent in several geophysical and astrophysical flows such as the solar tachocline. In the present study, we use linear spectral theory (LST) and investigate the energy partition, scale by scale, in MAC weak wave turbulence for a Boussinesq fluid. At the scale k^{-1}, the maximal frequencies of magnetic (Alfvén) waves, gravity (Archimedes) waves, and inertial (Coriolis) waves are, respectively, V_{A}k,N, and f. By using the induction potential scalar, which is a Lagrangian invariant for a diffusionless Boussinesq fluid [Salhi et al., Phys. Rev. E 85, 026301 (2012)PLEEE81539-375510.1103/PhysRevE.85.026301], we derive a dispersion relation for the three-dimensional MAC waves, generalizing previous ones including that of f-plane MHD "shallow water" waves [Schecter et al., Astrophys. J. 551, L185 (2001)AJLEEY0004-637X10.1086/320027]. A solution for the Fourier amplitude of perturbation fields (velocity, magnetic field, and density) is derived analytically considering a diffusive fluid for which both the magnetic and thermal Prandtl numbers are one. The radial spectrum of kinetic, S_{κ}(k,t), magnetic, S_{m}(k,t), and potential, S_{p}(k,t), energies is determined considering initial isotropic conditions. For magnetic Coriolis (MC) weak wave turbulence, it is shown that, at large scales such that V_{A}k/f≪1, the Alfvén ratio S_{κ}(k,t)/S_{m}(k,t) behaves like k^{-2} if the rotation axis is aligned with the magnetic field, in agreement with previous direct numerical simulations [Favier et al., Geophys. Astrophys. Fluid Dyn. (2012)] and like k^{-1} if the rotation axis is perpendicular to the magnetic field. At small scales, such that V_{A}k/f≫1, there is an equipartition of energy between magnetic and kinetic components. For magnetic Archimedes weak wave turbulence, it is demonstrated that, at large scales, such that (V_{A}k/N≪1), there is an equipartition of energy between magnetic and potential components, while at small scales (V_{A}k/N≫1), the ratio S_{p}(k,t)/S_{κ}(k,t) behaves like k^{-1} and S_{κ}(k,t)/S_{m}(k,t)=1. Also, for MAC weak wave turbulence, it is shown that, at small scales (V_{A}k/sqrt[N^{2}+f^{2}]≫1), the ratio S_{p}(k,t)/S_{κ}(t) behaves like k^{-1} and S_{κ}(k,t)/S_{m}(k,t)=1.

Instability in stratified accretion flows under primary and secondary perturbations.

We consider horizontal linear shear flow (shear rate denoted by Λ) under vertical uniform rotation (ambient rotation rate denoted by Ω(0)) and vertical stratification (buoyancy frequency denoted by N) in unbounded domain. We show that, under a primary vertical velocity perturbation and a radial density perturbation consisting of a one-dimensional standing wave with frequency N and amplitude proportional to w(0)sin(ɛNx/w(0))≈ɛNx(≪1), where x denotes the radial coordinate and ɛ a small parameter, a parametric instability can develop in the flow, provided N(2)>8Ω(0)(2Ω(0)-Λ). For astrophysical accretion flows and under the shearing sheet approximation, this implies N(2)>8Ω(0)(2)(2-q), where q=Λ/Ω(0) is the local shear gradient. In the case of a stratified constant angular momentum disk, q=2, there is a parametric instability with the maximal growth rate (σ(m)/ɛ)=3√[3]/16 for any positive value of the buoyancy frequency N. In contrast, for a stratified Keplerian disk, q=1.5, the parametric instability appears only for N>2Ω(0) with a maximal growth rate that depends on the ratio Ω(0)/N and approaches (3√[3]/16)ɛ for large values of N.

Nonlinear dynamics and anisotropic structure of rotating sheared turbulence.

