Continuous to intermittent flows in growing granular heaps.

If a granular material is poured from above on a horizontal surface between two parallel, vertical plates, a sand heap grows in time. For small piles, the grains flow smoothly downhill, but after a critical pile size X_{c}, the flow becomes intermittent: sudden avalanches slide downhill from the apex to the base, followed by an "uphill front" that slowly climbs up, until a new downhill avalanche interrupts the process. By means of experiments, controlling the distance between the apex of the sandpile and the container feeding it from above, we show that X_{c} grows linearly with the input flux, but scales as the square root of the feeding height. We explain these facts from a phenomenological model based on the experimental observation that the flowing granular phase forms a "wedge" on top of the static one, differently from the case of stationary heaps. Moreover, we demonstrate that our controlled experiments allow to predict the value of X_{c} for the common situation in which the feeding height decreases as the pile increases in size.

Sink versus tilt penetration into shaken dry granular matter: The role of the foundation.

We study the behavior of cylindrical objects as they sink into a dry granular bed fluidized due to lateral oscillations. Somewhat unexpectedly, we have found that, within a large range of lateral shaking powers, cylinders with flat bottoms sink vertically, while those with a "foundation" consisting of a shallow ring attached to their bottom, tilt besides sinking. The latter scenario seems to dominate independently from the nature of the foundation when strong enough lateral vibrations are applied. We are able to explain the observed behavior by quasi-2D numerical simulations, which also demonstrate the influence of the intruder's aspect ratio. The vertical sink dynamics is explained with the help of a Newtonian equation of motion for the intruder. Our findings may shed light on the behavior of buildings and other manmade structures during earthquakes.

Avalanches and extreme value statistics in interfacial crackling dynamics.

We study the avalanche and extreme statistics of the global velocity of a crack front, propagating slowly along a weak heterogeneous interface of a transparent polymethyl methacrylate block. The different loading conditions used (imposed constant velocity or creep relaxation) lead to a broad range of average crack front velocities. Our high-resolution and large dataset allows one to characterize in detail the observed intermittent crackling dynamics. We specifically measure the size S, the duration D, as well as the maximum amplitude [Formula: see text] of the global avalanches, defined as bursts in the interfacial crack global velocity time series. Those quantities characterizing the crackling dynamics follow robust power-law distributions, with scaling exponents in agreement with the values predicted and obtained in numerical simulations of the critical depinning of a long-range elastic string, slowly driven in a random medium. Nevertheless, our experimental results also set the limit of such model which cannot reproduce the power-law distribution of the maximum amplitudes of avalanches of a given duration reminiscent of the underlying fat-tail statistics of the local crack front velocities.This article is part of the theme issue 'Statistical physics of fracture and earthquakes'.

Thermally activated crack fronts propagating in pinning disorder: simultaneous brittle/creep behaviour depending on scale.

We study theoretically the propagation of a crack front in mode I along an interface in a disordered elastic medium, with a numerical model considering a thermally activated rheology, toughness disorder and long-range elastic interactions. This model reproduces not only the large-scale dynamics of the crack front position in fast or creep loading regimes, but also the small-scale self-affine behaviour of the front. Two different scaling laws are predicted for the front morphology, with a Hurst exponent of 0.5 at small scales and a logarithmic scaling law at large scales, consistently with experiments. The prefactor of these scaling laws is expressed as a function of the temperature, and of the quenched disorder characteristics. The cross-over between these regimes is expressed as a function of the quenched disorder amplitude, and is proportional to the average energy release rate, and to the inverse of temperature. This model captures as well the experimentally observed local velocity fluctuation probability distribution, with a high-velocity tail P(v)∼v -2.6 This feature is shown to arise when the quenched disorder is sufficiently large, whereas smaller toughness fluctuations lead to a lognormal-like velocity distribution. Overall, the system is shown to obey a scaling determined by two distinct mechanisms as a function of scale: namely, the large scales display fluctuations similar to an elastic line in an annealed noise excited as the average front travels through the pinning landscape, while small scales display a balance between thresholds in possible elastic forces and quenched disorder.This article is part of the theme issue 'Statistical physics of fracture and earthquakes'.

