Forced motion of a probe particle near the colloidal glass transition

We use confocal microscopy to study the motion of a magnetic bead in a dense colloidal suspension, near the colloidal glass transition volume fraction $\phi_g$. For dense liquid-like samples near $\phi_g$, below a threshold force the magnetic bead exhibits only localized caged motion. Above this force, the bead is pulled with a fluctuating velocity. The relationship between force and velocity becomes increasingly nonlinear as $\phi_g$ is approached. The threshold force and nonlinear drag force vary strongly with the volume fraction, while the velocity fluctuations do not change near the transition.Comment: 7 pages, 4 figures revised version, accepted for publication in Europhysics Letter

Internal displacement and the Syrian crisis: an analysis of trends from 2011–2014

BACKGROUND: Since the start of the Syrian crisis in 2011, civil unrest and armed conflict in the country have resulted in a rapidly increasing number of people displaced both within and outside of Syria. Those displaced face immense challenges in meeting their basic needs. This study sought to characterize internal displacement in Syria, including trends in both time and place, and to provide insights on the association between displacement and selected measures of household well-being and humanitarian needs. METHODS: This study presents findings from two complementary methods: a desk review of displaced population estimates and movements and a needs assessment of 3930 Syrian households affected by the crisis. The first method, a desk review of displaced population estimates and movements, provides a retrospective analysis of national trends in displacement from March 2011 through June 2014. The second method, analysis of findings from a 2014 needs assessment by displacement status, provides insight into the displaced population and the association between displacement and humanitarian needs. RESULTS: Findings indicate that while displacement often corresponds to conflict levels, such trends were not uniformly observed in governorate-level analysis. Governorate level IDP estimates do not provide information on a scale detailed enough to adequately plan humanitarian assistance. Furthermore, such estimates are often influenced by obstructed access to certain areas, unsubstantiated reports, and substantial discrepancies in reporting. Secondary displacement is not consistently reported across sources nor are additional details about displacement, including whether displaced individuals originated within the current governorate or outside of the governorate. More than half (56.4 %) of households reported being displaced more than once, with a majority displaced for more than one year (73.3 %). Some differences between displaced and non-displaced population were observed in residence crowding, food consumption, health access, and education. CONCLUSIONS: Differences in reported living conditions and key health, nutrition, and education indicators between displaced and non-displaced populations indicate a need to better understand migration trends in order to inform planning and provision of live saving humanitarian assistance

Direct visualization of aging in colloidal glasses

We use confocal microscopy to directly visualize the dynamics of aging colloidal glasses. We prepare a colloidal suspension at high density, a simple model system which shares many properties with other glasses, and initiate experiments by stirring the sample. We follow the motion of several thousand colloidal particles after the stirring and observe that their motion significantly slows as the sample ages. The aging is both spatially and temporally heterogeneous. Furthermore, while the characteristic relaxation time scale grows with the age of the sample, nontrivial particle motions continue to occur on all time scales.Comment: submitted to proceedings for Liquid Matter Conference 200

The Validity of Patient-Reported Short-Term Complications following Total Hip and Knee Arthroplasty

Introduction: Given the lack of national data on outcomes of on patients who undergo total joint arthroplasty (TJA) and the limitations of hospital databases to capture information on patients who seek post-TJA care elsewhere, there is growing interest in using patient self-report to identify possible complications following surgery. We examined the concordance between patients self-report of potential short-term complications with review of available medical records as well as the location of the reported post-operative care. Material & Methods: Patients undergoing primary hip or knee arthroplasty from 7/1/11 through 12/3/12 participating in a tertiary care center were identified. Patients completed a 6-month post-operative survey regarding needing evaluation at an emergency department, day surgery or hospitalization for possible medical or mechanical complications and the location of care. We reviewed available inpatient and outpatient medical records to identify the location of postoperative care as well as the validity of patient self-report (sensitivity, specificity, positive predictive values and negative predictive values). Results: There were 413 patients who had 431 surgeries and completed the 6-month questionnaire. Patients reported 40 medical encounters including emergency department, day surgery or inpatient care resulting in a 9% reported complication rate, of which 20% occurred at outside hospitals Overall patient self-report of emergency department, day surgery and inpatient care for possible complications was both sensitive (82%) and specific (100%). The positive predictive value was 100% and negative predictive value 98%. Conclusion: Given the prevalence of events requiring care at outlying hospitals and the accuracy of self-report, methods that directly engage patients can augment current surveillance procedures

Poor Pre-Operative Emotional Health Limits Gain in Function after Total Hip Replacement