Homogeneous turbulence in rotating shear flows is studied by means of pseudospectral direct numerical simulation and analytical spectral linear theory (SLT). The ratio of the Coriolis parameter to shear rate is varied over a wide range by changing the rotation strength, while a constant moderate shear rate is used to enable significant contributions to the nonlinear interscale energy transfer and to the nonlinear intercomponental redistribution terms. In the destabilized and neutral cases, in the sense of kinetic energy evolution, nonlinearity cannot saturate the growth of the largest scales. It permits the smallest scale to stabilize by a scale-by-scale quasibalance between the nonlinear energy transfer and the dissipation spectrum. In the stabilized cases, the role of rotation is mainly nonlinear, and interacting inertial waves can affect almost all scales as in purely rotating flows. In order to isolate the nonlinear effect of rotation, the two-dimensional manifold with vanishing spanwise wave number is revisited and both two-component spectra and single-point two-dimensional energy components exhibit an important effect of rotation, whereas the SLT as well as the purely two-dimensional nonlinear analysis are unaffected by rotation as stated by the Proudman theorem. The other two-dimensional manifold with vanishing streamwise wave number is analyzed with similar tools because it is essential for any shear flow. Finally, the spectral approach is used to disentangle, in an analytical way, the linear and nonlinear terms in the dynamical equations.

Instability of subharmonic resonances in magnetogravity shear waves.

We study analytically the instability of the subharmonic resonances in magnetogravity waves excited by a (vertical) time-periodic shear for an inviscid and nondiffusive unbounded conducting fluid. Due to the fact that the magnetic potential induction is a Lagrangian invariant for magnetohydrodynamic Euler-Boussinesq equations, we show that plane-wave disturbances are governed by a four-dimensional Floquet system in which appears, among others, the parameter ɛ representing the ratio of the periodic shear amplitude to the vertical Brunt-Väisälä frequency N(3). For sufficiently small ɛ and when the magnetic field is horizontal, we perform an asymptotic analysis of the Floquet system following the method of Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]. We determine the width and the maximal growth rate of the instability bands associated with subharmonic resonances. We show that the instability of subharmonic resonance occurring in gravity shear waves has a maximal growth rate of the form Δ(m)=(3√[3]/16)ɛ. This instability persists in the presence of magnetic fields, but its growth rate decreases as the magnetic strength increases. We also find a second instability involving a mixing of hydrodynamic and magnetic modes that occurs for all magnetic field strengths. We also elucidate the similarity between the effect of a vertical magnetic field and the effect of a vertical Coriolis force on the gravity shear waves considering axisymmetric disturbances. For both cases, plane waves are governed by a Hill equation, and, when ɛ is sufficiently small, the subharmonic instability band is determined by a Mathieu equation. We find that, when the Coriolis parameter (or the magnetic strength) exceeds N(3)/2, the instability of the subharmonic resonance vanishes.

[Reactive perforating collagenosis]. / Collagénose perforante réactionnelle.

BACKGROUND: Reactive perforating collagenosis (RPC) belongs to the group of perforating dermatoses, which comprises elastosis perforans serpiginosa, RPC, perforating folliculitis and Kyrle's disease. RPC was initially described as a distinctive form of transepithelial elimination of altered collagen related to superficial trauma. Two types are distinguished: a hereditary type (MIM 216700), which is rare and begins during early childhood, and a second type, called acquired RPC, which is more frequent, appears in adults and is associated with other diseases, diabetes mellitus, renal insufficiency, solid tumors, lymphomas and AIDS. We report the case of a young man whose illness began during infancy, militating in favor of a diagnosis of a hereditary form of RPC. The description of similar lesions in the patient's brother confirmed our diagnosis. PATIENTS AND METHODS: A 26-year-old man, the child of consanguinous parents, presented crusted papular lesions on his hands. The cutaneous lesions, located on the external side of the limbs, had been present since childhood, with flares during winter. Histologic analysis showed a cup-shaped depression in the epidermis containing keratinous material with extruded degenerated collagen towards the cutaneous surface. Treatment with topic retinoids did not result in any real resolution of the disease. The patient reported the presence of similar lesions in his brother, which was consistent with our diagnosis. DISCUSSION: The pathogenesis of hereditary RPC is still unknown, even if superficial trauma is suspected as the cause of RPC. In contrast, in diabetes, acquired RPC pathogenesis has recently been related to advanced glycation end-products of collagen.

Magnetized stratified rotating shear waves.