Sinking during earthquakes: Critical acceleration criteria control drained soil liquefaction.

This article focuses on liquefaction of saturated granular soils, triggered by earthquakes. Liquefaction is defined here as the transition from a rigid state, in which the granular soil layer supports structures placed on its surface, to a fluidlike state, in which structures placed initially on the surface sink to their isostatic depth within the granular layer. We suggest a simple theoretical model for soil liquefaction and show that buoyancy caused by the presence of water inside a granular medium has a dramatic influence on the stability of an intruder resting at the surface of the medium. We confirm this hypothesis by comparison with laboratory experiments and discrete-element numerical simulations. The external excitation representing ground motion during earthquakes is simulated via horizontal sinusoidal oscillations of controlled frequency and amplitude. In the experiments, we use particles only slightly denser than water, which as predicted theoretically increases the effect of liquefaction and allows clear depth-of-sinking measurements. In the simulations, a micromechanical model simulates grains using molecular dynamics with friction between neighbors. The effect of the fluid is captured by taking into account buoyancy effects on the grains when they are immersed. We show that the motion of an intruder inside a granular medium is mainly dependent on the peak acceleration of the ground motion and establish a phase diagram for the conditions under which liquefaction happens, depending on the soil bulk density, friction properties, presence of water, and peak acceleration of the imposed large-scale soil vibrations. We establish that in liquefaction conditions, most cases relax toward an equilibrium position following an exponential in time. We also show that the equilibrium position itself, for most liquefaction regimes, corresponds to the isostatic equilibrium of the intruder inside a medium of effective density. The characteristic time to relaxation is shown to be essentially a function of the peak ground velocity.

Determining Measurement Error for Bohler's Angle and the Effect of X-Ray Obliquity on Accuracy.

BACKGROUND: Bohler's angle (BA) is the most commonly utilized radiographic measurement in the study of calcaneus fractures and has been shown to be prognostic in nature. Therefore, it is critical that the measurement of BA be accurate as both therapeutic and prognostic information relies on it. Oblique lateral radiographs can be a cause of error in BA measurements. However, measurement error and the effects of X-ray beam obliquity on BA have not been established in the literature. The purpose of this study was to determine measurement error and understand the effects of X-ray beam's obliquity on the measurement of BA. METHODS: A cadaver specimen was imaged using a C-arm to obtain a perfect lateral radiograph of the ankle and slightly oblique lateral views in the anterior, posterior, cephalad, and caudad directions in 5° increments (21 images). Metallic beads were then placed on the anterior calcaneal process, posterior facet, and the superior aspect of the posterior tuberosity, and the same 21 images were then obtained. The metallic beads placed on the reference radiographs allowed the authors to accurately measure BA for each image and served as reference for the corresponding test radiographs. Thirty-four orthopaedic staff members participated in the study and used DICOM measurement tool to measure BA on each of the 21 test radiographs. The measurements were then compared to the measurements of BA from the reference radiographs to determine error in measurement. RESULTS: A total of 714 different measurements were obtained. Average measurement error was 6° (95% confidence interval = -4° to 15°). The difference between the observed BA measurements compared to the true BA measurements increased with increasing X-ray obliquity. CONCLUSIONS: Measurement error for BA is ±6° and increases most with cephalad oblique radiographs. Orthopaedic surgeons' ability to accurately measure BA significantly decreases with increasing obliquity of the lateral radiograph. LEVELS OF EVIDENCE: Level V: Cadaver bench study.

[Total hip and knee arthroplasty : Results of outpatient orthopedic rehabilitation]. / Hüft- und Knietotalendoprothesenversorgung : Ergebnisse ambulanter orthopädischer Rehabilitation.

