Sound-propagation gap in fluid mixtures

We discuss the behavior of the extended sound modes of a dense binary hard-sphere mixture. In a dense simple hard-sphere fluid the Enskog theory predicts a gap in the sound propagation at large wave vectors. In a binary mixture the gap is only present for low concentrations of one of the two species. At intermediate concentrations sound modes are always propagating. This behavior is not affected by the mass difference of the two species, but it only depends on the packing fractions. The gap is absent when the packing fractions are comparable and the mixture structurally resembles a metallic glass.Comment: Published; withdrawn since ordering in archive gives misleading impression of new publicatio

Dynamic structure factors of a dense mixture

We compute the dynamic structure factors of a dense binary liquid mixture. These describe dynamics on molecular length scales, where structural relaxation is important. We find that the presence of a few large particles in a dense fluid of small particles slows down the dynamics considerably. We also observe a deep narrowing of the spectrum for a disordered mixture composed of a nearly equal packing of the two species. In contrast, a few small particles diffuse easily in the background of a dense fluid of large particles. We expect our results to describe neutron scattering from a dense mixture

Veronesean representations of projective spaces over quadratic associative division algebras

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Proximal aortic stiffening in Turner patients may be present before dilation can be detected : a segmental functional MRI study

Background: To study segmental structural and functional aortic properties in Turner syndrome (TS) patients. Aortic abnormalities contribute to increased morbidity and mortality of women with Turner syndrome. Cardiovascular magnetic resonance (CMR) allows segmental study of aortic elastic properties. Method: We performed Pulse Wave Velocity (PWV) and distensibility measurements using CMR of the thoracic and abdominal aorta in 55 TS-patients, aged 13-59y, and in a control population (n = 38; 12-58y). We investigated the contribution of TS on aortic stiffness in our entire cohort, in bicuspid (BAV) versus tricuspid (TAV) aortic valve-morphology subgroups, and in the younger and older subgroups. Results: Differences in aortic properties were only seen at the most proximal aortic level. BAV Turner patients had significantly higher PWV, compared to TAV Turner (p = 0.014), who in turn had significantly higher PWV compared to controls (p = 0.010). BAV Turner patients had significantly larger ascending aortic (AA) luminal area and lower AA distensibility compared to both controls (all p < 0.01) and TAV Turner patients. TAV Turner had similar AA luminal areas and AA distensibility compared to Controls. Functional changes are present in younger and older Turner subjects, whereas ascending aortic dilation is prominent in older Turner patients. Clinically relevant dilatation (TAV and BAV) was associated with reduced distensibility. Conclusion: Aortic stiffening and dilation in TS affects the proximal aorta, and is more pronounced, although not exclusively, in BAV TS patients. Functional abnormalities are present at an early age, suggesting an aortic wall disease inherent to the TS. Whether this increased stiffness at young age can predict later dilatation needs to be studied longitudinally

Theorem on the Distribution of Short-Time Particle Displacements with Physical Applications

The distribution of the initial short-time displacements of particles is considered for a class of classical systems under rather general conditions on the dynamics and with Gaussian initial velocity distributions, while the positions could have an arbitrary distribution. This class of systems contains canonical equilibrium of a Hamiltonian system as a special case. We prove that for this class of systems the nth order cumulants of the initial short-time displacements behave as the 2n-th power of time for all n>2, rather than exhibiting an nth power scaling. This has direct applications to the initial short-time behavior of the Van Hove self-correlation function, to its non-equilibrium generalizations the Green's functions for mass transport, and to the non-Gaussian parameters used in supercooled liquids and glasses.Comment: A less ambiguous mathematical notation for cumulants was adopted and several passages were reformulated and clarified. 40 pages, 1 figure. Accepted by J. Stat. Phy

Square root singularity in the viscosity of neutral colloidal suspensions at large frequencies