Introduction: While total joint replacement surgery successfully reduce joint pain and is associated with a low complication rate, patients experience a wide variation in functional improvement. Pre-surgery emotional state correlates with post-surgical functional improvement in total knee replacement patients. We tested this concept against a national cohort of total hip replacement (THR) patients. Materials & methods: Patients undergoing primary THR from 7/1/11 through 12/6/13 with postoperative outcomes at 6 months were identified from FORCE-TJR, a US national research consortium. We obtained data on patient demographics, underlying type of arthritis, body mass index (BMI), Charlson Comorbidity Index, arthritic pain in contralateral hip and bilateral knees, back pain, Hip Disability and Osteoarthritis Outcome Score (HOOS), global function based on the Short Form 36 (SF-36) Physical Component Score (PCS) and emotional health using the SF-36 Mental Component Score (MCS). We performed descriptive statistics and multivariable linear regression models to identify factors associated with 6-month postoperative PCS global function scores. Results: The 1,426 THR patients identified were 60.7% female, 95.0% white, mean age 65.3 years, mean BMI of 29.0. Mean preoperative surgical joint pain, stiffness and function was 50.1 (± 19.2), 38.7 (± 21.9), 46.4 (±19.2) respectively. MCS was 51.56 (± 12.2) and PCS 31.6 (± 8.9). Pre-operative and post-operative functioning differed based on emotional health (MCS ≥50). In multivariable models, lower MCS levels were associated with worse PCS at 6 months (coefficient of 0.18. 95% CI 0.14-0.22) after controlling for demographics, medical comorbidity, baseline PCS and burden of musculoskeletal disease. Conclusion: Poorer emotional health is associated with poorer global function following surgery and a key factor in the recovery and rehabilitation following THR. Better emotional health screening for THR surgical candidates, and interventions to provide additional emotional support to those who need it, are necessary to ensure optimal functional gain

Dynamic fluctuations of elastic lines in random environments

We study the fluctuations of the two-time dependent global roughness of finite size elastic lines in a quenched random environment. We propose a scaling form for the roughness distribution function that accounts for the two-time, temperature, and size dependence. At high temperature and in the final stationary regime before saturation the fluctuations are as the ones of the Edwards-Wilkinson interface evolving from typical initial conditions. We analyze the variation of the scaling function within the aging regime and with the distance from saturation. We speculate on the relevance of our results to describe the fluctuations of other non-equilibrium systems such as models at criticality.Comment: 7 pages, 3 figure

Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics

We explore the existence of time reparametrization symmetry in p-spin models. Using the Martin-Siggia-Rose generating functional, we analytically probe the long-time dynamics. We perform a renormalization group analysis where we systematically integrate over short timescale fluctuations. We find three families of stable fixed points and study the symmetry of those fixed points with respect to time reparametrizations. One of those families is composed entirely of symmetric fixed points, which are associated with the low temperature dynamics. The other two families are composed entirely of non-symmetric fixed points. One of these two non-symmetric families corresponds to the high temperature dynamics. Time reparametrization symmetry is a continuous symmetry that is spontaneously broken in the glass state and we argue that this gives rise to the presence of Goldstone modes. We expect the Goldstone modes to determine the properties of fluctuations in the glass state, in particular predicting the presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature (non-symmetric) and low temperature (symmetric) renormalization group fixed points. Now 16 pages with 1 figure. v1: 13 page

Does Functional Gain and Pain Relief After TKR and THR Differ by Patient Obese Status?

Introduction: Obesity is an important predictor of functional status and pain after total knee (TKR) and total hip (THR) replacement. However, variations in pre-post TKR and THR changes in function and pain by obesity status remain to be examined. Material & Methods: Pre- and 6 month post surgery data were collected on 2,964 primary TKR and 2,040 primary THR patients between 5/2011 and 3/2013. Data included demographics, comorbidities, operative joint pain severity based on the Knee Injury or Hip Disability and Osteoarthritis Outcome Score (KOOS/HOOS), WOMAC pain (higher is better), physical function (SF-36 PCS, higher is better), mental health (SF-36 MCS), and musculoskeletal burden of illness. Pre-post changes in PCS and pain were analyzed using descriptive statistics. Results: TKR patients were average 67 years, 61% women, 93% whites, 13% under or normal weight, 33% overweight, 29% obese, 15% severely obese, 9% morbidly obese. Greater level of obesity was associated with lower PCS at baseline and 6 month, lower pain scores at baseline but larger improvement post-op. Pre to-6 month PCS did not differ by obesity status. At 6 months morbidly obese patients had slightly lower/worse pain score. THR patients were average 65 years, 62% women, 95% whites, 27% under/normal weight, 38% overweight, 23% obese, 9% severely obese, 4% morbidly obese. Greater level of obesity was associated with lower PCS at baseline and 6 month, poorer baseline pain score but larger improvement post-op. Mean changes in pre-to-6 month PCS did not differ by obesity status. Conclusion: At 6 months after TKR, severely obese patients (BMI\u3e35) reported improvements in both pain and function equal to or greater than patients with BMI35 had lower mean functional gain than those with BM

Fluctuations in glassy systems

We summarize a theoretical framework based on global time-reparametrization invariance that explains the origin of dynamic fluctuations in glassy systems. We introduce the main ideas without getting into much technical details. We describe a number of consequences arising from this scenario that can be tested numerically and experimentally distinguishing those that can also be explained by other mechanisms from the ones that we believe, are special to our proposal. We support our claims by presenting some numerical checks performed on the 3d Edwards-Anderson spin-glass. Finally, we discuss up to which extent these ideas apply to super-cooled liquids that have been studied in much more detail up to present.Comment: 33 pages, 7 figs, contribution to JSTAT special issue `Principles of Dynamical Systems' work-shop at Newton Institute, Univ. of Cambridge, U