AIM AND METHODOLOGY: For evaluation of outpatient rehabilitation after total hip and knee replacement, a multicenter study was performed to assess quality of life, general health as well as subjective and objective impairment at the beginning (T1), at the end (T2) and 3 months (T3) after rehabilitation: SF 36, EQ-5D, and WOMAC. The Knee Society and Harris Hip Score scores were documented at T1 and T2. RESULTS: A total of 721 patients were included (359 hips, 362 knees). The average age was 65 years, and 49 % of the patients were women. Both the results of the clinical scores and health statuses showed highly significantly positive changes in the rehabilitation course as well as sustainability in the further observation time period. An effect loss with declining results after rehabilitation was not observed. CONCLUSION: The study illustrates positive effects of outpatient rehabilitation following endoprosthetic treatment.

Note: "Lock-in accelerometry" to follow sink dynamics in shaken granular matter.

Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. While the penetration of intruders in two dimensional (2D) laboratory granular beds can be followed using video recording, this is useless in three dimensional (3D) beds of non-transparent materials such as common sand. Here, we propose a method to quantify the sink dynamics of an intruder into laterally shaken granular beds based on the temporal correlations between the signals from a reference accelerometer fixed to the shaken granular bed, and a probe accelerometer deployed inside the intruder. Due to its analogy with the working principle of a lock-in amplifier, we call this technique lock-in accelerometry.

The impact of psychiatric comorbidity on quality of life in patients undergoing herniated disc surgery.

BACKGROUND: Recent studies examined the role of psychiatric comorbidity in the process of rehabilitation in patients undergoing herniated disc surgery. These patients suffer from physical and psychosocial complaints or symptoms, which impact their everyday life negatively and the success of rehabilitation potentially. The objectives of this study are (1) to examine the quality of life (QoL) in disc surgery patients and to compare the findings with reference data from the general German population, and (2) to investigate the impact of psychiatric comorbidity on QoL of patients undergoing herniated disc surgery. METHODS: This study consists of 305 patients aged between 18 and 55 years who took part in face-to-face interviews during their hospital stay. Psychiatric comorbidity was assessed with the Composite International Diagnostic Interview (CIDI-DIA-X). By means of the 36-Item Short-Form Health Survey (SF-36), QoL was assessed in patients undergoing herniated disc surgery with and without psychiatric comorbidity. These findings were compared with the QoL of a representative sample of the general German population. RESULTS: Compared with the general population, QoL in patients with herniated disc surgery was lower in all domains of the SF-36. Psychiatric comorbidity impacts the QoL in patients with herniated disc surgery in all SF-36 domains except "physical function". The patients with psychiatric comorbidity showed significantly lower levels of QoL in the domains "bodily pain", "vitality", "social function", "role emotional", and "mental health". CONCLUSIONS: Psychiatric comorbidity has a substantial adverse effect on QoL in patients undergoing disc surgery. Therefore, it will be necessary to diagnose psychiatric comorbidities at an early stage and to include psychosocial interventions in the treatment of herniated disc patients aimed at improving deficits in psychosocial functioning and QoL.

Disaster triage after the Haitian earthquake.

In the aftermath of the devastating Haitian earthquake, we became the primary relief service for a large group of severely injured earthquake victims. Finding ourselves virtually isolated with extremely limited facilities and a group of critically injured patients whose needs vastly outstripped the available resources we employed a disaster triage system to organize their clinical care. This report describes the specific injury profile of this group of patients, their clinical course, and the management philosophy that we employed. It provides useful lessons for similar situations in the future.

Hydrothermal coupling in a self-affine rough fracture.