The asymptotic frequency $\omega$, dependence of the dynamic viscosity of neutral hard sphere colloidal suspensions is shown to be of the form $\eta_0 A(\phi) (\omega \tau_P)^{-1/2}$, where $A(\phi)$ has been determined as a function of the volume fraction $\phi$, for all concentrations in the fluid range, $\eta_0$ is the solvent viscosity and $\tau_P$ the P\'{e}clet time. For a soft potential it is shown that, to leading order steepness, the asymptotic behavior is the same as that for the hard sphere potential and a condition for the cross-over behavior to $1/\omega \tau_P$ is given. Our result for the hard sphere potential generalizes a result of Cichocki and Felderhof obtained at low concentrations and agrees well with the experiments of van der Werff et al, if the usual Stokes-Einstein diffusion coefficient $D_0$ in the Smoluchowski operator is consistently replaced by the short-time self diffusion coefficient $D_s(\phi)$ for non-dilute colloidal suspensions.Comment: 18 pages LaTeX, 1 postscript figur

THREE DIMENSIONAL ARTHROKINEMATIC ANALYSIS OF THE LATE PREPARATORY PHASE OF HANDBALL THROWING

INTRODUCTION: At full cocking, functional instability of the glenohumeral (GH) joint is commonly found in handball players. In the past, 2D radiography was used to examine the in vivo translation of the humeral head (HH) on the glenoid cavity (GC). Considering the restraint validity of 2D methods to estimate 3D motion, 3D intra-articular GH kinematical data were obtained on the late cocking phase of handball throwing, using fast helical CT scanning. METHODS: Based on the CT data, 3D bone reconstructions of 3 asymptomatic and 3 functionally unstable GH joints (1 internal impingement, 2 with minor anterior GH instability) in handball players were acquired from a position with the shoulder in 90° abduction and 90° external rotation, and from a position of full cocking assessed on an individual basis. Kinematic analysis was based on a least squares method and linked to the finite helical axis (FHA) concept. After virtual disarticulation, a local frame was embedded on the GC. Subsequently, the GH FHA parameters of direction, rotation and shift were decomposed on this local frame. The displacement of the center of curvature of the HH was related to the GC. Based on an analytic error propagation model, the estimates of the rotation angle, the direction vector and the shift showed highly accurate results. The estimate of the position vector was insufficient for a mathematical analysis and therefore obtained graphically in the finite plane of motion, perpendicularly situated on the FHA. Subsequently, GH contact areal displacement of the mating articular surfaces was analyzed in this finite plane of motion. RESULTS: Towards full cocking, the HH of the asymptomatic shoulders practically did not externally/internally rotate on the local GC frame. The internal impingement demonstrated an accentuated GH external rotation, attended by a dysfunction in scapular setting, with a normal posterior translation of the HH on the GC. Minor anterior GH instability showed a diminished posterior translation of the center of the HH on the GC, as well as an accentuated external rotation. GH contact areal displacement in the normal throwing shoulders and the test case with internal impingement revealed roll behavior. The test cases with minor anterior GH instability featured a pivot. CONCLUSIONS: This research demonstrated the use of helical CT data reconstruction of joint structures with the implementation of an FHA approach to study the 6 degrees of freedom of intra-articular motion assessing a local articular embedded frame and contact areal displacements. The study provided insight in the arthrokinematics of functional instability of the GH joint at late cocking

Short-wavelength collective modes in a binary hard-sphere mixture

We use hard-sphere generalized hydrodynamic equations to discuss the extended hydrodynamic modes of a binary mixture. The theory presented here is analytic and it provides us with a simple description of the collective excitations of a dense binary mixture at molecular length scales. The behavior we predict is in qualitative agreement with molecular-dynamics results for soft-sphere mixtures. This study provides some insight into the role of compositional disorder in forming glassy configurations.Comment: Published; withdrawn since already published. Ordering in the archive gives misleading impression of new publicatio

Extra-articular hip endoscopy: a review of the literature

The aim of this review is to evaluate the current available literature evidencing on periarticular hip endoscopy (the third compartment). A comprehensive approach has been set on reports dealing with endoscopic surgery for recalcitrant trochanteric bursitis, snapping hip (or coxa-saltans; external and internal), gluteus medius and minimus tears and endoscopy (or arthroscopy) after total hip arthroplasty. This information can be used to trigger further research, innovation and education in extra-articular hip endoscopy