We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity Ω), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k(1) = 0, axisymmetric disturbances) and a finite one (k(1) ≠ 0, nonaxisymmetric disturbances). In the former case (k(1) = 0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k(1) ≠ 0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the stability of the solution at infinite vertical wavelength (k(3) = 0): There is an oscillatory behavior for τ > 1+|K(2)/k(1)|, where τ = St is a dimensionless time and K(2) is the radial component of the wave vector at τ = 0. The model is suitable to describe instabilities leading to turbulence by the bypass mechanism that can be relevant for the analysis of magnetized stratified Keplerian disks with a purely azimuthal field. For initial isotropic conditions, the time evolution of the spectral density of total energy (kinetic + magnetic + potential) is considered. At k(3) = 0, the vertical motion is purely oscillatory, and the sum of the vertical (kinetic + magnetic) energy plus the potential energy does not evolve with time and remains equal to its initial value. The horizontal motion can induce a rapid transient growth provided K(2)/k(1)>>1. This rapid growth is due to the aperiodic velocity vortex mode that behaves like K(h)/k(h) where k(h)(τ)=[k(1)(2) + (K(2) - k(1)τ)(2)](1/2) and K(h) =k(h)(0). After the leading phase (τ > K(2)/k(1)>>1), the horizontal magnetic energy and the horizontal kinetic energy exhibit a similar (oscillatory) behavior yielding a high level of total energy. The contribution to energies coming from the modes k(1) = 0 and k(3) = 0 is addressed by investigating the one-dimensional spectra for an initial Gaussian dense spectrum. For a magnetized Keplerian disk with a purely vertical field, it is found that an important contribution to magnetic and kinetic energies comes from the region near k(1) = 0. The limit at k(1) = 0 of the streamwise one-dimensional spectra of energies, or equivalently, the streamwise two-dimensional (2D) energy, is then computed. The comparison of the ratios of these 2D quantities with their three-dimensional counterparts provided by previous direct numerical simulations shows a quantitative agreement.

[Osteoma cutis presenting as an erythematous and grainy, retroauricular plaque]. / Ostéome cutané primaire à type de plaque rétro-auriculaire érythémateuse et grenue.

BACKGROUND: Authentic bone tissue can be observed in the skin, in both the epidermis and dermis, where it produces cutaneous osteomas. These lesions are classed as either primary or secondary ossifications. Secondary ossifications are the consequence of inflammatory lesions such as acne or injuries while primary ossifications are neither preceded by preexisting lesions nor associated with other lesions. PATIENTS AND METHODS: A 22-year-old man with no prior history consulted for a grainy, erythematous, telangiectatic retroauricular plaque on the right side. Palpation revealed hard grainy lesions giving a tactile sensation of small stones. Histological analysis showed an ossification in the dermis resulting from mature bone in contact with dilated vessels. A diagnosis of venous malformation with osseous metaplasia was initially proposed, but the patient insisted that no vascular anomaly had preceded the grainy lesions. Further histological analysis demonstrated that the vascular anomalies were restricted to the ossified regions and the final diagnosis was of primary cutaneous osteoma. DISCUSSION: In our patient, the absence of any endocrine anomalies and of any vascular malformation supported the diagnosis of primary cutaneous osteoma. Certain vascular anomalies such as haemangiomas or venous malformation can lead to bone formation. The coexistence in the dermis of osteomas and dilated vessels initially led us to suspect osteomas secondary to venous malformation. However, the absence of any vascular anomalies preceding the cutaneous osteoma contradicted this diagnosis. In venous malformations, phleboliths are usually seen as a result of calcium deposits on thrombus rather than authentic osteomas. Our patient had no standard primary solitary osteoma of either the nodular or the plaque type, and this case thus constitutes a new original form of primary cutaneous osteoma.

A deterministic DNA database search.

This paper suggests a novel way for measuring the similarity between sequences of symbols from alphabets of small cardinality such as DNA and RNA sequences. The approach relies on finding one-to-one mappings between these sequences and a subset of the real numbers. Gaps in nonidentical sequences are easily detected. Computational illustrations on DNA sequences and a comparison with BLAST are included.

Magnetohydrodynamic instabilities in rotating and precessing sheared flows: an asymptotic analysis.