The influence of the multiscale fracture roughness on the heat exchange when a cold fluid enters a fractured hot solid is studied numerically on the basis of the Stokes equation and in the limit of both hydrolubrication and thermolubrication. The geometrical complexity of the fracture aperture is modeled by small self-affine perturbations added to a uniform aperture field. Thermal and hydraulic properties are characterized via the definition of hydraulic and thermal apertures both at microscopic and macroscopic scales and obtained by comparing the fluxes to the ones of flat fractures. Statistics over a large number of fracture configurations provide an estimate of the average behavior and its variability. We show that the long-range correlations of the fracture roughness induces strong channeling effects that significantly influence the hydraulic and thermal properties. An important parameter is the aspect ratio (length over width) of the fracture: we show, for example, that a downstream elongated rough fracture is more likely to inhibit the hydraulic flow and subsequently to enhance the thermal exchange. Fracture roughness might, in the opposite configuration, favor strong channeling which inhibits heating of the fluid. The thermal behavior is in general shown to be mainly dependent on the hydraulic one, which is expressed through a simple law.

Decompaction and fluidization of a saturated and confined granular medium by injection of a viscous liquid or gas.

We compare quantitatively two experimental situations concerning injection of a miscible fluid into an initially jammed granular medium saturated with the same fluid, confined in a Hele-Shaw cell. The two experiments are identical, apart from the interstitial and injected fluid, which is in one case air injected into a dry granular packing, and in the other case silicone oil injected into a dense suspension. In spite of the strong differences regarding the nature of the two fluids, strikingly similar dynamical and geometrical features are identified as functions of the control parameters: cell thickness and applied fluid injection pressure. In both cases an initial hydrodynamically driven decompaction process controls the unjamming and prepares the final displacement process characterized by fingerlike patterns empty of grains. The pattern shapes are comparable. In addition, the mobilities of the coupled fluid-grain flow, rescaled by the interstitial fluid viscosity and grain diameter squared, are of the same range and behave comparably. The mobility proves to depend on the initial solid fraction of the medium. Subtle differences are observed in geometrical aspects like the finger width with respect to the control parameters.

Revolving rivers in sandpiles: from continuous to intermittent flows.

In a previous paper [E. Altshuler, Phys. Rev. Lett. 91, 014501 (2003)], the mechanism of "revolving rivers" for sandpile formation is reported: As a steady stream of dry sand is poured onto a horizontal surface, a pile forms which has a river of sand on one side flowing from the apex of the pile to the edge of the base. For small piles the river is steady, or continuous. For larger piles, it becomes intermittent. In this paper we establish experimentally the "dynamical phase diagram" of the continuous and intermittent regimes, and give further details of the piles' "topography," improving the previous kinematic model to describe it and shedding further light on the mechanisms of river formation. Based on experiments in Hele-Shaw cells, we also propose that a simple dimensionality reduction argument can explain the transition between the continuous and intermittent dynamics.

Coupled air/granular flow in a linear Hele-Shaw cell.

We investigate experimentally the pattern formation process during injection of air in a noncohesive granular material confined in a linear Hele-Shaw cell. We characterize the features and dynamics of this pattern formation on the basis of fast image analysis and sensitive pressure measurements. Behaviors are classified using two parameters--injection pressure and plate opening--and four hydrodynamic regimes are defined. For some regions of the parameter space, flows of air and grains are shown to be strongly coupled and instable, and lead to channelization within the granular material with obvious large-scale permeability variations.

Nonsurgical complications after total hip and knee arthroplasty.

Postoperative medical complications after total hip arthroplasty (THA) and total knee arthroplasty (TKA) may occur in patients of any age. However, percentage of adverse events increases with increasing patient age and can cause significant morbidity and even mortality. It is important that the orthopedist identify risk factors and symptoms and be knowledgeable in the treatment of nonsurgical postoperative complications. Nonsurgical complications after THA and TKA include pulmonary embolism, fat embolism syndrome, pneumonia, myocardial infarction, postoperative delirium, cerebrovascular accident, urinary retention, urinary tract infections, and deep vein thrombosis.

Pattern formation during air injection into granular materials confined in a circular Hele-Shaw cell.

We investigate the dynamics of granular materials confined in a radial Hele-Shaw cell, during central air injection. The behavior of this granular system, driven by its interstitial fluid, is studied both experimentally and numerically. This allows us to explore the associated pattern formation process, characterize its features and dynamics. We classify different hydrodynamic regimes as function of the injection pressure. The numerical model takes into account the interactions between the granular material and the interstitial fluid, as well as the solid-solid interactions between the grains and the confining plates. Numerical and experimental results are comparable, both to reproduce the hydrodynamical regimes experimentally observed, as well as the dynamical features associated to fingering and compacting.

Roughness of stylolites: implications of 3D high resolution topography measurements.

Stylolites are natural pressure-dissolution surfaces in sedimentary rocks. We present 3D high resolution measurements at laboratory scales of their complex roughness. The topography is shown to be described by a self-affine scaling invariance. At large scales, the Hurst exponent is zeta(1) approximately 0.5 and very different from that at small scales where zeta(2) approximately 1.2. A crossover length scale at around L(c)=1 mm is well characterized. Measurements are consistent with a Langevin equation that describes the growth of a stylolitic interface as a competition between stabilizing long range elastic interactions at large scales or local surface tension effects at small scales and a destabilizing quenched material disorder.

Sacroiliac dysfunction in construction workers.

BACKGROUND: In the literature of manual medicine the sacroiliac joint is widely accepted as a potential source of low back pain. On the other hand, some investigations have detected sacroiliac joint dysfunction without concomitant low back pain. The prevalence of sacroiliac dysfunction in the population has been noted in the medical literature to be between 19.3% and 47.9%. However, the prevalence of sacroiliac dysfunction in the general population and for construction workers is unknown. OBJECTIVE: This article presents results from the Hamburg Construction Workers Study in respect to sacroiliac diagnostics. The prevalence of and connection between sacroiliac dysfunction and low back pain are particularly interesting. DESIGN AND PARTICIPANTS: The sacroiliac joint diagnostics were studied in a cross-section investigation of a cohort of 480 male construction workers. Manual examination is the standard in the diagnostics of sacroiliac joint conditions at present. The assessment of sacroiliac joint function by standing flexion test, the spine test, the iliac compression test, and the iliac springing test was operationalized as two categories: sacroiliac dysfunction I and II. RESULTS: A prevalence of 29.0% was found for dysfunction I and 6.3% for dysfunction II, whereas a prevalence of 7.9% was found for the coprevalence of low back pain and sacroiliac dysfunction on the day of examination. This study demonstrated no statistical associations between low back pain and sacroiliac joint dysfunction. CONCLUSIONS: The reason why symptomatic and asymptomatic sacroiliac dysfunctions exist has not yet been sufficiently explained. The identification of pain-provoking factors should be the aim of subsequent investigations. A further study with a prospective design will be necessary to answer the questions that remain.

Sacroiliac joint diagnostics in the Hamburg Construction Workers Study.

BACKGROUND: In the medical literature, test procedures for sacroiliac joint diagnostics are viewed as controversial. The provocation tests are based on provoked sacroiliac pain, whereas the palpation tests examine the motion of the sacroiliac joint or describe the condition indirectly if limitation of the sacroiliac function is present. It must be presumed that the use of different test results in the detection of varying functional phenomena of a sacroiliac dysfunction or, alternatively, that identical effects of a dysfunction are evaluated in differing ways. OBJECTIVE: This article presents results with regard to the consistency of tests for sacroiliac joint dysfunctions carried out on participants from the building trade. DESIGN AND PARTICIPANTS: The consistency of the tests (standing flexion test, spine test, iliac compression test, iliac springing test) used in a cross-section investigation of a cohort of 480 male construction workers is presented. To evaluate the degree of consistency of the test procedure the percentage agreement and the kappa value, including a confidence interval of 95%, are given. RESULTS: The consistency between the iliac compression test and the three sacroiliac palpation tests could not be shown to be statistically significant. The consistency between the three palpation tests was moderate to good and the percentage agreement was acceptable (87.4%, 88.6%, 80.9%). CONCLUSIONS: It may be assumed that the palpation tests characterize the same dysfunction of the sacroiliac joint. Standing flexion test, spine test, and iliac springing test seem to be valuable tools for sacroiliac joint diagnostics.