Linear magnetohydrodynamic instabilities are studied analytically in the case of unbounded inviscid and electrically conducting flows that are submitted to both rotation and precession with shear in an external magnetic field. For given rotation and precession the possible configurations of the shear and of the magnetic field and their interplay are imposed by the "admissibility" condition (i.e., the base flow must be a solution of the magnetohydrodynamic Euler equations): we show that an "admissible" basic magnetic field must align with the basic absolute vorticity. For these flows with elliptical streamlines due to precession we undertake an analytical stability analysis for the corresponding Floquet system, by using an asymptotic expansion into the small parameter ε (ratio of precession to rotation frequencies) by a method first developed in the magnetoelliptical instabilities study by Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]10.1086/420972. The present stability analysis is performed into a suitable frame that is obtained by a systematic change of variables guided by symmetry and the existence of invariants of motion. The obtained Floquet system depends on three parameters: ε , η (ratio of the cyclotron frequency to the rotation frequency) and χ=cos α, with α being a characteristic angle which, for circular streamlines, ε=0, identifies with the angle between the wave vector and the axis of the solid body rotation. We look at the various (centrifugal or precessional) resonant couplings between the three present modes: hydrodynamical (inertial), magnetic (Alfvén), and mixed (magnetoinertial) modes by computing analytically to leading order in ε the instabilities by estimating their threshold, growth rate, and maximum growth rate and their bandwidths as functions of ε, η, and χ. We show that the subharmonic "magnetic" mode appears only for η>square root of 5/2 and at large η (>>1) the maximal growth rate of both the "hydrodynamic" and magnetic modes approaches ε/2, while the one of the subharmonic "mixed" mode approaches zero.

Stability of rotating stratified shear flow: an analytical study.

We study the stability problem of unbounded shear flow, with velocity U(i)=Sx(3)delta(i1), subjected to a uniform vertical density stratification, with Brunt-Väisälä frequency N, and system rotation of rate Omega about an axis aligned with the spanwise (x(2)) direction. The evolution of plane-wave disturbances in this shear flow is governed by a nonhomogeneous second-order differential equation with time-dependent coefficients. An analytical solution is found to be described by Legendre functions in terms of the nondimensional parameter sigma(phi)(2)=R(R+1)sin(2) phi+R(i), where R=(2Omega/S) is the rotation number, phi is the angle between the horizontal wave vector and the streamwise axis, and R(i)=N(2)/S(2) is the Richardson number. The long-time behavior of the solution is analyzed using the asymptotic representations of the Legendre functions. On the one hand, linear stability is analyzed in terms of exponential growth, as in a normal-mode analysis: the rotating stratified shear flow is stable if R(i)>1/4, or if 00, or if R(R+1)<0

Precessing rotating flows with additional shear: stability analysis.

We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Omega(0)) and the additional "precessing" Coriolis force (with angular velocity -epsilonOmega(0)), normal to it. A "weak" shear flow, with rate 2epsilon of the same order of the Poincaré "small" ratio epsilon , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler's equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov's [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré's [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small epsilon . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet's theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small epsilon , but significant differences are obtained regarding growth rates and widths of instability bands, if larger epsilon values, up to 0.2, are considered. Finally, both flow cases are briefly discussed in view of a subsequent nonlinear study using pseudospectral direct numerical simulations, which is a natural continuation of RDT.

Heterodyne lock-in thermal coupling measurements in integrated circuits: Applications to test and characterization.

Heterodyne strategies can be used to characterize thermal coupling in integrated circuits when the electrical bandwidth of the dissipating circuit is beyond the bandwidth of the thermal coupling mechanism. From the characterization of the thermal coupling, two possible applications are described: extraction of characteristics of the dissipating circuit (the determination of the center frequency of a low-noise amplifier) and the extraction of the thermal coupling transfer function.

Linear increase of the modal gain in 1.3 µm InAs/GaAs quantum dot lasers containing up to seven-stacked QD layers.

The authors have recently demonstrated the enhancement of the quantum dot laser modal gain, linearly scaling with the number of stacked QD layers. These results allowed the achievement of multi-quantum dot (MQD) lasers, the zero-dimensional counterpart of MQW lasers, with a modal gain as high as 42 cm(-1), in a seven-layer structure. A detailed investigation of the structural and optical properties was performed on laser structures with three, five and seven QD layers. Such an investigation clearly shows that the high uniformity of QD layer features is responsible for the linear increase of the modal gain and its high value.

Laser scanning thermoreflectance imaging system using galvanometric mirrors for temperature measurements of microelectronic devices.

We present a thermoreflectance imaging system using a focused laser sweeping the device under test with a scanner made of galvanometric mirrors. We first show that the spatial resolution of this setup is submicrometric, which makes it adapted to microelectronic thermal measurements. Then, we studied qualitative temperature variations on two dissipative structures constituted of thin (0.35 microm) dissipative resistors, the distance between two resistors being equal to 0.8 or 10 microm. This technique combines sensitivity and speed: it is faster than a point classical thermoreflectance technique and, in addition, more sensitive than a charge-coupled device thermoreflectance imaging technique.

Time-dependent rotating stratified shear flow: exact solution and stability analysis.

A solution of the Euler equations with Boussinesq approximation is derived by considering unbounded flows subjected to spatially uniform density stratification and shear rate that are time dependent [S(t)= partial differentialU3/partial differentialx2]. In addition to vertical stratification with constant strength N(v)2, this base flow includes an additional, horizontal, density gradient characterized by N(h)2(t). The stability of this flow is then analyzed: When the vertical stratification is stabilizing, there is a simple harmonic motion of the horizontal stratification N(h)2(t) and of the shear rate S(t), but this flow is unstable to certain disturbances, which are amplified by a Floquet mechanism. This analysis may involve an additional Coriolis effect with Coriolis parameter f, so that governing dimensionless parameters are a modified Richardson number, R=[S(0)2+N(h)4(0)/N(v)2]1/2, and f(v)=f/N(v), as well as the initial phase of the periodic shear rate. Parametric resonance between the inertia-gravity waves and the oscillating shear is demonstrated from the dispersion relation in the limit R-->0. The parametric instability has connection with both baroclinic and elliptical flow instabilities, but can develop from a very different base flow.

Looking into the volcano with a Mid-IR DFB diode laser and Cavity Enhanced Absorption Spectroscopy.

We report on the first application of extended-wavelength DFB diode lasers to Cavity-Enhanced Absorption Spectroscopy in-situ trace measurements on geothermal gases. The emission from the most active fumarole at the Solfatara volcano near Naples (Italy) was probed for the presence of CO and CH(4). After passing through a gas dryer and cooler, the volcanic gas flow (98% CO(2)) was analysed in real time for the concentration of these species, whose relatively strong absorption lines could be monitored simultaneously by a single Distributed Feed-Back (DFB) GaSb-based diode laser emitting around 2.33 mum (4300 cm(-1)) at room temperature. The concentrations were found to be about 3 ppm and 75 ppm, respectively, while actual detection limits for these molecules are around 1 ppb. We discuss the possibility of detecting other species of interest for volcanic emission monitoring.

Residual lesions after Kasabach-Merritt phenomenon in 41 patients.

BACKGROUND: Kasabach-Merritt phenomenon (KMP) is the association of a vascular tumor and thrombocytopenic coagulopathy. Vascular tumors are either kaposiform hemangioendothelioma or tufted angioma but not "true" common hemangioma of infancy. There is a conspicuous absence in the literature regarding the late outcome and possible residual lesions after apparent clinical cure of KMP. OBJECTIVE: The purpose of the study was to analyze these residua in a large number of patients. METHODS: Clinical data on 41 patients who had KMP were accrued in an international cooperative study. The emphasis was on the residual lesions after resolution of the thrombocytopenia and other coagulation abnormalities. Imaging studies (follow-up magnetic resonance imaging studies available for 10 patients) and histologic specimens (30 specimens available for 26 patients, 18 biopsies done during the KMP and 12 concerning the sequelae) were reviewed. RESULTS: Residual lesions after "cure" of KMP were common. They exhibited 3 clinical patterns: type I lesions (n = 28) showed a cutaneous red stain, with or without associated red papules. The stain might overlap a minor fibrotic infiltration or a significant poorly delineated diffuse fibrotic infiltration. These cutaneous vascular lesions varied in size and appearance over time and were occasionally painful. Type II lesions were telangiectatic streaks and swelling (n = 5), and type III lesions showed a minor, firm, irregular, subcutaneous mass assessed by palpation or deep infiltration evidenced by computed tomography or magnetic resonance imaging (n = 8). A fourth feature was sequelae in muscles and/or joints. Histologically, tufted angioma was more common in the specimens from residual lesions, whereas kaposiform hemangioendothelioma was more common during the active phase of KMP. Imaging findings were remarkably reproducible and revealed a persistent vascular tumor. CONCLUSION: Residua of tumors associated with KMP are common after the resolution of thrombocytopenia and coagulopathy. They are (more or less) prominent dormant vascular tumors, not "scars" and, clinically as well as histologically, they differ markedly from involuted hemangioma.